News & Events

## About Seminars, Colloquia & Talks

This page contains an archive of all entries posted to Physics Announcements in the Seminars, Colloquia & Talks category. They are listed from newest to oldest.

Notable Achievements is the previous category.

Many more can be found on the main index page or by looking through the archives.

Movable Type 3.34

## April 23, 2014

### Seminar: Wednesday, April 23 at 3:30 pm

what can learn from these spectacular active galactic nuclei?
Marco Chiaberge
Space Telescope Science Institute

Radio galaxies are a spectacular class of Active Galactic Nuclei (AGN). They are powered by accretion of matter onto the most massive black holes and they are hosted by the largest galaxies in the Universe. I will focus on results from our studies of radio galaxies at all distances, from the closest objects to high redshifts, when the Universe was less than a quarter of the age it is now. I will show how low-redshift radio galaxies observed with HST and other instruments allowed us a better understanding of the innermost regions of AGNs and of their black holes. While we still don’t know the details of the physics of the jet launch, we learned that the nuclei of lower power objects are fundamentally different from all other AGNs. In recent years, we focused on the cosmological evolution of these sources. I will show the first results of the analysis of a new sample of high redshift (11, which will allow a detailed comparison of the properties of the environment of these sources over more than four decades in radio power.

Location: Physics Bldg., Room 401

## March 10, 2014

### Seminar: Monday, March 10 at 3:30 pm

Aircraft Observations and Modeling of Cloud and Aerosol Radiative Effects
Sebastian Schmidt
Laboratory for Atmospheric and Space Physics

Our ability to understand how solar energy is distributed and deposited on our planet has greatly improved over the past two decades, enabled by new global observing systems such as the NASA A-­‐Train satellite constellation. But some of the outstanding questions regarding the radiative effects of atmospheric constituents and the surface cannot be answered with satellite observations alone because the derivation of surface and atmospheric energy budget terms from remote sensing requires a number of assumptions and parameterizations. Aircraft observations can fill some of these gaps because they allow the direct measurement of flux densities above, below and inside atmospheric layers of interest – alongsidein-­‐situ measurements of atmospheric constituents and their optical properties. In my talk,I will show that the combination of airborne spectrally resolved radiation measurements with three-­‐dimensional radiative transfer modeling allowed the resolution of a long-­‐standing issue in so-­‐called radiation closure experiments where cloud absorption from measurements appeared to be consistently higher than expected from the calculations. This led to the discovery of “colored” or spectrally dependent net horizontal photon transport, which is relevant not only to energy budget parameters such as radiative forcing and absorption, but also to remote sensing. The radiative effect of aerosols in homogeneous or inhomogeneous cloud fields can be understood as a spectral perturbation to the radiative signature of the underlying cloud field. Interpreting the combined signal from aerosols and clouds by means of their distinct fingerprints has become one of the goals of an emerging focus area: “cloud-­‐aerosol spectrometry.” I will present some of the results of this new research direction and discuss how multiple observational techniques including spectral imaging and active sounding could be combined to gain a more complete understanding of the radiative effects of clouds, aerosols and gases in future research.

Location: Physics Bldg., Room 401

## March 5, 2014

### Seminar: Wednesday, March 5 at 3:30 pm

The far-reaching impacts of mineral dust: A satellite perspective
Hongbin Yu
ESSIC/University of Maryland and NASA Goddard Space Flight Center

Dust cycle is an emerging core theme in the Earth system science. Dust emitted from deserts and disturbed soils can have significant impacts on climate, human health, ecosystems, and biogeochemical cycle. On the other hand, dust emissions can be affected by changes in rainfall, wind speed, and vegetation cover. The impacts of dust are far-reaching because of the global movement of dust. Each year about 60 million tons of dust is imported into North America from both coasts, which is dominated by the trans-Pacific transport of dust with both Asian and African origins. This surprisingly large magnitude of dust import is comparable with domestic emissions in North America. Meanwhile, 43 ~ 58 million tons of trans-Atlantic dust from North Africa is deposited into the Amazon basin every year, providing nutrients needed for maintaining the health and productivity of Amazon rainforest, an important ecosystem in regulating global climate. The trans-Pacific aerosol transport, additional source of particulate pollution for the U.S., increases the surface concentration of fine particulate matter (PM2.5) by a magnitude that is much larger in the west than in the east, because of the geographical proximity and high topography of the west. However, when the influences on meteorology by imported aerosols are also considered, the more populous east shows the PM2.5 increase that is comparable to the west. In this presentation I will discuss how these impacts have been assessed utilizing advanced aerosol remote sensing measurements from the MODerate resolution Imaging and Spectroradiometer (MODIS) and the Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) in conjunction with a regional modeling system. Future research will also be discussed.

Location: Physics Bldg., Room 401

## February 26, 2014

### Seminar: Wednesday, Feb 26 at 3:30 pm

A Challenge We Must Face: A Cloudy Picture in Climate Science
Tianle Yuan
Goddard Space Flight Center

It is increasingly realized that clouds are at the heart of physical climate science. They are the most important player in the energy balance of the Earth by interacting with both shortwave and longwave radiation. Tiny changes in cloud properties can have major consequences for our climate.

Here I concentrate on how aerosols affect clouds, the so-called aerosol indirect effects (AIEs), which remain one of the most uncertain factors in our scientific understanding and projection of climate change. Two cloud regimes will be discussed.

In one, aerosols invigorate maritime tropical convection at a large scale. The invigoration effect manifests in characters of precipitation radar reflectivity vertical profiles, cloud top ice particle size and cloud glaciation temperature. Furthermore, lightning, as a hallmark of strong convection, increases at a rate of 20-40 times per unit increase of aerosol optical depth. Aerosol-induced lightning changes also have interesting implications for ozone chemistry and wildfire activity.

In the other, aerosols change cloud properties of trade cumuli at a large scale. They decreased cloud droplet size, decreased precipitation efficiency and increased cloud amount. In addition we find significantly higher cloud tops for polluted clouds. Changes in cloud properties caused by aerosols perturbed the energy balance by more than 20Wm-2, almost an order of magnitude higher than aerosol direct forcing alone. It highlights the strong leverage of AIE in this cloud regime. Furthermore, the precipitation reduction associated with enhanced aerosol leads to large changes in the energetics of air-sea exchange within trade wind boundary layer.

Results from both regimes open up new opportunities for future research in reducing uncertainty surrounding AIEs and climate adaptation/mitigation.

Location: Physics Bldg., Room 401

## February 19, 2014

### Seminar: Wednesday, Feb. 19 at 3:30 pm

Light, Ocean, and Life
Pengwang Zhai
SSAI, NASA Langley Research Center

Phytoplankton are unicellular organisms that are responsible for half of all photosynthetic activity on Earth. According to their functional types, phytoplankton are divided into several different conceptual groups that include calcifiers, nitrogen fixers, DMS producers and silicifiers. Coccolithophores belong to the calcifier group which plays important roles in global carbon cycle processes. When proper nutrition and light conditions are met, phytoplankton can produce massive blooms, which have large environmental impacts. I am primarily interested in how light interacts with particles, particularly phytoplankton and other oceanic particles, and how light can be used to remote sense and monitor ocean water optical properties. In this talk I will cover three general aspects of my research interests: light scattering, radiative transfer, and optical remote sensing. Light scattering studies the interaction of light with single particles within the classical electromagnetic theory and linear optics. Radiative transfer theory covers light field multiply scattered within turbid media consisting of individual particles. It is understood that optical properties of single particles are known knowledge in radiative transfer theory. Generally radiative transfer theory assumes incoherent scattering, which means that there is no systematic phase correlation among light waves scattered by a group of particles. Nonetheless, coherent scattering is significant in coherent backscattering and other phenomena. Optical remote sensing is to use light scattered by particles, singly or multiply, to retrieve information about particles’ properties. In other words, light scattering and radiative transfer theories are building blocks and diagnostic tools for optical remote sensing. I will present two examples of my research efforts in each of the three theoretical categories. In light scattering, the examples are invisible particles for monostatic lidar/radar detections and simulation of light scattering by nonspherical coccolithophores. In radiative transfer theory section, I will cover how polarization is treated and two methods are presented to solve light field in a turbid medium: Monte Carlo and the successive order of scattering. In the optical remote sensing section, two applications of polarized radiative transfer solutions are given for ocean color and aerosol remote sensing.

Location: Physics Bldg., Room 401

## February 12, 2014

### Seminar: Wednesday, Feb 12 at 3:30 pm

Climate and clean air in the 21st century:
Understanding and reducing uncertainties
in atmospheric change
Christopher D. Homes
Department of Earth System Science
University of California, Irvine

Rising concentrations of greenhouse gases are the main drivers of current and projected future climate change. Reactive gases, including methane (CH4) and ozone (O3), contribute substantially to climate forcing and the chemistry controlling their abundances also responds to climate change. Using multiple global chemical transport models we diagnose factors controlling the year-to-year variations in tropospheric hydroxyl (OH), the main sink for atmospheric CH4. The modeled variations over the last decade are then evaluated against our best observational constraints. Using factors that control OH in the recent past, we project CH4 lifetime and abundance forward in time for a range of future climate scenarios. This simple approach agrees with projections from fully coupled Earth System Models. All this information is combined into an uncertainty analysis of the future CH4 abundance and global warming potential. Key process uncertainties are identified and can guide future research priorities.

Location: Physics Bldg., Room 401

## February 3, 2014

### Seminar: Wednesday Feb 3 at 3:30 pm

Aerosol Remote Sensing:
Investing in the Next Generation of Scientists
Lorraine Remer
JCET

Through the stories of my interaction with four young scientists, I will explore different aspects of Aerosol Remote Sensing. These will include developing an operational algorithm for wide community use, developing a specialized product to retrieve that hard-to-acquire aerosol characterization of spectral absorption, and exploring aerosol-cloud interaction in two different ways. Aerosol remote sensing spans both data producers and data users, and both types of scientists discover new knowledge in pursuit of their projects. My four young scientists each made a significant contribution to science as they pursued their Ph.D.s and post-docs, and also enriched my experience in the process.

Location: Physics Bldg., Room 401

## December 4, 2013

### Seminar: Wednesday, Dec 4, 2013 at 3:30 pm

Relativistic Jets from Black Holes: Shooting movies of nature's great particle accelerators with the Hubble Space Telescope
Eileen Meyer
Space Telescope Science Institute

The super-massive black holes residing at the centers of many galaxies emit jets of relativistic plasma moving near the speed of light, a process which can deposit enormous amounts of energy into the host galaxy and inter-galactic medium. Yet the detailed physics behind these jets, including how they are launched and collimated, how long they remain relativistic, and their total energy content remain poorly understood. Using over 13 years of archival Hubble Space Telescope (HST) observations of the relativistic jet in the archetypal radio galaxy M87, we have produced astrometric speed measurements of the optically bright synchrotron emitting plasma components in the jet with unprecedented accuracy. Building on previous work showing the superluminal nature of the jet in the optical, we have found that the jet motion is incredibly complex, with both transverse motions and flux variations which can be seen by eye in the time series of deep exposures. These observations of M87 provide us with a unique dataset with which to refine theoretical models of the large-scale jet structure, potentially addressing open questions such as the jet collimation mechanism, bulk acceleration and deceleration in the jet, and the presence of a helical structure. I will also present very recent results using data from the HST archive on the optical counterjet and nuclear regions of M87 and discuss the larger implications of these detailed studies of one of the most nearby AGN jets.

Location: Physics Bldg., Room 401

## November 6, 2013

### Seminar: Wednesday, Nov. 6, 2013 at 3:30 pm

Isoprene: A Chemical Link between the Biosphere and the Atmosphere
Glenn M. Wolfe
UMBC

Air quality and climate change, two of the most pervasive environmental issues of the 21st century, are inextricably linked to our atmosphere. Near the surface, atmospheric composition is defined by the emission and transformation of a host of chemical species, including nitrogen oxides (NOx) and volatile organic compounds (VOC). While NOx is primarily a byproduct of anthropogenic activities (e.g. fossil fuel combustion), the vast majority (~90%) of global non-methane VOC emissions originate from the biosphere. Isoprene, a highly reactive hydrocarbon emitted by oak trees and other vegetation, comprises a full third of this budget. In many regions, isoprene and NOx fuel the photochemical processes responsible for production of secondary pollutants like ozone and organic aerosol, thereby impacting air quality and climate on a global scale.

Despite decades of research, our understanding of isoprene is still evolving. Emission inventories remain highly uncertain, and models struggle to reproduce observations in low-NOx, high-isoprene regions; however, much progress has been made. Recent laboratory studies have unveiled a wealth of novel reaction mechanisms, while field observations continue to challenge canonical chemistry and raise new questions. In this seminar I will highlight several such advances and demonstrate how new perspectives and measurement capabilities are helping to elucidate the details of isoprene chemistry. Completing this picture is critical for predicting and mitigating future impacts of anthropogenic activities on both the atmosphere and other Earth systems

Location: Physics Bldg., Room 401

## October 30, 2013

### Seminar: Wednesday, Oct. 30, 2013 at 3:30 pm

Global constraints on the fundamental radiative properties of ice clouds
Bastiaan van Diedenhoven
COLUMBIA UNIVERSITY

Inadequate representation of the macrophysical, microphysical and radiative properties of clouds in global circulation models is one of the largest sources of uncertainties in Earth’s climate projections. In the case of radiative properties, in particular those of ice clouds are highly uncertain because of the myriad of ice crystal shapes and sizes that can form and evolve in natural ice clouds. Currently, satellite instruments provide global estimates of two of the three fundamental radiative properties of ice clouds, namely optical thickness and effective ice crystal size near cloud top. However, very little is known about the natural variation of the third fundamental radiative property of ice clouds, the asymmetry parameter, which mainly depends on ice crystal shape. Moreover, current satellite retrievals of ice cloud optical thickness and effective ice crystal size are highly uncertain because they depend on an assumed, fixed asymmetry parameter that does not vary as in nature. In this talk, I will discuss a newly developed technique to simultaneously infer all three fundamental radiative properties of ice clouds from satellite measurements.

I will first explain the relation between the radiative and microphysical properties of ice crystals. I will review the current technique to infer ice cloud optical thickness and crystal size and will show how such retrievals can be greatly enhanced by simultaneous retrievals of the asymmetry parameter using multi-directional polarization measurements. Examples will be shown of this technique applied to detailed aircraft measurements, to satellite measurements over the Tropical West Pacific, and finally to global measurements. The variation of ice crystal size, shape and asymmetry parameter with atmospheric conditions will be discussed.

Location: Physics Bldg., Room 401

## October 23, 2013

### Seminar: Wednesday, Oct 23, 2013 at 3:30 pm

What Made the Big Bang so Big: Testing Physics With the Cosmic Microwave Background
Alan Kogut
NASA/GSFC

The cosmic microwave background (CMB) serves as a "backlight" throughout the evolution of the universe, encoding details of physics at energies up to a trillion times higher than any accessible to particle accelerators. New instrumentation now offers the tantalizing possibility of detecting the "smoking gun" signature of primordial inflation through its imprint on the linear polarization of the microwave background. A positive detection would have profound consequences for both cosmology and high-energy physics. It would not only establish inflation as a physical reality, but would probe physics at energies approaching Grand Unification. I will present the scientific motivation behind measurements of the CMB polarization and discuss how recent experimental progress could lead to a detection in the not-very-distant future.

Location: Physics Bldg., Room 401

## October 16, 2013

### Seminar: Wednesday, Oct .16, 2013 at 3:30 pm

Optical Studies of Nanoscale Physics
Matthew Pelton
UMBC

Semiconductor nanocrystals and metal nanoparticles are key building blocks for nanophotonics, because they both interact strongly with light in a way that can be tuned by changing the size, shape, and composition of the particles. Light incident on noble-metal nanoparticles excites surface-plasmon resonances, or collective oscillations of conduction electrons, and light incident on semiconductor nanocrystals interactions with excitons, or bound electron-hole pairs. Time-resolved optical measurements on these particles can thus be used to probe electronic, chemical, and mechanical processes on ultrafast time scales and nanometer length scales. I will discuss some examples of the nanoscale physics that can be studied in this way: (1) measurements of charge relaxation, separation, and localization in semiconductor nanoparticles; (2) studies of nanoscale mechanical energy dissipation using plasmons as an optical probe; and (3) new optical properties that emerge from coherent interactions between plasmons in metal nanoparticles and excitons in semiconductor nanoparticles.

Location: Physics Bldg., Room 401

### Seminar: Wednesday, Oct .16, 2013 at 3:30 pm

Optical Studies of Nanoscale Physics
Matthew Pelton
UMBC

Semiconductor nanocrystals and metal nanoparticles are key building blocks for nanophotonics, because they both interact strongly with light in a way that can be tuned by changing the size, shape, and composition of the particles. Light incident on noble-metal nanoparticles excites surface-plasmon resonances, or collective oscillations of conduction electrons, and light incident on semiconductor nanocrystals interactions with excitons, or bound electron-hole pairs. Time-resolved optical measurements on these particles can thus be used to probe electronic, chemical, and mechanical processes on ultrafast time scales and nanometer length scales. I will discuss some examples of the nanoscale physics that can be studied in this way: (1) measurements of charge relaxation, separation, and localization in semiconductor nanoparticles; (2) studies of nanoscale mechanical energy dissipation using plasmons as an optical probe; and (3) new optical properties that emerge from coherent interactions between plasmons in metal nanoparticles and excitons in semiconductor nanoparticles.

Location: Physics Bldg., Room 401

## October 9, 2013

### Seminar: Wednesday, Oct .9, 2013 at 3:30 pm

Exploring Fundamental Properties of Materials with Dusty Plasmas
Carlos A. Romero-Talamás
UMBC

Dusty plasmas are ionized gases in which charged multi-particle systems can be affected by electric and magnetic fields. They are found in a wide range of settings, from astrophysics to semiconductor manufacturing. In general, plasmas are sometimes referred to as the fourth state of matter, because of their high temperature and charge mobility. Dusty plasmas, however, force us to revisit our notion of states of matter given the wide range of temperatures and particle sizes. These can vary typically from 0.01 to 1 eV and 0.1 to 10 eV for the temperature of ions and electrons, respectively, and have charged micron-sized particles with room temperature, all coexisting and interacting in the same system.

In the laboratory, it is possible to create strongly coupled dusty plasmas that form crystalline arrays. These arrays fall in the realm of soft matter and exist within a background plasma that is dilute, resulting in practically undamped dynamics that allows for direct emulation and measurement of atomistic dynamics in solids. At UMBC, a new experimental facility is under construction that will allow us to create dusty plasmas in fluid or crystal form. The setup includes electrodes with adjustable separation and orientation with respect to gravity. The ability to add magnetic fields as high as 10 Tesla is under design. Planned experiments with dusty plasmas include: studies of friction of coefficient in crystals; compression, tension, and shock dynamics; waves with oscillating boundary conditions; and response to fast (> 10 eV) electrons penetrating the crystal lattice.

Location: Physics Bldg., Room 401

## October 2, 2013

### Seminar: Wednesday, Oct 2, 2013 at 3:30 pm

Enhancement of 3-rd Order Nonlinearities in Nanoplasmonic Metamaterials: Figures of Merit
Jacob Khurgin
Johns Hopkins University

A simple analytical theory of plasmonic enhancement of optical nonlinearities in various nanoplasmonic structures is developed. It is shown that in simple structures roughly two-to-three order enhancement of effective third order nonlinear susceptibility can be obtain, while in more complicated arrangements of plasmonic dimers and nanoantennae, enhancement can be as high as four-to-five orders of magnitude. At the same time, if one introduces a more practical figure of merit for nonlinearity, as a maximum attainable phase shift per 10dB loss, this phase shift can never exceed a few degrees, thus making photonic switching in metamaterials all but unattainable. This self-contradictory behavior is caused by a combination of inherently low values of nonlinear susceptibility and large loss in the metal. The conclusion is then that nanoplasmonic metamaterials may enhance weak nonlinearities for various sensing applications, but are rather ineffectual in photonic switching and modulation.

Location: Physics Bldg., Room 401

## September 25, 2013

### Seminar: Wednesday, Sept. 25, 2013 at 3:30 pm

Formation and properties of plasmonic nanomaterials
Sharka Prokes
NRL

There is significant interest in the growth of semiconductor nanowires, due to interesting and useful optical, electrical and mechanical properties. They are attractive for a variety of applications, including optical sensing. One of the interesting aspects of these nanostructures is an enhanced plasmonic response, which has been investigated using Surface Enhanced Raman Spectroscopy (SERS). The growth and formation of several nanowire/metal composite structures, the formation of random and ordered arrays of these structures, and their surface enhanced Raman (SERS) properties will be discussed. The effect of geometry will also be examined, and we will show, both experimentally and in electric field simulations, that the intersections of these nanowires are critical in generating the high electric fields necessary for this enhancement.

In addition, we recently developed another novel plasmonic material, based on Plasma Enhanced Atomic Layer Deposition (PEALD) of Ag, which results in strong plasmonic properties of flat Ag films. It will be shown as-deposited flat PEALD Ag films exhibit unexpected plasmonic properties and the plasmonic enhancement can differ significantly, depending on the microstructure of the Ag film. Electric field simulations suggest that the plasmonic behavior is due to air gaps that are an inherent property of the PEALD growth of Ag and account for the trends observed in SERS. This unusual plasmonic behavior is very similar to what would be expected in hybrid spoof plasmonics and suggests that PEALD Ag is a metamaterial.

Location: Physics Bldg., Room 401

## September 18, 2013

### Seminar: Wednesday, Nov 13, 2013 at 3:30 pm

Understanding and controlling electron-nuclear spin dynamics in a quantum dot
Ed Barnes
UMCP

The realization of a quantum computer would enable us to solve problems that cannot be solved with even the most powerful supercomputers based on classical technology. Building a quantum computer requires precise control over the state of a system possessing only a few quantum degrees of freedom. In this talk I will focus on a quantum bit represented by a single electron spin trapped in a semiconductor quantum dot. The electron interacts with up to a million nuclear spins in the surrounding material through the hyperfine interaction, leading to a rapid randomization of the electron spin state and a loss of the information it encodes. Understanding how an electron spin evolves in a bath of nuclear spins is an old, challenging problem in theoretical physics known as the Central Spin problem. I will present our recent nonperturbative solution to this problem, which reveals unusual many-body quantum dynamics and offers important lessons on how to reduce the rate of information loss in spin qubits. I will also discuss our new theoretical approach on the dynamic creation of nuclear spin polarization through manipulation of the electron spin, shedding light on recent experimental puzzles.

Location: Physics Bldg., Room 401

## September 11, 2013

### Seminar: Wednesday, Sept.11, 2013 at 3:30 pm

Exploring topological orders with photons
UMCP

Topological properties of physical systems can lead to natural protection against perturbations. Traditionally, this robustness is exemplified by quantized conductance in the electronic systems. In this talk, I demonstrate how similar physics can be observed for photons; specifically, how various quantum spin Hall Hamiltonians can be simulated with linear optical elements using a two dimensional array of coupled optical resonators. I report on the experimental progress towards the implementation of such ideas in silicon-on-insulator technology. Such systems allow the presence of photonic edge states which are insensitive to certain fabrication disorder and paves the way to develop robust integrated optical devices.

Furthermore, the addition of optical non-linearity to the system leads to the possibility of implementing fractional quantum Hall states of photons and anyonic states that have not yet been observed. In particular, I discuss a scheme to engineer three-body interaction, which is absent in nature, to implement some of fractional quantum Hall models in the context of circuit-QED.

Location: Physics Bldg., Room 401

## September 4, 2013

### Seminar: Wednesday, Sept. 4, 2013 at 3:30 pm

Quantum interference of expanding BEC in microgravity
Vincenzo Tamma
Institut fur Quantenphysik, Universitat Ulm

Interferometry with expanding Bose-Einstein condensate in microgravity can be exploited to probe fundamental physics at the border between quantum mechanics and general relativity.

In particular millions of atoms in a BEC can be described by a single macroscopic wave function which o ers itself for quantum interference experiments aimed to test the weak equivalence principle.

In this talk I will describe the physics behind the BEC expansion and interference in microgravity in the time-dependent Thomas-Fermi (TF) regime in generic interferometric con gurations and taking into account rst order corrections in perturbation theory.

In particular, by using an asymmetric Mach-Zehender con guration interference fringes for expanding BEC in microgravity have been recently observed in pioneering experiments within our QUANTUS collaboration

[1]. Such experiments not only represent a perfect test for future experiments in orbit but also gives us an important motivation in pursuing further exciting research based on quantum gravimeters for ground based applications.

[1] 1. H. Muentinga, et al., Phys. Rev. Lett. 110, 093602 (2013) (Viewpoint: M. Arndt, Physics 6, 23 (2013)).

Location: Physics Bldg., Room 401

## August 18, 2013

### Seminar: Wednesday, Sept. 18, 2013 at 3:30 pm

Are thermal and radiative heat equivalent?
Giovanna Scarel

Our Research Group is interested in harvesting infrared radiation from the solar spectrum and other infrared sources. We use a device called bi-junction power generator (bj-PG). This device behaves according to the Seebeck effect when activated by heat: the voltage produced depends linearly on the temperature difference between the two ends of the bj-PG. This behavior is thermoelectric (TEC) power generation. Surprisingly, the linear relationship is lost when infrared radiation activates the bj-PG. This behavior is infrared (IR) power generation. The experimentally-observed difference motivates the question whether thermal energy and radiative energy are equivalent. This talk will illustrate the journey of our Research Group in answering this question. Thermoelectric and IR power generation, and their difference will be described. Some possible hypotheses on the origin of the difference will be proposed: the interaction of heat and radiation with charged carriers, or the onset of chaotic phenomena affecting the oscillation of quasiparticles (polaritons and plasmons) in the bj-PG. Finally, methods to tune the voltage produced by the bj-PG will be briefly discussed. Among them is the use of atomic layer deposited (ALD) oxide films on various types of substrates.

Location: Physics Bldg., Room 401

## May 26, 2013

### Seminar: Wednesday, May 8, 2013 at 3:30 pm

Joseph F. Mulligan Lecture
Neutrinos: History and their Role in Astrophysics
Diana Marcu
UMBC

In 1930 beta decay - the process in which an electron is emitted from a radioactive nucleus - led to a “crisis”, an undetected new particle with zero mass that carries away the missing energy. Wolfgang Pauli suggested a “desperate remedy”: a new particle carrying away the missing energy. Enrico Fermi named the particle “neutrino”, Italian for “little neutral one”. Thus, an intense search for these mysterious particles began. Only in 1956 were neutrinos from a nuclear reactor first observed. In 1964 Ray Davis looked for solar neutrinos, and found fewer than theoretically expected. The solution to this “solar neutrino anomaly” was extreme since it involved reconsidering the Standard Model of particles, including whether or not neutrinos had mass. Now we know that neutrinos have an extremely small mass. They rarely interact with matter which makes them extremely hard to detect. I will present a detailed history of how neutrinos and their properties were discovered, along with the impact these discoveries have had on the physics community. I will also discuss the present work taking place on neutrino detections since they play an important role at the border of particle physics and astrophysics. Lastly, I will highlight some of the instrumentation and discoveries we can expect to see in the near future.

Location: Physics Bldg., Room 401

## April 24, 2013

### Seminar: Wednesday, April 24, 2013 at 3:30 pm

Nature's Accelerators and the Mysterious Origin of Galactic Cosmic Rays
John Hewitt
NASA Goddard

The origin of cosmic rays in our Galaxy is a century-long puzzle. Charged particles with energies up to a few PeV permeate interstellar space. It has long been thought that these cosmic rays are accelerated in the expanding shockwaves of supernovae. Observations with modern gamma-ray telescopes can be used to trace cosmic rays in interstellar space interacting with the ambient gas and low-energy radiation fields, turning our suspicion into certainty.

NASA's Fermi Gamma-ray Space Telescope has detected a variety of both expected and unexpected Galactic GeV gamma-ray sources, including supernova remnants, pulsars and their nebulae, and stellar novae. Importantly, in the two brightest supernova remnants we detect a low-energy pion-decay cutoff, a definitive signature of cosmic ray protons, finally proving that supernova remnants do accelerate Galactic cosmic rays. The growing number of identified supernova remnants by Fermi allows a comparative study of the effects of evolution and environment on acceleration efficiency. These new results promise to resolve the question of origin, and deepen our understanding of the physics of cosmic ray acceleration and transport in the interstellar medium.

Location: Physics Bldg., Room 401

## April 17, 2013

### Seminar: Wednesday, April 17, 2013 at 3:30 pm

Why are Pulsars observable
Constantinos Kalapotharakos
UNIV MARYLAND COLLEGE PARK

Pulsars are extraordinary objects powered by the fast rotation of huge magnetic fields. The resulting electric fields convert continuously part of the Pulsar rotational energy to electromagnetic radiation. At the same time they accelerate particles to energies sufficiently high to produce GeV photons. Their electromagnetic emission is in fact quite complex and ranges from the radio to the multi-GeV regime. It is essential, for the understanding of the Pulsar machine, to know the structure of the magnetosphere around these objects. I will present numerical models of 3D global pulsar magnetospheres covering the entire spectrum between the vacuum retarded dipole and the (ideal) force-free solutions. Finally, I will demonstrate how we exploit these solutions in order to explain the observations and,consequently, to understand the physical mechanisms that take place in pulsar magnetospheres.

Location: Physics Bldg., Room 401

## April 10, 2013

### Seminar: Wednesday, April 10, 2013 at 3:30 pm

Precise measurement and enhanced imaging with entangled .
and correlated photons observation, physics and consequences'
Sasha Sergienko
Boston University

The flexibility and high information capacity of entangled states has been so far demonstrated in several areas of quantum communication and quantum computing. We have recently concentrated on the development of several new techniques for high efficiency optical imaging and ultra-precise measurement in telecommunication and nanotechnology. The use of high dimensional quantum states of light helps to outperform traditional optical approaches in resolution and in the amount of information obtained about the system under evaluation.

We consider the benefit of using the high-dimensional Hilbert space of correlated orbital angular momentum (OAM) states. A typical imaging procedure requires a significant amount of energy to be registered pixel-by-pixel by a CCD camera before one could start recognizing the type of object that has registered. The new approach [1] enables one to recognize objects much faster and with less required energy (more information is obtained per detected photon).

The nonlinear process of spontaneous parametric down conversion (SPDC) has often been used as an effective source of optical entanglement, and is capable of generating entangled photon pairs that span higher order OAM states. The correlated (joint) detection of two photons in the OAM basis using coincidence counting reveals that the scattering occurs mainly between OAM states of orbital orders that have symmetry elements resonating with geometric structures present in the object.

Such a fast object recognition technology could become useful in situations where the presence or absence of objects with particular symmetry features must be quickly identified in the field of view. For example, some living cells, drug molecules, or viruses have particular rotational symmetries, so that their IEEE and LEOS.

Location: Physics Bldg., Room 401

## March 13, 2013

### Seminar: Wednesday, March 13, 2012 at 3:30 pm

The Microwave Response to Ice-Phase Precipitation
Dr. Benjamin Johnson
JCET

Present methods of passive and active microwave remote sensing of precipitation have a key problem: the uncertainty of the physical and associated radiative properties of ice- and mixed-phase hydrometeors. In nature, ice particles manifest themselves in an extraordinarily diverse variety of sizes, shapes, and habits -- ranging from simple crystals such as needles or plates to complex aggregates and rimed particles. As these complex particles fall into air that is warmer than freezing, they begin to melt. While the general thermodynamic and fluid mechanics aspects of melting snowflakes is fairly well understood, the complex interaction with incident microwave radiation remains largely unexplored. This area of research is attempting to address one of the largest sources of uncertainly in physically-based precipitation retrieval algorithms using microwave observations (e.g., radar / radiometer).

In this presentation, I will talk about simulated microphysical properties of a variety of ice- and mixed-phase precipitation particles, with particular emphasis on simulating the melting morphology of ice-phase particles, such as snowflake aggregates. There are three distinct parts to this research:

(1) Physical modeling, i.e., growing and simulating snowflake shapes, sizes, etc., in a way that is consistent with observations.
(2) Electromagnetic wave scattering -- how an incident plane wave (microwave -> submillimeter wavelengths) interacts with individual snow particles, and the general sensitivity of that interaction to the various physical properties.
(3) Sensitivity of observable quantities, such as radar reflectivity and passive microwave brightness temperatures to variations in the physical properties of the snow clouds being observed.

I will describe my efforts towards the above problem, and highlight the work of our group as we head towards a snowfall retrieval algorithm for the upcoming Global Precipitation Measurement mission (GPM), set to launch in 2014.

Location: Physics Bldg., Room 401

## December 5, 2012

### Seminar: Wednesday, Dec. 5, 2012 at 3:30 pm

"Spectral Imaging of Cultural Heritage Texts"
Dr. William Christens-Barry
Equipoise Imaging, LLC,

Techniques of spectral imaging that were originally developed for remote sensing and biological imaging have more recently been applied in studies of ancient textual materials of cultural and historical interest. Palimpsests, texts in which the original content has been intentionally erased or removed so that the writing substrate could be reused, are of particularly intense interest to scholars and the public. While manuscript leaves share much in common with traditional subjects of spectral imaging and subsequent processing, they exhibit many unique and problematic features that confound collaborative imaging projects. Extensive damage further limits the legibility of text, while constraints imposed by the location and setting often complicate efforts to capture and analyze images.

A self-organized group of scientists and scholars, including the speaker, have tapped and modified spectral imaging techniques to investigate numerous manuscripts and textual materials of interest, including: the Archimedes Palimpsest containing important methods written by Archimedes; the innovative Waldseemuller Map, which first established the name "America"; the Dead Sea Scrolls, whose condition and content is currently under study in Jerusalem; the very large collection of ancient palimpsests in the library of St. Catherine's Monastery of the Sinai; textual and cartographic treasures held at the Library of Congress, including drafts of the Declaration of Independence and the Gettysburg Address; David Livingstone's journals from East Africa; and numerous others.

The speaker will describe techniques used for image capture and analysis of palimpsests and other faint or damaged texts, and will discuss findings and current directions.

Location: Physics Bldg., Room 401

## November 28, 2012

### Seminar: Wednesday, Nov. 28, 2012 at 3:30 pm

The DARPA Shredder Challenge
Don Engel
UMBC

In November 2011, the Defense Advanced Research Projects Agency (DARPA) challenged civilians to come up with novel ways to reconstruct shredded documents. This talk will examine the strategy our team of two physicists developed, enabling us to place second out of about 9,000 teams. Our approach involved signal/noise analysis, computational linguistics, and innovative user interface design. DARPA has open competitions regularly and future competitions may be of interest to UMBC students, faculty, and staff.

Location: Physics Bldg., Room 401

## November 14, 2012

### Seminar: Wednesday, Nov. 14, 2012 at 3:30 pm

Signposts of Planets:
What can images of dusty disks tell us about extrasolar planets?
Marc Kuchner
NASA

Images of dusty debris disks around nearby stars from the Hubble Space Telescope and ALMA show warps, rings, and other spectacular patterns. Some of these patterns are probably caused by known extrasolar planets or undetected extrasolar planets hidden in the dust. So dynamical models of these images can sometimes allow us to constrain the properties of the planets we see and find planets that would otherwise be hidden.

But adding a bit of gas to our dynamical models of debris disks-- too little gas to detect--seems to change the story. Small amounts of gas lead to new dynamical instabilities that may mimic the narrow eccentric rings and other structures planets would create in a gas-free disk. Can we still use disk patterns to find hidden exoplanets?

Location: Physics Bldg., Room 401

## November 7, 2012

### Seminar: Wednesday, Nov. 7, 2012 at 3:30 pm

Multiple Exciton Generation in Lead-Salt Nanostructures
Paul D. Cunningham
U.S. Naval Research Laboratory

In a typical solar cell, only part of the energy from absorbed light is converted to electricity. Each absorbed photon produces an electron-hole pair, i.e. exciton, which ultimately cools till it possesses only the semiconductor bandgap energy. The excess energy that is typically wasted can be harnessed by exploiting multiple exciton generation, whereby the excess energy is used to excite additional excitons. This process was recently shown to be more efficient in nanocrystals than in the bulk. We have discovered that multiple exciton generation is significantly enhanced in quasi-one-dimensional nanorods compared to nanocrystals. Devices exploiting this enhancement have the potential to show enhanced photovoltaic efficiencies. I will discuss our transient absorption measurements of multiple exciton generation in PbSe nanostructures. Complications arising from the quasi-one dimensionality of these nanostructures will be explained. Multiple exciton dynamics and lifetimes will also be discussed, as well as promising future directions.

Location: Physics Bldg., Room 401

## October 31, 2012

### Seminar: Wednesday, Oct. 31, 2012 at 3:30 pm

"Violin Acoustics, Bowing, and Construction"
Joseph Sedlak

This talk will begin with a brief description of the violin's early history, evolution, and main structural characteristics. Next, we will look in more detail at two topics concerning the instrument's acoustics. The first is Helmholtz's solution for the waveform and spectrum of the bowed string, which we will compare with the plucked string. The second is a simple mathematical model describing the coupling of the air cavity resonance with the sound radiated from the violin body. This resonance is important for the richness of sound when playing the lowest notes. Finally, a slide-show will be presented showing the step-by-step construction of a violin.

Location: Physics Bldg., Room 401

## October 24, 2012

### Seminar: Wednesday, Oct. 24, 2012 at 3:30 pm

"The Higgs Boson"
University of Maryland, College Park

Last July, experimentalists reported on the observation of a new particle seen in proton proton experiments at CERN. This new particle might be the first observation of a fundamental scalar, and is very likely to be the long sought after Higgs boson. I will try to give an overview of the experiment and the impact of the measurement.

Location: Physics Bldg., Room 401

## October 17, 2012

### Seminar: Wednesday, Oct. 17, 2012 at 3:30 pm

Dust and volcanoes: Natural aerosols in human-induced climate change
Dr. Lorraine Remer
UMBC Joint Center for Earth Systems Technology

Aerosols are tiny suspended liquid and solid particles found in the atmosphere. These particles degrade air quality and are active in the climate system. Over the past 20 years, man-made aerosols, those particles emitted hand-in-hand with greenhouse gases, have been the focus of intense scrutiny by the aerosol-climate community.

Let’s not forget natural aerosols. The bulk of aerosol particles are natural, not man-made, and these natural aerosols are just as important to the climate system. Natural aerosols travel long distances and affect exceptionally pristine areas of the Earth where small changes in the aerosol environment can produce relatively large responses. Most importantly the processes producing natural aerosols such as dust and volcanic emissions are not constant. Therefore, there is no background aerosol environment from which to quantify the perturbation made by human activity and man-made particles. How do we calculate the aerosol forcing imposed by human activity if we do not know what the aerosol effect was before people became involved?

Location: Physics Bldg., Room 401

## October 10, 2012

### Seminar: Wednesday, Oct. 10, 2012 at 3:30 pm

From Random Walks to Brownian Motion to Diffusion and Entropy:
Statistical Principles in Introductory Physics
Mark Reeves
Department of Physics George Washington University

Introductory biology courses often begin with an exploration of the qualities of water that are important to living systems. One idea that is often not addressed is dominant contribution of the entropy of water molecules in driving biologically important processes towards equilibrium. Compounding the problem, many introductory physics courses have deemphasized entropy, almost to the point of eliminating it entirely. In contrast, we are teaching this concept in our introductory physics and biology classes, and are collaborating to bring the pedagogical approaches of Scale-Up Physics teaching into biology instruction. From a content point of view, we strive to bring quantitative modeling into the biology class and life into the physics course. To this end, students are introduced to prediction and random walk by first considering coin flips. We move on to a Java-based simulation of the random walk problem that mimics the diffusion of molecules in water. The simulations are complemented by lab experiments in which Brownian motion and dye diffusion in agarose gels are observed and quantitatively measured using ImageJ software. These measurements link the microscopic model of Brownian motion to its macroscopic realization in diffusion. Furthermore, this curricular unit, which is presented in both the introductory physics and biology classes, leads to the important conclusion that lipid bilayers and folded proteins are formed because of the entropic release of water molecules from the surfaces of hydrophobic moieties. Formative and summative assessments of the students’ learning provide perspectives to the challenges of our joint curricular reforms.

Location: Physics Bldg., Room 401

## October 3, 2012

### Seminar: Wednesday, Oct. 3, 2012 at 3:30 pm

Genius Machines: The Future of Artificial Intelligence,
Virtual reality, Robotics, and Biomechanics
Dr. Catherine Asaro
UMBC

Disruptive technologies are those innovations that create new markets or replace old ones. Such a technology applies a new set of scientific, social, or economic conditions that ultimately, and often unexpectedly, displaces an existing market. The car replaced the horse and buggy; CDs replaced LP records and cassette tapes; online social networking such as email and Facebook now dominate social interactions once confined to mailing hardcopy letters. The areas of artificial intelligence, virtual reality, robotics, and biomechanics are exploding in their expansion and will continue to disrupt current technologies over the next decades, changing how we live, do business, and even what it means to be human. Catherine Asaro is a member of SIGMA, a think tank of futurists that consults for the US government and private industry on such developments. In January of 2012, Asaro was one of four futurists, along with Arlan Andrews, Kathleen Goonan, and Mark O'Green, who were hosted as invited speakers at the Global Competitiveness Forum in Saudi Arabia, an annual gathering of several thousand of the world’s political, financial, academic and intellectual leaders. During their panel, “Disruptive Technologies,” Asaro spoke on the innovations of AI, VR, robotics, and biomechanics. The seminar presented by Asaro at UMBC is an expansion of her talk that she has adapted for seminars at venues such as Georgetown University, the Philadelphia Science Fiction Society, and the Naval Observatory in Washington DC.

Location: Physics Bldg., Room 401

## September 26, 2012

### Seminar: Wednesday, Sept. 26, 2012 at 3:30 pm

"From STEM To Stern(e)
Actually it was the other way around"
Dr. Susan Hoban
UMBC Joint Center for Earth Systems Technology

As an astronomer, I typically would be classified as a "Scientist," and of course, Technology and Engineering are at the heart of how scientists collect our data. We all agree that Mathematics is the language of science. It is the inextricable nature of these four subjects that is at the heart of the STEM education movement. The predicted need for scientists and engineers in America, and the corresponding lack of interest in these subjects demonstrated by American students, lends a sense of urgency to the movement. This talk will provide a brief summary of one astronomer's journey from the telescope to STEM teacher education and highlight some areas where university STEM faculty can contribute their expertise to the inspiration of the next generation of American scientists and engineers.

Location: Physics Bldg., Room 401

## September 19, 2012

### Seminar: Wednesday, Sept. 19, 2012 at 3:30 pm

Warm Events at Summit, Greenland During 2012 Relative to an
Evolving 25 Year Ice Sheet Temperature Record
Christopher A. Shuman
JCET

An evolving temperature record from the Greenland Summit, at approximately 3216 m in elevation, has documented unusual periods of near and above freezing air temperatures especially in July 2012. Since August 2005, data has been collected from well-calibrated and actively-ventilated temperature sensors at a NOAA-ESRL climate observatory. Comparison of these data from a nominal 2 m height above the ice sheet surface over the past seven summers reveals several periods of unusual warmth at the highest elevations of the ice sheet during 2012. Field observations from station personnel indicate slush formed during the period of greatest warmth and an ~2 cm thick ice crust has been preserved in the snow stratigraphy. The warm temperatures at Summit were independently assessed and mapped across Greenland using a combination of SSMIS passive microwave, Oceansat scatterometer, and MODIS infrared data. http://www.nasa.gov/topics/ earth/features/greenland-melt.html

Detailed analysis of the available data indicates that temperatures rose to or above freezing for almost 6.5 hours on July 11 at Summit Station. A maximum air temperature of 1 degree C was recorded repeatedly in the 1-minute averages during this period. NOAA’s data also indicated brief periods at or above zero on July 12th and 29th as well. These anomalously warm air-temperature periods can now be compared and contrasted with equivalent-quality data from earlier records (automatic weather stations began operating in May 1987 during the GISP2 project) and used to calibrate indications of warm surface temperatures derived from satellite sensors.

Location: Physics Bldg., Room 401

## September 12, 2012

### Seminar: Wednesday, Sept. 12, 2012 at 3:30 pm

Entropy, information and compressive
sensing in the quantum domain
John Howell
University of Rochester

It may seem somewhat surprising that information is governed by uncertainty. Put another way, if we know what someone is going to tell us, then there would be no need for listening. The uncertainty of that communication, entropy, is a measure of the information gained. In this presentation, I will discuss some basic concepts of entropy along with some of our recent experiments on studies of entanglement entropy and quantum imaging using compressive sensing. Lastly, I will present results on recent studies of quantum noise on compressive signals. These experiments will be couched in the ideas of entropy and the information gained as a function of the number of photons. Compressive sensing has a wide range of possible application including imaging through obscurants, hyperspectral imaging, and high resolution single pixel imaging in otherwise difficult regions of the spectrum to image. These concepts are crucial in understanding compressive sensing as a sensing paradigm. Based on these ideas, I will present details of a novel compressive sensing Lidar system.

Location: Physics Bldg., Room 401

## September 7, 2012

### Seminar: Wednesday, Nov. 7, 2012 at 3:30 pm

Multiple Exciton Generation in Lead-Salt Nanostructures
Paul D. Cunningham
U.S. Naval Research Laboratory

In a typical solar cell, only part of the energy from absorbed light is converted to electricity. Each absorbed photon produces an electron-hole pair, i.e. exciton, which ultimately cools till it possesses only the semiconductor bandgap energy. The excess energy that is typically wasted can be harnessed by exploiting multiple exciton generation, whereby the excess energy is used to excite additional excitons. This process was recently shown to be more efficient in nanocrystals than in the bulk. We have discovered that multiple exciton generation is significantly enhanced in quasi-one-dimensional nanorods compared to nanocrystals. Devices exploiting this enhancement have the potential to show enhanced photovoltaic efficiencies. I will discuss our transient absorption measurements of multiple exciton generation in PbSe nanostructures. Complications arising from the quasi-one dimensionality of these nanostructures will be explained. Multiple exciton dynamics and lifetimes will also be discussed, as well as promising future directions.

Location: Physics Bldg., Room 401

## May 9, 2012

### Seminar: Wednesday, May 9, 2012 at 3:30 pm

Joseph F. Mulligan Lecture
The Life and Work of Nikola Tesla
Erika Nesvold
UMBC

Nikola Tesla was a man of contradictions. He specialized in dramatic public demonstrations of his work, but led a largely solitary and very private personal life. He was a prolific inventor, an intuitive engineer, and a brilliant physicist, but was tormented by mental illness in the later years of his life. Despite personal setbacks and professional conflicts, Tesla was a pioneer in the field of electrical engineering and invented many of the devices we use today, including the alternating current induction motor, the remote control, and radio communication. He did early work with x-rays, robotics, and fluorescent lights. For this year’s Mulligan Lecture, I will present a brief overview of Nikola Tesla’s biography and discuss some of his most important discoveries and inventions.

Location: Physics Bldg., Room 401

## May 2, 2012

### Seminar: Wednesday, May 2, 2012 at 3:30 pm

Quantum Knots and Quantum Braids
Professor Samuel J. Lomonaco
UMBC

In this talk, we show how to reconstruct knot theory in such a way that it is intimately related to quantum physics. In particular, we give a blueprint for creating a quantum system that has the dynamic behavior of a closed knotted piece of rope moving in 3-space. Within this framework, knot invariants become physically measurable quantum observables, knot moves become unitary transformations, with knot dynamics determined by Schroedinger's equation. The same approach can also be applied to the theory of braids.

Toward the end of the talk, we briefly look at possible applications to superfluid vortices and to topological quantum computing in optical lattices.

Location: Physics Bldg., Room 401

## April 18, 2012

### Seminar: Wednesday, Apr 18, 2012 at 3:30 pm

Collective, virtual and nonlocal effects in
light emission by atomic ensembles
Dr. Anatoly Svidzinskyl
Texas A & M University

Collective nature of light emission by atomic ensembles yields fascinating effects such as superradiance and radiation trapping even at the single-photon level. Photon emission is influenced by virtual transitions which lead to collective Lamb shift. For large samples light emission is also affected by retardation due to the finite value of the speed of light. I will discuss collective emission of a single photon from a cloud of N atoms and show exact analytical solutions of this many-atom quantum mechanical problem for superradiant and trapped states. I will discuss how virtual and nonlocal effects modify evolution of the atomic system yielding peculiar temporal features and new kind of cavity QED. I will also show that fully quantum mechanical treatment of spontaneous emission of weakly excited atomic ensembles is analogous to emission of N classical harmonic oscillators.

Location: Physics Bldg., Room 401

## April 11, 2012

### Seminar: Wednesday, Apr 11, 2012 at 3:30 pm

Single Photons and Nonclassical Light in Tight
Binding Lattice Models
Dr. G. S. Agarwal
Department of Physics
Oklahoma State University

It is now recognized that arrays of classical waveguides are suitable elements for realizing a number of condensed matter and quantum optical effects like Bloch oscillations, Anderson localization, Hong-Ou-Mandel two photon interference, entanglement, quantum walks. Since various interactions can be controlled by design of the array such structures are especially useful to study physical effects in a region previously unrealized. This talk would focus on some of these developments with special emphasis on quantum fields in such structures.

Location: Physics Bldg., Room 401

## April 4, 2012

### Seminar: Wednesday, Apr 4, 2012 at 3:30 pm

Earth Science Research at NASA Langley Research Center
Dr. Bruce Doddridge
Science Directorate, NASA Langley Research Center

The Science Directorate at NASA Langley Research Center (LaRC) emphasizes an end-to-end approach where technology development, mission development, calibration and validation activities, and data analyses are carried out with the goal of deriving scientific information from space-based observations for decision support. This work includes scientific leadership in space-based missions; technology development; laboratory, surface and sub-orbital (aircraft) measurements; research and analyses projects; atmospheric science data stewardship; applied sciences research in developing decision support tools; and education and outreach activities, all in support of NASA’s Science Mission Directorate (SMD). The LaRC Science Directorate strengths include Earth observation, interdisciplinary research, Earth system modeling, data processing systems, and advanced technology development, with an overall focus on atmospheric science and climate. The Directorate also provides significant support to the SMD Applied Sciences program, particularly in areas of air quality management, energy forecasting, and aviation safety. This presentation will provide an introduction to the LaRC Science Directorate vision, goals, organizational structure and ongoing research and present key examples of basic and applied research, as well as data center and education/outreach activities. More information on the LaRC Science Directorate can be found at URL: http://science.larc.nasa.gov/.

Location: Physics Bldg., Room 401

## March 14, 2012

### Seminar: Wednesday, Mar 14, 2012 at 3:30 pm

The Heliophysics Quest (for Data and Answers)
Dr. Jan Merka
NASA Goddard Space Flight Center

The word Heliophysics is used by NASA for the study of Sun's heliosphere and the objects that interact with it, for example planetary atmospheres and magnetospheres, solar corona, or the interstellar medium. Heliophysics combines several disciplines, e.g. plasma physics, space physics and solar physics, when uncovering mysteries of the Sun's heliosphere and predicting space weather. In-situ measurements are the primary source of new discoveries and theory validation but they are sparse in both time and space. In my talk, I will discuss main research limitations imposed by existing data from space missions and illustrate them on selected topics, e.g. the Earth's bow shock wave, solar wind origin and space weather forecasting.

Location: Physics Bldg., Room 401

## March 7, 2012

### Seminar: Wednesday, Mar 7, 2012 at 3:30 pm

Control of Electron Transport in Molecular Bridges: Insight and Design by ab-initio Modeling
Dr. Barry Dunietz
Assistant Professor of Chemistry, University of Michigan

Molecular bridges may constitute the fundamental building blocks in nanotechnology. My group studies properties of nano-scale molecular bridges and interfaces that can improve thermal and solar energy conversion schemes. We have developed and employed state of the art ab-initio methods for modeling electron transport and transfer. In this talk, I will describe our modeling of transport switching properties in molecular devices. Several related leading edge experiments achieving molecular scale conductance are considered. Our studies provide both insight into the mechanisms underlying the electronic-transport switching activity and predictions useful for designing novel schemes to enhance the switching functionality. I will also discuss briefly our treatment of the challenging time-dependent aspects of electron transport by our newly-developed computational approach. We highlight conditions at the electronic-structure level for a molecular bridge to function optimally as a photo-induced electron pump. This functionality is fundamental to the development of greatly improved solar cell technology.

Location: Physics Bldg., Room 401

## January 26, 2012

### Seminar: Thursday, Jan 26, 2012 at 3:30 pm

Materials Design For Thermoelectric Applications
Massachusetts Institute of Technology

Thermoelectrics can directly convert heat into electricity and therefore have applications in waste heat recovery. These solid-state devices can also be integrated directly on chips and actively cool down hot spots of high-speed devices. In this talk, I will discuss modeling of electron and phonon transport inside thermoelectric legs to identify fundamental length scales such as carrier mean free path and momentum and energy relaxation lengths. Knowing the fundamental length scales, we can design nanostructured materials with enhanced hermoelectric figure of merit (Z=σS2/ K). I will discuss strategies to reduce the thermal conductivity via introducing interfaces and rattling atoms to scatter phonons, to increase the electrical conductivity by means of modulation doping and to improve the Seebeck coefficient by energy filtering and introducing sharp features in the density of states. In each strategy the challenge is to improve one property without deteriorating the other properties. We have fabricated and characterized bulk samples as well as superlattices, which were designed based on different strategies. The obtained experimental results are in agreement with theoretical predictions but there is still a lot of room for improvement in terms of materials designing. Finally, I will address the issue of heat management. By using a Monte Carlo algorithm, we have identified the energy relaxation length and the location of Peltier cooling/heating at heterointerfaces. We have also explored the nonlinearity of heat current when the applied electric field is strong and electrons are out of equilibrium with phonons. The nonlinearity of thermoelectric transport coefficients could be used to enhance the device performance significantly especially at low temperatures.

Location: Physics Bldg., Room 401

## December 7, 2011

### Seminar: Wednesday, Dec 7, 2011 at 3:30 pm

Metrology of and Metrology using Single Photon Detectors.
Dr. Alan Migall
NIST

Given the tiny energies involved, the generation and detection of one photon at a time is an extraordinary feat. Even with this difficulty, the development of single-photon technology is rapidly advancing. Because this technology involves dealing directly with individual quantum states, it opens up many areas that push the conventional limits, and thus is a strong motivation for this development. One big driver has been the field of quantum information which offers the potential of nothing less than revolutionizing our abilities to calculate here-to-fore intractable calculational problems, to test fundamental principles of the nature, to provide communication where absolute security is based on fundamental physical principles, and to make measurements beyond what are fundamental limits in the classical world. With all this potential, it is no wonder there is such interest in improving single-photon devices.

I will review single photon detector and source technology and some applications. One area of particular interest to us at NIST is their use in metrology. I will present techniques that use this technology for measurements that are not possible any other way and to, in turn, use the techniques made possible by these devices, to characterize the devices themselves. I will also discuss their use in a fundamental test of nature.

Location: Physics Bldg., Room 401

## November 30, 2011

### Seminar: Wednesday, Nov 30, 2011 at 3:30 pm

The Role of Physics in Industry
Research and Development Updated with Cold Fusion Discussion
Michael M. Fitelson
Chief Scientist, Micro-Systems Enablers
Northrop Grumman Electronic Systems

Today’s High Technology companies, particularly those involved in defense related research, are utilizing advances associated with physics research to an increasing extent. Many of the devices and technologies employed in advanced sensors and computing are leveraging breakthroughs in physics and related disciplines. These breakthroughs encompass quantum optics, quantum information, nano-science, solid state physics, superconductivity, materials science and many other disciplines. One of the more interesting recent developments are the significant advances being made in explaining low energy Nuclear Fusion and the associated experimental results. I will be summarizing some of the leading theoretical and experimental results in the area of “Cold Fusion”.

Location: Physics Bldg., Room 401

## November 16, 2011

### Seminar: Wednesday, Nov 16, 2011 at 3:30 pm

Towards High-Speed Optical Quantum Memories.
Dr. Virginia Lorenz
University of Delaware

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computing and quantum communication. The majority of quantum memories to date have operated with bandwidths that limit data rates to megahertz. I will present results demonstrating the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium vapor. The novel memory interaction takes place through a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field.

Location: Physics Bldg., Room 401

## November 2, 2011

### Seminar: Wednesday, Nov 2, 2011 at 3:30 pm

Gradient Magnetometry in Arbitrary Magnetic Fields.
Dr. Francesco Narducci
Naval Air Systems

Field-able scalar magnetometers have now reached impressive sensitivities on the order of0.1pT Hz  with laboratory versions promising a few orders of magnitude improvement. However, at this level, practical applications at low frequencies, e.g. anti-submarine warfare (ASW), are limited by environmental noise and not fundamental sensor noise. A standard technique to circumvent this limitation is to employ two magnetometers separated by a given distance (Δz) and subtract the measurements (ΔB), resulting in a so called gradient measurement (ΔB / Δz) that can cancel out common noise. Recently, I proposed a method to measure magnetic field gradients using an atom interferometer1. This method has the unique advantage of being an intrinsic gradiometer with a very short baseline. At the very heart of this device is an atom beam-splitter that can create super-positions of magnetic sensitive transitions using Raman pulses, in contrast with other existing atom interferometer sensors that use magnetically insensitive transitions. In this talk, I’ll discuss our work to measure Raman spectra in the presence of an arbitrary magnetic field. I’ll present the results (and pitfalls!) of our multi-level theoretical model and present the results of our recent measurements.

Location: Physics Bldg., Room 401

## October 26, 2011

### Seminar: Wednesday, Oct. 26, 2011 at 3:30pm

FAST‐CARS
Dr. George Welch
Texas A&M University

The vibrational structure of a molecule can be a useful signature or "fingerprint" of a substance. Inelastic scattering of light by molecules is an important tool for probing molecular vibrational structure. Thus, inelastic scattering of light from molecules can be a useful method for detecting particular molecular species. This effect is called Raman scattering after Chandrasekhara Venkata Raman, who received the 1930 Nobel Prize in Physics for its discovery.

The Raman effect is typically very weak, and coherence is a very powerful way to produce larger signals. Multiple photons can be used to excite and scatter from molecular vibrations, resulting in a signal that is sensitive to the same vibrations as in Raman scattering, but where the fields emitted from all molecules can add coherently, producing a very large signal that is quadratic in the number of scattering molecules. This effect is called coherent anti-Stokes Raman scattering, or CARS.

CARS is a third-order nonlinear optical process and may be masked by other nonlinear optical processes, such as four-wave mixing. Also, because of its large quadratic dependence, CARS may be unsuitable for detection of small amounts of a substance in the presence of a large background o other molecules.

There are many approaches for resolving the problems of CARS while preserving its high signal level. One method is to use femtosecond lasers with temporally shaped pulses to exploit the vibrational structure of molecules. We refer to these tricks as "FAST-CARS" for "femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman scattering".

I will introduce all these concepts, and present many results from various experiments we have performed over the last few years. I will also show how optical interference can be used for broad-band heterodyne detection of FAST-CARS signals, giving rise to interesting new effects.

Location: Physics Bldg., Room 401

## October 19, 2011

### Seminar: Wednesday, Oct 19, 2011 at 3:30 pm

New frontiers with ultra-cold molecules.
Paul S. Julienne
Joint Quantum Institute
NIST and the University of Maryland

Cold atoms have proved to be a highly successful workhorse for research in experimental and theoretical physics for over two decades now, touching on diverse areas such as atomic and molecular physics, precision measurement, condensed matter physics, and quantum information and computing. Recent developments in producing cold and ultra-cold molecules promise to open up many new aspects of studies with ultra-cold matter with temperature in the nanokelvin range. Molecules are much harder to cool and trap than atoms, because of their much more complex internal energy level structure of vibration and rotation. On the other hand, molecules can have relatively large dipole moments and consequently new ways of controlling and interacting them not available with atoms. This talk will review progress in making and using cold molecules, emphasizing the assembly of an ultra-cold molecule in its ground state from two already ultra-cold atoms. The quantum dynamics that determines the chemical reactions of two such molecules with nearly zero kinetic energy turns out in some cases to have a remarkably simple universal character, subject to experimental control using the bosonic or fermionic nature of the molecules or using electric fields to orient the molecules in various kinds of optical traps or lattices.

Location: Physics Bldg., Room 401

## October 12, 2011

### Seminar: Wednesday, Oct. 12, 2011 at 3:30pm

Beyond the Rayleigh limit in optical lithography
Dr. M. Suhail Zubairy
Texas A&M University
Institute for Quantum Studies and Department of Physics and Astronomy

It is well known that the classical schemes for microscopy and lithography are restricted by the diffraction limit. The precision with which a pattern could be etched in interference lithography is limited by the wavelength of the light. In recent years, a number of schemes have been proposed via quantum interferometry to improve the resolution. Some of these schemes are based on quantum entanglement and multiphoton processes. In this talk we shall discuss several schemes for 'quantum' lithography using classical light.

Location: Physics Bldg., Room 401

## October 5, 2011

### Seminar: Wednesday, Oct. 5, 2011 at 3:30pm

Pictures, Models, Approximations and Reality:
Phase transitions and our understanding of the physical world
Dr. Michael Fisher
UMCP, Institute for Physical Science and Technology

Ways in which theoretical physicists look at the real world and try to understand it will be explored. Through the medium of a domino game on a large checkerboard, the rapier-like specific heat of a superfluid helium, and the visual effects seen when a liquid and its vapor merge to form a supercritical fluid, the talk will address the question: "What is the role of the theorist in modern science?" The power of analogy based on physical pictures and simple models will be illustrated in the context of ideas concerning phase transitions and critical phenomena in fluids and magnets, in alloys and plasmas. The significance of the concepts of shape and singularity in the search for universality will be explained; the role of symmetry and dimensionality in our insights will be touched upon.

Location: Physics Bldg., Room 401

## September 28, 2011

### Seminar: Wednesday, Sept 28, 2011 at 3:30 pm

Polarization Entanglement, Special Reference Frames, and Advanced Waves
Dr. Robert French
Oakland Community College, Highland Lakes Campus, Waterford, MI.

This talk sketches a program towards giving a physically realist model of the photon in terms of properties of the electromagnetic field. It is both shown how to rework traditional wave and particle concepts so as to have a unified concept and how parallel electromagnetic fields can be associated with each charged particle. An account of both light propagation and of interactions with matter is sketched. A suggestion, utilizing advanced waves, is made as to how the account may be able to explain EPR correlations in the case of polarization entanglement. A possible empirical test, using a pockels cell with a fast driver is also discussed.

Location: Physics Bldg., Room 401

## September 21, 2011

### Seminar: Wednesday, Sep 21, 2011 at 3:30pm

Single Photon Frequency Up-Conversion and its Applications in Quantum Information Research
Xiao Tang
Information Technology Laboratory, National Institute of Standards and Technology

In this talk, we will present the recent efforts at NIST on the single photon frequency upconversion technique and its applications in quantum information research.

Silicon-based single photon detectors (Si-APDs) are high efficiency and low noise detectors for visible and near visible wavelengths, but do not work at the near infrared (NIR) wavelength range where the important telecom bands (mainly 1310 and 1550 nm) are. The performance of InGaAs based detectors for NIR photons needs to be improved. Upconversion detectors provide a good alternative, in which the NIR photons are converted to visible first and then detected by a Si-APD.

The single photon upconversion technique is based on the sum frequency generation (SFG) in nonlinear optics. A few years ago, NIST adapted the optical frequency upconversion technique to develop single photon detectors for the illusive NIR photons and used the detectors in a fiber-based high speed quantum key distribution (QKD) system. Since then, the devices have been significantly improved. In the recent years, the team’s effort is focused on the applications of the up-conversion technique in quantum information research. We will briefly introduce the applications in the research areas including the QKD system, the ultra sensitive NIR spectrometer, the entangled photon source, quantum dots, and higher-order NIR photon temporal correlations. A multiple wavelength pump technique for increasing system date rates beyond the initial limitation will be mentioned. We will also point out some potential applications of the upconversion technique in future quantum information systems.

Location: Physics Bldg., Room 401

## September 14, 2011

### Seminar: Wednesday, Sep.14, 2011 at 3:30pm

Imaging Infrared and Terahertz radiation using non-linear optics
Dr. Matthew DeCamp
University of Delaware, Dept. of Physics and Astronomy

Molecular vibrations are resonant with electromagnetic radiation in the infrared (IR) portion of the electromagnetic spectrum (0-100THz) making vibrational spectroscopy a very powerful tool for identifying complex molecular compounds, ranging from proteins to explosives. However, the photon energy of IR radiation is often too small to detect using standard room temperature semi-conductor devices. In addition, far-IR radiation (0-10THz) overlaps with the radiation of a blackbody at room temperature, making spectral separation from the thermal background difficult. For this reason, current IR detection technology often utilizes cryogenically cooled detectors, which in addition to being very expensive are not easily portable, making field and/or clinical applications very difficult. In this talk, I will be discussing new techniques for detecting infrared radiation using standard semi-conductor technology by utilizing non-linear optical methods. This new technology may lead to low-cost, portable detection tools for research, clinical, and security applications.

Location: Physics Bldg., Room 401

## May 11, 2011

### Seminar: Wednesday, May 11, 2011 at 3:30pm

Joseph F. Mulligan Lecture
The Life of Willard Gibbs: An American Scientist
Paul Corbitt
UMBC

Willard Gibbs is one of the least known, but most important scientists in the nineteenth century. At this time America was a scientific backwater compared to the research universities of Europe. Working alone at Yale, Gibbs made major contributions to the fields of thermodynamics, vector analysis, and statistical mechanics. This lecture will explore the life of Willard Gibbs and his contributions to science. Even, today, the methods devised by Willard Gibbs are still in use.

Location: Physics Bldg., Room 401

## May 4, 2011

### Seminar: Wednesday, May 4, 2011 at 3:30pm

Teaching Introductory Physics in Biological Context
Dr. Catherine Crouch
Swarthmore College

How can introductory physics best serve future life scientists and premedical students? Physics is an increasingly important foundation for today’s life sciences and medicine, as recognized by recent reports from professional societies such as the National Academy of Sciences, the Howard Hughes Medical Institute, and the American Association of Medical Colleges. However, the content and skills identified by these reports and other practitioners as most important for these fields are often not taught, or underemphasized, in traditional algebra-based college physics courses. Furthermore, such courses rarely make substantive connections between the physics taught and the life sciences. I propose (in general agreement with many innovators in this area) that an exemplary course for these students focuses on the most relevant physics content, which does not always match the traditional introductory physics syllabus; anchors that physics in rich biological contexts; and explicitly seeks to develop sophisticated scientific and problem-solving skills, both qualitative and quantitative. I will present the syllabus and key features of the course I offer at Swarthmore College, describe the process of developing that course in collaboration with my biology colleagues as well as many others, and identify directions for further development and research related to such courses.

Location: Physics Bldg., Room 401

## April 27, 2011

### Seminar: Wednesday, April 27, 2011 at 3:30pm

Decoherence of Polarization Entanglement in Optical Fibers
Dr. Misha Brodsky
AT&T Labs

Quantum mechanics permits the existence of unique correlations, or entanglement, between individual particles. For a pair of entangled photons, this means that performing a measurement on one photon appears to affect the state of the other. The ability of entangled particles to act in concert is preserved even when they are separated by large distances and serves as a resource for numerous applications. For example, distributing entangled photon pairs over fiber-optic cables enables secure communication between two remote parties or could offer the possibility of interconnecting quantum computers. The vast transparency band of the installed global fiber-optic network, consisting of over a Gigameter of optical fiber cables, presents a particularly attractive opportunity for this task. The bond between entangled photons is, however, very fragile and could be lost. How far could one send entangled photons while still maintaining the connection between them?

We investigate, theoretically and experimentally, how inherent defects and miniscule imperfections in fiber-optic cables degrade entanglement between two photons transmitted over fibers. We show that the loss of entanglement could be either gradual or surprisingly abrupt. We describe relation between local and non-local effects and suggest a novel non-local way to compensate for adverse effects that occur during propagation in fibers. The richness of the observed phenomena suggests that fiber-based entanglement distribution systems could serve as natural laboratories for studying entanglement decoherence.

A brief introduction to the topic of the talk is available on the front page of AT&T Labs website: www.research.att.com

Location: Physics Bldg., Room 401

## April 13, 2011

### Seminar: Wednesday, April 13, 2011 at 3:30pm

The Theoretical Modeling of Chemical Reactions
Dr. Millard Alexander
Department of Chemistry and Biochemistry and Institute for Physical Science and Technology
UMCP

A long-standing goal of physical chemistry is the understanding of how chemical reactions occur and the prediction of cross sections and thermal rate constants. Within the Born-Oppenheimer approximation this requires, firstly, the ability to determine the potential energy of the few-atom system as a function of geometry, and, consequently, the ability to solve the equations of motion for the rearrangement of the nuclei.

The F+H2→FH+H reaction is one of the most-studied elementary chemical reactions, because increasingly more-sophisticated experimental and theoretical techniques have been brought to bear on this system. Because the F atom has an unfilled 2p shell, more than one electronic state will contribute to this reaction.

We shall present a simple introduction to concepts which underly both the determination of the FHF potential energy function and then, subsequently, the quantum solution of the equations of motion for transfer of the H atom. We will then discuss our recent work on this, and related, hydrogen exchange reactions.

Location: Physics Bldg., Room 401

## April 6, 2011

### Seminar: Wednesday, April 6, 2011 at 3:30pm

Solitons, Self-Induced Transparency, and Modelocking in Quantum Cascade Lasers
Dr. Curtis Menyuk
UMBC/CSEE

Standard semiconductor lasers operate in a limited wavelength range, below about 4 microns. Quantum cascade lasers (QCLs) that operate in the mid-IR and far-IR have important applications to medicine, environmental sensing, and national security. While short pulse lasers (~100 fs) are available for standard semiconductor lasers, that is not the case for QCLs. Standard passive modelocking is hard to do in QCLs because of their long coherence times and short gain recovery times. We propose a fundamentally different approach, based on the self-induced-transparency (SIT) effect, that turns these weaknesses into strengths. Solitons, modelocking, and SIT are all reviewed at the beginning of the talk.

Location: Physics Bldg., Room 401

## March 30, 2011

### Seminar: Wednesday, March 30, 2011 at 3:30pm

Imaging Mechanical Properties of Tissue and Biomaterials
Dr. Giuliano Scarcelli
Harvard Medical School

The mechanical properties of biological tissues and biomaterials are closely related to their functional abilities, and thus play significant roles in many areas of medicine. For example, hardened coronary arteries by calcification can cause heart problems; changes in the elasticity of crystalline lens and cornea are central in the development of cataracts, presbyopia and corneal ectasia; biomechanical compatibility is crucial in tissue engineering procedures; and, the stiffness of extra-cellular matrix influences drug delivery and cell motility. However, measuring such biomechanical properties remains a significant challenge due to a dearth of non-invasive technologies. To address this need, we are developing a novel imaging technology, Brillouin confocal microscopy, to probe the biomechanical properties of tissue in vivo without contact, quantitatively, and with high spatial resolution. The first areas of biomedical applications we are exploring are in ophthalmology where Brillouin microscopy may enable measuring changes in corneal and lens elasticity by aging, by the progression of disease, or in response to treatment and drugs; and in tissue engineering for the optimization of procedures by mapping and monitoring in situ and in real time the micromechanical properties of host and implanted tissue.

Location: Physics Bldg., Room 401

## March 16, 2011

### Seminar: Wednesday, March 16, 2011 at 3:30pm

The Role of Medical Physics in Modern Neuroscience
Dr. Peter Kochunov
UT Health Science Center

Discoveries in neuro-biological science have been increasingly led by two forces: neuroimaging and genomics. A modern neuroscience research teams combine expertise from seemingly diverse areas of science including physics, biology, physiology, genetics and statistics. A recent graduate from a medical physics program is expected to have a polymathic background that prepared him/her to seamlessly integrate within the neuroscience community contributing knowledge and expertise in physics and physiology of underlying imaging signal. I will discuss a curriculum of modern medical physics doctorate training program that prepares students for a research carrier in neuroscience. This program builds upon the robust knowledge of physics and mathematics that new coming students are bringing with them with training in imaging technology, neuroscience, statistics and experimental design. The graduates of this program are working in diverse area from clinical science to academic research.

Location: Physics Bldg., Room 401

## February 23, 2011

### Seminar: Wednesday, February 23, 2011 at 3:30pm

Solar Forced Thermal Tides in the Atmosphere
Dr. Jian Du-Caines
University of Cambridge, UK

While gravitationally forced lunar tides generate significant amplitude periodic oscillations in the global oceans the corollary is not true for the atmosphere. In fact the lunar tides in the atmosphere are quite small in comparison to the thermally forced solar tides. These atmospheric tides are forced by the periodic absorption of solar radiation in the infra-red by water vapor in the troposphere and the ultraviolet by ozone in the stratosphere. Conserving energy and propagating vertically through the atmosphere these waves can reach significant amplitudes of 30-50 m/s in the horizontal wind field and 10-20K in the temperature field of the mesosphere before breaking or dissipating. This provides a mechanism for the redistribution of energy throughout the atmosphere.

In this talk I will provide a brief overview of the solar forced atmospheric tides, results from current modelling efforts and discuss recent observations from space and ground-based instruments. One of the potential generation mechanisms for the atmospheric tides – non-linear interactions between waves and the transport effect of atmospheric waves in the mesosphere are also briefly discussed.

Location: Physics Bldg., Room 401

## February 9, 2011

### Seminar: Wednesday, February 9, 2011 at 3:30pm

Remote Sensing of Global Cloud Properties from MODIS
Dr. Zhibo Zhang
GEST

Clouds cover about 2/3 of Earth’s surface. They play a crucial role in regulating Earth’s energy budget. Clouds reflect part of the sunlight back to space (i.e., albedo effect), which reduces the solar energy available to Earth’s surface. At the same time, clouds also act like greenhouse gases—they block the emission of heat to space and inhibit the ability of the planet to release its absorbed solar energy (i.e., greenhouse effect). The net radiative effect of clouds on the climate depends on the global distribution of clouds and their optical and microphysical properties. Satellite-based, long-term, global cloud observation is the key to understanding the role of clouds in the current climate system and how clouds will change with global warming.

In this talk, I will provide an overview of the remote sensing of global cloud properties using a NASA satellite sensor—MODIS (Moderate Resolution Imaging Spectroradiometer). In the first part, I will explain the fundamental physics behind the retrieval of two key cloud parameters, cloud optical thickness and cloud particle effective radius, from MODIS cloud reflection measurements. In the second part of this talk, I will present our recent studies on several key issues in MODIS cloud retrieval algorithm. Topics will include: i) an assessment of the uncertainties in MODIS ice cloud products due to the complex and variable nature of ice crystals; ii) an investigation of the influence of cloud vertical structure on cloud particle effective radius retrieval; and iii) a study on the 3-D radiative transfer effect on MODIS cloud particle effective radius retrieval.

Location: Physics Bldg., Room 401

## February 2, 2011

### Seminar: Wednesday, February 2, 2011 at 3:30pm

Clouds, Aerosols, and 3D Radiative Processes
Dr. Tamás Várnai
JCET

Some of the largest uncertainties in understanding human impacts on climate arise from difficulties in quantifying the effects of atmospheric aerosols on solar radiation and clouds. A better understanding of these effects will require accurate calculations of solar heating and accurate measurements of aerosol and cloud properties. The three-dimensional (3D) nature of radiative processes can create challenges such as accommodating computational demands and specifying necessary inputs—and as a result, both climate simulations and satellite data interpretation methods use one-dimensional (1D) radiation models that treat each atmospheric column separately, without considering their interactions.

The presentation will first discuss solar heating calculations for a multiyear dataset of clouds observed at three Department of Energy sites. These calculations indicate that horizontal radiative interactions cause 1D radiation models to underestimate average solar heating by a few W/m2. The talk will next present CALIOP and MODIS satellite data in examining atmospheric particles and 3D radiative processes near clouds. The results indicate that clouds are surrounded by a wide transition zone of increased particle size, enhanced light scattering, and significant 3D radiative interactions. The talk will also outline some possibilities for considering 3D radiative interactions in dynamical simulations and satellite remote sensing.

Location: Physics Bldg., Room 401

## December 8, 2010

### Seminar: Wednesday, December 8, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Patterns of mineral dust aerosols from North Africa over the Mid Atlantic Ocean
Drs. Y. Ben-Ami, I. Koren, O. Altaratz and Y, Lehahn
Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, Rehovot, Israel, Department of Geophysics and Planetary Sciences, Tel Aviv University, Tel Aviv, Israel.

While fluxes of North African dust travelling over the Atlantic have significant influence on climate processes, biogeochemical cycles and human lives, there are still many open questions such as:

- Where exactly the dust is originating from and where does it sink?
- What is the dust flux and how well is it quantified?
- What is the frequency of emission of the North African dust sources?

Inhomogeneous spatial, vertical and temporal distribution of dust aerosol in the atmosphere and the location of dust sources in remote regions harden our ability to understand and quantify its exact role in climatic processes.

Focusing on the inter-annual patterns of dust loading and height we are trying to answer some of the open questions by studying the spatial and vertical distribution of dust over the ocean and by following dust plumes from source to sink.

In this talk I will discuss inter-annual patterns of North African dust height and loading over the Mid Atlantic Ocean and dust sink over the Amazon forest.

## December 1, 2010

### Seminar: Wednesday, December 1, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Improving students' understanding through research
Dr. Chandralekha Singh
University of Pittsburgh
The goal of physics education research is to help close the gap between teaching and learning. I will discuss, drawing from my own research as examples, how the lessons learned from physics education research can be applied to all STEM disciplines. I will discuss my research that emphasizes the importance of understanding the relevant prior knowledge of students and designing instruction such that it builds on students' existing knowledge. Our research suggests that the difficulty of a problem not only depends on its inherent complexity but on the familiarity and intuition one has developed about it. Our research also suggests that students should be taught effective problem solving strategies explicitly while they acquire content knowledge because everyday life does not prepare students for the disciplined approach to problem solving required to solve complex problems in the STEM disciplines. Finally, I will discuss why instructional approach should value and encourage students to be actively engaged and work with each other and provide examples of how such collaboration gives students an opportunity to be able to solve problems that each student alone may not be able to solve.

## November 10, 2010

### Seminar: Wednesday, November 10, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Metal-Enhanced Fluorescence: A paradigm shift in how we think and use Fluorescence Spectroscopy today
Dr. Chris D. Geddes
Institute of Fluorescence, University of Maryland Baltimore County, Columbus Center
In recent years the IoF has described the favorable interactions and outcomes of both plasmon supporting particles (Ag, Au, Cu, Zn, Ni, Cr) and substrates with electronically excited states. These favorable effects have included significantly enhanced fluorescence emission from singlet states, S1 and S21, as well as enhanced phosphorescence yields from triplet, T1, states (MEP) 2. In addition, we have observed and described plasmon enhanced chemiluminescence intensities (MEC), as well as highly directional emission. As a result of enhanced triplet yields, we have also observed both enhanced singlet oxygen and superoxide anion yields3. These favorable influences on the photophysical properties of close proximity excited states to plasmon supporting substrates / particles has led to wealth of biochemical applications, such as the high sensitivity and ultra fast detection of proteins4, DNA5, RNA and ultra bright and photostable metal-enhanced fluorescence based particles for downstream cellular imaging applications. In addition, there are a lot downstream applications of MEP such as in photodynamic therapy by surface plasmon controlled single oxygen generation. Current thinking, describes Metal-Enhanced Fluorescence as the near-field coupling of electronic excited states to surface plasmons (a surface mirror dipole), the particle subsequently radiating the photophysical characteristics of the coupled excited state in the far-field, remarkably, even vibronic structure. In this presentation, we communicate our recent findings for metal-fluorophore interactions and our current thinking and progress towards developing a unified metal-fluorophore description.

## November 5, 2010

### Seminar: Friday, November 5, 2010 at 10:00 a.m

"Thermal emission from gamma-ray bursts"
Dr. Asaf Pe'er
CFA/ITC
I will discuss recent evidence for a thermal emission component that accompanies the non-thermal emission during the prompt phase of GRBs. I argue that this component is naturally explained by considering emission from the photosphere, taking into account high latitude emission from optically thick relativistically expanding plasma. The thermal flux is expected to decay at late times as F_BB ~ t^{-2}, and the observed temperature as T ~ t^{-\alpha}, with \alpha ~ 1/2 - 2/3. I will discuss some of the latest theoretical progress, including the theory of multicolor black body emission from relativistically expanding plasma. These theoretical predictions are in very good agreement with the observations. Finally, I will discuss three implications of this interpretation: (a) The relation between thermal emission and high energy, non-thermal spectra observed by FERMI, with particular emphasis on the peculiar GRB090902B. (b) The use of thermal emission to directly measure the Lorentz factor of the flow and the initial radius of the jet. (c) I argue that lack of detection of thermal component can be used to constrain the composition of GRB jets.

No Seminar

## October 27, 2010

### Seminar: Wednesday, October 27, 2010 at 3:30 p.m. Coffee 3:15 p.m.

"Hunting for Gamma-ray Binaries"
Dr. Robin Corbet
UMBC/CRESST
The X-ray sky (beyond the Sun) is dominated by emission from luminous binary star systems containing neutron stars and black holes. However, at higher gamma-ray energies (GeV to TeV) very few of these binaries are so far known to be sources.

The Fermi satellite, launched two years ago, carries the LAT, a much more sensitive detector than any previous gamma-ray astronomy spacecraft. I will present the results of LAT observations of the exotic binary systems that do produce gamma-ray emission, and discuss what we can learn from these sources. I will also describe our hunt for new members of this class, including the techniques we are developing to maximize our signal-to-noise in this search.

## October 20, 2010

### Seminar: Wednesday, October 20, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Parallel Computing for Long-Time Simulations of Calcium Waves in a Heart Cell
Dr. Matthias Gobbert
UMBC/Math
Parallel computing can fascilitate both solving larger problems and solving them faster than possible on a serial computer. This has the potential for new discoveries in many subject areas and highlights the opportunities arising from using state-of-the-art computational hardware and software. The numerical simulation for a model of calcium waves in a heart cell serves as example for the power of parallel computing to enable the faster solution of larger problems. Using this prototypical example, I will explain the ideas and considerations in the creation of the UMBC High Performance Computing Facility (www.umbc.edu/hpcf), the community-based, interdisciplinary core facility for scientific computing and research on parallel algorithms at UMBC. There will be plenty of time throughout the talk to discuss with the audience the hardware, software, structure, and user support in HPCF, and how researchers at UMBC can participate.

## October 13, 2010

### Seminar: Wednesday, October 13, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Compact Silica Microcavities for Sensing, Communications, and Information Processing
Dr. Lee Oesterling
Battelle
Dr. Lee Oesterling is the leader of a research team at Battelle that has been working on the development of high Q, small mode volume optical microcavities that can be produced in large arrays on silicon chips to support a wide variety of defense and commercial applications. Applications for this technology include filters, multiplexers, low threshold lasers, all optically controlled switches, buffers, chem/bio sensors, and optical microphones. In this seminar, Dr. Oesterling will discuss (1) the fabrication techniques to create high Q microcavities, (2) the integration of these microcavities into optical circuits to create sensors, lasers, and photon routers, and (3) research and developmental work that is currently being performed in this field at Battelle and leading universities.

Brief Bio: Dr. Lee Oesterling has 10 years of experience with the development of optical and photonic technologies, which includes work at JDS Uniphase and Battelle. He received his Ph.D. in Chemical Physics from The Ohio State University in 2009.

## October 6, 2010

### Seminar: Wednesday, October 6, 2010 at 3:30 p.m. Coffee 3:15 p.m.

New results on high energy cosmic ray electrons observed with Fermi LAT and their implications on the origin of cosmic rays
Dr. Alexis Moiseev
CRESST/UMCP
The Large Area Telescope on-board the Fermi Gamma-Ray Space Telescope has collected more than 10 million cosmic ray electrons with energy above 7 GeV since its science operation on orbit. High energy electrons rapidly lose their energy by synchrotron radiation on Galactic magnetic fields and by inverse Compton scattering on the interstellar radiation field. The typical distance over which a 1 TeV electron loses half its total energy is estimated to be 300-400 pc.This makes them a unique tool for probing nearby Galactic space. Observed spectrum has a harder spectral index than was previously reported and suggests the presence of nearby sources of high energy electrons. One of viable candidates are nearby pulsars, possibly some of recently discovered by Fermi. At the same time the dark matter origin of such sources cannot be ruled out. I will also report our current upper limits on cosmic ray electrons anisotropy which helps to set constraints on their local sources.

## September 29, 2010

### Seminar: Wednesday, September 29, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Ultra-high Resolution Functional Spectral-Domain Optical Coherence Tomography for Real-Time 4-D Imaging
Dr. Jin U. Kang
JHU
Optical coherence tomography has become a high-resolution, high-speed, and versatile tomographic imaging modality along with technological developments in high-performance optical sensors: CCD and CMOS cameras, high-quality, and low-coherent light source, such as ultrafast laser or superluminescent emission diodes (SLED). Due to superior imaging speed and higher sensitivity, Fourier domain OCT (FD OCT) is gradually supplanting time domain OCT (TD OCT) in most applications. We have been developing Spectral domain-based FDOCT (SD OCT), one subcategory of FD OCT for microsurgical applications. Surgeons require both physical and optical access to tight surgical space in order to perform microsurgery on delicate tissues such as retina. Our research effort is directed at providing microsurgeons with OCT based real-time high-resolution 4-D visualization that will enhance their ability to achieve surgical objectives, diminish surgical risk, and improve outcomes. Compared to other image-guiding modalities such as MRI, CT, and ultrasound, OCT is more compact and portable, allowing for integration with surgical tools. In this talk I will discuss challenges in achieving high resolution (~1 micron), high-speed (10 frames/s) functional 4-D SDOCT along with various hardware and signal processing methods we have developed to overcome the challenges.

## September 22, 2010

### Seminar: Wednesday, September 22, 2010 at 3:30 p.m. Coffee 3:15 p.m.

“The Beginnings of Everything: from the Big Bang to Planets”
Dr. John Mather
NASA/GSFC
The history of the universe in a nutshell, from the Big Bang to now, and on to the future – John Mather will tell the story of how we got here, how the Universe began with a Big Bang, how it could have produced an Earth where sentient beings can live, and how those beings are discovering their history. Mather was Project Scientist for NASA’s Cosmic Background Explorer (COBE) satellite, which measured the spectrum (the color) of the heat radiation from the Big Bang, discovered hot and cold spots in that radiation, and hunted for the first objects that formed after the great explosion. He will explain Einstein’s biggest mistake, show how Edwin Hubble discovered the expansion of the universe, how the COBE mission was built, and how the COBE data support the Big Bang theory. He will also show NASA’s plans for the next great telescope in space, the James Webb Space Telescope. It will look even farther back in time than the Hubble Space Telescope, and will look inside the dusty cocoons where stars and planets are being born today. It is capable of examining Earth-like planets around other stars using the transit technique, and future missions may find signs of life. Currently planned for launch in 2014, the JWST may lead to another Nobel prize for some lucky observer.

## September 15, 2010

### Seminar: Wednesday, September 15, 2010 at 3:30 p.m. Coffee at 3:15 pm

Gravitational-Wave Astronomy
Dr. Bernard Kelly
UMBC/CRESST
"Einstein's General Theory of Relativity is our best classical description of gravity, and informs modern astronomy and astrophysics at all scales: stellar, galactic, and cosmological. Among its surprising predictions is the existence of gravitational waves -- ripples in space-time that carry energy and momentum away from strongly interacting gravitating sources. In my talk, I will give an overview of the properties of this radiation, recent breakthroughs in computational physics allowing us to calculate the waveforms from galactic mergers, and the prospect of direct observation with interferometric detectors such as LIGO and LISA."

## September 8, 2010

### Seminar: Wednesday, September 8, 2010 at 3:30 p.m. Coffee 3:15 p.m.

Using molecular simulations to understand allosteric inhibition of the Hepatitis C viral polymerase
Dr. Ian Thorpe
UMBC/Chemistry Department
The general term "allostery" is often used to refer to processes which allow an event at one location in a macromolecule (such as a protein) to alter the properties of another location in that macromolecule. Allostery is important because it allows macromolecules such as proteins to sense and respond to their environment, providing a way to regulate their functional characteristics. Thus, understanding the physical principles which underlie allostery can be of significant utility in understanding how proteins and other macromolecules function. Allostery can occur because distant regions of a macromolecule are structurally connected, potentially allowing information to be communicated over long distances within the molecule. Allosteric inhibitors of the RNA-dependent RNA polymerase (RdRp) found in Hepatitis C Virus (HCV) have been identified which bind to the enzyme distant from the site of catalysis. The manner in which these ligands inhibit the enzyme is not well understood. I will describe efforts in my research group to understand the link between ligand binding and allosteric inhibition in RdRp by using molecular simulation methods to describe the structure and dynamics of this enzyme. The knowledge gained as a result of this study can improve our understanding of allosteric regulation of enzyme function and the manner in which the process may be modulated by small molecules. In addition, these studies may foster the development of new treatments for HCV infections.

## September 1, 2010

### Seminar: Wednesday, September 1, 2010 at 3:30 p.m.

Will Alien Life Resemble Us (and How Could We possible Know)? Astrobiology, Evolution and the Amino Acids
Dr. Stephen Freeland
University of Hawaii
A fundamental challenge for astrobiology is to establish the relative contributions of chance versus predictability in the origin and evolution of life on our own planet. Thus, for example, all Earth-life creates metabolism from an interacting network of protein molecules that catalyze various biochemical reactions. Furthermore, early during evolution it had arrived at a standard set of 20 amino acid building-blocks with which to build each of these proteins. We now have good reason to think that many of these amino acids are formed in significant quantities throughout the galaxy - but so are many others - so would alien life be like us, and how could we possibly know?

## May 5, 2010

### Seminar: Wednesday, May 5, 2010 at 3:30 pm

The Invention and 50th Anniversary of the Laser
Sheng Liu
UMBC
2010 is recognized as the 50th anniversary of laser after its first demonstration in 1960 by Theodore Maiman at Hughes Research Lab. From DVD players to eye surgery, the laser is one of the greatest inventions of the 20th century—one that has revolutionized the way we live.

The laser was not discovered from a single breakthrough by one individual, but from a series of developments incorporating hundreds of great minds’ efforts, starting from Albert Einstein’s paper of “On the quantum theory of radiation” in 1917. Then Richard Tolman, Rudolf Ladenburg, and V.A Fabrikant brought up the ideas of negative absorption, stimulated emission, and population inversion, respectively. However, population inversion was never achieved experimentally until 1954 when Charles H. Townes and James P. Gordon made the first MASER (Microwave Amplification by Stimulated Emission of Radiation). Immediately after that, scientists started wondering how to make a MASER working at optical frequencies.

Starting from 1957, the competition of inventing an optical MASER began heating up. Teams at half a dozen laboratories set out, each hoping to be the first to succeed. The term “laser” was first introduced to the public in Gordon Gould’s 1959 conference paper. In 1960, Theodore Maiman was the first one to a demonstrate laser in ruby, which by the way was considered as a dark horse in this laser race. Over the next 30 years, Gordon Gould fought with the United States Patent and Trademark Office to obtain patents for the laser and related technologies, and was finally issued forty-eight patents, with optical pumping, collisional pumping, and applications patents being the most important.

The competition of developing new types of lasers did not end there. A brief review of important laser breakthroughs over the last 50 years will be presented.

## April 28, 2010

### Seminar: Wednesday, April 28, 2010 at 3:30 pm

Optical Switches and Memories Using the Zeno Effect and Two-Photon Absorption
Dr. Bryan C. Jacobs
John Hopkins University
The quantum Zeno effect can be used to implement quantum logic operations using single photons. It is shown here that similar effects can occur in a resonant system subject to nonlinear dissipation, and that these effects can be used to implement classical logic and memory devices. Current progress toward the realization of these types of devices will be discussed.

## April 21, 2010

### Seminar, Wednesday, April 21, 2010 at 3:30 pm

Guided wave terahertz characterization of vibrational fingerprint lines in molecular solids
Dr. Joseph Melinger
Naval Research Laboratory

One of the outstanding problems of terahertz (THz) spectroscopy is the measurement of the underlying vibrational spectrum of a molecular solid, where individual vibrational transitions are often merged into broad absorption features by line broadening processes. In this talk I describe how this problem can be addressed using the technique of waveguide terahertz time-domain spectroscopy (THz-TDS). In this technique an analyte molecular film is deposited on one of the inner surfaces of a single-mode metal parallel plate waveguide (PPWG) with a 50 micron gap between the plates. The vibrational spectrum of the film is then measured in a sensitive manner using sub-picosecond THz pulses confined within the PPWG over a relatively long pathlength of a few centimeters. I will show how waveguide THz-TDS (applied at cryogenic temperatures) has proven useful in resolving the underlying vibrational fingerprint spectrum of a variety of explosives solids in the frequency range between 0.2 THz – 4.0 THz, with linewidths of individual transitions as narrow as 7 GHz (0.21 cm 1), and line frequencies determined to a precision of 1 GHz (0.03 cm-1). I’ll also discuss how these highly resolved spectra are currently being modeled using solid state computational methods.

## April 15, 2010

### Seminar: Thursday, April 15, 2010 at 4:00 pm

Hubble's Diverse Universe
Dr. Jarita Holbrook
University of Arizona

Hubble's Diverse Universe is a 40 minute documentary focused on nine African American and Hispanic American astronomers and astrophysicists. They discuss their research and their experiences being minority astronomers. They share their personal stories and give advice about how to succeed in the sciences. The film was conceived and produced by Jarita Holbrook and Romeel Dave' of the University of Arizona. Holbrook will be available for Q & A after the screening. The film has been presented at many institutions during the 2009 International Year of Astronomy. Holbrook who is the fourth African American woman to earn a Ph.D. in astrophysics in the USA appears in the film.

Location: Physics Bldg., room 401

## April 14, 2010

### Seminar: Wednesday, April 14, 2010 at 3:30 pm

Possibilities and challenges in using satellite aerosol data for surface air quality studies
Dr. Mian Chin
NASA Goddard

Surface concentration of aerosol particles, also known as particulate matter (PM), is a key component determining air quality, especially with small articles (diameter less than 2.5 µm, or PM2.5) which are known to cause respiratory diseases. Local emissions and long-range transport can both contribute to the PM2.5 levels at the surface. In the past decade, satellites remote sensing measurements of global aerosol distributions have become available, continuously providing large-scale “chemical weather” pictures, which can be potentially useful for estimating surface PM2.5 levels. In this presentation, we discuss the possibilities and challenges in using satellite data for air quality applications, in particular, we will address the following questions: (1) What is the relationship between column aerosol optical depth (AOD), which is the quantity measured by satellite, and surface PM2.5 concentrations? (2) How and why this relationship varies with time and location? (3) What is the optimal approach to use model and satellite data for air quality studies? We will present case studies over the U.S. using the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model, satellite data from MODIS and MISR, and surface PM2.5 concentration data from the U.S. EPA and IMPROVE monitoring networks. We will also explore the use of the lidar data from CALIPSO.

Location: Physics Bldg., room 401

## April 7, 2010

### Seminar: Wednesday, April 7, 2010 at 3:30 pm

The Fermi Large Area Telescope as a GeV gamma-ray all-sky monitor
Dr. Elizabeth Hays
NASA Goddard

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has been surveying the sky since August 2008. The LAT detects gamma rays from ~20 MeV to >300 GeV. The field of view is large (~2.4 sr) and provides all-sky coverage every 3 hours. The LAT data provide a rich multiwavelength resource. They also allow searches for new activity in the notoriously variable gamma-ray sky. LAT flare advocates monitor the data daily to track sources of interest and to watch for new gamma-ray outbursts. I will discuss highlights of the transient gamma-ray sky as viewed by the LAT with an emphasis on results for objects in the Galaxy.

Location: Physics Bldg., room 420

## March 31, 2010

### Seminar: Wednesday, March 31, 2010 at 3:30 pm

Lessons on galactic nuclear activity from cosmic voids
Dr. Anca Constantin

Galaxies in the most underdense regions of the universe, the voids, must have different evolutionary histories than those in denser regions, the walls. This is mainly because of the expected huge difference in their rate of interactions, which is believed to affect the nuclear activity, and thus the growth process of galaxies and their central black holes. It is therefore important to determine the degree to which the void galactic nuclear activity compares to its counterpart in denser environments. I will present the results of a comparison of void and wall systems based on a variety of physical properties and near neighbor statistics, together with spatial clustering calculations, which provide empirical evidence that both small and large scale environment influence the interplay between nuclear supermassive black hole accretion and surrounding stellar activity, and thus the optically dominant power source. I will present these ideas in the context of a potential sequence in the lives of galaxies that suggests a transformation from star-forming via supermassive black hole accretion to quiescence, and show support for this scenario with new Chandra X-ray measurements.

Physics Bldg., room 401

## March 24, 2010

TBA

### Seminar: Wednesday, March 24, 2010

Teaching Introductory Physics for the 21st Century: Matter & Interactions
Dr. Mark Haugan
Purdue University

Purdue University, North Carolina State University and the Georgia Institute of Technology are now using the new Matter & Interactions [1] curriculum in their calculus-based introductory physics courses for science and engineering majors. In this presentation I will discuss our reasons for concluding that this curriculum was right for our students, how we manage its use in courses taken by several thousand students each year and what our assessment data reveal about our students’ learning.

In part, the answer to the first of these questions is the way in which the M&I curriculum helps students to structure and to use the physics they learn. It lays a foundation of learning more advanced material by engaging students in physics’ central enterprise of systematically using a small number of fundamental principles to explain or predict a broad range of phenomena by constructing models of realistic physical systems. Such models must often address matter’s atomic structure, which brings accessible 20th century physics into our introductory courses and makes the courses more coherent by unifying topics like mechanics and thermal physics, like electrostatics and DC circuits and others.

Physics Bldg., room 401

## March 17, 2010

### Seminar: Wednesday, March 17, 2010 at 3:30 pm

No Seminar - Spring Break

## March 10, 2010

### Seminar: Wednesday, March 10, 2010 at 3:30 pm

Aerosol Remote Sensing From Space – What We’ve Learned, Where We’re Heading
Dr. Ralph Kahn
NASA Goddard

The MISR and MODIS instruments aboard the NASA Earth Observing System's Terra Satellite have been collecting data containing information about the state of Earth's atmosphere and surface for almost ten years. Among the retrieved quantities are amount and type of wildfire smoke, desert dust, volcanic effluent, urban and industrial pollution particles, and other aerosols. However, the broad scientific challenges of understanding aerosol impacts on climate and health place different, and very exacting demands on our measurement capabilities. And these data sets, though much more advanced in many respects than previous aerosol data records, are imperfect. In this presentation, I will summarize current understanding of MISR and MODIS aerosol product strengths and limitations, discuss how they relate to the bigger aerosol science questions we must address, and give my view of what we will need to do to progress further.

## March 3, 2010

### Seminar: Wednesday, March 03, 2010 at 3:30 pm

Magnetars: The Most Magnetic Stellar Objects in the Universe.
Dr. Fotis Gavrill
UMBC/CSST

Neutron stars are the compact cores of collapsed massive stars. They contain as much mass as our Sun but with radii of the size of the capital beltway. Pulsars are rapidly rotating neutron stars with magnetic fields on the order of 10^11 times that of our Sun. There exists a small population of pulsars with magnetic fields three orders of magnitude greater than canonical pulsars -- the aptly named magnetars. These fields are so high that exotic effects due to quantum electrodynamics cannot be neglected when modeling their emission. The enormous magnetic fields of magnetars power bright X-ray pulsations, clusters of bright X-ray bursts, as well as gamma-ray flares that are energetic enough to disturb the Earth's Ionosphere. I will review how our X-ray observations have cemented the magnetar model for a an enigmatic group of pulsars, for which the magnetar interpretation was controversial for several decades. I will also present recent results on a missing-link between canonical pulsars and magnetars.

Physics Bldg., room 401

## February 24, 2010

### Seminar: Wednesday, February 24, 2010 at 3:30 pm

“Lorentz-Lorenz under attack: atomic nano-riot against uniformity”
Dr. Alex Kaplan
John Hopkins ECE Department

A crystal, i. e. an ordered lattice of atoms or molecules is normally assumed to be almost uniformly excited by an incident light on a sub-wavelength scale. An interatomic interaction produces then a uniform local field (different from that of incident laser) at each atom as well. This is a major assumption in the Lorentz-Lorenz theory of interaction of light with dense matter.

We show that at certain critical conditions on the atomic density and dipole strength, a previously unexpected phenomenon emerges: the interacting atoms break the uniformity of interaction, and in a violent switch to a strong non-uniformity, their excitation and local field form nanoscale strata with a spatial period much shorter than that of laser wavelength, thus changing the entire paradigm of light-matter interaction. The most interesting effects can be observed for relatively small 1D-arrays or 2D-lattices if the laser is almost resonant to an atomic quantum transition. The effects include huge local field enhancement at size-related resonances at the laser frequencies near the atomic line, so that the strata are readily controlled by laser tuning. A striking feature is that for the shortest strata, the nearest atomic dipoles counter-oscillate, which is reminiscent of anti-ferromagnetism of magnetic dipoles in Ising model.

Our results also show the formation of "hybrid" modes, whereby at certain atoms in the lattice, their excitation and local field get completely suppressed. Due to those modes, at certain "magic" array size or configuration, the absorption of light at the exact resonant is almost fully canceled. The simplest magic 2D-shape is a six-point star made of 13 atoms (with one atom at the center). The resonant amplitude enhancement enables optical hysteresis and bistability at low light intensities; the tiniest known optical switch can be made of just two atoms. The new phenomenon promises a potential for nanoscale non-conductive computer elements, sensors for detecting bio-molecules, etc.

Physics Bldg., room 401

## February 17, 2010

### Seminar: Wednesday, February 17, 2010 at 3:30 pm

"A different view: polarization signaling in mantis shrimp"
Dr. Tom Cronin
UMBC

" While color and brightness patterns are widely used in animal communications, some animals have evolutionarily discovered the use of polarized-light patterns for signaling. In this talk, I will discuss the use of polarization signals in a group of marine crustaceans, the stomatopods (commonly called mantis shrimps). These animals have unusual biological polarizers, some based on principles that are poorly understood and are not used in any artificial polarization systems. Even more unusual is their use of circularly polarized light for communication. Mantis shrimps are the only animals known to sense the handedness of circularly polarized light, and use this sensory modality in their signaling behavior."

Physics Bldg., room 401

## February 3, 2010

### Seminar: Wednesday, February 3, 2010 at 3:30 pm

Biomass burning emissions from fire remote sensing
Dr. Charles Ichoku

Knowledge of the emission source strengths of different (particulate and gaseous) atmospheric constituents is one of the principal ingredients upon which the modeling and forecasting of their distribution and impacts depend. Biomass burning emissions are complex and difficult to quantify. However, satellite remote sensing is providing us tremendous opportunities to measure the fire radiative energy (FRE) release rate or power (FRP), which has a direct relationship with the rates of biomass consumption and emissions of major smoke constituents. In this presentation, we will show how the remote-sensing measurement of FRP is facilitating the development of various scientific studies relating to biomass burning, particularly the quantitative characterization of their emission rates and the implications of this unique capability for improving our understanding of smoke impacts on air quality, weather, and climate.

Physics Bldg., room 401

No Seminar

## December 14, 2009

### Seminar: Monday, December 14, 2009 at 2:00 p.m.

Precision Quantum Metrology and Optical Atomic Clock
Jun Ye
JILA, National Institute of Standards and Technology and University of Colorado

Quantum state engineering of ultracold matter and precise control of optical fields have allowed accurate measurement of light-matter interactions for applications ranging from precision tests of fundamental physics to quantum information science. State-of-the-art lasers now maintain optical phase coherence over one second. Optical frequency combs distribute this phase coherence across the entire visible and infrared parts of the electromagnetic spectrum, leading to direct visualization and measurement of light ripples. A new generation of light-based atomic clocks has been developed, with ultracold Sr atoms confined in an engineered optical lattice offering unprecedented coherence times for light-matter interactions. The uncertainty of this new clock has reached 1 x 10-16, a factor of 4 below the current best Cs primary standard. These developments represent a remarkable convergence of ultracold matter, laser technology, and ultrafast science. Further improvements are tantalizing, where quantum correlations and measurement protocols will enable explorations of the next frontiers in precision metrology and quantum information science.

Physics Bldg., room 401

## December 9, 2009

### Seminar: Wednesday, December 9, 2009 at 3:30 p.m.

Cloud and Aerosol Properties from IR and Lidar
Dr. Anne Garnier
LATMOS France

Location: Physics Bldg., room 401

## December 2, 2009

### Seminar: Wednesday, December 2, 2009 at 3:30 p.m.

Pulsars in the Fermi Era
Dr. Ozlem Celik
University of Maryland Baltimore County (CRESST)

Until the launch of Fermi Gamma-ray Space Telescope (Fermi) on 11 June 2008, only a few pulsars were known to have pulsed emission in the gamma-ray energy band compared to thousands of pulsars emitting in the radio band. With the excellent sensitivity of Large Area Telescope (LAT) on Fermi in the energy regime most relevant to the pulsar research, many new gamma-ray pulsars have been discovered after a year of sky-survey observations, increasing the number of known gamma-ray pulsars by nearly a factor of ten. Along with the detection of many known radio pulsars, some pulsars that had not seen in any other wavelengths before have been discovered through their gamma-ray pulsations alone. Gamma-ray pulsations have also been detected from a number of millisecond pulsars for the first time, confirming them as gamma-ray sources. Detailed studies of the pulse profiles and spectra of these pulsars improved our understanding of pulsed emission and allowed us to test the predictions of the current high-energy pulsed emission models. In this presentation, I will summarize the pulsar results from Fermi-LAT and our current understanding of the pulsars.

Location: Physics Bldg., room 401

## November 25, 2009

### Seminar: Wednesday, November 25, 2009

No Seminar - Thanksgiving Holiday

## November 18, 2009

### Seminar: Wednesday, November 18, 2009 at 3:30 p.m.

History and Optics of 3D Movies
Dr. Todd Pittman
University of Maryland Baltimore County

The 3-D movie experience has improved quite a bit since the “golden era” of the 1950’s…the special effects are now so realistic that you are almost guaranteed to spill your popcorn when the monster jumps off the screen! In this talk I will review the basic operating principles of modern 3-D movie systems, which are built upon the clever use of a few key concepts from undergraduate optics.

Location: Physics Bldg., room 401

## November 11, 2009

### Seminar: Wednesday, November 11, 2009 at 6:00 p.m.

Confessions of a Converted Lecturer
Dr. Eric Mazur
Harvard University

I thought I was a good teacher until I discovered my students were just memorizing information rather than learning to understand the material. Who was to blame? The students? The material? I will explain how I came to the agonizing conclusion that the culprit was neither of these. It was my teaching that caused students to fail! I will show how I have adjusted my approach to teaching and how it has improved my students' performance significantly.

Location: LH 5 (ECS Bldg)

### Seminar: Wednesday, November 11, 2009 at 3:30 p.m.

Nonlinear Optics at the Nanoscale
Dr. Eric Mazur
Harvard University

We explore nonlinear optical phenomena at the nanoscale by launching femtosecond laser pulses into long silica nanowires. Using evanescent coupling between wires we demonstrate a number of nanophotonic devices. At high intensity the nanowires produce a strong supercontinuum over short interaction lengths (less than 20 mm) and at a very low energy threshold (about 1 nJ), making them ideal sources of coherent white-light for nanophotonic applications. The spectral broadening reveals an optimal fiber diameter to enhance nonlinear effects with minimal dispersion. We also present a device that permits a number of all-optical logic operations with femtosecond laser pulses in the nanojoule range.

Location: Physics Bldg., Room 401

## November 4, 2009

### Seminar: Wednesday, November 4, 2009 at 3:30 p.m.

TBA

Location: Physics Bldg., Room 401

## October 28, 2009

### Seminar: Wednesday, October 28, 2009 at 3:30 p.m.

The Fermi Gamma-Ray Space Telescope and the Search for Dark Matter
Yvonne Edmonds
Stanford University

The Fermi Gamma-Ray Space Telescope launched in June 2008 opening a new window on the highest energy sources in the universe. I will give a brief overview of how Fermi’s primary instrument, the Large Area Telescope (LAT), detects gamma-rays and its topics of study. One of the most exciting possibilities for the Fermi-LAT is the indirect detection of dark matter. Well-motivated and popular dark matter theory assumes that a significant component of dark matter is Weakly Interacting Massive Particles (WIMPs). I will go over WIMP basics, and the strategies involved in dark matter searches. Finally, I will talk about my work on the possibility to observe gamma lines from WIMP annihilation into gamma-gamma and gamma-Z final states. Detection of these lines would give convincing evidence for the existence of WIMPs and the WIMP mass.

Location: Physics Bldg., Room 401

## October 21, 2009

### Seminar: Wednesday, October 21, 2009 at 3:30 p.m.

Lethal Landscapes: the Soviet-American history of plutonium, radiation and the communities that learned to love and then fight over the bomb
Dr. Kate Brown
University of Maryland Baltimore County

In 1944, brigades of construction workers, soldiers and prisoners transformed Richland, Washington from a ranch town to an ‘operators’ village’ exclusively reserved for workers at the new Hanford Engineering Works, a vast, ambling complex behind cyclone fencing that produced plutonium for the Manhattan Project. A few years later, inspired by Hanford, soldiers, prisoners and construction workers broke ground on another special city dedicated to plutonium workers. This one located in the thick, marshy forests of the southern Russian Urals. Both cities, Richland and Cheliabinsk-40*, existed to secure the secrets of plutonium. To keep the plutonium safe, plant employees were carefully-screened and closely-watched in isolated communities in remote locations. To keep the plutonium workers, engineers and scientists happy in these provincial locations, industrial leaders rewarded them handsomely and invested generously in the plutonium communities.

In short, it took a village (really a small city) to produce the few kilograms of plutonium necessary for a nuclear bomb. The cities existed for four decades in relative obscurity (Richland) or outright secrecy (Cheliabinsk-40). Chernobyl changed all that. When reactor number four blew in April 1986, it gave a pulse to anti-nuclear groups that had long demanded to know what went on behind the cyclone fencing of military nuclear installations. As American and Soviet documents were de-classified, the public learned that the plants had dumped, each day, tens of thousands of curies of radiation into rivers, air and soil. As the days had accumulated into decades, the total of spilled curies mounted into the millions and then hundreds of millions.

Since Chernobyl, the public memory of the plutonium cities has existed in a vortex of controversy. Commentators, residents, and activists characterize the plutonium cities variously—as radioactive and dangerous, or as safe and wholesome, “a great place to grow up.” People in towns surrounding the plutonium cities filed lawsuits for damage from what they charged were radiation-related health problems. Meanwhile, many residents in the cities fought against acknowledging a connection between the plutonium plants and local health problems.

Brown argues that the contentious legacy of the plutonium cities derive from the fact that the cities were built as model modern communities with novel new security regimes. Meanwhile radiation was also a modern contaminant--undetectable without sensitive equipment and the source of illness only after long latency periods. In short, the incongruity of the comfortable and thriving plutonium cities against an invisible, radioactive geography enabled the tragedy of massive environmental contamination, enabled too the personal tragedies of contaminated bodies to go unnoticed and unheeded for decades and remain controversial to this day.

Location: Physics Bldg., room 401

## October 14, 2009

### Seminar: Wednesday, October 14, 2009 at 3:30 p.m.

Interstellar Dust: The Universe through Rose-Colored Glasses
Dr. Ulysses J. Sofia
American University

Most astronomical observations are affected by interstellar dust, the submicron sized solid particles that live in the medium between stars. This is especially true as we observe increasingly distant objects with higher redshifts. The dominant method for accounting for light distortion by interstellar dust is an empirical correction which has a restricted range of validity. We are seeking to understand dust and its distorting affects in a context that is based in physics so that we may better correct for its effects on astronomical observations. We do this primarily through the study of the physical and chemical composition of dust, and radiative transfer models that relate potential dust grains to distortion effects. Data from the Hubble Space Telescope has allowed us to make great progress in this field over the past 18 years, but there are still fundamental pieces of the puzzle that do not fit together.

Location: Physics Bldg., Room 401

## October 7, 2009

### Seminar: Wednesday, October 7, 2009 at 3:30 p.m.

How do we know whether to believe model predictions?
Dr. Susan Strahan
Goddard Space Flight Center

Chemistry climate models (CCMs) embody the state of our knowledge of atmospheric chemistry and physics. They are used to predict future changes in atmospheric composition and climate based on estimates of future emissions of CO2, CH4, N2O, chlorofluorocarbons (CFCs), and other trace species. Every four years, chemistry climate modeling groups participate in an international effort sponsored by the World Meteorological Organization (WMO) to predict the future state of the stratospheric ozone. 13 CCMs participated in the most recent WMO assessment and they produced a wide range of predictions for benchmarks such as the date of the disappearance of the Antarctic ozone hole and the return of northern midlatitude ozone to 1980 levels. How do we know which, if any, of the model predictions to believe?
The answer lies in the use of observations to assess the ability of CCMs to represent key aspects of stratospheric circulation and chemistry. The analyses of several decades of aircraft, balloon, and satellite trace gas observations such as O3, H2O, CH4, and N2O have identified many important transport processes in the stratosphere. We use observational analyses to derive diagnostics for stratospheric transport processes, and because of them we now understand many aspects of stratospheric circulation, e.g, the rate at which air ascends in the tropical stratosphere and the existence of transport barriers in the subtropics and polar regions. Diagnostics are applied to model simulations to assess whether models realistically represent known processes. In recent years an international group of scientist has been systematically applying a growing set of stratospheric chemistry and transport diagnostic to CCMs in order to better understand their behavior and determine model credibility. This effort is providing a rational basis for distinguishing between model predictions of the future of stratospheric ozone.

Location: Physics Bldg., Room 401

## September 30, 2009

### Seminar: Wednesday, September 30, 2009 at 3:30 p.m.

Coherent Control of Electrical Current and Terahertz Radiation
Dr. Ki Yong Kim
University of Maryland College Park

Sandwiched between the traditional optical and microwave regimes, far infrared or terahertz (THz) frequency has recently drawn special attention due to its ubiquitous nature, as well as its potential for molecular sensing, biomedical imaging and spectroscopy, security scanners, and plasma diagnostics. For these applications, there is a present and growing need for high-energy, compact THz sources at a tabletop-scale. In this effort, I will present our recent demonstration of high-energy (>5 microjoule), super-broadband (>75 THz) THz radiation generation using a tabletop femtosecond laser [1]. In this scheme, an ultrafast pulsed laser’s fundamental and second harmonic fields are mixed in a gas of atoms or molecules, causing them to ionize. The resulting plasma can generate a directional electron current and simultaneous far-field THz radiation, all coherently controlled by the laser field amplitudes and relative phase. By controlling the relative phase, we can also switch the output energy between THz and harmonics.

Location: Physics Bldg., room 401

## September 23, 2009

### Seminar: Wednesday, September 23, 2009 at 3:30 p.m.

Er:YAG is a 2.46-level laser
Dr. Jeffrey O. White
Army Research Laboratory

For a high power solid state laser in the 1.6 micron spectral region, Er3+ is a natural choice for the active ion. One advantage is the possibility of low-quantum-defect pumping with diode lasers. A disadvantages is the presence of upconversion. I will discuss recent modeling and experiments on lasing, and z-scan measurements of upconversion. 'Level parameters' will be proposed for quantitative comparison of rare-earth-doped solid-state laser media, operating temperatures, pump and laser wavelengths.

Location: Physics Bldg., Room 401

## September 16, 2009

### Seminar: Wednesday, September 16, 2009 at 3:30 p.m.

Human Restructuring of the Terrestrial Biosphere, Surface Processes and Global Climate
Dr. Erle Ellis
University of Maryland Baltimore County

Humans have been altering terrestrial ecosystems for millennia, beginning with early use of fire for hunting and leading now to the wholesale restructuring of the terrestrial biosphere for use in agriculture and settlements. This presentation will explore the global implications of land use by humans, beginning with the first farmers and then detailing the global ecological patterns created by human activities from the 1700s to the present. Anthropogenic global patterns in ecosystem and land surface processes are likely causing global changes in atmospheric pattern and process- a fruitful pathway for future research.

Location: Physics Bldg., Room 401

## September 9, 2009

### Seminar: Wednesday, September 9, 2009 at 3:30 p.m.

Quantum Networks with Ions, Phonons, and Photons
Dr. Chris Monroe
Joint Quantum Institute, University of Maryland and NIST

Trapped atomic ions are among the most promising candidates for quantum information processing. All of the fundamental quantum operations have been demonstrated on this system, and the central challenge now is how to scale the system to larger numbers of qubits. By entangling atomic qubits through both deterministic phonon and probabilistic photon interfaces, the trapped ion system can be scaled in various ways for applications in quantum communication, quantum computing, and quantum simulations. I will discuss several options and issues for such atomic quantum networks, along with state-of-the-art experimental progress.

Location: Physics Bldg., Room 401

## May 6, 2009

### Seminar: Wednesday, May 6, 2009 at 3:30 p.m.

Joseph F. Mulligan Lecture
Lives and Discoveries of Lord Rayleigh and Gustav Mie
Gergely Dolgos
UMBC

The talk will introduce Lord Rayleigh and Gustav Mie in order to help us understand their work and character. Their research on light scattering by small objects is crucial to the understanding of radiative processes in the atmosphere, which motivated the joint investigation of the two scientists. Rayleigh worked out the details of light scattering by gases, whereas Mie set the foundation for the study of light scattering by clouds and aerosols.

Rayleigh was a talented theorist, experimenter, leader and administrator. An English landowner in the Victorian era, he had a very stable and prosperous environment. He fully took advantage of his financial situation for the benefit of science and humanity. He was an average student in middle school and developed his math skills by hard work. He always strived for economy, obtaining accurate results with cheap and simple equipment, since he worked from his own money. He touched almost every area of classical physics. The discovery of argon earned him the Nobel Prize and a number of physical phenomena and mathematical methods are named after him. Atmospheric scientists use his truly innovative and accurate results regarding light scattering by gas molecules from 1871. The answer to the fundamental question: “Why is the sky blue?” lies in his work.

A reserved academic genius, Mie led a middle class life in Germany in peaceful and during turbulent times during the first half of the 20th century. Some of his significant contributions are in field theory, general relativity and X-ray diffraction. Mie’s 1908 paper on light scattering by spherical particles (of any size) is a complete work by itself. He applies first principles, documents the computational method and its implementation, reaches numerical results, and successfully compares them to experimental work. His energetic work and studies made him a foremost expert of his day on electricity and magnetism. His textbook on electrodynamics ran into several editions. His computational method for modeling light scattering and absorption by spherical particles is used in atmospheric remote sensing today and it is the foundation and benchmark of more advanced methods for modeling radiative effects of small airborne particles.

Today, Rayleigh and Mie are linked through the importance of their work to atmospheric physics but they were two different men from different circumstances.

Location: Physics Bldg., Room 401

## April 29, 2009

### Seminar: Wednesday, April 29, 2009 at 3:30 p.m.

No Seminar - Wednesday, April 29, 2009

## April 21, 2009

### Seminar: Wednesday, April 22, 2009 at 3:30 p.m.

No Seminar - Wednesday, April 22, 2009

## April 13, 2009

### Seminar: Wednesday, April 15, 2009 at 3:30 p.m.

The Role of Physics in Industry Research and Development
Dr. Michael Fitelson
Northrop Grumman Corporation

Today’s High Technology companies, particularly those involved in defense related research, are utilizing advances associated with physics research to an increasing extent. Many of the devices and technologies employed in advanced sensors and computing are leveraging breakthroughs in physics and related disciplines. These breakthroughs encompass quantum optics, quantum information, nano-science, solid state physics, superconductivity, materials science and many other disciplines.

Physics Bldg., room 401

## April 7, 2009

### Seminar: Wednesday, April 8, 2009 at 3:30p.m.

There will be no seminar Wednesday, April 8, 2009

## April 1, 2009

### Seminar: Wednesday, April 1, 2009 at 3:30 p.m.

How to Plan a Spacecraft-Based Science Experiment: Cloud CubeSat
Dr. Joseph Sedlak
A.I. Solutions

One of the first steps in spacecraft mission design is the selection of orbit and attitude scenarios that enable the science. This selection process works best when scientists and engineers begin the dialog early to understand the geometry, the science measurements, and the platform orbit and attitude accuracy. Flight Dynamics analysis helps clarify accuracies available with particular sensor complements.

This affects costs both through the hardware and through the need for initial and ongoing ground support. In the first part, this talk presents an overview of general considerations needed for orbit and attitude analysis. The second part gives an introduction to Cloud CubeSat, a very small, but very exciting student spacecraft (picosat) for side-imaging of clouds.

Location: Physics Bldg., Room 401

## March 25, 2009

### Seminar: Wednesday, March 25, 2009 at 3:30 p.m.

Life's place in the universe
Dr. Steve Freeland
UMBC Department of Biology

One, relatively new interface between biology and physics occurs within astrobiology: the quest to develop a scientific understanding of life's relationship with the physical universe (i.e. its origin(s) and likely distribution.) At present we know only one example of life, and our understanding of its origin remains patchy at best.

However, science often challenges us to extrapolate from incomplete observations of the actual into reasoned inferences of what is possible. For astrobiology, this means developing our understanding of how and why we emerged on this planet. Answers require extensive interdisciplinarity: how typical is our solar system of other star-systems in the galaxy? what properties of Earth are typical or unusual for a planet? How are these properties related to life's emergence here? What can we learn about life's boundaries by examining the biodiversity we encounter today? Once life had evolved, what aspects of our 4 billion year evolutionary history were likely or even inevitable? In this talk I will approach these questions from a biologist's perspective, showing where my own research interests lie within this bigger topic. I hope to illustrate the sorts of questions that we are learning to answer (and the assumptions we still make). I will also encourage you to help me better understand what Physics can contribute to the bigger questions.

Location: Physics Bldg., Room 401

## March 18, 2009

### Seminar: Wednesday, March 18, 2009 at 3:30 p.m.

No Seminar - Wednesday, March 18, 2009

## March 11, 2009

### Seminar: Wednesday, March 11, 2009 at 3:30 p.m.

The life of a snowflake : Measuring snow from space
Dr. Benjamin Johnson
UMBC Joint Center for Earth Systems (JCET) and NASA Goddard Space Flight Center

On Earth, the vast majority of precipitation originates as snow particles in the atmosphere. At middle and high latitudes, snow falling on land contributes to snowpack; a critical source of freshwater for spring and summer months. Snow on the ground also provides an atmospheric cooling mechanism due to it's high visible-light albedo. In the middle and lower latitudes, falling snow often melts, becoming rain -- feeding our streams, rivers, and lakes. The growth and melting of snow also contributes to heating / cooling of the atmosphere through phase change, influencing atmospheric motions and stability. It is critical, especially given our changing climate, to be able to accurately measure atmospheric snow on a global basis for long time periods.

One of the key challenges to measurement is understanding how the physical characteristics a snowflake influence millimeter-wavelength observations made from a satellite-based remote sensing platform. On both the microscopic and synoptic scales, the physical aspects of the initiation, growth, and dissipation of an individual snowflake are reasonably well understood. However, when considering a precipitating cloud containing a wide variety of sizes, habits, orientations, phases, of snow, the problem of characterizing the 3-D scene in analytical fashion becomes troublesome.

In this talk I will focus the physical processes which contribute to the growth and eventual destruction of an individual snowflake, and I will describe how these individual processes are treated when considering a diverse ensemble of snow particles within, for example, a precipitating cloud. I will also briefly describe how the physical properties of snow particles influence incident electromagnetic waves at centimeter and millimeter wavelengths (~1-22 mm or 13 to 220 GHz), and the ramifications for inferring information about snow based on satellite observations at these wavelengths.

Location:
Physics Bldg., room 401

## March 4, 2009

### Seminar: Wednesday, March 4, 2009 at 3:30 p.m.

Open Source Physics: Computational Tools for Teaching
Dr. Mario Belloni
Over the past dozen years Davidson College has produced some of the most widely used interactive curricular materials for the teaching of introductory and advanced physics courses. These materials are based on Java applets called Physlets and the Open Source Physics (OSP) programs and applications. The new Open Source Physics Project has focused on the creation and dissemination of computational and educational tools for teaching. Specific examples of using modeling in intermediate classical mechanics with Easy Java Simulations (Ejs) and teaching other advanced courses (quantum mechanics and general relativity) with OSP-based programs will be shown. How the Open Source Physics Project is connected to existing Digitial Libraries like ComPADRE will also be discussed

Location: Physics Bldg., room 401

## February 25, 2009

### Seminar: Wednesday, February 25, 2009 at 3:30 p.m.

Peering into Galaxies with Gamma-Ray Glasses
Dr. Craig Markwardt
U. Maryland and NASA/Goddard Space Flight Center
Most galaxies are thought to have a supermassive black hole at their center, as a natural consequence of the formation of structure in the universe. Finding these black holes is not as easy as it may seem however, because the centers of galaxies are often shrouded by obscuring material, which preferentially absorb optical and X-ray light. Most active galaxies found by surveys in the optical and X-ray wavelengths will thus be biased toward unobscured objects. However, as we move towards shorter wavelength X-rays - "hard X-rays" - the obscuring clouds become transparent. We have exploited this fact to construct a survey of all local active galaxies with the Swift Burst Alert Telescope, free of previous biases. While Swift and BAT were designed to chase and study gamma-ray bursts, the most powerful explosions in the universe, BAT is able to pierce the veil of obscuration surrounding local galaxies as well. I will present a summary of these results and compare to the properties of the supermassive black hole at the center of our own galaxy.

Location: Physics Bldg., room 401

## February 18, 2009

### Seminar: Wednesday, February 18, 2009 at 3:30 p.m.

Physics in Games
Dr. Marc Olano
UMBC/CSEE

Modern computer games exhibit a number of elements of elementary physics. This is perhaps most visible in kinematic simulation of articulated bodies, the so-called "rag doll physics" for character animation. However, physics can also be found in fluid simulation, optical effects with participating media, and models of surface reflectance. These methods must run effectively on a range of consumer hardware, and must be fast, finishing within a fraction of the 10-30 ms time available per frame. This talk will present some of the currently popular methods and demonstrate their results, and discuss the state of consumer-level hardware to accelerate physics simulation.

Location Physics Bldg., room 401

## February 11, 2009

### Seminar: Wednesday, February 11, 2009 at 3:30 p.m.

The nano-optics of surface plasmon polaritons and their applications in cloaking and microscopy
Dr. Chris Davis, Professor of Electrical and Computer Engineering
University of Maryland College Park

In this talk I will describe what surface plasmon polaritons (SPPs) are, how they are excited, and how they can be used to produce both very large, and effectively negative, relative permittivities and group refractive indices. The effectively negative permittivities and refractive indices that can be produced in metal/dielectric composite nanostructures has allowed the first demonstration of 2-D cloaking in the visible part of the spectrum. The general principle and limitations of practical cloaking will also be discussed, and some of the approaches that are being considered for reducing the visibility of 3-D objects. The effectively large refractive indices that can be experienced by SPPs also allows the construction of super-resolution microscopes.

Location Physics Bldg., Room 401

## December 1, 2008

### Seminar: Wednesday, December 3, 2008 at 3:30pm

An Update on Stratospheric Ozone and Related Science Issues as We Approach the 2010 WMO/UNEP Scientific Assessment of Ozone Depletion
Mike Kurylo
Goddard Earth Sciences and Technology (GEST) Center, UMBC and NASA GSFC

The international Montreal Protocol on Substances that Deplete the Ozone Layer requires that the Parties assess the control measures on the basis of available scientific, environmental, technical, and economic information. To achieve this, the Parties are required to convene appropriate panels of experts who will report their conclusions to the Parties. The 2010 Scientific Assessment of Ozone Depletion is now underway and is the seventh in the set of major assessments prepared by the Scientific Assessment Panel as direct input to the Montreal Protocol process. This talk will highlight our current understanding of stratospheric ozone and its related science issues as we embark on this next assessment. Specific points of focus will include: ozone depleting substances, ozone observations and projections, ground level ultraviolet radiation, greenhouse gases and ozone, and scientific gaps and needs.

Location: Physics Bldg., Room 401

## November 24, 2008

### Seminar: Wednesday, November 26, 2008

Due to the Thanksgiving Holiday, there will be no seminar on Wednesday, November 26, 2008.

## November 19, 2008

### Seminar: Wednesday, November 19, 2008 at 3:30pm

Secret Lives of the Hidden Physicists: From Spandex to Spintronics
Gary White
American Institute of Physics

What is a physicist? A case is made for defining a physicist as anyone with a bachelor's degree (or higher) in physics. Under this definition, a large fraction of physicists are hidden, that is, they have left, or never belonged to, the traditional lot of Ph.D. academicians. Data from the Statistical Research Center at the American Institute of Physics and from a survey of members of the national physics honor society, Sigma Pi Sigma, show the vast array of actual career paths taken by physicists. From spandex to blackberries to bioinformatics to flight control to wind energy to spintronics, physicists can be found in nearly every job sector with some of the coolest careers around.

Location: Physics Bldg., Room 401

## November 10, 2008

### Seminar: Wednesday, November 12, 2008 at 3:30pm

Fossils of the first galaxies in the Local Group and the role of reionization feedback on suppressing the formation of dwarf galaxies
Massimo Ricotti
Department of Astronomy
University of Maryland College Park

In this talk I show results of cosmological simulations suggesting a possible identification of at least some dwarf spheroidal galaxies in the Local Group as the fossils of the first galaxies (pre-reionization fossils''). I also revisit the problem of gas accretion onto minihalos after reionization. I show that primordial minihalos with v_{cir}<20 km/s stop accreting gas after reionization, as it is usually assumed, but in virtue of their increasing concentration and the decreasing temperature of the intergalactic medium as redshift decreases, they may have a late phase (at redshift z<2) of gas accretion and possibly star formation. As a result we expect that pre-reionization fossils have a more complex star formation history than previously envisioned. The dwarf spheroidal galaxy Leo~T fits with this scenario. Another prediction of the model is the existence of a population of gas rich minihalos that never formed stars. A subset of compact high-velocity clouds may be identified as such objects but the bulk of them may still be undiscovered.

Location: Physics Bldg., Room 401

## November 3, 2008

### Seminar: Wednesday, November 5, 2008 at 3:30pm

A CCD Based Multiwavelength X-ray Diffractometer
Keith Gendreau
NASA Goddard Space Flight Center

We have made a new type of X-ray Diffractometer that uses CCD technology developed for X-ray astrophysics. The instrument provides X-ray diffraction and fluorescence information from unprepared samples. This can be used to identify minerals and provide surface texture information. The instrument is designed to minimize mass, power, and risk for planetary exploration.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## October 27, 2008

### Seminar: Wednesday, October 29, 2008 at 3:30pm

The BESS-Polar Program and the Search for Antimatter
Thomas Hams
NASA Goddard Space Flight Center

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) program is searching for antimatter in the galactic cosmic radiation by precisely measuring the elemental and isotopic composition of the light cosmic ray component. The experiment is a highly successful US-Japanese collaboration and over the past 15 years, the BESS payload has had eight low geomagnetic cutoff, northern latitude flights and two long duration balloon flights from Antarctica. The most recent flight of the BESS-Polar experiment was a long-duration Antarctica flight, which occurred between December 2007 and January 2008. This flight yielded 24.5 days of observation time at a time of low solar activity (solar minimum). We will review the BESS program and report the results of the antiproton and proton spectra measured in the BESS-Polar I flight, the search for cosmic antinuclei, and the status of the BESS-Polar II analysis.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## October 20, 2008

### Seminar: Wednesday, October 22, 2008 at 3:30pm

The NASA Constellation Program:
Deirdre Healey
Constellation Program Safety & Mission Assurance NASA HQ/OSMA

This seminar has been cancelled! There will be no seminar on Oct. 22, 2008.

## October 15, 2008

### Seminar: Wednesday, October 15, 2008 at 3:30pm

Quantum Entanglement and Particle Scattering
Dr. Nathan Harshman
Assistant Professor & Chair of Physics Department
American University

When the state of a quantum system cannot be separated into the states of its constituents, we say the system is entangled. In some cases, the presence of entanglement means that measurements on different parts of a system have correlations stronger than can be explained by any purely classical theory. Einstein derisively called this effect “spooky action at a distance,” but now we know that entanglement is a hallmark of quantum mechanics. In this talk, I will investigate entanglement in particle systems. Different types of entanglement can occur in such systems, and dynamical processes can change the amount of entanglement.

In particular, I will look at how entanglement is generated between particles by scattering, the fundamental experimental paradigm for particle physics.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## October 8, 2008

### Seminar: Wednesday, October 8, 2008 at 3:30pm

Freezing of Supercooled Cloud Drops
Dr. Alex Kostinski
Professor of Physics
Michigan Technological University

Supercooled cloud water is in a metastable thermodynamic state and, therefore, the associated phase transition (to ice) must be irreversible. Has this irreversibility been considered? Does it matter to atmospheric scientists? I'll argue No and Yes, respectively.

We used measured temperature-dependent heat capacities of supercooled water and ice to calculate the ice-(metastable) water entropy difference and to estimate a lower bound on the amount of latent heat, liberated by the freezing droplets. The calculation is compared with tabulated values of the latent heat of fusion with surprising results. Based on a novel physical picture of the freezing process, we suggest a simple estimate for the effective latent heat, suitable for heat budget calculations of glaciating clouds. In addition, we arrive at a quadratic dependence on supercooling for the irreversible contribution to heat exchange during the freezing process. Implications for optical properties of the "hurriedly made ice" will also be discussed.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## October 1, 2008

### Seminar: Wednesday, October 1, 2008 at 3:30pm

Solar Shield - Forecasting and Mitigating Solar Effects on Power Transmission Systems
Antti Pulkkinnen
Goddard Earth Sciences and Technology Center (GEST), UMBC

The Solar Shield project is a collaborative effort between the Electric Power Research Institute (EPRI) and NASA. It was launched to utilize state-of-the-art space physics models in experimental space weather forecasting. More specifically, Solar Shield is using an extensive pool of coupled space physics models hosted at the Community Coordinated Modeling Center (CCMC) at NASA/GSFC. The models propagate information obtained from solar observations to the interplanetary medium, from the interplanetary medium to the Earth’s magnetosphere and ionosphere and eventually all the way down to the surface of the Earth. Here is where geomagnetically induced currents (GIC) flowing in high-voltage power transmission systems are calculated. The two-level forecasting system provides both 2-3 day lead-time and 30-60 minute lead-time forecasts, and it is already capable of generating predictions of GIC flow at few individual nodes of the North American power transmission system.

An important special aspect of the project is the participation of the end-user, i.e. power transmission industry, in the development of the forecast products. The goal is to define a system, which, when integrated into EPRI’s SUNBURST decision support tool, will help power transmission system operators to make decisions about possible mitigation actions during “poor” space weather conditions. Industry participation will also enable quantification of the economic value of the generated GIC forecasting system. The result of the economic analysis can be used to indicate if there is a business case for transitioning the experiment into operations.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## September 24, 2008

### Seminar: Wednesday, September 24, 2008 at 3:30pm

Making Things With Light: Recent Progress in Multiphoton Absorption Polymerization
Dr. John Fourkas
Department of Chemistry and Biochemistry
University of Maryland College Park

Many new device applications in micro- and nanotechnology require the ability to fabricate complex, 3D structures. Conventional lithographic techniques are not well suited to the creation of many such structures, which has fueled interest in the development of novel fabrication techniques. One rapidly emerging technology for 3D fabrication is multiphoton absorption polymerization (MAP). In MAP, a tightly focused laser beam is used to exposure a photoresist exclusively at the laser focal point. By moving this focal point over a desired pattern in three dimensions, arbitrarily complex structures with feature sizes as small as 100 nm can be created. I will discuss some of our recent progress in expanding the capabilities of MAP as well as in creating functional devices.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## September 17, 2008

### Seminar: Wednesday, September 17, 2008 at 3:30pm

How much light was produced since the Universe was born? Finally, a way to measure it.
Dr. Markos Georganopoulos
Department of Physics, UMBC

The extragalactic background light (EBL) that permeates the Universe in the optical-IR is essentially an integral of the light produced from the time the first stars were formed in our Universe until now. As such, it is a quantity that is very closely connected to the galaxy/ large scale structure formation in our Universe. Unfortunately, measuring the EBL has been proven practically impossible, for very simple reasons that I will discuss in the first part of my talk. Luckily, we found an unexpected, parameter-free way to break the deadlock of measuring the EBL with GLAST, NASA's new gamma-ray satellite. This will be the second part of my talk. GLAST measurements are underway and the determination will take about two years.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## September 10, 2008

### Seminar: Wednesday, September 10, 2008 at 3:30pm

Linearized Electrooptic Phase Modulation for Microwave-Photonic Signal Transmission
Dr. Tom Murphy
Department of Electrical and Computer Engineering
University of Maryland College Park

Anyone who travels has likely heard the following warning: “FAA regulations prohibit the use of portable electronic devices during takeoff or landing.” The modern aircraft contains an ever-growing array of electronic sensors used in navigation and communication. At the same, time, we have seen a rapid explosion not only in the number of handheld electronic appliances carried by passengers, but also in their frequencies of operation. This has lead to growing concern that electromagnetic radiation from such devices could interfere with navigation and communication.

One potential solution to this problem is to replace the coaxial cables and wires normally used to transmit electronic signals in the aircraft with optical fibers. Compared to coaxial cables, optical fibers are smaller, lighter, and less expensive. The bandwidth available in a single fiber is large enough to accommodate the data from thousands of coaxial cables, and the loss in optical fiber is negligible in comparison to coaxial cables, especially at microwave frequencies. Most importantly, optical fibers are completely immune to electromagnetic interference, which makes them especially attractive for avionic sensor networks. The key challenge is to find a ways to modulate and demodulate analog microwave signals onto an optical carrier without distorting or impairing the microwave signal.

In this talk, I will discuss our recent research on using phase modulation instead of more commonly-used intensity modulation to impose a microwave signal on an optical carrier. To date, there has been very little research on developing low-distortion linearized phase-modulation systems. Unlike earlier intensity-modulation schemes, which often required multiple interconnected modulators or signal pre-distortion, our system is unique in that it uses only a single electrooptic phase modulator driven by an unmodified input signal, and could entirely eliminate the third-order intermodulation distortion that usually limits the dynamic range.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## September 3, 2008

### Seminar: Wednesday, September 3, 2008 at 3:30pm

Trace Elements In Matter Is What Actually Matters
Prof. Manfredo H. Tabacniks
Institute of Physics, University of Sao Paulo
2008 Yoram Kaufman GEST/UMBC-GSFC Research Fellow

In former times, materials were developed tuning their chemical composition to get the desired properties. Hence, material analysis was used to get the chemical composition in a broad sense. Though initially based on wet-chemistry processes, material analysis by physical methods turned into an ever-growing field. Ion Beam Analysis and Inductively Coupled Plasma Mass Spectrometry are just two examples of a field in which the detection limits, and sample sizes are being extraordinarily reduced enabling nowadays the measurement of sub-ppb levels of any element of the whole periodic table in microscopic samples. The billionaire semiconductor industry is just one of the applications of modern ultra low detection analysis by physical (dry) methods. Trace elements in materials can be used to trace archaeological technologies. Trace elements in blood serum may be used in the future to trace diseases, eventually cancer. Trace elements in aerosols can indicate its origins and transport properties. In this new era, the question whether an element is or is not present in a sample has changed to what are the elemental concentration levels and how they correlate to the bio-physical-chemical processes involved.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.

## August 27, 2008

### Seminar: Wednesday, August 27, 2008 at 3:30pm

Directional signatures of the Earth reflectances. Measurements, modeling and corrections.
Dr. François-Marie Bréon
CEA/DSM/LSCE, France

Earth reflectances are highly anisotropic. The most anisotropic signal is observed over water surfaces where the glint effect generates a reflectance that varies by several orders of magnitude as a function of the observation geometry. Over land surfaces, the variations are not as large, but nevertheless significant. The reflectance of a given target varies with the observation geometry by a factor of up to four. This anisotropy causes some difficulties for a quantitative analysis of satellite measurement time series as the variability due to the changing measurement geometry may be as large as the geophysical signal that is monitored.

The POLDER/Parasol spaceborne instrument is a great tool to monitor these effects. Indeed, it provides up to 16 measurements of the same targets, with varying view angles, as the satellite flies over it. We will present and discuss the directional reflectance measurements, and the model that was developed to reproduce the observed signatures. The model is then used to correct the time series, for a much better identification of the geophysical signal, such as the vegetation dynamic.

Location: Physics Bldg., Room 401
Coffee: 3:15 p.m.