Physics Announcements

Seminar: Wednesday, Apr 25, 2012 at 3:30 pm

2012-04-25T08:32:43Z

REMOTE SENSING OF TITAN FROM CASSINI
Dr. Conor Nixon
Univ. Maryland /NASA GSFC
Solar System Exploration Division Titan is the largest moon of Saturn, and the only moon in the solar system to have a significant atmosphere. Predominantly composed of nitrogen (N2), it has a 1.5 bar surface pressure, similar to the Earth in these respects. However there are important differences, as Titan's atmosphere is much colder and contains a variety of hydrocarbons and organic species as important minor constituents, but few oxygen compounds. With the arrival of the Cassini-Huygens space mission in 2004, our knowledge of Titan - previously derived mainly from the Voyager missions several decades earlier - expanded dramatically. The Huygens probe descended to the surface by parachute, making in situ atmospheric measurements, while Cassini continued to orbit Saturn, making regular encounters with Titan: more than 80 to date. In this talk I will introduce Titan and the Cassini mission in general, before zooming in to discuss the suite of four 'optical' remote sensing instruments in more detail. Together these cameras and spectrometers sense the EM spectrum from EUV to sub-millimeter wavelengths (not counting the RADAR and radio experiments.) I will highlight key findings from the mission so far, saying how they have changed our understanding of Titan as a world, and conclude with some open questions and expectations for the remainder of the mission duration (through 2017). Location: Physics Bldg., Room 401

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

2012-04-04T20:29:26Z

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

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

2012-03-07T20:29:26Z

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

PhD Proposal Defense - Neetika Sharma

2012-02-08T15:35:16Z

You are all invited to attend Neetika's PhD Proposal defense. Date: Wednesday, February 8, 2012 Time: 11:00 am Location: PHYS 401 TITLE: Diagnostics of Photoionized Gas in Seyfert Galaxies ABSTRACT: As their name implies Active Galactic Nuclei (AGN) reside in the centers of many (10%) galaxies. They are active in the sense that their spectra exhibit a broad (from radio to gamma-rays) non-stellar continuum which exceeds the luminosity of the host galaxy. Furthermore at some wavelengths intensity variations have been observed on timescales less than a day (minutes in extreme cases). The ultimate cause of this tremendous outflow of energy in the form of radiation is widely believed to be due to the accretion of matter onto a supermassive black hole (BH ~ 10⁶-10⁹ times the mass of the Sun). Unfortunately since all this activity takes place in such a relatively small region (<< 3lyr) the central engine of even the closest AGN cannot be imaged directly with current technology (eg. The central region of Circinus, the nearest active galaxy at a distance of about 40 million trillion miles, has an angular size of about 0.2" that is just resolvable with VLT of spatial resolution 0.1"-0.5" ). Nevertheless spectroscopic observations can help us constrain the conditions of the gas very close to the BH. Such observations reveal that, as expected from considerations of the angular momentum of the infalling matter, such material in the circumnuclear regions of an AGN is not in a spherically-symmetric distribution. The unified model of AGN comprises of different gas components surrounding the central engine and hence that leads to the classification of AGN depending upon their oreintations with respect to the observer on the Earth. My thesis focuses on constraining the physical conditions in the NLR of Seyfert galaxies. I propose to compare observational data with the predictions of a publically available software tool CLOUDY in order to further constrain the conditions within the circumnuclear regions of a number of nearby Seyfert Galaxies. Specifically I propose to use archival data in the soft X-ray band (6-38Å) obtained by the grating spectrometers onboard the XMM-Newton and Chandra observatories for this purpose. Some Seyfert galaxies (Seyfert 2 galaxies) emit a multitude of emission lines due to H-like and He-like ions of the cosmically abundant elements (C, N, O, Ne, Mg...etc). These line intensities are far in excess of those predicted by models of the gas in the standard Unied Model of Active Galactic Nuclei (AGN). It has been suggested that the lines are due to an additional amount of circumnuclear material. Some of this material is actually thought be co-located with the so-called Narrow-line region (NLR) of AGN. This has been dubbed the Xray NLR (XNLR) and is probably co-located with the regular NLR. Due to the intense continuum radiation, the XNLR gas is thought to be photoionized. Understanding this X-ray emitting component of gas is important, as it will help us understand the overall structure and dynamics of the circumnuclear regions of AGN.

PhD Defense - Sanjit Karmakar

2012-02-01T17:18:45Z

Sanjit successfully defended his PhD dissertation on February 1, 2012. TITLE: Ghost Imaging with Sunlight ABSTRACT: The main result of this dissertation is the first successful experimental demonstration of ghost imaging using the sun as a light source. This result supports the quantum theory of near-field thermal light ghost imaging and also clarifes the physics of near-field thermal light ghost imaging from the fundamental level. The quantum theory of two-photon interference is the key to understanding non-local ghost imaging with thermal light sources. Two-photon interference occurs between two different yet indistinguishable probability two-photon amplitudes, nonclassical entities produced by the joint-detection between two distant photo-detectors. On the other hand, the classical theory considers the reason behind thermal light ghost imaging to be an intensity fluctuation correlation. Interestingly, the physics of intensity fluctuation correlation was misled by the speckle-to-speckle picture. The experimental demonstration of ghost imaging with sunlight suggests that the nonlocal ghost-imaging effect of thermal light is caused by quantum-mechanical two-photon interference and it also proves that the idea of 'speckles" is unnecessary in near-field thermal light ghost imaging. Most importantly, the sun does not make any speckle and it is a near-field source. The experimental studies on sunlight-based ghost imaging is discussed in two steps: (1) an experimental demonstration as well as a quantum mechanical explanation of the nontrivial intensity correlation with the sun, a natural thermal source, as a light source and (2) the demonstration of the experimental observation of ghost imaging with sunlight with its quantum-mechanical explanation. These observations with their theoretical explanation are very helpful to understanding the physics of ghost imaging from a fundamental level. From the application point of view, sunlight-based ghost imaging may achieve a spatial resolution equivalent to that of a classical imaging system taking pictures at a distance of 10 km with a lens of 92 m size. So far ghost imaging using thermal light with one color are demonstrated. This dissertation also reports an experimental study of two-color, biphoton ghost imaging using an entangled photon pair source. The result of this experimental observation shows a ghost image with enhanced angular resolving power by means of a greater field of view compared with that of classical imaging. The experience gained in the two-color ghost imaging experiment with entangled photon pairs will be helpful to get a real color ghost image with sunlight. A proposal to achieve sunlight-based ghost imaging with real colors is also reported here. Potential real color sunlight-based ghost imaging with its nonlocal behavior and turbulence-free nature gives us a promise for its applications in distant imaging.

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

2012-01-26T18:32:01Z

Materials Design For Thermoelectric Applications Dr. Mona Zebarjadi
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

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

2011-12-07T20:29:23Z

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

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

2011-11-30T20:11:31Z

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

PhD Defense - Chris Wilson

2011-11-29T18:00:57Z

Chris successfully defended his PhD dissertation on November 29, 2011. TITLE: Multivariate Retrieval of Carbon Monoxide ABSTRACT: A new technique is presented here to retrieve carbon monoxide (CO) profiles from Atmospheric Emitted Radiance Interferometer (AERI) spectra. This retrieval version deviates from the previous AERI CO retrieval method, which utilized signal processing to determine a constant CO mixing ratio representative of the entire troposphere. Instead, this retrieval version utilizes linear mapping to ascertain an estimate of the CO profile. A detailed analysis is conducted to estimate the error from all aspects of the the linear mapping procedure including measurements, forward modeling of atmospheric radiation, and uncertainty from inputs to the forward model. It was found that the dominant sources of error were from cloud contaminated spectra and uncertainty in absorption line strengths inside the forward model, A new cloud flagging technique that uses a neural network to identify spectra affected by clouds was tested and compared to the previously used version based on brightness temperature contrast. The neural network method decreased uncertainty between AERI and forward model spectra by 30 percent when compared with the previously used version. First guess CO profiles to the AERI retrieval were from two different sources. One source was an a priori CO profile calculated as the mean profile from 56 individual measurements where each CO profile encompasses tower, aircraft, and satellite CO measurements. The other first guess CO profile came from the AIRS version 5 (AIRSv5) retrieved CO product. Incorporating the AIRS CO profile to the AERI retrieval provided a better estimate of free tropospheric CO when compared with the a priori profile. Using a better upper tropospheric CO estimate resulted in more accurate results from the AERI retrieval below 2 km, thus revealing that an AERI plus AIRS retrieved CO product is superior to either instrument's own CO retrieval working alone. The combined retrieval product is shown to have an RMSE of 10% in the first 2 km of the atmosphere.

PhD Proposal Defense - Erika Nesvold

2011-11-21T15:21:46Z

You are all invited to attend Erika's PhD Proposal defense. Date: Monday, November 21, 2011 Time: 12:00 pm Location: PHYS 401 TITLE: A Collisional Algorithm for Modeling Debris Disks ABSTRACT: Many stars harbor disks of debris, in the form of dust and planetesimals, left over from planet formation. Any planets orbiting in these debris disks will gravitationally perturb the planetesimals, creating morphological features in the disk. These features have a large angular extent on the sky compared to planets, and can be more easily resolved than the planets themselves. We can therefore use images of a resolved debris disk to predict the presence of a perturbing planet and constrain its mass and orbital elements, even when the planet is too faint to be observed. But to use this planet-finding technique, we need accurate models of the evolution of the disk as it is shaped by the planet. This problem has previously been addressed using N-body integrators to simulate the dynamics of a planet-disk system, but these models neglect or over-approximate the effects of catastrophic collisions between planetesimals. Such collisions affect the dynamics of the planetesimals as well as their size distribution as the kinetic energy of the colliding planetesimals is used to shatter them into smaller fragments. I propose to develop a debris disk model that combines an N-body integrator to solve the equations of motion for the planetesimals and planets in a disk and a collisional algo- rithm to correct the trajectories of colliding planetesimals and calculate the evolution of the planetesimal size distribution as fragments are created. My model will take as its inputs various parameters such as planetary and stellar mass, the planets’ initial orbital elements, and the initial distribution of planetesimals. The output of my model will be simulated images of the evolved disk. After the model has been completed and tested, I will apply it to archived data of several different resolved debris disks to constrain the mass and orbital elements of confirmed planets and to predict the presence, mass, and orbits of undetected planets.

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

2011-11-16T20:25:32Z

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

PhD Defense - Debra Kollonige

2011-11-10T19:00:01Z

Debra successfully defended her PhD dissertation on November 10, 2011. TITLE: The Impact of Upper Tropospheric Dynamics on Surface Air Quality over the United States ABSTRACT: Monitoring air quality and source attribution at the surface requires a vast understanding of radiative and dynamical effects in the lower atmosphere to capture influential processes affecting human health, the environment, and current pollutant standards. In order to accurately determine all sources impacting lower atmospheric composition, a more thorough comprehension of the dynamical, chemical, and radiative coupling of the stratosphere and troposphere is required. Particularly significant is the transport or exchange of trace gases, both natural and anthropogenic, between the stratosphere and troposphere also known as stratosphere-troposphere exchange (STE). During previous research campaigns, STE was found to contribute to the tropospheric ozone budget. In this work, a plan was designed to determine whether or not stratosphere-to-troposphere transport (STT) was a viable mechanism for elevated ozone at the surface, particularly in cases where unhealthy air quality conditions were detected. An investigation of several case studies in which high levels of surface ozone appear to originate from the stratosphere shows that a variety of dynamical processes from the boundary layer to the lower stratosphere are involved. Starting with the quasigeostrophic equations of vertical and horizontal motion, dynamical parameters can be derived and evaluated from the North American Regional Reanalysis (NARR) meteorological fields. Reanalysis diagnostics, such as Q-vector, can locate the prevailing STT mechanism and capture the extent of vertical transport and mixing into the lower troposphere. Back trajectories from the University of Maryland Baltimore County - Lagrangian Trajectory (UMBC-LT) model released at the ground sites present additional support. Along with the reanalysis dataset, a combination of satellite-retrieved and surface observations of chemical tracers were utilized to demonstrate the plausibility of a stratospheric source and to rule out anthropogenic surface contributions where possible. The practicality of Atmospheric InfraRed Sounder (AIRS), Tropospheric Emission Spectrometer (TES), and High Resolution Dynamics Limb Sounder (HIRDLS) satellite observations to infer stratospheric transport as the probable source was tested for these case studies and the results supported dynamical evidence of STE using tracer correlations, as in the ozone-water vapor relationship. The overall strategy of implementing satellite, reanalysis, and surface measurements together provided strong evidence that unhealthy ozone anomalies at the ground were incurred primarily by STE in these events and setup future studies of resulting ozone signatures.

Congratulations!

2011-11-02T20:46:34Z

Congratulations to our 2010-2011 Doctoral Candidates!

November 2, 2011: Congratulations to our Physics Graduate Students who passed into PhD Candidacy during the past year: Sheng Liu (mentor: Dr. Johnson), Felipe Vallejo Monsalve (mentor: Dr. Hayden), Tao Peng (mentor: Dr. Shih), Malachi Tatum (mentor: Dr. Turner), Anthony Davidson (mentor: Dr. Worchesky), Gergely Dolgos (mentor: Dr. Martins), Steven Buczkowski (mentor: Dr. Martins). These students were honored at the annual Graduate School Doctoral Candidates Reception last night. Pictured (left to right) are Anthony Davidson, Dr. T. Worchesky, and Malachi Tatum.

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

2011-11-02T20:25:32Z

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

Blast Off!

2011-11-02T04:30:02Z

UMBC's Prof. Strow, NPP/CrIS, & the future of weather predictions

On 2011 Oct 28 the NPP satellite was launched successfully from Vandenberg AFB. NPP is an acronym for the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project [acronyms can be your friend!]

NPP is the first of a new generation of satellites to monitor/predict the long-term climate change AND short-term weather conditions. One of the several instruments on board is the Cross-track Infrared Sounder (CrIS) that provides spectra in ~1300 bins in 3 important bands in the infrared part of the electromagnetic spectrum. UMBC Physics Professor Dr Larrabee Strow leads a team calibrate CrIS. The instrument can measure Earth's surface temperature and atmospheric parameters such as the major 'Greenhouse Gases' H₂0, CO₂ (carbon dioxide) & CH₄ (methane).