Subscribe to this blog's feed
- Seminar: Wednesday, May 8, 2013 at 3:30 pm
- Seminar: Wednesday, April 24, 2013 at 3:30 pm
- PhD Defense - Meimei Lai
- Seminar: Wednesday, April 17, 2013 at 3:30 pm
- Seminar: Wednesday, April 10, 2013 at 3:30 pm
- PhD Defense - Li Zhu
- Seminar: Wednesday, March 13, 2012 at 3:30 pm
- PhD Proposal - Thishan Dharshana
- PhD Proposal - Erin Balsamo
- Seminar: Wednesday, Dec. 5, 2012 at 3:30 pm
[What is this?
Announcements for the Department of Physics at UMBC
Joseph F. Mulligan Lecture
Neutrinos: History and their Role in Astrophysics
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
Nature's Accelerators and the Mysterious Origin of Galactic Cosmic Rays
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
Meimei successfully defended her dissertation on April 18, 2013.
Experiments Using Sub-Wavelength Diameter Tapered Optical Fibers in
In this work, we describe experimental research on a relatively new
nonlinear optics system comprised of a sub-wavelength diameter Tapered
Optical Fiber (TOF) suspended in atomic Rubidium (Rb) vapor. The
compression of the evanescent optical mode propagating along the TOF
enables a dramatic increase in the nonlinear interactions between the
fields and the surrounding Rb atoms, thereby allowing the observation of a
variety of nonlinear optical effects with very low-power fields.
Specifically, we report on the observation of saturated absorption with nW
power levels and, more significantly, the observation of two-photon
absorption using power-levels corresponding to only 10’s to 100’s of
photons interacting with the Rb atoms at a given time.
One significant drawback to this "TOF in Rb" system is that at the
relatively high atomic densities needed for many of these experiments, Rb
atoms accumulating on the TOF surface can cause a significant loss of
overall transmission through the fiber. Here we report direct measurements
of the time-scale associated with this transmission degradation for various
Rb density conditions. We find that transmission is affected almost
immediately after the introduction of Rb vapor into the system, and
declines rapidly as the density is increased.
More significantly, we show how a heating element designed to raise the
TOF temperature can be used to reduce this transmission loss and
dramatically extend the effective TOF transmission lifetime. Our results
indicate that it is possible to achieve relatively high TOF transmission,
even in the presence of the relatively high Rb vapor densities that would
be needed for many low-power nonlinear optics applications. This study
represents a significant step in moving the basic "TOF in Rb" system from a
laboratory setting towards a practical ultra-low-power nonlinear optics
Why are Pulsars observable
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
Precise measurement and enhanced imaging with entangled .
and correlated photons observation, physics and consequences'
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  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
Li successfully defended her dissertation on March 15, 2013.
Determination of the single scattering albedo and direct radiative forcing of biomass burning aerosol with data from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite instrument
Biomass burning aerosols absorb and scatter solar radiation and therefore affect the energy balance of the Earth-atmosphere system. The single scattering albedo (SSA), the ratio of the scattering coefficient to the extinction coefficient, is an important parameter to describe the optical properties of aerosols and to determine the effect of aerosols on the energy balance of the planet and climate. Aerosol effects on radiation also depend strongly on surface albedo. Large uncertainties remain in current estimates of radiative impacts of biomass burning aerosols, due largely to the lack of reliable measurements of aerosol and surface properties. In this work we investigate how satellite measurements can be used to estimate the direct radiative forcing of biomass burning aerosols. We developed a method using the critical reflectance technique to retrieve SSA from the Moderate Resolution Imaging Spectroradiometer (MODIS) observed reflectance at the top of the atmosphere (TOA). We evaluated MODIS retrieved SSAs with AErosol RObotic NETwork (AERONET) retrievals and found good agreements within the published uncertainty of the AERONET retrievals. We then developed an algorithm, the MODIS Enhanced Vegetation Albedo (MEVA), to improve the representations of spectral variations of vegetation surface albedo based on MODIS observations at the discrete 0.67, 0.86, 0.47, 0.55, 1.24, 1.64, and 2.12 µm channels. This algorithm is validated using laboratory measurements of the different vegetation types from the Amazon region, data from the Johns Hopkins University (JHU) spectral library, and data from the U.S. Geological Survey (USGS) digital spectral library. We show that the MEVA method can improve the accuracy of flux and aerosol forcing calculations at the TOA compared to more traditional interpolated approaches. Lastly, we combine the MODIS retrieved biomass burning aerosol SSA and the surface albedo spectrum determined from the MEVA technique to calculate TOA flux and aerosol direct radiative forcing over the Amazon region and compare it with Clouds and the Earth's Radiant Energy System (CERES) satellite results. The results show that MODIS based forcing calculations present similar averaged results compared to CERES, but MODIS shows greater spatial variation of aerosol forcing than CERES. Possible reasons for these differences are explored and discussed in this work. Potential future research based on these results is discussed as well.
The Microwave Response to Ice-Phase Precipitation
Dr. Benjamin Johnson
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
Date: Wednesday, January 9, 2013
Time: 2:00 pm
Location: PHYS 401
Improving estimates of CO emissions from biomass burning using FRP and its applicability to atmospheric models.
Biomass burning is responsible for the second largest source of Carbon emissions that include Carbon Dioxide (CO2), Carbon Monoxide (CO), and Methane (CH4) emissions. Despite the necessity of quantifying these emissions, a reliable and an efficient approach is unavailable. Hence, we are proposing a new approach, with the focus on CO, a trace gas where the remote sensing is well established and generated from a variety of satellite sensors. For comparison and validation purposes, ARCTAS field campaign is selected.
Despite the multi-sensor capability of several satellites, such as the Terra satellite that we are using at the primary stage of the analysis: MOPITT sensor to obtain CO data, MISR sensor for smoke plume height and MODIS sensor for FRP, there still remains constraints to be addressed. For example, MOPITT sensor is primarily sensitive only to the mid-troposphere so it is not capable of retrieving CO near the fire origin. However, when these high concentrations travel downwind and reach the altitude threshold sensitive to MOPITT, it is detectable by the MOPITT sensor. Throughout the transport, these CO fields move with visible smoke plumes detected by MISR. So, MODIS detected fire locations are connected to MISR detected smoke plumes, which in turn connected to MOPITT detected CO fields.
In applying the above methodology, GEOS-5 wind data will be used with WRF-Chem model to produce the forward transport and to link CO emissions from their sources to the current atmospheric distributions. Then to get the emission time frames, HYSPLITT back-trajectory analysis will be used. To validate the products, airborne measurements will be used with CO data from AQUA AIRS and AURA TES.
Date: Thursday, December 6, 2012
Location: PHYS 401
Developing and Characterizing X-ray Concentrators for Astronomical Observations and X-ray Polarization
Advancements in technology have caused a dramatic increase in the number of cosmic X-ray sources discovered and over the past half century. Dramatic increases in the sensitivity, and in the spatial, spectral, and temporal resolution of these instruments have led to numerous advances in our understanding of the physical conditions in almost every class of astronomical object. Several classes of such objects (such as neutron stars and supernova remnants) contain strong magnetic fields leading to a substantial fraction of the X-ray emission suspected of being polarized. Studies of polarized X-rays will therefore open up a new dimension in discovery space and help further constraint our models for these sources.
Unfortunately to date there have been minimal studies on X-ray polarization due to the lack of dedicated X-ray polarimeters on big missions. I am working with the X-ray advanced Concepts Testbed (XACT) sounding rocket project which will be launched next year to observe the Crab Nebula. The goal is to test the new technologies specifically designed to advance this field, specifically high throughout X-ray concentrators and a time projected gas chamber polarimeter. The Neutron star Interior Composition ExploreR (NICER) shares some of the same technology, yet for other scientific goals. I am working to develop a method to characterize and calibrate the technology with the instrument development teams. I will give a brief overview of the projects, explain the work I have completed so far, and describe the work planned for the remainder of my thesis.
"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