Physics Announcementstag:www.umbc.edu,2014:/blogs/physics//602014-02-18T14:52:10ZAnnouncements for the Department of Physics at UMBCMovable Type 3.34Seminar: Wednesday, April 23 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175282014-04-23T20:29:13Z2014-02-18T14:52:10Z Radio Galaxies near and far: 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...stignall
Radio Galaxies near and far:
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
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Seminar: Monday, March 10 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175182014-03-10T18:29:42Z2014-02-28T18:33:07Z Aircraft Observations and Modeling of Cloud and Aerosol Radiative Effects Sebastian Schmidt University of Colorado Laboratory for Atmospheric and Space Physics Our ability to understand how solar energy is distributed and deposited on our planet has greatly improved over...stignall
Aircraft Observations and Modeling of Cloud and Aerosol Radiative Effects
Sebastian Schmidt
University of Colorado
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
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Seminar: Wednesday, March 5 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175322014-03-05T20:30:01Z2014-02-25T15:00:44Z 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...stignall
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
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Seminar: Wednesday, Feb 26 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175312014-02-26T20:29:59Z2014-02-25T14:43:28Z 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...stignall
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
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Seminar: Wednesday, Feb. 19 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175172014-02-19T18:30:01Z2014-02-07T19:40:44Z 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...stignall
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
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Seminar: Wednesday, Feb 12 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175202014-02-12T20:28:55Z2014-02-07T20:40:01Z 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...stignall
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
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Seminar: Wednesday Feb 3 at 3:30 pmtag:www.umbc.edu,2014:/blogs/physics//60.175212014-02-03T20:30:30Z2014-02-07T20:04:44Z 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...stignall
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
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PhD Proposal - John Sullivantag:www.umbc.edu,2013:/blogs/physics//60.174932014-01-06T12:52:37Z2013-12-23T16:57:45ZDate: Monday, January 6, 2014 Time: 8:00 am Location: PHYS 401 TITLE: A New Differential Absorption Lidar Using Raman Cells to Measure Subhourly Variation of Tropospheric Ozone Profiles in the Baltimore - Washington D.C. region ABSTRACT: This proposal will detail...Jen Salmi
Date: Monday, January 6, 2014
Time: 8:00 am
Location: PHYS 401
TITLE:
A New Differential Absorption Lidar Using Raman Cells to Measure Subhourly Variation of Tropospheric Ozone Profiles in the Baltimore - Washington D.C. region
ABSTRACT:
This proposal will detail the theory and background necessary for the ground based tropospheric ozone Differential Absorption Lidar (DIAL) system at the NASA Goddard Space Flight Center (Greenbelt, MD 38.99° N, 76.84° W, 57 meters ASL), with initial results from 500 m to 10 km in Summer 2013. Current atmospheric satellites cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, NASA has funded the ground based Tropospheric Ozone Lidar Network (TOLNET) which currently consists of five stations across the US. The Goddard instrument is based on the Differential Absorption Lidar (DIAL) technique, which transmits three wavelengths, 266, 289 and 299 nm. Ozone is absorbed more strongly at 266 nm and 289 nm than at 299 nm. The DIAL technique exploits this difference between the returned backscatter signals to obtain the ozone number density as a function of altitude. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman Cells, filled with high pressure Hydrogen and Deuterium. Stimulated Raman Scattering within the focus shifts the pump wavelength and the first Stokes shift in each cell produces the required wavelengths. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range resolved number density can then be derived. A interesting scientific validation data set will be examined, which yields accurate initial results. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make continuous routine ozone profile measurements in the Washington, DC - Baltimore area.]]>
PhD Proposal - Diana Marcutag:www.umbc.edu,2013:/blogs/physics//60.174832013-12-12T14:43:03Z2013-12-03T14:46:51ZDate: Thursday, December 12, 2013 Time: 1:00 pm Location: PHYS 401 TITLE: Shedding New Light on Accreting Pulsars ABSTRACT: Neutron stars are remnants of stellar evolution, the collapsed cores of massive stars. They are extremely dense and sustained against further...Jen Salmi
Date: Thursday, December 12, 2013
Time: 1:00 pm
Location: PHYS 401
TITLE:
Shedding New Light on Accreting Pulsars
ABSTRACT:
Neutron stars are remnants of stellar evolution, the collapsed cores of massive stars. They are extremely dense and sustained against further gravitational collapse by neutron degeneracy pressure. Many have the strongest magnetic fields found in the universe. Accreting X-ray pulsars are rotating neutron stars which show regular flashes of X-ray emission powered by the accretion of material from a stellar companion onto the magnetic poles of the neutron star. The processes that take place at the poles involve strong gravitational fields, high temperatures and the most extreme magnetic fields. These are conditions that cannot take place naturally on Earth and cannot be reproduced in laboratories.
In recent years, considerable progress has been made regarding the development of physical models describing the accretion process onto the magnetic poles such that these new models can now be tested for the first time. These new models can now provide the first direct connection between physical parameters of the accretion process (magnetic field strength, plasma temperature, plasma density, mass accretion rate) and X-ray spectral shape. The standard empirical and new physical spectral models will be systematically applied to a sample of pulsars. Most of the chosen pulsars show a “cyclotron line”, a spectral feature that allows for a direct measurement of their magnetic fields. This detailed spectral analysis will be mainly based on observations from the Japanese X-ray satellite, Suzaku, due to its instruments’ high sensitivity, spectral resolution, and broad-band coverage. (The project will also include additional satellite data of a Symbiotic X-ray Binary, a member of a small, under-studied subclass of X-ray pulsars accreting from a dense stellar companion wind. Its study will involve modeling the spectrum as well as characterizing the variability and comparing the results with more common X-ray binaries.)
The goal of this project is provide the first steps towards a much needed improvement of our theories and observational analysis of magnetically dominated accretion, which can only be achieved by fitting the best physical models to the best available data.]]>
Seminar: Wednesday, Dec 4, 2013 at 3:30 pmtag:www.umbc.edu,2013:/blogs/physics//60.174792013-12-04T18:29:36Z2013-11-25T16:51:42Z 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...stignall
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
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PhD Proposal - Daniel Orozcotag:www.umbc.edu,2013:/blogs/physics//60.174772013-11-27T15:00:01Z2013-12-03T14:30:59ZDate: Wednesday, November 27, 2013 Time: 10:00 am Location: PHYS 401 TITLE: Study of the Relative Humidity Impact on Atmospheric Aerosols by Phase Function and Polarization Measurements Using the Polarized Imaging Nephelometer PI-Neph ABSTRACT: Atmospheric aerosols influence the Earth's radiation...stignall
Date: Wednesday, November 27, 2013
Time: 10:00 am
Location: PHYS 401
TITLE:
Study of the Relative Humidity Impact on Atmospheric Aerosols by Phase Function and Polarization Measurements Using the Polarized Imaging Nephelometer PI-Neph
ABSTRACT:
Atmospheric aerosols influence the Earth's radiation budget by scattering and absorbing sunlight radiation. Aerosols also modify the microphysical and radiative properties, as well as the water content and lifetime of clouds. In atmosphere conditions, aerosol particles experience hygroscopic growth due to the relative humidity (RH) influence. Wet aerosols particles are larger than their dry equivalents; therefore, they scatter more light. The quantitative knowledge of the RH effect on aerosols and its influence on the ability to scatter light is of substantial importance when comparing ground-based observations with other optical aerosol measurements techniques such satellite and photometry retrievals as well as for climate forcing calculations. This study focuses on measurements of aerosol optical properties under the effect of RH by performing different experiments where aerosols are humidified. Our next goal is to investigate the effect of water on aerosol phase function and polarized phase function using the UMBC Polarized Imaging Nephelometer (PI-Neph) designed and built by the LACO group. This study will produce the first reports of laboratory generated and ambient aerosol polarization measurements at high levels of RH.
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PhD Proposal - Jane Spriggtag:www.umbc.edu,2013:/blogs/physics//60.174732013-11-25T17:29:26Z2013-12-03T14:38:15ZDate: Monday, November 25, 2013 Time: 12:30 pm Location: PHYS 401 TITLE: New measurement scheme for second-order correlation measurements of thermal light ABSTRACT: Experiments using second order correlations have proven to be important for many applications, such as the Hanbury...stignall
Date: Monday, November 25, 2013
Time: 12:30 pm
Location: PHYS 401
TITLE:
New measurement scheme for second-order correlation measurements of thermal light
ABSTRACT:
Experiments using second order correlations have proven to be important for many applications, such as the Hanbury Brown Twiss interferometer which measures the angular size of stars, three dimensional LIDAR imaging, ghost imaging, quantum computing, and lithography. Of these experiments, only one regularly uses thermal light: the Hanbury Brown Twiss interferometer. The other experiments usually use lasers or entangled light sources, which are less than practical for many real-world applications. In addition, entangled experiments are typically performed at the single photon level and prone to decoherence. However, all of these experiments can also be performed with thermal light, such as sunlight, if one condition is met: the temporal coherence is increased allowing many measurements to be made within the coherence time. This is problematic for thermal light, as its temporal coherence is the inverse of its bandwidth, on the order of 10^-15. Our goal is to investigate the use of linear and nonlinear optics to stretch the time-scale of thermal light, reducing the bandwidth and increasing the temporal coherence without drastically reducing the intensity, allowing Hui Chen's Positive Negative Fluctuation Correlation Protocol to be used. This would result in a new method to achieve high intensity, high contrast second-order correlation measurements with broadband thermal light.
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PhD Defense - Malachi Tatumtag:www.umbc.edu,2013:/blogs/physics//60.174642013-11-14T16:45:02Z2013-12-03T14:31:45ZYou're invited to attend Malachi's dissertation defense. Date: Thursday, November 14, 2013 Time: 9:45 am Location: PHYS 401 TITLE: Examining the Role of the Compton-thick, X-ray reprocessor in Type 1 Active Galactic Nuclei ABSTRACT: Studies have indicated that black holes...stignall
You're invited to attend Malachi's dissertation defense.
Date: Thursday, November 14, 2013
Time: 9:45 am
Location: PHYS 401
TITLE:
Examining the Role of the Compton-thick, X-ray reprocessor in Type 1 Active Galactic Nuclei
ABSTRACT:
Studies have indicated that black holes and their host galaxies must co-evolve, although the mechanism linking the two is not yet clear. X-ray observations of the actively accreting systems (active galactic nuclei, hereafter AGNs) over a valuable probe of conditions in the inner environs of the supermassive black hole, as X-ray production within these systems comprises a significant fraction (5%-40%) of the bolometric luminosity and originates close to the nucleus. Detailed spectroscopy in this bandpass has established that the inner environs comprise multiple X-ray absorbing zones with column densities extending into the Compton-thick regime (N_H > 10^24 atoms cm^-2). Compton-thick absorbers are known to have outflowing velocities up to 0.3c. The kinetic energy of oufltowing material with velocities > 0.1c may possibly be comparable to the gravitational binding energy of the stellar bulge and serve as a link between the black hole and the host galaxy. In addition, weak outflows may have a signicant effect on star formation in the host galaxy.
In this study, we use X-ray observations of radio-quiet AGN to examine some aspects of the flow of material between the black hole and the host galaxy. First, we model a small sample of unabsorbed Seyfert galaxies, finding their X-ray spectra to be consistent with arising as reflection from tens to hundreds of r_g in a Compton-thick, accretion disk wind of solar abundances seen face-on. Then, we explore properties of the local AGN population in the very hard band, above 10 keV, where there has been scant data available to date. We finnd a high flux for local AGN above 10 keV, and thus a very hard spectral shape over the Suzaku bandpass. Taken together, the spectral hardness and equivalent width of Fe K emission are consistent with reprocessing by an ensemble of Compton-thick clouds that partially cover the continuum source. Simple considerations place the distribution of Compton-thick clouds at or within 10^17 cm.
This work demonstrates not only that a Compton-thick wind can have a profound effect on the observed X-ray spectrum of an AGN, even when the system is not viewed through the flow, but that at least 50% of the continuum in type 1 AGNs is partially-covered by Compton-thick gas, suggesting that type 1 AGNs may not offer a completely direct view of the primary continuum, as once thought.]]>
PhD Proposal - Alex Henegartag:www.umbc.edu,2013:/blogs/physics//60.174612013-11-11T19:08:39Z2013-12-03T14:34:52ZDate: Monday, November 11, 2013 Time: 2:00 pm Location: PHYS 401 TITLE: Investigation of Atomic Layer Deposition of Metal Oxides on III-V Semiconductors ABSTRACT: Atomic layer deposition (ALD) is becoming a leading technique for the fabrication of nanoscale materials because...stignall
Date: Monday, November 11, 2013
Time: 2:00 pm
Location: PHYS 401
TITLE:
Investigation of Atomic Layer Deposition of Metal Oxides on III-V Semiconductors
ABSTRACT:
Atomic layer deposition (ALD) is becoming a leading technique for the fabrication of nanoscale materials because of its precise thickness control and unprecedented capability of film uniformity and surface conformality. Applications for such materials are diverse, ranging from Li-ion batteries and dye-sensitized solar cells to coatings on 3D structures and replacing SiO2 with high dielectric constant materials in metal oxide semiconductor field effect transistors (MOSFETs).
Our current understanding of ALD is based on ideal, one-pathway mechanisms. However, recent studies have shown we know very little about what reactions actually take place during ALD. The purpose of this research is to widen our understanding of the fundamentals of ALD by characterizing specific ALD processes such as the deposition Ta2O5 on InAs(100), post-deposition annealing effects on TiO2 thin films, the diffusion phenomenon of III-V semiconductor substrate atoms through metal oxide overlayers and explore the diffusion barrier capabilities of Al2O3 in these thin film systems.
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Seminar: Wednesday, Nov. 6, 2013 at 3:30 pmtag:www.umbc.edu,2013:/blogs/physics//60.174142013-11-06T18:28:50Z2013-10-10T16:09:03Z 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,...stignall
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
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