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Date Location Seminar
Wednesday, Oct.12, 2011
3.30 pm
TKH Room 103

Lemming Black Holes

M.Coleman Miller
Department of Astronomy
University of Maryland at College Park

Black holes withbillions of solar masses have been discovered
at redshifts as high as z=6.4, when the universe was less than abillion years old.  Given the probable formation time of thefirststars, this may not be enough time for the holes to grow
fromstellar-mass seeds via conventional pathways.  Recently, wesuggested a new scenario.  In the redshift z>10universe,mergers between galaxies that already had massive and dense stellarclusters would commonly bring in several times as much mass in gas asthere was in stars.  This has been shown in computersimulationsto lead to instabilities that can shepherd the gas to the center of theclusters, leading to contraction of the clusters and subsequentdestruction of their binaries. Without binary interactions to hold theclusters up, they can
undergo core collapse, in which the centraldensity becomes so high that initially unbound stellar-mass black holesmerge with each other via the emission of gravitational radiation.
These mergers run away, with each black hole joining in a shorter timethan the previous one, until most of the original black holes, alongwith neutron stars and white dwarfs, form a massive black hole seed ina short time.  This scenario, although speculative, seems tohaveadvantages in explaining the early supermassive black holes that havebeen observed.

May 10, 2011
4:30 pm

Room 103, Thirkield Hall

Dr.Mengs H. Weldegaber
Department of Physics &Astronomy
Howard University

Investigation of stableand unstable boundary layer phenomena using observations and anumerical weather prediction model
Despite significant advances in the simulation of synoptic scaleweather events, current numerical weather prediction models show poorskill in their capability to accurately simulate sub-grid scaleprocesses, such as cloud-precipitation processes and planetary boundarylayer (PBL) evolution, because too many semi-empiricalparameterizations are involved. The goal of the work presented here isto evaluate the next-generation mesoscale Weather Research andForecasting (WRF) model in simulating mesoscale weather phenomena underdifferent PBL stratifications. This study investigates the performanceof the state-of-the-art mesoscale WRF model in simulating the structureand development of a daytime convective boundary layer phenomenon, (thedryline over the Southern Great Plains), and a nocturnal stableboundary layer phenomenon, (the low level jet (LLJ) over theMid-Atlantic region). The dryline and LLJ are two examples of boundarylayer phenomena that occur under very different conditions and thustogether they provide a good test of the PBL dynamics in the model.Extensive, high spatial and temporal resolution remote sensing datacollected during these case studies is used to evaluate the numericalresults. For the unstable boundary layer, a detailed observationalanalysis of a non-convective dryline investigates an incorrectforecast. For the stable boundary layer, the accuracy of the timing andspatial characteristics of the LLJ for different PBL parameterizationsis investigated and discussed in terms of the LLJ forcing mechanisms.

Refreshments will beserved at 3:15 pm

May 9, 2011
4:30 pm
Room 103,Thirkield Hall

Ms.Narcrisha Norman
Department of Physics &Astronomy
Howard University

MODELING MONTE CARLOENTRY DESCENT AND LANDING ANALYSIS USING RESPONSE SURFACE METHODOLOGY
A full and complete understanding of the planetary entry, descent andlanding (EDL) process is an essential component of planetaryexploration. Research in this area is ongoing and confidence in ourability to explore known celestial bodies is growing. Based on anunderstanding of the Martian atmosphere and the Viking Lander, thepurpose of this research was to develop a unique technique for modelingreconstructed EDL scenarios. For this research project a simulation wasdeveloped to reconstruct Martian EDL scenarios. Design of Experiments(DoE) was used to design an experiment around sixteen input variablesand thirty-eight output variables pertinent to EDL. Response SurfaceMethodology (RSM) was used in conjunction with the EDL simulation todevelop thirty-eight second order regression models based on the outputvariables. These models were reduced using the Multiple AdjustedR-Squared Reduction (MARR) method. The MARR method, an algorithmdeveloped in conjunction with this research, is a process of reducingregression models so that their calculated Adjusted R-Squared (ARS)values are as close to the target ARS (0.99 +/- 0.004) as possible.Eighteen of the thirty-eight models develop met the Adjusted R-Squaredtarget and were further used in Monte Carlo experiments to test thesensitivity of the models and to develop EDL pertinent trade studiesbased on the reduced models.

Refreshments will beserved at 3:15 pm

April 27, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Silvina Gatica
Department of Physics & Astronomy
Howard University

SIMULATIONS OF THE SOLID PHASE OFKRYPTON AND ARGON ON A CARBON NANOTUBE
Recentexperiments have found evidence of phase transitions of gases adsorbedon a single carbon nanotube. In order to understand the observations,we have carried out classical grand canonical Monte Carlo simulationsof this system. In this talk I will discuss the results of thesimulations for Ar and Kr on zigzag and armchair nanotubes with radiusR > 0.7 nm. The calculated behavior resembles the experimentalresults in the case of Ar. However, the prominent, ordered phase foundfor Kr in both simulations and (classical) energy minimizationcalculations differs from that deduced from the experimental data. Atentative explanation of the apparent discrepancy is that theexperiments involve a nanotube of rather large radius (>1.5 nm).

Refreshments will beserved at 3:15 pm

April 13, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Anand Swaroop, Ph.D.
Senior Investigator and Chief, Neurobiology-Neurodegeneration &Repair Laboratory (N-NRL)
National Eye Institute, National Institutes of Health
Bethesda, MD 20892, USA

Treatment Paradigms from BasicBiology
Retinaland macular neurodegenerative diseases are a major cause of untreatableblindness worldwide. In most retinal diseases, the dysfunction or deathof photoreceptors leads to vision loss. A better understanding ofregulatory networks that control photoreceptor differentiation andhomeostasis would allow development of new approaches for treatment ortherapies of retinal neurodegeneration. NRL is a bZIP transcriptionfactor that is essential for differentiation of rod photoreceptors.Loss of NRL leads to cone-only retina. Ectopic expression of NRL inearly photoreceptor precursors produces rods. We generated Nrl-GFP micethat can be used to enrich committed but functionally undifferentiatedGFP-tagged rod precursors. Transplantation of rod precursors todegenerating mouse retina revealed the feasibility of cell-basedtherapies for retinal diseases. Recent successes in generatingphotoreceptors from stem cells clearly demonstrate that it should bepossible to translate basic research findings into clinically relevanttherapies for retinal repair. Several critical questions remain.
 
Iwill discuss our studies on NRL, including its key role inphotoreceptor development, and outline new approaches to understandpathways of photoreceptor degeneration and design targets for treatment.

Refreshments will beserved at 3:15 pm

April 6, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.William Ratcliff
NIST - CNR

The MultiferroicRenaissance
As early as 1894, Pierre Curie found that there were materials in whichthe magnetic and dielectric properties were coupled. Thesemagnetoelectric materials were studied for some time, but the couplingwas relatively weak. Later, people studied multiferroic materials inwhich both spontaneous ferroelectric and magnetic ordering occurs. Inthese materials, the coupling could be much stronger, but the materialswere exceeding rare.

Recently, several new compounds suchas TbMnO3 have been discovered and the field has enjoyed a renaissance,culminating in the award of the 2010 James C. McGroddy Prize for NewMaterials for research on these compounds. During this talk, I willtalk about the history of this field and the current state of theresearch. I will focus on one of the most technologically promisingmaterials, BiFeO3 and the critical role neutron scattering has playedin understanding the physics of these materials.

Refreshments will beserved at 3:15 pm

March 30, 2011
3:30 PM
Thirkield Hall(Physics), room 103

Dr.Paul Mahaffy
NASA Goddard Spaceflight Center

A New Generation of Science on theSurface of Mars with the Curiosity Rover
The next mission to be sent to the surface of Mars is designed toexplore the habitability of a carefully selected site on the surface ofour neighboring planet. A suite of instruments is presently underdevelopment for use on this rover that has been named “Curiosity”. TheSample Analysis at Mars (SAM) suite of instruments on Curiosityconsists of a quadrupole mass spectrometer (QMS) coupled to asix-column gas chromatograph (GC) and a tunable laser spectrometer(TLS) that utilizes a common gas processing system with the otherinstruments.

The SAM investigation is designed to revealthe chemical and isotopic composition of samples from the Martiansurface and atmosphere and to search for organic molecules. Theinvestigation is part of a larger exploration program directed towardunderstanding habitability of diverse environments in our solar systemand the origin and evolution of planets and more primitive solar systemobjects.

The science goals of the 2011 Mars ScienceLaboratory (MSL) with the Curiosity Rover tie directly to the ongoingsearch for life on Mars. We wish to characterize the landing siteselected as a potential habitat for past or present life. The top-levelscientific mission goals and specific investigations required are (1)to assess biological potential of at least one target environment (pastor present), (2) to investigate the chemical, isotopic, andmineralogical composition of Martian surface and near-surfacegeological materials, and (3) to study planetary processes thatinfluence habitability. We support this mission with a program ofplanetary analog research that includes laboratory simulations of Marsenvironments and chemical, geochemical, and isotopic field studies ofanalog sites.

Refreshments will beserved at 3:15 pm

March 23, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Prabhakar Misra
Laser Spectroscopy Laboratory,Department of Physics & Astronomy
Howard University

High Resolution LaserSpectroscopy Of Polyatomic Free Radicals, Ions And Clusters In ASupersonic Jet Expansion
The technique of Laser-Induced Fluorescence (LIF) spectroscopy, inconjunction with a supersonic jet expansion, has afforded a detailedspectroscopic characterization of moderately-sized organic molecules ofsignificance for plasma physics and combustion phenomena.1 With thedevelopment of several high level ab initio computational techniques,it is now possible to analyze and interpret in detail the electronicabsorption-excitation-emission spectra of polyatomic molecules and ionsin terms of the transitions between vibrational and rotational levelsof associated electronic states.2 Clusters are considered to beweakly-bound aggregates of atoms or molecules held together bynon-covalent bonds and they help in the elucidation of weakinteractions associated with hydrogen bonding and van der Waals forcesin play in polyatomic species. The ultra-cold environment of thesupersonic jet expansion enables one to generate size-specific clustersin the gas phase. Detailed characterization of positively charged ionsin terms of the ro-vibrational energy levels is possible using ZeroKinetic Energy (ZEKE) photoelectron spectroscopy3 and Mass AnalyzedThreshold Ionization (MATI) spectroscopy. All of the above highresolution spectroscopic techniques will be illustrated for specificpolyatomic free radicals, ions and clusters in a jet-cooled environment.

1 P. Misra, X. Zhu, C.-Y. Hsueh, and J.B. Halpern, Chemical Physics178, 377-385 (1993).
2 Ultraviolet Spectroscopy and UV Lasers, P. Misra and M. Dubinskii(eds.), Marcel Dekker, New York, 2002.
3 S. Chakraborty, P. Misra, and S. Wategaonkar, J. Chem. Phys. 127,124317 (2007).

Refreshments will beserved at 3:15 pm

SeminarCancelled for Today
March 9, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Gregory Jenkins/Dr. Miliaritiana Robjhon

Multi-site troposphericozone measurements across the Tropical north Atlantic during the summerof 2010
Two Intensive observing periods (IOP I, II) were carried out usingozone soundings over Dakar, Senegal; Sao Vicente, Cape Verde; andHusbands St James, Barbados to investigate ozone variability across thenorth Atlantic during the summer of 2010. Emphases were placed upon howSaharan dust and African Easterly Waves (AEWs) affect atmospheric ozonein the tropics. Electrochemical cell ozonesondes were launched at eachsite on scheduled routines to sample tropospheric ozone amount. IOP Iperiod was from June 15-July 17 with a focus on Saharan dust events,while IOP II occurred from Aug 15- Sept 15 with a focus on AEWs andprovided ground support for several aircraft missions. This fieldcampaign also provided research opportunities for undergraduate andgraduate students at Howard and Hampton Universities. Preliminaryresults will be presented.

Refreshments will beserved at 3:15 pm

March 2, 2011
3:30 PM
Thirkield Hall(Physics), room 103 Mr. Tommy Owens
SAIC, NASA Goddard Spaceflight Center

Data Assimilation and Reanalysis atthe NASA Global Modeling and Assimilation Office
Data assimilation provides powerful constraints on predictive models.In assimilation, models are used to synthesize diverse in-situ andsatellite data streams into a single product (analysis) that combinesthe strengths of each data set with those of the model. In the GlobalModeling and Assimilation Office, we focus on using data assimilationto improve the use of NASA’s satellite data for Numerical WeatherPrediction as well as developing ocean and land data assimilationsystems for climate analyses and short-term climate prediction.

One application of data assimilation is retrospective-analysis (orreanalysis) Reanalyses blend the continuity and breadth of output dataof a numerical model with the constraint of vast quantities ofobservational data. The result is a long-term continuous data record.Retrospective analyses have been a critical tool in studying weatherand climate variability for the last 15 years. As part of our missionto bring a climate perspective to NASA’s satellite data, we recentlyconducted an atmospheric reanalysis of the satellite era using ourGEOS-5 data assimilation system - the Modern Era Retrospective Analysisfor Research and Applications (MERRA).

Refreshments will beserved at 3:15 pm

February 23, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Howard J. Wood
NASA Goddard Space flight Center, Greenbelt, U.S.A.

Hubble Anthology
Orbiting high above the turbulence of the earth's atmosphere, theHubble Space Telescope (HST) is providing breathtaking views ofastronomical objects never before seen in such detail. The steadyimages allow this medium-size telescope to reach the faintest galaxiesever seen by mankind. Some of these galaxies are seen as early as 2billion years after the Big Bang in a 13.7 billion year old universe.HST has provided dramatic advances in all fields of Astronomy andAstrophysics since its launch in April 1990. Servicing by the SpaceShuttle has allowed correction of the optics and installation of newstate-of-the-art instruments over the 20 years the telescope has beenin orbit.

Seventy years ago Joseph Lisle Woods inBaltimore began observing with his new homemade 12-inch telescope. Thebrass clock drive kept the telescope tracking at the star rate. Therotating dome was a curiosity for the mail man because the slit was ina different position every morning. Joe invited a neighbor, me,8-year-old Johnny Wood, to come look at the moon, Mars and nebulae.Need I say that I was enthralled by the beauty of the objects we couldsee? So enthralled was I that I made a life commitment to study thestars.

Now, after 20 years of successful operations inspace, the HST has provided me with another discovery: the meaning ofobjects in the sky. A selection of some of the most beautiful imageswill demonstrate the power and utility of the HST. And I hope that youwill leave with a greater understanding of the meaning of the images.

Refreshments will beserved at 3:15 pm

February 16, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Chanda Prescod-Weinstein
NASA Postdoctoral Program Fellow, Observational Cosmology Lab, GoddardSpace Flight Center, Greenbelt, U.S.A.

The New Era of PrecisionCosmology: Testing Gravity at Large Scales
Abstract: Cosmic acceleration may be the biggest phenomenologicalmystery in cosmology today. Various explanations for its cause havebeen proposed, including the cosmological constant, dark energy andmodified gravities. Structure formation provides a strong test of anycosmic acceleration model because a successful dark energy model mustnot inhibit the development of observed large-scale structures.Traditional approaches to studies of structure formation in thepresence of dark energy or a modified gravity implement the Press&Schechter formalism (PSF). However, does the PSF apply in allcosmologies? The search is on for a better understanding ofuniversality in the PSF. In this talk, I explore the potential foruniversality and talk about what dark matter haloes may be able to tellus about cosmology. I will also discuss the implications of this andnew cosmological experiments for better understanding our theory ofgravity.

Refreshments will beserved at 3:15 pm

February 9, 2011
3:30 pm
Thirkield Hall(Physics), room 103

Dr.Ted Burkhardt
Temple University

From Random Walks toRubber: The Physics of Long Polymer Chains
Polymers are macromolecules made up of many repeating units. They areof central importance in chemistry and biology, plastics and DNA beingprominent examples. In solution a long, flexible polymer chaincontinually changes its shape due to thermal agitation, somewhat like astrand of spaghetti in a pot of boiling water. I will discuss some ofthe basic physical properties of long polymer chains, concentrating on“universal” properties that are independent of chemical details andapply to all polymers.

Refreshments will beserved at 3:15 pm

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