Physics Commons^™

Linked-Cluster Expansion For The Green's Function Of The Infinite-U Hubbard Model, Ehsan Khatami, Edward Perepelitsky, Marcos Rigol, Sriram B. Shastry

Faculty Publications

We implement a highly efficient strong-coupling expansion for the Green's function of the Hubbard model. In the limit of extreme correlations, where the onsite interaction is infinite, the evaluation of diagrams simplifies dramatically enabling us to carry out the expansion to the eighth order in powers of the hopping amplitude. We compute the finite-temperature Green's function analytically in the momentum and Matsubara frequency space as a function of the electron density. Employing Padé approximations, we study the equation of state, Kelvin thermopower, momentum distribution function, quasiparticle fraction, and quasiparticle lifetime of the system at temperatures lower than, or of the …

Application Of An Isogeometric Boundary Element Method To The Calculation Of Acoustic Radiation Modes And Their Efficiencies, Candice Marie Humpherys

Theses and Dissertations

In contrast to the structural modes, which describe the physical motion of vibrating structures, acoustic radiation modes describe the radiated sound power. Radiation modes are beneficial in active noise control because reducing an efficiently radiating radiation mode guarantees the reduction of radiated sound power. Much work has been done to calculate the radiation modes for simple geometries, where analytic solutions are available. In this work, isogeometric analysis (IGA) is used to provide a tool capable of analyzing the radiation modes of arbitrarily complex geometries. IGA offers increased accuracy and efficiency by using basis functions generated from Non-Uniform Rational B-Splines (NURBS) …

Radiative Cooling Ii: Effects Of Density And Metallicity, Ye Wang, Gary J. Ferland, Matt Lykins, R. L. Porter, Peter A. M. Van Hoof, R. J. R. Williams

Physics and Astronomy Faculty Publications

This work follows Lykins et al. discussion of classic plasma cooling function at low density and solar metallicity. Here, we focus on how the cooling function changes over a wide range of density (n_H <10¹² cm⁻³) and metallicity (Z < 30 Z_⊙). We find that high densities enhance the ionization of elements such as hydrogen and helium until they reach local thermodynamic equilibrium. By charge transfer, the metallicity changes the ionization of hydrogen when it is partially ionized. We describe the total cooling function as a sum of four parts: those due to H&He, the heavy …

The Ninja-2 Project: Detecting And Characterizing Gravitational Waveforms Modelled Using Numerical Binary Black Hole Simulations, J. Aasi, B. Abbott, R. Abbott, T. Abbott, M. R. Abernathy, T. Accadia, Mario C. Diaz, Malik Rakhmanov, Joseph D. Romano, Soma Mukherjee, Volker Quetschke, Teviet Creighton, Robert Stone

Physics and Astronomy Faculty Publications and Presentations

The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational-wave (GW) astrophysics communities. The purpose of NINJA is to study the ability to detect GWs emitted from merging binary black holes (BBH) and recover their parameters with next-generation GW observatories. We report here on the results of the second NINJA project, NINJA-2, which employs 60 complete BBH hybrid waveforms consisting of a numerical portion modelling the late inspiral, merger, and ringdown stitched to a post-Newtonian portion modelling the early inspiral. In a ‘blind injection challenge’ similar to that conducted in recent Laser …

Veritas Very High Energy Observations Of The Distant Blazar 1es 0647+250, Margaret R. Molter, Jon Dumm, Lucy Fortson

Macalester Journal of Physics and Astronomy

We perform an analysis of the long- and short-term variability of the very high energy (VHE; above 100 GeV) gamma-ray emission from the newly-detected distant blazar 1ES 0647+250. Both new and archival data from the VERITAS telescope were examined, and no strong evidence for integral flux variability on any timescale was found. This lack of variability is consistent with the application of current ultra-high energy cosmic ray (UHECR) models, which can produce secondary gamma-ray emission along the line of sight from the blazar; it also allows averaging over multiyear timescales without bias, aiding in the construction of spectral energy distribution …

Finesse Measurement In Fabry-Perot Interferometers, Michael C. Darrow

Macalester Journal of Physics and Astronomy

STAR (Space-time Asymmetry Research) is an experimental satellite that will measure anisotropy in the speed of light to unprecedented resolutions using two orthogonal Fabry- Perot interferometers. In order to achieve the desired level of precision, the optical cavities must have finesse values greater than 100,000. Using two test interferometers, I tested and optimized two different experimental methods for measurement of finesse: full-width half max measurement and cavity ring-down spectroscopy. Although each technique proved valid in its own right, my work suggests that cavity ring-down spectroscopy may be more applicable for the needs of STAR.

Monte Carlo Simulations Of Atmospheric Loss By Stellar Winds From Exoplanets, Daniel P. Violette

University Scholar Projects

Hot Jupiters are a class of extra-solar planets. Massive gas giants on the same size scale as Jupiter, they orbit their host stars closely. This proximity results in large stellar winds capable of stripping away a planet’s atmosphere. Developing a more complete understanding of atmospheric mass loss and evolution in planetary bodies is critical, and Hot Jupiter systems are accessible analogues.

This project will seek to create a computational model capable of estimating mass loss rates due to stellar winds. A Monte Carlo method is utilized to take an ensemble of single, high-energy energetic neutral particles, produced by kilo-electronvolt stellar …

Monte Carlo Simulations Of Atmospheric Loss By Stellar Winds From Exoplanets, Daniel Violette

Honors Scholar Theses

Hot Jupiters are a class of extra-solar planets. Massive gas giants on the same size scale as Jupiter, they orbit their host stars closely. This proximity results in large stellar winds capable of stripping away a planet’s atmosphere. Developing a more complete understanding of atmospheric mass loss and evolution in planetary bodies is critical, and Hot Jupiter systems are accessible analogues.

This project will seek to create a computational model capable of estimating mass loss rates due to stellar winds. A Monte Carlo method is utilized to take an ensemble of single, high-energy energetic neutral particles, produced by kilo-electronvolt stellar …

Subaru Spectroscopy And Spectral Modeling Of Cygnus A, Matthew J. Merlo, Erik S. Perlman, Robert Nikutta, Christopher Packham, Moshe Elitzur, Masatoshi Imanishi, N. A. Levenson, James T. Radomski, Itziar Aretxaga

Physics and Astronomy Faculty Publications

We present high angular resolution (~0.''5) MIR spectra of the powerful radio galaxy, Cygnus A (Cyg A), obtained with the Subaru telescope. The overall shape of the spectra agree with previous high angular resolution MIR observations, as well as previous Spitzer spectra. Our spectra, both on and off nucleus, show a deep silicate absorption feature. The absorption feature can be modeled with a blackbody obscured by cold dust or a clumpy torus. The deep silicate feature is best fit by a simple model of a screened blackbody, suggesting that foreground absorption plays a significant, if not dominant, role in shaping …

On The Observability Of Optically Thin Coronal Hyperfine Structure Lines, Marios Chatzikos, Gary J. Ferland, R. J. R. Williams, A. C. Fabian

Physics and Astronomy Faculty Publications

We present CLOUDY calculations for the intensity of coronal hyperfine lines in various environments. We model indirect collisional and radiative transitions, and quantify the collisionally excited line emissivity in the density-temperature phase space. As an observational aid, we also express the emissivity in units of that in the 0.4-0.7 keV band. For most hyperfine lines, knowledge of the X-ray surface brightness and the plasma temperature is sufficient for rough estimates. We find that the radiation fields of both Perseus A and Virgo A can enhance the populations of highly ionized species within 1 kpc. They can also enhance line emissivity …

Electronic Device Incorporating Memristor Made From Metallic Nanowire, Douglas R. Strachan, Stephen L. Johnson

Physics and Astronomy Faculty Patents

An electronic device includes a first electrode, a second electrode and a nanowire connected between the first and second electrodes to allow electric current flow. The nanowire is made from a conductive material exhibiting a variable resistance due to electromigration. The nanowire is repeatably switchable between two states. A voltage clamp operates through feedback control to maintain the voltage across the nanowire and prevent thermal runaway.

Investigating Evidence For Different Black Hole Accretion Modes Since Redshift Z ∼ 1, A. Georgakakis, P. G. Pérez-González, N. Fanidakis, M. Salvato, J. Aird, H. Messias, J. M. Lotz, G. Barro, Li-Ting Hsu, K. Nandra, D. Rosario, M. C. Cooper, Dalibor D. Kocevski, J. A. Newman

Physics and Astronomy Faculty Publications

Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U − V versus V − J colours of X-ray AGN hosts in the redshift intervals 0.1 < z < 0.6 (mean z¯=0.40) and 0.6 < z < 1.2 (mean z¯=0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by theirU − V versus V − J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early- and late-type hosts. The position of AGN hosts on the U − V versusV − J diagram is then used to set limits on the accretion density of the …

Multidimensional Simulations Of Non-Linear Cosmic Ray Production In Supernova Remnant Evolution, Joshua Wood

All Dissertations

When a high-mass star (& 4Msun) explodes at the end of its life, a supernova occurs, leaving its degenerate core and a fast-moving shell of matter, known as a supernova remnant (SNR). The SNR shell lasts for many thousands of years, generating emissions from low-frequency radio (~ 10-7 eV) up to γ-ray regime (~ 1015 eV). It is also believed that SNRs are the predominant source of galactic cosmic rays, accelerating a population of thermal ions, primarily protons, up to relativistic energies by means of the diffusive shock acceleration (DSA) mechanism. The small population of thermal (Boltzmann) particles, p ~ …

Physics Of Gamma-Ray Bursts And Multi-Messenger Signals From Double Neutron Star Mergers, He Gao

UNLV Theses, Dissertations, Professional Papers, and Capstones

My dissertation includes two parts:

Physics of Gamma-Ray Bursts (GRBs): Gamma-ray bursts are multi-wavelength transients, with both prompt gamma-ray emission and late time afterglow emission observed by telescopes in different wavelengths. I have carried out three investigations to understand GRB prompt emission and afterglow. Chapter 2 develops a new method, namely, "Stepwise Filter Correlation" method, to decompose the variability components in a light curve. After proving its reliability through simulations, we apply this method to 266 bright GRBs and find that the majority of the bursts have clear evidence of superposition of fast and slow variability components. Chapter 3 gives …

Dust Properties Of Z~2 Infrared-Luminous Lyman Break Galaxies., Jennifer Leigh Wojno

Electronic Theses and Dissertations

Lyman break galaxies (LBGs) are well-known indicators of star formation. By analyzing the dust of moderate redshift (z ~ 2) LBGs, we can further investigate the properties of these strongly star forming galaxies at an epoch when global star formation is expected to peak. Using data observed by the Herschel satellite, we derive far-infrared fluxes for our color-selected sample of LBGs in the GOODS-S field, including a subsample of infrared-luminous LBGs (ILLBGs). This is one of the first samples of UV dropouts/partial dropouts, which are also infrared-luminous, to be studied for their far-IR properties. Fitting modified Planck curves and model …

Mri Characterization Of Cobalt Dichloride-N-Acetyl Cysteine (C4) Contrast Agent Marker For Prostate Brachytherapy, Tze Yee Lim, R. Jason Stafford, Rajat J. Kudchadker, Madhuri Sankaranarayanapillai, Geoffrey Ibbott, Arvind Rao, Karen S. Martirosyan, Steven J. Frank

Physics and Astronomy Faculty Publications and Presentations

Brachytherapy, a radiotherapy technique for treating prostate cancer, involves the implantation of numerous radioactive seeds into the prostate. While the implanted seeds can be easily identified on a CT image, distinguishing the prostate and surrounding soft tissues is not as straightforward. Magnetic Resonance Imaging (MRI) offers superior anatomical delineation, but the seeds appear as dark voids and are difficult to identify, thus creating a conundrum. Cobalt dichloride-N-acetylcysteine (C4) has previously been shown to be promising as an encapsulated contrast agent marker. We performed spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements of C4 solutions with varying cobalt dichloride …

Perihelion Precession In General Relativity, Charles G. Torre

Charles G. Torre

This is a Maple worksheet providing a relatively quick and informal sketch of a demonstration that general relativistic corrections to the bound Kepler orbits introduce a perihelion precession. Any decent textbook will derive this result. My analysis aligns with that found in the old text "Introduction to General Relativity", by Adler, Bazin and Schiffer. The plan of the analysis is as follows. * Model the planetary orbits as geodesics in the (exterior) Schwarzschild spacetime. * Compute the geodesic equations. * Simplify them using symmetries and first integrals. * Isolate the differential equation expressing the radial coordinate as a function of …

Experimental Observation Of Lasing Shutdown Via Asymmetric Gain, M. Chitsazi, S. Factor, J. Schindler, Hamidreza Ramezani, F. M. Ellis, T. Kottos

Physics and Astronomy Faculty Publications and Presentations

Using a pair of coupled RLC cavities we experimentally demonstrate that amplification action can be tamed by a spatially inhomogeneous gain. Under specific conditions we observe the counterintuitive phenomenon of stabilization of the system even when the overall gain provided is increased. This behavior is directly related to lasing shutdown via asymmetric pumping, recently proposed in M. Liertzer et al. [Phys. Rev. Lett. 108, 173901 (2012)]. The analysis of other simple systems reveals the universal nature of the lasing shutdown phenomenon as having its roots in managing impedance matching.

Event-Plane-Dependent Dihadron Correlations With Harmonic VN Subtraction In Au + Au Collisions At √SNn=200 Gev, H Agakishiev, M. M. Aggarwal, Z. Ahammed, A. V. Alakhverdyants, I. Alekseev, J. Alford, B. D. Anderson, C. D. Anson, D. Arkhipkin, G. S. Averichev, Renee H. Fatemi, Robert G. Fersch, Wolfgang Korsch, G. Webb, Wayne Otto Witzke

Physics and Astronomy Faculty Publications

STAR measurements of dihadron azimuthal correlations (Δϕ) are reported in midcentral (20–60%) Au + Au collisions at √^sNN = 200 GeV as a function of the trigger particle's azimuthal angle relative to the event plane, ϕ_s = |ϕ_t − ^ψEP |. The elliptic (^v2), triangular (^v3), and quadratic (^v4) flow harmonic backgrounds are subtracted using the zero yield at minimum (ZYAM) method. The results are compared to minimum-bias d + Au collisions. It is found that a finite near-side (|Δϕ| < π/2) long-range pseudorapidity correlation (ridge) is present in the in-plane direction (ϕ_s∼0). The …

Ds/Cft At Uniform Energy Density And A De Sitter “Bluewall”, Diptarka Das, Sumit R. Das, K. Narayan

Physics and Astronomy Faculty Publications

We describe a class of spacetimes that are asymptotically de Sitter in the Poincare slicing. Assuming that a dS/CFT correspondence exists, we argue that these are gravity duals to a CFT on a circle leading to uniform energy-momentum density, and are equivalent to an analytic continuation of the Euclidean AdS black brane. These are solutions with a complex parameter which then gives a real energy-momentum density. We also discuss a related solution with the parameter continued to a real number, which we refer to as a de Sitter “bluewall”. This spacetime has two asymptotic de Sitter universes and Cauchy horizons …

Lensed Type Ia Supernovae As Probes Of Cluster Mass Models, J Nordin, David Rubin, J Richard, E Rykoff, Greg Aldering, R Amanullah, H Atek, K Barbary, S Deustua, H K. Fakhouri, A S. Fruchter, A Goobar, I Hook, E Y. Hsiao, Xiaosheng Huang, J P. Kneib, C Lidman, J Meyers, S Perlmutter, C Saunders, A L. Spadafora, N Suzuki

Physics and Astronomy

Using three magnified Type Ia supernovae (SNe Ia) detected behind CLASH (Cluster Lensing and Supernovae with Hubble) clusters, we perform a first pilot study to see whether standardizable candles can be used to calibrate cluster mass maps created from strong lensing observations. Such calibrations will be crucial when next-generation Hubble Space Telescope cluster surveys (e.g. Frontier) provide magnification maps that will, in turn, form the basis for the exploration of the high-redshift Universe. We classify SNe using combined photometric and spectroscopic observations, finding two of the three to be clearly of Type Ia and the third probable. The SNe exhibit …

Dipole Bound Excited States Of Polycyclic Aromatic Hydrocarbons Containing Nitrogen And Their Relation To The Interstellar Medium, Mallory L. Theis

Honors College Theses

Polycyclic aromatic hydrocarbons (PAHs) are the most abundant type of molecule present in the interstellar medium (ISM). It has been hypothesized that nitrogen replacement within a ring is likely for PAHs present in the ISM. Additionally, electrons, protons, and hydrogen atoms are readily added to or removed from PAHs creating a truly diverse set of chemistries in various interstellar regions. The presence of a nitrogen within a PAH (called a PANH herein) that is additionally dehydrogenated leads to a neutral radical with a large dipole moment. It has recently been shown through the use of high-level quantum chemical computations for …

Single Spin Asymmetries Of Inclusive Hadrons Produced In Electron Scattering From A Transversely Polarized 3He Target, K. Allada, Y. X. Zhao, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, C. Dutta, Ameya Suresh Kolarkar, Wolfgang Korsch

Physics and Astronomy Faculty Publications

We report the first measurement of target single spin asymmetries (A_N) in the inclusive hadron production reaction, e+³He^↑→h+X, using a transversely polarized ³He target. The experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons (π^±, K^±, and proton) were detected in the transverse hadron momentum range 0.54 <p_T< 0.74 GeV/c. The range of x_F for pions was −0.29 <x_F< −0.23 and for kaons was −0.25 <x_F< −0.18. The observed asymmetry strongly depends on the type of hadron. A positive asymmetry is observed for π⁺ and K⁺. A negative asymmetry is observed for π⁻. The …

Dark Matter As An Integral Part Of An Alternative Gravity Model, Hontas Farmer

Hontas F Farmer

The purpose of this paper is to reconcile observations of dark matter effects on the galactic and cosmological scales with the null results of astroparticle physics observations such as CDMS and ANTARES. This paper will also provide a candidate unified and simpler mathematical formulation for the Lambda CDM model. Unification is achieved by a combination of the f(R) approach, with the standard LCDM approach and inflationary models. It is postulated that dark matter-energy fields depend on the Ricci curvature R. Standard methods of classical and quantum field theory on curved space time are applied. When this model is treated as …

Section Abstracts: Astronomy, Mathematics, And Physics With Materials Science

Virginia Journal of Science

Abstracts of the Astronomy, Mathematics, and Physics with Materials Science Section for the 92nd Annual Meeting of the Virginia Academy of Science, May 13-15, 2014, Virginia Commonwealth University, Richmond, Virginia

The Physics Of A Space Elevator, Trevor Hamer

Thinking Matters Symposium Archive

A space elevator is a hypothetical device consisting of a long cable attached to the surface of the earth that extends upward into space. Its purpose is to provide a tether on which a vehicle could be lifted up into orbit, greatly reducing the cost of space travel. This project explains the physical forces acting on the elevator along with the kinds of materials required to keep such a cable intact. It also examines different design aspects, as well as potential problems facing the construction and usage of the elevator, and whether or not it is something we should expect …

Forbidden Fe Ii Emission Line Fluxes From The Weigelt Knots Of Eta Carinae, S. Towers

Masters Theses

Eta Carinae is an unparalleled object crossing many divisions of astrophysics. It has multiple, complicated and dynamic processes leading to absorption and emission spectra across all wavelengths from radio to hard x-ray. The spectra differ spatially across Eta Carinae's extended envelope and are changing rapidly over time.

The Weigelt Knots of Eta Carinae's ejecta emit spectra of numerous forbidden iron species lines, rare on Earth, but prevalent in the unique conditions surrounding this star. The Weigelt Knots' unique conditions occur almost nowhere else, making Eta Carinae, useful not only for understanding massive stars similar to it, but for understanding the …

Fermi-Normal, Optical, And Wave-Synchronous Coordinates For Spacetime With A Plane Gravitational Wave, Malik Rakhmanov

Physics and Astronomy Faculty Publications and Presentations

Fermi-normal (FN) coordinates provide a standardized way to describe the effects of gravitation from the point of view of an inertial observer. These coordinates have always been introduced via perturbation expansions and were usually limited to distances much less than the characteristic length scale set by the curvature of spacetime. For a plane gravitational wave this scale is given by its wavelength which defines the domain of validity for these coordinates known as the long-wavelength regime. The symmetry of this spacetime, however, allows us to extend FN coordinates far beyond the long-wavelength regime. Here we present an explicit construction for …

Experimental Observation Of Lasing Shutdown Via Asymmetric Gain, M. Chitsazi, S. Factor, J. Schindler, Hamidreza Ramezani

Physics and Astronomy Faculty Publications and Presentations

Using a pair of coupled RLC cavities we experimentally demonstrate that amplification action can be tamed by a spatially inhomogeneous gain. Under specific conditions we observe the counterintuitive phenomenon of stabilization of the system even when the overall gain provided is increased. This behavior is directly related to lasing shutdown via asymmetric pumping, recently proposed in M. Liertzer et al. [Phys. Rev. Lett. 108, 173901 (2012)]. The analysis of other simple systems reveals the universal nature of the lasing shutdown phenomenon as having its roots in managing impedance matching.

Jet-Hadron Correlations In √SNn=200 Gev P+P And Central Au+Au Collisions, L. Adamczyk, James K. Adkins, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, I. Alekseev, J. Alford, C. D. Anson, A. Aparin, D. Arkhipkin, Renee H. Fatemi, Suvarna Ramachandran, G. Webb

Physics and Astronomy Faculty Publications

Azimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in Au+Au and p+p collisions at √^sNN=200  GeV in STAR are presented. The trigger jet population in Au+Au collisions is biased toward jets that have not interacted with the medium, allowing easier matching of jet energies between Au+Au and p+p collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum (p^assoc_T) and enhanced at low p^assoc_T in 0%–20% central …