Physics Commons^™

Table Of Contents, Michele Harmon

Journal of the South Carolina Academy of Science

No abstract provided.

Molecular Hydrogen Regulated Star Formation In Cosmological Smoothed Particle Hydrodynamics Simulations, Robert Thompson, Kentaro Nagamine, Jason Jaacks, Jun-Hwan Choi

Physics and Astronomy Faculty Publications

Some observations have shown that star formation (SF) correlates tightly with the presence of molecular hydrogen (H₂); therefore, it is important to investigate its implication on galaxy formation in a cosmological context. In the present work, we implement a sub-grid model (hereafter H₂-SF model) that tracks the H₂ mass fraction within our cosmological smoothed particle hydrodynamics code GADGET-3 by using an equilibrium analytic model of Krumholz et al. This model allows us to regulate the SF in our simulation by the local abundance of H₂ rather than the total cold gas density, which naturally …

Dose Dependent Effects Of Caffeine On Cognitive Performance And Neuronal Activation, Stephan Albrecht, Helen Morris, Michelle Vieyra

Journal of the South Carolina Academy of Science

Many students assume that the more caffeine you drink, the better your cognitive performance. Over-consumption of caffeine has many negative effects, so if there are no dose related cognitive benefits to large amounts of caffeine, then college students should limit their intake. This study looked at whether ingesting a medium dose (200 mg) versus a lower dose (100 mg) of caffeine improved short term memory as measured by Flanker and n-back tests, compared to a control group. In addition, we looked at whether larger doses of caffeine produced a difference in neuronal activation during these tests as measured by functional …

Fourier Analysis Of Phase Resetting Curves Of Neural Oscillators, Robert A. Raidt, Sorinel A. Oprisan

Journal of the South Carolina Academy of Science

We investigated the impact of changes in biologically relevant control parameters, such as the shape of an external perturbation or the conductance values of an individual model neuron, on the shape of the phase resetting curve (PRC) of that neuron. For that purpose, PRCs were generated for groups of Morris-Lecar (ML) model neurons with different conductance values but similar firing periods (within 0.005ms) using external rectangular, triangular, or trapezoidal perturbations of varying areas. These PRCs were numerically described and analyzed as a series of coefficient values using a Fourier Discrete Sine Transform (DST). We found that changes in the shape …

Atomic Data For S Ii—Toward Better Diagnostics Of Chemical Evolution In High-Redshift Galaxies, Romas Kisielius, Varsha P. Kulkarni, Gary J. Ferland, Pavel Bogdanovich, Matt L. Lykins

Physics and Astronomy Faculty Publications

Absorption-line spectroscopy is a powerful tool used to estimate element abundances in both the nearby and distant universe. The accuracy of the abundances thus derived is naturally limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state of the art quantal calculations. Here, we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and …

Sensitivity Curves For Searches For Gravitational-Wave Backgrounds, E. H. Thrane, Joseph D. Romano

Physics and Astronomy Faculty Publications and Presentations

We propose a graphical representation of detector sensitivity curves for stochastic gravitational-wave backgrounds that takes into account the increase in sensitivity that comes from integrating over frequency in addition to integrating over time. This method is valid for backgrounds that have a power-law spectrum in the analysis band. We call these graphs “power-law integrated curves.” For simplicity, we consider cross-correlation searches for unpolarized and isotropic stochastic backgrounds using two or more detectors. We apply our method to construct power-law integrated sensitivity curves for second-generation ground-based detectors such as Advanced LIGO, space-based detectors such as LISA and the Big Bang Observer, …

Development And Validation Of An Automated Directivity Acquisition System Used In The Acquisition, Processing, And Presentation Of The Acoustic Far-Field Directivity Of Musical Instruments In An Anechoic Space, Nicholas J. Eyring

Theses and Dissertations

A high spatial resolution acoustic directivity acquisition system (ADAS) has been developed to acquire anechoic measurements of the far field radiation of musical instruments that are either remote controlled or played by musicians. Building upon work performed by the BYU Acoustic Research Group in the characterization of loudspeaker directivity, one can rotate a musical instrument with sequential azimuthal angle increments under a fixed semicircular array of microphones while recording repeated notes or sequences of notes. This results in highly detailed and instructive directivity data presented in the form of high-resolution balloon plots. The directivity data and corresponding balloon plots may …

The Progenitors Of The Compact Early-Type Galaxies At High Redshift, Christina C. Williams, Mauro Giavalisco, Paolo Cassata, Elena Tundo, Tommy Wiklind, Yicheng Guo, Bomee Lee, Guillermo Barro, Stijn Wuyts, Eric F. Bell, Christopher J. Conselice, Avishai Dekel, Sandra M. Faber, Henry C. Ferguson, Norman A. Grogin, Nimish Hathi, Kuang-Han Huang, Dalibor D. Kocevski, Anton M. Koekemoer, David C. Koo, Swara Ravindranath, Sarah Salimbeni

Physics and Astronomy Faculty Publications

We use GOODS and CANDELS images to identify progenitors of massive (M > 10¹⁰ M _☉) compact early-type galaxies (ETGs) at z ~ 1.6. Because merging and accretion increase the size of the stellar component of galaxies, if the progenitors are among known star-forming galaxies, these must be compact themselves. We select candidate progenitors among compact Lyman-break galaxies at z ~ 3 on the basis of their mass, star-formation rate (SFR), and central stellar density, and we find that these account for a large fraction of, and possibly all, compact ETGs at z ~ 1.6. We find that …

The Unexpectedly Bright Comet C/2012 F6 (Lemmon) Unveiled At Near-Infrared Wavelengths, Lucas Paganini, Michael Disanti, Michael Mumma, Geronimo Villanueva, Boncho Bonev, Jacqueline Keane, Erika Gibb, Hermann Boehnhardt, Karen Meech

Physics Faculty Works

We acquired near-infrared spectra of the Oort cloud comet C/2012 F6 (Lemmon) at three different heliocentric distances (R h) during the comet's 2013 perihelion passage, providing a comprehensive measure of the outgassing behavior of parent volatiles and cosmogonic indicators. Our observations were performed pre-perihelion at R h = 1.2 AU with CRIRES (on 2013 February 2 and 4), and post-perihelion at R h = 0.75 AU with CSHELL (on March 31 and April 1) and R h = 1.74 AU with NIRSPEC (on June 20). We detected 10 volatile species (H2O, OH* prompt emission, C2H6, CH3OH, H2CO, HCN, CO, CH4, …

The Unexpectedly Bright Comet C/2012 F6 (Lemmon) Unveiled At Near-Infrared Wavelengths, Lucas Paganini, Michael A. Disanti, Michael J. Mumma, Geronimo L. Villanueva, Boncho P. Bonev, Jacqueline V. Keane, Erika L. Gibb, Hermann Boehnhardt, Karen J. Meech

Erika Gibb

Effects Of External Radiation Fields On Line Emission—Application To Star-Forming Regions, Marios Chatzikos, Gary J. Ferland, R. J. R. Williams, Ryan Porter, P. A. M. Vanhoof

Physics and Astronomy Faculty Publications

A variety of astronomical environments contain clouds irradiated by a combination of isotropic and beamed radiation fields. For example, molecular clouds may be irradiated by the isotropic cosmic microwave background, as well as by a nearby active galactic nucleus. These radiation fields excite atoms and molecules and produce emission in different ways. We revisit the escape probability theorem and derive a novel expression that accounts for the presence of external radiation fields. We show that when the field is isotropic the escape probability is reduced relative to that in the absence of external radiation. This is in agreement with previous …

Magneto-Transport Characteristics Of A 2d Electron System Driven To Negative Magneto-Conductivity By Microwave Photoexcitation, Ramesh G. Mani, Annika Kriisa

Physics and Astronomy Faculty Publications

Negative diagonal magneto-conductivity/resistivity is a spectacular- and thought provoking-property of driven, far-from-equilibrium, low dimensional electronic systems. The physical response of this exotic electronic state is not yet fully understood since it is rarely encountered in experiment. The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phenomena. Here, we examine the magneto-transport characteristics of this negative conductivity/ resistivity state in the microwave photo-excited two-dimensional electron system (2DES) through a numerical solution of the associated boundary value problem. The results suggest, surprisingly, that a bare …

Solar Energy Conversion And Control Using Organic Photovoltaic Cells, Kurt Wade Woods

Masters Theses & Specialist Projects

Organic photovoltaic (OPV) cells are advanced, newly emerging technologies that are lightweight, mechanically flexible devices with highthroughput processes from low cost material in a variety of colors. Rathnayake et al. of Western Kentucky University have developed a nanostructure-based OPV cell. Presented in this thesis is a model and simulation of a generalized PV powered system that can predict the performance of solar arrays in various environmental conditions. The simulation has been carried out in Matlab/Simulink, and upon entering the cell’s parameters, it provides key electrical characteristics such as the cell’s I-V curve and efficiency information. The total system that is …

An Integrated Multidisciplinary Nanoscience Concentration Certificate Program For Stem Education, Karen S. Martirosyan, Mikhail M. Bouniaev, Malik Rakhmanov, Ahmed Touhami, Nazmul Islam, Davood Askari, Tarek Trad, Dmitri Litvinov, Sergey E. Lyshevski

Physics and Astronomy Faculty Publications and Presentations

Integration of nanoscience and nanotechnology curricula into the College of Science, Mathematics, and Technology (CSMT) at the University of Texas at Brownsville (UTB) is reported. The rationale for the established multidisciplinary Nanoscience Concentration Certificate Program (NCCP) is to: (i) develop nanotechnology-relevant courses within a comprehensive Science, Engineering and Technology curriculum, and, to offer students an opportunity to graduate with a certificate in nanoscience and nanotechnology; (ii) to contribute to students' success in achieving student outcomes across all college's majors, and, improve the breath, depth and quality of science, technology, engineering and mathematics (STEM) graduates' education; (iii) through NCCP, recruit certificate- …

Directed Search For Continuous Gravitational Waves From The Galactic Center, J. Aasi, Daniel Bessis, Teviet Creighton, H. Daveloza, Mario C. Diaz, S. R. Morriss, Soma Mukherjee, W. Ortega Larcher, M. E. Normandin, Volker Quetschke, O. Puncken, Malik Rakhmanov, Joseph D. Romano, Robert Stone, A. S. Stroeer, Lappoon R. Tang, Cristina V. Torres, D. Vrinceanu

Physics and Astronomy Faculty Publications and Presentations

We present the results of a directed search for continuous gravitational waves from unknown, isolated neutron stars in the Galactic center region, performed on two years of data from LIGO’s fifth science run from two LIGO detectors. The search uses a semicoherent approach, analyzing coherently 630 segments, each spanning 11.5 hours, and then incoherently combining the results of the single segments. It covers gravitational wave frequencies in a range from 78 to 496 Hz and a frequency-dependent range of first-order spindown values down to −7.86×10−8  Hz/s at the highest frequency. No gravitational waves were detected. The 90% confidence upper limits …

The Stochastic Background: Scaling Laws And Time To Detection For Pulsar Timing Arrays, X. Siemens, Justin A. Ellis, Fredrick A. Jenet, Joseph D. Romano

Physics and Astronomy Faculty Publications and Presentations

We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the observation time T that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as . In addition, in this regime the quality of the pulsar timing data and the cadence become relatively unimportant. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime …

Searching For Millisecond Pulsars: Surveys, Techniques And Prospects, Kevin Stovall, Duncan R. Lorimer, R. S. Lynch

Physics and Astronomy Faculty Publications and Presentations

Searches for millisecond pulsars (which we here loosely define as those with periods < 20 ms) in the galactic field have undergone a renaissance in the past five years. New or recently refurbished radio telescopes utilizing cooled receivers and state-of-the art digital data acquisition systems are carrying out surveys of the entire sky at a variety of radio frequencies. Targeted searches for millisecond pulsars in point sources identified by the Fermi Gamma-ray Space Telescope have proved phenomenally successful, with over 50 discoveries in the past five years. The current sample of millisecond pulsars now numbers almost 200 and, for the first time in 25 years, now outnumbers their counterparts in galactic globular clusters. While many of these searches are motivated to find pulsars which form part of pulsar timing arrays, a wide variety of interesting systems are now being found. Following a brief overview of the millisecond pulsar phenomenon, we describe these searches and present some of …

Using Open Datasets And Simulations In Laboratories, Jim Crumley

Physics Faculty Publications

While advances in instrumentation physics have made many areas more accessible to undergraduate physics laboratories, other areas are still beyond reach. Open data sets and simulations can open up some other frontiers of physics, such as Space Physics and Astronomy. In this talk, I will give an overview of some resources for open data and simulations, and then describe my experiences using these tools in both introductory and advanced labs in our curriculum.

Detection Of Ch4 In The Gv Tau N Protoplanetary Disk, David Horne, Erika Gibb

Physics Faculty Works

T Tauri stars are low mass young stars that may serve as analogs to the early solar system. Observations of organic molecules in the protoplanetary disks surrounding T Tauri stars are important for characterizing the chemical and physical processes that lead to planet formation. Searches for undetected molecules, particularly in the inner, planet forming regions of these disks are important for testing protoplanetary disk chemical models and for understanding the evolution of volatiles through the star and planet formation process. We used NIRSPEC on Keck 2 to perform a high resolution (λ/Δλ ~ 25,000) L-band survey of T Tauri star …

Detection Of Ch4 In The Gv Tau N Protoplanetary Disk, Erika L. Gibb, David Horne

Erika Gibb

Rainich-Type Conditions For Null Electrovacuum Spacetimes Ii, Charles G. Torre

Research Vignettes

In this second of two worksheets I continue describing local Rainich-type conditions which are necessary and sufficient for the metric to define a null electrovacuum. In other words, these conditions, which I will call the null electrovacuum conditions, guarantee the existence of a null electromagnetic field such that the metric and electromagnetic field satisfy the Einstein-Maxwell equations. When it exists, the electromagnetic field is easily constructed from the metric. In this worksheet I consider the null electrovacuum conditions which apply when a certain null geodesic congruence determined by the metric is twisting. I shall illustrate the these conditions using a …

Gamma-Ray Observations Of X-Ray Binaries, Angelo Varlotta

Open Access Dissertations

The detection of GeV/TeV emission from X-ray binaries (XRBs) has established a new class of high-energy (HE, >0.1 GeV) and very-high-energy (VHE, >100 GeV) gamma-ray emitters. XRBs are formed by a compact object, either a neutron star or a black hole, and by an optical companion star. Some XRBs are known to possess collimated relativistic jets, and are called microquasars. VERITAS has conducted observations of the high-mass X-ray binary (HMXB) 1A 0535+262 and of the microquasar Cygnus X-3. Many theoretical models predict VHE emission when these sources manifest persistent relativistic jets or transient ejections. In light of these considerations, VERITAS …

Is The Brain’S Inertia For Motor Movements Different For Acceleration And Deceleration?, Bhim M. Adhikari, Kristen M. Quinn, Mukesh Dhamala

Physics and Astronomy Faculty Publications

The brain’s ability to synchronize movements with external cues is used daily, yet neuroscience is far from a full understanding of the brain mechanisms that facilitate and set behavioral limits on these sequential performances. This functional magnetic resonance imaging (fMRI) study was designed to help understand the neural basis of behavioral performance differences on a synchronizing movement task during increasing (acceleration) and decreasing (deceleration) metronome rates. In the MRI scanner, subjects were instructed to tap their right index finger on a response box in synchrony to visual cues presented on a display screen. The tapping rate varied either continuously or …

Detecting The Rapidly Expanding Outer Shell Of The Crab Nebula: Where To Look, Xiang Wang, Gary J. Ferland, J. A. Baldwin, E. D. Loh, C. T. Richardson

Physics and Astronomy Faculty Publications

We present a range of steady-state photoionization simulations, corresponding to different assumed shell geometries and compositions, of the unseen postulated rapidly expanding outer shell to the Crab Nebula. The properties of the shell are constrained by the mass that must lie within it, and by limits to the intensities of hydrogen recombination lines. In all cases the photoionization models predict very strong emissions from high ionization lines that will not be emitted by the Crab's filaments, alleviating problems with detecting these lines in the presence of light scattered from brighter parts of the Crab. The near-NIR [Ne VI] λ7.652 μ …

The Biophysical Effects Of Deuterium Oxide On Biomolecules And Living Cells Through Open Notebook Science., Anthony Salvagno

Physics & Astronomy ETDs

This dissertation explores various effects of deuterium oxide (D2O also known as heavy water) in nature. Water is everywhere and interacts with just about everything. As such, it would be quite a daunting task to characterize every effect that water exhibits on everything in the universe. This research is a small piece of the puzzle, and provides some fundamental understanding of how water interacts with other molecules. This is done from two viewpoints: (1) the effects of heavy water on living cells and (2) the effects of heavy water on molecules. Varying concentrations of deuterium oxide were used as the …

Conformal Tensors Via Lovelock Gravity, David Kastor

David Kastor

Constructs from conformal geometry are important in low dimensional gravity models, while in higher dimensions the higher curvature interactions of Lovelock gravity are similarly prominent. Considering conformal invariance in the context of Lovelock gravity leads to natural, higher-curvature generalizations of the Weyl, Schouten, Cotton and Bach tensors, with properties that straightforwardly extend those of their familiar counterparts. As a first application, we introduce a new set of conformally invariant gravity theories in D=4k dimensions, based on the squares of the higher curvature Weyl tensors.

Size-Dependent Giant-Magnetoresistance In Millimeter Scale Gaas/Algaas 2d Electron Devices, Ramesh G. Mani, Annika Kriisa, Werner Wegscheider

Physics and Astronomy Faculty Publications

Large changes in the electrical resistance induced by the application of a small magnetic field are potentially useful for device-applications. Such Giant Magneto-Resistance (GMR) effects also provide new insights into the physical phenomena involved in the associated electronic transport. This study examines a ‘‘bell-shape’’ negative GMR that grows inmagnitude with decreasing temperatures inmm-wide devices fabricated from the high-mobility GaAs/AlGaAs 2-Dimensional Electron System (2DES). Experiments show that the span of this magnetoresistance on the magnetic-field-axis increases with decreasing device width, W, while there is no concurrent Hall resistance, Rxy, correction. A multi-conduction model, including negative diagonalconductivity, and non-vanishing off-diagonal conductivity, reproduces …

The Deep2 Galaxy Redshift Survey: Design, Observations, Data Reduction, And Redshifts, Jeffery A. Newman, Michael C. Cooper, Marc Davis, S. M. Faber, Alison L. Coil, Puragra Guhathakurta, David C. Koo, Andrew C. Phillips, Charlie Conroy, Aaron A. Dutton, Douglas P. Finkbeiner, Brian F. Gerke, David J. Rosario, Benjamin J. Weiner, Renbin Yan, Justin J. Harker, Susan A. Kassin, N. P. Konidaris, Kamson Lai, Darren S. Madgwick, K. G. Noeske, Gregory D. Wirth, A. J. Connolly, N. Kaiser, Evan N. Kirby, Brian C. Lemaux, Lihwai Lin, Jennifer M. Lotz, G. A. Luppino, C. Marinoni

Physics and Astronomy Faculty Publications

We describe the design and data analysis of the DEEP2 Galaxy Redshift Survey, the densest and largest high-precision redshift survey of galaxies at z ~ 1 completed to date. The survey was designed to conduct a comprehensive census of massive galaxies, their properties, environments, and large-scale structure down to absolute magnitude M_B = –20 at z ~ 1 via ~90 nights of observation on the Keck telescope. The survey covers an area of 2.8 deg² divided into four separate fields observed to a limiting apparent magnitude of R_AB = 24.1. Objects with z ≲ 0.7 are readily …

Shadows In Time: A Study Of Temporal Metaphysics Through Hard Science Fiction And Its Restrictions On The Past And Future, Lindsey E. Mitchell

Oglethorpe Journal of Undergraduate Research

Through a series of essays, this body of work explores the varying theories concerning the nature of time and how each theory affects the possibility and outcome of time travel. Following these essays, a collection of short stories focuses on what the author considers the most probable theories concerning time and expands on how they might affect a time traveler's decisions and fate.

Supermassive Black Hole Formation At High Redshifts Via Direct Collapse: Physical Processes In The Early Stage, Jun-Hwan Choi, Isaac Shlosman, Mitchell C. Begelman

Physics and Astronomy Faculty Publications

We use numerical simulations to explore whether direct collapse can lead to the formation of supermassive black hole (SMBH) seeds at high redshifts. Using the adaptive mesh refinement code ENZO, we follow the evolution of gas within slowly tumbling dark matter (DM) halos of M_vir ~ 2 × 10⁸ M_☉ and R_vir ~ 1 kpc. For our idealized simulations, we adopt cosmologically motivated DM and baryon density profiles and angular momentum distributions. Our principal goal is to understand how the collapsing flow overcomes the centrifugal barrier and whether it is subject to fragmentation which can potentially …