Astrophysics and Astronomy Commons^™

Improving The Catalytic Activity Of Semiconductor Nanocrystals Through Selective Domain Etching, Elena Khon, Kelly Lambright, Rony S. Khnayzer, Pavel Moroz, Dimuthu Perera, Evgeniia Butaeva, Scott Lambright, Felix N. Castellano, Mikhail Zamkov

Physics and Astronomy Faculty Publications

Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of semiconductor nanocrystals. While many nanocrystal architectures can be obtained directly via colloidal growth, other nanoparticle morphologies require alternative processing strategies. Here, we show that chemical etching of colloidal nanoparticles can facilitate the realization of nanocrystal shapes that are topologically inaccessible by hot-injection techniques alone. The present methodology is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle dimer, constructed in a way that both CdSe and CdS semiconductor domains are exposed to the external environment. This structural morphology is highly desirable for catalytic applications as it enables both reductive …

Modeling The Spectral Energy Distribution Of Mrk 421, Randall L. Oglesby

Physics

Blazars are astronomical objects thought to be powered by the release of gravitational energy by accretion of material into a supermassive black hole located in the central region of the host galaxy. Some AGN present strong relativistic outflows in the form of jets, with blazars being the particular subset whose jets are aligned with our line of sight. Even though blazars account for only a small fraction of all AGN, they are the dominant class source in the high-energy sky. In this thesis we study the spectral energy distribution of Mrk 421, a prototypical blazar. Using publicly available numerical code …

Discovery Of A Relation Between Black Hole Mass And Soft X-Ray Time Lags In Active Galactic Nuclei, B. De Marco, G. Ponti, M. Cappi, M. Dadina, P. Uttley, E. M. Cackett, A. C. Fabian, G. Miniutti

Physics and Astronomy Faculty Research Publications

We carried out a systematic analysis of time lags between X-ray energy bands in a large sample (32 sources) of unabsorbed, radio quiet active galactic nuclei (AGN), observed by XMM-Newton. The analysis of X-ray lags (up to the highest/shortest frequencies/time-scales), is performed in the Fourier-frequency domain, between energy bands where the soft excess (soft band) and the primary power law (hard band) dominate the emission. We report a total of 15 out of 32 sources displaying a high-frequency soft lag in their light curves. All 15 are at a significance level exceeding 97 per cent and 11 are at a …

The Fine-Tuning Of Nomic Behavior In Multiverse Scenarios, Max Lewis Edward Andrews

Masters Theses

The multiverse hypothesis (the view that there is not just one world or universe in existence, bur rather that there are many) is the leading alternative to the competing fine-tuning hypothesis (the laws of physics and constants are fine-tuned for the existence of life). The multiverse dispels many aspects of the fine-tuning argument by suggesting that there are different initial conditions in each universe, varying constants of physics, and the laws of nature lose their known arbitrary values; thus, making the previous single-universe argument from fine- tuning incredibly weak. The position that will be advocated will be that a form …

Section Abstracts: Astronomy, Mathematics And Physics

Virginia Journal of Science

Abstracts of the Astronomy, Mathematics and Physics Section for the 91st Annual Virginia Journal of Science Meeting, May 2013

Tracers Of Chromospheric Structure.I. Ca Ii H&K Emission Distribution Of 13,000 F, G, And K Stars In Sdss Dr7 Spectroscopic Sample, J K. Zhao, Terry D. Oswalt, G Zhao, Q H. Lu, A L. Luo, L Y. Zhang

Aerospace, Physics, and Space Science Faculty Publications

We present chromospheric activity index SHK measurements for over 13,000 F, G, and K disk stars with high signal-to-noise ratio (>60) spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic sample. A parameter δS is defined as the difference between SHK and a “zero” emission line fitted by several of the most inactive stars. The SHK indices of subgiant stars tend to be much lower than dwarfs, which provide a way to distinguish dwarfs and giants with relatively low-resolution spectra. Cooler stars are generally more active and display a larger scatter than hotter stars. Stars …

Co-Production Of Nitrogen-15 And Oxygen-18 In Explosive Helium Burning And Implications For Supernova Graphite Grains, Michael Bojazi

All Theses

My Masters research involves simulations of a supernova whereby a shock wave of constant Mach number is sent through a 15-solar-mass star evolved to the point of core-collapse. The resulting nucleosynthesis is examined with the intent of explaining the overproduction, relative to solar values, of nitrogen-15 and oxygen-18 abundances in supernova presolar graphite grains, as experimentally determined by Groopman et al. via a NanoSIMS analysis. We find such overabundances to be present in the helium-rich zone. Oxygen-18 is leftover from presupernova helium burning while nitrogen-15 is produced by explosive helium burning. Interestingly, anomalous excesses in molybdenum-95 and molybdenum-97 abundances in …

Einstein A Coefficients For Rovibronic Lines Of The A2Π → X2Σ+ And B'2Σ+ → X 2Σ+ Transitions Of Mgh, Ehsan Gharibnezhad, Alireza Ahayesteh, Peter F. Bernath

Chemistry & Biochemistry Faculty Publications

Einstein A coefficients have been calculated for rovibronic lines of the A²Π →X²Σ⁺ and B'²Σ⁺ →X²Σ⁺ transitions of 24MgH. Using the experimentally determined analytic potential energy curve for the X²Σ⁺ state, and the Rydberg-Klein-Rees potentials for the A²Π and B'²Σ⁺ states, combined with the most recent ab initio transition dipole moments, rovibronic transition moments were computed. The rovibronic transition frequencies were obtained accurately by subtracting the published term values of the X²Σ⁺, A²Π and B' …

How Accurately Can The Inclination Angle, Position Angle, And Location Of The Dynamic Center Be Measured From The Neutral Hydrogen Disk In The Central Regions Of Dwarf Galaxies?, John Henry Boisvert

UNLV Theses, Dissertations, Professional Papers, and Capstones

Rotation curves measured using Hi emission are a powerful tool for probing the mass distribution of galaxies. We investigate the accuracy with which rotation curves can be determined using the tilted-ring model. We have examined the effect of varying the dynamic center on measured rotation velocities within the inner regions of galaxies where the disagreement between theory and observation is the greatest. We examine a sample of dwarf galaxies (and one spiral galaxy) from the THINGS high-resolution survey (Walter et al. 2008). We find that the measured rotation curve is quite sensitive to the location of the dynamic center. This …

Magnesium Isotopic Compositions Of The Moon And Achondrites: Implications For Their Origin And Evolution, Fatemeh Sedaghatpour

Graduate Theses and Dissertations

The main objectives of this thesis are to estimate Mg isotopic compositions of the Moon and achondrites, to understand the behavior of Mg isotopes during magmatic differentiation processes in different planetary bodies, and to evaluate the extent of Mg isotopic heterogeneity in the solar system. In order to achieve these goals, Mg isotopes have been measured for 47 well-characterized lunar samples and 22 differentiated meteorites by MC-ICPMS. The limited Mg isotopic variations among mare and highland regolith, mare breccias, and highland impact-melt rocks reflect negligible Mg isotope fractionation during lunar surface processes (e.g. solar wind, cosmic rays, micrometeorite bombardments, meteorite …

On Chlorine Salts: Their Detection, Stability And Implications For Water On Mars And Europa, Jennifer Hanley

Graduate Theses and Dissertations

Chlorine salts (e.g. chlorides, chlorates and perchlorates) are an important factor in the stability of water on the surfaces of planetary bodies. Here we have shown that perchlorate and chlorate salts will lower the freezing point of water, allowing it to be liquid down to ~204 K. These salts will also slow down the evaporation rate, extending the lifetime of the liquid water solution. Chlorine salts have been detected on Mars, which has significant implications for the stability of water and hence its habitability. To study their effects on the stability of water on planetary surfaces, we need to first …

Investigation Of A Lagrangian-Point Propellant Depot Rendezvous Approach For An Interplanetary Mission To Mars, Joshua W. Ehrlich

Doctoral Dissertations and Master's Theses

This thesis investigates the feasibility of a refueling station for a beyond Earth orbit (BEO) mission. The propellant depot is located at the L₂ -Lagrangian point within the Earth-Moon system. This investigation determines if a refueling mission will reduce propulsive energy requirements necessary for Earth departure of a BEO-vehicle to achieve an interplanetary transfer to Mars. Furthermore, this research presents a trade study which identifies approximate total requirements for a direct and rendezvous mission to Mars as well as the necessary fuel masses to complete each approach. This analysis provides conclusive information in determining the benefits in utilizing a …

Dissolution Rates Of Amorphous Al- And Fe-Phosphates And Their Relevance To Phosphate Mobility On Mars, Valerie Tu

UNLV Theses, Dissertations, Professional Papers, and Capstones

Phosphate is an essential element for life on Earth, and therefore if life exists or ever existed on Mars it may have required phosphate. Amorphous Al- and Fe-phosphates rapidly precipitate from acidic solutions and amorphous Al-phosphates likely control phosphate concentrations in some natural waters on Earth. Amorphous phases may be even more important on Mars than on Earth, and amorphous phosphates are therefore likely important in the phosphate cycle on Mars. Despite this importance, however, few dissolution rates exist for amorphous Al- and Fe- phosphates. In this study, dissolution rates of amorphous Al- and Fe-phosphates were measured in flow-through reactors …

Active Galactic Nuclei Mergers And Outflows: Observations From Optical And Ultraviolet Emission Lines, Robert Scott Barrows

Graduate Theses and Dissertations

I have investigated the nature of a subset of active galactic nuclei (AGN) which show double peaks in their characteristic optical and ultraviolet emission lines. I have performed this investigation through studies of the broad emission line regions (BLRs), which are produced less than 1 pc from the central supermassive black hole (SMBH), and the narrow emission line regions (NLRs), which originate at larger (kpc) distances. The BLR studies consist of detailed line modeling of two individual quasars with double-peaked broad emission line profiles. The modeling suggests there are two primary interpretations of the complex broad line profiles. The first …

Image Processing Algorithms For Improving Planetary Exploration And Understanding, Ali Pouryazdanpanah

College of Engineering: Graduate Celebration Programs

• To design a fully automated tool-set that allows to detect and extract the sky region in planetary images.

• To develop the new method for rock segmentation in planetary stereo images.
• To develop the new method for shadow detection in planetary images

Host Star Properties And Transit Exclusion For The Hd 38529 Planetary System, Gregory W. Henry, Stephen R. Kane, Sharon X. Wang, Jason T. Wright, Tabetha S. Boyajian, Kaspar Von Braun, David R. Ciardi, Diana Dragomir, Chris D. Farrington, Debra A. Fischer, Natalie R. Hinkel, Andrew W. Howard, Eric Jensen, Gregory Laughlin, Suvrath Mahadevan, Genady Pilyavsky

Information Systems and Engineering Management Research Publications

The transit signature of exoplanets provides an avenue through which characterization of exoplanetary properties may be undertaken, such as studies of mean density, structure, and atmospheric composition. The Transit Ephemeris Refinement and Monitoring Survey is a program to expand the catalog of transiting planets around bright host stars by refining the orbits of known planets discovered with the radial velocity technique. Here we present results for the HD 38529 system. We determine fundamental properties of the host star through direct interferometric measurements of the radius and through spectroscopic analysis. We provide new radial velocity measurements that are used to improve …

Neutral Pion Background Analysis At Star, Adam Clark

Symposium on Research and Creative Expression (SORCE)

The STAR detector at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory takes measurements of polarized proton collisions which can then be used to extract cross sections and spin asymmetries. The Endcap Electromagnetic Calorimeter (EEMC) in STAR allows measurements of electromagnetic particles in the forward direction, 1 < η < 2. The EEMC will be used to determine the neutral pion (π0) cross section and the double longitudinal spin asymmetry (ALL) which gives us information about the gluon contribution to the proton’s spin. The π0 cross section is an important supporting measurement to verify our signal reconstruction and the background characterization for the π0 asymmetry. In order to measure the π0 cross section and asymmetry, the backgrounds must be well understood (such as those from photon conversions and reconstruction errors where one photon reconstructs as two clusters). Efforts toward the π0 cross section and asymmetry measurements and, specifically, those to understand π0 backgrounds are discussed.

Stability Of The Gains Of The Star Endcap Calorimeter From 2006 To 2011, Kayla Kutz

Symposium on Research and Creative Expression (SORCE)

The Solenoid Tracker at RHIC (STAR) experiment, based at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC), uses polarized-proton collisions to investigate sea quark and gluon contributions to the fundamental proton property called “spin.” The STAR detector's Endcap Electromagnetic Calorimeter (EEMC) measures the energy of particles produced by those collisions using a lead-scintillator sampling calorimeter, consisting of several layers that include pre-shower, shower maximum, tower, and post-shower detectors. In these detectors, the energy gains, which convert a measured pulse into an energy deposition, have been determined using data taken from the years 2006, 2009, and 2011. Changes in the gains …

A Study Of Light Variability In Dying Stars, Hannah Rotter, Aaron Seider, Austin Bain

Symposium on Research and Creative Expression (SORCE)

In this research project, we observed and analyzed the light variability in a class of dying stars that are in the stage between Red Giant and White Dwarf in the evolution of stars like the Sun. Our observations were carried out during the summer and fall of 2012 at the Valparaiso Observatory. Thirty-two of these objects were observed in total. We analyzed a subset of 18 of these and found that they all varied in visual brightness by 10-70 percent. Periods for the variability were found for 8 out of 18 objects, and they range from 27 to 125 days, …

An Event-By-Event Comparison Of Clustering Algorithms For Photon Detection In The Star Endcap Calorimeter, William J. Pochron

Symposium on Research and Creative Expression (SORCE)

The STAR detector at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory uses polarized proton collisions to determine the origin of the proton spin, using measurements such as neutral pion asymmetries. The Endcap Electromagnetic Calorimeter (EEMC) in the STAR detector is especially useful for detecting photons from π° decays at forward angles. This latter measurement is obtained from the Shower Maximum Detector (SMD) in the EEMC where narrow crossed scintillator strips measure the energy deposited in them and can be used to identify the location of the photon shower. The electromagnetic shower most often deposits energy in a …

Dispersion Of Radon-222 Gas In Air, Erin Beckmeyer

Symposium on Research and Creative Expression (SORCE)

Radon-222 is a heavy radioactive gas with a half-life of 3.8 days, often found in basements and other enclosed, underground spaces. It is produced by decaying deposits of uranium-238, and presents a significant health risk to those who encounter it in their homes and places of work. The only gas in the uranium decay chain, radon atoms work their way through layers of soil, usually to dissipate harmlessly into the atmosphere. In buildings, however, the gas accumulates and causes dangerous environmental radiation. Much work has been done to measure the transmission of the gas through water and solid materials, but …

A Study Of Two Newly-Discovered Eclipsing Binary Systems, Austin Bain

Symposium on Research and Creative Expression (SORCE)

I have observed three newly-discovered variable stars using the 16-inch telescope and CCD at the Valparaiso University Observatory. Of these three variables, two have been verified as binary star systems, where one of the stars passes in front of the other. The third is found to be a pulsating variable, which varies due to a change in its size and temperature. One of the goals of this project has been to further refine the periods of these three variables. From my new data and some previous observations at the Valparaiso University Observatory, I have been able to determine that the …

Testing The Klein-Nishina Model For Compton Scattering Of 0.662 Mev Photons With A Focus On Lower Scattering Angles, Joel Rogers

Symposium on Research and Creative Expression (SORCE)

The Thomson and Klein-Nishina equations for obtaining the differential cross section by Compton scattering of photons from free electrons in aluminum will be tested using 0.662 MeV photons from a Cesium-137 source. A NaI detector will be used to count the number of photons scattering from the target as a function of the scattering angle. A previous experiment carried out by VU student Josh Vredevoogd showed good agreement with the Klein-Nishina theory for angles greater than 45 but discrepancies with angles less than 45 degrees. This experiment will concentrate on testing the Klein-Nishina theory at angles less than 45 degrees.

Generating A ‘Clean’ Pi0 Spectrum In Star, William J. Pochron

Symposium on Research and Creative Expression (SORCE)

The STAR detector at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider uses polarized proton collisions to investigate the origin of the proton spin, using measurements such as neutral pion (π0) asymmetries. STAR’s Endcap Electromagnetic Calorimeter (EEMC) is especially useful for detecting photons from π0 decays at forward-angle scattering from ≈15 to ≈40 degrees above the beam direction. We identify π0’s by constructing invariant mass spectra from these photons. Large background contributions are present in these spectra and distort the true value of the π0 invariant mass. By applying constraints (cuts) on parameters such as the opening angle of the photons …

Classification And Analysis Of Emission-Line Galaxies Using Mean Field Independent Component Analysis, James T. Allen, Paul C. Hewett, Chris T. Richardson, Gary J. Ferland, Jack A. Baldwin

Physics and Astronomy Faculty Publications

We present an analysis of the optical spectra of narrow emission-line galaxies, based on mean field independent component analysis (MFICA), a blind source separation technique. Samples of galaxies were drawn from the Sloan Digital Sky Survey (SDSS) and used to generate compact sets of ‘continuum’ and ‘emission-line’ component spectra. These components can be linearly combined to reconstruct the observed spectra of a wider sample of galaxies. Only 10 components – five continuum and five emission line – are required to produce accurate reconstructions of essentially all narrow emission-line galaxies to a very high degree of accuracy; the median absolute deviations …

Strongly Localized Magnetization Modes In Permalloy Antidot Lattices, J. Sklenar, V. S. Bhat, Lance E. De Long, O. Heinonen, J. B. Ketterson

Physics and Astronomy Faculty Publications

Antidot lattices (ADLs) patterned into soft magnetic thin films exhibit rich ferromagnetic resonance (FMR) spectra corresponding to many different magnetization modes. One of the predicted modes is highly localized at the edges of the antidots; this mode is difficult to detect experimentally. Here we present FMR data for a permalloy thin film patterned into a square array of square antidots. Comparison of these data with micromagnetic simulations permits identification of several edge modes. Our simulations also reveal the effect of the antidot shape on the mode dispersion.

Astronomy / Galactic Structure - Rensselaer Polytechnic Institute, Kathryn M. Dunn

Data Curation Profiles Directory

The researcher participates in large-scale astronomical survey projects, which are collaborative efforts of many institutions and individuals. Management of the raw and processed/calibrated data is handled by those projects, but data for specific research questions is handled by the researcher. The researcher would like to have a better way to share the data behind the figures in their published papers with other researchers. The effort involved in retrieving and documenting the data so it’s usable by others is a barrier to sharing the data. It would be easier to share data from publications if it could be deposited to a …

Suppression Of Dielectronic Recombination Due To Finite Density Effects, D. Nikolić, T. W. Gorczyca, K. T. Korista, Gary J. Ferland, N. R. Badnell

Physics and Astronomy Faculty Publications

We have developed a general model for determining density-dependent effective dielectronic recombination (DR) rate coefficients in order to explore finite-density effects on the ionization balance of plasmas. Our model consists of multiplying by a suppression factor those highly-accurate total zero-density DR rate coefficients which have been produced from state-of-the-art theoretical calculations and which have been benchmarked by experiment. The suppression factor is based upon earlier detailed collision-radiative calculations which were made for a wide range of ions at various densities and temperatures, but used a simplified treatment of DR. A general suppression formula is then developed as a function of …

Erratum: 'Improved He I Emissivities In The Case B Approximation', R. L. Porter, Gary J. Ferland, P. J. Storey, M. J. Detisch

Physics and Astronomy Faculty Publications

No abstract provided.

Tuning Electronic Structure Via Exipatial Strain In Sr2Iro4 Thin Films, J. Nichols, Jsaminka Terzic, Emily Geraldine Bittle, Oleksandr B. Korneta, Lance E. De Long, Joseph Brill, Gang Cao, Sung S. Ambrose Seo

Physics and Astronomy Faculty Publications

We have synthesized epitaxial Sr₂IrO₄ thin-films on various substrates and studied their electronic structure as a function of lattice-strain. Under tensile (compressive) strain, increased (decreased) Ir-O-Ir bond-angle is expected to result in increased (decreased) electronic bandwidth. However, we have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are shifted to higher (lower) energies under tensile (compressive) strain, indicating that the electronic-correlation energy is also affected by in-plane lattice-strain. The effective tuning of electronic structure under lattice-modification provides an important insight into the physics driven by the coexisting strong spin-orbit coupling and electronic …