Physics Commons^™

Dielectronic Recombination Calculations For Silicon-Like Ions And The S2+ Orion Nebula Abundance Conundrum, Jagjit Kaur

Dissertations

Modern astronomical spectroscopy and imaging data are of an unprecedented quality, and span the full electromagnetic spectrum. To take full advantage of these data and successfully model the physical conditions in and elemental abundances of astrophysical plasmas, an accurate and complete description of relevant atomic processes occurring in a wide range of cosmic environments is required. The primary focus of this project is to investigate one of the atomic processes, dielectronic recombination (DR), for the entire silicon-like isoelectronic sequence. Dielectronic recombination is generally the most important contribution to the total recombination rate of atomic ions. This study will serve as …

Department Of Physics Newsletter, Summer 2017, College Of Arts And Sciences

Physics Newsletter

• Message from Dr. Kirk Korista, Department Chair
• Science Olympiad draws 400 hundred students to WMU
• 2016 Alumni Achievement Award, Physics
• Department of Physics Award Ceremony
• Faces of Physics

Time-Dependent Photoionization Of Gaseous Nebulae, Ehab Elsayed Elhoussieny Ahmed

Dissertations

We study time-dependent photoionization of gaseous nebulae, i.e. the physical conditions and spectra of astronomical plasmas photoionized by a time-dependent source of ionizing radiation. Our study proceeds in two chief steps: First, we start with a simplified model of plasmas of pure H. Second, we develop a more realistic model of plasmas composed of a mixture of chemical elements. For the first step, we wrote a time-dependent photoionization code (TDP) that solves the coupled system of equations for ionization, energy balance, and radiation transfer in their full time-dependent forms For the second step, we developed a more realistic code (TDXSTAR) …

Type 1a Supernova Models And Galactic Chemical Evolution, Spencer Henning

Honors Theses

Multiple models of type Ia supernovae are discussed, as well as the properties of white dwarf formation, electron degeneracy pressure, nucleosynthesis, and galactic chemical evolution (GCE). A GCE computer model is used to produce nuclear abundance data corresponding to Chandra (W7) and sub-Chandra (WDD2) type Ia supernovae models for Ca, Sc, Ti, V, Cr, and Mn nuclei. Overall, a trend was found indicating that the WDD2 model had greater [x/Fe] abundance values than the W7 model at the end time of the model. Additionally, each model fit within total observed data, but observed data filtered to highlight white dwarf stars …

The Quantum Dancing Of Hot Atomic Nuclei: A New Theoretical Approach, Herlik Wibowo

Research and Creative Activities Poster Day

We study the nuclear excitation spectra in the two energy domains: the low energy region (below 10 MeV) and giant resonance (GR) region (10-30 MeV). In the low energy region, the experimentally discovered upbend of the radiative dipole strength function is very important as it has an impact on the rapid neutron capture cross sections, which are used, in particular, for the r-process nucleosynthesis studies.

Thermal continuum quasiparticle random-phase approximation (TCQRPA) is one of the models which attempts to explain this phenomenon. The deficiency of TCQRPA is the absence of quasiparticle vibration coupling (QVC) mechanism, which is already included in …

Crystallography And Magnetism Of Magnetocalorically Important Ni-Mn-X Based Heusler Alloys, Amila S. B. Madiligama

Dissertations

Ni-Mn-X Heusler alloys, demonstrating strong coupling between crystalline structure and magnetic state, were studied. They undergo field-induced, first-order transformations from a low symmetry martensite to a high-symmetry austenitic phase around room temperature. The substantial difference between the entropies of the two phases results in a large adiabatic temperature change, called “Giant Magnetocaloric Effect (GMCE)”. Consequently, these alloys are promising refrigerants for near-room temperature cooling systems. This magnetic cooling is an energy-efficient and eco-friendly technology.

Crystalline structures and magnetic states of these alloys, which determine their magnetocaloric performances, highly depend on their composition. To examine new paths to optimize their magnetocaloric …

An R-Matrix, Quantum Defect Theory Approach To The Photoionization Of Molecular Nitrogen, Gaetan L. Vangyseghem

Dissertations

No abstract provided.

Physics News, Winter 2016, College Of Arts And Sciences

Physics Newsletter

Contents:

Physics Alum Wins NSF Fellowship

Book Donation Noted

New Books... Familiar Authors

Physics Hosts Science Olympians

Students Recognized

Recent Graduates

Physics Department News

Recent Colloquia

Alumni Updates

Deposition And Characterization Of Carbon Nanotubes (Cnts) Based Films For Sensing Applications, Amila C. Dissanayake

Dissertations

The advent of carbon nanotubes (CNTs) has opened up lot of novel applications because of their unique electrical and mechanical properties. CNTs are well known material for its exceptional electrical, mechanical, optical, thermal and chemical properties. A single-wall nanotube (SWNT) can be either semiconducting, metallic or semi-metallic, based on its chirality and diameter. SWNTs can be used in transistor device as active channels due to high electron mobility (~10000 cm2/(V s), electrical interconnects, nano-scale circuits, field-emission displays, light-emitting devices and thermal heat sinks due to low resistivity, high current density (~109A cm-2) and high thermal conductivity (~3500 W m-1). Further, …

Electron Transmission Through Micrometer Sized Funnelshaped Tapered Glass Capillaries And Electron Micro-Beam Production, Samanthi Jayamini Wickramarachchi

Dissertations

The prime motivation of this work is to understand the fundamental transmission process of an electron beam through a funnel-shaped capillary taking into account its shape together with the energy, angular and time dependence of the transmitted electrons produce a microsized electron beam. The utilized capillaries had inlet/outlet diameters of 800/16 μm, 800/100 μm and lengths of 35 mm. Considerable transmission of 800 and 1000 eV electrons for tilt angles up to 1.5^o and only small transmission for 500 eV electrons was observed for the capillary with the smaller outlet diameter of 16 μm. Incident electrons with energies of …

Integrating Formative Assessment Into Physics Instruction: The Effect Of Formative Vs. Summative Assessment On Student Physics Learning And Attitudes, Chaiphat Plybour

Dissertations

Of many instructional strategies used to improve teaching and learning in science, formative assessment is potentially one of the most effective. A central feature is timely feedback during learning, giving students the opportunity to benefit and improve while also enabling teachers to adjust instruction to learner needs. By contrast, conventional assessment tends to be mostly summative, assigning point scores, grading and ranking students, and providing extrinsic motivation. For maximum effectiveness in enhancing learning, formative assessment should be designed into instruction from the start rather than being an add-on. This project comprised development, teaching, and research aspects. Two physics topic modules, …

Energy, Angular And Charge Deposition Dependence Of Electron Transmission Through Insulating Polyethylene Terephthalate Nanocapillaries For Narrow Beam Production, Darshika Keerthisinghe

Dissertations

This study analyzes the characteristic properties of electron transmission with incident energies of 300, 500 and 800 eV for the production of nanometer-sized beams through insulating polyethylene terephthalate (PET) nanocapillaries. More specifically, it investigates the transmission for very small tilt angles near zero degrees with the small step sizes revealing distinct regions of behavior, angular dependence, energy and the charge deposition dependence on transmission. Results were obtained for two Samples, 1 and 2, with different capillary diameters (100/200 nm) and pore densities (5 x 10⁸ /5 x 10⁷ /cm²), respectively, with the same foil thickness 12 …

Advantages Of A Finite Extensible Nonlinear Elastic Potential In Lattice Boltzmann Simulations, Tai-Hsien Wu, Dewei Qi

The Hilltop Review

A new structure, generalized lattice nonlinear spring model (GLNSM), which adopts non-linear FENE-LJ potential instead of harmonic potential, has been coupled with lattice Boltzmann simulation for solving fluid-solid interaction problem. In this article, a significant work is the relationship between the GLNSM (FENE-LJ potential) and Young’s modulus has been described in detail. A validation has also been presented to prove that GLNSM is reliable.

The Experiences Of Women In Post Graduate Physics And Astronomy Programs: The Roles Of Support, Career Goals, And Gendered Experiences, Ramón S. Barthelemy

Dissertations

In physics and astronomy the low representation of women is obvious at every stage of the educational pathway from undergraduate students to full professors. These low numbers perpetuate themselves by failing to create new mentors to foster the next generation of women. Women and men also have different experiences as they traverse into physics and astronomy careers. Women often experience chilly climates, discrimination, and challenges coordinating the demands of young families with their careers. In the literature exploring this topic, little focus is put on the experiences of women graduate students in physics and no focus is put on women …

Studies Of The Quantum Phase Transition In Chromium Using Inelastic X-Ray Scattering And Ab Initio Methods, Chengyang Li

Dissertations

In this project, inelastic x-ray scattering (IXS) was used to measure the phonon dispersion in chromium at high pressure and low temperature, and an ab initio method was used to simulate the phonon dispersion with different lattice constants and magnetic orders. The IXS measurements were carried out in Sector 30 at the Advanced Photon Source at Argonne National Laboratory. Data were taken at room temperature with pressures of 1.29 GPa, 8.15 GPa, 10.6 GPa, and at 5 K with a pressure of 18.36 GPa. The data shows similar phonon behavior in the antiferromagnetism (AFM) and the spin density wave (SDW) …

Time-Dependent Photoionization Of Gas Outflows In Agn, Ehab Elhoussieny, Manuel A. Bautista, J. Garcia, T. R. Kallman

Research and Creative Activities Poster Day

Gas outflows are fundamental components of Active Galactic Nuclei (AGN) activity. Time-variability of ionizing radiation, which is characteristic of AGN in various different time scales, may produce non-equilibrium photoionization conditions over a significant fraction of the flow and yields supersonically moving cooling/heating fronts. These fast fronts create pressure imbalances that can only be resolved by fragmentation of the flow and acceleration of such fragments. This mechanism can explain the kinematic structure of low ionization BAL systems (FeLoBAL). We will study these effects in detail by constructing time-dependent photoionization models of the outflows and incorporating these models into radiative-hydrodynamic simulations.

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 …

Electron Capture By Multiply Charged Ions From Molecular Targets, Justin Harris

Masters Theses

State-selective differential cross sections for single-electron capture processes in collisions of Ne^q+ (q=2, 3, 5) ions with H₂O and CO₂ have been studied experimentally at laboratory collisions energies between 45 and 250 eV, and at scattering angles between 0^o and 7:20^o by means of translational energy-gain spectroscopy technique. The translational energy spectra show that only a few final states are populated depending on the projectile's charge state, laboratory scattering angle, and the collision energy. In addition, these measurements show that the dominant reaction channels are due to non-dissociative electron capture into excited states of …

Research Report 2014-2015, College Of Arts And Sciences

Physics Research Reports

• Introduction
• From the Chair
• Research Spotlight: Zbigniew Chajecki, Ph.D.
• Refereed Publications
• Invited Presentations
• Contributed Presentations
• External Grant Activity (Submitted and Awarded)
• Notable Awards and Memberships
• Doctoral Dissertations
• Department Personnel

Development Of Polarization Analysis Of Resonant Inelastic X-Ray Scattering, Xuan Gao

Dissertations

Resonant inelastic x-ray scattering (RIXS) is a powerful technique in condensed matter physics for studying the electronic excitations in novel materials of interest. In currently operating hard x-ray RIXS instruments the energy and momentum transfers are measured while the outgoing polarization is not measured due to significant technical challenges. But the outgoing polarization of the scattered photons provides valuable information (excitation symmetry) about the states involved in the scattering which is difficult to determine without polarization analysis. Polarization analysis has proved extremely valuable in soft x-ray RIXS, and so a polarization analysis system is being developed to fill the technical …

Theoretical Modeling Of Near-Threshold Shape Resonance Behaviour In Photodetachment Experiments, Laurentiu Dan Dumitriu

Masters Theses

This thesis attempts to better understand the results obtained from photodetachment experiments of Fe-, made by the Western Michigan University experimental atomic physics group at the Advanced Light Source (ALS), Lawrence Berkeley National laboratory.

After a relevant description of the quantum mechanics and theoretical atomic physics concepts and formulas involved in this subject, a physically realistic model, based on the square well potential, is developed. Based on this model, the theoretical photodetachment cross section is computed in order to reproduce the qualitative behavior of the experimental photodetachment cross section measured at ALS.

This development, involving programming in Fortran and numerical …

Organic Solar Cells Based On High Dielectric Constant Materials: An Approach To Increase Efficiency, Khalil Jumah Tawfiq Hamam

Dissertations

The efficiency of organic solar cells still lags behind inorganic solar cells due to their low dielectric constant which results in a weakly screened columbic attraction between the photogenerated electron-hole system, therefore the probability of charge separating is low. Having an organic material with a high dielectric constant could be the solution to get separated charges or at least weakly bounded electron-hole pairs. Therefore, high dielectric constant materials have been investigated and studied by measuring modified metal-phthalocyanine (MePc) and polyaniline in pellets and thin films. The dielectric constant was investigated as a function of temperature and frequency in the range …

Study Of 14b Using (D,P) Reaction In Inverse Kinematics, Shadi Bedoor, Jonathan C. Lighthall, Scott T. Marley

Research and Creative Activities Poster Day

No abstract provided.

Microbeam Production Using Straight And Tapered Glass Capillaries, Asma M. Ayyad

Research and Creative Activities Poster Day

No abstract provided.

Compositional And Structural Analysis Of Nitrogen Incorporated And Ion Implanted Diamond Thin Films, Elias James Garratt

Dissertations

Significant progress in area of nano-structured thin film systems has taken place in recent decades. In particular, diamond thin film systems are being widely studied for their wear resistant, optical and electronic properties. Of the various methods researchers use to modify the structure of such films, three techniques in particular are of interest due to their versatility: modification of the growth atmosphere, growth on metalized substrates, providing an interfacial layer, and modification through post-growth ion implantation. The aim of this study is to investigate the effects each has to the structure and composition of elements. Different techniques are applied in …

Engineered Interfaces And Nano-Scale Thin Films For Solid Oxide Fuel Cell Electrolytes, Manjula I. Nandasiri

Dissertations

Solid state electrolytes with high oxygen ionic conductivity at low temperatures are required to develop cost effective and efficient solid oxide fuel cells. This study investigates the influence of engineered interfaces on the oxygen ionic conductivity of nano-scale multilayer thin film electrolytes. The epitaxial Sm₂O₃ doped C_eO₂ (SDC) and Sc₂O₃ stabilized ZrO₂ (ScSZ) are selected as the alternative layers for the proposed multilayer thin film electrolyte based on the optimum structural, chemical, and electrical properties reported in the previous studies. The epitaxial SDC(111)/ScSZ(111) multilayer thin films are grown on high …

Localized Surface Plasmon Resonance Induced Structure-Property Relationships Of Metal Nanostructures, Subramanian Vilayurganapathy

Dissertations

The confluence of nanotechnology and plasmonics has led to new and interesting phenomena. The industrial need for fast, efficient and miniature devices which constantly push the boundaries on device performance tap into the happy marriage between these diverse fields. Designing devices for real life application that give superior performance when compared with existing ones are enabled by a better understanding of their structure-property relationships. Among all the design constraints, without doubt, the shape and size of the nanostructure along with the dielectric medium surrounding it has the maximum influence on the response and thereby the performance of the device. Hence …

Research Report 2013-2014, College Of Arts And Sciences

Physics Research Reports

• Introduction
• From the Chai
• Research Spotlight: Elena Litvinova, Ph.D.
• Refereed Publications
• Invited Presentations
• Contributed Presentations
• External Grant Activity (Submitted and Awarded)
• Notable Awards and Memberships
• Doctoral Dissertations and Master’s Theses
• Department Personnel

Radiative Double Electron Capture In Collisions Of Fully-Stripped Fluorine Ions With Thin Carbon Foils, Tamer Mohammad Samy Elkafrawy

Dissertations

Radiative double electron capture (RDEC) is a one-step process in ion-atom collisions occurring when two target electrons are captured to a bound state of the projectile simultaneously with the emission of a single photon. The emitted photon has approximately double the energy of the photon emitted due to radiative electron capture (REC), which occurs when a target electron is captured to a projectile bound state with simultaneous emission of a photon. REC and RDEC can be treated as timereversed photoionization (PI) and double photoionization (DPI), respectively, if loosely-bound target electrons are captured. This concept can be formulated with the principle …

Physics Faculty Use Of Example Solutions In Teaching Introductory Physics, William O. Mamudi

Masters Theses

This study investigates how physics faculty perceive and use features of example problem solutions. Thirty physics instructors from diverse institutions participated in semi-structured interviews. In addition to open-ended questions, three example problem solution artifacts were used to focus on specific solution features. Data were analyzed to identify instructors’ goals for the use of example solutions and whether their goals were consistent with the solution features that they valued and used. The study concludes that many faculty have three major goals: keeping students cognitively involved, helping students become better problem solvers, and supporting students in learning physics. The study also found …