Raman Spectroscopy Of Oxygen Evolution Catalysts And Psii Manganese Model Compounds,
2017
Purdue University
Raman Spectroscopy Of Oxygen Evolution Catalysts And Psii Manganese Model Compounds, Sergei Shmakov, Daniel A. Hartzler, Alireza Karbakhsh Ravari, Yulia Pushkar
The Summer Undergraduate Research Fellowship (SURF) Symposium
Photosynthesis is the basis of life on earth, and oxygen evolution catalysts are key components of this complicated, yet not fully understood process. Photosystem II, a large membrane bound pigment-protein complex, is the key system that facilitates oxygenic photosynthesis via the oxygen evolving complex (a natural oxygen evolving catalyst). It is a key component in oxygen producing catalysts, which can be used in fields such as energy production and biomimetic catalysts. The oxygen evolution cycle, or Kok cycle going within it is still not studied completely. In this project, we were studying the vibrational (and structural) state of a Manganese …
Dielectronic Recombination Calculations For Silicon-Like Ions And The S2+ Orion Nebula Abundance Conundrum,
2017
Western Michigan University
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 …
Angular Distribution Of Single-Photon Superradiance In A Dilute And Cold Atomic Ensemble,
2017
Old Dominion University
Angular Distribution Of Single-Photon Superradiance In A Dilute And Cold Atomic Ensemble, A. S. Kuraptsev, I. M. Sokolov, M. D. Havey
Physics Faculty Publications
On the basis of a quantum microscopic approach we study the dynamics of the afterglow of a dilute Gaussian atomic ensemble excited by pulsed radiation. Taking into account the vector nature of the electromagnetic field we analyze in detail the angular and polarization distribution of single-photon superradiance of such an ensemble. The dependence of the angular distribution of superradiance on the length of the pulse and its carrier frequency as well as on the size and the shape of the atomic clouds is studied. We show that there is substantial dependence of the superradiant emission on the polarization and the …
Electron Paramagnetic Resonance Study Of Neutral Mg Acceptors In Β-Ga2O3 Crystals,
2017
Air Force Institute of Technology
Electron Paramagnetic Resonance Study Of Neutral Mg Acceptors In Β-Ga2O3 Crystals, Brant E. Kananen, Larry E. Halliburton, Elizabeth M. Scherrer, K. T. Stevens, G. K. Foundos, K. B. Chang, Nancy C. Giles
Faculty Publications
Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors (Mg0Ga) in a β-Ga2O3 crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors (Mg−Ga). Unintentionally present Fe3+ (3d5) and Cr3+ (3d3) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion …
Band Offsets At The Interface Between Crystalline And Amorphous Silicon From First Principles,
2017
University of Kentucky
Band Offsets At The Interface Between Crystalline And Amorphous Silicon From First Principles, Karol Jarolimek, E. Hazrati, R. A. De Groot, D. A. De Wijs
Center for Applied Energy Research Faculty and Staff Publications
The band offsets between crystalline and hydrogenated amorphous silicon (a−Si∶H) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature …
Optimizing An Electron's Path To Ionization Using A Genetic Algorithm,
2017
Ursinus College
Optimizing An Electron's Path To Ionization Using A Genetic Algorithm, Jason Bennett, Kevin Choice
Physics and Astronomy Summer Fellows
A Rydberg atom is an atom with a highly excited and weakly bound valence electron. A widespread method of studying quantum mechanics with Rydberg atoms is to ionize the electron and measure its arrival time. We use a Genetic Algorithm (GA) to control the electron's path to ionization. The Rydberg electron's energy levels are strongly shifted by the presence of an electric field. The energy levels shift and curve, but never cross. At an avoided crossing the electron can jump from one level to the next. By engineering the electric field's time dependence, we thereby control the path to ionization. …
Kinematical Vortices In Double Photoionization Of Helium By Attosecond Pulses,
2017
University of Nebraska-Lincoln
Kinematical Vortices In Double Photoionization Of Helium By Attosecond Pulses, Jean Marcel Ngoko Djiokap, A. V. Meremianin, N. L. Manakov, S. X. Hu, L. B. Madsen, Anthony F. Starace
Anthony F. Starace Publications
Two-armed helical vortex structures are predicted in the two-electron momentum distributions produced in double photoionization (DPI) of the He atom by a pair of time-delayed elliptically polarized attosecond pulses with opposite helicities. These predictions are based upon both a first-order perturbation theory analysis and numerical solutions of the two-electron, time-dependent Schrödinger equation in six spatial dimensions. The helical vortex structures originate from Ramsey interference of a pair of ionized two-electron wave packets, each having a total angular momentum of unity, and appear in the sixfold differential DPI probability distribution for any energy partitioning between the two electrons. The vortex structures …
Simulation Of Alnico Coercivity,
2017
Ames Laboratory
Simulation Of Alnico Coercivity, Liqin Ke, Ralph Skomski, Todd D. Hoffman, Lin Zhoue, Wei Tang, Duane D. Johnson, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang
Nebraska Center for Materials and Nanoscience: Faculty Publications
Micromagnetic simulations of alnico show substantial deviations from Stoner-Wohlfarth behavior due to the unique size and spatial distribution of the rod-like Fe-Co phase formed during spinodal decomposition in an external magnetic field. The maximum coercivity is limited by single-rod effects, especially deviations from ellipsoidal shape, and by interactions between the rods. Both the exchange interaction between connected rods and magnetostatic interaction between rods are considered, and the results of our calculations show good agreement with recent experiments. Unlike systems dominated by magnetocrystalline anisotropy, coercivity in alnico is highly dependent on size, shape, and geometric distribution of the Fe-Co phase, all …
One More Hard Three-Loop Correction To Parapositronium Energy Levels,
2017
University of Kentucky
One More Hard Three-Loop Correction To Parapositronium Energy Levels, Michael I. Eides, Valery A. Shelyuto
Physics and Astronomy Faculty Publications
A hard three-loop correction to parapositronium energy levels of order mα7 is calculated. This nonlogarithmic contribution is due to the insertions of one-loop photon propagator in the fermion lines in the diagrams with virtual two-photon annihilation. We obtained ΔE = 0.03297(2)(mα7 / π3) for this energy shift.
Non-Hermitian Matter-Wave Mixing In Bose-Einstein Condensates: Dissipation-Induced Amplification,
2017
Bilkent University
Non-Hermitian Matter-Wave Mixing In Bose-Einstein Condensates: Dissipation-Induced Amplification, S. Wuster, Ramy El-Ganainy
Department of Physics Publications
We investigate the nonlinear scattering dynamics in interacting atomic Bose-Einstein condensates under non-Hermitian dissipative conditions. We show that, by carefully engineering a momentum-dependent atomic loss profile, one can achieve matter-wave amplification through four-wave mixing in a quasi-one-dimensional nearly-free-space setup—a process that is forbidden in the counterpart Hermitian systems due to energy mismatch. Additionally, we show that similar effects lead to rich nonlinear dynamics in higher dimensions. Finally, we propose a physical realization for selectively tailoring the momentum-dependent atomic dissipation. Our strategy is based on a two-step process: (i) exciting atoms to narrow Rydberg or metastable excited states, and (ii) introducing …
Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins,
2017
University of Nebraska-Lincoln
Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins, Christian Binek
Christian Binek Publications
It is shown that in the ergodic regime, the temperature dependence of Young’s modulus is solely determined by the magnetic properties of a material. For the large class of materials with paramagnetic or diamagnetic response, simple functional forms of the temperature derivative of Young’s modulus are derived and compared with experimental data and empirical results. Superconducting materials in the Meissner phase are ideal diamagnets. As such, they display remarkable elastic properties. Constant diamagnetic susceptibility gives rise to a temperature independent elastic modulus for ceramic and single crystalline superconductors alike. The thermodynamic approach established in this report, paves the way to …
Atomistic Quantum Transport Simulation Of Multilayer Phosphorene Nanoribbon Field Effect Transistors,
2017
University of Kentucky
Atomistic Quantum Transport Simulation Of Multilayer Phosphorene Nanoribbon Field Effect Transistors, Hojjatollah Sarvari, Chaoyuan Liu, Amir Hossein Ghayour, Parham Shenavar, Zhi Chen, Rahim Ghayour
EKU Faculty and Staff Scholarship
Few-layer black phosphorus is a semiconductor material, where its allotrope is called phosphorene; a new two-dimensional material which is discovered in 2014. In this paper, first we use the tight-binding method to implement a matrix representation for single-layer and multilayer structures of phosphorene nanoribbon (PNR) to define the Hamiltonian of the system. Second, we investigate the band structure and the band gap of multilayer PNRs. The band gap of armchair PNRs with 16 atoms across the width of PNR for single-layer, bilayer, and three-layer structures are obtained as 1.899, 1.224, and 0.937 eV, respectively. Third, we use the atomistic description …
Vortex Circulation Patterns In Planar Microdisk Arrays,
2017
Lawrence Berkeley National Laboratory
Vortex Circulation Patterns In Planar Microdisk Arrays, Sven Velten, Robert Streubel, Alan Farhan, Noah Kent, Mi Young Im, Andreas Scholl, Scott Dhuey, Carolin Behncke, Guido Meier, Peter Fischer
Robert Streubel Papers
We report a magnetic X-ray microscopy study of the pattern formation of circulation in arrays of magnetic vortices ordered in a hexagonal and a honeycomb lattice. In the honeycomb lattice, we observe at remanence an ordered phase of alternating circulations, whereas in the hexagonal lattice, small regions of alternating lines form. A variation in the edge-to-edge distance shows that the size of those regions scales with the magnetostatic interaction. Micromagnetic simulations reveal that the patterns result from the formation of flux closure states during the nucleation process.
Quantum Optical Interferometry And Quantum State Engineering,
2017
CUNY Graduate Center
Quantum Optical Interferometry And Quantum State Engineering, Richard J. Birrittella Jr
Dissertations, Theses, and Capstone Projects
We highlight some of our research done in the fields of quantum optical interferometry and quantum state engineering. We discuss the body of work for which our research is predicated, as well as discuss some of the fundamental tenants of the theory of phase estimation. We do this in the context of quantum optical interferometry where our primary interest lies in the calculation of the quantum Fisher information as it has been shown that the minimum phase uncertainty obtained, the quantum Cramer-Rao bound, is saturated by parity-based detection methods. We go on to show that the phase uncertainty one obtains …
Improvements For The T0c+ Geometry Of The Fast Interaction Trigger (Fit) Upgrade To Alice At The Cern Lhc,
2017
California Polytechnic State University, San Luis Obispo
Improvements For The T0c+ Geometry Of The Fast Interaction Trigger (Fit) Upgrade To Alice At The Cern Lhc, Noah Miller
Physics
The purpose of the ALICE experiment at CERN is to investigate the properties of the strongly interacting quark-gluon plasma formed in the high-energy collisions of lead nuclei in the CERN Large Hadron Collider. ALICE has been collecting data since 2009. The upcoming upgrade of the CERN LHC injectors during 2019-20 will boost the luminosity and the collision rate beyond the design parameters for several of the key ALICE detectors including the forward trigger detectors. The new Fast Interaction Trigger (FIT) will enable ALICE to discriminate beam-beam interactions with a 99% efficiency for the collisions generated by the LHC at a …
My Contributions To The Cryogenic Underground Observatory For Rare Events Experiment And The Utilization Of Geant4 In Their Analysis,
2017
California Polytechnic State University, San Luis Obispo
My Contributions To The Cryogenic Underground Observatory For Rare Events Experiment And The Utilization Of Geant4 In Their Analysis, Kevin Armenta
Physics
First, a brief introduction and background of the basics of particle physics and the Standard Model is discussed in order to give context to nature of the neutrinoless double beta decay ($2\nu\beta\beta$) and why it is so interesting to particle physicists. Next, the Cryogenic Underground Observatory for Rare Events (CUORE) experiment is discussed in detail, explaining the rational behind the experimental setup and detection process. Finally, I conclude by discussing Geant4, an important software toolkit used in particle physics, and how it is utilized in the CUORE experiment.
Time-Dependent Photoionization Of Gaseous Nebulae,
2017
Western Michigan University
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) …
Implementation And Modeling Of A Femtosecond Laser-Activated Streak Camera,
2017
University of Nebraska-Lincoln
Implementation And Modeling Of A Femtosecond Laser-Activated Streak Camera, Omid Zandi, Kyle J. Wilkin, Martin Centurion
Martin Centurion Publications
8 June 2017) A laser-activated streak camera was built to measure the duration of femtosecond electron pulses. The streak velocity of the device is 1.89 mrad/ps, which corresponds to a sensitivity of 34.9 fs/pixels. The streak camera also measures changes in the relative time of arrival between the laser and electron pulses with a resolution of 70 fs RMS. A full circuit analysis of the structure is presented to describe the streaking field and the general behavior of the device. We have developed a general mathematical model to analyze the streaked images. The model provides an accurate method to extract …
Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2,
2017
University of Nebraska-Lincoln
Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, Zhiyong Xiao, Jingfeng Song, David K. Ferry, Stephen Ducharme, Xia Hong
Stephen Ducharme Publications
We exploit scanning-probe-controlled domain patterning in a ferroelectric top layer to induce nonvolatile modulation of the conduction characteristic of monolayer MoS2 between a transistor and a junction state. In the presence of a domain wall, MoS2 exhibits rectified I-V characteristics that are well described by the thermionic emission model. The induced Schottky barrier height ΦeffB varies from 0.38 to 0.57 eV and is tunable by a SiO2 global back gate, while the tuning range of ΦeffB depends sensitively on the conduction-band-tail trapping states. Our work points to a new route to achieving programmable …
Observing Orbital Angular Momentum Transfer From Electron Vortex Beams To Matter,
2017
Linfield College
Observing Orbital Angular Momentum Transfer From Electron Vortex Beams To Matter, Hannah Devyldere
Senior Theses
It is possible to produce electron beams with non-zero orbital angular momentum. Such beams, known as electron vortex beams, are theoretically able to transfer their orbital angular momenta to matter, causing the matter to rotate. Nanoparticles in an aqueous solution were observed with an electron vortex beam to detect the transfer of orbital angular momentum in a low-friction environment. Observing the transfer of orbital angular momentum to particles in solution is difficult due to the necessity of imaging the particles through a liquid and the random movement of particles in the solution. Thus, orbital angular momentum transfer to matter could …
