Numerical Analysis and Scientific Computing Commons^™

Contact Process With Temporal Disorder, Hatem Barghathi, Thomas Vojta, José A. Hoyos

Physics Faculty Research & Creative Works

We investigate the influence of time-varying environmental noise, i.e., temporal disorder, on the nonequilibrium phase transition of the contact process. Combining a real-time renormalization group, scaling theory, and large scale Monte-Carlo simulations in one and two dimensions, we show that the temporal disorder gives rise to an exotic critical point. At criticality, the effective noise amplitude diverges with increasing time scale, and the probability distribution of the density becomes infinitely broad, even on a logarithmic scale. Moreover, the average density and survival probability decay only logarithmically with time. This infinite-noise critical behavior can be understood as the temporal counterpart of …

Multiple Fermi Surfaces In Superconducting Nb-Doped Bi₂Se₃, B. J. Lawson, Paul Corbae, Gang Li, Fan Yu, Tomoya Asaba, Colin Tinsman, Y. Qiu, Julia E. Medvedeva, Yew San Hor, L. Li

Physics Faculty Research & Creative Works

Topological insulator Bi₂Se₃ has shown a number of interesting physical properties. Doping Bi₂Se₃ with copper or strontium has been demonstrated to make the material superconducting and potentially even a topological superconductor. The recent discovery of superconducting niobium-doped Bi₂Se₃ reveals an exciting new physical phenomenon, the coexistence of superconductivity and magnetic ordering, as well as signatures of an odd-parity p-wave superconducting order. To understand this new phenomenon, a detailed knowledge of the electronic structure is needed. We present an observation of quantum oscillations in the magnetization (the de Haas-van Alphen effect) of …

Spica: Stereographic Projection For Interactive Crystallographic Analysis, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

In numerous research fields, especially the applications of electron and X-ray diffraction, stereographic projection represents a powerful tool for researchers. SPICA is a new computer program for stereographic projection in interactive crystallographic analysis, which inherits features from the previous JECP/SP and includes more functions for extensive crystallographic analysis. SPICA provides fully interactive options for users to plot stereograms of crystal directions and crystal planes, traces, and Kikuchi maps for an arbitrary crystal structure; it can be used to explore the orientation relationships between two crystalline phases with a composite stereogram; it is also used to predict the tilt angles of …

Comparison Of Experimental And Theoretical Triple Differential Cross Sections For The Single Ionization Of Co₂ (1Πg) By Electron Impact, Zehra N. Ozer, Esam Ali, Mevlut Dogan, Murat Yavuz, Osman Alwan, Adnan Naja, Ochbadrakh Chuluunbaatar, Boghos B. Joulakian, Chuan-Gang Ning, James Colgan, Don H. Madison

Physics Faculty Research & Creative Works

Experimental and theoretical triple differential cross sections for intermediate-energy (250 eV) electron-impact single ionization of the CO₂ are presented for three fixed projectile scattering angles. Results are presented for ionization of the outermost 1πg molecular orbital of CO₂ in a coplanar asymmetric geometry. The experimental data are compared to predictions from the three-center Coulomb continuum approximation for triatomic targets, and the molecular three-body distorted wave (M3DW) model. It is observed that while both theories are in reasonable qualitative agreement with experiment, the M3DW is in the best overall agreement with experiment.

Experimental And Theoretical Triple-Differential Cross Sections For Tetrahydrofuran Ionized By Low-Energy 26-Ev-Electron Impact, Esam Ali, Xueguang Ren, Alexander Dorn, Chuangang Ning, James Colgan, Don H. Madison

Physics Faculty Research & Creative Works

We report an experimental and theoretical study of low-energy electron-impact ionization of tetrahydrofuran, which is a molecule of biological interest. The experiments were performed using an advanced reaction microscope specially built for electron-impact ionization studies. The theoretical calculations were performed within the molecular three-body distorted-wave model. Reasonably good agreement is found between experiment and theory.

Kinematically Complete Study Of Low-Energy Electron-Impact Ionization Of Argon: Internormalized Cross Sections In Three-Dimensional Kinematics, Xueguang Ren, Sadek Amami, Oleg Zatsarinny, Thomas Pflüger, Marvin Weyland, Alexander Dorn, Don H. Madison, Klaus Bartschat

Physics Faculty Research & Creative Works

As a further test of advanced theoretical methods to describe electron-impact single-ionization processes in complex atomic targets, we extended our recent work on Ne(2p) ionization [X. Ren, S. Amami, O. Zatsarinny, T. Pflüger, M. Weyland, W. Y. Baek, H. Rabus, K. Bartschat, D. Madison, and A. Dorn, Phys. Rev. A 91, 032707 (2015)PLRAAN1050-294710.1103/PhysRevA.91.032707] to Ar(3p) ionization at the relatively low incident energy of E₀ = 66 eV. The experimental data were obtained with a reaction microscope, which can cover nearly the entire 4π solid angle for the secondary electron emission. We present experimental data for detection angles of 10, …

Reply To "Comment On 'Classical Description Of H(1s) And H* (N=2) For Cross-Section Calculations Relevant To Charge-Exchange Diagnostics'", N. D. Cariatore, Sebastian Otranto, Ronald E. Olson

Physics Faculty Research & Creative Works

In reply to the Comment of Jorge et al. [Phys. Rev. A 93, 066701 (2016)], we agree and reconfirm that the alternative classical trajectory Monte Carlo method (called hydrogenic-Z-CTMC) radial distributions for H*(n = 2) we recently published are not stable in time. However, we show that such lack of stability which is more noticeable for H(2s) than for H(2p) is due to the initialization procedure employed and not to the hydrogenic-Z-CTMC method itself. A new set of completely stable hydrogenic-Z-CTMC calculations for H*(n = 2) is introduced and found in very good agreement with standard microcanonical results reinforcing our …

Experimental Building Demonstration Model With Viscous Fluid Dampers, Blake Thomas Reeve, Brianna Jean Kufa, Aden Malek Stepanians, Sophie Carmion Ratkovich

Architectural Engineering

The Architectural Engineering major places a heavy emphasis on structural dynamics and the role of wind and seismic loading in building analysis and design. Buildings of high importance that are critical to community function, such as hospitals, often utilize supplemental damping devices like supplemental viscous fluid dampers or base isolators to reduce the overall demands on the structural system. The design and analysis of these dampers are typically not taught at the undergraduate level, and is frequently performed by mechanical engineers, in lieu of structural engineers.

To better understand and research building behavior with supplemental damping devices, our multi-disciplinary team …

Contributing To Astropy: A Community Python Library For Astronomers, Asra Nizami

Macalester Journal of Physics and Astronomy

This paper discusses the author’s contributions to two packages affiliated with Astropy, a community Python library for astronomers. The packages the author contributed to were modeling, a sub-package within the core Astropy package, and WCSAxes, an Astropy affiliated package, outside the core package.

Spatio-Temporal Generalization Of The Harris Criterion And Its Application To Diffusive Disorder, Thomas Vojta, Ronald Dickman

Physics Faculty Research & Creative Works

We investigate how a clean continuous phase transition is affected by spatiotemporal disorder, i.e., by an external perturbation that fluctuates in both space and time. We derive a generalization of the Harris criterion for the stability of the clean critical behavior in terms of the space-time correlation function of the external perturbation. As an application, we consider diffusive disorder, i.e., an external perturbation governed by diffusive dynamics, and its effects on a variety of equilibrium and nonequilibrium critical points. We also discuss the relation between diffusive disorder and diffusive dynamical degrees of freedom in the example of model C of …

Random Field Disorder At An Absorbing State Transition In One And Two Dimensions, Hatem Barghathi, Thomas Vojta

Physics Faculty Research & Creative Works

We investigate the behavior of nonequilibrium phase transitions under the influence of disorder that locally breaks the symmetry between two symmetrical macroscopic absorbing states. In equilibrium systems such "random-field" disorder destroys the phase transition in low dimensions by preventing spontaneous symmetry breaking. In contrast, we show here that random-field disorder fails to destroy the nonequilibrium phase transition of the one- and two-dimensional generalized contact process. Instead, it modifies the dynamics in the symmetry-broken phase. Specifically, the dynamics in the one-dimensional case is described by a Sinai walk of the domain walls between two different absorbing states. In the two-dimensional case, …

Retrival Of Atmospheric Aerosol Size Distributions Using Stochastic Particle Swarm Optimization, Benjamin D. Nault-Maurer

All College Thesis Program, 2016-2019

A stochastic particle swarm optimization (SPSO) technique’s robustness is studied in regards to atmospheric aerosol size distribution estimations for a bimodal distribution that focuses on Aitken and accumulation mode aerosols. The SPSO method is used to calculate a set of 11 aerosol optical depth (AOD) values based on a size distribution and match them to an inputted set of AOD values. This method is tested using computer generated AOD values with fixed distribution parameters, generated AOD values with varying distribution parameters, two sets of AOD measurements in clear conditions, and one set of AOD values in hazy conditions. The SPSO …

Computational Progress Towards Maximum Distinguishability Of Bell States By Linear Evolution And Local Measurement, Victor Shang

HMC Senior Theses

Many quantum information protocols rely on the ability to distinguish between entangled quantum states known as Bell states. However, theoretical limits exist on the maximal distinguishability of these entangled states using linear evolution and local measurement (LELM) devices. In the case of two particles entangled in multiple qubit variables, the maximum number of distinguishable Bell states is known. However, in the more general case of two particles entangled in multiple qudit variables, only an upper bound is known under additional assumptions. I have written software in Matlab and Mathematica to explore computationally the maximum number of Bell states that can …

Role Of Composition And Structure On The Properties Of Metal/Multifunctional Ceramic Interfaces, Fang Yin Lin, Aleksandr V. Chernatynskiy, Juan Claudio Nino, Jacob L. Jones, Richard G. Hennig, Susan Sinnott

Physics Faculty Research & Creative Works

The formation of intermetallic secondary phases, such as Pt₃Pb, has been observed experimentally at PbTiO₃/Pt and Pb(Zr,Ti)O₃/Pt, or PZT/Pt, interfaces. Density functional theory calculations are used here to calculate the work of adhesion of these interfacial systems with and without the secondary intermetallic phase. The charge density maps of the interfaces reveal the electronic interactions at the interface and the impact of the secondary phase. In addition, Bader charge analysis provides a quantitative assessment of electron transfer from the perovskites to the Pt. Analysis of the band diagrams indicates an increase of the potential …

Electron Impact Ionization Dynamics Of Para-Benzoquinone, D. B. Jones, E. Ali, C. G. Ning, J. Colgan, O. Ingólfsson, Don H. Madison, M. J. Brunger

Physics Faculty Research & Creative Works

Triple differential cross sections (TDCSs) for the electron impact ionization of the unresolved combination of the 4 highest occupied molecular orbitals (4b_3g, 5b_2u, 1b_1g, and 2b_3u) of para-benzoquinone are reported. These were obtained in an asymmetric coplanar geometry with the scattered electron being observed at the angles −7.5°, −10.0°, −12.5° and −15.0°. The experimental cross sections are compared to theoretical calculations performed at the molecular 3-body distorted wave level, with a marginal level of agreement between them being found. The character of the ionized orbitals, through calculated momentum profiles, provides some qualitative …

Stereographic Visualization Of Bose-Einstein Condensate Clouds To Measure The Gravitational Constant, Ed Wesley Wells

College of Graduate Studies: Theses & Dissertations

This thesis describes a set of tools that can be used for the rapid design of atom interferometer schemes suitable for measuring Newton's Universal Gravitation constant also known as "Big G". This tool set is especially applicable to Bose--Einstein--condensed systems present in NASA's Cold Atom Laboratory experiment to be deployed to the International Space Station in 2017. These tools include a method of approximating the solutions of the nonlinear Schrödinger or Gross--Pitaevskii equation (GPE) using the Lagrangian Variational Method. They also include a set of software tools for translating the approximate solutions of the GPE into images of the optical …

High-Fidelity Simulations Of Long-Term Beam-Beam Dynamics On Gpus, B. Terzić, K. Arumugam, M. Aturban, C. Cotnoir, A. Godunov, D. Ranjan, M. Stefani, M. Zubair, F. Lin, V. Morozov, Y. Roblin, H. Zhang

Physics Faculty Publications

Future machines such as the Electron Ion Collider (MEIC), linac-ring machines (eRHIC) or LHeC are particularly sensitive to beam-beam effects. This is the limiting factor for long-term stability and high luminosity reach. The complexity of the non-linear dynamics makes it challenging to perform such simulations typically requiring millions of turns. Until recently, most of the methods have involved using linear approximations and/or tracking for a limited number of turns. We have developed a framework which exploits a massively parallel Graphical Processing Units (GPU) architecture to allow for tracking millions of turns in a sympletic way up to an arbitrary order. …

Infinite-Noise Criticality: Nonequilibrium Phase Transitions In Fluctuating Environments, Thomas Vojta, José A. Hoyos

Physics Faculty Research & Creative Works

We study the effects of time-varying environmental noise on nonequilibrium phase transitions in spreading and growth processes. Using the examples of the logistic evolution equation as well as the contact process, we show that such temporal disorder gives rise to a distinct type of critical points at which the effective noise amplitude diverges on long time scales. This leads to enormous density fluctuations characterized by an infinitely broad probability distribution at criticality. We develop a real-time renormalization-group theory that provides a general framework for the effects of temporal disorder on nonequilibrium processes. We also discuss how general this exotic critical …

Comparison Of Experimental And Theoretical Electron-Impact-Ionization Triple-Differential Cross Sections For Ethane, Esam Ali, Kate Nixon, Andrw Murray, Chuangang Ning, James Colgan, Don H. Madison

Physics Faculty Research & Creative Works

We have recently examined electron-impact ionization of molecules that have one large atom at the center, surrounded by H nuclei (H₂O, NH₃, CH₄). All of these molecules have ten electrons; however, they vary in their molecular symmetry. We found that the triple-differential cross sections (TDCSs) for the highest occupied molecular orbitals (HOMOs) were similar, as was the character of the HOMO orbitals which had a p-type "peanut" shape. In this work, we examine ethane (C₂H₆) which is a molecule that has two large atoms surrounded by H nuclei, so that …

Evidence For Unnatural-Parity Contributions To Electron-Impact Ionization Of Laser-Aligned Atoms, G. S. J. Armstrong, J. Colgan, M. S. Pindzola, S. Amami, Don H. Madison, J. Pursehouse, K. L. Nixon, A. J. Murray

Physics Faculty Research & Creative Works

Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this work we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. We demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionization from …

Simulations Of Hl-Lhc Crab Cavity Noise Using Headtail, Stanley Steeper

Physics

The High Luminosity Large Hadron Collider (Hi-Lumi LHC) upgrade -- scheduled to be completed by 2025 -- will improve the existing LHC in many ways. One such upgrade is the addition of Crab Cavities (CCs). The CCs are resonant structures that provide strong transverse kicks to the circulating clouds of particles around each interaction region. As such, the CCs result in a head-on collision of the clouds and a large increase in event rate, leading to reduced statistical uncertainty and potentially faster discoveries. However, the CC field will be modulated by phase and amplitude noise which can have detrimental effects …

Mapping Open Water Bodeis With Optical Remote Sensing, Mary Ellen O'Donnell, Erika Podest

STAR Program Research Presentations

There is interest in mapping open water bodies using remote sensing data. Coverage and persistence of open water is currently a poorly measured variable due to its spatial and temporal variability across landscapes, especially in remote areas. The presence and persistence of open water is one of the primary indicators of conditions suitable for mosquito breeding habitats. Predicting the risk of mosquito caused disease outbreaks is a required step towards their control and eradication. Satellite observations can provide needed data to support agency decisions for deployment of preventative measures and control resources. This study, which will try to map open …

Anharmonic Properties In Mg₂X (X= C, Si, Ge, Sn, Pb) From First-Principles Calculations, Aleksandr V. Chernatynskiy, Simon R. Phillpot

Physics Faculty Research & Creative Works

Thermal conductivity reduction is one of the potential routes to improve the performance of thermoelectric materials. However, detailed understanding of the thermal transport of many promising materials is still missing. In this paper, we employ electronic-structure calculations at the level of density functional theory to elucidate thermal transport properties of the Mg₂X (X=C, Si, Ge, Sn, and Pb) family of compounds, which includes Mg₂Si, a material already identified as a potential thermoelectric. All these materials crystallize into the same antifluorite structure. Systematic trends in the anharmonic properties of these materials are presented and examined. Our calculations …

Interference Effects For Intermediate Energy Electron-Impact Ionization Of H₂ And N₂ Molecules, Zehra Nur Ozer, Hari Chaluvadi, Don H. Madison, Mevlut Dogan

Physics Faculty Research & Creative Works

We have studied electron impact ionization of H₂ and N₂ molecules at intermediate energies to look for possible two center interference effects experimentally and theoretically. Here we report a study of the interference factor I for 250 eV electron-impact ionization. The experimental measurements are performed using a crossed-beam-type electron-electron coincidence spectrometer and theoretical calculations are obtained using the Molecular Three Body Distorted Wave Approximation (M3DW). We found that the I-factor demonstrated strong evidence for two-center interference effects for both H₂ and N₂. We also found that the I-factor is more sensitive to projectile angular scans …

Emerging Criticality In The Disordered Three-Color Ashkin-Teller Model, Qiong Zhu, Xin Wan, Rajesh Narayanan, José A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We study the effects of quenched disorder on the first-order phase transition in the two-dimensional three-color Ashkin-Teller model by means of large-scale Monte Carlo simulations. We demonstrate that the first-order phase transition is rounded by the disorder and turns into a continuous one. Using a careful finite-size-scaling analysis, we provide strong evidence for the emerging critical behavior of the disordered Ashkin-Teller model to be in the clean two-dimensional Ising universality class, accompanied by universal logarithmic corrections. This agrees with perturbative renormalization-group predictions by Cardy. As a byproduct, we also provide support for the strong-universality scenario for the critical behavior of …

Erratum: Theoretical And Experimental (E,2e) Study Of Electron-Impact Ionization Of Laser-Aligned Mg Atoms [Physical Review A 90, 062707 (2014)], Sadek Amami, Andrew J. Murray, Al Stauffer, Kate Nixon, Gregory Armstrong, James Colgan, Don H. Madison

Physics Faculty Research & Creative Works

We have recently reported a theoretical and experimental study of electron-impact ionization of laser-aligned magnesium. Results were presented for both ionization of the ground state, as well as for laser-aligned atoms in the 3p state. For ionization from the 3p state, theoretical results were presented using the distorted wave Born (DWBA) and three-body distorted wave (3DW) approximations. Unfortunately, after publication we learned that the theoretical results were incorrect due to one of the arrays in the computer code dimensioned too small. The figures affected by this error are Figs. 3–5 in the original paper. The present Figs. 3–5 …

Classical Description Of H(1s) And H* (N=2) For Cross-Section Calculations Relevant To Charge-Exchange Diagnostics, N. D. Cariatore, Sebastian Otranto, Ronald E. Olson

Physics Faculty Research & Creative Works

In this work, we introduce a classical trajectory Monte Carlo (CTMC) methodology, specially conceived to provide a more accurate representation of charge-exchange processes between highly charged ions and H(1s) and H* (n=2). These processes are of particular relevance in power fusion reactor programs, for which charge-exchange spectroscopy has become a useful plasma diagnostics tool. To test the methodology, electron-capture reactions from these targets by C⁶⁺,N⁷⁺, and O⁸⁺ are studied at impact energies in the 10-150keV/amu range. State-selective cross sections are contrasted with those predicted by the standard microcanonical formulation of the CTMC method, the CTMC …

Kinematically Complete Study Of Low-Energy Electron-Impact Ionization Of Neon: Internormalized Cross Sections In Three-Dimensional Kinematics, Xueguang Ren, Sadek Amami, Oleg Zatsarinny, Thomas Pflüger, Marvin Weyland, Woon Yong Baek, Hans Rabus, Klaus Bartschat, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Low-energy (E₀ 0=65eV) electron-impact single ionization of Ne (2p) has been investigated to thoroughly test state-of-the-art theoretical approaches. The experimental data were measured using a reaction microscope, which can cover nearly the entire 4π solid angle for the secondary electron emission energies ranging from 2 to 8 eV, and projectile scattering angles ranging from 8.5⁰ to 20.0⁰. The experimental triple-differential cross sections are internormalized across all measured scattering angles and ejected energies. The experimental data are compared to predictions from a hybrid second-order distorted-wave Born plus R-matrix approach, the distorted-wave Born approximation with the inclusion of postcollision interaction (PCI), …

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.

Composition-Dependent Structural And Transport Properties Of Amorphous Transparent Conducting Oxides, Rabi Khanal, D. Bruce Buchholz, Robert P. Chang, Julia E. Medvedeva

Physics Faculty Research & Creative Works

Structural properties of amorphous In-based oxides, In-X-O with X=Zn, Ga, Sn, or Ge, are investigated using ab initio molecular dynamics liquid-quench simulations. The results reveal that indium retains its average coordination of 5.0 upon 20% X fractional substitution for In, whereas X cations satisfy their natural coordination with oxygen atoms. This finding suggests that the carrier generation is primarily governed by In atoms, in accord with the observed carrier concentration in amorphous In-O and In-X-O. At the same time, the presence of X affects the number of six-coordinated In atoms as well as the oxygen sharing between the InO_{6 …}