Characterizing The Effects Of Radiation On Muscle Cells, 2017 Utah State University

#### Characterizing The Effects Of Radiation On Muscle Cells, Lori Caldwell, Elizabeth Vargis, Charles Harding, Jr Dennison

*Posters*

One of the primary concerns for those spending time in low gravity and high radiation environments is muscle atrophy. A major cause of muscular atrophy is oxidative stress which is amplified by increased levels of ionizing radiation during spaceflight. Additionally, high levels of radiation can damage DNA, increasing the risk of cancer. Utah State University’s Space Environment Test Facility was used to irradiate C2C12 myoblasts and human vascular endothelial cells with a beta-radiation dosage mimicking that on the International Space Station and a 3-year deep space mission.

Electron Yield Of A Carbon-Composite Nanodielectric, 2017 Utah State University

#### Electron Yield Of A Carbon-Composite Nanodielectric, Matthew Robertson, Justin Christensen, Greg Wilson, Jr Dennison

*Posters*

No abstract provided.

Characterizing The Effects Of Radiation On Muscle Cells, 2017 Utah State University

#### Characterizing The Effects Of Radiation On Muscle Cells, Lori Caldwell, Charles Harding, Jr Dennison, Elizabeth Vargis

*Posters*

As longer space missions become more desirable to public and private institutions, the physiological impact on astronauts must be considered. One of the primary concerns for those spending time in low gravity and high radiation environments is muscle atrophy. A major cause of muscular atrophy is oxidative stress which is amplified by increased levels of ionizing radiation during spaceflight. Additionally, high levels of radiation can damage DNA, increasing the risk of cancer. Utah State University’s Space Environment Test Facility was used to irradiate C2C12 myoblasts and human vascular endothelial cells with a dosage mimicking that on the International Space ...

Electron Yield Of Challenging Materials: Low Density Polyethylene And Carbon-Composite Nanodielectrics, 2017 Utah State University

#### Electron Yield Of Challenging Materials: Low Density Polyethylene And Carbon-Composite Nanodielectrics, Matthew Robertson, Jordan Lee, Jr Dennison

*Presentations*

The electron yield—the ratio of the number of emitted electrons to incident electrons—is a key material property that characterizes how materials will charge due to exposure to electron fluxes. The USU Materials Physics Group has developed expertise in measuring this for a wide array of conductors, semiconductors and insulators, including many challenging materials. The basic definitions associated with electron yield and how they are measured will be discussed. We will highlight many critical applications investigated at USU, particularly those associated with spacecraft charging as materials interact with space plasma environments. Electron irradiation experiments conducted to investigate the electron ...

Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, 2017 Iowa State University and Ames Laboratory

#### Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney

*Ames Laboratory Accepted Manuscripts*

Inelastic neutron scattering measurements on the itinerant antiferromagnet CaCo2−yAs2 at a temperature of 8 K reveal two orthogonal planes of scattering perpendicular to the Co square lattice in reciprocal space, demonstrating the presence of effective one-dimensional spin interactions. These results are shown to arise from near-perfect bond frustration within the J1-J2 Heisenberg model on a square lattice with ferromagnetic J1 and hence indicate that the extensive previous experimental and theoretical study of the J1-J2 Heisenberg model on local-moment square spin lattices should be expanded to include itinerant spin systems.

Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, 2017 Iowa State University and Ames Laboratory

#### Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield

*Ames Laboratory Accepted Manuscripts*

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0 ...

An Enhanced Operational Definition Of Dielectric Breakdown For Dc Voltage Step-Up Tests, 2017 Utah State University

#### An Enhanced Operational Definition Of Dielectric Breakdown For Dc Voltage Step-Up Tests, Allen Andersen, Jr Dennison

*Journal Articles*

The imprecise definition of breakdown in the ASTM D3755-14 standard can misidentify breakdown. If the recommended test circuit current sensing element threshold is set too high, breakdown may occur undetected. Conversely, false positives may result from designating a low current threshold. An operational definition of breakdown much less sensitive to these pitfalls is outlined herein. This enhanced definition of breakdown is based on the average rate of change of the leakage current with increasing voltage, rather than a simple current threshold, avoiding ambiguous association with anomalies in current traces. For tests that continuously monitor leakage current, breakdown can be detected ...

Highly Accelerated Test Method For Characterizing Likelihood Of Breakdown In Hvdc Dielectric Materials, 2017 Utah State University

#### Highly Accelerated Test Method For Characterizing Likelihood Of Breakdown In Hvdc Dielectric Materials, Allen Andersen, Jr Dennison

*Journal Articles*

Increasing application and development of HVDC technologies emphasizes the need for improved characterization of candidate insulating materials. Accurately predicting the lifetime to breakdown of dielectric materials by means of accelerated voltage step-up to breakdown tests can be prohibitively time consuming. Step-up to breakdown tests with sufficiently slow voltage ramp rates that continuously monitor leakage current have detected a distribution of DC partial discharge (DCPD) events occurring prior to breakdown, which increase with increasing field. These DCPD distributions are shown to correlate strongly with the likelihood of breakdown for four common polymers. Given that hundreds of DCPD events are typically observed ...

Detecting Majorana Fermion Induced Crossed Andreev Reflection, 2017 The Graduate Center, City University of New York

#### Detecting Majorana Fermion Induced Crossed Andreev Reflection, Lei Fang

*All Graduate Works by Year: Dissertations, Theses, and Capstone Projects*

This dissertation is devoted to a study of detecting the Majorana fermion induced crossed Andreev reflection.

Majorana fermions are particles that constitute their own antiparticles. In condensed matter physics, Majorana fermions are zero energy modes that reside at edges or around vortices of topological superconductors. The special properties of Majorana fermions result in their potential to conduct topological quantum computation, which has been attracting a lot of current research. One of the most important issues in the field of the Majorana fermion physics now is to detect their existence in realistic systems. Among many classes of detecting methods, a transport ...

Cubesat Space Environments Effects Studied In The Space Survivability Test Chamber, 2017 Utah State University

#### Cubesat Space Environments Effects Studied In The Space Survivability Test Chamber, Alexander Souvall, Gregory Wilson, Ben Russon, Katie Gamaunt, Jr Dennison

*Posters*

No abstract provided.

Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, 2017 University of Nothern Iowa

#### Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He

*Pavel Lukashev*

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We ...

Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, 2017 University of Nothern Iowa

#### Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He

*Rui He*

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We ...

Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, 2017 University of Nothern Iowa

#### Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He

*Rui He*

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We ...

Hopping Conductivity Of Electron Glass, 2017 University of Massachusetts Boston

#### Hopping Conductivity Of Electron Glass, Mingzhu Cui

*Graduate Masters Theses*

Hopping conductance between the sites in disordered systems is mapped to a random resistor network named Miller-Abrahams network. The conductance between two sites is in an exponential form depending on two parameters, the space separation and energy separation between sites. Our effort is focused on the visualization of the random resistor network. We find all the realizations for one electron hop and plot out the according random resistor networks. By comparing the random resistor network structures, we find that Coulomb interaction plays an important role in calculating the hopping conductance between sites. Furthermore, we rank the realizations by total energy ...

Machine Learning Phases Of Strongly Correlated Fermions, 2017 San Jose State University

#### Machine Learning Phases Of Strongly Correlated Fermions, Kelvin Ch'ng, Juan Carrasquilla, Roger Melko, Ehsan Khatami

*Faculty Publications*

Machine learning offers an unprecedented perspective for the problem of classifying phases in condensed matter physics. We employ neural network machine learning techniques to distinguish finite-temperature phases of the strongly-correlated fermions on cubic lattices. We show that a three-dimensional convolutional network trained on auxiliary field configurations produced by quantum Monte Carlo simulations of the Hubbard model can correctly predict the magnetic phase diagram of the model at the average density of one (half filling). We then use the network, trained at half filling, to explore the trend in the transition temperature as the system is doped away from half filling ...

Machine Learning Phases Of Strongly Correlated Fermions, 2017 San Jose State University

#### Machine Learning Phases Of Strongly Correlated Fermions, Kelvin Ch'ng, Juan Carrasquilla, Roger G. Melko, Ehsan Khatami

*Ehsan Khatami*

Permeability And Kinetic Coefficients For Mesoscale Bcf Surface Step Dynamics: Discrete Two-Dimensional Deposition-Diffusion Equation Analysis, 2017 Iowa State University

#### Permeability And Kinetic Coefficients For Mesoscale Bcf Surface Step Dynamics: Discrete Two-Dimensional Deposition-Diffusion Equation Analysis, Renjie Zhao, James W. Evans, Tiago J. Oliveira

*James W. Evans*

A discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessed as ...

Submonolayer Ag Films On Fe(100): A First-Principles Analysis Of Energetics Controlling Adlayer Thermodynamics And Kinetics, 2017 South University of Science and Technology of China

#### Submonolayer Ag Films On Fe(100): A First-Principles Analysis Of Energetics Controlling Adlayer Thermodynamics And Kinetics, Wei Li, Li Huang, James W. Evans, Yong Han

*James W. Evans*

Epitaxial growth of Ag on Fe(100) and postdeposition relaxation have been studied in several experiments. We provide a first-principles density functional theory analysis of key adatom interaction energies and diffusion barriers controlling growth and relaxation kinetics for the submonolayer regime, as these have not been assessed previously. A cluster expansion approach is used to obtain an extensive set of conventional lateral interactions between adatoms on fourfold hollow adsorption sites. We find robust oscillatory decay of pair interactions with increasing separation, and of trio interactions with increasing perimeter length. First- and second-nearest-neighbor pair interactions, as well as compact linear and ...

Diffusion Of Noninteracting Particles Into A Semi-Infinite Lattice, 2017 Iowa State University

#### Diffusion Of Noninteracting Particles Into A Semi-Infinite Lattice, James W. Evans

*James W. Evans*

Consider a gas of noninteracting particles diffusing into a semi-infinite lattice, Z+×ZD−1, subject to exclusion of double occupancy. An exact closed set of equations can be obtained and solved (in closed form) for the single-site occupancies or densities. Equations for the n-site occupancies couple only to such functions for n and n-1 sites, as for an infinite lattice. Their analysis reveals that negative pair correlations develop during this process, reflecting the propensity for diffusion to reduce density inhomogeneities and fluctuations.

Diffraction From Disordered One-Dimensional Islands With Domain Boundaries: Intensity Behavior For Various Statistical Approximations, 2017 Iowa State University

#### Diffraction From Disordered One-Dimensional Islands With Domain Boundaries: Intensity Behavior For Various Statistical Approximations, James W. Evans, R. S. Nord

*James W. Evans*

We consider the angular distribution of the diffracted intensity, I(q), for systems of disordered one-dimensional double-spaced islands with domain boundaries. Although I(q) is directly determined by the spatial pair correlations, it is often naturally reexpressed in terms of island size and separation distributions. We analyze the effect on I(q) of various approximate specifications of the island statistics. In particular, we highlight the approximations implicit in Guinier (-type) formulations, and provide a new very accurate approximation. Motivated by the scarcity of analysis for kinetically limited island growth (often seen in chemisorption), we consider such an irreversible cooperative filling ...