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Articles 1 - 30 of 135
Full-Text Articles in Condensed Matter Physics
Hexagonal Rare-Earth Manganites As Promising Photovoltaics And Light Polarizers, Xin Huang, Tula R. Paudel, Shuai Dong, Evgeny Y. Tsymbal
Hexagonal Rare-Earth Manganites As Promising Photovoltaics And Light Polarizers, Xin Huang, Tula R. Paudel, Shuai Dong, Evgeny Y. Tsymbal
Evgeny Tsymbal Publications
Ferroelectric materials possess a spontaneous electric polarization and may be utilized in various technological applications ranging from nonvolatile memories to solar cells and light polarizers. Recently, hexagonal rareearth manganites, h-RMnO3 (R is a rare-earth ion), have attracted considerable interest due to their intricate multiferroic properties and improper ferroelectricity characterized by a sizable remnant polarization and high Curie temperature. Here we demonstrate that these compounds can serve as very efficient photovoltaic materials and, in addition, possess remarkable optical anisotropy properties. Using first-principles methods based on density functional theory and considering h-TbMnO3 as a representative …
Spontaneously Generated Inhomogeneous Phases Via Holography, Kübra Yeter Aydeniz
Spontaneously Generated Inhomogeneous Phases Via Holography, Kübra Yeter Aydeniz
Doctoral Dissertations
We discuss a holographic model consisting of a U(1) gauge field and a scalar field coupled to a charged AdS (anti-de Sitter) black hole under a spatially homogeneous chemical potential. By turning on a higher-derivative interaction term between the U(1) gauge field and the scalar field, a spatially dependent profile of the scalar field is generated spontaneously. We calculate the critical temperature at which the transition to the inhomogeneous phase occurs for various values of the parameters of the system. We solve the equations of motion below the critical temperature, and show that the dual gauge theory on the boundary …
Hydrogen Bond-Mediated Structural Order In Hydroxylated Bis-Mpa Dendritic Polymers: Experimental And Molecular Dynamics Simulation Study, Maliha N. Syed
Hydrogen Bond-Mediated Structural Order In Hydroxylated Bis-Mpa Dendritic Polymers: Experimental And Molecular Dynamics Simulation Study, Maliha N. Syed
Dissertations
Dendritic architectures are echoed throughout nature. While the significance of these pervasive patterns is not entirely clear, connections between their structures and physical properties are fascinating to contemplate. Particular interest has been paid to a family of synthetically manufactured and commercially available dendritic polymers based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) as a monomer. Composed of two hydroxyls and a carboxyl group, bis-MPA based structures hydrogen bond (H-bond) profusely. Given the high concentration and unique spatial orientation of end-groups, as well as the multitude of carbonyl, ester, and ether interior H-bond acceptors, a set of distinct H-bond organizations may be observed …
Determination Of The Global Heat Transfer Coefficient Of A Double Heat Exchanger Battery In A Dry Mode., B. Dieng, G. Jaw, A. Kane, I. Diagne, M. Dieng, G. Sissoko
Determination Of The Global Heat Transfer Coefficient Of A Double Heat Exchanger Battery In A Dry Mode., B. Dieng, G. Jaw, A. Kane, I. Diagne, M. Dieng, G. Sissoko
Innovative Research Publications IRP India
The cold battery is a heat exchanger between two fluids, air (secondary fluid) and iced water (primary fluid).The cold battery is composed of two heat exchangers in series, one of which is made up of flat-plate in galvanized steel serving as a reservoir for the iced water and the other one a copper shelland-tube exchanger with aluminum cooling blades. The two heat exchangers a connected pipe of the same diameter. These pipes will permit the transit of the iced water coming from the flat-plate exchanger by gravitation towards the tubes of the second exchanger. These two heat exchangers are incorporated …
Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley, Jr Dennison
Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley, Jr Dennison
Senior Theses and Projects
A model developed by the Materials Research Group that calculates electron penetration range of some common materials, has been greatly expanded with the hope that such extensions will predict the range in other, perhaps, more interesting materials. Developments in this extended model aid in predicting the approximate penetration depth into diverse classes of materials for a broad range of energetic incident electrons (<10 eV to>10 MeV, with better than 20% accuracy). The penetration depth—or range—of a material describes the maximum distance electrons can travel through a material, before losing all of its incident kinetic energy. This model has started to predict …10>
Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley
Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley
Reports
A model developed by the Materials Research Group that calculates electron penetration range of some common materials, has been greatly expanded with the hope that such extensions will predict the range in other, perhaps, more interesting materials. Developments in this extended model aid in predicting the approximate penetration depth into diverse classes of materials for a broad range of energetic incident electrons (10 MeV, with better than 20% accuracy). The penetration depth—or range—of a material describes the maximum distance electrons can travel through a material, before losing all of its incident kinetic energy. This model has started to predict a …
Contact Resistance To Srruo3 And La0.67Sr0.33Mno3 Epitaxial Films, Mohammad Abuwasib, Hyungwoo Lee, Alexei Gruverman, Chang-Beom Eom, Uttam Singisetti
Contact Resistance To Srruo3 And La0.67Sr0.33Mno3 Epitaxial Films, Mohammad Abuwasib, Hyungwoo Lee, Alexei Gruverman, Chang-Beom Eom, Uttam Singisetti
Alexei Gruverman Publications
Contact resistance to the metallic oxide electrodes, SrRuO3 (SRO) and La0.67Sr0.33MnO3 (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρc) for Ti and Pt contact metals and the sheet resistance (Rsh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and …
The Role Of Space Materials Research In Spacecraft Charging And Satellite Survivability, Jr Dennison
The Role Of Space Materials Research In Spacecraft Charging And Satellite Survivability, Jr Dennison
Presentations
No abstract provided.
An Overview Of The Dynamic Interplay Between The Space Environment & Spacecraft Materials, Jr Dennison
An Overview Of The Dynamic Interplay Between The Space Environment & Spacecraft Materials, Jr Dennison
Presentations
No abstract provided.
Population Annealing Monte Carlo Studies Of Ising Spin Glasses, Wenlong Wang
Population Annealing Monte Carlo Studies Of Ising Spin Glasses, Wenlong Wang
Doctoral Dissertations
Spin glasses are spin-lattice models with quenched disorder and frustration. The mean field long-range Sherrington-Kirkpatrick (SK) model was solved by Parisi and displays replica symmetry breaking (RSB), but the more realistic short-range Edwards-Anderson (EA) model is still not solved. Whether the EA spin glass phase has many pairs of pure states as described by the RSB scenario or a single pair of pure states as described by two-state scenarios such as the droplet/scaling picture is not known yet. Rigorous analytical calculations of the EA model are not available at present and efficient numerical simulations of spin glasses are crucial in …
Elasticity And Geometry In Curved-Filament Assemblies, Luis Cajamarca Ospina
Elasticity And Geometry In Curved-Filament Assemblies, Luis Cajamarca Ospina
Doctoral Dissertations
In this dissertation we explore the effect of shape, mechanics and geometry in assemblies of tubular filaments by introducing the notion of cohesive contact. We first study the optimal geometry of cohesive interactions in straight flexible tubes by considering two interaction potentials. We find filaments adopt a locally skewed configuration, associated with a twist angle. The interaction energy decreases with the twist angle and ground states are found to be twisted. For pair-wise interactions, we find a generic behavior in the profile of the cohesive energy where the geometry of close-packed double helices dictates the shape of the assembly. By …
Emergent Structure Of Multi-Dislocation Ground States In Frustrated Assemblies, Amir Azadi
Emergent Structure Of Multi-Dislocation Ground States In Frustrated Assemblies, Amir Azadi
Doctoral Dissertations
In this dissertation we study the emergent patterns of multi-dislocation ground states in two geometrically related classes of frustrated assemblies, twisted filament bundles and crystalline spherical cap. We discuss the fundamental role played by characteristic patterns of dislocations in restructuring the ordered phase of theses geometrically frustrated systems in the presence of external stresses. Our analysis on the formation of grain boundary scars leads to universal predictions for the features of defect patterns and their underlying energetic principles.
Hohenberg-Kohn Theorems In Electrostatic And Uniform Magnetostatic Fields, Xiao-Yin Pan, Viraht Sahni
Hohenberg-Kohn Theorems In Electrostatic And Uniform Magnetostatic Fields, Xiao-Yin Pan, Viraht Sahni
Publications and Research
The Hohenberg-Kohn (HK) theorems of bijectivity between the external scalar potential and the gauge invariant nondegenerate ground state density, and the consequent Euler variational principle for the density, are proved for arbitrary electrostatic field and the constraint of fixed electron number. The HK theorems are generalized for spinless electrons to the added presence of an external uniform magnetostatic field by introducing the new constraint of fixed canonical orbital angular momentum. Thereby, a bijective relationship between the external scalar and vector potentials, and the gauge invariant nondegenerate ground state density and physical current density, is proved. A corresponding Euler variational principle …
Dependence Of Electrostatic Field Strength On Voltage Ramp Rates For Spacecraft Materials, Krysta Moser
Dependence Of Electrostatic Field Strength On Voltage Ramp Rates For Spacecraft Materials, Krysta Moser
Senior Theses and Projects
No abstract provided.
Effect Of Sm Content On Energy Product Of Rapidly Quenched And Oriented Smco5 Ribbons, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly
Effect Of Sm Content On Energy Product Of Rapidly Quenched And Oriented Smco5 Ribbons, Wenyong Zhang, Xingzhong Li, Shah R. Valloppilly
Nebraska Center for Materials and Nanoscience: Faculty Publications
The Sm-content dependence of phase composition, anisotropy, and other magnetic properties of Sm1+δCo5 (δ ≤ 0.12) ribbons melt spun at 10 m/s has been studied. The samples consist of hexagonal SmCo5 grains whose c axes are preferentially aligned along the long direction of the ribbon. The lattice parameter a and the cell volume (V) increase with increasing Sm content δ, whereas c decreases. Sm addition appears to improve the degree of the preferred orientation of the c-axis and to increase the mean grain size, which weakens the effective intergranular exchange …
Distributions Of Long-Lived Radioactive Nuclei Provided By Star-Forming Environments, Marco Fatuzzo, Fred Adams
Distributions Of Long-Lived Radioactive Nuclei Provided By Star-Forming Environments, Marco Fatuzzo, Fred Adams
Faculty Scholarship
Radioactive nuclei play an important role in planetary evolution by providing an internal heat source, which affects planetary structure and helps facilitate plate tectonics. A minimum level of nuclear activity is thought to be necessary—but not sufficient—for planets to be habitable. Extending previous work that focused on short-lived nuclei, this paper considers the delivery of long-lived radioactive nuclei to circumstellar disks in star forming regions. Although the long-lived nuclear species are always present, their abundances can be enhanced through multiple mechanisms. Most stars form in embedded cluster environments, so that disks can be enriched directly by intercepting ejecta from supernovae …
Force-Enhanced Atomic Refinement: Structural Modeling With Interatomic Forces In A Reverse Monte Carlo Approach Applied To Amorphous Si And Sio2, A. Pandey, Parthapratim Biswas, D. A. Drabold
Force-Enhanced Atomic Refinement: Structural Modeling With Interatomic Forces In A Reverse Monte Carlo Approach Applied To Amorphous Si And Sio2, A. Pandey, Parthapratim Biswas, D. A. Drabold
Faculty Publications
We introduce a structural modeling technique, called force-enhanced atomic refinement (FEAR). The technique incorporates interatomic forces in reverse Monte Carlo (RMC) simulations for structural refinement by fitting experimental diffraction data using the conventional RMC algorithm, and minimizes the total energy and forces from an interatomic potential. We illustrate the usefulness of the approach by studying a−SiO2 and a−Si. The structural and electronic properties of the FEAR models agree well with experimental neutron and x-ray diffraction data and the results obtained from previous molecular dynamics simulations of a−SiO2 and a−Si. We have shown that the method is more efficient …
Pre-Breakdown Arcing As A Proxy For Dc Dielectric Breakdown Testing Of Polymeric Insulators, Jr Dennison, Allen Andersen
Pre-Breakdown Arcing As A Proxy For Dc Dielectric Breakdown Testing Of Polymeric Insulators, Jr Dennison, Allen Andersen
Presentations
No abstract provided.
Mixed Weibull Distribution Model Of Dc Dielectric Breakdowns With Dual Defect Modes, Allen Andersen, Jr Dennison
Mixed Weibull Distribution Model Of Dc Dielectric Breakdowns With Dual Defect Modes, Allen Andersen, Jr Dennison
Journal Articles
This work provides physical insight into common statistical models for DC dielectric breakdown field strengths. Voltage step-up tests were performed on low density polyethylene films. The merits of generalizations to widely-used empirical Weibull models are discussed. The cumulative probability distributions of the breakdown fields were fit to standard two- and three-parameter Weibull distributions. Mixed two-parameter Weibull distributions, sometimes used in the literature to model multiple breakdown modes, were found to yield the best fits to the data. In addition, the same data were fit to a physically-motivated dual-defect mean field model incorporating both low- and high-energy defect modes with different …
Mixed Weibull Distribution Model Of Dc Dielectric Breakdowns With Dual Defect Modes, Allen Andersen, Jr Dennison
Mixed Weibull Distribution Model Of Dc Dielectric Breakdowns With Dual Defect Modes, Allen Andersen, Jr Dennison
Presentations
Purpose/Aim
This work proposes an enhanced statistical model for DC dielectric breakdown properties, which incorporates both shallow and deep defect modes. By incorporating these physics-based concepts into a traditionally empirical model, its accuracy and utility can be extended.
Experimental/Modeling methods
Voltage step-up tests were performed for various polymeric films. The distributions of the breakdown fields are fit to standard two- and three-parameter Weibull distributions. These are extended for a dual defect model, with separate mean energies for shallow and deep level traps, using mixed Weibull distributions.
Results/discussion
As shown in Fig 1, such enhanced physics-based statistical models can result in …
Hohenberg-Kohn Theorems In Electrostatic And Uniform Magnetostatic Fields, Xiao-Yin Pan, Viraht Sahni
Hohenberg-Kohn Theorems In Electrostatic And Uniform Magnetostatic Fields, Xiao-Yin Pan, Viraht Sahni
Publications and Research
The Hohenberg-Kohn (HK) theorems of bijectivity between the external scalar potential and the gauge invariant nondegenerate ground state density, and the consequent Euler variational principle for the density, are proved for arbitrary electrostatic field and the constraint of fixed electron number. The HK theorems are generalized for spinless electrons to the added presence of an external uniform magnetostatic field by introducing the new constraint of fixed canonical orbital angular momentum. Thereby a bijective relationship between the external scalar and vector potentials, and the gauge invariant nondegenerate ground state density and physical current density, is proved. A corresponding Euler variational principle …
Comparing Experimental Apples And Oranges With Quantile-Quantile Plots, Allen Andersen, Jr Dennison
Comparing Experimental Apples And Oranges With Quantile-Quantile Plots, Allen Andersen, Jr Dennison
Presentations
An important question often encountered in experimental physics is, are two observables related or not? Quantile-quantile (q-q) analysis compares the cumulative distributions of two observations (or one set of observations and a theoretical curve) in a way that is both visually apparent and statistically quantifiable. If the two observables follow the same distribution, the q-q plot will be linear; if they are identical the plot will have unity slope. Deviations from a linear q-q plot indicate that the two observables do not follow the same distribution. We show that the q-q analysis method is applicable to a wide range of …
Oxygen Vacancies In Lialo2 Crystals, Maurio S. Holston, I. P. Ferguson, John W. Mcclory, Nancy C. Giles, Larry E. Halliburton
Oxygen Vacancies In Lialo2 Crystals, Maurio S. Holston, I. P. Ferguson, John W. Mcclory, Nancy C. Giles, Larry E. Halliburton
Faculty Publications
Singly ionized oxygen vacancies are produced in LiAlO2 crystals by direct displacement events during a neutron irradiation. These vacancies, with one trapped electron, are referred to as V+O centers. They are identified and characterized using electron paramagnetic resonance (EPR) and optical absorption. The EPR spectrum from the V+O centers is best monitored near 100 K with low microwave power. When the magnetic field is along the [001] direction, this spectrum has a g value of 2.0030 and well-resolved hyperfine interactions of 310 and 240 MHz with the two 27Al nuclei that are adjacent to the oxygen vacancy. A second …
The Space Survivability Test Chamber, Katie Gamaunt, Heather Tippets, Alex Souvall, Ben Russon, Jr Dennison
The Space Survivability Test Chamber, Katie Gamaunt, Heather Tippets, Alex Souvall, Ben Russon, Jr Dennison
Posters
The Space Survivability Test chamber is a new ground-based research instrument being used for accelerated testing of environment-induced modifications of diverse samples. The chamber simulates space environment conditions, including neutral gas atmospheres and vacuum (<10-5 Pa) environments, temperature (~100 K to >450 K), ionizing radiation, electron fluxes (<10 eV to ~2½ MeV), and vacuum ultraviolet through mid-infrared photon fluxes. This versatile test chamber is well-suited for cost-effective testing of complete systems up to the size (< 20 cm dia.) of a 1U CubeSat, smaller components or electronics, and individual material samples. Multiple in-flux or in-situ space survivability and radiation exposure tests can be performed simultaneously, as well as extensive before and after ex-situ tests. Currently the chamber is performing a series of radiation experiments using a Sr90 beta radiation source which approximately mimics the geostationary high energy electron spectra at ~4-10X accelerated …10>10
Density Of State Models Of Steady-State Temperature Dependent Radiation Induced Conductivity, Jodie Corbridge Gillespie, Jr Dennison
Density Of State Models Of Steady-State Temperature Dependent Radiation Induced Conductivity, Jodie Corbridge Gillespie, Jr Dennison
Posters
Radiation induced conductivity (RIC) occurs when incident radiation deposits energy and excites electrons into the conduction band of insulators. The magnitude of the enhanced conductivity is dependent on a number of factors including temperature and the spatial- and energy-dependence and occupation of the material’s distribution of localized trap states within the band gap—or density of states (DOS). Expressions are developed for steady-state RIC over an extended temperature range, based on DOS models for highly disordered insulating materials. A general discussion of the DOS of disordered materials can be given using two simple distributions: one that monotonically decreases below the band …
Properties Of Spacecraft Materials Exposed To Ionizing Radiation, Alex Souvall, Gregory Wilson, Katie Gamaunt, Ben Russon, Heather Tippets, Jr Dennison
Properties Of Spacecraft Materials Exposed To Ionizing Radiation, Alex Souvall, Gregory Wilson, Katie Gamaunt, Ben Russon, Heather Tippets, Jr Dennison
Posters
The effects of ionizing radiation damage on the various properties of spacecraft materials resulting from exposure in the Space Survivability Testing chamber (SST) are being studied with both ex situ and in situ tests. The SST is a ground based test facility designed to mimic low earth orbit (LEO), and geosynchronous orbit to test potential environmental-induced modifications to small satellites , and materials. Tests described here expose spacecraft materials to a Sr90 ionizing beta radiation source at room temperature and in high vacuum. Ex situ optical transmission/reflectivity measurements glass samples will monitor optical darkening. Properties of polymeric samples will …
Dependence Of Electrostatic Field Strength On Voltage Ramp Rates For Spacecraft Material, Krysta Moser, Allen Andersen, Jr Dennison
Dependence Of Electrostatic Field Strength On Voltage Ramp Rates For Spacecraft Material, Krysta Moser, Allen Andersen, Jr Dennison
Posters
Previous tests done by the USU Materials Physics Group (MPG) using our electrostatic discharge (ESD) custom vacuum chamber have found that, for the polymeric materials polyimide and low density polyethylene (LDPE), the electrostatic field strength at breakdown depends on the voltage ramp rate applied across the materials. At ramp rates an order of magnitude lower than the maximum recommended rate of 500 V/s, the breakdown electrostatic field strength was also found to be significantly lower. The data from these tests were compared to a microscopic mean field theory for dielectric breakdown in highly disordered insulating materials. We present new ramp …
Measurement Of Effects Of Long Term Ionizing Radiation On High Efficiency Solar Arrays, Ben Russon, Heather Tippets, Gregory Wilson, Katie Gamaunt, Alex Souvall, Jr Dennison
Measurement Of Effects Of Long Term Ionizing Radiation On High Efficiency Solar Arrays, Ben Russon, Heather Tippets, Gregory Wilson, Katie Gamaunt, Alex Souvall, Jr Dennison
Posters
Degradation of power output efficiency for high-efficiency multilayer solar arrays due to ionizing radiation is measured using the Space Survivability Test chamber. Exposure to ionizing radiation disrupts the crystalline structure and can reduce solar array power output to the point that it no longer provides adequate output capacity. This can be a significant concern, particularly in the harsh environment of space where radiation dose rate is significantly higher and replacing components is often impossible. Ionizing radiation is simulated in a controlled environment to allow measurement and characterization of the power output of solar arrays, using a 100 mCi encapsulated Sr90 …
Enhanced Electron Yield Measurements Of Extremely Low-Conductivity High Yield Dielectrics, Justin Christensen, Jr Dennison
Enhanced Electron Yield Measurements Of Extremely Low-Conductivity High Yield Dielectrics, Justin Christensen, Jr Dennison
Presentations
An important question often encountered in experimental physics is, are two observables related or not? Quantile-quantile (q-q) analysis compares the cumulative distributions of two observations (or one set of observations and a theoretical curve) in a way that is both visually apparent and statistically quantifiable. If the two observables follow the same distribution, the q-q plot will be linear; if they are identical the plot will have unity slope. Deviations from a linear q-q plot indicate that the two observables do not follow the same distribution. We show that the q-q analysis method is applicable to a wide range of …
Hybridized Criticality And Elementary Excitations In Lihof4, Haifu Ma
Hybridized Criticality And Elementary Excitations In Lihof4, Haifu Ma
Dissertations, Theses, and Capstone Projects
In this dissertation, I study the magnetic properties of LiHoF4. Quantum criticality in rare earth ferromagnet LiHoF4 is complicated by the presence of strong crystal field and hyperfine interactions resulting, e.g., in incomplete mode softening reported by Rønnow et al. We construct a systematic framework for treating elementary excitations in this material across the phase diagram. These excitations interpolate between purely electronic, nuclear and lattice modes and exhibit two-types of quantum critical softening, both complete (as anticipated by elementary treatments, see e.g. Sachdev) but also incomplete, in close correspondence with nuclear scattering results.