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- Impact Ionization (14)
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- Physics Faculty Research & Creative Works (44)
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Articles 1 - 30 of 104
Full-Text Articles in Physical Sciences and Mathematics
Homogenization Of Plastic Deformation In Heterogeneous Lamella Structures, Rui Yuan, Irene J. Beyerlein, Caizhi Zhou
Homogenization Of Plastic Deformation In Heterogeneous Lamella Structures, Rui Yuan, Irene J. Beyerlein, Caizhi Zhou
Materials Science and Engineering Faculty Research & Creative Works
It has been shown that unlike its constituent nanocrystalline (NC) phase, a heterogeneous lamella (HL) composite comprising NC and coarse-grain layers exhibits greatly improved ductility. To understand the origin of this enhancement, we present a 3D discrete dislocation, crystal plasticity finite element model to study the development of strains across this microstructure. Here we show that the HL structure homogenizes the plastic strains in the NC layer, weakening the effect of strain concentrations. These findings can provide valuable insight into the effects of material length scales on material instabilities, which is needed to design heterogeneous structures with superior properties.
Inelastic Rate Coefficients For Collisions Of C₆Hˉ With H₂ And He, Kyle M. Walker, François Lique, Fabien Dumouchel, Richard Dawes
Inelastic Rate Coefficients For Collisions Of C₆Hˉ With H₂ And He, Kyle M. Walker, François Lique, Fabien Dumouchel, Richard Dawes
Chemistry Faculty Research & Creative Works
The recent detection of anions in the interstellar medium has shown that they exist in a variety of astrophysical environments -- circumstellar envelopes, cold dense molecular clouds and star-forming regions. Both radiative and collisional processes contribute to molecular excitation and de-excitation in these regions so that the ‘local thermodynamic equilibrium’ approximation, where collisions cause the gas to behave thermally, is not generally valid. Therefore, along with radiative coefficients, collisional excitation rate coefficients are needed to accurately model the anionic emission from these environments. We focus on the calculation of state-to-state rate coefficients of the C6H- molecule in …
Shape Analysis Of Traffic Flow Curves Using A Hybrid Computational Analysis, Wasim Irshad Kayani, Shikhar P. Acharya, Ivan G. Guardiola, Donald C. Wunsch, B. Schumacher, Isaac Wagner-Muns
Shape Analysis Of Traffic Flow Curves Using A Hybrid Computational Analysis, Wasim Irshad Kayani, Shikhar P. Acharya, Ivan G. Guardiola, Donald C. Wunsch, B. Schumacher, Isaac Wagner-Muns
Engineering Management and Systems Engineering Faculty Research & Creative Works
This paper highlights and validates the use of shape analysis using Mathematical Morphology tools as a means to develop meaningful clustering of historical data. Furthermore, through clustering more appropriate grouping can be accomplished that can result in the better parameterization or estimation of models. This results in more effective prediction model development. Hence, in an effort to highlight this within the research herein, a Back-Propagation Neural Network is used to validate the classification achieved through the employment of MM tools. Specifically, the Granulometric Size Distribution (GSD) is used to achieve clustering of daily traffic flow patterns based solely on their …
Passive Rifting Of Thick Lithosphere In The Southern East African Rift: Evidence From Mantle Transition Zone Discontinuity Topography, Cory A. Reed, Kelly H. Liu, Patrick R. N. Chindandali, Belarmino Massingue, Hassan Mdala, Daniel Mutamina, Youqiang Yu, Stephen S. Gao
Passive Rifting Of Thick Lithosphere In The Southern East African Rift: Evidence From Mantle Transition Zone Discontinuity Topography, Cory A. Reed, Kelly H. Liu, Patrick R. N. Chindandali, Belarmino Massingue, Hassan Mdala, Daniel Mutamina, Youqiang Yu, Stephen S. Gao
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
To investigate the mechanisms for the initiation and early-stage evolution of the nonvolcanic southernmost segments of the East African Rift System (EARS), we installed and operated 35 broadband seismic stations across the Malawi and Luangwa rift zones over a 2 year period from mid-2012 to mid-2014. Stacking of over 1900 high-quality receiver functions provides the first regional-scale image of the 410 and 660 km seismic discontinuities bounding the mantle transition zone (MTZ) within the vicinity of the rift zones. When a 1-D standard Earth model is used for time-depth conversion, a normal MTZ thickness of 250 km is found beneath …
Mantle Structure Beneath The Incipient Okavango Rift Zone In Southern Africa, Youqiang Yu, Kelly H. Liu, Zhouchuan Huang, Dapeng Zhao, Cory A. Reed, Moikwathai Moidaki, Jianshe Lei, Stephen S. Gao
Mantle Structure Beneath The Incipient Okavango Rift Zone In Southern Africa, Youqiang Yu, Kelly H. Liu, Zhouchuan Huang, Dapeng Zhao, Cory A. Reed, Moikwathai Moidaki, Jianshe Lei, Stephen S. Gao
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
Numerous investigations of the mature segments of the East African rift system (EARS) have significantly improved our understanding of the structure and processes associated with well-developed continental rifts. In contrast, knowledge of rifting processes at their early stage is still significantly limited. Here we present results from a teleseismic P-wave tomography investigation of the incipient Okavango rift zone (ORZ), which is located at the southwestern terminus of the EARS. P-wave relative travel-time residuals recorded by 17 recently deployed portable seismic stations were manually picked and inverted for three-dimensional upper-mantle and mantle transition-zone tomographic images beneath the ORZ and its adjacent …
Computational Fluid Dynamics Study Of Molten Steel Flow Patterns And Particle-Wall Interactions Inside A Slide-Gate Nozzle By A Hybrid Turbulent Model, Mahdi Mohammadi-Ghaleni, Mohsen Asle Zaeem, Jeffrey D. Smith, Ronald J. O'Malley
Computational Fluid Dynamics Study Of Molten Steel Flow Patterns And Particle-Wall Interactions Inside A Slide-Gate Nozzle By A Hybrid Turbulent Model, Mahdi Mohammadi-Ghaleni, Mohsen Asle Zaeem, Jeffrey D. Smith, Ronald J. O'Malley
Materials Science and Engineering Faculty Research & Creative Works
Melt flow patterns and turbulence inside a slide-gate throttled submerged entry nozzle (SEN) were studied using Detached–Eddy Simulation (DES) model, which is a combination of Reynolds–Averaged Navier–Stokes (RANS) and Large–Eddy Simulation (LES) models. The DES switching criterion between RANS and LES was investigated to closely reproduce the flow structures of low and high turbulence regions similar to RANS and LES simulations, respectively. The melt flow patterns inside the nozzle were determined by k–ε (a RANS model), LES, and DES turbulent models, and convergence studies were performed to ensure reliability of the results. Results showed that the DES model has significant …
A Dual-Porosity-Stokes Model And Finite Element Method For Coupling Dual-Porosity Flow And Free Flow, Jiangyong Hou, Meilan Qiu, Xiaoming He, Chaohua Guo, Mingzhen Wei, Baojun Bai
A Dual-Porosity-Stokes Model And Finite Element Method For Coupling Dual-Porosity Flow And Free Flow, Jiangyong Hou, Meilan Qiu, Xiaoming He, Chaohua Guo, Mingzhen Wei, Baojun Bai
Mathematics and Statistics Faculty Research & Creative Works
In this paper, we propose and numerically solve a new model considering confined flow in dual-porosity media coupled with free flow in embedded macrofractures and conduits. Such situation arises, for example, for fluid flows in hydraulic fractured tight/shale oil/gas reservoirs. The flow in dual-porosity media, which consists of both matrix and microfractures, is described by a dual-porosity model. And the flow in the macrofractures and conduits is governed by the Stokes equation. Then the two models are coupled through four physically valid interface conditions on the interface between dual-porosity media and macrofractures/conduits, which play a key role in a physically …
Quantum Critical Behavior Of The Superfluid-Mott Glass Transition, Thomas Vojta, Jack Crewse, Martin Puschmann, Daniel Arovas, Yury Kiselev
Quantum Critical Behavior Of The Superfluid-Mott Glass Transition, Thomas Vojta, Jack Crewse, Martin Puschmann, Daniel Arovas, Yury Kiselev
Physics Faculty Research & Creative Works
We investigate the zero-temperature superfluid to insulator transitions in a diluted two-dimensional quantum rotor model with particle-hole symmetry. We map the Hamiltonian onto a classical (2+1)-dimensional XY model with columnar disorder which we analyze by means of large-scale Monte Carlo simulations. For dilutions below the lattice percolation threshold, the system undergoes a generic superfluid-Mott glass transition. In contrast to other quantum phase transitions in disordered systems, its critical behavior is of conventional power-law type with universal (dilution-independent) critical exponents z=1.52(3), ν =1.16(5), ß/ν =0.48(2), γ/ν=2.52(4), and η = -0.52(4). These values agree with and improve upon earlier Monte Carlo results …
High-Frequency Instabilities Of Stationary Crossflow Vortices In A Hypersonic Boundary Layer, Fei Li, Meelan Choudhari, Pedro Paredes-Gonzalez, Lian Duan
High-Frequency Instabilities Of Stationary Crossflow Vortices In A Hypersonic Boundary Layer, Fei Li, Meelan Choudhari, Pedro Paredes-Gonzalez, Lian Duan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Hypersonic boundary layer flows over a circular cone at moderate incidence angle can support strong crossflow instability in between the windward and leeward rays on the plane of symmetry. Due to more efficient excitation of stationary crossflow vortices by surface roughness, such boundary layer flows may transition to turbulence via rapid amplification of the high-frequency secondary instabilities of finite-amplitude stationary crossflow vortices. The amplification characteristics of these secondary instabilities are investigated for crossflow vortices generated by an azimuthally periodic array of roughness elements over a 7° half-angle circular cone in a Mach 6 free stream. The analysis is based on …
Comparison Of Experimental And Theoretical Fully Differential Cross Sections For Single Ionization Of The 2s And 2p States Of Li By O⁸⁺ Ions, Ebrahim Ghanbari-Adivi, Daniel Fischer, Natalia Ferreira, Johannes Goullon, Renate Hubele, Aaron Laforge, Michael Schulz, Don H. Madison
Comparison Of Experimental And Theoretical Fully Differential Cross Sections For Single Ionization Of The 2s And 2p States Of Li By O⁸⁺ Ions, Ebrahim Ghanbari-Adivi, Daniel Fischer, Natalia Ferreira, Johannes Goullon, Renate Hubele, Aaron Laforge, Michael Schulz, Don H. Madison
Physics Faculty Research & Creative Works
This paper presents a full three-dimensional (3D) comparison between experiment and theory for 24 MeV O8+ single ionization of the 2s ground state of lithium and the 2p excited state. Two theoretical approximations are examined: the three-body continuum distorted-wave (3DW) and three-body continuum distorted-wave-eikonal initial state (3DW-EIS). Normally, there is a significant difference between these two approaches and the 3DW-EIS is in much better agreement with experiment. In this case, there is very little difference between the two approaches and both are in very good agreement with experiment. For the excited 2p state, the 3D cross sections would exhibit …
Contact Process With Temporal Disorder, Hatem Barghathi, Thomas Vojta, José A. Hoyos
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 …
The First Potential Energy Surfaces For The C₆Hˉ-H₂ And C₆Hˉ-He Collisional Systems And Their Corresponding Inelastic Cross Sections, Kyle M. Walker, Fabien Dumouchel, François Lique, Richard Dawes
The First Potential Energy Surfaces For The C₆Hˉ-H₂ And C₆Hˉ-He Collisional Systems And Their Corresponding Inelastic Cross Sections, Kyle M. Walker, Fabien Dumouchel, François Lique, Richard Dawes
Chemistry Faculty Research & Creative Works
Molecular anions have recently been detected in the interstellar and circumstellar media. Accurate modeling of their abundance requires calculations of collisional data with the most abundant species that are usually He atoms and H2 molecules. In this paper, we focus on the collisional excitation of the first observed molecular anion, C6H-, by He and H2. Theoretical calculations of collisional cross sections rely generally on ab initio interaction potential energy surfaces (PESs). Hence, we present here the first PESs for the C6H--H2 and C6H--He van …
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
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 …
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
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 …
A New Set Of Potential Energy Surfaces For Hco: Influence Of Renner-Teller Coupling On The Bound And Resonance Vibrational States, Steve Alexandre Ndengué, Richard Dawes, Hua Guo
A New Set Of Potential Energy Surfaces For Hco: Influence Of Renner-Teller Coupling On The Bound And Resonance Vibrational States, Steve Alexandre Ndengué, Richard Dawes, Hua Guo
Chemistry Faculty Research & Creative Works
It is commonly understood that the Renner-Teller effect can strongly influence the spectroscopy of molecules through coupling of electronic states. Here we investigate the vibrational bound states and low-lying resonances of the formyl radical treating the Renner-Teller coupled X2A' and Ã2A" states using the MultiConfiguration Time Dependent Hartree (MCTDH) method. The calculations were performed using the improved relaxation method for the bound states and a recently published extension to compute resonances. A new set of accurate global potential energy surfaces were computed at the explicitly correlated multireference configuration interaction (MRCI-F12) level and yielded remarkably close agreement with experiment in this …
Shear Wave Splitting Analyses In Tian Shan: Geodynamic Implications Of Complex Seismic Anisotropy, Solomon G. Cherie, Stephen S. Gao, Kelly H. Liu, Ahmed A. Elsheikh, Fansheng Kong, Cory A. Reed, Bin B. Yang
Shear Wave Splitting Analyses In Tian Shan: Geodynamic Implications Of Complex Seismic Anisotropy, Solomon G. Cherie, Stephen S. Gao, Kelly H. Liu, Ahmed A. Elsheikh, Fansheng Kong, Cory A. Reed, Bin B. Yang
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
The Tian Shan is a tectonically complex intracontinental orogenic belt situated between the Tarim Basin and the Kazakh Shield. The vast majority of the previous shear wave splitting (SWS) measurements were presented as station averages, which are only valid when the anisotropy structure can be approximated by a single layer of anisotropy with a horizontal axis of symmetry, i.e., a model of simple anisotropy. A variety of anisotropy-forming hypotheses have been proposed based on the station-averaged measurements. In this study, we measure the splitting parameters at 25 stations that recorded high-quality data from a wide back azimuthal range for the …
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
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, …
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
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.
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
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.
The Anisotropy Of Hexagonal Close-Packed And Liquid Interface Free Energy Using Molecular Dynamics Simulations Based On Modified Embedded-Atom Method, Ebrahim Asadi, Mohsen Asle Zaeem
The Anisotropy Of Hexagonal Close-Packed And Liquid Interface Free Energy Using Molecular Dynamics Simulations Based On Modified Embedded-Atom Method, Ebrahim Asadi, Mohsen Asle Zaeem
Materials Science and Engineering Faculty Research & Creative Works
This work aims to comprehensively study the anisotropy of the hexagonal close-packed (HCP)-liquid interface free energy using molecular dynamics (MD) simulations based on the modified-embedded atom method (MEAM). As a case study, all the simulations are performed for Magnesium (Mg). The solid-liquid coexisting approach is used to accurately calculate the melting point and melting properties. Then, the capillary fluctuation method (CFM) is used to determine the HCP-liquid interface free energy (γ) and anisotropy parameters. In CFM, a continuous order parameter is employed to accurately locate the HCP-liquid interface location, and the HCP symmetry-adapted spherical harmonics are used to expand γ …
The Mantle Transition Zone Beneath The Afar Depression And Adjacent Regions: Implications For Mantle Plumes And Hydration, Cory A. Reed, Stephen S. Gao, Kelly H. Liu, Y. Yu
The Mantle Transition Zone Beneath The Afar Depression And Adjacent Regions: Implications For Mantle Plumes And Hydration, Cory A. Reed, Stephen S. Gao, Kelly H. Liu, Y. Yu
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
The Afar Depression and its adjacent areas are underlain by an upper mantle marked by some of the world's largest negative velocity anomalies, which are frequently attributed to the thermal influences of a lower-mantle plume. In spite of numerous studies, however, the existence of a plume beneath the area remains enigmatic, partially due to inadequate quantities of broad-band seismic data and the limited vertical resolution at the mantle transition zone (MTZ) depth of the techniques employed by previous investigations. In this study, we use an unprecedented quantity (over 14 500) of P-to-S receiver functions (RFs) recorded by 139 stations from …
A Uniform Database Of Teleseismic Shear-Wave Splitting Measurements For The Western And Central United States: December 2014 Update, Bin B. Yang, Kelly H. Liu, Haider H. Dahm, Stephen S. Gao
A Uniform Database Of Teleseismic Shear-Wave Splitting Measurements For The Western And Central United States: December 2014 Update, Bin B. Yang, Kelly H. Liu, Haider H. Dahm, Stephen S. Gao
Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works
We present a new version of a shear-wave splitting (SWS) database for the western and central United States (WCUS) using broadband seismic data recorded up to the end of 2014 to update a previous version that used data recorded prior to the end of 2012, when the USArray Transportable Array stations were still recording in the easternmost region of theWCUS. A total of 7452 pairs of additional measurements recorded by 1202 digital broadband seismic stations are obtained, and all the measurements in the previous database are rechecked. The resulting uniform SWS database contains a total of 23,448 pairs of well-defined …
Spatio-Temporal Generalization Of The Harris Criterion And Its Application To Diffusive Disorder, Thomas Vojta, Ronald Dickman
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 …
Calculated Vibrational States Of Ozone Up To Dissociation, Steve Alexandre Ndengué, Richard Dawes, Xiaogang Wang, Tucker Carrington Jr., Zhigang Sun, Hua Guo
Calculated Vibrational States Of Ozone Up To Dissociation, Steve Alexandre Ndengué, Richard Dawes, Xiaogang Wang, Tucker Carrington Jr., Zhigang Sun, Hua Guo
Chemistry Faculty Research & Creative Works
A new accurate global potential energy surface for the ground electronic state of ozone [R. Dawes et al., J. Chem. Phys. 139, 201103 (2013)] was published fairly recently. The topography near dissociation differs significantly from previous surfaces, without spurious submerged reefs and corresponding van der Waals wells. This has enabled significantly improved descriptions of scattering processes, capturing the negative temperature dependence and large kinetic isotope effects in exchange reaction rates. The exchange reactivity was found to depend on the character of near-threshold resonances and their overlap with reactant and product wavefunctions, which in turn are sensitive to the potential. Here …
Random Field Disorder At An Absorbing State Transition In One And Two Dimensions, Hatem Barghathi, Thomas Vojta
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, …
Geometric Consideration Of Nanostructures For Energy Storage Systems, Jonghyun Park, Jie Li, Wei Lu, Ann Marie Sastry
Geometric Consideration Of Nanostructures For Energy Storage Systems, Jonghyun Park, Jie Li, Wei Lu, Ann Marie Sastry
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Battery performance and its fade are determined by various aspects such as the transport of ions and electrons through heterogeneous internal structures; kinetic reactions at the interfaces; and the corresponding interplay between mechanical, chemical, and thermal responses. The fundamental factor determining this complex multiscale and multiphysical nature of a battery is the geometry of active materials. In this work, we systematically consider the tradeoffs among a selection of limiting geometries of media designed to store ions or other species via a diffusion process. Specifically, we begin the investigation by considering diffusion in spheres, rods, and plates at the particle level, …
Silicon-Wall Interfacial Free Energy Via Thermodynamics Integration, Wan Shou, Heng Pan
Silicon-Wall Interfacial Free Energy Via Thermodynamics Integration, Wan Shou, Heng Pan
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We compute the interfacial free energy of a silicon system in contact with flat and structured walls by molecular dynamics simulation. The thermodynamics integration method, previously applied to Lennard-Jones potentials [R. Benjamin and J. Horbach, J. Chem. Phys. 137, 044707 (2012)], has been extended and implemented in Tersoff potentials with two-body and three-body interactions taken into consideration. The thermodynamic integration scheme includes two steps. In the first step, the bulk Tersoff system is reversibly transformed to a state where it interacts with a structureless flat wall, and in a second step, the flat structureless wall is reversibly transformed into an …
Coupled Crystal Orientation-Size Effects On The Strength Of Nano Crystals, Rui Yuan, Irene J. Beyerlein, Caizhi Zhou
Coupled Crystal Orientation-Size Effects On The Strength Of Nano Crystals, Rui Yuan, Irene J. Beyerlein, Caizhi Zhou
Materials Science and Engineering Faculty Research & Creative Works
We study the combined effects of grain size and texture on the strength of nanocrystalline copper (Cu) and nickel (Ni) using a crystal-plasticity based mechanics model. Within the model, slip occurs in discrete slip events exclusively by individual dislocations emitted statistically from the grain boundaries. We show that a Hall-Petch relationship emerges in both initially texture and non-textured materials and our values are in agreement with experimental measurements from numerous studies. We find that the Hall-Petch slope increases with texture strength, indicating that preferred orientations intensify the enhancements in strength that accompany grain size reductions. These findings reveal that texture …
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
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 …
Ionic And Electronic Conductivities Of Atomic Layer Deposition Thin Film Coated Lithium Ion Battery Cathode Particles, Rajankumar L. Patel, Jonghyun Park, Xinhua Liang
Ionic And Electronic Conductivities Of Atomic Layer Deposition Thin Film Coated Lithium Ion Battery Cathode Particles, Rajankumar L. Patel, Jonghyun Park, Xinhua Liang
Mechanical and Aerospace Engineering Faculty Research & Creative Works
It is imperative to ascertain the ionic and electronic components of the total conductivity of an electrochemically active material. A blocking technique, called the “Hebb-Wagner method”, is normally used to explain the two components (ionic and electronic) of a mixed conductor, in combination with the complex ac impedance method and dc polarization measurements. CeO2 atomic layer deposition (ALD)-coated and uncoated, LiMn2O4 (LMO) and LiMn1.5Ni0.5O4 (LMNO) powders were pressed into pellets and then painted with silver to act as a blocking electrode. The electronic conductivities were derived from the currents obtained using …