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The divergence of nearby trajectories in soft-sphere DEM

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Particuology 2022年第4期20卷 1-8页

作者： William D.Fullmer Roberto Porcu Jordan Musser Ann S.Almgren Ishan Srivastava national Energy Technology Laboratory MorgantownWV 26507USA NETL Support Contractor MorgantownWV 26507USA Center for Computational Sciences and Engineering.Lawrence Berkeley national Laboratory BerkeleyCA 94720USA

The n-body instability is investigated with the soft-sphere discrete element *** divergence of nearby trajectories is quantifed by the dynamical memory *** the inverse proportionality between the dynamical memory time and the largest Lyapunov exponent,the soft-sphere discrete ele-ment method results are compared to previous hard-sphere molecular dynamics data for the first *** agreement is observed at low concentrations and the degree of instability is shown to increase asymptotically with increasing spring *** particle concentrations above 30%,the soft-sphere Lya-punov exponents increase faster than the corresponding hard-sphere *** paper concludes with a demonstration of how this case study may be used in conjunction with regression testing and code verification activities.

关键词： Soft-sphere DEM Chaos Lyapunov exponent

A molecular dynamics study of laser-excited gold

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Matter and Radiation at Extremes 2022年第3期7卷 20-30页

作者： Jacob M.Molina T.G.White University of Nevada RenoNevada 89557USA

The structural evolution of laser-excited systems of gold has previously been measured through ultrafast MeV electron ***,there has been a long-standing inability of atomistic simulations to provide a consistent picture of the melting process,leading to large discrepancies between the predicted threshold energy density for complete melting,as well as the transition between heterogeneous and homogeneous *** make use of two-temperature classical molecular dynamics simulations utilizing three highly successful interatomic potentials and reproduce electron diffraction data presented by Mo et al.[Science 360,1451–1455(2018)].We recreate the experimental electron diffraction data,employing both a constant and temperature-dependent electron–ion equilibration *** all cases,we are able to match time-resolved electron diffraction data,and find consistency between atomistic simulations and experiments,only by allowing laser energy to be transported away from the interaction *** additional energy-loss pathway,which scales strongly with laser fluence,we attribute to hot electrons leaving the target on a timescale commensurate with melting。

关键词： diffraction. excited dynamics

Change of Electrical and Transport Properties of Nickel Oxide by Carrier Concentration and Temperature through First‑Principle Calculations

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Nanomanufacturing and Metrology 2023年第4期6卷 109-118页

作者： Nayem Md.Reza Shah Chang‑Dong Yeo Minyeong Choi Yang‑Ki Hong Jeong H.You Department of Mechanical Engineering Texas Tech UniversityLubbockTX 79409USA Department of Electrical and Computer Engineering and Material Science Ph.D.Program The University of AlabamaTuscaloosaAL 35487USA Department of Mechanical Engineering School of EngineeringUniversity of St.ThomasSt.PaulMN 55105USA

Nickel is typically used as one of the main components in electrical contact devices or *** oxide(NiO)is usually formed on the surfaces of electrodes and can negatively impact system performance by introducing electrical contact *** thermal,electrical,and transport properties of NiO,as a Mott insulator or a p-type semiconductor,can be altered by operating and environmental conditions such as temperature and stress/strain by *** this study,we inves-tigate the fundamental material properties of NiO through the first-principle ***,we obtain and compare the lattice parameter,magnetic moment,and electronic structure for NiO via the WIEN2K simulations with four different poten-tials(i.e.,GGA,GGA+U,LSDA,and LSDA+U).Then,using the WIEN2K simulation results with LSDA+U potential that produces a highly accurate bandgap for NiO,we calculate the electrical conductivity and electrical part of the thermal conductivity of nickel and NiO as a function of temperature and carrier concentration through the BoltzTraP *** simulation results revealed that the electrical conductivity relative to the relaxation time for NiO increases with the carrier concentration,while it shows a slightly decreasing trend with temperature under a fixed carrier *** contrast,the electrical part of the thermal conductivity shows an increasing trend considering carrier concentration and temperature.

关键词： Nickel oxide Magnetic moments Density of states Seebeck coefcient Electrical conductivity

Modular next generation fast-neutron detector for portal monitoring

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nuclear Science and Techniques 2022年第1期33卷 140-148页

作者： E.Aboud S.Ahn G.V.Rogachev V.E.Johnson J.Bishop G.Christian E.Koshchiy C.E.Parker D.P.Scriven Cyclotron Institute Texas A&M UniversityCollege StationTX 77843USA Department of Physics and Astronomy Texas A&M UniversityCollege StationTX 77843USA Department of Statistics Texas A&M UniversityCollege StationTX 77843USA

nuclear nonproliferation is of critical importance for global *** fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to *** interrogation techniques may result in much better sensitivity but are difficult with conventional portal monitors that rely on detecting thermal ***,most conventional portal monitoring systems rely on ^(3)He,which has a finite and continually decreasing *** designing a highly segmented array of organic scintillators,we posit that we can accurately and quickly identify fissile materials,including weapons-grade plutonium and highly enriched uranium,being *** propose a new design for a fast-neutron detector that overcomes the limitations of the current generation of portal ***6 simulations have been performed in conjunction with the UMPBT statistical model to determine the sensitivity limitations of the proposed *** suggest that the proposed detector may be 10 times more efficient than current-generation thermal neutron detectors and may be able to positively identify a 81 mg 235U source in as little as 192 seconds utilizing active interrogation techniques.

关键词： Fast-neutron detection Portal monitoring Nonproliferation

Modeling Fast Diffusion Processes in Time Integration of Stiff Stochastic Differential Equations

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Communications on Applied Mathematics and Computation 2022年第4期4卷 1457-1493页

作者： Xiaoying Han Habib N.Najm Department of Mathematics and Statistics Auburn University221 Parker HallAuburnAL 36849USA Sandia national Laboratories P.O.Box 969LivermoreCA 94551USA

Numerical algorithms for stiff stochastic differential equations are developed using lin-ear approximations of the fast diffusion processes,under the assumption of decoupling between fast and slow *** numerical schemes are proposed,all of which are based on the linearized formulation albeit with different degrees of *** schemes are of comparable complexity to the classical explicit Euler-Maruyama scheme but can achieve better accuracy at larger time steps in stiff *** analysis is conducted for one of the schemes,that shows it to have a strong convergence order of 1/2 and a weak convergence order of *** arriving at the other two schemes are *** experiments are carried out to examine the convergence of the schemes proposed on model problems.

关键词： Stiff stochastic differential equation Fast diffusion Linear diffusion approximation Mean-square convergence Weak convergence

Structure-Preserving Finite-Element Schemes for the Euler-Poisson Equations

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Communications in Computational Physics 2023年第3期33卷 647-691页

作者： Matthias Maier John N.Shadid Ignacio Tomas Department of Mathematics Texas A&M University3368 TAMUCollege StationTX 77843USA Sandia national Laboratories P.O.Box 5800MS 1320AlbuquerqueNM 87185USA Department of Mathematics and Statistics University of New MexicoMSC011115AlbuquerqueNM 87131USA Department of Mathematics&Statistics Texas Tech University2500 BroadwayLubbockTX 79409USA.

We discuss structure-preserving numerical discretizations for repulsive and attractive Euler-Poisson equations that find applications in fluid-plasma and selfgravitation *** scheme is fully discrete and structure preserving in the sense that it maintains a discrete energy law,as well as hyperbolic invariant domain properties,such as positivity of the density and a minimum principle of the specific entropy.A detailed discussion of algorithmic details is given,as well as proofs of the claimed *** present computational experiments corroborating our analytical findings and demonstrating the computational capabilities of the scheme.

关键词： Euler-Poisson equations operator splitting invariant domain preservation discrete energy balance.

Microstructural banding of directed energy deposition-additively manufactured 316L stainless steel

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Journal of Materials Science & Technology 2021年第10期69卷 96-105页

作者： Yoon Hwa Christopher S.Kumai Thomas M.Devine Nancy Yang Joshua K.Yee Ryan Hardwick Kai Burgmann Department of Materials Science and Engineering University of CaliforniaBerkeleyCA94720USA Sandia national Laboratory LivermoreCA.94551USA

The microstructures of 316L stainless steel created by rapid solidification are investigated by comparing the similar microstructures of individual hatches of directed energy deposition additive manufacturing(DED-AM)and those of single,laser surface-melted tracks formed on a solid *** recoil pressure,which is exponentially dependent on the laser beam power density,induces convection of the melt pool,which causes formation of microstructural bands in the as-solidified *** microstructural bands are associated with changes in the chromium concentration and are a significant component of the inhomogeneous microstructure of DED-AM.

关键词： Additive manufacturing Directed energy deposition Stainless steel Rapid solidification Recoil pressure Microstructure

Conceptual design of a 15-TW pulsed-power accelerator for high-energy-densityephysics experiments

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Matter and Radiation at Extremes 2017年第4期2卷 204-223页

作者： R.B.Spielman D.H.Froula G.Brent E.M.Campbell D.B.Reisman M.E.Savage M.J.Shoup III W.A.Stygar M.L.Wisher Laboratory for Laser Energetics University of RochesterRochesterNY14623USA Sandia national Laboratories AlbuquerqueNM 87185USA

We have developed a conceptual design of a 15-TW pulsed-power accelerator based on the linear-transformer-driver(LTD)architecture described by Stygar[*** et al.,*** *** 18,110401(2015)].The driver will allow multiple,high-energy-density experiments per day in a university environment and,at the same time,will enable both fundamental and integrated experiments that are scalable to larger *** this design,many individual energy storage units(bricks),each composed of two capacitors and one switch,directly drive the target load without additional pulse *** LTD modules in parallel drive the *** module consists of 16 LTD cavities connected in series,where each cavity is powered by 22 bricks connected in *** design stores up to 2.75 MJ and delivers up to 15 TW in 100 ns to the constant-impedance,water-insulated radial transmission *** transmission lines in turn deliver a peak current as high as 12.5 MA to the physics *** maximize its experimental value and flexibility,the accelerator is coupled to a modern,multibeam laser facility(four beams with up to 5 kJ in 10 ns and one beam with up to 2.6 kJ in 100 ps or less)that can provide auxiliary heating of the physics *** lasers also enable advanced diagnostic techniques such as X-ray Thomson scattering and multiframe and three-dimensional *** coupled accelerator-laser facility will be the first of its kind and be capable of conducting unprecedented high-energy-densityephysics experiments.

关键词： Pulsed power accelerator High energy density physics Conceptual design

Laser-direct-drive program: Promise, challenge, and path forward

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Matter and Radiation at Extremes 2017年第2期2卷 37-54页

作者： E.M.Campbell V.N.Goncharov T.C.Sangster S.P.Regan P.B.Radha R.Betti J.F.Myatt D.H.Froula M.J.Rosenberg I.V.Igumenshchev W.Seka A.A.Solodov A.V.Maximov J.A.Marozas T.J.B.Collins D.Turnbull F.J.Marshall A.Shvydky J.P.Knauer R.L.McCrory A.B.Sefkow M.Hohenberger P.A.Michel T.Chapman L.Masse C.Goyon S.Ross J.W.Bates M. Karasik J.Oh J.Weaver A.J.Schmitt K.Obenschain S.P.Obenschain S.Reyes B.Van Wonterghem Laboratory for Laser Energetics University of RochesterRochesterNYUSA Lawrence Livermore national Laboratory LivermoreCAUSA Naval Research Laboratory WashingtonDCUSA

Along with laser-indirect(X-ray)-drive and magnetic-drive target concepts,laser direct drive is a viable approach to achieving ignition and gain with inertial confinement *** the United States,a national program has been established to demonstrate and understand the physics of laser direct *** program utilizes the Omega Laser Facility to conduct implosion and coupling physics at the nominally 30-kJ scale and lasereplasma interaction and coupling physics at the MJ scale at the national Ignition *** article will discuss the motivation and challenges for laser direct drive and the broad-based program presently underway in the United States.

关键词： Inertial fusion Direct drive Laser interactions Hydrodynamics Omega national ignition facility