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Neutron Diffraction Study of Low-Cycle Fatigue Behavior in an Austenitic–Ferritic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2015年第10期28卷 1247-1256页

作者： Ming-Wei Zhu Nan Jia Feng Shi bjorn Clausen School of Materials Science and Engineering Shenyang Aerospace University Key Laboratory for Anisotropy and Texture of Materials(ATM) Northeastern University School of Science Northeastern University Los Alamos National Laboratory Los Alamos Neutron Science Center

By performing in situ neutron diffraction experiments on an austenitic-ferritic stainless steel subjected to lowcycle fatigue loading, the deformation heterogeneity of the material at microscopic level has been revealed. Based on the in situ neutron diffraction data collected from a single specimen together with the mechanical properties learned from the ex situ micro-hardness, a correlation has been found. The performance versus diffraction-profile correlation agrees with the cyclic-deformation-induced dislocation evolution characterized by ex situ TEM observation. Moreover, based on the refined neutron diffraction-profile data, evident strain anisotropy is found in the austenite. The high anisotropy in this phase is induced by the increase in dislocation density and hence contributes to the hardening of the steel at the first 10 *** 10 fatigue cycles, the annihilation and the rearrangement of the dislocations in both austenitic and ferritic phases softens the plastically deformed specimen. The study suggests that the evolution of strain anisotropy among the differently oriented grains and micro-strain induced by lattice distortion in the respective phases mostly affect the cyclic-deformationinduced mechanical behavior of the steel at different stages of fatigue cycles. The stress discrepancy between phases is not the dominant mechanism for the deformation of the steel.

关键词： Duplex steel Neutron diffraction Fatigue Plastic deformation Microstructure

A Cartesian Embedded Boundary Method for Hyperbolic Conservation Laws

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Communications in Computational Physics 2007年第6期2卷 1199-1219页

作者： bjorn Sjogreen N.Anders Petersson Center for Applied Scientific Computing Lawrence Livermore National LaboratoryLivermoreCA 94551USA.

We develop an embedded boundary finite difference technique for solving the compressible two-or three-dimensional Euler equations in complex geometries on a Cartesian *** method is second order accurate with an explicit time step determined by the grid size away from the *** limiters are used on the embedded boundary to avoid non-physical oscillations near shock *** show computed examples of supersonic flow past a cylinder and compare with results computed on a body fitted ***,we discuss the implementation of the method for thin geometries,and show computed examples of transonic flow past an airfoil.

关键词： Embedded boundary hyperbolic conservation law finite difference scheme shock wave.

Super-Grid Modeling of the Elastic Wave Equation in Semi-Bounded Domains

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Communications in Computational Physics 2014年第9期16卷 913-955页

作者： N.Anders Petersso bjorn Sjogreen Center for Applied Scientific Computing L-422LLNLP.O.Box 808LivermoreCA 94551USA

We develop a super-grid modeling technique for solving the elastic wave equation in semi-bounded two-and three-dimensional spatial *** this method,waves are slowed down and dissipated in sponge layers near the far-field ***,this is equivalent to a coordinate mapping that transforms a very large physical domain to a significantly smaller computational domain,where the elastic wave equation is solved numerically on a regular *** damp out waves that become poorly resolved because of the coordinate mapping,a high order artificial dissipation operator is added in layers near the boundaries of the computational *** prove by energy estimates that the super-grid modeling leads to a stable numerical method with decreasing energy,which is valid for heterogeneous material properties and a free surface boundary condition on one side of the *** spatial discretization is based on a fourth order accurate finite difference method,which satisfies the principle of summation by *** show that the discrete energy estimate holds also when a centered finite difference stencil is combined with homogeneous Dirichlet conditions at several ghost points outside of the far-field ***,the coefficients in the finite difference stencils need only be boundary modified near the free *** allows for improved computational efficiency and significant simplifications of the implementation of the proposed method in multi-dimensional *** experiments in three space dimensions show that the modeling error from truncating the domain can be made very small by choosing a sufficiently wide super-grid damping *** numerical accuracy is first evaluated against analytical solutions of Lamb’s problem,where fourth order accuracy is observed with a sixth order artificial *** then use successive grid refinements to study the numerical accuracy in the more complicated motion due to a point moment tensor source in a

关键词： Far field boundary conditions higher order methods elastic wave equation summation by parts.

Stable and Efficient Modeling of Anelastic Attenuation in Seismic Wave Propagation

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Communications in Computational Physics 2012年第6期12卷 193-225页

作者： N.Anders Petersson bjorn Sjogreen Center for Applied Scientific Computing L-422Lawrence Livermore National LaboratoryP.O.Box 808LivermoreCA 94551USA

We develop a stable finite difference approximation of the three-dimensional viscoelastic wave *** material model is a super-imposition of N standard linear solid mechanisms,which commonly is used in seismology to model a material with constant quality factor *** proposed scheme discretizes the governing equations in second order displacement formulation using 3N memory variables,making it significantly more memory efficient than the commonly used first order velocitystress *** new scheme is a generalization of our energy conserving finite difference scheme for the elastic wave equation in second order formulation[SIAM ***.,45(2007),pp.1902–1936].Our main result is a proof that the proposed discretization is energy stable,even in the case of variable material *** proof relies on the summation-by-parts property of the *** newscheme is implemented with grid refinement with hanging nodes on the *** experiments verify the accuracy and stability of the new ***-analytical solutions for a half-space problem and the LOH.3 layer over half-space problem are used to demonstrate how the number of viscoelastic mechanisms and the grid resolution influence the *** find that three standard linear solid mechanisms usually are sufficient to make the modeling error smaller than the discretization error.

关键词： Viscoelastic standard linear solid finite difference summation by parts

An Energy Absorbing Far-Field Boundary Condition for the Elastic Wave Equation

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Communications in Computational Physics 2009年第8期6卷 483-508页

作者： N.Anders Petersson bjorn Sjogreen Center for Applied and Scientific Computing L-550 Lawrence Livermore National LaboratoryLivermoreCA 94551USA

We present an energy absorbing non-reflecting boundary condition of Clayton-Engquist type for the elastic wave equation together with a discretization which is stable for any ratio of compressional to shear wave *** prove stability for a second-order accurate finite-difference discretization of the elastic wave equation in three space dimensions together with a discretization of the proposed non-reflecting boundary *** stability proof is based on a discrete energy estimate and is valid for heterogeneous *** proof includes all six boundaries of the computational domain where special discretizations are needed at the edges and *** stability proof holds also when a free surface boundary condition is imposed on some sides of the computational domain.

关键词： Elastic wave equation far-field boundary condition finite differences stability energy estimate

Stable Grid Refinement and Singular Source Discretization for Seismic Wave Simulations

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Communications in Computational Physics 2010年第10期8卷 1074-1110页

作者： N.Anders Petersson bjorn Sjogreen Center for Applied Scientific Computing L-422Lawrence Livermore National LaboratoryPO Box 808LivermoreCA 94551.

An energy conserving discretization of the elastic wave equation in second order formulation is developed for a composite grid,consisting of a set of structured rectangular component grids with hanging nodes on the grid refinement *** developed summation-by-parts properties are generalized to devise a stable second order accurate coupling of the solution across mesh refinement *** discretization of singular source terms of point force and point moment tensor type are also *** on enforcing discrete moment conditions that mimic properties of the Dirac distribution and its gradient,previous single grid formulas are generalized to work in the vicinity of grid refinement *** source discretization formulas are shown to give second order accuracy in the solution,with the error being essentially independent of the distance between the source and the grid refinement *** numerical examples are given to illustrate the properties of the proposed method.

关键词： Elastic wave equation mesh refinement stability summation by parts singular source term

F?(H2O)+CH3I Ligand Exchange Reaction Dynamics

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Chinese Journal of Chemical Physics 2020年第2期33卷 210-216,I0003,I0039-I0040页

作者： bjorn Bastian Tim Michaelsen Milan Oncák Jennifer Meyer Roland Wester Institut für Ionenphysik und Angewandte Physik Universitat InnsbruckTechnikerstraβe 256020 InnsbruckAustria

Single hydration of the gas phase F^-+CH3I→CH3F reaction allows to probe solvent effects on a fundamental nucleophilic substitution *** the same time,the addition of a solvent molecule opens alternative product ***,we present crossed beam imaging results on the dynamics of the F^-(H2O)+CH3I→[FCH3I]^-+H2O ligand exchange pathway at collision energies between 0.3 and 2.6 *** kinetic energies are constrained by the stability requirement of the weakly bound product *** implies substantial internal excitation of the water molecule and disfavors effcient energy redistribution in an intermediate complex,which is reflected by the suppression of low kinetic energies as collision energy *** 0.3 eV,internal nucleophilic displacement is important and is discussed in light of the competing nucleophilic substitution pathways that form I^- and I^-(H2O).

关键词： Reaction dynamics Ligand exchange Microsolvation Crossed beams Velocity map imaging

Immune responses to tumor-unrelated antigens might predict adverse effects in patients treated with anti-PD-1 immunotherapy

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Cellular & Molecular Immunology 2023年第4期20卷 313-315页

作者： bjorn Nuise Tim Holland Jochen Mattner Mikrobiologisches Institut-Klinische Mikrobiologie Immunologie und HygieneUniversitatsklinikum Erlangen and Friedrich-Alexander-Universitat(FAU)Erlangen-NurnbergErlangenGermany.2Medical Immunology Campus ErlangenFAU Erlangen-NurnbergErlangenGermany

The advent of checkpoint inhibition targeting programmed cell death protein 1(PD-1)or its ligand(PD-L1)revolutionized cancer immunotherapy and significantly improved the treatment of different ***,not all immune cell subsets that express PD-1 also target tumor *** the immune response of the germinal center reaction to seasonal influenza vaccination as a readout,Herati et *** vaccination as an analytical tool to predict adverse effects beyond anticancer responses[1]

关键词： immunotherapy al. vaccination

Linearized model for optimization of coupled electricity and natural gas systems

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Journal of Modern Power Systems and Clean Energy 2017年第3期5卷 364-374页

作者： Mathias SIRVENT Nikolaos KANELAKIS bjorn GEIßLER Pandelis BISKAS Discrete Optimization Friedrich-Alexander-Universitat Erlangen-Nurnberg(FAU)Cauerstr.1191058 ErlangenGermany School of Electrical and Computer Engineering Aristotle University of Thessaloniki54124 ThessalonikiGreece

In this paper,a combined optimization of a coupled electricity and gas system is *** the electricity network a unit commitment problem with optimization of energy and reserves under a power pool,considering all system operational and unit technical constraints is *** gas network subproblem is a medium-scale mixed-integer nonconvex and nonlinear programming *** coupling constraints between the two networks are nonlinear as *** resulting mixed-integer nonlinear program is linearized with the extended incremental method and an outer approximation *** resulting model is evaluated using the Greek power and gas system comprising fourteen gas-fired units under four different approximation accuracy *** results indicate the efficiency of the proposed mixed-integer linear program model and the interplay between computational requirements and accuracy.

关键词： Electricity system Natural gas system Mixed-integer(non)linear programming Extended incremental method Outer approximation