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Communications in Computational Physics 2009年第1期5卷 108-125页

作者： kristopher t.kim Electromagnetic Scattering Branch Sensors DirectorateAir Force Research LaboratoryHanscom AFBMA 01731-3010USA

We consider two existing FFt-based fast-convolution iterative solution techniques for the scalar t-matrix multiple-scattering equation[1].the use of the FFt operation requires field values be expressed on a regular Cartesian grid and the two techniques differ in how to go about achieving *** first technique[6,7]uses the nondiagonal translation operator[1,9]of the spherical multipole field,while the second method[11]uses the diagonal translation operator of Rokhlin[10].Because of its use of the non-diagonal translator,the first technique has been thought to require a greater number of spatial convolutions than the second *** establish that the first method requires only half as many convolution operations as the second method for a comparable numerical accuracy and demonstrate,based on an actual CPU time comparison,that it can therefore perform iterations faster than the second *** then consider the respective symmetry relations of the non-diagonal and diagonal translators and discuss a memory-reduction procedure for both FFt-based *** this procedure,we need to store only the minimum sets of near-field and far-field translation operators and generate missing elements on the fly using the symmetry *** show that the relative cost of generating the missing elements becomes smaller as the number of scatterers increases.

关键词： Multiple scattering iterative method FFt symmetry

Grain size and temperature effect on the tensile behavior and deformation mechanisms of non-equiatomic Fe(41)Mn(25)Ni(24)Co8Cr2high entropy alloy

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Journal of Materials Science & technology 2020年第7期42卷 190-202页

作者： H.t.Jeong W.J.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul121-791Republic of Korea

the effect of the grain size on the tensile properties and deformation mechanisms of a nonequiatomic Fe(41)Mn(25)Ni(24)Co8 Cr2 high-entropy alloy was studied in the temperature range between 298 and 1173 k by preparing the samples with three different grain sizes through severe plastic deformation and subsequent annealing:ultrafine(sub)grain size(≤0.5μm),8.1μm and 590.2μ*** the temperature between 298 and773 k,the material with the large grain size of 590.2μm exhibited the largest tensile ductility(57%-82%)due to its high strain hardening associated with mechanical twinning,but it exhibited the lowest strength due to its large grain *** material with the ultrafine(sub)grain size exhibited the lowest tensile ductility(3%-7%)due to a greatly reduced strain hardening ability after severe plastic deformation,but it exhibited the highest strength due to the dislocation strengthening and grain refinement *** tensile testing at temperatures above 973 k,recrystallization occurred in the material with the ultrafine(sub)grains during the sample heating and holding stage,leading to the formation of fine and equiaxed grains with the sizes of 6.8-13.5μ*** deformation behavior of the Fe(41)Mn(25)Ni(24)Co8 Cr2 with different grain sizes in the high temperature range between 973 and 1173 k,where pseudosteady-state flow was attained in the stress-strain curves,could be explained by considering the simultaneous contribution of grain boundary sliding and dislocation-climb creep to total plastic *** activation energies for plastic flow for the materials with different grain sizes were similar as^199 kJ/*** predicting the deformation mechanism,it was important to consider the change in grain size by rapid grain growth or recrystallization during the sample heating and holding stage because grain boundary sliding is a grain-size-dependent deformation *** sample with the ultrafine(sub)grains exhibited the large tensile elongations of 30%-85%due to it

关键词： High entropy alloys Grain size High temperature deformation mechanism tensile behavior Grain boundary sliding

Effects of grain size and Al addition on the activation volume and strain-rate sensitivity of CoCrFeMnNi high-entropy alloy

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Journal of Materials Science & technology 2023年第12期143卷 242-252页

作者： H.t.Jeong W.J.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul121-791Republic of Korea

the activation volume(V∗)and strain-rate sensitivity exponent(m)of CoCrFeMnNi and Al_(0.5)CoCrFeMnNi high entropy alloys(HEAs)with various grain sizes(ranging between 2.4 and 356μm)were measured at different strain rates and strain levels at room *** the strain rate decreased,the plastic strain decreased,and the grain size increased,V∗*** enhanced solid-solution strengthening by addition of aluminum decreased V∗.the Hassen plot was modified to capture the grain-size depen-dence of V∗by considering the grain-size dependence of the dislocation *** the plastic strain increased,the strain rate decreased,and the grain size decreased,m *** behavior of m could be quantitatively predicted by using equations derived for the grain-size-dependent V∗and flow *** difference in the grain-size dependence of m between conventional face centered cubic(FCC)metals and FCC HEAs over the nanograin size range could not be explained in terms of a relatively large Hall-Petch slope of the FCC HEAs compared with that of the FCC conventional metals,but was explainable in terms of a substantially higher probability of activation of grain-boundary diffusion-controlled grain-boundary-sliding mechanism at nanograin sizes in the FCC conventional metals than in the FCC HEAs.

关键词： Grain size High entropy alloys Activation volume Strain-rate sensitivity Solid solution

Effect of roll speed ratio on the texture and microstructural evolution of an FCC high-entropy alloy during differential speed rolling

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Journal of Materials Science & technology 2022年第16期111卷 152-166页

作者： H.t.Jeong W.J.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

A very coarse-grained(335μm)Fe_(41)Mn_(25)Ni_(24)Co_(8)Cr_(2)high-entropy alloy with a single FCC phase was cold rolling to a 80%reduction in thickness using the differential speed rolling technique with various speed ratios(SRs)ranging between 1 and *** the SR was increased,the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear *** SR=4,the entire thickness of the sheet was covered with micro-shear bands,and ultrafine(sub)grains with a size of1.4μm were uniformly formed along the shear bands.A continuous dynamic recrystallization(CDRX)mechanism occurred during rolling,and a higher SR accelerated the CDRX *** conventional rolling(at SR=1),a brasstorientation texture with minor components of S{123}and Cutorientations *** higher SRs,shear texture developed as the main type,while the development of rolling texture was *** microstructure at SR=4 obtained after annealing at973 k showed a fully recrystallized microstructure composed of a five times smaller grain size(4μm)with a higher intensity ofγfiber texture compared with that prepared by conventional *** samples processed with high SRs exhibited better tensile properties compared with the conventionally rolled sample in terms of strength and ductility after *** current results demonstrate that by using differential speed rolling with a high SR,one can achieve a significantly finer and more homogeneous microstructure,stronger shear texture,and superior tensile mechanical properties for an FCC high-entropy alloy compared to that obtained by conventional *** strength of the as-rolled and annealed samples was quantitatively explained by considering the contribution of grain size and dislocation density to strengthening.

关键词： High entropy alloys Differential speed rolling texture Grain refinement Strength Severe plastic deformation

Microstructure tailoring of Al_(0.5)CoCrFeMnNi to achieve high strength and high uniform strain using severe plastic deformation and an annealing treatment

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Journal of Materials Science & technology 2021年第12期71卷 228-240页

作者： H.t.Jeong W.J.kim Department of Materials Science and Engineering Hongik UniversityMapo-guSangsu-dong 72-1Seoul 121-791Republic of Korea

Ultrafine-grained alloys fabricated by severe plastic deformation(SPD)have high strength but often poor uniform *** via high-ratio differential speed rolling(HRDSR)followed by an annealing treatment was applied to Al_(0.5)CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be *** optimized microstructure was composed of an ultrafine-grained FCC matrix(1.7-2μm)with a high fraction of high-angle grain boundaries(61%-66%)and ultrafine BCC particles(with a size of 0.6-1μm and a volume fraction of8%-9.3%)distributed uniformly at the grain boundaries of the FCC *** the severely plastically deformed microstructure,the nucleation kinetics of the BCC phase was *** static recrystallization(CSRX)took place during the annealing process at 1273 *** of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC *** precipitation of the hard and brittleσphase was,however,*** annealed sample processed by HRDSR with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14%-20%.these tensile properties are comparable to those of transformation-induced plasticity *** mechanisms of the severely plastically deformed alloy before and after annealing were identified,and each strengthening mechanism contribution was *** calculated results matched well with the experimental results.

关键词： High entropy alloys Severe plastic deformation Uniform ductility High strength Dual phase Annealing

A Study of the Critical Nozzle for Flow Rate Measurement of High-Pressure Hydrogen Gas

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Journal of thermal Science 2007年第1期16卷 28-32页

作者： H.D.kim J.H.Lee k.A.Park t.Setoguchi S.Matsuo School of Mechanical Engineering Andong National University388Songchun-dongAndong 760-749Korea Dynamics Group Korea Research Institute of Standards and SciencePO Box 102YusongTaejon 305-606Korea Department of Mechanical Enginering.Saga University 1Honjo—machiSaga-shiSaga 840—8502Japan

the mass flow rate measurement using a critical nozzle shows the validity of the inviscid theory, indicating that the discharge coefficient increases and approaches unity as the Reynolds number increases under the ideal gas law However, when the critical nozzle measures the mass flow rate of a real gas such as hydrogen at a pressure of hundreds bar, the discharge coefficient exceeds unity, and the real gas effects should be taken into account. the present study aims at investigating the flow features of the critical nozzle using high-pressured hydrogen gas. the axisymmetric, compressible Navier-Stokes computation is employed to simulate the critical nozzle flow, and a fully implicit finite volume method is used to discretize the governing equation system. the real gas effects are simulated to consider the intermolecular forces, which account for the possibility of liquefying hydrogen gas. the computational results are compared with past experimental data. It has been found that the coefficient of discharge for real gas can be corrected properly below unity adopting the real gas assumption.

关键词： critical nozzle compressible flow hydrogen gas ideal gas law real gas effect

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空中英语教室（高级版．彭蒙惠英语） 2024年第8期 12-13,40,41页

作者： kim Rittberg 不详

我为了推广自己的拍摄视频培训业务而开始定期发布视频的时候,一个朋友问我:“你想尝试变成网红吗?”我确实想要影响别人。我想要帮助他们提升沟通能力、制作有创意的内容、帮助他们提高知名度,并且通过内容得到更多销售业绩和潜在客户。

关键词：培训业务销售业绩沟通能力网红视频潜在客户知名度

Hadrons from a hard wall AdS/QCD model

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Chinese Physics C 2010年第9期34卷 1520-1522页

作者： Hyun-Chul kim Youngman kim U.t.Yakhshiev Department of Physics Inha University Asia Pasific Center for theoretical Physics and Department of Physics Pohang University of Science and Technology Department of Nuclear and theoretical Physics National University of Uzbekistan

We review a recent work on masses of mesons and nucleons within a hard wall model of holographic QCD in a unified *** order to treat meson and nucleon properties on the same footing,we introduced the same infrared （IR） cut for both *** framework of present approach,the best fit to the experimental data is achieved introducing the anomalous dimension for baryons.

关键词： AdS/QCD nucleons mesons

Photoproduction of the Θ^+ and its vector andaxial-vector structure

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Chinese Physics C 2009年第12期33卷 1279-1284页

作者： H.-Ch. kim k. Goeke t. Ledwig S. i. Nam Department of Physics Inha University Incheon 402-751 Republic of Korea Institut fr theoretische Physik II Ruhr-Universitt Bochum D-44780 Bochum Germany Institut fr kernphysik Universitt Mainz D-55099 Mainz Germany Department of Physics Chung-Yuan Christian University (CYCU)

We present recent investigations on the vector and axial-vector transitions of the baryon antidecuplet within the framework of the self-consistent SU（3） chiral quark-soliton model, taking into account the 1/No rotational and linear mscorrections. the main contribution to the electric-like transition form factor comes from the wave-function corrections. this is a consequence of the generalized Ademollo-Gatto theorem. It is also found that in general the leading-order contributions are almost canceled by the rotational 1/No corrections. the results are summarized as follows： the vector and tensor k＇NO coupling constants, gk＊N= 0.74--0.87 and fk＊N =0.53--1.16, respectively, and F→kN = 0.71 MeV, based on the result of the kN coupling constant gkne =0.83. We also show the differential cross sections and beam asymmetries, based on the present results. We also discuss the connection of present results with the original work by Diakonov, Petrov, and Polyakov.

关键词： Baryon antidecuplet vector and axial-vector transition form factors chiral quark-soliton model,Photoproduction of the +

Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-Y magnesium alloys with different volume fractions of icosahedral phase

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Journal of Materials Science & technology 2019年第1期35卷 181-191页

作者： t.Y.kwak W.J.kim Department of Materials Science and Engineering Hongik University

the effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-Y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. the average grain sizes, fractions of dynamically recrystallized(DRXed) grains,and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller,higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. this was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. the constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in *** with the cast alloys, the onset of the power law breakdown(PLB) occurred at larger ZenerHolloman(Z) parameter values in the extruded alloys. this was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. the flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. this agreed with the microstructural observations.

关键词： Hot compression Magnesium alloy Processing map Grain refinement Dynamic recrystallization