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An Implicit LU-SGS Scheme for the Spectral Volume Method on Unstructured Tetrahedral Grids

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Communications in Computational Physics 2009年第10期6卷 978-996页

作者： Takanori Haga Keisuke Sawada Z.J.Wang Department of Aerospace Engineering Tohoku UniversitySendai 980-8579Japan Department of Aerospace Engineering Iowa State UniversityAmesIA 50011USA

An efficient implicit lower-upper symmetric Gauss-Seidel(LU-SGS)solution approach has been applied to a high order spectral volume(SV)method for unstructured tetrahedral *** LU-SGS solver is preconditioned by the block element matrix,and the system of equations is then solved with a LU *** compact feature of SV reconstruction facilitates the efficient solution algorithm even for high order *** developed implicit solver has shown more than an order of magnitude of speed-up relative to the Runge-Kutta explicit scheme for typical inviscid and viscous problems.A convergence to a high order solution for high Reynolds number transonic flow over a 3D wing with a one equation turbulence model is also indicated.

关键词： High-order unstructured grid spectral volume implicit method

A micromechanical damage model for rocks and concretes under triaxial compression

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Applied Mathematics and Mechanics(English Edition) 2009年第3期30卷 323-333页

作者：任中俊彭向和胡宁杨春和 Xing-ming GUO Department of Engineering Mechanics Chongqing University Chongqing 400044 P. R. China Department of Aerospace Engineering Tohoku University Sendai 980-8579 Japan 不详

Based on analysis of deformation in an infinite isotropic elastic matrix containing an embedded elliptic crack, subject to far field triaxial compressive stress, the energy release rate and a mixed fracture criterion are obtained by using an energy balance approach. The additional compliance tensor induced by a single closed elliptic microcrack in a representative volume element and its in-plane growth is derived. The additional compliance tensor induced by the kinked growth of the elliptic microcrack is also obtained. The effect of the microcracks, randomly distributed both in geometric characteristics and orientations, is analyzed with the Taylor＇s scheme by introducing an appropriate probability density function. A micromechanical damage model for rocks and concretes under triaxial compression is obtained and experimentally verified.

关键词： elliptic microcrack in-plane growth kinked growth energy release rate micro-macro damage model

Pseudogap,Fermi arc,and Peierls-insulating phase induced by 3D-2D crossover in monolayer VSe2

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Nano Research 2019年第1期12卷 165-169页

作者： Yuki Umemoto Katsuaki Sugawara Yuki Nakata Takashi Takahashi Takafumi Sato Department of Physics Tohoku UniversitySendai 980-8578Japan WPI-Advanced Institute for Materials Research Tohoku UniversitySendai 980-8577Japan Center for Spintronics Research Network Tohoku UniversitySendai 980-8577Japan

One of important challenges in condensed-matter physics is to realize new quantum states of matter by manipulating the dimensionality of materials,as represented by the discovery of high-temperature superconductivity in atomic-layer pnictides and room-temperature quantum Hall effect in *** sition-metal dichalcogenides(TMDs)provide a fertile platform for exploring novel quantum phenomena accompanied by the dimensionality change,since they exhibit a variety of electronic/magnetic states owing to quantum *** we report an anomalous metal-i nsulator transition in duced by three-dimensional(3D)-two-dimensional(2D)crossover in mono layer 1T-VSe2 grown on bilayer *** observed a complete insulating state with a finite energy gap on the entire Fermi surface in monolayer 1T-VSe2 at low temperatures,in sharp contrast to metallic nature of *** surprisingly,monolayer 1T-VSe2 exhibits a pseudogap with Fermi arc at temperatures above the charge-density-wave temperature,showing a close resemblanee to high-temperature *** similarity suggests a common underlying physics between two apparently different systems,pointing to the importance of charge/spin fluctuations to create the novel electronic states,such as pseudogap and Fermi arc,in these materials.

关键词： transition-metal dichalchogenides 1T-VSe2 charge density wave electronic states pseudogap Fermi arc

Ultrafast reorientation of the Néel vector in antiferromagnetic Dirac semimetals

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npj Computational Materials 2021年第1期7卷 1562-1568页

作者： Atsushi Ono Sumio Ishihara Department of Physics Tohoku UniversitySendai 980-8578Japan

Antiferromagnets exhibit distinctive characteristics such as ultrafast dynamics and robustness against perturbative fields,thereby attracting considerable interest in fundamental physics and technological ***,it was revealed that the Néel vector can be switched by a current-induced staggered(Néel)spin-orbit torque in antiferromagnets with the parity-time symmetry,and furthermore,a nonsymmorphic symmetry enables the control of Dirac ***,the real-time dynamics of the magnetic and electronic structures remain largely ***,we propose a theory of the ultrafast dynamics in antiferromagnetic Dirac semimetals and show that the Néel vector is rotated in the picosecond timescale by the terahertz-pulse-induced Néel spin-orbit torque and other torques originating from magnetic *** reorientation accompanies the modulation of the mass of Dirac fermions and can be observed in real time by the magneto-optical *** results provide a theoretical basis for emerging ultrafast antiferromagnetic spintronics combined with the topological aspects of materials.

关键词： materials Dirac metals

Marangoni Convection in the LiCaAIF_6 Crystal Growth by the Czochralski Technique

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Journal of Thermal Science 2002年第4期11卷 348-352页

作者： Hiroshi Mizuseki Touetsu Shishido Kyoko Ichinoseki Yoshiyuki Kawazoe Institute for Materials Research Tohoku UniversityInstitute for Materials Research Tohoku UniversityInstitute for Materials Research Tohoku UniversityInstitute for Materials Research Tohoku University Sendai 980-8577 Japan Sendai 980-8577 Japan Sendai 980-8577 Japan Sendai 980-8577 Japan

Numerical simulation of the mixed convection induced by buoyancy, crystal rotation, and also unbalanced surface tension at the melt-gas interface is conducted by means of the finite volume method in the model of the Czochralski crystal growth. The role of Marangoni convection in the heat and mass transfer is investigated by the comparison of the models with and without surface tension included, and our results indicate that Marangoni convection plays an important role in the heat and mass transfer near the interface of melt and crystal, and also the convection structure.

关键词： marangoni convection buoyancy convection Czochralski technique crystal growth computer simulation.

Mechanism of superlubricity of a DLC/Si_(3)N_(4) contact in the presence of castor oil and other green lubricants

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Friction 2022年第10期10卷 1693-1706页

作者： Yun LONG Yang WANG Volker WEIHNACHT Stefan MAKOWSKI Momoji KUBO Jean Michel MARTIN Maria-Isabel DE BARROS BOUCHET Ecole Centrale de Lyon Laboratory of Tribology and System DynamicsUniversity of LyonEcully 69134France Institute for Materials Research Tohoku UniversitySendai 980-8577Japan Department of Mechanical Systems Engineering Graduate School of EngineeringTohoku UniversitySendai 980-8579Japan Fraunhofer Institute for Material and Beam Technology(IWS) Dresden 01277Germany

To meet the surging needs in energy efficiency and eco-friendly lubricants,a novel superlubricious technology using a vegetable oil and ceramic materials is *** coupling different hydrogen-free amorphous carbon coatings with varying fraction of sp^(2) and sp^(3) hybridized carbon in presence of a commercially available silicon nitride bulk ceramic,castor oil provides superlubricity although the liquid vegetable oil film in the contact is only a few nanometres thick at *** a partial liquid film possibly separating surfaces in contact,local tribochemical reactions between asperities are essential to maintain superlubricity at low *** local pressure activates chemical degradation of castor oil generating graphitic/graphenic-like species on top of asperities,thus helping both the chemical polishing of surface and its chemical passivation by H and OH ***,the formation of the formation of–(CH_(2)–CH_(2))n–noligomers have been evidenced to have a major role in the friction *** simulation unveils that formation of chemical degradation products of castor oil on friction surfaces are favoured by the quantity of sp^(2)-hybridized carbon atoms in the amorphous carbon ***,tuning sp^(2)-carbon content in hydrogen-free amorphous carbon,in particular,on the top layers of the coating,provides an alternative way to control superlubricity achieved with castor oil and other selected green lubricants.

关键词： superlubricity diamond-like carbon(DLC) sp^(2)-hybridized carbon hydrogen passivation castor oil

Cultivation of aerobic granular sludge in a conventional, continuous flow, completely mixed activated sludge system

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Frontiers of Environmental Science & Engineering 2015年第2期9卷 324-333页

作者： Xi CHEN Linjiang YUAN Wenjuan LU Yuyou LI Pei LIU Kun NIE School of Environmental and Municipal Engineering Xi'an University of Architecture and Technology Xi'an 710055 China Department of Environmental Science Graduate School of Environmental Studies Tohoku University Sendai 980-8579 Japan

Aerobic granules were formed in a conven- tional, continuous flow, completely mixed activated sludge system （CMAS）. The reactor was inoculated with seed sludge containing few filaments and fed with synthetic municipal wastewater. The settling time of the sludge and the average dissolved oxygen （DO） of the reactor were 2 h and 4.2 mg. L 1, respectively. The reactor was agitated by a stirrer, with a speed of 250r·min^-1, to ensure good mixing . The granular sludge had good settleability, and the sludge volume index （SVI） was between 50 and 90 mL ·g ^-1. The laser particle analyzer showed the diameter of the granules to be between 0.18 and 1.25 mm. A scanning electron microscope （SEM） investigation revealed the predominance of sphere-like and rod-like bacteria, and only few filaments grew in the granules. The microbial community structure of the granules was also analyzed by polymerase chain reaction-denaturing gradient gel electro- phoresis （PCR-DGGE）. Sequencing analysis indicated the dominant species were α, β, and γ-Proteobacteria, Bacteroidetes, and Firmicutes. The data from the study suggested that aerobic granules could form, if provided with sufficient number of filaments and high shear force. It was also observed that a high height-to-diameter ratio of the reactor and short settling time were not essential for the formation of aerobic granular sludge.

关键词： aerobic granular sludge completely mixed activated sludge system (CMAS) continuous flow shear force filamentous bacteria polymerase chain reaction- denaturing gradient gel electrophoresis (PCR-DGGE)

Fe含量对粉末冶金Cu-Fe合金显微组织与性能的影响

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Transactions of Nonferrous Metals Society of China 2024年第5期34卷 1571-1587页

作者：张平袁晓波曾梓名滕剑威周芸合杨标标李云平中南大学粉末冶金国家重点实验室长沙410083 Institute for Materials Research Tohoku UniversitySendai 980-8577Japan IMDEA Materials Institute C/Eric Kandel 2GetafeMadrid 28906Spain Department of Materials Science Polytechnic University of Madrid/Universidad Politécnica de MadridE.T.S.de Ingenieros de CaminosMadrid 28040Spain

研究Fe含量对粉末冶金Cu-Fe合金显微组织及性能的影响。采用电火花等离子烧结、冷轧以及时效处理工艺制备4种不同铁含量(5%、10%、20%和40%,质量分数)的Cu-Fe合金。研究结果表明,随着Fe含量从5%(质量分数)增加到40%(质量分数),Fe相由离... 详细信息

研究Fe含量对粉末冶金Cu-Fe合金显微组织及性能的影响。采用电火花等离子烧结、冷轧以及时效处理工艺制备4种不同铁含量(5%、10%、20%和40%,质量分数)的Cu-Fe合金。研究结果表明,随着Fe含量从5%(质量分数)增加到40%(质量分数),Fe相由离散球形分布演变为连续交错分布,Fe相尺寸从0.29μm增加到1.20μm;时效态的Cu-Fe合金的屈服强度从411.5 MPa提高到788.8 MPa,电导率从62.5%(IACS)降低到42.0%(IACS)。在以上结果的基础上,提出一种混合法则计算Cu基体、初级Fe相和次级Fe相对屈服强度的贡献,可较好地预测Fe含量高于10%(质量分数)合金的力学性能。

关键词：铜铁合金粉末冶金快速凝固力学性能强度计算

Model Equation for Acoustic Nonlinear Measurement of Dispersive Specimens at High Frequency

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Chinese Physics Letters 2006年第10期23卷 2807-2810页

作者：章东 KUSHIBIKI Junichi 邹微 Laboratory of Modern Acoustics Institute of Acoustics Nanjing University Nanjing 210093 Department of Electrical Engineering Tohoku University Sendai 980-8579 Japan System and Technology Group IBM Corporation NY 12533 USA

We present a theoretical model for acoustic nonlinearity measurement of dispersive specimens at high frequency. The nonlinear Khokhlov-Zabolotskaya-Kuznetsov （KZK） equation governs the nonlinear propagation in the SiO2/specimen/SiO2 multi-layer medium. The dispersion effect is considered in a special manner by introducing the frequency-dependant sound velocity in the KZK equation. Simple analytic solutions are derived by applying the superposition technique of Gaussian beams. The solutions are used to correct the diffraction and dispersion effects in the measurement of acoustic nonlinearity of cottonseed oil in the frequency range of 33-96 MHz. Re- garding two different ultrasonic devices, the accuracies of the measurements are improved to ±2.0% and ±1.3% in comparison with ±9.8% and ±2.9% obtained from the previous plane wave model.

关键词： 2ND-HARMONIC SOUND FIELD ULTRASOUND PARAMETER LIQUIDS