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A NOVEL METHOD FOR EVALUATING PLANE STRESS DYNAMIC FRACTURE TOUGHNESS OF 0Cr18Ni10Ti STAINLESS STEEL WELDED jOINTS

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Acta Metallurgica Sinica(English Letters) 2008年第4期21卷 303-312页

作者： Z.j. xu Y.L. Li School of Aeronautics Northwestern Polytechnical University Xi＇an 710072 China

A novel method was proposed for the evaluation of Mode I dynamic fracture toughness （DFT） under plane stress and small scale yielding conditions for welded joints of stainless steel （SS）, 0Cr18Ni10Ti. In a hybrid experimental-numerical approach, the experiments were carried out on the Hopkinson pressure bar apparatus, and three dimensional （3D） transient numerical simulations were performed by a finite element （FE） computer program. Macroscopical plastic deformation was observed at the loading and supporting points, on the specimens, after the test, which could cause a large error if omitted in the numerical simulation. Therefore, elustic-viscoplustic analysis was performed on the specimen by adopting the johnson-Cook （j-C） model to describe the rate-dependent plastic flow behavior of the material. The material heterogeneity in the mismatched welded joints, induced by the difference in the base metal （BM） and the weld metal （WM） in yield stress, has also been taken into consideration by using the j-C models separately. Good accordance was obtained between the experimental and the computational results by the present approach. The relationship between plane stress DFT and loading rate was also obtained on the order of 108 MPa.m^1/2.s^-1.

关键词： 0Cr18Ni10Ti Welded joint High strain rate Dynamic fracture Plane stress

Scale Effects of Geographical Soil Datasets on Soil Carbon Estimation in Louisiana,USA:A Comparison of STATSGO and SSURGO

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Pedosphere 2011年第4期21卷 491-501页

作者： B. ZHONG Y. j. xu School of Renewable Natural Resources Louisiana State University Agricultural Center Baton Rouge LA 70803 (USA)

Estimation of soil organic carbon （SOC） pools and fluxes bears large uncertainties because SOC stocks vary greatly over geographical space and through time. Although development of the U.S. Soil Survey Geographic Database （SSURGO）, currently the most detailed level with a map scale ranging from 1：12 000 to 1：63 360, has involved substantial government funds and coordinated network efforts, very few studies have utilized it for soil carbon assessment at the large landscape scale. The objectives of this study were to 1） compare estimates in soil organic matter among SSURGO, the State Soil Geographic Database （STATSGO）, and referenced field measurements at the soil map unit; 2） examine the influence of missing data on SOC estimation by SSURGO and STATSGO; 3） quantify spatial differences in SOC estimation between SSURGO and STATSCO, specifically for the state of Louisiana; and 4） assess scale effects on soil organic carbon density （SOCD） estimates from a soil map unit to a watershed and a river basin scale. SOC was estimated using soil attributes of SSURGO and STATSGO including soil organic matter （SOM） content, soil layer depth, and bulk density. Paired t-test, correlation, and regression analyses were performed to investigate various relations of SOC and SOM among the datasets. There were positive relations of SOC estimates between SSURGO and STATSGO at the soil map unit （R2 = 0.56, n = 86, t = 1.65, P = 0.102; depth： 30 cm）. However, the SOC estimated by STATSGO were 9%, 33% and 36~ lower for the upper 30-cm, the upper l-m, and the maximal depth （up to 2.75 m） soils, respectively, than those from SSURGO. The difference tended to increase as the spatial scale changes from the soil map unit to the watershed and river basin scales. Compared with the referenced field measurements, the estimates in SOM by SSURGO showed a closer match than those of STATSCO, indicating that the former was more accurate than the latter in SOC estimation, both in spatial and temporal resoluti

关键词： carbon accounting climate change GIS soil organic carbon soil organic matter

Influence of Drying Methods on Fractal Geometric Characteristics of Mesoporous Silica Aerogels

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journal of Wuhan University of Technology(Materials Science) 2013年第3期28卷 476-482页

作者：赵善宇 xu Haixun WANG Lijiu j William Suggs School of Environmental and Safety Engineering Changzhou University School of Civil and Hydraulic Engineering Dalian University of Technology Department of Chemistry Brown University

Chemical modification/ambient drying method and freeze drying method were introduced to research the synthesis of mesoporous silica aerogels. By analyzing N2 gas adsorption/desorption isotherms, the fractal geometric characteristics of gels were focused. The overall surface fractal dimensions were determined by analyzing N2 gas adsorption branch and a Frenkel-Halsey-Hill （FHH） equation was empolyed to determine surface fractal dimension Df It is found that, during ambient drying process, VTMCS/VWetgel ratio plays a crucial role in the changes of geometric feature, the key point is 50%, when the ratio is lower, and surface roughness increases with the ratio, when it exceeds 50%, the surface is almost unaffected by the modification. While freeze drying always tends to get larger Df freeze drying process could cause a rough surface of the gels. Compared with traditional porosity and specific surface area analyses, fractal geometry may be expected to be favorable for mesoporous structural analyses of materials.

关键词： silica aerogel N2 gas adsorption surface fractal dimension mesoporous structure

Laser-induced microjet-assisted ablation for high-quality microfabrication

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International journal of Extreme Manufacturing 2022年第3期4卷 122-130页

作者： Yang Guo Pei Qiu Shaolin xu Gary j Cheng School of Mechatronics Engineering Harbin Institute of TechnologyHarbin 150001People’s Republic of China Department of Mechanical and Energy Engineering Southern University of Science and TechnologyShenzhen 518055People’s Republic of China School of Industrial Engineering Purdue UniversityWest LafayetteIN 47906United States of America

Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debris, and turbulent liquid flow generally deteriorate laser beam transmission stability, leading to low energy efficiency and poor surface quality. Here, we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer. The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region, and thus a very stable material removal process can be obtained. The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m sin its initial 500 μm displacement. The coupling effect of laser ablation, mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality. We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation(LIMjAA) based on its unique characteristics. High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMjAA with a single-pass laser scanning process in our experiments. LIMjAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels, square and circle microscale through-holes. The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.

关键词： liquid-assisted laser ablation laser-induced microjet cavitation bubbles laser microfabrication

Comprehensive insights into the thermal and mechanical effects of metallic glasses via creep

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journal of Materials Science & Technology 2022年第4期99卷 39-47页

作者： Z.R.xu j.C.Qiao j.Wang E.Pineda D.Crespo School of Mechanics Civil Engineering and ArchitectureNorthwestern PolytechnicalUniversityXi’an 710072China State Key Laboratory of Solidification Processing Northwestern PolytechnicalUniversityXi’an 710072China Department of Physics Barcelona Research Center in Multiscale Science and TechnologyInstitute of Energy TechnologiesUniversitat Politècnica de CatalunyaBarcelona 08019Spain

Evolution of deformation and relaxation behaviors of a prototypical Cu_(46)Zr_(46)A_(l8)metallic glass was explored by extensive creep tests under both physical aging and cyclic *** insights into the microstructure-induced dynamic heterogeneity which accommodates creep deformation were successively revealed via experimental measurements and spectral *** annihilation of local defects within metallic glass with increasing annealing time and cyclic numbers was observed through the reduction of amplitude in both activation energy spectra and relaxation-time spectra,which were also accompanied by an ascending value of β_(KWW).It is further found that the corresponding deformation units within the metallic glass do not disappear permanently,but are recoverable over the course of cyclic *** apparent suppressed relaxation process can be gradually alleviated with increasing resuming time between two consecutive cycles,behaving differently from physical aging,which indicates a notable discrepancy between thermal treatment and mechanical treatment.

关键词： Metallic glasses Creep Physical aging Cyclic loading Relaxation-time spectrum

Dissociation cross sections ofψ(3770),ψ(4040),ψ(4160),andψ(4415)mesons with nucleons

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Communications in Theoretical Physics 2024年第4期76卷 93-112页

作者： Ruo-Qing Ding Xiao-Ming xu H j Weber Department of Physics Shanghai UniversityBaoshanShanghai 200444China Department of Physics University of VirginiaCharlottesvilleVA 22904United States of America

We study the dissociation of ψ(3770), ψ(4040), ψ(4160), and ψ(4415) mesons in collision with nucleons, which takes place in high-energy proton-nucleus collisions. The quark interchange between a nucleon and a ■ meson leads to the dissociation of the ■ meson. We consider the reactions:■, and■, where R stands for ψ(3770), ψ(4040), ψ(4160), or ψ(4415). A reaction of a neutron and a ■ meson corresponds to a reaction of a proton and the ■ meson by replacing the up quark with the down quark and vice versa. Transition-amplitude formulas are derived from the S-matrix *** cross sections are calculated with the transition amplitudes for scattering in the prior form and in the post form. The cross sections relate to nodes in the radial wave functions of ψ(3770), ψ(4040), ψ(4160), and ψ(4415) mesons.

关键词： inelastic nucleon-charmonium scattering quark interchange relativistic constituent quark potential model

Molecular Dynamics Simulation of MgSiO_(3) Perovskite

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Chinese Physics Letters 1998年第6期15卷 444-446页

作者： ZHOU Lin-xiang j.R.Hardy xu Xin Department of Physics Xiamen UniversityXiamen 361005 Department of Physics and Center for Electro-Optics University of Nebraska-LincolnNE 68588-0111U.S.A State Key Laboratory for Physical Chemistry of Solid Surfaces Department of ChemistryXiamen UniversityXiamen 361005

Using molecular dynamics to simulate MgSiO_(3) perovskite is performed to investigate its phase transitions and *** simulations has used parameter-free Gordon-Kim potentials and a novel technique to monitor the motion of ions which clearly demonstrates the sublattice melting of ions O^(2-) and the rotations of SiO_(6) ***_(3) has to undergo a few of phase transitions,then enter into the cubic *** particular,there is a transitional phase between orthorhombic phase and cubic *** are a superionc phase and the cubic phase in magnesium-rich silicate *** superionic phase occurs after the onset of cubic phase before the melting *** onset temperature T_(c) for superionicity is about 200-700K below the melting point T_(m),T_(c)/T_(m)~0.92.

关键词： cubic perovskite transitions

Molecular Dynamics Simulation of Binary Fluorozirconate Glass ZrF_(4)·BaF_(2)

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Chinese Physics Letters 1998年第5期15卷 326-328页

Binary fluorozirconate glassZrF_(4)·BaF_(2) has been studied by molecular dynamical simulation using parameter-free Gordon-Kim *** these simulations a novel technique is employed to monitor the motion of ions,thus the structure pictures of glass and the microscopic motion mechanism of ionic conduction are clearly and directly *** glass networks commonly are formed by ZrF8,ZrF7 or ZrF6 polyhedra,cross linked by Ba-F ionic *** mean distance of the ionic nearest neighboring at 300K is about 3.90Å(Zr-Zr),3.87Å(Zr-Ba),and 1.96Å(Zr-F).The two stronger peaks of five main peaks of vibrational spectra are at about 540-600 and 460-510cm^(-1) and three weaker peaks at about 386-416,322-348,and 183-196cm^(-1).The other properties of glass:density,thermal expansion coefficient,polarization,and glass transition temperature are also examined.

关键词： zirconate glass Molecular

Frozen Landweber Iteration for Nonlinear Ill-Posed Problems

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Acta Mathematicae Applicatae Sinica 2007年第2期23卷 329-336页

作者： j.xu B.Han L.Li Academy of Mathematics and Systems Science Chinese Academy of SciencesBeijing 100080China Department of Mathematics Harbin Institute of TechnologyHarbin 150001China

In this paper we propose a modification of the Landweber iteration termed frozen Landweber iteration for nonlinear ill-posed problems. A convergence analysis for this iteration is presented. The numerical performance of this frozen Landweber iteration for a nonlinear Hammerstein integral equation is compared with that of the Landweber iteration. We obtain a shorter running time of the frozen Landweber iteration based on the same convergence accuracy.

关键词： Ill-posed problem regularization Landweber iteration