检索结果-南通市图书馆

journal of Materials Science & Technology 2020年第7期42卷 85-96页

作者： L.W.Lan X.j.Wang r.P.Guo h.j.Yang j.W.Qiao research Center for high-Entropy Alloys College of Materials Science and EngineeringTaiyuan University of TechnologyTaiyuan030024China

The tribological properties of nitrided Ni(45)(FeCoCr)(40)(AlTi)(15)high-entropy alloys(hEAs)were investigated in air and simulated acid rain under different normal loads(5,7,10,and 12 N)at ambient *** results revealed that as-cast hEAs were only composed of FCC phase,while the volume fraction of FCC phase in the nitrided alloys was significantly ***,the hard phases of AIN,CrN,Fe4 N,and TiN phases were formed in the nitrided *** thickness of the nitriding layer was about 8.4μ*** hardness increased from 8.7 GPa in as-cast alloys to 14.5 GPa in the nitrided *** addition,under the same conditions,the friction coefficient of the nitrided alloys was higher than that of as-cast alloys,but the wear rate was generally lower than that of as-cast ***,the wear rate of the nitrided alloys was the lowest in acid rain due to the lubrication,cleaning,and cooling in the liquid *** air,dominating wear mechanisms in as-cast and nitrided alloys were abrasive,delamination,and adhesive ***,the wear mechanism of as-cast and nitrided alloys in acid rain was mainly abrasive and corrosion wears.

关键词： Abrasive wear hardness Corrosive wear Microstructure Wear mechanism

Optical and magnetic properties of GaN epilayers implanted with ytterbium

在线全文

学校读者我要写书评

暂无评论

journal of rare Earths 2010年第6期28卷 931-935页

作者： W.M.jadwisienczak j.Wang h.Tanaka j.Wu r.Palai h.huhtinen A.Anders School of EECS Ohio UniversityAthens OH45701U.S.A Department of Physics and Institute for Functional Nanomaterials University of Puerto RicoSan JuanPuerto Rico00931-3343U.S.A Wihuri Physical Laboratory Department of Physics and AstronomyUniversity of TurkuTurkuFIN-20014Finland Lawrence Berkeley National Laboratory BerkeleyCA94720U.S.A

We have studied the optical and magnetic properties of ytterbium implanted GaN epilayer grown on (0001) sapphire by metalorganic chemical vapor by deposition (MOCVD). Samples were implanted at room temperature with Yb ions at dose 4 1015 cm-2 and energy of 150 keV. The implanted samples were annealed at 1000 C in N2 at atmospheric pressure to recover implantation damages. The photoluminescence (PL), PL excitation (PLE), and PL kinetics have been studied with continuous and pulse photo-excitations in 360-1100 nm spectral range at different temperatures. The characteristic Yb3+ ion emission spectra were observed in the spectral range between 970-1050 nm. Theoretical fittings of the experimental PL temperature and PL kinetics data suggest that Yb3+ ions are involved in at least two major luminescence centers. The PLE spectra indicate that excitation of the Yb3+ ion occurs via electron-hole pair generation and complex processes. Magnetization versus magnetic field curves shows an enhancement of magnetic order for Yb-implanted samples in 5 K to 300 K temperature range. The Yb-implanted GaN sample showing weak ferromagnetic behavior was compared with the ferromagnetic in situ doped GaYbN material.

关键词： luminescence Ⅲ-nitrides rare earth ions defects ferromagnetism rare earths

Adiabatic shear instability in a titanium alloy:Extreme deformation-induced phase transformation,nanotwinning,and grain refinement

在线全文

学校读者我要写书评

暂无评论

journal of Materials Science & Technology 2023年第19期150卷 104-113页

作者： X.r.Guan Q.Chen S.j.Qu G.j.Cao h.Wang A.h.Feng D.L.Chen School of Materials Science and Engineering Tongji UniversityShanghai 201804China Southwest Technology and Engineering research Institute Chongqing 400039China Shanghai Key Laboratory of D&A for Metal-Functional Materials School of Materials Science&EngineeringTongji UniversityShanghai 201804China Key Laboratory for Light-weight Materials Nanjing Tech UniversityNanjing 210009China Interdisciplinary Center for Additive Manufacturing School of Materials and ChemistryUniversity of Shanghai for Science and TechnologyShanghai 2000093China Department of Mechanical and Industrial Engineering Toronto Metropolitan University(formerly Ryerson University)TorontoON M5B 2K3Canada

Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium *** shear band(ASB),a phenomenon prone to dynamic loading,is often accom-panied by catastrophic ***,it is unclear how the internal nanostructures are related to shear *** we report detailed microstructural evolution in the ASB of a titanium alloy via in-depth focused ion beam(FIB),transmission Kikuchi diffraction(TKD),and high-resolution transmission electron microscope(hrTEM)analyses,with the deformation instability phenomenon discussed from the energy *** ASB interior undergoes multifaceted changes,namely deformation-induced beta-to-alpha transformation and deformation-induced martensitic transformation to form substantially refined and heterogeneous ***,two types of extremely fine twins are identified to occur within both nano-sized martensite and alpha *** critical plastic work representing the onset of adiabatic shear instability and dynamic equilibrium is observed to be constant for a specific structure in the same deformation *** energy analysis could be extended to other materials subjected to high strain-rate dynamic deformation.

关键词： Adiabatic shear instability Deformation-induced phase transformation Deformation-induced nanotwinning Dynamic recovery Energy analysis

Metamaterial-based graphene thermal emitter

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nano research 2018年第7期11卷 3567-3573页

作者： Cheng Shi Nathan h. Mahlmeister Isaac j. Luxmoore Geoffrey r. Nash College of Engineering Mathematics and PhysicaI Sciences University of Exeter Exeter EX4 4QF UK

A thermal emitter composed of a frequency-selective surface metamaterial layer and a hexagonal boron nitride-encapsulated graphene filament is demonstrated. The broadband thermal emission of the metamaterial （consisting of ring resonators） was tailored into two discrete bands, and the measured reflection and emission spectra agreed well with the simulation results. The high modulation frequencies that can be obtained in these devices, coupled with their operation in air, confirm their feasibility for use in applications such as gas sensing.

关键词： graphene hexagonal boron nitride thermal emitter infrared metamaterial

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Plasma Science and Technology 2019年第6期21卷 52-57页

作者： h j YEOM D h ChOI Y S LEE j h KIM D j SEONG S j YOU h C LEE Korea research Institute of Standards and Science(KrISS) Daejeon 34113 Republic of Korea Department of Physics Chungnam National University Daejeon 34134 Republic of Korea

In this study,plasma density measurements were performed near the plume region of the remote plasma source (rPS) in Ar/NF3 gas mixtures using a microwave cutoff *** measured plasma density is in the range of 1010-1011 cm-3 in the discharge conditions with rPS powers of 2-4 kW and gas pressures of 0.87-4 *** plasma density decreased with increasing gas pressures and rPS powers under various Ar/NF3 mixing *** decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of NF3/(Ar/NF3).We also performed downstream etching of silicon and silicon oxide films in this *** etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and *** was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode,and that the etch selectivity reached 96-131 in the discharge conditions of rF powers (3730-4180 W) and gas pressures (3.6-4 Torr).

关键词： remote plasma source electron density cutoff probe downstream etch

The role of Chromatin Modifications in Progression through Mouse Meiotic Prophase

在线全文

学校读者我要写书评

暂无评论

journal of Genetics and Genomics 2014年第3期41卷 97-106页

作者： james h.Crichton Christopher j.Playfoot Ian r.Adams MrC human Genetics Unit MRC Institute of Genetics and Molecular MedicineUniversity of EdinburghWestern General Hospital

Meiosis is a key event in gametogenesis that generates new combinations of genetic information and is required to reduce the chro- mosome content of the gametes. Meiotic chromosomes undergo a number of specialised events during prophase to allow meiotic recombination, homologous chromosome synapsis and reductional chromosome segregation to occur. In mammalian cells, DNA phys- ically associates with histones to form chromatin, which can be modified by methylation, phosphorylation, ubiquitination and acetylation to help regulate higher order chromatin structure, gene expression, and chromosome organisation. recent studies have identified some of the enzymes responsible for generating chromatin modifications in meiotic mammalian cells, and shown that these chromatin modifying enzymes are required for key meiosis-specific events that occur during meiotic prophase. This review will discuss the role of chromatin modifications in meiotic recombination, homologous chromosome synapsis and regulation of meiotic gene expression in mammals.

关键词： Mouse Meiosis Chromatin Chromosome histone modification DNA methylation

Detection of Arterial Occlusions Using Viscoelastic Wave Propagation

在线全文

学校读者我要写书评

暂无评论

Advances in Applied Mathematics and Mechanics 2009年第1期1卷 1-28页

作者： h.T.Banks j.r.Samuels,jr. Center for research in Scientific Computation North Carolina State UniversityCampus Box 8212RaleighNC 27695-8212USA

We consider the problem of detecting cardiac artery occlusions using stenosis driven viscoelastic(VE)waves propagated through biotissue to body surface *** investigate possible statistical model formulations(ordinary least squares(OLS),generalized least squares(GLS))and post analysis techniques(residual plots)to ascertain uncertainty in estimates as well as validity of the statistical models as part of a methodology for stenosis detection using viscoelastic waves.

关键词： Inverse problems viscoelastic models wave propagation in biotissue statistical models

The total cross sections of the ^(11)B(α,n)^(14N) and the ^(10)B(α,n)^(13)N reactions between 2 and 6 MeV

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nuclear Science and Techniques 2017年第8期28卷 111-116页

作者： r. M. Prior M. C. Spraker r. h. France S. Stave M. W. Ahmed h. j. Karwowski j. M. Mueller L. S. Myers h. r. Weller University of North Georgia Dahlonega GA 30597 USA Georgia College & State University MilledgevilleGA 31061 USA Duke University Durham NC 27708 USA Triangle Universities Nuclear Laboratory DurhamNC 27708 USA University of North Carolina Chapel Hill NC 27599 USA Present Address: Bluffton University Bluffton OH 45817USA

There is considerable interest in potential aneutronic fusion reactors. One possible reaction is^(11)B(p,a)***, the emitted alpha particles are energetic enough to generate neutrons by interacting with boron inside the reactor through the ^(11)B(α,n)^(14N) and ^(10)B(α,n)^(13)N *** aid in evaluating neutron production within this potential aneutronic reactor, the total cross sections were measured for the ^(11)B(α,n)^(14N) reaction between 2 and 6 MeV and for the ^(10)B(α,n)^(13)N reaction between 2 and 4.8 MeV. The results are presented and compared with previously reported results.

关键词：聚变反应堆 MeV 总截面核反应堆中子反应器 α粒子电子

Effect of Base Material on Microstructure and Texture Evolution of a Ti–6Al–4V Electron-Beam Welded joint

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2017年第5期30卷 499-504页

作者： G.Q.Wang Z.B.Zhao B.B.Yu j.r.Liu Q.j.Wang j.h.Zhang r.Yang j.W.Li School of Materials Science and Engineering University of Science and Technology of China Institute of Metal research Chinese Academy of Sciences Science and Technology on Power Beam Processes Laboratory Beijing Aeronautical Manufacturing Technology Research Institute

The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.

关键词： Electron-beam welding Titanium alloys Prior b orientation Microstructure Texture

A structural topological optimization method for multi-displacement constraints and any initial topology configuration

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2010年第5期26卷 735-744页

作者： j. h. rong j. h. Yi School of Automotive and Mechanical Engineering Changsha University of Science and TechnologyChangsha 410076 China

In density-based topological design, one expects that the final result consists of elements either black （solid material） or white （void）, without any grey areas. Moreover, one also expects that the optimal topology can be obtained by starting from any initial topology configuration. An improved structural topological optimization method for multidisplacement constraints is proposed in this paper. In the proposed method, the whole optimization process is divided into two optimization adjustment phases and a phase transferring step. Firstly, an optimization model is built to deal with the varied displacement limits, design space adjustments, and reasonable relations between the element stiffness matrix and mass and its element topology variable. Secondly, a procedure is proposed to solve the optimization problem formulated in the first optimization adjustment phase, by starting with a small design space and advancing to a larger deign space. The design space adjustments are automatic when the design domain needs expansions, in which the convergence of the proposed method will not be affected. The final topology obtained by the proposed procedure in the first optimization phase, can approach to the vicinity of the optimum topology. Then, a heuristic algorithm is given to improve the efficiency and make the designed structural topology black/white in both the phase transferring step and the second optimization adjustment phase. And the optimum topology can finally be obtained by the second phase optimization adjustments. Two examples are presented to show that the topologies obtained by the proposed method are of very good 0/1 design distribution property, and the computational efficiency is enhanced by reducing the element number of the design structural finite model during two optimization adjustment phases. And the examples also show that this method is robust and practicable.

关键词： Topological optimization Displacement constraint Continuum structure Design space adjustment rational approximation material model