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structure and p.op.rties of brazed joints on disp.rsion-strengthened cop.er

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China Welding 2014年第3期23卷 31-36页

作者： s. v. Maksymov. v. F. Khorunov E. O. p.ton Electric Welding Institute National Academy of Sciences of Ukraine Brazing

Dev.lop.ent of the technological p.ocess for brazing of heat-resistant cop.er alloy strengthened with Al2O3 oxide p.rticles is an imp.rtant task of fabrication of high-temp.rature ap.lication structures. As mechanical p.op.rties of the brazed joints directly dep.nd on the structural factor and morp.ological p.culiarities of the brazed seams, the latter are of technological interest in terms of making of p.rmanent joints. This study giv.s results of X-ray sp.ctral microanalysis of the brazed joints on disp.rsion-strengthened cop.er alloy （ Gridcop.Al-25 ） p.oduced by using the Ti-Cu system adhesion-activ. brazing filler alloy, different heat sources and temp.rature-time p.rameters of the brazing p.ocess. shown are differences in formation of structure of the seams made by v.cuum brazing using radiation and high-frequency heating. v.cuum brazing with radiation heating p.ov.des the homogeneous seams with crystallisation of the p.ases based on the CuTi and CuTi2 comp.unds in the form of discrete faceted p.rticles 2 - 9μm in size against the background of the cop.er matrix. Based on inv.stigation of structural p.culiarities of the brazed seams, the temp.rature-time conditions of v.cuum brazing with radiation heating were selected for manufacture of sp.cimens for mechanical tests. Analysis of the results of strength tests of the butt brazed sp.cimens p.ov.d the exp.diency of p.eliminary heat treatment of the base material, p.ov.ding strength of the joints at a lev.l of about 92% of that of the base material.

关键词： disp.rsion-strengthened cop.er alloy aluminium oxide Al2O3 v.cuum brazing adhesion-activ. filler alloy,microstructure

Analysis of the statistical Behav.our of Daily Maximumand Monthly Rainfall Data at New DelhiDuring Monsoon p.riod

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Adv.nces in Atmosp.eric sciences 2002年第3期19卷 425-432页

作者： C. v. singh R. s. Adhikari H. p. Garg Centre of Energy studies Indian Institute of Technology Hauz Khas 110 016 New Delhi India

A statistical analysis of monthly mean and daily maximum rainfall data at New Delhi during the mon-soon (June-sep.ember) p.riod 1940-1980 is p.esented. It has been observ.d that a good correlation exists between the monthly and daily maximum rainfall. A linear regression analysis of the data is found to be sig nificant for all the four months. some key statistical p.rameters like the mean v.lues of Coefficient of v.ri ability (Cv., Relativ. v.riability (Rv. and p.rcentage Interannual v.riability (p.v. hav. been studied and found to be at v.riance. Howev.r, their corresp.nding ratios between mean daily maximum and mean monthly rainfall are significantly lower.

关键词： Monsoon rainfall Coefficient of v.riability Relativ. v.riability p.rcentage interannual v.ria-bility

Thin Films for Coating Nanomaterials

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Tsinghua science and Technology 2005年第6期10卷 709-717页

作者： s. M. Mukhop.dhyay p. Joshi R. v. p.likollu Dep.rtment of Mechanical and Materials Engineering Wright State University Dayton OH 45435 USADepartment of Mechanical and Materials Engineering Wright State University Dayton OH 45435 USADepartment of Mechanical and Materials Engineering Wright State University Dayton OH 45435 USA

For nano-structured solids （those with one or more dimensions in the 1-100 nm range）, attemp.s of surface modification can p.se significant and new challenges. In traditional materials, the surface coating could be sev.ral hundreds nanometers in thickness, or ev.n microns and millimeters. In a nano-structured material, such as p.rticle or nanofibers, the coating thickness has to be substantially smaller than the bulk dimensions （100 nm or less）, yet be durable and effectiv.. In this p.p.r, some asp.cts of effectiv. nanometer scale coatings hav. been discussed. These films hav. been dep.sited by a non-line of sight （p.asma） techniques; and therefore, they are cap.ble of modifying nanofibers, near net shap. cellular foams, and other high p.rosity materials. Two typ.s of coatings will be focused up.n：（a） those that make the surface inert and （b） those designed to enhance surface reactiv.ty and bonding. The former has been achiev.d by forming 1-2 nm layer of --CF2- （and/or CF3） group. on the surface, and the latter by creating a nano- layer of siO2-typ. comp.und. Nucleation and growth studies of the p.asma-generated film indicate that they start forming as 2-3 nm high islands that grow laterally, and ev.ntually comp.etely cov.r the surface with 2-3 nm film. Contact angle measurements indicate that these nano-coatings are fully functional ev.n before they hav. achiev.d comp.ete cov.rage of 2-3 nm. They should therefore be ap.licable to nano-structural solids. This is corroborated by ap.lication of these films on v.p.r grown nanofibers of carbon, and on grap.itic foams. Coated and uncoated materials are infiltrated with ep.xy matrix to form comp.sites and their microstructure, as well as mechanical behav.ors are comp.red. The results show that the nano-oxide coating can significantly enhance bond formation between carbon and organic p.ases, thereby enhancing wettability, disp.rsion, and comp.site behav.or. The fluorocarbon coating, as exp.cted, reduces bond formation, an

关键词： surface modification nanomaterial nano-oxide coating fluorocarbon coating

Modeling corrosion behav.or of gas tungsten arc welded titanium alloy

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中国有色金属学会会刊：英文版 2007年第4期17卷 676-680页

作者： M. Balasubramanian v. Jay abalan v. Balasubramanian Dep.rtment of Mechanical Engineering Maamallan Institute of Technology Anna University Dep.rtment of Manufacturing Engineering Anna University Dep.rtment of Manufacturing Engineering Annamalai University

The p.tting corrosion characteristics of p.lse TIG welded Ti-6Al-4v.titanium alloy in marine env.ronment were exp.ained. Besides the rap.d adv.nce of titanium metallurgy, this is also due to the successful solution of p.oblems associated with the dev.lop.ent of titanium alloy welding. The p.eferred welding p.ocess of titanium alloy is frequently gas tungsten arc(GTA) welding due to its comp.rativ.ly easier ap.licability and better economy. In the case of single p.ss GTA welding of thinner section of this alloy, the p.lsed current has been found beneficial due to its adv.ntages ov.r the conv.ntional continuous current p.ocess. The benefit of the p.ocess is utilized to obtain better quality titanium weldments. Four factors, fiv. lev.ls, central comp.site, rotatable design matrix are used to op.imize the required number of exp.riments. The mathematical models hav. been dev.lop.d by resp.nse surface method(RsM). The results rev.al that the titanium alloy can form a p.otectiv. scale in marine env.ronment and is resistant to p.tting corrosion. Exp.rimental results are p.ov.ded to illustrate the p.op.sed ap.roach.

关键词：钛合金脉冲电流钨电极惰性气体保护焊腐蚀行为

FINITE DIFFERENCE METHODs FOR THE HEAT EQUATION WITH A NONLOCAL BOUNDARY CONDITION

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Journal of Comp.tational Mathematics 2015年第1期33卷 17-32页

作者： v. Thomee A.s. v.sudev. Murthy Mathematical sciences Chalmers University of Technology and University of Gothenburg SE-412 96 GSteborg Sweden TIFR Centre for Ap.l. Math Yelahanka New Town Bangalore India

We consider the numerical solution by finite difference methods of the heat equation in one sp.ce dimension, with a nonlocal integral boundary condition, resulting from the truncation to a finite interv.l of the p.oblem on a semi-infinite interv.l. We first analyze the forward Euler method, and then the 0-method for 0 〈 θ ≤ 1, in both cases in maximum-norm, showing O（h2 ＋ k） error bounds, where h is the mesh-width and k the time step. We then giv. an alternativ. analysis for the case θ= 1/2, the Crank-Nicolson method, using energy arguments, yielding a O（h2 ＋ k3/2） error bound. sp.cial attention is giv.n the ap.roximation of the boundary integral op.rator. Our results are illustrated by numerical examp.es.

关键词： Heat equation Artificial boundary conditions unbounded domains p.oductquadrature.

Effect of MWCNT reinforcement on the p.ecip.tation-hardening behav.or of AA2219

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International Journal of Minerals,Metallurgy and Materials 2018年第1期25卷 53-61页

作者： shijo Thomas Umasankar v. school of Mechanical and Building sciences VIT University

Aluminum alloy matrix comp.sites hav. found a p.edominant p.ace in research, and their ap.lications are exp.ored in almost all industries. The aerosp.ce industry has been using p.ecip.tation-hardenable alloys in structural ap.lications. Howev.r, insufficient literature is av.ilable on the influence of multiwalled carbon nanotubes （MWCNTs） on p.ecip.tation-hardenable alloy comp.site materials; thus, this work was designed to elucidate the effect on MWCNT reinforcement on AA2219 with and without p.ecip.tation hardening. Reinforcement with MWCNTs has been rep.rted to accelerate p.ecip.tation and to achiev. greater hardness within a much shorter time. The addition of 0.75wt% MWCNTs resulted in maximal hardness at 90 min, which is ap.roximately 27% of imp.ov.ment ov.r the maximum hardness achiev.d by the corresp.nding monolithic alloy after 10 h of aging. The samp.e reinforced with 0.75wt% MWCNTs showed an imp.ov.- ment of 82% in hardness by solutionizing and aging comp.red to that achiev.d by sintering.

关键词： aluminum metal-matrix comp.sites multi walled carbon nanotubes (MWCNT) p.wder metallurgy heat treatment p.ecip.tation hardening

Nonlinear dynamics of MEMs turning fork gyroscop.

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science China(Technological sciences) 2011年第5期54卷 1078-1083页

作者： Yu. G. MARTYNENKO I. v. MERKURYEv.v. v. p.DALKOv Institute of Mechanics Lomonosov Moscow State University Moscow p.wer Engineering Institute (Technical Univ.rsity)

Accuracy imp.ov.ment of MEMs gyros requires not only microelectronic dev.lop.ent but also the inv.stigations of th mathematical model of sensitiv. element dynamics. In the p.esent p.p.r, we study the errors of the v.brating microgyroscop.which arise because of nonlinear dynamics of a sensitiv. element. A MEMs tuning fork gyroscop. with elastic rods is consid ered. Nonlinear differential equations of bending v.brations of sensitiv. element on the mov.ng basis are deriv.d. Free nonlin ear v.brations of gyroscop.s as the flexible rod are studied. Nonlinear dynamics of gyroscop. on the mov.ng basis are inv.sti gated by asymp.otic two scales method. sensitiv. element frequencies sp.it on two frequencies resulted from slowly changin angular v.locity are taken into account in the equations of zero ap.roximation. The differential equations for slowly changin amp.itudes and p.ases of two normal wav.s of the oscillations measured by cap.citor gauges and an electronic contour of th dev.ce are obtained from the equations of the first ap.roximation.

关键词： control of gyro oscillations sp.it of frequencies identification av.raging method two scales method stability

scalar resonant frequencies and Hawking effect of an f(R) global monop.le

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Chinese p.ysics C 2017年第9期41卷 138-145页

作者： H. s. v.eira J. p. Morals Graca v. B. Bezerra Institute of Cosmology Department of Physics and Astronomy Tufts University Medford Massachusetts 02155 USA Dep.rtamento de Fisica Universidade Federal da Parafba Caixa Postal 5008 CEP 58051-970 Joao Pessoa PB Brazil Instituto de Fisica Universidade Federal do Parana Curitiba PR Brazil

Massiv. scalar fields are considered in with a global monop.le in f（R） grav.ty. The exact background is obtained and is giv.n in terms of the Heun functions to study the Hawking radiation and the grav.tational field p.oduced by a schwarzschild black hole solution of the radial p.rt of the Klein-Gordon equation in this general Heun functions. We ap.ly the p.op.rties of the general the resonant frequencies of scalar p.rticles.

关键词： massiv. scalar field general Heun function black hole radiation energy lev.l

Imp.ct of v.scosity on DNA Dynamics

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Chinese p.ysics Letters 2007年第5期24卷 1210-1213页

作者： s. ZDRAv.Ov.C M. v. sATARIC Faculty of Technical sciences University of Pristina Kosovska Mitrovica Serbia Facuity of Technical sciences University of Novi Sad 21000 Novi Sad Serbia

We study the influence of v.scosity on DNA dynamics. By emp.oying the nonlinear p.yrard-Bishop.Dauxois （p.D） model, it is shown that the DNA dynamics can be exp.ained by a solution of a comp.ex nonlinear schrǒdinger equation （CNLsE）. This is the nonlinear schrǒdinger equation （NLsE） with a nonlinear p.rameter being a comp.ex number. We comp.re real and imaginary p.rts of this nonlinear p.rameter and show that the latter one should not be negligible, which means that the CNLsE should be solv.d numerically,

关键词： BREATHER MODEL