共查询到20条相似文献,搜索用时 13 毫秒
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The evolution of elastic-plastic shock compression waves in a VT6 titanium alloy is measured at a distance of 0.16–17 mm at room temperature and 600°C. The results of measuring the decay of an elastic precursors and the compression rate in a plastic shock wave are used to determine the temperature–rate dependences of the flow stress in the strain-rate range 103–107s–1. New data for the spall strength of the alloy at normal and elevated temperatures are obtained. 相似文献
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Available data on the temperature and concentration dependence of critical resolved shear stress (CRSS) of KCl–KBr solid-solution crystals containing 9, 17, 27 and 45?mol% KBr in the temperature range 77–230?K have been analyzed within the framework of the kink-pair nucleation model of plastic flow in solid- solution crystals. It is found that CRSS τ decreases with increasing temperature T in accordance with the model relation lnτ?=?A???BT, where A and B are positive constants. The CRSS τ at a given temperature depends on solute concentration c as τ?∝?cp , where exponent p has a value between 0.33 and 0.57 as temperature T rises from 0 to 230?K. The model parameter W o, i.e. binding energy between the edge-dislocation segment L o involved in the unit activation process and the solute atoms close to it (T?→?0?K), which is inversely proportional to B, increases with solute concentration c monotonically as W o?∝?c 0.33 up to a critical value c m?=?35?mol% KBr, which is in reasonable agreement with the model prediction W o?∝?c 0.25. However, W o decreases with an increase in c beyond c m, which indicates somewhat ordered distribution of solute in the host lattice of concentrated KCl–KBr solid solutions with c?>?c m. 相似文献
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The deformation behaviour of an α + β Ti–6Al–4V (wt.%) alloy was investigated during in situ deformation inside a scanning electron microscopy (SEM). Tensile experiments were performed at 296 and 728 K (~0.4Tm), while a tensile-creep experiment was performed at 728 K and 310 MPa (σ/σys = 0.74). The active deformation systems were identified using electron backscattered diffraction-based slip-trace analysis and SEM images of the specimen surface. The distribution of the active deformation systems varied as a function of temperature. Basal slip deformation played a major role in the tensile deformation behaviour, and the relative activity of basal slip increased with increasing temperature. For the 296 K tension deformation, basal slip was less active than prismatic slip, whereas this was reversed at 728 K. Twinning was observed in both the 296 and 728 K tension experiments; however, no more than 4% of the total deformation systems observed was twins. The tension-creep experiment revealed no slip traces, however grain boundary ledge formation was observed, suggesting that grain boundary sliding was an active deformation mechanism. The results of this work were compared with those from previous studies on commercially pure Ti, Ti–5Al–2.5Sn (wt.%) and Ti–8Al–1Mo–1V (wt.%), and the effects of alloying on the deformation behaviour are discussed. The relative amount of basal slip activity increased with increasing Al content. 相似文献
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The temperature dependences of the lattice spacing and thermal expansion coefficient for five hexaborides MB6 (M=Ce, Pr, Nd, Gd, and Tb) are experimentally investigated. 相似文献
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The electrical conductances of very dilute solutions of the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4] and 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] in the low-permittivity solvent dichloromethane have been measured in the temperature range from 278.15 to 303.15 K at 5 K intervals. The data was analyzed assuming the possible presence of contact (CIP) and solvent-separated (SSIP) ion pairs in the solution on the basis of lcCM model to obtain ionic association constants, K A, and the limiting molar conductivities, Λo, of these electrolytes. The examined ionic liquids are strongly associated in dichloromethane over the whole temperature range. From the temperature dependence of the limiting molar conductivities, the Eyring’s activation enthalpy of charge transport was determined. The thermodynamic functions such as Gibbs energy, entropy, and enthalpy of the process of ion pair formation were calculated from the temperature dependence of the association constants. 相似文献
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We have determined the lattice parameters of perdeuterated melamine, C3N6D6, as a function of temperature (4.2–320?K) close to atmospheric pressure and as a function of pressure (0–5?GPa) at room temperature, using time-of-flight neutron powder diffraction methods. Our observations confirm that the ambient-pressure P21/a structure persists throughout this range of P and T. Both the thermal expansion and the compressibility are highly anisotropic; the principal directions of greatest thermal expansion and greatest compressibility are roughly perpendicular to the corrugated sheets of H-bonded melamine molecules that form the main structural motif. Complementary ab initio calculations (van der Waals corrected Density Functional Theory) provide an estimate of how the inter- and intra-molecular geometry may alter as a function pressure in the athermal limit. 相似文献
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Bhasker Gahtori S.K. Agarwal Tirthankar Chakraborty Ashok Rao Y.-K. Kuo 《Physica C: Superconductivity and its Applications》2009,469(1):27-29
In this communication we present some theoretical results of specific heat and thermoelectric power of the superconductor GdBa2(Cu1?xMnx)3O7?δ (for x ? 0.02). A model based on separate electronic and phononic contributions is used for the interpretation of the specific heat data while a narrow band model is used for the analysis of thermoelectric power. On the basis of these models two main conclusions have been drawn about the relative effects of different Mn contents: (1) the observed fluctuation effects near Tc whose strength increases with increasing Mn content and (2) Mn produces mainly electronic effects for lower Mn contents, while for higher doping levels (x > 0.0075) Mn predominantly causes carrier-Mn scattering process. 相似文献
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Ph. Gavillet R. Armenteros M. Aguilar-Benítez M. Mazzucato C. Dionisi 《Zeitschrift fur Physik C Particles and Fields》1982,16(2):119-128
Evidence is presented for a newK * \(\bar K\) +c.c. resonance with a mass of (1,526±6) MeV, a width of (107±15) MeV and quantum numbersIJ PC=01++. We call itD′ meson. Initially it is observed as aK * \(\bar K\) +c.c. enhancement in the reactionsK ? p→(K s 0 K ±π?)Λ at 4.2 GeV/c. The isospin assignmentI=0 comes from its further observation in the reactionsK ? p→(K s 0 K ±π?)Σ 0 andK ? p→(K s 0 K ±π?)Σ(1,385)0 but not inK ? p→(K + K ?π?)Σ+ orK ? p→(K s 0 K ±π?)Σ(1,385)+. A maximum likelihood analysis of the (K \(\bar K\) π) decay Dalitz plots in the reactionsK ? p→(K s 0 K ±π?) determines theJ PC of theD′ meson to be 1++. A satisfactorySU(3) fit is obtained to a 1++ nonet composed of theI-1A 1, theI=1/2Q A with theD(1,285) and theD′(1,526) as theI=0 members having a mixing angle close to the magic one. 相似文献
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B. Baatar A. S. Galoyan E. N. Kladnitskaya Lj. Simic V. V. Uzhinsky 《Physics of Atomic Nuclei》2006,69(6):956-970
Experiemntal data obtained by using the 2-m propane bubble chamber of the Joint Institute for Nuclear Research (JINR, Dubna) are used to study the effect collision centrality on the spectra of Λ hyperons and K S 0 mesons produced in carbon-carbon interactions at 4.2 A GeV/c. The multiplicity of participant protons having momenta in excess of 300 MeV/c is taken to be a measure of collision centrality. The features of pions and protons accompanying strange-particle production are also presented. The experimental data in question are compared with the prediction of a modified version of the FRITIOF model. It is shown that strange particles are predominantly produced in central and semicentral collisions. The average kinematical features of K S 0 mesons are found to be indepedent of collision centrality. At the same time, the average transverse momentum of Λ hyperons and the average value of their emission angle increase slowly with increasing degree of collision centrality. The anisotropy of the angular distributions of both Λ hypersons and K S/0 mesons in the c.m. frame of nucleon-nucleon collisions decreases with increasing collision centrality. The average transverse momentum of K S 0 mesons is approximately 1.6 times higher than the average transverse momentum of π ? mesons. 相似文献
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Aaltonen T Álvarez González B Amerio S Amidei D Anastassov A Annovi A Antos J Apollinari G Appel JA Apresyan A Arisawa T Artikov A Asaadi J Ashmanskas W Auerbach B Aurisano A Azfar F Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Barria P Bartos P Bauce M Bauer G Bedeschi F Beecher D Behari S Bellettini G Bellinger J Benjamin D Beretvas A Bhatti A Binkley M Bisello D Bizjak I Bland KR Blumenfeld B Bocci A Bodek A Bortoletto D Boudreau J Boveia A Brau B Brigliadori L Brisuda A Bromberg C 《Physical review letters》2011,106(19):191801
We present a search for a new particle T' decaying to top quark via T' → t + X, where X is an invisible particle. In a data sample with 4.8 fb(-1) of integrated luminosity collected by the CDF II detector at Fermilab in pp collisions with √s = 1.96 TeV, we search for pair production of T' in the lepton + jets channel, pp → tt + X + X → ?νbqq'b + X + X. We interpret our results primarily in terms of a model where T' are exotic fourth generation quarks and X are dark matter particles. Current direct and indirect bounds on such exotic quarks restrict their masses to be between 300 and 600 GeV/c2, the dark matter particle mass being anywhere below m(T'). The data are consistent with standard model expectations, and we set 95% confidence level limits on the generic production of T'T' → tt + X + X. For the dark matter model we exclude T' at 95% confidence level up to m(T') = 360 GeV/c2 for m(X) ≤ 100 GeV/c2. 相似文献
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Based on results obtained with event generators we have launched the core-corona model. It describes in a simplified way but quite successfully the centrality dependence of multiplicity and 〈p t 〉 of identified particles observed in heavy-ion reactions at beam energies between $\sqrt s = 17$ and 200 GeV. Also the centrality dependence of the elliptic flow, υ 2, for all charged and identified particles could be explained in this model. Here we extend this analysis and study the centrality dependence of single-particle spectra of K ? and $\bar p$ measured by the PHENIX, STAR, and BRAHMS Collaborations. We find that also for these particles the analysis of the spectra in the core-corona model suffers from differences in the data published by the different experimental groups, notably for the pp collisions. As for protons and K +, for each experience the data agree well with the prediction of the core-corona model but the values of the two necessary parameters depend on the experiments. We show as well that the average momentum as a function of the centrality depends in a very sensitive way on the particle species and may be quite different for particles which have about the same mass. Therefore the idea to interpret this centrality dependence as a consequence of a collective expansion of the system, as done in blast way fits, may be premature. 相似文献
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In this study we use the spectral relaxation method (SRM) for the solution of the steady von Kármán flow of a Reiner-Rivlin fluid with Joule heating and viscous dissipation. The spectral relaxation method is a new Chebyshev spectral collocation based iteration method that is developed from the Gauss-Seidel idea of decoupling systems of equations. In this work, we investigate the applicability of the method in solving strongly nonlinear boundary value problems of von Kármán flow type. The SRM results are validated against previous results present in the literature and with those obtained using the bvp4c, a MATLAB inbuilt routine for solving boundary value problems. The study highlights the accuracy and efficiency of the proposed SRM method in solving highly nonlinear boundary layer type equations. 相似文献
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Aaltonen T Adelman J Alvarez González B Amerio S Amidei D Anastassov A Annovi A Antos J Apollinari G Appel J Apresyan A Arisawa T Artikov A Asaadi J Ashmanskas W Attal A Aurisano A Azfar F Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Barria P Bartos P Bauer G Beauchemin PH Bedeschi F Beecher D Behari S Bellettini G Bellinger J Benjamin D Beretvas A Bhatti A Binkley M Bisello D Bizjak I Blair RE Blocker C Blumenfeld B Bocci A Bodek A Boisvert V Bortoletto D Boudreau J Boveia A Brau B 《Physical review letters》2010,105(19):191801
We present a search for supersymmetric neutrino ν production using the Tevatron pp collision data collected with the CDF II detector and corresponding to an integrated luminosity of 1 fb-1. We focus on the scenarios predicted by the R-parity violating (RPV) supersymmetric models in which sneutrinos decay to two charged leptons of different flavor. With the data consistent with the standard model expectations, we set upper limits on σ(pp→ν)×BR(ν→eμ,μτ,eτ) and use these results to constrain the RPV couplings as a function of the sneutrino mass. 相似文献
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The electron paramagnetic resonance g factors g i (i?=?x, y, z) of two rhombic Cu2+ centers, Cu2+(II) and Cu2+(III), in K2Zn1?x Cu x F4 crystals found at low temperature are calculated from the complete diagonalization (of energy matrix) method based on the cluster approach. The calculations show that the ground state wave function of the two rhombically compressed Cu2+ centers is $ | {d_{{z^{2} }} }\!\!> $ with a small admixture of $ | {d_{{x^{2} - y^{2} }} } \!\!> $ . The rhombic distortions for both Cu2+ centers are obtained from the calculations. The results are discussed. 相似文献
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Wenping Deng Didier Mondelain Franck Thibault Arlan W. Mantz 《Journal of Molecular Spectroscopy》2009,256(1):102-108
Helium broadening coefficients for the R(10) and the P(2) lines in the ν3 band of 13CO2 have been measured over a large range of temperature (70 K-300 K). Helium pressure shifts for the R(10) line at several temperatures between 100 K and 300 K have also been determined. These measurements were obtained with a cold Herriott cell, using the collisional cooling technique to reach the lowest temperatures. They provide an extended dataset for the temperature dependence of widths and shifts. This dataset was compared to theoretical He-broadening coefficients combining quantum scattering calculations and the latest potential energy surface for the system He-CO2 from Korona et al. [T. Korona, R. Moszynski, F. Thibault, J.-M. Maunay, B. Bussery-Honvault, J. Boissoles, P.E.S. Wormer, J. Chem. Phys. 115 (2001) 3074-3084]. 相似文献