共查询到19条相似文献,搜索用时 125 毫秒
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利用分子动力学方法,模拟了5000个表面轻微摩擦(μ=1×10-4)的弹性颗粒组成的体系在各向同性压缩过程中的堵塞(jamming)现象,研究了颗粒体系对边壁压强P和对关联函数第一个峰的高度g1随体积分数φ的变化规律. 结果表明,当体系的体积分数φ大于临界体积分数φc时,P(φ)曲线表现出明显的黏滑(stick-slip)行为,法向的力-力关联函数、切向的力-力关联函数和颗粒的位置-位置关联函数同时发生跳变,说明宏观黏滑现象源自内部的力位形和几何构形的调整. 体系在φ缓慢增大过程中得到了不同的堵塞态,随着颗粒粒径的缓慢减小,体系得以松弛(unjamming),实现松弛过程并得到相应的φc. 对于不同堵塞态,其边壁压强P与φ-φc遵从幂律标度P∝(φ-φc)0.964.
关键词:
堵塞相图
对关联函数
力-力关联函数
标度规律 相似文献
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本文在少粒子体系波函数数值解的基础上讨论了强磁场中二维电子气的二体关联函数.在数值计算的意义上给出了有限集团体系二体关联函数的计算公式.
关键词: 相似文献
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The Green—Kubo time correlation function for the shear viscosity in liquid CS2 has been simulated by molecular dynamics at several thermodynamic state points. The breakdown of this function into its kinetic and potential contributions as well as the cross-term between the two has been performed. Intermolecular interactions were obtained from a three-centre atom—atom (12/6) Lennard-Jones potential model. The time correlation functions for the potential part of the shear viscosity contain component two-, three- and four-body terms that were explicitly evaluated to show that they partially cancel each other at short times but at long times, they exhibit approximately exponential decays with magnitude ratios corresponding to nearly perfect cancellation. In this respect, the correlation functions for CS2 resemble those of liquid argon. In addition, the microscopic stress tensor was separated into the portions arising from the repulsive and attractive branches of the Lennard-Jones model. This split gives rise to positive autocorrelation functions involving the repulsive and the attractive forces plus a negative cross-correlation function between the two that partially cancels the contributions of the autocorrelation functions. It is argued that the breakdown of the potential part of the shear viscosity into its component parts is helpful in elucidating the role of molecular re-orientation in determining the separate short and long time behaviours of this time correlation function for liquids such as CS2. 相似文献
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The phase transition mechanism in squaric acid is reviewed from the viewpoint of the pressure dependence of the O—H—O bond length (2R). The two-dimensional pressure effect on Tc is extracted from the hydrostatic pressure behaviour by taking account of the uniaxial stress applied perpendicular to the layer planes. The result shows that if 2R(H2SQ) is stretched to 2R(D2SQ) the phase transition temperature 7H c of H2SQ coincides with TD c of D2SQ. This result supports the suggestion that the phase transition mechanism is of the order-disorder type. 相似文献
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The negative glow plasma has been found nearly field free in axial direction. Therefore plasma electrons in the stationary glow can thermalize down to the temperature of the neutral gas, whenever their diffusion—and recombination—lifetime is high enough. Applying Boltzmann's equation to this problem, the conditions of thermalization of plasma electrons are derived as a function of the outer parameters of the plasma: vessel diameter 2R, neutral gas pressurep and longitudinal magnetic fieldB. — If plasma electrons have a too short diffusion—and recombination—lifetime to be in thermal equilibrium with the neutral gas, the electron energy increases. For this case the distribution function of plasma electrons is derived using Boltzmann's equation. Approximating the calculated energy distribution by a Maxwellian distribution function, the electron temperature in the glow is obtained as a function of the parameters:R, p, B. OurT e -measurements carried out in the H2- and He-glows of different tube diameters, neutral gas pressures and magnetic fields agree closely with the theoretical results. TheT e -measurements have been performed with Langmuir probes and by the method of reversal of the radial ambipolar electric field in a longitudinal magnetic field. 相似文献
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W.H. Jeu de 《Molecular physics》2013,111(3):573-576
The I.R. and Raman bandwidths of the v(≡C-H) and v(C≡C) stretching modes of 1-hexyne and 1-decyne have been measured in dilute solutions in n C7H16 and CCl4 as a function of temperature. The I.R. spectrum is used, by comparison with the Raman spectrum, to verify the generally assumed absence of correlation between the rotational and vibrational relaxations. The important experimental findings is the opposite effect of temperature on the isotropic Raman linewidths of the two modes. The v(≡C-H) mode broadens with decreasing temperature and this is interpreted in a qualitative way by the isolated binary collision model of Fisher and Laubereau and the hydrodynamic model of Oxtoby. On the contrary, these models are unable to interpret the linewidth of the v(C≡C) mode. A possible explanation lies in an intramolecular energy relaxation between Fermi resonance levels. Finally, application of the Kubo stochastic line shape theory to the vibrational correlation function of the v(≡C-H) mode shows that the modulation is fast in n C7H16 specially at high temperature and intermediate between fast and slow limits in CCl4. 相似文献
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采用1948—2005年NCEP/NCAR全球温度资料构建温度关联矩阵,研究表明:为了滤除关联“噪声”,采用信度为001的统计检验是比较合适的.对日温度序列做step=5d,10d,…的滑动平均继而构建关联矩阵发现:365—730d可能是温度场时间尺度上的一个转折点;全球平均关联系数Cglobal的总体变化趋势是随step的增加而增大,但趋势逐渐变缓;相关系数绝对值大于03的正负强关联点对数也随之增加;位于赤道东太平洋海域的正关联中心(区域Ⅰ)(1625°W—775°E,75°N—125°S)和位于北太平洋海域的负关联中心(区域Ⅱ)(1575°W—325°E,275°—475°N )是值得重点关注的两个区域,二者之间存在较强的负相关;取长度为10 a滑动窗口研究Cglobal随时间的演变特征发现,Cglobal在1981—1987a之间发生了明显的跃变,并且这一跃变可能是年代际尺度上的行为;区域Ⅰ和Ⅱ对这一跃变也有清晰的反映,区域Ⅱ的跃变略滞后于区域Ⅰ;与此同时北太平洋海域关联系数的最小值点随时间演变还出现了明显的“位移”.
关键词:
温度场
关联矩阵
时间尺度
跃变 相似文献
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The lowest six momenta of the spectral function of the single-band s—d model in the low electron-concentration limit are expressed in terms of spin correlation functions. Using them, nontrivial information on electron quasiparticle subbands in the strong scattering régime is deduced. The temperature dependence and overall form of the spectrum is discussed. Comparison with experiment on CdCr2Se4 is made. 相似文献