C_(60)取向驰豫的极限动力学研究

用极限动力学模型研究了C60 分子在有序 -无序相变和玻璃态相变间的驰豫行为 .结果表明 :KWW方程的非指数因子 β与双取向态间的能极差有关 ,则其值与实验结果相符 ;导出了 38°取向态的密度表达式 ,计算结果在 85K和 90K与实验值吻合 ;讨论了双能级的C60 分子从非平衡态到平衡态的驰豫行为 ,其总的驰豫时间决定于其中一个较短的驰豫时间 ,伸展指数形式保持不变 .在 85K以下 ,具有较长驰豫时间的近邻分子会咬合跳跃单元以冻结取向态间的比例变化 .

波尔兹曼方程到欧拉方程黎曼解的流体动力学极限

文章回顾了Huang等关于波尔兹曼方程到欧拉方程一般黎曼解的流体动力学极限.黎曼解由激波、稀疏波和接触间断波的任意线性组合复合而成.通过引进两类双曲波并结合尺度变换及精细的能量估计方法,成功证明了以上流体动力学极限并得到了收敛速率.

二维玻尔兹曼方程的不可压缩极限

本文拟研究二维空间区域上玻尔兹曼方程的不可压缩Navier-Stokes-Fourier极限。由于有界区域上的玻尔兹曼方程的解没有高阶正则性,故本文拟采用最新的L2-L∞方法并结合解的宏观部分的L4估计,来获取余项方程线性部分的一致上界估计,进而通过迭代方法得到余项方程解的存在性,最后得出原玻尔兹曼方程解的存在性和收敛极限。

无序材料在液-玻相变区域的时间温度关系

运用极限动力学模型和Adam-Gibbs理论,由β的温度关系容易得出玻璃化液体的VFI方程.根据关联区域内构型熵S_c的概念及其与弛豫时间的基本关系式,可得出伸展因子与构型熵的关系式;描述了液-玻相变温区构型熵的温度变化规律及其与等压热容的关系.

轿车轮胎道路试验客观评价指标及方法概述

本文全面阐述在进行轮胎的对比评价试验和认证试验时,轿车轮胎的声学性能、滚动阻力、动力学极限和耐磨性等评价指标及相应的评价方法,为不同轮胎产品间的对比,以及与轮胎相关的整车舒适性、经济性、动力学性能和可靠性的提高提供参考。

Molecular dynamics analysis on bending mechanical behavior of alumina nanowires at different loading rates

The molecular dynamics(MD)model ofα-Al_(2)O_(3) nanowires in bending is established by using LAMMPS to calculate the atomic stress and strain at different loading rates in order to study the effect of loading rate on the bending mechanical behaviors of theα-Al_(2)O_(3) nanowires.Research results show that the maximum surface stress−rotation angle curves ofα-Al_(2)O_(3) nanowires at different loading rates are all divided into three stages of elastic deformation,plastic deformation and failure,where the elastic limit point can be determined by the curve symmetry during loading and unloading cycle.The loading rate has great influence on the plastic deformation but little on the elastic modulus ofα-Al_(2)O_(3) nanowires.When the loading rate is increased,the plastic deformation stage is shortened and the material is easier to fail in brittle fracture.Therefore,the elastic limit and the strength limit(determined by the direct and indirect MD simulation methods)are closer to each other.The MD simulation result ofα-Al_(2)O_(3) nanowires is verified to be valid by the good agreement with the improved loop test results.The direct MD method becomes an effective way to determine the elastic limit and the strength limit of nanoscale whiskers failed in brittle or ductile fracture at arbitrary loading rate.

Identifying Diffusion Limiting Current to Unravel the Intrinsic Kinetics of Electrode Reactions Affected by Mass Transfer at Rotating Disk Electrode

Rotating disk electrode systems are widely used to study the kinetics of electrocatalytic reactions that may suffer from insufficient mass transfer of the reactants.Kinetic current density at certain overpotential calculated by the Koutecky-Levich equation is commonly used as the metrics to evaluate the activity of electrocatalysts.However,it is frequently found that the diffusion limiting current density is not correctly identified in the literatures.Instead of kinetic current density,the measured current density normalized by diffusion limiting current density(j/jL)has also been frequently under circumstance where its validity is not justified.By taking oxygen reduction reaction/hydrogen oxidation reaction/hydrogen evolution reaction as examples,we demonstrate that identifying the actual diffusion limiting current density for the same reaction under otherwise identical conditions from the experimental data is essential to accurately deduce kinetic current density.Our analysis reveals that j/jLis a rough activity metric which can only be used to qualitatively compare the activity trend under conditions that the mass transfer conditions and the roughness factor of the electrode are exactly the same.In addition,if one wants to use j/jLto compare the intrinsic activity,the concentration overpotential should be eliminated.

Mixed Quark-Gluon Condensate Beyond Chiral Limit

Using the Dyson-Schwinger equation and perturbation theory, we calculate the mixed quark-gluon condensates in the chiral limit and in the case of nonzero quark current mass for the light quark u/d and strange quark s. The results show that the mixed quark-gluon condensate will decrease when the quark mass increases. For the quark with zero mass, we obtain mo2 = g（qσuvGuvq）/（qq） 0.68 GeV2, which is in good agreement with the QCD sum rules estimate mo2=（0.8± 0.2） GeV2.

A Note on Fundamental Limit of Quantum Dynamics Rate

The unified bound on the fundamental limit of quantum dynamics rate, as quietly recently obtainedby Levitin and Toffoli [Phys.Rev.Lett.103 (2009) 160502], is improved and refined.The improvement may bearbitrarily large in certain cases.In particular, this puts a limit on the operation rate of quantum gates allowed byquantum mechanics.

Determination of metformin in diabetic rat plasma by an improved ion-pair high-performance liquid chromatography: application to a pharmacokinetic study

An efficient and sensitive ion-pair HPLC-UV method using atenolol as internal standard （IS） was developed and validated for the determination of metformin in the plasma of diabetic rats. Plasma samples were deproteinated with 10% （v/v） perchloric acid. Separation was achieved on a UltimateTM AQ-C18 column （250 mm×4.6 mm, 5 μm） with a mobile phase （pH 5.05） composed of acetonitrile-water （31：69, v/v, containing 0.002 M sodium dodecyl sulfate, 0.0125 M potassium dihydrogen phosphate, 0.015 M triethylamine） at a flow rate of 1.0 mL/min. The calibration curve was linear （r〉0.994） between 7.5 and 4000 ng/mL. The lower limit of quantification （LLOQ） was 7.5 ng/mL. The precision was validated and the relative standard deviation was in the range of 1.87% to 15.70%; the accuracy was between 93.98%-106.89%. The mean recoveries were 95.40% and 95.31% for metformin and IS, respectively. The relative error （RE） of stability at different storage conditions was within ±9.00%. This method was used to determine the concentration-time profile of metformin in diabetic rat plasma following an oral administration of metformin at the dose of 10 mg/kg. Our results indicated that ion-pair HPLC-UV method using UltimateTM AQ-C18 column was effective for the pharmacokinetic studies of high polarity compounds like metformin.

Super-resolution imaging and tracking of TGF-β receptor II on living cells

Single-particle tracking photoactivated local- ization microscopy （sptPALM） has recently emerged as a powerful tool for high-density imaging and tracking of individual molecules in living cells. In this work, we have monitored and compared the diffusion dynamics of TGF-β type II receptor （TβRII） at high expression level using both traditional single-particle tracking （SPT） and sptPALM. The ligand-induced aggregation of TβRII oligomers was further indicated by sptPALM. Due to the capacity of distinguishing and tracking single molecules within diffraction limit, sptPALM outperforms traditional SPT by providing more accurate biophysical information,

Mean field limit of a dynamical model of polymer systems

This paper provides a mathematically rigorous foundation for self-consistent mean field theory of the polymeric physics. We study a new model for dynamics of mono-polymer systems. Every polymer is regarded as a string of points which are moving randomly as Brownian motions and under elastic forces. Every two points on the same string or on two different strings also interact under a pairwise potential V. The dynamics of the system is described by a system of N coupled stochastic partial differential equations （SPDEs）. We show that the mean field limit as N -＋ c~ of the system is a self-consistent McKean-Vlasov type equation, under suitable assumptions on the initial and boundary conditions and regularity of V. We also prove that both the SPDE system of the polymers and the mean field limit equation are well-posed.