Molecular dynamics simulation of adhesion forces in a dipalmitoylphosphatidylcholine membrane

Adhesion forces of Dipalmitoylphosphatidylcholine ( DPPC) membrane in the gel phase are investigated by molecular dynamics ( MD) simulation. In the simulations, individual DPPC molecules are pulled out of DPPC membranes with different rates and we get the maximum adhesion forces of DPPC membrane. We find that the maximum adhesion forces increase with pull rate, from about 400 to 700 pN when pull rates are from 0.001 to 0.03 nm/ps. We analyze the relationship between pull rate and adhesion forces of different origins using Brownian dynamics and notice that viscosity of solvent plays an important role in adhesion forces. Then we simulate the motion of a single DPPC molecule in solvent and it elucidates that the maximum drag force is almost linear with respect to the pull rate. We use Stokes' relation to describe the motion of a single DPPC molecule and deduce the effective length of a DPPC molecule. Conformational analyses indicate that the free energy variation of a DPPC molecule inside and outside of the DPPC membrane is an essential part of adhesion energy.

模拟MEMS中气体流动的工具——信息保存法

MEMS中气体流动因特征尺度小而是稀薄气体的领域,本文首先介绍处理低速稀薄气体流动的一些方法:线化Boltzmann方程,Lattice Boltzmann方法,加滑移边界的Navier-Stoks方程,以及DSMC方法,并讨论它们模拟MEMS中过渡领域低速流动所遇到的困难。信息保存法克服了流速低使得信息噪声比小引起统计模拟的困难,已成功模拟了一些一维和二维问题。MEMS中流速低和大的长宽比的特点还引起出入口边界条件相互影响需要协调的问题,通过微槽道流动的算例,在模拟中采用守恒形式的质量守恒方程和超松弛法成功地解决了这一问题。处理有温度变化的MEMS流动问题和跨越领域的混合算法是重要的问题,本文用信息保存法也进行了有益的尝试。

分岔管路内油水两相流动的研究

分岔管路大量存在于石油行业的输送管网中,油水两相流在分岔管路内的流动特性将对流程控制、动力匹配及下游处理设施产生显著的影响。对分岔管路内的油水两相流动进行了实验研究,采用不可压缩Nayier-Stokes方程结合双流体模型和混合k-ε模型对分岔管路内的油水两相流动进行了数值模拟,获得了初步的结果。计算表明,数值模拟能够较好地反映分岔管路内的油水两相流动,为工程设计提供参考。

理性力学基础

der="0" alt="" hspace="8" width="300" height="400" align="left" />《理性力学基础》为《中国科学院研究生教学丛书》之一。
    《理性力学基础》系统地介绍了理性力学的主要科学体系和基本理论。《理性力学基础》由四部分，共十五章组成。第一部分综合介绍了理性力学的科学意义、方法和特点，从理性力学角度概括论述变形几何学与运动学、力学基本定律与场方程以及本构方程的一般原理。着重阐明张量和场方程的时空无差异原理，以及本构方程所应遵循的客观性原理。第二部分着重介绍简单物质的理论体系。作为典型范例进一步阐明弹性物质和简单流体的本构方程以及弹性体有限变形边值问题的分析方法。第三部分详细介绍黏弹性物质、弹塑性物质及晶体塑性的基本理论。第四部分主要介绍含缺陷物质的本构理论。
    《理性力学基础》可作为力学、应用数学、理论物理等专业的研究生教材，也可供力学工作者及高等院校力学专业教师参考。

目录 

第一章 绪论
1·1 理性力学目的和意义
1·2 理性力学的特点与体系
1·3 理性力学的方法
1·4 符号
第二章 变形几何学和运动学
2·1 直角坐标系的张量
2·2 物体的构形与运动
2·3 变形梯度
2·4 应变度量和面元、体元变形
2·5 应变率
第三章 基本定律与场方程
3·1 质量守恒定律
3·2 应力原理与动量守恒定律
3·3 能量守恒定律和熵定律
3·4 功共轭与应力度量
3·5 场方程
3·6 随体坐标系
第四章 本构方程的一般原理
4·1 时空系的变换
4·2 基本定律的客观性
4·3 本构方程的一般原理
第五章 简单物质
5·1 张量函数
5·2 张量函数表示定理
5·3 简单物质的本构方程
5·4 本构方程的简化形式
5·5 各向同性物质
5·6 简单固体
5·7 简单流体和流晶
5·8 内部约束
5·9 特殊类型物质
5·10 衰退记忆
第六章 弹性物质
6·1 弹性物质的本构方程
6·2 物质对称性
6·3 各向同性弹性固体
6·4 超弹性物质
6·5 各向同性超弹性物质
6·6 主轴表示
6·7 储能函数表示式
6·8 二次弹性
6·9 均匀变形场
6·10 储能函数的实验确定
第七章 弹性体有限变形边值问题
7·1 边值问题的提法
7·2 若干典型问题
7·3 平面应变问题
7·4 不可压缩各向同性弹性体
第八章 简单流体
8·1 直线流动
8·2 曲线流动
8·3 伸长历史恒定运动
8·4 定常测黏流动
8·5 Poiseuille流动
8·6 Couette流动
8·7 圆锥-平板流动
8·8 端部正应力效应
8·9 Stokes流体测黏流动
8·10 定常拉伸流动
第九章 黏弹性物质
9·1 线性黏弹性理论
9·2 非线性黏弹性固体
9·3 本构泛函展开
9·4 非线性黏弹性流体
第十章 弹塑性物质
10·1 微小变形塑性理论
10·2 张量的时间导数
10·3 有限塑性变形的本构方程
10·4 塑性大变形基本方程
10·5 Drucker公设与有限塑性变形
第十一章 晶体塑性理论
11·1 晶体塑性变形运动学
11·2 硬化规律
11·3 硬化系数表示式
11·4 晶体塑性本构关系
11·5 滑移剪切率γ(α)的存在性与惟一性
11·6 率相关流动规律
第十二章 缺陷连续统的线性理论
12·1 张量场的微分运算
12·2 协调条件
12·3 缺陷的几何意义
12·4 位错弹性理论
12·5 位错塑性理论
12·6 一般缺陷塑性理论
12·7 晶体塑性位错理论
12·8 Nye张量及缺陷塑性理论小结
12·9 位错塑性理论二维公式及算例
第十三章 非黎曼几何及流形简介
13·1 Euler空间张量场的绝对微分
13·2 曲率张量
13·3 线性空间
13·4 仿射联络空间
13·5 非完整变换
13·6 拓扑空间
13·7 微分流形
第十四章 缺陷连续统的非线性理论
14·1 非Niemann物质流形的构造
14·2 缺陷的几何意义
14·3 缺陷连续统的弹性理论
14·4 缺陷连续统的塑性理论
14·5 晶体塑性位错理论
第十五章 理性力学若干应用
15·1 有限变形的精确描述
15·2 曲线坐标的相应公式
15·3 本构方程的客观性原理
15·4 物质对称性
15·5 主轴法
15·6 客观应力率
附录 曲线坐标
1 基向量与度量张量
2 逆变导数
3 应力张
4 运动方程

 

Numerical study on heavy rigid particle motion in a plane wake flow by spectral element method

Experimental particle dispersion patterns in a plane wake flow at a high Reynolds number have been predicted numerically by discrete vortex method (Phys. Fluids A 1992; 4:2244-2251; Int. J. Multiphase Flow 2000; 26:1583-1607). To address the particle motion at a moderate Reynolds number, spectral element method is employed to provide an instantaneous wake flow field for particle dynamics equations, which are solved to make a detail classification of the patterns in relation to the Stokes and Froude numbers. It is found that particle motion features only depend on the Stokes number at a high Froude number and depend on both numbers at a low Froude number. A ratio of the Stokes number to squared Froude number is introduced and threshold values of this parameter are evaluated that delineate the different regions of particle behavior. The parameter describes approximately the gravitational settling velocity divided by the characteristic velocity of wake flow. In order to present effects of particle density but preserve rigid sphere, hollow sphere particle dynamics in the plane wake flow is investigated. The evolution of hollow particle motion patterns for the increase of equivalent particle density corresponds to that of solid particle motion patterns for the decrease of particle size. Although the thresholds change a little, the parameter can still make a good qualitative classification of particle motion patterns as the inner diameter changes.

SPT方法在纳米粒子布朗运动观测中的应用

纳米粒子布朗运动特性对Micro-/Nano-PIV的使用和与粒子相关的物理现象的研究有重要意义.观测了200nm荧光粒子的布朗运动,利用单粒子追踪(SPT)算法和自编程序处理图像,获得粒子的均方位移,计算了实验扩散系数D_(exp)为2.09×10~(-12) m~2/s.与Stokes-Einstein公式估计的理论扩散系数D_(th)相比,二者量阶一致,但实验扩散系数的数值偏小约5%.对相关的实验误差进行了分析.

Large-eddy simulation of turbulent collision of heavy particles in isotropic turbulence

The small-scale motions relevant to the collision of heavy particles represent a general challenge to the conventional large-eddy simulation (LES) of turbulent particle-laden flows. As a first step toward addressing this challenge, we examine the capability of the LES method with an eddy viscosity subgrid scale (SGS) model to predict the collision-related statistics such as the particle radial distribution function at contact, the radial relative velocity at contact, and the collision rate for a wide range of particle Stokes numbers. Data from direct numerical simulation (DNS) are used as a benchmark to evaluate the LES using both a priori and a posteriori tests. It is shown that, without the SGS motions, LES cannot accurately predict the particle-pair statistics for heavy particles with small and intermediate Stokes numbers, and a large relative error in collision rate up to 60% may arise when the particle Stokes number is near St_K=0.5. The errors from the filtering operation and the SGS model are evaluated separately using the filtered-DNS (FDNS) and LES flow fields. The errors increase with the filter width and have nonmonotonic variations with the particle Stokes numbers. It is concluded that the error due to filtering dominates the overall error in LES for most particle Stokes numbers. It is found that the overall collision rate can be reasonably predicted by both FDNS and LES for St_K>3. Our analysis suggests that, for St_K<3, a particle SGS model must include the effects of SGS motions on the turbulent collision of heavy particles. The spectral analysis of the concentration fields of the particles with different Stokes numbers further demonstrates the important effects of the small-scale motions on the preferential concentration of the particles with small Stokes numbers.

Subgrid scale fluid velocity timescales seen by inertial particles in large-eddy simulation of particle-laden turbulence

Large-eddy simulation (LES) has emerged as a promising tool for simulating turbulent flows in general and, in recent years,has also been applied to the particle-laden turbulence with some success (Kassinos et al., 2007). The motion of inertial particles is much more complicated than fluid elements, and therefore, LES of turbulent flow laden with inertial particles encounters new challenges. In the conventional LES, only large-scale eddies are explicitly resolved and the effects of unresolved, small or subgrid scale (SGS) eddies on the large-scale eddies are modeled. The SGS turbulent flow field is not available. The effects of SGS turbulent velocity field on particle motion have been studied by Wang and Squires (1996), Armenio et al. (1999), Yamamoto et al. (2001), Shotorban and Mashayek (2006a,b), Fede and Simonin (2006), Berrouk et al. (2007), Bini and Jones (2008), and Pozorski and Apte (2009), amongst others. One contemporary method to include the effects of SGS eddies on inertial particle motions is to introduce a stochastic differential equation (SDE), that is, a Langevin stochastic equation to model the SGS fluid velocity seen by inertial particles (Fede et al., 2006; Shotorban and Mashayek, 2006a; Shotorban and Mashayek, 2006b; Berrouk et al., 2007; Bini and Jones, 2008; Pozorski and Apte, 2009).However, the accuracy of such a Langevin equation model depends primarily on the prescription of the SGS fluid velocity autocorrelation time seen by an inertial particle or the inertial particle–SGS eddy interaction timescale (denoted by $\delt T_{Lp}$ and a second model constant in the diffusion term which controls the intensity of the random force received by an inertial particle (denoted by C_0, see Eq. (7)). From the theoretical point of view, dTLp differs significantly from the Lagrangian fluid velocity correlation time (Reeks, 1977; Wang and Stock, 1993), and this carries the essential nonlinearity in the statistical modeling of particle motion. dTLp and C0 may depend on the filter width and particle Stokes number even for a given turbulent flow. In previous studies, dTLp is modeled either by the fluid SGS Lagrangian timescale (Fede et al., 2006; Shotorban and Mashayek, 2006b; Pozorski and Apte, 2009; Bini and Jones, 2008) or by a simple extension of the timescale obtained from the full flow field (Berrouk et al., 2007). In this work, we shall study the subtle and on-monotonic dependence of $\delt T_{Lp}$ on the filter width and particle Stokes number using a flow field obtained from Direct Numerical Simulation (DNS). We then propose an empirical closure model for $\delta T_{Lp}$. Finally, the model is validated against LES of particle-laden turbulence in predicting single-particle statistics such as particle kinetic energy. As a first step, we consider the particle motion under the one-way coupling assumption in isotropic turbulent flow and neglect the gravitational settling effect. The one-way coupling assumption is only valid for low particle mass loading.

Imaging and tracking single fluorescent nanobeads in solution

In single-particle tracking (SPT), fluorescence video microscopy is used to record the motion images of single particle or single molecule. Here, by using a total-internal-reflection microscope equipped with an argon ion laser and a charge-coupled device (CCD) camera with high-speed and high-sensitivity, video images of single nanobeads in solutions were obtained. From the trajectories, the diffusion coefficient of individual nanobead was determined by the mean square displacements as a function of time. The sizes of nanobeads were calculated by Stokes-Einstein equation, and the results were compared with the actual values.

两种新型芴类衍生物的三光子吸收特性研究

研究了两种新型芴类衍生物9，9-二(2-乙基已基)-2，7-二咔唑-9H-芴(简记为DCZF)和9，9-二(2-乙基已基)-2，7-二(2-(4-甲氧基)苯-2，1-乙烯基)芴(简记为BMOSF)在N，N-二甲基甲酰胺(DMF)中的线性吸收和单光子荧光行为，并用脉冲宽度为38ps，重复频率为10Hz的1064 nm Nd：YAG脉冲激光研究了两种化合物的三光子吸收性质．结果表明：两种新材料的最大线性吸收峰分别位于330和380nm，吸收区域覆盖了270-420nm波段．两种化合物的荧光带位于蓝-紫区，中心

532 nm激光泵浦硝酸钡晶体产生外腔拉曼激光

由于硝酸钡晶体具有很强的对称振动（频率1047 cm^-1）和较高的拉曼增益,可以用来产生受激拉曼激光.采用单端泵浦的外置拉曼振荡腔与双棱镜分光装置进行了硝酸钡晶体拉曼激光实验,泵浦源为倍频Nd： YAG的532 nm激光,硝酸钡晶体通过水溶液降温法生长,尺寸为10 mm×10 mm×48 mm,采用特殊镀膜的腔镜对各阶斯托克斯光进行优化选择.在泵浦源达到65 mJ时,获得21 mJ一阶斯托克斯光,输出波长为563 nm,以及16 mJ的二阶斯托克斯光,输出波长为599 nm,受激拉曼散射SRS最大的整体

高效率,窄脉冲1198.5nm Ba(NO_3)_2喇曼激光器(英文)

利用1 064 nm的Nd∶YAG激光抽运振荡腔内的硝酸钡晶体,获得高效率、窄脉冲的喇曼激光输出.硝酸钡晶体由水溶液降温法生长,长度为48 mm.喇曼振荡腔由对抽运光、一阶、二阶斯托克斯光有不同反射率的双色平面镜构成.当抽运光功率达到4.5 W时,获得最高的一阶斯托克斯喇曼激光功率为1.48 W,相应的转换效率为32.9%,并测得斜率效率为40%.由于受激喇曼散射的作用,喇曼脉冲光由抽运脉冲光的19.8 ns压缩为2.4 ns,获得的喇曼激光脉冲波形具有的＂上升沿陡峭、下降沿缓慢＂的特性,对其形成过程作了

偏振光斯托克斯参量的高速实时测量技术

为了满足对高速变化的偏振态的测量,提出一种能够对偏振态实现高速测量的技术。阐述了利用1/4波片与起偏器测量偏振光的斯托克斯参量常规的原理和方法,根据高速测量的要求推导出了新的斯托克斯参量计算公式,并依据此公式设计了基于多通道偏振态高速测量的方案,设计了具体的方法并编写了控制与算法程序。测试表明,该系统的测量速度达到了每秒700次偏振态测量,测量速度主要由电子线路的性能决定,测得的结果稳定可靠实现了光纤传输偏振态的高速测量。