胶体体系的固化及分离过程的计算机模拟

胶体体系是自然界很重要的组成部分，广泛应用于工业生产和日常生活中。胶体体系在固化的过程中，会形成有序的晶体结构或无序的玻璃态结构。对胶体的结晶和玻璃化的认识对研究相变理论，纳米材料以及自组装有着重要的意义。事实上，在这一领域存在着许多悬而未决的问题。另一方面，胶体的分离也是胶体科学研究中不可或缺的步骤。特别是近年来微流器件技术的进步为流体动力学色谱分离方法带来了进一步发展的机会，这为胶体的分离提供了非常有效的实验手段。然而，由于实际应用过程的复杂性，理论方法还不足以深入探讨胶体粒子体系固化和分离的本质。作为一种可以直接反映物理过程的研究方法，计算机模拟成为一种有效的研究胶体粒子固化和分离的手段。 硬球模型是一种最简单的胶体粒子体系，能够很好地描述具有体积排斥作用的胶体粒子的行为，因此，对于胶体粒子体系固化问题，我们采用分子动力学方法研究了硬球粒子体系的固化过程。此外，对于胶体和高分子体系的分离过程，我们主要采用耗散分子动力学（dissipative particle dynamics DPD）进行研究。论文的主要内容包括： 1)采用硬球分子动力学模型，研究了胶体颗粒在不同的压缩速率下得到的堆积态的结构异质性。我们应用Lubachevsky-Stillinger方法，在不同的压缩速率下得到了一系列的结构受限的硬球堆积状态。这些体系的有序度随着压缩速率的减小而增加，而体系的密度则是先增加后减小又增加，在中间压缩速率时出现最小值。通过测量体系中的局域序参量分布，粒子位置的均方根涨落分布和直接观察受限粒子的位置，发现这些状态中包含有无规区域和结晶区域，存在显著的结构异质性。特别的是低密度状态中许多小的有序区域互相连接成贯穿体系的逾渗网络，说明晶区之间的结构不匹配是生成这些状态的重要机理。 2)用DPD方法模拟了线性高分子链和星形高分子链在穿越纳米孔道的输运过程。对复合管道中小管的半径分别为2.5 和2.0 的两种情况进行了研究。在各种情况下我们都发现了存在一个临界流量Jc，只有当流量大于Jc的时候高分子才能进入纳米孔洞。对于线性高分子，长链的高分子进入同样粗细的小管所需要的临界流量比短链大。线性链和星形链在半径是2.0小管子中的临界流量比通过半径2.5的管子的临界流量大，或者近似相同。在半径2.5的小管中，星形高分子的临界流量要大于同等尺寸的线性高分子。此外，我们没有观察到不同接枝数的星形高分子的临界流量之间的差异。出现这种情况的原因可能是DPD模型中粒子间的相互作用势能很软，所以不能很好地体现出不同接枝数的星形高分子在位阻上的差异。 3）我们利用DPD方法模拟了圆柱形管道中线性高分子链的输运过程。比较了模拟得到的高分子保留时间和DG理论预测值之间的差异。发现分子量越大的高分子对DG理论的偏离越显著。计算了高分子链在流动过程中伸长的情况，发现了链的伸长率S与Weissenberg number 有着明确的标度关系。与狭缝中的情况类似，对于圆柱型管道中流动的线性高分子，如果采用修饰过的Peclet number，则能够更好地满足Aris-Taylor分散的标度关系。 4)我们建立了纳米粒子在DPD模拟的动力学模型，研究了在本体溶液中纳米粒子的自扩散系数和速度关联函数对与胶体粒子的半径定性关系。发现纳米粒子的扩散系数随粒子半径的增加而减小。纳米粒子的半径越大，其速度关联函数的衰减越慢，同样大小纳米粒子的质量越大，其速度关联函数衰减得越慢。我们进一步模拟了在狭缝中纳米粒子的输运过程。通过观察流体受限方向的流速曲线，我们发现由于与器壁之间的体积排斥作用，使得纳米粒子远离流体的边界。对Aris-Taylor分散的研究结果表明，在λ不大的时候，应用不同的Peclet numbers 对分散方程结果的影响不大。

Comparison of aggregation behaviors between branched and linear block polyethers: MesoDyn simulation study

The comparison of aggregation behaviors between the branched block polyether T1107 (polyether A) and linear polyether (EO)(60)(PO)(40)(EO)(60) (polyether B) in aqueous solution are investigated by the MesoDyn simulation. Polyether A forms micelles at lower concentration and has a smaller aggregation number than B. Both the polyethers show the time-dependent micellar growth behaviors. The spherical micelles appear and then change to rod-like micelles with time evolution in the 10 vol% solution of polyether A. The micellar cluster appears and changes to pseudo-spherical micelles with time evolution in the 20 vol% solution of polyether A. However, the spherical micelles appear and change to micellar cluster with time evolution in the 20 vol% polyether B solution. The shear can induce the micellar transition of both block polyethers. When the shear rate is 1x10(5) s(-1), the shear can induce the sphere-to-rod transition of both polyethers at the concentration of 10 and 20 vol%. When the shear rate is lower than 1x10(5) s(-1), the huge micelles and micellar clusters can be formed in the 10 and 20 vol% polyether A systems under the shear, while the huge micelles are formed and then disaggregated with the time evolution in the 20 vol% polyether B system.

耗散粒子动力学处理复杂固体壁面的一种有效方法

耗散粒子动力学(dissipative particle dynamics,DPD)作为一种介观尺度拉格朗日型粒子方法,已经成功地应用于微纳米流动和生化科技的研究中. 复杂固体壁面的处理和壁面边界条件的实施一直是DPD方法发展及应用的一个障碍. 提出了处理复杂固体壁面的一种新的方法. 复杂固体区域通过冻结随机分布并且达到平衡状态的DPD粒子代表;所冻结的DPD粒子位于临近流动区域的一个截距内;在靠近固体壁面的流动区域中设置流动反弹层,当流动DPD粒子进入此流动层后反弹回流动区域. 应用这种固体壁面处理方法.

The hyper-radiosensitivity effect of human hepatoma SMMC-7721 cells exposed to low dose gamma-rays and C-12 ions

Hypersensitive response of mammalian cells in cell killing to X- and gamma-rays has been reported at doses below 1 Gy. The purpose of this study was to examine the low dose sensitivity of human hepatoma SMMC-7721 cells irradiated with Co-60 gamma-rays and 50 MeV/u C-12 ions. Experiments using gamma-rays and charged particle irradiation were performed, particularly in the low dose range from 0 to 2 Gy. The survival effect of SMMC-7721 cells was measured by means of standard clonogenic assay in conjunction with a cell sorter. The result indicates SMMC-7721 cells showed hyper-radiosensitive response at low doses and increased radio-resistance at larger single doses for the carbon ions (LET = 45.2 keV/mu m) and the gamma-rays. However, the HRS/IRR effect caused by high-LET irradiation is different from that by low-LET radiation. This might possibly be due to the difference in the mode of energy deposition by particle beam and low-LET irradiation.

Design and simulation of charge sensitive preamplifier with CMOS FET implemented as feedback capacitor C-fp

In this paper, to design a new preamplifier for optimum performances with charged-particle or heavy-ion detectors, the CMOS FET is implemented as a feedback capacitor C-fp, so that the entire system should be built only with MOSFET. This work is a revolution design because to realize an ASIC for a preamplifier circuit, the capacitor will also be included. We succeed after a simulation to maintain a rise time less than 3 ns, the output resistance less than 94 Omega and the linearity almost good.

Balance functions from Au+Au, d+Au, and p+p collisions at root s(NN)=200 GeV

Balance functions have been measured for charged-particle pairs, identified charged-pion pairs, and identified charged-kaon pairs in Au + Au, d + Au, and p + p collisions at root s(NN) = 200 GeV at the Relativistic Heavy Ion Collider using the STAR detector. These balance functions are presented in terms of relative pseudorapidity, Delta eta, relative rapidity, Delta y, relative azimuthal angle, Delta phi, and invariant relative momentum, q(inv). For charged-particle pairs, the width of the balance function in terms of Delta eta scales smoothly with the number of participating nucleons, while HIJING and UrQMD model calculations show no dependence on centrality or system size. For charged-particle and charged-pion pairs, the balance functions widths in terms of Delta eta and Delta y are narrower in central Au + Au collisions than in peripheral collisions. The width for central collisions is consistent with thermal blast-wave models where the balancing charges are highly correlated in coordinate space at breakup. This strong correlation might be explained by either delayed hadronization or limited diffusion during the reaction. Furthermore, the narrowing trend is consistent with the lower kinetic temperatures inherent to more central collisions. In contrast, the width of the balance function for charged-kaon pairs in terms of Delta y shows little centrality dependence, which may signal a different production mechanism for kaons. The widths of the balance functions for charged pions and kaons in terms of q(inv) narrow in central collisions compared to peripheral collisions, which may be driven by the change in the kinetic temperature.

25MeV/A~(40)Ar+~(115)In反应中轻粒子发射研究及大面积位置灵敏闪烁探测器的研制

论文分为两个部分。第一部分：研究在25MeV/u ~(40)Ar+~(115)In反应中轻粒子发射机制。实验中，利用研制的轻粒子探测器测量了发射的P、#alpha#能谱。用三源模型拟合了轻粒子能谱，所提取的参数与费米气体模型的计算结果进行比较，分析了发射源形成和衰变的一些特点。第二部分：研制一种大面积幅度、时间、位置灵敏闪烁探测器。它是HIRFL上建成的第一阶段放射性核束物理实验终端的主要设备之一，在首次放射性核束调试中收到良好的效果。本文的目的是用经典理论研究了热核形成及衰变的一些性质，在即将开展的放射性核束物理研究中， 利用研制的大型探测器对经典理论普适性进行检验

Didodecyldimethylammonium bromide lipid bilayer-protected gold nanoparticles: Synthesis, characterization, and self-assembly

Didodecyldimethylammonium bromide (DDAB) lipid bilayer-protected gold nanoparticles (AuNPs), which were stable and hydrophilic, were synthesized by in situ reduction of HAuCl4 with NaBH4 in an aqueous medium in the presence of DDAB. As-prepared nanoparticles were characterized by UV-vis spectra, transmission electron microscopy, dynamic light scattering analysis, and X-ray photoelectron spectroscopy. All these data supported the formation of AuNPs. Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis/thermogravimetric analysis data revealed that DDAB existed in a bilayer structure formed on the particle surface, resulting in a positively charged particle surface. The FTIR spectra also indicated that the DDAB bilayer coated on the surface of AuNPs was probably in the ordered gel phase with some end-gauche defects. On the basis of electrostatic interactions between such AuNPs and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), we successfully fabricated (PSS/AuNP)(n) multilayers on a cationic polyelectrolyte poly(ethylenimine) coated indium tin oxide substrate via the layer-by-layer self-assembly technique and characterized as-formed multilayers with UV-vis spectra and atomic force microscopy.

大云室组动量选择器

采用“预选—寄存—运算再选”的方案,设计并完成了云南站大云室组的宇宙线事例选择系统.其中动量选择器应用了数字在线计算技术.设计了小型专用计算单元,根据荷电粒子在磁场中的偏转角与动量的对应关系,对寄存下来的描迹信号进行快速运算和逻辑判断,从而实现单个荷电粒子的动量选择.

Brownian dynamics simulation of the crystallization dynamics of charged colloidal particles

Crystal formation process of charged colloidal particles is investigated using Brownian dynamics (BD) simulations. The particles are assumed to interact with the pair-additive repulsive Yukawa potential. The time evolution of crystallization process and the crystal structure during the simulation are characterized by means of the radial distribution functions (RDF) and mean square displacement (MSD). The simulations show that when the interaction is featured with long-range, particles can spontaneously assemble into body-centered-cubic (BCC) arrays at relatively low particle number density. When the interaction is short-ranged, with increasing the number density particles become trapped into a stagnant disordered configuration before the crystallization could be actualized. The simulations further show that as long as the trapped configurations are bypassed, the face-centered-cubic (FCC) structures can be achieved and are actually more stable than BCC structures. (C) 2010 Elsevier Inc. All rights reserved.

An algorithm for coarse particle sedimentation simulation by Stokesian dynamics

Coarse Particle sedimentation is studied by using an algorithm with no adjustable parameters based on stokesian dynamics. Only inter-particle interactions of hydrodynamic force and gravity are considered. The sedimentation of a simple cubic array of spheres is used to verify the computational results. The scaling and parallelism with OpenMP of the method are presented. Random suspension sedimentation is investigated with Mont Carlo simulation. The computational results are shown in good agreement with experimental fitting at the lower computational cost of O(N In N).

Dynamics of collapsing fluidized beds and its application in the simulation of pulsed fluidized beds

A new method to study collapsing process of fluidized bed was proposed. The method is based on the analysis of the pressure variation during collapse. A model is proposed to describe the pressure variation on any location of the bed during collapse. Three kind of particles were fluidized by air and the pressure variation after shutting down the gas supply was measured by pressure transducers and simulated by the proposed model. The simulated results were in good agreement with the experimental data. The parameters of the fluidized bed, such as bubble fraction alpha(b), particle fraction in dense phase alpha(p), bubble velocity u(b) and slip velocity of particle u(i), can be estimated from the measured pressure data by using the proposed model. The model was also used to calculate the pressure variation in pulsed fluidized beds with low frequency.

Computer simulation on the collision-sticking dynamics of two colloidal particles in an optical trap

Collisions of a particle pair induced by optical tweezers have been employed to study colloidal stability. In order to deepen insights regarding the collision-sticking dynamics of a particle pair in the optical trap that were observed in experimental approaches at the particle level, the authors carry out a Brownian dynamics simulation. In the simulation, various contributing factors, including the Derjaguin-Landau-Verwey-Overbeek interaction of particles, hydrodynamic interactions, optical trapping forces on the two particles, and the Brownian motion, were all taken into account. The simulation reproduces the tendencies of the accumulated sticking probability during the trapping duration for the trapped particle pair described in our previous study and provides an explanation for why the two entangled particles in the trap experience two different statuses. (c) 2007 American Institute of Physics.

Drag on an ellipsoid particle in free-molecular plasma flow

Based on the analysis of molecular gas dynamics, the drag and moment acting on an ellipsoid particle of revolution X-2/a(2) + Y-2/a(2) + Z(2)/c(2) = 1, as an example of nonspherical particles, are studied under the condition of free-molecular plasma flow with thin plasma sheaths. A nonzero moment which causes nonspherical particle self-oscillation and self-rotation around its own axis in the plasma flow-similar to the pitching moment in aerodynamics-is discovered for the first time. When the ratio of axis length c/a is unity, the moment is zero and the drag formula are reduced to the well-known results of spherical particles. The effects of the particle-plasma relative velocity, the plasma temperature, and the particle materials on the drag and moment are also investigated.

Multi-scale Calculation of Settling Speed of Coarse Particles by Accelerated Stokesian Dynamics without Adjustable Parameter

The calculation of settling speed of coarse particles is firstly addressed, with accelerated Stokesian dynamics without adjustable parameters, in which far field force acting on the particle instead of particle velocity is chosen as dependent variables to consider inter-particle hydrodynamic interactions. The sedimentation of a simple cubic array of spherical particles is simulated and compared to the results available to verify and validate the numerical code and computational scheme. The improvedmethod keeps the same computational cost of the order O(N log N) as usual accelerated Stokesian dynamics does. Then, more realistic random suspension sedimentation is investigated with the help ofMont Carlo method. The computational results agree well with experimental fitting. Finally, the sedimentation of finer cohesive particle, which is often observed in estuary environment, is presented as a further application in coastal engineering.