一氧化碳、氢、甲醇和正乙烷体系的分子模拟

钟炳等将超临界流体引入固定床反应器进行催化分离一体化合成甲醇的研究,取得了良好的效果［１］．对于一氧化碳加氢合成甲醇这一体系,文献报导的相平衡实验数据十分缺乏,ＤｅＬｏｏｓ［２］和Ｚａｗｉｓｚａ［３］仅对甲醇和正己烷二元体系的相行为进行了研究．对于合...     

Critical behaviour of the ferromagnetic Ising model on a triangular lattice

We use a new updated algorithm scheme to investigate the critical behaviour of the two-dimensional ferromagnetic Ising model on a triangular lattice with the nearest neighbour interactions. The transition is examined by generating accurate data for lattices with L= 8, 10, 12, 15, 20, 25, 30, 40 and 50. The updated spin algorithm we employ has the advantages of both a Metropolis algorithm and a single-update method. Our study indicates that the transition is continuous at T_c= 3.6403({2}). A convincing finite-size scaling analysis of the model yields υ=0.9995(21), β / υ = 0.12400({17}), γ / υ = 1.75223(22), γ '/υ=1.7555(22), α/υ= 0.00077(420) (scaling) and α / υ = 0.0010(42) (hyperscaling). The present scheme yields more accurate estimates for all the critical exponents than the Monte Carlo method, and our estimates are shown to be in excellent agreement with their predicted values.     

Reverse Monte Carlo study on structural order in liquid and glassy AlFe alloys

This paper reports that anomalous local order in liquid and glassy AlFeCe alloy has been detected by x-ray diffraction measurements. The addition of the element Ce has a great effect on this local structural order. The element Ce favours interpenetration of the icosahedra by sharing a common face and edges. It argues that frustration between this short-range order and the long-range crystalline order controls the glass-forming ability of these liquids. The obtained results suggest that a system having a stronger tendency to show local icosahedral order should be a better glass-former. This scenario also naturally explains the close relationship between the local icosahedral order in a liquid, glass-forming ability, and the nucleation barrier. Such topological local order has also been analysed directly using the reverse Monte Carlo method. It also estimated the fraction of local ordered and disordered structural units in a glassy AlFeCe alloy.     

Theoretical investigation of synchronous totally asymmetric simple exclusion process on lattices with two consecutive junctions in multiple-input-multiple-output traffic system

In this paper, we study the dynamics of the synchronous totally asymmetric simple exclusion process (TASEP) on lattices with two consecutive junctions in a multiple-input-multiple-output (MIMO) traffic system, which consists of m sub-chains for the input and the output, respectively. In the middle of the system, there are N (nN synchronously increasing, the vertical phase boundary moves toward the right and the horizontal phase boundary moves toward the upside in the phase diagram. The boundary conditions of the system as well as the numbers of input and output determine the no-equilibrium stationary states, stationary-states phases, and phase boundaries. We use the results to compare with computer simulations and find that they are in very good agreement with each other.     

铁磁球/反铁磁纳米体系磁滞回线的Monte Carlo模拟

利用经典Heisenberg模型和Monte Carlo方法研究外磁场和反铁磁磁晶各向异性、交换相互作用对铁磁球均匀嵌入到反铁磁基体中的铁磁/反铁磁纳米体系磁滞回线的影响.模拟结果显示,外加反向最大磁场不同时,磁滞回线形状不同.当磁场正向增加时,体系的磁化强度会产生一个跃变,但跃变高度与反向场最大值无关.反铁磁磁晶各向异性越大,体系的交换偏置现象越明显,且磁化强度回到饱和值所需的外磁场越大.随着反铁磁基体交换相互作用的增大,在正向和负向磁场区域还可能出现新的磁滞现象.     

大空间生物组织透射的Monte Carlo模拟方法的加速

乳腺等类型生物组织的透射Monte Carlo模拟(简称MC模拟)耗时很长,这主要是由于被模拟的组织较厚和Monte Carlo模拟自身统计特性引起的所需光子数量多造成的。针对光源与接收面在同一直线上,采用光纤接收透射光的模型进行分析,通过考虑生物组织自身的光学特性,进行了边界约束和有效后向散射次数的限制来缩短仿真时间,经过多次实验验证,以两次散射所到位置为分界,并充分利用组织光学参数计算约束边界,计算相对比较简单,同时考虑到入射与出射的实际情况进行微扩,从而得到的约束边界。对光学参数相同但厚度不同的组织进行仿真,分析进入同一位置光纤的光子数所发生后向散射次数,发现后向散射次数随着组织厚度与散射系数的增大而增大,随着吸收系数与各向异性因子的增大而减小,通过限定后向散射次数来节省时间。仿真结果表明,在传统计算机上,该方法能够显著缩短MC模拟的运算时间50%左右,尤其适用于较厚且边界较为复杂的高散射物质的MC模拟。该提速方法主要应用于光源与接收面处于同一直线,且生物组织较厚,散射系数较大的情况,能够有效节约仿真所需时间,有利于分析组织透射成像。     

M_(αβ) X-ray production cross sections of Pb and B iby 9–40 keV electron impact

The experimental data of Mαβ X-ray production cross sections for Pb and Bi by 9–40 keV electron impact have been given. Thin films with thick carbon substrates are used in the experiment. The effects of target structure on the Mαβ X-ray production cross sections are corrected by using the Monte Carlo method. The corrected experimental data are compared with calculated cross sections in terms of the distorted-wave Born approximation(DWBA) theory. The measured Mαβ X-ray production cross sections for Pb and Bi are lower than the DWBA calculations. The atomic relaxation parameters used in comparing the DWBA values with experimental results affect the degree of difference.     

大分子拥挤下核酸单链的结构性质

通过粗粒化模型构建核酸单链,采用Monte Carlo方法系统地研究了拥挤大分子体积比和尺寸对中性核酸单链结构性质的影响,得到了核酸单链端-端距离Ree与大分子体积比Φc和半径Rc的关系曲线.实验结果表明,大分子拥挤可导致核酸单链形成更加紧凑的结构,拥挤分子的体积分数越大、尺寸越小,核酸单链的结构越紧凑,而且大分子拥挤对较长的核酸单链影响更大,并进一步通过分析拥挤大分子的分布,揭示了大分子拥挤效应产生的机制.     

基于检测光纤的漫射高光谱采集的Monte Carlo仿真

从漫射高光谱中可以获得被测物体成分、结构及其分布等信息。采用光纤光谱仪获取漫射高光谱是一种常用的方法。Monte Carlo方法在研究光在浑浊介质的传播方面得到了广泛的应用。然而,使用Monte Carlo方法研究漫射高光谱时,必须考虑实际的检测条件对信号采集的影响。将光纤参数引入到Monte Carlo模型中,研究了光纤参数对被检测光学信号的影响。仿真结果表明,孔径角和半径增大,检测的漫射高光谱随之增大,而光纤与被测物质表面的距离小于1 mm时对漫射高光谱的影响在一定程度上可以忽略。进一步研究发现存在固定的修正系数使不同孔径角的光纤所采集的漫射高光谱转化为孔径角为π/2的光纤对应的信号。同时,得到了实际光纤孔径角范围内的修正系数拟合曲线。不同半径的光纤通过面积归一化可以得到很好的一致性。研究检测光纤参数对漫射高光谱的影响对实际测量有重要的指导意义,而且不同光纤所对应的检测结果可以通过修正系数和面积归一化进行移植。     

体光源模拟标定法测O2（^1△）绝对浓度

O2(^1△)绝对浓度的测量,一直是SOG和COIL研究中的重要参数之一。体光源模拟标定法测O2(^1△)绝对浓度,是把发光气体以某一流速引入一已知体积的流动光池中,再通过具有低象差失真的光学系统,把该体光源成象在探测器的有效表面上。探测器和测量仪器组成的测量系统,要经过标准光源和电学标定。本方法可测出O2(^1△)绝对浓度及其分压,O2(^1△)产率等参数。其中O2(^1△)浓度测量结果的相对误差为20％。