Uncertain and negative evidence in continuous time Bayesian networks

The continuous time Bayesian network (CTBN) enables reasoning about complex systems by representing the system as a factored, finite-state, continuous-time Markov process. Inference over the model incorporates evidence, given as state observations through time. The time dimension introduces several new types of evidence that are not found with static models. In this work, we present a comprehensive look at the types of evidence in CTBNs. Moreover, we define and extend inference to reason under uncertainty in the presence of uncertain evidence, as well as negative evidence, concepts extended to static models but not yet introduced into the CTBN model.     

空气洁净度对点源透射比测试准确度的影响

为了进一步提高点源透射比测试准确度,明确点源透射比测试环境需求,提出了一种定量分析空气洁净度对点源透射比测试准确度影响的方法.该方法以Mie散射理论为基础,采用蒙特卡洛模拟方法,对空气中尘埃的尺寸和数量进行随机模拟,得到不同空气洁净度等级下空气中尘埃对点源透射比测试准确度的影响.以直径为800mm、点源透射比设计值为10-9量级的某太空望远镜为例进行定量分析,结果表明:为了满足该空间光学系统的点源透射比测试需求,空气洁净度等级应优于ISO class 6,此时空气中尘埃引起的点源透射比测试误差约为10-10量级;ISO class每升高一级,测试误差约增大10倍.     

PGNAA系统中D-T中子管的慢化装置优化设计

为了提高PGNAA系统中D-T中子管的中子慢化效率,获得更高的热中子产额,借助蒙特卡罗模拟,确定了以铅为中子反射层、5个聚乙烯层和铅层相互交替作为中子慢化层、碳化硼含量为3%的含硼聚乙烯作为中子吸收层以及铅作为γ屏蔽层的中子慢化装置模型。针对中子产额为3×107 n/s 的D-T中子管,该慢化装置输出面低于5 eV中子通量可达5.28×106 n/s,占总中子通量的30.8%,有效提高了中子慢化效率。经过验证模拟结果能够满足实验要求。To improve the moderating efficiency of D-T Neutron Generator in PGNAA system, and get higher thermal neutron yield, the Monte Carlo code MCNP was used to optimize the moderation setup. The lead was selected as neutron reflector and gamma absorber, 5 polyethylene layers and 4 lead layers constituted the neutron moderator and 3% boron-doping polyethylene was selected as neutron absorber. For the yield of 3107 n/s D-T Neutron Generator, this moderation setup can provide a yield of lower than 5 eV of 5.28106 n/s, accounting for 30.8% of total neutron yield, dramatically improves the moderating efficiency. It is proved that the simulation results can satisfy the requirement of PGNAA system by preliminary experimental verification.     

蒙特卡罗临界计算全局计数效率新算法研究

为提高蒙特卡罗临界计算时全局计数的整体效率, 对比分析了新提出的均匀计数密度算法、均匀径迹数密度算法和原有的均匀裂变点算法. 以大亚湾核反应堆pin-by-pin模型的全局体平均通量计数和中子沉积能计数为例, 前两种算法较均匀裂变点算法都获得了整体效率的提高. 上述算法已经在自主开发的并行蒙特卡罗输运程序JMCT上予以实现.     

线路保护装置SV直采传输方案研究

分析了当前智能变电站SV点对点发送处理机制,提出了一种满足过程层要求的高均匀性和一致性SV直采传输方法。应用FPGA实现DMA控制器和以太网MAC控制单元,对SV报文添加发送描述符,由FPGA根据描述符直接控制SV发送。采用Spartan-6系列架构FPGA,通过PCI Express总线,系统内部实现SV数据高速传输。此方案充分利用了FPGA的并行数据处理的特性及丰富的IP资源,设计实现了多路以太网点对点数据的高带宽和高可靠性传输,极大的提升了智能变电站系统的性能。     

受限导致硬椭球液体的取向有序

Monte Carlo模拟研究了两平行硬墙受限下各向异相的硬椭球液体形成的有序结构. 墙壁对椭球粒子的过量吸附和椭球的长短径之比有关;对于高密度的椭球液体,它在一个临界的长短径之比 a/b=2.9处达到最大值,表明在墙表面附近发生了取向有序. 墙表面附近的密度分布和取向序参量进一步证实这结论. 相同密度条件下体相中的取向序参量计算表明体相结构均为各向同性,这是由于体系的密度依然低于各向同性相向相列向转变的临界密度. 该受限椭球液体中墙表面的取向有序是由墙面的几何受限所导致的.     

A kinetic Monte Carlo simulation study of inositol 1,4,5-trisphosphate receptor (IP3R) calcium release channel

Most of the previously theoretical studies about the stochastic nature of the IP3R calcium release channel gating use the chemical master equation (CME) approach. Because of the limitations of this approach we have used a stochastic simulation algorithm (SSA) presented by Gillespie. A single subunit of De Young-Keizer (DYK) model was simulated using Gillespie algorithm. The model has been considered in its complete form with eight states. We investigate the conditions which affect the open state of the model. Calcium concentrations were the subject of fluctuation in the previous works while in this study the population of the states is the subject of stochastic fluctuations. We found out that decreasing open probability is a function of Ca(2+) concentration in fast time domain, while in slow time domain it is a function of IP3 concentration. Studying the population of each state shows a time dependent reaction pattern in fast and medium time domains (10(-4) and 10(-3)s). In this pattern the state of X(010) has a determinative role in selecting the open state path. Also, intensity and frequency of fluctuations and Ca(2+) inhibitions have been studied. The results indicate that Gillespie algorithm can be a better choice for studying such systems, without using any approximation or elimination while having acceptable accuracy. In comparison with the chemical master equation, Gillespie algorithm is also provides a wide area for studying biological systems from other points of view.     

Integration of continuous-flow sampling with microchip electrophoresis using poly(dimethylsiloxane)-based valves in a reversibly sealed device

Here we describe a reversibly sealed microchip device that incorporates poly(dimethylsiloxane) (PDMS)-based valves for the rapid injection of analytes from a continuously flowing stream into a channel network for analysis with microchip electrophoresis. The microchip was reversibly sealed to a PDMS-coated glass substrate and microbore tubing was used for the introduction of gas and fluids to the microchip device. Two pneumatic valves were incorporated into the design and actuated on the order of hundreds of milliseconds, allowing analyte from a continuously flowing sampling stream to be injected into an electrophoresis separation channel. The device was characterized in terms of the valve actuation time and pushback voltage. It was also found that the addition of sodium dodecyl sulfate (SDS) to the buffer system greatly increased the reproducibility of the injection scheme and enabled the analysis of amino acids derivatized with naphthalene-2,3-dicarboxaldehyde/cyanide. Results from continuous injections of a 0.39 nL fluorescein plug into the optimized system showed that the injection process was reproducible (RSD of 0.7%, n = 10). Studies also showed that the device was capable of monitoring off-chip changes in concentration with a device lag time of 90 s. Finally, the ability of the device to rapidly monitor on-chip concentration changes was demonstrated by continually sampling from an analyte plug that was derivatized upstream from the electrophoresis/continuous flow interface. A reversibly sealed device of this type will be useful for the continuous monitoring and analysis of processes that occur either off-chip (such as microdialysis sampling) or on-chip from other integrated functions.     

Coarse-graining: a procedure to generate equilibrated and relaxed models of amorphous polymers

We present a coarse-graining procedure to construct models of amorphous polymers. The method, which was applied to polyethylene, is based on a generation-relaxation strategy previously developed to provide independent atomistic microstructures. The coarse-graining was performed by assigning positions to mesoscopic particles denoted blobs, which represent groups of atoms, through distance, angle and dihedral distribution functions. The interaction energy between pairs of blobs was evaluated through a soft potential, whose parameters were derived from atomistic models. Three levels of coarse-graining that differ in the number of atoms included in the blob have been considered. The structural and energy-related properties calculated using the coarse-grained models developed in this study are in good agreement with those obtained using atomistic simulations.     

A diagnostic tool for determining the quality of accuracy validation. Assessing the method for determination of nitrate in drinking water

Realistic internal validation of a method implies the performance validation experiments under intermediate precision conditions. The validation results can be organized in an X _Nr×Ns (replicates×runs) data matrix, analysis of which enables assessment of the accuracy of the method. By means of Monte Carlo simulation, uncertainty in the estimates of bias and precision can be assessed. A bivariate plot is presented for assessing whether the uncertainty intervals for the bias (E ± U(E)) and intermediate precision (RSDi ± U(RSDi) are included in prefixed limits (requirements for the method). As a case study, a method for determining the concentration of nitrate in drinking water at the official level set by 98/83/EC Directive is assessed by use of the proposed plot.