Numerical simulation of catalytic combustion of methane using washcoat model and external model: a comparison study

This paper presents a comparison study of numerical simulation of catalytic combustion of methane on Pt catalyst using two different physical models. The external surface model and the washcoat model were employed. The simulations were conducted in a two-dimensional monolith reactor with detail surface kinetics. The agreement of simulation results of the washcoat model with the measured data is good. However, in contrast to experimental data, the external surface method will produce a lower result of conversion of CH₄ at low temperature due to the neglecting of the larger inner surface of the washcoat. Moreover, the effects of specific surface area and pore size of washcoat on reaction rate were discussed. It can be concluded that the washcoat model would provide a more realistic result and can enrich the contents of numerical simulation of catalytic reaction.     

Terahertz surface plasmon polaritons in textured metal surfaces formed by square arrays of metallic pillars

In this paper, we investigate numerically the characteristics of surface plasmon polaritons (SPPs) sustained by two-dimensional arrays of metallic pillars protruding out of planar metal surfaces at terahertz (THz) frequencies. Various shapes of the pillars are analyzed, and it is shown that the pillar shape only has weak influence on the dispersion of spoof SPPs. However, the loss of spoof SPPs is closely dependent on the pillar shape. It is also shown that spoof SPPs on textured surfaces with pillars can exhibit much better confinement than those on pierced surfaces with holes.     

基于高吸水／保水材料的红外隐身技术研究

介绍了基于高吸水／保水材料的红外隐身原理，对高吸水／保水材料的吸水／保水特性进行了研究，提出以高吸水／保水材料为基底的红外隐身复合材料的概念和模型设计，通过实验对其可行性和有效性进行了初步验证。结果表明，该复合材料能有效降低目标红外辐射特征，具有较好的红外隐身效果。     

Microfluidic pool structure for cell docking and rapid mixing

A microfluidic pool structure for cell docking and rapid mixing is described. The pool structure is defined as a microchamber on one structural layer of a bilayer chip and connects with two or more individual microchannels on the other structural layer. In contrast to the turbulent flow in a macroscale pool, laminar streams enter and exit this microfluidic pool structure with definite and controllable direction that may be influenced by the location and geometry of the pool. A simple microfluidic model was used to validate this hypothesis. In this model, a microscale pool structure was made on the lower layer of a chip and connected with three parallel microchannels in the upper layer. Simulation and experimental results indicated that the flow profile within the pool structure was determined by its geometry and location. This could be used as a flow control method and it was simpler than designs based on microvalve, hydraulic pressure, or electrokinetic force, and has some important applications. For example, controllable streams within this structure were used to immobilize biological cells along the microchannel walls. When different solution streams flowed through the pool, rapid diffusion of analytes occurred for short diffusion distance between vertical flow laminas. Furthermore, desired dilution (mixing) ratio could be obtained by controlling the geometry of the microfluidic pool.     

Investigation of the fill factor of dye-sensitized solar cell based on ZnO nanowire arrays

The fill factor of dye-sensitized solar cells based on the ZnO nanowire array is very low, which is usually ascribed to a rapid charge recombination. In this article, the influence on the fill factor of ZnO nanowire array cell is investigated and discussed by comparing dark current and decay rate of open circuit potential of the ZnO nanowire array cell with those of the ZnO nanoparticle cell, TiO₂ nanoparticle cell and TiO₂-coated ZnO nanowire array cell. The results demonstrate that the low fill factor of the ZnO nanowire array cell is largely caused by a rapid decrease of electron injection efficiency rather than a rapid charge recombination, which is decided by the absorption nature of Ru-complexed dye molecules on ZnO surface and repellency of radial electric field. The fill factor of the ZnO nanowire array cell can be improved by coating ZnO nanowires with a wide band gap semiconductor material or metal oxide insulator.     

基于高吸水/保水材料的红外隐身复合材料的可行性研究及效能评价

根据战场条件及红外材料的性能要求,在研究高吸水/保水材料特性的基础上对开发基于高吸水/保水材料的红外隐身复合材料的可行性进行研究分析,提出以高吸水/保水材料为基底的红外隐身复合材料的两种设计方案并制备出该红外隐身复合材料样板.通过对其进行红外效果评价,结果表明,该材料若作为军事目标的表面材料能有效改变目标的红外辐射特性...     

具有非抢占优先站点的轮询系统顾客队长

本文讨论轮询系统在系统平稳条件下,对于具有一个非抢占的优先权站点且采用穷尽服务方式下的轮询系统进行理论分析,给出服务员轮询到每个站点时该站点的队长及数学期望。     

Dimensionality reduction via variables selection – Linear and nonlinear approaches with application to vibration-based condition monitoring of planetary gearbox

Feature extraction and variable selection are two important issues in monitoring and diagnosing a planetary gearbox. The preparation of data sets for final classification and decision making is usually a multi-stage process. We consider data from two gearboxes, one in a healthy and the other in a faulty state. First, the gathered raw vibration data in time domain have been segmented and transformed to frequency domain using power spectral density. Next, 15 variables denoting amplitudes of calculated power spectra were extracted; these variables were further examined with respect to their diagnostic ability. We have applied here a novel hybrid approach: all subset search by using multivariate linear regression (MLR) and variables shrinkage by the least absolute selection and shrinkage operator (Lasso) performing a non-linear approach. Both methods gave consistent results and yielded subsets with healthy or faulty diagnostic properties.     

变时延移动Ad-Hoc网络容量非合作规划博弈模型的渐近稳定性

移动Ad-Hoc网络容量的稳定性是保证其服务质量的关键性质之一.本文提出一种新颖的考虑时变传播时延的非合作规划博弈移动Ad-Hoc网络容量分析模型稳定性控制技术.首先求得加入时变传播时延项的非合作规划博弈移动Ad-Hoc网络容量分析模型的源节点发送流量速率演化方程组—–一类非线性时变时滞微分方程组,在此基础上采用描述器技术结合线性矩阵不等式技术得到该模型的渐进稳定性准则,并设计了模型稳定性控制的迭代算法.由于是基于等价模型变换,所提出的渐近稳定性判别准则具有较小的保守性.仿真实验验证了本算法的有效性.本建模与分析方法虽以具体的非合作规划博弈移动Ad-Hoc网络容量分析模型为例,但其可以应用于一般的移动Ad-Hoc网络容量稳定性控制问题.     

Tb3+-Eu3+共掺杂2ZnO·2.2B2O3·3H2O的制备和发光性能

采用水热法合成了Tb3+和Eu3+共掺的2ZnO.2.2B2O3.3H2O红色荧光粉。通过固定Eu3+的掺杂浓度为3%(物质的量比:Eu∶Zn=3%),改变Tb3+的掺杂浓度(2%～15%),研究Tb3+掺杂浓度对红色荧光粉晶相结构和光学性能的影响。用X射线衍射和荧光光谱仪对样品的结构和发光性能进行表征,结果表明:随着Tb3+掺杂浓度的升高,样品由晶态向无定形的玻璃态转变;Eu3+的发光强度也逐渐增强;Tb3+与Eu3+之间存在能量传递的过程,且当采用不同的激发波长(220 nm和393 nm)激发时,其能量传递的过程也不一样。