图示仪在LED失效分析中的应用

本文基于图示仪的检测原理,说明了其测量LED参数的方法,提出了在LED失效分析中图示仪几个特殊的应用和操作方法.     

Extending potential flow modelling of flat-sheet geometries as applied in membrane-based systems

The efficiency of chemical reactors can be analysed using the residence time distribution. This research focusses on flat-sheet geometries applied in membrane-based systems. The residence time distribution depends mainly on the 2D velocity field, parallel to the membrane. The velocity average over the transversal direction is calculated using potential flow theory. A combination of real and virtual sources and sinks are used to model the internal inlets and outlets. Furthermore, a novel method is presented to calculate the residence time distribution. By ignoring diffusion and dispersion, every streamline is modelled to have a fixed residence time, which can be calculated with a simple quadrature based on a coordinate transformation. The model predicts the impact of the two-dimensional geometry on the residence time distribution, but it is demonstrated that large zones of nearly stagnant flow have only a limited impact on the residence time distribution. The new model can predict the travelling time from the inlet to each interior location, providing a better tool to analyse spatially distributed chemical reactions. The models agreed highly with pressure measurements (R² = 0.94–0.98) and they agreed well with tracer experiments for the residence time (R² = 0.73–0.99).     

Conference and Research Reports

Groundwater discharge into an open pit lignite mining lake was investigated using radon-222 as a naturally occurring environmental tracer. The chosen study site was a meromictic lake, i.e., a water body that is divided horizontally into two separate layers – the upper mixolimnion (with seasonal mixing) and the lower monimolimnion (without seasonal mixing). For the estimation of groundwater discharge rates into the lake, a simple box model including all radon sinks and sources related to each layer was applied. Two field investigations were performed. During the October campaign, the total groundwater discharge into the lake was found to be 18.9 and 0.7 m³ d^?1 for the mixolimnion and monimolimnion, respectively. During the December campaign, the groundwater discharge into the mixolimnion was 15.0 m³ d^?1, whereas no discharge at all was observed into the monimolimnion. Based on the given water volumes, the residence time of lake water was 5.3 years for the monimolimnion and varies between 0.9 and 1.1 years for the mixolimnion. The investigation confirmed radon to be a useful environmental tracer for groundwater and surface water interactions in meromictic lake environments.     

Experimental and theoretical investigation of oxygen diffusion in stabilised zirconia

Oxygen diffusion in stabilised zirconias is investigated by the simultaneous application of computer modelling and experimental techniques to yttria-stabilised zirconia. Using the Mott-Littleton method, migration pathways for oxygen ions have been calculated in perfect cubic zirconia. The oxygen migration occurs through a straight pathway, but not starting from the ideal lattice positions. The calculated activation energy of migration is about 0.2 v eV. Oxygen transport is investigated experimentally in YSZ containing 8-24 v mol% Y 2 O 3 as a function of stabiliser content by combining the stable isotope ( 18 O 2 ) method with ionic conductivity measurements. It was found that for a given temperature, diffusion and conductivity are highest for YSZ containing 8-10 v mol% yttria, but with differing activation energies which can be compared to the calculated values.     

基于Packet Tracer的中小企业融合通信仿真研究

基于Packet Tracer仿真软件模拟构建了一个中小分支企业融合通信的平台,给出具体规划和实施过程,实现了企业中数据、语音的融合通信,为相关的实训教学提供一种可行的参考解决方案。     

Experimental data on binary and ternary mixtures of perfluoro-1,3-dimethylcyclohexane with normal alkanes at 373.15 K

Phase behaviour measurement of binary mixtures of perfluoro-1,3-dimethylcyclohexane with methane and propane, and ternary mixtures of perfluoro-1,3-dimethylcyclohexane with methane + n-hexane and methane + n-decane at 373.15 K and over a wide range of concentration are presented. Measurements are made at the liquid bubble point and retrograde dew point pressures of the mixtures. A constant composition expansion test was carried out on perfluoro-1, 3-dimethylcyclohexane + methane mixture at 373.15 K.     

Imaging water fluxes in porous media by magnetic resonance imaging using D(2)O as a tracer

In this study, we investigate the usefulness of D(2)O as a conservative tracer for monitoring water flux by MRI in a heterogeneous sand column. The column consisted of a cylindrical 3x9-cm packing of fine sand in which an 8-mm diameter cylindrical obstacle was placed. Constant steady-state flux densities between J(w)=0.07 and 0.28 cm min(-1) corresponding to mean pore flow velocities between 0.20 and 0.79 cm min(-1) were imposed at the top of the sand column, and a constant hydraulic head of -39 cm was maintained at the lower boundary. We injected pulses of 0.01 M NiCl(2) and 55% D(2)O and monitored the motion of the tracer plumes by MRI using a fast spin echo sequence over a period of 20 min. We observed that the center of gravity of all plumes moved with the mean pore flow velocity, which showed that D(2)O behaves as a conservative tracer. The motion of the tracer plume at J(w)=0.14 cm min(-1) was validated by a numerical simulation using HYDRUS2D, which reproduced the experimentally observed behavior very satisfactorily.     

Elliptic random-walk equation for suspension and tracer transport in porous media

We propose a new approach to transport of the suspensions and tracers in porous media. The approach is based on a modified version of the continuous time random walk (CTRW) theory. In the framework of this theory we derive an elliptic transport equation. The new equation contains the time and the mixed dispersion terms expressing the dispersion of the particle time steps. The properties of the new equation are studied and the fundamental analytical solutions are obtained. The solution of the pulse injection problem describing a common tracer injection experiment is studied in greater detail. The new theory predicts delay of the maximum of the tracer, compared to the velocity of the flow, while its forward “tail” contains much more particles than in the solution of the classical parabolic (advection-dispersion) equation. This is in agreement with the experimental observations and predictions of the CTRW theory.     

Tracer (self)-diffusion of potassium ion in NaCl−KCl−H2O mixtures at 25°C

Tracer (self)-diffusion coefficients of K⁺ have been measured using the diaphragm cell in seven compositions of the NaCl–KCl–H₂O system. These data complete the full set of isothermal vector transport properties for five of these compositions.     

基于三层交换的两种VLAN间通信的设计与实现

文章依托思科Packet Tracer模拟器,采用两种方法来实现不同VLAN间通信,并通过对比分析,加深学生对VLAN划分、VLAN间通信、VLAN虚接口等VLAN相关技术的理解和掌握,增强学生对所学知识的实际运用能力。