基于QBD模型的混合信道分配技术研究

混合信道分配技术兼有同定信道分配技术和动态信道分配技术的优点.为提高信道资源利用率,通过建立拟生灭过程的数学模型,选择切换保留混合优先级算法,然后通过模型平稳分布的求解得出性能指标的数学表达式,通过仿真对其性能进行比较.结果表明混合信道分配略差于动态信道分配,但优于同定信道分配.     

组播环境下IPTV快速频道切换方法

为解决组播网络中基于网际互连协议的电视(IPTV)频道切换时间过长的问题,提出一种在组播环境下IPTV快速频道切换的方法. 该方法利用终端的上传带宽,为其他终端提供快速的数据流,在短时间内充满频道切换终端播放缓存,可减少频道切换时间. 理论分析与仿真验证的结果表明,在较高频道切换频率下,该方法用不足20%的新增带宽,使频道切换时间减小到原有的15%～45%.     

八面河地区河道砂体描述方法与应用

根据八面河地区的沉积特点,分析河道砂体的响应特征,引进先进的勘探技术与方法对河道砂体进行精细描述,预测河道砂体展布,寻找有利圈闭,形成一套适用于八面河地区的河道砂体描述方法,发现有利勘探目标区2个,其中面138北部地区含油河道已被钻井证实,新增探明石油地质储量176万吨。     

Effect of the geometry and pattern of the flow channel on the performance of polymer electrolyte membrane fuel cell

This research focuses on the effect of the geometry and patterns of the gas flow channel on the PEM fuel cell performance. Simulation was conducted and the results were verified by experiments. Three-dimensional, single phase, compressible and isothermal models of 5 cm² electrodes, anode and cathode, were developed and studied by utilizing a commercial Computational Fluid Dynamics (CFD) software, FLUENT 4.5. Two types of gas flow channel were investigated: conventional and interdigitated. The results showed that the flow channel pattern does not have a significant effect on the anode cell performance, whereas it has a strong effect/influence on the cathode cell performance. The interdigitated design provides a higher limiting current density and cell performance than the conventional design on the cathode side. Moreover, the cell performance does not depend on the inlet and outlet channel widths. On the contrary, for the interdigitated design, it was influenced by the shoulder width. Finally, experiments were conducted to validate the simulation results.     

东兴市江平新城水系风道对建筑布局的影响研究

文章采用CFD模拟方法对东兴市江平新城规划进行评价研究,发现城市水系风道对建筑布局具有着重要的作用,并提出一些针对性的新城规划对策和发展思路,为今后开展的新城规划提供参考与依据,起到一个抛砖引玉的作用。     

半导体GaN功率开关器件灵敏度测试技术

测试半导体GaN功率开关器件灵敏度对掌握器件性能具有重要意义,提出一种新的半导体GaN功率开关器件灵敏度测试技术。通过分析半导体GaN功率开关器件的导通电阻与击穿电压关系、空穴电流与栅极电流关系掌握功率开关器件击穿机理,在此基础上,测试半导体GaN功率开关器件灵敏度;根据灵敏度测试原理与微频通道衰减值周期检查原理,测量功率开关器件微频信号功率和微频通道衰减值,汇总微频通道衰减值和最后一次开关灵敏时的衰减值,得到半导体GaN功率开关器件灵敏度。实验结果表明：所提测试技术测量半导体GaN功率开关器件灵敏度过程中,平均测试误差为0.03 dB,仅平均花费9.42ms,是一种高效、可靠的半导体GaN功率开关器件灵敏度测试技术。     

小型子弹抛撒后的飞行力学特性影响研究

利用子弹尾翼展开过程风洞试验气动特性和尾翼在驱动力作用下在不同张开位置对应时间的测量结果,分析研究子弹抛撒引起的初始角速率对飞行攻角的影响;根据子弹飞行过程中最大攻角限制,确定子弹抛撒初始角速率控制范围。子弹抛撒初始角速率要求可进一步放宽,研究结果对子母弹药子弹抛撒设计中姿态调整具有现实意义。     

Effect of welding conditions on reduction in angular distortion by welding with trailing heat sink

Abstract

The effectiveness of welding with a trailing heat sink in reducing the angular distortion of a weld has been experimentally investigated with focus on the cooling position. A numerical model of welding with a trailing heat sink is constructed through the comparison of measured values of weld penetration, thermal cycles and angular distortion with those calculated. On the basis of this model, the effect of welding heat input conditions on the reduction in angular distortion is discussed to evaluate the versatility of welding with a trailing heat sink. The results indicate that the choice of an appropriate cooling position behind the welding heat source is essential for the effective reduction in angular distortion. The reduction in angular distortion by the heat sink at the appropriate cooling position increases with the heat input parameter Q_net/h, where Q_net is the weld heat input and h is the thickness of the plate.