基于二维网状结构的应用层组播协议研究

为了改善网状优先的应用层组播协议可扩展性差等缺点,提出一种新的应用组播协议,协议采用特殊的二维层次结构。在低层,将距离近的结点划分为同一个域,域内成员组织成车轮状,域成员只和邻居结点交换信息,减少了维护通信量。在高层,将距离较远的域首组织成网状结构,上下层通过不同的路由算法并行地传输数据,使得数据可以尽快到达远处的结点,提高了传输效率。仿真结果表明,该组播协议具有较小的控制开销、链路压力和端到端延迟。     

多层交换机在Intranet中的应用研究

摘要：本文针对路由器与第三层交换机在Intranet中应用的瓶颈问题，分析了第三层交换技术的工作机制和多层交换机在Intranet中的应用优势，提出了多层交换机在现实各VLAN间通信、与Intranet的互连、网络安全与管理及QoS等的应用方案。     

基于跨层竞争的PRMAC协议的优化研究

基于流水路由的MAC协议PRMAC(Pipelined Routing Medium Access Control)是无线传感网络WSNs(Wireless Sensor Networks)的典型的基于跨层竞争的同步MAC协议. PRMAC协议允许一个周期内进行多跳传输.但是,PRMAC协议的传输请求发送包RTSD(Request-To-Send Data)和确认发送数据包CTSD(Confirmation-To-Send Data)在同一个数据包窗口传输,降低了路由性能.为此,对 PRMAC 协议进行改进,提出面向多跳场景的 PRMAC 协议 MH-PRMAC(Multi-Hop PRMAC). MH-PRMAC协议采用新的周期结构,并在休眠窗口内设置两个独立窗口,再由它们分别传输RTSD和CTSD包.实验数据表明,提出的MH-PRMAC协议有效地降低了数据包传输时延,并提高了数据包传输率.     

Benefits of Membrane Electrode Assemblies with Asymmetrical GDL Configurations for PEM Fuel Cells

Membrane electrode assemblies (MEAs), based on commercial catalyst‐coated membranes combined with various gas diffusion layers (GDLs) on anode and cathode, were studied in terms of their specific advantages for different operations regimes of proton exchange membrane fuel cells (PEMFCs.) It is verified that MEAs with optimized gas diffusion layer designs (backing and micro‐porous layers) on anode and cathode are able to provide improved cell performance combined with a largely reduced sensitivity towards changes in the relative humidity as compared to MEAs with symmetrical gas diffusion layer configuration.     

Enhancement of the Passive Direct Methanol Fuel Cells Performance by Modification of the Cathode Microporous Layer Using Carbon Nanofibers

Mass transfer is a key parameter affecting the performance of the passive direct methanol fuel cells (DMFCs), which work under natural convection. In this study, effect of carbon nanofibers (CNFs) addition to the cathode microporous layer (MPL) on the performance of the passive DMFCs was investigated. The results indicated that CNFs content has a significant influence on both of the mass transport and the electrochemical surface area (ECSA). Interestingly, addition of the CNFs (20 wt.%) leads to increase the power density of the passive DMFC to 160% compared to pristine carbon black MPL. At low current density, the CNFs content has no influence on the performance, while at high current density the maximum performance can be obtained at 20 wt.% CNFs then the performance decreases with further increase in the CNFs content. Although the highest catalyst utilization is observed at 40 wt.% CNFs, a maximum power density of 36 mW cm^–2 can be obtained at 20 wt.% CNFs and this is related to the significant effect of the mass transfer resistance under the passive operation conditions. Overall, addition of CNFs to the MPL can be considered an effective strategy to modify the passive DMFCs performance.     

Suppressing methanol crossover with a deposited quaternary Pt-based catalyst on the Nafion surface

A Pt₄₉–Ru₃₅–Ir₆–Os₁₀ alloy layer is deposited on the Nafion membrane surface using the impregnation-reduction (IR) method to mitigate methanol crossover. The methanol crossover in a membrane electrode assembly (MEA) with a deposited Pt–Ru–Ir–Os layer is compared with a MEA without any layer on the proton exchange membrane (PEM). The deposited Pt₄₉–Ru₃₅–Ir₆–Os₁₀ layer functions like a catalytically active layer, a methanol barrier, and an electrode all at the same time. This layer yields up to a 30% suppression of methanol crossover and a 15% improvement in fuel cell voltage performance (@170 mA cm⁻²) at 80 °C. The porous metal alloy layer with a high surface area of the Pt–Ru layer suppresses methanol crossover by the catalytic activity of the deposited layer. The presence of the solid Pt₄₉–Ru₃₅–Ir₆–Os₁₀ layer on the Nafion membrane surface reduces the proton conductivity of the PEM (from 10.75 to 4.22 mS cm⁻¹), and degrades the output of the cell voltage performance (from 0.350 to 0.335 V at 90 mA cm⁻² of current density) at 60 °C, even though methanol crossover is reduced (from 6928 ppm to 4415 ppm (CO₂ concentration at cathode exhaust is proportional to methanol crossover)).     

高压水在焦炉气配套甲醇装置中的应用

通过高压水力切割煤气管线的盲端进行甩头、煤气管道在线割孔和高压水清洗炉门和循环氨水喷嘴、以及设备除锈的实际生产应用,总结了该技术的特点,可供同行在处理此类问题时借鉴。     

Molecular engineering to improve carrier lifetimes for organic photovoltaic devices with thick active layers

The morphology of the bulk heterojunction absorber layer in an organic photovoltaic (OPV) device has a profound effect on the electrical properties and efficiency of the device. Previous work has consistently demonstrated that the solubilizing side-chains of the donor material affect these properties and device performance in a non-trivial way. Here, using Time-Resolved Microwave Conductivity (TRMC), we show by direct measurements of carrier lifetimes that the choice of side chains can also make a substantial difference in photocarrier dynamics. We have previously demonstrated a correlation between peak photoconductance measured by TRMC and device efficiencies; here, we demonstrate that TRMC photocarrier dynamics have an important bearing on device performance in a case study of devices made from donor materials with linear vs. branched side-chains and with variable active layer thicknesses. We use Grazing-Incidence Wide Angle X-ray Scattering to elucidate the cause of the different carrier lifetimes as a function of different aggregation behavior in the polymers. Ultimately, the results help establish TRMC as a technique for screening OPV donor materials whose devices maintain performance in thick active layers (>250 nm) designed to improve light harvesting, film reproducibility, and ease of processing.     

紫外激光切割覆盖膜速度提升研究

文章针对基模激光束在切割运用中的特点,分别从激光频率,激光功率两个方面对紫外激光切割覆盖膜速度的影响条件进行研究,并进行相关的实验验证。同时运用我们的研究结果将39μm厚的覆盖膜切割速度由200 mm/s提升到350 mm/s。     

高含水期剩余油研究方法及影响因素分析

经过长期注水开采的油田已经基本进入了高含水期,研究剩余油的分布以及油田开发难度越来越大。高含水期剩余油对于增加可采储量和提高采收率具有很大的潜力,研究剩余油势在必行,主要从成因、影响因素、研究方法三方面进行。