A Novel Gateway Selection Technique for Throughput Optimization in Configurable Wireless Mesh Networks

Wireless mesh networks (WMNs) have attracted much attention due to their low up-front cost, easy network deployment, stable topology, robustness, reliable coverage, and so forth. These advantages are suitable for the disaster recovery applications in disaster areas, where WMNs can be advantageously utilized to restore network collapse after the disaster. In this paper, based on a new network infrastructure for WMNs, to guarantee high network performance, we focus on the issue of throughput optimization to improve the performance for WMNs. Owing to selecting different mesh router (MR) as the gateway will lead to different network throughput capacity, we propose a novel gateway selection technique to rapidly select the optimal MR as the gateway, in order to maximize the network throughput. In addition, we take into account the traffic distribution for the MR to eliminate traffic congestion in our method. The performance of our proposed method is evaluated by both numerical and simulated analysis. The simulation results demonstrate that the gateway selection method is effective and efficient to optimize the throughput for WMNs.     

Theatre in the Sky: a ubiquitous broadband multimedia‐on‐demand service over a novel constellation composed of quasi‐geostationary satellites

To meet an ever‐growing demand for wideband multimedia services and electronic connectivity across the world, development of ubiquitous broadband multimedia systems is gaining a tremendous interest at both commercial and academic levels. Satellite networks will play an indispensable role in the deployment of such systems. A significant number of satellite communication constellations have been thus proposed using Geostationary (GEO), Medium Earth Orbit (MEO), or Low Earth Orbit (LEO) satellites. These constellations, however, either require a potential number of satellites or are unable to provide data transmission with high elevation angles. This paper proposes a new satellite constellation composed of Quasi‐GeoStationary Orbit (Quasi‐GSO) satellites. The main advantage of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. Based on a combination of this Quasi‐GSO satellites constellation and terrestrial networks, the paper proposes also an architecture for building a global, large‐scale, and efficient Video‐on‐Demand (VoD) system. The entire architecture is referred to as a ‘Theatre in the Sky’. Copyright © 2006 John Wiley & Sons, Ltd.     

LED显示屏二次开发接口醮设计与实现

针对LED显示屏工程应用中对二次开发接口的需求,提出了一种二次开发接口的方法,归纳为通信通道、节目和命令三类接口,并介绍其基本的功能。据此方案,可在工程应用中简单、快速地实现二次开发,完成系统集成。     

LED显示屏网络直连的设计与实现

文章针对LED显示屏调试过程中对网络直连的需求,提出了一种网络直连的方法。该方法可自动匹配PC机与LED显示屏IP在同一网段,实现它们之间的网络直连通信,启动系统时自动保存PC机网络配置,退出系统时自动恢复PC机网络配置。通过这种方式使用户不用知道LED显示屏的IP地址,也不用修改PC机的IP,便可实现PC机与LED显示屏之间的网络通信,让用户方便、高效地调试LED显示屏,并为类似的应用提供了一种可借鉴的解决方案。     

THE CARBONITRIDE IN GAS CARBONITRIDING LAYER ON 18CrMnNiMoA STEEL

本文以电解提取-化学分离-X射线衍射逐层相分析及电子显微镜观察、电于衍射、化学分析等综合方法,研究了18CrMnNiMoA钢的气体碳氮共渗层中碳氮化物的形貌、结构、数量、组成、沿渗层的分布以及合金元素在各相间的分配,并对碳氮共渗层的强化机制作了某些讨论.     

On Efficient Traffic Distribution for Disaster Area Communication Using Wireless Mesh Networks

In recent time, a great deal of research effort has been directed toward promptly facilitating post-disaster communication by using wireless mesh networks (WMNs). WMN technology has been considered to be effectively exploited for this purpose as it provides multi-hop communication through an access network comprising wireless mesh routers, which are connected to the Internet through gateways (GWs). One of the critical challenges in using WMNs for establishing disaster-recovery networks is the issue of distributing traffic among the users in a balanced manner in order to avoid congestion at the GWs. To overcome this issue, we envision a disaster zone WMN comprising a network management center. First, we thoroughly investigate the problem of traffic load balancing amongst the GWs in our considered disaster zone WMN. Then, we develop traffic load distribution techniques from two perspectives. Our proposal from the first perspective hinges upon a balanced distribution of the bandwidth to be allocated per user. On the other hand, our second perspective considers the dynamic (i.e., varying) bandwidth demands from the disaster zone users that requires a more practical and refined distribution of the available bandwidth by following an intelligent forecasting method. The effectiveness of our proposals is evaluated through computer-based simulations.     

相转移催化合成乙酸苄酯

采用氯苄和乙酸钠三水合物为原料,二甲苯为溶剂,十二烷基三甲基氯化铵为相转移催化剂,对乙酸苄酯的合成反应进行了改进。在反应温度为120~130℃,n(氯苄)∶n(乙酸钠三水合物)∶n(催化剂)=1∶1.3∶0.03的较佳工艺条件下,氯苄转化率≥99.5%,产品收率≥98.3%,产品含量≥99.8%。     

Effective and simple recovery of 1,3-propanediol from a fermented medium by liquid–liquid extraction system with ethanol and K_3PO_4

1,3-Propanediol,traditionally obtained from fossils,has numerous industrial applications,including use in the production of high performance polymers.The microbial production of 1,3-propanediol presents several opportunities,and the final purity grade determines its price and commercial viability.The development of novel separation technology could improve the economic viability of the bioproduction of 1,3-propanediol.Thus,we investigated salting-out extraction as a novel process for 1,3-propanediol recovery from fermentation broth.Initially,a screening for the best salt/solvent combination was conducted and then optimized using the response surface methodology.The solvents studied were methanol,ethanol,isopropanol and acetone,and the salts examined were K_2HPO_4,Na_2CO_3,K_2CO_3,(NH_4)_2SO_4,NaHPO_4,K_3PO_4 and C_6H_5NaO_7.The optimal extraction system consisted of 34 wt%K_3PO_4,28 wt% ethanol,and 38 wt% fermentation broth containing 23.0 g·L~(-1)1,3-propanediol,which gave the highest partition coefficient of 33 and recovery yield of 97%.The results demonstrated that salting-out extraction was a promising method for 1,3-propanediol recovery from fermentation broth.     

Growth of ice crystals in frozen specimens

The formation of ice crystals, which might be the possible artefact in cryo-techniques for electron microscopy, was examined during the rewarming process of rapidly frozen erythrocytes. Intracellular ice formation, which is usually found in cells suspended in saline by rapid freezing, was inhibited by the addition of 30% glycerol. When such glycerinated cells, having no ice crystals at liquid nitrogen temperature, were rewarmed to higher temperatures above ? 80° C, recrystallization of ice occurred. Ice particles became visible within the cells even at ? 80°C and grew larger with a temperature rise. From the results obtained in the morphological and physiological investigations, it also became evident that the recrystallization of ice appeared prior to the increase in haemolysis during the rewarming process.     

φ3m分级机螺旋轴断裂分析

文章根据电机负荷理论对φ3m分级机螺旋轴进行受力分析，避免了复杂的推导计算和疲劳强度校核。根据现场实际，将机械技术与电气技术结合，分析其断裂原因，提出改进措施，具有较好的效果和借鉴价值。