Tree and Group Based Reliable Multicast Protocol

The paper proposes a reliable multicast protocol which is appropriate for real-time and interactive collaborative environment. The control tree and grouping mechanism are introduced to make error recovery localized, which can efficiently decrease the amount of packet stream on the backbone of network and the workload of host. Analysis shows that the protocol has perfect throughput and can be extended to very wide applications.     

TCP/IP在卫星通信系统中的应用研究

简要介绍了国际互联网的发展趋势及其在农业卫星指挥调度系统中的应用,分析了TCP/IP的特点,论述了卫星通信系统信道传输中效率较低的原因,提出了在网络层和链路层的解决方案。     

Irrigation scheduling performance by evapotranspiration-based controllers

Evapotranspiration-based irrigation controllers, also known as ET controllers, use ET information or estimation to schedule irrigation. Previous research has shown that ET controllers could reduce irrigation as much as 42% when compared to a time-based irrigation schedule. The objective of this study was to determine the capability of three brands of ET-based irrigation controllers to schedule irrigation compared to a theoretically derived soil water balance model based on the Irrigation Association Smart Water Application Technologies (SWAT) protocol to determine the effectiveness of irrigation scheduling. Five treatments were established, T1-T5, replicated four times for a total of twenty field plots in a completely randomized block design. The irrigation treatments were as follows: T1, Weathermatic SL1600 with SLW15 weather monitor; T2, Toro Intelli-sense; T3, ETwater Smart Controller 100; T4, a time-based treatment determined by local recommendations; and T5, a reduced time-based treatment 60% of T4. All treatments utilized rain sensors set at a 6 mm threshold. A daily soil water balance model was used to calculate the theoretical irrigation requirements for comparison with actual irrigation water applied. Calculated in 30-day running totals, irrigation adequacy and scheduling efficiency were used to quantify under- and over-irrigation, respectively. The study period, 25 May 2006 through 27 November 2007, was drier than the historical average with a total of 1326 mm of rainfall compared to 1979 mm for the same historical period. It was found that all treatments applied less irrigation than required for all seasons. Additionally, the ET controllers applied only half of the irrigation calculated for the theoretical requirement for each irrigation event, on average. Irrigation adequacy decreased when the ET controllers were allowed to irrigate any day of the week. All treatments had decreased scheduling efficiency averages in the rainy season with the largest decrease of 29 percentile points with a timer and rain sensor (T4) and an average decrease of 20 percentile points for the ET controllers, indicating that site specific rainfall has a significant effect on scheduling efficiency results. Rainfall did not drastically impact the average irrigation adequacy results. For this study, there were two controller program settings that impacted the results. The first setting was the crop coefficients where specific values were chosen for the location of the study when calculating the theoretical requirement whereas the controllers used default values. The second setting was the soil type that defines the soil water holding capacity of the soil. The ET controllers were able to regularly adjust to real-time weather, unlike the conventional irrigation timers. However, the incorporation of site specific rainfall measurements is extremely important to their success at managing landscape water needs and at a minimum a rain sensor should be used.     

凌源青龙河省级自然保护区现状及管护措施

辽宁省凌源青龙河保护区动植物资源异常丰富,具有独特性、稀有性和不可替代性。因此,如何提升资源管护品位,实现人与自然和谐共处,刻不容缓。     

机井施工管理中存在的问题及对策

阐述了机井施工管理过程中存在的问题,并提出了切实可行的对策。     

无线射频模块在曲轴臂距差测量中的应用

为了克服机械式拐档表和有线数显式臂距差测量仪的缺陷,设计了一种采用无线射频模块（nRF24L01）实现双向通信的无线臂距差测量系统．该系统采用SW—ARQ和连续发送相结合的无线通信协议,将霍尔式位移传感器采集的臂距差信号传输给主控单片机,实现了无线传输．实验结果表明该系统在提高测量方便性的同时,测量精度可达到0．005mm．     

基于SNMP舰船电力监控网络管理的实现

西方经济思想在中国的传播,既有推进中国政治经济学多元发展积极的一面,又有排斥阻碍发展的消极影响。新自由主义经济学派的去意识形态论、鼓吹自由化和私有化等思想严重冲击了中国政治经济学;凯恩斯经济学和新制度经济学的国家干预、福利国家、经济制度等思想对中国政治经济学的发展产生了积极的影响。     

安全协议中的潜在攻击

阐述了网络安全协议中一些常见的攻击方式,并论述了这些攻击产生的原因和避免此类攻击的方法.     

基于Windows系统的PPPoE协议的实现

提出了一种在 Windows2 0 0 0系统中实现 PPPo E(PPP over Ethernet)客户端软件的方案 ,该方案利用现有 Windows系统的资源 ,绕过 PPP的细节而实现 PPPo E协议 ,并使 PPPo E协议同 Windows之间达到无缝结合 ,解决了 PPPo E“服务器 /客户端”平台搭建问题。介绍了方案的实现 ,包括 PPPo E客户端软件的总体结构、工作流程以及 PPPo E协议驱动等主要功能模块。所完成的系统软件已通过实地检测 ,可使用户在Windows98/ SE/ 2 0 0 0 / ME上实现 ADSL (Asymmetric Digital Subscriber L ine,非对称数字用户专线 )的接入 ,各项数据传输参数都符合 ADSL传输指标     

谈随书附盘的管理与利用

本文通过对随书附盘的内容进行分析 ,指出应依据附盘内容管理附盘图书 ,方便读者利用。