Performance analysis and comparison of IEEE 802.11 distributed coordination function and improved schemes

To improve the media access control mechanism and enhance the performance of large scale wireless LANs, the distributed coordination function of IEEE802.11 standard and two typical improved schemes are studied extensively. Compared with the distributed coordination function, the fast collision resolution mechanism greatly enhances the throughput, but deteriorates the delay jitter and fairness of wireless LANs. The new self adaptive distributed coordination function markedly improves the delay jitter and fairness performance, while enhancing the throughput of wireless LANs to a certain degree. Hence, with further improvement, the new self adaptive distributed coordination function is more suitable for large scale wireless LANs for multimedia information transmission.     

Analysis and verification of TCP goodput of poisson distribution station over WLANs

By analyzing the throughput model of IEEE 802.11 MAC DCF put forward by Bianchi G, the retransmitting limit is extended and the state of direct transmission with no backing off is added in its discrete Markov chains to refine and perfect the classic model. The following assumption is proposed: the number of wireless stations accessing to AP in BSS met poisson distribution within a certain period of time. Under this assumption, both of the corresponding model and the quantified expression of calculating its goodput are provided. The rationality and effectiveness of the proposed model are verified with emulation of unidirectional TCP flow from AP to wireless stations.     

Performance Analysis of MIPv4 Regional Registration Combined with Low Latency Handoffs

The mechanism of MIPv4 regional registration and the low latency handoff protocols are introduced. Ways and procedure of pre-registration handoff and post-registration handoff are discussed also. The authors analyze the performance of the low latency handoff protocols combined with low latency handoffs over a wireless access based on IEEE 802. 11 standard in a tree-like network topology. The performance of pre-registration and post-registration scheme is given by simulation.     

壳聚糖铁(Ⅲ)配合物的合成及结构表征

【研究目的】为了利用高分子壳聚糖的生物活性,寻找理想的补铁制品,在均相反应条件下,以壳聚糖为载体与Fe3+离子配位,合成了壳聚糖铁(Ⅲ)配合物;【方法】用元素分析、UV光谱和IR光谱等研究了配合物的组成与性质,并优化了配合物的合成条件;【结果】壳聚糖对Fe3+的吸附具有较好的动力学性能,随着温度的升高,反应达到平衡的时间缩短;壳聚糖对Fe3+离子吸附等温线符合Langmuir吸附等温线方程,在室温下,pH为1.8时吸附8h的饱和吸附量Qmax = 62.89mg/g,b =4.969J/mg;壳聚糖铁(Ⅲ)配合物的UV光谱中出现了新的吸收峰,IR光谱分析显示,形成配合物后,壳聚糖的部分特征吸收峰也发生了一定的位移,光谱分析的结果表明壳聚糖与Fe3+离子之间可能发生了配位反应;壳聚糖中主要是-NH2和-OH参与了与金属离子的配位,部分乙酰氨基(-CONH2)也可能参与了配位。【结论】实验结果有望使壳聚糖铁(Ⅲ)配合物成为一种具有较好生物利用度的营养型补铁剂,使壳聚糖铁(Ⅲ)配合物成为具有多功能的保健药品。     

Building Wireless Sensor Networks(WSNs) by Zigbee Technology

ZigBee technology is a new and exoteric wireless interconnection technology . Sensor Networks is combined by senor technology , ZigBee, IEEE 1451.2 and route protocol. This paper puts forward the implementation of each module on the wireless gas meter data -transmitting system.     

Waiting for Broadband: Local Competition and the Spatial Distribution of Advanced Telecommunication Services in the United States

ABSTRACT With the passage of the Telecommunications Act of 1996, Congress directed the Federal Communications Commission and all fifty U.S. states to encourage the deployment of advanced telecommunication capability in a reasonable and timely manner. Today, with the rollout of advanced data services such as digital subscriber lines (xDSL), cable modems, and fixed wireless technologies, broadband has become an important component of telecommunication service and competition. Unfortunately, the deployment of last‐mile infrastructure enabling high‐speed access has proceeded more slowly than anticipated and competition in many areas is relatively sparse. More importantly, there are significant differences in the availability of broadband services between urban and rural areas. This paper explores aspects of broadband access as a function of market demand and provider competition. Data collected from the Federal Communications Commission is analyzed using a geographic information system and spatial statistical techniques. Results suggest significant spatial variation in broadband Internet access as a function of provider competition in the United States.     

无线网络接入点TCP流时间公平性

对无线网络接入点上下行TCP流存在的时间不公平性现象进行了研究,报告了无线网络接入有线网络存在的拥塞控制问题现状,提出了一种的无线网络TCP流公平调度算法。采用快速的TCP流优先发送方法,既保证了各流吞吐率公平性,又解决了慢速的TCP占用信道时间过多的问题,实现了各流占用信道的时间公平性。通过网络仿真实验证明,新的公平调度算法比传统的算法在性能上有较大的改进,达到了提高网络整体效率的目的。     

植物U-box蛋白在植物先天免疫反应中的作用及其研究进展

为了分析植物U-box蛋白在植物先天免疫反应中的作用及其机制,总结了U-box的结构特点及其与RING-finger结构的异同;归纳了植物U-box蛋白的分类及分类特点;并综述了SPL11、PUB12/PUB13、PUB17等U-box蛋白在植物PTI信号传导途径中的调控作用与调控机制,以及ACRE276、PUB17、CMPG1、MAC3A/MAC3B等U-box蛋白在植物ETI信号传导途径中的调控作用与调控机制。得出植物U-box蛋白的结构特点、生化功能及其在植物先天免疫反应中的作用与分子机制,并认为对植物U-box蛋白的研究可为植物抗病分子育种提供基因资源与参考信息。     

Analysis of Failure Behaviors in Glass under Shock Loading

The failure wave phenomena in glass media under shock loading are analyzed. The propagating mechanism and dynamic characteristics of failure wave and the property of failure layer are revealed. On the basis of experimental analysis, a damage accumulating model determinated by partial stress impulse is proposed, which describes the phenomenon of failure delay in materials being done with the Heaviside function. The propagating procedure, the evolution characters of transverse stress and longitudinal compression strain in failure layer are simulated. Furthermore a phenomenon is revealed that the failure wave velocity decreases after reflection of rarefaction wave at the boundary of failure layer.     

粮油食品专业毕业设计(论文)创新模式实施过程中的质量监控

河南工业大学粮油食品专业具有鲜明的专业和行业特色。为满足社会对高素质创新应用型人才的需求,粮油食品特色专业进行了毕业设计(论文)创新模式的研究和探索,主要从毕业设计(论文)选题、中期检查、论文写作及答辩等方面对创新模式的质量体系进行监控。     

耕作方式和施氮量对稻茬小麦产量构成和群体质量的影响

以苏麦188为材料,在水稻秸秆全量还田条件下研究板茬、旋耕、耕翻等耕作方式和施氮量210kg/hm2、240 kg/hm2、270 kg/hm2对小麦群体质量和产量及其结构的影响,为稻茬小麦大面积机械化栽培提供参考。结果表明：板茬方式产量显著高于旋耕和耕翻;随施氮量增加,产量逐渐提高。产量在不同耕作方式与施氮量间存在显著的互作效应。相比其他耕作方式,板茬方式每穗粒数和千粒重较高;群体茎蘖数多,但分蘖成穗率不高、源库协调水平偏低,花后具有较高的光合生产能力。随施氮量增加,穗数和每穗粒数、群体茎蘖数和分蘖成穗率、花后光合生产能力以及源库协调性均呈提高趋势。说明,通过合理增施氮肥可以进一步改善板茬方式下小麦群体质量,协同提升产量构成因素,实现增产。本试验条件下采用板茬方式配以施氮量270 kg/hm2或240 kg/hm2处理产量最高。     

冬小麦条锈病内外菌源的原理和效应研究

调查研究表明,冬小麦条锈病发生晚的麦田,病叶主要分布在上部,与早发麦田相比,同部位叶片发病轻,因而形成的本田菌源量低,不利于后期小麦条锈病暴发,控病效果明显。因此对早发麦田要早期挑治和中期控制,对晚发麦田要中期控制,阻止外部菌源的落户和本田菌源的形成,有效减轻后期发病程度, 中度以上发病年份,齐穗扬花期普防病田     

基于广义谐振理论的输电线路中波无源干扰谐振频率预测

现有IEEE（institute of electrical and electronics engineers）标准,目前只能明确0.5~1.7 MHz有限频段的输电线路无源干扰谐振机理。为拓展输电线路无源干扰谐振的研究频率,引入广义谐振理论,提出了一种基于电磁场能量平衡的干扰谐振频率预测构想。将大尺度空间下输电线路铁塔阵列及天线等效为广义封闭系统,从而基于复坡印廷定理,推导了电磁开放系统广义谐振因子的表达式,求解得到的广义谐振因子零值点为无源干扰谐振频点。该方法由于避开了传统将铁塔等效为半波天线的局限,因此可以实现中波频段无源干扰谐振预测。采用IEEE标准算例进行验证,结果表明：1.7 MHz频率以下,基于广义谐振理论的无源干扰谐振频率预测值和缩比模型实测值最大误差不超过±0.169 MHz。     

Parallel Operating the 13-Bit Lattice Gas Automata Model

The parallel operation mechanism of 13 Bit lattice gas automata model, which can quickly compute and include more sites, is presented. Via coding and computing for particles of sites by bit, the parallel computing is achieved by transfering the particles propagation and collision into its backup and reloading. This mechanism can simulate correctly and validly some fluid motion with complex geometry boundary, such as flow through coke porous media. [WT5HZ]     

Symbolic and social dimensions in the economic production of seaweed

Abstract: Based on the thesis of ‘deagrarianisation’ of farming economies, work on sustainable rural livelihoods (SRL) has successfully captured the agency of rural producers as they diversify their livelihoods to minimise risk. SRL captures a complex interplay of local and global factors, as well as the synergies emanating from natural (environmental), economic and social capital that underpin diversification. The framework has been found useful for analyses of change in coastal, marine‐based livelihoods. However, agency at the local level implies equal power to accept and reject development interventions. The way groups diversify or use the options open to them depends as much on access to resources (the means), as on how that access is interpreted (the meaning), and the latter dimension is a creative (unpredictable) one. New introduced forms of economic activities, in this case seaweed farming, can be assigned meaning by participants that were unanticipated by change agents. Livelihood diversification through seaweed cultivation on Banggi island off Kudat, northern Sabah (East Malaysia) is not attained by economic factors alone but also by the meaning attached to the activity.     

Testing and modal analysis on multi stage planetarygearbox housing of shield tunnelling machine

The finite element model is developed for the multi stage planetary gearbox housing in shield tunnelling machine (STM), and the the eigenvalue problem is solved by using block Lanczos method, and then the low order natural frequencies and corresponding modes are extracted. Based on the theory of experimental modal analysis, the modal testing is made for the gearbox housing by pulse excitation method. The least squares complex frequency domain (LSCF) estimation method is used to analyze the modal data, and the natural characteristics of housing is obtained. According to the modal assurance criterion (MAC), the experimental modal parameters are validated. Modal analysis shows that the experimental data is coincided with analytical results, which indicates the accuracy of the theoretical model and testing method. The coupling sympathetic vibration is disappearing between the gears train and housing, the local vibration is large at the high speed side of gearbox housing, and the torsional mode is outstanding under operating condition. The research results provide theoretical basis and experimental support for the structural optimization of the gearbox of STM.     

Research and implementation on WNXD database storage strategy

For the drawbacks of NativeXML, such as low data storage performance, low efficiency of querying and updating, a new kind of semi-structured information storage model, named WNXD, is proposed. The dynamic invert-sorting technique and data imaging mechanism are introduced to combine the record and the page storage mode, three structured indexes are established to achieve structural and dynamic growth with different ways. A practical storage mode is created to provide a comprehensive access strategy from global to local, and from elements, attributes to values, which guarantees effective and complete data storage, especially for the data with different types. The query number decreases I/O and the system performace is improved.     

Information Platform of Enterprise Office Based on Dynamic and Instantaneous Coordination Work

It is not able to provide the decision service information that should be instantaneous, exact and all-around for governor by means of traditional mode of information communication. And it is important problem faced by modernization office. In order to get the needed information instantaneously and satisfy requirement of coordination work, the paper presents a kind of enterprise office information platform based on dynamic coordination work. The platform can guarantee coordination work of the system dynamically and instantaneously, and it is stronger in functions, and facility in use. It is discussed in more details to the design of dynamic coordination workflow drive and coordination message service drive and so on. The application effect of practical engineering shows that the design is successful.     

Recommending Trust Model Based on Behavior for Distributed CA in MANET

Mobile Ad Hoc Networks(MANET) is a multi-ho Pand instant self-organized autonomous system of a collection of wireless mobile nodes.A multi-domain full-distributed Certification Authorities system model was proposed founding on its trait of territorial communication.The thesis researched this model and proposes a new model for the interoperability between virtual Certification Authorities named extended recommending trust model based on behavior.It can improve the system's security,retractility and robustness by dynamic trust chain maintenance with feedback information in the actual course.     

Research on Water Resource and City Construction in Chengdu

Integrated with the study on Chengdu space developing strategy, in this paper, the problem about Chengdu water resource is analyzed and it is concluded that the Chengdu water resource has comparative advantage and can support its great development.But the construction mode must be observed.On the microscopic layer, the water resource was deteriorated in Chengdu City.A fundamental of gradual eco-construction is suggested, which is adapted to the city space construction.The key of the city eco-construction is the coordination of water resource with the city development.