Performance Evaluation of IEEE 802.15.4 CSMA/CA Scheme Adopting a Modified LIB Model

Since the successful release of the IEEE 802.15.4 standard, a great convenience is offered to applications in low-power and low-rate wireless sensor networks (WSNs) which almost touch upon all aspects in our surrounding circumstances. For time-critical applications, we use a modified Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) mechanism called Linear Increase Backoff (LIB) to enhance the performance of packet delay, but not compromise the metrics of energy efficiency and throughput. An accurate and comprehensive Markov model is used to analyze the characteristics of our LIB scheme predicting packet delay, energy consumption and throughput of unsaturated, unacknowledged IEEE 802.15.4 networks in which the unsaturated state is dependent on the traffic condition rather than the depiction by a predetermined length. Simulation results are consistent with the predictions of this model. We also compare the performance of LIB with that of several mechanisms according to the optimal parameters selected from operating point, and find that packet delay is obviously superior to that of other schemes, while energy efficiency and throughput are superior to others for large number of nodes and high traffic arrivals.     

Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid

Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H₂O₂). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO₃ crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO₃ implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance.     

Studies on pharmacokinetics,body distribution,plasma protein binding rate,and excretion of 1-methyl hydantoin in rats in vivo

In this paper, plasma concentration, plasma protein binding rate, body distribution, and excretion of both oral and intravenous administration of rats were determined by high performance liquid chromatography (HPLC) combining with UV detector. The blood drug concentration of oral and intravenous administration was summarized. The bioavailability of T_1/2 was approximately 0.75?hr. At the meanwhile, the bioavailability was about 18.84?±?2.21%. The plasma protein binding rate of 1-methyl hydantoin was about 24.36?±?0.93%, belonging to low protein binding drug. The result shows that 1-methyl hydantoin can be rapidly distributed in various organs and tissues and quickly eliminated within 6?hr without accumulation in the organs. Its discharge from the urine and feces was 16.58?±?4.48% and 3.37?±?0.71%, respectively. All of the results showed that the recovery rate, liner relationship, specificity, stability, and precision of the method were good. The study also proved that 1-methyl hydantoin has been eliminated quite faster in rats.     

面向客户群的服务方案配置规则挖掘方法

产品/服务配置规则获取的主要方式是用数据挖掘技术从设计实例数据库中提取.客户化服务方案配置规则为服务功能需求和方案特征间的关联规则.考虑到常用关联规则挖掘算法Apriori具有运算复杂的缺点,提出基于PIETM(Principle of Inclusion—Exclusion and Transaction Mapping)算法的配置规则挖掘方法,考虑置信度和有趣度指标,提取强关联规则.针对配置实例数据库数据量较大时,配置规则挖掘的效率会降低且会产生大量冗余规则的问题,采用二元语义模型表达定性的服务功能需求,将同类客户群的功能需求进行合并,替换多样化的功能需求,减少规则的冗余.最后以一工程机械制造企业服务方案配置规则挖掘为例,验证了所提方法的有效性.     

Zhiber-Shabat方程的多辛几何和多辛隐式格式研究

Zhiber-Shabat方程,描述许多重要的物理现象,是一类重要的非线性方程,有着许多广泛的应用前景.本文给出Zhiber-Shabat方程的多辛几何结构和多辛Fourier拟谱方法.数值算例结果表明多辛离散格式具有较好的长时间的数值稳定性.