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针对如何提高车辆自组织网络无线信道资源利用率问题,提出了一种分布式车辆间通信信道接入控制算法,该算法具体表示为利用中国余数定理设计一种用户保障协议序列,车辆节点(亦称用户)依据该协议序列决定其对通信信道的接入,无需基站或中心节点的协调,所设计的协议序列确保每个车辆节点在一个序列周期内至少成功发送一次数据.仿真结果表明,采用本文提出的协议序列控制算法比无反馈时隙ALOHA接入控制算法具有更小的传输时延,能够满足车辆自组织网络通信实时性的要求. 相似文献
174.
王多姿 《中国水能及电气化》2014,(10)
分散性黏土是黏土中的一种,抵抗冲蚀能力较低,易形成管涌,破坏大堤整体安全,必须在大坝修筑中采取适当的反滤等措施降低其危害。目前国内外对于分散性黏土的认识和试验检测仍处于摸索阶段,对其定性判别方法和试验检测手段暂时也没有形成规范,多数均根据经验处理。笔者所在单位根据多年经验,在赤峰市东台子水库黏土心墙土料特性判别及检测中做了大量工作,取得了一定成果,本文以此为例介绍分散性黏土的判别方法,供同仁在试验工作中参考。 相似文献
175.
非平稳时间序列极值统计模型及其在气候-水文变化研究中的应用综述 总被引:2,自引:0,他引:2
伴随全球气候变暖和平均海平面持续上升,极端气象事件出现的频率增加、强度增大,气候变化已经成为导致水文极值非平稳性的一个重要原因。本文总结了气候-水文变化研究中常用非平稳时间序列极值统计模型的结构以及统计推断方法,从降雨极值变化、洪水极值变化等方面分析了非平稳时间序列极值统计模型在气候-水文变化研究中的典型应用案例。国内外研究表明:非平稳时间序列极值统计模型能体现水文极值随时间或协变量的变化情势,非平稳情况下水文极值重现期和风险的概念和计算方法与传统平稳时间序列的频率分析相比存在显著差异。最后对需要进一步研究的问题进行了展望。 相似文献
176.
Spinhoven Philip; Bamelis Lotte; Molendijk Marc; Haringsma Rimke; Arntz Arnoud 《Canadian Metallurgical Quarterly》2009,118(3):520
The study objective was to investigate whether, compared with nonclinical controls, participants with an avoidant, dependent, or obsessive–compulsive Cluster C personality disorder (PD) manifested reduced levels of memory specificity and whether the association of Cluster C PDs with memory specificity is mediated by repetitive negative thoughts and experiential avoidance. The Autobiographical Memory Test (R. J. McNally, N. B. Lasko, M. L. Macklin, & R. K. Pitman, 1995) was administered along with self-report measures (translated into Dutch) for repetitive, uncontrollable, and negative thinking in the form of worry (Penn State Worry Questionnaire; T. J. Meyer, M. L. Miller, R. L. Metzger, & T. D. Borkovec, 1990) and experiential avoidance (Acceptance and Action Questionnaire; S. C. Hayes et al., 2004) to 294 clinical participants diagnosed with Axis I disorders (assessed with the Structured Clinical Interview for DSM–IV Axis I Disorders [SCID-I]; M. B. First, R. L. Spitzer, M. Gibbon, & J. B. W. Williams, 1994) and Axis II disorders (assessed with the SCID-II; M. B. First, R. L. Spitzer, M. Gibbon, & J. B. W. Williams, 1997)—202 with avoidant, 49 with dependent, and 120 with obsessive–compulsive PD—and to 108 matched nonclinical controls. Participants with a Cluster C PD showed lower levels of memory specificity than did nonclinical controls. Depression and worry mediated the effect of Cluster C PDs on memory specificity. Besides depression severity, repetitive, uncontrollable, and negative thinking may constitute a general mechanism mediating the association of various Axis I and II disorders with memory specificity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
177.
The major objective of the paper is to address the main weakness of the reverse Monte-Carlo method applied to jet fire simulation; its slow convergence rate. This is done by replacing the use of a pseudo-random number generator for calculating ray orientations with a ray direction specification based on Sobol sequences. Sobol sequences produce sequences of points on the unit hemisphere that are not independent of each other in that new points in the sequence avoid previous points generated. This has the property that a more uniform pattern of rays on the unit hemisphere is produced, giving a ray convergence rate for the incident heat flux that is asymptotically equivalent to O(NRay−1). The use of Sobol sequences to accelerate convergence of the Monte-Carlo method has been applied in mathematical physics and financial modelling but the results presented here are the first study of quasi-Monte-Carlo methods applied to the incident heat flux integral. The use of Sobol sequences to generate ray directions means that the Central Limit Theorem no longer holds. In its place, it has been demonstrated that it is possible to construct a Gaussian variable from the incident intensity distributions calculated using Sobol sequences. This means it is possible to calculate confidence limits for a prediction of incident heat flux and the confidence limits contract with ray number at a rate of O(NRay−1 ln(NRay)). 相似文献
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Mohamed Hemida Abd-Alla Fatthy Mohamed Morsy Abdel-Wahab Elsadek El-Enany 《International Journal of Hydrogen Energy》2011,36(21):13518-13527
This study was devoted for H2 production from rotten fruits of date palm (Phoenix dactylifera L.) by three fermentation stages. A facultative anaerobe, Escherichia coli EGY was used in first stage to consume O2 and maintain strict anaerobic conditions for a second stage dark fermentative H2 production by the strictly anaerobic Clostridium acetobutylicum ATCC 824. Subsequently, a third stage photofermentation using Rhodobacter capsulatus DSM 1710 has been conducted for the H2 production. The maximum total H2 yield of the three stages (7.8 mol H2 mol−1 sucrose) was obtained when 5 g L−1 of sucrose was supplemented to fermentor as rotten date fruits. A maximum estimated cumulative H2 yield of the three stages (162 LH2 kg−1 fresh rotten dates) was estimated at the (5 g L−1) sucrose concentration. These results suggest that rotten dates can be efficiently used for commercial H2 production. The described protocol did not require addition of a reducing agent or flashing with argon which both are expensive. 相似文献
180.
The effect of repetitive processing on the mechanical properties and fracture toughness of dynamically vulcanized isotactic polypropylene/ethylene‐propylene‐diene rubber blends (TPVs) with and without addition of β‐nucleating agent (β‐NA) was studied. The results showed that the repetitive processing did not cause much loss in the mechanical properties of TPVs, especially for TPVs with β‐NA, and TPVs with β‐NA showed better performance stability than TPVs without β‐NA. Essential work of fracture (EWF) approach was used to study the fracture behavior, and the results showed that the value of we (the specific essential work of fracture) of TPVs without β‐NA showed a significant decrease while that of TPVs with β‐NA almost kept constant after repetitive processing. Differential scanning calorimetry and wide‐angle X‐ray diffraction were used to study the variation of crystalline structures, and the results indicated that the repetitive processing showed no significant influence on the crystalline structures of TPVs, and the β‐NA maintained high‐nucleating efficiency after repetitive processing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献