上海金山地区近50a雷暴气候特征分析

使用1959～2008年上海金山地区站点观测资料,分析近50a该地区雷暴的气候特征。结果表明:上海金山地区年雷暴日数年际变化大,平均27.8d,最多52d,最少12d;每10a减少1d,呈逐渐减少的趋势;该区雷暴季节性强,集中出现在3～10月,夏季雷暴发生次数占7成以上。雷暴初始日在3月中旬,终日在10月上旬,雷暴初(终)日年际间差异大。雷暴日数存在1～2a左右、准3a和准6a的年际尺度显著变化周期。候平均气温上升稳定通过6℃,是初雷暴日的温度阈值,候平均气温下降稳定通过18℃,是终雷暴日的温度阈值。     

填充氟塑料暨冶金液压缸密封应用

简要及综合性地叙述了,特瑞堡公司拥有知识产权的填充氟塑料密封材料;介绍典型的密封名称、结构及在治金液压缸中的应用方案。     

PVA纤维和纳米SiO2对地聚合物砂浆断裂性能的影响

针对72个尺寸为100mm×100mm×400mm的预切口小梁试件进行三点弯曲断裂试验,以临界有效裂缝长度、起裂断裂韧度、失稳断裂韧度和断裂能等参数为评价指标,研究了纳米SiO_2质量分数或聚乙烯醇(PVA)纤维体积分数对地聚合物砂浆断裂性能的影响.结果表明:在一定掺量范围内,纳米SiO_2或PVA纤维的掺入可以提高地聚合物砂浆的断裂性能;PVA纤维或纳米SiO_2掺入地聚合物砂浆后,能较大幅度地提高小梁试件的峰值荷载、临界有效裂缝长度、起裂断裂韧度、失稳断裂韧度和断裂能,这些断裂参数在纳米SiO_2掺量或PVA纤维掺量逐渐增大时皆呈现先增大后减小的趋势,并且在PVA纤维体积分数为1.0%或纳米SiO_2质量分数为1.5%的条件下达到最大值,此时小梁试件的荷载-裂缝口张开位移曲线最饱满,与坐标轴之间的包络面积最大.     

浅析业主对建设工程施工索赔的预防及处理

从业主的角度出发,对建设工程施工索赔管理的基本思路进行了论述,对索赔预防及处理的具体措施进行了分析,并对业主的施工索赔管理提出了几点思考。     

浅谈业主方工程施工合同的管理

从业主的角度出发，对工程施工合同及业主方工程施工合同管理的特点进行了分析，对业主方工程施工合同管理包括前期的合同策划以及施工过程中合同管理应注意的问题提出了自己的看法。     

铝塑复合板的发展现状与前景

简要的介绍了铝塑板在国外的发展概况；评述了国内铝塑板生产企业、原材料供应、应用和市场价格四方面情况。作者认为铝塑板是一种综合性能良好的新型装饰材料．目前处于快速增长阶段，预测到２０００年消费量将达 １８００万ｍ~２。由于国内现有生产能力已超过市场需求量，所以企业投资铝塑板项目应当慎重。     

Seeking powerful information initial spreaders in online social networks: a dense group perspective

The rapid growth of online social networks (OSNs) has ultimately facilitated information spreading and changed the economics of mobile networks. It is important to understand how to spread information as widely as possible. In this paper, we aim to seek powerful information initial spreaders with an efficient manner. We use the mean-field theory to characterize the process of information spreading based on the Susceptible Infected (SI) model and validate that the prevalence of information depends on the network density. Inspired by this result, we seek the initial spreaders from closely integrated groups of nodes, i.e., dense groups (DGs). In OSNs, DGs distribute dispersedly over the network, so our approach can be fulfilled in a distributed way by seeking the spreaders in each DG. We first design a DG Generating Algorithm to detect DGs, where nodes within the DG have more internal connections than external ones. Second, based on the detected DGs, we design a criterion to seek powerful initial spreaders from each DG. We conduct experiments as well as statistical analysis on real OSNs. The results show that our approach provides a satisfactory performance as well as computational efficiency.     

Unified fixed‐point analysis of IEEE 802.11 WLAN under saturated and unsaturated conditions

Most of analysis so far for IEEE 802.11 wireless local area networks (WLANs) focuses on saturated condition. However, it is of practical value to take into account the unsaturation case. In this paper, we modified Bianchi's Markov back‐off model to make it applicable to unsaturated condition and the analytic results are provided by employing the renewal‐reward theorem. Under our proposed model, we study the fixed‐point solution of the system and provide a condition to guarantee both the uniqueness and balance of the fixed point. From the fixed point, we find that under unsaturated condition, network parameters should be adjusted according to the traffic load. Then, we study the system throughput. In the case where there are a large number of nodes, we provide closed‐form formulas for the collision probability, the aggregate attempt rate, and the throughput. We find that in such a scenario, the system yields similar performance as that under saturated situation. Moreover, we compare all the results with those under saturated condition and find the latter is a special case of our results. Hence, all of our analysis based on unsaturated condition well covers saturated condition. Our analytical results are validated through ns2 simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

一类具有附加食物的Leslic - Gower捕食者-食饵模型的定性分析

研究了一类具有附加食物的Leslie - Gower捕食者-食饵模型平衡点的局部与全局渐进稳定性及其非双曲平衡点的分支行为,并利用数值模拟验证了所得结论的正确性.该研究结果可为应用额外食物进行生物防治提供参考.     

酸溶铝和铌含量对取向硅钢夹杂物特征的影响

摘 要：为了掌握Als（酸溶铝）和Nb含量对取向硅钢中夹杂物特征的影响,借助场发射扫描电镜(FE-SEM)结合能谱仪(EDS)和图像分析软件研究了钢中夹杂物类型、数量、尺寸及尺寸分布,结合钢液凝固过程中溶质元素的微观偏析模型,重点分析了Als和Nb含量影响钢中AlN和NbN析出的机制。结果表明,钢中的夹杂物以NbN、AlN和AlN-NbN为主,夹杂物尺寸分布由Als和Nb含量综合影响。Als含量的增加使含氧复合夹杂物中Al2O3含量增加,SiO2含量降低,促进了钢中硅酸盐类氧化物夹杂的去除,但大大增加了AlN和AlN-NbN夹杂的偏析析出。Nb含量的增加使夹杂物的平均尺寸变小,促进了钢中NbN在凝固前沿的提前析出和以氧化物为核心析出。Als主要影响钢中的氧化物和氮化物夹杂,Nb通过影响与Als结合的O和N的活度影响钢中氧化物和氮化物夹杂的析出特性。