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1.
会话初始协议（SIP）已经成为一种标准,而随着P2P技术的日趋成熟,SIP和P2P的结合已经成为一种趋势.介绍了一个基于JXTA的P2P-SIP原型系统,主要描述了P2P-SIP系统的基本原理,分析了呼叫流程和系统结构,给出了实现的主要代码以及测试结果 相似文献
2.
针对航天器姿态控制系统常见的传感器故障问题,基于增广P型学习观测器技术研究了故障重构问题,并对故障系统进行了容错控制器的设计.首先,考虑同时存在传感器故障和未知干扰输入的航天器姿控系统状态空间模型,将故障等效考虑成与前一时刻故障估计值和当前时刻输出误差有关的两项,借助Lyapunov定理设计观测器,并采用LMI方法给出了观测器参数矩阵系统化设计方法.然后,设计积分滑模面,将得到的等效控制律代入系统状态空间模型后,设计包含自适应故障补偿控制项和线性输出反馈控制项的容错控制律.最后通过仿真实例验证了所设计观测器和容错控制器的有效性. 相似文献
3.
通过对雷击建筑物所造成建筑物及其内部系统损害原因的分析,结合《雷电防护》GB/T21714系列标准,分析得知GB/T21714.2中损害概率PB和PSPD与雷电流的概率分布和LPL（Lighfning Pretection Level,雷电防护水平）对应的雷电流极值有关。PB的数值等于雷电流大于LPL对应雷电流最大值的概率,与其小于雷电流最小值的概率之和;PSPD的数值等于雷电流大于LPL对应雷电流最大值的概率。同时指出,《建筑物防雷设计规范》GB50057－2010中各个LPL的损害概率PB和PSPD不应直接采用GB/T21714.2中的规定值,应根据GB50057给出的雷电流参数进行计算,或利用雷电监测网的资料,获取建筑物附近一定范围内的云地闪数据,统计得到雷电流概率分布函数,依据该雷电流概率分布函数来计算PB和PSPD。 相似文献
4.
为了探索Ｂ－Ｐ网络的参数调整特性,进行了参数α、β的选取对Ｂ－Ｐ算法的收敛速度和模型的稳定性的影响研究。通过Ｂ－Ｐ网络用于气象预测建模的参数调整个例分析表明：参数α、β的取值对Ｂ－Ｐ模型的稳定性无显著影响,但参数值的调整尤其是β值的调整对建整对建模的收敛速度明显的影响。 相似文献
5.
人体热量平衡模型及其在人体舒适度预报中的应用 总被引：2，自引：1，他引：1
人对外界冷热的调节和舒适感,不能根据气温或其他单一的气象要素来评价.要真正全面表述环境对人体的影响必须运用人体热量平衡模型,人体热量平衡模型全面考虑了所有相关的气象要素、行为参数(活动和服装)和人体参数.运用上海有限域数值天气预报和热量平衡模型计算了体感温度,以衡量人体在环境中的热舒适状况. 相似文献
6.
用Priestley—Taylor公式估算作物农田蒸散量的研究 总被引：2，自引：0，他引：2
利用田间试验资料，综合考虑了影响农田蒸散的气象，作物和土壤因素，并以Ｐｒｉｅｓｔｌｅｙ－Ｔａｙｌｏｒ公式为基础，建立了不同作物（棉花、玉米冬小麦）的农田散估算模型。该模型仅需常规气象和农业气象资料，计算简便，具有一定的实用价值。 相似文献
7.
PC 因子是指雷电灾害风险评估中雷击建(构)筑物导致电气电子系统失效的概率参数值,该因子的选取方法直接影响评估结果的准确度。通过对PC因子的分析,从概念出发,探讨定量计算该因子参数值的方法,得出结论：选取PC 因子的参数值既要依据国家标准判断分析电涌保护器（SPD)的设计合理性及SPD的保护局限性,又需要通过当地闪电定位历史资料的统计分析来确定雷电流峰值的分布概率;PC值的选取应在确保评估对象SPD设计科学、有效的基础上,通过分析评估位置雷电流峰值概率,判断SPD的保护概率,以定量确定PC因子的参数值。 相似文献
8.
利用有青藏高原地形存在及没有青藏高原地形存在时的数值模拟结果，对比分析了它们环流E—P通量特征的差异。结果表明，这些差异与大地形对西风气流的阻挡、抬升作用有关；也与大地形在夏季季年环流中所起的热力作用有关。同时青藏高原对中纬度地区上传的E—P通量有激发作用。 相似文献
9.
利用Lorenz系统,初步研究了外源强迫和初始值在短期气候变化中的作用.结果表明,外源强迫的大小,对气候系统的长期行为有着重要的影响.在短期气候预测中,应该根据外源强迫的大小及其持续时间的长短,采取不同的短期气候预测方法即在大气外源强迫较弱、持续时间短时,可以只考虑初值的影响;在大气外源强迫强、持续时间长时,可不考虑初始条件的影响,而只考虑外源强迫的作用;在大气外源较强、持续时间较长时,必须同时考虑初值和外源的作用. 相似文献
10.
网格环境具有分布式、高度异构和动态变化等特点,为保证对网格资源访问的动态有效性,提供可靠的品质服务是目前网格技术研究的热点问题．提出了一种适用于网格环境的基于Ａｇｅｎｔ技术的资源调度模型,该模型借鉴信任管理技术在虚拟组织内部和不同组织的网格实体间建立了信任关系,并具有较低计算复杂度和良好的动态性可扩展性． 相似文献
11.
德国VDI3784的S/P模式为三维流体动力学积分模式,其方程主要描述了无穷小体积元素的质量、动量、静态污染物质量浓度及能量的守恒。利用德国模式进行了冷却塔烟气排放不同参数、不同大气条件下烟气抬升高度的敏感性试验。结果表明：在影响烟气抬升高度的3个气象要素（风速,气温和湿度）中,风速和气温的变化对结果影响较大,而湿度影响较小。在D类稳定度,当环境风速从0.1 m/s增加到15.0 m/s时,抬升高度将从711.7 m变为38.5 m。随着环境温度的升高,抬升高度明显单调变小;当稳定度为A类,环境温度从10℃升到40℃时,烟气抬升最大高度从688.9 m降低到45.1 m,降低了14倍多。而环境湿度的变化,对抬升高度的影响不是很明显。对于E和F类,当环境湿度从20 %增加到70 %,最大抬升高度分别从115.3 m和84.6m降到112.9 m和81.7m,分别降低了3.43 %和2.08 %。在影响烟气抬升高度的其他3个因素（凉水塔直径,烟气出口速度和混合气体温度）中,混合气体温度的变化对结果影响较大,而凉水塔直径和烟气出口速度的影响较小。在各类稳定度条件下,当出口温度从20 ℃变到90 ℃时,烟气抬升高度增加1.2-13.3倍;在各类稳定度条件下,当凉水塔直径从30 m变到90 m,烟气抬升高度仅增加0.63-1.40倍;在各类稳定度条件下,当出口速度从2.5 m/s变到8 m/s,烟气抬升高度增加0.24-0.74倍。 相似文献
12.
德国VDI3784的S/P模式为三维流体动力学积分模式,其方程主要描述了无穷小体积元素的质量、动量、静态污染物质量浓度及能量的守恒。利用德国模式进行了冷却塔烟气排放不同参数、不同大气条件下烟气抬升高度的敏感性试验。结果表明：在影响烟气抬升高度的3个气象要素（风速、气温和湿度）中,风速和气温的变化对结果影响较大,而湿度影响较小。在D类稳定度,当环境风速从0.1 m/s增加到15.0 m/s时,抬升高度从711.7 m变为38.5 m。随着环境温度的升高,抬升高度明显单调变小;当稳定度为A类,环境温度从10升到40时,烟气抬升最大高度从688.9 m降低到45.1 m,降低了14倍多。而环境湿度的变化,对抬升高度的影响不是很明显。对于E类稳定度和F类稳定度,当环境湿度从20%增加到70%,最大抬升高度分别从115.3 m和84.6 m降到112.9 m和81.7 m,分别降低了3.43%和2.08%。在影响烟气抬升高度的其他3个因素（凉水塔直径、烟气出口速度和混合气体温度）中,混合气体温度的变化对结果影响较大,而凉水塔直径和烟气出口速度的影响较小。在各类稳定度条件下,当出口温度从20变到90时,烟气抬升高度增加1.2—13.3倍;在各类稳定度条件下,当凉水塔直径从30 m变到90 m,烟气抬升高度仅增加0.63—1.40倍;在各类稳定度条件下,当出口速度从2.5 m/s变到8.0 m/s,烟气抬升高度增加了0.24—0.74倍。 相似文献
13.
Industrial phosphorus (P) fertilizer has substantially improved global food production, but has also led to environmental impacts. Intensive global agricultural trade has increased and the impacts of trade on aggravating or alleviating future P scarcity must be examined, especially for the most vulnerable countries. We combined data to estimate the global P trade among countries and its impacts on global P flows, based on global agricultural trade, cropland soil P budgets and crop P fertilizer footprints (the amount of industrial P fertilizer applied for producing one unit of P in the harvested crop). The global agricultural P trade represented a fraction of 16% of P in harvested crops in 2014, half of which was exported from the United States of America, Brazil and the European Union and one fifth imported by China. Virtual P fertilizer flows (about 2.60 Tg P y-1) referred to industrial P fertilizers applied to traded crops by exporting countries; thus, 1/3 of global virtual P fertilizer flows were associated with the international soybean trade. P use efficiency (PUE), the ratio of the harvested crop-P to the total external P inputs, is a larger problem for tropical than temperate countries. Global crop trade had brought in a net 0.2 Tg P y-1 savings of industrial P fertilizers globally, compared to crop production in export and import countries. >0.50 Tg y-1 of the gross global accumulation of soil P and P in freshwater were associated with global agricultural trade. Global PUE, however, could be improved considerably, and thus global cooperation and improving PUE could help to solve the problem of future P scarcity. Vulnerable countries should also propose urgent national plans to address their own situations of P scarcity or low PUE. 相似文献
14.
Minqiang ZHOU Qichen NI Zhaonan CAI Bavo LANGEROCK Jingyi JIANG Ke CHE Jiaxin WANG Weidong NAN Yi LIU Pucai WANG 《大气科学进展》2023,40(2):223-234
Measurements of carbon dioxide(CO2), methane(CH4), and carbon monoxide(CO) are of great importance in the Qinghai-Tibetan region, as it is the highest and largest plateau in the world affecting global weather and climate systems. In this study, for the first time, we present CO2, CH4, and CO column measurements carried out by a Bruker EM27/SUN Fourier-transform infrared spectrometer(FTIR) at Golmud(36.42°E, 94.91°N, 2808 m) in August 2021. The mean and... 相似文献
15.
介绍了冷却塔烟气排放原理及德国VDI 3784的S/P模式,结合实例研究了冷却塔烟气排放不同参数、不同大气条件下烟气抬升高度变化特征,并使用德国VDI 3945的Austal 2000模式对冷却塔和烟囱的排放浓度进行了对比。结果表明：烟气抬升高度主要取决于出口温度和环境温度之差;随着风速的增大,抬升高度明显变小;随着直径的增加,烟气抬升高度也增加;随着出口速度的增加,抬升高度增加的相对较多;随着出口温度的增加,烟气抬升高度在逐渐增加,稳定度决定增加的倍数;VDI 3945模拟结果表明：小时浓度差别相对较小,而年均浓度差别较大,日均值的差别介于小时和年均之间。 相似文献
16.
Public expectations of government influence private action for managing climate change risks. Institutional neglect or incompetence result in a loss of trust in public institutions, consequently discouraging the public from taking added responsibility for risk management. This has been explained in terms of social contract, but evidence suggests that a politics of distrust can reinforce alternative social drivers of action, rather than displacing action. This is empirically confirmed by the present study, which examines the tendencies for adopting private protective measures across a gradient of institutional trust. Surveys were conducted in four jurisdictions within China that operate under two different political-economic systems, namely, Hong Kong and Macao (liberal market economy), and Zhuhai and Sanya (socialist market economy). Structured interviews were conducted with 569 business operators to explore how their stated adaptation practice is related to institutional trust and social capital. We found that trust predicted action only in Sanya, which is characterized by a high level of public confidence in authorities. In places of lower institutional trust, social capital became a salient and powerful driver of action. The weakening of the social contracts in Hong Kong and Macao turned their people to alternative social mechanisms. We explain the results in terms of the development trajectories, socio-political norms and institutional settings of these jurisdictions. This study provides insights into how adaptation practice can be mediated by the consequences of a change in political leadership, policy, or governance arrangements that alters the relationship of trust. 相似文献
17.
Ecosystem-based management of fisheries and other transboundary natural resources require a number of organizations across jurisdictions to exchange knowledge, coordinate policy goals and engage in collaborative activities. Trust, as part of social capital, is considered a key mechanism facilitating the coordination of such inter-organizational policy networks. However, our understanding of multi-dimensional trust as a theoretical construct and an operational variable in environmental and natural resource management has remained largely untested. This paper presents an empirical assessment of trust and communication measures applied to the North American Great Lakes fisheries policy network. Using a scale-based method developed for this purpose, we quantify the prevalence of different dimensions of trust and in/formal communication in the network and their differentiated impacts on decision-making and goal consensus. Our analysis reveals that calculation-based ‘rational trust’ is important for aligning mutual goals, but relationship-based ‘affinitive trust’ is most significant for influencing decision-making. Informal communication was also found to be a strong predictor of how effectively formal communication will influence decision-making, confirming the “priming” role of informal interactions in formal inter-agency dealings. The results also show the buffering and interactive functions of these components in strengthening institutional resilience, with procedural trust undergirding the system to compensate for a lack of well-developed relationships. Overall, this study provides evidence to suggest that informal communication and multi-dimensional trust constitute a crucial element for improving collaboration and reducing conflict in the networked governance of transboundary natural resource systems. 相似文献
18.
在研究黄土高原东亚季风地质时期周期演变中,引入了用于定量检测周期的奇异谱分析方法,结合小波分析,对典型的黄土高原陕西省洛川黄土剖面、甘肃省灵台黄土剖面的磁化率中2.6 MaB.P.以来东亚季风的强信号进行了研究。结果表明:2.6-1.0 MaB.P.之间地质时期,除在1.87-1.37 MaB.P.之间可能存在一个周期演变不明显的缺失时段外,东亚季风演变的主导周期是40 ka,0.9-0.6 MaB.P.是40 ka周期和100 ka周期的调整过渡期。0.6 MaB.P.以来的主导周期是100ka。研究还发现,1.2 MaB.P.前后没有明显的周期差异,说明1.2 MaB.P.不是一次真正意义上的周期转型事件,而是周期演变过程中的触发事件,这一触发事件对0.9 MaB.P.以后出现的周期转型事件影响深刻。40 ka周期从1.2 MaB.P.开始衰减,至0.9MaB.P.时100 ka周期逐渐建立。0.6 MaB.P.开始东亚季风出现冷暖大幅振荡的100 ka演变周期,因而0.6MaB.P.具有气候振荡加剧的突变性质。 相似文献
19.
Climate change is expected to have particularly severe effects on poor agrarian populations. Rural households in developing countries adapt to the risks and impacts of climate change both individually and collectively. Empirical research has shown that access to capital—financial, human, physical, and social—is critical for building resilience and fostering adaptation to environmental stresses. Little attention, however, has been paid to how social capital generally might facilitate adaptation through trust and cooperation, particularly among rural households and communities. This paper addresses the question of how social capital affects adaptation to climate change by rural households by focusing on the relationship of household and collective adaptation behaviors. A mixed-methods approach allows us to better account for the complexity of social institutions—at the household, community, and government levels—which drive climate adaptation outcomes. We use data from interviews, household surveys, and field experiments conducted in 20 communities with 400 households in the Rift Valley of Ethiopia. Our results suggest that qualitative measures of trust predict contributions to public goods, a result that is consistent with the theorized role of social capital in collective action. Yet qualitative trust is negatively related to private household-level adaptation behaviors, which raises the possibility that social capital may, paradoxically, be detrimental to private adaptation. Policymakers should account for the potential difference in public and private adaptation behaviors in relation to trust and social capital when designing interventions for climate adaptation. 相似文献
20.
Carlos E. Canosa-mas Mark L. Flugge Dina Shah Alison Vipond Richard P. Wayne 《Journal of Atmospheric Chemistry》1999,34(1):153-162
A discharge-flow tube coupled with resonance fluorescence and chemiluminescence detection has been used to investigate the reactions IO + HO2 products (1) and IO + O(3P) I + O2(2), at T = 296 ± 1 K and P = 1.7 - 2 Torr. The rate constants k-1 and k2 have been found to be (7.1 ± 1.6) × 10-11 cm3 molecule-1 s-1 and (1.35 ± 0.15) × 10-10 cm3 molecule-1 s-1, respectively. 相似文献