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Propagation of passive worms in unstructured peer-to-peer (P2P) networks can result in significant damages and the loss of network security. This paper obtains the average delay for all peers in the entire transmitting process, and proposes a mathematical model for simulating unstructured P2P networks-based passive worms' propagation taking into account network throughput. According to the file popularity which follows the Zipf distribution, we propose a new healthy file dissemination-based defense strategy. Some parameters related to the propagation of passive worms are studied based on the proposed model. Finally, the simulation results verify the effectiveness of our model, which can provide an important guideline in the control of passive worms in unstructured P2P networks. 相似文献
43.
Correcting for the influence of frozen lakes in satellite microwave radiometer observations through application of a microwave emission model 总被引:1,自引:0,他引:1
Juha Lemmetyinen Anna Kontu Juho Vehviläinen Jouni Pulliainen 《Remote sensing of environment》2011,115(12):3695-3706
The spatial resolution of passive microwave observations from space is of the order of tens of kilometers with currently available instruments, such as the Special Sensor Microwave/Imager (SSM/I) and Advanced Microwave Scanning Radiometer (AMSR-E). The large field of view of these instruments dictates that the observed brightness temperature can originate from heterogeneous land cover, with different vegetation and surface properties.In this study, we assess the influence of freshwater lakes on the observed brightness temperature of AMSR-E in winter conditions. The study focuses on the geographic region of Finland, where lakes account for 10% of the total terrestrial area. We present a method to mitigate for the influence of lakes through forward modeling of snow covered lakes, as a part of a microwave emission simulation scheme of space-borne observations. We apply a forward model to predict brightness temperatures of snow covered sceneries over several winter seasons, using available data on snow cover, vegetation and lake ice cover to set the forward model input parameters. Comparison of model estimates with space-borne observations shows that the modeling accuracy improves in the majority of examined cases when lakes are accounted for, with respect to the case where lakes are not included in the simulation. Moreover, we present a method for applying the correction to the retrieval of Snow Water Equivalent (SWE) in lake-rich areas, using a numerical inversion method of the forward model. In a comparison to available independent validation data on SWE, also the retrieval accuracy is seen to improve when applying the influence of snow covered lakes in the emission model. 相似文献
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本文提出一种新型的Boost-Buck变换器,该变换器具有输入输出电流连续、输出电压可调范围大等优点。由于该变换器的输入电流连续,所以适合于功率因数校正电路,且其实现较为简单。该变换器的输出电压可调范围大,可以大于(或小于)输入电压,这就很好地克服了传统Boost变换器输出电压必须大于输入电压的缺点。理论分析、仿真和实验均验证了该变换器的实用性。 相似文献
46.
自动X射线检测(AXI)已经成为检测和评估复杂微机电系统(MEMS)和微光电子机械系统(MOEMS)的基本方法,在医疗、考古等领域也有了广泛应用,而稳定可靠高效的直流高压电源是AXI的核心组件。一般的高压直流电源为定值输出,它们在X射线管这样的宽负载变化范围下的稳态和暂态响应不能满足AXI的要求。基于AXI的需要,本文介绍了一种最新研制的可调高压电源,创新型的主电路拓扑结构由PFC(功率因数校正)模块、Buck模块、逆变电路、高频变压器和倍压电路组成。电源利用变压器的寄生参数谐振工作,利用软形状技术实现了ZCS低损耗。PFC模块能使此电源系统适用于国内外市场并且可减小对电网的谐波污染。电源的控制电路采用基于DSP的PI调解器,并基于RS232实现与PC的通信,从而实现本地控制和远程管理。 相似文献
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DCBM模式160瓦功率因数校正器的研制 总被引:1,自引:0,他引:1
张友军 《苏州大学学报(工科版)》2005,25(1):64-67
介绍了有源功率因数校正器(PFC)的拓扑结构和几种工作模式,分析了电流断续临界模式(DCBM)控制的PFC电路的工作原理,并给出了160WPFC电路参数的选取方法、实验波形和结果。实验结果表明此类PFC具有高效率、高功率因数及低成本等优点。 相似文献
49.
介绍了宝钢5m宽厚板轧机工作辊的弯辊/平衡系统,对这一系统的功能,机械、液压设备,压力补偿控制原理,闭环控制系统,参考值,板形及平直度控制,错误及警告等内容做了阐述,着重分析了弯辊系统的压力补偿控制原理。 相似文献
50.
When buildings are subjected to earthquakes, it is imperative to dissipate some of the input energy through pre-determined and well designed mechanisms. This study investigates the influence of mechanical control on structural systems through the application of strategically located component elements with reliable damping and stiffness properties that can modulate the response. The effects of installing such damping elements at two particular locations have been investigated. These positions are between the shear walls near the coupling beams and within cut out sections of the wall elements in multi-storey structures. Finite element time history analysis is used in the study and results indicate that the proposed procedure is able to achieve reasonable improvements in seismic response. 相似文献