PAIDD: a hybrid P2P-based architecture for improving data distribution in social networks

Rapid growth in social networks(SNs)presents a unique scalability challenge for SN operators because of the massive amounts of data distribution among large number of concurrent online users.A request from any user may trigger hundreds of server activities to generate a customized page and which has already become a huge burden.Based on the theoretical model and analytical study considering realistic network scenarios,this article proposes a hybrid P2P-based architecture called PAIDD.PAIDD fulfills effective data distribution primarily through P2P connectivity and social graph among users but with the help of central servers.To increase system efficiency,PAIDD performs optimized content prefetching based on social interactions among users.PAIDD chooses interaction as the criteria because user’s interaction graph is measured to be much smaller than the social graph.Our experiments confirm that PAIDD ensures satisfactory user experience without incurring extensive overhead on clients’network.More importantly,PAIDD can effectively achieve one order of magnitude of load reduction at central servers.     

Effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives for microelectronic applications

The effects of oxidation and particle shape on critical volume fractions of silver‐coated copper powders in conductive adhesives are investigated. Silver‐coated copper powders with spherical and flake‐shaped particles were oxidized at temperatures of 30°C, 175°C and 240°C for two hours and dispersed in an epoxy matrix. As silver‐coated copper powders are oxidized at 30°C and 175°C, the critical volume fractions of the conductive adhesives are slightly affected by oxidation and particle shape at these temperatures. As the oxidation temperature approaches 240°C, the critical volume fractions of the conductive adhesives are strongly affected by oxidation temperature and particle shape, owing to the formation of oxides such as Cu₂O on the surface of silver‐coated copper powder—Cu diffuses from the interior to the surface of silver‐coated copper powder and reacts with the oxygen in the air. Silver‐coated copper powder with flake‐shaped particles shows lower critical volume fractions in conductive adhesives than silver‐coated copper powder with spherically shaped particles. Polym. Eng. Sci. 44:2075–2082, 2004. © 2004 Society of Plastics Engineers.     

(1S,4S)-2-甲基-2,5-二氮杂二环[2.2.1]庚烷的合成

以N—位磺酰化的反—4—羟基—L—脯氨酸为原料,以硼氢化钾与氯化锌还原羧基,以三乙胺和丙酮代替吡啶进行羟基磺酰化和羟基氯代反应,“一锅煮”进行取代环合和去N—磺酰化合成(1S,4S)—2—甲基—2,5—二氮杂二环[2．2．1]庚烷,总收率达53％。该法操作简便,收率高,更有利于工业化生产。     

Explaining similarity for SPARQL queries

World Wide Web - Knowledge graph has gained significant popularity in recent years. As one of the W3C standards, SPARQL has become the de facto standard query language to retrieve the desired data...     

网络犯罪的检测分析技术

随着信息技术的高速发展,越来越多的生产生活逐渐转移到网络空间进行,国民经济对网络空间的依赖也日益凸显.互联网带来便利的同时,越来越多的犯罪从传统线下转移到网络空间中进行,威胁人民群众的日常生活安全.因此,如何理解、评估、预防、打击网络犯罪,成为学术界、工业界和相关执法部门的关注重点.近年来,研究人员持续关注各种网络犯罪及对应的防范、评估、反制技术.但目前针对网络犯罪总体综述研究较少,亟需对网络犯罪产业链组成部分进行全面且详细的梳理.将以钓鱼(phishing)、诈骗(scam)、恶意挖矿(cryptojacking)等经典网络犯罪攻击方式为切入点,深入分析包括黑帽搜索引擎优化(Blackhat SEO)、误植域名(typosquatting)在内的相关支撑技术,详细揭露地下市场(underground market)、僵尸网络(Botnet)和洗钱渠道(money laundering)等网络犯罪基础设施,剖析网络犯罪产业链,最后讨论了网络犯罪研究中仍存在的挑战,并展望未来研究方向.     

基于生成对抗网络的图像清晰度提升方法

视频监控、军事目标识别以及消费型摄影等众多领域对图像清晰度有很高的要求.近年来,深度神经网络在视觉和定量评估的应用研究中取得较大进展,但是其结果一般缺乏图像纹理的细节,边缘过度平滑,给人一种模糊的视觉体验.本文提出了一种基于生成对抗网络的图像清晰度提升方法.为了更好的传递图像的细节信息,采用改进的残差块和跳跃连接作为生成网络的主体架构,生成器损失函数除了对抗损失,还包括内容损失、感知损失和纹理损失.在DIV2K数据集上的实验表明,该方法在提升图像清晰度方面有较好的视觉体验和定量评估.     

A novel ADRC‑based design for a kind of fexible aerocraft

The paper presents a novel control design, which is based on the idea of active disturbance rejection control (ADRC), for a kind of fexible aerocraft whose controlled variable cannot be measured directly. Since the original frame of ADRC cannot be directly applied, the paper puts forward a new extended state observer (ESO) and the corresponding ADRC law. In order to assign the poles of the closed-loop system to ideal positions such that the vibration can be quickly suppressed, an elastic damping term is added into feedback law. The advantages of the new ESO for efectively estimating both the rigid mode and elastic mode from the measurements are discussed. Moreover, the analysis on the stability, the relative stability and the steady state of the closed-loop system is given. Finally, the efectiveness and robustness of the proposed ADRC are verifed by simulations.     

稻草强化生物膜浮床脱除工业尾水中氮素及COD的效果

工业污水处理厂排放的尾水中总氮含量偏高,容易引起地表水体的富营养化。为了提高尾水中总氮的去除效率,通过模拟稳定塘静态和动态试验,对比了不同稻草添加量(0,0.18,0.54 g/L)强化生物膜浮床脱除工业尾水中总氮(TN)的效果。静态试验结果表明:随着稻草量的增加,TN的去除率显著提高;10 d后,添加0(CK)、0.18 g/L(T1)和0.54 g/L(T2)稻草的尾水中,TN去除率分别为18%,40%,93%。动态试验结果显示,水力停留时间(HRT)为 4 d时,CK、T1和T2的平均TN去除率分别为10%,22%,49%,且3种情况下的进出水COD浓度无显著差异。这主要是由于稻草通过缓慢释放碳源为生物膜中异养反硝化细菌提供可利用的有机物。研究成果可为工业尾水深度处理脱氮技术提供参考。     

火电厂给水泵调速系统变频改造

以潘三电厂的给水泵调速系统变频改造为例,对改造的必要性及实施方案进行介绍论述。改造完成后,在对运行参数进行比对分析的基础上,从经济性角度对改造效果进行了评价,充分说明给水泵调速系统变频改造作为一种安全可靠的节能降耗技术值得推广应用。     

压印接头强度的有限元模型及理论计算方法

建立了压印接头拉剪强度模型并提出接头强度的理论计算方法。建立了压印连接成形的二维模型,模拟压印成型过程并分析金属流动规律,模拟结果与试验结果一致。由压印连接过程的模拟结果得到压印接头的三维模型,由此三维模型模拟接头的拉剪过程,得到接头的载荷-位移曲线和失效形式,模拟结果与试验结果一致,求解误差为3.4%。根据压印接头拉剪的两种失效形式(颈部断裂失效和上下板分离失效),提出了压印接头的理论计算公式。并由12种压印接头对计算公式进行验证,求解结果与试验结果吻合,最大强度误差为8.9%。