HPSIN: a new hybrid P2P spatial indexing network

Geographic information system(GIS)is increasingly managing very large sets of data,hence a centralized data index may not always provide the most scalable solution.Recently,the peer to peer(P2P)networks have become very popular for sharing information in a totally decentralized manner.In this paper,a new hybrid P2P spatial indexing network(HPSIN)is proposed,which combines distributed quad-tree with distributed Hash table(DHT)based Chord network to maintain both query efficiency and system load balance.In addition,a simple theoretical model based on opened queueing network for HPSIN is established.Assuming each peer as M/M/1 queueing processor in the model,fundamental characteristics of the system is captured,and expression of average query delay is obtained in close form.The theoretical analysis and numerical computing results show that there exists an optimum point of tradeoff between efficiency and load balance.By setting a proper value of start index level ls for different network scale and query rate,HPSIN will achieve the minimum overall query delay,therefore,can adapt to different P2P application environments.     

Synthesis,Morphology, and Properties of Poly(3‐hexylthiophene)‐block‐Poly(vinylphenyl oxadiazole) Donor–Acceptor Rod–Coil Block Copolymers and Their Memory Device Applications

Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) ( P3HT )‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) ( POXD ) are successfully synthesized by the combination of a modified Grignard metathesis reaction ( GRIM ) and atom transfer radical polymerization ( ATRP ). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐ b ‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT / POXD block ratio and the resulting morphology. The ITO/ P3HT₄₄ ‐b‐ POXD₁₈ /Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications.     

Optimization of Si NC/P3HT Hybrid Solar Cells

Silicon nanocrystals (Si NCs) are shown to be an electron acceptor in hybrid solar cells combining Si NCs with poly(3‐hexylthiophene) (P3HT). The effects of annealing and different metal electrodes on Si NC/P3HT hybrid solar cells are studied in this paper. After annealing at 150 °C, Si NC/P3HT solar cells exhibit power conversion efficiencies as high as 1.47%. The hole mobility in the P3HT phase extracted from space‐charge‐limited current measurements of hole‐only devices increases from 2.48 × 10^?10 to 1.11 × 10^?9 m² V^?1 s^?1 after annealing, resulting in better transport in the solar cells. A quenching of the open‐circuit voltage and short‐circuit current is observed when high work function metals are deposited as the cathode on Si NC/P3HT hybrid devices.     

Chord双向查找算法研究

Chord算法是一种典型的结构化P2P搜索算法,该算法简洁而且拓扑结构清晰,但该算法还存在着路由表信息冗余,查找效率不高的问题。在分析经典Chord算法的基础上,通过扩展Chord路由表,提出一种新的查找算法,该算法能够消除路由表的一些冗余信息,减少查找次数。通过理论分析,该算法提高了Chord的查找效率。     

适用于无线通信的动态拓扑感知性P2P网络

 在无线信道环境下,如何解决逻辑拓扑与物理拓扑之间的失配是设计P2P网络的主要挑战之一。本文提出一种适用于无线系统的P2P组网协议。在该协议中,首先,新入网节点从其邻居节点处获得一个数值上相近的节点标号,从而实现网络的瞬时拓扑感知。当节点的位置改变时,它们向中心节点更新自己的位置信息。然后,在中心节点处将节点标号的最优分配转换为旅行商问题,并用模拟退火算法对旅行商问题进行最优化求解,得到优化标号序列。最后,由中心节点向网络广播更新信息,引导节点进行标号和数据交换,从而使无线P2P网络在任何时刻都具有拓扑感知性。仿真结果表明,在基于该协议的无线P2P网络中,文件的定位路径明显缩短,定位延时明显减小。     

P2P网络中基于假名的匿名机制

In this paper, we proposed an anonymity scheme based on pseudonym where peers are motivated not to share their identity. Compared with precious scheme such as RuP (Reputation using Pseudonyms), our scheme can reduce its overhead and minimize the trusted center's involvement.     

BitTorrent在嵌入式系统中的应用

开发具有低功耗、微内核、体积小,并且具有下载功能的嵌入式系统,是非常具有商业价值的。BitTorrent系统是P2P文件共享技术中应用较为广泛的一种,本文在分析通用的BitTorrent软件基础上,给出一种适合嵌入式系统的BitTorrent下载模型,并通过编码在嵌入式Linux之上实现了稳定快速的下载。     

Regio‐ and Stereoselective Biohydroxylations with a Recombinant Escherichia coli Expressing P450pyr Monooxygenase of Sphingomonas Sp. HXN‐200

A recombinant Escherichia coli expressing P450_pyr monooxygenase of Sphingomonas sp. HXN‐200 was developed as a useful biocatalyst for regio‐ and stereoselective hydroxylations, with no side reaction and easy cell growth. The resting E. coli cells showed an activity of 4.1 U/g cdw and 9.9 U/g cdw for the hydroxylation of N‐benzylpyrrolidin‐2‐one 1 and N‐benzyloxycarbonylpyrrolidine 3 , respectively, being as active as the wide‐type strain. Biohydroxylation of N‐benzylpyrrolidin‐2‐one 1 with the resting cells gave (S)‐N‐benzyl‐4‐hydroxypyrrolidin‐2‐one 2 in >99% ee and 10.8 mM, a 2.6 times increase of product concentration in comparison with the wild‐type strain. Biohydroxylation of N‐tert‐butoxycarbonylpiperidin‐2‐one 5 , N‐benzylpiperidine 7 and N‐tert‐butoxycarbonylazetidine 9 with the E. coli cells afforded the corresponding 4‐hydroxypiperidin‐2‐one 6 , 4‐hydroxypiperidine 8 , and 3‐hydroxyazetidine 10 in 14 mM, 17 mM, and 21 mM, respectively. Moreover, hydroxylation of (−)‐β‐pinene 11 with the recombinant E. coli cells showed excellent regio‐ and stereoselectivity and gave (1R)‐trans‐pinocarveol 12 in 82% yield and 4.1 mM, which is over 200 times higher than that obtained with the best biocatalytic system known thus far. The recombinant strain was also able to hydroxylate other types of substrates with unique selectivity: biohydroxylation of norbornane 13 gave exo‐norbornaeol 14 , with exo/endo selectivity of 95%; tetralin 15 and 6‐methoxytetralin 17 were hydroxylated at the non‐activated 2‐position, for the first time, with regioselectivities of 83–84%.     

P2P流媒体系统中层次化网络拓扑推断技术的研究

目前基于P2P技术的应用已经远远超过了传统互联网应用,成为占用互联网带宽最多的网络应用. 因此,如何减少P2P应用、特别是P2P流媒体播放系统对骨干网带宽的过度消耗,成为P2P技术中一个急需解决的问题.本文提出利用一种基于网络断层扫描的分层推断方法,以将P2P流媒体系统中的流量限制在较小的网络范围内,从而减少跨网流量、同网之间的骨干网带宽消耗,缓解网络拥塞.在OPNET上的仿真表明,该方法能够适应P2P流媒体的高动态性,有效降低跨网流量以及对骨干网的带宽消耗速度.