基于p范式模型的检索

随着电子文本的大量涌现,人们对信息检索工具提出了更高的要求。本文介绍一种扩展的布尔检索模型及其在中文信息检索系统中的应用,并利用相关反馈技术改善检索系统性能。     

Tuples of Disjoint $\mathsf{NP}$ -Sets

Disjoint -pairs are a well studied complexity-theoretic concept with important applications in cryptography and propositional proof complexity. In this paper we introduce a natural generalization of the notion of disjoint -pairs to disjoint k-tuples of -sets for k≥2. We define subclasses of the class of all disjoint k-tuples of -sets. These subclasses are associated with a propositional proof system and possess complete tuples which are defined from the proof system. In our main result we show that complete disjoint -pairs exist if and only if complete disjoint k-tuples of -sets exist for all k≥2. Further, this is equivalent to the existence of a propositional proof system in which the disjointness of all k-tuples is shortly provable. We also show that a strengthening of this conditions characterizes the existence of optimal proof systems. An extended abstract of this paper appeared in the proceedings of the conference CSR 2006 (Lecture Notes in Computer Science 3967, 80–91, 2006). Supported by DFG grant KO 1053/5-1.     

P2P multicast for pervasive ad hoc networks

During the last few years, the proliferation of miniaturised devices with networking capabilities has provided the technological grounds for pervasive networking environments. It is not visionary to foresee a world of pervasive devices embedded in the environment interacting between them, and with those carried by users, via wireless communications. In addition, fostered by the diffusion of small-size, computational-rich mobile devices, the way content is generated, and accessed is changing with respect to the legacy-Internet paradigm. An ever-increasing share of the Internet content is generated directly by the users, and shared on the network (following the User-Generated Content model). While today the legacy Internet is still used to share user-generated content, it is reasonable to envision that pervasive networking technologies will represent the natural platform to support this new model. This will result in content being distributed on users’ devices rather than on centralised servers on the Internet, and in users creating ad hoc networks to share content. The p2p paradigm is particularly suitable for this scenario, because communications will occur directly among users, instead of being necessarily mediated by centralised servers. Motivated by these remarks, in this work we focus on p2p multicast services over ad hoc networks aimed at sharing content among groups of users interested in the same topics. Specifically, starting from a reference solution in legacy wired networks (Scribe), we design a cross-layer optimised protocol (XScribe) that addresses most of the Scribe problems on ad hoc networks. XScribe exploits cross-layer interactions with a proactive routing protocol to manage group membership. Furthermore, it uses a lightweight, structureless approach to deliver data to group members. By jointly using experimental results and analytical models, we show that, with respect to Scribe, XScribe significantly reduces the packet loss and the delay experienced by multicast receivers, and increases the maximum throughput that can be delivered to multicast groups.     

p范数正则化支持向量机分类算法

L2范数罚支持向量机(Support vector machine,SVM)是目前使用最广泛的分类器算法之一,同时实现特征选择和分类器构造的L1范数和L0范数罚SVM算法也已经提出.但是,这两个方法中,正则化阶次都是事先给定,预设p=2或p=1.而我们的实验研究显示,对于不同的数据,使用不同的正则化阶次,可以改进分类算法的预测准确率.本文提出p范数正则化SVM分类器算法设计新模式,正则化范数的阶次p可取范围为02范数罚SVM,L1范数罚SVM和L0范数罚SVM.     

广义Orlicz空间的λ—性质和一致λ—性质

根据各种不同理论和应用的需要,Orlicz空间有各种不同形式的推广,赋p—Amemiya范数的Orlicz空间是Orlicz空间的推广,记为LM,p空间.λ—性质和一致λ—性质是Banach空间几何理论中的重要概念,它与端点和严格凸性有着紧密的联系.本文中我们得出了LM,p空间具有λ—性质,并给出了LM,p空间具有一致λ—性质的充要条件.     

硫酸铈氧化对二甲苯制对甲基苯甲醛

用硫酸铈为媒质间接电氧化对二甲苯制对甲基苯甲醛。在优选的条件下，电氧化Ｃｅ（ＩＶ）的产率≥８５％。采用十二烷基硫酸钠等催化剂可以明显地加速合成对甲基苯甲醛的反应。     

Ser411磷酸化p70S6k的细胞免疫化学定位

培养NIH3T3细胞，结合免疫印迹和细胞免疫荧光染色法，对p70的S6激酶（p70^S6k）及其第411位丝氨酸（Ser^411）处于磷酸化状态的细胞定位进行研究．利用免疫荧光染色技术，发现p70^S6k存在于细胞的各个部分，而Ser^411磷酸化后的p70姒只存在细胞核内．将细胞核与细胞质分离，并利用抗磷酸化Ser^411的抗体进行免疫印迹分析，发现只有细胞核部分才出现免疫条带，说明Ser^411磷酸化后的p70^S6k特异性地存在于细胞核当中．     

GF(2p)LDPC编码的相位调制OFDM系统在瑞利衰落信道的性能

OFDM是一项能有效对抗高速无线通信中多径衰落的关键技术，为了进一步提高OFDM系统的误码性能，许多信道编码技术已被应用于OFDM系统中，二元域LDPC码以其近香农限的误码性能和较低的译码复杂度成为研究的热点。在AWGN信道下，多元域LDPC码比等效码长的二元域LDPC码有更好的纠错性能。本文提出了一种将多元域LDPC码经过MPSK调制后用于OFDM系统的新方法。仿真结果表明，在多径衰落信道下，通过合理选择多元LDPC码域的阶数和调制的方法，多元域LDPC编码的高阶调制OFDM系统比等效码长的二元域LDPC编码OFDM系统具有更好的性能，并且由于采用了多元域LDPC的快速BP译码，译码复杂度只是稍有增加。     

基于密度树的P2P视频流多播

应用层多插技术是互联网研究的一个重要方向．本文提出一种新的应用层多插模型DHCM，该模型采用改进的IHC算法，对cluster的密度进行层次划分，通过组建一个密度树实现最短路由，并把peer-to-peer技术用在数据传输上，最终把视频服务器的内容分发到密度树上的各个主机，实现应用层多插．这种密度层次划分的cluster满足单调性和同构性．实验证明DHCM可以在视频流传输上具有高效性和健壮性．