The Content Driven Mobile Internet

The development of future mobile networks will be driven, in large part, by content and web based services. In this paper, we examine several performance, scalability and architectural challenges faced by future mobile web applications and how advanced mobile content delivery techniques can address these challenges. We review existing content delivery using a taxonomy that consists of three categories: network scaling, end system acceleration, and content and protocol optimization. While wireline content delivery focuses on network and server scalability, mobile content delivery will likely benefit most from optimizing radio link usage. We also present our ongoing work in this area, which extends the functionality of edge caching to the terminal, uses user interest correlation information to maintain low terminal power consumption and adds a new dimension to radio resource management. This revised version was published online in August 2006 with corrections to the Cover Date.     

塔河渣油高温催化临氢热转化技术研究

以塔河减压渣油（简称塔河减渣）为原料，在实验室小型试验装置和中型连续试验装置上，对在较高温度条件下催化临氢热转化加工塔河减渣的工艺操作条件及改质效果进行了系统研究。采用高分散的油溶性催化剂，在高压釜反应器中考察了反应温度、反应压力、催化剂添加量、溶剂油添加量、反应时间以及助剂添加量对塔河减渣催化临氢热转化反应的转化率和缩合率的影响，优化了操作参数。在优化的操作条件下，进行了塔河减渣催化临氢热转化中型试验，得到初馏点大于524 ℃组分的裂化率为85.2%，馏分油收率为80%，金属（Ni+V）和沥青质脱除率均大于90%。     

Locality-preserving hash functions for general purpose parallel computation

Consider the problem of efficiently simulating the shared-memory parallel random access machine (PRAM) model on massively parallel architectures with physically distributed memory. To prevent network congestion and memory bank contention, it may be advantageous to hash the shared memory address space. The decision on whether or not to use hashing depends on (1) the communication latency in the network and (2) the locality of memory accesses in the algorithm.We relate this decision directly to algorithmic issues by studying the complexity of hashing in the Block PRAM model of Aggarwal, Chandra, and Snir, a shared-memory model of parallel computation which accounts for communication locality. For this model, we exhibit a universal family of hash functions having optimal locality. The complexity of applying these hash functions to the shared address space of the Block PRAM (i.e., by permuting data elements) is asymptotically equivalent to the complexity of performing a square matrix transpose, and this result is best possible for all pairwise independent universal hash families. These complexity bounds provide theoretical evidence that hashing and randomized routing need not destroy communication locality, addressing an open question of Valiant.This work was started when the author was a student at Oxford University, supported by a National Science Foundation Graduate Fellowship and a Rhodes Scholarship. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the views of the National Science Foundation or the Rhodes Trust.     

焊接构造对T型接头超低周疲劳性能的影响

为了研究焊接细节对钢结构超低周疲劳性能的影响,以T型接头为对象,在通用有限元程序Abaqus平台上,开发基于Arlequin算法的结构多尺度计算程序. 利用多尺度算法,开展焊接接头的局部弹塑性有限元分析. 比较焊趾半径、厚钢板未熔透长度及焊趾表面凹凸对局部塑性应变履历的影响,利用Coffin-Manson模型对T型接头的超低周疲劳特性进行定性讨论. 数值计算结果表明,焊趾位置是焊接接头的超低周疲劳易损位置,厚钢板的未熔透长度对焊接部位局部塑性应变的影响不大;焊趾半径对焊趾局部塑性应变有较大的影响,增大焊趾半径可以有效提升钢结构在循环荷载下的超低周疲劳性能;焊趾表面的平整性是影响焊趾局部塑性应变履历的重要因素,尖锐的凹坑会明显降低焊接接头的超低周疲劳性能,磨平的焊趾表面可以减少局部塑性应变,提高接头的超低周疲劳强度.     

无线传感器网络中的改进数据聚集调度算法

针对现有聚集数据调度近似算法具有较高延时上界的问题,提出一种改进的聚集数据调度近似算法。建立一棵根在中心结点的广度优先搜索树,分层构造一个最大独立集(MIS),使MIS中相邻的2个结点相距两跳。将MIS中的结点连接起来,形成一棵根在中心结点的数据聚集调度树,使结点按数据聚集调度树进行分层数据调度。在数据聚集调度树的构造过程中,对于任意支配点,以最小的结点连接其相距两跳的支配点。对于2个相邻支配点的公共邻居支配点,通过在距中心点最近的支配点加入数据聚集树,使其在数据调度过程中将数据发送给距中心点最近的支配点,从而降低数据的聚集延时。实验结果表明,与SAS算法、Guo’s算法和IAS算法相比,该算法的数据聚集延时更低,其延时上界为14R+△?10。     

车载安全应用广播性能分析*

在仿真软件NS-2.29和VanetMobiSim1.1下,搭建了车载通信网络仿真平台,讨论了广播信标信息在不同距离下的接收率,并对两类广播信息在EDCA方式下的接收率和接入时延进行了深入的分析和比较。仿真结果表明,隐藏终端导致广播数据的严重丢包而且不同竞争窗口对接入时延有很大的影响,尤其是在信道负荷比较重时。最后指出了可行的解决思路。     

An underwater acoustic MAC protocol using reverse opportunistic packet appending

Underwater communication primarily utilizes propagation of acoustic waves in water. Its unique characteristics, including slow propagation speed and low data rates, pose many challenges to Media Access Control (MAC) protocol design. In most existing handshaking-based underwater MAC protocols, only an initiating sender can transmit data packets to its intended receiver after a channel reservation through a Request-to-Send (RTS)/Clear-to-Send (CTS) handshake. This conventional single-node transmission approach is particularly inefficient in underwater environments, as it does not account for long propagation delays. To improve channel utilization in high latency environments, we propose a novel approach that exploits the idle waiting time during a 2-way handshake to set up concurrent transmissions from multiple nodes. The sender can coordinate multiple first-hop neighbors (appenders) to use the current handshake opportunity to transmit (append) their data packets with partially overlapping transmission times. After the sender finishes transmitting its packets to its own receiver, it starts to receive incoming appended packets that arrive in a collision-free packet train. This not only reduces the amount of time spent on control signaling, but it also greatly improves packet exchange efficiency. Based on this idea, we propose an asynchronous, single-channel handshaking-based MAC protocol based on reverse opportunistic packet appending (ROPA). From extensive simulations (single- and multi-hop networks) and comparisons with several existing MAC protocols, including MACA-U, MACA-UPT, BiC-MAC, Slotted-FAMA, DACAP, unslotted Aloha, we show that ROPA significantly increases channel utilization and offers performance gains in throughput and delay while attaining a stable saturation throughput.     

基于3D Mesh结构的一种静态路由算法

3D NoC在同构多核系统中相比2D NoC具有更为优越的性能.本文在研究3D Mesh结构的基础上,对拓扑结构中的平均延时和理想吞吐量进行了理论上的评估,并提出了一种基于3D Mesh的新的静态路由算法,最后运用NS2网络仿真软件对其进行仿真和比较.实验结果显示,新的路由算法可以有效地提高吞吐量,并在大规模数据传输时...     

近红外耳穴信号的超低频成份提取与分析

血氧超慢信号与脑神经递质的超慢振荡特点具有平行性与同源性。应用940 nm单波长近红外对管,检测识别耳颞穴的透射信息,可以帮助理解脑神经血管耦合的机制,同时发现新信号的特征以支持脑认知研究。具体工作包括:①基于输出能量的最大值寻优探头传感角度;②基于软件SPSS11.0统计描述谎实数据差异显著性的P分数;③利用Agilent54624A型示波器内嵌的FFT功能,提取近红外透射信息中0~100 mHz的超低频特征,以便显示谎和实的差异性。研究工作进一步细化了专用的近红外耳穴信息识别系统,为整机的SoC化奠定了基础。     

基于生成树的无线传感器网络MAC协议

简要分析了无线传感器网络(W SNs)MAC层协议,针对MAC协议在节能和时延方面的不足,提出了一种基于生成树的MAC协议(ST-MAC)。以汇聚点为根节点,创建一个由网络中所有节点组成的生成树。ST-MAC采用TDMA接入方式,其固有的低工作周期提高了网络性能。性能分析和实验结果表明:相对S-MAC,ST-MAC在能量节省和时延方面有较好的效果。