基于位置信息的非结构化overlay匹配方法研究*

在非结构化overlay中,由于底层物理网络和overlay的拓扑失配问题,产生了大量冗余网络负载。为了降低负载,提出了基于位置信息的方法动态构造overlay。通过分布部署用于维护已加入网络的节点信息的infoNode,在不引入较大冗余网络负载的情况下,能够较好地解决拓扑失配问题。实验表明,基于网络测量的方法能显著降低网络负载和查询响应时间。     

不锈钢堆焊层剥离断裂的金属学本质

通过电解充氢试验研究了不锈钢堆焊层剥离断裂的影响因素，并着重分析了这一断裂问题的金属学本质，结果显示，经过焊后热处理，堆焊过渡区碳，铬元素有迁移。在氢致剥离裂纹产生的区域，碳和合金元素分布有突变，研究也表明，碳化物沉淀，相变产物的存在及其与空位，位错等微观缺陷，应力，进入金属内部的氢交互作用，是剥离断裂产生和发展的主要原因。     

Fe3Al合金堆焊层的高温热腐蚀行为研究

用钨极氩孤焊方法在A304不锈钢基体上堆焊Fe3Al合金，对其相组成进行了XRD分析，对堆焊试样在750℃和950℃温度下分别进行了Na2SO4盐和NaCl盐的热腐蚀试验。结果表明：堆焊层金属主要由Fe3Al相构成，仅含有少量的α-Fe固溶体；堆焊层金属在NaCl盐中的热腐蚀程度明显高于在Na2SO4盐中的腐蚀，且堆焊层与基体的熔合区是最薄弱的区域。     

A smart spectrum utilization approach using multiantenna‐based cognitive relays in cognitive radio network

Efficient spectrum utilization is a promising technique for a prolonged unused radio frequency (RF) spectrum in a wireless network. In this paper, an adaptive spectrum sharing cognitive radio (CR) network has been proposed consisting of a primary user (PU) and secondary user transmitter (SU ? Tx) that communicates with secondary user receiver (SU ? Rx) via multiantenna‐based proactive decode‐and‐forward (DF) relay selection scheme. In our model, strategically an adaptable joint venture on underlay/overlay protocol is defined based on channel occupancy using spectrum sensing technique. Here, secondary transmitters (i.e., source transmitter) continuously sense the PU activities by energy detector and can simultaneously transmit to secondary receivers. Depending on sensing result secondary transmitters automatically switches in underlay mode if PU is active otherwise operates in overlay mode. The advantage of this scheme is that the joint mode of transmission allows the SUs to maximize their transmission rate. The outage performance at SU ? Rx and closed‐form expressions of joint underlay/overlay protocol has been evaluated. The power control policies at different transmitter nodes are taken care of. With the same diversity order, a trade‐off between multiantenna and multirelay is shown. This comparison shows improvement in outage behavior when the count in relays surpasses the number of antennas. Finally, the analytical model of smart efficient spectrum utilization without harming license users in CR is validated by MATLAB simulation.     

请求下降邻域叠加选取分布式P2P 视频点播调度

为实现对等架构的低成本视频流传输和实时播放要求,提出基于请求下降叠加选 取的分布式P2P 视频点播调度算法。首先,基于叠加技术构建P2P 视频点播的技术指标,充分 考虑输入邻域节点、输出邻域节点和媒体服务器负载3 组优化指标,构建叠加架构和分布式算 法流程;其次,利用请求下降策略对发送节点和服务节点选取进行改进,解决可能出现的带宽 低利用率和无效的视频播放问题;最后,通过BitTorrent 视频点播系统对所提算法的有效性进 行了验证。     

一种基于半透明颜色叠加与深度值的碰撞检测算法

为了快速验证虚拟装配仿真过程中零部件的可装配性,改进了一种基于图像空间的快速碰撞检测算法。该算法首先通过半透明颜色叠加实现对无碰撞装配体的快速滤除,并确定出潜在的碰撞区域;然后利用像素深度值求出遮挡对象与待装配物体在其运动方向的最小分离距离,弥补了基于图像空间的碰撞检测算法只能判断物体间是否发生碰撞而不能求距的缺点;最后针对求距环节提出了一种像素区域划分策略,以提高算法的检测精度。测试结果表明,所提算法在整体上能够满足虚拟装配系统实时性和精确性的要求。     

AR可变的有向传感器网络节点模型的研究*

针对以往采用的感知角度、感知半径固定的传感器节点模型在网络覆盖优化上的问题,提出了一种感知角度与感知半径（Angle and Radius,AR）可变的新型节点模型,在边界处理问题上提出边界模型,并对PFCEA算法进行了改进。通过网络初次部署稳定后进行二次部署改变传感器节点模型使其在有限节点上提高网络覆盖率。仿真实验表明,新型节点模型在提高监测区域覆盖率方面要比现有节点模型更加优越。     

Strain energy release rate at interface of concrete overlaid pavements

A new method for calculating energy release rate (ERR) at the interface of concrete overlaid pavements is proposed using crack closure and the nodal force technique. This method transforms a 3D pavement system into a 2D interfacial crack model via a theoretical conversion. The interfacial ERRs of steel fibre-reinforced, roller-compacted, polymer-modified concrete overlay pavement subjected to vehicular load were calculated and compared with the measured interfacial fracture toughness of the bi-material. It was found that the ERRs considerably decrease with the increase in overlay thickness and elastic modulus of foundation. Thin overlays (less than 100 mm) should not be considered in overlay pavement design to avoid interfacial delamination induced by heavy vehicular loading. For a typical overlay pavement system subjected to complex vehicular loads, an interfacial crack suffers mainly from damage due to mode-I, opening, compared to mode-II, sliding, while mode-III, tearing damage is negligible.     

A superimposed cohesive zone model for investigating the fracture properties of concrete–asphalt interface debonding

A cohesive zone model is proposed to simulate the interface debonding, a preponderant cause of failure for bonded concrete overlay of asphalt (BCOA). The model is constructed by superimposing four root models, each representing the mechanism of one subcritical failure at the interface zone observed in laboratory experiments. The model parameters are established through an inverse analysis of wedge splitting tests performed on BCOA specimens. These inputs are mainly a function of the materials at the interface zone, such as microtexture and macrotexture, and thus can be expected to be applicable to the numerical simulation of a full scale BCOA slab. For modeling across scales, the impact of specimen size, milling depth and initial flaw size on the model, in terms of peak traction and fracture energy, is also discussed.     

异构网络环境下的高稳定性应用层组播方案

针对异构网络环境中由于节点转发能力异构而引起的应用层组播稳定性不足的问题,对异构overlay拓扑建模进行了研究,分析出组播稳定所需满足的约束条件,提出了一种基于gossip协作机制的应用层组播方案。在所提机制能够均衡节点间负载,缓解能力弱的节点负载过重的问题;如果组播过程中有成员节点动态离开或转发能力不足,其他节点相互协作共同分担其负载以维持组播的稳定性。随后的链路强度分析表明,与传统的应用层组播方案相比,本方案能够大幅降低拓扑的平均链路强度,提高组播系统的稳定性。最后通过OMNeT 仿真平台对本方案进行仿真验证,实验证明在动态的异构overlay拓扑下,本方案能够显著提高数据分发成功率,保证组播的连续性和稳定性。