Efficient query execution on broadcasted index tree structures

The continuous broadcast of data together with an index structure is an effective way of disseminating data in a wireless mobile environment. The index allows a mobile client to tune in only when relevant data is available on the channel and leads to reduced power consumption for the clients. This paper investigates the execution of queries on broadcasted index trees when query execution corresponds to a partial traversal of the tree. Queries exhibiting this behavior include range queries and nearest neighbor queries. We present two broadcast schedules for index trees and two query algorithms executed by mobile clients. Our solutions simultaneously minimize tuning time and latency and adapt to the client’s available memory. Experimental results using real and synthetic data compare results for a broadcast with node repetition to one without node repetition and they show how a priority-based data management can help reduce tuning time and latency.     

Distributed clustering algorithms for data-gathering in wireless mobile sensor networks

One critical issue in wireless sensor networks is how to gather sensed information in an energy-efficient way since the energy is a scarce resource in a sensor node. Cluster-based architecture is an effective architecture for data-gathering in wireless sensor networks. However, in a mobile environment, the dynamic topology poses the challenge to design an energy-efficient data-gathering protocol. In this paper, we consider the cluster-based architecture and provide distributed clustering algorithms for mobile sensor nodes which minimize the energy dissipation for data-gathering in a wireless mobile sensor network. There are two steps in the clustering algorithm: cluster-head election step and cluster formation step. We first propose two distributed algorithms for cluster-head election. Then, by considering the impact of node mobility, we provide a mechanism to have a sensor node select a proper cluster-head to join for cluster formation. Our clustering algorithms will achieve the following three objectives: (1) there is at least one cluster-head elected, (2) the number of cluster-heads generated is uniform, and (3) all the generated clusters have the same cluster size. Last, we validate our algorithms through an extensive experimental analysis with Random Walk Mobility (RWM) model, Random Direction Mobility (RDM) model, and a Simple Mobility (SM) model as well as present our findings.     

Effect of Surface State on Nodular Corrosion Resistance of Zircaloy-4 Alloy

The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in superheated steam at 500 °C/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded specimens were observed by TEM and SEM. The results indicate that surface strained layer delays the appearance of nodular spots on the specimen surfaces and improves the nodular corrosion resistance. The columnar grains orientation of the oxide films formed on the specimens with surface strained layer was more consistent than that on the specimens without surface strained layer when a comparison was made on the same orientation of the grain surfaces. Such a kind of oxide microstructure formed on the specimens with surface strained layer can hinder the diffusion of oxygen ions along the grain boundaries and delay the growth of oxide films, therefore retard the formation process of nodular spots. This indicates that the microstructure of the initial oxide films has an important influence on the subsequent growth of the oxide films.     

Microstructural characterization of Cu-poor Cu (In, Ga)Se2 surface layer

Grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) are combined to investigate the microstructure and chemical composition of the surface layer in Cu(In, Ga)Se₂ (CIGS) thin films deposited using a three-stage co-evaporation process. According to the GIXRD and micro-region electron diffraction analyses, ordered defect chalcopyrite (ODC) structure does not exist in the surface layer and the surface and the bulk region of the CIGS film have the similar crystal structure. However, the results from the EDX data show that the compositional ratios of the Cu/(In + Ga) (Cu/III) have a gradient distribution across the whole surface layer. The surface layer shows a Cu-poor compositional characteristics and the Cu content increases gradually from the surface to the bulk of the material. The compositional depth profiles determined by XPS agree very well with the results of the EDX measurements. The thickness of the surface layer has been determined to be about 50-100 nm in consistence with that estimated from the compositional ratio of Cu/III. High density dislocations have been observed in the surface region of these samples by high resolution TEM analyses. Our results suggest that different compositions would induce different point defects in the surface layer.     

Roles of organic acids during exectrooxidation reaction over Pt-supported carbon electrodes in direct methanol fuel cells

A comprehensive study has been made to explore the role of organic acids on electrocatalytic performances of platinum (Pt) nanoparticles supported on carbon porous materials (CPMs) in proton exchange membrane fuel cells (PEMFCs). In particular, the effects of carboxylic acids (R–COOH), viz. formic acid, acetic acid, propionic acid, and butyric acid on catalytic activity, stability, and durability of anodic Pt/CPM electrocatalyst in direct methanol fuel cells (DMFCs) were investigated. In the presence of doped carboxylic acids, the electrooxidative activity of Pt/CPM follows the trend: HCOOH < CH₃COOH < C₂H₅COOH < C₃H₇COOH, revealing a consistent increase in the severity of catalyst deactivation with the number of carbons on the alkyl chain of the dopant. The Pt/CPM was found to exhibit electrocatalytic performances and tolerance for poisoning than a commercial Pt/XC-72 catalyst with a similar Pt loading (20 wt%). Moreover, a notable increase in mass activity up to ca. 150% over the spent Pt/CPM catalyst was observed up on removing the organic acid in the feed stream, indicating that catalyst poisoning by deactivation may be revived, even to its “intrinsic” activity.     

A group-based data-driven approach for data synchronization in unstructured mobile P2P systems

This paper addresses the problem of data consistency on mobile peer-to-peer (MP2P) systems (or MP2P networks). The considered MP2P system is based on a mobile ad-hoc network, where the energy and connectivity on the mobile devices are limited. Since different mobile nodes may store copies of shared information, data synchronization on an MP2P system becomes crucial and challenging due to frequent disconnection and change on network topology caused by node mobility. We propose an effective approach to improving the performance of data synchronization with a dynamic inverted data indexing structure and group-based data-driven consistency management. The proposed approach can effectively synchronize the data items without using a central cache node in each group (or cluster) and perform well in terms of the coverage of successfully synchronized nodes and the number of redundant messages. Last, the proposed approach is validated through extensive simulation experiments.     

采用改进高斯-牛顿法的视频弹性运动估计

运动估计是去除视频时间维冗余的编码技术,而目前通用的平移运动模型无法有效地表示物体的局部非刚性复杂运动.为此,提出一种基于改进高斯-牛顿法的弹性运动估计方法.首先,通过分析初始迭代点对高斯-牛顿迭代结果的影响,采用基于2bit深度像素的均匀搜索预测初始迭代点;其次,通过理论和实验分析发现,不同的迭代步长对弹性运动估计/补偿性能有明显的影响,采用离散余弦变换的低频能量比率估计步长的上限,再利用黄金分割法对步长进行求精.实验结果表明,对于具有不同场景特点的视频序列,该算法始终能够保持较高的估计精度,运动补偿的平均峰值信噪比,比基于块平移模型的全搜索算法和传统弹性运动估计算法分别提高1.73dB和1.42dB.并且,该算法具有更快的收敛速度,一般仅需1~3次迭代就能取得高于传统弹性运动估计和块平移全搜索的峰值信噪比.     

FGH96、FGH97粉末盘的无损检测

通过对FGH96粉末、FGH97粉末镍基高温合金涡轮盘、篦齿盘无损检测方法研究,确定了粉末盘超声检测和荧光检测工艺。通过检测结果研究发现,热等静压+锻造态合金有利于超声检测,并发现了缺陷显示;直接成型热等静压态合金有利于荧光检测,并发现了缺陷显示。     

Disseminating dependent data in wireless broadcast environments

In wireless mobile environments, data broadcasting is an effective approach to disseminate information to mobile clients. In some applications, the access pattern of all the data can be represented by a weighted DAG. In this paper, we explore how to efficiently generate the broadcast schedule in a wireless environment for the data set having a weighted DAG access pattern. Such a broadcast schedule not only minimizes the access latency but also is a topological ordering of the DAG. Minimized access latency ensures the quality of service (QoS). We prove that it is NP-hard to find an optimal broadcast schedule and provide some heuristics. After giving an analysis for these heuristics on the latency and complexity, we implement all the proposed heuristics to compare their performance. Recommended by: Sunil Prabhakar     

一种新的小波域视频可分级运动估计方案

首先提出了一种运动估计方法MLBS（Modified Low Band Shift），并在此基础上提出了基于MLBS的小波域视频可分级运动估计方案MLBSSME．利用MLBS方法，提高了运动估计的准确度．借助重叠块运动补偿方法，有效降低了最高分辨率下解码图像的块效应．根据小波变换的多分辨率特性，利用缩小了的搜索窗口提高了搜索速度．这种方法可有效应用于空间可分级和数率可分级的视频编码器中．实验结果证明，对于多种类型的标准测试视频流，MLBSSME算法始终能保持很高的估计精度．利用该算法补偿得到的预测帧，其PSNR较之基于下层LL子带的分层运动估计方法和子带直接运动估计方法平均要高出1～3dB，而对于空间细节较简单的视频，其PSNR比LBS方法提高了0．5～1dB，并且算法的时空复杂度是LBS方法复杂度的30％～40％．