多普勒频率补偿算法在GPS信号捕获中的应用

在GPS卫星高速运动和地面GPS接收机的移动中,由于卫星和接收机之间的径向速度引起了载波多普勒频移、C/A码的多普勒频移和数据码的多普勒频移,多普勒频移会对GPS接收机的信号捕获产生影响,使其准确度下降。针对上述情况,在常用的相干积分结合非相干积分的GPS信号捕获方案中引入一种多普勒频率补偿算法,并对此算法进行相应的仿真。结果表明该设计方案是可行的,引入的补偿算法能够有效消除多普勒频移对GPS信号捕获的影响,能够实现对GPS卫星信号的多普勒和码相的准确捕获。     

Addressing agent loss in vehicle formations and sensor networks

In this paper, we address the problem of agent loss in vehicle formations and sensor networks via two separate approaches: (1) perform a ‘self‐repair’ operation in the event of agent loss to recover desirable information architecture properties or (2) introduce robustness into the information architecture a priori such that agent loss does not destroy desirable properties. We model the information architecture as a graph G(V, E), where V is a set of vertices representing the agents and E is a set of edges representing information flow amongst the agents. We focus on two properties of the graph called rigidity and global rigidity, which are required for formation shape maintenance and sensor network self‐localization, respectively. For the self‐repair approach, we show that while previous results permit local repair involving only neighbours of the lost agent, the repair cannot always be implemented using only local information. We present new results that can be applied to make the local repair using only local information. We describe implementation and illustrate with algorithms and examples. For the robustness approach, we investigate the structure of graphs with the property that rigidity or global rigidity is preserved after removing any single vertex (we call the property as 2‐vertex‐rigidity or 2‐vertex‐global‐rigidity, respectively). Information architectures with such properties would allow formation shape maintenance or self‐localization to be performed even in the event of agent failure. We review a characterization of a class of 2‐vertex‐rigidity and develop a separate class, making significant strides towards a complete characterization. We also present a characterization of a class of 2‐vertex‐global‐rigidity. Copyright © 2008 John Wiley & Sons, Ltd.     

一种时频域联合捕捉主动声纳信号的方法

介绍了一种可应用于被动声纳的时频域联合捕捉主动声纳信号的方法及其工作流程。仿真相同噪声环境下使用该方法的发现距离与主动声纳探测距离,仿真结果表明使用该方法的发现距离远超过主动声纳探测距离,使用该方法可实现对目标的远程发现。     

Turbo spin-echo sequences in magnetic resonance imaging of the brain: Physics and applications

Fast SE imaging provides considerable measure time reduction, high signal-to-noise ratios as well as similar contrast behavior compared to conventional SE sequences. Besides TR and TE_eff, echo train length (ETL), interecho time , and-space trajectory determine image contrast and image quality in fast SE sequences. True proton density contrast (CSF hypointense) and not too strong T2 contrast are essential requirements in routine brain MRI. A Turbo SE sequence with very short echo train length (ETL=3), short TE_eff and short interecho time (17 ms), and TR=2000 ms was selected for proton density contrast; a Turbo SE sequence with ETL=7, TE_eff=90 ms, =22 ms, and TR=3250 ms was selected for T₂-weighted images. Using both single-echo Turbo SE sequences yielded 50% measure time reduction compared to the conventional SE technique. Conventional SE and optimized Turbo SE sequences were compared in 150 patients resulting in very similar signal and contrast behavior. Furthermore, reduced flow artifacts in proton density—and especially in T₂-weighted Turbo SE images—and better contrast of high-intensity lesions in proton density-weighted Turbo SE images were found. Slightly reduced edge sharpness—mainly in T₂-weighted Turbo SE images—did not reduce diagnostic reliability. Differences between conventional and Turbo SE images concerning image contrast and quality are explained regarding special features of fast SE technique.Address for correspondence: Institut für Röntgendiagnostik, Klinikum der Universität Regensburg, Franz-Josef-Strauß-Allee 11, 93042 Regensburg, Germany. Additional reprints of this chapter may be obtained from the Reprints Department, Chapman & Hall, One Venn Plaza, New York, NY 10119.     

Tariff reduction as a tool to increase the efficiency of electricity distributors: A case study in southern Brazil

The article aims to evaluate the consumer response to a reduction in the electricity tariffs as a hourly economic signal for the case of an electric utility in the state of Rio Grande do Sul, southern Brazil. Using Differences-in-differences method, the results were robust in showing that the change in the economic signal increased up to 81.01% the consumption at the time influenced by the change, improving the way in which the company's assets are used, in addition to reducing fuel oil consumption by users.     

智能车竞赛中道路的视频识别方案

视频信号的的采集和处理是一个复杂的过程,这需要程序设计者了解视频信号的构成,充分利用复合视频信号中的各种同步信息作为视频信号采集的控制信号,从而完成信号的采集。     

PIRF-Nav 2.0: Fast and online incremental appearance-based loop-closure detection in an indoor environment

This paper presents a fast and online incremental solution for an appearance-based loop-closure detection problem in a dynamic indoor environment. Closing the loop in a dynamic environment has been an important topic in robotics for decades. Recently, PIRF-Nav has been reported as being successful in achieving high recall rate at precision 1. However, PIRF-Nav has three main disadvantages: (i) the computational expense of PIRF-Nav is beyond real-time, (ii) it utilizes a large amount of memory in the redundant process of keeping signatures of places, and (iii) it is ill-suited to an indoor environment. These factors hinder the use of PIRF-Nav in a general environment for long-term, high-speed mobile robotic applications. Therefore, this paper proposes two techniques: (i) new modified PIRF extraction that makes the system more suitable for an indoor environment and (ii) new dictionary management that can eliminate redundant searching and conserve memory consumption. The results show that our proposed method can complete tasks up to 12 times faster than PIRF-Nav with only a slight percentage decline in recall. In addition, we collected additional data from a university canteen crowded during lunch time. Even in this crowded indoor environment, our proposed method has better real-time processing performance compared with other methods.     

Stabilizing switching design for switched linear systems: A state-feedback path-wise switching approach

This paper addresses the problem of switching stabilization for discrete-time switched linear systems. Based on the abstraction-aggregation methodology, we propose a state-feedback path-wise switching law, which is a state-feedback concatenation from a finite set of switching paths each defined over a finite time interval. We prove that the set of state-feedback path-wise switching laws is universal in the sense that any stabilizable switched linear system admits a stabilizing switching law in this set. We further develop a computational procedure to calculate a stabilizing switching law in the set.     

基于改进曲率尺度空间技术的图像水印算法

提出一种新的鲁棒性水印算法,利用改进的曲率尺度空间技术,提取图像的少量较顽强角点,用于重建受几何攻击的图像。选取2个chirp信号作为水印信息,将其嵌入图像的分数傅里叶变换（FRFT）域,选用变换阶次和水印嵌入位置矩阵作为算法密钥,根据chirp信号在FRFT域呈现的冲激特征检测水印信号。仿真实验结果表明,该算法具有较高不可见性、安全性和鲁棒性。     

基于能量估计的灰度水印系统分析

针对一类灰度水印系统设计理论存在的不足,给出指导该类灰度水印算法设计的一系列理论结果,包括嵌入强度、鲁棒性、不可见性三者之间定量关系的建立,提出水印算法不可见性和鲁棒性的折中方案,采用已有的算法对理论结果进行验证,结果表明,得出的理论结果对该类水印算法的设计具有较大的指导意义。