一种用于水下距离选通成像的变步长扫描方法

为了扫描时既减少"切片"数目又保证图像质量,采用一种用于距离选通水下激光成像的变步长的延迟递增方法,首先通过辐射探测理论和景深原理确定接收镜头的焦距和对焦位置以及系统需要扫描的范围,再依据水下激光脉冲时域展宽理论确定延迟递进的步长和相应的选通门宽,最后进行了仿真计算和实验.结果表明,在保证图像质量的同时,基于该方法的距...     

一种换能器频率跟踪与振幅稳定方法的研究

针对超声波换能器工作过程中换能器的谐振频率漂移及其振幅不稳定问题,对一种同时实现振幅稳定和频率跟踪的方法进行了研究。通过正交相关法对换能器匹配网络的复阻抗幅值与相位进行分析。通过比例-积分-微分(PID)控制算法对超声波发生器输出电压的频率和幅值进行调节,从而实现换能器频率的跟踪和振幅稳定。对频率28kHz的换能器进行了实验,实验表明,正交相关法和PID控制算法的结合能实现换能器的谐振频率跟踪和振幅稳定。     

一种改进RBF神经网络的机器人轨迹规划方法

在应用径向基函数RBF(Radial Basis Function)神经网络对机器人进行轨迹规划时,为解决一般学习算法中收敛速度慢、学习精度不高的问题,提出一种混合学习算法.该方法根据轨迹规划的具体要求,用最近邻聚类算法确定网络的结构和参数,通过在学习速率中加入自适应学习因子调整网络参数,以加快收敛速度.通过MATLAB软件进行仿真,结果表明混合学习算法收敛速度较快,逼近误差小,从而证明了该算法的可行性.     

Throughput Evaluation of a Novel Scheme to Mitigate the Congestion over WSNs

In recent years, due to fast development of wireless sensor networks (WSNs), the numbers of nodes are increasing, and their scope of applications is continuously expanding, including environmental monitoring, military and smart home applications. The power supply, memory and computing power of wireless sensor nodes are greatly hampered in WSNs so that the WSNs are classified as a task-oriented framework. This study focused on exploring problems caused by traffic congestion on the WSNs with a large amount of flow, such as packet loss, bandwidth reduction, and waste of energy on the sensor nodes. On the other hand, a cooperative strong node mechanism is presented and named as Cooperative Strong Node Mechanism, in which a threshold is set to determine whether the node traffic is over or not. When the load exceeds, the privilege of corresponding sensor nodes is upgraded so that it can command its child nodes to change the transmission path to distribute the traffic effectively. Furthermore, when the traffic exceeds preset overall network flow, new sensor nodes are added in the network to relieve the traffic. This novel proposed mechanism can not only increase network throughput and effectively prevent the occurrence from congestion problems, but is suitable for a variety of routing protocols.     

A Guideline to Mitigate Interfacial Degradation Processes in Solid-State Batteries Caused by Cross Diffusion

Diffusion of transition metals across the cathode–electrolyte interface is identified as a key challenge for the practical realization of solid-state batteries. This is related to the formation of highly resistive interphases impeding the charge transport across the materials. Herein, the hypothesis that formation of interphases is associated with the incorporation of Co into the Li₇La₃Zr₂O₁₂ lattice representing the starting point of a cascade of degradation processes is investigated. It is shown that Co incorporates into the garnet structure preferably four-fold coordinated as Co²⁺ or Co³⁺ depending on oxygen fugacity. The solubility limit of Co is determined to be around 0.16 per formula unit, whereby concentrations beyond this limit causes a cubic-to-tetragonal phase transition. Moreover, the temperature-dependent Co diffusion coefficient is determined, for example, D_{700 °C} = 9.46 × 10⁻¹⁴ cm² s⁻¹ and an activation energy E_a = 1.65 eV, suggesting that detrimental cross diffusion will take place at any relevant process condition. Additionally, the optimal protective Al₂O₃ coating thickness for relevant temperatures is studied, which allows to create a process diagram to mitigate any degradation with a minimum compromise on electrochemical performance. This study provides a tool to optimize processing conditions toward developing high energy density solid-state batteries.     

A Street Broadcast Reduction Scheme (SBR) to Mitigate the Broadcast Storm Problem in VANETs

In urban vehicular wireless environments, several vehicles can send warning messages and so every vehicle within the transmission range will receive the broadcast transmission, possibly rebroadcasting these messages to other vehicles. This increases the number of vehicles receiving the traffic warning messages. Hence, redundancy, contention, and packet collisions due to simultaneous forwarding (usually known as the broadcast storm problem), can occur. In the past, several approaches have been proposed to solve the broadcast storm problem in wireless networks such as Mobile ad hoc Networks MANETs. In this paper, we present Street Broadcast Reduction SBR, a novel scheme that mitigates the broadcast storm problem in VANETs. SBR also reduces the warning message notification time and increases the number of vehicles that are informed about the alert.     

Collaborative Polling based Routing Security Scheme to Mitigate the Colluding Misbehaving Nodes in Mobile Ad Hoc Networks

The recent advancements in the field of wireless communications makes the mobile devices to communicate with each other in a self organized manner without relying on stable infrastructure. It requires cooperation between the mobile devices in order to find routes between them when the nodes are not in the communication range of each other. The misbehaving node comes into existence due to scarcely available resources such as battery, bandwidth and computational power. When the nodes collude to misbehave then it further makes the routing process difficult due to frequent network partitioning and it also degrades the overall network throughput. This paper proposes a Collaborative Polling based Routing Security Scheme to detect and isolate the colluding misbehaving nodes in mobile ad hoc networks. The proposed system employs a timeout approach to detect the active neighbors in the neighborhood before monitoring the transmissions which involves it. It ensures that the false detection of a good node as a bad one has been greatly reduced which in turn decreases the send buffer drop because of the availability of alternate routes. The simulation result shows that the measured parameters such as packet drop ratio and malicious drop has been reduced due to the efficient detection and isolation of misbehaving nodes. This paper also presents an analytical and simulation results of the impact of node misbehavior.     

A New Scheme to Mitigate the OFDM High PAR Problem by Minimizing the Signal's Nonlinear Distortion Caused by HPA

How to mitigate the negative impact of high PAR in OFDM systems is an important issue. Most of recent works have focused on minimizing the PAR of OFDM signal to enhance performance. However, after relating this issue with the specific characteristics of HPA, we propose a new scheme to mitigate the high PAR problem. Rather than minimizing OFDM signal's PAR, the new scheme uses the amount of OFDM signal's nonlinear distortion to be caused by HPA as a new measure and increases the performance of OFDM system by minimizing this nonlinear distortion. The pre-calculation of the new measure is achieved by employing an adaptive nonlinear system identification process. Meanwhile, because the new scheme only changes the measure of the OFDM signal but not the frameworks of the prior PAR-reduction methods based on minimum PAR criterion, these prior PAR-reduction methods can be easily extended to incorporate the new scheme. A case study of the new scheme by adopting it in the SLM method shows its superiority over the conventional scheme     

衬底负偏置对FLASH器件耐久性退化的影响

研究了ETOXTM结构FLASH memory单元器件在VFG≈VD/2的热载流子写入应力条件下,衬底负偏置对单元器件耐久性退化的影响.结果表明:在既定的栅、漏偏置条件下,随着衬底负偏置的增加,器件耐久性退化会出现极小值.综合考虑了器件耐久性退化以及写入效率两方面的要求以后,确定了在VFG≈VD/2热载流子写入应力模式下,FLASH memory单元器件具有增强写入效率以及最小耐久性退化的最佳衬底负偏置条件.     

衬底负偏置对FLASH器件耐久性退化的影响

研究了ETOXTM结构FLASH memory单元器件在VFG≈VD/2的热载流子写入应力条件下,衬底负偏置对单元器件耐久性退化的影响.结果表明:在既定的栅、漏偏置条件下,随着衬底负偏置的增加,器件耐久性退化会出现极小值.综合考虑了器件耐久性退化以及写入效率两方面的要求以后,确定了在VFG≈VD/2热载流子写入应力模式下,FLASH memory单元器件具有增强写入效率以及最小耐久性退化的最佳衬底负偏置条件.     

中低轨卫星跨层激光链路二次同步切换方法

中低轨卫星之间跨层激光链路的无缝切换直接决定了双层卫星光网络的稳定性.异步切换方法会导致网络拓扑频繁重构,而集中同步切换将造成两层间连接中断,网络运行状态失控.为此,本文提出了中低轨卫星星座激光链路的二次同步切换方法,在保证中低轨道卫星连通的基础上,可降低网络拓扑重构频率.研究了整数周期比的中轨道和低轨道卫星空间位置特性,建立了中低轨卫星星座构形二阶非球摄动模型,确定了中低轨道之间轨道周期比为3的双层卫星星座构形.按连接和切换顺序将该星座构形中跨层激光链路分为两组,以相对周期的1/4为基准,每次令其中一组同步切换,通过交替完成切换.研究结果表明,二次同步切换方法使得网络拓扑重构频率降低到链路切换频率的1/7,比集中切换方法在网络平均时延方面降低了30ms.     

Data Randomization Scheme for Endurance Enhancement and Interference Mitigation of Multilevel Flash Memory Devices

In this letter, we propose a data randomization scheme for endurance and interference mitigation of deeply‐scaled multilevel flash memory. We address the relationships between data patterns and the raw bit error rate. An on‐chip pseudorandom generator composed of an address‐based seed location decoder is developed and evaluated with respect to uniformity. Experiments performed with 2x‐nm and 4x‐nm NAND flash memory devices illustrate the effectiveness of our scheme. The results show that the error rate is reduced up to 86% compared to that of a conventional cycling scheme. Accordingly, the endurance phenomenon can be mitigated through analysis of interference that causes tech shrinkage.