Influence of channel length on discharge performance of anode layer Hall thruster studied by particle-in-cell simulation

Hall thruster has the advantages of simple structure, high specific impulse, high efficiency, and long service life, and so on. It is suitable for spacecraft attitude control, North and South position keeping, and other track tasks. The anode layer Hall thruster is a kind of Hall thruster. The thruster has a longer anode area and a relatively short discharge channel. In this paper, the effect of the channel length on the performance of the anode layer Hall thruster is simulated by the PIC simulation method. The simulation results show that the change of the channel length has significant effect on the plasma parameters, such as potential and plasma density and so on. The ionization region mainly concentrates at the hollow anode outlet position, and can gradually move toward the channel outlet as the channel length decreases. The collision between the ions and the wall increases with the channel length increasing. So the proper shortening of the channel length can increase the life of the thruster. Besides, the results show that there is a best choice of the channel length for obtaining the best performance. In this paper, thruster has the best performance under a channel length of 5 mm.

Dependence of short channel length on negative/positive bias temperature instability (NBTI/PBTI) for 3D FinFET devices

A comprehensive study of the negative and positive bias temperature instability(NBTI/PBTI)of 3D FinFET devices with different small channel lengths is presented.It is found while with the channel lengths shrinking from 100 nm to 30 nm,both the NBTI characteristics of p-FinFET and PBTI characteristics of n-FinFET turn better.Moreover,the channel length dependence on NBTI is more serious than that on PBTI.Through the analysis of the physical mechanism of BTI and the simulation of 3-D stress in the FinFET device,a physical mechanism of the channel length dependence on NBTI/PBTI is proposed.Both extra fluorine passivation in the corner of bulk oxide and stronger channel stress in p-FinFETs with shorter channel length causes less NBTI issue,while the extra nitrogen passivation in the corner of bulk oxide induces less PBTI degradation as the channel length decreasing for n-FinFETs.The mechanism well matches the experimental result and provides one helpful guide for the improvement of reliability issues in the advanced FinFET process.

Shot Noise Suppression in a Quantum Point Contact with Short Channel Length

An experimental study on the current shot noise of a quantum point contact with short channel length is reported. The experimentally measured maximum energy level spacing between the ground and the first excited state of the device reached up to 7.5meV, probably due to the hard wall confinement by using shallow electron gas and sharp point contact geometry. The two-dimensionM non-equilibrium shot noise contour map shows noise suppression characteristics in a wide range of bias voltage. Fano factor analysis indicates spin-polarized transport through a short quantum point contact.

Anomalous Channel Length Dependence of Hot-Carrier-Induced Saturation Drain Current Degradation in n-Type MOSFETs

The dependencies of hot-carrier-induced degradations on the effective channel length Lch,eff are investigated for n-type metal-oxide-semiconductor field effect transistor （MOSFETs）. Our experiments find that, with decreasing Lch,eff, the saturation drain current （Iasat ） degradation is unexpectedly alleviated. The further study demonstrates that the anomalous Lch,eff dependence of Idsat degradation is induced by the increasing influence of the substrate current degradation on the lazar degradation with Lch,eff reducing.

Analysis on the positive dependence of channel length on ESD failure current of a GGNMOS in a 5 V CMOS

Contrary to general understanding, a test result shows that devices with a shorter channel length have a degraded ESD performance in the advanced silicided CMOS process. Such a phenomenon in a gate-grounded NMOSFET （GGNMOS） was investigated, and the current spreading effect was verified as the predominant factor. Due to transmission line pulse （TLP） measurements and Sentaurus technology computer aided design （TCAD） 2-D numerical simulations, parameters such as current gain, on-resistance and power density were discussed in detail.

Theoretical Study of Fully Developed Turbulent Flow in a Channel, Using Prandtl’s Mixing Length Model

This research used the common decomposition of the velocity and pressure in an average part and a fluctuating part, for high Reynolds number, of the Navier-Stokes equation, which leads to the classic problem of turbulent closure. The Prandtl’s mixing length model, based on the Boussinesq hypothesis and traditionally used for free shear flows, was chosen and adapted for internal flows to solve the closure problem. For channel flows, Johann Nikuradse proposed a model for the Prandtl mixing length. In the present paper, which has an academic character, the authors made a return to the model of the mixing length of Prandtl and the model of Nikuradse, to solve turbulent flows inside a plane channel. It was possible to develop an ordinary differential model for the velocity in the direction of the flow whose solution occurs computationally in a simple but extremely accurate way when compared with Direct Numerical Simulation databases. For the viscous stress on the wall, it was possible to determine the exact mathematical solution of the ordinary differential equation. It is a model of great academic value and even to be used as reference for verification of computational codes destined to the solution of complete numerical and computational models.

Proposed Equation to Estimate the Length of a Hydraulic Jump in a Rectangular Open Channel Hydraulic with Variable Slope, and Its Comparison with Seven Theoretical Equations of Specialized Literature

A hydraulic jump is a localized phenomenon that generates on an open hydraulic channel;however, its mathematical demonstration is not possible in the turbulent area of the phenomenon, especially in the area where the jump occurs and where its length is measured, so the data must be obtained with direct measurements in a laboratory and through empiric equations. This work presents the results of the generated hydraulic jumps and the measure of its length in a series of tests, where we input different flow rates in a transportable open channel hydraulic with a constant gate opening “a” and a slope of S = 0.0035, in the Engineering Faculty Research Centre of the Autonomous University of Chiapas. We also present the experimental method to generate a hydraulic jump, the measure of its length and a comparison with seven empirical equations, including the Sieñchi equation used in H-Canales, the most used software for hydraulic channels design in Latin America. The results show that the calculus of L with the proposed equation has a mean squared error (MSE) of 0.1337, a Bias of -0.0049, a model efficiency (ME) of 0.9991 and a determination coefficient (R2) of 0.9993 when compared with the experimental model. Meanwhile, the comparison of L calculated with the Sieñchi equation versus the experimental model resulted in a MSE of 0.1741, a bias of -0.0437, a ME of 0.9984 and a R2 of 0.9997. Both equations are highly recommended to estimate L in rectangular channels under the conditions presented in this paper, thus, the proposed equation can be applied if??y . Finally, it must be stated that we also proved that the Pavlosky equation is comparable in precision and accuracy concerning to proposed equation and Sieñchi equation.

Integrated Joint Source-Channel Symbol-by-Symbol Decoding of Variable-Length Codes Using 3-D MAP Sequence Estimation

Most of multimedia schemes employ variable-length codes （VLCs） like Huffman code as core components in obtaining high compression rates. However VLC methods are very sensitive to channel noise. The goal of this paper is to salvage as many data from the damaged packets as possible for higher audiovisual quality. This paper proposes an integrated joint source-channel decoder （I-JSCD） at a symbol-level using three-dimensional （3-D） trellis representation for first-order Markov sources encoded with VLC source code and convolutional channel code. This method combines source code and channel code state-spaces and bit-lengths to construct a two-dimensional （2-D） state-space, and then develops a 3-D trellis and a maximum a-posterior （MAP） algorithm to estimate the source sequence symbol by symbol. Experiment results demonstrate that our method results in significant improvement in decoding performance, it can salvage at least half of （50%） data in any channel error rate, and can provide additional error resilience to VLC stream like image, audio, video stream over high error rate links.

Crosstalk and Wire Length Reduction in the Non-Manhattan Channel Routing

A novel framework for non-Manhattan channel routing considering crosstalk and wire length reduction is proposed. To handle crosstalk and wire length reduction problem, an improved non-Manhattan router in the gridded routing model is developed, and a novel rerouting algorithm based on segment-rerouting technique and layer reassignment is presented. Simulation exDeriments demonstrate that our algorithm achieves verv good results.

Scaling of the bubble/slug length of Taylor flow in a meandering microchannel

In order to reduce or avoid the fluctuations from interface breakup, a meandering microchannel with curved multi-bends(44 turns) is fabricated, and investigations of scaling bubble/slug length in Taylor flow in a rectangular meandering microchannel are systematically conducted. Based on considerable experimental data,quantitative analyses for the influences of two important characteristic times, liquid phase physical properties and aspect ratio are made on the prediction criteria for the bubble/slug length of Taylor flow in a meandering microchannel. A simple principle is suggested to predict the bubble formation period by using the information of Rayleigh time and capillary time for six gas–liquid systems with average deviation of 10.96%. Considering physical properties of the liquid phase and cross-section configuration of the rectangular mcirochannel,revised scaling laws for bubble length are established by introducing Ca, We, Re and W/h whether for the squeezing-driven or shearing-driven of bubble break. In addition, a simple principle in terms of Garstecki-type model and bubble formation period is set-up to predict slug lengths. A total of 107 sets of experimental data are correlated with the meandering microchannel and operating range: 0.001 b CaTPb 0.05, 0.06 b WeTPb 9.0,18 b ReTPb 460 using the bubble/slug length prediction equation from current work. The average deviation between the correlated data and the experimental data for bubble length and slug length is about 9.42% and9.95%, respectively.

脉冲放电破岩等离子体通道长度预测方法

针对高压脉冲放电破岩电弧等离子体通道长度难以预测的问题,构建了高压脉冲放电破岩综合试验平台,测量了花岗岩-自来水组合介质下电弧等离子体通道发展特性及典型电流、电压参数,提取了不同电极间距和脉冲放电次数下岩石表面形成的破碎区域。基于能量平衡方程建立了岩石中电弧等离子体通道的阻抗模型,采用迭代优化算法获取阻抗模型参数的近似最优解,模型计算结果与试验结果的相对误差小于7%。基于优化参数,利用实测电流电压数据预测了等离子体通道的长度。模型预测的等离子体通道长度与实测值的绝对误差均处于毫米量级,且两者的相对误差小于10%,为高压脉冲放电破岩系统电源-电极负载的匹配设计提供了理论支撑。

基于概率球面判别分析的说话人识别信道补偿算法

在说话人识别任务中,概率线性判别分析(PLDA)模型是目前常用的分类后端,但由于高斯PLDA模型分布假设不能准确拟合真实说话人特征分布,导致基于高斯分布假设长度归一化的信道补偿方法会破坏说话人特征类内分布的独立性,使得高斯PLDA不能充分利用上游任务提取特征所包含的说话人信息,从而影响识别结果。针对这一问题,提出基于概率球面判别分析的信道补偿算法(CC-PSDA),通过引入冯·米塞斯-费希尔(VMF)分布假设的概率球面判别分析模型(PSDA)和特征变换方法代替高斯分布假设的概率线性判别分析方法,以避免信道补偿对说话人特征类内分布独立性的影响。首先,为了使说话人特征符合VMF分布先验假设拟合后端分类模型,在特征级利用非线性转换对说话人特征进行分布变换。之后,利用基于VMF分布假设的PLDA模型不会破坏说话人特征的类内分布结构的特点,将变换后的说话人特征定义到特定维度的超球面,最大化特征类间距离。所提算法通过期望最大化(EM)算法进行求解,最终完成分类任务。实验结果表明,改进算法在三个测试集上的识别等错误率相较于对比模型PSDA、高斯PLDA均最低。由此可见,所提模型可以有效区分说话人特征,提高识别性能。

基于深层神经网络的信道编码类型盲识别

为了解决当前识别算法只能识别一种或者两种码字类型以及人工提取特征复杂的问题,提出了两种基于深层神经网络模型的信道编码类型识别器,即卷积神经网络(convolutional neural network,CNN)识别器和递归CNN(recursive CNN,RCNN)识别器,用于识别接收数据中不同类型的信道码字。将待识别的软解调序列作为自然语言处理中文本分类问题的句子向量进行处理,输入到预先训练好的深层神经网络识别器中进行识别,并分析了字长度对识别准确率的影响,得出了最合适的字长度。实验结果表明,两种识别器都能够有效识别接收数据中多种类型的信道编码,且在信噪比为3 dB时CNN识别器的识别准确率能够达到99%以上,而RCNN识别器在1 dB时就能够达到99%以上的识别准确率。

滨里海盆地东缘北特鲁瓦油田石炭系碳酸盐岩储层裂缝网络连通性评价

基于岩心、成像测井及裂缝网络建模结果,应用拓扑学理论,对滨里海盆地东缘北特鲁瓦油田石炭系碳酸盐岩储层裂缝网络的连通性进行了评价,并分析了其对油田开发的影响。研究结果表明:(1)滨里海盆地东缘北特鲁瓦油田石炭系碳酸盐岩储层裂缝切割类型可划分为高高切割、高低切割和低低切割,研究区A2,A3,G1,G2,G3及G4小层裂缝切割较为发育,且主要分布在构造高部位。(2)裂缝网络连通性可通过连通体面积占比、裂缝体密度、裂缝的平均长度和平均节点数4个参数进行定量评价,根据连通体面积大小、裂缝体密度大小及裂缝类型可对裂缝连通体进行定性分析和命名,研究区A2小层主要发育低低大连通体、高中大连通体和高高大连通体。(3)裂缝网络连通性和储层物性的耦合作用是油田水窜的原因,裂缝网络连通性主要与裂缝长度和裂缝体密度有关。

The Estimation Method of Channel Quality

On the basis of the introduction about water saving irrigation that works as a kind of new irrigation pattern,the method of anti-seep quality estimation of the conveying water and distributing channel which acts as an important engineering measure of water saving irrigation will be introduced in te paper.that is,by means of unit length of channel's water utilization coefficient(η 0)to estimate the quality of channel,and the calculative method has been explained by the example of an actual project.It can be referred to irrigational workers.

Optimization of laser focused atomic deposition by channeling

Laser focused atomic deposition is a unique and effective way to fabricate highly accurate pitch standards in nanometrology.However,the stability and repeatability of the atom lithography fabrication process remains a challenging problem for massive production.Based on the atom-light interaction theory,channeling is utilized to improve the stability and repeatability.From the comparison of three kinds of atom-light interaction models,the optimal parameters for channeling are obtained based on simulation.According to the experimental observations,the peak to valley height of Cr nano-gratings keeps stable when the cutting proportion changes from 15%to 50%,which means that the channeling shows up under this condition.The channeling proves to be an effective method to optimize the stability and repeatability of laser focused Cr atomic deposition.

Integrated Joint Source-Channel Decoding for H.264 Video Transmission

This paper proposes an integrated joint source-channel decoder （I-JSCD） using Max-Log-MAP method for sources encoded with exp-Golomb codes and convolutional codes, and proposes a system applying this method to decoding the VLC data, e.g. motion vector differences （MVDs）, of H.264 across an AWGN channel. This method combines the source code state-space and the channel code state-space together to construct a joint state-space, develops a 3-D trellis and a maximum a-posterior （MAP） algorithm to estimate the source sequence symbol by symbol, and then uses max-log approximation to simplify the algorithm. Experiments indicate that the proposed system gives significant improvements on peak signal-to-noise ratio （PSNR） （maximum about 15 dB） than a separate scheme. This also leads to a higher visual quality of video stream over a highly noisy channel.

曲线路段平行式加速车道渐变段合理长度研究

渐变段长度直接影响高速公路合流区末端的交通安全,JTG D20—2017《公路路线设计规范》中对渐变段长度的规定没有考虑加速车道渐变段位于曲线路段时的需求,位于曲线路段的渐变段长度不足可能导致路侧护栏遮挡驾驶人视线,存在合流末端停车视距不足的安全隐患。分析合流末端渐变段小客车行驶轨迹特点及小车驾驶人的视线通视条件,采用符合实际换道轨迹的双曲正切换道模型,以渐变段满足小车驾驶人停车视距为控制要素,构建了曲线路段平行式加速车道渐变段长度计算模型,并基于国内外研究及相关合流末端车辆运行速度调查数据,确定了该模型中关键参数的取值,最后提出了曲线路段平行式加速车道渐变段合理长度取值。研究表明:曲线路段平行式加速车道渐变段最小长度与合流末端的小客车运行速度正相关,与主线行车道右侧硬路肩宽度和圆曲线半径负相关;JTG D20—2017《公路路线设计规范》规定的平行式加速车道渐变段最小长度能满足主线设计速度<100 km/h时小客车合流末端换道时停车视距的要求,当主线设计速度≥100 km/h时,不满足小客车合流末端换道时停车视距的要求,存在一定的行车安全风险,建议根据主线曲率半径及硬路肩宽度综合确定平行式加速车道渐变段长度。

通道弯数与长度对静脉曲张泡沫硬化疗法的泡沫稳定性影响实验研究

目的研究通道弯数与长度对静脉曲张泡沫硬化疗法的泡沫稳定性影响。方法设置3组实验:实验组1通道弯数不同(A、B、C组弯数分别为1、2、3)、实验组2(对照组)通道总长度不同(A、B、C组总长度分别为2、6、10)、实验组3通道长短比例不同(A、B、C组长短边比值分别为1∶1、5∶1、9∶1)。选用5 mL注射器,液气比1∶4,并在室温环境下进行CO_(2)和空气的Tessari法制备泡沫实验。每组实验全程摄像,设置重复实验5次,通过视频回放方式获取析水时间、半衰期、析水率曲线等数据。结果实验组2中,CO_(2)泡沫除析水率40%和80%,A组与B组、C组都具有显著性差异。空气泡沫中,析水率20%和50%的B组与A组具有显著性差异;所有析水率下,C组与A组具有显著性差异。通道总长度对CO_(2)泡沫的影响更为显著。通道总长度越长,泡沫越稳定。实验组1与对照组对比,CO_(2)泡沫的实验组1析水率曲线明显高于对照组,而空气泡沫出现重合和交叉,差异不明显。实验组3和对照组对比,CO_(2)泡沫实验组3的曲线明显高于对照组,而空气泡沫只在析水达到100%时,实验组明显高于对照组。通道长短比例的影响在CO_(2)泡沫中较为明显。半衰期在CO_(2)泡沫中存在较大影响。结论制备泡沫的通道弯数增强了泡沫的稳定性,通道总长度增加对泡沫稳定性具有积极意义,而通道长短比例对泡沫稳定性的影响较大。研究结果对于临床制备泡沫以及其他泡沫的稳定性研究具有一定意义。