First assessment of Noise-Equivalent Sigma-Zero in GF3-02 TOPSAR mode with sea surface wind speed retrieval

Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.

Linearized Phase Detector Zero Crossing DPLL Performance Evaluation in Faded Mobile Channels

Zero Crossing Digital Phase Locked Loop with Arc Sine block (AS-ZCDPLL) is used to linearize the phase difference detection, and enhance the loop performance. The loop has faster acquisition, less steady state phase error, and wider locking range compared to the conventional ZCDPLL. This work presents a Zero Crossing Digital Phase Locked Loop with Arc Sine block (ZCDPLL-AS). The performance of the loop is analyzed under mobile faded channel conditions. The mobile channel is assumed to be two path fading channel corrupted by additive white Gaussian noise (AWGM). It is shown that for a constant filter gain, the frequency spread has no effect on the steady state phase error variance when the loop is subjected to a phase step. For a frequency step and under the same conditions, the effect on phase error is minimal.

A New Accident Prediction Model for Highway-Rail Grade Crossings Using the USDOT Formula Variables

This paper presents the ZINDOT model,a methodology utilizing a zero-inflated negative binomial model with the variables used in the United States Department of Transportation(USDOT)accident prediction formula,to determine the expected accident count at a highway-rail grade crossing.The model developed contains separate formulas to estimate the crash prediction value depending on the warning device type installed at the crossing:crossings with gates,crossings with flashing lights and no gates,and crossings with crossbucks.The proposed methodology also accounts for the observed accident count at a crossing using the Empirical Bayes method.The ZINDOT model estimates were compared to the USDOT model estimates to rank the crossings based on the expected accident frequency.It is observed that the new model can identify crossings with a greater number of accidents with Gates and Flashing Lights and Crossbucks in both Illinois(data which were used to develop the model)and Texas(data which were used to validate the model).A practitioner already using the USDOT formulae to estimate expected accident count at a crossing could easily use the ZINDOT model as it employs the same variables used in the USDOT formula.This methodology could be used to rank highway-rail grade crossings for resource allocation and safety improvement.

Relative energy zero ratio-based approach for identifying pulse-like ground motions

Pulse-like ground motions are capable of inflicting significant damage to structures. Efficient classification of pulse-like ground motion is of great importance when performing the seismic assessment in near-fault regions. In this study, a new method for identifying the velocity pulses is proposed, based on different trends of two parameters: the short-time energy and the short-time zero crossing rate of a ground motion record. A new pulse indicator, the relative energy zero ratio(REZR), is defined to qualitatively identify pulse-like features. The threshold for pulse-like ground motions is derived and compared with two other identification methods through statistical analysis. The proposed procedure not only shows good accuracy and efficiency when identifying pulse-like ground motions but also exhibits good performance for classifying records with high-frequency noise and discontinuous pulses. The REZR method does not require a waveform formula to express and fit the potential velocity pulses;it is a purely signal-based classification method. Finally, the proposed procedure is used to evaluate the contribution of pulse-like motions to the total input energy of a seismic record, which dramatically increases the seismic damage potential.

MEASUREMENT OF 2-DIMENSIONAL DISPLACEMENT USING 2-D ZERO-REFERENCE MARKS

Several 2-D displacement sensing methods are reviewed. As to the crossdiffraction grating, there is no absolute zero-reference. In regards to the optical fiber method,the output signal is affected greatly by the quality of the reflecting surface and it is hard to gethigh resolution. Considering the concentric-circle gratings, the displacement can only be gainedwith complicated calculating of the experiment data. Compared with the advantages and limitations ofthe methods above, a novel 2-D zero-reference mark is especially proposed and demonstrated. Thiskind of mark has an absolute zero-reference when used in pair, and the experimental result is simpleto dispose. By superimposing a pair of specially coded 2-D marks, the correct alignment position ofthe two marks can be detected by the maximum output of the sharp intensity peak. And each slope ofthe peak is of good linearity which can be used to achieve high resolution in positioning andalignment in two dimensions. Design and fabrication of such 2-D zero-reference marks are introducedin detail. The experiment results are agreed with the theoretical ones.

Cross correlation mediated by distant Majorana zero modes with no overlap

Existing studies via shot noise calculation conclude that the cross correlation between the currents in the two leads connected by a pair of Majorana zero modes(MZMs)vanishes when their coupling energy𝜖∈_(M)→0.Motivated by the intrinsic nature of nonlocality of the MZMs,we revisit this important problem and propose an experimental scheme to demonstrate the nonvanishing cross correlation even at the limit𝜖∈_(M)→0.The proposed scheme employs the Andreevprocess-associated branch circuit currents,which are theoretically obtained by applying a decomposition analysis for the total currents while are accessible directly in practical measurement.For different bias voltage setup,we find intriguing results of both negative and positive correlations and carry out simple physical understanding using a quantum jump technique.Importantly,combining together with the evidence of the zero-bias-peak of conductance,the nonlocal cross correlation predicted in this work can help to confirm the existence of the nonlocal MZMs.

Variance Reduction Technique for Estimating Value-at-Risk based on the Cross - Entropy

Value-at-Risk （VaR） estimation via Monte Carlo （MC） simulation is studied here. The variance reduction technique is proposed in order to speed up MC algorithm. The algorithm for estimating the probability of high portfolio losses （more general risk measure） based on the Cross - Entropy importance sampling is developed. This algorithm can easily be applied in any light- or heavy-tailed case without an extra adaptation. Besides, it does not loose in the performance in comparison to other known methods. A numerical study in both cases is performed and the variance reduction rate is compared with other known methods. The problem of VaR estimation using procedures for estimating the probability of high portfolio losses is also discussed.

基于过零点斜率加窗解调的ACARS信号接收方法

飞机通信寻址与报告系统(ACARS)允许飞机和地面站之间发送和接收报文,在保障飞行安全、实现空中交通管制等方面具有重要意义。通信链路的噪声和频偏是影响ACARS信号接收性能的关键因素。针对ACARS信号接收过程中的失真等问题,深入研究频偏、噪声等因素与ACARS报文接收性能之间的关系;在充分考虑噪声与多普勒频移等因素的基础上,提出基于过零点斜率加窗解调的ACARS信号接收方法,并从理论和仿真分析2方面探讨不同方法的抗频偏抗噪声能力;设计并搭建基于软件无线电平台的ACARS信号接收系统。通过对ACARS报文接收性能的仿真分析和真实报文接收性能的对比分析,表明所提方法在提升抗噪声和频偏能力、降低误码率等方面均具有优势。

柔性直流输电系统的高频谐波保护方法与工程实践

柔性直流输电系统受电力电子设备本身特性以及控制系统影响,在多种运行工况下易出现不同频率的振荡问题。作为实现设备安全和电网稳定运行的决定因素,保护系统应实现对系统谐波的准确监测以及可靠动作。根据高频振荡时的电流能量累积作用,给出了基于反时限动作的电流类谐波保护算法。基于高频谐波电压特性,分别给出了过零点监测保护算法、谐波畸变率保护算法以及宽谐波保护算法,各保护算法相互配合,实现对不同电压振荡类型的全面保护。最后,给出了国内柔性直流工程实践中配置的高频谐波保护,结合保护原理对系统发生高频振荡后的动作特性进行分析,验证了高频谐波保护的有效性和准确性。

微波消解-零交截距导数分光光度法同时测定催化剂中钴和镍

采用微波法消解催化剂 ,研究确定了微波消解催化剂的最佳工作条件。应用零交截距导数分光光度法解决了 PAR- CO2 +、PAR- Ni2 +体系中 Co2 +、Ni2 +的同时测定。钴和镍的线性范围分别为 0～ 30 μg/ 2 5m L和 0～ 2 5μg/ 2 5m L,催化剂样品中钴和镍测定结果的相对标准偏差 (n=5)分别≤ 1 .5%和≤ 1 .0 % ,与标准值相对误差分别≤± 1 .5%和≤± 2 .1 %。本方法测定催化剂中钴和镍 ,酸用量少 。

基于短时幅度-过零率函数识别抽油井液面回波

基于液面回波短时过零率较低的显著特征和新定义的短时幅度函数,提出一种新的液面回波的综合识别方法,将含有幅度敏感因子的短时幅度函数与短时过零率函数相结合构造出了一个短时幅度-过零率函数,利用该函数逐帧地对回波信号进行计算,可识别出液面回波。与传统方法相比,可显著降低误判。通过阈值方法或其他方法可确定液面回波到达时刻。通过对比分析与实际计算给出了短时幅度-过零率函数的参数及帧长的选择范围。合适的函数参数和帧长可在一定程度上提高识别能力。现场应用表明该方法是可行的,与传统的单一幅值的识别方法相比,该方法对液面回波的正确识别能力有较大提高。

一种同步降压型DC-DC转换器驱动电路设计

设计了一种适用于同步整流降压型DC-DC转换器的驱动电路,包含电平移位、死区时间控制及过零检测等模块。分析了电路整体及各个模块的结构和工作原理,并基于0.35μm BCD工艺模型库,通过Cadence Spectre进行仿真验证。仿真结果表明,本电路可以有效地控制死区时间,抑制反向电流,提高转换器的效率。

增强依存结构表达的零样本跨语言事件论元角色分类

事件论元角色分类是事件抽取中的子任务,旨在为事件中的候选论元分配相应的角色。事件语料标注规则复杂、人力耗费大,在很多语言中缺少相关标注文本。零样本跨语言事件论元角色分类可以利用源语言的丰富语料建立模型,然后直接应用于标注语料匮乏的目标语言端。围绕不同语言的事件文本在依存结构上的表达共性,提出了使用BiGRU网络模块对触发词到候选论元的依存路径信息进行额外编码的方法。本文设计的编码模块能灵活地与当前主流的基于深度学习框架的事件论元角色分类模型相联合。实验结果表明,本文提出的方法能更有效地完成跨语言迁移,提高多个基准模型的分类性能。

基于K-L距离的两步固定音频检索方法

根据音频文件数据量大、数据间存在一定相关性的特点,提出一种基于K-L距离的两步固定音频检索方法。该方法采用基于可变门限的直方图检索方法快速筛选出相似度较高的语音文件,利用特征矩阵的K-L距离对剩余语音进行精确比较,取得较好的效果。实验结果证明,该方法能使检索准确率达到90%左右。

面向跨联盟链的隐私保护数据要素交易审计方案

随着企业数据资产化的发展,联盟链成为了企业联盟内部数据交易的核心基础设施.利用联盟链构建去中心化、不可篡改、访问可控的数据交易市场,可以提高数据交易的可信度,降低数据泄露风险.然而,随着企业联盟的增多,如何促进跨企业联盟的数据要素流通,抵御数据隐私泄露、数据欺诈和支付抵赖等安全威胁,成为了数据流通领域亟待解决的难题.为此,提出了一种面向跨联盟链的隐私保护数据要素交易审计方案.该方案利用联盟链进行数据存证,通过中继链上的智能合约进行数据验证和支付管理.结合Pedersen承诺和Shamir秘密分享技术,构建零知识证明机制,在不泄露数据要素的情况下防止数据欺诈的发生.此外,还引入了一种基于双线性映射的数据要素完整性审计机制,允许在不透露数据隐私的情况下验证数据要素的收据,有效解决支付抵赖问题.通过理论分析和实验评估,验证了所提方案的有效性和可靠性,在本地模拟实验环境下,实验结果表明所提方案是可行且高效的.

基于光伏充电的低压混合式断路器设计及仿真

直流断路器是实现直流系统电流故障清除和隔离的关键设备。基于人工过零点的直流断路器熄弧时刻具有不确定性,且换流电容需要更换辅助电源,降低断路器可靠性,增加维护成本。为此,在传统直流断路器基础上,提出了一种基于光伏充电的混合式直流断路器拓扑结构设计方案。该方案在断路器过零点未熄弧时闭锁IGBT开关,加速电弧熄灭,并设计光伏储能供电系统为换流电容预充电能,以保障断路器持续运行。同时对所提断路器的拓扑结构、开断时序、拓扑参数进行了设计,基于MATLAB/Simulink实验平台建立了150 V混合式直流断路器模型,讨论IGBT开关器件闭锁时刻及电阻电容二极管(resistance-capacitance diode,RCD)缓冲电路对断路器开断的影响。在此基础上,通过仿真实验分析了正常和短路工况下断路器开断过程,验证了所提方案的可行性。

基于零知识证明的跨链隐私智能合约

针对跨链智能合约的代码和数据在跨链交易中公开披露用户隐私信息的情景,设计具有隐私保护功能的跨链智能合约,该合约中每一个函数所涉及的用户隐私信息,将被用户加密后作为函数参数输入,同时引入零知识证明电路,用于证明用户输入密文的正确性。在合约执行过程中,合约调用者通过输入公共参数和隐私参数密文发起合约调用请求,跨链隐私智能合约的验证节点使用零知识证明电路来验证用户输入信息的正确性并执行智能合约,从而在保护用户隐私信息的同时确保智能合约的正确执行。

LCC-MMC型混合直流送端交流系统故障时直流电流的暂态过程解析

电网换相换流器和模块化多电平换流器(LCC-MMC)型混合直流输电解决了传统直流受端的换相失败问题,目前葛洲坝—上海直流系统正在进行受端柔性直流化改造的方案论证,而焦点在于送端交流系统故障引起直流电流快速下降的故障穿越问题。为此,首先根据送端交流系统故障时的系统等值电路得到其拉氏运算电路,基于回路电流法通过拉氏反变换求得直流电流的暂态过程,并分析了暂态电流的衰减分量及振荡分量。在PSCAD/EMTDC仿真平台上建立了葛洲坝—上海直流的电磁暂态仿真模型,仿真结果验证了分析的正确性。进一步地,忽略暂态电流的振荡分量,得到了直流电流及其过零时间的近似解析表达式。最后,利用解析表达式分析了交流电压跌落程度、平波电抗器和控制策略对直流电流过零时间的影响。所提方法可为LCC-MMC型混合直流输电的送端交流系统保护定值整定及平波电抗器参数的选取提供依据。

PWM-ON-PWM调制方式控制的无刷直流电机换相信号检测

为了实现PWM-ON-PWM调制方式控制的无位置传感器无刷直流电机转子位置信号的检测,在分析了该种调制方式控制的功率逆变器为桥式结构无刷直流电机端电压的基础上,提出一种通过检测线电压差的过零点,移相30°电角度获得换相信号的方法,并以此得到了相应的检测电路。通过应用该检测电路搭建无刷直流电机控制系统的仿真和实验结果表明:提出的方法在宽速度范围内,特别是低速时都能准确地检测到转子的位置,从而验证了该方法的有效性。

一种过零单边干涉图加权切趾函数对太阳观测中傅里叶变换光谱的影响分析

傅里叶变换光谱仪(FTS)因其出色的光谱分辨率而广泛用于太阳活动的观测。在使用过零单边干涉图进行光谱复原时,可能会出现频率泄漏、旁瓣效应以及对零光程差附近的采样数据重复利用,从而导致光谱线的平滑和畸变等问题。为了获得更准确的太阳光谱数据,必须对过零单边干涉图进行加权和切趾操作。对此,文章采用了一种奇次多项式非对称加权切趾函数来处理过零单边干涉图,并探讨了使用不同的切趾函数构建非对称加权切趾函数进行光谱恢复的效果。模拟数据实验的结果表明采用奇次多项式非对称加权切趾函数可以有效地恢复光谱。此外,与Griffiths、相里斌以及SP.Davis提出的加权切趾方法相比,文章中提出的方法表现出较小的误差。最后,将所提出的方法应用于Bruker IFS-125HR FTS采集的干涉图数据,与其他切趾方法相比,使用文中提出的方法可以有效地恢复光谱。