Shear-wave splitting in the crust:Regional compressive stress from polarizations of fast shear-waves

When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shear- wave （PFS） is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations.

Seismic anisotropy of the crust in Yunnan,China:Polarizations of fast shear-waves

Using seismic data recorded by Yunnan Telemetry Seismic Network from January 1, 2000 to December 31, 2003, the dominant polarization directions of fast shear-waves are obtained at 10 digital seismic stations by SAM technique, a systematic analysis method on shear-wave splitting, in this study. The results show that dominant directions of polarizations of fast shear-waves at most stations are mainly at nearly N-S or NNW direction in Yunnan. The dominant polarization directions of fast shear-waves at stations located on the active faults are consistent with the strike of active faults, directions of regional principal compressive strains measured from GPS data, and basically consistent with regional principal compressive stress. Only a few of stations.show complicated polarization pattern of fast shear-waves, or are not consistent with the strike of active faults and the directions of principal GPS compressive strains, which are always located at junction of several faults. The result reflects complicated fault distribution and stress field. The dominant polarization direction of fast shear-wave indicates the direction of the in-situ maximum principal compressive stress is controlled by multiple tectonic aspects such as the regional stress field and faults.

基于关键翻转集合的极化码Fast-SSC-Flip译码算法

为了降低极化码快速简化串行抵消翻转(Fast-SSC-Flip)译码算法的候选翻转比特集合大小,减小搜索复杂度,该文提出一种基于关键翻转集合的极化码Fast-SSC-Flip译码算法。基于快速简化串行抵消(Fast-SSC)译码过程中首位译码错误信息比特有极大的概率落于关键集合(CS)中,以及Fast-SSC-Flip译码算法的候选比特均为码字比特,所提算法利用极化码的生成矩阵得到与CS中信息比特相应的码字比特,并用这些码字比特构建关键翻转集合(CFS)作为候选翻转比特集合。实验结果表明,在使用相同候选比特可靠性度量准则的前提下,在码长N=1024及码率R=0.5时,该文所提基于关键翻转集合的Fast-SSC-Flip译码算法相较于传统Fast-SSC-Flip算法在不损失译码性能的情况下,候选翻转集合大小显著降低;相较于新的快速简化串行抵消翻转(N-Fast-SSC-Flip)算法有相近的译码性能,但候选翻转集合至少缩小了77.93%。

Preliminary analysis of the shear-wave splitting observations from the Qiaojia seismic array

A total of 351 shear-wave splitting results at 25 stations were obtained from the seismic data recorded in period of January,2013 to December,2016,by a broadband seismic array deployed in the northern segment of Xiaojiang Fault Zone(n-XJFZ).Meanwhile,the stress field of the n-XJFZ was determined by inverting 140 focal mechanism solutions of the small earthquakes within the study area which were recorded in the same period.This determination confirmed a compressive stress in NW-SE orientation and an extensional stress in the NE-SW orientation,with little difference from those released by previous studies.The shear-wave splitting results show a spatial complexity in polarization orientation,different from one site to another.How-ever,the polarization orientations integrated for the subareas suggest that the fault trends seemingly played important roles.All the subareas bear two dominant orientations,N10°E and N90°E,both of which are different from the azimuths of the principal compressive stress,due to the fault distribution.The time delay averaged over the entire region is 4.56 ms/km,close to that of the upper boundary of the generally accepted interval worldwide but larger than those in most of the investigated regions in the Chinese mainland,which probably implies an alignment of more micro-cracks in the n-XJFZ.Interestingly,the 2014 Ms6.5 Ludian earthquake was found to have caused a variation in the time delays of the slow shear waves within the study area though its epicenter was outside.This earthquake resulted in an evident drop of the time delays remaining for 4 months,however,lifted a bit the time-delay level with respect to that prior to the earthquake.

Power System State Estimation Solution With Zero Injection Constraints Using Modified Newton Method and Fast Decoupled Method in Polar Coordinate

如何保证零注入节点的注入功率在状态估计结果中严格为0是电力系统状态估计研究中的重要问题。在直角坐标下,由于零注入约束为线性约束,可使用修正牛顿法来有效地解决这一问题。因此,借鉴直角坐标下修正牛顿法的思路,提出了极坐标下的修正牛顿法和修正快速解耦估计。这些方法的计算流程与传统的极坐标下的牛顿法和快速解耦估计非常相似,计算速度与大权重法相当,同时能够保证零注入约束严格满足。仿真结果验证了所得结论。

Towards 640 Gbit/s wavelength conversion based on nonlinear polarization rotation in a semiconductor optical amplifier

Taking into account ultra-fast carrier dynamics, this paper models 640 Gbit/s wavelength conversion scheme based on nonlinear polarization rotation （NPR） in a single semiconductor optical amplifier （SOA） and investigates the performance of this kind of wavelength conversion scheme in detail. In this model, two carrier temperature equations are introduced to substitute two energy density equations, which reduce the complexity of calculation in comparison with the previous model. The temporary gain and phase shift dynamics induced by ultra-short optical pulses are numerically simulated and the simulated results are qualitatively in good agreement with reported experimental results. Simulated results show that non-inverted and inverted 640 Gbit/s wavelength conversions based on NPR are achieved with clear open eye diagrams. To further investigate the performance of the non-inverted wavelength conversion scheme, the dependence of output extinction ratio （ER） on some key parameters used in simulation is illustrated. Furthermore, simulated analyses show that high performance non-inverted wavelength conversion based on NPR can be achieved by using a red-shifted filtering scheme.

Improved Polar Decoder Utilizing Neural Network in Fast Simplified Successive-Cancellation Decoding

Polar codes using successive-cancellation decoding always suffer from high latency for its serial nature. Fast simplified successive-cancellation decoding algorithm improves the situation in theoretically but not performs well as expected in practical for the workload of nodes identification and the existence of many short blocks. Meanwhile, Neural network (NN) based decoders have appeared as potential candidates to replace conventional decoders for polar codes. But the exponentially increasing training complexity with information bits is unacceptable which means it is only suitable for short codes. In this paper, we present an improvement that increases decoding efficiency without degrading the error-correction performance. The long polar codes are divided into several sub-blocks, some of which can be decoded adopting fast maximum likelihood decoding method and the remained parts are replaced by several short codes NN decoders. The result shows that time steps the proposed algorithm need only equal to 79.8% of fast simplified successive-cancellation decoders require. Moreover, it has up to 21.2 times faster than successive-cancellation decoding algorithm. More importantly, the proposed algorithm decreases the hardness when applying in some degree.

RETRACTED: <i>Improved Polar Decoder Utilizing Neural Network in Fast Simplified Successive-Cancellation Decoding</i>

This article has been retracted to straighten the academic record. In making this decision the Editorial Board follows COPE's Retraction Guidelines. The aim is to promote the circulation of scientific research by offering an ideal research publication platform with due consideration of internationally accepted standards on publication ethics. The Editorial Board would like to extend its sincere apologies for any inconvenience this retraction may have caused. Please see the article page for more details. The full retraction notice in PDF is preceding the original paper which is marked "RETRACTED".

基于复数FastICA的双极化干扰对消算法研究

为解决卫星通信中极化复用导致的交叉极化干扰问题,提出了一种基于复数快速独立成分分析方法,根据传输信道的对称性对算法作了简化处理,减少了计算量。该算法依据发送端的两个线极化信号的不相关性,在无源信号及混合矩阵的先验信息情况下,构造负熵函数并使其最大化来分离出独立成分,进而实现交叉极化信号对消。仿真实验以正交相移键控调制信号为例,从误差向量幅度、信干噪比、交叉极化隔离度、性能指数这几个指标上进行仿真,仿真结果显示基于复数快速独立成分分析方法对解决交叉极化干扰问题具有良好的性能。

基于滤波算法的隧道全时域激发极化超前探测正演方法

为进一步提高隧道全时域激发极化多参数超前探测的效果,采用滤波算法进行计算时间域等效电阻率,采用有限单元法进行计算,提出一种基于滤波算法的隧道全时域激发极化超前探测正演方法。该方法针对时间域Cole-Cole表达式计算收敛性差的问题,引入滤波算法进行时间域激发极化等效电阻率的计算,提高算法的收敛性;针对正演过程中大型矩阵求解影响计算效率的问题,引入OpenMP并行算法,实现隧道全时域激发极化超前探测正演的加速运算。最后,开展数值算例和物理模型试验。研究结果表明:该正演方法对异常体有敏感响应,且在加快正演速度具有显著优势。通过基于滤波算法的隧道全时域激发极化超前探测获得的观测数据与实际探测数据较为相符,这为基于全时域激发极化隧道超前探测提供了一种可行的正演算法。

一种高性能极化码Fast-SSC译码器设计

为了进一步降低无线通信系统中信道编码极化码Fast-SSC译码器的译码延迟和硬件资源消耗,本文提出了两种对Fast-SSC译码算法的优化方法,基于FPGA硬件实现了码长N=1024优化的Fast-SSC译码器.基于Fast-SSC译码树上的四种特殊结点Rate0、Rate1、Rep和SPC,提出分别以Rate0结点和Rep结点为基础进行组合型特殊结点的拓展,使译码树上的特殊结点类型由原来的四种增加至十种以上,进一步加快了搜索译码树的速度;提出存储器资源复用的方法,相同译码树深度的结点使用相同的存储空间.综合结果表明最大工作频率为169 MHz,译码延迟为1.71μs,数据吞吐率为599 Mbps,存储器消耗为14.8 Kbit,有效提升了Fast-SSC译码器的整体性能.

FAST地锚基础工程中的若干问题探讨

FAST工程主动反射面为一半径300 m、口径500 m的球冠面,是一种基于柔性基底的预应力整体索网结构,索网包括2225个主索节点及下拉索驱动装置和地锚。由于台址岩土单元复杂,地锚点多、分布范围广、定位精度要求高、与场地其他基础设施的相互干涉大,给地锚基础的设计带来了一定的难题。本文针对FAST地锚基础中的特殊问题一一展开研究:以工程地质调查和测绘为基础,通过抓台址区主控因素,集合影响台址岩土性质的自然因素,对岩土单元进行了合理的分区;通过建立台址开挖后的BIM模型,利用极射投影技术实现了地锚中心点的精确定位;利用极射投影结果,对设备之间的相互干涉情况进行了调节和处理。研究成果最终确保了FAST地锚基础工程的顺利竣工。

基于FPGA的高速Fast-SSC译码器测试系统

为了满足Polar码高性能测试时大数据量的要求,设计了一种针对Fast-SSC译码器的FPGA硬件测试平台,包含信源、信道编码器、调制器、信道、解调器、译码器和统计模块,采用Verilog在Altera Stratix V 5SGXEA7N2F45C2上实现,并采用PCIe接口与上位机进行通信。该平台对码长1 024、码率1/2的Polar码进行测试,结果表明测试频率为300 MHz、测试数据为1.4×1010位时,译码耗时仅为19.18 s。

基于简化序列重复节点的极化码快速串行抵消译码算法

为了进一步降低串行抵消(SC)译码算法的译码时延,在序列重复(SR)节点的基础上,根据SR源节点的类型与译码复杂度,对不同类型的拓展类广义奇偶校验(EG-PC)节点进行分解、合并和简化,并使用快速简化串行抵消(Fast-SSC)译码对Rate-C节点进行裁剪处理,提出了基于简化SR节点的极化码快速SC译码算法(SSRFSC)。实验数据表明,在相近的译码性能下(在误帧率为10^(-3)时,约有0.1 dB的性能损失),与基于SR节点的快速SC(SRFSC)译码算法相比,所提算法的译码时延最多减少了28%;与Fast-SSC译码算法相比,译码时延最多减少了49%。

四川威远地区近震剪切波分裂特征

基于布设在四川威远地区的流动地震台站2019年11月至2020年5月记录的近震波形数据,利用剪切波分裂分析方法获得了研究区内23个地震台站的剪切波分裂参数。结果显示:威远地区地震台站快波偏振方向多数为北西向,与区域主压应力方向一致;有个别台站可能由于受到局部构造环境的影响,快波偏振方向为北东向。而在地壳速度变化明显的威远背斜附近,有6个台站结果显示为两个快波偏振优势方向,表明该地区快波偏振方向是区域应力场和局部构造环境共同作用的结果,威远地区慢波延迟时间均值为4.43 ms/km,威远背斜南侧区域的慢波延迟时间值普遍大于其北部区域,表明在威远地区南部区域的各向异性强度强于北部区域。

换流变阀侧套管极性反转暂态电场模型降阶

随着以新能源为主体的新型数字化电力系统建设,实现主设备的数字孪生体系是未来数字电网的重要发展趋势,使用模型降阶方法提高计算效率并实现快速实时仿真,是数字孪生应用于电力设备多物理场仿真领域的重要基础。为此提出了一种基于本征正交分解(proper orthogonal decomposition,POD)法求解换流变阀侧套管极性反转暂态电场的有限元快速计算方法,应用伽辽金有限元数值计算方法编程建立了换流变阀侧套管暂态电场刚度矩阵,提出了换流变阀侧套管芯体铝箔极板悬浮电位边界设置的强加虚拟齐次边界条件与稀疏矩阵联合的算法,通过矩阵奇异值分解对处理后的矩阵进行了主成分提取,构建了换流变阀侧套管电场降阶模型。研究结果表明,采用模型降阶方法得到的套管电场分布与商用软件计算的结果相近,同时,采用轻量化模型计算套管电场分布所需时间被大幅缩减,验证了模型降阶方法具有较高的准确性和计算效率,证明了采用模型降阶方法实现套管这种电力设备电场的快速计算和实时仿真的可行性。

混合阵列误差校正与快速极化MUSIC算法

为解决通道不一致性对传统极化敏感阵列长矢量模型的测向精度影响及传统长矢量多重信号分类(multiple signal classification,MUSIC)算法实时性不高的问题,本文在传统极化敏感测向系统基础上,在阵列中心增加一个标量平面螺旋天线,利用其天线方向图的增益稳定性,作为内部源对其他矢量通道不一致性进行实时校正;然后将结合标量圆阵和快速傅里叶变换(fastFouriertransform,FFT)的快速MUSIC算法推广到矢量阵列,提出降维快速极化MUSIC算法.仿真结果验证了此误差校正方法的有效性,且快速算法在保证测角精度前提下有效提高了算法实时性.本文为极化敏感阵列测向提供了一种误差校正方法及一种快速实用的测向算法.

Shear wave splitting analysis of local earthquakes from dense arrays in Shimian,Sichuan

The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.

S1P1在间断禁食抑制慢性脑低灌注大鼠海马星形胶质细胞极化中的作用

目的探讨间断禁食对慢性脑低灌注(CCH)大鼠海马星形胶质细胞极化的影响以及S1P1在其中的作用。方法将30只雄性SD大鼠随机分为3组:对照组、CCH组和CCH+间断禁食组。对照组给予假手术,CCH组大鼠给予双侧颈总动脉结扎手术处理,CCH+间断禁食组大鼠在手术后1周开始给予隔日间断禁食处理。术后8周取脑切片,进行C3d/GFAP双重荧光染色,并取新鲜海马组织进行WB检测S1P1、NeuN、PSD95蛋白水平。体外对小胶质细胞系BV2细胞给予慢性浓度梯度氯化钴(48 h)诱导处理,取其条件培养基(MCM)加入原代星形胶质细胞中,qPCR检测各组星形胶质细胞极化标志物表达。将星形胶质细胞条件培养基(ACM)加入神经元细胞系HT22中,CCK8及LDH活性测试检测其毒性,摸索体外慢性缺氧最佳药物浓度。对慢性缺氧诱导的星形胶质细胞给予S1P1抑制剂Ponesimod浓度梯度预处理,观察其是否能抑制星形胶质细胞极化及神经毒性。结果间断禁食可降低慢性脑低灌注大鼠海马C3d/GFAP双重标记细胞数量和S1P1蛋白表达,并恢复慢性脑低灌注引起的NeuN和PSD95蛋白下调(P<0.05)。慢性氯化钴刺激BV2细胞最佳浓度为100μmol/L,刺激后其MCM诱导星形胶质细胞毒性极化标志物C3、Serping1、H2D1转录水平明显增加(P<0.05),且刺激后星形胶质细胞ACM能降低神经元细胞系HT22细胞活性,增加LDH释放(P<0.05)。体外实验发现,10μmol/L浓度Ponesimod能够模拟间断禁食,下调慢性缺氧诱导的星形胶质细胞C3和Serping1转录,并改善慢性缺氧诱导的星形胶质细胞ACM对HT22细胞活性的抑制作用(P<0.05)。结论S1P1可能介导间断禁食对慢性脑低灌注大鼠海马星形胶质细胞毒性极化的抑制作用。

Large capacitance and fast polarization response of thin electrolyte dielectrics by spin coating for two- dimensional MoS2 devices

A spin-coating method was applied to obtain thinner and smoother poly（ethylene oxide） （PEO）/LiC104 polymer electrolyte films （EFs） with a lower level of crystallization than those obtained using a drop-casting method. When the applied frequency was as high as 10 kHz, the specific capacitance of such EFs with thicknesses of 1.5 μm was on the order of I μF·cm^-2 a value larger than most of the previously reported results achieved from the same material. We then combined the thin EFs with two-dimensional （2D） materials to fabricate a MoS2 transistor with a top gate right above the channel, defined by a shadowmask method, and an inverter device. This transistor showed excellent static characteristics and the inverter device showed excellent switching performance at 100 Hz, which indicates a fast polarization response of the thin EFs. Such device architecture is suitable for future low power and flexible electronics based on 2D materials.