Upper mantle seismic anisotropy beneath a convergent boundary:SKS waveform modeling in central Tibet

This study used SKS waveforms from the International Deep Profiling of Tibet and the Himalayas(INDEPTH) III dataset and a new 2D method for modeling seismic waves in anisotropic media to construct an image of anisotropic structures beneath central Tibet.A preferred model revealed three-segment anisotropic structures in the upper mantle beneath the study region.Waveform modeling demonstrated that the anisotropy was mainly generated by the lithosphere but not the asthenosphere,and that an anisotropic model with a flatter axis of symmetry provides a more consistent interpretation of the observations than models having steeply dipping symmetry axes.A relatively low velocity zone may underlie or intermingle with the anisotropic structures in the northern portion of the region.Synthetic tests also indicate that variations in the elastic constants and depth extent of the anisotropy assumed by the calculations do not affect the general conclusions,although trade-offs exist among certain model parameters.The modeling results suggest that the complex seismic structures in central Tibet were associated with underthrusting of the Indian lithosphere beneath the Asian lithosphere;the inferred flat symmetry axis of the anisotropy was likely generated during this collision process.If this were not the case,the inherited anisotropy would exhibit a steeply dipping axis of symmetry,parallel to the direction of underthrusting.

Construction of Energy-Optimal Smooth Monophasic Defibrillation Pulse Waveforms Using Cardiomyocyte Membrane Model

The goal is to help create smooth energy-optimal monophasic pulse waveforms for defibrillation using the Luo-Rudy cardiomyocyte membrane computer model. The waveforms were described with the help of the piecewise linear function. Each line segment provides a transition from one present level of the transmembrane potential to the next with a minimal energy value. The duration of the last segment was defined as a minimum duration at which an action potential occurs. Monophasic waveforms of segments 3, 10 and 29 were built using different increments of the transmembrane potential. The pulse energy efficiency was evaluated according to their threshold energy ratios in mA2·ms/cm4. There was virtually no difference between the threshold energy ratios of the three waveforms constructed and those of the previously studied energy-optimal half- sine waveform: 241 - 242 and 243 mA2·ms/cm4. The pulse waveform constructed is characterized by a low rise and fall as the duration of the rise is ~1.5 times longer than that of the fall. Conclusion: Energy-optimal smooth monophasic pulse waveforms have the same threshold energy ratio as the optimal half-sine one which was studied before. The latter is equivalent to the first phase of biphasic quasisinusoidal Gurvich-Venin pulse which has been used in Russia since 1972. Thus, the use of the Luo-Rudy cardiomyocyte membrane model appears to offer no possibilities for a substantial increase in the energy efficiency (threshold energy ratio reduction) of the classical monophasic defibrillation pulse waveforms.

Theoretical modeling of airways pressure waveform for dual-controlled ventilation with physiological pattern and linear respiratory mechanics

The present paper describes the theoretical treatment performed for the geometrical optimization of advanced and improved-shape waveforms as airways pressure excitation for controlled breathings in dual-controlled ventilation applied to anaesthetized or severe brain injured patients, the respiratory mechanics of which can be assumed linear. Advanced means insensitive to patient breathing activity as well as to ventilator settings while improved-shape intends in comparison to conventional square waveform for a progressive approaching towards physiological transpulmonary pressure and respiratory airflow waveforms. Such functional features along with the best ventilation control for the specific therapeutic requirements of each patient can be achieved through the implementation of both diagnostic and compensation procedures effectively carried out by the Advance Lung Ventilation System (ALVS) already successfully tested for square waveform as airways pressure excitation. Triangular and trapezoidal waveforms have been considered as airways pressure excitation. The results shows that the latter fits completely the requirements for a physiological pattern of endoalveolar pressure and respiratory airflow waveforms, while the former exhibits a lower physiological behaviour but it is anyhow periodically recommended for performing adequately the powerful diagnostic procedure.

Upper-mantle velocity structures beneath the Tibetan Plateau and surrounding areas inferred from triplicated P waveforms

P-wave waveforms in the distance range between 12°and 30°were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas.The waveform data from 504 earthquakes with magnitudes larger than 5.0 between 1990 and 2005 that occurred within 30°from the center of the Plateau were modelled.We divided the study area into 6 regions and modeled upper-mantle-distance P waveforms with turning points beneath each region separately.The results show that the uppermantle P-wave velocity structures beneath India,the Himalayas,and the Lhasa Terrane are similar and contain a high-velocity lid about 250 km thick.The upper-mantle velocities down to 200 km beneath the Qiangtang Terrane,the Tarim Basin,and especially the Songpan-GarzêTerrane are lower than those in the south.The 410-km discontinuity beneath these two terranes is elevated by about 20 km.Highvelocity anomalies are found in the transition zone below 500 km under the Lhasa and Qiangtang Terranes.The results suggest that the Tibetan Plateau was generated by thrusting of the Indian mantle lithosphere under the southern part of Tibet.Portions of the thickened Eurasian mantle lithosphere were delaminated;they are now sitting in the transition zone beneath southern Tibet and atop of the 410-km discontinuity underneath northern Tibet.

APPLICATION OF FRF ESTIMATOR BASED ON ERRORS-IN-VARIABLES MODEL IN MULTI-INPUT MULTI-OUTPUT VIBRATION CONTROL SYSTEM

The FRF estimator based on the errors-in-variables （EV） model of multi-input multi-output （MIMO） system is presented to reduce the bias error of FRF HI estimator. The FRF HI estimator is influenced by the noises in the inputs of the system and generates an under-estimation of the true FRF. The FRF estimator based on the EV model takes into account the errors in both the inputs and outputs of the system and would lead to more accurate FRF estimation. The FRF estimator based on the EV model is applied to the waveform replication on the 6-DOF （degree-of-freedom） hydraulic vibration table. The result shows that it is favorable to improve the control precision of the MIMO vibration control system.

考虑PWM波形特征的纳米晶磁心损耗模型的研究及验证

磁心损耗精确预测对于电力电子变压器的优化设计至关重要。然而,传统的磁心损耗模型在复杂激励下适用性较差,尤其对于占空比可调、高次谐波含量丰富的PWM波磁心损耗预测,计算精度显著下降。基于Jordan损耗分离模型,建立了一种考虑PWM波形特征的磁心损耗计算方法。首先,该方法根据激励波形特征,推导出相应的波形系数及等效频率来计算PWM波激励下的动态涡流损耗,将Jordan模型的适用范围从正弦拓展到PWM波激励下的磁心损耗计算;然后,分析了不同占空比激励下激励波形有效频率及高次谐波含量变化对损耗系数的影响,并对其进行数学表征,实现了整个占空比范围内磁心损耗的精确预测;最后,搭建了高频非正弦激励下软磁材料磁特性测量平台,针对1K107B纳米晶材料,测量了两种典型PWM波激励下的损耗数据。实验结果表明,所建立的磁心损耗模型具有较高的计算精度,相比于传统的Steinmetz改进公式,整体精度提高了25%。

Full-waveform Velocity Inversion Based on the Acoustic Wave Equation

Full-waveform velocity inversion based on the acoustic wave equation in the time domain is investigated in this paper. The inversion is the iterative minimization of the misfit between observed data and synthetic data obtained by a numerical solution of the wave equation. Two inversion algorithms in combination with the CG method and the BFGS method are described respectively. Numerical computations for two models including the benchmark Marmousi model with complex structure are implemented. The inversion results show that the BFGS-based algorithm behaves better in inversion than the CG-based algorithm does. Moreover, the good inversion result for Marmousi model with the BFGS-based algorithm suggests the quasi-Newton methods can provide an important tool for large-scale velocity inversion. More computations demonstrate the correctness and effectives of our inversion algorithms and code.

CRUST AND UPPER STRUCTURE OF QINGHAI-TIBET PLATEAU AND ITS ADJACENT REGIONS FROM SURFACE WAVEFORM INVERSION

In this paper,218 long period Rayleigh wave records from 7 seismic station of CDSN are selected.We applied a partitioned waveform inversion to these data in order to construct a 3\|D model of shear velocity down to 400km depth in the crust and upper mantle of Qinghai\|Tibet plateau and Its Adjacent Regions (22°～44°N,70°～110°E).The first step of the waveform inversion used involved the matching of the waveforms of fundamental and highermost Ravleigh waves with waveforms synthesized from stratified models;in the second stage,the 3\|D model was constructed by solve linear constrains equation. The major structural features inferred from the surface waveform inversions can be summarized as follows:(1) There is a great contrast between surface waveform through Qinghai—Thibet plateau and the others.Main frequency of the former is lower than the latter, which indicate the crust depth of Qinghai—Tibet plateau is deeper than the others. In addition,the amplitude of about 30s period and 50s period is lower than both sides,which implied these exist lower velocity layer at about 25km depth and about 50km depth in Qinghai—Tibet plateau Crust.The former is common,the latter was argued because resolution of most method can not prove it.

面向外辐射源雷达目标探测的非时变稀疏模型和深度展开网络实现方法

近年来,基于稀疏特征提取的目标探测方法成为了雷达领域的研究热点。基于正交频分复用调制的外辐射源雷达(简称“外源雷达”)由于发射波形不受控,一方面构建的稀疏模型会随未知发射波形时变,导致相应的目标探测方法计算量大;另一方面目标回波常常因被直达波等强杂波掩盖而面临探测困难。在此背景下,利用外源雷达的正交频分复用波形特点,使用导频位置处频域信道响应提出一种非时变稀疏模型。通过将稀疏模型求解的每一次迭代过程替代为一层神经网络,首次研究了基于深度展开网络的智能化外源雷达目标探测实现方法。仿真和实测数据结果表明:所提方法与传统杂波抑制方法在目标探测上性能相近,但有着更低的计算复杂度,且无需人工设计稀疏矩阵等稀疏模型求解参数。

全波形发射电流激发下地面瞬变电磁法磁场特征

在过去四十年,大部分关于瞬变电磁法的三维建模和反演研究都聚焦于磁场时间导数,而对于磁场数据研究并不多见.如今,随着超导量子干涉仪(SQUID)技术日益成熟,基于磁场数据的瞬变电磁法探测案例逐渐增多.基于矢量有限单元法,采用频谱法和时步法分别实现了适用于瞬变电磁法磁场数据的三维正演.以低阻覆盖层下的良导体和均匀半空间中板状良导体模型为例,研究了全波形发射电流激发的瞬变电磁法磁场及其时间导数特征,并探讨了二者对深部良导体的探测能力.正演计算结果表明:由于受发射电流全波形效应影响,晚延时磁场随目标体电导率增大而先增强、后减弱,然而即使不考虑全波形效应,磁场时间导数也呈现上述规律;在高阻和低阻围岩情形中,磁场比其时间导数对深部良导体反映更加灵敏,并且晚延时磁场比其时间导数更不易受地磁场背景噪声干扰,说明磁场比其时间导数更适合于深部良导体探测.需要注意的是,发射电流全波形效应降低了瞬变电磁法对深部良导体的识别能力,建议在瞬变电磁法对块状或脉状金属硫化物矿床探测时,尽量采用低基频发射电流波形.

多功能相控阵雷达行为辨识综述

多功能相控阵雷达是指具备相位控制阵列,能同时实现搜索、跟踪、制导等多种功能的雷达。随着雷达对抗的不断升级以及各国对于电子战的日益重视,作为获取多功能相控阵雷达信息的重要手段,其行为辨识技术的研究得到了进一步发展。结合目前多功能相控阵雷达行为辨识的背景与意义,对已有的不同多功能相控阵雷达信号模型进行梳理,对高密度、大噪声信号环境下的波形单元提取算法和基于深度学习的工作模式识别算法进行识别性能、适用场景等方面的系统性对比,并归纳了不同仿真数据集的实际应用情况,最后总结了该技术存在的问题并提出了未来展望。

基于局部存储策略的声波全波形反演方法

全波形反演作为一种高精度地下速度模型建模方法,自提出以来就受到了地震勘探领域的广泛关注.然而在时间域全波形反演中梯度计算需要存储或恢复震源波场,这会导致存储大量数据或额外的震源波场重构计算,使得全波形反演的实用化受到波场重构的制约.为此,本文提出了一种基于局部存储策略的声波全波形反演方法.依据奈奎斯特采样定理设置存储间隔,通过存储每个空间网格点有限时间区间内的有效波场来计算梯度,达到减少存储震源波场数据量、避免波场重构进而提升效率的目的.与其他方法相比,本方法无需波场重构且所需内存大小与正演模拟的差分精度和记录时长均无关.二维和三维推覆体模型合成数据的反演测试均表明:本方法能够在不重构波场的情况下保证反演结果的精度和信噪比,有效提高计算效率并显著降低对计算机内存的需求.

基于多通道卷积神经网络的甚低频/低频雷电辐射电场波形分类方法

雷电过程中产生多类雷电辐射电场波形,基于特征值的传统分类方法易误分类。为准确分类雷电辐射电场波形,该文提出了一种基于多通道卷积神经网络的甚低频/低频雷电辐射电场信号分类方法,该方法采用深度网络直接处理电场波形以减少先验知识依赖,设计多通道并行卷积核以有效提取雷电波形多尺度特征,引入shortcut连接以加速模型收敛。基于合肥地区实测雷电数据,该文建立了回击、初始预击穿、窄双极性脉冲以及云闪4分类波形数据集,模型训练结果表明该模型识别准确率达到99.4%,与经典机器学习方法以及主流深度神经网络模型分类性能相比,所提模型在分类准确率及训练收敛速度上均达更优水平。基于该模型,该文采用知识蒸馏方法获得了适用于低算力计算平台的部署模型,部署模型在合肥某雷暴活动中单次分类耗时仅59ms,算力需求降低66%,分类准确率为99.0%,实现了模型在低算力计算平台上的可靠应用。

快速变化的电能信号波形模态对直流电能表误差影响分析

针对直流非线性负载导致电压和电流波形的骤升或骤降、电流振荡或阶梯变化等的快速变化波形模态,文中采用机理建模的方法,首先建立直流电能表信号预处理单元、信号转换单元、功率测量单元和电能测量单元的数学模型;建立8种典型电流和电压单一波形模态的数学模型,及其3种典型电流和电压组合波形模态的数学模型;仿真分析11种动态电能信号波形模态对直流电能表动态误差的影响;给出了对电能表动态误差的影响最大的波形模态:单一波形模态中,尖顶骤升波形模态输入时电能表动态误差最大,达到-5.16×10^(-2),组合波形模态中,编号9组合波形模态动态误差最大,达到-1.05×10^(-3),以及对动态误差影响最大的功率滤波器类型;文中结论可为制定直流电能表动态误差的测试评价试验条件与改进电能表提供理论依据。

直流充电桩快速变化的电流和电压波形模态特性分析

针对电动汽车充电桩输出电流和电压呈现出“随机性、波动性、时变性”的快速变化特性,引发电能计量较大超差问题,文章建立充电桩快速变化直流电流和电压的随机信号数学模型及其时频域表征模型;提出快速变化波形模态提取方法,提取了6类12种快速变化直流波形模态,提出并构建了幅度域8个特征参量数学模型,表征影响电能计量的电流和电压特征;提取了典型特征参量数值和重要特性,该特征参量数值和特性可为制定直流电能表动态误差的测试评价试验条件提供理论依据。

基于Attention-UNet网络的速度模型构建方法研究

随着油气资源的不断勘探开发,相对易开采的油气矿逐渐建成,地震勘探的研究重点也向地下更深、构造更复杂的区域转移。目前,传统的地震速度建模方法在稳定性、准确性和计算效率方面都面临挑战。因此,笔者利用将地震数据映射到速度模型的思路,提出了一种基于Attention-UNet网络的深度学习速度建模方法。采用的这种方法利用有限差分正演得到反射波形数据,将反射波形数据和对应的速度模型(标签)对作为Attention-UNet网络的输入,建立地震数据和速度模型之间的映射关系。网络训练后对新输入的地震数据进行速度模型的估计。数值实验结果表明,与传统的FWI相比,笔者提出的方法表现出良好的性能;基于Attention-UNet网络模型训练完成后,不需要经过大量的计算,就可以快速执行与训练集中速度结构相似的地下结构的速度建模,这比传统方法计算效率更高。该方法在建立大量速度模型时具有很好的推广价值。

基于低中频采样的超宽带雷达波形产生器误差校正方法

针对超宽带(UWB)雷达波形合成中正交调制器、混频器、倍频器等模拟环节的误差因素特点,提出一种基于“低中频直接数字产生+倍频”途径的高质量UWB雷达LFM波形数字产生器方案。在频域建立该系统误差的数学模型,提出一种基于频谱对比途径的系统误差数字预失真校正方法,并进行实验验证和性能分析。该方法将系统失真的校正函数映射到系统数字输入端的波形库中,通过直接对存储的数字波形进行预失真融合处理实现系统误差的校正和补偿。结果表明该方法能够显著地提高产生UWB雷达LFM波形的质量和性能,证实提出的误差校正方法正确、有效和可行。

冲击试验机波形预测方法研究

在使用冲击试验机对产品进行考核时,其往往达不到规定脉冲波形的峰值加速度和脉宽,需要靠试验人员的经验以及多次重复试验进行调整。因此,为了在冲击试验前准确地预测冲击波形,节省调试时间和资源,提出了一种采用非线性回归模型对波形峰值加速度和脉宽进行预测的方法。首先,采用Mooney-Rivlin模型拟合了波形发生器超弹性本构参数,建立了冲击系统有限元模型,并进行了冲击试验,对有限元模型的准确性进行了验证;然后,采用有限元和正交实验法研究了波形发生器硬度、厚度、直径和冲击台跌落高度等参数对冲击波形的影响;最后,选用幂函数作为多元非线性回归的函数形式,并剔除了显著性较低因素项,建立了冲击波形峰值加速度和脉宽的预测模型,并通过冲击试验对预测模型的准确性进行了验证。研究结果表明:波形发生器的厚度和直径及其交互作用是影响冲击波形的主要因素;通过对比回归模型预测值与冲击试验数据,发现两者误差不超过10%,表明该冲击波形回归预测模型具有有效性。

超深水区基准面延拓驱动的反射波形反演成像

远离大陆架的海洋油气勘探与开发具有高风险、高投入的特征,对构造成像和储层预测精度要求很高,传统的基于射线理论的速度建模方法难以满足精细成像的需求。超深水探区地震观测受巨厚水层的影响,导致记录时间较长、数据规模和模型空间巨大,因此难以大规模应用基于波动理论的速度建模方法。为此,提出基准面延拓驱动的反射波形反演成像技术。该技术利用基准面延拓剥离水层影响,消除地震波在水中的传播效应,降低数据规模、压缩模型空间、缓解速度—深度多解性,使全波形反演在深海区的实际应用成为可能。考虑到超深水探区有限炮检距难以记录到穿透较深的初至波,无法利用初至波进行波形反演更新速度,因此选用反射波形反演对延拓后数据进行速度建模,以便得到高精度速度模型和成像结果。理论模型合成数据和南海A区块实际数据处理结果表明,该技术能够大规模缩减数据量,并提高高精度速度建模的效率,可在超深水油气勘探中发挥积极作用。

川中充西地区雷三^(2)亚段泥灰岩储层精细预测研究

川中充西地区多口钻井在雷三2亚段泥灰岩储层中油气显示好,测井解释储层发育,展示了良好的勘探潜力。为准确预测雷三2亚段泥灰岩储层纵横向分布,为下一步勘探部署提供指导,首先利用储层合成记录标定明确储层地球物理响应特征;接着围绕岩性和储层分别开展岩石物理分析,优选盐岩和泥灰岩储层的敏感参数,利用地震波形指示模拟预测盐岩的分布;最后利用波形指示反演预测泥灰岩储层的分布。结果表明:雷三2亚段顶部盐岩对应强波峰反射,储层底界对应弱波峰反射,储层与盐岩存在明显的波阻抗重叠,而盐岩与其他岩性在密度上存在明显差异,当去除盐岩的影响后,利用波阻抗可以较好地区分储层和非储层。因此,在利用波形指示模拟识别盐岩分布后,地震波形指示反演可有效识别储层。充西三维区储层大面积发育,厚30~60 m,发育岩性圈闭16个,总面积124 km 2,是下一步富有机质泥灰岩储层的现实勘探方向。