The efifect of wave breaking on surface wave imaging by Synthetic Aperture Radar

The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions （MTF） of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic （e.m.） wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle for HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%-60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization.

An Improved Coupling of Numerical and Physical Models for Simulating Wave Propagation

An improved coupling of numerical and physical models for simulating 2D wave propagation is developed in this paper. In the proposed model, an unstructured finite element model （FEM） based Boussinesq equations is applied for the numerical wave simulation, and a 2D piston-type wavemaker is used for the physical wave generation. An innovative scheme combining fourth-order Lagrange interpolation and Runge-Kutta scheme is described for solving the coupling equation. A Transfer function modulation method is presented to minimize the errors induced from the hydrodynamic invalidity of the coupling model and/or the mechanical capability of the wavemaker in area where nonlinearities or dispersion predominate. The overall performance and applicability of the coupling model has been experimentally validated by accounting for both regular and irregular waves and varying bathymetry. Experimental results show that the proposed numerical scheme and transfer function modulation method are efficient for the data transfer from the numerical model to the physical model up to a deterministic level.

A Wave Modulation Model of Ripples over Long Surface Waves

A study is presented on the modulation of ripples induced by a long surface wave (LW) and a new theoretical modula-tion model is proposed. In this model, the wind surface stress modulation is related to the modulation of ripple spectrum. The model results show that in the case of LW propagating in the wind direction with the wave age parameter of LW increasing, the area with enhanced shear stress shifts from the region near the LW crest on the upwind slope to the LW trough. With a smaller wave age parameter of LW, the ripple modulation has the maximum on the upwind slope in the vicinity of LW crest, while with a larger parameter the enhancement of ripple spectrum does not occur in that region. At low winds the amplitude of ripple modulation transfer function (MTF) is larger in the gravity wave range, while at moderate or high winds it changes little in the range from short gravity waves to capillary waves.

Heat, Resolvent and Wave Kernels with Multiple Inverse Square Potential on the Euclidian Space Rⁿ

In this paper, the heat, resolvent and wave kernels associated to the Schr?dinger operator with multi-inverse square potential on the Euclidian space Rn are given in explicit forms.

A TECHNIQUE FOR MEASURING THE LINEARITY OF A LINEARLY FREQUENCY-MODULATED SIGNAL

A technique for measuring the linearity of a linearly frequency-modulated continuous wave (LFM-CW) signal is presented. It uses a delay-line and a mixer to sense the slope of the output of a sweep oscillator, so that the original form of frequency function deviated from idealized linear slope is retrieved by means of spectrum analysis. Consequently,the linearity of the LFM signal is determined. The formulation is performed based on the principle that an angle-modulated signal can be approximated by an amplitude-modulated signal if the modulation coefficient is sufficiently small. To examine the validity of the procedure and to study the effect of each parameter on the accuracy of measurement, a number of computer simulations has been made. The results of simulation show that the error of the measurement is less than 2%.

The improved element-free Galerkin method forthree-dimensional wave equation

The paper presents the improved element-free Galerkin （IEFG） method for three-dimensional wave propa- gation. The improved moving least-squares （IMLS） approx- imation is employed to construct the shape function, which uses an orthogonal function system with a weight function as the basis function. Compared with the conventional moving least-squares （MLS） approximation, the algebraic equation system in the IMLS approximation is not ill-conditioned, and can be solved directly without deriving the inverse matrix. Because there are fewer coefficients in the IMLS than in the MLS approximation, fewer nodes are selected in the IEFG method than in the element-free Galerkin method. Thus, the IEFG method has a higher computing speed. In the IEFG method, the Galerkin weak form is employed to obtain a dis- cretized system equation, and the penalty method is applied to impose the essential boundary condition. The traditional difference method for two-point boundary value problems is selected for the time discretization. As the wave equations and the boundary-initial conditions depend on time, the scal- ing parameter, number of nodes and the time step length are considered for the convergence study.

A Novel Square-wave Pulse Rotation Modulation Strategy for Modular Multilevel Converters

悬浮直流电容电压的均衡问题是模块组合多电平变换器（modular multilevel converter,MMC）的关键问题之一。提出一种可实现MMC直流电容电压平衡的方波脉冲循环调制（square-wave pulse rotation modulation,SWPRM）策略,在保证合成的阶梯波输出波形不变的前提下,根据MMC的拓扑结构和工作原理,对传统方波脉冲列进行脉冲优化,并按照一定的次序和切换周期进行循环和判断反相调整,获得的循环方波脉冲列作为最终驱动脉冲用于实现对MMC的控制。实验结果表明,采用提出的方波脉冲循环调制策略无需任何电容电压控制措施,在较低开关频率下,实现了MMC各功率单元间有功能量的平均分配和直流电容电压的均衡。

A Study of Some Properties of Bottomonium

We apply matrix Numerov’s method to obtain the radial wave functions;from these wave functions we calculate the root mean square radius rms and β coefficients of bottomonium . The obtained results have implications for decay constants, decay widths and differential cross sections of heavy mesons.

Hilbert spectrum and intrinsic oscillation mode of dynamic response of a bilinear SDOF system: influence of harmonic excitation amplitude

Under harmonic wave excitation, the dynamic response of a bilinear SDOF system can be expressed by the Hilbert spectrum. The Hilbert spectrum can be formulated by (1) the inter-wave combination mechanism between the steady response and the transient response when the system behaves linearly, or (2) the intra-wave modulation mechanism embedded in one intrinsic mode function (IMF) component when the system behaves nonlinearly. The temporal variation of the instantaneous frequency of the IMF component is consistent with the system nonlinear behavior of yielding and unloading. As a thorough study of this fundamental structural dynamics problem, this article investigates the influence of the amplitude of the harmonic wave excitation on the Hilbert spectrum and the intrinsic oscillatory mode of the dynamic response of a bilinear SDOF system.

A new modulation transfer function for ocean wave spectra retrieval from X-band marine radar imagery

When imaging ocean surface waves by X-band marine radar, the radar backscatter from the sea surface is modulated by the long surface gravity waves. The modulation transfer function （MTF） comprises tilt, hydrodynamic, and shadowing modulations. A conventional linear MTF was derived using HH-polarized radar observations under conditions of deep water. In this study, we propose a new quadratic polynomial MTF based on W-polarized radar measurements taken from heterogeneous nearshore wave fields. This new MTF is obtained using a radar-observed image spectrum and in situ buoy-measured wave frequency spectrum. We validate the MTF by comparing peak and mean wave periods retrieved from X-band marine radar image sequences with those measured by the buoy. It is shown that the retrieval accuracies of peak and mean wave periods of the new MTF are better than the conventional MTF. The results also show that the bias and root mean square errors of the peak and mean wave periods of the new MTF are 0.05 and 0.88 s, and 0.32 and 0.53 s, respectively, while those of the conventional MTF are 0.61 and 0.98 s, and 1.39 and 1.48 s, respectively. Moreover, it is also shown that the retrieval results are insensitive to the coefficients in the proposed MTF.

EFFICIENT DESIGN METHOD OF COSINE-MODULATED QMF BANKS SATISFYING PR PROPERTY

In this paper the design problem of perfect-reconstruction cosine-modulated QMF banks has been formulated as a quadratic-constrained least-squares (QCLS) minimization problem in which all constrained matrices of the QCLS optimization problem are symmetric and positive definite. A cost function which is a convex function of desired prototype filter coefficients is constructed so that this kind of QCLS optimization problems can be efficiently solved. So a global minimizer of this problem can be easily obtained. Results of two design examples are presented to support the derivations and analyses.

Single Mode Periodic Wave Trains in Self-Gravitating Dusty Plasma

In this paper, we consider the dynamics of modulated waves in an unmagnetized, non-isothermal self-gravitating dusty plasma model. The varying charge on the moving dust, as it moves in and out of regions of differing electron and ion densities (due to changes in the electrostatic potential), will be out of phase with the equilibrium charge. The effect of the dust is to increase the phase velocity of the ion-acoustic (IA) waves i.e. decrease the Landau damping. In the low-amplitude limit and weak damping, we apply the reductive perturbation method on the model that resulted to the complex cubic Ginzburg-Landau (CCGL) equation. From these results, it is observed that, the plasma parameters strongly influence the properties of the solitary wave solution namely, the amplitude and the width. The effects of non-isothermal electrons, gravity, dust charge fluctuations and drifting motion on the ion-acoustic solitary waves are discussed with application in astrophysical contexts. It is also observed that the number of charges residing on the dust grains increases the modulational stability of the plane waves in the plasma, thus, enhancing the generation of modulated waves.

基于励磁电压方波调制的三级式同步起动/发电机转子初始位置估算方法

现有基于高频注入的三级式同步起动/发电机转子初始位置估算方法由于高频衰减,面临失效风险。该文基于主电机定转子互感,提出一种“基于励磁电压方波调制的三级式同步起动/发电机转子初始位置估算方法”,将励磁电压作为载波,用低频方波对其进行调制后,提取主电机定子侧低频响应电流用于转子初始位置估算。定子逆变器三相下管导通状态下,该方法分为2步:首先对励磁电压进行低频方波调制,采集主电机定子低频感应电流用于转子初始位置预估算;其次,由预估算初始位置,判断励磁电压断电前后相关电流特征,得到包含磁极信息的最终初始位置。所提方法通过虚拟角度变换和方差对采集低频电流进行处理。实验表明所提方法具有较高估算精度。

基于调制比自然过渡的多模式同步调制策略

轨道交通牵引变流器通常运行在低开关频率下,随着电机转速逐渐上升,传统空间矢量脉宽调制(Space Vector Pulse Width Modulation,SVPWM)由于开关频率恒定,其载波比会随着逆变器输出基波频率的增大而下降,造成输出电压脉冲数减少,导致其含有大量低次谐波,畸变严重,最终影响整个系统的控制性能。此时系统需要切换至脉冲数对称且固定的同步调制,保证逆变器输出波形的同步性与对称性,以实现谐波优化。现有同步调制策略需要涉及众多脉冲数之间的切换,且最终需要进入3脉冲调制才可自然进入方波工况,实现过程考虑因素较多、难度较大。基于开关角的方法,提出一种随着调制比增大,可由15脉冲同步调制平滑过渡至各脉冲数且最终能自动过渡至方波工况的同步调制策略。首先,根据SVPWM原理,将各矢量作用时间转换为0~2π范围下的角度,并计算传统空间矢量策略(Conventional Space Vector Strategy,CSVS)的15脉冲调制下对应的所有开关角。其次,对调制比进行分段,改变开关角随调制比变化的斜率,进而在调制比逐渐增大的同时,使得相邻开关角逐渐向所划分的扇区边界合并,窄脉冲成对消失,实现在设定调制比下平滑过渡至不同脉冲数并最终进入方波单脉冲。最后,通过仿真与硬件实验对所提方法和传统方法进行对比,验证了所提方法的自然过渡能力。

基于延迟断点映射FMCW的双功能雷达通信系统设计

基于调频连续波(Frequency Modulated Continuous Wave, FMCW)的双功能雷达通信(Dual-Functional RadarCommunication, DFRC)系统具有时频利用率高、抗多普勒性能强、距离旁瓣低的特点。现有的FMCW-DFRC波形系统产生双功能性能恶化,并增加通信接收机的链路复杂度。设计了一种基于延迟断点映射(Delayed Breakpoint Mapping, DBM)FMCW的DFRC系统,通过啁啾周期内延迟断点位置的映射和被分割的簇间的相位进行数据调制。通信接收端在载波混频和欠采样后,在数字域实现去啁啾、码片对齐和数据解调,极大降低了接收端生成相干信号和ADC性能的需求。在雷达处理链路中,设计了断点区域删除与拼接(Breakpoint Area Deletion and Splicing, BADS)方案,使DFRC的雷达性能与无调制的FMCW一致。仿真结果表明,与无补偿的方案相比,BADS方案距离图像的副瓣幅度减小约37 dB,且不受调制数据的影响。与现有基于啁啾波形的DFRC方案的通信性能相比,DBM-FMCW降低了约3 dB误符号率。

Cosine-modulated window function-based staggered-grid finite-difference forward modeling

The numerical dispersion and computational cost are high for conventional Taylor series expansion staggered-grid finite-difference forward modeling owing to the high frequency of the wavelets and the large grid intervals. In this study, the cosine-modulated binomial window function （CMBWF）-based staggered-grid finite-difference method is proposed. Two new parameters, the modulated time and modulated range are used in the new window function and by adjusting these two parameters we obtain different characteristics of the main and side lobes of the amplitude response. Numerical dispersion analysis and elastic wavefield forward modeling suggests that the CMBWF method is more precise and less computationally costly than the conventional Taylor series expansion staggered-grid finite-difference method.

强信号全覆盖环境高精密传感器微弱信号调制设计

在强信号的存在下,传感器微弱信号会被干扰、淹没或认为噪声,导致信号无法准确读取影响传感器的性能。为了解决这个问题,提出了一种强信号全覆盖环境高精密传感器微弱信号调制设计方法。该方法利用压缩感知技术重构完整的高精密传感器微弱信号集,通过自适应滤波器进行滤波以降低噪声,提高微弱信号的信噪比。利用基于正弦载波的扩频调制技术对微弱信号展开调制,将微弱信号扩展到宽频带中,以提高微弱信号的抗干扰能力和传输效率。实验结果表明,所提方法的信号重构精度高,能够有效滤除信号中的噪声,提高信号的抗噪声能力。并且信号调制性能好、抗干扰能力强。

Determination of Curcumin on Functionalized Carbon Nano Tube Modified Electrode and Probing its Interaction with DNA and Copper Ion

Voltammetry measurements have been employed to investigate the redox behaviour of curcumin in aqueous media using functionalized carbon nanotube(FCNTs)modified glassy carbon electrode(GCE).The electro-catalytic properties of FCNTs modified electrode are superior in comparison to the conventional electrode in generating the electrochemical response from curcumin.The oxidation process of the curcumin over the modified substrate is found to be p H dependent and shows 2e^(-)and 2H^(+)proton transfer electrochemical process.The oxidation peak is obtained at 0.37 V and the peak current is found to be linear with the varying concentration of curcumin.The limit of detection(LOD)and the limit of quantification(LOQ)for the curcumin are obtained as 60 and 200 nmol/L,respectively using the FCNTs modified GCE.The enhanced electrochemical response from the FCNTs modified GCE has been utilized in the evaluation of the chemical and biochemical behaviour of curcumin in presence of transition metal ions(Cu^(2+))and ds DNA,and the observation has been supported by the spectrochemical characteristics of the interactions.

共用模块的柔性多状态开关新型调制方法

柔性多状态开关作为取代传统机械开关的新型电力电子设备,具有响应速度快、潮流可控等优势。针对新型具有共用模块的级联型H桥变换器柔性多状态开关拓扑,简化其结构的同时节省部分模块,但是传统控制方法不再适用,因此文中提出新的适用于共用模块的类方波调制方法。首先根据具体工况计算出共用模块的调制波,然后协调计算得出非共用模块的调制波,实现对新型拓扑所有模块的调制。类方波调制在方波调制的基础上加入零电平时间,减小过零点时共用模块电压瞬时变化值,同时可以通过协调零电平时间与相位关系,使调制波的相位可变,避免非共用模块过调制。文中搭建共用模块柔性多状态开关拓扑的三相实验平台,验证了类方波调制策略的正确性和有效性。

高压器件封装用有机硅凝胶内气泡对其正极性方波电压下放电特性的影响

有机硅凝胶内气泡缺陷是高压IGBT器件封装的绝缘薄弱环节。该文针对有机硅凝胶内气泡缺陷对放电特性的影响,制备了指定位置含有气泡的有机硅凝胶实验样品,提出了有机硅凝胶内部气泡含量的量化方法,面向器件运行条件下所承受的正极性重复方波电压工况,建立了基于局部放电电流脉冲测量方法的有机硅凝胶局部放电特性实验平台,提出了方波电压下放电电流脉冲的准确测量与提取的方法,通过实验获得了有机硅凝胶内气泡含量对局部放电分布特性及电流脉冲波形参数的影响规律,并给出了气泡对有机硅凝胶局部放电特性的影响机理的定性解释。结果表明:正极性重复方波电压下,有机硅凝胶的局部放电起始电压与熄灭电压均随气泡含量的增加而显著下降,反向放电比例随气泡含量的增加而增加,脉冲上升时间、下降时间随气泡含量的增加而减小。该文成果可为IGBT器件有机硅凝胶灌封工艺的改进提供指导,并为有机硅凝胶气泡含量检测奠定基础。