基于载波和空间矢量调制之间联系的多电平VSI降低和消除共模电压的PWM策略

提出一种多电平逆变器降低和消除共模电压的调制方法。选择适当的开关状态,部分共模电压消除调制方法(PCMVPWM)能将共模电压降低到直流侧母线单电源电压的三分之一,完全共模电压消除调制方法(FCMVPWM)能完全消除共模电压。分析了这两种调制方法与基于载波的脉宽调制方法的关系。在NPC三电平逆变器的原型机上对算法进行了实验验证,仿真和实验结果表明该调制方法能够有效地降低共模电压。最后将算法拓展到任意电平逆变器的调制中。     

基于空间直角坐标系的逆变器调制波研究

基于空间直角坐标系,对逆变器三相调制波进行研究,提出三维空间调制波矢量的概念并讨论其特点。利用调制波矢量得到了SPWM和SVPWM的解析表达式,使调制方法、控制策略、主电路成为一个整体,便于进行统一建模,具有几何含义清晰、理解直观、计算简单等优点。利用Matlab/Simulink进行仿真和逆变器平台进行实验,结果证明研究方法正确有效。     

用于级联型大功率变流器的多变量组合控制方案

提出一种用于级联型大功率变流器的多变量组合控制方案，综合利用非对称直流母线电压控制、移相控制和脉冲宽度调制(PWM)。与传统的非对称电平、阶梯波合成以及混合型调制控制方案相比，该控制方案能更好地消除输出电压的低次谐波，且全部功率器件均低频工作。本文分析了该控制方案下的输出电压谐波特性和各逆变模块功率分配。该控制方案简洁可靠，开关频率低，可用于现有典型的级联型结构变流器。基于混合非对称级联型拓扑并结合SPWM、SHEPWM调制策略的实验样机验证控制方案的可行性和低次谐波消除效果，仿真和实验结果表明理论分析的正确性。     

混合角点检测算法用于脑磁共振图像配准

目的针对现有角点检测算法的不足,提出结合Harris、Susan的混合角点检测算法,并应用于脑MR图像配准中。方法首先通过Harris算子、Susan算子分别提取图像中Harris角点和Susan角点;然后对Harris角点和Susan角点取并集;通过引入两个加权因子ω1和ω2,分别对Harris角点响应值与Susan角点响应值进行加权计算,获得其角点强度,从而筛选出新的角点集合;通过归一化相关法和投票策略筛选出精确匹配的角点对;最后采用Powell算法进一步优化,获得图像最终配准参数值。结果混合角点检测算法应用于脑MR图像配准能获得较高的配准精度和较好的稳定性。结论相比于目前的角点检测算法,本文算法更适用于脑MR图像配准。     

不同电压下紫外线强度观察及消毒时间探讨

对13支使用中的石英紫外线灯管在不同电压下的紫外线强度进行观察，发现紫外线强度与电源电压呈正相关。通过相关回归分析，得出线性回归方程4个，以利用不同电压下紫外线强度计算电压为220V时的紫外线强度，并计算出合格紫外线灯管在不同电压下杀灭各类微生物所需的时间。建议：常规紫外线消毒最好在电压较高的大夜班进行，随时进行物体表面消毒时，应根据电压改变定量延长消毒时间。     

基于插入损耗的噪声源阻抗修正计算方法

为了使EMI滤波器能够实现有效的插入损耗，需要考虑噪声源阻抗的频谱特性。电压插入损耗法是最简单的测试噪声源阻抗的方法。本文分析了传统的电压插入损耗法在实现过程中采用的假设条件，部分假设在数学上并不严格成立，相应的简化近似计算可能导致较大误差；甚至有些计算结果会与假设条件矛盾，进而导致计算结果无效。在不改变传统插入损耗法的测试方案的前提下，对噪声源阻抗的计算方法进行修正，推导了源阻抗幅值的精确解析表达式，进而确定源阻抗幅值的最大值和最小值。解析计算结果经过数学验证成立。在此基础上，以电动汽车用DC-DC变换器为测试对象，实现了源阻抗幅值的测试和计算，验证了该方法的有效性和适用性。通过该测试和设计实例的分析可以发现，改进的电压插入损耗法可以获得更精确的噪声源阻抗，避免滤波器的过设计，便于滤波元件的设计和选型，并为滤波器体积、重量等的优化提供帮助。     

一种具有中点电位平衡可降低损耗的三电平空间矢量调制方法

对中点钳位式(NPC)三电平逆变器降低开关损耗的方法进行研究。提出一种新的不连续空间矢量脉宽调制(SVPWM)方法,在单位功率因数下实现大电流不开关原则,较大程度的降低开关损耗。另外由于中点电位平衡是三电平NPC的固有问题,基于不连续SVPWM,提出一种滞环控制策略,通过切换矢量序列方式控制中点电位平衡。仿真和实验结果证明了本文提出的新型调制方法的可行性和有效性。     

基于目标波形与逻辑编-译码的多电平变流器通用调制算法

考虑到传统的多电平变流器调制算法不能简单应用于各种新型多电平变流器拓扑结构，提出了基于目标波形与逻辑编-译码的多电平变流器通用调制算法。该算法首先确定与实际变流器电平数相同的等价变流器和目标波形，再通过编-译码确定原始工作波形和实际工作波形的逻辑关系，使实际变流器获得与目标波形一致的输出波形。以混合级联多电平变流器为例，对该调制算法进行了理论分析、仿真和试验验证。仿真和试验结果表明基于目标波形与逻辑编-译码的多电平变流器通用调制算法，具有不依赖于具体拓扑结构的通用性，算法简单且容易实现，适用于各种结构的多电平变流器。     

癌症痛治疗的进展及展望：癌症疼痛高级研讨会纪要

１９８２年，ＷＨＯ成立了癌痛专家委员会，探讨用现有的、为数有限的镇痛药物解除癌痛病人的问题，并提出了癌症病人三阶梯止痛疗法。之后，三阶梯方案成为全世界治疗癌痛的基本方法。１９９１年，中华人民共和国卫生部发文，要求在我国实施和开展癌症病人三阶梯止痛治疗...     

细胞分化抗原CD45辅助设门在白血病表型分析中的应用

目的建立在流式细胞仪上利用细胞分化抗原ＣＤ４５（ＣＤ４５）和侧向角光散射（ＳＳＣ）坐标图辅助门的方法，确保在白血病细胞免疫分型时设六的准确无误。方法根据ＣＤ４５在所有白细胞上都有表达，但在不同系成熟细胞和同系不同发育阶段细胞表面表达密度不同的特点，在不同荧光抗体检测组合中配以ＣＤ４５荧光单克隆抗有先按常规在前向角光散射（ＦＳＣ）与ＳＳＣ坐标图中设站，再利用ＣＤ４５－ＳＳＣ图辅助设门选择低ＣＤ４５表     

超低压井堵漏工艺技术研究与应用

针对开绕组永磁复合轮毂(Permanent Magnet Compact In-Wheel, PMCW)电机驱动系统中单开关管开路故障工况,在60°坐标系下,提出了基于双三相四开关逆变器的电压空间矢量调制(SVPWM)重构容错控制策略。该策略采用电压解析模型法进行故障诊断,通过桥臂冗余开关组合在线模拟开关管故障,依据矢量分解准则,在一个调制周期内,一个逆变器钳位于对应三角区域顶点的相同冗余开关状态,另一个逆变器进行电压矢量合成,两个逆变器交替运行在钳位和矢量合成状态,在不增加额外器件的情况下,实现了开绕组PMCW电机驱动系统单开关管开路故障容错运行,并兼顾了双逆变器之间的功率平衡。仿真和实验验证了该容错控制策略能够实现开绕组PMCW电机驱动系统从开关管故障状态到容错运行的平滑、可靠切换。     

Empirical mode decomposition and tissue harmonic imaging

Empirical mode decomposition (EMD) is a relatively new technique used in the analysis of nonlinear and nonstationary time series. Previous signal-processing methods used for medical ultrasound have been based on the assumption of a linear time-invariant system. More recently, the technique of tissue harmonic imaging (THI) has become prevalent. This technique relies on the nonlinear propagation of the sound wave through the medium to disperse the signal energy into the harmonic frequencies of the transmitted signal. In this paper, results are presented from using EMD to process received ultrasound echo signals that have passed through nonlinear media. The Hilbert spectrum is used to demonstrate an interpretation of the physical process underlying THI that is based on the concept of intrawave frequency modulation, rather then the spreading of signal energy into harmonic frequencies. The technique of EMD is shown to be able to produce superior results to the bandpass filtering method of THI, even when the band width of the transducer was such that the second harmonic would be suppressed.     

电压型PWM整流器无差拍预测直接功率控制

研究了一种用于电压型PWM整流器的无差拍预测直接功率控制方法。该方法根据无差拍功率预测模型，在每一个采样周期，实现对下一个周期开始时的功率给定值的跟踪控制。采用空间矢量脉宽调制方法调制目标电压矢量，实现了直接功率控制开关频率的恒定。并在系统中引入了基于内模原理的准积分反馈校正环节，在每个采样周期对系统有功功率和无功功率的预测给定值进行修正。仿真表明，该方法有功功率、无功功率响应迅速、平滑，而且没有静差；控制器对系统参数变化不敏感，系统鲁棒性好，控制器设计简单，具有工程应用前景。     

Ultrasound Attenuation Estimation in Harmonic Imaging for Robust Fatty Liver Detection

Accurate detection of liver steatosis is important for liver disease management. Ultrasound attenuation coefficient estimation (ACE) has great potential in quantifying liver fat content. The commonly used ACE methods (e.g., spectral shift methods, reference phantom methods) assume linear tissue response to ultrasound and were developed in fundamental imaging. However, fundamental imaging may be vulnerable to reverberation clutters introduced by the body wall. The clutters superimposed on liver echoes may bias the attenuation estimation. Here we propose a new ACE technique, the reference frequency method (RFM), in harmonic imaging to mitigate the reverberation bias. The accuracy of harmonic RFM was validated through a phantom study. In a pilot patient study, harmonic RFM performed more robustly in vivo compared with fundamental RFM, illustrating the potential of ACE in harmonic imaging.     

Optical Quantification of Harmonic Acoustic Radiation Force Excitation in a Tissue-Mimicking Phantom

Optical tracking was used to characterize acoustic radiation force-induced displacements in a tissue-mimicking phantom. Amplitude-modulated 3.3-MHz ultrasound was used to induce acoustic radiation force in the phantom, which was embedded with 10-μm microspheres that were tracked using a microscope objective and high-speed camera. For sine and square amplitude modulation, the harmonic components of the fundamental and second and third harmonic frequencies were measured. The displacement amplitudes were found to increase linearly with acoustic radiation force up to 10 μm, with sine modulation having 19.5% lower peak-to-peak amplitude values than square modulation. Square modulation produced almost no second harmonic, but energy was present in the third harmonic. For the sine modulation, energy was present in the second harmonic and low energy in the third harmonic. A finite-element model was used to simulate the deformation and was both qualitatively and quantitatively in agreement with the measurements.     

Bioimpedance harmonic analysis as a tool to simultaneously assess circulation and nervous control

Multicycle harmonic (Fourier) analysis of bioimpedance was employed to simultaneously assess circulation and neural activity in visceral (rat urinary bladder) and somatic (human finger) organs. The informative value of the first cardiac harmonic of the bladder impedance as an index of bladder circulation is demonstrated. The individual reactions of normal and obstructive bladders in response to infusion cystometry were recorded. The potency of multicycle harmonic analysis of bioimpedance to assess sympathetic and parasympathetic neural control in urinary bladder is discussed. In the human finger, bioimpedance harmonic analysis revealed three periodic components at the rate of the heart beat, respiration and Mayer wave (0.1 Hz), which were observed under normal conditions and during blood flow arrest in the hand. The revealed spectrum peaks were explained by the changes in systemic blood pressure and in regional vascular tone resulting from neural vasomotor control. During normal respiration and circulation, two side cardiac peaks were revealed in a bioimpedance amplitude spectrum, whose amplitude reflected the depth of amplitude respiratory modulation of the cardiac output. During normal breathing, the peaks corresponding to the second and third cardiac harmonics were split, reflecting frequency respiratory modulation of the heart rate. Multicycle harmonic analysis of bioimpedance is a novel potent tool to examine the interaction between the respiratory and cardiovascular system and to simultaneously assess regional circulation and neural influences in visceral and somatic organs.     

Force-plate based computation of ankle and hip strategies from double-inverted pendulum model

BACKGROUND: Using statistical characteristics of the centre of pressure displacement or of the ground reaction forces, it is difficult to have quantitative evaluation of the equilibrium strategy employed (ankle or hip). The purpose of this study is to validate a new force-plate based approach that allows to evaluate postural strategies employed through a method based on a double-inverted pendulum model. METHODS: This method allows to compute ankle and hip joint motion only from force plate data and relies on inverse kinematics with the centre of mass considered as the end effector. Furthermore, an index, depending on the covariance between hip and ankle angles, is proposed to quantify the strategy used. To validate the method and the strategy index, we compare the results of our computation to an optical stereophotogrammetry measurement of the angles considered as reference value. FINDINGS: The experiments demonstrate that our method provides acceptable results. The root mean square error between computed and measured hip and ankle angles stands between 4.5 x 10(-3)degrees for ankle angle in static condition and 1.1 x 10(-1) degrees for hip angle in hip forced condition. INTERPRETATION: The main interest of our method for clinicians is that it allows to retrieve the ankle and hip angles only using a simple and widespread device, the force-plate. Moreover, it proposes a new postural index that can be also be computed without videographic systems.     

Stokes vector based polarization resolved second harmonic microscopy of starch granules

We report on the measurement and analysis of the polarization state of second harmonic signals generated by starch granules, using a four-channel photon counting based Stokes-polarimeter. Various polarization parameters, such as the degree of polarization (DOP), the degree of linear polarization (DOLP), the degree of circular polarization (DOCP), and anisotropy are extracted from the 2D second harmonic Stokes images of starch granules. The concentric shell structure of a starch granule forms a natural photonic crystal structure. By integration over all the solid angle, it will allow very similar SHG quantum efficiency regardless of the angle or the states of incident polarization. Given type I phase matching and the concentric shell structure of a starch granule, one can easily infer the polarization states of the input beam from the resulting SH micrograph.OCIS codes: (180.4315) Nonlinear microscopy, (120.5410) Polarimetry, (320.0320) Ultrafast optics, (120.0120) Instrumentation, measurement, and metrology, (160.1435) Biomaterials