Ultrasound enhanced thrombolysis in acute arterial ischemia

In vitro and animal studies have shown that thrombolysis with intravenous tissue plasminogen activator (tPA) can be enhanced with ultrasound. Ultrasound delivers mechanical pressure waves to the clot, thus exposing more thrombus surface to circulating drug. Moreover, intravenous gaseous microspheres with ultrasound have been shown to be a potential alternative to fibrinolytic agents to recanalize discrete peripheral thrombotic arterial occlusions or acute arteriovenous graft thromboses. Small phase I-II randomized and non-randomized clinical trials have shown promising results concerning the potential applications of ultrasound-enhanced thrombolysis in the setting of acute cerebral ischemia. CLOTBUST was an international four-center phase II trial, which demonstrated that, in patients with acute ischemic stroke, transcranial Doppler (TCD) monitoring augments tPA-induced arterial recanalization (sustained complete recanalization rates: 38% vs. 13%) with a non-significant trend toward an increased rate of clinical recovery from stroke, as compared with placebo. The rates of symptomatic intracerebral hemorrhage (sICH) were similar in the active and placebo group (4.8% vs. 4.8%). Smaller single-center clinical trials using transcranial color-coded sonography (TCCD) reported recanalization rates ranging from 27% to 64% and sICH rates of 0-18%. A separate clinical trial evaluating the safety and efficacy of therapeutic low-frequency ultrasound was discontinued because of a concerning sICH rate of 36% in the active group. To further enhance the ability of tPA to break up thrombi, current ongoing clinical trials include phase II studies of a single beam 2 MHz TCD with perflutren-lipid microspheres. Moreover, potential enhancement of intra-arterial tPA delivery is being clinically tested with 1.7-2.1 MHz pulsed wave ultrasound (EKOS catheter) in ongoing phase II-III clinical trials. Intravenous platelet-targeted microbubbles with low-frequency ultrasound are currently investigated as a rapid noninvasive technique to identify thrombosed intracranial and peripheral vessels. Multi-national dose escalation studies of microspheres and the development of an operator independent ultrasound device are underway.     

On the signal-to-noise ratio enhancement of the Doppler process

The output signal-to-noise ratio (SNR) of the ultrasound Doppler process, with and without the commonly used sample and hold circuit, is calculated rigorously, and confirmed by experiment. On the basis of this result it is shown that the use of pulsed Doppler processing without increase of the transmitted power enhances the output SNR of a pulse-echo system observing moving particles by the factor f_rT_t, where f_r is the repetition rate of the pulse echo and Doppler systems and T_t is the transit time of the particles across the range cell. If nonlinear losses are significant, then changing to continuous Doppler operation and lowering the peak transmitted power to maintain the average power constant can produce additional improvement in SNR due to reduced non-linear losses in the transducer and the propagation medium, as well as reduced requirements for transducer damping.     

获取超短波长电磁辐射的新途径

在系统研究运动电子对迎面而来的圆偏振激光脉冲的汤姆逊散射的基础上，讨论了获取超短波长电磁辐射的两种新方案。其一是利用超强圆偏振激光在具有特定速度的电子的非线性散射所伴随的谐波频率上称，其二是利用激光在相对论电子反向散射所伴随的多普勒频移。     

Effects of electrode morphology on the slit flow of an electrorheological fluid

In this work the effects of electrode morphology on the slit flow of an electrorheological (ER) fluid via laser Doppler anemometry (LDA) are studied. For this purpose, oblique and corrugated electrodes were used. Under a.c.-conditions the ER-effect with the oblique and corrugated electrodes is greater in comparison to the case of smooth electrodes at the same voltage and pressure drop. An average factor of 2.0 and 2.5 (in the range 1–5 kV) describes the increase in the ER-effect for the oblique and corrugated electrodes, respectively. This increase in ER-effect is accompanied by a decrease in electric current. Under d.c.-conditions the ER-effect with the oblique and corrugated electrodes is somewhat better than with the smooth electrodes but only at a very low field strength. Increasing the field strength leads to a decreased ER-effect (in comparison to the smooth electrodes). This decrease of the ER-effect is always accompanied by a decrease in electric current (d.c.-field).     

Differential Discrimination Technique for Incoherent Doppler Lidar to Measure Atmospheric Wind and Backscatter Ratio

A new incoherent Doppler lidar scheme is proposed using a high resolution Mach-Zehnder interferometer discriminator with sinusoidal transmission functions. A two-channel differential discrimination technique is developed which provides high sensitive velocity measurement. The aerosol and molecular backscatter signals can be separately measured and the backscatter ratio obtained. Principle of the measurement is described and the characteristics of this technique are analyzed and compared. Numerical calculation for a moderate size 1.064 μ lidar shows that an accuracy better than 1 m/s for the velocity measurement and 18% for the backscatter ratio measurement can be obtained up to a height of 10 km by a 500 shot average.     

Denoising of quadrature ultrasound Doppler signal from bi-directional flow based on matching pursuit

Denoising of Doppler signal is a preliminary and important step in medical ultrasound imaging. To denoise quadrature Doppler signal from bi-directional flow, we propose a novel method based on matching pursuit in this paper. The proposed method is an iterative decomposition algorithm which decomposes the original Doppler signal into a linear expansion of atoms in a time-frequency dictionary. The time-frequency dictionary is similar to Fourier transform domain and the atoms are similar to orthogonal bases in Fourier transform. In each step of the iteration, the atom which gives the largest inner product with the analyzed signal is selected from the dictionary, and the contribution of this atom is subtracted from the Doppler signal. This process is repeated on the residue until the SNR reaches the maximum. The linear expansion of the selected atoms is the denoised signal. Simulations were conducted on a simulation model with a sampling rate of 12.8 kHz. When the original SNRs are 0 dB, 2 dB, 4 dB, 6 dB, 8 dB, 10 dB, the proposed method can improve the SNR for 7.9 dB, 7.8 dB, 7.5 dB, 7.3 dB, 7.05 dB, 6.8 dB respectively, reduce the root mean square error (RMSE) of the mean frequency waveform to 0.0441 kHz, 0.0303 kHz, 0.0245 kHz, 0.0215 kHz, 0.0161 kHz, 0.0125 kHz respectively, and suppress the RMSE of the spectral width waveform to 0.1774 kHz, 0.0591 kHz, 0.0486 kHz, 0.0170 kHz, 0.0145 kHz, 0.0117 kHz respectively. Preliminary in vivo evaluation was also carried out on a healthy 33-year-old male using B-K medical A/S 3535 ultrasound scanner, and the results showed that the proposed method can effectively enhance the Doppler spectrogram.     

粗糙微管道内液体流动特性的实验研究

利用实验方法研究了粗糙度对矩形截面微管道内液体流动阻力特性的影响，采用微观粒子图像测速技术测量了粗糙微管道内的流场结构.实验结果表明：在层流状态下，3%—7%的相对粗糙度可以导致微管道内流动阻力的明显增加，在粗糙单元附近形成的压差阻力是导致流动阻力增加的主要原因.粗糙单元还会引起微管道内的流动失稳，导致粗糙微管道内层流向湍流的转捩提前. 关键词： 微管道 粗糙度 微观粒子图像测速 转捩     

摆动式声多普勒效应实验仪

针对现有的声多普勒效应实验装置中存在的问题,设计并制作了摆动式声多普勒效应实验仪.该仪器能够分别进行声源运动和观察者运动的声多普勒效应实验,且可定量分析频偏和测量速度.本文详细介绍了该仪器的原理、构造、特点和实验过程,并对实验结果进行了较为全面的分析.     

PIV水下流场测试系统试验研究

基于粒子图像测速技术,设计研制了一套适用于水洞洞体内高速、封闭试验条件的流场测量与显示设备.该系统由光源、成像、图像处理与分析、控制和粒子投放等分系统组成，具有复杂环境下全流场的无接触、无扰动、高准确度测量和显示能力，流场测试误差小于2%，可为水下航行器外形设计及其改进提供相关的实测数据.     

纳米Fe3 O4 颗粒的正电子湮没谱学研究

测量了磁性纳米Fe₃O₄颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe₃O₄颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe₃O₄颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe₃O_{4< 关键词： 正电子 3}O₄')" href="#">Fe₃O₄ 寿命谱 多普勒展宽谱