Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method

A thermodynamic method for measuring the acoustic nonlinearity parameter B/A in tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20 degrees to 37 degrees C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues.     

A novel phase locked cavity resonator for B/A measurements in fluids

A new technique for the measurement in fluids of the acoustic non-linearity parameter B/A is presented, together with measured B/A values for several fluids. The non-linearity parameter is measured by phase locking radial modes within a PZT cylinder. The system, which implements the isentropic phase technique, uses continuous wave phase locking to measure the change in sound velocity that is typically associated with a change in ambient pressure under constant entropy. The method provides a means of measuring B/A in vitro both accurately and simply without the typical problems involved in time-of-flight systems. Fluid samples can remain small due to the nature of the cavity resonator, so the system is well suited to small volume, biological samples.     

氮化硅陶瓷层裂强度的研究

 用一级轻气炮冲击加载装置，对氮化硅陶瓷进行了冲击性能实验研究。发展了一种新的方法用于研究层裂特性，即通过在样品中埋设电磁粒子速度计来记录氮化硅陶瓷内部的层裂特性。该方法不同于常用的VISAR激光干涉法和锰铜计法，记录的是样品内部粒子速度的变化特征，位于层裂面后方的粒子速度计能清晰地表征材料的层裂特性。通过实验，得到了密度为3.12 g/cm³的氮化硅陶瓷的层裂强度为0.73 GPa，和Nahme等得到的强度较为接近，对称碰撞得到的裂片厚度与该次实验的飞片厚度相当。实验表明，电磁粒子速度计的方法可以用于研究非磁屏蔽材料的层裂特性。由于采用多个计进行记录，还得到了材料在弹性区内（1.8~3.6 GPa）的Hugoniot冲击绝热线。     

A brief study on the mixture rules of the acoustic non-linearity parameter B/A in binary biological mixtures

Using the improved thermodynamic method, the acoustic non-linearity parameter B/A of binary biological mixtures — such as pig blood, sheep blood and bovine blood — is measured in order to test the mixture rules proposed by Apfel and Sehgal. The results show that the B/A values of the above-mentioned blood decrease with an increasing volume fraction of water. The B/A value varies linearly with the volume fraction of protein. It is also shown that, treated as a binary mixture, the blood obeys the trend that the B/A value varies with the volume of water. This is in agreement with the rules proposed by Apfel and Sehgal. However, the measured B/A value is not exactly equal to that of the mixture rules.     

2 TPa压力下2169钢的冲击压缩测量

 利用地下爆炸产生的冲击波进行2169钢冲击压缩测量。测量是根据阻抗匹配解方法并且以铁作为标准材料。布置47根接触电探针以确定2169钢和标准材料中的冲击波速度以及冲击波阵面形状。测量出的2169钢冲击压缩参数是：冲击波速度u_s=22.12 km/s，波后粒子速度u_p=13.39 km/s，冲击波压力p=2.31 TPa和压缩比σ=2.53。本测量结果与较低压力下化爆测量结果的外推值的比较表明，两者基本一致。     

Microwave detection of spatial-dispersion effects in superconductors

A microwave method based on the use of microstrip retardation systems for detecting spatial-dispersion effects in superconductors is proposed. Strong phase velocity retardation in a microstrip resonator has been revealed, which is explained by the influence of sharp strip edges, near which high curvature occurs for the coordinate system introduced to search for wave solutions. This circumstance leads to a spatial dependence of the phase velocity on the scale factors of the curvilinear coordinate system and may significantly reduce the phase velocity. Comparative estimates of the spatial effects in samples of a single-crystal high-temperature superconductor (YBaCuO), Nb, and Cu have been obtained from measurements of the total value and increment of the resonance frequency during the transition of the cooling helium from the liquid to gaseous state, depending of the sample position in the field of the microstrip resonator.     

In vivo B/A determination in a mammalian organ

Investigations of the ultrasonic nonlinearity parameter B/A have been restricted previously to in vitro preparations. The parameter B/A has now been determined in vivo in cat liver and found to have the same value as in vitro determinations. The finite amplitude method was used, with a substitutional procedure to improve accuracy.     

A Wavelet-Based Processing method for simultaneously determining ultrasonic velocity and material thickness

Methods of measuring ultrasonic wave velocity in an elastic sample require data on the thickness of the sample and/or the distances between the transducers and the sample. The uncertainty of the ultrasonic wave velocity measurements generally depends on that of the data available. Conversely, to determine the thickness of a material, it is necessary to have a priori information about the wave velocity. This problem is particularly hard to solve when measuring the parameters of biological specimens such as bones having a greater acoustical impedance contrast (typically 3-5 MRayl) than that of the surrounding soft tissues (typically 1.5 MRayl). Measurements of this kind cannot easily be performed. But obtaining the thickness of a bone structure and/or the ultrasonic wave velocity is a important problem, for example, in biomechanical field for the calculation of elastic modulus, or in acoustical imaging field to parameterize the images, and to reference the grey or color level set to a physical parameter.The aim of the present study was to develop a method of simultaneously and independently determining the velocity of an ultrasonic wave in an elastic sample and the wave path across the thickness of this sample, using only one acquisition in pure transmission mode. The new method, which we have called the “Wavelet-Based Processing” method, is based on the wavelet decomposition of the signals and on a suitable transmitted incident wave correlated with the experimental device, and the mathematical properties such as orthonormality, of which lend themselves well to the time-scale approach. By following an adapted algorithm, ultrasonic wave velocities in parallelepipedic plates of elastic manufactured material and the apparent thicknesses were both measured using a water tank, a mechanical device and a matched pair of 1 MHz ultrasonic focused transducers having a diameter of 3 mm, a focal length of 150 mm and beam width of 2 × 2 mm at the focus (mean temperature 22°). The results were compared with those obtained with a conventional Pulse-mode method and with the control values, to check their validity. Measurements performed on bovine and human dry cortical bone samples are also presented to assess the limitations of the method when it is applied to elastic biological samples, including those of an equal-wavelength size (≈1.5 mm). The thicknesses and the ultrasonic wave velocities were then measured in this kind of (quasi-) parallelepipedic elastic materials with an mean estimated error ranged from 1% to 3.5% compared to the referenced values.     

Automatic measurement of the nonlinearity parameter B/A in liquid media

Using a 19-MHz focused Gaussian beam generated by a LiNbO(3) plate with an inverted polarization layer coupled to an acoustic lens, a method to automatically measure the nonlinearity parameter B/A in liquid media is presented. A liquid sample is poured into a cylindrical cell set with a glass tube on the lens surface. The focusing source emits burst waves. A tungsten rod immersed in the sample so that the top surface is normal to the beam axis behaves as a perfect reflector. The position of the reflector to maximize the amplitude receiving the returned wave determines the sound speed c of the sample. The amplitude measurement for the waves returned from the lens-sample interface and the reflector surface leads to the determination of the density rho and attenuation coefficient alpha, respectively. Then the B/A is finally derived by summarizing the measured result of the 38-MHz second harmonic amplitude contained in the sound returned back from the reflector, together with rho, c and alpha. All these are automatically processed in a short time less than 2 min with the performance of computer controlled instruments.     

六面顶压机高温高压弹性波速测量装置样品室温度梯度的校正

 大腔体六面顶压机波速测量装置的样品室内存在着较大的温度梯度。根据实验观测的样品室内的温度分布数据和在一定温度条件下波速随温度升高呈线性变化的特征，运用理论分析和计算相结合的方法对样品的弹性波速进行了校正。以斜长角闪岩为例，对其实验测量的纵波速度（v_P）进行了校正，并与原来的数据作了对比：波速校正量绝对值随着温度的升高逐渐增大；在2.0 GPa、530 ℃时，样品X和样品Y校正后的v_P比未校正的v_P分别减小了0.270 km/s（3.3%）和0.118 km/s（1.5%）。这种方法明显地提高了波速测量结果的精度，有助于更准确地进行地球物理资料的解释。     

CT-6B托卡马克等离子体角向转动的光谱测量

利用高分辨光谱测量系统，根据杂质离子谱线ＯⅡ４６４.２ｎｍ，ＣⅢ４６４.７ｎｍ和氢Ｈα谱线的多普勒位移，测量了ＣＴ-６Ｂ托卡马克等离子体角向转动速度的径向分布．结果表明：杂质离子的角向转动速度的方向在等离子体内部为电子逆磁漂移方向，其线速度在小半径约９ｃｍ处达到极大值３.５ｋｍ／ｓ；在接近孔阑ｒ＝１０ｃｍ处，反转为离子逆磁漂移方向．由此导出等离子体内部的径向电场向里，其最大值为１８Ｖ／ｃｍ．中性氢原子只存在其方向为电子逆磁漂移方向的角向转动分量，其数值较杂质离子谱线所得结果要低．最后对所得的结果作了初步的讨论 关键词：     

开态应力下电压和电流对AlGaN/GaN高电子迁移率晶体管的退化作用研究

通过采集等功率的两种不同开态直流应力作用下AlGaN/GaN高电子迁移率晶体管(HEMTs)漏源电流输出特性、源区和漏区大信号寄生电阻、转移特性、阈值电压随应力时间的变化, 并使用光发射显微镜观察器件漏电流情况, 研究了开态应力下电压和电流对AlGaN/GaN高电子迁移率晶体管的退化作用. 结果表明, 低电压大电流应力下器件退化很少, 高电压大电流下器件退化较明显. 高电压是HEMTs退化的主要因素, 栅漏之间高电场引起的逆压电效应对参数的永久性退化起决定性作用. 除此之外, 器件表面损坏部位的显微图像表明低电压大电流下器件失效是由于局部电流密度过高, 出现热斑导致器件损伤引起的.     

Measurement of the B/A nonlinearity parameter under high pressure: application to water

An experimental apparatus was developed to measure, over a wide range of pressure, the acoustical nonlinear parameter B/A with an uncertainty of 2.2% in order to study the influence of pressure on the value of this parameter in liquids. The experimental technique rests on an improved thermodynamic method which uses a highly sensitive phase comparison technique to measure the change in speed of sound with pressure. The apparatus was then used to measure B/A in water within the pressure range from 0.1 to 50 MPa and at temperatures of between 303.15 and 373.15 K. The data obtained were compared with those in the literature which come from numerical derivation of speed of sound measurements.     

基于分块速度域改进迭代运动目标检测算法的红外弱小目标检测

提出一种基于分块速度域的迭代红外运动目标检测算法来解决传统算法计算量巨大这一难题.首先,采用二维最小均方差滤波器对红外序列图像进行滤波,获得包含弱小目标以及残差的红外序列图像.然后,通过在序列图像块的速度域上应用改进的迭代运动目标检测算法进行能量累积,从而将弱小目标的运动速度在速度域进行累积增强,达到检测弱小运动目标的目的.最后在解算出的速度值附近进行搜索,得到弱小目标运动的精确速度.利用此速度进行空域能量累积,得到叠加图像,在此图上进行目标检测.与传统方法相比较,几组实验结果显示,本文提出的方法大大缩短了检测的时间,而且本文方法的检测效果也较好.     

钕铁硼的冲击压缩特性

 利用二级轻气炮对恒磁体钕铁硼进行冲击压缩,采用阻抗匹配法进行测量,获得了平均初始密度为7.346 g/cm³的钕铁硼Hugoniot关系数据。实验结果表明,该种钕铁硼在19~78 GPa范围内,其D-u_p满足线性变化关系,即：C₀、λ分别为3.686 km/s、1.059,是一种稳定的压缩过程,其间没有相变产生。而较小的λ值表明该种钕铁硼材料偏向于疏松体结构,且容易被压缩。同时实验结果也为其状态方程和脉冲功率源等方面的研究工作提供了可资参考的实验参数。     

A High-Resolution C 3D CSA-CSA-CSA Correlation Experiment by Means of Magic Angle Turning

It is shown in this paper that a previously reported 90° sample flipping ¹³C 2D CSA-CSA correlation experiment may be carried out alternatively by employing constant slow sample rotation about the magic angle axis and by synchronizing the read pulse to of the rotor cycle. A high-resolution 3D CSA-CSA-CSA correlation experiment based on the magic angle turning technique is reported in which the conventional 90° 2D CSA-CSA powder pattern for each carbon in a system containing a number of inequivalent carbons may be separated according to the isotropic chemical shift value. The technique is demonstrated on 1,2,3-trimethoxybenzene in which all of the overlapping powder patterns that cannot be segregated by the 2D CSA-CSA experiment are resolved successfully by the 3D CSA-CSA-CSA experiment, including even the two methoxy groups (M₁ and M₃) whose isotropic shifts, confirmed by high-speed MAS, are separated by only 1 ppm. A difference of 4 ppm in the principal value component (δ₃₃) between M₁ and M₃ is readily obtained.     

内爆圆柱套筒磁通量压缩的磁流体力学计算

在一维反应流体动力学程序SSS的基础上扩充编制一维磁流体力学计算编码SSS/MHD,并对炸药内爆驱动的圆柱形套筒磁通量聚积发生器(MC-1装置)进行了一维磁流体力学模拟计算。分析了空腔磁场向压缩套筒和样品套筒壁中的磁扩散现象,结果表明,在压缩套筒壁中距离空腔0.2mm处的磁感应强度最大值只有十几T;而在样品套筒壁中距离空腔0.2mm处的磁感应强度最大值达到几百T,这主要是内外套筒运动速度不同,电磁力与内爆作用力平衡引起的。计算了空腔中磁感应强度的变化曲线和样品套筒内壁的速度历程曲线,得到与实验测试符合的结果。     

A new approach for the estimation of the axial velocity using ultrasound

The most used estimation method for calculating the blood velocity in commercial scanners is the autocorrelation approach. The calculation of the mean velocity used in this method depends on the center frequency of the interacting ultrasound pulse which downshifts as a function of depth, introducing a bias. A new velocity estimator for the mean axial velocity is presented. The estimation principle is based on the 2D Fourier transform and the Radon transform. The input data are a sequence of RF data forming a 2D data input, one column for each pulse emission. A 2D segment is selected for a specific depth. This data segment is first transformed by a 2D Fourier transform, and the result is then transformed by a Radon transform. The center of gravity for the angles of the lines intersecting the origin of the R-theta coordinate system in the Radon domain gives the mean axial velocity for the data segment. The benefit of this method is an estimate of the mean axial velocity which is independent of the center frequency of the propagating ultrasound pulse. The estimate will only depend on f(s) and f(pr f). Results of the estimation method is presented based on both simple generated RF harmonic data for different signal/noise ratios and simulated acoustic RF responses from a 3D measurement situation with an array transducer and a tube with plug flow. The new method shows improvement with a factor of 1.5-4 on the standard deviation on the estimated mean velocity for the simulated case.     

A kinetic method for correcting the X-ray photoelectron spectra of radiation-sensitive compounds

A new method is proposed for determining the initial XPS spectra of compounds which are sensitive to X-ray irradiation, based on the first-order kinetics of the sample decomposition. The method simultaneously gives a value for the rate constant of the radiation-induced decomposition, which may itself be characteristic of the compound. The method is verified for the compounds cupric bis(8-quinolenethiol) and bis(dimethyl-glyoxime)triphenylphosphinecobalt(III) chloride, and a simple criterion for its use is given.