Ultrasonic studies in binary liquid mixtures of benzene and coconut oil near the critical region

Velocity and attenuation of ultrasonic waves have been measured in complex binary mixtures of benzene and multicomponent coconut oil near the critical temperature in the low MHz region. The experimental results are analysed in terms of theories developed by Kawasaki and Mistura. The characteristic frequency and amplitude parameter determined by fitting the data in the relations proposed by Kawasaki-Mistura are scaled at reduced temperature and these agree with scaling exponents. A small velocity dispersion is also observed.     

挠曲电效应对向列相液晶盒响应时间的影响

应用液晶动力学理论和差分迭代方法,考虑上液晶挠曲电特性情形下研究强锚泊混合排列向列相液晶盒撤掉电压时的动态响应过程,数值计算得到液晶盒透过率随时间的变化.结果表明:随展曲和弯曲挠曲电系数和的绝对值|e₁₁+e₃₃|的增加,液晶盒的响应时间逐渐减小,当|e₁₁+e₃₃|=50 pC·m^-1时,响应时间与忽略挠曲电效应的情况相比缩短了一半.     

三光子纠缠W态隐形传输令牌总线网的保真度计算

计算了三光子W态隐形传输令牌总线网的保真度.通过计算发现在整个量子网络通信过程中,对于给定的分析角θ,保真度仅与系数|a|2有关|随着分析角θ的增加,保真度出现最大值所对应的系数|a|2相应减小,取θ=π/4、π/2、3π/4时可使保真度达最大值1,此时对应的|a|2分别为0.724、0.5和0.276.对于给定的系数|a|,保真度仅与分析角θ有关|若|a|=0,则无论θ为何值,保真度始终为0|若|a|=|b|=0.707 1,则当θ=π/2、3π/2时保真度达最大值1.     

Ultrasonic absorption in critical binary mixture of perfluoromethylcyclohexane and carbon tetrachloride

The results of ultrasonic absorption and velocity measurements for the system perfluoromethylcyclohexane-carbon tetrachloride are presented. In addition, viscosity measurements were made. Ultrasonic absorption at 5, 7, 10, 15, 21, and 25 MHz, above critical temperature Tc, is analyzed using the dynamic scaling theory of Ferrell and Bhattacharjee. The values of alpha/f2 vs f-1.06 show a good agreement with the theory. The experimental values of alpha/alpha c for the binary mixture are compared to the scaling function F(omega*).     

PdSiAg非晶合金中切变波的超声衰减

一、引言 在迅速发展的非晶态金属材料中,钯硅系合金由于具有低声速、低声损耗特性而引起人们的很大兴趣。M.Dutoit和H.S.Chen(陈鹤寿)首先研究了φ1～2.5mm杆状PdSiAg样品中的超声衰减,G.Bellessa等测量了PdSiCu样品中纵波超声衰减和声速的温度关系,M.Bavmatz等测量了PdSi非晶合金的杨氏模量和低频内耗,这些实验研究工作对正确使用这类新材料和发展非晶固体理论无疑都有重要意义。但PdSiAg非晶合金中切变波超声衰减的温度关系和冷轧带状样品中的超声特性至今未见报道。     

Scattering-induced attenuation of an ultrasonic beam in austenitic steel

The scattering-induced attenuation coefficient of a beam of longitudinal waves propagating through an austenitic steel plate is measured as a function of the texture angle. The experimental data were obtained by mapping the incident and the transmitted ultrasonic field, and by evaluating the energy loss experienced by each plane wave component of the beam. Contrary to the behavior of data obtained by means of conventional techniques, that of the data reported in this work agrees qualitatively with the theoretical predictions. The reasons for the disagreement between theory and data obtained by means of conventional techniques are also discussed.     

液晶N相→SA相相变点附近的反常声衰减

本文考虑在N→S_A相变中,当T→T_c⁺(相交点)时,声在液晶中传播引起的压力效应。使用模-模耦合方法计算了声的衰减和色散,得到在高频区间,声的衰减有反常发散行为,在低频极限声衰减的临界指数为2.5.当T→T_c⁺时,本文的理论曲线大体上与实验结果相一致。     

Universal amplitude ratios of critical sound attenuation

The universal amplitude ratios for ultrasonic attenuation above and below the critical point are determined for uniaxial magnets, the gas liquid critical point, binary mixtures and related universality classes. For uniaxial ferromagnets also the scaling functions are computed. The theory is based on time dependent Ginzburg-Landau models and the ?=4?d-expansion. Depending on the universality class the universal amplitude ratio assumes values in the range 1/15 to 15. In systems with continuous internal symmetry Goldstone mode singularities are found.     

Ultrasonic attenuation by a thin film of high transition temperature Nb3Ge

The electron-phonon contribution to the ultrasonic attenuation coefficient of a 0.5 μm Nb₃Ge film has been measured using 1.2 GHz surface acoustic waves. Analysis of the attenuation data shows that the largest part of the film has a superconducting transition near the bulk transition temperature, 18 K, even though the total film has a high transition temperature, namely 21.5 K. The electron mean free path is calculated from the electron-phonon attenuation data and is found to be an order of magnitude higher than expected for high transition temperature Nb₃Ge films.     

Inelastic ultraviolet scattering from high frequency acoustic modes in glasses

The dynamic structure factor of vitreous silica and glycerol has been measured as a function of temperature and of the momentum transfer up to Q=0.105 nm(-1) using a novel experimental technique, the inelastic ultraviolet scattering. As in the case of Brillouin light scattering and ultrasonic measurements, the temperature dependence of the acoustic attenuation shows a plateau below the glass transition whose amplitude scales as Q2. Moreover, a slight temperature dependence of attenuation has been found in vitreous silica at about 130 K, which seems to be reminiscent of the peak measured at lower Qs. These two findings strongly support the idea that anharmonicity is responsible for sound attenuation at ultrasonic and hypersonic frequencies. Finally, we demonstrate that the attenuation mechanism should show a change of regime between 0.105 and 1 nm(-1).     

钢在疲劳过程中的超声衰减

测量了高强度钢的紧凑拉伸试样在疲劳过程中的10MHz超声衰减,研究了疲劳裂纹前端区域内的位错动态行为。 关键词：     

Attenuation of micro-wave ultrasonics in the film superconducting Pb

The ultrasonic attenuation of superconducting Pb film in the magnetic field was measured at frequency 9.4 GHz. The field dependence of the attenuation coefficient of the thin film Pb has been compared to theoretical expression.     

超声衰减法测量悬浊液中颗粒粒度和浓度

研究了由颗粒悬浊液中3个频率下声衰减系数测量颗粒粒度分布和浓度的方法。用FFT对测得的1,2和5 MHz 3个频率的声信号进行降噪后得到声幅度和声衰减系数,再根据描述不同频率下声衰减系数与颗粒粒径及浓度关系的ECAH模型,运用Philip-Twomey-NNLS算法和改进Chahine算法求解相关的第一类Fredholm方程,反演出颗粒的尺寸分布和浓度。用该方法对两种不同尺寸体积浓度为5%的玻璃微珠-水悬浊液颗粒进行测量,结果与显微镜法结果吻合。这表明:测量3个频率下的声衰减信号,结合Philip-Twomey-NNLS或改进的Chahine算法,可在较高浓度条件下较准确地测得颗粒粒度和浓度,从而简化了现有的高频率宽频带测量方法。     

Investigation of the HFS in the 4d 5p zP3,4 states of Mo and Mo by levelcrossing spectroscopy

The hyperfine structures of the z⁷P₃ and z⁷P₄ states of ⁹⁵Mo and ⁹⁷Mo have been investigated by levelcrossing spectroscopy. A fit of the experimental signal curves yields the magnetic and electric hfs coupling constants: ⁹⁵Mo z⁷P₃ |A| = 86.19(10) MHz, |B|=5.2(30) MHz, A/B0⁹⁵Mo z⁷P₄ |A|=64.05(30) MHz, |B|=4.3(30) MHz, A/B<0; ⁹⁷Mo z⁷P₃|A|= 88.0(1) MHz, |B|=60.0(20) MHz, A/B<0; ⁹⁷Mo z⁷P₄ |A|=65.4(3) MHz, |B|=50.0(50) MHz, A/B0. For the ratio of the electric quadrupole moments we fine ⁹⁷Q/⁹⁵ Q= -11.5(70).     

Time domain attenuation estimation method from ultrasonic backscattered signals

Ultrasonic attenuation is important not only as a parameter for characterizing tissue but also for compensating other parameters that are used to classify tissues. Several techniques have been explored for estimating ultrasonic attenuation from backscattered signals. In the present study, a technique is developed to estimate the local ultrasonic attenuation coefficient by analyzing the time domain backscattered signal. The proposed method incorporates an objective function that combines the diffraction pattern of the source/receiver with the attenuation slope in an integral equation. The technique was assessed through simulations and validated through experiments with a tissue mimicking phantom and fresh rabbit liver samples. The attenuation values estimated using the proposed technique were compared with the attenuation estimated using insertion loss measurements. For a data block size of 15 pulse lengths axially and 15 beamwidths laterally, the mean attenuation estimates from the tissue mimicking phantoms were within 10% of the estimates using insertion loss measurements. With a data block size of 20 pulse lengths axially and 20 beamwidths laterally, the error in the attenuation values estimated from the liver samples were within 10% of the attenuation values estimated from the insertion loss measurements.     

Absorption of ultrasound in the intermediate state of tin

We have measured the ultrasonic attenuation in the intermediate state of high purity single crystals of tin. Andreev's theory extended for arbitrary ql values has been applied to determine the sizes of the normal and superconducting regions, fraction of the normal material at a given filed and the demagnetisation coefficient of the specimen.     

Ultrasonic study on organic liquid and binary organic liquid mixtures by using Schaaffs＇ collision factor theory

Based on Schaaff's collision factor theory (CFT) in liquids, the equations for nonlinear ultrasonic parameters in both organic liquid and binary organic liquid mixtures are deduced. The nonlinear ultrasonic parameters, including pressure coefficient, temperature coefficients of ultrasonic velocity, and nonlinear acoustic parameter B/A in both organic liquid and binary organic liquid mixtures, are evaluated for comparison with the measured results and data from other sources. The equations show that the coefficient of ultrasonic velocity and nonlinear acoustic parameter B/A are closely related to molecular interactions. These nonlinear ultrasonic parameters reflect some information of internal structure and outside status of the medium or mixtures. From the exponent of repulsive forces of the molecules, several thermodynamic parameters, pressure and temperature of the medium, the nonlinear ultrasonic parameters and ultrasonic nature of the medium can be evaluated. When evaluating and studying nonlinear acoustic parameter B/A of binary organic liquid mixtures, there is no need to know the nonlinear acoustic parameter B/A of the components. Obviously, the equation reveals the connection between the nonlinear ultrasonic nature and internal structure and outside status of the mixtures more directly and distinctly than traditional mixture law for B/A, e.g. Apfel's and Sehgal's laws for liquid binary mixtures.     

The effect of grain size distribution on the frequency dependence of the ultrasonic attenuation in polycrystalline materials

An expression has been derived for the effect of the grain size distribution in polycrystalline materials on the frequency dependence of the ultrasonic attenuation. It has been shown that two specimens with the same mean grain size can have significantly different ultrasonic attenuations if their grain size distributions are different and that no unique solution in terms of the grain size exists for a particular ultrasonic attenuation against frequency curve. Qualitative agreement has been found between the theory and some of the experimental data available.     

基于双高斯衰减模型的超声回波处理方法

信号降噪与特征提取是超声检测数据处理的关键技术.基于超声信号有特定结构而噪声和超声信号的结构无关,本文提出一种旨在解决强噪声背景下超声回波的参数估计和降噪问题的方法.该方法将超声回波的参数估计和降噪问题转换为函数优化问题,首先根据工程经验建立超声信号的双高斯衰减数学模型,然后根据观测回波和建立的超声信号模型确定目标函数,接着选择人工蜂群算法对目标函数进行优化从而得到参数的最优估计值,最后由估计出的参数根据建立的超声信号数学模型重构出无噪的超声估计信号.通过仿真和实验表明本文方法可以准确估计出信噪比大于-10 dB的含噪超声回波中的无噪信号,且效果优于基于自适应阈值的小波降噪方法和经验模态分解方法;此外相比常用的指数模型和高斯模型,本文提出的双高斯衰减超声信号模型与实测超声信号更接近,其均方误差为9.4×10~(-5),波形相似系数为0.98.