测量液体非线性参量的光声方法

本文描述了一种用光声脉冲测量液体非线性参量B/A的新方法。用聚焦脉冲激光束通过光击穿机制在液体中激发光声脉冲。在测量距离范围内,光声脉冲声压幅值随传播距离的变化接近球面扩展衰减规律。根据光声脉冲传播一定距离后前沿上升时间的变化,测定了液体的B/A。和有限束宽的平面脉冲声波相比,用球面脉冲声波可以避免衍射的影响。用此法测量了水的非线性参量,得到了满意的结果。     

Study of acoustic nonlinearity parameter B/A for seawater

I.Introductionlnthcearlyfifties,thercweremanyresearchworksonpropagatingmechanismofultrasonicwaveinseawater,itssoundve1ocity,absorptionandattenuation.Withthedevelop-mcntandapp1icationofhigh-powersoundsourcc,suchasSONARinnavy,thenonlinearacousticaleffectscausedbyfiniteamplitudeu1trasonicwavetravellingthroughseawaterbecomemoreevident.Thcrcfore,tostudythesenonlinearacousticaleffectsandtheirinfluenccsalsobecomcsmuchmoreimportant.Moreover,ithasbeenexpccted'foralongtimetogetalowfrequencyandhighlydi…     

Acoustic nonlinearity parameter B/A determined by means of thermodynamic method under elevated pressures for alkanediols

The so-called Beyer nonlinearity parameter B/A is calculated for 1,2- and 1,3-propanediol, 1,2-, 1,3-, and 1,4-butanediol, as well as 2-methyl-2,4-pentanediol by means of a thermodynamic method. The calculations are made for temperatures from (293.15 to 318.15) K and pressures up to 100 MPa. The decrease in B/A values with the increasing pressure is observed. In the case of 1,3-butanediol, the results are compared with corresponding literature data. The consistency is very satisfactory. A simple relationship between the internal pressure and B/A nonlinearity parameter has also been studied.     

Influences of tissue composition and structural features of biological media on the ultrasonic nonlinearity parameter

The Acoustic nonlinearity parameter is an important parameter innonlinear acoustics.In this article,the nonlinearity parameter B/A of normaland eight kinds of pathological porcine liver tissues were measured by finiteamplitude insert-substitution method.The mixture law for nonlinearityparameter is used to analyze and predict the volume fractions of the compo-nents in a given tissue.It was found that the nonlinearity parameter is sensitiveto the pathological forms of biological tissues and the values of B/A dependon the tissue composition and structural features.     

混合算法中的耦合判据

混合算法是研究跨尺度流动问题的重要手段之一. 分界面位置以及分界面两侧的信息传递是混合算法需要解决的两个主要问题. 分析推导了现有耦合判据之间的关系,给出耦合判据的统一形式及参数的选取范围. 关键词： 混合算法 耦合判据     

Photoacoustic detection of microcracks induced in BK7 glass by focused laser pulses

An experimental investigation on the induced damage by accumulative pulses generated by a Nd:YAG laser beam focused into the bulk of the BK7 glass is reported in this work. The laser was operated at the single-pulse damage energy threshold of the sample. The optical detonation generates a shock wave emission and microcrack formation. The induced photoacoustic wave emerging from the sample was monitored by piezoelectric detection. These signals provide a simple, reliable and highly sensitive indication of damage, processes involved, and the most appropriate laser parameters for two- and three-dimensional engraving.     

Measurement under high pressure of the nonlinearity parameter B/A in glycerol at various temperatures

An experimental study of some assorted glycerol properties is carried out in order to determine, under high static pressure, the glycerol nonlinearity parameter B/A against temperature by a modified isentropic method. The static pressure and temperature ranges exploited in this experimental investigation, of various glycerol properties, are extended respectively from 0.1 to 100 MPa and from 10 to 100 °C. The static pressure step of two consecutive measurements is 10 MPa and the temperature step is 10 °C. The measured values show that, in glycerol, the density ρ₀ and the infinitesimal ultrasonic wave velocity c₀ increase monotonically with the imposed static pressure and decrease monotonically with temperature. The present investigation shows that the nonlinearity parameter B/A is a function of the imposed static pressure and temperature. The accuracy of the measured B/A values is estimated at about ±2%.     

基于不同频率成份衰减矫正的光声成像方法

根据超声衰减理论,研究了光声信号不同频率成份随距离的衰减差异,及其对光声图像重建的影响;提出了对光声信号不同频率成份进行衰减矫正的成像方法,此方法增强了光声信号的高频成份,突出了吸收体的边界变化和细微的结构特征,提高了成像系统分辨率,实验结果显示系统分辨率由0.3 mm提高到0.2 mm.实验所用的光源为YAG激光器,波长为1064 nm,重复频率为20 Hz,脉宽为6 ns,探测器为针状的PVDF膜水听器,接收面积的直径为1 mm.     

Effects of experimental parameters on elemental analysis of coal by laser-induced breakdown spectroscopy

The purpose of this work is to improve the precision of the elemental analysis of coal using laser-induced breakdown spectroscopy (LIBS). The LIBS technique has the ability to allow simultaneous elemental analysis and on-line determination, so it could be used in the elemental analysis of coal. Organic components such as C, H, O, N and inorganic components such as Ca, Mg, Fe, Al, Si, Ti, Na, and K of coal have been identified. The precision of the LIBS technique depends strongly on the experimental conditions, and the choice of experimental parameters should be aimed at optimizing the repeatability of the measurements. The dependences of the relative standard deviation (RSD) of the LIBS measurements on the experimental parameters including the sample preparation parameters, lens-to-sample distance, sample operation mode, and ambient gas have been investigated. The results indicate that the precision of LIBS measurements for the coal sample can be improved by using the optimum experimental parameters.     

Relationship between the molecular constant,isothermal volume derivative of thermodynamic Grüneisen parameter,nonlinearity parameter and intermolecular forces in liquids

The isochoric temperature derivative of sound velocity, Beyer’s nonlinearity parameter, the isothermal volume derivatives of thermodynamic Grüneisen parameter and isochoric heat capacity and the repulsive exponent of intermolecular potential are shown to be related to the molecular constant representing the ratio of internal pressure to cohesive pressure of liquids. The calculated values are reasonably satisfactory and explain the experimental results on sound propagation data of liquids. The results have been used to develop further understanding of the significance of molecular constant, fractional free volume and repulsive exponent of intermolecular potential in describing various thermoacoustic and nonlinear properties and the anharmonic behaviour with regard to molecular order and intermolecular interactions in liquids.     

A nondestructive method for estimation of the fracture toughness of CrMoV rotor steels based on ultrasonic nonlinearity

The objective of this paper is to develop a nondestructive method for estimating the fracture toughness (K(IC)) of CrMoV steels used as the rotor material of steam turbines in power plants. To achieve this objective, a number of CrMoV steel samples were heat-treated, and the fracture appearance transition temperature (FATT) was determined as a function of aging time. Nonlinear ultrasonics was employed as the theoretical basis to explain the harmonic generation in a damaged material, and the nonlinearity parameter of the second harmonic wave was the experimental measure used to be correlated to the fracture toughness of the rotor steel. The nondestructive procedure for estimating the K(IC) consists of two steps. First, the correlations between the nonlinearity parameter and the FATT are sought. The FATT values are then used to estimate K(IC) using the K(IC) versus excess temperature (i.e., T-FATT) correlation that is available in the literature for CrMoV rotor steel.     

Photoacoustic measurement of thermal properties and thickness of buried layers in a multilayer film

The photoacoustic model of multilayer with a strong-absorbing surface layer is developed. The phase of ph0toacoustie signal is measured as a function of modulated frequency using apparatus totally controlled by a computer system. The thermal diffusivity, effusivity as well as thickness of several buried layers are obtained independently through the best fit of experimental data according to the theoretical model. The multilayers of thin metal and alloy film are investigated. This method is proved to be valuable particularly in nondestructive examination of subsurface physical properties.     

Photoacoustic cell with black absorber as a detector for spectrophotometric studies

The PAS cell with carbon black absorber is used as a detector for spectrophotometry in an open room. This has immense potential of obtaining absorption speciation information from remote samples.     

Photoacoustic spectra of some laser dyes

Photoacoustic spectra of rhodamine 110, rhodamine 6 G, rhodamine B, rhodamine 101 and coumarin 102 laser dyes have been recorded at room temperature of 25°C in the spectral range of 350–750 nm. These samples were taken in powder as well as in solution forms. For this purpose the closed and the open photoacoustic cells have been used. It is hoped the present study would be useful for characterization of these dyes.     

Carbon as Reference for Normalizing Infrared Photoacoustic Spectra

Photoacoustic spectra of solids¹ are usually “source compensated,” i. e., normalized for differences in source emission at different wavelengths, and such compensation is done by comparing the photoacoustic spectrum of a sample to the emission spectrum of the source measured directly with, say, a photocell,² power meter,³ or photodiode,⁴ or to the photoacoustic spectrum of “carbon” recorded under the same conditions as that of the sample. A variety of carbons has been used for this purpose, including carbon black on silica,⁵ soot from a gas torch,⁶ and acatylene-sooted bakelite,⁷ such a reference substance being assumed to be a flat black absorber. That assumption appears to be valid, as indicated by the close     

多元线性回归提高激光诱导荧光辅助激光诱导击穿光谱技术的准确度

冶金、核工业、污染检测和环境监测等领域对元素分析的需求是必不可少.激光诱导击穿光谱技术作为一种新型的原子光谱分析技术,具有实时快速、对样品几乎无损、可多元素同时分析等特点,因此一直受到广泛的关注.但其分析灵敏度较差的缺点一直限制着该技术的发展.激光诱导荧光辅助激光诱导激光光谱技术能够通过激光共振激发提高分析灵敏度并高效...     

基于红外热辐射光源的光声气体分析仪

研制了一种基于红外热辐射光源的光声气体分析仪,给出了该光声气体分析仪的设计理论、硬件结构、软件系统和实验测试结果。根据红外热辐射光源的光谱特性,通过比较吸收气体在不同吸收带中多线的综合吸收系数,确定了光声池的最优设计参数、滤光片的中心波长和带宽。实验结果表明,该光声气体分析仪对CO,NO和H₂S的极限检测灵敏度分别达到1.6×10-6,4.5×10-6和4.0×10-4(被测气体与背景气体的分压比),并且对0～987×10-6 的CO测量显示了其良好的测量重复精度和线性度。此外,通过增加特定中心波长的滤光片还能够对其他多种小分子气体实现高灵敏度、实时、连续、自动地测量。     

The delay vector variance method for detecting determinism and nonlinearity in time series

A novel ‘delay vector variance’ (DVV) method for detecting the presence of determinism and nonlinearity in a time series is introduced. The method is based upon the examination of local predictability of a signal. Additionally, it spans the complete range of local linear models due to the standardisation to the distribution of pairwise distances between delay vectors. This provides consistent and easy-to-interpret diagrams, which convey information about the nature of a time series. In order to gain further insight into the technique, a DVV scatter diagram is introduced, which plots the DVV curve against that for a globally linear model (surrogate data). This way, the deviation from the bisector line represents a qualitative measure of nonlinearity, which can be used additionally for constructing a quantitative measure for statistical testing. The proposed method is compared to existing methods on synthetic, as well as standard real-world signals, and is shown to provide more consistent results overall, compared to other, established nonlinearity analysis methods.     

Photoacoustic Spectroscopy of Strongly Absorbing Solids: Bismuth Tri-Iodide

We found a need to optically characterize bismuth tri-iodide, BiI₃, which has been used in antireflective thin film coatings on potassium chloride laser windows. We received a 7mm thick, 18mm diameter disc shaped sample of BiI₃ which exhibited a dark gray, glassy, metallic appearance. Several commercial spectrophotometers in the laboratory showed it to be opaque from 0.3μm to 50μm. We therefore decided to see if relevant optical data could be obtained on the sample using an in-house built photoacoustic spectrometer.     

白血病人血液的光声光谱

利用光声光谱对不同类型的白血病患者和正常人的全血进行检测，发现白血病患者与正常人全血光谱图特征峰有明显差异，结果提示患者全血的光声光谱图可能对早期白血病诊断及白血病分型具有较大的临床意义。