生物物理条件变化对超声溶血的影响

如果生物组织中存在稳定的气泡,则声强低于空化阈值的超声波即可引起非热致的一些重要的生物效应。为深入了解其机理及评估其对医学超声技术安全性的关系,生物悬浮液常被用于低声强生物效应的研究。要在悬浮液内产生稳定气泡,可置一具有含气微孔的疏水薄膜于悬浮液中。本文研究在直径为3.7μm的微孔薄膜附近,由1.9MHz超声波所引起犬血球(密度为0.5％)的溶血现象,随生物物理环境的变化。 实验中,考虑到微孔结构(直径3.7μm,长12μm)的共振频率,超声波频率选在1.9MHz。一个高3.2mm,直径22.5mm的样品室被置于离换能器14cm     

超声波去除铝表面残留液滴的试验研究

对频率20 kHz的超声波作用下竖直铝表面残留液滴的去除过程进行了快速可视化观测。对不同超声功率下铝表面液滴的去除时间进行了对比分析,同时对超声波作用下不同粒径液滴的去除时间进行了对比研究。试验结果表明,超声波可以瞬间去除竖直铝表面附着液滴且铝表面液滴去除过程可分为动力变形期以及破碎雾化期两个阶段。随着超声功率的增大,液滴的动力变形期变短,液滴越早进入破碎雾化期;此外,液滴粒径的增大使得液滴的动力变形时间以及破碎雾化时间均显著增加。结果验证了超声波去除铝板表面残留液滴的可行性,为有效去除表面残留液滴提供了可能。     

弹黏塑性热点模型的冲击起爆临界条件

非均质炸药冲击起爆临界条件是武器传爆系列设计以及安全性能评估中十分关注的问题。基于Kim弹黏塑性热点模型,通过数值求解冲击波作用下炸药局部热点的温升模型,获得了TATB和HMX基炸药在不同冲击压力作用下的冲击起爆临界阈值,定量分析了孔隙度对炸药冲击起爆临界阈值的影响。与实验数据对比,结果表明:在1~10GPa范围内,采用该模型计算得到的冲击起爆临界阈值与一维短脉冲试验相符,对应的炸药冲击起爆临界阈值近似为一常量;当压力大于10GPa时,非均匀炸药的冲击起爆机制开始由局部热点机制向整体均匀加热机制转变;在一定压力范围内,炸药孔隙度越大,冲击起爆临界阈值越小。     

光动力治疗中热效应的理论分析与计算

基于Pennes传热方程，从理论上分析了光动力治疗中激光作用所引起的组织温升的变化.结果表明，激光照射在生物组织内形成热源，该热源在一维生物组织空间引起组织的温升一般随时间呈指数形式增大，随激光照射处的距离呈指数减少.激光照射生物组织产生热效应，存在一个最小阈值光剂量，仅当照射的激光剂量大于阈值光剂量时，才能产生热效应.阈值光剂量大小由生物组织的光学参量和热物性参量决定，并随激光照射处的距离呈指数增加     

基于蒙特卡罗模拟的超声辅助OCT成像研究

通过蒙特卡罗模拟方法研究了超声波提高OCT成像质量的机理,以宏观经典理论和微观量子理论分别阐述了光和超声的相互作用,建立了存在超声辅助时光在生物组织中传播的模型,模拟了有超声辅助和无超声辅助两种情况下生物组织多次散射光的分布.模拟结果表明,与光平行射入生物组织的超声波能够使OCT成像系统中的多次散射光降低80%,携带组织信息的单次散射光在组织返回光中所占比重增大为无超声辅助时的2倍,从而增大了OCT成像的探测深度及图像对比度.     

临界及非临界相位匹配KTP光学参量振荡器

报道了利用Nd:YAG激光器二次谐波532nm及基频波1064nm作抽运源,采用临界及非临界相位匹配方式抽运KTP光学参量振荡器的实验结果.实验中获得了具有实用价值的1.53-1.84um人眼安全激光,KTP光学参量振荡器输出总量最大达130mJ,最高能量转换效率64%.分析比较了调谐范围、离分角、接收角、阈值及转换效率,讨论离分角对参量输出的光束质量、转换效率的影响.     

生物组织电穿孔中的热效应研究

本文对生物组织电穿孔中的热效应问题进行了计算研究。结果表明生物组织电穿孔过程中,选用不当的脉冲电压参数,会对组织造成严重的热损伤。若采用相同的烧伤阈值来描述热损伤范围,则相同电脉冲参数条件下在体组织比离体组织受到的热损伤更大。     

石英玻璃球撞击刚性壁的破碎过程

利用高速枪对石英玻璃球撞击刚性靶板进行了实验研究,分析了不同速度下球体的破碎过程和失效模式。当冲击速度低于临界破坏速度时,石英玻璃球以略低于原速从靶板回弹;当超过临界破坏速度时,球体呈现“压缩破碎区-表面剥落区-剪切破坏区”的破坏结构;进一步提高碰撞速度,剪切破坏区的扩展导致球体碎裂为若干“月牙状”的碎块;更高撞击速度下,石英玻璃球发生坍塌式破碎,在远离撞击端处产生层裂现象。利用离散元软件对球体的撞击破坏过程进行了模拟研究,球体在高速碰撞下的破碎可以分为弹性压缩、整体破碎和二次撞击3个阶段。球体碎裂前Hertz接触理论可以较好描述其撞击力,而破碎后的撞击力由于碎裂卸载远小于理论值,且偏差随冲击速度逐渐增加。     

生物受激发光的管流实验研究

构建了管流场刺激下的生物受激发光实验平台,分析了管流场中的水动力特性和影响生物受激发光的水动力因素。采用光子计数器测量了3种腰鞭毛虫在管流刺激下的受激发光特性。实验结果表明:海洋生物体受激发光的水动力影响因素是流场剪应力,引起生物体发光的剪应力存在剪应力阈值,只有当剪应力大于阈值,生物体才能被激发发光。根据生物体种类的不同,刺激生物受激发光的剪应力阈值为0.05~0.29N/m2。通过对实验数据的分析得出了生物受激发光的发光强度与剪应力的关系。     

一类非线性神经网络系统的超阈值随机共振现象

超阈值随机共振可用来解释一些生物现象.本文对一类非线性多阈值神经网络模型的超阈值 随机共振现象进行了探讨. 首先推导出了系统输出互信息的表达式, 然后分析了系统参数及噪声对互信息量的影响.通过数值计算发现,在阈值系统的信息传递过程中, 根据乘性噪声和加性噪声对系统信息传递影响的不同, 对系统的阈值进行恰当选取是至关重要的. 此外, 还发现系统的阈值单元数目越多, 超阈值随机共振现象就越容易出现.     

超声滚压中的空化现象*

在超声滚压加工中引入切削液后可能会产生空化现象,由此产生的微射流和冲击波对超声表面强化将有积极作用。为研究超声滚压加工中空化现象是否存在及空化效应在超声滚压中的作用,本文首先分析了超声滚压中的空化阈值,然后进行了染色法试验和超声滚压后试样氧元素能谱分析,最后通过超声滚压加工对比试验研究了空化效应对加工后材料表面粗糙度和显微硬度的影响。研究发现,超声滚压加工中的声压幅值远大于空化阈值,满足空化存在的必要条件;超声滚压中发生了明显的卡纸染色现象,引入切削液后工件超声滚压加工表面氧元素含量显著提高,表明超声滚压中发生了空化现象。超声滚压加工中的空化效应能进一步降低工件表面粗糙度和提高表面显微硬度,有利于提高工件表面强化质量。本研究为空化效应在超声滚压中的积极利用提供了依据。     

Effect of sparse basis selection on ultrasonic signal representation

Recently, adaptive sparse representations of ultrasonic signals have been utilized to improve the performance of scanning acoustic microscopy (SAM), a common nondestructive tool for failure analysis of microelectronic packages. The adaptive sparse representation of an ultrasonic signal is generated by decomposing it in a learned overcomplete dictionary using a sparse basis selection algorithm. Detection and location of ultrasonic echoes are then performed on the basis of the resulting redundant representation. This paper investigates the effect of sparse basis selection algorithms on ultrasonic signal representation. The overcomplete independent component analysis, focal underdetermined system solver (FOCUSS), and sparse Bayesian learning algorithms are examined. Numerical simulations are performed to quantitatively analyze the efficiency of ultrasonic signal representations. Experiments with ultrasonic A-scans acquired from flip-chip packages are also carried out in the study. The efficiency of ultrasonic signal representations are evaluated in terms of the different criteria that can be used to measure its performance for different SAM applications, such as waveform estimation, echo detection, echo location and C-scan imaging. The results show that the FOCUSS algorithm performs best overall.     

Influence of thresholding procedures in ultrasonic grain noise reduction using wavelets

Wavelet transform based techniques are used for signal-to-noise ratio (SNR) enhancement in ultrasonic non-destructive testing and evaluation of strong sound scattering materials. The overall denoising performance of a wavelet signal processor is conditioned by several processing parameters, including the type of wavelet, thresholding method, and threshold selection rules. Different thresholding procedures and threshold selection rules are analysed in this paper using the discrete wavelet transform and decomposition level dependent thresholds. Global performance is evaluated by means of the SNR enhancement using synthetic grain noise registers with an incrusted flaw signal, with different values of the input SNR, and experimental ultrasonic traces acquired from a carbon fibre reinforced plastic composite block.     

碟形超声变幅杆的设计

优化超声变幅杆的形状结构可有效地提高水域声场分布和空化区域,提升对水域超声空化效果。通过模拟分析发现传统超声变幅杆在水域中具有声场分布均匀性差、变幅杆端部声压高等特征,不利于声波在水域中传播。基于此,提出并优化设计了一种具有碟形结构的变幅杆,位于变幅杆的最大振幅处的碟形结构,有更大的振动位移;模拟表明其水域声场和声压均衡度显著优于传统变幅杆,铝箔空化腐蚀实验进一步证实了其水域中的声压分布均匀性。同时,实验通过铝箔的空化腐蚀、KI剂量测定及工件表面油渍去除对比了传统变幅杆和碟形变幅杆,分析表明碟形变幅杆所在水域中有较大的空化腐蚀区域,腐蚀速率明显提升,声化学反应速率提高,油渍去除程度增强,说明了设计的碟形变幅杆能够促进空化泡的产生,增加水域空化区域。     

The efficiency of ultrasonic oscillations transfer into the load

The results of ultrasonic action to the substances have been presented. It is examined, the correlation between the electrical parameters of ultrasonic equipment and acoustic performances of the ultrasonic field in treating the medium, the efficiency of ultrasonic technological facility, and the peculiarities of oscillations introduced into the load under cavitation development. The correlation between the acoustic powers of oscillations securing the needed level of cavitation and desired technological effect, and the electrical parameters of the ultrasonic facility, first of all, the power, is established. The peculiarities of cavitation development in liquids with different physical-chemical properties (including the molten low-melting metals) have been studied, and the acoustic power of oscillations introduced into the load under input variation of electric power to the generator has been also estimated.     

超声波辅助酸蚀提高熔石英损伤阈值

为了提高熔石英元件表面抗激光损伤阈值,利用超声波辅助HF酸研究平滑光学元件表面缺陷形貌和去除刻蚀后残留物效果,通过扫描电子显微镜电镜和原子力显微镜记录表面形貌结构,以及单脉冲激光辐照测试抗损伤阈值确定实验参数。研究表明,超声波场的引入能催化HF酸的刻蚀速率、提高钝化效果并且更易剥离嵌入的亚μm级杂质粒子。经过实验测试,获得了熔石英类元件相匹配的超声辅助HF酸刻蚀实验参数,研究结果对应用超声波辅助HF酸研究熔石英表面抗激光损伤有重要意义。     

Double-structured ultrasonic high frequency reactor using an optimised slant bottom

The present work has been carried out in order to design a new type of ultrasonic reactor consisting of a double-structured tank. The inner working compartment is built with a slant bottom to allow a better ultrasonic transmission. This paper reports the effect of the inclination angle on acoustic efficiency for several different plates, e.g. two plates made of glass (2 mm and 3 mm thickness) and one made of PVC (3 mm thickness). The acoustic efficiency was determined as the ratio of the signal measured by a hydrophone in the presence of the plate to that signal in the absence of the plate. Having optimised the system, the ultrasonic powers in the inner and the outer compartments of the slant bottom reactor were determined by hydrogen peroxide dosimetry.     

Noise reduction in ultrasonic NDT using undecimated wavelet transforms

Translation-invariant wavelet processing is applied to grain noise reduction in ultrasonic non-destructive testing of materials. In particular, the undecimated wavelet transform (UWT), which is essentially a discrete wavelet transform (DWT) that avoids decimation, is used. Two different UWT processors have been specifically developed for that purpose, based on two UWT implementation schemes: the "à trous" algorithm and the cycle-spinning scheme. The performance of these two UWT processors is compared with that of a classical DWT processor, by using synthetic grain noise registers and experimental pulse-echo NDT traces. The synthetic ultrasonic traces have been generated by an own-developed frequency-domain model that includes frequency dependence in both material attenuation and scattering. The experimental ultrasonic traces have been obtained by inspecting a piece of carbon-fiber reinforced plastic composite in which we have mechanized artificial flaws. Decomposition level-dependent thresholds, which are suitable for correlated noise, are specifically determined in all cases. Soft thresholding, Daubechies db6 mother wavelet and the three well-known threshold selection rules, Universal, Minimax and SURE, are applied to the different decomposition levels. The performance of the different de-noising procedures for single echo detection has been comparatively evaluated in terms of signal-to-noise ratio enhancement.     

Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.     

Measurement of ultrasonic power of cylindrical horns

Monitoring high power ultrasonic equipment and the determination of the efficiency of transducers depends upon the methods used to measure ultrasonic power. This paper discusses several such methods used on longitudinally vibrating horns, and describes in detail a new electronic method of measuring acoustic power.