Weakly nonlinear focused ultrasound in viscoelastic media containing multiple bubbles

To facilitate practical medical applications such as cancer treatment utilizing focused ultrasound and bubbles, a mathematical model that can describe the soft viscoelasticity of human body, the nonlinear propagation of focused ultrasound, and the nonlinear oscillations of multiple bubbles is theoretically derived and numerically solved. The Zener viscoelastic model and Keller–Miksis bubble equation, which have been used for analyses of single or few bubbles in viscoelastic liquid, are used to model the liquid containing multiple bubbles. From the theoretical analysis based on the perturbation expansion with the multiple-scales method, the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation, which has been used as a mathematical model of weakly nonlinear propagation in single phase liquid, is extended to viscoelastic liquid containing multiple bubbles. The results show that liquid elasticity decreases the magnitudes of the nonlinearity, dissipation, and dispersion of ultrasound and increases the phase velocity of the ultrasound and linear natural frequency of the bubble oscillation. From the numerical calculation of resultant KZK equation, the spatial distribution of the liquid pressure fluctuation for the focused ultrasound is obtained for cases in which the liquid is water or liver tissue. In addition, frequency analysis is carried out using the fast Fourier transform, and the generation of higher harmonic components is compared for water and liver tissue. The elasticity suppresses the generation of higher harmonic components and promotes the remnant of the fundamental frequency components. This indicates that the elasticity of liquid suppresses shock wave formation in practical applications.     

Ultrasonic devulcanization of waste rubbers: Experimentation and modeling

Continuous ultrasonic devulcanization of ground tire rubber (GRT) and styrene-butadiene rubber (SBR) is considered. Experiments are performed under various processing conditions. Two recipes of SBR with different amounts of polysulfidic linkages are utilized. Gel fraction and crosslink density of devulcanized rubbers are measured and a unique relationship between them is established. Die characteristics with and without imposition of ultrasonic waves are determined. Devulcanized samples are revulcanized and mechanical properties are measured. In some cases, properties of revulcanized SBR samples exceeded those of virgin vulcanizates. This is explained based on the presence of a double network in the revulcanized rubber. A modification of acoustic cavitation and flow modeling of ultrasonic devulcanization of SBR and GRT is proposed using a concept of effective viscosity characterizing the flow of vulcanized particles before devulcanization combined with a shear rate, temperature and gel fraction-dependent viscosity of devulcanized rubber. Velocity, shear rate, pressure, and temperature field along with gel fraction, crosslink density and number of bonds broken are simulated. Predicted data on gel fraction, crosslink density, and pressure using the present modification of the model are found to be closer to experimental data then previously reported.Dedicated to the memory of Professor Tasos C. Papanastasiou     

Wave propagation in multi-wire strands by wavelet-based laser ultrasound

Methods based on guided ultrasonic waves are gaining increasing attention for the non-destructive inspection and condition monitoring of multi-wire strands used in civil structures such as prestressing tendons and cable stays. In this paper we examine the wave propagation problem in seven-wire strands at the level of the individual wires comprising the strand. Through a broad-band, laser ultrasonic setup and a time—frequency wavelet transform processing, longitudinal and flexural waves are characterized in terms of dispersive velocity and frequency-dependent attenuation. These vibrating frequencies propagating with minimal losses are identified as they are suitable for long-range inspection of the strands. In addition, the wave transmission spectra are found to be sensitive to the load level, suggesting the potential for continuous load monitoring in the field.     

Sonochemical Synthesis of Gold Nanoparticles by Using High Intensity Focused Ultrasound

The sonochemical synthesis of gold nanoparticles (GNPs) with different shapes and size distributions by using high‐intensity focused ultrasound (HIFU) operating at 463 kHz is reported. GNP formation proceeds through the reduction of Au³⁺ to Au⁰ by radicals generated by acoustic cavitation. TEM images reveal that GNPs show irregular shapes at 30 W, are primarily icosahedral at 50 W and form a significant amount of nanorods at 70 W. The size of GNPs decreases with increasing acoustic power with a narrower size distribution. Sonochemiluminescence images help in the understanding of the effect of HIFU in controlling the size and shapes of GNPs. The number of radicals that form and the mechanical forces that are generated control the shape and size of the GNPs. UV/Vis spectra and TEM images are used to propose a possible mechanism for the observed effects. The results presented demonstrate, for the first time, that the HIFU system can be used to synthesise size‐ and shape‐controlled metal nanoparticles.     

超声波辐射下光致变色螺噁嗪类化合物的快速合成

在超声波辐射条件下,以Fischer碱、1-亚硝基-2,7-二羟基萘为原料,无水乙醇为溶剂快速合成了三个螺嗪类光致变色化合物,通过1 H NMR、IR对目标产物的结构进行了表征,讨论了超声辐射时间对合成产率的影响,利用超声波法合成螺噁嗪类光致变色化合物反应速率快、产率有所提高.     

单模聚焦微波辅助合成1-乙基-3-羧甲基咪唑四氟硼酸盐离子液体

以1-乙基咪唑为原料,采用discover环形单模聚焦微波合成仪合成了1-乙基-3-羧甲基咪唑四氟硼酸盐离子液体,对产品结构进行了表征及热性分析,并测定了粘度、密度、表面张力、电化学窗口等物化性能,同时考察了合成离子液体对淀粉的溶解性能.结果表明,单模聚焦微波辐射合成具有速度快、时间短、反应条件温和等优点,产品产率为88.23％,其密度、粘度、表面张力与温度均呈线性关系,且随温度升高而减小.与水溶剂相比,合成的离子液体对可溶性淀粉具有较高的溶解度,为淀粉及其衍生物的均相衍生化反应提供了理论基础.     

超声刀在甲状腺手术中保护喉返神经及入喉处甲状腺组织的应用效果观察

目的探讨超声刀在甲状腺手术中对于喉返神经及入喉处甲状腺组织的保护作用。方法选取2016年1月至12月间广东省遂溪县人民医院收治的120例甲状腺疾病的患者,随机分为对照组和观察组,每组60例,对照组采用传统电刀手术,观察组采用超声刀进行手术,比较两种手术方式的效果以及对喉返神经及入喉处甲状腺组织的影响。结果相较于传统电刀手术,采用超声刀可明显缩短腺体切除时间和手术总时间,减少术中出血量,差异具有统计学意义(P0.05);两种手术方式在术后引流量和住院时间方面比较,差异无统计学意义(P0.05);观察组患者喉返神经损伤以及甲状旁腺功能低下的发生率低于对照组,但是两组间差异无统计学意义(P0.05),所有观察组患者的声音嘶哑现象均于术后3个月内恢复,而对照组有3例于3~6个月恢复,2例1年以上未好转。结论在甲状腺手术最终采用超声刀可明显缩短手术时间,减少术中出血量,利于术中对喉返神经和入喉处甲状腺组织的辨认和保护,是一种安全可行的手术方法。     

S波段微波热致超声成像系统研究

微波热致超声成像技术通过向物体发射微波脉冲, 导致物体吸收电磁波温度迅速升高, 产生瞬时压力波, 从而激发产生超声波信号, 通过传感器对产生的超声波信号进行采集并成像, 最终还原了反映物体吸收电磁波能量特性的图像, 由于此方法兼具了微波成像的高对比性和超声成像的高分辨率特点, 理论上验证了热声成像技术对早期乳腺肿瘤检测的可行性. 本实验兼顾系统成像深度和分辨率, 采用S波段的微波脉冲信号源对物体进行辐射, 利用圆形扫描方式对待测物体进行检测, 同时为了更好的验证成像性能, 本实验同时使用了肿瘤仿体及实际生物组织进行成像实验. 通过实验分析, 验证了该系统对肿瘤仿体和生物组织检测的有效性, 以及系统的高分辨率和高对比度特性, 为早期乳房肿瘤检测提供了进一步的理论支撑.     

超声浸渍对费托合成Co/Zr/SiO2催化剂性能的影响

采用超声浸渍法制备了费托合成Co/Zr/SiO2催化剂,考察了超声波功率对催化剂费托反应性能的影响,并运用N2物理吸附、X射线衍射、H2程序升温脱附、H2程序升温还原和透射电子显微镜对催化剂进行了表征,结果表明,超声波处理可以增大催化剂的比表面积,减小金属Co的粒径,并使其较为均匀地分散于载体表面,其中以高功率超声波作...