Ultrasonic waves in diluted and densified suspensions

A theory of propagation of stress waves in diluted and densified suspensions is developed to make the theoretical basis for analysis of ultrasonic waves through these media. The formulae for the phase velocity and the attenuation coefficient are determined as the function of wave frequency and the suspension structure parameter, which is the volume or mass fraction of the solid phase. These formulae can be use, after suitable calibration, for determination of the solid volume fraction in diluted suspensions, and the solid mass fraction or the water content in densified suspensions, that is, parameters that characterize the structure of a suspension. These structure parameters can be determined by measuring the transition time of ultrasonic wave through a given distance of suspension. The phase velocity dispersion curves and the attenuation coefficients determined theoretically and experimentally are plotted as a function of the volume fraction of the solid phase for dilute suspension, or the solid mass fraction for densified suspension.     

高密度超细颗粒高浓度悬浊液超声衰减的数值模拟分析

以拓展耦合相ECP理论模型为基础,通过对高浓度超细二氧化钛-水悬浊液和玻璃微珠-水悬浊液中超声衰减的数值计算分析,讨论了高密度差异颗粒两相介质在高浓度情况下,超声频率、颗粒粒径大小、颗粒浓度对超声波衰减的影响,为高密度超细颗粒在高浓度悬浊液中颗粒粒度和浓度的超声波测量提供理论支持。     

Device for aeration and mixing of cell and organelle suspensions during NMR experiments

A device for aeration and mixing of cell or organelle suspensions in a vertical bore NMR magnet is described. Multiple external sensors (e.g., ion-selective electrodes) may be immersed in the suspension within the bore of the magnet. The sensors are positioned to avoid noise due to contact with gas bubbles and proximity to the probe head. The required sample volume is minimised. The modular design of components permits the use of the device in magnets of various internal dimensions, or with probe heads of different sample tube diameter, by modification of the simpler components of the assembly.     

Size-selective separation of submicron particles in suspensions with ultrasonic atomization

Aqueous suspensions containing silica or polystyrene latex were ultrasonically atomized for separating particles of a specific size. With the help of a fog involving fine liquid droplets with a narrow size distribution, submicron particles in a limited size-range were successfully separated from suspensions. Performance of the separation was characterized by analyzing the size and the concentration of collected particles with a high resolution method. Irradiation of 2.4 MHz ultrasound to sample suspensions allowed the separation of particles of specific size from 90 to 320 nm without regarding the type of material. Addition of a small amount of nonionic surfactant, PONPE20 to SiO₂ suspensions enhanced the collection of finer particles, and achieved a remarkable increase in the number of collected particles. Degassing of the sample suspension resulted in eliminating the separation performance. Dissolved air in suspensions plays an important role in this separation.     

一种测量功率超声振动系统振速比的简单方法

本文提出了一种测量功率超声振动系统中振动速度比的简单方法。与传统的测量方法相比,本方法将力学量转变为电学量的测量,将绝对测量变成了相对测量,降低了对实验设备的要求,有利于提高测试精度。     

Study on rectangular ultrasonic radiator of flexural resonant vibration in high modes

Based on the theory of coupling vibration and flexural vibration of thin rod of rectangular cross section, the fiexural vibration of rectangular thin plate was studied. The frequency equation was derived under the condition of freeboundaries. The normal modes and the relation between the normal modes and the resonant frequency were obtained. Experiments showed that the calculated resonant frequencies agree well with the measured results, and the rectangular thin plate in flexural vibration has abundant resonant frequencies. The radiator of flexural vibration used in ultrasonic cleaning and other techniques has the advantages of large acoustic radiating area, uniform acoustic field and easy adjustment of resonant frequencies, proving that it is a promising ultrasonic source.     

序列脉冲激光中的原子共振辐射

本文详细研究了序列脉冲激光与二能级原子共振作用的Bloch方程的解。在此基础上,结合数值计算,求出了序列脉冲作用下二能级原子的共振辐射谱;并得出如下结论:对满足K_1/K=1的原子(如仅受自然展宽的气体原子),序列脉冲差不多等效于一单色激光场;而对满足K_1/K(?)=1的原子(比如一些固体原子)序列脉冲场中边频成份也表现出较强的作用,辐射谱呈现出多边峰现象。     

Universality in the critical dynamics of fluids: ultrasonic attenuation

In contrast to the binary liquids, the order-parameter relaxation rates in the pure fluids are greatly affected by a large non-critical component. With the appropriate crossover correction to dynamic scaling, we restore universality and demonstrate that the ultrasonic data for both the one- and two-component fluids fall on the same scaling plot.     

使用共振多程光声池的CO_2和SF_6的无多普勒饱和吸收光谱

本文使用共振多程池的光声探测法对CO_2和SF_6分子的无多普勒饱和吸收光谱进行了实验研究.测量CO_2的吸收凹陷约为2.5MHz,实验中观察到5个SF_6的吸收凹陷、凹陷深率约为1.9MHz.两种情况的分辨率均大于10~7.     

On the validity and improvement of the ultrasonic pulse-echo immersion technique to measure real attenuation

A fundamental assumption embraced in conventional use of the ultrasonic pulse-echo immersion technique to measure attenuation in solid materials is revisited. The cited assumption relies on perfect and immutable adhesion at the water to sample interface, a necessary condition that allows calculating the reflection coefficient at any interface from elastic wave propagation theory. This parameter is then used to correct the measured signal and obtain the real attenuation coefficient of the sample under scrutiny. In this paper, cases in which the perfectly cohesive interfacial condition is not satisfied are presented. It is shown also that in those cases, the repeatability of the conditions at the interface is always uncertain. This implies that the reflection coefficients are unknown, even when density is known. A new method of simultaneously measuring the reflection coefficients for both exposed interfaces that are normal to the transducer, and the attenuation coefficient of the specimen is developed and is presented here. The robustness of the new method is proven, as we demonstrate that the proper value of attenuation is achieved independently of the continuously varying interfacial conditions of these non-ideal cases.     

Filamentary coagulation of heavy particles suspended in water in an ultrasonic field

A stable formation of long thin filaments involving heavy particles (heavier than water) suspended in water in an acoustic resonator was observed. The filaments consisted of regularly spaced thin disks formed by coalescent particles. The particles in the disks were tightly packed forming almost solid structures. The disks were arranged perpendicularly to the filament axis and were spaced at half-sound-wavelength intervals. The diameter of the disks was about half-wavelength. The length of the filaments was about hundreds of the sound wavelength. Experiments were performed with particles of different natures and sizes. The filaments were not destroyed under wide variations of sound frequency, acoustic power, length of resonator, size and configuration of the mirror, or its angle of rotation. The particles suspended in water not only visualized the acoustic field but also affected its configuration. The formation of filaments was explained by a nonthermal self-focusing of sound in the resonator, which was caused by the decrease in sound velocity in the region of maximum concentration of particles due to coagulation in the inhomogeneous sound field.     

Cavitation intensity of water under practical ultrasonic cleaning conditions

When measuring cavitation during cooling of thermally degassed water cavitation maxima are frequently observed at various temperatures. Relations between this phenomenon and frequency and power of ultrasounds as well as air content in water have been examined. It was found out that the secondary water regassing with air is the reason.     

Characterization of TiO<Subscript>2</Subscript> nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO₂ deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO₂ nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3–2.5 wt.%) and at different shear rates ( = 10–250 s⁻¹). The influence of these parameters on the quality of TiO₂ films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO₂ nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s⁻¹). For the suspension with 1 wt.% TiO₂ containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕ_m) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕ_m = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO₂ deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1–9, being pH ≈ 5 the optimal value for this system in terms of EPD results.     

Dielectric and ultrasonic investigation of phase transition in cuinp2s6 crystals

Investigation results of dielectric and ultrasonic properties of layered CuInP₂S₆ crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4?K (0.635?eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order–disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP₂S₆ crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature.     

多腔虚阴极振荡器研究

 提出了一种具有预调制腔、主谐振腔和提取腔组成的多腔轴向提取虚阴极振荡器结构。腔体特性分析表明其在工作频段可以获得更高的提取效率。粒子模拟显示该结构在电压700 kV,电流23 kA的条件下,可输出功率大于1.7 GW,频率4.0 GHz,功率效率大于10％的微波。初步的实验研究获得了辐射功率约700 MW,频率约4.1 GHz的微波输出。对实验结果的进一步分析表明,通过适当加大器件虚阴极振荡工作区微波管直径的方法可以有效改善器件的谐振性能,从而获得更好的工作性能。     

Macroscopic resonant tunneling in an rf-SQUID flux qubit

We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit.The dependences of the macroscopic resonant tunneling on the barrier height of the potential well,the flux bias and the initial state are investigated.Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.     

Velocity study in an ultrasonic reactor

In order to determine the parameters required to describe and to optimize sonochemical reactors, we have investigated the water flow inside such a reactor. With this aim, the experimental velocity field has been measured by tomography laser. The influence of certain parameters such as the electric power, the water height and the fluid viscosity has been evaluated. At the same time, the water movement has been studied theoretically using Nyborg's model. We have tried to improve this model by considering a three-dimensional velocity.