Excitation of oscillations of an immiscible liquid interface by a pulsed ultrasound beam parallel to the interface

For several pairs of immiscible liquids, a new opportunity to excite oscillations of their interface by ultrasound pulses propagating parallel to the interface has been discovered experimentally. A plane ultrasound transducer is placed so that the interface between liquids halves its aperture. The evolution of the shape of the interface oscillations under the variation of the amplitude and duration of excitation pulses, as well as of the distance from the transducer, has been analyzed. The possibility of the excitation of various modes of the interface oscillations in a bounded volume has been revealed.     

Schlieren visualization of ultrasonic wave fields with high spatial resolution

The visualization of ultrasonic wave fields in optically transparent liquids using the acousto-optic interaction is a well proven tool for the experimental investigation of wave propagation including wave field interaction effects with certain discontinuities and obstacles like reflection, refraction, and diffraction effects as well as for transducer testing and design. For high resolution visualization of wave fields including pulsed waveforms, pulsed light sources and sensitive optical imaging sensors with certain specifications are needed. In this paper the technical requirements of optical and electronic components for high resolution visualization of ultrasound wave fields will be presented. Also, specifications and operation results of a new designed, inexpensive Schlieren optical system will be presented, which is capable of pulsed wave field visualization in the MHz frequency range. The spatial resolution is high enough, not only for accurate beam shape and wave pattern visualization, but also for a gray-scaled display of wave amplitudes including amplitude zero crossings in ultrasound pulses. Consequently, ultrasonic wavelengths can be visualized quantitatively as well as wavelength changes of the ultrasound pulses while traveling through transparent media with different sound velocities. Results to be presented will include 2 MHz and 10 MHz experiments using single transducers as well as linear arrays of commercial medical scanners during their standard operation showing the system beamforming characteristics.     

Monodisperse drop formation in square microchannels

The electrohydrodynamic instability of the interface between two liquids with different physical and electrical properties in plane Poiseuille flow is used to form monodisperse droplets in a square channel. The drop size and formation rate are controlled by simply controlling the flow rates and the amplitude of the electric field applied across the channel.     

Laser optoacoustic measurement of paper porosity

The propagation of broadband ultrasonic pulses in combined media that consist of printing paper of different porosity saturated with different liquids is studied. The experiments are performed with three types of paper, namely, Zoom Ultra (Stora Enso, Finland) with surface densities of 80 and 100 g/m² and Data Copy (Mo Do, Sweden) with a surface density of 160 g/cm², and with two types of saturating liquids: ethanol and transformer oil. To excite ultrasonic pulses and to detect them with a high time resolution, the laser optoacoustic spectroscopy method is used. For each type of liquid-saturated paper, the phase velocity of ultrasound is measured in the frequency range of 5–35 MHz. The absence of any noticeable frequency dispersion of the phase velocity is revealed. The possibility of measuring the porosity of printing paper on the basis of the theoretical model of a two-phase medium with the use of the corresponding experimental data is demonstrated.     

On the structure of the velocity field due to wave motion at a uniformly charged interface between two viscous immiscible liquids

An analytical solution to the problem of evolution of a capillary-gravitational wave on the uniformly charged interface between viscous immiscible liquids is found. It is shown that, away from the interface, both the total liquid flows and their wave-related eddy components on both sides of the interface decrease rapidly. The amplitude of the velocity field curl changes stepwise in going through the interface. The ratio between the amplitudes of the velocity field eddy components in the media being considered depends on the charge density at the interface, ratio of the kinematic viscosities, and densities of the upper and lower liquids.     

A computer interface for psychophysical and speech research with the Nucleus cochlear implant

A computer interface has been designed and implemented that allows presentation of biphasic pulse stimuli to patients with the Nucleus Ltd./Cochlear Corporation cochlear implant. The one version of the interface connects to a standard parallel output port of a PC or AT compatible computer, and another version plugs directly into a standard PC/XT bus slot. The host computer sends a stream of bytes to the parallel port that specifies the configuration of the desired output pulses. Upon receipt of the data, the interface generates the appropriate burst sequence that is delivered to the patient's external transmitter coil. The coded information is interpreted by the internal receiver that delivers the pulse to the specified electrodes at the specified amplitude and pulse width. This interface makes it possible to interleave pulses on two or more electrode pairs, to modulate the amplitude or timing of a pulse sequence, or to sweep a stimulus across the electrode array. Investigators can achieve stimulus control with this interface that allows them to conduct psychophysical, electrophysiological, and speech experiments not possible through the patient's speech processor or with available clinical interfaces.     

Effect of static pressure on acoustic energy radiated by cavitation bubbles in viscous liquids under ultrasound

The effect of static pressure on acoustic emissions including shock-wave emissions from cavitation bubbles in viscous liquids under ultrasound has been studied by numerical simulations in order to investigate the effect of static pressure on dispersion of nano-particles in liquids by ultrasound. The results of the numerical simulations for bubbles of 5 μm in equilibrium radius at 20 kHz have indicated that the optimal static pressure which maximizes the energy of acoustic waves radiated by a bubble per acoustic cycle increases as the acoustic pressure amplitude increases or the viscosity of the solution decreases. It qualitatively agrees with the experimental results by Sauter et al. [Ultrason. Sonochem. 15, 517 (2008)]. In liquids with relatively high viscosity (～200 mPa s), a bubble collapses more violently than in pure water when the acoustic pressure amplitude is relatively large (～20 bar). In a mixture of bubbles of different equilibrium radius (3 and 5 μm), the acoustic energy radiated by a 5 μm bubble is much larger than that by a 3 μm bubble due to the interaction with bubbles of different equilibrium radius. The acoustic energy radiated by a 5 μm bubble is substantially increased by the interaction with 3 μm bubbles.     

Acoustic dispersion and attenuation measurement using both transmitted and reflected pulses

Traditional broadband transmission method for measuring acoustic dispersion and attenuation requires the measurement of the thickness of the specimen, the transmission coefficient at the water–specimen interface, and the Fourier spectra of two transmitted pulses. A new method has recently been developed that can determine both the thickness and dispersion of the specimen by utilizing the phase spectra of two additional pulses reflected back from the front and back surfaces of the specimen. In this paper, the method is further extended to the measurement of attenuation. If the density of the specimen is known, the frequency-dependent transmission coefficient can be determined based on the measured phase velocity, and only the amplitude spectra of the two transmitted pulses are used to determine the attenuation. If the density of the specimen is unknown, the attenuation can be determined from the amplitude spectra of all the four pulses. In both cases, the thickness estimated from the phase spectra of the four pulses is utilized. Experimental results from two specimens are presented to demonstrate the application of the new method.     

Droplet ejection from an interface between two immiscible liquids under pulsed ultrasound

The emphasis of this study is on the ejection of single droplets of a certain size under pulsed ultrasound. Droplet ejection from an interface of two immiscible liquids in this mode, which differs from the well-known ultrasonic fountain (where liquid droplets arise spontaneously), has been experimentally implemented and investigated. The spatial and time evolution of the interface deformation and violation of interface integrity, caused by pulsed acoustic radiation pressure, has been recorded with a high-speed video camera. It is shown that, depending on the ultrasound intensity, three characteristic modes of interface response can be distinguished. In the first (low-intensity)mode, the interface undergoes forced oscillations, without violation of its integrity. In the second (intermediate-intensity) mode, which is in the focus of our study, the interface integrity is violated due to the ejection of a single droplet of a certain size; the latter continuously changes its shape when moving in the second liquid. In the third (high-intensity) mode, the predictable ejection of droplets of a predictable size turns into stochastic ejection of multiple droplets with unpredictable sizes. The dependence of the sizes of single droplets on the parameters of focused ultrasound beam have been measured in the second (stable) mode of ultrasound ejection. Based on these measurements, the range of ultrasound parameters providing controlled generation of single droplets of a specified size is estimated. Differences in the dynamics of interface motion and specific features of droplet generation for the liquid/liquid interface in comparison with the liquid/gas interface are indicated. Possible applications of the observed effects are discussed.     

Ultrafast electronic spectroscopy for chemical analysis near liquid water interfaces: concepts and applications

Electron spectroscopy for chemical analysis (ESCA) being conceptually a photoelectron spectroscopy is established as a chemically specific probe mostly for surface analysis. Liquid phase ESCA for volatile liquids has become possible through the development of the liquid microjet technique in vacuum enabling the measurement of liquid interface photoelectron emission at the high vapor pressure of volatile liquids. Recently we have been able to add the dimension of time to the liquid interface ESCA technique employing high-harmonics soft X-ray and UV/near IR femtosecond pulses in combination with liquid water micro beams in vacuum. The concepts as well as technical details are outlined and several characteristic applications are highlighted.     

Extraction of ions from polar solutions by high-strength electric field pulses

Extraction of ions from solutions of salts in ethylene glycol and water-glycerol mixture by high-strength electric field pulses is investigated. The conditions for stable extraction of ions from a polar liquid in the pulsed regime are ensured by using a track membrane with channels of a nanosize diameter as the interface between the liquid solution and vacuum. The possibility of barrier-free field evaporation of ions from polar liquids in electromembrane ion source for mass-spectrometric analysis of solutions is considered.     

Parallel flow in hele-shaw cells with ferrofluids

Parallel flow in a Hele-Shaw cell occurs when two immiscible liquids flow with relative velocity parallel to the interface between them. The interface is unstable due to a Kelvin-Helmholtz type of instability in which fluid flow couples with inertial effects to cause an initial small perturbation to grow. Large amplitude disturbances form stable solitons. We consider the effects of applied magnetic fields when one of the two fluids is a ferrofluid. The dispersion relation governing mode growth is modified so that the magnetic field can destabilize the interface even in the absence of inertial effects. However, the magnetic field does not affect the speed of wave propogation for a given wave number. We note that the magnetic field creates an effective interaction between the solitons.     

Photoacoustic method for the measurement of the nonlinearity parameter of liquids

I.IntroductionThenonlinearityparameterB/Aisanimportantacousticalparameteroffluids.Hitherto,manytheoreticalandexperimentalstudiesforthedeterminahonofthenon1inearityparamctersof1iquidshavebeenrcported.ThemcthodsfordetCrminationofthenonlinearityparamenterofthe1iquidcanbeseparatedintotwocategories:thermodynamicmethod[llandfinite-amp1itudeacousticwavcmethod.The1attercancseparatedfurtherintoharmonicwavemcthodt2]andpulsemethod.Karabutovetal.[31andBozkhovetaI.[4lusedthepulsedlasertogencratetheplane…     

声波在含气泡液体中传播特性及产热效应*

该文对含气泡液体中的声波方程采用线性分析方法,研究了超声波在含气泡液体中的传播特性以及产热效应。当声波在含气泡液体中传播时,气泡的存在会影响声波的传播,在声波频率接近气泡共振频率的频段内,声信号在液体中传播时剧烈衰减,而在声波频率远远高于或低于气泡共振频率时,声波的传播基本不受影响。在接近气泡共振的频段内,声波耗散的能量最终转化为热能。同时液体中的气泡会在声波驱动下径向振动并辐射声波,伴随气泡壁在液体中的粘滞振动,热量随之产生。结果表明,两种产热机制分别在不同频段起主导作用。     

Thermocapillary motion of a drop near a plane interface between liquids

The thermocapillary motion of a liquid drop immersed into another liquid near an infinite plane interface between two liquids is theoretically analyzed. The motion is considered under the conditions of a constant temperature gradient normal to the interface at infinity and small Reynolds and Peclet numbers. The problem is solved in bispherical coordinates. The analysis takes into consideration the thermal conductivity of the liquids and the thermocapillary motion of the liquids due to a nonuniform temperature distribution over the plane interface.     

Optical and acoustic monitoring of bubble cloud dynamics at a tissue-fluid interface in ultrasound tissue erosion

Short, high-intensity ultrasound pulses have the ability to achieve localized, clearly demarcated erosion in soft tissue at a tissue-fluid interface. The primary mechanism for ultrasound tissue erosion is believed to be acoustic cavitation. To monitor the cavitating bubble cloud generated at a tissue-fluid interface, an optical attenuation method was used to record the intensity loss of transmitted light through bubbles. Optical attenuation was only detected when a bubble cloud was seen using high speed imaging. The light attenuation signals correlated well with a temporally changing acoustic backscatter which is an excellent indicator for tissue erosion. This correlation provides additional evidence that the cavitating bubble cloud is essential for ultrasound tissue erosion. The bubble cloud collapse cycle and bubble dissolution time were studied using the optical attenuation signals. The collapse cycle of the bubble cloud generated by a high intensity ultrasound pulse of 4-14 micros was approximately 40-300 micros depending on the acoustic parameters. The dissolution time of the residual bubbles was tens of ms long. This study of bubble dynamics may provide further insight into previous ultrasound tissue erosion results.     

Scattering of atoms in a bichromatic field of oppositely propagating light pulses

The interaction of a two-level atom with two light pulses which have different carrier frequencies and propagate in opposite directions is studied in the adiabatic approximation. It is shown that when there is a delay between the light pulses, the momentum of the atom changes, as a result of the interaction with the laser field, by a definite amount that depends on the amplitude of the light pulses and on the difference of their carrier frequencies. It is predicted that the momentum transfer to the atom is a step function of the amplitude of the light pulses.     

Simultaneous measurement of sound velocity and wall thickness of a tube.

A method for simultaneously measuring the sound propagation velocity and the thickness of each wall on the opposite sides of a tube is presented. The method uses a pair of ultrasound transducers to produce two reflected pulses from the outer and inner surfaces of the tube wall on the each side, and two transmitted pulses, one with and one without the tube sample between the two transducers. Using the time-domain analysis, sound velocity and wall thickness of the tube are determined from the time delays between the three pairs of ultrasound pulses, whereas using the frequency-domain analysis, phase velocity, group velocity, and wall thickness of the tube are determined from the phase differences between the three pairs of ultrasound pulses. Results of measurements on five tube samples are reported.     

p型金属氧化物半导体场效应晶体管界面态的积累对单粒子电荷共享收集的影响

由于负偏置温度不稳定性和热载流子注入,p型金属氧化物半导体场效应晶体管(pMOSFET)将在工作中不断退化,而其SiO₂/Si界面处界面态的积累是导致其退化的主要原因之一. 采用三维器件数值模拟方法,基于130 nm体硅工艺,研究了界面态的积累对相邻pMOSFET之间单粒子电荷共享收集的影响. 研究发现,随着pMOSFET SiO₂/Si界面处界面态的积累,相邻pMOSFET漏端的单粒子电荷共享收集量均减少. 还研究了界面态的积累对相邻反相器中单粒子电荷共享收集 关键词： 负偏置温度不稳定性 电荷共享收集 双极放大效应 单粒子多瞬态     

Spin-wave reflection from an interface of two Fermi liquids

The boundary condition for the magnetization jump at an interface of two Fermi liquids and the spin current through the interface is rederived. With the use of the derived condition the coefficient of reflection of a spin wave from a boundary of two Fermi liquids for normal incidence is found and applied to the case of interface of phase separated liquid mixture of ³He in ⁴He. The effect of the phase separation boundary on the coherently precessing spin pattern is discussed.