摘要:

The generating mechanism of the relaxation oscillation in Multi-Bubble SonoLuminescence (MBSL) is experimentally investigated. The range of liquid temperature and sound pressure amplitude within which the phenomenon occurs are examined. It is found that one of the main causes for changeover from the radiation state to the vanishing state is the temperature rise during the radiating period. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309264

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Bubble collapse is an effective mechanism for the concentration of the diffuse energy of a sound field into localized hot spots. It has long been predicted that the interior temperatures of collapsing bubbles should reach thousands of K during collapse. Experimental measurements of conditions inside cavitating bubbles have been very limited. We report here the first use of multi-bubble sonoluminescence (MBSL) from metal atom excited states as a spectroscopic probe of temperatures inside cavitating bubbles. This intense atomic emission allows us to change the properties of the gas/vapor mixture within the bubble and thus vary the effective emission temperatures for MBSL from 5100 K to 2300 K. The observed emission temperatures are in accord with those expected due to simple compressional heating during cavitation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309265

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A catalytic reactor is considered, consisting of parallel capillaries on which a mixture of reactants flows. The catalyst is put on the internal surface of these capillaries. The possibility of increasing the effectiveness of the considered type of catalytic reactor is shown in the case of realization of the chemical reaction in artificially created non-steady-state conditions with simultaneous management of the distribution of active centres on an internal surface of the capillaries. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309266

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A sonochemical reaction field in a rectangular glass cell driven by two kinds of ultrasonic transducer was visualized optically and compared with a distribution of multi-bubble sonoluminescence. Fluid motion in the cell was measured using a laser Doppler velocimeter. In a standing-wave type reactor driven at 140 kHz, the reaction field formed layers and was not uniform accompanying fluid motion at high intensity. In a horn-type reactor of 19.5 kHz, the luminescing region was confined in very close vicinity to the horn tip in contrast with broad region of fast fluid motion. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309267

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Thermal safety indices for diagnostic ultrasound beams are calculated under the assumption that the sound propagates under linear conditions. A non-axisymmetric finite difference model is used to solve the KZK equation, and so to model the beam of a diagnostic scanner in pulsed Doppler mode. Beams from both a uniform focused rectangular source and a linear array are considered. Calculations are performed in water, and in attenuating media with tissue-like characteristics. Attenuating media are found to exhibit significant nonlinear effects for finite-amplitude beams. The resulting loss of intensity by the beam is then used as the source term in a model of tissue heating to estimate the maximum temperature rises. These are compared with the thermal indices, derived from the properties of the water-propagated beams. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309268

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In HIFU applications to ultrasound surgery, it is important to intensify acoustic energy absorption in the focal region without increase of heating in the prefocal region. This regime may be achieved by using the mechanism of nonlinear absorption, which is more pronounced when sharp shocks are developed in the waveform. In this report, results of an experimental study of nonlinear enhancement of ultrasound heating induced by a sawtooth wave are presented. A focused beam was radiated from a 1 MHz piezoceramic transducer with 10 cm diameter and 20 cm focal length. The wave was focused through water into a gelatin sample with a thermocouple implanted near the focal point of the beam. The transducer was excited by repetitive tone bursts. Cases with various amplitude and duration of the tone burst but with the same level of mean power were compared. It was shown that the heating was more efficient for higher amplitudes when shock fronts were formed at the focus. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309269

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Ultrasound image quality has experienced a significant improvement over the past years with the utilization of harmonic frequencies. This brings the need to understand the physical processes involved in the propagation of finite amplitude sound beams, and the issues for redesigning and optimizing the phased array transducers. New arrays with higher imaging performances are essential for tissue imaging and contrast imaging as well. This study presents measurements and simulations on a 4.6 MHz square transducer. The numerical scheme used solves the KZK equation in the time domain. Comparison of measured and computed data showed good agreement for low and high excitation levels. In a similar way, a numerical simulation was performed on a linear array with five elements. The simulation showed that the second harmonic beam is narrower than the fundamental with less energy in the near field. In addition, the grating lobes are significantly lower. Accordingly, selective harmonic imaging shows less near field artifacts and will lower the clutter, resulting in much cleaner images. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309270

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Exactly solvable wave dynamic models for liquids containing gas bubbles are presented. Lighthill’s generalized inhomogeneous wave equation is first derived for a host liquid where the gas phase is presented by an equivalent distribution of monopole sources. The complete effects of nonlinear bubble dynamics and the change of bubble number density in a pressure field are included. An exact numerical method, where individual bubbles are traced to estimate their radial dynamics and the full volumetric change of the wave phenomena, is developed and programmed for solution on a computer. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309271

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Bounded sound beam propagation in an inhomogeneous medium is treated by the nonsingular perturbation method. For a liquid with gas bubbles the analogue of the Khokhlov-Zabolotskaya equation with KdV dispersion term was derived. An equation with new coefficients which are revised for a compressible liquid is obtained. It is essential for the dynamics of a bubbly liquid with a small volume concentration of bubbles. Some explicit solutions that come from a connection of the resulting equation with the cylindrical Kadomtsev-Petviashvilli (Johnson) equation are discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309272

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The problem of the stochastisation of solitary waves due to the development of higher harmonics in a liquid with identical gas bubbles is investigated. An experimental and numerical study of wave structure and a spectrum are presented. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309273

出版商:AIP    

年代:1900

数据来源: AIP