摘要:

Experimental studies at the Cavendish Laboratory [1] and the Drittes Physikalisches Institut, Go¨ttingen [2] have shown the emission of light from the vigorous collapse of a cavitation bubble near a rigid boundary. The Go¨ttingen studies, using laser produced bubbles, indicate that a rapid increase in the emission of light occurs beyond a critical “stand-off” distance of the cavitation bubble from the boundary. This paper reports on theoretical studies using a modified boundary integral method approach that has been developed to allow for toroidal bubble geometry once the high speed jet has fully penetrated the bubble interior and impacted on the far side. This provides the framework to model the essential phenomena for the motion of a single cavitation bubble near a rigid boundary. Key physical characteristics of the bubble motion which include bubble shape, particle paths, velocities, pressures and gas temperature, are presented. In the context of single bubble cavitation luminescence (SCBL) it is found that maximum jet speeds occur at a critical distance from the boundary corresponding to jet impact occurring at minimum bubble volume. In bubbles further away from the boundary, the high speed jet does not penetrate the full width of the cavity, while for closer bubbles a vigorous toroidal bubble collapse leads to the highest pressures occurring on a ring, rather than at the point of impact. This may contribute to the understanding of the Go¨ttingen experiments. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309174

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In cases of severe injury, physicians speak of a “golden hour”—a brief grace period in which quickly applied, proper therapy can save the life of the patient. Much of this mortality results from exsanguination, i.e., bleeding to death—often from internal hemorrhage. The inability of a paramedic to treat breaches in the vascular system deep within the body or to stem the loss of blood from internal organs is a major reason for the high level of mortality associated with blunt trauma. We have undertaken an extensive research program to treat the problem of internal bleeding. Our approach is as follows: (a) We use scanning ultrasound to identify internal bleeding and hemorrhage, (b) we use ultrasound imaging to locate specific breaches in the vascular system, both from damaged vessels and gross damage to the capillary bed, and (c) we use High Intensity Focused Ultrasound (HIFU) to treat the damaged region and to induce hemostasis. We present a general review of this research with some emphasis on the role of nonlinear acoustics. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309175

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The first reports on the fragmentation of human calculi with ultrasound appeared in the fifties. Initial positive results with an extracorporeal approach with continuous wave ultrasound could, however, not be reproduced. A more promising result was found by generating the acoustic energy either in pulsed or continuous form directly at the stone surface. The method was applied clinically with success. Extracorporeal shock-wave generators unite the principle of using single ultrasonic pulses with the principle of generating the acoustic energy outside the body and focusing it through the skin and body wall onto the stone. Ha¨usler and Kiefer reported the first successful contact-free kidney stone destruction by shock waves. They had put the stone in a water filled cylinder and generated a shock wave with a high speed water drop which was fired onto the water surface. To apply the new principle in medicine, both Ha¨usler and Hoff’s group at Dornier company constructed different shock wave generators for the stone destruction; the former used a torus-shaped reflector around an explosion wire, the latter the electrode-ellipsoid system. The former required open surgery to access the kidney stone, the latter did not. It was introduced into clinical practice after a series of experiments in Munich. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309176

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This paper compares the different approaches used in acoustics to time reverse or to phase conjugate a wavefield. The basic principle of a time reversal mirror is an extension for broadband pulsed waves to the optical phase conjugated mirror designed for monochromatic waves. However, this equivalence is only valid mathematically and there are some fundamental differences between these two techniques that will be described in this paper. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309177

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The nonlinear phenomena, which are linked to finite-amplitude waves, are directly involved in the mechanisms that determine a great number of practical applications. In fact, high-intensity applications of sonic and ultrasonic energy constitute a wide field wherein the acoustic waves are used to produce permanent effects on the medium through which they propagate. This field is termed macrosonics. The use of finite-amplitude waves in industrial processing is generally based on the exploitation of high pressure variations together with the associated nonlinear effects, such as radiation pressure, streaming and cavitation, and a series of secondary effects, such as heat, agitation, mechanical rupture, etc. For technological applications the knowledge and control of these effects is essential in order to maximize or suppress them according to the application needs. The development of the systems for industrial use also requires a proper generation and distribution of finite amplitude acoustic fields. There is a wide range of potential macrosonic processing applications, but the majority of them still remain at laboratory stage. This is probably because of the problems related to the development of adequate macrosonic systems and to the deep knowledge of the mechanism of the processes. This paper reviews the main nonlinear problems involved in the development of macrosonic systems for industrial applications as well as the nonlinear effects related to the mechanisms of some specific applications. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309178

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A comprehensive theory based on Hamiltonian mechanics has been developed for a wide variety of nonlinear surface acoustic waves. The present paper reviews evolution equations and physical insight resulting from this body of work. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309179

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Cavitation bubbles are formed from small air bubbles, so-called nuclei, with the surrounding pressure reduction caused by the flow, and then, the bubbles shrink and collapse with the surrounding pressure rise. Such volumetric changes of bubbles are calculated in detail and it is found that they are significantly influenced by the internal phenomena, such as thermal diffusion, mist formation due to a homogeneous condensation, mass diffusion between vapor and noncondensable gas, heat and mass transfer through the bubble wall. The structure in cavitating flow interacts with the cavitation bubbles, and those bubbles form a cloud cavitation. It is well known that cloud cavitation is one of the most destructive forms. The behavior of bubble clouds is simulated numerically. An inward propagating shock wave is formed during the collapse of the bubble cloud, and the shock wave and its precursor are focused at the cloud center area. These phenomena associate high frequency pressure oscillations and violent bubble collapses. Those bubble collapses emit high pressure peaks, which are several hundreds times larger than that of a single bubble collapse. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309180

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This work describes several physical models of the mechanical properties of rocks resulting in macroscopic nonlinear behavior due to their mesoscopic-scale structure. Theoretical models include Hertzian grain contacts with multiple scales and hysteretic properties. A significant addition to the highly nonlinear response in these materials are fluids contained in the soft bond system. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309181

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The problems of nonlinear interaction between a linear medium and a vibrating boundary are discussed. Two types of problems are studied: excitation of waves into an unlimited medium and excitation of oscillations in resonators. Statistical properties of emitted waves are considered. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309182

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Both sonochemistry and sonoluminescence derive from acoustic cavitation. Bubble collapse in liquids results in an enormous concentration of energy from the conversion of the kinetic energy of liquid motion into heating of the contents of the bubble. The high local temperatures and pressures, combined with extraordinarily rapid cooling, provide a unique means for driving chemical reactions under extreme conditions. A diverse set of applications of ultrasound to enhance chemical reactivity has been explored, with important applications in mixed phase synthesis, materials chemistry, and biomedical uses. For example, the sonochemical decomposition of volatile organometallic precursors in low-volatility solvents produces nanostructured materials in various forms with high catalytic activities. Nanostructured metals, alloys, carbides and sulfides, nanometer colloids, and nanostructured supported-catalysts can all be prepared by this general route. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1309183

出版商:AIP    

年代:1900

数据来源: AIP