ISSN:0031-9228    

DOI:10.1063/1.2810314

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810315

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810316

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Many applications of ultrasound, such as welding plastics or sterilization of medical equipment, exploit cavitation, the rapid expansion and collapse of bubbles as sound waves pulse through a liquid. This phenomenon that has proved to be so utilitarian is also the source of great fascination and mystery: During cavitation the collapsing bubbles develop extremely high temperatures and pressures and emit visible radiation. Recent experiments have elucidated just how extreme the properties of cavitation bubbles are and have also suggested what potential new applications the bubbles might have. In one paper, Bradley Barber and Seth Putterman of the University of California at Los Angeles report that the light emitted during cavitation—known as sonoluminescence—emerges in flashes that are less than 50 picoseconds long, far shorter than anyone had expected, and that the pulses repeat with clocklike precision. In other work, Edward Flint and Kenneth Suslick of the University of Illinois at Urbana‐Champaign have confirmed, by the most direct measurements to date, the long‐standing expectation that the temperature during cavitation soars above 5000 K. A number of researchers have been exploiting these high temperatures for several years by using acoustic waves to accelerate various chemical reactions. Suslick and his colleagues recently reported a new application along these lines—the formation of amorphous iron.

ISSN:0031-9228    

DOI:10.1063/1.2810317

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

On 18 May 1990 my longtime friend and colleague Wolfgang Kra¨tschmer called from the Max Planck Institute for Nuclear Physics in Heidelberg with a startling suggestion. The elusive moleculeC60,which we had slowly come to realize was abundantly present in the carbonaceous smoke we had been making since 1983, was readily soluble in benzene, he told me. This would provide a simple technique for separating the molecule from the ordinary graphite that made up over 90&percent; of the soot we had been producing.

ISSN:0031-9228    

DOI:10.1063/1.881295

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The striking flow shown in figure 1 is produced in a simple apparatus: A fluid is confined between two concentric cylinders, with the inner and perhaps the outer cylinder able to rotate. The cellular motion that develops with rotation was discovered and described mathematically by Geoffrey I. Taylor in 1923. A similar apparatus, with the inner cylinder suspended from a torsion fiber and the outer cylinder rotating, was used even earlier as a viscometer. Maurice Couette described this arrangement in his thesis, which he presented in Paris in 1890. For this reason, modern investigators refer to flow between rotating cylinders as Taylor‐Couette flow. In this article I trace the beginnings of the subject back to Isaac Newton and, by discussing the contributions of Newton, George Stokes, Max Margules, Arnulph Mallock, Couette, Taylor, S. Chandrasekhar and others, show how the study of this flow evolved to its place of prominence today.

ISSN:0031-9228    

DOI:10.1063/1.881296

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Radioastronomy began in 1933 with Karl Jansky's accidental discovery of radio emission from the center of the Galaxy as he was studying the effect of thunderstorms on transatlantic telecommunications. Six decades later, telecommunications and other radio services are threatening the future of radioastronomy. Whether searching for the signature of a protogalaxy, studying the maseremission signposts of star formation or pursuing answers to any of the myriad questions of modern astrophysics, today's radioastronomer is often frustrated by man‐made radio interference. From satellites, radar, radio and television transmitters, and wireless personal communication systems of all sorts to microwave ovens, computers and even garage door openers, the same technology that lets us study the universe at radio wavelengths is producing a flood of man‐made signals. Figure 1 illustrates how noisy the radio spectrum has become at wavelengths around 1 meter. (The remedy offered in the figure is, alas, just an astronomer's fantasy.)

ISSN:0031-9228    

DOI:10.1063/1.881297

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810318

出版商:AIP    

年代:1991

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810319

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Some call it musical chairs. To the more cynical it's something like the Mad Tea Party inAlice in Wonderland, at which the participants changed seats at the direction of the Hatter. InAlice, the shuffling of seats had little effect on the individuals or on events. By contrast, the moves in Washington over the past few months are intended to make a difference at the White House Office of Science and Technology Policy and the Departments of Energy and Defense.

ISSN:0031-9228    

DOI:10.1063/1.2810320

出版商:AIP    

年代:1991

数据来源: AIP