ISSN:0031-9228    

DOI:10.1063/1.2808083

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808084

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808085

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808087

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thanks to the wave nature of matter, it's possible to build the atomic analog of an optical interferometer, although it's extremely difficult, because the de Broglie wavelengths of atoms are typically 10 000 times shorter than those of light. The feat was accomplished four years ago by a number of groups, each with a different scheme for splitting and recombining the matter waves. (SeePHYSICS TODAY, July 1991, page 17.) We are now starting to see the fulfillment of the hopes raised by those first atom interferometers as researchers hone their interferometers to yield ever more precise values of fundamental constants or explore fundamental aspects of quantum mechanics such as Berry's phase. For example, Steven Chu and his colleagues at Stanford University have measured the ratioh/mof Planck's constant to the mass of a cesium atom with a precision of one part in107,although the systematic errors are at the level of 1 part in106.An experiment to improve the absolute accuracy of theh/mmeasurement to a few parts in109is underway. This ratio is one factor in the determination of the finestructure constant.

ISSN:0031-9228    

DOI:10.1063/1.2808088

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Skyrmions—which can be thought of, loosely, as topological twists or kinks in a spin space—are one of those concepts that seem to jump restlessly from field to field. Technically, in a nonlinear field theory a Skyrmion is defined as a soliton with spin and statistics different from those of the underlying fields. Introduced by Tony H. R. Skyrme in 1958 as a way of representing the nucleon (a fermion) as a topological soliton of bosonic pion fields, skyrmions have sojourned in nuclear physics, particle physics and condensed matter physics.

ISSN:0031-9228    

DOI:10.1063/1.2808089

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We ordinarily think of a sound wave in a gas as consisting of coupled pressure and displacement oscillations. However, temperature oscillations always accompany the pressure changes. The combination of all these oscillations, and their interaction with solid boundaries, produces a rich variety of “thermoacoustic” effects. Although these effects as they occur in everyday life are too small to be noticed, one can harness extremely loud sound waves in acoustically sealed chambers to produce powerful heat engines, heat pumps and refrigerators. Whereas typical engines and refrigerators have crankshaft‐coupled pistons or rotating turbines, thermoacoustic engines and refrigerators have at most a single flexing moving part (as in a loudspeaker) with no sliding seals. Thermoacoustic devices may be of practical use where simplicity, reliability or low cost is more important than the highest efficiency (although one cannot say much more about their cost‐competitiveness at this early stage).

ISSN:0031-9228    

DOI:10.1063/1.881466

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Two of the greatest physics discoveries in the first half of the 20th century were superconductivity and superfluidity. Superconductivity involves the frictionless conduction of electricity in wires, and superfluidity the frictionless flow of superfluid liquid helium through channels. Both discoveries led to the arcane phenomenon of macroscopic quantization: the manifestation of the laws of quantum mechanics not just on atomic dimensions but also on the scale of common laboratory apparatus. Both discoveries required the liquefaction of helium, which was first done in 1908.

ISSN:0031-9228    

DOI:10.1063/1.881467

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808090

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808092

出版商:AIP    

年代:1995

数据来源: AIP