ISSN:0031-9228    

DOI:10.1063/1.2806741

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881621

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This month, Steven Chu, Claude Cohen‐Tannoudji and William Phillips will doff their laboratory clothes and don white tie and tails to receive the 1997 Nobel Prize in Physics in Stockholm. The Royal Swedish Academy of Sciences selected these three “for the development of methods to cool and trap atoms with laser light.” Thanks to these methods, neutral atoms have now been slowed to speeds below a few centimeters per second, corresponding, for helium atoms, totemperatures of a few hundred nanokelvin. To bring atoms to such a crawl, the researchers broke not one but two barriers originally thought to limit the temperatures to which atoms could be cooled.

ISSN:0031-9228    

DOI:10.1063/1.881626

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

At the Max Planck Institute for Quantum Optics in the Munich suburb of Garching, Theodor Hansch and colleagues have measured the ultraviolet transition frequency between the 1S and 2S states of atomic hydrogen to be2.466 061 413 187 34(84)×1015 Hz.With an uncertainty of only 3 parts in1013,this result exceeds the accuracy of the best previous measurement of the 1S‐2S transition by two orders of magnitude. It is, in fact, the most accurate measurement to date of any frequency in the visible or ultraviolet. It's so accurate that simply repeating the measurement a year from now would provide a better and more direct verification (or falsification) of the constancy of the fine‐structure constant over cosmological time than any astrophysical data we have.

ISSN:0031-9228    

DOI:10.1063/1.881627

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Comets—dubbed “dirty snowballs” by comet guru Fred Whipple—are among the last celestial bodies you'd expect to emit x rays, which typically come from matter at least as hot as106 K.But last year, to the surprise of astronomers, Carey Lisse (University of Maryland) and Mike Mumma (NASA's Goddard Space Flight Center) discovered faint x‐ray emission from comet Hyakutake. They observed the photogenic comet with the ROSAT satellite as the comet flew by Earth in March 1996. That same month, Mumma and Vladimir Krasnopolsky (Catholic University of America) detected the comet with the Extreme Ultraviolet Explorer (EUVE) satellite.

ISSN:0031-9228    

DOI:10.1063/1.882046

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Amazingly, individual grains of dust from stars that existed before the Sun was born have made their way to Earth in meteorites. When subjected to a battery of cutting‐edge laboratory techniques, these tiny grains provide thrilling new insights into such topics as the dynamics of supernova explosions, the age and chemical evolution of the Galaxy, fundamental nuclear physics and processes in the outer envelopes of stars. The path from dust grain to astrophysical insight is the subject of this article.

ISSN:0031-9228    

DOI:10.1063/1.882049

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

IfPHYSICS TODAYhad been launched just one year earlier—in 1947 rather than 1948—it might have begun life by soliciting a number of articles to commemorate the 50th anniversary of the discovery of the electron by J. J. Thomson. That 1897 event could surely have qualified as the start of the electronics discipline and the industry that followed. It was the new understanding of the properties of the electron that created the field of electronics and that, combined with our developing capability in the electrical, magnetic and mechanical arts, made possible a rich array of new products and services.

ISSN:0031-9228    

DOI:10.1063/1.881628

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Forty years ago the southern part of the San Francisco Bay area was predominantly an agricultural valley filled with apricot orchards. Today this region is the bustling high‐technology capital of the world—envied by governments around the globe for its creativity and productivity. How did this remarkable technological transformation occur? And why is Silicon Valley located southeast of San Francisco rather than in, say, northern New Jersey, the Boston area or near Dallas?

ISSN:0031-9228    

DOI:10.1063/1.881629

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881630

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.882048

出版商:AIP    

年代:1997

数据来源: AIP