ISSN:0031-9228    

DOI:10.1063/1.2806644

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881720

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881721

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

For over eight years, researchers at JILA and the University of Colorado, Boulder, have worked patiently and painstakingly to improve the precision with which they can detect a rare, parity‐violating atomic transition. The group, led by Carl Wieman, has finally been rewarded with a measurement of the transition amplitude that is precise to 0.35&percent;, a factor of seven better than their 1988 measurement of the same transition. The dominant uncertainty in the value of this term is now the uncertainty in the atomic theory, which reached 1.2&percent; in the early 1990s. The combined uncertainties bring the data into the realm where they place useful constraints on the Standard Model of electro weak interactions. As icing on the cake, the Boulder experiment also gives the first good evidence for a nuclear feature predicted years ago: the nuclear anapole moment.

ISSN:0031-9228    

DOI:10.1063/1.881714

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Over the last four years, the H1 and ZEUS detector groups at DESY in Hamburg have been studying the interaction of 27.5 GeV positrons colliding with 820 GeV protons in the Hadron‐Electron Ring Accelerator (HERA). The events at the highest 4‐momentum transfer explore a new kinematic regime, down to10−16 cm.As early as 1994, some deep inelastic scattering events at very high momentum transfer were seen. Late last year, rumors became rampant in labs outside DESY that the H1 and ZEUS detectors were finding leptoquarks. Both groups independently analyzed their data sample of high‐energy deep inelastic scattering collected from 1994 to 1996. The events they found have the signature of deep inelastic scattering—tne positron is scattered by a quark inside the proton through a large angle, almost completely back the way it came, and the struck quark generates a high‐energy jet of hadrons.

ISSN:0031-9228    

DOI:10.1063/1.881753

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

X‐ray astronomy has already provided us with about a dozen rather convincing stellar black hole candidates. (SeePHYSICS TODAY, November 1995, page 58.) But until now the evidence was simply that an object too compact to be an ordinary star was too massive to be just another neutron star. So, by elimination, what else could it be but a black hole? Convincing as that kind of evidence is, it does not address the defining exotic properties that general relativity attributes to black holes: the remorseless event horizon and the strongly curved spacetime leading down to it.

ISSN:0031-9228    

DOI:10.1063/1.881722

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

As optical communications systems get faster and faster, approaching 10 Gbit/second, near‐infrared receivers are struggling to keep pace with them. What's needed are avalanche photodetectors with enough gain to amplify the much shorter pulses that come in at these higher bit rates. Researchers from the University of California, Santa Barbara, and the Royal Institute of Technology in Kista, Sweden, hope that their new avalanche photodiode (APD) will fill the bill: Its gain‐bandwidth product is over 300 GHz. That's nearly double the best performance demonstrated up to now by an APD (the old record was held by a superlattice design introduced in the late 1980s) and almost quadruple that of commercial receivers.

ISSN:0031-9228    

DOI:10.1063/1.881723

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The concept of a galaxy as a vast organized system of stars originates with Galileo's Observation in 1610 that the Milky why cound be resolved into “innumerable” faint stars. Confirmation that many of the faint patches of light seen through small telescopes were actually galaxies like our own came in 1923, when Edwin Hubble, working with the just‐completed 2.4‐meter telescope at Mount Wilson in southern California, measured the brightnesses of individual stars in the Andromeda nebula. At about the same time, Vesto Slipher, working at the Lowell Observatory in Arizona, was making the first systematic measurements of the Doppler shifts of galaxies. Of several dozen galaxies measured, all but two were found to be receding. In 1929, Hubble showed that the recession velocities of Slipher's galaxies were directly proportional to their distances, thus introducing the concept of an expanding universe

ISSN:0031-9228    

DOI:10.1063/1.881724

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The careers of many physicists, particularly those engaged in applied or industrial research, depend on the cerns grow, they are increasingly being asked to help expand their employers' sources of income. In many cases, the most direct link between an organization's scientific research, development and application efforts and its financial objectives is its portfolio of patents. And so it would not be unreasonable to say that the professional success of many physicists is greatly affected by the number and quality of the patents resulting from their efforts.

ISSN:0031-9228    

DOI:10.1063/1.881725

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The discovery of high‐temperature superconductors has stimulated dramatic growth in our understanding of the physics of quantized vortex lines. These superconductors exclude magnetic fields weaker than a lower critical fieldHc1≤10−2tesla. Stronger fields penetrate as an array of vortices, each consisting of exactly one quantum of flux(&fgr;0 = hc/2e)surrounded in the plane perpendicular to the field by circulating supercurrents that extend radially a few hundred nanometers. The behavior of vortices dominates many physical properties of high‐temperature superconductors up to the upper critical fieldHc2∼102tesla, where superconductivity gives way to normal metallic behavior and magnetic fields penetrate uniformly.

ISSN:0031-9228    

DOI:10.1063/1.881715

出版商:AIP    

年代:1997

数据来源: AIP