ISSN:0031-9228    

DOI:10.1063/1.2810787

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810788

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810789

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Experimenters may finally have observed the crystalline phase of a degenerate electron gas. Electrons in such a phase do not move freely through the available space; they are confined to the sites of a lattice and their quantum mechanical zero‐point motions are limited to small oscillations about their mean positions. Eugene Wigner had proposed this phase based on his theoretical analyses in the 1930s. The “Wigner crystal” phase has been the focus of much discussion for twenty years, since experimenters have been able to fabricate a variety of systems where the phase might be realized.

ISSN:0031-9228    

DOI:10.1063/1.2810790

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Cornell and Stanford are competing to build a B‐meson “factory,” and Fermilab wants to build a new injector ring for its Tevatron Collider. These are the two principal new construction initiatives proposed by the US highenergy‐physics community for completion by the middle of this decade. They are intended to address the two remaining “dangling participles” of the spectacularly successful standard model of the elementary particles: Understanding the violation ofCPsymmetry would seem to require a new source of B mesons much more profuse than the existing electronpositron rings; and determining the properties of the (still missing) top quark in adequate detail appears to necessitate an order of magnitude increase in the luminosity of the Tevatron proton‐antiproton collider.

ISSN:0031-9228    

DOI:10.1063/1.2810791

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

As first suggested by Fritz London, superconductivity and superfluid flow in liquid helium are macroscopic quantum phenomena. They depend on the fact that the energy states of even macroscopic objects, although closely spaced, are discrete, and on the statistical mechanics of systems made up of identical particles. The electrons in a superconducting metal, with a spin of one‐half, obey Fermi‐Dirac statistics and the exclusion principle. Helium atoms of isotopic mass 4 obey Einstein‐Bose statistics, in which there can be many particles in the same quantum state, as is the case with photons, the quanta of radiation, if they are regarded as particles.

ISSN:0031-9228    

DOI:10.1063/1.881218

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

In science we like to emphasize the novelty and originality of our ideas. This is harmless enough, provided it does not blind us to the fact that concepts rarely arise out of nowhere. There is always a historical context, in which isolated precursors of the idea have already appeared. What we call “discovery” sometimes looks, in retrospect, more like emergence into the air from subterranean intellectual currents.

ISSN:0031-9228    

DOI:10.1063/1.881219

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Scientists often set the stage for their most productive advances by first developing simple models, even when sophisticated first‐principles tools are available. These models usually originate from the necessity to explain experimental observations. If the models are robust, then a variety of data fall into place, and successful predictions are made. If a model is “correct,” it is eventually found to be consistent with or derivable from fundamental theory. The Bohr model for atoms is a prime example. Ernest Rutherford's experiments showed that J. J. Thomson's “plum pudding” model of an atom, consisting of a positive spherical “pudding” embedded with negative electron “plums,” had to be replaced by Rutherford's nuclear picture, and subsequent optical data led to the Bohr model. Eventually quantum theory confirmed that the Bohr model is an excellent rudimentary representation for an atom. Although it has been superseded by more elaborate quantum theoretical approaches, this model is still taught to students of atomic physics because of the physical insight one gains by using the Bohr picture of an atom.

ISSN:0031-9228    

DOI:10.1063/1.881220

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810792

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810793

出版商:AIP    

年代:1990

数据来源: AIP