ISSN:0031-9228    

DOI:10.1063/1.881135

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811549

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Photographs of ions trapped by electric and magnetic fields are revealing ordered structures ranging from a few ions in crystalline arrays to thousands of ions arranged on the surfaces of concentric shells. In some experiments with a handful of singly charged ions, varying certain parameters of the trap causes the regular structures to dissolve rapidly into clouds and just as rapidly to recrystallize—behavior resembling a phase change or an order‐to‐chaos transition. All these regular structures occur in systems with well‐defined constituents and interactions. As such they can provide useful insights into collective phenomena such as cluster formation, Wigner crystallization and other strongly coupled plasmas.

ISSN:0031-9228    

DOI:10.1063/1.881130

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Almost eight years after the discovery of the quantum Hall effect, a group led by Daniel Tsui (Princeton University) has observed universal scaling behavior that might provide an important clue to how the effect could be reconciled with the quantum theory of electrical resistance. At issue is a scaling law of that theory. As enunciated in 1979, the law applies only to electrons in the absence of a magnetic field. If, however, the law also applied to electrons in the presence of the strong magnetic fields used in quantum Hall effect measurements, then both the Hall conductance and the longitudinal conductance of electrons confined in a plane would have a vanishingly small value. (In Hall effect measurements, the sample is placed in perpendicular electric and magnetic fields. The Hall conductance is a measure of the current flow in a direction normal to both the electric field and the magnetic field.)

ISSN:0031-9228    

DOI:10.1063/1.881131

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Hendrik A. Kramers was a major figure in the long and painful struggle that propelled quantum physics from the inspired but artful guessing game of the Bohr rules to a well‐defined, coherent and systematic quantum mechanics. Kramers's basic and deep contributions in this struggle are barely known nowadays, and he actually suffers in comparison with Niels Bohr and Louis de Broglie, let alone Paul Dirac, Werner Heisenberg and Wolfgang Pauli. Kramers is still known for a number of isolated and disconnected results, such as the WKB method, the Kramers degeneracy in magnetism and the Kramers‐Kronig relations. Although these are unquestionably significant and first‐rate contributions, they do not demonstrate Kramers's deep physical insight and his profound concern for fundamental questions. They show Kramers as an extraordinarily skillful craftsman rather than as a scientific innovator. This may be an important reason why Kramers's reputation has faded so markedly in comparison with those of, say, Heisenberg or Pauli, whose contemporary he was and who, as his fellow architects of quantum mechanics, recognized him as a talented physicist and deep thinker. For example, when Bartel L. van der Waerden started to collect what he believed were the seminal papers in quantum mechanics, Pauli, hardly a person known for his generosity in giving undeserved credit, alerted him to the importance of Kramers's investigations.

ISSN:0031-9228    

DOI:10.1063/1.881132

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Mistrust of technical experts by the general public is a growing problem in science policy. The National Science Board reports that whereas 80 percent of the public believes that scientists work for the good of humanity, 55 percent believes that their knowledge gives scientists a power that makes them dangerous. The image of the crazed scientist plotting to master and destroy remains a staple of both children's and adult fiction, as Spencer Weart explained in a recent article in this magazine (June, page 28).

ISSN:0031-9228    

DOI:10.1063/1.881133

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811550

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811551

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811552

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The recent intensification of Soviet interest in participating in international scientific activities is not merely a result of new policies introduced under Mikhail Gorbachev. Soviet scholars have sought out contacts with Western scholars since the first years of the Russian Revolution, although under Joseph Stalin and during times of heightened political tensions with the West these contacts have been reduced. On the eve of the revolution, the Russian empire had no more than a hundred physicists—including professors, docents and laboratory assistants with the equivalent of graduate degrees, but not including primary‐ or secondary‐school teachers—and very few well‐equipped laboratories. While creating conditions propitious to the long‐term growth of physics as a dispcipline, the revolution led to short‐term disruptions of research. Making matters worse, World War I cut physicists off from their customary contacts with Western scholars and laboratories, and the 1918–20 civil war between the Reds (the Bolsheviks and their allies) and the Whites (the monarchists and their sympathizers) atomized the domestic physics community.

ISSN:0031-9228    

DOI:10.1063/1.881134

出版商:AIP    

年代:1988

数据来源: AIP