ISSN:0031-9228    

DOI:10.1063/1.2808953

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808954

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808955

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808956

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Surprises abound when strong magnetic fields are imposed on two‐dimensional electron gases at low temperature. When the electron density approaches an integral multiple &ngr; of the density of magnetic flux quanta threading the plane, the resistivity of the electron system begins to vanish and its Hall resistance takes on the quantized valueh/ve2to a spectacular level of precision. That's the integral quantum Hall effect, for whose serendipitous discovery at Grenoble in 1980 Klaus von Klitzing won the 1985 Nobel Prize in Physics.

ISSN:0031-9228    

DOI:10.1063/1.2808957

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

No superconductor has broken the record for the highest critical temperature since 1988, when a thalliumbearing compound, exhibiting resistanceless conduction at temperatures as high as 125 K, laid claim to the title. (SeePHYSICS TODAY, April, 1988, page 21.) But in early May a group from ETH in Zurich reported measuring a superconducting transition several degrees above 130 K in a compound containing mercury together with barium, calcium, copper and oxygen. The researchers were not able to specify the exact stoichiometry of the new champion, because their sample consisted of several phases of the compound and they have been unable so far to separate out the phase that is responsible for the highTc.

ISSN:0031-9228    

DOI:10.1063/1.2808958

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

According to the standard model of the Big Bang, the only elements created during that event were hydrogen, helium and some lithium; the rest were brewed in the stars. Over the past few decades nuclear astrophysicists have sorted out the complex chain of stellar reactions responsible for the observed abundances of the isotopes, with remarkable success in all the most critical reactions but one:12C(&agr;,&ggr;)16O.This reaction is a key stepping‐stone in the synthesis of heavier elements, linking the stage that burns helium to produce carbon and oxygen with the later stages fueled by those elements. If helium burning yields more or less oxygen or carbon, it is predicted that the later stages will be strongly affected, and so will the ultimate fate of massive stars.

ISSN:0031-9228    

DOI:10.1063/1.2808959

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Physicists have always been fascinated by the very small. These days, the inner structures of everyday items such as the personal computer fall into that size category and warrant our interest. The critical dimensions of individual features of state‐of‐the‐art memory chips are now as small as 500 nanometers and are getting smaller. The microwave transistors in some satellite dish receivers require gates smaller than a quarter of a micron.

ISSN:0031-9228    

DOI:10.1063/1.881357

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Postmodern movements are well known in the arts. After a major artistic revolution, and after the “modern” innovations have been assimilated, the threads of premodern thought are always reconsidered. Much of value may be rediscovered and put to new use. The modern context casts new light on premodern thought, which in turn shades perspectives on modernism.

ISSN:0031-9228    

DOI:10.1063/1.881358

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Venus is the planet most similar to the Earth in mass, radius and solar distance. Current theories of the early evolution of the solar system suggest that Earth and Venus each formed by the accretion of planetesimals—small rocky or rock‐metal objects—that collectively constituted a well‐mixed sample of material condensed from the inner solar nebula. The bulk compositions of the two planets should thus be similar. The rates of internal heat generation and the energy available to drive interior convection should also be similar. An important difference between the two planets, however, is the character of their atmospheres. The mass of the dominantlyCO2atmosphere of Venus is two orders of magnitude greater, as a fraction of planet mass, than that of Earth's atmosphere, and the surface temperature is 450 K higher, a consequence of continuous global cloud cover and a runaway greenhouse effect. The mass ofH2Oin a vertical column of unit area is four to five orders of magnitude less for Venus's atmosphere than for the atmosphere and hydrosphere on Earth. As a result, the surface of Venus lacks a water cycle, and the processes of weathering, erosion and sediment transport that dominate terrestrial landforms are comparatively unimportant.

ISSN:0031-9228    

DOI:10.1063/1.881359

出版商:AIP    

年代:1993

数据来源: AIP