ISSN:0031-9228    

DOI:10.1063/1.2811308

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811309

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811311

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Spin a nucleus fast enough and it will stretch into an elongated shape. Spin it even faster and it will fission. But below the angular momentum at which fission can occur, some nuclei can be relatively stable, especially those whose lengths are twice their widths. Nuclear theory has long predicted such rapidly rotating, superdeformed states. Only recently, however, have experimenters been capable of producing such nuclei, through heavy‐ion collisions, and of observing them, with large arrays of highresolution germanium detectors. In 1986, a group working at the Daresbury Laboratory in Great Britain succeeded in measuring the largest angular momentum reported until then for a nucleus. They found dysprosium‐152 to be rotating with a spin of 60 ℏ—or about2×1020revolutions per second in a classical estimate. Several months ago the same team confirmed that this state of Dy152has a superdeformed shape: It resembles a prolate ellipsoid rotating about a minor axis. (A prolate ellipsoid has one major and two equal minor axes, and the length ratio of the major to minor axes is 2:1 for superdeformed nuclei.)

ISSN:0031-9228    

DOI:10.1063/1.2811312

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Lanthanum copper oxide, which is now regarded as the prototype for the new high‐temperature superconductors, undergoes a phase transition to an antiferromagnetic state. The critical temperature for this transition, at which the magnetic moments on copper ions begin to order antiferromagnetically, depends sensitively on the oxygen concentration. Confirmation of the existence of this antiferromagnetic phase inLa2CuO4−yand the determination, using neutron scattering, of the arrangement of magnetic moments in it provided definitive evidence last summer for the importance of magnetic phenomena in the new superconducting oxides. Philip Anderson (Princeton University) had proposed in January 1987 that superconductivity inLa2CuO4−ydoped with barium or strontium, which had been confirmed only two months earlier, arose from novel, short‐range antiferromagnetic correlations between copper spins.

ISSN:0031-9228    

DOI:10.1063/1.2811313

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A few days after the Challenger accident, on a Friday, I got a call from William Graham, who was the acting director of NASA. Mr. Graham had been a student of mine—at Caltech, and also at the Hughes Aircraft Company, where I gave a series of lectures—and thought maybe I would be of some use to the investigation. When I heard it would be in Washington, my immediate reaction was not to do it. I have a principle of not going anywhere near Washington or having anything to do with government.

ISSN:0031-9228    

DOI:10.1063/1.881143

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The recent passage of Comet Halley produced a great deal of scientific activity as well as the usual plethora of books, articles and diverse paraphernalia. So why add more? My excuse is that although Edmond Halley is famous for his comet—and rightly so—his contributions to scientific knowledge were much wider than is generally appreciated. Indeed, cometary matters represent a very small fraction of his work. Even if he had made none of his astronomical and other contributions, however, Halley would have left us an important legacy as one of the world's first geophysicists.

ISSN:0031-9228    

DOI:10.1063/1.881144

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811314

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811315

出版商:AIP    

年代:1988

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2811316

出版商:AIP    

年代:1988

数据来源: AIP