ISSN:0031-9228    

DOI:10.1063/1.2808195

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808196

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808197

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Take a bunch of granular particles, put them in a container on a rigid platform and shake the system vertically. You might find heaping, convective rolls, size segregation or traveling waves. Recent experiments with several layers of particles have produced, at a critical acceleration, a sharp transition from a flat surface to standing‐wave patterns oscillating at either one‐half or one‐quarter the excitation frequency.

ISSN:0031-9228    

DOI:10.1063/1.2808198

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

According to the standard model, shortly after the Big Bang, primordial hydrogen and helium were spread nearly uniformly throughout space. After matter began to coalesce into galaxies and other structures, nuclear cooking within massive stars produced heavier elements. But researchers still expect to see traces of the primordial elements if they look far out in intergalactic space, at distances corresponding to the earliest times. In 1971 they saw signs of hydrogen clumped in clouds located billions of light‐years away. Now, thanks to the availability of satelliteborne telescopes sensitive to ultravio let radiation, they have found hydrogen's primordial companion.

ISSN:0031-9228    

DOI:10.1063/1.2808199

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Neutron scattering research in Germany should get a boost from the construction of a new research reactor, called the FRM‐2, at the Technical University of Munich. The German federal government and the state of Bavaria have approved funding for the reactor, which, together with the beam hall and instruments, is expected to cost DM720 million. Although the reactor will have only about one‐third the power of the 57‐megawatt facility at the Institut Laue‐Langevin in Grenoble, France—the research reactor with the highest neutron flux—the FRM‐2 will have somewhat over half its flux (8×1014neutrons per square centimeter per second compared to1.5×1015 cm−2 s−1at the ILL). With a capacity for 30‐35 instruments, the reactor will provide additional neutron capability at a time when beam lines at ILL and other reactors are heavily oversubscribed. FRM‐2 will have a cold source to provide neutrons whose temperatures are below 60 K; the flux of these cold neutrons will be comparable to that at the ILL. A unique feature of the FRM‐2 will be a built‐in facility for treating human cancer with fission neutrons. The chief designer of the FRM‐2 is Klaus Boning of the Technical University of Munich.

ISSN:0031-9228    

DOI:10.1063/1.2808200

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thpheoretical computer scientists, like their counterparts in physics, suffer and benefit from a high level of intellectual machismo. They believe they have some of the biggest brains around, which they need to think about some of the hardest problems. Like mathematicians, they prove theorems and doubt the seriousness of those who don't. Lately, however, theoretical computer scientists have sought the help of physicists in understanding quantum mechanics, a hard part of physics which they now believe has great significance for their own field.

ISSN:0031-9228    

DOI:10.1063/1.881452

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

What powers the Sun? Why does it have spots? How long will it sustain life on Earth? Efforts to answer these questions about the astrophysical object that is of greatest importance to humanity have produced many advances in physics and helped lay the main foundations of astrophysics. The three questions, however, remain to be answered. For example, the best models of the Sun's nuclear power predict a significantly higher neutrino flux than is observed. (SeePHYSICS TODAYApril, page 19.) We do not know what causes sunspots and other solar activity or even why the Sun emits x rays. Modeling how stars evolve leads to age estimates for some stars that are greater than recent estimates of the age of the universe.

ISSN:0031-9228    

DOI:10.1063/1.881453

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Most theoretical physicists rely on interactions with others to stay abreast of theoretical and experimental advances. In classrooms and seminars, on blackboards and napkins, they exchange and clarify ideas with colleagues and students. Rare is the theoretical physicist who makes repeated and varied contributions apart from the throng; rarer still is one who not only contributes but also sets standards and priorities singlehandedly. Julian Seymour Schwinger, who died 16 July 1994 at the age of 76, was such an individual. Gentle but steadfastly independent, quiet but dramatically eloquent, self‐taught and self‐propelled, brilliant and prolific, Schwinger remained active and productive until his death. His ideas, discoveries and techniques pervade all areas of theoretical physics.

ISSN:0031-9228    

DOI:10.1063/1.881454

出版商:AIP    

年代:1995

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808201

出版商:AIP    

年代:1995

数据来源: AIP