ISSN:0031-9228    

DOI:10.1063/1.2808859

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808860

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For more than a decade now, experiments in high‐energy physics have yielded very few real surprises. Far from being a reproach to the experimenters, this state of affairs is a testament to the encompassing success of the standard model of the elementary particles that took its definitive shape in the 1970s. In the early 1980s the heavy vector bosons,W±andZ0,that mediate the weak interactions were found just about where they were expected, and the millions ofZ0screated since then have confirmed the predictions of the standard model in spectacular detail.

ISSN:0031-9228    

DOI:10.1063/1.2808861

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Some of the more subtle predictions of quantum mechanics have had to wait decades before experiments were capable of validating them. One of these is the so‐called retarded force between charges that are so far apart that it takes a relatively long time for a photon to travel between them. (See the article by Larry Spruch inPHYSICS TODAY, November 1986, page 37.) In the 1940s Hendrik B. G. Casimir and D. Polder (then at the scientific laboratory of N. V. Philips's Gloeilampenfabriken in Eindhoven, the Netherlands) analyzed interactions affected by the finite speed of light. They found that the van der Waals potential between two atoms, which goes asr−6,becomes a potential that varies asr−7when the atoms are separated by distances greater than a few hundred Bohr radii. A related prediction is that the interaction between a neutral atom and a conducting wall changes from anr−3to anr−4potential when the atom is far enough from the wall. Casimir subsequently formulated an expression for the force between two conducting plates which is now known as the Casimir force

ISSN:0031-9228    

DOI:10.1063/1.2808862

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For the first few million years of its life, the Sun was a large red star surrounded by a disk of gas and dust—the primitive solar nebula—that reached out beyond the boundaries of our present planetary system. Like all stars, the Sun was created by the collapse of a cold, dense core within a rotating cloud of interstellar material, debris from supernovae and other evolved stars of a previous generation. Angular momentum in the cloud allowed collapse along only one axis, thus leaving the material in a thin orbital plane around the new Sun. During the next hundred thousand years, the dust began to coagulate into larger particles, which eventually became planetesimals, the seeds for the nine planets. Over a further 10 million years, these planetesimals grew larger, clearing the residual gas and dust by dynamical sweeping and gravitational capture. Collisions led to further growth and the creation of a system of planets, comets and asteroids orbiting the young Sun. Within a billion years, the first life came into existence on one of those planets. Now, 5 billion years later, that life has developed to a degree of sophistication that seemingly defies the second law of thermodynamics.

ISSN:0031-9228    

DOI:10.1063/1.881387

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The last period of extensive curriculum reform in physics occurred about 30 years ago. The objectives of that earlier effort were sweeping. The high school physics course was an early target, and the Physical Science Study Committee was created to effect its reform. The Commission on College Physics, formed in June 1960, had as its objective the revitalization of the entire undergraduate physics curriculum. In the wake of this period of reform a new genre of introductory textbooks, modeled on the successful textbook authored by David Halliday and Robert Resnick, became standard. These texts followed the more mathematical emphasis favored after World War II but gave more attention to worked‐out examples and other pedagogical elements as well as more substantial exercises and problems than was characteristic of their predecessors

ISSN:0031-9228    

DOI:10.1063/1.881388

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808863

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808864

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808865

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808869

出版商:AIP    

年代:1993

数据来源: AIP