ISSN:0031-9228    

DOI:10.1063/1.2809025

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2809026

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Just before dawn on 28 June last year, the Mojave Desert 200 km east of Los Angeles was struck by a magnitude‐7.3 earthquake. Although the Landers earthquake, named for the small town nearest the epicenter, was stronger than the earthquake that had rocked San Francisco three years earlier, it attracted little public attention, because the region is so sparsely populated. But it made seismological history. The dense and extensive network of seismographic stations built up in the Far West during the 1980s has provided convincing evidence that the Landers quake triggered secondary tremors as far away as Yellowstone National Park, 1250 km to the northeast.

ISSN:0031-9228    

DOI:10.1063/1.2809027

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

At the Hanford Nuclear Reservation in Richland, Washington first steps are being taken toward mitigation of the threat posed by hydrogen buildup in a milliongallon tank of radioactive waste. Shown in the photograph is a 64‐foothigh pump being lowered on 4 July through a 40‐inch‐diameter pipe into tank 101‐SY, which is buried below ground. Of the 177 tanks of high‐level waste stored at Hanford, 101‐SY is the most notorious, because of the high concentrations of hydrogen that are produced by its mixture of radioactive materials and organic chemicals. (SeePHYSICS TODAY, March 1992, page 17.) The material in the tank forms a viscous slurry at the bottom, covered by a liquid layer and topped by thick pieces of crust. As the hydrogen is generated, it is trapped in the slurry, and about every three months it is released in a giant “burp.” Hydrodynamic models have indicated that the pump should be able to stir the tank contents enough to promote a continual release of hydrogen gas and prevent the accumulation of explosive concentrations.

ISSN:0031-9228    

DOI:10.1063/1.2809028

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The first practical solar cell was developed at Bell Laboratories in 1954. With the advent of the space program, photovoltaic cells made from semiconductor‐grade silicon quickly became the power source of choice for use on satellites. The systems were very reliable, and cost was of little concern. In the early 1970s, the disruption of oil supplies to the industrialized world led to serious consideration of photovoltaics as a terrestrial power source. This application focused research attention on improving performance, lowering costs and increasing reliability. These three issues remain important today even though researchers have made extraordinary progress over the years. This article details that progress.

ISSN:0031-9228    

DOI:10.1063/1.881362

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Given the success of Ludwig Boltzmann's statistical approach in explaining the observed irreversible behavior of macroscopic systems in a manner consistent with their reversible microscopic dynamics, it is quite surprising that there is still so much confusion about the problem of irreversibility. (See figure 1.) I attribute this confusion to the originality of Boltzmann's ideas: It made them difficult for some of his contemporaries to grasp. The controversies generated by the misunderstandings of Ernst Zermelo and others have been perpetuated by various authors. There is really no excuse for this, considering the clarity of Boltzmann's later writings. Since next year, 1994, is the 150th anniversary of Boltzmann's birth, this is a fitting moment to review his ideas on the arrow of time. In Erwin Schro¨dinger's words, “Boltzmann's ideas really give an understanding” of the origin of macroscopic behavior. All claims of inconsistencies that I know of are, in my opinion, wrong; I see no need for alternate explanations. for further reading I highly recommend Boltzmann's works as well as references 2–7. (See alsoPHYSICS TODAY, January 1992, page 44, for a marvelous description by Boltzmann of his visit to California in 1906.)

ISSN:0031-9228    

DOI:10.1063/1.881363

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The US played host in July to the XXIV International Physics Olympiad, in which 201 top high school physics students from 41 nations competed in theoretical and experimental exams. Although the weeklong event, held this year in Williamsburg, Virginia, naturally fosters some international rivalry, its purpose is just as much to build friendships around a common interest in physics. The US organizing committee worked particularly hard to promote these friendships (see the summary on pages 42–43 by Arthur Eisenkraft, the executive director of the XXIV Olympiad.)

ISSN:0031-9228    

DOI:10.1063/1.881364

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2809029

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2809030

出版商:AIP    

年代:1993

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2809031

出版商:AIP    

年代:1993

数据来源: AIP