ISSN:0031-9228    

DOI:10.1063/1.2916263

出版商:AIP    

年代:1984

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2916226

出版商:AIP    

年代:1984

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2916232

出版商:AIP    

年代:1984

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2916236

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

For the lonely among us who are eager to make contact with life elsewhere in the Universe, the abundance or scarcity of planetary systems around other stars is a particularly interesting question. Tentative reports of gravitational perturbations in the positions of a few nearby stars have been taken as very inconclusive evidence of planets, but until last summer we had no direct evidence of solid, non‐stellar material orbiting any star other than our own.

ISSN:0031-9228    

DOI:10.1063/1.2916237

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Over twenty years have elapsed since Leonard Schiff at Stanford and, independently, George E. Pugh at the Defense Department predicted that a gyroscope in orbit about Earth would precess as a consequence of Einstein's general theory of relativity. Such behavior depends on an aspect of the theory of gravity that remains untested to this day. Although the concept is simple, the experiment is formidable: The precession is about 44 milliarcsec/year, to be measured with an accuracy of 1 milliarc‐sec per year. Undaunted, Schiff, together with Stanford colleagues William Fairbank and Robert Cannon, respectively, set up a program to develop the experiment. Since 1962, a Stanford team led by Francis Everitt and later having the support of NASA's Marshall Space Flight Center, has patiently and persistently toppled many technical barriers, bringing the experiment from the realm of the improbable into the world of the possible. In late 1980, a committee of 16 scientists and engineers convened by NASA spent five days reviewing the technical readiness of the experiment, which is called the Gravity Probe B. They gave it a sound endorsement and concluded it was now ready to proceed to its flight phase.

ISSN:0031-9228    

DOI:10.1063/1.2916238

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

People frequently do more than one thing at a time: Driving a car while listening to the radio, cooking a meal so that several dishes are ready at once, or playing two lines of melody on a piano are all familiar examples. On a larger scale, many human activities, such as building a house or complicated experimental apparatus, or putting out a magazine, are separated into what might be called “units of activity” that are performed separately by people working in parallel. On a smaller scale, our brains control separately—but in a coordinated fashion—breathing, heartbeat and several different kinds of motor activity. In each of these cases, separate units of activity are carried out by separate processors (different people or different parts of the brain, for example) that work simultaneously (at the same time, but not in lockstep) and interact to produce the final effect or product.

ISSN:0031-9228    

DOI:10.1063/1.2916239

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Although the title of our article addresses engineeringlimits, we do not mean to convey a grim outlook. Over the past 20 years, the technology of computer systems has advanced dramatically in terms of performance, cost and reliability. There is every reason to expect this advance to continue, at a rate almost as shocking as we have experienced to date. However, the advance already achieved has pushed the mechanisms of switching, storage and communication close enough to fundamental physical limits to bring into awareness for the first time limitations in the engineering of high‐performance systems.

ISSN:0031-9228    

DOI:10.1063/1.2916240

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

We are on the verge of a revolution in computing, spawned by advances in computer technology. Progress in very‐large‐scale integration is leading not so much to faster computers, but to much less expensive and much smaller computers—computers contained on a few chips. These machines, whose cost‐effectiveness is expected to be staggering, will make it practical to build very‐high‐performance computers, or “supercomputers,” consisting of very many small computers combined to form a single concurrent processor.

ISSN:0031-9228    

DOI:10.1063/1.2916241

出版商:AIP    

年代:1984

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2916242

出版商:AIP    

年代:1984

数据来源: AIP