ISSN:0031-9228    

DOI:10.1063/1.2994909

出版商:AIP    

年代:1978

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2994860

出版商:AIP    

年代:1978

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2994862

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Arno Penzias and Robert W. Wilson of Bell Laboratories were awarded half the 1978 Nobel prize in physics for their discovery of the cosmic microwave background, which they found accidentally while attempting to measure the intensity of radio waves emitted from the halo of gas surrounding our galaxy. Their 20‐foot antenna had been built in Holmdel for satellite communications with Echo and Telstar. We recently discussed the discovery with Penzias and Wilson, who explained that their antenna was more directionally sensitive than other radio telescopes of the day. The Bell Labs antenna has back lobes more than 30 dB below an isotropic response. Thus, assuming the Earth to be at 300 K, 1/1000th of its radiation intensity (or about 0.3 K) would be received by this antenna from the ground. (Temperature and intensity are linearly related at radio wavelengths.) In an ordinary radio telescope, one might receive 20–30 K from the ground.

ISSN:0031-9228    

DOI:10.1063/1.2994864

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

More than ten years of painstaking measurements of the solar‐neutrino flux have been summarized, and at least as many years of future experimentation have been previewed, in conference talks and in journal articles over the last year. At the Conference on the Status and Future of Solar‐Neutrino Research held at Brookhaven National Laboratory in January, Raymond Davis Jr and his coworkers from Brookhaven presented a statistical average of the past eight years of measurements of the solar‐neutrino flux. The value was1.7 ± 0.4SNU (one solar‐neutrinounit = 10−36captures per target atom per second), about one‐third that predicted by the standard solar model (4.7 SNU). Unlike the first data that hinted at the unexpectedly low value, the current results have gained general acceptance because the careful refinements and checks in the intervening years have dispelled most doubts. No one knows whether the current discrepancy between theory and experiments reflects an inadequate understanding of the dynamics of the Sun's core or a lack of knowledge of some aspect of nuclear or neutrino physics (although there tends to be some mutual finger pointing!). To resolve the question, many research groups have advanced concepts for future experiments. Feasibility studies of these proposed experiments continue to be updated and debated.

ISSN:0031-9228    

DOI:10.1063/1.2994865

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The National Science Foundation has approved a grant of $1 million over the next three years for the construction of a synchrotron radiation facility at the Cornell Electron Storage Ring. The Cornell High Energy Synchrotron Source will produce x rays up to 100 keV, a higher energy than is available from other existing or planned sources in the US; it will thus complement synchrotron radiation facilities now operating or under construction at Brookhaven, Wisconsin and Stanford (see PHYSICS TODAY, March 1977, page 17). Conversion of the 12‐GeV electron synchrotron at Cornell to a colliding‐beam device for up to 8‐GeV electrons and 8‐GeV positrons is scheduled to be completed in the spring of 1979; the synchrotron‐radiation facility should then be ready for users in the summer of 1979.

ISSN:0031-9228    

DOI:10.1063/1.2994866

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

How many basic standards do we need? Standards are necessary to measurement, and for reasons of accuracy and convenience many measurements involve frequency. With atomic and molecular transitions serving as references, measurement precisions near10−16are possible. The duration of the second is determined by a resonance in the cesium atom, and international atomic time is the reference for all time and frequency measurements in the world. Furthermore, frequency measurements lead,viathe speed of light, to the measurement of wavelengths and,viatransducers, to the measurement of many other physical quantities such as temperature and pressure. As a result, time and frequency metrology is at the root of any thinking to revise or improve our system of basic standards of measurement.

ISSN:0031-9228    

DOI:10.1063/1.2994867

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Not just biological phenomena but most physical phenomena as well become drastically altered or impossible in spaces of fewer than three dimensions. As is well known, the cooperative behavior of many‐body systems depends very strongly on the coordination of the closely interacting particles and therefore on the number of spatial dimensions. As we shall see, not only does an examination of physics in fewer than three dimensions illuminate the familiar world of three dimensions, there are also real systems whose structure effectively reduces their dimensionality and for which, therefore, low‐dimensional physics is a prerequisite. As a consequence, a considerable effort has been expended in explaining the properties of lower‐dimensional and, especially, linear systems. During the last decade there has been a veritable explosion in the “one‐dimensional” literature. In this article we would like to discuss in the context of magnetism some of the motivating factors for this explosion and the progress that has been achieved so far.

ISSN:0031-9228    

DOI:10.1063/1.2994868

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Fifty years ago in theZeitschrift fu¨r Physik, two papers were published which laid the foundations for the modern quantum theory of solids. Arnold Sommerfeld quantized the theory of the electron gas, and Felix Bloch showed how this could be generalized to a realistic theory for electrons in solids. In a delightful article inPHYSICS TODAY(December 1976 page 23) Bloch has recounted the circumstances in which he came to work on the electron theory of metals in Leipzig as Heisenberg's first graduate student.

ISSN:0031-9228    

DOI:10.1063/1.2994869

出版商:AIP    

年代:1978

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2994870

出版商:AIP    

年代:1978

数据来源: AIP