ISSN:0031-9228    

DOI:10.1063/1.2807717

出版商:AIP    

年代:1996

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.881504

出版商:AIP    

年代:1996

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2807719

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A side from ordinary hydrogen, only four other nuclear species (2H,3He,4Heand7Liare left over from the Big Bang. Of these, deuterium(2H)is the one whose obsei^ved abundance provides the most accurate determination of the crucial cosmological parameter&rgr;b,the present‐day average mass density of ordinary baryonic matter (made up of protons and neutrons) in the universe. In principle, if one knows the primordial abundance of any one of these light nuclei, relative to1H,the theory of Big Bang nucleosynthesis specifies&rgr;b.(See the figure below.)

ISSN:0031-9228    

DOI:10.1063/1.881505

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Now that the rantare of simply creating a Bose–Einstein condensate in a dilute atomic gas has died down (see the “Reference Frame” column by Daniel Kleppner on page 11), the leading research groups are proceeding in earnest to map out the properties of their condensates. Four experimental groups reported their latest results in invited talks at a session on Bose–Einstein condensation (BEC) at the meeting of the American Physical Society's Division of Atomic and Molecular Physics (DAMOP) held in Ann Arbor in May.

ISSN:0031-9228    

DOI:10.1063/1.881506

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Two years after a group of researchers at Bell Labs successfully operated a novel infrared, semiconductor laser, they have the device putting out hundreds of milliwatts of power at temperatures near 50 °C. That's 40 °C warmer than the highest temperature at which its competitors in this wavelength region can operate, and then only at much lower power. The new laser is a quantum cascade laser developed by Jerome Faist, Federico Capasso and their colleagues at Bell Labs. Their modifications of the 1994 design have produced a laser that operates in a pulsed mode at 5.2 &mgr;m and generates maximum peak powers of about 200 mW at 27 °C and 100 mW at 47 °C.

ISSN:0031-9228    

DOI:10.1063/1.881507

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Technology is directly linked to our national economic growth, just as it is to the growth of other nations. The globalization of technology poses difficult challenges for policymakers, not just in technology policy, but in areas such as trade and regulatory policy. Technology‐related policy issues are made all the more difficult as one struggles to interpret our national interest; after all, much of the technology needed for national growth is developed and managed by multinational companies whose markets, operations and sources of capital are distributed throughout the globe.

ISSN:0031-9228    

DOI:10.1063/1.881508

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An important theme that threads through many areas of current interest in condensed matter physics is the effect of randomness and disorder. Prior to the 1960s, disorder and impurities were often viewed as unavoidable nuisances that masked the true behavior of ideal systems. We have since learned that disorder itself can bring forth fascinating and often unexpected new phenomena in condensed phases of matter. (See the December 1988 special issue ofPHYSICS TODAY, dedicated to disordered solids.)

ISSN:0031-9228    

DOI:10.1063/1.881509

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An elderly gentleman with heart disease was admitted to hospital for treatment of an abnormal heart rhythm called ventricular tachycardia. This potentially fatal rhythm can occur days, or even years, after a heart attack. It is associated with an abnormally rapid heartbeat that arises from tissue in the heart attack‐damaged portions of the ventricles—the two main pumping chambers of the heart. (See the box on page 41.)

ISSN:0031-9228    

DOI:10.1063/1.881510

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In a search some three years ago for an old catalog of optical instruments, I went to the science and technology division of the New York Public Library and requested a certain volume indexed under what seemed an appropriate category. What the libra 17 messenger delivered to me turned out to be a diverse collection of pamphlets on optics and laboratory instruments. The catalog I had hoped to locate was not in the collection, and the items were of no interest to me—with one exception: a seemingly misfiled eight‐page pamphlet that came as a stunning surprise. Its cover page announced a “Printer's Proof of General Outline Plan for Exhibition on Color.” The exhibition was scheduled to begin on 1 January 1931 at the “Museums [sic] of the Peaceful Arts (A Museum of Science and Industry)” at 220 East 42nd Street in New York City. The existence of such a museum was as surprising to me as the mounting of the exhibition.

ISSN:0031-9228    

DOI:10.1063/1.881511

出版商:AIP    

年代:1996

数据来源: AIP