ISSN:0031-9228    

DOI:10.1063/1.2808730

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808731

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808733

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808735

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2808736

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

More than 40 years ago Bertram N. Brockhouse and Clifford G. Shull started working separately at two of the world's first nuclear reactors, exploiting the opportunities to do basic research with the relatively large fluxes of neutrons from those machines. Their efforts helped launch the technique of neutron scattering, which is now widely used to study materials: Being uncharged, neutrons penetrate deeply to interact with the atomic nuclei of a sample, and having a magnetic moment, they also probe its magnetic structure. Today neutron scattering occupies thousands of researchers in condensed matter, materials physics, chemistry, biology and engineering (seePHYSICS TODAY, November, page 17).

ISSN:0031-9228    

DOI:10.1063/1.2808737

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

One of the “Key Projects” intended for the Hubble Space Telescope from the start was to pin down the distance to the Virgo cluster by measuring Cepheid variable stars in that massive assemblage of galaxies some 50‐million light‐years away. Cepheids are the primary yardsticks for astronomical distances beyond the reach of parallax measurement. The inability to determine cosmologically relevant distances with confidence has been the principal source of confusion in our knowledge ofHo,the Hubble constant. The HST's measurement of Cepheids in the Virgo cluster was to be the opening salvo in an assault that would soon pin down this fundamental parameter of cosmology to within 10&percent;, once and for all. Estimates of the Hubble constant in recent years have differed by as much as a factor of two, and the stakes are high. The reciprocal ofHois, after all, the first approximation to the age of the universe.

ISSN:0031-9228    

DOI:10.1063/1.2808738

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

On 1 October, four years after the National Science Foundation chose to build a new high‐magnetic‐field laboratory at Florida State University rather than upgrade the existing Francis Bitter National Magnet Laboratory at MIT (seePHYSICS TODAY, January 1991, page 53), the new laboratory was dedicated in Tallahassee.

ISSN:0031-9228    

DOI:10.1063/1.2808739

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Optical observations by ground‐based astronomers have long been limited by the distorting effects of the Earth's atmosphere. Primary mirrors have been polished to exquisite accuracy for telescopes with apertures as large as 10 meters, but at optical wavelengths these can deliver an angular resolution typically no better than that of a 25‐cm telescope, as atmospheric turbulence deforms the image on a millisecond time scale. One (highly expensive) approach to overcome this problem has been to loft instruments such as the Hubble Space Telescope above the atmosphere. Another approach, pursued by instrument builders in the astronomy community and their counterparts in the military, has been to design electro‐optical systems that measure and undo the effects of clear‐air turbulence in real time. (See figure 1.) A number of such adaptive optic devices have already been built and operated on large ground‐based telescopes, delivering near‐diffraction‐limited performance at infrared and visible wavelengths. With the first significant astronomical images beginning to appear from these adaptive optics systems (see the cover of this issue), the level of interest in this work is rising very rapidly in the astronomy community.

ISSN:0031-9228    

DOI:10.1063/1.881406

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Beginning in 1927 the University of Michigan's summer school in physics became famous astheinternational forum for learning about the latest advances in modern physics. Within a decade of its inception perhaps half of the most renowned European physicists had turned up for its sessions—scientists like Fermi, Dirac, Pauli, Sommerfeld, Goudsmit, Uhlenbeck, Ehrenfest and the astrophysicists Robert Atkinson and E. A. Milne.

ISSN:0031-9228    

DOI:10.1063/1.881407

出版商:AIP    

年代:1994

数据来源: AIP