PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Publ

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PHYSICS NEWS UPDATE A digest of physics news items prepared by Phillip F. Schewe, AIP Public Information Number 162 January 31, 1994 THE FIRST DIRECT OBSERVATION OF STRUCTURE IN THE COSMIC MICROWAVE BACKGROUND (CMB) has been made by a team of astronomers using a telescope at Tenerife, in the Canary Islands. Two years ago the Cosmic Background Explorer (COBE) detected structure in the CMB at a level of 1 part in 100,000 over angular swatches of 10 degrees. This structure, however, was inferred from statistical correlations in the underlying data and did not correspond to the blue and red clumps one saw in the famous COBE maps of the entire sky. The Tenerife measurements, in contrast, directly display primordial fluctuations in the temperature of the CMB (variations about an average value of 2.7 K) at a level of 2 parts in 100,000 over 5-degree chunks of the sky, for the portion of the sky covered by the Tenerife survey. These features would not correspond to any supercluster we would see today since the largest such structure would still subtend an angular size of less than 1 degree when projected onto the CMB. The Tenerife and COBE results are consistent with each other. For example, the quadrupole component of the CMB fluctuations is calculated to be 26 +/- 6 microkelvins for Tenerife and 17 +/-5 for COBE. (S. Hancock et al., Nature, 27 January 1994.) ATOM-BOMB SIZED METEOROID EXPLOSIONS in the Earth's atmosphere occur many times a year. In general, meteors will fragment upon entering the upper atmosphere because of friction. Smaller fragments will burn up but the larger ones may actually explode, at altitudes of 20 miles or so. Data from military satellites being made public for the first time reveal the scope of these meteoroid blasts: an average of 8 events a year were observed to have an energy equivalent to a small nuclear bomb, although the true occurrence may be 10 times larger. Scientists estimate that every 10 million years we should receive a catastrophic hit that would devastate life forms over much of the planet, much like the dinosaur-killing impact 65 million years ago. Much of the military data were originally gathered in an attempt to discriminate between meteoroid blasts and manmade nuclear explosions. (The New York Times, 25 Jan; Sky & Telescope, Feb 1994.) INTERMETALLIC SUPERCONDUCTORS operate in a much colder temperature regime than ceramic superconductors, but may still be important for industrial purposes. A Y-Pa-B-C material developed at AT&T Bell Labs (Robert Cava, 908-582-2180) is superconducting at 23 K, the highest transition temperature yet for a bulk intermetallic compound (Nature, 13 Jan. 1994). This material, at least for now however, is multi-phase, meaning that several phases---each with its own structure---are present in the sample. This complicates the study of superconductivity properties. The same team of scientists has now reported a single-phase material, Ln-Ni-B-C, which suerconducts at 16.6 K (Nature, 20 Jan). The AT&T scientists believe that these represent the first of what may be a new family of intermetallic superconductors with useful properties. For example, they might facilitate higher magnetic fields than are possible with existing low-temperature superconductors used in making wire, such as Nb-Sn.


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