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Extracts from the Internet | ||
Improving high-temperature superconductivity1 June 1998Along with new high-Tc materials, advanced fabrication technique for improving the efficiency of those already available are being actively sought for, with a particular view to increasing the critical current density, beyond which superconductivity is destroyed. D Larbalestier and his team at the Applied Superconductivity Centre of the University of Wisconsin, Madison, succeeded in identifying the critical-current-limiting factors. By using a novel magneto-optical visualization technique to monitor the current flow and the barriers it encounters in its way, microscopic defects and cracks and, to a somewhat lesser extent, grain boundaries were found to be the culprits. The development of materials free of these flaws holds the promise of considerably widening the scope of superconductivity applications. Source: http://unisci.com/ Metallic hydrogen1 June 1998The problem of making solid hydrogen metallic still remains an open one. The 1997 Berkeley experiment, the first to produce metallic hydrogen, started from gaseous hydrogen and did not pass through its solid phase. While theoretical analyses yield 340GPa as a metallization pressure for solid hydrogen, a Cornell research team reports that it remains an insulator even at 342GPa, thus challenging previous theories. Such pressure was achieved by using the so-called `diamond anvil cell' and could not be increased further because of the incipient cracking of diamond. Research into metallic hydrogen, believed to be abundant in the interiors of larger planets, is of special relevance to astrophysics. Source: Nature, May 7 An optical twin of a gamma burst1 June 1998Another gamma burst/optical source identification is reported, which differs in several important respects from two previous, February 1997 and May 1997, identifications. The gamma burst was detected by using the Compton Gamma Ray Observatory's BATSE device, and the accompanying X-ray burst, by the Italian/Dutch BeppoSAX satellite. X-ray observations allowed the burst to be localised with great precision on the celestial sphere. A few hours after the burst, a faint optical source was detected by ground-based optical telescopes at its location, whose brightness was decreasing more rapidly than in the previous identification cases. As the brightness became much lower, it turned out that the source is projected on a very distant galaxy, whose redshift was found to be z=4 using the Keck II telescope. It is this galaxy where both the gamma bursts and the optical source are most likely to have their origin. Apart from the source's being extremely distant, a surprising feature is that the gamma energy it releases is about a hundred times more than expected for a gamma burst. No sources with that high energy release are as yet known. The findings favour the cosmological origin of gamma bursts over the local (galaxy halo) model. Source: http://wwwssl.msfc.nasa.gov/default.htm Gravitational fields near neutron stars1 June 1998Neutron stars, first discovered in 1967, appear when an ordinary star is compressed and then explodes in a violent event known as supernova. About as massive as the Sun and as small as about 10 miles in diameter, a neutron star has its matter compressed to the point where space-time around is strongly (up to 30%) curved according to the theory of general relativity. Unlike Newton's theory of gravity, Einstein's also predicts the existence of an innermost circular orbit such that at distances closer to the star surface particles cannot orbit around the star and spiral down. This effect was confirmed by the Rossi Explorer observation of X-ray radiation from a binary star system located 20,000 light years from the Earth and having a neutron star as a component. The matter of the second, ordinary, star flows over to the neutron companion, emitting X-rays in doing so. Interestingly, the radiation shows periodic pulses which may be regarded as evidence of the innermost circular orbit. The finding appears to be the first ever test of a strong-field prediction of the general theory of relativity. Source: Physics News Update, Number 368 Radio-frequency burst1 June 1998An extremely powerful burst of radio-frequency radiation coming from the CI Cam, a variable star earlier known as an X-ray source only, was detected by the New-Mexico VLA radio telescope on March 31, 1998, along with an X-ray burst detected by the Rossi satellite. One explanation is that the burst was caused by a star that collapsed after having exhausted its nuclear fuel. Alternatively, the fall of a clump of matter on an invisible companion of the star - a black hole or a neutron star - might a possibility. Source: ABQjournal Science & Technology |
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources. | |
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