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| Issue 12, 2024 |
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Extracts from the Internet | ||
Measurement of Plank's constant1 October 1998The most accurate measurement of Plank's constant so far has been conducted by researchers at NIST, also providing more accuracy for other fundamental constants, such as the electron mass, Avogadro's number, etc. The experiment designed by B. Kibble of the National Physical Laboratory in England relies on using a solenoidal pendulum, a 1-kg mass attached to a metal solenoid in a magnetic field. The magnetic field of the solenoid balances the force of gravity acting on the mass. Decreasing the current through the solenoid wiring causes the mass to move downward, at which moment two quantities dependent on Planck's constant, namely, the velocity of the mass and the induced voltage, are measured. It proved possible to cancel out geometry sensible factors in conducting the experiment. Planck's constant is found to be h=6.62606891×10-34 Joule sec, with an uncertainty of 89×10-9, two times better than in the best measurements so far. Based on this experiment, the mass unit, kilogram, can now be defined in quantum language rather than relying on the mass standard stored in France. Source: Physical Review Letters, 21 September 1998 Kaons and supernova blasts1 October 1998Collisions of 1 Gev/nucleon gold nuclei were investigated at the GCI Lab in Darmstadt, Germany. For a period of 5×10-23 sec, the reaction zone is 3 times denser than normal nuclear matter. The micro-explosion that occurs during the collision causes gold nuclei to break up giving rise to strange mesons, mostly charged K mesons (kaons), which fly out predominantly perpendicular to the collision plane. As their paths suggest, the kaon effective mass alters at high energies, which is consistent with other experimental data and may be due to the fact that, along with kaons, antikaons are involved in the reaction. Exotic short-lived particles, kaons are of interest not only for high-energy physics but also for astrophysics, where their properties within dense nuclear matter place certain constraints on the dynamics of supernova collisions and the stability of neutron stars. Based on the results obtained, it is found that a star with a 1.5-2 solar mass iron core cannot survive a collision as a neutron star and collapses into a black hole instead. Source: http://xxx.lanl.gov/abs/nucl-ex/9807003 Nanolithography1 October 1998A Stanford research team led by H. Dai has developed a technique that uses carbon nanotubes for nanoscale image writing. Earlier, the only use of nanotubes was as AFM (atomic force microscope) tips in nanostructure studies. The new technique allows an image writing rate of 10 mm/sec. An electric field applied to the nanotube removes hydrogen atoms from the hydrogen layer deposited on the silicon substrate, after which the oxidation of the surface leads to the formation of a silicon substrate with SiO2 tracks deposited on it. With this technique, data storage at the nanometer scale becomes possible. Source: Physics News Update, Number 390 A red dwarf planet1 October 1998Red dwarfs, stars belonging to the spectral classes K and M, constitute about 70% of all stars in the Galaxy. The first discovery of an invisible companion - planet - orbiting an M- class dwarf was made by astronomers at the University of San Francisco and independently by their colleagues at the Geneva Observatory. The planet, which has 2 to 4 times the mass of Jupiter, is only 0.21 astronomical units from the star and orbits it in 61 days. The star, although only 15 light years from the Sun, is invisible to the naked eye. It is a hundred times less luminous than the Sun and three times less heavy. To date only a few stars, none of them red dwarfs, were found to have massive planets. All the planets were discovered only in an indirect way, either from perturbations in a star path or spectroscopically, from periodic fluctuations in a star's spectrum. It is hoped, however, that the new planet can be seen directly by the most powerful optical telescopes. As is the case with other massive extrasolar planets, the new planet is very close to its primary, a fact for which no interpretation is yet available. Source: Nature Science Update Acceleration anomaly1 October 1998Galileo and Ulysses spacecraft navigation data provide new evidence for the existence of the thus far unexplained acceleration of 8×10-8cm s-2 toward the Sun, which remains after contributions from all known or possible sources, such as the Sun, solar wind, planets, the Milky Way as a whole, and the dark matter of the solar system, are subtracted. The first evidence of this anomaly was provided by Pioneer 11 and 12 back in the 80s. While systematic data processing errors are still suspected, it is not ruled out that unknown gravitational effects may be behind the phenomenon. More careful analysis of the motion of planets, comets and the proposed Pluto Express craft is likely to clarify the matter. Source: Physics News Update, Number 391 |
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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