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| Issue 4, 2024 |
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Extracts from the Internet | ||
Neutron Phase Shift1 July 2002H Rauch and his colleagues at the Atomic Institute of the Austrian University (Vienna, Austria) and the Laue-Langevin Institute (Grenoble, France) performed an experiment which demonstrates for the first time a shift in the phase of a neutron passing through a narrow slit. The effect was predicted theoretically by J M Levy-Leblond and D Greenberger in the late 1980s. The motion of a neutron that has passed through a narrow horizontal slit is quantized in the vertical direction leading to a phase shift in the direction of motion. The experiment used an array of 186 slits 22.1 mkm in width and a neutron beam from a nuclear reactor. The beam was split into two components, one of which was sent through the slit system. The phase shift was measured from the interference of the beams in a neutron interferometer and found to be in good agreement with theoretical calculations. Earlier this year, discrete quantum states of neutrons in a gravitational field were observed by another team at the Laue-Langevin Institute (see Physics Uspekhi 45 233 (2002)). Source: Nature 417 630 (2002) Measuring the orbital angular momentum of a photon1 July 2002Along with the spin angular momentum, photons are characterised by an orbital angular momentum. M Padgett and his colleagues at the University of Glasgow (Scotland) have developed a technique for measuring the orbital momentum of a singular photon. Using a sequence of interferometers they split a beam of light into two, with an odd and even orbital angular momenta respectively. Repeating this procedure for both of these beams enabled researchers to distinguish photons with four different orbital momentum states. Measurements were even possible with such low initial beam intensities that only one photon reached the detector. Source: Phys.Rev.Lett. 88 257901 (2002) Crystalline Mobius strip1 July 2002Researchers at Hokkaido University (Japan) have succeeded in fabricating one-surface Mobius-strip-like crystalline structures. These structures are single-crystal entities having neither seems nor any other defects. Earlier, thin crystalline niobium-selenide ribbons had been synthesized by heating selenium and niobium in a vacuum-tight quartz tube. The Japanese team improved the technique by introducing a temperature gradient, with a consequence that selenium could be in the gaseous and liquid phases at one at the same time in the tube. The surface tension of the liquid led to the formation of various ring configurations, Mobius strips among them. The unusual crystals may find application in the study of topological effects in quantum mechanics. Source: Nature 417 397 (2002) Verification of special relativity1 July 2002According to the special theory of relativity, the speed of light is independent of the direction and magnitude of the observer's velocity v. The independence of light speed of the magnitude of v has been demonstrated recently with a record precision in experiments at the Universities of Konstanz and Dusseldorf in Germany (see Physics Uspekhi 45 233 (2002)). The same team now has performed an experiment to verify the direction independence (modern version of the Michelson-Morley experiment), whose accuracy, 1.7 x 10-15, is the best achieved to date and three times better than earlier. The researchers studied a standing electromagnetic wave in a liquid helium cooled cavity made of sapphire crystal. Two such resonant cavities were oriented at right angles to each other. The whole setup could be rotated - thus enabling the researchers to establish the direction independence of light speed. Source: Physics News Update, Number 590 Dark galaxies1 July 2002The theory of galaxy formation has long been plagued by a problem concerning small galaxies, i. e., the satellites of large ones: according to numerical simulations, their number is much larger than astronomical observations reveal. It was assumed that the lacking satellites exist in the form of concentrated dark matter which is unseen because stars in it are very few. This hypothesis has now been confirmed by gravitational lensing observations carried out by N Dalal of the University of California at San Diego and C Kochanek of Cambridge, Massachusetts. N Dalal and C Kochanek have studied 7 galaxies that act as gravitational lenses for still farther galaxies. Based on the configurations of additional images due to lensing, the researchers came to the conclusion that 6 of the 7 lensing galaxies have numerous dwarf galaxies around them and that for each of these six the dwarf galaxies have about 2% of the central galaxy's mass. Our Galaxy also may be expected to have many invisible satellites. The star formation process in them may have proved inefficient due to the low temperature (low virial velocity) of the galactic gas. Source: http://arXiv.org/abs/astro-ph/0111456 |
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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