 |
RSS feeds |
|
|||||
| Issue 4, 2024 |
|
||||||
|
|
|
||||||
Extracts from the Internet | ||
Decay of the Ds meson1 June 2008CLEO Collaboration (Cornell University) reported observations for the first time of the decay of a charmed meson (with a ñ quark in its composition) to a baryon-antibaryon pair. Ds mesons were created in the reaction e+e-→Ds*-anti-Ds+ when electron and positron beams collided at center-of-mass energy of about 4170 MeV. The CLEO detector recorded meson decays into protons and antineutrons Ds+→p anti-n. The probability of this process was measured: 1,30 ± 0,36) × 10-3. All in all, 13 decays were recorded. Among the known charm mesons, only Ds possesses a mass sufficiently large for decaying into a pair of nucleons. The decay proceeds through the annihilation channel and involves a virtual W+ boson. The results of the experiment are important for testing complicated theoretical models describing decays of charm mesons. Sources: Phys. Rev. Lett. 100 181802 (2008) Quantum Hall effect without magnetic field1 June 2008The quantum Hall effect was previously observed only in thin films placed in strong external magnetic field at temperatures close to absolute zero. Charles Kane and his colleagues made a theoretical prediction that this effect may arise in certain materials without external magnetic field, provided electrons are in certain states of motion and polarization, with strong spin-orbital interaction. The moving electron gas creates its own internal magnetic field responsible for the Hall effect. A group of researchers of Princeton University led by Z. Hasan observed for the first time the quantum Hall effect without external magnetic field in a crystalline bismuth-antimony compound Bi0,9Sb0,1. Scattering of ultrashort x-ray pulses on faces of the crystal was studied. The characteristics of scattering allowed an investigation of charge distribution in the crystal. This distribution is found to have the form typical of the Hall effect. Source: Nature 452 970 (2008) Radiation transmission through subwavelength holes1 June 2008In 1950 C.J. Bouwkamp developed a theory describing how electromagnetic waves pass through holes with below-wavelength diameter. Bouwkamp predicted the distribution of charge and electric field induced in the matter in the vicinity of the hole. Since than, numerous experiments studied the transmission of waves through small holes in metal plates but there was no direct testing of Bouwkamp's theoretical results. The first to measure the distribution of electric field near a hole were A. Adam (Delft University, The Netherlands) and his coworkers. Radio waves of frequency 1012 Hz were sent through holes in a gold plate. Radiation went through holes even when their diameters were a mere 1/50 of light wavelength. The gold plate was placed on the surface of a GaP crystal. The measurement method was based on the fact that the microwave radiation induced charges and an electric field in the gold plate and these in their turn induced changes in the optical refractive index of the GaP crystal in the proximity of the hole. These small changes were recorded by means of a laser beam. Laser pulses were synchronized with the radio wave source and served to determine the dynamic pattern of charge and electric field distribution on the metal surface close to the hole with spatial resolution less than one wavelength and temporal resolution better than one period of oscillations of the microwave radiation. The results of measurements confirm the theoretical calculations of C.J. Bouwkamp. The approach used in this experiment may find practical applications in microscopy using electromagnetic waves of the teraherz range, THz. Source: Optics Express 16 7407 (2008) Memristor1 June 2008S. Williams and his colleagues at Hewlett Packard created a new type of passive element of electric circuits which change their electric resistance depending on the amount of charged passed. The concept of this instrument, given the name memristor (Memory Resistor), was suggested by L. Chua (Califonia University) in 1971. The electric properties of the memristor resemble the hysteresis; similar behavior of resistance was earlier observed in current-voltage characteristics of microelectronic devices based on thin films. S. Williams and his colleagues built the memristor of two parts of titanium dioxide — a semiconductor — in contact with each other, one of which was doped with impurity atoms. Electric field causes impurities to drift, producing a typical hysteresis. Memristors may find applications alongside ordinary electronic components as, for instance, electronic switches and memory elements. Source: Nature 453 80 (2008) Intergalactic gas1 June 2008The totality of available observational data (including the measurements of microwave background anisotropy) and their theoretical interpretation established quite reliably that baryons make up approximately 4.5% of the mass of matter in the Universe. However, we see only about half of this amount as stars, gas clouds in galaxies and hot gas in galaxy clusters. It is most likely that the missing baryons reside in the intergalactic gas. Detailed computer simulation showed that gravitation must force the non-baryon dark matter (hidden mass), the galaxies and the intergalactic gas to gather into filament-like structures and that huge galaxy clusters must be located where filaments intersect one another. The gas temperature is predicted to be about 105-107 K. Filament-like distribution of matter is indeed revealed by the distribution of galaxies and weak gravitational lensing but no data was obtained until recently on the presence of baryonic gas in such filaments. The reason was its very low density and consequently very weak emission intensity. Favorable conditions for recording x-ray emission may arise when a filament is oriented close to the direction of the line of sight and its apparent surface brightness is correspondingly relatively high. This situation is realized for the filament of matter connecting two galaxy clusters Abell 222 and Abell 223 having red shift z = 0,21. Weak x-ray emission from the region between clusters was already detected earlier by the ROSAT telescope. New detailed observations of the x-ray space telescope ÕÌÌ-Newton confirm these data and point to the presence of weakly luminous gas in the filament. The gas density and temperature correspond to theoretically expected values. Evidence has thus been obtained that the missing baryons may indeed reside in the intergalactic gas. Source: ArXiv:0803.2525 |
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. | |
|
© 1918–2024 Uspekhi Fizicheskikh Nauk Email: ufn@ufn.ru Editorial office contacts About the journal Terms and conditions |