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| Issue 10, 2024 |
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Extracts from the Internet | ||
Parity violation in nuclear collisions1 January 2010The “chiral magnetic effect”, predicted in 1998 by D. Kharzeev, R.D. Pisarski and M.H.G. Tytgat was first detected at the RHIC accelerator (Relativistic Heavy Ion Collider) in the US using the STAR detector of the Brookhaven National Laboratory. The effect consists in parity violation (violation of the symmetry under mirror reflection) which manifests itself in a partial spatial separation of positively and negatively charged quarks along the direction of the orbital angular momentum of the colliding nuclei. The separation of charges is caused by the difference between the numbers of quarks of different chirality in the new metastable domains and by the strong magnetic field of intensity up to ≈ 1015 T which arises in nonzero impact parameter collisions of nuclei. The experimenters collided nuclei of Au + Au and Cu + Cu with center-of-mass energy of 200 GeV. The distribution of charges on the two sides of the plane of reaction (i.e. along the direction of the angular momentum) was measured using correlation analysis. Possible sources of background noise and experimental uncertainty such as the contribution of scattering of three or more particles and of resonance decays were studied and eliminated. This resulted in identification of statistically significant correlations which could correspond to parity violation. As predicted by theoretical calculations, the measured effect was found to be stronger in the case of copper nuclei than with gold nuclei. Source: Phys. Rev. Lett. 103 251601 (2009) Measurement of ultralow temperatures1 January 2010D.M. Weld and coworkers at the Massachusetts Institute of Technology developed a sufficiently universal technique of thermometry of ultracold atoms in optical lattices. The method of spin-gradient thermometry was tested successfully in nonuniform magnetic field on the gas of 87Rb atoms trapped in a three-dimensional laser beam lattice. The gas was maintained in the Mott insulator regime in which conductivity is zero due to strong repulsion between particles. The width of the transition zone between atom clouds in different spin states (and having different magnetic moments) depends on temperature; these clouds separated in the gradient of the external magnetic field. As temperature decreases, the transition becomes sharper; incomplete separation at finite temperatures is caused by spin excitations. Therefore, the temperature of the gas can be found from observations of the transition zone. In this particular experiment it was possible to measure temperatures down to 1 nK and the researchers predict that the new technique will allow measuring temperatures down to ≈ 50 pK. The study of atoms in optical lattices at ultralow temperatures is important for implementing quantum spin Hamiltonians which model materials with unique properties, such as high-temperature superconductors. Source: Phys. Rev. Lett. 103 245301 (2009) Relativistic plasma “mirror”1 January 2010Ì. Kando and coworkers at the Advanced Photon Research Center (Kioto, Japan) and the P.N. Lebedev Physical Institute of the RAS (Moskow, Russia) studied the reflection of laser pulses from relativistically moving “mirror”. The “mirror” was the plasma wave (modulation of electron density) generated by the high-power laser pulse. When laser light propagates toward the “mirror”, the double Doppler effect increases the frequency of the reflected light by a factor of 37 to 66. The frequency jump of this magnitude may prove useful in a number of practical applications, for instance, for laser acceleration of ions or for generation of ultrashort pulses. The reflection coefficient in this experiment was 1.3 × 10-4 to 0.6 × 10-3 which is close to the quantity predicted by the theory for this experiment. The experiment with reflection by a relativistic plasma “mirror” was first carried out in 2007. In this new experiment it proved possible to achieve considerably higher reflectivity and to investigate in detail the characteristics of the reflected light. Source: Phys. Rev. Lett. 103 235003 (2009) A close pair of compact stars1 January 2010Ñ. Badenes and his coworkers in the US and Israel discovered a binary system at a distance of about 50 pc from the Earth in which one object is a white dwarf with a mass of about 0.9M☉ and the second object is a neutron star or a black hole with a mass higher than 1.6M☉. This system therefore contains the nearest to the Earth known compact remnant of supernova explosion. The binary system SDSS 1257 + 5428 with the orbital period of 4.6 hours was found by studying the spectral features of objects of the Sloan Digital Sky Survey catalog and was then additionally investigated by the DIS spectrograph on the 3.5-meter ARC telescope in New Mexico. The components of the pair gradually move closer because of the emission of gravitational waves. Estimates of the orbital parameters make it possible to conclude that these compact stars will collide not later than about 500 million years. Ò.A. Thompson and his colleagues at the Ohio State University used this data to evaluate the total number and rate of mergers of binary systems of this type. By their calculations, the Galaxy contains about 106 such systems and the rate of mergers in the Galaxy is estimated as ≈ 5 × 10-4 yr-1. It cannot be excluded that a collision of a white dwarf and a compact object generate gamma bursts, powerful neutrino flashes and also ultrahigh-energy cosmic rays. Binary systems with white dwarfs might constitute the principal source of background gravitational wave signal in the currently planned space interferometer LISA. Sources: arXiv:0910.2709v1 [astro-ph.SR], arXiv:0912.0009v1 [astro-ph.HE] Waves on a cell membrane1 January 2010The propagation of wave excitations along the outer shell of live cells depends on many physical and chemical factors, some of them nonlinear, so that the observation and theoretical explanation of the properties of waves on cell membranes is an interesting and complex problem of biophysics. Surface waves are directly linked to the ability of cells to move. Researchers at the Institute of Biophotonics Engineering and Research Center for Applied sciences (Taipei, Taiwan) were able to clarify how waves propagate on the surface of fibroblasts, i.e. cells of connective tissue. The method of observation they used is known as noninterferometric wide-field optical profilometry (NIWOP). It is based on using the interval of linear dependence of light intensity on the amount of spatial shifting out of focal point of the microscope. This technique made it possible to achieve the required resolution in the three-dimensional picture of wave propagation. The experimenters measured wave profiles and their speed (≈ 100 nm s-1), their dispersion and other characteristics. Observations confirm the detailed theory of wave propagation suggested by R. Shlomovitz and N.S. Gov in 2007. Their model was based on the interaction between the force of repulsion that arises when the protein actin polymerizes, and the compressive force produced by the protein myosin which forms links between actin fibers. The researchers discovered that waves disappeared when they added reagents blocking myosin and polymerization of actin, which confirms the decisive role of these proteins in the wave process. The outlined results may lead to important applications in medical sciences and biotechnologies. Source: Phys. Rev. Lett. 103 238101 (2009) |
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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