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| Issue 4, 2024 |
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Extracts from the Internet | ||
Two-proton decay1 July 2008Researchers at the University of Catania and Istituto Nazionale di Fisica Nucleare (Italy) obtained for the first time unambiguous data proving the existence of the two-proton decay. They studied collisions of a beam of 20Ne nuclei with beryllium foil. Some of these 20Ne nuclei lost two neutrons in collisions and transformed into 18Ne nuclei which then fragmented on collisions with a lead target. This decay went with probability 31% through the diproton resonance when a nucleus ejected a bound pair of protons which can be regarded as a short-lived 2He isotope that rapidly decays into two individual protons. The formation of 2He was established unambiguously by analyzing the kinematics of the processes, the energies of nuclear fragments and the correlation of trajectories of ejected protons. Earlier experiments already established simultaneous ejection of two protons but there was no exact evidence of these two first forming a bound state. Source: Phys. Rev. Lett. 100 192503 (2008) Quasiparticles with a charge of e/41 July 2008Ì. Dolev, V. Umansky and their colleagues at the Weizmann Institute of Science in Israel observed for the first time quasiparticles (collective electronic excitations) with a charge that is a simple fraction with an even denominator — 1/4 in units of electron charge e. Only quasiparticles with charges of 1/3, 1/5 etc were observed earlier. The object of study was highly purified gallium arsenide placed in a magnetic field at a temperature of about 1 K. Electrons in the semiconductor moved in two-dimensional layers and their collective excitations effectively behaved as quasiparticles with fractional charge of 1/4. There were five electrons per each quantum of magnetic flux. The quasiparticle charge was calculated from the characteristics of fluctuations of electric current. As followed from theoretical calculations, quasiparticles with even denominators in the fractional charge possess properties different from those of quasiparticles with odd denominators. Thus quasiparticles with 1/4 electron charge can be used to create a ‘topographical quantum computer’. Source: http://arxiv.org/abs/0802.0930 Bose glass1 July 2008One usually assumes that the Bose – Einstein condensate of quasiparticles and the corresponding to it superfluidity of matter set in at the same temperature. However, Ê. Shirahama and his coworkers in Japan discovered that on the nanometer scale these phenomena may arise at different temperatures. They studied helium-4 contained in a porous material with pore diameter of about 2.5 nm. The transition to the Bose – Einstein condensate state was detected by monitoring the heat capacity of helium-4 while superfluidity manifested itself by a drop in the moment of inertia and hence by a change in the period of torsional oscillations of a specimen. The temperature dependence of heat capacity is adequately described by a model in which phonons and rotons are excited in helium-4. It was discovered that the temperature of transition to the Bose – Einstein condensate is considerably higher than the temperature of superconducting transition. It is possible that this experiment observed for the first time the state of the so-called ‘Bose glass’ whose properties were predicted in theoretical papers and stem from the disordered nature of the small-scale structure of the specimen. Hypotheses are advanced that a state of similar type may exist in high-temperature superconductors. This discovery may also find practical applications for the creation of quantum interference devices. Source: http://arxiv.org/abs/0711.3969 Anderson localization in Bose – Einstein condensate1 July 2008Electrons possessing certain momenta can move freely through the periodic potential of crystalline lattice (Bloch waves). About 50 years ago P.W. Anderson predicted theoretically that if the periodicity of this potential is disrupted, electrons will be trapped (i.e. wave functions will be localized) in the vicinity of some groups of atoms. This effect, known as Anderson localization, was observed in experiments with light and sound waves but until recently it was impossible to observe it with massive particles. Two independent groups of researchers observed Anderson localization for the first time in the Bose – Einstein condensate. A. Aspect and his colleagues in France studied the condensate of rubidium atoms flying freely from the center of a magnetic trap after magnetic field is turned off. However, atoms stayed in the trap if laser beams created an irregular potential inside the trap. The irregularity was achieved by reflecting laser light from a rough surface. The researchers concluded that retention of atoms was caused by the Anderson localization. The second group of researchers in Florence studied the Bose – Einstein condensate in a one-dimensional periodic potential created by laser beams. Atoms were able to move in the course of diffusion. Irregularity was introduced by a second beam which interfered with the first. The intensity of the second beam was varied and when it reached a certain level, atomic diffusion stopped, which again was explained in terms of the Anderson localization. Both groups of researchers intend to improve their experimental techniques and extend them for observing the Anderson localization in two- and three-dimensional systems and in the case of interacting atoms. Sources: Nature 453 891 (2008) , Nature 453 891 (2008) Supernova SN 2008D1 July 2008Scheduled observations in January 2008 by the NASA Swift space observatory accidentally recorded an x-ray burst which proved to be the initial phase of the explosion of a supernova in the spiral galaxy NGC 2770 (redshift z=0,007). Optical observations which made it possible to identify the x-ray source as a supernova were made 1.77 days after the x-ray burst. The powerful burst was probably produced due to the shockwave breakout. It is the first time that a type-Ib supernova was observed at a very early stage of explosion. Shape of spectrum, luminosity function (evolution of luminosity with time) and spectral lines were measured in detail; this will help to better understand the physical mechanisms active during the explosion and to evaluate the statistics of such events. Source: Nature 453 469 (2008) |
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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