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| Issue 12, 2024 |
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Extracts from the Internet | ||
Testing Lorentz invariance in decays of K0S mesons1 December 2010A. de Angelis (Physics Institute of the Max Planck Society, Germany) and his colleagues from Italy obtained new constraints on the hypothetical effect of violation of Lorentz invariance in K0S → π+π- decays. They analyzed 62.3 million events permitting reliable reconstruction at the synchrotron accelerator of the National Laboratory in Frascati (Italy). Researcers measured K0S meson lifetime as a function of the direction of motion relative to the reference frame fixed to the microwave background radiation, i.e. the frame in which the microwave background radiation has zero dipole component. The measured degree of asymmetry, A = (- 0.13 ± 0.40) × 10-3, is compatible with the zero value A = 0, i.e. no dependence of the lifetime of K0S mesons on their direction of motion has been found at the confidence level 95%. This result improves previously calculated upper limits by about an order of magnitude. Source: arXiv:1011.3720v1 [astro-ph.CO] Heat production in nuclear fuel1 December 2010Of the heat released in nuclear reactors, approximately 8% is contributed by decays of radionuclides, i.e. products of the main reactions. Uncertainties still survive in the characteristics of these processes and their removal may significantly improve the safety of storing and processing of nuclear materials, plus this may generate an appreciable economic gain. The new experiment carried out by the international team of scientists at the IGISOL isotope separator at the Jyvaskyla University (Finland) studied heat release in decays of nuclides 102, 104-107Tc, 105Mo and 101Nb. The total-absorption gamma spectrometer designed at the B.P. Konstantinov Petersburg Nuclear Physics Institute was directly coupled to a Penning trap into which all nuclides generated in the cyclotrone were sent and which recorded the total-absorption γ-cascades that followed β-decays. For the nuclei 104-107Tc and 105Mo the amount of heat removed by gamma radiation was found to be greater than that yielded by earlier measurements with germanium detectors. The new measurements removed much of the uncertainty in energy release in decays of 239Pu and daughter nuclei in the time interval from 4 to 3000 s after the termination of fission in the reactor. The results are also useful for improving the accuracy of the spectrum of the antineutrino signal from nuclear reactors, which is important for studying neutrino oscillations. Source: Phys. Rev . Lett. 105 202501 (2010) Magnetic excitations in cuprate-based superconductors1 December 2010Ì. Greven (University of Minnesota, USA) and his colleagues, using the method of inelastic scattering of spin-polarized neutrons, found a new type of magnetic wave (magnetic excitations) characterized by low dispersion in high-temperature superconductor HgBa2CuO4+δ. The energy of these exitations is 52-56 meV and they are observed at temperatures below T* at which a pseudogap is formed in the electron spectrum of the material. The study of the pseudogap state is permanently important problem as the mecanism of its generation may hide a clue to the mechanism of high-temperature superconductivity. The discovered magnetic excitations are likely to be directly connected with the pseudogap as their intensity begins to increase as the material is cooled to temperatures below T*. Electron-phonon excitation may prove to be the mechanism responsible for these excitations. The energy of excitations is close to the energy of one of the resonances of the compound HgBa2CuO4+δ, which explains why they were not observed in earlier experiments. Source: Nature 468 283 (2010) Information is used to increase free energy1 December 2010Ì. Sano (University of Tokyo, Japan) and his colleagues demonstrated that the free energy of a Brownian particle can be increased by using information on the direction of its velocity. A dimer particle — a pair of polystirene beads 287 nm in diameter — was fixed to the wall of a chamber filled with buffer solution and could rotate around its axis. A rotating ellipsoidal electric field was created in the chamber, which applied angular moment to the particle. Molecules of the buffer solution caused the particle to execute rotational Brownian motion which was monitored through a microscope and high-speed video camera. The particle was allowed to rotate in the direction of increase of potential energy (against the angular moment) while in the opposite direction its motion was artificially blocked by changing the phase of the electric field. This created a feedback loop that controlled the motion of the particle by using the information on its direction. As a result the particle was raised to a state with greater and greater potential energy. This process resembles the thought experiment with “Maxwell's demon” who sorts out molecules according to their energy. In terms of L. Szillard's interpretation, information is consumed to create temperature difference, which results in growth of entropy in the compound larger system that includes the ``demon'' itself. Thus, the second law of thermodynamics is not violated here. Quantitative measurements conducted by M. Sano et al. confirmed the theoretical relations derived by Ñ. Jarzynski (Maryland University, USA) that characterize the efficiency of obtaining free energy from information. In this experiment, the “demon” is a cumbersome system involving a video camera, computers and other pieces of equipment. Moving the whole experiment to nanoscale could be the next step, e.g. by creating a microscopic control system for “molecular motors”. Source: Nature Physics 6 988 (2010) Massive neutron star1 December 2010P. Demorest (National Radio Observatory, USA) and his colleagues using the Green Bank radio telescope discovered a neutron star with record large mass of 1.97 ± 0.04 solar masses. The astronomers studied the PSR J1614-2230 millisecond pulsar in a binary system at a distance of about 3000 light years from Earth. A new technique of coherent filtering of signal fading caused by dispersion in interstellar gas was used. Owing to a favorable orientation of the plane of orbit (seen from Earth almost perfectly edge-on) it proved possible to use the timing technique (measurement of pulse rate) for high-precision measurements of the Shapiro effect, i.e. the delay of signals propagating in a gravitational field. Taking this effect and the expected characteristics of the orbital motion into account, the mass of the neutron star has been inferred. Measuring the masses and radii of neutron stars makes it possible to determine constraints on the equation of state of matter at nuclear densities of which they consist. Hypotheses were advanced on the presence in neutron stars of an exotic hadron matter — hyperons or kaon condensate. The fact that a neutron star with a mass of ≈ 1.97M☉ does exist rules out these models and imposes severe constraints on models with quark matter, without as yet ruling them out completely. Source: Nature 467 1081 (2010) |
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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