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| Issue 12, 2024 |
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Extracts from the Internet | ||
Structure of Λ(1405)-resonance1 May 2015The Λ(1405)-resonance particle which was considered to be the lower excited state of Λ-baryon with quark composition uds was discovered in 1961. Up to the present time its structure remains disputable because the mass of this particle is less than expected in the three-quark model. In the 1960s, R. Dalitz with colleagues supposed that Λ(1405) is actually not a three-quark particle, but a “subatomic molecule” consisting of the bound state of a meson (K- or anti-K0) and a nucleon (a proton or a neutron). The hypothesis of R. Dalitz and his colleagues had been neither proved nor disproved, but the belief in its validity increased with time. J.M.M. Hall (University of Adelaide, Australia) et al. accomplished new super-computer ab initio calculations by the “lattice QCD” method and calculated for the first time rather accurately the electromagnetic form factors of Λ(1405). s-quark was found not to contribute to the magnetic moment of Λ(1405). This is only possible if s-quark resides inside a spin-zero meson forming a bound system with a nucleon. The calculation of Λ(1405) mass in the molecular model also shows better agreement with experiment. However, a comprehensive proof of the molecular Λ(1405) structure needs further investigation. Source: Phys. Rev. Lett. 114 132002 (2015) Quantum entanglement of 3000 atoms1 May 2015Researchers from Serbia and USA generated quantum entanglement of about 3000 atoms in their interaction with a single photon. R. McConnell with colleagues placed ultracold 87Rb atomic gas into an optical cavity, transmitted weak laser radiation through the cavity and measured the output photon polarization. The turn of polarization through 90 degrees relative to the original direction corresponded to passing over to an entangled state of almost all the atoms upon their interaction with a single photon. Nearly 94 % out of 3100 atoms in the cavity were brought into an entangled state, which is a record for systems of a large number of massive particles. The experiment was carried out many times, and the characteristics of escaping photons were used to measure the Wigner function for atoms in the cavity characterizing their probability distribution. In a certain region, the Wigner function was negative, which was indicative of a nonclassical system. The distribution also showed a non-Gaussian character, which testified to entanglement in the directions of atomic spins. Large quantum-entangled ensembles of atoms can find application in the high-accuracy atomic clock and in precision measurements. Source: Nature 519 439 (2015) Water ice between graphene layers1 May 2015The structure of water ice locked in a narrow spacing (three-water-molecules thick) between two graphene layers was investigated in the experiment guided by I.V. Grigorieva and A.K. Geim (University of Manchester, Great Britain). Owing to the fact that mutual attraction of graphene layers by Van der Waals forces creates pressure of ≈ 1 GPa between them the water freezes under these conditions already at room temperature. The ice structure was examined by a high-resolution transition electron microscope. The ice turned out to have a square crystal lattice with the lattice constant (the distance between oxygen atoms) of 2.83 A in contrast to the hexagonal structure of ordinary ice. No co-orientation of the crystal directions of ice and carbon was then observed. It is possible that square-lattice ice can also appear in natural conditions in microcapillaries of some hydrophobic rocks. Source: Nature 519 443 (2015) Propagation of shock perturbation in granular medium1 May 2015R.P. Behringer (Technological Institute of New Jersey, USA) and his colleagues used the photoelasticity method to study the propagation of force effect in a granular medium. As distinct from elastic media where weak perturbations propagate as linear waves, in a granular medium one observes considerable nonlinearity even upon a weak impact. A substance changing its optical properties under deformation was powdered between two transparent plecsiglas plates, which allowed one to observe the propagation of mechanical stress in the medium. The velocity and spatial structure of the perturbation running through the medium after the impact by a downfalling load was measured using high-speed photography. The character of perturbation propagation turned out to depend on the dimensionless parameter M = tcv0/d, where v0 is the velocity of falling load upon an impact, d is the diameter of particles of the medium, and tc is the characteristic time of collision between pairs of particles. For M << 1 the force perturbation propagates in the medium along solitary chains of particles. The point is that because of the loose contact of particles, especially in the upper part of the vessel, the forces are transported along separate lines only. If M ≥ 0.6, the chains are located thickly, and a well pronounced collective front of perturbation propagation is observed. Source: Phys. Rev. Lett. 114 144502 (2015) Gravitational lensing of relic radiation1 May 2015Gravitational lensing of microwave background radiation onto the dark matter halo was revealed for the first time by the radio telescope Atacama Cosmology Telescope (Chile) on the scale of masses of galactic groups and clusters ≈ 1013-1014M☉. These objects represent large density perturbations and are already at the nonlinear stage of their evolution. The gravitational lensing of relic radiation has already been observed earlier by other telescopes, but only on scales of only tens and hundreds of megaparsec (galactic superclusters). The map of relic radiation fluctuations measured by Atacama Cosmology Telescope and calibrated by the Planck telescope data was compared with the distribution of 12000 galaxies from the SDSS-III/BOSS optical review, and the lensing effect was revealed at the confidence level of 3.2 σ. Observation of gravitational lensing of relic radiation opens up prospects of dark matter distribution study on the scale of galactic groups and clusters. Source: Phys. Rev. Lett. 114 151302 (2015) |
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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