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| Issue 4, 2024 |
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Extracts from the Internet | ||
Search for new physical effects using optical resonator1 January 2017The researchers from the University of Dusseldorf E. Weins, A.Yu. Nevsky, and S. Schiller obtained restrictions on the new physical effects from stability of the oscillation frequency in an optical resonator that might result in a change in its length. The resonator, 25 cm long, was fabricated from crystalline silicon, and its resonance frequency was determined by the inverse time of electromagnetic wave propagation from the laser. The resonator frequency was periodically compared within a year with the frequency of hydrogen maser located in the laboratory and also with the time readings obtained from the GPS system in which they are formed by atomic clock. This gives comparison of stability of the local process frequency in atoms with stability of the resonator length. For the relative frequency drift the restriction | df / dt | / f < 1,4×10-20s-1 was obtained which is two orders of magnitude stronger than the Universe expansion rate H0 ≈ 2,3×10-18s-1. The change in the local scales at the H0 level had already been excluded in preceding experiments. It is known that in the framework of General Relativity the Hubble expansion only proceeds on the average on cosmological scales. However, a local expansion of even coupled objects is sometimes formally considered as an effect of new physics. The described experiment also gave restrictions on violation of the principle of local spatial invariance (under Earth motion) and also on the magnitude of hypothetical space-time fluctuations with frequencies of ≈10-6 Hz. Source: arXiv:1612.01467 [gr-qc] Local flutter mode in plasma1 January 2017In their experiment, K. Ida (National Institute of Natural Sciences, Japan) with colleagues confirmed the theoretical prediction that L.A. Artsimovich made in 1968 concerning the development in plasma of local “tongue”-shaped deformations at a pressure exceeding the magnetic pressure. This type of instability is due to flute instability. The experiment was carried out in a superconducting stellarator (Large Helical Device). Plasma perturbations were observed by magnetometers and through registration of cyclotron radio emission of ions that increased sharply upon the development of instability. The “tongue”-shaped deformation of the magnetic surface began 100 µs and reached its maximum 30 µs before the plasma collapse. Furthermore, observed was a deformation of proton distribution in the phase space due to a fast variation of the radial electric field. For flute instability see, e.g., the book by L.A. Artsimovich “Closed plasma configurations” and the review by M.S. Ioffe and B.B. Kadomtsev in Sov. Phys. Usp. 13 225 (1970). Source: Scientific Reports 6 36217 (2016) Quasi-liquid layer on the ice surface1 January 2017As far back as 1850s M. Faraday supposed that a thin liquid-water layer exists on the ice surface below the bulk ice melting temperature of 273 K. The hypothesis was based on the fact that adjoining pieces of ice fuse together. The presence of a quasi-liquid layer was later confirmed in a lot of experiments, but its origin and thickness remained the subject of discussion. M.A. Sancheza (Max Planck Institute for Polymer Research, Germany) with colleagues used the spectroscopic methods to study the properties of the quasi-liquid layer within the temperature range of 235-273 K. It turned out that already at 235 K (-38°C) a double molecular layer (bilayer) of liquid water exists on the ice surface, and upon heating above 257 K two such bilayers appear. Such a jump-like thickness variation was predicted in theoretical calculations by the method of molecular dynamics. The measurements also showed that in the character of the net of hydrogen bonds the liquid water in the surface layer looks more like ice than overcooled water in the volume at the same temperature. Source: Proc. Nat. Ac. Sci. 117 203003 (2016) “Chip” gravimeter1 January 2017E.M. Rasel (the University of Hannover, Germany) with colleagues designed a quantum gravimeter located “on a chip”, that is, within one microcircuit and operating in an effective volume of only 1 cm3 by analogy with the atomic Mach – Zehnder interferometer. Approximately 15000 87Rb atoms fell from the height of 1 cm and were transferred by laser pulses to different interfering states. The fact that the condensate in the laser wave field was again thrown up was a new element. This prolonged the time of its fall to several tens of ms, which is of great importance for measurements in such a compact device. Atomic interference was observed by the resonance absorption and the free fall acceleration was found. Although the new gravimeter is an order of magnitude inferior in sensitivity to the now exploited devices it is envisaging further development for its compactness. Source: Phys. Rev. Lett. 117 203003 (2016) Gamma ray emission from the center of Galaxy1 January 2017In 2013-2014 the gas cloud G2 passed in close proximity (2200 Schwarzschild radii) to the supermassive black hole in the center of Galaxy. The gas accretion from the cloud to the black hole was expected to induce flare activity in a wide energy range. However, no increase in the level of emission from the center of Galaxy was observed in X-ray, IR, or radio range upon the passage of G2 through the orbit pericenter because the cloud was not notably destructed. M.L. Ahnen (Swiss Federal Institute of Technology in Zurich) with colleagues used the Cherenkov telescope MAGIC to observe the center of Galaxy in 2012-2015 in very-high-energy (VHE) gamma-ray range not below 100 GeV. However, the same as in other ranges no G2 effect on VHE gamma-ray emission was now observed. Nevertheless, in these MAGIC observations some concomitant results were obtained, namely, the spectrum of background (continuous) VHE gamma-ray emission from the central region of the Galaxy was measured, the presence of the gamma-ray source spatially coincident with G0.9+0.1 supernova remnant and the existence of a gamma-ray source near the radio arc in the galactic center were confirmed. Source: arXiv:1611.07095 [astro-ph.HE] |
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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