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| Issue 4, 2024 |
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Extracts from the Internet | ||
p11B fusion reaction in a stellarator1 April 2023Naturally occurring isotopes participate in the nuclear fusion reaction p11B→3α+8.7 MeV with no neutrons at the output, and therefore this reaction is fairly attractive for fusion energy. However, this reaction requires a 30 times higher temperature than in the deuterium-tritium scheme. This results in a high-power electromagnetic plasma radiation preventing a positive energy release. Nevertheless, theoretical calculations have shown that the radiation loss can be decreased by violation of thermal equilibrium between electrons and positive ions through electron temperature lowering. Till now, the p11B reaction was only observed in plasma produced by powerful laser pulses and at accelerators. R.M. Magee (National Institute for Fusion Science, Japan and TAE Technologies, USA) and their co-authors demonstrated for the first time the p11B reaction in a magnetically confined plasma [1]. Boron powder in a glow discharge was introduced in a superconducting stellarator LHD (Large Helical Device) (plasma boronization process) and was concentrated near the core of the confined plasma. High-energy protons were also injected there. Nuclear reactions were registered by a silicon detector by bursts of alfa particle fluxes. Solution of many complicated technical problems are needed for a practical application of p11B reaction in a reactor. [1] Magee R M et al. Nature Communications 14 955 (2023) Room-temperature hydride superconductivity1 April 2023Some data indicate that hydrides can have a high superconducting transition temperature Tc, and CaH6 superconductivity at Tc=220-235 K has already been revealed at a pressure of 150 ÃGPa. Along with # increase, topical is the problem of pressure lowering resulting in the occurrence of high-temperature superconductivity. Doping that heightened atomic lattice stability was considered as a promising method. The new experiment performed by N. Dasenbrock-Gammon (University of Rochester, USA) and their co-authors confirmed this expectation [2]. In nitrogen-doped lutetium hydride, room-temperature Tc=294 K (21°C) superconductivity was observed at a pressure of only 10 kbar. The presence of superconductivity was shown in several ways: by the lack of electric resistance, by the behavior of magnetic susceptibility and thermal capacity, etc. The structure of nitrogen-doped lutetium hydride has not yet been completely clarified. To understand it, investigation using the neutron diffraction method will be needed. Obtaining room-temperature superconductivity is now one of the most topical problems of modern physics [3]. For ambiguous results in examination of superconductivity in carbonaceous sulfur hydride, see [4]. [2] Dasenbrock-Gammon N et al. Nature 615 244 (2023) [3] Ginzburg V L Phys. Usp. 47 1155 (2004); UFN 174 1240 (2004) [4] Sadakov A V, Sobolevsky O A, Pudalov V M Phys. Usp. 65 1313 (2022); UFN 192 1409 (2022) Light localization in a moire lattice1 April 2023Moire lattices are structures formed by identical sublattices mutually twisted at a certain angle in their plane. Unusual superconductivity and other interesting effects were observed in systems with atomic layers in the form of moire lattices. A.A. Arkhipova (Institute of Spectroscopy RAS and the Physics Department of the Higher School of Economics) and her co-authors demonstrated for the first time a photon moire lattice created with a femtosecond laser [5]. The moire lattice was limited to a square area, which made it possible to investigate edge excitations in both linear and nonlinear regimes for different orientations of the primary lattice. The moire lattice was found to maintain linear modes localized in the corners and at the edges of the lattice with a weak background inside, and the transfer from the linear quasi-localized states to surface solitons occurring at higher light intensities was observed. [5] Arkhipova A A et al. Phys. Rev. Lett. 130 083801 (2023) Time reflection1 April 2023The ordinary signal reflection proceeds from a spatial interface between media with different properties. However, the version of “time reflection” after a synchronous variation of the properties of a homogeneous medium was theoretically considered. In this case, the reflection occurs not at the spatial but at the temporal boundary. A similar effect was earlier observed for monochromatic signals only, when the properties of the medium were modulated by another signal with double frequency. H. Moussa (City University of New York, USA) and their co-authors were the first to demonstrate the time reflection effect for broadband electromagnetic signals [6]. Employed to this end was a metamaterial - a large array of microchips simultaneously connecting additional capacitors, thus changing the electric properties of the medium. As a result, the incoming signal was divided to reflected and transmitted signals with frequency conversion. The use of two such metamaterials made it possible to observe interference of transmitted and time reflected signals. [6] Moussa H et al. Nature Physics, published on-line March 13, 2023 ã. Black holes and cosmology1 April 2023In the theory of gravitation, models of nonsingular black holes (BH) exist with masses increasing due to the Universe expansion. D. Farrah (University of Hawaii, USA) and his co-authors verified this mass growth hypothesis for BH in galactic nuclei at redshifts 0 < z < 2.7 [7]. Evidence was found that within this time the BH masses did actually increase 8 to 20 times relative to the galactic star masses, the whole increase being hard to explain by gas accretion. If the BH mass dependence on the Universe scale factor is expressed in the exponential form M ∝ ak, then k = 3.11+1.19−1,33. For k ≈ 3, the internal part of the space-time of such BH under the horizon can be determined by a certain type of dark energy [8-10]. Another interesting possibility is to explain the accelerated expansion of the Universe by the increase in the total BH mass, including the BH resulted from the stellar evolution. The authors of [7] have shown that an increase in BH mass by the law M ∝ ak with k ≈ 3 can imitate the presence of dark energy in the Universe, leading to an accelerated expansion. To verify this model, further studies are needed using more extensive statistical material. [7] Farrah D et al. The Astrophysical Journal Letters 944 L31 (2023) [8] Gliner E B JETP 22, 378 (1966) [9] Gliner E B Phys. Usp. 45 213 (2002); UFN 172 221 (2002) [10] Dymnikova I General Relativity and Gravitation 24 235 (1992) |
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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