Cooper pairs as resonances

Using the Bethe-Salpeter (BS) equation, Cooper pairing can be generalized to include contributions from holes as well as particles from the ground state of either an ideal Fermi gas (IFG) or of a BCS many-fermion state. The BCS model interfermion interaction is employed throughout. In contrast to the better-known original Cooper pair problem for either two particles or two holes, the generalized Cooper equation in the IFG case has no real-energy solutions. Rather, it possesses two complex-conjugate solutions with purely imaginary energies. This implies that the IFG ground state is unstable when an attractive interaction is switched on. However, solving the BS equation for the BCS ground state reveals two types of {\it real} solutions: one describing moving (i.e., having nonzero total, or center-of-mass, momenta) Cooper pairs as resonances (or bound composite particles with a {\it finite} lifetime), and another exhibiting superconducting collective excitations sometimes known as Anderson-Bogoliubov-Higgs (ABH) modes. A Bose-Einstein-condensation-based picture of superconductivity is addressed.Comment: 5 pages in PS, including 3 figures. In press Physica

Transient Cherenkov radiation from an inhomogeneous string excited by an ultrashort laser pulse at superluminal velocity

An optical response of one-dimensional string made of dipoles with a periodically varying density excited by a spot of light moving along the string at the superluminal (sub-luminal) velocity is theoretically studied. The Cherenkov radiation in such system is rather unusual, possessing both transient and resonant character. We show that under certain conditions, in addition to the resonant Cherenkov peak another Doppler-like frequency appears in the radiation spectrum. Both linear (small-signal) and nonlinear regimes as well as different string topologies are considered.Comment: accepted to Phys. Rev.

Development of Small and Medium-Sized Regional Enterprises: Creation of Priority Areas (the Case of Sverdlovsk Region)

This article presents the results of the research which deals with the current level of development of small and medium enterprises (SMEs) in Sverdlovsk region. The study analyses the statistics of entrepreneurship development as well as Russian and international experience in this sphere. It also includes a sociological survey of entrepreneurs’ satisfaction with the business climate in the region. The research was aimed at elaborating guidelines for the long-term development of a regional entrepreneurship support system. This system seeks to facilitate the implementation of the ‘Strategy for the Development of Small and Medium Enterprises in Sverdlovsk Region before 2030’. As a result, an amalgam of strategic responses for the development of SMEs is presented. The completed response comprises measures intended to address the problems entrepreneurs face by developing SME support tools; to solve the endemic problems of the sector by improving the system of regional SME support; and to promote the realization of concrete priority areas for entrepreneurship development.The research work was carried out in collaboration with the Ural Federal University n.a. the First President of Russia B. N. Yeltsin and OOO “Analytical Centre Expert-Ural’” at the request of Sverdlovsk Regional Entrepreneurship Support Fund. The research was conducted in the period of September-November 2014. The state programme of Sverdlovsk region ‘Development of Industry and Science in Sverdlovsk Region Before 2020’ (approved by the Order of Sverdlovsk government of 24 October 2013 № 1293-ПП)

Generation of unipolar pulses in a circular Raman-active medium excited by few-cycle optical pulses

We study theoretically a new possibility of unipolar pulses generation in Raman-active medium excited by a series of few-cycle optical pulses. We consider the case when the Raman-active particles are uniformly distributed along the circle, and demonstrate a possibility to obtain a unipolar rectangular video pulses with an arbitrarily long duration, ranging from a minimum value equal to the natural period of the low frequency vibrations in the Raman-active medium

Superflares of H2_2O Maser Emission in the Protostellar Object IRAS 18316−-0602

The results of the study of the maser emission source IRAS 18316$-$0602 in the H$_2$O line at $\lambda =1.35$ cm are reported. The observations have been carried out at the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory (Russia) since June 2002 until March 2017. Three superflares have been detected, in 2002, 2010, and 2016, with peak flux densities of 3400, 19,000, and 46,000 Jy, respectively. The results of the analysis of the superflares are given. The flares took place during periods of high maser activity in a narrow interval of radial velocities (40.5-42.5 km/s) and could be associated with the passage of a strong shock wave. During our monitoring the emission of three groups of features at radial velocities of about 41, 42, and 43 km/s dominated. The flare of 2016 was accompanied by a considerable increase in the flux densities of several features in an interval of 35--56 km/s.Comment: 7 pages, 9 figures; submitted to Astronomy Report

Experiments on Sonoluminescence: Possible Nuclear and QED Aspects and Optical Applications

Experiments aimed at testing some hypothesis about the nature of Single Bubble Sonoluminescence are discussed. A possibility to search for micro-traces of thermonuclear neutrons is analyzed, with the aid of original low-background neutron counter operating under conditions of the deep shielding from Cosmic and other sources of background. Besides, some signatures of QED-contribution to the light emission in SBSL are under the consideration, as well as new approaches to probe a temperature inside the bubble. An applied-physics portion of the program is presented also, in which an attention is being paid to single- and a few-pulse light sources on the basis of SBSL.Comment: 4 pages; to be published by AIP in the Proc. ISNA-1

High-efficiency optical pumping of nuclear polarization in a GaAs quantum well

The dynamic polarization of nuclear spins by photoexcited electrons is studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high efficiency of the spin transfer from the electrons to the nuclei as reflected by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T strength only. This high efficiency is due to a low leakage of spin out of the polarized nuclear system, because mechanisms of spin relaxation other than the hyperfine interaction are strongly suppressed, leading to a long nuclear relaxation time of up to 1000 s. A key ingredient to that end is the low impurity concentration inside the heterostructure, while the electrostatic potential from charged impurities in the surrounding barriers becomes screened through illumination by which the spin relaxation time is increased compared to keeping the system in the dark. This finding indicates a strategy for obtaining high nuclear spin polarization as required for long-lasting carrier spin coherence.Comment: 6 pages, 4 figure