39,944 research outputs found

    The KCAL VERA 22 GHz calibrator survey

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    We observed at 22 GHz with the VLBI array VERA a sample of 1536 sources with correlated flux densities brighter than 200 mJy at 8 GHz. One half of target sources has been detected. The detection limit was around 200 mJy. We derived the correlated flux densities of 877 detected sources in three ranges of projected baseline lengths. The objective of these observations was to determine the suitability of given sources as phase calibrators for dual-beam and phase-referencing observations at high frequencies. Preliminary results indicate that the number of compact extragalactic sources at 22 GHz brighter than a given correlated flux density level is twice less than at 8 GHz.Comment: Accepted for publication by the Astronomical Journal. 6 pages, 3 figures, 3 table. The machine readable catalogue file, kcal_cat.txt can be extracted from the source of this submissio

    The catalogue of positions of optically bright extragalactic radio sources OBRS-1

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    It is expected that the European Space Agency mission Gaia will make possible to determine coordinates in the optical domain of more than 500000 quasars. In 2006, a radio astrometry project was launched with the overall goal to make comparison of coordinate systems derived from future space-born astrometry instruments with the coordinate system constructed from analysis of the global very long baseline interferometry (VLBI) more robust. Investigation of their rotation, zonal errors, and the non-alignment of the radio and optical positions caused by both radio and optical structures are important for validation of both techniques. In order to support these studies, the densification of the list of compact extragalactic objects that are bright in both radio and optical ranges is desirable. A set of 105 objects from the list of 398 compact extragalactic radio sources with declination > -10 deg was observed with the VLBA+EVN with the primary goal of producing their images with milliarcsecond resolution. These sources are brighter than 18 magnitude at V band, and they were previously detected at the European VLBI network. In this paper coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these VLBI observations following the method of absolute astrometry. The catalogue of positions of 105 target sources is presented. The accuracies of sources coordinates are in the range of 0.3 to 7 mas, with the median 1.1 mas.Comment: 6 pages, 1 figure, accepted by the Astronomical Journal, ID: AJ-10606. Electronic table 2 with the catalogue is available in the source code of this submissio

    From the exclusive photoproduction of heavy quarkonia at HERA to the EDDE at TeVatron and LHC

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    Exclusive photoproduction of heavy quarkonia at HERA is analyzed in the framework of the Regge-eikonal approach together with the nonrelativistic bound state formalism. Total and differential cross-sections for the process γ+p(QQˉ)1S+p\gamma+p\to (Q\bar{Q})_{1S}+p are calculated. The model predicts cross-sections of Exclusive Double Diffractive Events (EDDE) at TeVatron and LHC.Comment: 14 pages, 6 figures, reference is adde

    Energetics of a strongly correlated Fermi gas

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    The energy of the two-component Fermi gas with the s-wave contact interaction is a simple linear functional of its momentum distribution: E_\text{internal}=\hbar^2\Omega C/4\pi am+\sum_{\vect k\sigma}(\hbar^2 k^2/2m)(n_{\vect k\sigma}-C/k^4) where the external potential energy is not included, aa is the scattering length, Ω\Omega is the volume, n_{\vect k\sigma} is the average number of fermions with wave vector \vect k and spin σ\sigma, and C\equiv\lim_{\vect k\to\infty} k^4 n_{\vect k\up} =\lim_{\vect k\to\infty} k^4 n_{\vect k\down}. This result is a \textit{universal identity}. Its proof is facilitated by a novel mathematical idea, which might be of utility in dealing with ultraviolet divergences in quantum field theories. Other properties of this Fermi system, including the short-range structure of the one-body reduced density matrix and the pair correlation function, and the dimer-fermion scattering length, are also studied.Comment: 28 pages, 1 figur

    Current - voltage characteristics of break junctions of high-TcT_c superconductors

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    The current-voltage (II-VV) characteristics of break junctions of polycrystalline La1.85_{1.85}Sr0.15_{0.15}CuO4_4, Y0.75_{0.75}Lu0.25_{0.25}Ba2_2Cu3_3O7δ_{7-\delta}, Bi1.8_{1.8}Pb0.3_{0.3}Sr1.9_{1.9}Ca2_2Cu3_3Ox_x and composite YBa2_2Cu3_3O7δ_{7-\delta} + Ag are investigated. The experimental II-VV curves exhibit the specific peculiarities of superconductor/normal-metal/superconductor junctions. The relation between an II-VV characteristic of network of weak links and II-VV dependencies of typical weak links is suggested to describe the experimental data. The II-VV curves of typical weak links are calculated by the K\"{u}mmel - Gunsenheimer - Nicolsky model considering the multiple Andreev reflections.Comment: 9 pages, 5 figures, 2 Table
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