39,944 research outputs found

### The KCAL VERA 22 GHz calibrator survey

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

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

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
$\gamma+p\to (Q\bar{Q})_{1S}+p$ 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

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, $a$ is the scattering length, $\Omega$ is the volume, n_{\vect
k\sigma} is the average number of fermions with wave vector \vect k and spin
$\sigma$, 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-$T_c$ superconductors

The current-voltage ($I$-$V$) characteristics of break junctions of
polycrystalline La$_{1.85}$Sr$_{0.15}$CuO$_4$,
Y$_{0.75}$Lu$_{0.25}$Ba$_2$Cu$_3$O$_{7-\delta}$,
Bi$_{1.8}$Pb$_{0.3}$Sr$_{1.9}$Ca$_2$Cu$_3$O$_x$ and composite
YBa$_2$Cu$_3$O$_{7-\delta}$ + Ag are investigated. The experimental $I$-$V$
curves exhibit the specific peculiarities of
superconductor/normal-metal/superconductor junctions. The relation between an
$I$-$V$ characteristic of network of weak links and $I$-$V$ dependencies of
typical weak links is suggested to describe the experimental data. The $I$-$V$
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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