975 research outputs found
Constraining the parameters of the putative supermassive binary black hole in PG 1302-102 from its radio structure
We investigate the pc-scale kinematics and kpc-scale radio morphology of the
quasar PG 1302-102, which may harbour a sub-pc separation supermassive binary
black hole system at its centre as inferred from optical variability.
High-resolution radio interferometric measurements obtained with the Very Long
Baseline Array (VLBA) in the Monitoring Of Jets in Active galactic nuclei with
VLBA Experiments (MOJAVE) programme at 15 GHz at 20 epochs spanning 17 years
were analysed to investigate the pc-scale radio structure. Archival
observations with the Very Large Array (VLA) at 1.4 GHz and 5 GHz were obtained
to study the kpc-scale morphology. We find that the pc-scale jet is inclined
within ~2.2 deg to the line of sight and has a half-opening angle of about 0.2
deg. The parameters derived from the pc-scale radio jet are qualitatively
consistent with those obtained from the analysis of the optical light curve of
PG 1302-102. We obtain at least 0.08 for the mass ratio of the two black holes
in the system. We find some indication for a helical jet structure on
kpc-scale, but the directions of the inner and the extended radio jets are
significantly different, obstructing a straightforward connection of the pc-
and kpc-scale jets within the binary scenario.Comment: 9 pages, 4 figures, 1 table, accepted to MNRA
Probing the Active Massive Black Hole Candidate in the Center of NGC 404 with VLBI
Recently Nyland et al. (2012) argued that the radio emission observed in the
center of the dwarf galaxy NGC 404 originates in a low-luminosity active
galactic nucleus (LLAGN) powered by a massive black hole (
M). High-resolution radio detections of MBHs are rare. Here we
present sensitive, contemporaneous Chandra X-ray, and very long baseline
interferometry (VLBI) radio observations with the European VLBI Network (EVN).
The source is detected in the X-rays, and shows no long-term variability. If
the hard X-ray source is powered by accretion, the apparent low accretion
efficiency would be consistent with a black hole in the hard state. Hard state
black holes are known to show radio emission compact on the milliarcsecond
scales. However, the central region of NGC 404 is resolved out on 10
milliarcsecond (0.15-1.5 pc) scales. Our VLBI non-detection of a compact,
partially self-absorbed radio core in NGC 404 implies that either the black
hole mass is smaller than M, or the source
does not follow the fundamental plane of black hole activity relation. An
alternative explanation is that the central black hole is not in the hard
state. The radio emission observed on arcsecond (tens of pc) scales may
originate in nuclear star formation or extended emission due to AGN activity,
although the latter would not be typical considering the structural properties
of low-ionization nuclear emission-line region galaxies (LINERs) with confirmed
nuclear activity.Comment: Accepted for publication in the Astrophysical Journal. 7 pages, 2
figures, 1 tabl
VLBI observation of the newly discovered z=5.18 quasar SDSS J0131-0321
Few high-redshift, radio-loud quasars are known to date. The extremely
luminous, radio-bright quasar, SDSS J013127.34-032100.1 was recently discovered
at a redshift of . We observed the source with high resolution very
long baseline interferometry (VLBI) at 1.7 GHz with the European VLBI Network
(EVN) and found a single compact radio component. We estimated a lower limit to
the brightness temperature of the detected radio component, T_B~10^{11} K.
Additionaly, when compared to archival radio data, the source showed
significant flux density variation. These two findings are indicative of the
blazar nature of the source.Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter
Importance of assisted reproductive technologies in the conservation of wild, rare or indigenous ungulates: Review article
Biodiversity is increasingly threatened by intensive agriculture, environmental pollution, extinction of natural habitats and several other factors. Several mammalian species including ungulates have disappeared or are threatened by extinction. However, ungulates play an important role both in the ecosystem and in the economy. In general, species or breeds are considered endangered if their population does not exceed 1,000 individuals. In these cases conservation programmes should be initiated in order to maintain or even increase their number. This review deals with the possibilities and limitations of assisted reproductive technologies (ART) in the conservation of ecologically valuable wild, rare and indigenous ungulates. The methods discussed here are artificial insemination, cryopreservation of semen and embryos, embryo recovery and transfer,in vitroproduction of embryos, as well as micromanipulation techniques including sperm injection, assisted hatching and cloning. Some of these procedures are already being exploited in the breeding of farm ungulates, but more basic information about the reproductive patterns of wild, rare and indigenous animal species is needed before the routine use of ARTs
Studies on factors affecting superovulation and embryo transfer in Hungarian Merino ewes
The objectives of this study were (a) to assess the ovulatory response and embryo production of Hungarian Merino ewes after superovulation, (b) to investigate the factors influencing the efficiency of embryo transfer (ET) in Hungarian Merino ewes, (c) to compare the results of two ovarian stimulation protocols (PMSG and PMSG+FSH treatment) in Hungarian Merino ewes, and (d) to study how superovulation, laparoscopic insemination and surgical embryo retrieval (ER) affect the subsequent reproduction of Hungarian Merino donor females after an ET programme. There was no significant difference between the ovarian stimulation protocols in the ratio of donor ewes responding to superovulation nor in the average number of corpora lutea. However, the number of transferable embryos recovered per donor ewe was higher in the PMSG+FSH group. The proportion of transferable embryos, unfertilised oocytes and degenerated embryos did not differ between the treatment protocols. The total pregnancy rate was 53.4% (179/335). Neither the developmental stage of the embryo nor the number of transferred embryos affect the implantation of embryos. However, the increased number of transferred embryos positively influenced the pregnancy rate. No difference was found in the pregnancy rate between synchronised and nonsynchronised groups of recipients. Thirty-six out of 45 donor ewes (80%) became pregnant within one year after the ET programme, indicating that ovarian stimulation and surgical ER did not affect adversely their reproduction
A schematic model for QCD I: Low energy meson states
A simple model for QCD is presented, which is able to reproduce the meson
spectrum at low energy. The model is a Lipkin type model for quarks coupled to
gluons. The basic building blocks are pairs of quark-antiquarks coupled to a
definite flavor and spin. These pairs are coupled to pairs of gluons with spin
zero. The multiplicity problem, which dictates that a given experimental state
can be described in various manners, is removed when a particle-mixing
interaction is turned on. In this first paper of a series we concentrates on
the discussion of meson states at low energy, the so-called zero temperature
limit of the theory. The treatment of baryonic states is indicated, also.Comment: 29 pages, 6 figures. submitted to Phys. Rev.
Proxy-SU(3) symmetry in the shell model basis
The proxy-SU(3) symmetry has been proposed for spin-orbit like nuclear shells
using the asymptotic deformed oscillator basis for the single particle
orbitals, in which the restoration of the symmetry of the harmonic oscillator
shells is achieved by a change of the number of quanta in the z-direction by
one unit for the intruder parity orbitals. The same definition suffices within
the cartesian basis of the Elliott SU(3) model. Through a mapping of the
cartesian Elliott basis onto the spherical shell model basis, we translate the
proxy-SU(3) approximation into spherical coordinates, proving, that in the
spherical shell model basis the proxy-SU(3) approximation corresponds to the
replacement of the intruder parity orbitals by their de Shalit--Goldhaber
partners. Furthermore it is shown, that the proxy-SU(3) approximation in the
cartesian Elliott basis is equivalent to a unitary transformation in the
z-coordinate, leaving the x-y plane intact, a result which in the asymptotic
deformed oscillator coordinates implies, that the z-projections of angular
momenta and spin remain unchanged. The present work offers a microscopic
justification of the proxy-SU(3) approximation and in addition paves the way,
for taking advantage of the proxy-SU(3) symmetry in shell model calculations.Comment: 15 pages, 7 tables, 1 figur
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