903 research outputs found
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
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
Heavy-element yields and abundances of Asymptotic Giant Branch models with a Small Magellanic Cloud metallicity
We present new theoretical stellar yields and surface abundances for
asymptotic giant branch (AGB) models with a metallicity appropriate for stars
in the Small Magellanic Cloud (SMC, , [Fe/H] ). New
evolutionary sequences and post-processing nucleosynthesis results are
presented for initial masses between 1 and 7, where the
7 is a super-AGB star with an O-Ne core. Models above
1.15 become carbon rich during the AGB, and hot bottom burning
begins in models . We present stellar surface abundances
as a function of thermal pulse number for elements between C to Bi and for a
selection of isotopic ratios for elements up to Fe and Ni (e.g.,
C/C), which can be compared to observations. The integrated
stellar yields are presented for each model in the grid for hydrogen, helium
and all stable elements from C to Bi. We present evolutionary sequences of
intermediate-mass models between 4--7 and nucleosynthesis results
for three masses () including -process elements for
two widely used AGB mass-loss prescriptions. We discuss our new models in the
context of evolved AGB stars and post-AGB stars in the Small Magellanic Clouds,
barium stars in our Galaxy, the composition of Galactic globular clusters
including Mg isotopes with a similar metallicity to our models, and to
pre-solar grains which may have an origin in metal-poor AGB stars.Comment: 19 pages, accepted for publication in MNRA
Relation between the phenomenological interactions of the algebraic cluster model and the effective two--nucleon forces
We determine the phenomenological cluster--cluster interactions of the
algebraic model corresponding to the most often used effective two--nucleon
forces for the O + system.Comment: Latex with Revtex, 1 figure available on reques
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
New and simple algorithms for stable flow problems
Stable flows generalize the well-known concept of stable matchings to markets
in which transactions may involve several agents, forwarding flow from one to
another. An instance of the problem consists of a capacitated directed network,
in which vertices express their preferences over their incident edges. A
network flow is stable if there is no group of vertices that all could benefit
from rerouting the flow along a walk.
Fleiner established that a stable flow always exists by reducing it to the
stable allocation problem. We present an augmenting-path algorithm for
computing a stable flow, the first algorithm that achieves polynomial running
time for this problem without using stable allocation as a black-box
subroutine. We further consider the problem of finding a stable flow such that
the flow value on every edge is within a given interval. For this problem, we
present an elegant graph transformation and based on this, we devise a simple
and fast algorithm, which also can be used to find a solution to the stable
marriage problem with forced and forbidden edges.
Finally, we study the stable multicommodity flow model introduced by
Kir\'{a}ly and Pap. The original model is highly involved and allows for
commodity-dependent preference lists at the vertices and commodity-specific
edge capacities. We present several graph-based reductions that show
equivalence to a significantly simpler model. We further show that it is
NP-complete to decide whether an integral solution exists
Association of PPAR Alpha Intron 7 G/C, PPAR Gamma 2 Pro12Ala, and C161T Polymorphisms with Serum Fetuin-A Concentrations
BACKGROUND: Both peroxisome activator proteins (PPARs) and fetuin-A play a role in lipid and glucose metabolism. AIMS: We investigated whether PPARalpha intron 7 G2468/C and PPARgamma2 Pro12Ala and PPARgamma exon 6 C161T polymorphisms are associated with serum fetuin-A concentrations. PATIENTS AND METHODS: The PPARalpha intron 7 G/C polymorphism was studied in cohort 1 (79 reference individuals, 165 postinfarction patients). The two PPARgamma polymorphisms were investigated in cohort 2 (162 reference individuals, 165 postinfarction patients). Fetuin-A levels and PPAR polymorphisms were determined by radial immunodiffusion and polymerase chain reaction-restriction fragment length polymorphism techniques. RESULTS: The C allele variant of PPARalpha intron 7 G2467C was associated with higher fetuin-A levels (p = 0.018). Postinfarction status (p = 0.001), PPARalpha intron 7 GG/GC/CC genotypes (p = 0.032), and the C allele (p = 0.021) were the strongest determinants of fetuin-A concentration in a multiple regression model. Higher fetuin-A levels were associated with the Pro variant of PPARgamma2 (p = 0.047). Postinfarction status (p = 0.041) and BMI (p < 0.001) but not PPARgamma2 Pro were the strongest determinants of fetuin-A concentrations. PPARgamma exon 6 C161T genotypes were not associated with fetuin-A levels. CONCLUSIONS: Fetuin-A was determined mainly by the PPARalpha intron 7C allele and postinfarction status in cohort 1 and the BMI and postinfarction in cohort 2. The PPARalpha intron 7C and PPARgamma2 Pro variants are associated with fetuin-A levels
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