1,755 research outputs found
A Search for Optical Variability of Type 2 Quasars in SDSS Stripe 82
Hundreds of Type 2 quasars have been identified in Sloan Digital Sky Survey
(SDSS) data, and there is substantial evidence that they are generally galaxies
with highly obscured central engines, in accord with unified models for active
galactic nuclei (AGNs). A straightforward expectation of unified models is that
highly obscured Type 2 AGNs should show little or no optical variability on
timescales of days to years. As a test of this prediction, we have carried out
a search for variability in Type 2 quasars in SDSS Stripe 82 using
difference-imaging photometry. Starting with the Type 2 AGN catalogs of
Zakamska et al. (2003) and Reyes et al. (2008), we find evidence of significant
g-band variability in 17 out of 173 objects for which light curves could be
measured from the Stripe 82 data. To determine the nature of this variability,
we obtained new Keck spectropolarimetry observations for seven of these
variable AGNs. The Keck data show that these objects have low continuum
polarizations (p<~1% in most cases) and all seven have broad H-alpha and/or
MgII emission lines in their total (unpolarized) spectra, indicating that they
should actually be classified as Type 1 AGNs. We conclude that the primary
reason variability is found in the SDSS-selected Type 2 AGN samples is that
these samples contain a small fraction of Type 1 AGNs as contaminants, and it
is not necessary to invoke more exotic possible explanations such as a
population of "naked" or unobscured Type 2 quasars. Aside from misclassified
Type 1 objects, the Type 2 quasars do not generally show detectable optical
variability over the duration of the Stripe 82 survey.Comment: 14 pages, 8 figures. Accepted for publication in A
RAPTOR observations of delayed explosive activity in the high-redshift gamma-ray burst GRB 060206
The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos
National Laboratory observed GRB 060206 starting 48.1 minutes after gamma-ray
emission triggered the Burst Alert Telescope (BAT) on-board the Swift
satellite. The afterglow light curve measured by RAPTOR shows a spectacular
re-brightening by ~1 mag about 1 h after the trigger and peaks at R ~ 16.4 mag.
Shortly after the onset of the explosive re-brightening the OT doubled its flux
on a time-scale of about 4 minutes. The total R-band fluence received from GRB
060206 during this episode is 2.3e-9 erg/cm2. In the rest frame of the burst (z
= 4.045) this yields an isotropic equivalent energy release of ~0.7e50 erg in
just a narrow UV band 130 +/- 22 nm. We discuss the implications of RAPTOR
observations for untriggered searches for fast optical transients and studies
of GRB environments at high redshift.Comment: Submitted to ApJ Letter
5-Fluoro-1,3-dihydro-2,1-benzoxaborol-1-ol
In the crystal structure of the title compound, C7H6BFO2, a broad-spectrum antifungal drug (AN2690), the planar [maximum deviation 0.035 (1) Å] molecules form centrosymmetric R
2
2(8) dimers via strong O—H⋯O hydrogen bonds. The dimers are arranged into layers by weak intermolecular C—H⋯O and C—H⋯F hydrogen bonds. The symmetry of this two-dimensional supramolecular assembly can be described by the layer group p
and topologically classified as a simple uninodal four-connected two-dimensional network of a (4.4.4.4.6.6) topology. Further weak C—H⋯O interactions build up the three-dimensional structure
The Optical Gravitational Lensing Experiment. Short Distance Scale to the LMC
We present {\it UBVI} photometry of the eclipsing binary HV2274 - the system
which has been recently used for distance determination to the LMC by Guinan et
al. (1998). We determine the interstellar reddening to the star,
E(B-V)=0.149+/-0.015 mag, based on observed colors of the star. This value is
in excellent agreement with the mean reddening towards HV2274 obtained from
photometry of the red clump stars in the surrounding field. The reddening is
almost twice as large as determined by Guinan et al. (1998).
We discuss the consequences of reddening underestimate. Most likely HV2274 is
located much closer with the distance modulus to the star and the LMC: m-M =
18.22+/-0.13 mag supporting the short distance scale to the LMC. Such a
distance modulus is in excellent agreement with the recent distance
determinations with RR Lyr and red clump stars.Comment: 11 pages, Latex, 2 Figures. Accepted for publication in Astrophysical
Journal Letters. New version - trimmed to fit ApJL. Additional determination
of the reddening towards HV2274 with OB star
Generalised Decision Level Ensemble Method for Classifying Multi-media Data
In recent decades, multimedia data have been commonly generated and used in various domains, such as in healthcare and social media due to their ability of capturing rich information. But as they are unstructured and separated, how to fuse and integrate multimedia datasets and then learn from them eectively have been a main challenge to machine learning. We present a novel generalised decision level ensemble method (GDLEM) that combines the multimedia datasets at decision level. After extracting features from each of multimedia datasets separately, the method trains models independently on each media dataset and then employs a generalised selection function to choose the appropriate models to construct a heterogeneous ensemble. The selection function is dened as a weighted combination of two criteria: the accuracy of individual models and the diversity among the models. The framework is tested on multimedia data and compared with other heterogeneous ensembles. The results show that the GDLEM is more exible and eective
The relationship between successional vascular plant assemblages and associated microbial communities on coal mine spoil heaps
The aim of the study was to investigate the relationships between the vascular plant species and the associated soil microbial properties at various stages of vegetation development on unclaimed hard coal mine spoil heaps in Upper Silesia (south Poland). The spontaneous vegetation, soil chemistry as well as the activity and structure of microbial communities were recorded on this specific habitat. The colliery heaps were divided into four age classes and the plant species composition and cover abundance were recorded on established plots (2 m × 2 m). The soil microbial activity under the vegetation patches was assessed using fluorescein diacetate hydrolytic activity (FDHA) and the soil microbial biomass and community composition were determined by phospholipid fatty acid (PLFA) biomarkers. Total microbial biomass in soils from the older vegetation plots was significantly higher than those in soils from the younger plots. In all studied samples, microbial communities consisted primarily of bacteria with the dominance of Gram negative bacteria over Gram positive and aerobic microorganisms were more dominant than anaerobic ones. Statistical analysis revealed a correlation between the type of vegetation and microbial community structure
Subcellular distribution and expression of cofilin and ezrin in human colon adenocarcinoma cell lines with different metastatic potential
The dynamic reorganization of the actin cytoskeleton is regulated by a number of actin binding proteins (ABPs). Four human colon adenocarcinoma cell lines – parental and three selected sublines, which differ in motility and metastatic potential, were used to investigate the expression level and subcellular localization of selected ABPs. Our interest was focused on cofilin and ezrin. These proteins are essential for cell migration and adhesion. The data received for the three more motile adenocarcinoma sublines (EB3, 3LNLN, 5W) were compared with those obtained for the parental LS180 adenocarcinoma cells and fibroblastic NRK cells. Quantitative densitometric analysis and confocal fluorescence microscopy were used to examine the expression levels and subcellular distribution of the selected ABPs. Our data show distinct increase in the level of cofilin in adenocarcinoma cells accompanied by the reduction of inactive phosphorylated form of cofilin. In more motile cells, cofilin was accumulated at cellular periphery in co-localization with actin filaments. Furthemore, we indicated translocation of ezrin towards the cell periphery within more motile cells in comparison with NRK and parental adenocarcinoma cells
The initial zones of the atrioventricular node: really neglected anatomical features of potential clinical significance?
The constant evolution of medical knowledge and accompanying development
of diagnostic and treatment possibilities for arrhythmias and conduction disturbances
has reawakened interest in the structure and function of the conduction
system of the human heart, especially in the region of the atrioventricular (AV)
junction and within the junction itself. Of the large number of studies dealing
with the AV junction few focus on the initial zones of the AV node. These were
described for the first time by Tawara in 1906. Similarly, Anderson et al. distinguished
two origins of the AV node, the left one running towards the basis of
the mitral valve and the right one leading towards the tricuspid valve. The differences
in length and scale could be the result of the adoption of different reference
points.
The study was carried out on the material of 50 human hearts, of both sexes
and ranging in age from 22 to 93, which were fixed in 10% formalin and 98%
ethanol solution. The tissue obtained was fixed in the 10% formalin solution
and, after being sunk in the paraffin, was cut into layers of about 10 μm thick.
According to the age of the hearts, every 10th or 6th section was stained by the
Masson-Goldner method. The preparations were examined under a LEICA 2000
and BIOLAR 2 microscope at magnifications of 2× to 400×.
Each of the 50 examined hearts contained the atrioventricular node and its initial
parts. We observed that the initial zone of the AV node is created by an
assembly of cells typical for a conduction system that can create three groups
that are initially independent of each other and are always arranged around the
AV nodal artery. In all the hearts examined we found at least two initial parts of
the node: the superior and inferior. These two groups were present in 45 hearts
(90%). In the last 5 cases (10%) there was also a middle group. No cases were
found either with a single initial group or without any initial groups. In the
sections examined the superior group appeared to be first in 27 hearts (54%),
while in 23 cases (46%) the inferior group was first. The length of each group
was measured from its first appearance to its first direct contact with the second
part. The length of the superior part varied from 0.15 to 2.91 mm (mean 0.90 ± 0.6 mm), the inferior from 0.11 to 2.41 mm (mean 0.88 ± 0.6 mm) and the middle from 0.67 to 2.21 mm (mean 1.04 ± 0.7 mm). As mentioned above, in
all 50 hearts there was a direct connection between the atrial muscle and the
upper origin of AV node. Furthermore, in all sections (100%) the same part of
the interatrial septal muscle was connected to the compact part of the node.
Additionally, in 3 cases (6%) we were able to observe direct connections between
the muscle fibres running from the fasciculus limbicus inferior to the
initial zone of the AV node: in 2 cases (4%) with the superior group and in
1 case (2%) with the inferior group. In 8% of the material the atrial muscle of
the supra-orificial zone made direct contact with the superior initial group and
the compact zone of the node and in 10% there was contact between the
suborificial muscle and the inferior group and the compact part of the node.
This configuration was not observed in relation to the middle and inferior groups
The quest for companions to post-common envelope binaries. II. NSVS14256825 and HS0705+6700
We report new mid-eclipse times of the two close binaries NSVS14256825 and
HS0705+6700, harboring an sdB primary and a low-mass main-sequence secondary.
Both objects display clear variations in the measured orbital period, which can
be explained by the action of a third object orbiting the binary. If this
interpretation is correct, the third object in NSVS14256825 is a giant planet
with a mass of roughly 12 M_Jup. For HS0705+6700, we provide evidence that
strengthens the case for the suggested periodic nature of the eclipse time
variation and reduces the uncertainties in the parameters of the brown dwarf
implied by that model. The derived period is 8.4 yr and the mass is 31 M_Jup,
if the orbit is coplanar with the binary. This research is part of the
PlanetFinders project, an ongoing collaboration between professional
astronomers and student groups at high schools.Comment: Accepted by Astron. and Astrophy
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