626 research outputs found
Study of oxidative stress biomarkers in obese children
Background: The objective is to study the oxidative stress in obese and non-obese children by assessing the biomarkers of lipid peroxidation and antioxidant status, Malondialdehyde (MDA) and Ascorbic acid (vitamin C) respectively. Childhood obesity is a growing global epidemic that requires attention due to the burden placed on the healthcare system for children and adults. Consumption of fatty foods and a high sugar, fat diet, and no exercise qualify as the main reasons for obesity among children and adults. Childhood obesity is connected with an increased risk of various diseases such as diabetes, cardiovascular, stroke, certain types of cancer later in life, social problems and depression among youths. Obesity is also characterized by chronic low grade inflammation with permanently increased oxidative stress (OS). Over-expression of oxidative stress damages cellular structures together with under-production of anti-oxidant mechanisms, leading to the development of obesity-related complications.Methods: The study involved 25 obese children for Vitamin C, 20 obese children for Malondialdehyde (MDA) and 18 non obese children for both Vitamin C and MDA in the age group of 5-14 years, without any complications. This study was conducted at L.T.M.M College. Plasma Ascorbic Acid was estimated colorimetrically by using 2,6- dicholrophenol indophenol dye and similarly Malondialdehyde was estimated colorimetrically by MDA-TBA colored complex.Results: The study showed significantly higher values of MDA and lower level of Vitamin C in obese children as compared with non-obese children.Conclusions: The levels of lipid peroxidation marker Malondialdehyde (MDA) is higher and level of antioxidant marker Ascorbic Acid (Vitamin C) is lower in obese children as compared with non-obese children. Thereby increasing oxidative stress and hence the oxidative damage to cells
The soft X-ray properties of quasars in the Sloan Digital Sky Survey
We use the ROSAT All Sky Survey (RASS) to study the soft X-ray properties of
a homogeneous sample of 46,420 quasars selected from the third data release of
the Sloan Digital Sky Survey (SDSS). Optical luminosities, both at rest-frame
2500\AA () and in [OIII] () span more than three
orders of magnitude, while redshifts range over . We detect 3366
quasars directly in the observed 0.1--2.4 keV band. Sub-samples of radio-loud
and radio-quiet objects (RLQs and RQQs) are obtained by cross-matching with the
FIRST catalogue. We study the distribution of X-ray luminosity as a function of
optical luminosity, redshift and radio power using both individual detections
and stacks of complete sets of similar quasars. At every optical luminosity and
redshift \log L_{2\kev} is, to a good approximation, normally distributed
with dispersion , at least brightwards of the median X-ray
luminosity. This median X-ray luminosity of quasars is a power law of optical
luminosity with index for and for
. RLQs are systematically brighter than RQQs by about a factor
of 2 at given optical luminosity. The zero-points of these relations increase
systematically with redshift, possibly in different ways for RLQs and RQQs.
Evolution is particularly strong at low redshift and if the optical luminosity
is characterised by . At low redshift and at given
the soft X-ray emission from type II AGN is more than 100
times weaker than that from type I AGN.Comment: 16 pages, 15 figures, 3 tables, replaced with final version accepted
by MNRA
Compact Nuclei in Galaxies at Moderate Redshift:II. Their Nature and Implications for the AGN Luminosity Function
This study explores the space density and properties of active galaxies to
z=0.8. We have investigated the frequency and nature of unresolved nuclei in
galaxies at moderate redshift as indicators of nuclear activity such as Active
Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged
galaxies with multi-component models using maximum likelihood estimate
techniques to determine the best model fit. We select those galaxies requiring
an unresolved point-source component in the galaxy nucleus, in addition to a
disk and/or bulge component, to adequately model the galaxy light. We have
searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies
containing compact nuclei. In our survey of 1033 galaxies, the fraction
containing an unresolved nuclear component greater than 5% of the total galaxy
light is 9+/-1% corrected for incompleteness. In this second of two papers in
this series, we discuss the nature of the compact nuclei and their hosts.
We present the upper limit luminosity function (LF) for low-luminosity AGN
(LLAGN) in two redshift bins to z=0.8. Mild number density evolution is
detected for nuclei at -18 -16
and this flatness, combined with the increase in number density, is
inconsistent with pure luminosity evolution. Based on the amount of density
evolution observed for these objects, we find that almost all present-day
spiral galaxies could have hosted a LLAGN at some point in their lives. We also
comment on the likely contribution of these compact nuclei to the soft X-ray
background.Comment: 50 pages, 14 figures, to appear in ApJ, April 199
Boson Stars as Gravitational Lenses
We discuss boson stars as possible gravitational lenses and study the lensing
effect by these objects made of scalar particles. The mass and the size of a
boson star may vary from an individual Newtonian object similar to the Sun to
the general relativistic size and mass of a galaxy close to its Schwarzschild
radius. We assume boson stars to be transparent which allows the light to pass
through them though the light is gravitationally deflected. We assume boson
stars of the mass to be on non-cosmological distance from
the observer. We discuss the lens equation for these stars as well as the
details of magnification. We find that there are typically three images of a
star but the deflection angles may vary from arcseconds to even degrees. There
is one tangential critical curve (Einstein ring) and one radial critical curve
for tangential and radial magnification, respectively. Moreover, the deflection
angles for the light passing in the gravitational field of boson stars can be
very large (even of the order of degrees) which reflects the fact they are very
strong relativistic objects. We also propose a suitable formula for the lens
equation for such large deflection angles, and with the reservation that large
deflection angle images are highly demagnified but in the area of the
tangential critical curve, their existence may help in observational detection
of suitable lenses possessing characteristic features of boson stars which
could also serve as a direct evidence for scalar fields in the universe.Comment: accepted by Astrophys. J., 31 pages, AASTeX, 6 figure
The first joint ESGAR/ ESPR consensus statement on the technical performance of cross-sectional small bowel and colonic imaging
Objectives: To develop guidelines describing a standardised approach to patient preparation and acquisition protocols for magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound (US) of the small bowel and colon, with an emphasis on imaging inflammatory bowel disease. Methods: An expert consensus committee of 13 members from the European Society of Gastrointestinal and Abdominal Radiology (ESGAR) and European Society of Paediatric Radiology (ESPR) undertook a six-stage modified Delphi process, including a detailed literature review, to create a series of consensus statements concerning patient preparation, imaging hardware and image acquisition protocols. Results: One hundred and fifty-seven statements were scored for agreement by the panel of which 129 statements (82 %) achieved immediate consensus with a further 19 (12 %) achieving consensus after appropriate modification. Nine (6 %) statements were rejected as consensus could not be reached. Conclusions: These expert consensus recommendations can be used to help guide cross-sectional radiological practice for imaging the small bowel and colon. Key points: • Cross-sectional imaging is increasingly used to evaluate the bowel • Image quality is paramount to achieving high diagnostic accuracy • Guidelines concerning patient preparation and image acquisition protocols are provided
The XMM-Newton view of IRAS 09104+4109: evidence for a changing-look Type 2 quasar?
We analyzed the spectroscopic data from the PN and the MOS cameras in the
0.4-10 keV band. We also used an archival BeppoSAX 1-50 keV observation of IRAS
09104+4109 to investigate possible variations of the quasar emission. The X-ray
emission in the EPIC band is dominated by the intra-cluster medium thermal
emission. We found that the quasar contributes ~35% of the total flux in the
2-10 keV band. Both a transmission- (through a Compton-thin absorber with a
Compton optical depth of \tau_C~0.3, i.e. Nh~5 x 10^{23} cm^-2) and a
reflection-dominated (\tau_C>1) model provide an excellent fit to the quasar
continuum emission. However, the value measured for the EW of Fe Kalpha
emission line is only marginally consistent with the presence of a
Compton-thick absorber in a reflection-dominated scenario, which had been
suggested by a previous, marginal (i.e. 2.5\sigma) detection with the hard
X-ray (15-50 keV), non-imaging BeppoSAX/PDS instrument. Moreover, the value of
luminosity in the 2-10 keV band measured by the transmission-dominated model is
fully consistent with that expected on the basis of the bolometric luminosity
of IRAS 09104+4109. From the analysis of the XMM-Newton data we therefore
suggest the possibility that the absorber along the line of sight to the
nucleus of IRAS 09104+4109 is Compton-thin. Alternatively, the absorber column
density could have changed from Compton-thick to -thin in the five years
elapsed between the observations. If this is the case, then IRAS 09104+4109 is
the first 'changing-look' quasar ever detected.Comment: Accepted by Astronomy and Astrophysic
Warming and elevated CO2 promote rapid incorporation and degradation of plant-derived organic matter in an ombrotrophic peatland
Rising temperatures have the potential to directly affect carbon cycling in peatlands by enhancing organic matter (OM) decomposition, contributing to the release of CO2 and CH4 to the atmosphere. In turn, increasing atmospheric CO2 concentration may stimulate photosynthesis, potentially increasing plant litter inputs belowground and transferring carbon from the atmosphere into terrestrial ecosystems. Key questions remain about the magnitude and rate of these interacting and opposing environmental change drivers. Here, we assess the incorporation and degradation of plant- and microbe-derived OM in an ombrotrophic peatland after 4 years of whole-ecosystem warming (+0, +2.25, +4.5, +6.75 and +9°C) and two years of elevated CO2 manipulation (500 ppm above ambient). We show that OM molecular composition was substantially altered in the aerobic acrotelm, highlighting the sensitivity of acrotelm carbon to rising temperatures and atmospheric CO2 concentration. While warming accelerated OM decomposition under ambient CO2, new carbon incorporation into peat increased in warming × elevated CO2 treatments for both plant- and microbe-derived OM. Using the isotopic signature of the applied CO2 enrichment as a label for recently photosynthesized OM, our data demonstrate that new plant inputs have been rapidly incorporated into peat carbon. Our results suggest that under current hydrological conditions, rising temperatures and atmospheric CO2 levels will likely offset each other in boreal peatlands
A forming disk at z~0.6: Collapse of a gaseous disk or major merger remnant?
[Abridged] We present and analyze observations of J033241.88-274853.9 at
z=0.6679, using multi-wavelength photometry and imaging with FLAMES/GIRAFFE 3D
spectroscopy. J033241.88-274853.9 is found to be a blue, young (~320Myr)
stellar disk embedded in a very gas-rich (fgas=73-82% with
log(Mstellar/Mo)=9.45) and turbulent phase that is found to be rotating on
large spatial scales. We identified two unusual properties of
J033241.88-274853.9. (1) The spatial distributions of the ionized gaseous and
young stars show a strong decoupling; while almost no stars can be detected in
the southern part down to the very deep detection limit of ACS/UDF images,
significant emission from the [OII] ionized gas is detected. (2) We detect an
excess of velocity dispersion in the southern part of J033241.88-274853.9 in
comparison to expectations from a rotating disk model. We considered two disk
formation scenarios, depending on the gaseous phase geometry. In the first one,
we examined whether J033241.88-274853.9 could be a young rotating disk that has
been recently collapsed from a pre-existing, very gas-rich rotating disk. This
scenario requires two (unknown) additional assumptions to explain the
decoupling between the distribution of stars and gas and the excess of velocity
dispersion in the same region. In a second scenario, we examine whether
J033241.88-274853.9 could be a merger remnant of two gas-rich disks. In this
case, the asymmetry observed between the gas and star distributions, as well as
the excess of velocity dispersion, find a common explanation. Shocks produced
during the merger in this region can be ionized easily and heat the gas while
preventing star formation. This makes this scenario more satisfactory than the
collapse of a pre-existing, gas-rich rotating disk.Comment: Accepted for publication in A&A. 8 pages & 5 figure
A census with ROSAT of low-luminosity X-ray sources in globular clusters
I analyze 101 observations from the ROSAT archive to search for X-ray sources
in or near 55 globular clusters. New sources are found in the cores of NGC362
(a double source), NGC6121 (marginally significant), NGC6139, and NGC6266; and
outside the cores of NGC6205, NGC6352 and NGC6388. More accurate positions are
determined for the X-ray sources in some ten clusters. The improved position
for the source in NGC6341 excludes the suggested ultraviolet counterpart. It is
shown that one of the two sources reported near the core NGC6626 is spurious,
as is the detection of a pulsar period in the PSPC data of this cluster; the
central source is resolved in three sources. One source reported previously in
NGC6304 is demoted to an upper limit. For 20 cluster cores better upper limits
to the X-ray luminosity are obtained.
From a statistical analysis I argue that several sources outside the cluster
cores may well belong to the clusters. All spectral energy distributions
observed so far are relatively soft, with bremsstrahlung temperatures =~0.9keV;
there is evidence however that bremsstrahlung spectra do not correctly describe
the spectra. The X-ray luminosity per unit mass for the cluster as a whole does
not depend on the concentration; the luminosity per unit mass for the core may
increase with the cluster concentration.Comment: 24 pages, 8 figures, 5 tables, accepted for publication in Astronomy
and Astrophysic
CAIXA: a Catalogue of AGN In the XMM-Newton Archive II. Multiwavelength correlations
We presented CAIXA, a Catalogue of AGN in the XMM-Newton Archive, in a
companion paper. Here, a systematic search for correlations between the X-ray
spectral properties and the multiwavelength data was performed for the sources
in CAIXA. All the significant (>99.9% confidence level) correlations are
discussed along with their physical implications on current models of AGN. Two
main correlations are discussed in this paper: a) a very strong
anti-correlation between the FWHM of the H optical line and the ratio
between the soft and the hard X-ray luminosity. Although similar
anti-correlations between optical line width and X-ray spectral steepness have
already been discussed in the literature (see e.g., Laor et al. 1994, Boller et
al. 1996, Brandt et al. 1997), we consider the formulation we present in this
paper is more fundamental, as it links model-independent quantities. Coupled
with a strong anti-correlation between the V to hard X-ray flux ratio and the
H FHWM, it supports scenarios for the origin of the soft excess in AGN,
which require strong suppression of the hard X-ray emission; b) a strong (and
expected) correlation between the X-ray luminosity and the black hole mass. Its
slope, flatter than 1, is consistent with Eddington ratio-dependent bolometric
corrections, such as that recently proposed by Vasudevan & Fabian (2009).
Moreover, we critically review through various statistical tests the role that
distance biases play in the strong radio to X-ray luminosity correlation found
in CAIXA and elsewhere; we conclude that only complete, unbiased samples (such
as that recently published by Behar & Laor, 2008) should be used to draw
observational constraints on the origin of radio emission in radio-quiet AGN.Comment: 12 pages, 11 figures, accepted for publication in Astronomy and
Astrophysics; two figures erroneously attached by astroph to the paper were
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