224 research outputs found
Probing the extragalactic fast transient sky at minute timescales with DECam
Searches for optical transients are usually performed with a cadence of days
to weeks, optimised for supernova discovery. The optical fast transient sky is
still largely unexplored, with only a few surveys to date having placed
meaningful constraints on the detection of extragalactic transients evolving at
sub-hour timescales. Here, we present the results of deep searches for dim,
minute-timescale extragalactic fast transients using the Dark Energy Camera, a
core facility of our all-wavelength and all-messenger Deeper, Wider, Faster
programme. We used continuous 20s exposures to systematically probe timescales
down to 1.17 minutes at magnitude limits (AB), detecting hundreds of
transient and variable sources. Nine candidates passed our strict criteria on
duration and non-stellarity, all of which could be classified as flare stars
based on deep multi-band imaging. Searches for fast radio burst and gamma-ray
counterparts during simultaneous multi-facility observations yielded no
counterparts to the optical transients. Also, no long-term variability was
detected with pre-imaging and follow-up observations using the SkyMapper
optical telescope. We place upper limits for minute-timescale fast optical
transient rates for a range of depths and timescales. Finally, we demonstrate
that optical -band light curve behaviour alone cannot discriminate between
confirmed extragalactic fast transients such as prompt GRB flashes and Galactic
stellar flares.Comment: Published in MNRA
Contribution of hierarchical clustering techniques to the modeling of the geographic distribution of genetic polymorphisms associated with chronic inflammatory diseases in the Québec population
Objectives:
The purpose of this project was to evaluate the potential of the downward hierarchical clustering analysis (DHCA) for studying genetic heterogeneity, i.e. differences in allele frequency in subpopulations, such as the 15 public health regions of the province of Québec (Canada).
Methods:
The study relied on an anonymized sample of 1,680 individuals who had participated in the Québec Heart Health Survey in 1990-1991. The genotyping of 11 variants in 8 candidate genes known to be involved in chronic inflammatory diseases, namely asthma and cardiovascular diseases, was performed using the amplification refractory mutation system and restriction fragment length polymorphism techniques. Only variants showing an allelic frequency >2% in the Québec Heart Health Survey (n = 8) were selected. DHCA techniques were then applied to model the geographical distribution of these 8 genetic variants in 15 Québec public health regions and to study genetic heterogeneity.
Results:
The DHCA allowed to group public health regions and gene variants on the basis of genetic variability. For both asthma and cardiovascular diseases, 3 significant clusters of public health regions and 1 cluster of gene variants were identified.
Discussion:
This study suggests that DHCA might be useful in studying genetic heterogeneity at the population level and for public health activities
Probing the extragalactic fast transient sky at minute time-scales with DECam
Searches for optical transients are usually performed with a cadence of days to weeks, optimized for supernova discovery. The optical fast transient sky is still largely unexplored, with only a few surveys to date having placed meaningful constraints on the detection of extragalactic transients evolving at sub-hour time-scales. Here, we present the results of deep searches for dim, minute-time-scale extragalactic fast transients using the Dark Energy Camera, a core facility of our all-wavelength and all-messenger Deeper, Wider, Faster programme. We used continuous 20 s exposures to systematically probe time-scales down to 1.17 min at magnitude limits g > 23 (AB), detecting hundreds of transient and variable sources. Nine candidates passed our strict criteria on duration and non-stellarity, all of which could be classified as flare stars based on deep multiband imaging. Searches for fast radio burst and gamma-ray counterparts during simultaneous multifacility observations yielded no counterparts to the optical transients. Also, no long-term variability was detected with pre-imaging and follow-up observations using the SkyMapper optical telescope. We place upper limits for minute-time-scale fast optical transient rates for a range of depths and time-scales. Finally, we demonstrate that optical g-band light-curve behaviour alone cannot discriminate between confirmed extragalactic fast transients such as prompt GRB flashes and Galactic stellar flares
PPARα L162V underlies variation in serum triglycerides and subcutaneous fat volume in young males
<p>Abstract</p> <p>Background</p> <p>Of the five sub-phenotypes defining metabolic syndrome, all are known to have strong genetic components (typically 50–80% of population variation). Studies defining genetic predispositions have typically focused on older populations with metabolic syndrome and/or type 2 diabetes. We hypothesized that the study of younger populations would mitigate many confounding variables, and allow us to better define genetic predisposition loci for metabolic syndrome.</p> <p>Methods</p> <p>We studied 610 young adult volunteers (average age 24 yrs) for metabolic syndrome markers, and volumetric MRI of upper arm muscle, bone, and fat pre- and post-unilateral resistance training.</p> <p>Results</p> <p>We found the PPARα L162V polymorphism to be a strong determinant of serum triglyceride levels in young White males, where carriers of the V allele showed 78% increase in triglycerides relative to L homozygotes (LL = 116 ± 11 mg/dL, LV = 208 ± 30 mg/dL; p = 0.004). Men with the V allele showed lower HDL (LL = 42 ± 1 mg/dL, LV = 34 ± 2 mg/dL; p = 0.001), but women did not. Subcutaneous fat volume was higher in males carrying the V allele, however, exercise training increased fat volume of the untrained arm in V carriers, while LL genotypes significantly decreased in fat volume (LL = -1,707 ± 21 mm<sup>3</sup>, LV = 17,617 ± 58 mm<sup>3 </sup>; p = 0.002), indicating a systemic effect of the V allele on adiposity after unilateral training. Our study suggests that the primary effect of PPARα L162V is on serum triglycerides, with downstream effects on adiposity and response to training.</p> <p>Conclusion</p> <p>Our results on association of PPARα and triglycerides in males showed a much larger effect of the V allele than previously reported in older and less healthy populations. Specifically, we showed the V allele to increase triglycerides by 78% (p = 0.004), and this single polymorphism accounted for 3.8% of all variation in serum triglycerides in males (p = 0.0037).</p
Apertif 1.4 GHz continuum observations of the Bo\"otes field and their combined view with LOFAR
We present a new image of a 26.5 square degree region in the Bo\"otes
constellation obtained at 1.4 GHz using the Aperture Tile in Focus (Apertif)
system on the Westerbork Synthesis Radio Telescope. We use a newly developed
processing pipeline which includes direction-dependent self-calibration which
provides a significant improvement of the quality of the images compared to
those released as part of the Apertif first data release. For the Bo\"otes
region, we mosaic 187 Apertif images and extract a source catalog. The mosaic
image has an angular resolution of 2711.5 arcseconds and a median
background noise of 40 Jy/beam. The catalog has 8994 sources and is
complete down to the 0.3 mJy level. We combine the Apertif image with LOFAR
images of the Bo\"otes field at 54 and 150 MHz to study spectral properties of
the sources. We find a spectral flattening towards low flux density sources.
Using the spectral index limits from Apertif non-detections we derive that up
to 9 percent of the sources have ultra-steep spectra with a slope steeper than
-1.2. Steepening of the spectral index with increasing redshift is also seen in
the data showing a different dependency for the low-frequency spectral index
and the high frequency one. This can be explained by a population of sources
having concave radio spectra with a turnover frequency around the LOFAR band.
Additionally, we discuss cases of individual extended sources with an
interesting resolved spectral structure. With the improved pipeline, we aim to
continue processing data from the Apertif wide-area surveys and release the
improved 1.4 GHz images of several famous fields.Comment: 13 pages, 9 figures; to be published in A&
Disturbance in uniformly 13C-labelled DHA metabolism in elderly human subjects carrying the apoE ε4 allele
Carrying the apoE ε4 allele (E4+) is the most important genetic risk for Alzheimer's disease. Unlike non-carriers (E4 − ), E4+ seem not to be protected against Alzheimer's disease when consuming fish. We hypothesised that this may be linked to a disturbance in n-3 DHA metabolism in E4+. The aim of the present study was to evaluate [13C]DHA metabolism over 28 d in E4+v. E4 − . A total of forty participants (twenty-six women and fourteen men) received a single oral dose of 40 mg [13C]DHA, and its metabolism was monitored in blood and breath over 28 d. Of the participants, six were E4+ and thirty-four were E4 − . In E4+, mean plasma [13C]DHA was 31 % lower than that in E4 − , and cumulative β-oxidation of [13C]DHA was higher than that in E4 − 1–28 d post-dose (P≤ 0·05). A genotype × time interaction was detected for cumulative β-oxidation of [13C]DHA (P≤ 0·01). The whole-body half-life of [13C]DHA was 77 % lower in E4+ compared with E4 − (P≤ 0·01). In E4+ and E4 − , the percentage dose of [13C]DHA recovered/h as 13CO2 correlated with [13C]DHA concentration in plasma, but the slope of linear regression was 117 % steeper in E4+ compared with E4 − (P≤ 0·05). These results indicate that DHA metabolism is disturbed in E4+, and may help explain why there is no association between DHA levels in plasma and cognition in E4+. However, whether E4+ disturbs the metabolism of 13C-labelled fatty acids other than DHA cannot be deduced from the present study
Continuum source catalog for the first APERTIF data release
The first data release of Apertif survey contains 3074 radio continuum images
covering a thousand square degrees of the sky. The observations were performed
during August 2019 to July 2020. The continuum images were produced at a
central frequency 1355 MHz with the bandwidth of 150 MHz and angular
resolution reaching 10". In this work we introduce and apply a new method to
obtain a primary beam model using a machine learning approach, Gaussian process
regression. The primary beam models obtained with this method are published
along with the data products for the first Apertif data release. We apply the
method to the continuum images, mosaic them and extract the source catalog. The
catalog contains 249672 radio sources many of which are detected for the first
time at these frequencies. We cross-match the coordinates with the NVSS,
LOFAR/DR1/value-added and LOFAR/DR2 catalogs resulting in 44523, 22825 and
152824 common sources respectively. The first sample provides a unique
opportunity to detect long term transient sources which have significantly
changed their flux density for the last 25 years. The second and the third ones
combined together provide information about spectral properties of the sources
as well as the redshift estimates.Comment: 12 pages, 9 figures; accepted for publication in A&
PPARα: energy combustion, hypolipidemia, inflammation and cancer
The peroxisome proliferator-activated receptor α (PPARα, or NR1C1) is a nuclear hormone receptor activated by a structurally diverse array of synthetic chemicals known as peroxisome proliferators. Endogenous activation of PPARα in liver has also been observed in certain gene knockout mouse models of lipid metabolism, implying the existence of enzymes that either generate (synthesize) or degrade endogenous PPARα agonists. For example, substrates involved in fatty acid oxidation can function as PPARα ligands. PPARα serves as a xenobiotic and lipid sensor to regulate energy combustion, hepatic steatosis, lipoprotein synthesis, inflammation and liver cancer. Mainly, PPARα modulates the activities of all three fatty acid oxidation systems, namely mitochondrial and peroxisomal β-oxidation and microsomal ω-oxidation, and thus plays a key role in energy expenditure. Sustained activation of PPARα by either exogenous or endogenous agonists leads to the development of hepatocellular carcinoma resulting from sustained oxidative and possibly endoplasmic reticulum stress and liver cell proliferation. PPARα requires transcription coactivator PPAR-binding protein (PBP)/mediator subunit 1(MED1) for its transcriptional activity
Characterising the Apertif primary beam response
Context. Phased Array Feeds (PAFs) are multi element receivers in the focal
plane of a telescope that make it possible to form simultaneously multiple
beams on the sky by combining the complex gains of the individual antenna
elements. Recently the Westerbork Synthesis Radio Telescope (WSRT) was upgraded
with PAF receivers and carried out several observing programs including two
imaging surveys and a time domain survey. The Apertif imaging surveys use a
configuration, where 40 partially overlapping compound beams (CBs) are
simultaneously formed on the sky and arranged in an approximately rectangular
shape. Aims. This manuscript aims to characterise the response of the 40
Apertif CBs to create frequency-resolved, I, XX and YY polarization empirical
beam shapes. The measured CB maps can be used for image deconvolution, primary
beam correction and mosaicing of Apertif imaging data. Methods. We use drift
scan measurements to measure the response of each of the 40 CBs of Apertif. We
derive beam maps for all individual beams in I, XX and YY polarisation in 10 or
18 frequency bins over the same bandwidth as the Apertif imaging surveys. We
sample the main lobe of the beams and the side lobes up to a radius of 0.6
degrees from the beam centres. In addition, we derive beam maps for each
individual WSRT dish as well. Results. We present the frequency and time
dependence of the beam shapes and sizes. We compare the compound beam shapes
derived with the drift scan method to beam shapes derived with an independent
method using a Gaussian Process Regression comparison between the Apertif
continuum images and the NRAO VLA Sky Survey (NVSS) catalogue. We find a good
agreement between the beam shapes derived with the two independent methods.Comment: Accepted for publication by A&A, 14 pages, 15 figure
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