228 research outputs found
Scaling Relations of Spiral Galaxies
We construct a large data set of global structural parameters for 1300 field
and cluster spiral galaxies and explore the joint distribution of luminosity L,
optical rotation velocity V, and disk size R at I- and 2MASS K-bands. The I-
and K-band velocity-luminosity (VL) relations have log-slopes of 0.29 and 0.27,
respectively with sigma_ln(VL)~0.13, and show a small dependence on color and
morphological type in the sense that redder, early-type disk galaxies rotate
faster than bluer, later-type disk galaxies for most luminosities. The VL
relation at I- and K-bands is independent of surface brightness, size and light
concentration. The log-slope of the I- and K-band RL relations is a strong
function of morphology and varies from 0.25 to 0.5. The average dispersion
sigma_ln(RL) decreases from 0.33 at I-band to 0.29 at K, likely due to the
2MASS selection bias against lower surface brightness galaxies. Measurement
uncertainties are sigma_ln(V)~0.09, sigma_ln(L)~0.14 and somewhat larger and
harder to estimate for ln(R). The color dependence of the VL relation is
consistent with expectations from stellar population synthesis models. The VL
and RL residuals are largely uncorrelated with each other; the RV-RL residuals
show only a weak positive correlation. These correlations suggest that scatter
in luminosity is not a significant source of the scatter in the VL and RL
relations. The observed scaling relations can be understood in the context of a
model of disk galaxies embedded in dark matter halos that invokes low mean spin
parameters and dark halo expansion, as we describe in our companion paper
(Dutton et al. 2007). We discuss in two appendices various pitfalls of standard
analytical derivations of galaxy scaling relations, including the Tully-Fisher
relation with different slopes. (Abridged).Comment: Accepted for publication at ApJ. The full document, with
high-resolution B&W and colour figures, is available at
http://www.astro.queensu.ca/~courteau/papers/VRL2007ApJ.pdf . Our data base
for 1303 spiral galaxies is also available at
http://www.astro.queensu.ca/~courteau/data/VRL2007.da
Low-Surface-Brightness Galaxies in the Sloan Digital Sky Survey. I. Search Method and Test Sample
In this paper we present results of a pilot study to use imaging data from
the Sloan Digital Sky Survey (SDSS) to search for low-surface-brightness (LSB)
galaxies. For our pilot study we use a test sample of 92 galaxies from the
catalog of Impey et al. (1996) distributed over 93 SDSS fields of the Early
Data Release (EDR). Many galaxies from the test sample are either LSB or dwarf
galaxies. To deal with the SDSS data most effectively a new photometry software
was created, which is described in this paper. We present the results of the
selection algorithms applied to these 93 EDR fields. Two galaxies from the
Impey et al. test sample are very likely artifacts, as confirmed by follow-up
imaging. With our algorithms, we were able to recover 87 of the 90 remaining
test sample galaxies, implying a detection rate of 96.5%. The three
missed galaxies fall too close to very bright stars or galaxies. In addition,
42 new galaxies with parameters similar to the test sample objects were found
in these EDR fields (i.e., 47% additional galaxies). We present the main
photometric parameters of all identified galaxies and carry out first
statistical comparisons. We tested the quality of our photometry by comparing
the magnitudes for our test sample galaxies and other bright galaxies with
values from the literature. All these tests yielded consistent results. We
briefly discuss a few unusual galaxies found in our pilot study, including an
LSB galaxy with a two-component disk and ten new giant LSB galaxies.Comment: 36 pages, 16 figures, accepted for publication by AJ, some figures
were bitmapped to reduce the siz
Structural Properties of Central Galaxies in Groups and Clusters
Using a representative sample of 911 central galaxies (CENs) from the SDSS
DR4 group catalogue, we study how the structure of the most massive members in
groups and clusters depend on (1) galaxy stellar mass (Mstar), (2) dark matter
halo mass of the host group (Mhalo), and (3) their halo-centric position. We
establish and thoroughly test a GALFIT-based pipeline to fit 2D Sersic models
to SDSS data. We find that the fitting results are most sensitive to the
background sky level determination and strongly recommend using the SDSS global
value. We find that uncertainties in the background translate into a strong
covariance between the total magnitude, half-light size (r50), and Sersic index
(n), especially for bright/massive galaxies. We find that n depends strongly on
Mstar for CENs, but only weakly or not at all on Mhalo. Less (more) massive
CENs tend to be disk (spheroid)-like over the full Mhalo range. Likewise, there
is a clear r50-Mstar relation for CENs, with separate slopes for disks and
spheroids. When comparing CENs with satellite galaxies (SATs), we find that low
mass (<10e10.75 Msun/h^2) SATs have larger median n than CENs of similar Mstar.
Low mass, late-type SATs have moderately smaller r50 than late-type CENs of the
same Mstar. However, we find no size differences between spheroid-like CENs and
SATs, and no structural differences between CENs and SATs matched in both mass
and colour. The similarity of massive SATs and CENs shows that this distinction
has no significant impact on the structure of spheroids. We conclude that Mstar
is the most fundamental property determining the basic structure of a galaxy.
The lack of a clear n-Mhalo relation rules out a distinct group mass for
producing spheroids, and the responsible morphological transformation processes
must occur at the centres of groups spanning a wide range of masses. (abridged)Comment: 22 pages, 14 figures, submitted to MNRA
UDP-N-Acetylglucosamine 2-Epimerase/N-Acetylmannosamine Kinase (GNE) Binds to Alpha-Actinin 1: Novel Pathways in Skeletal Muscle?
Hereditary inclusion body myopathy (HIBM) is a rare neuromuscular disorder caused by mutations in GNE, the key enzyme in the biosynthetic pathway of sialic acid. While the mechanism leading from GNE mutations to the HIBM phenotype is not yet understood, we searched for proteins potentially interacting with GNE, which could give some insights about novel putative biological functions of GNE in muscle. We used a Surface Plasmon Resonance (SPR)-Biosensor based assay to search for potential GNE interactors in anion exchanged fractions of human skeletal muscle primary culture cell lysate. Analysis of the positive fractions by in vitro binding assay revealed alpha-actinin 1 as a potential interactor of GNE. The direct interaction of the two proteins was assessed in vitro by SPR-Biosensor based kinetics analysis and in a cellular environment by a co-immunoprecipitation assay in GNE overexpressing 293T cells. Furthermore, immunohistochemistry on stretched mouse muscle suggest that both GNE and alpha-actinin 1 localize to an overlapping but not identical region of the myofibrillar apparatus centered on the Z line. The interaction of GNE with alpha-actinin 1 might point to its involvement in alpha-actinin mediated processes. In addition these studies illustrate for the first time the expression of the non-muscle form of alpha-actinin, alpha-actinin 1, in mature skeletal muscle tissue, opening novel avenues for its specific function in the sarcomere. Although no significant difference could be detected in the binding kinetics of alpha-actinin 1 with either wild type or mutant GNE in our SPR biosensor based analysis, further investigation is needed to determine whether and how the interaction of GNE with alpha-actinin 1 in skeletal muscle is relevant to the putative muscle-specific function of alpha-actinin 1, and to the muscle-restricted pathology of HIBM
Centers For Mendelian Genomics: a Decade of Facilitating Gene Discovery
PURPOSE: Mendelian disease genomic research has undergone a massive transformation over the past decade. With increasing availability of exome and genome sequencing, the role of Mendelian research has expanded beyond data collection, sequencing, and analysis to worldwide data sharing and collaboration.
METHODS: Over the past 10 years, the National Institutes of Health-supported Centers for Mendelian Genomics (CMGs) have played a major role in this research and clinical evolution.
RESULTS: We highlight the cumulative gene discoveries facilitated by the program, biomedical research leveraged by the approach, and the larger impact on the research community. Beyond generating a list of gene-phenotype relationships and participating in widespread data sharing, the CMGs have created resources, tools, and training for the larger community to foster understanding of genes and genome variation. The CMGs have participated in a wide range of data sharing activities, including deposition of all eligible CMG data into the Analysis, Visualization, and Informatics Lab-space (AnVIL), sharing candidate genes through the Matchmaker Exchange and the CMG website, and sharing variants in Genotypes to Mendelian Phenotypes (Geno2MP) and VariantMatcher.
CONCLUSION: The work is far from complete; strengthening communication between research and clinical realms, continued development and sharing of knowledge and tools, and improving access to richly characterized data sets are all required to diagnose the remaining molecularly undiagnosed patients
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Syndecan 4 Is Involved in Mediating HCV Entry through Interaction with Lipoviral Particle-Associated Apolipoprotein E
Hepatitis C virus (HCV) is a major cause of liver disease worldwide and HCV infection represents a major health problem. HCV associates with host lipoproteins forming host/viral hybrid complexes termed lipoviral particles. Apolipoprotein E (apoE) is a lipoprotein component that interacts with heparan sulfate proteoglycans (HSPG) to mediate hepatic lipoprotein uptake, and may likewise mediate HCV entry. We sought to define the functional regions of apoE with an aim to identify critical apoE binding partners involved in HCV infection. Using adenoviral vectors and siRNA to modulate apoE expression we show a direct correlation of apoE expression and HCV infectivity, whereas no correlation exists with viral protein expression. Mutating the HSPG binding domain (HSPG-BD) of apoE revealed key residues that are critical for mediating HCV infection. Furthermore, a novel synthetic peptide that mimics apoE's HSPG-BD directly and competitively inhibits HCV infection. Genetic knockdown of the HSPG proteins syndecan (SDC) 1 and 4 revealed that SDC4 principally mediates HCV entry. Our data demonstrate that HCV uses apoE-SDC4 interactions to enter hepatoma cells and establish infection. Targeting apoE-SDC interactions could be an alternative strategy for blocking HCV entry, a critical step in maintaining chronic HCV infection
Evidence from GC-TRFLP that Bacterial Communities in Soil Are Lognormally Distributed
The Species Abundance Distribution (SAD) is a fundamental property of ecological communities and the form and formation of SADs have been examined for a wide range of communities including those of microorganisms. Progress in understanding microbial SADs, however, has been limited by the remarkable diversity and vast size of microbial communities. As a result, few microbial systems have been sampled with sufficient depth to generate reliable estimates of the community SAD. We have used a novel approach to characterize the SAD of bacterial communities by coupling genomic DNA fractionation with analysis of terminal restriction fragment length polymorphisms (GC-TRFLP). Examination of a soil microbial community through GC-TRFLP revealed 731 bacterial operational taxonomic units (OTUs) that followed a lognormal distribution. To recover the same 731 OTUs through analysis of DNA sequence data is estimated to require analysis of 86,264 16S rRNA sequences. The approach is examined and validated through construction and analysis of simulated microbial communities in silico. Additional simulations performed to assess the potential effects of PCR bias show that biased amplification can cause a community whose distribution follows a power-law function to appear lognormally distributed. We also show that TRFLP analysis, in contrast to GC-TRFLP, is not able to effectively distinguish between competing SAD models. Our analysis supports use of the lognormal as the null distribution for studying the SAD of bacterial communities as for plant and animal communities
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