2,114 research outputs found
Is the EGRET source 3EG J1621+8203 the radio galaxy NGC 6251?
We discuss the nature of the unidentified EGRET source 3EG J1621+8203. In an
effort to identify the gamma-ray source, we have examined X-ray images of the
field from ROSAT PSPC, ROSAT HRI, and ASCA GIS. Of the several faint X-ray
point sources in the error circle of 3EG J1621+8203, most are stars or faint
radio sources, unlikely to be counterparts to the EGRET source. The most
notable object in the gamma-ray error box is the bright FR I radio galaxy NGC
6251. If 3EG J1621+8203 corresponds to NGC 6251, then it would be the second
radio galaxy to be detected in high energy gamma rays, after Cen A, which
provided the first clear evidence of the detection above 100 MeV of an AGN with
a large-inclination jet. If the detection of more radio galaxies by EGRET has
been limited by its threshold sensitivity, there exists the exciting
possibility that new high energy gamma-ray instruments, with much higher
sensitivity, will detect a larger number of radio galaxies in the future.Comment: 7 pages, 6 figures. Accepted for publication in The Astrophysical
Journal, August 2002 issu
A comparison of static vs dynamic surface topography measurements in the evaluation of scoliosis
A sample of radio-loud QSOs at redshift ~ 4
We obtained spectra of 60 red, starlike objects (E< 18.8) identified with
FIRST radio sources, S_{1.4GHz} > 1 mJy. Eight are QSOs with redshift z>
3.6.Combined with our pilot search (Benn et al 2002), our sample of 121
candidates yields a total of 18 z > 3.6 QSOs (10 of these with z > 4.0). 8% of
candidates with S_{1.4GHz} 10
mJy are QSOs with z > 3.6. The surface density of E 1mJy,
z> 4 QSOs is 0.003 deg^{-2}. This is currently the only well-defined sample of
radio-loud QSOs at z ~ 4 selected independently of radio spectral index. The
QSOs are highly luminous in the optical (8 have M_B < -28, q_0 = 0.5, H_0 = 50
kms^{-1}Mpc^{-1}). The SEDs are as varied as those seen in optical searches for
high-redshift QSOs, but the fraction of objects with weak (strongly
self-absorbed) Ly alpha emission is marginally higher (3 out of 18) than for
high-redshift QSOs from SDSS (5 out of 96).Comment: Accepted for publication in MNRAS, 9 pages, Latex, 5 postscript
figures, 1 landscape table (postscript
A novel class of CoA-transferase involved in short-chain fatty acid metabolism in butyrate-producing human colonic bacteria
Peer reviewedPublisher PD
The Stellar Mass Distribution in the Giant Star Forming Region NGC 346
Deep F555W and F814W Hubble Space Telescope ACS images are the basis for a
study of the present day mass function (PDMF) of NGC346, the largest active
star forming region in the Small Magellanic Cloud (SMC). We find a PDMF slope
of Gamma=-1.43+/-0.18 in the mass range 0.8-60 Mo, in excellent agreement with
the Salpeter Initial Mass Function (IMF) in the solar neighborhood. Caveats on
the conversion of the PDMF to the IMF are discussed. The PDMF slope changes, as
a function of the radial distance from the center of the NGC 346 star cluster,
indicating a segregation of the most massive stars. This segregation is likely
primordial considering the young age (~3 Myr) of NGC346, and its clumpy
structure which suggests that the cluster has likely not had sufficient time to
relax. Comparing our results for NGC346 with those derived for other star
clusters in the SMC and the Milky Way (MW), we conclude that, while the star
formation process might depend on the local cloud conditions, the IMF does not
seem to be affected by general environmental effects such as galaxy type,
metallicity, and dust content.Comment: 26 pages, 7 figures, 1 table, accepted for publication in A
A More Open Approach Is Needed to Develop Cell-Based Fish Technology: It Starts with Zebrafish
Adhesion Stimulates Direct PAK1/ERK2 Association and Leads to ERK-dependent PAK1 Thr 212 Phosphorylation
The Rac1/Cdc42 effector p21-activated kinase (PAK) is activated by various signaling cascades including receptor-tyrosine kinases and integrins and regulates a number of processes such as cell proliferation and motility. PAK activity has been shown to be required for maximal activation of the canonical Ras/Raf/MEK/ERK Map kinase signaling cascade, likely because of PAK co-activation of Raf and MEK. Herein, we found that adhesion signaling also stimulates an association between PAK1 and ERK1/2. PAK1 and ERK1/2 co-immunoprecipitated from rat aortic smooth muscle cells (SMC) plated on fibronectin, and the two proteins co-localized in membrane ruffles and adhesion complexes following PDGF-BB or sphingosine 1-phosphate treatment, respectively. Far Western analysis demonstrated a direct association between the two proteins, and peptide mapping identified an ERK2 binding site within the autoinhibitory domain of PAK1. Interestingly, deletion of a major ERK binding site in PAK attenuates activation of an ERK-dependent serum-responsive element (SRE)-luciferase reporter gene, indicating that association between PAK and ERK is required to facilitate ERK signaling. We also show that ERK2 phosphorylates PAK1 on Thr(212) in vitro and that Thr(212) is phosphorylated in smooth muscle cells following PDGF-BB treatment in an adhesion- and MEK/ERK-dependent fashion. Expression of a phosphomimic variant, PAK-T212E, does not alter ERK association, but markedly attenuates downstream ERK signaling. Taken together, these data suggest that PAK1 may facilitate ERK signaling by serving as a scaffold to recruit Raf, MEK, and ERK to adhesion complexes, and that subsequent growth factor-stimulated phosphorylation of PAK-Thr(212) by ERK may serve to provide a negative feedback signal to control coordinate activation of ERK by growth factor- and matrix-induced signals
PhylomeDB: a database for genome-wide collections of gene phylogenies
The complete collection of evolutionary histories of all genes in a genome, also known as phylome, constitutes a valuable source of information. The reconstruction of phylomes has been previously prevented by large demands of time and computer power, but is now feasible thanks to recent developments in computers and algorithms. To provide a publicly available repository of complete phylomes that allows researchers to access and store large-scale phylogenomic analyses, we have developed PhylomeDB. PhylomeDB is a database of complete phylomes derived for different genomes within a specific taxonomic range. All phylomes in the database are built using a high-quality phylogenetic pipeline that includes evolutionary model testing and alignment trimming phases. For each genome, PhylomeDB provides the alignments, phylogentic trees and tree-based orthology predictions for every single encoded protein. The current version of PhylomeDB includes the phylomes of Human, the yeast Saccharomyces cerevisiae and the bacterium Escherichia coli, comprising a total of 32 289 seed sequences with their corresponding alignments and 172 324 phylogenetic trees. PhylomeDB can be publicly accessed at http://phylomedb.bioinfo.cipf.e
WFPC2 Observations of the Hubble Deep Field-South
The Hubble Deep Field-South observations targeted a high-galactic-latitude
field near QSO J2233-606. We present WFPC2 observations of the field in four
wide bandpasses centered at roughly 300, 450, 606, and 814 nm. Observations,
data reduction procedures, and noise properties of the final images are
discussed in detail. A catalog of sources is presented, and the number counts
and color distributions of the galaxies are compared to a new catalog of the
HDF-N that has been constructed in an identical manner. The two fields are
qualitatively similar, with the galaxy number counts for the two fields
agreeing to within 20%. The HDF-S has more candidate Lyman-break galaxies at z
> 2 than the HDF-N. The star-formation rate per unit volume computed from the
HDF-S, based on the UV luminosity of high-redshift candidates, is a factor of
1.9 higher than from the HDF-N at z ~ 2.7, and a factor of 1.3 higher at z ~ 4.Comment: 93 pages, 25 figures; contains very long table
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