375 research outputs found
Palomar 13: a velocity dispersion inflated by binaries ?
Recently, combining radial velocities from Keck/HIRES echelle spectra with
published proper motion membership probabilities, Cote et al (2002) observed a
sample of 21 stars, probable members of Palomar 13, a globular cluster in the
Galactic halo. Their projected velocity dispersion sigma_p = 2.2 +/-0.4 km/s
gives a mass-to-light ratio M/L_V = 40 +24/-17, about one order of magnitude
larger than the usual estimate for globular clusters. We present here radial
velocities measured from three different CCD frames of commissioning
observations obtained with the new ESO/VLT instrument FLAMES (Fibre Large Array
Multi Element Spectrograph). From these data, now publicly available, we
measure the homogeneous radial velocities of eight probable members of this
globular cluster. A new projected velocity dispersion sigma_p = 0.6-0.9 +/-0.3
km/s implies Palomar 13 mass-to-light ratio M/L_V = 3-7, similar to the usual
value for globular clusters. We discuss briefly the two most obvious reasons
for the previous unusual mass-to-light ratio finding: binaries, now clearly
detected, and more homogeneous data from the multi-fibre FLAMES spectrograph.Comment: 9 pages, 2 Postscript figure
Effect of regrouping unfamiliar pigs at weaning on immune function
Pigs weaned at 3 weeks of age and regrouped with unfamiliar individuals had a 4-fold increase in plasma cortisol when compared to pigs that remained in a litter group. However, cellular measures of immune function were not altered by regrouping.; Swine Day, Manhattan, KS, November 10, 198
Recoiling black holes: prospects for detection and implications of spin alignment
Supermassive black hole (BH) mergers produce powerful gravitational wave (GW)
emission. Asymmetry in this emission imparts a recoil kick to the merged BH,
which can eject the BH from its host galaxy altogether. Recoiling BHs could be
observed as offset active galactic nuclei (AGN). Several candidates have been
identified, but systematic searches have been hampered by large uncertainties
regarding their observability. By extracting merging BHs and host galaxy
properties from the Illustris cosmological simulations, we have developed a
comprehensive model for recoiling AGN. Here, for the first time, we model the
effects of BH spin alignment and recoil dynamics based on the gas-richness of
host galaxies. We predict that if BH spins are not highly aligned,
seeing-limited observations could resolve offset AGN, making them promising
targets for all-sky surveys. For randomly-oriented spins, less than about 10
spatially-offset AGN may be detectable in HST-COSMOS, and > 10^3 could be found
with Pan-STARRS, LSST, Euclid, and WFIRST. Nearly a thousand velocity-offset
AGN are predicted within the SDSS footprint; the rarity of large broad-line
offsets among SDSS quasars is likely due in part to selection effects but
suggests that spin alignment plays a role in suppressing recoils. Nonetheless,
in our most physically motivated model where alignment occurs only in gas-rich
mergers, hundreds of offset AGN should be found in all-sky surveys. Our
findings strongly motivate a dedicated search for recoiling AGN.Comment: 30 pages, 19 figures. Accepted to MNRAS after minor revision
Imaging Active Infection in vivo Using D-Amino Acid Derived PET Radiotracers.
Occult bacterial infections represent a worldwide health problem. Differentiating active bacterial infection from sterile inflammation can be difficult using current imaging tools. Present clinically viable methodologies either detect morphologic changes (CT/ MR), recruitment of immune cells (111In-WBC SPECT), or enhanced glycolytic flux seen in inflammatory cells (18F-FDG PET). However, these strategies are often inadequate to detect bacterial infection and are not specific for living bacteria. Recent approaches have taken advantage of key metabolic differences between prokaryotic and eukaryotic organisms, allowing easier distinction between bacteria and their host. In this report, we exploited one key difference, bacterial cell wall biosynthesis, to detect living bacteria using a positron-labeled D-amino acid. After screening several 14C D-amino acids for their incorporation into E. coli in culture, we identified D-methionine as a probe with outstanding radiopharmaceutical potential. Based on an analogous procedure to that used for L-[methyl-11C]methionine ([11C] L-Met), we developed an enhanced asymmetric synthesis of D-[methyl-11C]methionine ([11C] D-Met), and showed that it can rapidly and selectively differentiate both E. coli and S. aureus infections from sterile inflammation in vivo. We believe that the ease of [11C] D-Met radiosynthesis, coupled with its rapid and specific in vivo bacterial accumulation, make it an attractive radiotracer for infection imaging in clinical practice
Expression and cytosolic assembly of the S-layer fusion protein mSbsC-EGFP in eukaryotic cells
BACKGROUND: Native as well as recombinant bacterial cell surface layer (S-layer) protein of Geobacillus (G.) stearothermophilus ATCC 12980 assembles to supramolecular structures with an oblique symmetry. Upon expression in E. coli, S-layer self assembly products are formed in the cytosol. We tested the expression and assembly of a fusion protein, consisting of the mature part (aa 31–1099) of the S-layer protein and EGFP (enhanced green fluorescent protein), in eukaryotic host cells, the yeast Saccharomyces cerevisiae and human HeLa cells. RESULTS: Upon expression in E. coli the recombinant mSbsC-EGFP fusion protein was recovered from the insoluble fraction. After denaturation by Guanidine (Gua)-HCl treatment and subsequent dialysis the fusion protein assembled in solution and yielded green fluorescent cylindric structures with regular symmetry comparable to that of the authentic SbsC. For expression in the eukaryotic host Saccharomyces (S.) cerevisiae mSbsC-EGFP was cloned in a multi-copy expression vector bearing the strong constitutive GPD1 (glyceraldehyde-3-phosophate-dehydrogenase) promoter. The respective yeast transfomants were only slightly impaired in growth and exhibited a needle-like green fluorescent pattern. Transmission electron microscopy (TEM) studies revealed the presence of closely packed cylindrical structures in the cytosol with regular symmetry comparable to those obtained after in vitro recrystallization. Similar structures are observed in HeLa cells expressing mSbsC-EGFP from the Cytomegalovirus (CMV IE) promoter. CONCLUSION: The mSbsC-EGFP fusion protein is stably expressed both in the yeast, Saccharomyces cerevisiae, and in HeLa cells. Recombinant mSbsC-EGFP combines properties of both fusion partners: it assembles both in vitro and in vivo to cylindrical structures that show an intensive green fluorescence. Fusion of proteins to S-layer proteins may be a useful tool for high level expression in yeast and HeLa cells of otherwise instable proteins in their native conformation. In addition the self assembly properties of the fusion proteins allow their simple purification. Moreover the binding properties of the S-layer part can be used to immobilize the fusion proteins to various surfaces. Arrays of highly ordered and densely structured proteins either immobilized on surfaces or within living cells may be advantageous over the respective soluble variants with respect to stability and their potential interference with cellular metabolism
Two distinct ancient components in the Sculptor Dwarf Spheroidal Galaxy: First Results from DART
We have found evidence for the presence of two distinct ancient stellar
components (both geq 10 Gyr old) in the Sculptor dwarf spheroidal galaxy. We
used the ESO Wide Field Imager (WFI) in conjunction with the VLT/FLAMES
spectrograph to study the properties of the resolved stellar population of
Sculptor out to and beyond the tidal radius. We find that two components are
discernible in the spatial distribution of Horizontal Branch stars in our
imaging, and in the [Fe/H] and v_hel distributions for our large sample of
spectroscopic measurements. They can be generally described as a ``metal-poor''
component ([Fe/H] -1.7). The
metal-poor stars are more spatially extended than the metal-rich stars, and
they also appear to be kinematically distinct. These results provide an
important insight into the formation processes of small systems in the early
universe and the conditions found there. Even this simplest of galaxies appears
to have had a surprisingly complex early evolution.Comment: accepted for publication in ApJL 12 pages, 4 figure
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