853 research outputs found
The Giant Branches of Open and Globular Clusters in the Infrared as Metallicity Indicators: A Comparison with Theory
We apply the giant branch slope-[Fe/H] relation derived by Kuchinski et al.
[AJ, 109, 1131 (1995)] to a sample of open clusters. We find that the slope of
the giant branch in K vs. (J-K) color-magnitude diagrams correlates with [Fe/H]
for open clusters as it does for metal-rich globular clusters but that the open
cluster data are systematically shifted to less negative values of giant branch
slope, at constant [Fe/H]. We use isochrone models to examine the theoretical
basis for this relationship and find that for a given value of [Fe/H], the
slope of the relationship remains constant with decreasing population age but
the relation shifts to less negative values of giant branch slope with
decreasing age. Both of these theoretical predictions agree with the trends
found in the data. Finally, we derive new coefficients for the giant branch
slope-[Fe/H] relation for specific members of 3 populations, metal-rich
globular clusters, bulge stars and open clusters.Comment: 16 pages including 3 figures (AASTEX), AJ Accepted, also available at
http://www.astronomy.ohio-state.edu/~martini/pubs.htm
Uncertainties of size measurements in electron microscopy characterization of nanomaterials in foods
Electron microscopy is a recognized standard tool for nanomaterial characterization, and recommended by the European Food Safety Authority for the size measurement of nanomaterials in food. Despite this, little data have been published assessing the reliability of the method, especially for size measurement of nanomaterials characterized by a broad size distribution and/or added to food matrices. This study is a thorough investigation of the measurement uncertainty when applying electron microscopy for size measurement of engineered nanomaterials in foods. Our results show that the number of measured particles was only a minor source of measurement uncertainty for nanomaterials in food, compared to the combined influence of sampling, sample preparation prior to imaging and the image analysis. The main conclusion is that to improve the measurement reliability, care should be taken to consider replications and matrix removal prior to sample preparation
The Metallicity and Reddening of Stars in the Inner Galactic Bulge
We present a preliminary analysis of K, J-K color magnitude diagrams (CMDs)
for 7 different positions on or close to the minor axis of the Milky Way at
Galactic latitudes between +0.1^\circ and -2.8^\circ. From the slopes of the
(linear) giant branches in these CMDs we derive a dependence of on
latitude for b between -0.8^\circ and -2.8^\circ of -0.085 \pm 0.033
dex/degree. When combined with the data from Tiede et al. we find for
-0.8^\circ \leq b \leq -10.3^\circ the slope in is -0.064 \pm 0.012
dex/degree. An extrapolation to the Galactic Center predicts [Fe/H] = +0.034
\pm 0.053 dex. We also derive average values for the extinction in the K band
(A_K) of between 2.15 and 0.27 for the inner bulge fields corresponding to
average values of E(J-K) of between 3.46 and 0.44. There is a well defined
linear relation between the average extinction for a field and the star-to-star
scatter in the extinction for the stars within each field. This result suggests
that the typical apparent angular scale size for an absorbing cloud is small
compared with the field size (90\arcsec on a side). Finally, from an
examination of the luminosity function of bright giants in each field we
conclude that the young component of the stellar population observed near the
Galactic center declines in density much more quickly than the overall bulge
population and is undetectable beyond 1^\circ from the Galactic center.Comment: accepted for publication in Astron. Jour. Compressed file contains
the text, 9 figures, and 6 tables prepared with AAS Latex macros v. 4.
Implications of New JHK Photometry and a Deep Infrared Luminosity Function for the Galactic Bulge
We present deep near-IR photometry for Galactic bulge stars in Baade's
Window, and another minor axis field at . We combine our data with previously published photometry
and construct a luminosity function over the range ,
deeper than any previously published. The slope of this luminosity function and
the magnitude of the tip of the first ascent giant branch are consistent with
theoretical values derived from isochrones with appropriate age and
metallicity.
We use the relationship between [Fe/H] and the giant branch slope derived
from near-IR observations of metal rich globular clusters by Kuchinski {\it et
al.} [AJ, 109, 1131 (1995)] to calculate the mean metallicity for several bulge
fields along the minor axis. For Baade's Window we derive , consistent with the recent estimate of
McWilliam \& Rich [ApJS, 91, 749 (1994)], but somewhat lower than previous
estimates based on CO and TiO absorption bands and the colors of M giants
by Frogel {\it et al.} [ApJ, 353, 494 (1990)]. Between and
we find a gradient in of dex/degree or dex/kpc for kpc, consistent with
other independent derivations. We derive a helium abundance for Baade's Window
with the and methods and find that implying
.
Next, we find that the bolometric corrections for bulge K giants () are in excellent agreement with empirical derivations based on observations
of globular cluster and local field stars. However, for the redder M giants weComment: Accepted by the Astronomical Journal. 43 pages, uuencoded compressed
PostScript, no figures or tables. A complete (text, figs and tables) preprint
is also available at
ftp://bessel.mps.ohio-state.edu/pub/terndrup/bwphot.tar.Z (compressed tar
file with PostScript
Vimentin expression influences flow dependent VASP phosphorylation and regulates cell migration and proliferation
The cytoskeleton plays a central role for the integration of biochemical and biomechanical signals across the cell required for complex cellular functions. Recent studies indicate that the intermediate filament vimentin is necessary for endothelial cell morphogenesis e.g. in the context of leukocyte transmigration. Here, we present evidence, that the scaffold provided by vimentin is essential for VASP localization and PKG mediated VASP phosphorylation and thus controls endothelial cell migration and proliferation. Vimentin suppression using siRNA technique significantly decreased migration velocity by 50% (videomicroscopy), diminished transmigration activity by 42.5% (Boyden chamber) and reduced proliferation by 43% (BrdU-incorporation). In confocal microscopy Vimentin colocalized with VASP and PKG in endothelial cells. Vimentin suppression was accompanied with a translocation of VASP from focal contacts to the perinuclear region. VASP/Vimentin and PKG/Vimentin colocalization appeared to be essential for proper PKG mediated VASP phosphorylation because we detected a diminished expression of PKG and p(Ser239)-VASP in vimentin-suppressed cells, Furthermore, the induction of VASP phosphorylation in perfused arteries was markedly decreased in vimentin knockout mice compared to wildtypes. A link is proposed between vimentin, VASP phosphorylation and actin dynamics that delivers an explanation for the important role of vimentin in controlling endothelial cell morphogenesis
Distances to Populous Clusters in the LMC via the K-Band Luminosity of the Red Clump
We present results from a study of the distances and distribution of a sample
of intermediate-age clusters in the Large Magellanic Cloud. Using deep
near-infrared photometry obtained with ISPI on the CTIO 4m, we have measured
the apparent K-band magnitude of the core helium burning red clump stars in 17
LMC clusters. We combine cluster ages and metallicities with the work of
Grocholski & Sarajedini to predict each cluster's absolute K-band red clump
magnitude, and thereby calculate absolute cluster distances. An analysis of
these data shows that the cluster distribution is in good agreement with the
thick, inclined disk geometry of the LMC, as defined by its field stars. We
also find that the old globular clusters follow the same distribution,
suggesting that the LMC's disk formed at about the same time as the globular
clusters, ~ 13 Gyr ago. Finally, we have used our cluster distances in
conjunction with the disk geometry to calculate the distance to the LMC center,
for which we find (m-M)o = 18.40 +/- 0.04_{ran} +/- 0.08_{sys}, or Do = 47.9
+/- 0.9 +/- 1.8 kpc.Comment: 31 pages including 5 figures and 7 tables. Accepted for publication
in the August 2007 issue of A
The Clustering of Extragalactic Extremely Red Objects
We have measured the angular and spatial clustering of 671 K5
Extremely Red Objects (EROs) from a 0.98 square degree sub-region of the NOAO
Deep Wide-Field Survey (NDWFS). Our study covers nearly 5 times the area and
has twice the sample size of any previous ERO clustering study. The wide field
of view and BwRIK passbands of the NDWFS allow us to place improved constraints
on the clustering of z=1 EROs. We find the angular clustering of EROs is
slightly weaker than in previous measurements, and w(1')=0.25+/-0.05 for
K<18.40 EROs. We find no significant correlation of ERO spatial clustering with
redshift, apparent color or absolute magnitude, although given the
uncertainties, such correlations remain plausible. We find the spatial
clustering of K5 EROs is well approximated by a power-law, with
r_0=9.7+/-1.1 Mpc/h in comoving coordinates. This is comparable to the
clustering of 4L* early-type galaxies at z<1, and is consistent with the
brightest EROs being the progenitors of the most massive ellipticals. There is
evidence of the angular clustering of EROs decreasing with increasing apparent
magnitude, when NDWFS measurements of ERO clustering are combined with those
from the literature. Unless the redshift distribution of K>20 EROs is very
broad, the spatial clustering of EROs decreases from r_0=9.7+/-1.1 Mpc/h for
K20 EROs.Comment: Accepted for publication in the ApJ. 29 pages with 10 figures. The
NOAO Deep Wide-Field Survey Bootes data release is available online at
http://www.noao.edu/noao/noaodeep
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