6,473 research outputs found
Magnetic friction due to vortex fluctuation
We use Monte Carlo and molecular dynamics simulation to study a magnetic
tip-sample interaction. Our interest is to understand the mechanism of heat
dissipation when the forces involved in the system are magnetic in essence. We
consider a magnetic crystalline substrate composed of several layers
interacting magnetically with a tip. The set is put thermally in equilibrium at
temperature T by using a numerical Monte Carlo technique. By using that
configuration we study its dynamical evolution by integrating numerically the
equations of motion. Our results suggests that the heat dissipation in this
system is closed related to the appearing of vortices in the sample.Comment: 6 pages, 41 figure
Discovery in IC10 of the farthest known symbiotic star
We report the discovery of the first known symbiotic star in IC10, a
starburst galaxy belonging to the Local Group, at a distance of ~750kpc. The
symbiotic star was identified during a survey of emission-line objects. It
shines at V = 24.62+-0.04, V - R_C = 2.77+-0.05 and R_C - I_C = 2.39+-0.02 and
suffers from E(B-V) = 0.85+-0.05 reddening. The spectrum of the cool component
well matches that of solar neighborhood M8III giants. The observed emission
lines belong to Balmer series, [SII], [NII] and [OIII]. They suggest a low
electronic density, negligible optical depth effects and 35,000K < T_eff <
90,000K for the ionizing source. The spectrum of the new symbiotic star in IC10
is an almost perfect copy of that of Hen 2-147, a well known Galactic symbiotic
star and Mira.Comment: 5 pages including 3 figures. MNRAS Letters accepted. Also available
at http://pessoais.ov.ufrj.br/denise
3,3âČ-BithioÂphene
The title compound, C8H6S2, is disordered [occupancy ratio = 0.839â
(2):0.161â
(2)] and sits across a centre of symmetry. In the crystal, the molÂecules are linked by a weak CâHâŻÏ interÂaction
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Expression divergence measured by transcriptome sequencing of four yeast species
<p>Abstract</p> <p>Background</p> <p>The evolution of gene expression is a challenging problem in evolutionary biology, for which accurate, well-calibrated measurements and methods are crucial.</p> <p>Results</p> <p>We quantified gene expression with whole-transcriptome sequencing in four diploid, prototrophic strains of <it>Saccharomyces </it>species grown under the same condition to investigate the evolution of gene expression. We found that variation in expression is gene-dependent with large variations in each gene's expression between replicates of the same species. This confounds the identification of genes differentially expressed across species. To address this, we developed a statistical approach to establish significance bounds for inter-species differential expression in RNA-Seq data based on the variance measured across biological replicates. This metric estimates the combined effects of technical and environmental variance, as well as Poisson sampling noise by isolating each component. Despite a paucity of large expression changes, we found a strong correlation between the variance of gene expression change and species divergence (R<sup>2 </sup>= 0.90).</p> <p>Conclusion</p> <p>We provide an improved methodology for measuring gene expression changes in evolutionary diverged species using RNA Seq, where experimental artifacts can mimic evolutionary effects.</p> <p>GEO Accession Number: GSE32679</p
A neutral hydrogen survey of polar ring galaxies IV. Parkes observations
A total of 33 polar ring galaxies and polar ring galaxy candidates were
observed in the 21-cm HI line with the 64-m Parkes radio telescope. The
objects, selected by their optical morphology, are all south of declination -39
degrees and in only 5 of them HI had been reported previously. HI line emission
was detected towards 18 objects, though in 3 cases the detection may be
confused by another galaxy in the telescope beam, and one is a marginal
detection. Eight objects were detected for the first time in HI, of which 5 did
not have previously known redshifts.Comment: Accepted by Astronomy and Astrophysics, 12/2/2002; new references
added on 20/2/200
A model of diffuse Galactic Radio Emission from 10 MHz to 100 GHz
Understanding diffuse Galactic radio emission is interesting both in its own
right and for minimizing foreground contamination of cosmological measurements.
Cosmic Microwave Background experiments have focused on frequencies > 10 GHz,
whereas 21 cm tomography of the high redshift universe will mainly focus on <
0.2 GHz, for which less is currently known about Galactic emission. Motivated
by this, we present a global sky model derived from all publicly available
total power large-area radio surveys, digitized with optical character
recognition when necessary and compiled into a uniform format, as well as the
new Villa Elisa data extending the 1.4 GHz map to the entire sky. We quantify
statistical and systematic uncertainties in these surveys by comparing them
with various global multi-frequency model fits. We find that a principal
component based model with only three components can fit the 11 most accurate
data sets (at 10, 22, 45 & 408 MHz and 1.4, 2.3, 23, 33, 41, 61, 94 GHz) to an
accuracy around 1%-10% depending on frequency and sky region. Both our data
compilation and our software returning a predicted all-sky map at any frequency
from 10 MHz to 100 GHz are publicly available at
http://space.mit.edu/home/angelica/gsm .Comment: Accuracy improved with 5-year WMAP data. Our data, software and new
foreground-cleaned WMAP map are available at https://ascl.net/1011.01
Defective cancellous bone structure and abnormal response to PTH in cortical bone of mice lacking Cx43 cytoplasmic C-terminus domain
Connexin 43 (Cx43) forms gap junction channels and hemichannels that allow the communication among osteocytes, osteoblasts, and osteoclasts. Cx43 carboxy-terminal (CT) domain regulates channel opening and intracellular signaling by acting as a scaffold for structural and signaling proteins. To determine the role of Cx43 CT domain in bone, mice in which one allele of full length Cx43 was replaced by a mutant lacking the CT domain (Cx43(ÎCT/fl)) were studied. Cx43(ÎCT/fl) mice exhibit lower cancellous bone volume but higher cortical thickness than Cx43(fl/fl) controls, indicating that the CT domain is involved in normal cancellous bone gain but opposes cortical bone acquisition. Further, Cx43(ÎCT) is able to exert the functions of full length osteocytic Cx43 on cortical bone geometry and mechanical properties, demonstrating that domains other than the CT are responsible for Cx43 function in cortical bone. In addition, parathyroid hormone (PTH) failed to increase endocortical bone formation or energy to failure, a mechanical property that indicates resistance to fracture, in cortical bone in Cx43(ÎCT) mice with or without osteocytic full length Cx43. On the other hand, bone mass and bone formation markers were increased by the hormone in all mouse models, regardless of whether full length or Cx43(ÎCT) were or not expressed. We conclude that Cx43 CT domain is involved in proper bone acquisition; and that Cx43 expression in osteocytes is dispensable for some but not all PTH anabolic actions
An Attempt to Determine the Largest Scale of Primordial Density Perturbations in the Universe
Inflationary cosmology predicts that the particle horizon should be
generically much bigger than the present-day Hubble radius, . This
implies a special regime of super-Hubble scale energy density fluctuations
imprinted on the cosmic microwave background radiation (CMBR), which from
present theory could only be explained by inflation Causality constraints are
used to determine models for the power spectrum that accommodate a suppression
scale. A three parameter likelihood analysis is performed of the COBE-DMR
4-year data with respect to the amplitude, spectral index, and suppression
scale. It is found that all suppression length scales larger than are
consistent with the data, but that scales of order are slightly
preferred, at roughly the one-sigma level. Many non-inflation models would be
consistent with a small suppression length scale, whereas for standard
inflation models, the duration of the inflation epoch would have to be bounded
by a fairly small upper limit. Suppression scales smaller than are
strongly excluded by the anisotrophy data.Comment: 9 pages, Latex, 1 figure, additional tests reporte
A new picture on (3+1)D topological mass mechanism
We present a class of mappings between the fields of the Cremmer-Sherk and
pure BF models in 4D. These mappings are established by two distinct
procedures. First a mapping of their actions is produced iteratively resulting
in an expansion of the fields of one model in terms of progressively higher
derivatives of the other model fields. Secondly an exact mapping is introduced
by mapping their quantum correlation functions. The equivalence of both
procedures is shown by resorting to the invariance under field scale
transformations of the topological action. Related equivalences in 5D and 3D
are discussed. A cohomological argument is presented to provide consistency of
the iterative mapping.Comment: 13 page
Reversal of loss of bone mass in old mice treated with mefloquine
Aging is accompanied by imbalanced bone remodeling, elevated osteocyte apoptosis, and decreased bone mass and mechanical properties; and improved pharmacologic approaches to counteract bone deterioration with aging are needed. We examined herein the effect of mefloquine, a drug used to treat malaria and systemic lupus erythematosus and shown to ameliorate bone loss in glucocorticoid-treated patients, on bone mass and mechanical properties in young and old mice. Young 3.5-month-old and old 21-month-old female C57BL/6 mice received daily injections of 5âŻmg/kg/day mefloquine for 14âŻdays. Aging resulted in the expected changes in bone volume and mechanical properties. In old mice mefloquine administration reversed the lower vertebral cancellous bone volume and bone formation; and had modest effects on cortical bone volume, thickness, and moment of inertia. Mefloquine administration did not change the levels of the circulating bone formation markers P1NP or alkaline phosphatase, whereas levels of the resorption marker CTX showed trends towards increase with mefloquine treatment. In addition, and as expected, aging bones exhibited an accumulation of active caspase3-expressing osteocytes and higher expression of apoptosis-related genes compared to young mice, which were not altered by mefloquine administration at either age. In young animals, mefloquine induced higher periosteal bone formation, but lower endocortical bone formation. Further, osteoclast numbers were higher on the endocortical bone surface and circulating CTX levels were increased, in mefloquine- compared to vehicle-treated young mice. Consistent with this, addition of mefloquine to bone marrow cells isolated from young mice led to increased osteoclastic gene expression and a tendency towards increased osteoclast numbers in vitro. Taken together our findings identify the age and bone-site specific skeletal effects of mefloquine. Further, our results highlight a beneficial effect of mefloquine administration on vertebral cancellous bone mass in old animals, raising the possibility of using this pharmacologic inhibitor to preserve skeletal health with aging
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