838 research outputs found
Generalized Advanced Propeller Analysis System (GAPAS). Volume 2: Computer program user manual
The Generalized Advanced Propeller Analysis System (GAPAS) computer code is described. GAPAS was developed to analyze advanced technology multi-bladed propellers which operate on aircraft with speeds up to Mach 0.8 and altitudes up to 40,000 feet. GAPAS includes technology for analyzing aerodynamic, structural, and acoustic performance of propellers. The computer code was developed for the CDC 7600 computer and is currently available for industrial use on the NASA Langley computer. A description of all the analytical models incorporated in GAPAS is included. Sample calculations are also described as well as users requirements for modifying the analysis system. Computer system core requirements and running times are also discussed
Global Existence and Regularity for the 3D Stochastic Primitive Equations of the Ocean and Atmosphere with Multiplicative White Noise
The Primitive Equations are a basic model in the study of large scale Oceanic
and Atmospheric dynamics. These systems form the analytical core of the most
advanced General Circulation Models. For this reason and due to their
challenging nonlinear and anisotropic structure the Primitive Equations have
recently received considerable attention from the mathematical community.
In view of the complex multi-scale nature of the earth's climate system, many
uncertainties appear that should be accounted for in the basic dynamical models
of atmospheric and oceanic processes. In the climate community stochastic
methods have come into extensive use in this connection. For this reason there
has appeared a need to further develop the foundations of nonlinear stochastic
partial differential equations in connection with the Primitive Equations and
more generally.
In this work we study a stochastic version of the Primitive Equations. We
establish the global existence of strong, pathwise solutions for these
equations in dimension 3 for the case of a nonlinear multiplicative noise. The
proof makes use of anisotropic estimates, estimates on the
pressure and stopping time arguments.Comment: To appear in Nonlinearit
The VMC survey - XV : The Small Magellanic Cloud-Bridge connection history as traced by their star cluster populations
Date of Acceptance: 19/03/2015We present results based on YJKs photometry of star clusters located in the outermost, eastern region of the Small Magellanic Cloud (SMC). We analysed a total of 51 catalogued clusters whose colour-magnitude diagrams (CMDs), having been cleaned from field-star contamination, were used to assess the clusters' reality and estimate ages of the genuine systems. Based on CMD analysis, 15 catalogued clusters were found to be possible non-genuine aggregates. We investigated the properties of 80 per cent of the catalogued clusters in this part of the SMC by enlarging our sample with previously obtained cluster ages, adopting a homogeneous scale for all. Their spatial distribution suggests that the oldest clusters, log(t/yr) ≥ 9.6, are in general located at greater distances to the galaxy's centre than their younger counterparts - 9.0 ≤ log(t/yr) ≤ 9.4 - while two excesses of clusters are seen at log(t/yr) ~9.2 and log(t yr-1) ˜ 9.7. We found a trail of younger clusters which follow the wing/bridge components. This long spatial sequence does not only harbour very young clusters, log(t yr-1) ~7.3, but it also hosts some of intermediate ages, log(t/yr) ~9.1. The derived cluster and field-star formation frequencies as a function of age are different. The most surprising feature is an observed excess of clusters with ages of log(t/yr) < 9.0, which could have been induced by interactions with the LMC.Peer reviewedFinal Accepted Versio
STEP: the VST survey of the SMC and the Magellanic Bridge - I : Overview and first results
STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guaranteed Time Observation survey being performed at the VST (the ESO VLT Survey Telescope). STEP will image an area of 74 sq. deg. covering the main body of the Small Magellanic Cloud (32 sq. deg.), the Bridge that connects it to the Large Magellanic Cloud (30 sq. deg.) and a small part of the Magellanic Stream (2 sq. deg.). Our g, r, i, Hα photometry is able to resolve individual stars down to magnitudes well below the main-sequence turn-off of the oldest populations. In this first paper, we describe the observing strategy, the photometric techniques and the upcoming data products of the survey. We also present preliminary results for the first two fields for which data acquisition is completed, including some detailed analysis of the two stellar clusters IC 1624 and NGC 419.Peer reviewedFinal Accepted Versio
Multiple stellar populations in Magellanic Clouds clusters. I. An ordinary feature for intermediate age globulars in the LMC?
The discovery of multiple MSs in NGC2808 and Omega Centauri, and multiple
SGBs in NGC1851 and NGC6388 has challenged the long-held paradigm that GCs
consist of simple stellar populations. This picture has been further
complicated by recent studies of the LMC intermediate-age clusters, where the
MSTO was found to be bimodal or broadened. We have undertaken a study of
archival HST images of LMC and SMC clusters with the aim of measuring the
frequency of clusters with evidence of multiple or prolonged star formation
events and determining their main properties. In this paper, we analyse the CMD
of 16 intermediate-age LMC clusters. We find that 11 clusters show an anomalous
spread (or split) in color and magnitude around the MSTO. We demonstrate that
the observed feature is unequivocally associated to the clusters and that it is
not an artifact due to photometric errors, differential reddening or binaries.
We confirm that NGC 1806 and NGC 1846 clearly exhibit two distinct MSTOs and
observe, for the first time, a double MSTO in NGC 1751. In these three clusters
the population corresponding to the brighter MSTO includes more than two-thirds
of cluster stellar population. We confirm the presence of multiple stellar
populations in NGC 1783 and suggest that the MSTO of this cluster is formed by
two distinct branches. In 7 clusters (ESO057-SC075, HODGE7, NGC1852, NGC1917,
NGC1987, NGC2108, and NGC2154) we observed an intrinsic broadening of the MSTO
that may suggest that these clusters have experienced a prolonged period of
star formation (150-250 Myr). The CMDs of IC2146, NGC1644, NGC1652, NGC1795 and
NGC1978 show no evidence of spread or bimodality. In summary 7025% of our
sample are not consistent with the simple, single stellar population hypotesis.Comment: 28 pages, 39 figures, accepted for publication on A&A, full
resolution images at ftp://ftp.stsci.edu/outside-access/out.going/bedin/LMC
An integrated analysis of genes and functional pathways for aggression in human and rodent models
Human genome-wide association studies (GWAS), transcriptome analyses of animal models, and candidate gene studies have advanced our understanding of the genetic architecture of aggressive behaviors. However, each of these methods presents unique limitations. To generate a more confident and comprehensive view of the complex genetics underlying aggression, we undertook an integrated, cross-species approach. We focused on human and rodent models to derive eight gene lists from three main categories of genetic evidence: two sets of genes identified in GWAS studies, four sets implicated by transcriptome-wide studies of rodent models, and two sets of genes with causal evidence from online Mendelian inheritance in man (OMIM) and knockout (KO) mice reports. These gene sets were evaluated for overlap and pathway enrichment to extract their similarities and differences. We identified enriched common pathways such as the G-protein coupled receptor (GPCR) signaling pathway, axon guidance, reelin signaling in neurons, and ERK/MAPK signaling. Also, individual genes were ranked based on their cumulative weights to quantify their importance as risk factors for aggressive behavior, which resulted in 40 top-ranked and highly interconnected genes. The results of our cross-species and integrated approach provide insights into the genetic etiology of aggression
Testing Newtonian Gravity with AAOmega: Mass-To-Light Profiles and Metallicity Calibrations From 47 Tuc and M55
Globular clusters are an important test bed for Newtonian gravity in the
weak-acceleration regime, which is vital to our understanding of the nature of
the gravitational interaction. Recent claims have been made that the velocity
dispersion profiles of globular clusters flatten out at large radii, despite an
apparent paucity of dark matter in such objects, indicating the need for a
modification of gravitational theories. We continue our investigation of this
claim, with the largest spectral samples ever obtained of 47 Tucanae and M55.
Furthermore, this large sample allows for an accurate metallicity calibration
based on the equivalent widths of the calcium triplet lines and K band
magnitude of the Tip of the Red Giant Branch. Assuming an isothermal
distribution, the rotations of each cluster are also measured with both
clusters exhibiting clear rotation signatures. The global velocity dispersions
of NGC 121 and Kron 3, two globular clusters in the Small Magellanic Cloud, are
also calculated. By applying a simple dynamical model to the velocity
dispersion profiles of 47 Tuc and M55, we calculate their mass-to-light
profiles, total masses and central velocity dispersions. We find no
statistically significant flattening of the velocity dispersion at large radii
for M55, and a marked increase in the profile of 47 Tuc for radii greater than
approximately half the tidal radius. We interpret this increase as an
evaporation signature, indicating that 47 Tuc is undergoing, or has undergone,
core-collapse, but find no requirement for dark matter or a modification of
gravitational theories in either cluster.Comment: 11 pages, 12 figures, 4 tables. Accepted by MNRA
Virgo cluster early-type dwarf galaxies with the Sloan Digital Sky Survey. II. Early-type dwarfs with central star formation
Despite the common picture of an early-type dwarf (dE) as a quiescent galaxy
with no star formation and little gas, we identify 23 dEs that have blue
central colors caused by recent or ongoing star formation in our sample of 476
Virgo cluster dEs. In addition, 14 objects that were mostly classified as
(candidate) BCDs have similar properties. Among the certain cluster members,
the dEs with blue centers reach a fraction of more than 15% of the dE
population at brighter (B<=16) magnitudes. A spectral analysis of the centers
of 16 galaxies reveals in all cases an underlying old population that dominates
the mass, with M(old)>=90% for all but one object. Therefore the majority of
these galaxies will appear like ordinary dEs within ~one Gigayear or less after
the last episode of star formation. Their overall gas content is less than that
of dwarf irregular galaxies, but higher than that of ordinary dEs. Their
flattening distribution suggests the shape of a thick disk, similar to what has
been found for dEs with disk features in Paper I of this series. Their
projected spatial distribution shows no central clustering, and their
distribution with projected local density follows that of irregular galaxies,
indicative of an unrelaxed population. This is corroborated by their velocity
distribution, which displays two side peaks characteristic of recent infall. We
discuss possible formation mechanisms (ram-pressure stripping, tidally induced
star formation, harassment) that might be able to explain both the disk shape
and the central star formation of the dEs with blue centers.Comment: 16 pages + 15 figures. Accepted for publication in AJ. We recommend
downloading the full resolution version from
http://www.virgo-cluster.com/lisker2006b.ps.g
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