3,208 research outputs found
A Data Exchange Standard for Optical (Visible/IR) Interferometry
This paper describes the OI Exchange Format, a standard for exchanging
calibrated data from optical (visible/infrared) stellar interferometers. The
standard is based on the Flexible Image Transport System (FITS), and supports
storage of the optical interferometric observables including squared visibility
and closure phase -- data products not included in radio interferometry
standards such as UV-FITS. The format has already gained the support of most
currently-operating optical interferometer projects, including COAST, NPOI,
IOTA, CHARA, VLTI, PTI, and the Keck Interferometer, and is endorsed by the IAU
Working Group on Optical Interferometry. Software is available for reading,
writing and merging OI Exchange Format files.Comment: 26 pages, 1 figur
Entire solutions of hydrodynamical equations with exponential dissipation
We consider a modification of the three-dimensional Navier--Stokes equations
and other hydrodynamical evolution equations with space-periodic initial
conditions in which the usual Laplacian of the dissipation operator is replaced
by an operator whose Fourier symbol grows exponentially as \ue ^{|k|/\kd} at
high wavenumbers . Using estimates in suitable classes of analytic
functions, we show that the solutions with initially finite energy become
immediately entire in the space variables and that the Fourier coefficients
decay faster than \ue ^{-C(k/\kd) \ln (|k|/\kd)} for any . The
same result holds for the one-dimensional Burgers equation with exponential
dissipation but can be improved: heuristic arguments and very precise
simulations, analyzed by the method of asymptotic extrapolation of van der
Hoeven, indicate that the leading-order asymptotics is precisely of the above
form with . The same behavior with a universal constant
is conjectured for the Navier--Stokes equations with exponential
dissipation in any space dimension. This universality prevents the strong
growth of intermittency in the far dissipation range which is obtained for
ordinary Navier--Stokes turbulence. Possible applications to improved spectral
simulations are briefly discussed.Comment: 29 pages, 3 figures, Comm. Math. Phys., in pres
Cross-Disorder Genome-Wide Analyses Suggest a Complex Genetic Relationship Between Tourette\u27s Syndrome and OCD
OBJECTIVE: Obsessive-compulsive disorder (OCD) and Tourette\u27s syndrome are highly heritable neurodevelopmental disorders that are thought to share genetic risk factors. However, the identification of definitive susceptibility genes for these etiologically complex disorders remains elusive. The authors report a combined genome-wide association study (GWAS) of Tourette\u27s syndrome and OCD. METHOD: The authors conducted a GWAS in 2,723 cases (1,310 with OCD, 834 with Tourette\u27s syndrome, 579 with OCD plus Tourette\u27s syndrome/chronic tics), 5,667 ancestry-matched controls, and 290 OCD parent-child trios. GWAS summary statistics were examined for enrichment of functional variants associated with gene expression levels in brain regions. Polygenic score analyses were conducted to investigate the genetic architecture within and across the two disorders. RESULTS: Although no individual single-nucleotide polymorphisms (SNPs) achieved genome-wide significance, the GWAS signals were enriched for SNPs strongly associated with variations in brain gene expression levels (expression quantitative loci, or eQTLs), suggesting the presence of true functional variants that contribute to risk of these disorders. Polygenic score analyses identified a significant polygenic component for OCD (p=2x10(-4)), predicting 3.2% of the phenotypic variance in an independent data set. In contrast, Tourette\u27s syndrome had a smaller, nonsignificant polygenic component, predicting only 0.6% of the phenotypic variance (p=0.06). No significant polygenic signal was detected across the two disorders, although the sample is likely underpowered to detect a modest shared signal. Furthermore, the OCD polygenic signal was significantly attenuated when cases with both OCD and co-occurring Tourette\u27s syndrome/chronic tics were included in the analysis (p=0.01). CONCLUSIONS: Previous work has shown that Tourette\u27s syndrome and OCD have some degree of shared genetic variation. However, the data from this study suggest that there are also distinct components to the genetic architectures of these two disorders. Furthermore, OCD with co-occurring Tourette\u27s syndrome/chronic tics may have different underlying genetic susceptibility compared with OCD alone
Measurements of binary stars with coherent integration of NPOI data
In this paper we use coherently integrated visibilities (see separate paper
in these proceedings, Jorgensen et al. 2008) to measure the properties of
binary stars. We use only the phase of the complex visibility and not the
amplitude. The reason for this is that amplitudes suffer from the calibration
effect (the same for coherent and incoherent averages) and thus effectively
provide lower accuracy measurements. We demonstrate that the baseline phase
alone can be used to measure the separation, orientation and brightness ratio
of a binary star, as a function of wavelength.Comment: 2008 SPIE Astronomical Telescopes and Instrumentatio
Disentangling the Cosmic Web I: Morphology of Isodensity Contours
We apply Minkowski functionals and various derived measures to decipher the
morphological properties of large-scale structure seen in simulations of
gravitational evolution. Minkowski functionals of isodensity contours serve as
tools to test global properties of the density field. Furthermore, we identify
coherent objects at various threshold levels and calculate their partial
Minkowski functionals. We propose a set of two derived dimensionless
quantities, planarity and filamentarity, which reduce the morphological
information in a simple and intuitive way. Several simulations of the
gravitational evolution of initial power-law spectra provide a framework for
systematic tests of our method.Comment: 26 pages including 12 figures. Accepted for publication in Ap
A measure of centrality based on the spectrum of the Laplacian
We introduce a family of new centralities, the k-spectral centralities.
k-Spectral centrality is a measurement of importance with respect to the
deformation of the graph Laplacian associated with the graph. Due to this
connection, k-spectral centralities have various interpretations in terms of
spectrally determined information.
We explore this centrality in the context of several examples. While for
sparse unweighted networks 1-spectral centrality behaves similarly to other
standard centralities, for dense weighted networks they show different
properties. In summary, the k-spectral centralities provide a novel and useful
measurement of relevance (for single network elements as well as whole
subnetworks) distinct from other known measures.Comment: 12 pages, 6 figures, 2 table
The Mid-Infrared Colors of the ISM and Extended Sources at the Galactic Center
A mid-infrared (3.6-8 um) survey of the Galactic Center has been carried out
with the IRAC instrument on the Spitzer Space Telescope. This survey covers the
central 2x1.4 degree (~280x200 pc) of the Galaxy. At 3.6 and 4.5 um the
emission is dominated by stellar sources, the fainter ones merging into an
unresolved background. At 5.8 and 8 um the stellar sources are fainter, and
large-scale diffuse emission from the ISM of the Galaxy's central molecular
zone becomes prominent. The survey reveals that the 8 to 5.8 um color of the
ISM emission is highly uniform across the surveyed region. This uniform color
is consistent with a flat extinction law and emission from polycyclic aromatic
hydrocarbons (PAHs). Models indicate that this broadband color should not be
expected to change if the incident radiation field heating the dust and PAHs is
<10^4 times that of the solar neighborhood. The few regions with unusually red
emission are areas where the PAHs are underabundant and the radiation field is
locally strong enough to heat large dust grains to produce significant 8 um
emission. These red regions include compact H II regions, Sgr B1, and wider
regions around the Arches and Quintuplet Clusters. In these regions the
radiation field is >10^4 times that of the solar neighborhood. Other regions of
very red emission indicate cases where thick dust clouds obscure deeply
embedded objects or very early stages of star formation.Comment: 37 pages, 15 Postscript figures (low resolution). Accepted for
publication in the Ap
Constraining Disk Parameters of Be Stars using Narrowband H-alpha Interferometry with the NPOI
Interferometric observations of two well-known Be stars, gamma Cas and phi
Per, were collected and analyzed to determine the spatial characteristics of
their circumstellar regions. The observations were obtained using the Navy
Prototype Optical Interferometer equipped with custom-made narrowband filters.
The filters isolate the H-alpha emission line from the nearby continuum
radiation, which results in an increased contrast between the interferometric
signature due to the H-alpha-emitting circumstellar region and the central
star. Because the narrowband filters do not significantly attenuate the
continuum radiation at wavelengths 50 nm or more away from the line, the
interferometric signal in the H-alpha channel is calibrated with respect to the
continuum channels. The observations used in this study represent the highest
spatial resolution measurements of the H-alpha-emitting regions of Be stars
obtained to date. These observations allow us to demonstrate for the first time
that the intensity distribution in the circumstellar region of a Be star cannot
be represented by uniform disk or ring-like structures, whereas a Gaussian
intensity distribution appears to be fully consistent with our observations.Comment: 23 pages, 14 figures, accepted for publication in A
The HgMn Binary Star Phi Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary
Observations of the Mercury-Manganese star Phi Herculis with the Navy
Prototype Optical Interferometer (NPOI) conclusively reveal the previously
unseen companion in this single-lined binary system. The NPOI data were used to
predict a spectral type of A8V for the secondary star Phi Her B. This
prediction was subsequently confirmed by spectroscopic observations obtained at
the Dominion Astrophysical Observatory. Phi Her B is rotating at 50 +/-3
km/sec, in contrast to the 8 km/sec lines of Phi Her A. Recognizing the lines
from the secondary permits one to separate them from those of the primary. The
abundance analysis of Phi Her A shows an abundance pattern similar to those of
other HgMn stars with Al being very underabundant and Sc, Cr, Mn, Zn, Ga, Sr,
Y, Zr, Ba, Ce, and Hg being very overabundant.Comment: Accepted to ApJ, 45 pages, 11 figure
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