456 research outputs found
Introducing BAX: a database for X-ray clusters and groups of galaxies
We present BAX, Base de Donnees Amas de Galaxies X
(http://webast.ast.obs-mip.fr/bax), a multi-wavelength database dedicated to
X-ray clusters and groups of galaxies allowing detailed information retrieval.
BAX is designed to support astronomical research by providing access to
published measurements of the main physical quantities and to the related
bibliographic references: basic data stored in the database are cluster/group
identifiers, equatorial coordinates, redshift, flux, X-ray luminosity (in the
ROSAT band) and temperature, and links to additional linked parameters (in
X-rays, such as spatial profile parameters, as well as SZ parameters of the hot
gas, lensing measurements,and data at other wavelengths, such as optical and
radio). The clusters and groups in BAX can be queried by the basic parameters
as well as the linked parameters or combinations of these. We expect BAX to
become an important tool for the astronomical community. BAX will optimize
various aspects of the scientific analysis of X-ray clusters and groups of
galaxies, from proposal planning to data collection, interpretation and
publication, from both ground based facilities like MEGACAM (CFHT), VIRMOS
(VLT) and space missions like XMM-Newton, Chandra and Planck.Comment: Accepted for publication in Astronomy and Astrophysics Journal.
Contains 4 pages and 1 figur
SHELS: The Hectospec Lensing Survey
The Smithsonian Hectospec Lensing Survey (SHELS) combines a large deep
complete redshift survey with a weak lensing map from the Deep Lens Survey
(Wittman et al. 2002; 2005). We use maps of the velocity dispersion based on
systems identified in the redshift survey to compare the three-dimensional
matter distribution with the two-dimensional projection mapped by weak lensing.
We demonstrate directly that the lensing map images the three-dimensional
matter distribution obtained from the kinematic data.Comment: Astrophysical Journal Letters 9pages, 3 figures, accepted, corrected
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The Incidence of Highly-Obscured Star-Forming Regions in SINGS Galaxies
Using the new capabilities of the Spitzer Space Telescope and extensive
multiwavelength data from the Spitzer Infrared Nearby Galaxies Survey (SINGS),
it is now possible to study the infrared properties of star formation in nearby
galaxies down to scales equivalent to large HII regions. We are therefore able
to determine what fraction of large, infrared-selected star-forming regions in
normal galaxies are highly obscured and address how much of the star formation
we miss by relying solely on the optical portion of the spectrum. Employing a
new empirical method for deriving attenuations of infrared-selected
star-forming regions we investigate the statistics of obscured star formation
on 500pc scales in a sample of 38 nearby galaxies. We find that the median
attenuation is 1.4 magnitudes in H-alpha and that there is no evidence for a
substantial sub-population of uniformly highly-obscured star-forming regions.
The regions in the highly-obscured tail of the attenuation distribution
(A_H-alpha > 3) make up only ~4% of the sample of nearly 1800 regions, though
very embedded infrared sources on the much smaller scales and lower
luminosities of compact and ultracompact HII regions are almost certainly
present in greater numbers. The highly-obscured cases in our sample are
generally the bright, central regions of galaxies with high overall attenuation
but are not otherwise remarkable. We also find that a majority of the galaxies
show decreasing radial trends in H-alpha attenuation. The small fraction of
highly-obscured regions seen in this sample of normal, star-forming galaxies
suggests that on 500pc scales the timescale for significant dispersal or break
up of nearby, optically-thick dust clouds is short relative to the lifetime of
a typical star-forming region.Comment: Accepted for publication in ApJ; emulateapj style, 30 pages, 18
figures (compressed versions), 3 table
Lack of phenotypic and evolutionary cross-resistance against parasitoids and pathogens in Drosophila melanogaster
BackgroundWhen organisms are attacked by multiple natural enemies, the evolution of a resistance mechanism to one natural enemy will be influenced by the degree of cross-resistance to another natural enemy. Cross-resistance can be positive, when a resistance mechanism against one natural enemy also offers resistance to another; or negative, in the form of a trade-off, when an increase in resistance against one natural enemy results in a decrease in resistance against another. Using Drosophila melanogaster, an important model system for the evolution of invertebrate immunity, we test for the existence of cross-resistance against parasites and pathogens, at both a phenotypic and evolutionary level.MethodsWe used a field strain of D. melanogaster to test whether surviving parasitism by the parasitoid Asobara tabida has an effect on the resistance against Beauveria bassiana, an entomopathogenic fungus; and whether infection with the microsporidian Tubulinosema kingi has an effect on the resistance against A. tabida. We used lines selected for increased resistance to A. tabida to test whether increased parasitoid resistance has an effect on resistance against B. bassiana and T. kingi. We used lines selected for increased tolerance against B. bassiana to test whether increased fungal resistance has an effect on resistance against A. tabida.Results/ConclusionsWe found no positive cross-resistance or trade-offs in the resistance to parasites and pathogens. This is an important finding, given the use of D. melanogaster as a model system for the evolution of invertebrate immunity. The lack of any cross-resistance to parasites and pathogens, at both the phenotypic and the evolutionary level, suggests that evolution of resistance against one class of natural enemies is largely independent of evolution of resistance against the other
Bayesian inference of biochemical kinetic parameters using the linear noise approximation
Background
Fluorescent and luminescent gene reporters allow us to dynamically quantify changes in molecular species concentration over time on the single cell level. The mathematical modeling of their interaction through multivariate dynamical models requires the deveopment of effective statistical methods to calibrate such models against available data. Given the prevalence of stochasticity and noise in biochemical systems inference for stochastic models is of special interest. In this paper we present a simple and computationally efficient algorithm for the estimation of biochemical kinetic parameters from gene reporter data.
Results
We use the linear noise approximation to model biochemical reactions through a stochastic dynamic model which essentially approximates a diffusion model by an ordinary differential equation model with an appropriately defined noise process. An explicit formula for the likelihood function can be derived allowing for computationally efficient parameter estimation. The proposed algorithm is embedded in a Bayesian framework and inference is performed using Markov chain Monte Carlo.
Conclusion
The major advantage of the method is that in contrast to the more established diffusion approximation based methods the computationally costly methods of data augmentation are not necessary. Our approach also allows for unobserved variables and measurement error. The application of the method to both simulated and experimental data shows that the proposed methodology provides a useful alternative to diffusion approximation based methods
Arene C−H Bond Activation and Arene Oxidative Coupling by Cationic Palladium(II) Complexes
N,N‘-Diaryl-α-diimine-ligated Pd(II) dimethyl complexes (^(tBu)2^(Ar)DAB^(Me))PdMe_2 and {(CF_3)_2^(Ar)DAB^(Me)}PdMe_2 {^(tBu)2^(Ar)DAB^(Me): ArNC═(CH_3)−C(CH_3═NAr, Ar=3,5-di-tert-butylphenyl; (CF_3)_2^(Ar)DAB^(Me):Ar = 3,5-bis(trifluoromethyl)phenyl} undergo protonolysis with HBF_4(aq) in trifluoroethanol (TFE) to form cationic complexes [(α-diimine)Pd(CH_3)(H_2O)][BF_4]. The cations activate benzene C−H bonds at room temperature. Kinetic analyses reveal trends similar to those observed for the analogous platinum complexes: the C−H activation step is rate-determining (KIE = 4.1 ± 0.5) and is inhibited by H_2O. The kinetic data are consistent with a mechanism in which benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway. Following benzene C−H activation under 1 atm O_2, the products of the reaction are biphenyl and a dimeric μ-hydroxide complex, [(α-diimine)Pd(OH)]_2[BF_4]_2. The Pd(0) formed in the reaction is reoxidized by O_2 to the dimeric μ-hydroxide complex after the oxidative C−C bond formation. The regioselectivity of arene coupling was investigated with toluene and α,α,α-trifluorotoluene as substrates
Spectroscopy of the neighboring massive clusters Abell 222 and Abell 223
We present a spectroscopic catalog of the neighboring massive clusters Abell
222 and Abell 223. The catalog contains the positions, redshifts, R magnitudes,
V-R color, as well as the equivalent widths for a number of lines for 183
galaxies, 153 of them belonging to the A 222 and A 223 system. We determine the
heliocentric redshifts to be z=0.2126+/-0.0008 for A 222 and z=0.2079+/-0.0008
for A 223. The velocity dispersions of both clusters in the cluster restframe
are about the same: sigma = 1014^{+90}_{-71} km/s and sigma = 1032^{+99}_{-76}
km/s for A 222 and A 223, respectively. While we find evidence for substructure
in the spatial distribution of A 223, no kinematic substructure can be
detected. From the red cluster sequence identified in a
color--magnitude--diagram we determine the luminosity of both clusters and
derive mass--to--light ratios in the R--band of (M/L)_A222 = (202+/-43) h_70
M_{su}n/L_{sun} and (M/L)_A223 = (149+/-33) h_70 M_{sun}/L_{sun}. Additionally
we identify a group of background galaxies at z ~ 0.242.Comment: Accepted for publication in A&A, 10 pages, 9 figures, full version of
table 2 included in source distribution, version with higher quality images
available from http://www.astro.uni-bonn.de/~dietrich
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