511 research outputs found
Identification de ligands de la protéase adénovirale de type 2 à l'aide d'une peptothÚque de phages ("phage library")
Une peptothĂšque de phages a Ă©tĂ© utilisĂ©e afin d'identifier des ligands Ă la protĂ©ase de lâAd2. La peptothĂšque de phages contient une rĂ©gion alĂ©atoire de 15 a.a. bordĂ©e par deux rĂ©sidus cystĂ©ine qui forment un pont disulfure. Le criblage de la peptothĂšque contre la protĂ©ase de lâAd2, a dĂ©gagĂ© 29 sĂ©quences de peptides de 15 a.a. de longueur Ă partir de 63 phages vĂ©rifiĂ©s. Parmi ces sĂ©quences, il a Ă©tĂ© possible de distinguer certaines sĂ©quences connues, telles les sites de clivage de la protĂ©ase (M,I,L)XGG^X et (M,I,L)XGX^G. Une sĂ©quence homologue au peptide pVIct, un stimulateur de la protĂ©ase, a aussi Ă©tĂ© mise en Ă©vidence. Une rĂ©gion de grande homologie entre plusieurs des sĂ©quences obtenues met en Ă©vidence une sĂ©quence qui ressemble au site de clivage, cette sĂ©quence Ă©tant VEGGS. Le peptide VEGGS a Ă©tĂ© synthĂ©tisĂ© afin de vĂ©rifier son effet sur la protĂ©ase in vitro et in vivo. A partir d'une recherche avec le logiciel Blast dans les banques de donnĂ©es Swissprot et Genbank, l'homologie entre les protĂ©ines avec les sĂ©quences provenant des phages isolĂ©s ont Ă©tĂ© relevĂ©es. Parmi les sĂ©quences protĂ©iques obtenues de ces banques de donnĂ©es, on observe une homologie avec la protĂ©ine 100kD et la protĂ©ine Tp de lâAd2, ainsi qu'une homologie avec la protĂ©ine Tp de lâAd5
Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
With the unprecedented photometric precision of the Kepler Spacecraft,
significant systematic and stochastic errors on transit signal levels are
observable in the Kepler photometric data. These errors, which include
discontinuities, outliers, systematic trends and other instrumental signatures,
obscure astrophysical signals. The Presearch Data Conditioning (PDC) module of
the Kepler data analysis pipeline tries to remove these errors while preserving
planet transits and other astrophysically interesting signals. The completely
new noise and stellar variability regime observed in Kepler data poses a
significant problem to standard cotrending methods such as SYSREM and TFA.
Variable stars are often of particular astrophysical interest so the
preservation of their signals is of significant importance to the astrophysical
community. We present a Bayesian Maximum A Posteriori (MAP) approach where a
subset of highly correlated and quiet stars is used to generate a cotrending
basis vector set which is in turn used to establish a range of "reasonable"
robust fit parameters. These robust fit parameters are then used to generate a
Bayesian Prior and a Bayesian Posterior Probability Distribution Function (PDF)
which when maximized finds the best fit that simultaneously removes systematic
effects while reducing the signal distortion and noise injection which commonly
afflicts simple least-squares (LS) fitting. A numerical and empirical approach
is taken where the Bayesian Prior PDFs are generated from fits to the light
curve distributions themselves.Comment: 43 pages, 21 figures, Submitted for publication in PASP. Also see
companion paper "Kepler Presearch Data Conditioning I - Architecture and
Algorithms for Error Correction in Kepler Light Curves" by Martin C. Stumpe,
et a
Pointwise Bounds for Steklov Eigenfunctions
Let (Ω,g) be a compact, real-analytic Riemannian manifold with real-analytic boundary âΩ. The harmonic extensions of the boundary Dirichlet-to-Neumann eigenfunctions are called Steklov eigenfunctions. We show that the Steklov eigenfunctions decay exponentially into the interior in terms of the Dirichlet-to-Neumann eigenvalues and give a sharp rate of decay to first order at the boundary. The proof uses the Poisson representation for the Steklov eigenfunctions combined with sharp h-microlocal concentration estimates for the boundary Dirichlet-to-Neumann eigenfunctions near the cosphere bundle SââΩ. These estimates follow from sharp estimates on the concentration of the FBI transforms of solutions to analytic pseudodifferential equations Pu=0 near the characteristic set {Ï(P)=0}
Verification of the Kepler Input Catalog from Asteroseismology of Solar-type Stars
We calculate precise stellar radii and surface gravities from the
asteroseismic analysis of over 500 solar-type pulsating stars observed by the
Kepler space telescope. These physical stellar properties are compared with
those given in the Kepler Input Catalog (KIC), determined from ground-based
multi-color photometry. For the stars in our sample, we find general agreement
but we detect an average overestimation bias of 0.23 dex in the KIC
determination of log (g) for stars with log (g)_KIC > 4.0 dex, and a resultant
underestimation bias of up to 50% in the KIC radii estimates for stars with
R_KIC < 2 R sun. Part of the difference may arise from selection bias in the
asteroseismic sample; nevertheless, this result implies there may be fewer
stars characterized in the KIC with R ~ 1 R sun than is suggested by the
physical properties in the KIC. Furthermore, if the radius estimates are taken
from the KIC for these affected stars and then used to calculate the size of
transiting planets, a similar underestimation bias may be applied to the
planetary radii.Comment: Published in The Astrophysical Journal Letter
Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
Kepler provides light curves of 156,000 stars with unprecedented precision.
However, the raw data as they come from the spacecraft contain significant
systematic and stochastic errors. These errors, which include discontinuities,
systematic trends, and outliers, obscure the astrophysical signals in the light
curves. To correct these errors is the task of the Presearch Data Conditioning
(PDC) module of the Kepler data analysis pipeline. The original version of PDC
in Kepler did not meet the extremely high performance requirements for the
detection of miniscule planet transits or highly accurate analysis of stellar
activity and rotation. One particular deficiency was that astrophysical
features were often removed as a side-effect to removal of errors. In this
paper we introduce the completely new and significantly improved version of PDC
which was implemented in Kepler SOC 8.0. This new PDC version, which utilizes a
Bayesian approach for removal of systematics, reliably corrects errors in the
light curves while at the same time preserving planet transits and other
astrophysically interesting signals. We describe the architecture and the
algorithms of this new PDC module, show typical errors encountered in Kepler
data, and illustrate the corrections using real light curve examples.Comment: Submitted to PASP. Also see companion paper "Kepler Presearch Data
Conditioning II - A Bayesian Approach to Systematic Error Correction" by Jeff
C. Smith et a
Overview of the Kepler Science Processing Pipeline
The Kepler Mission Science Operations Center (SOC) performs several critical
functions including managing the ~156,000 target stars, associated target
tables, science data compression tables and parameters, as well as processing
the raw photometric data downlinked from the spacecraft each month. The raw
data are first calibrated at the pixel level to correct for bias, smear induced
by a shutterless readout, and other detector and electronic effects. A
background sky flux is estimated from ~4500 pixels on each of the 84 CCD
readout channels, and simple aperture photometry is performed on an optimal
aperture for each star. Ancillary engineering data and diagnostic information
extracted from the science data are used to remove systematic errors in the
flux time series that are correlated with these data prior to searching for
signatures of transiting planets with a wavelet-based, adaptive matched filter.
Stars with signatures exceeding 7.1 sigma are subjected to a suite of
statistical tests including an examination of each star's centroid motion to
reject false positives caused by background eclipsing binaries. Physical
parameters for each planetary candidate are fitted to the transit signature,
and signatures of additional transiting planets are sought in the residual
light curve. The pipeline is operational, finding planetary signatures and
providing robust eliminations of false positives.Comment: 8 pages, 3 figure
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