870 research outputs found
Construction and Characterization of a cDNA Library from Wheat Infected with Fusarium graminearum Fg 2
Total RNA from wheat spikes infected with F. graminearum Fg2 was extracted and the mRNA was purified. Switching Mechanism at 5′ end of the RNA Transcript (SMART) technique and CDS Ill/3′ primer were used for first-strand cDNA synthesis using reverse transcriptase by RT-PCR. Primer extension polymerase chain reaction was used to construct the double-strand cDNA that was digested by proteinase K, then by Sfi I and fractionated. cDNAs longer than 0.5 kb were collected and ligated to λTriplEx2 vector followed λ phage packaging reaction and library amplification. The qualities of both unamplified and amplified cDNA libraries were strictly checked by conventional titer determination. One hundred and sixty five plaques were randomly picked and tested using PCR with universal primers derived from the sequence flanking the vector. A high quality cDNA library from wheat spikes that have been infected by F. graminearum was successfully constructed
Chandra Detects the Rare Oxygen-type Wolf-Rayet Star WR 142 and OB Stars in Berkeley 87
We present first results of a Chandra X-ray observation of the rare
oxygen-type Wolf-Rayet star WR 142 (= Sand 5 = St 3) harbored in the young,
heavily-obscured cluster Berkeley 87. Oxygen type WO stars are thought to be
the most evolved of the WRs and progenitors of supernovae or gamma ray bursts.
As part of an X-ray survey of supposedly single Wolf-Rayet stars, we observed
WR 142 and the surrounding Berkeley 87 region with Chandra ACIS-I. We detect WR
142 as a faint, yet extremely hard X-ray source. Due to weak emission, its
nature as a thermal or nonthermal emitter is unclear and thus we discuss
several emission mechanisms. Additionally, we report seven detections and eight
non-detections by Chandra of massive OB stars in Berkeley 87, two of which are
bright yet soft X-ray sources whose spectra provide a dramatic contrast to the
hard emission from WR 142.Comment: To appear in the Astrophysical Journa
Lower bounds for several online variants of bin packing
We consider several previously studied online variants of bin packing and
prove new and improved lower bounds on the asymptotic competitive ratios for
them. For that, we use a method of fully adaptive constructions. In particular,
we improve the lower bound for the asymptotic competitive ratio of online
square packing significantly, raising it from roughly 1.68 to above 1.75.Comment: WAOA 201
High pressure mechanical seal
A relatively impervious mechanical seal is formed between the outer surface of a tube and the inside surface of a mechanical fitting of a high pressure fluid or hydraulic system by applying a very thin soft metal layer onto the outer surface of the hard metal tube and/or inner surface of the hard metal fitting, prior to swaging the fitting onto the tube. The thickness of such thin metal layer is independent of the size of the tube and/or fittings. Many metals and alloys of those metals exhibit the requisite softness, including silver, gold, nickel, tin, platinum, indium, rhodium and cadmium. Suitably, the coating is about 0.0025 millimeters (0.10 mils) in thickness. After swaging, the tube and fitting combination exhibits very low leak rates on the order or 10.sup.-8 cubic centimeters per second or less as meaured using the Helium leak test
X-ray Variability in the Young Massive Triple theta2 Ori A
Massive stars rarely show intrinsic X-ray variability. The only O-stars
credited to be intrinsically variable are theta1 Ori C due to effects from
magnetic confinement of its wind, and theta2 Ori A suspected of similar
activity. Early Chandra observations have shown that the most massive star
system in the Orion Trapezium Cluster, theta2 Ori A, shows rapid variability on
time scales of hours. We determine X-ray fluxes and find that the star shows
very strong variability over the last 5 years. We observed a second large X-ray
outburst in November 2004 with the high resolution transmission grating
spectrometer on-board Chandra. In the low state X-ray emissivities indicate
temperatures well above 25 MK. In the high state we find an extended emissivity
distribution with high emissivities in the range from 3 MK to over 100 MK. The
outburst event in stellar terms is one of the most powerful ever observed and
the most energetic one in the ONC with a lower total energy limit of 1.5x10^37
ergs. The line diagnostics show that under the assumption that the line
emitting regions in the low states are as close as within 1 -- 2 stellar radii
from the O-star's photosphere, whereas the hard states suggest a distance of 3
-- 5 stellar radii. The two outbursts are very close to the periastron passage
of the stars. We argue that the high X-ray states are possibly the result of
reconnection events from magnetic interactions of the primary and secondary
stars of the spectroscopic binary. Effects from wind collisions seem unlikely
for this system. The low state emissivity and R-ratios strengthen the
predicament that the X-ray emission is enhanced by magnetic confinement of the
primary wind. We also detect Fe fluorescence indicative of the existence of
substantial amounts of neutral Fe in the vicinity of the X-ray emission.Comment: 11 pages, 8 figures, accepted for publication in The Astrophysical
Main Journa
An Atlas of K-line Spectra for Cool Magnetic CP Stars: The Wing-Nib Anomaly (WNA)
We present a short atlas illustrating the unusual Ca {\sc ii} K-line profiles
in upper main sequence stars with anomalous abundances. Slopes of the profiles
for 10 cool, magnetic chemically peculiar (CP) stars change abruptly at the
very core, forming a deep "nib." The nibs show the same or nearly the same
radial velocity as the other atomic lines. The near wings are generally more
shallow than in normal stars. In three magnetic CP stars, the K-lines are too
weak to show this shape, though the nibs themselves are arguably present. The
Ca {\sc ii} H-lines also show deep nibs, but the profiles are complicated by
the nearby, strong H absorption. The K-line structure is nearly
unchanged with phase in CrB and Cir. Calculations, including
NLTE, show that other possibilities in addition to chemical stratification may
yield nib-like cores.Comment: 6 pages, 2 figures, and 8 figures; accepted for publication in ApJ
Focusing by blocking: repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes
Over the past few years the displacement statistics of self-propelled
particles has been intensely studied, revealing their long-time diffusive
behavior. Here, we demonstrate that a concerted combination of boundary
conditions and switching on and off the self-propelling drive can generate and
afterwards arbitrarily often restore a non-stationary centered peak in their
spatial distribution. This corresponds to a partial reversibility of their
statistical behavior, in opposition to the above-mentioned long-time diffusive
nature. Interestingly, it is a diffusive process that mediates and makes
possible this procedure. It should be straightforward to verify our predictions
in a real experimental system.Comment: 6 pages, 6 figure
Color LAR codec : a color image representation and compression scheme based on local resolution adjustment and on self-extracting region representation
This LAR (Locally Adaptive Resolution) color image coding scheme yields to an efficient progressive compression with a
better subjective quality than Jpeg2000. Additionally, it offers region functionalities for low bit rate coding and decoding.
From highly compressed luminance, a region description, without contours encoding, can be obtained through a
segmentation process performed at both coder and decoder. Considering color results, controlled chrominance
components segmentation provides a better data consistency simultaneously with a low bit rate compression. As regions
and their encoding are based on a same representation grid, enhancement of image quality can be global, or only
restricted to a Region Of Interest.Cet article présente un schéma original de codage progressif d'images couleur apportant à la fois une
efficacité en termes de compression (meilleure qualité subjective que Jpeg2000) et des fonctionnalités au
niveau région à bas débits pour le codeur et le décodeur. À partir de l'image des luminances codée à bas
débit par le codec LAR (Locally Adaptive Resolution), une description en régions, sans codage des contours,
est obtenue à travers un procédé de segmentation effectué au codeur et au décodeur. Cette segmentation
peut être contrôlée par les composantes chromatiques pour une meilleure cohérence du résultat d'un point de
vue couleur. Un codage basé régions appliqué sur les images de chrominance produit alors une compression
de ces composantes à très bas débit. Comme les régions et le codage de leur contenu partagent une même
grille de représentation, l'amélioration de la qualité de l'image peut être globale, ou limitée à une zone
d'intérêt
Predictions for mass-loss rates and terminal wind velocities of massive O-type stars
Mass loss forms an important aspect of the evolution of massive stars, as
well as for the enrichment of the surrounding ISM. Our goal is to predict
accurate mass-loss rates and terminal wind velocities. These quantities can be
compared to empirical values, thereby testing radiation-driven wind models. One
specific issue is that of the "weak-wind problem", where empirically derived
mass-loss rates fall orders of magnitude short of predicted values. We employ
an established Monte Carlo model and a recently suggested new line acceleration
formalism to solve the wind dynamics consistently. We provide a new grid of
mass-loss rates and terminal wind velocities of O stars, and compare the values
to empirical results. Our models fail to provide mass-loss rates for
main-sequence stars below a luminosity of log(L/Lsun) = 5.2, where we run into
a fundamental limit. At luminosities below this critical value there is
insufficient momentum transferred in the region below the sonic point to
kick-start the acceleration. This problem occurs at the location of the onset
of the weak-wind problem. For O dwarfs, the boundary between being able to
start a wind, and failing to do so, is at spectral type O6/O6.5. The direct
cause of this failure is a combination of the lower luminosity and a lack of Fe
V lines at the wind base. This might indicate that another mechanism is
required to provide the necessary driving to initiate the wind. For stars more
luminous than log(L/Lsun) = 5.2, our new mass-loss rates are in excellent
agreement with the mass-loss prescription by Vink et al. 2000. This implies
that the main assumption entering the method of the Vink et al. prescriptions -
i.e. that the momentum equation is not explicitly solved for - does not
compromise the reliability of the Vink et al. results for this part of
parameter space (Abridged).Comment: 10 pages, 10 figures, Astronomy & Astrophysics (in press
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