240 research outputs found
Forging the endothelium during inflammation: pushing at a half-open door?
During an inflammatory response, changes in the adhesive properties of the endothelium occur that enable normally non-adherent blood-borne leukocytes to adhere and subsequently to traverse the endothelium through small gaps at inter-cellular junctions. This review concentrates on the role played by inter-endothelial adhesion molecules during transmigration and the way in which their expression may be regulated during inflammation. We show that the final "open" signals that lead to the formation of clefts between adjacent endothelial cells may be derived from inflamed tissue underlying the endothelium and from activated leukocyte
LPS differentially regulates adhesion and transendothelial migration of human monocytes under static and flow conditions
One of the key components of the innate immune response is the recognition of microbial products such as LPS by Toll-like receptors on monocytes and neutrophils. We show here that short-term stimulation of primary human monocytes with LPS led to an increase in adhesion of monocytes to endothelial cells and a dramatic decrease in transendothelial migration under static conditions. In contrast, under normal physiological flow, monocyte adhesion and migration across a human umbilical vein endothelial cell monolayer appeared to be unaffected by LPS treatment. LPS stimulation of monocytes activated β1 and β2 integrins, but did not increase their surface expression levels. During septic shock, reduction in blood flow as a result of vasodilation and vascular permeability leads to adhesion and accumulation of LPS-stimulated circulating monocytes onto the blood vessel walls. The different findings of monocyte migration under static and flow conditions in our study may offer one explanation for this phenomenon. The rapid engagement of LPS-activated monocytes preventing transendothelial migration could represent a novel mechanism of bacterial exclusion from the vasculature. This occurs during the early stages of sepsis, and in turn may modulate the severity of the pathophysiolog
Development and Characterisation of a Gas System and its Associated Slow-Control System for an ATLAS Small-Strip Thin Gap Chamber Testing Facility
A quality assurance and performance qualification laboratory was built at
McGill University for the Canadian-made small-strip Thin Gap Chamber (sTGC)
muon detectors produced for the 2019-2020 ATLAS experiment muon spectrometer
upgrade. The facility uses cosmic rays as a muon source to ionise the quenching
gas mixture of pentane and carbon dioxide flowing through the sTGC detector. A
gas system was developed and characterised for this purpose, with a simple and
efficient gas condenser design utilizing a Peltier thermoelectric cooler (TEC).
The gas system was tested to provide the desired 45 vol% pentane concentration.
For continuous operations, a state-machine system was implemented with alerting
and remote monitoring features to run all cosmic-ray data-acquisition
associated slow-control systems, such as high/low voltage, gas system and
environmental monitoring, in a safe and continuous mode, even in the absence of
an operator.Comment: 23 pages, LaTeX, 14 figures, 4 tables, proof corrections for Journal
of Instrumentation (JINST), including corrected Fig. 8b
Spreading of Latex Particles on a Substrate
We have investigated both experimentally and theoretically the spreading
behavior of latex particles deposited on solid substrates. These particles,
which are composed of cross-linked polymer chains, have an intrinsic elastic
modulus. We show that the elasticity must be considered to account for the
observed contact angle between the particle and the solid substrate, as
measured through atomic force microscopy techniques. In particular, the work of
adhesion computed within our model can be significantly larger than that from
the classical Dupr\'{e} formula.Comment: 7 pages, 7 figures, to appear in Europhys. Let
Multi-object spectroscopy of stars in the CoRoT fields II: The stellar population of the CoRoT fields IRa01, LRa01, LRa02, and LRa06
With now more than 20 exoplanets discovered by CoRoT, it has often been
considered strange that so many of them are orbiting F-stars, and so few of
them K or M-stars. Although transit search programs are mostly sensitive to
short-period planets, they are ideal for verifying these results. To determine
the frequency of planets as a function of stellar mass, we also have to
characterize the sample of stars that was observed. We study the stellar
content of the CoRoT-fields IRa01, LRa01 (=LRa06), and LRa02 by determining the
spectral types of 11466 stars. We used spectra obtained with the multi-object
spectrograph AAOmega and derived the spectral types by using template spectra
with well-known parameters. We find that 34.8+/-0.7% of the stars observed by
CoRoT in these fields are F-dwarfs, 15.1+/-0.5% G-dwarfs, and 5.0+/-0.3%
K-dwarfs. We conclude that the apparent lack of exoplanets of K- and M-stars is
explained by the relatively small number of these stars in the observed sample.
We also show that the apparently large number of planets orbiting F-stars is
similarly explained by the large number of such stars in these fields. Our
study also shows that the difference between the sample of stars that CoRoT
observes and a sample of randomly selected stars is relatively small, and that
the yield of CoRoT specifically is the detection one hot Jupiter amongst
2100+/-700 stars. We conclude that transit search programs can be used to study
the relation between the frequency of planets and the mass of the host stars,
and that the results obtained so far generally agree with those of radial
velocity programs.Comment: 231 pages with 6 figures, A&A accepte
Multi-object spectroscopy of stars in the CoRoT fields I: Early-type stars in the CoRoT-fields IRa01, LRa01, LRa02
Observations of giant stars indicate that the frequency of giant planets is
much higher for intermediate-mass stars than for solar-like stars. Up to now
all known planets of giant stars orbit at relatively far distances from their
host stars. It is not known whether intermediate-mass stars also had many
close-in planets when they were on the main sequence, which were then engulfed
when the star became a giant star. To understand the formation and evolution of
planets it is therefore important to find out whether main-sequence stars of
intermediate-mass have close-in planets or not. A survey for transiting planets
of intermediate-mass stars would be ideal to solve this question, because the
detection of transiting planets is not affected by the rapid rotation of these
stars. As a first step for an efficient survey we need to identify
intermediate-mass stars in the CoRoT-fields, which can then be used as an input
list. To compile the input list we derived the spectral types of essentially
all O, B and A stars down to 14.5 mag in the CoRoT fields IRa01, LRa01, LRa02
taken with the multi-object spectrograph AAOmega. We determined the spectral
types by comparing the spectra with template spectra from a library. In total
we identify 1856 A and B stars that have been observed with CoRoT. Given the
number of planets that have been detected in these fields amongst late-type
stars, we estimate that there are one to four transiting planets of
intermediate-mass stars waiting to be discovered. Our survey not only allows us
to carry out a dedicated planet search programme but is also essential for any
types of studies of the light curves of early-type stars in the CoRoT database.
We also show that it would be possible to extend the survey to all fields that
CoRoT has observed using photometrically determined spectral types.Comment: 57 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
An educated search for transiting habitable planets: (Research Note) Targetting M dwarfs with known transiting planets
Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. We investigate here the potential of this approach for the M dwarf GJ 1214 that hosts a transiting super-Earth. For this system, we infer the transit probabilities as a function of orbital periods. Using Monte-Carlo simulations we address both the cases for fully coplanar and for non-coplanar orbits, with three different choices of inclinations distribution for the non-coplanar case. GJ 1214 reveals to be a very promising target for the considered approach. Because of its small size, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring could detect any transiting habitable planet down to the size of Mars. The mass measurement of such a small planet would be out of reach for current facilities, but we emphasize that a planet mass would not be needed to confirm the planetary nature of the transiting object. Furthermore, the radius measurement combined with theoretical arguments would help us to constrain the structure of the planet
Characterizing Transiting Extrasolar Planets with Narrow-Band Photometry and GTC/OSIRIS
We report the first extrasolar planet observations from the 10.4-m Gran
Telescopio Canarias (GTC), currently the world's largest, fully steerable,
single-aperture optical telescope. We used the OSIRIS tunable filter imager on
the GTC to acquire high-precision, narrow-band photometry of the transits of
the giant exoplanets, TrES-2b and TrES-3b. We obtained near-simultaneous
observations in two near-infrared (NIR) wavebands (790.2 and 794.4 +/- 2.0 nm)
specifically chosen to avoid water vapor absorption and skyglow so as to
minimize the atmospheric effects that often limit the precision of ground-based
photometry. Our results demonstrate a very-high photometric precision with
minimal atmospheric contamination despite relatively poor atmospheric
conditions and some technical problems with the telescope. We find the
photometric precision for the TrES-2 observations to be 0.343 and 0.412 mmag
for the 790.2 and 794.4 nm light curves, and the precision of the TrES-3
observations was found to be 0.470 and 0.424 mmag for the 790.2 and 794.4 nm
light curves. We also discuss how future follow-up observations of transiting
planets with this novel technique can contribute to the characterization of
Neptune- and super-Earth-size planets to be discovered by space-based missions
like CoRoT and Kepler, as well as measure atmospheric properties of giant
planets, such as the strength of atmospheric absorption features.Comment: 9 pages, including 3 figures and 2 tables; accepted for publication
in MNRA
Transition from Cassie to Wenzel state in patterned soft elastomer sliding contacts
In this paper, we presented an experimental and theoretical analysis of the
formation of the contact between a smooth elastomer lens and an elastomer
substrate micropatterned with hexagonal arrays of cylindrical pillars. We show
using a JKR model coupled with a full description of the deformation of the
substrate between the pillars that the transition between the top to the full
contact is obtain when the normal load is increased above a well predicted
threshold. We have also shown that above the onset of full contact, the
evolution of the area of full contact was obeying a simple scaling.Comment: 4 pages, 6 figures. Submitte
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