2,567 research outputs found
Adherence to and Invasion of Human Intestinal Cells by Arcobacter Species and Their Virulence Genotypes
The genus Arcobacter is composed of 17 species which have been isolated from various sources. Of particular interest are A. butzleri, A. cryaerophilus, and A. skirrowii, as these have been associated with human cases of diarrhea, the probable transmissionrroutes being through the ingestion of contaminated drinking water and food. To date, only limited studies of virulence traits in this genus have been undertaken. The present study used 60 Arcobacter strains isolated from different sources, representing 16 of the 17 species of the genus, to investigate their ability to adhere to and invade the human intestinal cell line Caco-2. In addition, the presence of five putative virulence genes (ciaB, cadF, cj1349, hecA, and irgA) was screened for in these strains by PCR. All Arcobacter species except A. bivalviorum and Arcobacter sp. strain W63 adhered to Caco-2 cells, and most species (10/16) were invasive. The most invasive species were A. skirrowii, A. cryaerophilus, A. butzleri, and A. defluvii. All invasive strains were positive for ciaB (encoding a putative invasion protein). Other putative virulence genes were present in other species, i.e., A. butzleri (cadF, cj1349, irgA, and hecA), A. trophiarum (cj1349), A. ellisii (cj1349), and A. defluvii (irgA). No virulence genes were detected in strains which showed little or no invasion of Caco-2 cells. These results indicate that many Arcobacter species are
potential pathogens of humans and animals
Instability and new phases of higher-dimensional rotating black holes
It has been conjectured that higher-dimensional rotating black holes become
unstable at a sufficiently large value of the rotation, and that new black
holes with pinched horizons appear at the threshold of the instability. We
search numerically, and find, the stationary axisymmetric perturbations of
Myers-Perry black holes with a single spin that mark the onset of the
instability and the appearance of the new black hole phases. We also find new
ultraspinning Gregory-Laflamme instabilities of rotating black strings and
branes.Comment: 5 pages, 5 figures. The instability of the black hole is argued to
appear at the second zero mode. The first zero mode is not associated to a
new branch of black hole solution
Kinematic groups across the MW disc: insights from models and from the RAVE catalogue
With the advent of the Gaia data, the unprecedented kinematic census of great
part of the Milky Way disc will allow us to characterise the local kinematic
groups and new groups in different disc neighbourhoods. First, we show here
that the models predict a stellar kinematic response to the spiral arms and bar
strongly dependent on disc position. For example, we find that the kinematic
groups induced by the spiral arm models change significantly if one moves only
~ 0.6 kpc in galactocentric radius, but ~ 2 kpc in azimuth. There are more and
stronger groups as one approaches the spiral arms. Depending on the spiral
pattern speed, the kinematic imprints are more intense in nearby vicinities or
far from the Sun. Secondly, we present a preliminary study of the kinematic
groups observed by RAVE. This sample will allow us, for the first time, to
study the dependence on Galactic position of the (thin and thick) disc moving
groups. In the solar neighbourhood, we find the same kinematics groups as
detected in previous surveys, but now with better statistics and over a larger
spatial volume around the Sun. This indicates that these structures are indeed
large scale kinematic features.Comment: 4 pages, 3 figures, to appear in the proceedings of "Assembling the
Puzzle of the Milky Way", Le Grand Bornand (April 17-22, 2011), C. Reyle, A.
Robin, M. Schultheis (eds.
Endpoint of the Gregory-Laflamme instability of black strings revisited
We reproduce and extend the previous studies of Lehner and Pretorius of the endpoint of the Gregory-Laflamme instability of black strings in five space-time dimensions. We consider unstable black strings of fixed thickness and different lengths, and in all cases we confirm that at the intermediate stages of the evolution the horizon can be interpreted as a quasistationary self-similar sequence of black strings connecting spherical black holes on different scales. However, we do not find any evidence for a global timescale relating subsequent generations. The endpoint of the instability is the pinch off of the horizon in finite asymptotic time, thus confirming the violation of the weak cosmic censorship conjecture around black string spacetimes
PREFACE: The Milky Way Unravelled by Gaia: GREAT Science from the Gaia Data Releases
International audiencePREFAC
The Low Velocity Wind from the Circumstellar Matter Around the B9V Star sigma Herculis
We have obtained FUSE spectra of sigma Her, a nearby binary system, with a
main sequence primary, that has a Vega-like infrared excess. We observe
absorption in the excited fine structure lines C II* at 1037 A, N II* at 1085
A, and N II** at 1086 A that are blueshifted by as much as ~30 km/sec with
respect to the star. Since these features are considerably narrower than the
stellar lines and broader than interstellar features, the C II and N II are
circumstellar. We suggest that there is a radiatively driven wind, arising from
the circumstellar matter, rather than accretion as occurs around beta Pic,
because of sigma Her's high luminosity. Assuming that the gas is liberated by
collisions between parent bodies at 20 AU, the approximate distance at which
blackbody grains are in radiative equilibrium with the star and at which 3-body
orbits become unstable, we infer dM/dt ~ 6 * 10^-12 M_{sun}/yr. This wind
depletes the minimum mass of parent bodies in less than the estimated age of
the system.Comment: 6 pages, 3 figures, ApJ in pres
BGM FASt: Besan\c{c}on Galaxy Model for Big Data. Simultaneous inference of the IMF, SFH and density in the Solar Neighbourhood
We develop a new theoretical framework to generate Besan\c{c}on Galaxy Model
fast approximate simulations (BGM FASt) to address fundamental questions of the
Galactic structure and evolution performing multi-parameter inference. As a
first application of our strategy we simultaneously infer the IMF, the star
formation history and the stellar mass density in the Solar Neighbourhood. The
BGM FASt strategy is based on a reweighing scheme, that uses a specific
pre-sampled simulation, and on the assumption that the distribution function of
the generated stars in the Galaxy can be described by an analytical expression.
To validate BGM FASt we execute a set of tests. Finally, we use BGM FASt with
an approximate Bayesian computation algorithm to obtain the posterior PDF of
the inferred parameters, by comparing synthetic versus Tycho-2 colour-magnitude
diagrams. Results: The validation shows a very good agreement between BGM FASt
and the standard BGM, with BGM FASt being times faster. By
analysing Tycho-2 data we obtain a thin disc star formation history decreasing
in time and a present rate of . The resulting total
stellar mass density in the Solar Neighbourhood is and the local dark matter density is . For the composite IMF we obtain a slope of
in the mass range between and
. The results of the slope at the high mass range are trustable up
to and highly depend on the choice of the extinction map (obtaining
and respectively,
for two different extinction maps). Systematic uncertainties are not included.
Conclusions: The good performance of BGM FASt demonstrates that it is a very
valuable tool to perform multi-parameter inference using Gaia data releases.Comment: Accepted for publication by A&A. 30 pages (23 pages of main body and
7 pages of Appendixes) , 15 figures and 4 table
Fracciones en la recta numérica: un acercamiento didáctico usando applets
En este trabajo se exponen resultados de las actuaciones de alumnos de educación secundaria que participaron en un estudio cuyo propósito es coadyuvar en la construcción de mejores objetos mentales sobre las fracciones, en el sentido de Freudenthal (1983). Para la indagación se diseñó una secuencia de enseñanza dirigida a estudiantes de 10 a 14 años de edad, apoyada fundamentalmente en el uso de applets construidos con Geogebra. Dos elementos se distinguen en el diseño de los applets: (a) la interfaz gráfica, diseñada con una intención didáctica, con la que interactúa el estudiante, y (b) una colección de rutinas programadas en JavaScript que permiten recoger de una manera no invasiva las acciones de los alumnos en tiempo real. Dicho registro posibilita analizar las respuestas y los procesos usados durante la interacción estudiante/applet
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