1,299 research outputs found
Multi-object spectroscopy of low redshift EIS clusters. I
We report the results of the first multi-object spectroscopic observations at
the Danish 1.54m telescope at La Silla, Chile. Observations of five cluster
candidates from the ESO Imaging Survey Cluster Candidate Catalog are described.
From these observations we confirm the reality of the five clusters with
measured redshifts of 0.11<=z<=0.35. We estimate velocity dispersions in the
range 294-621km/s indicating rather poor clusters. This, and the measured
cluster redshifts are consistent with the results of the matched filter
procedure applied to produce the Cluster Candidate Catalog.Comment: 7pages, accepted by Astronomy and Astrophysic
A2163: Merger events in the hottest Abell galaxy cluster II. Subcluster accretion with galaxy-gas separation
Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster
medium (ICM) that exhibits extraordinary properties, including an exceptionally
high X-ray luminosity, average temperature, and a powerful and extended radio
halo. The irregular and complex morphology of its gas and galaxy structure
suggests that this cluster has recently undergone major merger events that
involve two or more cluster components. In this paper, we study the gas
structure and dynamics by means of spectral-imaging analysis of X-ray data
obtained from XMM-Newton and Chandra observations. From the evidence of a cold
front, we infer the westward motion of a cool core across the E-W elongated
atmosphere of the main cluster A2163-A. Located close to a galaxy over-density,
this gas 'bullet' appears to have been spatially separated from its galaxy (and
presumably dark matter component) as a result of high-velocity accretion.
From gas brightness and temperature profile analysis performed in two
opposite regions of the main cluster, we show that the ICM has been
adiabatically compressed behind the crossing 'bullet' possibly because of shock
heating, leading to a strong departure of the ICM from hydrostatic equilibrium
in this region. Assuming that the mass estimated from the Yx proxy best
indicates the overall mass of the system and that the western cluster sector is
in approximate hydrostatic equilibrium before subcluster accretion, we infer a
merger scenario between two subunits of mass ratio 1:4, leading to a present
total system mass of M500 . The exceptional
properties of A2163 present various similarities with those of 1E0657-56, the
so-called 'bullet-cluster'. These similarities are likely to be related to a
comparable merger scenario.Comment: A&A, in pres
Mannose-Specific Lectins from Marine Algae: Diverse Structural Scaffolds Associated to Common Virucidal and Anti-Cancer Properties.
To date, a number of mannose-specific lectins have been isolated and characterized from seaweeds, especially from red algae. In fact, man-specific seaweed lectins consist of different structural scaffolds harboring a single or a few carbohydrate-binding sites which specifically recognize mannose-containing glycans. Depending on the structural scaffold, man-specific seaweed lectins belong to five distinct structurally-related lectin families, namely (1) the griffithsin lectin family (beta-prism I scaffold); (2) the Oscillatoria agardhii agglutinin homolog (OAAH) lectin family (beta-barrel scaffold); (3) the legume lectin-like lectin family (beta-sandwich scaffold); (4) the Galanthus nivalis agglutinin (GNA)-like lectin family (beta-prism II scaffold); and, (5) the MFP2-like lectin family (MFP2-like scaffold). Another algal lectin from Ulva pertusa, has been inferred to the methanol dehydrogenase related lectin family, because it displays a rather different GlcNAc-specificity. In spite of these structural discrepancies, all members from the five lectin families share a common ability to specifically recognize man-containing glycans and, especially, high-mannose type glycans. Because of their mannose-binding specificity, these lectins have been used as valuable tools for deciphering and characterizing the complex mannose-containing glycans from the glycocalyx covering both normal and transformed cells, and as diagnostic tools and therapeutic drugs that specifically recognize the altered high-mannose N-glycans occurring at the surface of various cancer cells. In addition to these anti-cancer properties, man-specific seaweed lectins have been widely used as potent human immunodeficiency virus (HIV-1)-inactivating proteins, due to their capacity to specifically interact with the envelope glycoprotein gp120 and prevent the virion infectivity of HIV-1 towards the host CD4+ T-lymphocyte cells in vitro
On the Nature of the EIS Candidate Clusters: Confirmation of z<0.6 candidates
We use public V-band imaging data from the wide-angle surveys conducted by
the ESO Imaging Survey project (EIS) to further investigate the nature of the
EIS galaxy cluster candidates. These were originally identified by applying a
matched-filter algorithm which used positional and photometric data of the
galaxy sample extracted from the I-band survey images. In this paper, we apply
the same technique to the galaxy sample extracted from V-band data and compare
the new cluster detections with the original ones. We find that ~75% of the
low-redshift cluster candidates (z<0.6) are detected in both passbands and
their estimated redshifts show good agreement with the scatter in the redshift
differences being consistent with the estimated errors of the method. For the
``robust'' I-band detections the matching frequency approaches ~85%. We also
use the available (V-I) color to search for the red sequence of early-type
galaxies observed in rich clusters over a broad range of redshifts. This is
done by searching for a simultaneous overdensity in the three-dimensional
color-projected distance space. We find significant overdensities for ~75% of
the ``robust'' candidates with z_I<0.6. We find good agreement between the
characteristic color associated to the detected "red sequence" and that
predicted by passive evolution galaxy models for ellipticals at the redshift
estimated by the matched-filter. The results presented in this paper show the
usefulness of color data, even of two-band data, to both tentatively confirm
cluster candidates and to select possible cluster members for spectroscopic
observations. Based on the present results, we estimate that ~150 EIS clusters
with z_I<0.6 are real, making it one of the largest samples of galaxy clusters
in this redshift range currently available in the southern hemisphere.Comment: 11 pages, 10 figures, accepted for publication in A&
New spectroscopic confirmations of high-redshift galaxy clusters
We present new spectroscopic data in the field of five high-redshift (z>=0.6)
candidate galaxy clusters, drawn from the EIS Cluster Candidate Catalog. A
total of 327 spectra were obtained using FORS1 at the VLT, out of which 266 are
galaxies with secure redshifts. In this paper, we use these data for confirming
the existence of overdensities in redshift space at the approximate same
location as the matched-filter detections in the projected distribution of
galaxies from the EIS I-band imaging survey. The spectroscopic redshifts,
associated to these overdensities, are consistent but, in general, somewhat
lower than those predicted by the matched-filter technique. Combining the
systems presented here with those analyzed earlier, we have spectroscopically
confirmed a total of nine overdensities in the redshift range 0.6<z<1.3,
providing an important first step in building an optically-selected,
high-redshift sample for more detailed studies, complementing those based on
the few available X-ray selected systems.Comment: 14 pages, Accepted for publication in A&
A refined stable restriction theorem for vector bundles on quadric threefolds
Let E be a stable rank 2 vector bundle on a smooth quadric threefold Q in the
projective 4-space P. We show that the hyperplanes H in P for which the
restriction of E to the hyperplane section of Q by H is not stable form, in
general, a closed subset of codimension at least 2 of the dual projective
4-space, and we explicitly describe the bundles E which do not enjoy this
property. This refines a restriction theorem of Ein and Sols [Nagoya Math. J.
96, 11-22 (1984)] in the same way the main result of Coanda [J. reine angew.
Math. 428, 97-110 (1992)] refines the restriction theorem of Barth [Math. Ann.
226, 125-150 (1977)].Comment: Ann. Mat. Pura Appl. 201
Phase transition curves for mesoscopic superconducting samples
We compute the phase transition curves for mesoscopic superconductors.
Special emphasis is given to the limiting shape of the curve when the magnetic
flux is large. We derive an asymptotic formula for the ground state of the
Schr\"odinger equation in the presence of large applied flux. The expansion is
shown to be sensitive to the smoothness of the domain. The theoretical results
are compared to recent experiments.Comment: 8 pages, 1 figur
Certainty Closure: Reliable Constraint Reasoning with Incomplete or Erroneous Data
Constraint Programming (CP) has proved an effective paradigm to model and
solve difficult combinatorial satisfaction and optimisation problems from
disparate domains. Many such problems arising from the commercial world are
permeated by data uncertainty. Existing CP approaches that accommodate
uncertainty are less suited to uncertainty arising due to incomplete and
erroneous data, because they do not build reliable models and solutions
guaranteed to address the user's genuine problem as she perceives it. Other
fields such as reliable computation offer combinations of models and associated
methods to handle these types of uncertain data, but lack an expressive
framework characterising the resolution methodology independently of the model.
We present a unifying framework that extends the CP formalism in both model
and solutions, to tackle ill-defined combinatorial problems with incomplete or
erroneous data. The certainty closure framework brings together modelling and
solving methodologies from different fields into the CP paradigm to provide
reliable and efficient approches for uncertain constraint problems. We
demonstrate the applicability of the framework on a case study in network
diagnosis. We define resolution forms that give generic templates, and their
associated operational semantics, to derive practical solution methods for
reliable solutions.Comment: Revised versio
Vortex matter in superconducting mesoscopic disks: Structure, magnetization, and phase transitions
The dense vortex matter structure and associated magnetization are calculated
for type-II superconducting mesoscopic disks. The magnetization exhibits
generically first-order phase transitions as the number of vortices changes by
one and presents two well-defined regimes: A non-monotonous evolution of the
magnitude of the magnetization jumps signals the presence of a vortex glass
structure which is separated by a second-order phase transition at
from a condensed state of vortices (giant vortex) where the magnitude of the
jumps changes monotonously. We compare our results with Hall magnetometry
measurements by Geim et al. (Nature 390, 259 (1997)) and claim that the
magnetization exhibits clear traces of the presence of these vortex glass
states.Comment: 4 pages, 3 figure
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