614 research outputs found
The definability criterions for convex projective polyhedral reflection groups
Following Vinberg, we find the criterions for a subgroup generated by
reflections \Gamma \subset \SL^{\pm}(n+1,\mathbb{R}) and its finite-index
subgroups to be definable over where is an integrally
closed Noetherian ring in the field . We apply the criterions for
groups generated by reflections that act cocompactly on irreducible properly
convex open subdomains of the -dimensional projective sphere. This gives a
method for constructing injective group homomorphisms from such Coxeter groups
to \SL^{\pm}(n+1,\mathbb{Z}). Finally we provide some examples of
\SL^{\pm}(n+1,\mathbb{Z})-representations of such Coxeter groups. In
particular, we consider simplicial reflection groups that are isomorphic to
hyperbolic simplicial groups and classify all the conjugacy classes of the
reflection subgroups in \SL^{\pm}(n+1,\mathbb{R}) that are definable over
. These were known by Goldman, Benoist, and so on previously.Comment: 31 pages, 8 figure
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
Transcriptomes of the B and T lineages compared by multiplatform microarray profiling
T and B lymphocytes are developmentally and functionally related cells of the immune system, representing the two major branches of adaptive immunity. Although originating from a common precursor, they play very different roles: T cells contribute to and drive cell-mediated immunity, whereas B cells secrete Abs. Because of their functional importance and well-characterized differentiation pathways, T and B lymphocytes are ideal cell types with which to understand how functional differences are encoded at the transcriptional level. Although there has been a great deal of interest in defining regulatory factors that distinguish T and B cells, a truly genomewide view of the transcriptional differences between these two cells types has not yet been taken. To obtain a more global perspective of the transcriptional differences underlying T and B cells, we exploited the statistical power of combinatorial profiling on different microarray platforms, and the breadth of the Immunological Genome Project gene expression database, to generate robust differential signatures. We find that differential expression in T and B cells is pervasive, with the majority of transcripts showing statistically significant differences. These distinguishing characteristics are acquired gradually, through all stages of B and T differentiation. In contrast, very few T versus B signature genes are uniquely expressed in these lineages, but are shared throughout immune cells.National Institute of Allergy and Infectious Diseases (U.S.) (National Institutes of Health (R24 AI072073
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
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
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
Influence of the confinement geometry on surface superconductivity
The nucleation field for surface superconductivity, , depends on the
geometrical shape of the mesoscopic superconducting sample and is substantially
enhanced with decreasing sample size. As an example we studied circular,
square, triangular and wedge shaped disks. For the wedge the nucleation field
diverges as with decreasing angle () of
the wedge, where is the bulk upper critical field.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev.
Dilation of the Giant Vortex State in a Mesoscopic Superconducting Loop
We have experimentally investigated the magnetisation of a mesoscopic
aluminum loop at temperatures well below the superconducting transition
temperature . The flux quantisation of the superconducting loop was
investigated with a -Hall magnetometer in magnetic field intensities
between . The magnetic field intensity periodicity observed in
the magnetization measurements is expected to take integer values of the
superconducting flux quanta . A closer inspection of the
periodicity, however, reveal a sub flux quantum shift. This fine structure we
interpret as a consequence of a so called giant vortex state nucleating towards
either the inner or the outer side of the loop. These findings are in agreement
with recent theoretical reports.Comment: 12 pages, 5 figures. Accepted for publication in Phys. Rev.
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