4,583 research outputs found
Contact Moishezon threefolds with second Betti number one
We prove that the only contact Moishezon threefold having second Betti number
equal to one is the projective space.Comment: 5 pages. v2: exposition improved as suggested by the referee. To
appear in Archiv der Mat
Maximum solutions of normalized Ricci flows on 4-manifolds
We consider maximum solution , , to the normalized
Ricci flow. Among other things, we prove that, if is a smooth
compact symplectic 4-manifold such that and let
, be a solution to (1.3) on whose Ricci curvature
satisfies that and additionally , then there exists an , and a sequence of points
, , satisfying that, by passing to a
subsequence, , in the -pointed
Gromov-Hausdorff sense for any sequence , where
, , are complete complex hyperbolic orbifolds
of complex dimension 2 with at most finitely many isolated orbifold points.
Moreover, the convergence is in the non-singular part of
and
, where
(resp. ) is the Euler characteristic (resp. signature) of
.Comment: 23 page
Open TURNS: An industrial software for uncertainty quantification in simulation
The needs to assess robust performances for complex systems and to answer
tighter regulatory processes (security, safety, environmental control, and
health impacts, etc.) have led to the emergence of a new industrial simulation
challenge: to take uncertainties into account when dealing with complex
numerical simulation frameworks. Therefore, a generic methodology has emerged
from the joint effort of several industrial companies and academic
institutions. EDF R&D, Airbus Group and Phimeca Engineering started a
collaboration at the beginning of 2005, joined by IMACS in 2014, for the
development of an Open Source software platform dedicated to uncertainty
propagation by probabilistic methods, named OpenTURNS for Open source Treatment
of Uncertainty, Risk 'N Statistics. OpenTURNS addresses the specific industrial
challenges attached to uncertainties, which are transparency, genericity,
modularity and multi-accessibility. This paper focuses on OpenTURNS and
presents its main features: openTURNS is an open source software under the LGPL
license, that presents itself as a C++ library and a Python TUI, and which
works under Linux and Windows environment. All the methodological tools are
described in the different sections of this paper: uncertainty quantification,
uncertainty propagation, sensitivity analysis and metamodeling. A section also
explains the generic wrappers way to link openTURNS to any external code. The
paper illustrates as much as possible the methodological tools on an
educational example that simulates the height of a river and compares it to the
height of a dyke that protects industrial facilities. At last, it gives an
overview of the main developments planned for the next few years
Deformation of LeBrun's ALE metrics with negative mass
In this article we investigate deformations of a scalar-flat K\"ahler metric
on the total space of complex line bundles over CP^1 constructed by C. LeBrun.
In particular, we find that the metric is included in a one-dimensional family
of such metrics on the four-manifold, where the complex structure in the
deformation is not the standard one.Comment: 20 pages, no figure. V2: added two references, filled a gap in the
proof of Theorem 1.2. V3: corrected a wrong statement about Kuranishi family
of a Hirzebruch surface stated in the last paragraph in the proof of Theorem
1.2, and fixed a relevant error in the proof. Also added a reference [24]
about Kuranishi family of Hirzebruch surface
A Kaehler Structure on the Space of String World-Sheets
Let (M,g) be an oriented Lorentzian 4-manifold, and consider the space S of
oriented, unparameterized time-like 2-surfaces in M (string world-sheets) with
fixed boundary conditions. Then the infinite-dimensional manifold S carries a
natural complex structure and a compatible (positive-definite) Kaehler metric h
on S determined by the Lorentz metric g. Similar results are proved for other
dimensions and signatures, thus generalizing results of Brylinski regarding
knots in 3-manifolds. Generalizing the framework of Lempert, we also
investigate the precise sense in which S is an infinite-dimensional complex
manifold.Comment: 13 pages, LaTe
EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6
We present a study of the high-energy diffuse emission observed toward Orion
by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton
Gamma-Ray Observatory. The total exposure by EGRET in this region has increased
by more than a factor of two since a previous study. A simple model for the
diffuse emission adequately fits the data; no significant point sources are
detected in the region studied ( to and ) in either the composite dataset or in two separate
groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion
is found to be for E > 100 MeV,
and the differential emissivity is well-described as a combination of
contributions from cosmic-ray electrons and protons with approximately the
local density. The molecular mass calibrating ratio is .Comment: 16 pages, including 5 figures. 3 Tables as three separate files.
Latex document, needs AASTEX style files. Accepted for publication in Ap
Discovery of a new INTEGRAL source: IGR J19140+0951
IGR J19140+0951 (formerly known as IGR J19140+098) was discovered with the
INTEGRAL satellite in March 2003. We report the details of the discovery, using
an improved position for the analysis. We have performed a simultaneous study
of the 5-100 keV JEM-X and ISGRI spectra from which we can distinguish two
different states. From the results of our analysis we propose that IGR
J19140+0951 is a persistent Galactic X-ray binary, probably hosting a neutron
star although a black hole cannot be completely ruled out.Comment: 4 pages, 4 figures. Accepted for publication in A&A
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