377 research outputs found
Optimal eigenvalue estimate for the Dirac-Witten operator on bounded domains with smooth boundary
Eigenvalue estimate for the Dirac-Witten operator is given on bounded domains
(with smooth boundary) of spacelike hypersurfaces satisfying the dominant
energy condition, under four natural boundary conditions (MIT, APS, modified
APS, and chiral conditions). This result is a generalisation of Friedrich's
inequality for the usual Dirac operator. The limiting cases are also
investigated.Comment: 2007, 18 pages, submitted 02 June 200
The Dirac operator on untrapped surfaces
We establish a sharp extrinsic lower bound for the first eigenvalue of the
Dirac operator of an untrapped surface in initial data sets without apparent
horizon in terms of the norm of its mean curvature vector. The equality case
leads to rigidity results for the constraint equations with spherical boundary
as well as uniqueness results for constant mean curvature surfaces in Minkowski
space.Comment: 16 page
IntegraciĂłn continua y su aplicaciĂłn a gvHIDRA utilizando Selenium y Hudson
Hijazi, YMT. (28-0). IntegraciĂłn continua y su aplicaciĂłn a gvHIDRA utilizando Selenium y Hudson. http://hdl.handle.net/10251/14854.Archivo delegad
Extended Formulations in Mixed-integer Convex Programming
We present a unifying framework for generating extended formulations for the
polyhedral outer approximations used in algorithms for mixed-integer convex
programming (MICP). Extended formulations lead to fewer iterations of outer
approximation algorithms and generally faster solution times. First, we observe
that all MICP instances from the MINLPLIB2 benchmark library are conic
representable with standard symmetric and nonsymmetric cones. Conic
reformulations are shown to be effective extended formulations themselves
because they encode separability structure. For mixed-integer
conic-representable problems, we provide the first outer approximation
algorithm with finite-time convergence guarantees, opening a path for the use
of conic solvers for continuous relaxations. We then connect the popular
modeling framework of disciplined convex programming (DCP) to the existence of
extended formulations independent of conic representability. We present
evidence that our approach can yield significant gains in practice, with the
solution of a number of open instances from the MINLPLIB2 benchmark library.Comment: To be presented at IPCO 201
The Cauchy problems for Einstein metrics and parallel spinors
We show that in the analytic category, given a Riemannian metric on a
hypersurface and a symmetric tensor on , the metric
can be locally extended to a Riemannian Einstein metric on with second
fundamental form , provided that and satisfy the constraints on
imposed by the contracted Codazzi equations. We use this fact to study the
Cauchy problem for metrics with parallel spinors in the real analytic category
and give an affirmative answer to a question raised in B\"ar, Gauduchon,
Moroianu (2005). We also answer negatively the corresponding questions in the
smooth category.Comment: 28 pages; final versio
Spectral Bounds for Dirac Operators on Open Manifolds
We extend several classical eigenvalue estimates for Dirac operators on
compact manifolds to noncompact, even incomplete manifolds. This includes
Friedrich's estimate for manifolds with positive scalar curvature as well as
the author's estimate on surfaces.Comment: pdflatex, 14 pages, 3 figure
Instantons and Killing spinors
We investigate instantons on manifolds with Killing spinors and their cones.
Examples of manifolds with Killing spinors include nearly Kaehler 6-manifolds,
nearly parallel G_2-manifolds in dimension 7, Sasaki-Einstein manifolds, and
3-Sasakian manifolds. We construct a connection on the tangent bundle over
these manifolds which solves the instanton equation, and also show that the
instanton equation implies the Yang-Mills equation, despite the presence of
torsion. We then construct instantons on the cones over these manifolds, and
lift them to solutions of heterotic supergravity. Amongst our solutions are new
instantons on even-dimensional Euclidean spaces, as well as the well-known
BPST, quaternionic and octonionic instantons.Comment: 40 pages, 2 figures v2: author email addresses and affiliations adde
World Health Organization Guidelines for Management of Acute Stress, PTSD, and Bereavement: Key Challenges on the Road Ahead
Wietse Tol and colleagues discuss some of the key challenges for implementation of new WHO guidelines for stress-related mental health disorders in low- and middle-income countries. Please see later in the article for the Editors' Summar
The Energy Application Domain Extension for CityGML: enhancing interoperability for urban energy simulations
The road towards achievement of the climate protection goals requires, among the rest, a thorough rethinking of the
energy planning tools (and policies) at all levels, from local to global. Nevertheless, it is in the cities where the largest
part of energy is produced and consumed, and therefore it makes sense to focus the attention particularly on the cities
as they yield great potentials in terms of energy consumption reduction and efficiency increase. As a direct
consequence, a comprehensive knowledge of the demand and supply of energy resources, including their spatial
distribution within urban areas, is therefore of utmost importance. Precise, integrated knowledge about 3D urban
space, i.e. all urban (above and underground) features, infrastructures, their functional and semantic characteristics, and
their mutual dependencies and interrelations play a relevant role for advanced simulation and analyses.
As a matter of fact, what in the last years has proven to be an emerging and effective approach is the adoption of
standard-based, integrated semantic 3D virtual city models, which represent an information hub for most of the abovementioned
needs. In particular, being based on open standards (e.g. on the CityGML standard by the Open Geospatial
Consortium), virtual city models firstly reduce the effort in terms of data preparation and provision. Secondly, they offer
clear data structures, ontologies and semantics to facilitate data exchange between different domains and applications.
However, a standardised and omni-comprehensive urban data model covering also the energy domain is still missing
at the time of writing (January 2018). Even CityGML falls partially short when it comes to the definition of specific
entities and attributes for energy-related applications.
Nevertheless, and starting from the current version of CityGML (i.e. 2.0), this article describes the conception and the
definition of an Energy Application Domain Extension (ADE) for CityGML. The Energy ADE is meant to offer a unique
and standard-based data model to fill, on one hand, the above-mentioned gap, and, on the other hand, to allow for
both detailed single-building energy simulation (based on sophisticated models for building physics and occupant
behaviour) and city-wide, bottom-up energy assessments, with particular focus on the buildings sector. The overall
goal is to tackle the existing data interoperability issues when dealing with energy-related applications at urban scale.
The article presents the rationale behind the Energy ADE, it describes its main characteristics, the relation to other
standards, and provides some examples of current applications and case studies already adopting it
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