13,015 research outputs found
Mean Curvature Flow of Spacelike Graphs
We prove the mean curvature flow of a spacelike graph in of a map from a closed Riemannian
manifold with to a complete Riemannian manifold
with bounded curvature tensor and derivatives, and with
sectional curvatures satisfying , remains a spacelike graph,
exists for all time, and converges to a slice at infinity. We also show, with
no need of the assumption , that if , or if and
, constant, any map is trivially
homotopic provided where
, in case , and
in case . This largely extends some known results for
constant and compact, obtained using the Riemannian structure
of , and also shows how regularity theory on the mean
curvature flow is simpler and more natural in pseudo-Riemannian setting then in
the Riemannian one.Comment: version 5: Math.Z (online first 30 July 2010). version 4: 30 pages:
we replace the condition by the the weaker one .
The proofs are essentially the same. We change the title to a shorter one. We
add an applicatio
Dynamics of the giant planets of the solar system in the gaseous proto-planetary disk and relationship to the current orbital architecture
We study the orbital evolution of the 4 giant planets of our solar system in
a gas disk. Our investigation extends the previous works by Masset and
Snellgrove (2001) and Morbidelli and Crida (2007, MC07), which focussed on the
dynamics of the Jupiter-Saturn system. The only systems that we found to reach
a steady state are those in which the planets are locked in a quadruple mean
motion resonance (i.e. each planet is in resonance with its neighbor). In total
we found 6 such configurations. For the gas disk parameters found in MC07,
these configurations are characterized by a negligible migration rate. After
the disappearance of the gas, and in absence of planetesimals, only two of
these six configurations (the least compact ones) are stable for a time of
hundreds of millions of years or more. The others become unstable on a
timescale of a few My. Our preliminary simulations show that, when a
planetesimal disk is added beyond the orbit of the outermost planet, the
planets can evolve from the most stable of these configurations to their
current orbits in a fashion qualitatively similar to that described in Tsiganis
et al. (2005).Comment: The Astronomical Journal (17/07/2007) in pres
Functional kernel estimators of conditional extreme quantiles
We address the estimation of "extreme" conditional quantiles i.e. when their
order converges to one as the sample size increases. Conditions on the rate of
convergence of their order to one are provided to obtain asymptotically
Gaussian distributed kernel estimators. A Weissman-type estimator and kernel
estimators of the conditional tail-index are derived, permitting to estimate
extreme conditional quantiles of arbitrary order.Comment: arXiv admin note: text overlap with arXiv:1107.226
Effective models of quantum gravity induced by Planck scale modifications in the covariant quantum algebra
In this paper we introduce a modified covariant quantum algebra based in the
so-called Quesne-Tkachuk algebra. By means of a deformation procedure we arrive
at a class of higher derivative models of gravity. The study of the particle
spectra of these models reveals an equivalence with the physical content of the
well-known renormalizable and super-renormalizable higher derivative gravities.
The particle spectrum exhibits the presence of spurious complex ghosts and, in
light of this problem, we suggest an interesting interpretation in the context
of minimal length theories. Also, a discussion regarding the non-relativistic
potential energy is proposed.Comment: Small corrections were made; improved figures; results unchanged;
published versio
Reaction of potato cultivars to Meloidogyne Hapla and M. Morocciensis.
Edição dos Proceedings do 6th International Congress of Nematology, Cape Town, South Africa, May 2014
Structural properties of crumpled cream layers
The cream layer is a complex heterogeneous material of biological origin
which forms spontaneously at the air-milk interface. Here, it is studied the
crumpling of a single cream layer packing under its own weight at room
temperature in three-dimensional space. The structure obtained in these
circumstances has low volume fraction and anomalous fractal dimensions. Direct
means and noninvasive NMR imaging technique are used to investigate the
internal and external structure of these systems.Comment: 9 pages, 4 figures, accepted in J. Phys. D: Appl. Phy
Planning a sustainable reverse logistics system: balancing costs with environmental and social concerns
The present work aims to support tactical and operational planning decisions of reverse logistics systems while considering economical, environmental and social objectives. In the literature, when addressing such systems economical aspects have been often used, while environmental concerns have been only recently emerging. The social component is the one less studied, and rarely the combination of the three concerns has been analyzed. This work address the three objectives and was motivated by the challenge of supporting decisions makers when managing a real case study of a recyclable waste collection system, where strategic decisions on the number and location of depots, vehicles and containers were taken beforehand. Tactical and operational decisions are studied involving the establishment of service areas for each depot and the definition and scheduling of collection routes for each vehicle. Such decisions should represent a compromise solution between the three objectives considered and support a sustainable reverse logistics plan. A multi-objective solution approach based on mixed-integer linear programming models is developed. Trade-offs between the objectives are discussed. Moreover the solutions obtained when each objective is tackled individually are compared between themselves and with the balanced solution.info:eu-repo/semantics/publishedVersio
Economic and environmental concerns in planning recyclable waste collection systems
This paper addresses the planning of recyclable waste collection systems while accounting for economic and environmental concerns. Service areas and vehicle routes are defined for multiple-depot logistics networks where different products have to be collected. The problem is modeled as a multi-product, multi-depot vehicle routing problem with two objective functions: distance and CO2 emissions minimization. A decomposition solution method is developed and applied to a real case-study. Six scenarios are studied regarding different service areas configuration and different objective functions. Savings up to 22% in distance and 27% in CO2 emissions are achieved, excelling economical and environmental goals.info:eu-repo/semantics/publishedVersio
T-Duality in 2-D Integrable Models
The non-conformal analog of abelian T-duality transformations relating pairs
of axial and vector integrable models from the non abelian affine Toda family
is constructed and studied in detail.Comment: 14 pages, Latex, v.2 misprints corrected, reference added, to appear
in J. Phys.
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