3,845 research outputs found
On Nonexistence of Magnetic Charge in Pure Yang-Mills Theories
We prove that magnetic charge does not exist as a physical observable on the
physical Hilbert space of the pure SU(2) gauge theory. The abelian magnetic
monopoles seen in lattice simulations are then interpreted as artifacts of
gauge fixing. The apparent physical scaling properties of the monopole density
in the continuum limit observed on the lattice are attributed to the correct
scaling properties of physical objects - magnetic vortices, as first argued by
Greensite et. al. We can show that a local gauge transformation of a certain
type can " create" abelian monopole-antimonopole pairs along magnetic vortices.
This gauge transformation exists in pure SU(N) gauge theory at any .Comment: Some references and comments adde
A numerical analysis of the relation between CTOD and fatigue crack growth
El cálculo de la vida a fatiga durante la etapa de propagación de la grieta se suele realizar relacionando da/dN con ΔK. Sin embargo, la influencia que en estos análisis tiene el parámetro ΔK debe recaer en algún otro parámetro no lineal cercano al frente de la grieta, ya que estos son los que realmente controlan la velocidad de crecimiento de la grieta. El principal objetivo del presente artÃculo es intentar mejorar la comprensión del crecimiento de grieta en fatiga empleando el desplazamiento de apertura de la punta de la grieta (CTOD). Este parámetro no ha sido muy empleado en el problema del cierre de grieta y su propagación en fatiga, teniendo un gran potencial. Por este motivo, se ha realizado un análisis numérico para un amplio rango de cargas de amplitud constante en dos aleaciones de aluminio (6016-T4 y 6082-T6). Cuando no se considera el contacto entre los flancos de la grieta se puede observar una relación bien definida entre el valor máximo de CTOD y ΔK, lo cual indica que no existe influencia de la relación de cargas y valida la mecánica de la fractura elástica lineal. Se ha encontrado una relación lineal entre los valores de CTOD y ΔK al considerar una doble escala logarÃtmica. Los valores de CTOD cuando se considera el contacto se superpone a los resultados sin contacto, únicamente cuando se emplea el ΔK efectivo, lo cual valida el concepto del cierre de grieta. Se ha encontrado una relación lineal entre da/dN y CTOD cuando se considera una doble escala logarÃtmica para la aleación de aluminio 6082-T6.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
A note on the Markoff condition and central words
We define Markoff words as certain factors appearing in bi-infinite words satisfying the Markoff condition. We prove that these words coincide with central words, yielding a new characterization of Christoffel words
Bidimensionality of Geometric Intersection Graphs
Let B be a finite collection of geometric (not necessarily convex) bodies in
the plane. Clearly, this class of geometric objects naturally generalizes the
class of disks, lines, ellipsoids, and even convex polygons. We consider
geometric intersection graphs GB where each body of the collection B is
represented by a vertex, and two vertices of GB are adjacent if the
intersection of the corresponding bodies is non-empty. For such graph classes
and under natural restrictions on their maximum degree or subgraph exclusion,
we prove that the relation between their treewidth and the maximum size of a
grid minor is linear. These combinatorial results vastly extend the
applicability of all the meta-algorithmic results of the bidimensionality
theory to geometrically defined graph classes
An evaluation of location management procedures
This paper gives a comparative description of two scenarios for location management in a mobile telecommunications system. The first scenario uses fixed location and paging areas. Mobiles perform a location update as they enter a new location area. The second scenario uses a time-out based location updating scheme. Mobiles start their timer as they leave the paging area they are currently registered in. As the timer elapses, the mobile performs a location update. Both scenarios also differ in the way paging is performed. In the first scenario it is only necessary to page in the location area the mobile is currently registered in. In order to do this efficiently, the paging is done in a 2-step fashion: mobiles are paged first in the paging area in which they were registered in, and next in the entire location area they are registered in. In the second scenario the mobile is paged in multiple steps: first in the paging area it is registered in, next in a circle of paging areas surrounding that area, and so on, until the mobile is found, or the number of steps has reached a certain upper limit. Results comprise a quantitative and qualitative comparison of these scenarios, and guidelines for optimal applicatio
Backbone colorings for networks: tree and path backbones
We introduce and study backbone colorings, a variation on classical vertex colorings: Given a graph and a spanning subgraph of (the backbone of ), a backbone coloring for and is a proper vertex coloring of in which the colors assigned to adjacent vertices in differ by at least two. We study the cases where the backbone is either a spanning tree or a spanning path
Planar graph coloring avoiding monochromatic subgraphs: trees and paths make things difficult
We consider the problem of coloring a planar graph with the minimum number of colors such that each color class avoids one or more forbidden graphs as subgraphs. We perform a detailed study of the computational complexity of this problem
Comment on Mott Scattering in strong Laser Field
The first differential cross section for Mott scattering of a Dirac-Volkov
electron is reviewed. The expression (26) derived by Szymanowski et al.
[Physical Review A {\bf 56}, 3846,(1997)] is corrected. In particular, we
disagree with the expression of they obtained and
we give the exact coefficients multiplying the various Bessel functions
appearing in the scattering differential cross section.Comment: 16 pages, LaTex, added reference for section 3, corrected some
typosReport no: LPHEA 02-0
Connecting Terminals and 2-Disjoint Connected Subgraphs
Given a graph and a set of terminal vertices we say that a
superset of is -connecting if induces a connected graph, and
is minimal if no strict subset of is -connecting. In this paper we prove
that there are at most minimal -connecting sets when and that
these can be enumerated within a polynomial factor of this bound. This
generalizes the algorithm for enumerating all induced paths between a pair of
vertices, corresponding to the case . We apply our enumeration algorithm
to solve the {\sc 2-Disjoint Connected Subgraphs} problem in time
, improving on the recent algorithm of Cygan et
al. 2012 LATIN paper.Comment: 13 pages, 1 figur
A numerical analysis of the plastic wake influence on plasticity induced crack closure
Fatigue crack closure has been studied by means of finite element method since long time
ago. Most work has been performed considering bi-dimensional models. Lately, the use of threedimensional
models has been extended. Nevertheless, the methodology employed has been taken from
that developed for bi-dimensional cases.
There are a great number of previous bi-dimensional studies which analyse different numerical
parameters and optimise them. The current computational capabilities allow a comprehensive study of
the influence of the different modelling parameters in a similar way to those studies carried out with bidimensional
models, with the advantage, that the evolution along the thickness of the analysed
parameters can be taken into consideration.
In particular, one of the key issues is related to the plastic wake length which is developed during the
previous loading cycles. This residual stresses have a great influence on the crack opening and closure
values. As the numerical analysis are complex and computationally expensive, the length of the
simulated wake is a critical parameter.
In this work, a comprehensive study of the effect of the plastic wake in fatigue crack closure is made.
On this purpose, a CT aluminium specimen has been modelled three-dimensionally and several
calculations have been made in order to evaluate the influence of the simulated plastic wake length. The
numerical analysis is made in terms of crack closure and opening values as in terms of the stress and
strain fields near the crack front.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
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