275 research outputs found
The Hawking-Penrose singularity theorem for -Lorentzian metrics
We show that the Hawking--Penrose singularity theorem, and the generalisation
of this theorem due to Galloway and Senovilla, continue to hold for Lorentzian
metrics that are of -regularity. We formulate appropriate weak
versions of the strong energy condition and genericity condition for
-metrics, and of -trapped submanifolds. By regularisation, we
show that, under these weak conditions, causal geodesics necessarily become
non-maximising. This requires a detailed analysis of the matrix Riccati
equation for the approximating metrics, which may be of independent interest.Comment: Minor amendments in v4: Removed non-equivalent condition from Def.
2.2 and adapted Lemma 3.5 and the proof of Lemma 3.
On the Geroch-Traschen class of metrics
We compare two approaches to semi-Riemannian metrics of low regularity. The maximally 'reasonable' distributional setting of Geroch and Traschen is shown to be consistently contained in the more general setting of nonlinear distributional geometry in the sense of Colombea
The Phase Effect in Electronic Stopping: A Survey of the Contributing Physical Processes
The phase effect in electronic stopping deals with the question whether the energy loss of an ion due to the interaction with electrons depends on the state of aggregation of the target. It is commonly accepted that charge changing collisions of the projectile and changes in the electronic states of the target contribute to the phase effect In addition, the energy loss measurements might possibly be influenced by different impact parameter selection in the two experiments (solid and gas phase). Quantitative results of our calculations show that generally the impact parameter selection inherently present in a transmission experiment is quenched by the inevitable multiple scattering of the projectiles. Thus, electronic excitation and ionization in the projectile and the target are the only processes that contribute significantly to the phase effect
The future is not always open
We demonstrate the breakdown of several fundamentals of Lorentzian causality
theory in low regularity. Most notably, chronological futures (defined
naturally using locally Lipschitz curves) may be non-open, and may differ from
the corresponding sets defined via piecewise -curves. By refining the
notion of a causal bubble from [CG:12],we characterize spacetimes for which
such phenomena can occur, and also relate these to the possibility of deforming
causal curves of positive length into timelike curves (push-up). The phenomena
described here are, in particular, relevant for recent synthetic approaches to
low regularity Lorentzian geometry where, in the absence of a differentiable
structure, causality has to be based on locally Lipschitz curves.Comment: Minor amendments. Final version. 17 pages, 4 figure
Geodesics in spacetimes with expanding impulsive gravitational waves
We study geodesic motion in expanding spherical impulsive gravitational waves
propagating in a Minkowski background. Employing the continuous form of the
metric we find and examine a large family of geometrically preferred geodesics.
For the special class of axially symmetric spacetimes with the spherical
impulse generated by a snapping cosmic string we give a detailed physical
interpretation of the motion of test particles.Comment: 12 pages, Revtex, final versio
Aichelburg-Sexl boost of an isolated source in general relativity
A study of the Aichelburg--Sexl boost of the Schwarzschild field is described
in which the emphasis is placed on the field (curvature tensor) with the metric
playing a secondary role. This is motivated by a description of the Coulomb
field of a charged particle viewed by an observer whose speed relative to the
charge approaches the speed of light. Our approach is exemplified by carrying
out an Aichelburg-- Sexl type boost on the Weyl vacuum gravitational field due
to an isolated axially symmetric source. Detailed calculations of the boosts
transverse and parallel to the symmetry axis are given and the results, which
differ significantly, are discussed.Comment: 25 pages, LateX2
Isomorphisms of algebras of Colombeau generalized functions
We show that for smooth manifolds X and Y, any isomorphism between the
special algebra of Colombeau generalized functions on X, resp. Y is given by
composition with a unique Colombeau generalized function from Y to X. We also
identify the multiplicative linear functionals from the special algebra of
Colombeau generalized functions on X to the ring of Colombeau generalized
numbers. Up to multiplication with an idempotent generalized number, they are
given by an evaluation map at a compactly supported generalized point on X.Comment: 10 page
Symmetries and geodesics in (anti-)de Sitter spacetimes with nonexpanding impulsive waves
We consider a class of exact solutions which represent nonexpanding impulsive
waves in backgrounds with nonzero cosmological constant. Using a convenient
5-dimensional formalism it is shown that these spacetimes admit at least three
global Killing vector fields. The same geometrical approach enables us to find
all geodesics in a simple explicit form and describe the effect of impulsive
waves on test particles. Timelike geodesics in the axially-symmetric
Hotta-Tanaka spacetime are studied in detail. It is also demonstrated that for
vanishing cosmological constant, the symmetries and geodesics reduce to those
for well-known impulsive pp-waves.Comment: 16 pages, 3 figures, LaTeX 2e. To appear in Class. Quantum Gra
Evolución de las infecciones de transmisión sexual en la ciudad de Valencia. Periodo 2004-2009
Las infecciones de transmisión sexual (ITS) han aumentado en los últimos años en toda la Unión Europea. La puesta en marcha de sistemas de notificación y registro de las enfermedades de declaración obligatoria (AVE) y sistemas de notificación automatizada de resultados de microbiología(RedMiVa) han permitido una mejora de la exhaustividad en la detección de casos y por tanto una mejor identificación y prevención de la transmisión de estas enfermedades.Un diseño clásico de vigilancia de salud pública para los registros de Sífilis del periodo 2005-2009 y de Infección gonocócica del periodo 2004-2009, nos permite analizar las características de los sujetos, su evolución temporal y hábitos sexuales en la ciudad de Valencia. Durante el periodo fueron notificados 321 casos de Sífilis y 596 de Infección Gonocócica. La evolución temporal de la incidencia pasó de 2,13 (2005) a 15,60 (2009) para la Sífilis; y de 2,13 (2004) a 26,36 (2009) para la Infección gonocócica. La introducción de la notificación microbiológica incrementó la detección de nuevos casos de ITS.La desproporción por género muestra una evolución creciente de la Razón de masculinidad. La Sífilis presenta cifras superiores entre los inmigrantes tanto en varones como en mujeres, mientras que para la Infección Gonocócica destaca una incidencia superior en mujeres autóctonas que entre las inmigrantes. El factor sexual de riesgomás frecuente para ambas enfermedades fue la existencia de parejas múltiples. El 42,68% de los pacientes con Sífilis y el 36,91% de los pacientes con Infección Gonocócica indicaron esta conducta.La tendencia creciente observada, con independencia de lo anterior, es concordante con informes de similar origen en nuestro país. No obstante, nuestras cifras de Incidencia Anual son sustancialmente mayores que las registradas en el conjunto de la nación.Esta evolución sugiere la necesidad de incrementar las estrategias activas de prevención y uso de preservativos. De igual modo la detección temprana y el tratamiento correcto de las ITS requieren, en nuestra opinión, unamayor difusión de la información epidemiológica sobre ITS a los profesionales clínicos
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