The Hawking-Penrose singularity theorem for C1,1C^{1,1}-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 $C^{1, 1}$-regularity. We formulate appropriate weak versions of the strong energy condition and genericity condition for $C^{1,1}$-metrics, and of $C^0$-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 $C^1$-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

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

Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions

Background Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals. Results Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall. Conclusions The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions