Null cone evolution of axisymmetric vacuum spacetimes

We present the details of an algorithm for the global evolution of asymptotically flat, axisymmetric spacetimes, based upon a characteristic initial value formulation using null cones as evolution hypersurfaces. We identify a new static solution of the vacuum field equations which provides an important test bed for characteristic evolution codes. We also show how linearized solutions of the Bondi equations can be generated by solutions of the scalar wave equation, thus providing a complete set of test beds in the weak field regime. These tools are used to establish that the algorithm is second order accurate and stable, subject to a Courant-Friedrichs-Lewy condition. In addition, the numerical versions of the Bondi mass and news function, calculated at scri on a compactified grid, are shown to satisfy the Bondi mass loss equation to second order accuracy. This verifies that numerical evolution preserves the Bianchi identities. Results of numerical evolution confirm the theorem of Christodoulou and Klainerman that in vacuum, weak initial data evolve to a flat spacetime. For the class of asymptotically flat, axisymmetric vacuum spacetimes, for which no nonsingular analytic solutions are known, the algorithm provides highly accurate solutions throughout the regime in which neither caustics nor horizons form.Comment: 25 pages, 6 figure

IMPORT PRICES AND HARD CURRENCY CONSTRAINTS IN EASTERN EUROPE: IMPLICATIONS FOR COARSE GRAIN IMPORTS AND PRODUCTION OF MEAT

The objectives of this study were (a) to determine the degree to which hard currency earnings constrained overall imports and coarse grain imports in command economies; (b) to measure the importance of import prices on grain imports and to trace the link of grain availability to meat production; and (c) to determine how economic and political reforms in the selected countries may have affected the hard currency constraint, the importance of import prices, and grain imports and meat production. The results indicate that import demand was constrained by earnings of hard currency, but was not responsive to world prices, and meat production was affected by total grain availability, including imports.Coarse grain imports, Hard currency, Eastern Europe, Import prices, Meat production, Political reforms, International Relations/Trade,

Colliding black holes from a null point of view: the close limit

We present a characteristic algorithm for computing the perturbations of a Schwarzschild spacetime by means of solving the Teukolsky equations. Our methods and results are expected to have direct bearing on the study of binary black holes presently underway using a fully {\em nonlinear} characteristic code \cite{Gomez98a}.Comment: 2 pages, contribution to the 9th Marcel Grossmann meeting (MG9), Rome, July 200

Physiological Bases of Plant Shrinkage and Its Demographic Implications

Perennial plants are plastic organisms and can vary greatly in size within and between years. While much attention has been paid to the factors that maximize plant growth, plant shrinkage has been bluntly overlooked. Here we study anatomy, physiology, demography and comparative biology to understand how often plants shrink, mechanisms by which plants may internally regulate their architecture to shrink, and shrinkage’s demographic implications. We explored belowground resource uptake, hydraulic transport and demographic contributions of shrinkage of individuals of Cryptantha flava (Boraginaceae) in the Great Basin desert. We used a database with \u3e700 species to explore shrinkage’s frequency and ecological consequences by examining demographic parameters such as population growth rate, longevity and reproductive output for species with and without shrinkage. We show that C. flava can forage the heterogeneous desert space by uptaking via some roots but not others, and that individuals become sectored with age (i.e., individual roots transport resources only to specific canopy regions). The switch in hydraulic design with ontogeny may explain why large individuals are more likely to shrink after droughts than juveniles. Perturbation analyses demonstrated that large individuals contribute very little to the population growth rate (λ) and that growth to large classes can negatively affect λ in C. flava. The comparative analyses indicated that shrinkage correlates positively with lifespan, survival, fecundity and growth. Finally, we found a significant number of candidate herbaceous species where shrinkage might be under selection because in them shrinking increases λ. We have linked anatomical traits, physiological mechanisms and population dynamics to offer a mechanistic explanation of how and why plants shrink. We argue that sectoriality in Cryptantha flava may allow individuals to minimize respiratory demands during harsh conditions by shedding sectors. Thus shrinkage, being preferable over mortality, is a survival mechanism that helps individuals buffer stochasticity. The finding that large individuals of C. flava contribute very little to λ in comparison to medium-sized individuals and that positive shrinkage vital-rate sensitivities occur frequently in the plant kingdom, together with recent demographic analytical developments, make exploring plant shrinkage a very promising venue of ecological and evolutionary research

Nanocrystalline glass-like carbon thin films may be an useful tool in nerve cells regeneration

Abstract en el libro de Abstract de la International Conference, p. 99The interest in carbon nanomaterials with high transparency and electrical conductivity has grown within the last decade in view of a wide variety of applications, including biocompatible sensors, diagnostic devices and bioelectronic implants. The aim of this work is to test the biocompatibility of particular nanometer-thin nanocrystalline glass-like carbon films (NGLC), a disordered structure of graphene flakes joined by carbon matrixUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. We thank Prof. Arenas, Karolinska Institutet, Stockholm, Sweden, for SN4741 cell line. R.G.V. gratefully acknowledges Spanish Ministry of Science and Innovation for funding through a Ramon y Cajal fellowship

Extending Message Passing Interface Windows to Storage

This work presents an extension to MPI supporting the one-sided communication model and window allocations in storage. Our design transparently integrates with the current MPI implementations, enabling applications to target MPI windows in storage, memory or both simultaneously, without major modifications. Initial performance results demonstrate that the presented MPI window extension could potentially be helpful for a wide-range of use-cases and with low-overhead

An improved habitat suitability index for the great crested newt Triturus cristatus

Great crested newts Triturus cristatus are a European protected species whose conservation depends on the provision and protection of their breeding habitat. The species is in decline internationally, partly due to loss of suitable breeding habitat (European Environment Agency, 2019). A habitat suitability index (HSI) developed in 2000 is extensively used in great crested newt conservation to assess breeding habitat quality in the UK. Here, we introduce a new HSI with an improved ability to reflect T. cristatus presence/absence in UK ponds. This proposed HSI is easier to use, requires less data and predicts T. cristatus presence/absence better than the previous index. To inform the new index, we used a dual approach to identify the relative importance of environmental criteria to predict T. cristatus presence/absence. Firstly, we conducted a survey of 288 HSI users to assess the perceived strengths and limitations of the existing index. Secondly, we analysed national datasets of T. cristatus presence/absence and associated environmental data. Using these findings, we then tested various index modifications. The final modifications of the new HSI include (i) using an arithmetic (instead of geometric) mean, to reduce calculation errors and allow compensation between variables; (ii) excluding water quality and waterfowl impact, as these lacked significant power to predict T. cristatus presence/absence and were deemed inaccurate by HSI users; and (iii) changing the scoring relationship for pond area to better reflect current data and provide scores for ponds over 2000m2. We compared scores from the new and original HSIs using an independent dataset for validation, showing that the new HSI better reflects T. cristatus presence/absence (larger effect sizes and R-squared values) in comparison to the old HSI. Adopting this improved HSI will enable more effective conservation of the protected species via better-informed decision-making and monitoring

Ill-posedness in the Einstein equations

It is shown that the formulation of the Einstein equations widely in use in numerical relativity, namely, the standard ADM form, as well as some of its variations (including the most recent conformally-decomposed version), suffers from a certain but standard type of ill-posedness. Specifically, the norm of the solution is not bounded by the norm of the initial data irrespective of the data. A long-running numerical experiment is performed as well, showing that the type of ill-posedness observed may not be serious in specific practical applications, as is known from many numerical simulations.Comment: 13 pages, 3 figures, accepted for publication in Journal of Mathematical Physics (to appear August 2000

Una marca de agua inteligente aplicada al dinero electrónico

International audienceEl uso de las marcas de agua se ha incrementado, principalmente por la necesidad de proteger los derechos de autor, detener copias ilegales o medir la integridad de los datos de ciertos archivos. Es bien sabido que se puede insertar código ejecutable en imágenes, pero hasta ahora solamente se ha estudiado como una amenaza de seguridad para el usuario. Nosotros proponemos utilizar esta característica de manera segura para expandir las aplicaciones actuales de las marcas de agua, dándoles exibilidad a través del código ejecutable. Presentamos el modelo de marca de agua inteligente para resolver problemas de incompatibilidad de funciones y demostramos cómo se puede aplicar este modelo a un escenario de dinero electrónico. En dicho escenario el beneciario puede manejar diferentes implementaciones de dinero electrónico mediante una aplicación estándar. Como parte de este escenario, también proponemos una máquina expendedora de dinero electrónico para ofrecer una opción de pago a los usuarios que no tienen cuenta bancaria

Action principles for higher and fractional spin gravities

We review various off-shell formulations for interacting higher-spin systems in dimensions 3 and 4. Associated with higher-spin systems in spacetime dimension 4 is a Chern-Simons action for a superconnection taking its values in a direct product of an infinite-dimensional algebra of oscillators and a Frobenius algebra. A crucial ingredient of the model is that it elevates the rigid closed and central two-form of Vasiliev's theory to a dynamical 2-form and doubles the higher-spin algebra, thereby considerably reducing the number of possible higher spin invariants and giving a nonzero effective functional on-shell. The two action principles we give for higher-spin systems in 3D are based on Chern-Simons and BF models. In the first case, the theory we give unifies higher-spin gauge fields with fractional-spin fields and an internal sector. In particular, Newton's constant is related to the coupling constant of the internal sector. In the second case, the BF action we review gives the fully nonlinear Prokushkin-Vasiliev, bosonic equations for matter-coupled higher spins in 3D. We present the truncation to a single, real matter field relevant in the Gaberdiel-Gopakumar holographic duality. The link between the various actions we present is the fact that they all borrow ingredients from Topological Field Theory. It has bee conjectured that there is an underlying and unifying 2-dimensional first-quantised description of the previous higher-spin models in 3D and 4D, in the form of a Cattaneo-Felder-like topological action containing fermionic fields.Comment: 41+1 pages. References added and reorganized, corrected typos, last paragraph of section 2 re-written. Contribution to the proceedings of the International Workshop on Higher Spin Gauge Theories (4-6 November 2015, Singapore