Homogeneous and locally homogeneous solutions to symplectic curvature flow

J. Streets and G. Tian recently introduced symplectic curvature flow, a geometric flow on almost K\"ahler manifolds generalising K\"ahler-Ricci flow. The present article gives examples of explicit solutions to this flow of non-K\"ahler structures on several nilmanifolds and on twistor fibrations over hyperbolic space studied by J. Fine and D. Panov. The latter lead to examples of non-K\"ahler static solutions of symplectic curvature flow which can be seen as analogues of K\"ahler-Einstein manifolds in K\"ahler-Ricci flow.Comment: 15 page

Semiparametrically efficient rank-based inference for shape I. optimal rank-based tests for sphericity

We propose a class of rank-based procedures for testing that the shape matrix $\mathbf{V}$ of an elliptical distribution (with unspecified center of symmetry, scale and radial density) has some fixed value ${\mathbf{V}}_0$; this includes, for ${\mathbf{V}}_0={\mathbf{I}}_k$, the problem of testing for sphericity as an important particular case. The proposed tests are invariant under translations, monotone radial transformations, rotations and reflections with respect to the estimated center of symmetry. They are valid without any moment assumption. For adequately chosen scores, they are locally asymptotically maximin (in the Le Cam sense) at given radial densities. They are strictly distribution-free when the center of symmetry is specified, and asymptotically so when it must be estimated. The multivariate ranks used throughout are those of the distances--in the metric associated with the null value ${\mathbf{V}}_0$ of the shape matrix--between the observations and the (estimated) center of the distribution. Local powers (against elliptical alternatives) and asymptotic relative efficiencies (AREs) are derived with respect to the adjusted Mauchly test (a modified version of the Gaussian likelihood ratio procedure proposed by Muirhead and Waternaux [Biometrika 67 (1980) 31--43]) or, equivalently, with respect to (an extension of) the test for sphericity introduced by John [Biometrika 58 (1971) 169--174]. For Gaussian scores, these AREs are uniformly larger than one, irrespective of the actual radial density. Necessary and/or sufficient conditions for consistency under nonlocal, possibly nonelliptical alternatives are given. Finite sample performances are investigated via a Monte Carlo study.Comment: Published at http://dx.doi.org/10.1214/009053606000000731 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

"Movimientos en Andalucía para prohibir los transgénicos" : pasos para incidir en la prohibición de los transgénicos en un territorio. El caso de Andalucía

Una vez levantada la moratoria europea para la siembra de cultivos genéticamente modificados en 2004, varias organizaciones que habían trabajado en la lucha contra los transgénicos entran en una nueva fase de lucha, en la que se buscan alianzas civiles más estables en Andalucía. Pero no es hasta noviembre de 2007, fecha en la que tienen lugar en Sevilla la "3º Conferencia Internacional de Coexistencia de Organismos Modificados Genéticamente" organizada por la Comisión Europea y la contra-conferencia "Contaminación genética: la imposible coexistencia", el momento en el que se establecen las bases del trabajo coordinado que luego impulsarían el trabajo de la PALT.El objetivo general de la PALT es conseguir una Andalucía Libre de Transgénicos, libre de cultivos comerciales y de experimentación y libre de importaciones de granos y alimentos elaborados a partir de cultivos transgénicos. Para contribuir a este objetivo general se ha puesto en marcha la campaña "Con Soberanía Alimentaria, sin Transgénicos" que se concreta en tres objetivos específicos: 1) Incidencia y presión política; 2) información y sensibilización a la ciudadanía; y 3) Denuncia, visibilización y movilización

Existencia y unicidad de soluciones periódicas para una ecuación de Liénard discontinua lineal a trozos

En esta comunicación se establece un resultado de existencia y unicidad de soluciones periódicas en una ecuación de tipo Liénard, donde las funciones involucradas son lineales a trozos discontinuas. Para ello, se ha transformado la ecuación inicial en un sistema plano de Liénard y se ha seguido el método convexo de Filippov para extender las órbitas que alcanzan la línea de discontinuidad. Nos hemos limitado a considerar sistemas que no poseen soluciones deslizantes (sliding motions) en el sentido de Filippov

Solving moving-boundary problems with the wavelet adaptive radial basis functions method

Moving boundaries are associated with the time-dependent problems where the momentary position of boundaries needs to be determined as a function of time. The level set method has become an effective tool for tracking, modelling and simulating the motion of free boundaries in fluid mechanics, computer animation and image processing. This work extends our earlier work on solving moving boundary problems with adaptive meshless methods. In particular, the objective of this paper is to investigate numerical performance the radial basis functions (RBFs) methods, with compactly supported basis and with global basis, coupled with a wavelet node refinement technique and a greedy trial space selection technique. Numerical simulations are provided to verify the effectiveness and robustness of RBFs methods with different adaptive techniques

Material calavera

En el mes de octubre de 2010 los proyectos “Arte Libre y Sin Barrotes y Matapalo Cartonera”, coordinaron una semana de trabajo conjunto en el interior del Centro de Rehabilitación de Varones de Guayaquil. El objetivo fundamental de esta labor consistía en trabajar junto a los internos del Pabellón ‘El Buen Samaritano’ un álbum de memoria en el cuál se plasmaran las “historias” de los internos, a partir de objetos que apelaban a sus recuerdos

Asymmetric Network Effects

When platforms compete for consumers, two types of consumer heterogeneity will matter: consumers value the presence of other consumers on a platform differently, and consumers contribute to the value of the platform differently. The optimal discriminatory pricing policy for platforms will depend on whether those two dimensions of consumer heterogeneity are positively or negatively correlated, which is an empirical question. In a companion paper (Cantillon and Yin, 2008), we study membership decisions of trading firms for two competing exchanges: LIFFE and DTB. Our analysis shows that different traders care about liquidity differently. In this paper, we estimate the heterogeneous contribution to liquidity by different types. We combine the estimates from both papers of heterogeneous preferences and contributions to liquidity

Moving-boundary problems solved by adaptive radial basis functions

The objective of this paper is to present an alternative approach to the conventional level set methods for solving two-dimensional moving-boundary problems known as the passive transport. Moving boundaries are associated with time-dependent problems and the position of the boundaries need to be determined as a function of time and space. The level set method has become an attractive design tool for tracking, modeling and simulating the motion of free boundaries in fluid mechanics, combustion, computer animation and image processing. Recent research on the numerical method has focused on the idea of using a meshless methodology for the numerical solution of partial differential equations. In the present approach, the moving interface is captured by the level set method at all time with the zero contour of a smooth function known as the level set function. A new approach is used to solve a convective transport equation for advancing the level set function in time. This new approach is based on the asymmetric meshless collocation method and the adaptive greedy algorithm for trial subspaces selection. Numerical simulations are performed to verify the accuracy and stability of the new numerical scheme which is then applied to simulate a bubble that is moving, stretching and circulating in an ambient flow to demonstrate the performance of the new meshless approach. (C) 2010 Elsevier Ltd. All rights reserved