Hamiltonian Dynamics of Linearly Polarized Gowdy Models Coupled to Massless Scalar Fields

The purpose of this paper is to analyze in detail the Hamiltonian formulation for the compact Gowdy models coupled to massless scalar fields as a necessary first step towards their quantization. We will pay special attention to the coupling of matter and those features that arise for the three-handle and three-sphere topologies that are not present in the well studied three torus case -in particular the polar constraints that come from the regularity conditions on the metric. As a byproduct of our analysis we will get an alternative understanding, within the Hamiltonian framework, of the appearance of initial and final singularities for these models.Comment: Final version to appear in Classical and Quantum Gravit

A Generalization of Chetaev's Principle for a Class of Higher Order Non-holonomic Constraints

The constraint distribution in non-holonomic mechanics has a double role. On one hand, it is a kinematic constraint, that is, it is a restriction on the motion itself. On the other hand, it is also a restriction on the allowed variations when using D'Alembert's Principle to derive the equations of motion. We will show that many systems of physical interest where D'Alembert's Principle does not apply can be conveniently modeled within the general idea of the Principle of Virtual Work by the introduction of both kinematic constraints and variational constraints as being independent entities. This includes, for example, elastic rolling bodies and pneumatic tires. Also, D'Alembert's Principle and Chetaev's Principle fall into this scheme. We emphasize the geometric point of view, avoiding the use of local coordinates, which is the appropriate setting for dealing with questions of global nature, like reduction.Comment: 27 pages. Journal of Mathematical Physics (to zappear

Symmetries in Classical Field Theory

The multisymplectic description of Classical Field Theories is revisited, including its relation with the presymplectic formalism on the space of Cauchy data. Both descriptions allow us to give a complete scheme of classification of infinitesimal symmetries, and to obtain the corresponding conservation laws.Comment: 70S05; 70H33; 55R10; 58A2

Avances de investigación en frutales tropicales promisorios para el departamento de Meta.

El estudio presenta la recolección de germoplasma divididos en 4 grupos de la siguiente manera: en el grupo 1 se presentan los frutales tradicionales no cultivados en el departamento del Meta, en el grupo 2 se presentan los frutales tropicales promisorios poco conocidos en el mercado como arazá, borojó, chontaduro, cocona y carambolo, en el grupo 3 se presentan los frutales con alta potencialidad en el mercado nacional e internacional como el langostino y el camu-camú y en el grupo 4 se presentan los frutales poco conocidos en los mercados y que no se cultivan en huertos o son de reciente introducción a los Llanos. También se presentan las recomendaciones para la realización de germoplasma de frutales promisorios y exóticos para los Llanos Orientales, entre otros

Testing the comet nature of main belt comets. The spectra of 133P/Elst-Pizarro and 176P/LINEAR

We present the visible spectrum of MBCs 133P/Elst-Pizarro and 176P/LINEAR, as well as three Themis family asteroids: (62) Erato, (379), Huenna and (383) Janina, obtained in 2007 using three telescopes at "El Roque de los Muchachos"' Observatory, in La Palma, Spain, and the 8m Kueyen (UT2) VLT telescope at Cerro Paranal, Chile. The spectra of 133P and 176P resemble best those of B-type asteroid and are very similar to those of Themis family members and are significantly different from the spectrum of comet 162P/Siding-Spring and most of the observed cometary nuclei. CN gas emission is not detected in the spectrum of 133P. We determine an upper limit for the CN production rate Q(CN) = $= 2.8 \times 10^{21}$ mol/s, three orders of magnitude lower than the Q(CN) of Jupiter family comets observed at similar heliocentric distances. The spectra of 133P/Elst-Pizarro and 176P/LINEAR confirm that they are likely members of the Themis family of asteroids, fragments that probably retained volatiles, and unlikely have a cometary origin in the trans-neptunian belt or the Oort cloud.Comment: Paper sumbmited to A&A. 7 pages and 6 figure

XANES and EXAFS study of the local order in nanocrystalline yttria-stabilized zirconia

The local order around Zr and Y atoms of nanocrystalline yttria-stabilized zirconia (YSZ) powders with different grain sizes has been investigated by x-ray absorption spectroscopies. The samples were prepared by means of mechanical alloying with or without subsequent sintering treatment and also by milling commercial YSZ. Our study is motivated by the interest in the electrical properties of grain boundaries and the controversy about the level of disorder in the intergrain regions in nanocrystalline YSZ. The x-ray absorption near edge structure (XANES) analysis indicates that the local order of all the sintered samples is independent of the grain size. This is confirmed by the analysis of the extended x-ray absorption fine structure, which points out also that, in contrast to that found in sintered samples, the local order around the cation in the samples milled without further sintering treatment extends only to the first coordination shell. Finally, the results of ab initio Zr K-edge XANES calculations lead us to conclude that the observed changes of the shape of the white line are not related to a phase transformation but reflects the short-range order present in the as-milled samples

Human bony labyrinth is an indicator of population history and dispersal from Africa.

The dispersal of modern humans from Africa is now well documented with genetic data that track population history, as well as gene flow between populations. Phenetic skeletal data, such as cranial and pelvic morphologies, also exhibit a dispersal-from-Africa signal, which, however, tends to be blurred by the effects of local adaptation and in vivo phenotypic plasticity, and that is often deteriorated by postmortem damage to skeletal remains. These complexities raise the question of which skeletal structures most effectively track neutral population history. The cavity system of the inner ear (the so-called bony labyrinth) is a good candidate structure for such analyses. It is already fully formed by birth, which minimizes postnatal phenotypic plasticity, and it is generally well preserved in archaeological samples. Here we use morphometric data of the bony labyrinth to show that it is a surprisingly good marker of the global dispersal of modern humans from Africa. Labyrinthine morphology tracks genetic distances and geography in accordance with an isolation-by-distance model with dispersal from Africa. Our data further indicate that the neutral-like pattern of variation is compatible with stabilizing selection on labyrinth morphology. Given the increasingly important role of the petrous bone for ancient DNA recovery from archaeological specimens, we encourage researchers to acquire 3D morphological data of the inner ear structures before any invasive sampling. Such data will constitute an important archive of phenotypic variation in present and past populations, and will permit individual-based genotype-phenotype comparisons

Diagnóstico al sector de alimentos balanceados para animales en Colombia

La Facultad de Administración de la Universidad del Rosario viene adelantando desde el año 2004 una serie de estudios orientados a comprender, de una mejor manera, la perdurabilidad empresarial. Una diversidad de sectores han sido analizados: financiero, salud, comercio, confecciones y aeronáutico, entre otros. La principal herramienta implementada ha sido el Análisis Estructural de Sectores Estratégicos (AESE), cuya metodología permite percibir, de una mejor manera, el estado del sector a través de cuatro pruebas: hacinamiento, panorama competitivo, análisis de fuerzas de mercado y estudio de competidores. En la primera fase de la investigación se realizaron estudios en diferentes sectores económicos; la siguiente fase consistirá en realizar un análisis cruzado entre sectores y entre países, el cual permitirá aportar elementos para la generación de una teoría sobre la perdurabilidad empresarial. De manera paralela, se seguirán realizando estudios de sectores con estudiantes de pregrado y posgrado. El presente estudio fue desarrollado, conjuntamente, con estudiantes de la Especialización en Gerencia de Negocios Internacionales del convenio Universidad del Rosario-Universidad CES, y es resultado del trabajo elaborado para la asignatura Análisis Estratégico, coordinada por el profesor Hugo Alberto Rivera, director de la línea de investigación en perdurabilidad empresarial. El sector estudiado es el de las empresas de alimentos balanceados para animales, base del sector pecuario en Colombia; estas se encargan de convertir materias primas de origen agrícola en alimento para la producción de animales. La producción de alimentos balanceados ha mantenido una dinámica importante en el país durante los últimos años, jalonada, principalmente, por el incremento en el consumo de carne de pollo, y, en menor proporción, el de otras líneas de producción (peces y codornices, entre otros). Las turbulencias indicadas en el presente informe exponen la complejidad, dinamismo e incertidumbre que se tiene al momento de reflejar la toma de decisiones en cuanto a inversión, ventas, fusiones e integraciones. Esto se debe a que el sector estudiado es un sector donde la incertidumbre sobre los eventos futuros está dada por factores exógenos que no son atribuibles al control humano, sino al control de la naturaleza; para esto, las empresas ajustan sus condiciones de producción y estrategias de venta de acuerdo a las necesidades de sus consumidores finales, evidenciando así un alto componente de investigación y desarrollo junto a la versatilidad de adaptación a los cambios del entorno, y desencadenando, a su vez, una imitación de las empresas pequeñas frente a las tradicionales y representativas del sector. Para poder realizar un correcto análisis, es necesario partir de las diferentes especies que tienen explotación pecuaria en Colombia, agrupándolas en grandes grupos representativos con la finalidad de reconocer las potencialidades de cada uno de los actores y poder hacer una evaluación con un mayor grado de certeza. A lo largo del documento, se podrá evidenciar una lectura crítica, basada en los datos analizados y con opiniones fundamentadas en la lectura del mercado y en la literatura proporcionada por las agremiaciones y entes reguladores

Neutron polarizabilities investigated by quasi-free Compton scattering from the deuteron

Measuring Compton scattered photons and recoil neutrons in coincidence, quasi-free Compton scattering by the neutron has been investigated at MAMI (Mainz) at $theta^{lab}_\gamma=136^o$ in an energy range from 200 to 400 MeV. From the data a polarizability difference of $\alpha_n - \beta_n = 9.8 \pm 3.6(stat)^{+2.1}_{-1.1}(syst)\pm 2.2(model)$ in units of $10^{-4}fm^3$ has been determined. In combination with the polarizability sum $\alpha_n+\beta_n= 15.2\pm 0.5$ deduced from photo absorption data, the neutron electric and magnetic polarizabilities, $\alpha_n=12.5\pm 1.8(stat)^{+1.1}_{-0.6}(syst)\pm 1.1(model)$ and $\beta_n = 2.7\mp 1.8(stat)^{+0.6}_{-1.1}(syst)\mp 1.1(model)$, are obtained