Canonical Equivalence of a Generic 2D Dilaton Gravity Model and a Bosonic String Theory

We show that a canonical tranformation converts, up to a boundary term, a generic 2d dilaton gravity model into a bosonic string theory with a Minkowskian target space.Comment: LaTeX file, 9 pages, no figure

Salida de doble en plancha con pirueta en barra de Manuel Carballo y Rafael Martínez

En el entrenamiento díario de los gimnastas del equipo nacional se utilizan muchas veces la comparación entre gimnastas que realizan un elemento y otros que están aprendiendo a a realizar este mismo elemento. Como apoyo a esta labor se ha realizado una comparativa en la ejecución que una salida de barra de dos gimnastas del equipo nacional. Tomando a una como la ejecución modelo, definida por el seleccionador nacional, se han comparado los datos obtenidos por el otro gimnasta para intentar determinar que factor técnica dificultad de la buena realización de este elemento por parte del gimnasta que lo está aprendiendo

Quantitative Estimates of Environmental Effects on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies

A simple model is constructed to evaluate the change of star formation rate of a disk galaxy due to environmental effects in clusters of galaxies. Three effects, (1) tidal force from the potential well of the cluster, (2) increase of external pressure when the galaxy plows into the intracluster medium, (3) high-speed encounters between galaxies, are investigated. General analysis indicates that the star formation rate increases significantly when the pressure of molecular clouds rises above $\sim 3\times 10^5 cm^{-3} K$ in $\sim 10^8$ yr. The tidal force from the potential well of the cluster increases pressures of molecular clouds in a disk galaxy infalling towards the cluster center. Before the galaxy reaches the cluster center, the star formation rate reaches a maximum. The peak is three to four times larger than the initial value. If this is the main mechanism of the Butcher-Oemler effect, blue galaxies are expected to be located within $\sim 300$ kpc from the center of the cluster. However this prediction is inconsistent with the recent observations. The increase of external pressure when the galaxy plows into the intracluster medium does not change star formation rate of a disk galaxy significantly. The velocity perturbation induced by a single high-speed encounter between galaxies is too small to affect star formation rate of a disk galaxy, while successive high-speed encounters (galaxy harassment) trigger star formation activity because of the accumulation of gas in the galaxy center. Therefore, the galaxy harassment remains as the candidate for a mechanism of the Butcher-Oemler effect.Comment: 12 pages, 13 figures. To be published in Ap

Análisis comparativo para la búsqueda de un patrón en la realización de un doble mortal atrás con pirueta de salida en anillas

El presente estudio ha sido realizado gracias a la colaboración del INEF de Madrid con el Equipo Nacional de Gimnasia Artística. Empleando fotogrametría tridimensional se ha comparado la técnica de ejecución de un doble mortal atrás con pirueta de salida en anillas de 3 gimnastas. El patrón de eficacia que vamos a utilizar la nota que el entrenador, haciendo las veces de juez, va a determinar, así catalogamos en un primer momento las ejecuciones analizadas. Como premisas suponemos que una mayor altura del Centro de Gravedad (CDG) en la suelta va a dar más tiempo de vuelo y una velocidad angular en el extremo distal (en este caso el pie) mayor va a permitir más rotación en dicho tiempo de vuelo. Como conclusión obtuvimos que la velocidad de la punta del pie en el suspensión vertical del impulso previo determinará la velocidad angular final y la altura máxima del CDG. Así también, el momento y empuje de las anillas determinará la altura y trayectoria del movimiento.Peer Reviewe

Glide Effects on Low Speed Unmanned Aerial Vehicles with Ice Formation

This paper builds on the research that was previously presented and defended at a conference and adds to the depth of glide characteristics and aerodynamics. The basic assumed theory of low speed flight is used as the starting point and determined if this holds true for low speed. Traditionally, flight has always been about achieving faster and high flight operations. Unmanned Aerial Vehicles (UAV) are not typically designed to fly fast, the construction and power units are limiting, added to the lack of complexity in propulsion systems prevents high speeds in most cases. Here, aerodynamic data for Ice on leading edge and top surfaces were analysed, the characteristics obtained and thus the limitations. Furthermore, the influences of this to for unmanned aerial vehicles when subjected to surface environmental conditions such as ice on the leading edge and upper surface. Tested in a wind tunnel to see how theory compares with practice at various speed including take-off, landing and operational applications where head winds substantially alter parameters and this is data used to determine glide paths for landing. It also recommends design and operational changes to limited situations

Psychologie sociale et psychologie environnementale : confrontations et complémentarités

International audienc

Diffeomorphisms, Noether Charges and Canonical Formalism in 2D Dilaton Gravity

We carry out a parallel study of the covariant phase space and the conservation laws of local symmetries in two-dimensional dilaton gravity. Our analysis is based on the fact that the Lagrangian can be brought to a form that vanishes on-shell giving rise to a well-defined covariant potential for the symplectic current. We explicitly compute the symplectic structure and its potential and show that the requirement to be finite and independent of the Cauchy surface restricts the asymptotic symmetries.Comment: 14 pages, latex with psfig macro, one figur

Properties of galaxy dark matter halos from weak lensing

We present the results of a study of weak lensing by galaxies based on 45.5 deg$^2$ of $R_C$ band imaging data from the Red-Sequence Cluster Survey (RCS). We present the first weak lensing detection of the flattening of galaxy dark matter halos. We use a simple model in which the ellipticity of the halo is $f$ times the observed ellipticity of the lens. We find a best fit value of $f=0.77^{+0.18}_{-0.21}$, suggesting that the dark matter halos are somewhat rounder than the light distribution. The fact that we detect a significant flattening implies that the halos are well aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of $=0.33^{+0.07}_{-0.09}$, in fair agreement with results from numerical simulations of CDM. This result provides strong support for the existence of dark matter, as an isotropic lensing signal is excluded with 99.5% confidence. We also study the average mass profile around the lenses, using a maximum likelihood analysis. We consider two models for the halo mass profile: a truncated isothermal sphere (TIS) and an NFW profile. We adopt observationally motivated scaling relations between the lens luminosity and the velocity dispersion and the extent of the halo. The best fit NFW model yields a mass $M_{200}=(8.4\pm0.7\pm0.4)\times 10^{11} h^{-1} M_\odot$ and a scale radius $r_s=16.2^{+3.6}_{-2.9} h^{-1}$ kpc. This value for the scale radius is in excellent agreement with predictions from numerical simulations for a halo of this mass.Comment: Significantly revised version, accepted for publication in ApJ 11 pages, 6 figure

Free Fields for Chiral 2D Dilaton Gravity

We give an explicit canonical transformation which transforms a generic chiral 2D dilaton gravity model into a free field theory.Comment: LaTeX file, 4 pages, to appear in Phys. Rev.

Catalog of Galaxy Morphology in Four Rich Clusters: Luminosity Evolution of Disk Galaxies at 0.33<z<0.83

Hubble Space Telescope (HST) imaging of four rich, X-ray luminous, galaxy clusters (0.33<z<0.83) is used to produce quantitative morphological measurements for galaxies in their fields. Catalogs of these measurements are presented for 1642 galaxies brighter than F814W(AB)=23.0 . Galaxy luminosity profiles are fitted with three models: exponential disk, de Vaucouleurs bulge, and a disk-plus-bulge hybrid model. The best fit is selected and produces a quantitative assessment of the morphology of each galaxy: the principal parameters derived being B/T, the ratio of bulge to total luminosity, the scale lengths and half-light radii, axial ratios, position angles and surface brightnesses of each component. Cluster membership is determined using a statistical correction for field galaxy contamination, and a mass normalization factor (mass within boundaries of the observed fields) is derived for each cluster. In the present paper, this catalog of measurements is used to investigate the luminosity evolution of disk galaxies in the rich-cluster environment. Examination of the relations between disk scale-length and central surface brightness suggests, under the assumption that these clusters represent a family who share a common evolutionary history and are simply observed at different ages, that there is a dramatic change in the properties of the small disks (h < 2 kpc). This change is best characterized as a change in surface brightness by about 1.5 magnitude between z=0.3 and z=0.8 with brighter disks at higher redshifts.Comment: 53 pages, including 13 figures and 7 tables. Accepted for publication in the Astrophysical Journal Supplement Serie