Mostrando recursos 141 - 160 de 487

  1. Observational and Numerical Simulation Study of a Sequence of Eight Atmospheric Density Currents in Northern Spain

    Soler Duffour, Maria Rosa; Udina, Mireia; Ferreres Soler, Enriqueta
    A sequence of eight atmospheric density current fronts occurred in consecutive days are identified and analyzed using micrometeorological time series and numerical simulations. Observations were collected in the context of the INTERCLE project, which took place from September 2002 to November 2003 at the CIBA (Research Centre for the Lower Atmosphere) site located over the northern Spanish plateau. Numerical simulations used the Weather Research and Forecast (WRF) model with fine horizontal resolution (1 km). Both observations and simulations agree that the arrival of the density currents are characterized by a sharp change in temperature, wind velocity, wind direction and specific...

  2. Observational and Numerical Simulation Study of a Sequence of Eight Atmospheric Density Currents in Northern Spain

    Soler Duffour, Maria Rosa; Udina, Mireia; Ferreres Soler, Enriqueta
    A sequence of eight atmospheric density current fronts occurred in consecutive days are identified and analyzed using micrometeorological time series and numerical simulations. Observations were collected in the context of the INTERCLE project, which took place from September 2002 to November 2003 at the CIBA (Research Centre for the Lower Atmosphere) site located over the northern Spanish plateau. Numerical simulations used the Weather Research and Forecast (WRF) model with fine horizontal resolution (1 km). Both observations and simulations agree that the arrival of the density currents are characterized by a sharp change in temperature, wind velocity, wind direction and specific...

  3. Cobalt-56 gamma-ray emission lines from the type Ia supernova 2014J

    Churazov, Eugene; Sunyaev, Rashid; Isern Vilaboy, Jordi; Knodlseder, Jurgen; Jean, Pierre; Lebrun, François; Chugai, Nikolai; Grebenev, Sergei; Bravo Guil, Eduardo; Sazonov, Sergei; Renaud, Matthieu
    A type Ia supernova is thought to be a thermonuclear explosion of either a single carbon–oxygen white dwarf or a pair of merging white dwarfs. The explosion fuses a large amount of radioactive 56Ni. After the explosion, the decay chain from 56Ni to 56Co to 56Fe generates gamma-ray photons, which are reprocessed in the expanding ejecta and give rise to powerful optical emission. Here we report the detection of 56Co lines at energies of 847 and 1,238 kiloelectronvolts and a gamma-ray continuum in the 200–400 kiloelectronvolt band from the type Ia supernova 2014J in the nearby galaxy M82. The line...

  4. Comparison of theoretical white dwarf cooling timescales (Research Note)

    Salaris, Maurizio; Althaus, Leandro Gabriel; García-Berro Montilla, Enrique
    Context. An accurate assessment of white dwarf cooling times is paramount so that white dwarf cosmochronology of Galactic populations can be put on more solid grounds. This issue is particularly relevant in view of the enhanced observational capabilities provided by the next generation of extremely large telescopes, that will offer more avenues to use white dwarfs as probes of Galactic evolution and test-beds of fundamental physics. Aims. We estimate for the first time the consistency of results obtained from independent evolutionary codes for white dwarf models with fixed mass and chemical stratification, when the same input physics is employed in...

  5. The post-merger magnetized evolution of white dwarf binaries: The double-degenerate channel of sub-Chandrasekhar type Ia supernovae and the formation of magnetized white dwarfs

    Ji, Suoqing; Fisher, Robert T.; García-Berro Montilla, Enrique; Tzeferacos, Petros; Jordan, George C.; Lee, Dongwook; Loren Aguilar, Pablo; Cremer, Pascal; Behrends, Jan
    Type Ia supernovae (SNe Ia) play a crucial role as standardizable cosmological candles, though the nature of their progenitors is a subject of active investigation. Recent observational and theoretical work has pointed to merging white dwarf binaries, referred to as the double-degenerate channel, as the possible progenitor systems for some SNe Ia. Additionally, recent theoretical work suggests that mergers which fail to detonate may produce magnetized, rapidly rotating white dwarfs. In this paper, we present the first multidimensional simulations of the post-merger evolution of white dwarf binaries to include the effect of the magnetic field. In these systems, the two...

  6. Automatic source detection in astronomical images

    Masias Moyset, Marc
    The use of automatic algorithms to detect astronomical sources (stars, galaxies, gas, dust or cosmic rays) becomes of great importance because of the increasing amount of astronomical images and the inefficiency and inaccuracy of manual inspection. We exhaustively analyze the state of the art on this topic, presenting a new classification of techniques and pointing out their main strengths and weaknesses. A complementary quantitative evaluation of some of the most remarkable methods found in the literature is also provided. Moreover, we present three different proposals based on different strategies to detect faint sources in radio images, and another proposal to...

  7. Astronomia e Astrofísica em figuras

    Petry, Mauricio Gasparin

  8. The effects of metallicity on the Galactic disk population of white dwarfs

    Cojocaru, Elena Ruxandra; Torres Gil, Santiago; Isern Vilaboy, Jordi; García-Berro Montilla, Enrique
    Context. It has been known for a long time that stellar metallicity plays a significant role in the determination of the ages of the different Galactic stellar populations, when main sequence evolutionary tracks are employed. Aims. Here, we analyze the role that metallicity plays on the white dwarf luminosity function of the Galactic disk, which is often used to determine its age. Methods. We employ a Monte Carlo population synthesis code that accounts for the properties of the population of Galactic disk white dwarfs. Our code incorporates the most up-to-date evolutionary cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient...

  9. O ensino de fundamentos de astronomia e astrofísica na modalidade a distância para alunos de graduação

    Müller, Alexei Machado
    O número de cursos na modalidade a distância tem aumentado consideravelmente no mundo, porém existe um grande receio por parte de muitos que o ensino nessa modalidade tenha qualidade inferior ao apresentado na modalidade presencial. Contudo a qualidade do ensino não decorre da presença de todos os envolvidos num mesmo local, e sim da implementação de ações que facilitem o processo de aprendizagem. Esse trabalho teve como objetivo produzir um módulo didático, em hipermídia, para a disciplina de Fundamentos de Astronomia e Astrofísica, a ser ministrada na modalidade a distância aos alunos do curso de licenciatura em Física e a...

  10. A search for neutrino emission from the Fermi bubbles with the ANTARES telescope

    Adrian Martinez, Silvia; Albert, A.; Al Samarai, Imen; André, Michel; Anton, G.; Anvar, S.; Ardid, M.; Astraatmadja, T.; Baret, B.; Basa, S.; Bertin, V.; Biagi, S.; Bogazzi, C.; Bouhou, B.; Brunner, J.; Morganti, M.; Schmidt, J.; Stolarczyk, Th.
    Analysis of the Fermi-LAT data has revealed two extended structures above and below the Galactic Centre emitting gamma rays with a hard spectrum, the so-called Fermi bubbles. Hadronic models attempting to explain the origin of the Fermi bubbles predict the emission of high-energy neutrinos and gamma rays with similar fluxes. The ANTARES detector, a neutrino telescope located in the Mediterranean Sea, has a good visibility to the Fermi bubble regions. Using data collected from 2008 to 2011 no statistically significant excess of events is observed and therefore upper limits on the neutrino flux in TeV range from the Fermi bubbles...

  11. Extracción de conocimiento en bases de datos astronómicas mediante redes de neuronas artificiales: aplicaciones en la misión Gaia

    Fustes Villadóniga, Diego
    En la llamada era de las TIC, las capacidades de los sistemas de adquisición de datos han aumentado enormemente, de forma que resulta complicado almacenar toda la información que producen, así como su análisis posterior. Esta explosión de datos ha aparecido recientemente en el campo de la Astronomía, donde cada vez se observan un número mayor de objetos, con mayor periodicidad. Un ejemplo de esto es la próxima misión Gaia, que observará múltiples propiedades de hasta mil millones de estrellas, cuya información tendrá un volumen del orden del petabyte. Por lo tanto, para analizar tal cantidad de datos, es necesario...

  12. Light enhancements in nano-structured solar cells

    Pastorelli, Francesco
    Cotutela ICFO-Universitat Politècnica de Catalunya i Institut Fresnel-Université Aix-Marseille

  13. A systematic approach to airborne sensor orientation and calibration: method and models

    Blázquez González, Marta
    Tesi per compendi de publicacions

  14. Numerical modelling of a parabolic trough solar collector

    Hachicha, Ahmed Amine
    Concentrated Solar Power (CSP) technologies are gaining increasing interest in electricity generation due to the good potential for scaling up renewable energy at the utility level. Parabolic trough solar collector (PTC) is economically the most proven and advanced of the various CSP technologies. The modelling of these devices is a key aspect in the improvement of their design and performances which can represent a considerable increase of the overall efficiency of solar power plants. In the subject of modelling and improving the performances of PTCs and their heat collector elements (HCEs), the thermal, optical and aerodynamic study of the fluid...

  15. Contributions to ionospheric determination with global positioning system: solar flare detection and prediction of global maps of total electron content

    García Rigo, Alberto
    Two research studies have been addressed in this thesis. Both of them are of actual scientific interest and are based on processing GNSS data. The first part of this thesis is devoted to GNSS detection and monitoring of solar flares. The second one is devoted to GNSS prediction of ionospheric Total Electron Content. Regarding the first study, a new solar flare detector called SISTED has been designed and implemented. Its goal is to provide a simple and efficient way of detecting the most number of powerful X-class solar flares in real time operation. In addition, it can send early warning messages...

  16. Microstructural characterization & viscoelastic properties of AlZnMg & AlCuMg alloys

    Rojas Gregorio, José Ignacio
    The comprehension of the viscoelastic behaviour of metals is of high interest as these materials are subjected to dynamic loads in most of their structural applications, and also because it enables a deeper understanding of several technologically essential properties, like mechanical damping and yielding. Thus, research on this field is needed not only because it may lead to new potential applications of metals, but also because predictability of the fatigue response may be greatly enhanced. Indeed, fatigue is the consequence of microstructural effects induced in a material under dynamic loading, while the viscoelastic behaviour is also intimately linked to the microstructure. Accordingly, the characterization of...

  17. Precise GPS-based position, velocity and acceleration determination: algorithms and tools

    Salazar Hernández, Dagoberto José
    Esta tesis doctoral llevó a cabo el estudio, desarrollo e implementación de algoritmos para la navegación con sistemas globales de navegación por satélite (GNSS), enfocándose en la determinación precisa de la posición, velocidad y aceleración usando GPS, en modo post-procesado y lejos de estaciones de referencia. Uno de los objetivos era desarrollar herramientas en esta área y hacerlas disponibles a la comunidad GNSS. Por ello el desarrollo se hizo dentro del marco del proyecto preexistente de software libre llamado GPS Toolkit (GPSTk). Una de las primeras tareas realizadas fue la validación de las capacidades de la GPSTk para el procesado del pseudorango, realizando comparaciones con una...

  18. Evolution formalisms of Einstein equations: Numerical and Geometrical Issues

    Cordero Carrión, Isabel
    The topic treated along this thesis is the theoretical and numerical study of formalisms of Einstein equations, with the final aim of applications to black holes and gravitational waves. The General Relativity theory of Einstein (1915) postulated that light and trajectories of all particles are curved by the geometry of spacetime. Schwarzschild a few months later and Kerr in 1963 found solutions which describe non-rotating and rotating black holes. From an astrophysical point of view, a stellar black hole can be seen as the final result of some kind of collapse of massive stars or merger of compact binaries objects. One...

  19. Análisis de las anisotropías de la Radiación Cósmica del Fondo de Microondas mediante el uso de Filtros Adaptados

    Herranz Muñoz, Diego
    El estudio de las anisotropías de la Radiación Cósmica del Fondo de Microondas es una de las piedras de toque de la Cosmología actual. Una fase importante de dicho estudio consiste en el análisis previo de los datos mediante técnicas deprocesado estadístico que permiten identificar, separar y estudiar de forma independiente las diferentes componentes físicas que contribuyen a la emisión del cielo. En esta Tesis se propone una nueva técnica de filtrado, los Filtros Adaptados a la Escala, que permite detectar la emisión de fuentes compactas(galaxias y cúmulos de galaxias) de forma robusta atendiendo alas particularidades de su estructura espacial...

  20. Calibration Validation and Polarimetry in 2D Aperture Synthesis. Application to MIRAS

    Ribó i Vedrilla, Serni
    La missió SMOS de l'Agència Europea de l'Espai (ESA) té com a objectiu mesurar la humitat del sòl i la salinitat dels oceans, paràmetres fonamentals per tal d'entendre el canvi climàtic global.MIRAS (Radiòmetre de microones generador d'imatges pel mètode de síntesi d'obertura) és un tipus d'instrument nou per a l'observació de la terra i és l'únic instrument de la missió SMOS. Consisteix en un agrupació aprimada (thinned array) en forma d'i grega amb 21 elements per braç. Amb aquesta tècnica s'aconsegueixen grans obertures sintètiques amb una massa relativament reduida.Aquesta nova tecnologia ha estat triada per a la missió SMOS, per...

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