Colloquia

Talks given by high profile astronomers and scientists.


Video
Thursday November 5, 2009
Prof. Rony Keppens
Centre for Plasma-Astrophysics, K. U. Leuven, Belgium

Abstract

I will present grid-adaptive computational studies of both magnetized and unmagnetized jet flows, with significantly relativistic bulk speeds, as appropriate for AGN jets. Our relativistic jet studies shed light on the observationally established classification of Fanaroff-Riley galaxies, where the appearance in radio maps distinguishes two types of jet morphologies. We investigate how density changes in the external medium can induce one-sided jet decelerations, explaining the existence of hybrid morphology radio sources. Our simulations explore under which conditions highly energetic FR II jets may suddenly decelerate and continue with FR I characteristics. In a related investigation, we explore the role of dynamically important, organized magnetic fields in the collimation of the relativistic jet flows. In that study, we concentrate on morphological features of the bow shock and the jet beam, for various jet Lorentz factors and magnetic field helicities. We show that the helicity of the magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. For the high speed jets considered, significant jet deceleration only occurs beyond distances exceeding hundred jet radii, as the axial flow can reaccelerate downstream to internal cross-shocks. This reacceleration is magnetically aided, due to field compression across the internal shocks which pinch the flow.

Video
Tuesday October 20, 2009
Prof. Matthias Rempel
Matthias Rempel, National Center for Atmospheric Research, USA

Abstract

For a long time radiative MHD simulations of entire sunspots from first principles were out of reach due to insufficient computing resources. Over the past 4 years simulations have evolved from 6x6x2 Mm size domains focusing on the details of umbral dots to simulations covering a pair of opposite polarity sunspots in a 100x50x6 Mm domain. In this talk I will discuss the numerical challenges encountered in comprehensive radiative MHD simulations of active regions and summarize the recent progress. Numerical simulations point toward a common magnetoconvective origin of umbral dots and filaments in the inner and outer penumbra. Most recent simulations also capture the processes involved in the formation of an extended outer penumbra with strong horizontal outflows averaging around 5 km/s in the photosphere. I will discuss in detail the magneto convective origin of penumbral fine structure as well as the Evershed flow. I will conclude with a brief summary of recent helioseismic studies based on realistic MHD simulations as well as inferences on the sub surface structure of sunspots.

Video
Thursday September 10, 2009
Prof. Piergiorgio Picozza
University of Roma, Italy

Abstract

New results on the antiproton-to-proton and positron-to-all electron ratios over a wide energy range (1 – 100 GeV) have been obtained by the PAMELA mission. These data are mainly interpreted in terms of dark matter annihilation or pulsar contribution. The instrument PAMELA, in orbit since June 15th, 2006 on board the Russian satellite Resurs DK1, is daily delivering to ground 16 Gigabytes of data. The apparatus is designed to study charged particles in the cosmic radiation, with a particular focus on antiparticles for searching antimatter and signals of dark matter annihilation. A combination of a magnetic spectrometer and different detectors allows antiparticles to be reliably identified from a large background of other charged particles. The talk will illustrate the most important scientific results obtained by PAMELA, together with some of the more recent theoretical interpretations.


Video
Thursday July 16, 2009
Prof. David Koo
University of California Observatories, Lick Observatory, USA

Abstract

AEGIS (All-wavelength Extended Groth strip International Survey: aegis.ucolick.org) is on-going survey that opens up new views of the development of galaxies and AGN's at redshifts z about 1. AEGIS is panchromatic like GOODS, with coverage ranging from X-ray to radio, and nearly as deep but more panoramic by covering a 4x larger region. Its backbone is the most Northern (accessible to the GTC) of the four fields of the DEEP2 Keck spectroscopic survey, which provides not only precision redshifts that yield reliable pairs, groups, and environments, but also internal kinematics and chemical abundances. After an overview of the DEEP and AEGIS surveys, I will share some recent highlights, including using a new kinematic measure for distant galaxies to track Tully-Fisher-like evolution; discovering metal poor, massive, luminous galaxies; finding ubiquitous galactic gas outflows among distant star forming galaxies; and exploring the nature of distant x-ray AGNs.

Video
Thursday June 11, 2009
Prof. Roger Davies
Department of Physics, University of Oxford, UK

Abstract

The SAURON survey has revised our view of early type galaxies discovering that central disks and multiple kinematic components are common; 75% of the sample have extended ionized gas, often misaligned with the stars; half of S0s and 25% of Es have intermediate age populations. There is a tight relationship between the escape velocity and Mg line strength which holds both within and between galaxies raising uncomfortable questions for hierarchical assembly. Many of the properties of ETGs are related to a measure of their specific angular momentum : slow rotators are triaxial, close to spherical, isotropic and frequently exhibit decoupled central kinematics, whereas fast rotators are intrinsically flatter, oblate, have disk-like (anisotropic) kinematics and often have Mg enhanced disks. In general the slow rotators are more massive and have older populations Only half of the elliptical galaxies exhibit slow rotation, the remainder have stellar disks showing that the historic division by morphological class is physically misleading. We suggest that the contrasting physical properties of fast and slow rotators arise through distinct assembly histories with slow rotators forming in gas free, dry mergers and fast rotators retaining a disk component through a dissipative merger.

Video
Thursday March 26, 2009
Dr. Michael Atiyah
University of Edinburgh, UK

Abstract


Video
Thursday March 26, 2009
Prof. Sebastiá Xambó
Universidad Politécnica de Cataluña, Spain

Abstract

En una parte preliminar se recordarán unos pocos hechos experimentales obtenidos durante las últimas décadas, con énfasis en fenómenos puramente cuánticos como el entrelazamiento y el teletransporte, y también algunos hechos matemáticos elementales, con énfasis en las matrices hermíticas y unitarias. En una segunda parte se presentará un modelo matemático de la noción de q-ordenador y de conceptos subordinados como puertas q-lógicas, q-computación y q-algoritmos programas, con énfasis en los ejemplos, incluyendo la q-transformada de Fourier y el q-algoritmo de Shor de factorización en tiempo polinómico de números enteros positivos. A continuación se sumarizará un enfoque axiomático de la mecánica cuántica y se usará para relacionar las q-nociones anteriores con sus posibles realizaciones físicas, con énfasis en algunos problemas abiertos y en posibles líneas de trabajo futuro. La base de este material es la tesis de máster de Juanjo Rué,  "Un modelo matemático para la computación cuántica: fundamentos, algoritmos y aplicaciones" (julio de 2007), dirigida por Lluís Torner y el conferenciante.


Video
Thursday March 12, 2009
Dr. Nick Scoville
California Institute of Technology, USA

Abstract

The COSMOS survey is the largest high redshift galaxy evolution survey ever done -- imaging 2 square degrees with all major space-based and ground based observatories. I will describe the key data in the survey and then present recent results on large-scale structures, the dark matter distributions and galaxy evolution.

Video
Thursday February 19, 2009
Prof. Carlos Frenk
Institute for Computational Cosmology, Physics Dept, Durham University

Abstract

The standard model of cosmology -- the ``Lambda cold dark matter'' model -- is based on the idea that the dark matter is a collisionless elementary particle, probably a supersymmetric particle. This model (which mostly dates back to an early workshop in Santa Barbara in the 1980s) has been famously verified by observations of the cosmic microwave background radiation and the large-scale distribution of galaxies. However, the model has yet to be tested conclusively on the small scales appropriate to most astronomical objects, such as galaxies and clusters. I will review our current understanding of the distribution of dark matter on small scales which derives largely from large cosmological N-body simulations and I will discuss prospects for detecting dark matter, either through its gravitational effect on galaxies and clusters or, more directly, through gamma-ray annihilation radiation.

Video
Sunday January 18, 2009
Prof. Juan Torres López
University of Sevilla, Spain

Abstract

Aunque en otras ocasiones se habían producido episodios financieros muy críticos, en los últimos meses se viene sufriendo una perturbación de las finanzas internacionales muy singular por su extraordinaria magnitud y por los efectos que está produciendo sobre el resto de la economía. Se puede conocer ya con suficiente rigor sus causas pero los gobiernos y los organismos internacionales no aciertan a la hora de ponerle remedios. En la conferencia se pondrán de relieve sus orígenes y las opciones políticas disponibles para afrontarla.


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