Recent Talks

The matter within a few Schwarzschild radii of accreting neutron stars and black holes is moving under the influence of a strong gravitational field, and, in stellar mass compact objects, through strongly curved spacetime. The X-rays emitted in the accretion process can be used to diagnose this motion, using both spectroscopy and rapid time variability. Similarly, X-rays emitted from the surface of accreting neutron stars can be used to diagnose neutron star mass, radius and even internal structure. I discuss these ways to probe strong gravitational fields and ultradense matter from an empirical perspective and in the context of proposed future X-ray observatories, in particular, LOFT.

Following the observational and theoretical evidence that points at core collapse supernovae as major producers of dust, we calculate the hydrodynamics of the matter reinserted within young and massive super stellar clusters under the assumption of gas and dust radiative cooling. The large supernova rate expected in massive clusters allows for a continuous replenishment of dust immersed in the high temperature thermalized reinserted matter and warrants a stationary presence of dust within the cluster volume during the type II supernova era (~ 3 Myr - 40 Myr). Such a balance determines the range of dust to gas mass ratio and this the dust cooling law. We then search for the critical line in the cluster mechanical luminosity (or cluster mass) vs cluster size, that separates quasi- adiabatic and strongly radiative cluster wind solutions from the bimodal cases. In the latter, strong radiative cooling reduces considerably the cluster wind mechanical energy output and affects particularly the cluster central regions, leading to frequent thermal instabilities that diminish the pressure and inhibit the exit of the reinserted matter. Instead matter accumulates there and is expected to eventually lead to gravitational instabilities and to further stellar formation with the matter reinserted by former massive stars. The main outcome of the calculations is that the critical line is almost two orders of magnitude or more, depending on the assumed value of V\infty, lower than when only gas radiative cooling is applied. And thus, massive clusters (M_sc > 10^5 Msun) are predicted to enter the bimodal regime.

Many images (and signals) admit sparse representations in the sense that they are well approximated by linear combinations of a small number of functions taken from know sets. The topic of sparse and redundant representations, often termed as a sparse regression or sparse coding, has attracted tremendous interest from the research community in the last ten years. This interest stems from the role that the low dimensional models play in many signal and image areas such as compression, restoration, classification, and design of priors and regularizers, just to name a few. In this talk we use the sparse approximations for phase and magnitude of a complex-valued wavefield. While our techniques are quite general here they are illustrated for processing phase-shifting interferometry measurements. It is assumed that the observations are Poissonian (photon counting). In this way we are targeting at optimal sparse reconstruction of both phase and magnitude taking into consideration all details of the observation formation. Contrary to the standard variational approaches we propose a vector optimization with two objective functions leading to decoupling of inverse and denoising operations. This reconstruction is framed as a maximum likelihood constrained nonlinear optimization problem. It is demonstrated by simulation that proposed recursive algorithm is efficient, demonstrates high accuracy and better imaging performance in comparison with the current state-of-the-art.

Jorge Juan y Santacilia (Novelda, 1713; Madrid, 1773) participó en la expedición científica organizada por la Academia de Ciencias de París al Ecuador (Virreinato del Perú, entonces) para determinar 'definitivamente' la forma y tamaño de la Tierra, con la intención de resolver la perturbadora pugna científica entre los partidarios de las ideas de Descartes y Newton. A su regreso publicó con Antonio de Ulloa la obra, que se estableció como 'histórica', Observaciones astronómicas y físicas, que precedió a las referencias francesas. Con Louis Godin, académico francés director de la referida expedición científica, en la Academia de Caballeros Guardias Marinas de Cádiz, estableció el primer Observatorio Astronómico del sur de Europa (hoy Real Instituto y Observatorio Astronómico de la Armada, en San Fernando), y su discípulo José Celestino Mutis construiría en Santa Fe de Bogotá el primer Observatorio Astronómico de las Américas.