Polytechnic University of Catalonia

About: Polytechnic University of Catalonia is a education organization based out in Barcelona, Spain. It is known for research contribution in the topics: Finite element method & Population. The organization has 16006 authors who have published 45325 publications receiving 949306 citations. The organization is also known as: UPC - BarcelonaTECH & Technical University of Catalonia.

Cobalt-56 γ-ray emission lines from the type Ia supernova 2014J

Abstract: We report the first ever detection of 56 Co lines at 847 and 1237 keV and a continuum in the 200-400 keV band from the Type Ia supernova SN2014J in M82 with INTEGRAL observatory. The data were taken between 50th and 100th day since the SN2014J outburst. The line fluxes suggest that 0.62 ± 0.13 M of radioactive 56 Ni were synthesized during the explosion. Line broadening gives a characteristic ejecta expansion velocity Ve ∼ 2100 ± 500 km s −1. The flux at lower energies (200-400 keV) flux is consistent with the three-photon positronium annihilation, Compton downscattering and absorption in the ∼ 1.4 M ejecta composed from equal fractions of iron-group and intermediate-mass elements and a kinetic energy Ek ∼ 1.4 10 51 erg. All these parameters are in broad agreement with a " canonical " model of an explosion of a Chandrasekhar-mass White Dwarf (WD), providing an unambiguous proof of the nature of Type Ia supernovae as a thermonuclear explosion of a solar mass compact object.

Study of the transfer from the Earth to a halo orbit around the equilibrium pointL 1

Abstract: The purpose of this paper is to study a transfer strategy from the vicinity of the Earth to a halo orbit around the equilibrium pointL 1 of the Earth-Sun system. The study is done in the real solar system (we use the DE-118 JPL ephemeris in the simulations of motion) although some simplified models, such as the restricted three body problem (RTBP) and the bicircular problem, have been also used in order to clarify the geometrical aspects of the problem. The approach used in the paper makes use of the hyperbolic character of the halo orbits under consideration. The invariant stable manifold of these orbits enables the transfer to be achieved with, theoretically, only one manoeuvre: the one of insertion into the stable manifold. For the total Δv required, the figures obtained are similar to the ones given by the standard procedures of optimization.

Uniform power allocation in mimo channels: a came-theoretic approach

Abstract: When transmitting over multiple-input-multiple-output (MIMO) channels, there are additional degrees of freedom with respect to single-input-single-output (SISO) channels: the distribution of the available power over the transmit dimensions. If channel state information (CSI) is available, the optimum solution is well known and is based on diagonalizing the channel matrix and then distributing the power over the channel eigenmodes in a "water-filling" fashion. When CSI is not available at the transmitter, but the channel statistics are a priori known, an optimal fixed power allocation can be precomputed. This paper considers the case in which not even the channel statistics are available, obtaining a robust solution under channel uncertainty by formulating the problem within a game-theoretic framework. The payoff function of the game is the mutual information and the players are the transmitter and a malicious nature. The problem turns out to be the characterization of the capacity of a compound channel which is mathematically formulated as a maximin problem. The uniform power allocation is obtained as a robust solution (under a mild isotropy condition). The loss incurred by the uniform distribution is assessed using the duality gap concept from convex optimization theory. Interestingly, the robustness of the uniform power allocation also holds for the more general case of the multiple-access channel.