Three-dimensional simulations of solar magneto-convection including effects of partial ionization

Over the last decades, realistic 3D radiative-MHD simulations have become the dominant theoretical tool for understanding the complex interactions between the plasma and the magnetic field on the Sun. Most of such simulations are based on approximations of magnetohydrodynamics, without directly considering the consequences of the very low degree of ionization of the solar plasma in the photosphere and bottom chromosphere. The presence of large amount of neutrals leads to a partial decoupling of the plasma and the magnetic field. As a consequence of that, a series of non-ideal effects (ambipolar diffusion, Hall effect and battery effect) arises. The ambipolar effect is the dominant one in the solar chromosphere. Here we report on the first three-dimensional realistic simulations of magneto-convection including ambipolar diffusion and battery effects. The simulations are done using the newly developed Mancha3D code. Our results reveal that ambipolar diffusion causes measurable effects on the amplitudes of waves excited by convection in the simulations, on the absorption of Poynting flux and heating and on the formation of chromospheric structures. We provide a low limit on the chromospheric temperature increase due to the ambipolar effect using the simulations with battery-excited dynamo fields.Comment: To appear in Astronomy & Astrophysic

Numerical simulations of quiet Sun magnetic fields seeded by Biermann battery

The magnetic fields of the quiet Sun cover at any time more than 90\% of its surface and their magnetic energy budget is crucial to explain the thermal structure of the solar atmosphere. One of the possible origins of these fields is due to the action of local dynamo in the upper convection zone of the Sun. Existing simulations of the local solar dynamo require an initial seed field, and sufficiently high spatial resolution, in order to achieve the amplification of the seed field to the observed values in the quiet Sun. Here we report an alternative model of seeding based on the action of the Bierman battery effect. This effect generates a magnetic field due to the local imbalances in electron pressure in the partially ionized solar plasma. We show that the battery effect self-consistently creates from zero an initial seed field of a strength of the order of micro G, and together with dynamo amplification, allows the generation of quiet Sun magnetic fields of a similar strength to those from solar observations.Comment: To appear in Astronomy & Astrophysic

Study of the derivative expansions for the nuclear structure functions

We study the convergence of the series expansions sometimes used in the analysis of the nuclear effects in Deep Inelastic Scattering (DIS) proccesses induced by leptons. The recent advances in statistics and quality of the data, in particular for neutrinos calls for a good control of the theoretical uncertainties of the models used in the analysis. Using realistic nuclear spectral functions which include nucleon correlations, we find that the convergence of the derivative expansions to the full results is poor except at very low values of $x$

Experimental characterization of the structural response of adobe arches

Earth was one of the first construction materials used by mankind and has been used as a building material since ancient times until the present days. Its qualities related to thermal comfort, low cost or simple construction techniques have contributed to such a long tradition throughout the world with several different architectural expressions, integrating the culture and history of each region. With the wide propagation of steel and concrete structures, there has been a general loss of the traditional knowledge in earth construction. This type of construction presents important structural fragilities and requires a special maintenance to preserve its qualities. In order to understand the structural behaviour of this type of structures, the associated construction methods and processes have to be considered. Aveiro University has been developing studies on adobe constructions, with research on the material mechanical characterization, experimental study of the structural behaviour of adobe masonry walls and, more recently, in the development of a detailed survey methodology for the characterization of buildings in Aveiro district. Integrated in these studies, arches with different geometries were built using adobe blocks and traditional construction methods. These arches were tested under different types of vertical loading (distributed symmetrical, distributed non-symmetrical and point load) until collapse. The experimental tests performed reproduce the typical loading conditions of these structures during construction and use. The tests conducted, the results obtained and the main conclusions attained are described in this paper

Local analysis of a new multipliers method

http://www.sciencedirect.com/science/article/B6VCT-45X2SGP-1/1/1571cb1c8b840e1e82cd33e423a0e19

Local Convergence of the Affine-Scaling Interior-Point Algorithm for Nonlinear Programming

This paper addresses the local convergence properties of the affine-scaling interior-point algorithm for nonlinear programming. The analysis of local convergence is developed in terms of parameters that control the interior-point scheme and the size of the residual of the linear system that provides the step direction. The analysis follows the classical theory for quasi-Newton methods and addresses q-linear, q-superlinear, and q-quadratic rates of convergence

Implicitly and densely discrete black-box optimization problems

This paper addresses derivative-free optimization problems where the variables lie implicitly in an unknown discrete closed set. The evaluation of the objective function follows a projection onto the discrete set, which is assumed dense rather than sparse. Such a mathematical setting is a rough representation of what is common in many real-life applications where, despite the continuous nature of the underlying models, a number of practical issues dictate rounding of values or projection to nearby feasible figures. We discuss a definition of minimization for these implicitly discrete problems and outline a direct search algorithm framework for its solution. The main asymptotic properties of the algorithm are analyzed and numerically illustrated.FCT POCI/MAT/59442/2004, PTDC/MAT/64838/200