Stability and mode analysis of solar coronal loops using thermodynamic irreversible energy principles

We study the modes and stability of non - isothermal coronal loop models with different intensity values of the equilibrium magnetic field. We use an energy principle obtained via non - equilibrium thermodynamic arguments. The principle is expressed in terms of Hermitian operators and allow to consider together the coupled system of equations: the balance of energy equation and the equation of motion. We determine modes characterized as long - wavelength disturbances that are present in inhomogeneous media. This character of the system introduces additional difficulties for the stability analysis because the inhomogeneous nature of the medium determines the structure of the disturbance, which is no longer sinusoidal. Moreover, another complication is that we obtain a continuous spectrum of stable modes in addition to the discrete one. We obtain a unique unstable mode with a characteristic time that is comparable with the characteristic life-time observed for loops. The feasibility of wave-based and flow-based models is examined.Comment: 29 pages 10 figure

Hopf bifurcations in coronal loops I. Stability conditions for static equilibrium

We study the coupling between the hot plasma confined in a coronal loop and the much colder chromospheric plasma at the footpoints. Considering the coronal heating rate as a control parameter, we find that the static equilibrium becomes unstable for heating rates below a critical value, giving rise to the appearance of a stable limit cycle. Starting from the hydrodynamic equations, we derive a model which generalizes the analysis of Kuin and Martens and consistently takes into account the condensation-evaporation process. In this paper, we linearize our equations in order to find the bifurcation point where the stability of the static equilibrium is lost. We also show that this model can provide a natural explanation for the excess widths of EUV spectral lines formed in the transition region. Moreover, we can predict the observed reduction in the broadening of these lines when they form in certain active regions, like quiescent prominences or sunspots.Fil:Gómez, D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Sicardi Schifino, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Ferro Fontán, C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Energy performance and climate control in mechanically ventilated greenhouses: A dynamic modelling-based assessment and investigation

Controlled environment agriculture in greenhouse is a promising solution for meeting the increasing food demand of world population. The accurate control of the indoor environmental conditions proper of greenhouses enhances high crop productivity but, contemporarily, it entails considerable energy consumption due to the adoption of mechanical systems. This work presents a new modelling approach for estimating the energy consumption for climate control of mechanically ventilated greenhouses. The novelty of the proposed energy model lies in its integrated approach in simulating the greenhouse dynamics, considering the dynamic thermal and hygric behaviour of the building and the dynamic response of the cultivated crops to the variation of the solar radiation. The presented model simulates the operation of the systems and the energy performance, considering also the variable angular speed fans that are a new promising energy-efficient technology for this productive sector. The main outputs of the model are the hourly thermal and electrical energy use for climate control and the main indoor environmental conditions. The presented modelling approach was validated against a dataset acquired in a case study of a new fully mechanically controlled greenhouse during a long-term monitoring campaign. The present work contributes to increase the knowledge about the dynamics and the energy consumption of greenhouses, and it can be a valuable decision support tool for industry, farmers, and researchers to properly address an energy efficiency optimisation in mechanically ventilated greenhouses to reach the overall objective of decreasing the rising energy consumption of the agricultural sector

Quantum random walk on the line as a markovian process

We analyze in detail the discrete--time quantum walk on the line by separating the quantum evolution equation into Markovian and interference terms. As a result of this separation, it is possible to show analytically that the quadratic increase in the variance of the quantum walker's position with time is a direct consequence of the coherence of the quantum evolution. If the evolution is decoherent, as in the classical case, the variance is shown to increase linearly with time, as expected. Furthermore we show that this system has an evolution operator analogous to that of a resonant quantum kicked rotor. As this rotator may be described through a quantum computational algorithm, one may employ this algorithm to describe the time evolution of the quantum walker.Comment: few typos corrected, 13 pages, 2 figures, to appear in Physica

Markovian Behaviour and Constrained Maximization of the Entropy in Chaotic Quantum Systems

The separation of the Schr\"{o}dinger equation into a Markovian and an interference term provides a new insight in the quantum dynamics of classically chaotic systems. The competition between these two terms determines the localized or diffusive character of the dynamics. In the case of the Kicked Rotor, we show how the constrained maximization of the entropy implies exponential localization.Comment: 8 pages, 2 figure

Estudio de modos de oscilación

El objeto de este trabajo es estudiar las oscilaciones y la estabilidad en la situación más general posible, es decir abarcando las oscilaciones radial y no radial en los casos adiabáticos y no adiabáticos. Para ello se han preparad códigos computacionales, que se aplican a los modelos más sencillos de pulsaciones estelares descriptos en la literatura, con el fin de ajustarlos para luego extender su aplicación a casos más complejos.Asociación Argentina de Astronomí

Thermal stability analysis of coronal loops

The coronal loops confine a low density (n=10¹⁰ cm⁻³) and hot plasma (T=10⁶ K), whose ends interact with the much denser and hotter photospheric fluid. The linear stability of the dynamical and thermal equilibria of the coronal plasma is analyzed. A formalism based on methods of irreversible thermodynamics was used, which systematically builds up (whenever it is possible) a variational principle for studying the stability. The stability conditions derived in this work are compared with results available in the literature, which were obtained by standard stability methods.Asociación Argentina de Astronomí

Sobre administradores de recursos redundantes en sistemas distribuídos

La tolerancia a las fallas es una característica importante que presentan los sistemas distribuidos. Uno de los mecanismos mas utilizados para ello es la replicación, sea de datos, de procesamiento o de comunicación. La replicación de datos ha sido una de las más estudiadas por lo que ofrece en cuanto a disponibilidad y rendimiento. La replicación de comunicación se ha utilizado para proveer servicios confiables de mensajes. Sin embargo es poco lo que se ha hecho en cuanto a la rep1icación de procesamiento. Por ello este trabajo propone un diseño de administradores de procesamiento redundante en un ambiente de sistemas distribuidosEje: Sistemas distribuidosRed de Universidades con Carreras en Informática (RedUNCI