Modelling Structural Flexure Effects in CPV Sun Trackers

Nowadays CPV trends mostly based in lens parqueted flat modules, enable the separate design of the sun tracker. To enable this possibility a set of specifications is to be prescribed for the tracker design team, which take into account fundamental requisites such as the maximum service loads both permanent and variable, the sun tracking accuracy and the tracker structural stiffness required to maintain the CPV array acceptance angle loss below a certain threshold. In its first part this paper outlines the author’s approach to confront these issues. Next, a method is introduced to estimate the acceptance angle losses due to the tracker’s structural flexure, which in last instance relies in the computation of the minimum enclosing circle of a set of points in the plane. This method is also useful to simulate the drifts in the tracker’s pointing vector due to structural deformation as a function of the aperture orientation angle. Results of this method when applied to the design of a two axis CPV pedestal tracker are presented.

Optical Multistability and Oscillations in Hybrid Optical Bistable Systems with Short Delay Times

Optical instabilities in the output light from a bistable optical device (BOD) with a delayed feedback was predicted by Ikeda [1]. Gibbs et al. [2] gave the first experimental verification of this type of instabilities. From that time several groups have studied the instabilities of the BOD for different relations between the delay time tR and the time constant ح of the system. In a previous paper [3] an empirical and analytical study of instabilities in hybrid BOD was reported by us. The employed set up is shown in Fig. 1.

Utzon and the sun path as an organizing element of life in a house

The present text intends to analyze the hypothesis stating that the path of the sun can be an organizing element for how you live in the houses designed by Jørn Utzon. To do so, I have selected twenty houses and building complexes designed by him between the years 1950-94, in Denmark, Sweden, The United Kingdom and Spain. In these projects I will look for elements which are repeated and their possible meaning. The aim is to reach practical conclusions that could help us decide how to orientate a house.

Where is photonics going? Reflections under the sun

After a short personal view of the first years of the photonics in Spain, some references about its present situation are given. As a possible future, the first steps towards a Photonics based on the study of the employed mechanisms in the visual system of the living beings are presented.

Change factors that may influence sun and beach destinations in a low-growth scenario

Análisis de los principales factores de cambio que previsiblemente incidirán en los destinos turísticos de sol y playa en un escenario de bajo crecimiento.

First order mem-circuits: modeling, nonlinear oscillations and bifurcations

This paper presents a theoretical framework intended to accommodate circuit devices described by characteristics involving more than two fundamental variables. This framework is motivated by the recent appearance of a variety of so-called mem-devices in circuit theory, and makes it possible to model the coexistence of memory effects of different nature in a single device. With a compact formalism, this setting accounts for classical devices and also for circuit elements which do not admit a two-variable description. Fully nonlinear characteristics are allowed for all devices, driving the analysis beyond the framework of Chua and Di Ventra We classify these fully nonlinear circuit elements in terms of the variables involved in their constitutive relations and the notions of the differential- and the state-order of a device. We extend the notion of a topologically degenerate configuration to this broader context, and characterize the differential-algebraic index of nodal models of such circuits. Additionally, we explore certain dynamical features of mem-circuits involving manifolds of non-isolated equilibria. Related bifurcation phenomena are explored for a family of nonlinear oscillators based on mem-devices.

Temperature-depnedent disruption of circadian oscillations in woody plants-A mathematical approach

Poster

EL AIRE SE SERENA Y VISTE DE HERMOSURA Y LUZ NO USADA. De cómo el espacio arquitectónico es como el instrumento musical. Dedicado a Luis Suñén.

Se intenta en este texto establecer un paralelismo entre el instrumento musical y el espacio arquitectónico. El instrumento musical mediante el aire produce el regalo de la música. El espacio arquitectónico mediante la luz produce ese algo inefable que es la arquitectura.

Foresight in designing sun-beach destinations

Planteamiento de un Nuevo enfoque metodológico para incorporar la prospectiva en la planificación de destinos turísticos de sol y playa.

Vortex pinning vs superconducting wire network: origin of periodic oscillations induced by applied magnetic fields in superconducting films with arrays of nanomagnets

Hybrid magnetic arrays embedded in superconducting films are ideal systems to study the competition between different physical (such as the coherence length) and structural length scales such as are available in artificially produced structures. This interplay leads to oscillation in many magnetically dependent superconducting properties such as the critical currents, resistivity and magnetization. These effects are generally analyzed using two distinct models based on vortex pinning or wire network. In this work, we show that for magnetic dot arrays, as opposed to antidot (i.e. holes) arrays, vortex pinning is the main mechanism for field induced oscillations in resistance R(H), critical current Ic(H), magnetization M(H) and ac-susceptibility χ ac(H) in a broad temperature range. Due to the coherence length divergence at Tc, a crossover to wire network behaviour is experimentally found. While pinning occurs in a wide temperature range up to Tc, wire network behaviour is only present in a very narrow temperature window close to Tc. In this temperature interval, contributions from both mechanisms are operational but can be experimentally distinguished.

Reseña. Architecture of the Sun: Los Angeles Modernism 1900-1970

Reseña bibliográfica de Architecture of the Sun: Los Angeles Modernism 1900-1970

Numerical study of ultrasound induced non-linear shape and size bubble oscillations in viscoelastic media

The theoretical study of forced bubble oscillations is motivated by the importance of cavitation bubbles and oscillating encapsulated microbubbles (i.e. contrast agents) in medical sciences. In more details,theoretical studies on bubble dynamics addressing the sound-bubble interaction phenomenon provide the basis for understanding the dynamics of contrast agent microbubbles used in medical diagnosis and of non-linearly oscillating cavitation bubbles in the case of high-intensity ultrasound therapy. Moreover, the inclusion of viscoelasticity is of vital importance for an accurate theoretical analysis since most biological tissues and fluids exhibit non-Newtonian behavior.

Magnetic Attitude Control for Satellites in Polar or Sun-Synchronous Orbits

In this work, a new law for magnetic control of satellites in near-polar orbits is presented. This law has been developed for the UMPSat-2 microsatellite, which has been designed and manufactured by Universidad Politécnica de Madrid, Madrid. The control law is a modification of the B-dot strategy that enables the satellite to control the rotation rate. Besides, the satellite?s equilibrium state is characterized by having the rotation axis perpendicular to the orbit?s plane. The control law described in the present work only needs magnetometers and magnetorquers, as sensors and actuators, respectively, to carry out a successful attitude control on the spacecraft. A description of the analysis is included. Performance and applicability of the proposed method have been demonstrated by control dynamics together with Monte Carlo techniques and by implementing the control law in the UPMSat-2 mission simulator. Results show good performance in terms of acquisition and stability of the satellite rotation rate and orientation with respect to its orbit?s plane.

Electron transport and azimuthal oscillations in hall thrusters

The Hall Effect Thruster (HET) is a type of satellite electric propulsion device initially developed in the 1960’s independently by USA and the former USSR. The development continued in the shadow during the 1970’s in the Soviet Union to reach a mature status from the technological point of view in the 1980’s. In the 1990’s the advanced state of this Russian technology became known in western countries, which rapidly restarted the analysis and development of modern Hall thrusters. Currently, there are several companies in USA, Russia and Europe manufacturing Hall thrusters for operational use. The main applications of these thrusters are low-thrust propulsion of interplanetary probes, orbital raising of satellites and stationkeeping of geostationary satellites. However, despite the well proven in-flight experience, the physics of the Hall Thruster are not completely understood yet. Over the last two decades large efforts have been dedicated to the understanding of the physics of Hall Effect thrusters. However, the so-called anomalous diffusion, short name for an excessive electron conductivity along the thruster, is not yet fully understood as it cannot be explained with classical collisional theories. One commonly accepted explanation is the existence of azimuthal oscillations with correlated plasma density and electric field fluctuations. In fact, there is experimental evidence of the presence of an azimuthal oscillation in the low frequency range (a few kHz). This oscillation, usually called spoke, was first detected empirically by Janes and Lowder in the 1960s. More recently several experiments have shown the existence of this type of oscillation in various modern Hall thrusters. Given the frequency range, it is likely that the ionization is the cause of the spoke oscillation, like for the breathing mode oscillation. In the high frequency range (a few MHz), electron-drift azimuthal oscillations have been detected in recent experiments, in line with the oscillations measured by Esipchuk and Tilinin in the 1970’s. Even though these low and high frequency azimuthal oscillations have been known for quite some time already, the physics behind them are not yet clear and their possible relation with the anomalous diffusion process remains an unknown. This work aims at analysing from a theoretical point of view and via computer simulations the possible relation between the azimuthal oscillations and the anomalous electron transport in HET. In order to achieve this main objective, two approaches are considered: local linear stability analyses and global linear stability analyses. The use of local linear stability analyses shall allow identifying the dominant terms in the promotion of the oscillations. However, these analyses do not take into account properly the axial variation of the plasma properties along the thruster. On the other hand, global linear stability analyses do account for these axial variations and shall allow determining how the azimuthal oscillations are promoted and their possible relation with the electron transport.

The forced oscillations of submerged bodies

The increasing use of very light structures in aerospace applications are given rise to the need of taking into account the effects of the surrounding media in the motion of a structure (as for instance, in modal testing of solar panels or antennae) as it is usually performed in the motion of bodies submerged in water in marine applications. New methods are in development aiming at to determine rigid-body properties (the center of mass position and inertia properties) from the results of oscillations tests (at low frequencies during modal testing, by exciting the rigid-body modes only) by using the equations of the rigid-body dynamics. As it is shown in this paper, the effect of the surrounding media significantly modifies the oscillation dynamics in the case of light structures and therefore this effect should be taken into account in the development of the above-mentioned methods. The aim of the paper is to show that, if a central point exists for the aerodynamic forces acting on the body, the motion equations for the small amplitude rotational and translational oscillations can be expressed in a form which is a generalization of the motion equations for a body in vacuum, thus allowing to obtain a physical idea of the motion and aerodynamic effects and also significantly simplifying the calculation of the solutions and the interpretation of the results. In the formulation developed here the translational oscillations and the rotational motion around the center of mass are decoupled, as is the case for the rigid-body motion in vacuum, whereas in the classical added mass formulation the six motion equations are coupled. Also in this paper the nonsteady motion of small amplitude of a rigid body submerged in an ideal, incompressible fluid is considered in order to define the conditions for the existence of the central point in the case of a three-dimensional body. The results here presented are also of interest in marine applications.