Lattice effects and current reversal in superconducting ratchets

Competition between the vortex lattice and a lattice of asymmetric artificial defects is shown to play a crucial role in ratchet experiments in superconducting films. We present a novel and collective mechanism for current reversal based on a reconfiguration of the vortex lattice. In contrast to previous models of vortex current reversal, the mechanism is based on the global response of the vortex lattice to external forces.Comment: 12 pages, 7 figure

Modelo presa-depredador y su contextualización en el ámbito nacional e internacional

Este trabajo se enfoca en la construcción de un modelo presa-depredador a través de datos reales para luego proceder a simularlo y controlarlo mediante Matlab/Simulink; para alcanzar este objetivo es necesario conocer modelos realistas derivados del modelo de Lotka-Volterra a través de la revisión bibliográfica de artículos no solo nacionales sino también internacionales, de esta forma se hace posible determinar un modelo adecuado para los datos con los que se trabajan. De forma paralela se realizan algunas simulaciones de los modelos hallados con el fin de conocer su comportamiento y así definir el sentido biológico de las acciones de control realizadas sobre ellos. Luego de obtener los datos reales, se desarrolla un algoritmo genético como método para identificar un sistema presa-depredador, que devuelva salidas de presas y depredadores similares a las reales. Con este proceso será posible proponer un modelo matemático capaz de describir el comportamiento de un sistema biológico real

Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy

Stripe domains are studied in perpendicular magnetic anisotropy films nanostructured with a periodic thickness modulation that induces the lateral modulation of both stripe periods and inplane magnetization. The resulting system is the 2D equivalent of a strained superlattice with properties controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy. This allows us to observe, experimentally for the first time, the continuous structural transformation of a grain boundary in this 2D magnetic crystal in the whole angular range. The magnetization reversal process can be tailored through the effect of misfit strain due to the coupling between disclinations in the magnetic stripe pattern and domain walls in the in-plane magnetization configuration

Criterios de robustez para sistemas lineales

Al construir un modelo de un sistema, éste siempre incluye algún grado de incertidumbre con respecto al sistema real y a su entorno. El sistema puede cambiar de manera inesperada o estar sujeto a perturbaciones inesperadas. Debido a factores como los cambios en los parámetros, las dinámicas y retardos no modeladas, los cambios en los puntos de operación, el ruido en los sensores o las perturbaciones no predichas, el modelo de un proceso no puede ser una representación completamente acertada del sistema real [1]

A novel Fireworks Algorithm with wind inertia dynamics and its application to traffic forecasting

Fireworks Algorithm (FWA) is a recently contributed heuristic optimization method that has shown a promising performance in applications stemming from different domains. Improvements to the original algorithm have been designed and tested in the related literature. Nonetheless, in most of such previous works FWA has been tested with standard test functions, hence its performance when applied to real application cases has been scarcely assessed. In this manuscript a mechanism for accelerating the convergence of this meta-heuristic is proposed based on observed wind inertia dynamics (WID) among fireworks in practice. The resulting enhanced algorithm will be described algorithmically and evaluated in terms of convergence speed by means of test functions. As an additional novel contribution of this work FWA and FWA-WID are used in a practical application where such heuristics are used as wrappers for optimizing the parameters of a road traffic short-term predictive model. The exhaustive performance analysis of the FWA and FWA-ID in this practical setup has revealed that the relatively high computational complexity of this solver with respect to other heuristics makes it critical to speed up their convergence (specially in cases with a costly fitness evaluation as the one tackled in this work), observation that buttresses the utility of the proposed modifications to the naive FWA solver

Spectropolarimetric multi line analysis of stellar magnetic fields

In this paper we study the feasibility of inferring the magnetic field from polarized multi-line spectra using two methods: The pseudo line approach and The PCA-ZDI approach. We use multi-line techniques, meaning that all the lines of a stellar spectrum contribute to obtain a polarization signature. The use of multiple lines dramatically increases the signal to noise ratio of these polarizations signatures. Using one technique, the pseudo-line approach, we construct the pseudo-line as the mean profile of all the individual lines. The other technique, the PCA-ZDI approach proposed recently by Semel et al. (2006) for the detection of polarized signals, combines Principle Components Analysis (PCA) and the Zeeman Do ppler Imaging technique (ZDI). This new method has a main advantage: the polarized signature is extracted using cross correlations between the stellar spectra nd functions containing the polarization properties of each line. These functions are the principal components of a database of synthetic spectra. The synthesis of the spectra of the database are obtained using the radiative transfer equations in LTE. The profiles built with the PCA-ZDI technique are denominated Multi-Zeeman-Signatures. The construction of the pseudo line as well as the Multi-Zeeman-Signatures is a powerful tool in the study of stellar and solar magnetic fields. The information of the physical parameters that governs the line formation is contained in the final polarized profiles. In particular, using inversion codes, we have shown that the magnetic field vector can be properly inferred with both approaches despite the magnetic field regime.Comment: Accepted for publication in Astronomy and Astrophysic

Crossed-ratchet effects and domain wall geometrical pinning

The motion of a domain wall in a two dimensional medium is studied taking into account the internal elastic degrees of freedom of the wall and geometrical pinning produced both by holes and sample boundaries. This study is used to analyze the geometrical conditions needed for optimizing crossed ratchet effects in periodic rectangular arrays of asymmetric holes, recently observed experimentally in patterned ferromagnetic films. Geometrical calculations and numerical simulations have been used to obtain the anisotropic critical fields for depinning flat and kinked walls in rectangular arrays of triangles. The aim is to show with a generic elastic model for interfaces how to build a rectifier able to display crossed ratchet effects or effective potential landscapes for controlling the motion of interfaces or invasion fronts.Comment: 13 pages, 18 figure

Evolution of Martensitic Microstructure on Carbon Steel Tempered at Low Temperatures

This work presents the microstructural changes of a carbon steel during tempering at low temperatures (first stage of tempering), and its effects in the second and third stages. These changes are determined by internal friction. Internal friction is measured in a forced vibration mode at 5 Hz, in a temperature range from 300 to 600K. Four internal friction peaks appear: S1 at 350K, P1 at 380K, P2 at 440K, P3 at 480K. S1 only appears in the sample tempered at 380K for 20 hours, and this can be related to the reduction of the martensite tetragonality. The height of P1 is lowest when the intensity of tempering is increased. This height can be related to the quantity of epsilon carbide than precipitate. The heights of P2 and P3 are not changed significantly, but the difference of temperature between both is lowest when the tempering intensity is increased. This suggests than the dissolution of epsilon carbide and formation of cementite takes places in a lowest range of temperature.Fil: Hoyos, J.. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina. Universidad Nacional de Cuyo; ArgentinaFil: Ghilarducci, Ada Albertina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina. Universidad Nacional de Cuyo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Salva, Horacio Ramon. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Vélez, J. M.. Universidad Nacional de Colombia; Colombi