Control of bistability in a directly modulated semiconductor laser using delayed optoelectronic feedback

We show numerically that direct delayed optoelectronic feedback can suppress hysteresis and bistability in a directly modulated semiconductor laser. The simulation of a laser with feedback is performed for a considerable range of feedback strengths and delays and the corresponding values for the areas of the hysteresis loops are calculated. It is shown that the hysteresis loop completely vanishes for certain combinations of these parameters. The regimes for the disappearance of bistability are classified globally. Different dynamical states of the laser are characterized using bifurcation diagrams and time series plots.

Numerical study of reverse period doubling route from chaos to stability in a two-mode intracavity doubled Nd-YAG laser

We have numerically studied the behavior of a two-mode Nd-YAG laser with an intracavity KTP crystal. It is found that when the parameter, which is a measure of the relative orientations of the KTP crystal with respect to the Nd-YAG crystal, is varied continuously, the output intensity fluctuations change from chaotic to stable behavior through a sequence of reverse period doubling bifurcations. The graph of the intensity in the X-polarized mode against that in the Y-polarized mode shows a complex pattern in the chaotic regime. The Lyapunov exponent is calculated for the chaotic and periodic regions.

Existence of multiple attractors and the nature of bifurcations in a discontinuous logistic map

We present the analytical investigations on a logistic map with a discontinuity at the centre. An explanation for the bifurcation phenomenon in discontinuous systems is presented. We establish that whenever the elements of an n-cycle (n > 1) approach the discontinuities of the nth iterate of the map, a bifurcation other than the usual period-doubling one takes place. The periods of the cycles decrease in an arithmetic progression, as the control parameter is varied. The system also shows the presence of multiple attractors. Our results are verified by numerical experiments as well.

Evidence for the existence of Sarkovskii ordering in a two-dimensional map

We analyse numerically the bifurcation structure of a two-dimensional noninvertible map and show that different periodic cycles are arranged in it exactly in the same order as in the case of the logistic map. We also show that this map satisfies the general criteria for the existence of Sarkovskii ordering, which supports our numerical result. Incidently, this is the first report of the existence of Sarkovskii ordering in a two-dimensional map.

Universal behaviour in a ``modulated'' logistic map

We study the period-doubling bifurcations to chaos in a logistic map with a nonlinearly modulated parameter and show that the bifurcation structure is modified significantly. Using the renormalisation method due to Derrida et al. we establish the universal behaviour of the system at the onset of chaos.

Multifractal dimension of chaotic attractors in a driven semiconductor superlattice

The multifractal dimension of chaotic attractors has been studied in a weakly coupled superlattice driven by an incommensurate sinusoidal voltage as a function of the driving voltage amplitude. The derived multifractal dimension for the observed bifurcation sequence shows different characteristics for chaotic, quasiperiodic, and frequency-locked attractors. In the chaotic regime, strange attractors are observed. Even in the quasiperiodic regime, attractors with a certain degree of strangeness may exist. From the observed multifractal dimensions, the deterministic nature of the chaotic oscillations is clearly identified.

Onset And Characterisation Of Chaos In A Two Dimensional Nonlinear Deterministic Model

Nature is full of phenomena which we call "chaotic", the weather being a prime example. What we mean by this is that we cannot predict it to any significant accuracy, either because the system is inherently complex, or because some of the governing factors are not deterministic. However, during recent years it has become clear that random behaviour can occur even in very simple systems with very few number of degrees of freedom, without any need for complexity or indeterminacy. The discovery that chaos can be generated even with the help of systems having completely deterministic rules - often models of natural phenomena - has stimulated a lo; of research interest recently. Not that this chaos has no underlying order, but it is of a subtle kind, that has taken a great deal of ingenuity to unravel. In the present thesis, the author introduce a new nonlinear model, a ‘modulated’ logistic map, and analyse it from the view point of ‘deterministic chaos‘.

" Nonlinear Signal Processing of Electroencephalogram .' Application in the Study of Neurodynamics. "

Interfacings of various subjects generate new field ofstudy and research that help in advancing human knowledge. One of the latest of such fields is Neurotechnology, which is an effective amalgamation of neuroscience, physics, biomedical engineering and computational methods. Neurotechnology provides a platform to interact physicist; neurologist and engineers to break methodology and terminology related barriers. Advancements in Computational capability, wider scope of applications in nonlinear dynamics and chaos in complex systems enhanced study of neurodynamics. However there is a need for an effective dialogue among physicists, neurologists and engineers. Application of computer based technology in the field of medicine through signal and image processing, creation of clinical databases for helping clinicians etc are widely acknowledged. Such synergic effects between widely separated disciplines may help in enhancing the effectiveness of existing diagnostic methods. One of the recent methods in this direction is analysis of electroencephalogram with the help of methods in nonlinear dynamics. This thesis is an effort to understand the functional aspects of human brain by studying electroencephalogram. The algorithms and other related methods developed in the present work can be interfaced with a digital EEG machine to unfold the information hidden in the signal. Ultimately this can be used as a diagnostic tool.

Semi-algebraic methods for symbolic analysis of complex reaction networks

The identification of chemical mechanism that can exhibit oscillatory phenomena in reaction networks are currently of intense interest. In particular, the parametric question of the existence of Hopf bifurcations has gained increasing popularity due to its relation to the oscillatory behavior around the fixed points. However, the detection of oscillations in high-dimensional systems and systems with constraints by the available symbolic methods has proven to be difficult. The development of new efficient methods are therefore required to tackle the complexity caused by the high-dimensionality and non-linearity of these systems. In this thesis, we mainly present efficient algorithmic methods to detect Hopf bifurcation fixed points in (bio)-chemical reaction networks with symbolic rate constants, thereby yielding information about their oscillatory behavior of the networks. The methods use the representations of the systems on convex coordinates that arise from stoichiometric network analysis. One of the methods called HoCoQ reduces the problem of determining the existence of Hopf bifurcation fixed points to a first-order formula over the ordered field of the reals that can then be solved using computational-logic packages. The second method called HoCaT uses ideas from tropical geometry to formulate a more efficient method that is incomplete in theory but worked very well for the attempted high-dimensional models involving more than 20 chemical species. The instability of reaction networks may lead to the oscillatory behaviour. Therefore, we investigate some criterions for their stability using convex coordinates and quantifier elimination techniques. We also study Muldowney's extension of the classical Bendixson-Dulac criterion for excluding periodic orbits to higher dimensions for polynomial vector fields and we discuss the use of simple conservation constraints and the use of parametric constraints for describing simple convex polytopes on which periodic orbits can be excluded by Muldowney's criteria. All developed algorithms have been integrated into a common software framework called PoCaB (platform to explore bio- chemical reaction networks by algebraic methods) allowing for automated computation workflows from the problem descriptions. PoCaB also contains a database for the algebraic entities computed from the models of chemical reaction networks.

La Universidad en el siglo XX : Espa??a e Iberoam??rica

Actas correspondientes al d??cimo Coloquio de Historia de la Educaci??n organizado por la Sociedad Espa??ola del mismo nombre y el departamento correspondiente de la Universidad de Murcia, dedicado a la Universidad Espa??ola e Iberoamericana en el siglo XX. En las actas se recogen tanto las ponencias que se ocuparon de la vocaci??n cient??fica, el centralismo y la autonom??a y la pol??tica universitaria, como las comunicaciones presentadas en cada uno de las cuatro secciones del Congresos: pol??tica universitaria, curriculum, profesores y estudiantes y la Historia de la Educaci??n como disciplina acad??mica y campo de investigaci??n.

En el deseo de vivir : familia y primera infancia.

Esta guía de consulta para la familia pretende ser una aproximación al mundo de la educación familiar y al desarrollo de la primera infancia. El autor considera de interés divulgar una serie de reflexiones sobre la educación con el objeto de profundizar en la comprensión de lo que caracteriza la convivencia familiar. La estructura del libro se dispone en capítulos breves encabezados por las preguntas más frecuentes de las familias sobre los hijos pequeños: la comunicación, el juego, el sueño, el llanto, el chupete, el lenguaje, etc..

Investigaci??n, educaci??n y desarrollo profesional

Los autores abordan la relevancia de la producci??n de conocimiento educativo y su recreaci??n en la pr??ctica educativa a la que no pueden ser ajenos los profesionales de la educaci??n. El libro se estructura en tres partes: la primera dedicada a investigaci??n y conocimiento en educaci??n, en la que se abordan los temas relacionados con la investigaci??n-acci??n, el aprendizaje autodirigido y la generaci??n de conocimiento. En la segunda se trata de la experiencia educativa y de los m??todos de investigaci??n alternativos como el aprendizaje vivencial, el aprendizaje para la diversidad, la investigaci??n participativa y la educaci??n ambiental. La tercera, dedicada al desarrollo profesional, trata de participaci??n y epistemolog??a..

Transport of Sub-micron Aerosols in Bifurcations

The convective-diffusive transport of sub-micron aerosols in an oscillatory laminar flow within a 2-D single bifurcation is studied, using order-of-magnitude analysis and numerical simulation using a commercial software (FEMLAB®). Based on the similarity between momentum and mass transfer equations, various transient mass transport regimes are classified and scaled according to Strouhal and beta numbers. Results show that the mass transfer rate is highest at the carinal ridge and there is a phase-shift in diffusive transport time if the beta number is greater than one. It is also shown that diffusive mass transfer becomes independent of the oscillating outer flow if the Strouhal number is greater than one.

El área Matemática en primero de EGB : globalización y construcción de técnicas operatorias.

Elaborar y llevar a la práctica programaciones globalizadas y cíclicas en las que los objetivos del área de expresión matemática en primero de EGB se vayan logrando, partiendo de actividades directamente relacionadas con los centros de interés elegidos según el área de experiencia. Conseguir que sean los niños quienes elaboren las técnicas operatorias habituales de la adición y sustracción partiendo de procedimientos provisionales para llegar al dominio de técnicas usuales. Grupo experimental de dos cursos de primero de EGB del Colegio Nacional de Contrueces (Gijón), con 28 y 32 alumnos. Grupo de control constituido por dos cursos de primero de EGB del Colegio Nacional de Las Palmeras (Gijón), con 25 y 24 alumnos que siguen una metodología tradicional. Se desarrollan 11 programaciones cíclicas centradas en otros tantos centros de interés: la familia, el cuerpo humano, el cuidado del cuerpo, el otoño, la escuela, la calle, la casa, el invierno, los alimentos, el movimiento, la primavera. Se controla la variable aptitudes cognoscitivas antes de aplicar las programaciones y se trata de comprobar la influencia de la aplicación de éstas en el razonamiento matemático y el rendimiento escolar en esta área. Test de aptitudes cognoscitivas, tres subtests de Primaria I. Una prueba objetiva de Matemática elaborada y aplicada en la investigación: diseño de un programa de Educación Compensatoria en función de los determinantes del rendimiento escolar en el primer ciclo de EGB. Por Mario de Miguel y col. Dos pruebas colectivas de 12 ítems cada una y una individual elaboradas por el Institut Romand de Recherches et Documentation Pedagogiques y adaptadas para esta investigación. Las diferencias de partida en el test de aptitudes cognoscitivas no son significativas. Los resultados en la prueba objetiva de Matemáticas y en las del Institut Romand, colectivas e individuales, son significativos a favor del grupo experimental, lo que sirve para validar la hipótesis de que el desarrollo del área de Matemática en primero de EGB de forma globalizada y cíclica incrementa la capacidad de razonamiento matemático del alumno, tanto en la utilización de nociones conjuntistas como en las numéricas y operacionales, así como en la utilización de nociones topológicas y geométricas. Se comprueba un mayor rendimiento del grupo experimental que no se puede achacar a diferencias previas ya que no eran significativas. Es posible desarrollar el área Matemática en este nivel partiendo de actividades relacionadas con centros de interés seleccionados desde el área de experiencias. La conveniencia de dicha globalización es resaltada por muchos autores, pero faltan modelos válidos para que puedan ser llevados a la práctica escolar. El que se presenta es uno de tantos que se pueden concebir y aplicar, pero en este sentido hay que desterrar enfoques parciales, que se suelen basar en cursos a base de asignaturas aisladas, para tratar de favorecer el proceso de construcción de conocimientos de los alumnos planteando actividades que les motiven a poner en juego sus recursos y a construir nociones siguiendo su ritmo individual.