1,721,128 research outputs found
Chaos generation, synchronization and communications using an integrated source with an air gap
No full text
Nonlinear Dynamics of Semiconductor Laser Systems with Feedback: Applications to Optical Chaos Cryptography, Radar Frequency Generation, and Transverse Mode Control
No full textTesis doctoral de la Universidad de las Islas Baleares, Facultad de Física y del Departamento de Física Interdisciplinar del Instituto Mediterráneo de Estudios Avanzados (IMEDEA-CSIC/UIB).-- Fecha de lectura: 15-12-2006.The simple fact to introduce and account for a delay time in a dynamical system increases its dimensionality to infinity, and thereby opens the way to a wide variety of very complex behaviors. Despite the huge advances of physics and mathematics in the twentieth century, in is only at the early sixties that delay differential equations gained sufficient attention from the scientific community. In the first years, though, the interest was purely mathematical and these equations where studied under the terminology of Functional Differential Equations, mainly by Krasovskii and Hale. Then, these new ideas rapidly started to spread in various areas of applied science, particularly in control theory. In physics, in particular, delay differential equations have been found to be the idoneous tool to investigate the behavorial properties of dynamical systems
where delays had to be taken into account. Far beyond the scope of physics, delay differential systems have been successfully used to investigate a very large spectrum of problems, ranging from predator/prey ecosystems to neurology.It has resulted from thirty years of theoretical and experimental investigations that the delay may globally have two opposite effects: either a destabilization effect, through the excitation of many of the latent degrees of freedom; or either a stabilization effect by somehow acting as a selective energy sink. In both cases, there is a plethora of applications where one of these effects may be highly desired. Within the frame of this thesis, we will lay emphasis upon those of these applications which are related to semiconductor laser systems.This PhD thesis has been funded by a fellowship from the Govern de les Illes Balears
Dynamics of spatial structures in nonlinear optics
No full textTesis doctoral de la Universidad de las Islas Baleares,Instituto Mediterráneo de Estudios Avanzados (IMEDEA-CSIC/UIB).-- Texto en inglés, agradecimientos en catalán.-- 181 pages, 3 appendixes.-- Fecha de lectura: 11-02-2003.The formation of spatial structures in systems out of thermodynamical equilibrium
has been the subject of a large amount of scienti c research in the last quarter
of the 20'th century [101, 39, 245]. Examples include patterns in hydrodynamic
systems, granular media, nonlinear optics, oscillatory chemical reactions and biological
systems. De nite progress has been made in the understanding of the common
general theory behind the emergence and evolution of spatial structures. Methods
of nonlinear dynamics and bifurcation theory such as amplitude equations, that describe
the dynamics close to bifurcation points, or \phase equations", that describe
the slow distortions of patterns even far from the instability threshold, have been
essential tools in the development of a universal description of pattern formation
and their dynamics.However, these analytical techniques have limitations, and interesting
phenomena often take place beyond their range of validity. For instance,
instabilities of patterns (secondary bifurcations) may take place far away from the
pattern formation instability where the dynamics of the systems is not properly
reproduced by the the amplitude equations obtained at the primary instability.
Furthermore, amplitude equations are usually derived using the relevant modes, in
general, from a Fourier decomposition, so that they are not useful to describe states
without spatial periodicity such as those containing localized structures. An alternative
tool is the numerical simulation of the partial di erential equations that govern
the evolution of a extended system. But these numerical simulations are very time
consuming and, by themselves, do not allow for a complete understanding of the
dynamics of a system. For this reason, more appropriated methods of analysis have
to be used and developed. Here we address this kind of problems using a powerful
combination of analytical and numerical techniques.Aquesta tesi ha estat realitzada a l'Institut Mediterrani d'Estudis Avan çats
(IMEDEA, CSIC-UIB) i finan çada per una beca FPI del Ministeri de Ci ència i Tecnologia
associada al projecte PB97-0141-C02-02, així com per tota una s érie de projectes
d'investigaci ó: BFM2001-0341-C02-02, BFM2000-1108, Accions integrades
Hispano-Alemanes HA98-29, Accions integrades Hispano-Italianes i les xarxes europeas
QSTRUCT (FMRXCT960077) i PHASE.Peer reviewe
Modelo de agentes en economía basado en el juego de la minoría
No full text[spa] El Minority Game es un modelo simple basado en agentes. Consiste en un colectivo de agentes que
a cada paso de tiempo tienen que decidir que acci´on realizar entre dos opciones posibles, y se premia a
la minor´ıa. En los ´ultimos a˜nos se ha estudiado bien a fondo este modelo, haciendo modificaciones sobre
´el para estudiar y replicar el mercado financiero. A pesar de que este es su uso m´as com´un (mercado
financiero), se puede emplear para estudiar campos como el transporte, la gen´etica o el arbitraje en el
mercado energ´etico. En los ´ultimos a˜nos el mercado el´ectrico ha cambiado su organizaci´on hacia estructuras
m´as autoorganizadas y centralizadas para intentar obtener el m´aximo beneficio. Esto puede dar lugar
a posibilidades de arbitraje en el mercado el´ectrico, lo que puede ocasionar una desestabilizaci´on en la red
f´ısica. Debido a la naturaleza del arbitraje, este mercado se puede entender como un juego de minor´ıas
por lo que se usar´a el Minority Game para entender el funcionamiento de este. Primero se explicar´a el
modelo y estudiaremos sus distintas propiedades, destacando una transici´on de fase que divide el juego
en dos reg´ımenes diferentes. Por ´ultimo, se emplear´a el Minority Game para analizar el arbitraje en el
mercado de la energ´ıa el´ectrica y como poder reducirlo para que el mercado sea lo m´as estable posible
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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