Analytical study of coherence in seeded modulation instability

We derive analytical expressions for the coherence in the onset of modulation instability, in excellent agreement with thorough numerical simulations. As usual, we start by a linear perturbation analysis, where broadband noise is added to a continuous wave (CW) pump; then, we investigate the effect of adding a deterministic seed to the CW pump, a case of singular interest as it is commonly encountered in parametric amplification schemes. Results for the dependence of coherence on parameters such as fiber type, pump power, propagated distance, seed signal-to-noise ratio are presented. Finally, we show the importance of including higher-order linear and nonlinear dispersion when dealing with generation in longer wavelength regions (mid IR). We believe these results to be of relevance when applied to the analysis of the coherence properties of supercontinua generated from CW pumps.Comment: 6 pages, 8 figure

On the beneficial role of noise in resistive switching

We study the effect of external noise on resistive switching. Experimental results on a manganite sample are presented showing that there is an optimal noise amplitude that maximizes the contrast between high and low resistive states. By means of numerical simulations, we study the causes underlying the observed behavior. We find that experimental results can be related to general characteristics of the equations governing the system dynamics.Comment: 4 pages, 5 figure

Pseudocoloring with BSO crystals

A new pseudocoloring technique is proposed using pho torefractive BSO crystals biased under the influence of an externally applied electric field with coherent or incoherent illumination

Aplicaciones del efecto fotorrefractivo del cristal BSO al procesamiento óptico de imágenes a tiempo real

Presentamos en este trabajo algunas aplicaciones al procesamiento óptico de imágenes usando un cristal fotorrefractivo BSO. Para ello en el capítulo 1 estudiamos las propiedades físicas del cristal BSO, describiendo aspectos generales del mismo, sus propiedades ópticas y la estructura de niveles de energía . En el capítulo 2 se estudia el efecto fotorrefractivo haciendo un análisis del efecto electroóptico tanto en el caso general como en el caso particular del cristal BSO en aquellas configuraciones más utilizadas. También se hace un análisis de la generación del campo de cargas espaciales fotoinducidas. Todo ello nos permitió arrivar a una ecuación integrodiferencial que relaciona la distribución de intensidad incidente sobre el cristal con el campo de cargas espaciales fotoinducidas. Esta relación junto con las nociones de birrefringencia nos permitió entender al sistema formado por el cristal entre polarizadores lineales como un filtro de intensidad. Este filtro tiene la ventaja de poder ser modificado desde el exterior. En el capítulo 3 desarrollamos por medio del modelo propuesto en el capítulo anterior el estudio de la distribución de transmitancia del filtro de intensidad controlado por una distribución de intensidad luminosa unidimensional. En particular lo adaptamos para una distribución de intensidad que simula una rendija en movimiento. Finalmente, en el capítulo 4 presentamos aplicaciones clásicas en forma novedosa tales como el pseudocoloreado de niveles de gris y el filtrado de frecuencias espaciales a tiempo real. Por otra parte mostramos una aplicación de desarrollo más reciente como es el filtrado renovador.Doctor en Ciencias Física

Shape resonances in nested diffraction gratings

The diffraction problem of a plane wave impinging on a grating formed by nested cavities is solved by means of the modal method, for $s$ and $p$ polarization modes. The cavities are formed by perfectly conducting sheets that describe rectangular profiles. The electromagnetic response of the grating is analyzed, paying particular attention to the generation of resonances within the structure. The dependence of the resonances on the geometrical parameters of the grating is studied, and results of far and near field are shown. The results are checked and compared with those available in the literature for certain limit cases.Comment: 18 pages, 8 figure

Probabilistic approaches for modeling text structure and their application to text-to-text generation

Since the early days of generation research, it has been acknowledged that modeling the global structure of a document is crucial for producing coherent, readable output. However, traditional knowledge-intensive approaches have been of limited utility in addressing this problem since they cannot be effectively scaled to operate in domain-independent, large-scale applications. Due to this difficulty, existing text-to-text generation systems rarely rely on such structural information when producing an output text. Consequently, texts generated by these methods do not match the quality of those written by humans – they are often fraught with severe coherence violations and disfluencies. In this chapter, I will present probabilistic models of document structure that can be effectively learned from raw document collections. This feature distinguishes these new models from traditional knowledge intensive approaches used in symbolic concept-to-text generation. Our results demonstrate that these probabilistic models can be directly applied to content organization, and suggest that these models can prove useful in an even broader range of text-to-text applications than we have considered here.National Science Foundation (U.S.) (CAREER grant IIS- 0448168)Microsoft Research. New Faculty Fellowshi

Situation based strategic positioning for coordinating a team of homogeneous agents

. In this paper we are proposing an approach for coordinating a team ofhomogeneous agents based on a flexible common Team Strategy as well as onthe concepts of Situation Based Strategic Positioning and Dynamic Positioningand Role Exchange. We also introduce an Agent Architecture including a specifichigh-level decision module capable of implementing this strategy. Ourproposal is based on the formalization of what is a team strategy for competingwith an opponent team having opposite goals. A team strategy is composed of aset of agent types and a set of tactics, which are also composed of several formations.Formations are used for different situations and assign each agent a defaultspatial positioning and an agent type (defining its behaviour at several levels).Agents reactivity is also introduced for appropriate response to the dynamicsof the current situation. However, in our approach this is done in a way thatpreserves team coherence instead of permitting uncoordinated agent behaviour.We have applied, with success, this coordination approach to the RoboSoccersimulated domain. The FC Portugal team, developed using this approach wonthe RoboCup2000 (simulation league) European and World championshipsscoring a total of 180 goals and conceding none