Transverse Patterns in Nonlinear Optical Resonators

The book is devoted to the formation and dynamics of localized structures (vortices, solitons) and extended patterns (stripes, hexagons, tilted waves) in nonlinear optical resonators such as lasers, optical parametric oscillators, and photorefractive oscillators. The theoretical analysis is performed by deriving order parameter equations, and also through numerical integration of microscopic models of the systems under investigation. Experimental observations, and possible technological implementations of transverse optical patterns are also discussed. A comparison with patterns found in other nonlinear systems, i.e. chemical, biological, and hydrodynamical systems, is given. This article contains the table of contents and the introductory chapter of the book.Comment: 37 pages, 14 figures. Table of contents and introductory chapter of the boo

Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled cavity

In this paper we have considered the problem of parametric sound generation in an acoustic resonator flled with a fluid, taking explicitely into account the influence of the nonlinearly generated second harmonic. A simple model is presented, and its stationary solutions obtained. The main feature of these solutions is the appearance of bistable states of the fundamental field resulting from the coupling to the second harmonic. An experimental setup was designed to check the predictions of the theory. The results are consistent with the predicted values for the mode amplitudes and parametric thresholds. At higher driving values a self-modulation of the amplitudes is observed. We identify this phenomenon with a secondary instability previously reported in the frame of the theoretical model.Comment: 5 figures. Submitted to JAS

CORROSION ATMOSFÉRICA MARINA DE ACEROS AL CARBONO

Ciclo de Conferencias. 50 Aniversario Revista de MetalurgiaLa investigación fundamental en corrosión atmosférica marina de aceros al carbono es un campo científico relativamente joven que presenta grandes lagunas de conocimiento. La formación de akaganeita como producto de corrosión del acero en atmósferas marinas conduce a un incremento notable de la velocidad de corrosión. En la conferencia se abordan las siguientes cuestiones: • La formación y transporte del aerosol marino (salinidad atmosférica). • Condiciones ambientales necesarias para la formación de akaganeita. • Caracterización de la akaganeita en los productos de corrosión mediante XRD, SEM/EDS, TEM/ED, Espectroscopía Mössbauer y SEM/MicroRaman. • Exfoliación de las capas de herrumbre formadas en atmósferas marinas muy agresivas. • Mecanismos de corrosión. • Predicción del comportamiento a largo plazo del acero al carbono. • Comportamiento de aceros patinables en atmósferas marinas. La investigación de campo se lleva a cabo en el Parque Eólico de Cabo Vilano (Camariñas, Galicia) en un amplio rango de salinidades atmosféricas.Revista de MetalurgiaN

Cow Conundrum: the science behind lactose intolerance

We’ve all heard those words before - lactose intolerant. You, a close friend, or even a random stranger at d-hall mutters those words and with it comes the inability to eat milk, cheese, and ice cream. But what does being lactose intolerant actually mean? Besides special access to that one refrigerator in d-hall you’ve always wondered about, lactose intolerance means that you lack a special enzyme needed to digest lactose - a sugar present in many of your favorite foods