Localized Dispersive States in Nonlinear Coupled Mode Equations for Light Propagation in Fiber Bragg Gratings.

Dispersion effects induce new instabilities and dynamics in the weakly nonlinear description of light propagation in fiber Bragg gratings. A new family of dispersive localized pulses that propagate with the group velocity is numerically found, and its stability is also analyzed. The unavoidable different asymptotic order of transport and dispersion effects plays a crucial role in the determination of these localized states. These results are also interesting from the point of view of general pattern formation since this asymptotic imbalance is a generic situation in any transport-dominated (i.e., nonzero group velocity) spatially extended system

Nearly inviscid Faraday waves in containers with broken symmetry

In the weakly inviscid regime parametrically driven surface gravity-capillary waves generate oscillatory viscous boundary layers along the container walls and the free surface. Through nonlinear rectification these generate Reynolds stresses which drive a streaming flow in the nominally inviscid bulk; this flow in turn advects the waves responsible for the boundary layers. The resulting system is described by amplitude equations coupled to a Navier-Stokes-like equation for the bulk streaming flow, with boundary conditions obtained by matching to the boundary layers, and represents a novel type of pattern-forming system. The coupling to the streaming flow is responsible for various types of drift instabilities of standing waves, and in appropriate regimes can lead to the presence of relaxations oscillations. These are present because in the nearly inviscid regime the streaming flow decays much more slowly than the waves. Two model systems, obtained by projection of the Navier-Stokes-like equation onto the slowest mode of the domain, are examined to clarify the origin of this behavior. In the first the domain is an elliptically distorted cylinder while in the second it is an almost square rectangle. In both cases the forced symmetry breaking results in a nonlinear competition between two nearly degenerate oscillatory modes. This interaction destabilizes standing waves at small amplitudes and amplifies the role played by the streaming flow. In both systems the coupling to the streaming flow triggered by these instabilities leads to slow drifts along slow manifolds of fixed points or periodic orbits of the fast system, and generates behavior that resembles bursting in excitable systems. The results are compared to experiments

Weakly nonlinear nonaxisymmetric oscillations of capillary bridges at small viscosity

Weakly nonlinear nonaxisymmetric oscillations of a capillary bridge are considered in the limit of small viscosity. The supporting disks of the liquid bridge are subjected to small amplitude mechanical vibrations with a frequency that is close to a natural frequency. A set of equations is derived for accounting the slow dynamics of the capillary bridge. These equations describe the coupled evolution of two counter-rotating capillary waves and an associated streaming flow. Our derivation shows that the effect of the streaming flow on the capillary waves cannot be a priori ignored because it arises at the same order as the leading (cubic) nonlinearity. The system obtained is simplified, then analyzed both analytically and numerically to provide qualitative predictions of both the relevant large time dynamics and the role of the streaming flow. The case of parametric forcing at a frequency near twice a natural frequency is also considere

Service-Learning as an Approach to Educating for Sustainable Development

Higher education has an essential role in the promotion of sustainable development. For this to be possible, the use of methodologies in accordance with principles of sustainability must be fostered. This article theoretically analyzes the characteristics that make service-learning an effective tool in education for sustainable development. In order to understand the challenges involved in its implementation in higher education, first of all, the concepts of sustainable development and sustainability are defined. Next, the use of education for sustainable development and curricular sustainability in higher education is contextualized. Finally, the pedagogical proposal of servicelearning is addressed and linked to the principles of sustainability in the university environment. To conclude, in relation to prospective applications of service-learning, it is argued that it is an optimal methodology to educate about, for, and from sustainability and that its institutionalization in higher education is highly desirabl

Low-dimensional modeling of streaks in a wedge flow boundary layer

This paper is concerned with the low dimensional structure of optimal streaks in a wedge flow boundary layer, which have been recently shown to consist of a unique (up to a constant factor) three-dimensional streamwise evolving mode, known as the most unstable streaky mode. Optimal streaks exhibit a still unexplored/unexploited approximate self-similarity (not associated with the boundary layer self-similarity), namely the streamwise velocity re-scaled with their maximum remains almost independent of both the spanwise wavenumber and the streamwise coordinate; the remaining two velocity components instead do not satisfy this property. The approximate self-similar behavior is analyzed here and exploited to further simplify the description of optimal streaks. In particular, it is shown that streaks can be approximately described in terms of the streamwise evolution of the scalar amplitudes of just three one-dimensional modes, providing the wall normal profiles of the streamwise velocity and two combinations of the cross flow velocity components; the scalar amplitudes obey a singular system of three ordinary differential equations (involving only two degrees of freedom), which approximates well the streamwise evolution of the general streaks

Optimal streaks in a Falkner-Skan boundary layer

This paper deals with the optimal streaky perturbations (which maximize the perturbed energy growth) in a wedge flow boundary layer. These three dimensional perturbations are governed by a system of linearized boundary layer equations around the Falkner-Skan base flow. Based on an asymptotic analysis of this system near the free stream and the leading edge singularity, we show that for acute wedge semi-angle, all solutions converge after a streamwise transient to a single streamwise-growing solution of the linearized equations, whose initial condition near the leading edge is given by an eigenvalue problem first formulated in this context by Tumin (2001). Such a solution may be regarded as a streamwise evolving most unstable streaky mode, in analogy with the usual eigenmodes in strictly parallel flows, and shows an approximate self-similarity, which was partially known and is completed in this paper. An important consequence of this result is that the optimization procedure based on the adjoint equations heretofore used to define optimal streaks is not necessary. Instead, a simple low-dimensional optimization process is proposed and used to obtain optimal streaks. Comparison with previous results by Tumin and Ashpis (2003) shows an excellent agreement. The unstable streaky mode exhibits transient growth if the wedge semi-angle is smaller than a critical value that is slightly larger than $\pi/6$, and decays otherwise. Thus the cases of right and obtuse wedge semi-angles exhibit less practical interest, but they show a qualitatively different behavior, which is briefly described to complete the analysis

Low-Dimensional Modelling for optimal streaks in the blasius boundary layer

This paper is concerned with the low dimensional structure of optimal streaks in the Blasius boundary layer. Optimal streaks are well known to exhibit an approximate self-similarity, namely the streamwise velocity re-scaled with their maximum remains almost independent of both the spanwise wavenumber and the streamwise coordinate. However, the reason of this self-similar behavior is still unexplained as well as unexploited. After revisiting the structure of the streaks near the leading edge singularity, two additional approximately self-similar relations involving the velocity components and their wall normal derivatives are identified. Based on these properties, we derive a low dimensional model with two degrees of freedom. The comparison with the results obtained from the linearized boundary layer equations shows that this model is consistent and provide good approximations

Modal Description of Internal Optimal Streaks.

This paper deals with the definition and description of optimal streaky (S) perturbations in a Blasius boundary layer. First, the asymptotic behaviours of S-perturbations near the free stream and the leading edge are studied to conclude that the former is slaved to the solution inside the boundary layer. Based on these results, a quite precise numerical scheme is constructed that allows concluding that S-perturbations produced inside the boundary layer, near the leading edge, can bedefined in terms of just one stream wise-evolving solution of the linearized equations, associated with the first eigenmode of an eigenvalue problem first formulated by Luchini (J. Fluid Mech., vol. 327, 1996, p. 101). Such solution may be seen as an internal unstable streaky mode of the boundary layer, similar to eigenmodes of linearized stability problems. The remaining modes decay stream wise. Thus, the definition of streaks in terms of an optimization problem that is used nowadays is not necessary

Red articuladora de espacios públicos para mejorar la calidad de vida en la Localidad de Suba, a partir de la recreación

"El trabajo consiste en generar una red articuladora que conecta 4 elementos de la estructura ecológica principal (Cerros de Suba, Humedal Juan Amarillo, Humedal La Conejera y Río Bogotá) y además, el desarrollo de 3 puntos principales que la componen. 1. El tramo general de la red tanto en calles como en otros parques, 2. La intersección de la red con una vía de la malla vial principal, 3. El tramo de la red cuando se encuentra dentro de la estructura ecológica principal. La investigación parte de la búsqueda del mejoramiento de la calidad de vida para una población (poco favorecida) en Bogotá. Se analiza la calle 80 y sus alrededores, hasta llegar a las UPZ Tibabuyes (No.71) y El Rincón (No.28), en la Localidad de Suba, que se encuentran en tratamiento de Mejoramiento Integral, debido a que ""como consecuencia de su origen informal no planificado, cerecen de malla vial, infraestructura de servicios públicos, zonas para estacionamiento, espacios recreativos, equipamientos de salud, educación, etc., y por lo tanto, requieren acciones dirigidas a complementar su urbanismo y mejorar la calidad de vida de sus habitantes""."Espacio PúblicoBogotáCA111

Reflexiones sobre el aprendizaje-servicio en la educación superior europea

Over the last two decades, there has been a growing emphasis on the transformation of higher education within Europe. The promotion of active and democratic citizenship through formal higher education is a primary concern. Service-learning (SL) has proven to be a powerful didactic methodology for achieving these ideals. The objective of this paper is to highlight some reflections that permeate SL european experiences, published in the European Observatory of Service-Learning in Higher Education, between January 2020 and September 2021. The counting and percentages of the valued attitudes of SL experiences were collected to explore the guiding philosophy, historical roots, purposes, and underpinning features of SL, contextual factors affecting the practice of SL in the partner institutions and countries, and future challenges and opportunities. Conclusionsfocus onSLgrowth and mainstreaming; SL as a core strategic pillar for developing deeper community-higher education partnerships and for strengthening civic engagement across higher education; the need to develop future research to explore these connections and the potential that SLcan play in terms of increased civic, work-life and theoretical understandings and skillsDurante las últimas dos décadas, ha habido un énfasis creciente en la transformación de la educación superior en Europa. La promoción de una ciudadanía activa y democrática a través de la educación superior formal es una preocupación primordial. El aprendizaje-servicio (ApS) ha demostrado ser una poderosa metodología didáctica para lograr estos ideales. El objetivo de este trabajo es resaltar algunas reflexiones que impregnan las experiencias europeas de ApS, publicadas en el Observatorio Europeo de Aprendizaje-Servicio en EducaciónSuperior, entre enero de 2020 y septiembre de 2021. Se recogieron los recuentos y porcentajes de las actitudes valoradas de las experiencias de ApS,explorandola filosofía rectora, las raíces históricas, los propósitos y las características fundamentalesdel ApS, los factores contextuales que afectan la práctica delApSen las instituciones y países socios, y los desafíos y oportunidades futuras. Las conclusiones se centran en el crecimiento y la integración del ApS; el ApScomo un pilar estratégico central para desarrollar asociaciones más profundas entre la comunidad y la educación superior y para fortalecer el compromiso cívico en la educación superior; la necesidad de desarrollar investigaciones futuras para explorar estas conexiones y el potencial que el ApSpuede jugar en términos de una mayor comprensión y habilidades cívicas, laborales y teóricasDurant les dues últimes dècades, hi ha hagut un èmfasi creixent en la transformacióde l'educaciósuperior a Europa. La promocióde la ciutadania activa i democràtica a través de l'educaciósuperior formal és una preocupacióprimordial. L'aprenentatge servei (ApS) ha demostrat ser una potent metodologia didàctica per assolir aquests ideals. L'objectiu d'aquest article és destacar algunes reflexions que impregnen les experiències europees d'ApS, publicades a l'Observatori Europeu de l'Aprenentatge-Servei al'EducacióSuperior, entre gener de 2020 i setembre de 2021. El recompte i els percentatges de les actituds valorades de les experiències d'ApS es van recollir per explorar la filosofia rectora, les arrels històriques, els propòsits i les característiques subjacents de l’ApS, els factors contextuals que afecten la pràctica de l’ApSa les institucions i països associats, i els reptes i oportunitats futurs. Les conclusions se centren en el creixement de l’ApS; l’ApScom a pilar estratègic bàsic per desenvolupar associacions més profundes entre la comunitat i l'educaciósuperior i per enfortir el compromís cívic en l'educaciósuperior; la necessitat de desenvolupar investigacions futures per explorar aquestes connexions i el potencial que l'ApSpot tenir en termes d'augment de les competències i habilitats cíviques, laborals i teòrique