Periodic orbits in tall laterally heated rectangular cavities

This study elucidates the origin of the multiplicity of stable oscillatory flows detected by time integration in tall rectangular cavities heated from the side. By using continuation techniques for periodic orbits, it is shown that initially unstable branches, arising at Hopf bifurcations of the basic steady flow, become stable after crossing Neimark-Sacker points. There are no saddle-node or pitchfork bifurcations of periodic orbits, which could have been alternative mechanisms of stabilization. According to the symmetries of the system, the orbits are either fixed cycles, which retain at any time the center symmetry of the steady flow, or symmetric cycles involving a time shift in the global invariance of the orbit. The bifurcation points along the branches of periodic flows are determined. By using time integrations, with unstable periodic solutions as initial conditions, we determine which of the bifurcations at the limits of the intervals of stable periodic orbits are sub- or supercritical.Postprint (author's final draft

Torsional solutions of convection in rotating fluid spheres

A numerical study of the nonlinear torsional solutions of convection in rotating, internally heated, self-gravitating fluid spheres is presented. Their dependence on the Rayleigh number has been found for two pairs of Ekman (E) and small Prandtl (Pr) numbers in the region of parameters where, according to Zhang et al. [J. Fluid Mech. 813, R2 (2017)], the linear stability of the conduction state predicts that they can be preferred at the onset of convection. The bifurcation to periodic torsional solutions is supercritical for sufficiently small Pr. They are not rotating waves, unlike the nonaxisymmetric case. Therefore they have been computed by using continuation methods for periodic orbits. Their stability with respect to axisymmetric perturbations and physical characteristics have been analyzed. It was found that the time- and space-averaged equatorially antisymmetric part of the kinetic energy of the stable orbits splits into equal poloidal and toroidal parts, while the symmetric part is much smaller. Direct numerical simulations for E=10-4 at higher Rayleigh numbers (Ra) show that this trend is also valid for the nonperiodic flows and that the mean values of the energies remain almost constant with Ra. However, the modulated oscillations bifurcated from the quasiperiodic torsional solutions reach a high amplitude, compared with that of the periodic, increasing slowly and decaying very fast. This repeated behavior is interpreted as trajectories near heteroclinic chains connecting unstable periodic solutions. The torsional flows give rise to a meridional propagation of the kinetic energy near the outer surface and an axial oscillation of the hot nucleus of the metallic fluid sphere.Postprint (published version

O projecto do espaço público: uma mediação entre a(s) memória(s) e o lugar

info:eu-repo/semantics/publishedVersio

Cambios en elrango de distribución dePotentilla tucumanensis (Rosaceae), una especie críptica en peligro de extinción

Una correcta identificación taxonómica es esencial para la preservación de la biodiversidad. En este trabajo se presentan caracteres morfológicos sencillos para diferenciar la nueva especip, Potentilla tucumanensis recientemente descripta. Esta especie, cuyo período reproductivo ocupa el 10% final de su ciclo de vida, es considerada críptica debido a que puede ser confundida por su similitud en estado vegetativo, con especies con las cuales cohabita y está aislada reproductivamente. Además, se muestra que en los últimos cien años, P. tucumanensis ha sufrido una dramática retracción de su hábitat: desde 1900 a 1925 se encontraron ejemplares de esta planta distribuidos en diferentes ambientes ecológicos de la reglón del noroeste argentino, mientras que en la actualidad, esta especie es raramente encontrada y siempre confinada a un sólo tipo de hábitat. Se discuten las posibles causas de este proceso de retracción. Si P. tucumanensis no hubiese sido reconocida como una especie nueva, probablemente hubiese desaparecido sin dejar rastro de su existencia.: A correct taxonomic identification is essential for the preservation of biodiversity. In this paper we present simple morphological characters for the identification of the new species recently described, Potentilla tucumanensis. The reproductive period of this species occupies about 10% of the last part of its lifecycle, is considered cryptic because in the vegetative stage it has many morphological similarities with other cohabiting related species; it can be easily confused with them and it is reproductively isolated. Our study also revealed that for the last hundred years P. tucumanensis has suffered a dramatic habitat retraction. Possible causes of this area retraction are discussed. IfPtucumanensis had not been recognized asa new species, it would have most likely disappeared without being noticed.Fil: Arias, Marta Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; ArgentinaFil: Diaz Ricci, Juan Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; ArgentinaFil: Castagnaro, Atilio Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentin

Spontaneous emergence of contrarian-like behaviour in an opinion spreading model

We introduce stochastic driving in the Sznajd model of opinion spreading. This stochastic effect is meant to mimic a social temperature, so that agents can take random decisions with a varying probability. We show that a stochastic driving has a tremendous impact on the system dynamics as a whole by inducing an order-disorder nonequilibrium phase transition. Interestingly, under certain conditions, this stochastic dynamics can spontaneously lead to agents in the system who are analogous to Galam's contarians.Comment: 4 eps figs, EuroPhys Lett styl

Formas da urbanização de baixa densidade entre Braga e Barcelos: a matriz histórica do território: informar a intervenção

info:eu-repo/semantics/draf

Formas da urbanização de baixa densidade entre Braga e Barcelos: uma proposta de leitura a partir da matriz histórica e geográfica do território

O processo de acumulação entre formas de urbanização recentes e dispersão antiga no território da urbanização de baixa densidade entre Braga e Barcelos motiva-nos uma reflexão sobre as potencialidades de uma leitura atenta à conformação do suporte no tempo longo. Começamos com a contextualização do problema e com os fundamentos que justificam o campo argumentativo. Definimos uma estratégia metodológica que parte da delimitação geográfica do objecto de estudo, para estabelecer as coordenadas de observação entre os assentamento proto-históricos e o período medieval, na perspectiva de selecionar processos e materiais que nos informam sobre a pertinência da matriz cognitiva. Na segunda parte tratamos questões que interessam à problematização da forma urbana relacionadas com os factores sistémicos de ocupação do território e com a possibilidade de trabalhar a partir dos valores formais do suporte geográfico. Refletimos sobre um entendimento de base morfológica vinculado à hipótese de estruturar campos de relações a partir dos processos de sedimentação das formas, segundo um processo onde a continuidade se passa a estabelecer por relações de significado.From the process that combines recent urban forms and old fragments in the territory of low density urbanisation between Braga and Barcelos drives a reflection about the potential of a reading that is attentive to the construction of the territory over time. We start with contextualising the problem and the foundations that justify the argumentative field. We define a methodological strategy that starts with the geographical delimitation of the object of this study, in order to establish the boundaries of this analysis: the proto-historic settlements and the medieval period. From here we select processes and materials that inform the pertinence of the subject-matter. In the second part we raise questions that concern the problematisation of the urban form as they relate to systemic factors of occupation of the territory, and to the possibility of working from the formal values of the geographical support. We ponder the understanding of this morphological basis associated to the hypothesis of structuring relationship fields through the processes of shape sedimentation, following a process where continuity is established by meaning.info:eu-repo/semantics/publishedVersio