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Search Results: 1 - 10 of 598146 matches for " J. M. Miranda "
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Spatiotemporal phase synchronization in a large array of convective oscillators
M. A. Miranda,J. Burguete
Physics , 2009, DOI: 10.1142/S0218127410026125
Abstract: In a quasi-1D thermal convective system consisting of a large array of nonlinearly coupled oscillators, clustering is the way to achieve a regime of mostly antiphase synchronized oscillators. This regime is characterized by a spatiotemporal doubling of traveling modes. As the dynamics is explored beyond a spatiotemporal chaos regime with weak coupling, new interacting modes emerge through a supercritical bifurcation. In this new regime, the system exhibits coherent subsystems of antiphase synchronized oscillators, which are stationary clusters following a spatiotemporal beating phenomena. This regime is the result of a stronger coupling. We show from a phase mismatch model applied to each oscillator, that these phase coherent domains undergo a global phase instability meanwhile the interactions between oscillators become nonlocal. For each value of the control parameter we find out the time-varying topology (link matrix) from the contact interactions between oscillators. The new characteristic spatiotemporal scales are extracted from the antiphase correlations at the time intervals defined by the link matrix. The interpretation of these experimental results contributes to widen the understanding of other complex systems exhibiting similar phase chaotic dynamics in 2D and 3D.
An experimental route to spatiotemporal chaos in an extended 1D oscillators array
M. A. Miranda,J. Burguete
Physics , 2009, DOI: 10.1103/PhysRevE.79.046201
Abstract: We report experimental evidence of the route to spatiotemporal chaos in a large 1D-array of hotspots in a thermoconvective system. Increasing the driving force, a stationary cellular pattern becomes unstable towards a mixed pattern of irregular clusters which consist of time-dependent localized patterns of variable spatiotemporal coherence. These irregular clusters coexist with the basic cellular pattern. The Fourier spectra corresponding to this synchronization transition reveals the weak coupling of a resonant triad. This pattern saturates with the formation of a unique domain of great spatiotemporal coherence. As we further increase the driving force, a supercritical bifurcation to a spatiotemporal beating regime takes place. The new pattern is characterized by the presence of two stationary clusters with a characteristic zig-zag geometry. The Fourier analysis reveals a stronger coupling and enables to find out that this beating phenomena is produced by the splitting of the fundamental spatiotemporal frequencies in a narrow band. Both secondary instabilities are phase-like synchronization transitions with global and absolute character. Far beyond this threshold, a new instability takes place when the system is not able to sustain the spatial frequency splitting, although the temporal beating remains inside these domains. These experimental results may support the understanding of other systems in nature undergoing similar clustering processes.
Parallel flow in Hele-Shaw cells with ferrofluids
J. A. Miranda,M. Widom
Physics , 1999, DOI: 10.1103/PhysRevE.61.2114
Abstract: Parallel flow in a Hele-Shaw cell occurs when two immiscible liquids flow with relative velocity parallel to the interface between them. The interface is unstable due to a Kelvin-Helmholtz type of instability in which fluid flow couples with inertial effects to cause an initial small perturbation to grow. Large amplitude disturbances form stable solitons. We consider the effects of applied magnetic fields when one of the two fluids is a ferrofluid. The dispersion relation governing mode growth is modified so that the magnetic field can destabilize the interface even in the absence of inertial effects. However, the magnetic field does not affect the speed of wave propagation for a given wavenumber. We note that the magnetic field creates an effective interaction between the solitons.
Consideraciones sobre los posibles mecanismos de corrosión de las estructuras de hormigón armado y sobre los factores que controlan su cinética
González, J. A.,Miranda, J. M.
Revista de Metalurgia , 2004,
Abstract: It is well known that in normal circumstances steel remains passive in concrete, due to the highly alkaline pH, and that the passivity of the rebars guarantees the practically unlimited durability of reinforced concrete structures (RCS). However, a number of matters continue to cause controversy, with the risk of promoting the acceptance of behaviours or mechanisms that cannot be extended to all circumstances; for instance: a) that when carbonation is ruled out, concrete "always" imposes a highly alkaline pH on rebars. b) that in RCSs corroding active state, cathodic control by oxygen diffusion in the aqueous phase of the pore network is "usual", c) that the influence of galvanic macrocouples strongly conditions the rebar corrosion process, d) that the concrete coating "always" has a protective effect on rebars. e) that the initial grade of corrosion of rebars does not matter, since the concrete's great alkalinity guarantees their passivation. This paper presents results which demonstrate that the response of RCSs in the above cases is variable, at times contradictory, depending on the set of experimental conditions. Resulta bien conocido que el acero permanece pasivo en el hormigón, en circunstancias normales, debido al pH fuertemente alcalino, y que la pasividad de las armaduras garantiza la durabilidad prácticamente ilimitada de las estructuras de hormigón armado (EHA). Sin embargo, existen cuestiones que siguen planteando, aún, activas controversias, con el riesgo de propiciar la aceptación de comportamientos o mecanismos que no son extensibles a todas las circunstancias, por ejemplo: a) que, descartada la carbonatación, el hormigón impone "siempre" un pH muy alcalino a los refuerzos, b) que, en las EHA que se corroen en estado activo, es "usual" un control catódico por difusión del oxígeno en la fase acuosa de la red de poros, c) que la influencia de los macropares galvánicos condiciona fuertemente el proceso de corrosión de las armaduras, d) que el recubrimiento de hormigón tiene "siempre" un efecto protector sobre las armaduras, e) que no importa el grado de corrosión inicial de las armaduras, porque la gran alcalinidad del hormigón garantiza su pasivación. En el trabajo presente se aportan resultados que demuestran que la respuesta de las EHA a las cuestiones anteriores es variada, a veces contradictoria, dependiendo del conjunto de condiciones experimentales.
Revision of the Portuguese catalog of tsunamis
M. A. Baptista,J. M. Miranda
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2009,
Abstract: Catastrophic tsunamis are described in historical sources for all regions around the Gulf of Cadiz, at least since 60 BC. Most of the known events are associated with moderate to large earthquakes and among them the better studied is 1 November 1755. We present here a review of the events which effects, on the coasts of the Portuguese mainland and Madeira Island, are well described in historical documents or have been measured by tide gauges since the installation of these instruments. For a few we include new relevant information for the assessment of the tsunami generation or effects, and we discard events that are included in existing compilations but are not supported by quality historical sources or instrumental records. We quote the most relevant quantitative descriptions of tsunami effects on the Portuguese coast, including in all pertinent cases a critical review of the coeval sources, to establish a homogenous event list. When available, instrumental information is presented. We complement all this information with a summary of the conclusions established by paleo-tsunami research.
Exporting "failure": why research from rich countries may not benefit the developing world
Miranda,J Jaime; Zaman,M Justin;
Revista de Saúde Pública , 2010, DOI: 10.1590/S0034-89102010000100020
Abstract: the '10/90 gap' was first highlighted by the global forum for health research. it refers to the finding that 90% of worldwide medical research expenditure is targeted at problems affecting only 10% of the world's population. applying research results from the rich world to the problems of the poor may be a tempting, potentially easy and convenient solution for this gap. this paper had the objective of presenting arguments that such an approach runs the risk of exporting failure. health interventions that are shown to be effective in the specific context of a western industrialized setting will not necessarily work in the developing world.
Jets of closed orbits of Ma?é generic Hamiltonian flows
C. M. Carballo,J. A. G. Miranda
Mathematics , 2011,
Abstract: We prove a perturbation theorem for the $k$-jets, $k\geq 2$, of the Poincar\'e map of a closed orbit of the Hamiltonian flow of a Tonelli Hamiltonian $H: T^*M\to \R$, on a closed manifold $M$. As a consequence we obtain Ma\~n\'e generic properties of Hamiltonian and Lagrangian flows.
Cardiac Pacemaker and Wireless Capsule Endoscopy Interference: Case Report in a Patient with Gastric Vascular Ectasias  [PDF]
A. G. Gravina, R. Bozzi, I. J. Romano, E. Pezzullo, A. Miranda, M. G. Merola, M. Romano, A. Pezzullo
Wireless Sensor Network (WSN) , 2010, DOI: 10.4236/wsn.2010.23027
Abstract: Wireless capsule endoscopy is a new endoscopic tool for the diagnosis and management of small bowel diseases. The main indication at present is the evaluation of GI bleeding of obscure origin, Crohn’s disease, coeliac disease and small bowel tumors. Studies suggest that capsule endoscopy is associated with few adverse events. Whether cardiac pacemaker may interfere with capsule endoscopy is still a controversial issue. We here report a case showing that there is a possibility of interference between the two procedures, cardiac pacemaker affecting the proper functioning of capsule endoscopy and that this is related to the distance between the pacemaker and the recorder.
Degradación y durabilidad del acero en el hormigón: Evaluación por técnicas electroquímicas
González, J. A.,Miranda, J. M.,Feliu, S.
Revista de Metalurgia , 2005,
Abstract: A brief analysis is made of the technical and economic importance of reinforced concrete structures, the corrosion factors that can limit their durability, and the ways of evaluating deterioration kinetics using electrochemical techniques in the laboratory and in-situ on real structures. Attention is drawn to the work performed at CENIM since the 1970's, in collaboration with the ICCET, developing electrochemical techniques for studying corrosion that are applicable to the steel/concrete system. These techniques are enormously sensitive compared to those previously available and have allowed a quantitative content to be given to much of the qualitative knowledge acquired hitherto. Se analiza someramente la importancia técnica y económica de las estructuras de hormigón armado (EHA), los factores de corrosión que pueden limitar su durabilidad, así como las formas de evaluar la cinética de deterioro mediante técnicas electroquímicas, en el laboratorio y directamente, in-situ sobre las estructuras reales. Se resalta la labor desarrollada en el CENIM, en colaboración con el ICCET, desde el decenio de los 70, desarrollando técnicas electroquímicas de estudio de la corrosión aplicables al sistema acero/hormigón, de enorme sensibilidad en comparación con las técnicas precedentes, lo que ha permitido dar un contenido cuantitativo a multitud de conocimientos cualitativos adquiridos hasta entonces.
Reflexiones sobre los métodos electroquímicos de rehabilitación de las estructuras corroídas de hormigón armado
Miranda, J. M.,Otero, E.,González, J. A.
Revista de Metalurgia , 2005,
Abstract: Electrochemical realkalinisation and electrochemical chloride removal have shown their capacity to eliminate, in just a few weeks, the causes of corrosion of reinforced concrete structures (RCS), and for this reason are currently receiving very special attention. This communication seeks to answer some fundamental questions that continue to arouse great controversy, which are summarized in the question: removing the causes of corrosion in RCS suffice to stop rusting? To this end an analysis is made of the responses of clean and precorroded electrodes in a solution that simulates the aqueous phase of the concrete pore network. According to the results obtained, the efficiency of electrochemical rehabilitation methods depends heavily on the degree of precorrosion of the rebars. La realcalinización electroquímica (RAE) y la extracción electroquímica de cloruros (EEC) han mostrado su capacidad de eliminar, en pocas semanas, las causas de la corrosión de las estructuras de hormigón armado (EHA), razón por la cual reciben, actualmente, una especialísima atención. La comunicación presente intenta la búsqueda de respuestas a cuestiones fundamentales que siguen planteando fuertes controversias, que se sintetizan en la siguiente pregunta: Garantiza la eliminación de las causas de la corrosión el cese de la misma?. Para ello, se analizan las respuestas de electrodos limpios y precorroídos en solución que simula la fase acuosa de la red de poros del hormigón. La eficacia de los métodos de rehabilitación electroquímica depende, fuertemente, de acuerdo con los resultados obtenidos, del grado de precorrosión de las armaduras.
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