1,887 research outputs found
Recent Mediterranean Outflow Water and Atlantic Meridional Overturning Circulation correlations
The Atlantic Meridional Overturning Circulation (AMOC) is the main contributor to the heat interchange in the North Atlantic, carrying around 1.5 PW at 25°N, which helps to regulate the climate, especially in Europe. Any slowdown of the AMOC would produce an important decrease in the temperature in the regions around the North Atlantic and also in other parts of the world.
A factor that affects the strength of the AMOC is the input of water. While an input of freshwater would produce a reduction in the transport of the AMOC, a supply of salty water, such as the Mediterranean Outflow Water (MOW), would enhance the formation of deep water, strengthening the AMOC, and even stabilizing it.
The aim of this work is to determine if the variation of the volume of the MOW is having any effect in the fluctuation of the transport of the AMOC. In order to achieve this, we developed a method to estimate the volume of MOW in the North Atlantic using the Roemmich-Gilson Argo Climatology and compared it with the observations of the AMOC from the RAPID array. Although statistically, there was a low correlation, the similarities between the MOW and RAPID time series were evident, especially for the period 2012-2017. A possible explanation of this resemblance is that the changes that occur in the AMOC also affect the interchange between the Atlantic and the Mediterranean, and therefore the volume of MOW in the Atlantic
Identificación y descripción de procesos reales en la universidad EAFIT bajo la perspectiva de sistemas dinámicos
Este trabajo está enfocado hacia el estudio de los sistemas dinámicos en la universidad EAFIT, a partir de visitas realizadas a los laboratorios de la universidad, haciendo una breve descripción de máquinas y procesos bajo la teoría de los sistemas dinámicos, teniendo en cuenta las características más importantes de un sistema dinámico como lo son: entrada, salidas, posibles perturbaciones. Dejando así un importante apoyo para quienes después se puedan interesar tanto en describir como llegar a un posible control de algunos de los procesos, dada la necesidad en la universidad por personas interesadas en este tipo de estudios, pues en las visitas realizadas a dichos laboratorios se pudo observar la falta de interés tanto de los estudiantes como de la misma universidad para realizar un mejor estudio de los procesos, viendo así como muchos de los procesos no son desarrollados de la mejor manera.
Hecha la descripción de los procesos, se procederá a un estudio mucho más detallado de dos de estos procesos reales empezando con la modelación y simulación del mismo, bajo la teoría de los sistemas lineales usando como herramienta de simulación MATLAB SIMULINK
Remodelado estructural y de GAP Junctions en un modelo 3D de aurícula humana
Introducción:la fibrilación auricular (AF), es la más común de la arritmia cardiaca sostenida y un factor de riesgo para el accidente cerebro vascular y otras morbilidades, si no es tratada. Estudios epidemiológicos muestran que la AF tiende a perpetuarse con el tiempo, generando cambios electrofisiológicos y anatómicos denominados: remodelados auriculares. Se ha demostrado que estos cambios provocan variaciones de la velocidad de conducción (CV), en el tejido auricular.
Objetivo:estudiar el efecto del remodelado de gap junctions en la propagación del potencial de acción, implementando un modelo 3D de aurícula humana altamente realista.
Materiales y Métodos:se incorporaron los cambios generados por el remodelado eléctrico a un modelo de potencial de acción (AP) de miocito auricular, acoplado con un modelo tridimensional anatómicamente realista de aurícula humana dilatada. Mediante simulaciones de la propagación del AP en condiciones de remodelado eléctrico y anatómico, y de remodelado de gap junctions, se midieron las ventanas vulnerables de generación de reentradas en la base de las venas pulmonares izquierdas de la aurícula.
Resultados:los resultados obtenidos indican que la ventana vulnerable en el remodelado de gap junctions, se desplazó 38 ms con relación al modelo dilatado, lo que nos muestra el impacto de la dilatación con remodelado de gap junction.
Conclusiones:el remodelado eléctrico generó una disminución del 70 % en la duración del potencial de acción y una disminución de las velocidades de conducción entre un 14.6 y un 26 %, que fueron medidas en diferentes regiones de la aurícula dilatada. El foco disparado en la base de las venas pulmonares izquierdas, generó un frente de onda que mantiene una actividad reentrante debido a la anatomía subyacente de las venas pulmonares.Introduction:Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and a significant risk factor for cerebrovascular accident and other morbidities if left untreated. Epidemiological studies show that AF tends to persist over time, creating electrophysiological and anatomical changes called atrial remodeling. It has been shown that these changes result in variations in conduction velocity (CV) in the atrial tissue.
Objective:to study the effect of remodeling of gap junctions in the propagation of the action potential by implementing a highly realistic 3D human atrial model.
Materials and methods:the changes caused by electrical remodeling were incorporated in an atrial myocyte action potential (AP) model coupled with an anatomically realistic three-dimensional model of dilated human atria. Through simulations of the AP spread in variations of anatomical and electrical remodeling and of gap junctions remodeling, vulnerable windows of reentry generation were measured at the base of the atrium left pulmonary veins.
Results:the results obtained indicate that vulnerable window in the gap junctions remodeling moved 38 ms in relation with the expanded model which shows the impact of the dilatation gap junction remodeling.
Conclusions:the electrical remodeling produced 70% decrease in action potential duration and decreased conduction velocities between 14.6 and 26 %, which were measured in different regions of the dilated atrium. The focus shot at the base of the left pulmonary veins created a wave which maintains a reentering activity due to the underlying anatomy of the pulmonary veins
Ammonia Borane Dehydrogenation Promoted by a Pincer-Square-Planar Rhodium(I) Monohydride: A Stepwise Hydrogen Transfer from the Substrate to the Catalyst
The pincer d8-monohydride complex RhH{xant(PiPr2)2} (xant(PiPr2)2 = 9, 9-dimethyl-4, 5-bis(diisopropylphosphino)xanthene) promotes the release of 1 equiv of hydrogen from H3BNH3 and H3BNHMe2 with TOF50% values of 3150 and 1725 h–1, to afford [BH2NH2]n and [BH2NMe2]2 and the tandem ammonia borane dehydrogenation–cyclohexene hydrogenation. DFT calculations on the ammonia borane dehydrogenation suggest that the process takes place by means of cis-¿2-PP-species, through four stages including: (i) Shimoi-type coordination of ammonia borane, (ii) homolytic addition of the coordinated H–B bond to afford a five-coordinate dihydride-boryl-rhodium(III) intermediate, (iii) reductive intramolecular proton transfer from the NH3 group to one of the hydride ligands, and (iv) release of H2 from the resulting square-planar hydride dihydrogen rhodium(I) intermediate
Crossed-ratchet effects and domain wall geometrical pinning
The motion of a domain wall in a two dimensional medium is studied taking
into account the internal elastic degrees of freedom of the wall and
geometrical pinning produced both by holes and sample boundaries. This study is
used to analyze the geometrical conditions needed for optimizing crossed
ratchet effects in periodic rectangular arrays of asymmetric holes, recently
observed experimentally in patterned ferromagnetic films. Geometrical
calculations and numerical simulations have been used to obtain the anisotropic
critical fields for depinning flat and kinked walls in rectangular arrays of
triangles. The aim is to show with a generic elastic model for interfaces how
to build a rectifier able to display crossed ratchet effects or effective
potential landscapes for controlling the motion of interfaces or invasion
fronts.Comment: 13 pages, 18 figure
Analysis of tidal strain observations in Lanzarote Island
Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002.The strain response of the Earth to tidal forces is observed in the Geodynamics Laboratory of Lanzarote Island.
The instruments, installed in a gallery inside the lava tunnel of Cueva de los Verdes, are kind of horizontal
ceramic-tube extensometers. Their base fines comprise from 8 to 38 m length and are orientated in two orthogonal
directions (45º.2 N Y 135°.2 N), which depend on the situation in the gallery. The reliability of this instruments,
which measure the variation of distance between two fixed points with a resolution of 10 -10, allow us to dispose
long term series of tidal strains since 1992. The data series are analysed in order to study the stability of the
instruments. Also, with these data we can determine the tidal strain models, as well as the tidal deformation and the
long-term variations of strains in this island. Due to the dependence of the local conditions of the station, which is
located in an island, the oceanic influence will be investigated together with local atmospheric disturbing effects.
These effects are carefully studied for this station, in order to allow the identification and, if possible, its separation
from other signals of interest, given the volcanic feature of the island.Peer reviewe
The role of temperature in the magnetic irreversibility of type-I Pb superconductors
Evidence of how temperature takes part in the magnetic irreversibility in the
intermediate state of a cylinder and various disks of pure type-I
superconducting lead is presented. Isothermal measurements of first
magnetization curves and magnetic hysteresis cycles are analyzed in a reduced
representation that defines an equilibrium state for flux penetration in all
the samples and reveals that flux expulsion depends on temperature in the disks
but not in the cylinder. The magnetic field at which irreversibility sets in
along the descending branch of the hysteresis cycle and the remnant
magnetization at zero field are found to decrease with temperature in the
disks. The contributions to irreversibility of the geometrical barrier and the
energy minima associated to stress defects that act as pinning centers on
normal-superconductor interfaces are discussed. The differences observed among
the disks are ascribed to the diverse nature of the stress defects in each
sample. The pinning barriers are suggested to decrease with the magnetic field
to account for these results
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