Implementation of position assimilation for ARGO floats in a realistic Mediterranean Sea OPA model and twin experiment testing

In this paper, a Lagrangian assimilation method is presented and implemented in a realistic OPA OGCM with the goal of providing an assessment of the assimilation of realistic Argo float position data. We focus on an application in the Mediterranean Sea, where in the framework of the MFSTEP project an array of Argo floats have been deployed with parking depth at 350 m and sampling interval of 5 days. In order to quantitatively test the method, the "twin experiment" approach is followed and synthetic trajectories are considered. The method is first tested using "perfect" data, i.e. without shear drift errors and with relatively high coverage. Results show that the assimilation is effective, correcting the velocity field at the parking depth, as well as the velocity profiles and the geostrophically adjusted mass field. We then consider the impact of realistic datasets, which are spatially sparse and characterized by shear drift errors. Such data provide a limited global correction of the model state, but they efficiently act on the location, intensity and shape of the described mesoscale structures of the intermediate circulation

Wind-driven ocean circulation and equilibrium statistical mechanics

In this paper, we show that numerical solutions of the single-layer quasigeostrophic equation in a beta-plane basin approach the state predicted by equilibrium statistical mechanics when the forcing and dissipation are (unrealistically) zero. This equilibrium state, which we call Fofonoff flow, consists of a quasi-steady uniform westward interior flow closed by inertial boundary layers. When wind stress and bottom drag are switched on, we find that the nonlinear terms in the quasigeostrophic equation still try to drive the flow toward Fofonoff flow, but their success at this depends strongly on the geometry of the wind stress. If the prescribed wind stress exerts a torque with the right sign to balance the bottom-drag torque around every closed streamline of the Fofonoff flow, then solutions to the wind-driven quasigeostrophic equation are energetic, Fofonoff-like, and nearly steady. If, on the other hand, the wind opposes Fofonoff flow, the wind-driven solutions are turbulent, with small mean flows, and much less energy. Our results suggest that integral conservation laws (on which the equilibrium statistical mechanics is solely based) largely define the role of the nonlinearities in the quasigeostrophic equation. To support this viewpoint, we demonstrate a resemblance between the solutions of the quasigeostrophic equation and the solutions of a stochastic model equation. The stochastic model equation, in which the advected vorticity is replaced by a random variable, has only gross conservation laws in common with the quasigeostrophic equation

Nonlinear general circulation of an ocean model driven by wind with a stochastic component

The effects of the stochastic component of the large-scale wind on the climatological mean of the nonlinear ocean circulation are studied, using a set of numerical solutions for the single-layer, quasi-geostrophic equation in a closed basin with a flat bottom. In the absence of a steady wind, the purely stochastic wind is found to drive the solutions toward a nonlinear mean flow similar to that of the free system (i.e. without forcing and dissipation). This equilibrium mean flow (Fofonoff flow), is predicted by statistical mechanics and is characterized by a westward interior closed by inertial boundary layers along the coast. When a steady component of the wind is present, the effects of the stochastic wind depend on the geometry of the steady wind. If the steady wind is compatible with Fofonoff flow, the stochastic wind tends to reinforce the Fofonoff-like mean solution obtained with the steady wind alone. When the steady wind opposes Fofonoff flow, the contribution of the stochastic wind does not increase the energy of the mean solution, but instead tends to change the spatial structure of the mean flow. An example of steady wind opposing Fofonoff flow is the classical double-gyre wind, often used to represent the realistic mean wind in mid-latitude ocean regions. We study the double-gyre wind case in detail. The stochastic wind is found to weaken the recirculating regions and the meandering jet between the two gyres, and the homogenization of potential vorticity in the recirculations is inhibited. These changes are explained in terms of increased mixing of the probability density in phase space due to the stochastic wind, causing an increased tendency toward the equilibrium state predicted by statistical mechanics

Acoustically-induced slip in sheared granular layers: application to dynamic earthquake triggering

A fundamental mystery in earthquake physics is ``how can an earthquake be triggered by distant seismic sources?'' Here, we use discrete element method simulations of a granular layer, during stick-slip, that is subject to transient vibrational excitation to gain further insight into the physics of dynamic earthquake triggering. Using Coulomb friction law for grains interaction, we observe delayed triggering of slip in the granular gouge. We find that at a critical vibrational amplitude (strain) there is an abrupt transition from negligible time-advanced slip (clock advance) to full clock advance, {\it i.e.}, transient vibration and triggered slip are simultaneous. The critical strain is order of $10^{-6}$, similar to observations in the laboratory and in Earth. The transition is related to frictional weakening of the granular layer due to a dramatic decrease in coordination number and the weakening of the contact force network. Associated with this frictional weakening is a pronounced decrease in the elastic modulus of the layer. The study has important implications for mechanisms of triggered earthquakes and induced seismic events and points out the underlying processes in response of the fault gouge to dynamic transient stresses

Kinematic optimization for the design of a collaborative robot end-effector for tele-echography

Tele-examination based on robotic technologies is a promising solution to solve the current worsening shortage of physicians. Echocardiography is among the examinations that would benefit more from robotic solutions. However, most of the state-of-the-art solutions are based on the development of specific robotic arms, instead of exploiting COTS (commercial-off-the-shelf) arms to reduce costs and make such systems affordable. In this paper, we address this problem by studying the design of an end-effector for tele-echography to be mounted on two popular and low-cost collaborative robots, i.e., the Universal Robot UR5, and the Franka Emika Panda. In the case of the UR5 robot, we investigate the possibility of adding a seventh rotational degree of freedom. The design is obtained by kinematic optimization, in which a manipulability measure is an objective function. The optimization domain includes the position of the patient with regards to the robot base and the pose of the end-effector frame. Constraints include the full coverage of the examination area, the possibility to orient the probe correctly, have the base of the robot far enough from the patient’s head, and a suitable distance from singularities. The results show that adding a degree of freedom improves manipulability by 65% and that adding a custom-designed actuated joint is better than adopting a native seven-degrees-freedom robot

Predictability of Lagrangian particle trajectories: Effects of smoothing of the underlying Eulerian flow

The increasing realism of ocean circulation models is leading to an increasing use of Eulerian models as a basis to compute transport properties and to predict the fate of Lagrangian quantities. There exists, however, a significant gap between the spatial scales of model resolution and that of forces acting on Lagrangian particles. These scales may contain high vorticity coherent structures that are not resolved due to computational issues and/or missing dynamics and are typically suppressed by smoothing operators. In this study, the impact of smoothing of the Eulerian fields on the predictability of Lagrangian particles is first investigated by conducting twin experiments that involve release of clusters of synthetic Lagrangian particles into true (unmodified) and model (smoothed) Eulerian fields, which are generated by a QG model with a flow field consisting of many turbulent coherent structures. The Lagrangian errors induced by Eulerian smoothing errors are quantified by using two metrics, the difference between the centers of mass (CM) of particle clusters, ρ, and the difference between scattering of particles around the center of mass, s. The results show that the smoothing has a strong effect on the CM behavior, while the scatter around it is only partially affected. The QG results are then compared to results obtained from a multi-particle Lagrangian Stochastic Model (LSM) which parameterizes turbulent flow using main flow characteristics such as mean flow, velocity variance and Lagrangian time scale. In addition to numerical results, theoretical results based on the LSM are also considered, providing asymptotics of ρ, s and predictability time. It is shown that both numerical and theoretical LSM results for the center of mass error (ρ) provide a good qualitative description, and a quantitatively satisfactory estimate of results from QG experiments. The scatter error (s) results, on the other hand, are only qualitatively reproduced by the LSM

Estimates of turbulence parameters from Lagrangian data using a stochastic particle model

A new parametric approach for the study of Lagrangian data is presented. It provides parameter estimates for velocity and transport components and is based on a stochastic model for single particle motion. The main advantage of this approach is that it provides more accurate parameter estimates than existing methods by using the a-priori knowledge of the model. Also, it provides a complete error analysis of the estimates and is valid in presence of observation errors. Unlike nonparametric methods (e.g. Davis, 1991b), our technique depends on a-priori assumptions which require that the model validity be checked in order to obtain reliable estimates. The model used here is the simplest one in a hierarchy of “random flight” models (e.g. Thomson, 1987), and it describes the turbulent velocity as a linear Markov process, characterized by an exponential autocorrelation. Experimental and numerical estimates show that the model is appropriate for mesoscale turbulent flows in homogeneous regions of the upper ocean. More complex models, valid under more general conditions, are presently under study. Estimates of the mean flow, variance, turbulent time scale and diffusivity are obtained. The properties of the estimates are discussed in terms of biases and sampling errors, both analytically and using numerical experiments. Optimal sampling for the measurements is studied and an example application to drifter data from the Brazil/Malvinas extension is presented

La participación vecinal en las políticas deportivas y recreativas en la Ciudad de Córdoba, Argentina

El presente artículo analiza la participación de los centros vecinales en las políticas deportivas yrecreativas locales de la Municipalidad de Córdoba. A pesar de los cambios de gestión, y de denominación del programa, se observa una continuidad en las lógicas de implementación del mismo.Si bien podríamos considerar aquí un modelo de gestión asociada, la participación de los centros vecinales refiere más a un uso pragmático e instrumental de su figura y de sus instalaciones, que de sus capacidades de gestión y acción territorial. Para su indagación hemos utilizado normativas, informes de gestión, documentación institucional e información publicada en el sitio web de la municipalidad.Para contextualizar el análisis, recuperaremos la Carta Orgánica Municipal, donde se contempla la participación de los centros vecinales en la gestión de las políticas públicas, y las ordenanzas que regulan el funcionamiento de estas instituciones barriales

Las Políticas Locales De Recreación Y Deporte Social En Córdoba, Argentina

This article proposes to carry out a first exploratory survey of the local policies of recreation and social sports in the city of Córdoba in the period 1980-2020. This work is part of the research project "Public policies for recreation in the province of Córdoba" that we carry out from the Faculty of Physical Education of the Provincial University of Córdoba, Argentina. Through the investigation and analysis of management reports, regulations, websites, institutional documentation, and some first exploratory interviews with members of technical teams and program managers, we can observe that despite management changes in the municipal government and in the province, it is possible to identify a continuity in recreation and social sports policies, as well as the sustained link with social institutions, mainly neighborhood centers, in their implementation. Other aspects that deserve our attention and analysis refer to the decentralization of these policies, the construction of infrastructure to carry out sports and recreational activities, and the participation of various actors in their management and development. In this article we will also refer to the institutional structure from which these policies were carried out in the city of Córdoba, the organizations that constitute them and the management models that have been designed and implemented for this purpose.El presente artículo se propone realizar un primer rastreo exploratorio de las políticas locales de recreación y deporte social en la ciudad de Córdoba, Argentina, en el período 1980-2020. Este trabajo forma parte del proyecto de investigación “Políticas públicas de recreación en la provincia de Córdoba”2 que llevamos adelante desde la Facultad de Educación Física de la Universidad Provincial de Córdoba, República Argentina. A través de la indagación y análisis de informes de gestión, normativas, sitios web, documentación institucional, y unas primeras entrevistas exploratorias a miembros de equipos técnicos y responsables de programas, podemos observar que a pesar de los cambios de gestión en el gobierno municipal y provincial es posible identificar una continuidad en las políticas de recreación y deporte social, así como también del vínculo sostenido con instituciones sociales, principalmente centros vecinales, en la implementación de las mismas. Otros aspectos que merecen nuestra atención y análisis refieren a la descentralización de estas políticas, a la construcción de infraestructura para la realización de actividades deportivas y recreativas, y a la participación de diversos actores en su gestión y desarrollo. En este artículo haremos referencia también a la estructura institucional desde las cuales se llevaron a cabo estas políticas en la ciudad de Córdoba, los organismos que las constituyen y los modelos de gestión que han sido diseñados e implementados para tal fin