55 research outputs found
Controllability of the linear 1D-wave equation with inner moving forces
No full textThis paper deals with the numerical computation of distributed null controls for the 1D wave equation. We consider supports of the controls that may vary with respect to the time variable. The goal is to compute approximations of such controls that drive the solution from a prescribed initial state to zero at a large enough controllability time. Assuming a geometric optic condition on the support of the controls, we first prove a generalized observability inequality for the homogeneous wave equation. We then introduce and prove the well-posedness of a mixed formulation that characterizes the controls of minimal square-integrable norm. Such mixed formulation, introduced in [\textit{Cindea and Münch, A mixed formulation for the direct approximation of the control of minimal -norm for linear type wave equations}], and solved in the framework of the (space-time) finite element method, is particularly well-adapted to address the case of time dependent support. Several numerical experiments are discussed
A mixed formulation for the direct approximation of the control of minimal -norm for linear type wave equations
No full textThis paper deals with the numerical computation of null controls for the wave equation with a potential. The goal is to compute approximations of controls that drive the solution from a prescribed initial state to zero at a large enough controllability time. In [\textit{Cindea, Fernandez-Cara \& Münch, Numerical controllability of the wave equation through primal methods and Carleman estimates, 2013}], a so called primal method is described leading to a strongly convergent approximation of boundary controls : the controls minimize quadratic weighted functionals involving both the control and the state and are obtained by solving the corresponding optimality condition. In this work, we adapt the method to approximate the control of minimal square-integrable norm. The optimality conditions of the problem are reformulated as a mixed formulation involving both the state and his adjoint. We prove the well-posedeness of the mixed formulation (in particular the inf-sup condition) then discuss several numerical experiments. The approach covers both the boundary and the inner controllability. For simplicity, we present the approach in the one dimensional case
A mixed formulation for the direct approximation of the control of minimal -norm for linear type wave equations
No full textThis paper deals with the numerical computation of null controls for the wave equation with a potential. The goal is to compute approximations of controls that drive the solution from a prescribed initial state to zero at a large enough controllability time. In [\textit{Cindea, Fernandez-Cara \& Münch, Numerical controllability of the wave equation through primal methods and Carleman estimates, 2013}], a so called primal method is described leading to a strongly convergent approximation of boundary controls : the controls minimize quadratic weighted functionals involving both the control and the state and are obtained by solving the corresponding optimality condition. In this work, we adapt the method to approximate the control of minimal square-integrable norm. The optimality conditions of the problem are reformulated as a mixed formulation involving both the state and his adjoint. We prove the well-posedeness of the mixed formulation (in particular the inf-sup condition) then discuss several numerical experiments. The approach covers both the boundary and the inner controllability. For simplicity, we present the approach in the one dimensional case
Andragogía en los Estudios Sociales: su incidencia en el desarrollo del aprendizaje significativo con poblaciones estudiantes adultas de décimo año en el CINDEA Alberto Manuel Brenes Mora, durante el 2020-2021
No full textEl presente proyecto de investigación propone la andragogía como alternativa educativa, a
través de la incorporación del aprendizaje significativo, para una educación integral, que atienda a las
necesidades educativas de las personas estudiantes que asisten al CINDEA Alberto Manuel Brenes
Mora.
El mismo se enmarca dentro de la investigación socioeducativa y parte de la Licenciatura en la
Enseñanza de los Estudios Sociales y la Educación Cívica, bajo la modalidad de Seminario de
Graduación. Este presenta por eje de investigación: Los Estudios Sociales y La Educación Cívica para
el Nuevo Milenio, desafíos desde una Perspectiva crítica, respondiendo al problema de investigación:
¿cómo incorporar el enfoque andragógico desde el programa de estudio de los Estudios
Sociales de décimo año del MEP, para lograr un aprendizaje significativo en la población
estudiantil adulta del CINDEA Alberto Manuel Brenes Mora, durante el período lectivo del
2020?
Se sustenta, teóricamente, en las posturas de D. Ausubel, M. Knowless, I. Sánchez, L.
Rodríguez, M. Villaruel, para desarrollar conceptos como Andragogía, Aprendizaje Significativo,
Mediación, Mediador y Currículo. Metodológicamente, parte del Paradigma naturalista, Enfoque
cualitativo, Diseño de Investigación narrativo y Tipo de Estudio etnográfico. En la aplicación de
instrumentos para la recolección de información se utilizó cuestionarios, grupo focal y un análisis de
los programas de estudio aplicados en el CINDEA.
En última instancia, para el contraste de la información se utiliza la triangulación para
evidenciar las realidades de las personas estudiantes adultas en relación con el tipo de educación que se
impulsa desde el MEP, para el caso específico del CINDEA Alberto Manuel Brenes Mora. De esta
manera, se logró evidenciar que existen vacíos teóricos y prácticos en la educación que reciben las
personas adultas dado que la misma no se ajusta a su contexto y cotidianidad.This research project proposes andragogy as an educational alternative, through the incorporation of meaningful learning, for a comprehensive education that meets the educational needs of students who attend CINDEA Alberto Manuel Brenes Mora. It is part of the socio-educational research and part of the Bachelor's Degree in Teaching Social Studies and Civic Education, under the modality of Graduation Seminar. This presents by research axis: Social Studies and Civic Education for the New Millennium, challenges from a critical perspective, responding to the research problem: how to incorporate the andragogic approach from the study program of Social Studies of the tenth year of the MEP, to achieve significant learning in the adult student population of CINDEA Alberto Manuel Brenes Mora, during the 2020 school period? It is based, theoretically, on the positions of D. Ausubel, M. Knowless, I. Sánchez, L. Rodríguez, M. Villaruel, to develop concepts such as Andragogy, Meaningful Learning, Mediation, Mediator and Curriculum. Methodologically, part of the Naturalist Paradigm, Qualitative Approach, Narrative Research Design and Ethnographic Study Type. In the application of instruments for the collection of information, questionnaires, a focus group and an analysis of the study programs applied at CINDEA were used. Ultimately, to contrast the information, triangulation is used to show the realities of adult students in relation to the type of education promoted by the MEP, for the specific case of CINDEA Alberto Manuel Brenes Mora. In this way, it was possible to show that there are theoretical and practical gaps in the education that adults receive since it does not fit their context and daily life.Universidad Nacional, Costa RicaEscuela de Histori
PUBLIC – PRIVATE PARTNERSHIP IN PROVIDING PUBLIC GOODS AND SERVICES
No full textLocal administrations are searching for new ways to efficiently deliver services and to develop and maintain the infrastructure that allows economic development. Increasingly, they are turning to public-private partnerships to do so. PPPs covers a wide range of partnerships arrangements, such as: outsourcing, joint ventures, concessions, sales of equity stakes in state owned business, privatization, private finance initiative, but these forms of PPPs are not adopted by all specialists. Some organizations and specialists exclude privatization from the PPPs, because in their opinion PPPs are viable alternatives to privatization. The concept of PPP is very ambiguous.public-private partnership, concession, outsourcing, privatization
Treatment with flow diverter stent during pregnancy
No full textIntracranial aneurysms are rarely diagnosed during pregnancy. If treatment is necessary, surgery was traditionally preferred over embolization in case of ongoing pregnancy, due to concerns regarding foetal radiation exposure. We present a case of 21 mm unruptured carotid-ophthalmic aneurysm diagnosed during pregnancy and treated with flow diversion. Foetal radiation dose was estimated between 1 and 5 mGy, well below recommended limits. Double antiplatelet therapy with prasugrel and aspirin was administered between week 17 and week 37, followed by uneventful vaginal delivery at 39 weeks. The new-born infant did not present any clinical abnormalities. Post-natal angiography showed complete aneurysm occlusion. To our knowledge, this is the first report of flow diverter stent placement during ongoing pregnancy. Although a good outcome was observed in this case, this result should be interpreted with caution. Further studies are needed in order to better define the safety profiles of intracranial stents and double antiplatelet therapies during pregnancy
Inverse problems for linear hyperbolic equations via a mixed formulation
No full textWe introduce in this document a direct method allowing to solve nu-merically inverse type problems for linear hyperbolic equations. We first consider the reconstruction of the full solution of the wave equation posed in Ω × (0, T) -Ω a bounded subset of R N -from a partial distributed observation. We employ a least-squares technic and minimize the L 2 -norm of the distance from the observa-tion to any solution. Taking the hyperbolic equation as the main constraint of the problem, the optimality conditions are reduced to a mixed formulation involving both the state to reconstruct and a Lagrange multiplier. Under usual geometric optic conditions, we show the well-posedness of this mixed formulation (in partic-ular the inf-sup condition) and then introduce a numerical approximation based on space-time finite elements discretization. We prove the strong convergence of the approximation and then discussed several example for N = 1 and N = 2. The problem of the reconstruction of both the state and the source term is also addressed
APPROXIMATION OF CONTROLS FOR LINEAR WAVE EQUATIONS: A FIRST ORDER MIXED FORMULATION
No full textInternational audienceThis paper deals with the numerical approximation of null controls for the wave equation posed in a bounded domain of R n. The goal is to compute approximations of controls that drive the solution from a prescribed initial state to zero at a large enough controllability time. In [Cindea & Münch, A mixed formulation for the direct approximation of the control of minimal L 2-norm for linear type wave equations], we have introduced a space-time variational approach ensuring strong convergent approximations with respect to the discretization parameter. The method, which relies on generalized ob-servability inequality, requires H 2-finite element approximation both in time and space. Following a similar approach, we present and analyze a variational method still leading to strong convergent results but using simpler H 1-approximation. The main point is to preliminary restate the second order wave equation into a first order system and then prove an appropriate observability inequality
Deciphering simplified regional anticoagulation with citrate in intermittent hemodialysis: a clinical and computational study
No full textInternational audienceRegional citrate anticoagulation use in intermittent hemodialysis is limited by the increased risk of metabolic complications due to faster solute exchanges than with continuous renal replacement therapies. Several simplifications have been proposed. The objective of this study was to validate a mathematical model of hemodialysis anticoagulated with citrate that was then used to evaluate different prescription scenarios on anticoagulant effectiveness (free calcium concentration in dialysis filter) and calcium balance. A study was conducted in hemodialyzed patients with a citrate infusion into the arterial line and a 1.25 mmol/L calcium dialysate. Calcium and citrate concentrations were measured upstream and downstream of the citrate infusion site and in the venous line. The values measured in the venous lines were compared with those predicted by the model using Bland and Altman diagrams. The model was then used with 22 patients to make simulations. The model can predict the concentration of free calcium, bound to citrate or albumin, accurately. Irrespective of the prescription scenario a decrease in free calcium below 0.4 mmol/L was obtained only in a fraction of the dialysis filter. A zero or slightly negative calcium balance was observed, and should be taken into account in case of prolonged use
An approximation method for exact controls of vibrating systems
No full textInternational audienceWe propose a new method for the approximation of exact controls of a second order infinite dimensional system with bounded input operator. The algorithm combines Russell's ''stabilizability implies controllability" principle with the Galerkin's method. The main new feature brought in by this work consists in giving precise error estimates. In order to test the efficiency of the method, we consider two illustrative examples (with the finite element approximations of the wave and the beam equations) and we describe the corresponding simulations
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