Parameter estimation using ensemble based data assimilation in the presence of model error

This work explores the potential of online parameter estimation as a technique for model error treatment under an imperfect model scenario, in an ensemble-based data assimilation system, using a simple atmospheric general circulation model, and an observing system simulation experiment (OSSE) approach. Model error is introduced in the imperfect model scenario by changing the value of the parameters associated with different schemes. The parameters of the moist convection scheme are the only ones to be estimated in the data assimilation system. In this work, parameter estimation is compared and combined with techniques that account for the lack of ensemble spread and for the systematic model error. The OSSEs show that when parameter estimation is combined with model error treatment techniques, multiplicative and additive inflation or a bias correction technique, parameter estimation produces a further improvement of analysis quality and medium-range forecast skill with respect to the OSSEs with model error treatment techniques without parameter estimation. The improvement produced by parameter estimation is mainly a consequence of the optimization of the parameter values. The estimated parameters do not converge to the value used to generate the observations in the imperfect model scenario; however, the analysis error is reduced and the forecast skill is improved.Fil: Ruiz, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; Argentina. Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos; Argentina. Advanced Institute for Computational Science ; JapónFil: Pulido, Manuel Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnologica; Argentina. Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos; Argentin

El "IMACO": un índice mensual líder de la actividad económica en Colombia

En este trabajo se describe la construcción de un nuevo indicador mensual líder de la actividad económica en Colombia (IMACO). El procedimiento se basa en un algoritmo de búsqueda heurístico que identifica siete variables líderes del nivel de actividad, que anticipan los movimientos del PIB con cinco meses de adelanto y una correlación del 93%. Asimismo, el IMACO tiene otras propiedades predictivas deseables: anticipa los puntos de quiebre del ciclo económico colombiano sin arrojar señales falsas, y minimiza los errores de pronóstico sobre el crecimiento del PIB. Dada su simplicidad y bajo costo computacional, el IMACO provee una herramienta para el seguimiento continuo de la coyuntura y el diseño de la política económica, que puede ser replicado tanto para otros agregados macroeconómicos en Colombia así como en otros países de la región.Índice líder, ciclo económico, componentes principales. Classification JEL: E23, E27, E37.

Estimating Model Parameters with Ensemble-Based Data Assimilation: A Review

In this work, various methods for the estimation of the parameter uncertainty and the covariance between the parameters and the state variables are investigated using the local ensemble transform Kalman filter (LETKF). Two methods are compared for the estimation of the covariances between the state variables and the parameters: one using a single ensemble for the simultaneous estimation of model state and parameters, and the other using two separate ensembles; for the initial conditions and for the parameters. It is found that the method which uses two ensembles produces a more accurate representation of the covariances between observed variables and parameters, although this does not produce an improvement of the parameter or state estimation. The experiments show that the former method with a single ensemble is more efficient and produces results as accurate as the ones obtained with the two separate ensembles method. The impact of parameter ensemble spread upon the parameter estimation and its associated analysis is also investigated. A new approach to the optimization of the estimated parameter ensemble spread (EPES) is proposed in this work. This approach preserves the structure of the analysis error covariance matrix of the augmented state vector. Results indicate that the new approach determines the value of the parameter ensemble spread that produces the lowest errors in the analysis and in the estimated parameters. A simple low-resolution atmospheric general circulation model known as SPEEDY is used for the evaluation of the different parameter estimation techniques.Fil: Ruiz, Juan Jose. Universidad Nacional del Nordeste; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pulido, Manuel Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; ArgentinaFil: Miyoshi, Takemasa. University of Maryland; Estados Unidos de América

Diabetic Macular Edema: From Old Concepts to New Therapeutic Avenues

Diabetic macular edema (DME) is an important cause of blindness in the working population and is currently challenging to treat. Current interventions include focal laser or intravitreal injections. This article outlines a new treatment protocol based on the concept that peripheral ischemia is the introduction to angiogenesis, that will ultimately gather its momentum at the fovea. Performing extreme peripheral light laser panretinal photocoagulation (PRP) back to the equator reduces excessive expression of the vascular endothelial growth factor (VEGF) in the eye. Subsequently, this decreases VEGF-induced DME and provides long-term protection for the development of neovascularization. Initial exacerbation of DME often accompanies PRP, Therefore; first injections of anti-VEGF agents (with or without dexamethasone implant) can forestall worsening of DME preventing loss of vision. However, on the other hand, applying peripheral PRP and intraocular injections can induce posterior vitreous detachment (PVD). This could help release vitreomacular adhesions (VMA) and vitreomacular traction (VMT), decreasing DME severity and improving response to intravitreal injections. The current approach works by laser ablation of the peripheral retina that should stop the drive for VEGF release; moreover, laser ablation should produce secondary, accidental and beneficial PVD. This approach precludes focal laser therapy and paves the path for prolonged anti-VEGF therapy

Detection of Elevated Signaling Amino Acids in Human Diabetic Vitreous by Rapid Capillary Electrophoresis

Elevated glutamate is implicated in the pathology of PDR. The ability to rapidly assess the glutamate and amino acid content of vitreous provides a more complete picture of the chemical changes occurring at the diabetic retina and may lead to a better understanding of the pathology of PDR. Vitreous humor was collected following vitrectomies of patients with PDR and control conditions of macular hole or epiretinal membrane. A capillary electrophoresis method was developed to quantify glutamate and arginine. The analysis is relatively fast (<6 minutes) and utilizes a poly(ethylene)oxide and sodium dodecylsulfate run buffer. Both amino acid levels show significant increases in PDR patients versus controls and are comparable to other reports. The levels of vitreal glutamate vary inversely with the degree of observed hemorrhage. The results demonstrate a rapid method for assessment of a number of amino acids to characterize the chemical changes at the diabetic retina to better understand tissue changes and potentially identify new treatments

EVALUATION OF POSTURAl STABILITY AND ITS RELATION TO ISOKINETIC PERFORMANCE IN PERSONS WITH CEREBRAL PALSY

There are several studies targeting to the functional evaluation of lower extremities in Cerebral Palsy (CP). However there is lack of information concerning the relationship of lower-limb weakness and certain limitations in functional abilities like postural stability (Mauishi et al. 2001; Engsberg et al. 2000; Nardone, 2001; Wiley and Damiano, 1998; Damiano and Kelly, 1995). The main purpose of this study is to determine the level of neuromuscular potential, assessed by isokinetic tests and its relation to postural stability in persons affected by different types of CP

POSTURAL STABILITY IN PERSONS WITH CEREBRAL PALSY AND ITS RELATIONSHIP WITH THE PERfORMANCE IN VERTICAL JUMPING

The main purpose of this study was to evaluate the quality of postural stability of persons affected by different symptoms of cerebral palsy, and, on the other hand, to determine its relationship with the level of the neuromuscular potential of the subjects, evaluated on the base of their performance in the two-legged countermovement jump. The obtained results confirmed, first, significant differences between the subjects affected by hemiplegia and those affected by tetraparesis concerning the quality of postural stability, and, second, that the higher capacity for neuromuscular activity of the lower extremities is correlated with more stable posture. In this way, muscle strength seems to be a limiting factor in standing posture