Repositorio institucional - Concytec
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Handling missing values in interrupted time series analysis of longitudinal individual-level data
No full textBackground: In the interrupted time series (ITS) approach, it is common to average the outcome of interest at each time point and then perform a segmented regression (SR) analysis. In this study, we illustrate that such ‘aggregate-level’ analysis is biased when data are missing at random (MAR) and provide alternative analysis methods. Methods: Using electronic health records from the UK, we evaluated weight change over time induced by the initiation of antipsychotic treatment. We contrasted estimates from aggregate-level SR analysis against estimates from mixed models with and without multiple imputation of missing covariates, using individual-level data. Then, we conducted a simulation study for insight about the different results in a controlled environment. Results: Aggregate-level SR analysis suggested a substantial weight gain after initiation of treatment (average short-term weight change: 0.799kg/week) compared to mixed models (0.412kg/week). Simulation studies confirmed that aggregate-level SR analysis was biased when data were MAR. In simulations, mixed models gave less biased estimates than SR analysis and, in combination with multilevel multiple imputation, provided unbiased estimates. Mixed models with multiple imputation can be used with other types of ITS outcomes (eg, proportions). Other standard methods applied in ITS do not help to correct this bias problem. Conclusion: Aggregate-level SR analysis can bias the ITS estimates when individual-level data are MAR, because taking averages of individual-level data before SR means that data at the cluster level are missing not at random. Avoiding the averaging-step and using mixed models with or without multilevel multiple imputation of covariates is recommended. © 2020 Bazo-Alvarez et al.Fondo Nacional de Desarrollo Científico y Tecnológico - Fondecy
Ambient lighting generation for flash images with guided conditional adversarial networks
No full textTo cope with the challenges that low light conditions produce in images, photographers tend to use the light provided by the camera flash to get better illumination. Nevertheless, harsh shadows and non-uniform illumination can arise from using a camera flash, especially in low light conditions. Previous studies have focused on normalizing the lighting on flash images; however, to the best of our knowledge, no prior studies have examined the sideways shadows removal, reconstruction of overexposed areas, and the generation of synthetic ambient shadows or natural tone of scene objects. To provide more natural illumination on flash images and ensure high-frequency details, we propose a generative adversarial network in a guided conditional mode. We show that this approach not only generates natural illumination but also attenuates harsh shadows, simultaneously generating synthetic ambient shadows. Our approach achieves promising results on a custom FAID dataset, outperforming our baseline studies. We also analyze the components of our proposal and how they affect the overall performance and discuss the opportunities for future work.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte
Capacitance voltage curve simulations for different passivation parameters of dielectric layers on silicon
No full textSurface passivation is a widely used technique to reduce the recombination losses at the semiconductor surface. The passivating layer performance can be mainly characterized by two parameters: The fixed charge density (Q(ox)) and the interface trap density (D-it) which can be extracted from Capacitance-Voltage measurements (CV). In this paper, simulations of High-Frequency Capacitance-Voltage (HF-CV) curves were developed using simulated passivation parameters in order to examine the reliability of measured results. The D-it was modelled by two different sets of functions: First, the sum of Gaussian functions representing different dangling bond types and exponential tails for strained bonds. Second, a simpler U-shape model represented by the sum of exponential tails and a constant value function was employed. These simulations were validated using experimental measurements of a reference sample based on silicon dioxide on crystalline silicon (SiO2/c-Si). Additionally, a fitting process of HF-CV curves was proposed using the simple U-shape D-it model. A relative error of less than 0.4% was found comparing the average values between the approximated and the experimentally extracted D-it's. The constant function of the approximated D-it represents an average of the experimentally extracted D-it for values around the midgap energy where the recombination efficiency is highest.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte
Characterization and comparison of Porphyridium sordidum and Porphyridium purpureum concerning growth characteristics and polysaccharide production
No full textMicroalgae as photosynthetic microorganisms are the source of valuable compounds such as proteins, carotenoids, lipids and carbohydrate polymers. Among the different phyla, Porphyridium as part of the red microalgae (Rhodophyta) are of high importance as producers of sulfated polysaccharides. As the name suggests these microalgae are typically red; however, Porphyridium sordidum has an olive-green color and was recently described as a putative exopolysaccharide producer. Exopolysaccharides (EPS) are sugars polymers excrete to the culture medium. In this study P. sordidum is evaluated for the first time in detail as newly described EPS producer in direct comparison to the already characterized EPS producer Porphyridium purpureum. The evaluation was performed on several aspects, such as morphological differences between the two strains followed by the comparison of the growth behavior, nitrate and phosphate uptake during cultivation of both strains, and a detailed analysis of the EPS. P. purpureum consumed 51 ± 4.6% of nitrate and 95 ± 2.1% of phosphate compared to P. sordidum which utilized 17 ± 0.1% of nitrate and 68 ± 0.1% of phosphate at day 30 of cultivation. The produced EPS were analyzed and revealed the major constitutional carbohydrate monomers of the EPS to be xylose, galactose, glucose and glucuronic acid. In addition, other substituents that decorate the EPS were identified as sulfate and methyl groups. Finally, rheological measurements (viscosity curves and amplitude sweeps) were performed to analyze the physicochemical properties.Fondo Nacional de Desarrollo Científico y Tecnológico - Fondecy
Acidic pretreatment of a copper-silver ore and its beneficial effect on cyanide leaching
No full textThe presence of copper in ores containing noble metals results in a high consumption of cyanide during leaching, which is undesirable from economic and environmental standpoints. Substantial previous work targets copper-gold ores, but the present study focuses on a copper-silver ore, which will be leached following acidic pretreatment (sulfuric acid at pH 1) to assess the effect of copper in cyanide consumption and silver extraction. The ore is mainly composed of hematite/goethite and silicates, with copper (0.15%) and silver (250 ppm) mostly present as sulfides and sulfosalts. The acidic pretreatment dissolves 18% of the copper content, which in turn decreases the cyanide consumption from 7 to 3 kg NaCN/ton in a five-hour leaching. Mineralogical changes, followed by polarization microscopy, are only minimal and restricted to iron oxides, while silicates and sulfides remain unchanged. However, X-ray photoelectron spectroscopy shows that surface copper oxides and calcium are removed during acidic pretreatment, without removing silver or copper sulfides. While no significant increase in silver extraction is observed after pretreatment, silver extraction takes place at a significantly faster rate, which demonstrates that copper decreases the kinetics of leaching and is responsible for a high consumption of cyanide during leaching. This work highlights the need for understanding the solubility of copper compounds to design strategies aimed at improving the efficiency of cyanide leaching in copper-silver ores.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte
Presentación del Comité del Portal SciELO Perú
No full textPresenta al comité de la colección SciELO Perú, quien entre otras funciones realizará la inclusión y exclusión de las revistas indizadas y postulantes. Asimismo, propondrá lineamientos para el fortalecimiento de la colección
Control de oscilaciones inter-área en sistemas de potencia de gran escala mediante mediciones de área amplia
No full textPropone diseñar un control de amortiguamiento de área amplia (WADC, por sus siglas en inglés) para sistemas eléctricos de potencia de gran escala. El control se realiza con base a la identificación del modelo lineal del sistema dinámico alrededor de una condición operativa. La identificación se lleva a cabo mediante el método de interpolación de matrices de Loewner (LIM, por sus siglas en inglés), que utiliza mediciones del sistema de potencia para obtener el modelo lineal
SciELO Perú: una mirada quince años después
No full textPresenta una revisión histórica de la colección SciELO Perú desde su conformación en el año 2004 a la fecha. Presenta datos cualitativos y cuantitativos de la colección
Guía práctica para la formulación y ejecución de proyectos de investigación y desarrollo experimental (I+D)
No full textContiene pautas sobre la estructura de un proyecto de investigación, criterios básicos a considerar en su evaluación, indicadores de producción científica y procesos de gestión de un proyecto de I+D, contribuyendo además a un adecuado cierre del mismo. La finalidad del documento es Contribuir a la calidad y originalidad del conocimiento y productos generados por losproyectos de I+D desarrollados en las instituciones del país, promoviendo así investigaciones de impacto científico, tecnológico, ecológico y socioeconómico a nivel regional, nacional e internacional
RENATI: Registro Nacional de Trabajos conducentes a Grados y Títulos
No full textProporciona información en torno al Registro Nacional de Trabajos conducentes a Grados y Títulos (RENATI). Esta presentación fue realizada como parte del taller virtual: "Sensibilización sobre la normativa ALICIA y RENATI"