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Virtual education customized to learning styles and problem-based learning (PBL): A neural network-based approach [Educación virtual personalizada a estilos de aprendizaje y ABP: Una aproximación basada en redes neuronales]
No full text[No abstract available
A Search for Ultra-high-energy Neutrinos from TXS 0506+056 Using the Pierre Auger Observatory
No full textResults of a search for ultra-high-energy neutrinos with the Pierre Auger Observatory from the direction of the blazar TXS 0506+056 are presented. They were obtained as part of the follow-up that stemmed from the detection of high-energy neutrinos and gamma rays with IceCube, Fermi-LAT, MAGIC, and other detectors of electromagnetic radiation in several bands. The Pierre Auger Observatory is sensitive to neutrinos in the energy range from 100 PeV to 100 EeV and in the zenith-angle range from θ = 60° to θ = 95°, where the zenith angle is measured from the vertical direction. No neutrinos from the direction of TXS 0506+056 have been found. The results were analyzed in three periods: One of 6 months around the detection of IceCube-170922 A, coinciding with a flare period of TXS 0506+056, a second one of 110 days during which the IceCube collaboration found an excess of 13 neutrinos from a direction compatible with TXS 0506+056, and a third one from 2004 January 1 up to 2018 August 31, over which the Pierre Auger Observatory has been taking data. The sensitivity of the Observatory is addressed for different spectral indices by considering the fluxes that would induce a single expected event during the observation period. For indices compatible with those measured by the IceCube collaboration the expected number of neutrinos at the Observatory is well below one. Spectral indices as hard as 1.5 would have to apply in this energy range to expect a single event to have been detected. © 2020. The American Astronomical Society. All rights reserved
Role of Transition Metals on TM/Mo2C Composites: Hydrogen Evolution Activity in Mildly Acidic and Alkaline Media
No full textModification of electronic and chemical properties of a material by the introduction of another element into its lattice is one of the most common methods for designing new catalysts for different applications. In this work the effect of modifying molybdenum carbide with transition metals (Fe, Co, Ni, Cu), TM-Mo2C composites, upon the catalytic activity toward hydrogen evolution reaction (HER) in mild acidic and alkaline media has been studied. Catalysts were prepared by carbothermal reduction of molybdenum and TM oxides precursors and were characterized by different physicochemical techniques. Results evidenced a strong pH effect on the catalytic performance of TM-Mo2C, while, at pH = 5, inclusion of TM into the Mo2C lattice has a deleterious effect on the HER activity and, at pH = 9, a promoting effect was observed, highlighting the importance of considering specific operation conditions during the catalyst design process. Analysis of in situ near-edge X-ray adsorption data reveals a decrease on the oxidation state and average bond ionicity of dopant metal upon a pH increase, shedding light of the different effects of TMs on the resulting HER activity in acidic and alkaline media. Finally, stability tests demonstrated no deterioration on catalysts' performance after 8 h of continuous cycling within the HER working range, confirming the suitability of Mo2C materials as promising HER catalysts
Enhanced geothermal systems: Review and analysis of case studies
No full textThis article reviews the characteristics of the EGS, sources of clean energy that promise to be an alternative to face the problems related to global warming caused by the use of fossil fuels like oil and natural gas. Currently in Colombia the geothermal systems of interest are hydrothermal, so there are no plans for the development of EGS yet, however, this article pretends to be an introduction to the reader interested in EGS and to be a reference to future projects developed in the national territory, describing the most significant places in the world where this technique has been used, along with its social perception and associated impacts. In addition, it seeks to analyze the differences between the hydraulic stimulation technique in the EGS and the fracking used for the extraction of shale gas. © 2020 Universidad Industrial de Santander
Impact of Electricity Regulation on Distributed Generation in Latin American and Caribbean Countries
No full textThis work shows the impact of electricity regulation inside the context of distributed generation in Latin American and Caribbean countries through the analysis of the current regulation and the projects registered in each of the countries. Information was collected about the updated regulation in each country and the distributed generation projects derived from said regulation. Based on this information, the percentage of the potential capacity of the distributed generation projects was identified with respect to the total installed power within each country, obtaining in this way the results that allow to make a comparison between the countries of the region regarding the impact of the regulatory framework of distributed generation. © 2020 IEEE
The social discount rate and the environment [La tasa social de descuento y el medio ambiente]
No full text[No abstract available
Altitude and fertilization type: concentration of nutrients and production of biomass in Stevia rebaudiana Bertoni
No full textAgricultural production systems demand techniques that allow reducing uncertainty in decision-making. A factor that adds uncertainty in agricultural systems is altitude since it influences the nutrient uptake by plants. This work aimed to evaluate the influence of two altitudinal gradients (2569 and 1487 m.a.s.l.) and two fertilizers: an organo-mineral fertilizer (composted poultry manure mixed with inorganic fertilizer) and mineral fertilizer (control) on the nutrient uptake and biomass production in commercial stevia crops. The effect of altitude and fertilizers was evaluated after 60 days, under greenhouse conditions, assessing macro and micronutrient levels in the plant leaves (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, manganese, zinc, iron, and boron) and biomass production. The results of this work showed the effect of altitude (2569 m.a.s.l.) and organo-mineral fertilization on crop productivity and yield. The application of the organo-mineral fertilizer decreased the differences of nutrient uptake between the altitudinal gradients and provided both better nutrient uptake levels, mainly of N (79%), Ca (115%), and Mg (162%), and increased biomass production (49%), than mineral fertilization at both experimental sites. Likewise, the organo-mineral fertilizer enhanced the soils’ cation exchange capacity, increased nutrient availability, and minimizing the risks of contamination by nutrient leaching. An important conclusion of this work is that stevia plants grown at different altitudes differ in nutrient uptake (mostly nitrogen 79%); therefore, fertilizer dosing must be adjusted to crop altitude, especially for mineral fertilizers. Thus, fertilizer design should consider not only the plant nutrition requirements but also its environmental conditions. © 2020 Taylor & Francis Group, LLC
Memory as an open story. Political challenges of the work of memory centers and truth commissions [La memoria como relato abierto. Retos políticos del trabajo de los centros de memoria y las comisiones de verdad]
No full textThis article is based on the recognition of the need for the work of a memory center or a truth commission to analyze the political challenge that this entails, bearing in mind that the institutional circumstances that condition the production of a final report turn its exercise of memory into a hegemonic narrative, while it is expected to contribute to the construction of the symbolic framework of post-conflict. The text presents arguments to show that the existence of victims not integrated in the institutional narrative opens the possibility of a politics of memory, as a task that must be incurred by society, that assumes the challenges left by the work of a truth commission. The text concludes that it is a citizen’s task to open the space for the political action of those victims not included in the regime of memory produced institutionally. © 2018, Universidad Nacional de Colombia. All rights reserved
A Direct Role for the CD1b Endogenous Spacer in the Recognition of a Mycobacterium tuberculosis Antigen by T-Cell Receptors
No full textLipids, glycolipids and lipopeptides derived from Mycobacterium tuberculosis (Mtb) are presented to T cells by monomorphic molecules known as CD1. This is the case of the Mtb-specific sulfoglycolipid Ac2SGL, which is presented by CD1b molecules and is recognized by T cells found in tuberculosis (TB) patients and in individuals with latent infections. Our group, using filamentous phage display technology, obtained two specific ligands against the CD1b-Ac2SGL complex: (i) a single chain T cell receptor (scTCR) from a human T cell clone recognizing the CD1b-AcSGL complex; and (ii) a light chain domain antibody (dAbκ11). Both ligands showed lower reactivity to a synthetic analog of Ac2SGL (SGL12), having a shorter acyl chain as compared to the natural antigen. Here we put forward the hypothesis that the CD1b endogenous spacer lipid (EnSpacer) plays an important role in the recognition of the CD1b-Ac2SGL complex by specific T cells. To support this hypothesis we combined: (a) molecular binding assays for both the scTCR and the dAbκ11 antibody domain against a small panel of synthetic Ac2SGL analogs having different acyl chains, (b) molecular modeling of the CD1b-Ac2SGL/EnSpacer complex, and (c) modeling of the interactions of this complex with the scTCR. Our results contribute to understand the mechanisms of lipid presentation by CD1b molecules and their interactions with T-cell receptors and other specific ligands, which may help to develop specific tools targeting Mtb infected cells for therapeutic and diagnostic applications. © Copyright © 2020 Camacho, Moreno, Garcia-Alles, Chinea Santiago, Gilleron, Vasquez, Choong, Reyes, Norazmi, Sarmiento and Acosta
Linear programming for aggregate production planning in a textile company
No full textThis article aims to propose and implement an aggregated production planning model to provide optimal strategies in the medium term for a textile company, for which a linear programming model is proposed to minimise total costs associated with labour and inventory levels. The model proposed takes into account characteristics associated with fabric contraction, wastes in the process, the efficiency of new employees, and training requirements. The model is implemented and solved in GAMS, supported on an MSExcel interface, to find the optimal solution, which is to apply a hybrid strategy to the production plan, and also some strategies for improving the production process are generated. © 2018, Institute of Biopolymers and Chemical Fibres. All rights reserved