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Evaluation of 3B42V7 and IMERG daily-precipitation products for a very high-precipitation region in northwestern South America
No full textThe availability of water is critical in determining the distribution of species by favoring or limiting their development, and leading to the formation of different ecosystems. Thus, analyzing the trends and fluctuations of the precipitation is a key factor to understanding our planet's biodiversity. Different physical conditions exist in northwestern South America that cause extreme climate conditions, especially on the west coast of the continent. This region, known as Biogeographic Chocó has high annual precipitation caused by interactions between the humid currents of the Pacific Ocean and the Andes Mountains. A limited network of hydro-meteorological stations are available in the region to monitor precipitation. Satellite precipitation products can provide valuable information in the absence of field stations, complementing the network of field stations in remote areas, and completing time series for stations that have stopped working. However, remote sensing data must be validated before being used. The goal of this study is thus to evaluate the accuracy of the products of the Tropical Rainfall Measuring Mission 3B42V7 and the Integrated Multi-satellite Retrievals for Global Precipitation Measurement (IMERG), under very high precipitation conditions, and evaluate their strengths and shortcomings. These programs provide daily-precipitation information with a spatial resolution of 0.25° for the former and 0.1° for the latter. The validation was done by using a time series of daily-precipitation data obtained from 185 hydro-meteorological stations distributed over the Biogeographic Chocó. Different statistic metrics were used in the evaluation and comparison: error metrics (mean difference MD, relative mean difference RMD, and root mean square error RMSE), a correlation metric (Pearson correlation CP), contingency metrics (probability of detection POD, false-alarm ratio FAR, and critical success index CSI). We also evaluate the grid and areal scale. The results show that (i) the 3B42V7 and IMERG daily-precipitation products represent well the spatial and temporal distribution of mean daily precipitation over the Biographic Chocó and both products are accurate for detecting precipitation events. (ii) Mean daily precipitation tends to be overestimated in areas with relative low precipitation and medium-to-high altitude whereas, on the contrary, mean daily precipitation tends to be underestimated in areas with very high precipitation and medium-to-low altitude. (iii) Finally, copious precipitation (i.e., an annual accumulated precipitation over 5000 mm, which is common for over 55% of the study area) strongly affects the accuracy of the satellite products, leading to significant errors in estimates of daily precipitation for some regions. This study constitutes one of the first exhaustive validation of the IMERG daily precipitation product over the Biogeographic Chocó and the results provide important information about the potential for using this product in the study area and over regions with high precipitation. © 201
Dangling-to-Interstitial Oxygen Transition and Its Modifications of the Electronic Structure in Few-Layer Phosphorene
No full textIn this work, oxidation processes are correlated with the current-voltage characteristics of few-layer black phosphorus obtained by liquid-phase exfoliation. Black phosphorous (BP), a room-temperature p-type semiconductor, exhibits an anomalous switching behavior between 373 and 448 K. The anomalous increase in electrical resistance is explained using a combined spectroscopic and DFT approach. The activation energy for thermally activated electrical conductance was calculated from the current-voltage characteristics and correlated with the oxidation processes. The activation energy for thermally activated electrical conductance in the dangling oxide BP phase was found to be 79.7 meV, ∼40 times lower than that in the interstitial counterpart. First-principles calculations reveal electronic differences between dangling and interstitial oxides, and electrical resistance measurements reveal a Schottky-to-ohmic contact formation related to the differences in the calculated work function of dangling and interstitial oxides. We propose that this phenomenon can be exploited as a fast, economical method for the evaluation of the oxidation processes in few-layer BP.
Assessing school principal leadership practices. Validity and reliability of a rubric [Evaluación de las prácticas directivas en directores escolares: validez y confiabilidad de una rúbrica]
No full textBasic education has several priorities, such as improving students’ levels of reading, calculation, and social interaction; changing pedagogical practices traditionally based on oral expositions and content learning; building a more inclusive school environment; improving security conditions; and ensuring that schools operate well. Although it is well known that rubrics are tools that allow for verifying achievements and accurately defining improvement needs, however, there are no available rubrics to assess principals’ management regarding these priorities in basic education. The purpose of the present study was to design and validate an analytical rubric that could be used by principals to self-assess their practices and establish improvement actions that would benefit learning in elementary schools. The instrument was assessed by 10 judges. Aiken’s V values higher than 0.75 were obtained in relevance, intelligibility of wording, and satisfaction with the instrument. The rubric was administered to a group of 645 elementary school principals, who found every item satisfactory, relevant, intelligibly worded, and suitable for use to help them to improve their managerial practices. A factor analysis was then carried out, and, in accordance with what was expected at the theoretical level, a single factor was found. Finally, it was established that the rubric has reliability of 0.877. It is concluded that the rubric for management practices self-assessment has adequate levels of content validity, construct validity, and reliability. © 2020, Universidad Nacional de Educacion a Distancia. All rights reserved
On the principle of planning in public contracting: A theoretical and factual analysis in the colombian legal order [Del principio de planeación en la contratación estatal: Un análisis teórico y fáctico en el orden jurídico colombiano]
No full textThe present work has two objectives: (i) to illustrate how the constitutional and principlistic paradigm of our legal system reliably conditions the entire scaffolding of public contracting and, (ii) to demonstrate, by means of a theoretical and factual analysis, how the principle of planning, without the mediation an explicit declaration in law, whether or not it is an essential criterion to develop all other principles, values, duties and functions of public contracting in Colombia. © 2020
Effect of the concentration ratio on energetic and exergetic performance of concentrating solar collectors with integrated transparent insulation materials
No full textThe effect of the concentration ratio on the performance of parabolic trough and central receiver collectors with integrated transparent insulation materials (TIMs) is analyzed in this work. A model based on optical, energy, and exergy analyses is developed to determine thermal and second law efficiencies of concentrated solar collectors as a function of the absorber temperature and concentration ratio. The results are compared with the respective traditional collector configurations without TIM. In general, high concentration ratios are fundamental to maintain high efficiencies. The incorporation of a TIM into concentrated solar collectors leads to higher thermal efficiencies at high operating temperatures even at low concentration ratios. An equivalent second law efficiency to that of the reference collector configuration can be achieved at lower concentration ratios by incorporating a TIM in parabolic trough or a TIM and a glass envelope in central receiver collectors. The idea of using a TIM deserves further exploration as it seems to be a promising alternative that contributes to a more efficient and cost-effective technology. © 2019 Elsevier Lt
Nominalismo y temporalidad en el mono gramático (1970) de octavio paz
No full text[No abstract available
System dynamics baseline model for determining a multivariable objective function optimization in Wireless Sensor Networks
No full textWireless Sensor Networks (WSN) are dedicated networks used in applications where environmental information must be collected, such as temperature, humidity, level, flow, pressure, rain, radiation, among others. These kinds of networks are constrained regarding power, bandwidth, number of nodes per area unit, etc. It is desirable that they operate without supervision and can work steadily in time, because they are normally located in difficult or far places. Nonetheless, some of these metrics are conflicting with others, so if one improves, some of the others get worse. So, it is mandatory to know what is the best combination of metrics that in conjunction can fit an application the best. Literature reports works where \neg optimization is used as a mathematical scheme to solve this problem, and two scenarios are provided: First, where a single objective function is proposed regarding one metric, and the other metrics are restricted via constraints, and second, where multi-objective optimization (MOOP) approaches are proposed, but without considering the whole set of significant metrics involved in WSN, so there is not a definitive solution that finds a real optimal set of metrics. System Dynamics (SD) is a computer-aided approach to design and analyze (mostly) social, economic and enterprise systems, that allows proposing a mathematical framework to analyze such complex systems, by using relationships of interdependence, mutual interaction, feedback and causality. This work aims to show a first dynamic hypothesis of a model that considers important metrics ofWSN, in order to find a set of equations that serve as objective functions in a MOOP context. By applying this methodology is possible to find some difficult relations between metrics, that are not clearly reported by previous work so far. © 2020 AISTI
LA «pRESIDENCIA IMPERIAL» Y SU EVOLUCIÓN EN LA ESTRUCTURA CONSTITUCIONAL DE LOS ESTADOS UNIDOS DE AMÉRICA
No full textThis article analyzes «Imperial Presidency» in US Constitutional Law from a historical and institutional perspective. This is firstly made from a philosophical foundation of American constitutionalism and secondly from an evolution of the Presidential government. These two parts try to answer the question about the limits of the Federal presidency. It should be noted that these are not enough, because the executive orders promote the President's role, allowing the US to become a powerful country. The conclusion of this work that the «imperial presidency» is opposed to the moderate republic of the Founding Fathers; the blur limits of the executive department always adjust to the political power facts and situations. © 2019 Universidad Nacional de Educacion a Distancia. All rights reserved
Subgeneric comedy during Spanish transition: Paradoxes into the storm [La comedia subgenérica de la Transición española: Paradojas en la tormenta]
No full textThe period of the Spanish Transition was as prolific in film production as in analysis of those works that were born in a turbulent time. But there was a group of films that took advantage of the new freedom but they were ideologically anchored in the past. These films rarely have been studied. We refer to what we call the Subgeneric Transition Comedy, a group of remarkable box office hits with an undeniable force as ideological weapon. We will try to demonstrate this through an analysis of the 30 most representative examples of that subgenre. © 2018 Universidad Complutense de Madrid. All rights reserved
Structural Relaxation and Crystalline Phase Effects on the Exchange Bias Phenomenon in FeF2/Fe Core/Shell Nanoparticles
No full textIn this study, the power of first-principles methods along with molecular dynamics and atomistic Monte Carlo simulations is employed to elucidate the effects of the structural relaxation on the exchange bias (EB) behavior of FeF2/Fe core/shell nanoparticles. The effects of the crystalline phase are also explored by studying the EB features on the related nanoparticles modeled through simple cubic, body centered cubic, and face centered cubic systems. The results indicate that effects of both structural relaxation and crystalline phase on the EB phenomenon are crucial. Noticeable differences are found in the quantitative and qualitative results, as well as in conclusions from studies which, for the sake of simplicity, have used simple cubic crystalline structures for modeling the sample of study instead of its own crystalline model. To compare these results with experimental systems, hysteresis behaviors under field cooling procedures and for a sample made up by a particle diameter distribution D = 4.3 ± 0.7 nm, which is easily affordable at present, are presented. In that sense, this study raises a warning about the conclusions derived from previous works, and offers a suggestion to pay close attention to both the crystalline model and the structural relaxation of the nanoparticle systems exhibiting EB effects. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei