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Vanadium carbide (VC) coatings were deposited on AISI H13 and AISI D2 steel substrates via thermo-reactive deposition/diffusion (TRD) in order to evaluate their mechanical properties as a function of the vanadium content. The coatings were produced with different percentages of ferrovanadium in the reactive mixture. The chemical composition of the coatings was determined through X-ray fluorescence (XRF), the crystal structure was analyzed using X-ray diffraction (XRD), the morphology was characterized using scanning electron microscopy (SEM), the hardness was measured with nanoindention, and the tribological behavior was studied using the ball-on-disc test. The XRF analysis indicated that the coatings grown on D2 steel decreased the atomic percentage of vanadium when the coating was made with 20% ferrovanadium. The XRD analysis established that the coatings were polycrystalline, with a cubic structure. The SEM images revealed that the coatings grown on D2 steel were more compact than those grown on H13 steel. Finally, the wear tests established that the friction coefficient decreased with an increase of vanadium in the coating. © The author; licensee Universidad Nacional de Colombia. Source

Gonzalez Navarrete J.C.,Fundacion Universitaria Los Libertadores | Salamanca J.,University of Caldas
Revista Mexicana de Fisica

A procedure to compute total ozone estimation by applying Dobson method, with a data set obtained from a global ultraviolet radiometer -GUV2511 Biospherical Instruments- is presented here. Dobson method is applied by using four different spectral lines in the UV-B range that are measured by the radiometer. This procedure involves a proposal for a calculation of direct -and diffuse-spectral radiation from a global spectral radiation measurement. The enhancement of this total ozone calculation model can also provide elements to study clouds behavior in tropical high mountain zones. In our case, it is affected furthermore by the intertropical confluence zone. Source

Avila C.A.,Fundacion Universitaria Los Libertadores | Franco R.,National University of Colombia | Silva-Valencia J.,National University of Colombia
Physica B: Condensed Matter

We study the quantum phase transition in the one-dimensional Bose-Hubbard model with three-body local interactions for densities ρ=2, 3, 4 and 5 by implementing the Density Matrix Renormalization Group method. This system shows two types of phases. One phase is incompressible (corresponding to the Mott insulator state) and the other compressible (the superfluid state). The critical points found correspond to a value of the hopping parameter for which the gap energy is equal to zero. We found that the critical point increases slowly as the density of the system increases. © 2014 Published by Elsevier B.V. Source

Anzola J.P.A.,Fundacion Universitaria Los Libertadores | Rojas L.A.R.,Fundacion Universitaria Los Libertadores | Bermudez G.M.T.,University of Caldas
Lecture Notes in Business Information Processing

The bibliometric technics allow us to illustrate aspects of interpretation of data obtained through data bases that are focus in science spreading, which offers an aggregated value to researchers. In this article, we explore the importance of such obtained information from articles’ query; in this particular case study the Internet of Things (IoT). The obtained and preprocessed metadata is used to feed the decision tree classification (J48) algorythms, as a result of the training stage, we generated a decision tree/classification where the subjects of research are visualized within a four year time frame. The construction of this classification tree is based in entropy, thus, the order or disorder in which the subjects of research can be interpreted within a level of relevancy in the time frame mentioned. We conceived the visualization and interpretation as the state of the art for the subjects addressed for a particular case, which help researchers to infer tendencies within specific subjects of research. © Springer International Publishing Switzerland 2015. Source

Rolon J.E.,Fundacion Universitaria Los Libertadores | Cendales E.D.,Fundacion Universitaria Los Libertadores | Cruz I.M.,University
Journal of Physics: Conference Series

Cracking of metallic engineering materials is of great importance due cost of replacing mechanical elements cracked and the danger of sudden structural failure of these elements. One of the most important parameters during consideration of the mechanical behavior of machine elements having cracking and that are subject to various stress conditions is the stress intensity factor near the crack tip called factor Kic. In this paper a computational model is developed for the direct assessment of stress concentration factor near to the crack tip and compared with the results obtained in the literature in which other models have been established, which consider continuity of the displacement of the crack tip (XBEM). Based on this numerical approximation can be establish that computational XBEM method has greater accuracy in Kic values obtained than the model implemented by the method of finite elements for the virtual nodal displacement through plateau function. Source

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