Artículos (Gema)

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Deposition and characterization of duplex treated coating system applied on hot work steel AISI H13
(Universidad Simón Bolívar, 201-08-08) Bejarano Gaitán, Gilberto; Arroyave Franco, Mauricio; Gómez Botero, Maryori; Universidad EAFIT. Departamento de Ciencias Básicas; marroya5@eafit.edu.co; Electromagnetismo Aplicado (Gema)
AISI H13 steel is widely used for extrusion moulds and other hot work tools fabrication, due to its high toughness, strength and hardness around 56 HRC (Rockwell C) -- However, this steel possesses a relatively low wear resistance, which reduces its life time under high loading conditions -- The aim of this work was to enhance the wear resistance of the steel H13 using the following surface treatments:austenitizing + quenching + tempering (further called “tempering”), tempering and bath nitriding, tempering and coated with chromium nitride (CrN), tempering + bath nitriding + coated with CrN (further called “Duplex coating”) -- The properties of the treated samples were compared with each other in dependence of the made surface treatment -- The coatings were deposited using the r.f. balanced magnetron sputtering deposition technique -- The total thickness of the coatings was maintained at 5 µm, while the thickness of the nitrided zone was approximately 140 µm -- The microstructure and the crystalline phase composition were investigated by Scanning -- Electron Microscopy (SEM) and X-ray diffraction (XRD) technique, respectively -- The hardness and the adhesion of the coatings were determined by micro indentation measurements and the Rockwell indentation test, respectively -- The wear resistance of the coatings was evaluated using ball on disc tests -- The duplex treated samples presented a hardness three order of magnitude higher and showed a wear rate six times smaller than those samples only tempered
Recuperación de la energía radiada por conductores de corriente alterna
(Sociedad Colombiana de Física, 2001-06-01) Marulanda, José Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Plasma etching of DLC films for microfluidic channel
(2003-01-01) JARAMILLO, JUAN MANUEL; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Experimentos en el aula de clase para enseñanza de la física
(Sociedad Colombiana de Física, 2006-01-01) J. I. Marulanda; Gómez, Luis A.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Considerando la importancia de los aspectos fenomenológicos como motivación para elaborar modelos formales en la enseñanza de la física, la experimentación se convierte en un recurso didáctico valioso en este proceso.
Identification by force modulation microscopy of nanoparticles generated in vacuum arcs
(Fondo Editorial Universidad EAFIT, 2006-01-01) Arroyave, Mauricio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Caracterización y calibración de un instrumento AFM utilizado para producir nanodeformación en superficies altamente rígidas
(2006-02-01) Arroyave, Mauricio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
MEJORAMIENTO DEL DESEMPEÑO DE UN SISTEMA DE COMUNICACIONES ÓPTICAS FFH-OCDMA UTILIZANDO REDES DE BRAGG APODIZADAS FUERTES
(Sociedad Colombiana de Física, 2006-04-01) Marulanda, José Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Síntesis de reforzantes carbonosos para materiales compuestos a partir de fibras vegetales colombianas
(2007-01-01) JARAMILLO, JUAN MANUEL; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Diseño de un conversor AC/DC para excitación con pulsos rectangulares de un piezoactuador de PZT
(2008-04-01) JARAMILLO, JUAN MANUEL; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Diseño de un conversor AC/DC para excitación con pulsos rectangulares de un piezopactuador de PZT
(2008-04-01) Arroyave, Mauricio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
La microscopía de barrido por sondas: Herramienta básica en las nanociencias
(Fondo Editorial Universidad EAFIT, 2008-09-01) Arroyave, Mauricio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Simulación Gráfica de Sistemas Oscilatorios no Lineales
(Sociedad Colombiana de Física, 2009-04-01) VELASQUEZ, ALVARO ANDRES; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Structural characterization of the (methanol)4 potential energy surface
(AMER CHEMICAL SOC, 2009-09-24) David, Jorge; Guerra, Doris; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
In this paper, we report the geometries and properties of the structural isomers obtained from a random walk of the potential energy surface (PES) of the methanol tetramer. Thirty-three structures were obtained after B3LYP/6-31+g* optimization of 94 candidate structures generated from a stochastic search of the PM3 conformational space. The random search was carried out using a recently proposed modified Metropolis acceptance test in the simulated annealing (SA) procedure. Corrections for the basis set superposition error (BSSE) show improvements on the binding energies of the clusters in an average of approximately 2.0 kcal/mol, while geometries are predicted to be less sensitive to BSSE corrections. MP2/aug-cc-pvdz calculations on representative structures did not change the geometries but predicted better binding energies. Highly correlated CCSD(T) energies were calculated on the B3LYP and MP2 stationary points and used to establish relative stabilities. We report several new conformations and group the structures into six distinct geometrical motifs. Only the cyclic tetramers with four primary hydrogen bonds in the same plane are predicted to have significant populations. Secondary hydrogen bonds, those for which the donated proton comes from an alkyl group, lead to a rich conformational space.
Structure and Reactivity of the Au6Pt Clusters
(AMER CHEMICAL SOC, 2010-01-01) David, Jorge Leon; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Insights into the structure and stability of the carbonic acid dimer
(ROYAL SOC CHEMISTRY, 2010-01-01) Murillo, Juliana; David, Jorge; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
In this paper we report the geometries and properties of 40 structural isomers located on the MP2/6-311++G** PES of the carbonic acid dimer. All six possible combinations of carbonic acid monomers were considered. The dimers are divided into six geometrical motifs. Our data suggests that combinations of anti-anti monomers do not necessarily lead to larger stabilization energies in the formation of the dimers. MP2 underestimates the relative binding energies with respect to CCSD(T) by as much as 3.2 kcal mol-1. At least 3 different dimers which may contribute to the stability of carbonic acid are predicted to have significant populations. Binding energy is only directly related to relative stability when comparing dimers formed from the same monomers. Overall stabilization is mainly dictated by attractive electrostatic interactions via cooperative polarization by virtue of the spatial arrangement of the dipole moment components along the polar bonds. Shorter O…H bond distances and larger bond orders predicted for the hydrogen bonds directed towards carbonyl groups make for stronger hydrogen bonding than in O…H bonds directed towards hydroxyl groups. © the Owner Societies.
Density functional based reactivity parameters: Thermodynamic or kinetic concepts?
(ELSEVIER SCIENCE BV, 2010-03-15) Fuentealba, Patricio; David, Jorge; Guerra, Doris; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
The Density Functional Theory of chemical reactivity has provided and effective way to develop a mathematical framework for many empirical chemical concepts. In this work, the relation of some of the proposed indexes with the thermodynamic and kinetic effects on a chemical reaction will be discussed. In order to give a numerical support to the discussion, families of SN2 reactions and Diels-Alder reactions have been studied. It is concluded that the theoretical proposed indexes represent neither thermodynamic nor kinetic effects but a combination of both depending on the type of reaction. © 2009 Elsevier B.V. All rights reserved.
Caracterización de Imanes para aplicación en sistemas de sensado de posición
(Sociedad Colombiana de Física, 2010-06-25) Guarin, Nicolas; Velásquez, A. A.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
This paper reports the characterization of a set of Neodymium magnets with different sizes and geometries, which is devoted to determine the influence of the former parameters both in the magnitude as in the direction of the magnetic field
Structural studies of the water hexamer
(AMER CHEMICAL SOC, 2010-07-29) Hincapie, Gina; Acelas, Nancy; Castano, Marcela; David, Jorge; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
In this paper we report the geometries and properties of 24 structural isomers located on the MP2/6-311++g**potential energy surface of the water hexamer. At least 15 structural patterns are located within 3 kcal/mol of the most stable conformation, leading to a very complex potential energy surface, several isomers having significant contributions. A quadratic correlation between the distance from the proton to the center of the hydrogen bond with the distance between oxygen atoms for all clusters is reported. MP2/6-311++g**and CCSD(T)/aug-cc-pvdz//MP2/6-311++g**predict different stabilization orderings but are in good agreement for binding energies. Compact structures are energetically favored by electronic energies with zero point energy corrections, while noncompact cyclic structures are preferred when temperature and entropy are accounted for. © 2010 American Chemical Society.
Dielectric properties characterization of high dielectric constant thick films
(John Wiley & Sons, 2010-10-01) Demenicis, Luciene S.; J. I. Marulanda; Lima, Rodolfo A. A.; Carvalho, Maria Cristina R.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
A technique for the characterization of microwave dielectric properties of high dielectric constant thick films at room temperature is proposed, using multilayered coplanar waveguide transmission lines with high dielectric constant thick films deposit
Structure and reactivity of the (1)Au6Pt clusters
(AMER CHEMICAL SOC, 2010-10-07) David, Jorge; Guerra, Doris; Hadad, C. Z.; Restrepo, Albeiro; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
In this paper we report the geometries, properties, and reactivity descriptors of 12 structural isomers located on the MP2/SDDALL potential energy surface of the (1)Au(6)Pt binary clusters. A nonplanar, D(3d) symmetry, cyclohexane chairlike structure is predicted to be the global minimum. Binding energies per atom in the range approximately 44-51 kcal/mol account for very stable clusters. The relative stability of the clusters is directly related to all global and local reactivity descriptors. All structures are predicted to have large electron affinities. The chemical environment of the Pt atom on the structures plays a central role in the resulting relative stabilities and global and local reactivities. Our results show that more peripheral Pt atoms are more likely to be involved in electron-accepting processes.

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