Artículos (Gema)

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https://hdl.handle.net/10784/2867

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Análisis de la respuesta mecánica de recubrimientos elaborados mediante proyección térmica por plasma usando la medición de esfuerzos residuales y el método de elementos finitos a escala estructural: Efecto de la Red de Poros.
(Universidad de Tarapaca, 2011-01-01) C. C. Palacio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
En el presente trabajo se estudia la respuesta mecánica de recubrimientos elaborados mediante proyección térmica por plasma ante la presencia de esfuerzos residuales y campos de esfuerzos generados por deformaciones
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
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)
Characterization of SrTiO3 thin films at microwave frequencies using coplanar waveguide linear resonator method
(John Wiley & Sons Inc., 2011-07-01) Marulanda, José Ignacio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Comportamiento Dielérctrico de un Hidrogel de Alcohol Polivinílico Obtenidos por la Técnica Congelamiento/Descongelamiento
(UNIV NAC COLOMBIA, FAC NAC MINAS, 2011-02-01) JARAMILLO, JUAN MANUEL; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
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.
Deposition and characterization of duplex treated coating system applied on hot work steel AISI H1
(Universidad Simon Bolivar, 2012-01-01) Arroyave, Mauricio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Deposition and characterization of duplex treated coating system applied on hot work steel AISI H13
(Universidad Simon Bolivar, 2012-01-01) Gaitan, G.B.; Botero, M.G.; Franco, M.A.; Universidad EAFIT. Departamento de Ciencias Básicas; 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. © 2012 Universidad Simón Bolívar.
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
Design and construction of an electromechanical velocity modulator for Mössbauer spectroscopy
(SPRINGER, 2011-11-01) Velasquez, A. A.; Carmona, A.; Velasquez, D.; Angel, L.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
In this paper we report the design, construction and characterization of an electromechanical velocity modulator for application in Mössbauer spectroscopy. The modulator was constructed with copper coils, Neodymium magnets, steel cores and polymeric membranes. The magnetic field in the driving and velocity sensing stages was analyzed by the finite element method, which showed a linear relation between the magnetic field in the region of motion of both coils and the position of the coils within the steel cores. The results obtained by computational simulation allowed us to optimize geometries and dimensions of the elements of the system. The modulator presented its first resonance frequency at 16. 7 Hz, this value was in good agreement with that predicted by a second order model, which showed a resonant frequency of 16. 8 Hz. The linearity of the velocity signal of the modulator was analyzed through an optical method, based on a Michelson-Morley interferometer, in which the modulator moved one of the mirrors. Results showed a satisfactory linearity of the velocity signal obtained in the sensing coil, whose correlation with a straight line was around 0. 99987 for a triangular reference waveform. © 2011 Springer Science+Business Media B.V.
Design and thermal modeling of a cold finger open cycle cryostat for Mössbauer spectroscopy
(SPRINGER, 2019-01-01) Andrade N.A.G.; Torres Á.A.V.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
In this work we present the design and thermal modeling of a cold finger open cycle cryostat that operates with liquid nitrogen, intended to be implemented into the Mössbauer spectrometer available at the Universidad EAFIT of Medellín, Colombia, with the purpose of obtaining a low cost and good performance system for the acquisition of low temperature Mössbauer spectra. Initially, we propose a design that meets the requirements of the spectrometer, afterward, based on the initial design, we develop the calculations of heat flow into the system. The results of the thermal model allowed us to define the dimensions of the vessels, as well as calculate the evaporation time of a given column of liquid nitrogen in the cryogenic vessel. Finally, some progresses in the construction of the physical prototype are presented. © 2019, Springer Nature Switzerland AG.
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
Dielectric properties of poly(vinyl alcohol) hydrogels prepared by freezing/thawing technique
(Escuela de Ingeniería de Antioquia, 2012-07-01) Londoño, Martha Elena; Ocampo, J.M.J.; Sabater, Roser; Vélez, Juan Manuel; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Por medio de espectroscopia dieléctrica (DRS) y calorimetría diferencial de barrido (DSC) se investigaron las propiedades dieléctricas de los hidrogeles de alcohol polivinílico -PVA- entrecruzados por ciclos repetidos de la técnica congelamiento/descongel
DIELECTRIC PROPERTIES OF POLY(VINYL ALCOHOL) HYDROGELS PREPARED BY FREEZING/THAWING TECHNIQUE
(Escuela de Ingeniería de Antioquia, 2011-02-01) JARAMILLO, JUAN MANUEL; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Dipolar interactions among magnetic dipoles of iron oxide particles dispersed in mili-size hydrogel beads
(Elsevier B.V., 2020-01-01) Actis, D.G.; Muñoz Medina, G.A.; Velásquez, A.A.; Pereda, C.; Sanchez, L.M.; Alvarez, V.A.; Muñetón Arboleda, D.; Mendoza Zélis, P.; Sánchez, F.H.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
The recently published Mean Field Interacting Superparamagnet Model (MFISP model), which introduces the effective demagnetizing factor NE, is tested in specimens having a random-like spatial distribution of magnetic nanoparticles, where different hierarchies of clustering are present. These specimens are ferrogel PVA/iron oxide beads synthesized by a one-pot route, having spheroidal shapes and sizes of about 1 mm, and chain and disk-like arrays (superstructures) of beads. Raman analyses indicated that magnetic nanoparticles are composed by a mixture of magnetite and maghemite. Beads swell 208% by hydration in about 40 min. The increase of the ac susceptibility as a function of hydration time closely reflects the effect of bead swelling, in agreement with the expected diminution of dipole–dipole interactions. Measured susceptibility is analyzed in terms of the susceptibility ? of non-interacting particles and the effective demagnetizing factor NE of the specimen, which depends on swelling. The Specific Absorption Rate of electromagnetic power by the beads grows with the hydration time in agreement with ac susceptibility behavior. For long hydration times susceptibility and high field magnetization decrease. This is explained by the occurrence of oxidation of magnetite/maghemite to hematite. Isothermal magnetization experiments are performed on each superstructure in two perpendicular principal directions each. Results are consistently described with the MFISP model by considering two hierarchies of clustering: beads themselves and clusters within the beads. From the whole set of experiments, it is possible to estimate values for the volume fractions of particles in clusters and clusters in beads, given by xpc=0.46(15) and xcb=0.16(5). The susceptibility of non-interacting particles, ?=13(4), is also obtained, which results about five times larger than the measured (apparent) one. The MFISP model proves to be a convenient and efficient tool for the analysis of magnetization studies of complex 3d dispersions of magnetic nanoparticles, allowing an experimental determination of relevant physical information, otherwise not accessible by magnetic measurements. © 2020 Elsevier B.V.
Diseño conceptual de una sonda langmüir para caracterización de plasmas fríos mediante diseño estadístico de experimentos.
(IMPRENTA UNIV ANTIOQUIA, 2013-01-01) Camargo, Victor Hugo; Acosta, Diego A.; JARAMILLO, JUAN MANUEL; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
The characterization and control of plasma-assisted processes, has become increasingly urgent to adapt this kind technology to industrial contexts. This work presents the design and construction of a cold plasma characterization system by electrostatic means (Langmuir probe), based on concepts of plasma physics and tools of engineering, design of experiments and conceptual design. The result of this work is a functional prototype probe and some measurements on the reactor.
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)
Diseño e implementación de un reactor de deposición química de vapor para producir películas delgadas
(Universidad de Tarapaca, 2015-01-01) Arroyave, Mauricio; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
Diseño e implementación de un reactor PECVD para producir películas delgadas a partir de un horno microondas casero
(Universidad de Tarapaca, 2015-01-01) Arroyave, M.; Ocampo, J.M.J.; Arenas, Monica; Jaramillo, Juliana; saldarriaga, Clarita; Londoño, Valentina; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)
El presente trabajo describe el desarrollo y la implementación de un reactor de deposición química de vapor asistido por plasma PECVD (Plasma Enhanced Chemical Vapor Deposition). La construcción se realizó a partir del diseño de los diferentes componentes

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