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Search Results: 1 - 10 of 168412 matches for " Jarol E; Hoyos "
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Modelo Matemático de la Nucleación Electroquímica con Ondas de Corriente Pulsante
Molina,Jarol E; Hoyos,Bibian A;
Información tecnológica , 2007, DOI: 10.4067/S0718-07642007000500005
Abstract: a mathematical model has been established for the description of concentration overpotential, nucleation rate and nucleus size formed on metallic substrates when four types of pulse current waveforms are used: rectangular, ramp-down, ramp-up and triangular. the mathematical model was developed considering that the species diffusion in the limit layer is the rate determining step of the process. the model predicts that when using wave current with the same current average and the same time of application, the ramp-down current produces the shortest transition time, with the highest rise of overpotential concentration, this drives to high nucleation rates with small nucleus size. for the case of current wave forms with the same pick and average current, the rectangular and ramp-down waves show practically the same transition time, with equivalent nucleation rate and deposit size.
Modelo Matemático de la Nucleación Electroquímica con Ondas de Corriente Pulsante Mathematical Model for the Electrochemical Nucleation with Pulse Current Waveforms
Jarol E Molina,Bibian A Hoyos
Información Tecnológica , 2007,
Abstract: Se presenta un modelo matemático para describir el sobrepotencial de concentración, la velocidad de nucleación y el tama o de núcleos formados sobre sustratos metálicos, cuando se emplean cuatro tipos de ondas de corriente pulsante: rectangular, rampa ascendente, rampa descendente y triangular. Para el desarrollo del modelo, se considera que la etapa que controla el proceso es la difusión de especies en la capa limite. El modelo predice que, cuando se emplean ondas con igual corriente promedio e igual tiempo de aplicación, la rampa descendente produce tiempos de transición más cortos, con mayor aumento en el sobrepotencial de concentración, lo que lleva a mayores velocidades de nucleación con tama os de núcleos más peque os. Para el caso de ondas con igual corriente pico y promedio, las ondas rectangular y descendente presentan prácticamente el mismo tiempo de transición, con velocidades de nucleación y tama o de los depósitos equivalentes. El modelo desarrollado, constituye una herramienta ágil y flexible para la determinación del tama o y la velocidad de formación de núcleos de electrodepositos y, puede ser extendida para estudiar otro tipo de ondas de corriente. A mathematical model has been established for the description of concentration overpotential, nucleation rate and nucleus size formed on metallic substrates when four types of pulse current waveforms are used: rectangular, ramp-down, ramp-up and triangular. The mathematical model was developed considering that the species diffusion in the limit layer is the rate determining step of the process. The model predicts that when using wave current with the same current average and the same time of application, the ramp-down current produces the shortest transition time, with the highest rise of overpotential concentration, this drives to high nucleation rates with small nucleus size. For the case of current wave forms with the same pick and average current, the rectangular and ramp-down waves show practically the same transition time, with equivalent nucleation rate and deposit size.
EFECTO DE LAS FORMAS DE ONDAS DE CORRIENTE PULSANTE EN LA ELECTRODEPOSITACIóN DE NANOCRISTALES
MOLINA,JAROL; HOYOS,BIBIAN;
DYNA , 2009,
Abstract: a mathematical model has been developed for describing the effect of pulse current wave forms on size and hardness of electroplated nanocrystals. the model relates in a direct form the typical wave variables (frequency, duty cycle and peak current) with harness of generated deposits by means of direct current and by four pulse current wave forms: rectangular, ramp up, ramp down and triangular. the results of the model were evaluated for duty cycles of 20 and 80%, with frequencies of 50 and 150 hz and peak currents of 4 and 8 ka/m2.the model predicts that small increases in the concentration overpotential drives to increase the nucleation rate significantly, diminishing the growth of the nanocrystals and generating a hardness increase. the increase of the duty cycle and the wave?s frequency produces a behavior increasingly close to that produced by direct current, with a diminution in the nanocrystals hardness. any modification in the waveform variables that increases the peak current produces higher hardness values.
EFECTO DE LAS FORMAS DE ONDAS DE CORRIENTE PULSANTE EN LA ELECTRODEPOSITACIóN DE NANOCRISTALES
JAROL MOLINA,BIBIAN HOYOS
DYNA , 2009,
Abstract: Se desarrolló un modelo matemático para establecer el efecto que tiene la forma de las ondas de corriente pulsante en el tama o y dureza de nanocristales electrodepositados. El modelo relaciona de forma directa las variables típicas de las ondas (frecuencia, ciclo de trabajo y corriente pico) con la dureza de los depósitos generados mediante corriente continua y con cuatro tipos de ondas de corriente pulsante: rectangular, rampa ascendente, rampa descendente y triangular. Se evaluaron los resultados del modelo para ciclos de trabajo de 20 y 80%, con frecuencias de 50 y 150 Hz y corrientes pico de 4 y 8 kA/m2. El modelo predice que peque os aumentos en el sobrepotencial de concentración incrementan significativamente la velocidad de nucleación, disminuyen el crecimiento de los nanocristales y generan un aumento en la dureza. El aumento del ciclo de trabajo y la frecuencia de las ondas produce un comportamiento cada vez más cercano al producido por la corriente continua, con una disminución en la dureza de los nanocristales. Cualquier modificación en las variables de las ondas, que tenga como consecuencia el incremento de la corriente pico, produce valores de dureza más altos.
New approaches to presenting information in the agrarian sector and country areas – Technological solution of the agris web portal
P. ?imek,J. Vanek,E. Cervenková,J. Jarolímek
AGRIS on-line Papers in Economics and Informatics , 2010,
Abstract: The present paper brings an overview of both technological and functional upgrade of the agrarian web portalAGRIS (http://www.agris.cz). Agris 4.0 version has been developed, tested and launched in the course of 2010.Agris 4.0 is built and runs on Microsoft technologies within the framework of MS IIS web server. Model-View-Controller (MVC) architectural pattern, an inherent part of the technology .NET framework 3.5, has been used.
Freud. Una vida de nuestro tiempo
Hoyos Z. Julio E.
Desde el Jardín de Freud , 2010,
Abstract:
Evaluation of data box introduction process in the Czech Republic
J. Jarolímek,E. ?ervenková,J. Vaněk,V. Smí?ková
AGRIS on-line Papers in Economics and Informatics , 2010,
Abstract: One of base building stones of eGovernment development in the Czech Republic is so called Data boxes which were introduced to unify communication and to increase efficiency in public administration. The aim of a study carried out by the Department of Information Technologies was to analyze the implementation procedure and to use data boxes. The questioning took place in December 2009, i.e. c.6 weeks after introduction of duty to use a data box.Obtained results are important above all because the development process of eGovernment still does not end. The suggestion from data box implementation can significantly facilitate introduction of basic registers and other applications.
Phase diagrams and universality classes of random antiferromagnetic spin ladders
J. A. Hoyos,E. Miranda
Physics , 2004, DOI: 10.1103/PhysRevB.69.214411
Abstract: The random antiferromagnetic two-leg and zigzag spin-1/2 ladders are investigated using the real space renormalization group scheme and their complete phase diagrams are determined. We demonstrate that the first system belongs to the same universality class of the dimerized random spin-1/2 chain. The zigzag ladder, on the other hand, is in a random singlet phase at weak frustration and disorder. Otherwise, we give additional evidence that it belongs to the universality class of the random antiferromagnetic and ferromagnetic quantum spin chains, although the universal fixed point found in the latter system is never realized. We find, however, a new universal fixed point at intermediate disorder.
Random Antiferromagnetic SU(N) Spin Chains
J. A. Hoyos,E. Miranda
Physics , 2004, DOI: 10.1103/PhysRevB.70.180401
Abstract: We analyze random isotropic antiferromagnetic SU(N) spin chains using the real space renormalization group. We find that they are governed at low energies by a universal infinite randomness fixed point different from the one of random spin-1/2 chains. We determine analytically the important exponents: the energy-length scale relation is $\Omega\sim\exp(-L^{\psi})$, where $\psi=1/N$, and the mean correlation function is given by $\bar{C_{ij}}\sim(-1)^{i-j}/|i-j|^{\phi}$, where $\phi=4/N$. Our analysis shows that the infinite-N limit is unable to capture the behavior obtained at any finite N.
To the Validation of Some Syntaxa of the Loiseleurio-Vaccinietea from the Western Carpathians Published in Hacquetia 2006, 5/1: 37-71
Jozef ibík , Ján Kliment , Ivan Jarolímek , Zuzana Dúbravcová , Radmila Bělohlávková , Libu e Paclová
Hacquetia , 2007, DOI: 10.2478/v10028-007-0005-9
Abstract:
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