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San Jeronimo Ixtepec, Mexico

Cortina-Marrero H.J.,National Autonomous University of Mexico | Martinez-Alonso C.,National Autonomous University of Mexico | Hechavarria-Difur L.,Istmo University of Mexico | Hu H.,National Autonomous University of Mexico
EPJ Applied Physics | Year: 2013

Bilayer hybrid solar cells were prepared by solution deposition of CdS thin films on conductive glass substrates (ITO), followed by spin-coating or drop-casting poly (3-hexylthiophene) (P3HT) solution on a CdS surface. After a slow drying process, the P3HT films of different thicknesses (from 100 to 725 nm) were annealed at temperatures (T1) from 110 to 190 C, called pre-metal contact annealing. Then carbon paint was collocated on top of P3HT and gold was evaporated. The whole structure was annealed for the second time, called post-metal contact annealing, at temperature (T2) between 110 and 190 C. The continuous increase of the (1 0 0) crystalline plane and the optical absorption coefficient of P3HT films with annealing temperatures indicates the improvement of molecular order inside the polymer films induced by the thermal annealing process. The better ordered P3HT films lead to lower series resistance and higher fill factor in the corresponding solar cells, suggesting the enlargement of charge carrier mobility in annealed P3HT films. On the other hand, the photovoltaic performance is also affected by T2 temperature; a low T2 improves the ohmic contact between P3HT and the metal contact to benefit the charge carrier extraction, whereas a high T2 may deteriorate that union. The same observation was obtained in CdS/P3HT solar cells with P3HT films of different thicknesses. The best energy conversion efficiency of 0.44% was obtained in CdS/P3HT cells with 305 nm thick P3HT annealed at T1 = 190 C and T2 = 110 C for 10 min each. © 2013 EDP Sciences. Source

Campos-Garcia M.,National Autonomous University of Mexico | Moreno-Oliva V.I.,Istmo University of Mexico | Diaz-Uribe R.,National Autonomous University of Mexico | Granados-Agustin F.,National Institute of Astrophysics, Optics and Electronics | Santiago-Alvarado A.,Technological University of Mixteca
Applied Optics | Year: 2011

A method for testing fast aspheric convex surfaces with dynamic null screens using LCDs is shown. A flat null screen is designed and displayed on an LCD monitor with drop-shaped spots in such a way that the image, which is formed by reflection on the test surface, becomes an exactly square array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the surface. Here the whole surface is tested at once. The position of the spots on the LCD can be changed in a dynamic way, to perform point-shifting of the image spots. The proposed procedure improves the dynamic point-shifting method. As has been shown previously, this process reduces the numerical error during the integration procedure, thereby improving the sensitivity of the test. The positioning accuracy for the screen spots is related to the LCD's spatial resolution. Results of the evaluation of a parabolic convex surface with f/# = 0.22 are shown. © 2011 Optical Society of America. Source

Lumbreras J.A.,Istmo University of Mexico | Huirache-Acuna R.,National Autonomous University of Mexico | Rivera-Munoz E.M.,National Autonomous University of Mexico | Berhault G.,CNRS Research on Catalysis and Environment in Lyon | Alonso-Nunez G.,National Autonomous University of Mexico
Catalysis Letters | Year: 2010

Unsupported Ni/MoS2 and Ni/WS2 HDS catalysts were prepared by in situ activation of hexamethylenediammonium thiometallates promoted with Ni. The method involved an aqueous solution reaction of ammonium thiomolybdate (ATM) or ammonium thiotungstate (ATT) with Ni(NO3) 2•6H2O and hexamethylenediamine. Ni-promoted precursors were then in situ activated during the hydrodesulfurization (HDS) of dibenzothiophene (DBT) producing Ni/MoS2 and Ni/WS2 catalysts. Solids were analyzed after the in situ activation by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and for textural properties by using the BET and BJH methods. Catalysts with relatively high surface area and type IV N2 adsorption-desorption isotherms were obtained. The use of the hexamethylenediammonium precursor led to a significant nickel promotion of MoS2 and WS2 catalysts. For Ni/MoS2, the use of this carbon-containing precursor was found to be more beneficial for the final HDS catalytic activity than using the classical ammonium tetrathiomolybdate (ATM) without carbon. For Ni/WS 2, compared to tetraalkylammonium thiosalts, the lower amount of carbon in excess formed during the decomposition of the hexamethylenediammonium precursor coupled with a lower crystallization rate of WS2 favors a correct nickel accommodation on the WS2 edges. © 2009 Springer Science+Business Media, LLC. Source

Campos-Garcia M.,National Autonomous University of Mexico | Cossio-Guerrero C.,National Autonomous University of Mexico | Moreno-Oliva V.I.,Istmo University of Mexico | Huerta-Carranza O.,National Autonomous University of Mexico
Applied Optics | Year: 2015

In order to measure the shape of fast convex aspherics, such as the corneal surface of the human eye, we propose the design of a conical null-screen with a radial point distribution (spots similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the evaluated surface. We present the target array design and the surface evaluation algorithm. The precision of the test is increased by performing an iterative process to calculate the surface normals, reducing the numerical errors during the integration. We show the applicability of the null-screen based topographer by testing a spherical calibration surface of 7.8 mm radius of curvature and 11 mm in diameter. Here we obtain an rms difference in sagitta between the evaluated surface and the best-fitting sphere less than 1 μm. © 2015 Optical Society of America. Source

Mezura-Montes E.,Laboratorio Nacional Of Informatica Avanzada Lania Ac | Miranda-Varela M.E.,Istmo University of Mexico | Del Carmen Gomez-Ramon R.,University Del Carmen
Information Sciences | Year: 2010

Motivated by the recent success of diverse approaches based on differential evolution (DE) to solve constrained numerical optimization problems, in this paper, the performance of this novel evolutionary algorithm is evaluated. Three experiments are designed to study the behavior of different DE variants on a set of benchmark problems by using different performance measures proposed in the specialized literature. The first experiment analyzes the behavior of four DE variants in 24 test functions considering dimensionality and the type of constraints of the problem. The second experiment presents a more in-depth analysis on two DE variants by varying two parameters (the scale factor F and the population size NP), which control the convergence of the algorithm. From the results obtained, a simple but competitive combination of two DE variants is proposed and compared against state-of-the-art DE-based algorithms for constrained optimization in the third experiment. The study in this paper shows (1) important information about the behavior of DE in constrained search spaces and (2) the role of this knowledge in the correct combination of variants, based on their capabilities, to generate simple but competitive approaches. © 2010 Elsevier B.V. All rights reserved. Source

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