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Search Results: 1 - 10 of 9709 matches for " Jaime;Zelaya-Angel "
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Crystallization of II-VI semiconductor compounds forming long microcrystalline linear assemblies
Becerril, Marcelino;Portillo-Moreno, óscar;Lozada-Moráles, Rosendo;Ramírez-Bon, Rafael;Ochoa-Landín, Ramón;Sánchez-Sinencio, Feliciano;Santoyo-Salazar, Jaime;Zelaya-Angel, Orlando;
Materials Research , 2013, DOI: 10.1590/S1516-14392013005000011
Abstract: in this work we report the formation of long microcrystalline linear self-assemblies observed during the thin film growth of several ii-vi compounds. polycrystalline cdte, cds, cdco3, and nanocrystalline cdte:al thin films were prepared on glass substrates by different deposition techniques. in order to observe these crystalline formations in the polycrystalline materials, the thin film growth was suspended before the grains reached to form a continuous layer. the chains of semiconductor crystals were observed among many isolated and randomly distributed grains. since cdte, cdte:al, cds and cdco3 are not ferroelectric and/or ferromagnetic materials, the relevant problem would be to explain what is the mechanism through which the grains are held together to form linear chains. it is well known that some nanocrystalline materials form rods and wires by means of electrostatic forces. this occurs in polar semiconductors, where it is assumed that the attraction forces between surface polar faces of the small crystals are the responsible for the chains formation. since there are not too many mechanisms responsible for the attraction we assume that a dipolar interaction is the force that originates the formation of chain-like grain clusters. the study of this property can be useful for the understanding of nucleation processes in the growth of semiconductor thin films.
Aluminum doping of CdTe polycrystalline films starting from the heterostructure CdTe/Al
Becerril, M;Vigil-Galán, O;Contreras-Puente, G;Zelaya-Angel, O;
Revista mexicana de física , 2011,
Abstract: aluminum doped cdte polycrystalline films were obtained from the heterostructure cdte/al/corning glass. the aluminum was deposited by thermal vacuum evaporation and the cdte by sputtering of a cdte target. the aluminum was introduced into the lattice of the cdte from a thermal annealed to the cdte/al/corning glas heterostructure. the electrical, structural, and optical properties were analyzed as a function of the al concentrations. it found that when al is incorporated, the electrical resistivity drops and the carrier concentration increases. in both cases the changes are several orders of magnitude. from the results, we conclude that, using this deposition techniques, n-type al doped cdte polycrystalline films can be produced.
Aluminum doping of CdTe polycrystalline films starting from the heterostructure CdTe/Al
M. Becerril,O. Vigil-Galán,G. Contreras-Puente,O. Zelaya-Angel
Revista mexicana de física , 2011,
Abstract: Aluminum doped CdTe polycrystalline films were obtained from the heterostructure CdTe/Al/Corning glass. The aluminum was deposited by thermal vacuum evaporation and the CdTe by sputtering of a CdTe target. The aluminum was introduced into the lattice of the CdTe from a thermal annealed to the CdTe/Al/Corning glas heterostructure. The electrical, structural, nd optical properties were analyzed as a function of the Al concentrations. It found that when Al is incorporated, the electrical resistivity drops and the carrier concentration increases. In both cases the changes are several orders of magnitude. From the results, we conclude that, using this deposition techniques, n-type Al doped CdTe polycrystalline films can be produced.
The effect of Er3+ doping on the physical properties of CdSe thin films deposited by chemical bath
López-Flores, R.B;Portillo-Moreno, O;Lozada-Morales, R;Palomino-Merino, R;Hernández Espinosa, M.A;Korneev Zabello, N;Rojas Hernández, A.G;Tomas, S.A;Zelaya-Angel, O;
Revista mexicana de física , 2006,
Abstract: cdse thin films were prepared by a chemical bath on glass substrates and doped with erbium during the growing process at 70°c. eight impurity levels were obtained by changing the relative volume of the salt solution containing er in the total cdse growing solution. the relative volume of the er-salt solution had the values: 2, 5, 8, 10, 15, 18, 25 and 30%. the electrical, structural, optical and photoconductive properties were characterized. important changes in the energy band gap, in the photoconductance, and in the refractive index were observed in the cdse layers as a result of the concentration level of er in the semiconductor.
Band gap energy in Zn-rich Zn1 xCdxTe thin films grown by r.f. sputtering
M. Becerril,H. Silva López,O. Zelaya Angel
Revista mexicana de física , 2004,
Abstract: Películas semiconductoras de Zn1 xCdxTe fueron crecidas por la técnica de co-erosión catódica de radio frecuencia sobre substratos de vidrio Corning 7059 a temperatura ambiente a partir de un blanco de ZnTe-Cd. Peque as laminillas de Cd fueron colocadas sobre la superficie del blanco cubriendo un área del 0% - 4%. Las propiedades ópticas y estructurales de las películas fueron analizadas en función de la concentración de Cd (x). El patrón de difracción de rayos-X nos indica preferentemente la fase cúbica del ZnTe. Cuando el cadmio es incorporado dentro de la red del ZnTe, la brecha de energía (Eg) decrece desde 2.2748 eV (x = 0) hasta 2.2226 eV (x = 0.081). A partir de los datos obtenidos se encuentra una relación lineal Eg vs (x) en el intervalo de (x) estudiado, el cual predice un parámetro de curvatura b en la relación Eg(x) = Eg0 + ax + bx2, que coincide con el valor de b calculado para el mismo estudio en las películas de Zn1 xCdxTe. Este resultado es interesante dado el gran número de valores reportados para b y a de Eg para este material ternario.
Fractal Cracks Propagation in Aluminum  [PDF]
Francisco Casanova del Angel, Jaime Retama Velasco
Modeling and Numerical Simulation of Material Science (MNSMS) , 2013, DOI: 10.4236/mnsms.2013.33A004
Abstract: The theory of the fractal structure characterizing propagation of a crack through identification of its generator is presented. It’s generating fractal, the peculiarities of its construction and the way to measure its segments are defined, and a theorem on the inverse scale property of such and other of the axial symmetry property of the fractal generator are presented and demonstrated. The theory is applied on 6061-T6 aluminum samples, using SENB probes. Direction of crack propagation and its fractal dimension are calculated numerically. Results obtained from modeling the direction of crack propagation through mechanics of elastic linear fracture and the one proposed here, called geometrical fractal fracture, are compared, thus developing the mirror case.

Improving the Efficiency of Abdominal Aortic Aneurysm Wall Stress Computations
Jaime E. Zelaya, Sevan Goenezen, Phong T. Dargon, Amir-Farzin Azarbal, Sandra Rugonyi
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0101353
Abstract: An abdominal aortic aneurysm is a pathological dilation of the abdominal aorta, which carries a high mortality rate if ruptured. The most commonly used surrogate marker of rupture risk is the maximal transverse diameter of the aneurysm. More recent studies suggest that wall stress from models of patient-specific aneurysm geometries extracted, for instance, from computed tomography images may be a more accurate predictor of rupture risk and an important factor in AAA size progression. However, quantification of wall stress is typically computationally intensive and time-consuming, mainly due to the nonlinear mechanical behavior of the abdominal aortic aneurysm walls. These difficulties have limited the potential of computational models in clinical practice. To facilitate computation of wall stresses, we propose to use a linear approach that ensures equilibrium of wall stresses in the aneurysms. This proposed linear model approach is easy to implement and eliminates the burden of nonlinear computations. To assess the accuracy of our proposed approach to compute wall stresses, results from idealized and patient-specific model simulations were compared to those obtained using conventional approaches and to those of a hypothetical, reference abdominal aortic aneurysm model. For the reference model, wall mechanical properties and the initial unloaded and unstressed configuration were assumed to be known, and the resulting wall stresses were used as reference for comparison. Our proposed linear approach accurately approximates wall stresses for varying model geometries and wall material properties. Our findings suggest that the proposed linear approach could be used as an effective, efficient, easy-to-use clinical tool to estimate patient-specific wall stresses.
La expansión de universidades privadas en el caso argentino The expansion of private universities: the Argentinian case
Marisa Zelaya
Pro-Posi??es , 2012, DOI: 10.1590/s0103-73072012000200012
Abstract: Este trabajo aborda el tema de la privatización de la educación superior en el caso argentino. Se presentan, en primer lugar, los cambios producidos en el contexto latinoamericano y en nuestro país, en especial en el campo educativo, a partir de la instalación del paradigma neoliberal. A continuación, se describen dos momentos de expansión de universidades privadas en el caso argentino: uno es el período 1989- 1995, durante el cual crece el número de universidades privadas con sus especificidades; el segundo, abarca desde el a o 1995 hasta la actualidad, y se caracteriza por la expansión del sector privado de la educación por medio de la creación de "ofertas distantes" o "Extensiones áulicas". Por último, se aborda la dimensión espacial vinculada a la expansión de las extensiones. This paper addresses the issue of higher education privatization in the Argentinian case. Firstly, we present the changes that have taken place in the latinoamerican context, particularly in our own educational field since the beginning of the neoliberal paradigm. In addition, two stages of the expansion of private universities in Argentina are described: one stage covers the expansion period that took place from 1989 to 1995 in which the number of private universities together with their specificities increased, and the other stage covers the period from 1995 up to now which is characterized by the expansion of private sector of education through "ofertas distantes" or "extensions extraterritoriales/áulicas." Finally, the spatial dimension linked to the expansion of extensions are discussed.
On the (3,N) Maurer-Cartan equation
Mauricio Angel,Jaime Camacaro,Rafael Diaz
Mathematics , 2007, DOI: 10.1080/jnmp.2007.14.4.4
Abstract: Deformations of the 3-differential of 3-differential graded algebras are controlled by the (3,N) Maurer-Cartan equation. We find explicit formulae for the coefficients appearing in that equation, introduce new geometric examples of N-differential graded algebras, and use these results to study N Lie algebroids.
Thermodynamics of a Shallow Solar Still  [PDF]
Juan Cristóbal Torchia-Nú?ez, Jaime Cervantes-de-Gortari, Miguel Angel Porta-Gándara
Energy and Power Engineering (EPE) , 2014, DOI: 10.4236/epe.2014.69022
Abstract: A detailed summary of the most relevant aspects of the thermodynamics of a shallow solar still is presented, including historical features not often found in the literature. Solar distillation has grown from applying empirical knowledge to advanced modeling and simulation. Geometrical, environmental and operational parameters of the solar still to heat transfer phenomena including evaporation and condensation, are taken into account in this overview, giving a comprehensive structure and classification to the study of solar stills from the thermodynamic point of view. The article describes global parameters, such as solar radiation, wind speed and thermal insulation among others and how they have been taken into account in the literature. Also, a distinction between internal and external heat transfer phenomena is proposed for clarification. Exergy balance is included to account for thermodynamic imperfections in the several processes inside the solar still.
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