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Tuxtla Gutierrez, Mexico

Ibanez G.,University of Arts and Science of Chiapas | Lopez A.,Chiapas Polytechnic University | Cuevas S.,National Autonomous University of Mexico
International Communications in Heat and Mass Transfer | Year: 2012

The influence of the geometrical and physical parameters on entropy generation for a viscous flow between infinite parallel walls of finite thickness is studied by solving the momentum and energy conservation equations. The conjugate heat transfer problem in the fluid and solid walls is solved analytically using thermal boundary conditions of the third kind at the outer surfaces of the walls and continuity of temperature and heat flux across the fluid-wall interfaces. Analytic solutions for the velocity and temperature fields in the fluid and walls are used to calculate the local and global entropy generation rate. Conditions under which this quantity is minimized are determined for certain suitable combination of geometrical and physical parameters of the system. Special attention has been given to the effect of the wall thickness on the entropy generation rate. It is found that the global entropy generation reaches a minimum for specific values of the wall thickness ratio, when the other parameters are fixed. © 2012 Elsevier Ltd.

Mendoza-Perez A.F.,Chiapas Polytechnic University | Hernandez-Lerma O.,CINVESTAV
Mathematical Methods of Operations Research | Year: 2010

This paper deals with discrete-time Markov control processes in Borel spaces, with unbounded rewards. The criterion to be optimized is a long-run samplepath (or pathwise) average reward subject to constraints on a long-run pathwise average cost. To study this pathwise problem, we give conditions for the existence of optimal policies for the problem with "expected" constraints. Moreover, we show that the expected case can be solved by means of a parametric family of optimality equations. These results are then extended to the problem with pathwise constraints. © 2010 Springer-Verlag.

Ramos-Quintana F.,Autonomous University of the State of Morelos | Guerrero J.A.,Autonomous University of the State of Morelos | Rizo-Aguilar A.,Autonomous University of the State of Morelos | Urzua-Vazquez E.,Autonomous University of the State of Morelos | And 2 more authors.
Ecological Indicators | Year: 2016

We propose in this work a novel approach aiming at assessing cause and effect relationships between variables that can affect target biodiversity issues. These cause–effect relations are used to build a network whose nodes represent variables linked by directed arcs. The arcs have associated a value that represents trends of cause–effect relations. An important novelty of this approach is the use of product and addition operations between trends of cause–effect relations for assessing factors that can affect target variables. For the analysis of the network we use the concept of paths. Paths are defined as sequences of cause–effect relations from source variables to target variables. For example, the path from population increment that causes effects on the increment of transport routes, which in turn causes effects on the loss of vegetation cover. This approach was applied to the assessment of vegetation cover in the Morelos State, México during the period 2000–2010. The results show a promising practical alternative to assess the potential effects on biodiversity issues based on the analysis of the paths represented in the network. © 2016 Elsevier Ltd

Muniz J.,Chiapas Polytechnic University | Castillo R.,Chiapas Polytechnic University | Robles J.B.,Chiapas Polytechnic University | Sansores E.,National Autonomous University of Mexico
International Journal of Quantum Chemistry | Year: 2016

This DFT study examined the interaction of a sulfated zirconia (SZ) slab model system (heterogeneous catalyst) and triacetin (a precursor in biodiesel production) using explicit methanol solvent molecules. Full geometry optimizations of the systems were performed at the B3LYP level of theory. Gibbs free energies provide insight into the spontaneity of the reactions along a three-step reaction mechanism for the transesterification of triacetin. Charge decomposition analysis revealed electronic charge transfer between the metallic oxide and the organic moieties involved in the reaction mechanism. Fukui indices indicate the likely locations on the SZ surface where catalysis may occur. The quadratic synchronous transit scheme was used to locate transition structures for each step of the transesterification process. The results are in agreement with the strongly acidic catalytic character of zirconium observed experimentally in the production of biodiesel. © 2016 Wiley Periodicals, Inc.

Muniz J.,Chiapas Polytechnic University | Sansores E.,National Autonomous University of Mexico | Castillo R.,Chiapas Polytechnic University
Theoretical Chemistry Accounts | Year: 2013

The prediction of the series of [Au3X3M2] compounds (with X = H, F, Cl, Br, I and M = Li, Na, K, Rb, Cs) has been carried out by ab initio and DFT calculations. The systems are chemically stable due to their high chemical hardness. An unusual Au-Au attraction was found on each of the compounds along the series, addressing a strong metalophilic interaction of the aurophilic type. A strong aromatic character on the center of the [Au3X3]2-ring was also detected in the compounds under study, enhancing the stability of the species. The mechanism behind the bonding of the systems is mainly ruled by an electrostatic interaction among the 2 M+ cations and the [Au3X3]2-monolayer sheet in accordance with CDA and Ziegler analysis; only a slight orbital contribution yielded by back-donation from the alkaline metals to the [Au3X3]2-monolayer sheet is involved. It was shown that the [Au3Cl3M2] group has the highest Fukui indexes, indicating that a catalytic reaction may rise from an electrophilic attack centered at the Au atoms or a nucleophilic attack on the alkaline-earth metals. The latter was tested with the most stable system of this group, namely [Au3Cl3Li2], allowing it to interact with a CO molecule; the optimized [Au3Cl3Li2] [CO] system represents a bound state that highlights the reactive properties of the species. An extended-M-S-M-S-M- (with S representing the [Au3X3]2-system) linear chain model was also predicted at DFT level. Considering its spatial representation of the frontier molecular orbitals, it was found that a possible electronic transfer along the chain may take place via the triggering of an electron, suggesting the existence of a nanowire. © Springer-Verlag Berlin Heidelberg 2013.

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