Autonomous University of Occidente

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Ramirez-Villegas J.F.,Autonomous University of Occidente | Ramirez-Moreno D.F.,Autonomous University of Occidente
Neurocomputing | Year: 2012

This work develops a support vector and neural-based classification of mammographic regions by applying statistical, wavelet packet energy and Tsallis entropy parameterization. From the first four wavelet packet decomposition levels, four different feature sets were evaluated using two-sample Kolmogorov-Smirnov test (KS-test) and, in one case, principal component analysis (PCA). Feature selection was performed applying a hybrid scheme integrating non-parametric KS-test, correlation analysis, a logistic regression (LR) model and sequential forward selection (SFS). The top selected features (depending on the selected wavelet decomposition level) produced the best classification performances in comparison to other well-known feature selection methods. The classification of the data was carried out using several support vector machine (SVM) schemes and multi-layer perceptron (MLP) neural networks. The new set of features improved significantly the classification performance of mammographic regions using conventional SVMs and MLPs. © 2011 Elsevier B.V.


Lain S.,Autonomous University of Occidente | Sommerfeld M.,Autonomous University of Occidente | Sommerfeld M.,Martin Luther University of Halle Wittenberg
International Journal of Multiphase Flow | Year: 2012

The present study deals with pneumatic conveying of spherical particles in horizontal ducts, a 6. m long rectangular cross-section horizontal channel and a circular pipe, from a numerical perspective. The three-dimensional numerical computations were performed by the Euler-Lagrange approach in connection with the k- ε and a Reynolds Stress turbulence model accounting for full two-way coupling. For the calculation of the particle motion all relevant forces (i.e. drag, slip-shear and slip-rotational lift and gravity), inter-particle collisions and particle-rough wall collisions were considered. For all considered cases an average air velocity of 20. m/s was selected. Calculations are carried out for spherical glass beads with a diameter of 130 μm at a mass loading of 1.0 (kg particles/kg air). Additionally, different wall roughnesses are considered. The agreement of the computations with experiments was found to be satisfactory for mean and fluctuating velocities of both phases as well as for the normalised particle mass flux in the case of the channel flow. The main part of this contribution is related to a detailed analysis on the differences between pneumatic conveying properties in the rectangular channel and the circular pipe. For that the influence of wall roughness and the degree of coupling (i.e. two- or four-way) was analysed by visualising the cross-sectional distributions of air and particle properties. The observed focussing effect has a remarkable influence on particle concentration distribution in the pipe cross-section and the wall collision frequency over the circumference. Distinct differences in the velocity profiles of both phases (mean velocities and fluctuating components), as well as the concentration profiles, for channel and pipe flow are identified. The particle fluctuating velocities in the pipe are higher than in the channel for all situations, yielding mostly higher wall collision frequencies. As a consequence, in all the considered cases, the pressure drop in the pipe is larger than in the channel, especially for high wall roughness. © 2011 Elsevier Ltd.


Lain S.,Autonomous University of Occidente
Indian Journal of Chemical Technology | Year: 2013

The present study deals with pneumatic conveying of spherical particles in a six meter long horizontal channel with rectangular cross-section from a numerical perspective. Calculations are done for spherical glass beads of different sizes with a mass loading of 1.0 kg particles/kg gas. Additionally, different wall roughnesses are considered. Air volume flow rate is kept constant in order to maintain a fixed gas average velocity of 20 m/s. The numerical computations are performed by the Euler/Lagrange approach in connection with a Reynolds stress turbulence model accounting for two-way coupling and inter-particle collisions. For the calculation of the particle motion, all relevant forces (drag, slip-shear and slip-rotational lift and gravity), inter-particle collisions and particle-rough wall collisions are considered. The agreement of the computations with the findings or earlier experiments are found to be satisfactory for mean and fluctuating velocities of both phases as well as for the normalized particle mass flux.


Nunez E.E.,Autonomous University of Occidente | Polycarpou A.A.,Texas A&M University
Wear | Year: 2015

Blended Polyetheretherketone (PEEK) and polyimide-based polymers are excellent lighter tribomaterials that make possible the replacement of sliding metallic components in machinery. In this work a quantitative analysis of the effect of surface roughness on the transfer of polymer films was investigated using a specialized tribometer, under air-conditioning and refrigeration specific operating conditions. Specifically, polyimide (Vespel SP-21), polyimide (Vespel SP-211), PEEK with carbon fibers, and Aromatic Thermosetting Polyester (ATSP) polymer pins were tested against gray cast iron disks under unlubricated unidirectional conditions. It was found that a continuous transfer layer of polymer on the surface of the cast iron disks with mirror finish (low surface roughness) was produced in all the combinations of tested blended polymers. In the case of the polymer pins tested against cast iron disks with high surface roughness, a discontinuous transfer layer was observed. © 2015 Elsevier B.V.


Zhang H.,Arizona State University | Vittal V.,Arizona State University | Heydt G.T.,Arizona State University | Quintero J.,Arizona State University | Quintero J.,Autonomous University of Occidente
IEEE Transactions on Power Systems | Year: 2012

The transmission expansion planning (TEP) problem in modern power systems is a large-scale, mixed-integer, non-linear and non-convex problem. Although remarkable advances have been made in optimization techniques, finding an optimal solution to a problem of this nature can still be extremely challenging. Based on the linearized power flow model, this paper presents a mixed-integer linear programming (MILP) approach that considers losses, generator costs and the $N - 1$ security constraints for the multi-stage TEP problem. The losses and generator cost are modeled as piecewise linear functions of the line flows and the generator outputs, respectively. The IEEE 24-bus system is used to compare the lossy and the lossless model. The results show that the lossy model provides savings in total cost in the long run. The selection of the best number of piecewise linear sections L is also shown. Then a complete planning framework is presented and a multi-stage TEP is performed on the IEEE 118-bus test system. Simulation results show that the proposed approach is accurate and efficient, and has the potential to be applied to large-scale power system planning problems. © 2012 IEEE.


Caballero A.D.,Autonomous University of Occidente | Lain S.,Autonomous University of Occidente
Cardiovascular Engineering and Technology | Year: 2013

It has long been recognized that the forces and stresses produced by the blood flow on the walls of the cardiovascular system are central to the development of different cardiovascular diseases (CVDs). However, up to now, the reason why arterial diseases occur at preferential sites is still not fully understood. This paper reviews the progress, made largely within the last decade, towards the use of 3D computational fluid dynamics (CFD) models to simulate the blood flow dynamics and its interaction with the arterial wall within the human thoracic aorta (TA). We describe the technical aspects of model building, review methods to create anatomic and physiologic models, obtain material properties, assign boundary conditions, solve the equations governing blood flow, and describe the assumptions used in running the simulations. Detailed comparative information is provided in tabular format about the model setup, simulation results, and a summary of the major insights and contributions of each TA article reviewed. Several syntheses are given that summarize the research carried out by influential research groups, review important findings, discuss the methods employed, limitations, and opportunities for further research. We hope that this review will stimulate computational research that will contribute to the continued improvement of cardiovascular health through a strong interaction and cooperation between engineers and clinicians. © 2013 Biomedical Engineering Society.


Contreras J.P.,Autonomous University of Occidente | Ramirez J.M.,CINVESTAV
IEEE Transactions on Smart Grid | Year: 2014

This paper presents a Multi-Fed Power Electronic Transformer (MF-PET) for use in power distribution electrical systems. The MF-PET is a power electronic transformer with two or more AC/DC rectifiers at its input port, which may be connected to different feeders. Thus, it is possible to share the demand among feeders. Through a proper control, the AC/DC rectifiers may handle active power from the feeders (independently of the load type), may protect the load from sag/swell events, and may transfer power among feeders. This paper presents a three-phase MF-PET model. A small-scale laboratory prototype is shown and its application to distribution electrical system is discussed, exhibiting the MF-PET as a power electronic building block (PEBB) for its integration into electrical grids, enhancing the distribution system flexibility and contributing to the smart grid concept. © 2010-2012 IEEE.


Ramirez-Villegas J.F.,Autonomous University of Occidente | Ramirez-Moreno D.F.,Autonomous University of Occidente
Biological Cybernetics | Year: 2013

Itti and Koch's (Vision Research 40:1489-1506, 2000) saliency-based visual attention model is a broadly accepted model that describes how attention processes are deployed in the visual cortex in a pure bottom-up strategy. This work complements their model by modifying the color feature calculation. Evidence suggests that S-cone responses are elicited in the same spatial distribution and have the same sign as responses to M-cone stimuli; these cells are tentatively referred to as red-cyan. For other cells, the S-cone input seems to be aligned with the L-cone input; these cells might be green-magenta cells. To model red-cyan and green-magenta double-opponent cells, we implement a center-surround difference approach of the aforementioned model. The resulting color maps elicited enhanced responses to color salient stimuli when compared to the classic ones at high statistical significance levels. We also show that the modified model improves the prediction of locations attended by human viewers. © 2012 Springer-Verlag Berlin Heidelberg.


Lain S.,Autonomous University of Occidente | Sommerfeld M.,Autonomous University of Occidente | Sommerfeld M.,Martin Luther University of Halle Wittenberg
Powder Technology | Year: 2013

This paper deals with the transport of solid particles in pneumatic conveying systems, namely a 5. m horizontal pipe, a 90° bend and 5. m a vertical pipe. The pipe diameter is 150. mm in all cases and the average conveying velocity is 27. m/s. Three-dimensional stationary numerical computations were performed by the Euler/Lagrange approach in connection with the k-ε turbulence model accounting for full two-way coupling. Particle transport is calculated by considering all the relevant forces (including drag, gravity and transverse lift forces) and dispersion due to turbulence. Particle-wall collisions and wall roughness are modelled according to Sommerfeld and Huber [1] and inter-particle collisions are described by the stochastic modelling approach of Sommerfeld [2]. The objective of the present contribution is to demonstrate the capability of this computational approach for accurately predicting more complex pneumatic conveying systems where the transported powder has a rather wide size distribution. In particular the effect of inter-particle collisions will be demonstrated.As known from many single-phase studies a secondary flow is developing along the pipe bend. Since in the present study rather small glass powder is considered (i.e. 15μm


Patent
Autonomous University of Occidente | Date: 2012-03-27

The invention relates to a ceramic biocomposite for bone regeneration, having a pH range of between 6.5 and 8.5, with an initial plasticity that allows the biocomposite to be easily moulded in situ and to set after 7 minutes, meaning that it can remain at the indicated location during the healing process. In addition, the biocomposite has demonstrated an ability to stimulate bone formation in hard-to-heal wounds. The material can act alone or in combination with other types of bone graft such as autografts, homografts or xenografts which act as a vehicle, as a binding material for endosseous prostheses or as a covering for endosseous implants or prostheses.

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