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Artículos publicados en: 2015

Arrhythmias detection based on wavelet transform
International Journal of Engineering Science and Innovative Technology
Fátima Moumtadi 1 , Nicté Mandujano Mayoral 1 , Gabriela Díaz Cartas 1 , Rogelio Alcántara Silva 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: ECG signals, R-R interval, Wavelet transform
Abstract: Currently in Mexico the heart attacks occurs every four seconds and in the adult population (20-69 years) are more than 17 million hypertensive therefore becomes a fundamental part, the detection and diagnosis of heart diseases [14]. In spite of telemedicine progress on the issue of electrocardiographs, the reading to ECG signals is reserved for specialists, delaying the diagnosis and the treatment of patients is getting complicated. Therefore the design and development of a strategy for the classification of arrhythmias: Tachycardia, Bradycardia, and Ventricular Flutter, by detecting the R-R interval of the ECG signal and calculating the heart rhythm in the Wavelet transform representation.
Fabrication Process for PDMS Polymer/Silica Long-Period Fiber Grating Sensors
IEEE Photonics Technology Letters
A. Martínez Gaytán 1 , J. Soto Olmos 1 , Laura Oropeza Ramos 1 , J. Hernández Cordero 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales

Keywords: Optical fiber gratings, Tapered fibers, Polymer Optical Gratings
Abstract: We present a long-period fiber grating sensor composed of a tapered optical fiber embedded in a polymeric grating. The fabrication process is based on a mold-replica approach, thus yielding low-cost reproducible structures. We evaluate the sensitivity to temperature and refractive index changes showing that the proposed structures could render useful for developing sensors with biocompatible polymers.
A decision support system based in multi-agent technology for gene expression analysis
International Journal of Intelligence Science
Edna Márquez 1 , Jesús Savage Carmona 1 , Jaime Berumen 2 , Christian Lemaitre 3 , Ana Lilia Laureano Cruces 4 , Ana Espinosa 2 , Ron Leder 1 , Alfredo Weitzenfeld 5
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Hospital General de México, Unidad de Medicina Genómica
3 Universidad Autónoma Metropolitana, Departamento de Ciencias de la Comunicación
4 Universidad Autónoma Metropolitana, Departamento de Sistemas
5 University of South Florida, Departmente of Computer Science and Engineering

Keywords: Multi-Agent Systems, Machine Learning, Bioinformatics, Gene expression analysis
Abstract: The genetic microarrays give to researchers a huge amount of data of many diseases represented by intensities of gene expression. In genomic medicine gene expression analysis is guided to find strategies for prevention and treatment of diseases with high rate of mortality like the different cancers. So, genomic medicine requires the use of complex information technology. The purpose of our paper is to present a multi-agent system developed in order to improve gene expression analysis with the automation of tasks about identification of genes involved in a cancer, and classification of tumors according to molecular biology. Agents that integrate the system, carry out reading files of intensity data of genes from microarrays, pre-processing of this information, and with machine learning methods make groups of genes involved in the process of a disease as well as the classification of samples that could propose new subtypes of tumors difficult to identify based on their morphology. Our results we prove that the multi-agent system requires a minimal intervention of user, and the agents generate knowledge that reduce the time and complexity of the work of prevention and diagnosis, and thus allow a more effective treatment of tumors.
Compound Hidden Markov Model for Activity Labelling
International Journal of Intelligence Science
José Israel Figueroa Angulo 1 , Jesús Savage Carmona 2 , Ernesto Bribiesca 2 , Boris Escalante Ramírez 2 , Luis Enrique Sucar 3
1 Universidad Nacional Autónoma de México, Laboratorio de Biorobotica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería
3 Instituto Nacional de Astrofísica, ?ptica y Electrónica, Departamento de Ciencias Computacionales

Keywords: Hidden Markov Model, Compound Hidden Markov Model, Activity Recognition, Human Activity, Human Motion, Motion Capture, Skeleton, Computer Vision, Machine Learning, Motion Analysis
Abstract: This research presents a novel way of labelling human activities from the skeleton output computed from RGB-D data from vision-based motion capture systems. The activities are labelled by means of a Compound Hidden Markov Model. The linkage of several Linear Hidden Markov Models to common states, makes a Compound Hidden Markov Model. Each separate Linear Hidden Markov Model has motion information of a human activity. The sequence of most likely states, from a sequence of observations, indicates which activities are performed by a person in an interval of time. The purpose of this research is to provide a service robot with the capability of human activity awareness, which can be used for action planning with implicit and indirect Human-Robot Interaction. The proposed Compound Hidden Markov Model, made of Linear Hidden Markov Models per activity, labels activities from unknown subjects with an average accuracy of 59.37%, which is higher than the average labelling accuracy for activities of unknown subjects of an Ergodic Hidden Markov Model (6.25%), and a Compound Hidden Markov Model with activities modelled by a single state (18.75%).
Fault tolerant control allocation via continuous integral sliding-modes: A HOSM-Observer approach
Héctor Ríos 1 , Shyam Kamal 2 , Leonid Fridman Golredich 3 , Ali Zolghadri 4
1 INRIA Lille - Nord Europe, Parc Scientifique de la Haute Borne
2 Indian Institute of Technology, Systems and Control Engineering
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 Université de Bordeaux, Automatic Control Group

Keywords: Fault tolerant systems, Sliding-mode control, State observers
Abstract: In this paper a continuous fault tolerant control allocation is proposed. This approach is based on a uniform High-Order Sliding-Mode Observer where only measurable outputs are used. The fault tolerant control scheme is developed using, for the first time, a continuous integral sliding-mode and a fixed control allocation technique which provides an approximate estimation of matched faults. The conditions for stability are found by ensuring the stability of the closed loop system in the presence of possible faults in the components, and actuator faults or failures. The effectiveness of the proposed approach is verified through simulation of a linear version of the benchmark B747??100/200 civil aircraft model.
Una estrategia de inversión y cobertura mediante la combinación de notas estructuradas
Panorama Económico
Isabel Patricia Aguilar Juárez 1 , Francisco Venegas Martínez 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Instituto Politécnico Nacional, Escuela Superior de Economía

Keywords: notas estructuradas, inversión privada, portafolios
Abstract: El presente trabajo desarrolla una estrategia de inversión compuesta por un portafolio de notas estructuradas. El portafolio considera dos dimensiones: primero, una vertical que consiste en la combinación de notas estructuradas con el mismo periodo de vigencia que garanticen un flujo de efectivo pro- nosticable al vencimiento de esta estructura, y una dimensión horizontal que considera la integración en la estructura final de una nueva nota es- tructurada cuya vigencia inicia al vencimiento de la estructura vertical. Esta estructuración permite actualizar el precio del activo subyacente en el trans- curso de la vigencia de la estructura propuesta, así como ampliar el plazo de la inversión, garantizando el capital inicial y ofreciendo la posibilidad de un rendimiento mayor al del mercado con bajo nivel de riesgo. Por último, con fines ilustrativos, se desarrolla en detalle una aplicación de la propuesta y se compara con otras alternativas disponibles en el mercado.
Caracterización de la capa de boruros formada durante la austenización de un hierro nodular austemperizado
Ingeniería Mecánica
Urbano Ordóñez Hernández 1 , Sarah Parada De la Puente 2 , Carlos Figueroa Hernández 1 , Francisco Mondelo García 1 , Arturo Barba Pingarrón 3 , Alfredo Del Castillo Serpa 1
1 Instituto Superior Politécnico José Antonio Echeverría, Facultad de Ingeniería Mecánica
2 Case New Holland
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: hierro nodular, borurado, austenización, austemperizado
Abstract: En este trabajo se ha investigado el efecto de la austenitización y el borurado simultáneos, a 950 °C, en la microestructura, la microdureza Vickers y el espesor de la capa borurada en medio líquido de un hierro nodular austemperizado no aleado. Se demostró que es posible obtener una capa de boruros de hierro muy bien estructurada con la microdureza Vickers suficientemente alta (1400 HV) y con adecuado espesor de capa de 67 μm, sobre un sustrato de ausferrita típico de las fundiciones nodulares austemperizadas. Por medio de un ensayo pin on disc modificado, se comprobó la superior resistencia al desgaste abrasivo de la capa de boruros depositada durante la austenización del ADI, comparada con la máxima obtenida durante el austempering de éste sin aplicar el recubrimiento.
Corrosion behavior of hybrid sol-gel films reinforced with electrospun nanofibers
Solid State Phenomena
Alba Covelo Villar 1 , Juan Genesca 2 , Arturo Barba Pingarrón 1 , Carmina Menchaca 3 , Jorge Uruchurtu 3 , Miguel Ángel Hernández Gallegos 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Facultad de Química
3 Universidad Autónoma del Estado de Morelos, CIICAp

Keywords: AA2024-T3, Corrosion, EIS, Electrospinning, Sol-Gel
Abstract: The aim of this paper is to evaluate the efficiency of hybrid sol-gel coatings reinforced with electrospinning nanofibers doped with cerium nitrate and ceria particles to increase the corrosion properties of the coating. Poly(vinyl alcohol) solutions doped with cerium nitrate and ceria were electrospun onto clean commercial aluminum alloy AA2024-T3 plates and then coated with a hybrid sol-gel system using the dip-coating procedure. The hybrid materials synthesized via sol-gel chemistry were prepared from inorganic-organic precursors: zirconium (IV) propoxide and 3-glycidoxypropyltrimetoxysilane. The electrochemical impedance spectroscopy technique was applied to evaluate the electrochemical properties of the film whereas scanning electron microscopy and atomic force microscopy were employed to characterize the surface characteristics. The incorporation of nanofibers into the sol-gel system provides good barrier properties that increase the corrosion resistance of the aluminum at longer exposure times in saline media. This protection depends of the type of inhibitor loaded within the electrospun nanofibers.
Cinemática Diferencial de un Manipulador Paralelo Plano 3RRR-(RRR)v con Actuación Virtual Indirecta
Ingeniería Mecánica, Tecnología y Desarrollo
Patricio Martínez Zamudio 1 , Víctor J. González Villela 1 , Alejandro Cuauhtémoc Ramírez Reivich 1 , Marcelo López Parra 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Cinemática de robots, robots paralelos, cadenas virtuales, variables de estado, controlabilidad
Abstract: En este artículo, se presenta un enfoque nuevo para obtener el modelo de la cinemática diferencial, matriz jacobiana: por un lado, el modelo de un manipulador paralelo delta plano de configuración 3RRR-(RRR)v y por el otro, el modelo de su cadena virtual serial (RRR)v. Ambos modelos se presentan en variables de estado y en función de las variables articulares de la cadena virtual. El primer modelo facilita el análisis completo de ambos: la cinemática y la controlabilidad del robot delta plano con su cadena virtual. El segundo modelo se utiliza para obtener su cinemática inversa, para, retroalimentar al primero. Esta retroalimentación es llamada "actuación virtual indirecta?. El enfoque propuesto garantiza que cuando el efector final de la cadena virtual serial (RRR)v es controlado alrededor de una trayectoria, el efector final del robot paralelo plano 3RRR también sigue dicha trayectoria; esto se debe a que comparten el mismo punto de análisis. Los resultados muestran que es posible controlar un robot paralelo delta plano 3RRR-(RRR)v a partir de controlar la cadena virtual (RRR)v. El método presentado aquí promete, por lo tanto, ser una herramienta útil para resolver robots complejos, como el caso de los robots manipuladores híbridos.
Estimation of the Groundwater Recharge in the Aquifer of Mexico City
Procedia Environmental Sciences
Gerardo Ruiz Solorio 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: groundwater recharge, water-table fluctuation method, groundwater flow modeling, groundwater system, groundwater recharge
Abstract: This work used several methodologies to evaluate the vertical groundwater recharge from precipitation in the aquifer of the Mexico City, Mexico. Firstly, the spatial variation of the recharge was evaluated and then the temporal variation in the recharge was analyzed in a station located in the center region of the study area. Several independent methods were applied to evaluate recharge: water-table fluctuation method and groundwater flow modeling in steady-state and in transient conditions. The results obtained show that the temporal variation in the recharge, measured in annual periods, was considerably greater than the variability in the precipitation that generated it, for all the applied methods and all the analyzed periods. The annual mean groundwater recharge varied from over 20% of the annual mean precipitation in the upper basin to less than 3% of the precipitation in the plains. A conceptual model of the groundwater system is proposed and its relationship to the recharges in each sector of the basin. This model identifies a regional flow system and local systems of different sizes.
Viscoelastic Characterization of Bovine Trabecular Bone Samples
Engineering and Technology International Journal of Mechanical and Mechatronics Engineering
Edgar I. Ramirez D. 1 , José J. Ángeles H. 1 , Osvaldo Ruiz C. 1 , Víctor Hugo Jacobo Armendáriz 1 , Armando Ortiz Prado 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Bone viscoelasticity, fatigue test, stress relaxation test, trabecular bone properties.
Abstract: Knowledge of bone mechanical properties is important for bone substitutes design and fabrication, and more efficient prostheses development. The aim of this study is to characterize the viscoelastic behavior of bone specimens, through stress relaxation and fatigue tests performed to trabecular bone samples from bovine femoral heads. Relaxation tests consisted on preloading the samples at five different magnitudes and evaluate them for 1020 seconds, adjusting the results to a KWW mathematical model. Fatigue tests consisted of 700 load cycles and analyze their status at the end of the tests. As a conclusion we have that between relaxation stress and each preload there is linear relation and for samples with initial Young´s modulus greater than 1.5 GPa showed no effects due fatigue test loading cycles.
Contraction based identification for nonlinear systems
Anahí Flores Pérez 1 , Yu Tang Xu 1 , Ileana Grave 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Nonlinear parameterization, systems identification, contraction theory
Abstract: A top-down approach to identification for systems with nonlinear parameterizations has been recently developed in Flores-Perez et al. (2014, 2015) based on contraction analysis where, at the top-level, the contraction analysis is carried out to ensure the proposed estimation algorithm possess the desired contraction properties, then, at the down-level, the estimation algorithm is realized through a proportional plus integral (PI) form. The realization of estimation schemes however relies on the assumption that state time derivatives are available. In this paper, by filtering signals involved in the system, an alternative to the realization of estimation algorithms without requiring the state time derivatives is given.
Security enhancement of medical imaging via imperceptible and robust watermarking
IEICE Transactions on Information and Systems
Manuel Cedillo Hernández 1 , Antonio Cedillo Hernández 2 , Francisco Javier García Ugalde 2 , Mariko Nakano Miyatake 1 , Héctor Pérez Meana 1
1 Instituto Politécnico Nacional, Sección de Estudios de Posgrado e Investigación
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: digital watermarking, medical imaging, authentication
Abstract: In this letter we present an imperceptible and robust watermarking algorithm that uses a cryptographic hash function in the authentication application of digital medical imaging. In the proposed scheme we combine discrete Fourier transform (DFT) and local image masking to detect the watermark after a geometrical distortion and improve its imperceptibility. The image quality is measured by metrics currently used in digital image processing, such as VSNR, SSIM and PSNR.
Copyright protection of color imaging using robust-encoded watermarking
Manuel Cedillo Hernández 1 , Antonio Cedillo Hernández 2 , Francisco Javier García Ugalde 2 , Mariko Nakano Miyatake 1 , Héctor Pérez Meana 1
1 Instituto Politécnico Nacional, Sección de Estudios de Posgrado e Investigación
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Digital watermarking, image normalization, geometric and signal processing distortions, convolutional encoder, Viterbi decoder, discrete cosine transform.
Abstract: In this paper we present a robust-encoded watermarking method applied to color images for copyright protection, which presents robustness against several geometric and signal processing distortions. Trade-off between payload, robustness and imperceptibility is a very important aspect which has to be considered when a watermark algorithm is designed. In our proposed scheme, previously to be embedded into the image, the watermark signal is encoded using a convolutional encoder, which can perform forward error correction achieving better robustness performance. Then, the embedding process is carried out through the discrete cosine transform domain (DCT) of an image using the image normalization technique to accomplish robustness against geometric and signal processing distortions. The embedded watermark coded bits are extracted and decoded using the Viterbi algorithm. In order to determine the presence or absence of the watermark into the image we compute the bit error rate (BER) between the recovered and the original watermark data sequence. The quality of the watermarked image is measured using the well-known indices: Peak Signal to Noise Ratio (PSNR), Visual Information Fidelity (VIF) and Structural Similarity Index (SSIM). The color difference between the watermarked and original images is obtained by using the Normalized Color Difference (NCD) measure. The experimental results show that the proposed method provides good performance in terms of imperceptibility and robustness. The comparison among the proposed and previously reported methods based on different techniques is also provided.
Traditional Method and Multi-Taper to Feature Extraction Using Mel Frequency Cepstral Coefficients
International Journal of Information and Electronics Engineering
José Trangol 1 , Abel Herrera Camacho 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Feature extraction, mel frequency cepstral coefficients, multi-taper
Abstract: This paper makes a comparison of two methods in speech processing that aims to obtain cepstral coefficients that represent characteristics of each speaker, in order to obtain a greater difference between each speaker (to build a representative model, in a next step), traditionally feature extraction is performed through a single periodic window function (generally hamming windows), we compare the traditional method with multi-taper, which has been used in verification speakers tasks and language recognition. The results obtained using 40 speakers indicate a reduction of the variance by using multi-taper and better separation between speakers; with this we have more robust coefficients. To feature extractions we use Mel Frequency Cepstral Coefficients.
Creating a Grammar-Based Speech Recognition Parser for Mexican Spanish Using HTK, Compatible with CMU Sphinx-III System
International Journal of Electronics and Electrical Engineering
Carlos Hernandez Mena 1 , Abel Herrera Camacho 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: speech recognition, mexican spanish, HTK, CMU Sphinx-III, grammar based system
Abstract: In this paper, we present the creation of a novel language model for automatic speech recognition based on HTK but compatible with the CMU Sphinx-III speech recognition system. This recognizer works with user defined grammars in the HTK format for speaker dependent recognition in Mexican Spanish. Input files are based on the Sphinx format, so you can use them with no modification in both systems. We provide with the recognizer a "live decode? module based on the Japanese speech recognition system called Julius for live recognition. We will also explain the phonetic alphabet chosen for the system and we will explore some of the new resources that are now available for the Mexican Spanish language. This software is available for free use and it is compatible with the most common operating systems (Windows, GNU-Linux and MAC OS).
Robust watermarking method in DFT domain for effective management of medical imaging
Signal, Image and Video Processing
Manuel Cedillo Hernández 1 , Francisco Javier García Ugalde 2 , Mariko Nakano Miyatake 1 , Héctor Pérez Meana 1
1 Instituto Politécnico Nacional, Sección de Estudios de Posgrado e Investigación
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Digital watermarking, Discrete Fourier transform, Medical imaging, DICOM imaging, Robust watermarking, Authentication, Detachment detection
Abstract: In general, management of medical data is achieved by several issues of medical information such as authentication, security, integrity, privacy, among others. Because medical images and their related electronic patient record (EPR) data are stored separately; the probability of corruption of this information or their detachment from the corresponding EPR data could be very high. Losing data from the corresponding medical image may lead to a wrong diagnostic. Digital watermarking has recently emerged as a suitable solution to solve some of the problems associated with the management of medical images. This paper proposes a robust watermarking method for medical images to avoid their detachment from the corresponding EPR data in which the watermark is embedded using the digital imaging and communications in medicine standard metadata together with cryptographic techniques. In order to provide a high robustness of the watermark while preserving at the same time a high quality of the watermarked images, the generated watermark is embedded into the magnitude of the middle frequencies of the discrete Fourier transform of the original medical image. During the detection process, the watermark data bits are recovered and detected using the bit correct rate criterion. Extensive experiments were carried out, and the performance of the proposed method is evaluated in terms of imperceptibility, payload, robustness and detachment detection. Quantitative evaluation of the watermarked images is performed by using three of the more common metrics: the peak signal-to-noise ratio, structural similarity index and visual information fidelity. Experimental results show the watermark robustness against several of the more aggressive geometric and signal processing distortions. The receiver operating characteristics curves also show the desirable detachment detection performance of the proposed method. A comparison with the previously reported methods with similar purposes respect to the proposed method is also provided.
Single DC-Sourced 9-level DC/AC Topology as Transformerless Power Interface for Renewable Sources
Juan Ramón Rodríguez Rodríguez 1 , Edgar Lenimirko Moreno Goytia 2 , Vicente Venegas Rebollar 3
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Instituto Tecnológico de Morelia, División de Estudios de Posgrado e Investigación
3 Instituto Tecnológico de Morelia, Programa de Graduados e Investigación en Ingeniería Eléctrica (PGIIE)

Keywords: multilevel converters, buck converter, cascaded cells, transformerless, micro-grids, FPGA control
Abstract: This paper introduces an advanced transformerless multilevel hybrid-conversion topology intended for the interconnection of renewable DC sources at small-scale. The most important contribution presented in this paper is the generation of two isolated DC sources from a single DC source without the use of any type of transformer. The DC sources feed a nine-level DC/AC hybrid cascade multilevel converter. This advanced topology is achieved by redesigning the conventional DC/DC Buck topology, attached to the multilevel converter, and embedding a suitable switching strategy along with a Field Programmable Gate Array (FPGA)-based control. The advantages of the proposed structure, when compared to other proposals in the literature, are higher efficiency, reduced number of power switches, and high power density derived of transformerless characteristic. As a way to highlight differences and advantages of this converter over other options recently available in the literature, this paper carries out a quantitative evaluation comparing the number of voltage levels and the number of elements involved in the structure of DC/AC multilevel converters. The mathematical model and control strategy of the converter are explained and analyzed by means of simulations. Finally experimental results, obtained from a laboratory-scale prototype, show the performance of the system and demonstrate its relative advantages.
Current-sensorless control of an SPWM H-Bridge-based PFC rectifierdesigned considering voltage sag condition
Electric Power Systems Research
Juan Ramón Rodríguez Rodríguez 1 , Edgar Lenimirko Moreno Goytia 2 , Vicente Venegas Rebollar 3 , David Campos Gaona 4 , Ramón Felix 5 , Luis E. Ugalde Caballero 6
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Instituto Tecnológico de Morelia, División de Estudios de Posgrado e Investigación
3 Instituto Tecnológico de Morelia, Programa de Graduados e Investigación en Ingeniería Eléctrica (PGIIE)
4 University of British Columbia, Electrical and Computer Engineering
5 Universidad de Colima, Facultad de Ingeniería Mecánica y Eléctrica
6 Instituto Tecnológico de Morelia, Ingeniería Eléctrica

Keywords: AC??DC power conversion, PFC converter, SPWM rectifier, Sensorless current, Single-loop PI, DC regulation
Abstract: This paper presents and details the H-Bridge PFC rectifier control scheme. This control is a step forward in sensorless current control schemes for performance improvements of single-phase bidirectional rectifiers. The H-Bridge PFC rectifier is designed based on a single PI controller loop fed by DC reference signals. Regarding dynamic operating conditions, the proposed control can maintain a regulated DC voltage under varying conditions at input (voltage sags) and output (load step changes) ports while maintaining an unitary power factor (PF) and constant THD current input at any of these conditions. Different to other investigations, this control proposal uses SPWM, does not require a variable transformation into the dq0 reference frame, and the complex compensators accompanying to the PI controller stage are no longer needed. Therefore, this proposal is aimed to reduce the complexity of the control scheme and to improve the overall dynamic response of the PFC rectifier. The experimental results obtained from the scaled-down prototype setup, which was built for research purposes, validate the control law, mathematical model and quantitative comparison between simulation and experiment, both considering the parasitic resistances of the inductor and semiconductor switches.
Propiedades de sistemas tipo M/G/1/K con estaciones en serie
Ingeniería Investigación y Tecnología
Salvador Hernández González 1 , Manuel Darío Hernández Ripalda 1 , Idalia Flores De La Mota 2 , José Antonio Vázquez López 1
1 Instituto Tecnológico de Celaya, Departamento de Ingeniería Industrial
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: líneas de espera, análisis, descomposición, buffer, estaciones múltiples, arreglo en serie
Abstract: En este trabajo se presenta una adecuación al método de Buzacott y Shanthikumar (1993) para calcular analíticamente las propiedades de sistemas de líneas de espera tipo M/G/1/K y arreglo en serie. Se realizaron pruebas de validación empleando simulación y se observó que, con la modificación propuesta, el método tiene un grado de exactitud aceptable para obtener las propiedades de sistemas M/G/1/K en serie, con lo que se puede considerar como una alternativa a otro método propuesto en la literatura para dicha clase de sistemas. Al ser un procedimiento que requiere menos cálculos, es de gran utilidad para responsables en la toma de decisiones, que requieren implementar herramientas para analizar el desempeño de sistemas de líneas de espera en ambientes de producción y servicios.
Second-Order Sliding Mode Control of a Perturbed-Crane
Journal of Dynamic Systems, Measurement, and Control
Carlos Vázquez 1 , Leonid Fridman Golredich 2 , Ismael Castillo 2
1 Umea University, Department of Applied Physics and Electronics
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Nonlinear systems, Control
Abstract: A five degrees-of-freedom overhead crane system affected by external perturbations is the topic of study. Existing methods just handle the unperturbed case or, in addition, the analysis is limited to three or two degrees-of-freedom. A wide range of processes cannot be restricted to these scenarios and this paper goes a step forward proposing a control solution for a five degrees-of-freedom system under the presence of matched and unmatched disturbances. The contribution includes a model description and a second-order sliding mode (SOSM) control design ensuring the precise trajectory tracking for the actuated variables and at the same time the regulation of the unactuated variables. Furthermore, the proposed approach is supported by the design of strong Lyapunov functions providing an estimation of the convergence time. Simulations and experiments, including a comparison with a proportional-integral-derivative (PID) controller, verified the advantages of the methodology.
Sliding-Mode Based Disturbance Estimation, Attenuation and Fault Detection
IET Control Theory & Applications
Leonid Fridman Golredich 1 , Shihua Li 2 , Arie Levant 3 , Xinkai Chen 4 , Xinhguo Yu 5
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Southeast University, School of Automation
3 Tel-Aviv University, School of Mathematical Sciences
4 Shibaura Institute of Technology, Department of Electronic and Infromation, Systems
5 RMIT University, Platform Technologies Research Institute

Abstract: Sliding-mode control and observation theory has received an influx of new results owing to the development of arbitrary order differentiators. Such differentiators ensure the best possible asymptotic accuracy in the presence of discrete sampling and measurement noises, while only requiring the knowledge of a Lipschitz constant of the highest estimated derivative.
Output tracking of systems subjected to perturbations and a class of actuator faults based on HOSM observation and identification
Alejandra Ferreira De Loza 1 , Jérome Cieslak 2 , David Henry 2 , Ali Zolghadri 2 , Leonid Fridman Golredich 3
1 Instituto Politécnico Nacional, CITEDI
2 Université de Bordeaux
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Disturbance rejection, Fault-tolerant systems, Sliding-mode control
Abstract: This paper deals with the output tracking problem of a MIMO system subjected to a class of actuator faults and unmatched perturbations. The proposed methodology is based on high order sliding mode observation and identification techniques. A dynamic sliding surface is proposed using a backstepping-like design strategy in order to counteract the effects of the unmatched perturbations. Whereas a continuous sliding mode control is designed to steer the states toward the sliding surface. The identified value of the fault is injected to alleviate the control gain while accomplishing fault accommodation. As a consequence, the chattering is attenuated. A simulation example for a 3-DOF helicopter highlights the efficiency of the present method.
Transparent bilateral master-slave control based on virtual surfaces: Stability analysis and experimental results
International Journal of Robotics and Automation
Alejandro Rodríguez Angeles 1 , Marco Antonio Arteaga Pérez 2 , Rogelio Portillo Vélez 1 , Carlos A. Cruz Villar 3
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería
3 Instituto Politécnico Nacional, Centro de Investigación y de Estudios Avanzados

Keywords: Teleoperation, master-slave systems, position??force tracking control,transparency, force re?ecting
Abstract: This work develops a bilateral master??slave control approach based on virtual surfaces for the master and direct force re?ecting from the slave robot. Real and virtual surfaces are modeled by holonomic constraints, allowing joint orthogonal decomposition into force and position spaces to be considered. A stability analysis is provided and convergence properties for position and force errors are drawn, yielding transparency of the bilateral master??slave system. The reaction force between the real surface and the slave robot is measured by a force sensor and this signal is sent for force re?ecting to the master robot. On the master robot, a holonomic constraint generates a virtual surface. Between the operator and the virtual surface, a virtual force arises and it is obtained via a Lagrange multiplier. The virtual force is regulated to converge to the measured reaction force at the slave robot. Thus, the operator feels the virtual force as a reaction force, and convergence from the virtual to the slave reaction force makes the user feels the environment reaction force. Inclusion of the virtual force allows decoupling of the operator and the real re?ected slave reaction force, which helps to improve the force bandwidth and stability of the bilateral system, mainly at transient stage. The virtual surface and the virtual reaction force allow the integration of a force sensor at the master robot to determine the desired force exerted by the operator by direct measurement.
On the Observability and the Observer Design of Differential Pneumatic Pistons
Journal of Dynamic Systems, Measurement, and Control
Marco Antonio Arteaga Pérez 1 , Alejandro Gutiérrez Giles 1 , Jens Weist 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Volkswagen AG

Keywords: Design, generalized proportional integral, pneumatic pistons
Abstract: In this paper, an observability analysis for differential pneumatic pistons is presented, together with the design and implementation of linear observers of the Luenberger type. To avoid as much as possible the knowledge of the system model parameters, the generalized proportional integral (GPI) approach is employed for the estimation of unmeasured variables. Experimental results show the good performance of the proposed scheme.
3D Visual Servoing Control for Robot Manipulators Without Parametric Identification
IEEE Latin America Transactions
Marco Antonio Arteaga Pérez 1 , Maximiliano Bueno López 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad de La Salle

Keywords: 3D Vision, No Cameras Calibration, Observer Design, Unknown Dynamic Model, Visual Servoing Control
Abstract: Visual servoing control of robot manipulators represents a natural option in unstructured environments and it is specially attractive when the task to achieve can be expressed directly in image coordinates. In the present work a control law is developed for trajectory tracking of three degrees of freedom robot manipulators. The main characteristic of the proposed algorithm is that it does not need any dynamic model of the system and image coordinates are employed directly for feedback, while an observer is designed for velocity estimation. To carry out 3D movements no stereoscopic vision is used. Rather, a simpler configuration employing two fixed cameras is proposed which makes unnecessary their calibration and helps avoid occlusions for most of the robots workspace. The developed theory was successfully tested in an industrial manipulator.
An immersed free-surface boundary treatment for seismic wave simulation
Longfei Gao 1 , Romain Brossier 1 , Banjamin Pajot 2 , Josué Tago Pacheco 3 , Jean Virieux 4
1 Université Grenoble Alpes, ISTerre
2 Center for Excellence in Parallel Programming Bull
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 Universite Grenoble Alpes, Institut des Sciences de la Terre

Keywords: Wave equation, free surface, immersed-boundary methods, extrapolation, staggered grid, instability
Abstract: Finite-difference methods are popular for wave simulation within the seismic exploration community, thanks to their efficiency. However, difficulties arise when encountering complex topography due to the regular grid pattern of the finite-difference schemes. Despite alternatives that can handle the free surface with little effort, such as the spectral element or discontinuous Galerkin??s methods, incorporating a free-surface boundary condition within the finite-difference framework is still appealing, even at the cost of extra algorithm complexity and stronger requirement of computational resources. We present a free-surface boundary treatment within the finite-difference framework, belonging to the family of the immersed-boundary methods. Inherently, the presented boundary treatment is separated from the rest of the wave simulation, which makes it easy to be integrated in existing finite-difference codes. Specifically, we construct an extrapolation operator for each grid point above the free surface, if requested by the finite-difference stencil, to estimate its fictitious wavefield value at each time step. These operators are constructed only once and remain unchanged for all the time steps and source locations. The memory requirement of these operators is significant. Fortunately, grouping together multiple simulations concerning different source locations makes it possible to dilute the memory burden to a negligible level. Additionally, applying these operators incurs numerical noise, which may lead to long time instabilities. In such a scenario, additional numerical procedures, for instance, introducing artificial diffusion, are necessary to control the instability and obtain sensible simulation results. Successful applications of the presented boundary treatment to elastic-wave equations on domains with nontrivial topographies, in 2D and 3D, are presented. Robust and efficient numerical techniques to control high-frequency numerical noise remain to be investigated.
La relación de subsidencia del terreno InSAR-GPS y el abatimiento del nivel estático en pozos de la zona Metropolitana de la Ciudad de México
Boletín de la Sociedad Geológica Mexicana
Darío Solano Rojas 1 , Enrique Cabral Cano 2 , Antonio Hernández Espriú 3 , Shimon Wdowinski 1 , Charles DeMets 4 , Luis Salazar Tlaczani 2 , Giacomo Falorni 5 , Adrian Bohane 5
1 University of Miami, Rosenstiel School of Marine and Atmospheric Science
2 Universidad Nacional Autónoma de México, Instituto de Geofísica
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 University of Wisconsin, Department of Geoscience
5 TRE Canada Inc.

Keywords: subsidencia, abatimiento, GPS, InSAR, Ciudad de México
Abstract: El proceso de subsidencia en la zona metropolitana de la Ciudad de México ha sido reconocido desde principios del siglo pasado y sus efectos tienen graves consecuencias para la operación y mantenimiento de la infraestructura de la ciudad. En este trabajo se presentan las velocidades de subsidencia del terreno obtenidas de Dispersores Persistentes (Persistent Scatterers, PSs) derivados del análisis interferométrico SqueeSAR de datos ENVISAT-ASAR de Radar de Apertura Sintética adquiridos entre los años 2003 ?? 2010 y de nueve estaciones GPS de operación continua. A partir de estos datos se investigó la relación existente entre las velocidades de subsidencia observadas con el abatimiento del nivel estático obtenidos de hidrógrafos de 180 pozos de abastecimiento distribuidos en la zona metropolitana de la Ciudad de México. Los resultados geodésicos muestran diversos comportamientos del proceso de subsidencia en las inmediaciones de las estaciones GPS que van desde lo estable (zonas no subsidentes), zonas de baja velocidad de subsidencia, hasta zonas de muy alta velocidad de subsidencia. Las zonas de mayor velocidad de subsidencia se encuentran en regiones de gradiente horizontal de subsidencia muy bajo, dentro de la zona lacustre, con velocidades verticales de GPS tan altas como -273 mm/año. Áreas con gradientes horizontales de subsidencia locales muy altos inducen a su vez el potencial de desarrollo de grietas y fallas de tensión en la superficie. El análisis de los datos de hidrógrafos de los últimos 20 años indica que el nivel del agua subterránea ha descendido hasta 30 m en los casos más severos; sólo en algunos cuantos casos se registra la recuperación del nivel estático y es únicamente en aquellos pozos ubicados en áreas de baja velocidad de subsidencia. La caída de los niveles del agua subterránea se aprecia en todo el rango de velocidades de subsidencia, sugiriendo que el sistema acuífero-acuitardo se encuentra bajo severo estrés debido a la extracción extrema de agua subterránea que excede por mucho la magnitud de la recarga natural. La baja correlación entre la velocidad de subsidencia del terreno y la caída del nivel estático sugiere que existen variables adicionales que condicionan de manera importante los procesos de subsidencia, tales como la litología, la potencia del acuitardo, el contenido de agua, el comportamiento elasto-plástico de la hidroestratigrafía, la reducción de la presión de poro y el volumen de extracción. Al analizar la relación del espesor del acuitardo superior con las velocidades de subsidencia se observa una correlación positiva entre ambas variables.
Stability and Consensus of Electrical Circuits via Structural Properties
Sofía Ávila Becerril 1 , Gerardo Espinosa Pérez 1 , Paul Fernández Carrillo 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Electrical circuits, Hamiltonian systems, Consensus, Graph theory
Abstract: In this paper stability and consensus on electrical circuits is approached. The novelty of the presented results lies in the fact that, contrary to the usual practice of establishing these properties for a given circuit, generic features of this class of networks are interpreted in terms of interconnections of the circuit elements to conceive specific topologies for which both stability and consensus are guaranteed. Fundamental for this achievement is the Hamiltonian structure exhibited by the circuits, since the features enjoyed by this kind of dynamical systems allow to systematically state the structural (interconnection) properties under which stability is assured while conditions to conclude consensus are derived from the analysis of its equilibria.
Revisión de los últimos eventos magmáticos del Cenozoico del sector norte-central de la Sierra Madre del Sur y su posible conexión con el subsuelo profundo de la Cuenca de México
Boletín de la Sociedad Geológica Mexicana
Enrique Alejandro González Torres 1 , Dante J. Morán Zenteno 2 , Laura Mori 1 , Barbara M. Martiny 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Instituto de Geología

Keywords: Hamiltonian systems
Abstract: En el presente trabajo se revisa la posible correlación de las unidades del subsuelo profundo de la Cuenca de México (CM) que forman las sucesiones inferiores de pozos de perforación, con el registro estratigráfico del Cenozoico anterior a la Faja Volcánica Trans-Mexicana (FVTM) expuesto en la parte norte de la Sierra Madre del Sur (SMS). En años recientes se han realizado estudios estratigráficos y geocronológicos de algunos centros eruptivos del sector norte-central de la SMS, que forman los campos volcánicos de Taxco y Huautla, y la caldera de Tilzapotla. En dichos campos se encuentra el registro de los últimos episodios volcánicos anteriores a la formación de la FVTM, y que constituye el extinto arco del Paleógeno de la SMS. Con base en las analogías litológicas, la posición estratigráfica y el espesor del registro litológico obtenido, se pueden relacionar las partes inferiores de los pozos con las unidades distales de los centros volcánicos referidos. De la misma forma, en Tepoztlán y Malinalco (estados de Morelos y de México), al sur de la CM, se encuentran expuestos los primeros episodios volcánicos de la FVTM, con edades que varían entre los ~22.8 y 18.8 Ma, para los cuales se ha sugerido en trabajos previos una correlación temporal con las edades reportadas en varios pozos profundos de la CM. A partir de la información geológica disponible, se argumenta que el proceso de subsidencia observado en la CM es un rasgo tectónico contemporáneo a la FVTM, que no se encuentra relacionado a la tectónica del Paleógeno de la región. La ausencia de espesores significativos (no superiores a 1000 m) de rocas volcánicas o sedimentarias cuya edad probable es del Paleógeno entre las sucesiones del Neógeno y las capas marinas del Cretácico en el subsuelo de la CM sugiere que la subsidencia ocurrió principalmente durante el Neógeno.
Geochronology of Mexican mineral deposits. III: the Taxco epithermal deposits, Guerrero
Boletín de la Sociedad Geológica Mexicana
José Farfán Panamá 1 , Antoni Camprubi 2 , Eduardo González Partida 3 , Alexander Iriondo 3 , Enrique Alejandro González Torres 4
1 Universidad Autónoma de Guerrero, Unidad Académica de Ciencias de la Tierra
2 Universidad Nacional Autónoma de México, Instituto de Geología
3 Universidad Nacional Autónoma de México, Centro de Geociencias
4 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Taxco, Mexico, epithermal deposits, intermediate sulfidation, 40Ar/39Ar ages, U-Pb ages, zircon
Abstract: New 40Ar/39Ar (34.96 ± 0.19 Ma) and U-Pb ages (35.44 ± 0.24 and 34.95 ± 0.37 Ma) obtained in this study for the Calavera group of dikes, which predate intermediate sulfidation epithermal mineralization in the Taxco mining district, constrain the formation of such deposits to less than 34.96 Ma (latest Eocene). These deposits might arguably have formed at ~ 33 Ma, thus coinciding in age with the La Azul fluorite deposits, within the same district. Although this age is significantly younger than previously existing estimations, the deposits at Taxco consistently cluster into a Late Eocene to Oligocene metallogenic event. Such event was closely associated with the volcanism in the northern part of the Sierra Madre del Sur, specifically to the most prominent flare-up of subduction-derived volcanism before it ceased in the region and refashioned into the Trans-Mexican Volcanic Belt.
Early Mesozoic Southern Mexico??Amazonian connection based on U??Pb ages from detrital zircons: The La Mora Paleo-River in the Mixteca Terrane and its paleogeographic and tectonic implications
Gondwana Research
Gilberto Silva Romo 1 , Claudia Cristina Mendoza Rosales 1 , Emiliano Campos Madrigal 1 , Elena Centeno García 2 , Rosario Peralta Salazar 3
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Instituto de Geología
3 Petroanalisis, S.A. de C.V.

Keywords: La Mora Formation, Late Triassic??Early Jurassic, Amazonian craton, Amazon basin, Tolimán submarine fan
Abstract: The La Mora Formation is the oldest Mesozoic floodplain succession in the Mixteca Terrane of Southern Mexico. The presence of Amazonian detrital zircons in the La Mora Formation and in the overlying volcanic Diquiyú Unit indicates a major fluvial system that drained the Mixteca Terrane. The La Mora Paleo-River crossed the Oaxaquia microcontinent and the Mixteca Terrane prior to the breakup of Pangea, during Late Triassic??Early Jurassic time, when the Acatlán??Oaxaquia block was part of the northwestern portion of the Amazonian craton. Detrital zircons in the La Mora Formation have ages between 3307 ± 31 and 210 ± 12 Ma, which suggest that they originated in Amazonia and Southern Mexico: 33.2% of the detrital zircons have ages that are found only in Amazonian sources; whereas 66.7% of the zircons may be associated with either the Amazonian craton, the Andean Basement, or Southern Mexico. We propose that the La Mora fluvial system drained the Amazon basin in a westward direction, with its mouth in central Pangea, and that it most likely fed the Tolimán submarine fan. The inferred location of the Acatlán??Oaxaquia tectonic block at the time of the La Mora fluvial system implies that the basement of Southern Mexico experienced a right lateral displacement of at least 2300 km with respect to South America during the Mesozoic.
Towards an Aptian (Lower Cretaceous) ammonite biostratigraphy of the Mina Texali section, Central Atlantic province (Puebla State, Central Mexico)
Cretaceous Research
Josep A. Moreno Bedmar 1 , Claudia Cristina Mendoza Rosales 2 , K. P. Minor 3 , G. Delanoy 4 , R. Barragán 1 , Oscar González León 5
1 Universidad Nacional Autónoma de México, Instituto de Geología
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería
3 Sovereign Pharmaceuticals
4 Université de Nice-Sophia Antipolis, Département des Sciences de la Terre
5 Universidad Nacional Autónoma de México, Facultad de Estudios Superiores Iztacala

Keywords: Ammonites, Biostratigraphy, Aptian, Lower Cretaceous, Mexico
Abstract: This work is a study of the ammonite record of a new stratigraphic section of Aptian age, at the Mina Texali (Puebla State, Central Mexico). A detailed biostratigraphic analysis was carried out on 309 specimens systematically sampled on a bed-by-bed basis. An Aptian ammonite zonation is proposed for the Mina Texali (= MT) section with two interval zones, Dufrenoyia justinae and Caseyella sp., and one informal biostratigraphic unit represented by the Huastecoceras trispinosoides beds. We also analyze the taxonomic composition, paleoecology and some systematic issues of the ammonite record of the MT section. The first record in Mexico of the genera Pseudosaynella, Xerticeras and the nautiloid Heminautilus is identified in this section. The ammonite assemblage is assigned to the proximal part of the outer neritic region of the continental shelf. The ammonite record of the studied section is diagnostic in establishing the lower-upper Aptian transition, and the local zonation of the MT provides important data for the development of an Aptian standard ammonite zonation for the Central Atlantic province.
Two algorithms to compute the electric resistivity response using Green's fuctions for 3D structures
Geofísica Internacional
Leticia Flores Máquez 1 , Claudia Arango Galván 1 , René E. Chávez Segura 1 , Andrés Tejero Andrade 2 , A. León Sánchez 2
1 Universidad Nacional Autónoma de México, Instituto de Geofísica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: 3D electrical model, Green??s functions, integral method, Gauss theorem, Boundary conditions
Abstract: An integral solution of the forward DC geoelectric response for three-dimensional target-bodies in a half-space, based on Green??s functions, is introduced. The first algorithm presented is based on a volume integral method (VIM); here, only the primary electrical current is involved to compute the electric potential. The second one employs the surface integral method (SIM), and it is assumed the induced charge is due to the primary electrical field. Both algorithms are a combination of boundary and volume integrals. This paper shows the applicability of these algorithms to generate resistivity profile images reproducing some electrode arrays for traditional synthetic examples, and then these images were compared with already published results. Finally, the comparison between results shows the concept of induced charge used in SIM produces a better approach than VIM scheme in computing the electrical potential.
L- and CORNER-arrays for 3D electric resistivity tomography: an alternative for geophysical surveys in urban zones
Near Surface Geophysics
Andrés Tejero Andrade 1 , Gerardo Cifuentes Nava 2 , René E. Chávez Segura 2 , Aideé López González 2 , Cecilia Delgado Solórzano 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Instituto de Geofísica

Abstract: Three?dimensional electric resistivity tomography surveys carried out on heavily urbanized areas represent a cumbersome task since buildings, houses, or other types of obstacles do not allow parallel electric resistivity tomography lines to be deployed. This paper proposes applying any four?electrode configuration to provide subsurface information in complex urban areas. Such a procedure allows acquiring information beneath a construction by simply surrounding the structure of interest by a series of electric resistivity tomography profiles. Apparent resistivity is obtained from ??L??? and ??Corner???shaped profiles, where alternations between current and potential electrodes are carried out in an automatic way. Four ??L???arrays and four ??Corner???arrays are employed in a square geometry that allows surrounding the studied target to cover the subsurface. The first mentioned array will provide deep information. The second array will cover more of the shallow subsurface information. For the ??L??? and ??Corner???arrays, a mixture of traditional arrays are employed, like the Wenner??Schlumberger, axial, equatorial, azimuthal, and perpendicular dipole arrays. Two synthetic examples are presented to demonstrate the possibilities of the proposed electric arrays. A resistive cube set at the centre of a working cube is modelled. The ??L??? and ??Corner??? arrays are capable to detect such a model; however, dimensions are exaggerated. Later on, an extended wall model is dealt with. Similar results as in the first synthetic example are obtained in terms of geometry and resistivity. However, depth to the top of the wall model is not adequately recovered in comparison with the traditional methodology. Finally, the ??L??? and ??Corner???arrays are applied in an archaeological site named El Pahñu, located in Central Mexico. The new methodology described here is compared with the traditional 3D procedure employing a grid of electric resistivity tomography transects. As expected, the approach discussed in this investigation produced a reasonable solution towards the central portion of the working cube. However, shallow resistive anomalies (size about the electrode interval) were not fully detected, in comparison to a traditional 3D survey, where parallel lines forming a grid could be deployed. The reason is that no electrodes were set towards the central portions of the structure under study. However, the L? and Corner?arrays are more sensitive to anomalies produced by deeper objects, which cannot be observed in the traditional method, especially when objects are located in between the electric resistivity tomography transects.
Consideraciones en la definición del modelo específico al paciente de la tibia
Revista Cubana de Investigaciones Biomédicas
Raide Alfonso González Carbonell 1 , Armando Ortiz Prado 2 , Víctor Hugo Jacobo Armendáriz 2 , Yosbel Angel Cisneros 1 , Lázaro Morales Acosta 2
1 Universidad de Camagüey, Facultad de Electromecánica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: modelo específico al paciente, elementos finitos, densidad de la malla, biomecánica ortopédica
Abstract: Introducción: los análisis por elementos finitos se usan para entender y predecir los procesos biológicos. En la biomecánica ortopédica, los modelos específicos al paciente se generan a partir de Tomografía Computarizada y empleados en la toma de decisiones médicas. Algunos procesos correctivos ortopédicos pueden simularse a través, de los análisis por elementos finitos. Para obtener modelos biomecánicos confiables, es muy recomendable reducir los errores en la definición del modelo en la etapa de pre-procesamiento del análisis por elementos finitos. Objetivo: analizar la influencia de la densidad del mallado y las propiedades mecánicas durante la definición del modelo específico al paciente en los resultados del análisis por elementos finitos. Métodos: se empleó el Método de Elementos Finitos en la simulación de la tibia a compresión. La geometría de la tibia del paciente se generó a partir de Tomografía Computarizada. Se emplearon mallas con tamaño de elementos no uniforme y uniforme. Al modelo se le aplicaron propiedades mecánicas homogéneas y no homogéneas. Resultados: los elementos de bajo orden convergen a la solución, las tensiones para las mallas con estos elementos son inferiores a las correspondientes las mallas con elementos de tamaño uniforme y de alto orden. Por otra parte, las propiedades mecánicas no homogéneas reducen la diferencia en el cálculo de las tensiones. Conclusiones: para obtener modelos específicos al paciente confiables se recomienda, generar la geometría del hueso con superficies suavisadas, controlar la calidad de la malla superficial, usar propiedades mecánicas no homogéneas, y utilizar la malla generada directo en Abaqus con elementos de bajo orden y tamaño no uniforme.
Critical analysis of a coaxial configuration for the characterization of adhesive wear and its application to Al and Al-Sn alloys
Tribology Letters
Carlos Gabriel Figueroa 1 , Víctor Hugo Jacobo Armendáriz 2 , Armando Ortiz Prado 2 , Rafael Schouwenaars Franssens 2
1 Universidad Nacional Autónoma de México, Facultad de Estudios Superiores Aragón
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Adhesive wear, Wear testing devices, Aluminium??tin, Journal bearings, Surface roughness, Tribolayer
Abstract: One of the main challenges of a tribological design is to find suitable pairs of materials to minimize friction and wear under specific operating conditions. To reproduce conditions of sliding and adhesive wear, a coaxial tribometer was developed. The equipment uses real-time data acquisition and feedback, allowing continuous control over a wide range of loads and rotational speed. Finite element analysis and experiments on selected materials are used to present a critical assessment of the advantages and drawbacks of the proposed configuration. Specifically, the tribological behaviour of cold-rolled and recrystallized AA1100 Al alloy and Al??Sn alloys is revisited. Worn surfaces are characterized by optical roughness measurement and SEM observation. Optical profilometry shows higher values of roughness in cold-rolled materials and confirms the essential contribution of Sn to the reduction of adhesive wear in Al-based alloys. At the surface of the SAE 783 alloy, severe mechanical mixing of the Al and Sn phases was observed in the worn zones as the result of severe plastic deformation during the formation of the tribologically modified surface layer.
Searching for enrichment and gadolinia distributions in BWR fuel lattices through a Heuristic-Knowledge Method
Progress in Nuclear Energy
José Luis Montes Tadeo 1 , Raúl Perusquía Del Cueto 1 , Cecilia Martín del Campo 2 , Alejandro Castillo 1 , Juan Luis François Lacouture 2 , Juan José Ortiz Servin 1
1 Instituto Nacional de Investigaciones Nucleares
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Fuel lattice design, Heuristic-Knowledge Method, BWR
Abstract: A Heuristic-Knowledge Method was developed to determine the enrichment and gadolinia distribution in a fuel lattice of boiling water reactors. The method was called S15 and is based on the experience obtained for the fuel lattice design for this kind of nuclear reactors. It also takes advantage of the symmetry aspects found in a typical BWR fuel lattice. An objective function was used throughout the searching process, as well as the same degrees of freedom used by five different meta-heuristic techniques based on evolutionary algorithms. Using the S15 method forty iterations were needed to obtain the best solution i.e., the smallest value of the objective function through a minimization process. In order to assess the performance of the S15 method, it was compared to five other evolutionary techniques. The two-dimensional CASMO-4 code was used to obtain the neutronic parameters employed by the objective function. The objective function value was the main criterion used to qualify all the techniques. All the methods were applied to fuel lattices charged in three different real operation cycles of the nuclear reactors at the Laguna Verde Nuclear Power Plant (LVNPP). The results generated with S15 surpass those obtained by the five evolutionary techniques.
Acomodo de figuras irregulares en áreas irregulares para el corte de cuero
Ingeniería Investigación y Tecnología
Luis Guevara Palma 1 , Saúl Daniel Santillán Gutiérrez 1 , Yu Tang Xu 1 , Jesús Manuel Dorador González 1 , Claudia Ivette Lara Jiménez 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: corte de cuero, optimización en acomodo de figuras irregulares, nesting, sistema de producción
Abstract: El problema del acomodo de figuras irregulares dentro de áreas irregulares se ha estudiado desde varios enfoques debido a su aplicación en diferentes industrias. El caso particular del corte de cuero implica varias restricciones que hacen difícil la automatización de este problema, pues es necesario cumplirlas para poder generar productos con la calidad requerida por los clientes. El presente documento presenta una metodología para el acomodo de figuras irregulares en un área irregular (piel) considerando las restricciones establecidas por la industria del calzado, así como los resultados de dicha metodología al aplicarlos mediante un sistema de cómputo. El alcance del sistema es desarrollar un algoritmo que pueda integrarse en un prototipo funcional, que opere bajo los lineamientos de una línea de producción de una industria patrocinadora. Pruebas de laboratorio del sistema de cómputo arrojan reducciones del tiempo de 70% con respecto a sistemas comerciales y una mejora de 5 a 7% del área que puede lograr utilizar un operario.
Life cycle assessment of hydrogen production from a high temperature electrolysis process coupled to a high temperature gas nuclear reactor
International Journal of Hydrogen Energy
Mario Giraldi 1 , Juan Luis François Lacouture 1 , Cecilia Martín del Campo 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Hydrogen production, LCA, GHG, Nuclear energy chain, High temperature electrolysis, High temperature gas reactor
Abstract: The life cycle analysis (LCA) is a versatile tool to evaluate process and production systems, and is useful to compare environmental burdens. For the purposes of this LCA, a high temperature electrolysis process was coupled to a high temperature gas nuclear reactor. The system function is the production of hydrogen using electricity and heat from nuclear power, with a functional unit of 1 kg of hydrogen, at the plant gate. The product system consists of the following steps: (i) the extraction and manufacturing of raw materials (upstream flows), (ii) the electrolytic cell fabrication, (iii) the nuclear fuel cycle, and, (iv) the hydrogen production plant. Particular attention was paid to those processes where there was limited information available on inventory data, for example mining and processing of rare earth metals, and electrolytic cell assembly, which are the primary components of a hydrogen generation plant. The environmental impact assessment focuses on the emissions of greenhouse gases (GHGs), as related to global warming. Additionally, other environmental loads, to complete the environmental profile of the product system, were included. The results were low GHGs emissions, with a value of 416 g of CO2eq kg-1H2. As to the process components, the electrolytic cell showed the highest environmental impact.
Transient electroosmotic flow of Maxwell fluids in a slit microchannel with asymmetric zeta potentials
European Journal of Mechanics - B/Fluids
Juan P. Escandón Colín 1 , Edson M. Jiménez 2 , Clara Hernández 1 , Oscar Eladio Bautista Godínez 1 , Federico Méndez Lavielle 2
1 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Maxwell fluid, Transient electroosmotic flow, Microchannel, Zeta potential
Abstract: In this work, the transient electroosmotic flow through a slit microchannel formed by two parallel walls with asymmetric zeta potentials is studied. An appropriate combination of the momentum equation together with the rheological Maxwell model leads to a hyperbolic partial differential equation that permits to determine the velocity profile, which is found analytically by the method of separation of variables. Adopting the nondimensionalized version of the governing equations allows us to obtain the following dimensionless parameters that control the fluid flow conditions: the dimensionless relaxation time of the fluid, l1 , and the ratio of the zeta potentials for both walls of the microchannel, Rz. The significance of the former is based on that the fluid flow of Maxwell fluids reaches the steady state just controlled by the value of this parameter. For the Newtonian case, the steady state is directly established depending on values of Rz. The velocity profiles of the fluid flow exhibit a symmetric or asymmetric shape and a peculiar oscillatory behavior in the transient stage, depending on the competition between the viscous and elastic forces.
Automatic segmentation of the cerebellum in ultrasound volumes of the fetal brain
Revista Mexicana de Ingeniería Biomédica
G. Velázquez Rodríguez 1 , Fernando Arámbula Cosío 1 , Mario E. Guzmán Huerta 2 , L. Carmargo Marín 2 , Héctor Borboa Olivares 2 , Boris Escalante Ramírez 3
1 Universidad Nacional Autónoma de México, Instituto de Ciencias Aplicadas y Tecnología
2 Instituto Nacional de Perinatología
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: 3D fetal ultrasound segmentation, fetal cerebellum, statistical shape models, spherical harmonics
Abstract: The size of the cerebellum in ultrasound volumes of the fetal brain has shown a high correlation with gestational age, which makes it a valuable feature to detect fetal growth restrictions. Manual annotation of the 3D surface of the cerebellum in an ultrasound volume is a time-consuming task, which needs to be performed by a highly trained expert. In order to assist the experts in the evaluation of cerebellar dimensions, we developed an automatic scheme for the segmentation of the 3D surface of the cerebellum in ultrasound volumes, using a spherical harmonics model. In this work, we present our validation results on 10 ultrasound volumes in which we have obtained an adequate accuracy in the segmentation of the cerebellum (mean Dice coefficient of 0.689). The method reported shows potential to effectively assist the experts in the assessment of fetal growth in ultrasound volumes.
Robustification of time varying linear quadratic optimal control based on output integral sliding modes
IET Control Theory & Applications
Rosalba Galván Guerra 1 , Leonid Fridman Golredich 2
1 Instituto Politécnico Nacional, Unidad Profesional Interdisciplinaria de Ingeniería campus Hidalgo
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: linear quadratic control, observers, robust control, time-varying systems, uncertain systems, variable structure systems
Abstract: A hierarchical observer for an uncertain linear time-varying system is designed generalising the output integral sliding-mode approach. The observer is based on a step by step reconstruction of the output and its derivatives, to reconstruct the state theoretically exactly right after the initial time, eliminating completely the effects of the uncertainties/perturbations. The observed state is used in linear quadratic control with an output integral sliding-mode technique, allowing the uncertain system to behave as a nominal (uncertainties/perturbations free) one. The proposed approach is tested by computer simulations.
Asymptotic Formulas for the Reflection/Transmission of Long Water Waves Propagating in a Tapered and Slender Harbor
Journal of Applied Mathematics
Eric Gustavo Bautista Godínez 1 , Federico Méndez Lavielle 2 , Oscar Eladio Bautista Godínez 1
1 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Abstract: We obtain asymptotic formulas for the reflection/transmission coefficients of linear long water waves, propagating in a harbor composed of a tapered and slender region connected to uniform inlet and outlet regions. The region with variable character obeys a power-law. The governing equations are presented in dimensionless form. The reflection/transmission coefficients are obtained for the limit of the parameter k2<1, which corresponds to a wavelength shorter than the characteristic horizontal length of the harbor. The asymptotic formulas consider those cases when the geometry of the harbor can be variable in width and depth: linear or parabolic among other transitions or a combination of these geometries. For harbors with nonlinear transitions, the parabolic geometry is less reflective than the other cases. The reflection coefficient for linear transitions just presents an oscillatory behavior. We can infer that the deducted formulas provide as first approximation a practical reference to the analysis of wave reflection/transmission in harbors.
Automated pollen identification using microscopic imaging and texture analysis
Víctor Marcos 1 , Rodrigo Nava 2 , Gabriel Cristóbal 1 , Rafael Redondo 1 , Boris Escalante Ramírez 3 , Gloria Bueno 4 , ?scar Déniz 4 , Amelia González Porto 5 , Cristina Pardo 6 , François Chung 7 , Tomás Rodríguez 7
1 Spanish National Research Council, Instituto de ?ptica
2 Luxembourg Institute of Science and Technology
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 Universidad de Castilla La Mancha, VISILAB
5 Centro de Investigación Apícola y Agroambiental
6 Universidad Complutense de Madrid, Facultad de Farmacia
7 Tecnologías Avanzadas Inspiralia

Keywords: Texture analysis, Pollen identification, Gray-level co-occurrence matrix, Log-Gabor filters, Local binary patterns, Discrete Tchebichef moments
Abstract: Pollen identification is required in different scenarios such as prevention of allergic reactions, climate analysis or apiculture. However, it is a time-consuming task since experts are required to recognize each pollen grain through the microscope. In this study, we performed an exhaustive assessment on the utility of texture analysis for automated characterisation of pollen samples. A database composed of 1800 brightfield microscopy images of pollen grains from 15 different taxa was used for this purpose. A pattern recognition-based methodology was adopted to perform pollen classification. Four different methods were evaluated for texture feature extraction from the pollen image: Haralick's gray-level co-occurrence matrices (GLCM), log-Gabor filters (LGF), local binary patterns (LBP) and discrete Tchebichef moments (DTM). Fisher's discriminant analysis and k-nearest neighbour were subsequently applied to perform dimensionality reduction and multivariate classification, respectively. Our results reveal that LGF and DTM, which are based on the spectral properties of the image, outperformed GLCM and LBP in the proposed classification problem. Furthermore, we found that the combination of all the texture features resulted in the highest performance, yielding an accuracy of 95%. Therefore, thorough texture characterisation could be considered in further implementations of automatic pollen recognition systems based on image processing techniques.
Fault detection and isolation for nonlinear systems via high-order-sliding-mode multiple-observer
International Journal of Robust and Nonlinear Control
Héctor Ríos 1 , Jorge Dávila Montoya 2 , Leonid Fridman Golredich 3 , C. Edwards 4
1 INRIA Lille - Nord Europe, Parc Scientifique de la Haute Borne
2 Instituto Politécnico Nacional, Sección de Estudios de Posgrado e Investigación
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 University of Exeter, College of Engineering, Mathematics and Physical Sciences

Keywords: high?order sliding?mode observers, fault detection, fault isolation
Abstract: In this paper, fault detection and isolation problems are studied for a certain class of nonlinear systems. Under some structural conditions, multiple high?order sliding?mode observers are proposed. The value of the equivalent output injection is used for detecting faults and the multiple?model approach for isolating particular faults in the system. The proposed method provides fast detection and isolation of actuator and plant faults. Simulation results support the proposed approach.
Theoretical analysis of coupled thermal and denaturation processes in living tissues subject to a uniform surface heating condition
International Journal of Heat and Mass Transfer
Sergio Sánchez 1 , Oscar Eladio Bautista Godínez 2 , Federico Méndez Lavielle 3
1 Instituto Politécnico Nacional, ESIME Azcapotzalco
2 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Denatured tissue, Non-linear Penne??s equation, Blood perfusion, Temperature-dependent properties
Abstract: In this work, we develop a theoretical study of the thermal and denaturation processes in a biological tissue subject to a surface heating, when coupled effects of dynamic changes of blood perfusion and temperature-dependent physical properties are taken into account. To analyze this phenomenon, the governing equations were appropriately nondimensionalized, where a suitable Damköhler number appears, which measures the competition between the denaturation time and the characteristic thermal diffusive time of tissue. In order to determine the denaturation front, situation that occurs when tissue has been completely denatured, we show the existence of a critical value of this dimensionless number for each time, which represents an eigenvalue in the mathematical model. Important results of the proposed model indicate that the denatured region, and the time required for carrying out this thermal process are substantially modified in comparison with the case of constant physical properties. In addition, the magnitude of the applied thermal energy source, the biological resistance of tissue to thermal attack and the blood perfusion are very important aspects that must be considered in those medical treatments that make use of rehabilitation therapies by thermal processes.
Imaging Fractures beneath a Residential Complex Using Novel 3-D Electrical Resistivity Arrays
Journal of Environmental and Engineering Geophysics
René E. Chávez Segura 1 , Andrés Tejero Andrade 2 , Gerardo Cifuentes Nava 1 , Esteban Hernández Quintero 1 , Diego Aguilar 1
1 Universidad Nacional Autónoma de México, Instituto de Geofísica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Federal District Mexico, geophysical methods, fractures, land subsidence, Mexico state, Mexico City, Mexico
Abstract: Typical 3-D electrical resistivity tomography sampling schemes, which require a grid of electrode lines to be deployed, are limited by physical conditions of the area under study. New array techniques are needed to characterize the subsoil beneath anthropogenic or natural structures to define hazardous zones. Use of multiple L-shaped arrays overcome the need for a grid of electrodes by surrounding an area in a square of electrode lines; however, in some instances, the physical environment does not allow closure of a square of electrodes. An alternative array introduced in this investigation is termed the horseshoe array. The horseshoe array combines the L-shaped arrays with equatorial and minimum coupling arrays to overcome array closure problems. Three synthetic examples were investigated to establish the limitations of the horseshoe array, and to describe the geological conditions of the subsoil, e.g., building foundations and fractures. The first two examples represent two resistive cubes initially located in the southern and northern positions of the array, and then are moved to a diagonal of the array. In both examples, the cube located near the electrode lines was well defined, while the cube located near the line with no electrodes was not detected. On the other hand, a weak signal for the cube located along the diagonal was observed, but only when located near the electrode line. This alternative array revealed a low tri-dimensional resolution zone possessing an inverted triangular-shaped geometry towards the line with no electrodes. A third example consisted of a low resistivity thin fracture embedded in a highly resistive infill. The solution computed demonstrated that the horseshoe array can resolve the infill close to the surface; however, the thin fracture is masked by the infill. The above-mentioned methodology was applied on a residential complex named La Concordia. Several buildings within the residential area suffered strong structural damage caused by fractures and subsidence within the subsurface. The residential complex, consisting of six four-story buildings in an area 33 ? 80 m2, is located towards the eastern region of Mexico City. The horseshoe geometry, combined with Wenner-Schlumberger, dipole-dipole, equatorial-dipole, and minimum-coupling arrays, was used to investigate the subsurface beneath the buildings. A maximum depth of 8 m was investigated. A pattern of elongated resistivity anomalies (northwest-southeast direction) were associated with possible fracturing or differential compaction. Such features are caused by intense water extraction of the poorly consolidated clays that cover most of the central portion of the Mexican Basin.
Pollen segmentation and feature evaluation for automatic classification in bright-field microscopy
Computers and Electronics in Agriculture
Rafael Redondo 1 , Gloria Bueno 2 , François Chung 3 , Rodrigo Nava 4 , Víctor Marcos 1 , Gabriel Cristóbal 1 , Tomás Rodríguez 3 , Amelia González Porto 5 , Cristina Pardo 6 , ?scar Déniz 2 , Boris Escalante Ramírez 7
1 Spanish National Research Council, Instituto de ?ptica
2 Universidad de Castilla La Mancha, VISILAB
3 Tecnologías Avanzadas Inspiralia
4 Luxembourg Institute of Science and Technology
5 Centro de Investigación Apícola y Agroambiental
6 Universidad Complutense de Madrid, Facultad de Farmacia
7 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Apiculture, Pollen, Bright-field microscopy, Morphology descriptors, Statistical descriptors, Texture descriptors
Abstract: Besides the well-established healthy properties of pollen, palynology and apiculture are of extreme importance to avoid hard and fast unbalances in our ecosystems. To support such disciplines computer vision comes to alleviate tedious recognition tasks. In this paper we present an applied study of the state of the art in pattern recognition techniques to describe, analyze, and classify pollen grains in an extensive dataset specifically collected (15 types, 120 samples/type). We also propose a novel contour??inner segmentation of grains, improving 50% of accuracy. In addition to published morphological, statistical, and textural descriptors, we introduce a new descriptor to measure the grain??s contour profile and a logGabor implementation not tested before for this purpose. We found a significant improvement for certain combinations of descriptors, providing an overall accuracy above 99%. Finally, some palynological features that are still difficult to be integrated in computer systems are discussed.
Frequency Response based Adaptive Vibration Control of Nonlinear Systems
Suresh Thenozhi 1 , Yu Tang Xu 2
1 Universidad Autónoma de Querétaro
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Adaptive control, convergence analysis, cubic stiffness, frequency response function, satelitte, vibration control
Abstract: The problem of active vibration control for a class of nonlinear mechanical system is addressed. A recently developed nonlinear frequency response analysis technique is utilized for the vibrational analysis and controller design. Unlike the linear case, the nonlinear system oscillations are complex, which can be observed via the nonlinear Frequency Response Function (FRF). In order to achieve a satisfactory vibration attenuation, an adaptive tuning method based on the FRF, for selecting the controller gains is proposed. The proposed algorithm performs sufficiently well for a given range of input excitation magnitudes and frequencies. A physically motivated example is given to demonstrate the application of these results. Finally, the feasibility of the proposed algorithm in a satellite vibration control application has been examined.
Dynamics and acoustic energy dissipation in conical bubble collapse
International Journal of Multiphase Flow
Manuel Navarrete 1 , Francisco Antonio Godínez Rojano 1 , F. Castellanos 2 , E. V. Mejía Uriarte 3 , Jorge Luis Naude De la Llave 4 , Federico Méndez Lavielle 4
1 Universidad Nacional Autónoma de México, Instituto de Ingeniería
2 Universidad de Alberta
3 Universidad Nacional Autónoma de México, Instituto de Ciencias Aplicadas y Tecnología
4 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Conical bubble collapse, Bubble dynamics, Cavitation cloud, Luminescence, Shock waves
Abstract: We follow the dynamics and acoustics of conical bubble collapse (CBC) in a U-tube device, to understand its associated phenomena such as: light emission, turbulence, bubble cloud formation, strong rebound pressures, shock wave emission, and liquid??gas interface behaviour. High-speed video frames linked with the waveforms acquired by piezoelectric transducers and photomultipliers during the collapse are analysed. All of the data acquisition is synchronised to the same timeline. Acoustic energy dissipation is investigated in detail by analysing the piezoelectric waveforms using Fourier transforms and wavelets. The primary experimental results demonstrate that as the compression proceeds, (a) the liquid meniscus reaches the conical zone in cavitation conditions; (b) the liquid meniscus undergoes a geometric transformation (2D to 3D), it becomes a "bulb with a nozzle?, wherein the instabilities are dragged and confined inside it; (c) the nozzle is retained as part of the new meniscus that continues to push the gas pocket; and (d) both structures (bulb and gas pocket) are connected by a neck/nozzle and will eventually form a "slug?. Furthermore, during the collapse, the bulb eventually becomes a bubble cloud, and the bubble structures exhibit their own expansion??contraction rate. These phenomena are widely discussed. A detailed analysis of the acquired signals yields frequencies and scales, which are associated with the onset of shock waves and its propagation, as well as the frequency bands that occur when the energy has dissipated. Good agreement was found between the experimental measurements and two different models for CBC dynamics. From the analysis of the dynamics and acoustics, we consider that various light emission mechanisms are activated during the collapse of a conical bubble, these are: thermal, chemical, and electrical in nature.
A new observer for perspective vision systems under noisy measurements
IEEE Transactions on Automatic Control
Ileana Grave 1 , Yu Tang Xu 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Observers, Noise, Synchronization, Noise measurement, Convergence, Machine vision, Jacobian matrices
Abstract: A simple design of observers for the range identification problem in perspective vision systems is given based on nonlinear contraction theory and synchronization. Exponential convergence to the object coordinates is achieved. In the presence of significant measurement noise, the performance is improved by synchronization among a group of observers.
Surface tension effects on a conjugate laminar filmcondensation process for a vertical fin placed in a porous medium
Journal of Porous Media
A. Hernández 1 , José Carlos Arcos Hernández 1 , Federico Méndez Lavielle 2 , Oscar Eladio Bautista Godínez 1
1 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: conjugate heat transfer, film condensation, fin, surface tension, porous medium
Abstract: In this work we treat theoretically the conjugate film-condensation process on a vertical fin embedded in a homogeneous porous medium filled with a saturated vapor. The presence of the solid matrix results in the occurrence of a two-phase flow region governed by gravity and capillarity. In order to predict the influence of surface tension on the condensed thickness, an overall energy balance in the liquid, the two-phase region, and through the fin was conducted. Therefore, the conservation equations of mass, momentum, and energy for the condensed film, together with the energy equation in the fin are reduced to a nonlinear system of two differential equations containing five dimensionless numbers: the Bond number, Bo; the Jakob number, Ja; the Rayleigh number Ra; a conjugate heat transfer parameter, α, which represents the competition between the heat conducted by the fin in the longitudinal direction and the heat conducted through the condensate film, and the aspect ratio of the fin, ε. Using the limit of Ja « 1 with Ra » 1, and finite values of Bo, together with the boundary layer approximation for the film condensation process, the non-dimensional heat transfer or Nusselt number and the overall mass flow rates of the condensed fluid have been obtained as functions of the involved dimensionless parameters.
Identification of nonlinear discrete systems by a state-space recurrent neurofuzzy network with a convergent algorithm
Marcos González Olvera 1 , Yu Tang Xu 2
1 Universidad Autónoma de la Ciudad de México, Colegio de Ciencia y Tecnología
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Neural-network models, Fuzzy modeling, System identification, Discrete-time systems
Abstract: Recurrent neurofuzzy networks have proven to be useful in identification of systems with unknown dynamics when only input??output information is available. However, training algorithms for these structures usually require also the measurement of the actual states of the system in order to obtain a convergent algorithm and then obtain a scheme to approximate its dynamic behavior. When states are not available and only input??output information can be obtained, the stability of the training algorithm of the recurrent networks is hard to establish, as the dynamics is driven by the internal recurrent dynamics of each connection. In this paper, we present a structure and an ultimately stable training algorithm inspired by adaptive observer for black-box identification based on state-space recurrent neural networks for a class of dynamic nonlinear systems in discrete-time. The network catches the dynamics of the unknown plant and jointly identifies its parameters using only output measurements, with ultimately bounded identification and parameter error. Numerical examples using simulated and experimental systems are included to illustrate the effectiveness of the proposed method.
Continuous Nested Algorithms : The Fifth Generation of Sliding Mode Controllers
Recent Advances in Sliding Modes
Leonid Fridman Golredich 1 , Jaime Alberto Moreno Pérez 2 , Bijnan Bandyopadhyay 3 , Shyam Kamal 3 , Asif Chalanga 3
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Instituto de Ingeniería
3 Indian Institute of Technology, Systems and Control Engineering

Abstract: The history and evolution of Sliding Mode Controllers in the last three decades is revisited. The new generation of continuous sliding-mode controllers, and continuous nested sliding-mode controllers is presented. Such controllers generate an continuous control signal, ensuring, for the systems with relative degree r, the finite??time convergence to the (r??+??1)??????th sliding-mode set using only information on the sliding output and its derivatives up to the (r??????1) order. In this book it is natural to recall the past and to think about the future. This chapter is an attempt to give a viewpoint on the stages of development of the Sliding-Mode Control(SMC) theory in the last decades. We will show that each decade the SMC community has been able to generate families of controllers with much better properties than before, and propose arbitrary-order continuous SMC algorithms which can significatively reduce the chattering and improve the precision.
Drop deformation in two-roll mills considering wall effects
Journal of Physics
C. A. Escalante Velázquez 1 , M. A. Huesca Reyes 2 , I. Yescas Rosas 1 , E. Geffroy 1
1 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Abstract: Experimental, theoretical and numerical results of dynamics of drop deformation in strong flows generated by a co-rotating two-roll mill and considering the influence of near rigid walls are presented. The drop dynamics is altered, with respect to a drop free of wall effects, by the proximity of the rigid boundaries as well as caused by a non-linear and non-uniform flow due to gradients of flow-type parameter and shear rate. Simulations were carried out using the Boundary Element Method (BEM). Since the inclusion of the whole boundaries (drop and rollers surfaces) is not an easy and trivial task, bi-dimensional numerical simulations was performed as a first approach. The experimental and numerical results were obtained for a flow type of α = 0.03 and two values of viscosity ratio λ = 0.012 and 16. In general, numerical results for the stationary deformation parameters, up to intermediate confinements, are in agreement with the experiments, with and without wall effects. Since the case of drops with a high viscosity ratio did not match existing theoretical models, the wall-effect theory of Shapira and Haber was modified, considering Cox's second-order theory as the converging theory without wall effects. From low to intermediate confinements, the new Cox-Shapira-Haber model fitted the observed experimental deformations.
Negative vortices: The formation of vortex rings with reversed rotation in viscoelastic liquids
Physics of Fluids
Carlos Alberto Palacios Morales 1 , Christophe Barbosa 2 , Francisco Javier Solorio Ordaz 1 , Roberto Zenit 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales

Abstract: The formation process of vortex rings in a viscoelastic liquid is studied experimentally considering a piston-cylinder arrangement. Initially, a vortex ring begins to form as fluid is injected from the cylinder into the tank in a manner similar to that observed for Newtonian liquids. For later times, when the piston ceases its motion, the flow changes dramatically. A secondary vortex with reversed spinning direction appears and grows to be as large in size as the original one. The formation process is studied by contrasting the evolution with that obtained for Newtonian liquids with equivalent Reynolds numbers and stroke ratios. We argue that the reversing flow, or negative vortex, results from the combined action of shear and extension rates produced during the vortex formation, in a process similar to that observed behind ascending bubbles and falling spheres in viscoelastic media.
Alternatives of management and disposal for mercury thermometers at the end of their life from Mexican health care institutions
Journal of Cleaner Production
Irma Cruz Gavilán García 1 , Georgina Fernández Villagómez 2 , Arturo Gavilán García 3 , Víctor Alcántara Conce 3
1 Universidad Nacional Autónoma de México, Facultad de Química
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería
3 Instituto Nacional de Ecología y Cambio Climático

Keywords: Mercury thermometers, Mercury-containing products, Mercury emissions, Mercury recycling, Life cycle assessment
Abstract: Mercury releases from used thermometers at the end of their life in the Mexican health sector are estimated to be 2166 kg/year. Some actions are being implemented at the hospital level to eliminate the use of mercury thermometers in some cities. This study evaluated the impact of policy alternatives for the sound management of mercury released from used thermometers using a life cycle assessment with Umberto software and Ecoinvent databases. The results identified that the elimination of open dumping and increasing the recycling rate of mercury up to 60% will lead to the highest net benefits compared with the use of virgin materials in new products. This study showed different scenarios of recycling and end of life practices in the management of mercury waste from glass thermometers in Mexico to know the environmental burdens of each treatment strategy and identified recommendations for development of public policies for handling of this type of waste with focus in the decrease of associated risks. It was demonstrated that increase of recycling allows reducing the environmental impacts caused by the use of raw materials and that decrease of landfills for deposit of mercury waste, preventing uncontrolled emissions of mercury to the atmosphere.
Pennsylvanian biota of the Sierra Agua Verde, Sonora, Mexico: Biostratigraphic and paleogeographic considerations
Revista Mexicana de Biodiversidad
Blanca Buitrón Sánchez 1 , Omar Chacón Wences 2 , Daniel Vachard 3 , Juan José Palafox Reyes 4 , José Carlos Jiménez López 5 , Francisco Sour Tovar 6
1 Universidad Nacional Autónoma de México, Instituto de Geología
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería
3 Université Lille, Géosystémes
4 Universidad de Sonora, Departamento de Geología
5 Universidad Nacional Autónoma de México, Ciencias de la Tierra
6 Universidad Nacional Autónoma de México, Facultad de Ciencias

Keywords: Carboniferous, NW Sonora, Pennsylvanian, Upper Paleozoic
Abstract: The marine biota from the middle Pennsylvanian outcrops of the Sierra Agua Verde, located in mid-eastern Sonora, consists of phylloid algae of the genera Komia and Eugonophyllum and a number of invertebrates. These species include bioaccumulations of chaetetids; brachiopods of the genera Dielasma sp., Reticulariina sp., Anthracospirifer sp., Antiquatonia sp.; bryozoans of the genus Thamniscus; tabulate corals such as Syringopora and solitary corals such as Zaphrentis; fusulinid foraminifera such as Pseudostaffella, Eoshubertella texana, Fusulinella llanoensis, and Zellerella; gastropods of the genus Euomphalus and Donaldina; and the crinoid genera Cyclocaudex, Cyclocrista, Heterosteleschus, Lamprosterigma, Mooreanteris, Pentagonopternix, Preptopremium, Cycloscaspus, and Pentaridica. The material was collected from outcrops in the first 512 m of the La Joya Formation, and their sediments have a total thickness of 780 m and consist of limestone interbedded with calcareous mudstone and sandstone lenses. The age of the middle Pennsylvanian strata corresponds to that of the Atokan stage (311 million years). The species assemblages are typical of a shallow tropical marine benthos. The analysis of the distribution of the species allowed for the determination of their paleogeographic relationships with the components of the biota of the Carboniferous strata of Texas and Kansas in the United States of America, which belong to the province of the North American Craton.
Surveillance System Mobile Object Using Segmentation Algorithms
IEEE Latin America Transactions
Roman Osorio Comparan 1 , Ismael López Juárez 2 , Jesús Savage Carmona 3 , Mario Peña 1 , Víctor Lomas 1 , Gastón Lefranc 4
1 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas
2 Instituto Politécnico Nacional, Centro de Investigación y de Estudios Avanzados
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 Pontificia Universidad Católica del Valparaíso, Escuela de Ingeniería Eléctrica

Keywords: image processing, Robot Visión, segmentation algorithm, Visual Surveillance
Abstract: In this paper a segmentation algorithm is used to detect moving objects and to integrate it to a supervision and surveillance systems, in a parking lot, as a first step. One of the way to moving detection in image sequences is the moving object segmentation by background model, very well-known technique that it permit to know what objects are moving. This can be employed, in the second stage, to identify and to follow objects.
Performance of a Composite Thermoelectric Generator with Different Arrangements of SiGe, BiTe and PbTe under Different Configurations
Alexander Vargas Almeida 1 , Miguel Angel Olivares Robles 2 , Federico Méndez Lavielle 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica

Keywords: thermoelectric module, thermoelectric properties, figure of merit
Abstract: In this study, we analyze the role of the thermoelectric (TE) properties, namely Seebeck coefficient α, thermal conductivity κ and electrical resistivity ρ, of three different materials in a composite thermoelectric generator (CTEG) under different configurations. The CTEG is composed of three thermoelectric modules (TEMs): (1) two TEMs thermally and electrically connected in series (SC); (2) two branches of TEMs thermally and electrically connected in parallel (PSC); and (3) three TEMs thermally and electrically connected in parallel (TEP). In general, each of the TEMs have different thermoelectric parameters, namely a Seebeck coefficient α, a thermal conductance K and an electrical resistance R. Following the framework proposed recently, we show the effect of: (1) the configuration; and (2) the arrangements of TE materials on the corresponding equivalent figure of merit Zeq and consequently on the maximum power Pmax and efficiency η of the CTEG. Firstly, we consider that the whole system is formed of the same thermoelectric material (α1,K1,R1 = α2,K2,R2 = α3,K3,R3) and, secondly, that the whole system is constituted by only two different thermoelectric materials Entropy 2015, 17 7388 (αi,Ki,Ri ? αj ,Kj ,Rj 6= αl,Kl,Rl, where i, j, l can be 1, 2 or 3). In this work, we propose arrangements of TEMs, which clearly have the advantage of a higher thermoelectric figure of merit value compared to a conventional thermoelectric module. A corollary about the Zeq-max for CTEG is obtained as a result of these considerations. We suggest an optimum configuration.
Numerical study on buoyancy and inclination effects on transient laminar opposing mixed convection in rectangular channels with symmetric and discrete heating
International Journal of Heat and Mass Transfer
J. Marroquín Desentis 1 , César Treviño 2 , Juan Carlos Cajas García 3 , Erick Salcedo 4 , Lorenzo Martínez Suástegui 1
1 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica
2 Universidad Nacional Autónoma de México, Facultad de Ciencias
3 Barcelona Supercomputing Center
4 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Mixed convection, Discrete heating, Inclination angle, Flow bifurcation, Unsteady convective flows
Abstract: Detailed numerical simulations are carried out for transient laminar opposing mixed convection in a rectangular inclined channel with both walls suddenly subjected to discrete isothermal flush-mounted heat sources simulating electronic components. Using the vorticity-stream function formulation of the unsteady two-dimensional Navier??Stokes and energy equations, the governing equations are solved numerically using the control volume method. Simulations are performed for fixed values of the geometrical parameters, Reynolds number of Re = 500, Prandtl number of Pr = 7 and channel inclination of 0° < g < 90°. Results illustrate the effects of buoyancy strength or Richardson number Ri = Gr/Re2 and channel inclination angle on the overall flow structure and nondimensional heat flux (Nusselt number) from the heated slabs. It is found that for the horizontal configuration ( g= 0°), due to the indirect effect of buoyancy, much higher threshold values of buoyancy strength are required for the appearance of the recirculation flows that take place downstream of the heated slabs. However, for increasing values of the inclination angle, vortex migration to higher positions inside the channel occurs and higher heat transfer rates are obtained. In addition, transition from steady to time-periodic flow takes place for values of the buoyancy parameter larger than a critical one, and the threshold value between the two regimes strongly depends on the value of the Reynolds number and channel orientation. The results include the effects of Reynolds and Prandtl numbers along with heat losses to the channel walls on the evolution of the final flow and thermal response.
Electrochemical corrosion behavior of a Co20Cr alloy in artificial saliva
International Journal of Electrochemical Science
R. A. Rodríguez Díaz 1 , A. L. Ramírez Ledesma 2 , M. A. Aguilar Méndez 3 , J. Uruchurtu Chavarin 4 , Miguel Ángel Hernández Gallegos 3 , J. A. Juárez Islas 2
1 Universidad Politécnica del Estado de Morelos
2 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería
4 Universidad Autónoma del Estado de México, Centro de Investigación en Ingeniería y Ciencias Aplicadas

Keywords: Corrosion, Co-Cr alloy, dental materials, electrochemical techniques, artificial saliva
Abstract: The corrosion behavior of Co20Cr (at. %) together with 316L stainless steel (SS) in artificial saliva solution during nine immersion days at room temperature have been studied and assessed by means of electrochemical techniques. Techniques included potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) measurements. Results have shown that the corrosion rate of Co20Cr alloy resulted higher as compared with that of stainless steel 316L biomaterial, using polarization curves. Besides, corrosion potential of Co-20Cr alloy resulted more active. 316 L stainless steel exhibited a more defined passivation zone, while the Co20Cr alloy exhibited a pseudo-passivation zone. Although the pitting potential of binary alloy is higher. The measured values of Rp at the end of the exposure time are related to a higher stability of the film composed by the corrosion products formed on Co20Cr alloy as compared with those of the 316 L SS, which is related to a minor corrosion rate of the CoCr alloy after the third day of immersion. Corrosion behavior is explained in terms of the stability of the corrosion products formed film.
Computer-controlled Two-Roll Mill flow cell for the experimental study of particle and drop dynamics
Experimental Thermal and Fluid Science
Israel Rosas 1 , Marco Reyes 2 , Antonmaría Minzoni 1 , Enrique Geffroy 1
1 Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Two-Roll Mill, Flow-type parameter, Nonlinear control, Drop deformation
Abstract: In this paper, we present for the deformation of a drop under flow, using an experimental device based on the Two-Roll Mill geometry. To study the drop deformation for extended periods of time, the use of this device requires implementation of a non-linear control scheme that has not previously been used. The device and control scheme generate well characterized flow fields, which present a richness of behavior of the drop dynamics that smoothly varies from that observed in simple shear flows, where the vorticity dominates, to those observed in purely Hyperbolic flows. The Two-Roll Mill flow cell allows detailed studies such as the critical capillary number versus the critical viscosities ratio for elongational flows with significant vorticity. As well, the experimental device is able to track the time evolution of the drop shape permitting to study its complex time evolutions. Experiments were performed for sub-millimeter size drops with the determination of the surface tension with high accuracy.
Active Dual-Band Frequency Selective Surfaces with Close Band Spacing Based on Switchable Ring Slots
IEEE Microwave and Wireless Components Letters
Henry Fabian Gongora 1 , Alexander Martynyuk 1 , Jorge Rodríguez Cuevas 1 , José Ismael Martínez López 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Active frequency selective surfaces, PIN diodes, reconfigurable arrays, ring slot resonators
Abstract: This letter presents active dual-band frequency selective surfaces (AFSS) with close band spacing based on two switchable ring slots loaded by PIN diode switches. The close band response is achieved by splitting the outer ring slot, and then shifting upward its fundamental resonance beyond the resonance of the inner ring slot. The proposed AFSS can provide four states of operation including lower single-band, upper single-band, dual-band with close band spacing, and reflective mode. Experimental results based on the waveguide simulator show that a frequency ratio of 1.14, with insertion loss lower than 0.82 dB at resonant frequencies, is obtained in the X-band.
Extrusion blow molding of a starch-gelatin polymer matrix reinforced with cellulose
European Polymer Journal
Wendy Rodríguez Castellanos 1 , Fernando Martínez Bustos 2 , Denis Rodrigue 1 , Magdalena Trujillo Barragán 3
1 Université Laval
2 Instituto Politécnico Nacional, Centro de Investigación y de Estudios Avanzados
3 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: Extrusion blow molding, Starch-gelatin, Cellulose, Processing, Dimensional stability, Natural polymers
Abstract: This work investigated the possibility of using hydrolyzed corn starch??gelatin as a base matrix and cellulose as reinforcement, to produce containers by extrusion blow molding. First, the compounds were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) to determine their viscoelastic behavior and thermal stability. The results showed that the most suitable processing temperature should be less than 120 °C to avoid degradation. Furthermore, the addition of cellulose decreased the viscosity of the starch??gelatin polymer matrix allowing the compounds to be processed at temperatures as low as 100 °C. Then, parisons were obtained by extrusion blow molding and presented suitable processing characteristics. Overall, the best containers were found to have 44% higher energy at break and better dimensional stability when cellulose was added.
Wideband-reconfigurable reflectarrays based on rotating loaded split rings
Journal of Electromagnetic Waves and Applications
Lourdes Martínez López 1 , Jorge Rodríguez Cuevas 1 , Alexander Martynyuk 1 , José Ismael Martínez López 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: reflectarrays, reflective periodic surfaces, antenna arrays, reconfigurable antennas
Abstract: In this paper, reflective periodic arrays with rotating spiraphase-type elements based on loaded split rings are analyzed. It is proven that these arrays can be reconfigured over a wide frequency band with high reflection elevation angles, low conversion losses, and low axial ratios. A full-wave mathematical model has been developed to calculate their reflection characteristics. This model has been used to design a Ka-band reflectarray. The analysis of the designed reflectarray shows that an incident circularly polarized wave can be redirected at reflection elevation angles as high as 40° with conversion losses less than 1.8 dB and axial ratios less than 2 dB over the frequency band from 26.6 to 46.3 GHz. Additionally, the rotation of the reflectarray elements using minimotors is analyzed and discussed. In order to study the velocity properties of the electromechanical actuation, minimotor-driven antenna elements in the X-band have been designed, fabricated, and tested.
Influence of slip wall effect on a non-isothermal electro-osmotic flow of a viscoelastic fluid
International Journal of Thermal Sciences
Andrés Matías 1 , Sergio Sánchez 1 , Federico Méndez Lavielle 2 , Oscar Eladio Bautista Godínez 3
1 Instituto Politécnico Nacional, ESIME Azcapotzalco
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería
3 Instituto Politécnico Nacional, Escuela Superior de Ingeniería Mecánica y Eléctrica

Keywords: Slip velocity, Hydrophobic microchannels, Electro-osmotic flow, Non-isothermal, Joule heating, Viscoelastic fluid
Abstract: We present an analytical model that predicts the influence of Joule heating on the slip velocity in an electro-osmotic flow (EOF) of viscoelastic fluids. The viscoelasticity of the fluid is taken into account by employing the simplified Phan-Thien and Tanner constitutive model (sPTT). The Joule heating induces temperature gradients along the microchannel making properties non-uniform and hence alters the electric potential and the flow field. In consequence, the slip velocity and the velocity gradient on the microchannel surface are drastically modified in comparison with the case of uniform properties. Using the well-known lubrication theory, the momentum equations together with the energy, Poisson and Ohmic current conservation equations are considerably simplified. The dimensionless mathematical model is solved by using a regular perturbation technique, which is compared against a numerical solution. The results show that using hydrophobic microchannels, for the used values of the parameters involved in this analysis, the volumetric flow rate through microchannels can be massively amplified in about 400%, in comparison with the case of non-slipping surfaces. In addition, by using hydrophobic microchannels, the maximum temperature in the microchannel can be substantially reduced.
Spiraphase-Type Reflectarray for Large Reflection Elevation Angles
IEEE Transactions on Antennas and Propagation
Jovanni Silva Montero 1 , José Ismael Martínez López 1 , Jorge Rodríguez Cuevas 1 , Alexander Martynyuk 1
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: reflectarrays, antenna arrays, aperture efficiency, cross-polarization
Abstract: This paper presents a spiraphase-type reflectarray based on reactively loaded ring slot resonators. The infinite array approach was used to optimize the unit cell geometry to obtain high aperture efficiencies and low cross-polarization levels at large reflection elevation angles θo . The results of the optimization were used to design four 367-element reflectarrays for θo of 0°, 20°, 40°, and 60° operating at 36.5 GHz. The designed reflectarrays were then fabricated and tested. The experimental investigation of the fabricated reflectarrays revealed that aperture efficiencies of 0.60, 0.51, 0.42, and 0.21 along with cross-polarization levels of -25.8, -24.0, -17.8, and -10.9 dB were obtained for the reflectarrays with reflection elevation angles of 0°, 20°, 40°, and 60°, respectively, at 36.5 GHz. Additionally, it was experimentally demonstrated that for certain planes of scanning the cross-polarization level can be reduced to -19 dB even for reflection elevation angles θo as high as 60°.
On the Provision of Frequency Regulation in Low Inertia AC Grids using VSC-HVDC links
IEEE Transactions on Smart Grid
Luis Miguel Castro González 1 , Enrique Acha Daza 2
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Tampere University of Applied Sciences, Faculty of Information Technology and Communication Sciences - Electrical Engineering

Keywords: Dynamic simulations, Newton-Raphson method, frequency control, low inertia ac grids, voltage source converterhigh voltage dc (VSC-HVDC) link
Abstract: This paper proposes an improved model of a high voltage dc (HVDC) link capable of providing frequency support to networks with no inertia or near-zero inertia; for instance, ac grids with small synchronous generators. The model is useful to carry out steady-state and dynamic simulations of ac grids described by their positive-sequence representation using phasorial information. The core of the frequency control scheme put forward in this paper uses the angular aperture that exists between the internal phase-shifting angle of the voltage source converter (VSC)-HVDC rectifier and the voltage angle at its ac terminal. This is amenable to power flow regulation in the dc link and, hence, to frequency control in the low-inertia grid. A feature of this model is that the developed VSC-HVDC link model may also be used to feed an island system; for instance, a system with dead load, where the inverter station provides the electrical angular reference. Hence, the inverter acts as a virtual synchronous generator with frequency regulation capabilities as seen from the low-inertia ac grid. The dynamic control scheme that enables the VSC-HVDC to provide frequency control in such operating environments has been comprehensively investigated under a wide range of credible scenarios. Overall, the dynamic system of equations describing the VSC-HVDC and the synchronous generators are discretized using the trapezoidal rule, and the ensuing equations are combined together with the algebraic equations of the ac and dc grids in a linearized reference frame amenable to iterative solutions using the Newton-Raphson method.
A novel VSC-HVDC Link Model for Dynamic Power System Simulations
Electric Power Systems Research
Luis Miguel Castro González 1 , Enrique Acha Daza 2 , Claudio Rubén Fuerte Esquivel 3
1 Universidad Nacional Autónoma de México, Facultad de Ingeniería
2 Tampere University of Applied Sciences, Faculty of Information Technology and Communication Sciences - Electrical Engineering
3 Universidada Michoacana de San Nicolás de Hidalgo, Posgrado en Ingeniería Eléctrica

Keywords: VSC, HVDC, FACTS, Newton??Raphson method, Dynamic power system simulations
Abstract: This paper introduces a new RMS model of the VSC-HVDC link. The model is useful for assessing the steady-state and dynamic responses of large power systems with embedded back-to-back and point-to-point VSC-HVDC links. The VSC-HVDC model comprises two voltage source converters (VSC) linked by a DC cable. Each VSC is modelled as an ideal phase-shifting transformer whose primary and secondary windings correspond, in a notional sense, to the AC and DC buses of the VSC. The magnitude and phase angle of the ideal phase-shifting transformer represent the amplitude modulation ratio and the phase shift that exists in a PWM converter to enable either generation or absorption of reactive power purely by electronic processing of the voltage and current waveforms within the VSC. The mathematical model is formulated in such a way that the back-to-back VSC-HVDC model is realized by simply setting the DC cable resistance to zero in the point-to-point VSC-HVDC model. The Newton??Raphson method is used to solve the nonlinear algebraic and discretised differential equations arising from the VSC-HVDC, synchronous generators and the power grid, in a unified frame-of-reference for efficient, iterative solutions at each time step. The dynamic response of the VSC-HVDC model is assessed thoroughly; it is validated against the response of a detailed EMT-type model using Simulink®. The solution of a relatively large power system shows the ability of the new dynamic model to carry out large-scale power system simulations with high efficiency.
Generalized State Estimation of Flexible AC Power Systems Considering Wind Generators and Primary Frequency Control
Electric Power Components and Systems
Boris Alejandro Alcaide Moreno 1 , Claudio Rubén Fuerte Esquivel 1 , Luis Miguel Castro González 2 , Enrique Arnoldo Zamora Cárdenas 1
1 Universidada Michoacana de San Nicolás de Hidalgo, Posgrado en Ingeniería Eléctrica
2 Universidad Nacional Autónoma de México, Facultad de Ingeniería

Keywords: State estimation, wind generator, primary frequency regulation, facts controllers
Abstract: This paper proposes a practical approach to incorporate the mathematical models of both fixed-speed and variable-speed wind turbine generators, automatic load frequency controls as well as voltage magnitude and frequency dependent loads into a weighted least squares-based state estimation algorithm suitable for the analysis of flexible alternating current (AC) transmission systems. As opposed to conventional static state estimators, where the inclusion of these electric components has been neglected so far, the proposed approach permits the determination of the steady state operation of a power system in the event of a supply-demand unbalance by estimating the magnitude of the frequency deviation from its nominal value. The state estimation is based on measurements related to those that should be obtained by a supervisory control and data acquisition (SCADA) system and phasor measurement units. For the purpose of this paper, the set of values associated with SCADA measurements (nodal power injections, power flows, and voltage magnitudes) and phasor measurement unit (PMU) measurements (voltage and current phasors) are generated from a power flow analysis of the network under study. Lastly, numerical simulations are reported to demonstrate the effectiveness of the proposed approach.