Instituto Tecnológico y de Estudios Superiores de Occidente

This article examines how people learn by actively observing and "listening-in" on ongoing activities as they participate in shared endeavors. Keen observation and listening-in are especially valued and used in some cultural communities in which children are part of mature community activities. This intent participation also occurs in some settings (such as early language learning in the family) in communities that routinely segregate children from the full range of adult activities. However, in the past century some industrial societies have relied on a specialized form of instruction that seems to accompany segregation of children from adult settings, in which adults "transmit" information to children. We contrast these two traditions of organizing learning in terms of their participation structure, the roles of more- and less-experienced people, distinctions in motivation and purpose, sources of learning (observation in ongoing activity versus lessons), forms of communication, and the role of assessment.

This article introduces predefined-time stable dynamical systems which are a class of fixed-time stable dynamical systems with settling time as an explicit parameter that can be defined in advance. This concept allows for the design of observers and controllers for problems that require to fulfil hard time constraints. An example is encountered in the fault detection and isolation problem, where mode detection in a timely manner needs to be guaranteed in order to apply a recovery action. Furthermore, through the notion of strong predefined-time stability, the approach hereinafter presented permits to overcome the problem of overestimation of the convergence time bound encountered in previous methods for the analysis of finite-time stable systems, where the stabilization time is often an unbounded function of the initial conditions of the system. A Lyapunov analysis is provided together with a detailed discussion of the applications to consensus and first order sliding mode controller design.

The contribution of this paper is a dynamic controller that enforces predefined-time stabilization of robotic manipulators by exploiting the passivity property inherent to their dynamical structure. The proposed scheme is continuous and provides exact predefined-time stabilization in the case of full knowledge of the robot dynamics. Nonetheless, even in the case of dynamic uncertainties and nonvanishing disturbances, exact predefined-time stabilization can be assured by using an additional unit-vector-like control term, and alternatively, a predefined-time predefined-bounded convergence can be achieved into a vicinity of the origin by means of a continuous controller. Numerical results based on simulations highlight the feasibility of the proposed scheme.

This paper reviews the current state-of-the-art in electromagnetic (EM)-based design and optimization of microwave circuits using artificial neural networks (ANNs). Measurement-based design of microwave circuits using ANNs is also reviewed. The conventional microwave neural optimization approach is surveyed, along with typical enhancing techniques, such as segmentation, decomposition, hierarchy, design of experiments, and clusterization. Innovative strategies for ANN-based design exploiting microwave knowledge are reviewed, including neural space-mapping methods. The problem of developing synthesis neural networks is treated. EM-based statistical analysis and yield optimization using neural networks is reviewed. The key issues in transient EM-based design using neural networks are summarized. The use of ANNs to speed up "global modeling" for EM-based design of monolithic microwave integrated circuits is briefly described. Future directions in ANN techniques to microwave design are suggested.

The Active Healthy Kids Canada (AHKC) Report Card on Physical Activity for Children and Youth has been effective in powering the movement to get kids moving by influencing priorities, policies, and practice in Canada. The AHKC Report Card process was replicated in 14 additional countries from 5 continents using 9 common indicators (Overall Physical Activity, Organized Sport Participation, Active Play, Active Transportation, Sedentary Behavior, Family and Peers, School, Community and Built Environment, and Government Strategies and Investments), a harmonized process and a standardized grading framework. The 15 Report Cards were presented at the Global Summit on the Physical Activity of Children in Toronto on May 20, 2014. The consolidated findings are summarized here in the form of a global matrix of grades. There is a large spread in grades across countries for most indicators. Countries that lead in certain indicators lag in others. Overall, the grades for indicators of physical activity (PA) around the world are low/poor. Many countries have insufficient information to assign a grade, particularly for the Active Play and Family and Peers indicators. Grades for Sedentary Behaviors are, in general, better in low income countries. The Community and Built Environment indicator received high grades in high income countries and notably lower grades in low income countries. There was a pattern of higher PA and lower sedentary behavior in countries reporting poorer infrastructure, and lower PA and higher sedentary behavior in countries reporting better infrastructure, which presents an interesting paradox. Many surveillance and research gaps and weaknesses were apparent. International cooperation and cross-fertilization is encouraged to tackle existing challenges, understand underlying mechanisms, derive innovative solutions, and overcome the expanding childhood inactivity crisis.

Summary In this paper, we provide a new nonconservative upper bound for the settling time of a class of fixed‐time stable systems. To expose the value and the applicability of this result, we present four main contributions. First, we revisit the well‐known class of fixed‐time stable systems, to show the conservatism of the classical upper estimate of its settling time. Second, we provide the smallest constant that the uniformly upper bounds the settling time of any trajectory of the system under consideration. Third, introducing a slight modification of the previous class of fixed‐time systems, we propose a new predefined‐time convergent algorithm where the least upper bound of the settling time is set a priori as a parameter of the system. At last, we design a class of predefined‐time controllers for first‐ and second‐order systems based on the exposed stability analysis. Simulation results highlight the performance of the proposed scheme regarding settling time estimation compared to existing methods.

Summary This paper addresses the problem of optimal predefined‐time stability. Predefined‐time stable systems are a class of fixed‐time stable dynamical systems for which the minimum bound of the settling‐time function can be defined a priori as an explicit parameter of the system. Sufficient conditions for a controller to solve the optimal predefined‐time stabilization problem for a given nonlinear system are provided. These conditions involve a Lyapunov function that satisfies a certain differential inequality for guaranteeing predefined‐time stability. It also satisfies the steady‐state Hamilton–Jacobi–Bellman equation for ensuring optimality. Furthermore, for nonlinear affine systems and a certain class of performance index, a family of optimal predefined‐time stabilizing controllers is derived. This class of controllers is applied to optimize the sliding manifold reaching phase in predefined time, considering both the unperturbed and perturbed cases. For the perturbed case, the idea of integral sliding mode control is jointly used to ensure robustness. Finally, as a study case, the predefined‐time optimization of the sliding manifold reaching phase in a pendulum system is performed using the developed methods, and numerical simulations are carried out to show their behavior. Copyright © 2017 John Wiley & Sons, Ltd.

The inspection of high voltage power transmission lines is mainly carried out by manned aerial vehicles or foot patrol. However, these maintenance methodologies for inspection are somehow inefficient and expensive. Moreover, helicopter assisted inspection endangers the human life. Recently, unmanned aerial vehicles have been under development in several research centers all over the world due to its potential applications. In this paper, we present an unmanned aerial system based on the quadrotor helicopter for high voltage power line inspection. Our interest is to equip the quadrotor helicopter with the necessary payload in order to be able to carry out a qualitative inspection, therefore the hardware architecture of the aerial robotic system is presented. Finally, some experimental results are shown to demonstrate the feasibility of the proposed system.

A computationally efficient method for highly accurate electromagnetics-based statistical analysis and yield estimation of RF and microwave circuits is described in this paper. The statistical analysis is realized around a space-mapped nominal solution. Our method consists of applying a constrained Broyden-based linear input space-mapping approach to design, followed by an output neural space-mapping modeling process in which not only the responses, but the design parameters and independent variable are used as inputs to the output neural network. The output neural network is trained using reduced sets of training and testing data generated around the space-mapped nominal solution. We illustrate the accuracy and efficiency of our technique through the design and statistical analysis of a classical synthetic problem and a microstrip notch filter with mitered bends

AIMS: To study how the antimicrobial and antioxidant activities of Lippia graveolens essential oils with different composition are affected after the microencapsulation process with beta-cyclodextrin (beta CD). METHODS AND RESULTS: Three Mexican oregano essential oils (EOs) with different carvacrol/thymol/p-cymene ratios (38 : 3 : 32, 23 : 2 : 42, 7 : 19 : 35) were used in this study. Microencapsulation was carried out by spray-drying. Antimicrobial activities were measured as MBC (minimal bactericidal concentration) using 0.05%/0.10%/0.20% (w/v) dilutions of EOs against Escherichia coli ATCC 11229, Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538. Antioxidant activities were determined by the 2,2'-diphenyl-1-picrylhydrazil (DPPH) method. EOs showed antimicrobial and antioxidant activity, but microencapsulation preserved the antimicrobial activity in all cases and increased the antioxidant activity from four- to eightfold. CONCLUSIONS: Although the Lippia essential oils were from the same species, their composition affects the biological activities before and after the microencapsulation process, as well as encapsulation efficiency. Our study supports the fact that microencapsulation of EOs in beta-cyclodextrin preserves the antimicrobial activity, improves the antioxidant activity and acts as a protection for EOs main compounds. SIGNIFICANCE AND IMPACT OF THE STUDY: Microencapsulation affects positively EOs main compounds, improves antioxidant activity and retains antimicrobial activity, enhancing the quality of the oils.

This article addresses cultural differences in children's initiative in helping in their home. Many 6- to 8-year-old children from an Indigenous-heritage community in Guadalajara, Mexico, were reported to engage, on their own initiative, in complex work for the benefit of the whole family (such as tending younger siblings, cooking, or running errands). In contrast, few children from a cosmopolitan community in Guadalajara, in which families had extensive experience with Western schooling and associated practices, were reported to contribute to family household work, and seldom on their own initiative. They were more often reported to be involved in activities managed by adults, and to have limited time to play, compared with the children in the Indigenous-heritage community, who were often reported to have plenty of time for free play and often planned and initiated their own after-school activities. The differences in children's contributions on their own initiative support the idea that children in some Indigenous American communities have opportunities and are expected and allowed to learn with initiative by observing and pitching in to collaborative endeavors of their families and communities.

We propose a solution to the menu planning problem adapting the bacterial foraging-based optimization algorithm. We design a mathematical model which satisfies the nutritional needs of individuals while enforcing the “Laws of Nutrition”, a set of postulates used by virtually all nutrition scientists in Latin America. This model corresponds to a constrained numerical optimization problem. We design a menu generator software prototype to set up a custom menu for 15 users with different characteristics. Results obtained by our proposal were satisfactory from an expert's point of view.

We propose in this work a general procedure to efficient EM-based design of single-layer SIW interconnects, including their transitions to microstrip lines. Our starting point is developed by exploiting available empirical knowledge for SIW. We propose an efficient SIW surrogate model for direct EM design optimization in two stages: first optimizing the SIW width to achieve the specified low cutoff frequency, followed by the transition optimization to reduce reflections and extend the dominant mode bandwidth. Our procedure is illustrated by designing a SIW interconnect on a standard FR4-based substrate.

This paper deals with the predefined-time stabilisation problem for a class of uncertain chained-form nonholonomic systems. Based on a novel generalised Lyapunov-like characterisation of predefined-time stability, new predefined-time controllers are introduced for a class of first and second order systems with matched perturbations. Contrary to existing finite-time and fixed-time schemes, an upper bound of the settling time is an easily tuneable control parameter. Then, these results for first and second order systems are used to design a switching strategy, which guarantees the predefined-time stability of the closed-loop system. The switching time and the settling-time can be easily tuned according to the control parameters. A benchmark example is presented to show the effectiveness of the proposed method.

This note presents a new characterization for predefined-time-stable systems based on Lyapunov stability. In contrast to the previous results in predefined-time stability, the proposed characterization allows the construction of predefined-time stabilizing controllers with polynomial terms instead of exponential ones, removing the exponential nature hypothesis of predefined-time-stable systems. Moreover, the existing Lyapunov characterization of predefined-time stability is shown to be a consequence of the new theorem presented in this paper. Finally, the proposed approach is used for the construction of robust predefined-time stabilizing controllers for first-order systems. A simulation example shows the feasibility of the proposed methods.

In this paper, we outline the historical evolution of RF and microwave design optimization and envisage imminent and future challenges that will be addressed by the next generation of optimization developments. Our journey starts in the 1960s, with the emergence of formal numerical optimization algorithms for circuit design. In our fast historical analysis, we emphasize the last two decades of documented microwave design optimization problems and solutions. From that retrospective, we identify a number of prominent scientific and engineering challenges: 1) the reliable and computationally efficient optimization of highly accurate system-level complex models subject to statistical uncertainty and varying operating or environmental conditions; 2) the computationally-efficient EM-driven multi-objective design optimization in high-dimensional design spaces including categorical, conditional, or combinatorial variables; and 3) the manufacturability assessment, statistical design, and yield optimization of high-frequency structures based on high-fidelity multi-physical representations. To address these major challenges, we venture into the development of sophisticated optimization approaches, exploiting confined and dimensionally reduced surrogate vehicles, automated feature-engineering-based optimization, and formal cognition-driven space mapping approaches, assisted by Bayesian and machine learning techniques.

This paper presents a grid synchronization scheme aimed to provide an estimation of the angular frequency and both the positive and negative sequences of the fundamental component of an unbalanced three-phase signal. These sequences are provided in fixed-reference-frame coordinates, and thus, the proposed algorithm is referred to as fixed-reference-frame phase-locked loop (PLL) (FRF-PLL). In fact, the FRF-PLL does not require transformation of variables into the synchronous frame coordinates as in most PLL schemes. Therefore, the proposed scheme is not based on the phase angle detection. Instead, the angular frequency is detected and used for synchronization purposes. The design of the FRF-PLL is based on a complete description of the source voltage involving both positive and negative sequences in stationary coordinates and considering the angular frequency as an uncertain parameter. Therefore, the FRF-PLL is intended to perform properly under severe unbalanced conditions and to be robust against angular frequency variations, sags, and swells in the three-phase utility voltage signal. Due to the selective nature of the scheme, it shows certain capability to alleviate the effect of harmonic distortion that is present in the utility voltage signal.

A general formulation to develop electromagnetic-based polynomial surrogate models in the frequency domain utilizing the multinomial theorem is presented in this paper. Our approach is especially suitable when the number of learning samples is very limited and no physics-based coarse model is available. We compare our methodology against four other surrogate modeling techniques: response surface modeling, support vector machines, generalized regression neural networks, and Kriging. Results confirm that our modeling approach has the best performance among these techniques when using a very small amount of learning base points on relatively small modeling regions. We illustrate our technique by developing a surrogate model for a substrate integrated waveguide interconnect with transitions to microstrip lines, a dual-band T-slot planar inverted-F handset antenna, and a high-speed package interconnect. Examples are simulated on a commercially available 3-D FEM simulator.

El objetivo de este trabajo es presentar una revisión crítica de las maneras en que se tiende a evaluar el desempeño de los docentes universitarios. Por lo general, las instituciones enuncian propósitos de la evaluación que suelen no coincidir con lo que se evalúa y con el uso que se hace de los resultados. Se incluye la revisión de distintos modelos de evaluación Para mostrar los desfases entre objetivos y prácticas, es decir, la pobre relación de lo que se hace, con el modelo del declarado. Se tiende a enunciar que el objetivo de la evaluación está centrado en la mejora continua. Uno de los instrumentos más utilizados es el cuestionario, con el que se pretende hacer una evaluación precisa, pero que, por lo general, no evalúa el desempeño docente, sino, en el mejor de los casos, la opinión de los estudiantes. Si se declara que la evaluación debe servir para mejorar la práctica docente, convendría privilegiar el modelo constructivista que permitiría favorecer los cambios que se requieren a través de la reflexión que surja de la revisión de la autoevaluación, la hetero-evaluación y la co-evaluación.

This research focuses on seeking the most important Critical Success Factors (CSF) that influence the implementation process of an Enterprise Resource Planning System (ERP) system. Based on a literature review, a reference list of 14 CSFs considered important in previous studies is identified. An experience survey, using a questionnaire, was conducted to verify whether these CSFs are also important and relevant for Mexican enterprises in the city of Guadalajara, Mexico. The sample consisted of 48 medium and large enterprises. The main results are as follows: (a) all the 14 CSFs in the reference list proved to be relevant for the Mexican enterprises; (b) no additional CSFs were added to the reference list by the participants, which implies that these 14 CSFs are the most important for the Mexican enterprises; and (c) cultural aspects is a likely cause of the differences in the ordering of CSF priority levels in different world regions. © 2007 Wiley Periodicals, Inc.