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https://hdl.handle.net/10669/1419

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4th graders’ working on a functional context: generalization levels and influence of stimuli
(2018) Ureña Alpízar, Jason de Jesús; Molina González, Marta; Ramírez Uclés, Rafael
In the last decades studies about the early algebra proposal have provided evidences of elementary students’ algebraic skills since early ages. Some of these studies (e.g. Blanton & Kaput, 2011) address algebra from a functional approach. In this context, one of the main focus of interest is the students’ ability to generalize a relationship between covariating quantities and how it is expressed by the students. Within this approach, in our study we analyze the generalization levels shown by eight 4th grade COUNTRY students while working, during an interview, on a task based on the functional relationship x+2. The task had an inductive structure and asked about the relation between the hours of stay of a car in a parking lot and the money to be paid. At the same time we study how the stimuli made by the interviewer (e.g. suggest, summarize information, redirect, etc.) influence the manifestation of generalizations. The results indicate that all the students manifested several generalization levels while solving the task. We detect facility to express the functional relationship by referring to specific numbers. When being asked about indeterminate quantities, they manifested generalization by means of referring to generic examples or using verbal expressions to allude indeterminacy. However, most of them required the interviewer’s stimuli. Four students accepted the use of a symbolic representation of the relationship when suggested and were able to explain its meaning or reproduce it with another letter. Our results evidence that the proposal of a functional task with inductive organization was useful to structure students’ ideas and reasoning with the final purpose of expressing the generalization of the relationship involved. At the same time they show that stimuli like suggesting processes or redirecting observations were determinant to obtain different answers from the students, to consolidate their ideas, and to provoke and promote the mobilization between generalization levels.
A aprendizagem dos conceitos de acontecimentos disjuntos e complementares com recurso ao Geogebra
(2019) Ramírez Montes, Guillermo Enrique; Henriques, Ana Cláudia Correia Batalha
Nesta comunicação, apresentamos os resultados de um estudo que visa compreender como alunos costarriquenhos do 10.º ano aprendem conceitos básicos de Probabilidade, no âmbito de uma experiência de ensino apoiada em tarefas exploratórias com recurso à simulação no Geogebra. Analisamos, em particular, as aprendizagens evidenciadas pelos alunos na resolução de uma tarefa que envolve os conceitos de acontecimentos disjuntos e complementares e os contributos do GeoGebra para essas aprendizagens. O estudo, de natureza qualitativa e interpretativa, teve por base os dados recolhidos através da observação participante, das resoluções escritas dos alunos da tarefa e de um questionário aplicado aos alunos no final da experiência de ensino. Os resultados evidenciam que o trabalho em torno da tarefa exploratória promoveu a aprendizagem dos alunos destes conceitos, ajudando-os a inferirem algumas propriedades de probabilidades associadas aos acontecimentos disjuntos e complementares. Ainda assim, o conceito de acontecimentos complementares revelou-se difícil para os alunos que, no final da experiência de ensino, mantêm algumas dificuldades. O Geogebra permitiu a visualização de representações dos conceitos e a sua exploração dinâmica, facilitando a inferência das referidas propriedades e motivando os alunos.
A comparison of bio-inspired optimization methodologies applied to the tuning of industrial controllers
(2016-11-09) Céspedes, Macarena; Contreras, Mónica; Cordero, Joaquín; Montoya, Gustavo; Valverde, Karen; Rojas Fernández, José David
A comparison of different bio-inspired methods is presented for the problem of tuning the parameters of a PID industrial controller for second order plus time delay plants. The compared algorithms are representative of three different kind of methodologies (evolutionary, swarm-based and ecology-based). Al methods are briefly explained and are fully implemented to solve the control problem at hand. It was found that all methods are well suited to solve the problem, but they differ in its computational cost. However in all cases, the different methodologies tested were able to find similar minimum values for different families of plants
A DMC implementation for a binary distillation column: a MIMO approach
(2022-11) Villalobos Herra, Elena; Chacón Vásquez, Mercedes
Distillation columns are essential equipment for many industries, they are in charge of separating liquid mixtures based on the volatility differences of their components. Traditional PID control techniques have proven not to be the best fit for operating distillation columns when trying to obtain pure components, since they are a very complex process. In order to test MPC control with distillation columns, a real pilot-scale model is chosen and a multiple-input multiple-output DMC algorithm is developed in MATLAB®. Additionally, a fuzzy logic controller is created based on previous work, in order to compare the distillation column control performance. Simulation results show good performance of the MPC.
A few additional reasons why vertical jump height should not be used to predict leg power
(2023-02) Aragón Vargas, Luis Fernando; González Lutz, María Isabel
Jump height continues to be widely used to predict power in humans. Individual progress is often monitored on the basis of estimated power, but prediction equations are based on group data. Objectives: to show that vertical jump performance (VJP) and mechanical power are poorly associated, particularly within individuals. Design: regression analysis. Methods: Two experiments are presented. First, 52 physically active male college students performed five maximal vertical jumps each. Second, three young male participants performed 50 maximal jumps each. Participants rested for 1 minute between jumps. VJP was calculated from kinematic data as peak body center of mass (BCOM) minus standing BCOM; peak power (PEAKPWR) was calculated from the vertical ground reaction force registered by a force plate, and average power (MEANPWR) during propulsion from the change in potential energy of BCOM. Regression analyses used standardized VJP scores as the predictor variable and standardized power scores as the resulting variables, expecting an identity function of y = x (intercept = 0, slope = 1) and R2 = 1. Results: In experiment 1, the model for zPEAKPWR R2 = 0.9707 (p < 0.0001) but slope (0.3452) ≠ 1 (p = 8.7x10-15). The model for zMEANPWR R2 = 0.9239 (p < 0.0001); nevertheless, slope (0.4257) ≠ 1 (p = 1.15x10-5). In experiment 2, all individual models for zPEAKPWR and zMEANPWR resulted in poor associations (R2 ≤ 0.21) and slopes ≠ 1 (p≤0.001). Conclusion: Regression analysis for individuals, and even for groups, confirms that VJP is a poor predictor of mechanical power.
A mobile application for improving the delivery process of notifications
(2021-01) Ureña Madrigal, Heriberto; López Herrera, Gustavo; Díaz Oreiro, Ignacio; Quesada Quirós, Luis
At present, there are systems in charge of classifying and sending notifications to smart devices at different times. However, there are not many studies that demonstrate the effectiveness of these systems in real world settings. We propose a method that classifies and prioritizes notifications by analyzing only the content of the notification and the sender of the message. We also developed a system implementing this method. User diaries were used to analyze the behavior of the system in real world situations, and the results showed that the implemented system significantly reduces interruptions to users. Additionally, the user experience of the system was evaluated through the standardized questionnaire UEQ (User Experience Questionnaire). The results obtained were positive in most of the scales of this instrument, above the average according to UEQ benchmarks. However, aspects such as stimulation and creativity can be improved in the future to motivate users to use the system.
A modeling methodology to evaluate the impact of temperature on Solar Home Systems for rural electrification
(2018) Narayan, Nishant; Vega Garita, Víctor; Qin, Zian; Popovic Gerber, Jelena; Bauer, Pavol; Zeman, Miroslav
Solar Home Systems (SHS) have recently gained prominence as the most promising solution for increasing energy access in remote, off-grid communities. However, the higher than standard testing conditions (STC) temperatures have a significant impact on the SHS components like PhotoVoltaic (PV) module and battery. A modeling methodology is described in this study for quantifying the temperature impact on SHS. For a particular location with high irradiation and temperatures and a given load profile, an SHS model was simulated, and the temperature-impact was analyzed on the performance and lifetime of the SHS components. Different PV module temperature estimation models were applied, and the corresponding dynamic PV outputs were compared. The nominal operating cell temperature (NOCT) model was found inadequate for estimating PV module temperatures under high irradiance conditions. The PV yield was found to be affected by almost 10% due to thermally induced losses. When different levels of temperature variations were considered, the battery lifetime was seen to be up to 33% less than that at 25°C. The modeling methodology presented in this paper can be used to include the thermal losses in SHS for rural electrification, which can further help accordingly in system sizing.
A note event-based decomposition of polyphonic recordings applied to single-channel audio source separation
(2020-07-14) Delgado Castro, Alejandro; Szymanski, John Edward
In this work, a novel decomposition method for single-channel polyphonic recordings is presented and applied to the separation of harmonic or nearly-harmonic sources from within an audio mixture. The proposed method is based on the iterative estimation and extraction of note events, where each event is defined as a section of audio containing largely harmonic energy identified as coming from a single sound source. In every iteration, the pitch trajectory of the predominant note event is automatically selected from an array of fundamental frequency estimates and used to guide the separation of the event’s spectral content, using two different methods: time-frequency masking and time-domain subtraction. A residual signal is then generated and used as the input mixture for the next iteration. This iterative stage continues until a predefined maximum number of iterations is reached. After convergence, all detected note events are clustered into individual sources by exploiting end-user interaction. Performance evaluation is carried out on a set of test recordings, containing excerpts of real music performances with different levels of polyphony, and the obtained results are compared with those generated with an alternative semi-automatic algorithm.
A novel control strategy for modular multilevel-based drives considering the system operating point
(2018-11-01) Espinoza Bolaños, Mauricio; Donoso Urrutia, Felipe Ignacio; Espina González, Enrique; Díaz Díaz, Matías; Cárdenas Dobson, Jesús Roberto Pedro Alejandro
Modular Multilevel Converters (MMC) are considered an attractive solution for high-power mediumvoltage drives. However, in drive applications, the influence of the loading conditions leads to more complex control systems than the required ones for constant frequency applications. To solve this issue, a novel control methodology for the MMC-based drive is presented in this paper. The proposed scheme defines the best control structure to balance the voltage of the converter capacitors considering the drive operating point (e.g. the loading conditions and the machine frequency). The design of the converter parameters considering the desired behaviour of the converter is also discussed in this paper. Experimental results with an 18-power cells MMC are used to validate the proposed control strategy.
A novel distributed secondary control strategy applied to hybrid ac/dc microgrids
(2019-11-28) Espina González, Enrique; Cárdenas Dobson, Jesús Roberto Pedro Alejandro; Donoso Urrutia, Felipe Ignacio; Urrutia Ortiz, Matías Alonso; Espinoza Bolaños, Mauricio
In this paper, a distributed secondary control strategy for hybrid ac/dc-microgrids is proposed. The control strategy restores the variables modified by the primary control loop, i.e. voltage on the DC-side and voltage amplitude and frequency of the AC-side, to their nominal values while maintaining a good power-sharing capability between AC- and DC-units, A distributed communication network among the generation units is needed for the proper performance of the control strategy, however, a high bandwidth communication network is not needed to ensure a good behaviour of the proposed control scheme. The effectiveness of the control scheme is validated through simulation of a 9.0kW hybrid ac/dc-microgrid.
A novel LVRT control strategy for Modular Multilevel Matrix Converter based high-power Wind Energy Conversion Systems
(2015-06-01) Díaz Díaz, Matías; Cárdenas Dobson, Jesús Roberto Pedro Alejandro; Espinoza Bolaños, Mauricio; Mora Castro, Andrés Felipe; Rojas Lobos, Félix Eduardo
The trend of multimegawatt wind turbines has positioning multilevel converters as a promising solution for high-power Wind Energy Conversion Systems (WECSs). Furthermore, due to the high penetration of wind energy into the electrical network, some rather strict grid regulations have been development in case of fault into the grid power. Mainly, grid codes set Low Voltage Ride Through (LVRT) requirements for grid connected WECS. In this scenario, this paper presents a novel modelation and control strategy to fulfil Low Voltage Ride Through requirements using a Modular Multilevel Matrix Converter for interfacing a high power wind turbine.
A novel topology and control system for Interconnected Wave Energy converters (IWECS)
(2019-11-28) Rodríguez Vindas, Mauricio; Espinoza Bolaños, Mauricio; Cárdenas Dobson, Jesús Roberto Pedro Alejandro; McDonald, Stephen P.; Baker, Nick J.
Recently, the extraction of energy from the incoming waves has taken more importance in the energy generation based on renewable resources. However, most of the attention has been directed towards the Power-Take-Off systems more than in the interaction between several generating units. Consequently, in this work, there are presented and carefully analysed a novel topology of Interconnected Wave-Energy Converters (IWECs) and its associated control system. A representative set of data of a real wave frequency and height variation from the South Uist island, in Scotland, and a proof-of-concept simulation show that the energy requirements of the proposed IWEC are lower than those required for individual WECs.
A performance evaluation of several artificial neural networks for mapping speech spectrum parameters
(2020) Yeom Song, Victor; Zeledón Córdoba, Marisol; Coto Jiménez, Marvin
In this work, we compare different neural network architectures, for the task of mapping spectral coefficients of noisy speech signals with those corresponding to natural speech. In previous works on the subject, fully-connected multilayer perception (MLP) networks and recurrent neural networks (LSTM & BLSTM) have been used. Several references report some initial trial and error processes to determine which architecture to use. Finding the best network type and size is of great importance due to the considerable training time required by some models of recurrent networks. In our work, we conducted extensive tests training more than five hundred networks, with several architectures to determine which cases present significant differences. The results show that for this application of neural networks, the architectures with more layers or the greater number of neurons are not the most convenient, both for the time required in their training and for the adjustment achieved. These results depend on the complexity of the task (the signal-to-noise ratio or SNR) and the amount of data available. This exploration can guide the most efficient use of these types of neural networks in future mapping applications, and can help to optimize resources in future studies by reducing computational time and complexity.
A risk-based methodology for defining the time of intentional controlled islanding
(2015-10-05) Fernández Porras, Pablo; Panteli, Mathaios; Quirós Tortós, Jairo
Power systems are operated close to their stability limits and this increases the probability of cascading outages leading to large-area blackouts. To mitigate these phenomena, intentional controlled islanding (ICI) has been suggested as an effective corrective strategy that splits the system into sustainable subsystems (islands). There are two primary aspects associated with ICI: i) where to island, and ii) when to island? This work focuses on the latter and proposes a risk-based methodology that compares in a real-time fashion (i.e., quickly enough) the overall risk of the system without and with islanding (i.e., when an ICI scheme is activated) in order to define a suitable time for system splitting. Simulation results on the IEEE 9-bus system demonstrate the effectiveness of the methodology in determining a suitable time for the creation of islands, which in turn corresponds to the crossing point between the risks of the system without and with islanding.
A simple methodology for estimating battery lifetimes in Solar Home System design
(2017) Narayan, Nishant; Papakosta, Thekla; Vega Garita, Víctor; Popovic Gerber, Jelena; Bauer, Pavol; Zeman, Miroslav
The proliferation of Solar Home Systems (SHS) in recent times hopes to provide an alleviating solution to the global problem of energy poverty. Battery is usually the most expensive but important part of an SHS; it is also normally the first part to fail. Estimating the battery lifetime can help make informed system design choices, and it is therefore an important exercise for an SHS designer. Battery lifetime modelling is often a complex task requiring empirical data or reliance on modelling cell level electrochemical phenomena. This paper presents a simple battery lifetime estimation method specific to the application and candidate battery choices at hand. An SHS application specific simulation is carried out for a year and the effect of microcycles on the battery activity is analyzed. The concept of active Depth-of-Discharge (DOD) is introduced. Cyclic ageing of the battery is thus quantified and relative cycle lives of 2 battery technologies are compared. A delicate trade-off is demonstrated between battery sizing and lifetime. The described methodology is also compared with an empirical model and the lifetime results are found to be within 3.85%. The methodology described in this paper can potentially help SHS designers in making quick, reasonable estimations of battery lifetimes based on the intended application and battery manufacturer's data.
A solid state transformer based on a three-phase to single-phase modular multilevel converter for power distribution networks
(2018-04-09) Espinoza Bolaños, Mauricio; Díaz Díaz, Matías; Rojas Lobos, Félix Eduardo; Cárdenas Dobson, Jesús Roberto Pedro Alejandro
To properly integrate electric vehicles and distributed generation systems in a massive scale, new revolutionary features and unprecedented transformations has to be implemented in power distribution networks, such as: access to LV DC interconnection point, reconfiguration capability for power flow management, disturbance isolation, low power-losses, high reliability, high power-quality, smart protection and low failure rate. In this paper, an innovative topology for a Solid State Transformer based on AC/AC Modular Multilevel Converter (MMC) is proposed. The proposed topology uses only one centralized singlephase Medium Frequency Transformer (MFT), which reduces the footprint of the SST. Furthermore, it provides three-phase balanced low-voltage system under unbalanced and non-linear loads. Simulation results validate the proposed topology and the control of the MMC to modulate a medium frequency mediumvoltage to provide a desired power flow.
A survey on 3D Perception for robot object manipulation tasks
(2019) Peralta Sáenz, Javier Ignacio; Ruiz Ugalde, Federico
Un sistema confiable de manipulación de objetos requiere de percepción sofisticada. Aspectos importantes de este sistema es ser capaz de detectar la forma, tamaño y pose de los objetos a manipular. Estas capacidades se han mostrado antes en la literatura pero sin demostrar altos grados de confiabilidad en ambientes no controlados. Las soluciones actuales tienen muchas limitaciones para lograr un manejo adecuado de los objetos. El objetivo principal de este estudio es revisar las técnicas de percepción más relevantes al problema, sus características y limitaciones. Esto será de utilidad para dirigir el trabajo futuro a los aspectos que un robot (como el desarrollado en el ARCOS-Lab) necesita para manipular objetos en ambientes humanos no controlados cotidianos, como las cocinas
A systematic literature review of methodologies used for the design of serious games. A comparative analysis
(2020-06-26) Sandí Delgado, Juan Carlos; Bazán, Patricia Alejandra
This article of systematic literature review presents the analysis of a series of methodological proposals, suggested for the design of educational video games. Nine different methodologies are analyzed. As part of the analysis, criteria are defined to describe and compare them, linked with the possibilities they have for the design of serious games. Criteria include: requirements elicitation and specification, pedagogical intention, pedagogical and ludic objectives definition, educational level and target public, roles identification, feedback type, user experiences analysis, objectives and methodologies validation. Main results indicate the following. 1) It is of vital importance, in the initial phase of a methodology design to incorporate the requirements elicitation and specification, as well as to define and assign roles of the different parties involved in the game production, all of this jointly and by consensus. 2) The definition of pedagogical objectives is closely related to the context use and it is important that it be done in the initial stage and then asses the game quality in the final stage. 3) It is important to incorporate the definition of pedagogical elements in the design. They will be helpful to assess the efficiency, learning and the user experience in relation with the interaction with the game. In addition, these pedagogical elements will facilitate the development of a quantitative record of learning to know the process and its quality by the user. It is concluded that the set of methodologies analyzed provide information in regards to the considerations when proposing a methodology for the design of a serious games. As a future work, there will be a methodological proposal, which will facilitate the integration of the aspects identified through the revision of the methodologies analyzed to guide systematically the design process of a serious game, specifically targeted to the teaching of digital competencies.
El acceso abierto a la información: una premisa indispensable para desarrollar la investigación en diversidad cultural y estudios regionales
(2013-06-28) Córdoba, Saray
En el año 1998 escribíamos que la información es fundamental para apoyar la investigación sobre la identidad cultural. Este texto incluía una propuesta para agilizar los procesos que permitirían un fácil acceso a la producción científica que generaba el Centro de Investigaciones en Identidad y Cultura Latinoamericanas (CIICLA, UCR) único en su género en ese momento. Sin embargo, 14 años después, en que la tecnología ha hecho variar el panorama notablemente para alcanzar ese propósito, se retoma la idea y se actualiza de acuerdo con las posibilidades que se encuentran disponibles en este momento. Las costumbres de los y las investigadoras en Humanidades y Ciencias Sociales (o cultura epistémica como lo denomina Cronin (2005)) muestran una gama amplia de posibilidades para publicar su producción científica, que va desde las monografías hasta los textos de creación cultural, que se esconden fácilmente y se mimetizan. Para ello se incluyen datos para justificar cómo el acceso abierto multiplica la generación de conocimiento en diferentes campos, pero aún más en el caso de estudios sobre estos temas, dado que el ámbito de acción es tan específico y amplio como lo desee el y la investigadora, y la situación de dispersión en que se encuentran las fuentes hace difícil su ubicación. Se ofrece ejemplos concretos de experiencias sobre el tema y se aclaran las diferentes posibilidades que deben generarse dentro y fuera de la UCR. Asimismo, se insiste en que el acceso abierto es la única posibilidad para lograr que el conocimiento se multiplique para favorecer la generación de otros estudios similares.
Actitudes de la población general en Costa Rica hacia las personas mayores como aprendices y usuarias TIC
(2022) Castro Rojas, María Dolores; Smith Castro, Vanessa
En Costa Rica se pueden identificar varios factores básicos que dificultan el aprendizaje sobre las TIC y su uso en la vida cotidiana por parte de las Personas Adultas Mayores, entre ellos destaca apoyo inadecuado o falta de apoyo por parte de familiares y amistades para el aprendizaje de las TIC (PROSIC, 2010). También se ha identificado que las dificultades en el aprendizaje TIC se relacionan con la falta de experiencia previa con TIC, miedo y vergüenza asociados con el proceso de aprendizaje y restricciones para recibir apoyo individual por parte de familiares, amigos y docentes para aprender a usar las TIC (Castro-Rojas, 2018a; Castro-Rojas, et al., 2016, 2018; Coto, et al., 2017). Las Personas Mayores señalan que el miedo y la vergüenza, así como la falta de apoyo social durante el aprendizaje, se relaciona con actitudes y estereotipos negativos sobre las personas mayores y sus capacidades para aprender y usar las TIC.

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