Colecciones Institucionales

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1-D memristor-based cellular automaton for pseudo-random number generation
(IEEE, 2017) Karamani, Rafailia Eleni; Ntinas, Vasileios; Vourkas, Ioannis; Sirakoulis, Georgios C.
Cellular Automata (CAs) is a well-known parallel, bio-inspired, computational model. It is based on the capability of simpler, locally interacting units, i.e. the CAs cells, to evolve in time, giving rise to emergent computation, suitable to model physical system behavior, prediction of natural phenomena and multi-dimensional problem solutions. Moreover, at the same time CAs constitute a promising computing platform, beyond the von Neumann architecture. In this paper, a memristor device is considered to be the basic module of a CA cell circuit implementation, performing as a combined memory and processing element to implement CA-based circuits, able to model sufficiently systems and applications as mentioned above, targeting tentatively to a more energy efficient design compared to the conventional electronics. In particular and as a proof of concept, the results of elementary CAs modeling and simulation for the generation of pseudo-random numbers are presented using a 1-D memristor-based CAs array to illustrate the robustness and the efficacy of the proposed computing approach.
23-Level Inverter for Electric Vehicles Using a Single Battery Pack and Series Active Filters
(IEEE, 2012) Pereda Torres, Javier Eduardo; Dixon, Juan
Cascaded H-bridge (CHB) multilevel inverters have been conceived as an alternative to reduce total harmonic distortion (THD) in medium-voltage drives. The reduced THD makes them useful for electric vehicle (EV) applications, but the main problem with the CHB is the large amount of isolated power sources required to feed each of the H-bridges. An improved variant known as the asymmetrical CHB (ACHB) inverter uses H-bridges of different sizes and then needs fewer isolated power sources than the CHB. However, in battery-powered EVs, only one power supply (fuel cell or battery pack) is desirable. This work presents a solution to solve the problem, operating some of the small H-bridges (Aux-bridges) as series active filters and using a small high-frequency link (HFL). With this solution, only one dc source is required to feed the inverter, and if the control is adjusted to work at particular switching points, more than 98% of power is transferred through the larger H-bridges (MAIN bridges). The proposed ACHB topology can produce any number of levels, and the M AIN bridges always commutate at fundamental frequency. As the number of levels must remain constant for all output voltages, a variable dc source is required to control the amplitude of the motor voltage. This work shows some simulations and experiments on a 2-kW 27-level ACHB working with only 23 levels. The concept is being implemented in a small EV with an ACHB drive of 18 kW.
27-level converter for electric vehicles using only one power supply
(IEEE, 2010) Dixon Rojas, Juan; Pereda Torres, Javier Eduardo
The main advantage of asymmetrical multilevel inverters is the optimization of levels with a minimum number of power supplies. However, this optimized multilevel system still needs a large number of isolated and floating DC supplies, which makes these converters complicated to implement in electric vehicles (EVs), because the system will require many independent battery packs. In this paper, a very simple scheme, based on a small and cheap high frequency link (HFL), allows the utilization of only one power supply for the complete multilevel inverter drive, with an inherent regulation of the voltages supplied among the H-bridges. It also allows voltage control with full number of levels if the DC power supply is of variable voltage characteristic. This work is focused on a 27-level asymmetric inverter but the strategy, using only one power supply, can be applied to converters with any number of levels. In particular, an asymmetrical 27-level converter needs nine isolated power supplies and the proposed system reduces these nine sources to only one: the battery car. The topology also permits full regenerative braking working as a three-level converter. The proposed system is intended for application in electric vehicles from power ratings up to 150 kW. Simulations and experimental results show the feasibility to implement this â€œone-sourceâ€ multilevel system.
3-D CNC trajectory interpolation using Bresenham's algorithm
(IEEE, 1994) Chiang Sánchez, Luciano Eduardo
This article describes a 3D extension of Bresenham's algorithm and its implementation in the linear trajectory interpolation of CNC paths. The resulting algorithm has been successfully applied to a CNC milling machine that uses stepper motors as actuators, resulting in minimal contour errors for a given step motor resolution. A numerical control system that uses the algorithm implementation has been built as part of a wider effort which is to test the feasibility of building or retrofitting machine tools with CNC capabilities at an affordable price tag for a developing country.<>
3D Quantification of Wall Shear Stress and Oscillatory Shear Index Using a Finite-Element Method in 3D CINE PC-MRI Data of the Thoracic Aorta
(2016) Sotelo Parraguez, Julio Andrés; Urbina, Jesus; Valverde, Israel; Tejos Nunez, Cristian Andres; Irarrázaval Mena, Pablo; Andia Kohnenkampf, Marcelo Edgardo; Uribe Arancibia, Sergio A.; Hurtado Sepúlveda, Daniel
Several 2D methods have been proposed to estimate WSS and OSI from PC-MRI, neglecting the longitudinal velocity gradients that typically arise in cardiovascular flow, particularly on vessel geometries whose cross section and centerline orientation strongly vary in the axial direction. Thus, the contribution of longitudinal velocity gradients remains understudied. In this work, we propose a 3D finite-element method for the quantification of WSS and OSI from 3D-CINE PC-MRI that accounts for both in-plane and longitudinal velocity gradients. We demonstrate the convergence and robustness of the method on cylindrical geometries using a synthetic phantom based on the Poiseuille flow equation. We also show that, in the presence of noise, the method is both stable and accurate. Using computational fluid dynamics simulations, we show that the proposed 3D method results in more accurate WSS estimates than those obtained from a 2D analysis not considering out-of-plane velocity gradients. Further, we conclude that for irregular geometries the accurate prediction of WSS requires the consideration of longitudinal gradients in the velocity field. Additionally, we compute 3D maps of WSS and OSI for 3D-CINE PC-MRI data sets from an aortic phantom and sixteen healthy volunteers and two patients. The OSI values show a greater dispersion than WSS, which is strongly dependent on the PC-MRI resolution. We envision that the proposed 3D method will improve the estimation of WSS and OSI from 3D-CINE PC-MRI images, allowing for more accurate estimates in vessels with pathologies that induce high longitudinal velocity gradients, such as coarctations and aneurisms.
A baseline restorer for charge-sensitive amplifiers in a 500-nm CMOS process
(IEEE, 2018) Abusleme Hoffman, Ángel Christian; Barraza Altamirano, Renzo Ignacio; Kuleshov, S.
Charge-sensitive amplifiers (CSAs), widely used as front-ends in pulse processors for capacitive detectors, require a feedback network to set the operation point, deal with leakage currents and restore the baseline voltage upon the arrival of signals. Passive feedback networks are simple and reliable solutions that accomplish the task, but cannot modify the operation point in order to accommodate an input with different polarity, and do not offer sufficient flexibility to deal with a wide range of leakage current or input rates. The Krummenacher feedback solves these drawbacks at the cost of a large compensation capacitor, which is required for stability purposes. In this work, a novel configurable feedback network is presented. Based on the same principle as the Krummenacher network, this circuit relies on the design parameters to ensure stability. This work shows analysis, design and test results from a recent implementation in a 500-nm CMOS process.
A Blind Calibration Scheme for Switched-Capacitor Pipeline Analog-to-Digital Converters
(IEEE, 2020) Bozzo Jiménez Juan Andrés; Abusleme Hoffman, Ángel Christian; Martinez, J. S.
A foreground calibration algorithm is proposed to digitally self-calibrate a switched-capacitor (SC), pipelined, analog-to-digital converter (ADC). Static errors resulting from capacitor mismatch, charge transfer loss (from limited amplifier dc gain) and variance in Multiplying DAC (MDAC) voltages are estimated and compensated for. The proposed algorithm reuses the electrical components of the pipeline stages to instantiate Î”Î£ converters in the stages' interfaces. By feeding to those converters self-generated input signals and storing the output stream of codes, the algorithm is able to infer the electrical parameters of the reused elements. The algorithm does not require external stimulus or specialized circuitry to be used as true ground but depends on the stages sub-ADC threshold levels precision, diminishing its performance in circuits where error is dominated by sub-ADC input offset. A number of 10-bit ADC's with a mean uncalibrated Effective Number Of Bits (ENOB) of 6.3 bits where simulated, and a resolution improvement between 2.5 bits, for the best case, and 1 bit for the worst, were observed.
A clean four-quadrant sinusoidal power rectifier using multistage converters for subway applications
(2005) Dixon, Juan; Morán, Luis
A special 27-level four-quadrant rectifier for subway applications is analyzed. The arrangement uses only three H-bridges per phase, common dc bus, and independent input transformers for each H-bridge. The transformers allow galvanic isolation and power escalation to obtain high-quality voltage waveforms, with total harmonic distortion of less than 1%. Some advantages of this 27-level rectifier are: 1) only one of the three H-bridges, called the main converter, manages more than 80% of the total active power in each phase and 2) it switches at fundamental frequency, reducing the switching losses at a minimum value. The rectifier analyzed in this paper is a current-controlled voltage-source type, with a conventional feedback control loop. Some simulations in a rectifier substation, including power reversal at full load are displayed (750 Vdc, 1200 A). The rectifier shows the ability to produce clean ac and dc waveforms without any ripple, and fast reversal of power. Some experimental results with a small prototype, showing voltage and current waveforms, are finally displayed.
A Compact Answer Set Programming Encoding of Multi-Agent Pathfinding
(IEEE, 2021) Gómez Araya, Rodrigo Nicolás Teófilo; Hernández, Carlos; Baier Aranda, Jorge Andrés
Multi-agent pathfinding (MAPF) is the problem of finding k non-colliding paths connecting k given initial positions with k given goal positions on a given map. In its sum-of-costs variant, the total number of moves and wait actions performed by agents before they definitely reach the goal is minimized. Not surprisingly, since MAPF is combinatorial, a number of compilations to Boolean Satisfiability (SAT) and Answer Set Programming (ASP) exist. In this article, we describe in detail the first family of compilations to ASP that solve sum-of-costs MAPF over 4-connected grids. Compared to existing ASP compilations, a distinguishing feature of our compilation is that the number of total clauses (after grounding) grow linearly with the number of agents, while existing compilations grow quadratically. In addition, the optimization objective is such that its size after grounding does not depend on the size of the grid. In our experimental evaluation, we show that our approach outperforms search-based sum-of-costs MAPF solvers when grids are congested with agents. We also show that our approach is competitive with a SAT-based approach when follow conflicts are taken into account. We also explore the potential of our solver when finding makespanoptimal solutions, in which makespan is minimized first and then cost is minimized. Our results show that makespan-optimal solutions are slightly suboptimal in most benchmarks. Moreover, our MAPF solver, when run in that mode, is faster and scales better.
A comparison of gradient versus color and texture analysis for lane detection and tracking
(IEEE, 2009) Tapia Espinoza, Rodolfo Antonio; Torres Torriti, Miguel Attilio
Accurate lane detection in real-time is a critical task in autonomous vehicle guidance and lane departure warning for driver assistance. Existing vision-based approaches rely mostly on some analysis of the spatial gradient of the image. However, if the road structure is not regular and well delimited, edges may not be easy to extract and other features must be employed. This paper evaluates the use of color and textural features as a way to improve the standard gradient-based lane detection. Textural features are generated using a bank of Gabor filters. A benefit of using color and texture is that the sky regions of the image, as well as side elements, can be detected. The results obtained from testing the approaches on city roads show that color and texture analysis yields a more accurate road segmentation.
A Comparison of Path Planning Algorithms for Omni-Directional Robots in Dynamic Environments
(IEEE, 2006) Haro, F.; Torres Torriti, Miguel Attilio
The scope of this paper is to analyze and compare three path planning methods for omni-directional robots, which are based on a) the bug algorithm, b) the potential fields algorithm, and c) the A* algorithm for minimum cost path with multiresolution grids. The approaches are compared in terms of computational costs and the resulting path lengths. Results obtained indicate that the bug algorithm is a suitable choice for this type of application as its computational cost is lower than that of the other methods. Furthermore, minor modifications of the standard bug algorithm, such as the tangent following modification, allow the path planner to handle well the situations encountered in typical multi-robot environments
A Container-based IoT-oriented Programmable Logical Controller
(IEEE, 2020) Mellado Aceitón, Jacob Enrique; Núñez Retamal, Felipe Eduardo
The programmable-logical-controller (PLC) has been the key building block of industrial control systems throughout the whole automation revolution, where its role has been mainly to command low-level regulatory feedback control loops. Modernized versions of PLCs aim at facilitating its integration with cloud-based solutions, in the context of the Industrial Internet of Things (IIoT) paradigm. This work is a step forward in this direction and presents a container-based formulation of an IoT-oriented programmable controller, named IoT-PLC, in which each functionality works within a separate container. This IoT-PLC device has regulatory control capabilities, fog-computing functionalities as filtering and field data storage, and multiple wireless interfaces managed independently by individual containers. A virtual device model is used as an abstraction method to represent real entities, and OPC-UA is available for straightforward compatibility with the upper control layers.
A CSP-theoretic Framework of Checking Conformance of Business Processes
(IEEE, 2012) Roy, S.; Bihary, S.; Corso Laos, José Alfonso
In this paper, we tackle the problem of conformance checking which verifies if the event logs (observed) match/fit the reference (arbitrary) process. We use concepts from Communicating Sequential Processes (CSP), which facilitates automated analysis using PAT toolkit. By this technique one can identify all the logs which cannot be properly replayed on the process. We illustrate our approach with an example. Finally, we introduce some metrics based on conformance checking. They are related to fitness, closeness, and appropriateness of the event logs vis-a-vis reference process models.
A customizable collaborative virtual environment on the Web
(IEEE, 1999) Portugal Portugal, Roberto Carlos; Guerrero, Luis A.; Fuller Padilla, David Alfredo
Collaborative virtual environments (CVE) support the collaboration, communication and social interaction among users in virtual spaces. We present a customizable CVE implemented on top of the Web that allows for the creation of various interactive environments. This CVE is designed mainly, from the perspective of the desk, rooms and hall metaphors. The architecture of our CVE is based on design patterns and integrates a group of tools in order to support interaction among users in both synchronous and asynchronous ways.
A DAC reconstruction filter for narrowband long distance Communications
(IEEE, 2014) Aldunate Varela, Joaquín Pablo; Feres Ducci, Carlos Jose; Vlahoyiannatos, Spyros; Oberli Graf, Christian Robert; de Villers-Grandchamps Zaldivar, Jean-Paul Idesbald; Guarini Hermann, Marcelo Walter
There are applications that require long-range, low data rate and low power consumption communications that could be implemented with wireless sensor networks equipped with multiple antennas. We are implementing a transceiver for that purpose. The transceiver requires a specific reconstruction filter which isn't commercially available for our target technology, XFAB XH018. An integrated active DAC reconstruction filter was designed and implemented on the target technology using Synopsys design tools. This document present the design, implementation and testing of the reconstruction filter. The filter achieved the design requirements.
A Deep Learning Based Behavioral Approach to Indoor Autonomous Navigation
(IEEE, 2018) Sepulveda Villalobos, Gabriel Andres; Niebles, Juan Carlos; Soto Arriaza, Álvaro Marcelo
We present a semantically rich graph representation for indoor robotic navigation. Our graph representation encodes: semantic locations such as offices or corridors as nodes, and navigational behaviors such as enter office or cross a corridor as edges. In particular, our navigational behaviors operate directly from visual inputs to produce motor controls and are implemented with deep learning architectures. This enables the robot to avoid explicit computation of its precise location or the geometry of the environment, and enables navigation at a higher level of semantic abstraction. We evaluate the effectiveness of our representation by simulating navigation tasks in a large number of virtual environments. Our results show that using a simple sets of perceptual and navigational behaviors, the proposed approach can successfully guide the way of the robot as it completes navigational missions such as going to a specific office. Furthermore, our implementation shows to be effective to control the selection and switching of behaviors.
A delicate balance in South America
(2008) Rudnick, Hugh; Barroso, Luiz; Mocarquer, Sebastian; Bezerra, Bernardo
This article deals with the challenges of balancing the need for hydroelectricity with the impact on the environment. Economic efficiency, energy security, and environmental sustainability are concerns that must be considered in any energy policy in any given country. These key aspects remain challenged currently in South America. High energy consumption growth worldwide rising fossil fuels prices, strong environmentalist pressure toward reducing greenhouse gas effects, and promotion of renewable energy production have been a common challenge in South American energy markets. The development of vast unexploited hydroelectric resources is also at the center of attention, where its renewable character is being confronted with its environmental impact.
A density-based approach for effective pedestrian counting at bus stops
(IEEE, 2009) García Bunster, Guillermo; Torres Torriti, Miguel Attilio
Accurately counting people waiting at bus stops is essential for automated bus fleet scheduling and dispatch. Estimating the passenger demand in regular open bus stops is a nontrivial problem because of the varying conditions, such as illumination, crowdedness, people poses, to name a few. This paper presents a simple, but very effective approach to estimate the passenger count using people density estimates. People density is obtained from foreground segmentation using a Gaussian mixture background model. A linear model, which is employed to correct the densities due to perspective scaling for people far from the camera position, yields the final people count estimates. The approach is compared to the well-know Viola-Jones detector and shown to yield better people count estimates despite its simplicity, because it is more robust to occlusions, pose changes, and due to the fact that it does not attempt to find body parts. The proposed method is general and can be employed to count people in other public spaces, such as buildings.
A Digital Memristor Emulator for FPGA-Based Artificial Neural Networks
(IEEE, 2016) Vourkas, Ioannis; Abusleme Hoffman, Ángel Christian; Ntinas, Vasileios; Sirakoulis, Georgios C.; Rubio, Antonio
FPGAs are reconfigurable electronic platforms, well-suited to implement complex artificial neural networks (ANNs). To this end, the compact hardware (HW) implementation of artificial synapses is an important step to obtain human brain-like functionalities at circuit-level. In this context, the memristor has been proposed as the electronic analogue of biological synapses, but the price of commercially available samples still remains high, hence motivating the development of HW emulators. In this work we present the first digital memristor emulator based upon a voltage-controlled threshold-type bipolar memristor model. We validate its functionality in low-cost yet powerful FPGA families. We test its suitability for complex memristive circuits and prove its synaptic properties in a small associative memory via a perceptron ANN.
A Framework for Transmission Expansion Planning: A Complex Problem Clouded by Uncertainty
(IEEE, 2016) Velásquez Guerino, Constantin Sebastián Klaus; Watts Casimis, David; Rudnick van de Wyngard, Hugh; Bustos Sölch, Cristián Pablo
Transmission Expansion Planning (TEP), a complex problem that is vital to ensure the proper functioning of restructured electricity markets, is clouded by uncertainties. Timely and cost-effective transmission expansion is necessary for providing secure and reliable electricity service to customers, enhancing competition, and ensuring market efficiency in electricity markets. Given the irreversibility and long lifetimes of transmission investments, TEP requires addressing uncertainties on future system conditions several years ahead. Because of these fundamental properties of transmission, the importance of developing tools and models to assist power system planning under uncertainty has long been recognized. As any decision under uncertainty is made before the uncertainty is revealed, addressing uncertainties allows hedging against risks caused by the outcomes of decisions taken under uncertainty.

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