Artículos de publicaciones periódicas

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Time delay properties of stochastics-resonance information transmission line
(2008) Ibáñez, Santiago Agustín; Fendrik, Alejandro J.; Fierens, Pablo Ignacio; Grosz, Diego; Perazzo, Roberto P. J.
"In this paper we analyze the properties of a chain of forward-coupled bi-stable over-damped oscillators. It is well known that this system displays stochastic resonance and behaves as a transmission line when an adequate amount of noise is added to each oscillator, and the first oscillator is driven by a periodic (sine) modulating signal. By driving the first oscillator with a modulated sequence of random non-return-to-zero (NRZ) bits, we start by showing that the system exhibits a stochastic-resonance behavior. Then we show that bit delays can be adjusted by either changing the amount of noise and/or the coupling intensity between adjacent oscillators. We find that the system can be regarded as a tunable delay line for a broad range of noise and coupling parameters, a feature that may find applications in information processing and bit regeneration."
On the dynamics of a single-bit stochastic-resonance memory device
(2010-07) Ibáñez, Santiago Agustín; Fierens, Pablo Ignacio; Perazzo, Roberto P. J.; Patterson, Germán; Grosz, Diego
"The increasing capacity of modern computers, driven by Moore’s Law, is accompanied by smaller noise margins and higher error rates. In this paper we propose a memory device, consisting of a ring of two identical overdamped bistable forward-coupled oscillators, which may serve as a building block in a larger scale solution to this problem. We show that such a system is capable of storing a single bit and its performance improves with the addition of noise. The proposed device can be regarded as asynchronous, in the sense that stored information can be retrieved at any time and, after a certain synchronization time, the probability of erroneous retrieval does not depend on which oscillator is being interrogated. We characterize memory persistence time and show it to be maximized for the same noise range that both minimizes the probability of error and ensures synchronization. We also present experimental results for a hard-wired version of the proposed memory, consisting of a loop of two Schmitt triggers. We show that this device is capable of storing a single bit and does so more efficiently in the presence of noise."
Analysis and design of a tilted rotor hexacopter for fault tolerance
(IEEE, 2016) Giribet, Juan I.; Sanchez-Peña, Ricardo; Ghersin, Alejandro S.
A proof is presented of how a hexagon-shaped hexacopter can be designed to keep the ability to reject disturbance torques in all directions while counteracting the effect of a failure in any of its motors. The method proposed is simpler than previous solutions, because it does not require change of the motor rotation direction or in-flight mechanical reconfiguration of the vehicle. It consists of tilting the rotor a small fixed angle with respect to the vertical axis. Design guidelines are presented to calculate the tilt angle to achieve fault-tolerant attitude control without losing significant vertical thrust. It is also formally proved that the minimum number of unidirectional rotating motors needed to have fault tolerance is 6 and that this can be achieved by tilting their rotors. This proof is essentially a control allocation analysis that recovers in a simple way a result already known: the standard configuration (without tilting the motors) is not fault tolerant. A simulation example illustrates the theory.
Reverberation chambers through the magnifying glass: an overview and classification of performance indicators
(2017) Serra, Ramiro
"The present paper follows on a previously published one in the theme section of the IEEE EMC Magazine's last issue. In this Part II, we will address the main body of the different metrics and methodologies there exist in order to assess reverberation chambers (RC) performance."
Quaternions and dual quaternions: singularity-free multirobot formation control
(2017-09) Mas, Ignacio; Kitts, Christopher
"Cluster space control is a method of multirobot formation keeping that considers a group of robots to be a single entity, defining state variables to represent characteristics of the group, such as position, orientation, and shape. This technique, however, suffers from singularities when a minimal state representation is used. This paper presents three alternative implementations of this control approach that eliminate singularities through changes in the control architecture or through redundant formation definitions. These proposed solutions rely on quaternions, dual quaternions, and control implementations that produce singularity-free trajectories while maintaining a cluster level abstraction that allows for simple specification and monitoring. A key component of this work is a novel concept of representing formation shape parameters with dual quaternions. Simulation results show the feasibility of the proposed solutions and illustrate their differences and limitations."
Pedestrian tracking using probability fields and a movement feature space
(2017-12) Negri, Pablo; Garayalde, Damián
"Retrieving useful information from video sequences, such as the dynamics of pedestrians, and other moving objects on a video sequence, leads to further knowledge of what is happening on a scene. In this paper, a Target Framework associates each person with an autonomous entity, modeling its trajectory and speed by using a state machine. The particularity of our methodology is the use of a Movement Feature Space (MFS) to generate descriptors for classifiers and trackers. This approach is applied to two public sequences (PETS2009 and TownCentre). The results of this tracking outperform other algorithms reported in the literature, which have, however, a higher computational complexity."
Experimental validation of a fault-tolerant hexacopter with tilted rotors
(2018) Giribet, Juan I.; Pose, Claudio D.; Ghersin, Alejandro S.; Mas, Ignacio
"Recently, research reporting the advantages of flying with tilted-motor multicopters has surfaced. Particularly, it has been theoretically proven that in the case of a complete failure of one of the motors in a hexagon-shaped hexacopter, complete altitude and attitude control can be maintained. In this work, these theoretical results were experimentally validated."
Control system to balance internal currents of a multilevel current-source inverter
(2018-03) Cossutta, Pablo; Aguirre, Miguel Pablo; Angélico Engelhardt, Mathias; Valla, María Inés
"Multilevel current-source inverters have proved to be a high-performance option for industrial applications due to reliability, fault-tolerant capabilities, quasi soft switching, and the use of lower filter capacitor values. One of its major challenges is to balance the internal currents that feed each module. Imbalances could be caused by manufacturing deviations of the reactive components, temperature drift or aging, nonlinear loads, and modulation errors, among others. Using the well-known phase-shift carrier sinusoidal pulse width modulation, a slight change in the amplitude of the carrier signals produces a variation in the average value of the internal currents. In this paper, we introduce a control strategy to balance the current of the inductors and its implementation in a prototype. Simulation and experimental results at different operating conditions show a robust behavior of the control system along with a low distortion in the output voltages and currents of the converter."
Diseño de un autopiloto para pequeños vehículos no tripulados
(2019-06) Garberoglio, Leonardo; Pose, Claudio D.; Mas, Ignacio; Giribet, Juan I.
"En este trabajo se presenta el diseño de un autopiloto para pequeños vehículos autónomos. El trabajo está enfocado principalmente en la arquitectura del sistema, pero se presentan también algunos detalles del firmware desarrollado para el autopiloto. En particular, el firmware incluye el paquete rosserial, que permite una conexión simple con ROS (Robot Operating System), resultando beneficioso para diversas aplicaciones. El desarrollo se valida experimentalmente en un vehículo aéreo no tripulado (UAV1) del tipo multi-rotor y en un vehículo acuático de superficie (ASV2). Estos vehículos han sido desarrollados por nuestro grupo, y en este trabajo puede encontrarse información sobre estos proyectos, lo cual puede ser de utilidad para los interesados en el desarrollo de UAV o ASV."
A dual-stator winding induction generator based wind-turbine controlled via super-twisting sliding mode
(2019-11) Talpone, Juan I.; Puleston, Paul F.; Cendoya, Marcelo G.; Barrado-Rodrigo, José A.
"The dual-stator winding induction generator (DWIG) is a promising electrical machine for wind energy conversion systems, especially in the low/mid power range. Based on previous successful results utilising feed forward control, in this article, a super-twisting (ST) sliding mode improved control set-up is developed to maximise power extraction during low wind regimes. To accomplish this objective, via constant volts/hertz implementation, a ST controller was designed to command the DWIG control winding, such that the tip-speed ratio is robustly maintained at its optimal value. The proposed super-twisting control set-up was experimentally assessed to analyse its performance and to verify its efficiency in an actual generation test bench. The results showed a fast convergence to maximum power operation, avoiding chattering and offsets due to model uncertainties"
Hardware in the loop and software in the loop testing of the MOVE-II CubeSat
(2019-12) Kiesbye, Jonis; Messmann, David; Preisinger, Maximiliam; Reina Kiperman, Gonzalo Julián; Nagy, Daniel; Schummer, Florian; Mostad, Martin; Kale, Tejas; Langer, Martin
"This article reports the ongoing work on an environment for hardware-in-the-loop (HIL) and software-in-the-loop (SIL) tests of CubeSats and the benefits gained from using such an environment for low-cost satellite development. The satellite tested for these reported efforts was the MOVE-II CubeSat, developed at the Technical University of Munich since April 2015. The HIL environment has supported the development and verification of MOVE-II’s flight software and continues to aid the MOVE-II mission after its launch on 3 December 2018. The HIL environment allows the satellite to interact with a simulated space environment in real-time during on-ground tests. Simulated models are used to replace the satellite’s sensors and actuators, providing the interaction between the satellite and the HIL simulation. This approach allows for high hardware coverage and requires relatively low development effort and equipment cost compared to other simulation approaches. One key distinction from other simulation environments is the inclusion of the electrical domain of the satellite, which enables accurate power budget verification. The presented results include the verification of MOVE-II’s attitude determination and control algorithms, the verification of the power budget, and the training of the operator team with realistic simulated failures prior to launch. This report additionally presents how the simulation environment was used to analyze issues detected after launch and to verify the performance of new software developed to address the in-flight anomalies prior to software deployment."
A literature review on embedded systems
(2020-02) De Micco, Luciana; Vargas, Fabian; Fierens, Pablo Ignacio
"Embedded system design is crucial for the development of industry, technology, and science, and it is an area that has significantly grown in recent years throughout Latin America, both in academia and in industry. Embedded System (ES) refers to electronic equipment with a computing core which, unlike a personal computer, is designed to meet a specific function and is usually optimized to satisfy strict requirements of processing time, reliability, power consumption, size, and cost. With the advancement of research on the domains of Internet of Things (IoT), Computing Edge (CE) and Cloud Computing (CC) and their endless application possibilities, ESs have gained new roles and assumed unquestionable importance in our daily lives. In this article, we make a brief review of the relevant literature in the area of embedded systems in the Latin America region during recent years."
Guest editorial special issue on embedded systems
(2020-02) De Micco, Luciana; Vargas, Fabian; Fierens, Pablo Ignacio
"La temática de sistemas embebidos (SE) tiene una enorme relevancia debido al gran número de aplicaciones en muy diversas áreas. En los últimos años ha habido un interés especial animado por las áreas emergentes de la Internet de las Cosas (IoT, según la sigla en inglés) y la Industria 4.0."
A non-centralized predictive control strategy for wind farm active power control: a wake-based partitioning approach
(2020-05) Siniscalchi-Minna, Sara; Bianchi, Fernando D.; Ocampo-Martínez, Carlos; Domínguez-García, José Luis; De Schutter, Bart
"Owing to wake effects, the power production of each turbine in a wind farm is highly coupled to the operating conditions of the other turbines. Wind farm control strategies must take into account these couplings and produce individual power commands for each turbine. In this case, centralized control approaches might be prone to failures due to the high computational burden and communication dependency. To overcome this problem, this paper proposes a non-centralized scheme based on splitting the wind farm into almost uncoupled sets of turbines by solving a mixed-integer partitioning problem. In each set of turbines, a model predictive control strategy seeks to optimize the distribution of the power set-points among turbines such that the impact of the power losses due to the wake effect is reduced. Then, a supervisory controller coordinates the generation of each group to satisfy the power demanded by the grid operator. The effectiveness of the proposed control scheme in terms of reduction of computational costs and power regulation is confirmed by simulations for a wind farm of 42 turbines."
Modulation instability in waveguides with an arbitrary frequency-dependent nonlinear coefficient
(2020-05) Linale, N.; Bonetti, Juan I.; Sánchez, Alfredo D.; Hernández, Santiago M.; Fierens, Pablo Ignacio; Grosz, Diego
"In this Letter, we present, for the first time, to the best of our knowledge, the modulation instability (MI) gain spectrum of waveguides with an arbitrary frequency-dependent nonlinear coefficient ensuring strict energy and photon-number conservation of the parametric process. This is achieved by starting from a linear stability analysis of the recently introduced photon-conserving nonlinear Schrödinger equation. The derived MI gain is shown to predict some unique features, such as a nonzero gain extending beyond a zero-nonlinearity wavelength and a complex structure of the MI gain spectrum. Analytical results are shown to be in excellent agreement with numerical simulations."
Fault tolerance analysis for a class of reconfigurable aerial hexarotor vehicles
(2020-08) Pose, Claudio D.; Giribet, Juan I.; Mas, Ignacio
"Several works have addressed the issue of fault tolerance in multirotors in case of a rotor total failure, particularly their ability to keep full independent control of attitude and altitude. It has been proven that to achieve this, a minimum of six rotors is needed. In this work, the performance of several standard and nonstandard hexarotor structures is analyzed, both for a nominal case (without failure) and in the case where one of the actuators is under failure (incapability to exert thrust). The performance is shown in terms of maximum rotational torque and vertical force that the vehicle can exert. The main contribution of this work is the proposal and analysis of converting these vehicles into reconfigurable ones through the addition of a minimum number of servomotors, to deal with failures and to greatly improve the maneuverability under these conditions, in order to identify the reconfigurable structure with the best performance. An experimental demonstration in an outdoor environment is shown for the proposed reconfigurable structure with best performance in case of a full rotor failure."
Multi-UAV specification and control with a single pilot-in-the-loop
(2020-10) Moreno, Patricio; Esteva, Santiago; Mas, Ignacio; Giribet, Juan I.
"This work presents a multi-unmanned aerial vehicle formation implementing a trajectory-following controller based on the clusterspace robot coordination method. The controller is augmented with a feed-forward input from a control station operator. This teleoperation input is generated by means of a remote control, as a simple way of modifying the trajectory or taking over control of the formation during flight. The cluster-space formulation presents a simple specification of the system’s motion and, in this work, the operator benefits from this capability to easily evade obstacles by means of controlling the cluster parameters in real time. The proposed augmented controller is tested in a simulated environment first, and then deployed for outdoor field experiments. Results are shown in different scenarios using a cluster of three autonomous unmanned aerial vehicles."
Training a gaming agent on brainwaves
(2020-12-07) Bartolomé, Francisco; Moreno, Juan; Navas, Natalia; Vitali, José; Ramele, Rodrigo; Santos, Juan Miguel
"Error-related potential (ErrP) are a particular type of Event-Related Potential (ERP) elicited by a person attending a recognizable error. These Electroencephalographic (EEG) signals can be used to train a gaming agent by a Reinforcement Learning (RL) algorithm to learn an optimal policy. The experimental process consists of an observational human critic (OHC) observing a simple game scenario while their brain signals are captured. The game consists of a grid, where a blue spot has to reach a desired target in the fewest amount of steps. Results show that there is an effective transfer of information and that the agent successfully learns to solve the game efficiently, from the initial 97 steps on average required to reach the target to the optimal number of 8 steps. Our results are expressed in threefold: (i) the mechanics of a simple grid-based game that can elicit the ErrP signal component, (ii) the verification that the reward function only penalizes wrong steps, which means that type II error (not properly identifying a wrong movement) does not affect significantly the agent learning process; (iii) collaborative rewards from multiple observational human critics can be used to train the algorithm effectively and can compensate low classification accuracies and a limited scope of transfer learning schemes."
Analysis of the Impact of the monitoring equipment on the common-mode to differential-mode conversion in bulk current injection tests
(2021) Gardella, Pablo; Marini, Eduardo
"In this paper, the common-mode to differential mode conversion in a Bulk Current Injection (BCI) test setup is analyzed in the presence of an optical fiber transmitter. A modular-basis analysis based on S-parameters measurements and Electromagnetic simulations has been performed. It is shown that the loading effects can change the insertion losses from the RF amplifier to the Devices Under Test, even at frequencies as low as 10MHz by 2dB and up to 23dB at worst cases. The study has been undertaken with the substitution and closed-loop methods. Quantification of this problem as well as mitigation strategies are proposed, analyzed and evaluated with the aim of improving the accuracy of BCI simulations at early-design stages. Considering the significant cost of redesigning at an advanced point in the product development cycle, the presented work expects to raise awareness about how even small changes in the BCI setup can remarkably compromise the outcome."
Revisiting soliton dynamics in fiber optics under strict photon-number conservation
(2021) Linale, N.; Fierens, Pablo Ignacio; Grosz, Diego F.
"We revisit the complex interplay between the Raman-induced frequency shift (RIFS) and the effect of selfsteepening (SS) in the propagation of solitons, and in the framework of an equation that ensures strict conservation of the number of photons. The generalized nonlinear Schrödinger equation (GNLSE) is shown to severely fail in preserving the number of photons for sub-100-fs solitons, leading to a large overestimation of the frequency shift. Furthermore, when considering the case of a frequency-dependent nonlinear coefficient, the GNLSE also fails to provide a good estimation of the time shift experienced by the soliton. We tackle these shortcomings of the GNLSE by resorting to the recently introduced photon-conserving GNLSE (pcGNLSE) and study the interplay between the RIFS and selfsteepening. As a result, we make apparent the impact of higherorder nonlinearities on short-soliton propagation and propose an original and direct method for the estimation of the second-order nonlinear coefficient."

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