A comparison among different Hill-type contraction dynamics formulations for muscle force estimation

El músculo es un tipo de tejido capaz de contraerse y, por lo tanto, acortarse, produciendo una fuerza capaz de generar movimiento. El análisis de su actividad es esencial para entender cómo se genera la fuerza para realizar un movimiento y cómo esa fuerza puede ser estimada a partir de las medidas directas o indirectas. El modelo muscular Hill-tipo es uno de los modelos más utilizados para describir el mecanismo de producción de fuerza. Está compuesto por diferentes elementos que describen el comportamiento del músculo contráctil (serie, paralelo y elástica elemento elástico) y el tendón. En este trabajo analizamos las diferencias entre diferentes formulaciones encontradas en la literatura para estos elementos. Para evaluar las diferencias, un flexo-movimiento de extensión del brazo se realiza, utilizando como entrada a los distintos modelos de electromiografía de superficie de la señal grabada y del músculo-tendón longitudes y por las velocidades de contracción obtenida a partir del análisis dinámico inverso. Los resultados muestran que la fuerza predicha por los diferentes modelos es similar y las principales diferencias en la predicción de la fuerza muscular se observaron en la flexión completa. Se espera que los resultados contribuyan a seleccionar las diferentes formulaciones del modelo muscular tipo Hill para resolver un problema específico.Muscle is a type of tissue able to contract and, thus, shorten, producing a pulling force able to generate movement. The analysis of its activity is essential to understand how the force is generated to perform a movement and how that force can be estimated from direct or indirect measurements. Hill-type muscle model is one of the most used models to describe the mechanism of force production. It is composed by different elements that describe the behaviour of the muscle (contractile, series elastic and parallel elastic element) and tendon. In this work we analyze the differences between different formulations found in the literature for these elements. To evaluate the differences, a flexo-extension movement of the arm was performed, using as input to the different models the surface electromyography signal recorded and the muscle-tendon lengths and contraction velocities obtained by means of inverse dynamic analysis. The results show that the force predicted by the different models is similar and the main differences in muscle force prediction were observed at full-flexion. The results are expected to contribute in the selection of the different formulations of Hill-type muscle model to solve a specific problem.• Ministerio de Economía y Competitividad y Fondos FEDER. Proyecto DPI2012-38331-C03 • Unión Europea. Fondos FEDERpeerReviewe

Estimation of muscular forces from SSA smoothed sEMG signals calibrated by inverse dynamics-based physiological static optimization

The estimation of muscular forces is useful in several areas such as biomedical or rehabilitation engineering. As muscular forces cannot be measured in vivo non-invasively they must be estimated by using indirect measurements such as surface electromyography (sEMG) signals or by means of inverse dynamic (ID) analyses. This paper proposes an approach to estimate muscular forces based on both of them. The main idea is to tune a gain matrix so as to compute muscular forces from sEMG signals. To do so, a curve fitting process based on least-squares is carried out. The input is the sEMG signal filtered using singular spectrum analysis technique. The output corresponds to the muscular force estimated by the ID analysis of the recorded task, a dumbbell weightlifting. Once the model parameters are tuned, it is possible to obtain an estimation of muscular forces based on sEMG signal. This procedure might be used to predict muscular forces in vivo outside the space limitations of the gait analysis laboratory.Postprint (published version

Design, control and evaluation of a low-cost active orthosis for the gait of spinal cord injured subjects

Robotic gait training after spinal cord injury is of high priority to maximize independence and improve the living conditions of the patients. Current rehabilitation robots are expensive and heavy, and are generally found only in the clinical environment. To overcome these issues, we present the design of a low-cost, low-weight and personalized robotic orthosis for incomplete spinal cord injured subjects. The paper also presents a preliminary experimental evaluation of the assistive device on one subject with spinal cord injury that can control hip flexion to a certain extent, but lacks control of knee and ankle muscles. Results show that gait velocity, stride length and cadence of walking increased (24,11%, 7,41% and 15,56%, respectively) when wearing active orthoses compared to the case when the subject used the usual passive orthoses.Postprint (published version

Low-cost active orthosis for gait assistance of subjects with spinal cord injury

Postprint (published version

Mechanical discrete simulator of the electro-mechanical lift with n:1 roping

El proceso de diseño de nuevos productos de ingeniería de elevación es una tarea difícil debido, principalmente, a la complejidad y esbeltez del sistema de elevación, exigiendo una herramienta predictiva para la elevación mecánica. Una mecánica ad-hoc simulador discreto, como una alternativa a la "mecánica" de propósito general simuladores está propuesto. En primer lugar, la síntesis y la experimentación, proceso que ha llevado a establecer un modelo adecuado capaz de simular con precisión la respuesta del ascensor electromecánico es discutido. Entonces, las ecuaciones de movimiento se derivan. El modelo consta de un sistema discreto de 5 masas desplazables verticalmente (coche, contrapeso, bastidor del vehículo, los pasajeros/carga y accionamiento de elevación), una masa inercial de la asamblea del eje del rotor de la polea de tensión que puede girar alrededor del eje de la máquina y 6 conectores mecánicos con diseño de suspensión 1:1. El modelo se extiende a cualquier n:1 roping estableciendo 6 equivalente de elevación mecánica (sistemas de suspensión para automóviles y contrapeso, accionamiento de elevación bloques silenciosos, polea tensora-accionamiento de elevación el estator y pasajeros/carga equivalente muelle-amortiguador) por inferencia inductiva de 1:1 y 2:1 generalizado del sistema de soga. La aplicación para simular sistemas elevador real es propuesto por la integración numérica de las ecuaciones que rigen utilizando el algoritmo Kutta-Meden e implementado en un programa informático de simulación de elevador ad-hoc denominada ElevaCAD.The design process of new products in lift engineering is a difficult task due to, mainly, the complexity and slenderness of the lift system, demanding a predictive tool for the lift mechanics. A mechanical ad-hoc discrete simulator, as an alternative to ‘general purpose’ mechanical simulators is proposed. Firstly, the synthesis and experimentation process that has led to establish a suitable model capable of simulating accurately the response of the electromechanical lift is discussed. Then, the equations of motion are derived. The model comprises a discrete system of 5 vertically displaceable masses (car, counterweight, car frame, passengers/loads and lift drive), an inertial mass of the assembly tension pulley-rotor shaft which can rotate about the machine axis and 6 mechanical connectors with 1:1 suspension layout. The model is extended to any n:1 roping lift by setting 6 equivalent mechanical components (suspension systems for car and counterweight, lift drive silent blocks, tension pulley-lift drive stator and passengers/load equivalent spring-damper) by inductive inference from 1:1 and generalized 2:1 roping system. The application to simulate real elevator systems is proposed by numeric time integration of the governing equations using the Kutta-Meden algorithm and implemented in a computer program for ad-hoc elevator simulation called ElevaCAD.peerReviewe

Information and complexity analysis of spatial data

This work was supported by MCIU/AEI/ERDF, EU, Spain grant PGC2018-098860-B-I00, and by grant A-FQM-345-UGR18 cofinanced by the ERDF Operational Programme 2014–2020 and the Economy and Knowledge Council of the Regional Government of Andalusia, Spain .Information Theory provides a fundamental basis for analysis, and for a variety of subsequent methodological approaches, in relation to uncertainty quantification. The transversal character of concepts and derived results justifies its omnipresence in scientific research, in almost every area of knowledge, particularly in Physics, Communications, Geosciences, Life Sciences, etc. Information-theoretic aspects underlie modern developments on complexity and risk. A proper use and exploitation of structural characteristics inherent to spatial data motivates, according to the purpose, special considerations in this context. In this paper, some relevant approaches introduced regarding the informational analysis of spatial data, related aspects concerning complexity analysis, and, in particular, implications in relation to the structural assessment of multifractal point patterns, are reviewed under a conceptually connective evolutionary perspective.MCIU/AEI/ERDF, EU, Spain PGC2018-098860-B-I00ERDF Operational Programme 2014–2020 A-FQM-345-UGR18Regional Government of Andalusia, Spai

Homogeneity and isotropy in the 2MASS Photometric Redshift catalogue

Using the 2MASS Photometric Redshift catalogue we perform a number of statistical tests aimed at detecting possible departures from statistical homogeneity and isotropy in the large-scale structure of the Universe. Making use of the angular homogeneity index, an observable proposed in a previous publication, as well as studying the scaling of the angular clustering and number counts with magnitude limit, we place constraints on the fractal nature of the galaxy distribution. We find that the statistical properties of our sample are in excellent agreement with the standard cosmological model, and that it reaches the homogeneous regime significantly faster than a class of fractal models with dimensions $D<2.75$. As part of our search for systematic effects, we also study the presence of hemispherical asymmetries in our data, finding no significant deviation beyond those allowed by the concordance model.Comment: 18 pages, 13 figures, published in MNRA

Implementation of a Surgery Congress for Medical Students to Learn Transversal Competences. A Case of Student-Led Teaching Activity

Background: A dynamic training approach close to clinical work and research is highly requested by health sciences students. The aim of this paper is to present the organizational model of a student-promoted and student-managed surgical congress that encourages the acquisition of transversal competencies among the students in charge of the organization of the Congress. Methods: A two-day surgical congress for medical students organized by themselves was held. Each day comprised two separate sections corresponding to different surgical specialties; sections included three types of activities: conferences, round tables with guest professors, and practical workshops. Once the Congress had finished, an online survey was carried out to evaluate 10 items scored from 1 to 4. To assess the acquisition of transversal competences among the students organizing the congress, three evaluations were carried out by the professor involved in the organization of the congress. Results: The congress had great acceptance among the students, filling 150 available places with an attendance rate of 100%. The survey showed a high assessment of the subjects (3.48/4), conferences (3.48/4) and workshops (3.27/4). Evaluation of the round tables was significantly lower (2/4). A total of 99% considered the congress to have been useful in its formation process and 100% would recommend it. The grade of transversal competences among the students organizing the congress showed a significant increase between the first and the third evaluation, being between 1.24 and 7.25 times higher. Conclusions: the student-led student surgical congress is a well-evaluated activity for medical students, and promotes, among its organizers, the acquisition of transversal competences.The congress organization was partially supported by the Vice-rectorate of the Biscay Campus, the Student Council of the Faculty of Medicine and Nursing and the Student Council of the University of the Basque Country for their support

One-dimensional Convolutional Neural Networks for Detecting Transiting Exoplanets

The transit method is one of the most relevant exoplanet detection techniques, which consists of detecting periodic eclipses in the light curves of stars. This is not always easy due to the presence of noise in the light curves, which is induced, for example, by the response of a telescope to stellar flux. For this reason, we aimed to develop an artificial neural network model that is able to detect these transits in light curves obtained from different telescopes and surveys. We created artificial light curves with and without transits to try to mimic those expected for the extended mission of the Kepler telescope (K2) in order to train and validate a 1D convolutional neural network model, which was later tested, obtaining an accuracy of 99.02 % and an estimated error (loss function) of 0.03. These results, among others, helped to confirm that the 1D CNN is a good choice for working with non-phased-folded Mandel and Agol light curves with transits. It also reduces the number of light curves that have to be visually inspected to decide if they present transit-like signals and decreases the time needed for analyzing each (with respect to traditional analysis)

Reconfiguration Algorithm to Reduce Power Losses in Offshore HVDC Transmission Lines

The race to increase the efficiency and reduce the power losses in transmission systems has resulted in the substantial growth of high-voltage direct current (HVDC) transmission systems. Moreover, the interconnection of these transmission systems significantly increases their reliability. However, the control of these meshed grids is a key problem that usually is managed through the control of the VSCs in those grids, but the control of the VSC can be complemented with a reconfiguration algorithm. This paper proposes the use of the particle swarm optimization algorithm, in order to reconfigure meshed HVDC transmission systems and reduce losses. The proposed algorithm has been tested in the CIGRE benchmark grid, which comprises of several offshore wind farms that generate energy sent to the grid through several HVDC transmission lines. The results show that as the energy generation changes due to wind changes, the grid topology must be reconfigured in order to achieve the maximum efficiency. Doing this reconfiguration, power savings around 18&#8211;19% could be achieve