201 research outputs found
Schumann's resonances: A particular example of a spherical resonant cavity
No full textThe resonances between the Earth as one boundary and the ionosphere as the other, known as Schumann's resonances, represent an interesting example of a spherical cavity. We consider a simple model in which the boundaries behave as perfect conductors and then take into account the finite conductivity of the boundaries. Numerical results are obtained for both models and compared with available data. Good agreement is shown to exist between the analytical results and the experimental values when finite conductivity of the walls is considered.Fil: Ciappina, Marcelo Fabián. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentin
A finite extensibility nonlinear oscillator
No full textThe dynamics of a finite extensibility nonlinear oscillator (FENO) is studied analytically by means of two different approaches: a generalized decomposition method (GDM) and a linearized harmonic balance procedure (LHB). From both approaches, analytical approximations to the frequency of oscillation and periodic solutions are obtained, which are valid for a large range of amplitudes of oscillation. Within the generalized decomposition method, two different versions are presented, which provide different kinds of approximate analytical solutions. In the first version, it is shown that the truncation of the perturbation solution up to the third order provides a remarkable degree of accuracy for almost the whole range of amplitudes. The second version, which expands the nonlinear term in Taylor's series around the equilibrium point, exhibits a little lower degree of accuracy, but it supplies an infinite series as the approximate solution. On the other hand, a linearized harmonic balance method is also employed, and the comparison between the approximate period and the exact one (numerically calculated) is slightly better than that obtained by both versions of the GDM. In general, the agreement between the results obtained by the three methods and the exact solution (numerically integrated) for amplitudes (A) between 0 < A ≤ 0.9 is very good both for the period and the amplitude of oscillation. For the rest of the amplitude range (0.9 < A < 1), an exponentially large L2 error demonstrates that all three approximations do not represent a good description for the FENO, and higher order perturbation solutions are needed instead. As a complement, very accurate asymptotic representations of the period are provided for the whole range of amplitudes of oscillation. © 2011 Elsevier Inc. All rights reserved.Fil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentin
Harmonic response of a class of finite extensibility nonlinear oscillators
No full textFinite extensibility oscillators are widely used to simulate those systems which can not be extended to infinity. For example, they are used when modelling the bonds between molecules in a polymer or DNA molecule or when simulating filaments of non-Newtonian liquids. In this work, the dynamic behavior of a harmonically driven finite extensibility oscillator is presented and studied. To this end, the harmonic balance method is applied to determine the amplitude-frequency and the amplitude-phase equations. The distinguishable feature in this case is the bending of the amplitude-frequency curve to the frequency axis, making it to approach asymptotically to the limit of maximum elongation of the oscillator, which physically represents the impossibility for the systemto reach this limit. Also, the stability condition which defines stable and unstable steady-states solutions is derived. The study of the effect of the system parameters in the response reveals that a decreasing value of damping coefficient or an increasing value of excitation amplitude leads to the appearance of a multi-valued response and to the existence of a jump phenomenon. In this sense, the critical amplitude of the excitation, which refers to here as a certain value of external excitation that results in the occurrence of jump phenomena, is also derived. Numerical experiments to observe the effects of the system parameters on the frequency-amplitude response are performed to compare them to analytical calculations. For a low value of damping coefficient or a high value of excitation amplitude the agreement is poor for low frequencies but good for high frequencies.It is demonstrated that the disagreement is caused by neglecting the higher-order harmonics in the analytical formulation. These higher-order harmonics, which appear as distinguishable peaks at certain values in the frequency response curves, are possible to calculate considering not the linearized frequency of the oscillator but its actual frequency which is strongly amplitude-dependent. On the other side, for a high value of damping coefficient or a low value of excitation amplitude, the agreement between numerical and analytical calculations is excellent. For these cases, the system is prevented to explore large amplitudes of vibration and, therefore, thenonlinearity is not too much manifested.Fil: Febbo, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin
An upper limb Functional Electrical Stimulation controller based on Reinforcement Learning: A feasibility case study.
No full textControllers for Functional Electrical Stimulation (FES) are still not able to restore natural movements in the paretic arm. In this work, Reinforcement Learning (RL) is used
for the first time to control a hybrid upper limb robotic system for stroke rehabilitation in a real environment. The feasibility of the FES controller is tested on one healthy subject during elbow flex-extension in the horizontal plane. Results showed an absolute position error <1.2° for a maximum range of motion of 50°
Reinforcement Learning Control of Functional Electrical Stimulation of the upper limb: a feasibility study.
No full textControllers for Functional Electrical Stimulation are still not able to produce natural movements of the paretic arm. In this work, Reinforcement Learning was used to design a non-linear controller for a hybrid upper limb robotic system thought for stroke rehabilitation. The performance of the controller was tested on one healthy subject during elbow extensions in the horizontal plane. Experimental results showed an absolute position error <0.7° for a maximum range of motion of 40° and stability against perturbation induced by simulated muscle spasms. Promising results must be confirmed on a broader population
IoT ink pen for ecological monitoring of daily life handwriting
No full textThe analysis of the writing gesture has been successfully investigated in the diagnosis of age-related diseases, but the current technologies and methods still do not allow the ecological daily monitoring of handwriting, mostly because they rely on standardized writing protocols. In this study, we first designed and validated a novel electronic ink pen, equipped with motion and writing force sensing, for the ecological daily-life monitoring of handwriting in uncontrolled environments. We used the pen to acquire writing activities from healthy adults, from which we computed useful handwriting and tremor indicators. We evaluated the reliability of our measurements by computing the intraclass correlation coefficients (ICC) and the minimal detectable changes (MDC). Moderate to excellent reliability were obtained for all the handwriting indicators computed in two different writing tasks. MDC values can be used as reference to discriminate a real change in the handwriting parameters from a measurement error in longitudinal studies. These results pave the way towards the use of the pen for daily life handwriting monitorin
A decision support system for Rey-Osterrieth complex figure evaluation
No full textObjective: The Rey Osterrieth complex figure (ROCF) is one of the most used neuropsychological tests for the assessment of mild cognitive impairment (MCI) and dementia. In the copy test, the patient has to draw a replica of a 18-pattern image and the outcome is a score based on the accuracy of the overall drawing. The standard scoring system however have limitations related to its subjective nature and its inability to evaluate other cognitive domains than constructional abilities. Previous works addressed those problems by proposing tablet-based automated evaluation systems. Even promising, such methods are still far away from clinical validation and translation. In this work, we developed a decision support system (DSS) for the evaluation of the ROCF copy test in the common practice using retrospective information from previously performed drawings. The goal of our system was to support the professionals providing a qualitative judgement for each of the 18 patterns, estimating the most probable diagnosis for the patient, and identifying the main signs associated to the obtained diagnosis. Methods: A total of 250 human evaluated ROCF copies were scanned from 57 healthy subjects, 131 individuals with MCI, and 62 individuals with dementia. The images were pre-processed and analysed using both computer vision and deep learning techniques to assign a qualitative label to the 18 patterns. Then, the 18 labels were used as features in 3 binary (healthy VS MCI, healthy VS dementia, MCI VS dementia) and a 3-class classifications with model explanation (SHAP).Results: Very good to excellent performance were obtained in all the diagnosis classification tasks. Indeed, an accuracy of about 85%, 91%, and 83% was obtained in discriminating healthy subjects from MCI, healthy subjects from dementia and MCI from dementia respectively. An accuracy of 73% was achieved in the 3-class classification. The model explanation showed which patterns are responsible for each prediction and how the importance of some patterns changes according to the severity of the cognitive decline. Significance: The proposed DSS enriches the standard evaluation and interpretation of the ROCF copy test. Being trained with retrospective knowledge, the performance of the DSS can be further enhanced by extending the dataset with existing ROCF copies
WRITING INSTRUMENT, SYSTEM AND METHOD FOR TRANSPARENT MONITORING AND ANALYSIS OF WRITING
No full textThe present invention relates to a writing instrument comprising: - a writing element comprises a writing end configured for depositing a writing materiai on a support; - a plurality of sensors comprising at least: - a force sensor configured to measure a force applied to said writing element, and - a movement sensor configured to measure movement of the instrument in a three- dimensionai space; - a communication unit configured to exchange data with a remote device via a wireless communication channel; - a control unit connected to the plurality of sensors and to the communication unit configured to control said plurality of sensors and said communication unit in order to transmit to the remote device the measures provided of the plurality of sensors in presence of a connection between the communication unit and the remote device, - a memory unit connected to the control unit and configured to store one or more measures of said plurality of sensors, and - a hollow casing
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