On the critical forcing amplitude of forced nonlinear oscillators

© Versita sp. z o.o. The steady-state response of forced single degree-of-freedom weakly nonlinear oscillators under primary resonance conditions can exhibit saddle-node bifurcations, jump and hysteresis phenomena, if the amplitude of the excitation exceeds a certain value. This critical value of excitation amplitude or critical forcing amplitude plays an important role in determining the occurrence of saddle-node bifurcations in the frequency-response curve. This work develops an alternative method to determine the critical forcing amplitude for single degree-of-freedom nonlinear oscillators. Based on Lagrange multipliers approach, the proposed method considers the calculation of the critical forcing amplitude as an optimization problem with constraints that are imposed by the existence of locations of vertical tangency. In comparison with the Gröbner basis method, the proposed approach is more straightforward and thus easy to apply for finding the critical forcing amplitude both analytically and numerically. Three examples are given to confirm the validity of the theoretical predictions. The first two present the analytical form for the critical forcing amplitude and the third one is an example of a numerically computed solution

Clinical and biochemical response to neridronate treatment in a patient with osteoporosis-pseudoglioma syndrome (OPPG)

Osteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive syndrome characterized by juvenile-onset osteoporosis and ocular abnormalities due to a low-density lipoprotein receptor-related protein 5 (LRP5) gene mutation. Treatment with bisphosphonates, particularly with pamidronate and risedronate, has been reported to be of some efficacy in this condition. We report on a patient with OPPG due to an LRP5 gene mutation, who showed an encouraging response after a 36-month period of neridronate therapy. We report a case of a patient treated with bisphosphonates. Bisphosphonates should be administered in OPPG patients as a first-line therapy during early childhood

An upper limb Functional Electrical Stimulation controller based on Reinforcement Learning: A feasibility case study.

Controllers 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°

Effects of stimulant drugs on self-control choices in pigeons : determining behavioral mechanisms of drug action

The present study attempted to identify behavioral mechanisms of stimulant effects on “self-control” choices in pigeons. The experimental procedure required pigeons to respond on a single random interval (RI) 1 min schedule in order to choose between a smaller, more immediate reinforcer (1 s food after 2 s delay) and a larger, more delayed reinforcer (4 s food after 2 to 40 s delay). While the signaled delay to the smaller option remained 2 s throughout the session, the signaled delay associated with the larger option increased across five, 10 min blocks from 2 s to 40 s. In this way delay-discount functions were obtained within each experimental session. Once stable delay-discount functions were obtained, methylphenidate (MPD) (0.0 – 17.0 mg/kg) and methamphetamine (METH) (0.0 – 3.0 mg/kg) were administered via i.m. injections. Using a logarithmic variation of Herrnstein’s matching law, an attempt was made to separate changes in the sensitivity to delay (SD) from changes in the sensitivity to amount (SA). Overall, MPD and METH increased choices of the larger, more delayed reinforcer. Moreover, MPD’s and METH’s primary effects were a decrease in SD, although concomitant decreases in SA occasionally occurred. It is concluded that quantitative methods such as those used here may prove useful in elucidating behavioral mechanisms of drug action

A decision support system for Rey-Osterrieth complex figure evaluation

Objective: 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

Local attitudes toward Apennine brown bears: Insights for conservation issues

Human-carnivore coexistence is a multi-faceted issue that requires an understanding of the diverse attitudes and perspectives of the communities living with large carnivores. To inform initiatives that encourage behaviors in line with conservation goals, we focused on assessing the two components of attitudes (i.e., feelings and beliefs), as well as norms of local communities coexisting with Apennine brown bears (Ursus arctos marsicanus) for a long time. This bear population is under serious extinction risks due to its persistently small population size, which is currently confined to the long-established protected area of Abruzzo, Lazio and Molise National Park (PNALM) and its surrounding region in central Italy. We interviewed 1,611 residents in the PNALM to determine attitudes and values toward bears. We found that support for the bear's legal protection was widespread throughout the area, though beliefs about the benefits of conserving bears varied across geographic administrative districts. Our results showed that residents across our study areas liked bears. At the same time, areas that received more benefits from tourism were more strongly associated with positive feelings toward bears. Such findings provide useful information to improve communication efforts of conservation authorities with local communities

Formulación de elementos finitos para modelar dispositivos recolectores de energía rotantes

Los dispositivos recolectores de energía piezoeléctricos convierten la energía mecánica en energía eléctrica debido a las deformaciones mecánicas de las estructuras. Los prototipos de recolección de energía se utilizan para alimentar dispositivos y sensores electrónicos de baja potencia. En este trabajo, se desarrolla un elemento finito unidimensional para el modelado de recolectores de energía tridimensionales rotantes. La viga piezoeléctrica rotante se formula mediante un elemento finito geométricamente no lineal con seis grados de libertad mecánicos y un grado de libertad eléctrico por nodo. Utilizando la teoría de viga de Timoshenko para el dominio mecánico y una teoría de primer orden para el campo eléctrico, las ecuaciones de equilibrio electromecánico se derivan usando el principio D'Alembert. Con el fin de validar la formulación de elementos finitos, se construyen y ensayan dos dispositivos de recolección de energía, obteniéndose información sobre la generación de energía eléctrica, las frecuencias naturales y las respuestas temporales de las variables dinámicas. Una placa Arduino se implementa como sistema de adquisición de datos que transfiere la señal de voltaje a través de Bluetooth. Finalmente, los resultados de nuestra formulación se comparan con los obtenidos utilizando un software comercial (Abaqus) y los resultados experimentales. Se obtiene una buena correlación entre los tres métodos, proporcionando evidencia de que la formulación propuesta predice con precisión el comportamiento de los recolectores de energía rotantes.Publicado en: Mecánica Computacional vol. XXXV, no. 25Facultad de Ingenierí

Aplicación de un recolector de energía piezoeléctrico en un sistema giratorio

En este trabajo se presenta un recolector de energía piezoeléctrico de baja frecuencia para ser aplicado en sistemas rotativos. En especial, el propósito del recolector es la provisión de energía de un sistema de monitoreo inalámbrico para un aerogenerador de 30 KW que gira entre 50 y 150 rpm, bajo diferentes condiciones de viento. El prototipo mecánico consiste en dos vigas flexibles con masas ubicadas en sus extremos con el fin de incrementar su deformación y unidas por medio de un resorte. Además, se incorpora un límite elástico de desplazamiento con el fin de evitar grandes deformaciones. La transformación de energía mecánica en eléctrica se realiza mediante una lámina piezoeléctrica comercial PZT-5H que es adherida a una de las vigas. La fuerza de excitación del prototipo se debe a la fuerza gravitatoria que actúa principalmente sobre las masas. Por lo tanto se alcanza un movimiento oscilatorio sostenido en las vigas flexibles siempre que haya un movimiento rotativo. Con el objetivo de recuperar el mayor porcentaje de la energía de rotación el prototipo mecánico es diseñado a partir de la modificación de sus parámetros físicos y geométricos. Para ello, se realiza un estudio analítico exhaustivo del movimiento rotatorio que evidencia la influencia de las fuerzas centrifuga y gravitacional a medida que aumenta la velocidad de rotación. Asimismo, se derivan las ecuaciones gobernantes que predicen la dinámica y la potencia de salida. De los resultados obtenidos, es posible expresar que las predicciones analíticas concuerdan en buena medida con los experimentos. En cuanto a la generación de energía, el voltaje obtenido es aceptable para el rango esperado. Esto permite concluir que el sistema propuesto es apto para generar energía en un entorno giratorio de baja frecuencia.Publicado en: Mecánica Computacional vol. XXXV, no. 28.Facultad de Ingenierí

Reinforcement Learning Control of Functional Electrical Stimulation of the upper limb: a feasibility study.

Controllers 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

Dynamics of a stretched nonlinear polymer chain

We study the relaxation dynamics of a coarse-grained polymer chain at different degrees of stretching by both analytical means and numerical simulations. The macromolecule is modelled as a string of beads, connected by anharmonic springs, subject to a tensile force applied at the end monomer of the chain while the other end is fixed at the origin of coordinates. The impact of bond non-linearity on the relaxation dynamics of the polymer at different degrees of stretching is treated analytically within the Gaussian self-consistent approach (GSC) and then compared to simulation results derived from two different methods: Monte-Carlo (MC) and Molecular Dynamics (MD). At low and medium degrees of chain elongation we find good agreement between GSC predictions and the Monte-Carlo simulations. However, for strongly stretched chains the MD method, which takes into account inertial effects, reveals two important aspects of the nonlinear interaction between monomers: (i) a coupling and energy transfer between the damped, oscillatory normal modes of the chain, and (ii) the appearance of non-vanishing contributions of a continuum of frequencies around the characteristic modes in the power spectrum of the normal mode correlation functions.Comment: 17 pages, 9 figure