A Mean-Field Method for Generic Conductance-Based Integrate-and-Fire Neurons with Finite Timescales

The construction of transfer functions in theoretical neuroscience plays an important role in determining the spiking rate behavior of neurons in networks. These functions can be obtained through various fitting methods, but the biological relevance of the parameters is not always clear. However, for stationary inputs, such functions can be obtained without the adjustment of free parameters by using mean-field methods. In this work, we expand current Fokker-Planck approaches to account for the concurrent influence of colored and multiplicative noise terms on generic conductance-based integrate-and-fire neurons. We reduce the resulting stochastic system from the application of the diffusion approximation to a one-dimensional Langevin equation. An effective Fokker-Planck is then constructed using Fox Theory, which is solved numerically to obtain the transfer function. The solution is capable of reproducing the transfer function behavior of simulated neurons across a wide range of parameters. The method can also be easily extended to account for different sources of noise with various multiplicative terms, and it can be used in other types of problems in principle.Comment: 11 pages, 6 figures, research articl

Integración temporal explícita con grandes pasos de tiempo de la ecuación de transmisión del calor

We present a novel fully explicit time integration method that remains stable for large time steps, requires neither matrix inversions nor solving a system of equations and therefore allows for nearly effort-less parallelization. In this first paper the proposed approach is applied to solve conduction heat transfer problems, showing that it is stable for any time step as is the case with implicit methods but with a much lower computation time.We present a novel fully explicit time integration method that remains stable for large time steps, requires neither matrix inversions nor solving a system of equations and therefore allows for nearly effort-less parallelization. In this first paper the proposed approach is applied to solve conduction heat transfer problems, showing that it is stable for any time step as is the case with implicit methods but with a much lower computation time.Fil: Becker, Pablo Javier. Universitat Politècnica de Catalunya; EspañaFil: Nigro, Norberto Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Idelsohn, Sergio Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin

Classificação e caracterização das dinâmicas em redes neuronais recorrentes quando o balanço excitatório-inibitório é alterado

Redes neuronais são capazes de exibir uma grande variedade de comportamentos dinâmicos, os quais costumam ser classificados com base nos seus níveis de sincronia e regularidade de disparos. Acredita-se que o tipo de dinâmica exibido por essas redes seja resultado do balanço entre as correntes excitatórias e inibitórias em cada neurônio, de modo que disparos sejam frutos da média e das flutuações temporais dessas correntes. Nesse processo, a inibição desempenha um importante papel, controlando a excitação que advém das conexões internas e da entrada externa. Dessa forma, a relação entre as conexões excitatórias e inibitórias em ambas as direções se torna importante. Outro fator de possível relevância é a escala de tempo das correntes excitatórias, as quais podem ser moduladas pela proporção de canais AMPA e NMDA. Nesse trabalho, buscamos caracterizar os diferentes tipos de dinâmicas exibidos frente à alteração no acoplamento entre as populações excitatória e inibitória, bem como modificações na proporção de canais AMPA e NMDA. Observamos a maior relevância das conexões excitatória-inibitória na determinação do regime dinâmico em que a rede opera. Entretanto, esse efeito tende a diminuir à medida que introduzimos canais NMDA em neurônios inibitórios, de modo que a excitação nesses neurônios tornase menos precisa. As redes foram capazes de exibir uma grande riqueza de dinâmicas, sendo que as transições entre estados tornam-se possíveis pela simples alteração de alguns parâmetros da rede, o que pode ser alcançado fisiologicamente por mecanismos plásticos celulares.Neuronal networks are capable of exhibiting a great variety of behaviors which are typically classified on the basis of the synchrony and regularity of their spikes. It is believed that the type of dynamics exhibited by these networks are the result of the balance between the excitatory and inhibitory currents in the neurons so that spikes are the results of the average and the temporal fluctuations of these currents. In this process, the inhibition plays an important role, controlling the excitation that comes from the internal connections and the external input. In this way, the relation between the inhibitory and excitatory connections in both directions become important. Another factor of possible relevance is the time scale of the excitatory currents, which can be modulated by the AMPA and NMDA channels proportion. Here we aimed to characterize the different types of dynamics exhibited by the change in the coupling between de excitatory and inhibitory populations, as well as modifications in proportions of the AMPA and NMDA channels. We observed higher importance of the excitatory-inhibitory connections in determining the dynamical regime in which the network operates. However, this effect tends to decrease as we introduce NMDA channels in the inhibitory neurons so that the excitation in these neurons becomes less accurate. The networks were able to display a great wealth of dynamics, such that the transitions between states become possible by the simple alteration of some parameters of the network, which can be attained physiologically by cell plasticity mechanisms

Projeto eletromagnético ótimo de gerador síncrono de imãs permanentes para aplicações com dispositivos com ondas de mar

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2016.Este trabalho apresenta o dimensionamento elétrico e magnético de um gerador síncrono de ímãs permanentes de fluxo magnético radial que será acoplado em um dispositivo de conversão eletromecânica de energia, cuja energia primária é proveniente do movimento das ondas do mar. Primeiramente, calcula-se a geometria do rotor e do estator a partir de especificações das induções magnéticas, da tensão tangencial do rotor, da densidade máxima de corrente nos enrolamentos, e das características elétricas do gerador na condição nominal. Em seguida, aplica-se uma técnica de otimização a fim de maximizar a potência transferida no entreferro considerando como restrição o valor máximo de densidade linear de corrente do gerador na condição nominal. A otimização permite redimensionar a geometria do estator e diminuir a massa de aço elétrico utilizado, reduzindo assim o custo do gerador. Com a geometria e os materiais definidos, realiza-se a modelagem do gerador usando o método de elementos finitos para verificar se as grandezas como induções magnéticas, força eletromotriz induzida (em vazio), tensões elétricas (com carga), e torque eletromagnético atendem as especificações do projeto. Analisando os resultados das simulações, conclui-se que as induções da máquina estão em faixas de operação aceitáveis e que não há saturação magnética no gerador na condição nominal, e que as condições de potência e torque especificadas são atendidas.Abstract : This work presents the electric and magnetic sizing of a permanent magnet synchronous generator of radial flux, which will operate coupled to an electromechanical device for energy conversion whose primary source of power are sea waves. Initially, the rotor and stator geometry is calculated based on specifications of magnetic induction, rotor tangential tension, maximum current density on windings and electrical characteristics of the generator at rated condition. Then, an optimization technique is employed to maximize the air-gap power, considering as a restriction the maximum value of current linear density of the generator at rated condition. The optimization process allows the adjustment of the stator geometry in order to reduce the weight of the magnetic core, thus reducing the cost of the generator. Once the geometry and the materials are defined, the generator is modeled through the finite element method in order to verify if the values of magnetic induction, induced voltage at no load condition, voltage under load and electromagnetic torque meet the project specifications. From the analysis of the simulation results it is concluded that the values of magnetic induction stand within acceptable operating ranges without magnetic saturation and that the specified power and torque conditions are met

2D laser-based probabilistic motion tracking in urban-like environments

All over the world traffic injuries and fatality rates are increasing every year. The combination of negligent and imprudent drivers, adverse road and weather conditions produces tragic results with dramatic loss of life. In this scenario, the use of mobile robotics technology onboard vehicles could reduce casualties. Obstacle motion tracking is an essential ability for car-like mobile robots. However, this task is not trivial in urban environments where a great quantity and variety of obstacles may induce the vehicle to take erroneous decisions. Unfortunately, obstacles close to its sensors frequently cause blind zones behind them where other obstacles could be hidden. In this situation, the robot may lose vital information about these obstructed obstacles that can provoke collisions. In order to overcome this problem, an obstacle motion tracking module based only on 2D laser scan data was developed. Its main parts consist of obstacle detection, obstacle classification, and obstacle tracking algorithms. A motion detection module using scan matching was developed aiming to improve the data quality for navigation purposes; a probabilistic grid representation of the environment was also implemented. The research was initially conducted using a MatLab simulator that reproduces a simple 2D urban-like environment. Then the algorithms were validated using data samplings in real urban environments. On average, the results proved the usefulness of considering obstacle paths and velocities while navigating at reasonable computational costs. This, undoubtedly, will allow future controllers to obtain a better performance in highly dynamic environments.Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES