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Simulated Activation Patterns of Biological Neurons Cultured onto a Multi-Electrode Array Based on a Modified Izhikevich's Model

Saito J. H., Mari J.-F., Pedrino E., Destro-Filho J. B., Nicoletti M. C.

Fundamenta Informaticae

2013

Vol. 124, nr 1/2

111--132

Recently we have witnessed research efforts into developing real-time hybrid systems implementing interactions between computational models and live tissues, in an attempt to learn more about the functioning of biological neural networks. A fundamental role in the development of such systems is played by Multi-Electrode Array (MEA). In vitro cultures of neurons on MEAs, however, have some drawbacks such as: needing a rigorous adherence to sterile techniques, careful choice and replenishment of media and maintenance of pH, temperature, and osmolarity. An alternative way to study and investigate live tissues which partially circumvent some of the problems with in vitro cultures is by simulating them. This paper describes the proposal of Sim-MEA, a system for modeling and simulating neuron's communications in a MEA-based in vitro culture. Sim-MEA implements a modified Izhikevich model that takes into account both: distances between neurons and distances between microelectrodes and neurons. The system also provides ways of simulating microelectrodes and their recorded signals as well as recovering experimental MEA culture data, from their images. The soundness of the Sim-MEA simulation procedure was empirically evaluated using data from an experimental in vitro cultured hippocampal neurons of Wistar rat embryos. Results from simulations, compared to those of the in vitro experiment, are presented and discussed. The paper also describes a few experiments (varying several parameter values) to illustrate and detail the approach.

Polish day-ahead electricity market prices. Features analysis

Bobinaite V., Juozapaviciene A., Staniewski M., Szczepankowski P.

Rynek Energii

2012

Nr 5

101--111

The goal of this article is to better understand electricity market price formation processes in Poland through an analysis of the features (volatility and spikes) of Polish day-ahead electricity market prices. The following indicators have been calculated to determine electricity market price volatility: the oscillation coefficient; the coefficient of variation; the standard deviation indicator; the daily velocity indicator, which is based on the overall average price; and the daily velocity indicator, which is based on daily average price. Critical values for electricity market price have been calculated to evaluate price spikes. This analysis reveals that Polish electricity market price volatility is moderate. Electricity price spikes have been an observable phenomenon in Polish day-ahead electricity markets, encompassing 3.15% of the time period analysed in Poland.

Artykuł przedstawia wyniki analizy wybranych czynników (cech) kształtujących ceny energii elektrycznej dnia następnego. Ma na celu przybliżenie i lepsze zrozumienie procesów kształtujących ceny rynkowe energii elektrycznej w Polsce. Analizę oparto m.in. na badaniu zmienności cen energii elektrycznej i wyliczono w tym zakresie następujące współczynniki: wahań cen, ich zmienności statystycznej, odchylenia standardowego oraz dziennej szybkości zmiany cen, związanej z porównywaniem ich średnich dziennych wielkości. Wartości krytyczne rynkowej ceny energii elektrycznej zostały obliczone w celu oszacowania wielkości skoków cenowych. Analiza pokazuje, że zmienność cen energii elektrycznej na rynku polskim jest umiarkowana. Zaobserwowane zjawisko skoków cen dnia następnego na rynku energii elektrycznej w Polsce opisuje nieco ponad 3% ogólnej zmiany cen w całym analizowanym okresie.