Eri Ioka

Noise characteristic of the chaotic double loop delta sigma modulator

The chaotic delta sigma modulator is a way to suppress the limit cycle oscillation caused by the input of a null or constant signal. By changing integrator gains, the output sequence becomes chaotic and the noise characteristic of the output is changed. This noise characteristic is an important factor for evaluating the performance of delta sigma modulation. The aim of this study is to analyze the noise characteristic of chaotic double loop delta sigma modulation when the null signal is input. We use a bifurcation diagram and FFT analysis to obtain the parameter dependence of the output state and noise characteristic, respectively. The output status of the chaotic double loop delta sigma modulation can be guessed from a bifurcation diagram with the brute force method. We also investigate the noise characteristic of the output signal of the chaotic modulator with FFT analysis and classify the various noise characteristics by changing the integrator gains of the double loop delta sigma modulator. We use FFT and the bifurcation diagram to classify these noise characteristics into three categories: suppressed tone (affected by the chaos), divergence, and the appearance of the limit cycle oscillation. We also confirm the existence of an unusual noise-shaping characteristic caused by the intermittent chaos.

Generation Mechanism of Alternans in Luo–Rudy Model

Electrical alternans is the alternating amplitude from beat to beat in the action potential of the cardiac cell. It has been associated with ventricular arrhythmias in many clinical studies; however, its dynamical mechanisms remain unknown. The reason is that we do not have realistic network models of the heart system. Recently, Yazawa clarified the network structure of the heart and the central nerve system in the crustacean heart. In this study, we construct a simple model of the heart system based on Yazawa’s experimental data. Using this model, we clarify that two parameters (the conductance of sodium ions and free concentration of potassium ions in the extracellular compartment) play the key roles of generating alternans. In particular, we clarify that the inactivation gate of the time-independent potassium channel is the most important parameter. Moreover, interaction between the membrane potential and potassium ionic currents is significant for generating alternate rhythms. This result indicates th...

Bifurcation in mutually coupled three neurons with inhibitory synapses

We investigate a system of mutually coupled three neurons in a line with the inhibitory synapses as a basic motif of complex networks. For class I and class II neurons, bifurcation structure is analyzed when we change the external DC current of a middle neuron. In both classes, the neurons have a wide parameter region in which stable 1∶2 cluster synchronous firing is observed as the external DC current of a middle neuron becomes larger than that of outer neurons. For only class I neurons, we observe the stable non-in-phase synchronous firing between three neurons.