College of Science (COS)

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Browsing College of Science (COS) by Department "Academy of Integrated Science"

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    Implications of Noise on Neural Correlates of Consciousness: A Computational Analysis of Stochastic Systems of Mutually Connected Processes
    Kraikivski, Pavel (MDPI, 2021-05-08)
    Random fluctuations in neuronal processes may contribute to variability in perception and increase the information capacity of neuronal networks. Various sources of random processes have been characterized in the nervous system on different levels. However, in the context of neural correlates of consciousness, the robustness of mechanisms of conscious perception against inherent noise in neural dynamical systems is poorly understood. In this paper, a stochastic model is developed to study the implications of noise on dynamical systems that mimic neural correlates of consciousness. We computed power spectral densities and spectral entropy values for dynamical systems that contain a number of mutually connected processes. Interestingly, we found that spectral entropy decreases linearly as the number of processes within the system doubles. Further, power spectral density frequencies shift to higher values as system size increases, revealing an increasing impact of negative feedback loops and regulations on the dynamics of larger systems. Overall, our stochastic modeling and analysis results reveal that large dynamical systems of mutually connected and negatively regulated processes are more robust against inherent noise than small systems.
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    The origin of impedance rise in Ni-Rich positive electrodes for lithium-ion batteries
    Lee, Rung-Chuan; Franklin, Joseph; Tian, Chixia; Nordlund, Dennis; Doeff, Marca M.; Kostecki, Robert (2021-06-30)
    The cycling performance of nickel-rich lithium nickel cobalt manganese oxide (NMC) electrodes in Li-ion batteries (LIBs) partially depends on the control of the kinetics of degradation processes that result in impedance rise. The impedance contribution from surface film formation at the NMC/electrolyte interfaces is highly dependent on the initial chemical composition and the structure of the NMC surfaces. Through comparison of film quantity and electrochemical performance of composite electrodes made of pristine- and surface treated-NMC materials, we are able to demonstrate that a simple surface treatment suppressed the subsequent film formation and reduced impedance rise of the Li/NMC half-cells during cycling. Detailed modelling of factors affecting cell impedance provide further insights to index individual interphase resistance, highlighting the underlying positive effects of the proposed surface treatment, and demonstrating the importance of homogeneous, electronically conducting matrices throughout the composite electrode.
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    Structure-preserving interpolation of bilinear control systems
    Benner, Peter; Gugercin, Serkan; Werner, Steffen W. R. (2021-06)
    In this paper, we extend the structure-preserving interpolatory model reduction framework, originally developed for linear systems, to structured bilinear control systems. Specifically, we give explicit construction formulae for the model reduction bases to satisfy different types of interpolation conditions. First, we establish the analysis for transfer function interpolation for single-input single-output structured bilinear systems. Then, we extend these results to the case of multi-input multi-output structured bilinear systems by matrix interpolation. The effectiveness of our structure-preserving approach is illustrated by means of various numerical examples.