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Detecting K-Complexes in Brain Signals Using WSST2-DETOKS
Published in Mridu Sahu, G. R. Sinha, Brain and Behavior Computing, 2021
Zahra Ghanbari, Mohammad Hassan Moradi
K-complex is one of the most underlying micro-events in the sleep EEG, which was introduced around 80 years ago. It is known as the largest grapho-element in the EEG signal. K-complex, according to the American Academy of Sleep Medicine (AASM) is a “well delineated negative sharp wave immediately followed by a positive component standing out from the background EEG, with total duration ≥500 ms, usually maximal in amplitude over the frontal regions” [8]. A duration of 500 ms to 1,500 ms is usually considered for K-complex patterns. However, a maximum duration of 1,000 ms to 3,000 ms is imposed for it. The K-complex pattern has a crucial role in scoring sleep stages. Moreover, it has a sleep protection role; i.e., preventing brain form awaking in response to sensory inputs recognized harmless, while sleeping. In addition, K-complex serves as a predecessor of the slow wave activity which has a reactive homeostatic function in the brain. From a practical perspective, K-complex is important in studying the functional role of sleep as well as diagnosing sleep disorders. In addition, K-complex alongside sleep spindle are hallmarks in the second stage of the nonrapid eye movement (NREM) sleep [9,10]. Therefore, precise identification of K-complexes is essential for reliable projection of the sleep macrostructure and then for the analysis of sleep quality.
Neurophysiology of the Human Scalp EEG
Published in Kaushik Majumdar, A Brief Survey of Quantitative EEG, 2017
Delta band EEG is known to be a low-frequency, high-amplitude wave, which among others is associated with slow wave sleep (SWS). SWS in turn is associated with declarative memory consolidation (Marshall et al., 2006). Declarative memory is the memory of events in one’s life. This indicates that delta wave may have implication in memory consolidation. In the adult brain, delta activity is originated in the frontal cortex, hippocampus, and thalamus. Delta EEG is important in sleep research because it is associated with the deepest stage of sleep known as nonrapid eye movement (NREM) sleep. K-complex is a distinctive pattern of sleep EEG, which precedes delta waves.
Assessment of subgrid scale mixing models used in LES at high pressures
Published in Journal of Turbulence, 2018
Neelakantan Padmanabhan, Richard S. Miller
where A represents the amplitude of forcing signal which is chosen to be a value between 0.001 and 0.002 (larger amplitudes cause production of stronger numerical waves that corrupt the flow, while perturbations with smaller amplitudes get dampened quickly) and f represents the most unstable frequency which determines the distance away from the inlet at which flow transition takes place. Based on a number of simulations performed, a value of f between 0.25 and 0.4 is chosen such that the distance of flow transition is less than from the inlet. However, these perturbation frequencies work only for velocities (). For flows with different velocities, the most unstable frequency may be determined from linear stability analysis [18]. The circular spatial forcing term induces three dimensional spatial instability. Instability in spatial flows is induced when the wave number is complex and wave frequency is real (, with k -- complex, ω -- real). Since the boundaries in the spanwise directions are periodic, a forcing method without θ does not induce cascading. The flow evolution and the flow statistics measured from the DNS are presented in Section 4.1