Statistical Analysis of Slow-Drift Responses

1983 ◽  
Vol 105 (3) ◽  
pp. 310-317 ◽  
Author(s):  
C. T. Stansberg
Keyword(s):  
Probability Density ◽  
Low Frequency ◽  
Mathematical Expression ◽  
General System ◽  
Analytical Signal ◽  
Second Order ◽  
Induced Response ◽  
Frequency Spectra ◽  
Slow Drift ◽  
Continuous Frequency

The statistical properties of second-order wave-induced response processes are investigated theoretically. Emphasis is placed on the slow-drift components. The assumed forcing waves are irregular with continuous frequency spectra. A spectral analysis of the response of a general system is made. It is shown that the slow-drift components are closely connected to the complex analytical signal and the Hilbert envelope of the wave elevation. A simple mathematical expression exists for the slow-drift components, based on the complex wave signal and the second-order impulse response of the system. By use of this explicit formula, the theoretical probability functions of slow-drift responses are investigated. The analysis is based on the Kac-Siegert method. A similar approach has earlier been applied to study the sum of both the low-frequency and the high-frequency second-order responses. Final calculations of the probability density functions are in general very complicated, but it can be simplified by the use of a simple idealized model for the second-order transfer function. Probability density curves for a few simple cases are presented.

Second-Order Wave Loads on a LNG Carrier in Multi-Directional Waves

2008 ◽  
Author(s):  
Mathieu Renaud ◽  
Fla´via Rezende ◽  
Olaf Waals ◽  
Xiao-Bo Chen ◽  
Radboud van Dijk
Keyword(s):  
Low Frequency ◽  
Model Tests ◽  
Second Order ◽  
Wave Loads ◽  
Wave Kinematics ◽  
Directional Waves ◽  
Slow Drift ◽  
Wave Directionality ◽  
Offshore Industry ◽  
Cross Waves

Due to the installation of LNG terminals moored in proximity to the coast, the wave kinematics in shallow water and the consequence on the behavior of those terminals have recently became a major concern of the offshore industry. One key issue is the accurate simulation of the low-frequency motions of LNG carriers, specially the surge, for which the vessel presents low damping, in order to perform the design of the mooring system. The present paper focuses on the effect of wave directionality on second-order slow-drift loads and the related response of the vessel. The paper describes results of model tests in regular cross waves — monochromatic but coming from two directions separated by 90 degrees, as well as bichromatic cross waves. The new “middle field” formulation extended to the case of cross waves, is used to compute the wave drift loads and low-frequency Quadratic Transfer Function (QTF). The results are compared with those from the model tests.

Effect of the Second-Order Potential in the Slow-Drift Oscillation of a Floating Structure in Irregular Waves

1986 ◽  
Vol 30 (02) ◽  
pp. 103-122
Author(s):  
J. A. P. Aranha ◽  
C. P. Pesce
Keyword(s):  
Water Depth ◽  
Narrow Band ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Second Order ◽  
Irregular Waves ◽  
Leading Order ◽  
Floating Structure ◽  
Slow Drift ◽  
The Waves

The slow-drift phenomenon is important when the waves are irregular and the sea spectrum has a relatively narrow band. In this paper an expression is derived for the low-frequency force due to the second-order potential. This expression is the leading-order contribution in the wave spectrum bandwidth and can be exactly determined without computing the second-order potential. It is shown that this effect is of importance when the water depth is relatively shallow or the typical wave period relatively long.

Heart Rate Variability, Emotions, and Music

2010 ◽  
Vol 24 (2) ◽  
pp. 112-119 ◽  
Author(s):  
F. Riganello ◽  
A. Candelieri ◽  
M. Quintieri ◽  
G. Dolce
Keyword(s):  
Data Mining ◽  
Heart Rate ◽  
Heart Rate Variability ◽  
Vegetative State ◽  
Low Frequency ◽  
Emotional Reactions ◽  
Heart Beat ◽  
Healthy Controls ◽  
Frequency Spectra ◽  
Emotional Value

The purpose of the study was to identify significant changes in heart rate variability (an emerging descriptor of emotional conditions; HRV) concomitant to complex auditory stimuli with emotional value (music). In healthy controls, traumatic brain injured (TBI) patients, and subjects in the vegetative state (VS) the heart beat was continuously recorded while the subjects were passively listening to each of four music samples of different authorship. The heart rate (parametric and nonparametric) frequency spectra were computed and the spectra descriptors were processed by data-mining procedures. Data-mining sorted the nu_lf (normalized parameter unit of the spectrum low frequency range) as the significant descriptor by which the healthy controls, TBI patients, and VS subjects’ HRV responses to music could be clustered in classes matching those defined by the controls and TBI patients’ subjective reports. These findings promote the potential for HRV to reflect complex emotional stimuli and suggest that residual emotional reactions continue to occur in VS. HRV descriptors and data-mining appear applicable in brain function research in the absence of consciousness.

scholarly journals Rheology of rounded mammalian cells over continuous high-frequencies

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gotthold Fläschner ◽  
Cosmin I. Roman ◽  
Nico Strohmeyer ◽  
David Martinez-Martin ◽  
Daniel J. Müller
Keyword(s):  
High Frequency ◽  
Mammalian Cells ◽  
Mechanical Response ◽  
Cell Mass ◽  
Low Frequency ◽  
Mass Measurements ◽  
High Frequencies ◽  
Polymer Relaxation ◽  
Continuous Frequency ◽  
Rheological Experiments

AbstractUnderstanding the viscoelastic properties of living cells and their relation to cell state and morphology remains challenging. Low-frequency mechanical perturbations have contributed considerably to the understanding, yet higher frequencies promise to elucidate the link between cellular and molecular properties, such as polymer relaxation and monomer reaction kinetics. Here, we introduce an assay, that uses an actuated microcantilever to confine a single, rounded cell on a second microcantilever, which measures the cell mechanical response across a continuous frequency range ≈ 1–40 kHz. Cell mass measurements and optical microscopy are co-implemented. The fast, high-frequency measurements are applied to rheologically monitor cellular stiffening. We find that the rheology of rounded HeLa cells obeys a cytoskeleton-dependent power-law, similar to spread cells. Cell size and viscoelasticity are uncorrelated, which contrasts an assumption based on the Laplace law. Together with the presented theory of mechanical de-embedding, our assay is generally applicable to other rheological experiments.

scholarly journals Analysis of stimulus-related activity in rat auditory cortex using complex spectral coefficients

2013 ◽  
Vol 110 (3) ◽  
pp. 621-639 ◽  
Author(s):  
Bryan M. Krause ◽  
Matthew I. Banks
Keyword(s):  
Low Frequency ◽  
Phase Changes ◽  
Induced Response ◽  
Top Down ◽  
Time Frequency ◽  
State Dependent ◽  
Spectral Coefficients ◽  
The Mean ◽  
Sensory Responses ◽  
Mean Variance

The neural mechanisms of sensory responses recorded from the scalp or cortical surface remain controversial. Evoked vs. induced response components (i.e., changes in mean vs. variance) are associated with bottom-up vs. top-down processing, but trial-by-trial response variability can confound this interpretation. Phase reset of ongoing oscillations has also been postulated to contribute to sensory responses. In this article, we present evidence that responses under passive listening conditions are dominated by variable evoked response components. We measured the mean, variance, and phase of complex time-frequency coefficients of epidurally recorded responses to acoustic stimuli in rats. During the stimulus, changes in mean, variance, and phase tended to co-occur. After the stimulus, there was a small, low-frequency offset response in the mean and modest, prolonged desynchronization in the alpha band. Simulations showed that trial-by-trial variability in the mean can account for most of the variance and phase changes observed during the stimulus. This variability was state dependent, with smallest variability during periods of greatest arousal. Our data suggest that cortical responses to auditory stimuli reflect variable inputs to the cortical network. These analyses suggest that caution should be exercised when interpreting variance and phase changes in terms of top-down cortical processing.

scholarly journals A Low-Power Opamp-Less Second-Order Delta-Sigma Modulator for Bioelectrical Signals in 0.18 µm CMOS

Sensors ◽  
2021 ◽  
Vol 21 (19) ◽  
pp. 6456
Author(s):  
Fernando Cardes ◽  
Nikhita Baladari ◽  
Jihyun Lee ◽  
Andreas Hierlemann
Keyword(s):  
Low Power ◽  
Low Frequency ◽  
Cmos Technology ◽  
Low Noise ◽  
Second Order ◽  
Frequency Noise ◽  
Voltage Controlled Oscillator ◽  
Noise Shaping ◽  
Delta Sigma Modulator ◽  
Delta Sigma

This article reports on a compact and low-power CMOS readout circuit for bioelectrical signals based on a second-order delta-sigma modulator. The converter uses a voltage-controlled, oscillator-based quantizer, achieving second-order noise shaping with a single opamp-less integrator and minimal analog circuitry. A prototype has been implemented using 0.18 μm CMOS technology and includes two different variants of the same modulator topology. The main modulator has been optimized for low-noise, neural-action-potential detection in the 300 Hz–6 kHz band, with an input-referred noise of 5.0 μVrms, and occupies an area of 0.0045 mm2. An alternative configuration features a larger input stage to reduce low-frequency noise, achieving 8.7 μVrms in the 1 Hz–10 kHz band, and occupies an area of 0.006 mm2. The modulator is powered at 1.8 V with an estimated power consumption of 3.5 μW.

scholarly journals In search for the most optimal EEG method: A practical evaluation of a water-based electrode EEG system

2021 ◽  
Vol 5 ◽  
pp. 239821282110536
Author(s):  
Marta Topor ◽  
Bertram Opitz ◽  
Philip J. A. Dean
Keyword(s):  
Signal To Noise Ratio ◽  
Flanker Task ◽  
Low Frequency ◽  
Noise Levels ◽  
Slow Drift ◽  
Practical Evaluation ◽  
Beta Power ◽  
Water Based ◽  
High Beta ◽  
Frequency Power

The study assessed a mobile electroencephalography system with water-based electrodes for its applicability in cognitive and behavioural neuroscience. It was compared to a standard gel-based wired system. Electroencephalography was recorded on two occasions (first with gel-based, then water-based system) as participants completed the flanker task. Technical and practical considerations for the application of the water-based system are reported based on participant and experimenter experiences. Empirical comparisons focused on electroencephalography data noise levels, frequency power across four bands (theta, alpha, low beta and high beta) and event-related components (P300 and ERN). The water-based system registered more noise compared to the gel-based system which resulted in increased loss of data during artefact rejection. Signal-to-noise ratio was significantly lower for the water-based system in the parietal channels which affected the observed parietal beta power. It also led to a shift in topography of the maximal P300 activity from parietal to frontal regions. The water-based system may be prone to slow drift noise which may affect the reliability and consistency of low-frequency band analyses. Practical considerations for the use of water-based electrode electroencephalography systems are provided.

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