11,579 research outputs found
Do Complexity Measures of Frontal EEG Distinguish Loss of Consciousness in Geriatric Patients Under Anesthesia?
While geriatric patients have a high likelihood of requiring anesthesia, they carry an increased risk for adverse cognitive outcomes from its use. Previous work suggests this could be mitigated by better intraoperative monitoring using indexes defined by several processed electroencephalogram (EEG) measures. Unfortunately, inconsistencies between patients and anesthetic agents in current analysis techniques have limited the adoption of EEG as standard of care. In attempts to identify new analyses that discriminate clinically-relevant anesthesia timepoints, we tested 1/f frequency scaling as well as measures of complexity from nonlinear dynamics. Specifically, we tested whether analyses that characterize time-delayed embeddings, correlation dimension (CD), phase-space geometric analysis, and multiscale entropy (MSE) capture loss-of-consciousness changes in EEG activity. We performed these analyses on EEG activity collected from a traditionally hard-to-monitor patient population: geriatric patients on beta-adrenergic blockade who were anesthetized using a combination of fentanyl and propofol. We compared these analyses to traditional frequency-derived measures to test how well they discriminated EEG states before and after loss of response to verbal stimuli. We found spectral changes similar to those reported previously during loss of response. We also found significant changes in 1/f frequency scaling. Additionally, we found that our phase-space geometric characterization of time-delayed embeddings showed significant differences before and after loss of response, as did measures of MSE. Our results suggest that our new spectral and complexity measures are capable of capturing subtle differences in EEG activity with anesthesia administration-differences which future work may reveal to improve geriatric patient monitoring
Nonlinear dynamics of a regenerative cutting process
We examine the regenerative cutting process by using a single degree of
freedom non-smooth model with a friction component and a time delay term.
Instead of the standard Lyapunov exponent calculations, we propose a
statistical 0-1 test analysis for chaos detection. This approach reveals the
nature of the cutting process signaling regular or chaotic dynamics. For the
investigated deterministic model we are able to show a transition from chaotic
to regular motion with increasing cutting speed. For two values of time delay
showing the different response the results have been confirmed by the means of
the spectral density and the multiscaled entropy
Self-Assembly of Nanocomponents into Composite Structures: Derivation and Simulation of Langevin Equations
The kinetics of the self-assembly of nanocomponents into a virus,
nanocapsule, or other composite structure is analyzed via a multiscale
approach. The objective is to achieve predictability and to preserve key
atomic-scale features that underlie the formation and stability of the
composite structures. We start with an all-atom description, the Liouville
equation, and the order parameters characterizing nanoscale features of the
system. An equation of Smoluchowski type for the stochastic dynamics of the
order parameters is derived from the Liouville equation via a multiscale
perturbation technique. The self-assembly of composite structures from
nanocomponents with internal atomic structure is analyzed and growth rates are
derived. Applications include the assembly of a viral capsid from capsomers, a
ribosome from its major subunits, and composite materials from fibers and
nanoparticles. Our approach overcomes errors in other coarse-graining methods
which neglect the influence of the nanoscale configuration on the atomistic
fluctuations. We account for the effect of order parameters on the statistics
of the atomistic fluctuations which contribute to the entropic and average
forces driving order parameter evolution. This approach enables an efficient
algorithm for computer simulation of self-assembly, whereas other methods
severely limit the timestep due to the separation of diffusional and complexing
characteristic times. Given that our approach does not require recalibration
with each new application, it provides a way to estimate assembly rates and
thereby facilitate the discovery of self-assembly pathways and kinetic dead-end
structures.Comment: 34 pages, 11 figure
Statistical mechanics characterization of spatio-compositional inhomogeneity
On the basis of a model system of pillars built of unit cubes, a
two-component entropic measure for the multiscale analysis of
spatio-compositional inhomogeneity is proposed. It quantifies the statistical
dissimilarity per cell of the actual configurational macrostate and the
theoretical reference one that maximizes entropy. Two kinds of disorder
compete: i) the spatial one connected with possible positions of pillars inside
a cell (the first component of the measure), ii) the compositional one linked
to compositions of each local sum of their integer heights into a number of
pillars occupying the cell (the second component). As both the number of
pillars and sum of their heights are conserved, the upper limit for a pillar
height hmax occurs. If due to a further constraint there is the more demanding
limit h <= h* < hmax, the exact number of restricted compositions can be then
obtained only through the generating function. However, at least for systems
with exclusively composition degrees of freedom, we show that the neglecting of
the h* is not destructive yet for a nice correlation of the h*-constrained
entropic measure and its less demanding counterpart, which is much easier to
compute. Given examples illustrate a broad applicability of the measure and its
ability to quantify some of the subtleties of a fractional Brownian motion,
time evolution of a quasipattern [28,29] and reconstruction of a laser-speckle
pattern [2], which are hardly to discern or even missed.Comment: 17 pages, 5 figure
Range entropy: A bridge between signal complexity and self-similarity
Approximate entropy (ApEn) and sample entropy (SampEn) are widely used for
temporal complexity analysis of real-world phenomena. However, their
relationship with the Hurst exponent as a measure of self-similarity is not
widely studied. Additionally, ApEn and SampEn are susceptible to signal
amplitude changes. A common practice for addressing this issue is to correct
their input signal amplitude by its standard deviation. In this study, we first
show, using simulations, that ApEn and SampEn are related to the Hurst exponent
in their tolerance r and embedding dimension m parameters. We then propose a
modification to ApEn and SampEn called range entropy or RangeEn. We show that
RangeEn is more robust to nonstationary signal changes, and it has a more
linear relationship with the Hurst exponent, compared to ApEn and SampEn.
RangeEn is bounded in the tolerance r-plane between 0 (maximum entropy) and 1
(minimum entropy) and it has no need for signal amplitude correction. Finally,
we demonstrate the clinical usefulness of signal entropy measures for
characterisation of epileptic EEG data as a real-world example.Comment: This is the revised and published version in Entrop
- …