5,745 research outputs found
Multimodal oscillations in systems with strong contraction
One- and two-parameter families of flows in near an Andronov-Hopf
bifurcation (AHB) are investigated in this work. We identify conditions on the
global vector field, which yield a rich family of multimodal orbits passing
close to a weakly unstable saddle-focus and perform a detailed asymptotic
analysis of the trajectories in the vicinity of the saddle-focus. Our analysis
covers both cases of sub- and supercritical AHB. For the supercritical case, we
find that the periodic orbits born from the AHB are bimodal when viewed in the
frame of coordinates generated by the linearization about the bifurcating
equilibrium. If the AHB is subcritical, it is accompanied by the appearance of
multimodal orbits, which consist of long series of nearly harmonic oscillations
separated by large amplitude spikes. We analyze the dependence of the
interspike intervals (which can be extremely long) on the control parameters.
In particular, we show that the interspike intervals grow logarithmically as
the boundary between regions of sub- and supercritical AHB is approached in the
parameter space. We also identify a window of complex and possibly chaotic
oscillations near the boundary between the regions of sub- and supercritical
AHB and explain the mechanism generating these oscillations. This work is
motivated by the numerical results for a finite-dimensional approximation of a
free boundary problem modeling solid fuel combustion
Excitable Dynamics in the Presence of Time Delay
The spiking properties of a subcritical Hopf oscillator with a time delayed
nonlinear feedback is investigated. Finite time delay is found to significantly
affect both the statistics and the fine structure of the spiking behavior.
These dynamical changes are explained in terms of the fundamental modifications
occurring in the bifurcation scenario of the system. Our mathematical model can
find useful applications in understanding the dynamical behaviour of various
real life excitable systems where propagation delay effects are ubiquitous.Comment: 10 pages including 7 figure
Tensor Analysis and Fusion of Multimodal Brain Images
Current high-throughput data acquisition technologies probe dynamical systems
with different imaging modalities, generating massive data sets at different
spatial and temporal resolutions posing challenging problems in multimodal data
fusion. A case in point is the attempt to parse out the brain structures and
networks that underpin human cognitive processes by analysis of different
neuroimaging modalities (functional MRI, EEG, NIRS etc.). We emphasize that the
multimodal, multi-scale nature of neuroimaging data is well reflected by a
multi-way (tensor) structure where the underlying processes can be summarized
by a relatively small number of components or "atoms". We introduce
Markov-Penrose diagrams - an integration of Bayesian DAG and tensor network
notation in order to analyze these models. These diagrams not only clarify
matrix and tensor EEG and fMRI time/frequency analysis and inverse problems,
but also help understand multimodal fusion via Multiway Partial Least Squares
and Coupled Matrix-Tensor Factorization. We show here, for the first time, that
Granger causal analysis of brain networks is a tensor regression problem, thus
allowing the atomic decomposition of brain networks. Analysis of EEG and fMRI
recordings shows the potential of the methods and suggests their use in other
scientific domains.Comment: 23 pages, 15 figures, submitted to Proceedings of the IEE
Optimal set of EEG features for emotional state classification and trajectory visualization in Parkinson's disease
In addition to classic motor signs and symptoms, individuals with Parkinson's disease (PD) are characterized by emotional deficits. Ongoing brain activity can be recorded by electroencephalograph (EEG) to discover the links between emotional states and brain activity. This study utilized machine-learning algorithms to categorize emotional states in PD patients compared with healthy controls (HC) using EEG. Twenty non-demented PD patients and 20 healthy age-, gender-, and education level-matched controls viewed happiness, sadness, fear, anger, surprise, and disgust emotional stimuli while fourteen-channel EEG was being recorded. Multimodal stimulus (combination of audio and visual) was used to evoke the emotions. To classify the EEG-based emotional states and visualize the changes of emotional states over time, this paper compares four kinds of EEG features for emotional state classification and proposes an approach to track the trajectory of emotion changes with manifold learning. From the experimental results using our EEG data set, we found that (a) bispectrum feature is superior to other three kinds of features, namely power spectrum, wavelet packet and nonlinear dynamical analysis; (b) higher frequency bands (alpha, beta and gamma) play a more important role in emotion activities than lower frequency bands (delta and theta) in both groups and; (c) the trajectory of emotion changes can be visualized by reducing subject-independent features with manifold learning. This provides a promising way of implementing visualization of patient's emotional state in real time and leads to a practical system for noninvasive assessment of the emotional impairments associated with neurological disorders
The Hunt for Exomoons with Kepler (HEK): I. Description of a New Observational Project
Two decades ago, empirical evidence concerning the existence and frequency of
planets around stars, other than our own, was absent. Since this time, the
detection of extrasolar planets from Jupiter-sized to most recently Earth-sized
worlds has blossomed and we are finally able to shed light on the plurality of
Earth-like, habitable planets in the cosmos. Extrasolar moons may also be
frequent habitable worlds but their detection or even systematic pursuit
remains lacking in the current literature. Here, we present a description of
the first systematic search for extrasolar moons as part of a new observational
project called "The Hunt for Exomoons with Kepler" (HEK). The HEK project
distills the entire list of known transiting planet candidates found by Kepler
(2326 at the time of writing) down to the most promising candidates for hosting
a moon. Selected targets are fitted using a multimodal nested sampling
algorithm coupled with a planet-with-moon light curve modelling routine. By
comparing the Bayesian evidence of a planet-only model to that of a
planet-with-moon, the detection process is handled in a Bayesian framework. In
the case of null detections, upper limits derived from posteriors marginalised
over the entire prior volume will be provided to inform the frequency of large
moons around viable planetary hosts, eta-moon. After discussing our
methodologies for target selection, modelling, fitting and vetting, we provide
two example analyses.Comment: 21 pages, 8 figures, 4 tables, accepted in Ap
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