nonlinear
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elektronický časopis
- MeSH
- optika a fotonika MeSH
- Konspekt
- Fyzika
- NLK Obory
- fyzika, biofyzika
- NLK Publikační typ
- elektronické časopisy
Předmětem článkuje nelineární robustní 3D filtrace MR obrazu, která umožňuje realizaci vysokého prostorového rozlišení při zachování únosné míry šumu. Důraz je kladen na rozdílné vlastnosti 2D a 3D filtrů a na rozdíl mezi lineárními a nelineániími robustními technikami filtrace. Základní pojmy jsou vysvětleny v matematicky odlehčené podobě a postupy nelineární filtrace jsou dokumentovány na číselných příkladech. Rozdíly mezi jednotlivými metodami jsou zobrazeny v grafické formě. Software pro nelineární filtraci 3D MR obrazů je realizován v prostředí Matlab a zahrnuje čtení souborů podle normy Interfile, vlastní numerické výpočty, grafickou prezentaci a archivaci výsledků.
Nonlinear robust 3D filtering of MR image is a subject of the paper. It enables to realize high space resolution with guaranteed acceptable level of noise. Different properties of 2D and 3D filters plus the difference between linear and nonlinear robust techniques are pointed. Basic terms are explained in simple and „light" mathematical form and the procedures of nonlinear filtering are explained on numerical examples. The method differences are depicted using graphical form. The software for nonlinear filtering of 3D MR images is realized in Matlab environment including Interfile reading, numeric calculations, graphical presentation and result archivation.
We extended the linearized model of electromigration, which is used by PeakMaster, by calculation of nonlinear dispersion and diffusion of zones. The model results in the continuity equation for the shape function ϕ(x,t) of the zone: ϕ(t) = -(v(0) + v(EMD) ϕ)ϕ(x) + δϕ(xx) that contains linear (v(0)) and nonlinear migration (v(EMD)), diffusion (δ), and subscripts x and t stand for partial derivatives. It is valid for both analyte and system zones, and we present equations how to calculate characteristic zone parameters. We solved the continuity equation by Hopf-Cole transformation and applied it for two different initial conditions-the Dirac function resulting in the Haarhoff-van der Linde (HVL) function and the rectangular pulse function, which resulted in a function that we denote as the HVLR function. The nonlinear model was implemented in PeakMaster 5.3, which uses the HVLR function to predict the electropherogram for a given background electrolyte and a composition of the sample. HVLR function also enables to draw electropherograms with significantly wide injection zones, which was not possible before. The nonlinear model was tested by a comparison with a simulation by Simul 5, which solves the complete nonlinear model of electromigration numerically.
1st ed. x, 654 s., grafy
elektronický časopis
- Konspekt
- Psychologie
- NLK Obory
- psychologie, klinická psychologie
- biologie
- NLK Publikační typ
- elektronické časopisy
Oscillatory phenomena in the brain activity and their synchronization are frequently studied using mathematical models and analytic tools derived from nonlinear dynamics. In many experimental situations, however, neural signals have a broadband character and if oscillatory activity is present, its dynamical origin is unknown. To cope with these problems, a framework for detecting nonlinear oscillatory activity in broadband time series is presented. First, a narrow-band oscillatory mode is extracted from a broadband background. Second, it is tested whether the extracted mode is significantly different from linearly filtered noise, modelled as a linear stochastic process possibly passed through a static nonlinear transformation. If a nonlinear oscillatory mode is positively detected, further analysis using nonlinear approaches such as the phase synchronization analysis can potentially bring new information. For linear processes, however, standard approaches such as the coherence analysis are more appropriate and provide sufficient description of underlying interactions with smaller computational effort. The method is illustrated in a numerical example and applied to analyze experimentally obtained human EEG time series from a sleeping subject.
- MeSH
- biologické hodiny fyziologie MeSH
- časové faktory MeSH
- elektroencefalografie metody MeSH
- lidé MeSH
- modely neurologické MeSH
- mozek fyziologie MeSH
- nelineární dynamika MeSH
- počítačové zpracování signálu MeSH
- spánek fyziologie MeSH
- spektrální analýza MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
We study effects of oscillatory convective flow in extracellular space on the velocity of chemical signal propagation having a form of a front wave above a cellular layer. We found that the time-averaged propagation velocity under oscillatory flow for a particular Péclet number amplitude is slower than the velocity under steady laminar flow regime for the same value of the Péclet number, but significantly faster than under no-flow conditions. We derive asymptotic values of the propagation velocity and asymptotic characteristics of the corresponding concentration fronts in high- and low-frequency regimes and show that the reason for the observed velocity increase under the oscillatory flow stems from a nonlinear dependence of the propagation velocity on the Péclet number, particularly from the convex character of the dependence. Our findings suggest that the specific responses of cellular cultures to different flow conditions in the extracellular space (for example, expression of atherosclerosis protective genes under steady laminar flow but not under oscillatory flow) is a consequence of a nonlinear coupling between the extracellular transport and complex intracellular reaction cascades forming a positive feedback loop of the autocrine signaling. This mechanism can operate independently of, or in conjunction with, a direct stress-sensing due to mechanotransduction.
- MeSH
- autokrinní signalizace * MeSH
- biologické modely * MeSH
- hydrodynamika * MeSH
- konvekce * MeSH
- lidé MeSH
- nelineární dynamika MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
This work is focused on investigation of applicability of two widely used model equations for description of nonlinear standing waves in constant-cross-sectioned resonators. The investigation is based on the comparison of numerical solutions of these model equations with solutions of more accurate model equations whose validity has been verified experimentally in a number of published papers.
- MeSH
- akustika * MeSH
- časové faktory MeSH
- nelineární dynamika * MeSH
- numerická analýza pomocí počítače MeSH
- počítačová simulace MeSH
- pohyb těles MeSH
- reprodukovatelnost výsledků MeSH
- tlak MeSH
- vibrace MeSH
- zvuk * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
Recent findings in cognitive neuroscience indicate that activation of anterior cingulate cortex (ACC) is related to detecting cognitive conflict. Conflict related ACC activation elicits responses in central autonomic network which can be assessed by psychophysiological measures such as heart rate variability (i.e. beat to beat R-R intervals--RRI). Recent findings in neuroscience also suggest that cognitive conflict is related to specific nonlinear chaotic changes of the signal generated by the neural systems. The present study used Stroop word-colour test as an experimental approach to the study of cognitive conflict in connection with RRI measurement, psychometric measurement of dissociation (DES) and calculation of largest Lyapunov exponents in nonlinear data analysis of RRI time series in 40 patients with unipolar depression and 35 healthy controls. Significant correlation 0.58 (p<0.01) between largest Lyapunov exponents and DES found in depressive patients indicate that cognitive conflict related neural interference during conflicting Stroop task is closely related to dissociative processes. These results present first supportive evidence that degree of chaos could be related to dissociation.
- MeSH
- depresivní poruchy komplikace patofyziologie psychologie MeSH
- disociační poruchy komplikace patofyziologie MeSH
- dospělí MeSH
- financování organizované MeSH
- kognice MeSH
- konflikt (psychologie) MeSH
- lidé středního věku MeSH
- lidé MeSH
- nelineární dynamika MeSH
- srdeční frekvence fyziologie MeSH
- Check Tag
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
