In this work, we introduce an exact calculation method and an approximation technique for tracing the invariant manifolds of unstable periodic orbits of planar maps. The exact method relies on an adaptive refinement procedure that prevents redundant calculations occurring in other approaches, and the approximated method relies on a novel interpolation approach based on normal displacement functions. The resulting approximated manifold is precise when compared to the exact one, and its relative computational cost falls like the inverse of the manifold length. To present the tracing method, we obtain the invariant manifolds of the Chirikov-Taylor map, and as an application we illustrate the transition from homoclinic to heteroclinic chaos in the Duffing oscillator that leads from localized chaos to global chaotic motion.
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http://dx.doi.org/10.1063/1.5027698 | DOI Listing |
Eur J Radiol
December 2024
Division of Endocrinology and Metabolism, Department of Medicine III, Medical University of Vienna, Austria.
Objectives: To explore texture analysis' ability on T and T relaxation maps to classify liver fibrosis into no-to-mild liver fibrosis (nmF) versus severe fibrosis (sF) group using machine learning algorithms and histology as reference standard.
Materials And Methods: In this single-center study, patients undergoing 3 T MRI who also had histology examination were retrospectively enrolled. SNAPSHOT-FLASH sequence for T1 mapping, radial turbo-spin-echo sequence for T2 mapping and spin-echo echo-planar-imaging magnetic resonance elastography (MRE) sequences were analyzed.
Pediatr Radiol
December 2024
Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH, 45229, USA.
Background: Diagnostically adequate contrast and spatial resolution in brain MRI require prolonged scan times, leading to motion artifacts and image degradation in awake children. Rapid multi-parametric techniques can produce diagnostic images in awake children, which could help to avoid the need for sedation.
Objective: To evaluate the utility of a rapid echo-planar imaging (EPI)-based multi-inversion spin and gradient echo (MI-SAGE) technique for generating multi-parametric quantitative brain maps and synthetic contrast images in awake pediatric participants.
Comput Biol Med
December 2024
Dept. of Mechanical Engineering, University of Washington, Seattle, WA, USA; Center for Cardiovascular Biology, University of Washington School of Medicine, Seattle, WA, USA; Division of Cardiology, University of Washington School of Medicine, Seattle, WA, USA. Electronic address:
Intraventricular vector flow mapping (VFM) is an increasingly adopted echocardiographic technique that derives time-resolved two-dimensional flow maps in the left ventricle (LV) from color-Doppler sequences. Current VFM models rely on kinematic constraints arising from planar flow incompressibility. However, these models are not informed by crucial information about flow physics; most notably the forces within the fluid and the resulting accelerations.
View Article and Find Full Text PDFEng Comput
May 2024
Institute of Mathematics, École Polytechnique Fédérale de Lausanne, Rte Cantonale, 1015 Lausanne, Vaud Switzerland.
This paper presents a parameterisation framework based on (inverted) elliptic PDEs for addressing the planar parameterisation problem of finding a valid description of the domain's interior given no more than a spline-based description of its boundary contours. The framework is geared towards isogeometric analysis (IGA) applications wherein the physical domain is comprised of more than four sides, hence requiring more than one patch. We adopt the concept of harmonic maps and propose several PDE-based problem formulations capable of finding a valid map between a convex parametric multipatch domain and the piecewise-smooth physical domain with an equal number of sides.
View Article and Find Full Text PDFMed Phys
November 2024
CNRS, CRMSB, UMR 5536, IHU Liryc, University of Bordeaux, Bordeaux, France.
Background: Quantitative real-time MRI-based temperature mapping techniques are hampered by abdominal motion. Intrascan motion can be reduced by rapid acquisition sequences such as 2D echo planar imaging (EPI), and inter-scan organ displacement can be compensated by image processing such as optical flow (OF) algorithms. However, motion field estimation can be seriously affected by local variation of signal intensity on magnitude images inherent to tissue heating, potentially leading to erroneous temperature estimates.
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