scholarly journals The Role of Chaos in Barred Galaxies

1996 ◽  
Vol 157 ◽  
pp. 321-338 ◽  
Author(s):  
G. Contopoulos ◽  
N. Voglis
Keyword(s):  
Initial Conditions ◽  
Characteristic Number ◽  
Dissipative Systems ◽  
Barred Galaxies ◽  
Chaotic Orbits ◽  
Self Consistency ◽  
Lyapunov Characteristic Number ◽  
Stretching Numbers ◽  
Lyapunov Characteristic Numbers

AbstractOrdered orbits in barred galaxies appear along the bar and between the −4/1 and −2/1 resonances of the outer spiral. Chaotic orbits appear mainly near corotation. Such orbits support the bar and the spiral for long times and they are important for self-consistency. There are three main mechanisms for transition from order to chaos: (a) infinite bifurcations, (b) infinite gaps, and (c) infinite spirals. The Lyapunov characteristic number is zero for ordered orbits and positive for chaotic orbits. But much more information is provided by the distribution of the stretching numbers (one-period Lyapunov characteristic numbers). The spectrum of stretching numbers is invariant with respect to initial conditions in a connected chaotic domain. We provide examples of such spectra for 2-D maps, plane galactic orbits, 2-D dissipative systems, 3-D systems (represented by 4-D maps), and systems depending periodically on the time.

scholarly journals Distribution of Kolmogorov-Sinaï Entropy in Self-Consistent Models of Barred Galaxies

1999 ◽  
Vol 172 ◽  
pp. 149-158
Author(s):  
H. Wozniak ◽  
D. Pfenniger
Keyword(s):  
Star Formation ◽  
Building Blocks ◽  
Maximum Extension ◽  
Star Forming ◽  
Barred Galaxies ◽  
Chaotic Orbits ◽  
Self Consistent ◽  
Elementary Building

AbstractThe properties of chaos in 2D self-consistent models of barred galaxies are investigated using Kolmogorov-Sinai entropy hKS. These models are constructed with Schwarzschild’s method which combines orbits as elementary building blocks.Most models are dominated by chaos near the 2/3 of the length of the bar and close to corotation. These locations correspond to regions where star-forming HII regions are observed because gas clouds could shock, shrink and fragment such that star formation could be ignited.The model the most similar to N-body models shows a peak of hKS between the corners of the rectangular-like x1 orbits and the maximum extension points of the Lagrangian orbits. This emphasizes the role of Lagrangian orbits in the morphology of bars. Most models essentially contain ‘semi-chaotic’ orbits confined inside the corotation.

scholarly journals Detection of Ordered and Chaotic Motion using The Dynamical Spectra

1999 ◽  
Vol 172 ◽  
pp. 211-220
Author(s):  
N. Voglis ◽  
G. Contopoulos ◽  
C. Efthymiopoulos
Keyword(s):  
Phase Space ◽  
Characteristic Number ◽  
Space Structure ◽  
Initial Deviation ◽  
Phase Space Structure ◽  
Spectral Distance ◽  
Chaotic Orbits ◽  
Dynamical Spectra ◽  
Lyapunov Characteristic Number ◽  
Number Of Iterations

AbstractTwo simple and efficient numerical methods to explore the phase space structure are presented, based on the properties of the “dynamical spectra”. 1) We calculate a “spectral distance”Dof the dynamical spectra for two different initial deviation vectors.D→ 0 in the case of chaotic orbits, whileD→const≠ 0 in the case of ordered orbits. This method is by orders of magnitude faster than the method of the Lyapunov Characteristic Number (LCN). 2) We define a sensitive indicator called ROTOR (ROtational TOri Recongnizer) for 2D maps. The ROTOR remains zero in time on a rotational torus, while it tends to infinity at a rate ∝N= number of iterations, in any case other than a rotational torus. We use this method to locate the last KAM torus of an island of stability, as well as the most important cantori causing stickiness near it.

Transport and fluctuations in nonlinear-dissipative systems: role of interparticle collisions

1999 ◽  
Vol 4 ◽  
pp. 31-86 ◽  
Author(s):  
R. Katilius ◽  
A. Matulionis ◽  
R. Raguotis ◽  
I. Matulionienė
Keyword(s):  
Electric Fields ◽  
Carrier Density ◽  
Experimental Results ◽  
Dissipative Systems ◽  
Doped Semiconductors ◽  
Electron Diffusion ◽  
Electron Collisions ◽  
Electric Noise ◽  
Diffusion Phenomena

The goal of the paper is to overview contemporary theoretical and experimental research of the microwave electric noise and fluctuations of hot carriers in semiconductors, revealing sensitivity of the noise spectra to non-linearity in the applied electric field strength and, especially, in the carrier density. During the last years, investigation of electronic noise and electron diffusion phenomena in doped semiconductors was in a rapid progress. By combining analytic and Monte Carlo methods as well as the available experimental results on noise, it became possible to obtain the electron diffusion coefficients in the range of electric fields where inter-electron collisions are important and Price’s relation is not necessarily valid. Correspondingly, a special attention to the role of inter-electron collisions and of the non-linearity in the carrier density while shaping electric noise and diffusion phenomena in the non-equilibrium states will be paid. The basic and up-to-date information will be presented on methods and advances in this contemporary field - the field in which methods of non-linear analytic and computational analysis are indispensable while seeking coherent understanding and interpretation of experimental results.

Reassessment of transient permeability measurement for tight rocks: The role of boundary and initial conditions

2021 ◽  
pp. 104173
Author(s):  
Yue Wang ◽  
Zhiguo Tian ◽  
Steffen Nolte ◽  
Alexandra Amann-Hildenbrand ◽  
Bernhard M. Krooss ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Permeability Measurement ◽  
Tight Rocks

scholarly journals The role of masks in reducing the risk of new waves of COVID-19 in low transmission settings: a modeling study

2020 ◽  
Author(s):  
Robyn M Stuart ◽  
Romesh G Abeysuriya ◽  
Cliff C Kerr ◽  
Dina Mistry ◽  
Daniel J Klein ◽  
...  
Keyword(s):  
Initial Conditions ◽  
High Mobility ◽  
Baseline Scenario ◽  
New Wave ◽  
Policy Environment ◽  
Agent Based ◽  
Low Transmission ◽  
South Wales ◽  
Community Transmission

Objectives: To evaluate the risk of a new wave of coronavirus disease 2019 (COVID-19) in a setting with ongoing low transmission, high mobility, and an effective test-and-trace system, under different assumptions about mask uptake. Design: We used a stochastic agent-based microsimulation model to create multiple simulations of possible epidemic trajectories that could eventuate over a five-week period following prolonged low levels of community transmission. Setting: We calibrated the model to the epidemiological and policy environment in New South Wales, Australia, at the end of August 2020. Participants: None Intervention: From September 1, 2020, we ran the stochastic model with the same initial conditions (i.e., those prevailing at August 31, 2020), and analyzed the outputs of the model to determine the probability of exceeding a given number of new diagnoses and active cases within five weeks, under three assumptions about future mask usage: a baseline scenario of 30% uptake, a scenario assuming no mask usage, and a scenario assuming mandatory mask usage with near-universal uptake (95%). Main outcome measure: Probability of exceeding a given number of new diagnoses and active cases within five weeks. Results: The policy environment at the end of August is sufficient to slow the rate of epidemic growth, but may not stop the epidemic from growing: we estimate a 20% chance that NSW will be diagnosing at least 50 new cases per day within five weeks from the date of this analysis. Mandatory mask usage would reduce this to 6-9%. Conclusions: Mandating the use of masks in community settings would significantly reduce the risk of epidemic resurgence.

A mechanism for jet drift over topography

2018 ◽  
Vol 845 ◽  
pp. 392-416 ◽  
Author(s):  
Hemant Khatri ◽  
Pavel Berloff
Keyword(s):  
Bottom Topography ◽  
Vertical Shear ◽  
Dissipative Systems ◽  
Dynamical Equations ◽  
Nonlinear Stress ◽  
Multiple Jets ◽  
Baroclinic Model ◽  
The One ◽  
Constant Slope

The dynamics of multiple alternating oceanic jets has been studied in the presence of a simple bottom topography with constant slope in the zonal direction. A baroclinic quasi-geostrophic model forced with a horizontally uniform and vertically sheared background flow generates mesoscale eddies and jets that are tilted from the zonal direction and drift with constant speed. The governing dynamical equations are rewritten in a tilted frame of reference moving with the jets, and the cross-jet time-mean profiles of the linear and nonlinear stress terms are analysed. Here, the linear stress terms are present because of the zonally asymmetric topography. It is demonstrated that the linear dynamics controls the drift mechanism. Also, it is found that the drifting jets are directly forced by the imposed vertical shear, whereas the eddies oppose the jets, although this is limited to continuously forced dissipative systems. This role of the eddies is opposite to the one in the classical baroclinic model of stationary, zonally symmetric multiple jets. This is expected to be more generic in the ocean, which is zonally asymmetric nearly everywhere.

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