422 research outputs found
Formation of Ionization-Cone Structures in Active Galactic Nuclei: I. Stationary Model and Linear Stability Analysis
We discuss causes of the formation of the observed kinematics and morphology
of cones of ionized matter in the neighborhood of the nuclei of Seyfert
galaxies. The results of linear stability analysis of an optically thin conic
jet where radiation cooling and gravity play an important part are reported.
The allowance for radiation cooling is shown to result in strong damping of all
acoustic modes and to have insignificant effect on unstable surface
Kelvin--Helmholtz modes. In the case of waveguide--resonance internal gravity
modes radiative cooling suppresses completely the instability of waves
propagating away from the ejection source and, vice versa, reduces
substantially the growth time scale of unstable sourceward propagating modes.
The results obtained can be used to study ionization cones in Seyfert galaxies
with radio jets. In particular, our analysis shows that surface
Kelvin--Helmholtz modes and volume harmonics are capable of producing regular
features observed in optical emission-line images of such galaxies.Comment: 13 pages, published in Astrophysical Bulleti
01. Introduction: Maps
Part one of course materials for Nonequilibrium Statistical Physics (Physics 626), taught by Gerhard Müller at the University of Rhode Island. Entries listed in the table of contents, but not shown in the document, exist only in handwritten form. Documents will be updated periodically as more entries become presentable.
Updated with version 2 on 5/3/2016
Characterizing chaos in a type of fractional duffing's equation
We characterize the chaos in a fractional Duffing’s equation computing the Lyapunov exponents and the dimension of the strange attractor in the effective phase space of the system. We develop a specific analytical method to estimate all Lyapunov exponents and check the results with the fiduciary orbit technique and a time series estimation method
Generalized Neighbor-Interaction Models Induced by Nonlinear Lattices
It is shown that the tight-binding approximation of the nonlinear
Schr\"odinger equation with a periodic linear potential and periodic in space
nonlinearity coefficient gives rise to a number of nonlinear lattices with
complex, both linear and nonlinear, neighbor interactions. The obtained
lattices present non-standard possibilities, among which we mention a
quasi-linear regime, where the pulse dynamics obeys essentially the linear
Schr{\"o}dinger equation. We analyze the properties of such models both in
connection with their modulational stability, as well as in regard to the
existence and stability of their localized solitary wave solutions
Study of instabilities and transition to turbulence in a linear hall accelerator
Magnetospheric instabilities and transition to plasma turbulence in Hall current accelerator
Nonlinear optical lattices with a void impurity
We examine a one-dimensional nonlinear (Kerr) waveguide array which contains
a single "void" waveguide where the nonlinearity is identically zero.
We uncover a new family of nonlinear localized modes centered at or near the
void, and their stability properties. Unlike a usual impurity problem, here the
void acts like a repulsive impurity causing the center of the simplest mode to
lie to the side of the void's position. We also compute the stability of
extended nonlinear modes showing significant differences from the usual
homogeneous nonlinear array. The transmission of a nonlinear pulse across the
void shows three main regimes, transmission, reflection and trapping at the
void's position, and we identify a critical momentum for the pulse below
(above) where the pulse gets reflected (transmitted), or trapped indefinitely
at the void's position. For relatively wide pulses, we observe a steep increase
from a regime of no transmission to a regime of high transmission, as the
amplitude of the soliton increases beyond a critical wavevector value. Finally,
we consider the transmission of an extended nonlinear wave across the void
impurity numerically, finding a rather complex structure of the transmission as
a function of wavevector, with the creation of more and more transmission gaps
as nonlinearity increases. The overall transmittance decreases and disappears
eventually, where the boundaries separating passing from non-passing regions
are complex and fractal-like.Comment: 9 pages, 10 figure
Nonlinear wave propagation in disordered media
We briefly review the state-of-the-art of research on nonlinear wave propagation in
disordered media. The paper is intended to provide the non-specialist reader with a flavor
of this active field of physics. Firstly, a general introduction to the subject is made. We
describe the basic models and the ways to study disorder in connection with them.
Secondly, analytical and numerical techniques suitable for this purpose are outlined. We
summarize their features and comment on their respective advantages, drawbacks and
applicability conditions. Thirdly, the Nonlinear Klein-Gordon and Schrbdinger equations
are chosen as specific examples. We collect a number of results that are representative of
the phenomena arising from the competition between nonlinearity and disorder. The
review is concluded with some remarks on open questions, main current trends and
possible further developments.This work has been supported in part by the C.I.C. y T. (Spain) under project MAT90-0S44. A S. was also supported by fellowships from the Universidad Complutense and the Ministerio de Educacion y Ciencia.Publicad
An evaluation of planarity of the spatial QRS loop by three dimensional vectorcardiography: its emergence and loss
Aims:
To objectively characterize and mathematically justify the observation that vectorcardiographic QRS loops in normal individuals are more planar than those from patients with ST elevation myocardial infarction (STEMI).
Methods:
Vectorcardiograms (VCGs) were constructed from three simultaneously recorded quasi-orthogonal leads, I, aVF and V2 (sampled at 1000 samples/s). The planarity of these QRS loops was determined by fitting a surface to each loop. Goodness of fit was expressed in numerical terms.
Results:
15 healthy individuals aged 35–65 years (73% male) and 15 patients aged 45–70 years (80% male) with diagnosed acute STEMI were recruited. The spatial-QRS loop was found to lie in a plane in normal controls. In STEMI patients, this planarity was lost. Calculation of goodness of fit supported these visual observations.
Conclusions:
The degree of planarity of the VCG loop can differentiate healthy individuals from patients with STEMI. This observation is compatible with our basic understanding of the electrophysiology of the human heart
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