9,593 research outputs found
Parametric uncertainty analysis of pulse wave propagation in a model of a human arterial network
Accepted versio
Numerical Study of Nonlinear Dispersive Wave Models with SpecTraVVave
In nonlinear dispersive evolution equations, the competing effects of
nonlinearity and dispersion make a number of interesting phenomena possible. In
the current work, the focus is on the numerical approximation of traveling-wave
solutions of such equations. We describe our efforts to write a dedicated
Python code which is able to compute traveling-wave solutions of nonlinear
dispersive equations of the general form \begin{equation*} u_t + [f(u)]_{x} +
\mathcal{L} u_x = 0, \end{equation*} where is a self-adjoint
operator, and is a real-valued function with .
The SpectraVVave code uses a continuation method coupled with a spectral
projection to compute approximations of steady symmetric solutions of this
equation. The code is used in a number of situations to gain an understanding
of traveling-wave solutions. The first case is the Whitham equation, where
numerical evidence points to the conclusion that the main bifurcation branch
features three distinct points of interest, namely a turning point, a point of
stability inversion, and a terminal point which corresponds to a cusped wave.
The second case is the so-called modified Benjamin-Ono equation where the
interaction of two solitary waves is investigated. It is found that is possible
for two solitary waves to interact in such a way that the smaller wave is
annihilated. The third case concerns the Benjamin equation which features two
competing dispersive operators. In this case, it is found that bifurcation
curves of periodic traveling-wave solutions may cross and connect high up on
the branch in the nonlinear regime
Algebraic approach in the study of time-dependent nonlinear integrable systems: Case of the singular oscillator
The classical and the quantal problem of a particle interacting in
one-dimension with an external time-dependent quadratic potential and a
constant inverse square potential is studied from the Lie-algebraic point of
view. The integrability of this system is established by evaluating the exact
invariant closely related to the Lewis and Riesenfeld invariant for the
time-dependent harmonic oscillator. We study extensively the special and
interesting case of a kicked quadratic potential from which we derive a new
integrable, nonlinear, area preserving, two-dimensional map which may, for
instance, be used in numerical algorithms that integrate the
Calogero-Sutherland-Moser Hamiltonian. The dynamics, both classical and
quantal, is studied via the time-evolution operator which we evaluate using a
recent method of integrating the quantum Liouville-Bloch equations \cite{rau}.
The results show the exact one-to-one correspondence between the classical and
the quantal dynamics. Our analysis also sheds light on the connection between
properties of the SU(1,1) algebra and that of simple dynamical systems.Comment: 17 pages, 4 figures, Accepted in PR
Stochastic foundations of undulatory transport phenomena: Generalized Poisson-Kac processes - Part II Irreversibility, Norms and Entropies
In this second part, we analyze the dissipation properties of Generalized
Poisson-Kac (GPK) processes, considering the decay of suitable -norms and
the definition of entropy functions. In both cases, consistent energy
dissipation and entropy functions depend on the whole system of primitive
statistical variables, the partial probability density functions , while the corresponding energy
dissipation and entropy functions based on the overall probability density
do not satisfy monotonicity requirements as a function of time.
Examples from chaotic advection (standard map coupled to stochastic GPK
processes) illustrate this phenomenon. Some complementary physical issues are
also addressed: the ergodicity breaking in the presence of attractive
potentials, and the use of GPK perturbations to mollify stochastic field
equations
Truncated decompositions and filtering methods with Reflective/Anti-Reflective boundary conditions: a comparison
The paper analyzes and compares some spectral filtering methods as truncated
singular/eigen-value decompositions and Tikhonov/Re-blurring regularizations in
the case of the recently proposed Reflective [M.K. Ng, R.H. Chan, and W.C.
Tang, A fast algorithm for deblurring models with Neumann boundary conditions,
SIAM J. Sci. Comput., 21 (1999), no. 3, pp.851-866] and Anti-Reflective [S.
Serra Capizzano, A note on anti-reflective boundary conditions and fast
deblurring models, SIAM J. Sci. Comput., 25-3 (2003), pp. 1307-1325] boundary
conditions. We give numerical evidence to the fact that spectral decompositions
(SDs) provide a good image restoration quality and this is true in particular
for the Anti-Reflective SD, despite the loss of orthogonality in the associated
transform. The related computational cost is comparable with previously known
spectral decompositions, and results substantially lower than the singular
value decomposition. The model extension to the cross-channel blurring
phenomenon of color images is also considered and the related spectral
filtering methods are suitably adapted.Comment: 22 pages, 10 figure
Open problems, questions, and challenges in finite-dimensional integrable systems
The paper surveys open problems and questions related to different aspects
of integrable systems with finitely many degrees of freedom. Many of the open
problems were suggested by the participants of the conference “Finite-dimensional
Integrable Systems, FDIS 2017” held at CRM, Barcelona in July 2017.Postprint (updated version
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