50,325 research outputs found
Convective instabilities in two superposed horizontal liquid layers heated laterally
This work is devoted to the theoretical study of the stability of two
superposed horizontal liquid layers bounded by two solid planes and subjected
to a horizontal temperature gradient.
The liquids are supposed to be immiscible with a nondeformable interface.
The forces acting on the system are buoyancy and interfacial tension. Four
different flow patterns and temperature profiles are found for the basic state.
A linear perturbative analysis with respect to two and three dimensional
perturbations reveals the existence of three kind of patterns. Depending on the
relative height of both liquids several situations are predicted: either wave
propagation from cold to the hot regions, or waves propagating in the opposite
direction or still stationary longitudinal rolls. The behavior of three
different pairs of liquids which have been used in experiments on bilayers
under vertical gradient by other authors have been examined. The instability
mechanisms are discussed and a qualitative interpretation of the different
behaviors exhibited by the system is provided. In some configurations it is
possible to find a codimension-two point created by the interaction of two Hopf
modes with different frequencies and wavenumbers. These results suggest to
consider two liquid layers as an interesting prototype for the study of
propagation and interaction of waves in the context of the B\'enard-Marangoni
problem.Comment: 21 pages, 9 figures, 2 tables;accepted to be published in PR
Traveling wave solutions for wave equations with two exponential nonlinearities
We use a simple method that leads to the integrals involved in obtaining the
traveling wave solutions of wave equations with one and two exponential
nonlinearities. When the constant term in the integrand is zero, implicit
solutions in terms of hypergeometric functions are obtained while when that
term is nonzero all the basic traveling wave solutions of Liouville, Tzitzeica
and their variants, as well as sine/sinh-Gordon equations with important
applications in the phenomenology of nonlinear physics and dynamical systems
are found through a detailed study of the corresponding elliptic equationsComment: 9 pages, 7 figures, 42 references, version matching the published
articl
Correlations in nuclear energy recurrence relations
The excitation energies of states belonging to the ground state bands of
heavy even-even nuclei are analysed using recurrence relations. Excellent
agreement with experimental data at the 10 keV level is obtained by taking into
account strong correlations which emerge in the analysis. This implies that the
excitation energies can be written as a polynomial of maximum degree four in
the angular momentum.Comment: 4 pages, 1 figure, 1 table, 9 reference
Dynamic heterogeneity in the glass-like monoclinic phases of some halogen methane compounds
In this work we study the heterogeneity of the dynamics on the low-temperature monoclinic phases of the simple molecular glassy systems CBrnCl4−nCBrnCl4−n, n = 0, 1, 2. In these systems the disorder comes exclusively from reorientational jumps mainly around the C3 molecular axes. The different time scales are determined by means of the analysis of the spin-lattice relaxation time obtained through Nuclear Quadrupole Resonance (NQR) technique. Results are compared with those obtained from dielectric spectroscopy, from which two α- and β-relaxation times appear. NQR results enable us to ascribe with no doubt that the existence of two relaxations is due to dynamical heterogeneities which are the consequence of the different molecular surroundings of the molecules in the asymmetric unit cell of systems here studied.Fil: Zuriaga, Mariano Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Perez, S. C.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Pardo, L. C.. Universidad Politecnica de Catalunya; EspañaFil: Tamarit, J. L.. Universidad Politecnica de Catalunya; Españ
Multifractal properties of elementary cellular automata in a discrete wavelet approach of MF-DFA
In 2005, Nagler and Claussen (Phys. Rev. E 71 (2005) 067103) investigated the
time series of the elementary cellular automata (ECA) for possible
(multi)fractal behavior. They eliminated the polynomial background at^b through
the direct fitting of the polynomial coefficients a and b. We here reconsider
their work eliminating the polynomial trend by means of the multifractal-based
detrended fluctuation analysis (MF-DFA) in which the wavelet multiresolution
property is employed to filter out the trend in a more speedy way than the
direct polynomial fitting and also with respect to the wavelet transform
modulus maxima (WTMM) procedure. In the algorithm, the discrete fast wavelet
transform is used to calculate the trend as a local feature that enters the
so-called details signal. We illustrate our result for three representative ECA
rules: 90, 105, and 150. We confirm their multifractal behavior and provide our
results for the scaling parametersComment: 8 pages, 5 figures, 21 reference
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