71 research outputs found
Comparison of methods for estimating continuous distributions of relaxation times
The nonparametric estimation of the distribution of relaxation times approach
is not as frequently used in the analysis of dispersed response of dielectric
or conductive materials as are other immittance data analysis methods based on
parametric curve fitting techniques. Nevertheless, such distributions can yield
important information about the physical processes present in measured
material. In this letter, we apply two quite different numerical inversion
methods to estimate the distribution of relaxation times for glassy \lila\
dielectric frequency-response data at 225 \kelvin. Both methods yield unique
distributions that agree very closely with the actual exact one accurately
calculated from the corrected bulk-dispersion Kohlrausch model established
independently by means of parametric data fit using the corrected modulus
formalism method. The obtained distributions are also greatly superior to those
estimated using approximate functions equations given in the literature.Comment: 4 pages and 4 figure
How can one probe Podolsky Electrodynamics?
We investigate the possibility of detecting the Podolsky generalized
electrodynamics constant . First we analyze an ion interferometry apparatus
proposed by B. Neyenhuis, et al (Phys. Rev. Lett. 99, (2007) 200401) who looked
for deviations from Coulomb's inverse-square law in the context of Proca model.
Our results show that this experiment has not enough precision for measurements
of . In order to set up bounds for we investigate the influence of
Podolsky's electrostatic potential on the ground state of the Hydrogen atom.
The value of the ground state energy of the Hydrogen atom requires Podolsky's
constant to be smaller than 5.6 fm, or in energy scales larger than 35.51 MeV.Comment: 12 pages, 2 figure
Estudo de filtros RC para baixas e altas freqüências por meio de um circuito para superposição de sinais
Quasinormal modes of plane-symmetric anti-de Sitter black holes: a complete analysis of the gravitational perturbations
We study in detail the quasinormal modes of linear gravitational
perturbations of plane-symmetric anti-de Sitter black holes. The wave equations
are obtained by means of the Newman-Penrose formalism and the Chandrasekhar
transformation theory. We show that oscillatory modes decay exponentially with
time such that these black holes are stable against gravitational
perturbations. Our numerical results show that in the large (small) black hole
regime the frequencies of the ordinary quasinormal modes are proportional to
the horizon radius (wave number ). The frequency of the purely
damped mode is very close to the algebraically special frequency in the small
horizon limit, and goes as in the opposite limit. This result
is confirmed by an analytical method based on the power series expansion of the
frequency in terms of the horizon radius. The same procedure applied to the
Schwarzschild anti-de Sitter spacetime proves that the purely damped frequency
goes as , where is the quantum number characterizing
the angular distribution. Finally, we study the limit of high overtones and
find that the frequencies become evenly spaced in this regime. The spacing of
the frequency per unit horizon radius seems to be a universal quantity, in the
sense that it is independent of the wave number, perturbation parity and black
hole size.Comment: Added new material on the asymptotic behavior of QNM
Extracting spectral density function of a binary composite without a-priori assumption
The spectral representation separates the contributions of geometrical
arrangement (topology) and intrinsic constituent properties in a composite. The
aim of paper is to present a numerical algorithm based on the Monte Carlo
integration and contrainted-least-squares methods to resolve the spectral
density function for a given system. The numerical method is verified by
comparing the results with those of Maxwell-Garnett effective permittivity
expression. Later, it is applied to a well-studied rock-and-brine system to
instruct its utility. The presented method yields significant microstructural
information in improving our understanding how microstructure influences the
macroscopic behaviour of composites without any intricate mathematics.Comment: 4 pages, 5 figures and 1 tabl
Quantum mechanical virial theorem in systems with translational and rotational symmetry
Generalized virial theorem for quantum mechanical nonrelativistic and
relativistic systems with translational and rotational symmetry is derived in
the form of the commutator between the generator of dilations G and the
Hamiltonian H. If the conditions of translational and rotational symmetry
together with the additional conditions of the theorem are satisfied, the
matrix elements of the commutator [G, H] are equal to zero on the subspace of
the Hilbert space. Normalized simultaneous eigenvectors of the particular set
of commuting operators which contains H, J^{2}, J_{z} and additional operators
form an orthonormal basis in this subspace. It is expected that the theorem is
relevant for a large number of quantum mechanical N-particle systems with
translational and rotational symmetry.Comment: 24 pages, accepted for publication in International Journal of
Theoretical Physic
Theoretical Aspects of Transient Electromagnetic Field in Finite Sized Conducting Media
It is generally accepted that electromagnetic disturbances diffuse into the bulk region of highly conducting media instead of propagating with wave-like characteristics [1]. This can be explained based on the fact that the high frequency components of the electromagnetic field decay rapidly, leaving the electromagnetic state in the bulk material quasistatic. For the application of this phenomena to practical testing, Ross et al. developed a formalism describing the diffusion of electromagnetic field in a finite thickness conductor and demonstrated the effect of thickness on the time rate of damping of field amplitude [2]
Mathematical Constraint on Functions with Continuous Second Partial Derivatives
A new integral identity for functions with continuous second partial
derivatives is derived. It is shown that the value of any function f(r,t) at
position r and time t is completely determined by its previous values at all
other locations r' and retarded times t'<t, provided that the function vanishes
at infinity and has continuous second partial derivatives. Functions of this
kind occur in many areas of physics and it seems somewhat surprising that they
are constrained in this way.Comment: 10 pages, 6 figure
Diffraction of light by topological defects in liquid crystals
We study light scattering by a hedgehog-like and linear disclination
topological defects in a nematic liquid crystal by a metric approach. Light
propagating near such defects feels an effective metric equivalent to the
spatial part of the global monopole and cosmic string geometries. We obtain the
scattering amplitude and the differential and total scattering cross section
for the case of the hedgehog defect, in terms of the characteristic parameters
of the liquid crystal. Studying the disclination case, a cylindrical partial
wave method is developed. As an application of the previous developments, we
also examine the temperature influence on the localization of the diffraction
patterns.Comment: Correcting some typos,15 pages, 3 figures, accepted for publication
in Liquid Crystal
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