19,417 research outputs found
Effective model of the electronic Griffiths phase
We present simple analytical arguments explaining the universal emergence of
electronic Griffiths phases as precursors of disorder-driven metal-insulator
transitions in correlated electronic systems. A simple effective model is
constructed and solved within Dynamical Mean Field Theory. It is shown to
capture all the qualitative and even quantitative aspects of such Griffiths
phases.Comment: 9 pages, 7 figures, one reference corrected; minor corrections
include
Dependence of the critical temperature of laser-ablated YBa2Cu3O(7-delta) thin films on LaAlO3 substrate growth technique
Samples of LaAlO3 made by flame fusion and Czochralski method were subjected to the same temperature conditions that they have to undergo during the laser ablation deposition of YBa2Cu3O(7 - delta) thin films. After oxygen annealing at 750 C, the LaAlO3 substrate made by two methods experienced surface roughening. The degree of roughening on the substrate made by Czochralski method was three times greater than that on the substrate made by flame fusion. This excessive surface roughening may be the origin of the experimentally observed lowering of the critical temperature of a film deposited by laser ablation on a LaAlO3 substrate made by Czochralski method with respect to its counterpart deposited on LaAlO3 substrates made by flame fusion
Massive Black Hole Binary Systems in Hierarchical Scenario of Structure Formation
The hierarchical scenario of structure formation describes how objects like
galaxies and galaxy clusters are formed by mergers of small objects. In this
scenario, mergers of galaxies can lead to the formation of massive black hole
(MBH) binary systems. On the other hand, the merger of two MBH could produce a
gravitational wave signal detectable, in principle, by the Laser Interferometer
Space Antenna (LISA). In the present work, we use the Press-Schechter
formalism, and its extension, to describe the merger rate of haloes which
contain massive black holes. Here, we do not study the gravitational wave
emission of these systems. However, we present an initial study to determine
the number of systems formed via mergers that could permit, in a future
extension of this work, the calculation of the signature in gravitational waves
of these systems.Comment: to match the published version in International Journal of Modern
Physics
Biot-Savart-like law in electrostatics
The Biot-Savart law is a well-known and powerful theoretical tool used to
calculate magnetic fields due to currents in magnetostatics. We extend the
range of applicability and the formal structure of the Biot-Savart law to
electrostatics by deriving a Biot-Savart-like law suitable for calculating
electric fields. We show that, under certain circumstances, the traditional
Dirichlet problem can be mapped onto a much simpler Biot-Savart-like problem.
We find an integral expression for the electric field due to an arbitrarily
shaped, planar region kept at a fixed electric potential, in an otherwise
grounded plane. As a by-product we present a very simple formula to compute the
field produced in the plane defined by such a region. We illustrate the
usefulness of our approach by calculating the electric field produced by planar
regions of a few nontrivial shapes.Comment: 14 pages, 6 figures, RevTex, accepted for publication in the European
Journal of Physic
Mode-coupling approach to non-Newtonian Hele-Shaw flow
The Saffman-Taylor viscous fingering problem is investigated for the
displacement of a non-Newtonian fluid by a Newtonian one in a radial Hele-Shaw
cell. We execute a mode-coupling approach to the problem and examine the
morphology of the fluid-fluid interface in the weak shear limit. A differential
equation describing the early nonlinear evolution of the interface modes is
derived in detail. Owing to vorticity arising from our modified Darcy's law, we
introduce a vector potential for the velocity in contrast to the conventional
scalar potential. Our analytical results address how mode-coupling dynamics
relates to tip-splitting and side branching in both shear thinning and shear
thickening cases. The development of non-Newtonian interfacial patterns in
rectangular Hele-Shaw cells is also analyzed.Comment: 14 pages, 5 ps figures, Revtex4, accepted for publication in Phys.
Rev.
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
An experimental route to spatiotemporal chaos in an extended 1D oscillators array
We report experimental evidence of the route to spatiotemporal chaos in a
large 1D-array of hotspots in a thermoconvective system. Increasing the driving
force, a stationary cellular pattern becomes unstable towards a mixed pattern
of irregular clusters which consist of time-dependent localized patterns of
variable spatiotemporal coherence. These irregular clusters coexist with the
basic cellular pattern. The Fourier spectra corresponding to this
synchronization transition reveals the weak coupling of a resonant triad. This
pattern saturates with the formation of a unique domain of great spatiotemporal
coherence. As we further increase the driving force, a supercritical
bifurcation to a spatiotemporal beating regime takes place. The new pattern is
characterized by the presence of two stationary clusters with a characteristic
zig-zag geometry. The Fourier analysis reveals a stronger coupling and enables
to find out that this beating phenomena is produced by the splitting of the
fundamental spatiotemporal frequencies in a narrow band. Both secondary
instabilities are phase-like synchronization transitions with global and
absolute character. Far beyond this threshold, a new instability takes place
when the system is not able to sustain the spatial frequency splitting,
although the temporal beating remains inside these domains. These experimental
results may support the understanding of other systems in nature undergoing
similar clustering processes.Comment: 12 pages, 13 figure
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