592 research outputs found
Electronic transport through ballistic chaotic cavities: reflection symmetry, direct processes, and symmetry breaking
We extend previous studies on transport through ballistic chaotic cavities
with spatial left-right (LR) reflection symmetry to include the presence of
direct processes. We first analyze fully LR-symmetric systems in the presence
of direct processes and compare the distribution w(T) of the transmission
coefficient T with that for an asymmetric cavity with the same "optical" S
matrix. We then study the problem of "external mixing" of the symmetry caused
by an asymmetric coupling of the cavity to the outside. We first consider the
case where symmetry breaking arises because two symmetrically positioned
waveguides are coupled to the cavity by means of asymmetric tunnel barriers.
Although this system is asymmetric with respect to the LR operation, it has a
striking memory of the symmetry of the cavity it was constructed from.
Secondly, we break LR symmetry in the absence of direct proceses by
asymmetrically positioning the two waveguides and compare the results with
those for the completely asymmetric case.Comment: 15 pages, 8 Postscript figures, submitted to Phys. Rev.
Dynamics of Enceladus and Dione inside the 2:1 Mean-Motion Resonance under Tidal Dissipation
In a previous work (Callegari and Yokoyama 2007, Celest. Mech. Dyn. Astr.
vol. 98), the main features of the motion of the pair Enceladus-Dione were
analyzed in the frozen regime, i.e., without considering the tidal evolution.
Here, the results of a great deal of numerical simulations of a pair of
satellites similar to Enceladus and Dione crossing the 2:1 mean-motion
resonance are shown. The resonance crossing is modeled with a linear tidal
theory, considering a two-degrees-of-freedom model written in the framework of
the general three-body planar problem. The main regimes of motion of the system
during the passage through resonance are studied in detail. We discuss our
results comparing them with classical scenarios of tidal evolution of the
system. We show new scenarios of evolution of the Enceladus-Dione system
through resonance not shown in previous approaches of the problem.Comment: 36 pages, 12 figures. Accepted in Celestial Mechanics and Dynamical
Astronom
The random phase property and the Lyapunov Spectrum for disordered multi-channel systems
A random phase property establishing in the weak coupling limit a link between quasi-one-dimensional random Schrödinger operators and full random matrix theory is advocated. Briefly summarized it states that the random transfer matrices placed into a normal system of coordinates act on the isotropic frames and lead to a Markov process with a unique invariant measure which is of geometric nature. On the elliptic part of the transfer matrices, this measure is invariant under the unitaries in the hermitian symplectic group of the universality class under study. While the random phase property can up to now only be proved in special models or in a restricted sense, we provide strong numerical evidence that it holds in the Anderson model of localization. A main outcome of the random phase property is a perturbative calculation of the Lyapunov exponents which shows that the Lyapunov spectrum is equidistant and that the localization lengths for large systems in the unitary, orthogonal and symplectic ensemble differ by a factor 2 each. In an Anderson-Ando model on a tubular geometry with magnetic field and spin-orbit coupling, the normal system of coordinates is calculated and this is used to derive explicit energy dependent formulas for the Lyapunov spectrum
Internal quality of commercial eggs stored under conditions that simulate storage from laying to consumption
This study evaluated the effects on the internal quality of eggs of various storage environments through which eggs may pass between being laid and being consumed. Commercial eggs (N = 648) from Dekalb White hens were used. Treatments consisted of T1: 28 days at 4 °C; T2: 28 days at 20 °C; T3: 7 days at room temperature (27 °C ± 2 °C) (humidity 55%) and 21 days at 4 °C; T4: 7 days at room temperature and 21 days at 20 °C; T5: 14 days at room temperature and 14 days at 4 °C; T6: 14 days at room temperature and 14 days at 20 °C; T7: 21 days at room temperature and 7 days at 4 °C; T8: 21 days at room temperature and 7 days at 20 °C; and T9: 28 days at room temperature. The characteristics that were evaluated consisted of Haugh unit (HU), yolk index (YI), colour (L*, a* and b*), albumen pH, yolk pH and lipid oxidation. Eggs stored 28 days were darker (L*), and had greater yolk pH and lipid oxidation than fresh eggs. Eggs stored under T1 and T3 conditions had greater HU and YI than eggs stored in the other environments. The albumin pH of eggs stored at room temperature (T9) was highest of the treatments. Yellowness was increased in eggs stored under T4, T6, T8, and T9 conditions. Eggs should be stored under refrigeration as this promotes maintenance of internal quality and mitigates negative effects of previous storage conditions
On the statistical significance of the conductance quantization
Recent experiments on atomic-scale metallic contacts have shown that the
quantization of the conductance appears clearly only after the average of the
experimental results. Motivated by these results we have analyzed a simplified
model system in which a narrow neck is randomly coupled to wide ideal leads,
both in absence and presence of time reversal invariance. Based on Random
Matrix Theory we study analytically the probability distribution for the
conductance of such system. As the width of the leads increases the
distribution for the conductance becomes sharply peaked close to an integer
multiple of the quantum of conductance. Our results suggest a possible
statistical origin of conductance quantization in atomic-scale metallic
contacts.Comment: 4 pages, Tex and 3 figures. To be published in PR
The embedding method beyond the single-channel case: Two-mode and Hubbard chains
We investigate the relationship between persistent currents in multi-channel
rings containing an embedded scatterer and the conductance through the same
scatterer attached to leads. The case of two uncoupled channels corresponds to
a Hubbard chain, for which the one-dimensional embedding method is readily
generalized. Various tests are carried out to validate this new procedure, and
the conductance of short one-dimensional Hubbard chains attached to perfect
leads is computed for different system sizes and interaction strengths. In the
case of two coupled channels the conductance can be obtained from a statistical
analysis of the persistent current or by reducing the multi-channel scattering
problem to several single-channel setups.Comment: 14 pages, 13 figures, submitted for publicatio
Quantum master equation for a system influencing its environment
A perturbative quantum master equation is derived for a system interacting
with its environment, which is more general than the ones derived before. Our
master equation takes into account the effect of the energy exchanges between
the system and the environment and the conservation of energy in a finite total
system. This master quantum describes relaxation mechanisms in isolated
nanoscopic quantum systems. In its most general form, this equation is
non-Markovian and a Markovian version of it rules the long-time relaxation. We
show that our equation reduces to the Redfield equation in the limit where the
energy of the system does not affect the density of state of its environment.
This master equation and the Redfield one are applied to a spin-environment
model defined in terms of random matrices and compared with the solutions of
the exact von Neumann equation. The comparison proves the necessity to allow
energy exchange between the subsystem and the environment in order to correctly
describe the relaxation in isolated nanoscopic total system.Comment: 39 pages, 10 figure
Minimal surfaces and Reggeization in the AdS/CFT correspondence
We address the problem of computing scattering amplitudes related to the
correlation function of two Wilson lines and/or loops elongated along
light-cone directions in strongly coupled gauge theories. Using the AdS/CFT
correspondence in the classical approximation, the amplitudes are shown to be
related to minimal surfaces generalizing the {\em helicoid} in various
backgrounds. Infra-red divergences appearing for Wilson lines can be factorized
out or can be cured by considering the IR finite case of correlation functions
of two Wilson loops. In non-conformal cases related to confining theories,
reggeized amplitudes with linear trajectories and unit intercept are obtained
and shown to come from the approximately flat metrics near the horizon, which
sets the scale for the Regge slope. In the conformal case the absence of
confinement leads to a different solution. A transition between both regimes
appears, in a confining theory, when varying impact parameter.Comment: 22 pages, 2 eps figures, expanded discussion, conclusions unchanged,
version to be published in Nuclear Physics
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