13,374 research outputs found
Performance of dynamical decoupling in bosonic environments and under pulse-timing fluctuations
We study the suppression of qubit dephasing through Uhrig dynamical
decoupling (UDD) in nontrivial environments modeled within the spin-boson
formalism. In particular, we address the case of (i) a qubit coupled to a
bosonic bath with power-law spectral density, and (ii) a qubit coupled to a
single harmonic oscillator that dissipates energy into a bosonic bath, which
embodies an example of a structured bath for the qubit. We then model the
influence of random time jitter in the UDD protocol by sorting
pulse-application times from Gaussian distributions centered at appropriate
values dictated by the optimal protocol. In case (i) we find that, when few
pulses are applied and a sharp cutoff is considered, longer coherence times and
robust UDD performances (against random timing errors) are achieved for a
super-Ohmic bath. On the other hand, when an exponential cutoff is considered a
super-Ohmic bath is undesirable. In case (ii) the best scenario is obtained for
an overdamped harmonic motion. Our study provides relevant information for the
implementation of optimized schemes for the protection of quantum states from
decoherence.Comment: 8 pages, 5 figure
G\"odel-type Spacetimes in Induced Matter Gravity Theory
A five-dimensional (5D) generalized G\"odel-type manifolds are examined in
the light of the equivalence problem techniques, as formulated by Cartan. The
necessary and sufficient conditions for local homogeneity of these 5D manifolds
are derived. The local equivalence of these homogeneous Riemannian manifolds is
studied. It is found that they are characterized by three essential parameters
, and : identical triads correspond to
locally equivalent 5D manifolds. An irreducible set of isometrically
nonequivalent 5D locally homogeneous Riemannian generalized G\"odel-type
metrics are exhibited. A classification of these manifolds based on the
essential parameters is presented, and the Killing vector fields as well as the
corresponding Lie algebra of each class are determined. It is shown that the
generalized G\"odel-type 5D manifolds admit maximal group of isometry
with , or depending on the essential parameters ,
and . The breakdown of causality in all these classes of homogeneous
G\"odel-type manifolds are also examined. It is found that in three out of the
six irreducible classes the causality can be violated. The unique generalized
G\"odel-type solution of the induced matter (IM) field equations is found. The
question as to whether the induced matter version of general relativity is an
effective therapy for these type of causal anomalies of general relativity is
also discussed in connection with a recent article by Romero, Tavakol and
Zalaletdinov.Comment: 19 pages, Latex, no figures. To Appear in J.Math.Phys.(1999
Efeito de isolados de Baculovirus em lagartas de Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) e sua caracterização utilizando PCR.
xEdição dos resumos do Congresso Nacional de Genética, Gramado, 1999
Susceptibilidade da lagarta do cartucho do milho, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) a isolados de baculovirus.
Tuned liquid dampers simulation for earthquake response control of buildings
This paper is focused on the study of an earthquake protection system, the Tuned Liquid Damper (TLD), which
can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking
into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated
Tuned Liquid Damper, subjected to a sinusoidal excitation at its base, with different displacement amplitudes,
was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses
Linear Theory of Electron-Plasma Waves at Arbitrary Collisionality
The dynamics of electron-plasma waves are described at arbitrary
collisionality by considering the full Coulomb collision operator. The
description is based on a Hermite-Laguerre decomposition of the velocity
dependence of the electron distribution function. The damping rate, frequency,
and eigenmode spectrum of electron-plasma waves are found as functions of the
collision frequency and wavelength. A comparison is made between the
collisionless Landau damping limit, the Lenard-Bernstein and Dougherty
collision operators, and the electron-ion collision operator, finding large
deviations in the damping rates and eigenmode spectra. A purely damped entropy
mode, characteristic of a plasma where pitch-angle scattering effects are
dominant with respect to collisionless effects, is shown to emerge numerically,
and its dispersion relation is analytically derived. It is shown that such a
mode is absent when simplified collision operators are used, and that
like-particle collisions strongly influence the damping rate of the entropy
mode.Comment: 23 pages, 10 figures, accepted for publication on Journal of Plasma
Physic
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