21,263 research outputs found
Efficient Schemes for Reducing Imperfect Collective Decoherences
We propose schemes that are efficient when each pair of qubits undergoes some
imperfect collective decoherence with different baths. In the proposed scheme,
each pair of qubits is first encoded in a decoherence-free subspace composed of
two qubits. Leakage out of the encoding space generated by the imperfection is
reduced by the quantum Zeno effect. Phase errors in the encoded bits generated
by the imperfection are reduced by concatenation of the decoherence-free
subspace with either a three-qubit quantum error correcting code that corrects
only phase errors or a two-qubit quantum error detecting code that detects only
phase errors, connected with the quantum Zeno effect again.Comment: no correction, 3 pages, RevTe
Self-discharge characteristics of spacecraft nickel-cadmium cells at elevated temperatures
The effects of heat generation were determined in NiCd cells during high temperature storage on open circuits. The testing was designed to determine the extent to which thermal stability is a valid concern, at temperature of exposure (externally effected) between 40 and 120 C
Cosmological Vorticity in a Gravity with Quadratic Order Curvature Couplings
We analyse the evolution of the rotational type cosmological perturbation in
a gravity with general quadratic order gravitational coupling terms. The result
is expressed independently of the generalized nature of the gravity theory, and
is simply interpreted as a conservation of the angular momentum.Comment: 5 pages, revtex, no figure
A conserved variable in the perturbed hydrodynamic world model
We introduce a scalar-type perturbation variable which is conserved in
the large-scale limit considering general sign of three-space curvature (),
the cosmological constant (), and time varying equation of state. In a
pressureless medium is {\it exactly conserved} in all scales.Comment: 4 pages, no figure, To appear in Phys. Rev.
Relativistic Hydrodynamic Cosmological Perturbations
Relativistic cosmological perturbation analyses can be made based on several
different fundamental gauge conditions. In the pressureless limit the variables
in certain gauge conditions show the correct Newtonian behaviors. Considering
the general curvature () and the cosmological constant () in the
background medium, the perturbed density in the comoving gauge, and the
perturbed velocity and the perturbed potential in the zero-shear gauge show the
same behavior as the Newtonian ones in general scales. In the first part, we
elaborate these Newtonian correspondences. In the second part, using the
identified gauge-invariant variables with correct Newtonian correspondences, we
present the relativistic results with general pressures in the background and
perturbation. We present the general super-sound-horizon scale solutions of the
above mentioned variables valid for general , , and generally
evolving equation of state. We show that, for vanishing , the
super-sound-horizon scale evolution is characterised by a conserved variable
which is the perturbed three-space curvature in the comoving gauge. We also
present equations for the multi-component hydrodynamic situation and for the
rotation and gravitational wave.Comment: 16 pages, no figure, To appear in Gen. Rel. Gra
Analysis of recent type Ia supernova data based on evolving dark energy models
We study characters of recent type Ia supernova (SNIa) data using evolving
dark energy models with changing equation of state parameter w. We consider
sudden-jump approximation of w for some chosen redshift spans with double
transitions, and constrain these models based on Markov Chain Monte Carlo
(MCMC) method using the SNIa data (Constitution, Union, Union2) together with
baryon acoustic oscillation A parameter and cosmic microwave background shift
parameter in a flat background. In the double-transition model the Constitution
data shows deviation outside 1 sigma from LCDM model at low (z < 0.2) and
middle (0.2 < z < 0.4) redshift bins whereas no such deviations are noticeable
in the Union and Union2 data. By analyzing the Union members in the
Constitution set, however, we show that the same difference is actually due to
different calibration of the same Union sample in the Constitution set, and is
not due to new data added in the Constitution set. All detected deviations are
within 2 sigma from the LCDM world model. From the LCDM mock data analysis, we
quantify biases in the dark energy equation of state parameters induced by
insufficient data with inhomogeneous distribution of data points in the
redshift space and distance modulus errors. We demonstrate that location of
peak in the distribution of arithmetic means (computed from the MCMC chain for
each mock data) behaves as an unbiased estimator for the average bias, which is
valid even for non-symmetric likelihood distributions.Comment: 12 pages, 6 figures, published in the Phys. Rev.
Unified Analysis of Cosmological Perturbations in Generalized Gravity
In a class of generalized Einstein's gravity theories we derive the equations
and general asymptotic solutions describing the evolution of the perturbed
universe in unified forms. Our gravity theory considers general couplings
between the scalar field and the scalar curvature in the Lagrangian, thus
includes broad classes of generalized gravity theories resulting from recent
attempts for the unification. We analyze both the scalar-type mode and the
gravitational wave in analogous ways. For both modes the large scale evolutions
are characterized by the same conserved quantities which are valid in the
Einstein's gravity. This unified and simple treatment is possible due to our
proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure
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