5,428 research outputs found
Spectral Transformation Algorithms for Computing Unstable Modes of Large Scale Power Systems
In this paper we describe spectral transformation algorithms for the
computation of eigenvalues with positive real part of sparse nonsymmetric
matrix pencils , where is of the form \pmatrix{M&0\cr 0&0}. For
this we define a different extension of M\"obius transforms to pencils that
inhibits the effect on iterations of the spurious eigenvalue at infinity. These
algorithms use a technique of preconditioning the initial vectors by M\"obius
transforms which together with shift-invert iterations accelerate the
convergence to the desired eigenvalues. Also, we see that M\"obius transforms
can be successfully used in inhibiting the convergence to a known eigenvalue.
Moreover, the procedure has a computational cost similar to power or
shift-invert iterations with M\"obius transforms: neither is more expensive
than the usual shift-invert iterations with pencils. Results from tests with a
concrete transient stability model of an interconnected power system whose
Jacobian matrix has order 3156 are also reported here.Comment: 19 pages, 1 figur
Magnetization in quasiperiodic magnetic multilayers with biquadratic exchange and uniaxial anisotropy
A theoretical study is made of the magnetization versus applied field curves
of ferromagnetic/nonmagnetic multilayers constructed according to a Fibonacci
quasiperiodic sequence. The ferromagnetic films are assumed to have uniaxial
anisotropy and are coupled by both bilinear and biquadratic effective exchange.
The effects of quasiperiodicity in the magnetic phases are illustrated
numerically for Fe/Cr systems.Comment: 5 pages, 3 ps figures, Elsevier Latex2e Style. To appear in Journal
of Magnetism and Magnetic Materials (proceedings of the 4th International
Symposium on Metallic Multilayers, MML'01, Aachen, June 24-29, 2001
On the extension of Jackiw's scalar theory to (2+1)- dimensional gravity
We study some aspects of three-dimensional gravity by extending Jackiw's
scalar theory to (2+1)-dimensions and find a black hole solution. We show that
in in general this teory does not possess a Newtonian limit except for special
metric configurations.Comment: 11 pages, LATEX fil
Quantum Brownian motion in an analog Friedmann-Robertson-Walker geometry
In this paper we study the effects of quantum scalar field vacuum
fluctuations on scalar test particles in an analog model for the
Friedmann-Robertson-Walker spatially flat geometry. In this scenario, the cases
with one and two perfectly reflecting plane boundaries are considered as well
the case without boundary. We find that the particles can undergo Brownian
motion with a nonzero mean squared velocity induced by the quantum vacuum
fluctuations due to the time dependent background and the presence of the
boundaries. Typical singularities which appears due to the presence of the
boundaries in flat spacetime can be naturally regularized for an asymptotically
bounded expanding scale function. Thus, shifts in the velocity could be, at
least in principle, detectable experimentally. The possibility to implement
this observation in an analog cosmological model by the use of a Bose-Einstein
condensate is also discussed.Comment: 26 pages, 7 figures. Accepted for Publication in Phys. Rev.
Light-Cone Fluctuations in the Cosmic String Spacetime
In this paper we consider light-cone fluctuations arising as a consequence of
the nontrivial topology of the locally flat cosmic string spacetime. By setting
the light-cone along the z-direction we are able to develop a full analysis to
calculate the renormalized graviton two-point function, as well as the mean
square fluctuation in the geodesic interval function and the time delay (or
advance) in the propagation of a light-pulse. We found that all these
expressions depend upon the parameter characterizing the conical topology of
the cosmic string spacetime and vanish in the absence of it. We also point out
that at large distances from the cosmic string the mean square fluctuation in
the geodesic interval function is extremely small while in the opposite limit
it logarithmically increases, improving the signal and thus, making possible
the detection of such quantity.Comment: 19 pages, 1 figur
Vaccum Polarization for a Massless Scalar Field in the Global Monopole Spacetime at Finite Temperature
In this paper we calculate the effects produced by temperature in the
renormalized vaccum expectation value of the square of the massless scalar
field in the pointlike global monopole spacetime. In order to develop this
calculation, we had to construct the Euclidean thermal Green function
associated with this field in this background. We also calculate the
high-temperature limit for the thermal average of the zero-zero component of
the energy-momentum tensor.Comment: 21 pages in LATEX and 3 figures in poscrip
Measurement of Effective using Baseline Differences of Daya Bay, RENO and Double Chooz Reactor Neutrino Experiments
In 2011 and 2012, three reactor neutrino experiments, Double Chooz, Daya Bay
and RENO showed positive signals of reactor neutrino disappearance and measured
a mixing parameter sin^2(2th13) at average baselines 1.05, 1.65 and 1.44km,
respectively. It is possible to measure effective Dm31^2 from distortion of
neutrino energy spectrum (E dependence of the oscillation) in those
experiments. However, since it requires a precise energy calibration, such
measurements have not been reported yet. Dm31^2 can also be measured from
baseline (L) dependence of the neutrino oscillation. In this paper, Dm31^2 is
measured from disappearance probabilities of the three reactor experiments
which have different baselines, to be 2.99^{+1.13}_{-1.58}(^{+0.86}_{-0.88}) X
10^{-3}eV^2, where the errors are two (one) dimensional uncertainties. This is
consistent with Dm32^2 measured by \nu_{\mu} disappearance in accelerator
experiments. Importance of Dm31^2 measurement and future possibilities are also
discussed.Comment: 6 pages, 5 figures. Presented as poster (ID250-1) in Neutrino2012.
v2: A reference is added. Minor typos corrected. No change for value
Surface impedance and the Casimir force
The impedance boundary condition is used to calculate the Casimir force in
configurations of two parallel plates and a shpere (spherical lens) above a
plate at both zero and nonzero temperature. The impedance approach allows one
to find the Casimir force between the realistic test bodies regardless of the
electromagnetic fluctuations inside the media. Although this approach is an
approximate one, it has wider areas of application than the Lifshitz theory of
the Casimir force. The general formulas of the impedance approach to the theory
of the Casimir force are given and the formal substitution is found for
connecting it with the Lifshitz formula. The range of micrometer separations
between the test bodies which is interesting from the experimental point of
view is investigated in detail. It is shown that at zero temperature the
results obtained on the basis of the surface impedance method are in agreement
with those obtained in framework of the Lifshitz theory within a fraction of a
percent. The temperature correction to the Casimir force from the impedance
method coincides with that from the Lifshitz theory up to four significant
figures. The case of millimeter separations which corresponds to the normal
skin effect is also considered. At zero temperature the obtained results have
good agreement with the Lifshitz theory. At nonzero temperature the impedance
approach is not subject to the interpretation problems peculiar to the
zero-frequency term of the Lifshitz formula in dissipative media.Comment: 2 figures; to appear in Phys. Rev.
Loop variables and gravitational Berry's quantum phase in the space-time of a rotating massive body
In this paper we compute the holonomies along curves in the gravitational
field of a slowly rotating massive body. We use our results to study the
gravitational analogue of Aharanov-Bohm effect in this space-time. We also
investigate the behaviour of a scalar quantum particle in this space-time and
determine Berry's quantum phase acquired by this particle when transported
along a closed curve surrounding the body.Comment: 8 pages, iopart styl
Casimir effect due to a slowly rotating source in the weak field approximation
We calculate the renormalized vacuum energy density for a massless scalar
field confined between two nearby parallel plates formed by ideal uncharged
conductors, placed very close to the surface of a rotating spherical
gravitational source with mass , radius and momentum angular , at the
equatorial region. We consider that the source rotates slowly and that the
gravitational field is weak. Corrections to the Casimir energy density induced
by the gravitational field generated by this source are calculated up to
order. The obtained results show us that there is an important
modification in the Casimir energy only in this order of approximation, which
depends on the surface gravity as well as on the rotation of the source.
Thermal corrections to the Casimir energy found also are calculated in all
these orders.Comment: 15 pages. To appear in Physical Review
- …