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 $(J,L)$, where $L$ 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 Δm312\Delta m_{31}^2 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 $M$, radius $R$ and momentum angular $J$, 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 $M/R^2$ 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