755 research outputs found
The basis of nonlocal curvature invariants in quantum gravity theory
A complete basis of nonlocal invariants in quantum gravity theory is built to
third order in spacetime curvature and matter-field strengths. The nonlocal
identities are obtained which reduce this basis for manifolds with
dimensionality . The present results are used in heat-kernel theory,
theory of gauge fields and serve as a basis for the model-independent approach
to quantum gravity and, in particular, for the study of nonlocal vacuum effects
in the gravitational collapse problem.Comment: 28 pages, REVTeX, Alberta Thy 14-9
Thermal radiation of conducting nanoparticles
The thermal radiation of small conducting particles was investigated in the
region where the Stephan-Boltzmann law is not valid and strongly overestimates
radiation losses. The new criterion for the particle size, at which black body
radiation law fails, was formulated. The approach is based on the magnetic
particle polarization, which is valid until very small sizes (cluster size)
where due to drop of particle conductivity the electric polarization prevails
over the magnetic one. It was also shown that the radiation power of clusters,
estimated on the basis of the experimental data, is lower than that given by
the Stephan-Boltzmann law.Comment: 12 pages, 5 figures, 1 tabl
Non-reciprocal light scattering by lattice of magnetic vortices
We report on experimental study of optical properties of two-dimensional
square lattice of triangle Co and CoFe nanoparticles with a vortex
magnetization distribution. We demonstrate that intensity of light scattered in
diffraction maxima depends on the vorticity of the particles magnetization and
it can be manipulated by applying an external magnetic field. The experimental
results can be understood in terms of phenomenological theory.Comment: 10 pages, 4 figure
How to reduce the suspension thermal noise in LIGO without improving the Q's of the pendulum and violin modes
The suspension noise in interferometric gravitational wave detectors is
caused by losses at the top and the bottom attachments of each suspension
fiber. We use the Fluctuation-Dissipation theorem to argue that by careful
positioning of the laser beam spot on the mirror face it is possible to reduce
the contribution of the bottom attachment point to the suspension noise by
several orders of magnitude. For example, for the initial and enhanced LIGO
design parameters (i.e. mirror masses and sizes, and suspension fibers' lengths
and diameters) we predict a reduction of in the "bottom" spectral
density throughout the band of serious thermal noise. We then
propose a readout scheme which suppresses the suspension noise contribution of
the top attachment point. The idea is to monitor an averaged horizontal
displacement of the fiber of length ; this allows one to record the
contribution of the top attachment point to the suspension noise, and later
subtract it it from the interferometer readout. For enhanced LIGO this would
allow a suppression factor about 100 in spectral density of suspension thermal
noise.Comment: a few misprints corrected; submitted to Classical and Quantum Gravit
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