216,174 research outputs found
Generalized constraints on quantum amplification
We derive quantum constraints on the minimal amount of noise added in linear
amplification involving input or output signals whose component operators do
not necessarily have c-number commutators, as is the case for fermion currents.
This is a generalization of constraints derived for the amplification of
bosonic fields whose components posses c-number commutators.Comment: 4 pages, 1 figure, submitted to Physical Review Letter
Construction and application of a questionnaire for the social scientific investigation of environmental noise effects
A social psychological questionnair has been developed to study the effects of environmental noise and was applied to 636 people living in 19 different areas of Hamburg. The theoretical foundations and the statistical means employed in its development are described. Four main reactions to noise are isolated statistically, and it is determined that these are moderated by several intervening variables, chief of which are coping capacity for noise, the perceived dangerousness of the noise souce, other daily loads and the individual's liability
Diamagnetic orbital response of mesoscopic silver rings
We report measurements of the flux-dependent orbital magnetic susceptibility
of an ensemble of 10^5 disconnected silver rings at 217 MHz. Because of the
strong spin-orbit scattering rate in silver this experiment is a test of
existing theories on orbital magnetism. Below 100 mK the rings exhibit a
magnetic signal with a flux periodicity of h/2 e consistent with averaged
persistent currents, whose amplitude is estimated to be of the order of 0.3 nA.
The sign of the oscillations indicates diamagnetism in the vicinity of zero
magnetic field. This sign is not consistent with theoretical predictions for
average persistent currents unless considering attractive interactions in
silver. We propose an alternative interpretation taking into account spin orbit
scattering and finite frequency.Comment: 4 pages, 4 figures, revtex4, accepted for publication in Physical
Review Letter
Equivalence of stationary state ensembles
We show that the contact process in an ensemble with conserved total particle
number, as simulated recently by Tome and de Oliveira [Phys. Rev. Lett. 86
(2001) 5463], is equivalent to the ordinary contact process, in agreement with
what the authors assumed and believed. Similar conserved ensembles and
equivalence proofs are easily constructed for other models.Comment: 5 pages, no figure
Complete phase diagram of the spin-1/2 -- model (with ) on the honeycomb lattice
We use the coupled cluster method to investigate the ground-state (GS)
properties of the frustrated spin-1/2 -- model on the
honeycomb lattice, with nearest-neighbor exchange coupling plus
next-nearest-neighbor () and next-next-nearest-neighbor () exchanges
of equal strength. In particular we find a direct first-order phase transition
between the N\'eel-ordered antiferromagnetic phase and the ferromagnetic phase
at a value when , compared to the
corresponding classical value of -1. We find no evidence for any intermediate
phase. From this and our previous CCM studies of the model we present its full
zero-temperature GS phase diagram.Comment: 4 pages, 4 figure
Coulomb corrections and multiple e+e- pair production in ultra-relativistic nuclear collisions
We consider the problem of Coulomb corrections to the inclusive cross
section. We show that these corrections in the limiting case of small charge
number of one of the nuclei coincide with those to the exclusive cross section.
Within our approach we also obtain the Coulomb corrections for the case of
large charge numbers of both nuclei.Comment: 7 pages, REVTeX
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