430 research outputs found
Detectability of dissipative motion in quantum vacuum via superradiance
We propose an experiment for generating and detecting vacuum-induced
dissipative motion. A high frequency mechanical resonator driven in resonance
is expected to dissipate energy in quantum vacuum via photon emission. The
photons are stored in a high quality electromagnetic cavity and detected
through their interaction with ultracold alkali-metal atoms prepared in an
inverted population of hyperfine states. Superradiant amplification of the
generated photons results in a detectable radio-frequency signal temporally
distinguishable from the expected background.Comment: 4 pages, 2 figure
Quantum dissipative effects in moving mirrors: a functional approach
We use a functional approach to study various aspects of the quantum
effective dynamics of moving, planar, dispersive mirrors, coupled to scalar or
Dirac fields, in different numbers of dimensions. We first compute the
Euclidean effective action, and use it to derive the imaginary part of the
`in-out' effective action. We also obtain, for the case of the real scalar
field in 1+1 dimensions, the Schwinger-Keldysh effective action and a
semiclassical Langevin equation that describes the motion of the mirror
including noise and dissipative effects due to its coupling to the quantum
fields.Comment: References added. Version to appear in Phys. Rev.
Exact Casimir interaction between eccentric cylinders
The Casimir force is the ultimate background in ongoing searches of
extra-gravitational forces in the micrometer range. Eccentric cylinders offer
favorable experimental conditions for such measurements as spurious
gravitational and electrostatic effects can be minimized. Here we report on the
evaluation of the exact Casimir interaction between perfectly conducting
eccentric cylinders using a mode summation technique, and study different
limiting cases of relevance for Casimir force measurements, with potential
implications for the understanding of mechanical properties of nanotubes.Comment: 5 pages, 4 figure
Black hole mass estimates in quasars - A comparative analysis of high- and low-ionization lines
The inter-line comparison between high- and low-ionization emission lines has
yielded a wealth of information on the quasar broad line region (BLR) structure
and dynamics, including perhaps the earliest unambiguous evidence in favor of a
disk + wind structure in radio-quiet quasars. We carried out an analysis of the
CIV 1549 and Hbeta line profiles of 28 Hamburg-ESO high luminosity quasars and
of 48 low-z, low luminosity sources in order to test whether the
high-ionization line CIV 1549 width could be correlated with Hbeta and be used
as a virial broadening estimator. We analyze intermediate- to high-S/N,
moderate resolution optical and NIR spectra covering the redshifted CIV and
H over a broad range of luminosity log L ~ 44 - 48.5 [erg/s] and
redshift (0 - 3), following an approach based on the quasar main sequence. The
present analysis indicates that the line width of CIV 1549 is not immediately
offering a virial broadening estimator equivalent to H. At the same time
a virialized part of the BLR appears to be preserved even at the highest
luminosities. We suggest a correction to FWHM(CIV) for Eddington ratio (using
the CIV blueshift as a proxy) and luminosity effects that can be applied over
more than four dex in luminosity. Great care should be used in estimating
high-L black hole masses from CIV 1549 line width. However, once corrected
FWHM(CIV) values are used, a CIV-based scaling law can yield unbiased MBH
values with respect to the ones based on H with sample standard
deviation ~ 0.3 dex.Comment: 43 pages, 15 Figures, submitted to A&
Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry
We have performed precision electrostatic calibrations in the sphere-plane
geometry and observed anomalous behavior. Namely, the scaling exponent of the
electrostatic signal with distance was found to be smaller than expected on the
basis of the pure Coulombian contribution and the residual potential found to
be distance dependent. We argue that these findings affect the accuracy of the
electrostatic calibrations and invite reanalysis of previous determinations of
the Casimir force.Comment: 4 pages, 4 figure
Functional integral treatment of some quantum nondemolition systems
In the scheme of a quantum nondemolition (QND) measurement, an observable is
measured without perturbing its evolution. In the context of studies of
decoherence in quantum computing, we examine the `open' quantum system of a
two-level atom, or equivalently, a spin-1/2 system, in interaction with quantum
reservoirs of either oscillators or spins, under the QND condition of the
Hamiltonian of the system commuting with the system-reservoir interaction. For
completeness, we also examine the well-known non-QND spin-Bose problem. For all
these many-body systems, we use the methods of functional integration to work
out the propagators. The propagators for the QND Hamiltonians are shown to be
analogous to the squeezing and rotation operators, respectively, for the two
kinds of baths considered. Squeezing and rotation being both phase space
area-preserving canonical transformations, this brings out an interesting
connection between the energy-preserving QND Hamiltonians and the homogeneous
linear canonical transformations.Comment: 16 pages, no figure
Shape deformations and angular momentum transfer in trapped Bose-Einstein condensates
Angular momentum can be transferred to a trapped Bose-Einstein condensate by
distorting its shape with an external rotating field, provided the rotational
frequency is larger than a critical frequency fixed by the energy and angular
momentum of the excited states of the system. By using the Gross-Pitaevskii
equation and sum rules, we explore the dependence of such a critical frequency
on the multipolarity of the excitations and the asymmetry of the confining
potential. We also discuss its possible relevance for vortex nucleation in
rotating traps.Comment: 4 pages revtex, 2 figures include
Current status of ticks and tick-host relationship in domestic and wild animals from Pantanal wetlands in the state of Mato Grosso do Sul, Brazil.
This is a commented list of tick?s species collected on various wild and domestic animals, including the reports on scientifi c literature for the studied region. Most of animals were small or medium mammals. Carnivores were the main taxa group examined. Although, the pampas deer (Ozotocerus bezoarticus) and giant anteater (Mymercophaga tridactyla) also has a good representation on study. Among domestic animals, dogs, horses and cattle were examined. Summing up, 18 tick species were listed for the region. Sixteen were hard ticks (Ixodidae) and two soft ticks (Argasidae). Amblyomma sculptum was the most common and abundant hard tick. Ornithodoros rostratus (Argasidae) was very abundant, being the more important Argasidae tick on the study region. The following species were colleted or reported on scientifi c literature: Argas miniatus Koch, 1844; Ornithodoros rostratus Aragão, 1911; Dermacentor nitens Newmann, 1897; Rhipicephalus (Boophilus) microplus Canestrini, 1887; Amblyomma tigrinum Koch, 1844; A.dissimile Koch, 1844; A. ovale Koch, 1844; A. pauvum Aragão, 1908; A. sculptum Berlese, 1888; A. calcaratum Neumann, 1899; A. coelebs Neumann, 1899; A. dubittatum Newmann, 1899; A. scalpturatum Newmann, 1906; A. naponense Packard, 1869; A. nodosum Newmann, 1899; A. pseudoconcolor Aragão, 1908; A. rotundatum Koch, 1844; A. triste Koch, 1844.Título em português: Estado atual dos carrapatos em relação a seus animais-hospedeiros domésticos e selvagens do Pantanal no Estado do Mato Grosso do Sul, Brasil
Hertz potentials approach to the dynamical Casimir effect in cylindrical cavities of arbitrary section
We study the creation of photons in resonant cylindrical cavities with time
dependent length. The physical degrees of freedom of the electromagnetic field
are described using Hertz potentials. We describe the general formalism for
cavities with arbitrary section. Then we compute explicitly the number of TE
and TM motion-induced photons for cylindrical cavities with rectangular and
circular sections. We also discuss the creation of TEM photons in non-simply
connected cylindrical cavities.Comment: 13 pages, 3 figures, revtex
Narrow-line Seyfert 1s: what is wrong in a name?
Narrow-line Seyfert 1s (NLSy1s) are an ill-defined class. Work done over the
past 20 years as well as recent analyses show a continuity in properties (e.g.,
Balmer line profiles, blueshifts of high-ionization lines) between sources with
FWHM above and below 2000 km/s, the defining boundary of NLSy1s. This finding
alone suggests that comparisons between samples of NLSy1s and rest of
broad-line AGNs are most likely biased. NLSy1s can be properly contextualized
by their location on the quasar main sequence originally defined by Sulentic et
al 2000. At one end, NLSy1s encompass sources with strong FeII emission and
associated with high Eddington ratio that hold the promise of becoming useful
distance indicators; at the other end, at least some of them are sources with
broad profiles seen face-on. Any rigid FWHM limit gives rise to some physical
ambiguity, as the FWHM of low-ionization lines depends in a complex way on
mass, Eddington ratio, orientation, and luminosity. In addition, if the scaling
derived from luminosity and virial dynamics applies to the broad line regions,
NLSy1s at luminosity higher than 1E47 erg/s become physically impossible.
Therefore, in a broader context, a proper subdivision of two distinct classes
of AGNs and quasars may be achieved by the distinction between Pop. A and B
with boundary at = 4000 km/s in samples at z < 1, or on the basis of
spectrophotometric properties which may ultimately be related to differences in
accretion modes if high-luminosity quasars are considered.Comment: Contribution presented at the meeting Revisiting narrow-line Seyfert
1 galaxies and their place in the Universe, held at the Padova Botanical
Garden, Italy, on 9-13 April 201
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