4,918 research outputs found
Exotic looped trajectories via quantum marking
We provide an analytical and theoretical study of exotic looped trajectories
(ELTs) in a double-slit interferometer with quantum marking. We use an excited
Rydberg-like atom and which-way detectors such as superconducting cavities,
just as in the Scully-Englert-Walther interferometer. We indicate appropriate
conditions on the atomic beam or superconducting cavities so that we determine
an interference pattern and fringe visibility exclusive from the ELTs. We
quantitatively describe our results for Rubidium atoms and propose this
framework as an alternative scheme to the double-slit experiment modified to
interfere only these exotic trajectories.Comment: 10 pages, 5 figure
Noise models for superoperators in the chord representation
We study many-qubit generalizations of quantum noise channels that can be
written as an incoherent sum of translations in phase space. Physical
description in terms of the spectral properties of the superoperator and the
action in phase space are provided. A very natural description of decoherence
leading to a preferred basis is achieved with diffusion along a phase space
line. The numerical advantages of using the chord representation are
illustrated in the case of coarse-graining noise.Comment: 8 pages, 5 .ps figures (RevTeX4). Submitted to Phys. Rev. A. minor
changes made, according to referee suggestion
Fungiform Papillae of the Pig and the Wild Boar Analyzed by Scanning Electron Microscopy
Fungiform papillae of wild boar and pig were studied by scanning electron microscopy (SEM). Four regions were defined on the tongue: rostral, medial and caudal thirds and lateral sides. Morphologically the fungiform papillae correspond with their denomination. Rostral and lateral tongue regions presented the largest average number of fungiform papillae. Taste pores opened onto the upper surface of the papillae and were easily identifiable by SEM. The total number of fungiform taste pores from both animals was the highest reported in the literature. The lateral papillae of wild boar and pig contained the largest average number of pores per papilla. This region must be important in taste sensitivity. Lateral and rostral papillae from both animals can provide a source of taste buds for study since each fungiform papilla presents numerous taste buds and these papillae are very abundant
UV properties of early-type galaxies in the Virgo cluster
We study the UV properties of a volume limited sample of early-type galaxies
in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet
(2310 A) data with spectro-photometric data available at other wavelengths. The
sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range
in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude
relations (CMR) are similar to those observed at optical wavelengths, with a
monotonic reddening of the color index with increasing luminosity, the (FUV-V)
and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An
even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For
ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and
with increasing reddening of the optical or near-IR color indices. For the
dwarfs the opposite trend is observed. These observational evidences are
consistent with the idea that the UV emission is dominated by hot, evolved
stars in giant systems, while in dwarf ellipticals residual star formation
activity is more common.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in
Astrophysical Journal Letter
Extremely Inefficient Star Formation in the Outer Disks of Nearby Galaxies
(Abridged) We combine data from The HI Nearby Galaxy Survey and the GALEX
Nearby Galaxy Survey to study the relationship between atomic hydrogen (HI) and
far-ultraviolet (FUV) emission outside the optical radius (r25) in 17 spiral
and 5 dwarf galaxies. In this regime, HI is likely to represent most of the ISM
and FUV emission to trace recent star formation with little bias due to
extinction, so that the two quantities closely trace the underlying
relationship between gas and star formation rate (SFR). The azimuthally
averaged HI and FUV intensities both decline with increasing radius in this
regime, with the scale length of the FUV profile typically half that of the HI
profile. Despite the mismatch in profiles, there is a significant spatial
correlation (at 15" resolution) between local FUV and HI intensities; near r25
this correlation is quite strong, in fact stronger than anywhere inside r25,
and shows a decline towards larger radii. The star formation efficiency (SFE) -
defined as the ratio of FUV/HI and thus the inverse of the gas depletion time -
decreases with galactocentric radius across the outer disks, though much
shallower than across the optical disks. On average, we find the gas depletion
times to be well above a Hubble time (~10^11 yr). We observe a clear
relationship between FUV/HI and HI column in the outer disks, with the SFE
increasing with increasing HI column. Despite observing systematic variations
in FUV/HI, we find no clear evidence for step-function type star formation
thresholds. When compared with results from inside r25, we find outer disk star
formation to be distinct in several ways: it is extremely inefficient
(depletion times of many Hubble times) with column densities and SFRs lower
than found anywhere inside the optical disks. It appears that the HI column is
one of, perhaps even the key environmental factor in setting the SFR in outer
galaxy disks.Comment: Accepted for Publication in The Astronomical Journa
Experimental proposal for measuring the Gouy phase of matter waves
The Schr\"odinger equation for an atomic beam predicts that it must have a
phase anomaly near the beam waist analogous to the Gouy phase of an
electromagnetic beam. We propose here a feasible experiment which allows for
the direct determination of this anomalous phase using Ramsey interferometry
with Rydberg atoms. Possible experimental limitations are discussed and shown
to be completely under control within the present day technology. We also
discuss how this finding can open the possibility to use the spatial mode
wavefunctions of atoms as q-dits, since the Gouy phase is an essential
ingredient for making rotations in the quantum states.Comment: 9 pages and 3 figure
InfluĂŞncia do fĂłsforo e de diferentes regimes de corte sobre a digestibilidade in vitro do capim-de-raiz (Chloris orthonoton, Doell).
O presente trabalho objetivou avaliar a digestibilidade do capim-de-raiz submetido a diferentes doses de fĂłsforo, frequĂŞncias e intensidades de corte
Extinction law variations and dust excitation in the spiral galaxy NGC 300
We investigate the origin of the strong radial gradient in the
ultraviolet-to-infrared ratio in the spiral galaxy NGC 300, and emphasize the
importance of local variations in the interstellar medium geometry, concluding
that they cannot be neglected with respect to metallicity effects. This
analysis is based upon a combination of maps from GALEX and Spitzer, and from
the ground (UBVRI, Halpha and Hbeta). We select ionizing stellar clusters
associated with HII regions of widely varying morphologies, and derive their
fundamental parameters from population synthesis fitting of their spectral
energy distributions, measured to eliminate local backgrounds accurately. From
these fits, we conclude that the stellar extinction law is highly variable in
the line of sight of young clusters of similar ages. In the particular model
geometry that we consider most appropriate to the sampled regions, we checked
that our findings are not significantly altered by the correct treatment of
radiative transfer effects. The variations are systematic in nature: extinction
laws of the Milky Way or LMC type are associated with compact HII regions (the
compacity being quantified in two different ways), while clusters surrounded by
diffuse HII regions follow extinction laws of the 30 Doradus or SMC type. The
Calzetti starburst attenuation law, although most often degenerate with the 30
Doradus extinction law, overpredicts ionizing photon fluxes by large amounts.
We also find that the extinction law variations are correlated with the column
density of dust species emitting in the near- and mid-infrared. Finally, we
briefly discuss the nebular to stellar extinction ratios, and the excitation of
aromatic band carriers, invalidating their claimed association with cold dust.Comment: accepted for publication in ApJ -- figure 6 abridged her
Recommended from our members
Cool dust heating and temperature mixing in nearby star-forming galaxies
Physical conditions of the interstellar medium in galaxies are closely linked
to the ambient radiation field and the heating of dust grains. In order to
characterize dust properties in galaxies over a wide range of physical
conditions, we present here the radial surface brightness profiles of the
entire sample of 61 galaxies from Key Insights into Nearby Galaxies:
Far-Infrared Survey with Herschel (KINGFISH). The main goal of our work is the
characterization of the grain emissivities, dust temperatures, and interstellar
radiation fields responsible for heating the dust. After fitting the dust and
stellar radial profiles with exponential functions, we fit the far-infrared
spectral energy distribution (SED) in each annular region with
single-temperature modified black bodies using both variable (MBBV) and fixed
(MBBF) emissivity indices beta, as well as with physically motivated dust
models. Results show that while most SED parameters decrease with radius, the
emissivity index beta also decreases with radius in some galaxies, but in
others is increasing, or rising in the inner regions and falling in the outer
ones. Despite the fixed grain emissivity (average beta~ 2.1) of the
physically-motivated models, they are well able to accommodate flat spectral
slopes with beta<= 1. We find that flatter slopes (beta<= 1.5) are associated
with cooler temperatures, contrary to what would be expected from the usual
Tdust-beta degeneracy. This trend is related to variations in Umin since beta
and Umin are very closely linked over the entire range in Umin sampled by the
KINGFISH galaxies: low Umin is associated with flat beta<=1. Both these results
strongly suggest that the low apparent \beta values (flat slopes) in MBBV fits
are caused by temperature mixing along the line-of-sight, rather than by
intrinsic variations in grain properties. Abstract truncated for arXiv.Comment: 28 pages, 20 figures, accepted for publication in A&
Quantum Rolling Down out of Equilibrium
In a scalar field theory, when the tree level potential admits broken
symmetry ground states, the quantum corrections to the static effective
potential are complex. (The imaginary part is a consequence of an instability
towards phase separation and the static effective potential is not a relevant
quantity for understanding the dynamics). Instead, we study here the equations
of motion obtained from the one loop effective action for slow rollover out of
equilibrium.
We considering the case in which a scalar field theory undergoes a rapid
phase transition from to . We find that, for slow rollover
initial conditions (the field near the maximum of the tree level potential),
the process of phase separation controlled by unstable long-wavelength
fluctuations introduces dramatic corrections to the dynamical evolution of the
field. We find that these effects slow the rollover even furtherComment: 33 pages, Latex,LPTHE-PAR 92-33 PITT 92-0
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