5,589 research outputs found
Second order reductions of the WDVV Equations related to classical Lie algebras
We construct second order reductions of the generalized
Witten-Dijkgraaf-Verlinde-Verlinde system based on simple Lie algebras. We
discuss to what extent some of the symmetries of the WDVV system are preserved
by the reduction.Comment: 6 pages, 1 tabl
Experimental Detection of Entanglement with Polarized Photons
We report on the first experimental realization of the entanglement witness
for polarization entangled photons. It represents a recently discovered
significant quantum information protocol which is based on few local
measurements. The present demonstration has been applied to the so-called
Werner states, a family of ''mixed'' quantum states that include both entangled
and non entangled states. These states have been generated by a novel high
brilliance source of entanglement which allows to continuously tune the degree
of mixedness
Ultraviolet and soft X--ray photon--photon elastic scattering in an electron gas
We have considered the processes which lead to elastic scattering between two
far ultraviolet or X--ray photons while they propagate inside a solid, modeled
as a simple electron gas. The new ingredient, with respect to the standard
theory of photon--photon scattering in vacuum, is the presence of low--energy,
nonrelativistic electron--hole excitations. Owing to the existence of
two--photon vertices, the scattering processes in the metal are predominantly
of second order, as opposed to fourth order for the vacuum case. The main
processes in second order are dominated by exchange of virtual plasmons between
the two photons. For two photons of similar energy , this gives
rise to a cross section rising like up to maximum of around
~cm, and then decreasing like . The maximal cross
section is found for the photon wavevector , the Fermi surface
size, which typically means a photon energy in the keV range.
Possible experiments aimed at checking the existence of these rare but
seemingly measurable elastic photon--photon scattering processes are discussed,
using in particular intense synchrotron sources.Comment: 33 pages, TeX, Version 3.1, S.I.S.S.A. preprint 35/93/C
Neutral Gas Outflows and Inflows in Infrared-Faint Seyfert Galaxies
Previous studies of the Na I D interstellar absorption line doublet have
shown that galactic winds occur in most galaxies with high infrared
luminosities. However, in infrared-bright composite systems where a starburst
coexists with an active galactic nucleus (AGN), it is unclear whether the
starburst, the AGN, or both are driving the outflows. The present paper
describes the results from a search for outflows in 35 infrared-faint Seyferts
with 10^9.9 < L_IR/L_sun < 10^11, or, equivalently, star formation rates (SFR)
of ~0.4 -- 9 solar masses per year, to attempt to isolate the source of the
outflow. We find that the outflow detection rates for the infrared-faint
Seyfert 1s (6%) and Seyfert 2s (18%) are lower than previously reported for
infrared-luminous Seyfert 1s (50%) and Seyfert 2s (45%). The outflow kinematics
of infrared-faint and infrared-bright Seyfert 2 galaxies resemble those of
starburst galaxies, while the outflow velocities in Seyfert 1 galaxies are
significantly larger. Taken together, these results suggest that the AGN does
not play a significant role in driving the outflows in most infrared-faint and
infrared-bright systems, except the high-velocity outflows seen in Seyfert 1
galaxies. Another striking result of this study is the high rate of detection
of inflows in infrared-faint galaxies (39% of Seyfert 1s, 35% of Seyfert 2s),
significantly larger than in infrared-luminous Seyferts (15%). This inflow may
be contributing to the feeding of the AGN in these galaxies, and potentially
provides more than enough material to power the observed nuclear activity over
typical AGN lifetimes.Comment: 17 pages, 12 figures, published in ApJ (article updated 12/30/09
Single photon generation by pulsed excitation of a single dipole
The fluorescence of a single dipole excited by an intense light pulse can
lead to the generation of another light pulse containing a single photon. The
influence of the duration and energy of the excitation pulse on the number of
photons in the fluorescence pulse is studied. The case of a two-level dipole
with strongly damped coherences is considered. The presence of a metastable
state leading to shelving is also investigated.Comment: 17 pages, 4 figures, submitted to PR
Radial Velocity Offsets Due to Mass Outflows and Extinction in Active Galactic Nuclei
We present a study of the radial velocity offsets between narrow emission
lines and host galaxy lines (stellar absorption and H I 21-cm emission) in
Seyfert galaxies with observed redshifts less than 0.043. We find that 35% of
the Seyferts in the sample show [O III] emission lines with blueshifts with
respect to their host galaxies exceeding 50 km/s, whereas only 6% show
redshifts this large, in qualitative agreement with most previous studies. We
also find that a greater percentage of Seyfert 1 galaxies show blueshifts than
Seyfert 2 galaxies. Using HST/STIS spatially-resolved spectra of the Seyfert 2
galaxy NGC 1068 and the Seyfert 1 galaxy NGC 4151, we generate geometric models
of their narrow-line regions (NLRs) and inner galactic disks, and show how
these models can explain the blueshifted [O III] emission lines in collapsed
STIS spectra of these two Seyferts. We conclude that the combination of mass
outflow of ionized gas in the NLR and extinction by dust in the inner disk
(primarily in the form of dust spirals) is primarily responsible for the
velocity offsets in Seyfert galaxies. More exotic explanations are not needed.
We discuss the implications of this result for the velocity offsets found in
higher redshift AGN.Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical
Journa
Correlative Microscopy Of Bone In Implant Osteointegration Studies.
Routine morphological analyses usually include investigations by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Each of these techniques provides specific information on tissue morphology and all the obtained results are then combined to give an in-depth morphological overview of the examined sample. The limitations of this traditional comparative microscopy lie in the fact that each technique requires a different experimental sample, so that many specimens are necessary and the combined results come from different samples. The present study describes a technical procedure of correlative microscopy, which allows us to examine the same bone section first by LM and then, after appropriate processing, by SEM or TEM. Thanks to the possibility of analyzing the same undecalcified bone sections both by LM and SEM, the approach described in the present study allows us to make very accurate evaluations of old/new bone morphology at the bone-implant interface
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