23,574 research outputs found
The Bizarre Spectral Variability of Central Stars of Planetary Nebulae
A radial velocity (RV) survey to detect central stars in binary systems was
carried out between 2002 and 2004. De Marco et al. (2004) reported that 10 out
of 11 monitored stars exhibited strong RV variability, but periods were not
detected. Since other mechanisms, such as wind variability, can cause apparent
RV variations, we monitored 4 of the 10 RV-variable stars at echelle
resolutions to determine the origin of the variability. Although RV changes are
confirmed for all four stars, none of them can be ascribed to binarity at this
time. However, only for IC4593 is wind variability able to explain most (though
not all) spectral variability. For BD+332642, no wind and no pulsations appear
to be the origin of the RV changes. Finally, M1-77 and M2-54, both known to be
irregular photometric variables, exhibit dramatic RV and line shape variability
of the hydrogen and HeI absorption lines, as well as large RV variability of
weaker lines, which do not change in shape. There is no satisfactory
explanation of this variability, though a combination of wind variability and
pulsations is still the best guess at what makes these stars so variable. We
suggest that luminous central stars are ill suited to detect spectroscopic
binaries, because winds (and possibly pulsations) are pervasive and would mask
even strong periodicities. It it likely that a sample of intrinsically faint
central stars would more readily yield binary information.Comment: 7 pages, 3 figures. To appear in the proceedings of the conference
"Asymmetric Planetary Nebulae IV
Second-order quantum nonlinear optical processes in single graphene nanostructures and arrays
Intense efforts have been made in recent years to realize nonlinear optical
interactions at the single-photon level. Much of this work has focused on
achieving strong third-order nonlinearities, such as by using single atoms or
other quantum emitters while the possibility of achieving strong second-order
nonlinearities remains unexplored. Here, we describe a novel technique to
realize such nonlinearities using graphene, exploiting the strong per-photon
fields associated with tightly confined graphene plasmons in combination with
spatially nonlocal nonlinear optical interactions. We show that in properly
designed graphene nanostructures, these conditions enable extremely strong
internal down-conversion between a single quantized plasmon and an entangled
plasmon pair, or the reverse process of second harmonic generation. A separate
issue is how such strong internal nonlinearities can be observed, given the
nominally weak coupling between these plasmon resonances and free-space
radiative fields. On one hand, by using the collective coupling to radiation of
nanostructure arrays, we show that the internal nonlinearities can manifest
themselves as efficient frequency conversion of radiative fields at extremely
low input powers. On the other hand, the development of techniques to
efficiently couple to single nanostructures would allow these nonlinear
processes to occur at the level of single input photons.Comment: 25 pages, 6 figure
Basin scale assessment of landslides geomorphological setting by advanced InSAR analysis
An extensive investigation of more than 90 landslides affecting a small river basin in Central
Italy was performed by combining field surveys and remote sensing techniques. We thus defined the
geomorphological setting of slope instability processes. Basic information, such as landslides mapping
and landslides type definition, have been acquired thanks to geomorphological field investigations
and multi-temporal aerial photos interpretation, while satellite SAR archive data (acquired by ERS
and Envisat from 1992 to 2010) have been analyzed by means of A-DInSAR (Advanced Differential
Interferometric Synthetic Aperture Radar) techniques to evaluate landslides past displacements
patterns. Multi-temporal assessment of landslides state of activity has been performed basing
on geomorphological evidence criteria and past ground displacement measurements obtained by
A-DInSAR. This step has been performed by means of an activity matrix derived from information
achieved thanks to double orbital geometry. Thanks to this approach we also achieved more detailed
knowledge about the landslides kinematics in time and space
Follow-up study of over three years of patients with uveitis after cataract phacoemulsification: outcomes and complications
Purpose: To evaluate the rate and onset of intraoperative and postoperative complications post-phacoemulsification.
Methods: One hundred sixty-two eyes of 145 patients with uveitis who underwent phacoemulsification
between 2006 and 2009 were identified through surgical record review. Fifty-nine eyes of 46 patients met
the inclusion criteria. Hazard ratio (HR) and Kaplan-Meier survival probability were calculated for each class
of uveitis. Results: Macular edema (ME) resulted to be associated to chronic postoperative inflammation
(r = 0.6; p = 0.00) and mostly related to patients who presented more than one postoperative relapse/year (r = 0.2;
p = 0.02). Fuchs uveitis resulted to be a risk factor for posterior capsule opacification (PCO) (HR 3.36
IC95%1.0-10.5; p = 0.03). Hypotony and elevated intraocular pressure (IOP) were detected in the anterior uveitis
group (0.02 EY). Conclusion: The HR to develop ME was significantly related to chronic anterior uveitis. PCO
and elevated IOP are
Hot Quark Matter with an Axial Chemical Potential
We analyze the phase diagram of hot quark matter in presence of an axial
chemical potential, . The latter is introduced to mimic the chirality
transitions induced, in hot Quantum Chromodynamics, by the strong sphaleron
configurations. In particular, we study the curvature of the critical line at
small , the effects of a finite quark mass and of a vector interaction.
Moreover, we build the mixed phase at the first order phase transition line,
and draw the phase diagram in the chiral density and temperature plane. We
finally compute the full topological susceptibility in presence of a background
of topological charge.Comment: 12 pages, 7 figures. Few references added, short discussion included.
Final version appearing on Phys. Rev.
Analysis of second harmonic generation in photonic-crystal-assisted waveguides
We study second harmonic generation in a planar dielectric waveguide having a
low-index, polymer core layer, bounded by two multilayer stacks. This geometry
allows exceptionally strong confinement of the light at the fundamental
wavelength inside the core region with virtually zero net propagation losses
for distances that exceed several centimeters, provided material and scattering
losses are neglected. A phase-matched configuration of the waveguide is
reported in which the pump signal is the lowest-order mode of the waveguide,
and the generated second harmonic signal corresponds to the third propagation
mode of the waveguide. Using a polymer waveguide core, having chi(2)=100 pm/V,
we predict a conversion efficiency of approximately 90% after a propagation
distance of 2 mm, using peak pump intensities inside the core of the waveguide
of 1.35 GW/cm^2. If the waveguide core contains polymer layers with different
glass transition temperatures, the layers can be poled independently to
maximize the overlap integral, and similar pump depletions may be achieved over
a distance of approximately 500 microns.Comment: 20 pages, 7 figures, 330k
Constitutional Challenges to Washington\u27s Limit on Noneconomic Damages in Cases of Personal Injury and Death
This Comment considers the constitutionality of the Washington cap on noneconomic damages. The Comment briefly reviews the recent legislation of medical malpractice and tort reform damages ceilings and judicial decisions on the constitutionality of such ceilings. The Comment then analyzes the constitutionality of the Washington limit under the substantive due process and equal protection guarantees of the federal and state constitutions. Because under the federal constitution a court should give the statute only minimal scrutiny, the statute probably does not offend fourteenth amendment protections. Under the Washington Constitution, however, a court should give the statute intermediate scrutiny. Under intermediate scrutiny a court probably will hold that the limit violates the state equal protection guarantee, but a court probably will not hold the limit violative of substantive due process. Under the right of trial by jury guarantee of the state constitution, the statute also is unconstitutional
Facial displays in young tufted capuchin monkeys (Cebus apella): appearance, meaning, context and target
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