23,963 research outputs found
New line-interactive UPS system with DSP-based active power-line conditioning
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Deep optical imaging of AGB circumstellar envelopes
We report results of a program to image the extended circumstellar envelopes
of asymptotic giant branch (AGB) stars in dust-scattered Galactic light. The
goal is to characterize the shapes of the envelopes to probe the mass-loss
geometry and the presence of hidden binary companions. The observations consist
of deep optical imaging of 22 AGB stars with high mass loss rates: 16 with the
ESO 3.5 m NTT telescope, and the remainder with other telescopes. The
circumstellar envelopes are detected in 15 objects, with mass loss rates > 2E-6
Msun/year. The surface brightness of the envelopes shows a strong decrease with
Galactic radius, which indicates a steep radial gradient in the interstellar
radiation field. The envelopes range from circular to elliptical in shape, and
we characterize them by the ellipticity (E = major/minor axis) of iso-intensity
contours. We find that about 50 percent of the envelopes are close to circular
with E
1.2. We interpret the shapes in terms of populations of single stars and
binaries whose envelopes are flattened by a companion. The distribution of E is
qualitatively consistent with expectations based on population synthesis models
of binary AGB stars. We also find that about 50 percent of the sample exhibit
small-scale, elongated features in the central regions. We interpret these as
the escape of light from the central star through polar holes, which are also
likely produced by companions. Our observations of envelope flattening and
polar holes point to a hidden population of companions within the circumstellar
envelopes of AGB stars. These companions are expected to play an important role
in the transition to post-AGB stars and the formation of planetary nebulae.Comment: 19 pages, 13 figures, color pictures in Appendix, accepted by A&
The consistency condition for the three-point function in dissipative single-clock inflation
We generalize the consistency condition for the three-point function in
single field inflation to the case of dissipative, multi-field, single-clock
models. We use the recently introduced extension of the effective field theory
of inflation that accounts for dissipative effects, to provide an explicit
proof to leading (non-trivial) order in the generalized slow roll parameters
and mixing with gravity scales. Our results illustrate the conditions necessary
for the validity of the consistency relation in situations with many degrees of
freedom relevant during inflation, namely that there is a preferred clock.
Departures from this condition in forthcoming experiments would rule out not
only single field but also a large class of multi-field models.Comment: 26+11 page
Atmospheric hydroxyl radical (OH) abundances from ground-based ultraviolet solar spectra: an improved retrieval method
The Fourier Transform Ultraviolet Spectrometer (FTUVS) instrument has recorded a long-term data record of the atmospheric column abundance of the hydroxyl radical (OH) using the technique of high resolution solar absorption spectroscopy. We report new efforts in improving the precision of the OH measurements in order to better model the diurnal, seasonal, and interannual variability of odd hydrogen (HOx) chemistry in the stratosphere, which, in turn, will improve our understanding of ozone chemistry and its long-term changes. Until the present, the retrieval method has used a single strong OH absorption line P1(1) in the near-ultraviolet at 32,341 cm−1. We describe a new method that uses an average based on spectral fits to multiple lines weighted by line strength and fitting precision. We have also made a number of improvements in the ability to fit a model to the spectral feature, which substantially reduces the scatter in the measurements of OH abundances
A Naturally Large Four-Point Function in Single Field Inflation
Non-Gaussianities of the primordial density perturbations have emerged as a
very powerful possible signal to test the dynamics that drove the period of
inflation. While in general the most sensitive observable is the three-point
function in this paper we show that there are technically natural inflationary
models where the leading source of non-Gaussianity is the four-point function.
Using the recently developed Effective Field Theory of Inflation, we are able
to show that it is possible to impose an approximate parity symmetry and an
approximate continuos shift symmetry on the inflaton fluctuations that allow,
when the dispersion relation is of the form , for a unique
quartic operator, while approximately forbidding all the cubic ones. The
resulting shape for the four-point function is unique. In the models where the
dispersion relation is of the form a similar construction
can be carried out and additional shapes are possible.Comment: 13 pages, 1 figure. v2: extended discussion on near-de-Sitter model
Structure of a liquid crystalline fluid around a macroparticle: Density functional theory study
The structure of a molecular liquid, in both the nematic liquid crystalline
and isotropic phases, around a cylindrical macroparticle, is studied using
density functional theory. In the nematic phase the structure of the fluid is
highly anisotropic with respect to the director, in agreement with results from
simulation and phenomenological theories. On going into the isotropic phase the
structure becomes rotationally invariant around the macroparticle with an
oriented layer at the surface.Comment: 10 pages, 6 figues. Submitted to Phys. Rev.
The Scaling Behavior of Classical Wave Transport in Mesoscopic Media at the Localization Transition
The propagation of classical wave in disordered media at the Anderson
localization transition is studied. Our results show that the classical waves
may follow a different scaling behavior from that for electrons. For electrons,
the effect of weak localization due to interference of recurrent scattering
paths is limited within a spherical volume because of electron-electron or
electron-phonon scattering, while for classical waves, it is the sample
geometry that determine the amount of recurrent scattering paths that
contribute. It is found that the weak localization effect is weaker in both
cubic and slab geometry than in spherical geometry. As a result, the averaged
static diffusion constant D(L) scales like ln(L)/L in cubic or slab geometry
and the corresponding transmission follows ~ln L/L^2. This is in contrast
to the behavior of D(L)~1/L and ~1/L^2 obtained previously for electrons
or spherical samples. For wave dynamics, we solve the Bethe-Salpeter equation
in a disordered slab with the recurrent scattering incorporated in a
self-consistent manner. All of the static and dynamic transport quantities
studied are found to follow the scaling behavior of D(L). We have also
considered position-dependent weak localization effects by using a plausible
form of position-dependent diffusion constant D(z). The same scaling behavior
is found, i.e., ~ln L/L^2.Comment: 11 pages, 12 figures. Submitted to Phys. Rev. B on 3 May 200
Conformal consistency relations for single-field inflation
We generalize the single-field consistency relations to capture not only the
leading term in the squeezed limit---going as 1/q^3, where q is the small
wavevector---but also the subleading one, going as 1/q^2. This term, for an
(n+1)-point function, is fixed in terms of the variation of the n-point
function under a special conformal transformation; this parallels the fact that
the 1/q^3 term is related with the scale dependence of the n-point function.
For the squeezed limit of the 3-point function, this conformal consistency
relation implies that there are no terms going as 1/q^2. We verify that the
squeezed limit of the 4-point function is related to the conformal variation of
the 3-point function both in the case of canonical slow-roll inflation and in
models with reduced speed of sound. In the second case the conformal
consistency conditions capture, at the level of observables, the relation among
operators induced by the non-linear realization of Lorentz invariance in the
Lagrangian. These results mean that, in any single-field model, primordial
correlation functions of \zeta are endowed with an SO(4,1) symmetry, with
dilations and special conformal transformations non-linearly realized by \zeta.
We also verify the conformal consistency relations for any n-point function in
models with a modulation of the inflaton potential, where the scale dependence
is not negligible. Finally, we generalize (some of) the consistency relations
involving tensors and soft internal momenta.Comment: 26 pages, 1 figure. v2. Corrected typos, notably a sign error in eq.
(54). Matches JCAP published versio
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