4,313 research outputs found
When is a surface foam-phobic or foam-philic?
By integrating the Young-Laplace equation, including the effects of gravity,
we have calculated the equilibrium shape of the two-dimensional Plateau borders
along which a vertical soap film contacts two flat, horizontal solid substrates
of given wettability. We show that the Plateau borders, where most of a foam's
liquid resides, can only exist if the values of the Bond number and
of the liquid contact angle lie within certain domains in
space: under these conditions the substrate is
foam-philic. For values outside these domains, the substrate cannot support a
soap film and is foam-phobic. In other words, on a substrate of a given
wettability, only Plateau borders of a certain range of sizes can form. For
given , the top Plateau border can never have greater
width or cross-sectional area than the bottom one. Moreover, the top Plateau
border cannot exist in a steady state for contact angles above 90. Our
conclusions are validated by comparison with both experimental and numerical
(Surface Evolver) data. We conjecture that these results will hold, with slight
modifications, for non-planar soap films and bubbles. Our results are also
relevant to the motion of bubbles and foams in channels, where the friction
force of the substrate on the Plateau borders plays an important role.Comment: 20 pages, 14 figure
What is the shape of an air bubble on a liquid surface?
We have calculated the equilibrium shape of the axially symmetric meniscus along which a spherical bubble contacts a flat liquid surface, by analytically integrating the Young-Laplace equation in the presence of gravity, in the limit of large Bond numbers. This method has the advantage that it provides semi-analytical expressions for key geometrical properties of the bubble in terms of the Bond number. Results are in good overall agreement with experimental data and are consistent with fully numerical (Surface Evolver) calculations. In particular, we are able to describe how the bubble shape changes from hemispherical, with a shallow flat bottom, to lenticular, with a deeper, curved bottom, as the Bond number is decreased
Information-theoretic postulates for quantum theory
Why are the laws of physics formulated in terms of complex Hilbert spaces?
Are there natural and consistent modifications of quantum theory that could be
tested experimentally? This book chapter gives a self-contained and accessible
summary of our paper [New J. Phys. 13, 063001, 2011] addressing these
questions, presenting the main ideas, but dropping many technical details. We
show that the formalism of quantum theory can be reconstructed from four
natural postulates, which do not refer to the mathematical formalism, but only
to the information-theoretic content of the physical theory. Our starting point
is to assume that there exist physical events (such as measurement outcomes)
that happen probabilistically, yielding the mathematical framework of "convex
state spaces". Then, quantum theory can be reconstructed by assuming that (i)
global states are determined by correlations between local measurements, (ii)
systems that carry the same amount of information have equivalent state spaces,
(iii) reversible time evolution can map every pure state to every other, and
(iv) positivity of probabilities is the only restriction on the possible
measurements.Comment: 17 pages, 3 figures. v3: some typos corrected and references updated.
Summarizes the argumentation and results of arXiv:1004.1483. Contribution to
the book "Quantum Theory: Informational Foundations and Foils", Springer
Verlag (http://www.springer.com/us/book/9789401773027), 201
Synthesizing Speech from Intracranial Depth Electrodes using an Encoder-Decoder Framework
Speech Neuroprostheses have the potential to enable communication for people
with dysarthria or anarthria. Recent advances have demonstrated high-quality
text decoding and speech synthesis from electrocorticographic grids placed on
the cortical surface. Here, we investigate a less invasive measurement modality
in three participants, namely stereotactic EEG (sEEG) that provides sparse
sampling from multiple brain regions, including subcortical regions. To
evaluate whether sEEG can also be used to synthesize high-quality audio from
neural recordings, we employ a recurrent encoder-decoder model based on modern
deep learning methods. We find that speech can indeed be reconstructed with
correlations up to 0.8 from these minimally invasive recordings, despite
limited amounts of training data
On the Classical Stability of Orientifold Cosmologies
We analyze the classical stability of string cosmologies driven by the
dynamics of orientifold planes. These models are related to time-dependent
orbifolds, and resolve the orbifold singularities which are otherwise
problematic by introducing orientifold planes. In particular, we show that the
instability discussed by Horowitz and Polchinski for pure orbifold models is
resolved by the presence of the orientifolds. Moreover, we discuss the issue of
stability of the cosmological Cauchy horizon, and we show that it is stable to
small perturbations due to in-falling matter.Comment: 40 pages, 13 figures. Reference and conclusion added. Published
versio
PHANGS CO kinematics: disk orientations and rotation curves at 150 pc resolution
We present kinematic orientations and high resolution (150 pc) rotation
curves for 67 main sequence star-forming galaxies surveyed in CO (2-1) emission
by PHANGS-ALMA. Our measurements are based on the application of a new fitting
method tailored to CO velocity fields. Our approach identifies an optimal
global orientation as a way to reduce the impact of non-axisymmetric (bar and
spiral) features and the uneven spatial sampling characteristic of CO emission
in the inner regions of nearby galaxies. The method performs especially well
when applied to the large number of independent lines-of-sight contained in the
PHANGS CO velocity fields mapped at 1'' resolution. The high resolution
rotation curves fitted to these data are sensitive probes of mass distribution
in the inner regions of these galaxies. We use the inner slope as well as the
amplitude of our fitted rotation curves to demonstrate that CO is a reliable
global dynamical mass tracer. From the consistency between photometric
orientations from the literature and kinematic orientations determined with our
method, we infer that the shapes of stellar disks in the mass range of log()=9.0-10.9 probed by our sample are very close to circular
and have uniform thickness.Comment: 19 figures, 36 pages, accepted for publication in ApJ. Table of
PHANGS rotation curves available from http://phangs.org/dat
Resolved observations at 31 GHz of spinning dust emissivity variations in Oph
The Oph molecular cloud is one of the best examples of spinning dust
emission, first detected by the Cosmic Background Imager (CBI). Here we present
4.5 arcmin observations with CBI 2 that confirm 31 GHz emission from Oph
W, the PDR exposed to B-type star HD 147889, and highlight the absence of
signal from S1, the brightest IR nebula in the complex. In order to quantify an
association with dust-related emission mechanisms, we calculated correlations
at different angular resolutions between the 31 GHz map and proxies for the
column density of IR emitters, dust radiance and optical depth templates. We
found that the 31 GHz emission correlates best with the PAH column density
tracers, while the correlation with the dust radiance improves when considering
emission that is more extended (from the shorter baselines), suggesting that
the angular resolution of the observations affects the correlation results. A
proxy for the spinning dust emissivity reveals large variations within the
complex, with a dynamic range of 25 at 3 and a variation by a factor of
at least 23, at 3, between the peak in Oph W and the location of
S1, which means that environmental factors are responsible for boosting
spinning dust emissivities locally.Comment: 12 pages, 7 figures, 8 tables. Accepted for publication in MNRA
Carnegie Supernova Project-II: Extending the Near-Infrared Hubble Diagram for Type Ia Supernovae to
The Carnegie Supernova Project-II (CSP-II) was an NSF-funded, four-year
program to obtain optical and near-infrared observations of a "Cosmology"
sample of Type Ia supernovae located in the smooth Hubble flow (). Light curves were also obtained of a "Physics"
sample composed of 90 nearby Type Ia supernovae at selected for
near-infrared spectroscopic time-series observations. The primary emphasis of
the CSP-II is to use the combination of optical and near-infrared photometry to
achieve a distance precision of better than 5%. In this paper, details of the
supernova sample, the observational strategy, and the characteristics of the
photometric data are provided. In a companion paper, the near-infrared
spectroscopy component of the project is presented.Comment: 43 pages, 10 figures, accepted for publication in PAS
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