2,333 research outputs found
Energies and widths of atomic core-levels in liquid mercury
High-resolution measurements of the photoinduced X-ray emission of liquid mercury were performed, using a transmission DuMond-type crystal spectrometer for transitions above 11 keV and a reflection von Hamos-type crystal spectrometer for transitions below 11 keV. The target X-ray fluorescence was produced by irradiating the sample with the Bremsstrahlung from X-ray tubes. The energies and natural linewidths of 6 K-shell, 26 L-shell and 2 M-shell X-ray transitions were determined. Using a least-squares-fit method to solve the two sets of equations derived from the observed transition energies and transition widths the binding energies of the subshells K to M5 and O1 and the level widths of the subshells K to N5 and O1 could also be determine
Multiple Molecular H2 Outflows in AFGL 618
We report high spatial (0.5 arcsec) and high spectral (9 km/s) resolution
spectro-imaging of the 2.12 micron H2 1-0 S(1) line in the proto-planetary
nebula AFGL 618 using BEAR at the CFHT. The observations reveal the presence of
multiple, high-velocity, molecular outflows that align with the remarkable
optical jets seen in HST images. The structure and kinematics of the outflows
show how jets interact with circumstellar gas and shape the environment in
which planetary nebulae form.Comment: 14 pages, 5 figures. To appear in The Astrophysical Journal Letter
Deuterium on Venus: Observations from Earth
In view of the importance of the deuterium-to-hydrogen ratio in understanding the evolutionary scenario of planetary atmospheres and its relationship to understanding the evolution of our own Earth, we undertook a series of observations designed to resolve previous observational conflicts. We observed the dark side of Venus in the 2.3 micron spectral region in search of both H2O and HDO, which would provide us with the D/H ratio in Venus' atmosphere. We identified a large number of molecular lines in the region, belonging to both molecules, and, using synthetic spectral techniques, obtained mixing ratios of 34 plus or minus 10 ppm and 1.3 plus or minus 0.2 ppm for H2O and HDO, respectively. These mixing ratios yield a D/H ratio for Venus of D/H equals 1.9 plus or minus 0.6 times 10 (exp 12) and 120 plus or minus 40 times the telluric ratio. Although the detailed interpretation is difficult, our observations confirm that the Pioneer Venus Orbiter results and establish that indeed Venus had a period in its early history in which it was very wet, perhaps not unlike the early wet period that seems to have been present on Mars, and that, in contrast to Earth, lost much of its water over geologic time
The saga of the Ising susceptibility
We review developments made since 1959 in the search for a closed form for
the susceptibility of the Ising model. The expressions for the form factors in
terms of the nome and the modulus are compared and contrasted. The
generalized correlations are defined and explicitly
computed in terms of theta functions for .Comment: 19 pages, 1 figur
Artificial dry surface biofilm (DSB) models for testing the efficacy of cleaning and disinfection
Dry surface biofilms (DSB) harbouring pathogens are widespread in healthcare settings, difficult to detect and resistant to cleaning and disinfection interventions. Here, we describe a practical test protocol to palliate the lack of standard efficacy test methods for DSB.
Staphylococcus aureus DSB were produced over a 12‐day period, grown with or without the presence of organic matter, and their composition and viability were evaluated. Disinfectant treatment was conducted with a modified ASTM2967‐15 test and reduction in viability, transferability, and biofilm regrowth post treatment were measured. Dry surface biofilms produced over a 12‐day period had a similar carbohydrates, proteins and DNA content, regardless the presence or absence of organic matter. The combination of sodium hypochlorite (1,000 ppm) and a microfiber cloth was only effective against DSB in the absence of organic load. With the increasing concerns of the uncontrolled presence of DSB in healthcare settings, the development of effective interventions is paramount. We propose that our DSB model in the presence of organic load is appropriate for the testing of biocidal products, while the use of three parameters, log10 reduction, transferability and regrowth, provides an accurate and practical measurement of product efficacy
Random Matrix Theory and Classical Statistical Mechanics. I. Vertex Models
A connection between integrability properties and general statistical
properties of the spectra of symmetric transfer matrices of the asymmetric
eight-vertex model is studied using random matrix theory (eigenvalue spacing
distribution and spectral rigidity). For Yang-Baxter integrable cases,
including free-fermion solutions, we have found a Poissonian behavior, whereas
level repulsion close to the Wigner distribution is found for non-integrable
models. For the asymmetric eight-vertex model, however, the level repulsion can
also disappearand the Poisson distribution be recovered on (non Yang--Baxter
integrable) algebraic varieties, the so-called disorder varieties. We also
present an infinite set of algebraic varieties which are stable under the
action of an infinite discrete symmetry group of the parameter space. These
varieties are possible loci for free parafermions. Using our numerical
criterion we have tested the generic calculability of the model on these
algebraic varieties.Comment: 25 pages, 7 PostScript Figure
Near-infrared oxygen airglow from the Venus nightside
Groundbased imaging and spectroscopic observations of Venus reveal intense near-infrared oxygen airglow emission from the upper atmosphere and provide new constraints on the oxygen photochemistry and dynamics near the mesopause (approximately 100 km). Atomic oxygen is produced by the Photolysis of CO2 on the dayside of Venus. These atoms are transported by the general circulation, and eventually recombine to form molecular oxygen. Because this recombination reaction is exothermic, many of these molecules are created in an excited state known as O2(delta-1). The airglow is produced as these molecules emit a photon and return to their ground state. New imaging and spectroscopic observations acquired during the summer and fall of 1991 show unexpected spatial and temporal variations in the O2(delta-1) airglow. The implications of these observations for the composition and general circulation of the upper venusian atmosphere are not yet understood but they provide important new constraints on comprehensive dynamical and chemical models of the upper mesosphere and lower thermosphere of Venus
A Fast and Efficient Incremental Approach toward Dynamic Community Detection
Community detection is a discovery tool used by network scientists to analyze
the structure of real-world networks. It seeks to identify natural divisions
that may exist in the input networks that partition the vertices into coherent
modules (or communities). While this problem space is rich with efficient
algorithms and software, most of this literature caters to the static use-case
where the underlying network does not change. However, many emerging real-world
use-cases give rise to a need to incorporate dynamic graphs as inputs.
In this paper, we present a fast and efficient incremental approach toward
dynamic community detection. The key contribution is a generic technique called
, which examines the most recent batch of changes made to an
input graph and selects a subset of vertices to reevaluate for potential
community (re)assignment. This technique can be incorporated into any of the
community detection methods that use modularity as its objective function for
clustering. For demonstration purposes, we incorporated the technique into two
well-known community detection tools. Our experiments demonstrate that our new
incremental approach is able to generate performance speedups without
compromising on the output quality (despite its heuristic nature). For
instance, on a real-world network with 63M temporal edges (over 12 time steps),
our approach was able to complete in 1056 seconds, yielding a 3x speedup over a
baseline implementation. In addition to demonstrating the performance benefits,
we also show how to use our approach to delineate appropriate intervals of
temporal resolutions at which to analyze an input network
New Results on the Helium Stars in the Galactic Center Using BEAR Spectro-Imagery
Integral field spectroscopy of the central parsec of the Galactic Center was obtained at 2.06 microns using BEAR, an imaging Fourier Transform Spectrometer, at a spectral resolution of 74 km/s. Sixteen stars were confirmed as helium stars by detecting the He I 2.058 microns line in emission, providing a homogeneous set of fully resolved line profiles. These observations allow us to discard some of the earlier detections of such stars in the central cluster and to add three new stars. The sources detected in the BEAR data were compared with adaptive optics images in the K band to determine whether the emission was due to single stars. Two sub-classes of almost equal number are clearly identified from the width of their line profiles, and from the brightness of their continuum. Most of the emission lines show a P Cygni profile. From these results, we propose that the latter group is formed of stars in or near the LBV phase, and the other one of stars at the WR stage. The division into two groups is also shown by their spatial distribution, with the narrow-line stars in a compact central cluster (IRS 16) and the other group distributed at the periphery of the central cluster of hot stars. In the same data cube, streamers of interstellar helium gas are also detected. The helium emission traces the densest parts of the SgrA West Mini-Spiral. Several helium stars have a radial velocity comparable to the velocity of the interstellar gas in which they are embedded. In the final discussion, all these findings are examined to present a possible scenario for the formation of very massive stars in the exceptional conditions of the vicinity of the central Black Hole
Holonomic functions of several complex variables and singularities of anisotropic Ising n-fold integrals
Lattice statistical mechanics, often provides a natural (holonomic) framework
to perform singularity analysis with several complex variables that would, in a
general mathematical framework, be too complex, or could not be defined.
Considering several Picard-Fuchs systems of two-variables "above" Calabi-Yau
ODEs, associated with double hypergeometric series, we show that holonomic
functions are actually a good framework for actually finding the singular
manifolds. We, then, analyse the singular algebraic varieties of the n-fold
integrals , corresponding to the decomposition of the magnetic
susceptibility of the anisotropic square Ising model. We revisit a set of
Nickelian singularities that turns out to be a two-parameter family of elliptic
curves. We then find a first set of non-Nickelian singularities for and , that also turns out to be rational or ellipic
curves. We underline the fact that these singular curves depend on the
anisotropy of the Ising model. We address, from a birational viewpoint, the
emergence of families of elliptic curves, and of Calabi-Yau manifolds on such
problems. We discuss the accumulation of these singular curves for the
non-holonomic anisotropic full susceptibility.Comment: 36 page
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