3,790 research outputs found
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
Robust Online Monitoring of Signal Temporal Logic
Signal Temporal Logic (STL) is a formalism used to rigorously specify
requirements of cyberphysical systems (CPS), i.e., systems mixing digital or
discrete components in interaction with a continuous environment or analog com-
ponents. STL is naturally equipped with a quantitative semantics which can be
used for various purposes: from assessing the robustness of a specification to
guiding searches over the input and parameter space with the goal of falsifying
the given property over system behaviors. Algorithms have been proposed and
implemented for offline computation of such quantitative semantics, but only
few methods exist for an online setting, where one would want to monitor the
satisfaction of a formula during simulation. In this paper, we formalize a
semantics for robust online monitoring of partial traces, i.e., traces for
which there might not be enough data to decide the Boolean satisfaction (and to
compute its quantitative counterpart). We propose an efficient algorithm to
compute it and demonstrate its usage on two large scale real-world case studies
coming from the automotive domain and from CPS education in a Massively Open
Online Course (MOOC) setting. We show that savings in computationally expensive
simulations far outweigh any overheads incurred by an online approach
Exoplanet science with the LBTI: instrument status and plans
The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument
of the LBT designed for high-sensitivity, high-contrast, and high-resolution
infrared (1.5-13 m) imaging of nearby planetary systems. To carry out a
wide range of high-spatial resolution observations, it can combine the two
AO-corrected 8.4-m apertures of the LBT in various ways including direct
(non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging,
non-redundant aperture masking, and nulling interferometry. It also has
broadband, narrowband, and spectrally dispersed capabilities. In this paper, we
review the performance of these modes in terms of exoplanet science
capabilities and describe recent instrumental milestones such as first-light
Fizeau images (with the angular resolution of an equivalent 22.8-m telescope)
and deep interferometric nulling observations.Comment: 12 pages, 6 figures, Proc. SPI
Adaptive Optics Imaging of the AU Microscopii Circumstellar Disk: Evidence for Dynamical Evolution
We present an H-band image of the light scattered from circumstellar dust
around the nearby (10 pc) young M star AU Microscopii (AU Mic, GJ 803, HD
197481), obtained with the Keck adaptive optics system. We resolve the disk
both vertically and radially, tracing it over 17-60 AU from the star. Our AU
Mic observations thus offer the possibility to probe at high spatial resolution
(0.04" or 0.4 AU per resolution element) for morphological signatures of the
debris disk on Solar-System scales. Various sub-structures (dust clumps and
gaps) in the AU Mic disk may point to the existence of orbiting planets. No
planets are seen in our H-band image down to a limiting mass of 1 M_Jup at >20
AU, although the existence of smaller planets can not be excluded from the
current data. Modeling of the disk surface brightness distribution at H-band
and R-band, in conjunction with the optical to sub-millimeter spectral energy
distribution, allows us to constrain the disk geometry and the dust grain
properties. We confirm the nearly edge-on orientation of the disk inferred from
previous observations, and deduce an inner clearing radius <=10 AU. We find
evidence for a lack of small grains in the inner (<60 AU) disk, either as a
result of primordial disk evolution, or because of destruction by
Poynting-Robertson and/or corpuscular drag. A change in the power-law index of
the surface brightness profile is observed near 33 AU, similar to a feature
known in the profile of the beta Pic circumstellar debris disk. By comparing
the time scales for inter-particle collisions and Poynting-Robertson drag
between the two systems, we argue that the breaks are linked to one of these
two processes.Comment: 17 pages, 7 figures, 1 table; accepted by Ap
The Beetle Genus Paralimulodes Bruch in North America, with Notes on Morphology and Behavior (Coleoptera: Limulodidae)
ASTRA: ASTrometry and phase-Referencing Astronomy on the Keck interferometer
ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the
existing Keck Interferometer which aims at providing new self-phase referencing
(high spectral resolution observation of YSOs), dual-field phase referencing
(sensitive AGN observations), and astrometric (known exoplanetary systems
characterization and galactic center general relativity in strong field regime)
capabilities. With the first high spectral resolution mode now offered to the
community, this contribution focuses on the progress of the dual field and
astrometric modes.Comment: 10 pages, 6 figures, 2 tables, SPIE 201
Mid-InfraRed imaging of the circumstellar dust around three Herbig Ae stars : HD135344, CQTau, HD163296
Planet formation has been known for many years to be tied to the spatial
distribution of gas and dust in disks around young stars. To constrain planet
formation models, imaging observations of protoplanetary disks are required. In
this framework, we have undertaken a mid-infrared imaging survey of Herbig Ae
stars, which are pre-main sequence stars of intermediate mass still surrounded
by a large amount of circumstellar material. The observations were made at a
wavelength of 20.5 m with the CAMIRAS camera mounted at the Cassegrain
focus of the Canada France Hawaii Telescope.
We report the observations of three stars, HD135344, CQTau and HD163296. The
circumstellar material around the three objects is spatially resolved. The
extensions feature a disk like shape. The images provide direct information on
two key parameters of the disk : its inclination and its outer radius. The
outer radius is found to be quite different from the one deduced from disk
models only constrained by fitting the Spectral Energy Distribution of the
object. Other parameters of the disk, such as flaring, dust mass have been
deduced from fitting both the observed extension and the spectral energy
distribution with sophisticated disk models.
Our results show how important imaging data are to tighten constraints on the
disk model parameters.Comment: 10 pages, Accepted in A&
Modelling the black hole silhouette in Sgr A* with ion tori
We calculate the "observed at infinity" image and spectrum of the accretion
structure in Sgr A*, by modelling it as an optically thin, constant angular
momentum ion torus in hydrodynamic equilibrium. The physics we consider
includes a two-temperature plasma, a toroidal magnetic field, as well as
radiative cooling by bremsstrahlung, synchrotron and inverse Compton processes.
Our relativistic model has the virtue of being fully analytic and very simple,
depending only on eight tunable parameters: the black hole spin and the
inclination of the spin axis to our line of sight, the torus angular momentum,
the polytropic index, the magnetic to total pressure ratio, the central values
of density and electron temperature and the ratio of electron to ion
temperatures. The observed image and spectrum are calculated numerically using
the ray-tracing code GYOTO. Our results demonstrate that the ion torus model is
able to account for the main features of the accretion structure surrounding
Sgr A*.Comment: 11 pages, 10 figures, submitted to A &
The origin of hydrogen line emission for five Herbig Ae/Be stars spatially resolved by VLTI/AMBER spectro-interferometry
To trace the accretion and outflow processes around YSOs, diagnostic spectral
lines such as the BrG 2.166 micron line are widely used, although due to a lack
of spatial resolution, the origin of the line emission is still unclear.
Employing the AU-scale spatial resolution which can be achieved with infrared
long-baseline interferometry, we aim to distinguish between theoretical models
which associate the BrG line emission with mass infall or mass outflow
processes. Using the VLTI/AMBER instrument, we spatially and spectrally
(R=1500) resolved the inner environment of five Herbig Ae/Be stars (HD163296,
HD104237, HD98922, MWC297, V921Sco) in the BrG emission line as well as in the
adjacent continuum. All objects (except MWC297) show an increase of visibility
within the BrG emission line, indicating that the BrG-emitting region in these
objects is more compact than the dust sublimation radius. For HD98922, our
quantitative analysis reveals that the line-emitting region is compact enough
to be consistent with the magnetospheric accretion scenario. For HD163296,
HD104237, MWC297, and V921Sco we identify a stellar wind or a disk wind as the
most likely line-emitting mechanism. We search for general trends and find that
the size of the BrG-emitting region does not seem to depend on the basic
stellar parameters, but correlates with the H-alpha line profile shape. We find
evidence for at least two distinct BrG line-formation mechanisms. Stars with a
P-Cygni H-alpha line profile and a high mass-accretion rate seem to show
particularly compact BrG-emitting regions (R_BrG/R_cont<0.2), while stars with
a double-peaked or single-peaked H-alpha-line profile show a significantly more
extended BrG-emitting region (0.6<R_BrG/R_cont<1.4), possibly tracing a stellar
wind or a disk wind.Comment: 20 pages; 11 figures; Accepted by A&A; a high quality version of the
paper can be obtained at
http://www.skraus.eu/papers/kraus.HAeBe-BrGsurvey.pd
Socioeconomic differentials in the immediate mortality effects of the national Irish smoking ban
This article has been made available through the Brunel Open Access Publishing Fund.Background: Consistent evidence has demonstrated that smoking ban policies save lives, but impacts on health inequalities are uncertain as few studies have assessed post-ban effects by socioeconomic status (SES) and findings have been inconsistent. The aim of this study was to assess the effects of the national Irish smoking ban on ischemic heart disease (IHD), stroke, and chronic obstructive pulmonary disease (COPD) mortality by discrete and composite SES indicators to determine impacts on inequalities. Methods: Census data were used to assign frequencies of structural and material SES indicators to 34 local authorities across Ireland with a 2000–2010 study period. Discrete indicators were jointly analysed through principal component analysis to generate a composite index, with sensitivity analyses conducted by varying the included indicators. Poisson regression with interrupted time-series analysis was conducted to examine monthly age and gender-standardised mortality rates in the Irish population, ages ≥35 years, stratified by tertiles of SES indicators. All models were adjusted for time trend, season, influenza, and smoking prevalence. Results: Post-ban mortality reductions by structural SES indicators were concentrated in the most deprived tertile for all causes of death, while reductions by material SES indicators were more equitable across SES tertiles. The composite indices mirrored the results of the discrete indicators, demonstrating that post-ban mortality decreases were either greater or similar in the most deprived when compared to the least deprived for all causes of death. Conclusions: Overall findings indicated that the national Irish smoking ban reduced inequalities in smoking-related mortality. Due to the higher rates of smoking-related mortality in the most deprived group, even equitable reductions across SES tertiles resulted in decreases in inequalities. The choice of SES indicator was influential in the measurement of effects, underscoring that a differentiated analytical approach aided in understanding the complexities in which structural and material factors influence mortality
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