404 research outputs found
A Genetic Algorithm-Based Exploration of Three Filament Models: A Case for the Magnetic Support of the G11.11-0.12 Infrared-Dark Cloud
The G11.11-0.12 infrared-dark cloud has a filamentary appearance, both in
extinction against the diffuse infrared emission of the Galactic plane and in
emission at 850 microns. We use a novel computational technique based on an
advanced genetic algorithm to explore thoroughly 3 different models of
self-gravitating, pressure truncated filaments and to constrain their
parameters. Specifically, the models tested are the non-magnetic Ostriker
(1964) model, a generalized version of the magnetic Stodolkiewicz (1963) model,
and the magnetic Fiege & Pudritz (2000) model. Previous results showed that
G11.11-0.12 has a much steeper r^{-4} radial density profile than other
filaments, where the density varies approximately as r^{-2}, and that this
steep density profile is consistent with the Ostriker (1964) model. We present
a more complete analysis that shows that the radial structure of G11.11-0.12 is
consistent with regimes of each of these models. All of the magnetic models
that agree with the data are threaded by a dominant poloidal magnetic field,
and most have dynamically significant fields. Thus, G11.11-0.12 is an excellent
candidate for radial support by a magnetic field that is predominantly
poloidal. We predict the polarization patterns expected for both magnetic
models and show that the two magnetic models produce different polarization
patterns that should be distingished by observations.Comment: To appear in Ap.J. Dec. 1 edition, volume 616. 40 pages and 42
figures. Figures are severely reduced to satisfy astro-ph size limits. A
version with higher quality figures is available by contacting the first
autho
Dynamics of an Intruder in Dense Granular Fluids
We investigate the dynamics of an intruder pulled by a constant force in a
dense two-dimensional granular fluid by means of event-driven molecular
dynamics simulations. In a first step, we show how a propagating momentum front
develops and compactifies the system when reflected by the boundaries. To be
closer to recent experiments \cite{candelier2010journey,candelier2009creep}, we
then add a frictional force acting on each particle, proportional to the
particle's velocity. We show how to implement frictional motion in an
event-driven simulation. This allows us to carry out extensive numerical
simulations aiming at the dependence of the intruder's velocity on packing
fraction and pulling force. We identify a linear relation for small and a
nonlinear regime for high pulling forces and investigate the dependence of
these regimes on granular temperature
Discovery of a massive SCUBA core with both inflow and outflow motions
We report the discovery of a massive SCUBA core with evidence of inflow and
outflow motions. This core is detected by SCUBA at both 450 and 850 micro
meter. Barely resolved by the telescope beam at 450 micro meter, it has a size
of 10 arcsec, corresponding to 0.28 pc at a distance of 5.7 kpc. The dust
temperature is estimated to be less than 29 K, the total mass is 820 solar mass
and the average density is 1.1e-6 per cube-cm in a region with a radius of 5
arcsec. Follow-up spectral line observations, including HCN (3-2), HCO+ (3-2),
H13CO+ (3-2) and C17O (2-1) reveal a typical blue profile which indicates that
this core is collapsing. The CO (3-2) line profile is as broad as 38 km/s,
indicating outflow motions in this region. This core is approximately 1.5 pc
away from the known HII region G25.4NW, but there are no obvious radio, IRAS,
MSX or Spitzer sources associated with it. We suggest that this core is at a
very early stage of massive star or cluster formation.Comment: 12 pages, 2 figures, 1 table, accepted by ApJ
The G11.11-0.12 Infrared-Dark Cloud: Anomalous Dust and a Non-Magnetic Isothermal Model
The G11.11-0.12 Infrared-Dark Cloud has a filamentary appearance, both in
absorption against the diffuse 8micron Galactic background, and in emission
from cold dust at 850micron. Detailed comparison of the dust properties at
these two wavelengths reveals that standard models for the diffuse interstellar
dust in the Galaxy are not consistent with the observations. The ratio of
absorption coefficients within the cloud is kappa_8/kappa_850 <= 1010, which is
well below that expected for the diffuse ISM where kappa_8/kappa_850 ~ 1700.
This may be due to the formation of ice mantles on the dust and grain
coagulation, both of which are expected within dense regions of molecular
clouds. The 850micron emission probes the underlying radial structure of the
filament. The profile is well represented by a marginally resolved central
region and a steeply falling envelope, with Sigma(r) proportional to r^(-a),
where a <= 3, indicating that G11.11-0.12 is the first observed filament with a
profile similar to that of a non-magnetic isothermal cylinder.Comment: 13 pages, 4 figures, accepted for publication by ApJ Letter
Radiative transfer models of non-spherical prestellar cores
We present 2D Monte Carlo radiative transfer simulations of prestellar cores.
We consider two types of asymmetry: disk-like asymmetry, in which the core is
denser towards the equatorial plane than towards the poles; and axial
asymmetry, in which the core is denser towards the south pole than the north
pole. We limit our treatment to cores with mild asymmetries, which are exposed
directly to the interstellar radiation field or are embedded inside molecular
clouds.
The isophotal maps of a core depend strongly on the viewing angle. Maps at
wavelengths longer than the peak of the SED (e.g. 850 micron) essentially trace
the column-density. Thus, for instance, cores with disk-like asymmetry appear
elongated when mapped at 850 micron from close to the equatorial plane.
However, at wavelengths near the peak of the SED (e.g. 200 micron), the
emissivity is more strongly dependent on the temperature, and therefore, at
particular viewing angles, there are characteristic features which reflect a
more complicated convolution of the density and temperature fields within the
core.
These characteristic features are on scales 1/5 to 1/3 of the overall core
size, and so high resolution observations are needed to observe them. They are
also weaker if the core is embedded in a molecular cloud (because the range of
temperature within the core is then smaller), and so high sensitivity is needed
to detect them. Herschel, to be launched in 2007, will in principle provide the
necessary resolution and sensitivity at 170 to 250 micron.Comment: 16 pages, 22 figures, accepted by A&A, also available (with high
resolution figures) at
http://www.astro.cf.ac.uk/pub/Dimitrios.Stamatellos/publications
Screening of melon genotypes for resistance to vegetable leafminer and your phenotypic correlations with colorimetry.
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Efficient Passive ICS Device Discovery and Identification by MAC Address Correlation
Owing to a growing number of attacks, the assessment of Industrial Control
Systems (ICSs) has gained in importance. An integral part of an assessment is
the creation of a detailed inventory of all connected devices, enabling
vulnerability evaluations. For this purpose, scans of networks are crucial.
Active scanning, which generates irregular traffic, is a method to get an
overview of connected and active devices. Since such additional traffic may
lead to an unexpected behavior of devices, active scanning methods should be
avoided in critical infrastructure networks. In such cases, passive network
monitoring offers an alternative, which is often used in conjunction with
complex deep-packet inspection techniques. There are very few publications on
lightweight passive scanning methodologies for industrial networks. In this
paper, we propose a lightweight passive network monitoring technique using an
efficient Media Access Control (MAC) address-based identification of industrial
devices. Based on an incomplete set of known MAC address to device
associations, the presented method can guess correct device and vendor
information. Proving the feasibility of the method, an implementation is also
introduced and evaluated regarding its efficiency. The feasibility of
predicting a specific device/vendor combination is demonstrated by having
similar devices in the database. In our ICS testbed, we reached a host
discovery rate of 100% at an identification rate of more than 66%,
outperforming the results of existing tools.Comment: http://dx.doi.org/10.14236/ewic/ICS2018.
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