550 research outputs found
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
The active galaxy NGC 4151 has a crucial role as one of only two active
galactic nuclei for which black hole mass measurements based on emission line
reverberation mapping can be calibrated against other dynamical methods.
Unfortunately, effective calibration requires an accurate distance to NGC 4151,
which is currently not available. Recently reported distances range from 4 to
29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distance
very uncertain, and the geometry of the galaxy and its nucleus prohibit
accurate measurements using other techniques. Here we report a dust-parallax
distance to NGC 4151 of Mpc. The measurement is
based on an adaptation of a geometric method proposed previously using the
emission line regions of active galaxies. Since this region is too small for
current imaging capabilities, we use instead the ratio of the
physical-to-angular sizes of the more extended hot dust emission as determined
from time-delays and infrared interferometry. This new distance leads to an
approximately 1.4-fold increase in the dynamical black hole mass, implying a
corresponding correction to emission line reverberation masses of black holes
if they are calibrated against the two objects with additional dynamical
masses.Comment: Authors' version of a letter published in Nature (27 November 2014);
8 pages, 5 figures, 1 tabl
The dusty heart of nearby active galaxies. I. High-spatial resolution mid-IR spectro-photometry of Seyfert galaxies
We present 8-13 micron imaging and spectroscopy of 9 type 1 and 10 type 2 AGN
obtained with the VLT/VISIR instrument at spatial resolution <100 pc. The
emission from the host galaxy sources is resolved out in most cases. The
silicate absorption features are moderately deep and emission features are
shallow. We compare the mid-IR luminosities to AGN luminosity tracers and found
that the mid-IR radiation is emitted quite isotropically. In two cases, IC5063
and MCG-3-34-64, we find evidence for extended dust emission in the narrow-line
region. We confirm the correlation between observed silicate feature strength
and Hydrogen column density recently found in Spitzer data. In a further step,
our 3D clumpy torus model has been used to interpret the data. We show that the
strength of the silicate feature and the mid-IR spectral index can be used to
get reasonable constraints on the dust distribution in the torus. The mid-IR
spectral index, alpha, is almost exclusively determined by the radial dust
distribution power-law index, a, and the silicate feature depth is mostly
depending on the average number of clouds, N0, along an equatorial
line-of-sight and the torus inclination. A comparison of model predictions to
our type 1 and type 2 AGN reveals typical average parameters a=-1.0+/-0.5 and
N0=5-8, which means that the radial dust distribution is rather shallow. As a
proof-of-concept of this method, we compared the model parameters derived from
alpha and the silicate feature to more detailed studies of IR SEDs and
interferometry and found that the constraints on a and N0 are consistent.
Finally, we might have found evidence that the radial structure of the torus
changes from low to high AGN luminosities towards steeper dust distributions,
and we discuss implications for the IR size-luminosity relation. (abridged)Comment: 22 pages, 13 figues, 6 tables; Accepted for publication in A&A; Note
that this is the second submitted paper from the series, but we changed paper
order. This one will be referred to as paper I, the previously submitted
arXiv:0909.4539 will become paper I
The dusty torus in the Circinus galaxy: a dense disk and the torus funnel
(Abridged) With infrared interferometry it is possible to resolve the nuclear
dust distributions that are commonly associated with the dusty torus in active
galactic nuclei (AGN). The Circinus galaxy hosts the closest Seyfert 2 nucleus
and previous interferometric observations have shown that its nuclear dust
emission is well resolved.
To better constrain the dust morphology in this active nucleus, extensive new
observations were carried out with MIDI at the Very Large Telescope
Interferometer.
The emission is distributed in two distinct components: a disk-like emission
component with a size of ~ 0.2 1.1 pc and an extended component with a
size of ~ 0.8 1.9 pc. The disk-like component is elongated along PA ~
46{\deg} and oriented perpendicular to the ionisation cone and outflow. The
extended component is elongated along PA ~ 107{\deg}, roughly perpendicular to
the disk component and thus in polar direction. It is interpreted as emission
from the inner funnel of an extended dust distribution and shows a strong
increase in the extinction towards the south-east. We find no evidence of an
increase in the temperature of the dust towards the centre. From this we infer
that most of the near-infrared emission probably comes from parsec scales as
well. We further argue that the disk component alone is not sufficient to
provide the necessary obscuration and collimation of the ionising radiation and
outflow. The material responsible for this must instead be located on scales of
~ 1 pc, surrounding the disk.
The clear separation of the dust emission into a disk-like emitter and a
polar elongated source will require an adaptation of our current understanding
of the dust emission in AGN. The lack of any evidence of an increase in the
dust temperature towards the centre poses a challenge for the picture of a
centrally heated dust distribution.Comment: 30 pages, 12 figures; A&A in pres
Diagnostics of hydraulic fluids used in aviation
ArticleDiagnostics is a maintenance industry that monitors performance, parameters, and
follow
–
up. Diagnosing hydraulic fluids means comparing the parameters of the used hydr
aulic
fluid sample to the parameters of the clean fluid. It is also essentia
l to monitor the limit values
either by the aircraft manufacturer or by the manufacturer of the hydraulic fluid. This means
that the manufacturer recommends the limitations of the
liquid parameters. The measurements
of the fluid samples give an overview of the liquid quality. Most businesses focus on so
–
called
proactive maintenance. The main senses and objectives of proactive maintenance are: lubricant
sample analysis, lubricant sta
tus, machine status, next step recommendation, database saving
and trend analysis. This article focuses on the quality of hydraulic fluid focused in aviation. The
aim of the article was to determine the properties of the hydraulic fluid used in the A320 ai
rcraft
family, determine the interval of its exchange. Monitoring the state of the hydraulic fluid could
contribute to the timely detection of the problem, thus avoiding a failure of the device or the
system as a
whole. The tracking proposal is an integral
part of this article
Energy analysis of hydrogen as a fuel in the Czech Republic
ArticleThe concept of ‘hydrogen economy’ dates back to the 1970s. It was first introduced as
s response to the first oil crisis. In the context of the hydrogen economy, it is important to calculate
how much hydrogen would be needed to power all motor vehicles in the Czech Republic. This is
main topics of this paper. To calculate the amount of hydrogen, we used two different methods.
One is based on thermodynamic laws and the other on normal operating conditions. Both
approaches yielded comparable results. It was found out that even with the use of all the electricity
produced in the Czech Republic in 2016, we would not be able to cover the amount of energy
that is required for production. It would cover only 75% resp. 76% depending on the calculation
method used. Eventually, the Czech Republic could buy necessary amount of hydrogen and it
would cost between 11 and 29 billion euros which is between 6% and 16% of GDP of the Czech
Republic. In the calculations, authors found out that most fuel is burnt in the passenger cars.
Therefore, we made a sensitivity analysis to find out how much our results would differ if fuel
consumption changed. It turns out that with an increase in consumption of 1l per 100 km,
hydrogen production coverage will decrease by about 4% (again with the use of all electricity
produced in the Czech Republic)
Mapping the radial structure of AGN tori
We present mid-IR interferometric observations of 6 type 1 AGNs at multiple
baseline lengths of 27--130m, reaching high angular resolutions up to
lambda/B~0.02 arcseconds. For two of the targets, we have simultaneous near-IR
interferometric measurements as well. The multiple baseline data directly probe
the radial distribution of the material on sub-pc scales. Within our sample,
which is small but spans over ~2.5 orders of magnitudes in the UV/optical
luminosity L of the central engine, the radial distribution clearly and
systematically changes with luminosity. First, we show that the brightness
distribution at a given mid-IR wavelength seems to be rather well described by
a power law, which makes a simple Gaussian or ring size estimation quite
inadequate. Here we instead use a half-light radius R_1/2 as a representative
size. We then find that the higher luminosity objects become more compact in
normalized half-light radii R_1/2 /R_in in the mid-IR, where R_in is the dust
sublimation radius empirically given by the L^1/2 fit of the near-IR
reverberation radii. This means that, contrary to previous studies, the
physical mid-IR emission size (e.g. in pc) is not proportional to L^1/2, but
increases with L much more slowly, or in fact, nearly constant at 13 micron.
Combining the size information with the total flux specta, we infer that the
radial surface density distribution of the heated dust grains changes from a
steep ~r^-1 structure in high luminosity objects to a shallower ~r^0 structure
in those of lower luminosity. The inward dust temperature distribution does not
seem to smoothly reach the sublimation temperature -- on the innermost scale of
~R_in, a relatively low temperature core seems to co-exist with a slightly
distinct brightness concentration emitting roughly at the sublimation
temperature.Comment: accepted for publication in A&
Chemical priming of plant defense responses to pathogen attacks
Plants can acquire an improved resistance against pathogen attacks by exogenous application of natural or artificial compounds. In a process called chemical priming, application of these compounds causes earlier, faster and/or stronger responses to pathogen attacks. The primed defense may persist over a stress-free time (lag phase) and may be expressed also in plant organs that have not been directly treated with the compound. This review summarizes the current knowledge on the signaling pathways involved in chemical priming of plant defense responses to pathogen attacks. Chemical priming in induced systemic resistance (ISR) and systemic acquired resistance (SAR) is highlighted. The roles of the transcriptional coactivator NONEXPRESSOR OF PR1 (NPR1), a key regulator of plant immunity, induced resistance (IR) and salicylic acid signaling during chemical priming are underlined. Finally, we consider the potential usage of chemical priming to enhance plant resistance to pathogens in agriculture
High-Spatial Resolution SED of NGC 1068 from Near-IR to Radio. Disentangling the thermal and non-thermal contributions
We investigate the ideas that a sizable fraction of the interferometrically
unresolved infrared emission of the nucleus of NGC 1068 might originate from
other processes than thermal dust emission from the torus. We examine the
contribution of free-free or synchrotron emissions to the central mid- and
near-IR parsec-scale emitting region of NGC 1068. Each mechanism is constrained
with parsec scale radio data available for NGC 1068 in the 10^9 - 10^11 Hz
regime, and compared to the highest-resolution interferometric data available
in the mid-infrared. It is shown that the unresolved emission in the
interferometric observation (<~1pc) is still dominatedd by dust emission and
not by contributions from synchrotron or free-free emission. As recent studies
suggest, the interferometric observations prefer a clumpy structure of the dust
distribution. Extrapolation of the radio free-free or synchrotron emission to
the IR indicates that their contribution is <20% even for the unresolved
fraction of the interferometric flux. The slope of the available radio data is
consistent with a power law exponent alpha = 0.29 +/- 0.07 which we interprete
in terms of either free-free emission or synchrotron radiation from
quasi-monochromatic electrons. We apply emission models for both mechanisms in
order to obtain physical parameters. (abridged)Comment: 8 pages, 3 figures; accepted by A&
Flying Adversarial Patches: Manipulating the Behavior of Deep Learning-based Autonomous Multirotors
Autonomous flying robots, e.g. multirotors, often rely on a neural network
that makes predictions based on a camera image. These deep learning (DL) models
can compute surprising results if applied to input images outside the training
domain. Adversarial attacks exploit this fault, for example, by computing small
images, so-called adversarial patches, that can be placed in the environment to
manipulate the neural network's prediction. We introduce flying adversarial
patches, where an image is mounted on another flying robot and therefore can be
placed anywhere in the field of view of a victim multirotor. For an effective
attack, we compare three methods that simultaneously optimize the adversarial
patch and its position in the input image. We perform an empirical validation
on a publicly available DL model and dataset for autonomous multirotors.
Ultimately, our attacking multirotor would be able to gain full control over
the motions of the victim multirotor.Comment: 6 pages, 5 figures, Workshop on Multi-Robot Learning, International
Conference on Robotics and Automation (ICRA
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