237 research outputs found
Torus models for obscuration in type 2 AGN
We discuss a clumpy model of obscuring dusty tori around AGN. Cloud-cloud
collisions lead to an effective viscosity and a geometrically thick accretion
disk, which has the required properties of a torus.
Accretion in the combined gravitational potential of central black hole and
stellar cluster generates free energy, which is dissipated in collisions, and
maintains the thickness of the torus. A quantitative treatment for the torus in
the prototypical Seyfert 2 nucleus of NGC 1068 together with a radiative
transfer calculation for NIR re-emission from the torus is presented.Comment: 6 pages, 2 figures, contributed paper to Proceedings of the
Conference "Growing Black Holes" held in Garching, Germany, June 21-25, 2004,
edited by A. Merloni, S. Nayakshin and R. Sunyaev, Springer-Verlag series of
"ESO Astrophysics Symposia
Advection-Dominated Accretion with Infall and Outflows
We present self-similar solutions for advection-dominated accretion flows
with radial viscous force in the presence of outflows from the accretion flow
or infall. The axisymmetric flow is treated in variables integrated over polar
sections and the effects of infall and outflows on the accretion flow are
parametrised for possible configurations compatible with the self-similar
solution. We investigate the resulting accretion flows for three different
viscosity laws and derive upper limits on the viscosity parameter alpha. In
addition, we find a natural connection to non-rotating and spherical accretion
with turbulent viscosity, which is assumed to persist even without differential
rotation. Positive Bernoulli numbers for advection-dominated accretion allow a
fraction of the gas to be expelled in an outflow and the upper limit on the
viscosity predicts that outflows are inevitable for equations of state close to
an ideal gas.Comment: 17 pages, 9 figures, accepted for publication in the Astrophysical
Journa
Why context matters in a changing social media environment: The role of placement prominence as a moderator of disclosure effects in sponsored influencer content
Social media influencers have marked a significant change in advertising in recent years. By integrating sponsored content from advertisers into their feeds, they create awareness and favorable attitudes for products and brands. The effectiveness of this sponsored content builds on close adaptation to the original content of the specific media platform. To ensure transparency, influencers are required to disclose sponsored content. While effects of such disclosure labels and disclaimers have been widely examined, less attention has been paid to context factors that may influence these effects, such as placement prominence. Building on the propositions of the Persuasion Knowledge Model (PKM), this study aims to investigate the role of placement prominence as a moderator of disclosure effects. Results of an experimental study revealed that prominent placements support disclosure labels in reducing perceived deceptiveness of sponsored content, which positively affects influencer credibility and recipients’ attitudes toward the promoted brand. In contrast, disclosure effects on perceived persuasive intent vanished, when placement prominence was high. The results emphasize the importance of context factors in the processing of sponsored content and disclosures in a constantly changing social media environments
The Power of Jets: New Clues from Radio Circular Polarization and X-rays
Jets are ubiquitous in accreting black holes. Often ignored, they may be a
major contributor to the emitted spectral energy distribution for sub-Eddington
black holes. For example, recent observations of radio-to-X-ray correlations
and broad band spectra of X-ray binaries in the low/hard state can be explained
by a significant synchrotron contribution from jets also to their IR-to-X-ray
spectrum as proposed by Markoff, Falcke, Fender 2001. This model can also
explain state-transitions from low/hard to high/soft states. Relativistic
beaming of the jet X-ray emission could lead to the appearance of seemingly
Super-Eddington X-rays sources in other galaxies. We show that a simple
population synthesis model of X-ray binaries with relativistic beaming can well
explain the currently found distribution of off-nucleus X-ray point sources in
nearby galaxies. Specifically we suggest that the so-called ultra-luminous
X-ray sources (ULXs, also IXOs) could well be relativistically beamed
microblazars. The same model that can be used to explain X-ray binaries also
fits Low-Luminosity AGN (LLAGN) and especially Sgr A* in the Galactic Center.
The recent detection of significant circular polarization in AGN radio cores,
ranging from bright quasars down to low-luminosity AGN like M81*, Sgr A* and
even X-ray binaries, now places additional new constraints on the matter
contents of such jets. The emerging picture are powerful jets with a mix of hot
and cold matter, a net magnetic flux, and a stable magnetic north pole.Comment: to appear in: ``Lighthouses of the Universe'', Springer Verlag, ESO
Astrophysics Symposia, Eds: R.Sunyaev, M.Gilfanov, E.Churazov, LaTex, 8
pages, 5 figures, also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#lighthouse
Algae Biorefinery – Material and energy use of algae
Algae offer as much as 30 times greater biomass productivity than terrestrial plants, and are able to fix carbon and convert it into a number of interesting products.
The numerous challenges in algae production and use extend across the entire process chain. They include the selection of suitable algal phyla, cultivation (which takes place either in open ponds or in closed systems), extraction of the biomass from the suspension, through to optimal use of the obtained biomass. The basic suitability of aquatic biomass for material use and energy supply has been demonstrated in a large number of studies. Numerous research projects are concerned with identifying the optimal processes to enable its widespread implementation. [... aus der Einleitung
Anomalous Nernst effect in perpendicularly magnetised {\tau}-MnAl thin films
-MnAl is interesting for spintronic applications as a ferromagnet with
perpendicular magnetic anisotropy due to its high uniaxial magnetocrystalline
anisotropy. Here we report on the anomalous Nernst effect of sputter deposited
-MnAl thin films. We demonstrate a robust anomalous Nernst effect at
temperatures of 200 K and 300 K with a hysteresis similar to the anomalous Hall
effect and the magnetisation of the material. The anomalous Nernst coefficient
of (0.60.24) V/K at 300 K is comparable to other perpendicular
magnetic anisotropy thin films. Therefore -MnAl is a promising candidate
for spin-caloritronic research
Perspectives for applications of quantum imaging
Quantum imaging is a multifaceted field of research that promises highly efficient imaging in extreme spectral ranges as well as ultralow‐light microscopy. Since the first proof‐of‐concept experiments over 30 years ago, the field has evolved from highly fascinating academic research to the verge of demonstrating practical technological enhancements in imaging and microscopy. Here, the aim is to give researchers from outside the quantum optical community, in particular those applying imaging technology, an overview of several promising quantum imaging approaches and evaluate both the quantum benefit and the prospects for practical usage in the near future. Several use case scenarios are discussed and a careful analysis of related technology requirements and necessary developments toward practical and commercial application is provided
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Probing magnetic properties at the nanoscale: in-situ Hall measurements in a TEM
We report on advanced in-situ magneto-transport measurements in a transmission electron microscope. The approach allows for concurrent magnetic imaging and high resolution structural and chemical characterization of the same sample. Proof-of-principle in-situ Hall measurements on presumably undemanding nickel thin films supported by micromagnetic simulations reveal that in samples with non-trivial structures and/or compositions, detailed knowledge of the latter is indispensable for a thorough understanding and reliable interpretation of the magneto-transport data. The proposed in-situ approach is thus expected to contribute to a better understanding of the Hall signatures in more complex magnetic textures
Carbon Valuation: Alternatives, Alternations and Lateral Measures?
This article refers to carbon valuation as the practice of ascribing value to, and assessing the value of, actions and objects in terms of carbon emissions. Due to the pervasiveness of carbon emissions in the actions and objects of everyday lives of human beings, the making of carbon offsets and credits offers almost unlimited repertoires of alternatives to be included in contemporary carbon valuation schemes. Consequently, the article unpacks how discussions of carbon valuation are interpreted through different registers of alternatives - as the commensuration and substitution of variants on the one hand, and the confrontational comparison of radical difference on the other. Through the reading of a wide selection of the social science literature on carbon markets and trading, the article argues that the value of carbon emissions itself depends on the construction of alternative, hypothetical scenarios, and that emissions have become both a moral and a virtual measure pitting diverse forms of actualised actions or objects against each other or against corresponding nonactions and non-objects as alternatives
Phase Referencing in Optical Interferometry
One of the aims of next generation optical interferometric instrumentation is
to be able to make use of information contained in the visibility phase to
construct high dynamic range images. Radio and optical interferometry are at
the two extremes of phase corruption by the atmosphere. While in radio it is
possible to obtain calibrated phases for the science objects, in the optical
this is currently not possible. Instead, optical interferometry has relied on
closure phase techniques to produce images. Such techniques allow only to
achieve modest dynamic ranges. However, with high contrast objects, for faint
targets or when structure detail is needed, phase referencing techniques as
used in radio interferometry, should theoretically achieve higher dynamic
ranges for the same number of telescopes. Our approach is not to provide
evidence either for or against the hypothesis that phase referenced imaging
gives better dynamic range than closure phase imaging. Instead we wish to
explore the potential of this technique for future optical interferometry and
also because image reconstruction in the optical using phase referencing
techniques has only been performed with limited success. We have generated
simulated, noisy, complex visibility data, analogous to the signal produced in
radio interferometers, using the VLTI as a template. We proceeded with image
reconstruction using the radio image reconstruction algorithms contained in
AIPS IMAGR (CLEAN algorithm). Our results show that image reconstruction is
successful in most of our science cases, yielding images with a 4
milliarcsecond resolution in K band. (abridged)Comment: 11 pages, 36 figure
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