3,734 research outputs found
Multi-band implications of external-IC flares
Very fast variability on scales of minutes is regularly observed in Blazars.
The assumption that these flares are emerging from the dominant emission zone
of the very high energy (VHE) radiation within the jet challenges current
acceleration and radiation models. In this work we use a spatially resolved and
time dependent synchrotron-self-Compton (SSC) model that includes the full time
dependence of Fermi-I acceleration. We use the (apparent) orphan -ray
flare of \textit{Mrk501} during MJD 54952 and test various flare scenarios
against the observed data. We find that a rapidly variable external radiation
field can reproduce the high energy lightcurve best. However, the effect of the
strong inverse Compton (IC) cooling on other bands and the X-ray observations
are constraining the parameters to rather extreme ranges. Then again other
scenarios would require parameters even more extreme or stronger physical
constraints on the rise and decay of the source of the variability which might
be in contradiction with constraints derived from the size of the black hole's
ergosphere.Comment: accepted for publication in Astroparticle Physic
A spatially resolved SSC Shock-in-Jet model
In this paper a spatially resolved, fully self-consistent SSC model is
presented. The observable spectral energy distribution (SED) evolves entirely
from a low energetic delta distribution of injected electrons by means of the
implemented microphysics of the jet. These are in particular the properties of
the shock and the ambient plasma, which can be varied along the jet axis. Hence
a large variety of scenarios can be computed, e.g. the acceleration of
particles via multiple shocks. Two acceleration processes, shock acceleration
and stochastic acceleration, are taken into account. From the resulting
electron distribution the SED is calculated taking into account synchrotron
radiation, inverse Compton scattering (full cross section) and synchrotron self
absorption. The model can explain SEDs where cooling processes are crucial. It
can verify high variability results from acausal simulations and produce
variability not only via injection of particles, but due to the presence of
multiple shocks. Furthermore a fit of the data, obtained in the 2010
multi-frequency campaign of Mrk501, is presented.Comment: 4 pages, 2 figures; appeared in the proceedings of the conference:
"High Energy Phenomena in Relativistic Outflows (HEPRO) III", held in
Barcelona, Spain, June 27th-July 1st 2011 (IJMPCS
The radio morphology of a spatially resolved SSC model
One of the main, unresolved questions about the nature of quasars is the
position of the acceleration site responsible for the highest energies. The
attempt to investigate this question in the energy regime with the highest
resolution, the radio band, has the downside that no theoretical model exists
that can connect these two regimes. The model in this work tries to shrink this
gap by extending the general synchrotron self Compton (SSC) model up to length
scales in the order of the resolution of radio observations. The resulting
spectral energy distributions (SED) show a qualitative improvement in the
representation of the radio spectrum. Furthermore the obtained emission
morphology shows similar properties to the radio structures observed in jets of
quasars. A complete and quantitative connection will however need either much
higher numerical effort or an improved methodology
What about the Women? Female Headship, Poverty and Vulnerability in Thailand and Vietnam
This paper investigates whether different types of female?headed households in Thailand and Vietnam are disadvantaged in terms of current consumption, exposure to shocks, consumption smoothing capacities, as well as vulnerability to poverty and downside risk. Using a unique panel data set of over 4000 rural households in both countries, we find that female headed households with an absent husband appear to be better off in terms of current consumption in both countries (suggesting a positive impact of remittances). However, de jure female headed households in Thailand and Vietnam are more exposed to shocks and are less able to insure their consumption against income shocks than other households. In line with this finding de jure female headed households are also more vulnerable to perceived downside risk. Instead, de facto female headed households are less vulnerable to poverty and not worse off in terms of vulnerability to perceived downside risk. --Poverty,Gender Analysis,Vulnerability to Poverty,Inter?generational Poverty
Osmotic stress-dependent serine phosphorylation of the histidine kinase homologue DokA
BACKGROUND: Two-component systems consisting of histidine kinases and their corresponding receivers are widespread in bacterial signal transduction. In the past few years, genes coding for homologues of two-component systems were also discovered in eukaryotic organisms. DokA, a homologue of bacterial histidine kinases, is an element of the osmoregulatory pathway in the amoeba Dictyostelium. The work described here addresses the question whether DokA is phosphorylated in vivo in response to osmotic stress. RESULTS: We have endogenously overexpressed individual domains of DokA to investigate post-translational modification of the protein in response to osmotic shock in vivo. Dictyostelium cells were labeled with [(32)P]-orthophosphate, exposed to osmotic stress and DokA fragments were subsequently isolated by immunoprecipitation. Thus, a stress-dependent phosphorylation could be demonstrated, with the site of phosphorylation being located in the kinase domain. We demonstrate biochemically that the phosphorylated amino acid is serine, and by mutational analysis that the phosphorylation reaction is not due to an autophosphorylation of DokA. Furthermore, mutation of the conserved histidine did not affect the osmostress-dependent phosphorylation reaction. CONCLUSIONS: A stimulus-dependent serine phosphorylation of a eukaryotic histidine kinase homologue was demonstrated for the first time in vivo. That implies that DokA, although showing typical structural features of a bacterial two-component system, might be part of a eukaryotic signal transduction pathway that involves serine/threonine kinases
Entwicklungsstufen des Unternehmensarchitekturmanagements
Zusammenfassungen: Je nach Ausgestaltung kann Unternehmensarchitekturmanagement (UAM) eine wichtige Komponente des strategischen IT-Managements bilden — oder auch nicht. Um die Ausgestaltungsmöglichkeiten besser zu verstehen, führen wir zunächst UAM-Dimensionen ein und beschreiben auf dieser Grundlage vier zentrale UAM-Entwick-lungsstufen, deren letzte >>strategisches UAM<< ist. Die vier Entwicklungsstufen ermöglichen dem Leser die Positionierung des jeweils realisierten UAM im eigenen Unternehmen sowie die Definition eines angemessenen Zielzustands. Drei Kurzfallstudien zeigen konkret auf, in welchen Variationen strategisches UAM umgesetzt und in welcher Weise dadurch strategisches Informationsmanagement unterstützt werden kan
Inelastic electron backscattering in a generic helical edge channel
We evaluate the low-temperature conductance of a weakly interacting
one-dimensional helical liquid without axial spin symmetry. The lack of that
symmetry allows for inelastic backscattering of a single electron, accompanied
by forward-scattering of another. This joint effect of weak interactions and
potential scattering off impurities results in a temperature-dependent
deviation from the quantized conductance, . In addition,
is sensitive to the position of the Fermi level. We determine
numerically the parameters entering our generic model for the
Bernevig-Hughes-Zhang Hamiltonian of a HgTe/CdTe quantum well in the presence
of Rashba spin-orbit coupling.Comment: 4+ pages, 3 figures, published versio
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