1,858 research outputs found
AGN dust tori at low and high luminosities
A cornerstone of AGN unification schemes is the presence of an optically and
geometrically thick dust torus. It provides the obscuration to explain the
difference between type 1 and type 2 AGN. We investigate the influence of the
dust distribution on the Eddington limit of the torus. For smooth dust
distributions, the Eddingtion limit on the dust alone is 5 orders of magnitudes
below the limit for electron scattering in a fully ionized plasma, while a
clumpy dust torus has an Eddington limit slightly larger than the classical
one. We study the behaviour of a clumpy torus at low and high AGN luminosities.
For low luminosities of the order of ~10^42 erg/s, the torus changes its
characteristics and obscuration becomes insufficient. In the high luminosity
regime, the clumpy torus can show a behaviour which is consistent with the
"receding torus" picture. The derived luminosity-dependent fraction of
type-2-objects agrees with recent observational results. Moreover, the
luminosity-dependent covering factor in a clumpy torus may explain the presence
of broad-line AGN with high column densities in X-rays.Comment: 5 pages, 0 figures; Accepted for publication in MNRA
Poisson-Lie T-duality: Open Strings and D-branes
Global issues of the Poisson-Lie T-duality are addressed. It is shown that
oriented open strings propagating on a group manifold are dual to -brane
- anti--brane pairs propagating on the dual group manifold \ti G. The
-branes coincide with the symplectic leaves of the standard Poisson
structure induced on the dual group \ti G by the dressing action of the group
. T-duality maps the momentum of the open string into the mutual distance of
the -branes in the pair. The whole picture is then extended to the full
modular space of the Poisson-Lie equivalent \si-models which is the
space of all Manin triples of a given Drinfeld double.T-duality rotates the
zero modes of pairs of -branes living on targets belonging to . In
this more general case the -branes are preimages of symplectic leaves in
certain Poisson homogeneous spaces of their targets and, as such, they are
either all even or all odd dimensional.Comment: 15 pages, LaTeX (references added
Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
We describe the diffusion and random velocities of solid particles due to
stochastic forcing by turbulent gas. We include the orbital dynamics of
Keplerian disks, both in-plane epicycles and vertical oscillations. We obtain a
new result for the diffusion of solids. The Schmidt number (ratio of gas to
particle diffusivity) is Sc = 1 + (Omega t_stop)^2, in terms of the particle
stopping time, t_stop, and the orbital frequency, Omega. The standard result,
Sc = 1 + t_stop/t_eddy, in terms of the eddy turnover time, t_eddy, is shown to
be incorrect. The main difference is that Sc rises quadratically, not linearly,
with stopping time. Consequently, particles larger than ~ 10 cm in
protoplanetary disks will suffer less radial diffusion and will settle closer
to the midplane. Such a layer of boulders would be more prone to gravitational
collapse. Our predictions of RMS speeds, vertical scale height and diffusion
coefficients will help interpret numerical simulations. We confirm previous
results for the vertical stirring of particles (scale heights and random
velocities), and add a correction for arbitrary ratios of eddy to orbital
times. The particle layer becomes thinner for t_eddy > 1/Omega, with the
strength of turbulent diffusion held fixed. We use two analytic techniques --
the Hinze-Tchen formalism and the Fokker-Planck equation with velocity
diffusion -- with identical results when the regimes of validity overlap. We
include simple physical arguments for the scaling of our results.Comment: 17 pages, 7 figures, 2 tables, accepted to Icaru
Structure and thermodynamics of associating rods solutions
Thermoreversible sol-gel transitions in solutions of rod-like associating
polymers are analyzed by computer simulations and by mean field models. The
sol-gel transition is determined by the divergence of the cluster weight
average. The analytically determined sol-gel transition is in good agreement
with the simulation results. At low temperatures we observe a peak in the heat
capacity, which maximum is associated with the precipitation transition. The
gelation transition is sensitive to the number of associating groups per rod
but nearly insensitive to the spatial distribution of associating groups around
the rod. The precipitation is strongly dependent on both the number and
distribution of associating groups per rod. We find negligible nematic
orientational order at the gelation and precipitation transitions
Superconducting nanowire photon number resolving detector at telecom wavelength
The optical-to-electrical conversion, which is the basis of optical
detectors, can be linear or nonlinear. When high sensitivities are needed
single-photon detectors (SPDs) are used, which operate in a strongly nonlinear
mode, their response being independent of the photon number. Nevertheless,
photon-number resolving (PNR) detectors are needed, particularly in quantum
optics, where n-photon states are routinely produced. In quantum communication,
the PNR functionality is key to many protocols for establishing, swapping and
measuring entanglement, and can be used to detect photon-number-splitting
attacks. A linear detector with single-photon sensitivity can also be used for
measuring a temporal waveform at extremely low light levels, e.g. in
long-distance optical communications, fluorescence spectroscopy, optical
time-domain reflectometry. We demonstrate here a PNR detector based on parallel
superconducting nanowires and capable of counting up to 4 photons at
telecommunication wavelengths, with ultralow dark count rate and high counting
frequency
Transient reconnection in the cusp during strongly negative IMF B y
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94721/1/jgra16996.pd
Neutral and Charged Polymers at Interfaces
Chain-like macromolecules (polymers) show characteristic adsorption
properties due to their flexibility and internal degrees of freedom, when
attracted to surfaces and interfaces. In this review we discuss concepts and
features that are relevant to the adsorption of neutral and charged polymers at
equilibrium, including the type of polymer/surface interaction, the solvent
quality, the characteristics of the surface, and the polymer structure. We pay
special attention to the case of charged polymers (polyelectrolytes) that have
a special importance due to their water solubility. We present a summary of
recent progress in this rapidly evolving field. Because many experimental
studies are performed with rather stiff biopolymers, we discuss in detail the
case of semi-flexible polymers in addition to flexible ones. We first review
the behavior of neutral and charged chains in solution. Then, the adsorption of
a single polymer chain is considered. Next, the adsorption and depletion
processes in the many-chain case are reviewed. Profiles, changes in the surface
tension and polymer surface excess are presented. Mean-field and corrections
due to fluctuations and lateral correlations are discussed. The force of
interaction between two adsorbed layers, which is important in understanding
colloidal stability, is characterized. The behavior of grafted polymers is also
reviewed, both for neutral and charged polymer brushes.Comment: a review: 130 pages, 30 ps figures; final form, added reference
Catálogo sinonímico de los táxones ibero-baleares de la familia Meloidae (Coleoptera)
We present an up to date synonymic list of the Iberian and Balearic fauna of Meloidae (Coleoptera). This current list includes all synonymies for 65 taxa at the species level. We have checked most of the original references for all taxa and names cited in the catalogue. This revision leads to various corrections and changes in the spelling of some names and in publication dates and pagination of original references with respect to previous catalogues. The work is illustrated with photographs of 13 type specimens. Some nomenclatural and taxonomic problems require additional work, and their solution might produce further changes in the current list. Most relevant among these problems are the revision of <i>M. maculosopunctata</i> nomenclature, the confirmation of the specific identification of the single Iberian record for <i>M. tricincta</i>, the revision of the taxonomic status of <i>Meloe ibericus</i>, herein maintained at the species level while waiting for the needed revision of the <i>M. brevicollis</i> species group, the evaluation of the taxonomic status of <i>Sitaris melanura</i> and the taxonomic problem of the subgenus <i>Meloe</i> in the Balearic Islands.<br><br>En este trabajo presentamos un listado sinonímico actualizado de la fauna de Meloidae (Coleoptera) de la Península Ibérica e Islas Baleares. En el listado actual se recogen las sinonimias correspondientes a 65 táxones de nivel especie. Se han revisado las publicaciones donde se incluyen las descripciones originales de la mayoría de los táxones y nombres de las especies ibero baleares de Meloidae. Esta revisión ha llevado a diversas correcciones y actualizaciones tanto en la grafía de algunos nombres, como en las las referencias originales, incluyendo cambios de fechas o de paginación con respecto a catálogos anteriores. El trabajo se ilustra con fotografías de 13 ejemplares tipo. Existen una serie de problemas nomenclaturales y taxonómicos aún por resolver, que podrían producir cambios en el listado actual. Entre estos problemas destacan el caso de la nomenclatura de <i>M. maculosopunctata</i> que requiere revisión, la adscripción específica correcta de la cita ibérica de <i>M. tricincta</i>, la revisión del estatus taxonómico de <i>Meloe ibericus</i>, que se mantiene a nivel específico en espera de la revisión del grupo de especies afines a <i>M. brevicollis</i>, la revisión del estatus de <i>Sitaris melanura</i> y el problema taxonómico del subgénero <i>Meloe</i> en las Islas Baleares
Les Houches 2011: Physics at TeV Colliders New Physics Working Group Report
We present the activities of the "New Physics" working group for the "Physics
at TeV Colliders" workshop (Les Houches, France, 30 May-17 June, 2011). Our
report includes new agreements on formats for interfaces between computational
tools, new tool developments, important signatures for searches at the LHC,
recommendations for presentation of LHC search results, as well as additional
phenomenological studies.Comment: 243 pages, report of the Les Houches 2011 New Physics Group; fix
three figure
Hadron Energy Reconstruction for the ATLAS Calorimetry in the Framework of the Non-parametrical Method
This paper discusses hadron energy reconstruction for the ATLAS barrel
prototype combined calorimeter (consisting of a lead-liquid argon
electromagnetic part and an iron-scintillator hadronic part) in the framework
of the non-parametrical method. The non-parametrical method utilizes only the
known ratios and the electron calibration constants and does not require
the determination of any parameters by a minimization technique. Thus, this
technique lends itself to an easy use in a first level trigger. The
reconstructed mean values of the hadron energies are within of the
true values and the fractional energy resolution is . The value of the ratio
obtained for the electromagnetic compartment of the combined calorimeter is
and agrees with the prediction that for this
electromagnetic calorimeter. Results of a study of the longitudinal hadronic
shower development are also presented. The data have been taken in the H8 beam
line of the CERN SPS using pions of energies from 10 to 300 GeV.Comment: 33 pages, 13 figures, Will be published in NIM
- …