3,121 research outputs found
Observations of shallow convective clouds generated by solar heating of dark smoke plumes
The SEVIRI instrument on the Meteosat Second Generation satellite with both fine spatial and temporal resolution allows to detect and follow the dynamics of fast developing meteorological events like spreading smoke plumes and the lifecycles of convective clouds. Smoke plumes have the ability to change the atmospheric heat content due to absorption and reduced reflection of solar radiation. By these means they can trigger formation of shallow convective clouds at their edge. A heavy smoke plume emerging from burning Lebanese oil tanks and spreading over adjacent deserts on 17 July 2006 has been observed as an example of such an effect. This study suggests a physical explanation of the observed convection along the edge of the smoke plume, namely the strong thermal contrast resulting from solar heating of the smoke layer
OGO-3 observations of ELF noise in the magnetosphere - Part 1 - Spatial extent and frequency of occurrence
OGO-3 spectrum analyzer measurements of magnetic noise in magnetospher
A study of waves in the earth's bow shock
The perturbation vectors of waves up and downstream from the region of maximum compression in the bow shock were examined on OGO-5 under particularly steady solar wind conditions. The polarization of the upstream waves was RH, circular and of the downstream waves LH, elliptical in the spacecraft frame. By observing that the polarization of the waves remained unchanged as the shock motion swept the wave structure back and forth across the satellite three times in eight minutes, it was found that the waves were not stationary in the shock frame. A study of the methods of determining the shock normal indicates that the normal estimated from a shock model should be superior to one based upon magnetic coplanarity. The propagation vectors of the waves examined did not coincide with the shock model normal, the average magnetic field, or the plasma flow velocity. However, the major axis of the polarization ellipse of the downstream wave was nearly parallel to the upstream propagation vector
Collisionless solar wind protons: A comparison of kinetic and hydrodynamic descriptions
Kinetic and hydrodynamic descriptions of a collisionless solar wind proton gas are compared. Heat conduction and viscosity are neglected in the hydrodynamic formulation but automatically included in the kinetic formulation. The results of the two models are very nearly the same, indicating that heat conduction and viscosity are not important in the solar wind proton gas beyond about 0.1 AU. It is concluded that the hydrodynamic equations provide a valid description of the collisionless solar wind protons, and hence that future models of the quiet solar wind should be based on a hydrodynamic formulation
Investigations on the individual and maternal components of calving performance in cattle
International audienc
Towards Collaborative Conceptual Exploration
In domains with high knowledge distribution a natural objective is to create
principle foundations for collaborative interactive learning environments. We
present a first mathematical characterization of a collaborative learning
group, a consortium, based on closure systems of attribute sets and the
well-known attribute exploration algorithm from formal concept analysis. To
this end, we introduce (weak) local experts for subdomains of a given knowledge
domain. These entities are able to refute and potentially accept a given
(implicational) query for some closure system that is a restriction of the
whole domain. On this we build up a consortial expert and show first insights
about the ability of such an expert to answer queries. Furthermore, we depict
techniques on how to cope with falsely accepted implications and on combining
counterexamples. Using notions from combinatorial design theory we further
expand those insights as far as providing first results on the decidability
problem if a given consortium is able to explore some target domain.
Applications in conceptual knowledge acquisition as well as in collaborative
interactive ontology learning are at hand.Comment: 15 pages, 2 figure
Measurements of heavy ion beam losses from collimation
The collimation efficiency for Pb ion beams in the LHC is predicted to be
lower than requirements. Nuclear fragmentation and electromagnetic dissociation
in the primary collimators create fragments with a wide range of Z/A ratios,
which are not intercepted by the secondary collimators but lost where the
dispersion has grown sufficiently large. In this article we present
measurements and simulations of loss patterns generated by a prototype LHC
collimator in the CERN SPS. Measurements were performed at two different
energies and angles of the collimator. We also compare with proton loss maps
and find a qualitative difference between Pb ions and protons, with the maximum
loss rate observed at different places in the ring. This behavior was predicted
by simulations and provides a valuable benchmark of our understanding of ion
beam losses caused by collimation.Comment: 12 pages, 20 figure
The acceleration and propagation of solar flare energetic particles
Observations and theories of particle acceleration in solar flares are reviewed. The most direct signatures of particle acceleration in flares are gamma rays, X-rays and radio emissions produced by the energetic particles in the solar atmosphere and energetic particles detected in interplanetary space and in the Earth's atmosphere. The implication of these observations are discussed. Stochastic and shock acceleration as well as acceleration in direct electric fields are considered. Interplanetary particle propagation is discussed and an overview of the highlights of both current and promising future research is presented
Low temperature dynamics of kinks on Ising interfaces
The anisotropic motion of an interface driven by its intrinsic curvature or
by an external field is investigated in the context of the kinetic Ising model
in both two and three dimensions. We derive in two dimensions (2d) a continuum
evolution equation for the density of kinks by a time-dependent and nonlocal
mapping to the asymmetric exclusion process. Whereas kinks execute random walks
biased by the external field and pile up vertically on the physical 2d lattice,
then execute hard-core biased random walks on a transformed 1d lattice. Their
density obeys a nonlinear diffusion equation which can be transformed into the
standard expression for the interface velocity v = M[(gamma + gamma'')kappa +
H]$, where M, gamma + gamma'', and kappa are the interface mobility, stiffness,
and curvature, respectively. In 3d, we obtain the velocity of a curved
interface near the orientation from an analysis of the self-similar
evolution of 2d shrinking terraces. We show that this velocity is consistent
with the one predicted from the 3d tensorial generalization of the law for
anisotropic curvature-driven motion. In this generalization, both the interface
stiffness tensor and the curvature tensor are singular at the
orientation. However, their product, which determines the interface velocity,
is smooth. In addition, we illustrate how this kink-based kinetic description
provides a useful framework for studying more complex situations by modeling
the effect of immobile dilute impurities.Comment: 11 pages, 10 figure
- …