453 research outputs found
On manifolds with nonhomogeneous factors
We present simple examples of finite-dimensional connected homogeneous spaces
(they are actually topological manifolds) with nonhomogeneous and nonrigid
factors. In particular, we give an elementary solution of an old problem in
general topology concerning homogeneous spaces
Spin and energy transfer in nanocrystals without transport of charge
We describe a mechanism of spin transfer between individual quantum dots that
does not require tunneling. Incident circularly-polarized photons create
inter-band excitons with non-zero electron spin in the first quantum dot. When
the quantum-dot pair is properly designed, this excitation can be transferred
to the neighboring dot via the Coulomb interaction with either {\it
conservation} or {\it flipping} of the electron spin. The second dot can
radiate circularly-polarized photons at lower energy. Selection rules for spin
transfer are determined by the resonant conditions and by the strong spin-orbit
interaction in the valence band of nanocrystals. Coulomb-induced energy and
spin transfer in pairs and chains of dots can become very efficient under
resonant conditions. The electron can preserve its spin orientation even in
randomly-oriented nanocrystals.Comment: 13 pages, 3 figure
Critical point network for drainage between rough surfaces
In this paper, we present a network method for computing two-phase flows between two rough surfaces with significant contact areas. Low-capillary number drainage is investigated here since one-phase flows have been previously investigated in other contributions. An invasion percolation algorithm is presented for modeling slow displacement of a wetting fluid by a non wetting one between two rough surfaces. Short-correlated Gaussian process is used to model random rough surfaces.The algorithm is based on a network description of the fracture aperture field. The network is constructed from the identification of critical points (saddles and maxima) of the aperture field. The invasion potential is determined from examining drainage process in a flat mini-channel. A direct comparison between numerical prediction and experimental visualizations on an identical geometry has been performed for one realization of an artificial fracture with a moderate fractional contact area of about 0.3. A good agreement is found between predictions and observations
Sigref – A Symbolic Bisimulation Tool Box
We present a uniform signature-based approach to compute the most popular bisimulations. Our approach is implemented symbolically using BDDs, which enables the handling of very large transition systems. Signatures for the bisimulations are built up from a few generic building blocks, which naturally correspond to efficient BDD operations. Thus, the definition of an appropriate signature is the key for a rapid development of algorithms for other types of bisimulation.
We provide experimental evidence of the viability of this approach by presenting computational results for many bisimulations on real-world instances. The experiments show cases where our framework can handle state spaces efficiently that are far too large to handle for any tool that requires an explicit state space description.
This work was partly supported by the German Research Council (DFG) as part of the Transregional Collaborative Research Center “Automatic Verification and Analysis of Complex Systems” (SFB/TR 14 AVACS). See www.avacs.org for more information
Guidelines for the Selection of Physical Literacy Measures in Physical Education in Australia
Assessment of physical literacy poses a dilemma of what instrument to use. There is currently no guide regarding the suitability of common assessment approaches. The purpose of this brief communication is to provide a user's guide for selecting physical literacy assessment instruments appropriate for use in school physical education and sport settings. While recommendations regarding specific instruments are not provided, the guide offers information about key attributes and considerations for the use. A decision flow chart has been developed to assist teachers and affiliated school practitioners to select appropriate methods of assessing physical literacy. School PE and sport scenarios are presented to illustrate this process. It is important that practitioners are empowered to select the most appropriate instrument/s to suit their needs
Defining Physical Literacy for Application in Australia: A Modified Delphi Method
Purpose.
The development of a physical literacy definition and standards framework suitable for implementation in Australia.
Method.
Modified Delphi methodology.
Results
. Consensus was established on four defining statements:
Core – Physical literacy is lifelong holistic learning acquired and applied in movement and physical activity contexts;
Composition – Physical literacy reflects ongoing changes integrating physical, psychological, cognitive and social capabilities;
Importance – Physical literacy is vital in helping us lead healthy and fulfilling lives through movement and physical activity;
Aspiration – A physically literate person is able to draw on their integrated physical, psychological, cognitive, and social capacities to support health promoting and fulfilling movement and physical activity, relative to their situation and context, throughout the lifespan. The standards framework addressed four learning domains (physical, psychological, cognitive, and social), spanning five learning configurations/levels.
Conclusion.
The development of a bespoke program for a new context has important implications for both existing and future program
Radiation fields of disk, BLR and torus in quasars and blazars: implications for gamma-ray absorption
The radiation fields external to the jets and originating from within a few
parsecs from the black hole, are discussed in this paper. They are the direct
radiation from an accretion disk in symbiosis with jets, the radiation field
from the broad line region (BLR) surrounding the accretion disk, and the
infrared radiation from a dusty torus. The jet/disk symbiosis modifies the
energetics in the central parsec of AGN such that for a given accretion rate, a
powerful jet would occur at the expense of the disk luminosity, and
consequently the disk would less efficiently ionize the BRL clouds or heat the
dust in the torus, thereby affecting potentially important target photon fields
for interactions of gamma-rays, accelerated electrons and protons along the
jet.
Motivated by unification schemes of active galactic nuclei, we briefly review
the evidence for the existence of broad line regions and small-scale dust tori
in BL Lacs and Fanaroff-Riley Class I (FR-I) radio galaxies. We propose that an
existing jet-accretion disk symbiosis can be extrapolated to provide a large
scale-symbiosis between other important dusty constituents of the blazar/FR-I
family. In the present paper, we discuss in the context of this symbiosis
interactions of GeV and TeV gamma-rays produced in the jet with the various
radiation fields external to the jet in quasars and blazars, taking account the
anisotropy of the radiation.Comment: 27 pages, 12 figures. submitted to Astroparticle Physic
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