4,634 research outputs found
A learning community two years on: reflecting on successes and framing futures
This paper reports the results of a participatory action research (PAR) evaluation conducted with the members of the Granite Belt Learners Group in their rural 'learning community' in South East Queensland, and presents an action research and evaluation framework to guide the community on the next stage of its journey
Approximation by finite mixtures of continuous density functions that vanish at infinity
Given sufficiently many components, it is often cited that finite mixture
models can approximate any other probability density function (pdf) to an
arbitrary degree of accuracy. Unfortunately, the nature of this approximation
result is often left unclear. We prove that finite mixture models constructed
from pdfs in can be used to conduct approximation of various
classes of approximands in a number of different modes. That is, we prove
approximands in can be uniformly approximated, approximands
in can be uniformly approximated on compact sets, and
approximands in can be approximated with respect to the
, for . Furthermore, we also prove
that measurable functions can be approximated, almost everywhere
Reviews
J. Combrink en J. Spies. SARA. Sakboek van regte Afrikaans, 2de uitgawe,lste druk 1994, 214 pp. ISBN 0 624 03252 3. Kaapstad: TafelbergUitgewers.Prys R49,95
Die nuwe AWS in die praktyk: 'n gebruikersoorsig na twee jaar
English Title: The Afrikaanse Woordelys en Spelreëls in Practice: A user's view after two years of useEnglish AbstractA language practitioner takes a critical look at the eighth improved edition of the Afrikaanse Woordelys en Spelreëls, the authoritative Afrikaans spelling list and spelling rules, after using it intensively for two years. The first impression contains many confusing typographical errors, but these have for the most part been corrected in the second. In many respects the Eighth Edition is an improvement on its predecessor; the rules are explained more comprehensively and the spelling list and abbreviations list are greatly expanded. The spelling list contains more information for the user, for example more diminutives, degrees of comparison, attributive past participles and certain compounds the styling of which often presents problems for writers of Afrikaans. However, some of these rules create problems: they complicate established usage unnecessarily, are formulated inadequately and are difficult to apply in practice, and the examples are too simplistic. The list also contains many apparent inconsistencies the ordinary user may find incomprehensible and confusing. The conclusion is that, while the publication is in many respects more user-friendly than its predecessor, it lacks the necessary consistency and cohesion. Many shortcomings could have been eliminated if the complete draft had been submitted to language practitioners to use and evaluate in practice.Keywords: abbreviations, comprehensive explanations, degrees of comparison, diminutives, editing, expansions, inconsistencies, index, language designations, link phonemes, new rules, new words, numerals, overall impression, past participles, proper-name rule, separated compounds, spelling list, spelling rules, terms, vulgar fraction
Hooke's law correlation in two-electron systems
We study the properties of the Hooke's law correlation energy (\Ec),
defined as the correlation energy when two electrons interact {\em via} a
harmonic potential in a -dimensional space. More precisely, we investigate
the ground state properties of two model systems: the Moshinsky atom (in
which the electrons move in a quadratic potential) and the spherium model (in
which they move on the surface of a sphere). A comparison with their Coulombic
counterparts is made, which highlights the main differences of the \Ec in
both the weakly and strongly correlated limits. Moreover, we show that the
Schr\"odinger equation of the spherium model is exactly solvable for two values
of the dimension (), and that the exact wave function is
based on Mathieu functions.Comment: 7 pages, 5 figure
Finite-size effects on the Hamiltonian dynamics of the XY-model
The dynamical properties of the finite-size magnetization M in the critical
region T<T_{KTB} of the planar rotor model on a L x L square lattice are
analyzed by means of microcanonical simulations . The behavior of the q=0
structure factor at high frequencies is consistent with field-theoretical
results, but new additional features occur at lower frequencies. The motion of
M determines a region of spectral lines and the presence of a central peak,
which we attribute to phase diffusion. Near T_{KTB} the diffusion constant
scales with system size as D ~ L^{-1.6(3)}.Comment: To be published in Europhysics Letter
Migrations of sandy beach meiofauna
The meiofauna at higher tide levels on a sheltered beach has been found to undergo vertical migrations correlated with the alternate drying and wetting of the sand during the tidal cycle. This movement may be modified by temperature differences between summer and winter and day and night. No major horizontal up/downshore movement of the meiofauna has been found during the tidal cycle and it appears that rain also has little effect on the meiofauna
Calibration of the Ames Anechoic Facility. Phase 1: Short range plan
A calibration was made of the acoustic and aerodynamic characteristics of a small, open-jet wind tunnel in an anechoic room. The jet nozzle was 102 mm diameter and was operated subsonically. The anechoic-room dimensions were 7.6 m by 5.5 m by 3.4 m high (wedge tip to wedge tip). Noise contours in the chamber were determined by various jet speeds and exhaust collector positions. The optimum nozzle/collector separation from an acoustic standpoint was 2.1 m. Jet velocity profiles and turbulence levels were measured using pressure probes and hot wires. The jet was found to be symmetric, with no unusual characteristics. The turbulence measurements were hampered by oil mist contamination of the airflow
Casimir-Polder interaction of atoms with magnetodielectric bodies
A general theory of the Casimir-Polder interaction of single atoms with
dispersing and absorbing magnetodielectric bodies is presented, which is based
on QED in linear, causal media. Both ground-state and excited atoms are
considered. Whereas the Casimir-Polder force acting on a ground-state atom can
conveniently be derived from a perturbative calculation of the atom-field
coupling energy, an atom in an excited state is subject to transient force
components that can only be fully understood by a dynamical treatment based on
the body-assisted vacuum Lorentz force. The results show that the
Casimir-Polder force can be influenced by the body-induced broadening and
shifting of atomic transitions - an effect that is not accounted for within
lowest-order perturbation theory. The theory is used to study the
Casimir-Polder force of a ground-state atom placed within a magnetodielectric
multilayer system, with special emphasis on thick and thin plates as well as a
planar cavity consisting of two thick plates. It is shown how the competing
attractive and repulsive force components related to the electric and magnetic
properties of the medium, respectively, can - for sufficiently strong magnetic
properties - lead to the formation of potential walls and wells.Comment: 16 pages, 6 figures, minor additions and correction
Enhanced dispersion interaction in confined geometry
The dispersion interaction between two point-like particles confined in a
dielectric slab between two plates of another dielectric medium is studied
within a continuum (Lifshitz) theory. The retarded (Casimir-Polder) interaction
at large inter-particle distances is found to be strongly enhanced as the
mismatch between the dielectric permittivities of the two media is increased.
The large-distance interaction is multiplied due to confinement by a factor of
at zero temperature, and by
at finite temperature, \gamma=\ein(0)/\eout(0)
being the ratio between the static dielectric permittivities of the inner and
outer media. This confinement-induced amplification of the dispersion
interaction can reach several orders of magnitude.Comment: 4 page
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