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 $\mathcal{C}_{0}$ can be used to conduct approximation of various classes of approximands in a number of different modes. That is, we prove approximands in $\mathcal{C}_{0}$ can be uniformly approximated, approximands in $\mathcal{C}_{b}$ can be uniformly approximated on compact sets, and approximands in $\mathcal{L}_{p}$ can be approximated with respect to the $\mathcal{L}_{p}$, for $p\in\left[1,\infty\right)$. 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 $D$-dimensional space. More precisely, we investigate the $^1S$ 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 ($D = 1 \text{and} 3$), 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 $(33\gamma^{5/2}+13\gamma^{-3/2})/46$ at zero temperature, and by $(5\gamma^2+\gamma^{-2})/6$ 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