10,954 research outputs found
The development and application of the Explanatory Model of School Dysfunctions
This article develops the Explanatory Model of School Dysfunctions based on 80 essays of school principals and their representatives in Gauteng. It reveals the degree and kinds of school dysfunctions, as well as their interconnectedness with actors, networks, and domains. The model provides a basis for theory-based analyses of specific dysfunctions, and for context and culture-sensitive interventions. The main dysfunctions relate to rules (dysfunctional rules, rule bending, and rule breaking), competences (management, finances, and conflict resolution), and roles (role confusion and conflict, abuse of power). The model was developed to invite researchers to explore these and other dysfunctions in relation to their antecedents, motivations, and consequences, as well as to formulate evidence-based interventions and policies
Magnetoresistance of Three-Constituent Composites: Percolation Near a Critical Line
Scaling theory, duality symmetry, and numerical simulations of a random
network model are used to study the magnetoresistance of a
metal/insulator/perfect conductor composite with a disordered columnar
microstructure. The phase diagram is found to have a critical line which
separates regions of saturating and non-saturating magnetoresistance. The
percolation problem which describes this line is a generalization of
anisotropic percolation. We locate the percolation threshold and determine the
t = s = 1.30 +- 0.02, nu = 4/3 +- 0.02, which are the same as in
two-constituent 2D isotropic percolation. We also determine the exponents which
characterize the critical dependence on magnetic field, and confirm numerically
that nu is independent of anisotropy. We propose and test a complete scaling
description of the magnetoresistance in the vicinity of the critical line.Comment: Substantially revised version; description of behavior in finite
magnetic fields added. 7 pages, 7 figures, submitted to PR
Winding effects on brane/anti-brane pairs
We study a brane/anti-brane configuration which is separated along a compact
direction by constructing a tachyon effective action which takes into account
transverse scalars. Such an action is relevant in the study of HQCD model of
Sakai and Sugimoto of chiral symmetry breaking, where the size of the compact
circle sets the confinement scale. Our approach is motivated by string theory
orbifold constructions and gives a route to model inhomogeneous tachyon decay.
We illustrate the techniques involved with a relatively simple example of a
harmonic oscillator on a circle. We will then repeat the analysis for the
Sakai-Sugimoto model and show that by integrating out the winding modes will
provide us with a renormalized action with a lower energy than that of
truncating to zero winding sector.Comment: 21 pages, 3 figures. v3: discussion and references added, published
versio
On fluctuations of closed string tachyon solitons
We discuss fluctuations on solitons in the dilaton/graviton/tachyon system
using the low energy effective field theory approach. It is shown that closed
string solitons are free of tachyons in this approximation, regardless of the
exact shape of the tachyon potential.Comment: 13 pages, 1 figure, uses JHEP3.cl
THE NORDIC MARKET: SIGNS OF STRESS?
The supply shock that hit the Nordic electricity market in 2002-2003 put the market to a severe test. A sharp reduction in inflow to hydro reservoirs during the normally wet months of late autumn pushed electricity prices to unprecedented levels. We take this event as the starting point for analysing some potential weaknesses of the Nordic market. We conclude that fears regarding supply security and adequacy are likely to be unfounded. Nevertheless, as inherited over-capacity is eroded, and new market-based environmental regulation takes effect, tighter market conditions are to be expected. It is then crucial that retail markets are fully developed so as to allow consumers to adequately protect themselves from occurrences of price spikes.Production; Pricing; and Market Structure; Size Distribution of Firms; Firm Performance: Size; Diversification; and Scope; Retail and Wholesale Trade; e-Commerce; Air Transportation; Organizational Behavior; Transaction Costs; Property Rights; Oligopoly and Other Forms of Market Imperfection.
Generalized Paraxial Ray Trace Procedure Derived from Geodesic Deviation
Paraxial ray tracing procedures have become widely accepted techniques for
acoustic models in seismology and underwater acoustics. To date a generic form
of these procedures including fluid motion and time dependence has not appeared
in the literature. A detailed investigation of the characteristic curves of the
equations of hydrodynamics allows for an immediate generalization of the
procedure to be extracted from the equation form geodesic deviation. The
general paraxial ray trace equations serve as an ideal supplement to ordinary
ray tracing in predicting the deformation of acoustic beams in random
environments. The general procedure is derived in terms of affine
parameterization and in a coordinate time parameterization ideal for
application to physical acoustic ray propagation. The formalism is applied to
layered media, where the deviation equation reduces to a second order
differential equation for a single field with a general solution in terms of a
depth integral along the ray path. Some features are illustrated through
special cases which lead to exact solutions in terms of either ordinary or
special functions.Comment: Original; 40 pages (double spaced), 1 figure Replaced version; 36
pages single spaced, 7 figures. Expanded content; Complete derivation of the
equations from the equations of hydrodynamics, introduction of an auxiliary
basis for three dimensional wave-front modeling. Typos in text and equations
correcte
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
Experimental archeology and serious games: challenges of inhabiting virtual heritage
Experimental archaeology has long yielded valuable insights into the tools and techniques that featured in past peoplesâ relationship with the material world around them. However, experimental archaeology has, hitherto, confined itself to rigid, empirical and quantitative questions. This paper applies principles of experimental archaeology and serious gaming tools in the reconstructions of a British Iron Age Roundhouse. The paper explains a number of experiments conducted to look for quantitative differences in movement in virtual vs material environments using both âvirtualâ studio reconstruction as well as material reconstruction. The data from these experiments was then analysed to look for differences in movement which could be attributed to artefacts and/or environments. The paper explains the structure of the experiments, how the data was generated, what theories may make sense of the data, what conclusions have been drawn and how serious gaming tools can support the creation of new experimental heritage environments
Lectures on Non-BPS Dirichlet branes
A comprehensive introduction to the boundary state approach to Dirichlet
branes is given. Various examples of BPS and non-BPS Dirichlet branes are
discussed. In particular, the non-BPS states in the duality of Type IIA on K3
and the heterotic string on T4 are analysed in detail.Comment: 46 pages, 5 figures, LaTeX; lectures given at the TMR network school
on `Quantum aspects of gauge theories, supersymmetry and quantum gravity',
Torino, 26 January - 2 February 2000, and at the `Spring workshop on
Superstrings and related matters', Trieste, 27 March - 4 April 2000;
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