Semantic modelling of learning objects and instruction

We introduce an ontology-based semantic modelling framework that addresses subject domain modelling, instruction modelling, and interoperability aspects in the development of complex reusable learning objects. Ontologies are knowledge representation frameworks, ideally suited to support knowledge-based modelling of these learning objects. We illustrate the benefits of semantic modelling for learning object assemblies within the context of standards such as SCORM Sequencing and Navigation and Learning Object Metadata

Mean flow and spiral defect chaos in Rayleigh-Benard convection

We describe a numerical procedure to construct a modified velocity field that does not have any mean flow. Using this procedure, we present two results. Firstly, we show that, in the absence of mean flow, spiral defect chaos collapses to a stationary pattern comprising textures of stripes with angular bends. The quenched patterns are characterized by mean wavenumbers that approach those uniquely selected by focus-type singularities, which, in the absence of mean flow, lie at the zig-zag instability boundary. The quenched patterns also have larger correlation lengths and are comprised of rolls with less curvature. Secondly, we describe how mean flow can contribute to the commonly observed phenomenon of rolls terminating perpendicularly into lateral walls. We show that, in the absence of mean flow, rolls begin to terminate into lateral walls at an oblique angle. This obliqueness increases with Rayleigh number.Comment: 14 pages, 19 figure

Pairwise Force SPH Model for Real-Time Multi-Interaction Applications

In this paper, we present a novel pairwise-force smoothed particle hydrodynamics (PF-SPH) model to allow modeling of various interactions at interfaces in real time. Realistic capture of interactions at interfaces is a challenging problem for SPH-based simulations, especially for scenarios involving multiple interactions at different interfaces. Our PF-SPH model can readily handle multiple kinds of interactions simultaneously in a single simulation; its basis is to use a larger support radius than that used in standard SPH. We adopt a novel anisotropic filtering term to further improve the performance of interaction forces. The proposed model is stable; furthermore, it avoids the particle clustering problem which commonly occurs at the free surface. We show how our model can be used to capture various interactions. We also consider the close connection between droplets and bubbles, and show how to animate bubbles rising in liquid as well as bubbles in air. Our method is versatile, physically plausible and easy-to-implement. Examples are provided to demonstrate the capabilities and effectiveness of our approach

Phase transition in Schwarzschild-de Sitter spacetime

Using a static massive spherically symmetric scalar field coupled to gravity in the Schwarzschild-de Sitter (SdS) background, first we consider some asymptotic solutions near horizon and their local equations of state(E.O.S) on them. We show that near cosmological and event horizons our scalar field behaves as a dust. At the next step near two pure de-Sitter or Schwarzschild horizons we obtain a coupling dependent pressure to energy density ratio. In the case of a minimally couplling this ratio is -1 which springs to the mind thermodynamical behavior of dark energy. If having a negative pressure behavior near these horizons we concluded that the coupling constant must be $\xi<{1/4}$ >. Therefore we derive a new constraint on the value of our coupling $\xi$ . These two different behaviors of unique matter in the distinct regions of spacetime at present era can be interpreted as a phase transition from dark matter to dark energy in the cosmic scales and construct a unified scenario.Comment: 7 pages,no figures,RevTex, Typos corrected and references adde

Probing neutrino masses with future galaxy redshift surveys

We perform a new study of future sensitivities of galaxy redshift surveys to the free-streaming effect caused by neutrino masses, adding the information on cosmological parameters from measurements of primary anisotropies of the cosmic microwave background (CMB). Our reference cosmological scenario has nine parameters and three different neutrino masses, with a hierarchy imposed by oscillation experiments. Within the present decade, the combination of the Sloan Digital Sky Survey (SDSS) and CMB data from the PLANCK experiment will have a 2-sigma detection threshold on the total neutrino mass close to 0.2 eV. This estimate is robust against the inclusion of extra free parameters in the reference cosmological model. On a longer term, the next generation of experiments may reach values of order sum m_nu = 0.1 eV at 2-sigma, or better if a galaxy redshift survey significantly larger than SDSS is completed. We also discuss how the small changes on the free-streaming scales in the normal and inverted hierarchy schemes are translated into the expected errors from future cosmological data.Comment: 14 pages, 7 figures. Added results with the KAOS proposal and 1 referenc

Electrical and ultraviolet characterization of 4H-SiC Schottky photodiodes

Fabrication and electrical and optical characterization of 4H-SiC Schottky UV photodetectors with nickel silicide interdigitated contacts is reported. Dark capacitance and current measurements as a function of applied voltage over the temperature range 20 °C – 120 °C are presented. The results show consistent performance among devices. Their leakage current density, at the highest investigated temperature (120 °C), is in the range of nA/cm2 at high internal electric field. Properties such as barrier height and ideality factor are also computed as a function of temperature. The responsivities of the diodes as functions of applied voltage were measured using a UV spectrophotometer in the wavelength range 200 nm - 380 nm and compared with theoretically calculated values. The devices had a mean peak responsivity of 0.093 A/W at 270 nm and −15 V reverse bias

Neutrinoless Double Beta Decay in Light of SNO Salt Data

In the SNO data from its salt run, probably the most significant result is the consistency with the previous results without assuming the 8B energy spectrum. In addition, they have excluded the maximal mixing at a very high confidence level. This has an important implication on the double beta decay experiments. For the inverted or degenerate mass spectrum, we find |_{ee}| > 0.013 eV at 95% CL, and the next generation experiments can discriminate Majorana and Dirac neutrinos if the inverted or degenerate mass spectrum will be confirmed by the improvements in cosmology, tritium data beta decay, or long-baseline oscillation experiments.Comment: REVTEX4, three figures. Now uses the updated SK atmospheric data rather than naive rescaling. Conclusion unchanged. References adde

Fine-Tuning Solution for Hybrid Inflation in Dissipative Chaotic Dynamics

We study the presence of chaotic behavior in phase space in the pre-inflationary stage of hybrid inflation models. This is closely related to the problem of initial conditions associated to these inflationary type of models. We then show how an expected dissipative dynamics of fields just before the onset of inflation can solve or ease considerably the problem of initial conditions, driving naturally the system towards inflation. The chaotic behavior of the corresponding dynamical system is studied by the computation of the fractal dimension of the boundary, in phase space, separating inflationary from non-inflationary trajectories. The fractal dimension for this boundary is determined as a function of the dissipation coefficients appearing in the effective equations of motion for the fields.Comment: 10 pages, 4 eps figures (uses epsf), Revtex. Replaced with version to match one in press Physical Review

Distribution and density of the partition function zeros for the diamond-decorated Ising model

Exact renormalization map of temperature between two successive decorated lattices is given, and the distribution of the partition function zeros in the complex temperature plane is obtained for any decoration-level. The rule governing the variation of the distribution pattern as the decoration-level changes is given. The densities of the zeros for the first two decoration-levels are calculated explicitly, and the qualitative features about the densities of higher decoration-levels are given by conjecture. The Julia set associated with the renormalization map is contained in the distribution of the zeros in the limit of infinite decoration level, and the formation of the Julia set in the course of increasing the decoration-level is given in terms of the variations of the zero density.Comment: 8 pages,8figure

Sign-reversal of drag in bilayer systems with in-plane periodic potential modulation

We develop a theory for describing frictional drag in bilayer systems with in-plane periodic potential modulations, and use it to investigate the drag between bilayer systems in which one of the layers is modulated in one direction. At low temperatures, as the density of carriers in the modulated layer is changed, we show that the transresistivity component in the direction of modulation can change its sign. We also give a physical explanation for this behavior.Comment: 4 pages, 4 figure