Weak refinement in Z

An important aspect in the specification of distributed systems is the role of the internal (or unobservable) operation. Such operations are not part of the user interface (i.e. the user cannot invoke them), however, they are essential to our understanding and correct modelling of the system. Various conventions have been employed to model internal operations when specifying distributed systems in Z. If internal operations are distinguished in the specification notation, then refinement needs to deal with internal operations in appropriate ways. However, in the presence of internal operations, standard Z refinement leads to undesirable implementations. In this paper we present a generalization of Z refinement, called weak refinement, which treats internal operations differently from observable operations when refining a system. We illustrate some of the properties of weak refinement through a specification of a telecommunications protocol

Classical and quantum dynamics of a model for atomic-molecular Bose--Einstein condensates

We study a model for a two-mode atomic-molecular Bose--Einstein condensate. Starting with a classical analysis we determine the phase space fixed points of the system. It is found that bifurcations of the fixed points naturally separate the coupling parameter space into four regions. The different regions give rise to qualitatively different dynamics. We then show that this classification holds true for the quantum dynamics.Comment: 13 pages, 7 eps figure

The ACIGA Data Analysis programme

The Data Analysis programme of the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) was set up in 1998 by the first author to complement the then existing ACIGA programmes working on suspension systems, lasers and optics, and detector configurations. The ACIGA Data Analysis programme continues to contribute significantly in the field; we present an overview of our activities.Comment: 10 pages, 0 figures, accepted, Classical and Quantum Gravity, (Proceedings of the 5th Edoardo Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July 2003

Pattern formation in binary fluid mixtures induced by short-range competing interactions

Molecular dynamics simulations and integral equation calculations of a simple equimolar mixture of diatomic molecules and monomers interacting via attractive and repulsive short-range potentials show the existence of pattern formation (microheterogeneity), mostly due to depletion forces away from the demixing region. Effective site-site potentials extracted from the pair correlation functions using an inverse Monte Carlo approach and an integral equation inversion procedure exhibit the features characteristic of a short-range attractive and long-range repulsive potential. When charges are incorporated into the model, this becomes a coarse grained representation of a room temperature ionic liquid, and as expected, intermediate range order becomes more pronounced and stable

Eight-band calculations of strained InAs/GaAs quantum dots compared with one, four, and six-band approximations

The electronic structure of pyramidal shaped InAs/GaAs quantum dots is calculated using an eight-band strain dependent $\bf k\cdot p$ Hamiltonian. The influence of strain on band energies and the conduction-band effective mass are examined. Single particle bound-state energies and exciton binding energies are computed as functions of island size. The eight-band results are compared with those for one, four and six bands, and with results from a one-band approximation in which m(r) is determined by the local value of the strain. The eight-band model predicts a lower ground state energy and a larger number of excited states than the other approximations.Comment: 8 pages, 7 figures, revtex, eps

Mighty ducts: Final report

Mechanical engineering undergraduate education traditionally included a substantial amount of experimental work. However, a shift of focus towards a more theory based curriculum led to a loss of practical "gut feeling"-type understanding of the material. A laboratory setup will be developed as part of this project to support future generations of undergraduate students in obtaining such practical understanding of class material. The final product should be targeted towards a future HVAC systems class at the undergraduate level and include the necessary laboratory documentation for the students to execute experiments.The objective of this project is to develop a system for the characterization of fan performance and ductwork fittings (subsequently called system) that includes the following aspects:1. Measurement of fan curves (pressure vs. volumetric flowrate) at various fan speeds2. Determination of pressure loss for various different duct components (including elbows and straight sections). You may choose to express the loss coefficients in terms of equivalent straight duct length.3. Determination of interaction between fittings arranged in series (aka system effect) expressed in pressure vs. air velocity relative to baseline4. Integration into an overall learning environment with predefined 50 minute laboratory modules as mentioned above including the required instructional material.5. An automated controller to emulate constant torque, constant fan speed, and constant flowrate behavior of the fan (teams that include an electrical engineer only)

Multiple-scattering effects on incoherent neutron scattering in glasses and viscous liquids

Incoherent neutron scattering experiments are simulated for simple dynamic models: a glass (with a smooth distribution of harmonic vibrations) and a viscous liquid (described by schematic mode-coupling equations). In most situations multiple scattering has little influence upon spectral distributions, but it completely distorts the wavenumber-dependent amplitudes. This explains an anomaly observed in recent experiments

Electronic structure of strained InP/GaInP quantum dots

We calculate the electronic structure of nm scale InP islands embedded in $Ga_{0.51}In_{0.49}P$. The calculations are done in the envelope approximation and include the effects of strain, piezoelectric polarization, and mixing among 6 valence bands. The electrons are confined within the entire island, while the holes are confined to strain induced pockets. One pocket forms a ring at the bottom of the island near the substrate interface, while the other is above the island in the GaInP. The two sets of hole states are decoupled. Polarization dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia

Thin-film flow of a Bingham fluid over topography with a temperature-dependent rheology

We consider the flow of a viscoplastic fluid on a horizontal or an inclined surface with a flat and an asymmetric topography. A particular application of interest is the spread of a fixed mass – a block – of material under its own weight. The rheology of the fluid is described by the Bingham model which includes the effect of yield stress, i.e. a threshold stress which must be exceeded before flow can occur. Both the plastic viscosity and the yield stress are modelled with temperature-dependent parameters. The flow is described by the lubrication approximation, and the heat transfer by a depthaveraged energy conservation equation. Results show that for large values of the yield stress, only the outer fraction of the fluid spreads outward, the inner fraction remaining unyielded. We also present an analysis which predicts the threshold value of the yield stress for which partial slump occurs