Molecular dynamics for fluid mechanics in arbitrary geometries

Simulations of nanoscale systems where fluid mechanics plays an important role are required to help design and understand nano-devices and biological systems. A simulation method which hybridises molecular dynamics (MD) and continuum computational fluid dynamics (CFD) models is able to accurately represent the relevant physical phenomena and be computationally tractable. An MD code has been written to perform MD simulations in systems where the geometry is described by a mesh of unstructured arbitrary polyhedral cells that have been spatially decomposed into irregular portions for parallel processing. The MD code that has been developed may be used for simulations on its own, or may serve as the MD component of a hybrid method. The code has been implemented using OpenFOAM, an open source C++ CFD toolbox (www.openfoam.org). The requirements for two key enabling components are described. 1) Parallel generation of initial configurations of molecules in arbitrary geometries. 2) Calculation of intermolecular pair forces, including between molecules that lie on mesh portions assigned to different, and possibly non-neighbouring processors. A case study of flow in a realistic nanoscale mixing channel, where the geometry is drawn and meshed in engineering CAD tools is simulated to demonstrate the capabilities of the code

Global Competition, Institutions, And The Diffusion Of Organizational Practices: The International Spread Of Iso 9000 Quality Certificates

We use panel data on ISO 9000 quality certification in 85 countries between 1993 and 1998 to better understand, the cross-national diffusion of an organizational practice. Following neoinstitutional theory, we focus on the coercive, normative, and mimetic effects that result from the exposure of firms in a given country to a powerful source of critical resources, a common pool of relevant technical knowledge, and the experiences of firms located in other countries. We use social network theory to develop a systematic conceptual understanding of how firms located in different countries influence each other's rates of adoption as a result of cohesive and equivalent network relationships. Regression results provide support for our predictions that states and foreign multinationals are the key actors responsible for coercive isomorphism, cohesive trade relationships between countries generate coercive and normative effects, and role-equivalent trade relationships result in learning-based and competitive imitation.Business Administratio

Patients' advocacy: the development of a service at the State Hospital, Carstairs, Scotland

Advocacy is part of the process of empowering patients and involving them in the development of services. This paper describes the development of an advocacy service in the State Hospital at Carstairs and explores the issues involved in advocacy in a maximum secure environment. Using a model of citizen advocacy the service was started in September 1997. Patient involvement throughout the hospital was high with approximately 88% of patients having some contact with the service by January 2000. Most of the issues raised by patients are similar to those in any mental health advocacy project. Entrapment is a particular issue for some patients. Safety and security issues influence every aspect of the service. This ranges from advocates having to do more for patients rather than enable them to do things for themselves (e.g. make telephone calls) to the principle of the patients' wishes being paramount being tempered by security demands

Molecular dynamics in arbitrary geometries : parallel evaluation of pair forces

A new algorithm for calculating intermolecular pair forces in molecular dynamics (MD) simulations on a distributed parallel computer is presented. The arbitrary interacting cells algorithm (AICA) is designed to operate on geometrical domains defined by an unstructured, arbitrary polyhedral mesh that has been spatially decomposed into irregular portions for parallelisation. It is intended for nano scale fluid mechanics simulation by MD in complex geometries, and to provide the MD component of a hybrid MD/continuum simulation. The spatial relationship of the cells of the mesh is calculated at the start of the simulation and only the molecules contained in cells that have part of their surface closer than the cut-off radius of the intermolecular pair potential are required to interact. AICA has been implemented in the open source C++ code OpenFOAM, and its accuracy has been indirectly verified against a published MD code. The same system simulated in serial and in parallel on 12 and 32 processors gives the same results. Performance tests show that there is an optimal number of cells in a mesh for maximum speed of calculating intermolecular forces, and that having a large number of empty cells in the mesh does not add a significant computational overhead

A classification of primitive permutation groups with finite stabilizers

We classify all infinite primitive permutation groups possessing a finite point stabilizer, thus extending the seminal Aschbacher-O'Nan-Scott Theorem to all primitive permutation groups with finite point stabilizers.Comment: Accepted in J. Algebra. Various changes, some due to the author, some due to suggestions from readers and others due to the comments of anonymous referee

The Origin and Significance of Reverse Zoning in Melilite from Allende Type B Inclusions

In many Type B Allende inclusions, melilite is reversely-zoned over restricted portions of each crystal. Textural relationships and the results of dynamic crystallization experiments suggest that the reverselyzoned intervals in these Type melilites result from the co-precipitation of melilite with clinopyroxene from a melt, prior to the onset of anorthite precipitation. When clinopyroxene begins to precipitate, the Al/Mg ratio of the melt rises, causing the crystallizing melilite to become more gehlenitic, an effect which is negated by crystallization of anorthite. Because the equilibrium crystallization sequence in these liquids is anorthite before pyroxene, melilite reverse zoning can occur only when anorthite nucleation is suppressed relative to pyroxene. This has been achieved in our experiments at cooling rates as low as 0.5°C/hour. Our experiments further indicate, however, that reverse zoning does not form at cooling rates ≥50°C/hour , probably because the clinopyroxene becomes too Al-rich to drive up the Al/Mg ratio of the liquid. Type inclusions with reversely-zoned melilites must have cooled at rates greater than those at which anorthite begins to crystallize before clinopyroxene but <50°C/hour. Such rates are far too slow for the Type droplets to have cooled by radiation into a nebular gas but are much faster than the cooling rate of the solar nebula itself. One possibility is that Type B's formed in local hot regions within the nebula, where their cooling rate was equal to that of their surrounding gas. Other possibilities are that their cooling rates reflect their movement along nebular temperature gradients or the influence of a heat source. The sun or viscous drag on inclusions as they moved through the nebular gas are potential candidates for such heat sources

Some aspects of analytical chemistry as applied to water quality assurance techniques for reclaimed water: The potential use of X-ray fluorescence spectrometry for automated on-line fast real-time simultaneous multi-component analysis of inorganic pollutants in reclaimed water

The potential use of isotopically excited energy dispersive X-ray fluorescence (XRF) spectrometry for automated on line fast real time (5 to 15 minutes) simultaneous multicomponent (up to 20) trace (1 to 10 parts per billion) analysis of inorganic pollutants in reclaimed water was examined. Three anionic elements (chromium 6, arsenic and selenium) were studied. The inherent lack of sensitivity of XRF spectrometry for these elements mandates use of a preconcentration technique and various methods were examined, including: several direct and indirect evaporation methods; ion exchange membranes; selective and nonselective precipitation; and complexation processes. It is shown tha XRF spectrometry itself is well suited for automated on line quality assurance, and can provide a nondestructive (and thus sample storage and repeat analysis capabilities) and particularly convenient analytical method. Further, the use of an isotopically excited energy dispersive unit (50 mCi Cd-109 source) coupled with a suitable preconcentration process can provide sufficient sensitivity to achieve the current mandated minimum levels of detection without the need for high power X-ray generating tubes

Time, Number, Space, and the Domestic Dog

Over the past 20 years, the field of animal cognition has seen a dramatic increase in the attention given to the study of cognition in the domestic dog. Since their origin at least 10, 000 years ago, dogs have been artificially selected by humans to protect our homes, guard our livestock, pull our sleds, and a multitude of other functions. Given their close relationship with humans, much of the current research in the area of dog cognition to date has focused on aspects of social cognition. Considerably less attention has been paid to domains that have traditionally been areas of heavy focus in the animal cognition literature. This dissertation focuses on three areas, which are addressed as “fundamental” aspects of cognition—namely, numerical discrimination, interval timing, and spatial memory. These areas were chosen because a.) they are basic processes fundamental to the daily existence of an animal in the wild, and b.) because these topics have been studied rigorously in traditional animal cognition research, yet have received little attention in the area of dog cognition. In the first set of studies, a numerical discrimination task using sequential presentation of stimuli was used, in which subjects watched as a different number of food items were dropped into each of two bowls. The subjects were then allowed to select and consume the contents of one of the bowls. Although dogs excelled in a 1 vs 0 condition, their performance did not significantly surpass chance across all other ratios. In a second experiment with a single subject, a simultaneous task was used in which stimuli were presented on two magnet boards. Using this simultaneous presentation, ratio effects consistent with both Weber’s Law and the Approximate Number System were demonstrated. In the second set of studies, interval timing was demonstrated using a fixed interval 30-s schedule, with either a light or a tone + light compound signalling the beginning of each fixed interval. When dogs in the compound group were subsequently tested with 60-s tone-only probe trials, the dogs’ rate of responding peaked near 30 s. When the same dogs were tested with light-only probes, however, no evidence of timing was found, revealing an overshadowing effect of tone over light. In a second experiment, a bi-section task was used in which dogs had to learn to approach one feeder when given an 8-s tone + light signal, and another feeder when given a 2-s tone + light signal. When subsequently tested at intermediate durations, psychophysical curves again showed clear control of timing by the tone stimulus but not by the light stimulus. The final set of studies were an attempt to investigate both reference and working memory, within a spatial memory task. A win/shift design was used, in which dogs searched for food within the four corners of a large area (an empty classroom in Experiment 1, and an outdoor field in Experiment 2). Food items were hidden under plastic flower pots, which the dogs had previously been trained to knock over. The dogs’ performance in locating rewards hidden consistently in the same location during the test phase (reference memory), was compared to their performance for locating rewards hidden in a different randomly-selected location from trial to trial (working memory). Dogs’ performance varied across subjects, and implications of these individual differences are discussed