Turbulent kinetic energy equation and free mixing

Calculation of free shear flows was carried out to investigate the usefulness of several concepts which were previously successfully applied to wall flows. The method belongs to the class of differential approaches. The turbulence is taken into account by the introduction of one additional partial differential equation, the transport equation for the turbulent shear stress. The structure of turbulence is modeled after Bradshaw et al. This model was used successfully in boundary layers and its applicability to other flows is demonstrated. The work reported differs substantially from that of an earlier attempt to use this approach for calculation of free flows. The most important difference is that the region around the center line is treated by invoking the interaction hypothesis (concerning the structure of turbulence in the regions separated by the velocity extrema). The compressibility effects on shear layer spreading at low and moderate Mach numbers were investigated. In the absence of detailed experiments in free flows, the evidence from boundary layers that at low Mach numbers the structure of turbulence is unaffected by the compressibility was relied on. The present model was tested over a range of self-preserving and developing flows including pressure gradients using identical empirical input. The dependence of the structure of turbulence on the spreading rate of the shear layer was established

Emergence of Kinetic Behavior in Streaming Ultracold Neutral Plasmas

We create streaming ultracold neutral plasmas by tailoring the photoionizing laser beam that creates the plasma. By varying the electron temperature, we control the relative velocity of the streaming populations, and, in conjunction with variation of the plasma density, this controls the ion collisionality of the colliding streams. Laser-induced fluorescence is used to map the spatially resolved density and velocity distribution function for the ions. We identify the lack of local thermal equilibrium and distinct populations of interpenetrating, counter-streaming ions as signatures of kinetic behavior. Experimental data is compared with results from a one-dimensional, two-fluid numerical simulation.Comment: 8 pages, 6 figure

Assessment of closure coefficients for compressible-flow turbulence models

A critical assessment is made of the closure coefficients used for turbulence length scale in existing models of the transport equation, with reference to the extension of these models to compressible flow. It is shown that to satisfy the compressible 'law of the wall', the model coefficients must actually be functions of density gradients. The magnitude of the errors that result from neglecting this dependence on density varies with the variable used to specify the length scale. Among the models investigated, the k-omega model yields the best performance, although it is not completely free from errors associated with density terms. Models designed to reduce the density-gradient effect to an insignificant level are proposed

Creating Spaces of Imaginative Engagement for Gifted High School Honors and Advanced Placement English Students

Gifted students may have safety needs beyond the universal needs for security that all students have in order to learn. I investigated the needs of gifted students first hand through interviews with nine gifted students with diverse backgrounds. Interview questions and findings were organized around five major themes: characterization of self, characterization of classmates, characterization of teachers, characterization of classroom, and characterization of strategies and activities. Conclusions show that gifted students share commonalities in personality, needs, and characteristics as well as commonalities among the challenges they face, conditions in which they learn, and the environment in which they feel safe to learn. Features in classroom, teachers, and activities create conditions for excitement about learning and student engagement in learning. The most salient findings were the importance gifted students place on a learning community that includes learning through interaction and conversation as well as through classroom discussions, the need that gifted students place on being in gifted classes with their peers throughout the day, and the focus gifted students put on trusting a teacher to teach what is needed as the gifted students further pursue their educations

A Relationship Between Spin and Geometry

In a recent paper, algebraic descriptions for all non-relativistic spins were derived by elementary means directly from the Lie algebra \specialorthogonalliealgebra{3}, and a connection between spin and the geometry of Euclidean three-space was drawn. However, the details of this relationship and the extent to which it can be developed by elementary means were not expounded. In this paper, we will reveal the geometric content of the spin algebras by realising them within a novel, generalised form of Clifford-like algebra. In so doing, we will demonstrate a natural connection between spin and non-commutative geometry, and discuss the impact of this on the measurement of hypervolumes and on quantum mechanics.Comment: 12 pages, includes work presented at the 13th Annual Conference on Clifford Algebras and Their Applications in Mathematical Physics (ICCA13

Developing mental health education for health volunteers in a township in South Africa

Reproduced with permission of the publisher. © Cambridge University Press 2006.South Africa like many countries is moving towards a system of community care for people with mental health problems. This is set against a backdrop of under-resourced and overburdened services. These problems are particularly apparent in the township communities. The aim of this study was to devise an education programme for South African volunteer health workers using principles adapted from the UK evidence base for psychosocial intervention (PSI) and to evaluate the impact of the education programme on community volunteer health workers' knowledge about mental health issues. A stakeholder consultation exercise was held to explore: the context of South African services; the transferability of the UK evidence base and educational strategies to South Africa; and to inform the design of an educational programme. Evaluation of the community volunteer educational programme was undertaken using pre- and post-education focus groups. Twenty-one volunteers working with mentally ill people in the community from one township attended a three-day, six module course. After the course, volunteers: were able to articulate a greater range of aetiological and contributing factors to the development of mental health problems, including stress vulnerability and traditional belief frameworks; could describe a more humanistic model of mental health identification; identified a wider range of both formal and informal helping strategies; were more aware of the negative impact of interpersonal behaviours for people with mental health problems. Volunteer involvement has been confined to communicable diseases in South Africa. Volunteers educated about mental health care could assist in the South African policy of ‘horizontal’ integration of services into primary care from their current ‘vertical’, specialist-orientated structures

Evaluating parameterization protocols for hydration free energy calculations with the AMOEBA polarizable force field

Hydration free energy (HFE) calculations are often used to assess the performance of biomolecular force fields and the quality of assigned parameters. The AMOEBA polarizable force field moves beyond traditional pairwise additive models of electrostatics and may be expected to improve upon predictions of thermodynamic quantities such as HFEs over and above fixed point charge models. The recent SAMPL4 challenge evaluated the AMOEBA polarizable force field in this regard, but showed substantially worse results than those using the fixed point charge GAFF model. Starting with a set of automatically generated AMOEBA parameters for the SAMPL4 dataset, we evaluate the cumulative effects of a series of incremental improvements in parameterization protocol, including both solute and solvent model changes. Ultimately the optimized AMOEBA parameters give a set of results that are not statistically significantly different from those of GAFF in terms of signed and unsigned error metrics. This allows us to propose a number of guidelines for new molecule parameter derivation with AMOEBA, which we expect to have benefits for a range of biomolecular simulation applications such as protein ligand binding studie

Could the extensive use of rare elements in renewable energy technologies become a cause for concern?

The energy transformation process beginning to take place in many countries as a response to climate change will reduce substantially the consumption of fossil fuels, but at the same time cause a large increase in the demand for other raw materials. Whereas it is difficult to estimate the quantities of, for example, iron, copper and aluminium required, the situation is somewhat simpler for the rare elements that might be needed in a sustainable energy economy based largely on photovoltaic sources, wind and possibly nuclear fusion. We consider briefly each of these technologies and discuss the supply risks associated with the rare elements required, if they were to be used in the quantities that might be required for a global energy transformation process. In passing, we point out the need in resource studies to define the terms “rare”, “scarce” and “critical” and to use them in a consistent way