Dependence of SWNT Growth Mechanism on Temperature and Catalyst Particle Size: Bulk versus Surface Diffusion

MD simulations reveal that many aspects of SWNT nucleation and growth from solid and liquid metal particles are similar. In both cases graphitic islands lift off the cluster surface to form caps that grow into SWNTs. However, in contrast to liquid particles, where C atoms primarily diffuse into the bulk of the cluster before adding to the growing SWNT, incorporation of C into SWNTs on solid particles occurs predominantly via surface diffusion

Technology for the 21st Century Workforce: A Case Study of a Rural East Tennessee Workforce Community

The purpose of this study was to assess technology use, on-the-job technology training, education levels, and salary ranges of employees in low-, middle-, and high- skill jobs in a rural county in East Tennessee to create an example of a small town workforce. For this study, technology included computers, robotics, and mobile technology. A survey determined the technology used, training provided, salaries, and job skill levels based on education obtained and required by major employers. The study identified the level of jobs requiring more technology skills and salaries or training related to these job skill levels. Participants included 336 persons who completed an electronic survey. Participants represented twenty-eight different companies in healthcare, education, manufacturing, banking, and other small businesses in an East Tennessee rural county. The major findings of the study included: a) use of multiple forms of technology in all job skill levels; b) more time spent in on-the-job training for higher job skill levels; c) participants in lower job skill levels more likely to be overqualified for their position; d) participants in higher paying jobs used more types of technology; and e) participants in higher skill level jobs tend to have higher salaries. The study concluded that, while technology affected all skill levels, there was a significantly positive relationship between salary, technology use, technology training, and job skill level

Use of CFD to Calculate the Dynamic Resistive End Correction for Microperforated Materials

The classical Maa theory for microperforated materials was initially formulated for constant diameter, cylindrical holes. Since then, a number of ad hoc corrections have been suggested to account for different hole shapes, in particular, rounding of the aperture. Here it is shown that the resistance and reactance of small apertures may be calculated using relatively simple CFD models in which a single hole is modeled. The fluid is assumed to be viscous but incompressible, and the geometry is assumed to be axisymmetric. It will be shown that this approach essentially reproduces the classical theory of Maa for circular, sharp-edged apertures. However, it will also be shown that the empirical correction to the resistive end correction, in particular, exhibits a clear dependence on frequency and geometrical parameters that is neglected in conventional microperforated material models

Fast, large volume, GPU enabled simulations for the Ly-alpha forest: power spectrum forecasts for baryon acoustic oscillation experiments

High redshift measurements of the baryonic acoustic oscillation scale (BAO) from large Ly-alpha forest surveys represent the next frontier of dark energy studies. As part of this effort, efficient simulations of the BAO signature from the Ly-alpha forest will be required. We construct a model for producing fast, large volume simulations of the Ly-alpha forest for this purpose. Utilising a calibrated semi-analytic approach, we are able to run very large simulations in 1 Gpc^3 volumes which fully resolve the Jeans scale in less than a day on a desktop PC using a GPU enabled version of our code. The Ly-alpha forest spectra extracted from our semi-analytical simulations are in excellent agreement with those obtained from a fully hydrodynamical reference simulation. Furthermore, we find our simulated data are in broad agreement with observational measurements of the flux probability distribution and 1D flux power spectrum. We are able to correctly recover the input BAO scale from the 3D Ly-alpha flux power spectrum measured from our simulated data, and estimate that a BOSS-like 10^4 deg^2 survey with ~15 background sources per square degree and a signal-to-noise of ~5 per pixel should achieve a measurement of the BAO scale to within ~1.4 per cent. We also use our simulations to provide simple power-law expressions for estimating the fractional error on the BAO scale on varying the signal-to-noise and the number density of background sources. The speed and flexibility of our approach is well suited for exploring parameter space and the impact of observational and astrophysical systematics on the recovery of the BAO signature from forthcoming large scale spectroscopic surveys.Comment: 16 pages, 11 figures, accepted to MNRA

Hybrid Two-Dimensional Finite Element Model of Tires

It has been shown that the vibrational response of a tire can be represented by a set of decaying waves, each associated with a particular cross-sectional mode shape in the region near the contact patch. Thus, it can be concluded that tires can be effectively modeled as lossy waveguides. It has also been shown that the sound radiation from tires is mainly from the region close to the contact patch. In consequence, it may be computationally efficient to analyze tire vibration and sound radiation in the region close to the contact patch by using a hybrid finite element model in which the cross-section of a tire is approximated by 2-D finite elements while an analytical wave solution is assumed in the circumferential direction of the tire. In this article, a hybrid finite element was formulated based on a composite shell model. The dispersion relations for sample structures obtained by using the hybrid FE model were then compared with those obtained by using a full, three-dimensional FE model. It has been shown that the FE analysis made using the hybrid 2-D finite elements yields results in close agreement with the three-dimensional model