An adaptive computation mesh for the solution of singular perturbation problems

In singular perturbation problems, control of zone size variation can affect the effort required to obtain accurate, numerical solutions of finite difference equations. The mesh is generated by the solution of potential equations. Numerical results for a singular perturbation problem in two dimensions are presented. The mesh was used in calculations of resistive magnetohydrodynamic flow in two dimensions

Plasma sheet structure in the magnetotail: kinetic simulation and comparison with satellite observations

We use the results of a three-dimensional kinetic simulation of an Harris current sheet to propose an explanation and to reproduce the ISEE-1/2, Geotail, and Cluster observations of the magnetotail current sheet structure. Current sheet flapping, current density bifurcation, and reconnection are explained as the results of the kink and tearing instabilities, which dominate the current sheet evolution.Comment: Submitted to Geophys. Res. Lett. (2003

Experimental investigation on the effects of surface roughness on microscale liquid flow

Microfluidics has become of interest recently with shrinking device sizes. Roughness structures left from machining processes on the inside of tubes and channels that were once not a concern may now create relative roughness that exceeds 5%. Confusion still exists in the literature as to the extent of the effects of roughness on laminar flow. This work aims to experimentally examine the effects of different roughness structures on internal flows in high aspect ratio rectangular microchannels. A total of four test sections were fabricated to test samples with different patterned rough surfaces, and to also vary the two opposite surfaces forming the long faces of the channel. These test sections allowed the same roughness samples to be tested at varying relative roughnesses and allowed a systematic study on their effects on pressure drop. The first test section looked at sawtooth effects on laminar flow. The second looked at uniform roughness on laminar flow. The third looked at sawtooth roughness in turbulent flow, and the fourth looked at varying pitch sawtooth roughness in laminar flow. Rough surfaces were formed in one of two ways. The first involved making structured repeating sawtooth ridges with a ball end mill on a CNC machine. The second was using sandpaper in a crosshatch pattern to make a more unpatterned roughened surface. In this study, the Reynolds number was varied from 30 to 15,000 with degassed, deionized water as the working fluid. The experimental uncertainty in the experimental data is at worst 7.58% for friction factor and 2.67% for Reynolds number. Roughness structures varied from a lapped smooth surface with 0.2 μm roughness height to sawtooth ridges of height 117 μm. Hydraulic diameters from 198 μm to 2,349 μm were tested. The highest relative roughness tested was 24.8%. As a result of the first and second experiments, it was shown that using constricted parameters, sawtooth and uniform roughness performance could be predicted in the laminar regime. In the third experiment, it was shown that certain sawtooth roughness samples cause the results to converge to a single line for friction factor. In the fourth experiment, the pitch of sawtooth elements was shown to be a key parameter in showing when each parameter is applicable. It was found that roughness has an effect even at relative roughness values less than 5%. Lapped smooth samples showed no departure from macroscale theory at all channel diameters tested, which implies that no departure from continuum mechanics occurred at the length scales tested. This fit with what was expected. Early transitions to turbulence were seen however, showing decreasing transition Reynolds number with increasing relative roughness. The lowest turbulent transition occurred at a Reynolds number of 210, with a relative roughness of 24.8%. Most all of the roughness structures studied were found to have experimental results that were well predicted with the use of constricted parameters. However, samples with roughness elements placed at higher pitches were seen to have experimental results approaching theory calculated with root parameters of the channel

The Network Structure Of Collective Innovation

Prior research on how to design collaboration networks among scientists, engineers, and strategists surprisingly predicts that inefficient networks that slow down the rate of collaboration will lead to better performance on complex problems. However, empirical research has provided mixed evidence for these ideas. Here, we test this theory using an online Data Science Competition that experimentally manipulates the network efficiency of teams working on a complex problem. The results support the idea that less efficient collaboration networks increase collective performance on complex problems. The results have important implications for designing problem-solving teams in numerous domains

An Intercomparison Between Divergence-Cleaning and Staggered Mesh Formulations for Numerical Magnetohydrodynamics

In recent years, several different strategies have emerged for evolving the magnetic field in numerical MHD. Some of these methods can be classified as divergence-cleaning schemes, where one evolves the magnetic field components just like any other variable in a higher order Godunov scheme. The fact that the magnetic field is divergence-free is imposed post-facto via a divergence-cleaning step. Other schemes for evolving the magnetic field rely on a staggered mesh formulation which is inherently divergence-free. The claim has been made that the two approaches are equivalent. In this paper we cross-compare three divergence-cleaning schemes based on scalar and vector divergence-cleaning and a popular divergence-free scheme. All schemes are applied to the same stringent test problem. Several deficiencies in all the divergence-cleaning schemes become clearly apparent with the scalar divergence-cleaning schemes performing worse than the vector divergence-cleaning scheme. The vector divergence-cleaning scheme also shows some deficiencies relative to the staggered mesh divergence-free scheme. The differences can be explained by realizing that all the divergence-cleaning schemes are based on a Poisson solver which introduces a non-locality into the scheme, though other subtler points of difference are also catalogued. By using several diagnostics that are routinely used in the study of turbulence, it is shown that the differences in the schemes produce measurable differences in physical quantities that are of interest in such studies

Architecture As Gateway: A Cultural Center in Annapolis, Maryland

I contend that a gateway can be created to link the two polar conditions without necessarily creating a physical passageway from one condition to the other, but by creating a link between past and present; A link between humanity and nature; a link between ignorance and understanding

Advanced Conducting Project

Chapter 1: Celebration Tribalesque, by Randall D. Standridge, pg. 2 Chapter 2: Nimrod from Enigma Variations, by Edward Elgar, arr. Alfred Reed, pg. 18 Chapter 3: Daedalus\u27 Labyrinth, by Sean O\u27Loughlin, pg. 37 Chapter 4: Lightning Field, by John Mackey, pg. 56 Chapter 5: Mambo from West Side Story, by Leonard Bernstein, arr. Michael Sweeney, pg. 7 4 Chapter 6: Prairie Dances, by David R. Holsinger, pg. 91 Chapter 7: Alchemy, by Andrew Boysen, Jr., pg. 110 Chapter 8: Symphonic Suite, by James Clifton Williams, pg. 130 Chapter 9: Vesuvius, by Frank Ticheli, pg. 16