Raman spectroscopy of acoustic phonons in periodic and Fibonacci superlattices

Results of Raman scattering experiments on (a) periodic superlattices made up of GaAs/In_xGa_1−xAs layers with high indium concentrations, (b) GaAs/Ga_1−xAl_xAs Fibonacci superlattices, are presented. We discuss the observed peak positions and intensities using the continuum theory of acoustic wave propagation in layered media and the photo-elastic coupling model.     

Electron tunneling in ensembles of silicon nanocrystals

Results from our calculations of the electron tunneling rates between silicon nanocrystals are presented. It is shown that tunnel transitions can be more efficient than radiative interband recombination and substantially influence emission in ensembles of silicon nanocrystals.     

Infrared spectroscopy of self-assembled monolayer films on silicon

Infrared vibrational spectroscopy in an attenuated total reflection (ATR) geometry has been employed to investigate the presence of organic thin layers on Si-wafer surfaces. The phenomena have been simulated to show there can be a field enhancement with the presented single-reflection ATR (SR-ATR) approach which is substantially larger than for conventional ATR or specular reflection. In SR-ATR, a discontinuity of the field normal to the film contributes a field enhancement in the lower index thin film causing a two order of magnitude increase in sensitivity. SR-ATR was employed to characterize a single monolayer of undecylenic acid self-assembled on Si(1 1 1) and to investigate a two monolayer system obtained by adding a monolayer of bovine serum albumin protein.     

Extended magnetic reconnection across the dayside magnetopause

The extent of where magnetic reconnection (MR), the dominant process responsible for energy and plasma transport into the magnetosphere, operates across Earth's dayside magnetopause has previously been only indirectly shown by observations. We report the first direct evidence of X-line structure resulting from the operation of MR at each of two widely separated locations along the tilted, subsolar line of maximum current on Earth's magnetopause, confirming the operation of MR at two or more sites across the extended region where MR is expected to occur. The evidence results from in-situ observations of the associated ion and electron plasma distributions, present within each magnetic X-line structure, taken by two spacecraft passing through the active MR regions simultaneously.     

A Model,Algorithms and Strategy for Train Pathing

We set out a model, algorithms and strategies for the train pathing and timetabling problem for rail lines of the type normally found in Britain and Europe; that is, lines having separate tracks for trains in each direction. As the pathing problem is combinatorially difficult we propose solution heuristics and strategies analogous to those which have enabled ‘expert’ train pathers to plan large-scale complex rail systems by traditional manual graphical methods. This approach also has the potential advantage of facilitating user interaction, understanding and acceptance. We report computational results for several examples. Without the above strategies we found even very small problems intractable. With these strategies we could solve realistic size problems in acceptable times, while exploring more options and trade-offs than do traditional methods. More work is needed and we suggest natural extensions, and directions for further research and development.