The laminar-to-turbulent transition process in swept-wing boundary layers is often dominated by an inflectional instability arising from crossflow. It is now known that freestream turbulence and surface roughness are two of the key disturbance sources in the crossflow instability problem. Recent experimental findings have suggested that freestream turbulence of low intensity (less than 0.2%) may have a larger influence on crossflow instability than was previously thought. The present work involves experimental measurement of stationary and traveling crossflow mode amplitudes in freestream turbulence levels between 0.02% and 0.2%. A 1.83 m chord, 45-degree swept-wing model is used in the Klebanoff-Saric Wind Tunnel to perform these experiments. The turbulence intensity and length scales are documented. Although a significant amount of research on the role of turbulence has been completed at higher turbulence levels, comparatively little has been done at the low levels of the present experiments, which more closely reflect the flight environment. It is found that growth of the traveling crossflow mode is highly dependent on small changes to the freestream turbulence. Additionally, previously studied attenuation of saturated stationary disturbance amplitudes is observed at these low turbulence levels. The extent of laminar flow is also observed to decrease in moderate freestream turbulence.

The pressure between two parallel planar surfaces at equal electric potentials is derived using the modified Poisson-Boltzmann (MPB) equation to account for finite ion size. The effects of finite ion size are presented for a z:z symmetric electrolyte and compared with the pressure derived by the classical Poisson-Boltzmann (PB) equation. The pressures predicted by the two models differ more as the bulk ion concentration, surface potential, and ion size increase. The ratio of the pressures predicted by the two models is presented by varying the ion concentration, surface potential, ion size and distance of separation. The ratio of pressures is relatively independent of the distance of separation between the two surfaces. An elastic beam suspended horizontally over a substrate in liquid electrolyte is subjected to electric, osmotic, and van der Waals forces. The continuous beam structure, not a discrete spring, which is governed by four nondimensional parameters, is solved using the finite element method. The effects of ion concentration and electric potentials to the pull-in instability are especially focused by parametric studies with a carbon nanotube cantilever beam. The pull-in voltage of a double-wall carbon nanotube suspended over a graphite substrate in liquid can be less than or greater than the pull-in voltage in air, depending on the bulk ion concentration. The critical separation between the double-walled carbon nanotube (DWCNT) and the substrate increases with the bulk ion concentration. However, for a given bulk ion concentration, the critical separation is independent of the electric potentials. Furthermore, the critical separation is approximately equal in liquid and air. Stiction, the most common failure mode of the cantilever-based devices, is studied in a liquid environment, including elastic energy, electrochemical work done, van der Waals work done and surface adhesion energy. We extend the classical energy method of the beam peeling for micro-electro-mechanical systems (MEMS) in the air to an energy method for nano-electro-mechanical systems (NEMS) in liquid electrolyte. We demonstrate a useful numerical processing method to find the parameters to free the stiction of the beams and to obtain the detachment length of the beams.

Myotonic dystrophy type 2 (DM2) is caused by the extreme expansion (from < 30 repeats in normal individuals to ~ 11,000 for the full mutation in certain patients) of the repeating tetranucleotide CCTG•CAGG sequence in the intron of the zinc finger protein 9 (ZNF9) gene. The genetic instabilities of the CCTG•CAGG repeats were investigated to evaluate the molecular mechanisms responsible for these massive expansions. The effects of replication, recombination, repair and transcription on the genetic instabilities have been investigated in COS-7 cells and E. coli model systems. A replication assay was established in COS-7 cells wherein the CCTG•CAGG repeats cloned proximal to the SV40 origin of replication resulted in expansions and deletions in a length and orientation-specific manner, whereas the repeats cloned distal to the same origin were comparatively stable. These results fit with our data obtained from biochemical studies on synthetic oligonucleotides since these biochemical studies revealed that the d(CAGG)26 oligomer had a marked propensity to adopt a hairpin structure as opposed to its complementary d(CCTG)26 that lacked this capacity. Furthermore, a genetic assay in E. coli was used to monitor the intramolecular frequency of recombination. This assay revealed that the tetranucleotide repeats were indeed hot spots for recombination. Moreover, studies conducted in SOS-repair mutants showed that recombination frequencies were much lower in a SOS¯ strain as compared to a SOS+ strain. However, experiments conducted to ascertain the level of induction of the SOS response revealed that the SOS pathway was not stimulated in our studies. These results revealed that although breaks may occur within the repeats, the damage is most likely repaired without induction of the SOS response contrary to previous beliefs. Thus, a complex interplay of replication, recombination, and repair is likely responsible for the expansions observed in DM2.

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Zimbabwe is currently experiencing unprecedented hyperinflation, which is impacting on the effectiveness and efficiency of businesses operating in this unstable economic climate. The current skewed economic policies are producing unusual threats for these businesses but are also providing unusual opportunities for exploitation. Some of these threats can be summarised as the breakdown of social infrastructure, which has worsened the effects on these operations of low world market prices for primary products. There is a large amount of strategic systems and controls theory about management in turbulent operating environments. Most of these focus on survival against fast moving competition from rivals and substitutes, rapid pace of technological change and similar developed country problems. Conventional strategic theory relies on stable currency and procurement environments and is not well adapted to operations in hyperinflation situations. This paper reports the results of a study of strategic changes introduced as survival mechanism by four businesses with a long operating cycle in primary agricultural production. The study examines the relevance of specific strategic theories to each of the respondents. The respondents questioned all expect that the economic situation will return to "normal" and that these strategic adjustments will be replaced with conventional theory soon thereafter. / Thesis (MBA)-University of Natal, 2003.

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