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Environmental Influences on Crossflow InstabilityDowns, Robert 1982- 14 March 2013 (has links)
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.
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Mechanics of nanoscale beams in liquid electrolytes: beam deflections, pull-in instability, and stictionLee, Jae Sang 15 May 2009 (has links)
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.
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The molecular mechanisms involved in the genetic instability of the CCTG. CAGG repeats associated with myotonic dystrophy type 2Dere, Ruhee J. 16 August 2006 (has links)
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 CCTGÂCAGG sequence in the intron of the zinc finger
protein 9 (ZNF9) gene. The genetic instabilities of the CCTGÂCAGG 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 CCTGÂCAGG 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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Generation, propagation and breaking of an internal gravity wave beamClark, Heather A Unknown Date
No description available.
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Survival strategies : changes to systems and controls in agricultural based businesses during a period of economic instability and hyperinflation in Zimbabwe.Kotze, Carrol. January 2003 (has links)
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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Agricultural diversification and economic development in MauritiusFowdar, Narud January 1994 (has links)
No description available.
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Pattern formation in nonlinear opticsMcIntyre, Ross January 1996 (has links)
No description available.
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The damping of inter-area oscillations in power systems with controllable phase shiftersSo, Ping Lam January 1997 (has links)
No description available.
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Instability and Breakup of Non-Newtonian Viscoelastic Liquid JetsSai Ramesh, Prassanna 21 September 2012 (has links)
No description available.
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Beyond Family Structure: Examining the Association between Family Instability and Childhood DelinquencyEnglehart, Michael 25 October 2016 (has links)
No description available.
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