Stability and Limit Cycle Oscillation Amplitude Prediction for Simple Nonlinear Aeroelastic Systems

in Proceedings of the 45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference (2004, April)

The prediction of the bifurcation and post-bifurcation behaviour of nonlinear aeroelastic systems is becoming a major area of research in the aeroelastic community due to the need for improved transonic ... [more ▼]

The prediction of the bifurcation and post-bifurcation behaviour of nonlinear aeroelastic systems is becoming a major area of research in the aeroelastic community due to the need for improved transonic aeroelastic prediction, the use of non-linear control systems, and new construction techniques that reduce the amount of inherent damping. In this paper, a novel application of the Centre Manifold Theorem is used to accurately predict bifurcation conditions and Limit Cycle Oscillation amplitudes for simple aeroelastic systems with various types of nonlinearity. A simple aeroelastic system with hardening cubic stiffness nonlinearity is considered and is demonstrated to display a wide variety of bifurcation phenomena. These make it dif cult for some of the standard existing methods, such as Normal Form, Cell Mapping and Tangential Linearisation, to quantify the Limit Cycle Oscillation amplitudes through the entire speed range of the system. Then, the proposed approach is introduced and applied to the same system. It is shown that it can accurately predict the limit cycle amplitudes of the system undergoing all types of bifurcation. Finally, the new technique is applied to the same system but with softening cubic stiffness nonlinearity. It is shown that the method can accurately predict both the static and dynamic divergence boundaries and that it can be used to draw a worst-case stability boundary, inside which the solution is always stable. [less ▲]

Stability and variability of teaching behavior: A case study

in Teaching & Teacher Education (1988), 4(4), 289-303

Stability domains, substrate-induced conformational changes, and hinge-bending motions in a psychrophilic phosphoglycerate kinase: A microcalorimetric study

in Journal of Biological Chemistry (2005), 280(50), 41307-41314

The cold-active phosphoglycerate kinase from the Antarctic bacterium Pseudomonas sp. TACII18 exhibits two distinct stability domains in the free, open conformation. It is shown that these stability ... [more ▼]

The cold-active phosphoglycerate kinase from the Antarctic bacterium Pseudomonas sp. TACII18 exhibits two distinct stability domains in the free, open conformation. It is shown that these stability domains do not match the structural N- and C-domains as the heat-stable domain corresponds to about 80 residues of the C-domain, including the nucleotide binding site, whereas the remaining of the protein contributes to the main heat-labile domain. This was demonstrated by spectroscopic and microcalorimetric analyses of the native enzyme, of its mutants, and of the isolated recombinant structural domains. It is proposed that the heat-stable domain provides a compact structure improving the binding affinity of the nucleotide, therefore increasing the catalytic efficiency at low temperatures. Upon substrate binding, the enzyme adopts a uniformly more stable closed conformation. Substrate-induced stability changes suggest that the free energy of ligand binding is converted into an increased conformational stability used to drive the hinge-bending motions and domain closure. [less ▲]

Stability limit of a granular monolayer

in European Physical Journal E -- Soft Matter (2005), 17(1), 77-81

A granular monolayer is composed by spherical grains on a horizontal plate. The plate is then tilted until the monolayer breaks down. This critical angle has been measured for different widths and heights ... [more ▼]

A granular monolayer is composed by spherical grains on a horizontal plate. The plate is then tilted until the monolayer breaks down. This critical angle has been measured for different widths and heights of the rectangular monolayer. The highest critical angles are found when one of these two characteristic lengths is less than about 30 bead diameters. When the polydispersity is less than one percent, the monolayer may be stable till angles close to 90 degrees. Arches induce large critical angles. On the other hand, for a large and high monolayer, the critical angle saturates towards a lower value. This angle is related to the static friction of a grain on the plate. A model based on the block dynamics is proposed to describe the behavior of the avalanche angle as a function of the size of the monolayer and the polydispersity of the beads. [less ▲]

Stability of a FBTCS Scheme Applied to the Propagation of Shallow-Water Inertia-Gravity Waves on Various Space Grids

in Journal of Computational Physics (1993), 108(1), 94-104

The equations governing the propagation of inertia-gravity waves in geophysical fluid flows are discretized on the A, B, C, and D grids according to the classical forward-backward on time and centered on ... [more ▼]

The equations governing the propagation of inertia-gravity waves in geophysical fluid flows are discretized on the A, B, C, and D grids according to the classical forward-backward on time and centered on space (FBTCS) numerical scheme. The von Neumann stability analysis is performed and it is shown that the stability condition of the inertia-gravity waves scheme is more restrictive, at least by a factor of , than that concerning pure gravity waves, whatever the magnitude of the Coriolis parameter. Finally, the general necessary and sufficient stability condition is derived for the A, B and C grids, while, on the D grid, the stability condition has been obtained only in particular cases. [less ▲]

The stability of alluaudite in granitic pegmatites

Conference (2004)

Stability of g+ Modes in a 30 M_solar Star

in Bulletin de la Société Royale des Sciences de Liège (1975), 8

Stability of gut microbiota over time in Crohn's disease patients compared to healthy relatives

in Gastroenterology (2008), 134(4), 653-653

Stability of intact parathyroid hormone in samples from hemodialysis patients

in Kidney International (2007), 72(3), 370-372

The determination of intact parathyroid hormone levels is used for diagnosis and in the management of renal osteodystrophy. Pre-analytical and analytical conditions are important in the overall confidence ... [more ▼]

The determination of intact parathyroid hormone levels is used for diagnosis and in the management of renal osteodystrophy. Pre-analytical and analytical conditions are important in the overall confidence of the assay. Unfortunately, there are no clear recommendations for the use of serum samples or samples anticoagulated with ethylenediaminotetraacetic acid (EDTA) for the best preservation of intact parathyroid hormone. In our study, the Roche Elecsys assay was used to measure intact hormone in both serum and EDTA plasmas from 16 hemodialysis patients over the span of a month. Parathyroid hormone stability was determined in samples kept frozen for 1-5 days or after 8-24 h at room temperature. There was no difference in hormone stability between serum and EDTA samples after 1 day in frozen storage. After 5 days frozen, hormone degradation was significantly greater after EDTA anticoagulation than in serum aliquots. When samples were stored at room temperature, intact parathyroid hormone was significantly more stable in EDTA-treated samples than in clotted serum samples, especially after 24 h. We conclude that optimum results are achieved in the measurement of intact parathyroid hormone levels depending on the workflow of the lab. If the lab works with intermittent batches of samples, frozen serum is the best. If the lab services general practitioners and/or several hospitals and has a continuous flow of samples, EDTA-treated samples stored at room temperature are the best. [less ▲]

Stability of Ondansetron Hydrochloride and Dexamethasone Sodium Phosphate in 0.9% Sodium Chloride Injection and in 5% Dextrose Injection

in American Journal of Health-system Pharmacy (1997), 54(9), 1065-8