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Opposite Behaviour (opposite + behaviour)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

The role of methylnaphthalene in EHV cable oil as related to oil breakdown and discharge velocity

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2002
A. Al-Sulaiman
This experimental investigation explores the effect of high voltage lightning surges on the insulating oil used in the oil filled extra high voltage cables that serve electric power networks worldwide. Using non-uniform electrode configuration, the breakdown voltage and corresponding discharge propagation velocities in oil samples that are doped with trace amounts of 1-Methylnaphthalene are investigated under both polarities of applied stresses in gap spacing of up to 10 mm. Two distinct ranges of additive concentrations are observed which effect these characteristics. Generally, the positive discharge growth decreases with increase in gap spacing while the negative ones show opposite behaviour. Anomalous behaviour of discharge growth is observed at an optimum concentration of additive, as it attains supersonic velocity which increases with the increase in gap spacing. A correlation between the positive impulse breakdown voltage and the discharge propagation velocity is also established. [source]

Fatigue behaviour of friction stir welded AA2024-T3 alloy: longitudinal and transverse crack growth

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2008
M. T. MILAN
ABSTRACT The fatigue crack growth properties of friction stir welded joints of 2024-T3 aluminium alloy have been studied under constant load amplitude (increasing -,K), with special emphasis on the residual stress (inverse weight function) effects on longitudinal and transverse crack growth rate predictions (Glinka's method). In general, welded joints were more resistant to longitudinally growing fatigue cracks than the parent material at threshold ,K values, when beneficial thermal residual stresses decelerated crack growth rate, while the opposite behaviour was observed next to KC instability, basically due to monotonic fracture modes intercepting fatigue crack growth in weld microstructures. As a result, fatigue crack growth rate (FCGR) predictions were conservative at lower propagation rates and non-conservative for faster cracks. Regarding transverse cracks, intense compressive residual stresses rendered welded plates more fatigue resistant than neat parent plate. However, once the crack tip entered the more brittle weld region substantial acceleration of FCGR occurred due to operative monotonic tensile modes of fracture, leading to non-conservative crack growth rate predictions next to KC instability. At threshold ,K values non-conservative predictions values resulted from residual stress relaxation. Improvements on predicted FCGR values were strongly dependent on how the progressive plastic relaxation of the residual stress field was considered. [source]

Large-scale cosmic microwave background anisotropies and dark energy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003
J. Weller
ABSTRACT In this paper we investigate the effects of perturbations in a dark energy component with a constant equation of state on large-scale cosmic microwave background (CMB) anisotropies. The inclusion of perturbations increases the large-scale power. We investigate more speculative dark energy models with w < ,1 and find the opposite behaviour. Overall the inclusion of perturbations in the dark energy component increases the degeneracies. We generalize the parametrization of the dark energy fluctuations to allow for an arbitrary constant sound speed, and we show how constraints from CMB experiments change if this is included. Combining CMB with large-scale structure, Hubble parameter and supernovae observations we obtain w=,1.02 ± 0.16 (1,) as a constraint on the equation of state, which is almost independent of the sound speed chosen. With the presented analysis we find no significant constraint on the constant speed of sound of the dark energy component. [source]

Steady Flow of Power Law Fluids across a Circular Cylinder

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2006
Ram Prakash Bharti
Abstract The momentum equations describing the steady cross-flow of power law fluids past an unconfined circular cylinder have been solved numerically using a semi-implicit finite volume method. The numerical results highlighting the roles of Reynolds number and power law index on the global and detailed flow characteristics have been presented over wide ranges of conditions as 5 , Re , 40 and 0.6 , n , 2. The shear-thinning behaviour (n < 1) of the fluid decreases the size of recirculation zone and also delays the separation; on the other hand, the shear-thickening fluids (n > 1) show the opposite behaviour. Furthermore, while the wake size shows non-monotonous variation with the power law index, but it does not seem to influence the values of drag coefficient. The stagnation pressure coefficient and drag coefficient also show a complex dependence on the power law index and Reynolds number. In addition, the pressure coefficient, vorticity and viscosity distributions on the surface of the cylinder have also been presented to gain further physical insights into the detailed flow kinematics. Les équations de mouvement décrivant l'écoulement transversal permanent de fluides de loi de puissance en aval d'un cylindre circulaire non confiné ont été résolues numériquement par une méthode de volumes finis semi-implicite. Des résultats numériques soulignant le rôle du nombre de Reynolds et de l'indice de loi de puissance sur les caractéristiques d'écoulement globales et détaillées sont présentés pour de vastes gammes de conditions, soit 5 , Re , 40 et 0,6 , n , 2. Le comportement rhéofluidifiant (n < 1) du fluide réduit la taille de la zone de recirculation et accroît également la séparation; d'autre part, les fluides rhéoépaississants (n > 1) montrent un comportement opposé. En outre, alors que la taille du sillage varie de manière non monotone avec l'indice de loi de puissance, elle ne semble pas influencer les valeurs du coefficient de traînée. Le coefficient de pression de stagnation et le coefficient de traînée montrent aussi une dépendance complexe envers l'indice de loi de puissance et le nombre de Reynolds. Les distributions des coefficients de pression, de la vorticité et de la viscosité sur la surface du cylindre sont également présentées afin de mieux comprendre les cinématiques d'écoulement détaillées. [source]

2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical Approach

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010
Miglena K. Georgieva
Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source]