Vortex structure in laminar boundary layers on a concave wall

Naturally occurring Görtler vortices have been investigated, using laser anemometry, in the laminar concave-surface boundary layers of water channels with 90° bends. Distributions of streamwise and spanwise velocities are presented, supported by flow visualization. Amplification was found to cease at Görtler numbers in the region of 9, followed by increasing distortion and spanwise wandering of the vortices. Development of a vortex system from an imposed disturbance has also been predicted by numerical computations.     

Campestarenes: novel shape-persistent Schiff base macrocycles with 5-fold symmetry

A simple 1-step procedure yields a family of easily modifiable, stable, conjugated Schiff base macrocycles with 5-fold symmetry mediated by 3-center hydrogen bonding.     

Towards conformationally dependent redox-responsive molecular switches. New polyferrocene bis benzo crown ether receptors

New polyferrocene bis benzo-15-crown-5 ligands have been prepared and shown to form 1:1 intramolecular sandwich complexes with the potassium cation. Electrochemical investigations reveal that both receptors undergo small anodic perturbations of the respective ferrocene-ferrocenium redox couples in the presence of alkali metal cations.     

Flow past a stretching plate

Zusammenfassung Eine Platte aus plastischem Material fliesst aus einem Spalt mit einer Geschwindigkeit, die proportional zum Abstand vom Spalt ist. Eine exakte Lösung der Grenzschichtgleichungen für die von der Platte erzeugte Luftbewegung wird gegeben. Oberflächenreibung und Wärmeleitungskoeffizient werden berechnet.     

The accuracy of finite difference schemes for the numerical solution of the Navier-Stokes equations

Comparisons are made between various finite difference algorithms used for the numerical solution of two-dimensional viscous flow. Central difference algorithms recently developed by the authors are compared with the well established upwind difference algorithms. Some analytical solutions to the Navier-Stokes equations have been produced in order for meaningful comparisons to be made. On the basis of the results, the new central difference algorithms are recommended as being more accurate whilst requiring little additional computational effort. There is an upper limit on the grid Reynolds number for which these new methods will converge, but this will usually be when the flow would in practice be turbulent.     

Natural convection from a vertical cylinder at very small Prandtl numbers

Summary The flow arising from the natural convection from an isothermal vertical cylinder, valid for very small Prandtl numbers, is determined.

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Zusammenfassung Das Problem der freien konvektiven Grenzschichtströmung entlang eines vertikalen isothermen Zylinders wird für den Fall gelöst, dass die Prandtl'sche Zahl sehr klein ist, und die Grenzschicht dick im Vergleich zum Radius des Zylinders.

     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.