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Nonsolenoidal flow in a liquid diffusion couple (1997)

Perera, P. S.

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 9 (1997), S. 376-391

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: Advective nonsolenoidal ((bold del)⋅v≠0) flow driven by diffusion-induced density changes in strictly zero gravity is studied in a two-dimensional rectangular box. Our model, which is more general than the Oberbeck–Boussinesq model, is a precursor for the study of fluid flow that occurs due to density changes during isothermal interdiffusion in a binary liquid under the influence of stochastic microgravity (g-jitter). We consider perturbation expansions of mass fraction (w) of the second chemical component of a binary solution, pressure (p), velocity (v), and chemical flux (j) with respect to a small parameter α [=ρ0∂(1/ρ)/∂w], where ρ is the density and ρ0 is its value for some average composition. The total barycentric velocity field is given by the sum of an average flow, having a nonzero divergence, and a solenoidal flow derived from a pseudo-stream-function. At first order in α, we obtain a fourth order partial differential equation for this pseudo-stream-function. We solve this equation analytically in a quasi-steady-state approximation for an infinitely long diffusion couple by using transform techniques. We also solve it numerically for the full time-dependent problem for a finite domain. We conclude that such nonsolenoidal flows will dominate for sufficiently small gravity, for which the Oberbeck–Boussinesq approximation will certainly not be valid. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.869238

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Thin layer chromatographic studies of the pungent principles of Ceylon chillies (Capsicum species) (1972)

Tirimanna, A. S. L. ; Perera, P. S. S.

Springer

Plant foods for human nutrition 22 (1972), S. 1-5

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ISSN: 1573-9104

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Description / Table of Contents: Zusammenfassung Auf Ceylon wird eine Reihe von Paprikasorten kultiviert, deren Schärfe deutlich mit der Sorte, der Farbe und der Größe variiert. Mit Hilfe der Dünnschichtchromatographie wurden die die Schärfe bedingenden Komponenten der auf Ceylon vorkommenden Capsicum-Spezies untersucht. Diese Untersuchungen ergaben, daß in den Capsicumsorten drei von Capsaicin abweichende Komponenten vorliegen, die ähnliche Farbreaktionen wie das Capsaicin ergeben. In Capsicum annuum var. grossum konnte mit dieser Methode Capsaicin nicht nachgewiesen werden, statt dessen jedoch zwei andere Komponenten, die in einem konzentrierten Extrakt für die Schärfe der Früchte verantwortlich sind. Die große Variationsbreite der relativen Konzentration dieser scharfen, halbquantitativ bestimmten Komponenten ceylonesischer Paprikasorten wird diskutiert.

Abstract: Résumé Il'y a plusieurs variétés des piments cultivés a Ceylan et le piquent de fruit varie selon l' éspèce, la couleur, et la taille. Une étude chromatographique sur couche mince des composants (piquents) d' espèce Capsicume de Ceylan indique trois composants sans compter ‘capsaicin’ (l'acide isoduenoic de vanillyl amide) qui repondent dans la même façon vis à vis der réactions colorantes. Dans le cas du Capsicum annuum de varieté grossum, le composant piquent ‘capsaicin’ n'est pas décelé par cette methode, par contre, on y trouve deux autres composants qui, dans un extrait concentré, sont responsables pour le piquent du fruit. Les variations relatives des concentrations de composants piquents, determinées semi-quantitativement dans les differents variétés des piments de Ceylan sont décrites.

Notes: Abstract There are many varieties of cultivated chillies in Ceylon and the pungency of the fruit varies markedly with species, colour and size. A thin layer chromatographic study has been undertaken of the hot principles of Capsicum species found in Ceylon. This study shows that there are three compounds in Capsicum species other than capsaicin (vanillyl amide of isodecenoic acid) which give similar colour reactions as capsaicin. In Capsicum annuum, variety grossum, the hot principle, capsaicin is not detected by this method but instead, two other compounds are present which in a concentrated extract are responsible for the pungency of the fruit. Major variations in the relative concentrations of those pungent principles as determined semi-quantitatively, in the different varieties of Ceylon chillies have been discussed.