Semileptonic (Λ b → Λcev) decay in a field theoretic quark model

The semileptonic decay width of heavy baryons such as (Λ _b → Λcev) has been estimated in the framework of a nonrelativistic field theoretic quark model where four component quark field operators along with a harmonic oscillator wave function are used to describe translationally invariant hadronic states. The present estimation does not make an explicit use of heavy quark symmetry and has a reasonable agreement with the experimentally measured decay width, polarisation ratio and form factors with the harmonic oscillator radii and quark momentum distribution inside the hadron as free parameters.     

Viscous flow through microfabricated hyperbolic contractions

We study the flow of a Newtonian fluid through microfabricated hyperbolic contractions followed by a sudden expansion, with the aim of investigating the potential of this geometry to serve as an extensional microrheometer. A set of planar converging geometries, with total Hencky strains ranging from 1.0 to 3.7, were fabricated in order to produce a homogeneous extensional flow field within the contraction. The velocity field in various planes of the hyperbolic contraction was quantified by means of microparticle image velocimetry (μPIV) and the pressure drop across the converging geometry was also measured and found to vary approximately linearly with the flow rate. Additionally, an extensive range of numerical calculations were carried out using a finite-volume method to help assess the performance of this geometry as a microfluidic elongational rheometer. The measured velocity fields in the contraction and associated pressure drops compare very well (to within 10%) with the numerical predictions. For the typical dimensions used in the microfluidic devices, the steady viscous flow through the contraction is shown to be three-dimensional and it is demonstrated that regions with nearly constant strain rate can only be achieved using geometries with large total Hencky strains under Hele–Shaw (potential-like) flow conditions.     

Determination of phosphorus in organic compounds: A new micro procedure

Summary A new micro procedure for the determination of phosphorus in organic compounds has been developed. It is based on the yellow complex produced by mixing ammonium vanadate, molybdate, and phosphate. The procedure is rapid, simple, and suited for series determinations; the reagents and the colored compounds are stable. A precision of ± 0.2% phosphorus is obtained with samples of 3 to 10 mg weight.

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Zusammenfassung Das beschriebene Mikroverfahren für die Phosphorbestimmung in organischen Substanzen beruht auf der photometrischen Auswertung des gelben Komplexes mit Vanadat und Molybdat. Es ist einfach, schnell, und für Serienbestimmungen geeignet. Die dafür nötigen Reagenzien sind gut haltbar, die gefärbte Verbindung ist beständig. Eine Genauigkeit von ± 0.2% Phosphor wird mit Probemengen von 3 bis 10 mg erhalten.

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Résumé On présente un micro-procédé de dosage du phosphore dans des composés organiques. Il repose sur le complexe jaune produit en mélangeant des vanadate, molybdate et phosphate d'ammonium. Le procédé est rapide, simple et convenable pour les dosages en série. Les réactifs et les composés colorés sont stables. Une précision de ± 0,2% sur le phosphore est obtenue avec des échantillons allant de 3 à 10 mg.