The Separation Problem, originally posed by K. Bezdek in , asks for the minimum number s(O, K) of hyperplanes needed to strictly separate an interior point O in a convex body K from all faces of K. It is conjectured that s(O, K) ≦ 2d in d-dimensional Euclidean space. We prove this conjecture for the class of all totally-sewn neighbourly 4-dimensional polytopes.
After summarising the techniques available generally in analytical chemistry for the separation and pre-concentration of trace
elements, reasons are given why some of these procedures have achieved greater prominence in particular radiochemical separations.
Examples of contemporary practice and current trends in a wide variety of radiochemical separation problems are then illustrated
by reference to papers that have appeared in recent literature.
The objective of this paper is to report a new procedure for separation of complex mixtures by combining different modes of multidimensional planar chromatography on silica plates. Initially the complex mixture was separated into five groups of compounds. Mobile phases for separation of these different groups were then optimized by regarding each group as an individual separation problem. By use of this new procedure 22 compounds from a complex mixture were separated on 10 cm × 10 cm TLC and HPLC plates.
Four chromatographic support materials from the production of GDR firms, one polytetrafluoroethylene support from USSR, polytrifluorochlorethylene
and Hyflo-Super-Cel were investigated for suitability under conditions of separation of uranium from other constituents of
irradiated uranium fuel solutions with tributylphosphate as an extracting agent. Among the supports there is a new material
developed in GDR on the basis of polytetrafluoroethylene with some favorable properties. The experimental results are discussed
in connection with the problem of comparison criteria for columns with supports differing in chemical nature, particle size
and other parameters. Reduced plate height and velocity were used to arrange experiments under comparable conditions. The
results indicate the fluorocontaining supports to be the most suitable ones from the investigated materials for the considered
Authors:Long Han, Deepak Doraiswamy and Rakesh K. Gupta
Light emitting devices containing conjugated polymers are conveniently fabricated using ink-jet printing. A common problem in the processing of these materials is that the Newtonian viscosity of the polymer solution is not sufficient to describe the jetting performance because the molecular weights and concentrations employed are such that the resulting solutions are elastic. These differences in fluid elasticity levels cannot be measured using traditional techniques like dynamic mechanical experiments or the first normal stress difference in shear, but strongly impact the jetting behavior of the liquid. In this study, a variety of polystyrene solutions in DECALIN having a shear viscosity of ~5 mPa s but different elasticity levels were examined for their jetting behavior. The jetting behavior of these solutions was studied visually using drop-on-demand jetting equipment and their rheology was characterized using a custom extensional rheometer designed for measuring the elasticity of such low viscosity liquids. If elasticity effects are absent as in Newtonian liquids (corresponding to a Trouton ratio of 3) satellite drops are formed resulting in loss of liquid and poor positioning. On the other hand, if elasticity effects are very large (Trouton ratios ≫4) separation problems occur at the nozzle with undesirable “tailing.” The optimum range for stable, efficient jetting occurs at Trouton ratios in a narrow band between 3 and ~5. A very slight degree of elasticity corresponding to a Trouton Ratio around four thus seems to be optimum for the jetting process. This appears to be the first time that such a design criterion has been outlined for this process. Such an approach complements thermal techniques for elucidating the role of molecular and flow properties on the processing behavior of polymeric systems.