The reactions of CH2 and ketene with CH2 and H have been investigated at elevated temperatures in the postshock region behind reflected shocks. Atomic (ARAS) and molecular resonance absorption spectrometry was used to record simultaneously H-atom and CO-molecule concentration profiles. The thermal decomposition of very low initial concentrations of ketene (2-50 ppm CH2CO/Ar) served as a source for methylene. The experiments were conducted in the temperature range of 1650-2800 K at total densities of 5 X 10"6 to 1.3 X 10~s mol cm"3. For temperatures above 2000 K the following rate coefficients (k in cm3 mol"' s"1) were deduced: CH2 + CH2 = C2H2 + 2H, k = (10 ± 2) X 1013; CH2 + H = CH + H2, k = (8 ± 2) X 1012. For temperatures between 1650 and 1850 K a value of (1.8 ± 0.6) X 1013 is deduced for the reaction of ketene with H atoms.

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The present work deals with the experimental investigation of entrainment characteristics of confined/semiconfined circular and noncircular jets. The jet fluid, after issuing out of a nozzle of circular or noncircular cross section, enters a circular mixing tube of larger area, and during this process it entrains some ambient fluid into the mixing tube. The flow is incompressible and isothermal at a jet Reynolds number of 7200. The experimental results obtained in the study are first validated with the approximate theoretical analysis of Pritchard et al. (1997) and also with the similarity solution proposed by Becker et al. (1963) for circular nozzles. It is observed that the similarity solution is applicable for circular as well as noncircular jets in the region close to the jet axis and away from the nozzle exit plane. The entrainment ratio increases to a maximum value as the jet location is shifted away from the tube inlet; for the configurations studied, enhancement up to 30% has been observed in the entrainment ratio with shift in jet location. For a smaller mixing tube diameter and jet located at the inlet of the mixing tube, the circular jet entrains more than noncircular jets. For a larger mixing tube or shifted jet locations, the noncircular jets entrain more of ambient fluid, in general. Among the different noncircular geometries considered, the jet having the cross section of an isosceles triangle causes maximum entrainment.

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SUMMARY: The variations in Vibrio cholerae studied included changes from Ogawa to Inaba type, smooth+rough, and motile-+non-motile. With a sloppy-agar technique it was possible to estimate the rate of formation of thcse variants (i.e. probable mutation rate 1 in 1 0 5 and 1 in lo4, respectively). It was possible to show that the action of antiserum in promoting the change from Ogawa to Inaba was selective rather than mutagenic. With the other two variations studied no selective process had to be considered owing to their high spontaneous rate of appearance. It may be said that all three variations studied were due to spontaneous mutants in the parent cultures giving rise to these forms.The studies of Gardner & Venkatraman (1935) showed that vibrio species could be separated on the basis of their somatic '0' antigens, while the flagellar 'H' antigens were widely shared. Since then the differentiation of Vibrio cholerae, the pathogen of cholera, from similar cholera-like vibrios, rests on its agglutinability with specific '0 ' antisera. V . cholerae constituted 0 group I, in this scheme of classification, along with certain haemolytic 'El Tor' vibrios. The definition of V. cholerae as a non-haemolytic vibrio belonging to 0 group I (Gardner & Venkatraman) is now generally accepted, and 0 antisera prepared with heat-killed suspensions are almost universally used for the identification of V . cholerae, in the absence of any reliable biochemical critera. Gardner & Venkatraman (1935) also confirmed the observations of early Japanese workers (Kabeshima, 1918; Nobechi, 1923) when they defined subtypes Inaba, Ogawa and Hikojima in V. cholerae which, while sharing group-specific 0 antigens, differed in minor type-specific 0 antigens. Types Inaba and Ogawa were the 'end' types, usually designated by the antigenic symbols AC and AB respectively, while Hikojima formed the intermediate type ARC. I n view of the poor content of antigen C in Hikojima strains, as well as its presence in Ogawa type cultures when grown a t ZOO, Kauffmann (1950) suggested that Ogawa-Hikojima types constituted one form of V . cholerae, as distinct from the Inaba form.Cholera outbreaks in India are usually confined to a single type of Vibrio cholerae in localized areas, though the type may vary from place to place and epidemic to epidemic. Hikojima-type strains seem to be of rare occurrence while Inaba and Ogawa types have contributed to most epidemic outbreaks. The shift between these two types, over several years, in the cholera endemic