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Amorphous ferri-aluminosilicates in some tropical ferruginous soils
- G. S. R. Krishna Murti, V. A. K. Sarma, P. Rengasamy
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- Journal:
- Clay Minerals / Volume 11 / Issue 2 / June 1976
- Published online by Cambridge University Press:
- 09 July 2018, pp. 137-146
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The amorphous mineral selectively dissolved from the clay (<2 μm) fractions of twenty-six ferruginous soils contains considerable iron in addition to silicon and aluminium. SiO2/Al2O3 and SiO2/R2O3 molar ratios are between 2·03-3·52 and 1·72-2·95 respectively. The model of the amorphous ferri-aluminosilicate (AFAS) consists mainly of negatively charged tetrahedrally coordinated silica-alumina phase Si3AlO6(OH)4 containing domains of neutral FeOOH, with an outer positively charged hydroxyaluminium polymeric component [Al(OH)2.5]n.The calculated hydroxyl water content of the AFAS averages 17·8%; cation exchange capacity varies from 48·6 to 112·0 mEq/100 g and shows a negative correlation with the outer hydroxyaluminium octahedral component and a positive correlation with the ratio of the tetrahedral Si-Al component to the octahedral hydroxyaluminium component. The K-fixation capacity (1·9-6·1 mEq/100 g) of the AFAS does not appear to be related to the chemical composition. The genesis of the amorphous mineral is discussed.
Ascaridia galli: lactic acid production, glycogen content, glycolytic enzymes and properties of purified aldolase, enolase and glucose-6-phosphate dehydrogenase*
- V. M. L. Srivastava, S. Ghatak, C. R. Krishna Murti
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- Journal:
- Parasitology / Volume 60 / Issue 2 / April 1970
- Published online by Cambridge University Press:
- 06 April 2009, pp. 157-180
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Glycogen reserves of whole worms and their body wall, intestines, ovarian and testicular tubules of the avian intestinal nematode, Ascaridia galli, were assayed and on dry-weight basis found to be 14–20 %, except in the testicular tissue which contained only 7 % glycogen.
Segments of whole male worms or testicular tubules were found to produce more lactic acid than segments of whole female worms or ovarian tubules. The body wall and intestine of the worms had also appreciable glycolytic activity. Whereas in the segments of whole worms, male and female alike, glycolysis was more active under anaerobic conditions, no differences in glycolytic rates were seen between aerobiosis and anaerobiosis when isolated tissues were used. Exogenously added glucose did not stimulate glycolysis either aerobically or anaerobically to any extent greater than observed in the absence of glucose.
Homogenates of whole worms or their different anatomical parts were assayed for enzymic activities associated with the Embden-Meyerhof pathway of glucose assimilation. The crude extracts prior to differential centrifugation, were found to contain glycogen phosphorylase, aldokinases, pyruvate kinase, phosphatases acting on glucose 6-phosphate and hexose diphosphate and 6-phospho-gluconate dehydrogenase. The 105000 g particulate-free supernate was found to have significant activities of the following enzymes: fructokinase, phosphoglucomutase, phosphoglucoseisomerase, phosphofructokinase, aldolase, glyceraldehyde 3-phosphate dehydrogenase, lactic dehydrogenase and glucose-6-phosphate dehydrogenase. This fraction was devoid of NADH or NADPH oxidase activities in the absence of added substrates.
Although there was some indication of a negative correlation between low glycogen reserves and high glycolytic activity in the testicular tubules, in general, there was no relationship between glycogen reserve and glycolytic activity on the one hand or between the rate of glycolysis and the specific activities of some of the key glycolytic enzymes in either whole worm or in tissues other than the testicular tubules.
The 105000 g supernate was fractionated with ammonium sulphate. The fraction precipitating between 25 and 80 % saturation of the salt was recovered, dialysed and chromatographed on DEAE cellulose column. By a step-wise elution schedule using increasing molarity of NaCl in tris-HCl buffer, pH 7·4, three main protein fractions were obtained representing respectively enolase, aldolase and glucose-6-phosphate dehydrogenase.
The recovery of enzyme activity after chromatography on DEAE cellulose was higher than the amount applied to the column suggesting that during the fractionation some naturally occurring inhibitors were removed. About 10- to 20-fold purification of the enzymes was achieved by anion-exchange chromatography.
Some properties of the purified enzymes were studied with respect to the affects of enzyme and substrate concentrations, temperature of preincubation and action of divalent cations, some anions, metal chelating agents and SH reagents. The Km values of enolase, aldolase and glucose-6-phosphate dehydrogenase of A. galli were 5·9 × 10−4M, 4·5 × 10−3M and 2·4 × 10−3M respectively. Glucose-6-phosphate dehydrogenase was found to be very sensitive to both heat and cold losing activity rapidly even at 43 °C or by freezing and thawing.
The SH groups of aldolase were readily blocked by pCMB and presumably by o–phenanthroline. No requirement of any divalent cations was shown by this enzyme which was, however, inhibited by borate ions.
Enolase of A. galli showed a requirement of Mg2+ for full activation. Phosphate, fluoride, EDTA, o–phenanthroline, αα-bipyridyl inhibited the enzyme. Veronal was found to inactivate the enzyme.
Glucose-6-phosphate dehydrogenase of A. galli was also found to be sensitive to SH reagents and metal chelating agents. The enzyme was activated by Co2+, Mn2+ and Mg2+.
The evidence presented indicates that segments of whole worms of A. galli or its anatomical parts are equipped with the enzymatic machinery required to mediate anaerobic breakdown of glucose and to derive energy by this mechanism.
The authors are grateful to Dr R. K. Kaushik for help in identifying the worms, to Mr P. A. George for help in the statistical analysis of the data and to Messrs A. C. Kol and S. K. Bose for skilful technical assistance.
Vibrations of Tapered Cantilever Beams and Shafts
- A. V. Krishna Murty, K. R. Prabhakaran
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- Journal:
- The Aeronautical Quarterly / Volume 20 / Issue 2 / May 1969
- Published online by Cambridge University Press:
- 07 June 2016, pp. 171-177
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- May 1969
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Vibration characteristics of a linearly tapered cantilever beam and a shaft have been studied by using the lumped inertia force method; a linear displacement distribution is considered over each element. The results are compared with some of those in the literature and with experimental observations. These comparisons indicate that, even using a few elements, a reasonable degree of accuracy can be obtained in the natural frequency, although it is essential to consider more elements in order to determine mode shape accurately.
A Lumped Inertia Force Method for Vibration Problems
- A. V. Krishna Murty
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- Journal:
- The Aeronautical Quarterly / Volume 17 / Issue 2 / May 1966
- Published online by Cambridge University Press:
- 07 June 2016, pp. 127-140
- Print publication:
- May 1966
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A rational method of lumping inertia forces by considering the equilibrium of the vibrating element has been developed. This method requires the selection of a suitable displacement distribution function over each element. The closer it is to the true mode shape, the better the result.
Considering a linear displacement distribution function over each element, the natural frequencies and mode shapes are obtained for transverse vibrations of a stretched string, torsional vibrations of a cantilever shaft (fixed at one end and free at the other) and transverse vibrations of a uniform cantilever beam. It is found that, even with a few elements, a reasonable accuracy can be obtained in the natural frequency, while the mode shapes are exact in the first two cases and almost exact in the third at the points considered.
In Appendix A, it is shown that, for the torsional vibration of a uniform cantilever shaft and with a linear displacement function over each element, this method gives exact mode shapes at the points considered, while the natural frequency is always an upper bound and the error follows an inverse square law when the number of elements considered is large.
In Appendix B, it is shown that a combination of this method with the conventional lumped mass method reduces the error in the natural frequency. The error follows an inverse fourth-power law when the number of elements considered is large and the mode shapes are exact at the points considered.
This method can incorporate better displacement distribution functions, to obtain better results and convergence, and can easily be adapted to the buckling of columns, the vibration of beam columns and forced vibrations, as well as more complicated problems such as the vibration or buckling of plates and shells.