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  • Author or Editor: T. Srinivasan x
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A laboratory experiment was conducted at the Biocontrol laboratory, Coconut Research Station, Aliyarnagar to study the life table parameters of Bracon brevicornis Wesmael, a parasitoid of the coconut blackheaded caterpillar, Opisina arenosella Walker on its established laboratory host, Corcyra cephalonica Stainton. Studies at 28.3±0.1 °C and 59.6±0.6% r.h. revealed that the net reproductive rate (Ro) of B. brevicornis was 39.52 females/female when reared on C. cephalonica larvae. The precise generation time (T) was 13.33 days. The intrinsic rate of natural increase (rm) was 0.2758 which was slightly higher than the innate capacity for increase (rc=0.2504). The weekly multiplication rate was 6.893 numbers while 1561.83 females could be expected in the F2 generation. Higher net reproductive rate, coupled with shorter population doubling time of B. brevicornis indicate the efficacy of the parasitoid as a suitable candidate for the management of coconut black headed caterpillar, O. arenosella, its intended host under field conditions.

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A method for the determination of free acidity in process solutions containing hydrolyzable ions like U(VI), Pu(IV), etc., has been developed. This method involves the titration of the free acid with electrogenerated hydroxide ions to a preset value of pH after complexing the metal ions with sodium sulfate. This method can by easily automated, requires small sample volumes and gives accurate results with good precision for samples with [UI]/[acid] mole ratios ranging from 0.25 to 16.

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Differential pulse voltammetric methods have been developed for the simultaneous estimation of the constituents of uranium-iron and uranium-cadmium mixtures in solution. A mixture of 1M H3PO4–1M KH2PO4 (with a pH1.5), was found to be the most ideal supporting electrolyte for both methods, among many that were evaluated for their suitability. In uranium-iron mixtures the calibration for iron was found to be linear up to 150 g ml–1 (r2=0.9986), while that of uranium up to 500 g ml–1 (r2=0.999). Iron at 6.7 g ml–1 level could be determined in the presence of 800 fold uranium (wt/wt) without significant interference. Uranium at 21 g ml–1 level could be analyzed with 5-fold iron (wt/wt). This upper limit of iron was due to the precipitation of iron as phosphate. In the case of uranium — cadmium mixtures, cadmium calibration for cadmium was found to be linear up to 1300 g ml–1 (r2=0.9993). Concentration levels of 4.6 g ml–1 Cd could be determined at a 500-fold excess (wt/wt) of uranium. Uranium calibration was linear up to 500 g ml–1 (r2=0.999) and 21 g ml–1 uranium could tolerate up to a 1000-fold excess of cadmium (wt/wt). Both procedures could tolerate 10 g ml–1 levels of metal ions, such as chromium, copper, manganese, molybdenum and vanadium.

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Mesoporous silica (MCM-41) with d (100) interplanar distance of 38 Å was prepared by a room temperature process through low surfactant templation technique. The surface of MCM-41 was functionalized with dithiocarbamate (dtc) ligand, named as MCM-41-dtc and this was characterized by X-ray diffraction, BET surface area, particle size analysis, 29Si MAS NMR spectra and sulphur analysis. The sorption of mercury from 0.1M HCl solution by MCM-41-dtc was studied as a function of pH, [Hg2+], time and temperature. The sorption data obtained at various initial concentrations of mercury were fitted into Langmuir adsorption model. Mercury speciation in solution and the sorption capacity measurements indicated possible formation of a 1 : 1 square planar complex in the solid phase. A very rapid sorption of mercury was observed in the initial stages of equilibration, which can be attributed to the large surface area, wide porosity and fine particle size of MCM-41-dtc, facilitating facile accessibility of mercury into the inner pores of the sorbent. The enthalpy change accompanied by the sorption of mercury was found to decrease from 83.7 to 6.2 kJ/mol, when the initial concentration of mercury was increased from 5.10-4M to 1.5.10-3M.

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A fast and accurate method for the determination of oxygen to metal ration (O/M) in U3O8 is described. The method involves dissolution of the sample in 85% phosphoric acid containing sulfate ions and measurement of the U(IV) absorbance directly and after reducing the U(VI) in the sample to U(IV) with Fe(II). The O/M is calculated from the ratio of the two absorbances. Elaborate calibrations for U(IV) and U(VI) are avoided and the sample requirement is a minimum. The method gives the oxygen to metal ratio with an accuracy better than ±0.004 O/M units and precision better than ±0.004 O/M units.

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The electrochemical behavior of ruthenium(III) and rhodium(III) in nitric acid medium has been studied at platinum and stainless steel electrodes by cyclic voltammetry. The cyclic voltammograms consisted of surge in cathodic current occurring at potentials of −0.13 V (Vs. Pd) and −0.15 V (Vs. Pd), which culminates into peaks at −0.47 V and −0.5 V due to the reductions of Ru(III) and Rh(III) to their metallic forms, respectively. Electrodeposition was carried out at stainless steel electrode and unlike palladium, the recovery of ruthenium and rhodium was limited to ~4% and ~14%, respectively. However, a different scenario was observed in case of electrodeposition from a ternary solution containing all these platinum metals. Ruthenium and rhodium deposited underpotentially in the presence of palladium and the recovery of ~20% and ~5% was observed for ruthenium and rhodium, respectively. Evolution of RuO4 at the anode and deposition of RuO2 in the anodic side was observed in all cases during electrolysis of ruthenium(III) containing solutions.

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The extraction of nitric acid by tri-n-butyl phosphate (TBP), tri-sec-butyl phosphate (TsBP) and tri-iso-amyl phosphate (TiAP) solutions in n-dodecane are reported. The results indicate that increase in carbon chain length of the alkyl group of the phosphate as well as introduction of branching near the phosphoryl (P=O) group of the phosphate do not affect significantly the extraction of nitric acid.

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Extraction of europium(III) from nitric acid medium by a solution of tri-n-butylphosphate (TBP) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in the room temperature ionic liquid, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (amimNTf2 where a = butyl or hexyl or octyl), was studied. The distribution ratio of (152+154)Eu(III) in TBP-CMPO/bmimNTf2 was measured as a function of various parameters such as the concentrations of nitric acid, CMPO and NaNO3. Remarkably large distribution ratios were observed for the extraction of europium(III) when bmimNTf2 acted as diluent. The stoichiometry of metal-solvate in organic phase was determined by the slope analysis of extraction data.

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The commercially available crystalline silicotitanate inorganic ion exchanger, IONSIV IE-911, and its parent precursor, TAM-5, have been evaluated for the removal of 137Cs from nitric acid medium and simulated high-level liquid waste. The distribution coefficient (K d) of cesium decreased with increasing nitric acid concentration and at 3.0 M nitric acid, a distribution coefficient of 1150 mL/g and 2600 mL/g were obtained for IONSIV IE-911 and TAM-5, respectively. Rapid uptake of cesium followed by the establishment of equilibrium occurring within three hours. Loading of cesium in ion exchangers increased with the increase in the concentration of cesium in aqueous phase and from Langmuir adsorption model the apparent capacity of cesium was 69 mg/g and 82 mg/g for IONSIV IE-911 and TAM-5, respectively. The performance of the sorbent under dynamic conditions was assessed by following a breakthrough (BT) curve up to C/C o = 1, where C and C o are the concentrations of cesium in the effluent and feed, respectively.

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Burn-up measurements on thermal as well as fast reactor fuels were carried out using high performance liquid chromatography (HPLC). A column chromatographic technique using di-(2-ethylhexyl) phosphoric acid (HDEHP) coated column was employed for the isolation of lanthanides from uranium, plutonium and other fission products. Ion-pair HPLC was used for the separation of individual lanthanides. The atom percent fissions were calculated from the concentrations of the lanthanide (neodymium in the case of thermal reactor and lanthanum for the fast reactor fuels) and from uranium and plutonium contents of the dissolver solutions. The HPLC method was also used for determining the fractional fissions from uranium and plutonium for the thermal reactor fuel.

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