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  • Author or Editor: A. K. Verma x
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Summary A comparative study of the non-isothermal decomposition of the dl-lactate hydrates of magnesium, calcium and strontium has been made with that of the dl-lactate hydrates chromium(III), manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) keeping dry air as the purge gas and the heating rate maintained at 10 K min-1. While the dl-lactates of manganese(II), cobalt(II) and copper(II) followed single step decomposition scheme suggesting that dehydration and decomposition steps overlapped, the dehydration steps of the other compounds were distinct. &-T plots of none of the dehydration steps showed any induction period, indicating no physical desorption, nucleation or branching. Neither the & max-values nor the onset temperatures of the dehydration steps did show any pattern. The TG data of the dehydration steps have also been analyzed using the Freeman-Carroll, Horowitz-Metzger, Coats-Redfern, Zsakó, Fuoss-Salyer-Wilson and Karkhanavala-Dharwadkar methods. Values of order of reaction, activation energy and Arrhenius factor have been approximated and compared. There are similarities in the activation energy values for the dehydration steps (< 60 kJ mol-1 in general). It is higher with group 2 metals and lower in transition metals (maximum in magnesium and lowest in chromium and iron lactates). In cases of overlapping of dehydration and decomposition steps, the activation energy values are on the lower side with the same trend (lower in cobalt and copper cases).

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The results obtained showed that there was severe competition between potato and the predominant weed species Coronopus didymus, Chenopodium album, Fumaria parviflora, Melilotus indica and Spergula arvensis. Competition by other weed species was nominal. The maximum reduction in tuber yield due to weed competition was 50.5% in 1997–98 and 63.4% in 1998–99. Weed control treatments lowered the weed density and weed biomass and scaled up tuber yield in both the years, but their effect on weed species differed. Metribuzin killed all the Chenopodium album plants and gave excellent control of Coronopus didymus (94%) and effective control of other weed species. Pendimethalin inhibited the germination of Chenopodium album, gave good control of arvensis and lowered the density of other weed species. Fluchloralin completely inhibited the germination of Fumaria parviflora and gave good control of Chenopodium album and Spergula arvensis, but was least effective against other weed species. The highest yield was recorded in the weed-free treatment, which was significantly superior to all other treatments. Hand weeding + earthing up, isoproturon (1.0 kg/ha), metribuzin and pendimethalin caused an identical increase in tuber yield, which was significantly higher than the increase in the rest of the treatments. Atrazine at 0.25 kg ha –1 resulted in a higher increase than when applied at 0.5 kg ha –1 . Fluchloralin, paraquat and paddy straw mulch boosted up production, but the increase in tuber yield was not significant.

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Abstract

Chromite Spinel materials were synthesized in this study by the citrate precursor method using four divalent cations (Ni2+, Co2+, Zn2+, and Cu2+). Citrate precursors consisting of mixed chromium citrates were first subjected to a thermogravimetric (TG) analysis for determining optimum temperatures for annealing. TG of coprecipitated chromium(III) citrate–zinc citrate gel has been carried out separately in N2 and O2 atmospheres. In both the cases, dehydration is followed by a four-step decomposition. The TG data were subjected to kinetic/mechanistic analysis, and the values of activation energy and Arrhenius factor were approximated. TG curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N2 atmosphere. A large coercivity of 2701.01 Oe was observed for NiCr2O4 at 650 °C. On the basis of the results, 450 °C has been chosen for annealing treatment of the four gels. The samples were accordingly annealed at two different temperatures (450 and 650 °C) in a muffle furnace for 1 h in each case. The annealed powders were characterized using X-ray diffraction (XRD), SEM, and vibrating sample magnetometer (VSM). The XRD patterns show that annealing of CuCr2O4, NiCr2O4, and CoCr2O4 at 450 °C yields very small crystallites with poor Bragg reflections, although ZnCr2O4 samples show better peaks in XRD data. Annealing at 650 °C resulted in particle size range of 8–89 nm in the four cases. In the case of ZnCr2O4, the particle size was 8 nm.

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The results obtained showed that there was severe competition between wheat and the predominant weed species Phalaris minor, Avena ludoviciana and Melilotus indica. Competition by other weed species was normal. The maximum reduction in grain and straw yields due to weed competition was 34.8% and 43.7%, respectively. Weed control treatments lowered the weed population and weed biomass accumulation and boosted up the crop yield. A significant reduction in the weed population and weed dry weight was observed with increasing doses of both atrazine and metribuzin. Metribuzin at 200 g ha-1 killed all the plants of M. indica and gave excellent control of both P. minor (98%) and A. ludoviciana (89%). Atrazine at higher doses had an almost similar effect on P. minor, A. ludoviciana and M. indica with 83-87% control. Pendimethalin gave good control of P. minor and M. indica (75-83%) but poor control of A. ludoviciana (55%). The highest yield was recorded in hand weeding which was significantly superior to all other treatments. Metribuzin at 100 g ha-1 was the next best treatment, and this rate was superior to the higher doses. Pendimethalin and atrazine also brought about a marked increase in the crop yield. Higher doses of atrazine and metribuzin had a phytotoxic effect on the crop, reducing the number of productive tillers and finally lowering the crop yield, despite their excellent control of dominant weed species.

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Abstract  

Large sample neutron activation analysis of dross from India Government Mint, Mumbai was carried out for quantification of gold (Au) and silver (Ag) using graphite reflector position of Advanced Heavy Water Reactor critical facility at Bhabha Atomic Research Centre, Mumbai. The k 0-based internal monostandard NAA was used to calculate concentration ratios of Au and Ag with respect to sodium (Na), which was used as an internal monostandard. The concentration ratio values of Au to Na of varying mass of dross showed that mass ≥2 g was the representative sample size for analysis. Concentrations of gold and silver were found to be in the range of 200–400 and 1200–1700 mg kg−1, respectively in three different samples.

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Abstract

Magnetic nanoparticles of cobalt ferrite have been synthesized by citrate precursor method. TG-DSC studies have been made to get the idea of the optimum temperature of annealing that could lead to the formation of nanoparticles. Annealing the citrate precursor was done at 450, 650, and 973 °C. The X-ray diffraction (XRD) studies and the scanning electron microscopy (SEM) have been used for characterization. The data from vibrating sample magnetometer and photoluminescence spectrometer (PL) have been analyzed for exploring their applications. Using the Scherrer formula, the crystallite size was found to be 25, 32, and 43 nm, respectively, using the three temperatures. The particle size increased with annealing temperature. Rietveld refinements on the X-ray (XRD) data were done on the cobalt ferrite nanoparticles (monoclinic cells) obtained on annealing at 650 °C, selecting the space group P2/M. The values of coercivity (1574.4 G) and retentivity (18.705 emu g−1) were found out in the sample annealed at 650 °C while magnetization (39.032 emu g−1) was also found in the sample annealed at 973 °C. The photoluminescence (PL) property of these samples were studied using 225, 330, and 350 nm excitation wavelength radiation source. The PL intensity was found to be increasing with the particle size.

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Summary

An online-hyphenated high-performance liquid chromatography-photodiode array-mass spectrometry (HPLC-PDA-MS) analytical method was developed for the simultaneous determination of six lignans of therapeutic importance in four Phyllanthus spp. (P. amarus, P. maderaspatensis, P. urinaria, and P. virgatus). HPLC with monolithic reverse phase silica column (4.6 × 100 mm) and simple isocratic elution of methanol-water mixed with dioxane facilitated the separation of lignans of diverse nature such as diarylbutyrolactone, tetrahydrofuran, isomeric aryltetralin, and diarylbutane type for quantitative analysis. Targeted lignans viz. heliobuphthalmin lactone (1), virgatusin (2), hypophyllanthin (3), phyllanthin (4), nirtetralin (5), and niranthin (6) were confirmed unambiguously in four Phyllanthus species by their abundant molecular adduct ions, retention time, UV, and mass spectra as compared with those of reference compounds. Advantages and limitations of both detection techniques for qualitative (fingerprinting) and quantitative analysis of the above mentioned lignans in four Phyllanthus spp. are discussed. The method was validated following international guidelines. The described method can be utilized for assays and stability tests of P. amarus extracts as well as traditional Indian medicine based on Phyllanthus herb.

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Abstract

Two aluminate spinel materials (ZnAl2O4 and NiAl2O4) were synthesized by the citrate precursor method. The citrate precursors consisting of coprecipitated citrates of Zn2+ or Ni2+ and aluminum were first subjected to thermal analysis (TG-DSC) for determining the optimum temperature for annealing. Two step decomposition was observed incorporating dehydration and formation of the aluminate. The second step gives an endo peak (−2937 J/g) at 356 °C in the DSC curve of the coprecipitated nickel(II) citrate–aluminum citrate gel in O2 atmosphere. Kinetic/mechanistic analysis of the TG data has also been carried out and values of E a, ΔS #, ΔG #, and A were approximated. On the basis of the findings, 450 °C has been chosen for annealing of the gels. Annealing has also been done at 650 °C for 1 h in muffle furnace in an attempt to obtain nanometric particles of aluminates (MAl2O4) {M = Ni, Zn} and to find out their magnetic properties which could render them useful for chemical sensing applications, etc. The TG-DSC curves of various powders which were obtained on annealing at the two temperatures did exhibit thermal instability when carried out in N2 atmosphere. NiAl2O4 and ZnAl2O4 spinels (particle size 17 and 34 nm, respectively) are obtained in pure crystalline phase at 650 °C. ZnAl2O4 prepared this way shows coercivity values of 470 and 58.37 G and NiAl2O4, 107 and 23.24 G when annealed at 450 and 650 °C, respectively. ZnAl2O4 prepared by a polymer precursor method and annealed at 1000 °C, has earlier been reported to have coercivity value of 469 G. Thus, the citrate precursor method is good for the synthesis of ZnAl2O4, producing single phase nanocrystalline powder of high quality and crystallinity. The value of magnetization was found to be small in the present case for the NiAl2O4 spinel obtained at 450 °C.

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Abstract  

Thorium along with its daughter products present in the soil is one of the major contributors to the external gamma dose in the environment. To establish the dose levels, quantification of thorium contents in soil samples is very important. As a part of pre-operational environmental radiological surveillance, a total of 23 soil and six sand samples were collected from different locations around the proposed nuclear power plant site of Jaitapur, Maharashtra. Thorium concentrations in these samples were determined by instrumental neutron activation analysis (INAA). Samples were irradiated with neutrons in Apsara reactor at a neutron flux of ~5 × 1011 cm−2 s−1 and radioactive assay was carried out using high resolution gamma ray spectrometry. Relative method of INAA was used for quantification of thorium utilizing 311.9 keV gamma ray of 233Pa, the daughter product of 233Th. The concentrations of thorium in the soil and sand samples were in the ranges of 4.0–18.8 and 1.2–6.2 mg kg−1 respectively.

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Abstract  

For standardization of k 0-based instrumental neutron activation analysis, k 0-factors for short-lived nuclides (half-lives—11 s to 37 min) of elements F, Se, Sc, Al, V, Ti, Cu, Ca, Mg, I, and Cl with respect to gold (197Au) were determined using pneumatic carrier facility (PCF) at CIRUS reactor of BARC, Mumbai. Characterization of PCF was carried out by cadmium-ratio method using Au and Zr. The experimental k 0-factors of the isotopes were found to be in good agreement with the recommended k 0-factors in most of the cases, as evident from the values of % error and U-score at 95% confidence level. The method was validated by determining concentrations of elements through their short-lived nuclides in one type of the synthetic multielement standards (SMELS-I) obtained from SCK-CEN, Belgium. The method was also applied for determination of concentrations of some of the elements in two reference materials of IAEA, SL-3, and SL-1.

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