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Abstract  

After a brief description of the PUREX process as a starting point, this paper aims to point out some of its most recent developments, always from the viewpoint of the chemistry involved in the solvent extraction methods. In addition to PUREX, other well-known technological approaches devoted to the reprocessing of irradiated uranium and thorium nuclear fuels and general radioactive wastes — TRUEX, DIAMEX, TRPO, DIDPA and UNEX — are also presented and discussed.

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Abstract  

The extraction behavior of uranium, thorium and lanthanides, represented by cerium and ytterbium, by Cyanex-923 has been investigated. The effect of different variables like the concentration of acids, metal ion and extractant, nature of diluent and temperature has been studied. A composition for the extracted U(VI) and Th(IV) species has been proposed. Based on the partition data some important binary and ternary separations involving the aforesaid metal ions have been achieved. The proposed procedure has been applied for the recovery of uranium, thorium and lanthanide fraction from monazite sand. The stability and regeneration capacity of the extractant have been evaluated.

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Abstract  

Natural radioactivity in the aquatic media has been determined by collecting samples of river, stream and drinking water from the northwestern areas of Pakistan. The concentrations of 40K, 226Ra and 232Th have been measured using a low background gamma-spectrometer and a 10 cm3 planar intrinsic high purity germanium detector. The annual ingestion of these radionuclides, using local consumption rates (average over the whole population) of 0.9 l.d-1, were estimated to be 49.2, 6.2 and 1.1 Bq.y-1 for 40K, 226Ra and 232Th, respectively. A comparison of the annual intakes of these radionuclides, using annual consumption rates of NCRP, ICRP and FBSP shows that the contribution from natural radionuclides to annual intake is slightly greater for NCRP than for ICRP and FBSP consumption rates. However, the estimated values and weighted means of these radionuclides compare well with the world average. The annual effective dose equivalent from drinking water was found to be 3.6.10-6 mSv.y-1 (226Ra), 3.2.10-12 mSv.y-1 (232Th) and 2.1.10-6 mSv.y-1 (40K). These values are lower than those given by NCRP.

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Polymerase chain reaction (PCR) was used to amplify the spacer regions between the 16S and 23S genes of rRNA genetic loci of Salmonella serovars for their rapid identification. These genetic loci revealed a significant level of polymorphism in length across the species/serovar lines. When the 16S-23S spacer region amplification products were subjected to agarose electrophoresis, the patterns observed could be used to distinguish all the serovars of Salmonella tested. Unique elements obtained in amplification products were mostly clustered at serovar level, although certain genus-specific patterns were also observed. On the basis of the results obtained, the amplification of 16S-23S ribosomal spacer region could suitably be used in a PCR-based identification method for Salmonella serovars.

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Apart from the issue of sustainability and resource drain, the yield plateau in the rice-wheat cropping system of south-east Asia is the major area of concern. Realizing that genetic gain is a remote possibility, efforts are directed to management options for yield improvement. Adequate crop nutrition in general and nitrogen (N) in particular figure at the top among various management issues. A survey was conducted covering the rice-wheat belt of Haryana state, India representing Trans-Gangetic plains to know about on-farm practices related to N management in wheat crop and how far it deviates from the blanket recommendations given by State Agricultural Universities. The survey revealed that about 42.7 per cent farmers used either recommended dose of N (150 kg/ha) or less and others used higher dose of N. Positive correlation between the size of the farm and extent of N used was established. Whenever the farmers tended to use higher dose of N, they also tended to partition it in more number of splits (up to 3 splits, excluding basal application) staggering upto 54 days after sowing (DAS) as against the recommended practice of two splits (including basal application) within 35 DAS. The study confirmed deviation from the recommended practices of N management but major revelation came about reverse gap holding that the practice of N management in wheat crop being followed by the farmers is better in terms of grain yield. The NPhysical optimum and NEconomic optimum exceeded the current use (165.7 kg/ha) and recommended levels. This study suggests a fit case for the upward revision of recommended dose of N in wheat crop involving no element of risk as arising from aggravated problem of insect pest and disease complex. Nearly half of the farmers use either recommended dose of N or less than that and it is here, where opportunity lies in augmenting the wheat productivity by enhancing the existing level of N use.

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Cereal Research Communications
Authors: B. Kumar, K.S. Hooda, R. Gogoi, V. Kumar, S. Kumar, A. Abhishek, P. Bhati, J.C. Sekhar, K.R. Yathish, V. Singh, A. Das, G. Mukri, E. Varghese, H. Kaur, V. Malik, and O.P. Yadav

Maydis leaf blight (MLB), a serious foliar fungal disease of maize, may cause up to 40% losses in yield. The present studies were undertaken to identify the stable sources of MLB resistance, its inheritance study, and testing of MLB resistance linked markers from diverse background in the Indian adapted tropical maize genotypes. A set of 112 inbred lines were screened under artificially created epiphytotics conditions at three hotspot locations. Analysis across multi-locations revealed significant effects of genotypes and environments, and non-significant effects due to genotypes × environment interaction on disease incidence. A total of 25 inbred lines with stable resistance were identified across multi-locations. Inheritance of resistance was studied in six F1s and two F2s of resistant and susceptible parents. The null hypothesis of segregation of resistance and susceptible for mono and digenic ratios in two F2 populations was rejected by Chi-square test. The non-significant differences among the reciprocal crosses depicted the complete control of nuclear genome for MLB resistance. Partial dominance in F1s and normal distribution pattern in F2s of resistant and susceptible parents suggested polygenic nature of MLB resistance. Correlation studies in F2 populations exhibited significant negative correlation between disease score and days to flowering. Five simple sequence repeats (SSRs) markers, found associated to MLB resistance in different studies were unable to differentiate amongst MLB resistance and susceptible parents in our study. This emphasizes the need of fine mapping for MLB resistance in Indian germplasm. The identified stable sources of resistance and information on inheritance study can be used further in strengthening of resistance breeding against MLB.

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