Search

Cadmium selenide (CdSe) nanostructures with different growth temperature viz. 25 °C, 60 °C, 100 °C, 150 °C and 200 °C have been synthesized through chemical route. The results of XRD reveals that as synthesized CdSe nanostructures possess polycrystalline cubic zinc blende structure. The particle sizes obtained from Scherer formula as well as W-H plot and are found to be 2.81 nm and 4.6 nm respectively. The strain induced in the crystal is obtained as −1.8 × 10−3 from the W-H plot. The results of UV–Vis and photoluminescence (PL) spectra show that growth temperature has a significant impact on the optical properties of the synthesized nanoparticles. Both the UV and PL spectra initially show a blue shift with the increase of temperature but after a particular temperature around 100 °C it starts showing red shift. The PL intensity also increases and possesses a maximum at growth temperature 100 °C but afterwards it again decreases at very high temperatures. From the observation of absorption, PL emission along with intensity it has been inferred that growth temperature ranging from 25 °C to 100 °C may be a suitable technique to modulate the optical properties of chemically synthesized CdSe nanoparticles.

Biodegradation of crude oil in reservoirs has been extensively studied and is usually considered to be a quasi-stepwise process. The process is known to increase the acidity of the oil. In this paper, results from the analysis of crude oils and co-produced waters from the reservoir surrounding the Troll C platform in the Norwegian North Sea are presented. Based on the concentrations of light hydrocarbons in the Troll oils, simultaneous biodegradation of n-alkanes, branched alkanes, cycloalkanes, alkyl benzenes, alkyl naphthalenes and methyl phenanthrenes is suggested. Pronounced relative enrichment of methylcyclopentane, cyclohexane and methylcyclohexane provide evidence for a specific recalcitrance of cycloalkanes to biodegradation in this field. Biodegradation can also be seen in the carbon isotopic signature of the lighter hydrocarbons, e.g., heavy signatures for n-pentane and iso-pentane. The composition of the aromatic acids in the produced waters suggests biodegradation to be their predominant source in the reservoir. The occurrence of reduced naphthoic acids previously shown to be specific indicators of anaerobic biodegradation of naphthalene, 2-methylnaphthalene and tetralin indicates that the biodegradation took place under anoxic conditions.

The effect of Bi on the structural and optical properties of Se82−xBixTe18 glassy alloys is studied, theoretically. Cohesive energy is calculated by using chemical bond approach and is found to decrease with increasing Bi content. Optical band gap of thin films is calculated by Shimakawa’s relation. The optical band gap decreases with increase in Bi content.

Effect of Bismuth (Bi) doping on the optical constants of Se‐Te thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index decreases with wavelength, for all compositions and the absorption coefficient increases with increase in optical energy. On the other hand the optical band gap is found to decreases with increase in Bi content.

Aquatic insects play important role in ecosystem functioning viz. nutrient cycling, primary production, decomposition and material translocation. The functional feeding group (FFG) approach is an attempt to classify organisms, especially insects, according to their role in the processing of organic matter. An investigation during 2011–2013 was carried out on aquatic insects in different stretches of a stream of Chakrashila Wildlife Sanctuary located in western Assam, North East India which is designated as Key Biodiversity Area (KBA) by IUCN. Physico-chemical properties of water of the stream like water temperature, dissolved oxygen, free-carbondioxide, pH, total alkalinity, electrical conductivity, phosphate and nitrate were estimated to correlate the aquatic insects of specific functional feeding groups with water quality. A total of seventeen species was recorded during the study period. Record of nine species in first year and fourteen species in second year under different functional feeding groups (FFG) showed altitudinal variation. Highest percentage of predators was found in upstream. Collectors were recorded in upstream and downstream and shredders were recorded in midstream.

Experimental studies have been carried out on fluidization of irregular particle mixtures of different size and density. The mixing and segregation phenomena could be interpreted on the basis of the diffusion model of Kennedy and Bretton. The dependence of computed particle dispersion coefficient on liquid velocity, particle density and size has been discussed. Nous avons effectue des etudes experimentales sur la fluidisation de melanges de particules de taille et de densite differentes. Les phenomenes de segregation et de melange peuvent ere interpretes a partir du modele de diffusion de Kennedy et Bretton. Nous avons etudie l'influence de la vitesse du liquide ainsi que de la densite de la taille des particules sur le coefficient de dispersion des particules calcule.