Analysis of startup oscillations in natural circulation boiling systems

The aim of the present work is to get an insight of the phenomena behind the low-pressure low-power transients that occur during startup of a natural circulation boiling system. A RELAP5 model developed for a test facility and its prototype is used to record additional system parameters that were not included in the data obtained from experiments. The flow oscillations observed during experimental and numerical studies are analyzed and classified. It is inferred that the low amplitude oscillations are not condensation induced geysering instabilities, but a density wave instability supported by flashing. The similarity between the nature of startup transients observed in the test facility and the prototype is also examined. The effect of flashing is more pronounced in the prototype due to the strong variation of saturation temperature as the length scale is 4 times that of the model. The time series data obtained from experimental observations and numerical simulations are analyzed to identify the structural nature of flow oscillations. The power spectral density estimated using fast Fourier transform (FFT) algorithm illustrates the chaotic nature of the signals. The nonlinear time series analysis (TISEAN) package has been used for the estimation of Lyapunov exponent and the Poincaré section. The Poincaré section and the Lyapunov exponent confirm the chaotic nature of the flow oscillations.     

Ionic liquid-induced synthesis of selenium nanoparticles

A simple wet chemical method has been used to synthesize selenium nanoparticles by the reaction of ionic liquid with sodium selenosulphate, a selenium precursor, in the presence of polyvinyl alcohol stabilizer, in aqueous medium. The method is capable of producing spherical selenium nanoparticles in the size range of 76-150 nm under ambient conditions. This is a first report on the production of nano-selenium assisted by an ionic liquid. The synthesized nanoparticles can be separated easily from the aqueous sol by a high-speed centrifuge machine, and can be re-dispersed in an aqueous medium. The synthesized selenium nanoparticles have been characterized by X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry and transmission electron microscopy techniques.     

Impedance studies of polycrystalline tin oxide

Polycrystalline SnO₂ samples prepared in the laboratory were irradiated with 2 MeV He ions having doses of 3.62 × 10¹⁵ ion/cm². The ac small-signal electrical data acquired for the polycrystalline SnO₂ in the frequency (f) range 100 Hz ≤ f ≤ 1 MHz and temperature (T) range 26°C ≤ T ≤ 100°C revealed one semicircular relaxation in the impedance plane for the He implanted sample. However, two semicircular relaxations were obtained in the same plane for the samples without He implantation. The He implantation indicated enhancement in the donor density in the polycrystalline SnO₂ as depicted via terminal conductance (or resistance). An erratum to this article can be found at     

Study of uranium sorption using D2EHPA‐impregnated polymeric beads

The extractant‐impregnated polymeric beads (EIPBs), containing Di(2‐ethylhexyl) phosphonic acid (D2EHPA) as an extractant and polyethersulfone as base polymer, were prepared by phase‐inversion method. These beads were characterized by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM) analysis to gain insight into the composition and morphology of beads. The beads exhibited good acid stability as no significant structural deformation or leaching out of the extractant was observed in 6M HNO₃ solution, up to the studied equilibration time of 15 days. The synthesized EIPBs were evaluated, for their ability to absorb uranium from aqueous solution, at different concentration and pH values. The kinetics measurement showed that about 90 min of equilibration time was enough to remove saturation amount of uranium from the solution. Kinetic modeling analysis of the extraction results was carried out using pseudo‐first‐order, pseudo‐second‐order, and intraparticle diffusion equations and the corresponding rate constants were determined. The equilibrium data were fitted into different isotherm models and were found to be represented well by the Freundlich isotherm equation. Reusability of the beads was also established by multiple sorption–desorption experiments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3355–3364, 2013     

Determination of Solvent Contamination and Characterization of Ultrafine HNS Particles after Solvent Recrystallization

Solvent–antisolvent recrystallization employed for size reduction of HNS has been described and the effect of various parameters such as stirring rate, effect of antisolvent type, antisolvent temperature, ultrasonication, etc. was investigated. Purified HNS, produced by hot solvent recrystallization of production grade crude HNS, of mean particle size ∼95 μm was used for preparation of ultrafine particles of HNS. Solvent contamination in terms of residual solvent was determined by ¹H NMR and GC‐MS analysis. In addition, ultrafine HNS has been characterized for purity (HPLC, ¹H NMR), particle size and shape (PSA and SEM), specific surface area (BET analysis), thermal behavior (TGA, DSC), sensitivity (impact, friction), etc. The results have been compared with C‐HNS. UF‐HNS was >99% pure with mean particle size <1 μm. SEM showed submicrometer size rods like particles of HNS as the final material.     

An outlier detection approach in large-scale data stream using rough set

Outlier detection has become an important research area in the field of stream data mining due to its vast applications. In the literature, many methods have been proposed, but they work well for simple and positive regions of outliers, where boundary regions are not given much importance. Moreover, an algorithm which processes stream data must be effective and able to compute infinite data in one pass or limited number of passes. These problems have motivated us to propose an outlier detection approach for large-scale data stream. The proposed algorithm employs the concept of relative cardinality, entropy outlier factor theory of information-based system, and size-variant sliding window in stream data. In addition, we propose a new methodology for concept drift adaptation on evolving data streams. The proposed method is executed on nine benchmark datasets and compared with six existing methods that are EXPoSE, iForest, OC-SVM, LOF, KDE, and FastAbod. Experimental results show that the proposed method outperforms six existing methods in terms of receiver operating characteristic curve, precision recall, and computational time for positive regions as well as for boundary regions.

     

Reactivity of Hydroxamate Ions in Cationic Vesicular Media for the Cleavage of Carboxylate Esters

The hydrolysis of carboxylate esters viz. p‐nitrophenyl acetate (PNPA), p‐nitrophenyl butyrate (PNPB) and p‐nitrophenyl octanoate (PNPO) in the presence of cationic vesicles of the surfactant dioctadecyldimethylammonium bromide (DODAC) by different hydroxamate ions i.e. acetohydroxamate (AHA^?), benzohydroxamate (BHA^?) and salicylhydroxamate (SHA^?) were studied. The kinetic data was supported by spectrophotometric measurements. The effects of vesicular size on the reaction have been discussed. The differential reactivity under endo‐ and exovesicular conditions has also been evaluated. Critical vesicle concentrations (CVC) of cationic vesicular surfactants were determined from conductometric and fluorimetric measurements at 300 K. Fluorescence probe pyrene and pyrene‐1‐carboxaldehyde have been used for determination of CVC. Further, thermodynamic parameters viz. Standard Gibb's energy (?G°), enthalpy (?H°), and entropy (?S°) of vesicles has also been evaluated within a temperature range of 303.15–328.15 K.     

Proximate Composition and Fatty Acid Profile of <Emphasis Type="Italic">Pongamia pinnata</Emphasis>, a Potential Biodiesel Crop

The chemical characteristics of Pongamia pinnata seeds, focussing on proximate composition and the fatty acid profile of its oil, are presented. The proximate composition of P. pinnata seeds was: 3.8% ash, 9.7% sugar, 7.07% protein, 24% oil, 10.7% free amino acids, and 0.24% free fatty acids. The oil was extracted from seeds by use of different solvents and the highest yield (29%) was obtained by use of n-hexane. Monounsaturated and polyunsaturated fatty acids accounted for 63.3 and 22.9%, respectively, of the seed oil. Oleic acid was the major fatty acid but a substantial amount of erucic acid was also detected; this was not reported in previous studies. The level of erucic acid and the presence of toxic flavonoids, for example karanjin, pongapin, and pongaglabrin, render the oil inedible according to WHO recommendations. However, low levels of saturated and polyunsaturated fatty acids with desirable cetane number and iodine value suggest potential for application as a biodiesel fuel.