Evidence of low-symmetry phases in pressure-dependent Raman spectroscopic study of BaTiO<Subscript>3</Subscript>

In the earlier pressure-dependent Raman spectroscopic studies, it has been reported that BaTiO₃ undergoes a tetragonal to cubic phase transition above ~ 2 GPa, whereas pressure-dependent X-ray absorption, X-ray diffuse scattering studies and pair distribution function studies have reported the presence of a low-symmetry rhombohedral phase above ~ 2.3 GPa. In this report, we present our pressure-dependent Raman spectroscopic studies on polycrystalline BaTiO₃ which shows that it first undergoes a transition from tetragonal to orthorhombic/rhombohedral phase above ~ 2.6 GPa and then finally goes to the cubic phase above 8.4 GPa. Pressure-dependent synchrotron X-ray diffraction (SXRD) studies have also been carried out that provided rate of change of volume as a function of pressure resulting in bulk modulus of 215 ± 9 GPa.     

Geometric optimization of trapezoidal thermoelectric heat pump considering contact resistances through genetic algorithm

An alternate option for improving the performance of the thermoelectric heat pump (TEHP) is the variation in thermoelectric leg configuration. In this paper, the thermodynamic model based on first and second law of thermodynamics for an exoreversible TEHP including influence of Thomson effect as well as leg geometry on the coefficient of performance and heating load of the device has been developed and optimized. Modified expressions have been derived analytically for dimensionless heating load, irreversibilities, figure of merit, energy, and exergy efficiency. The effects of operating and geometry parameters such as shape parameter (A_c/A_h), temperature ratio (T_c/T_h), Thomson effect, thermal and electrical contact resistances on the coefficient of performance, and heating load of the TEHP have been analysed. The results indicate that the Thomson effect has adverse effect on heating load of the system. The optimal parameters obtained through GA optimization process have been compared with the optimal parameters obtained through analytical method which proved the validity of GA optimization method for optimization of TEHP. After the testing, the GA optimization has been performed to determine the optimum parameters corresponding to maximum energy efficiency and maximum heating load. It was found that the GA population converges quickly after 20 runs only which proved the GA as time and cost‐effective optimization tool. This study will be useful for designing of practical TEHP systems of different leg geometries.     

Studies on the production of B. thuringiensis based biopesticides using wastewater sludge as a raw material

Growth and delta-endotoxin yield of Bacillus thuringiensis (Bt) subsp kurstaki in tryptic soy yeast extract (TSY) medium, soybean meal based commercial medium and wastewater sludge medium were studied. The viable spores (VS) count in sludge medium was comparable to that obtained in laboratory and commercial media. The entomotoxicity of the fermentation liquid (Bt grown sludge) against Choristoneura fumiferana was comparable to the concentrated commercial Bt formulation available in the market (Foray 48B). A higher entomotoxicity was observed in a sludge medium than in the TSY or soybean meal media. The secondary and mixed (mixture of primary and secondary) sludges from various wastewater treatment plants were also evaluated for spore formation and entomotoxicity yield. The VS count was higher in a mixed sludge compared to the secondary sludge at a similar sludge solids concentration. Both VS count and entomotoxicity yield was found to be a function of sludge solids concentration in the medium. The optimum value of solids concentration for Bt production was found to be 25 g (-1) (dry weight basis). Beyond this concentration, a drop in VS count and entomotoxicity yield was observed. A low C:N ratio in the secondary sludge and a high C:N ratio in the mixed sludge resulted in a higher entomotoxicity. The optimum value of C:N ratio in combined sludge for Bt production was found to be 7.9-9.9. Relationships between entomotoxicity and maximum specific growth as well as with specific sporulation rate were developed.     

Efficacy of organophosphorus derivatives containing chalcones/chalcone semicarbazones against fungal pathogens of sugarcane

Ten newly synthesized organophosphorus derivatives containing substituted chalcones and substituted chalcone semicarbazones were tested for their antifungal efficacy against Colletotrichum falcatum, Fusarium oxysporum, Curvularia pallescens (all sugarcane pathogens). The O,O-diethylphosphate derivatives containing 2-chlorochalcone and 2-chlorochalcone semicarbazone exhibited 70-85% mycelial inhibition against all the test fungi at 1000 ppm. The screening results were correlated with structural features of the tested compounds.     

Preparation, thermal expansion, high pressure and high temperature behavior of Al2(WO4)3

The titled compound Al₂(WO₄)₃ was synthesized by a conventional solid state reaction and characterized by powder XRD. It crystallizes in an orthorhombic (Pbcn, No. 60) lattice, with unit cell parameters as 12.582(2), 9.051(1), 9.128(2) Å, and V = 1039.5(3) (Å)³. The compound was found to show negative thermal expansion (NTE) behavior in the temperature range of 25 to 850°C. The average linear NTE coefficient (₁), in this temperature range, was –1.5 × 10^–6 K^–1. The effect of pressure at ambient temperature, was studied by a Bridgman Anvil (BA) apparatus, to reveal that there is no irreversible phase transition up to 8 GPa. The effect of high pressure and high temperature on this compound was studied by a Toroid Anvil (TA) apparatus. This compound has a limited stability under high pressure and temperature, as it undergoes a decomposition to AlWO₄ and WO_3–x with a partial oxygen loss. As an off-shoot of this work, certain new modifications of WO_3–x under pressure and temperature were observed, viz., monoclinic, tetragonal and an orthorhombic modifications at 5 GPa/1400°C, 3 GPa/900°C and 1.8 GPa/1030°C, respectively. The detailed XRD studies of the products are presented here.     

Effect of surface recombination on the transient decay of excess carriers produced by short wavelength laser pulses

Effect of surface recombination on the transient decay of excess carriers injected very near to the surface region has been analysed for a semi-infinite semiconductor sample. The one dimensional continuity equation for the excess minority carriers has been solved analytically assuming that the surface recombination is important only on the front surface from which the excess carriers are injected. The decay of total excess carrier charge as a function of time is calculated for various values of the surface recombination velocities. It is found that values of S lower than 10³ cm/sec. have little effect on the decay of total excess charge and the decay is exponential. For values of S larger than 10⁴ cm/sec. the initial decay of excess charge is much faster and is dominated by the surface recombination. However, if one waits long enough for the excess carrier to diffuse into the semiconductor the decay becomes exponential when the excess charge decays to about 5% of its initial value. This exponential decay can be used to determine the excess carrier lifetime fairly accurately. A source of error in such experiments may arise from the heating of the silicon sample by the laser pulse. This effect, however is negligible for short duration pulses of low average power.     

Wastewater treatment sludge as a raw material for the production of Bacillus thuringiensis based biopesticides

Seven wastewater sludges of different origins and types were used as an alternate culture medium for producing Bacillus thuringiensis variety kurstaki HD-1. The sludge samples were used under three different preparations: without pre-treatment, with acid treatment (hydrolysed sludge) and the supernatant obtained after centrifugation of the hydrolysed sludge. The sludge composition varied widely with origin and the type of sludge. Growth and sporulation were evaluated by the total viable cell count and spore count of the preparations. Growth, sporulation and endotoxin production were affected by the sludge origin. Hydrolysed sludge gave the highest viable cell and spore counts while the liquid phase (supernatant) gave the lowest. Non-hydrolysed primary sludge from Valcartier was unable to sustain bacterial growth because of its low pH. Bioassays were conducted against larvae of spruce budworm to evaluate entomotoxic potential of the preparations obtained. In general, sludge hydrolysis increased the entomotoxicity yields. Similar entomotoxicity was observed in Black Lake secondary sludge (4100 IU/microL) as that obtained in the reference soya medium (3800 IU/microL). The use of the sludge supernatant (liquid phase) was not recommended due to the low entomotoxic potential obtained.     

Microbicidal activity of TiO2 nanoparticles synthesised by sol–gel method

In this study, the authors investigated antimicrobial activity of TiO₂ nanoparticles (NPs) synthesised by sol–gel method. As synthesised TiO₂ NPs were characterised by X‐ray diffraction, scanning electron microscopy and ultraviolet‐visible absorption spectroscopy. The antimicrobial activity of calcined TiO₂ nanoparticle samples was examined in day light on Gram positive bacteria (Staphylococcus aureus, Streptococcus pneumonia and Bacillus subtilis), Gram negative bacteria (Proteus vulgaris, Pseudomonas aeruginosa and Escherichia coli) and fungal test pathogen Candida albicans. The synthesised TiO₂ NPs were found to be effective in visible light against Streptococcus pneumonia, Staphylococcus aureus, Proteus vulgaris, Pseudomonas aeruginosa and Candida albicans.Inspec keywords: titanium compounds, microorganisms, nanomedicine, biomedical materials, nanofabrication, sol‐gel processing, ultraviolet spectra, visible spectra, X‐ray diffraction, scanning electron microscopy, nanoparticles, antibacterial activityOther keywords: microbicidal activity, titanium dioxide nanoparticle, sol‐gel method, antimicrobial activity, X‐ray diffraction, scanning electron microscopy, ultraviolet‐visible absorption spectroscopy, Gram positive bacteria, Staphylococcus aureus, Streptococcus pneumonia, Bacillus subtilis, TiO₂ , Candida albicans, fungal test pathogen, Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Gram negative bacteria     

Linear-code multicast on parallel architectures

Parallel architectures involve communication with the aim of fast receiving of complete information at each node. Several architectures have been proposed to overcome the problem of high communicational and computational time complexity for transferring and receiving information. To reduce the complexity of such communication, we have implemented Linear Network Coding (LNC) in the parallel environment. For verification of our approach, we have considered some parallel architecture for implementing network coding approach and examined our results on these networks in a generic environment. We have formulated a standard approach for parallel networks, showing that by applying this approach effect of faulty nodes, information size and communication complexity exponentially decreases with code length.