Magnetoconductance response in unipolar and bipolar organic diodes at ultrasmall fields

We measured magnetoconductance (MC) response in a number of unipolar and bipolar organic diodes based on π-conjugated polymers and small molecules at fields |B|<100 mT and various bias voltages and temperatures. Similar to magneto-electroluminescence, the MC(B) response in bipolar diodes shows a sign reversal at ultrasmall |B|<1-2 mT due to interplay of hyperfine and Zeeman interactions in opposite-charge polaron pairs. Surprisingly, similar MC(B) response was also measured in unipolar devices, indicating the existence of like-charge polaron pairs, however, with a clear difference between the hyperfine interaction constants of electron polaron and hole polaron.     

Radioisotope‐induced EDXRF investigation of elemental uptake in cauliflower grown at MSW‐contaminated site

A ¹⁰⁹Cd radioisotope‐induced energy dispersive X‐ray fluorescence (EDXRF) study has been performed on samples of cauliflower consisting of the flower, the leaves and the associated root soil. The cauliflowers are collected from farms near the main dumping site of municipal solid waste (MSW) in the city of Kolkata, India, and also from uncontaminated farms about 50 km away from the city. The systematic investigation is primarily aimed at achieving two correlated objectives. Firstly, a unified calibration approach is undertaken for the study tool viz., EDXRF spectrometer, through the use of same instrumental scattering constants for quantification in widely differing matrices like soil and plant. Quality control was done by quantitative reproduction of National Institute of Standards and Technology–Standard Reference Materials (NIST–SRMs). Subsequently, the second objective is to comparatively study elemental uptake in the cauliflower samples from contaminated and uncontaminated farms using the same calibration. This study suggests that the elemental concentrations in the root soils and leaves of the samples vary from farm to farm, whereby the concentrations of Cu, Zn and Pb in root soils of MSW‐contaminated farms are higher by almost an order of magnitude compared to uncontaminated farms. But the most notable feature of this study is the strikingly similar elemental concentrations in the edible flower part of all samples irrespective of the soil type. Plots of the ratio of concentrations of elements in leaf to soil and in flower to leaf, observed from the present EDXRF study suggests that a preferential uptake of elements takes place at different stages. Copyright © 2010 John Wiley & Sons, Ltd.     

A modeling approach to describe the adhesion of rough, asymmetric particles to surfaces

A combined theoretical and experimental study of the adhesion of alumina particles and polystyrene latex spheres to silicon dioxide surfaces was performed. A boundary element technique was used to model electrostatic interactions between micron-scale particles and planar surfaces when the particles and surfaces were in contact. This method allows quantitative evaluation of the effects of particle geometry and surface roughness on the electrostatic interaction. The electrostatic interactions are combined with a previously developed model for van der Waals forces in particle adhesion. The combined model accounts for the effects of particle and substrate geometry, surface roughness and asperity deformation on the adhesion force. Predictions from the combined model are compared with experimental measurements made with an atomic force microscope. Measurements are made in aqueous solutions of varying ionic strength and solution pH. While van der Waals forces are generally dominant when particles are in contact with surfaces, results obtained here indicate that electrostatic interactions contribute to the overall adhesion force in certain cases. Specifically, alumina particles with complex geometries were found to adhere to surfaces due to both electrostatic and van der Waals interactions, while polystyrene latex spheres were not affected by electrostatic forces when in contact with various surfaces.     

Phase behavior, interfacial composition and thermodynamic properties of mixed surfactant (CTAB and Brij-58) derived w/o microemulsions with 1-butanol and 1-pentanol as cosurfactants and n-heptane and n-decane as oils

Phase diagrams of pseudo-quaternary systems of cetyltrimethylammonium bromide (CTAB)/polyoxyethylene(20)cetyl ether (Brij-58)/water/1-butanol (or 1-pentanol)/n-heptane (or n-decane) at fixed omega (=[water]/[surfactant]) of 55.6 were constructed at different temperatures (293, 303, 313, and 323 K) and different mole fraction compositions of Brij-58 (X(Brij-58)=0, 0.5, and 1.0 in CTAB + Brij-58 mixture). Pure CTAB stabilized systems produced larger single-phase domains than pure Brij-58 stabilized systems. Increasing temperature increased the single-phase domain in the Brij-58 stabilized systems, whereas the domain decreased in the CTAB stabilized systems. For mixed surfactant systems (with X(Brij)=0.5) negligible influence of temperature in the studied range of 293 to 323 K on the phase behavior was observed. Interfacial compositions of the mixed microemulsion systems at different temperature and different compositions were evaluated by the dilution method. The n(a)(i) (number of moles of alcohol at the interface) and n(a)(o) (number of moles of alcohol in the oil phase) determined from dilution experiments were found to decrease and increase respectively for CTAB stabilized systems, whereas an opposite trend was witnessed for Brij-58 stabilized systems. The energetics of transfer of cosurfactants from oil to the interface were found to be exothermic and endothermic for CTAB and Brij-58 stabilized systems, respectively. At equimolar composition of CTAB and Brij-58, the phase diagrams were temperature insensitive, so that the enthalpy of the aforesaid transfer process was zero.     

Interface of AOT/Brij mixed reverse micellar systems: conductometric and spectrophotometric investigations

Solubilization and conductivity studies are carried out with AOT/Brijs (Brij-30, Brij-35, Brij-52, Brij-56, Brij-58, Brij-72, Brij-76, Brij-78)/isooctane/water mixed reverse micellar systems. Replacement of AOT molecules with large head group Brij molecules (Brij-30, Brij-35, Brij-56, Brij-58, Brij-76, Brij-78) decreases the solubilization capacity, whereas those with smaller polar head groups (Brij-52 and Brij-72) increases it. The former blends assist the conductance percolation whereas the latter retard it. An attempt has been taken to obtain more insight on the interfacial composition of the mixed interface with the help of spectrophotometric studies using 7-hydroxycoumarin as the fluorophore. The results obtained from the solubilization and conductometric studies have been correlated with those obtained from the spectroscopic studies.     

Manifestations of drag reduction by polymer additives in decaying, homogeneous, isotropic turbulence

The existence of drag reduction by polymer additives, well established for wall-bounded turbulent flows, is controversial in homogeneous, isotropic turbulence. To settle this controversy, we carry out a high-resolution direct numerical simulation of decaying, homogeneous, isotropic turbulence with polymer additives. Our study reveals clear manifestations of drag-reduction-type phenomena: On the addition of polymers to the turbulent fluid, we obtain a reduction in the energy-dissipation rate, a significant modification of the fluid energy spectrum especially in the deep-dissipation range, a suppression of small-scale intermittency, and a decrease in small-scale vorticity filaments.     

Monitoring of atmospheric 3H around Narora Atomic Power Station

Atmospheric tritium activity is measured regularly around Narora Atomic Power Station (NAPS) since gaseous waste, which contains tritium, is being released through a 145 m high stack at NAPS site. Atmospheric data collected during 2004–2008 shows a large variation of ³H concentration in air, fluctuating in the range of ≤0.2–91.6 Bq m^?3. Significantly, higher tritium levels were measured in samples near the site boundary (1.6 km) of NAPS compared to off-site locations. The atmospheric dilution factor was found to be in the range of 1.1 × 10^?7–7.3 × 10^?7 s m^?3. The scavenging ratio of NAPS site was found to be varying from 0.2 × 10⁴ to 14.1 × 10⁴ (Bq m^?3 rain water per Bq m^?3 air). The inhalation dose to a member of general public at different distances (1.6–30 km) from NAPS site was found to be ranged from 0.08–0.21 μSv year^?1.     

Value-Added Production of Nisin from Soy Whey

The objective of this study was to evaluate the potential of low/negative value soy whey (SW) as an alternative, inexpensive fermentation substrate to culture Lactococcus lactis subsp. lactis for nisin production. Initially, a microtiter plate assay using a Bioscreen C Microbiology Plate Reader was used for rapid optimization of culture conditions. Various treatments were examined in efforts to optimize nisin production from SW, including different methods for SW sterilization, ultrasonication of soy flake slurries for possible nutrient release, comparison of diluted and undiluted SW, and supplementation of SW with nutrients. In subsequent flask-based experiments, dry bacterial mass and nisin yields obtained from SW were 2.18 g/L and 619 mg/L, respectively, as compared to 2.17 g/L and 672 mg/L from a complex medium, de Man–Rogosa–Sharpe broth. Ultrasonication of soybean flake slurries (10% solid content) in water prior to production of SW resulted in ∼2% increase in biomass yields and ∼1% decrease in nisin yields. Nutrient supplementation to SW resulted in ∼3% and ∼7% increase in cell and nisin yields, respectively. This proof-of-concept study demonstrates the potential for use of a low/negative value liquid waste stream from soybean processing for production of a high-value fermentation end product.     

Synthon evolution and unit cell evolution during crystallisation. A study of symmetry-independent molecules (Z' > 1) in crystals of some hydroxy compounds

A kinetically favoured crystal, with many molecules in the asymmetric unit, may be a fossil relic of the crystal nucleus of a more stable polymorph.