Novel Nanocomposites Made of Boron Nitride Nanotubes and a Physical Gel

This article describes successful incorporation of multiwalled boron nitride nanotubes (BNNTs) and various functionalized BNNTs by Lewis bases such as trioctylamine (TOA), tributylamine (TBA), and triphenylphosphine (TPP), etc., in organogels formed by triphenylenevinylene (TPV)-based low molecular weight gelator (LMWG) in toluene and consequent characterization of the resulting gel nanocomposites. Functionalized BNNTs were synthesized first,and the presence of tubular structures with high aspect ratio and increased diameter compared to the starting BNNTs was confirmed by SEM. TEM, and Raman spectroscopy. The micrographs of composites of I and BNNTs showed evidence of wrapping of the gelator molecules on to the BNNT surface presumably brought about by pi-pi stacking and van der Waals interactions, This leads to the formation of densely packed and directionally aligned fibrous networks. Such ``reinforced'' aggregation of the gelator molecules in presence of doped BNNTs led to an increase in the sot-to-gel transition temperature and the solidification temperature of the gel nanocomposites as revealed from differential scanning calorimetry. Rheological investigations of the gel nanocomposites indicate that the flow properties of the resulting materials become resistant to applied stress upon incorporation of even a very low wt % of BNNTs. Finally, the increase in thermal conductivity of the nanocomposite compared to the gelator alone was observed for the temperature range of 0-60 degrees C which may make these composites potentially useful in various applications depending on the choice and the amount of BNNT loading in the composite.

Adsorption behaviour of an oxidised starch onto haematite in the presence of calcium

The adsorption behaviour of an oxidised starch AP as well as that of calcium onto haematite have been studied both individually and together. While the adsorption density of starch AP onto haematite is enhanced in the presence of calcium, the adsorption of calcium onto haematite is not promoted by starch AP. Flocculation tests on haematite ore fines in the presence of starch AP and calcium chloride reveal that the sequence in which calcium and starch are added governs the settling rates and turbidity values. Zeta potential, viscosity and conductivity measurements, and calcium ion binding studies with starch AP indicate calcium-starch interactions. Possible mechanisms involved in such interactions with respect to haematite flocculation have been discussed.

A physical mechanism for North Atlantic SST influence on the Indian summer monsoon

A link between the Atlantic Multidecadal Oscillation (AMO) and multidecadal variability of the Indian summer monsoon rainfall is unraveled and a long sought physical mechanism linking Atlantic climate and monsoon has been identified. The AMO produces persistent weakening (strengthening) of the meridional gradient of tropospheric temperature (TT) by setting up negative (positive) TT anomaly over Eurasia during northern late summer/autumn resulting in early (late) withdrawal of the south west monsoon and persistent decrease (increase) of seasonal monsoon rainfall. On inter-annual time scales, strong North Atlantic Oscillation (NAO) or North Annular mode (NAM) influences the monsoon by producing similar TT anomaly over Eurasia. The AMO achieves the interdecadal modulation of the monsoon by modulating the frequency of occurrence of strong NAO/NAM events. This mechanism also provides a basis for explaining the observed teleconnection between North Atlantic temperature and the Asian monsoon in paleoclimatic proxies. Citation: Goswami, B. N., M. S. Madhusoodanan, C. P. Neema, and D. Sengupta (2006), A physical mechanism for North Atlantic SST influence on the Indian summer monsoon

Preparation and characterization of silane-stabilized, highly uniform, nanobimetallic Pt-Pd particles in solid and liquid matrixes

Highly uniform, stable nanobimetallic dispersions are prepared in a single si ep in the form of sols, gels, and monoliths, using organically modified silicates as the matrix and the stabilizer. The Pt-Pd bimetallic dispersions are characterized by W-vis, TEM, SEM, and XRD measurements. The evolution of silicate was followed by IR spectroscopy. XPS and CO adsorption studies reveal that the structure of the particles consists of a palladium core and a platinum shell. Electrocatalysis of ascorbic acid oxidation has been demonstrated using thin films of silicate containing the nanobimetal particles on a glassy carbon electrode.

Use of Polyazaheterocycles in the Assembly of New Cadmium Sulfate Frameworks: Synthesis, Structure, and Properties

The reaction of cadmium sulfate in the presence of polyazaheterocyclic organic molecules gave rise to a variety of new cadmium sulfate phases in water containing solvothermal reaction. The compounds have two- (I) and three-dimensionally (II-VI) extended structures. All the compounds have structures built up by the connectivity involving the cadmium octahedra and the sulfate tetrahedra in which the heterocyclic organic molecules act as the ligand. The linkages between the Cd2+ and (SO4)2- ions form one- (II), two- (I, III, and IV), and three- (V and VI) dimensionally extended cadmium sulfate phases. The connectivity between Cd2+ ion and the heterocyclic ligand also gives rise to one- and two-dimensional structures. The inter-connectivity between the two units gives rise to the observed structures. The presence of Cd-O-Cd chains and Cd-O-Cd layers in some of the structures is noteworthy. The adsorption/desorption studies suggest that the cadmium sulfate phases adsorb/desorb anionic dyes selectively in the presence of water/ethanol, respectively. The photocatalytic degradation studies on cationic dyes under UV-irradiation indicate modest activity. The cyanosilylation of imines using the present compounds as heterogeneous catalyst indicate good catalytic behavior. The various properties exhibited by the cadmium sulfate phases suggest that these compounds are versatile. All the compounds were characterized by powder X-ray diffraction, thermogravimetric analysis, infrared (IR) and UV-visible studies.

The physical properties of SnS films grown on lattice-matched and amorphous substrates

The development of high-quality tin monosulphide (SnS) layers is one of the crucial tasks in the fabrication of efficient SnS-based optoelectronic devices. Reduction of strain between film and the substrate by using an appropriate lattice-matched (LM) substrate is a new attempt for the growth of high-quality layers. In this view, the SnS films were deposited on LM Al substrate using the thermal evaporation technique with a low rate of evaporation. The as-grown SnS films were characterized using appropriate techniques and the obtained results are discussed by comparing them with the properties of SnS films grown on amorphous substrate under the same conditions. From structural analysis of the films, it is noticed that the SnS films deposited on amorphous substrate have crystallites that were oriented along different directions. However, the SnS crystallites grown on Al substrate exhibited epitaxial growth along the 101] direction. Photoluminescence (PL) and Raman studies reveal that the films grown on Al substrate have better optical properties than those of the films grown on amorphous substrates. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic evaluation of mitigation of petroleum hydrocarbon contamination by soil medium

Present in situ chemical treatment technologies for mitigation of petroleum hydrocarbon contamination are in the developmental stage or being tested. To devise efficient strategies for restricting the movement of petroleum hydrocarbon (PHC) molecules in the contaminated soil, it is proposed to utilize the sorption–interaction relationships between the petroleum contaminants and the soil substrate. The basic questions addressed in this paper are as follows (i) What are the prominent chemical constituents of the various petroleum fractions that interact with the soil substrate? (ii) What are the functional groups of a soil that interact with the contaminants? (iii) What are the bonding mechanisms possible between the soil functional groups and the PHC contaminants? (iv) What are the consequent changes brought about the soil physical properties on interaction with PHC's? (v) What are the factors influencing the interactions between PHC molecules and clay particles of the soil substrate? (vi) What is the possibility of improving the soil's attenuation ability for PHC's? The development of answers to the basic questions reveal that petroleum hydrocarbons comprise a mixture of nonpolar alkanes and aromatic and polycyclic hydrocarbons, that have limited solubility in water. The bonding mechanism between the nonpolar PHC's and the clay surface is by way of van der Waals attraction. The adsorption of the nonpolar hydrocarbons by the clay surface occurs only when their (i.e., the hydrocarbon molecules) solubility in water is exceeded and the hydrocarbons exist in the micellar form. Dilute solutions of hydrocarbons in water, i.e., concentrations of hydrocarbons at or below the solubility limit, have no effect on the hydraulic conductivity of clay soils. Permeation with pure hydrocarbons invariably influences the clay hydraulic conductivity. To improve the attenuation ability of soils towards PHC's, it is proposed to coat the soil surface with "ultra" heavy organic polymers. Adsorption of organic polymers by the clay surface may change the surface properties of the soil from highly hydrophilic (having affinity for water molecules) to organophilic (having affinity for organic molecules). The organic polymers attached to the clay surface are expected to attenuate the PHC molecules by van der Waals attraction, by hydrogen bonding, and also by adsorption into interlayer space in the case of soils containing swelling clays.

Physical mapping of the genomic DNA of the Oryctes rhinoceros baculovirus, KI

A non-occluded baculovirus, OBV-KI has been isolated from the insect pest, Oryctes rhinoceros. The viral genome is estimated to be 123 kb, with a G + C content of 43 mol% and no detectible methylated bases. A restriction map of the OBV-KI genome for BamHI, EcoRI, HindIII, PstI, SalI and XbaI has been constructed.

Experimental analysis of thermo-physical processes in acoustically levitated heated droplets

An experimental setup using radiative heating has been used to understand the thermo-physical phenomena and chemical transformations inside acoustically levitated cerium nitrate precursor droplets. In this transformation process, through infrared thermography and high speed imaging, events such as vaporization, precipitation and chemical reaction have been recorded at high temporal resolution, leading to nanoceria formation with a porous morphology. The cerium nitrate droplet undergoes phase and shape changes throughout the vaporization process. Four distinct stages were delineated during the entire vaporization process namely pure evaporation, evaporation with precipitate formation, chemical reaction with phase change and formation of final porous precipitate. The composition was examined using scanning and transmission electron microscopy that revealed nanostructures and confirmed highly porous morphology with trapped gas pockets. Transmission electron microscopy (TEM) and high speed imaging of the final precipitate revealed the presence of trapped gases in the form of bubbles. TEM also showed the presence of nanoceria crystalline structures at 70 degrees C. The current study also looked into the effect of different heating powers on the process. At higher power, each phase is sustained for smaller duration and higher maximum temperature. In addition, the porosity of the final precipitate increased with power. A non-dimensional time scale is proposed to correlate the effect of laser intensity and vaporization rate of the solvent (water). The effect of acoustic levitation was also studied. Due to acoustic streaming, the solute selectively gets transported to the bottom portion of the droplet due to strong circulation, providing it rigidity and allows it become bowl shaped. (C) 2010 Elsevier Ltd. All rights reserved.

Thermal decomposition of ethylene diamine diperchlorate

Thermal decomposition of ethylene diamine diperchlorate (EDDP) has been studied by differential-thermal analysis (DTA), thermogravimetric analysis (TGA), isothermal weight-loss measurements and mass-spectrometric analysis of the decomposition products. It has been observed that EDDP decomposes in two temperature regions. The low-temperature decomposition stops at about 35 to 40 percent weight loss below 250°C. The reason for the low-temperature cessation may be the adsorption of excess ethylene diamine on the crystal surface of EDDP. An overall activation energy of 54 kcal per mole has been calculated for the thermal decomposition of EDDP. Mass-spectrometric analysis shows that the decomposition products are mainly CO2, H2O, HCl and N2. The following stoichiometry has been proposed for the thermal decomposition of EDDP: (−CH2NH3CIO4)2→2CO2O+2HCl+N2

An electron spectroscopic study of the adsorption of nitrogen on a Ni/TiO2 catalyst prepared in situ in the spectrometer: evidence for dissociative adsorption in the strong-metal-support-interaction (SMSI) state

Nitrogen is dissociatively adsorbed on an annealed Ni/TiO2 surface just as on a Ti–Ni alloy surface while it is molecularly adsorbed on a Ni/Al2O3 surface.

Effect of HCl on the adsorption of oxygen on Cu(110) surface: An eels study

Oxygen is shown to adsorb molecularly on a clean Cu(110) surface at 80 K and dissociate around 150 K forming atomic oxygen. Adsorption of oxygen on an HCl covered surface at low temperatures results in the formation of adsorbed hydroxyl groups and water in addition to adsorbed molecular oxygen. The molecular oxygen species is stable up to 190 K on the HCl covered surface.

Impact of physical processes on the chlorophyll distribution in the Bay of Bengal

Satellite-derived chlorophyll a concentration (chl a) maps show three regions with high chl a in the Bay of Bengal. First among these is close to the coast, particularly off river mouths, with high values coinciding with the season of peak discharge; second is in the southwestern bay during the northeast monsoon, which is forced by local Ekman pumping; and the third is to the east of Sri Lanka in response to the summer monsoon winds. Chlorophyll-rich water from the mouths of rivers flows either along the coast or in an offshore direction, up to several hundred kilometers, depending on the prevailing ocean current pattern. The Irrawady River plume flows toward offshore and then turns northwestward during October–December, but it flows along the coast into the Andaman Sea for the rest of the year. From the Ganga-Brahmaputra river mouth, chl a–rich water flows directly southward into the open bay during spring but along the Indian coast during summer and winter. Along the Indian coast, the flow of chl a–rich water is determined by the East India Coastal Current (EICC). Whenever the EICC meanders off the Indian coast, it leads to an offshore outbreak of chl a–rich water from the coastal region into open ocean. The EICC as well as open ocean circulation in the bay is made up of several eddies, and these eddies show relatively higher chl a. Eddies near the coast, however, can often have higher chl a because of advection from the coastal region rather than generation within the eddy itself. The bay experiences several cyclones in a year, most of them occurring during October–November. These cyclones cause a drop in the sea surface temperature, a dip in the sea level, and a local increase in chl a. The impact of a cyclone is weaker in the northern part of the bay because of stronger stratification compared to the southern parts.

Low frequency oscillations in power systems: A physical account and adaptive stabilizers

This paper presents a physical explanation of the phenomenon of low frequency oscillations experienced in power systems. A brief account of the present practice of providing fixed gain power system stabilizers (PSS) is followed by a summary of some of the recent design proposals for adaptive PSS. A novel PSS based on the effort of cancelling the negative damping torque produced by the automatic voltage regulator (AVR) is presented along with some recent studies on a multimachine system using a frequency identification technique.