Covalent Grafting of Polydimethylsiloxane over Surface-Modified Alumina Nanoparticles

The synthesis of ``smart structured'' conducting polymers and the fabrication of devices using them are important areas of research. However, conducting polymeric materials that are used in devices are susceptible to degradation due to oxygen and moisture. Thus, protection of such devices to ensure long-term stability is always desirable. Polymer nanocomposites are promising materials for the encapsulation of such devices. Therefore, it is important to develop suitable polymer nanocomposites as encapsulation materials to protect such devices. This work presents a technique based on grafting between surface-decorated gamma-alumina nanoparticles and polymer to make nanocomposites that can be used for the encapsulation of devices. Alumina was functionalized with allyltrimethoxysilane and used to conjugate polymer molecules (hydride-terminated polydimethylsiloxane) through a platinum-catalyzed hydrosilylation reaction. Fourier transform infrared spectroscopy, X-ray-photoelectron spectroscopy, and Raman spectroscopy were used to characterize the surface chemistry of the nanoparticles after surface modification. The grafting density of alkene groups on the surface of the modified nanoparticles was calculated using CHN and thermogravimetric analyses. The thermal stability of the composites was also evaluated using thermogravimetric analysis. The nanoindentation technique was used to analyze the mechanical characteristics of the composites. The densities of the composites were evaluated using a density gradient column, and the morphology of the composites was evaluated by scanning electron microscopy. All of our studies reveal that the composites have good thermal stability and mechanical flexibility and, thus, can potentially be used for the encapsulation of organic photovoltaic devices.

Mo3O5(OH)(2)(AsO4)2: A new solid with a structure related to beta VOPO4

Mo3O5(OH)(2)(AsO4)(2) was prepared at 100 degrees C from an aqueous solution of MoO3 containing arsenic and nitric acids. It crystallises in the monoclinic system, a = 13.024(1)Angstrom, b = 7.2974 (2) Angstrom, c = 13.281(1) Angstrom, beta = 121.124(8)degrees, Z = 4, space group C2/c. The structure was determined by Rietveld refinement from X-ray powder diffraction data. The three-dimensional structure is built up from MoO6 and MoO5OH octahedra and AsO4 tetrahedra sharing corners. The octahedra share two opposite vertices forming zigzag chains that run parallel to [10(1) over bar]. Each AsO4 tetrahedron is connected to four octahedra, two of which belong to the same chain, thus linking three chains. The resulting covalent framework is similar to that of beta VOPO4 in which one tetrahedral P site for every three is empty. The two protons are likely to be bonded to two (out of four) unshared oxygen atoms surrounding this empty site. All the Mo atoms are strongly off-centred in the octahedra; and the off-centring is disordered. The disorder is discussed in terms of Mo shifts perturbed by a disordered hydrogen bonding scheme.

Airborne measurements of aerosol scattering properties above the MABL over Bay of Bengal during W_ICARB - characteristics and spatial gradients

Realizing the importance of aerosol characterization and addressing its spatio-temporal heterogeneities over Bay of Bengal (BoB), campaign mode observations of aerosol parameters were carried out using simultaneous cruise, aircraft and land-based measurements during the Winter Integrated Campaign for Aerosols gases and Radiation Budget (W_ICARB). Under this, airborne measurements of total and hemispheric backscatter coefficients were made over several regions of coastal India and eastern BoB using a three wavelength integrating nephelometer. The measurements include high resolution multi-level (ML) sorties for altitude profiles and bi-level (BL) sorties for spatial gradients within and above the Marine Atmospheric Boundary Layer (MABL) over BoB. The vertical profiles of the scattering coefficients are investigated in light of the information on the vertical structure of the atmospheric stability, which was derived from the collocated GPS (Global Positioning System) aided radiosonde ascents. In general, the altitude profiles revealed that the scattering coefficient remained steady in the convectively well-mixed regions and dropped off above the MABL. This decrease was quite rapid off the Indian mainland, while it was more gradual in the eastern BoB. Investigation on horizontal gradients revealed that the scattering coefficients over northern BoB are 3 to 4 times higher compared to that of central BoB within and above the MABL. A north-south gradient in scattering coefficients is observed over Port Blair in the eastern BoB, with values decreasing from south to north, which is attributed to the similar gradient in the surface wind speed, which can be replicated in the sea salt abundance. The gradients are parameterized using best-fit analytical functions.

Latitude variation of boundary layer height over Indian Ocean during pre- and First Field Phase (FFP-98) of INDOEX

This paper describes the results of the measurement of the Marine Boundary Layer (MBL) height from spectral analysis of the u and v components of the wind and from CLASS/radiosonde temperature profiles. The data were collected on ORV Sagar Kanya during the pre-INDOEX (27 December 1996 through 31 January 1997) and FFP-98 (18 February to 31 March 1998) over the latitude range 15 degrees N to 14 degrees S and 15 degrees N to 20 degrees S respectively. During the pre-INDOEX, the MBL heights gradually decrease from 2.5 km at 13 degrees N to around 500 to 600 m at 10 degrees S, Similar results are observed in the return track. The MBL heights (0.5 to 1 km) obtained during FFP-98 are less compared to those obtained during pre-INDOEX. The MBL heights during FFP-98 are less compared to the pre-INDOEX and are believed to be due to the presence of stratus, stratocumulus and cumulus clouds during the cruise period, compared to a relatively cloud free pre-INDOEX cruise.

Levitation of a drop over a film flow

A vertical jet of water impinging on a horizontal surface produces a radial film flow followed by a circular hydraulic jump. We report a phenomenon where fairly large (1 mi) drops of liquid levitate just upstream of the jump on a thin air layer between the drop and the film flow. We explain the phenomenon using lubrication theory. Bearing action both in the air film and the water film seems to be necessary to support large drops. Horizontal support is given to the drop by the hydraulic jump. A variety of drop shapes is observed depending on the volume of the drop and liquid properties. We show that interaction of the forces due to gravity, surface tension, viscosity and inertia produces these various shapes.

Localized data gathering paradigms for small and marginal farm lands in Semi-Arid region – Issues and Concerns

In this work we explore the application of wireless sensor technologies for the benefit of small and marginal farmers in semi-arid regions. The focus in this paper is to discuss the merits and demerits of data gathering & relay paradigms that collect localized data over a wide area. The data gathered includes soil moisture, temperature, pressure, rain data and humidity. The challenge to technology intervention comes mainly due to two reasons: (a) Farmers in general are interested in crop yield specific to their piece of land. This is because soil texture can vary rapidly over small regions. (b) Due to a high run-off, the soil moisture retention can vary from region to region depending on the topology of the farm. Both these reasons alter the needs drastically. Additionally, small and marginal farms can be sandwiched between rich farm lands. The village has very little access to grid power. Power cuts can extend up to 12 hours in a day and upto 3 or 4 days during some months in the year. In this paper, we discuss 3 technology paradigms for data relaying. These include Wi-Fi (Wireless Fidelity), GPRS (General Packet Radio Service) and DTN (Delay and Disruption Tolerant Network) technologies. We detail the merits and demerits of each of these solutions and provide our final recommendations. The project site is a village called Chennakesavapura in the state of Karnataka, India.

Vesicle formation from dimeric ion-paired amphiphiles. Control over vesicular thermotropic and ion-transport properties as a function of intra-amphiphilic headgroup separation

A novel series of vesicle-forming ion-paired amphiphiles, bis(hexadecyldimethylammonium)alkane dipalmitate (1a-1h), containing four chains were synthesized with two isolated headgroups. In each of these amphiphiles, the two headgroup charges are separated by a flexible polymethylene spacer chain -[(CH2)(m)]- of varying lengths (m) such that the length and the conformation of the spacer chain determine the intra-"monomer" headgroup separation. Transmission electron microscopy indicated that each of these forms bilayer membranes upon dispersion in aqueous media. The vesicular properties of these aggregates have been examined by differential scanning calorimetry and temperature-dependent fluorescence anisotropy measurements. Interestingly, their T-m values decreased with the increase in the m value. Thus while the apparent T-m of the lipid with m = 2 (1a) is 74.1 degrees C, the corresponding value observed for the lipid with m = 12 (1h) is 38.9 degrees C. The fluorescence anisotropy values (r) for 1b-1g were quite high (r similar to 0.3) compared to that of 1h (r similar to 0.23) at 20-30 degrees C in their gel states. On the other hand, the r value for vesicular 1b beyond melting was higher (0.1) compared to any of those for 1c-1h (similar to 0.04-0.06). X-ray diffraction of the cast films was performed to understand the nature and the thickness of these membrane organizations. The membrane widths ranged from 30 to 51 A as the m values varied. The entrapment of a small water-soluble solute, riboflavin, by the individual vesicular aggregates, and their sustenance: under an imposed transmembrane pH gradient have also been examined. These results show that all lipid vesicles entrap riboflavin and that generally the resistance to OH- permeation decreases with the increase in m value. Finally,all the above observations were comparatively analyzed, and on the basis of the calculated structures of these lipids, it was possible to conclude that membrane propel-ties can be modulated by spacer chain length variation of the ion-paired amphiphiles.

Aerosol radiative forcing over land: effect of surface and cloud reflection

It is now clearly understood that atmospheric aerosols have a significant impact on climate due to their important role in modifying the incoming solar and outgoing infrared radiation. The question of whether aerosol cools (negative forcing) or warms (positive forcing) the planet depends on the relative dominance of absorbing aerosols. Recent investigations over the tropical Indian Ocean have shown that, irrespective of the comparatively small percentage contribution in optical depth (similar to11%), soot has an important role in the overall radiative forcing. However, when the amount of absorbing aerosols such as soot are significant, aerosol optical depth and chemical composition are not the only determinants of aerosol climate effects, but the altitude of the aerosol layer and the altitude and type of clouds are also important. In this paper, the aerosol forcing in the presence of clouds and the effect of different surface types (ocean, soil, vegetation, and different combinations of soil and vegetation) are examined based on model simulations, demonstrating that aerosol forcing changes sign from negative (cooling) to positive (warming) when reflection from below (either due to land or clouds) is high.

Fast-Group-Decodable STBCs via Codes over GF(4)

In this paper we construct low decoding complexity STBCs by using the Pauli matrices as linear dispersion matrices. In this case the Hurwitz-Radon orthogonality condition is shown to be easily checked by transferring the problem to $\mathbb{F}_4$ domain. The problem of constructing low decoding complexity STBCs is shown to be equivalent to finding certain codes over $\mathbb{F}_4$. It is shown that almost all known low complexity STBCs can be obtained by this approach. New codes are given that have the least known decoding complexity in particular ranges of rate.

Neighbor oblivious link reversal over duty-cycled WSNs

We propose partial and full link reversal algorithms to bypass voids during geographic routing over duty-cycled wireless sensor networks. We propose a distributed approach that is oblivious to one-hop neighbor information. Upon termination of the algorithm, the resulting network is guaranteed to be destination-oriented. Further, to reduce the delays incurred under reactive link reversal, we propose the use of `pseudo-events', a preemptive link reversal strategy, that renders the network destination-oriented before the onset of a real event. A simulation study of the effectiveness of pseudo-events is also provided.

Dielectric barrier discharge plasma interaction with the airflow over an airfoil

The effect of various parameters on the velocity of the induced jet produced by a dielectric barrier discharge (DBD) plasma was studied experimentally. The glow discharge was created at atmospheric conditions by using a high voltage RF power supply. Flow visualization and photographic studies of the plasma were performed. The parametric investigation of the characteristics of the plasma show that the width of the plasma in the uniform glow discharge regime was an indication of the velocity induced under stagnant conditions. It was observed that the spanwise overlap of the two electrodes, dielectric thickness, voltage and frequency of the applied voltage are the major parameters that govern the velocity and the extent of plasma in the streamwise direction.

Enhanced aerosol loading over Arabian Sea during the pre-monsoon season: Natural or anthropogenic?

[1] Recent experiments conducted over the oceanic regions adjacent to the Indian sub continent have revealed the presence of anthropogenic aerosol haze during January to March. It has been suggested that the major source of this aerosol is South and Southeast Asia. Here we show from long term, multi-station and ship borne observations that aerosols transported from regions northwest of Indian subcontinent especially Arabian and Saharan regions (mostly natural dust) along with the locally produced sea-salt aerosols by sea-surface winds constitute a more significant source of aerosols during April-May period. The radiative forcing due to Arabian/Saharan aerosols (mostly natural) during April May period is comparable and often exceed (as much as 1.5 times) the forcing due to anthropogenic aerosols during January to March period. The presence of dust load over the Arabian Sea can influence the temperature profile and radiative balance in this region.

Icosahedral quasicrystalline and hexagonal approximant phases in the Al-Mn-Be alloy system

We report the formation of a primitive icosahedral quasicrystal with increased stability in Al Mn-Be alloys close to the compound Al15Mn13Be2, by melt spinning and injection casting. The crystal structure of this compound was unknown. We show that in as-cast as well as heat treated condition the intermetallic phase H1 has a hexagonal structure with lattice parameters a = 1.2295 run and c = 2.4634 nm. The space group is P6(3)/mmc In the injection-cast samples, the quasicrystal coexists with another closely related hexagonal phase H2 with a = 1.2295 nm and c = 1.2317 nm with a possible space group of P6/mmm. This phase exhibits specific orientation relationships with the icosahedral quasicrystal given by [0001](hex)//2f(QC) and [01 (1) over bar0](hex)//5f(QC) where 2f(QC) and 5f(QC) represent twofold and fivefold axes respectively. Electron diffraction patterns from both phases exhibit a close resemblance to the quasicrystalline phase. It is shown that the H1 phase is closely related to mu-Al4Mn with the same e parameter while the a parameter is reduced by tau. Following Kreiner and Franzen, it is postulated that both structures (H1 and H2) can be understood by a simple hexagonal packing of I13 clusters.

MHD flow over a moving plate in a rotating fluid with magnetic field, Hall currents and free stream velocity

The non-similar boundary layer flow of a viscous incompressible electrically conducting fluid over a moving surface in a rotating fluid, in the presence of a magnetic field, Hall currents and the free stream velocity has been studied. The parabolic partial differential equations governing the flow are solved numerically using an implicit finite-difference scheme. The Coriolis force induces overshoot in the velocity profile of the primary flow and the magnetic field reduces/removes the velocity overshoot. The local skin friction coefficient for the primary flow increases with the magnetic field, but the skin friction coefficient for the secondary flow reduces it. Also the local skin friction coefficients for the primary and secondary flows are reduced due to the Hall currents. The effects of the magnetic field, Hall currents and the wall velocity, on the skin friction coefficients for the primary and secondary flows increase with the Coriolis force. The wall velocity strongly affects the flow field. When the wall velocity is equal to the free stream velocity, the skin friction coefficients for the primary and secondary flows vanish, but this does not imply separation. (C) 2002 Published by Elsevier Science Ltd.

Oxidation and decomposition of NH3 over combustion synthesized Al2O3 and CeO2 supported Pt, Pd and Ag catalysts

The catalytic oxidation and decomposition of NH3 have been carried out over combustion synthesized Al2O3 and CeO2 supported Pt, Pd and Ag catalysts using temperature programmed reaction (TPR) technique in a packed bed tubular reactor. Metals are ionically dispersed over CeO2 and fine metal particles are found on Al2O3. NH3 oxidation occurs over 1% Pt/Al2O3, 1% Pd/Al2O3 and 1% Ag/Al2O3 at 175, 270 and 350 C respectively producing N-2, NO, N2O and H2O, whereas 1% Pt/CeO2, 1% Pd/CeO2 and 1% Ag/CeO2 give N-2 along with NO, N2O and H2O at 200, 225 and 250degreesC respectively. N-2 predominates over other nitrogen-containing products during the reaction on all catalysts. At less O-2 concentration, N-2 and H2O are the only products obtained during NH3 Oxidation. NH3 decomposition over all the catalysts occurs above 450degreesC.