Three-Dimensional Unsteady Flow With Heat and Mass Transfer Over a Continuous Stretching Surface

A numerical solution of the unsteady boundary layer equations under similarity assumptions is obtained. The solution represents the three-dimensional unsteady fluid motion caused by the time-dependent stretching of a flat boundary. It has been shown that a self-similar solution exists when either the rate of stretching is decreasing with time or it is constant. Three different numerical techniques are applied and a comparison is made among them as well as with earlier results. Analysis is made for various situations like deceleration in stretching of the boundary, mass transfer at the surface, saddle and nodal point flows, and the effect of a magnetic field. Both the constant temperature and constant heat flux conditions at the wall have been studied.

Adsorption of oxygen and reactivity with HCl on a barium-doped lead surface

X.p.s. studies on the adsorption of oxygen on a barium-covered Pb surface have shown the presence of two distinct types of oxygen species: oxidic, O2–, and the peroxo-like O2–2(ads), and the surface has been identified as a composite of PbO and BaPbO3. On a barium pre-covered surface, the sticking probability of oxygen on Pb is increased. The O2–(ads) species preferentially reacts with HCl forming PbCl2(ads)via proton abstraction, whereas O2–2(ads) is not reactive with HCl vapour. On the Pb surface, the PbCl2 overlayer reacts with excess HCl, forming a volatile compound believed to be Pb(ClHCl)2, while in the presence of coadsorbed barium, the stability of PbCl2 is increased and the activation energy for the reaction: PbCl2(ads)+ 2HCl(g) Pb(ClHCl)2(g) is increased. Stronger intermetallic interaction is suggested to be the reason for higher PbCl2 stability.

Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface

The electronic structure of the insulating sodium tungsten bronze, Na0.025WO3, is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E-F states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO3 lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system

Surface modifications in single crystal surfaces of YBa2Cu3O7-delta upon high energy ion irradiation

Atomic force microscopy investigations on swift heavy ion (200 MeV An) irradiated surfaces of a high T-c single crystal YBa2Cu3O7-delta are presented. Results obtained revealed an ion-induced erosion/sputtering clearly confirming our earlier observation on grain boundary dominated thin films. Apart from sputtering, notable effects were seen with many defect structures like dikes/hillocks surrounded by craters, dikes, holes, pearl like structures and ripple formation of sub-micron undulations, all in one crystal. Results are discussed in the light of co-operative phenomena of material re-distribution mechanism related to mass transfer and crater formations.

Correlation between stick-slip frictional sliding and charge transfer

A decade ago, Budakian and Putterman [Phys. Rev. Lett. 85, 1000 (2000)] ascribed friction to the formation of bonds arising from contact charging when a gold tip of a surface force apparatus was dragged on polymethylmethacrylate surface. We propose a stick-slip model that captures the observed correlation between stick-slip events and charge transfer, and the lack of dependence of the scale factor connecting the force jumps and charge transfer on normal load. Here, stick-slip dynamics arises as a competition between the viscoelastic and plastic deformation time scales and that due to the pull speed with contact charging playing a minor role. Our model provides an alternate basis for explaining most experimental results without ascribing friction to contact charging.

Surface diffusion driven nanoshell formation by controlled sintering of mesoporous nanoparticle aggregates

We report a general method for the synthesis of hollow structures of a variety of functional inorganics by partial sintering of mesoporous nanocrystal aggregates. The formation of a thin shell initiates the transport of mass from the interior leading to growth of the shell. The principles are general and the hollow structures thus produced are attractive for many applications including catalysis, drug delivery and biosensing.

Deformation and friction of MoS2 particles in liquid suspensions used to lubricate sliding contact

Tribology of a well known solid lubricant molybdenum disulphide is studied here in water and oil medium, over a large range of contact dimensions. Lateral force microscopy is used to identify the deformation modes, intra-crystalline slip, plastic grooving, fragmentation and fracture, of single particles The medium and agglomeration were found to dictate the deformation mode Steel on steel tribology lubricated by suspensions of these particles in liquid media was conducted over a range of contact pressure and sliding velocity. A scrutiny of the frictional data with the aid of Raman spectroscopy to identify the transfer film, suggested that the particle size, as it is at contact, is an important tribological parameter Ultrasonication of the suspension and dispersion of the particle by surfactants were used to control the apriori particle size fed into the suspension.Correspondence of friction data of the gently sonicated suspension with that of the ultrasonicated suspension with dispersants indicated the importance of liquid ingestion by these particles as it controls their mode of deformation and consequent tribology. (C) 2010 Elsevier B V All rights reserved.

Changes to near-surface region of PTFE during dry sliding against steel

PTFE specimens were slid against an EN24 disc. The unworn and worn surfaces as well as the wear debris were examined by X-ray diffraction. Sliding was found to introduce (i) shrinkage of the unit cell, (ii) enlargement of crystallites and (iii) residual stresses in the slid PTFE surface. No conformational changes in the 157 helix could be observed due to sliding. The wear debris was found to be 1 mgrm thick warped laminates.

Design and performance evaluation of a systolic architecture for hidden-surface removal

In this paper, we propose a systolic architecture for hidden-surface removal. Systolic architecture is a kind of parallel architecture best known for its easy VLSI implementability. After discussing the design details of the architecture, we present the results of the simulation experiments conducted in order to evaluate the performance of the architecture.

High temperature deformation processing maps for boron modified Ti-6Al-4V alloys

The alloy, Ti-6Al-4V is an alpha + beta Ti alloy that has large prior beta grain size (similar to 2 mm) in the as cast state. Minor addition of B (about 0.1 wt.%) to it refines the grain size significantly as well as produces in-situ TiB needles. The role played by these microstructural modifications on high temperature deformation processing maps of B-modified Ti64 alloys is examined in this paper.Power dissipation efficiency and instability maps have been generated within the temperature range of 750-1000 degrees C and strain rate range of 10(-3)-10(+1) s(-1). Various deformation mechanisms, which operate in different temperature-strain rate regimes, were identified with the aid of the maps and complementary microstructural analysis of the deformed specimens. Results indicate four distinct deformation domains within the range of experimental conditions examined, with the combination of 900-1000 degrees C and 10(-3)-10(-2) s(-1) being the optimum for hot working. In that zone, dynamic globularization of alpha laths is the principle deformation mechanism. The marked reduction in the prior beta grain size, achieved with the addition of B, does not appear to alter this domain markedly. The other domains, with negative values of instability parameter, show undesirable microstructural features such as extensive kinking/bending of alpha laths and breaking of beta laths for Ti64-0.0B as well as generation of voids and cracks in the matrix and TiB needles in the B-modified alloys. (C) 2010 Elsevier B.V. All rights reserved.

In situ surface modification of molybdenum-doped organic-inorganic hybrid TiO2 nanoparticles under hydrothermal conditions and treatment of pharmaceutical effluent

Molybdenum-doped TiO2 organic-inorganic hybrid nanoparticles were synthesized under mild hydrothermal conditions by in situ surface modification using n-butylamine. This was carried out at 150 degrees C at autogeneous pressure over 18 h. n-Butylamine was selected as a surfactant since it produced nanoparticles of the desired size and shape. The products were characterized using powder X-ray diffraction, Fourier transform infrared spectrometry, dynamic light-scattering spectroscopy, UV-Vis spectroscopy and transmission electron microscopy. Chemical oxygen demand was estimated in order to determine the photodegradation efficiency of the molybdenum-doped TiO2 hybrid nanoparticles in the treatment of pharmaceutical effluents. It was found that molybdenum-doped TiO2 hybrid nanoparticles showed higher photocatalytic efficiency than untreated TiO2 nanoparticles.

Laser Surface Alloying of a Creep Resistant Magnesium Alloy MRI 230D with Al and Al2O3

A creep resistant permanent mould cast Mg alloy MRI 230D was laser surface alloyed with Al and a mixture of Al and Al2O3 using pulsed Nd:YAG laser irradiation at four different scan speeds in order to improve the corrosion and wear resistance. The microstructure, corrosion and wear behavior of the laser surface alloyed material is reported in this manuscript. The coating comprised of a featureless microstructure with cellular-dendritic microstructure near the interface and exhibited good interfacial bonding. A few solidification cracks reaching down to substrate were also observed. The two step coating with Al followed by a mixture of Al and Al2O3 exhibited a slightly better corrosion resistance than the single step coating with Al. In the long run, however, corrosion resistance of both the coatings became comparable to the as-cast alloy. The corroded surface of the laser surface alloyed specimens revealed a highly localized corrosion. The laser surface alloyed specimens exhibited an improvement in wear resistance. The laser scan speed did not exhibit a monotonic trend either in corrosion or wear resistance.

Interannual Variations of Sea Surface Temperature over the Arabian Sea and the Indian Monsoon: A New Perspective

The interannual variation of surface fields over the Arabian Sea and Bay of Bengal are studied using data between 1900 and 1979. It is emphasized that the monthly mean sea surface temperature (SST) over the north Indian Ocean and monsoon rainfall are significantly affected by synoptic systems and other intraseasonal variations. To highlight the interannual signals it is important to remove the large-amplitude high-frequency noise and very low frequency long-term trends, if any. By suitable spatial and temporal averaging of the SST and the rainfall data and by removing the long-term trend from the SST data, we have been able to show that there exists a homogeneous region in the southeastern Arabian Sea over which the March�April (MA) SST anomalies are significantly correlated with the seasonal (June�September) rainfall over India. A potential of this premonsoon signal for predicting the seasonal rainfall over India is indicated. It is shown that the correlation between the SST and the seasonal monsoon rainfall goes through a change of sign from significantly positive with premonsoon SST to very small values with SST during the monsoon season and to significantly negative with SST during the post-monsoon months. For the first time, we have demonstrated that heavy or deficient rainfall years are associated with large-scale coherent changes in the SST (although perhaps of small amplitude) over the north Indian 0cean. We also indicate possible reasons for the apparent lack of persistence of the premonsoon SST anomalies.