Measuring mechanical properties of plasma-sprayed alumina coatings by nanoindentation technique

AISI 1020 steel substrate is coated with alumina as feedstock material using plasma spraying process in order to correlate the microstructural features with mechanical properties of coating. The present work focuses on the effects of microstructural inhomogeneity on mechanical properties of alumina coating through nanoindentation technique. Young’s modulus and hardness of the alumina coating are analytically evaluated. Indentation stress–strain curves are generated from the experimentally obtained load–displacement curves to characterise the mechanical properties of the coating. The results have shown large variation in hardness and Young’s modulus of alumina due to microstructural inhomogeneity of the coating.     

Structural characteristics,fluorescence quenching,and antioxidant activity of the arabinogalactan protein-rich fraction from senna (<Emphasis Type="Italic">Cassia angustifolia</Emphasis>) leaves

Senna (Cassia angustifolia) is widely used in Indian folk medicine for the prevention of various disorders. Herein, we have demonstrated that water extracted arabinogalactan protein (AGP) rich fraction possesses strong antioxidative activity. The AGP rich fraction was analyzed using chemical, chromatographic, and spectroscopic methods. Effect of water extracted polymers on bovine serum albumin spectrum was determined using excitation wavelength of 282 nm. The antioxidant capacity of this fraction was studied by ferric reducing antioxidant power (FRAP) and DPPH radical assays. This polymeric fraction, ≥88% of which gets precipitated with Yariv reagent, consisted mainly of (1→5)-/(1→3,5)-linked α-arabinosyl, (1→3)-/(1→3,6)-linked-galactosyl residues and terminal arabinofuranosyl residues. Its in vitro antioxidant capacity is comparable to that of standard antioxidants. Fluorescence quenching studies furnishes evidence for the interaction of the arabinogalactan protein with bovine serum albumin.     

Emulsion-based synthesis of NaA zeolite nanocrystals and its integration towards NaA membranes

NaA zeolite nanoparticles (seed crystals) of size 50–65 nm were synthesized using water-in-oil (w/o) type emulsions at a considerably low temperature of 65 ± 1°C in a short duration of 2 h. The emulsions were stabilized using non-ionic surfactants e.g. sorbitan monooleate (Span 80), sorbitan monolaurate (Span 20), polyoxyethylene(5)nonylphenylether with ethoxy numbers of 5 (Igepal CO-520) and polyoxyethylene sorbitan monooleate (Tween 80) of hydrophilic-lipophilic balance (HLB) values of 4.3, 8.6, 10 and 15 respectively. Among the surfactants, the intermediate HLB values of 8.6 (Span 20) and 10 (Igepal CO-520) were effective in synthesizing highly dispersible NaA nanoparticles of size 50–65 nm. The membrane prepared hydrothermally in multi-steps at 65 ± 1°C, using the Span 20-derived seed crystals deposited on porous support, showed the formation of high quality interlocked NaA coating. Single gas nitrogen (N₂) permeation of the membrane exhibited a permeance value of 1.01 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ at ambient temperature (30°C).     

Development of integrated ΔE-E silicon detector telescope using silicon planar technology

An integrated ΔE-E silicon detector telescope using silicon planar technology has been developed. The technology developed is based on standard integrated circuit technology and involves double sided wafer processing. The ΔE and E detectors have been realized in a PIN configuration with a common buried N⁺ layer. Detectors with ΔE thicknesses of 10, 15 and 25 μm, and E detector with thickness of 300 μm have been fabricated and tested with alpha particles using ²³⁸Pu-²³⁹Pu dual alpha source. The performance of the detector with ΔE detector of thickness 10 μm and E detector of thickness 300 μm has been studied for identification of charged particles using 12 MeV ⁷Li⁺ ion beam on carbon target. The results of these tests demonstrate that the integrated detector telescope clearly separates the charged particles, such as alpha particles, protons and ⁷Li. Due to good energy resolution of the E detector, discrete alpha groups corresponding to well known states of ¹⁵N populated during the reaction could be clearly identified.     

Image-based quality monitoring system of limestone ore grades

In this study, an image analysis-based ore quality monitoring system was developed. The study was conducted at a limestone mine located in India. The samples were collected based on a stratified random sampling method, and images of these samples were taken in a simulated environment in a laboratory. The image preprocessing and segmentation were performed using different segmentation methods to extract morphological, colour and textural features. A total of 189 features was extracted during this study. Principal components analysis was conducted to reduce the feature vector for modeling purposes. Five principal components, which were extracted from the feature vectors, captured 95% of the total feature variance. A neural network model was used as a mapping function for ore grade prediction. The five principal components were used as input, and four grade attributes of limestone (CaO, Al₂O₃, Fe₂O₃ and SiO₂) were used as output. The developed model was then used for day to day quality monitoring at 3 different face locations of the mine. Results revealed that this technique can be successfully used for ore grade monitoring at the mine level in a controlled environment.     

Metal-semiconductor nanojunctions and their rectification characteristics

Junctions of silver-copper oxide and silver-zinc oxide, respectively were prepared within the pores of diameters, 20 nm, in anodic aluminium oxide membranes. Voltage-current characteristics were measured over the temperature range 373–573 K which showed rectification behaviour. Using the standard equation the difference between the work functions of the metal and the semiconductor was calculated. This showed a variation with the temperature of measurement. This is explained as arising due to the effect of pressure generated as a result of thermal expansion of the metallic phases concerned between the electrodes. This is consistent with the theoretical prediction of Fermi level shifting of the semiconductor within the bandgap as a function of pressure. Dedicated to Prof. C N R Rao     

Re-examining the prospects of aluminous cements based on alkali-earth and rare-earth oxides

In the family of aluminous cements the potential of strontium aluminate, the strontium–barium aluminate and the barium aluminate cements have been sporadically and incoherently studied over several decades in various parts of the world and more particularly in the East European countries without much wide-spread commercial success. Attempts had also been made to extend the exploratory studies to the (Ca, Sr, Ba)O–Al₂O₃–ZrO₂–HfO₂ system to synthesize super-refractory binders.In fact, the above compositions, prima facie, seem to have the potential of arriving at cementitious formulations that, apart from being super-refractory, may as well be highly resistant to seawater, X-rays and gamma radiation.Looking at these potentials, quite a few experimental studies have been carried out under the guidance and supervision of the present author. The present paper is an endeavour to collate the data on some of these systems both from the published literature as well as from the author's findings. The prime motive has been to review and re-assess the prospects of manufacturing a range of new aluminous binders with superior properties.     

A novel high-power low-distortion synchronous link converter-basedload compensator without the requirement of VAr calculator

A high-power low-distortion static VAr compensator based on a synchronous link converter has been proposed, where the harmonics are eliminated by incorporating a low-power insulated-gate-bipolar-transistor-based controlled current auxiliary converter in conjunction with a high-power gate-turn-off-thyristor-based converter. In this paper, a new load compensator based on this topology is proposed which does not require the information of the voltampere required by the load. As the requirement of the reactive voltampere calculator is eliminated, the scheme becomes insensitive to system frequency variations, temperature, and component aging. The control scheme required for the compensator is developed. The operation of the scheme is validated through extensive simulation studies. Experimental results obtained from a laboratory prototype are provided to demonstrate the viability of the scheme     

Efficiency, speed, and scaling of two-dimensional passive-dynamic walking

We address performance limits and dynamic behaviours of the two dimensional passive-dynamic bipedal walking mechanisms of Tad McGeer. The results highlight the role of heelstrike in determining the mechanical efficiency of gait, and point to ways of improving efficiency. We analyse several kneed and straight-legged walker designs, with round feet and and point-feet. We present some necessary conditions on the walker mass distribution to achieve perfectly efficient (zero-slope-capable) walking for both kneed and straight-legged models. Our numerical investigations indicate, consistent with a previous study of a simpler model, that such walkers have two distinct gaits at arbitrarily small ground-slopes, of which the longer-step gait is stable at small slopes. Energy dissipation can be dominated by a term proportional to (speed) 2 from tangential foot velocity at heelstrike and from kneestrike, or a term proportional to (speed) 4 from normal foot collisions at heelstrike, depending on the gait, ground-slope, and walker design. For all zeroslope capable straight-legged walkers, the long-step gaits have negligible tangential foot velocity at heelstrike and are hence especially fast at low power. Some apparently chaotic walking motions are numerically demonstrated for a kneed walker.