Emission constrained power system planning: a pinch analysis based study of Indian electricity sector

In the light of rising electricity demands and a need to curb carbon dioxide emissions, this article investigates the problem of power system planning with emission targeting. A pinch analysis based approach is utilised here. The key aspect of this study is investigating the parameters that decide the priority of one type of power plant over another. For this, a quantity called prioritised cost, a trade off between cost incurred and emission from a new power plant is identified. In addition to cost and emission factor of a power plant, a third parameter, the present state of the system, also plays a significant role in deciding a power plant’s prioritised cost. The analysis done proves that new power plants can be added to the system in the order of their prioritised cost. This methodology is applied to Indian power sector as a case study. Two different problems, involving minimisation of investment and annualised cost, are considered. It is observed that renewables are slightly more favoured when the objective is to minimise overall cost and not just the capital investment. In both cases, the energy mix is still dominated by coal-based power generation. The share of renewables was seen to increase with more stringent emission targets when the objective was to minimise overall cost.     

Multiple-band large-signal characterization of millimeter-wave double avalanche region transit time diode

A large-signal method based on non-sinusoidal voltage excitation model is used to study the DC and RF characteristics of Double Avalanche Region (DAR) Silicon Transit Time diode. A large-signal simulation program based on drift-diffusion model is developed for this study. The simulation results show the existence of several distinct negative conductance bands in the admittance characteristics separated by positive conductance. Thus the DAR device is capable of delivering RF power not only at the design frequency but also at several frequency bands higher than the design frequency band in the mm-wave regime. A comparative study with DDR Si device designed to deliver RF power at a particular mm-wave frequency band shows that DAR Si device is capable of delivering significantly higher RF power not only at the designed mm-wave frequency band, but also at higher frequency bands.     

Alkali metal modified nano-silicalite-1: an efficient catalyst for transesterification of triacetin

Nanocrystalline Silicalite-1 was synthesized by conventional hydrothermal method and transformed into efficient solid base catalyst by modification with alkali metals like lithium, potassium and cesium. The synthesized and modified catalyst was characterized by X-ray diffraction, scanning electron microscopy, nitrogen adsorption/desorption, Infra-red spectroscopy, thermogravimetry and basicity determination. The catalysts were tested for transesterification reaction of short triglyceride triacetin with methanol. 1–3 wt% alkali metal ions have been loaded on nano Silicalite-1 and used for transesterification reaction. Among the tested catalyst, 3 % potassium loaded Silicalite-1 (KS-3) showed highest reactivity giving 94 % triacetin conversion, and 98 mol% selectivity for methyl acetate. Reaction parameters such as triglyceride/alcohol molar ratio, catalyst amount, time and temperature were optimized with KS-3 catalyst. Kinetic studies were also done and found that transesterification of triacetin follows first order dependence.     

A combined experimental and theoretical approach to establish the relationship between shear force and clay platelet delamination in melt-processed polypropylene nanocomposites

In this article, a combined experimental and theoretical approach has been proposed to establish a relationship between the required shear force and the degree of delamination of clay tactoids during the melt-processing of polymer nanocomposites. Polypropylene (PP) was selected as a model polymer, and nanocomposites of PP with organically modified clay were prepared by a master batch dilution technique in a twin-screw extruder. The effect of PP throughput during the dilution of the master batch on the dispersion and orientation of clay platelets were studied in detail. Powder X-ray diffraction, small and wide angle X-ray scattering and high resolution transmission electron microscopy were used to study the structure and morphology of the obtained nanocomposites. The results showed that a lower feeding rate led to the orientation of clay platelets almost in the direction of extrusion. The adhesive force and the interaction energy between the clay platelets were theoretically calculated using the Hamaker approach. The analysis showed that the peeling mechanism is a practical explanation for the delamination of clay platelets during melt extrusion and that the dimensions of the clay platelet tactoids play an important role in the peeling due to the shear stress.     

Synthesis of nanocrystalline hydroxyapatite using surfactant template systems: Role of templates in controlling morphology

Hydroxyapatite (HA) nanopowder was synthesized by reverse microemulsion technique using calcium nitrate and phosphoric acid as starting materials in aqueous phase. Cyclohexane, hexane, and isooctane were used as organic solvents, and Dioctyl sulfosuccinate sodium salt (AOT), dodecyl phosphate (DP), NP5 (poly(oxyethylene)₅ nonylphenol ether), and NP12 (poly(oxyethylene)₁₂ nonylphenol ether) as surfactants to make the emulsion. Effect of synthesis parameters, such as type of surfactant, aqueous to organic ratio (A/O), pH and temperature on powder characteristics were studied. It was found that the surfactant templates played a significant role in regulating the morphology of the nanoparticle. Hydroxyapatite nanoparticle of different morphologies such as spherical, needle shape or rod-like were obtained by adjusting the conditions of the emulsion system. Synthesized powder was characterized using X-ray diffraction (XRD), BET surface area and transmission electron microscopy (TEM). Phase pure HA nanopowder with highest surface area of 121 m²/g were prepared by this technique using NP5 as a surfactant. Densification studies showed that this nanoparticle can give about 98% of their theoretical density. In vitro bioactivity of the dense HA compacts was confirmed by excellent apatite layer formation after 21 days in SBF solution. Cell material interaction study showed good cell attachment and after 5 days cells were proliferated on HA compacts in OPC1 cell culture medium. The results imply this to be a versatile approach for making hydroxyapatite nanocrystals with controlled morphology and excellent biocompatibility.     

Bone cell–materials interaction on alumina ceramics with different grain sizes

The objective of this work was to study adhesion, proliferation and differentiation of osteoblast cells (OPC1) on alumina ceramic, a bio-inert material. Alumina ceramic with different average grain sizes, 1 μm and 12 μm, respectively, were used in as-prepared condition without any grinding and polishing to understand the influence of grain size on cell–material interactions. Scanning electron microscopy and confocal imaging were used to study attachment, adhesion and differentiation of OPC1 cells. Cells attached, proliferated and differentiated well on both the substrates. Adhesion of cells, as assessed by observing the production of vinculin, was found to be a consistent phenomenon on both the substrates. On day 5 of cell culture, significant cell-attachment was observed and vinculin was detected throughout cytoplasm. MTT assay showed that proliferation of OPC1 cells was consistently higher in the case of 12 μm-alumina. Cells of different morphology, nodular, plate-like as well as elongated, were found to get anchored at grains, grain boundaries as well as pores. On day 16, there were clear signs of mineralization as well. Over all, alumina with average grain size of 12 μm showed better cell-attachment, growth and differentiation compared to 1 μm grain size samples.     

Wear Performance of Laser Processed Tantalum Coatings

This first generation investigation evaluates the in vitro tribological performance of laser-processed Ta coatings on Ti for load-bearing implant applications. Linear reciprocating wear tests in simulated body fluid showed one order of magnitude less wear rate, of the order of 10(-4)mm(3)(N.m)(-1), for Ta coatings compared to Ti. Our results demonstrate that Ta coatings can potentially minimize the early-stage bone-implant interface micro-motion induced wear debris generation due to their excellent bioactivity comparable to that of hydroxyapatite (HA), high wear resistance and toughness compared to popular HA coatings.