Preparation and characterization of magnesium-aluminium-silicate glass ceramics

Synthesis of machinable quality magnesium aluminium silicate (MgO-Al₂O₃-SiO₂) for fabrication of insulators/spacers usable in high voltage applications under high vacuum conditions has been carried out following two different routes i.e. (i) sintering route, and (ii) glass route. A three-stage heating schedule involving calcination, nucleation and crystallization, has been evolved for the preparation of magnesium aluminium silicate (MAS) glass ceramic with MgF₂ as a nucleating agent. The effect of sintering temperature on the density of compacted material was studied. Microstructure and machinability of samples obtained from both routes were investigated. They were also characterized for microhardness. Initial studies on material obtained by glass route reveal that these samples are superior to those obtained from sintered route in respect of their high voltage breakdown strength and outgassing behaviour. Outgassing rate of 10⁻⁹ Torr l·s⁻¹ cm⁻² and breakdown strength of 160 kV/cm were obtained. Different types of spacers, lugs, nuts and bolts have been prepared by direct machining of the indigenously developed glass ceramic.     

Accurate estimation of statistical parametric variation in microelectronic test structures

Advanced technologies of microelectronic device fabrication need accurate determination of process parameters and their analysis. Test structures which represent individual process steps are incorporated in the design. Independent measurements can be carried out on these structures and the information is used as a feedback in order to achieve perfection at different stages of fabrication. This note presents an algorithm for analysis of measurement data and identification of defective sites on the wafer leading to an accurate yield analysis.     

Numerical assessment of heat transfer coefficient for preterm infant nursed under a radiant warmer

Body heat loss management is the primary concern with respect to a newborn, as excess heat loss or gain leads to hypo- or hyperthermia, respectively. The aim of this article is to numerically investigate the convection and radiation heat transfer coefficient of a newborn nursed under a radiant warmer. The preterm neonate manikin has five body segments (head, trunk, leg, arms, and back) placed in a relaxed spine position. In the present study, numerical simulations are carried out for body temperature ranging between 32.5°C and 40.1°C. Ambient air temperature is chosen from 22.77°C to 30°C as preferred room temperature in the analysis. Airflow and heat transfer under the radiant warmer are analyzed in two operational modes, that is, power-off and power-on modes. In the power-on mode, the convective heat transfer coefficient varies between 1.45 and 4.06 W/m² K, whereas the radiative heat transfer coefficient varies between 0.08 and 3.28 W/m² K under various operating conditions. The results obtained are numerically validated and found to be in fair agreement with the experimental results available in the open literature.     

On an interesting variant of the IMT quadrature

We indicate an interesting variant of the IMT quadrature. The IMT quadrature is known to converge exponentially in the presence of an end-point integrable singularity. The variant of IMT quadrature we indicate here retains this property and in addition it has exponential convergence for an integrand which has poles lying just below or above the mid-point of the integration interval.     

Network Lifetime Improved Optimal Routing in Wireless Sensor Network Environment

Wireless Personal Communications - In the field of Wireless Sensor Networks, major problem arises due to the unbalanced consumption of energy. The unbalanced consumption will reduce the lifetime of...     

Novel carbazole phenoxy-based methacrylates to produce high-refractive index polymers

A novel, high-refractive index homopolymer was produced by incorporating carbazole and phenol into the methacrylate monomer structure. The reaction of phenol with 9-(2,3-epoxypropyl)-carbazole, followed by the reaction of the carbazole phenoxy-based intermediate with methacryloyl chloride or methacrylic anhydride, and recrystallization from methanol, produced a good yield of highly pure carbazole phenoxy functionalized methacrylate monomer. Subsequent free radical polymerization or UV photopolymerization of the functionalized methacrylate monomer, in addition to copolymerizations with methyl methacrylate, provided for high-refractive index materials well suited for lightweight optical applications. Unlike N-vinyl carbazole, the novel carbazole phenoxy-based methacrylate readily copolymerized with methyl methacrylate. Statistical copolymers of carbazole based methacrylates with methyl methacrylate were produced by free radical solution polymerization in DMAC or by photopolymerization in DMF. The carbazole phenoxy-based methacrylate monomer was characterized for molecular weight using gel permeation chromatography (GPC), for melting point and glass transition temperature using differential scanning calorimetry (DSC), for decomposition using thermal gravimetric analysis (TGA), and for chemical composition by one- and two-dimensional ¹H nuclear magnetic resonance (NMR) spectroscopy and by elemental analysis. The AIBN initiated carbazole phenoxy-based methacrylate polymerization was followed using in situ FTIR, which showed the reaction to be complete within 40 min in DMAC at 90 °C. Refractive indices of the carbazole based methacrylate homopolymers and copolymers ranged from 1.52 to 1.63. PhotoDSC was used to determine the heat of polymerization (ΔH_p) for the carbazole phenoxy-based methacrylate (ΔH_p=−39.4 kJ/mol). The carbazole phenoxy-based methacrylate homopolymer had a surprisingly high onset of decomposition temperature (T_onset=316 °C). ¹³C NMR spectroscopy experiments and molecular modeling were used to explore the configuration of the polymerized carbazole phenoxy-based methacrylate. The lack of head-to-head linkages due to steric considerations reasonably explains the high thermal stability observed for the carbazole phenoxy-based methacrylate polymer.     

Knowledge coordination in transnational engineering projects:a practice-based study

Several multinational engineering firms offshore the delivery of engineering design or structural detail drawings to their globally distributed delivery centres. Studies have reported knowledge-sharing challenges when such work is co-ordinated across boundaries. This study takes a practice-based approach to explore knowledge-coordinating challenges across two multinational engineering firms that offshore projects to their global delivery centres in India. Data was collected from six infrastructure projects in the two delivery centres through direct observations augmented with real-time interviews and reviews of e-mails and project documents. This data was analysed qualitatively using ethnographic-coding techniques. Empirical findings identified a set of eight coordinating practices, many of which were emergent, which the teams creatively recombined and enacted as co-ordinating mechanisms that spanned organisational boundaries. Seven practices served to transfer knowledge and one practice transformed knowledge across onshore and offshore units. The study contributes to our understanding of co-ordinating by identifying emergent and informal coordinating practices in offshored construction projects and provides insights to practitioners on the boundary spanning capabilities of these practices.     

A review on particulate slurry erosive wear of industrial materials: In context with pipeline transportation of mineral−slurry

Pipeline transportation of slurry is being carried out all over the world. Slurry pipeline wear is one of the major problems associated with it. The wear rate of the slurry pipeline depends upon factors such as slurry properties, slurry particle properties, flow properties, and pipeline wall properties. Any change in these properties results in change in pipeline wear rate. There is a need to study the effect of individual properties, for predicting the slurry pipeline life span and also to find the methods to minimize the wear rate. In this review paper, an attempt has been made to discuss the parameters which are believed to be the primary factors that affect material wear rate. Several mechanisms and equations suggested by various researchers for the prediction of wear of materials are also reviewed. Most of the models incorporate the effects of only few parameters involved during the wear process. These equations are specific and valid up to limited operating conditions. No general equation have been evolved which can be used under any operating condition, with better accuracy. This can be attributed to lack of data at microscopic level and also to change in the wear mechanisms under various operating conditions.