Effect of sillimanite beach sand composition on mullitization and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

Mullite was developed by reaction sintering of sillimanite beach sand and calcined alumina. Two varieties of sillimanite beach sand viz. S and Z having different compositions were selected. Synthesis and properties of mullite were very much dependent on the sillimanite beach sand composition. Presence of higher amount of impurities in the Z-variety of sillimanite sand favours the densification by liquid phase formation. Presence of zircon in Z-variety increases the hardness and fracture toughness. Alumina addition improves the mechanical/thermomechanical properties of the samples. Mullite retains the usual orthorhombic habit of sillimanite. Rounded to sub rounded zirconia dispersed within the mullite matrix of the sample ZA is noticed.     

A model for accurate predictions of self-diffusivities in liquid metals, semimetals, and semiconductors

By combining the modified Stokes-Einstein formula with the authors’ model for the melting-point viscosity, the authors present a model for accurate predictions of self-diffusivity of liquid metallic elements. The model is expressed in terms of well-known physical quantities and has been applied to various liquid metallic elements for which experimental data are available. The results of calculations show that agreement with experimental data is excellent; the uncertainties in the calculations of the self-diffusivities in various liquid metallic elements are equal to the uncertainties associated with experimental measurements. Also, the authors propose an expression for the temperature dependence of self-diffusivity in liquid metallic elements in terms of melting-point temperature. Using the model, self-diffusivity data are predicted for liquid iron, cobalt, nickel, titanium, aluminum, magnesium, silicon, and so forth.     

Performance analysis of long-lived transaction processing systemswith rollbacks and aborts

Increasing the parallelism in transaction processing and maintaining data consistency appear to be two conflicting goals in designing distributed database systems (DDBSs). This problem is especially difficult if the DDBS is serving long-lived transactions (LLTs). A special case of LLTs, called sagas, has been introduced that addresses this problem. A DDBS with sagas provides high parallelism to transactions by allowing sagas to release their locks as early as possible. However, it is also subject to an overhead, due to the efforts needed to restore data consistency in the case of failure. We conduct a series of simulation studies to compare the performance of LLT systems with and without saga implementation in a faulty environment. The studies show that saga systems outperform their nonsaga counterparts under most of conditions, including heavy failure cases. We thus propose an analytical queuing model to investigate the performance behavior of saga systems. The development of this analytical model assists us to quantitatively study the performance penalty of a saga implementation due to the failure recovery overhead. Furthermore, the analytical solution can be used by system administrators to fine-tune the performance of a saga system. This analytical model captures the primary aspects of a saga system, namely data locking, resource contention and failure recovery. Due to the complicated nature of the analytical modeling, we solve the model approximately for various performance metrics using decomposition methods, and validate the accuracy of the analytical results via simulations     

An improved bacterial foraging algorithm for combined static/dynamic environmental economic dispatch

Economic dispatch is carried out at the energy control center to find out the optimal output of thermal generating units such that power balance criterion is met, unit operating limits are satisfied and the fuel cost is minimized. With growing environmental awareness and strict government regulations throughout the world, it has become essential to optimize not only the total fuel cost but also the harmful emissions, both, under static as well as dynamic conditions. The static environment economic dispatch finds the optimal output of generating units for a fixed load demand at a given time, while the dynamic environmental economic dispatch schedules the output of online generators with changing power demands over a certain time period (normally one day) so as to minimize these two conflicting objectives, simultaneously. In this paper, the price penalty factor approach is employed for simultaneous minimization of cost and emission. The generator ramp rate constraints, non-convex and discontinuous nature of cost function and the large number of generators in practical power plants, make this problem very difficult to solve. Here, a fuzzy ranking approach is employed to identify the solution which offers the best compromise between cost and emission objectives.     

Effect of laser irradiation on the electrical properties of amorphous germanium films

Amorphous films of germanium were grown using a vacuum evaporation technique, on glass substrates kept at room temperature. As-grown films were irradiated with Q-Switched Nd-YAG laser pulses (=1.06 m, 20nsec, 10 to 50Jcm^–2). The d.c. conductivity measurements were made in the temperature range 77 to 300 K. It was observed that the effect of laser irradiation was similar to the effect caused by the thermal annealing of the films. The d.c. conductivity data were analysed in the light of Mott's theory of a variable range hopping conduction process.     

Dual segment rectangular dielectric resonator antenna with metamaterial for improvement of bandwidth and gain

The simulation and experimental studies of an aperture‐coupled wideband dual segment rectangular dielectric resonator antenna with metamaterial for C‐band applications are presented in this paper. The antenna consists of Alumina (Al₂O₃) ceramic as upper segment and Teflon as lower segment. The combination of circular‐shaped coplanar split‐ring resonator and conducting strip has been used as metamaterial superstrate. With the use of metamaterial superstrate, the bandwidth of the antenna is increased by 48% through simulation and 22% experimentally. The broadside radiation pattern of the antenna is converted into directive radiation pattern with reduced beamwidth when metamaterial superstrate is used. The peak gain of the antenna is also enhanced by 33% through simulation and 31% experimentally with the use of metamaterial superstrate. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:646–655, 2014.     

Studies on bitumen production from North Rumaila crude oil

In the present investigation, the effect of three process variables viz., air rate, temperature and time of oxidation has been studied to determine the possibility of making paving bitumens from North Rumaila Crude Oil. In order to have flexibility in the choice of proper feedstock for bitumen production, the effect of these process parameters was studied on three different vacuum residues. Air rate and temperature of oxidation were optimised to produce a bitumen product having less temperature susceptibility. The composition studies of typical feeds and oxidised products indicate that mainly “saturates” components get converted to “asphaltics” on air blowing.     

Synthesis and densification of magnesium aluminate spinel: effect of MgO reactivity

Stoichiometric magnesium aluminate spinel was synthesized by reaction sintering of alumina with caustic and sintered magnesia. The volume expansion of 5–7% during MgAl₂O₄ formation was utilized to identify the starting temperature of spinel formation and densification by high temperature dilatometry. The magnesia reactivity was determined by measurement of crystallite size and specific surface area. Caustic magnesia and sintered magnesia behave differently vis-à-vis phase formation and densification of spinel. Densification of stoichiometric Mag-Al spinel was carried out between 1650 and 1750 °C. Attempts were made to correlate the MgO reactivity with microstructure and densification of spinel.