Preferential grain growth and improved fatigue endurance in Sr substituted PZT thin films on Pt(1 1 1)/TiOx/SiO2/Si substrates

Pb(Zr_0.5Ti_0.5)O₃ and (Pb_0.9Sr_0.1)(Zr_0.5Ti_0.5)O₃ thin films were grown on Pt/TiO_x/SiO₂/Si substrates by chemical solution deposition. 10% Sr substituted PZT film showed high degree of (0 0 1) type preferential grain growth. Surface morphology revealed a clear correlation between preferred grain orientation and grain size. Room temperature dielectric constant was 1200 and 700 for the PZT and PSZT films, respectively. Dielectric loss reduced with Sr substitution. PZT film showed severe fatigue, and hence the polarization reduced to 20% of the initial value (24 μC/cm²) after 10⁸ cycles where as PSZT showed less fatigue, 75% of the initial polarization (12 μC/cm²) was retained after 10⁸ switching cycles.     

Microwave-assisted synthesis and electrochemical characterization of TiNb2O7 microspheres as anode materials for lithium-ion batteries

TiNb₂O₇ microspheres are prepared via a microwave-assisted solvothermal method. The microwave irradiation lowers the compound formation temperature to 600°C, and highly crystalline TiNb₂O₇ powders are obtained upon calcination at 800°C. Morphological analysis of the sample shows uniformly distributed microspheres with a particle size of around 1 μm. The Li⁺-ion diffusion coefficient calculated from the electrochemical impedance result is around 1.21 × 10⁻¹³ cm² s⁻¹, which is 1.5 times higher than the sample obtained from the conventional solvothermal method. The TiNb₂O₇ sample derived from microwave yields a high discharge capacity of 299 mA h g⁻¹ at 0.1 C, whereas the sample synthesized via the conventional solvothermal process yields only 278 mA h g⁻¹ at 0.1 C. Excellent rate capabilities such as 220 mA h g⁻¹ at 5 C and 180 mA h g⁻¹ at 10 C are also observed for the microwave-assisted solvothermal sample. Moreover, the sample exhibits a large capacity retention of 95.5% after 100 discharge–charge cycles at 5 C. These results reveal the appropriateness of the microwave-assisted solvothermal process to prepare TiNb₂O₇ powders with superior properties for battery applications.     

Thermal Decomposition Of Carbonyl Sulfide At Temperatures Encountered In The Front End Of Modified Claus Plants

Understanding the kinetics of the formation and consumption of COS and CS₂ in the front end of the modified Claus process will be a significant step towards reducing the environmental impact of these plants. Specifically, homogeneous intrinsic rate expressions are needed for engineering design and simulation, which will lead to new, optimized ways of operating these plants. Hence, a high-temperature kinetic study of the COS decomposition reaction was carried out. Experiments were performed with inlet COS compositions in the range of 0.20-2.33 mol%, with pressures at 101-150 kPa and temperatures at 800-1100°C; these conditions cover the conditions typically encountered in the front end of the modified Claus process. The experimental results showed that COS conversion is dependent on the inlet concentration of COS, which contrasts with previously reported higher temperature studies. Finally, the COS decomposition kinetics were modeled as the sum of two reactions, which provided a satisfactory representation of experimental data.     

Some estimators of finite population variance using information on two auxiliary variables

Some estimators using information on two auxiliary variables for finite population variance are proposed, their bias and mean square error (MSE) are found, and their properties are analysed. As an illustration, an empirical study is also included.     

Geometrically non-linear formulation for two dimensional curved beam elements

This paper presents a geometrically non-linear formulation using a total lagrangian approach for the two dimensional curved beam elements. The beam element is derived using linear, paralinear and cubic-linear plane stress elements. The basic element geometry is constructed using the coordinates of the nodes on the element center line (η = 0) and the nodal point normals. The element displacement field is described using two translations of the node on the center line and a rotation about the axes normal to the plane containing the center line of the element. The existing beam element formulations are restricted to small nodal rotations between two successive load increments. The element formulation presented here removes such a restriction. This is accomplished by retaining non-linear nodal rotation terms in the definition of the displacement field and the consistent derivation of the element properties. The formulation presented here is very general and yet can be made specific by selecting appropriate non-linear functions representing the effects of nodal rotations. The element properties are derived and presented in detail. Numerical examples are also presented to demonstrate the behavior and the accuracy of the two dimensional beam elements for geometrically non-linear applications. In all cases comparisons made with theory and/or other published data show that the beam elements product accurate results and permit large load increments with good convergence characteristics.     

The oviposition and development of Sitophilus oryzae (L.) in different high-yielding varieties of wheat

Studies on the oviposition and development of Sitophilus oryzae in high-yielding varieties of wheat (PV-18, Sonora-64, Kalyan Sona, S-308 and S-307) were conducted at all combinations of the three temperatures, 19°C, 25°C and 30°C and four relative humidities, 45, 60, 75 and 90 per cent. Oviposition and development of the weevil were better on larger kernels. The rates of oviposition and development were affected by certain other factors besides the physical nature of the kernel and its bran and endosperm. According to the development index ($\text{log}\text{n}\text{Av}$) and number of eggs deposited, varieties in increasing order of suitability were Sonora-64 > PV-18 > Kalyan Sona > S-308 > S-307. Oviposition and development were best in varieties with the highest moisture content at any level of relative humidity. Oviposition and development were best at 75% r.h. or 15·0–15·5 per cent moisture content in all varieties. Oviposition and development rates were greater at 30°C and slower at 18°C than at 25°C. Of the conditions examined 30°C and 75% r.h. was the best for oviposition and development of S. oryzae.     

Step multiple quantum well enabled performance enhancement in InGaN/GaN based light-emitting diodes

In this work, we propose and investigate numerically InGaN/GaN based multiple quantum well (QW) blue light-emitting diodes (LEDs) with step quantum well (InGaN)/barrier (GaN) structures. We design four LED structures—(LED-A) InGaN/GaN rectangular quantum well, (LED-B) one down step in the middle of the QW created using sharp increase in In contents, (LED-C) one down step in the middle of the QW and the other down step in the right barrier away from QW and (LED-D) similar to LED-C barring one down step in the left barrier facing the QW. Using well-calibrated APSYS simulation program we compare the variation of output power and internal quantum efficiency of LEDs with input injection current and analyze them in the light of energy band diagram, electric field distribution, carrier concentration and radiative recombination rate. The proposed LED-D exhibits significant improvement in optical output power ~ 180.7% compared to conventional LED-A. Furthermore unlike other three LED structures, LED-D shows a very low internal quantum efficiency droop of 5.1% only at injection current of 120 mA.

     

Lumped mass matrices with non−zero inertia for general shell and axisymmetric shell elements

A diagonal lumped mas formulation with non?zero inertia terms is presented for Ahmad's general shell element. The effect of co?ordinate transformation of the mas matrix is demonstrated. Due to arbitray co?ordinate transformation on nodal variables, the diagonal lumped mas matrix becomes a banded matrix of half bandwidth three. It is shown that with some approximations this matrix can be made diagnoal without effecting the results appreciably. Numerical examples are presented to illustrate the accuracy of the formulation. Similar lumped mass matrix formulation is also given for axisymmetric shell elements.