Quenching-circumvented ergodicity in relaxor Na1/2Bi1/2TiO3-BaTiO3-K0.5Na0.5NbO3

Quenching alkaline bismuth titanates from sintering temperatures results in increased lattice distortion and consequently higher depolarization temperature. This work investigates the influence of quenching on the ergodicity of relaxor Na_1/2Bi_1/2TiO₃-BaTiO₃-K_0.5Na_0.5NbO₃. A distinct departure from ergodicity is evidenced from the increase in remanent polarization and the absence of frequency dispersion in the permittivity response of poled samples. Further, the samples exhibit enhanced negative strain upon application of electric field, indicating proclivity towards correlated polar nanoregions, corroborated by the enhanced tetragonal distortion. As a result, ergodic relaxor Na_1/2Bi_1/2TiO₃-6BaTiO₃-3K_0.5Na_0.5NbO₃ exhibits a depolarization temperature of 85°C with a 60% increase in remanent polarization and approximately a threefold increase in remanent strain upon quenching. Quenching-induced changes in the local environment of Na⁺ and Bi³⁺ cations hinder the development of ergodicity promoted by the A-site disorder. These results provide new insight into tailoring ergodicity of relaxor ferroelectrics.     

Uses of α-Fe2O3 and fly ash as solid adsorbents

Solid adsorbents have shown great promise for control of particulate and non-particulate matter and as gas sensing devices in recent times. In the present study, adsorption of environmental toxic pollutant such as lead ions on solid adsorbents viz. α-Fe₂O₃ and fly ash, are reported. Considerable adsorption was observed on fly ash when compared to α-Fe₂O₃ surface. These studies are characterized by employing solid state and solution studies.     

Integrated Placement and Skew Optimization for Rotary Clocking

The clock distribution network is a key component of any synchronous VLSI design. High power dissipation and pressure volume temperature-induced variations in clock skew have started playing an increasingly important role in limiting the performance of the clock network. Rotary clocking is a novel technique which employs unterminated rings formed by differential transmission lines to save power and reduce skew variability. Despite its appealing advantages, rotary clocking requires flip-flop locations to match predesigned clock skew on rotary clock rings. This requirement poses a difficult chicken-and-egg problem which prevents its wide application. In this paper, we propose an integrated placement and skew scheduling methodology to break this hurdle, making rotary clocking compatible with practical design flows. A network flow based flip-flop assignment algorithm and a cost-driven skew optimization algorithm are developed. We also present an integer linear programming formulation that minimizes maximum capacitance loaded at any of the rotary rings, thereby maximizing the operating frequency. Experimental results on benchmark circuits show that our method can reduce the tapping cost (measured as the total length of the wire segments connecting the rotary rings to the clock sinks) for rotary clocking by 33%-53%     

Heat transfer at the metal/substrate interface during solidification of Pb-Sn solder alloys

Heat transfer analysis during the solidification of lead, tin, and two lead-base solder alloys against two different chill materials (steel and copper) was carried out with and without flux coating on the chill surface. Temperatures at two known locations inside the chill and casting were recorded as the casting started solidifying, and the acquired chill temperature data were used for solving a one-dimensional heat conduction equation inversely to yield the metal/chill interfacial heat flux and chill surface temperature as a function of time. The initial heat flux was high due to good contact at the metal/chill interface. As the casting started solidifying, there was a reduction in the heat flux due to the nonconforming contact at the interface. Chills with flux coating resulted in finer microstructures near the solder/substrate interface compared to those obtained with uncoated chills. The fineness of the microstructure also increased when copper was used as the chill material. The estimated total heat flow was found to be higher with flux-coated and copper chills. This was in good agreement with the finer microstructures obtained near the solder/chill interfacial region for solidification against copper chills and chills with flux coating on their surface.     

Atmospheric stagnation,recirculation and ventilation characteristics at Kakrapar atomic power station site

This paper describes the meteorological characteristics of Kakrapar Atomic Power Station (KAPS) site (inland site) by using the integral parameters developed by Allwine and Whiteman. Meteorological data measured during the period 1995–2000, were analysed. The integral quantities related to the occurrence of stagnation, recirculation and ventilation characteristics were studied for KAPS site to asses the dilution potential of the atmosphere. Wind run and recirculation factors were calculated for a 24-h transport time using 6 years of hourly surface measurements of wind speed and direction. The occurrence of stagnation, recirculation and ventilation characteristics during 1995–2000 at KAPS site is observed to be 19.2% of the time, 21.0% of the time and 40.0% of the time, respectively. The presence of strong monsoon winds with predominant wind direction SW during monsoon season lead to higher ventilation (60.4% of the monsoon season). The presence of light winds and more dispersed winds during winter season with predominant wind directions E and ENE resulting more stagnation (26.5% of the winter season) and recirculation (32.6% of the winter season). Thus this study will serve as an essential meteorological tool to understand the transport mechanism of atmospheric releases from any industry including nuclear industry.     

Novel Fast Lithium Ion Conduction in Garnet-Type Li5La3M2O12 (M = Nb, Ta)

Lithium metal oxides with the nominal composition Li₅La₃M₂O₁₂ (M = Nb, Ta), possessing a garnetlike structure, have been investigated with regard to their electrical properties. These compounds form a new class of solid-state lithium ion conductors with a different crystal structure compared with all those known so far. The materials are prepared by solid-state reaction and characterized by powder XRD and ac impedance to determine their lithium ionic conductivity. Both the niobium and tantalum members exhibit the same order of magnitude of bulk conductivity (∼10⁻⁶ S/cm at 25°C). The activation energies for ionic conductivity (<300°C) are 0.43 and 0.56 eV for Li₅La₃Nb₂O₁₂ and Li₅La₃Ta₂O₁₂, respectively, which are comparable to those of other solid lithium conductors, such as Lisicon, Li₁₄ZnGe₄O₁₆. Among the investigated materials, the tantalum compound Li₅La₃Ta₂O₁₂ is stable against reaction with molten lithium. Further tailoring of the compositions by appropriate chemical substitutions and improved synthesizing methods, especially with regard to minimizing grain-boundary resistance, are important issues in view of the potential use of the new class of compounds as electrolytes in practical lithium ion batteries.     

A Grüneisen Relation on Constant-Pressure Lines

Grüneisen's constant, γ, is ideally temperature-independent on constant-volume lines; a similar constant, λ, which is ideally temperature-independent on isobaric lines, has been found. The comparison between γ and λ shows that both expressions contain the ratio of the volumetric thermal expansion coefficient to the specific heat capacity; γ has an additional temperature dependence due to the thermal part of the compressibility, whereas λ has only a slight thermal component due to the volume per unit mass. λ has been chosen so that λ=γ at the point where the temperature and pressure are both zero. For most materials it is expected that λ≥γ with a different temperature dependence. It is shown empirically for a selection of ceramics that λ is nearly temperature-independent and has a value between 0.7 and 1.4.     

Controlling failure using structural fuses for predictable progressive failure of composite laminates

Structural fuses have been used to bias and control failures in structural applications where predictability of the progressive failure or collapse response is important. Tailoring structural fuses by trial and error in large structures that have numerous possible load and failure paths is not possible because the optimum failure sequence is not known a priori. Using nondeterministic methods to tailor structural fuses is computationally expensive. A procedure for developing deterministic measures to optimize structural fuses is presented here. The progressive failure of composite laminates is used for demonstration. Structural fuses are optimized using a reliability optimization. The failure response characteristics of the laminate with optimum structural fuses are used to identify deterministic measures that correlate with high progressive failure predictability. The deterministic measures are validated by using them as surrogate design criteria in a deterministic optimization to optimize structural fuses that control failure and improve progressive failure predictability. The improvement in predictability of the deterministic optimum design achieved by using optimized structural fuses is better than that obtained by optimizing the ply angles of the laminate explicitly for predictability.     

Comprehensive approach to modeling threshold voltage of nanoscale strained silicon SOI MOSFETs

A comprehensive approach for modeling the threshold voltage of nanoscale strained silicon-on-insulator (SSOI) and strained Si-on-SiGe-on-insulator (SSGOI) MOSFETs is presented. The model includes the effect of strain in terms of Ge mole fraction and various other device parameters—channel length, channel doping, strained silicon film thickness, gate oxide thickness and gate work function. The accuracy of the proposed threshold voltage model is verified using two-dimensional numerical simulations. We have also demonstrated that our model can accurately predict the DIBL effects.     

Optimization of axisymmetric elastic modulus distributions around a hole for increased strength

Holes in engineering structures cause stress concentrations that often lead to failure. In nature, however, blood vessel holes (foramina) in load-bearing bones are not normally involved in structural failures. It has been found that this behavior is linked to the material distribution near the hole. In the present paper, we have investigated the effectiveness of optimizing the radial distribution of the isotropic elastic modulus around a circular hole to increase load-carrying capacity. Bezier curves were used to describe the radial distribution of the elastic modulus. Since changing the elastic modulus usually affects the strength, the ratio of maximum principal stress to strength was chosen as the objective function for optimization. Using non-dimensional analysis of the 2-D elasticity equations, we identified three parameters that govern the optimum design and are applicable to a wide range of materials, loading, and geometries. The first is a material parameter that describes the relationship between the strength and elastic modulus, the second is the geometric parameter given by the ratio of the optimized field to the hole radius, and the third is the biaxial load ratio. The effect of failure criterion choice on the optimum elastic modulus distribution is also investigated. Optimum elastic modulus distributions for materials whose strength increases faster than the stiffness, as density and/or composition is varied, completely eliminated the effect of the hole by locally stiffening areas that experience high stresses. When the strength lagged behind the stiffness, optimum designs were similar to those found in bones, and relied on modulus distributions that direct the loads away from the hole.