Study of Na2O-SiO2-Fe2O2-Y2O3 glass by Mössbauer and EPR spectroscopy

Mössbauer, EPR and magnetization experiments have been carried out on the glass composition Na₂O-SiO₂-Fe₂O₂-Y₂O₃ in which yttrium iron garnet (YIG) can be precipitated by suitable heat-treatment. The measurements have been carried out on the as-quenched sample as well as samples heat-treated for 4 h at 400, 500, 600, 650, 700, 750, 810 and 850 C. Mössbauer spectra from the as-quenched sample as well as the first six samples showed a quadrupole splitting while the last two samples, as well as the sample heat-treated (i) by a two-stage process at 600 C and then at 750 C for 4 h each, and (ii) at 700 C for 40 h, showed a hyperfine as well as quadrupole splitting. The behaviour of the isomer shift (IS) and quadrupole splitting (E) with the heat-treatment temperature show significant changes at the glass transition and crystallization temperatures. The Mössbauer data have been found consistent with optical and electron micrographs which show a large variation in particle size of the precipitated magnetic phase. This has been further correlated with EPR and magnetization data.     

ParFUM: a parallel framework for unstructured meshes for scalable dynamic physics applications

Unstructured meshes are used in many engineering applications with irregular domains, from elastic deformation problems to crack propagation to fluid flow. Because of their complexity and dynamic behavior, the development of scalable parallel software for these applications is challenging. The Charm++ Parallel Framework for Unstructured Meshes allows one to write parallel programs that operate on unstructured meshes with only minimal knowledge of parallel computing, while making it possible to achieve excellent scalability even for complex applications. Charm++’s message-driven model enables computation/communication overlap, while its run-time load balancing capabilities make it possible to react to the changes in computational load that occur in dynamic physics applications. The framework is highly flexible and has been enhanced with numerous capabilities for the manipulation of unstructured meshes, such as parallel mesh adaptivity and collision detection.     

Microstrip bandpass filter design using split‐path method and optimized curvature corrections

Bandpass filters with wide pass‐band are an essential requirement in various equipments of satellite and defence communication sectors. Here a method of split‐path interactions is proposed to approximately predict the resonant frequency and topology of bandpass filters which otherwise fall under the category of heuristic designs. Curved transmission lines are often required to make filter structures physically compact; however, curvature effects create errors in the theoretical (design) prediction of resonant or central frequencies for bandpass filter design. Earlier propositions on curvature corrections had been considerably precise, but recent design standards demand even higher accuracies. The prime feature of this work is the use of a meta‐heuristic optimization (i.e. Particle Swarm Optimization) technique in curvature corrections for the first time which brings accuracies of over 99% in the corrected results. The split paths used in this design are suitably curved, with the proposed optimized curvature correction technique, so as to attain a compact size of the filter. The resulting filter has a low insertion loss of around −1.00 dB and a sharp stopband cut‐off. Fabrication was done on a FR4 microstrip substrate with a good agreement between measured and simulated results. Copyright © 2015 John Wiley & Sons, Ltd.     

Using TCP flow-aggregation to enhance data experience of cellular wireless users

All over the world Global System for Mobile Communication (GSM) cellular mobile networks have been upgraded to support the "always-on" general packet radio service (GPRS). Despite the apparent availability of levels of bandwidth not dissimilar to that provided by conventional fixed-wire telephone modems, the user experience using GPRS is still considerably poor. In this paper, we examine the performance of protocols such as transmission control protocol (TCP) over GPRS, and show how certain network characteristics interact badly with TCP to yield problems such as: link underutilization for short-lived flows, excess queueing for long-lived flows, acknowledgment bunching, poor loss recovery, and gross unfairness between competing flows. We present the design and implementation of a transparent TCP proxy that mitigates many of these problems without requiring any changes to the TCP implementations in either mobile or fixed-wire end systems. The proxy is interposed in the cellular provider's network, and splits TCP connections transparently into two halves-the wired and wireless sides. Connections destined for the same mobile host are treated as an aggregate due to their statistical dependence. We demonstrate packet scheduling and flow control algorithms that use information shared between the connections to maximize performance of the wireless link, while interworking with unmodified TCP peers. We also demonstrate how fairness between flows and response to loss is improved, and that queueing and, hence, network latency is reduced. We discuss how TCP enhancing proxies could be transparently deployed, and conclude that installing such a proxy into GPRS network would be of significant benefit to users.     

Metal-semiconductor nanojunctions and their rectification characteristics

Junctions of silver-copper oxide and silver-zinc oxide, respectively were prepared within the pores of diameters, 20 nm, in anodic aluminium oxide membranes. Voltage-current characteristics were measured over the temperature range 373–573 K which showed rectification behaviour. Using the standard equation the difference between the work functions of the metal and the semiconductor was calculated. This showed a variation with the temperature of measurement. This is explained as arising due to the effect of pressure generated as a result of thermal expansion of the metallic phases concerned between the electrodes. This is consistent with the theoretical prediction of Fermi level shifting of the semiconductor within the bandgap as a function of pressure. Dedicated to Prof. C N R Rao     

Fem Analysis of Progressive Failure for Composite Hypar Shells

Strength of Materials - The finite element method is used to to study progressive failure aspects of laminar composite skewed hypar shells with straight edges employing the eight-node isoparametric...     

Effect of Cold Deformation on the Machinability of a Free Cutting Steel

The effect of cold deformation on the machinability of a free cutting steel has been investigated through characterization of the variation in size and morphology of the sulfide inclusions. The machinability has been indexed in terms of cutting force, surface roughness, and chip characteristics. The possible interrelations between inclusion characterizing parameters and machinability indices have been examined. Increased cold deformation was found to increase interinclusion spacing as well as aspect ratio of the inclusions. These variations in inclusion characteristics, in turn, were found to reduce the cutting forces and the chip length up to a critical amount of deformation. The results highlight the influence of inclusion characterizing parameters on machinability characteristics of free cutting steels.     

Bending of Composite Stiffened Hypar Shell Roofs under Point Load

The present paper applies a combination of an eight noded shell element with a three noded beam element, both curved and isoparametric to solve a bending problem of a composite stiffened hypar shell subjected to a concentrated load. Benchmark problems are solved to validate the suitability of the approach and a wide spectrum of stiffened hypar shell problems are solved by varying the lamination and curvature of simply supported and clamped shell surfaces. Different positions of stiffeners, both in plan and section, are considered together with variation of stiffener depth. Both static deflections and force/moment resultants are examined thoroughly. The performances of the different shell options are studied by arranging them rankwise and through a typical relative performance matrix, which will enable a designer to make a rational choice between a number of options.     

Finite element free vibration analysis of conoidal shells

Doubly curved conoidal shells are increasingly used for various industrial structures. Conoidal shells are aesthetically appealing and, being ruled surfaces, provide ease of casting. The variation of curvature is the difficulty enountered in the analysis of these shells. The finite element method is used here for the analysis of generalized doubly curved shells and is applied to truncated and full conoids of different boundary conditions, aspect ratios and degrees of truncation. An eight-noded isoparametric finite element with five degrees of freedom per node, including three translations and two rotations, is utilized. The accuracy is checked by comparing the results obtained by the present analysis with those existing in the literature. Results are presented for different conoidal shells and a set of conclusions are arrived at based on a parametric study.     

Rapid melting and solidification of a surface layer

A one-dimensional computer heat flow model is used to investigate the effect of high intensity heat fluxes,e.g. those achieved via continuous CO2 laser radiation, on the important surface layer melting and subsequent solidification variables of three substrate materials: aluminum, iron, and nickel. Temperature profilesvs time, melting, and solidification interface velocities, heating, and cooling rates in the surface layers of the three metals are calculated. Results are presented in a general form to permit determination of these variables for large ranges of absorbed heat fluxes and times. General trends established show that temperature gradients in the liquid and solid phases and interface velocities are directly proportional to the absorbed heat flux, whereas melt depth is inversely proportional to the absorbed heat flux. Average cooling rates comparable to splat cooling can be achieved by increasing the heat flux and reducing the dwell time of the incident radiation. An order of magnitude increase in the absorbed heat flux results in a corresponding two orders of magnitude increase in average cooling rates in the liquid during solidification of crystalline and noncrystalline structures. Formerly Research Associate, Formerly Research Associate, Formerly Research Associate,