Melting characteristics of magnesium—lithium alloys

Mg-Li-Al alloys containing 4–14 wt% Li and 1.5 wt% Al have been prepared by melting Mg/Mg-Al master alloy and Li separately under MgCl2 + KCl + MgO + CaF₂ and LiCl + LiF flux covers, respectively, and mixing the two together. The observed lithium loss and the pick-up of impurity elements in the melt have been correlated with various physico-chemical phenomena occurring during melting. The effect of holding time on melt composition was also examined. The results indicate that it is possible to control the alloy composition within specified limits by the selection of proper melting fluxes and crucible materials and by restricting the holding time to the minimum possible. These findings suggest that flux-cover melting is a viable route for the production of sound cast ingots of highly reactive magnesium—lithium alloys.     

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.     

A mobile bazaar for wide-area wireless services

We introduce MoB, an infrastructure for collaborative wide-area wireless data services. MoB proposes to change the current model of data services in the following fundamental ways: (1) it decouples infrastructure providers from services providers and enables fine-grained competition, (2) it allows service interactions on arbitrary timescales, and, (3) it promotes flexible composition of these fine-grained service interactions based on user and application needs. At the heart of MoB is an open market architecture in which mobile users can opportunistically trade various services with each other in a flexible manner. In this paper we first describe the overall architecture of MoB including various enablers like user reputation management, incentive management, and accounting services. We next present our experience from both simulations as well as our prototype implementation of MoB in enhancing application performance in multiple different scenarios—file transfers, web browsing, media streaming, and location-enhanced services. This work is supported in part by NSF grants CNS-0520152, CNS-0639434, CNS-0627589 and CNS-0627102. Rajiv Chakravorty received the B.E. degree from Nagpur University, Nagpur, India, in 1997 and the M.Tech. degree form the Indian Institute of Technology, Delhi in 1999. He is working towards the Ph.D. degree at the Computer Laboratory, University of Cambridge, U.K. In 2005 he was a visiting research scholar in the Department of Computer Sciences, University of Wisconsin, Madison. He has worked with Philips Research, ASA Laboratories, Eindhoven, The Netherlands. He also pursued research at ComNets, RWTH-Aachen, Germany. His current interests include mobile and wireless systems, and networking. He is a recipient of DAAD Scholarship Award from Germany, and the Sun Microsystems Scholarship and the Hughes Hall Commonwealth scholarhip from Cambridge Univeristy. Sulabh Agarwal received the B.Tech. degree in Computer Science and Engineering from Indian Institute of Technology, Delhi in 2000, and the M.S. degree in Computer Science from University of Maryland, College Park in 2002. His research interest is in the area of computer networking. Suman Banerjee received the B.Tech. degree in Computer Science and Engineering from Indian Institute of Technology, Kanpur in 1996, and the M.S. and the Ph.D. degrees in Computer Science from University of Maryland, College Park in 1999 and 2003 respectively. He is an Assistant Professor of Computer Sciences at University of Wisconsin-Madison and heads the Wisconsin Wireless and NetworkinG Systems (WiNGS) laboratory. His broad research interests are in the areas of networking and distributed systems with a special focus in the area of wireless and mobile networking systems. Ian Pratt received the Ph.D. in Computer Science from University of Cambridge, Cambridge, U.K. He was elected a Fellow of King’s College, Cambridge, U.K., in 1996. He is a Senior Faculty member at the Computer Loboratory, University of Cambridge, Cambridge, U.K. He is a a leader of the Systems Research Group, where he has been architect of a number of influential projects, including the Desk Area Network workstation, the Cambridge Open Mobile System, the Xen Virtual Machine Monitor, and the XenoServer infrastructure for global computing. His research interests cover a broad range if systems topics, including computer architecture, operating system design, mobile systems, and networking.     

Rapid melting and solidification of a surface layer

Metallurgical and Materials Transactions B - 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...     

Microstructural studies of glass-metal composites produced by ion-exchange and hydrogen treatments

Detailed electron micrographic studies have been carried out on float glass surface subjected to sodium ? copper ion-exchange in molten salts followed by a reduction treatment in hydrogen. Spherical copper particles of diameters ranging from 50 to 300 å are formed in the glass matrix depending on the ion-exchange and reduction temperatures. The nucleus density of these particles is maximum at around 450?C. Phase separation in glasses whether incipient or induced by ion-exchange, increases considerably the nucleus density when such samples are subsequently reduced. This is ascribed to the increase in the number of copper atoms surrounding the nucleation sites in the phase separated glasses. The optical absorption spectra of the glass-metal composites show two bands, namely at 17 400 cm^?1 and 23 000 cm^?1 respectively. The absorption maxima for both the bands occur for specimens reduced at temperatures between 450 and 500? C corresponding to the temperature of maximum nucleus density. The bands at 17 400 cm^?1 and 23 000 cm^?1 are assigned to the conduction resonance and plasma resonance respectively as predicted by Maxwell-Garnet theory on aggregated metal systems dispersed in a dielectric matrix.     

Glass-metal particulate composites

Oxide glasses containing ultrafine metal particles have interesting physical properties and have been widely used in practical systems. The various preparational techniques developed so far for making these materials are discussed. Electrical conduction in these composites is controlled by electron tunnelling between the metal islands. At high electric fields certain glasses containing bismuth granules show a memory switching effect. The latter has been explained by a particle stretching model. Optical absorption characteristics of these composites can be explained on the basis of various effective medium theories developed so far for inhomogeneous materials. Glasses containing ferromagnetic metal grains show a superparamagnetic behaviour with a transition temperature below 300 K. Improvement in the mechanical properties of glasses can be achieved by incorporating metal particles of suitable characteristics within them. In this paper the present state of understanding of all these properties is reviewed.     

Mechanical properties of glass fibres containing aluminium dispersoids

Glass fibres containing metallic aluminium dispersoids up to 7.5 at% AI have been made using ceramic bushings. The metallic granules have diameters ranging from 5 to 40 nm. A new technique based on strength-strain regression analysis has been used to determine the Young's moduli of the glass fibres. The Weibull parameters have been evaluated by both the graphical regression (GRE) and maximum likelihood (MLE) techniques. Fracture studies have also been carried out. The presence of aluminium particles increases the Young's modulus of the fibres but reduces the strength. The latter arises due to the metallic particles acting as stress concentrators within the glass matrix.