Solder engineering for optoelectronic packaging

In addition to providing electrical connections, solder is useful in the formation of passive, precision alignments for optoelectronic packaging. Different designs have demonstrated micrometer-level alignment accuracies, and the aligned structures are becoming more and more complex. Solder engineering has been successfully introduced into the field of optoelectronics, and it is expected to be applied to many other areas demanding low-cost, precision alignments.     

Adaptive state-based multi-radio multi-channel multi-path routing in Wireless Mesh Networks

Wireless Mesh Networks (WMNs) are envisioned to seamlessly extend the network connectivity to end users by forming a wireless backbone that requires minimal infrastructure. Unfortunately for WMNs, frequent link quality fluctuations, excessive load on selective links, congestion, and limited capacity due to the half-duplex nature of radios are some key limiting factors that hinder their deployment. To address these problems, we propose a novel Adaptive State-based Multi-path Routing Protocol (ASMRP), which constructs Directed Acyclic Graphs (DAGs) from each Mesh Router (MR) to Internet Gateways (IGWs) and effectively discovers multiple optimal path set between any given MR-IGW pair. A congestion aware traffic splitting algorithm to balance traffic over these multiple paths is presented which synergistically improves the overall performance of the WMNs. We design a novel Neighbor State Maintenance module that innovatively employs a state machine at each MR to monitor the quality of links connecting its neighbors in order to cope with unreliable wireless links. We also employ a 4-radio architecture for MRs, which allows them to communicate over multiple radios tuned to non-overlapping channels and better utilize the available spectrum. Through extensive simulations using ns-2, we observe that ASMRP substantially improves the achieved throughput (～5 times gain in comparison to AODV), and significantly minimizes end-to-end latencies. We also show that ASMRP ensures fairness in the network under varying traffic load conditions.     

Mechanism of titanium sponge formation in the kroll reduction reactor

The Kroll process of magnesium reduction of titanium tetrachloride is used the world over the production of titanium metal in the form of sponge. Although the process has been in practice for the last five decades, there is no clear understanding of the reaction mechanism and sponge formation. The present study involved reduction experiments in a 2000 kg titanium sponge-capacity prototype reactor to develop a better understanding of TiCl₄ reduction of magnesium with respect to the process parameters. Experiments were also conducted in two smaller experimental reactors to study the temperature evolution during the process as a function of the TiCl₄ feed rate. Based on the results of all these experiments, a model has been proposed for the mechanism of sponge formation in the Kroll process.     

Design of vessels subjected to external pressure

An analytical procedure, developed to simulate the graphic method for the design of vessels subjected to external pressure or vacuum, suggested by the ASME Code, Section VIII, Division 1, is presented in this contribution. A comprehensive computer program based on this method is also presented. The program also covers the design of stiffener rings. The procedure can be easily extended to include other international standards such as the British and German codes, since the method is based on the concept of the number of lobes at collapse. The method produced reproducible results over the entire range of L/D₀ and D₀/t ratios of the code. The deviation observed at any point in this range is less than 0.5% for factor A. The variation in allowable pressure is less than 2%.     

Studies on urethane–allophanate networks based on hydroxyl‐terminated polybutadiene: Modeling of network parameters and correlation to mechanical properties

Hydroxyl‐terminated polybutadiene (HTPB)‐based allophanate–urethane networks were prepared by reacting HTPB with di‐isocyanates, such as toluene–di‐isocyanate (TDI), isophorone–di‐isocyanate (IPDI), and 4,4′‐di(socyanatocyclohexyl)methane (H₁₂MDI) at stoichiometric ratios (r‐values) ranging from 1.0 to 1.5. The networks were characterized for mechanical and swell properties. The network parameters, such as “X,” which is the fraction of urethane groups involved in the allophanate formation, and effective chain length (L_x) were calculated from experimental crosslink density values determined from swell data, using α‐model equations developed by Marsh. Excellent linear correlations were obtained between mechanical properties and the calculated network parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2986–2994, 2006     

Application of electromagnetic impact technique for welding copper-to-stainless steel sheets

The ability to manufacture a product using different metal combinations greatly increases flexibility in design and production. Joining of dissimilar metal combinations like Copper-to-Stainless Steel (Cu-to-SS) is, however, a challenging task owing to the large differences in physical and chemical properties. The application of electromagnetic (EM) impact technique is demonstrated for welding copper (Cu) to stainless steel (SS) sheets. The welding Cu-to-SS is accomplished by using Al drivers to accelerate Cu and SS work sheets. The tensile shear strength test and the metallographic studies are carried out for Cu-to-SS EM welds.     

Electric field effect on metallic particle contamination in a common enclosure gas insulated busduct

Sulphur hexaflouride (SF₆) is generally found to be very sensitive to field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. A study of CIGRE group suggests that 20% of failures in gas insulated substations (GIS) is due to the existence of various metallic contaminations in the form of loose particles. The presence of contamination can therefore be a problem with gas-insulated substations operating at high fields. If the effects of these particles could be eliminated, then this would improve the reliability of compressed gas insulated substation. It would also offer the possibility of operating at higher fields to affect a potential reduction in the GIS size with subsequent savings in the cost of manufacture and installation. The purpose of this paper is to develop techniques, which will formulate the basic equations that will govern the movement of metallic particles like aluminum and copper in a bus duct. The simulation considers the electric field effect on particle movement and the results have been presented and analyzed     

Seismic retrofitting of nonductile beam-column sub-assemblage using FRP wrapping and steel plate jacketing

The paper discusses the aspects of repair and retrofitting technique adopted for a damaged reinforced concrete beam-column joint specimen under cyclic loading. A specimen designed based on Indian Standard specifications with consideration of seismic load but without adopting ductile detailing (NonDuctile) was investigated under reverse cyclic loading. Then, the damaged nonductile specimen was repaired with epoxy mortar and grouted using low viscous polymer, and retrofitted using fiber reinforced plastic (FRP) wrapping in beam and column components and steel plate jacketing in joint region. The experimental results showed that the retrofitted specimen not only regained its original strength and stiffness but also has overcome the deficiencies of nonductile detailing. The present study shows that a proper repair and adequate retrofitting technique can be used for strengthening and improvement of damaged regions in reinforced concrete structures.     

Patterns of various modes of delivery in relation to presence of different risk factors in term pregnant mothers--a case-control study

A case-control study, was carried out, which aimed to determine whether a relation exists between risk factors present in mother and the mode of delivery i.e., outcome. Cases were those mothers who had one or more risk factors present during pregnancy (namely, short stature, malpresentation, antepartum haemorrhage, pre-eclamptic toxaemia/eclampsia, anaemia-haemoglobin less than 10 g/dl, twins, bad obstetric history, prolonged pregnancy, history of previous caesarean section and instrumental delivery, pregnancy associated with general diseases, prolonged difficult labour and RH-iso-immunisation). Controls were those mothers who did not have any of the above mentioned risk factors. Total of 250 cases and 250 controls were taken. Results showed that surgical and instrumental deliveries were strongly associated with presence of risk factors (odd's ratio: 5.94; attributable risks: 72%). Out of risk factors among cases, most common indication of caesarean section, was previous caesarean section followed by malpresentation, prolonged difficult labour and short statured mothers in descending order.