Investigation of Eccentric Open Eye Formation in a Slab Caster Tundish

Metallurgical and Materials Transactions B - Inert gas shrouding in tundish can result in the formation of a tundish open eye (TOE) due to the presence of reversed flows on the upper surface of the...     

An enhanced Radial Basis Function Network for voltage stability monitoring considering multiple contingencies

This paper proposes a scheme for online voltage stability monitoring using an enhanced Radial Basis Function Network (RBFN). A single RBFN is used to predict MW margins for different contingencies. A sequential learning strategy is used along with a regularization technique to design the RBFN and the weights in the output layer are determined by using linear optimization. The proposed network can be adapted with changing operating scenario of the power system. A network pruning strategy is used to limit the growth of the network size due to adaptive training. The proposed scheme is applied on the New England 39-bus power system model.     

Factors controlling the time evolution of the corrosion potential of aluminum in alkaline solutions

The mechanism of corrosion of 99.99% purity aluminum in alkaline solutions was investigated, through detailed examination of open-circuit potential transients. These transients displayed a characteristic time dependence, in which the potential first decreased over a few seconds to a minimum of −1.7 to −1.9 V vs. Ag/AgCl, and then slowly increased over a period of hours. The value of the minimum potential of electropolished foils, along with its dependence on pH and aluminate ion concentration, indicated that it was determined by the Nernst potential for the oxidation of surface aluminum hydride (AlH₃). This finding supports the direct role of hydride in the dissolution process. The increase of anodic polarization after the minimum potential occurred in two stages, the first correlated with the buildup of surface hydride, and the second with surface enrichment of Cu and Fe impurities.     

Effect of curing conditions and ionic additives on properties of fly ash-lime compacts

In the present work the reaction between fly ash and lime in fly ash-lime compacts under water curing and steam curing conditions was studied thoroughly in relation to the processing conditions. Fly ash from different sources were collected, characterized, mixed with lime in different ratios and compacted. The compacts were cured with water and steam separately. The reduction in the free CaO content in these compacts was measured as a function of curing time and curing process. Role of two ionic additives, FeCl₃ and MgCl₂, on the reaction between fly ash and lime was also investigated by measuring the free CaO content. Kinetics of these reactions was studied by determining the reaction order and rate constants with respect to the free CaO content and it was observed that the curing conditions and additives affected the reaction kinetics significantly.     

An Efficient and Scalable Quasi-Aggregate Signature Scheme Based on LFSR Sequences

Aggregate signatures can be a crucial building block for providing scalable authentication of a large number of users in several applications like building efficient certificate chains, authenticating distributed content management systems, and securing path vector routing protocols. Aggregate signatures aim to prevent resources (signature and storage elements, and computation) from growing linearly in the number of signers participating in a network protocol. In this paper, we present an efficient and scalable quasi-aggregate signature scheme, {rm CLFSR}- {rm QA}, based on third-order linear feedback shift register (cubic LFSR) sequences that can be instantiated using both XTR and GH public key cryptosystems. In the proposed {rm CLFSR}-{rm QA} construction, signers sign messages sequentially; however, the verfier need not know the order in which messages were signed. The proposed scheme offers constant length signatures, fast signing, aggregation, and verification operations at each node, and requires the least storage elements (public keys needed to verify the signature), compared to any other aggregate signature scheme. To the best of our knowledge, {rm CLFSR}- {rm QA} is the first aggregate signature scheme to be constructed using LFSR sequences. We believe that the {rm CLFSR}- {rm QA} signature scheme can be catalytic in improving the processing latency as well as reducing space requirements in building secure, large-scale distributed network protocols. We perform extensive theoretical analysis including correctness and security of {rm CLFSR}- {rm QA} and also present a performance (computation and communication costs, storage overhead) comparison of the proposed scheme with well-known traditional constructions.     

Validating for Liveness in Hidden Adversary Systems

Multi-stream interactive systems can be seen as “hidden adversary” systems (HAS), where the observable behaviour on any interaction channel is affected by interactions happening on other channels. One way of modelling HAS is in the form of a multi-process I/O automata, where each interacting process appears as a token in a shared state space. Constraints in the state space specify how the dynamics of one process affects other processes. We define the “liveness criterion” of each process as the end objective to be achieved by the process. The problem now for each process is to achieve this objective in the face of unforeseen interferences from other processes. In an earlier paper, it was proposed that this uncertainty can be mitigated by collaboration among the disparate processes. Two types of collaboration philosophies were also suggested: altruistic collaboration and pragmatic collaboration. This paper addresses the HAS validation problem where processes collaborate altruistically.     

Role of V2O5 on the formation of chemical mullite from aluminosilicate precursor

Aluminosilicate precursor for the processing of mulite ceramics was synthesized chemically from inorganic salts following colloidal route. V₂O₅ was used as a sintering additive in different ratios with the precursor powder. The powder mixes were compacted and sintered at different elevated temperatures. The sintered masses were characterized by measuring the bulk density, porosity, flexural strength and fracture toughness. The extent of mullitization and final microstructure of the sintered masses were investigated by scanning electron microscopy and XRD analysis. It was observed that V₂O₅ exhibited favourable effect on the formation of properly crystallized mullite and in the improvement of different mechanical properties.     

Hydroformylation of 1-octene using rhodium–phosphite catalyst in a thermomorphic solvent system

The use of a liquid–liquid biphasic thermomorphic or temperature-dependent multicomponent solvent (TMS) system, in which the catalyst accumulates in one of the liquid phases and the product goes preferably to the other liquid phase, can be an enabling strategy of commercial hydroformylation processes with high selectivity, efficiency and ease of product separation and catalyst recovery. This paper describes the synthesis of n-nonanal, a commercially important fine chemical, by the hydroformylation reaction of 1-octene using a homogeneous catalyst consisting of HRh(PPh₃)₃(CO) and P(OPh)₃ in a TMS-system consisting of propylene carbonate (PC), dodecane and 1,4-dioxane. At a reaction temperature of 363 K, syngas pressure of 1.5 MPa and 0.68 mM concentration of the catalyst, HRh(CO)(PPh₃)₃, the conversion of 1-octene and the yield of total aldehyde were 97% and 95%, respectively. With a reaction time of 2 h and a selectivity of 89.3%, this catalytic system can be considered as highly reactive and selective compared to conventional ones. The resulting total turnover number was 600, while the turnover frequency was 400 h^?1. The effects of increasing the concentration of 1-octene, catalyst loading, partial pressure of CO and H₂ and temperature on the rate of reaction have been studied at 353, 363 and 373 K. The rate was found to be first order with respect to concentrations of the catalyst and 1-octene, and the partial pressure of H₂. The dependence of the reaction rate on the partial pressure of CO showed typical substrate inhibited kinetics. The kinetic behavior differs significantly from the kinetics of conventional systems employing HRh(CO)(PPh₃)₃ in organic solvents. Most notable are the lack of olefin inhibition and the absence of a critical catalyst concentration. A mechanistic rate equation has been proposed and the kinetic parameters evaluated with an average error of 5.5%. The activation energy was found to be 69.8 kJ/mol.     

Modeling the Interaction Between Fly Ash and Lime Under Water Curing by an Artificial Neural Network

An artificial neural network was used to model the chemical interaction between fly ash and lime with different ratios in water-cured compacts. As inputs for the model, different process parameters like pozzolanicity, surface area, unburnt carbon content of the ash samples, water-curing periods, and the proportion of initial lime content in the fly ash–lime mixes were used. Free lime remaining in the compacts after different curing periods was used as the output parameter. A generalized feedforward back-propagation three-layered neural network model was used with a tanhyperbolic transfer function at both the input and the output layer with 400 exemplars. For the training data, after 3500 iterations, the error value was found to be the minimum for the prediction mode. When the model was tested for the test data, the difference between the actual value of the strength and the predicted value of the strength was found to be within ±15%.