Thermal stability in bulk cryomilled ultrafine-grained 5083 Al alloy

Thermal stability in bulk ultrafine-grained (UFG) 5083 Al that was processed by gas atomization followed by cryomilling, consolidation, and extrusion, and that exhibited an average grain size of 305 nm, was investigated in the temperature range of 473 to 673 K (0.55 to 0.79 T _m , where T _m is the melting temperature of the material) for different annealing times. Appreciable grain growth was observed at temperatures > 573 K, whereas there was limited grain growth at temperatures < 573 K even after long annealing times. The values of the grain growth exponent, n, deduced from the grain growth data were higher than the value of 2 predicted from elementary grain growth theories. The discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination of the microstructure of the alloy suggests that the origin of the pinning forces is most likely related to the presence of dispersion particles, which are mostly introduced during cryomilling. Two-grain growth regimes were identified: the low-temperature region (<573 K) and the high-temperature region (>573 K). For temperatures lower than 573 K, the activation energy of 25 ± 5 kJ/mol was determined. It is suggested that this low activation energy represents the energy for the reordering of grain boundaries in the UFG material. For temperatures higher than 573 K, an activation energy of 124 ± 5 kJ/mol was measured. This value of activation energy, 124 ± 5 kJ/mol, lies between that for grain boundary diffusion and lattice diffusion in analogous aluminum polycrystalline systems. The results show that the strength and ductility of bulk UFG 5083 Al, as obtained from tensile tests, correlate well with substructural changes introduced in the alloy by the annealing treatment.     

Process optimisation in sunflower oil extraction by supercritical CO2

A continuous process for the extraction of sunflower oil using supercritical CO₂, featuring multiple extractors, one oil separator and three cascaded CO₂ recovery vessels operating at different pressures, was devised and studied. For every single equipment of the plant making up the process a mathematical model was built. Experimental tests—consisting in measurements of oil solubility in supercritical CO₂—were carried out in a laboratory-scale apparatus to characterise the behaviour of sunflower oil in the separation from the supercritical fluid. The mathematical model of the whole process was coded in the commercial gPROMS process modelling environment where both its simulation and optimisation—this latter assuming the overall oil production cost as the objective function—were carried out. The process- and economics-related results are discussed and compared with those obtained with traditional and cold-pressing extraction.     

Kinetics of discontinuous precipitation in a Zn-2.5 at % Cu alloy

The morphology and growth kinetics of discontinuous precipitation in a Zn-2.5 at % Cu alloy have been studied in the temperature range 383–583 K by optical and scanning electron microscopy. The precipitate phase has a lamellar morphology, and maintains a statistically constant interlamellar spacing under isothermal growth conditions. The interlamellar spacing increases with an increase in temperature. The isothermal growth kinetics in terms of reaction front migration rate is maximum at 523 K. The upper temperature limit for the occurrence of reaction in this alloy has been predicted to be 643 K. A detailed kinetic analysis of the experimental data using several analytical models has confirmed discontinuous precipitation in this system to be a boundary diffusion controlled reaction, and enabled the determination of the grain boundary chemical diffusivity of Cu in a Zn-rich Zn-Cu alloy in the temperature range studied. The corresponding activation energy values determined in this study, range between 65 to 86 kJ/mol^–1, which compare well with the relevant data in the literature.     

Group technology based adaptive cell formation using predator-prey genetic algorithm

In recent years, there has been a considerable growth of application of group technology in cellular manufacturing. This has led to investigation of the primary cell formation problem (CFP), both in classical and soft-computing domain. Compared to more well-known and analytical techniques like mathematical programming which have been used rigorously to solve CFPs, heuristic approaches have yet gained the same level of acceptance. In the last decade we have seen some fruitful attempts to use evolutionary techniques like genetic algorithm (GA) and Ant Colony Optimization to find solutions of the CFP. The primary aim of this study is to investigate the applicability of a fine grain variant of the predator-prey GA (PPGA) in CFPs. The algorithm has been adapted to emphasize local selection strategy and to maintain a reasonable balance between prey and predator population, while avoiding premature convergence. The results show that the algorithm is competitive in identifying machine-part clusters from the initial CFP matrix with significantly less number of iterations. The algorithm scaled efficiently for large size problems with competitive performance. Optimal cluster identification is then followed by removal of the bottleneck elements to give a final solution with minimum inter-cluster transition cost. The results give considerable impetus to study similar NP-complete combinatorial problems using fine-grain GAs in future.     

Deductive verification of alternating systems

Alternating systems are models of computer programs whose behavior is governed by the actions of multiple agents with, potentially, different goals. Examples include control systems, resource schedulers, security protocols, auctions and election mechanisms. Proving properties about such systems has emerged as an important new area of study in formal verification, with the development of logical frameworks such as the alternating temporal logic ATL*. Techniques for model checking ATL* over finite-state systems have been well studied, but many important systems are infinite-state and thus their verification requires, either explicitly or implicitly, some form of deductive reasoning. This paper presents a theoretical framework for the analysis of alternating infinite-state systems. It describes models of computation, of various degrees of generality, and alternating-time logics such as ATL* and its variations. It then develops a proof system that allows to prove arbitrary ATL* properties over these infinite-state models. The proof system is shown to be complete relative to validities in the weakest possible assertion language. The paper then derives auxiliary proof rules and verification diagrams techniques and applies them to security protocols, deriving a new formal proof of fairness of a multi-party contract signing protocol where the model of the protocol and of the properties contains both game-theoretic and infinite-state (parameterized) aspects.     

High power GaN‐HEMT SPDT switches for microwave applications

In this article, the design, fabrication, and on‐wafer test of X‐Band and 2–18 GHz wideband high‐power SPDT MMIC switches in AlGaN/GaN technology are presented. The switches have demonstrated state‐of‐the‐art performance and RF fabrication yield better than 65%. Linear and power measurements for different control voltages have been reported and an explanation of the dependence of the power performances on the control voltage is given. In particular, the X‐band switch exhibits a 0.4 dB compression level at 10 GHz when driven by a 38 dBm input signal. The wideband switch shows a compression level of 1 dB at an input drive higher than 38 dBm across the entire bandwidth. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

AVCOL: Availability-aware information aggregation in large distributed systems under uncollaborative behavior

Aggregation of system-wide information in large-scale distributed systems, such as p2p systems and Grids, can be unfairly influenced by nodes that are selfish, colluding with each other, or are offline most of the time. We present AVCOL, which uses probabilistic and gossip-style techniques to provide availability-aware aggregation. Concretely, AVCOL is the first aggregation system that: (1) implements any (arbitrary) global predicate that explicitly specifies any node’s probability of inclusion in the global aggregate, as a mathematical function of that node’s availability (i.e., percentage time online); (2) probabilistically tolerates large numbers of selfish nodes and large groups of colluders; and (3) scales well with hundreds to thousands of nodes. AVCOL uses several unique design decisions: per-aggregation tree construction where nodes are allowed a limited but flexible probabilistic choice of parents or children, probabilistic aggregation along trees, and auditing of nodes both during aggregation as well as in gossip-style (i.e., periodically). We have implemented AVCOL, and we experimentally evaluated it using real-life churn traces. Our evaluation and our mathematical analysis show that AVCOL satisfies arbitrary predicates, scales well, and withstands a variety of selfish and colluding attacks.     

Preprogramming Floating Time of Liquid Marble

Non-sticking droplets wrapped with fine hydrophobic particles, namely liquid marbles, can be transported both on solid and water pool without an undesired spill of the inner encapsulated liquid. While the stimuli-responsive release of the inner liquid in the target area is proposed, the time-programmed release is not yet achieved. Herein, the hydrophobicity of nanoclay is modulated via a catalyst-free 1,4-conjugate addition reaction to form liquid marbles. This nanoclay liquid marble is robust and stable in air but collapses on the liquid pool with a specific lifetime. The lifetime of the liquid marble can be modulated over seconds to hours scale depending on the selection of chemically modulated wettability of the nanoclay. The critical mechanism of lifetime modulation is responsible for controlling the coalescence kinetics between the water pool and inner liquid by nanoclays’ high diffusion length and chemically varied water spreading potential. The NC liquid marble's programmable lifetime to ‘time-bomb’ type drug release and cascade chemical reaction is applied—without requiring any external intervention.     

Parallel crypto-devices for GF(p) elliptic curve multiplication resistant against side channel attacks

All elliptic curve cryptographic schemes are based on scalar multiplication of points, and hence its faster computation signifies faster operation. This paper proposes two different parallelization techniques to speedup the GF(p) elliptic curve multiplication in affine coordinates and the corresponding architectures. The proposed implementations are capable of resisting different side channel attacks based on time and power analysis. The 160, 192, 224 and 256 bits implementations of both the architectures have been synthesized and simulated for both FPGA and 0.13μ CMOS ASIC. The final designs have been prototyped on a Xilinx Virtex-4 xc4vlx200-12ff1513 FPGA board and performance analyzes carried out. The experimental result and performance comparison show better throughput of the proposed implementations as compared to existing reported architectures.