Effect of annealing atmosphere on leakage and dielectric characteristics of multiferroic gallium ferrite

Mutliferroic and magnetoelectric gallium ferrite (GaFeO₃) is plagued by substantial electrical leakage in polycrystalline form. Here, we report on understanding the conduction mechanism in gallium ferrite ceramic samples vis‐à‐vis processing conditions. The results show that oxygen annealed samples exhibit minimum electrical leakage as compared to air or nitrogen annealed samples suggesting the role of oxy3gen vacancies on electrical conduction. Detailed time and temperature‐dependent impedance spectroscopy analysis of the samples showed higher activation energy of conduction in oxygen annealed samples than in air or nitrogen annealed samples. The lower activation energies of 0.3‐0.4 eV in nitrogen/air annealed samples were attributed to higher oxygen vacancy concentration while oxygen annealed samples with low oxygen vacancy concentration exhibited higher activation energy of ~0.50 eV (high frequency, i.e., grain) and 0.98 eV (low frequency, i.e., grain boundary), latter due to superior level of oxygenation at the grain boundaries. Further, X‐ray photoelectron spectroscopy revealed that the oxygen vacancies are compensated by the valence fluctuation between Fe²⁺/Fe³⁺ ions whose extent is higher in air/nitrogen annealed samples than in oxygen annealed samples. The conduction mechanisms that could be active are most likely to be double ionization of oxygen vacancies and hopping from Fe²⁺ to Fe³⁺ states, latter especially in oxygen deficient samples.     

An approach for reliability analysis of industrial systems using PSO and IFS technique

The main objective of this paper is to present a technique for computing the membership functions of the intuitionistic fuzzy set (IFS) by utilizing imprecise, uncertain and vague data. In literature so far, membership functions of IFS are computed via using fuzzy arithmetic operations within collected data and hence contain a wide range of uncertainties. Thus it is necessary for optimizing these spread by formulating a nonlinear optimization problem through ordinary arithmetic operations instead of fuzzy operations. Particle swarm optimization (PSO) has been used for constructing their membership functions. Sensitivity as well as performance analysis has also been conducted for finding the critical component of the system. Finally the computed results are compared with existing results. The suggested framework has been illustrated with the help of a case.     

Transient analysis of rock bed air heaters for intermediate temperature applications

This paper deals with the transient analysis of rock bed air heaters in three different configurations. The analysis has been carried out for both summer and winter weather conditions to explore the feasibility of their use in summer for crop-drying applications and in winter for space-heating and water-heating applications. A parallel study has also been performed on the conventional empty channel air heater to compare its performance with that of rock bed air heaters.     

Efficient dependency tracking for relevant events in concurrent systems

In a concurrent system with N processes, vector clocks of size N are used for tracking dependencies between the events. Using vectors of size N leads to scalability problems. Moreover, association of components with processes makes vector clocks cumbersome and inefficient for systems with a dynamic number of processes. We present a class of logical clock algorithms, called chain clock, for tracking dependencies between relevant events based on generalizing a process to any chain in the computation poset. Chain clocks are generally able to track dependencies using fewer than N components and also adapt automatically to systems with dynamic number of processes. We compared the performance of Dynamic Chain Clock (DCC) with vector clock for multithreaded programs in Java. With 1 % of total events being relevant events, DCC requires 10 times fewer components than vector clock and the timestamp traces are smaller by a factor of 100. For the same case, although DCC requires shared data structures, it is still 10 times faster than vector clock in our experiments. We also study the class of chain clocks which perform optimally for posets of small width and show that a single algorithm cannot perform optimally for posets of small width as well as large width.This is a revised and extended version of the paper “Efficient Dependency Tracking for Relevant Events in Shared Memory System” which appeared in PODC 2005. Anurag Agarwal received his B.Tech. degree in computer science and engineering from the Indian Institute of Technology, Kanpur in 2003. He is currently a student in the Department of Computer Science at the University of Texas, Austin. His research interests include distributed systems, program verification and security. Vijay K. Garg received his B.Tech. degree in computer science from the Indian Institute of Technology, Kanpur in 1984 and M.S. and Ph.D. degrees in electrical engineering and computer science from the University of California at Berkeley in 1985 and 1988, respectively. He is currently a full professor in the Department of Electrical and Computer Engineering and the director of the Parallel and Distributed Systems Laboratory at the University of Texas, Austin. His research interests are in the areas of distributed systems and discrete event systems. He is the author of the books Concurrent and Distributed Computing in Java (Wiley & Sons, 2004), Elements of Distributed Computing (Wiley & Sons, 2002), Principles of Distributed Systems (Kluwer, 1996) and a co-author of the book Modeling and Control of Logical Discrete Event Systems (Kluwer, 1995). Prof. Garg is also an IEEE Fellow.     

Partial Order Trace Analyzer (POTA) for Distributed Programs

Checking the correctness of software is a growing challenge. In this paper, we present a prototype implementation of Partial Order Trace Analyzer (POTA), a tool for checking execution traces of both message passing and shared memory programs using temporal logic. So far runtime verification tools have used the total order model of an execution trace, whereas POTA uses a partial order model. The partial order model enables us to capture possibly exponential number of interleavings and, in turn, this allows us to find bugs that are not found using a total order model. However, verification in partial order model suffers from the state explosion problem – the number of possible global states in a program increases exponentially with the number of processes.POTA employs an effective abstraction technique called computation slicing. A slice of a computation (execution trace) with respect to a predicate is the computation with the least number of global states that contains all global states of the original computation for which the predicate evaluates to true. The advantage of this technique is that, it mitigates the state explosion problem by reasoning only on the part of the global state space that is of interest. In POTA, we implement computing slicing algorithms for temporal logic predicates from a subset of CTL. The overall complexity of evaluating a predicate in this logic upon using computation slicing becomes polynomial in the number of processes compared to exponential without slicing.We illustrate the effectiveness of our techniques in POTA on several test cases such as the General Inter-ORB Protocol (GIOP)[18] and the primary secondary protocol[32]. POTA also contains a module that translates execution traces to Promela[16] (input language SPIN). This module enables us to compare our results on execution traces with SPIN. In some cases, we were able to verify traces with 250 processes compared to only 10 processes using SPIN.     

A critique of Java for concurrent programming

The number of processors in a commercial microprocessor chip has been increasing by a factor of two every year, so our desktop has at least a thousand processors. Furthermore, the desktop is connected to millions of other processors. In this article, the author explains the features of a concurrent programming language - Avaj. The author also explores how Avaj differs from Java.     

Pulse multiplication in AC-DC converters for harmonic mitigation in vector-controlled induction motor drives

In this paper, an autotransformer with reduced kilovoltampere rating for 24-pulse ac-dc converter fed vector controlled induction motor drives (VCIMDs) is presented for harmonic current reduction. The 24-pulse operation is achieved using dc ripple reinjection technique in 12-pulse ac-dc converters. The proposed novel harmonic mitigator is found capable of suppressing up to 21st harmonic in the supply current. The procedure for the design of autotransformer for proposed ac-dc converter is presented to show the flexibility in the design for making it a cost-effective replacement suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from other 24-pulse ac-dc converters are also given to compare their performance. The laboratory prototypes of proposed autotransformers based 12-pulse and 24-pulse ac-dc converters are developed and test results are presented to validate the developed design procedure and the simulation models of these ac-dc converters under varying loads.     

Characterizing particulate drug-delivery carriers with atomic force microscopy.

This work discusses the benefits of employing an atomic force microscope (AFM) in the characterization of the particulate-type drug-delivery carriers. AFM can provide invaluable information about the physicochemical characteristics of the carriers that play an important role in determining the performance of the drug delivery systems (DDS). A lot of this information cannot be obtained from other characterization techniques due to the unique ability of the AFM to probe nanometer scale features at the molecular level. There has already been a significant amount of work in the development of the DDS and the upcoming of AFM as a powerful characterizing tool provides a new inspiration in this area. This will definitely add to the understanding of the DDS and will influence the future designs of the drug carriers towards the development of better and more efficient DDS.     

Surface wave propagation in a double liquid layer over a liquid-saturated porous half-space

The frequency equation is derived for surface waves in a liquid-saturated porous half-space supporting a double layer, that of inhomogeneous and homogeneous liquids. Asymptotic approximations of Bessel functions are used for long and short wavelength cases. Certain other problems are discussed as special cases. Velocity ratio (phase and group velocity) is obtained as a function of wavenumber and the results are shown graphically.     

Fe2+ and Fe3+ adsorption on 2‐vinylpyridine–divinylbenzene copolymers and acrylonitrile–methyl methacrylate–divinylbenzene terpolymers

The adsorption of Fe²⁺ and Fe³⁺ ions on 2‐vinylpyridine–divinylbenzene copolymer and acrylonitrile–methyl methacrylate–divinylbenzene terpolymer was investigated. In general, the adsorption of Fe²⁺ and Fe³⁺ in both resins increased with the enhancement of hydrochloric acid and metal concentration. The metal adsorption on the terpolymer increased sharply with the addition of small portions of ethanol, whereas the adsorption on the copolymer practically was not affected by the presence of the alcohol. An increase in temperature produced a small increase in iron adsorption for both resins. Fourier transform infrared spectra showed that nitrile and ester groups of the terpolymer did not suffer hydrolysis during metal adsorption, even for the highest HCl concentration and the highest temperature applied. A mechanism of iron adsorption through the ion exchange of chloride anions by tetrahedral [FeCl₄]^2? or [FeCl₄]^? anions is proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3905–3912, 2003