Annular crack surrounding an elastic fibre in transversely isotropic elasticity

The axisymmetric problem of an infinitely long transversely isotropic elastic fibre perfectly bonded to a dissimilar transversely isotropic elastic matrix containing an annular crack is considered. The annular crack, surrounding the fibre, is subjected to prescribed longitudinal tension. A potential function approach is used to find the solution of the basic equations. The mixed boundary value problem is reduced to the solution of a singular integral equation, which is further reduced, by using Chebyshev polynomials, to a system of algebraic equations.     

Effect of chemical composition and initial heat treatment on the structure and properties of a few dual-phase steels

Dual-phase structures are produced in the three experimental steels, namely A1, A2 and A3, a) by air-cooling from the austenitising temperature (910°C) and then intercritically annealing the ferrite-pearlite structure at 750°C and 810°C followed by water quenching, and b) by water-quenching from the same austenitising temperature and then intercritically annealing the martensitic structure again at 750°C and 810°C followed by water quenching. The ferrite phases present in the alloys A1 and A2 have formed in two different ways: i) before and/or during intercritical annealing (old ferrite) and ii) during cooling of the alloys from the intercritical annealing temperature (new ferrite). The amount of new ferrite has been found to be larger in alloy A1 as compared to alloy A2. Alloy A3 did not show any measurable amount of new ferrite. TEM studies did not reveal any significant difference in microstructure in any of the alloys as a result of the initial heat treatment. The volume percent of martensite is maximum in alloy A2 and minimum in alloy A1, with alloy A3 coming in between. Although the amount of martensite in alloy A1 is somewhat lower than that in alloy A3, the overall strength of alloy A1 is higher than that of alloy A3 due possibly to the significant solid solution hardening of the ferritic matrix caused by silicon. Alloy A2 has been found to have the highest strength amongst the three alloys.     

Uncertainty management in expert systems using fuzzy Petri nets

The paper aims at developing new techniques for uncertainty management in expert systems for two generic class of problems using fuzzy Petri nets that represent logical connectivity among a set of imprecise propositions. One class of problems deals with the computation of fuzzy belief of any proposition from the fuzzy beliefs of a set of independent initiating propositions in a given network. The other class of problems is concerned with the computation of steady-state fuzzy beliefs of the propositions embedded in the network, from their initial fuzzy beliefs through a process called belief revision. During belief revision, a fuzzy Petri net with cycles may exhibit “limit cycle behavior” of fuzzy beliefs for some propositions in the network. No decisions can be arrived at from a fuzzy Petri net with such behavior. To circumvent this problem, techniques have been developed for the detection and elimination of limit cycles. Further, an algorithm for selecting one evidence from each set of mutually inconsistent evidences, referred to as nonmonotonic reasoning, has also been presented in connection with the problems of belief revision. Finally, the concepts proposed for solving the problems of belief revision have been applied successfully for tackling imprecision, uncertainty, and nonmonotonicity of evidences in an illustrative expert system for criminal investigation     

Dielectric properties of epoxy nanocomposites

The dielectric properties of epoxy nanocomposites with insulating nano-fillers, viz., TiO₂, ZnO and AI₂O₃ were investigated at low filler concentrations by weight. Epoxy nanocomposite samples with a good dispersion of nanoparticles in the epoxy matrix were prepared and experiments were performed to measure the dielectric permittivity and tan delta (400 Hz-1 MHz), dc volume resistivity and ac dielectric strength. At very low nanoparticle loadings, results demonstrate some interesting dielectric behaviors for nanocomposites and some of the electrical properties are found to be unique and advantageous for use in several existing and potential electrical systems. The nanocomposite dielectric properties are analyzed in detail with respect to different experimental parameters like frequency (for permittivity/tan delta), filler size, filler concentration and filler permittivity. In addition, epoxy microcomposites for the same systems were synthesized and their dielectric properties were compared to the results already obtained for nanocomposites. The interesting dielectric characteristics for epoxy based nanodielectric systems are attributed to the large volume fraction of interfaces in the bulk of the material and the ensuing interactions between the charged nanoparticle surface and the epoxy chains.     

Erratum to: Malaria infected erythrocyte classification based on a hybrid classifier using microscopic images of thin blood smear

Multimedia Tools and Applications -     

An evolutionary approach for personalization of content delivery in e-learning systems based on learner behavior forcing compatibility of learning materials

This paper presents an evolutionary approach for personalizing learning content for individual learners from a very large database in an e-learning system. The proposed work improves the quality of the self-learning process in an adaptive e-learning system by providing the most suitable content for individual learners. The paper depicts the results of personalizing the learning process by tuning the compatibility level of the learning objects with respect to the learning style of the learner, the complexity level of the learning objects with respect to the knowledge level of the learner and the interactivity level of the learner based on the satisfaction level of the learner during the learning process using a modified form of genetic algorithm named as Compatible Genetic Algorithm (CGA). The proposed work improves the efficiency of the genetic algorithms by forcing compatibility in the learning objects which has not been implemented so far in existing systems. Forcing compatibility into the search space not only helps to reduce the search space but also fills the search space with better chromosomes. The results show improvement in scores of the learners and also in their satisfaction levels. A comparison with the standard algorithms shows improvement in execution time, number of executing generations and fitness values. The results indicate that personalization of content delivery based on behavioral traits of learners leads to better learning.     

Fast formation of high-purity methyl esters from vegetable oils

Experiments have confirmed that the base-catalyzed methanolysis of vegetable oils occurs much slower than butanolysis because of the two liquid phases initially present in the former reaction. For the same reason, second-order kinetics are not followed. The use of a cosolvent such as tetrahydrofuran or methyl tertiary butyl ether speeds up methanolysis considerably. However, like one-phase butanolysis, one-phase methanolysis initially exhibits a rapid formation of ester, but then slows drastically. Experiments show that the half-life of the hydroxide catalyst is too long to explain the sudden slowing of the reaction. Similarly, lower rate constants for the methylation of the mono- and diglycerides are not a reasonable explanation. Instead the cause has been identified as the fall in polarity which results from the mixing of the nonpolar oil with the methanol. This lowers the effectiveness of both hydroxide and alkoxide catalysts. Increasing the methanol/oil molar ratio to 27 in the one-phase system raises the polarity such that the methyl ester content of the ester product exceeds 99.4 wt% in 7 min. This has obvious implications for the size of new methyl ester plants as well as the capacity of existing facilities.     

Individual differences in humans responding under a cocaine discrimination procedure: Discriminators versus nondiscriminators.

Twenty-six cocaine-abusing volunteers were trained to discriminate cocaine (80 mg/70 kg, p.o.) from placebo. On the basis of a discrimination acquisition criterion (i.e., >80% drug-appropriate responding for 4 consecutive sessions within 8–10 sessions), 18 participants were classified as discriminators (Ds) and 8 as nondiscriminators (NDs). Relative to Ds, NDs reported a greater amount of cocaine use per time. During the training phase, NDs showed significantly lower ratings than Ds on a stimulant ratings scale, regardless of the training drug condition. During the test-of-acquisition phase, cocaine-induced increases in scores on ratings of drug strength, anxious-nervous and cocaine high, as well as on a euphoria ratings scale, were significantly greater in Ds than NDs, relative to placebo. These results suggest that drug use history, general arousal level, and drug sensitivity may be important variables influencing the acquisition of cocaine versus placebo discrimination in cocaine abusers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)