Influence of fibre-aggregate interaction on some properties of steel fibre reinforced concrete

In the practical applications of fibre reinforced concrete, particularly for load-bearing purposes, it is desirable to incorporate coarse aggregates for economic and other reasons. Tests are reported in this paper in which the fibre-aggregate interaction is related to the properties of steel fibre concrete both in the fresh and hardened states. It is shown that compactibility, flexural and compressive strengths are reduced progressively by the presence of coarse aggregates. From the test results, a mix design for fibre concrete containing coarse aggregates to produce twice the flexural strength of the unreinforced matrix without bundling of fibres is presented. The data presented on flexural strength show good agreement with theory.     

Modification of shanks conjecture on stability of 2-D planar least-square inverse polynomials

In the letter we state a theorem modifying the Shanks conjecture on the stability of the planar least-square inverse of a 2-D polynomial based on our observation of various counterexamples.     

Approximation of 2-D analog and digital transfer functions using doubly terminated cascade-separable network properties

This paper considers certain useful approximations which can be obtained by doubly terminated two-variable cascade-separable networks. Since such networks can be transformed into 2-D wave digital filters, these approximations provide useful magnitude responses in the 2-D digital domain, also. Two approximation methods are discussed, and these can produce near quadrantal symmetry.     

Adsorption of Cr(VI) using thermally activated weed Salvinia cucullata

Cr(VI) removal studies were carried out by using activated carbon obtained from waste weed, Salvinia cucullata. Effects of various parameters, such as pH, contact time, temperature, adsorbate concentration, adsorbent dose and particle size of the adsorbent on percentage of adsorption were studied. The adsorption studies were carried out at an agitation speed of 600 rpm to minimize the film diffusion. The adsorption kinetics followed dual rate; it was fast during a first stage and then it was reduced. The equilibrium was achieved in 12 h. The kinetics increased with decrease in pH. Adsorbate and adsorbent concentration also influenced the kinetics. The adsorption process was endothermic in nature. The reaction kinetics followed pseudo-second-order kinetic equation. Empirical rate equation developed, which explained the effect of various adsorption parameters, was studied. Theoretical numbers of stages were calculated based on the results. Intra-particle diffusion was found to be the rate-controlling step. Optimization studies were also carried out to establish the upper and lower breakthrough points.     

Influence of aggressive exposure conditions on the behaviour of adhesive bonded concrete–GFRP joints

This paper presents the interim results of an on-going study on the influence of aggressive exposure conditions on the behaviour of epoxy adhesive bonded concrete–glass fibre reinforced polymers (GFRP) joints. The type of specimen used in this study is a push-off double lap shear specimen. Twenty-four of these push-off specimens consisting of concrete prisms, 100×100×300-mm, bonded with 470-mm long, 90-mm wide, and 3.5-mm thick GFRP plates on two opposite faces were tested. The bond length of the plate over the concrete surface was 200 mm. Two different concrete strengths were used, and they were suitably air entrained. The specimens were subjected to three accelerated ageing regimes in the laboratory for approximately 9 months. The accelerated tests consisted of exposing the specimens to alternate wet–dry cycling in 5% sodium chloride solution, cyclic freeze–thaw in air with a temperature of 20°C and −17.8°C, and a combination of chloride immersion and freeze–thaw cycles. The specimens were comprehensively instrumented, and tested to failure after the exposure regime. The structural performance of the exposed specimens is then compared with that of similar control specimens kept in laboratory environment in terms of load carrying capacity, longitudinal force distribution, shear stress development in the plate, plate end slip, and differential movements between the plate and the concrete substrate. There was clear indication that all the exposure regimes increased the bond transfer length, the magnitude of the shear stress distribution and the plate slip. The combined chloride immersion/freeze–thaw cycles produced the largest differential movements between the plate and the concrete substrate. The duration of exposure, however, was not long enough to affect the strength of the joints. Overall, the results were very consistent, and showed that accelerated tests could inflict deterioration in the adhesive bonded concrete–GFRP joints.     

Mixed convection heat and mass transfer over a vertical plate in a power‐law fluid‐saturated porous medium with radiation and chemical reaction effects

Mixed convection heat and mass transfer from a vertical plate embedded in a power‐law fluid‐saturated Darcy porous medium with chemical reaction and radiation effects is studied. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and then solved numerically using the shooting method. A parametric study of the physical parameters involved in the problem is conducted and a representative set of numerical results is illustrated graphically. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21058     

Sorption and diffusion of chlorinated aliphatic hydrocarbon penetrants into diol chain extended polyurethane membranes

Sorption and diffusion of a number of chlorinated alkanes through a diol chain extended polyurethane (PU) membranes have been investigated at 25, 40 and 60 degrees C, based on an immersion weight gain method. From the sorption result, the diffusion (D) and permeation (P) coefficients of halogenated hydrocarbon penetrants have been calculated. Molecular transport data depends on membrane-solvent interactions, size of the penetrants, temperature and also morphology of the chain extended PUs. The temperature dependence of the transport coefficient has been used to estimate the activation parameters for the process of diffusion (E(D)) and permeation (E(P)) from the Arrhenius plots. Furthermore, the sorption results have been interpreted interms of the thermodynamic parameters such as enthalpy and entropy.     

Behavior of acidogenesis during biohydrogen production with formate and glucose as carbon source: Substrate associated dehydrogenase expression

Experiments were designed to enumerate variation in biohydrogen (H₂) production pattern with formate and glucose as carbon source under acidogenic mixed microenvironment. High H₂ production was observed with glucose (180 ml) when compared to formate (152 ml). The process was validated with modified Gompertz model (R² = 0.98). Substrate degradation also showed higher removal of glucose (ξ_COD, 82%) compared to formate (ξ_COD, 53%). Nevertheless, specific H₂ yield of formate (6.6 mol H₂/kg COD_R) obtained was comparatively higher than glucose (5 mol H₂/kg COD_R). Variation in H₂ production was manifested by change in fatty acid composition and substrate degradation pattern. Acetate was obtained as a major metabolic intermediate from the degradation of glucose and a shift in the biochemical pathway towards formation of butyrate occurred after maximum substrate degradation. The role of substrate-dependent dehydrogenase activity was deciphered during H₂ production and was evidenced with bio-electrochemical analysis.     

A Study on Friction Stir Multi Spot Welding Techniques to Join Commercial Pure Aluminum and Mild Steel Sheets

To achieve significant improvement in the shear strength of dissimilar joints between aluminum and mild steel sheets, four methods of friction stir multi-spot welding processes, were investigated. Initially, in all these methods, plasticized aluminum layer was deposited on the steel side by friction surfacing. Subsequently, the deposited aluminum was compacted by friction forming. After dressing, spot welding with different tool configurations was performed. Tool rotational speeds of 900, 1120, 1400 and 1800 rpm were used to analyze their effects on the weld nugget. Different mechanical and metallurgical characterizations were done on the welds thus made. The process with aluminum layer on grooved mild steel followed by friction stir multi-spot welding using concave tipped welding tool resulted in welds. These welds had better metallurgical bonding characteristics and higher shear strength, which at a rotational speed of 1120 rpm was more than twice that of the welds made with conventional friction stir spot welding.     

L(p) norm design of stack filters.

Addresses the problem of designing optimal stack filters by employing an L(p) norm of the error between the desired signal and the estimated one. It is shown that the L(p) norm can be expressed as a linear function of the decision errors at the binary levels of the filter. Thus, an L(p)-optimal stack filter can be determined as the solution of a linear program. The conventional design of using the mean absolute error (MAE), therefore, becomes a special ease of the general L(p) norm-based design developed here. Other special cases of the proposed approach, of particular interest in signal processing, are the problems of optimal mean square error (p=2) and minimax (p-->infinity) stack filtering. Since an Linfinity optimization is a combinatorial problem, with its complexity increasing faster than exponentially with the filter size, the proposed L(p ) norm approach to stack filter design offers an additional benefit of a sound mathematical framework to obtain a practical engineering approximation to the solution of the minimax optimization problem. The conventional MAE design of an important subclass of stack filters, the weighted order statistic filters, is also extended to the L(p) norm-based design. By considering a typical application of restoring images corrupted with impulsive noise, several design examples are presented, to illustrate the performance of the L(p)-optimal stack filters with different values of p. Simulation results show that the L(p)-optimal stack filters with p=/>2 provide a better performance in terms of their capability in removing impulsive noise, compared to that achieved by using the conventional minimum MAE stack filters.