Optimization of bead geometry of submerged arc weld using fuzzy based desirability function approach

The present study highlights application of Taguchi’s robust design coupled with fuzzy based desirability function approach for optimizing multiple bead geometry parameters of submerged arc weldment. Fuzzy inference system has been adapted to avoid uncertainly, imprecision and vagueness in experimentation as well as in data analysis by traditional Taguchi based optimization approach. Detailed methodology and unique features of the proposed method has been highlighted through a case study. The said approach can efficiently be used in off-line quality control of any production process as well as automation of the process.     

Software bottlenecking in client-server systems and rendezvousnetworks

Software bottlenecks are performance constraints caused by slow execution of a software task, in typical client-server systems a client task must wait in a blocked state for the server task to respond to its requests, so a saturated server will slow down all its clients. A rendezvous network generalizes this relationship to multiple layers of servers with send-and-wait interactions (rendezvous), a two-phase model of task behavior, and to a unified model for hardware and software contention. Software bottlenecks have different symptoms, different behavior when the system is altered, and a different cure from the conventional bottlenecks seen in queueing network models of computer systems, caused by hardware limits. The differences are due to the “push-back” effect of the rendezvous, which spreads the saturation of a server to its clients. The paper describes software bottlenecks by examples, gives a definition, shows how they can be located and alleviated, and gives a method for estimating the performance benefit to be obtained. Ultimately, if all the software bottlenecks can be removed, the performance limit will be due to a conventional hardware bottleneck     

Deformation and fracture of a particle-reinforced aluminum alloy composite: Part II. Modeling

In this article, the tensile and fracture properties of a discontinuously reinforced aluminum (DRA) alloy composite are modeled to determine the influence of constituent parameters on material behavior. Comparison of the elastic-modulus calculations to the experimental data suggest that the angular particles are more effective in load transfer than spherical particles, and that a unit cylinder geometry is a good representation of the particles under elastic conditions. This same geometry is used in the finite element-based elastic-plastic model of Bao et al., and reasonably good agreement is obtained between the experimental and predicted yield strengths. A fracture-mechanics model is proposed for predicting the elongation to failure. The model assumes the existence of particle cracks, and criticality is based on the strain required for matrix rupture between cracked particles. The damage criterion of Cockcroft and Latham is utilized, and model predictions are compared to data from different investigations. It is shown that the volume fraction of particles and the work-hardening coefficient of the matrix have a strong influence on the strain to failure. Fracture toughness modeling once again exposes the limitations of existing zero-degree crack-propagation models, such as that of Hahn and Rosenfield, which predict increased toughness with yield strength rather than a decrease, which is observed experimentally. A shear-failure model along a 45-deg direction is proposed for the higher-strength conditions, where concentrated slip bands were observed. The model exhibits the inverse toughness dependence on strength and better correlation to peak-aged (PA) data, but shows poorer agreement with underaged (UA) data. Thus, a transition from zero-degree propagation to 45-deg propagation with increasing strength is suggested. A simplified method for extracting particle stresses is illustrated and is used to estimate a Weibull modulus of 4.9 and a Weibull strength of 2450 MPa for the SiC particles of an average diameter of 10 μm. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.     

Glass and glass-ceramic coatings, versatile materials for industrial and engineering applications

Among various coating systems for industrial and engineering applications, glass and glass-ceramic coatings have advantages of chemical inertness, high temperature stability and superior mechanical properties such as abrasion, impact etc as compared to other coating materials applied by thermal spraying in its different forms viz. PVD, CVD, plasma, etc. Besides imparting required functional properties such as heat, abrasion and corrosion resistance to suit particular end use requirements, the glass and glass-ceramic coatings in general also provide good adherence, defect free surface and refractoriness. Systematic studies covering the basic science of glass and glass-ceramic coatings, the functional properties required for a particular end-use along with the various fields of application have been reviewed in this paper.     

Laboratory-simulation experiment for optical communication through low-visibility atmosphere using a diode laser

A laboratory-simulation experiment has been performed to determine the feasibility of exploiting the scattered (in addition to the unscattered) radiation to improve optical communication through low-visibility atmosphere. A multiple field-of-views (FOV) (0.043-0.945degfull angle) optical receiver was designed which utilizes a narrow-band interference filter (Deltalambda sim 15Å) for background-light suppression. The laser transmitter was a CW GaAlAs laser diode (lambda = 0.8486 mum) capable of emitting ∼ 7 mW power output of 15° divergent beam. Both polydisperse (particle diameters,din the range ofsim0.2-5.17 mum) and monodisperse (d sim 0.2 mum andd = 3.01 mum) latex spheres in water were used for simulating haze, fog, etc. Results include signal-to-noise ratio (SNR) and scattered-to-unscattered signal ratio as a function of field-of-view of reception for various optical thickness of the medium. Also, SNR is plotted as a function of optical thickness for various FOV's. The unique feature of this simulation is that it can simulate worst case solar background where the sun enters the FOV of receiver. Finally a new technique of estimating forward-scattering efficiency and root-mean-square forward scatter angle has also been presented with examples.     

Isolation of type II epithelial cells from rabbit fetal lungs by adherence on an IgG-coated surface

The lung is comprised of about 40 different cell types, of which only 15% are type II cells. These are the major, if not the sole, source of synthesis and secretion of lung surfactant. To date a large number of methods have been described for the isolation of pure populations of type II cells using a wide variety of techniques, but most of these have employed differential centrifugation methods and have used adult rodents. The present study reports the isolation of type II cells from fetal rabbit lungs by the immunoglobin G plating method. Pure populations of fetal type II cells in high yield and with good viability were obtained by the procedure for the first time from rabbit fetal tissue.     

In vitro transcorneal permeation of ketorolac tromethamine from buffered and unbuffered aqueous ocular drops

In vitro transcorneal permeation of ketorolac tromethamine from 0.5% w/v solutions containing equimolar (0.02 M) concentrations of citrate (pH 6.5), phosphate (pH 6.5 and 7), citrate-phosphate (pH 7) and borate (pH 7) buffers was studied using goat cornea. Cumulative % permeation was maximum with phosphate buffered drops of pH 6.5. The effect of pH and ionic strength on permeation of ketorolac tromethamine from buffered (phosphate) drops was next investigated. Cumulative % permeation of ketorolac tromethamine from buffered drops was pH dependent being maximum at pH 4.5. Adjustment of ionic strength of drops to 0.2 resulted in decreased permeation of drug. Permeation of ketorolac tromethamine from unbuffered drops of varying pH and ionic strength 0.2 was also pH dependent and was maximum at pH 4.5. Buffered drops of pH between 4.5-5.5, ionic strength 0.2, provided better permeation of drug compared to unbuffered drops of same pH and ionic strength. Above pH 6.5 unbuffered drops showed better permeation than buffered drops. Increase in molarity of phosphate buffer (pH 4.5) used in making drops, between 0 to 0.15 M increased permeation. Aqueous drops of ketorolac tromethamine formulated in 0.15 M phosphate buffer of pH 4.5 and ionic strength 0.2 showed maximum cumulative % permeation in vitro. Considering lacrimation induced drug loss in vivo, by buffer of high concentration, ketorolac tromethamine drops formulated in buffer of low molarity, pH 4.5 and ionic strength 0.2 appear suitable.     

Effect of concentration, pH, and preservative on in vitro transcorneal permeation of ibuprofen and flurbiprofen from non-buffered aqueous drops

Influence of drug concentration, pH of aqueous drops and some commonly used preservatives on in vitro transcorneal permeation of ibuprofen and flurbiprofen were investigated using goat cornea. Increase in drug concentration in the drops made in normal saline resulted in increase in quantity permeated but decrease in cumulative percent permeation of both drugs. Permeation of each drug from 0.5% drops was maximum at acidic pH (6.4) and decreased with increase in pH of the drops. Normal saline, as a vehicle, favoured permeation of each drug, hence retained in the formulation. Benzalkonium chloride and chlorobutanol enhanced cumulative percent permeation of ibuprofen while benzalkonium chloride and phenyl mercuric nitrate increased permeation of flurbiprofen. Benzalkonium chloride being incompatible with 0.5% drops (pH 6.4) of either drug, chlorobutanol appears suitable for ibuprofen drops and phenyl mercuric nitrate for flurbiprofen drops.