Particle distribution control in cast aluminium alloy-mica composites

A suspension of mica particles (40m diameter and 3.7 thick) obtained in a mechanically stirred Al-4 wt % Cu-1.5 wt % Mg melt was poured and solidified in a variety of moulds under different heat flow configurations. The resulting cast structure showed a non-uniform distribution of dispersed mica particles with mica-depleted and segregated zones due to their flotation before and during solidification. The experimentally observed profiles of mica-free regions deviate significantly from those computed on the basis of Stokes's law and freezing-time computations. In relatively thick castings, segregation of mica could be minimized by using low pouring temperatures and/or side as well as bottom chilling. It was found, however, that thin castings (12.5 mm) could easily be produced with a homogeneous distribution of mica particles.     

Minimization and identification of conducted emission bearing current in variable speed induction motor drives using PWM inverter

The recent increase in the use of speed control of ac induction motor for variable speed drive using pulse width modulation (PWM) inverter is due to the advent of modern power electronic devices and introduction of microprocessors. There are many advantages of using ac induction motor for speed control applications in process and aerospace industries, but due to fast switching of the modern power electronic devices, the parasitic coupling produces undesirable effects. The undesirable effects include radiated and conducted electromagnetic interference (EMI) which adversely affect nearby computers, electronic/electrical instruments and give rise to the flow of bearing current in the induction motor. Due to the flow of bearing current in the induction motor, electrical discharge machining takes place in the inner race of the bearing which reduces the life of the bearing. In high power converters and inverters, the conducted and radiated emissions become a major concern. In this paper, identification of bearing current due to conducted emission, the measurement of bearing current in a modified induction motor and to minimize the bearing current are discussed. The standard current probe, the standard line impedance stabilization network (LISN)), the electronics interface circuits are used to measure high frequency common mode current, bearing current and to minimize the conducted noise from the system. The LISN will prevent the EMI noise entering the system from the supply source by conductive methods, at the same time prevents the EMI generated if any due to PWM, fast switching in the system, will not be allowed to enter the supply line. For comparing the results with Federal Communications Commission (FCC) and Special Committee on Radio Interference (CISPR) standards, the graphs are plotted with frequency Vs, line voltage in dBμ V, common mode voltage in dBμ V and the bearing current in dBμ A with out and with minimizing circuits.     

Predicting Transient Storage Model Parameters of Rivers by Genetic Algorithm

The presence of transient storage zone modifies the riverine pollutant transport. In the present work, new empirical expressions for three key parameters of transient storage model (TSM), an important method for predicting concentration variation of pollutants in rivers, have been derived employing genetic algorithm on published hydraulic data on river reaches and TSM parameters. The proposed expressions use few hydraulic and geometric characteristics of rivers that are usually available. Based on various performance indices, it can be concluded that the proposed expressions predict TSM parameters more reliably in comparison to the other empirical expressions for predicting TSM parameters.     

Fe-Nd-B magnets via the hot extrusion of amorphous powders

A rapid solidification melt spinning technique has been developed to produce amorphous powders of Fe-Nd-B alloys modified with hafnium diboride. The amorphous powders are consolidated by the hot extrusion technique into bulk magnets of various cross sections. Consolidated magnets show ultrafine grain structure stabilized by ultrafine submicron hafnium diboride particles. The extruded magnets develop strong texture-induced magnetic anisotropy which leads to attractive energy product values of up to 16MGOe. Significant improvement in coercivity is also achieved due to ultrafine grain structure of the extruded magnets.     

CHARACTERIZATION AMD POTENTIAL UTILIZATION OF WHITEROCKS (DTAB) TAR SAND BITUMEN II. PYROLYSIS MASS SPECTROMETRY AND NUCLEAR MAGNETIC RESONANCE ANALYSES

The proton and carbon-13 nuclear magnetic resonance characteristics of the native Whiterocks bitumen were determined by comparing the spectra of the samples to literature assignments. The tentative structural assignments of pyrolysis products were also obtained from the spectra of Curie-point low voltage mass spectrometric analysis. The results obtained from proton and carbon-13 nuclear magnetic resonance and pyrolysis-mass spectrometry analysis suggested that the native bitumen consists mostly of short- and long-chain (i.e., normal and isoprenoid chains) alkylsubstituents attached to polycyclic naphthenic, naphtheno-aromatic and/or aromatic moieties.     

Analytical formulation of small signal stability analysis of power systems with nonlinear loads

The online version of the original article can be found at     

Optimisation of the alkaline peroxide pretreatment for the delignification of rice straw and its applications

Alkaline peroxide pretreatment for the delignification of rice straw was optimised by varying the concentrations of H₂O₂ and NaOH and changing the temperature and duration of the pretreatment. Changes in the lignin content, content of total carbohydrates and weight loss were measured during the pretreatments. Maximum delignification of 62% was obtained by pretreating rice straw at 50°C for 5h with 1.5% (w/v) NaOH and 1% (v/v) H₂O₂, The preferential loss of hemicellulose and lignin from the straw resulted in an increase in the cellulose content of the insoluble residue after pretreatment from 47% (untreated) to 67.79% (treated). The product of this treatment is characterised by having higher cellulose digestibility than untreated rice straw. It also has use as a carbohydrate source in ruminant feed since the in-vivo digestibility by the cow increased from 56.85 % to 76.54% (P < 0.001). The treated rice straw could also be used for commercial process such as the generation of Single Cell Protein. Growth of Sporotrichum pulverulentum on treated rice straw gave a protein product of 24.41 % as compared to 3.8% on untreated rice straw.     

Estimation of reliability of stress-strength model with non-identical component strengths

An attempt has been made in this paper to estimate the reliability of an s-out-of-k system with non-identical component strengths when component strengths follow an exponential distribution. A further assumption is made that all the components are subjected to a common random stress which also follow an exponential distribution. Bayes and maximum likelihood estimators of such system reliability are considered. A Bayes estimate is obtained by using Lindley's approximation. Comparisons are made on the basis of efficiency and Pitman nearness probability through a Monte-Carlo study.     

Surfactants, polymers and their nanoparticles for personal care applications

A 'touch me not' plant folding up rapidly upon being attacked or microbes depositing on teeth or ocean vessels even under hostile conditions are examples in nature that provide inspiration for developing new classes of personal care release or deposition systems. In this paper, development of such systems based on polymer/surfactant colloid chemistry is explored for achieving transport and release of cosmetic and pharmaceutical molecules at desired rates at desired sites. The successful development of products depends upon understanding and utilizing key interactions among surfactants, polymers and hybrid polymers that are relevant to personal care products. Thus, the absorbed layers or tethers on the particulates can be manipulated for desired dispersion of actives or depositions on substrate under any and all conditions. New hybrid polymers and nanogels have been synthesized for tuning up nanodomains that can extract and deliver at will cosmetics/drugs/toxins by perturbing pH, temperature or ionic strength of the system. Particularly, hydrophobically modified polymers have features of both polymers and surfactants and due to the associative nature of the hydrophobic groups, such polymers can form intramolecular nanodomains for performing carrier functions. Nanogels developed recently include that of polyacrylamide, poly(acrylic acid) and starch nanogels modified for extraction and subsequent slow release of fragrances and overdosed toxic drugs. Binding and release processes were investigated using surface plasmon resonance and fluorescence spectroscopies, powerful techniques for monitoring short term and long term changes.