Generation of square and triangular wave with independently controllable frequency and amplitude using OTAs only and its application in PWM

This paper presents a self-generating square/triangular wave generator using only the CMOS Operational Transconductance Amplifiers (OTAs) and a grounded capacitor. The output frequency and amplitude of the proposed circuit can be independently and electronically adjusted. The proposed circuit validates its advantage by consuming less amount of power, which is about 71.3 µW. The theoretical aspects are authentically showcased using the PSPICE simulation results. The performance of the proposed circuit is also verified through pre layout and post layout simulation results using the 90 nm GPDK CMOS parameters. A prototype of this circuit has been made using commercially available IC CA3080 for experimental verification. Experimentation also gives the similar output as per the theoretical proposition. The designed circuit is also made applicable to perform pulse width modulation (PWM).     

Analysing the patterns of spatial contrast discontinuities in natural images for robust edge detection

Pattern Analysis and Applications - The pattern of spatial contrast discontinuities in natural images has been analysed in the present work, and based on it, a new adaptive model of the...     

One pot synthesis of nano Ag in calcium alginate beads and its catalytic application in p‐Nitrophenol reduction with kinetic parameter estimation and model fitting

In this work, one step process of synthesis of silver nanoparticles (Agnp) embedded in insitu formed calcium alginate (CA) beads is stated. CA, formed from the reaction between sodium alginate and calcium hydroxide, acts as reducing and stabilizing agent as well as support for nanoparticles. The reaction mechanism for the formation and stabilization of Agnp is proposed where the vicinal dihydroxy groups of alginate are assumed to act as the reducing agent for Ag⁺ to Ag°. Transmission electron microscopy (TEM), x‐ray diffraction (XRD), UV‐vis spectroscopy, field emission scanning electron microscopy (FESEM), and atomic absorption spectroscopy (AAS) were used to characterize the Agnp. The formation of spherical nanoparticles with average size range of 4‐5 nm was confirmed by TEM. Catalytic activity of this nano silver‐calcium alginate (Agnp‐CA) composite was evaluated in the reduction of p‐nitrophenol. Concentrations of sodium alginate, calcium hydroxide, and AgNO₃ are found to be the parameters that critically affect the synthesis of Agnp. The efficacy of the catalyst is expressed on the basis of suitable reaction parameters. Both pseudo‐homogeneous and heterogeneous kinetic models are proposed for the reaction to find the best model and the Eley‐Riedel model is found to fit well with the experimental data. The novelty of this work is that the tandem process of CA bead formation, Agnp formation, and Agnp entrapment in CA have been transformed into a single‐step process. Moreover, elaborations of each step of the ionic mechanisms of Agnp formation and p‐NP reduction with Agnp and the establishment of a heterogeneous kinetic model for the reaction are reported for the first time here.     

Slow release polymer–iodine tablets for disinfection of untreated surface water

Simple water treatment devices are designed to treat small amounts of drinking water for home use. This study was undertaken to develop an iodine‐releasing polymeric formulation and examine its potential as a domestic water purifier for untreated surface water. The antimicrobial tablet formulation was made from gum arabic (GA), poly(vinylalcohol) (PVA), ethyl cellulose (EC), and poly(vinylpyrrolidone)‐iodine (PVP‐I). The formulation consisted of a dispersible core tablet surrounded by a hydrophilic coating of EC and poly(ethylene glycol) mixture. These stable, non‐vaporizing, and water‐insoluble tablets slowly release iodine through diffusion over 48 h when suspended in water. The swelling behavior and release were observed to be the functions of excipient composition, iodine loading, and coating materials. Iodine release was determined by UV–VIS spectroscopy and volumetric titrations. The tablets were also assessed for antimicrobial activity against Escherichia coli, Staphylococcus aureus, Listeria monocytogenes Scott A, and Salmonella typhimurium. The disinfection efficiency of the developed tablets was compared with a commercial formulation (Potable Aqua®) as both contain iodine‐releasing active compounds and work on the antimicrobial property of released iodine. The difference between the two formulations is that water‐dispersible Potable Aqua® has a higher amount of free iodine quickly available in water thereby making it a fast‐action emergency water purifier, whereas the developed water‐insoluble polymer–iodine tablets act slowly and require 24 h to show the same disinfection efficacy with lower content of iodine in water. Overnight release of iodine in water from polymer–iodine tablets was effective in 99.9% reduction of an initial cell count of ～ 10⁷ colony forming units (cfu)/mL. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Reduction of Cr(VI) to Cr(III) and removal of total chromium from wastewater using scrap iron in the form of zerovalent iron(ZVI): Batch and column studies

This work experimentally investigates Cr(VI) reduction to Cr(III) using waste scrap iron in the form of zerovalent iron (ZVI) collected from the mechanical workshop of the Institute, both in batch and continuous operation. The reduction of Cr(VI) to Cr(III) was found to be complete (～100%) depending on the experimental conditions. Lower pH values favour Cr(VI) reduction. Two concurrent reactions take place, that is reduction of Cr(VI) by Fe⁰ (ZVI) and by Fe²⁺ generated due to H⁺ corrosion of iron. Maximum around 22%, 11% and 2% Cr(III) remained dissolved in solution while the experiments were carried out at initial pH of 2, 4.67 and 7. Higher ZVI loading increases Cr(VI) reduction rate, however, consumption of iron is noted to be higher. The results indicate that the bed is exhausted rapidly at higher pH, initial Cr(VI) concentration and flow rate. This is attributable to predominance passivation of ZVI surface forming Cr(III)–Fe(III)‐oxide layer. SEM analysis of ZVI before and after the experiments confirms formation of passive oxide on iron surface is responsible for deterioration of Cr(VI) reduction efficiency due to its blanketing effect.     

A Robust Experimental Methodology for Polymer Bubble Inflation

In thermoforming technique thermoplastic sheets are heated up well above their glass transition temperature and formed to the required shape by using an appropriate mold. Characterization of thermoplastic materials for thermoforming can be accomplished by employing polymer bubble inflation and rheology tests instead of undertaking expensive biaxial tensile testing. Polymer bubble inflation technique is very sensitive to process condition variations, so a robust experimental methodology is essential. Design and development of one such experimental system was undertaken by carrying out a variety of preliminary tests. This paper presents the experimental methodology developed for polymer bubble inflation. The developed experimental system demonstrates highly repeatable polymer bubble inflations. Bubble inflations were conducted at different temperatures and different diameter circular clamping using acrylonitrile butadiene styrene (ABS) thermoplastic. Polymer sheet initial sag due to heating and its influence on bubble inflation have been captured by using the experimental system.     

Effect of aspect ratio on bed expansion in pirticulate fluidization

The effect of aspect ratio on the degree of bed expansion in particulate fluidization has been studied. For unicomponent solid systems of crushed particles with water as the fluidizing medium, the degree of bed expansion is independent of aspect ratio. Coal and limestone have been taken as the solid while aspect ratio has been varied from 1.10 to 4.67. The result is in full conformity with previous work with steel balls.     

Physical and mathematical modelling of flow and residence time distributions in different tundish designs

A steady state, three‐dimensional, turbulent flow model has been developed in‐house for analysis of melt flow and residence time distribution phenomena in steelmaking tundish system. The governing equations of flow, turbulence and tracer dispersion were derived in terms of the Cartesian co‐ordinate systems and solved numerically with their associated boundary conditions adapting a control volume based finite difference procedure. In the numerical solution scheme, the pressure‐velocity coupling was treated via the popular Simple (semi implicit method for pressure linked equations) algorithm. Prior to carrying out elaborate numerical predictions for tundish geometry, the model was applied to several standard test problems and evaluated against corresponding bench mark results. Thus, several typical test problems such as, flows in a cubic cavity, flows in ducts of rectangular cross‐section, flow over flat plate and so on were simulated numerically to assess the adequacy and appropriateness of the computational procedure developed. Results thus obtained together with the bench mark solutions indicated that the mathematical model is internally consistent and sufficiently robust. Accordingly, the turbulent flow model was applied to simulate flow and Residence Time Distributions (RTD) in four different tundish designs . These included, a single strand and a two strand slab casting tundish systems, a six strand rectangular shaped tundish and a six strand delta shaped billet casting tundish. Various RTD parameters (e.g., minimum break through time, t_min, time at which peak concentration occurs, t_peak and average residence time, t_av) were computed numerically in the four tundish systems and these were subsequently compared with corresponding experimental measurements derived from equivalent water model tundish systems. Except for the single strand tundish system, large differences between measurements and prediction (particularly on t_min and t_peak) were noted for the other three tundish geometries. Furthermore, the extent of such discrepancy was found to be relatively more pronounced for the multi‐strand tundish system. The possible reasons for such discrepancy is discussed in the text and it was shown computationally that relatively better agreement between theory and measurement can be achieved if, instead of the high Reynolds number k‐ε turbulence model, a low Reynolds number turbulence model is applied in the computational procedure.