Synthesis and characterization of stable aqueous dispersions of graphene

A stable aqueous dispersion (5 mg ml^?1) of graphene was synthesized by a simple protocol based on three-step reduction of graphene oxide (GO) dispersion synthesized using the modified version of Hummers and Offeman method. Reduction of GO was carried out using sodium borohydride, hydrazine hydrate and dimethyl hydrazine as reducing agents. The chemically synthesized graphene was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopy, thermogravimetric analysis (TGA), optical microscopy. The stability of aqueous dispersions of graphene was confirmed through zeta potential measurements and the negative zeta potentials of 55–60 mV were obtained indicating the high stability of aqueous graphene dispersions.     

A Simple Technique for Scaling Up Pneumatic Conveying Systems

A brief survey has shown that although scaling-up techniques in pneumatic conveying systems have generally been based on laboratory-scale test data, there still exists a divergence of opinions about the right choice of certain basic parameters such as solids friction factor and air friction factor. In this article, a simple model for pressure drop calculation has been proposed based on the classical Darcy's equation with some modifications. A parameter K, called pressure drop coefficient, has been shown to be independent of pipe diameter and hence suitable for scaling up to pipe sizes different from those used in laboratory-scale tests. For each of the bulk material and pipe size combinations used in this study, we calculated the standard deviation of predicted pressure values from the experimental values along the central 45° line passing through the origin; it varied from±165 mbar to a maximum±285 mbar. It has been shown that the model can be used for both horizontal and vertical pneumatic conveying.     

A multi-stage production inventory system,including service time

The basic objective in this paper is to bring down inventory carrying cost, in a multistage production inventory system, by incorporating the idea of service time in the model. The paper considers models with two types of information flow: the serial information flow, in which the inventories at each stage are measured against, orders placed by the following stage, and the parallel information flow, in which they are measured against customer orders materializing at the finished goods stage.

The optimization involved, considering the service times, smoothing of the production rate, etc., would serve to specify which points in the manufacturing process should be inventory points and which points should not. Also, it determines how big should the in-process inventories be for maximum operating efficiency.     

Magneto-dielectric effect in Pb(Zr0·52Ti0·48)O3 filled nanoporous Ni 0 ·5Zn 0 ·5Fe 2 O 4 composite

Nanoporous Ni_0·5Zn_0·5Fe₂O₄ particles of diameter, ~ 9·5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m² g^???1 and the average pore diameter was 2·5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr_0·52Ti_0·48)O₃ was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2·4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni_0·5Zn_0·5Fe₂O₄ which exerted a compressive strain on Pb(Zr_0·52Ti_0·48)O₃ thereby lowering the tetragonality in its crystal structure.     

Deposition and characterization of diamond-like nanocomposite coatings grown by plasma enhanced chemical vapour deposition over different substrate materials

Diamond-like nanocomposite (DLN) coatings have been deposited over different substrates used for biomedical applications by plasma-enhanced chemical vapour deposition (PECVD). DLN has an interconnecting network of amorphous hydrogenated carbon and quartz-like oxygenated silicon. Raman spectroscopy, Fourier transform–infra red (FT–IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used for structural characterization. Typical DLN growth rate is about 1  ${\upmu} $ m/h, measured by stylus profilometer. Due to the presence of quartz-like Si:O in the structure, it is found to have very good adhesive property with all the substrates. The adhesion strength found to be as high as 0·6 N on SS 316 L steel substrates by scratch testing method. The Young’s modulus and hardness have found to be 132 GPa and 14· 4 GPa, respectively. DLN coatings have wear factor in the order of 1 × 10^???7 mm ³ /N-m. This coating has found to be compatible with all important biomedical substrate materials and has successfully been deposited over Co–Cr alloy based knee implant of complex shape.     

Phase Transitions in LiAl5O8

LiAl₅O₈ exists in many forms. The equilibrium high-temperature form (I) has a spinel structure. It undergoes a first-order reconstructive transformation at 1295°× 5°C to an equilibrium low-temperature form (II) with primitive cubic symmetry, the unit edge changing from a ₀= 7.921 A (I) to a ₀= 7.907 A (II). In addition, a whole series of phases (II-metastable) exist with the same symmetry as II but with a disorder different from I → II disorder.     

Computerless optimal control of Ward Leonard drive system

The optimal control of a Ward Leonard drive system has been studied in this paper from the stand-point of a control engineer rather than that of the theoretical control scientist. The outcome of the Pontryagin principle was the design of an optimizing controller which may be a collection of commonly available electronic components. The equation of the optimizing controller of a Ward Leonard drive has been derived. No computer is required in the scheme.     

HEATING UNIFORMITY AND RATES IN A DOMESTIC MICROWAVE COMBINATION OVEN

Physics-based modeling complemented with magnetic resonance imaging (MRI) for validation can provide a novel means to understand and thereby optimize combination heating processes. The objectives of this study were to compare heating patterns in a combination of radiant, forced air and microwave oven measured by MRI with those predicted by coupled electromagnetics-heat transfer model; quantify speed and uniformity of heating for the different combination modes; determine the effect of food dielectric properties on heating patterns; and delineate the nature of individual heating modes and their combinations. The modes of radiant heating through heating elements and forced convection by fan led to a more uniform heating compared with the faster (but less uniform) heating method provided by the microwaves. Combination methods were faster than radiant, forced-air and microwave-only heating. Although the speed of heating increased appreciably for combination modes, the nonuniformity of heating did not increase as much.

PRACTICAL APPLICATIONS

The results from the study can be used to develop design recommendations/guidelines for combination heating for different thermal processes such as baking, broiling, roasting and reheating of different materials, grouping them based on their properties. The research can benefit the consumers, food services and equipment manufacturers to understand the combination heating process in a better way and to, thereby, use it efficiently. Without a fundamental understanding of the effect of various combinations, optimization of heating can be intractable. The fundamental approach used in this study would, therefore, help consumers and food services in preparation of safe and high-quality foods through combination heating. The work would also help equipment manufacturers in optimizing the designs of combination-heating ovens.     

Analysis of time-delay systems via shifted Chebyshev polynomials of the first and second kinds

A novel and general approach for obtaining the delay operational matrix of shifted Chebyshev polynomials of first or second kind is presented. This operational matrix is exact in the sense that it does not involve any approximation. Next, this paper shows the application of the delay operational matrix in the analysis of time-delay systems. Two illustrative examples are included and the results are compared with those obtained by the exact method.     

A Static Variable-Frequency Three-Phase Source Using the Cycloconverter Principle for the Speed Control of an Induction Motor

This paper describes a variable-frequency source employing the cycloconverter principle. SCR's have been used as the principal switching and voltage-regulating devices. The logic of the firing circuit has been discussed. The factor affecting output frequency stability has also been presented. A three-phase variable low-frequency oscillator has been used as the reference to achieve the variation of frequency. Voltage variation has been affected by phase delaying of the firing pulses in a manner similar to that in a phase-controlled rectifier. Provision has been made for changing the phase sequence at the output in order to facilitate reversal of the direction of rotation of the motor. Experimental results include output waveforms of various frequencies (0-30 Hz), and speed variations of the experimental motor (1 hp, 100 V, 1700 r/min) in either direction of rotation thereby providing the practical feasibility of the SCR cycloconverter for speed control of induction motors.