Showing papers by "Indian Institute of Technology Kharagpur published in 1985"

Input impedance of annular ring microstrip antenna using circuit theory approach

Abstract: Input impedance and bandwidth of an annular ring microstrip antenna have been determined by modeling the antenna as a section of radial line loaded with wall admittances. The effect of mutual coupling between the radiating apertures has been taken into account. The theoretically calculated values of input impedance for TM 12 -mode are compared with measurements. The agreement is good. Higher order modes have been found to be present in the vicinity of TM 12 -mode. The reactance due to these modes can be utilized to increase the voltage standing-wave ratio (VSWR) bandwidth of the antenna.

The turbulent drag reduction by graft copolymers of guargum and polyacrylamide

Abstract: Commercial guargum is known to be a shear stable drag reducing agent. However, the aqueous solutions of guargum start degrading within 8 hrs. of their preparation and after 65 hrs., they degrade completely. In the present investigation, the graft copolymers of guargum and polyacrylamide have been prepared. It has been shown that the purification and grafting enhance the drag reduction effectiveness and biodegradation resistance considerably in guargum.

Layer type tungsten dichalcogenide compounds: their preparation, structure, properties and uses

Abstract: Tungsten dichalcogenides constitute a well defined family of compounds which crystallize in a layer type structure. These compounds find a wide range of applications in the field of catalysis and as a lubricant at high temperatures and pressures. They have also been investigated successfully as cathode and anode materials in photoelectrochemical cells for solar energy conversion. The layered tungsten dichalcogenides also exhibit superconducting behaviour when intercalated with alkali or alkaline earth metals and different divalent rare earth metals. In the present paper an attempt has been made to review the preparation, crystal structure and band models of tungsten dichalcogenides. Furthermore, we have tried to incorporate the physical, chemical, optical and electrical properties along with intercalation, thermal stability and uses of these compounds.

Production and purification of silicon by calcium reduction of rice-husk white ash

Abstract: Polycrystalline silicon of reasonable purity has been prepared by metallothermic reduction of purified rice-husk white ash (amorphous silica) by using calcium. The mechanism of reduction of the silica with calcium was investigated using simultaneous thermogravimetric analysis and differential thermal analysis, which revealed the reduction temperature to be around 720‡ C. The paper also discusses the method of preparation of silicon and its purification procedure. Characterization of the silicon sample thus prepared was made by X-ray diffraction, scanning electron microscopy and emission spectrography.

Studies on the melt flow behavior of thermoplastic elastomers from polypropylene—Natural rubber blends

Abstract: The melt flow behavior of thermoplastic polypropylenenatural rubber blends has been evaluated with specific reference to the effects of blend ratio, extent of dynamic crosslinking of the rubber phase and temperature, on viscosity, flow behavior index, and deformation of the extrudate. The proportion of rubber in the blend and the extent of dynamic crosslinking of the rubber phase were found to have profound influence on the viscosity of the blends at lower shear stresses. But at higher shear stresses, the effect of blend ratio on viscosity was comparatively less for the uncrosslinked blends than that for the crosslinked blends. At lower shear stress, the viscosity of the blend increased with increase in degree of crosslinking but at higher shear stress, the effect of crosslinking on viscosity was found to vary depending on the ratio of the plastic and rubber components in the blend. The deformation of the extrudates was also very much dependent on both blend ratio and degree of crosslinking.

Buckling analysis of anisotropic sandwich plates faced with fiber-reinforced plastics

Abstract: The small-deflection theory of orthotropic sandwich plates developed by Libove and Batdorf is extended to highly anisotropic sandwich plates with thin faces. Buckling coefficients of a simply supported rectangular symmetrical anisotropic sandwich plate under combined longitudinal compression and bending are evaluated using the Rayleigh-Ritz method. The results show that the multi-ply-faced orthotropic sandwich plate is stronger than a single-ply-fac ed anisotropic one and that the maximum longitudinal buckling strength occurs in plates with lower aspect ratios when the reinforcing fibers are longitudinal and in plates of higher aspect ratios when the fibers are oriented at about 40 deg with respect to the longitudinal axis.

Improvements in grinding steels by cryogenic cooling

Abstract: The intensive temperatures in high-speed machining and grinding not only limit the tool life but also impair the machined surface by inducing tensile residual stresses, micro-cracks and thermal damage. This problem becomes acute when the components are made of hard and strong materials and used in dynamic loading. In such cases drastic cooling is essential during machining. The authors have employed liquid nitrogen in the form of a jet in the surface grinding of a number of steels and found appreciable improvement, though to varying degrees, in their surface quality without significant change in specific energy requirement.

Effect of thermal stabilization on redox equilibria and colour of glass

Abstract: Oxidation-reduction equilibria in glass forming melts change with temperature, fugacity of oxygen, concentration of the redox ion and chemical composition of the melt. Near the glass transition temperature the rate of diffusion of oxygen into the melt is slow and no significant change of oxidation state takes place with conventional rates of cooling. However, if more than one redox oxide is present then during cooling the melt, mutual interaction takes place causing changes in the oxidation state and colour of the glass; the extent of the interaction depends upon the rate of cooling. Rate of cooling of the melt vis-a-vis “Fictive Temperature” also affects the coordination equilibria of some transition metal ions and thus causes a change of colour of the glass. Mutual interaction of manganese-arsenic in a silicate glass is discussed.

Drag reduction effectiveness and shear stability of polymer-polymer and polymer-fibre mixtures in recirculatory turbulent flow of water

Abstract: The turbulent drag reduction caused by polymer-polymer and polymerfibre mixtures has been measured in recirculatory flow of water. Shear stability studies have also been made on a number of drag reducing polymers, asbestos fibres and their mixtures in recirculatory turbulent flow of water. Reynolds numbers ranged from 20,000 to 57,000. Both positive and negative deviations from linear additive behaviour have been observed in drag reduction caused by the polymer-polymer mixtures depending upon their compositions, flow rate and polymer species in the mixture. The drag reduction by the mixtures has been predicted by using simple mixture rule equations including an interaction parameter. This interaction parameter is believed to depend upon the polymer interaction in the polymer mixture. The random coil size and rigidity of the polymer molecules appear to be responsible for the synergism observed in the drag reduction caused by the mixture. In general, mixtures having larger solvation number seem to give positive synergism.

Spectral domain analysis of wall admittances for circular and annular microstrip patches and the effect of surface waves

Abstract: Wall admittances for circular and annular ring microstrip antennas have been determined, including the effect of the substrate. The magnetic current model is used and the analysis is carried out in Hankel transform domain. The final expressions for wall admittances are obtained in integral form. The contributions of the surface wave to the wall conductances have been determined by evaluating the integrals near the singularity using the singularity extraction technique. The radiation conductance has been determined by simple integration. The value of wall susceptance, obtained in this paper, agrees well with Kirchhoff's equivalent extension formula. A closed form expression for wall susceptance for the TM_{1n} mode has been obtained by curve fitting the numerical values. The effect of the substrate on wall admittance has been found to be significant for higher order modes and is shown to explain the measured input impedance of an annular ring microstrip antenna.

Scanning electron microscopy studies on tensile, tear and abrasion failure of thermoplastic elastomers

Abstract: The tensile strength, tear resistance and abrasion resistance of four different types of commercial thermoplastic elastomers have been studied and their fracture surfaces examined by scanning electron microscopy. Thermoplastic polyurethane (TPU) showed elastic deformation under tensile fracture, whereas in 1,2 polybutadiene (1,2 PB) the fracture was initiated by craze formation and propagated by tear failure. Styrene-isoprene-styrene block copolymer (K1107) showed ductile type failure whereas in styrene-butadiene-styrene block copolymer containing a higher proportion of styrene and silica filler (K5152), the fracture occurred by shearing action. The tear failure surfaces of the thermoplastic elastomers showed different fracture patterns which could be correlated with the tear strength of the materials. The tear fracture surface of 1,2 PB showed stick-slip tear lines and that of TPU had a broad tear path with vertical striations. The fracture surfaces of K5152 and K1107 had the characteristics of laminar tearing and uninterrupted continuous tearing processes, respectively. The abrasion resistance of the samples was in the order TPU>1,2 PB>K5152, which was manifested through the type of ridge patterns formed on the abraded surfaces. Abraded surfaces of TPU, 1,2 PB and K5152 showed closely spaced stable ridges, widely spaced ridges bridged by elongated fibrils and highly deformed ridges, respectively.

Synthetic ion-exchange resins

Abstract: This review highlights the developments in the field of cation-exchange, anion-exchange, composite and thermally regenerable resins. The main focus is on the literature on synthesis and physico-chemical properties. Cation-exchange and anion-exchange resins have been discussed on the basis of the nature of monomers involved in the synthesis of polymeric matrices of the resins. Composite ion-exchange resins which incorporate inert materials and magnetic particles are discussed. The polymerization techniques adopted to synthesize thermally regenerable ion-exchange resins possessing the maximum possible thermally regenerable capacity are dealt with.

Composite stage effects in unbalancing of series production systems

Abstract: Earlier studies on production systems had indicated that the output is optimum when the less variable stages are loaded slightly more than the more variable stages. It is shown in this paper that this guideline is violated in systems consisting of a hyperexponential stage. From a comparative study of several two-stage systems it is shown that the unusual unbalancing behaviour of the hyperexponential distribution is due neither to its negative memory nor to any abnormality in the plot of its higher moments but to the fact that it is a composite distribution. Considering a general two-stage system, in which each of the stages is composite to an arbitrary degree, it is shown that the mean cycle time of such a system can be written as a linear combination of the mean cycle times of the several sub-systems into which it can be decomposed. The unbalancing pattern of the overall system is shown to violate the conventional guideline because the component subsystems are in general grossly misbalanced when the over...

Effect of complete plant submergence at different growth stages on grain yield, yield components and nutrient content of rice

Abstract: Of the three growth stagesviz., seedling establishment, maximum tillering and flowering, complete submergence of plant at flowering stage was found to be most critical followed by seedling estabilishment and maximum tillering stages. Among the three stages of reproductive growth phase, booting stage was found to be most susceptible to complete submergence followed by flowering and post-flowering. The submergence at booting for 4 days was equally detrimental as that of 6 or 8 days at flowering. Irrespective of the growth stages, the plants subjected to complete submergence showed higher nitrogen content (in plant as well as in grain) as compared to those grown under control conditions (5±2 cm) and increased with the increase in duration of submergence. The P and K contents in the plant decreased under submergence.

Synthetic design of policy decisions in system dynamics models: A modal control theoretical approach

Abstract: Researchers and practitioners in system dynamics usually follow a trial-and-error process to design new policy decisions. They mainly use influence diagrams for this purpose. However, these diagrams portray the direction of influence but not its strength. Therefore, the process of policy design becomes time-consuming, especially for beginners and those working with insufficient computer facilities. This paper presents an alternative approach for policy design using modal control theory. Policy variables are treated as control variables by delinking them from other variables. This generally leads to greatly simplified models that are free from many nonlin-earities. Provided that this reduced system is linear and controllable, it is possible to synthetically generate control policies by modal control theory to ensure any prescribed degree of stability. These theoretical control policies then can be used to design realistic policy decisions. This approach has been used in a test example.

A gradient algorithm for center-frequency adaptive recursive bandpass filters

Abstract: Mean-square output of a center-frequency variable bandpass filter is employed as the performance criterion to make the filter self-adjusting to the center frequency of the input signal. A gradient ascending algorithm is proposed to update the center-frequency-dependent coefficients of the filter to maximize the performance function.

Effect of flow maldistribution on multipassage heat exchanger performance

Abstract: Multipassage heat exchangers are normally designed with the assumption that the fluid stream is uniformly divided among all the parallel channels. But, in practice, an improper entrance configuration or imperfect flow passages create a flow maldistribution. Paired-channel exchangers in which the channels are continuously distributed as a function of flow rate have been investigated. Two cases of continuous maldistribution have been considered: (1) “one-side” nonuniformity, the other side having a uniform flow distribution, and (2) “both-sides” nonuniformity, where each channel pair serves as a balanced counterflow exchanger. Comparison with discrete distribution models investigated by other authors shows that a two-size model is adequate to predict the overall effectiveness of the heat exchangers in most cases of practical interest.

Structural characterization of tin selenide thin films

Abstract: Etude de la microstructure de couches minces de SnSe, de 2 epaisseurs differentes (100 et 200 nm). Determination de la taille des cristallites, des microcontraintes, de la densite des dislocations et de l'espacement moyen entre plans cristallographiques. Influence de la temperature de depot

Synthesis of a novel polyesterimide

Abstract: A new polyesterimide has been synthesized from trimellitic acid anhydride, diaminodiphenylsulfone, and bisphenol-A following three different routes. Solubility behavior in different solvents, solution viscosity, density, crystallinity, and thermal and electrical properties of the polyesterimide have been discussed. Results indicate that the polyesterimide thus prepared has medium thermal stability.

Energetics of hydration of cordierite and water barometry in cordierite-granulites

Abstract: The Gibbs free energy and volume changes attendant upon hydration of cordierites in the system magnesian cordierite-water have been extracted from the published high pressure experimental data at \(P_{{\text{H}}_{\text{2}} {\text{O}}} \)=Ptotal, assuming an ideal one site model for H2O in cordierite. Incorporating the dependence of ΔG and ΔV on temperature, which was found to be linear within the experimental conditions of 500°–1,000°C and 1–10,000 bars, the relation between the water content of cordierite and P, T and \(f_{{\text{H}}_{\text{2}} {\text{O}}} \) has been formulated as $$\begin{gathered} X_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{crd}}} = \hfill \\ \frac{{f_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{P, T}}} }}{{\left[ {{\text{exp}}\frac{1}{{RT}}\left\{ {64,775 - 32.26T + G_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{1, }}T} - P\left( {9 \times 10^{ - 4} T - 0.5142} \right)} \right\}} \right] + f_{{\text{H}}_{\text{2}} {\text{O}}}^{{\text{P, T}}} }} \hfill \\ \end{gathered} $$ The equation can be used to compute H2O in cordierites at \(P_{{\text{H}}_{\text{2}} {\text{O}}} \)<1. Our results at different P, T and partial pressure of water, assuming ideal mixing of H2O and CO2 in the vapour phase, are in very good agreement with the experimental data of Johannes and Schreyer (1977, 1981).

A microstrip array of concentric annular rings

Abstract: Analysis of an array of concentric annular ring microstrip antennas is presented. The feasibility of such an array is based on the observation that annular rings with different mean radii can be designed to resonate at the same frequency for the TM 12 mode. The ring array can be excited by means of a single feed by interconnecting two consecutive rings with an impedance transformer. The design procedure for the rings and the impedance transformers for a particular amplitude distribution is discussed. An experiment with an array of two rings has been performed and is found to agree with the theoretical predictions.

Effects of complete plant submergence on vegetative growth, grain yield and some biochemical changes in rice plants

Abstract: Complete plant submergence for 6 or 9 days at 20 days after transplanting effected the same decrease in grain yield as submergence for 12 days at 40 days after transplanting. With increasing duration of submergence, tiller number, green leaves and dry weight of all varieties tested decreased. The decrease was less in the flood tolerant variety FR 13A than in other varieties. Contents of reducing sugars and amylase activity also decreased with increasing duration of submergence. The reducing sugar contents and amylase activity were higher and peroxidase activity was lower in flood tolerant variety FR 13A than in other varieties. The N contents increased and P and K contents decreased with duration of submergence.