Showing papers by "Indian Institute of Technology Kharagpur published in 1986"

The preparation and thermoluminescence of alkaline earth sulphide phosphors

Abstract: The present article offers a review of the material preparation and thermoluminescence (TL) of alkaline earth sulphide phosphors. Different methods of material preparation and characterization of alkaline earth sulphides in the form of polycrystalline powders, films, single crystals and pellets are described. In the process of impurity doping, the role of flux is explained. The general theory of TL and the different methods used to calculate the trapping parameters (E and s) from the TL glow curves are presented. The effects of impurities, flux, grain size, preparative parameters etc. on the TL of these materials are reported. The types of traps and trapping parameters obtained by various workers are given. Considering the results presented by various authors, possible impurity complexes are proposed. The potential applications of these phosphors in TL and OSL dosimetry, cathode ray tubes, electroluminescence panels and infrared sensors are briefly discussed.

Feature Extraction Methods for Character Recognition

Abstract: Feature extraction is an important stage in the recognition of characters particularly for handprinted characters Based on a study of the extensive literature in handwritten character recognition,

Short fiber-reinforced thermoplastic elastomers from blends of natural rubber and polyethylene

Abstract: Thermoplastic elastomer blends of natural rubber (NR) with high density polyethylene (HDPE) and with low density polyethylene (LDPE) were reinforced with short silk fiber Processing characteristics such as torque and temperature developed during mixing and the effect of processing parameters such as nip gap and number of passes in the mill necessary to secure maximum orientation of the fibers in the blends were studied A small nip gap and a single pass in the mill were found to give best results Of the different mixing sequences studied, the sequence where short fibers followed by rubber were added to the molten thermoplastic was found to give a uniform dispersion of fibers Fiber breakage and the change in aspect ratio of the fibers after mixing were also examined It was observed that, as a direct consequence of the mixing sequence, each fiber was coated with a layer of thermoplastic Although the properties improved on the addition of the dry bonding system of silica–resorcinol–hexamethylenetetramine, the comparatively long curing time required for full development of adhesion between the fibers and the matrix proved to be a major disadvantage associated with the incorporation of the bonding system The tensile and tear properties were substantially enhanced, but the ultimate elongation decreased sharply with increasing loading of short fibers in the blends The effect of fiber orientation and the development of anisotropy in the properties was also noted Scanning electron microscopy (SEM) studies of the benzene-extracted surfaces of the NR/HDPE (high density polyethylene) blends substantiated the theory of fibers behaving like “mechanical anchors” between the rubber and thermoplastic phase The effect of fiber loading on the tear and tensile properties of the blends of NR/LDPE with varying blend ratios was studied Most pronounced improvement in the properties on the addition of short fibers was observed in the high rubber blends As the plastic content in the blends increased, the short fibers were found to have a lesser influence on the properties SEM photomicrographs of the tensile and tear fracture surfaces indicated the fiber orientations and the effect of orientation, fiber loading, and blend ratios on the nature of fracture

Analysis of arbitrarily shaped microstrip patch antennas using segmentation technique and cavity model

Abstract: Arbitrarily shaped microstrip patch antennas have been analyzed for resonant frequency, input impedance, and radiation patterns. The segmentation technique and the cavity model have been used for this purpose. The usefulness and the accuracy of the method are shown through comparison with experimental results for a rectangular ring antenna. The agreement is seen to be very good. Ihe method appears to be more efficient compared to those reported so far for arbitrary shapes. Moreover, feed reactance is built into the analysis. The method presented here can also be used to analyze microstrip antennas with various types of loadings, e.g., shorting pins, matched loads, etc.

Jointly Optimal Block-Replacement and Spare Provisioning Policy

Abstract: This paper deals with the problem of finding a jointly optimal, block preventive replacement and spare provisioning policy for a system consisting of several like equipments. It studies the effect of inventory of spares on the optimal block replacement interval. For a single period replacement model, the jointly optimal preventive replacement interval is appreciably different from the corresponding optimal preventive replacement interval where only the replacement related costs are considered. For a multiperiod replacement model, the jointly optimal preventive replacement interval decreases from its single period optimal interval as the multiplicity of the period increases. This shows that a trade-off exists between the replacement related costs and the inventory related costs. Therefore, we get a replacement interval which is much lower than the optimal replacement interval in a single period model. There exists a finite optimal interval between two inventory replenishments not necessarily equal to the basic preventive replacement interval.

Drag reduction characteristics of graft copolymers of xanthangum and polyacrylamide

Abstract: Graft copolymers of xanthangum and polyacrylamide have been prepared by grafting acrylamide onto xanthangum using ceric-ion-initiated solution polymerization technique. These graft copolymers have been tested for their drag reduction effectiveness, shear stability, and biodegradability. It has been shown that the grafting enhances the drag reduction effectiveness and biodegradation resistance of xanthangum considerably.

Effect of cryo‐ground rubber on melt flow and mechanical properties of polypropylene

Abstract: The influence of cryo-ground rubber (CGR) on melt flow and mechanical properties of polypropylene has been investigated. Cryo-ground rubber was incorporated in the polypropylene matrix (a) in powder form and (b) as masterbatch with natural rubber. Natural rubber was found essential as a dispersing agent. The loading of cryo-ground rubber has no significant effect on viscosity at high shear rates (>61 s−1) but at lower shear rates (>61 s−1), viscosity functions change shape with increasing cryo-ground rubber content. The dynamic mechanical properties revealed that polypropylene is thermodynamically incompatible with natural rubber and cryo-ground rubber. Cryo-ground rubber in the powder form shows poor adhesion to polypropylene matrix and, therefore, decreases the impact strength at higher loading. Addition of masterbatch of cryo-ground rubber and natural rubber improves the impact strength of polypropylene.

Effect of cryoground rubber on properties of nr

Abstract: The influence of cryoground rubber (CGR) on the curing characteristics, physical properties, network structure, and failure behavior of natural rubber (NR) has been investigated. CGR was added at two different levels of curatives and in two different ways (i) in powder form and (ii) in mill-sheeted form (obtained by mechanical treatment of CGR in a two-roll mill). The form of CGR and level of curatives affect the processing characteristics and technical properties of CGR–NR blends. The acetone extractables in the CGR were found to affect the curing characteristics, but no significant effect on the physical properties was observed. Model mixes were prepared by adding partially vulcanized NR compound in the matrix of the same compound. A three-layer model was set up to study the diffusion of sulfur from the NR matrix phase to the CGR phase. Scanning electron microscope studies of the fractured surface revealed that the mechanical treatment of CGR effects improved adhesion of CGR to NR matrix and the compatibility between the two phases. CGR acts as an inert filler in NR.

Dynamic mechanical properties of thermoplastic elastomers from polypropylene–natural rubber blend

Abstract: The dynamic mechanical properties of thermoplastic elastomers from polypropylene natural rubber blends have been evaluated with special reference to the effect of blend ratio and extent of dynamic crosslinking of the elastomer phase The effects of HAF black and silica fillers have also been studied It has been found that increasing the proportion of elastomer phase reduced the storage modulus and increased the loss tangent values of the blends The effect of dynamic crosslinking was found to be more prominent in blends containing higher proportion of elastomer phase The improvement in storage modulus and decrease in loss tangent values were quite remarkable with increase in extent of crosslinking in these blends The 70:30 NR:PP blend was found to exist as a two-phase system, both the components forming continuous phases of the blend

Effect of substrate on the efficiency of an arbitrarily shaped microstrip patch antenna

Abstract: A general approach is presented for the determination of power radiated via the space wave and surface wave from the aperture of an arbitrarily shaped microstrip antenna. The magnetic current model is used for this, and the analysis is carried out in the Fourier domain to determine the effect of the substrate. It has been shown that, in the Fourier domain, the longitudinal components of electric and magnetic displacement vectors follow the transmission line equation and can be solved by inspection. An expression for total radiated power has been derived. The singularities of the integral for power radiation indicate the presence of surface wave modes, and the associated power has been obtained using a singularity extraction technique. The effect of the substrate on space wave power has also been determined. This theory has been applied to a rectangular patch antenna. The results are in conformity with those reported in the literature. It has been found that for the frequency range ( h/\lambda, ), the effect of dielectric substrate can be neglected.

Excitation of Waveguide by Stripline- and Microstrip-Line-Fed Slots

Abstract: This paper presents investigations on coupling between stripline/microstrip line and a rectangular waveguide coupled through a slot in the ground plane which is fixed in the cross-sectional plane of the waveguide. A closed-form expression for the impedance loading on stripline/microstrip line is evaluated from knowledge of the complex power flowing down the rectangular waveguide supporting the dominant mode and discontinuity in the modal voltage in stripline/microstrip line. The reactance cancellation is obtained by terminating the stripline/microstrip tine exciting the slot in a short-circuited stub. The structure under this condition forms a transition between stripline/microstrip line and a waveguide. The design curves on slot length versus frequency are presented for different values of dielectric constants. The variation of coupling as a function of frequency and also the location of the slot is evaluated. Numerical results for slot coupling useful for the design of waveguide simulators are also presented.

A conformal cylindrical microstrip array for producing omnidirectional radiation pattern

Abstract: Radiation patterns of rectangular microstrip patches arranged circumferentially on a circular cylinder have been computed. Both the axial patches and circumferential patches have been used. It has been found that the number of circumferential patches required for a given ripple in gain pattern is considerably less, thus simplifying the feed network. Comparison with experimental measurements shows good agreement.

Studies on physical and thermal properties of rice husk related to its industrial application

Abstract: The physical and thermal properties namely, bulk density, true density, angle of repose, specific heat and thermal conductivity of both unground and ground rice husk at different moisture contents ranging from 10 to 20%, wet basis (wb) have been found. Except for the angle of repose, the values of the other properties were higher for the ground husk than those of the unground ones. Various possible industrial applications of both unground and ground husk (e.g. production of insulation board, packing material and ceramics) have been discussed.

Some geobarometers involving cordierite in the FeO-Al2O3-SiO2(±H2O) system: refinements, thermodynamic calibration, and applicability in granulite facies rocks

Abstract: Five geobarometers involving cordierite have been formulated for quantitative pressure sensing in high grade metapelites. The relevant reactions in the FeO-Al2O3-SiO2 (±H2O) system are based on the assemblages (A) cordierite-garnet-sillimanite-quartz, (B) cordierite-spinel-quartz, (C) cordierite-garnet-spinel-sillimanite, (D) cordierite-garnet-orthopyroxene-quartz and (E) cordierite-orthopyroxene-sillimanite-quartz. Application of the barometric formulations to a large number of granulite grade rocks indicates that the cordierite-garnet-sillimanite-quartz equilibrium is widely applicable and registers pressures which are in good agreement with the “consensus” pressure estimates. The dispersion in the computed P values, expressed as one standard deviation, is within ±1.2 kbar. The geobarometers (B) and (C) also yield pressures which are reasonable and compare well with those computed from equilibrium (A). The estimated pressures from (D) and (E), both involving orthopyroxene, are at variance with these estimates. It has been argued that the discrepancy in pressures obtained from these geobarometers stems from an inadequate knowledge of activity-composition relations and/or errors in input thermodynamic data of aluminous orthopyroxene. The convergence of pressure values estimated from the barometric formulations, especially (A), (B) and (C), implies that the present formulations are more dependable than the existing formulations and are also capable of setting limits on P values in response to varying $$\begin{gathered} {\text{1/2Fe}}_{\text{2}} {\text{Al}}_{\text{4}} {\text{Si}}_{\text{5}} {\text{O}}_{{\text{18}}} \hfill \\ {\text{ = 1/3Fe}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} {\text{ + 2/3Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + 5/6SiO}}_{\text{2}} {\text{. (A)}} \hfill \\ {\text{1/2Fe}}_{\text{2}} {\text{Al}}_{\text{4}} {\text{Si}}_{\text{5}} {\text{O}}_{{\text{18}}} {\text{ = FeAl}}_{\text{2}} {\text{O}}_{\text{4}} {\text{ + 5/2SiO}}_{\text{2}} {\text{. (B)}} \hfill \\ {\text{Fe}}_{\text{2}} {\text{Al}}_{\text{4}} {\text{Si}}_{\text{5}} {\text{O}}_{{\text{18}}} {\text{ + FeAl}}_{\text{2}} {\text{O}}_{\text{4}} \hfill \\ = {\text{Fe}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} {\text{ + 2Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{. (C)}} \hfill \\ {\text{1/2Fe}}_{\text{2}} {\text{Al}}_{\text{4}} {\text{Si}}_{\text{5}} {\text{O}}_{{\text{18}}} {\text{ + Fe}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} \hfill \\ = {\text{Fe}}_{\text{3}} {\text{Al}}_{\text{2}} {\text{Si}}_{\text{3}} {\text{O}}_{{\text{12}}} {\text{ + 3/2SiO}}_{\text{2}} .{\text{ (D)}} \hfill \\ {\text{1/2Fe}}_{\text{2}} {\text{Al}}{}_{\text{4}}{\text{Si}}_{\text{5}} {\text{O}}_{{\text{18}}} \hfill \\ = 1/2{\text{Fe}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} {\text{ + Al}}_{\text{2}} {\text{SiO}}_{\text{5}} {\text{ + 1/2SiO}}_{\text{2}} .{\text{ (E)}} \hfill \\ \end{gathered}$$ . The present communication addresses the calibration, applicability and reliability of these barometers with reference to granulite facies metapelites.

Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters

Abstract: Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in LD and Q-BOP furnaces using six different circular tuyere arrangements. Splashing and ‘spitting’ were also examined with a view to finding a quiet bath with minimum mixing time and maximum mass transfer rate. Froude’s similarity criterion was fulfilled to determine gas flow rate and bath depth. Complete mixing time of water determined by tracer technique had been 0.9 second to 1.8 seconds for Q-BOP as compared to 6 seconds to 13 seconds for LD. This shows that the stirring intensity in Q-BOP is remarkably larger than that of LD. A simple relationship τ = 5.9(Q/N) −0.49 was obtained with gas flow rateQ and number of tuyereN. This indicates that flow rate of gas per tuyere should be intensified to realize better mixing. Mass transfer coefficient KBa for bottom blowing was found to be almost double that for top blowing. Of all the tuyere configurations studied for Q-BOP’s, a half circular tuyere arrangement was found to be the best considering all aspects of mixing, mass transfer, and bath agitation.

Rectangular microstrip antenna for circular polarization

Abstract: Richmond's reaction integral equation method is used to design a rectangular microstrip patch to produce a circular polarization. A rectangular patch with the aspect ratio a = W_{x}/W_{y} , in the range 1.015- 1.02 and corner fed by a microstrip line, produces circular polarization. For substrate with thickness d = 0.16 cm, a = 1.017 the nearly square patch gives maximum bandwidth.

Properties of cis- and trans-polyisoprene blends

Abstract: Measurements of thermodynamic compatibility, technological properties, stress-strain isotherms at high elongation, birefringence, and wide-angle x-ray diffraction have been made on blends of guayule rubber (cis-1,4-polyisoprene) and trans-polyisoprene (t-PI). Both cross-linked and un-cross-linked systems, prepared by mechanical mixing and solution mixing, have been used. Blends of cis-and trans-polyisoprene show complete thermodynamic compatibility above the mp of t-PI. The technological properties measured at room temperature deteriorate with the incorporation of 20% of trans-polyisoprene. Tensile strength of blend vulcanizate measured at temperature above the melting point of t-PI crystals is increased and the values of compression set are comparable. The critical value of λ at which the upturn occurs in the Mooney-Rivlin plot decreases with increase in t-PI. Studies on WAXD and birefringence show that t-PI does not act as a nucleating site for crystallization of cis-PI. Intensity of a new ring...