Showing papers by "Indian Institute of Technology Kharagpur published in 1974"

Concrete Bearing Strength—Support, Mix, Size Effect

Abstract: Although the problem of large forces acting over limited contact areas of concrete is often encountered in engineering design, a theoretical rendering of the behavior and ultimate bearing strength of concrete is extremely difficult because of the overall complexity of the problem. Experimental studies are, therefore, imperative. The bearing strength of concrete is affected by several diverse factors. In this paper, the nature of bed (rigid or yielding) supporting the specimen, supported area of specimen, concrete properties, and size of specimen are considered as the principal variables, and their effect on the bearing strength ratio, i.e., the ration of ultimate local bearing stress to the concrete cube strength is presented on the basis of comprehensive tests.

Origin of garnet in the basic granulites around Saltora, W. Bengal, India

Abstract: Garnetiferous basic granulites occur, as parts of hornblende-pyroxene- and pyroxene granulites, in a Precambrian terrain around Saltora. The chemistry of the garnetiferous basic granulites is broadly similar to that of the hornblende-pyroxene granulites, their immediate precursors, but in detail they have distinctly higher Fe/Mg ratios. The compositions of the major mafic silicates of the garnetiferous varieties do not reflect higher pressures of formation: the Jd/Ts ratios in calcic pyroxenes are similar to those from the non-garnetiferous varieties, and the pyrope contents of garnets are low.

On the analysis of thermoluminescence glow pattern

Abstract: In the case of a thermoluminescence (TL) glow pattern which exhibits several overlapping glow maxima at different regions of temperature, the available methods cannot be used profitably to calculate trap depth (E) and frequency factor (S) for the different glow peaks of the pattern unless they are made well separated. A simple method is suggested by which it becomes possible to analyse such a complex TL pattern from its high temperature end and get well separated peaks. An analysis of the TL patterns of pure and doped CaF2 crystals (excited by 10 kV electrons in the temperature range 300 to 450 K) indicates that the glow peaks, observed between 300 and 700 K, are associated with traps having depths (E) in the range 0.52 to 1.65 eV and frequency factors (S or S′n0) in the range 6.1 × 105 to 1.2 × 1013 s−1. Im Falle einer Thermolumineszenz (TL)-Glowkurve, die mehrere uberlappende Glowmaxima in verschiedenen Temperaturbereichen besitzt, konnen die ublichen Methoden zur Berechnung der Haftstellentiefe (E) und des Frequenzfaktors (S) fur verschiedene Glowmaxima der Kurve nicht erfolgreich benutzt werden, wenn diese nicht gut getrennt werden. Es wird eine einfache Methode vorgeschlagen, mit der es moglich ist, eine solche komplexe TL-Kurve von ihrem Hochtemperaturende her zu analysieren und gut getrennte Maxima zu erhalten. Eine Analyse der TL-Kurven von reinen und dotierten CaF2-Kristallen (Anregung durch 10 kV-Elektronen im Temperaturbereich 300 bis 450 K) zeigt, das die Glowmaxima, die zwischen 300 und 700 K beobachtet werden, mit Haftstellen verknupft sind, deren Tiefe (E) im Bereich 0,52 bis 1,65 eV liegt mit Frequenzfaktoren (S oder S′n0) im Bereich 6,1 × 105 bis 1,2 × 1013 s−1.

Late Stress Systems Deduced from Conjugate Folds and Kink Bands in the ‘Main Raialo Syncline,’ Udaipur District, Rajasthan, India

Abstract: Two sets of conjugate folds and kink bands of different orientation are present in the mica schist flanked by marble of the “main Raialo syncline” in central Rajasthan. The region shows the effect of two systems of large-scale folding; west-trending isoclinal folds with variable axial surface have been involved in upright folding on north- to northeast-striking axial planes. These folds have been followed by the movements that generated the kink bands and conjugate folds. The mica schists showing the late-phase structures are in a zone of well-developed vertical schistosity striking northeast. The first set of conjugate folds and kink bands (F 3 ) has its axial planes dipping gently northeast and southwest, whereas the paired axial planes of the later set (F 4 ) are vertical with north-northwest–south-southeast and east-west strikes. Determination of the orientation of the principal stress axes during the late phases of movement indicates that the F 3 conjugate structures developed when the maximum compressive stress was vertical and the intermediate compressive stress direction almost normal to the schistosity plane. In the last phase of movement (F 4 ), the stress system was reoriented in such a way that the maximum compressive stress direction became horizontal parallel to the strike of the schistosity, and the intermediate compressive stress direction became vertical.

Analysis of Externally Pressurized Gas Porous Bearings

Abstract: An analytical solution is presented to predict the performance of an externally pressurized porous gas thrust bearing. When the wall thickness of the pad is small compared to its radius, the expressions for the bearing characteristics can be given in a closed form. The bearing number Λ—a dimensionless design variable—can adequately describe the performance of the bearing. The load capacity and mass flow rate progressively increase with the bearing number; the static stiffness increases with the bearing number up to Λ ∼ 4.0 and then gradually decreases. The decisive influence of permeability of the pad material in controlling the performance of the bearing is discussed and the interesting behaviour of the static stiffness as the film thickness is reduced is pointed out. It is found that there is near perfect agreement between the predicted performance of the bearing and the one experimentally evaluated. The characteristics are plotted over a wide range for the bearing number (.01 ≤ Λ ≤ 2500) in such a way that the information is of direct use to designers and applications engineers. Also, the results are given in tabular form to facilitate interpolation of the values as required.

A Review of Some Geochemical Characters of the Type Area (Pallavaram, India) Charnockite

Abstract: Available good quality data on the major element chemistry of charnockitic rocks of the type area and their minerals, though few, permit generalising on some significant aspects of their geochemistry hitherto not focussed upon. Rocks belonging to even the 'charnockite suite' of Subramaniam (1959) exhibit migmatitic rather than magmatic chemistry; migmatisation is also reflected in subtle changes in the chemistry of some minerals such as hornblendes. The grand average of all charnockitic rocks of the type area correspond to an intermediate composition like that ofa diorite and is similar to the average compositions of other well-studied charnockite areas. The lower crust, according to current belief, is probably of such composition; and in as much as charnockites-granulites make substantial contribution to the Precambrian shield areas, they should be included in computing the average chemical composition of the shields and the continental crust. This would result in lower Si for shield averages, and lower K, Ti, Fe and higher Si for the continental crust.

Two Loop Adaptive Delta Modulation Systems

Abstract: Two adaptive delta modulation (ADM) coders, one for A/D conversion of speech and the other for fiat spectrum signals, have been developed by incorporating a second adaptive feedback loop around the basic delta modulation (DM) coder. The dynamic range of the coder for integrated spectrum has been extended to more than 35 dB with a signal-to-noise ratio (SNR) > 28 dB, for a pulse-repetition frequency (PRF) of 32 kbits/s only, by using an adaptive circuit consisting of digital/analog slope detector and an FET expander. For flat spectrum signals, similar results with constant SNR over the band are obtained at a bit rate of 40 kbits/s. Thus the coders have performances equivalent to those of a 7-digit PCM, using only 32 and 40 kbits/s, respectively.

Fourier transforms of magnetic anomalies of two-dimensional Bodies

Abstract: Fourier transforms of theoretical magnetic anomalies of two-dimensional bodies (vertical fault and horizontal cylinder of infinite length) are computed. In both cases it is shown that for a particular body the amplitude spectra of horizontal and vertical anomalies are the same and the phase spectra differ by π/2. Different parameters like depth and susceptibility contrast can be calculated from the amplitude spectrum.

Kinetic study of silver iodide film growth on silver at low temperatures (30-73° C)

Abstract: Studies on tarnishing of silver in iodine atmosphere both for thinner (<6000A) and thicker (5500 to 30000A) silver iodide film formation in the temperature and pressure ranges of 30° to 73°C and 0.019 to 1.241 mm Hg, respectively, show the validity of a parabolic growth law. While the rate constant value for the thinner halide film range has been found to be proportional top 1.5 I2 the same for the thicker film growth follows a modified √pI2 relation. These unusual pressure dependences suggest a situation of non-attainment of steady state conditions at the phase boundaries of the films. An activation energy value of 6.3 ± 1.5 kcal mole-1 in the above temperature range atp I2 = 0.039 mm Hg is in accord with that obtained by analyzing others’ data, thereby supporting the hole diffusion controlled process of Wagner. The presence of moisture in the atmosphere has been found to reduce the rate of iodination. Comparison of tarnishing behavior between annealed and cold deformed silver samples demonstrates a reduction in rate of iodination with percentage cold work.

Studies on Dicumyl Peroxide Vulcanization of Styrene—Butadiene Rubber in Presence of Sulfur and 2-Mercaptobenzothiazole

Abstract: The effect of sulfur, MBT, zinc oxide, and stearic acid on the DCP vulcanization of SBR has been studied. DCP decomposition obeys first order kinetics in all cases, but its rate constant i...

On the thermal bending of a thin elastic simply supported rectangular plate resting on an elastic foundation

Abstract: Deflection and bending moments of a thin isotropic rectangular plate, having its edges simply supported and maintained at zero temperature, have been investigated in this paper. The upper surface is kept at a constant temperature while the lower surface, which is in contact with an elastic foundation, is thermally insulated.

Glass formation in the system CaO-Al2O3-CaF2

Abstract: The formation of glass in the system CaO-Al2O3-CaF2 has been investigated in sealed platinum capsules having about one atmosphere pressure of AlF3 vapour. Transparent colourless glass could be obtained in the low-fluoride moderate-alumina region of the system (Al2O3 35 to 60%, CaF2 0 to 20%). With the concentration of CaF2 exceeding 20% considerable amount of quench crystals of CaF2 appeared in the glass. Moderate-alumina low-lime melts containing more than 35% CaF2 occur in an immiscibility zone. At the low-fluoride periphery of the liquid immiscibility zone a small zone of metastable liquid immiscibility has been found. The results of electron microscopic and infra-red spectroscopic studies of a few selected glasses have been analysed in combination with the molar refractivity data to reflect upon the co-ordination characteristics of aluminium in these glasses.

Some Digitally Controlled Devices for Adaptive Control

Abstract: In adaptive control systems the controller parameters are to be adjusted in real time in accordance with the information received from the measurements on system dynamics. A special purpose or general purpose digital computer is often necessary for generating the signals for controller parameter adjustments. In this paper we describe a few electronic devices whose parameters are directly under the control of digital signals. These devices will be of great use for many applications including adaptive control. The devices described in this paper are, digitally controlled variable gain amplifier, digitally controlled compensating network and digitally controlled variable frequency sampler.

Thermoluminescence of electron-irradiated CaF2

Abstract: Storage of excitation energy in CaF2 crystals, irradiated by low- energy electrons, is found to be very much less compared to x-ray irradiation; the TL (thermoluminescence) yield is, in general, very poor for all the temperatures of excitation between 300 and 500 deg K. While the crystal, excited by electrons at RT, shows a complex distribution of glow maxima in the temperature region between 300 and 700 deg K, it does not seem to show any TL for excitation at about 500 deg K or above; in the latter case the crystal becomes densely colored and shows alpha and BETA absorption bands. The comparatively low intense glow peaks occurring below 500 deg K may be associated with the trapping states related with the trace impurities. Absence of TL in the colored crystal is explained by assuming that, during the process of excitation at or above 450 deg K trapped holes diffuse away from the affected layer and facilitate the formation of alpha and BETA absorption bands.