Showing papers by "Indian Institute of Technology Kharagpur published in 1975"

Hydromagnetic flow past a porous flat plate with hall effects

Abstract: An investigation is made of the flow of a conducting liquid past an infinite porous flat plate taking Hall effects into account, the liquid being permeated by a transverse magnetic field. It is shown that asymptotic solution for the velocity and magnetic field exists both for suction or blowing at the plate. Further when the magnetic Reynolds number is very small, the flow pattern is remarkably similar to that for a non-conducting flow past a flat plate in a rotating frame.

On the mean production rate of a two-stage production system of the tandem type

Abstract: SUMMARY Analytical solutions for the mean cycle time of a two-stage series production system with variable operation times at the stages are presented. Although the methodology is applicable to any type of service time distribution at the stages, typical cases of Erlang and normal distributions are worked out in detail. It is shown that the problem of a multi-stage unpaced belt production system can, in principle, be reduced to one of integration, for arbitrary service time distributions at the stages. Detailed expressions are obtained for the mean cycle time and in process inventory of a two-stage series production system with provision for an arbitrary level of interstage inventory. The service time at one of the stages is assumed to be constant and the other distributed exponentially. The analysis leads to the conclusion that at high values of coefficient of variation, the type of service time distribution has a considerable effect on the overall throughput of the system and unbalancing has a favourabl...

Dielectric Properties of Single Crystals of Al2O3 and Al2O3 Doped with Chromium or Vanadium

Abstract: Dielectric constant (K), loss (tan δ), and conductivity (σ) of single crystals of Al2O3, Al2O3: Cr (0.03 and 2 mol%) and Al2O3:V (2 mol%) have been measured as a function of frequency in the range 102 to 107 Hz and at temperatures between 30 and 450 °C, (where the electric field is always perpendicular to the optic axis). The K value of Al2O3, at 30 °C is 9.4 and frequency-independent. Doping by chromium or vanadium produces no detectable change in the K value of Al2O3. The dielectric loss of all these samples at 30 °C is below detection level (tan δ < 0.0005) throughout this frequency region. In these crystals, the dielectric constant increases with temperature exhibiting a frequency dependence from about 200 °C; the changes in K with temperature being larger at lower frequencies (similar behaviour is exhibited by the dielectric loss). This behaviour of K is attributed to space charge polarisation due to crystal defects. The plots of log σ vs. 1/T at different frequencies for these crystals do not coincide indicating the conduction in this temperature region is due to impurities. The activation energies for conduction — in the high temperature region — are calculated to be 0.77, 0.69, 0.64, and 0.62 eV respectively for the above mentioned solids. The lower activation energy values for conduction in doped crystals may be attributed to a larger charge carrier concentration in them (compared to Al2O3). Dielektrizitatskontsante (K), Verlustfaktor (tan Δ) und Leitfahigkeit (σ) von Al2O3-. Al2O3:Cr (0.03 und 2 Mol%)- und Al2O3:V (2 Mol%)-Einkristallen wurden im Frequenzbereich 102 bis 107 Hz bei Temperaturen von 30 bis 450 °C gemessen (wobei das elektrische Feld immer senkrecht zur optischen Achse orientiert war). Der K-Wert von Al2O3 betragt 9,4 bei 30 °C und ist frequenzunabhangig. Chrom- und Vanadiumdotierung verursacht keine nachweisbare anderung im K-Wert von Al2O3. Der dielektrische Verlustfaktor aller untersuchten Proben bei 30 °C liegt unterhalb der Nachweisgrenze (tan δ < 0,0005) im angegebenen Frequenzbereich. In diesen Kristallen nimmt die Dielektrizitatskonstante mit der Temperatur zu und zeigt von etwa 200 °C an eine Frequenzabhangigkeit, wobei die anderungen von K mit der Temperatur bei niedrigen Frequenzen groser sind (ein ahnliches Verhalten zeigt der Verlustfaktor). Dieses Verhalten von K wird der Raumladungspolarisation durch Kristalldefekte zugeschrieben. Die Kurven von log σ uber 1/T bei verschiedenen Frequenzen fallen fur diese Kristalle nicht zusammen und zeigen, das die Leitfahigkeit in diesem Temperaturbereich durch Storstellen verursacht wird. Die Aktivierungsenergien der Leitfahigkeit werden — im Hochtemperaturbereich — zu 0,77, 0,69, 0,64 bzw. 0,62 eV berechnet, fur die oben angegebenen Substanzen. Die niedrigen Werte fur die Aktivierungsenergien der Leitfahigkeit in dotierten Kristallen lassen sich mit einer groseren Ladungstragerkonzentration (im Vergleich zu Al2O3) erklaren.

Bearing Strength of Reinforced Concrete Blocks

Abstract: The problem of large forces acting over limited contact areas of concrete arises frequently in engineering design. Although several papers have appeared on the subject, information regarding the effect of reinforcement on the local bearing strength of concrete is rather insufficient. The present paper aims at removing this lack of information by reporting a fairly extensive series of bearing tests on reinforced concrete blocks, where the form and amount of reinforcement were the principal variables.

Digital Computer Simulation of an Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

Abstract: This paper deals with a digital computer-simulation study of a complex drive-system which incorporates a thyristor cycloconverter-type frequency-converter in the rotor circuit of a slip-ring induction motor for speed variation in the subsynchronous as well as the supersynchronous region by secondary voltage control The action of the frequency converter is analogous to that of a normal commutator in the stator-fed ac commutator motor while the circuit behavior is similar to that of a cycloconverter. A rotor-position detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. Simulation involves solution of a set of generalized performance equations of an ideal induction machine in an appropriate reference frame under the control conditions imposed by the thyristor-commutator which is simulated using simple logical and limiting statements. Differential equations are solved by the well-known Runge-Kutta numerical integration method. Initial simulation results assuming thyristors as ideal switches and neglecting source impedances show very similar characteristics to the case when a pure sine-wave slip-frequency voltage is injected to the rotor. Rigorous simulation results include the physical thyristor behavior, effect of source impedances, overlap, and logical control of the circulating currents that may occur. Simulation results are presented together with the experimental performance of the drive.

Photostimulated Glow Curve Method of Isolating Thermoluminescence Peaks

Abstract: The photostimulated glow curve method in which the glow curve is recorded after high temperature irradiation followed by room temperature F-illumination is shown to be a simple and unique method to obtain pure thermoluminescence (TL) peaks. A pure TL peak enables not only a more accurate determination of the thermal activation energy (E) but also to establish the order of kinetics through the geometric or shape factor (μg). For such peaks, since all the parameters τ, Δ, and Ω can be determined unambiguously, Chen's formulas for general order kinetics can be used to give consistent values for E and μg; the consistency of the latter offers a test for the purity of the peaks as well, a phenomenon usually rare in TL experiments. The effect of F-illumination on the behaviour of electron traps formed in X-irradiated KCl crystals is also discussed. Es wird gezeigt, das die Methode der photostimulierten Glowkurven, bei der die Glowkurve nach einer Hochtemperaturbestrahlung gefolgt von einer Raumtemperatur-F-Belichtung aufgepommen wird, eine einfache und einheitliche Methode zur Gewinnung reiner Thermolumineszenz(TL)-Maxima darstellt. Ein reines TL-Maximum liefert nicht nur eine exaktere Bestimmung der thermischen Aktivierungsenergie (E), sondern ergibt auch die Ordnung der Kinetik durch den Geometrie- oder Formfaktor (μg). Da alle Parameter τ, δ und ω eindeutig bestimmt werden konnen, last sich fur solche Maxima Chen's Formel fur Kinetik allgemeiner Ordnung anwenden und liefert konsistente Werte fur E und μg; die Konsistenz der letzteren ergibt ebenfalls einen Test fur die Reinheit dieser Maxima, eine Erscheinung, die gewohnlich selten ist bei TL-Experimenten. Der Einflus von F-Belichtung auf das Verhalten von Elektronenhaftstellen, die in rontgenbestrahlten KCl-Kristallen erzeugt wurden wird diskutiert.

The Admittance Characteristics of Longitudinal Shunt Slots in the Broad Face of Rectangular Waveguide

Abstract: The paper presents investigation on the admittance characteristics of a thin displaced longitudinal slot in the broad face of an X-band rectangular waveguide. The complex radiated power is calculated from the angular spectrum of plane waves. The admittance of the slot is found by dividing the complex radiated power by the square of the discontinuity in the modal current, for two types of field distribution in the aperture plane of the slot. The admittance calculated for the slot length in the range from 0.4λ to 0.6λ is found to be in good agreement with the experimental results.

Wall conductance effects on convective horizontal channel flow

Abstract: An exact solution has been found for the fully developed combined free and forced convection flow of electrically conducting fluids between two horizontal conducting walls under a transverse magnetic field. It is found that with the increase of the wall conductance the velocity decreases while the current density and the temperature increase. There is an incipient reversed flow for a critical Grashof number which is positive for the upper wall and negative for the lower wall. The magnitude of the critical Grashof number decreases with the increase of the wall conductance.

Effectiveness and efficiency of ethyl methanesulphonate and ethylene oxide for the induction of mutations in rice

Abstract: A comparison of the mutagenic efficiency and effectiveness of ethyl methanesulphonate (EMS) and ethylene oxide (EO) on two different genotypes of rice showed that the mutagenic efficiency sharply decreased with increase in the concentration of EO whereas the efficiency of EMS increased with an increase in the concentration. The effectiveness was inversely proportional to dose of EO whereas it varied little with an increased dose of EMS.

Instability of a horizontal layer of viscoelastic liquid on an oscillating plane

Abstract: Secular instability of unsteady flow of a horizontal layer of viscoelastic liquid set in motion by simple harmonic motion of the lower boundary in its own plane is investigated. Using an extension of Floquet's theory for ordinary differential equations, the stability of long waves is studied by a regular perturbation method. The elastic parameter of the fluid is found to be destabilizing and stabilizing in different ranges of frequency.

Electrical conductivity and dielectric properties of NaCl, KCl, and KBr single crystals near their melting temperatures

Abstract: The dielectric constant (K′) and loss (K″) of single crystals of NaCl, KCl, and KBr have been measured in the frequency region 104 to 107 Hz and in the temperature range 25 to 8 °C below their melting temperatures. The electrical conductivity of these crystals has also been measured at 104 Hz near their melting temperatures. The activation energy values for conduction in the temperature vicinity of the melting points of these solids are calculated to be 2.15, 2.35, and 2.55 eV for NaCl, KCl, and KBr, respectively; these values are larger than those reported in literature. Two points are emphasized: 1) the electrical conduction in these crystals near their melting temperatures appears to be mainly due to the generation and movement of negative ion vacancies and 2) these crystals do not show any dipole relaxation effects up to a frequency of 107 Hz.

An Analysis of Series Inverter Circuits

Abstract: This paper presents an unified approach to obtain the steady-state solutions for some inverter circuits. It is also proved incidentally that these systems actually exhibit a stable limit cycle phenomena.

Hall effects on free convection between vertical parallel plates

Abstract: Hall effects on the hydromagnetic fully-developed laminar free convection in a vertical parallel plate channel with asymmetric heating is analyzed. The effects of Hall current and the wall temperature difference ratio on the velocity and the magnetic field is discussed. The resultant shear stress at the cooler wall increases while that at the hotter wall decreases with increase in Hall parameter. With increase in Hall parameter, there occurs a change of sign in the Nusselt number at both the plates.

Acoustic waves in pulsed microwave discharge

Abstract: Sound waves were detected in a low-pressure gas ionized by a pulsed microwave field. The detection was made by means of a condenser microphone with a damped probe located in the 1 cm glass tube containing the plasma and about 60 cm away from it. The microphone output was monitored on a frequency counter and on a wave or frequency analyser, for frequency and amplitude analysis. The sound wave frequency was equal to the pulsation rate, and its pressure amplitude was dependent on the type, mean pressure and flow condition of the ionized gas, as well as on the incident microwave power. For example, in argon at static condition and at a mean pressure of 27 mm Hg, a sound pressure amplitude of 124 dB was measured. Results of other quantitative measurements in nitrogen and argon are reported.