Three-dimensional elastic analysis of cracked thick plates under bending fields

A three-dimensional analysis is presented for the bending problem of finite thick plates with through-the-thickness cracks. A general solution is obtained for Navier's equations of the theory of elasticity. It is found that the in-plane stresses and the transverse normal stress at the crack front are singular with an inverse square root singularity, while the transverse shear stresses are of the order of unity. Results from a numerical study indicate that the stress intensity factor, which varies across the thickness, is influenced by the thickness ratio in a significant manner. Results from a parametric study and those from a comparative study with existing finite element values are presented.

Surface waves in the presence of external high frequency fields

The system equations of a collisionless, unmagnetized plasma, contained in a box where a high frequency (h.f.1 electric field is incident, are solved in the electrostatic approximation. The surface modes of the plasma in the semi-infinite and box geometry are investigated. In the high frequency limit, the mode frequencies are not significantly changed by the h.f. field but their group velocities can be quite different. Two long wavelength low frequency modes, which are not excited in the absence of h.f. field, are found. These modes are true surface modes (decaying on one wavelength from the surface) unlike the only low frequency ion acoustic mode in the zero field case. In the short wavelength limit the low frequency mode occurs at &/2, oi being the ion plasma frequency, a result similar to the case of no h.f. field.

Prediction of Breakdown Voltages of Binary Gas Mixtures in Uniform Electric Fields

A simple equation to predict the breakdown voltages for binary mixtures (Vmix) of electronegative gases (SF6, CCl2F2) and buffer gases (N2, N2O, CO2, air) under uniform electric field has been proposed. Values of Vmix evaluated using this equation for mixtures of SF6-N2, SF6-air, SF6-N2O, SF6-CO2 and CCl2F2-N2 over a wide range of pd show an excellent agreement with the experimentally measured data available in the literature.

A Huge Effect of Weak dc Electrical Fields on Grain Growth in Zirconia

We show that the application of a modest dc electrical field, about 4 V/cm, can significantly reduce grain growth in yttria-stabilized polycrystalline zirconia. These measurements were made by annealing samples, for 10 h at 1300°C, with and without an electrical field. The finding adds a new dimension to the role of applied electrical fields in sintering and superplasticity, phenomena that are critical to the net-shape processing of ceramics. Grain-growth retardation will considerably enhance the rates of sintering and superplasticity, leading to significant energy efficiencies in the processing of ceramics.

Calculation of Sparking Potentials of SF6 and SF6-GAS Mixtures in Uniform and Non-Uniform Electric Fields

A simple formula is developed to predict the sparking potentials of SF6 and SF6-gas mixture in uniform and non-uniform fields. The formula has been shown to be valid over a very wide range from 1 to 1800 kPa·cm of pressure and electrode gap separation for mixtures containing 5 to 100% SF6. The calculated values are found to be in good agreement with the previously reported measurements in the literature. The formula should aid design engineers in estimating electrode-spacings and clearances in power apparatus and systems.

Surface instability in a semi-infinite plasma in the presence of high frequency fields

The surface instability of a semi-infinite plasma immersed in a high frequency field is investigated. When the natural Langmuir frequency of the surface is nearly equal to the frequency of the high frequency field, the dispersion relation predicts build-up of oscillations with a growth rate comparable with the real part of the frequency. Threshold values above which the instability is possible are derived.

Note on the stability of parallel magnetic fields

The stability characteristics of parallel magnetic fields when fluid motions are present along the lines of force is studied. The stability criterion for both symmetric (m=0) and asymmetric (m=1) modes are discussed and the results obtained by Trehan and Singh (1978) are amended in the present study. The results obtained for the cylindrical geometry are shown to play an important role forka<4, wherek is the wave number,a is the radius of the cylinder, compared to the results obtained by Geronicolas (1977) for the slab geometry.

Influence of Band Non-Parabolicity on Few Ballistic Properties of III-V Quantum Wire Field Effect Transistors Under Strong Inversion

A simplified yet analytical approach on few ballistic properties of III-V quantum wire transistor has been presented by considering the band non-parabolicity of the electrons in accordance with Kane's energy band model using the Bohr-Sommerfeld's technique. The confinement of the electrons in the vertical and lateral directions are modeled by an infinite triangular and square well potentials respectively, giving rise to a two dimensional electron confinement. It has been shown that the quantum gate capacitance, the drain currents and the channel conductance in such systems are oscillatory functions of the applied gate and drain voltages at the strong inversion regime. The formation of subbands due to the electrical and structural quantization leads to the discreetness in the characteristics of such 1D ballistic transistors. A comparison has also been sought out between the self-consistent solution of the Poisson's-Schrodinger's equations using numerical techniques and analytical results using Bohr-Sommerfeld's method. The results as derived in this paper for all the energy band models gets simplified to the well known results under certain limiting conditions which forms the mathematical compatibility of our generalized theoretical formalism.

Effect of magnetic and electrical fields on dendritic freezing of aqueous solutions of sodium chloride

Aqueous solutions of sodium chloride were solidified under the influence of magnetic and electrical fields using two different freezing systems. In the droplet system, small droplets of the solution are introduced in an organic liquid column at −20°C which acts as the heat sink. In the unidirectional freezing system the solutions are poured into a tygon tube mounted on a copper chill, maintained at −70°C, from which the freezing initiates. Application of magnetic fields caused an increase in the spacing and promoted side branching of primary ice dendrites in the droplet freezing system, but had no measurable effect on the dendrites formed in the unidirectional freezing system. The range of electric fields applied in this investigation had no measurable effect on the dendritic structure. Possible interactions between external magnetic and electrical fields have been reviewed and it is suggested that the selective effect of magnetic fields on dendrite spacings in a droplet system could be due to a change in the nucleation behaviour of the solution in the presence of a magnetic field.

Generation of High Magnetic Fields Using Thyristors

This paper describes the use of high-power thyristors in conjunction with a low-voltage supply for generating pulsed magnetic fields. A modular bank of electrolytic capacitors is charged through a programmable solid-state power supply and then rapidly discharged through a bank of thyristors into a magnetizing coil. The modular construction of capacitor banks enables the discrete control of pulse energy and time. Peak fields up to 15 telsa (150 KOe) and a half period of about 200 microseconds are generated through the discharges. Still higher fields are produced by discharging into a precooled coil ( 77°K). Measurement method for a pulsed field is described.

Mössbauer Lineshape in the Presence of Radio-Frequency Fields

A general expression for the Mössbauer lineshape in the presence of a radio frequency field is derived. As an example the effect of the rf field on Fe57 nuclei is discussed for a situation where the 3/2 sublevel of 14.4 keV state of Fe57 is selectively populated. At resonance, both the diagonal and non-diagonal matrix elements contribute to the correlation function. As a result, in addition to a slight rf induced distortion of the main Mössbauer line. additional transition lines are obtained. Thus the present calculation supports the experimental observations of Heiman et al.

Experimental investigation of interaction of strong shock heated oxygen gas on the surface of ZrO2 - a novel method to understand re-combination heating

Interaction of shock heated test gas in the free piston driven shock tube with bulk and thin film of cubic zirconium dioxide (ZrO2) prepared by combustion method is investigated. The test samples before and after exposure to the shock wave are analyzed by X-ray diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope (SEM). The study shows transformation of metastable cubic ZrO2 to stable monoclinic ZrO2 phase after interacting with shock heated oxygen gas due to the heterogeneous catalytic recombination surface reaction.

Strong gravity and the Yukawa field

A study of strong gravity field coupled to the Yukawa field is carried out for a conformally flat space-time. A quantitative relation between the strong interaction coupling constantg 2/hstrokc and the strong gravity constants (Lambda f~1028 cm–2,G f ~6.6×1030 C.G.S. units) is obtained givingg 2/hstroksim17, which is of the right order of magnitude. This justifies the contention that strong gravity is relevant for elementary particles (e.g., hadrons).

Effect of some "strong" excitants of central neurones on the uptake of L-glutamate and L-aspartate by synaptosomes

"Strong" excitants of central neurones such as β N-oxalyl L α,β-diaminopropionic acid (ODAP), N-methyl-D-aspartic acid (NMDA) and kainic acid (KA) were found to inhibit the high affinity uptake of glutamate and aspartate in synaptosomes isolated from young rat brain. The potency of these "strong" excitants as convulsants appear to parallel their ability to inhibit glutamate uptake by synaptosomes. The data suggest the possibility that the convulsive effect of these "strong" excitants could be mediated by glutamate/aspartate.