Plane-wave scattering by a magnetoplasma cylinder

The scattering of H-polarised plane waves by an infinitely long axially magnetised cylinder of uniform plasma is investigated for the case in which the radius of the cylinder is small in comparison with the wavelength of the incident wave. The scattering amplitude is found to be a maximum at two frequencies, which are shown to be related to the familiar dipolar resonant frequency of an isotropic plasma column. Approximate expressions for the two resonant frequencies are derived.     

T.W.T.-type radiation from a uniformly moving charge in an isotropic plasma environment

The characteristics of the travelling-wave-tube-type radiation produced by a point charge moving with uniform velocity along the axis of an infinite cylindrical cavity of free space in an otherwise unbounded, isotropic, cold and homogeneous plasma are investigated. For sufficiently small radius of the free-space column, the frequency of the emitted radiation is close to the plasma frequency, and the radiated energy is of significant strength and progresses in a direction opposite to that of the motion of the charge.     

Design Trade-Offs in VAX-11 Translation Buffer Organization

A major feature of the VAX-11 is its large virtual address space. This trace-driven simulation scheme evaluates address translation hardware that supports this feature cost-effectively.     

Diffraction by a circular aperture in a unidirectionally conducting screen

The diffraction of a normally incident plane electromagnetic wave with wave numberkby a circular aperture of radiusain a unidirectionally conducting plane screen of zero thickness and infinite extent is considered. In the limit of largeka, the ratio of the transmission cross section to the geometrical optics valuepi a^{2}, is found up to the order(ka)^{-3/2}.     

Heavy-ion effect on the e.l.f. propagation beneath a loss-less anisotropic ionosphere

The heavy-ion effect on the spectrum of the surface waves guided along a vacuum-plasma boundary is discussed. The e.l.f. terrestrial propagation is shown to take place via this surface-wave mode, which is only very slightly perturbed by the presence of the Earth. As a result of the inclusion of the heavy-ion motion, the guided e.l.f. waves are found to acquire a low-frequency cutoff.     

Radiation from an electromagnetic source in a half-space of compressible plasma-surface waves

The radiation characteristics of a line source of magnetic current are studied for the case in which the source is situated in a half-space of isotropic, compressible plasma which is bounded on one side by a perfectly conducting, rigid plane screen. In addition to the electromagnetic and plasma space waves, the line source excites a boundary wave. This boundary wave is a coupled wave. It has associated with it both a magnetic field component and the pressure term. This is in contrast to the space waves which can be decomposed into an electromagnetic (EM) mode with no pressure term and a plasma (P) mode with no magnetic field associated with it. The characteristics of this boundary wave are evaluated. The boundary wave propagates for all frequencies and the power carried by the boundary wave becomes smaller as the frequency is increased.     

Radiation from electromagnetic sources in a plasma

The radiation from electromagnetic sources in an unbounded, isotropic plasma is treated. Using a two-fluid magnetohydrodynamic approach, the problem is formulated in terms of three orthogonal modes, namely, i) the electromagnetic mode, ii) the electron plasma mode and iii) the ion plasma mode. When formulated in this manner, the radiation from simple electromagnetic sources are obtained easily. Three specific sources are treated, namely, i) a point source of electric current, ii) a uniformly moving charge and iii) a short filament with prescribed current distribution. For the case of the electric dipole and the current filament, the total power radiated in each of the three modes are obtained. A point charge moving uniformly with the velocity of sound, for example, is found to excite only the ion plasma mode. The frequency and the angular spectrum of the emitted radiation are obtained. It is found that at frequencies less than a critical frequency which is approximately equal tosqrt{2}times the ion plasma frequency, the radiation has the character of a simple sound wave.     

Thermodynamics of carbon dioxide hydrate formation in media with broad pore-size distributions

Equilibrium pressures for the dissociation of carbon dioxide hydrates confined in silica gel pores of nominal radii 7.5, 5.0, and 3.0 nm were measured over a wide temperature range and were observed to be higher than those for bulk carbon dioxide hydrate. Models that have been previously reported in the literature are used to determine the pore radius involved in each equilibrium associated with these data, exactly reproducing the experimental equilibrium pressure. Based on these models, pore volume distributions are reconstructed and compared to those obtained from nitrogen desorption isotherms. This comparison indicates that in the nominal 7.5 nm pores the hydrate formed nearly uniformly in the available pores, while in the nominal 5.0 and 3.0 nm pores it did not.     

Drag reduction in dilute fibre suspensions: Some mechanistic aspects

Long hair-like fibres were injected at the boundary and centreline of a turbulent pipe flow of water and polymeric solution. Pressure drop and mean velocity profiles were measured at various Reynolds numbers and injection rates in order to study some mechanistic aspects of drag reduction in these additive systems. Drag reduction in a fibre-water system is attributed to a decrease in the momentum transfer in the turbulent-core region, whereas synergism has been found to be a wall phenomenon.     

Electromagnetic modified Bessel-Gauss beams and waves

The transverse magnetic (TM) modified Bessel-Gauss beams and their full-wave generalizations are treated. Attention is paid to the spreading properties on propagation of the null in the radiation intensity pattern for the azimuthal mode numbers m=0 and 1. The rate of spreading of the null in the propagation direction is significantly less for the TM modified Bessel-Gauss waves than those for the corresponding TM Bessel-Gauss waves. The total power transported by the waves is determined and compared with that of the corresponding paraxial beam to estimate the quality of the paraxial beam approximation of the wave. The dependence of the quality of the paraxial beam approximation on the azimuthal mode number, the beam shape parameter, and the ratio of the beam waist to the wavelength has a regular pattern for the TM Bessel-Gauss wave and not for the TM modified Bessel-Gauss wave.