Maximum Amplifications Research Articles

Electrodynamic instability of a self-gravitating dielectric fluid cylinder embedded in a different dielectric self-gravitating fluid

The electrodynamic instability of a gravitational dielectric fluid cylinder embedded in a different self-gravitating infinite fluid is developed. The eigenvalue relation, valid to all symmetric and asymmetric modes, is derived and is based on the linear perturbation technique. Recent reported work is recovered as limiting case from the present result. The electric field has no direct influence on the gravitational instability of the present model. That is not only because no volume and surface charges are assumed to be present in the bulk and at the interface of the fluids but also because the electrodynamic forces acting on the fluids cancel each other, whether the pervading longitudinal electric fields are different or not. Gravitationally the model is marginally stable if the density of the cylinder is equal to that of the surrounding dielectric fluid. If the cylinder is less dense, the system is purely unstable for all (long and short!) wavelengths and the instability domains have their maximum temporal amplifications and critical wave numbers at infinity. If the cylinder is ambient with self-gravitating vacuum, the electrodynamic stabilizing influence can suppress the gravitational instability and stability arises. These results are confirmed numerically and interpreted physically.

Hollow Cathode Effect in a Long Perforated Cylindrical Cathode with External Coaxial Anode

AbstractThe paper presents the main characteristics of transverse mode HCE glow discharges in spectral pure helium and neon and in a He/Ne mixture in a long perforated cylindrical cathode with an external coaxial anode. At optimum values of gas pressure, when HCE gets its climatic stage, the compact negative glow evenly “fills” the cathode cavity with maximum amplifications of current and radiation.

Hollow Cathode Effect with Double Axial Electron Injection

AbstractThe paper presents a new type of HCE glow discharge obtained with double plane‐conical cathodes. The two identical cathodes are tronconical and screened with 1 mm2 mailed wire net with a 3.5 mm diameter central washer each. The discharge is obtained between the two cathodes and a ring shaped anode equally distant from both. Optimum intercathodic span is 4 mm, allowing for maximum amplifications at the optimum pressure values for the two gases. Employed helium and argon are spectral pure. At the given distance and depending on voltage and gas pressure, a double axial electron self injection cathode effect is obtained between the electrodes, consisting of very large increase of current and radiations.

On the low-pressure operation of multistep avalanche chambers

It is demonstrated that in the double-step parallel-plate structure filled with pure low-pressure isobutane or methane, the gas preamplification-and-tranfer mechanism occurs with an efficiency close to 100%, probably due to the electron diffusion process. Amplification in successive steps in isobutane and methane at pressures of 2–10 Torr is shown to be possible. An increase in total gain of 10–80 as compared to maximum amplifications attainable in a single-step structure is observed with 5.5 MeV alpha particles and single electrons. The possible applications of multistep low-pressure counters for single-electron (photoelectron) imaging are discussed.

Velocity measurements and order of magnitude estimates of the flow between two buildings in a simulated atmospheric boundary layer

In this paper we describe an experimental and theoretical investigation into the flow between a long low cuboid building placed upwind of a tall cuboid in a simulated atmospheric boundary layer. Measurements were made of the instantaneous longitudinal (along the axis of the tunnel) velocities using a pulsed hot-wire anemometer. The experiments have confirmed the existence of amplified ground level mean winds and turbulence for this building configuration. The results are compared with the flow around the two buildings in isolation. A simple order of magnitude argument has been developed which predicts the maximum amplifications observed.

Some results on the approach of a slowly-varyng gravity wave to a beach

Results from the theory of slowly-varying solutions of the non-linear shallow water equations (Varley et al. (1971)) are used to estimate maximum wave height amplifications on a beach of arbitrary ...

An experiment on the stability of hypersonic laminar boundary layers

An experimental investigation of the hydrodynamic stability of the laminar hypersonic boundary layer was carried out with the aid of a hot-wire anemometer. The case investigated was that of a flat surface at zero angle of attack and no heat transfer.The streamwise amplitude variation of both natural disturbances and of disturbances artifically excited with a siren mechanism was studied. In both cases it was found that such small fluctuations amplify for certain ranges of frequency and Reynolds numberRθ, and damp for others. The demarcation boundaries for the amplification (instability) zone were found to resemble the corresponding limits of boundary-layer instability at lower speeds. A ‘line of maximum amplification’ of disturbances was also found. The amplification rates and hence the degree of selectivity of the hypersonic layer were found, however, to be considerably lower than those at the lower speeds. The disturbances selected by the layer for maximum amplifications have a wavelength which was estimated to be about twenty times the boundary-layer thickness δ.