Table of contents

Peripheral scanning is compared with column scanning for the point over-relaxation calculation of the potential in a simple magnetic electron lens, and is shown to be faster than column scanning.

The possibility of formation of thin oxide films on silicon in a microwave magnetoactive oxygen plasma at pressures of 5*10^-5-1 Torr is described, and the corresponding experimental results are presented.

The note is a review of studies of the shear coefficient K occurring in Timoshenko's differential equation for flexural vibrations of beams. Expressions of K hitherto proposed for circular and rectangular cross sections are tabulated, together with new expressions hitherto overlooked and unknown, and compared with one another. It is pointed out that the expressions of K=(6+12 sigma +6 sigma ²)/(7+12 sigma +4 sigma ²) for the circle and K=(5+5 sigma )/(6+5 sigma ) for the rectangle, where sigma is Poisson's ratio, which have been found in Timoshenko's (1922) paper, will be the most probable ones at the present stage of theories and experiments.

Direct correlation experiments are reported which show no evidence for harmonic generation in the 1/f noise of a variety of specimens.

A carbon dioxide spray, containing particles as well as gas, produces an electric current when it impinges on a metal surface. This current was measured for a series of metals. Care was taken to provide a pure carbon dioxide atmosphere for the spraying process and to control the roughness and temperature of the sprayed surface. The surfaces were prepared by evaporating metals on to polished brass plates. With a nozzle pressure of 4.37*10⁴ torr and a flow rate of 2.5*10^-4 m³ s^-1, currents of the order 10^-10-10^-8 A were obtained. A correlation between current and the work-functions of the metals was found. The current can be explained in terms of electron transfer induced by the contact of substances having different work functions.

The basis of the impedance modelling technique for studying the magnetic forces and power loss in an electrodynamic levitation system is examined. Methods for predicting the magnetic lift and drag based on impedance measurements are discussed and are verified by experiments.

Measurements of the upper and lower level populations for the 351.1 nm line of an argon Z-pinch discharge are described. The populations are calculated from experimentally determined values of the small-signal gain, spontaneous emission intensity and fluorescence line width. The population inversion ratio, which must be known with the laser operating in some reference condition, is found by the addition of nitrogen to the discharge. The effects of initial argon pressure, the addition of oxygen or neon to the discharge and the time dependence of the upper and lower level populations are described. The method should be applicable to other pulsed gas lasers.

Low density argon plasma is studied in an electric discharge T tube. In the experimental conditions the shock wave and the contact surface merge. The wave trajectory determined from measurements obtained by a rotating-mirror camera, is described by a similarity solution of blast waves; it enables the authors to calculate the fraction of energy transferred to the gas. The temperature and the electron density are deduced from spectroscopic measurements.

The propagation of a Gaussian electromagnetic pulse in a growing/decaying (time-dependent) plasma has been studied when the duration of the pulse is comparable with the decay/growing time of the plasma. Because of the different group velocities of the front and tail portions of the pulse, the pulse is compressed/broadened in a time-dependent plasma. The effect of absorption on the compression/broadening is found to be negligible. However, the peak value of the pulse is suppressed by attenuation.

Radial temperature profiles for pulsed SF₆ arcs burning in high-pressure, approximately 5 bar, supersonic gas flow have been measured in the range 10 kA-1.0 kA. The temperature distribution was obtained from the emission intensities of spectral lines due to excited fluorine and ionized sulphur. The results for currents above 3.5 kA show that the axis temperature is 20000K+or-1000K and is independent of the arc current. Also the temperature profile is essentially parabolic, and any increase in arc current is accompanied by a corresponding increase in arc cross section to maintain a constant current density. Below 3.5 kA the axis temperature falls rapidly with current down to 15500K+or-1000K at kA and the temperature profiles show very steep temperature gradients less than 1 mm from the arc axis.

Three theories are outlined to explain the observed forces in fluids. A systematical analysis, via a number of appropriate experiments with liquids, shows that only one of them is substantially correct. A new method for studying the electrostriction in liquids is presented.

The paper gives experimental results showing the dependence of conduction currents and current pulses in liquid paraffin on temperature, dissolved gases, aromatic additives and hydrostatic pressure. The results support the theory that a gaseous phase is evolved at some stage in the breakdown of hydrocarbon liquids. The gaseous phase is most likely hydrogen bubbles produced by dissociation of the liquid molecules by energetic electrons.