Index of content:
Volume 13, Issue 3, 01 March 1942
13(1942); http://dx.doi.org/10.1063/1.1714846View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714847View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714848View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714849View Description Hide Description
An idealized yarn composed of fibers with specified properties is treated analytically with the aim of determining the yarn strength at any degree of twist. The results are presented in the form of equations and curves which relate the yarn strength to the fiber properties and the degree of twist. Two cases are studied: (1) All fibers alike; (2) fiber properties variable from fiber to fiber. In the latter case the mathematical expectation of the yarn strength at any yarn cross section is obtained. It is found that the optimum twist multiplier is largely determined by the fiber length, fiber fineness, and coefficient of friction, whereas the maximum yarn strength (corresponding to the optimum twist multiplier) is more strongly dependent upon the intrinsic fiber strength than upon the other fiber properties studied.
13(1942); http://dx.doi.org/10.1063/1.1714850View Description Hide Description
Simple energy considerations, which have previously been employed to provide a rational basis for the principle of Saint‐Venant, are shown to lead to the conclusion that forces applied in the neighborhood of a rigidly fixed portion of an elastic solid can cause only local stress and strain. This principle indicates useful features of certain problems encountered in engineering, and is used here in the calculation of the stiffness of a thin layer of elastic material confined between rigid plates, under any kind of load applied to the plates.
13(1942); http://dx.doi.org/10.1063/1.1714851View Description Hide Description
Thyratrons of FG‐41 type were tested at over‐voltage for arcback in a circuit which simulates operating conditions very closely. Memory oscillograms showed the time in the cycle at which the arcbacks occurred. At a mercury‐control temperature of 45°C, the distribution was nearly random, with a maximum at the time of highest negative anode voltage, and depending on voltage in the same manner as the average arcback rate, taken over a long period. When the mercury‐control temperature was raised to 64°C, all the arcbacks occurred at the beginning of negative voltage application. These results are interpreted on the theory recently advanced by Kingdon and Lawton, which attributes arcback to charging up of small non‐conducting particles on the surface of the anode. At low vapor pressure, where the ions remaining from the discharge have time to diffuse to the electrodes before negative voltage is applied, the charging is produced by processes such as glow discharge and field emission, which depend on voltage; hence arcback is correlated with voltage. At higher pressure,diffusion is interfered with by molecular collision, so that ions are present when negative voltage is applied. In this condition arcback occurs at the beginning of the negative cycle.
13(1942); http://dx.doi.org/10.1063/1.1714852View Description Hide Description
The problem of determining electrical earth conductivity from the surface, in the case where it is a function of the depth only, is solved by a perturbation method, which formally at least, allows the unperturbed functions to be perfectly arbitrary. Numerical work, however, is restricted to those functions which are available as solutions of the so‐called ``inverse'' problem, a group of which is given. Of this group the case in which the unperturbed conductivity varies exponentially is treated in detail and two examples showing the success of the method are presented. A numerical method of solving integral equations of the Laplace type, which occur in the above, is also submitted.
13(1942); http://dx.doi.org/10.1063/1.1714854View Description Hide Description
Various possible sources of Po for industrial use are discussed and reasons for selection of active lead salts for this purpose are given. Methods of measurement of the amounts of Po present on plated metal foils and in electrode alloy are described. The RaD/Pb ratio was found to vary from 1.2×10−8 to 1.9×10−8 for various samples of active lead from the Great Bear Lake region. Methods for extraction of Po from active lead salts are discussed and a large scale plating method is described. Results of experiments on the rate of Po‐plating from boiling solutions of active lead salts as related to the acid concentration, exposed foil area, foil composition, etc., are presented. Chemical methods for producing soluble active lead salts are described.
A method of introducing Po into electrode alloy is described. In a typical experiment, it was found that 94 percent of the Po introduced into the melt was retained in the final alloy. Contact radiographs of electrode alloy samples showing the affect of various heat treatments and surface condition are presented.
13(1942); http://dx.doi.org/10.1063/1.1714856View Description Hide Description
The Maxwellrelaxationtheory leading to the concept of a viscous‐elastic body is briefly stated. Extensions to systems built up from several such viscous‐elastic components with different relaxation times are discussed. In the case of high molecular weight materials, it is more appropriate to assume a continuous distribution of relaxation rates. Equations are formulated whose solution gives the distribution function in terms of the rate of deformation and of the applied stress or the elongation in terms of the two other quantities. The connection with the corresponding distribution of dielectric relaxation times, molecular inhomogeneity and chain branching, and effects at mechanical frequencies large compared with the relaxation rates, are pointed out.