Index of content:
Volume 15, Issue 6, 01 June 1944
15(1944); http://dx.doi.org/10.1063/1.1707457View Description Hide Description
In friction experiments material is exchanged between the sliding surfaces. A study of this transfer of material was made possible by the development of a radioactive tracer method by means of which one could detect quantities of metal as small as 10−4 microgram. Spherical or hemispherical specimens were slid over an activated base surface. After the friction experiments, the riders were tested for the presence of radioactive material, and the quantity of metal deposited on the rider was determined as a function of various parameters. A copper‐beryllium base surface was used for all measurements reported here. For the materials investigated it was found that the amount of base metal adhering to the rider was proportional to the load and increased with the distance of travel. Under otherwise identical conditions the amount of base metal deposited on the rider depended on surface finish and hardness of the rider. If the rider was harder than the base, the transferred material increased with surface roughness. If, on the other hand, the rider was softer than the base, surface finish was found to be of secondary importance. Measurements made with steel specimens showed that the amount of metal deposited on them was inversely proportional to their Brinell hardness. For riders of different materials, but having the same hardness and surface finish, the amount of transferred metal increased with the solid solubility of the base metal in that of the rider. Lubrication decreased the transfer; the reduction depended on load and, for the same load, on the material of the rider. The influence of lubrication was greater for smaller loads.
15(1944); http://dx.doi.org/10.1063/1.1707458View Description Hide Description
Mathematical relations between a few geometric yarn properties are used to develop the concept of relative density. With the aid of this idea it is possible to deal with yarns made of different materials but having the same relative density as though they were made of the same material, so far as their geometric properties are concerned. A simple formula is derived to convert twist multiples from one yarn count system to another. The figure obtained for the twist to be put into the new yarn is only an ``educated guess,'' but it is hoped that it will shorten the amount of experimentation necessary for determining the optimum twist in new yarns.
15(1944); http://dx.doi.org/10.1063/1.1707460View Description Hide Description
A general theory for the current in coupled antennas is formulated in terms of the vector potential and applied to determine the self‐impedance Z s1 and the mutual impedance Z 12 of a center‐driven antenna in the presence of a second parallel, identical antenna which may be center‐driven or center‐loaded in an arbitrary way. Each antenna has a half‐length h, a radius a, and the distance between them is b. Curves are shown for Z s1 and Z 12 for h=λ/4; Ω=2 ln (2h/a) = ∞, 30, 20, 10; ; and for h=λ/2; Ω=2 ln (2h/a) = 30, 20, 10; . It is shown that except for the special case of an indefinitely thin antenna (Ω= ∞) the self‐impedance Z s1 of an antenna in the presence of a second antenna differs from the self‐impedance Z 0 when the antenna is isolated and varies with b/λ. The input impedance Z lin is determined and plotted for the same values of h and Ω, and the same ranges of b/λ for the following special cases: 1. The antennas are both center‐driven in phase by identical generators. 2. The antennas are both center‐driven in opposite phase by identical generators; or a driven antenna is parallel to a perfectly conducting plane. 3. Antenna 1 is center‐driven; antenna 2 is parasitic and unloaded. 4. Antenna 1 is center‐driven, antenna 2 is parasitic and center‐tuned to self‐resonance (h=λ/2 only).
15(1944); http://dx.doi.org/10.1063/1.1707462View Description Hide Description
The powder method of x‐ray analysis has been applied to a series of slowly cooled copper‐manganese alloys to ascertain whether anomalous physical effects of these alloys, detected by the Metallurgical Division of the United States Bureau of Mines, may be ascribed to the presence of superstructures. The x‐ray analysis does not indicate superstructures, but it presents results quite different from those one would expect from examination of the accepted equilibrium diagram of the copper‐manganese binary alloy system. Slowly cooled and annealed samples both give identical results; namely, that copper enters into a continuous series of solid solutions with manganese,crystallizing in a face‐centered cubic lattice with a gradually increasing parameter as the manganese content is increased from zero to sixty percent. Above sixty percent manganese, and up to ninety percent manganese, the lattice is face‐centered tetragonal. Between ninety and one hundred percent manganese, two phases are present, one phase being the solid solution phase corresponding to an alloy with ninety percent manganese, the other phase being that of alpha‐manganese.
15(1944); http://dx.doi.org/10.1063/1.1707463View Description Hide Description
The directional characteristic of a goniometer using two half‐wave doublet antennas mounted at right angles is derived. It is shown that, unlike the double loop goniometer, the directional characteristic is not identical with that of a single half‐wave doublet that can be rotated, although the variation from such a case is very small.