Index of content:
Volume 11, Issue 9, 01 September 1940
11(1940); http://dx.doi.org/10.1063/1.1712835View Description Hide Description
The anomalous flow of certain suspensions through narrow tubes, known as the ``sigma'' phenomena, for which no fully satisfactory explanation has yet been given, is discussed. If it be assumed that the streamlining layers are not infinitely thin, so that a summation treatment takes the place of an integration, a series of equations can be derived depending on the relation assumed to exist between velocity gradient and shearing stress and on the nature of the friction between the layers. These equations reduce, in the limiting case of infinitely thin layers to the well‐known forms of Poiseuille, Buckingham‐Reiner, etc., and the general equation of Schofield‐Scott Blair can also be derived. For finite thicknesses of layer, the equation derived adequately explains the sigma‐phenomenon, and this is shown quantitatively by applying it to the data given in the original paper.
11(1940); http://dx.doi.org/10.1063/1.1712836View Description Hide Description
It is postulated that (A) the material is isotropic, (B) the volume change and hysteresis are negligible, and (C) the shear is proportional to the traction in simple shear in a plane previously deformed, if at all, only by uniform dilatation or contraction. It is deduced that the general strain‐energy function, W, has the formwhere the λ i 's are the principal stretches (1+principal extension), G is the modulus of rigidity, and H is a new elastic constant not found in previous theories. The differences between the principal stresses are σ i [minus]σ i =λ i ∂ W/∂λ i [minus]λ i ∂ W/∂λ i .
Calculated forces agree closely with experimental data on soft rubber from 400 percent elongation to 50 percent compression.
11(1940); http://dx.doi.org/10.1063/1.1712837View Description Hide Description
Starting potentials for hydrogen, nitrogen, helium, and argon of commercial purity at frequencies up to one million cycles per second were investigated using a discharge tube with spherical electrodes. Five gap distances were employed, ranging from 10 mm to 50 mm. The slope of the log pressure versus log distance curve was found to be independent of frequency and also of the gas for small gap distances.
11(1940); http://dx.doi.org/10.1063/1.1712838View Description Hide Description
11(1940); http://dx.doi.org/10.1063/1.1712839View Description Hide Description
The radiation properties of hollow pipes and horns are analyzed. The vector Kirchhoff formula is employed. The radiation fields from the transverse electric wave in hollow pipes of circular and rectangular cross sections are derived. For the TE 1, 1 wave in circular pipe and the TE 0, 1 wave in the rectangular pipe, the directivities are analytically expressed in terms of beam angle and power gain. It is found that the two waves have substantially equal power gains on the basis of equal areas of openings. The formulae for the radiation fields of TE 0, 1 and TE 1, 0 waves in a sectoral horn are given, of which, curves illustrating the radiation properties have been published previously.
11(1940); http://dx.doi.org/10.1063/1.1712840View Description Hide Description
Rotating anode x‐ray tubes for medical roentgenography require bearing operation in high vacuum. A method of lubricating such bearings by vaporizing a thin film of low vapor pressure material, such as pure bariummetal, onto them in the final vacuum is described. The results of tests with a great many different metals as the vaporizing films and combination films, as well as different base materials, are given. Experimental evidence is presented that indicates the lubricating film to be a liquid alloy of barium and metals such as cobalt,chromium, or aluminum.
11(1940); http://dx.doi.org/10.1063/1.1712841View Description Hide Description
The frequency spectrum of electronic oscillations in a large power triode having cylindrical plate and grid, and a filament consisting of four wires arranged at the corners of a square has been investigated. Experimental curves are displayed showing that two distinct primary frequencies may be generated at the same time, and that each of these may be replaced by two coupling frequencies, which also may be observed simultaneously, when the secondary circuit is near resonance with the primary clouds of electrons. The curves are interpreted in terms of a doubly resonant space‐charge region, and in terms of coupled‐circuit theory. Wave‐lengths extending from 50 to 250 cm have been recorded.