Volume 12, Issue 11, 01 November 1941
Index of content:
12(1941); http://dx.doi.org/10.1063/1.1712867View Description Hide Description
Dyadic algebra, because it has been designed for three‐dimensional systems, must undergo further development to be effective for more than three‐mesh networks. There is little point in carrying out such a development, since the much used cross product and the symbolism of dyadics both lose their simplicity for more than three dimensions. Of the outstanding properties of tensor analysis, only the special technique of linear transformations has been used in electrical network studies. But linear transformations are basic to the theory and manipulations of matrix algebra. Therefore, the simplest and most effective approach to network transformations is through matrix algebra. The primitive‐network impedance matrix of tensor treatments is in reality nothing more than the matrix of the branch impedances of a network, and the linear transformation employed to formulate the mesh‐current impedance matrix is simply the transformation which relates mesh and branch currents. Furthermore, the ``interconnection of networks'' transformation is merely a transformation from more than the minimum number of mesh currents to the minimum number. Matrix transformations may be used to establish networks which are equivalent.
12(1941); http://dx.doi.org/10.1063/1.1712868View Description Hide Description
The selection of filament material from which another metal can be evaporated successfully depends largely upon the three properties of wetting (W), reaction or alloying (R), and evaporation (E). Nine filament materials and twenty‐seven evaporated metals have been investigated and the results summarized in a table using the above symbols with subscripts 1, 2 and 3 to indicate the degree of favorable properties. A second table lists satisfactory filament materials for the evaporation of twenty‐six metals.
12(1941); http://dx.doi.org/10.1063/1.1712869View Description Hide Description
Starting with the fundamental field equations of Maxwell, the various approximations involved in the usual engineering formulation of the multiconductor problem are examined. Subject to these approximations, the set of differential equations which is taken as the starting point of the classical transmission theory in the steady state are derived and the character of the various parameters involved in these equations is studied. By the use of the Laplacian transformation and certain theorems of matrix algebra these equations are solved for the case of general terminal conditions. Certain special cases where the system exhibits symmetry are discussed.
12(1941); http://dx.doi.org/10.1063/1.1712870View Description Hide Description
Starting with the fundamental field equations of Maxwell, the equations governing the propagation of electromagnetic waves along two parallel wires are derived. The treatment is greatly facilitated by the use of the Laplacian transformation or modern rigorous operational calculus. First the case of waves traveling along perfectly conducting wires is considered and the dissipative case is treated as a perturbation of the ideal perfectly conducting one. An expression for the deformation of the front of an initially rectangular wave due to the ``skin‐effect'' is derived and the manner in which the wave progresses along the wire is studied.
12(1941); http://dx.doi.org/10.1063/1.1712871View Description Hide Description
The Young's modulus and specific energy loss of Lucite and Karolith were measured at different frequencies in the neighborhood of 50 kc/sec. as a function of temperature. The temperature range for Lucite was from −55°C to 65°C, and for Karolith, 25°C to 110°C. It was found that the reciprocal of Young's modulusversus temperature curves showed positive curvatures at higher temperatures for both materials. At room temperature the Young's moduli of Lucite and Karolith were 4.72 and 6.14×1010 dynes/cm2, respectively. The specific loss was found to vary with frequency for both materials and varied in a linear fashion for Lucite at room temperature. Absorbed water seemed to have a pronounced effect on the Young's modulus of Karolith.
12(1941); http://dx.doi.org/10.1063/1.1712872View Description Hide Description
An x‐ray study has been made of precipitation‐hardened, 7.16 percent tungsten, iron‐tungsten alloys. It is concluded that the precipitation reaction is of the discontinuous type. On the basis of diffraction evidence a mechanism for the formation and growth of the precipitate is proposed and a picture of the crystallographic form of the precipitate deduced.