Volume 14, Issue 2, 01 February 1943
Index of content:
14(1943); http://dx.doi.org/10.1063/1.1714953View Description Hide Description
This paper is a continuation of the description of problems arising in the development and design of an electrostaticelectron microscope. The present article discusses depth of focus, lens and field stops, shielding, manufacturing tolerances, the choice of the number of stages of magnification, and alternative methods of viewing and recording the final image. A following paper will describe a completed instrument.
14(1943); http://dx.doi.org/10.1063/1.1714954View Description Hide Description
Studies of the surface damage caused by the sliding of clean metals on one another show that penetration and distortion occur to some depth beneath the surface. Micro‐examination shows that welding of the metals takes place quite readily even at low speeds of sliding when the surface temperature‐rise due to frictional heat cannot be very high. In some cases the welded junctions may pluck out portions of the harder metal. These and other results have led to a more quantitative theory of metallic friction. It is suggested that in general the frictional force between clean metal surfaces is made up of two parts. The first is the force required to shear the metallic junctions formed between the surfaces; the second is the ploughing force required to displace the softer metal from the path of the harder. By using steel sliders of various shapes and sizes on a soft metal like indium, these two factors have been estimated separately, and it is shown that an approximate calculation of the friction between metal surfaces may be made in terms of the known physical properties of the metals. The effect of surface contamination is also discussed.
14(1943); http://dx.doi.org/10.1063/1.1714955View Description Hide Description
A solution of the problem of Dirichlet for a two‐dimensional region that can be mapped conformally on a circle is given by the formula of Schwarz. This formula is specialized to yield a complete solution of the torsion problem of St. Venant, and it is demonstrated that the results obtained formally by R. M. Morris are deducible rigorously from the general results of N. Muschelisvili. It is shown that the solution of the torsion problem for a prism whose cross section is the inverse of an ellipse, offered by T. J. Higgins, can be obtained more easily by utilizing the method outlined in this paper rather than by following the procedure of R. M. Morris.
Probable X‐Ray Mass Absorption Coefficients for Wave‐Lengths Shorter Than the K Critical Absorption Wave‐Length14(1943); http://dx.doi.org/10.1063/1.1714956View Description Hide Description
Absorption coefficients of all elements may be calculated, from short wave‐lengths up to the K critical absorption wave‐length by the expression:.This formula holds for all elements when suitable values for α and β are chosen. Factors α and β are related to the atomic number, Z, by the expressions α=(aZ 2+bZ−c), and β=(dZ 2−eZ+f). Different values of the constants a, b, c, d, e, and f are required for each side of the critical absorption wave‐lengths and for either side of Z=5, and are given for the short wave‐length side of the K critical absorption wave‐lengths. The values of αZ 2(2Z/A) and βZ 5(2Z/A) computed for all elements, are shown in the tables. The calculated mass absorption coefficients of a few elements are also furnished together with comparison of calculated mass absorption coefficients with published experimental data. No anomalies were found and the average agreement is of the order of 1 to 2 percent for all elements and all wave‐lengths on the short wave‐length side of the K critical absorption wave‐length. Values for the region between the K and L 1 critical absorption wave‐lengths will be published later.