Volume 19, Issue 6, 01 June 1948
Index of content:
Qualitative Experimental Verification of the Change of Burning Rate of Rocket Powders with Radiation Path Length19(1948); http://dx.doi.org/10.1063/1.1698165View Description Hide Description
Experimental studies on step‐machined powder grains indicate a small increase in the average burning rate of solid fuel rocket propellants with an increase in the radiation path length. This result is in agreement with theoretical predictions.
Universal Curves for Dielectric‐Filled Wave Guides and Microwave Dielectric Measurement Methods for Liquids19(1948); http://dx.doi.org/10.1063/1.1698166View Description Hide Description
The characteristics of wave guides containing a non‐ideal dielectric medium are expressed in terms of a dissipation factor, D, the effect of which is analogous to that of the loss tangent of the medium, tanδ, for coaxial or two‐conductor transmission lines. A set of universal curves may then be constructed for the variation of the wave‐guide parameters as functions of the dielectric loss factor in terms of D. These curves are independent of the dielectric constant, ε′, and of the frequency and mode of operation.
An experimental method is described for the measurement of the dielectric constants of medium and high loss liquids using a variable length of liquid dielectric column contained in a section of wave guide or coaxial line and terminated by a perfectly reflecting plane. Either a unidirectional coupler or slotted line may be used to observe the variation of the magnitude of the reflection coefficient with the dielectric sample length. An exact analytical expression is given for the determination of the constants of the medium using the dielectric constant, ε′, and the dissipation factor, D, as the primary independent parameters instead of ε′ and tanδ. A graphical method of solution is also given.
Erratum: On the One‐Dimensional Theory of Steady Compressible Fluid Flow in Ducts with Friction and Heat Addition19(1948); http://dx.doi.org/10.1063/1.1698167View Description Hide Description
19(1948); http://dx.doi.org/10.1063/1.1698168View Description Hide Description
A method is presented for determining the angle of arrival of the direct and reflected wave for line of sight cases. The method assumes one direct and one reflected wave. The phase difference equipment, as developed by the Electrical Engineering Research Laboratory, measures the difference in phase at 3.2‐cm wave‐length between two points separated vertically by ten feet [F. E. Brooks, Jr. and C. W. Tolbert, Equipment for Measuring Angle‐of‐Arrival by the Phase Difference Method, Electrical Engineering Research Laboratory, Report No. 2, May 1946] and the signal strength at each point. The normal procedure involves the raising of either transmitter or receiver while the other is held at a fixed level. The data to which the method is applied were collected at the Navy Electronics Laboratory desert site near Gila Bend, Arizona, during April 1947. The results are compared to calculations based on the meteorologically measured distribution of the refractive index and ray theory.
19(1948); http://dx.doi.org/10.1063/1.1698169View Description Hide Description
Experimental studies of the wave‐length spacing between modes of the spectrum of arrays of 10 and 16 cavities with different cavity‐to‐cavity couplings have been made. The results indicate greatest mode separation near the center, π/2 mode of the mode spectrum making this mode best for operation. Use of the end π‐mode of the spectrum should lead to a limiting length of approximately 3 to 6 ft., while choice of the center π/2 mode would result in a limiting accelerator length of 10 to 20 ft. at 10.7 cm.
19(1948); http://dx.doi.org/10.1063/1.1698170View Description Hide Description
Typical theories of plastic flow and plastic deformation are discussed, and the concept of neutral change of stress is introduced. A neutral change of stress can be considered as a limiting case of either loading or unloading. It therefore seems reasonable to demand that the stress‐strain relations for both loading and unloading should predict the same change of strain when applied to a neutral change of stress. It is shown that this condition is satisfied by the theories of plastic flow but not by the theories of plastic deformation.
The Theory of Extreme Values and Its Implications in the Study of the Dielectric Strength of Paper Capacitors19(1948); http://dx.doi.org/10.1063/1.1698171View Description Hide Description
In this paper it is shown that the statistical theory of the distribution of extreme values is pertinent to the study of the way in which the breakdown strengths of paper capacitors depend on capacitor size. The theory presented in this paper permits a quantitative explanation of this phenomenon and results are given which should be useful to design engineers.
19(1948); http://dx.doi.org/10.1063/1.1698172View Description Hide Description
The magnetic properties of an iron specimen under the influence of perpendicularly superposed direct and alternating fields are investigated. For the low and intermediate values of direct longitudinal magnetic field intensity the steady component of the longitudinal intensity of magnetization first increases, goes through a maximum, and then diminishes as the transverse alternating magnetic field intensity is increased. Static hysteresis loops in the longitudinal direction show a suppression of hysteresis with increasing transverse alternating magnetic field intensity. However, dynamic hysteresis loops in the transverse direction indicate that this suppression is merely apparent. Curves of the dynamic longitudinal magnetic inductionvs. transverse magnetic field intensity and transverse magnetic induction are included.
19(1948); http://dx.doi.org/10.1063/1.1698173View Description Hide Description
Explosives detonated in contact with thick steel plates produce much deeper holes in the steel when there is a cavity in the explosive in contact with the plate. While this phenomenon has been known for more than 150 years, the enormous increase in penetrating power that can be produced by lining the explosive cavity with thin metal has been discovered only recently. During the war a number of light, low velocity, antitank weapons (e.g., the rocket‐propelled Bazooka) were developed which made use of this phenomenon to perforate thick armor plate.
A fairly complete mathematical theory of this essentially new phenomenon is presented together with some of the experimental data that aided in the formulation and testing of the theory. The process is separated into two phases: first, the formation of part of the metal liner into a long thin jet traveling longitudinally at very high velocities (30,000 ft./sec.) and, second, the forcing aside of the target material by the extremely high pressures (0.3‐million atmos.) produced by the impact of the high speed jet.
The theories of both of these phases are based upon the classical hydrodynamics of perfect fluids, which is applicable because the strength of the metals involved can be neglected at the high pressures encountered.
19(1948); http://dx.doi.org/10.1063/1.1698174View Description Hide Description
A method is described for forming cathodes by means of a cataphoresis process wherein a thin layer of thoria is deposited over an underlying metal. A temperature scale determination yields for the relation between true temperature (°K) and brightness temperature (°C) at λ = 0.65 micron: Tt = 1.172Tb + 177.5. Electron emission studies yield for the constants of the Richardson equations:Information was also obtained regarding the resistivity of thoria at high temperatures.
19(1948); http://dx.doi.org/10.1063/1.1698175View Description Hide Description
19(1948); http://dx.doi.org/10.1063/1.1698176View Description Hide Description