Volume 22, Issue 10, 01 October 1951
Index of content:
22(1951); http://dx.doi.org/10.1063/1.1699831View Description Hide Description
An investigation of factors which influence the formation of a cavity when a sphere enters water vertically is described. It was found that cavities are formed at much lower entry speeds for contaminated spheres than for clean ones, but that there is little dependence on the type of the contaminant. In regard to the scaling of this effect, the tendency to form a cavity varies little with change of size or specific gravity of the sphere. Water‐entry cavities are observed to form at velocities much lower than those required for incipient cavitation in the water tunnel; consequently, a relation between the two effects appears improbable. Some dependence of cavity formation on viscosity might be inferred from the observation that cavities were formed at lower entry speeds by spheres coated with liquids of high viscosity than by spheres without this coating.
22(1951); http://dx.doi.org/10.1063/1.1699832View Description Hide Description
A numerical procedure is presented for the calculation, by diffusiontheory, of the critical size of a nuclear reactor, and of the time‐dependent distribution of neutrons in the reactor as a function of position (one‐dimensional space) and neutron energy. The partial differential equations for diffusiontheory are approximated by a system of ordinary differential equations, for which a stepwise convergent solution for neutron distribution is obtained. The critical size of the reactor is found from a comparison of the magnitude of the slowing down densities of the thermal and fission energy limits. The procedure is applied, by way of example, to a reflected sphere.
This method for calculating neutron distribution is thought to be new in that an integration technique is developed and used for the solution instead of differentiation. Primarily because of this, the convergence to the correct solution is rapid. In a one‐dimensional space all physical quantities can be considered as either continuous or discontinuous functions of both position and energy. Such items as fission and nonproductive capture in the slowing down range can be included as part of a standardized procedure. Certain transient and steady‐state perturbation like motion of control rods can be studied.
22(1951); http://dx.doi.org/10.1063/1.1699833View Description Hide Description
High accuracy of measurement in the electrolytic tank can be achieved by a suitable ratio of impedance as between tank and measuring circuit. With this requirement fulfilled, the axial distribution of the symmetrical lens was explored and found to satisfy a relation Vz =V 0+Ae −bz(2), where V 0 is the potential of the outers with respect to the middle electrode, `z,' the distance from the center of the lens, while A and b are constants from any one geometry.
The effect of varying the separation between the elements was specially investigated. It was found that the maximum value of the gradient between electrodesincreases as the separation between them increases, reaches a flat maximum between 0.8 and 0.4 D (D, bore diameter) and then decreases with further increase in spacing. This means that a decrease in separation produces a weaker field and an increased focal length.
The potential at the saddle point is very sensitive to changes in separation in the region up to about 0.5 D; it was also found to vary linearly with bore up to 3 D.
The relaxation method of field plotting was also applied to map the distribution; the results are compared with those given by the tank.
22(1951); http://dx.doi.org/10.1063/1.1699834View Description Hide Description
A solution is given for the problem of the scattering of plane electromagnetic waves from a sphere with a concentric spherical shell. The solution is general, and under appropriate conditions is reduced to the well‐known solution for scattering from a single sphere.
An Experimental Investigation of the Dielectric Rod Antenna of Circular Cross Section Excited in the Dominant Mode22(1951); http://dx.doi.org/10.1063/1.1699835View Description Hide Description
The radiation pattern and the gain were measured for four series of dielectricantennas of circular cross section. These antennas were excited by a TE 11 mode in a circular metallic wave guide at a frequency of 9275 mcps. Only one parameter was changed in each series of rods so that the effect of this parameter on the pattern and gain could be studied. Measurements of gain are presented for two further series of rods in which the length is varied. The measurements showed that a polystyrene rod of length 6λ0 and constant cross section has maximum gain and best pattern for a diameter of approximately 2λ0. On the other hand when the taper of a Lucite rod was varied while the length and the maximum diameter were held constant at 6λ0 and 0.87λ0, respectively, the gain and the pattern behavior improved as the minimum diameter was decreased to zero. It is shown that losses in the dielectric produce a significant decrease in the gain.
22(1951); http://dx.doi.org/10.1063/1.1699836View Description Hide Description
The design for a highly versatile dynamic load simulator is described, in which the correct resultant load is computed electrically and applied through a hydraulicservomechanism. One of the significant features of this machine is that virtually all of the power absorbed from the unit to which the load is applied is conserved in the form of electrical energy and returned to the power lines. A complete analysis of this electrohydraulic system is presented for the case in which coulomb friction is negligible. Two basic applications for this simulator are a servo test stand designed primarily for testing autopilots and an aircraft control load simulator for both design and test of control systems.
22(1951); http://dx.doi.org/10.1063/1.1699837View Description Hide Description
Internal friction studies have been made of an alloy 88 percent Mn‐12 percent Cu. This alloy when annealed at 925°C and quenched to room temperature has a tetragonal structure of axial ratio 0.97. Twins are readily formed along the (101) and (011) planes. It has been suggested that relaxation across these twin boundaries would account for certain observed internal friction. Verification of this is shown.
22(1951); http://dx.doi.org/10.1063/1.1699838View Description Hide Description
In order to gain an insight into the structure and properties of grain boundaries,diffusion along grain boundaries has been studied as a function of relative orientation of the grains and of the boundary. Experiments were made by comparing the depth of penetration of silver along the boundaries of columnar copper in the columnar direction . The results indicate that, for angles of misfit between the grains, greater than 20° and smaller than 70°, diffusion along grain boundaries is greater than volume diffusion (near 700°C) and reaches a maximum around 45°. Outside of that range of relative orientation the rate of grain boundarydiffusion is not greater than volume diffusion. These results are correlated with the information available about the energy of grain boundaries, and it is concluded that at small angles the dislocation model of grain boundaries describe satisfactorily the situation, while at larger angles the grain boundaries are better described in terms of areas of fit and misfit.
22(1951); http://dx.doi.org/10.1063/1.1699839View Description Hide Description
The electrical properties of selenium have been studied in their dependence on history of preparation, i.e., as functions of temperature of initial liquid selenium, quench procedure, nucleation procedure, temperature of crystallization, and time of crystallization.
The electrical properties of melt single crystals and the microcrystalline matrix of these crystals have been compared.
The influence of nonmetals S, O2, I2, in small quantities on the electrical properties has been determined.
Carrier densities and effective mobilities as functions of temperature of measurement have been estimated from data on thermoelectric powers and resistivities. The order of the carrier densities have been checked by measurements of the voltage dependence of capacity of completely vacuum prepared rectifiers.
The frequency dependence of resistivity has been determined to gain insight into the nature of the effective mobilities.
22(1951); http://dx.doi.org/10.1063/1.1699840View Description Hide Description
Approximate closed form analytical expressions are derived for the total and differential scattering cross sections of cylindrical, prolate spheroidal, and disk‐shaped scatterers which subject scalar plane waves to only a small phase shift.
When a plane wave excites a sphere or infinite cylinder, the internal field of these objects can be expressed as an infinite series of bessel functions. By making an approximation in coefficient of the nth bessel function which is valid for either 2πa/λ0»n (a = sphere or cylinder radius, λ0 = wavelength of incident plane wave) or |m−1| «1 (m = λ0/λ1, λ1 = wavelength of plane wave in medium composed of material of scatterer), it is possible to obtain a closed form expression for the series. The scattered field is obtained by integrating over these internal fields.
The scattered fields for long but finite cylinders and prolate spheroids are calculated by approximating their internal fields by those of infinite cylinders of the same radius. The scattered fields of thin disks are obtained by assuming the internal fields to be that of an infinite flat plate of the same thickness.
22(1951); http://dx.doi.org/10.1063/1.1699844View Description Hide Description
22(1951); http://dx.doi.org/10.1063/1.1699846View Description Hide Description
22(1951); http://dx.doi.org/10.1063/1.1699849View Description Hide Description
22(1951); http://dx.doi.org/10.1063/1.1699850View Description Hide Description