Volume 20, Issue 12, 01 December 1949
Index of content:
20(1949); http://dx.doi.org/10.1063/1.1698284View Description Hide Description
20(1949); http://dx.doi.org/10.1063/1.1698285View Description Hide Description
This paper describes some of the phenomena found to have their origin in electrically induced fibration of small particles in fluid liquid suspension. Particular attention is given to induced shear resistances found in layers of the fluid (0.01 to 0.15 cm) when bounded by potentialized electrodesurfaces. Ingredients and manner of compounding concentrated fluids capable of reversible shear resistance up to several hundred grams per cm2 are described. Dynamic induced shear resistance or the corresponding induced bulk viscosity are shown to be a parabolic function of field strength wherein parameters dependent on surface conditions of the particles are involved. Various properties of these fluids are discussed with regard to the mechanism of induced fibration, its application in slip clutches and other hydraulic devices, and some of the factors for best results. Consideration is given to the analogous magnetically induced fibration of ferromagnetic particles in fluidsuspension. It is found that the observed values of induced shear resistance approximate those predictable from the well‐known formulas for tractive force in both the electric and magnetic cases. Mention is also made of fluidsuspensions of ferrite powders which respond to both electric and magnetic fields.
20(1949); http://dx.doi.org/10.1063/1.1698286View Description Hide Description
An empirical method of calculating mass absorption coefficients is given. Complete tables of constants are presented for calculating μ/ρ for all elements and for wave‐lengths less than the K critical absorption wave‐length. Partial tables give constants for wave‐lengths between the L 1 and M 1 critical wave‐lengths.
Calculated mass absorption coefficients are given for the common elements.
20(1949); http://dx.doi.org/10.1063/1.1698287View Description Hide Description
From information about space‐charge‐limited currents, the transit time of electrons between a cylindrical cathode and an external coaxial anode has been computed. Taylor's series expansions of the functions useful in the calculations are given. These together with the tabulated values permit rapid calculation of electron transit times with an accuracy of 0.1 percent.
Bending of a Thin Circular Plate of an Aeolotropic Material under Uniform Lateral Load (Supported Edge)20(1949); http://dx.doi.org/10.1063/1.1698288View Description Hide Description
The bending problem is solved mathematically for a thin circular plate subjected to a uniform load. The material of the plate is assumed to have three symmetrical planes with respect to its elastic properties.
The solution is carried out in the case when the edge is simply supported, and it involves some numerical calculations. An empirical formula for the deflection is also given in a simpler form.
20(1949); http://dx.doi.org/10.1063/1.1698289View Description Hide Description
The torsion problem is theoretically treated for a prismatic cylinder with a star‐shaped section. To simplify the calculation, the bounding curve is assumed to be composed of logarithmic spirals. In one example the stress distributions on the boundary and on the symmetrical radial lines, and the torque are calculated. The result is confirmed by an experiment.
20(1949); http://dx.doi.org/10.1063/1.1698290View Description Hide Description
A special powder is used to show how static electricity is distributed on materials such as paper. Red particles of this powder are attracted to positively charged areas and blue particles are attracted to negatively charged areas. Paper from heat‐set printing presses shows streaks of static electricity generated by idling rollers and shifting patterns of static electricity generated in the folder, often with opposite charges on the same sheet of paper.
20(1949); http://dx.doi.org/10.1063/1.1698291View Description Hide Description
It has been shown experimentally that the mechanism of sintering of spherical glass particles is that of viscous flow. The viscosities of the investigated glass were determined for a range of temperatures from 575°C to 744°C. These viscosities remain in good agreement with those obtained by other methods.
20(1949); http://dx.doi.org/10.1063/1.1698292View Description Hide Description
An experiment was performed in order to determine the magnitude of that portion of dry, kinetic friction which is contributed by Coulomb friction, or the mechanical interlocking of surface irregularities. The results indicate that the work of the mechanical component of friction accounts for only a few percent of the work of total measured friction.
20(1949); http://dx.doi.org/10.1063/1.1698302View Description Hide Description
Golddeposited in vacuum at liquid air temperature contained defects and strain. The number of defects and their characteristic decay energy increased rapidly with increasing rate of deposit in the range from 1 to 5 micrograms/cm2/min. The defects decayed with rising temperature but the relief of strain did not occur until after most of the defects had disappeared. Electron micrographs showed that the goldfilm was made up of aggregations of discreet particles rather than a smooth continuous film.
20(1949); http://dx.doi.org/10.1063/1.1698303View Description Hide Description
Two techniques have been devised for the exploration of electrostatic and magnetic fields where conventional methods fail. Both use electron lens systems to magnify the deflecting effect of the fields on electron beams. One technique is the electron optical analog of the ``Schlieren'' method; the other involves deformed shadows of a thin obstruction.
For several reasons the ``Schlieren'' patterns obtained experimentally thus far have been interpreted only qualitatively. The patterns obtained by the shadow method, however, have been used for quantitative evaluation of field strengths. Experimental patterns of both types, produced by the fields of magnetized recording wires, are shown.
The shadow method is theoretically applicable to the quantitative evaluation of a wide variety of electric and magnetic fields. It utilizes formulas based on relations between field distribution and electron deflection, and between the latter and the geometrical parameters of a focusing system. Such formulas are derived and applied to several simple types of field.
An application of the theory to the magnetized wires used in the experiments yields relations from which each field distribution is evaluated by fitting a line to experimentally determined points. The theory also predicts the geometrical properties of the experimental patterns.
The agreement between theory and experiment is sufficiently good to justify the underlying theoretical assumptions and approximations.
20(1949); http://dx.doi.org/10.1063/1.1698304View Description Hide Description
Threshold detectors (In115, Ag107, and C12) were used to determine the relative intensities of neutrons at various distances inside a large water tank. Neutrons with energies up to 30 Mev were produced by (d, n) reactions. At distances in the water >20 cm the ``half‐thickness'' of water was found to be almost independent of neutron energy (about 8 cm).
20(1949); http://dx.doi.org/10.1063/1.1698305View Description Hide Description
20(1949); http://dx.doi.org/10.1063/1.1698306View Description Hide Description
An experimental investigation of dielectric rod as wave guide indicates that the guiding effect is retained even when the rod is only a fraction of a wave‐length in diameter. The greater part of the guided energy is then outside the dielectric, so that a very low loss wave guide results. Measurements of performance made at 1.25 cm indicate attenuations down to 0.004 decibel per meter in polystyrene rod, and show good agreement with theoretical predictions. A resonator utilizing the dielectric‐rod wave guide is described, in which a maximum Q of approximately 53,000 was observed.
20(1949); http://dx.doi.org/10.1063/1.1698307View Description Hide Description
Analysis of the non‐radiative modes propagated along a circular dielectric rod is accompanied by a discussion of dielectric loss. The attenuation for the three lowest modes in polystyrene is computed and agrees with the experimental data of Chandler given in the preceding paper.
20(1949); http://dx.doi.org/10.1063/1.1698308View Description Hide Description
The traveling‐wave amplifier is a typical structure where E‐M waves and electrons, traveling with approximately the same velocity, exhibit a strong interaction. The problem has usually been discussed for the case of weak waves with approximations corresponding to a small signal theory. It is interesting to state the limitations of this theory and to discuss the behavior of such tubes for strong signals. It seems that the amplified wave obtained in the case of small signals is progressively distorted until a final stage is reached where no further amplification is possible. The type of final distorted wave depends essentially upon all the details of the structure. In many cases where a complete investigation was possible, some strange types of shock waves were obtained, with a complete bunching of the space charge. A similar solution also applies to the linear accelerators or to the synchrotrons.
20(1949); http://dx.doi.org/10.1063/1.1698309View Description Hide Description
The quasi‐equilibrium distribution of a disperse phase, B, within a polycrystalline second phase, A, is investigated by methods of statistical thermodynamics. Phase B is assumed to consist of spherical particles of uniform size within the A crystals, and of lenticular particles of uniform size at the boundaries between two A crystals. The concentration (Mf) of B at the grain boundaries of A is found to be related to the sizes (r 1 and r 2) of the B particles at and away from grain boundaries, in terms of the interfacial energies (γ aa and γ ba ), the temperature (T), the over‐all concentration (M), and the size of the A crystals (R), by,wherewhere.Temperature will significantly affect the distribution only if γ aa r 1 2 is of the order of kT, or if γ ba /γ aa ∼½.
20(1949); http://dx.doi.org/10.1063/1.1698310View Description Hide Description
A technique of specimen preparation especially suited to the study of polymeric molecules and aggregates is presented. With slight modifications it is applicable to the preparation of replicas of a wide variety of surfaces where the action of heat, pressure, and solvents must be minimized. The method owes its superiority to the use of an aluminum‐beryllium alloy of high strength, low scattering power and nearly amorphous structure. A layer of evaporated hydrophilic material facilitates the separation of the metalfilm from the mounting surface. Micrographs are presented showing certain applications of the method.
20(1949); http://dx.doi.org/10.1063/1.1698311View Description Hide Description
The quantitative evaluation of the constituents of mixtures from x‐ray powder diffraction patterns has been highly successful in certain cases, but has been found subjected to limitations as an analytical tool of more general use. These arise from a number of effects which interfere with a simple interpretation of the patterns. The paper discusses the basic aspects of these interferences, in particular of those which result from superpositions of lines, and develops a method which takes account of them. The method is adapted to meet such cases where the constituents or impurities which interfere with the regular patterns are unknown.
20(1949); http://dx.doi.org/10.1063/1.1698312View Description Hide Description
The resistivity and the total emissivity of commerical titanium have been measured over the temperature range from room temperature to 1400°K. The resistivity at 20°C is 78.6 microhm cm. Above this temperature it increases to a flat maximum of 182 microhm cm at the temperature of the hexagonal‐body‐centered cubic transformation. The total emissivity is about 0.31 at low temperatures and there is some indication that it shows a maximum near the transition temperature. The spectral emissivity and the brightnesstemperature scale are also determined over the range of 1000°K–1400°K.