Volume 18, Issue 4, 01 April 1947
Index of content:
18(1947); http://dx.doi.org/10.1063/1.1697655View Description Hide Description
A detailed description of the preparation of silica replicas and substrates and their many and varied uses is presented with photographs and electron micrographs. A method of preparing silica replicas of specimens which cannot be subjected to the temperatures and pressures of the ordinary technique is described. It consists of applying a polystyrene lacquer to the specimen surface in place of the conventional molding. The question of ``up and down'' in stereo pictures of silica replicas is definitely settled by adding a metal oxide smoke (MgO) to the polystyrene replica before the silica evaporation. A successful powder dispersing technique consists of dispersing the powder in an ethyl cellulose lacquer and depositing upon a silica substrate. Several other techniques are also included.
18(1947); http://dx.doi.org/10.1063/1.1697656View Description Hide Description
An application of the characteristics of infra‐red storage phosphors to radiography is described, whereby the expense and trouble of x‐ray film processing may be partially or completely eliminated. The properties of these materials to store x‐ray energy for periods of time and release that energy upon exposure to infra‐red radiation have proved practical for either temporary and permanent recording of the latent x‐ray image. One distinct feature of this method is the complete removal of harmful x‐radiation to the technician. The possibility of a new field of radiography in ``flash fluoroscopy'' is also suggested by the authors. Graphs and charts exhibiting the characteristic behavior of infra‐red phosphors to x‐ray energy are included as well as actual photographs and radiographs comparing radiography with phosphorography.
A Flux Plotting Method for Obtaining Fields Satisfying Maxwell's Equations, with Applications to the Magnetron18(1947); http://dx.doi.org/10.1063/1.1697657View Description Hide Description
In this report the flux plotting methods which have previously been applied to fields satisfying Laplace's and Poisson's equations are extended to fields satisfying Maxwell's equations. Application is made to the hole and slot, and vane types of magnetron tubes.
18(1947); http://dx.doi.org/10.1063/1.1697658View Description Hide Description
Magnetron oscillators can provide very high frequency power for dielectric heating. Factors determining the choice of frequency for particular jobs are discussed. The design of a magnetron having 5 kw continuous output at 1050 megacycles is described, and performance data on the tube are given.
18(1947); http://dx.doi.org/10.1063/1.1697659View Description Hide Description
In determining molecular weights with the ultracentrifuge by the equilibrium method, it is necessary to drive the rotor at relatively high speeds for very long periods of time. It would be a real advantage to be able to deduce molecular weights from the distribution of concentration within a cell placed in a rotor without waiting for equilibrium. The solution of a certain differential equation gives the theoretical distribution within the cell at any time, and a comparison of the experimentally determined concentrations with those deduced from theory should yield molecular weights without waiting for equilibrium. The exact solution of this differential equation is known, but it is not suitable for numerical work. The present paper presents an approximate solution from which numerical results can be obtained with ease.
18(1947); http://dx.doi.org/10.1063/1.1697660View Description Hide Description
The elongations and natural frequencies of conically‐shaped coil springs are derived theoretically for several dynamic boundary conditions. Frequencies are verified experimentally on nickel and piano wire springs, attesting the reliability of the computations.
18(1947); http://dx.doi.org/10.1063/1.1697661View Description Hide Description
The paper aims at introducing the reader to the principal theories of plasticity. Since a presentation of the general stress‐strain relations used in these theories would require too much space, the discussion is restricted to the mechanical behavior of plasticmaterials under shear. Theories of plastic deformation (Hencky, Nadai) and theories of plastic flow (Saint Venant‐Lévy‐Mises, Prandtl‐Reuss, Prager) are illustrated by the example of a prismatic bar under torsion.
18(1947); http://dx.doi.org/10.1063/1.1697662View Description Hide Description
For the video output V of a receiver, consisting of an i‐f stage, a quadratic detector, and a video amplifier, the probability densityP(V) has been obtained for noise alone and for noise and signal. The results are expressed in terms of eigenvalues and eigenfunctions of the integral equation,where ρ(τ) is the i‐f correlation function (i.e., the Fourier transform of the i‐f power spectrum) and K(t) is the response function of the video amplifier (i.e., the Fourier transform of the video amplitude spectrum). Two special cases are discussed in which the integral equation can be solved explicitly. Approximations for general amplifiers are given in the limiting cases of wide and narrow videos. Some applications of the method to other problems are shown in Sections 7B and 9.
18(1947); http://dx.doi.org/10.1063/1.1697663View Description Hide Description
The analogy between thermal and electrical networks is used to obtain solutions to problems relating to the heating and cooling of air‐backed and solid‐backed bolometer elements exposed to radiation of periodically fluctuating intensity. From the equations derived, thermal response‐frequency characteristics are computed for ``typical'' bolometer elements. Features of these characteristics are discussed, and the physical influences of the various thermal properties of the bolometermaterial and of the backing material are pointed out.
18(1947); http://dx.doi.org/10.1063/1.1697664View Description Hide Description
18(1947); http://dx.doi.org/10.1063/1.1697665View Description Hide Description
A review of the literature indicates that a method of geologic mapping by means of observing the effect of geologic anomalies on electromagnetic field intensity should be practical. Field equipment is designed and assembled for that purpose and proves accurate and simple to use. Preliminary investigations with it successfully locate several anomalies.
18(1947); http://dx.doi.org/10.1063/1.1697666View Description Hide Description
An infinite sum transformation is defined and applied to a system of linear difference equations discussed by Faust and Beck in their paper on single tuned amplifiers. Some transforms of the more common functions are given and points of superiority of the transform method over the classical methods of solution of difference equations are emphasized.
18(1947); http://dx.doi.org/10.1063/1.1697667View Description Hide Description
Measurements were made of the internal friction of single crystal rods when vibrating longitudinally at 45 kilocycles per second. The decrement, or ratio of energy dissipated per cycle to twice the total vibrational energy, was used as a measure of the internal friction. At strain amplitudes below about 10−5 or 10−6 the decrement was independent of strain amplitude. The value of the constant decrement at low amplitudes, and the changes which occurred as the amplitude was increased, were both greatly dependent on the history of the specimen. The constant decrement for different crystals ranged from 7×10−5 to values higher than could be measured (about 200×10−5). For some of the initially high‐decrement crystals, values decreased with time (room temperature anneal). In general, for annealed crystals the decrement, measured as a function of increasing strain amplitude, remained almost constant up to and beyond the static elastic limit and then rose rapidly. It returned to the initial value when the strain amplitude was again reduced. On a second run, however, the rise in decrement occurred at much lower amplitude than on the initial one. It is concluded that the decrement is the result of two separate processes. The changing decrement at higher strain amplitudes is qualitatively explained with the use of dislocation theory.