Volume 17, Issue 9, 01 September 1946
Index of content:
17(1946); http://dx.doi.org/10.1063/1.1707775View Description Hide Description
This paper presents data on the internal friction of four single crystals of zinc while oscillating longitudinally, and a description of various slow speed tension tests on a fifth crystal within and beyond the elastic limit. In the first named measurements the behavior of the crystals bears little resemblance to that of crystals of zinc of greater purity prepared by another method, which has previously been reported (see reference 1). The most outstanding feature is that the decrement, although higher at the lowest stress amplitude than for the previous ones, shows very little rise with increasing stress amplitude, even up to stresses far beyond the statically‐determined elastic limit. The difference in behavior seems to be caused by the difference in purity of the zincs. An optically mosaic structure, such as that described by Schilling (see reference 4), does not appear to be responsible. In the slow speed tension tests the zinc crystal, after a period of self‐annealing at room temperature, has a Hooke's law region up to about 70 g/mm2 (R.S.S.=28 g/mm2) and at greater stress shows transient and steady creep. Under some circumstances the transient creep is in two parts, a slow starting creep followed by much more rapid creep. The crystal, when measured following a permanent strain, shows creep at loads well below the previous elastic limit and has a large amount of hysteresis. Self‐annealing occurs during rest periods and the initial elastic limit is gradually regained while the hysteresis disappears.
17(1946); http://dx.doi.org/10.1063/1.1707776View Description Hide Description
This paper is a continuation of a previous article on the design of broad band I.F. amplifiers of the stagger‐tuned type. The analysis is extended to unrestricted band width. It is shown that an exact solution is possible for either an oscillatory or a monotonic response, with this result: 1. The necessary number of stages (t) for a given minimum attenuation in the cut‐off region depends again only on the gain tolerance and the desired response. 2. Attentuation minima and maxima again appear at frequencies within the band, easily located and dependent only on the number of stages. 3. The amplifier consists of a number of pairs of circuits, which have the same figure of merit Qn and tune at resonant frequencies f 0n disposed in geometric symmetry around the middle band frequency f 0 thus making f 0n equal to δ n f 0 and f 0/δ n , respectively. Formulas for Qn and δ n are derived. The circuit impedances are calculated from a prescribed gain or from the maximum obtainable gain. A formula for the maximum gain band width product is given. A comparison is made between the performance of amplifiers with monotonic and oscillatory response. A practical example is worked out.
17(1946); http://dx.doi.org/10.1063/1.1707777View Description Hide Description
An analytical method is developed which yields key values of a harmonic function U in rectangular figures in terms of certain simple combinations of known boundary values, which we call Laplacian perimeters and denote by P. From the key values all the remaining interior values can be directly and rapidly calculated. The basic ideas consist of the introduction of four elementary figures of variable lengths: 3(2+δ), 3(3+δ), 4(2+δ), and 4(3+δ), where 0≤δ≤1, for which the key values are found algebraically, Eqs. (9.1) to (9.8) inclusive, and of combining analytically these elementary cases to obtain continuous solutions for rectangles (3×n′) and (4×n′) for any number n′ greater than 2. The general expression for any key value (ui ) m×n′ in a rectangle (m×n′) is
17(1946); http://dx.doi.org/10.1063/1.1707778View Description Hide Description
17(1946); http://dx.doi.org/10.1063/1.1707779View Description Hide Description
A simple theoretical treatment is given for the emission of light and associated variations of dark current that occur on warming zinc sulphide and zinc silicate type phosphors previously irradiated with ultraviolet light at low temperatures. Reasonably good agreement is found between the calculated and observed glow curve for Willemite. The same type of treatment is applied to the case of infra‐red illumination of phosphors at low temperatures.
17(1946); http://dx.doi.org/10.1063/1.1707780View Description Hide Description
An application of the calculus of finite differences has been made in obtaining the complete expression for the voltage gain of an n‐stage amplifier having identical grid‐to‐plate impedances and plate loads when driven by a generator of any given internal impedance. An application of these results was made in determining the conditions of oscillation in a multi‐stage amplifier using single‐tuned circuits. It was found that there is a certain minimum grid‐to‐plate capacitance required to cause oscillation. If the actual grid‐to‐plate capacitances are below this value, the system will not oscillate. There also exists a region of stable gain, zero to 21/n , wherein it is impossible to make the amplifier oscillate even with grid‐to‐plate capacitance arbitrarily large.