ISSN:0021-8979    

DOI:10.1063/1.1699631

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

This paper describes the results of radio angle‐separation measurements on a 2.50‐mile path over Lake Buchanan near Austin, Texas. The measurements were made to test the angle‐separation equipment developed at The University of Texas, and to compare these results with measurements obtained by rocking a 20‐foot parabolic antenna.

ISSN:0021-8979    

DOI:10.1063/1.1699632

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

When an electric arc is driven by a magnetic field, under special conditions, curious phenomena are observed. An electric arc cannot be driven by the magnetic field when it is established at very small gaps between the electrodes. Neither can it be driven by the magnetic field for the instant just after the contacts have been broken. These phenomena are called immobility phenomena. In the present work, the immobility time and the driving velocity of the electric arc were measured under various air pressures. As the air pressure decreases, the immobility time increases and the driving velocity decreases. Under a certain low air pressure, the arc cannot be driven by the magnetic field. When the air pressure is lower than this critical value, the arc can be driven again by the magnetic field; but in this case, the arc moves in a direction that is opposite to the direction of the electromagnetic force. This phenomenon is called the reverse driving phenomenon. The causes for these phenomena are considered.

ISSN:0021-8979    

DOI:10.1063/1.1699633

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Apparatus has been developed for measuring the dynamic viscosity and rigidity of soft rubber‐like solids in small oscillating deformations. A plate rigidly attached between two identical coils in two permanent magnets shears a pair of disk‐shaped samples when a driving current is passed through one coil. The open circuit voltage from the other coil is compared in amplitude and phase with the driving current by a method in which all measurements are in the form of settings of a potential divider. The apparatus has two advantages over the more familiar resonance devices: (a) the amplitudes of motion, which need not be measured directly, are extremely small, thus minimizing any non‐linear effects, or temperature change due to heat dissipation; (b) a continuous range of frequencies, spaced as closely as desired, is available without adjusting masses. The dynamic rigidity and viscosity of two samples of polyisobutylene, of molecular weights 1.2 and 0.47 million, have been measured at 15, 25, and 35°C at frequencies from 20 to 600 cycles/ sec., with a reproducibility of five percent or better. The rigidity increases and the viscosity decreases with increasing frequency. Both decrease with increasing temperature, and are almost independent of molecular weight. The temperature dependence is quantitatively explained by the assumption that stresses relax by flow processes whose apparent activation energies are all identical with that characterizing the steady flow viscosity.

ISSN:0021-8979    

DOI:10.1063/1.1699634

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The sixty‐cycle dielectric strengths of some gaseous fluorocarbons have been measured between three differently shaped electrode pairs at pressures up to three atmospheres. The breakdown potentials for propforane, butforane, and pentforane were found, in most instances, to be equal to or greater than those for sulfur hexafluoride under comparable conditions, and to be far greater than those for nitrogen. Fluorocarbons thus have possible uses as gaseous insulators in high voltage apparatus.

ISSN:0021-8979    

DOI:10.1063/1.1699635

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Polyethylene of such molecular weight and structure that it readily fibers or cold draws to 300–600 percent elongation by usual uniaxial, tensile stressing may react quite differently under biaxial tension. When biaxial tension in 1:1 ratio is applied to a diaphragm, some polymers show brittle fracture with <20 percent elongation at break. However, if the average molecular weight of such polyethylenes is shifted upward by crude fractionation, or an initially higher average is used, the polymers orient under complex stresses. Then, they usually elongate several hundred percent before rupture. Variations in crystallinity are also significant, although most technical polyethylene soon attains at room temperature enough crystallinity so that this factor does not cause big differences.Although the whole study is so far preliminary, x‐ray scattering of stressed samples suggests that preferred glide on certain crystallite planes tends to occur as the yield point approaches. These are such as to inhibit smooth alignment of the long chain axis in the direction of stressing. This could lead to brittleness.Apparatus for complex stressing of sheets and tubes is described. Strains are taken from coordinates printed on the sample by the silk screen process. High speed stressing was also observed. The speed of retraction of amorphous polyethylene chains approaches that of rubber.

ISSN:0021-8979    

DOI:10.1063/1.1699636

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Typical d.c. current‐voltage characteristics obtained for Si and Ge crystal rectifiers are described. A survey of the published theories of the rectifier shows that none of them will account for the principal features of the observed characteristics. The most obvious discrepancy is in the low resistance direction of flow where the logarithm of the current rises with increasing voltage at only a fraction of the rate indicated by the theories. The need for a more flexible theory is pointed out and the conditions which it must meet, both as a function of voltage and temperature are outlined.

ISSN:0021-8979    

DOI:10.1063/1.1699637

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The electric breakdown in CO2has been investigated from low pressures through the critical point into the liquid state. Paschen's similarity law is verified for low pressures. At high pressures small departures are observed for long gap‐lengths and large departures for small gap‐lengths. Simultaneously the scatter of the breakdown voltage becomes independent of illumination and the breakdown strength dependent on the cathode material; this appears due to the onset of field emission. Measurements of prebreakdown currents have yielded values for Townsend's first coefficient as well as for the field emission constants. For small gap‐lengths the prebreakdown currents are higher than the normal field emission equation predicts, indicating some new process effective at short gap‐lengths. The transition from the gaseous to the liquid state does not produce a discontinuous change of the breakdown voltage.

ISSN:0021-8979    

DOI:10.1063/1.1699638

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The equations of hydrodynamics are modified by the inclusion of additional terms which greatly simplify the procedures needed for stepwise numerical solution of the equations in problems involving shocks. The quantitative influence of these terms can be made as small as one wishes by choice of a sufficiently fine mesh for the numerical integrations. A set of difference equations suitable for the numerical work is given, and the condition that must be satisfied to insure their stabilty is derived.

ISSN:0021-8979    

DOI:10.1063/1.1699639

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

By elementary and obvious methods a differential equation is obtained, which in general is non‐linear and usually affords a solution which is a simple sinusoidal function of the independent variable (i.e., simple harmonic motion). Two particular examples are studied briefly although no physical realizations are presented. One is led to speculate that new types of oscillators having a sinusoidal output are described by these equations, and that practical applications, such as to frequency metering, may eventually be evolved. However, the writer's speculations along these lines have as yet borne no fruit and his primary object in publishing this material is to bring to the attention of those interested in non‐linear phenomena, about which our understanding is so essentially imperfect, an analysis which, though itself possibly trivial, conceivably may prove of service in setting someone else off on a productive investigation.

ISSN:0021-8979    

DOI:10.1063/1.1699640

出版商:AIP    

年代:1950

数据来源: AIP