摘要:

The telegraphist's or long line equations are derived from the Maxwell field equations for ultra‐high frequencies. By taking into account retardation and the time rate of change of current, a new circuit parameter is obtained in addition to the four usually found in the conventional low frequency equations. This new parameter integrates into the radiation resistance of the parallel wires. The approximations involved are discussed, and application is made to a specific example.

ISSN:0021-8979    

DOI:10.1063/1.1745301

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

Observations by Schonland and Collens with Boys' camera show that the luminous tip of the leader stroke of the lightning discharge advances with a high velocity sometimes exceeding 3×109cm per second. From the fact that electrons traveling 109cm per second produce about 6000 new electrons per cm of actual path and that 6000 new electrons per cm in the direction of the field (i.e., &agr;=6000) requires 4×106volts per cm shows that to give the electrons a velocity in the direction of the field of 109cm per second would require a field exceeding 4×106volts per cm even at the tip of the stroke. The fields, and therefore the electron velocities, are certainly far less than this value. Accordingly the velocity of the tip greatly exceeds the velocity of the electrons in the tip. It is possible to account for this velocity as follows: Calculations based on justified assumptions concerning the conditions known to exist in a lightning stroke show that if the field just ahead of the tip averages 105volts per cm for about one centimeter, ionization by collision by the electrons present in the gas before the stroke would be great enough to advance the tip at the observed rate. Such a field is found not too high to be consistent with the low conductivity of the leader path. In this way a propagation of the leader stroke of a velocity many times higher than the velocity of the electrons can be attained.

ISSN:0021-8979    

DOI:10.1063/1.1745302

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

The coercive force of magnetite powder is increased by mere mechanical grinding. Measurements on sized powders of one natural and one artificial magnetite give a linear relation between coercive force and mean specific surface of the grains. It is suggested that this relation between coercive force and specific surface may prove to be important in deciding between theories of ferromagnetism.

ISSN:0021-8979    

DOI:10.1063/1.1745303

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

A method is given for obtaining a power series expansion in the wavelength for the Rayleigh wave velocity in a half‐space whose density &rgr; and elastic constants &lgr; and &mgr; are functions of depth. This is followed by a discussion of the Rayleigh wave problem in media where &lgr; = &mgr; and &mgr;(z) and &rgr;(z) are special cases of the type (&rgr;/&rgr;0) = (&mgr;/&mgr;0) =Acosh2(&agr;+&bgr;z).

ISSN:0021-8979    

DOI:10.1063/1.1745304

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

The expression for the temperature distribution in a semi‐infinite bar with heat supplied to the surfacex=0 at a rate given byH=ktn(n=0, 1, 2 ···) is derived, assuming no radiation to the surrounding medium and an initial temperature of zero. Curves are given which enable the distribution in a bar of any material to be readily computed forn=0 andn=1. The solution serves equally well to determine the voltage variation in a semi‐infinite non‐inductive cable with entering current proportional totnprovided the heat constants are replaced by the appropriate electrical parameters.

ISSN:0021-8979    

DOI:10.1063/1.1745305

出版商:AIP    

年代:1935

数据来源: AIP

摘要:

This paper presents the results of investigations of dissipation of energy in vibrating solids, mostly metals, by means of longitudinal and torsional vibrations of cylindrical rods. The amplitudes of strain used have been kept between 10−5cm/cm and 10−8cm/cm, in which range the dissipation of energy is proportional to the square of the strain. The specific dissipative property of a material is expressed in three different ways: (1) Equivalent viscosity or the ratio of stress to dissipative component of strain rate; (2) hysteretic constant defined as the area in ergs of the cyclic stress‐strain diagram; and (3) elastic phase constant defined as the ratio of specific elastic reactance to equivalent viscosity. Within a range of frequencies 100 to 100,000 cycles per second the results show that the hysteretic constant is proportional to some power &Dgr; of the frequency, the numerical value of the exponent &Dgr; varying between the limits − ⅓ and + ½, depending on the kind of material and its internal structural condition. Measurements made with longitudinal and torsional vibration indicate that dissipation is associated with dilatation as well as with pure shear. Preliminary studies are described showing the correlation between internal dissipation in metals and temperature hardness effects of annealing and aging.

ISSN:0021-8979    

DOI:10.1063/1.1745306

出版商:AIP    

年代:1935

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1745307

出版商:AIP    

年代:1935

数据来源: AIP