摘要:

A number of methods of numerical solution of systems of partial differential equations are surveyed. The size and speed of computing machines required to solve problems of varying complexity is discussed. Finally, a number of typical problems which have been solved numerically by various authors are described.

ISSN:0021-8979    

DOI:10.1063/1.1721257

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The authors present the design and construction of an analog computer unit which is particularly well adapted for solving nonlinear differential equations. The units are readily combined to solve simultaneous nonlinear differential equations. The unit is carefully checked by using it to solve some nonlinear differential equations for which known solutions exist. Finally the unit is used to find the solution to some nonlinear differential equations whose solutions are not given in the literature.

ISSN:0021-8979    

DOI:10.1063/1.1721258

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The effect of electron encounters on the velocity distribution in an electron beam after passage through an accelerating grid is calculated by direct integration of the Boltzmann equation. It is found, with electron densities and velocities typical of traveling wave tubes and diodes, that the electron encounters have a negligible effect, that the formulas of the usual kinetic theory for heat conduction do not hold, and that the longitudinal component of the electron gas pressure is negligible.

ISSN:0021-8979    

DOI:10.1063/1.1721259

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The drift velocity of electrons in an electric field in argon and alcohol mixtures has been measured. The measurement has been taken observing on the screen of a triggered sweep oscillograph the rise time of pulses as given by &agr;‐particles in an ionization chamber. The results give, for the 10 percent mixture, a behavior of thew(E/p) function, of thew=aE/ptype up toE/p=2 v cm−1mm Hg−1values, and of thew=const type for larger values ofE/p. Measurements at 0.5 and 5 percent alcohol concentrations are also reported.

ISSN:0021-8979    

DOI:10.1063/1.1721260

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Artificial dielectrics have been constructed with indices of refraction as high as 7.2 at a frequency of 9364 mc/sec by imbedding microscopic conducting flakes in paraffin wax. When good conductors such as Cu and Al are used, the resulting permeability is observed to be complex while the permittivity is substantially real. This phenomenon is in agreement with the theoretical results of Lewin. It is indicated that a low loss, high refractive index, artificial dielectric can be constructed by using powdered conductors if the particles are very small and possess a high electric polarizability.

ISSN:0021-8979    

DOI:10.1063/1.1721261

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

It is shown that the electromagnetic field in a loss‐free cavity excited through holes cannot be completely expressed in terms of the short‐circuit modes of the cavity satisfying the condition that the tangential component of the electric field is zero on the boundary of the cavity including the openings. For a complete expansion it is necessary to add an irrotational magnetic field, which contributes a term inversely proportional to the frequency, to the usual admittance matrix. If the cavity is presumed to include a reasonable portion of the guides feeding the openings, this irrotational component becomes almost diagonal.

ISSN:0021-8979    

DOI:10.1063/1.1721262

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A few formal observations are made concerning wave propagation through an inhomogeneous medium. A modification of Kirchoff's formula is suggested and an integral equation derived which, if certain integrals can be evaluated, gives an estimate of the error made in the usual approximate methods. Applications are indicated to the equivalent earth's radius model and to the flat earth, modified index model.

ISSN:0021-8979    

DOI:10.1063/1.1721263

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

An extension of the Emmons numerical method for temperature fields is developed for application in cases of solid‐fluid heat transfer in which a gas or fluid passes through a porous wall generating nonuniform heat. The numerical approach is first presented in general form and then applied to the two specific cases of a porous power‐producing cylindrical pipe and porous power‐producing plain wall.

ISSN:0021-8979    

DOI:10.1063/1.1721264

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The dynamics of a line of traffic composed ofnvehicles is studied mathematically. It is postulated that the movements of the several vehicles are controlled by an idealized ``law of separation.'' The law considered in the analysis specifies that each vehicle must maintain a certain prescribed ``following distance'' from the preceding vehicle. This distance is the sum of a distance proportional to the velocity of the following vehicle and a certain given minimum distance of separation when the vehicles are at rest. By the application of this postulated law to the motion of the column of vehicles, the differential equations governing the dynamic state of the system are obtained.The solution of the dynamical equations for several assumed types of motion of the leading vehicle is effected by the operational or Laplace transform method and the velocities and accelerations of the various vehicles are thus obtained. Consideration is given to the use of an electrical analog computer for studying the dynamical equations of the system.

ISSN:0021-8979    

DOI:10.1063/1.1721265

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Quantitative studies of the influence of the surface composition on the creep of zinc single crystals under constant loads have been carried out. The creep curves of crystals with clean and oxidized surfaces were obtained in air and in acid. It is shown that a continuous layer of oxide strengthens the crystal only at low loads, and that the presence of cracks in this layer allows the metal to creep at its normal rate. These facts support the theory that the oxide film acts to relieve the metal of part of the load. An increase in creep rate is observed when the pure metal surface is treated with dilute mineral acids. The heat liberated by the reaction is considered as a possible explanation of the sudden increase in creep rate when the surface layer of the crystal is removed. The normal creep curves of unoxidized crystals in air may be described by an empirical equation of a new form, and its application to other types of curves obtained is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721266

出版商:AIP    

年代:1953

数据来源: AIP