摘要:

The formal solutions of problems involving transient heat conduction in infinite internally bounded cylindrical solids may be obtained by the Laplace transform method. Asymptotic series representing the solutions for large values of time are given in terms of functions related to the derivatives of the reciprocal gamma function. The results are applied to the case of the internally bounded infinite cylindrical medium with, (a) the boundary held at constant temperature; (b) with constant heat flow over the boundary; and (c) with the ``radiation'' boundary condition. A problem in the flow of gas through a porous medium is considered in detail.

ISSN:0021-8979    

DOI:10.1063/1.1722288

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A method is presented of measuring the equivalent nitrogen vapor pressure of polymeric materials over a range of temperatures. It is found that, for the range of temperatures investigated (300–450°K), the vapor pressure‐temperature characteristics of the polymeric materials studied are described by the empirical relationlogP=A−B/T.The values of the constantsAandBin this equation are determined for a number of materials including nylon, Teflon, saran, polyethylene, and mylar.

ISSN:0021-8979    

DOI:10.1063/1.1722289

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

In this paper there are described solutions of the three‐dimensional equations of elasticity and the equations of generalized plane stress pertaining to vibrations of crystal rectangular parallelepipeds and thin plates with traction‐free faces. The modes of motion exist in crystals of certain classes for specific orientations and length‐ratios of the edges. Since the solutions are exact and in closed form, they may be used to advantage in connection with the measurement of elastic constants. Special disposition of electrodes is required for piezoelectric excitation.

ISSN:0021-8979    

DOI:10.1063/1.1722290

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Bethe's equation for the change of entropy in waves of finite amplitude is shown to be inapplicable for an initial state of temperature arbitrarily close to absolute zero, for a degenerate substance possessing a zero‐point pressure (or energy). Thermodynamic functions for such a substance at low temperature are formulated in general terms applicable to the Fermi‐Dirac gas, the Thomas‐Fermi atom, the Debye solid, and the Mie‐Gru¨neisen solid as special cases. The conditions under which the equation of state satisfies the Bethe‐Weyl conditions are given. Of the usual four basic properties of the shock transition under the Bethe‐Weyl conditions, two must be modified for the class of substances in question, for an initial state arbitrarily close to zero temperature. The argument follows from extension of Bethe's method, by Taylor expansion of the Hugoniot function about the initial state. The results are shown to be consistent with Weyl's procedure.

ISSN:0021-8979    

DOI:10.1063/1.1722291

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Extremely low‐frequency (ELF) radio waves (10–500 cycles) originating in lightning were received over distances in excess of 15 000 km. Transmission conditions were equally good, day or night. Propagation distances were ascertained by analysis of higher frequency components (>1700 cycles) according to known methods. The receiving antenna employed an arrangement of grounded electrodes which uniquely determined the azimuthal direction of the source. Two distinct classes of ELF pulses are described which are attributed to different conditions of propagation.

ISSN:0021-8979    

DOI:10.1063/1.1722292

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Properties of electromagnetic propagation at extremely low frequencies (below 500 cycles) are deduced from analysis of pulse distortion. The source of the transmitted pulse is lightning. Two distinct transmission types are analyzed. Normal, or type I, propagation is shown to behave as if the earth's surface and ionosphere constitute a wave guide composed of two plane parallel surfaces, with one surface partially conducting. This wave guide has no low‐frequency limit on progagation; attenuation formulas are given. The transmission properties of type II, or anomalous propagation, are derived and seen to be inexplicable by means of this wave‐guide model. The analysis leads to a determination of the effective conductivity of the ionospheric reflector at these frequencies: the daytime reflecting layer (Dlayer) conductivity is 104esu; the nighttime conductivity (Elayer) is 5×104esu; both results are far lower than deduced by other means.

ISSN:0021-8979    

DOI:10.1063/1.1722293

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Tensile tests have been performed on whiskers of iron, copper, and silver 1.2 to 15 &mgr; in diameter. The strongest whiskers which were less than 4 &mgr; in diameter exhibited resolved elastic shear strengths of from two to six percent of their shear moduli. Stress‐strain determinations on iron have shown that large deviations from Hooke's law occur beyond two percent strain. As the whiskers increase in size, their strengths decrease with considerable scatter.

ISSN:0021-8979    

DOI:10.1063/1.1722294

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

This investigation is primarily concerned with the study of electromagnetic transmission characteristics of a lattice of infinitely long conducting cylinders. Four approaches to the general problem have been employed and the advantages, disadvantages, and realms of validity of each have been studied. Several of these methods constitute a substantial improvement over previous analyses and are supported by wave‐guide and free‐space experimental work.The four approaches are: (1) A molecular analogy with a consideration of dipole interactions leading to the Clausius‐Mosotti relations, (2) A transmission line formulation which considers the thick obstacle for both polarizations, (3) An analysis based on the summation of scattered fields which demonstrates that the Clausius‐Mosotti relations are a special case of a more general relation which accounts for the effects of higher order multipoles, and (4) A solution formally valid for all values of spacing and cylinder radius based on integral equation formulation of variational principle.

ISSN:0021-8979    

DOI:10.1063/1.1722295

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A complete solution is given for the problem of constructing a plane stratified dielectric medium having that the property that at a fixed frequency and polarization a plane wave at any angle of incidence will be transmitted without reflection by the medium. This problem can also be interpreted quantum‐mechanically. The dielectric medium of the first interpretation becomes, in the second interpretation, a potential for the one‐dimensional Schro¨dinger equation such that a particle which is sent in from ‐ ∞ is transmitted with probability one of getting through to + ∞, no matter what the initial kinetic energy of the particle may be.In addition, the results can be applied to the problem of finding perfectly matched nonuniform transmission lines.

ISSN:0021-8979    

DOI:10.1063/1.1722296

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Zinc crystals were bent either by wrapping them around a mandrel or by the application of a concentrated load in a direction perpendicular to the basal plane. The structure of the bent crystals was studied by means of suitable x‐ray diffraction techniques, namely the Lambot technique and the Schulz technique. It was found that, after bending around a mandrel of sufficiently small radius, the zinc crystals were subdivided into subgrains, with an average disorientation between neighboring subgrains of approximately 3 minutes of arc. In the dimples formed by a concentrated load the radius of bending is quite large and there is hardly any observable substructure. However, the substructure does develop upon annealing by the polygonization mechanism. The diameter of the dimples formed by a concentrated load increases linearly with the logarithm of the time of load application, for a constant load, and it increases linearly with the load if the time of load application is constant.

ISSN:0021-8979    

DOI:10.1063/1.1722297

出版商:AIP    

年代:1956

数据来源: AIP