摘要:

A sensitive and accurate method for determining the real part of the dielectric constant of gases at microwave frequencies is described. The method eliminates some possible sources of systematic error inherent in earlier methods.The dielectric constant of dry air at N.T.P. has been determined as 1.000569, at a frequency of 3000 Mc/sec. This is in good agreement with other results, at 24,000 Mc/sec, at 9000 Mc/sec, and at low frequencies, thus verifying that the dielectric constant is independent of frequency up to nearly 30,000 Mc/sec An earlier result suggesting the contrary was found to be in error because of insufficient drying of the air.

ISSN:0021-8979    

DOI:10.1063/1.1702240

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

We consider the shorted‐line method as applied to general samples, not restricted to quarter‐wave, half‐wave, thin, or low loss. The complex dielectric constant can be obtained by combination of two measurements, the sample being followed by short and open circuit, respectively. The equation is simple, nontranscendental, and unambiguous (Eqs. (5), (11), (19), (22)). It lends itself to complete graphical representation (Table I, Fig. 2). When only a single measurement is made, as in conventional practice, a change of variable leads to great simplification of detail ((14), (15), (16), Figs. 2, 3, 4). With due regard to the nature and magnitude of experimental errors, we analyze the conditions for optimum graphical representation, and give a reasoned determination of scale ranges. Large scale curves have been constructed, but only reductions are given here.

ISSN:0021-8979    

DOI:10.1063/1.1702241

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

1. The high limiting contact voltage of 40 to 50 volts in contacts between silicon carbide members (single crystals of the black‐green variety) is explained on the basis of the known temperature‐voltage relation.2. Practically clean silicon carbide possesses a superficial layer which functions as a potential hill for the electrons. Because of its thinness the hill is penetrable for the electric current by means of the tunnel effect. The tunnel resistance per unit area was investigated with terminal areas of the order of 2 mm2. Being constant at small voltages, it drops down through some orders of magnitude within the voltage range of 0.5 to 5 volts, showing that the work function for emission of electrons into the barrier material from the adjacent metal is of the order of 3 electron volts. From the amount of the tunnel resistance it is concluded that the thickness of the potential hill is of the order of 10 to 20 Angstrom units. The simultaneity of applied voltage and tunnel current is demonstrated.

ISSN:0021-8979    

DOI:10.1063/1.1702242

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The hypothesis is suggested that initiation of high voltage breakdown in vacuum is due to traversal of the high voltage gap by a clump of loosely adhering material. The implication of this hypothesis for uniform‐field gaps is that the breakdown voltage is proportional to the square root of the gap length. A summary the literature is presented which supports this conclusion for a range of voltages from 20 kilovolts to 7 megavolts, and for a range of gap distance from 0.2 mm to 6 meters. Additional qualitative evidence is presented which tends to support the proposed hypothesis.

ISSN:0021-8979    

DOI:10.1063/1.1702243

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A method of estimating magnetization losses due to eddy‐currents in solid cylindrical cores of ferromagnetic material is given. The conception of complex permeability is introduced to show the effects which hysteresis has upon the degree of flux penetration. A formula is given for the effective permeability which should be used in the classical treatment in which nonlinearities have been ignored.An arbitrary case in which the permeability changes across the core section is considered and the solution is extended to a core which is homogeneous, but whose permeability changes with the degree of magnetization. In this way errors due to a nonlinearB‐Hcurve are reduced and the complex permeability notation is shown to lead to a more reasonable Steinmetz relationship.The eddy‐current anomaly is mentioned and it is noted that the theory developed is suited to a consideration of the anomaly as explained in terms of time‐lag effects.

ISSN:0021-8979    

DOI:10.1063/1.1702244

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A possible source of confusion between the concept of information content and entropy in the theory of information is discussed and resolved. Information theory is then applied to the problem of taxonomy or classification of data and several models are discussed, representative of various possible methods of filing data with the purpose of determining the optimum size of filing‐unit in relation to the given data. The possible fields of application envisaged include the classification of faults in a system, the statistical analysis of data or the indexing of books, letters, etc.

ISSN:0021-8979    

DOI:10.1063/1.1702245

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

An article by Birkhoff, MacDougall, Pugh, and Taylor (see reference 1) presented hydrodynamic theories of jet formation and target penetration by explosives with lined conical cavities. However, it was unable to explain satisfactorily why the jets produced are several times as long and, therefore, several times as effective as the steady‐state theory predicts. It is shown here that these difficulties are overcome by assuming a variable instead of a constant collapse velocity for the walls of the conical liner. The variability in the collapse velocity produces a surprisingly large change in the process of jet formation.

ISSN:0021-8979    

DOI:10.1063/1.1702246

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Experimental evidence is presented that verifies the assumptions and conclusions of the article, ``Theory of Jet Formation by Charges with Lined Conical Cavities,'' by Pugh, Eichelberger, and Rostoker. A graphical method of predicting the shape of the jet and slug at every instant is presented.

ISSN:0021-8979    

DOI:10.1063/1.1702247

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

An observation of the creeping of a liquid past a mercury seal is reported. The conditions under which such a phenomenon might be expected to occur are discussed in terms of the thermodynamics of surfaces.

ISSN:0021-8979    

DOI:10.1063/1.1702248

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The subject is an unconventional method of heating and melting metals without a crucible, by suspension in space with an electromagnetic field. Operating conditions for certain cases are given. The results obtained by means of the new technique encourage the thought of melting, purifying, alloying, and agitating of inert and reactive metals without resort to crucibles, and thereby avoiding the contamination of reactive metals by crucible materials. Preliminary results with various forms and masses of metal are described. Considerations concerning the atmosphere in which levitation occurs are included.

ISSN:0021-8979    

DOI:10.1063/1.1702249

出版商:AIP    

年代:1952

数据来源: AIP