摘要:

This paper discusses a method for finding an integral transformation applicable to certain time‐varying systems. Examples of transformations derived by the method, including Laplace, Mellin, and Meijer, are given. A convolution theorem for the general method is presented, and its use in general representation of time‐varying systems is illustrated.

ISSN:0021-8979    

DOI:10.1063/1.1721727

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The physical characteristics, thermoelectric power, resistivity, specific heat conductivity, and the temperature difference between hot and cold junctions determine the efficiency of thermocouple materials. These data have been determined for ChromelP‐constantan, bismuth alloys, and the intermetallic compound ZnSb, containing small amounts of added metals.The optimum characteristics of flat‐plate type solar energy collectors have been evaluated in combination with thermocouples, designed for maximum energy conversion. Using flat‐plate collectors with 2 glass panes, an efficiency of 0.63 percent was obtained with the ZnSb‐type alloys in combination with a negative Bi‐alloy. The commercially available ductile alloys ChromelP‐constantan, produced ten times lower efficiency. Calculations indicate that the efficiency may be increased to 1.05 percent by using 4 panes of low‐reflection characteristics.With solar energy concentrating means (lenses), the efficiency was increased to 3.35 percent, using the above mentioned best alloy combination.The maximum allowable cost of thermoelectric generators has been evaluated, by comparison with present methods of electric power generation.Solar thermoelectric generators may find useful application in the tropics, as they do not contain moving parts and require very little attention. Further development is needed to determine their economical value.

ISSN:0021-8979    

DOI:10.1063/1.1721728

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Hardness measurements were made along radii of circular cross sections of an annealed thick‐walled low‐carbon steel cylinder internally loaded with an explosive charge. The degree of work‐hardening in the cylinder wall was found to decrease nonuniformly with an increase in distance from the surface in contact with the explosive. Each hardnessversusdistance curve exhibited a series of plateaus along which the hardness remained constant. The plateaus appear to be related to Neumann bands which are present in the steel. The maximum number of twin directions in a single grain increases with the magnitude of the stress. The presence of the hardness plateaus and the increase in the number of twin directions with hardness and stress level point to the existence of critical stresses for twinning.

ISSN:0021-8979    

DOI:10.1063/1.1721729

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The impedanceEm2/2&bgr;m2Pof the backward wave on helical structures is considered from the point of view of the design of backward‐wave oscillators. Curves of impedanceversus ka(circumference to free‐space wavelength ratio) for single and bifilar helices are presented. Both the case of thin tape and that of round wire are treated. The impedance curves are calculated on the basis of an approximation to the actual distribution of rf current over the surface of the conductors; the use of this approximation is justified by comparison with an exact solution at specific values ofka. A proof is presented which demonstrates that the backward‐wave impedances of two tape helices are identical if the gap width of one is equal to the tape width of the other. Expressions are derived for effects of dielectric supports upon the velocity and impedance of the backward wave.

ISSN:0021-8979    

DOI:10.1063/1.1721730

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Loss measurements were made on ten dielectric coated wires used as surface wave transmission lines at a frequency of 9365 mc/sec. The purpose of these measurements was (1) to develop a satisfactory method for making the loss measurements, and (2) to compare the measured loss with the calculated or predicted value obtained from theoretical analysis made by Goubau. A resonance method, in which theQof a resonator formed by short circuiting both ends of a length of line is determined, was found to be most desirable. The loss in the resonator end plates was taken into account in determining the wire loss.A description of the apparatus required and the experimental procedures used is given. A brief discussion of alternative methods for making the loss measurements, some of which have been tried, is also given.The losses of the wires measured ranged from about 3.0 db/100 feet for thin dielectric coatings to about 11.5 db/100 feet for thick dielectric coatings. The agreement between measured and calculated losses of wires for which the constants of the dielectric coating are known is considered good.

ISSN:0021-8979    

DOI:10.1063/1.1721731

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Thin films of antimony were condensed onto substrates at various temperatures. Films deposited at liquid oxygen temperatures showed large negative temperature coefficients of resistance. In general, reversible resistance changes occurred if the films were cooled below a temperature previously reached; irreversible changes took place if the films were heated above that at which they were prepared. Activation energies were calculated from logR vs1/Tcurves and gave values of ∼0.07 ev for low temperatures and ∼0.13 ev for high temperatures. There appeared to be little or no influence of evaporation rate or thickness on the activation energies. A theory based on lattice defects is proposed in order to explain the electrical behavior of the films.

ISSN:0021-8979    

DOI:10.1063/1.1721732

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The Wiener‐Khintchine theorem which connects the autocorrelation function and the power spectrum of a stationary time series by means of a Fourier cosine transform is well known. It is the purpose of this paper to generalize the theorem to deal with nonstationary time series.

ISSN:0021-8979    

DOI:10.1063/1.1721733

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721736

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721737

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721738

出版商:AIP    

年代:1954

数据来源: AIP