摘要:

The conductivity of liquid selenium has been measured in the temperature range 200°–500°C. The resistivity was expressed by log10&rgr;=A+(B/T). Average values for different selenium lots and melts ofAandBwere −3.81 and 5850. The maximum deviations from the averages were 10 percent and 3.4 percent respectively. The resistivity was a function of temperature alone.Various non‐metal impurities Cl2, I2, P lowered the resistivities and produced different values ofBin different temperature ranges. Mercury addition caused no change in eitherAorBalthough that metal greatly influences the resistance of solid hexagonal selenium. Melts doped with Cl2or Br2, along with Hg exhibited behaviors different from those with single additions.It was concluded that selenium is an ideal semiconductor in the range of measurement.

ISSN:0021-8979    

DOI:10.1063/1.1699747

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Mean specific heats were determined from 20°C to 800°C for MgO, TiO2, and ZrO2. True specific heats were then calculated assuming thatCT=A+BT+CT2. At 350°C the true specific heats were calculated to be MgO 0.276; TiO20.210; ZrO20.140.

ISSN:0021-8979    

DOI:10.1063/1.1699748

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The effects of inserting a video filter of finite width on the observability of pulsed signals in random noise are examined. It is found that at match (when the pulse and IF filter are each other's conjugate Fourier transforms) no improvement is gained from such a video: the infinitely wide response yields the optimum results. This is strictly true when the second detector is a quadratic rectifier; (a slight improvement on narrowing the video is noted, however, for strong signals when a half‐wave linear rectifier is used). Away from match a video filter does give noticeable improvement when the pulses are overlong, i.e., narrower spectrally than the IF (&lgr;>1); more noise than signal is then removed by the narrower video filter. The greatest gain over the infinite video is observed for final filters slightly wider than the original pulse. On the other hand, for pulses that are too short (&lgr;<1) the performance is worsened. The mean maximum signal level is decreased more rapidly than the interfering noise background. In all instances the familiar phenomenon of modulation suppression arises. Two different pulse shapes are considered: (1) Gaussian and (2) rectangular, but for wide videos pulse shape is not a critical factor. Curves showing the output signal‐to‐noise ratios as a function of the input ratio are included for conditions of match (&lgr;=1) and mismatch (&lgr;≠1).

ISSN:0021-8979    

DOI:10.1063/1.1699749

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The corona characteristics of air and methyl chloride were studied in a modified type of Cottrell precipitator at temperatures from room temperature to 500°C and pressures from 1 to 5 atmospheres. Within this range the corona current is a power function of voltage with gas density as a parameter. This power is independent of density. Values are given for air and methyl chloride.

ISSN:0021-8979    

DOI:10.1063/1.1699750

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

General results obtained previously for slots of arbitrary shape are applied to the case of a transverse rectangular slot in a circular cylinder. It is shown that the principal transverse plane pattern of such a slot in which the excitation has only a circumferential tangential electric field component is the same as the pattern generated by an infinite axial slot with the same circumferential excitation. Theoretical and experimental curves are given for the narrow‐width half‐wave‐length slot.

ISSN:0021-8979    

DOI:10.1063/1.1699751

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The thermal conductivity of soils of varying moisture content is calculated on a physical basis. The results of this computation are, in a range of moisture contents from 5 to 25 percent, in agreement with experimental data in the literature. The influence of soil composition on conductivity is also explained by the theory. The use for practical purposes of an average resistivity value of 60 to 70 thermal ohms appears justified in the light of this analysis.

ISSN:0021-8979    

DOI:10.1063/1.1699752

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The differential equation is considered which determines the position of a vehicle from dynamical measurements of the non‐gravitational accelerationbmade internally. Three linear approximations to the gravitational fieldg(r) of the earth, which lead to explicit solutions of this equation, are considered and their limitations are discussed. An interval‐wise solution (linear continuation) for trajectories of extended range is described, which is based on such linear approximations and has definite advantages in this application. The theory is applied to the trajectory of the German A10 vehicle.

ISSN:0021-8979    

DOI:10.1063/1.1699753

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Measurements were made of the diffraction patterns of circular apertures from one to eight wave‐lengths in diameter in the planes of the apertures and in the neighborhood of the apertures when a plane polarized electromagnetic wave was incident upon them. From Thomas Young's theory that the diffraction pattern is an interference pattern between the incident plane wave and wavelets from the edge of the aperture, the positions of maximum intensity have been predicted in the neighborhood of the aperture and the values of the intensities over the apertures checked with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1699754

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The motion of the cathode spot in a direction opposite to that predicted by Ampe`re's law depends on the arc current, gas pressure, kind of gas, and magnetic field strength. Studies of the effects of these variables have been made, including measurements of velocity and the critical pressure at which reversal of motion occurs. The phenomena observed have not been clearly explained by any of the pictures presented to date. The existence of the retrograde motion indicates very strongly that the positive‐ion space charge outside the cathode is all important in determining the mechanism of current transfer.

ISSN:0021-8979    

DOI:10.1063/1.1699755

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Even under the assumptions of irrotational, isentropic flow, which have been found generally useful for subsonic and supersonic cases, the equations of gas flow are relatively intractable for mixed, transonic situations. Approximate methods of solution used by a number of investigators are reviewed briefly, as well as the hodograph technique, which yields exact solutions of the equations for plane flow. It is pointed out that all the methods predict smooth, potential mixed flows involving imbedded regions of supersonic speed and both acceleration and deceleration through the speed of sound. There is no experimental verification of the existence of such flows.Three possible explanations for this sharp discrepancy between experiment and perfect‐fluid theory have been advanced; namely, (a) effects of viscosity, (b) non‐existence of neighboring solutions, and (c) temporal instability. These are reviewed in turn. None has led to a complete explanation, to date. Kuo's stability calculations are described briefly. His results indicate that stable, smooth, mixed flows may exist if certain conditions are satisfied.

ISSN:0021-8979    

DOI:10.1063/1.1699756

出版商:AIP    

年代:1950

数据来源: AIP