摘要:

This paper gives the results of measurements of the fields diffracted from a long narrow slit in a large conducting plane, when a uniform plane is incident. The results for two polarizations are shown.

ISSN:0021-8979    

DOI:10.1063/1.1721951

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Solutions are obtained for the diffraction of the waves radiated by scalar and vector point sources on the axis of a semi‐infinite cone. The scalar problems are solved by the method of characteristic Green's functions to yield directly various alternative representations whose different convergence properties are discussed; the vector problem is solved by an application of spherical transmission line theory. To evaluate the plane wave scattering observed far from the cone tip, a highly convergent contour integral representation is selected and evaluated approximately for the special case of backscattering from cones having large and small apex angles. The results for the large‐angle cone exhibit the transition from a backscattered spherical wave to a plane wave as the cone degenerates into an infinite plane.

ISSN:0021-8979    

DOI:10.1063/1.1721952

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The diffraction of plane electromagnetic waves by apertures in a plane screen which is infinitesimally thin and perfectly conducting is studied both theoretically and experimentally. The theoretical analysis employs a dyadic Green's function to develop vector formulas for the scattered fields, and from these formulas integral equations are obtained for the aperture distributions. The vector representation makes possible a compact demonstration of the electromagnetic form of Babinet's principle by means of which one may extend the aperture analysis to complementary disks. The integral equations are then used to construct a variational principle for the aperture transmission coefficient.Detailed analysis and numerical computations are carried out for two configurations. For the circular aperture a first‐order vector trial function with frequency dependent coefficients is chosen for the aperture distribution. The approximate transmission coefficient is found to agree closely with the exact value in the region 2&pgr;a/&lgr;≤3. For elliptical apertures a zeroth‐order approximation is evaluated using a one‐component trial function. Numerical results are given for minor‐to‐major axis ratios of ½ and ⅓.Transmission coefficient measurements were carried out in the 24 000 megacycle band (&lgr;=1.25 cm) using an image plane technique. The apparatus was first calibrated with the exact solution of the circular aperture. The approximate results calculated for elliptical apertures are then seen to be in good agreement with the measurements over the accessible range.

ISSN:0021-8979    

DOI:10.1063/1.1721953

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The relation of transmission of thin films of antimony as a function of thickness expressed in micrograms per cm2has been determined for blue, red, and white illumination. An abrupt change in optical properties of the antimony layer has been noted at the phase change. The transition occurs at a transmission of approximately 30 percent. Photosurfaces have been prepared by activating the deposited antimony films with cesium. The photoelectric yield for both regular and reverse illumination has been determined for different antimony thicknesses. For reverse illumination the peak response occurs between 5.5 and 6.0 micrograms per cm2of antimony. Expressing the photoresponse for reverse illumination of green light with decreasing transmission of the original antimony layer for blue, white, and red light shows peaks at 82, 88, and 92 percent, respectively. The transmission of the photosurface, which is substantially independent of processing or photoelectric efficiency of the surface, is given for blue, green, and white light.

ISSN:0021-8979    

DOI:10.1063/1.1721954

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A proton‐rich sample placed in a strong inhomogeneous magnetic field of mean strengthH0was subjected to a pattern of relatively weak radio‐frequency pulses at the Larmor frequency of the protons in the fieldH0. The pattern was then recalled by applying a strong rf pulse at a later time as in the spin‐echo technique. It is shown both mathematically and experimentally that such a series of pulses, varying in amplitude can be ``memorized'' by the spin system of protons for times as long as one second and then repeated, preserving both shape and relative amplitude.

ISSN:0021-8979    

DOI:10.1063/1.1721955

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The author's previous theory of elasticity and consolidation for isotropic materials [J. Appl. Phys.12, 155–164 (1941)] is extended to the general case of anisotropy. The method of derivation is also different and more direct. The particular cases of transverse isotropy and complete isotropy are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721956

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The mechanism of radiation of plasma noise inherent to arc discharge is studied experimentally. Intense electromagnetic radiation of random noise character is observed at the frequency of plasma oscillation of the ion sheath formed at the cathode drop. Maximum radiation occurs when the external circuit connected to the cathode is in resonance with the plasma frequency. The oscillating current in the external circuit is concluded to be generated by the periodic electron emission from the cathode caused by small perturbation of potential gradient at the cathode surface as a result of the variation in the ion sheath potential. This conclusion is supported by several experiments under various air pressures, electrode materials, current densities, etc.

ISSN:0021-8979    

DOI:10.1063/1.1721957

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The decay of photoconductivity has been used to measure the lifetime of excess carriers in rectangular samples of germanium and silicon. The sample is illuminated by a short pulse of light and the sample lifetime obtained from an oscilloscope display of the decay of photoconductivity. Analysis of the solution of the diffusion equation yields methods of measuring the bulk lifetime, the surface recombination velocity, and the diffusion constant.

ISSN:0021-8979    

DOI:10.1063/1.1721958

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Any instrumentation for measuring the mean frequency of a narrow‐band random signal presents an output quantity which inherently fluctuates about that value which represents the true mean frequency, due to the finite measuring time. In comparing the accuracy of various instrumentations for short‐time frequency measurement a useful figure of merit isvariance of the output/(sensitivity)2. In this paper the figure of merit is obtained for an instrumentation which measures frequency by determining the average number of zero crossings of the signal in a short time. The significant problem is the determination of the mean square number of zeros of a random function in timeT. The general result is presented in the form of an integral. For an assumed Gaussian power spectrum the integral is integrated graphically to obtain a figure of merit which is compared with previously published figures of merit of an autocorrelator and frequency discriminator.

ISSN:0021-8979    

DOI:10.1063/1.1721959

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Semiquantitative calculations were made of that portion of the internal friction of annealed and moderately cold‐worked metal single crystals which is due to dislocation motion. The calculations were made on the basis of a qualitative theory of Nowick. It is shown that Nowick's theory leads to reasonable orders of magnitude of the observed internal friction and changes of the modulus of elasticity. At low temperature or at high frequencies (megacycle range) Nowick's hysteresis mechanism becomes inoperative and theories of Koehler and of Eshelby have to be considered to calculate the internal friction.

ISSN:0021-8979    

DOI:10.1063/1.1721960

出版商:AIP    

年代:1955

数据来源: AIP