摘要:

The well‐known Kronig‐Kramers integral relations between the real and imaginary parts of the susceptibility are generalized to the case where the susceptibility is a tensor. The consequences of the principle of energy conservation are discussed. The case of a ferrite is discussed in some detail.

ISSN:0021-8979    

DOI:10.1063/1.1722731

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A photographic investigation of combustion in gases was undertaken to observe experimentally the mechanism of initiation and structure of detonation waves. Streak schlieren photographs of hydrogen‐oxygen and carbon monoxide‐oxygen explosions were made in a rectangular shock tube using precision optics and a rotating mirror camera.The photographs show that compression waves generated during the early stages of propagation of the explosion soon steepen into a shock wave which travels ahead of the combustion wave (zone of chemical reaction). This combination of shock and combustion wave is characteristic of a nonsteady detonation state in the moments before stable detonation is initiated. The distance between the two waves narrows as the explosion progresses down the tube due to the continued formation of new combustion centers ahead of the combustion wave by means of auto‐ignitions. Eventually the combustion wave overtakes the shock wave and supplies it directly with energy from the chemical reaction; at this moment stable detonation is initiated.The internal structure of steady state detonations is found to be different from nonsteady state detonations; for example, whereas the distance between the shock and the zone of chemical reaction is of the order of several centimeters in the nonsteady state detonation, this distance in the steady state detonation is too small to be resolved by the optical system (i.e., less than 1 mm). Other structural features such as spinning detonation and a high‐frequency oscillation of propagation velocity are also illustrated.

ISSN:0021-8979    

DOI:10.1063/1.1722732

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A microwave radiometer of the Dicke type for the 6‐mm wavelength range has been built and operated to measure radiation from the sun and attenuation in the earth's atmosphere. The total vertical attenuation in the earth's atmosphere on four clear summer days averages 1.2 db. It is presumably due principally to oxygen, since the 6‐mm wavelength is well up on one wing of the 5‐mm absorption line. The quoted values are in agreement with a line‐width constant of 0.02 cm−1. Attenuation in clouds is highly variable. An additional 1 db above the fair‐weather value is typical for a thin overcast.Measurements during the summer of 1956 indicate an effective solar temperature of about 4500°K. This value is appreciably lower than temperatures reported at 7.5 and 8.5 mm, and it favors a model of the lower chromosphere which assumes temperatures well below the optical surface value of 5700°K.

ISSN:0021-8979    

DOI:10.1063/1.1722733

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A procedure is presented for finding by successive approximation the current distribution, and thus the electromagnetic field, of the lowest mode of the microstrip transmission line. The approximation is valid provided that the strip is not too wide and the dielectric sheet not too thick. Each iteration consists of essentially solving two electrostatic problems.

ISSN:0021-8979    

DOI:10.1063/1.1722734

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A rigorous formulation of Babinet's Principle has been found by Copson and by Meixner for perfect conductors. A recently published theory of diffraction by holes in absorbing and transparent screens suggests a generalization of Babinet's Principle to absorbing and transparent materials. The generalized form of Babinet's Principle is not a rigorous statement; it holds only for certain approximate solutions. In this paper it is used to calculate backscattering by circular disks of various reflection coefficients from zero to unity. Experimental results by Severin and v.Baeckmann support this theory. It is expected that, in a succeeding paper, it can be shown that scattering by solid bodies may be calculated in a similar way if the bodies are bounded by plane surfaces large compared to wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1722735

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The dynamic motion of a spinning rocket of varying moments of inertia under the influence of a varying torque is analyzed. The varying moments of inertia result from the rapid expenditure of fuel. The varying torque is produced by a constant rocket thrust asymmetrically applied while the body center of gravity location varies as the fuel burns. Aerodynamic forces are assumed negligible. The analysis is performed through the direct application of Euler's equations, which have a special applicability to this type of problem. The resulting motion is described in terms of Euler angles and resembles the motion of an ordinary top with nonsteady precession. The motion is compared to that of a body of fixed moments of inertia caused by a torque of fixed magnitude. It is shown that the variable aspects of the general problem create important characteristics of the resulting motion.

ISSN:0021-8979    

DOI:10.1063/1.1722736

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Electroluminescence intensity of phosphor layers decreases with running time; this decay can be described by the empirical expression, proposed by Roberts,L=L0/(1+t/t½), wheret½is the time to half‐intensity. It is also observed that, during electroluminescence decay at room temperature, (1) photoluminescence remains constant, (2) a component of the dark capacitance decreases in proportion to the light output, (3) photoconductivity and dark conductivity show a similar decrease, and (4) the light output wave form shows marked progressive changes. Also, (5) decay at 80°K proceeds at a much slower rate. An approximate derivation of an expression describing trap or donor depletion by electrolysis serves to correlate the data and the empirical expression in the foregoing.

ISSN:0021-8979    

DOI:10.1063/1.1722737

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Oxides having the magnetoplumbite structure and a wide range of magnetic properties have been examined. The magnetic saturations of the compositions MIIFe12O19can be lowered by replacing part of the iron with the ions Al3+, Ga3+, Mn3+, Cr3+, and Ge3+amongst others. MIIin the above formula can be Ba2+, Sr2+, or Pb2+. Calcium can replace these ions in part. Even the samples with magnetic saturations below 200 gauss can be prepared as crystallographically oriented compacts. Contrary to its behavior in ferrites, Ga3+does not appear to occupy tetrahedral sites in the magnetoplumbite structure.Evidence is presented for the occurrence of points of magnetic compensation in the BaAlxFe12−xO19series. As the aluminum contents of the materials increase toward such a point, the ratio 2K/I(whereKis the magnetocrystalline anisotropy constant andIis the saturation magnetization) also increases. As a consequence the ferromagnetic resonance frequencies associated with the materials move to higher frequencies, and extremely high coercive forces are realized.

ISSN:0021-8979    

DOI:10.1063/1.1722738

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Magnesium‐manganese‐aluminum ferrites prepared by dry pressing techniques are usually fired in the temperature range between 1350 and 1400°C for extended periods of time to obtain samples having high relative densities. When about ten percent of the magnesium in such a system is replaced by copper, as in the series Mg0.9Cu0.1AlxFe1.75−xMn0.04O4±, it is possible to obtain samples with high relative densities and dc resistivities by firing in the 1250 to 1300°C range. Such materials are suitable for microwave applications.The preparation of ferrites of this type is discussed and data presented on the saturation inductions, Curie temperatures, densities, and dc resistivities.

ISSN:0021-8979    

DOI:10.1063/1.1722739

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Thermionic emission measurements on polycrystalline hafnium in the temperature range 1250 to 1820°K have yielded a work function of 3.60 ev and a thermionic constantAof 22.9 amp cm−2deg−2. Intermittent heating thereafter for a total of 46 hours at temperatures above 2100°K and at pressures below 1×10−9mm Hg did not change these parameters appreciably. No gas was desorbed from the hafnium when it was flashed to 2150°K after having been cold for 64 hours. A second sample of hafnium was used as a target in apparatus for studying electron ejection by ions. It was more brittle than the first and thus more contaminated with gas. Its work function was found to be 3.91 ev and the constantAto be 20.5 amp cm−2deg−2after repeated flashing to 2150°K. Evidence from the electron ejection work indicates that the surface of this second hafnium sample was covered with an appreciable fraction of a monolayer immediately after cooling from high temperature. One can conclude that the work function of hafnium increases as the metal irreversibly absorbs gas on heating.

ISSN:0021-8979    

DOI:10.1063/1.1722740

出版商:AIP    

年代:1957

数据来源: AIP