ISSN:0021-8979    

DOI:10.1063/1.1699937

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The main effort in the work described has been directed towards the measurement of the electric field distribution in a cut‐off magnetron, based on the electron optical shadow method. The space charge distribution can be determined qualitatively from the measured electric field distribution. The first objective is the development of a convenient method for such a study. In this work an elementary magnetron was investigated by sending an electron beam axially through the tube.The conclusions of the study are that the space charge distribution does not conform to Hull's classical theory (which predicts that the space charge density is approximately constant out to a well‐defined radius and zero beyond this cloud radius). Three different space charge distributions have been observed. One distribution has a sharp maximum near the cloud radius. Another falls off gradually toward the cathode; a third is time‐variant. The shape of the space charge distribution is closely related to the symmetry of the magnetron.

ISSN:0021-8979    

DOI:10.1063/1.1699938

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The quantities characterizing wave propagation through the interface of two media or through a transmission line containing obstacles are the two reflection coefficientsr1andr2and the two transmission coefficientst1andt2. It is shown that for any lossless discontinuity |r1| = |r2|, argt1= argt2, and that argr1+argr2−2 argt1= ±&pgr;. These relations are applied to the calculation of reflections from sheets of dielectric and metal‐plate media, the latter being distinguished by the fact that argt1≠0.

ISSN:0021-8979    

DOI:10.1063/1.1699939

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The theory of Carlson and Heins has been extended; an expression is found for the reflection coefficient applicable in the presence of a diffracted beam. Tables and graphs are included for the coefficients associated with electromagnetic phenomena at the surface of metal‐plate media. The magnitude of the reflection coefficient was measured at normal incidence and the phase of the transmission coefficient for angles of incidence from 0 to 25°. A satisfactory agreement with theory is obtained.

ISSN:0021-8979    

DOI:10.1063/1.1699940

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A method of measuring the reflection coefficient of metal‐plate media at 3 cm is described. The technique differs from that presented in the preceding paper in that the measurements are made in a closed system and back reflections are eliminated by an absorbing wedge. Angle of incidence and the plate thickness are varied. The agreement with the Carlson‐Heins theory is excellent for very thin plates. For plates of moderate thickness near normal incidence the measured reflection is higher than that predicted for an infinitely thin set of plates with identical index of refraction.

ISSN:0021-8979    

DOI:10.1063/1.1699941

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Amplitude bounds are obtained for the unique periodic solution of the generalized Lienard equationx¨+f(x)x˙+g(x)=0, when the functionsf(x) andg(x) are restricted suitably. The restrictions are less severe for the lower than for the upper bounds. A class of equations is exhibited which includes the van der Pol equation and satisfies all the restrictions. Numerical results are given for the van der Pol equation.

ISSN:0021-8979    

DOI:10.1063/1.1699942

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The well‐known problem of the end effects in a cylinder of finite length has been circumvented by the use of spheroidal rather than cylindrical apparatus. After a general theory of heat flow is given, applications demonstrate the mathematical difficulties caused by discontinuities in the curvature of the surface of the heat conductor. The suitability of the spheroidal shape is demonstrated, and corresponding heat flow equations are derived demonstrating the effects of the variable distance between any two isotherms on the amount of heat crossing any unit area of an isotherm. It is proven that the amount of heat flowing through a slice of a spheroidal isotherm made perpendicular to the axis of the spheroid is proportional to the width of the slice, and independent of the position of the slice with respect to the spheroid. This theorem is applied to find the heat distribution necessary to keep the core of the apparatus at uniform temperature. Because all measurements are made at thermal equilibrium, a rough estimate is given for the time necessary to reach equilibrium.

ISSN:0021-8979    

DOI:10.1063/1.1699943

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Measurements have been made on single crystals of CuZn and Cu3Au held at various temperatures belowTcto decide whether there is a single‐ordered phase whose order changes with temperature, or whether there is an ordered and a disordered phase the relative amounts changing with temperature. Precision measurements were made of the position and width of the (222) CuZn and (400) Cu3Au reflections. The disordered phase has a larger cell dimension, so that reflections from the ordered and disordered phases are slightly displaced from one another. For both materials, a single peak was observed which was too narrow to correspond to the existence of two phases. At the stoichiometric compositions, it is concluded that belowTcthere is only an ordered phase whose long‐range order varies with temperature. Measurements of the long‐range order in Cu3Au have been made on briquets of filings, using quenched samples, and on a sample held at temperature.

ISSN:0021-8979    

DOI:10.1063/1.1699944

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The equilibria between phases in platinum alloys containing 42, 48, and 54 atomic percent cobalt were determined at temperatures below 1000°C. This system of alloys exhibits an order‐disorder transition analogous to that for CuAu. A temperature range in which ordered and disordered phases coexist in equilibrium was determined for each alloy. These data were incorporated in the phase diagram. The Co‐Pt system is the first ordering alloy system in which it has been shown that this reaction is a true phase transformation contrary to the prevalent concepts of the phenomena.

ISSN:0021-8979    

DOI:10.1063/1.1699945

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The thermionic emission properties of the borides of the alkaline‐earth and rare‐earth metals and thorium have been investigated. These compounds all have the same formula MB6and the same crystal structure consisting of a three‐dimensional boron framework in whose interlattice spaces the metal atoms are embedded. The valence electrons of the metal atoms are not accepted by the B6complex, thus giving rise to the presence of free electrons which impart a metallic character to these compounds. This, together with the strong bonds between the boron atoms in the framework, produces a series of compounds which have high electrical conductivities and high thermal and chemical stabilities—ideal properties for a cathode material. When this structure is heated to a sufficiently high temperature, the metal atoms at the surface evaporate away. They are, however, immediately replaced by diffusion of metal atoms from the underlying cells. The boron frame work does not evaporate but remains intact. This process gives a mechanism for constantly maintaining an active cathode surface. Thermionic emission measurements made on these materials show the rare‐earth metal borides to be superior to the others. The highest emission was obtained from lanthanum boride. Its emission constants for the Dushman equation were &fgr;=2.66 volts andA=29 amps/cm2/degK2. This is higher than the emission normally obtained from thoria. Lanthanum boride has a relatively low evaporation rate corresponding to a latent heat of evaporation of 169 kilocalories per mole. If the hexaborides are operated at high temperature in contact with the refractory metals, boron diffuses into their metal lattices forming interstitial boron alloys with them. When this occurs, the boron framework which holds the alkaline‐earth or rare‐earth metal atoms collapses, permitting the latter to evaporate. However, the hexaboride cathodes may be operated at high temperatures in contact with tantalum carbide or graphite. Lanthanum boride cathodes are especially useful in applications where high current densities are required. They are also suitable for high voltage applications because they stand up well under positive ion bombardment. Since they are atmospherically stable and activate easily, they have found wide use in experimental demountable systems.

ISSN:0021-8979    

DOI:10.1063/1.1699946

出版商:AIP    

年代:1951

数据来源: AIP