摘要:

The general theory of stationary beams of prescribed shape is developed taking into account the electrostatic interaction between the particles. The Hamilton‐Jacobi equation, expressed in a particular system of coordinates, allows the determination of the potential distribution inside the beam. Compatibility conditions for the equations are obtained, as well as a general rule for the determination of the feasibility of arbitrarily chosen trajectories. A theoretical expression results for the proportionality coefficientkin Child's law (J=kV32) which relates current densityJwith the potential differenceVbetween electrodes. The theory was applied to the particular case of a plane beam with hyperbolic boundaries. The beam was experimentally reproduced, providing values forkin close agreement with the theoretical ones.

ISSN:0021-8979    

DOI:10.1063/1.1735845

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Several experimental tests dealing with the effects of stress waves initiated in solids by high explosives or by impacts are described. The tests indicate that stress waves which are initiated solely as compression commonly acquire tensile components which are not due to reflections.

ISSN:0021-8979    

DOI:10.1063/1.1735846

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The emissivities and thermal conductivities of high purity arc melted molybdenum and tantalum and powder metallurgy tantalum and tungsten were measured between 2300°K and their respective melting points. A method is presented for the determination of spectral and total emissivities from the determination of brightness temperature at the center of an electrically heated rod as a function of heat flow rate. The method does not depend on the experimental achievement of blackbody conditions. Spectral emissivities were also determined by measurement of brightness temperatures at the respective melting points. Thermal conductivities of electrically heated rods were determined by the Jain and Krishnan longitudinal heat flow method. The spectral emissivities of tantalum and tungsten decrease linearly with increase in temperature. The spectral emissivity of molybdenum is constant. The total emissivities of molybdenum, tantalum, and tungsten increase with increasing temperature. For any of the metals the spectral and total emissivities are closest to each other at the melting point. The melting point of tantalum is significantly lowered by small increase in impurity content. The thermal conductivities of molybdenum, tantalum, and tungsten decrease linearly with increasing temperature. The ranges of spectral emissivity, total emissivity, and thermal conductivity above 2300°K are as follows:&egr;&lgr;&egr;TK(cal. cm−1sec.−1∘K−1)Molybdenum0.300.271–0.2850.34–0.32Tantalum0.361–0.3500.288–0.3240.15–0.11Tungsten0.37 –0.360.268–0.3520.38–0.30

ISSN:0021-8979    

DOI:10.1063/1.1735847

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A magnetic memory effect is observed in a low Curie point ferrimagnetic spinel (∼NiFe0.15Cr1.85O4) containing a coherent antiferromagnetic impurity (NiO) with a high Ne´el point. It is explained in terms of the Meiklejohn‐Bean exchange anisotropy coupling the two phases. The past magnetic history is remembered in the spontaneous reacquisition of a fraction of the past remanent state despite prolonged storage at temperatures above the ferrimagnetic Curie point. A feature of the explanation is the condition that antiferromagnetic domains in NiO rotate irreversibly in accessible fields.

ISSN:0021-8979    

DOI:10.1063/1.1735848

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Forces arising on ion‐bombarded electrodes have been measured with a torsion balance immersed in a low‐pressure Hg plasma. The force curves obtained for 22 metals in the range of 20 to 300 ev bombarding energy indicate that Hg+‐ions are completely accommodated (&agr;=1) on clean metal surfaces and the forces originate essentially from the ejection of sputtered atoms. On comparing the forces with the sputtering yields, one obtains information on the average ejection velocities of sputtered atoms which are found to be much higher than those of thermally evaporated atoms. Oxide‐covered surfaces exhibit a quite different behavior inasmuch as the accommodation coefficient for Hg+‐ions seems to be less than unity.

ISSN:0021-8979    

DOI:10.1063/1.1735849

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The space charge theory of Langmuir has been extended to include the effects of anode emission on the performance of a vacuum thermionic power converter. The basic equation is similar to Langmuir's &xgr;—&eegr; equation, but it involves two additional parameters which depend on the temperatures and thermionic properties of the electrodes. An iterative technique is described for obtaining solutions in specific cases, and some sample calculations based on hypothetical diodes are presented. The calculations indicate that the effect of the anode temperature is considerably more pronounced if the cathode‐anode work function difference is large.

ISSN:0021-8979    

DOI:10.1063/1.1735850

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Effects of magnetoresistance and extraordinary Hall effect on the propagation of electromagnetic waves through very thin sheets of ferromagnetic conductors are studied. These contributions to the conductivity produce electric fields varying like products of current and magnetization and introduce nonlinear interactions, which are particularly large in the neighborhood of ferromagnetic resonance. Detailed first‐order dc electric fields are obtained for the configuration of a very thin ferromagnetic sheet very close to a conducting wall. The results predict signals strictly proportional to incident microwave power, and mostly inversely proportional to film thickness, becoming independent of thickness for the thinnest films. Their magnetic field or frequency dependence gives typical resonance curves modulated by slowly varying amplitudes. The maxima and zeros of these amplitudes are very sensitive to the local field configuration. Once this latter is well known, however, these effects can be employed to study conveniently the high‐frequency conduction and magnetic properties of the thinnest films.

ISSN:0021-8979    

DOI:10.1063/1.1735851

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The temperature dependence of Young's modulus of vitreous GeO2has been determined by a dynamic resonance method from −195°C to 540°C. The modulus increases with increasing temperature from about −120°C to 400°C. Below and above this range the modulus decreases with increasing temperature. Young's modulus for vitreous SiO2also increases from about −190°C to 1175°C and decreases with increasing temperature outside this range.In view of the similarity in structures and bond energies of these two materials, the similarity in the elastic modulus‐temperature relations is believed to be significant; especially when contrasted with the lack of agreement in another commonly measured anharmonic property, thermal expansion.

ISSN:0021-8979    

DOI:10.1063/1.1735852

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The thermal conductivity of eight halide crystals has been measured over the temperature range 220°K to 390°K. The thermal conductivities of potassium bromide, potassium chloride, and sodium chloride vary inversely with temperature for the lower part of this temperature range, and are nearly independent of temperature for the higher temperatures of the range measured. The thermal conductivities of cesium bromide, cesium iodide, and silver chloride are nearly independent of temperature throughout the entire temperature range. The thermal conductivities of barium fluoride and calcium fluoride vary more rapidly with temperature than anticipated from aT−1relationship; however, the accuracy of the data is not sufficient to establish the exact form of the variation of the thermal conductivity with temperature. The comparative method used for these measurements is described.

ISSN:0021-8979    

DOI:10.1063/1.1735853

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Dislocation densities and arrangements were studied, as a function of specimen thickness, in metal crystals grown from the melt. Aluminum crystals containing fewer than 104dislocations per cm2were produced by this method. The results of this study are consistent with the mechanism of collapsing vacancy disks for generating dislocations in crystals grown from the melt.It was found, in aluminum, that below a dislocation density of about 106lines per cm2, dislocations remain in a random network and do not form sub‐boundary arrays. The range of effective interaction between dislocations, to form arrays, thus appears to be limited to the average distance between dislocations when the density is about 106lines per cm2, or about 10 &mgr;.

ISSN:0021-8979    

DOI:10.1063/1.1735854

出版商:AIP    

年代:1960

数据来源: AIP