摘要:

A method for visual observation and photographic recording of electron beams that involves the dropping of fluorescent powder through the beam is illustrated by photographs of convergence in Pierce guns, an electron beam profile, and electron trajectories in an Einzel lens. It has the following advantages: (a) The photographic exposure time under all normal circumstances is much less than 1 sec. (b) It is applicable in any degree of vacuum. (c) Spatial resolution of less than 100 &mgr; is readily obtained. (d) The electron beam is not perturbed. (e) It is applicable to electron beams in less accessible regions—between closely spaced electrodes for example. (f) Satisfactory photographs may be obtained for electron beams of any perveance provided the beam potential exceeds 100 V.

ISSN:0021-8979    

DOI:10.1063/1.1713015

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An electron beam passing through a gas ionizes the gas, and the electrons and ions so produced collect in the vicinity of the beam to form a plasma with a number density that can be much greater than the density of the beam. A one‐dimensional static theory for such a system, with a beam either partially or completely filling the space between two parallel planes, gives the plasma density and potential distribution in the space. The theory requires only minor modifications of the Langmuir‐Tonks free‐fall theory of the positive column. A plasma filling the space occupied by the beam is separated by a low potential sheath from a somewhat lower density plasma that extends to the walls where a second higher potential sheath is formed. A comparison between the results of this theory and some density measurements on beam‐generated plasmas reported in the literature gives reasonable agreement.

ISSN:0021-8979    

DOI:10.1063/1.1713016

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The effect of microstructure on the ionic conductivity of Zr0.84Ca0.16O1.84ceramic specimens was evaluated. At low temperatures (<800°C), those specimens of smaller grain size exhibited a higher electrical conductivity. These data suggest high grain boundary conductivity owing to a higher diffusion rate for the oxygen ion along the grain boundary. Activation energy vs logarithm of average grain diameter data gave a linear plot; thus, an estimate of the activation energy for grain boundary conduction could be obtained by extrapolation. This value was found to be about 0.96 eV, whereas the activation energy for the bulk specimen lies in the range 1.24 to 1.30 eV. At temperatures of 1000°C or higher, the difference between grain boundary and bulk conductance is insignificant.

ISSN:0021-8979    

DOI:10.1063/1.1713017

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The rate of emission and the radiation pattern of coherent phonon radiation were obtained for a charged particle traveling along the symmetry axis of a piezoelectric crystal of hexagonal symmetry. The phonon power per unit frequency radiated by a charged particle is proportional to frequency. Macroscopic equations used in the derivation permit solution of a phonon radiation problem which otherwise would be quite complicated.

ISSN:0021-8979    

DOI:10.1063/1.1713018

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A multiple probe technique is described for the accurate measurement of the retarding potential characteristics of probes in high‐frequency electrodeless plasmas. Earlier multiple probe methods are discussed along with their advantages, assumptions, and limitations. The improved triple probe technique, developed for diagnostic measurements in plasma lasers, allows the complete probe characteristic to be traced rapidly. From the retarding potential characteristic for the electrons, the electron temperature and density can be determined for the low‐energy electrons, together with the electron energy distribution function.

ISSN:0021-8979    

DOI:10.1063/1.1713019

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The dielectric susceptibility of an atomic vapor in the presence of a magnetic field is expressed as a three by three tensor. The gain coefficient in the absence of external fields and thegandJvalues of the atomic levels are shown to be sufficient to determine all the tensor elements. An illustrative example for aJ=1 toJ=0 transition and formulae for generalizing the results are given.

ISSN:0021-8979    

DOI:10.1063/1.1713020

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Wave energy moving faster than the phase velocity of the wave in the medium becomes negative. Such a wave field can equally well be treated as an ensemble of quanta with negative energy. Amplification of waves by mode coupling is represented by pair creation of a negative quantum and a positive quantum. Interaction of an electron stream with a dissipative medium creates the negative quanta.

ISSN:0021-8979    

DOI:10.1063/1.1713054

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The semiempirical equation which was shown by Weissberg to be a very close approximation to the rigorous variational calculation of the pressure drop for creeping flow of incompressible viscous fluids through short tubes has been generalized to take into account the slip of a rarefied gas at the tube wall. The generalized equation is&ohgr;=&ohgr;s+&bgr;a/&lgr;¯, whereais the tube radius,&lgr;¯=(&mgr;/P¯)(12&pgr;RT/M)12, and&ohgr;=F/[14&pgr;a2&Dgr;P(8RT/&pgr;M)12]. Here, &mgr; andMare the viscosity and molecular weight of the gas, &Dgr;Pis the pressure dropP1−P2,P¯is the average pressure ½(P1+P2),Ris the gas constant per mole,Tis the absolute temperature, andF=P¯QwhereQis the volume flow. The coefficient &bgr; and the slip parameterwsdepend only onL/a, the length to radius ratio of the tube:&bgr;=(&pgr;/8)/[(L/a)+(3&pgr;/8)], &ohgr;s=(&bgr;2/3&pgr;)[(128L/a)+(27&pgr;2/4)]. Excellent agreement is noted between values ofwcalculated from the equation given here and values obtained by Knudsen for long tubes and by Lund for short tubes.

ISSN:0021-8979    

DOI:10.1063/1.1713055

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A theoretical and experimental study is described for the optical birefringence associated with the propagation of a plane shear wave in a viscoelastic medium. The shear wave propagation is characterized by a complex propagation constant from which the complex coefficient of shear viscosity of the medium may be derived. The optical birefringence is related to the mechanical action of the shear wave by a complex mechano‐optic coefficient. In the experiment the birefringence due to the shear wave is analyzed by transmitting circularly polarized light through the material at right angles to the direction of shear wave propagation and to the direction of particle displacement. The modified, circularly polarized light is then analyzed by a plane analyzer and a photomultiplier detector. The mechanical and mechano‐optic constants for the medium are determined for an aqueous milling yellow solution and for a polystyrene solution and are compared with independent determinations of these same factors from other experiments.

ISSN:0021-8979    

DOI:10.1063/1.1713056

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The boundary value problem for velocity of propagation and attenuation of capillary ripples over viscoelastic surface films is set up and solved from the viewpoint of continuum hydrodynamics. Both soluble and insoluble films are treated. Successive approximation methods are used to derive explicit formulas for velocity of propagation and amplitude attenuation; formulas for these quantities, accurate to second order, are given for slightly viscoelastic and highly viscoelastic films, and formulas, accurate to first order, are given for films of intermediate viscoelasticity.

ISSN:0021-8979    

DOI:10.1063/1.1713057

出版商:AIP    

年代:1964

数据来源: AIP