摘要:

The problem of two‐stream instability in plasma is studied by specifying the importance of initial magnetic field associated with the motion of the charged particles and the boundary effects. In Part I the accurate initial steady state is studied when the streams of electrons and ions move with different uniform speeds in plasmas with plane and cylindrical geometry. In Part II, in order to show the effects of finiteness and inhomogeneity of the system, small transverse plasma oscillations are studied in the case of plane plasmas. The role of plasma‐sheath oscillations at the boundaries is found to be very important in driving the instabilities associated with the electromagnetic modes. The numerical estimates of the growth rates of the instability are given for the specific case of the physical data in discharge tubes.

ISSN:0021-8979    

DOI:10.1063/1.1709019

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A method is presented for solving problems of one‐dimensional heat flow in regions with plane, spherical, or cylindrical boundaries. It is based on the physical concept of a uniform continuous‐source distribution on the boundary, whose strength varies with time in such a way as to meet the prescribed boundary condition. Examples of the method are given, including the solution for the temperature in a half‐space with an initial steady gradient of temperature and the boundary condition (∂T/∂x) −w(∂T/∂t) −hT= −h&thgr;.

ISSN:0021-8979    

DOI:10.1063/1.1709020

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

TheH‐Iccharacteristics of Nb‐15 at. % Zr‐45 at. % Ti alloys are experimentally discussed in relation to metallurgical structure, particularly, precipitation. Peak effect may be due to the random distribution in barrier heights and the interaction between flux lines at the magnetic fields nearHc2.

ISSN:0021-8979    

DOI:10.1063/1.1709021

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The magnetic field,Hfj, of the first flux jump during the initial magnetization of synthetic high‐field superconductors, composed of indium in porous glass, has been measured as a function of the temperature and the field‐sweep ratedH/dt. The behavior is reasonably well described byHfj∝log(dH/dt). At low values ofdH/dt, logHfjis approximately proportional to 1/(dH/dt). It is shown that under rather special conditions the flux‐jumping behavior depends upon the condition of the sample surface.

ISSN:0021-8979    

DOI:10.1063/1.1709022

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A complete analysis is given of the propagation of acoustic waves in crystals of the tetragonal system. The determination of the elastic constants from measurements of longitudinal‐ and shear‐wave velocities in selected directions is discussed and experimental results for calcium molybdate are presented. The elastic constants in units of 1011dyn/cm2at 25°C are found to bec11=+14.47 ±2%,c33=+12.65±0.17%,c44=+3.69±0.17%,c66=+4.51±5%,c16=+1.34±50%,c12=+6.64±50%,c13=+4.46±2%.

ISSN:0021-8979    

DOI:10.1063/1.1709023

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

This paper describes an investigation of the diffraction of 100–500‐Mc/sec longitudinal elastic waves in anisotropic materials, using the techniques of optical (Bragg) scattering, which allow direct measurement of ultrasonic intensity distributions along the path of the beam. Such measured distributions for beams propagating along pure mode axes in crystal quartz, silicon, and potassium bromide are shown to agree very well with intensity distributions predicted using a diffraction integral derived from a rigorous solution of the related problem of electromagnetic diffraction in uniaxially anisotropic media. In addition, it is demonstrated that cylindrical crystal surfaces, symmetric about the proper pure‐mode axis, are appropriate excitation surfaces for cylindrically focused ultrasonic beams. The focusing properties of thin‐film CdS and ZnO transducers evaporated on cylindrical surfaces of crystal quartz and silicon are described and compared with the properties of focused beams in isotropic materials.

ISSN:0021-8979    

DOI:10.1063/1.1709024

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The initial response of solid models to low‐Mach, high‐mass‐flow shock waves was analyzed. A rapid‐response piezoelectric load cell was mounted in a series assembly behind the models to directly measure resultant loading. The load history was analyzed and correlated with model geometry and shock‐wave velocity for rectangular wood models of various length and weight and for the effects caused by changing the front surface material. The front surface of the model was in some cases bare and in other cases covered with plastic foam or thin foam rubber. It was observed that the coatings produced increased loading effects. The maximum loading force was determined for various overpressures and found to be in linear relationship to a dimensionless ratio involving shock‐tube and shock‐wave pressure parameters.

ISSN:0021-8979    

DOI:10.1063/1.1709025

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Transients in the ring‐rate changes, which take place when the temperature of a field‐electron emitter is varied, have been observed for several crystal directions on bcc, fcc, and hcp crystals. It is proposed that these transients are the result of changes in the size of small surface facets which are in turn related to anisotropies in the surface tension.

ISSN:0021-8979    

DOI:10.1063/1.1709026

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Gravimetric and Seebeck‐effect measurements have been made on CoO single crystals doped with Li in the temperature range of 900°–1200°C and partial pressures of oxygen up to 1 atm.For low‐doped crystals and high oxygen pressures, the gravimetric and Seebeck‐effect results confirm a simple model by which the positive‐charge carriers are given at equilibrium by the singly ionized vacancies and the Li ions. By this model the concentration of holes is increased, and the concentration of vacancies is decreased by the addition of Li.The results at low pressures of oxygen for the low‐doped samples as well as the results in all the range of oxygen pressures for the heavier‐doped samples show that the model has to be enlarged, taking into account the contribution of Co interstitials to the defect structure of CoO(Li) and that of electrons to the conductivity in CoO(Li).

ISSN:0021-8979    

DOI:10.1063/1.1709027

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Ionic diffusion currents measured in a metal‐insulator‐metal structure yield an activation energy of 1.60 eV at 550°K for alumium ions diffusing into alumium oxide. Aluminum evaporated at 10−10Torr on aluminum oxide, formed by chemical reaction of pure oxygen with the base electrode, produces a structure with a graded alumium‐concentration profile at the lower interface and a relatively abrupt aluminum‐concentration profile at the upper interface. Thermal activation of aluminum ions from the electrodes produces a transient current of diffusing metal ions when an external short circuit prevents charge accumulation on the electrodes. Analysis of the diffusion‐current data of aluminum into aluminum oxide gave values of 1.60 eV for activation energy and 5.8×10−19cm2/sec for the diffusion constant.

ISSN:0021-8979    

DOI:10.1063/1.1709028

出版商:AIP    

年代:1967

数据来源: AIP