摘要:

Prebreakdown electron current between electrodes closing at voltages below the minimum which can give breakdown by successive ionization of air molecules has been measured by two different methods. This field emission current varies widely in successive experiments, increasing in general with decreasing voltage, with maximum values of the order of 10−7amp. At the small electrode separations characteristic of breakdown at voltages below 300, it is shown that the ions necessary for breakdown come from the anode surface. The number of ions in the space at one time is so small that they cannot cooperate to enhance the gross field at the cathode, which is a conclusion having important consequences for the theory of breakdown.

ISSN:0021-8979    

DOI:10.1063/1.1734973

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Two mechanisms have been proposed to account for the observed large yield of secondary electrons in gaseous breakdown at high electric fields. In one of these a single ion in approaching the cathode surface creates a ``pass'' by decreasing the width of the potential barrier. In the other the increased over‐all field due to a large number of ions in the gap is supposed to account for the increased emission. The first effect is re‐examined and appears to be effective in the observed breakdowns of extremely small gaps in air. It may also be effective in breakdown at high pressure and in liquid and solid dielectrics.

ISSN:0021-8979    

DOI:10.1063/1.1734974

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

An appreciable concentration of unpaired electrons has been found in colloidal carbon blacks through the application of electron spin resonance spectroscopy. The unpaired electrons in a typical channel process carbon black, Spheron 6, have been studied by noting the changes in the electron spin resonance spectrum produced by heat treatment (HT) to 3000°C and by various degrees of evacuation of the sample. The results indicate that the unpaired electrons in the original material are mobile &pgr; electrons, which are stabilized by condensed aromatic ring structures. Their concentration decreases slowly to 750°C HT and then declines more rapidly and vanishes above 1400°C HT. A different species of unpaired electrons arises at 1400°C HT. These are believed to be immobile &sgr; electrons resulting from broken carbon‐carbon bonds at lattice defects. The unpaired electrons present in several commercial carbon blacks have been examined and are believed to be &pgr; electrons also. A tentative theory of the origin of the unpaired electrons is given.

ISSN:0021-8979    

DOI:10.1063/1.1734975

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The relative rms deviation &sgr; of the intensity of a rapidly rotating polycrystallite specimen is &sgr;=[6.5Rsin&thgr;]/[h(mNeff)½], whereR=goniometer radius, &thgr;=Bragg angle,h=(hf+hs)/2,hf=length of focal spot,hs=length of receiving slit,m=multiplicity factor, andNeffthe effective number of irradiated crystallites. Experimental data on silicon powder specimens are presented to show the dependence of &sgr; on crystallite sizes, choice of x‐ray wavelengths and various other experimental parameters. Comparisons of data for rapidly rotating and stationary specimens having crystallite sizes in the 30–50 &mgr; range show that rotation improves &sgr; by a factor of 7 or 8 for peak intensities and 4 or 5 for integrated intensities, using a standard diffractometer.

ISSN:0021-8979    

DOI:10.1063/1.1734976

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A study of the more quantitative aspects of the behavior of suspended polymer particles in a real dielectric is presented. While it is recognized that nonuniform fields exert an attractive force of appreciable magnitude upon particles of high dielectric constant suspended in a liquid medium of lower dielectric constant, the limits of such behavior are not precisely known. This report presents some quantitative data on the subject. The results show that in real dielectrics there is an appreciable effect due to the very small currents, about 1013amperes at applied voltages in the kilovolt range [R. Coelho, Progress Report No. 22, pp. 13–17, Laboratory for Insulation Research, Massachusetts Institute of Technology (December, 1957)] which even a good liquid insulator supports.It is shown that the initial attraction to the central electrode due to the nonuniform field and its polarizing induction is gradually overcome by the repulsive effects of charge accumulated on the particles resulting from ionic conduction and related events in the liquid. The experimental observations include the study of the effects of field strength, electrode size, cell size, and particle size. Field strength, electrode size, and particle size show criticality. At certain upper limiting voltages, smaller central electrode diameters and small particle sizes, all precipitation appears to be prohibited. Use of the newly discovered ``sluff‐off'' voltage for making particle size separations is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1734977

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

An infinity in the input admittance of linear antennas owing to the use of an idealized delta‐function generator is investigated. It is shown that the infinity may be interpreted in terms of an infinite capacitance between the two halves of the antenna. The conclusion is reached that conventionally used iterative procedures are not invalidated by difficulties with respect to the driving point.

ISSN:0021-8979    

DOI:10.1063/1.1734978

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The relaxation of a nearly plane surface to flatness is discussed under the assumption that all surface properties are independent of orientation. A general solution is obtained for the combined action of the transport processes of viscous flow, evaporation‐condensation (in a closed system), volume diffusion, and surface diffusion. Green's function solutions are developed for each of the transport processes separately, and criteria are obtained to decide which process dominates. The initial forms of these solutions represent point concentrations (particles), or line concentrations (wires) of material set upon an infinite plane. The progressive topographical developments described by the formulas are idealized representations of the latter stages of the sintering of small wires and particles to a plane.

ISSN:0021-8979    

DOI:10.1063/1.1734979

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

In the absence of spin, natural convection between two horizontal surfaces in mercury heated from below is found to be given by the formulaN=0.051R⅓whereNis the Nusselt number andRthe Rayleigh number. Spinning the mercury about a vertical axis reduces the amount of convection after a certain value of the spin (Taylor number) is exceeded. This value of the Taylor number increases with increasing heat flux.Turbulent fluctuation of the temperatures of the bounding surfaces are observed and under some circumstances periodic oscillations of the temperature of the bounding surface are also noted.

ISSN:0021-8979    

DOI:10.1063/1.1734981

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A method of revealing screw component dislocations involving low‐energy cathodic sputtering with argon ions is presented. It is observed that hillocks having the shape of truncated cones with a spiral pattern on their tops form at the sites of intersection of screw dislocations with the surface. The hillocks probably form by mobile surface atoms attaching themselves to the step provided at the intersection of a screw dislocation with the surface. It is shown that the density of screw dislocations on a given plane depends on the orientation of the plane with respect to the crystal growth axis.

ISSN:0021-8979    

DOI:10.1063/1.1734982

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Experiments have demonstrated that the basic noise quantities of an electron beam can be transformed and optimized by varying the field configuration and flow characteristics in the multivelocity region near the cathode. Tube noise figures as low as 2.9 db and numerical values of beam noisiness 2&pgr;/kTc(S−&Pgr;) <0.27 have been attained at microwave frequencies (Sband). A detailed investigation of the conditions for minimum beam noisiness is presented. The beam is injected from the edge of the cathode into a highly divergent electric field and results in a distorted potential profile which greatly extends the low‐velocity region below ½ v. It is shown that these features satisfy the physical conditions necessary for realizing a quasi‐one‐dimensional model in which the transforming properties of a ``multivelocity noise transducer'' can be adjusted by varying the rate of acceleration through this region. The experiments also suggest other models and possible approaches for further theoretical and experimental investigation.

ISSN:0021-8979    

DOI:10.1063/1.1734983

出版商:AIP    

年代:1959

数据来源: AIP