摘要:

We have investigated ions emitted from molybdenum and tungsten surfaces in CO when the surfaces are bombarded by electrons. The surfaces, in the form of ribbons, can be cleaned at will by heating, and bombarded by an electron stream in which current and energy are controlled separately. The product ions are observed in a mass spectrometer whose envelope contains the experimental filament. Electron bombardment liberates only the O+ion from adsorbed CO with any abundance; it may be 50–100 times more abundant from the surface than from space. No CO+nor C+ions are detected nor any negative ions of CO or its fragments. Carbon atoms remain on the surface. Significant amounts of F+and Cl+are also liberated from new filaments; these diffuse from the interior and are more tightly bound than CO, and disappear only after prolonged heating. Their surface abundance is so slight that they do not interfere with the O+process. The threshold electron energy for liberation of O+ions and the dependence of O+ion current on electron current and energy are given. The method might be useful for studying kinetics of complex adsorption phenomena, although precautions are necessary to avoid perturbing the adsorbed film by the incoming electrons. The following phenomena are readily observed and probably understood: (a) The growth of a monomolecular film of CO from the ambient following a flash of the filament. (b) Competition for available sites by chlorine, fluorine, carbon, and CO. (c) Poisoning of the surface, for adsorption of CO, by carbon atoms freed by departure of O+ions. A simple theory reproduces the experimental kinetics of adsorption and poisoning semiquantitatively.

ISSN:0021-8979    

DOI:10.1063/1.1736212

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The electric breakdown strengths of thin, unsupported vinyl chloride‐acetate films in the thickness range of 1200 to 50 000 A have been measured. No dependence of breakdown strength on thickness is found in this region. Composite films composed of alternate layers of plastic film and thin conducting layers of silver show essentially the same breakdown strength as do single films. Five and six layer laminates which do not contain metal layers show a breakdown strength greater by a factor of 2 than that of single films of the same total thickness.

ISSN:0021-8979    

DOI:10.1063/1.1736213

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A solution to the problem of the stress distribution on the boundary of an elliptical hole in a large plate during passage of a compressive stress pulse of relatively long duration is presented. The major axis of the ellipse is normal to the wave front. The solution was experimentally obtained by using a low modulus model material in a combined photoelasticity and moire´ analysis. The long‐duration stress pulse was applied by loading a small region on an edge of the plate with a falling weight. The results of the investigation indicate that the falling weight loading generates a biaxial state of stress at every point in the plate, which varies with time. The maximum dynamic compressive stresses on the hole boundary can be computed with a fair degree of accuracy by using: (a) the equation of Inglis for the static stress distribution on the boundary of an elliptical hole in any two‐dimensional uniform and axial system of combined stress and (b) the biaxial stresses, at the same instant of time, that would have been present at the center of the ellipse if there had been no hole (free‐field stresses). The maximum dynamic tensile stresses on the hole boundary were always smaller than the values computed using this same procedure.

ISSN:0021-8979    

DOI:10.1063/1.1736214

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Ferromagnetic domain wall images have been observed in a variety of ferromagnetic materials by an electron transmission technique employing defocusing of the objective lens. Image formation and contrast effects are interpreted on the basis of charged particle motion through a magnetic field and electron microscope imaging. Observations are consistent with magnetic domain theory; domain sizes and wall geometry have been confirmed by the Bitter pattern technique.

ISSN:0021-8979    

DOI:10.1063/1.1736215

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

In view of recent interest in the effect of creep on the coefficient of self‐diffusion, measurements have been made on the electrical conductivity of NaCl in the intrinsic range during and after deformation by creep. The conductivity is proportional to the diffusion coefficient for Na. At about 550°C, no change in conductivity was observed, even at steady state creep rates approaching 10%/min. This negative result is shown to be in accord with theoretical estimates.

ISSN:0021-8979    

DOI:10.1063/1.1736216

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Initial magnetization curves, remanence, coercivity, reversible susceptibility, and rotational hysteresis have been measured for CrO2in the form of small particles. The measurements allow rough division into three types of behavior with decreasing particle size: multidomain, or bulk behavior, for ∼100‐&mgr; particles; few‐domain behavior for ∼1−10‐&mgr; particles; and single‐domain behavior for particles with a length/diameter ratio ∼5 and a diameter ≤0.2 &mgr;. The smaller particles studied were acicular and showed coercivity dominated by shape anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.1736217

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A high‐energy exploding wire facility has been used to investigate pinch effects in thin‐walled aluminum tubing. The experiments carried out consisted of subjecting the tubing to the discharge of a 141‐kj capacitor bank and observing its motion by flash radiography and by high‐speed sequential photography. Each tube first imploded uniformly, then broke down into an arc discharge in a manner similar to that of solid exploding wires. The implosion or pinch phase is adequately accounted for by the magnetic forces of the current discharge first acting against the mechanical strength of the tube walls and then, after melting, against the wall inertia and the retarding force of the air being compressed within the tube.

ISSN:0021-8979    

DOI:10.1063/1.1736218

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A method of growing doped single crystals of II–VI compounds a few cm3in size is described. The crystal is grown from the vapor phase in a closed moving crucible which permits an efficient utilization of the charge and flexibility in the dimensions of the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1736219

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The orientation of a monomer unit of a polystyrene molecule is specified in terms of seven orientation functions, of which five are independent in the general case. The birefringence and infrared dichroism are expressed in terms of these orientation functions. The expression for infrared dichroism is dependent on the angle which the direction of dipole moment change for the normal mode of vibration concerned makes with the axes of the molecule. Experimental possibilities for determining these orientation functions are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1736220

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Magnetoresistivity measurements employing ``Corbino disk'' geometry have been made, at temperatures of 77°, and 203°K, and at approximately room temperature, on a slice of fairly high‐purity, single‐crystal,n‐type InSb (probably compensated) with excess impurity concentrationND—NAof about 7×1015. In a series of measurements the ratios of the resistance at 20 kgauss to that at zero field, for the temperatures and in the order listed above, were found to be approximately 23, 23, and 33. The maximum magnetic coefficients of resistance, in the same order, were approximately 0.87, 0.70, and 0.50 per kgauss occurring approximately at fields of 0.7, 1.0, and 2.6 kgauss, respectively. Mobilities were determined by both Hall effect and low‐field magnetoresistivity, and were found to agree within a few percent. The values were, in the same temperature order, 7.3, 5.3, and 4.5 m2/v sec. Temperature cycling and aging appear to cause a reduction in area of soldered contacts to the specimen. Very slight variations of magnetoresistance with the polarity of current through the specimen were observed. An explanation is given; calculations are of the same order of magnitude as experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.1736221

出版商:AIP    

年代:1961

数据来源: AIP