摘要:

The lack of observable adhesion between most metal surfaces in air has been explained in the past by invoking the effect of released elastic stresses. In this work, the effect of released elastic stresses on adhesion has been investigated experimentally by evaporating thin films of gold on substrates of different hardness and measuring the adhesion as a function of the load. It has been found that the magnitude of the released elastic stresses is insufficient to account for the lack of observable adhesion in air. In the case of copper, it was found that adhesion became observable when the oxide film on the surface was ruptured. It was concluded that a protective film formed in the atmosphere prevented adhesion. It is suggested, therefore, that a class of frictional phenomena exists which cannot be explained by the adhesion theory. For electropolished Cu surfaces in particular, it is found that a mechanism based on plastic deformation may account for the frictional force observed where the oxide remains intact.

ISSN:0021-8979    

DOI:10.1063/1.1702460

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The mechanism of spin‐wave instability in an rf magnetic field applied parallel to the dc field is explained by simple, physical arguments. These spin waves give rise to rf and dc magnetic moments parallel to the dc field. The major part of the rf magnetic moment lags a quarter‐period behind the rf magnetic field so that the susceptibility is almost purely imaginary. The real part of the susceptibility vanishes unless the frequency of the unstable spin waves differs from half the pump frequency. The dc magnetic moment induced by the rf field is always larger than the amplitude of the rf magnetic moment. The theoretically expected variation of the susceptibility with the rf magnetic field is discussed and compared with experimental data.

ISSN:0021-8979    

DOI:10.1063/1.1702461

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The high‐power susceptibility has been measured as a function of the dc field at three frequencies on yttrium iron garnet with and without substitutions of holmium and gallium. The structure of the observed curves is attributed to relaxation processes in which two parametrically excited magnons coalesce into a third magnon under conservation of energy and momentum.

ISSN:0021-8979    

DOI:10.1063/1.1702462

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Antiphase boundaries have been observed in thin foils of a Fe3Al superlattice prepared from the bulk material, using transmission electron microscopy techniques. This particular alloy forms two distinct types of superlattice; the first is a high temperature modification based on an imperfectB2‐type lattice, while the second is a lower temperature modification based on the more perfectDO3‐type lattice. A distinct type of antiphase boundary has been found to be associated with each ordered configuration, and their geometry and energy have been analyzed in detail. The critical conditions necessary to reveal these antiphase boundaries by transmission electron microscopy have been treated. In particular, it is found that antiphase boundary contrast is obtained only when the foil is critically oriented for diffraction from a strong superlattice reflection. Furthermore, the detailed dynamical theory of electron diffraction has been applied successfully to the present observations. Finally, some contrast effects associated with intersecting antiphase boundaries have been observed and interpreted using the kinematical theory of electron diffraction.

ISSN:0021-8979    

DOI:10.1063/1.1702463

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The effects of displacement currents on ferromagnetic resonance are investigated for perfectly insulating slabs magnetized normal to their surfaces. The surface spins are assumed to be free. It is found that, at constant frequency, the usual ferromagnetic resonance shifts to higher fields. Also, for sufficiently thick samples, new resonances may be excited on the low‐field side of the main resonances. For thinner samples, these additional resonances may not be resolved from the main resonance, but may contribute significantly to its intrinsic linewidth.

ISSN:0021-8979    

DOI:10.1063/1.1702464

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Shock‐induced phase transformations in iron have been investigated in the temperature range 78° to 1158°K. The pressure for transformation over this temperature range has been determined by a technique that depends on microstructural changes associated with a phase transformation. A discontinuity in the temperature‐pressure relationship was observed at 115 kbars and 775°K. Two distinct transformation microstructures were observed. It is postulated that the results obtained above 775°K are due to the expected transformation from alpha iron to gamma iron whereas the results below 775°K are related to a transformation from alpha iron to a presently undetermined new phase.

ISSN:0021-8979    

DOI:10.1063/1.1702465

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Photoelectric emission from a 5‐mil single‐crystal molybdenum wire was measured at 1000°K with accelerating fields from 0.8 to 142 kv/cm and monochromatic light in the range 238 to 297 m&mgr;. Above 3.6 kv/cm, the data are in good agreement with Fowler‐Schottky theory. Apparent threshold energies increase from 4.44 to 4.52 ev with increasing illumination energy, as is expected from emitters of nonuniform work function. Two illumination directions, separated azimuthally by 90°, give identical results. Fowler plots yield identical thresholds of 4.41 ev at room temperature and 1000°K and a Richardson‐plot determination of the thermionic emission constants yieldse&fgr;**=4.33 ev andA**=38 amp/cm2‐deg2. The multiplicity of apparent work functions measured on a single specimen, as well as the marked dissimilarity in the emission constants of molybdenum in sheet and wire form, are explained in terms of patch effect. The theory for the periodic deviation from the photoelectric Schottky effect is extended to describe emitters at elevated temperatures. No evidence for the predicted deviation appears in the experimental photoelectric Schottky data.

ISSN:0021-8979    

DOI:10.1063/1.1702466

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Transmission electron micrographs of (111) prismatic loops in gold‐diffused silicon have been obtained. The loops were about 2 &mgr; in diameter. From the contrast effects seen and for a number of other reasons it is concluded that the loops surround a stacking fault rather than coherent platelets of gold.

ISSN:0021-8979    

DOI:10.1063/1.1702467

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Light scattering by an irregular cubical network of dislocations, represented by identical rods, along thex, y, andzdirections is computed by a method which is similar to the Patterson analysis of x‐ray diffraction. It is assumed that the spacingdbetween neighboring dislocations has a Gaussian distribution of width &dgr;d¯about the average spacingd¯, and it is shown that shallow maxima of the scattering intensity exist near the Laue spots of the regular lattice with spacingd¯. From these peaks the dislocation densityd¯−2may be calculated. The width of the peaks and the intensity ratio of scattering maxima and minima is found as a function ofd¯, &dgr;, and the wavelength &lgr;, and it is concluded that the peaks could be experimentally resolved if (&lgr;/&dgr;d¯) >&pgr;. This condition could be satisfied for fairly irregular networks, e.g., &dgr;¯=1/&pgr;, by infrared radiation of wavelength &lgr;≅d¯.

ISSN:0021-8979    

DOI:10.1063/1.1702468

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The resonant behavior of a cylindrical microwave cavity partially filled with a cold plasma of arbitrarily large density is studied theoretically and experimentally. Curves showing the resonant frequencies as functions of the plasma density are given for the lower order modes. The modes are generally not pureTEorTMmodes but are of hybrid character. In addition to the modes that are related to those of the empty cavity, there is a class of modes of surface wave character that do not exist in the empty cavity. Experiments have been performed and are generally in agreement with the theory. However, for some modes great discrepancies are observed. These correspond to the unexplained additional resonances obtained in plasma resonance experiments.

ISSN:0021-8979    

DOI:10.1063/1.1702469

出版商:AIP    

年代:1962

数据来源: AIP