摘要:

Amplification of surface wave has been experimentally observed in a composite structure consisting of a quartz plate, a thin liquid layer, and a piezoelectric semiconductor. An additional time delay is also observed in such a composite structure.

ISSN:0021-8979    

DOI:10.1063/1.1658306

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The Fourier‐Moment method developed by King and Mullins has been applied to the case of an isolated scratch decaying by viscous flow in an amorphous material such as a simple glass. Using the Stokes‐Einstein equation to relate the diffusivity and viscosity coefficients, a comparison of rates suggests that viscous flow would predominate over volume or surface diffusion as the mechanism of scratch healing in simple amorphous materials for scratch widths above approximately 0.1 &mgr;.

ISSN:0021-8979    

DOI:10.1063/1.1658338

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The resonant sphere technique has been used to measure the temperature variation of the acoustic shear loss of vitreous silica up to 1100°C. The acoustic loss near room temperature, which is on the high temperature end of the 50°K loss peak, was found to be dependent upon fictive temperature, the state of oxidation, and, through the state of oxidation, may be dependent upon the OH or Cl content. A minimum loss occurs above room temperature and for synthesized silicas the loss level is comparable to single‐crystal materials. Above the minimum loss, the loss process appears to be thermally activated with an approximate activation energy of 0.5 eV. This low activation energy suggests the diffusion of a network modifier such as hydrogen as a possible cause of the high temperature loss.

ISSN:0021-8979    

DOI:10.1063/1.1658378

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The structure of noncrystalline electrodeposited Ni&sngbnd;P alloys, 73.8–81.4 at.% Ni, has been investigated by x‐ray scattering and by physical density measurements. The x‐ray interference functions,I(k), are qualitatively inconsistent with those calculated for fcc‐, hcp‐, and Ni3P‐type crystallites. Calculated radial distribution functions RDF(r) indicate that the alloys have a better defined short‐range order than that observed in liquid noble metals above their melting points. The observedI(k) are very similar to theI(k) calculated by Dixmier, Doi, and Guinier [inPhysics of Noncrystalline Solids, J. A. Prins, Ed. (North‐Holland Publ. Co., Amsterdam, 1965), p. 67] from their model. However, the parameters needed to fit the experimental results are inconsistent with the atomic sizes expected for nickel and phosphorus. The noncrystalline alloys are between 0.6% and 1.4% less dense than the corresponding mixtures of fcc Ni and Ni3P, both of which are essentially close packed. A grain boundary density deficit model has been developed which relates the fractional density difference between the microcrystalline and macrocrystalline forms of a close‐packed metal to the minimum average microcrystal grain size. The fractional density differences of between 0.6% and 1.4% observed for the noncrystalline Ni&sngbnd;P alloys would correspond to minimum average microcrystal grain sizesDof between 133 and 57 Å. Stored elastic energy calculations indicate that rms strains⟨&egr;2⟩1/2greater than 0.03 and due to simple compressive and dilatory stresses are inconsistent with the reported energy of transformation of noncrystalline Ni&sngbnd;P to crystalline nickel and Ni3P. Crystallite size broadening withD≥57 Å and strain broadening with⟨&egr;2⟩1/2≤0.03are insufficient to produce fcc, hcp, or Ni3P modelI(k) consistent with the observed Ni&sngbnd;PI(k). The high densities of the noncrystalline Ni&sngbnd;P alloys suggest that the alloys have a continuous structure rather than one in which internal boundaries separate small well‐ordered regions. These limitations on structural models for noncrystalline Ni&sngbnd;P alloys may apply to the other noncrystalline metallic alloys with similar diffraction patterns.

ISSN:0021-8979    

DOI:10.1063/1.1658310

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Discrepancies with theory revealed by recent nucleation experiments have been examined. It is suggested that a minor deviation between experimental nucleation rate and the atomistic theoretical model, may be ascribed to a value between 1 and 5×1011sec−1(instead of 1013sec−1) for the desorption rate pre‐exponential. The much larger deviation with the spherical cap classical model is shown to be due to inability of the model to adequately evaluate the Gibb's free energy of formation from the monomer, &Dgr;Gn′, for nuclei in the rangen= 1–3 atoms, which is the actual critical size in these experiments. If, for Bi on C, the surface energy term is chosen to give the observed values ofn*, then evaluating &Dgr;Gn′ forn= 1 gives &Dgr;G1′ = −20 kcal/mole, whereas it should be zero. If the surface energy is chosen to make &Dgr;G1′ = 0, then the calculated values ofn* and the nucleation rate do not agree with experiments. A modified form of the monolayer disc classical model gives good agreement between theory and experiment but is less satisfactory than the atomistic model. The experimental temperature variation of the maximum number density of nuclei disagrees with that expected as a result of depletion of single atoms. The results can be explained by depletion of mobile nuclei by mutual capture.

ISSN:0021-8979    

DOI:10.1063/1.1658339

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Thin, chemically grown (111) Ag platelets were deformed and studied by high‐voltage electron microscopy. Dislocation networks of two kinds were found to form in the plane of the foil. The first type was the usual disclocation network of contracted and extended nodes and was usually observed in regions of light deformation. After heavier deformation a new, more complex dislocation configuration, which divides the crystal into intrinsically and extrinsically faulted regions, was observed. In some instances these dislocations form a very regular pattern. A formation mechanism for such networks is discussed in terms of present theories.

ISSN:0021-8979    

DOI:10.1063/1.1658346

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Expressions are derived for the equilibrium elastic strain of an overgrowth film in terms of the Burgers vectors of imperfect misfit dislocations and their associated stacking faults. It is shown that under most experimentally encountered conditions, the effect of the stacking fault on the equilibrium spacing of the dislocations is unimportant.

ISSN:0021-8979    

DOI:10.1063/1.1658353

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The deformation‐induced damping spectrum has been studied in nickel single crystals from 77° to 290°K. There is a strong correlation between the peaks observed and the stages of deformation. Peak X (Bordoni) rises linearly with resolved shear stress in Stages I and II, the slope in Stage I being probably higher than in Stage II, and then falls in Stage III. The orientation dependence in Stages I and II is consistent with the hypothesis that dislocations in the primary glide system are responsible for it. This linear rise is shown to follow, with the aid of well‐known relations, from Pare´'s version of Seeger's double‐kink theory, which predicts that the damping should be proportional to&rgr;l, where &rgr; is the dislocation density andlthe average loop length. Other theories (Brailsford, Seeger) give other powers ofl(l2,l0respectively). The fall of Peak X in Stage III, and its behavior on annealing, are shown to be consistent with pinning (or unpinning) by point defects. Peak Y, which we no longer believe to be the Niblett‐Wilks Peak, is associated almost entirely with Stage III, and has an orientation dependence for which there is no immediate explanation.

ISSN:0021-8979    

DOI:10.1063/1.1658359

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Single crystals of muscovite have been studied by x‐ray Berg‐Barrett topography. Remarkably sharp contrasting stripes exhibiting anomalous x‐ray contrast were observed. From a detailed study of these as well as rocking curve experiments, it is concluded that the contrast is due to the corrugation of basal planes of mica, as a consequence of irregularity in the slip. The relation between the corrugations and the elastic properties of muscovite is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658376

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The experimentally observed frequency dispersions of the complex dielectric coefficient for some samples of artificial saline ice (of a type similar to natural sea ice) are examined with a view to identifying major contributing mechanisms. The simultaneous integral equations describing the linear superposition of relaxation processes having a continuum of relaxation times were inverted numerically to yield histogram representations of the relaxation time distribution function between 10−9and 10−1sec. These functions exhibited three main features: (1) an abrupt peak near 10−9sec, responsible in part for the high frequency dispersion (above 1 MHz), and which is attributed to polarization of the elongated conductive brine cells within the ice (Maxwell‐Wagner‐Sillars dispersion); (2) a hump between 10−6and 10−4sec which shifts towards shorter relaxation times at higher temperatures, showing an activation energy similar to that of protons in pure ice—this mechanism is seen at midfrequencies (1 KHz‐1 MHz); and (3) a wide mass at longer relaxation times commencing between 10−4and 10−3sec which is probably associated with space‐charge polarization arising from movement of the ions within continuous brine channels reaching from one electrode to the other.

ISSN:0021-8979    

DOI:10.1063/1.1658377

出版商:AIP    

年代:1970

数据来源: AIP