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Journal of Applied Physics

Issue 2 • Date Feb 1962

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Displaying Results 1 - 25 of 70
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Mechanism of Friction

    Page(s): 519 - 526
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    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. View full abstract»

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  • Longitudinal Susceptibility of Ferromagnets in Strong rf Fields

    Page(s): 527 - 534
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    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. View full abstract»

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  • Susceptibility of Ferromagnets in a Strong rf Magnetic Field Applied Parallel to the dc Field

    Page(s): 535 - 537
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    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. View full abstract»

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  • Direct Observation of Antiphase Boundaries in the Fe3Al Superlattice

    Page(s): 537 - 552
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    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 imperfect B2‐type lattice, while the second is a lower temperature modification based on the more perfect DO3‐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. View full abstract»

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  • Propagation Effects on Ferromagnetic Resonance in Dielectric Slabs

    Page(s): 553 - 556
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    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. View full abstract»

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  • Temperature Dependence of Shock‐Induced Phase Transformations in Iron

    Page(s): 557 - 561
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    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. View full abstract»

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  • Field Dependence of Photoelectric Emission from Molybdenum

    Page(s): 562 - 568
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    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 mμ. 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 yields eϕ**=4.33 ev and A**=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. View full abstract»

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  • Electron Microscopy of Prismatic Dislocations in Silicon

    Page(s): 568 - 569
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    Transmission electron micrographs of (111) prismatic loops in gold‐diffused silicon have been obtained. The loops were about 2 μ 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. View full abstract»

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  • Theoretical Analysis of Light Scattering by Irregular Dislocation Networks

    Page(s): 570 - 574
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    Light scattering by an irregular cubical network of dislocations, represented by identical rods, along the x, y, and z directions is computed by a method which is similar to the Patterson analysis of x‐ray diffraction. It is assumed that the spacing d between neighboring dislocations has a Gaussian distribution of width δd¯ about the average spacing d¯, and it is shown that shallow maxima of the scattering intensity exist near the Laue spots of the regular lattice with spacing d¯. From these peaks the dislocation density d¯-2 may be calculated. The width of the peaks and the intensity ratio of scattering maxima and minima is found as a function of d¯, δ, and the wavelength λ, and it is concluded that the peaks could be experimentally resolved if (λ/δd¯) ≫π. This condition could be satisfied for fairly irregular networks, e.g., δ¯=1/π, by infrared radiation of wavelength λ≅d¯. View full abstract»

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  • Resonances of a Microwave Cavity Partially Filled with a Plasma

    Page(s): 575 - 581
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    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 pure TE or TM modes 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. View full abstract»

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  • Thermoelectric Phenomena Associated with Electron‐Field Emission

    Page(s): 582 - 587
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    The equilibrium temperature distribution in an ideal metal rod, one end of which is subjected to an intense electric field, is studied. Particular attention is focused on the case where the emitting end cools down, and the necessary conditions for this effect are derived. Viewed as a ``heat pump,'' the maximum rate of heat flow as a function of emitter temperature is derived, and it is found that rates in excess of 0.1 cal/sec/cm2 are possible at room temperature if the emitter work function is less than an electron volt. View full abstract»

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  • Effect of Reflecting Boundaries on the Transport of Resonance Radiation

    Page(s): 587 - 596
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    The Holstein‐Biberman theory of the transport of resonance radiation in gases is generalized to include the case in which the boundary is partially reflecting. The problem is formulated in a manner which follows conventional transport theory somewhat more closely than the earlier treatments of Holstein and Biberman. Using the incoherent scattering approximation, we first write down the two coupled Boltzmann equations describing the mutual transport of excited atoms and resonance photons. The photon equation is then solved, with (diffuse) reflecting boundary conditions, by a slight extension of the interreflection method, and inserting the result into the excited atom equation leads at once to the appropriate generalization of the Holstein‐Biberman transport equation. The kernel of this integrodifferential equation, G(r,r′), represents the mean probability that a resonance quantum emitted at r′ is absorbed at r, taking into account the contribution of paths which strike the boundary an arbitrary number of times; G(r,r′) is expressed quite generally in terms of the resolvent kernel of the interreflection equation. The theory is used to calculate the effect of a slightly reflecting boundary on the imprisonment time in a gas discharge. View full abstract»

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  • Measurement of the Thermal Diffusivity of Thermoelectric Materials

    Page(s): 597 - 600
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    A simple modification of Angstrom's classical method for the determination of the thermal diffusivity of thermoelectric materials is described. Using the Peltier heat generated at the junction of the specimen and a current lead as a periodic heat source, symmetrical temperature variations may be established in the specimen and the diffusivity derived from the propagation constants of the variations. Results of measurements at room temperature on lead telluride are presented. View full abstract»

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  • Point Defects in p‐Type Germanium as Introduced by Deformation, Quenching, and Electron Bombardment

    Page(s): 600 - 605
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    In order to compare point defect formation in germanium through different modes of production, Hall measurements have been made on germanium after different treatments. The same starting material was used in all experiments, namely, 5 ohm‐cm p‐type germanium. Markedly different behavior was observed. For the electron bombarded material, the number of carriers is reduced at all temperatures below room temperature, while the quenched material shows an increase at all temperatures. The deformed material exhibits intermediate behavior, with the carrier concentration increased at high temperatures and decreased at low temperatures. This is accounted for by an energy level scheme similar to that of James and Lark‐Horovitz. View full abstract»

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  • Some Considerations of Dynamic Behavior in the Plasma Thermocouple

    Page(s): 606 - 613
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    An analysis is presented of the role which stable electron oscillations of large amplitude may play in determining observed ``steady‐state'' characteristics of a plasma‐filled thermionic diode. The mechanism considered is that of coupling between electrostatic plasma oscillations, driven by the energy of the entrant electron ``beam'' from the emitter surface, and the potential distribution in the emitter sheath region. In operation such that net current flow is controlled by the sheath potential distribution, it is found that the time‐averaged net current may increase markedly in transition from nonoscillatory to oscillatory operation, with a concurrent change in cell and load potential drops such that the diode acts as a negative resistance source of potential over a limited range. Conditions which restrict attainment of the oscillatory mode are discussed, and it is found that large amplitude electron waves may be generated and maintained over a fairly wide, and experimentally accessible range of plasma electron density. Comparison is made with some experimental results, and an experiment is suggested for direct test of the driven‐wave hypothesis discussed herein. View full abstract»

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  • Influence of F‐Center Concentration on the Electrification of the Dust of KCl Monocrystals Irradiated with β Rays

    Page(s): 613 - 615
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    The electrification of the dust of KCl monocrystals irradiated with β rays is influenced by 3 factors: absorption of electrons in the crystal, creation of F centers, and secondary emission. The F‐center concentration in crystals irradiated with β rays for various irradiation times was measured spectrophotometrically. Based on the F‐center model and with the help of statistical calculations the relationship between the F‐center concentration in the crystal and the surface charge due to F centers was found. View full abstract»

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  • Thermodynamics for Nonequilibrium Systems. The Principle of Macroscopic Separability and the Thermokinetic Potential

    Page(s): 616 - 624
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    The consequence of the principle of microscopic reversibility used for deriving the reciprocal relations in the linear phenomenological coefficients is derived from the classical hypothesis of the separability of individual processes. The application of the separability principle to nonlinear systems is illustrated with an example, and its ability to suggest microscopic mechanisms is demonstrated. The nature of independence among the processes is discussed in more detail than has been done before, and the number of unknowns, conditions, and the minimum number of experimental coefficients are calculated in the process of finding the independent fluxes and forces. The inapplicability of the principle of minimum entropy production to nonlinear systems is confirmed, and a new dissipation function is found which is a minimum with respect to variations in all the unprescribed forces in a steady state. Such a function is found to be the integral of part of the change of the rate of entropy production with respect to the forces as discussed by Prigogine. The integrability of such a change is due to the classical principle of separability. Since this function can only decrease with time in all natural processes, it is given the name of thermokinetic potential. A possible separation between phonon drag and the energy of transport, and also that between the charge of transfer and the electron wind effect, by measuring higher‐order phenomenological coefficients is also discussed. View full abstract»

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  • Effect of Solutes on Polygonization in Bent Zinc Crystals

    Page(s): 625 - 629
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    The development of a reagent for dislocation etching of high‐purity zinc alloys with copper or aluminum, not requiring decoration of the dislocations, allowed the study of dislocation arrangements in bent alloy crystals. Most of the dislocations were found in the unannealed condition to be arranged in disconnected wall segments perpendicular to the basal plane, showing that the solutes had little, if any, effect on mechanical polygonization during bending. Their effect on the rate of subsequent thermal polygonization and of subgrain growth was also found to be surprisingly slight. View full abstract»

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  • Temperature Distribution in a Hollow Cylindrical Cup with a Stem

    Page(s): 629 - 633
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    An approximate analytical approach for determining the temperature distribution in a hollow cylindrical cup of radius C, having a base thickness H, with a stem of radius A, and length L, is given. The outer radial surface of the cup is held at a temperature T0 and the temperature at the bottom of the stem is Ts. All other surfaces are adiabatic. This geometrical arrangement is used to observe marker motion under the influence of a large thermal gradient in a thermal diffusion experiment described in the following paper. In this setup, only the sink temperature Ts and the temperature at the bottom of the cup Tm can be measured. Equations are presented which enable one to calculate the temperature and its gradient along the axis of this arrangement with relative ease for the physically important case A/C≪¼. In the region along the axis above the cup‐stem interface, the temperature at any point is given in terms of Tm, Ts, and functions which depend only upon the ratio A/H. A table of these functions is presented for the cases πA/H=0.4, 0.8, and 1.2. View full abstract»

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  • Diffusion of Au and Cu in a Temperature Gradient

    Page(s): 634 - 641
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    Measurements have been made of relative marker movements in Au and Cu in the presence of temperature gradients of the order of 1200°K/cm. These experiments yielded results which indicate that a net vacancy current is established in these metals under appropriate experimental conditions. The magnitude and direction of the observed effects are consistent with kinetic theory predictions in conjunction with previously determined vacancy energies. A three‐dimensional extension of existing kinetic theory is developed and important factors which do not appear in one‐dimensional treatments are discussed. Porosity development in Cu was found under certain conditions and this may be a visual demonstration of the existence of a thermal diffusion effect in Cu. View full abstract»

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  • Folded Molecules in Lamellas Crystallized from Molten Polymers

    Page(s): 642 - 643
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    Single crystals of polypropylene consisting of lamellas have been grown from the melt. Electron diffraction patterns indicate that the molecules are folded within the lamellas and have crystallized in a hexagonal unit cell. View full abstract»

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  • Thermodynamics of a Superconducting Energy Converter

    Page(s): 643 - 647
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    A thermodynamic analysis is given for an energy conversion process which employs the phase transition in a superconductor. The conversion process is a cyclic one. An expression for the conversion efficiency is obtained. Quantitative estimates are calculated from the formula for several superconducting materials. These indicate that conversion efficiencies as high as 44% may be obtainable under ideal conditions. View full abstract»

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  • Some Theoretical Considerations on the Geometry of Low‐Angle Dislocation Boundaries

    Page(s): 648 - 654
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    Frank's vector formula defining low‐angle boundaries is rewritten into six independent scalar equations which can be represented in the form of three simple two‐dimensional vector diagrams. These diagrams facilitate the discussion and construction of low‐angle boundaries, and in particular allow to construct four‐grid boundaries due to glide dislocations on arbitrary planes. View full abstract»

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  • Ultimate Yield Strength of Copper

    Page(s): 654 - 665
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    Copper specimens were subjected to large dynamic tensions by colliding relatively thin plates with thick plates holding the samples. The collision first produces strong shock waves, from 300 to 600 kbar, that propagate in both directions from the impact interface. Subsequent interaction of the two rarefaction waves resulting from these shock waves produces tensions that cause the material to disintegrate rather than to break in the ordinary manner. Comparison of these recovery experiments with corresponding hydrodynamic calculations show that the yield strength of copper is in excess of 150 kbar. The equation of state of copper used in the calculations is discussed. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory