Showing papers in "Journal of Applied Physics in 1949"
TL;DR: In this article, a general treatment of the scattering of radiation by an inhomogeneous material is developed, where scattering measurements can be used to obtain the average square of the fluctuations in refractive index or electron density and a correlation function which measures the degree of correlation between two fluctuations as a function of their distance of separation.
Abstract: A general treatment of the scattering of radiation by an inhomogeneous material is developed. It is shown how scattering measurements can be used to obtain the average square of the fluctuations in refractive index or electron density and a correlation function which measures the degree of correlation between two fluctuations as a function of their distance of separation.The scattering of visible light by Lucite and two glass samples has been investigated. The data are analyzed in terms of the quantities mentioned above. It is found that the extensions in space of the inhomogeneities in the Lucite sample are much greater than those in the optical glass samples investigated. The magnitudes of the fluctuations in refractive index are found to be dependent on the composition of the sample.
1,367 citations
TL;DR: In this article, the authors describe some of the phenomena found to have their origin in electrically induced fibration of small particles in fluid liquid suspension, including the induced shear resistances found in layers of the fluid when bounded by potentialized electrode surfaces.
Abstract: This paper describes some of the phenomena found to have their origin in electrically induced fibration of small particles in fluid liquid suspension. Particular attention is given to induced shear resistances found in layers of the fluid (0.01 to 0.15 cm) when bounded by potentialized electrode surfaces. Ingredients and manner of compounding concentrated fluids capable of reversible shear resistance up to several hundred grams per cm2 are described. Dynamic induced shear resistance or the corresponding induced bulk viscosity are shown to be a parabolic function of field strength wherein parameters dependent on surface conditions of the particles are involved. Various properties of these fluids are discussed with regard to the mechanism of induced fibration, its application in slip clutches and other hydraulic devices, and some of the factors for best results. Consideration is given to the analogous magnetically induced fibration of ferromagnetic particles in fluid suspension. It is found that the observe...
1,151 citations
TL;DR: In this paper, the radius of a spherical precipitate particle growing in a solid solution of initially uniform composition was shown to be equal to α(Dt)½, where D is the atomic diffusion coefficient, t the time of growth, and α, the growth coefficient, is a dimensionless function of the pertinent compositions.
Abstract: The radius of a spherical precipitate particle growing in a solid solution of initially uniform composition may be shown to be equal to α(Dt)½, where D is the atomic diffusion coefficient, t the time of growth, and α, the growth coefficient, is a dimensionless function of the pertinent compositions. In this paper the precise dependence is found of this function upon the pertinent concentrations. A similar computation is made for the growth coefficient corresponding to the one‐dimensional growth of a plate.
961 citations
TL;DR: The resolving power of the electron microscope and the contrast in the image are calculated for different conditions of focusing, illumination and aperture as mentioned in this paper, which can change the limit of resolution by a factor of about 3.
Abstract: The resolving power of the electron microscope and the contrast in the image are calculated for different conditions of focusing, illumination and aperture. These conditions can change the limit of resolution by a factor of about 3. The contrast in the image of an atom is appreciably increased by defocusing and spherical aberration. Nevertheless, the contrast improves when the numerical value of the aberration constant is diminished. The effect of different methods of spherical correction is discussed briefly.
854 citations
TL;DR: In this article, a new reflection method is described for determining pole figures of flat samples with a Geiger counter x-ray spectrometer, which can be used directly without corrections for changes in geometry during rotation of the sample.
Abstract: A new reflection method is described for determining pole figures of flat samples with a Geiger counter x‐ray spectrometer. The chief advantage of the method is that the experimental data may be used directly without corrections for changes in geometry during rotation of the sample. Beginning from an initial position identical with the usual reflection arrangement the sample is rotated about an axis defined by the intersection of the sample surface with the plane of the spectrometer. During this motion a randomly oriented sample of sufficient thickness will yield a constant counting rate because the absorption and effective scattering volume of the sample remain unchanged. As a result, no correction formula is required. The experimental arrangement requires three horizontal slits; two are used to collimate the incident beam, and the third is placed in front of the counter. A mathematical analysis of the optical elements of the arrangement is given together with the results from a practical application.
731 citations
TL;DR: In this article, the authors considered the case where the mechanical state is determined by the components of stress and permanent strain, and the conditions of continuity, uniqueness, irreversibility, and consistency can be used to extract rather far-reaching information regarding the structure of the stress-strain law.
Abstract: The first part of the paper (Sections I to V) is concerned with the general technique used in the discussion of stress‐strain laws for inviscid elastic‐plastic materials with work hardening. It is postulated that when the ``mechanical state'' of such a material is known a given infinitesimal change of stress produces a uniquely defined infinitesimal change of strain. Once the assumption is made as to which variables determine the mechanical state, the conditions of continuity, uniqueness, irreversibility, and consistency can be used to extract rather far‐reaching information regarding the structure of the stress‐strain law. The procedure is applied to the case where the mechanical state is determined by the components of stress and permanent strain.The second part of the paper (Sections VI to VIII) is concerned with various problems of plastic equilibrium. Structural stability in the plastic range is discussed and the difficulties arising in the formulation of stability problems for nonconservative system...
392 citations
TL;DR: In this paper, the power dissipation by eddy currents in a metallic surface at microwave frequencies in the presence of regular parallel grooves or scratches whose dimensions are comparable to the eddy current skin depth was investigated.
Abstract: A theoretical investigation has been made of the power dissipation by eddy currents in a metallic surface at microwave frequencies in the presence of regular parallel grooves or scratches whose dimensions are comparable to the eddy current skin depth. The eddy current equation has been integrated numerically for grooves of various shapes and sizes transverse to the direction of induced current flow, and the corresponding losses are calculated and plotted. The power dissipation is increased by about 60 percent over its value for a smooth surface when the root‐mean‐square deviation of the grooved surface from an average plane is equal to the skin depth; the exact shape of the grooves is not critical. The increase in eddy current losses caused by grooves parallel to the current is shown in a particular case to be only about one‐third as great as the increase caused by transverse grooves of similar size. The effect on losses of an isolated narrow crack or fissure transverse to the current is briefly discussed.
301 citations
242 citations
TL;DR: In this paper, it has been shown experimentally that the mechanism of sintering of spherical glass particles is that of viscous flow and the viscosities of the investigated glass were determined for a range of temperatures from 575°C to 744°C.
Abstract: It has been shown experimentally that the mechanism of sintering of spherical glass particles is that of viscous flow. The viscosities of the investigated glass were determined for a range of temperatures from 575°C to 744°C. These viscosities remain in good agreement with those obtained by other methods.
205 citations
TL;DR: In this article, a general expression for the flow process in an idealized mixture is developed and the general thermo-hydrodynamic relations for flow through a de Laval nozzle are developed.
Abstract: A gas‐water mixture, when expanded through a de Laval nozzle, acts as a compressible fluid. A general expression for the flow process in an idealized mixture is developed. The general thermo‐hydrodynamic relations for flow through a de Laval nozzle are developed. The magnitude of the velocity of an energy pulse or signal through the mixture is determined and is compared with the velocity of flow. Experimental results are compared with those predicted using the equations developed.
192 citations
TL;DR: In this article, an electrolytic method for preparing thin metal sections for electron microscopy and diffraction is introduced and its application to the structure of cold-worked aluminum and an aluminum-copper alloy is demonstrated.
Abstract: Bethe's dynamical theory of electron diffraction in crystals is developed using the approximation of nearly free electrons and Brillouin zones.The use of Brillouin zones in describing electron diffraction phenomena proves to be illuminating since the energy discontinuity at a zone boundary is a fundamental quantity determining the existence of a Bragg reflection. The perturbation of the energy levels at a corner of a Brillouin zone is briefly discussed and the manner in which forbidden reflections may arise at a corner pointed out. It is concluded that the kinematic theory is inadequate for interpreting electron images of crystalline films.An electrolytic method for preparing thin metal sections for electron microscopy and diffraction is introduced and its application to the structure of cold‐worked aluminum and an aluminum‐copper alloy demonstrated. It is concluded that cold‐worked aluminum initially consists of small, inhomogeneously strained and disoriented blocks about 200A in size. These blocks are n...
TL;DR: In this paper, the formation of precipitates from the solid solutions of C and N in α-iron has been studied by means of the internal friction peak associated with the stress-induced interstitial diffusion of the solute atoms.
Abstract: The formation of precipitates from the solid solutions of C and N in α‐iron has been studied by means of the internal friction peak associated with the stress‐induced interstitial diffusion of the solute atoms. A transformation law has been found to fit the experimental data. The data are interpreted as showing the following: (1) Fe3C precipitates in the shape of spheres; (2) an intermediate phase in the precipitation of nitrogen forms in the shape of disks; and (3) within the experimental error there is indicated no continuous nucleation. Using the results of a derivation made by Zener, the mean distance between nuclei is calculated for Fe3C. For carbon concentrations of about 0.016 wt. percent, this distance is about 800, 2000, and 7000 Angstroms at 27°C, 102°C, and 312°C, respectively. With appropriate experimental conditions, the temperature dependence of the precipitation rate is found to be about the same as the temperature dependence of the diffusion rate of the solute atoms.
TL;DR: In this article, an empirical method of calculating mass absorption coefficients is given for all elements and for wave lengths less than the K critical absorption wave length, and partial tables give constants for wave length between the L 1 and M 1 critical wave lengths.
Abstract: An empirical method of calculating mass absorption coefficients is given. Complete tables of constants are presented for calculating μ/ρ for all elements and for wave‐lengths less than the K critical absorption wave‐length. Partial tables give constants for wave‐lengths between the L1 and M1 critical wave‐lengths.Calculated mass absorption coefficients are given for the common elements.
TL;DR: The aerodynamic forces on golf balls were studied by dropping spinning balls through the horizontal wind stream of the B. F. Goodrich wind tunnel as discussed by the authors, and the results showed that the lift varied with the rotational speed of the balls.
Abstract: The aerodynamic forces on golf balls were studied by dropping spinning balls through the horizontal wind stream of the B. F. Goodrich wind tunnel. The lift, L, and drag, D, were calculated from the drift of the balls, rotating at speeds, N, up to 8000 r.p.m. while falling through a wind stream having a velocity of 105 feet per second. For a standard dimple or mesh golf ball weighing 0.1 lb., the lift varied with the rotational speed as L=0.064 ×[1−exp(−0.00026N)], with a maximum observed value of 0.055 lb. or more than half the weight of the ball. The drag increased nearly linearly from about 0.06 lb. for no spin to about 0.1 lb. at 8000 r.p.m.For a smooth ball the lift was negative at all rotational speeds below 5000 r.p.m. Above this speed, the lift was positive but was less than for the standard ball. The drag for these balls was nearly constant at about 0.08 lb. Balls with shallower dimples than standard gave intermediate results. Driving tests were consistent with the wind tunnel results.These result...
TL;DR: In this article, an apparatus is described which produces homogeneous mists or clouds of solid particles of any desired size, which are then sprayed by a Beams high speed air-driven top.
Abstract: An apparatus is described which produces homogeneous mists or clouds of solid particles of any desired size. As in Walton's original model liquid is sprayed by a Beams high speed air‐driven top, but an improved performance has been achieved by utilizing a property of high speed air films so that automatic extraction of unwanted satellite droplets, better running characteristics over a wider range, simplified construction, and low air consumption are obtained.
TL;DR: In this paper, a grain boundary model is described in which the transition region at the boundary is considered as consisting of numerous disordered groups of atoms or diffused holes, and the intercrystalline slip occurs through the atomic rearrangement by thermal agitation within each ''disordered group'' by a shear process involving as units of flow only a few atoms.
Abstract: A study of the activation energy associated with the viscous intercrystalline slip shows that the conventional theories of grain boundary, e.g., the intercrystalline amorphous cement theory and the abrupt transitional theory, are both untenable. A grain boundary model is described in which the transition region at the boundary is considered as consisting of numerous disordered groups of atoms or diffused holes. The intercrystalline slip occurs through the atomic rearrangement by thermal agitation within each ``disordered group'' by a shear process involving as units of flow only a few atoms. This grain boundary model and slip mechanism are consistent with experimental facts and furnish, furthermore, a unified viewpoint as to the mechanism of the viscous intercrystalline slip, the volume diffusion in metals, and the constant rate creep of metal crystals under small stress. Further experiments are described concerning the influence of previous deformation and impurities on grain boundary viscosity. It has b...
TL;DR: In this article, the structure of thin metallic films was studied by means of electron diffraction and electron microscopy, and the effects of varying experimental conditions on the film structure of selected metals were reported.
Abstract: The structure of thin metallic films was studied by means of electron diffraction and electron microscopy. Microcrystal size can be correlated with the melting point of the metals, those with high melting points producing continuous films of small unoriented microcrystals while those with low melting points produce large microcrystals oriented preferentially with respect to the substrate. The effects of varying experimental conditions on the film structure of selected metals are reported. The electron beam of the electron microscope affects metals with low melting points most directly, producing melting, sublimation or crystallization. Variations in the velocity of the impinging atom, obtained by passing thermal atoms through a mechanical velocity selector, produce no effect for metals whose vapor is monatomic. Antimony whose vapor is found to consist of polyatomic molecules as well as atoms produces films whose grain size seems to vary with the size of the molecules forming the antimony film. The rate of...
TL;DR: In this paper, the attenuation for the three lowest modes in polystyrene is computed and agreement with the experimental data of Chandler given in the preceding paper is given. And the analysis of the non-radiative modes propagated along a circular dielectric rod is accompanied by a discussion of die-lectric loss.
Abstract: Analysis of the non‐radiative modes propagated along a circular dielectric rod is accompanied by a discussion of dielectric loss. The attenuation for the three lowest modes in polystyrene is computed and agrees with the experimental data of Chandler given in the preceding paper.
TL;DR: In this article, a method that makes possible the attainment of a very high degree of precision in the determination of lattice constants (in some cases more than 1:200,000, even with crystals of lower symmetry) is described.
Abstract: A method that makes possible the attainment of a very high degree of precision in the determination of lattice constants (in some cases more than 1:200,000, even with crystals of lower symmetry) is described. The method and its applications, which has been in steady development since 1934 (in Riga, University of Latvia), tries to eliminate the errors of the Debye‐Scherrer‐Hull and rotating crystal methods by a careful experimental technique, based on:(1) Very exactly built cameras of a reasonable diameter (64 mm);(2) Elimination of all well‐known errors of the powder and rotating crystal methods (e.g., elimination of film shrinkage errors by a new method of putting the film into the camera);(3) Locating the camera in a specially constructed thermostat so that the temperature some hours before and during exposure is kept constant.The films obtained in this way are very clear, especially in the important back‐reflection region, with distinct lines (or spots) that can be measured exactly. As no standard subs...
TL;DR: In this paper, the problem of the scattering of electromagnetic waves by a spherical obstacle is discussed, and a reasonable system of approximations yields the well known ''Babinet's principle''.
Abstract: The problem discussed in this paper is that of the scattering of electromagnetic waves by a spherical obstacle. The classical theory is well known. Stratton's ``Electromagnetic Theory,'' for instance, contains a very good summary of that discussion. The computation of the scattering cross section, according to this theory, leads to some difficulties. In the case of large spheres, where geometrical optics should apply, the rigorous theory yields a scattering cross section equal to twice the actual cross section of the sphere!The discussion presented in this paper explains this strange result and shows the role played by the shadow and by the diffraction fringes surrounding the shadow. A reasonable system of approximations yields the well known ``Babinet's principle.'' The physical interpretation is of such general character that it must certainly apply to a variety of similar problems in acoustics or wave mechanics. The spherical shape of the obstacle is essential in the present discussion, but similar res...
TL;DR: In this paper, a simplified version of van der Waals' equation, (P+π)(V−ω)=nRT, where π is the internal pressure (or cohesive energy density) and ω is the volume at absolute zero, by extrapolation.
Abstract: Practical considerations emphasize the desirability of formulating an adequate equation of state for polystyrene. A fairly satisfactory one is this simplified version of van der Waals' equation, (P+π)(V−ω)=nRT, where π is the internal pressure (or cohesive energy density) and ω is the volume at absolute zero, by extrapolation. Evaluating constants from thermal expansion data and expressing P in p.s.i., V in cc per gram, and T in degrees Kelvin, this becomes (P+27,000)(V−0.822)=11.6T. Agreement with compressibility measurements, which are described in some detail, is good. Discrepancies with room temperature values of sound velocity and cohesive energy density by swelling measurements are discussed briefly.
TL;DR: In this article, a method employing a diverging x-ray beam is described for the determination of preferred orientation in flat transmission samples with a Geiger counter xray spectrometer and it is shown that for a certain range of sample thickness the counting rate is independent of the rotation of the samples, and therefore no correction formula is required.
Abstract: A method employing a diverging x‐ray beam is described for the determination of preferred orientation in flat transmission samples with a Geiger counter x‐ray spectrometer. It is shown that for a certain range of sample thickness the counting rate is independent of the rotation of the samples, and therefore, no correction formula is required.
TL;DR: In this article, the relationship between intrinsic viscosity and dilatometric properties was established for polyethylene terephthalate, and the most pronounced property change associated with increasing intrinsic viscoity was observed to be the second-order transition temperature.
Abstract: By means of a density balance, the relationship between intrinsic viscosity and dilatometric properties is established for polyethylene terephthalate. The most pronounced property change associated with increasing intrinsic viscosity was observed to be the second‐order transition temperature. The relationship between crystallinity and dilatometric properties is presented for 3 aromatic polyesters. In every case, increased crystallinity in the polymers is associated with higher second‐order transition temperatures, larger transition range, higher density, and lower volume coefficients of expansion. Second‐order transition temperatures, densities at 0°C, and volume of coefficients of expansion are presented for a number of polyesters and vinyl polymers to illustrate the effects of chemical structure as well as physical state on these dilatometric properties. Illustration of the effect of copolymerization on second‐order transition temperatures is made with a copolyester system.
TL;DR: In this article, it has been shown that a palladium-platinum mixture is the most satisfactory material for use in the pre-shadowed replica technique, and that films of this mixture in a thickness of about 6A produce adequate shadows in which there is no sign of granulation.
Abstract: The lower limit of size of biological objects which can be photographed with the electron microscope, by the aid of shadow‐casting, is shown to depend upon the smoothness of substrate upon which they can be mounted, and upon the continuity of structure of the thin films with which they are shadowed. Numerous attempts to improve the existing deficiencies are reported, both with respect to producing smoother substrate films, and to producing films for shadow‐casting of high efficiency and continuity of structure. No success has been encountered in producing a usable substrate film perceptibly smoother than the collodion and Formvar films commonly used. It is found that the best shadow‐casting material for this type of film is uranium or uranium oxide. Verification has been obtained of the severe granulation of goldfilms previously used in the pre‐shadowed replica process, when subjected to the electron current of a biased‐beam electron gun. Attempts to reduce the granulation to a satisfactory level have failed. Various methods of preparing pre‐shadowed replicas are reported. The factors affecting the tenacity of evaporated films to glass surfaces are discussed. It is found that elements which oxidize readily are relatively adherent to glass, while the elements gold,palladium,platinum, and rhodium are not. Uranium sulfide can be used as a pre‐shadowed replica material, but only with some uncertainty, owing to its chemical instability. It has been found that a palladium‐platinum mixture is the most satisfactory material for use in the pre‐shadowed replica technique, and that films of this mixture in a thickness of about 6A produce adequate shadows in which there is no sign of granulation. The surface of clean glass is again found to have the smoothest structure of any material known, with practically no sharp discontinuities in elevation as great as 10A. An appendix is given, in which technical details of shadow‐casting and replica production are described.
TL;DR: In this paper, an experimental investigation of dielectric rod as wave guide indicates that the guiding effect is retained even when the rod is only a fraction of a wave length in diameter, so that a very low loss wave guide results.
Abstract: An experimental investigation of dielectric rod as wave guide indicates that the guiding effect is retained even when the rod is only a fraction of a wave‐length in diameter. The greater part of the guided energy is then outside the dielectric, so that a very low loss wave guide results. Measurements of performance made at 1.25 cm indicate attenuations down to 0.004 decibel per meter in polystyrene rod, and show good agreement with theoretical predictions. A resonator utilizing the dielectric‐rod wave guide is described, in which a maximum Q of approximately 53,000 was observed.
TL;DR: In this article, it was shown that surfaces of various metals can be activated by vapors of certain unsaturated organic compounds, and in the active condition they give arcs even when the circuit inductance is greater than this limiting value by a factor of more than 103.
Abstract: When an electric current is set up by bringing two contacts together, they necessarily discharge a capacity. If the discharge takes place through an arc before the metallic circuit is established, erosion of the electrodes results. In a low voltage circuit the occurrence of an arc is dependent upon the condition of the electrode surfaces and upon the circuit inductance. For ``inactive'' surfaces, and a voltage of the order of 50, an arc does not occur if the inductance is greater than about 3 microhenries. Surfaces of various metals can be ``activated'' by vapors of certain unsaturated organic compounds, and in the active condition they give arcs even when the circuit inductance is greater than this limiting value by a factor of more than 103. The study of arcs between active metal surfaces is not yet complete, and most of this paper and all of the remainder of this abstract have to do with surfaces which are inactive.When an arc occurs at the make of inactive metal surfaces, its energy, which in low volt...
TL;DR: In this paper, the propagation of supersonic waves in bulk rubbers has been studied from 40 kc/sec. to 10 Mc/sec and from −60°C to 60°C.
Abstract: The propagation of supersonic waves in bulk rubbers has been studied from 40 kc/sec. to 10 Mc/sec. and from −60°C to 60°C. The wave velocity was found to increase with decreasing temperature, leveling off both at high and low temperatures, and was found to increase slightly with frequency. Peaks in attenuation as a function of either temperature or frequency were observed, the peaks occurring at lower temperatures for lower frequencies. The peaks for butyl, a high loss rubber, are broader and higher than those for GR‐S and Hevea, which are lower loss rubbers. The results are in qualitative agreement with data obtained by strip methods at audiofrequencies. However, for bulk waves the real and imaginary parts of two elastic constants, the bulk and shear moduli, determine wave velocity and attenuation; hence, independent measurements of shear wave properties are necessary to evaluate these constants. A three constant theory is discussed, assuming a shear viscosity only, so that an effective modulus K+4μ/3 is...