Showing papers in "Journal of Applied Physics in 1947"
TL;DR: A silver iodide smoke generator has been constructed in this paper, which consumes 1 mg of SilverIodide per second and produces 1013 effective nuclei per second, and the maximum temperature at which the SilverIid particles serve as nuclei is approximately −4°C for particles one micron in diameter, and −8°c for particles 100 Angstrom units in diameter.
Abstract: Silver iodide particles have been found to serve as nuclei for the formation of ice crystals in super‐cooled water and in water vapor super‐saturated with respect to ice. It is believed that silver iodide serves as a very effective nucleus because it very closely resembles ice in crystal structure. Both dimensions of the unit cell of ice and silver iodide are the same to within approximately one percent. The maximum temperature at which the silver iodide particles serve as nuclei is approximately −4°C for particles one micron in diameter, and −8°C for particles 100 Angstrom units in diameter. A silver iodide smoke generator has been constructed which consumes 1 mg of silver iodide per second and produces 1013 effective nuclei per second.
356 citations
TL;DR: In this paper, a method is presented whereby the adiabatic compressibility of a finely divided material can be found from sound velocity and density measurements of a suspension of the particles in a liquid.
Abstract: A method is presented whereby the adiabatic compressibility of a finely divided material can be found from sound velocity and density measurements of a suspension of the particles in a liquid. The method is based on the assumption that the velocity of sound in a suspension is the same as it would be in an ideal solution of the two substances. This is verified experimentally by measurements of sound velocity in kaolin‐water suspensions and xylene‐water emulsions, and the method is illustrated by the determination of compressibility of the oil droplets in an oil emulsion and of the blood corpuscles in horse blood. Considerable accuracy is attainable for materials which are not too incompressible compared to the suspending liquid.
342 citations
TL;DR: For the video output V of a receiver, consisting of an i‐f stage, a quadratic detector, and a video amplifier, the probability density P(V) has been obtained for noise alone and for noise and signal as mentioned in this paper.
Abstract: For the video output V of a receiver, consisting of an i‐f stage, a quadratic detector, and a video amplifier, the probability density P(V) has been obtained for noise alone and for noise and signal. The results are expressed in terms of eigenvalues and eigenfunctions of the integral equation ∫ 0∞K(t)ρ(s−t)f(t)dt=λf(s), where ρ(τ) is the i‐f correlation function (i.e., the Fourier transform of the i‐f power spectrum) and K(t) is the response function of the video amplifier (i.e., the Fourier transform of the video amplitude spectrum). Two special cases are discussed in which the integral equation can be solved explicitly. Approximations for general amplifiers are given in the limiting cases of wide and narrow videos. Some applications of the method to other problems are shown in Sections 7B and 9.
263 citations
TL;DR: In this paper, general expressions for the modulus of rigidity, λ2, and compressibility, k, of a medium of Lame's constants, i.e., λ 1 and λ 2, loaded with a volume fraction, φ of a filler of constants i.i.d.
Abstract: General expressions are given for the modulus of rigidity, λ2, and compressibility, k, of a medium of Lame's constants, λ1 and λ2, loaded with a volume fraction, φ, of a filler of constants λ1′ and λ2′. To terms in the first power of φ λ2=λ2(1+15(λ2′−λ2)(λ1−2λ2)2λ2′(3λ1+8λ2)+λ2(9λ1+14λ2)φ)k=k+3+4λ2k′3+4λ2k(k′−k)φ. If the ``filler'' is a gas at a pressure, p, in a nearly incompressible medium, these give Young's modulusĒ=E(1−E9p+4Eφ).Modulus of rigidityλ2=λ2(1−53φ).Compressibilityk=k+33p+4λ2φ.Poisson's ratioσ=σ(1−3E9p+4Eφ), where φ is the volume loading, p is the pressure within the spherical cavities in the deformed state. Barred symbols refer to the properties of the loaded material; unbarred, to the medium alone. Expressions for the displacements and stresses within the medium and the particles, neglecting interactions between particles, are also given.
169 citations
TL;DR: The bird navigation theory as presented implies an organ or organs in the bird's physiology which are sensitive to the effect of its motion through the vertical component of the earth's magnetic field and to the effort exerted to overcome the coriolis force, due to theearth's rotation.
Abstract: The bird navigation theory as presented implies an organ or organs in the bird's physiology which are sensitive to the effect of its motion through the vertical component of the earth's magnetic field and to the effort exerted to overcome the coriolis force, due to the earth's rotation. Both these influences involve a set of lines which together form a navigational gridwork. By correlating its instantaneous land speed with the two above effects, a bird can fly to its home which is a unique point in this gridwork, or to related companion points existing in the gridwork at positions other than its home. Experimentation with homing pigeons between the home and spurious home points (conjugate or companion points) has yielded data which supports the theory.
161 citations
TL;DR: In this paper, a right-circular cylinder of incompressible, highly elastic material, which is isotropic in its undeformed state, cannot be held in a state of pure torsional deformation by means of a torsion couple alone, and normal surface tractions must be exerted over the plane ends of the cylinder.
Abstract: It has been predicted theoretically that, in general, a right‐circular cylinder of incompressible, highly elastic material, which is isotropic in its undeformed state, cannot be held in a state of pure torsional deformation by means of a torsional couple alone. In addition, normal surface tractions must be exerted over the plane ends of the cylinder. These normal surface tractions depend on the amount of torsion and on position on the plane ends of the cylinder. Experiments are reported here in which this phenomenon is observed in a right‐circular cylinder of pure gum compound. The dependence of the surface traction on amount of torsion and its distribution over the surface of the cylinder is studied by measuring the bulging of the rubber into small holes in a metal plate on one end of the cylinder.
148 citations
TL;DR: In this paper, it is shown that the creep and the relaxation function of linear systems are mutually connected in a simple way. And the results of the theory are applied to a detailed discussion of the relaxation process in a particular case.
Abstract: The creep and the relaxation function of linear systems, for which the principle of superposition is valid, are mutually connected in a simple way. This makes it possible to calculate the distribution function of relaxation times of stress and the distribution function of retardation times of strain, when the relaxation function or the creep function is given. It also allows a transformation formula to be established for the conversion of one distribution function into another. The results of the theory are applied to a detailed discussion of the relaxation process in a particular case.
139 citations
TL;DR: In this article, high speed motion photography of the rapid movement of a glass rod (5 mm diameter) in a narrow (16 mm inside diameter) glass tube of water was used to study the tensile strength of water.
Abstract: Phenomena involving the tensile strength of water have been studied by a kinetic method—high speed motion photography of the rapid movement of a blunt glass rod (5 mm diameter) in a narrow (16 mm inside diameter) glass tube of water. Special precautions have been taken to remove all hydrophobic patches and small gas masses (gas nuclei) but to retain the dissolved gas (air at one atmosphere) in the water. If the rod surface contained gas nuclei, or was hydrophobic and free of gas nuclei, cavitation occurred at the rear end when the velocity was less than 3 meters/sec., but if completely hydrophilic and free of gas nuclei, the velocity could be 37 meters/sec. or 83 miles/hour without cavitation. Addition of a detergent (diactyl sodium succinate) to the water did not prevent cavitation at a low velocity with the hydrophobic rod free of gas nuclei. Movement of a rod in pure corn syrup (viscosity 20.1 poises), free of gas nuclei, left a large cylindrical cavity that collapsed in a matter of hundredths of a sec...
124 citations
TL;DR: The theory of robots or reproducing power‐amplifying systems is considered and special emphasis is placed on the specification of conditions for optimum performance, i.e., minimum deviation or maximum fidelity after any given time.
Abstract: The theory of robots or reproducing power‐amplifying systems is considered. After a general terminological orientation the study in the first part is confined to simple robots, the theory of which is equivalent to that of non‐linear springs with inertia and friction. The alacrity and fidelity of control are well exhibited by studying the behavior of a robot under constant tracking. Special emphasis is placed on the specification of conditions for optimum performance, i.e., minimum deviation or maximum fidelity after any given time. Curves are given for both proportional and on‐off robots, from which the parameter values for optimum performance may be read.In Part II the theory of proportional robots is analyzed in detail, especially from the point of view of conditions for optimum performance. Two subsequent papers will contain the theory for the on‐off case and the general non‐linear robot case. The paper is organized as follows:Part I. Descriptive accountA. Terminology and kinematic descriptionB. Dynamical equation of robots with usual loadC. Optimum performance curves. Practical examplesPart II. Theory of simple robots with proportional controlA. Complete solutions as functions of time. Optimum performance curvesB. Path curves in the position‐velocity plane
121 citations
TL;DR: In this article, a theoretical and experimental investigation of contour phenomena observed in electron microscope images near focus has been carried out and an explanation for the apparent reversal of the Fresnel fringes at exact focus is given.
Abstract: A theoretical and experimental investigation of contour phenomena observed in electron microscope images near focus has been carried out. An explanation for the apparent reversal of the Fresnel fringes at exact focus is given and a method is described for the determination of the degree of asymmetry from the fringe patterns. A procedure for empirically correcting the asymmetries usually present in magnetic electron microscope objectives is outlined and some of the results obtained with a compensated lens are shown. A number of instrumental defects which may prevent the attainment of the ultimate resolving power of an instrument, together with methods for their elimination, are listed.
118 citations
TL;DR: In this article, an arrangement permitting the fracture of brittle materials under the action of tensile stress superposed on hydrostatic pressure was described, and it was shown that in all cases of fracture produced at pressures above 25,000 kg/cm2 the net stress at fracture was compressive.
Abstract: An arrangement is described permitting the fracture of brittle materials under the action of tensile stress superposed on hydrostatic pressure. The hydrostatic pressures range up to 30,000 kg/cm2. The tensile stress superposed on the pressure required to break Pyrex glass is a strong function of the material by which pressure is transmitted to the lateral surface of the glass, but in all cases of fracture produced at pressures above 25,000 kg/cm2 the net stress at fracture was compressive, that is, tensile fracture takes place against the direction of the stress. Beryllium and phosphor bronze lose the brittleness which characterize them at atmospheric pressure and fracture in tension under pressure after marked plastic deformation. Carboloy remains brittle in tension under pressure, but its tensile strength may increase by a factor of three. NaCl elongates plastically in tension under pressure with no obvious disturbance of the optical homogeneity. Pipestone remains completely brittle under pressure and o...
TL;DR: In this article, a review of the theoretical efficiency calculations shows that higher efficiencies can be attained with thermocouple materials to which the Wiedemann-Franz-Lorenz relation is applicable, when their thermoelectric power is greater than 200 microvolts/°C.
Abstract: The generation of electrical energy from thermal energy by thermoelectric means cannot be accomplished with thermocouples made of the available alloys generally used for temperature measurements, their efficiency being less than one percent. A review of the theoretical efficiency calculations shows that higher efficiencies can be attained with thermocouple materials to which the Wiedemann‐Franz‐Lorenz relation is applicable, when their thermoelectric power is greater than 200 microvolts/°C. Some zinc‐antimony alloys with added metals approach the above conditions and have produced an experimental efficiency in excess of five percent, in accordance with the theoretical calculations. The criteria of higher efficiency are applied to semi‐conductors, deriving the optimum conditions. Lead sulfide with excess lead was found to be the only suitable material at present, which in combination with the zinc‐antimony alloy produces an efficiency of seven percent. Higher thermoelectric efficiencies can be produced only by developing new materials which can attain the theoretically required high values of thermoelectric power, low heat conductivity, and low specific resistance.
TL;DR: In this paper, the dielectric properties of some common plastic and ceramic materials at 10 cm and 3 cm wave lengths were measured using a short circuited end of the transmission line, and the properties of the sample, calculated from the position of a minimum of the standing wave and the ratio of the minimum field strength to the maximum field strength, were given.
Abstract: The method of measurement of the dielectric properties of solid dielectrics described by S. Roberts and A. von Hippel has been applied with 3‐cm wave‐length waves in a rectangular wave guide. In this method the dielectric sample is placed at a short circuited end of the transmission line, and the dielectric properties of the sample, calculated from the position of a minimum of the standing wave and the ratio of the minimum field strength to the maximum field strength of the standing wave. A simplified procedure for calculating the dielectric properties from the measurements is presented. Values are given of the dielectric properties of some common plastic and ceramic materials at 10‐cm wave‐length and 3‐cm wave‐length, which were measured with this method.
TL;DR: In this article, the general approximate theory of x-ray scattering at small angles by finely divided solids is reviewed and several procedures for obtaining a size distribution from the experimental scattering data are described.
Abstract: The general approximate theory of x‐ray scattering at small angles by finely divided solids is reviewed. It is assumed that the x‐ray scattering data can be interpreted in terms of a particle size distribution, with particle‐to‐particle scattering negligible. Scattered intensity curves for Maxwellian, Gaussian, and rectangular size distributions are calculated, and several procedures for obtaining a size distribution from the experimental scattering data are described. Details of the experimental technique are given, and evidence is presented to show that appreciable error can result if crystal‐monochromated radiation is not used. General procedures are given for applying corrections to the experimental data for the slit geometry used. Scattering data, mass distribution curves, and average particle sizes are presented for amorphous silica gels and for crystalline oxides of alumina, nickel and iron. These data are shown to correlate well with the results of crystal size measurements by x‐ray diffraction li...
TL;DR: In this article, it was shown that at higher breakdown voltages, the cathode gradient has diminished far below the value for field emission, and the possibilities of predicting and improving the insulating strength of electrode gaps in high vacuum by the study of the coefficients of the electrode materials are discussed.
Abstract: Breakdown studies have been made between electrodes in high vacuum at constant voltages from 50 to 700 kv. These further demonstrate the inadequacy of the field emission theory to account generally for high voltage breakdown in vacuum. Experiments are described which investigate some of the ``total voltage'' breakdown mechanisms, including positive‐ion emission by electron impact, electron emission by positive‐ion impact and by photons. In the d.c. case these processes contribute to a steady interchange of charged particles between cathode and anode which increases with voltage until breakdown ensues. At higher breakdown voltages the cathode gradient has diminished far below the value for field emission. Measurements of electron emission by electrons with energies up to 300 kv for tungsten, steel, aluminum, and graphite are reported. The possibilities of predicting and of improving the insulating strength of electrode gaps in high vacuum by the study of the coefficients of the electrode materials are discussed.
TL;DR: In this article, the angular dependence of the cross-section of randomly oriented wires and the mean cross-sections of thin metallic strips were investigated. But the results were limited to the case when the dimensions of the wire were determined only through the two ratios 2la = length of wireequivalent radius of wire, and 2lλ=length of wire wave length.
Abstract: Knowledge of the radar response of wires or thin metallic strips, as a function of their length and thickness, and of the radar frequency is important in the design of reflectors for radar. In view of the difficulty of this theoretical problem and the necessity of making approximations, as well as the dearth of adequate experimental data, two independent procedures for solution are presented. Detailed quantitative results are obtained for the angular dependence of the cross section, and also for the mean cross section, of randomly‐oriented wires or, more generally, of metallic strips, which behave electromagnetically like cylindrical wires of a certain ``equivalent radius.'' When expressed in terms of a unit of area equal to the square of the wave‐length, these cross sections depend on the dimensions of the wire only through the two ratios 2la=length of wireequivalent radius of wire, 2lλ=length of wirewave−length. >The mean cross section is shown to take on maximum values when 4l/λ is slightly less than a...
TL;DR: In this article, the theory of the scattering of x-rays at small angles is given for a continuous distribution in size of randomly spaced and oriented spheroidal particles having arbitrary, but fixed, shape.
Abstract: The theory of the scattering of x‐rays at small angles is given for a continuous distribution in size of randomly spaced and oriented spheroidal particles having arbitrary, but fixed, shape. Families of scattering curves are presented for spheres, and for spheroids ranging in shape from flat disks to long rods. Both Maxwellian and rectangular types of particle mass distribution are used. A fit between the experimental and a calculated scattering curve enables one, under favorable circumstances, to determine the mass distribution in the test sample. However, an unambiguous interpretation of the experimental scattering curve on the basis of the small angle scattering theory is not possible without additional evidence from independent investigations of such quantities as particle shape and sample specific surface.
TL;DR: A significant change in mean particle size and shape characteristics of carbon black due to specimen contamination while under examination in electron microscopes is reported in this paper, and the effect is observed in other materials but is more pronounced in carbon black.
Abstract: A significant change is reported in mean particle size and shape characteristics of carbon black due to specimen contamination while under examination in electron microscopes. The effect is described for a number of well‐known commercial blacks and examples are given in graphical form to illustrate expected variations in mean particle size with continued bombardment at normal focusing intensities. The effect is observed in other materials but is more pronounced in carbon black. Suggestions are made for minimizing the effect.
TL;DR: In this paper, the authors presented an approximate solution from which numerical results can be obtained with ease, and a comparison of the experimentally determined concentrations with those deduced from theory should yield molecular weights without waiting for equilibrium.
Abstract: In determining molecular weights with the ultracentrifuge by the equilibrium method, it is necessary to drive the rotor at relatively high speeds for very long periods of time It would be a real advantage to be able to deduce molecular weights from the distribution of concentration within a cell placed in a rotor without waiting for equilibrium The solution of a certain differential equation gives the theoretical distribution within the cell at any time, and a comparison of the experimentally determined concentrations with those deduced from theory should yield molecular weights without waiting for equilibrium The exact solution of this differential equation is known, but it is not suitable for numerical work The present paper presents an approximate solution from which numerical results can be obtained with ease
TL;DR: The properties of circular wave guides loaded with apertured disks are discussed both qualitatively and quantitatively in this paper, where the wave and group velocities, attenuation, and power flow are investigated.
Abstract: The properties of circular wave guides loaded with apertured disks are discussed both qualitatively and quantitatively. Formulae and curves are given for various quantities including the wave and group velocities, the attenuation, and the power flow.
TL;DR: The cathode-ray oscilloscope is usually regarded as a means for displaying data in one or two variables as a function of time as discussed by the authors, and it is possible to present three variable electrical data in the form of isometric or other conventional projections or as true perspective drawings.
Abstract: The cathode‐ray oscilloscope is usually regarded as a means for displaying data in one or two variables as a function of time. By means of simple transformations which are easily performed electrically, it is possible to present three variable electrical data in the form of isometric or other conventional projections or as true perspective drawings. It is further possible to change the observer's viewpoint in the presentation coordinate system at will by turning range, elevation, and azimuth controls.A more elaborate but similar set of transformations permits presentation of separate pictures to the two eyes. These pictures are optically superimposed but differ in such a way as to yield stereoscopically correct perspective pictures. These pictures are fully acceptable to the eye as patterns in space.
TL;DR: In this paper, a theory connecting the stress, f, required to break a brittle material in simple tension, with its duration of application, t, was proposed, where the slow process preceding fracture was shown to be the orientation of the atomic network contained in an elementary prism of length r=λ 0E/f, where E is Young's modulus and λ 0 is the critical elongation required for fracture.
Abstract: A theory is proposed which connects the stress, f, required to break a brittle material in simple tension, with its duration of application, t. The slow process preceding fracture is shown to be the orientation of the atomic network contained in an elementary prism of length r=λ0E/f, where E is Young's modulus and λ0 is the critical elongation required for fracture. The rate‐controlling factor is the activation energy, Eα/f, for the orientation or rearrangement of the atomic network under the stress, f. Moisture on glass, and moisture plus oxygen on certain metals, are important catalytic or fatigue‐promoting factors because they reduce the unit activation energy, α. The theory leads to the equations t=(1/k0)eEα/fkT and logt=−logk0+(Eα/2.3kT)/f, where t is the time for fracture (duration of the stress), k is the Boltzmann constant, T the absolute temperature, and α and k0 are experimentally determined constants. The logarithmic expression has the same form as the Glathart‐Preston [J. App. Phys. 17, 189 (1...
TL;DR: In this article, the transmission loss in a long waveguide and the Q's of resonant cavities were measured at 1.25 cm for a number of metals and showed that deviations from d.c. conductivity are due to surface roughness.
Abstract: Methods of measuring effective conductivities at microwave frequencies are described. These consist of either measuring the transmission loss in a long waveguide, or in measuring the Q's of resonant cavities. Both methods have been applied to measurements at 1.25 cm. Results for a number of metals are presented. Deviations from d.c. conductivity are thought to be due to surface roughness.
TL;DR: The absolute energy of the light from a fluorescent calcium tungstate x-ray screen, its spectral distribution, and the efficiency of conversion from x-rays to light have been determined as discussed by the authors.
Abstract: The absolute energy of the light from a fluorescent calcium tungstate x‐ray screen, its spectral distribution, and the efficiency of conversion from x‐rays to light have been determined. The absolute energy and its spectral distribution were obtained spectrographically by comparison with a standard tungsten filament lamp. Equations are given for determining the distribution of light in the diffusing screen material, and calculation of the light losses are made for varying screen thickness and x‐ray absorption. The data for energy distribution of the ingoing x‐rays were taken from measurements obtained in this laboratory by a new method to be published elsewhere. Allowance for scattering and secondary x‐radiation was made and a conversion efficiency of 5.0 percent was obtained for this calcium tungstate phosphor.
TL;DR: In this article, synthetic manganese-activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation.
Abstract: Synthetic manganese‐activated calcites are shown to be practically inert to ultraviolet excitation in the range 2000–3500A, while they are luminescent under cathode‐ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural calcites is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave‐length ultraviolet‐excited luminescence of all natural calcites to the action of an auxiliary impurity. The essential identity of the cathode‐ray excited luminescence spectra of CaCO3:Mn, CaCO3: (...
TL;DR: In this paper, an equation for the steady-state rate of creep of pure annealed polycrystalline metals is derived through dislocation theory and the theory of rate processes.
Abstract: An equation for the steady‐state rate of creep of pure annealed polycrystalline metals is derived through dislocation theory and the theory of rate processes The rate of generation of dislocations is shown to be the rate‐determining process A specific mechanism for the generation of a dislocation is presented, from which the heat and entropy of activation of the process are expressed in terms of physical constants of the material In addition the lowering under stress of the potential energy barrier, which yields the stress‐dependent term, is given in terms of constants of the material and a ``back‐stress'' term The creep equation thus obtained is found to be in good agreement with data in the literature
TL;DR: In this article, a variable capacitor is described for measuring small displacements, small volume changes, and pressure differences, which can be used for displacement measurements, either by a point contact from a mechanical link to the observed system, or by a uniform pressure load from a fluid link.
Abstract: A variable capacitor is described for measuring (1) small displacements, (2) small volume changes, and (3) pressure differences. The capacitor consists of a deflectable diaphragm and a fixed electrode. The diaphragm is metallic, plane‐parallel, clamped at the edges, and at ground potential; the electrode, at an a.c. potential, has a plane surface parallel to the undeflected plate across an air gap. For use in displacement measurements, the diaphragm's center is deflected by a point contact from a mechanical link to the observed system, or by a uniform pressure load from a fluid link to the system. The fluid link is used also when measuring volume changes and pressure differences. The plate deflection results in a change in the air gap, and thus generates a capacitance signal. This signal is measured by electrical methods.A theoretical analysis of this variable capacitor is presented; sensitivity and alinearity factors for the three uses of the device are derived. The experimental performance shows reasona...
TL;DR: In this article, the preparation, heat treatment, and properties of supermalloy, a magnetic alloy of iron, nickel, and molybdenum, were described.
Abstract: This paper describes the preparation, heat treatment, and properties of supermalloy, a magnetic alloy of iron, nickel, and molybdenum In the form of 0014 in sheet it has an initial permeability of 50,000 to 150,000, a maximum permeability of 600,000 to 1,200,000, coercive force of 0002 to 0005 oersted, and a hysteresis loss of less than 5 ergs/cm3/cycle at B=5000 Transformer cores made of insulated 0001 in tape, spirally wound, have about the same initial permeability and a maximum permeability of 200,000 to 400,000 The alloy has a Curie point of 400°C and appears to have an order‐disorder transformation temperature somewhat above 500°C