bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Noise Observation Using a Photoconductive Pickup Tube
Authors: Cope A. D. , Rose A.
Published: April 2005

A television pickup tube arrangement using a Vidicon for the direct recording of x-ray images is described. The transmitted x-ray picture shows noise characteristics that are clearly those of the absorbed x-ray photons. The internal conversion gain (number of carriers generated per absorbed x-ray photon) is estimated by two independent methods, one of which is based on a measurement of x-ray noise. Both methods give a gain of about 500 for a 100 kv x-ray photon. The agreement between the two methods is evidence for the validity of the simple electron-multiplier model for the noise current in the photoconductive selenium target. The appearance of x-ray noise means that all the information contained in the absorbed fraction of the x-ray beam is being transmitted. Thirty pictures per second are transmitted when irradiating the Vidicon with a 5 ma, 100 kv x-ray beam at a distance of two feet. Wires of one mil diameter were clearly observable.
On the Focusing of High-Current Electron Beams
Authors: Brewer George R.
Published: April 2005

The focusing of high-current electron beams by means of a system of periodically spaced magnetic lenses has been studied. The trajectories of the electrons under the influence of magnetic and space charge forces have been obtained by the use of an analog computer. Graphs have been prepared which permit the design of a lens focusing system for given values of current, voltage, and beam diameter. The solutions are obtained for the Glaser magnetic lens with longitudinal field variation of the form Bz=B0(1+(z/a)2)[minus]1. The conditions of operation appropriate to the minimum chromatic aberration are obtained, and the entrance conditions to the lens system discussed.
Solution of Nonlinear Differential Equations by the Reversion Method through the First Thirteen Terms
Authors: Cohn George I. , Saltzberg Bernard
Published: April 2005

By the use of the reversion method, certain types of ordinary nonlinear differential equations can be reduced to a set of ordinary linear differential equations which may be conveniently solved by the Laplace transform. The first thirteen equations of this reduced set are tabulated in this paper.
Distortion of a Crystal by Point Imperfections
Authors: Eshelby J. D.
Published: April 2005

The expression u=cr/r3, (where c is a constant) sometimes assumed for the displacement around a point imperfection (interstitial or substitutional impurity, lattice vacancy) gives a nonzero stress at the surface of the solid. The additional ``image displacement'' necessary to insure that this stress vanishes is usually neglected, but may be important. For example, it accounts for from 30 to 50 percent of the volume change produced by such defects. This and other effects of the image term are discussed. Miller and Russel have pointed out that for a point imperfection near the center of a sphere the apparent volume change deduced from measurements of the x-ray lattice constant is greater than the geometrical volume change. It is shown that the reverse is true when the defect is near the surface, and that for a large number of defects scattered uniformly through the sphere the geometrical and x-ray expansions are equal. It can be shown quite generally that a body of arbitrary shape is expanded uniformly by a statistically uniform distribution of point imperfections, and that the x-ray diffraction pattern is altered in the way to be expected for such an expansion. To establish this, however, it is essential to take the image terms into account.
Potential Distribution and Prevention of a Space-Charge-Induced Minimum Between a Plane Secondary Electron Emitter and Parallel Control Grid
Authors: Sponsler George C.
Published: April 2005

Formulas are developed which define the profile of the electrostatic potential distribution in the semi-infinite, space-charge-filled region between a plane emitter of secondary electrons and a parallel retarding-field control grid. The calculation assumes a known secondary-electron energy distribution and a cosine angular distribution. In practical application, the formulas must be evaluated numerically or graphically since the energy distribution cannot be expressed analytically except over limited regions. A method of determining the critical spacing between electrodes which will prevent formation of a space-charge-induced minimum in the potential distribution between the emitter and control grid is presented.
Approximations in Linear Viscoelasticity Theory: Delta Function Approximations
Authors: Leaderman Herbert
Published: April 2005

The relationships between certain approximations that have been proposed recently in connection with the linear viscoelastic behavior of noncrosslinked amorphous polymers are discussed. The approximations reviewed here are applicable with slight modifications to other types of linear response, for example, dielectric behavior.
16 Percent Aluminum-Iron Alloy Cold Rolled in the Order-Disorder Temperature Range
Authors: Nachman Joseph F. , Buehler William J.
Published: April 2005

The methods of fabricating 16 percent Al-Fe from cast slab to thin-gauge sheet are described in some detail. The melting, casting, homogenizing, hot rolling, and cold rolling at 575°C and room temperature are described. Particular attention is focused upon the 575°C cold rolling from the standpoint of the possible beneficial effects derived from an ordering reaction which occurs in this alloy. The technique of cold reduction from 0.007 in. to 0.0005 in. at room temperature is discussed.

Magnetic data on a limited number of heat-treated laminated cores are given. Useful physical properties, other than magnetic, of previous limited interest because of the inability to fabricate the alloy into ductile strong thin sheets, are discussed. These properties include excellent oxidation resistance at high temperatures, good wet-corrosion resistance to certain chemical solutions, and high electrical resistivity.
Apparent Density of Thin Evaporated Films
Authors: Blois M. S. , Rieser L. M.
Published: April 2005

Measurements of the apparent densities of copper and silver films formed by evaporation are described. The interpretation of the results and the manifestations of low apparant densities in physical experiments are discussed.
Noise in Semiconductors: Spectrum of a Two-Parameter Random Signal
Authors: Machlup Stefan
Published: April 2005

With intended application to the theory of current noise in semiconductors, the spectrum is calculated of a random signal which may be in one of two states (YES-NO: random telegraph signal), where the mean lives σ and τ of the two states may be different. The form of the spectrum is the same as for the case with equal lives, the single parameter τ for that (classical) case now being replaced by 2[(1/σ)+(1/τ)]−1; i.e., the rates of transition are additive.
Experimental Study of Low-Frequency Effects on the Dynamic Modulus of a Buna-N Rubber
Authors: Hutton Allen Q. , Nolle A. W.
Published: April 2005

The linear dynamic Young's modulus of a vulcanized Buna-N gum rubber is measured at frequencies of 0.05, 0.10, and 1.00 cps, in the temperature range −22°C to 30°C, by a method in which a small differential sinusoidal elongation is superimposed on a 5 percent static elongation. The width of the dispersion range on the temperature scale (the range in which the logarithm of the modulus increases steeply with decreasing temperature) is only about 10°C, as contrasted with widths as great as 25°C found in previous measurements on a similar compound at frequencies of several kilocycles. The modulus-temperature plot shifts upward by only about 4°C per decade of frequency increase in the present range, as contrasted with about 10°C per decade in the previous measurements at higher frequencies. It is concluded that this elastomer cannot be described properly by means of the ``method of reduced variables,'' in which the dynamic properties are ascribed to mechanisms having identical temperature dependence, and that the low-temperature behavior is governed by mechanisms distinct from those effective in the audio-frequency range at room temperature.
On the Electric Strengths of Aliphatic Hydrocarbons
Authors: Crowe R. W. , Bragg J. K. , Sharbaugh A. H.
Published: April 2005

Paschen's similarity law, which expresses a certain relationship between the breakdown voltage of a gas, the gas pressure, and the distance between electrodes, is known to fail at high pressures. This is owing, at least in part, to a change in the way in which electrons dissipate energy to the gas molecules. At high enough pressure, the electron transfers energy principally to molecular vibrations. In condensed phases this vibrational barrier is dominant, and one should expect a new kind of similarity law to hold under certain controlled conditions. The liquid aliphatic hydrocarbons provide an illustration of such a law. The electric strengths of nine hydrocarbons of various densities were measured and found to depend linearly upon density. It has also been found that the temperature dependence of the electric strength of a liquid aliphatic hydrocarbon can be accounted for by the change in density of the liquid due to thermal expansion.
Electromagnetic Velometry. II. Elimination of the Effects of Induced Currents in Explorations of the Velocity Distribution in Axially Symmetrical Flow
Authors: Kolin Alexander , Reiche Fritz
Published: April 2005

The distribution of electrical potential in a conduit carrying an axially symmetrical flow through an homogeneous magnetic field, which is perpendicular to the flow, is analyzed. It is shown that it is possible to eliminate the difficulties arising from induced currents in electromagnetic determinations of the velocity distribution by measuring the potential gradient ∂ψ/∂y (y being ⊥H and ⊥v) along a diameter bisecting the angle between the H axis and the Y axis. The knowledge of the distribution of (∂ψ/∂y)45° at a known discharge through the conduit determines the velocity distribution v=f(r).
Determination of the Resultant Dipole of the Heart from Measurements on the Body Surface
Authors: Gabor D. , Nelson C. V.
Published: April 2005

By means of the vector calculus, it is proved that the magnitude, orientation, and location of the resultant dipole of a system of sources and sinks inside a finite volume conductor is given by an integration over the bounding surface. The method is applied to finding the ``heart vector,'' or the resultant dipole moment of the human heart. The theory was checked in two- and three-dimensional electrolytic tank models of the human thorax.
The Secondary Electron Resonance Mechanism of Low-Pressure High-Frequency Gas Breakdown
Authors: Hatch Albert J. , Williams H. Bartel
Published: April 2005

Breakdown field strengths have been measured in air and hydrogen at pressures of the order of 1 micron Hg and frequencies from 25 to 90 Mc/sec between flat metal electrodes at separations from 1 to 4 cm. By suddenly applying a high voltage and then lowering it slowly an upper breakdown curve has been observed. This new curve can be combined with the lower breakdown curve and cut-off frequency such as reported previously by the Guttons, and by Gill and von Engel to form the boundaries of a breakdown region in the frequency-field strength domain.

The simple secondary electron resonance theories developed by Danielsson and Gill and von Engel have been extended by the semi-empirical determination of minimum and maximum limiting values of the electron-emission phase angle, a minimum limiting value of electron arrival energy, and a ratio between electron arrival and emission velocities.
Dynamics of Corona Discharge between Cylindrical Electrodes
Authors: Colli L. , Facchini U. , Gatti E. , Persano A.
Published: April 2005

The qualitative explanation by Loeb of the constancy of the amplification factor with increasing corona currents with coaxial cylindrical electrodes used, as in conventional Geiger counters, is placed on a quantitative basis. As anticipated, it is shown that it is the screening action of the space charge which is responsible for the constancy and the stability of the average discharge current. The fluctuations superposed on the constant current, previously reported by us, are explained as a response of the system having a definite resonance frequency to the statistical fluctuations of the photoelectric current. The theoretical predictions are confirmed by experimental data.
Studies on the Creep Recovery and Annealing of Zinc Single Crystals
Authors: Tanenbaum M. , Kauzmann W.
Published: April 2005

Part I is a description of some of the factors involved in the recovery by pure zinc single crystals at 35°C of the ability to creep following plastic deformation. The following observations were made: (1) Complete recovery of the ability to show an initial instantaneous plastic extension occurs much less readily than recovery of the ability to show transient creep. (2) Once the quasi-viscous creep stage is reached no recovery of transient creep occurs when the load is partially or completely removed for two minutes, but removal of only 6 percent of the load for 100 minutes permits partial recovery of transient creep at the full load. A 300 minute ``rest'' at 91.5 percent of the full load resulted in complete recovery of the transient creep at full load, even though creep occurred at the reduced stress. (3) The recovery of quasi-viscous creep at a reduced stress after exposure to a higher stress was also investigated. The recovery was slower, the larger the initial load. (4) The rate of the time-dependent contraction of zinc crystals on removal of the load probably follows a power law in the time. There is also an instantaneous nonelastic contraction which is about ten times larger than the elastic contraction.

These results show that the role of thermal fluctuations in activating the units of flow is very different from the role of the stress. The applications of the Eyring rate equation to quasi-viscous creep which have been made in the past are, therefore, not valid. A variable activation energy must be postulated in order to account for the kinetics of creep and recovery. These results are interpreted in terms of the dislocation theory of plastic flow.

In Part II a phenomenon is described in which pure zinc single crystals are consistently found to become temporarily hardened by annealing in vacuum above 200–260°C. The hardness thus introduced can be removed by straining the crystal and then allowing it to stand at temperatures below 200°C. The crystal is in this way returned to its normal plastic state. The hardening is not removed by electropolishing the crystal, so is not a surface phenomenon. Though similar to Orowan's thermal hardening effect, it differs by requiring a much higher temperature and by not requiring the addition of impurities.
Growth of a Vapor Bubble in a Superheated Liquid
Authors: Forster H. K. , Zuber N.
Published: April 2005

The integro-differential equation for the growth of a vapor bubble in a superheated liquid is formulated and discussed. It is shown that two distinct time domains exist: one, of the order of 10−4 second, during which the effect of the hydrodynamic forces may be an important factor in the growth of the bubble, and another, during which this effect is unimportant. An integral equation is formulated for the latter domain. A solution of the problem, in closed form, valid for the entire interval of interest is presented; it agrees very well with experimental data for various superheats.
The Necking of a Tension Specimen in Plane Plastic Flow
Authors: Onat E. T. , Prager W.
Published: April 2005

A linearized version of the equations of plasticity is used to discuss the symmetrical necking of a tension specimen in plane plastic flow. The material is treated as perfectly plastic, and elastic strains are neglected.
Contact Charging Between a Borosilicate Glass and Nickel
Authors: Peterson John W.
Published: April 2005

The charging of borosilicate glass spheres rolling on clean nickel has been studied under controlled conditions of cleanliness, humidity, and gas pressure. Strong evidence indicates the process of charge transfer to be a type of contact electrification akin to that operating between two metals. The observed charging is, however, influenced by other factors. The amount of charge acquired increases with surface areas in contact and hence with distance rolled until other factors intervene. The rate of charging depends on rolling speed and surface conductivity of the borosilicate glass, while the maximum equilibrium charge depends on the pressure of the ambient gas. The gas pressure effect is shown to be caused by electrical discharge of the highly charged sections of the borosilicate glass to the metal, as suggested by E. W. B. Gill, and this causes a minimum equilibrium charge to occur about 1 mm air pressure, as observed by D. E. Debeau. The effect of transverse electrical fields reported by E. W. B. Gill and G. F. Alfrey is negligible for low surface conductivity but becomes important at higher surface conductivity, in particular above 40 percent relative humidity at 20°C.
Circumferential Gap in a Circular Wave Guide Excited by a Dominant Circular-Electric Wave
Authors: Sheingold Leonard S. , Storer James E.
Published: April 2005

The scattering matrix of a 360-degree circumferential slot in an infinitely long circular wave guide with an incident dominant circular-electric wave is obtained by a variational principle. The theory which should by very good for small gaps is shown to be in good agreement with the obtained experimental results.
Impedance of a Top-Loaded Antenna of Arbitrary Length over a Circular Grounded Screen
Authors: Wait James R. , Surtees Walter J.
Published: April 2005

The problem of a vertical monopole situated over a circular perfectly conducting screen lying on a finitely conducting ground is considered. An approximate method employed originally by Abbott to calculate the self-impedance is discussed. Using this formula explicit expressions are derived for the self-impedance of a thin, top-loaded vertical monopole. Sinusoidal current distribution is assumed.
Tube Noise under Large Transit-Time Conditions
Authors: Yadavalli S. V.
Published: April 2005

That the noise convection current in a diode would be the same as the noise current in a triode under the conditions θ1≫1 and θ2≪1 (θ1 and θ2 are transit angles in radians of the potential minimum-to-grid and grid-to-plate regions, respectively) is shown by following the approach indicated by Rack and applying the Llewellyn-Peterson small signal theory to study the noise in a triode. Although the general trend of the experimental results agrees very well with the prediction from the Rack approach, the measured value of noise power is found to be about 2 db below the predicted value. The experimental results are applicable to triodes as well under certain conditions.
Diffusion in Bimetal Vapor-Solid Couples
Authors: Balluffi R. W. , Seigle L. L.
Published: April 2005

The intrinsic diffusivities of individual components in several binary systems have been determined with vapor-solid type diffusion couples. In this type of couple a high vapor-pressure component is diffused from the vapor phase into a slab of lower vapor pressure initially containing inert markers on its surface. Diffusivities may then be calculated from marker movement and diffusion-penetration curve data. Equations necessary for analysis of such couples are developed.

The alpha brass, copper-nickel, and silver-gold systems were investigated. Observations of polygonization during diffusion and dimensional changes normal to the diffusion direction were also made. Porosity formation, which occurred only in the vapor-solid silver-gold couples, was investigated in detail and was compared to porosity formation in corresponding sandwich couples. The general use and limitations of such couples in diffusion studies are discussed.
Propagation of Microwaves between a Parallel Pair of Doubly Curved Conducting Surfaces
Authors: Kunz K. S.
Published: April 2005

Microwaves propagated between two doubly-curved parallel conducting surfaces, in the geometrical optics approximation, follow rays obeying Fermat's principle. The optical distance in this case is determined both by the index of refraction of the material between the surfaces and by the curvature of the surfaces. The focusing properties of such a parallel plate lens is fully specified by giving the metric of the two-dimensional optical space associated with the mean surface of the guide. A family of equivalent lenses is shown to exist, and formulas are obtained that permit one to go from any one of these lenses to any other. Furthermore, conditions are given for there to exist in a family of equivalent lenses a lens employing a unit index of refraction everywhere. Of particular interest is the demonstration that the Rinehart analog of the Luneberg lens and the RCA ``R-2R'' lens are members of a two-parameter family of lenses with analogous focusing properties.
Approximate Emissivity Calculations for Polyatomic Molecules. I. CO2
Authors: Penner S. S.
Published: April 2005

Approximate emissivity calculations for CO2 have been carried out, as a function of optical density, at 300 and at 600°K. The calculations involve the assumption that the rotational lines overlap extensively. This condition appears to be satisfied at total pressures above about 1 atmos. Comparison of the values calculated from spectroscopic data with the emissivities tabulated by Hottel and his collaborators shows satisfactory agreement. The analysis presented in this manuscript emphasizes the fact that it is possible to obtain reasonable estimates for the engineering emissivity without performing extensive analytical work, provided the physical principles are understood and the needed spectroscopic data are available.
Cross Section of Pulled Crystals
Authors: Pohl Robert G.
Published: April 2005

An equation for the radius of a crystal grown by the Czochralski technique is derived by considering the mechanical and thermal equilibrium at the liquid-solid interface. The results agree qualitatively with experimentally known functional dependencies.
Relativistic Dynamics of a Charged Particle in Crossed Magnetic and Electric Fields with Application to the Planar Magnetron
Authors: Gold Louis
Published: April 2005

Complete characterization of planar magnetron behavior is achieved for intermediate relativistic energies where radiation loss is of no serious consequence. The cut-off condition in the neighborhood of the rest energy of the particle shows a linear dependency on the product of electrode separation and magnetic field LH rather than the classical (LH)2. The modified period assumes a particularly simple form (2π/ω[1/(1−γ2)3/2], γ being the ratio of electric and magnetic fields which reflects a voltage dependency of the period not encountered in the classical case.

A parametric solution for the periodic orbits is derived on the basis of a transformation related to the delineation of the velocity space and, as such, represents a new variety of transcendental curve which degenerates into the cycloid for the limiting case of γ→0.

The spatial-time dependent mass, momenta, and energy relations take on especially straightforward forms in terms of the trajectory parametric solution.
Sputtering at Low Ion Velocities
Authors: Wehner Gottfried , Medicus Gustav
Published: April 2005

Low sputtering rates are measured by means of the probe technique in a plasma. The displacement of the probe curve along the voltage axis (and its change in shape) when the probe is covered with a material of different work function, sputtered from a sputtering electrode, is a dependable measure for the thickness of the sputtered layer. The method is very sensitive, generally applicable, and was applied especially to answer the question of a threshold voltage U0 for sputtering. The sputtering rate for Pt in Xe, in the region of low ion energies (50<Us<200 ev) is roughly proportional to (Us−U0)2 with U0=40 ev.
Kinetics of the Circulating-Fuel Nuclear Reactor
Authors: Ergen William Krasny
Published: April 2005

In a circulating-fuel reactor, the circulation of the fuel causes a damping of power oscillations of the reactor. This is demonstrated under the assumption that there is no mechanical vibration coupled with the oscillation of reactor power, and that the shape of the hydrodynamic flow does not vary with time.
Electromagnetic Field of a Dipole Source above a Grounded Dielectric Slab
Authors: Lo Y. T.
Published: April 2005

A theoretical investigation of the electromagnetic waves due to a dipole source above a grounded dielectric slab has been made by integral transforms. The solutions in integral form have been evaluated asymptotically for distant field. It is found that the fields consist of a space wave and a surface wave. The former, spherical in nature, predominates in the free space, while the latter, cylindrical in nature and with a finite number of modes, is guided along the dielectric. As a result of the existence of at least one pole of the integrand, this surface wave always exists. At the dielectric surface, the zero-order spherical wave has a null value except the case of critical thickness; then it should be referred to the next-order solution.
Hardness Plateaus and Twinning in Explosively Loaded Mild Steel
Authors: Pearson John , Rinehart John S.
Published: April 2005

Hardness measurements were made along radii of circular cross sections of an annealed thick-walled low-carbon steel cylinder internally loaded with an explosive charge. The degree of work-hardening in the cylinder wall was found to decrease nonuniformly with an increase in distance from the surface in contact with the explosive. Each hardness versus distance curve exhibited a series of plateaus along which the hardness remained constant. The plateaus appear to be related to Neumann bands which are present in the steel. The maximum number of twin directions in a single grain increases with the magnitude of the stress. The presence of the hardness plateaus and the increase in the number of twin directions with hardness and stress level point to the existence of critical stresses for twinning.
The Helix as a Backward-Wave Circuit Structure
Authors: Watkins D. A. , Ash E. A.
Published: April 2005

The impedance Em2/2βm2P of the backward wave on helical structures is considered from the point of view of the design of backward-wave oscillators. Curves of impedance versus ka (circumference to free-space wavelength ratio) for single and bifilar helices are presented. Both the case of thin tape and that of round wire are treated. The impedance curves are calculated on the basis of an approximation to the actual distribution of rf current over the surface of the conductors; the use of this approximation is justified by comparison with an exact solution at specific values of ka. A proof is presented which demonstrates that the backward-wave impedances of two tape helices are identical if the gap width of one is equal to the tape width of the other. Expressions are derived for effects of dielectric supports upon the velocity and impedance of the backward wave.
Semiconducting Films of Antimony
Authors: Cohen Julius
Published: April 2005

Thin films of antimony were condensed onto substrates at various temperatures. Films deposited at liquid oxygen temperatures showed large negative temperature coefficients of resistance. In general, reversible resistance changes occurred if the films were cooled below a temperature previously reached; irreversible changes took place if the films were heated above that at which they were prepared. Activation energies were calculated from logR vs 1/T curves and gave values of ∼0.07 ev for low temperatures and ∼0.13 ev for high temperatures. There appeared to be little or no influence of evaporation rate or thickness on the activation energies. A theory based on lattice defects is proposed in order to explain the electrical behavior of the films.
Molecular Structure and the Crystallinity of Long-Chain Polymers
Authors: Bunn C. W.
Published: April 2005

The molecular characteristics which determine whether a long-chain polymer will crystallize at all—and if so, how readily—are considered. The criterion for crystallization is geometrical regularity of molecular structure; but absolute regularity is not essential, for certain copolymers, as well as certain homopolymers with geometrically irregular structures, do crystallize; the requirement is that the different units which indiscriminately occupy corresponding positions in the structure must be not too different in size and shape (as in monomeric ``mixed crystals''); an approximation to regularity is sufficient.

It is unlikely that quite regular molecules can be incapable of crystallizing; when such substances are reported as noncrystalline, it is more likely that they crystallize only with difficulty, and the right conditions have not been found. Reluctance to crystallize is associated with a small interval between relaxation transition (``second-order transition'') and melting points; this interval appears to be influenced by the general shape of the molecule (though shape is not the only factor). The temperature range within which crystallization proceeds at an appreciable rate may be still further restricted if the chain repeat distance of the molecules is long; and this same factor may make crystallization at any temperature very slow.
Crystallization Kinetics in High Polymers. I. Bulk Polymers
Authors: Mandelkern Leo , Quinn Fred A. , Flory Paul J.
Published: April 2005

The rates of crystallization of five polymers, poly-(ethylene oxide), poly-(decamethylene adipate), and three poly-(N,N′-sebacoyl piperazine)'s differing in molecular weight, have been observed dilatometrically at various temperatures ranging from 5.5 to 24° below the respective melting points Tm. The crystallization isotherms are remarkably reproducible, and the previous thermal history above the melting point is without effect provided that melting is completed before the crystallization experiment is begun. The crystallization isotherms display induction periods. The very large temperature coefficients observed are uniform throughout the crystallization process, i.e., isotherms at different temperatures are superimposable by rescaling the time. It is inferred from this and other evidence that steady-state nucleation and growth occur simultaneously throughout the process. The results are satisfactorily interpreted by applying conventional nucleation theory and assuming that nuclei grow at rates proportional to their surface areas. The treatment resembles that applied to crystallization in metals. Spherical and disk-shaped nuclei are considered, but the data do not discriminate between them. An extension of the theory accounts for the maximum commonly observed in the crystallization rate as the temperature is decreased below the range of the present measurements.
X-Ray and Infrared Studies on the Extent of Crystallization of Polymers
Authors: Nichols J. B.
Published: April 2005

The current x-ray and infrared techniques for estimation of the crystalline-amorphous ratio in polymers are surveyed. Representative data are assembled for some of the common crystallizing polymers. Advantages and limitations of the methods are pointed out.
Certain Transmission and Reflection Theorems
Authors: Twersky V.
Published: April 2005

The well-known relation between the total energy cross section of a scatterer and its forward scattered amplitude is extended to obtain an approximate transmission coefficient for a uniform planar distribution of parallel cylinders. An analogous reflection theorem for an arbitrary cylindrical boss on a perfectly reflecting plane is then derived; here the total cross ssction of the boss is related to the scattering amplitude in the specular direction of reflection of the plane. This is extended to obtain an approximate reflection coefficient for a uniform distribution of cylindrical bosses on a plane.
Information Theory and Uncertainty Principle
Authors: Brillouin L.
Published: April 2005

The methods of information theory are used in the discussion of observations under a microscope. Conclusions are similar to those obtained in a previous paper and exemplify again the difficulty of measuring extremely small distances. A comparison with the discussion of uncertainty relations shows that quantum uncertainties can be very much higher than the theoretical limit, especially when material screens or shutters are not being used and the observation is made on a free particle. This correction to uncertainty relations, however, does not introduce any change in the theory of quantized fields of Bohr and Rosenfeld.
Measurement of the Conductivity of a Jet Flame
Authors: Adler Fred P.
Published: April 2005

A method for the measurement of the complex conductivity of a rocket exhaust flame is described. Typical results are shown for an acid-aniline rocket motor and a frequency of 200 mc/sec. The importance of sodium impurities is pointed out and illustrated experimentally.
Contact Charging between Nonconductors and Metal
Authors: Peterson John W.
Published: April 2005

An investigation has been made of the charging of fused quartz and borosilicate glass spheres rolling on a clean nickel surface. The results indicate that the process of acquiring charge depends only upon the nature and surface condition of the materials in contact and is independent of the pressure of an atmosphere of dry N2. The total charge, however, is limited by gaseous discharge to the metal and therefore does depend upon the pressure. Such gaseous discharge has been verified by the observation of individual discharge pulses. The rate of acquiring charge and maximum charge in vacuum has been found to depend upon rolling speed, both reaching a maximum at an intermediate speed, and to decrease with increasing surface conductivity. Since both fused quartz and borosilicate glass charge negatively in contact with clean nickel, it is inferred that both have higher effective work functions than nickel. The surface conductivity of borosilicate glass has been found to be three of four orders of magnitude higher than that of quartz. Therefore, since the charging of the two materials is of the same order of magnitude, the effective work function of the glass appears to be considerably higher than that of fused quartz.
Instability of Liquid Surfaces and the Formation of Drops
Authors: Keller Joseph B. , Kolodner Ignace
Published: April 2005

The theory of Taylor instability is extended to take account of surface tension, and the most unstable mode is determined. The resulting theory is then used to estimate the size of drops which might be formed as a result of this instability.
Factors Determining the Permanent Magnet Properties of Single Crystals of Fe2NiAl
Authors: Nesbitt E. A. , Williams H. J. , Bozorth R. M.
Published: April 2005

It is shown that fine precipitated particles present in single crystals of Fe2NiAl are elongated and that the shape anisotropy of these particles is a major factor in determining the coercive force of Fe2NiAl. For fields of less than 7000 oersteds, 〈111〉 directions are the directions of easy magnetization in the (110) plane of the crystal; this is due to the effect of the shape of the precipitated particles, which are oriented in three mutually perpendicular directions. In higher fields, the torque due to this effect decreases and then the [001] direction is the direction of easy magnetization because of intrinsic crystal anisotropy. These conclusions are based on an analysis, and on measurements, of the torque on three mutually perpendicular rods of magnetic material. These rods simulate the preciptated particles in the actual crystal.
Short-Time Frequency Measurement of Narrow-Band Random Signals in the Presence of Wide-Band Noise
Authors: Schultheiss Peter M. , Wogrin Conrad A. , Zweig Felix
Published: April 2005

In certain applications it is necessary to measure the center frequency of a symmetrical power spectrum in the shortest possible time. Two instrumentations for short-time frequency measurement, the autocorrelator and the frequency discriminator, are examined for their ability to accomplish this task. The analysis compares the performance of the two systems and indicates the effect of such factors as signal-to-noise ratio and filter adjustment.
A Theorem Concerning Noise in Electron Streams
Authors: Pierce J. R.
Published: April 2005

It is proposed that if Imax and Imin are the maximum and minimum noise currents in a noise standing wave on an electron stream, then the product of their magnitudes cannot be smaller than |Imax||Imin|=αeI0B(ωωq)(kTceV0). Various assumptions lead to a factor α ranging between 0.8 and 1. I0 is beam current, B is band width, ω is frequency, ωq is effective plasma frequency, Tc is cathode temperature, and V0 is the voltage specifying the velocity of the electrons.
Geometrical Acoustics. I. The Theory of Weak Shock Waves
Authors: Keller Joseph B.
Published: April 2005

In the first part the discontinuity conditions in an arbitrary continuous material are deduced for a general (i.e., possibly curved) discontinuity surface. It is then shown that only three types of discontinuities are possible—shocks, contact discontinuities, and phase-change fronts. In the second part the acoustic discontinuity conditions are deduced and specialized to a perfect fluid without heat conduction. Then a first-order partial differential equation is obtained for the location of an acoustic shock front. This equation can be solved, as in optics, by means of rays. The variation of shock strength along a ray is then determined (this is one main result of this paper). Coefficients of reflection and transmission for an acoustic shock at a contact discontinuity in the basic flow are also obtained. Finally, the results are exemplified by an analysis of the shock tube.
Transient Wave Analysis in a Linear Time-Dependent Material
Authors: Glauz R. D. , Lee E. H.
Published: April 2005

We consider a body which under stress exhibits an elastic, a viscous, and a retarded elastic response. For the particular case of a constant velocity applied at the end of a semi-infinite bar, the transient stresses, strains and velocities are found by the method of characteristics. From this solution can also be obtained the stresses for the case of a constant stress applied at the end of a semi-infinite bar. By superposition we can also solve problems involving finite bars. For a constant velocity applied at the end of the bar an integral expression is derived for the stress at that end as a function of time.
Thermionic Emission and Electron Diffraction from Thin Films of Barium Oxide
Authors: Russell Paul N. , Eisenstein A. S.
Published: April 2005

A high-vacuum, sealed-off glass, electron diffraction tube was developed for observing the physical structure of evaporated BaO films on a nickel substrate. Simultaneously, measurements of thermionic emission could be made. The thermionic activity of the deposited film increased until approximately 20 monolayers (measured using a radioactive tracer technique) had been laid down, and no further increase was found up to 50 monolayers. This emission density (0.4A/cm2 at 1000°K) is comparable with that obtainable from sprayed oxide coatings. With the receiver at less than 450°K the oxide film showed an amorphous structure. With the receiver at 800°K the film was crystalline and was believed to exist in clumps. This crystalline structure became amorphous if the films were heated to 1070°K and this form persisted as the oxide film was removed by evaporation. The relation of the thermionic emission from thin BaO films to that from sprayed oxide cathodes is discussed.
Experimental Procedures for Determining the Efficiency of Four-Terminal Networks
Authors: Mathis H. F.
Published: April 2005

Five experimental procedures which may be used for determining the efficiency of four-terminal networks, by means of circular loci plotted in the impedance or reflection coefficient planes, are presented.
On the Chromatic Field Aberration of the Magnetic Electron Lens in the Electron Microscope
Authors: Morito Nozomu
Published: April 2005

The chromatic field aberration of the magnetic lens in the electron microscope is theoretically studied.

Good results are obtained for the coefficient of the chromatic difference in magnification of the objective, taking into account the inclination of the principal illuminating rays. The same coefficient of the intermediate lens increases rapidly as the magnification is reduced by the intermediate lens. The calculated results agree well with experimental results.

Calculated results are given for the coefficients of chromatic difference in rotation of all lenses as well as for the coefficient of chromatic difference in magnification of the projection lens.
Statistical Hydrodynamics in Porous Media
Authors: Scheidegger Adrian E.
Published: April 2005

The statistics of disordered phenomena as exemplified by Einstein's theory of the Brownian motion is applied to the flow of fluids through porous media.

It is shown that such a statistical treatment of the hydrodynamics in porous media automatically explains some well-known phenomena in a more satisfactory manner than do capillaric models. The statistical theory leads to a differential equation of motion of the fluid which is a modification of that of Darcy; notably a new macroscopic quantity is introduced which is termed ``dispersivity.'' This quantity is indicative of the sideways dispersion which a stream of fluid undergoes when it is passing through the porous medium. Under certain statistical assumptions outlined in the paper, the dispersivity becomes a constant of the porous medium.

The new differential equation of motion of the fluid is discussed in detail and some indications about applications are given.
Composition of Apparent Shearing Forces During Shear Degradation of Polymers
Authors: Bestul A. B.
Published: April 2005

An investigation has been made of the degradation of Vistanex polyisobutenes having viscosity-average molecular weights from about 500 000 to 2 500 000 by shearing in solution in cetane at polymer concentrations from 5 to 20 weight percent, at nominal rates of shear from 9000 to 66 000 sec−1, and at temperatures from 20° to 80°C. The initial apparent shearing loads, observed at the beginning of the degradation process, vary in unexpected ways with variations in nominal rate of shear, temperature, concentration, and initial molecular weight of the polymer. In some cases the observed variations are opposite to those which would be expected on the basis of viscoelastic resistance to shearing. These results can be explained on the basis of the hypothesis that the observed apparent shearing forces include some contribution associated with the energy used up in breaking chemical bonds in the polymer molecules during the degradation process. If this hypothesis is correct, valid viscosity values cannot be obtained directly from observed apparent shearing forces in viscometry measurements under conditions where shear degradation occurs.
The Rheological Unit in Raw Elastomers
Authors: Mooney M. , Wolstenholme W. E.
Published: April 2005

Reasons are adduced for suspecting that in a raw elastomer subjected to continuous shear there exist groups of molecules which are held together by entanglement or by thixotropic attachments and move and rotate essentially as elastic solid bodies. Such coherent molecular groups are called rheological units.

If an elastomer in continuous shear consists essentially of closely-packed rheological units, such units, rolling on each other, will transfer a rubber soluble dye across the shear planes as the ink rollers transfer ink in a printing press. This predicted phenomena has been observed with a Mooney viscometer fitted with a smooth rotor, the face of which is covered with a thin film of dried cement containing a dye in high concentration. From the velocity of the color front a rough value can be computed for the mean diameter of the rheological units. The diameters for a series of different elastomers lie in the range from 1 to 35 microns.
Effect of Rheological Behavior on Thermal Stresses
Authors: Freudenthal Alfred M.
Published: April 2005

Since the conventional elastic analysis of thermal stress problems coupled with limiting creep rates and time-dependent fracture stresses as (inelastic) design criteria, results in design procedures for thermal stresses (in heat exchangers, nuclear reactors, flight structures at supersonic speeds, etc.) of considerable unreality, the effect of various types of rheological behavior (viscoelastic, plastic, work hardening) on the level of thermal stresses is analyzed under simplified assumptions, such as uniaxial stress and polar or cylindrical symmetry. The effect on the thermal stress intensity of the rheological behavior of the material is shown to be very significant, particularly with respect to stress relaxation and the development of residual stresses.
Internal Friction and Dynamic Modulus of Cold-Worked Metals
Authors: Nowick A. S.
Published: April 2005

The complexities of the internal friction and dynamic modulus of metals in the cold-worked condition may be understood reasonably well by separation of the phenomena into the following three distinct effects: (1) the ``nonlinear'' effect, characterized by strong amplitude dependence, frequency independence, and its disappearance after severe deformation; (2) the Köster effect, which shows rapid recovery after deformation, at temperatures well below the recrystallization temperature; (3) the ``viscosity'' effect, characterized by strong frequency and temperature dependence. The origin of each of these effects is briefly discussed from the point of view of dislocation theory.
The Rheology of Suspensions
Authors: Sweeny Keith H. , Geckler Richard D.
Published: April 2005

The rheological properties of concentrated suspensions of sized glass spheres in an equal-density medium has been investigated with the rotational viscosimeter. It has been found that the variation of fluidity with rate of shear can be expressed satisfactorily by a form of an expression suggested by Reiner relating the fluidity to the shearing stress, the fluidity at rest, and the fluidity at infinite shearing stress. It is also shown that values of the apparent fluidity are influenced by the time of shearing, the aging of the suspensions, and temperature effect attributed to the work of shearing.

The viscosity of suspensions of sized spheres at concentrations as great as 55 volume percent solids may be satisfactorily represented by either the relation of Mooney or of Maron, Madow, and Krieger; the identity of their relations is also shown. The constants for the equation relating viscosity and concentration are shown to be in satisfactory agreement with those predicted by Mooney. Constants for the viscosity-concentration equation are also given for several examples of experimental work selected from the literature; the form of equation proposed by Mooney relating viscosity and concentration is generally useful though the constants may not agree with the predicted values.

It has been found that the apparent fluidity of the glass bead suspensions decreases with an increase in particle diameter when the suspending fluid is zinc bromide in aqueous glycerol though the viscosity is independent of particle diameter when the suspending fluid is the nonaqueous mixture of ethylene tetrabromide and diethylene glycol.

The viscosity of a bimodal system of glass beads was shown to decrease very significantly as the bulk density was increased by packing progressively smaller spheres into the interstices of the larger spheres of the bimodal system, in qualitative agreement with a relation proposed by Mooney.