bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation of Diffraction and Transmission Experiments for X-Ray and Neutron Elastic Scattering
Authors: Keating D. T. , Antal J. J.
Published: April 2005

The correlation of a neutron cross-section plot in the cut-off region and a diffraction pattern has been considered. The cross section for elastic scattering by a sample as determined from transmission experiments has been related to its diffraction pattern. A cross-section plot can be transformed into a diffraction pattern by combining the cross section and its derivative. Examples of neutron cutoffs exhibiting strain and particle size broadening (carbonyl iron) and exhibiting particle size broadening alone (MgO) have been transformed. The patterns derived by the relation show good agreement with the x-ray diffraction patterns. Cross-section plots are sensitive to the state of crystalline perfection of the sample to the same degree as are diffraction patterns. Comparisons between the two should be made by performing the transformations given in the paper.
Dependence of the Coercive Force on the Density of Some Iron Oxide Powders
Authors: Morrish A. H. , Yu S. P.
Published: April 2005

An experimental investigation has been made of the dependence of the coercive force on the density of some magnetite and gamma ferric oxide powders consisting of different sized and shaped particles. Various aspects of the data are discussed. In particular, an interpretation based on a calculation of the critical single domain size of iron oxide particles with a prolate spheroidal shape is consistent with the experimental results.
Measurement of Excess Ba in Practical Oxide Coated Cathodes
Authors: Wooten L. A. , Moore George E. , Guldner W. G.
Published: April 2005

These papers, designated I and II, discuss measurements of excess Ba (and/or Sr) in practical oxide coated cathodes. More than 300 cathodes of various designs were prepared, aged for periods up to 50 000 hours, tested thermionically, and then analyzed chemically.

Despite its great importance, the accurate measurement of excess Ba in practical cathodes is a problem whose complexity has not been adequately realized. Although the methods of the present experiments avoided many difficulties, limitations still exist. The difficulties and limitations, as well as the capabilities, can best be discussed in terms of typical measurements; we emphasize this aspect in I.
Excess Ba Content of Practical Oxide Coated Cathodes and Thermionic Emission
Authors: Moore George E. , Wooten L. A. , Morrison J.
Published: April 2005

Using methods given in paper I, emission and Ba content are given on (a) 125 coated cathodes, (b) 15 coated filaments; H2 evolution by 19 uncoated cathodes was also measured. For analysis, each was isolated from the remainder of its tube. Coatings varied in composition from pure SrO to pure BaO and in density from 1 to 5 mg per cm2. Ba was also measured in cathode coatings removed from their support metal. Essentially all cathodes contained excess Ba, but no cathode structure gave any correlation between Ba content and emission.

These experiments contribute the following toward understanding practical oxide cathodes: If excess Ba (or Sr) is important, the significant amounts are probably less than one atom of Ba in 106 molecules of (BaSr)O. Because essentially all cathodes, including some with extremely low emission, contained at least this amount, we believe that performance is seldom limited by excess Ba. The concentration of Ba (or Sr) was not affected by using pure BaO or SrO coatings or Pt supports, although each of these steps led to very low emission; the highest emissions were obtained by operating at relatively low temperature during life, but this retained no more Ba in the coat. These major effects require interpretation.
Geometrical Acoustics. II. Diffraction, Reflection, and Refraction of a Weak Spherical or Cylindrical Shock at a Plane Interface
Authors: Friedrichs K. O. , Keller Joseph B.
Published: April 2005

The method of a previous paper is applied to the reflection and refraction of a weak spherical or cylindrical shock wave at a plane interface and by a plane slab. The method is also extended to apply to the diffracted wave which appears in these problems whenever total reflection occurs. From the results the leading terms in the asymptotic expansions for high frequency of the fields produced by periodic point or line sources over a plane interface are also obtained. These terms, which apply to electromagnetic as well as acoustic fields, are in exact agreement with results previously obtained by much more complicated methods.
Weak Detonations and Condensation Shocks
Authors: Heybey W. H. , Reed S. G.
Published: April 2005

The absence of weak detonations in available experience is felt to pose a problem since the well-known rapid condensation processes encountered in the flow of expanding gases have all the characteristics and present, in fact, examples of weak detonations. As such, they would suggest that the initiation mechanism producing weak detonations will have to be different from that commonly adopted for strong detonations. The physical aspects of rapid condensation processes are discussed and compared with the conditions obtained by Friedrichs for the existence of weak detonations.
On the Reflection of Shock Waves from an Open End of a Duct
Authors: Rudinger George
Published: April 2005

The readjustment of the mean exit pressure to its steady-flow equilibrium level, following the arrival of a shock wave at an open end of a duct, has been investigated. For a cylindrical duct in which the gas is initially at rest, a solution based on acoustic theory was obtained in the form of a Fourier integral. The nature of this solution was established as a series of damped harmonic oscillations superposed on an exponential pressure decay. The actual pressure decay curve was obtained by numerical integrations. The same problem was also attacked experimentally using a shock tube of 3.23 inches i.d. From pressure records taken some distance from the open end, the ``effective'' exit pressure was derived.

It was found that the exit pressure deviates appreciably from its steady-flow equilibrium value during a time in which a sound wave could travel about three duct diameters. Satisfactory agreement between theory and experiment was observed for shock pressure ratios up to about 1.9 (in air) although, near this limit, significant deviations owing to wall friction were observed toward the end of the pressure decay region. For still stronger shocks, the influence of the decay time on the phenomena inside the duct becomes unimportant while friction effects dominate. The possible significance of the lag in the establishment of steady-flow boundary conditions in practical applications is discussed, in particular, for cases where the acceleration of the gas by the reflected expansion wave may be of importance.
X-Ray Diffraction Studies of Crystallization in Elastomers
Authors: Alexander Leroy E. , Ohlberg Stanley , Taylor G. Russell
Published: April 2005

In general, extension of an elastomer results in a degree of preferred orientation of the molecular chains composing the amorphous phase. Therefore the amorphous fraction of a partially crystalline elastomer must be related to the integrated intensity of the amorphous diffraction halo rather than to the intensity at any one azimuth. A noteworthy exception is natural rubber, for which simple meridional measurements suffice.

A Geiger-counter apparatus with beam monitor and temperature-controlling accessories is described for making accurate measurements of the x-ray intensities scattered at any azimuth and at small or moderate Bragg angles. Measurements of crystallinity in natural rubber are in essential agreement with the findings of previous workers. When polybutadiene is extended at room temperature, molecular orientation occurs, but little if any crystallization. Measurements at lowered temperatures show that the crystalline fraction becomes appreciable at about 0°C and that it increases with further reduction in temperature and with increasing extension ratio. Preferred orientation of the crystalline regions in extended polybutadiene has been measured quantitatively with the object of providing jointly with birefringence measurements a value of the birefringence of a single crystal of polybutadiene.
Birefringence and Crystallization in Elastomers
Authors: Taylor G. Russell , Darin Stephen R.
Published: April 2005

The semitheoretical expression, fc=Δn0−csFΔnc0−cs,where fc=volume fraction crystalline, Δn0=observed birefringence, c=the stress-optical coefficient, s=the stress on actual cross section, F=a known function of crystallite orientation, and Δnc0=the birefringence of a single polymer crystal, is proposed for relating birefringence, stress, and degree of crystallinity in polycrystalline elastomers under tensile stress. This expression is shown to yield results in substantial agreement with x-ray results for the degree of crystallinity of 5°C polybutadiene when Δnc0=0.157. Birefringencedensity data on natural rubber (due to L. R. G. Treloar) are shown to be a special case of the foregoing expression, yielding a value Δnc0=0.218 for natural rubber which is in good agreement with the theoretical value for this quantity.
Friction of Teflon Sliding on Teflon
Authors: Flom D. G. , Porile N. T.
Published: April 2005

The low coefficient of friction for Teflon sliding on Teflon, as observed previously by others, has been found in this study to hold only if low sliding speeds and newly prepared surfaces are used. At high sliding speed, the nature of the surface is irreversibly changed such that subsequent sliding at low speed reveals a two- to threefold increase in the friction coefficient.

In addition to the effect of high speed sliding, there are reversible changes in the friction of Teflon on Teflon dependent in part on temperature. As the temperature of Teflon is increased from below room temperature, a sharp and pronounced increase in the coefficient of friction is observed in the vicinity of 20°C. The existence of a phase transition in Teflon at this temperature indicates a close correlation between the frictional and the structural properties of this material.
Unilateral Compression of Rubber
Authors: Forster Michael J.
Published: April 2005

One-dimensional compression measurements have been made on samples of natural rubber gum stock. The experimental stress-strain curve and the theoretical relation f=G(L−1/L2) agreed quite well over the entire range (0%–32%) studied. No hysteresis loop was evident.

The friction at the faces of the sample was eliminated by a new method of lubrication. The sample essentially floated between two thin films of a liquid which flowed under pressure between the sample and compressing plates allowing uniform lateral expansion of the sample.
Effects of Attenuating Materials on Detonation Induction Distances in Gases
Authors: Evans Marjorie W. , Given Frank I. , Richeson William E.
Published: April 2005

The effectiveness of acoustic absorbing wall materials in delaying the onset of detonation in gases is explored. Experiments are reported for stoichiometric H2–O2 mixtures in two-inch diameter cylindrical tubes. The results show that the detonation induction distance may be increased by as much as a factor of two by making the walls of the tube of porous sintered bronze.
Effect of Nitrides on the Coercive Force of Iron
Authors: Kerr J. , Wert C.
Published: April 2005

The effect of plates of nitrides on the coercive force of iron has been determined. A pronounced particle size effect was observed. The maximum effect on the coercive force was produced by particles whose largest dimension was of the order of the domain wall thickness, δ. For particles much larger than δ, an expression given by Néel for the effect of inclusions is found to be valid. The results of this study are in good agreement with earlier results reported for the effect of carbides on the coercive force of iron.
Application of the Wiedemann Effect to the Magnetostrictive Coupling of Crossed Coils
Authors: Gianola U. F.
Published: April 2005

A new construction for an electromechanical transducer makes use of the Wiedemann effect to produce a magnetostrictive coupling between an input and an output winding, which are orthogonally disposed so that there is no direct inductive coupling between them. A first-order theory of the operation of the transducer is given, and is used to derive an equivalent electrical circuit. The more important characteristics of the transducer are discussed in terms of the equivalent circuit, and are shown to be verified by experimental models. A method for deriving the equivalent circuit components by experiment is outlined, and the performance of a representative model is presented.
Oxide-Impregnated Nickel-Matrix Cathode
Authors: Balas W. , Dempsey J. , Rexer E. F.
Published: April 2005

A new cathode is described consisting of an oxide-impregnated nickel matrix. A sintered nickel matrix of controllable porosity is prepared and impregnated with solutions which precipitate a mixed carbonate within the matrix. The resulting cathode is a dispenser type with a minimum of surface coating. The cathodes can be activated by schedules which approximate those of a normal oxide-coated cathode. Pulse-emission tests of these cathodes show properties intermediate between the oxide-coated cathode and the L-cathode, and of the same order as the molded cathode described by McNair, Lynch, and Hannay.
Penetration of Electrons and Ions in Aluminum
Authors: Young J. R.
Published: April 2005

The depth of penetration of 0.5- to 11-kev electrons and 1- to 25-kev H+, H2+, and He+ ions in aluminum has been measured. It has been found that the Thompson-Whiddington law for electrons does not hold for electrons having energies less than 10 kev. The practical range-energy relation obtained for electrons in aluminum was found to be R = KE1.3, where K is 0.042 if E is expressed in kev and R in microns. The practical range-energy relation for light ions in aluminum was found to be R = KE0.83 where K = 0.020 for H+, K = 0.021 for He+, and K = 0.015 for H2+ if E is expressed in kev and R in microns. Results are compared with those obtained by previous observers.
Photoneutrons from U233 and Pu239 Fission Products in Heavy Water
Authors: Bernstein S. , Leslie J. K. , McKinney C. R. , Jackson H. K.
Published: April 2005

The yield of photoneutrons from U235, U233, and Pu239 fission products in heavy water were compared. The number of photoneutrons per delayed neutron was found to be approximately the same for all three, in spite of the previously known large variations in the relative numbers of delayed neutrons from these isotopes.
Dielectric Properties of a Lattice of Anisotropic Particles
Authors: Kaprielian Zohrab A.
Published: April 2005

The constitutive dielectric parameters for uniform space arrays of generalized structural geometry composed of similarly oriented elements of completely generalized material and shape are derived. The theoretical procedure employed in evaluating these parameters is analogous to the classical method applied to the study of the dielectric properties of nonpolar media and assumes that the disturbing action of each particle on a uniform static field can be allowed for, if each particle is replaced by a set of dipoles. Consequently, the results are applicable to microwave frequencies only if the cross-sectional dimensions and interelemental spacings remain small compared to the wavelength. The general result is particularized for the case in which the elements are spherical objects with a tensor permeability and scalar dielectric constant. The results have several applications to the design of artificial dielectrics and some of these are given.
On the Thermal Aspect of Fatigue
Authors: Freudenthal A. M. , Weiner J. H.
Published: April 2005

An attempt is made to show that the highly localized temperature and associated thermal stress gradients in front of active slip planes, resulting from the conversion into heat of the work in slip of the resolved shear stress, are of sufficient severity to account for the initiation of micro-cracks parallel to the slip planes if, as in fatigue, slip under repeated stress cycles is concentrated into ``striations.'' The effect of the thermal characteristics of the metal on its fatigue performance is discussed.
Plasma Oscillations at Extremely High Frequencies
Authors: Lampert Murray A.
Published: April 2005

Plasma oscillations are here treated for a frequency range having application not only to gaseous discharges but also to solids such as impurity semiconductors.

Amplification of longitudinal electrostatic waves in a plasma may be achieved through energy exchange with a synchronously traveling electron beam, this being the same mechanism which underlies amplification in the traveling-wave tube. The dispersion equation describing this beam-plasma interaction, first derived by Bohm and Gross, is studied systematically to obtain the characteristics of the growth-in-time, ω vs κ, of standing plasma waves and the complex propagation constant κ vs ω for traveling plasma waves, at extremely high frequencies (high plasma densities). The problem of collision damping is also discussed. The possible application of plasma oscillations to the solution of the problem of the generation of millimeter wave power is considered, both for plasmas in gaseous discharges and for the thermally generated plasmas in impurity semiconductors.
Mechanism by Which Cobalt Ferrite Heat Treats in a Magnetic Field
Authors: Williams H. J. , Heidenreich R. D. , Nesbitt E. A.
Published: April 2005

Magnetic torque measurements and electron diffraction patterns on several cobalt ferrite and cobalt-zinc ferrite crystals show that those compositions which respond to heat treatment in a magnetic field contain precipitated particles of a second phase. Response of these crystals to heat treatment in a magnetic field is apparently due to the tendency of the precipitated particles to grow preferentially along the field direction in a manner similar to that previously reported by Heidenreich and Nesbitt [J. Appl. Phys. 23, 352 (1952)] for Alnico 5. When the crystals are heat treated without a magnetic field the precipitated particles are oriented along the crystal axes, and the shape anisotropy of the particles arrayed in this manner causes a reversal in sign of the torque as the measuring field is increased from zero. This anomalous variation of the torque with field was previously observed with Fe2NiAl and explained on the same basis. Thus a single mechanism explains the aforementioned magnetic phenomena observed in Fe2NiAl, Alnico 5, and the cobalt ferrites.
Noise in Silicon p-n Junction Photocells
Authors: Pearson G. L. , Montgomery H. C. , Feldmann W. L.
Published: April 2005

A silicon p-n junction photocell prepared by the gaseous diffusion process and biased in reverse showed no noise in excess of shot noise down to a frequency of 80 cycles per second in a dry atmosphere. In a humid atmosphere the excess noise was a factor of 3×105 above shot noise at 100 cycles and showed the familiar 1/f spectrum.
Determination of Dynamic Plastic Strain through the Use of Diffraction Gratings
Authors: Bell James F.
Published: April 2005

A new method is given for measuring dynamic plastic strain in metals under impact loading. Strain-time curves for initial and reflected wave fronts have been determined using a gauge length of 132 in. The measurements are made by observing the behavior during strain of the diffracted and central images of an 8300 line reflection grating ruled on the specimen surface.
Transient Electric Currents from Plastic Insulators
Authors: Munick R. J.
Published: April 2005

Change of voltage across a solid insulator produces a transient electric current. Measurements of such currents from the polymers of methyl methacrylate, monochlorotrifluoroethylene, ethylene, styrene, and tetrafluoroethylene were made for times from 10 to 104 seconds after change in voltage at 25°C, 47°C, and several points below room temperature. The current produced by applying a constant voltage to an undisturbed specimen decays as the negative nth power of the time, where n is a constant between 0.7 and 1.1. The currents from polyethylene and polytetrafluoroethylene do not conform to the superposition principle, in contradistinction to what is usually reported for solid insulators. The currents at 100 seconds exhibit maxima at −32°C for polymethyl methacrylate and at −50°C for polymonochlorotrifluoroethylene. It is suggested that permanent electric dipoles play an important role in the currents from polymethyl methacrylate and polymonochlorotrifluoroethylene.
Correction Factor for the Quantitative Determination of Fiber Textures
Authors: Chernock W. P. , Singer Joseph , Mueller Melvin H. , Beck Paul A.
Published: April 2005

Experimental texture data were collected for a titanium and a uranium rod in order to test the applicability of the sinφ correction factor to be used with pole charts for fiber textures. Comparison of the corrected and uncorrected integrated intensity values for pole charts corresponding to various reflections with the calculated intensity values indicates that the agreement is greatly improved when the sinφ correction factor is used.
Investigation of the Mechanism of MoS2 Lubrication in Vacuum
Authors: Johnson Virgil R. , Vaughn George W.
Published: April 2005

In contrast to graphite, MoS2 retains its lubrication properties in vacuum. The coefficient of friction of MoS2 powder, compressed into pellets, has been measured under high vacuum conditions. Well run-in surfaces, which have been stationary for a period of time, show higher friction initially upon resumption of sliding. Presence of an amorphous layer of sulfur during sliding is postulated.
Dynamic Elastic Moduli of Iron, Aluminum, and Fused Quartz
Authors: Hughes D. S. , Maurette Christian
Published: April 2005

The dynamic elastic constants of Armco iron, pure aluminum, and fused quartz have been measured with a supersonic pulse technique as functions of pressure and temperature over the range 1 to 9000 bars and 25°C to 300°C (200°C for quartz).

Within the experimental accuracy the dynamic elastic moduli of these materials can be represented by linear functions of pressure and temperature.

The isothermal bulk moduli of other observers have been used to compute the equivalent adiabatic moduli by use of the thermodynamic relations. Comparison shows that at high pressures the dynamic moduli agree with the adiabatic moduli within the experimental accuracy for iron and aluminum. At low pressure the dynamic modulus of Armco iron is less than the adiabatic. The deviation is small but is about four times the estimated probable error.
Creep of Tin Single Crystals
Authors: Weertman J. , Breen J. E.
Published: April 2005

The activation energy of creep was determined for a series of tin single crystals oriented with the specimen axis close to a [110] direction. Two activation energies were found. A value of approximately 22 000 cal/m was obtained for temperatures above 130°C; a value of about 11 000 cal/mole for temperatures below 130°C.
Viscoelastic Properties of Ice
Authors: Jellinek H. H. G. , Brill R.
Published: April 2005

An apparatus has been constructed for the study of deformation under tension of single and polycrystalline ice. Deformations down to 10−5 cm could be measured. Deformation of single and polycrystals was investigated as a function of time, stress, and temperature. Whereas the strain rate for polycrystalline ice decreases with time, that for single glacier ice increases linearly with time. The deformation for fine-grained polycrystalline ice consists of an instantaneous elastic deformation, a transient creep and a steady state creep. Deformation curves can be represented by empirical equations. The recovery curves on removal of the loads have also been investigated and the plastic flow has been deduced from the residual deformation after complete recovery. This plastic flow was found to be Newtonian within the range of stresses investigated and the viscosity coefficients can be represented by an exponential relationship as follows: η1 = 7.5·e+16100/RT poises, where 16 100 calories is the energy of activation for the plastic flow. The total deformation can be represented satisfactorily by a large number of Voigt units representing a distribution of retardation times, in series with a Maxwell unit.

The experimental results are further discussed in the light of current theories of dislocations and tentative mechanisms for the deformation of single and polycrystalline ice are proposed.
Frequency Dependence of Ultrasonic Attenuation in Germanium
Authors: Granato A. , Truell R.
Published: April 2005

The attenuation of compressional waves traveling in the [100] direction in germanium has been measured in the frequency range from 5 to 300 Mc/sec. Below 20 Mc/sec, the loss was found to be mostly due to diffraction. The remaining attenuation can be described by an expression of the form α=Kfn, where α is the attenuation, f the frequency, n a constant near but somewhat less than two, and K a constant. The attenuation is attributed to the damped forced oscillation of dislocation segments. The value of the damping constant found from the data (about 1.1×10−4 g-sec−1-cm−1) is in agreement with the estimate of Leibfried and Nabarro.
Photoconductivity Speed of Response for High Intensity Excitation in Cadmium Sulfide and Selenide
Authors: Bube Richard H.
Published: April 2005

The rise and decay time of photoconductivity in single crystals, sintered layers, and evaporated layers of cadmium sulfide and cadmium selenide with a wide range of sensitivities, has been measured for excitation at room temperature by a 1900°K incandescent source giving 1740 ft-c illumination on the sample. The data thus obtained are useful for determining the dependence of the speed of response on the sample's photosensitivity and for estimating a practical upper limit to the speed of response of these photoconductors. The minimum response times found for the samples tested were rise time of 250 μsec and decay time of 300 μsec for cadmium sulfide and rise time of 17 μsec and decay time of 8 μsec for cadmium selenide.
Simple Way to Obtain the Velocity Distribution of the Electrons in Gas Discharge Plasmas from Probe Curves
Authors: Medicus G.
Published: April 2005

Until now no simple technique of determining the velocity- or energy-distribution function of the electrons in gas discharge plasmas was known. Here a method of quickly finding this function from probe curves (preferably automatically plotted ones) is described.

It is shown that for a given probe current-voltage curve J(U) the energy distribution function g(U) of the electrons is proportional to a simple function which may be graphically determined from J(U). This function is U−½ΔJ0/ΔU, where ΔJ0 is the distance between the intersections of the two tangents to the probe curve J(U) at the ends of the voltage interval ΔU with the current axis, and U is the (retarding) voltage in the middle of ΔU. It can be used for a determination of the energy distribution g(U) in a simple and straightforward one-step procedure which is faster and in practice more accurate than the two-step procedure previously used for finding g(U) by means of ∂2J/∂U2.

A set of probe curves which stem from a Maxwellian distribution is evaluated in both the conventional and the new way. The electron temperatures obtained check excellently. A set of probe curves from strongly non-Maxwellian distributions in a Ne fireball discharge is evaluated. The presence of a fast and a slow group of electrons is revealed. The results are interpreted to some extent. Errors and dependability are discussed.
High Speed Coincident-Flux Magnetic Storage Principles
Authors: Hunter L. P. , Bauer E. W.
Published: April 2005

In conventional coincident-current magnetic storage systems, a specific storage element is selected by simultaneously applying, to two or more intersecting wires, currents of magnitudes such that their sum will produce a magnetic field sufficient to switch the element and such that the presence of any one of the selecting currents alone will not cause the element to switch. In the system described here, a coincident summation of magnetic flux causes the element to switch, and the magnitudes of the currents inducing the flux are not critical. This allows the switching time to be freed of the current-selection-ratio limitation typical of the coincident-current selection systems. In the coincident-flux system, one may use selecting flux densities representing fields very much greater than the coercive field, giving very fast switching times.
Accurate Mathematical Treatment of the Analyzer of the RF Mass Spectrometer Tube
Authors: Cannon W. W. , Testerman M. K.
Published: April 2005

A mathematical treatment of the Bennett-type rf mass spectrometer has been developed which is appreciably simpler to handle when dealing with a multistage analyzer. This simplification is a result of changing the point of reference in the tube from that previously used. The resulting form of the equation is soluble by the use of a very simple analog computer which is described.
Some Results on the Analysis of Random Signals by Means of a Cut-Counting Process
Authors: Miller Irwin , Freund John E.
Published: April 2005

The variance of the number of zeros of a Gaussian signal on a short time interval was derived in a recent paper by Steinberg, et al. This result is generalized to include the covariance of the number of zeros of a Gaussian signal at the values θ1 and θ2, using a somewhat different mathematical approach. A special case with θ1=θ2=θ gives the variance of the number of times the signal equals θ on a given time interval.
Effect of Neutron Interaction on Criticality
Authors: Stuart G. W.
Published: April 2005

A general method is developed to allow calculation of the critical buckling of an assemblage of fissile regions coupled by neutron leakage. Consideration is given both to regions embedded in vacuum and in material media. Several cases of simple geometry are further developed to illustrate the theory.
Preparation and Properties of Thin Film MgO Secondary Emitters
Authors: Wargo P. , Haxby B. V. , Shepherd W. G.
Published: April 2005

Some simple methods of preparing MgO thin films on Mg–Ag alloy with high secondary emission ratios are discussed. The oxidation procedure and a discussion of the underlying phenomena are presented. Films with a secondary yield of 12 at 600 v may be produced by oxidation in either oxygen or carbon dioxide. Results of a study of some of the factors influencing the life of a secondary emitter are given. These include the effects on the secondary emitting characteristics of evaporation products from an oxide-coated cathode and the deterioration of the thin film under electron bombardment.
Emission of Oxide Cathodes Supported on a Ceramic
Authors: Moore G. E. , Allison H. W.
Published: April 2005

To reduce the physical and chemical complexity of the oxide coated cathode, the support metal and interface were eliminated by applying the (BaSr)O layer to a MgO ceramic which is electrically and chemically inert to (BaSr)O. The three interacting chemical phases of the usual oxide coated cathode are thereby reduced to a single phase—the oxide coat alone. At 1000°K, thermionic emission, measured by a pulse technique, is about 1 order of magnitude less than from modern commercial cathodes but considerably greater than from any other cathode system. The emission capability is unaffected by treatment in either atomic hydrogen or methane, which reduce BaO to Ba metal and thereby increase the Ba content of the oxide. The experiments were an attempt to test the usual assumption that emission in conventional oxide coated cathodes is determined by the composition of the (BaSr)O phase. The results suggest strongly that much of the complexity of practical cathodes is in the oxide layer itself and that factors other than the content of excess Ba are decisive for thermionic emission.
Quantitative Study of Substructure Characteristics and Correlation to Tensile-Property of Nickel and Nickel Alloy
Authors: Weissmann Sigmund
Published: April 2005

The application of a method combining x-ray microscopy and diffraction analysis to the study of the substructure of nickel and nickel alloys disclosed the coexistence of three orders of magnitude of substructural entities. These three orders are structurally interrelated and distinguished by different ranges of size, disorientation angle, and lattice misalignment. The statistical analysis of the data disclosed that for the two largest orders of substructural entities increasing amounts of room temperature deformation cause (1) a decrease in the mean size and a decrease in the spread of the size distribution, (2) an increase in the mean disorientation angle between substructural entities of the same order and an increase in the spread of the distribution of angles, and (3) an increase in the mean lattice misalignment and spread in the distribution of misalignment. Progressive room temperature deformation causes the low-angle boundaries to become increasingly unsymmetrical and greatly increases the number of the smallest substructural entities. The rise of flow stress as a function of room temperature deformation was correlated to the systematic modification of substructure characteristics.
Shock Produced by a Spherical Piston of Radius a(t)
Authors: Evans G. W. , Faulkner F. D. , Lockhart B. J. , Perry C. L.
Published: April 2005

The numerical solution for a spherical shock in water produced by spherical piston of known expanding motion and initial nonzero radius is described. This solution is of interest during the time when the radius of the shock and that of the piston are of the same order of magnitude, that is, when point source solutions do not hold. Calculations are carried out for a constant velocity piston and for a piston with decreasing velocity.
The Resistance of Semitransparent Photocathodes
Authors: Harper W. J. , Choyke W. J.
Published: April 2005

The resistance of the semitransparent photoemissive films Sb–Cs, Sb–Rb, Bi–Cs, Bi–Rb, Te–Cs, Te–Rb, and Ag–O–Cs was measured as a function of temperature. A thermal activation energy associated with conductivity was determined for each of the materials.
Dislocation Etch Pits in Silicon Crystals
Authors: Vogel F. L. , Lovell L. Clarice
Published: April 2005

A method for suitably etching dislocations in silicon crystals is reported. Using this etch, dislocations in various arrays were observed: low angle boundaries, slip lines, polygonization walls, and bent crystal distributions.
Electrical Conductivity of Barium Oxide Single Crystals as a Function of Temperature and Excess Barium Density
Authors: Dolloff R. T.
Published: April 2005

Four-electrode conductivity measurements over the temperature range from 500 to 1000°K have been made on clear BaO single crystals and on crystals colored blue by excess barium densities between 0.3 and 6×1017 per cc. Barium was introduced into the crystals by heating in a barium atmosphere and the excess barium densities were computed by the Smakula formula from the 2.0-ev optical absorption band following the method of Sproull, Bever, and Libowitz. The conductivities of the clear crystals attain values of 10−4 mho/cm at 1000°K whereas the blue crystals show a conductivity maximum of about 1 mho/cm at about 900°K. The assumption of an electron mobility of 5 cm2/volt sec leads to an agreement of the saturation electron density and the excess barium density to within a factor of three.
Simple Modes of Vibration of Crystals
Authors: Mindlin R. D.
Published: April 2005

In this paper there are described solutions of the three-dimensional equations of elasticity and the equations of generalized plane stress pertaining to vibrations of crystal rectangular parallelepipeds and thin plates with traction-free faces. The modes of motion exist in crystals of certain classes for specific orientations and length-ratios of the edges. Since the solutions are exact and in closed form, they may be used to advantage in connection with the measurement of elastic constants. Special disposition of electrodes is required for piezoelectric excitation.
Properties of the Shock Transition at Low Temperature
Authors: Gilvarry J. J.
Published: April 2005

Bethe's equation for the change of entropy in waves of finite amplitude is shown to be inapplicable for an initial state of temperature arbitrarily close to absolute zero, for a degenerate substance possessing a zero-point pressure (or energy). Thermodynamic functions for such a substance at low temperature are formulated in general terms applicable to the Fermi-Dirac gas, the Thomas-Fermi atom, the Debye solid, and the Mie-Grüneisen solid as special cases. The conditions under which the equation of state satisfies the Bethe-Weyl conditions are given. Of the usual four basic properties of the shock transition under the Bethe-Weyl conditions, two must be modified for the class of substances in question, for an initial state arbitrarily close to zero temperature. The argument follows from extension of Bethe's method, by Taylor expansion of the Hugoniot function about the initial state. The results are shown to be consistent with Weyl's procedure.
Tensile Strength of Whiskers
Authors: Brenner S. S.
Published: April 2005

Tensile tests have been performed on whiskers of iron, copper, and silver 1.2 to 15 μ in diameter. The strongest whiskers which were less than 4 μ in diameter exhibited resolved elastic shear strengths of from two to six percent of their shear moduli. Stress-strain determinations on iron have shown that large deviations from Hooke's law occur beyond two percent strain. As the whiskers increase in size, their strengths decrease with considerable scatter.
Electromagnetic Transmission Characteristics of a Lattice of Infinitely Long Conducting Cylinders
Authors: Kaprielian Zohrab A.
Published: April 2005

This investigation is primarily concerned with the study of electromagnetic transmission characteristics of a lattice of infinitely long conducting cylinders. Four approaches to the general problem have been employed and the advantages, disadvantages, and realms of validity of each have been studied. Several of these methods constitute a substantial improvement over previous analyses and are supported by wave-guide and free-space experimental work.

The four approaches are: (1) A molecular analogy with a consideration of dipole interactions leading to the Clausius-Mosotti relations, (2) A transmission line formulation which considers the thick obstacle for both polarizations, (3) An analysis based on the summation of scattered fields which demonstrates that the Clausius-Mosotti relations are a special case of a more general relation which accounts for the effects of higher order multipoles, and (4) A solution formally valid for all values of spacing and cylinder radius based on integral equation formulation of variational principle.
Reflectionless Transmission through Dielectrics and Scattering Potentials
Authors: Kay I. , Moses H. E.
Published: April 2005

A complete solution is given for the problem of constructing a plane stratified dielectric medium having that the property that at a fixed frequency and polarization a plane wave at any angle of incidence will be transmitted without reflection by the medium. This problem can also be interpreted quantum-mechanically. The dielectric medium of the first interpretation becomes, in the second interpretation, a potential for the one-dimensional Schrödinger equation such that a particle which is sent in from - ∞ is transmitted with probability one of getting through to + ∞, no matter what the initial kinetic energy of the particle may be.

In addition, the results can be applied to the problem of finding perfectly matched nonuniform transmission lines.
Structure of Bent Zinc Crystals
Authors: Wei C. T. , Beck Paul A.
Published: April 2005

Zinc crystals were bent either by wrapping them around a mandrel or by the application of a concentrated load in a direction perpendicular to the basal plane. The structure of the bent crystals was studied by means of suitable x-ray diffraction techniques, namely the Lambot technique and the Schulz technique. It was found that, after bending around a mandrel of sufficiently small radius, the zinc crystals were subdivided into subgrains, with an average disorientation between neighboring subgrains of approximately 3 minutes of arc. In the dimples formed by a concentrated load the radius of bending is quite large and there is hardly any observable substructure. However, the substructure does develop upon annealing by the polygonization mechanism. The diameter of the dimples formed by a concentrated load increases linearly with the logarithm of the time of load application, for a constant load, and it increases linearly with the load if the time of load application is constant.
Focusing of Low-Energy Electron Beams
Authors: Clarke W. W. H. , Jacob L.
Published: April 2005

Conventional electrostatic and magnetic lenses were used to focus electron beams in the range of energies 30–70 v, produced by a specially designed experimental tube. The electron distribution in the focused beam was resolved by a series of concentric end collectors and a convention introduced to assess effective beam widths.

With near-symmetrical lenses of the electrostatic type and for energies above 30 v, the beam, if inside the aberration limits of the lens, appears to be acted on as a whole by the field and a definite focus is obtained; for 30-v beams, on the other hand, there is no unique focus since maximum and minimum values of effective beam width were recorded as the focus voltage was varied. Such a periodic variation might arise from the existence of standing wave patterns in the space charge in front of the cathode.

A characteristic feature of the focusing which is most marked in the magnetic case is the disappearance on focus of the Gaussian core of the incident beam distribution. With magnetic lenses having apertures in the ratio 2/1, it was remarkable to find that the smaller aperture lens was the most efficient in bringing beams to a focus. In general, the power of magnetic lenses had to be greatly increased (in the measurements, by a factor of 30) over any expected thin lens performance to achieve a focus. Space charge forces, nonhomocentricity, and potential depression are held to be responsible for the abnormal conditions of focus.
Underwater Sound Reflection from a Corrugated Surface
Authors: LaCasce E. O. , Tamarkin P.
Published: April 2005

Theories of rough surface reflection by Rayleigh, Eckart, and Brekhovskikh are utilized to calculate the dependence, on surface and radiation parameters, of the amplitudes of reflected radiation when an acoustic beam is incident on a pressure-release surface with sinusoidal corrugations. The results of these theories are compared, with emphasis on the assumptions used. Experimental results for the reflection of an underwater acoustic beam from this type of surface are presented and compared with each of the theories. The best agreement between theory and experiment is obtained for surfaces of small slope, indicating that this criterion is basic to the validity of the theories. However, surprisingly similar results are obtained for surfaces of large slope. The theories seem to predict the behavior of the lower orders of reflection more closely than that of the higher orders. Good agreement between theory and experiment is obtained for directions of reflection and for cut-off frequencies.
Shock Location in Front of a Sphere as a Measure of Real Gas Effects
Authors: Schwartz R. N. , Eckerman J.
Published: April 2005

Spheres were fired at supersonic speeds into monatomic gases and into chlorine gas. The position of the shock wave which forms in front of the sphere depends on the Mach number and gas state before and after crossing the shock wave. Measurements of position made in monatomic gases agree fairly well with aerodynamic theory. As the shock position depends on the actual gas state attained, and thus molecular excitation times, measurements in more complicated gases than a monatomic gas can give information as to amount and rates of excitation. The vibrational energy excitation in chlorine was singled out for study. This excitation involves a well-known rate process. By carrying out shock position measurements at several different pressures, it is possible to infer the order of magnitude of the vibrational relaxation time in chlorine; the present results are in agreement with shock tube measurements of the relaxation time.
Two-Group Diffusion in Slab Lattice Reactors
Authors: Estabrook Frank B.
Published: April 2005

Criticality calculations for heterogeneous reactor media are usually based on a single-cell calculation of f, the thermal utilization, followed by a ``homogenized'' treatment of the macroscopic neutron migration. A changed approach is here advocated, in which diffusion theory is applied only to the multiply-connected moderator portions of the reactor, the fuel is treated by the use of multiplying boundary conditions, and no arbitrary averaging need be done. As an example, the one-dimensional case of plane fuel slabs in moderator is treated, and the material buckling characteristic of the fundamental mode is obtained using two-group theory. The equation for this case readily allows a comparison between neutron migration lengths parallel to and perpendicular to the fuel slabs: considerable anistropy is found, in magnitude greatly dependent on fuel slab separation.
Ultrasonic Relaxation in Normal Propyl Alcohol
Authors: Lyon T. , Litovitz T. A.
Published: April 2005

Ultrasonic relaxation has been investigated in normal propyl alcohol using pulse techniques. Measurements of velocity and absorption were made at frequencies from 1 to 82 megacylces and over a temperature range 0 to −155°C. The data could be explained by assuming a distribution of relaxation times, and it was suggested that the distribution of relaxation times is but a reflection of the distribution of activation energies for the elementary molecular processes involved. A theory based on the assumption of a uniform distribution of activation energies for compressional processes and a single relaxation time for the shear process was presented. The agreement between the values calculated from this theory and the experimental data is good except at very high viscosities. The compressional viscosity calculated from the theory was found to be nearly equal to the shear viscosity except at very high viscosities. This is in agreement with the compressional viscosity calculated from the ``excess'' absorption in the nondispersion region.
On the Measurement of Electric Constants of Thin Metallic Films
Authors: Bonfiglioli G. , Coen E. , Malvano R.
Published: April 2005

The present work deals with Hall effect and specific conductivity measurements in the case of a nonuniform current density field (that is, when the specimen is not a parallelepiped but has irregularly waved surfaces). It is then impossible to measure separately RH (Hall coefficient) and σ (conductivity); it is possible, however, to get their product, the Hall mobility of the carriers. These conclusions are important when dealing with thin films, where the actual geometry of the surface is completely unknown. The preceding remarks are used to interpret the results of some experiments on Au films evaporated on mica. An almost constant mobility is found versus mean thickness, but its magnitude is about ¼ the bulk mobility. This behavior raises some question about the structure of thin films, and some connection seems to hold between the experiments here described and the results of the measurements of the optical constants of metals.