bluuebunny/crossref_metadata_2025 huggingface dataset:
Shadowing Technique for Electron Microscopy—A Possible Substitute for the High-Vacuum Evaporation Technique
Authors: Bills Alvin E. , Lefker Robert
Published: April 2005

A method of shadowing samples directly within the electron microscope has been developed in this Laboratory. This method, which uses thallium chloride immersed in distilled water as the shadowing material, is much less time consuming than is the usual method that involves high-vacuum metal evaporation; the results obtained are not of the same high quality as those of the usual method, but the time saving often justifies the method. Polystyrene Latex (batch No. 580) is introduced on the specimen screen, to provide an internal calibration standard; this standard makes it possible to measure the angle of shadowing.
Charge Storage in Junction Diodes
Authors: Steele Earl L.
Published: April 2005

A calculation is made which relates the physical properties of a junction diode to the troublesome spike current arising from hole storage in the germanium. This spike current results when the diode is suddenly switched from the conducting to the nonconducting state. For small germanium pellets, this current decay is exponential with a decay considerably shorter than that indicated by the hole lifetime in the material. For larger pellets the decay is a sum of exponentials giving a considerably longer decay time, still shorter, however, than the hole lifetime.
The Joint Distribution of n Successive Outputs of a Linear Detector
Authors: Hoffman William C.
Published: April 2005

The joint probability density function of n successive outputs of a linear detector is derived for the case of dependent Gaussian inputs.
Application of Ideal Gas Theory to the Gaseous Expansion from an Electric Spark
Authors: Edmonson R. B. , Olsen H. L. , Gayhart E. L.
Published: April 2005

The gaseous expansion from an electric spark is described in this paper in terms of ideal gas theory. The assumption is made that a quantity of energy is injected into a small gas volume in an infinitesimally short time and that the initial volume of gas then expands until it reaches the pre-spark pressure at an elevated temperature. Experimental results are given for a condenser discharge illustrating the dependence of the pressure equilibrated gas volume upon initial pressure and condenser energy. These results are interpreted using the ideal gas model presented. The significance of this expansion to the problem of spark ignition in combustible gases is discussed.
On the Nature of Radiation Damage in Metals
Authors: Brinkman John A.
Published: April 2005

The nature of the permanent damage retained in metals from irradiation has been investigated in somewhat greater detail than has been done in the past. The usual assumption has been that the damage in all metals consists chiefly of interstitial-vacancy pairs. The model presented in this paper reduces to this picture for the light elements but introduces a new concept in the case of damage in the heavy metals, called a displacement spike. Calculations are made from which one can estimate the relationship between the density of interstitial-vacancy pairs and the temperature of the associated thermal spike. An assumption regarding the extent to which interstitial-vacancy pairs persist throughout the duration of the thermal spike has been made, based upon these calculations. The number of interstitial-vacancy pairs predicted in the heavy elements is considerably smaller than that predicted by the former model. A mechanism is proposed by which small dislocation loops can be produced in the heavier metals by irradiation.

This article is based upon studies conducted for the U. S. Atomic Energy Commission under Contract AT-11–1-GEN-8.
Relaxation Time Spectrum of Dough and the Influence of Temperature, Rest, and Water Content
Authors: Cunningham J. R. , Hlynka I.
Published: April 2005

The effect of temperature, rest period, and water content on stress relaxation in doughs held at constant extension has been studied with a relaxometer previously described. Temperature was varied from 13 to 35°C, rest period from 2 to 120 min, and water content from 74.4 percent to 86.0 percent dry basis. It is found that the shape of the relaxation curves on a log time plot does not change with temperature in the above range but that the curve is shifted laterally along the log time axis. This permits the construction of master curves valid in the temperature range and extends the time scale of observation. The long relaxation time end of the distribution of relaxation times is affected most by rest period, decreasing as rest period is increased, and the short time end increases as water content is decreased. Activation energies from 11 to 24 kcal per mole are calculated for relaxation from the shift of the curve on the log time axis. There is an indication that the activation energy depends on temperature and increases with rest period.

A mathematical framework, based on the general Maxwell model, is discussed and the distribution function on the log time axis is interpreted in terms of viscosity and modulus of the relaxing mechanisms. Special reference is made to the ``box distribution'' and a viscosity is calculated.
Constant Stress Elongation of Soft Polymers: Plasticizer Studies
Authors: Hatfield Marshall R. , Rathmann George B.
Published: April 2005

Constant stress measurements have been made on lightly cross linked GR-S and polyisobutylene of 7 million molecular weight. The modulus values as a function of temperature, time, and concentration of mineral oil plasticizer have been treated according to the ``reduced variables'' principles.

Since both plasticized and unplasticized samples showed the expected equivalence of temperature and time, the modulus values could be shifted to produce master curves for each composition. In the case of GR-S the concentration of plasticizer could be similarly reduced to yield a single curve for all the data.

The polyisobutylene results, however, showed quite clearly that the plasticizer had a unique effect not paralleled by temperature or time. This effect has been attributed to the pseudoequilibrium modulus which apparently results from chain entanglements. Since the pseudoequilibrium modulus should be proportional to the number of chain entanglements per gram of polymer, it should vary as the square of the volume fraction of polymer. It is shown that a correction of this type improves the shift of the curves for polyisobutylene.

Changes in activation energy with the addition of plasticizer are apparently within experimental error (±2 kcal) in all cases.
Further Dynamic Investigations on Polymers
Authors: Philippoff Wladimir
Published: April 2005

Using the vibration tester of The Franklin Institute, a check of the proportionality between stress and strain in dynamic testing disclosed that a proportionality exists when heating is eliminated. A comparison of values of the dynamic test and steady-state experiment in the same range of rates of shear and shearing stress showed that the behavior is basically different; whereas in the dynamic test the viscosity is independent of both amplitude and shearing stress, in the steady-state test experiment a very high dependence exists. The curve of viscosity vs rate of shear (D) is very similar to the one of dynamic viscosity vs frequency (f). A frequency shift of the order of two is involved in comparing D and f. The application of Ferry's method of reduced variables to a polyisobutylene solution, liquid polyesters, and solid plastics showed its validity. A precision test on the polyester showed that the temperature shift, Tρ/T0ρ0, is necessary to make experimental values at different temperatures fit. The reduced curve of G′ vs frequency for different plastics has an S shape with different slopes in a very wide range of frequency around 1024.
Flow of Melts in ``Crosshead''-Slit Dies; Criteria for Die Design
Authors: Carley James F.
Published: April 2005

``Crosshead''-slit dies are widely used for the extrusion of polymer sheeting, flat film, and blown film. In this paper we analyze the laminar flow of liquids in such dies, deriving an equation relating pressure to position along the slit for materials that obey the ``power law.'' The equation yields an index of uniformity (UI), which is the ratio of the rate of extrusion at the far end to that at the feed end, given by UI={1−[(1+0.05n)nαL](n+1)/n(1+0.05n)(n+1)}n,where n=the exponent of the power law, L=the length of the die from feed end to far end, and α=a parameter depending on the other die dimensions and the exponent n, having the unit (in)−1. An illustrated procedure is given for designing dies that will make film whose caliper is satisfactorily uniform over its whole width. We show that the UI for center-fed dies is always greater than for end-fed dies of the same length.
Rotational Plastometry Applied to Molten Polyethylene
Authors: Dexter F. D.
Published: April 2005

A concentric cylinder rotational plastometer which automatically plots the shear strain vs time curve for each of a number of shear stresses is described. The flow behavior of molten polyethylene resins, measured with this instrument from 130°C to 210°C, is discussed. It is shown that, at each shear stress, the shear strain vs time curve for these resins is describable in terms of a viscosity, an elastic shear strain and a retardation time. As the shear stress is raised both the viscosity and retardation time decrease, while the elastic shear strain increases. The shear stress dependency of the viscosity and elastic shear strain are shown to be related and in a manner which suggests that the viscosity change is the result of an entropy effect.
The Statistical Properties of the Output of a Frequency Sensitive Device
Authors: Arthur George R.
Published: April 2005

Frequently it is desirable to know the statistical properties of the output of certain frequency sensitive devices when some type of random signal is impressed. Since most devices of this type are followed by low pass filters, this problem is one of determining the statistics of a filtered signal.

The problem of finding the probability density of the difference of two dependent random variables has not been solved in any general way. Also, the problem of finding the statistical properties of the output of a linear filter upon which a non-Gaussian random signal is impressed has been considered by only a very few writers.

The first sections of this paper gives a solution of the case of a frequency discriminator with no low pass filter, excited by a narrow band spectrum, and is solved by expressing the output of the device as the difference of two independent random quantities, which allows the use of the characteristic function method.

The later sections contain a solution of the problem when a low pass filter is present at the discriminator output. This is done by obtaining the predominant moments of the density from a series expansion which gives a good approximation to the nature of that density Also, in this regard, the approach of the density to a Gaussian one, as the output filter band is made very narrow, is clearly shown.
Amplification Factor and Perveance of an Elliptic Triode
Authors: Deb S. , Sanyal G. S.
Published: April 2005

An attempt has been made to derive, in terms of valve geometry, theoretical expressions for the constants of an elliptic triode, the shape of the electrodes of which belongs to a family of confocal ellipses. The amplification factor (μ) is derived by following the method of conformal transformation. Result shows that in general it varies with the parametric angle θ of the ellipse—decreasing from the direction of minor to that of the major axis. The average value of μ increases with increasing value of the eccentricity of the grid and with decreasing value of the eccentricity of the anode. Curves for ready evaluation of μ for any value of θ are given. The problem of design of an elliptic triode having a constant μ for all values of θ is also considered and its method of solution indicated. An expression for the perveance (P) has also been obtained by adopting the procedure followed by O'Neill for determining the perveance of a plane diode having filamentary cathode. The expression shows that the value of perveance is determined mainly by the eccentricity of the grid and the focal distance.

To illustrate the practical applications of the various deductions made, a numerical example, involving the design of a 6C5-GT/G type triode, is given.
Theory and Probe Measurements in a Magnetic Ion Source
Authors: Hoyaux Max , Lemaitre Robert , Gans Paul
Published: April 2005

The ``superstate'' in a magnetic ion source has been investigated experimentally and theoretically. The space-charge density is approximately constant throughout the source. The radial plasma density does not differ significantly from a Gaussian distribution. The radial distribution of space potential is approximately parabolic. The theoretical results have been tested by probe measurements, and good agreement has been found.
Analysis of Turbulent Density Fluctuations by the Shadow Method
Authors: Uberoi Mahinder S. , Kovasznay Leslie S. G.
Published: April 2005

Shadow pictures of turbulent flow regions give a particular kind of information about the three-dimensional density field. If homogeneity and isotropy of the fluctuation field can be assumed, the statistical properties of the picture uniquely determine the correlation function or power spectrum of the three dimensional turbulent density field. Shadow pictures obtained in the wake of a supersonic projectile were analyzed in this manner and encouraging results were obtained. In order to check the validity of the method, the density fluctuations in a heated jet were measured both by the shadow method and by the more conventional hot-wire technique.
Qualitative Evaluation of Correlation Coefficients from Scatter Diagrams
Authors: Burford Thomas M.
Published: April 2005

Middleton and Sugar have shown that the scatter diagram of two random electrical quantities may be oscilloscopically displayed, and that a simple relation exists between the resulting pattern and the correlation coefficient, if a Gaussian distribution is assumed. The present paper shows that qualitative information concerning the correlation coefficient may be found from the scatter diagram, no matter what distribution is assumed.
Measurements of Electrical Polarization in Thin Dielectric Materials
Authors: Tyler R. W. , Webb J. H. , York W. C.
Published: April 2005

Electrical polarization in thin, dielectric sheet material induced by handling or other means is not readily observed because the external field from a dipole charge layer is very weak compared with the field from net charges that are usually present. A method is described for measuring polarization in the presence of net charges by placing the dielectric sheet in contact with a grounded metal backing plate and by placing a field meter at a short distance in front of the dielectric. The grounded metal backing plate has the effect of almost completely annulling the external field of any net charge by induction, and of doubling the external field of a dipole charge layer of polarization.
Magnetic Materials for Digital-Computer Components. I. A Theory of Flux Reversal in Polycrystalline Ferromagnetics
Authors: Menyuk N. , Goodenough J. B.
Published: April 2005

It is proposed that magnetization reversal in polycrystalline ferro- and ferrimagnetic materials is primarily due to the nucleation and growth of 180° Bloch walls. The origin of domains of reverse magnetization is discussed. The rate of growth of these domains is determined by a study of the elastic and frictional forces which retard the motion of their 180°-Bloch-wall boundaries. This theoretical model successfully explains the output-voltage wave forms of polycrystalline materials. A figure of merit for the magnetization reversal of magnetic cores is defined as the switching coefficient Sw=(Hm−H0)τ, where τ is the time required to reverse the magnetization, Hm is the applied magnetic field, and H0 is the threshold field value at which the average domain-wall velocity is zero. Sw is composed of an eddy-current contribution Swe and a spin-relaxation contribution Swr. The value of Sw is derived in terms of various fundamental parameters of the material. It is shown that in ferrites and ultra-thin metal tapes, Swe«Swr. Theoretical relationships expressing the contributions of spin-relaxation, eddy-current, and hysteresis effects to energy losses are derived on the basis of this model. A study of the factors which affect the magnetization-reversal time of materials with square hysteresis loops indicates that a better figure of merit will result if the proper hysteresis shape is obtained by grain alignment rather than by the techniques currently employed in ferrites. A number of experiments are presented in support of this model.
An Approximate Theory of Armor Penetration
Authors: Thomson William T.
Published: April 2005

The problem of armor penetration of thin plates is considered from a quasi-dynamical approach. Equations are derived for the energy dissipation due to plastic deformation and for heating of the projectile target interface. Both the conical and the ogival head are considered in the application of the general equations.
Spectroscopic Studies of Highly Ionized Argon Produced by Shock Waves
Authors: Petschek H. E. , Rose Peter H. , Glick Herbert S. , Kane Anne , Kantrowitz Arthur
Published: April 2005

For the study of high-temperature gas dynamics, shock-tube techniques have been developed earlier to produce shock waves strong enough to heat gases to high and accurately known enthalpy (for argon up to 18 000°K or 40 percent ionization at equilibrium). This paper reports a study of the visible radiation from the highly luminous argon following strong shock waves.

Preliminary spectrograms showed a strong continuum and that the prominent argon lines were broadened and shifted to the red. Correlation of the frequency shifts with theoretical treatments permitted an evaluation of the ion density in the gas. Development of a drum camera spectrograph (film speed 700 ft/sec) in which time effects could be resolved to about 1 μsec indicated that equilibrium ion density was reached rapidly, and provided a rough measurement of the rate of decline of ion density due to cooling.

Absolute photoelectric spectrophotometric measurements of the continuum radiation were made and correlated with theoretical expectations. Confirmation of the expected variation of continuum intensity with wavelength and temperature was obtained and an undetermined factor on the theoretical intensity was evaluated. Determinations of the cooling rate of the high-temperature argon from time variation of the continuum intensity, the line shift, and the electrical conductivity (by others) are in agreement and show that continuum radiation was the dominant heat loss.
Methods for the Correction of X-Ray Intensities for Primary and Secondary Extinction in Crystal Structure Analysis
Authors: Vand Vladimir
Published: April 2005

The theory of x-ray extinction in diffraction studies is reviewed, and application to small crystals completely bathed in the incident beam is considered. Using a suitable approximation to a sum of Bessel functions, a correction formula is obtained, valid in the region of small Bragg angle θ where the extinction is likely to be greatest. The formula is discussed; and it is shown that when the crystal structure is essentially known, as in later stages of refinement, it is possible to separate the effects of primary from secondary extinction and to correct the experimental data accordingly.
On Zone Refining
Authors: Birman Joseph L.
Published: April 2005

A matrix method is used to solve the difference equations which describe the zone refining of a bar. The matrix method is designed for direct numerical calculation of the solute distribution, after any number of passes, with any initial solute distribution. The method is illustrated with a simple example.
Hysteresis Effect in Multiplier Phototube Noise
Authors: Ziegler C. A. , Seliger H. H.
Published: April 2005

A hysteresis effect in multiplier phototube noise as a function of tube gain has been found for both RCa 5819 and DuMont 6292 tubes. The effect is a function of both temperature and the length of time that a tube has ``rested.'' The hysteresis is seen to be a noise buildup with time but not a change in dynode multiplication. The reasons for this effect are not clear. Several possible mechanisms are discussed. Conditions are determined for obtaining reproducible noise counts for liquid scintillation counting of low-energy beta emitters.
On Electron Mirror Microscopy
Authors: Mayer Ludwig
Published: April 2005

This paper deals with a new kind of electron microscopy in which the specimen constitutes an electron mirror. The low velocity of the electrons in front of this mirror-specimen enables pictorial representations of potential distributions on surfaces. A resolving power comparable to that of the light microscope has been obtained. Sample micrographs depicting surface reliefs, potential distributions on surfaces, and the distribution of electrical conductivity are shown. The peculiar kind of image formation is briefly discussed and reference is made to the potentialities of such a research tool for surface physics and metallurgy.
Spatial Distribution of Thermal Neutrons from a Polonium-Beryllium Source in Water-Zirconium Mixtures
Authors: Baer William
Published: April 2005

The spatial distribution of neutrons emitted by a Po–Be source and moderated by water-zirconium mixtures has been measured for four water-zirconium volume ratios. From these data, migration areas of source neutrons to energies below the cadmium cutoff have been determined with an uncertainty of ±2%. The experimental values of the migration area M2 are: Zr/H2O ratioM2(cm2)0.0069.60.2581.30.5089.71.00112.8
Outgassing of Glass
Authors: Todd B. Johnson
Published: April 2005

The gas evolved from glass at temperatures below the softening point, which is of interest in bake-out problems, is primarily water. The water evolved from unit surface at constant temperature above 300°C is linear with respect to the square root of the time of bake-out. The intercept of the linear plot, which can be altered by different surface treatments, is a measure of the easily removed water residing at the surface. The slope is a measure of the rate of evolution of water that has diffused to the surface from the interior.

Values of the diffusion constant for water and concentration gradients after bake-out have been calculated for a soda-lime glass. The diffusion constant is an exponential function of the reciprocal of the absolute bake-out temperature. Values of the activation energy for the diffusion process are given for eight glasses.

A method of calculating the amount of water that will diffuse from glass for any time-temperature conditions following any bake-out is presented.
Prebreakdown Current and Noise in Insulators
Authors: Powers D. A. , Suita T.
Published: April 2005

The frequency spectrum of the noise associated with prebreakdown currents in insulators has been investigated in the audio-frequency range. Most of the noise is due to surface discharges which can be eliminated by special types of electrodes and careful experimentation. The remaining noise has a frequency spectrum with the highest amplitudes at very low frequencies; it falls rapidly to the Johnson noise level in the measuring resistor at about 104 cps. This noise apparently originates from fluctuations in the field-emission current.
Conduction and Breakdown in Hexane
Authors: Green W. B.
Published: April 2005

Conduction currents in hexane, studied as a function of spacing, metal, and heat treatment of the electrodes over the field-strength range from 0 to 250 kv/cm, obey neither a field-enhanced thermionic emission nor the customary field emission relation. The most important factor determining the currents appears to be a surface layer on the cathode. Exposing the liquid to gamma rays increases the current in a fashion that indicates a decrease of the effective work function rather than merely a collection of ionization products. Heat treatment of the cathode, by changing the nature of the surface layer, changes the emission. It appears that positive ions collect on the more or less insulating surface layer and build up intense local fields that cause electron emission. The size of the local field depends on the number of the ions arriving per second and on the thickness, homogeneity, and conductivity of the surface layer.

For some electrodes the current increases with gap width for constant field; previous investigators have interpreted this fact as evidence of impact ionization in the liquid. However, change of current with gap width proves to be an electrode property; some electrodes do not show it.

In one case the current was measured up to breakdown (1060 kv/cm). There is an indication that impact ionization may exist above 800 kv/cm; if so, the ionization factor is very small.

A variety of purification systems was tried but no influence of the purification treatment on the conduction currents was found.
Effect of Water Vapor on Grown Germanium and Silicon np Junction Units
Authors: Law J. T. , Meigs P. S.
Published: April 2005

The effect of water vapor on the photoresponse curves and reverse current characteristics of germanium and silicon np junction units has been investigated. It is concluded that changes in surface recombination velocity are only important at low relative humidities. Channel conduction accounts for the increased current of a silicon unit but another mechanism must be postulated for the germanium case. The possibility of this being ionic conduction is discussed.
Restoration of Resistivity and Lifetime in Heat Treated Germanium
Authors: Logan R. A. , Schwartz M.
Published: April 2005

Experiments are described in which minority carrier lifetime and resistivity of germanium are altered by the addition of copper by diffusion, under conditions where extraneous chemical contamination is minimized. This copper is then gettered by heating the samples in contact with liquid lead or gold, and the resistivity and lifetime are substantially restored. The gettering process in interpreted in terms of the low distribution coefficient of copper in the ternary system which copper and germanium form with the getter.
Variation of Elastic Wave Velocity with Frequency in Fused Quartz and Armco Iron
Authors: Hughes D. S. , Kennel J. M.
Published: April 2005

The velocity dispersion in fused quartz and in Armco iron was investigated by measuring the resonant frequency of small cylinders using quartz crystals on the ends as drivers and detectors. With x-cut crystals and y-cut crystals the computed velocities of the dilatational waves in the range 2.0–5.0 Mc and shear waves in the range 1.5–3.0 Mc decrease with frequency. This decrease in both cases is regarded as unreasonably large and is ascribed primarily to sample geometry. Simple standing plane waves, either dilatational or shear, cannot satisfy the boundary conditions in a free cylinder. A mosaic crystal was then constructed of sectors of y-cut crystals such that the driver generated and the detector transmitted only torsional waves. With these crystals and viscous coupling between the crystals and sample, the velocity in fused quartz was constant within ±1 m/s for the frequency range 0.6–3.0 Mc. The velocity in Armco iron was constant within ±2 m/s in the range 0.5–1.5 Mc and decreased about 10 m/s in the range 1.5–3.0 Mc.
Influence of Pulsed Magnetic Fields on the Reversal of Magnetization in Square-Loop Metallic Tapes
Authors: Rodbell D. S. , Bean C. P.
Published: April 2005

Reversal of magnetization in square-loop metallic tapes is described in terms of the domain geometry and the dependence of this geometry upon the applied magnetic field wave shape. For a steady field whose amplitude is slightly greater than the coercive force, the reversal is accomplished by growth of a single axial domain originating at the thin tape edge. For steady fields of much greater amplitude, the reversal domain grows in from all tape surfaces. Because of the finite nucleation time required to establish the reversal domain, short duration, high amplitude field pulses can be used to investigate the mechanism of nucleation of the high field reversal domain configuration. A model which accounts for the nucleation process is suggested. The compatability of this model with various experimental results is presented. From these results an understanding of the high field reversal-domain configuration and the kinetics of the nucleation and growth of these domains in lamellar materials is obtained. An auxiliary result obtained is the value of the ``intrinsic mobility'' of a domain wall which for a 65 Permalloy specimen is determined to be about 100 cm/sec oe.
Theory of Remagnetization of Thin Tapes
Authors: Ekstein H.
Published: April 2005

It is assumed that the velocity of the domain wall is proportional to the difference between the magnetic field intensity at the wall and the coercive force. The local magnetic field, which is not equal to the external field, is calculated from the eddy-current equations. The rate of change of the magnetic flux as a function of time is determined. The total switching time is expressed in terms of two phenomenological constants: the retardation constant α mentioned above, and a delay time τ, the duration of the formative phase during which the plane walls are formed.
On the Transient Behavior of Semiconductor Rectifiers
Authors: Gossick B. R.
Published: April 2005

If the forward current through a p-n junction suddenly ceases, an emf appears due to nonequilibrium carrier concentrations at the junction barrier. Measurements of the barrier emf have been made with a wide range of injection currents and yield current vs barrier voltage characteristic curves. The open circuit case of voltage decay across a p-n junction in the range V≫kT/q is discussed. The voltage decay is observed to be linear with time with a slope kT/qτ. It follows from an analysis based on a simple model that the excess minority carrier concentrations decrease exponentially with the time constant τ. The floating emitter and collector voltages, VE(t) and VC(t), of p-n-p transistors are observed to decay like the open circuit voltage across a p-n junction, and it is noted that VE(t) ≈ VC(t) in the range V≫kT/q. The transient response of a semiconductor rectifier connected in parallel with a large external capacitance is analyzed. The response calculated for large negative excursions of voltage gives a simple relation by which the saturation current may be determined. Measurements are presented and discussed.
Photoelectric Yields in the Vacuum Ultraviolet
Authors: Walker W. C. , Wainfan N. , Weissler G. L.
Published: April 2005

Absolute photoelectric yields of Ni, Cu, Pt, Au, W, Mo, Ag, and Pd are presented for the spectral region from 1400 to 473 A. Measurements were obtained for commercially pure polycrystalline surfaces which were treated in various ways including heat treatment in vacuo and in various gas atmospheres at reduced pressures. Surfaces, heat treated in vacuo, gave reproducible yields ranging from 10−3 electrons per photon at 1400 A to 10−1 electrons per photon at 500 A. Although untreated samples exhibited a maximum in the region studied, this maximum disappeared after heat treatment resulting in most cases in a broad plateau extending from 1000 A to 500 A. At wavelengths longer than 1000 A a decrease in yield was observed. Representative experiments with a Ni cathode, heat treated in vacuo then exposed to O2 at reduced pressures, indicated that the maxima for untreated surfaces were caused by adsorbed gases and metallic oxide formation. The absolute error in the values of the photoyields was estimated to be within ±15%.
Space-Charge Distribution in a Static Magnetron
Authors: Nedderman Howard C.
Published: April 2005

The space-charge distribution in a static magnetron was investigated by a method involving measurement of the radiation intensity from excited gas atoms at low pressure. Results of the measurements show that space charge extends to the anode under all conditions. Evidence is presented to show that a considerable fraction of the space charge consists of electrons that are trapped for exceedingly long times within the interaction space.
Thickness-Shear and Flexural Vibrations of Rectangular Crystal Plates
Authors: Mindlin R. D. , Deresiewicz H.
Published: April 2005

Equations governing thickness-shear and flexural vibrations of crystal plates are solved for the infinite plate, the simply-supported rectangular plate and the rectangular plate with one pair of parallel edges free and the other pair simply-supported. The equations permit three types of sinusoidal waves, with sinusoidal crests, in an infinite plate. Each of these undergoes a simple reflection upon normal incidence at a simply-supported straight edge, so that the frequency spectrum of a simply-supported rectangular plate has a relatively simple character. The results of a typical computation are given for the AT-cut of quartz. At a free edge each type of incident wave gives rise, in general, to all three types of reflected wave. Consequently, the frequency spectrum of a plate with a pair of parallel, free edges exhibits an intricate coupling of three infinite systems of modes. The development of the coupling is traced continuously by means of a solution involving elastically supported edges.
Space-Charge Effects in Electron Optical Systems
Authors: Dolder K. T. , Klemperer O.
Published: April 2005

Beams consisting of charged particles which are all directed towards a given virtual focus will generally not reach this focus but, due to their mutual repulsion, they will pass through a waist and then become divergent. Ray tracing shows that either positive or negative spherical aberration is introduced in a beam passing through a waist. This aberration is caused by the interaction of the electrons; its sign depends on voltage, current, and on the angle of initial convergence of the beam. For sufficiently high voltages or low currents, waist formation no longer occurs, but the electron rays cross the axis of the beam. With decreasing current density, the transition from waist to crossover is found to occur first for the inner rays of the beam while the outer rays still form a waist. All experimental results are found to be in approximate agreement with theoretical predictions.
Ferroelectric Hysteresis in Barium Titanate Single Crystals
Authors: Wieder H. H.
Published: April 2005

The properties of the dynamic hysteresis loop of a c-domain BaTiO3 single crystal are examined as a function of temperature. Experimental results indicate that the coercivity and hysteresis losses decrease sharply as the crystal passes through a phase transition to a lower order of symmetry. This occurs without a substantial loss in loop rectangularity. The properties of a theoretical model for the hysteresis loop are derived from the Devonshire thermodynamic equations and previously defined experimental parameters. In the tetragonal and orthorhombic crystal phases, good agreement is obtained between the behavior predicted for the theoretical model and the experimental observations made on a c-domain.
Calculation of the Complex Modulus of Linear Viscoelastic Materials from Vibrating Reed Measurements
Authors: Bland D. R. , Lee E. H.
Published: April 2005

Two methods of determining the variation of real and complex modulus with frequency from vibrating reed test results are detailed. One is based on measurements of the relative amplitude and phase lag of the motion of the free and driven ends of the reed, the other on amplitude resonance measurements only. The analysis is based on a general linear viscoelastic law, and takes into account the influence of the frequency dependent moduli of the material on the frequency and amplitude of the resonance peaks. This influence has not been correctly accounted for in previous analyses which have included the assumption that the material behaves according to a particular, simple viscoelastic law, which will in general not be borne out by the final results.

The method is applied to a series of tests. For the material and frequency range used the imaginary part of the complex modulus was small compared with the real part, and the influence mentioned in the foregoing was small. A simpler method of analysis might thus be justified, but in other cases it will be necessary to carry out the complete analysis in order to obtain a satisfactory interpretation of test results.
Short-Time Frequency Measurement of Narrow-Band Random Signals by Means of a Zero Counting Process
Authors: Steinberg Herbert , Schultheiss Peter M. , Wogrin Conrad A. , Zweig Felix
Published: April 2005

Any instrumentation for measuring the mean frequency of a narrow-band random signal presents an output quantity which inherently fluctuates about that value which represents the true mean frequency, due to the finite measuring time. In comparing the accuracy of various instrumentations for short-time frequency measurement a useful figure of merit is variance of the output/(sensitivity)2. In this paper the figure of merit is obtained for an instrumentation which measures frequency by determining the average number of zero crossings of the signal in a short time. The significant problem is the determination of the mean square number of zeros of a random function in time T. The general result is presented in the form of an integral. For an assumed Gaussian power spectrum the integral is integrated graphically to obtain a figure of merit which is compared with previously published figures of merit of an autocorrelator and frequency discriminator.
Anomalous Forward Switching Transient in p-n Junction Diodes
Authors: Jones N. T. , Kingston R. H. , Neustadter S. F.
Published: April 2005

A delay in the flow of forward current when a grown-crystal p-n junction diode is switched from reverse to forward bias is explained on the basis of an extra p-n barrier in the grown-crystal bar. This effect was observed in 10 out of 24 production units, while no such anomaly was found in fused-junction diodes. A mathematical theory of the effect gives good agreement with the experimental results.
Methods of Measuring Dielectric Constants Based upon a Microwave Network Viewpoint
Authors: Oliner A. A. , Altschuler H. M.
Published: April 2005

Dielectric samples located in wave guide are represented by network four-poles whose admittance determinant is related simply to the dielectric constant. The four-pole viewpoint, which has heretofore not been adequately exploited, makes possible the utilization of the whole body of transmission line four-pole measurement techniques, including those of precision and invariance. New measurement procedures based on these techniques have been formulated which are either length invariant or location invariant; that is, the dielectric constant is determinable without the knowledge of either the length or the location of the sample. Four specific measurement procedures are presented which incorporate the precision as well as the invariance aspects.
Information Theory Aspects of Propagation through Time-Varying Media
Authors: Feinstein Joseph
Published: April 2005

The channel capacity of a communications system which utilizes wave propagation through a time-varying medium such as the ionosphere or troposphere is evaluated in terms of the statistical properties of the medium and of the noise. The signal fading in such a system reduces the capacity. Rayleigh fading is found to give rise to an equivalent signal to noise ratio of 1.72, while shallow fading of the Gaussian type augments the noise in the channel by a fraction of the signal power proportional to the fading depth. An optimum manner of band width subdivision is shown to exist when selective fading is present.

Information theory concepts are broadened to include the possibility of multiple reception at spaced receiving sites, and the consequent increase in theoretical channel capacity is computed as a function of the number of such sites and the signal statistics. The method of maximum liklihood is utilized to obtain optimum combinatorial laws for the multiple signals. The commonly employed maximum signal selection diversity system is shown to perform as well as the optimum system in the presence of Rayleigh fading, for a small number of receiving sites.
Analog Computer Construction of Conformal Maps in Fluid Dynamics
Authors: Tomlinson N. P. , Horowitz M. , Reynolds C. H.
Published: April 2005

A general-purpose electronic analog computer has been used extensively to construct the streamlines around two-dimensional airfoil shapes immersed in an incompressible, nonrotating, nonviscous fluid. The computer generates a circular Lissajous pattern on a plotting table, and then transforms the coordinates of the circle into the airfoil shape by a conformal transformation. Two samples of the variety of airfoil shapes so constructed are shown. The accuracy of the process, which has been checked by a digital computer and a desk calculator, is quite satisfactory; the speed of the actual mapping process is highly advantageous to thorough exploration of a variety of airfoil shapes.
Effect of Temperature on Total Resonance Absorption of Neutrons by Spheres of Uranium Oxide
Authors: Creutz E. , Jupnik H. , Wigner E. P.
Published: April 2005

In the expression 1/α=c[1+(κ/ρR)] for the advantage (α) of decreased resonance absorption of uranium in a dE/E neutron spectrum brought about by lumping UO2 into spheres, the temperature dependence of c is measured and κ is measured also. ρ is the density of UO2 in g/cm3; R the radius of the sphere in cm. In the range 20° to 1000°C, Δc/ΔT averages 1.8×10−6 per degree centigrade and is positive as expected. This temperature dependence decreases by about a factor of three from the lowest to the highest measured temperatures. κ is 5.06 g/cm3 leading to a value of μ in the expression [Phys. Today 5, 32 (May, 1952)] ( ∫ σ(E)dEE)eff=A[1+μSM]of 1.69 g/cm2. ΔAΔT is 4×10−4barnsC∘.
Analysis of Scintillation Spectrometer Observations of the Penetration of Cs137 Gamma Radiation through Water
Authors: Theus R. B. , Beach L. A. , Faust W. R.
Published: April 2005

Spectral modifications of Cs137 gamma radiations produced by penetration and diffusion through water have been observed. A single crystal of NaI(Tl) was used to observe the pulse-height distributions produced by radiation from both plane parallel and point isotropic sources. Inversion of the pulse-height distribution was carried out by use of an analog computer to obtain the spectral distribution of radiation.
Gap Problem in Antenna Theory
Authors: King Ronold
Published: April 2005

The so-called gap problem in antenna theory is considered critically. It is shown that whereas there exist problems related to transmission-line end-effect and coupling between antenna and line, there is no gap, and hence no gap problem, when a physically realizable complete transmitting system is considered rather than an antenna with a fictitious mathematically convenient driving mechanism.
Use of Space Charge in Electron Optics
Authors: Ash E. A.
Published: April 2005

The electron optical properties of a cylindrical space charge cloud are derived. The possibility of achieving a system free from either spherical or chromatic aberration by combining a space charge lens with a space charge free converging lens is examined. It is concluded that the achromatization of a thin electric or magnetic lens is possible only if the resultant action of the combination is divergent. The correction of the spherical aberration of a high quality lens, such as an electron microscope objective, is shown to be impossible on account of electron interaction effects.
Radiation Characteristics of a Conical Helix of Low Pitch Angle
Authors: Chatterjee J. S.
Published: April 2005

The present work is an extension of the author's prior work on the radiation characteristics of and current distribution in a conical helix, the helix used in the present case having a pitch angle much lower than of that studied previously. In this case the condition of the phase velocity adjusting itself automatically to maintain maximum directivity condition (which enables the radiation to be confined in the axial mode over a large band of frequencies) does not hold. Nevertheless the major fraction of energy could be radiated in the axial direction when the geometry of the helix and the distance of the apex from the ground were properly chosen, the conical helix together with the ground being regarded as tapered transmission lines (with the ground as one and the helix wire—with the distance of its elements from the ground line increasing continually,—as the other line).

Measurements of the field intensity and the current distribution were made in the frequency range of 100 Mc/sec to 500 Mc/sec with a conical helix antenna arrangement as follows. The helix was of six turns, the radius increasing uniformly from 5 cm at the apex to 65 cm at the base within an axial distance of 60 cm. The apex of the helix was placed at a distance of 17.5 cm from the ``ground'' provided by a 6-ft square copper netting of close mesh. It was found that within the range of frequency measured the major fraction of the energy was radiated in the axial direction. Theoretical expressions for Eφ and Eθ were derived by assuming a linear current distribution, and the calculated radiation patterns were found to agree with the experimentally determined ones.
Studies of the Diffraction of Electromagnetic Waves by Circular Apertures and Complementary Obstacles: The Near-Zone Field
Authors: Ehrlich Morris J. , Silver Samuel , Held Gedeliahu
Published: April 2005

The diffraction of electromagnetic waves by circular apertures in extended conducting screens and by complementary obstacles was investigated experimentally to determine the structure of the field in the near zone. Techniques for measuring both the electric and magnetic field distributions are presented and the general experimental problems are discussed. Data are given for the tangential components of the electric and magnetic vectors in the principal planes in the immediate neighborhood of the diffracting structures, and axial distributions for the corresponding components. The results extend the range of the data available previously. The predicted uniformity of the tangential magnetic field in the aperture plane, for the case of a wave incident normally, is verified. An experimental test was made also of the electromagnetic Babinet principle.
Rate of Formation of Film on Metals and Alloys
Authors: Chatterjee G. P.
Published: April 2005

The rate of atmospheric corrosion of Cu–Zn and Cu–Mg alloys are retarded by Al or Mn, and the law of the growth of film in the case of Cu–Zn alloys changes over from the parabolic to the logarithmic law on the addition of Al or Mn. For Cu–Mg alloys under a given set of conditions the law of the growth of film is governed by x12=k1logt+k2,where x is the film thickness, t is time, and k1 and k2 are constants. It has been indicated that some experimental data on the corrosion of metals and alloys may be quantitatively represented if two or more functions, representing different mechanisms of the growth of film, are taken into consideration simultaneously.
Creep of Aluminum under Cyclotron Irradiation
Authors: Jeppson M. R. , Mather R. L. , Andrew A. , Yockey H. P.
Published: April 2005

The effect of cyclotron irradiation by 38-Mev alpha particles on the steady-state creep rate (ca 10−6 per second) of aluminum has been measured at beam densities up to 1.2×1013 particles per cm2 per second. The data, which were taken on a 0.016-inch thick aluminum specimen for a stress range of 600 to 2500 psi and over a temperature range of 160° to 330°C, showed a slight decrease in rate (up to 19 percent) during irradiation. Since the effect is small, apparently independent of beam density, and is comparable to the usual deviations in the absence of radiation, it can be considered a null result.