bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Boiling in Short Narrow Channels and Its Application to Design of Magnets Cooled by Liquid H2 and N2
Authors: Sydoriak S. G. , Roberts T. R.
Published: April 2005

A study has been made of the critical heat input, Q̇c, to liquid H2 and N2 boiling in an annular gap, of cross-section area, A, between a vertical cylindrical heater of height, Z, and various concentric plugs. The data are in approximate agreement with calculations based on an assumption of homogeneous and frictionless two phase flow. The pressure drop across the channel is spent primarily to accelerate the vapor being formed and the liquid carried with it. The derived relation does not contain any empirical coefficients or exponents. For ρv,2≪ρL the general equation reduces to Q̇=AL(ρV,2 ρLZegf2)12,where L is the latent heat of vaporization, ρv,2 the exit vapor density, ρL the liquid density, g the gravitational acceleration, Ze the hydrostatic head equivalent to the pressure drop across the heater, and f2 the mass fraction of vapor in the fluid leaving the heater.

Forced flow experiments give f2. At Q̇c equal to that found in natural convection boiling, f2=̇0.5 for both liquids. For Z=3 or 6 in. and a channel thickness of 0.022 in. the ratio of observed to calculated Q̇ is 0.95 for N2 and 0.70 for H2. The calculation is equally good for critical natural convection experiments, Ze=Z, and for subcritical as well as critical forced flow measurements, which extend up to Ze=70 Z.

The optimum operating vapor pressure is discussed for magnets cooled by ideal natural convection boiling. A simple roll-type of coil is discussed and is shown to be superior in some respects to more conventional windings.
Special Theory of Ultrasonic Machining
Authors: Miller George E.
Published: April 2005

A model is proposed for the mechanism of material removal in ultrasonic machining. From this model and fundamental physical principles, a machining rate equation is derived for the special case where solid, circular tools are used in conjunction with a puddled slurry. A comparison of the predictions of the theory with the experimental data shows that the theory gives the correct relationship between the machining rate and the variables involved in the machining process. Suggestions for the improvement of the ultrasonic machining process are presented, and the method to be used in generalizing the theory is outlined. The poor reproducibility of the machining rate measurements is explained on the basis of the machining rate equation.
Work-Function Studies of Germanium Crystals Cleaned by Ion Bombardment
Authors: Dillon J. A. , Farnsworth H. E.
Published: April 2005

The work functions of germanium single crystals have been obtained by measuring the contact potential differences between the germanium crystals and a gold reference whose work function was measured by the Fowler method. Work function values for the bombardment-cleaned surfaces of three samples having comparable resistivities were the same within experimental error (4.78±0.015 ev). Variation in the doping concentration resulted in work-function changes smaller than those predicted by a simple Fermi level shift. Adsorption of oxygen at pressures of about 1×10−7 mm Hg resulted in work-function increases of about 0.20 ev. The clean surface work-function values could be restored after O2 adsorption by heating at 500°C for 15 min. For those cases in which changes were noted, adsorption of hydrogen and nitrogen at higher pressures (10−3 mm Hg) resulted in decreases of work function, while CO adsorption increased the work function. Measurements of the effects of strong electric fields and intense illumination on the work function suggested that these effects were associated with rather thick surface layers which could be removed by vacuum heating or ion-bombardment cleaning. The photoelectric-threshold level was near or slightly above the Fermi level for the ion-bombardment cleaned surfaces. After oxygen adsorption the threshold level was below the Fermi level.
Angular Averages in the Scattering of Slow Neutrons by Gases
Authors: Volkin Howard C.
Published: April 2005

A procedure is developed for averaging over the thermal translational motion of a gas scatterer in order to obtain observed angular averages from a knowledge of the differential cross section in the center-of-mass system. The results are applied to the simple case of spherically symmetrical elastic scattering with constant cross section.
Dependence of the Ferromagnetic Resonance Line Width on the Shape of the Specimen
Authors: Berk A. D.
Published: April 2005

The dependence of line width of the ferromagnetic resonance on the shape of the sample is examined on phenomenological grounds. If a damping term of the Bloch-Bloembergen type is assumed in the equation of motion of the magnetization, the line width for an ellipsoidal sample is given by ΔH=[1+Ms2γ2(Nx−Ny)2/4ω2]−122/γT2. The Landau-Lifshitz form of damping leads to a line width which is independent of the shape of the specimen.
Annealing of Cold-Worked Copper by Electron Irradiation
Authors: Meechan C. J.
Published: April 2005

Copper wires were cold worked at room temperature to approximately a 15% reduction in area and were then irradiated at temperatures between 100° and 150°C with 1.25-Mev electrons. The residual resistivity was observed to decrease as a function of exposure at temperatures above 100°C. The higher the temperature at which the irradiation was performed, the greater was the rate of resistivity decrease. From these data, it is concluded that one of the primary defects produced by electron irradiation becomes mobile in the temperature range, 100°–150°C. It is suggested that interstitials and vacancies produced by the irradiation initiate a process which results in the annihilation of dislocations. From an analysis of the temperature dependence of the rate of decrease, a value for the activation energy for vacancy migration in copper has been deduced: 1.28±0.10 ev.
Linear Dissipation in Solids
Authors: Lomnitz C.
Published: April 2005

In solid materials the properties of transient creep, internal friction and dispersion can be correlated on the basis of a linear theory, if the strains are small throughout. The theory, first given by Boltzmann, is developed in some detail. Dissipative properties of the material are shown to depend on a function of time called the ``creep function'' φ(t).

The general condition 1/Q≅constant is examined. This condition is compatible with a creep function of logarithmic type. Velocity dispersion of plane or spherical waves is very small in such a medium. Graphs of 1/Q, phase and group velocities vs frequency are given, and a quantitative relationship between creep and internal friction constants is derived. The results are substantially applicable to the problem of losses in dielectrics, by carrying out the electromechanical analogy.
Grain Boundaries for Field Emission Microscopy
Authors: Brock E. G.
Published: April 2005

Heretofore the observation of grain boundaries with the field emission microscope has been limited by the accidental and infrequent appearance of suitable specimens. A process for preparing polycrystalline tungsten samples by bending a tungsten wire, etching a tip at the bend and heating is described. Both large and small angle grain boundaries result. As many as five tungsten grains may share a cross section of less than one micron in diameter. All the parameters required to describe the geometry of the boundaries may be obtained experimentally. Detailed observations on the dislocation structure of boundaries with angles as great as 6° are potentially possible. However, the field emission intensity from the region immediately adjoining and including the grain boundary must first be increased appreciably. Possible methods for achieving improved electron emission from the grain boundary region are discussed.
Effect of Annealing in Various Gases on the Bulk Lifetime of Germanium
Authors: Weiser Kurt
Published: April 2005

High resistivity germanium single crystals were annealed at 500°C in various gases. For an oxygen atmosphere with a trace of water vapor present, the bulk lifetime more than doubled, then decreased to below the initial value. For dry oxygen and for nitrogen, helium, hydrogen, or argon in the presence of water vapor, the lifetime first remained constant, and then decreased. Prolonged annealing in dry helium did not affect the lifetime. The data have been interpreted in terms of a ``leaching out'' of an impurity recombination center by a water catalyzed surface oxidation, and a simultaneous formation of an oxide of germanium which diffuses into the bulk and on precipitation acts as a recombination center.
Theory of Thermal Grooving
Authors: Mullins W. W.
Published: April 2005

A theory is presented which describes the development of surface grooves at the grain boundaries of a heated polycrystal. The mechanisms of evaporation-condensation and surface diffusion are discussed with the use of the Gibbs-Thompson formula and the assumption that the properties of an interface do not depend on its orientation. For the idealized case in which only one of the mechanisms is operative, the groove profile is shown to have a time-independent shape whose linear dimensions are proportional to t½ for evaporation-condensation, and to t½ for surface diffusion. The proportionality constants are evaluated, and criteria are developed which permit one to estimate which process predominates in practice. Order of magnitude agreement is obtained with estimates of actual grooving speeds and profiles.
Reproducing the Properties of Alnico Permanent Magnet Alloys with Elongated Single-Domain Cobalt-Iron Particles
Authors: Luborsky F. E. , Mendelsohn L. I. , Paine T. O.
Published: April 2005

Single-domain particles of 40:60 cobalt-iron alloy have been prepared with a median diameter of 200 angstrom units, a median elongation of 5.4:1, and an intrinsic coercive force of 1950 oersteds. By compacting these particles to various packing densities and degrees of alignment, shape anisotropy fine-particle magnets have been made with magnetic properties duplicating those of each of the Alnico permanent magnet alloys, including maximum energy product values above five million gauss-oersteds. It is concluded that the Alnico alloys and the fine-particle magnets derive their properties from very similar, but not identical, shape anisotropy effects.
Steady-State Creep through Dislocation Climb
Authors: Weertman J.
Published: April 2005

A dislocation climb creep model is considered which does not require the production of immobile dislocations. The creep equation that results from the analysis is creep rate=Aσ3sinh(Bσ1.5/kT)exp(−Q/kT),where A and B are constants, σ is the stress, Q is the activation energy of creep and kT has its usual meaning. This equation is quite similar to one previously proposed.
Thermoelastic Damping at the Boundary between Dissimilar Solids
Authors: Lessen Martin
Published: April 2005

The problem of thermoelastic damping at the boundary between dissimilar solids is investigated for the case of small, sinusoidal, longitudinal disturbances of long-wavelength propagating normally through the interface. The relevant equations are derived from thermodynamic considerations, and it is found that the mechanical energy absorption per unit time is proportional to the square root of the disturbance frequency.
Activation Field and Coercivity of Ferroelectric Barium Titanate
Authors: Wieder H. H.
Published: April 2005

The activation field of BaTiO3 c-domain crystals may be calculated from an experimental determination of the frequency dependence of the coercivity. The ratio of activation fields above and below the orthorhombic transition is equal to the respective ratio of coercivities. The decrease in coercivity in passing through this transition is related to the change in thickness of the space charge layer within the ferroelectric.
Etching Behavior of Pile-Irradiated Germanium and Silicon Single Crystals
Authors: Chang Roger
Published: April 2005

Germanium single crystals pile-irradiated at 20°C and 1014 to 1017 n/cm2 etch differently from similar crystals which have not been irradiated. The irradiated crystals when etched with CP-4 show a finer surface granulation. This difference in etching behavior is reduced on annealing. Kinematic studies indicate an activation energy for the annealing process between 1.6 and 1.8 ev. The etching behavior of silicon single crystals shows a similar change on pile irradiation. The present work, though preliminary in nature, suggests a new experimental approach to the study of radiation damage.
On Transition from Laminar to Turbulent Flow
Authors: Hama Francis R. , Long James D. , Hegarty John C.
Published: April 2005

Water-tank observations of the flow phenomena associated with boundary-layer transition have revealed that a two-dimensional discrete vortex line, which is considered to be the consequence of an amplified perturbation wave, has a strong tendency, in shear flows, to form three-dimensional vortex loops with a marked transverse wavelength. The formation and development of the vortex loop is found to be the essential feature preceding the creation of a turbulent spot which takes place near the top of the vortex loop and near the outer edge of the boundary layer. This formation and development provides the guiding principle of laminar-to-turbulent transition in wakes and jets as well as in the boundary layer.
Deposit Spot Patterns from Low-Index Planes of Metal Single Crystals in a New Theory of Cathode Sputtering
Authors: Henschke Erich B.
Published: April 2005

The generation of the deposit spot patterns from low-index planes at lower and higher ion energy is explained by mechanical double and triple collisions of the perpendicularly incident ions with lower and upper surface atoms of the target plane. The effective collision spheres are assumed to be determined by the largest closed electronic shells of the ion and the target atom with radii smaller than the radii of the largest electronic orbits of these shells. A second factor has to be taken into account for the explanation of the shape and other features of the single spots of the patterns. This is the attenuating influence of the different electron densities in the paths of the ion within the lattice, because the largest closed electronic shells exceed the size of the collision spheres and produce the highest electron density in close-packed rows of the lattice.

These two concepts are sufficient to explain the number and arrangements of the spots in the patterns of low-index planes, the specific shape of the single spots, the alterations of the spot patterns connected with higher ion energy or with accidental deviations of the prepared crystal plane from the ideal crystallographic plane, the deviation of the symmetry axis of the single spots in (110) fcc patterns from the diagonal direction of the unit area, and finally the different shape and size of the single spots in (111) spot patterns of silver and copper.
On the Cause of the Anomalous Flicker Effect
Authors: Lindemann W. W. , Van Der Ziel A.
Published: April 2005

This paper extends earlier work by Johnson and Donal on the anomalous flicker effect, observed in tubes with a tungsten cathode under space charge limited condition, and attributed to positive ions emitted by the cathode. This extension involves the observation of the individual current pulses causing the effect and the measurement of the flicker effect noise spectrum over a wide frequency range. The results indicate that these pulses are due to sudden bursts of about 104 positive ions emitted by the cathode in less than 1 μsec and trapped in the space charge for many μsec. The trapping time of the ions is determined from the shape of the pulses and from the noise spectrum, and the results are found to agree. An experiment that verifies directly that the effect is caused by positive ions also shows the way to eliminate the effect. A discussion of the nature of these sudden bursts is offered and various mechanisms for the observed decay of the pulses are presented.
Form of Polder Tensor for Single Crystal Ferrite with Small Cubic Symmetry Anisotropy Energy
Authors: Seidel H. , Boyet H.
Published: April 2005

The Polder tensor susceptibility is derived for a single crystal ferrite possessing cubic symmetric anisotropy energy. The tensor is derived for the 110 plane of the cube and its elements are exhibited as a function of the angle that the applied field makes with a cube edge, as well as of saturation magnetization, applied field, anisotropy constant, and frequency. The analysis is valid for ferrites with anisotropy fields much less than externally applied magnetic fields. The tensor is no longer diagonal for circular polarizations, except along the 100 and 111 axes.
Exact Current-Voltage Relation for the Metal-Insulator-Metal Junction with a Simple Model for Trapping of Charge Carriers
Authors: Suits Gwynn H.
Published: April 2005

The exact solution to the diffusion equation for one kind of charge carrier is obtained for the metal-insulator-metal junction where trapping of the charge carriers may occur in the body of the insulator. The effect of surface states is not considered. The electric potential distribution is given in closed form and the exact dc current-voltage relation is given in parametric form for any degree of trapping. A graph of the current-voltage relation is shown for the special case where the two boundary metals are the same.

A brief description of some experimental difficulties is given when test junctions were prepared entirely by the vacuum evaporation method.
Magnetic Anisotropy and Rotational Hysteresis in Elongated Fine-Particle Magnets
Authors: Jacobs I. S. , Luborsky F. E.
Published: April 2005

Various aspects of the magnetic anisotropy of electrodeposited elongated single-domain Fe and FeCo alloy particles are examined with a view to better understanding their process of magnetization. The initial increase of coercivity with increase of the angle between alignment direction and measuring field is in qualitative accord with the prediction of the chain-of-spheres model with fanning, as previously proposed, and in contrast to coherent rotation models. Analyses of high-field torque curves and of the fields at which rotational hysteresis vanishes suggest that an anisotropy is present which is a little greater than predicted by the chain-of-spheres model but less than that predicted by the Stoner-Wohlfarth ellipsoid model, for the observed dimensional ratios. Calculations of the rotational hysteresis in single domain-particles are extended to the chain-of-spheres model. A study of the rotational hysteresis enables a relatively sensitive choice between several models of the magnetization process. Comparison of the observed and predicted values for the rotational hysteresis integral, ∫(Wr/Is)d(1/H), indicates strongly that a nonuniform rotation process, like fanning in a chain-of-spheres, is operative in electrodeposited elongated single-domain particles.
Transverse Scaling of Electron Beams
Authors: Herrmann Gabriel
Published: April 2005

Under certain conditions an electron beam can be subjected to a process of scaling in which the transverse components of position, velocity, and force are scaled by a common factor while longitudinal components remain unchanged. In analyzing beams produced by electron guns under conditions where thermal velocity effects have to be taken into consideration, the application of transverse scaling simplifies the treatment by allowing a reduction in the number of independent parameters required. Design curves for Pierce-type guns are reproduced in normalized and condensed form. These curves may be used in choosing design parameters to produce a prescribed beam.
Permanent Magnet Oxides Containing Divalent Metal Ions. II
Authors: Van Uitert L. G. , Swanekamp F. W.
Published: April 2005

The dependence of saturation induction at room temperature upon composition for the substitution of nonmagnetic ions into BaFe12O19, into BaM2Fe16O27 (where M2=Ni2, Ni1.5Cu0.5, Zn2), and into the mixture BaNiFe14O23 is given. Evidence is presented for the existence of points of magnetic compensation in a number of series wherein aluminum is substituted for iron. The distribution that gallium takes in these structures appears to depend upon the sites occupied by divalent metal ions.
On the Origin of Certain Spirals of Large Step-Height Observed on Crystal Surfaces
Authors: Lang A. R.
Published: April 2005

Periodic bunching together of advancing or retreating atomic sheets frequently occurs on crystal surfaces inclined at small angles with densely packed atomic planes, and it causes microscopically observable steps to appear. Around a domed surface, in the case of growth, or around an etch pit, in the case of solution or evaporation, such steps usually form concentric rings. It is shown, however, that a simple ``mistake'' in the early stages of step formation will produce, instead of rings, a continuous spiral step. No screw dislocations, therefore, are required for the production of this spiral step.
Pinch Effect
Authors: Burkhardt Louis C. , Dunaway Robert E. , Mather Joseph W. , Phillips James A. , Sawyer George A. , Stratton Thomas F. , Stovall Emory J. , Tuck James L.
Published: April 2005

Some early studies of the pinch effect, made with a view to its application to the problem of developing a thermonuclear reaction are here presented, together with experimental arrangements for producing pinched discharges in toroidal and straight discharge tubes. Dynamical properties of the pinch and its instabilities are demonstrated, and the possibility of stabilizing the latter is mentioned.
Electrical Resistivity of Nickel-Palladium Alloys
Authors: Overhauser A. W. , Schindler A. I.
Published: April 2005

The concentration dependence of the residual resistivity of Ni–Pd alloys might be expected to obey a simple Nordheim law since the number of holes in the d band and the number of electrons in the s band are approximately independent of composition. Measurements have indicated, however, that the maximum resistivity occurs at 70 atomic percent Pd instead of 50%. This behavior can be explained by the spin dependence of electron scattering processes associated with the fact that the alloys with greater than 3% Ni are ferromagnetic. Quantitative fit of the data is possible if it is assumed that the density of states at the Fermi energy in the d band is approximately proportional to the number of holes, rather than to the cube root of this number. Data on the resistivity and paramagnetic susceptibility of Ag–Pd alloys support this hypothesis. The relative strength of s-d scattering to s-s scattering must be assumed to be about 5:1.
Long-Wave Neutron Spectrum of the Materials Testing Reactor
Authors: Borst L. B. , Miller L. G.
Published: April 2005

The long-wave spectrum of a neutron beam from the Be reflector of the Materials Testing Reactor (MTR) has been measured from 3 A to 10 A by a total reflection technique. The spectrum was found to vary as λ−3.9.
Microwave Gas Discharge Breakdown in Air, Nitrogen, and Oxygen
Authors: Rose D. J. , Brown Sanborn C.
Published: April 2005

The microwave breakdown electric field has been measured for pure air uncontaminated by discharge products (presumably oxides of nitrogen), and for nitrogen and oxygen separately. The breakdown field for pure air is significantly higher than that previously observed, in which cases such contamination could be suspected.

The breakdown field for pure air lies between those for nitrogen and oxygen. A calculation of the high-frequency breakdown field in air is made from dc data, using the measured Townsend ionization coefficient, electron attachment coefficient, and average electron energy. The present data agree well with this calculation.
Electron Beam Analyzer
Authors: Ashkin A.
Published: April 2005

A new technique is described for measuring the charge distribution of an electron beam in a magnetic field. The method is especially applicable to the long, thin, high-current beams commonly used in traveling wave tubes and backward wave oscillators. It consists of making the beam trace out its own characteristics by sweeping it across a pinhole in crossed electric and magnetic fields. The data are presented in the form of oscilloscope pictures of the actual charge distribution. Quantitative measurements of the charge distribution are also obtainable.
Electrical Properties of Arc-Evaporated Carbon Films
Authors: Blue M. D. , Danielson G. C.
Published: April 2005

Uniform thin films of carbon in the thickness range 100 to 2300 A have been prepared by arc-evaporation in vacuum. Evaporation rates were about 50 A/sec. The electrical properties of these films suggest that unannealed arc-evaporated carbon had less long-range order and was, therefore, more truly amorphous in structure than any other form of carbon yet obtained. After the films had been heated to 1200°K, however, their properties were similar to ordinary fine-particle carbon blacks, apparently as a result of increased ordering. The electrical resistivity of unannealed films followed Ohm's law, was not photosensitive, and could be well represented in the temperature range 77°K to 300°K by the equation R=AT−b, where b=5. When the carbon films were heated above room temperature, the resistivity and the exponent b were both decreased substantially. After the films had been annealed at 1200°K, the resistivity was reduced by a factor exceeding 800, and could be best represented, in the temperature range 77°K to 1200°K, by the equation R=α—βT. The values of the resistivity, temperature coefficient of resistivity, and thermoelectric power of the annealed films were then more nearly in agreement with the corresponding values for ordinary fine-particle carbon blacks. Other properties and applications of the films are discussed.
Radiation Effect of Positive Ion Bombardment on Glass
Authors: Hines R. L.
Published: April 2005

Bombardment of a silica-soda-lime glass (nD=1.5246) by more than 5×1016 A+ ions/cm2 with an energy of 33.5 kev reduces the reflection coefficient to 0.36 of its normal value for light of wavelength λ=0.6 μ. The change in reflection coefficient is attributed to the formation of an altered glass layer. For a bombardment by 40-kev A+ ions, the layer has a thickness of 0.095 μ and an effective refractive index of 1.343. The depth of the layer is determined by the ion energy and agrees approximately with the theoretical range of the incident ions. The refractive index of the altered layer is determined by the integrated flux of positive ions and the type of ion. The magnitude of the positive ion flux employed here is shown to be orders of magnitude larger than the flux of primary ``knocked-on'' atoms produced by fast neutron bombardment in a reactor.
Strength and Fatigue of Glass at Very Low Temperatures
Authors: Kropschot R. H. , Mikesell R. P.
Published: April 2005

The strength and fatigue properties of borosilicate crown (BSC-2) optical glass were measured at various temperatures within the range 20°K to 296°K. Simple beam specimens with two-point loading were tested in both the abraded and unabraded condition. The breaking stress for a given condition increases with decreasing temperature. The fatigue decreases with decreasing temperature but still exists at 76°K.
Infrared Emissivities and Absorptivities of Gases
Authors: Penner S. S. , Thomson A.
Published: April 2005

Approximate analytic expressions are obtained for the ``effective band widths'' and emissivities of diatomic molecules at elevated pressures.

The absorptivities of molecular vibration-rotation bands are evaluated for radiation emitted by similar molecular vibration-rotation bands and for radiation emitted by blackbodies. The results obtained for the absorptivity calculations compare favorably with available empirical correlations for H2O.

The postulated model does not apply to CO2 and, therefore, no satisfactory theoretical formula has been derived for the absorptivities of this molecule. The appendix (by A. Thomson) is devoted to a critical examination of the limits of validity of the effective band-width concept for different molecules.
Correction for the Finite Magnetic Modulation Amplitude in Paramagnetic and Nuclear Magnetic Resonance Lines
Authors: Spry W. J.
Published: April 2005

A general method of correcting for the finite magnetic modulation amplitude in line shape analyses of paramagnetic or nuclear magnetic resonance lines is described. The method consists of determining the proper ``folding'' function for the detection system. Once this has been determined, the numerical ``unfolding'' procedure of A. R. Stokes can be used to compute the true line shape from the observed shape of an arbitrary experimental line.
Glow-Arc Transition in Current-Stabilized Electrical Discharges
Authors: Jenkins Jobe , Jones T. Benjamin
Published: April 2005

The purpose of this investigation was to measure the limits with regard to currents and time duration of the glow and arc modes for the low current discharge at atmospheric pressure. In addition, some indications were obtained as to the conditions at the cathode which lead to such transitions. Accurate measurements in the normally unstable transition region were made possible through the use of a current stabilized power supply, together with special instrumentation for determining the magnitude and duration of the arc or glow voltage for periods as short as 0.02 microsecond.

It is shown that glow-arc transitions can occur for currents as low as 0.002 amp and for currents at least as high as 1.0 amp in the atmospheric pressure argon discharge. The duration of the arc mode at low currents is usually less than 5 microseconds. These low current transitions occur only when an oxide film is present on the cathode and are caused by the action of high fields created by positive ions across the bulk of the thin oxide films.
Effect of Neutron Interaction on Criticality. II
Authors: Stuart G. W.
Published: April 2005

A method for calculating the criticality conditions for spatially disconnected fissile regions based on the multiplication constant k is presented. To illustrate the method, the case of two interacting infinite water-tamped fissile slabs containing solutions of pure U235 in water is considered.
Small Signal Power Theorem for Electron Beams
Authors: Haus H. A. , Bobroff D. L.
Published: April 2005

An analysis is presented of a filament beam in arbitrary dc electric and magnetic fields. The trajectory of the filament beam in the absence of ac fields may thus follow an arbitrary curve. It is shown that the electromagnetic power delivered by the filament beam is, within the assumptions of small signal theory, balanced by a decrease in the beam of a quantity, the ``generalized ac power'' in the beam. This ac power involves products of the small signal beam-excitation amplitudes.

The ac power theorem for a filament beam can be extended to a thick beam. This is done to find the small signal ac power theorem for a two-dimensional rectilinear beam of finite thickness. The power theorem presented here is applicable to M-type and E-type traveling-wave devices. Applications to the noise theory and signal analysis of electron beams are indicated.
Minimum Saturating Fields for Ferromagnetic Crystals
Authors: Kouvel J. S.
Published: April 2005

The conditions for magnetic saturation are investigated analytically for a very thin ferromagnetic single-crystal disk or spheroid of cubic crystalline symmetry and positive magnetic anisotropy constant K1, whose axis of revolution is perpendicular to a {100} or {110} plane. Contrary to some previous work, it is found that an external field ranging in magnitude from NIs to NIs+2K1/Is (where NIs is the demagnetizing field) is sufficient for saturation in any direction in either of these planes. Above this field, the crystal behaves as a single magnetic domain. The applicability of the calculated minimum saturating fields to torque measurements is discussed.
Microwave Measurements of the Properties of a dc Hydrogen Discharge
Authors: Udelson Burton J. , Creedon John E. , French Judson C.
Published: April 2005

Microwave measurements of the properties of thin cross-sectional elements of a dc hydrogen discharge have been made. These measurements were accomplished by exposure of portions of the discharge in the gap between the cones of an S-band re-entrant cavity operating in the TM010 mode. The equipment and techniques for making the microwave measurements employing the re-entrant cavity are described. Measurements in the positive column of a dc hydrogen discharge showed the following results: Electron density increases with increasing tube current and also with increasing gas pressure in the pressure range measured (2 to 8-mm Hg). Electron collision frequency is approximately equal to 4.6×109 multiplied by the gas pressure in mm Hg, and is independent of tube current. When measurements were made in the negative glow region, several anomalous effects including a negative frequency shift were observed. These have been explained qualitatively as being caused by plasma resonance phenomena. The fact that these plasma resonance phenomena were also observed at a frequency of 8550 Mc demonstrates that the electron density in portions of the negative glow is at least 300 times greater than the density in the positive column.
Potential and Capacity of Concentric Coaxial Capped Cylinders
Authors: Kirkham Don
Published: April 2005

An exact solution is obtained for the potential in the space between two finite concentric coaxial right circular capped cylinders; and from the potentials an exact solution of the capacity is found. A set of infinite equations is involved but detailed numerical calculations, made for nine different geometries, show that if the ratio of height of the outer cylinder to diameter of the inner cylinder is less than about unity only the first eight equations and the first eight unknowns in them need be considered for obtaining three figure accuracy of the capacity. The theory is correct when the inner cylinder shrinks to a disk and also when the radius of the outer cylinder goes to infinity. Thus the theory yields the capacity for a horizontal disk midway between infinite conducting planes. When the planes become infinitesimally close to the disk the problem becomes two-dimensional, and the three-dimensional capacity expression goes over to an expression obtained by a conformal transformation. A table of coefficients for 1st, 2nd, 3rd, 4th, 6th, and 8th order approximations is given for computing quantities of interest and to show the rapidity of convergence of results for the nine geometries considered. For one of the cases the equipotentials and lines of force are computed and diagrammed.
Tensile Strength of Plastics below the Glass Temperature
Authors: Bueche F.
Published: April 2005

The times taken for two plastics, polystyrene and polyethyl methacrylate, to break under various constant loads are reported for both the glassy and rubbery states. A theory is presented which describes the strength properties of plastics in the glassy state. The theory predicts that the logarithm of the time taken for the sample to break is proportional to the applied load. Such behavior is actually found by experiment. The tensile data in the rubbery range are adequately represented by a theory previously developed for that region.
Electrical Conductivity of Fused Quartz
Authors: Cohen Julius
Published: April 2005

The electrical conductivities of two specimens of clear fused quartz were measured in vacuo in the temperature range of 600 to 1400°C. The method of potential probes was used to evaluate the platinum contacts and eliminate effects of high contact resistance. One specimen obeyed Ohm's law as evidenced by the linear dependence of the current on the potential between probes and the uniform potential distribution. This behavior established the specimen as an electronic conductor. The value of specific conductivity was ∼10−4 mho/cm over the interval from 1000 to 1400°C. Ohm's law was not found applicable for the other specimen, which displayed many dielectric anomalies and polarization effects such as polarization voltages, anomalous potential distributions, reverse currents, and current decays immediately after application of a voltage. The phenomena indicated the presence of space-charge polarization and here the conductivity appeared to be substantially ionic. Heat treatment of this specimen stabilized the electrical behavior and caused increased or decreased resistance, depending on voltage, polarity, and temperature of measurement. The heating was also found to produce partial crystallization. It is suspected that the marked contrasts in the behavior of the two specimens are due to differences in the impurity contents.
Reflection of Plane Waves of Sound from a Sinusoidal Surface
Authors: Heaps H. S.
Published: April 2005

When a plane wave of sound is incident upon a sinusoidal surface, part of the reflected radiation consists of undamped plane waves that travel away from the boundary. Under the assumption that no other reflected radiation is present the amplitudes of the plane waves are chosen to minimize the mean square value of the surface pressure. The amplitudes so obtained agree with the experimental results of LaCasce and Tamarkin. Except in the case of the specularly reflected wave the agreement is better than that obtained in previous analyses.
Role of Atmospheric Oxidation in High Speed Sliding Phenomena
Authors: Cocks M.
Published: April 2005

An experimental study of the role of oxidation in inhibiting metallic interaction between metal surfaces sliding at high speeds (up to 66 m/sec) is described. Metallic interaction was detected by microscopic examination of the surface damage after sliding. By using hardened steel, information concerning surface temperatures was deduced from subsequent hardness measurements. At light loads the metal surfaces were severely torn, but at higher loads the tearing became less severe. Above a certain load which depended on the speed tearing was almost eliminated from at least one of the surfaces. Other experiments supported the conclusion that this was due to the increased oxidation associated with the greater frictional heating, and that severe wear at high loads was due to a process of oxide disintegration. Under these conditions the wear rate increased rapidly with increase in load or speed, whereas the wear associated with metallic tearing at light loads showed little increase with load, and decreased with increasing speed. The friction coefficient decreased with increasing load and with increasing speed. The shapes of the underlying bodies influenced the average surface temperatures and therefore the wear and surface damage and create differences even for a pair of mating surfaces.
X-Ray Study of Polygonization in Copper Single Crystals
Authors: Wei C. T. , Parthasarathi M. N. , Beck P. A.
Published: April 2005

Single crystals of electrolytic tough pitch copper and of high purity (99.999%) copper were deformed by bending. The substructure in the as-bent and annealed crystals was studied by means of sensitive x-ray techniques. It was found that regardless of purity, crystals of certain orientations in the as-bent condition do not have sub-boundaries detectable by the methods used. Polygonization took place only upon prolonged annealing at around 97% of the absolute melting point and, at least in one high purity crystal, not even under those conditions. The sluggishness of the polygonization in copper is experimental evidence for the low rate of climb of extended dislocations predicted by Seeger.
Studies in Newtonian Flow. V. Further Verification of the Free-Space Viscosity Equation
Authors: Doolittle Arthur K. , Doolittle Dortha B.
Published: April 2005

Values of the limiting specific volume v0 calculated by a trial-and-error procedure from n-alkane viscosity data using the author's free-space viscosity equation, lnη=B(v0/vf)+lnA,agree substantially with previously published values obtained by extrapolation of density data. Values of v0 for mercury, sodium, benzene, carbon tetrachloride, dichlorodifluoromethane, and water were calculated by the same trial-and-error procedure. In all cases the free-space equation gave a much better fit than the corresponding Andrade temperature equation, lnη=B/T+lnA.
Trapping of Helium Ions and the Re-Emission of Trapped Atoms from Molybdenum
Authors: Varnerin L. J. , Carmichael J. H.
Published: April 2005

The electrical cleanup of helium on molybdenum surfaces has been investigated. In this case, the phenomenon can be described by a trapping of ions upon impact with the surface. Measurements of the trapping efficiency η (atoms removed/ions collected) have been made over a range of ion energies from 150 to 2600 ev. The re-emission of trapped helium atoms was investigated in detail. The contribution of re-emission to the pumping process is described by a phenomenological theory. The results indicate that the trapping efficiency is lowered by a short time re-emission of trapped atoms. Through the long-time re-emission of atoms, the theory accounts quantitatively for the observed saturation of the cleanup process.
New Method of Flow Visualization for Low-Density Wind Tunnels
Authors: Evans R. A.
Published: April 2005

A new method of visualizing low-density flows is described which employs the absorption by oxygen of radiation in the wavelength region 1400 A to 1500 A. It was developed for use in the low-density supersonic continuous flow wind tunnels at Berkeley because the conventional methods (shadowgraph, schlieren, and interferometer) were predicted to have inadequate sensitivity at the unusually low densities in the test section. A xenon discharge is used for the source of radiation, its 1470 A resonance line being isolated by a calcium fluoride vacuum monochromator. A 26 mm diameter beam of parallel radiation is passed through the test section where it is absorbed more or less depending on the oxygen density along the radiation path. The center of the test section is then focused by a calcium fluoride vacuum camera on an ultraviolet-sensitive photographic plate. Pictures of shock waves from cylinders ⅛ and ¼ inch in diameter and from a 60° ⅜ inch wedge were obtained with exposure times of about 4 minutes. Development of a stronger source would reduce the exposure time appreciably. This oxygen absorption method is shown to be suitable, in principal, for general wind tunnel work where the absolute pressures are below about 1 mm Hg.
Rotational Model of Flux Reversal in Square Loop Ferrites
Authors: Gyorgy E. M.
Published: April 2005

The present paper analyzes a rotational model of flux reversal in ferromagnetic materials. A brief review of the experimentally established details of the flux reversal process in square loop ferrites is given. The discrepancies between the experimental results and the predictions of the domain wall motion theory are discussed. The switching coefficient Sw is examined in detail.

The rotational model is based on the solution of the modified Landau and Lifshitz equation and predicts the shape of the output voltage pulse, the relationship between the flux reversal time and the applied field, and the minimum switching coefficient that can be obtained for a given ferrite. The switching coefficients determined experimentally are within a factor of three of the minimum value of Sw predicted by this model.
Note on Krishnan's Reciprocity Relation in Light Scattering
Authors: Stevenson A. F.
Published: April 2005

Krishnan's relation is deduced rigorously from Maxwell's equations when scattering by a single body is considered and an average overa-ll orientation of the body is taken. When scattering by a large number of randomly-oriented particles is considered, Krishnan's relation holds true either if multiple scattering and the effect of the container walls are neglected, or if a certain symmetry condition is satisfied. Where this condition is not satisfied, deviations from Krishnan's relation may be expected at high concentrations. The desirability of extrapolating experimental results to zero concentration is emphasized. Relations analogous to Krishnan's are also deduced which do not require any averaging over orientations, but involve instead the interchange of the dielectric constant and magnetic permeability, relative to the surrounding medium, at each point of the scattering system.
Plastic Deformation of Copper and Silver Whiskers
Authors: Brenner S. S.
Published: April 2005

By rapidly reducing the stress after yielding, it was possible to study the plastic deformation of copper and silver whiskers. The whiskers exhibit extremely sharp yield points and extensive easy ``glide'' regions which are due to the propagation of Lüders bands. It is unlikely that the sharp yield points are caused by dislocation pinning. The propagation of the Lüders bands often becomes obstructed giving rise to repeated yielding in the plastic region. The nature of these obstructions and the mechanism of Lüders band propagation are not clear.
Performance of Composite Peltier Junctions of Bi2Te3
Authors: Shilliday Theodore S.
Published: April 2005

An experimental Peltier refrigerator utilizing thermoelements of annular configuration has been designed, constructed, and operated. The thermoelectric materials used are p- and n-type Bi2Te3 with ρp=2×10−3 ohm-cm, ep=180 μvolts/°C, ρn=8.5×10−4 ohm-cm, and en=−150 μvolts/°C. The device has been operated under ``no-load'' conditions over a range of power inputs and has exhibited a maximum ΔT of 49°C. A simple theory relating to the performance of Peltier thermocouples is derived. Experimental performance of the device is shown to agree with theoretical predictions within experimental error.
The Reaction Field and Its Use in Some Solid-State Amplifiers
Authors: Anderson P. W.
Published: April 2005

It is shown that the theory of the maser can be simply presented in terms of the concept of the radiation reaction field. This is the radiation field produced in a cavity or wave guide by the presence of the sample's electromagnetic moment. Its reaction back on the sample causes coherence effects such as those called ``superradiance'' by Dicke.

Two amplifiers using the radiation reaction field in different ways from the usual solid-state maser are discussed. One of them takes advantage of the nonlinearity of the equations of motion to make a modulated coupling between two cavity modes by means of a sample with three energy levels such as is used in Bloembergen's maser. The resulting amplifying mixer behaves the same as (but is different in principle from) Suhl's ferromagnetic amplifier. A second type of amplifier employs the reaction field to destroy the circular polarization of a paramagnetic resonance. It is then possible to make an amplifier from this using the principle of the subharmonic generator.
Effect of Edge Dislocations on the Alloying of Indium to Germanium
Authors: Pankove Jacques I.
Published: April 2005

H. Kettering observed that indium fused to germanium spreads more extensively on material with a low edge-dislocation density than on high dislocation density material. A detailed study of the alloying mechanism shows that: (1) Edge dislocations and other crystal disturbances enhance the dissolution of germanium in indium. Hence, under equilibrium conditions, deep alloying results with smaller spread of the indium than in the case where the crystal is free from these defects. (2) The recrystallized structure over an edge dislocation differs considerably from the structure at undisturbed sites. (3) The shape of the alloy front is determined by surface tension forces and a tendency to terminate in (111) planes.