bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth from the Melt. III. Dendritic Growth
Authors: Bolling G. F. , Tiller W. A.
Published: April 2005

A mathematical treatment of steady-state dendritic growth from pure and alloy liquids has been developed for isothermal and nonisothermal dendrites. The velocity of dendritic growth, dendrite size, dendrite direction, and the alloy content of the dendrite have been calculated as a function of the bath supercooling, the alloy content of the bulk liquid, and the atomic kinetics of the material. To specify the problem completely it was necessary to choose some ``optimization'' condition. We have chosen the condition of ``maximum velocity.'' Comparison of the theoretical predictions with experimental data for pure nickel, tin, and ice, and for KCl and acetic acid solutions have been made. Satisfactory agreement with experiment was found using the atomic mechanism of ``uniform interface advance.''
Space-Charge Instabilities in Electron Diodes and Plasma Converters
Authors: Birdsall Charles K. , Bridges William B.
Published: April 2005

Space-charge instabilities in diodes have been found to produce variations in potential and current that are larger than predicted from classical static analyses and, moreover, which produce sustained electrokinetic oscillations. This report reviews the classical static solution and presents the new transient solution briefly. As applications, tentative explanations are offered for recent observations of extra shot-noise smoothing and of oscillations in thermionic converters.
Influence of Surface Energy on Friction and Wear Phenomena
Authors: Rabinowicz E.
Published: April 2005

A number of friction and wear phenomena are explicable in terms of the surface energy of adhesion of the contacting materials. In the friction field, it is found qualitatively that high friction coefficients are found for sliding materials with high surface energy/hardness ratios and conversely. Unfortunately, it is not easy to test this relationship quantitatively because the derived expression contains parameters which cannot be independently controlled. However, in the wear field, it has been found possible to derive an expression for the size of loose wear particles which can be readily tested; namely, that the average size of loose wear particles is proportional to the surface energy/hardness ratio, the nondimensional constant of proportionality being 60 000. Experiments with 15 different materials show the validity of this expression. Another phenomenon, adhesion, which also seems to be governed by surface energy considerations, is discussed in qualitative terms.
Lubrication of Polymers
Authors: Rubenstein C.
Published: April 2005

Previous work on the lubrication of polymers is reviewed and the explanations which have been advanced are examined and are shown to be inadequate. An alternative mechanism of polymer lubrication is proposed which is based on the hypothesis that when a lubricant is applied to a polymer it is possible for the lubricant molecules to penetrate the polymer and alter its mechanical properties. An investigation into the lubrication behavior of textile polymers is described and an explanation of the results of this and other investigations is offered in terms of the proposed mechanism.
Frictional Behavior of a Simple Rheological Material
Authors: Spurr R. T.
Published: April 2005

Simple experiments made on a hard bitumen support the adhesion theory of friction. The static friction of the bitumen depends upon its rheological properties, and for hemispherical specimens, μs is determined by the shear strength and flow pressure of the bitumen, the latter being obtained from identation measurements. For nominally flat specimens, the time and temperature dependence of μs can be determined from indentation measurements. At low sliding speeds the dynamic friction can be related to the static friction, and to the rheological properties of the bitumen; at higher speeds frictional heating complicates interpretation of results.
Use of Graphite Whiskers in a Study of the Atmosphere Dependence of Graphite Friction
Authors: Rollins F. R.
Published: April 2005

Several physical properties of graphite whiskers have been measured in ultra-high vacuum and other controlled atmospheres. The properties which have been studied include elasticity, electrical resistance, and cohesion between whiskers. The atmosphere dependence of these properties suggests that surface adsorption of contaminants is the most important factor in producing changes in graphite friction. There is some evidence that the adsorbed gases reduce surface roughness on an atomic scale. This ability of the adsorbed film to smooth out surface asperities may be used to explain some of the friction and wear characteristics of graphite.
Operation of the Field Ion Microscope with a Dynamic Gas Supply
Authors: Waclawski B. J. , Müller E. W.
Published: April 2005

The brightness level of the field ion microscope has been increased two orders of magnitude with little loss of resolution by the addition of a dynamic gas supply system. Space charge at the emitter is not a limiting factor. Cathode sputtering by the imaging helium ions may release negative ions which are accelerated toward the tip. These ions gain sufficient kinetic energy so that irrespective of subsequent multiple ionization in the high field region near the tip they are capable of striking the tip surface and cause damage to the tip lattice. This effect can be eliminated by proper electrode design.
Surface Kinetics and Physics Investigation of the Reaction between Single-Crystal Germanium and Iodine
Authors: Heinecke W. J. , Ing S.
Published: April 2005

A study of the kinetics of the reaction between iodine and single-crystal germanium and the resulting electrical surface has been undertaken. An activation energy of 18.5 kcal/mol has been found for the reaction of each of the three crystallographic planes studies. However, frequency factors were found to differ with orientation. An aging effect of the surface was found through field-effect surface measurements. A surface acceptorlike trap having an energy level (Et—Ev) of 0.44 ev was found and investigated. The density of the trap was found to be 1.4×1012 cm−2.
Back Scattering of Electrons
Authors: Archard G. D.
Published: April 2005

The behavior of a stream of electrons penetrating a solid target is studied with a view to determining the proportion which return to the surface and pass back into space. Two existing theories (diffusion and large-angle single elastic scattering) are adapted to this end. These theories predominate for high and low atomic numbers, respectively. A combination of the two theories agrees well with experiment.
Etch Pits in Electroluminescent Zinc Sulfide Crystallites
Authors: Goldberg Paul
Published: April 2005

Through suitable etching techniques, triangular etch pits are developed on the surfaces of electroluminescent ZnS:Cu,Cl powder crystallites at densities in the range 106−108/cm2. These pits, seen by means of the electron microscope, are essentially absent in similarly etched nonelectroluminescent ZnS:Cu,Cl crystallites. Also present on the electroluminescent particles are surface striations. The etch pits appear physically related to the striations in that the pits from only on those faces bearing the striations. All triangular pits on a given face point in the same direction, which is normal to the striation direction. This direction is one of the crystallographic polar axes in sphalerite and the c axis in wurtzite. The pits have also been found in other electroluminescent compositions such as ZnS:Cu,Al; ZnS:Cu, Cl–Pb; and ZnS:Cu, Cl–Mn. The possible interpretations of the pits and striations are discussed in terms of defect structures (e.g., dislocations and stacking faults) which may be of importance to the nature of the barriers believed to reside within the volume of electroluminescent particles. Some experiments with large crystal specimens are reported.
Nonlinear Damping Losses in YIG
Authors: Conger Robert L.
Published: April 2005

High-power ferromagnetic resonance in a flat plate has a small component of the precession parallel to the applied dc field. This component causes frequency doubling and also coherent amplification of some scattered spin waves. These spin waves then cause a linear damping of the parallel component of the precession, which in turn causes a nonlinear damping of the principal component of the precession. The nonlinear damping causes the microwave susceptibility to decrease with increasing power and to become approximately inversely proportional to the rf field at high power levels.
Acceleration of Rigid, Conducting, Diamagnetic Bodies by a Magnetic Field
Authors: Ayres R. U.
Published: April 2005

A scheme is developed for treating very fast acceleration processes involving plasmoids. The plasmoid is assumed to move approximately as a rigid body during the acceleration. Two coupled nonlinear differential equations must be solved simultaneously. A power series development valid for short times is given. Two examples are treated which are reminiscent, respectively, of exploding wires in the one case, and certain propulsion devices in the other case. Apart from an analysis of the first two terms in the power series development, no numerical work is attempted. The result of the analysis is that the kinetic energy acquired by the plasmoid can quite generally be expressed as a function of distance traveled, in the form 12mẋ2(x)=C′[12(∂L/∂x)|x=0]12{x32+13[(∂2L/∂x2)/(∂L/∂x)|x=0]x52+···}, where L(x) is the inductance of the total circuit, depending on the location of the plasmoid and its shape, and C′ is an experimentally determined constant depending on the circuit parameters and plasmoid mass prior to acceleration. The above expression is only valid for short distances (times).
Nanosecond Triggering of Air Gaps with Intense Ultraviolet Light
Authors: Godlove Terry F.
Published: April 2005

Measurements are presented of the breakdown time of a conventional two-electrode air gap. The applied voltage is maintained below the sparking threshold and breakdown is caused by the emission of a 6-nanosec burst of photoelectrons from the cathode, which produces space-charge distortion of the electric field. An auxiliary trigger spark provides the necessary light and results in cathode emission up to ∼10 ma/cm2. The dominant wavelength region is found to be ∼1100 A because of the relatively low air absorption and high photoelectric yield in this region. For a fixed gap spacing and using the highest light intensity available, the time delay is typically found to decrease from ∼5t- to a minimum delay t- as the main gap voltage is increased from ∼8% below threshold up to threshold. The minimum delay ranges from 10–60 nanosec for the gap spacings studied and agrees with calculated values of gap spacing/electron drift velocity. The techniques developed have direct application to the triggering of conventional spark-gap switches and to pulsed light sources and may provide an additional tool for investigating some of the basic parameters of gaseous electronics.
Mosaic Size in Lead from X-Ray Measurements
Authors: Hiki Yosio , Hasiguti Ryukiti R.
Published: April 2005

The size of mosaic blocks in lead powder was determined on the basis of the primary extinction effect of x rays. Integrated intensities of nine reflection lines in the Debye-Scherrer spectrum with CuKα radiation were measured with a Geiger counter spectrometer. The mosaic size was calculated by comparing these values with theoretical values of the intensities. Correction for absorption of x rays in the specimen powder was especially important because of the large absorption coefficient of lead. The order of magnitude of the mosaic size was found to be 10−4 cm. From this value, the dislocation density was calculated to be of the order of 108 cm−2. The dislocation density decreased slightly when the specimen was annealed in vacuo at 150°C for a long time.
Electrical Conduction and Breakdown in High-Pressure (0.25–300 mm) Rare Gases
Authors: Forman R.
Published: April 2005

The current-voltage characteristics of high-pressure (0.25–300 mm) rare-gas diodes have been measured. Data have been taken on diodes containing xenon, argon, and helium as the ambient gas, and tungsten, tantalum, rhenium, thoriated tungsten, and an oxide cathode as filamentary cathodes. Some unexpected phenomena have been observed and some of these general results can be summarized as: (1) The current vs voltage characteristics of argon- and xenon-filled diodes, at gas pressure above 1 mm, do not obey any space-charge law if the cathode temperature is above 2400°K. (2) The above violation of space-charge relations in argon- and xenon-filled diodes is found with tungsten, tantalum, or rhenium filaments, which can be operated above 2400°K. When thoriated tungsten or the oxide cathode, which operate below 2400°K, are used as filaments, the current-voltage characteristics of the diode follow a space-charge relation (current-voltage characteristics independent of temperature). (3) The current vs voltage characteristics of helium-filled diodes, however, do obey the space-charge relations at all filament temperatures available with the present cathode materials. (4) Some very unusual early breakdown phenomena (breakdown at potentials below ionization potential) were observed in these high-pressure rare-gas diodes employing a hot cathode. These data can be explained qualitatively by postulating the existence of thermally generated xenon or argon gas ions at temperatures in the range of 2400°K. An attempt will be made to justify this assumption by a semiquantitative theoretical treatment based on Saha's thermal ionization theory rather than the surface ionization theory of Langmuir and Kingdon.
Role of Crystal Structure in Diffusion. I. Diffusion Paths in Closest-Packed Crystals
Authors: Azároff Leonid V.
Published: April 2005

A consideration of the crystal structures of simple binary compounds shows that they can be represented by closest packings of the larger anions in which two kinds of interstices are available for occupation by the metal atoms. In hexagonal closest packings, the octahedral voids form continuous chains by sharing opposite faces while the tetrahedral voids form isolated pairs. In cubic closest packings, each kind of void shares faces only with unlike voids. The specific diffusion paths available in these compounds depend, therefore, on the manner in which the voids are occupied. Continuous diffusion paths comprised of normally unoccupied voids exist in ZnO and α-ZnS type structures so that voidal diffusion can take place without requiring defect formation. Similarly, voidal diffusion can occur in BiO3, CrCl3, and CdI2 type structures. Conversely, all possible continuous diffusion paths are blocked by metal atoms in the NiAs, NaCl, and antifluorite-type structures so that vacancy or interstitialcy mechanisms are necessary to account for diffusion.
Flash Method of Determining Thermal Diffusivity, Heat Capacity, and Thermal Conductivity
Authors: Parker W. J. , Jenkins R. J. , Butler C. P. , Abbott G. L.
Published: April 2005

A flash method of measuring the thermal diffusivity, heat capacity, and thermal conductivity is described for the first time. A high-intensity short-duration light pulse is absorbed in the front surface of a thermally insulated specimen a few millimeters thick coated with camphor black, and the resulting temperature history of the rear surface is measured by a thermocouple and recorded with an oscilloscope and camera. The thermal diffusivity is determined by the shape of the temperature versus time curve at the rear surface, the heat capacity by the maximum temperature indicated by the thermocouple, and the thermal conductivity by the product of the heat capacity, thermal diffusivity, and the density. These three thermal properties are determined for copper, silver, iron, nickel, aluminum, tin, zinc, and some alloys at 22°C and 135°C and compared with previously reported values.
Thermal Conductivity of Porous Media. II. Consolidated Rocks
Authors: Woodside W. , Messmer J. H.
Published: April 2005

Measurements have been made of the effective thermal conductivity of porous sandstones. The method is based on the transient heating effect resulting from use of a line heat source. Data are presented for six sandstones ranging in porosity from 3 to 59% and show the variation of thermal conductivity with porosity, the conductivity of the saturating fluid, the pressure of the gas filling the pore space, and overburden pressure. The results are compared with those previously obtained for unconsolidated sands. All samples, except one, exhibited a lower thermal conductivity when saturated with a gas at atmospheric pressure than when saturated with a liquid of the same conductivity as the gas. An explanation for this effect, in terms of the kinetic theory of gases, is advanced and substantiated by other data. Finally, the validity of certain equations for the thermal conductivity of two-phase systems is examined; the weighted geometric mean of the two constituent conductivities is found to agree well with the measured effective conductivities.
Cross-Section Ratios of Sensitizing Centers in Photoconductors
Authors: Bube Richard H.
Published: April 2005

The ratio of the capture cross section of a sensitizing center for a photoexcited hole to the subsequent capture cross section for a free electron, in n-type photoconductors, can be determined from the measurement of the thermal quenching of photoconductivity as a function of excitation intensity. The magnitude of the ratio gives information about the charged state of the sensitizing center. A summary of many such measurements on seven different photoconductors of type II–VI or III–V supports the hypothesis that doubly charged sensitizing centers are present in some of these materials, but that singly charged sensitizing centers are present in the majority.
Electromagnetic Surface Waves on a Plane Interface
Authors: Lengyel B. A. , Mitzner K. M.
Published: April 2005

Surface waves are defined as waves exponentially decreasing on both sides of a plane interface. It is shown how all such waves can be generated from a single Hertz vector perpendicular to the interface. The relations between the propagation parameters of the waves and the material constants are derived in a general case which includes media with different magnetic permeabilities. The condition for the existence of surface waves is derived.
Precipitation Sites in Aluminum Alloys
Authors: Frank G. R. , Robinson D. L. , Thomas G.
Published: April 2005

Frank sessile dislocations surrounding a region of stacking fault are shown to be nucleation sites for γ′ phase precipitation in aluminum-silver alloys. The segregation of silver to these regions is explained in terms of extinction fringe contrast. Direct evidence for ``pipe'' diffusion along dislocations to a grain boundary is also presented.
Transitions and Relaxations in Polytetrafluoroethylene
Authors: Eby R. K. , Sinnott K. M.
Published: April 2005

The modulus and internal friction of polytetrafluoroethylene were measured with longitudinal waves at a frequency of 12 Mc between 248° and 548°K and the fluorine magnetic resonance was studied between 77° and 375°K. The samples covered a wide range of crystallinities and included a specimen which had not been sintered (as polymerized material which had not been heated above the melting temperature). The results resolve discrepancies which existed in the literature and introduce new information about the relaxations and first-order transitions in polytetrafluoroethylene. In the ultrasonic work it is shown that the ``19°C'' and ``30°C'' diffuse first-order crystalline transitions can be studied independently of the crystalline relaxation which occurs at 418°K at 12 Mc. The ``19°C'' transition is not observed but the ``30°C'' transition causes an appreciable decrease in the modulus. X-ray data show that this accompanies a decrease in the rotational order of the lattice. This transition is found to occur over a wider temperature range in unsintered polymer (possibly because of a distribution of the lengths of the molecular segments in the ordered regions). An NMR absorption line from the crystalline regions is resolved and its narrowing above 280°K is attributed to rotational motions associated with the first-order transitions. Comparison with published data shows that the narrowing occurs over a wider temperature range in unsintered polymer. Consideration of a distribution of relaxation times suggests that the narrowing above 190°K of an NMR absorption line from the amorphous regions results from the molecular motion which gives rise to a relaxation observed at 263°K in the ultrasonic measurements. Another amorphous relaxation is observed at 470°K in the ultrasonic measurements and the activation parameters are obtained. Examination of these parameters for the two relaxations suggests that the higher-temperature relaxation should be assigned to the larger molecular segments. For all the relaxations, the parameters follow a relation which obtains for activated processes in inorganic solids.
Slip Patterns on Boron-Doped Silicon Surfaces
Authors: Queisser H. J.
Published: April 2005

Diffusion of a high concentration of boron impurities into a shallow surface layer of silicon and subsequent etching reveals regular arrays of etched lines with crystalline symmetries. These patterns are interpreted as slip lines introduced by the stress from the nonuniformly distributed, undersized substitutional boron impurities in the silicon lattice.
Nature of the Valley Current in Tunnel Diodes
Authors: Brody T. P.
Published: April 2005

An explanation of the ``excess current'' up to and including the valley point, observed in tunnel diodes, is suggested in terms of tunneling between impurity band states of the heavily doped p and n regions. Density-of-states curves are constructed, based on several different models of impurity bands, and the tunneling current between such bands is computed and compared with experiment. The effect of different base materials and impurities on the valley current is discussed. Some aspects of impurity band formation in heavily doped semiconductors are considered, and possible modifications and difficulties of the present approach are indicated. The possibility of obtaining information about impurity band structure from tunnel diode measurements is discussed. Experimental evidence is presented about the position of the Fermi level in heavily doped semiconductors and is shown to agree with that postulated by the present model. The Appendix gives the theory of locating the Fermi levels from measurements of the temperature variation of the diode characteristic.
Direct Observation of Outward-Progressing Flux Change in Tape-Wound Cores at Power Frequencies
Authors: Brownell R. M.
Published: April 2005

This brief preliminary report shows by a simple experiment that major flux changes in tape-wound, magnetic-amplifier-type cores begin near the core's inner perimeter and progress outward, at power frequencies, as has been predicted [R. C. Barker, Trans. Am. Inst. Elec. Engrs. 79-I, 482 (1960), with accompanying discussion]. It also shows, when the core is operated on a minor hysteresis loop, that at the start of every odd half-cycle of excitation additional small inward-progressing flux changes occur near the outer boundary of the region in which flux was reversed during the preceding even half-cycle. This reduces slightly the hysteresis loss in the odd half-cycles, and the resulting energy unbalance causes the minor loop to cling to one end of the major loop—a phenomenon well known in rectangular-loop materials. The cause of the energy unbalance was hitherto unknown, however. The method used for the experiments is observation of the voltage that appears between two probes touched to the side of the core when the core is excited by a conventional winding. This method is known to other investigators but scantily reported in the literature. It is not analyzed here, but some experimental justification is given.
Tensile Behavior of Lithium Fluoride
Authors: Hoover Donald B. , Washburn Jack
Published: April 2005

Tensile stress strain curves were obtained for single crystals of lithium fluoride. The specimens were elongated at room temperature along a 〈100〉 axis. The number of slip-band sources was controlled by surface treatment. Both the yield stress and the flow stress in the plastic range were found to depend on the number of active slip bands. The shapes of the stress-strain curves were related to the behavior of individual dislocations in lithium fluoride.
Phase Instability in Dilute Interstitial Solid Solutions of Nitrogen in Tantalum
Authors: Seraphim D. P. , Stemple N. R. , Novick D. T.
Published: April 2005

An ordered structure is found in interstitial solid solutions as dilute as 0.1 at. % nitrogen in tantalum. On the basis of the symmetry of the ordered structure, tetrahedral rather than the usual octahedral sites are considered appropriate for the nitrogen atoms. The effect of the ordered structure on the properties of the solid solution are discussed.
A Calculation of the Elastic Shear Constants of Beryllium
Authors: Bernstein B. T.
Published: April 2005

The contributions to the elastic shear constants of beryllium at 0°K were calculated on the basis of an energy band model for this metal proposed by Herring and Hill. The results are compared with those obtained assuming nearly-free-electron and free-electron behavior for the valence electrons. It was found that the valence electron contribution was very sensitive to the shape of the energy bands and hence the Fermi contribution to the elastic shear constants was strongly dependent upon the energy band model chosen. On the basis of the model proposed by Herring and Hill the elastic shear constants of beryllium, like the alkali metals, are predominantly determined by the electrostatic energy of the ion-cores.
Frequency Spectra of Low-Frequency Fluctuations in a Plasma
Authors: Crawford F. W.
Published: April 2005

Observations have been made of the low-frequency fluctuations occurring in hot-cathode dc mercury-vapor discharges at a pressure of approximately 1 μ. A spectrum analyzer was employed to study frequency spectra from three widely differing experimental tubes and to determine the effects of variations in tube geometry, electrode spacing, and anode current. Similar measurements were also made at points along a long discharge column with the aid of a capacitive probe sliding on the outside of the tube. The character of the spectrum is markedly dependent on tube geometry, substantially independent of column length and position along the column, and may be coarse or contain relatively pure frequency components. Two mechanisms observed involved frequency variation proportional to the square and cube roots of anode current, and possible explanations are given. There is, however, evidence for the existence of other basic mechanisms of generation.
On the Nature of Dislocation Etch Pits in Tungsten
Authors: Berlec Ivan
Published: April 2005

Some details on dislocation etch pits in tungsten are presented. Etch pits are produced electrolytically with 2% NaOH solution and the Millner-Sass reagent, and chemically with a potassium ferricyanide etchant. All three etchants can reveal dislocations, but only on certain crystallographic planes. In addition to etch pits, pyramids are produced on octahedral, or nearly octahedral planes. These pyramids do not seem to be related to dislocations. There is no guarantee that all pits correspond to dislocations since impurities, such as carbon, markedly affect the size, shape, and density of etch pits. It was observed that the density of etch pits depends also on the current density during electrolytic etching.
Thermionic Current Transmission in a Strong Magnetic Field
Authors: Schock Alfred , Eisen Charles L.
Published: April 2005

In an earlier analysis of the effect of magnetic fields on thermionic diodes, numerical results indicated that under certain conditions the fraction of emitted electrons reaching the collector equals the sine of the angle at which the magnetic field intersects the emitting surface. An analytic proof of this relation has since been found and is presented here.
Impedance Characteristics of a Mercury-Vapor Plasma
Authors: Crawford F. W.
Published: April 2005

Measurements have been made of the impedance/frequency characteristics of a hot-cathode, dc, mercury-vapor plasma at a pressure of approximately 1 μ. The experimental tube contained a directly-heated cathode from a commercial mercury-vapor rectifier and provided a discharge column 80 cm long. Bridge techniques were used to obtain impedance loci extending to 2 Mc/sec for several values of anode current. These appeared to normalize, the magnitudes of the components being approximately inversely proportional to current. A basic equivalent circuit can be deduced, its parameters being dependent on physical processes occurring in the discharge. Prominent frequency components of the low-frequency voltage fluctuations present in the tube appear to be closely related to the impedance characteristics.
Elastic Moduli of Cadmium Telluride
Authors: McSkimin H. J. , Thomas D. G.
Published: April 2005

The elastic moduli of cadmium telluride at 25°C have been determined by measurement of ultrasonic wave velocities in the frequency range 40–300 Mc/sec. Preparation of the crystal specimens is described, and factors affecting the accuracy of results are considered. The question of possible piezoelectric stiffening and its effect on measured wave velocities is also considered. Based on a density of 5.854 g/cm3 as computed from the lattice constant (and taken as exact with respect to uncertainty estimates) the zero field elastic moduli are: ModulusValue d/cm2Uncertainty in %c115.351×10110.15c123.6810.2c441.9940.15
Work Function Variation of Metals Coated by Metallic Films
Authors: Gyftopoulos Elias P. , Levine Jules D.
Published: April 2005

A theoretical correlation is derived to account for the variation of the work function of refractory metals coated by metallic films for all degrees of coverage. This correlation is based on an extension of the concept of electronegativity to composite surfaces and use of Pauling's rule about electronegativity and dipole moment of complex molecules. A series of theoretical curves is given for different crystallographically ideal surfaces of refractory metals such as W, Mo, and Ta coated by Cs, Sr, Ba, and Th.

The derived correlation is compared with available experimental data for which the experimenters specify the exact conditions under which the experiment is performed and excellent agreement between theory and experiment is established.

It is shown for the first time that the maximum work function variation does not necessarily always occur either when a full monolayer is reached or at a definite fractional coverage. The exact position of the maximum variation is a function of the adsorbate and substrate materials and the type of the substrate surfaces. It is also shown that it is erroneous to characterize a monolayer as the point at which maximum emission (or maximum work function variation) is achieved because such a maximum may be flat and extend from half a monolayer to one monolayer.
Electron Optics in Accelerating Tubes
Authors: Morikawa Minoru
Published: April 2005

The focusing properties of the multi-stage system of weak lenses, such as in the accelerating tubes, are considered. The lens system is treated as one thick lens in the paraxial ray approximations. By assuming that the field distribution of each lens is the same, the simple expressions for the focal lengths and the locations of the focal points of this lens system as a whole are given.
Cranberg Hypothesis of Vacuum Breakdown as Applied to Impulse Voltages
Authors: Farrall G. A.
Published: April 2005

If the Cranberg hypothesis for breakdown in vacuum is valid, measurements made using impulse and dc voltages may yield different results depending in part upon the rate of rise of the impulse and the nature of the attachment of the clumps to the parent electrode. It is assumed that metallic clumps are instantaneously detached from an electrode surface at a voltage dependent upon gap length as described by Cranberg. Consideration of the rise in impulse voltage occurring during the transit time of the clump to the opposing electrode yields the following results. For an over-volting impulse of constant rise rate the breakdown voltage of a vacuum gap depends upon the ⅚ power of the gap length in the limiting case of large gap length and clump radii, and fast rise impulses. For the same limiting conditions, with an impulse of constant rise time, breakdown voltage was found to be related to the 52 power of the gap length. A brief comparison of calculated results with experimental data in the literature indicates limited, although not conclusive, support for the Cranberg hypothesis in its application to impulse breakdown in vacuum.
Oxygen-Nickel Structures on the (110) Face of Clean Nickel
Authors: Germer L. H. , MacRae A. U.
Published: April 2005

The adsorption of oxygen on clean nickel (110) surfaces has been studied by low-energy electron diffraction. Several successive structures are formed before the first monolayer is completed. These structures consist of both oxygen and nickel atoms, with each having more oxygen atoms and fewer nickel than the preceding. With increasing oxygen content the sticking probability becomes progressively lower, from about unity for the (1×2) structure to 0.01 for the final most oxygen-rich structure. The temperature necessary for the degradation of any structure to that previously formed decreases from a value near the melting point of nickel for the (1×2) structure to about 250°C for the most oxygen-rich structure. Normal cubic nickel oxide can be grown on top of the most stable of these oxygen-nickel structures, but only at rather high temperatures and pressures. The oxide is oriented with a [100] direction normal to the (110) surface of the crystal, and with a [110] direction parallel to the [100] nickel direction in the surface plane.
Potential Form of the Small Signal Power Theorem
Authors: Klüver J. W.
Published: April 2005

The small signal power theorem for electron beams is transformed into a form which lends itself nicely to practical applications. This is achieved by the introduction of scalar and vector potentials and in four-vector notations the theorem becomes particularly appealing. As an example of the application of the theorem, the one-dimensional excitation of a cylindrical beam is discussed.
Space-Charge-Limited Tunnel Emission into an Insulating Film
Authors: Geppert D. V.
Published: April 2005

Expressions are derived that enable calculation of the effects of space charge on the current density of electrons tunneling from a metal into the conduction band of an insulating film. The effect of electron traps in the insulating material is considered. It is shown that if the insulating film contains a high trap density, space charge can severely limit the tunnel current density that can be achieved, even for very thin films.
The Effect of Zirconium on Internal Friction in Columbium
Authors: Bunn Patricia M. , Cummings D. G. , Leavenworth H. W.
Published: April 2005

The effect of zirconium on internal friction in columbium was investigated over the frequency range of 0.5 to 10 cps. An entirely new peak was observed which was attributed to the diffusion of oxygen in the vicinity of zirconium atoms. The normal columbium oxygen peak was not observed until approximately 0.14 wt% oxygen was added to the specimens. The normal columbium-nitrogen peak was readily observed, but a zirconium-nitrogen peak was not observed until oxygen concentration was reduced below 0.1 wt%. These observations are explained on the basis of a strong attraction between zirconium and oxygen atoms. As a preliminary to this investigation, the diffusivity of zirconium in columbium at 1930°C was determined. A value for D0 and the activation energy were calculated so that the diffusivity at any temperature could be obtained from the expressionD=0.57 exp 87 000/RT.
Dislocation Loops in Fission Fragment Bombarded Lead Iodide
Authors: Chadderton Lewis T.
Published: April 2005

Bombardment of thin crystals of lead iodide with uranium fission fragments does not produce distinct linear tracks but randomly distributed dislocation loops which are inclined to the surface of the crystals. These loops are formed by the aggregation of highly mobile point defects. Further point defects are produced by high intensity electron beams and the original loops are observed to move and grow, eventually coalescing.
Nucleation Fields of an Infinitely Long Square Ferromagnetic Prism
Authors: Brown William Fuller
Published: April 2005

When a homogeneous ferromagnetic specimen possesses an equilibrium state of uniform magnetization, the equilibrium becomes unstable at a certain (usually negative) value of the field component along the magnetization. This ``nucleation field'' is known for a longitudinally magnetized circular cylinder; the mode of deviation from the initial state is ``magnetization curling'' at large diameters and, to a good approximation, ``rotation in unison'' at small diameters. Values for square cross section would be useful for interpreting measurements on iron whiskers; but here the modes are more complicated, and rigorous solution would be difficult. The present calculation establishes upper and lower bounds to the nucleation fields for the modes described. The term that must be added to the crystalline-anisotropy term is determined to within a factor π/2 for ``rotation in quasi-unison'' and to within a factor 2 for curling; the corresponding values for a cylinder of the same cross section lie at the upper bound for the former mode and slightly above the lower bound for the latter; the critical thickness for change of mode is between 0.85 and 1.51 times the critical diameter for a cylinder.
Measurement of the Easy-Axis and Hk Probability Density Functions for Thin Ferromagnetic Films Using the Longitudinal Permeability Hysteresis Loop
Authors: Torok E. J. , White R. A. , Hunt A. J. , Oredson H. N.
Published: April 2005

A new method of measuring the inhomogeneity in easy-axis orientation and in the magnitude of the uniaxial anisotropy in thin ferromagnetic films has been found. Correlation between the two can also be obtained by this method. Apparatus has been built to measure the probability density of finding a part of the film with a given easy-axis orientation, as well as a given Hk, and to plot this probability density function on an x-y recorder. The Hk probability density function is found to be symmetric, contrary to popular belief. Measured values of easy-axis inhomogeneity agree within experimental error with values obtained by conventional methods. Previous methods of measuring Hk inhomogeneity, based on either radio-frequency resonance linewidth or on reversible limit, are discussed and found to be questionable.
Dielectric Anomaly in ZnS Films
Authors: Hacskaylo Michael , Feldman Charles
Published: April 2005

The dielectric constant of vacuum-deposited ZnS films was measured as a function of thickness in the range of 350 Å to 4 μ. For room temperature deposition, a sharp anomaly was found in the dielectric constant vs thickness curve. The highest measured constant was 34.7 at a thickness of 900 Å. As the thickness increased, the dielectric constant dropped sharply and a shallow minimum less than bulk value (8.3) was observed. This minimum was 5.3 at about 1 μ. At thickness greater than 2 μ the dielectric constant was about 10. For increasing substrate deposition temperatures, 150° and 250°C, the dielectric constant approached bulk values, the anomalous peak broadened, and the maximum occurred at greater film thicknesses. The dielectric loss curves showed minima at film thicknesses corresponding to the region on the thicker side of the anomalous peaks where the dielectric constant first became or approached bulk value. It is postulated that the departure of dielectric constant from bulk values is related to the stresses generated in the film during deposition, and that the effect is enhanced because of the piezoelectric nature of ZnS.
Space-Charge Neutralization and Negative Resistance in Thermionic Diodes Containing Radioactive Krypton
Authors: Forman R. , Ghormley J. A.
Published: April 2005

Anode current-voltage characteristics of gas-filled thermionic diodes containing fission-product krypton were compared with characteristics of the same tubes containing natural krypton. Significant increases in current were observed in the diodes when radioactive krypton was substituted for natural krypton at pressures in the range of 20–340 mm Hg. In addition, diodes containing radioactive krypton displayed negative resistance.
Diffraction from Layer Faults in bcc and fcc Structures
Authors: Wagner C. N. J. , Tetelman A. S. , Otte H. M.
Published: April 2005

Calculations, using the Warren-Mering method, of the broadening and shift of the x-ray diffraction peaks in powder patterns have been performed for the situation in which an interplanar spacing change occurs at the fault plane. Deformation-spacing faults on the {211} layers of the bcc lattice and the {111} layers of the fcc lattice, and spacing faults are discussed in detail. The principal effect of the spacing change is to introduce additional broadening and peak shifts, the magnitude (and direction, in the case of the peak shifts) of which depends on the reflection. In bcc structures the effect is particularly striking because no peak shifts are expected in the presence of stacking faults whose interplanar spacing is unchanged.

Measurements were made on three cold-worked bcc materials: Ta, Nb, and a stainless steel martensite. No measurable peak shifts were found in Ta. In Nb and in the martensite, however, small shifts were observed and were in directions predicted from the theory; the shifts could therefore be interpreted and indicated an expansion of the layer spacing at the fault.
Temperature Generated in Aluminum Rods Undergoing Torsional Oscillations
Authors: Dillon Oscar W.
Published: April 2005

Experimental data on the heat generated during torsional oscillations of annealed aluminum rods are presented. These results demonstrate the necessity of including coupling between the temperature field and the deviatoric components of strain when the material is deformed beyond the linear elastic region. The experiments are of sufficient duration that an approximate balance of the heat generation and the losses by conduction is finally reached. Temperatures in excess of five hundred degrees (F) are observed. It is also found that heat is generated during the loading parts of the cycle but that none is created when the material is unloading.
Effect of Grain Boundaries on Solute Partitioning During Progressive Solidification
Authors: Tiller W. A.
Published: April 2005

It can be shown that significant grain boundary segregation occurs during progressive solidification only when constitutional supercooling is present in the liquid ahead of the freezing interface. An extension of the analysis to cell boundary grooves shows that steep-walled grooves are stable only when a certain degree of constitutional supercooling in the liquid is exceeded.
Radiation Induced Hump Structure in the I-V Characteristics of Esaki Diodes
Authors: Pierce C. B. , Sander H. H. , Kantz A. D.
Published: April 2005

Well-defined hump structure is produced in the excess current region of Si, Ge, and GaAs Esaki diodes by irradiation with two MeV electrons, when the I-V characteristic is observed at low temperature. Si diodes develop humps at 0.35, 0.63, and 0.90 V at irradiation temperatures from 77° to 300°K. Ge diodes show humps at 0.23 and 0.51 V when irradiated at low temperature, but only a hump at 0.23 V after room temperature irradiation. GaAs diodes show humps at approximately 0.4 and 0.9 V. Diodes of approximately one mA peak current generally show hump current changes comparable to the peak current with an integrated flux of approximately 1017 electrons/cm2. On the basis of a simple model postulating direct tunneling of electrons from the conduction band of the n material to defect levels in the p material, generally good agreement is found with previous work on location of defect levels in Ge and Si. The technique shows promise as a tool for locating deep lying defect levels in the less thoroughly studied compound semiconductors. The first two humps in Si anneal from slightly above room temperature to above 250°C. The third hump does not anneal significantly to 250°C. The two humps produced on low temperature irradiation of Ge both anneal rapidly just below 0°C, while a third hump at 0.60 V appears in this temperature range. Hump structure produced or remaining in Ge at room temperature is stable to above 100°C, where anneal takes place with second-order kinetics and apparently goes to completion.
A Variational Approach to the Theory of the Effective Magnetic Permeability of Multiphase Materials
Authors: Hashin Z. , Shtrikman S.
Published: April 2005

Variational theorems are established and applied to the derivation of bounds for the effective magnetic permeability of macroscopically homogeneous and isotropic multiphase materials. For reasons of mathematical analogy the results are also valid for the dielectric constant, electric conductivity, heat conductivity, and diffusivity of such materials. For the case of two-phase materials, the bounds derived are the most restrictive ones that can be given in terms of the phase permeabilities and volume fractions. Comparison of present theoretical results with existing experimental data shows good agreement.
An Experimental Investigation on the Thermal Conductivity of Consolidated Porous Materials
Authors: Sugawara A. , Yoshizawa Y.
Published: April 2005

The thermal conductivity of porous materials consisting of the solid-fluid phase system, particularly the effect of porosity and of the saturating fluid occupying the pore space, has been investigated. Thirteen sand-stones and six fire bricks having different porosity were selected as typical examples of porous materials, and the experiment was carried out on these samples. A comparison method was used for measurement. Data were reported showing the variation of thermal conductivity relative to the porosity and conductivity of the saturating fluid. The variation according to the porosity of the samples is in complete agreement with the general formula previously derived by Sugawara and Yoshizawa.
The State of the Art of Magnetic Memories
Authors: Simkins Q. W.
Published: April 2005

A broad range of magnetic memories finds extensive use in today's data processing equipment. The most significant factors in evaluating a memory for a given application are reliability, cost, size, speed, and function. Ferrite core memories with capacities of 103 to 106 bits and with cycle times as short as 0.5 μsec are in use. Recent developments in this area, including partial switching, 2 cores/bit, and new core fabrication techniques, will be discussed.

There have been extensive development efforts recently in many forms of magnetic metal film devices. Many geometries, modes of operation, fabrication techniques, substrate materials, and film compositions are being used. A comparison of some of the resulting devices will be made, and the effects of the factors listed above will be discussed. The application of metal film memory devices will be considered and a comparison drawn with ferrite devices.

Techniques for achieving special purpose functions such as nondestructive readout, read-only and associative memory using magnetic elements, will also be described and compared.