bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave Analog to the Scattering of Light by Nonspherical Particles
Authors: Greenberg J. Mayo , Pedersen Norman E. , Pedersen Jeanne C.
Published: April 2005

A microwave technique has been developed for obtaining total cross sections and angular distributions for the scattering of electromagnetic radiation by nonspherical particles whose size is of the order of the wavelength. The scattering by spheroidal and cylindrical refracting particles has been measured for three orthogonal orientations of the symmetry axis. Comparison of the results with exact and approximate theoretical calculations for spheres, spheroids, and finite and infinite cylinders indicates the possibility of developing useful approximation methods. Some interesting effects have been noted, particularly a very large resonance in the scattering by finite cylinders. The results have been given preliminary application to the problem of the nature of the interstellar material which absorbs and polarizes starlight.
Coupled Mode Theory of Electron-Beam Parametric Amplification
Authors: Gould R. W. , Johnson C. C.
Published: April 2005

A theory of parametric amplification in a filamentary electron beam by transverse fields is developed in coupled mode form. Space charge effects are neglected. In addition to beam modes at the signal frequency, beam modes at frequencies ωn=ω+ωp, n=0, ±1, ±2…, where ωp is the pump frequency, are coupled together. A discussion of the general form of the equations is given and reveals the circumstances under which exponential gain or periodic energy transfer between various modes can occur. When applied to quadrupole electric pump fields, a description of the quadrupole amplifiers of Adler, Wade, and Gordon is obtained. This theory is then used to evaluate the noise contribution from synchronous beam modes and higher cyclotron idler modes. Coupling by axially symmetric electric fields and by axially symmetric magnetic fields is discussed, and other amplification schemes suggested. The theory of coupling by axially symmetric fields can also be used to study lens effects on noise in the gun region.
Backward Waves in Longitudinally Magnetized Ferrite Rods
Authors: Trivelpiece A. W. , Ignatius A. , Holscher P. C.
Published: April 2005

A quasi-static approximation (▿×H=0) is used to investigate the backward waves that propagate along a longitudinally magnetized ferrite rod. These waves propagate in the frequency range where the perme-ability of the ferrite is negative, γH0<ω<γH0[1 + (M0/μ0H0)]½, and can have a phase velocity much smaller than the velocity of light. The quasi-static approximation is shown to be valid whenever the free-space wavelength is greater than the circumference of the ferrite rod. Traveling-wave interaction of a drifting electron stream with these backward waves is considered, and a start-oscillation length of 1 in. at 4000 Mc is shown to be theoretically possible for a 600-v, 0.4-ma electron beam. Experimental verification of these waves is provided by measuring the phase velocity and signal strength along a longitudinally magnetized ferrite rod that completely fills a waveguide. Phase velocities as small as one one-hundredth of the velocity of light are measured.
Note on Ferromagnetic Relaxation Equations
Authors: Suhl H. , Fletcher R. C.
Published: April 2005

An amplitude formulation is employed for determining the motion of the electron spins in a ferromagnetic insulator in the presence of scattering from inhomogeneities. This formulation justifies the omission of an explicit back reaction term in previous ``energy'' and ``number of quanta'' formulations in the usual case where a large number of spin waves are excited by the scattering centers. The excited spin waves add up in such an incoherent fashion that they do not react back on the principal mode.
Transient Response of a Thermocouple Circuit Under Steady Currents
Authors: Reich Allen D. , Madigan John R.
Published: April 2005

Heat transfer calculations for a thermocouple circuit functioning as a Peltier cooler have been carried out. The calculations depend upon the exact solution of a one-dimensional time-dependent heat equation. It is shown that for an unloaded couple the temperature at the cold junction will be less than or equal to the reference junction temperature only for currents in the range from zero to twice the optimum current (i.e., the current that produces the minimum cold junction temperature). The temperature at the cold junction has been investigated as a function of time, and shown to approach the steady-state values appropriate to any particular multiple of the optimum current at that point with increasing time. It has been shown that one cannot produce a transient thermal spike at the cold junction which is greater in magnitude than the steady-state temperature for the optimum current by initially applying currents greater than the optimum. The possibility of achieving such thermal spikes by superposing a current pulse upon the steady-state current is discussed. The possibility of using the transient response of thermocouple junctions for the measurement of thermal conductivity is examined.
Thermionic Emission Constants and Their Interpretation
Authors: Hensley Eugene B.
Published: April 2005

A critical review of the procedures used in the measurement and interpretation of thermionic emission with particular reference to nonmetallic cathodes is presented. Definitions are proposed for the terms ``true work function,'' ``effective work function,'' and ``Richardson work function.'' The use of Schottky plots is criticized and the advantages of effective work function plots over the conventional Richardson plots are discussed. Factors relating to the interpretation of the thermionic emission constants which are discussed include reflection coefficients, nonuniform true work functions, temperature dependence of the electron affinity, and temperature dependence of the Fermi energy.
Study of the Bordoni Internal Friction Peaks in Copper
Authors: Paré Victor K.
Published: April 2005

The internal friction of several cold-worked copper single crystals was measured between 4° and 300°K at 4 kc. Vibrational strain amplitudes ranging from 10−7−2×10−5 were used. In pure samples the height of the Bordoni relaxation peak increased slightly with strain amplitude, but in all samples the activation energy of the relaxation process was not affected. This conclusion may be reconciled with the theory of Donth—and some other aspects of the measurements (e.g., peak width) can be clarified—by assuming that the dislocations participating in the relaxation process are under internal stresses resulting from the prior cold work. An activation energy of 0.12 ev is consistent with the present data, but the range of frequency represented in the comparison is not sufficient to determine the value accurately. It is shown that the subsidiary peak consists of two separate peaks at about 30° and 40°K.
Limitations of the Magneto-Optic Kerr Technique in the Study of Microscopic Magnetic Domain Structures
Authors: Treves D.
Published: April 2005

After considering the various factors that limit the performance of the Kerr technique in the observation of magnetic domains, it is concluded that the ellipticity caused by metallic reflection is of major importance. A detailed calculation of this effect is carried out, including the case of normal incidence. It is theoretically found that, for microscopic observation of magnetic domains using the longitudinal Kerr effect, the contrast is practically independent of the angle of incidence, and that there is an upper limit to the resolution obtainable, which is a function of the minimum contrast needed for observation. This resolution is usually of the order of a few microns. A detailed description of a Kerr instrument designed for microscopic observations is included.
Sputtering Yields of Metals for Ar+ and Ne+ Ions with Energies from 50 to 600 ev
Authors: Laegreid Nils , Wehner G. K.
Published: April 2005

Sputtering yields for polycrystalline metal and semiconductor targets under normally incident Ar+ and Ne+ ion bombardment were measured in the energy range from 50 to 600 ev. The yields (atoms/ion) were determined by measuring the weight loss of spherical targets immersed like large negative Langmuir probes in a dense low-pressure plasma (2–5 μ in Ar and ∼40 μ in Ne), created in a demountable thermionic cathode, low-voltage discharge tube. The yields were found to be independent of gas pressure and ion current density. Sputtering sets in substantially at approximately the same ion energy for the various metal-gas combinations (40 to 60 ev) but with increasing ion energy rises differently for different materials. Comparing various materials, it is found that the yields increase consistently as the d shells are filled, with Cu, Ag, and Au having the highest yields.
Magnetization of Iron-Nickel Alloys Under Hydrostatic Pressure
Authors: Kouvel J. S. , Wilson R. H.
Published: April 2005

Magnetization measurements were made on iron, nickel, and their alloys in hydrostatic pressures up to 3000 atm and in fields up to 12 000 oe. The results of these room-temperature measurements, combined with Patrick's results on the pressure dependence of the Curie temperatures, indicate that σ0, the saturation moment at 0°K, as well as θ, the Curie temperature, is rapidly decreased by compression in the fcc alloys of about 30% Ni. This is in agreement with the recent low-temperature pressure measurements of Kondorsky and Sedov. For these alloys, both σ0 and θ are decreasing with increasing Fe concentration. When the 30% Ni alloy is partially transformed to bcc, its σ0 and θ rise to much higher values but its magnetization is much less pressure dependent. It is concluded that unlike the more simple ferromagnetic bcc alloys, the fcc Fe-Ni alloys have a coexistence of ferromagnetic and antiferromagnetic order, similar to that recently proposed for the Ni-Mn alloys.
Recombination of Excess Carriers at Twin Structures in Germanium
Authors: McKelvey J. P.
Published: April 2005

A study of recombination of excess charge carriers at twin structures in germanium is made. The continuity equation is solved for a thin (one-dimensional) slab with a twin boundary of arbitrary recombination velocity bisecting the slab and parallel to the large faces of the sample. The results of lifetime measurements made on samples cut to approximate this geometry may then be made to yield the twin boundary recombination velocity, provided that suitable assumptions about the recombination velocity at the outer surfaces of the sample are made. Upper limits to the twin boundary recombination velocity are inferred from experimental evidence, and the case of a ``double'' or ``second-order'' twin boundary is investigated.
Effect of Pressure on emf of Thermocouples
Authors: Bundy F. P.
Published: April 2005

``Pressure'' thermal emf's have been measured for constantan, Pt, Ni, alumel, Pt 10% Rh, Cu, chromel, and Ni 18% Mo for a ΔT of 100°C over a pressure range 0 to 72 kbar. Corrections due to pressure for common thermocouples made of pairs of these metals have been deduced. A number of thermocouple pairs have been compared at temperatures up to 1200°C and pressures up to 58 kbar. Below 200 to 300° the deviations between them agree quite well with the absolute data on single metals taken at ΔT of 100°C. At higher temperatures the deviations diminish and generally reverse. It appears that the deviation δT of the readings of two thermocouples at a given pressure follow roughly the relationship δT = A (P)ΔT+B(P)ΔT2, where ΔT is the temperature interval in the pressurized zone, A (P) and B (P) are functions of pressure (roughly linear), and B (P) is generally opposite in sign to A (P) and is large enough to dominate the A (P) term at higher ΔT's.
Determination of the Semiconductor Surface Potential under a Metal Contact
Authors: Harrick N. J.
Published: April 2005

It is shown that through the use of the infrared absorption technique to measure the added carrier density in a semiconductor bulk adjacent to a metal contact coupled with simultaneous measurement of the floating potential of the contact, a reliable determination of the semiconductor surface barrier height under the metal contact can be obtained.
Man-Made Heating and Ionization of the Upper Atmosphere
Authors: Clavier P. A.
Published: April 2005

Absorption of radio signals by cyclotron resonance is shown to be possible within a very narrow layer of the atmosphere (20 km thick just below 100 km). For a plane-polarized signal only 25% of the power can be absorbed. Better results are obtained (50%) with a circularly polarized radio wave. The absorbable power is limited by the effects obtained so that an electron density of 3000 cm−3 and an electron temperature of 1600°K cannot be exceeded. The reason for this is the weakness of the earth's magnetic field.
Surface Electrical Changes Caused by the Adsorption of Hydrogen and Oxygen on Silicon
Authors: Law J. T.
Published: April 2005

Measurements of conductance, lifetime, change in contact potential with light, and contact potential have been carried out on bombardment-cleaned silicon surfaces and during the adsorption of molecular oxygen and atomic hydrogen. In the case of oxygen adsorption, the work function increased linearly with coverage. A change of 0.35 ev was obtained in going from θ=0 to θ=1. Very small changes in the transport properties were observed. Hydrogen atoms produced an initial decrease in work function of 0.1 ev for coverages below θ=0.35. From θ=0.35 to θ=1.0 the work function was increased by 0.3 ev. The changes in the transport properties were substantial and indicated a downward movement of the energy bands at the surface by about 0.08 ev. In the clean condition, the valence band edge was 0.12–0.14 ev below the Fermi level at the surface compared to 0.36 ev in the interior. The effect of hydrogen adsorption is discussed in terms of the adsorption data previously obtained on this system.
Current Flow across Grain Boundaries inn-Type Germanium. II
Authors: Mueller R. K.
Published: April 2005

The current flow across grain boundaries in n-type germanium has been measured in the temperature range of 350−200°K. Precisely oriented bicrystals have been grown for this study with 4, 6, and 25° tilt boundaries and 6° twist boundaries. The experimental data were found to be in good agreement with theoretical calculations given in the accompanying article [R. K. Mueller, J. Appl. Phys. 32, 635 (1961)]. The current across the boundary is mainly carried by electrons crossing the barrier, and it increases with decreasing boundary angle. The activation energy was found to be 0.71±0.01 ev for all boundaries. A lower limit of NB≥1013 (cm−2 ev−1) was found for the density of boundary states of 6 and 25° boundaries. No significant difference between tilt and twist boundaries has been observed.
Mobility of Radiation-Induced Defects in Germanium
Authors: Baruch P.
Published: April 2005

The motion of irradiation-produced defects in germanium has been observed under the influence of the electric field of a reverse-biased p-n junction. The defects were created with 1-Mev electrons or Co60 gamma rays, and the spatial distribution of the defects was obtained from the bias dependence of the junction capacity. Motion in the electric field was observable between 40–70°C and corresponds to negatively charged centers with a mobility of 2.6×10−14 cm2/v sec at 65°C. The activation energy of the mobility is about 1 ev. The centers are thought to be those which have previously been observed to anneal thermally. No observable effect was found for those defects which anneal at lower temperatures. Tentative interpretations are given.
Subsidiary Absorption above Ferrimagnetic Resonance
Authors: Fletcher P. C. , Silence Neal
Published: April 2005

The interaction between magnetostatic modes and spin waves was first discussed by Suhl [H. Suhl, J. Phys. Chem. Solids 1, 209 (1957)] and was shown to be the source of nonlinear effects at high power in ferrimagnetic resonance. It is the purpose of this article to extend Suhl's results on the threshold for subsidiary absorption to dc magnetic fields greater than that required for ferrimagnetic resonance. Some numerical results on the threshold for subsidiary absorption are presented for shapes other than spheres and for magnetostatic modes other than the uniform precession on a sphere. Some general conclusions regarding the shape dependence of nonlinear effects are stated. The theory is then compared with experimental results on YIG and MnZn ferrite.
Confirmation of Lifetimes by Noise and by Haynes-Shockley Method
Authors: Okazaki Susumu
Published: April 2005

Values of minority carrier lifetime in germanium filaments deduced from noise produced by photogeneration of carriers agree well with the values obtained by the Haynes-Shockley method.
End Effect Losses in dc Magnetohydrodynamic Generators
Authors: Boucher Roland A. , Ames Dennis B.
Published: April 2005

In this paper the end effect loss in a dc magnetohydrodynamic generator with rectangular cross section is considered. The case for nonconducting walls is examined, and a simple expression for the losses in terms of the maximum power output is obtained. The end effect loss is compared to viscous and turbulent flow losses and it is shown to be the predominant loss over a wide range of operating conditions.
Stability of Pressure-Supported Molten Zones in Horizontal Sheets
Authors: Kramer H. P. , Bogert B. P. , Hagelbarger D. W.
Published: April 2005

It is shown that the stability limit for pressurized horizontal floating zones is related to the eigenvalues of a membrane of the same shape. In particular, a rectangle of length a and width b is stable if π2(4/a2+1/b2)≥ρg/γ,and a circle of radius R is stable if (β11/R)2≥ρg/γ,where ρ is the density, g is the acceleration of gravity, γ is the surface tension constant, and β11=3.8317 is the first root of the Bessel function J1(x). This latter case checks with experiments on melted circular zones of tin.
Stacking Fault Probability of Noble Metal-Zinc Alloys
Authors: Vassamillet L. F.
Published: April 2005

The stacking fault probability has been measured by x-ray means on a number of alloys of gold, silver, and copper with varying zinc content. By using these probabilities, the relative magnitudes of the stacking fault energies have been deduced.
Investigation of the Sputtering of Silicon
Authors: Wolsky S. P. , Zdanuk E. J.
Published: April 2005

A sensitive vacuum microbalance was used to determine the sputtering yields for the argon-silicon system over an energy range of 34–800 ev. Preliminary data for the ion bombardment of silicon with CO2 was also obtained. Variation of the discharge voltage provided information on the relative sputtering effectiveness of Ar+ and Ar2+ ions. Extrapolation of the low-energy data indicates a probable threshold energy of 15–20 ev. The sputtering data indicate that the target surfaces were clean and reproducible. The experimental method is shown to be well suited for sputtering studies.
Sintering Crystalline Solids. II. Experimental Test of Diffusion Models in Powder Compacts
Authors: Coble R. L.
Published: April 2005

During sintering in alumina powder compacts, the density has been found to increase linearly with the logarithm of time, and the grain size increases with the one-third power of time. Incorporation of the time dependence of grain size increase into latestage bulk diffusion sintering models (from Part I) [R. L. Coble, J. Appl. Phys. 32, 787 (1961)] leads to corrected models by which a semilogarithmic behavior is predicted. The presence of density gradients in normally fabricated pellets makes impossible the deduction of whether theoretical density will be achieved from the early stages of the course of densification. Diffusion coefficients calculated from the intermediate and later stages of sintering bear order-of-magnitude agreement with those calculated from the initial-stage sintering measurements in alumina. All diffusion coefficients from sintering data are higher than Kingery's measured diffusion coefficients for oxygen. It is hypothesized that the sintering process must then be controlled by bulk diffusion of aluminum ions while the oxygen transport takes place along the grain boundaries. In controlling the sinterability of alumina to theoretical density, it appears that magnesia does not ``inhibit'' discontinuous grain growth, but instead increases the sintering rate such that discontinuous growth nuclei do not have time to form.
Effect of Neutron Irradiation on the Plastic Deformation of Copper Single Crystals
Authors: Greenfield I. G. , Wilsdorf H. G. F.
Published: April 2005

Copper single crystals subjected to a neutron dose of 3×1018 nvt (total flux) at pile temperature have been examined after deformation by the following experimental techniques: (a) observation of the load-extension relationships, (b) investigation of the slip-line structure with the electron microscope, and (c) diffraction electron microscopy of thinned-down single crystals before and after deformation. The critical resolved yield stress is in the order of 1.6 kg/mm2. In the early stages of deformation, the load-extension curves show serrations which are as large as 1.0% of the critical resolved shear stress. In the linear portion of the stress-strain curve, the rate of work hardening is less for irradiated single crystals than for the nonirradiated. The stress-strain curves of the irradiated and the nonirradiated specimens are similar in the parabolic region of the curves. The slip-line structure, at low deformations, consists of fine slip lines that are clustered together; the distances between the slip lines are, on the average, 100 A and often less; the distances between the clusters are in the order of 4μ. This structure is quite different than the alpha-brass structure, which in the past had been considered typical for irradiated copper. Cross slip, which is most abundant in the linear hardening region of the stress-strain curve, is found to be orientation dependent. The slip-line structures for the irradiated and nonirradiated crystals at high strains are very similar. Prismatic dislocation loops, apparently resulting from the condensation of vacancies, are found to be the most frequently produced radiation defect. The interaction between loops and glide dislocations results in heavily kinked dislocations which are probably responsible for the observed high yield stress. The glide dislocations were seen to remove the radiation damage. Because of this cleaning out of radiation-produced defects and the ability of the dislocations to multiply from new sources, the prolonged ``easy glide range'' can be explained. Further, the proposed mechanism provides an explanation of the work hardening in the linear and parabolic parts of the stress-strain curve.
Self-Diffusion in Silver during Plastic Deformation in Torsion
Authors: Darby J. B. , Tomizuka C. T. , Balluffi R. W.
Published: April 2005

Self-diffusion of Ag110 in silver polycrystals subjected to simultaneous torsion was studied near 700° and 800°C using the sectioning technique. Strains ⩽ 0.50 and strain rates ⩽ 13.8×10−5 sec−1 were employed. Specimen structures before and after deformation were also examined. The effects of straining on diffusion were relatively small in all cases. At 800°C the diffusivity was increased by no more than ∼50%. At 700°C the increase was no more than ∼100%. A substantial part of this observed enhancement was undoubtedly only apparent and due to difficulties associated with surface roughness. The results agreed generally with our previous work involving deformation in extension and compression but were in marked disagreement with recent results of Lee and Maddin and Forestieri and Girifalco [C. H. Lee and R. Maddin, Trans. AIME 215, 397 (1959); A. F. Forestieri and L. A. Girifalco, J. Phys. Chem. Solids 10, 99 (1959)], who have reported enhancements larger by one to two orders of magnitude. No simple explanation for these differences was found. Estimates of dislocation short-circuiting and the generation of extra point defects indicated that only small enhancements should be expected in agreement with the present results.
Some Experiments Using a Vacuum-Cleaned Silicon p-n Junction
Authors: Law J. T.
Published: April 2005

Measurements of the junction characteristics and the transport properties on either side of a vacuum-cleaned silicon p-n junction have been carried out. The changes in these properties during the adsorption of oxygen and hydrogen have also been investigated. In the clean condition, the value of (EF−EV) for both 21.5 ohm-cm n type and 27 ohm-cm p type was found to be 0.13–0.14 ev. When the silicon surface was clean, a large excess current across the junction was observed which disappeared during the adsorption of gas.
First Magnetocrystalline Anisotropy Constants of Some Iron-Silicon Alloys
Authors: Arajs Sigurds , Chessin Henry , Miller D. S.
Published: April 2005

First magnetocrystalline anisotropy constants K1∞ of 3.6, 6.7, 8.8, and 12.4 wt% silicon in iron alloys have been measured at 77°K and 297°K by determining the torque exerted on {100} single-crystal disks in uniform magnetic fields. The following results on disordered alloys have been obtained: Composition (wt%Si)Temperature (∘K)K1∞×103(erg cm−3)3.677430±10297360±106.777290±10297205±108.877245±10297165±1012.477120±529778±5

The measurements of this investigation are compared with the previously known studies. The agreement, where an overlap occurs, is satisfactory.
Interaction of Slow Electrons with Insulating Crystals. I. Absorption Coefficient for Cleaved Alkali Halides; Experimental Techniques
Authors: Cook C. J. , Fredericks William J.
Published: April 2005

Techniques have been developed that will permit a unique determination of an absorption coefficient δa for 0.2- to 20-ev electrons on cleaved, insulating crystals. Two classes of electron trapping levels, one that empties rapidly and one that does not empty at room temperature, may exist in the target and if they do, effects caused by them may perturb the data. Experimental techniques were developed to compensate for each characteristic effect. Pure and nonstoichiometric KBr and KCl crystals were studied. The probability that a crystal-incident electron results in a charge influx was found to vary makedly as a function of the impact energy and in a manner characteristic of the target. This feasibility study indicates that slow electron beams could be a powerful tool for diagnosing surface and bulk properties of insulating crystals.
Electron Microscope Study of Radiation Damage in Graphite
Authors: Bollmann W.
Published: April 2005

Neutron-induced defects in the graphite lattice are studied by dark-field transmission electron microscopy. The annealing is followed and the appearance of the defects is interpreted on the basis of the kinematical theory of electron diffraction. A physical interpretation of the observations based on displacement spikes and their annealing is given.
Textural Properties of Germanium Films
Authors: Davey John E.
Published: April 2005

The textural properties of thin germanium films vacuum evaporated onto hot fused-quartz substrates have been investigated in detail over the temperature range from ambient to 650°C. The strongest texture characteristic of these films is the [110], which is obtained at substrate temperatures as low as 175°C, and prevails up to about 350°C. For temperatures between 350° and 575°C, competition for growth occurs and the texture varies principally between being powder, [110] and [111]. Above 575°C the [111] texture becomes dominant.
Vacuum-Ultraviolet Absorption Studies of Irradiated Silica and Quartz
Authors: Nelson C. M. , Weeks R. A.
Published: April 2005

The optical absorption properties of Co60-irradiated fused silica and crystalline quartz have been studied in the vacuum-ultraviolet region. The most prominent absorption band found in both materials has a maximum at 7.6 ev (1620 A). Optical and thermal bleaching experiments indicate that this band is not necessarily complementary to a band at 5.9 ev (2100 A), as has been assumed. Though the 7.6-ev band has approximately the same intensity in both materials for the same irradiation, the 5.9-ev band is >20 times more intense in fused silica. The 7.6-ev band is still present after the 5.9-ev band has been thermally bleached. Additional absorption bands occur at 8.0 and 8.2 ev. Also, optical and thermal bleaching experiments suggest other absorption bands at 7.2, 7.4, 7.8, and 7.9 ev. Since these bands (particularly the 7.6-, 8.0-, and 8.2-ev bands) occur in high-purity silica and quartz, it is suggested that they are associated with defects in the quartz structure and are not caused by impurities.
Low-Frequency Measurements on the Bordoni Internal Friction Peak in Copper
Authors: Niblett D. H.
Published: April 2005

An apparatus is described for the measurement of the internal friction of metals over the temperature range of 4°–300°K at a frequency of the order of 10 cps. The Bordoni internal friction peak was observed in pure polycrystalline copper at 62°K at a frequency of 13.4 cps. By comparison with measurements at higher frequencies, a value of 0.14 ev is deduced for the activation energy. The width of the Bordoni peak is discussed in terms of distributions of activation energies and attempt frequencies.
Growth of Single-Crystal Iron Ferrites by the Czochralski Method
Authors: Horn F. H.
Published: April 2005

The growth of pure single crystals of ferrites by the Czochralski method is reported. Problems encountered are discussed and a practical solution indicated.
Traveling Wave Analysis of a Class of Parametric Amplifiers Based upon the Hill Equation
Authors: Fredricks R. W.
Published: April 2005

A general traveling wave analysis is given for electron beam parametric amplifiers in which the electron dynamical equation in the pump is a Hill's differential equation. Formulas are given for the complex wave number of beam waves, and clear conditions for growing wave solutions are presented. The special case of a sinusoidal pump field variation is treated, and the optimum pumping condition is found to result when the pump frequency is twice the beam natural frequency. It is shown that growing wave solutions exist at pump frequencies which are rational fractions of the beam natural frequency, but that the growth constants for these pumping conditions (at fixed pump power) are orders of magnitude less than under the optimum condition.
Discharge Photocells for the Detection of Resonance Radiation
Authors: Bell W. E. , Bloom A. L.
Published: April 2005

Penning discovered many years ago that a discharge whose characteristics depend on maintenance of a population of metastables can have its operation altered drastically when the metastables are removed by incident light. We have re-examined the effect in the light of more modern techniques with a view toward developing a highly efficient, narrow-band photodetector. A detector has been built which has sensitivity for the 20 581-A line of He comparable with that of commercially available detectors, but an acceptance bandwidth of only 0.1 cm−1.
On the Growth of Sapphire Microcrystals
Authors: Hargreaves C. M.
Published: April 2005

Thermodynamical considerations on the vapor-phase growth of whisker and platelet crystals of α-Al2O3 by the oxidation of aluminum lead to the conclusion that the vapor-phase mass transport is probably due to the suboxide Al2O and not AlO as previously suggested. Electron microscope observations confirm the optical evidence that spiral growth steps do not occur on the (0001) surfaces of Al2O3 crystals grown in this way.
Smooth Spalls and the Polymorphism of Iron
Authors: Erkman John O.
Published: April 2005

When Armco iron is loaded with a transient wave in which the pressure exceeds 0.131 megabar, smooth spalls may be observed. The two distinct compression shocks which are transmitted by the iron are followed by a steep rarefaction which may be called a rarefaction shock. At a free surface, the first compression shock is reflected as a backward-facing rarefaction wave. This wave may also steepen into a rarefaction shock which eventually meets the forward-facing rarefaction shock. The interaction of these waves results in a localized tension of destructive magnitude, which produces a smooth fracture. Location of the plane of this interaction was calculated by applying the theory of hydrodynamics. These calculations are inexact because the speed of sound for relief waves was taken from Hugoniot data since other data are not available. Fair agreement was obtained between experimental and calculated results. The work indicates that, in the case of a double spall, the fracture most remote from the original free surface may sometimes be formed first.
Semiconducting Properties of Inorganic Amorphous Materials
Authors: Uphoff H. L. , Healy J. H.
Published: April 2005

Ten compositions were prepared in the systems As:Se:Te and As:S:Te. Nine of these compositions were amorphous in structure. The resistivities and Seebeck coefficients of these materials were measured as functions of temperature. The resistivity varied exponentially with temperature, while the Seebeck coefficient varied linearly. At 298°K, the resistivity values for the amorphous samples ranged from 4.7×104−2.5×1013 ohm-cm, while the Seebeck coefficient values ranged from 830–1625 μv/°K (p type). At any temperature, the resistivity decreased with increase in tellurium content. For the amorphous materials, the thermal conductivity values ranged from 2.4–4.4 mw/cm-°K.
Theory of Magnetostatic Modes in Long, Axially Magnetized Cylinders
Authors: Joseph R. I. , Schlömann E.
Published: April 2005

The characteristic equation determining the eigenfrequencies of the magnetostatic modes is derived from the equations of motion and the boundary conditions. The solutions may be classified as pertaining to surface and to volume modes. Surface-mode solutions exist only for sufficiently small wave numbers, and their eigenfrequencies are larger than those of volume modes. The eigenfrequencies generally decrease with increasing wave number. Approximate, analytic expressions for the dependence of the eigenfrequencies on wave number have been obtained for the regions in which the wavelength is either much smaller or much larger than the cylinder radius. The approximate expressions are compared with numerical results obtained by means of an electronic computer.
Effects of Monolayer Adsorption and Bombardment Damage on Auger Electron Ejection from Germanium
Authors: Hagstrum Homer D.
Published: April 2005

Data are presented which show how the adsorption of carbon monoxide and oxygen on atomically clean germanium affect the process of Auger neutralization of He+ and Ne+ at the surface. Measurements of both total yield and kinetic-energy distribution of ejected Auger electrons have been made. The effect of ion bombardment alone without subsequent anneal, including the presence of absorbed noble gas in the surface layers of the crystal, has been investigated. Photomicrographs of the germanium target surface are reproduced.
Resistance Heating in the Arc Cathode Spot Zone
Authors: Rich J. A.
Published: April 2005

For an understanding of the arc cathode spot mechanism, it is essential to determine the relative importance of Joule heating within the cathode and the energy input from the arc discharge. The problem of a source of uniform current density acting over a circular area on the surface of a semi-infinite solid of conducting material is formulated and solved with the following results: (1) The Joule heat developed in the hemispherical volume directly under the cathode spot amounts to 38% of the total Joule heat developed in the electrode. This concentration of the heating leads to high average power densities in the cathode spot zone which amount, in the case of mercury, to 5×107 w/cm3 and 5×109 w/cm3 for current densities of 106 and 107 amp/cm2, respectively. (2) A comparison of the energy input to the cathode spot zone due to Joule heating and the energy input due to positive ion bombardment shows that for current densities of the order of 106 amp/cm2, the former amounts to some 10–20% of the latter for such high-resistivity metals as bismuth, antimony, and mercury. As the current density is increased to 107 amp/cm2, the two energy sources become comparable for metals other than the low resistivity metals such as copper and silver. (3) The time required to bring typical electrode materials to the melting point with resistance heating alone is relatively short. For J=106 amp/cm2 and a spot radius of 2×10−3 cm, bismuth (271°C) requires 4 μsec, antimony (631°C) 35 msec. The boiling point of mercury (357°C) is reached in 18 μsec.
Bismuth-Silver-Oxygen-Cesium Photocathode
Authors: Sommer A. H. , Spicer W. E.
Published: April 2005

The Bi–Ag–O–Cs photocathode has been used for many years because of its high and reasonably uniform sensitivity throughout the visible spectrum. Chemical and physical studies are reported which were made to gain an understanding of the chemical nature and of the energy band model of the material. It was found that the Bi–Ag–O–Cs cathode consists of the semiconductor Cs3Bi, elementary Ag, one or more Cs oxides, and possibly some elementary Cs. The Ag, but not the Bi, can be replaced by several other metals. Energy band models were determined by using considerations which have been successful in the interpretation of the alkali antimonide photoemitters. From optical and photoelectric measurements, values for band-gap energy and electron affinity were thus obtained for Cs3Bi as well as for the more complex materials represented by the symbols Cs3Bi(O), Cs3Bi(Ag), and Bi–Ag–O–Cs. A band gap of approximately 0.7 ev was found for all of these materials. It was shown that the oxygen reduces the electron affinity of Cs3Bi from 1.3 to 1.0 ev but does not greatly enhance the photoelectric yield. The addition of Ag to Cs3Bi or Cs3Bi(O) greatly increases the yield without appreciably reducing the electron affinity. A hypothesis is suggested to explain these effects.
Thermoelectric Measurements at Small-Area Contacts
Authors: Cutler M.
Published: April 2005

The measurement of the effects of heating a substance in the vicinity of a metal contact by means of an electrical current leads to the determination of various combinations of the thermoelectric parameters sufficient to determine the electrical conductivity, the thermal conductivity, and the Seebeck coefficient. If the metal contact is small, radiation causes negligible error in the determination of the thermal conductivity. One of the combinations obtained directly is the thermoelectric figure of merit. Equations are derived which relate to the heating current an observed thermoelectric voltage or change in resistance caused by a change in temperature at a small area contact. Geometric factors are found to cancel out of these equations. Quantitative relations are also presented which set limits on the effects of radiation. An experimental method is described which has been used for making such measurements, and some experimental results are reported which permit comparison to conventional measurements in accuracy. Ways in which measurements of thermal diffusivity can be combined with the other measurements are also discussed.
Dislocations and Stacking Faults in Aluminum Nitride
Authors: Delavignette P. , Kirkpatrick H. B. , Amelinckx S.
Published: April 2005

Dislocations in thin platelets of aluminum nitride grown from the vapor phase appear to be of two types. Some are dissociated into partials of the Shockley type; others are undissociated. A model is given for both types. The stacking fault associated with the dissociated dislocations consists of one lamella of the sphalerite structure. The stacking fault energy is deduced from the width of the ribbons and from the shape of the extended nodes; its value is γ ≈ 4 ergs/cm2.
Negative Resistance and Hot Electrons
Authors: Adawi I.
Published: April 2005

Current-voltage characteristics of hot electrons are analyzed for negative resistance regions. Electrons in a homogeneous semiconductor are assumed to interact only with acoustical phonons and charged centers of heavy mass. These charged centers could be ionized impurities or heavy holes with a negligible contribution to the current. A distribution function which ignores electron-electron collision almost certainly does not lead to negative resistance. A postulated Maxwellian distribution may lead to a current discontinuity, but does not lead to a stable region of negative resistance, contrary to previous conclusions. For any physical distribution it is shown that the average electron energy increases monotonically with field strength. These results also apply to situations in gaseous discharge where hot electrons are scattered by neutral molecules and ions.
Polarization and Diffusion in a Silicate Glass
Authors: Charles R. J.
Published: April 2005

The self-diffusion of alkali ions in alkali silicate glasses is discussed in terms of the formation, migration, and ultimate annihilation of defects. These defects exhibit a combination of the properties exhibited by Frenkel defects in alkali halides and Bjerrum defects in ice, and are treatable by many of the analytical techniques which are applicable to defects in crystalline solids. By utilizing the defect concept, relationships between self-diffusion, ac and dc conductivity, and orientational polarization are obtained.
Experimental Confirmation of Lamb Waves at Megacycle Frequencies
Authors: Worlton D. C.
Published: April 2005

A theory formulated in 1916 by Horace Lamb predicting that plates may vibrate in up to an infinite number of modes is confirmed by a method described. The theory is extended to correlate experimental observations. Equations are developed relating phase velocity to frequency and plate thickness in terms of longitudinal and shear wave velocity. Families of curves are obtained for aluminum and zirconium. The distinguishing characteristics of the various modes are discussed in the light of potential nondestructive testing applications. It is shown that the interior particles are displaced in elliptical orbits, with vertical motions existing at the surfaces when the wave velocity is (2)½ shear wave velocity, and horizontal surface motions existing for wave velocities equal to longitudinal wave velocity.
Flow of Gas through Porous Media in the Region between Molecular and Viscous Condition
Authors: Hirsch E. H.
Published: April 2005

Experiments on the flow of gases through porous Pyrex disks at pressures in the range of a few mm Hg are described. For air, hydrogen, and carbon dioxide the specific flow is found to be given by Q=A(MT)12+BηTp̄+CM12{1−exp[α0−βT12]p̄}The significance of this result is discussed.
Theory of Microplasma Instability in Silicon
Authors: McIntyre R. J.
Published: April 2005

A statistical theory is presented to explain microplasma instability at the onset of avalanche in reversebiased silicon linearly graded and step junctions. An expression is derived which relates the turnoff probability of the microplasma to the differential resistance of the diode in its conducting state and to other physically measurable diode parameters. Measurements of the turnoff probability as a function of the pulse current are presented for several diodes and are shown to agree well with the derived theory. To explain the turnon probability, three expressions, each involving slightly different approximations, are derived for the probability that a carrier entering the breakdown region will initiate an avalanche. In each case, this probability is found to be proportional to the excess of the applied voltage over a uniquely definable sustaining voltage Vs, in poor agreement with experiment. The various mechanisms which determine the diode's differential impedance in the conducting state are discussed and approximate expressions for the contributions of each mechanism to the differential impedance are derived. Multilevel pulses, previously interpreted as indicating more than one conducting state for a microplasma, are explained in terms of parallel breakdowns of more than one microplasma.
Mass Spectrographic Analysis of Insulators Using a Vacuum Spark Positive Ion Source
Authors: Ahearn A. J.
Published: April 2005

Serious limitations are encountered in the analysis of insulators when conducting tubes packed with the powdered insulator are the electrodes of the vacuum spark. A general method of forming a vacuum spark directly between a conductor and a slab of insulator, which removes the above limitations, is presented. Mass spectral data of the insulators steatite and quartz are presented showing the presence of bulk impurities and surface contamination.
Surface Layers on Barium Titanate Single Crystals above the Curie Point
Authors: Schlosser H. , Drougard M. E.
Published: April 2005

Dielectric dispersion measurements have been carried out on barium titanate single crystals of different thicknesses at temperatures above the Curie point ranging up to 180°C. In the high-frequency range of the measurements (100 kc), the measured dielectric constant of thin crystals is consistently much smaller than that of thick samples. The effect is ascribed to the presence of a layer of low dielectric constant on the surface of the crystals, with a capacitance of the order of 0.5 μf/cm2 in the temperature range explored. The relaxation time of this surface layer is found to be at least 10−4 sec at 120°C on crystals which have not been ``aged'' recently.
Stress Distribution on the Boundary of an Elliptical Hole in a Large Plate during Passage of a Stress Pulse of Long Duration (Major Axis Normal to the Wave Front)
Authors: Durelli A. J. , Riley W. F.
Published: April 2005

A solution to the problem of the stress distribution on the boundary of an elliptical hole in a large plate during passage of a compressive stress pulse of relatively long duration is presented. The major axis of the ellipse is normal to the wave front. The solution was experimentally obtained by using a low modulus model material in a combined photoelasticity and moiré analysis. The long-duration stress pulse was applied by loading a small region on an edge of the plate with a falling weight. The results of the investigation indicate that the falling weight loading generates a biaxial state of stress at every point in the plate, which varies with time. The maximum dynamic compressive stresses on the hole boundary can be computed with a fair degree of accuracy by using: (a) the equation of Inglis for the static stress distribution on the boundary of an elliptical hole in any two-dimensional uniform and axial system of combined stress and (b) the biaxial stresses, at the same instant of time, that would have been present at the center of the ellipse if there had been no hole (free-field stresses). The maximum dynamic tensile stresses on the hole boundary were always smaller than the values computed using this same procedure.
Transmission Electron Microscope Observations of Magnetic Domain Walls
Authors: Michalak J. T. , Glenn R. C.
Published: April 2005

Ferromagnetic domain wall images have been observed in a variety of ferromagnetic materials by an electron transmission technique employing defocusing of the objective lens. Image formation and contrast effects are interpreted on the basis of charged particle motion through a magnetic field and electron microscope imaging. Observations are consistent with magnetic domain theory; domain sizes and wall geometry have been confirmed by the Bitter pattern technique.
Optical Properties of Oriented Polystyrene
Authors: Stein Richard S.
Published: April 2005

The orientation of a monomer unit of a polystyrene molecule is specified in terms of seven orientation functions, of which five are independent in the general case. The birefringence and infrared dichroism are expressed in terms of these orientation functions. The expression for infrared dichroism is dependent on the angle which the direction of dipole moment change for the normal mode of vibration concerned makes with the axes of the molecule. Experimental possibilities for determining these orientation functions are discussed.