bluuebunny/crossref_metadata_2025 huggingface dataset:
Time Dependence of Mechanical Breakdown in Bundles of Fibers. II. The Infinite Ideal Bundle under Linearly Increasing Loads
Authors: Coleman Bernard D. , Marquardt Donald W.
Published: April 2005

This article contains an extension of the theory of the previous paper to the calculation of the behavior of an infinite ideal bundle in a constant rate of loading experiment. It is assumed throughout that the bundle is composed of filaments which have been randomly selected from a first-order ensemble for which the average lifetime under separate dead loads is an exponential function of the applied load. The differential equation which describes the breakdown of such a bundle has been numerically investigated with a CPC digital computer using a fourth-order Runge-Kutta method. It has been found that, throughout the practical range in rates of loading, the bundle's tensile strength (units of force at break per initial unit area) is about 90% of the strength of the individual filaments. It also was found that the strength of the bundle is approximately an increasing linear function of the logarithm of the rate of loading.
Frictional Heating and Its Influence on the Wear of Steel
Authors: Welsh N. C.
Published: April 2005

High frictional temperatures during the dry or imperfectly lubricated rubbing of steel produce gross structural changes and intense hardening of the surface layers. In consequence of these changes the wear time curve shows a marked inflexion, the wear rate of soft steel on soft steel diminishing by more than an order of magnitude as the hardened skin develops. The protective layer establishes itself more readily as the carbon content of the steel increases, a feature explained by the ease with which eutectoid pearlite transforms to austenite, and thence to martensite, during the rapid temperature cycle. By simulating the hot spots during wear by the thermal action of electric sparks, the hardness change is shown to be intensified by nitrogen or carbon absorbed from the atmosphere or lubricant.
Random Interchange of Circuits with Applications to Counting Rate Meters and Function Generators
Authors: Lichtenstein Roland M.
Published: April 2005

Two identical linear circuits are excited by generators furnishing equal and opposite voltages. Homologous portions of the two circuits are interchanged at random times with, on the average, r interchanges per unit time. Because of these interchanges, the currents in the remaining portions are irregular. A theorem is derived that permits one to calculate the statistical averages of these currents. It states that one may disregard the interchanging; instead, one merely replaces the complex frequency s by s+2r in the circuit functions [e.g., the impedances Z(s)] of the portions that were being interchanged. On the basis of this theorem one may design counting rate meters with nonlinear (e.g., logarithmic) scale, useful in reactor instrumentation, and function generators for functions of practical importance, such as the logarithmic and exponential functions, and powers with arbitrary exponent. The nature of the function depends only on linear passive circuit elements, such as resistors and capacitors.
Condensation Interfaces in Two-Phase Flows
Authors: Chiarulli P. , Dressler R. F.
Published: April 2005

The condensation zone of a condensing vapor flowing in a channel is idealized as an interface separating vapor and liquid phases of the fluid with a concentrated friction, heat removal, and cold liquid injector mechanism at the interface. Rankine-Hugoniot relations are obtained including effects of the mass, momentum, and energy sources at the interface. For a stationary interface, an explicit approximate solution is obtained giving the final liquid state in terms of the other parameters. In addition, a rapidly converging iterative procedure is presented with this solution as a first approximation and utilizing directly thermodynamic tables of the vapor and liquid. Examples corresponding to steam flow in a pipe and to an underwater steam jet are considered and their Hugoniot curves are computed and compared to similar curves obtained in detonation theory. The thermodynamic requirements of the existence of a steam-water interface limit these curves in extent and result in upper and lower bounds on the values of the cooling parameters.
Nucleation and Growth in a Photosensitive Glass
Authors: Maurer R. D.
Published: April 2005

The nucleation and growth of particles can be independently determined by simultaneous measurement of two quantities having different functional dependencies upon particle number and size. Light scattering and optical absorption are the two quantities chosen to observe the precipitation kinetics of a gold colloid. When an exposed photosensitive glass is treated at high temperatures, gold precipitates on a fixed number of sites. On the other hand, increasing the concentration of reactants causes spontaneous gold precipitation in which growth sites form continuously throughout the precipitation process. This indicates that the photosensitive reaction forms nuclei in a supersaturated solution which cannot nucleate spontaneously. In agreement with this, the experiment shows that the number of growth sites increases with exposure while the growth rate is the same for all exposures. Finally, assuming that the particles are spheres, absolute values are derived for the initial change of particle size with time and for the number of nuclei as a function of exposure.
Influence of Wall Losses on Pulse Propagation in Wave Guides
Authors: Gajewski Ryszard
Published: April 2005

Assuming that the resistivity of wave guide walls is not too large, the influence which energy losses have upon the shape of a pulse propagating along the wave guide is discussed. It is found that pulses are damped with a damping factor equal in the first approximation to that in a steady state.
Analysis of the Effect of Nuclear Radiation on Transistors
Authors: Loferski J. J.
Published: April 2005

The behavior of germanium transistors in nuclear radiation fields is predicted by combining transistor theory and the experimentally observed changes in irradiated semiconductors. It is shown that the decay of minority carrier lifetime τ in the base region usually controls the useful life of a transistor in a radiation field. Radiation induced changes of the conductivity place an ultimate limit on transistor life, but these changes occur at a much slower rate than those in τ. The analysis predicts the following: (a) αcb−1 should be a linear function of bombardment time in a constant flux field; (b) p-n-p units should decay faster than n-p-n units; (c) for a given resistivity type and structure the decay rate is proportional to the square of the transistor base width which in turn, is inversely proportional to the cutoff frequency of the amplification factor. Thus, high-frequency units with their thin base regions decay more slowly than low-frequency units. The predictions of the theory are compared with experimental observations on the behavior of irradiated transistors, and the agreement is found to be reasonably good.
X-Ray Study of Faults in Body-Centered Cubic Metals
Authors: Guentert O. J. , Warren B. E.
Published: April 2005

The effect on the x-ray diffraction pattern of deformation faults and twin faults occurring at random on the (211) planes of a b.c.c. lattice has been investigated. In single crystal reflections, deformation faults produce peak shifts and peak broadening, and twin faults produce a peak asymmetry and peak broadening. For a powder pattern it is necessary to average over the different components of a powder-pattern peak; the peak shifts average out to zero, and the peak asymmetries to a quantity which is generally too small to measure. Both types of fault produce a line broadening which varies strongly from one powder peak to another. The hkl dependence of the broadening is the same for the two kinds of faults, and only a combination of the two probabilities can be measured. Measurements were made on samples of cold-worked β-brass filings in different states of annealing. There were no measurable peak shifts or peak asymmetries. The ratios of the effective particle size values could be explained only if a major part of the particle size broadening is due to faulting. The results are discussed in connection with measurements on other cold-worked b.c.c. metals.
Numerical Calculation of Certain Small Electrostatic Effects
Authors: Cade R. , Small K. A.
Published: April 2005

A numerical method is described which enables the effect of thin wires upon a given electrostatic field to be calculated, in the case when the wires are straight and of uniform circular cross section. A brief description is given of a problem to which the method has been applied, and of the results obtained.
Transparency Factor for Weakly Absorbing Samples in X-Ray Diffractometry
Authors: Milberg M. E.
Published: April 2005

Equations have been developed for the transparency factor applicable to the intensity of x-rays scattered from very weakly absorbing materials in the standard diffractometric technique. The expressions differ from the standard absorption correction because of the variation of effective scattering volume with angle. Both equations and illustrative curves are presented.
Method for Measuring Saturation Magnetization in Ring Samples
Authors: Graham C. D.
Published: April 2005

A method is described for measuring saturation magnetization in a ring sample. This permits the measurement of saturation and of low-field magnetic properties in the same sample. The method consists of saturating the sample in a strong field directed perpendicular to the plane of the ring, changing the direction of the magnetization slightly with a circumferential field, and measuring the resultant flux change in the ring. The procedure also gives an accurate value for the cross-sectional area of the secondary winding on the specimen.
Some Aspects of Surface Boiling
Authors: Faneuff C. E. , McLean E. A. , Scherrer V. E.
Published: April 2005

An experiment is described in which the growth of vapor bubbles at a surface is followed in detail. Growth curves are obtained and shown to agree, within experimental error, with current theories of growth under idealized conditions, provided an average superheat present at the initiation of growth is used in the calculation. A criterion is proposed to permit an estimate of a delay time for vapor formation. The estimated delays are found to be in qualitative agreement with those measured.
Propagation of Waves in Helical Wave Guides
Authors: Chu Chiao-Min
Published: April 2005

The field configuration near the conductors of a helical wave guide is obtained from the solution of the spatial-wave equation for a developed helix. This solution is first obtained for the case of tape conductors and then adapted to elliptical (including circular) conductors by conformal transformation. By comparing this solution with that of a developed-sheath helix, the impedance, attenuation, and other parameters of a wire helix are deduced approximately. These are expressed as the product of the corresponding sheath-helix parameter times a proper correction factor depending on frequency, conductor size, and shape. The analysis is extended to the multifilar helix. The results of this analysis provide a means of calculating the attenuation of wire helices and of choosing optimum wire configurations in the design of helical wave guides.
Cooling Time of Strong Glass Fibers
Authors: Anderson O. L.
Published: April 2005

Simplified equations for the cooling time of glass fibers to the solid state are deduced from the theory of heat conduction. The approximations made are based upon a value of the order of 1 for Nusselt's number. This value of Nu holds for comparable metallic fibers, as measured by Mueller, and is assumed to hold for glass fibers. The relation of pulling speed and flow rate to cooling time is shown. Calculations of cooling time of typical small glass fibers show that they are of the same order as the Maxwell relaxation time of the glass at roughly 900°C. The consequence of this correlation is discussed in terms of the high strength of fibers, and the high ``fictive'' temperature of fibers.
Segmental Motion in Polypropylene
Authors: Sauer J. A. , Wall R. A. , Fuschillo N. , Woodward A. E.
Published: April 2005

Molecular motion in polypropylene has been studied both by measurements of dynamic mechanical properties and by observations of nuclear magnetic resonance line shapes. The mechanical measurements were made in the audio-frequency region over the temperature range from 80°K to the melting point. Both completely amorphous and highly crystalline samples of polypropylene were investigated. In the amorphous sample, two transitions were observed, a broad but weak secondary one near 235°K and a relatively sharp primary one occurring near 270°K. For the highly crystalline polypropylene, two transitions centered at 250°K and 300°K, respectively, are associated with increased mobility in the amorphous regions and a third higher temperature transition is associated with crystalline melting. These transitions have also been investigated by observing the changes occurring in NMR line shapes as the temperature is varied.
Free Volume Approach to Polystyrene Melt Viscosity
Authors: Williams Malcolm L.
Published: April 2005

The Doolittle approach to Newtonian viscosity assumes η=A expB/f, where A and B are constants independent of temperature and f, the relative free volume, is (v−v0)/v0. Here v is the specific volume and v0 is the occupied volume. Using machine computations, this equation was applied to published data on polystyrene, replacing v by its equivalent vg+(dv/dT)(T−Tg), where vg is the specific volume at the glass temperature Tg. The agreement between calculated and observed viscosities is at least as good, and perhaps better, than that afforded by other existing empirical expressions. The constant B is independent of molecular weight and temperature while v0 depends slightly on molecular weight. A log-log plot of A against molecular weight M produces two straight lines intersecting at M=35 000. At higher values of M, the slope is 3.4; at lower values, it is slightly greater than one. This treatment separates the melt viscosity of polystyrene into two factors, A, dependent only on structural parameters, and f, which is determined by the specific volume and is a function of temperature.
Measurement of the Isothermal Volume Dilation Accompanying the Unilateral Extension of Rubber
Authors: Hewitt Fred G. , Anthony Robert L.
Published: April 2005

Using a torsion balance immersed in water and natural rubber ring specimens cured with di-tertiary-butyl-peroxide, measurements were made of the isothermal volume dilation of rubber for mean extensions ε=14, 33, and 51%, thus extending the results of Gee, Stern, and Treloar to lower strains. Chain molecular weights Mc=3000, 4400, 5100, and 5500 were employed. The chain molecular weights were determined by swelling in benzene, the uncertainty in each determination being about 10%. Observed fractional volume increases ranged from 3.2×10−5 for ε=14% and Mc=5500 to 14×10−5 for ε=51% and Mc=3000. Using Gee's expression for the volume dilation, but obtaining the slope of the stress-strain curve from the statistical theory, curves were fitted to the data. The fitting process constituted a determination of Young's modulus E for each rubber specimen. The resulting curves are in good agreement with those of Gee, Stern, and Treloar. Additional determinations of E were made from rough stress-strain curves and from the swelling data, the internal agreement between the three determinations being fair.
Dynamic Mechanical Behavior of Irradiated Polyethylene
Authors: Deeley C. W. , Sauer J. A. , Woodward A. E.
Published: April 2005

Samples of a ``high-density'' polyethylene (ρ=0.964 g/cc) irradiated in a nuclear reactor to thermal neutron doses as high as 2.9×1018 nvt and of ``low-density'' polyethylene (ρ=0.915 g/cc) subjected to gammaray bombardment from a Co60 source up to a dosage of 1×109 rep have been investigated by dynamic mechanical methods from 80°K to 450°K at audio-frequencies. Degrees of cross-linking were estimated from the observed changes in resonance frequency at temperatures where the specimens were ``rubber-like.'' Densities and x-ray crystallinities at 25°C were also measured.

For the pile-irradiated ``high-density'' polyethylene the γ peak found around 165°K shows a marked increase in height and area at dosages above 1018 nvt. The α peak at about 390°K decreases markedly upon receiving a thermal neutron dose of 0.6×1018 nvt. Further changes in this absorption with higher dosages are obscured by the appearance of a β peak around 330°K which is almost absent in the unirradiated material; the appearance of the β region is attributed to the creation of branch points and cross-link points in the essentially linear polymer by the irradiation.

The irradiated ``low-density'' specimens exhibit three damping peaks. Over the dosage range studied the γ peak (165°K) increases in height and area, the β peak (270°K) shifts to higher temperatures, and the α peak (360°K) shifts to lower temperatures with increasing dose. The cross-linking degree is not proportional to dose and to the highest dosages studied, there is very little, if any, reduction in x-ray crystallinity.
Theoretical Values of the Dynamic Stretch Moduli of Fiber-Forming Polymers
Authors: Lyons W. James
Published: April 2005

Employing concepts first applied to textile fibers by Meyer and Lotmar in calculating the elastic stretch modulus of the crystalline domain of cellulose, the moduli of crystalline polyhexamethylene adipamide (α form), and polyethylene terephthalate have been derived. The treatment employs interatomic force constants for the stretching and bending of primary valence bonds, applied to molecular geometries deduced from the crystal structures of these polymers as determined by Bunn and co-workers. The modulus of the crystal cell of the first material (nylon 66) is calculated to be 15.7×1011 dyne cm−2, while that of the second is 14.6×1011 dyne cm−2. Supposedly these are approximately the modulus values which fibers having perfectly oriented, efficiently packed molecules would have. In both cases the theoretical value is at least an order of magnitude larger than that found experimentally for actual production samples.
Molecular Motion in Polypropylene, Isotactic and Atactic
Authors: Slichter W. P. , Mandell Elaine R.
Published: April 2005

Molecular order and motion in isotactic and atactic polypropylene molecules have been studied by proton magnetic resonance methods over the temperature range 77–400°K, and by x-ray diffraction. It is shown that some motion persists at the lowest temperatures, and becomes pronounced in the temperature interval 77–110°K. This behavior is ascribed to motion of the methyl groups about the threefold axis. The resonance undergoes further narrowing near room temperature for the atactic polymer, presumably owing to rotational and translational motions of chain segments. The isotactic compound possesses a narrow resonance superposed on a broad absorption over a wide temperature range. The former, ascribed to the amorphous regions, narrows at higher temperatures than for the atactic polymer, presumably owing to constraints imposed by the crystalline regions. The chains of the isotactic compound are less mobile than in polyethylene, as shown by the resonance studies and by x-ray diffraction comparisons of the rate of crystallization.
Magnetic Writing with an Electron Beam
Authors: Mayer Ludwig
Published: April 2005

Experimental evidence is presented that magnetic writing with an electron beam is possible. The method is based on Curie-point writing which permits local reversal of the direction of magnetization in suitable, premagnetized magnetic films by temporarily elevating the temperature above the Curie point. By utilizing the dissipation energy of a focused electron beam for this purpose, quite well-defined traces of reversed magnetization could be recorded on MnBi films. The traces were erasable magnetically. Writing speeds corresponding to 3·104 bits/sec and information densities corresponding to 105 bits/cm2 could be achieved in these first experiments. Considerably higher writing speeds and some increase in information density should be feasible.

By means of an electron mirror micrograph of the electronically recorded magnetic trace, evidence is presented which shows that, in addition to read-in with an electron beam, electronic read-out of the magnetically stored information is also possible.

Electronic writing of magnetic half-tone images by controlling the size of the spots of reversed magnetization appears to be feasible also.
Diffusion of Gallium in Silicon
Authors: Kurtz A. D. , Gravel C. L.
Published: April 2005

The diffusion of gallium into silicon has been investigated over a temperature range of 1130°C–1358°C using an open-tube vapor-solid diffusion technique at atmospheric pressure. A p-n junction method combined with incremental conductivity measurements of the diffused layer was used to determine the diffusion constant. Lower diffusivities and a somewhat higher activation energy, (ΔH=95 kcal) were obtained than those reported previously.

The difference is attributed to variation of diffusivity with surface concentration and is discussed on the basis of substitutional diffusion proceeding by a vacancy mechanism.
Thin Film Magnetization Reversal by Coherent Rotation
Authors: Gillette P. R. , Oshima K.
Published: April 2005

Several theoretical analyses of the process of magnetization reversal in thin films by coherent rotation of the magnetization vector have been published. However, these analyses suffer from the use of questionable assumptions and from a lack of generality. This paper presents results obtained by employing an electronic digital computer to solve differential equations of greater accuracy and generality than those previously used. These results show how the optimum damping factor (which, as defined herein, differs slightly from the critical damping factor), the peak output voltage, and the reversal time vary with the magnitude and direction of a field applied to a thin ferromagnetic film with uniaxial anisotropy. The results for a particular direction of applied field show that the optimum damping factor and the peak voltage increase and the reversal time decreases with increasing magnitude of the field; and that a plot of reciprocal reversal time versus field magnitude is a parabola if the damping factor is always equal to its optimum value, but a hyperbola if the damping factor is a constant.
Ferroelectric Switching Time of BaTiO3 Crystals at High Voltages
Authors: Stadler H. L.
Published: April 2005

The ferroelectric switching time of two BaTiO3 single crystals has been measured at voltages up to 1300 v across the crystals' thicknesses, 0.108 and 0.076 mm. The switching time, ts, can be represented approximately as ts=kV−32 from V equals 100 v to 1300 v applied. The shortest switching time, 7.0×10−9 sec, was less than half the time taken by a dilatational wave front to traverse the crystal's thickness, 14.9×10−9 sec. The results imply that ferroelectric switching in this voltage range does not involve the movement of elastic waves from one side of the crystal to the other.
Observations of Dislocations in Iron Whiskers
Authors: Coleman R. V.
Published: April 2005

The etching of iron whiskers in picral and nital etchants has been studied and etch-pit configurations in certain areas of as-grown whiskers have been observed. Dislocations introduced by plastic deformation of the whisker have been investigated and arrays of dislocations produced by annealing the deformed whiskers have been studied. Whiskers with axes in [100], [110], and [111] directions have been used in these experiments.
Crystal Growth on Cathode Sputtered Copper Films by Pairs of Double Spiral Mechanisms Analogous to Frank-Read Sources
Authors: Henschke Erich B.
Published: April 2005

Unique crystal growth patterns with closed loops, partly concentric and partly eccentric, with very large step heights between the ledges were observed on microblisters of copper films sputtered onto glass substrate. While the primary cause for the generation of the blisters is explained as due to diffusion-oil deposits present on the glass substrate and to heat from secondary electrons released by the target producing a high vapor pressure underneath the sputtered film, the generation of the loop patterns on the flat circular surface of the blisters is considered to be caused by alternative slips induced by the inside pressure which affect a triangular part of the {111} surface with two sides of {111} slip planes, one in radial <110> direction and the other in a <110> direction along the rim of the blister. Two alternately generated monatomic radial steps on the flat part of the blister produce two superposing spirals of opposite sense each due to one-half of two Frank-Read sources and create by repetition of this process the observed patterns with very large step heights of the ledges.
Thermal Conductivity and Thermoelectric Power of Germanium-Silicon Alloys
Authors: Steele M. C. , Rosi F. D.
Published: April 2005

Thermal conductivity measurements have been made on a series of germanium-silicon alloys. At 300°K for an alloy containing 56 atomic percent Si, the thermal conductivity was found to be six times smaller than the value for pure Ge. Measurements of the thermoelectric power on some alloys are also reported. It is then shown that solid-solution alloying can significantly increase the figure of merit of thermoelectric materials.
Anomalous Dispersion in Artificial Dielectrics
Authors: Wickersham Arthur F.
Published: April 2005

Measurements have been made of the anomalous dispersion occurring in certain types of artificial dielectrics. To a limited extent the dependence of dispersion on array and scattering element geometry has been determined and an attempt made to control dispersion by changing the array configuration. Applications are mentioned briefly.
Static Fatigue of Glass. I
Authors: Charles R. J.
Published: April 2005

Water vapor corrosion of a simple soda-lime glass has been studied in regard to its effect on static fatigue of the same glass. A mechanism of dissolution has been proposed in which alkali ion self-diffusion controls the initial steps of water corrosion and leads to breakdown of the glass network. Since experiments show that an expansion of a glass network enhances corrosion rate, it is postulated that asymmetrical contitions of expansion around a surface flaw, brought about by applied stress, could lead to growth of the flaw in a preferential direction to bring about delayed failure.
n-Type and p-Type Conduction in Alkali-Antimonide Photoemitters
Authors: Sommer A. H.
Published: April 2005

Conductivity measurements were made during the formation of alkali antimonides to deduce whether these materials are p-type or n-type conductors. Reproducible results were obtained, indicating that K3Sb and Na3Sb are n type while Cs3Sb and the multialkali antimonides are p type. A correlation between high-quantum efficiency of photoemission and p-type conduction is suggested.
Generation-Recombination Noise in a Two-Level Impurity Semiconductor
Authors: Teitler S.
Published: April 2005

A general expression for the generation-recombination noise in a two-level impurity semiconductor is derived. Application is then made to zinc-doped germanium in the dark from 20°K to 100°K. The total white noise in this case exhibits a maximum and a minimum as the temperature is increased and the contributions to the noise which can be associated with the individual levels vary.
Calculations on the Shape and Extent of Space Charge Regions in Semiconductor Surfaces
Authors: Dousmanis G. C. , Duncan R. C.
Published: April 2005

The shape and extent of space charge regions in semiconductor surfaces are briefly discussed. Curves describing the potential as a function of distance inside the semiconductor are obtained by numerical integration of the Poisson equation. The curves apply to all semiconductors. They show the effects of different resistivities and the increased depth of the space charge regions expected in pure III-V compounds over those encountered in Ge and Si.
Generation of High-Velocity Projectiles
Authors: Cook Melvin A. , Keyes Robert T.
Published: April 2005

A technique of controlling the shape of detonation wave fronts in high explosives by inert wave control inserts was applied to generate discrete ultrahigh-velocity pellets. Tests to determine the most suitable pellet shape as well as the optimum charge configuration are described, and velocities up to 7600 m/sec were realized for 0.95-g aluminum pellets. The mechanism whereby pellets are accelerated by ``shaped'' waves is discussed, and the conclusion is reached that a simple model based upon the transmission of shock from the detonation wave to the pellet is not applicable.
Arc Cathode Movement in a Magnetic Field
Authors: Guile A. E. , Secker P. E.
Published: April 2005

An arc cathode spot in a transverse magnetic field may move either in the Amperian (forward) direction, or in the opposite (retrograde) direction. Experiments are described which show that forward continuous motion is caused by magnetic fields at the cathode surface, as is the case with retrograde motion, and that both of these motions depend upon the material and surface condition of the cathode. Forward cathode velocity both when continuous and when moving in a stepping process is independent of arc current over a wide range.

The theories so far suggested for retrograde motion do not appear to be able to account for the dependence of retrograde cathode movement on the nature of the cathode surface.
Magnetostriction of Low-Density Cobalt Rondel
Authors: Stauss H. E.
Published: April 2005

A dimensional change that simulates magnetostriction can be expected when a porous or spongy ferromagnetic body is placed in a magnetic field. Such an effect has been observed. Polycrystalline cobalt with a density less than 50% of normal developed a strain of −139×10−6, whereas cobalt of normal density developed a strain of −28×10−6. This finding appears to open the way for the development of materials with enhanced values of strain in a magnetic field.
Microwave Faraday Rotation: Design and Analysis of a Bimodal Cavity
Authors: Portis A. M. , Teaney Dale
Published: April 2005

The design and analysis of a bimodal cavity for the observation of microwave Faraday rotation is presented. An equivalent circuit of lumped elements is developed and the coupling between degenerate cavity modes is expressed in terms of the elements of the susceptibility tensor of the material producing the rotation. The theory is checked against experimental results with a paramagnetic salt and substantial agreement is obtained. A cavity of this type when used in conjunction with superheterodyne detection appears to provide a high sensitivity spectrometer for the observation of magnetic resonance.
Shape Distribution of Magnetic Powders
Authors: Johnson Clark E. , Brown William Fuller
Published: April 2005

In work reported earlier, the average length-to-diameter ratios determined magnetically did not agree with those observed under the electron microscope; this was thought due to magnetic interactions. This paper describes further shape determination measurements on γ-Fe2O3 samples of increasing dilution by the original method and by two analogous methods described by Wohlfarth. The results show a slight increase of mean length-to-diameter ratio with dilution and a considerable broadening of the distribution toward large length-to-diameter ratios. The different methods of measurement described do not yield the expected congruent curves at very low concentration. This indicates a deviation from Stoner-Wohlfarth rotation in these particles. The details of the mathematical methods are also described.
Noise in Oxide Cathode Coatings
Authors: Hannam H. J. , Van Der Ziel A.
Published: April 2005

Noise measurements have been performed on oxide-coated cathodes at frequencies of 8 Mc and of 30 cycles. At 8 Mc, where thermal noise and shot noise predominate, the measurements show thermal noise at high cathode temperatures (pore conduction region) and at low cathode temperatures (grain conduction region) with a pronounced noise peak caused by shot noise in the temperature range where pore conduction switches over to grain conduction.

Noise measurements at 30 cycles where flicker noise (with a 1/f noise spectrum) predominates, indicate that the pore noise corresponds to the flicker noise expected for a semiconductor with a voltage-independent conductivity, whereas the grain noise corresponds to the flicker noise expected for a semiconductor with voltage-dependent conductivity. The measurements also show that the pores are inherently noisier than the grains at low frequencies. The results agree with a qualitative theoretical analysis.
Radiation Enhanced Diffusion in Solids
Authors: Dienes G. J. , Damask A. C.
Published: April 2005

A simple theory of radiation enhanced diffusion has been worked out which describes the dependence of this enhancement on flux and temperature under steady-state conditions. The theoretical study also shows that the measurement of enhanced diffusion as a function of temperature can indicate the mechanism by which defects are removed from the lattice. Alpha-brass was chosen for the experimental work because it is a kinetically simple system, not complicated by nucleation, in which diffusion is easily followed by measuring the electrical resistivity changes associated with changes in short-range order. The enhanced diffusion rate during irradiation in the Brookhaven reactor has been measured in this alloy at several temperatures in the range 0 to 190°C. This enhancement is independent of temperature from 0 to 150°C, in excellent agreement with the theoretical predictions for the case where the radiation induced defects finally disappear at internal surfaces. Some implications of radiation enhanced diffusion and suggestions for further study are also discussed.
Photoconductive Response of Single Crystal Germanium Layers Prepared by the Pyrolytic Decomposition of GeI2
Authors: Cronemeyer Donald C.
Published: April 2005

Layers of single crystal germanium have been prepared by pyrolytic decomposition of GeI2 at about 350°C upon single crystal seeds of germanium by J. C. Marinace. The substrate germanium could be removed and the resultant thin layers (∼5×10−3 cm) studied. The Hall coefficient and resistivity measured on these layers by Dunlap et al. showed that the layers as grown were usually n type and contained about 1016 donors/cm3. These donors are situated at 0.22±0.04 ev below the conduction band.

In the work reported here, the photoresponse of such layers at 77°K was found to extend to about 6 μ in substantial agreement with this thermal activation energy. The 0.2-ev donors apparently can be annealed out by prolonged heating at 550°C. The layers could also be intentionally doped with standard acceptors such as Al during formation. It was hoped that it would be possible to obtain the incorporation of Au into the layers. For this purpose, layers for which Au doping was attempted were annealed to remove the 0.2-ev donors. Although some of the layers became p type, a comparison of the photoresponse at 77°K with the photoresponse obtained for a 5×10−3 cm thick p-type plate of regularly Au-doped germanium showed no evidence for the 0.15 ev Au level. Likewise, annealed layers for which Ag doping was attempted were examined but yielded no positive identification of the 0.14-ev level of Ag.
Effect of Statically Applied Stresses on the Velocity of Propagation of Ultrasonic Waves
Authors: Bergman R. H. , Shahbender R. A.
Published: April 2005

The paper gives the results of an experimental investigation of the changes in the velocities of ultrasonic waves propagating transverse to the direction of applied stress in an aluminum column. The ultrasonic modes considered are longitudinal waves, shear waves with particle motion along the direction of applied stress, and shear waves with particle motion transverse to the direction of applied stress. The experimental results indicate that the relevant elastic constant for longitudinal waves is independent of stress, while that for the shear waves is stress dependent and also depends on the relative orientation of the particle motion and the direction of applied stress.
Nucleation of Dislocations Accompanying Electric Breakdown in LiF Crystals
Authors: Gilman J. J. , Stauff D. W.
Published: April 2005

``Dislocation Lichtenberg figures'' have been discovered on the surfaces of LiF crystals subjected to high inhomogeneous electric fields. The figures consist of thousands of dislocation loops arranged along [100] dendritic branches which are terminated by [110] branches. Etching is necessary to reveal the figures.

It is shown that electric fields can nucleate dislocations in LiF crystals.
Experimental Evaluation of the Oxygen Microwave Absorption as a Possible Atomic Frequency Standard
Authors: Richardson John M.
Published: April 2005

A microwave absorption line of O2 near 60 000 Mc has been experimentally investigated as a possible atomic frequency standard of high precision. Theoretical design, actual design, and results for an oxygen microwave spectrometer for use either in observing the line frequency or as a discriminator in a frequency control loop synchronizing an oscillator are described. Essential characteristics are the rate of change of spectrometer output signal with frequency and the output noise level. General expressions for these quantities for a wide range of experimental arrangements are obtained, and may be used to predict the attainable frequency precision. Characteristics in complete agreement with the theoretical values, capable of precision to less than 1 part in 109, were experimentally observed with relatively crude apparatus. These characteristics involved line widths of around 560 kc and signal/noise ratios of 83 db. Improvement by a few orders of magnitude can be confidently expected by engineering refinements. An additional result was close confirmation of the theoretical absolute intensity of the N+=7 line and a precision measurement of its frequency as (60 434.70±0.05) Mc.
Rapid X-Ray Determination of a Complete Pole Figure
Authors: Newkirk J. B. , Bruce L.
Published: April 2005

The Decker, Asp, and Harker technique and the Schultz technique for obtaining pole figure x-ray data in the transmission and back-reflection regions, respectively, are shown to give sufficient data for a complete pole figure, with consistent intensity contours in a 15° annulus of overlap. An improved integrating specimen holder, based on the design of Geisler, was found to perform satisfactorily for transmission and back-reflection operation.

A powder method for making all-metal sheet specimens with randomly oriented crystals is described. The use of this type of random sample for establishing background and 1X intensity levels for a corresponding textured specimen is shown to give results which are only semiquantitative when normal filtered radiation is used.
Maximum Performance of High-Resistivity Photoconductors
Authors: Redington R. W.
Published: April 2005

It is shown that the transit time in a photoconductor cannot be less than the charge relaxation or storage time if the photoconductor has contacts of the ``space charge,'' or ohmic, type. The principal consequence of the observation is that the photoconductor cannot simultaneously act as a detector, an amplifier, and a storage element and still have a response time as short as the storage time. This puts a restriction on the performance of high-resistivity photoconductive devices. For example, with present television standards and acceptable response times, the maximum quantum efficiency possible for a photoconductive camera tube of the vidicon type with space charge limited dark current is less than unity. [Note added in proof.—These same general conclusions have also been reached by A. Rose, Helv. Phys. Acta 30, 242–244 (1957)].
X-Ray Study of Cold Work in Molybdenum
Authors: Despujols J. , Warren B. E.
Published: April 2005

Filings from a molybdenum rod, pressed into a briquet, were used as the cold worked sample. Satisfactory peak shapes for 110, 200, 211, 220, and 310 were obtained with filtered CuKα. Peak shapes for 400 and 422 obtained with filtered MoKα were not satisfactory, partly because of fluorescence radiation. Peaks were recorded with a Norelco diffractometer, and instrumental broadening corrected by the Stokes method. The Fourier coefficients indicate approximately isotropic incoherent domains L=260 A, and strains inversely as Young's modulus. Molybdenum is similar to tungsten in that there is no evidence for faulting on (211) as a result of cold work.
An Improved X-Ray Method for Determining Cation Distribution in Ferrites
Authors: Skolnick L. P. , Kondo S. , Lavine L. R.
Published: April 2005

Cation distribution in many ferrites has been difficult to determine by x-ray diffraction since the scattering factors of such cations as Ni, Co, Mn, and Cu are close to that of Fe. By using radiation of a wavelength close to the absorption edge of one of the cations, as suggested by Bertaut, sufficient difference in x-ray scattering factors can be developed because of anomalous dispersion, thus allowing the cation distribution to be ascertained. This method was employed in the case of nickel ferrite.

As a modification of Bertaut's technique, ratios of intensities of the diffracted peaks for FeKα and FeKβ radiation from nickel ferrite were used to eliminate certain factors in the intensity equation which are difficult to calculate, for example, the absorption and temperature factors.

A least-squares technique was used to determine the best values of the cation distribution and the oxygen position for the intensity ratios obtained for seven reflections. It was found that the cation distribution coefficient was 0.48±0.02, in agreement with the results obtained by magnetic-moment measurements and neutron diffraction. The oxygen positional parameter was found to be 0.240±0.002 of the lattice parameter with an octahedral position at the origin, which is in good agreement with the value obtained using neutron diffraction.

The method appears to be of general value in distinguishing between two elements distributed over nonequivalent positions in a crystal lattice when their x-ray scattering factors are almost equal.
Spontaneous Magnetization of Some Garnet Ferrites and the Aluminum Substituted Garnet Ferrites
Authors: Pauthenet R.
Published: April 2005

Magnetic properties of 5Fe2O3·3M2O3 where M represents Gd-Tb-Dy-Ho-Er-Tm-Yb-Lu-Y-Sm-Eu are reported. The results are interpreted using Néel's molecular field model. A study of the Al substituted gadolinium garnets shows a preference for Al ions to occupy d sites.
Paramagnetic Faraday Effect
Authors: Soutif-Guicherd Jeanne
Published: April 2005

A theory is given for the Faraday rotation in paramagnetic salts and curves for the rotation angle as a function of applied field are calculated. For comparison with theory, results are given of measurements made on several manganese salts at a wavelength of 9.9 cm and the agreement is good.
Static and Dynamic Behavior of Thin Permalloy Films
Authors: Smith D. O.
Published: April 2005

Thin magnetic films (∼1000 A) evaporated onto a heated glass substrate in the presence of a dc magnetic field develop a uniaxial magnetic anisotropy energy of the form Ek=Ksin2φ, with φ measured from the deposition field. Such films promise to outperform ferrite cores in digital-computer memory-systems by several orders of magnitude. A detailed static and dynamic theory based on the above anisotropy energy and the Landau-Lifshitz dynamical equation is presented. The static theory contains the unique feature of the coercive force parallel to the easy axis being dependent on a field in the plane of the film and perpendicular to the easy axis. Experimental verification of the theory is given.

The dynamic theory considers both steady-state and pulse response. The steady-state solution is well known; the pulse solution must take very careful account of all the important torques acting in a switching experiment, and numerical results are obtained by the use of a digital computer. Experimentally, steady-state resonance is measured from 100 to 10 000 Mc and pulse switching down to 3 mμsec. Both types of experiment are in good agreement with each other and with the theory.
Flux Reversal in Thin Films of 82% Ni, 18% Fe
Authors: Olson C. D. , Pohm A. V.
Published: April 2005

The magnetization reversal process of iron-nickel films (nominally 82% Ni-18% Fe) deposited in the presence of a magnetic field to a thickness of about 1000 A to 4000 A have been examined by the application of appropriate fields. Experimental results indicate that at least two different magnetization reversal mechanisms are effective. The first, characterized by relatively long remagnetization periods, involves domain-wall movement; the second, characterized by relatively short remagnetization periods, is consistent with the rotation of the magnetization in the plane of the film. The threshold for the rotational process is altered by the application of transverse magnetic field in a manner consistent with a simple energy model.
Domain-Wall Structure in Permalloy Films
Authors: Huber E. E. , Smith D. O. , Goodenough J. B.
Published: April 2005

Domain-wall structure in Permalloy films in the thickness range 25 to 2000 A has been studied by the Bitter technique. A new type of 180° wall has been observed: the main wall is cut at regular intervals by short, right-angle ``cross ties'' which terminate in free, single ends. The cross-tie period and length are dependent on film thickness, each becoming shorter with decreasing thickness. These patterns can be understood in terms of a new model for the structure of domain walls in thin films of low-anisotropy material. In the conventional model the atomic moments within the wall rotate about an axis perpendicular to the wall. In a thin film such a configuration leads to a large energy contribution from the large demagnetization factor normal to the film. In the new model, the axis of rotation is itself thought to rotate about the axis of the wall to give a ``corkscrew'' configuration of spins and a large decrease in associated magnetostatic energy. Of several experiments which have been performed which support this model, one is briefly described.
Effects of Magnetic Fields upon Anisotropic Iron Crystals
Authors: Watson John H. L. , Arrott Anthony , Freeman Michael W.
Published: April 2005

Problems inherent to magnetic alignment of alpha iron crystals are discussed and explained by electron microscopic observation of the behavior of the single domain crystals under the effect of magnetic fields. With these specimens, which possess a fraction of magnetically unfavorable dendrites, intrinsic coercive forces of over 1700 oersteds have been measured without alignment.

``By no endeavour can a magnet ever attract a silver churn''

(W. S. Gilbert: Patience, Act II).
Study of Precipitate Particles in Cu–Co Employing Ferromagnetic Resonance
Authors: Rodbell D. S.
Published: April 2005

The dependence of the ferromagnetic resonance upon specimen anisotropies (shape and magnetocrystalline) is well known. Observations of the ferromagnetic resonance absorption of submicroscopic particles may be interpreted to yield useful information about these anisotropies. The alloy 2% Co–Cu heat treated to precipitate cobalt containing about ten percent copper from the nonmagnetic solid solution has been studied using ferromagnetic resonance techniques. In the early stages of growth the precipitate particles are shown to be essentially spherical in shape. Further growth of the precipitate particles (by subsequent heat treatment) is accompanied by aspherical shape changes which modify the resonance spectra. The magnetocrystalline anisotropy of the cobalt precipitate in single crystals of this alloy has been determined. This anisotropy is cubic with K1/Ms=−665 oe at room temperature. The cobalt-rich precipitate retains its cubic crystal structure to at least 4.2°K, apparently stabilized by the copper matrix.