bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric Properties of Alkaline Earth Fluoride Single Crystals
Authors: Rao K. V. , Smakula A.
Published: April 2005

Dielectric constant κ′ and dielectric loss κ″ of CaF2, SrF2, and BaF2 single crystals were determined as a function of frequency from 102 to 106 (partly to 1010) cps, in the temperature range from –193° to 500°C. κ′ in all three crystals is frequency independent at 25°C. The dielectric loss κ″ varies only slightly with frequency, having the greatest values at lowest and highest frequencies. The temperature has a striking effect on κ′ and κ″. κ′ increases continuously from 6.4, 6.1, and 6.9 (extrapolated values at absolute zero) to 8.07, 7.70, and 8.46 at 500°C at frequencies above 106 cps for CaF2, SrF2, and BaF2, respectively. Below about 25°C, κ′ is frequency-independent; at higher temperatures it increases with decreasing frequency, κ″ increases with temperature exponentially and decreases with frequency. A detailed interpretation of the frequency and temperature influence on κ′ and κ″ is given. Using expansion and density variation with temperature, a separation of electronic from atomic and dipolar contributions was made. The total dielectric constant is subdivided into six terms (three electronic and three atomic).
Behavior of Superconducting Coil Subjected to Steady Local Heating within the Windings
Authors: Stekly Z. J. J.
Published: April 2005

The steady-state heat conduction equation in a nonisotropic solid is solved for the relationship between local heat imput, the size of the heated region and the Joule heating in the resultant normal region. The results are used to derive the steady terminal voltage-current characteristics of a superconducting coil with heat generation within the windings. These terminal characteristics exhibit both a positive as well as a negative slope of the voltage versus current curve. A map of the expected behavior of a current carrying superconducting coil with heat generation in the windings shows that the coil can do one of three things: (1) remain fully superconducting; (2) operate in a stable manner with a nonpropagating normal region; (3) go fully normal (quench).

The analytical results are compared with measurements taken with a noninductive and an inductive coil. The measured terminal characteristics as well as over-all coil behavior agreed well with the result derived analytically.
A Plasma Instability Induced by Electron-Hole Generation in Impact Ionization
Authors: Toda Minoru
Published: April 2005

Existence of a new kind of plasma density instability, caused by the dependence of the plasma generation rate on the electric field, is predicted, and lower frequency oscillations believed due to it have been observed experimentally. The observed oscillations, induced by shunting the plasma with an external capacitance, are damped and of frequency 2∼10 Mc/sec in n-InSb at 77°K. The electron-hole generation rate has been calculated from the observations and is found to vary approximately as the eighth power of the electric field, with values from about 106 to 108 sec−1 for electric fields between 2.3 and 4.0×104 V/m. When a small external transverse magnetic field was applied, the generation rate increased, but obeyed the identical relationship as a function of electric field as observed in zero magnetic field. Evaluation of the threshold conditions for instability indicates that the microwave radiation observed from an impact-ionization plasma in InSb can be the result of this density instability.
Injection and Transport of Added Carriers in Silicon at Liquid-Helium Temperatures
Authors: Brown J. M. , Jordan A. G.
Published: April 2005

Single-carrier, space-charge-limited conduction is observed in compensated n-type silicon when used in n+nn+ samples at liquid-helium temperatures. The variation of the traps-filled-limit voltage (VTFL) with sample length follows the familiar square-law relationship until the presence of impact ionization of impurities, which occurs at a constant field, becomes the predominant conduction mechanism. A surface current is observed at voltages below VTFL when the n+nn+ samples are in contact with the liquid and no similar effect is observed on p+pp+ samples of similar dimensions and fabrication. Two-carrier injection in compensated n-type silicon at liquid-helium temperatures is also observed when used in n+np+ diodes. A modification of the Lampert-Ashley theory is proposed to include two distinct deep impurity levels. From these double-injection experiments, information about the neutral capture cross sections for boron and phosphorous as well as about the attractive capture cross sections is obtained. The field dependence of the capture cross sections is also established. A surface current is also observed when the n+np+ samples are in contact with the liquid helium.
Stress-Optical Behavior of Rubber Networks at Large Deformations
Authors: Smith K. J. , Puett D.
Published: April 2005

The birefringence of natural rubber networks at large deformations has been investigated experimentally and compared with the simultaneously determined stress-strain behavior. Our data is analyzed using a statistical theory of flexibly jointed chains, derived herein, which is believed to be more significant for the particular range of deformation used than the theories of Treloar and of Kuhn and Grün. In addition, the experimental data of Saunders is commented on in light of our theoretical development. We find that for network extensions exceeding those of the Gaussian region there is little correlation between the observed and theoretical behavior of the stress and birefringence (based upon the theory of flexibly jointed chains) and this lack of agreement is attributed to the fact that the statistical parameters needed for the description of the optical chain properties differ in magnitude from those required for the mechanical properties. Furthermore, by considering the points of incipient crystallization the strain behavior of the stress-optical coefficient is highly indicative of non-Gaussian behavior rather than crystallization, and therefore yields strong support for the position that non-Guassian behavior does not exist in rubber networks.
Inversion of Pole Figures for Materials Having Orthorhombic Symmetry
Authors: Morris Peter R.
Published: April 2005

A method for obtaining inverse pole figures from pole figures for materials having orthorhombic symmetry is presented. The method entails expansion of the axis distribution function in a series of spherical surface harmonics of appropriate symmetry, even in x1, x2, x3. Truncation of the series at order n=2, 4, 6, …, 2m, where m is a nonnegative integer, gives rise to ½n systems of 2,3,(½n)+1 simultaneous linear equations in a like number of variables, requiring a minimum of (½n)+1 pole figures for solution. A method for evaluating the goodness of fit is suggested. Data obtained by Mueller and Knott for alpha uranium are used to illustrate the method.
Wave Nature of Moving Striations
Authors: Lee D. A. , Bletzinger P. , Garscadden A.
Published: April 2005

The results are presented of time- and space-resolved measurements on self-excited moving striations and on the response of the positive column of a low-pressure glow discharge to externally excited pulses. From these the profile, structure, and the backward-wave nature of moving striations are clearly indicated. A new method of solution to the equation originally presented by Pekarek is shown to contain all of the experimental results, including the dispersion of a pulse disturbance. A stability criterion is derived; especially useful is that the onset of striations in a discharge can be calculated from a simple quadratic equation. The coupling with other oscillations in the plasma is investigated and it is shown that they cause phase modulation and mode jumping. The relationship of these results to other recent reports is considered. In general, the phenomena previously reported can be explained and points of conflict can be reconciled.
Radiation by an Electron Beam Interacting with a Diffraction Grating. Two-Dimensional Theory
Authors: Barnes Casper W. , Dedrick K. G.
Published: April 2005

Expressions are obtained for the power radiated by a modulated electron beam passing near the surface of a (perfectly conducting) diffraction grating. The electromagnetic fields are calculated in terms of the two-dimensional scalar Green's function for the grating surface. The grating profile may be chosen as any function that can be represented by a Fourier series, and the Green's function is developed as a power series in the grating groove depth. By superposition, the radiation by a moving line charge is also considered. The results are compared with those of previous treatments.
Some Remarks on Hysteresis
Authors: Biorci G. , Pescetti D.
Published: April 2005

This paper considers two approaches by which the Preisach distribution function may be obtained from experimental hysteresis curves, and then compares the results of these approaches with Bate's experimental results.

The first method, based upon the assumption that φ(a,b) = φ1(a)·φ2(b), was proposed by the authors in 1958. The second method is valid under other assumptions, and requires simple computations only. The comparison shows good agreement between the two methods, and with experimental data.
Production by Fission Fragments of Large Tracks in Crystals
Authors: Caspar P. E.
Published: April 2005

Thin crystals of two nonmetallic compounds have been irradiated with uranium fission fragments and the resulting damage investigated using the electron microscope. The light-contrast tracks observed were wider by a factor of over two than any previously reported and appeared to be directly produced by the passage of the fission fragments. Considerations of the rate of energy loss strongly suggest that the damage was produced by an ionization mechanism and that even these track widths are not the maximum which may be observed.
Numbers Theory for Lead Sulfide Photoconducting Films
Authors: Mahlman G. W.
Published: April 2005

This communication comments on some of the work of Fleming and Alberg, and presents some data tending to substantiate a ``numbers'' theory for photoconduction in certain types of chemically prepared photoconducting films of lead sulfide. The data were obtained some years ago but were not published, and were taken during an extensive program of measurements of the basic properties of PbS films, some of the results of which were published [G. W. Mahlman, Phys. Rev. 103, 1619 (1956); J. C. Slater, ibid. 103, 1631 (1956)].
Direct Measurement of the Nernst-Ettingshausen Dimensionless Figure of Merit
Authors: Guthrie G. L. , Palmer R. L.
Published: April 2005

A method is given for obtaining the Nernst-Ettingshausen dimensionless figure of merit, in a direct measurement, as the ratio of two voltages. A discussion of the method is given for experiments involving rectangular sample geometries and also for more general geometrical configurations. Both isotropic and anisotropic materials are considered. The method is based on measurements of the ratio of the adiabatic electrical resistance to the isothermal electrical resistance. The superposition of the voltage of the Peltier-Seebeck effect is avoided by arranging for the completion of the experiments in a length of time which is short compared to the Peltier-Seebeck time constant for the sample. The required equipment and circuitry are simple, being similar to a four-probe resistivity measurement circuit with the voltage being determined by use of an oscilloscope.
Stress Field Near a Dislocation Slip Plane in an Orthotropic Medium
Authors: Ahmed Nazeer
Published: April 2005

The elastic stress field in the vicinity of a dislocation slip plane in an infinite orthotropic medium subjected to uniform shear at infinity is determined using a formulation in integral equations. It is assumed that a slip plane is different from a traction-free surface crack in that it has uniform shear on its surface and remains closed under the applied stress field. However, the use of these mixed boundary conditions under the restrictions of plane stress in linear elasticity is found to give the same stress distribution as that for a shear crack. Although a shear crack under an applied uniform shear opens up into an ellipse, the opening per unit length is shown to be so small that for most engineering applications it can be considered closed and the equivalence of a shear crack and a slip plane is established. It is pointed out that this correspondence is not valid between a shear crack in a thick elastic plate and a slip plane in an infinite elastic medium. Results for an isotropic body are given as a limiting case of an orthotropic body.
Effect of Structure on the Superconducting Properties of Eutectic Alloys
Authors: Levy S. A. , Kim Y. B. , Kraft R. W.
Published: April 2005

The superconducting properties of twelve eutectic alloys have been studied. The seven alloys which were eutectics between terminal solid solutions were found to behave as type I superconductors irrespective of the solidification rate. Five other eutectic systems, all of which contained at least one intermetallic compound, were found to behave as type II superconductors. For the type II alloys a linear variation between the current-carrying capacity and the interphase boundary area per unit volume was observed. Of the type II alloys, eutectics containing one superconducting and one nonsuperconducting phase were found to be more structure sensitive than those having both phases superconducting.
Epitaxial Deposition of Germanium by Both Sputtering and Evaporation
Authors: Krikorian E. , Sneed R. J.
Published: April 2005

The structural characteristics of germanium films deposited onto germanium (111) and CaF2 (111) substrates have been characterized as a function of sputtering and evaporation parameters. Diagrams defining epitaxial temperatures and amorphous-polycrystalline transition temperatures have been obtained both for sputtered and evaporated films. It is demonstrated that these transitions are a function of the growth rate and background pressure only. Neither the particular deposition conditions which control the growth rate (voltage and current in sputtering, source temperature, and source-substrate distance in evaporation) nor the deposition techniques influence the transitions as long as the background pressure and growth rates are identical.

A qualitative model based on the relation between growth rate and surface mobility is presented which appears to adequately describe the growth-rate-epitaxial-temperature relations, including background pressure effects. The experimental data yield an activation energy for the onset of epitaxy at very low background pressures (evaporation) of 18 000 cal/mole, which is in good agreement with the activation energy for surface diffusion of germanium on germanium. Other activation energies ranging from 10 800 cal/mole at 65 μ argon pressure to 17 400 cal/mole at 8 μ argon pressure, have been obtained for sputtered films. The pressure dependence of the activation energy has been accounted for by the model presented.

It is also demonstrated that the growth rates in all states of the film (amorphous, polycrystalline, and monocrystalline) are decreasing functions of substrate temperature. At any given temperature, the observed growth rates are dependent only on the incidence rate, and are independent of the technique (sputtering or evaporation) and of the conditions used to achieve the incidence rate. The dependence of growth rate on substrate temperature is consistent with established nucleation theory and yields activation energies for single-crystal growth of approximately 10 000 cal/mole, for polycrystalline growth of approximately 3000 cal/mole, and for amorphous growth of approximately 600 cal/mole. These activation energies are independent of the deposition technique (evaporation or sputtering), the deposition conditions, and the incidence rate.
Electron Diffraction Studies of the Epitaxy of Cu Single Crystals. I. Epitaxy of Evaporated Cu Films on Cu Crystals
Authors: Krause G. O.
Published: April 2005

The epitaxy of evaporated Cu films on Cu single crystals has been investigated in situ under high-vacuum conditions with reflection HEED techniques. Spherically shaped Cu single crystals with high quality surfaces were used as substrates. The effects of condensation temperature and the annealing behavior were studied for the main low-index planes. A completely developed twin orientation of the film was found in all cases. For films deposited at room temperature the diffraction diagrams additionally contained a complete set of double diffraction spots.
Electron Diffraction Studies of the Epitaxy of Cu Single Crystals. II. Early Stages of Epitaxy and Interfacial Dislocation Networks
Authors: Krause G. O.
Published: April 2005

The first stages of epitaxy were investigated with reflection HEED methods for continuous Cu, Cu2O, and Ag films on Cu single-crystal substrates. A new kind of diffraction pattern was obtained from the Cu{111} planes. It is produced by networks of interfacial dislocations. In case of the Cu layers, hexagonal arrangements of screw dislocations are formed in a pure twist boundary. The corresponding Burgers vectors are of the type ½〈110〉. For the Cu2O and Ag films, hexagonal and rhombohedric networks, respectively, of interfacial edge dislocations with Burgers vectors ⅙〈112〉 are probably present. The dislocation densities and modifications in the film lattice constants for the latter two epitaxial systems are in good agreement with values predicted by the theory of interfacial dislocations.
Simplified Theory of Reflectometric Thickness Measurement of Structured Soap and Related Films
Authors: Frankel Stanley P. , Mysels Karol J.
Published: April 2005

The intensity of reflected light is now used in the exploration of the structure of soap films, and of the forces responsible for it. An accurate interpretation must take into account the complicated sandwich structure of these films whose surfaces are formed by monomolecular layers upon an aqueous core. A direct simple approach assuming only that the surface layers are very thin compared to the wavelength of light shows that each layer of thickness d and refractive index n is optically equivalent to an increase of the thickness of the core having a refractive index m by a thickness d′=d(n2−1)/(m2−1), in agreement both with a physical picture of the phenomenon and with results obtained by more complicated calculations. This approach also permits immediate generalization to a structure formed by any number of very thin layers and also to closely related films of lipids in water which are used as model biological membranes.
Interfacial Polarization in Single-Crystal NaCl
Authors: Wimmer J. M. , Tallan N. M.
Published: April 2005

Capacitance and conductance dispersions and a dissipation factor maximum were observed in single-crystal NaCl specimens at temperatures between 300° and 400°C. Probe measurements of the potential profile across these specimens in a dc field revealed the presence of a large potential drop in a very thin region adjacent to each electrode comparable in magnitude to the linear potential drop throughout the entire bulk of the crystal. The observed effects are shown to be consistent with an interpretation based on interfacial polarization arising from the presence of a surface layer having a higher resistivity than the bulk of the crystal. Interpretations based on dipole rotation or charge-carrier blocking at the electrodes are shown to be in disagreement with the observed polarization data.
Injection Electroluminescence in (AlxGa1−x)As Diodes of Graded Energy Gap
Authors: Ku S. M. , Black J. F.
Published: April 2005

p-n junction diodes were made from AlAs-GaAs mixed crystals of graded composition (energy gap). The energy gap vs composition was determined from measurements of the diode band-edge emission peaks vs electron microprobe analysis of p-n junction composition. A linear energy-gap variation was observed throughout the composition range 0–0.45 mole fraction AlAs. Measurements of the injection-current dependence and the temperature dependence of the emission spectra of these diodes, interpreted according to a simple model of injection electroluminescence, indicate that the AlAs-GaAs mixed crystals are of direct band nature to at least 0.25 mole fraction of AlAs. Diodes of 0.40–0.45 mole fraction AlAs junction composition, i.e., in the vicinity of the ``direct-indirect'' crossover, produced emission which requires more complex analysis.
Thickness of Cs-Sb Films Relative to the Original Sb Films
Authors: Hagino Minoru , Takahashi Tadashi
Published: April 2005

A simple method of measuring the thickness of Cs-Sb films in various compositions is described. The relation between composition ratio Cs/Sb and the increased thickness of the Cs-Sb film relative to the original thickness of the Sb film is obtained. This relative thickness measured in Cs3Sb films is about seven, which agrees with the result predicted by the crystal structure of Cs3Sb.
High-Temperature Internal Friction in Potassium Chloride
Authors: Robinson William Henry , Birnbaum H. K.
Published: April 2005

A theory for the strain-amplitude-independent damping due to electrically charged dislocations oscillating within their surrounding charge clouds and for the strain-amplitude-dependent damping caused by the dislocations ``breaking away'' from their charge clouds is discussed. Damping experiments on single crystals of KCl [〈100〉, 〈111〉, and 〈110〉 orientations] at temperatures of 450° to 760°C, frequencies ranging from 40 to 200 kc/sec, and strain amplitudes from 2.1×10−8 to 1.7×10−4 are reported. The damping φ in the amplitude-independent region could be represented by [open phi]=[open phi]0 exp−(Eeff/kT),where Eeff is frequency-dependent and orientation-independent. At 750°C the amplitude-independent damping rose extremely rapidly with temperature; this rise is attributed to approaching the intrinsic isoelectric temperature. Amplitude dependence was found above a strain amplitude of 3×10−6 and the damping at high strain amplitudes was observed to decrease with time. The strain amplitude at which amplitude dependence was first detected did not vary noticeably with temperature or frequency. The experimental results are shown to be in general agreement with the proposed theory.
Thermodynamic Aspects of the Temperature—Pressure Phase Diagram of InTe
Authors: Banus M. D. , Robinson P. M.
Published: April 2005

The heat of transformation at one atmosphere from the metastable high-pressure phase of InTe to the low-pressure phase has been measured by metal solution calorimetry to be 0.44±0.01 kcal/g·atom and by differential scanning calorimetry to be 0.42±0.03 kcal/g·atom. These values are compared to the heat of transformation at 30 kbar obtained by applying the Clausius—Clapeyron equation to the temperature—pressure phase diagram of InTe.

The volume change on fusion of the low-pressure phase, InTe(I), at one atmosphere was measured to be 0.80 cc/mole. The initial slope of the liquidus in the phase diagram calculated using this value is in close agreement with the previously determined experimental slope. It is estimated that the triple point between the liquidus and the InTe(I)—InTe(II) phase boundary occurs at 718°C and 11 kbar.
Exact Solution for the Eigenfrequencies of a Microwave Cavity Partially Filled with a Magnetized Plasma
Authors: Shohet J. L.
Published: April 2005

Pure TE and TM waves do not, in general, exist in a microwave cavity partially filled with a magnetized plasma. The scalar wave equations are coupled (the equation for Ez has a term involving Hz and vice versa). Uncoupling of the two equations results in two fourth-order wave equations which are biquadratic. The solution of this equation can be obtained by factoring the fourth-order expression into the product of two second-order wave equations. The result is two solutions for Ez and Hz. From these terms, all other field components may be found. A set of six boundary conditions on the field components gives a determinantal expression for the eigenvalues. These can be presented in mode chart form and show the splitting of degenerate modes along with resonances at the electron-cyclotron frequency. The technique is applicable to any form of the dielectric tensor if it can be specified in complex notation.
Anomalous Thermal Conductivity of Cd3As2 and the Cd3As2−Zn3As2 Alloys
Authors: Spitzer Donald P. , Castellion George A. , Haacke Gottfried
Published: April 2005

The room-temperature lattice thermal conductivity of Zn3As2 is 0.012 W/cm·°C; that of Cd3As2 is 0.014 W/cm·°C or less. Anomalously low thermal conductivities (as much as 30% below calculated values) are found for samples of Cd3As2 and Cd-rich alloys of Cd3As2 with Zn3As2 where the electrical conductivity is high (>103 Ω−1 cm−1). Thermal conductivities for Cd3As2 samples fall into two groups: Samples doped with an element which is expected to enter the anion sublattice have normal thermal conductivities, while undoped samples or those doped with an element which should enter the cation sublattice tend to have anomalously low thermal conductivities. High electron mobilities and general lack of correlation of carrier concentration with thermal conductivity indicate that the anomaly is not in the electronic component of thermal conductivity. Instead, doping experiments, as well as the temperature dependencies of thermal conductivities indicate that the anomaly is entirely in the lattice component and is due to a lattice defect in the anion sublattice, probably an As vacancy. Although the lattice thermal conductivity of some samples of Cd3As2 appears to be only 0.003–0.004 W/cm·°C, their electron mobility is 104 cm2/V·sec. To explain the apparently enormous phonon scattering cross-section of the lattice defect, it is suggested that the phonon scattering may involve the transitions of localized electrons from one type of As site (vacancy) to another (there are three different types of As sites in Cd3As2).
Effect of Crystallite Size on Coercive Force of Thin Ferromagnetic Films
Authors: Heinzel C. O. , Walker G. A.
Published: April 2005

This paper describes the effect crystallite size has on the coercive force Hc of thin ferromagnetic films. Crystallite size was determined by the use of x-ray diffraction using a small angle between the x-ray beam and film samples. Films in this study ranged in thickness from 150 to 1750 Å with crystallite size from 50 to 950 Å and Hc values of 2.1 to 8.4 Oe.

It was found that Hc is dependent on the crystallite size for films that have domain wall widths larger than the crystallite size. The data exhibits a decreasing Hc as the crystallite size increases for films with Néel or crosstie domain walls. For films with Bloch walls and crystallite size greater than the domain wall width, there is no apparent dependence on crystallite size of Hc.

To a first approximation, the results of this study are shown to agree with the anisotropy constant variation term from Middelhoek's semiquantitative theory for coercive force of thin magnetic films. For films with domain wall widths larger than the crystallite size, this term contributes to the over-all coercive force.
Magnetic Flux Compression by Magnetically Imploded Metallic Foils
Authors: Cnare Eugene C.
Published: April 2005

A 136-kJ capacitor-bank energy source was used to implode metallic foils in a ``theta'' pinch. Aluminum foils accelerated by this scheme attained a velocity of 2.3 mm/μsec and a capacitive-to-kinetic energy conversion efficiency of 23%. An upper limit for the foil velocity depended upon the foil thickness and density, together with a parameter which accounted for electrical heating of the foil. This parameter was determined in exploding wire studies.

Experiments with and without auxiliary injection of magnetic flux are described. Thick, imploding foils have been found to be capable of compressing enclosed magnetic flux to more than 2 MG.
Domain Structure of Hexagonal Ferrimagnetic Oxides with High Anisotropy Field
Authors: Rosenberg M. , Tănăsoiu C. , Florescu V.
Published: April 2005

The changes in domain structure as a function of the thickness L of the single crystals of the SrO·(6−x)Fe2O3·xAl2O3 compositional series were investigated. On the strontium ferrite single crystals, the same four models of Bitter patterns as in the case of magnetoplumbite and barium ferrite were observed. For the other compositions the limits of appearance of these four models shift towards higher values of the thickness as x increases as a result of the increased anisotropy field/saturation magnetization ratio. The thickness dependence of the domain width D changes from a D∼L⅔ dependence to a D∼L½ one for x≥1.8. In the case of crystals with x=2, the Bloch walls are parallel to the hexagonal axis everywhere. The finite dimensions of the samples may considerably influence the domain structure, which makes it possible for structures with two or even one domain only to be obtained, regarding relatively large samples.
Lithium Niobate: A High-Temperature Piezoelectric Transducer Material
Authors: Fraser D. B. , Warner A. W.
Published: April 2005

The high piezoelectric coupling and high Curie point of LiNbO3 make it an excellent transducer material for acoustic measurements at high temperatures. A single-crystal plate of LiNbO3 has been used as a shear mode transducer in measuring the acoustic properties of an Al2O3 ceramic sphere up to 1050°C.
Plasticity of Oriented Glassy Polymers
Authors: Robertson Richard E. , Joynson Catherine W.
Published: April 2005

The stress-strain properties of uniaxially oriented, glassy polycarbonate and polyphenylene oxide were measured in shear vs the angle between the shear plane and the orientation axis. The results are interpreted in terms of a model that emphasizes the microscopic graininess of glassy polymers. It is concluded that at least four of the five independent slip systems required for a general deformation of each grain involve kinking and the flexing of bonds. This confirms the importance of bond flexing in the plasticity of glassy polymers, as was assumed in a recently proposed theory.
Further Studies of Intercrystalline Links in Polyethylene
Authors: Keith H. D. , Padden F. J. , Vadimsky R. G.
Published: April 2005

A previous study of intercrystalline links in polyethylene, carried out using fractionated polymer only, has now been extended to mixtures of fractions and to whole polymer. There is little difference between links grown from concentrated (50%) solutions of polyethylene in n-C32H66, regardless of the molecular weight distribution of the polymer. These links exhibit surfaces that are more or less featureless and the evidence indicates that they are composed of molecules crystallized, for the most part, with extended conformations. However, when these links are used as substrates upon which polyethylene is deposited epitaxially from dilute (1% or less) solution in later, quite separate, crystallization experiments, lamellar overgrowths are formed which demonstrate unambiguously the crystallization of molecules in folded conformations.

The marked difference between these cases is attributed to entanglements which, as crystallizing molecules are ``reeled in'' to growth fronts, cause neighboring molecules to become extended and partly aligned in directions normal to these fronts. Links grown from concentrated solutions are built up from such molecules whose conformations are grossly disturbed by this crystallization-induced orientation. However, epitaxial overgrowths deposited from dilute solution are built up from molecules whose conformations in solution are unaffected, and these then crystallize conventionally with folded conformations.
Screw Dislocations in Anisotropic Media
Authors: Peterson J. M. , Lindenmeyer P. H.
Published: April 2005

Material displacements for screw dislocations in anisotropic media with orthorhombic symmetry have been derived for those cases where the Burgers vectors lie along the crystallographic axes. From these displacements electron diffraction contrast patterns are calculated and compared to those observed in polyethylene. It is shown that under certain assumptions it is possible to determine relationships between the elastic constants of the material using this technique; e.g., it can be concluded that interlamellar slip along the a axis is approximately 50 times easier than intralamellar shear, whereas interlamellar slip is only 10 times easier when the shear direction is along the b axis.
Dislocations Caused by Chain Ends in Crystalline Polymers
Authors: Predecki Paul , Statton W. O.
Published: April 2005

The molecular arrangement in the immediate vicinity of a chain end in a crystalline polymer such as 66 nylon is considered. It is shown that four simple kinds of line defect can be generated by such a chain end. One of these, called a coupled-screw dislocation, is unique to long chain structures and has not been proposed before. The remaining three are (1) vacant chain site or coupled-edge dislocation, (2) and (3) the more conventional screw and edge dislocations. These dislocations run from one chain end to another and create a three-dimensional defect network, possibly explaining the anomaly of weak x-ray diffraction intensity from (010) planes. If the ends are randomly distributed, the network may disorder the structure sufficiently to make it appear ``amorphous'' to x rays.

When sufficient segmental mobility exists, it is probable that this network will rearrange itself into a more ordered substructure of lower energy. Such a substructure might include: (a) clusters of chain ends and associated defects, (b) chain ends which are condensed into line defects, (c) boundaries between adjacent misaligned crystalline regions.
Anomalous Shock-Induced Demagnetization of Nickel Ferrite
Authors: Royce E. B.
Published: April 2005

Measurements of the demagnetization of nickel ferrite under explosively generated shock conditions have been made. Samples were biased close to saturation by a permanent magnet. The shock-induced reduction in magnetic flux through the sample was detected by pickup coils wound on the ferrite cores which completed the magnetic circuit between the sample and biasing magnet. The experiments show an apparent complete destruction of the spontaneous magnetization of the material at all shock pressures between 43 and 430 kbar. The susceptibility of the shocked material, however, is found to be an order of magnitude larger than the calculated paramagnetic susceptibility. The effect of shock pressure on the Néel temperature combined with the effect of shock heating would lead to total demagnetization only at shock pressures well above 400 kbar. The most plausible mechanism for the observed anomalous demagnetization is shown to be a shock-induced magnetic anisotropy, arising from the anisotropic microscopic strain associated with the shock. Equation-of-state data needed for the interpretation of the magnetic work are also presented.
Magnetostatic Mode Echo by Subsidiary Absorption
Authors: Comstock R. L. , Raymond J. J.
Published: April 2005

Experiments are described on microwave echoes observed in axially magnetized yttrium iron garnet cylinders following the application of two pulses in which the second is twice the frequency of the first. The echoes result from the radiation from the manifold of magnetostatic modes excited to resonance by the first pulse and selectively amplified by the second pulse. The parametric amplification results from the Suhl subsidiary absorption. The echo experiment differs from the previous magnetostatic mode echo experiments of Kaplan because of the difference in frequency of the second pulse, and it differs from that of Damon and van de Vaart because the excitations are nonpropagating magnetostatic modes. An analysis of the three-pulse magnetostatic mode echo experiment is presented in order to demonstrate the necessity for the above interpretation of the present experiment.
Laser Interferometer for Repetitively Pulsed Plasmas
Authors: Hooper E. B. , Bekefi G.
Published: April 2005

A three-mirror laser interferometer for measuring electron densities in repetitively pulsed plasmas is described and analyzed. The instrument has a sensitivity equivalent to a density of 1013/d cm−3, where d is the length of the plasma in centimeters. It has a time resolution of a few microseconds. The response of the laser intensity to a changing dielectric (e.g., plasma) is calculated in the quasistatic approximation, and the factors contributing to the finite time response are considered. The analysis applies to laser interferometers in general, as well as to the present instrument.
Generation of Vacancies in MgO by Deformation
Authors: Klein Mark J. , Gager W. B.
Published: April 2005

Electron spin resonance and x-ray line broadening were used to measure the deformation-induced vacancies and dislocation densities, respectively, in MgO. The vacancy concentration was found to increase with increasing deformation rate and dislocation density. The generation of vacancies is explained by the nonconservative motion of dislocation jogs created by dislocation intersections in regions where the dislocation density is high.
Transient Determinations of Thermal Diffusivities and Dissipations of Metal Foils
Authors: Jacovelli Paul B. , Zinke Otto H.
Published: April 2005

A technique for measuring the diffusivities and surface dissipations of transient heat in metal foils through the use of the total temperature—time curve is tested using foils of Al, Ag, Cu, Pb, Ni, and Fe, which are found to have diffusivities at room temperatures in general agreement with those expected. The surface dissipations from untreated surfaces of all these foils are calculated.
Variational Method of Determining Effective Moduli of Polycrystals with Tetragonal Symmetry
Authors: Meister Robert , Peselnick Louis
Published: April 2005

Variational principles have been applied to aggregates of randomly oriented pure-phase polycrystals having tetragonal symmetry. The bounds of the effective elastic moduli obtained in this way show a substantial improvement over the bounds obtained by means of the Voigt and Reuss assumptions. The Hill average is found to be a good approximation in most cases when compared to the bounds found from the variational method. The new bounds reduce in their limits to the Voigt and Reuss values.
Electron and Ion Emission from Polycrystalline Surfaces of Nb, Mo, Ta, W, Re, Os, and Ir in Cesium Vapor
Authors: Wilson R. G.
Published: April 2005

Full temperature range electron and ion emission data from seven refractory metals in cesium vapor are reported in the range of cesium arrival flux from 1012 to 1018 atoms/cm2·sec, as determined from measurements between 1013 and 1017 atoms/cm2·sec. Electron-emission S curves and cesium surface ionization critical temperature envelopes are shown.
Structure of Superconductive Vortices near a Metal-Air Interface
Authors: Pearl Judea
Published: April 2005

The current distribution along a vortex line emerging from a bulk superconductor is computed. The current density at the metal-air interface was found to follow a 1/r2 law at far distances from the vortex axis, while deep inside the metal it falls off exponentially. The effect of this structure on the macroscopic behavior of superconductors is discussed.
Two-Stream Flow in Diodes
Authors: Derfler H. , Holmstrom R.
Published: April 2005

The stability of counterstreaming flow of electrons and ions in heavily biased diodes is investigated theoretically. Space-charge wave analysis is used to find the rf impedance function. The impedance function has first-order poles and zeroes. Nyquist analysis is used to see if any of them lie in the lower (unstable) half of the frequency plane. Some systems are stable for most passive terminations but can be made unstable for others. Other systems are absolutely unstable. The differences between instability induced by addition of passive circuit elements and absolute instability are discussed.
Cold-Beam-Plasma Interaction Theory for Finite Transverse Dimensions and Finite Magnetic Fields
Authors: Simpson J. E. , Dunn D. A.
Published: April 2005

The dispersion relation for interaction between a cold electron beam and the electrons of a cold, uniform density plasma of a circular cylindrical cross section and of a radius equal to that of the beam inside a conducting pipe of a larger radius has been solved on a computer for a number of values of finite magnetic field, the ratio of plasma density to beam density, and beam perveance. Complete ω-k diagrams are given for various cases along with more extensive data on the growing wave gain that occurs below the plasma frequency and the cyclotron frequency.

A comparison with experimental data on a beam-generated plasma is given and the theory is shown to provide a satisfactory explanation for the onset of oscillations in such a system with a finite length.
Annealing of Dislocation Pinning Centers in the Temperature Range 120° to 180°K in Alkali Halide Crystals
Authors: Shaw R. W. , Mackay W. F. , Woo D. S. , Welsh W. , Dionne G.
Published: April 2005

The ultrasonic attenuation of several alkali halides has been studied at temperatures between 120° and 180°K and at frequencies of 10 and 30 Mc/sec. The effects of γ irradiation and light in pinning and unpinning dislocations are in agreement with the observations at lower frequencies of Bauer and Gordon. In addition a thermal annealing of the γ-ray-induced pinning has been found in NaCl, KCl, and, to a limited extent, in KI. The effect was not present to a measurable extent in NaBr or KBr. The annealing is analyzed in terms of a concentration of pinning points which appear to anneal with two activation energies in NaCl and in KCl, all in the range from 0.01 to 0.15 eV. Following the model of Bauer and Gordon, we suggest that the anneal is related to the changes occurring in this temperature range in the V bands and that the activation energies may correspond to thermal ionization of holes from V centers.
Mobility and Loss Mechanisms for Domain Wall Motion in Thin Ferromagnetic Films
Authors: Patton Carl E. , Humphrey Floyd B.
Published: April 2005

Domain-wall mobility for Ni–Fe alloy films has been measured as a function of film thickness from 300 to 1650 Å. Between 300 and 800 Å, the mobility decreases with increasing film thickness, ranging from 8×103 cm/sec·Oe at 300 Å to 3×103 cm/sec·Oe at 800 Å. Between 900 and 1000 Å, the mobility increases rapidly with increasing film thickness to about 7×103 cm/sec·Oe. Above 1000 Å, the mobility increases slowly with film thickness. These mobility data have been compared with predictions based on intrinsic and eddy-current loss mechanisms utilizing available static domain wall-shape information. Predictions based on a 180° Bloch or Néel wall model in which the magnetization rotates linearly through the wall are in disagreement with the present data over the entire range of film thickness. For the 300–800 Å thickness range, predictions based on Lorentz microscopy wall-shape measurements are in good agreement with the measured mobility values. The crosstie structure associated with Néel walls in this thickness range does not appear to affect the mobility. Bitter patterns indicate that the sharp increase in mobility between 900 and 1000 Å may be associated with a wall structure transition in this region. For thicker films, mobility predictions based on static Bloch wall-shape calculations are an order of magnitude lower than the observed mobilities. Lorentz microscopy wall-shape measurements for 1200-Å films yield wall widths of about 3000 Å significantly wider than calculated Bloch wall widths. Predictions based on these measured widths are in good agreement with the data. Although the calculation includes both intrinsic and eddy-current losses, intrinsic losses dominate for crosstie or Néel wall motion in the 300–800-Å thickness range and for Bloch wall motion in the 1000–1600 Å thickness range.
Structure of Very Thin Tantalum and Molybdenum Films
Authors: Denbigh P. N. , Marcus R. B.
Published: April 2005

Observations of thin-film growth in a continuously recording electron diffraction instrument show fcc phases in very thin films of tantalum and molybdenum. These films transform slowly to the expected bcc structures as the thickness is increased. The bcc phase is first detected in films 40 and 80 Å thick for molybdenum and tantalum, respectively; no fcc tantalum has been detected in films thicker than 250 Å. fcc tantalum films have been prepared in another high-vacuum station on different substrates at various temperatures. Epitaxial fcc tantalum has been grown on MgO.
Evaporation and Deposition Rates, Sticking Probability, and Background Pressure during the Production of Thin Films in Vacuum
Authors: Schwarz Helmut
Published: April 2005

The evaporation ratemeter as described by the author is used in a special circuit so that the background pressure and the rate of evaporation can be monitored simultaneously and continuously with the same specially designed ionization gauge. Both can be displayed on the screen of an oscilloscope or recorder; the rate appears as an ac ripple superimposed on the dc signal which is a measure of the background pressure at the substrate. A quartz oscillator ratemeter is used to measure the deposition rate. From the readings of the two ratemeters the sticking probability has been determined. Relations between background pressure, i.e., gas load, and sticking probability are being observed for silver on silicon monoxide substrates as these relations change with the buildup of the deposited film.
Field Ion Microscopic Observations of Dislocation Structures at Grain Boundaries
Authors: Ranganathan S.
Published: April 2005

The nature of dislocation contrast in field ion micrographs is examined and it is shown that spirals should be observed in most orientations. This analysis is extended to the spiral structures observed at boundaries and evidence for dislocations at a low angle boundary, a noncoherent twin, and a random boundary is presented in the context of lattice coincidence.
Evaluation of Some Transport Integrals. II.
Authors: Glasser M. L. , Wood V. E.
Published: April 2005

The transport integrals ∫0∞xl(ax+1)−1ex(ex±1)−2dx are tabulated and discussed. As an example, application is made to thermomagnetic effects in metals.
Magnetization and Anisotropy in Gallium Iron Oxide
Authors: Pinto A.
Published: April 2005

The magnitude and direction of the magnetization (M) of a single crystal of orthorhombic Ga2−xFexO3(x≈1.08) were measured separately in a magnetic field (H) which was applied in various crystallographic directions and ranged up to 23 kOe in magnitude. Temperatures (T) between 77° and 300°K were used. The apparatus included a vibrating sample magnetometer equipped with two mutually orthogonal pairs of pickup coils mounted on a rotating base. Analyses of the data show that M depends on H as well as on H/H, and that the uniaxial anisotropy coefficients (K) are such that the ratios KA/M2A and KB/M2B, which refer to the ac and bc planes, respectively, are independent of H within experimental error (<4%) and independent of H/H within experimental error (∼20%). The analyses show, moreover, that these ratios increase monotonically with increasing T, and that KA and KB, when extrapolated to H=0, are linear functions of T between 110° and 295°K. At 77°K, the values of KA and KB are determined to be 2.43×106 erg/cm3 and 4.37×106 erg/cm3, respectively.
Mass-Scattering Cross Section of Thin Carbon Films
Authors: Sarkar N. H.
Published: April 2005

Mass-scattering cross sections of thin carbon films have been determined experimentally for 60- and 80-kV electrons at the scattering angles of 2.23×10−3, 4.25×10−3, 9.76×10−3, and 1.86×10−2 rad. This was done by densitometric determination of the contrast in the electron microscope (Siemens Elmiskop I) negatives of thin carbon films of known mass thickness, on the basis of a rigorous contrast-density relationship. These experimental results and those due to Leisegang, Lippert, and Komoda have been compared with the values calculated from the theories of Lenz, of Burge and Smith, and of Sarkar. The experimental results are found to agree quite well with the theory of Sarkar.