bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Dislocations on X-Ray Diffraction Properties of Copper
Authors: Bachmann K. J. , Baldwin T. O. , Young F. W.
Published: February 2004

The effect of dislocations on both integrated intensities and rocking-curve half-widths has been studied in an (n, −n) double-crystal spectrometer arrangement on copper crystals of 103<N<108 dislocations per cm2. The results show that the rocking curve provides a suitable means of characterization of the density and the type of dislocations in this range. The changes in half-width of the rocking curve and the integrated intensity produced by the dislocations can be described satisfactorily by the model of independently scattering perfect crystal blocks up to a dislocation density of 2×105/cm2, and at higher dislocation densities, lattice tilts produced by the dislocations appear to be the main source of line broadening.
Diffusion Models for Hot Pressing with Surface Energy and Pressure Effects as Driving Forces
Authors: Coble Robert L.
Published: February 2004

Models for initial-, intermediate-, and final-stage densification under pressure have been developed, which explicitly include both the surface energy and applied pressure as driving forces. For the initial stage, the time dependences and size effects given by the integrated equations are identical to those reported earlier for surface energy (alone) as the driving force. The only modification is that the surface energy (γ) is expanded into (γ+PaR/π), where Pa is the applied pressure and R is the particle radius. For the intermediate stage of the process, the Nabarro-Herring and Coble creep models may be adapted to give approximate (∼4×) densification rates for lattice and boundary diffusion models, respectively. In these cases the complex driving force is written as: (Pa/D+γk), where D is the relative density, and k is the pore surface curvature. At the final stage of the process those models are invalid; an alternate model is developed based on diffusive transport between concentric spherical shells which will give a better assessment of the time dependence of densification high density (>95%); the driving force is (Pa/D+γk) in this case also. Because of the fact that the pore size is some unknown function of density, the rate equations cannot be integrated without further information. It is shown that of the various relations which have been assumed in development of models for hot pressing, for the effective stress in relationship to the applied stress and the porosity, (Pa/D) is the only form which satifies the criteria demanded by self-consistency in generation of steady-state diffusion models.
Method for Determining the Maximum Emission Depth of True Secondary Electrons by Means of Retarding Characteristics
Authors: Goto Keisuke , Ishikawa Kazuo
Published: February 2004

A method has been developed to determine the maximum emission depth of true secondary electrons λ. The method is based on observing the retarding potential characteristics as a function of film thickness of a specimen which was deposited on a substrate. With this method values of λ for DC-705, DC-704, and Octoil-S (diffusion pump oils) were determined to be about 30, 40, and 70 Å, respectively. No clear dependence of the λ on primary-electron energy was found for 200–1500 eV. These λ values well agree those obtained by means of δ-η analysis. This fact gives an experimental evidence for the validity of δ-η analysis in which a film thickness where a break occurs on a δ-η curve is assumed to correspond to λ.
Cathodic Interaction of an Electrode with Dense Plasma
Authors: Rohatgi Vijay K.
Published: February 2004

Current partitioning at a tungsten cathode in a 1-atm argon plasma is studied experimentally. Both ions and electrons are found to contribute to the cathode current in this case. The ion current is supplied by the plasma whereas the electron current is controlled by the thermoinic emission laws. The work function of the emitter is reduced due to the presence of an ion space-charge field in a manner described by the Schottky effect.
Temperature of the Restrike Channels of Exploding Wires
Authors: Lundquist Stig , Vlastós Antonios E.
Published: February 2004

The temporal behavior of the temperature, the electron density and the thermal conductivity of the restrike channel of a thin exploding wire were studied, using the electrical conductivity of the restrike channel, which was determined by simultaneous measurements of the current through the channel, the voltage drop cross the channel and the channel radius assuming that the current distribution within the channel was homogeneous. In this study, in which the channel plasma was assumed to be fully and singly ionized, the Spitzer equations for the electrical and thermal conductivity of a fully ionized plasma and a modified pinch relation for the restrike channel were used. The results show:

(a) that the electrical conductivity reaches its maximum before the current maximum on the ledge observed on the voltage oscillograms;

(b) that the temperature and thermal conductivity reach their maxima at the conductivity maximum;

(c) that the electron density reaches its maximum after the conductivity maximum and near the current maximum;

(d) that the maximum values of the electrical conductivity, the temperature, the electron density and the thermal conductivity increase when the energy-input rate to the channel increases;

(e) that the validity of the assumptions made is in general confirmed.

For restrikes initiated at the exterior of the 13-cm-long 0.005-cm-diam constantan wires, the maximum values of the temperature and the electron density were found at 5 kV to the about 2×104 °K and 1023 electrons/m3 respectively, and at 23 kV to be about 4×104 °K and 1025 electrons/m3, respectively.
Low-Voltage Arc and Breakdown Effects in Xenon-Filled Thermionic Diodes
Authors: Forman Ralph
Published: February 2004

Breakdown phenomena and the low-voltage xenon arc have been studied in xenon-filled thermionic diodes. These measurements were made at gas pressures ranging from 1 Torr to atmospheric pressure and with diodes having interelectrode spacings of 0.05, 0.1, and 0.75 cm. Most of the results were obtained on tubes with a unipotential thoriated-tungsten cathode operating at approximately 1700°C. The results showed that breakdown in xenon leading to the low-voltage arc can occur at voltages even lower than the first excitation potential of xenon. No minimum spacing effect was observed; the low-voltage arc occurred for interelectrode spacings down to 0.05 cm. At 0.05-cm spacing and a cathode temperature of 1700°C, the low-voltage xenon arc could be induced over the pressure range 1–500 Torr. Under some conditions of pressure and spacing the low-voltage xenon arc could be sustained at voltages as low as 1–2 V.
Magnetization Measurements on Twisted Superconducting Composite Conductors
Authors: Critchlow P. R. , Zeitlin B.
Published: February 2004

Magnetization measurements are reported on twisted multistrand NbTi superconducting composites. Data for copper matrix composites when fitted to the theoretical predictions give reasonable values for the matrix resistivity. Data for a CuNi matrix composite and data on the rate of decay of the magnetization at small twist rates do not agree with simple theory. An explanation based on the presence of an untwisted core removes the disagreement. Finally, the data are plotted to show a linear dependence of magnetization on filament diameter over the range 0.00036–0.015 in.
Domain-Wall Processes in SmCo5 Powders
Authors: Zijlstra H.
Published: February 2004

Measurements of minor loops of SmCo5 powders have revealed that wall motion is predominant in the magnetization process. A relation between the reversible susceptibility χ of the minor loops and the coercivity Hc has been found, showing that the coercivity of the investigated material is determined by the pinning of domain walls, rather than nucleation. The relation χHc2=const has been found in a wide range of coercivities obtained by aging of the material. The aging process is interpreted as a decrease of the density of pinning sites, each site retaining its pinning force. Hysteresis loops measured on single particles of a few microns size confirm these interpretations and allow for a refined model of pinned-wall coercivity of SmCo5 powders.
Noncharacteristic Defects in Thin Films of Cobalt Ferrites
Authors: De Jonghe L. C. , Thomas G.
Published: February 2004

High-voltage transmission electron microscopy has been used to study the structure of thin films of cobalt ferrites of various compositions. Small defects have been identified to result from a combination of chemical polishing used to prepare foils and subsequent radiation damage in the electron microscope. Such defects must be distinguished from the characteristic defects, such as small precipitates, since they are representative only of the preparation and examination techniques.
Bending Behavior and Tensile Strength of Carbon Fibers
Authors: Williams Wendell S. , Steffens D. A. , Bacon Roger
Published: February 2004

The strength of anisotropic polycrystalline carbon fibers was investigated. Theoretical estimates of the strength of graphite are far higher than observed values for carbonized rayon fibers, and we have searched for an explanation. Internal ``grain boundaries'' in the fibers can account for the reduced strength inasmuch as the fracture appears to be intergranular. The ``grains'' are believed to be axially oriented fibrils, ap-approximately 500-Å across. Experimental evidence for some inelastic behavior in carbon fibers at room temperature was obtained from bending experiments on single filaments. The results were interpreted in terms of local ``yielding'' or rupture of cross-link bonds between adjacent fibrils. The stress at which such ``yielding'' takes place in bending is approximately equal to the failure stress in a tensile test. Although a Griffith model of completely brittle fracture in tensile tests was considered, the possibility that local ``yielding'' might precede tensile fracture seemed more likely. Consideration of the brittle failure model and the localized plastic flow model both lead to the same conclusion: The tensile strength of carbonized rayon fibers is limited by the fibrillar microstructure and cannot be expected to approach the theoretical estimates for graphite single crystals.
Role of Constitutive Equations of Function Type in Modelling Some Commonplace Mechanical Behavior
Authors: Appleby E. J.
Published: February 2004

The materials considered in this paper exhibit the following phenomena: (1) a time-dependent stress approaching a steady value with increasing time in a simple-tension relaxation test, and (2) a time-dependent strain rate approaching a steady value with increasing time in a simple-tension creep test. They are also substantially isotropic and incompressible. Such materials are very common, but, as is shown in this paper, continuum models which will represent them are not. Even very general models such as the Rivilin-Ericksen and hygrosteric models are shown to be inadequate for this purpose. Models of function type, which do admit the phenomena described above, are considered here within the domain of finite deformations and nonlinear material response. The level of generality of the models is such that the variables appearing in the constitutive equation may be chosen but the form of the function relating them may not. This level forms the groundwork for specialized classification, and leaves open the possibility that a theoretical program of experimentation may be constructed which allows a given material to numerically identify the form of its function within the framework of the general model. As a first step in the search for a continuum model for these materials, the following question arises. Within the level of generality described, what is the simplest model of function type which will represent the material behavior discussed? Re-expressed: what is the least number of variables which must appear in the constitutive equation, and what are these variables? These questions are answered in this paper.
Optical Detection of Surface Damage in GaAs Induced by Argon Ion Implantation
Authors: Sell D. D. , MacRae A. U.
Published: February 2004

Surface damage in GaAs has been studied by measuring the room-temperature reflectance in the 3-eV spectral region. Controlled levels of damage were created by implanting samples with known doses of 75-keV argon ions. The damage from doses as low as 1011 ions/cm2 has been observed by studying the energy derivative of the reflectance (dR/dE)/R. As the damage level is increased, the optical reflectance structure broadens and hence the amplitude of (dR/dE)/R decreases. The sensitivity of this technique is comparable to or greater than that obtainable with other damage measurement techniques. The results for three other techniques (ellipsometry, channeling, and photoluminescence) are briefly discussed. Possible applications of the reflectance method are considered.
Effects of Growth Atmosphere on Photovoltaic Properties of ZnS Crystals
Authors: Shachar G. , Brada Y. , Steinberger I. T.
Published: February 2004

ZnS crystals were grown by sublimation in the presence of either H2S (``group S'') or a mixture of Ar and HCl (``group Cl''). Electroabsorption and polar rectification measurements indicate that permanent, high internal electrical fields exist in crystals of both groups. The anomalous photovoltaic effect (APE) is, however, observed only in the crystals of group S. For both groups, the sign of carriers excited by ir illumination was established by point-contact rectification. The Fermi level in the dark, in group S crystals, was found to be within 0.9 eV of the valence band, while in group Cl it lies in the upper half of the forbidden gap. These measurements, along with photoluminescence results indicate that the free-electron lifetime is considerably longer in group Cl crystals than in group S crystals. This difference in lifetime furnishes a simple explanation for the absence of the APE in crystals of group Cl.
Electron Density of Relativistic Electron Beam Produced Plasmas
Authors: Rizzo J. E.
Published: February 2004

A multiple-pass Mach-Zehnder laser-illuminated interferometer has been constructed and used to measure the electron density profile of plasmas produced by a self-confined propagating electron beam. Spatial and time resolved data were taken perpendicular to the electron beam axis at two longitudinal positions. Densities of 1016 cm−3 have been seen in air between 0.15 and 0.3 Torr as early as 150 nsec after the electron beam entrance. Peak densities of 1017 cm−3 were typically reached at around 2 μsec. Plasma compression was observed under some conditions.
Studies of Cavity Resonators Containing Magnetoplasmas
Authors: Kent Gordon , Thomas Donald
Published: February 2004

This paper deals with cylindrical cavity resonators containing weakly ionized gases, principally argon, in the pressure range of 0.03–0.70 Torr. The plasma, produced either by microwave or dc power, is magnetized by a uniform axial field. Measurements of resonant frequency, made over a range of plasma densities and magnetic field, are compared with the calculations of the theory given by Kent [J. Appl. Phys. 39, 5919 (1968)]. The agreement is good providing the cylindrical degeneracy of the cavity is preserved and the plasma is reasonably uniform. Experimental and analytical results are used to evaluate perturbation theory, and some simple formulas, useful for diagonostic purposes, are given. A perturbation method for correcting the theory to account for symmetrical nonuniformities is proposed, and it is applied to the experimental data with apparent success. The method offers the possibility of determining both uniformity and density from measurements of frequency in one microwave band.
Effect of Hydrostatic Pressure on Excess Carrier Lifetimes in Germanium
Authors: Eresian W. J. , McKelvey J. P.
Published: February 2004

The effect of hydrostatic pressure up to 10 000 kg/cm2 on excess carrier lifetime in single-crystal samples of n- and p-type germanium has been studied over a temperature range of 200°–350°K. The results of the experiments are interpreted in terms of existing theories of charge carrier recombination via recombination centers, and expressions for the variation of recombination level energies within the forbidden energy gap as a function of pressure are inferred. These variations are understandable on the basis of a simple Bohr model of defect levels in a dielectric medium whose dielectric constant varies with pressure. Tentative suggestions relating the recombination centers in the experimentally investigated samples to the presence of interstitial and substitutional impurity atoms are advanced.
Influence of Contacts on the High-Field Microwave Emission from InSb
Authors: Bonek Ernst , Albert Richard
Published: February 2004

Experiments are reported demonstrating the importance of contact characteristics for the high-field (average field≳ionization field) microwave emission from InSb. Large voltage drops across the contacts are associated with low threshold currents for the onset of microwave emission. Thermal overloading the contacted sample by high pulse currents results in both a drop in overall resistance and a rise in threshold current and threshold magnetic field. Cessation of microwave emission after a thermal overload may be due to an annealing process in the contact region and is not necessarily connected with any damage to the crystal structure.
Beta- and Gamma-Induced Conductivity in Semiconductors: Application to CdS Neutron Detectors
Authors: Johnson Ralph T.
Published: February 2004

Methods for determining the mobility-lifetime (μτ) product of high-resistivity n- or p-type semiconductors using induced conductivity resulting from high-energy beta and gamma irradiations are developed. The μτ product is determined, under conditions of steady-state excitation, from the measured induced conductivity and the calculated electron-hole generation rate g. The carrier free lifetime τ is determined from these results using the measured Hall mobility. For gamma irradiation g is determined from the exposure rate, density, mass energy-absorption coefficients, and radiation-ionization energy (ε). For beta irradiation gβ is determined for the case of ionization resulting from the beta decay of radioisotopes which are produced by neutron irradiation and which are randomly distributed throughout the semiconductor. gβ is determined from the radioactive decay rate, energy of the beta radiation, and ε. The absorbed dose rates resulting from these radiations are also determined. Gamma-induced conductivity experiments were performed using 60Co gamma irradiation on high-resistivity n-type CdS, CdSe, GaAs, and ZnS single crystals. The measured μτ products ranged from ∼10−5 to 25 cm2/V; τ varied from ∼10−8 to 10−1 sec. Some reduction in μτ resulting from high-temperature annealing of CdS and GaAs was also observed. Beta- and gamma-induced conductivity experiments (32P beta decay and 60Co gamma irradiation) were performed on neutron-irradiated CdS single crystals. Comparison of these results show that: (1) The μτ products determined at a given dose rate from the beta and gamma irradiations are in very good agreement (within 15%). Thus, the theories developed here for determining g and gβ are valid. (2) For samples which have considerable neutron damage, μτ is very dependent upon exposure rate (or absorbed dose rate); decreasing with increasing exposure rate. This is in contrast to samples which have minimal (or no) neutron damage, where very little dependence on exposure rate is observed. (3) The μτ product is also dependent upon the conductivity or Fermi level position. For irradiated high-resistivity crystals μτ is 1–6 cm2/V, and τ is of the order of tens of msec. However, for irradiated low-resistivity crystals μτ is larger by a factor of ∼102, and τ is of the order of seconds. The dependence of μτ on the excitation intensity, defect concentration, and Fermi level position in neutron-damaged samples results from sensitizing centers associated with neutron-induced defects. The concepts developed here have resulted in new techniques for measuring neutron fluences using electrical changes associated with induced radioactivity in semiconductors. Gamma-induced conductivity provides a valuable technique for ``calibrating'' these detectors (i.e., determining the μτ product).
Mechanism of Work-Function Reduction by Oxygen Adsorption
Authors: Chen J. M.
Published: February 2004

A model is proposed to explain the reduction in work function of an Na-covered W (112) surface by oxygen adsorption. It is proposed that oxygen atoms are adsorbed directly to the W (112) substrate, forcing the Na atoms to the second layer. Since the dipole moment of an O–Na bond is much larger than that of a W–Na bond, it is believed that the W–O–Na bonding has larger dipole moment than that of the W–Na bond thus causing a decrease in work function. LEED results consistent with the proposed model is presented.
Vibrational Effects in the Thermal Expansion of Noncubic Solids
Authors: Barron T. H. K.
Published: February 2004

The thermodynamics of thermal expansion and of the related Grüneisen function γ(T, V) is discussed first for cubic and isotropic solids. Vibrational effects are treated in the quasiharmonic approximation. For central force models two effects are distinguished-that of the anharmonicity of the pair potential, normally contributing positively to the expansion, and that of the bond ``tensions,'' contributing negatively. The extension of the theory to noncubic solids is summarized, the strongly anisotropic example of zinc being used to illustrate the roles played by anisotropy in the elasticity and in the Grüneisen tensor. Recent work on central force lattice models, both ionic and nonionic, is reviewed. For ``internal expansion,'' in which the disposition of atoms within a unit cell varies with temperature, it is convenient to treat both internal and external strains on the same footing.
Low-Temperature Phase Transitions in Alpha Uranium
Authors: Steinitz M. O. , Burleson C. E. , Marcus J. A.
Published: February 2004

Strain-gauge thermal expansion and anisotropy of susceptibility measurements indicate the existence of three phase transitions below 50°K in alpha uranium. Two of the transitions are of first order and one is of second order.
Thermoelastic Expansion and Creep of Polyethylene Terephthalate and Polypyromelitimide Film and Polyethylene Terephthalate Fibers from 20 to 295 K
Authors: McConnell P. M. , Daney D. E. , Kirgis J. B.
Published: February 2004

A quartz tube dilatometer was used to measure the lineal thermal expansion and creep of single lengths of polyethylene terephthalate (PETP) film, polypyromelitimide (PPMI) film, and PETP multifiber yarn, while stressed under constant tension. Tensions below and above the conventionally defined yield strength were used and the sample temperature ranged from 20 to 295 K. Relative creep strain measurements, taken at the constant temperatures 77, 195, and 295 K were found to obey the equation ε=exp[−2.3 exp(A′y)]where y is a function of stress, time, and temperature and A′ is a constant depending on the material. This equation was used to correct the thermoelastic expansion measurements for creep at the higher stresses. PETP multifiber yarn subjected to a slight tension was found to elongate during cooldown from 293 to 20 K. Higher stresses caused less elongation; i.e., the coefficient of expansion increased with stress. This result is believed to be due to changes in crystallinity at the higher stresses. A similar stress effect was found with PETP film but not with PPMI film. The thermoelastic expansion of the film samples was also found to be sensitive to the thickness.
Anisotropic Thermal Expansion of Refractory Carbides by High-Temperature Neutron Diffraction
Authors: Bowman A. L. , Arnold G. P. , Krikorian N. H.
Published: February 2004

The anisotropic thermal expansion of U2PtC2 (tetragonal), and UMoC2 (orthorhombic) has been measured using a high-temperature neutron diffractometer. Coefficients of thermal expansion (units of 10−6/°C) are U2PtC2, α11=9.3±0.1, α33=10.1±0.8; UMoC2, α11=8.6±0.2, α22=15.5±0.5, α33=10±3.
Thermal Expansivity and Isothermal Compressibility Measurements on Rare Gas Solids by an Optical Method
Authors: Coufal H. J. , Veith R. , Korpiun P. , Lüscher E.
Published: February 2004

The thermal expansivity and isothermal compressibility at p=0 of solid rare gases can be measured interferometrically in the temperature region between 2° and 150°K. The experimental errors are about 1% in the whole temperature region. First measurements have been done on solid Kr. We have found that the volume thermal expansion coefficient varies from (3.80±0.02)×10−5 °K−1 at 5°K to (1.82±0.012)×10−3 °K−1 at 115°K (triple point). The isothermal compressibility at p=0 varies from (2.93±0.022)×10−11 dyn−1 cm2 at 5°K to (8.83±0.10)×10−11 dyn−1 cm2 at 115°K.
Volume Dependence of the Thermal Expansion of Polymers
Authors: Pastine D. John
Published: February 2004

Recent theoretical developments dealing with the equation of state of polymers make it possible to obtain some estimate of the volume dependence of the thermal expansion α of these materials. It is clear at this point that α should depend not only on the volume V and temperature T, but also on the degree of crystallinity Fc of the polymer in question. The calculations presented take this latter parameter into account and theoretical values of α for polyethylene (PE) are given as a function of V, T, and Fc. The values of α for crystalline PE are converted into values for poly chloro tri fluoro ethylene (Kel F) by simple corresponding states relations. The efficacy of these relations is shown by accurately converting P-V data on PE to P-V data on Kel F.
Thermal Expansion of Polycrystalline Graphite
Authors: Naum Robert G. , Jun Choll K.
Published: February 2004

Thermal expansion characteristics of a group of polycrystalline graphites have been measured to 2400°C by a method which permits acquisition of meaningful expansion data without resorting to reference standards. Direct measurements on specimens while in the furnace were accomplished by using two 8-in. focal length Gaertner optical micrometers. Thermal expansion behavior is discussed in relation to orientation, impurity, degree of crystallinity, and grain size. Specimens were heated from room temperature to 2400°C, then cooled to room temperature, taking measurements of thermal expansion throughout both heating and cooling cycles. The existence of hysteresis is observed and discussed.
Effects of High Pressure on the Thermal Expansion of Solids with a Linear Us-up Relationship
Authors: O'Keeffe David J.
Published: February 2004

A theoretical technique for determining the volume dependence of the thermal expansion coefficient α along an isotherm is developed for solids which exhibit a linear Us-up (i.e., shock velocity-particle velocity) relationship. The method is founded on an accurate Grüneisen equation of state utilizing the temperature-independent Grüneisen parameter γ which has been calculated from experimental shock data. Detailed results are presented for several isotherms at pressures as high as 1 Mbar. Based on the accuracy of the Grüneisen parameter, the accuracy of the calculated thermal coefficient α is estimated to be within ±10% down to 20% compression with greater accuracy for lower compressions.
Thermal Expansion: A Review of Test Methods, Standards, and Data Availability
Authors: Pears C. D.
Published: February 2004

The purpose of this paper is to encourage agreement as to where we are and suggest a few ways that this symposium can contribute to some future requirements. Thermal expansion of solids is a subject of interest to a wide range of disciplines from those conducting basic studies of lattice behaviors to those analyzing temperature stresses on re-entry. Temperatures of interest range from cryogenic to 6500°F. Pressures range from 10−12 Torr to several atmospheres. The chemistry of the environment is also concerned. Thus the total environment is important. As a result of this broad scope, many different test methods are involved, different precisions and accuracies are required, and data are difficult to relate. This paper describes the applicability of some of the major test methods in terms of some of the above requirements, the standards that are available, and some sources of data for the different regimes. Particular emphasis is placed on engineering behavior since that represents the bulk of the authors experience. The observations are made that we need some base line understanding as to where we now stand and as to the areas where the thermal expansion symposium could systematically attack the problems by (1) encouraging papers and discussions of the various test methods, their environments, and limitations, (2) resolving by discussion and by encouraged personal round robins the obtainable precision and accuracy of methods and standards, (3) making known sources of data through author references, (4) communicating needs to groups that develop standards, (5) providing a forum where the facts can emerge and (6) publishing informal bound proceedings for a few years to gather the existing information and then bound abstracts eventually to provide references of more detail. After this sorting of information, more sophisticated studies will be possible by more people.
Use of Critically Evaluated Data on Copper to Test the Mie-Grüneisen Equation of State
Authors: Kirby Richard K.
Published: February 2004

Thermal expansion data that is now available for copper is believed to be accurate within the range 0–1000 K. Using this data and other critically evaluated data on thermodynamics and elastic properties various approximations of the Mie-Grüneisen equation of state PV=−V[∂φ(V)/∂V]+γEhave been evaluated. These approximations, assuming zero pressure, are usually written as (V−V0V0)=(K0γ0/V0)E1−A(K0γ0/V0)E,[(V−V0)/V0]−A[(V−V0)V0]2=(K0γ0/V0)E. Both of these approximations fail to provide a reasonable fit to the data, especially in the low-temperature region. If, contrary to the normal usage of these approximations, the Grüneisen parameter is allowed to be temperature dependent then a better fit, both qualitative and quantitative, to the data is obtained, [(V−V0)/V0]−A[(V−V0)/V0]2=(K0/V0)γE. This form of the Mie-Grüneisen equation also provides a means of estimating the temperature dependence of the Grüneisen parameter when compressibility data is only available at room temperature γ=a(V−V0)/V0E[1−b(V−V0V0)].
Thermal Expansion of Composite Materials
Authors: Tummala R. R. , Friedberg A. L.
Published: February 2004

An equation for predicting the thermal expansion coefficient of dilute binary composites is presented treating the dispersed particles as elastic spheres and taking into consideration the physical interactions between the dispersed phase and the matrix. Application of this particular equation to a variety of systems such as ceramic-glass, glass-metal, metal-metal, and organic-metal, is discussed, as well as the application of other equations to other material systems extant in the literature.
Thermal-Expansion Behavior of Two-Phase Solids
Authors: Fahmy A. A. , Ragai A. N.
Published: February 2004

The thermal expansion behavior of the two duplex systems, lead-fused silica and aluminum-silicon, has been investigated experimentally above and below room temperature. The microstructure in the first case consisted of fused silica particles in a lead matrix, while silicon constituted the dispersed phase in the second. The expansion coefficients always fell below those predicted by the simple rule of mixtures. A model is proposed and a new formula for the calculation of the thermal expansion coefficient of duplex materials is derived. The new formula fits experimental results better than Turner's formula. The role of microplastic yielding in high-inclusion-content composites is discussed.
Thermal Expansion of Graphite-Epoxy Composites
Authors: Fahmy A. A. , Ragai A. N.
Published: February 2004

The thermal expansion behavior of unidirectional, balanced angle-ply, and complex laminated graphite-epoxy composites, is studied. The expansion coefficient of the unidirectional composites is determined as a function of fiber orientation and is found to follow the simple equation αθ=αL cos2θ+αT sin2θ. Results obtained on angle-ply composites are in agreement with the predictions based on Halpin and Pagano's analysis. The applicability of the same approach to a panel of more complex construction is discussed. Hysteresis effects, observed in this panel, may be caused by interlayer stress relaxation.
Effect of Reduced Pressure on Thermal-Expansion Behavior of Rocks and Its Significance to Thermal Fragmentation
Authors: Thirumalai K. , Demou S. G.
Published: February 2004

Rock is a complex composite solid generally consisting of heterogeneous granular aggregates of polycrystalline mineral constituents which are characteristically anisotropic. Thermal stresses induced during the heating or cooling of rocks cause fracture and fragmentation. Thermal expansion is a significant parameter for the creation of thermal stresses to fragment rocks by heat. A method for experimentally measuring rock response to induced thermal stresses from cyclic thermal expansion of the rock surface is developed using strain-gauge technique. Rock fracture caused by internal thermal stresses during heating and cooling in atmosphere and vacuum environment is examined. The response of rock material to induced thermal stresses is shown to be independent of reduced environmental pressure down to 10−5 Torr. The results of reduced environmental pressure on thermal expansion behavior of some simulated lunar rocks are presented. These results provide a new insight on the feasibility of fragmenting rock with thermal energy in vacuum environment.
Elastoresistance Effect of a Nickel Single Crystal
Authors: Martin M. C.
Published: February 2004

The effect of tension T applied in a direction parallel to that of the current on the resistance of a nickel single crystal (elastoresistance) was determined at 77.4°K. Correction for strain permitted the calculation of the more informative physical characteristic, the elastoresistivity. The fact that the elastoresistivity coefficient [(1/T) (Δρ/ρ)] was negative indicated that a greater part of the resistance change of nickel under tensile stress is due to magnetic domain reorientation than to lattice distortions and other effects.
Structure of the (a/2) 〈111〉 Screw Dislocation in α Iron
Authors: Gehlen P. C.
Published: February 2004

The atomic positions around the core of the (a/2) 〈111〉 screw dislocation in α iron have been investigated using a new interatomic potential with a cutoff distance between third and fourth neighbors. A radical expansion term has been included in specifying the boundary conditions. Two configurations with about the same core energy were discovered; only one of these retained the threefold symmetry of the lattice around the dislocation line. The energy barrier between the two configurations is about 0.2 eV. The core radius is found to be between one and two Burgers vectors and the core energy between 0.3 and 0.45 eV/atom plane.
Internal Friction in Westerley Granite: Relation to Dislocation Theory
Authors: Mason Warren P. , Beshers Daniel N. , Kuo John T.
Published: February 2004

Compressional wave-velocity and attenuation measurements have been made for fine-grained Westerley granite over a frequency range from 25 kHz to 2.5 MHz. The internal friction Q−1 varies by a factor of 10 over this frequency range, increasing from 0.80×10−2 around 25 kHz to 6.5×10−2 at 2.5 MHz. The measurements are consistent with the low- and high-frequency components associated with kink motion of dislocations. The constants evaluated from the measurements are consistent with values obtained for polycrystalline metals.
Parametric Behavior of the Atmospheric Pressure Pulsed CO2 Laser
Authors: Smith David C. , DeMaria A. J.
Published: February 2004

Megawatt peak powers have recently been reported from a pulsed electrical discharge CO2 laser operating at atmospheric pressure [A. J. Beaulieu, Laser Focus 6, 14 (1970)]. The electrical discharge was struck across the transverse dimension of the laser producing the large electric field strengths required for laser excitation at high gas pressures. This paper describes the small signal gain, pulse energy, and duration as a function of gas pressure and discharge voltage of a 1.5-m laser tube utilizing 60 separate capacitor discharges along the axis of the tube. The gain coefficient is of the order of 1% per cm or less, typical of dc excited CO2 lasers. The peak power increases approximately as the square of the total gas pressure as a result of an increase in pulse energy and decrease in pulse duration with gas pressure.
Schottky Barrier Probe Tunneling into Superconductors
Authors: Thompson W. A. , von Molnar S.
Published: February 2004

This paper describes some GaAs probe tunneling experiments which exhibit the usefulness and reliability of this bulk tunneling method. Tunneling characteristics were observed for all superconducting counter-electrodes, and the measured ratios of superconducting energy gap to transition temperature were in good agreement with measurements by other techniques. Also described are the effects of contact pressure and a novel in situ surface cleaning technique for removing chemically contaminated surface layers.
Low-Temperature Electronic Transport Properties of Tl5Te3
Authors: Cruceanu E. , Lück R. , Schwarz H.
Published: February 2004

Measurements of the electrical resistivity, transverse magnetoresistivity, and Hall effect between 4.2° and 293°K were carried out on zone-melted Tl5Te3 single crystals, which had undergone heat treatments in different gas atmospheres. The results indicate that the electrical transport properties of Tl5Te3 are influenced by the absorbed nitrogen gas. The temperature dependence of the ideal resistivity is discussed in terms of the Grüneisen-Bloch relation. Using a characteristic temperature θR=115°K, a rather close agreement between the computed and the experimental curves is found. The transverse magnetoresistivity at 4.2°K is positive and varies as B2. The Hall coefficient decreases with increasing temperature by about a factor of 4, remaining positive throughout the whole temperature range investigated.
Effects of Various Heating Rates on Glow Curves
Authors: Chen R. , Winer S. A. A.
Published: February 2004

Methods for evaluating activation energies and escape frequency factors from glow curves by the use of various heating rates are discussed. For first-order peaks, the method of finding the glow parameters by measuring the shift of the maximum temperature with changing heating rate is generalized. This method, known to be true for linear and exponential heating rates, is shown in the present paper to hold true for any monotonically increasing heating function. The method using the variations in the maximum intensity with changing heating rates, previously known to apply for certain thermally stimulated current peaks is proved to be true for all first-order peaks. Analogous methods are found for general-order peaks, an important special case of which are the second-order peaks. Computer calculations as well as experimental results in ZnS:Er3+ samples are given as a check. These methods are of special value when the peaks are not ``clean'' since the quantities used are measured only at the maximum point.
Ferromagnetic Domain Wall Width Measurements Using Lorentz Electron Microscopy
Authors: Ray S. P. , Paul D. I.
Published: February 2004

Ferromagnetic domain walls in thin foils of iron and Fe-6.5-wt%-Si alloys have been imaged by out-of-focus Lorentz electron microscopy. By analysis of the variation of the electron beam intensity across the domain wall width an estimate has been made of the domain wall width of the materials. The mean width on (100) planes of 180° domain walls in Battelle iron is 1720 Å and for 90° walls is 770 Å while the same for 6.5% SiFe alloy is 2530 and 1140 Å, respectively. The mean wall width ratio of the iron-silicon alloy to the Battelle iron is 1.48 which yields a value of 1.06 for the ratio of the exchange constant for iron with respect to the iron silicon alloy. Further, using our value of 770 Å for the 90° wall width of Battelle iron, we obtain a value of 2.51×10−14 ergs for the exchange constant.
Characteristics of Magnetostatic Surface Waves for a Metalized Ferrite Slab
Authors: De Wames R. E. , Wolfram T.
Published: February 2004

Detailed calculations of the characteristics of the magnetostatic surface waves in a ferrite slab with a metalized surface are presented. The region of validity of the effective boundary condition model (EBCM) discussed by Seshadri is established. It is shown that the dispersion characteristics of overlayed magnetic systems can be modified and tailored to have a variety of frequency-versus-wavenumber properties. In general the modes are lossy and the degree of damping depends critically on the characteristic lengths of the problem.
Sintering of Die-Pressed Co5Sm Magnets
Authors: Cech R. E.
Published: February 2004

An experimental program was carried out to establish the conditions necessary to achieve successful sintering of Co5Sm powder. The objective was to sinter the as-pressed powder to the highest possible density without having the powder suffer a loss of coercive force. It was found that to maintain coercive force it was necessary to have an oxygen scavenging agent intimately dispersed throughout the powder. This was accomplished by adding either samarium metal or samarium hydride powder to nominally stoichiometric Co5Sm to give an average composition in the range of 36–37.5 wt% Sm. In addition it was found that highest sintered densities were achieved with a total samarium content slightly greater than that needed to maintain a high coercive force in the densified compacts.
Disclination Structures in Bloch Wall Lattices in BaFe12O19 and SmCo5
Authors: Hirth J. P. , Wells R. G.
Published: February 2004

Domain walls in barium hexaferrite (BaFe12O19) and SmCo5 are shown to form a lattice. Defects observed in the Boch wall patterns are interpreted geometrically as dislocations and disclinations. The elastic properties of these defects are briefly discussed. The faceted appearance of some Bloch wall patterns is analyzed on the basis of a surface energy torque term arising from an anisotropy in the Bloch wall energy. The anisotropy is deduced to arise from high-order coefficients in the anisotropy energy and the magnetostriction.
Raman Spectra of α Quartz Under Uniaxial Stress
Authors: Harker Y. D. , She C. Y. , Edwards David F.
Published: February 2004

The experimental results of the stress-dependent frequency and linewidth of two E and three A1 Raman active vibrations in α quartz are reported and their behavior is qualitatively discussed. The observed nonmonotonic frequency dependence of the stress induced shifts of the A1 lines can be understood based on the proposed modified valence-force model that includes the effects of an anharmonic potential and the applied stress.
Band Structure of InGaP from Pressure Experiments
Authors: Hakki B. W. , Jayaraman A. , Kim C. K.
Published: February 2004

Positive identification of the Γ and X conduction-band minima in InGaP has been made by performing hydrostatic-pressure experiments on forward-biased p-n junction diodes. The Γ and X valleys are coincident in energy at a composition of In0.37Ga0.63P, and the corresponding bandgap is (2.17±0.02) eV at 300°K. The indirect bandgap EX in InP is inferred from the measurements to be 2.0 eV at 300°K. In addition, the pressure coefficients of the direct and indirect bandgaps, ∂EΓ/∂P and ∂EX/∂P, respectively, have been measured at various In(1−x)GaxP compositions. For InP, ∂EΓ/∂P is 8.7×10−3 eV/kbar and this coefficient increases to 13×10−3 eV/kbar for compositions close to In0.5Ga0.5P. On the other hand, ∂EX/∂P = −1.25×10−3 eV/kbar for GaP and shows little change for compositions in the range 0.4<x<1. The deformation potential is 5.7 eV for the Γ valley in InP, and increases to about 9 eV for direct bandgap ternary compositions.
Trapping in Germanium and Silicon
Authors: Curtis O. L.
Published: February 2004

Various analyses have been performed in the past for transient photoconductivity decay in the presence of trapping. One which is potentially of great use, performed by Baicker, yields both trap concentration and energy-level position from transient decay measurements performed at a single temperature. (With the usual analyses, temperature variation measurements are required to determine energy-level position.) Comparison between this and other analyses is performed, and criteria are developed to determine the validity of Baicker's solution. Several sets of data are presented, of which those for one trapping level meet the stated criteria, while the others do not. The discrepancy arises because of the use by Baicker of the condition of thermal equilibrium between the traps and the minority carrier band. The most interesting data presented are probably those for certain irradiated and unirradiated silicon samples which display trapping above room temperature, and show an apparent activation energy of ∼1.6 eV, substantially larger than the silicon bandgap. Such a strong dependence is partially explained using Baicker's analysis. Data for irradiated silicon and germanium are also given, including trap annealing for gamma-irradiated Sb-doped germanium.
Shock Compression of Shoal Granite
Authors: Dennen Robert S.
Published: February 2004

Experiments utilizing explosives with and without flyer plates have been used to determine the shock compression properties of shoal granite. High-speed framing camera records were used to determine the free surface angles which occur in wedge-cut samples upon the emergence of the resulting shock waves. The shock equations are given for the oblique geometry. Previously observed yield point data are used to obtain the Hugoniot of shoal granite in the range between 0 and 400 kbars.
Optical Spectra of Rare-Earth Orthoferrites
Authors: Wood D. L. , Remeika J. P. , Kolb E. D.
Published: February 2004

The rare-earth orthoferrites form a class of optical materials having intrinsically good transmission in the infrared between about 1.3 and about 8 μ. In thin sections they have enough transparency to be useful in the visible region. Optical absorption loss can be less than α=0.5 cm-−1 in the infrared, but Fe valence changes can reduce the transparency drastically. Doping experiments with Sn, Bi, Sb, Mg, and H+ are reported and their effect on optical transparency is given.
Spectral Emissivity of Tantalum in the Red and in the Green, and the Change in Emissivity Resulting from a Change in Surface Structure Induced by Heat Treatment
Authors: Martinez J. M. , Madjid A. H.
Published: February 2004

The spectral emissivity ελ of tantalum for λ=0.645 μ and λ=0.546 μ has been measured by using a De Vos blackbody in ultrahigh vacuum. Changes of the emissivity with heat treatment are related to changes in surface structure, and the reproducibility of results is demonstrated by making measurements on two different blackbodies of identical construction that have been subjected to similar heat treatment. The data presented are compared to previously published results. It is found that ε0.645μ between 1100° and 1700°K for tantalum that is not heated above 1700°K ranges from 0.420 to 0.411; that ε0.645μ between 1100° and 2400°K for tantalum that is heat treated one hour at 2450°K ranges between 0.394 and 0.370; and that ε0.546μ in the latter temperature interval, also for heat-treated tantalum, ranges from 0.456 to 0.423.