Showing papers by "Sandia National Laboratories published in 1976"

Adiabatic Theory of an Electron in a Deformable Continuum

Abstract: A scaling analysis of the adiabatic eigenstates of an electron placed in a deformable continuum with and without the presence of a Coulombic defect is set forth. This procedure enables us to obtain exact information about the system's adiabatic eigenstates for various models of the electron-lattice interaction.

On some alternative procedures using ranks for the analysis of experimental designs

Abstract: The analysis of data from eseperisental designs is often hampered by the lack of more than one procedure available for the analysis, especially when that procedure is based on assumptions which do not apply in the situation at hand. In this paper tvo classes of alternative procedures are discussed and compared, One is the aligned ranks procedure which first standardises the data by subtracting an appropriate estimate of location, then replaces the data with ranks t and finally uses an appropriate test statistic which has asymptotically a chi-square distribution The second procedure is the rank transform which first replaces all of the data with the ranks, and then employs the usual parametric methods, but computed on the ranks instead of the data Some Monte Carlo simulations for a test of interaction in a two way layout with replication enable the robustness and pover of these tvo methods to be compared with the usual analysis of variancs.

Surface Area Reduction During Isothermal Sintering

Abstract: A kinetic model for the reduction in specific surface area during isothermal sintering is examined in detail. Experimental data for a variety of materials including A12O3, B, Ni, Cu, ZnO, TiO2, Fe2O3, and As-Se-S glasses are analyzed by the technique provided. The results of this technique agree well with those for previously identified sintering mechanisms for each material. The kinetic model is based on sintering driven by the curvature gradient in the interparticle neck region associated with initial-stage sintering. At the intermediate stage of sintering, a diminished curvature gradient shifts the sintering driving force to the excess surface free energy.

Computer-aided numerical analysis of silicon solar cells

Abstract: The application of a proven semiconductor device analysis computer code to the study of silicon solar cells is described. The code, which simultaneously solves Poisson's equation and the hole and electron continuity equations in one dimension, provides an effective analysis capability for solar cells that does not require limiting assumptions or approximations. Numerical solutions of the carrier transport problem in the illuminated solar cell illustrate where and how improvements in cell design can be achieved. The reliability of the analyses is demonstrated through a simulation of the conventional silicon solar cell. Results of this analysis are examined, and most practical design modifications to effect improvements in cell performance are identified and evaluated. This systematic technique is used with succeeding computer-aided analyses to identify the post-process silicon characteristics required to achieve a power-conversion efficiency greater than 20%.

New ab initio potential curve and quasibound states of HeH

Abstract: The ground state energy of HeH+ has been calculated in the Born—Oppenheimer approximation for 0.9 ⩽ R ⩽ 4.5 au by using an 83-term variational wavefunction in elliptic coordinates and including the interelectronic distance. The resulting potential curve has been used to compute the quasibound state spectrum of the ion.

Temperature and pressure dependences of the dielectric properties of Pb F 2 and the alkaline-earth fluorides

Abstract: The effects of temperature and hydrostatic pressure on the real (${\ensuremath{\epsilon}}^{\ensuremath{'}}$) and imaginary (${\ensuremath{\epsilon}}^{\ensuremath{'}\ensuremath{'}}$) parts of the static dielectric constant of single crystals of Pb${\mathrm{F}}_{2}$, Ba${\mathrm{F}}_{2}$, Sr${\mathrm{F}}_{2}$, and Ca${\mathrm{F}}_{2}$ were investigated. In all cases ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ decreases with increasing pressure. However, unlike the alkaline-earth fluorides and other normal ionic dielectrics where ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ increases slowly with increasing temperature, ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ of cubic Pb${\mathrm{F}}_{2}$ exhibits a relatively large decrease with increasing temperature and obeys a Curie-Weiss law over a substantial temperature range. It is suggested that this anomalous temperature dependence and the large value of ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ (\ensuremath{\sim}30) are associated with a soft longwavelength transverse optic phonon, i.e., a ferroelectric (FE) mode, although the crystal remains stable with respect to this mode down to the lowest temperatures. This is the first example of a soft FE mode in a crystal having the relatively simple cubic fluorite structure. The measured isobaric temperature dependence of ${\ensuremath{\epsilon}}^{\ensuremath{'}}$ is separated into its pure-volume and pure-temperature contributions. For the alkaline-earth fluorides both contributions are positive and additive, whereas for cubic Pb${\mathrm{F}}_{2}$ the pure-temperature contribution is negative and dominates the measured ${\ensuremath{\epsilon}}^{\ensuremath{'}}(T)$ response. This is attributed to the dominance of quartic anharmonicities in this crystal---a circumstance similar to that in other soft-FE-mode crystals. The Szigeti effective charges were calculated and the validity of the Lyddane-Sachs-Teller relationship was tested for all crystals. The effects of the pressure-induced cubic ($\mathrm{Fm}3m\ensuremath{-}{O}_{h}^{5}$) to orthorhombic ($\mathrm{Pm}nb\ensuremath{-}{V}_{2h}^{16}$) phase transition on the dielectric properties of Pb${\mathrm{F}}_{2}$ and Ba${\mathrm{F}}_{2}$ were also investigated, and the possible lattice-dynamical origin of the transition is briefly discussed. In Pb${\mathrm{F}}_{2}$ the orthorhombic phase is recovered at ambient conditions after releasing the pressure, and the effects of temperature and pressure on the dielectric properties of this phase were investigated. Unlike cubic Pb${\mathrm{F}}_{2}$, the orthorhombic phase behaves as a normal ionic dielectric. At $T\ensuremath{\ge}300$\ifmmode^\circ\else\textdegree\fi{}K the dielectric loss in both phases of Pb${\mathrm{F}}_{2}$ becomes very large due to the high ionic conductivity of the material. The activation energies deduced from the loss data are in excellent agreement with those obtained from ionic conductivity measurements.

Fracture-toughness testing of limestone

Abstract: Fracture-toughness measurements were made on standard three-point-bend fracture specimens of Indiana limestone. Specimen dimensions, experimental techniques, and methods of data reduction were chosen to comply as closely as possible to the Tentative Method of Test for Plane Strain Fracture Toughness of Metallic Materials (ASTM Designation: E399-72T). Typical strain-gage-type clip-in displacement gages were found to lack the necessary sensitivity for measuring the crack-opening displacement while an LVDT displacement transducer having a linear range of ±0.25 mm (±0.010 in.) was found to be ideal.

R-Domination in Graphs

Abstract: The problem of finding a minimum k-basis of graph G is that of selecting as small a set B of vertices as possible such that every vertex of G is at distance k or less from some vertex in B. Cockayne, Goodman, and Hedetniemi previously developed a linear algorithm to find a minimum 1-basis (a minimum dominating set) when G is a tree. In this paper the k-basis problem is placed in a more general setting, and a linear algorithm is presented that solves the problem for any forest.

Transient combined laminar free convection and radiation in a rectangular enclosure

Abstract: The mass, momentum and energy-transfer equations are solved to determine the response of a rectangular enclosure to a fire or other high-temperature heat source. The effects of non-participating radiation, wall heat conduction, and laminar natural convection are examined. The results indicate that radiation dominates the heat transfer in the enclosure and alters the convective flow patterns significantly. At a dimensionless time of 5·0 the surface of the wall opposite a vertical heated wall has achieved over 99% of the hot-wall temperature when radiation is included but has yet to change from the initial temperature for pure convection in the enclosure. At the same time the air at the centre of the enclosure achieves 33% and 13% of the hot-wall temperature with and without radiation, respectively. For a hot upper wall the convection velocities are not only opposite in direction but an order of magnitude larger when radiation transfer between the walls is included.

EPR of a 〈 001 〉 Si interstitial complex in irradiated silicon

Abstract: This paper deals with an electron-paramagnetic-resonance study of the $\mathrm{Si}\ensuremath{-}B3$ center, which was first reported by Daly. The $\mathrm{Si}\ensuremath{-}B3$ center is a secondary defect which forms upon annealing between 50 and 175\ifmmode^\circ\else\textdegree\fi{}C in irradiated boron-doped silicon and is stable up to $\ensuremath{\approx}500$\ifmmode^\circ\else\textdegree\fi{}C. Our studies indicate that the $\mathrm{Si}\ensuremath{-}B3$ center exhibits only a high-temperature stress response which is indicative of a thermally activated atomic reorientation at $T\ensuremath{\gtrsim}400$\ifmmode^\circ\else\textdegree\fi{}C. This defect does not exhibit a low-temperature stress response indicative of Jahn-Teller effects; consequently, the $\mathrm{Si}\ensuremath{-}B3$ center has inherent ${D}_{2d}$ symmetry by virtue of its molecular structure. The kinetics of this defect, the nature of the $^{29}\mathrm{Si}$ hyperfine interactions, and the symmetry of the defect suggest that the $\mathrm{Si}\ensuremath{-}B3$ corresponds to either a $〈001〉$ Si di-interstitial or a $〈001〉$ Si split interstitial. The $\mathrm{Si}\ensuremath{-}B3$ center appears to be similar but not identical to the $\mathrm{Si}P6$ center, which Lee and Corbett have recently suggested corresponds to a $〈001〉$ Si di-interstitial.

Enhanced low-temperature sintering of tungsten

Abstract: The effects of various transition metal additions on the sintering of a well-characterized, fine tungsten powder were analyzed using both isothermal and constant heating rate experiments in the temperature range 900 to 1400°C. Approximately four atomic mono-layers of palladium on the tungsten powder surface were found to be the optimal enhancer, followed by nickel, cobalt, platinum, and iron. The addition of Cu to the tungsten had no appreciable effect on the sintering kinetics. Sintering enhancement by these transition metals is related to their periodic chart position (i.e., electron structure). An overall non-Arrhenius shrinkage temperature dependence is attributed to grain growth in the activator-treated specimens. The activation energy for tungsten densification was determined to be 430 to 450 kJ/mol, which is in general agreement with a grain boundary diffusion process.

Global Error Estimates for Ordinary Differential Equations

Abstract: The user of a code for solving the initial value problem for ordinary differential equations is normally interested in the global error, i.e. the difference between the solution of the problem posed and the numerical result returned by the code. This paper describes a way of estimating the global error reliably while still solving the problem with acceptable efficiency. Global extrapolation procedures are applied to parallel solutions obtained by a Runge-Kutta-Fehlberg method. These ideas are implemented in a Fortran program called GERK, which is ACM Algomthm 504.

Effects of the Pauli principle on electron scattering by open‐shell targets

Abstract: The semiclassical exchange approximation and two free‐electron–gas exchange approximations are applied to electron scattering from the hydrogen atom. In the triplet spin state the results are similar to our previous findings [M. E. Riley and D. G. Truhlar, J. Chem. Phys. 63, 2182 (1975)] for electron scattering by closed‐shell atoms. However these results, already of useful accuracy, are improved by the inclusion of one‐electron exchange terms or an orthogonality constraint. For the singlet spin state it is essential to include the one‐electron exchange terms except at high impact energies (greater than about 50 eV). The approximation of Lippmann, Schey, Burke, and Chandra for treating exchange in closed‐shell systems is tested and found to be less accurate than the present approximations.

Exact microscopic theory of surface contributions to the reflectivity of a jellium solid

Abstract: Exact microscopic formulas are derived for the surface optical properties of a jellium solid. The comparison of these formulas to those derived classically by McIntyre and Aspnes shows that for $s$-polarized light, the parametrization of surface-reflectance data using the classical theory is a valid procedure, but that for $p$-polarized light, because short-wavelength fields are induced in the surface region, the classical assumption of local dielectric response is invalid, and thus the classical prescription for parametrizing surface reflectance data is unphysical.

The turbulent radial jet

Abstract: A hot-film anemometer has been used to investigate the mean velocity and turbulence intensity distributions in turbulent radial jets. A geometric parameter termed the constraint ratio, defined as the ratio of nozzle diameter to separation distance, is shown to characterize radial-jet behaviour. Large values of the constraint ratio typify ‘constrained’ radial jets, for which the nozzle walls constrain the flow leaving the orifice to be parallel; a small constraint ratio is representative of two opposing free axisymmetric jets, the collision of which produces an ‘impinged’ radial jet. It is found that the well-behaved constrained radial jet spreads at the same rate as does the familiar plane jet, whereas the impinged radial jet spreads at a rate more than three times as fast. Neither type of radial jet is amenable to a self-similar analytic solution; however, while the impinged jet is shown to require numerical solution techniques, an empirical solution for the constrained jet is demonstrated.

Influence of the electronic structure on the titanium-vanadium-hydrogen phase diagram☆☆☆

Abstract: Calculations have been carried out for cubic TiH 2 and VH 2 and the tetragonally-distorted TiH 2 in an attempt to explain the phase diagram of the TiVH system. The calculations demonstrate that the distortion is caused by the existence of degenerate states at the Fermi level, degeneracy of which is lifted by the tetragonal distortion- -an example of the Jahn-Teller effect in a metal. The effect of varying vanadium concentration and varying hydrogen concentration on the position of the phase boundaries is discussed in terms of the calculated results.

Series analysis of corrections to scaling for the spin-pair correlations of the spin-s Ising model: Confluent singularities, universality, and hyperscaling

Abstract: We report a detailed study of twelve-term, high-temperature series for the second moment of spin-pair correlations ${\ensuremath{\mu}}_{2}(t)$ and the specific heat ${c}_{H}(t)$ of the nearest-neighbor spin-$s$ Ising model in zero magnetic field on the fcc lattice. Near criticality we find ${\ensuremath{\mu}}_{2}(t)={A}_{2}(s)t{(s)}^{\ensuremath{-}(\ensuremath{\gamma}+2\ensuremath{ u})}[1 + {B}_{2}(s)t{(s)}^{{\ensuremath{\Delta}}_{1}}+ \ensuremath{\cdots}]$, {$t(s)=\frac{[T\ensuremath{-}{T}_{c}(s)]}{T}$}, showing a confluent correction to the dominant scaling singularity. To within uncertainties the exponents have the universal (i.e., spin-independent) values $\ensuremath{ u}={0.638}_{\ensuremath{-}0.008}^{+0.002}$ (with $\ensuremath{\gamma}={1.250}_{\ensuremath{-}0.007}^{+0.003}$) and ${\ensuremath{\Delta}}_{1}=0.6\ifmmode\pm\else\textpm\fi{}0.1$. The confluent exponent ${\ensuremath{\Delta}}_{1}$ is in reasonable agreement with the correction-to-scaling index derived from earlier analysis of the susceptibility, as predicted by renormalization-group arguments. A similar analysis of the specific heat ${c}_{H}$ for the same model finds no detectable confluent singularities in rather noisy, high-temperature series and gives $\ensuremath{\alpha}=0.125\ifmmode\pm\else\textpm\fi{}0.020$ in general confirmation of earlier $s=\frac{1}{2}$ estimates. With $\ensuremath{ u}$ as quoted above the hyperscaling relation $d\ensuremath{ u}=2\ensuremath{-}\ensuremath{\alpha}$ at $d=3$ requires $\ensuremath{\alpha}={0.086}_{\ensuremath{-}0.006}^{+0.024}$ so the validity of hyperscaling remains problematical.

Modeling of enhanced diffusion under ion irradiation

Abstract: The differential equations which govern enhanced diffusion under ion irradiation are solved using recently developed numerical techniques. Accurate time‐dependent profiles for vacancies, interstitials, and diffusing atoms are generated thereby with minimal computer time. The theoretical description is improved further by incorporating refined calculations of the atomic displacement rate by energetic ions. Three representative cases of enhanced diffusion are treated in detail: Al diffusion in Al under 100‐keV Al irradiation, Al diffusion in Al under uniform irradiation, and W diffusion in W under 100‐keV proton irradiation. It is shown that more information may be obtained from the diffused atomic profiles if the irradiation damage rate varies with depth in a known way over the diffusion region. Under this condition, both the shape and the time dependence of the atomic profile are sensitive to the rate coefficient for point‐defect annihilation. When the annihilation coefficient is so determined, the point‐...

Effects of contamination on the interaction of hydrogen gas with palladium: A review

Abstract: The role of contamination in the interaction of hydrogen gas with palladium is reviewed. Emphasis has been placed on correlation of the fragmentary information available in the palladium literature. Several different types of contamination problems are described; general precautions, palladium treatments, and hydrogen-gas purification procedures for the minimization of the problems are detailed. Finally, specific recommendations for future work are outlined.

Helium Migration in Sodium Aluminosilicate Glasses

Abstract: Helium permeation, diffusion, and solubility have been measured for a number of sodium aluminosilicate glasses. The results indicate that a major change in the glass structure occurs when the alumina-to-soda ratio exceeds unity. It also appears that small substitutions of alumina (Al/Na<0.5) have a different effect on the glass structure than do larger (0.5

Lattice-site location of ion-implanted impurities in copper and other fcc metals

Abstract: The backscattering-channeling technique has been used to study the lattice location of various heavy atoms implanted in a channeling direction to high doses in copper and other fcc metals Gold implanted into Cu, Pd, and Ag is found to be (100 \ifmmode\pm\else\textpm\fi{} 1)% on substitutional sites (in Ni, Au is 96% substitutional) Investigations of the lattice location of heavy metallic atoms implanted in Cu (Ag, Sb, W, Pt, Au, Hg, Tl, Pb, and Bi) show that these impurities occupy with a high probability (\ensuremath{\ge} 60%) regular fcc lattice sites for atomic concentrations \ensuremath{\lesssim} 1% In contrast, I shows a lower probability for occupying Cu lattice sites and the substitutionality is a function of depth, whereas Xe is entirely nonsubstitutional There is no implantation temperature dependence of the substitutionality of Au, W, or Xe in Cu between 15 K and room temperature These results are compared with criteria such as the size, electronegativity, and the binary phase diagrams of the implanted systems involved, but it is concluded that the final position of metallic atoms is determined mainly by nonequilibrium processes occurring near the end of the ion range For atomic concentrations g 10%, Au remains 100% substitutional in Cu but W produces a highly disordered layer in which the W atoms occupy no regular lattice site Low levels of damage are seen in the host copper crystals after high-dose channeled implantations of heavy ions The results indicate an absence of displaced host atoms and a layer of dechanneling centers which is approximately coincident in depth with the implanted species These results suggest that lattice strain around the implanted atoms is the major cause of dechanneling