Showing papers by "Sandia National Laboratories published in 1986"
TL;DR: A consistent set of embedding functions and pair interactions for use with the embedded-atom method was determined empirically by fitting to the sublimation energy, equilibrium lattice constant, elastic constants, and vacancy-formation energies of the pure metals and the heats of solution of the binary alloys as discussed by the authors.
Abstract: A consistent set of embedding functions and pair interactions for use with the embedded-atom method [M.S. Daw and M. I. Baskes, Phys. Rev. B 29, 6443 (1984)] have been determined empirically to describe the fcc metals Cu, Ag, Au, Ni, Pd, and Pt as well as alloys containing these metals. The functions are determined empirically by fitting to the sublimation energy, equilibrium lattice constant, elastic constants, and vacancy-formation energies of the pure metals and the heats of solution of the binary alloys. The validity of the functions is tested by computing a wide range of properties: the formation volume and migration energy of vacancies, the formation energy, formation volume, and migration energy of divacancies and self-interstitials, the surface energy and geometries of the low-index surfaces of the pure metals, and the segregation energy of substitutional impurities to (100) surfaces.
3,734 citations
TL;DR: In this article, a two-phase mixture theory is presented which describes the deflagration-to-detonation transition (DDT) in reactive granular materials, based on the continuum theory of mixtures formulated to include the compressibility of all phases and the compaction behavior of the granular material.
1,155 citations
TL;DR: In this article, the authors show that non-explosive eruption of lava appears to result from rapid, sub-surface gas release from magma ascending as a permeable foam.
Abstract: Silicic magma can erupt quietly, as vapour-poor lava, despite petrological evidence that it once contained ample dissolved water to drive violent venting of tephra. Non-explosive eruption of lava appears to result from rapid, sub-surface gas release from magma ascending as a permeable foam. The degassed foam then collapses during extrusion. Conditions of shallow ascent, rather than pre-eruption volatile concentrations, control eruptive behaviour.
582 citations
TL;DR: In this paper, the kinetics of the CO-O2 and CO-NO reactions over single crystal Rh(111) and over alumina-supported Rh catalysts have been compared at realistic reactant pressures.
444 citations
TL;DR: In this article, a method to calculate the first-order sensitivities of the mole fractions and temperature with respect to the rate constants is discussed and applied to nitric oxide production in the presence of hydrocarbons.
410 citations
TL;DR: Using small-angle x-ray scattering, it is shown that porous silica aerogel has a fractal backbone structure that is traced to the underlying chemical and physical growth processes.
Abstract: Using small-angle x-ray scattering, we show that porous silica aerogel has a fractal backbone structure. The observed structure is traced to the underlying chemical (polymerization) and physical (colloid aggregation) growth processes. Comparison of scattering curves for aerogel with silica aggregates confirms this interpretation.
401 citations
TL;DR: In this article, the authors developed a computational constitutive model which simulates the dynamic fracture behavior of brittle rock, where the damage mechanism has been attributed to the micro-cracking in the rock medium.
Abstract: This paper is concerned with the development of a computational constitutive model which simulates the dynamic fracture behavior of brittle rock. The essential feature of this model is the treatment of the dynamic fracture process in rock as a continuous accrual of damage, where the damage mechanism has been attributed to the microcracking in the rock medium. Detailed descriptions of the model and its numerical implementation are given. A method is presented for determining the three additional material constants governing the damage accumulation. All of the numerical algorithms are amenable to vectorization for a vector processing computer and the model is computationally very efficient. A numerical example of an oil-shale blasting experiment is presented and compared to field observations. Results demonstrate that the model is applicable to the prediction of dynamic rock-fracture behavior.
325 citations
TL;DR: Hall-petch strengthening has been observed for the microhardness of electrodeposited nickel material extending to a finest grain diameter of approximately 12 nm as mentioned in this paper, which is the smallest grain size known.
292 citations
TL;DR: In this paper, stable state two-dimensional results obtained from numerical solutions to the transient Navier-Stokes equations are given for laminar convective motion of a gas in an enclosed vertical slot with large horizontal temperature differences.
Abstract: Steady-state two-dimensional results obtained from numerical solutions to the transient Navier-Stokes equations are given for laminar convective motion of a gas in an enclosed vertical slot with large horizontal temperature differences. We present results for air using the ideal-gas law and Sutherland-law transport properties, although the results are also valid for hydrogen. Wide ranges of aspect-ratio, Rayleigh-number and temperature-difference parameters are examined. The results are compared in detail with the exact solution in the conduction and fully developed merged boundary-layer limits for arbitrary temperature difference, and to the well-established Boussinesq limit for small temperature difference. It is found that the static pressure, and temperature and velocity distributions are very sensitive to property variations, even though the average heat flux is not. In addition we observe a net vertical heat flux to be the same as that obtained from the Boussinesq equations. We concentrate on the boundary-layer regime, but we present a rather complete picture of different flow regimes in Rayleigh-number, aspect-ratio and temperaturedifference parameter space. We observe that, with increasing temperature difference, lower critical Rayleigh numbers for stationary and oscillatory instabilities are obtained. In addition we observe that in some cases the physical nature of the instability changes with increasing temperature difference.
253 citations
01 Jan 1986
TL;DR: The first surface acoustic wave (SAW) sensor that functions via changes in conductivity of a thin surface film is reported in this article, where a lead phthalocyanine (PbPc) thin film is deposited on the acoustic propagation path of a LiNbO 3 SAW delay line, which serves as the feedback element of an oscillator circuit.
Abstract: The first surface acoustic wave (SAW) sensor that functions via changes in conductivity of a thin surface film is reported. A lead phthalocyanine (PbPc) thin film is deposited on the acoustic propagation path of a LiNbO 3 SAW delay line, which serves as the feedback element of an oscillator circuit. Reaction with strongly oxidizing gases, in particular NO 2 , increases the conductivity of the PbPc film. Acousto-electric coupling of the traveling electric potential wave associated with the SAW to charge carriers in the PbPc film slows the acoustic wave velocity, altering the oscillation frequency of the circuit. This sensor is about 1000 times more sensitive, in terms of the number of NO 2 molecules that can be detected (10 16 molecules/cm 3 of PbPc film), than an identical SAW sensor functioning via mass loading would be. Sensitivity to a few ppm of NO 2 in N 2 has been demonstrated.
245 citations
TL;DR: In this article, both experimental measurements and a theoretical model for the thermal conductivity of a consolidated mixture of two-metal powders were presented, and the authors applied the technique of volume averaging to produce working equations applicable to the general problem of thermal conduction through mixtures.
TL;DR: This algorithm is a package of subroutines for Computing Bessel functions for orders v and complex z in −πz) and their double-precision counterparts are provided.
Abstract: This algorithm is a package of subroutines for Computing Bessel functions Hv(1)(z), Hv(2)(z), Iv(z), Jv(z), Kv(z), Yv(z) and Airy functions Ai(z), Ai′(z), Bi(z), Bi′(z) for ordersv≥0 and complex z in −p
TL;DR: In this paper, a new chemical process capable of completely removing NOx from the products of combustion is described, and the effectiveness of this process is established in flow tube experiments, and it is shown that this process for rapid reduction of nitrogen oxides could play a major role in controlling NOx emissions from most combustion devices.
Abstract: Nitrogen oxides (NOx) play a major role in the formation of photochemical smog and in acid rain production1. Some progress has been made in reducing NOx emissions through the use of combustion and exhaust control schemes, including three-way catalyst, staged combustion, and ammonia injection. Nevertheless, estimates indicate that the production of nitrogen oxides will continue to increase until the end of the century and beyond, if current trends continue2. We describe here a new chemical process capable of completely removing NOx from the products of combustion. The effectiveness of this process is established in flow tube experiments. Further, we demonstrate the practical feasibility of this method by eliminating NOx from a portion of the exhaust from a single-cylinder diesel engine. Based on these results we conclude that this process for rapid reduction of nitrogen oxides could play a major role in controlling NOx emissions from most combustion devices.
TL;DR: In this article, high-resolution inverse Raman spectroscopy measurements of nitrogen Q-branch linewidths in pure nitrogen at temperatures up to 1500 K and at pressures from 20 to 760 Torr were reported.
Abstract: We report high-resolution inverse Raman spectroscopy measurements of nitrogen Q-branch linewidths in pure nitrogen at temperatures up to 1500 K and at pressures from 20 to 760 Torr. Transitions from J = 0 to J = 30 have been measured with a resolution of 1.5 × 10−3 cm−1 and a Raman shift accuracy of 1 × 10−3 cm−1. Fits to the data using a Galatry line-shape model provide J-dependent collisional-broadening coefficients. A modified exponential-gap scaling law accurately describes the dependence of these coefficients on temperature and rotational quantum number.
TL;DR: In situ Raman spectroscopy and cyclic voltammetry have been used simultaneously to study anodic film growth and dissolution on Cu and Ag in strongly alkaline solution as mentioned in this paper.
Abstract: In situ Raman spectroscopy and cyclic voltammetry have been used simultaneously to study anodic film growth and dissolution on Cu and Ag in strongly alkaline solution. On copper, Cu/sub 2/O and another species, believed to be a hydroxide, were detected spectroscopically during anodic film formation. Raman spectra of electrochemically formed hydroxides on copper have not previously been reported. On silver, AgO was detected. Neither CuO nor Ag/sub 2/O was observed by Raman spectroscopy, although for certain potentials. AgO was apparently produced by photochemical conversion of Ag/sub 2/O. Experiments were performed using both the 488 nm line from an argon laser and the 647.1 nm line from a krypton laser. It was concluded that the detection of these thin film oxides was by spontaneous or resonant Raman scattering and did not involve surface enhanced Raman scattering (SERS).
TL;DR: In this paper, the structure of a two-dimensional, axisymmetric, laminar methane-air diffusion flame with detailed transport and finite rate chemical kinetics is investigated, where a cylindrical fuel stream is surrounded by a coflowing oxidizer jet.
Abstract: We investigate computationally the structure of a two-dimensional, axisymmetric, laminar methane-air diffusion flame with detailed transport and finite rate chemical kinetics. We consider flames in which a cylindrical fuel stream is surrounded by a coflowing oxidizer jet. Unlike some models in which diffusion in the axial direction is neglected, we treat the fully elliptic problem. A discrete solution is obtained on a two-dimensional grid by combining a steady-state and a time-dependent solution method. A time- dependent approach is used to help obtain a converged numerical solution on an initial coarse grid using a flame sheet starting estimate. Grid points are then inserted adaptively and Newton’s method is used to complete the problem.
TL;DR: In this article, the welding metallurgy of HASTELLOY* alloys C-4, C-22, and C-276 has been determined, and an equivalent chemistry model is proposed to account for the microstructures observed in each alloy's weld metal.
Abstract: The welding metallurgy (solidification and solid state transformations) of HASTELLOY* Alloys C-4, C-22, and C-276 has been determined. Varestraint hot-cracking tests performed on commercial alloys revealed a weldability ranking as follows: C-4 > C-22 > C-276. All alloys would be expected to have good weldability, with Alloy C-4 having a very low hot-cracking tendency, comparable to 304L stainless steel. Microstructures of gas-tungsten-arc welds of these alloys have been characterized by scanning electron microscopy and analytical electron microscopy. Intermetallic secondary solidification constituents have been found associated with weld metal hot cracks in Alloys C-276 and C-22. In Alloy C-276, this constituent is a combination ofP and ώ phases, and in Alloy C-22, this constituent is composed of σ,P, and ώ phases. With phase composition data obtained by AEM techniques and available ternary (Ni-Cr-Mo) phase diagrams, an equivalent chemistry model is proposed to account for the microstructures observed in each alloy's weld metal.
TL;DR: ITS as discussed by the authors is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-integrated coupled electron/photon radiation transport problems.
Abstract: ITS is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-integrated coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence Our goal has been to simultaneously maximize operational simplicity and physical accuracy Through a machine portable utility that emulates the basic features of the CDC UPDATE processor, the user selects one of eight codes for running on a machine of one of four (at least) major vendors The ease with which this utility is applied combines with an input scheme based on order-independent descriptive keywords that makes maximum use of defaults and internal error checking to provide experimentalists and theorists alike with a method for the routine but rigorous solution of sophisticated radiation transport problems Physical rigor is maximized by employing the best available cross sections and sampling distributions, and the most complete physical model for describing the production and transport of the electron/photon cascade from 10 GeV down to 10 keV Flexibility of construction permits the more sophisticated user to tailor the codes to specific applications and to extend the capabilities of the codes to more complex applications through simple update procedures
TL;DR: Using small-angle x-ray scattering, a simple model is developed which both is consistent with silicate chemistry and generates fractally rough structures in solution and in a porous solid made from the solution precursor.
Abstract: We report the growth and structure of fractally rough silicate particles in solution. Using small-angle x-ray scattering, we find fractal surfaces both in solution and in a porous solid made from the solution precursor. Finally, we develop a simple model which both is consistent with silicate chemistry and generates fractally rough structures.
TL;DR: In this article, the adsorption and growth of Cu films on the Ru(0001) surface were studied by work function measurements, low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and thermal programmed desorption (TPD).
TL;DR: The dependence of the nonequilibrium partition coefficient k of Bi in Si upon solidification velocity v has been measured with sufficient accuracy to distinguish between proposed solute-trapping mechanisms.
Abstract: The dependence of the nonequilibrium partition coefficient $k$ of Bi in Si upon solidification velocity $v$ has been measured with sufficient accuracy to distinguish between proposed solute-trapping mechanisms. For the range of measured velocities, 2-14 m/s, we observe a much more gradual increase in $k$ with increasing $v$ than those previously reported and no evidence for a "saturation" effect, i.e., $\frac{\mathrm{dk}}{\mathrm{dv}}\ensuremath{\rightarrow}0$ at $kl1$. The continuous-growth model of Aziz fits the data quite well; the Aziz stepwise-growth model and the two-level Baker model yield values of $\frac{\mathrm{dk}}{\mathrm{dv}}$ that are too high.
TL;DR: The Particle Beam Fusion Accelerator II (PBFA II) is presently under construction and is the only existing facility with the potential of igniting thermonuclear fuel in the laboratory.
Abstract: The Particle Beam Fusion Accelerator II (PBFA II) is presently under construction and is the only existing facility with the potential of igniting thermonuclear fuel in the laboratory. The accelerator will generate up to 5 megamperes of lithium ions at 30 million electron volts and will focus them onto an inertial confinement fusion (ICF) target after beam production and focusing have been optimized. Since its inception, the light ion approach to ICF has been considered the one that combines low cost, high risk, and high payoff. The beams are of such high density that their self-generated electric and magnetic fields were thought to prohibit high focal intensities. Recent advances in beam production and focusing demonstrate that these self-forces can be controlled to the degree required for ignition, break-even, and high gain experiments. ICF has been pursued primarily for its potential military applications. However, the high efficiency and cost-effectiveness of the light ion approach enhance its potential for commercial energy application as well.
TL;DR: The leaching behavior of several sodium borosilicate glasses has been characterized using a combination of pH stat titrations, elemental solution analyses, elemental depth profiling via elastic recoil detection analysis and Rutherford backscattering.
Abstract: The leaching behavior of several sodium borosilicate glasses has been characterized using a combination of pH stat titrations. elemental solution analyses, elemental depth profiling via elastic recoil detection analysis and Rutherford backscattering. sodium diffusion measurements, and 11B NMR measurements on both leached and unleached glass. Leaching results indicate that the molecular structure of the glass controls glass dissolution by establishing the distribution of ion exchange sites, hydrolysis sites, and the access of water to those sitas. There is no correlation between sodium leaching and sodium diffusion in the unaltered glass. For most borosilicates in most environments, network hydrolysis controls the kinetics of glass dissolution.
TL;DR: An adaptive IIR structure for processing a sinusoidal signal in broad-band noise is introduced that contains three adaptive processors, each of which is computationally very simple.
Abstract: An adaptive IIR structure for processing a sinusoidal signal in broad-band noise is introduced. The structure contains three adaptive processors, each of which is computationally very simple. Useful features of the structure include enhancement, frequency estimation, and detection.
TL;DR: The need for a fast, sensitive method of measuring IDD during each test vector is examined and problems confronting CMOS IC designers, test engineers and test instrumentation designers as they work to meet these demands are discussed.
Abstract: Gate oxide shorts are defects that must be detected to produce high-reliability ICs. These problems will continue as devices are scaled down and oxide thicknesses are reduced to the 100-A range. Complete detection of gate oxide shorts and other CMOS failure mechanisms requires measuring the IDD current during the quiescent state after each test vector is applied to the IC. A 100-percent stuck-at fault test set is effective only if each test vector is accompanied by an IDD measurement. This article examines the need for a fast, sensitive method of measuring IDD during each test vector and discusses problems confronting CMOS IC designers, test engineers and test instrumentation designers as they work to meet these demands.
TL;DR: The interesting structural and electronic properties of superlattices are reviewed in this paper, where the authors consider the case of a strained-layer super lattice with a single lattice.
Abstract: The interesting structural and electronic properties of strained-layer superlattices are briefly reviewed.
TL;DR: Based on structural studies of cyclic model compounds and MO calculations of ring strain energies, the authors concluded that 3 and 4-fold siloxane rings are responsible for the strong Raman bands at 608 and 490 cm−1, respectively.
Abstract: Raman spectroscopy and DSC were used to determine the structure and average heat of formation of siloxane species formed during the gel-to-glass conversion. Based on structural studies of cyclic model compounds and MO calculations of ring strain energies, we conclude that 3 and 4-fold siloxane rings are responsible for the strong Raman bands at 608 and 490 cm−1, respectively.
TL;DR: In this article, the authors developed closed-form solutions for forces on projectiles that penetrated geological targets using a linear hydrostat and a Mohr-Coulomb failure criterion with a tension cutoff.
TL;DR: The hydrogen uptake kinetics in the ..cap alpha..-phase region are found to be rate limited by diffusion of atomic H into the bulk rather than by dissociative chemisorption of H/sub 2/ at the surface as previously reported.
Abstract: A coupled high-pressure--ultrahigh-vacuum technique is employed to make the first kinetic measurements of high-pressure hydrogen absorption through an atomically clean palladium surface, Pd(110). The hydrogen uptake kinetics in the \ensuremath{\alpha}-phase region are found to be rate limited by diffusion of atomic H into the bulk rather than by dissociative chemisorption of ${\mathrm{H}}_{2}$ at the surface as previously reported. Our findings strongly suggest that previous high-pressure measurements of hydrogen absorption by palladium may be suspect due to uncharacterized surface contamination. The bulk diffusivity of hydrogen in palladium determined in this study has an activation barrier of 5.39\ifmmode\pm\else\textpm\fi{}0.30 kcal/mol with a preexponential factor of (2.83\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{2}$/s.