scispace - formally typeset
Search or ask a question

Showing papers by "Sandia National Laboratories published in 1975"


Journal ArticleDOI
TL;DR: Applications of gradient estimation to pattern recognition are presented using clustering and intrinsic dimensionality problems, with the ultimate goal of providing further understanding of these problems in terms of density gradients.
Abstract: Nonparametric density gradient estimation using a generalized kernel approach is investigated. Conditions on the kernel functions are derived to guarantee asymptotic unbiasedness, consistency, and uniform consistency of the estimates. The results are generalized to obtain a simple mcan-shift estimate that can be extended in a k -nearest-neighbor approach. Applications of gradient estimation to pattern recognition are presented using clustering and intrinsic dimensionality problems, with the ultimate goal of providing further understanding of these problems in terms of density gradients.

3,125 citations


Journal ArticleDOI
TL;DR: The Hartree-Fock wavefunctions were used in the numerical calculations for atomic numbers 1 ≤ Z ≤ 36 and relativistic Dirac-Hartree Fock wave functions for atomic number 36 ≤ Z ≥ 102.

734 citations



Journal ArticleDOI
TL;DR: In this paper, four new exchange potentials (the semiclassical exchange approximation, the asymptotically adjusted free-electron-gas approximation, second-order freeelectron gas approximation, and high-energy exchange approximation) are derived.
Abstract: Four new exchange potentials (the semiclassical exchange approximation, the asymptotically adjusted free‐electron–gas exchange approximation, the second‐order free‐electron–gas exchange approximation, and the high‐energy exchange approximation) are derived. Calculations are performed for elastic electron scattering from helium and argon. The results are compared to one another and to calculations using Hara’s free‐electron–gas approximation and the exact nonlocal exchange potential. Three of the approximations to exchange are in good agreement with the exact exchange —except at very low energy— but are much easier to use. Thus they should be very useful in electron–atom and electron–molecule scattering calculations.

367 citations


Journal ArticleDOI
TL;DR: In this paper, a fluid-transport calculation by computer simulation, via nonequilibrium molecular dynamics, of laboratory methods of transport measurement is described, and a new fluid perturbation theory of transport is described.
Abstract: A novel fluid-transport calculation by computer simulation, via nonequilibrium molecular dynamics, of laboratory methods of transport measurement is described. Shear viscosity of soft-sphere (${r}^{\ensuremath{-}12}$ potential) and Lennard-Jones particles (${r}^{\ensuremath{-}12}\ensuremath{-}{r}^{\ensuremath{-}6}$ potential) has been obtained from molecular dynamic modeling of Couette flow. Soft-sphere deviations from Enskog theory are similar to those found for hard spheres by Alder, Gass, and Wainwright, using time-correlations of equilibrium molecular dynamic system fluctuations. For the Lennard-Jones shear viscosity near the triple-point region, there is agreement between the equilibrium calculation of Levesque, Verlet, and Kurkijarvi and the nonequilibrium results using 108 atoms in a cube. However, systems two and three cubes wide give lower results, which, when extrapolated with inverse width, yield close agreement with the experimental argon shear viscosity. Comparison of the Lennard-Jones shear viscosity with experimental argon data along the saturated vapor-pressure line of argon confirms our successful simulation of macroscopic viscous flow with few-particle nonequilibrium molecular dynamic systems. A new result of the nonequilibrium molecular dynamics is the characterization of nonequilibrium distribution functions, which might provide the basis for a perturbation theory of transport. Since momentum transport is primarily accomplished by the repulsive potential core for high temperatures, the Lennard-Jones shear viscosity must behave like the soft-sphere system for high temperatures [viscosity divided by ${(\mathrm{t}\mathrm{e}\mathrm{m}\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e})}^{\frac{2}{3}}$ is a function of density divided by ${(\mathrm{temperature})}^{\mathrm{\textonequarter{}}}$]. In fact, the calculated excess shear viscosity (that part above the zero-density temperature dependence) has been successfully correlated in terms of the 12th-power scaling variables for temperatures as low as the critical value (along the freezing line). The utilization of soft-sphere scaling variables yields relatively simple functions for describing both the excess shear viscosity and the thermal-conductivity behavior throughout the fluid phase. The introduction of these scaling variables also clearly reveals two features: (i) weak temperature dependence, and (ii) the sign of the temperature derivative at constant density (negative for shear viscosity and positive for thermal conductivity). While both of these features have been experimentally observed in simple fluid experimental data, their cause has not been previously traced to the dominance of the core potential. Thus, the soft-sphere scaling variables should be useful for correlating experimental data.

331 citations


Journal ArticleDOI
TL;DR: In this paper, an extensive calculation of the optical-phonon-assisted transition rates for non-adiabatic electronic hopping motion in a solid is presented, which involves no restrictions on either the magnitude of the electron-lattice coupling strength, the temperature or the difference between the electronic energies of the initial and final sites.
Abstract: An extensive calculation of the optical-phonon-assisted transition rates for non-adiabatic electronic hopping motion in a solid is presented. Holstein's Molecular Crystal Model is used as a basis for study and the computation involves no restrictions on either the magnitude of the electron-lattice coupling strength, the temperature, or the difference between the electronic energies of the initial and final sites. In the strong-coupling small-polaron regime, the jump rates, associated d.c. conductivity, a.c. conductivity, and electric-field dependence of the d.c. conductivity, for a crystal are all calculated. These transport properties manifest qualitatively distinct behaviours corresponding to whether the temperature is above or well below the optical-phonon temperature. In the low-temperature regime the energy-conserving processes which involve the absorption of the minimum amount of vibrational energy provide the dominant contribution to the thermally activated jump rates. At sufficiently high...

287 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented the results of the first comprehensive two-dimensional numerical analysis of the split Hopkinson pressure bar and quantitatively described the effects of realistic friction and of variations in both the specimen geometry and the imposed strain-rate on the validity of the assumptions used in analyzing experimental data.
Abstract: T he split Hopkinson pressure bar is widely used to measure the dynamic properties of solid materials. This paper presents the results of the first comprehensive two-dimensional numerical analysis of the technique, and quantitatively describes the effects of realistic friction and of variations in both the specimen geometry and the imposed strain-rate on the validity of the assumptions used in analyzing experimental data. A two-dimensional axisymmetric numerical analysis is used to compute all components of the stress, strain and strain-rate tensors at each mesh point within the specimen and the elastic bars. The calculated response of the pressure bars is used to reconstruct the stress-strain behavior of the specimen and this is compared to both the input stress-strain curve and the actual calculated stress-strain states in the specimen. Thus, the validity of the assumptions and the corrections used in the analysis of the data is determined. Inertia and friction between the specimen and the elastic bars affect the response of the specimen differently for different length-to-diameter ratios. Inertia effects produce stress waves propagating radially and axially in the specimen and may result in an oscillating reconstructed stress-strain curve. If the ends of the specimen are well lubricated and care is taken to minimize the effects of inertia, the reconstructed stress-strain curve agrees with the input. However, serious stress and strain nonuniformity exists when the ends are not lubricated and this results in a reconstructed stress-strain curve where, for any given strain, the stress magnitude is larger than the correct value. A comparison of the calculations with experiment shows excellent agreement for various interface conditions. Finally, the inertia correction of E.D.H. Davies and S.C. Hunter (1963) is found to be reasonable.

234 citations


Journal ArticleDOI
TL;DR: In this article, the transition temperature decreases with hydrostatic pressure for those transitions associated with soft zone-center optic phonons and increases for those transition associated with the soft zone boundary optic phonon.
Abstract: On the basis of an analysis of data on a large number of compounds exhibiting displacive phase transitions, it is observed (with no known exceptions) that the transition temperature decreases with hydrostatic pressure for those transitions associated with soft zone-center optic phonons and increases for those transitions associated with soft zone-boundary optic phonons. This difference in behavior is tentatively interpreted in terms of a reversal in the roles of the short-range and long-range forces in the lattice dynamics of the two cases.

219 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of processing steps on the radiation hardness of MOS devices have been systematically investigated, where quantitative relationships between the radiation-induced voltage shifts and processing parameters have been determined, where possible.
Abstract: The effects of processing steps on the radiation hardness of MOS devices have been systematically investigated. Quantitative relationships between the radiation-induced voltage shifts and processing parameters have been determined, where possible. Using the results of process optimization, a controlled baseline fabrication process for aluminum-gate CMOS has been defined. CMOS inverters which can survive radiation exposures well in excess of 108 rads (Si) have been fabricated. Restrictions that the observed physical dependences place upon possible models for the traps responsible for radiation-induced charging in SiO2 are discussed.

190 citations


Journal ArticleDOI
TL;DR: In this paper, the total elastic and momentum transfer cross sections for 24 selected elements are presented in tabular form in the energy range 1 to 256 keV at values of 2n keV.

188 citations


Journal ArticleDOI
TL;DR: In this paper, the inverse isotope effect in superconducting transition temperature is not simply a result of the relative volume of Pd and D. The lattice constants of the $\ensuremath{\beta}$ phase of the Pd phase were measured at 77 K using a powder x-ray diffraction technique.
Abstract: Lattice constants of the $\ensuremath{\beta}$ phase of $\mathrm{Pd}{\mathrm{H}}_{x}$ and $\mathrm{Pd}{\mathrm{D}}_{x}$ for the concentration range $0.8lxl0.98$ have been measured at 77 K using a powder x-ray diffraction technique. The lattice constant ${a}_{0}$ of $\mathrm{Pd}{\mathrm{H}}_{x}$ is slightly larger (\ensuremath{\sim} 0.1%) than that of $\mathrm{Pd}{\mathrm{D}}_{x}$ and $\frac{d\mathrm{ln}{a}_{0}}{\mathrm{dx}}=0.044$ for both $\mathrm{Pd}{\mathrm{H}}_{x}$ and $\mathrm{Pd}{\mathrm{D}}_{x}$; extrapolated ${a}_{0}$ values for $x=1.0$ are 4.090 and 4.084 A for PdH and PdD, respectively. This study shows that the inverse isotope effect in the superconducting transition temperature is not simply a result of the relative volume of $\mathrm{Pd}{\mathrm{H}}_{x}$ and $\mathrm{Pd}{\mathrm{D}}_{x}$.

Journal ArticleDOI
01 Jun 1975-Carbon
TL;DR: In this paper, the relations between chemical vapor deposition (CVD) parameters and the resultant pyrolytic carbon microstructures have been examined for matrix deposition in fibrous carbon substrates.

Journal ArticleDOI
TL;DR: Nonparametric estimation of the Bayes risk R^\ast using a k -nearest-neighbor ( k -NN) approach is investigated and the mean-squared error of the conditional Bayes error estimate is reduced significantly.
Abstract: Nonparametric estimation of the Bayes risk R^\ast using a k -nearest-neighbor ( k -NN) approach is investigated. Estimates of the conditional Bayes error r(X) for use in an unclassified test sample approach to estimate R^\ast are derived using maximum-likelihood estimation techniques. By using the volume information as well as the class representations of the k -NN's to X , the mean-squared error of the conditional Bayes error estimate is reduced significantly. Simulations are presented to indicate the performance of the estimates using unclassified testing samples.

Journal ArticleDOI
TL;DR: In this article, the behavior of implanted hydrogen in Si has been investigated by differential infrared transmittance measurements using multiple internal-reflection (MIR) plates, where seven absorption bands between 4.5 and 5.5 µm after implantation with 1016 H+/cm2 at ion energies between 70 and 400 keV.
Abstract: The behavior of implanted hydrogen in Si has been investigated by differential infrared transmittance measurements using multiple-internal-reflection (MIR) plates. Si-H bonding of implanted hydrogen is detected by seven absorption bands between 4.5 and 5.5 µm after implantation with 1016 H+/cm2 at ion energies between 70 and 400 keV. The absorption bands are close in frequency to those for SiH stretching modes for silane, and they are produced only by hydrogen implantation. Implantation with deuterium gave absorption bands shifted to lower frequencies in accord with the square root of the reduced mass ratio for Si-H relative to Si-D.


Journal ArticleDOI
TL;DR: In this article, the performance of A-286 stainless steel with small variations in chemistry were tested to assess whether the ductility performance of this type of stainless steel, which shows a ductility loss of about 48 pct when hydrogen charged, could be improved.
Abstract: Eleven alloys similar to commercial A-286 but with small variations in chemistry were tested to assess whether the performance of this type of stainless steel, which shows a ductility (RA) loss of about 48 pct when hydrogen charged, could be improved. It was found that removal of Mn resulted in anRA loss of only 15 pct; low Mn plus a 5 pct increase in Ni gave further improvement to 11 pctRA loss. Reductions in C, Si and B had little effect on theseRA losses. None of the above changes had significant effect on strength. Other chemistry changes were unsuccessful: additions of Al, Ti, Ti + Mo, or decreases in Ni, increased the ductility loss. Extensive examination of thin foils permitted a structural rationale for behavior in hydrogen in terms of the effects of second-phase particles on ductile fracture, particularly as affected by the misfit between the austenite and the γ’ precipitates. This rationale was consistent with fractographic observations.

Journal ArticleDOI
TL;DR: In this paper, an infinite elastic solid containing a double-periodic rectangular array of slit-like cracks is considered, and the cracks are represented as suitable distributions of dislocations which are determined from a singular integral equation.
Abstract: An infinite elastic solid containing a double-periodic rectangular array of slit-like cracks is considered. The solid is subjected to a uniform stress resulting in a state of plane strain. The cracks are represented as suitable distributions of dislocations which are determined from a singular integral equation. This equation is solved numerically in an efficient manner using an expansion of the non-singular part of the kernel in a series of Chebyshev polynomials. Values of the stress intensity factors are presented, as well as the change in strain energy due to the presence of the cracks. Also, the effective elastic constants of a sheet having a rectangular array of cracks are given as functions of the crack spacing.

Journal ArticleDOI
TL;DR: In this paper, the soft-mode Raman spectra of KDP in both the paraelectric (PE) and ferroelectric (FE) phases are reported, and the results demonstrate that the proton motion remains coupled to an optic mode of the lattice for $Tl{T}_{C}
Abstract: Measurements of the pressure and temperature dependences of the soft-mode Raman spectra of potassium dihydrogen phosphate (KDP) in both the paraelectric (PE) and ferroelectric (FE) phases are reported. The soft-mode response is overdamped throughout the PE phase at atmospheric pressure, but can be made underdamped with pressure in this phase. Measurements at high pressure in the PE phase where the response is underdamped therefore allow a more accurate determination of the parameters for the coupled-mode system than one can obtain from measurements at atmospheric pressure. Measurement of the pressure dependence in the FE phase allows one to identify the soft mode of the system in this phase, and the results demonstrate that the proton motion remains coupled to an optic mode of the lattice for $Tl{T}_{C}$. The temperature and pressure dependences of the microscopic parameters are examined within the framework of both the pure tunneling and the coupled proton-optic-mode models for the phase transition. It is found that the pure tunneling model is inadequate for a detailed description of the spectra, whereas the modified tunneling model, or coupled-mode model, gives a more quantitative description of the results. While this model can be used for quantitative comparison between the Raman scattering and dielectric measurements in these materials, there are inadequacies of the model in describing the microscopic interactions. These features are discussed in detail.

Journal ArticleDOI
TL;DR: In this article, the composites have a relatively high density (1.70 g/cm3), a crystallite size LC = 150 A and an interlayer spacing d002 = 3.35 A.
Abstract: Composites of boron nitride (BN) have been made by the chemical vapor deposition (CVD) of a BN matrix on a BN felt fiber substrate. Reactant gases were boron trifluoride and ammonia. The composites have a relatively high density (1.70 g/cm3), a crystallite size LC = 150 A and an interlayer spacing d002 = 3.35 A. Measurements of elastic modulus and thermal conductivity and expansion showed some anisotropy as a result of the preferred fiber orientation of the substrate.

Journal ArticleDOI
TL;DR: The thermocompression gold bonding process was found to be highly temperature dependent when organic films, which are barriers to metallic bonding, are present as discussed by the authors, and much of this temperature dependence could be eliminated by rernoving the contaminant films by uV radiation prior to thermocolompression bonding.
Abstract: The recent development of a microshear test has made possible the quantitative study of the effect of surface contamination on thermocompression ball bonding of gold to gold metallization. Contarninant films were characterized by Auger electron spectroscopy and low energy ion spectroscopy. The thermocompression gold bonding process was found to be highly temperature dependent when organic films, which are barriers to metallic bonding, are present. Much of this temperature dependence could.be eliminated by rernoving the contaminant films by uV radiation prior to thermocompression bonding. Post-heat treatment resulted in the growth of metallic bond inter'faces, presumably by sintering mechanisms.

Journal ArticleDOI
TL;DR: In this article, the performance of ion-beam: irradiated fusion targets consisting of a high-density spherical shell containing DT gas has been calculated and shown to be Breakeven with 10-MeV protons irradiating 1: 2mm-diam targets with a beam current around 10 MA.
Abstract: The performance of ion-beam: irradiated fusion targets consisting of a high-density spherical shell containing DT gas has been calculated. Breakeven with 10-MeV protons irradiating 1: 2-mm-diam targets can be produced with a beam current around 10 MA. Results for various target sizes and other beam particles and voltages are also discussed.

Journal ArticleDOI
TL;DR: In this article, a finite element scheme suitable for incompressible fluid flow in plane and axisymmetric geometries is constructed by using a Galerkin method, which can be used for problems with or without free surfaces.

Journal ArticleDOI
TL;DR: In this article, the crystal structure and atomic arrangement of uranyl acetate dihydrate, UO2(CH3COO)2·2H2O, have been determined by a single-crystal X-ray diffraction study.


Journal ArticleDOI
TL;DR: A theory of the thermoelectric power associated with electronic phonon-assisted tunneling motion between inequivalent sites has been developed in this paper, and general results have been applied to some prototype situations characteristic of hopping in disordered solids.
Abstract: A theory of the thermoelectric power associated with electronic phonon-assisted tunneling (hopping) motion between inequivalent sites has been developed. The general results have been applied to some prototype situations characteristic of hopping in disordered solids. (auth)

Journal ArticleDOI
TL;DR: Inelastic light scattering is used to study the dynamics of an ordered suspension of macromolecules as mentioned in this paper, and it has been shown that light scattering can be used to measure the inelastic properties of ordered suspensions.
Abstract: Inelastic light scattering is used to study the dynamics of an ordered suspension of macromolecules. (auth)

Journal ArticleDOI
TL;DR: In this paper, the response of low-density plasmas when subjected to the very high electric fields of relativistic-electron-beam-accelerator diodes was studied.
Abstract: A study has been made of the response of low-density (\ensuremath{\sim} ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) plasmas when subjected to the very high electric fields of relativistic-electron-beam-accelerator diodes. An anomalous resistive behavior has not been seen. Instead, sheath formation at the cathode and electron-beam generation across the sheath has been found. This has important applications to the design of diodes for future electron-beam machines.

Journal ArticleDOI
TL;DR: In this paper, the electron-hole pairs are generated in the bulk of the oxide by a 3 ns x-ray pulse and the separation of the electron and hole photocurrents is made possible by the large difference in mobility.
Abstract: Hole and electron transport are reported for three different kinds of MOS oxides: wet, dry, and ion-implanted. The electron-hole pairs are generated in the bulk of the oxide by a 3 ns x-ray pulse and the separation of the electron and hole photocurrents is made possible by the large difference in mobility. The electrons are so mobile that they are swept from the oxide (or trapped in a heavily ion-implanted region) during the x-ray pulse. The holes, on the other hand, have much lower mobilities which depend strongly on the preparation of the oxide. In the dry oxide the nominal mobility at room temperature is several orders of magnitude higher than in the wet oxide. The mobility is strongly activated by temperature in the oxides, and at liquid N$sub 2$ temperature no hole motion could be detected even though the electrons are still swept out. The low temperature charging of oxides can be understood in terms of the bulk trapped holes, but room temperature charging seems to be dominated by trapping close to the Si/SiO$sub 2$ interface rather than the transport of the holes from the bulk to the interface. Ion implantation provides electron traps which seem to be associatedmore » with the lattice damage rather than the ion. The electron traps can be successfully annealed out at 900$sup 0$C in 20 minutes. (auth)« less

Journal ArticleDOI
TL;DR: In this article, a theoretical model to study the growth characteristics of a train of closely-spaced macrosteps is presented, where volume diffusion in the parent phase is assumed to be the rate controlling factor, and numerical calculations are performed to assess the effect of neighboring steps on the velocity of a given step.

Journal ArticleDOI
TL;DR: In this paper, the temperature and thickness dependence of low temperature electrical transport of amorphous silicon thin films measured in-situ in ultra-high vacuum are presented, and an extended range of ln ϱ ∝ T − 1 4 for thin films with S 2 ∝ d − 1 3 as expected from a variable range tunneling mechanism.