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Showing papers by "Sandia National Laboratories published in 1974"


Journal ArticleDOI
TL;DR: In this article, a large number of computer solutions of various types of resistor networks were presented, analogous to physical problems such as impurity conduction in lightly compensated semiconductors and variable-range hopping in amorphous semiconductor devices.
Abstract: In this paper we present a large number of computer solutions of various types of resistor networks. Some of these are analogous to physical problems such as impurity conduction in lightly compensated semiconductors and variable-range hopping in amorphous semiconductors. A significant extension of the standard relaxation techniques was required to implement these solutions. The results of these calculations are compared to percolation-model predictions based on concepts developed in the first paper of this series. A simple criterion is found for the applicability of the critical-percolation-path analysis to problems of this type and this is used to formulate an accurate prediction for the impurity-conduction case. Arguments based on percolation models are also given to show that the ${T}^{\ensuremath{-}\frac{1}{4}}$ and ${T}^{\ensuremath{-}\frac{1}{3}}$ dependence of ${log}_{10}\ensuremath{\sigma}$ often predicted for three-dimensional and two-dimensional variable-range hopping are indeed expected to be observed, and results on resistivity networks analogous to these problems are shown to be consistent with these arguments. Accurate empirical formulas are deduced from these computer calculations and we use them to analyze some recent data on films of $a$-Ge. Employing the results of the preceding paper, several experimental studies, and our computer models we have also examined the utility of the critical-volume-fraction rule of Sher and Zallen in solving various types of mixture conduction problems. We find that application of this rule is appropriate only in rather limited circumstances, and that in general a knowledge of the topological properties of these problems must be employed in finding the percolation threshold.

934 citations


Journal ArticleDOI
TL;DR: In this paper, the development of a generalized quadrilateral finite element that includes a singular point at a corner node is presented, and the global-local concept of finite elements is used to formulate the complete set of equations.
Abstract: The development of a generalized quadrilateral finite element that includes a singular point at a corner node is presented. Inter-element conformability is maintained so that monotone convergence is preserved. The global-local concept of finite elements is used to formulate the complete set of equations. Examples of crack tip singularities are given.

299 citations


Journal ArticleDOI
TL;DR: In this article, an exact calculation of the acoustic-phonon-assisted jump rate has been carried out, and it is found that while the Miller-Abrahams approximation is adequate for the study of shallow-impurity conduction at helium temperatures, it is typically inappropriate for hopping between deep states in noncrystalline solids.
Abstract: An exact calculation of the acoustic-phonon-assisted jump rate has been carried out. It is found that while the Miller-Abrahams (single-phonon) approximation is adequate for the study of shallow-impurity conduction at helium temperatures, it is typically inappropriate for the study of hopping between deep states in noncrystalline solids. In particular, the multiphonon jump rate will display a nonactivated temperature dependence below the Debye temperature which is similar to the often-seen $\mathrm{exp}[\ensuremath{-}{(\frac{{T}_{0}}{T})}^{\frac{1}{4}}]$ behavior.

255 citations


Journal ArticleDOI
TL;DR: In this paper, the long-time dependence of the time correlation functions is taken to be Gaussian, and the resulting short and long time parts are joined together in a manner similar to that used by Gulley, Hone, Scalapino, and Silbernagel.
Abstract: Electron-spin-resonance (ESR) measurements are reported in the two-dimensional Heisenberg magnet ${\mathrm{K}}_{2}$Mn${\mathrm{F}}_{4}$ and compared with a theory developed here. Results are in excellent agreement with calculated values and, we feel, give strong confirmation of recent theories of spin dynamics. The theory treats the linewidth $\ensuremath{\Delta}H$ and line shape in a two-dimensional Heisenberg system by assuming diffusive motion for the long-time dependence of the time correlation functions. The short-time dependence is taken to be Gaussian, and the resulting short- and long-time parts are joined together in a manner similar to that used by Gulley, Hone, Scalapino, and Silbernagel. An angular dependence roughly of the form $\ensuremath{\Delta}H\ensuremath{\propto}{(3{cos}^{2}\ensuremath{\theta}\ensuremath{-}1)}^{2}+(\mathrm{const}.)$ ($\ensuremath{\theta}$ is the angle of dc field with respect to the perpendicular to the plane) is observed at high temperature, as predicted by the theory. This angular dependence cannot be explained by either the secular or nonsecular parts of the second moment. Rather, it is due explicitly to the dominance of wave-vector $q\ensuremath{\rightarrow}0$ modes in the long-time decay of correlations in a two-dimensional system. As temperature is lowered toward the antiferromagnetic ordering temperature ${T}_{N}=45$ \ifmmode^\circ\else\textdegree\fi{}K, the linewidth initially decreases, passes through a minimum, and then increases rapidly near ${T}_{N}$. The angular dependence is also temperature-dependent such that $\ensuremath{\Delta}H$ ($\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}$) becomes less than $\ensuremath{\Delta}H$ ($\ensuremath{\theta}=55\ifmmode^\circ\else\textdegree\fi{}$) below about 65 K. These features of the temperature dependence are consistent with the theory. Indeed, we find absolute agreement between theory and experiment to within 20% or better at all angles over a broad range of temperature. The theory contains no adjustable parameters since classical dipolar coupling is taken as the sole source of broadening and we use the same exchange constant $J$ as obtained from susceptibility measurements. The room-temperature line shape, which is Lorentzian at $\ensuremath{\theta}=55\ifmmode^\circ\else\textdegree\fi{}$ and non-Lorentzian at $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}$, and the frequency dependence of $\ensuremath{\Delta}H$, measured at 9.8 and 23.4 GHz, are also in agreement with theory. Shift of the resonance field with angle has been measured as well. This effect can be explained quantitatively by the net dipolar field and, contrary to the other phenomena, does not, in the main, reflect two-dimensional spin dynamics.

205 citations


Journal ArticleDOI
TL;DR: In this paper, an empirically determined formulation for the eddy viscosity is introduced into the turbulent axially symmetric compressible free jet theory of Kleinstein, which is applicable to the main region of most classes of free jets, including heterogeneous, nonisothermal, and subsonic and properlyexpanded supersonic flows.
Abstract: Theme A empirically determined formulation for the eddy viscosity is introduced into the turbulent axially symmetric compressible free jet theory of Kleinstein. * The easily evaluated algebraic equation that results shows excellent agreement with an extensive compilation of experimental data for the centerline velocity decay in the main region. It is found that the eddy viscosity can be treated as constant, with functional dependence on only the exit Mach number and the jet-to-freestream density ratio. The theory presented is applicable to the main region of most classes of free jets, including heterogeneous, nonisothermal, and subsonic and properly-expanded supersonic flows.

190 citations


Journal ArticleDOI
TL;DR: In this paper, effective potentials to replace the Ar core electrons of Fe and Ni were obtained from ab initio ground state wavefunctions of the two core electrons and tested by comparing with SCF calculations for excited states of Fe, Fe +, Fe 2+, Fe 3+, Ni, Ni +, Ni 2+ and Ni 2 +, and the FeH + molecule.

135 citations


Journal ArticleDOI
TL;DR: Germanium diffusion was measured in SiGe alloys of 100/0, 77.3/77.7, 22.6/22.4, 69.2/30.8, 44.6 /55.4.
Abstract: Germanium diffusion was measured in SiGe alloys of 100/0, 77.6/22.4, 69.2/30.8, 44.6/55.4, and 22.3/77.7 silicon to germanium atomic-percent ratios by the use of the radioisotope $^{71}\mathrm{Ge}$ and a thin-sectioning technique. As expected from the calculated, small, strain-energy contributions from the $^{71}\mathrm{Ge}$ impurities, the diffusion is similar to silicon self-diffusion for the silicon end member. Since the results fit an Arrhenius plot for the compositions and temperature ranges studied, activation energies and pre-exponentials were determined. These diffusion parameters indicate that the $^{71}\mathrm{Ge}$ diffusion is compatible with the monovacancy mechanism up to 70-at.% silicon in the SiGe alloys. For more silicon-rich material, the diffusion is quite analogous to the extended-defect mechanism previously suggested for high-temperature silicon self-diffusion.

123 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed neutron-scattering study of the spin dynamics in Cu${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}2N(${C}}_{5}$${\mathhem{D}}_{ 5}$), a physical realization of the one-dimensional Heisenberg antiferromagnet, is presented.
Abstract: We report a detailed neutron-scattering study of the spin dynamics in Cu${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}2N(${\mathrm{C}}_{5}$${\mathrm{D}}_{5}$), a physical realization of the one-dimensional $S=\frac{1}{2}$ Heisenberg antiferromagnet. At $T=1.3$ K well-defined excitations are observed over the whole zone with energies given by $E(q)=\ensuremath{\pi}{J}_{\mathrm{nn}}sin(\mathrm{qc})$, the celebrated des Cloizeaux-Pearson exact solution for the spectrum of first excited states, but with intensities approximately those expected from classical spin-wave theory. At $T=8$ K the excitations are broad and ill defined.

119 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of microstructure on the strength, fracture toughness and low cycle fatigue behavior of 17-4 PH stainless steel has been examined, and it was shown that fracture toughness increased with increasing strength level and humidity but were not a function of toughness level.
Abstract: The influence of microstructure on the strength, fracture toughness and low cycle fatigue behavior of 17-4 PH stainless steel has been examined. Aging hardening involves initial formation of coherent copper-rich clusters which transform to incoherent fee ∈-copper precipitates upon further aging. The changes in strength level and strain hardening rates observed during aging are consistent with previously suggested models for precipitation hardening based on differing elastic moduli. The fracture toughness and fatigue crack growth rates were shown to be a function of microstructure and environment. At equivalent strength levels overaging resulted in a higher fracture toughness than did underaging. The fatigue crack growth rates increased with increasing strength level and humidity but were not a function of toughness level. Attempts to correlate the fatigue crack growth rates with monotonie tensile properties were unsuccessful. However when final failure obeyed a critical strain criteria, the fracture toughness behavior could be reasonably described and related to preferential void nucleation and growth at δ-ferrite-matrix interfaces.

108 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of prestrain on the tensile strength of Ti-6 Al-4 V and its alloys were investigated at 295 K on the solution treated and aged (4 h at 815 K) condition and in the as-welded condition.
Abstract: Creep tests were conducted at 295 K on Ti-6 Al-4 V in the solution treated and aged (4 h at 815 K) condition, and in the as-welded condition Some aged specimens were tested after pre-straining Creep stresses ranged from 40 to 90 pct of the aged material yield strength Results showed that creep was of the primary or transient kind in all cases, and was much greater in welded than in aged material In general, pre-strains reduced creep, although a strain larger than 10-3 was needed to do this at the highest creep stress Activation areas A* were between 10 and 20 b2, and thus were similar to tensile results on titanium and its alloys The microstructural rationale applied to Ti-5 Al-25 Sn in earlier work, based on the character of dislocation sources, proved successful in understanding the effects of prestrain in this work

103 citations


Journal ArticleDOI
19 Jul 1974-Science
TL;DR: Contrary to the hypothesis that the platinum-like catalytic activity of tungsten carbide results from the contribution of carbon valence electrons to the 5d band ofTungsten, the width of the unfilled portion of the d band increases on going from tundsten to tungsen carbide.
Abstract: The local electronic structures of the surface regions of tungsten, tungsten carbide, and platinum have been compared. Contrary to the hypothesis that the platinum-like catalytic activity of tungsten carbide results from the contribution of carbon valence electrons to the 5d band of tungsten, the width of the unfilled portion of the d band increases on going from tungsten to tungsten carbide.

Journal ArticleDOI
TL;DR: There exists an infinite binary sequence having no identical adjacent blocks of length 3 or greater and every infinitebinary sequence has arbitrarily long adjacent blocks that are permutations of each other.

Journal ArticleDOI
TL;DR: In this article, a modification of this model is suggested to explain the data and the thermal expansion coefficients of the Na2O-GeO2 glasses also exhibit a minimum at < 5 mol% Na 2 O 2.
Abstract: Transformation-range viscosities are reported for Na2O-, K2O-, Rb2O-, and Cs2O-GeO2 glasses. A minimum in viscosity occurs between 1 and 5 mol% alkali oxide and a maximum between 17 and 22 mol% alkali oxide. The thermal-expansion coefficients of the Na2O-GeO2 glasses also exhibit a minimum at < 5 mol% Na2O. The accepted structural model for alkali germanate glasses does not predict the minimum at low R2O concentrations. A modification of this model is suggested to explain these data.

Journal ArticleDOI
TL;DR: In this article, the authors applied the method of superposition of configurations to the singlet sigma states of HeH+ which correlate to the separated atom states of principal quantum number less than or equal to 3.
Abstract: The method of superposition of configurations is applied to the singlet sigma states of HeH+ which correlate to the separated atom states of principal quantum number less than or equal to 3. The calculations are carried out for internuclear separations in the ranges 0(.1)34.5, 35.0(.5)50.0 bohr. Energy eigenvalues and the expectation values of the electron coordinate along the internuclear line are discussed in this paper. Dipole transition matrix elements and radial coupling matrix elements are presented in a companion paper. The quality of the calculations is exhibited by comparisons of the length and velocity forms of the dipole matrix elements, by the Hellmann‐Feynman theorem, and by the approach to atomic properties at large internuclear separations. Supplementary calculations of higher quality wavefunctions for the lowest states are also reported. These are used to help estimate the extent to which the results of the main calculations have converged toward the exact values. Comparisons with other work are given. It is shown that for internuclear separations greater than about 3 bohr a one‐electron electron model potential approach is quite successful for the excited states. At smaller internuclear separations, and as the united atom limit is approached, current model potential methods cannot be trusted. In this region the model potential, being based on the separated atoms, cannot describe the actual changing charge distributions of the core electron. This work demonstrates the feasibility, for simple systems, of the ab initio structure calculations required for the quantitative description of low‐energy atom‐atom collisions.

Journal ArticleDOI
TL;DR: In this article, the authors verified the existence of an inverse isotope effect between homogeneous bulk PdH and PdD and obtained the maximum superconducting transition temperatures of the two isotopes.
Abstract: We have verified the existence of an inverse isotope effect between homogeneous bulk $\mathrm{Pd}{\mathrm{H}}_{x}$ and $\mathrm{Pd}{\mathrm{D}}_{x}$. Maximum $x$ values achieved by high-pressure charging were 0,99 and 0.97 for the hydride and deuteride, respectively. Our extrapolated values for the superconducting transition temperatures of PdH and PdD are 8 and 10 K, respectively.

Journal ArticleDOI
TL;DR: In this article, the authors examined the effect of hydrogen charging on 3.309S in the solution treated and quenched condition and after heat treatment at 975 K for either 15 or 300 min.

Journal ArticleDOI
TL;DR: In this paper, it is shown that speed distributions from many diverse sites possess a quasi-universal shape which, when approximated analytically, can be adjusted to yield a distribution of wind speeds which have some specified mean value.
Abstract: Estimation of long-term average concentrations from fixed sources is completely straightforward using standard dispersion formulas and occurrence statistics of wind speed classes and wind directions. However, in many cases of practical interest, only the fraction of time within a direction interval and its associated mean wind speed are available from a standard wind rose. While this information is sufficient to make an estimate of the mean concentration, estimates that better reflect the distributed nature of wind speeds can be made using some observed properties of the wind speed distribution. In particular, it is shown that speed distributions from many diverse sites possess a quasi-universal shape which, when approximated analytically, can be adjusted to yield a distribution of wind speeds which have some specified mean value. The distributions are shown to be satisfactorily described with a log-normal function having a typical geometric standard deviation of 1.9 which, in turn, yields a valu...

Journal ArticleDOI
TL;DR: In this paper, the authors show that the long-time tail of the velocity autocorrelation function has the form of a polygonal system, where the time and the coefficient depending on the kinematic viscosity and on the diffusion coefficient.
Abstract: By a molecular-dynamics simulation of a three-dimensional system of 4000 particles, we show that the long-time tail of the velocity autocorrelation function has the form ${\ensuremath{\alpha}}_{0}{t}^{\ensuremath{-}\frac{3}{2}}$, where $t$ is the time and ${\ensuremath{\alpha}}_{0}$ a coefficient depending on the kinematic viscosity and on the diffusion coefficient.

Journal ArticleDOI
TL;DR: In this article, a technique using nuclear microanalysis has been developed to determine 2D an 3He concentrations versus depth profiles in the near surface regions (∼2 μm) of solids.

Journal ArticleDOI
01 Sep 1974
TL;DR: In this paper, the effects of ionizing radiation on MOS structures were investigated and design techniques for minimizing the radiation-induced degradation of semiconductor-device performance were evaluated, and the present degree of understanding of radiation effects in silicon devices was summarized.
Abstract: The radiation-induced degradation of semiconductor material parameters is reviewed. These results are related to the degradation of semiconductor-device performance. Design techniques for minimizing the radiation-induced degradation are evaluated. Emphasis is placed on the effects of neutron-produced displacement damage on devices and on the effects of ionizing radiation on MOS structures. Transient ionization effects and circuit latchup are considered. The present degree of understanding of radiation effects in silicon devices is summarized.

Journal ArticleDOI
TL;DR: In this paper, a time-dependent conservation of energy equation is formulated for the general situation of n semitransparent contiguous liquid and solid phases, where dimensionless parameters governing phase change are identified and the effects of their variation are ascertained by a finite difference solution of the rigorously formulated energy and radiative transfer equations.
Abstract: Employing the assumptions of one-dimensional energy transfer, equilibrium phase change, and negligible convection in liquid regions, the time-dependent conservation of energy equation is formulated for the general situation of n semitransparent contiguous liquid and solid phases The dimensionless parameters governing phase change are identified and the effects of their variation are ascertained by a finite difference solution of the rigorously formulated energy and radiative transfer equations The chief conclusions of this investigation are that for the range of parameters encountered in the melting and solidification of many optical materials, radiant transfer has a significant effect, and that during solidification, radiation can force the temperature profile within the liquid phase to assume a shape which leads to unstable interfacial growth

Journal ArticleDOI
TL;DR: In this paper, the operation and theory for collisionless and transitional electric probes are reviewed, and the following topics are discussed: (1) orbital motion limit, (2) cold ion approximation, exact theories for current collection by spherical and cylindrical probes in the collisionless limit, collisional effects on probe response, and (5) the effect of flow on aligned cylinrical probes under collisionless conditions.
Abstract: The operation and theory for collisionless and transitional electric probes are reviewed. The following topics are discussed: (1) orbital motion limit, (2) cold ion approximation, (3) exact theories for current collection by spherical and cylindrical probes in the collisionless limit, (4) collisional effects on probe response, and (5) the effect of flow on aligned cylindrical probes under collisionless conditions. (MOW)

Journal ArticleDOI
TL;DR: In this article, a general irreversible thermodynamic framework for the description of electrophoresis experiments is provided, and the third problem is to show how number fluctuation experiments can be used to study the correlation lengths of polyelectrolyte solutions.
Abstract: Light scattering provides a sensitive tool for the study of solutions of charged macromolecules. This chapter deals with three separate problems involving polyelectrolyte solutions. The first problem is to interpret the spectrum of solutions in which the coulombic interactions between highly charged spherical polyions leads to long range spatial and dynamic correlations. The second problem is to provide a general irreversible thermodynamic framework for the description of electrophoresis experiments, and the third problem is to show how number fluctuation experiments can be used to study the correlation lengths as well as electrophoresis in charged systems. All of these problems are connected.

Journal ArticleDOI
TL;DR: In this paper, He re-emission was measured during 150 keV H+ implantation of Mo, V, and 316 SS between −90°C and 115 °C.

Journal ArticleDOI
TL;DR: In this article, the authors measured the pressure and temperature dependences of the six elastic constants of single-crystalline rutile (TiO2) lattice modes.

Journal ArticleDOI
TL;DR: In this article, a variable grid scheme is applied to a flat plate laminar to turbulent boundary layer flow with a rapidly changing grid interval across the layer, and the accuracy of the solution is determined for a different number of intervals and compared to results obtained with the Keller box scheme.

Journal ArticleDOI
TL;DR: In this paper, the mechanical response of x-cut quartz in the vicinity of the Hugoniot elastic limit was determined from measurements of the piezoelectric current from samples impact loaded from 26 to 130 kbar.

Journal ArticleDOI
TL;DR: The first direct determination of the lattice location of implanted deuterium in single-crystal chromium has been made for the first time in this paper, where ion channeling measurements of the angular distributions along the axial and planar directions indicate that implanted D occupies the octahedral position in bcc Cr. This contrasts to the expected tetrahedral interstitial position recently observed under the same conditions for bcc W.
Abstract: Direct determination of the lattice location of implanted deuterium in single-crystal chromium has been made for the first time. Ion-channeling measurements of the angular distributions along the $〈100〉$ axial and {100} planar directions indicate that implanted D occupies the octahedral position in bcc Cr. This contrasts to the expected tetrahedral interstitial position recently observed under the same conditions for bcc W. These results further clarify the apparent anomaly in the thermodynamic data for hydrogen solubility in Cr.

Journal ArticleDOI
TL;DR: In this article, a method for predicting deployment and inflation of reefed ribbon parachutes is presented based on integration of axial and radial momentum equations developed in the paper, which is assumed to be describable by drag and radial force coefficients.
Abstract: A method for predicting deployment and inflation of reefed ribbon parachutes is presented. The method is based on integration of axial and radial momentum equations developed in the paper. Axial and radial forces are assumed to be describable by drag and radial force coefficients. Computer solutions of the equations are compared to measured parachute loads and to parachute mouth and maximum diameters from tests of 23and 76-ft-diam conical ribbon parachutes. Comparison of load histories indicates that snatch loads depend to a large extent on deployment bag design and packing influences. Computed loads and parachute size histories for the inflation process compared favorably with flight data. The concept of a radial force coefficient appears to have considerable merit as a means of computing inflation for most types of parachutes.

Journal ArticleDOI
TL;DR: In this paper, structural and thermal properties have been examined as a function of composition throughout the glass forming region of the AsTe binary system, and evidence is presented to support the conclusion that a new face-centered cubic crystalline structure has the binary stoichiometry AsTe.