Showing papers by "Argonne National Laboratory published in 1983"
01 Jan 1983
TL;DR: The theoretical and practical results available for trust region methods are surveyed and the relevance of these results to the implementation oftrust region methods is discussed.
Abstract: Trust region methods are an important class of iterative methods for the solution of nonlinear optimization problems. Algorithms in this class have been proposed for the solution of systems of nonlinear equations, nonlinear estimation problems, unconstrained and constrained optimization, nondifferentiable optimization, and large scale optimization. Interest in trust region methods derives, in part, from the availability of strong convergence results and from the development of software for these methods which is reliable, efficient, and amazingly free of ad-hoc decisions. In this paper we survey the theoretical and practical results available for trust region methods and discuss the relevance of these results to the implementation of trust region methods.
363 citations
TL;DR: In this article, a constitutive relation for active nucleation site density is developed in pool boiling and extended to forced convective nucleate boiling, which is in relatively good agreement with direct measurements available in the literature.
318 citations
TL;DR: In this paper, the results of variational calculations of 3 H, 3 He, 4 He and nuclear matter with the Urbana v 14 two-nucleon interaction and realistic models of the TNI were reported.
312 citations
TL;DR: In this article, the electronic structure of CeO2 and PrO2 was determined by performing SCF band calculations, and it was shown that in both systems there are metal f-and d- electrons in the oxygen 2p bands.
243 citations
TL;DR: In this paper, a model was developed for predicting which sites and how many of them could be occupied by hydrogen atoms in each of the intermetallic compounds listed, and the resulting stoichiometries were determined by experimentally filling the interstices of model lattices constructed of Friauf polyhedra without violating either of the adopted geometric criteria.
Abstract: Hole sizes and intersite distances were calculated at various hydrogen concentrations for the interstices in hydrides of TiCr 1.8 , ZrTi 2 , ZrV 2 , ZrCr 2 , ZrFe 2 , HfV 2 and TaV 2 with the cubic MgCu 2 C15 structure and of ZrMn 2 and ErMn 2 with the hexagonal MgZn 2 C14 structure. From a survey of other metallic hydrides, empirical criteria were chosen for the minimum hole size (0.40 A) and the minimum H-H distance (2.1 A) for hydrogen atom occupancy in stable hydrides. With these criteria, a model was developed for predicting which sites and how many of them could be occupied by hydrogen atoms in each of the intermetallic compounds listed. The resulting stoichiometries were determined by experimentally filling the interstices of model lattices constructed of Friauf polyhedra without violating either of the adopted geometric criteria. For each of the compounds rationales are presented to explain the experimental observations reported by other researchers.
236 citations
TL;DR: In this paper, the potential energy surface for the reaction Cl+HCl was predicted by using a rotated Morse-oscillator spline fit for collinear geometries plus an analytic bend potential.
Abstract: Ab initio POL–CI calculations, augmented by a dispersion term, are used to predict the potential energy surface for the reaction Cl+HCl. The saddle point is found to be nonlinear. The surface is represented by a rotated‐Morse‐oscillator spline fit for collinear geometries plus an analytic bend potential. Variational transition state theory calculations, based on a linear reference path, are carried out, and they yield much smaller rate constants than conventional transition state theory, confirming that earlier similar results for this heavy–light–heavy mass combination were consequences of the small skew angle and were not artifacts of the more approximate potential energy surfaces used in those studies. Transmission coefficients are calculated using approximations valid for large‐reaction‐path curvature and the potential along the reference path is scaled so that the calculated rate constant agrees with experiment. The resulting surface is used to compute the H/D kinetic isotope effect which is in qualitative agreement with experiment.
231 citations
TL;DR: Theoretical values of electric and magnetic susceptibilities ( α 1, α 2, χ 1 ) and shielding factors ( γ 1, γ 2, 1 ) calculated in the relativistic random-phase approximation are presented in tabular form for ions with closed 1 s, 2 p, 3 p, 4 d, 4 p, 4 d, and 5 p shells.
230 citations
TL;DR: In this article, the authors studied the phase transition in AgI with use of the new molecular-dynamics technique which allows for a dynamical variation of the shape and size of the cell.
Abstract: The $\ensuremath{\alpha}\ensuremath{\rightleftarrows}\ensuremath{\beta}$ phase transition in AgI is studied with use of the new molecular-dynamics technique which allows for a dynamical variation of the shape and size of the cell. In the present model, upon heating of $\ensuremath{\beta}$-AgI, the iodine ions undergo a hep \ensuremath{\rightarrow} bee transformation and silver ions become mobile, whereas the reverse transformation is observed on cooling of $\ensuremath{\alpha}$-AgI. The calculated $\ensuremath{\alpha}\ensuremath{\rightleftarrows}\ensuremath{\beta}$ transition temperature and structural and dynamical properties are in good agreement with experiments.
211 citations
Journal Article•
205 citations
TL;DR: In this paper, a detailed model of the droplet size in annular flow was developed based on the above assumption and correlations for the volume mean diameter as well as the size distribution were obtained in collaboration with a large number of experimental data.
Abstract: The mean droplet size and size distribution are important for detailed mechanistic modeling of annular two-phase flow. A large number of experimental data indicate that the standard Weber number criterion based on the relative velocity between droplets and gas flow predicts far too large droplet sizes. Therefore, it was postulated that the majority of the droplets were generated at the time of entrainment and the size distribution was the direct reflection of the droplet entrainment mechanism based on roll-wave shearing off. A detailed model of the droplet size in annular flow was then developed based on the above assumption. The correlations for the volume mean diameter as well as the size distribution were obtained in collaboration with a large number of experimental data. A comparison with experimental data indicated that indeed the postulated mechanism has been the dominant factor in determining the drop size. Furthermore, a large number of data can be successfully correlated by the present model. These correlations can supply accurate information on droplet size in annular flow which has not been available previously.
194 citations
TL;DR: In this paper, anomalies have been observed in the lattice spacings, elastic moduli, and electrical resistivity versus modulation wavelength at the same superlattice wavelength.
Abstract: Metallic superlattices of nickel and molybdenum have been synthesized for a wide range of layer thicknesses by alternate sputtering. X-ray examination shows that they are composed of layers of fcc nickel and bcc molybdenum oriented along [111] and [110] directions, respectively. Anomalies have been observed in the lattice spacings, elastic moduli, and electrical resistivity versus modulation wavelength. These anomalies occur simultaneously at the same superlattice wavelength. The anomalies have been interpreted as due to strains in the nickel lattice.
TL;DR: In this paper, a review of qualitative and quantitative models that have been used to rationalize observed hydrogen atom site occupancies is critically reviewed, emphasizing the need for theoretical treatment leading to fundamental understanding of such systems.
Abstract: Numerous attempts have been made to explain the observed stabilities, stoichiometries and preferred hydrogen atom sites in hydrides of intermetallic compounds. The stabilities of some of these hydrides have been shown to correlate with cell volume or hole size or elastic properties or heat of formation for the intermetallic compound itself. It appears that each of these factors may influence the stability, but none plays the dominant role for all systems. The development of qualitative and quantitative models (based on the concept of imaginary binary hydrides) that have been used to rationalize observed hydrogen atom site occupancies is critically reviewed. The basis of these models is empirical and thus the successes reported for them may possibly be fortuitous. The example of LaNi5H6.5 is used to demonstrate a geometric model that uses only a minimum hole radius (0.40 A) and a minimum H-H distance (2.10 A) in the development of a rationale for the observed stoichiometries in hydrides of intermetallic compounds. This review emphasizes the need for theoretical treatment leading to fundamental understanding of such systems.
01 Jan 1983
TL;DR: This chapter presents a critical review of the general theory of density functional theory together with some illustrative examples and discusses several important areas of application.
Abstract: Over the course of the last 15 years density functional theory (DFT)* has evolved as a conceptually and practically useful method for studying the electronic properties of many-electron systems. In this chapter we present a critical review of the general theory together with some illustrative examples.† More complete discussions of several important areas of application may be found in other chapters of this book.
TL;DR: In this article, the ground states of droplets of $N$ atoms of $^{4}\mathrm{He}$ were calculated using variational Monte Carlo and Green's function Monte Carlo methods.
Abstract: Quantum mechanical calculations of the ground states of droplets of $N$ atoms of $^{4}\mathrm{He}$ are reported. The calculations have been made by the variational Monte Carlo method for $4l~Nl~728$ and by the Green's function Monte Carlo method for $3l~Nl~112$. The energies, rms radii, and density distributions are reported; liquid-drop fits to the energies and radii are discussed.
TL;DR: The coupled-cluster single and double excitation model (CCSD) is applied to an energy path for the insertion of Be into H2 and compared to the full configuration interaction (FCI) and full valence-multiconfiguration self-consistent field (FV-MCSCF) results as mentioned in this paper.
Abstract: The coupled-cluster single and double excitation model (CCSD) is applied to an energy path for the insertion of Be into H2 and compared to the full configuration interaction (FCI) and full valence–multiconfiguration self-consistent field (FV–MCSCF) results. This model problem is a severe test of a single-reference-function correlated method since two configurations are heavily weighted in the FCI description. CCSD is demonstrated to describe the FCI results using a single reference function which, however, changes orbital characteristics along the sampling path. In this case CCSD gives excellent agreement with the FCI results.
TL;DR: In this paper, the authors used time-of-flight neutron diffraction, using the General Purpose Powder Diffractometer at the IPNS (Intense Pulsed Neutron Source) at the Argonne National Laboratory, to measure residual stresses in deformed, polycrystalline Zircaloy-2.
TL;DR: In this paper, the authors measured the low energy cross section for the 7Be(p, γ)8B reaction by detecting the delayed α particles from the 8B beta decay.
Abstract: The low energy cross section for the 7Be(p, γ)8B reaction has been measured by detecting the delayed α particles from the 8B beta decay. Detailed discussion is presented of the analysis of the radioactive 7Be target including the use of two independent methods to determine the 7Be areal density. The direct capture part of the cross section is subtracted from the total cross section to deduce resonance parameters for the 1+ first excited state in 8B. The zero-energy astrophysical S factor inferred from the present experiment is compared with previous values. The effect on the 37Cl solar neutrino capture rate, predicted by the standard solar model, is also discussed.
TL;DR: The characteristics of dynamic recrystallization in χ sf μb becomes important; it makes Ni more like Cu than Al as discussed by the authors, and a change in the substructures observed both before and after dynamic re-stallization occurs at the same transition temperature.
TL;DR: In this article, molecular dynamics computer simulations have been performed to study properties of low-energy displacement cascades in Cu, including instantaneous number of Frenkel pairs, partitioning of kinetic and potential energies, distribution of atom kinetic energies, cascade expansion rate and Frenkel pair distributions.
TL;DR: In this article, the tracer diffusion coefficients of 22Na and 137Cs, and the electrical conductivity have been measured in the (Na, Cs)2O:3SiO2 glasses as a function of temperature and Cs/Na ratio.
Abstract: The tracer diffusion coefficients of 22Na and 137Cs, and the electrical conductivity have been measured in the (Na, Cs)2O:3SiO2 glasses as a function of temperature and Cs/Na ratio. Complex impedance analysis was used for the conductivity measurements. The Haven ratio at 396.5°C increases from 0.3–0.4 in single-alkali glasses to 0.8 for the mixed-alkali compositions. The results are explained in terms of a single-jump mechanism; interactions between alkali ions and non-bridging oxygen ions, and between different alkali ions, produce the observed correlation effects.
TL;DR: In this paper, the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures.
Abstract: Measurements of the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures. The temperature dependence of the resonant dt..mu..-molecular formation process has been determined in the range 100 to 540 K. Mesomolecular formation is found to be resonant for DT as well as D/sub 2/ target molecules. The sticking probability and other fundamental parameters have been measured for the first time.
TL;DR: In this article, the fluid-force coefficients for a row of cylinders and a square array are determined from available experimental data and critical flow velocities are calculated as a function of system parameters.
Abstract: The fluid-force coefficients for a row of cylinders and a square array are determined from available experimental data and critical flow velocities are calculated as a function of system parameters. Experimental data for critical flow velocities are found to be in good agreement with the analytical results. It is concluded that different stability criteria have to be utilized in different parameter ranges because of different instability mechanisms. 25 refs.
TL;DR: In this paper, it has been recognized that the 56Fe recoils will also cause significant displacement damage, which can nearly double the displacement damage in nickel in HFIR at high neutron fluences.
TL;DR: In this article, the interstitial hole radii, trigonal saddle point radii and intersite distances were calculated for the compounds LaNi 5 D 6.5, LaNi 4 AlD 4.8 and La Ni 4 MnD 5.9.
Abstract: Interstitial hole radii, trigonal saddle point radii and intersite distances were calculated for the compounds LaNi 5 D 6.5 , LaNi 4 AlD 4.8 and LaNi 4 MnD 5.9 in space group P 6/ mmm and for LaNi 5 D 6 in space group P 31 m . Two criteria, a minimum hole size of 0.4 A and a minimum H-H distance of 2.1 A, were adopted to allow rationalization of the observed interstitial occupancies and stoichiometries of each of these deuterides. The rationale includes consideration of diffusion mechanisms and their ramifications for site occupancy.
TL;DR: In this article, a more general melting and solidification model is proposed to account for an interesting phenomenon, namely, the existence of a two-phase zone in which partial phase change can occur.
TL;DR: In this paper, the interaction between structural metals and non-metallic elements in liquid alkali metals is analyzed in terms of equilibrium distribution coefficients and the concentrations of nonmetallic impurity elements that are sufficient for compound formation with the structural metals.
TL;DR: The absolute total cross section for the reaction of the reaction was measured in this article, where two independent methods have been used to determine the areal density of the $7}-mathrm{Be} target.
Abstract: The absolute total cross section for the reaction $^{7}\mathrm{Be}(p, \ensuremath{\gamma})^{8}\mathrm{B}$ has been measured for ${E}_{\mathrm{c}.\mathrm{m}.}=117\ensuremath{-}1230$ keV by detecting the delayed $\ensuremath{\alpha}$ particles following the $^{8}\mathrm{B}$ $\ensuremath{\beta}$ decay. Two independent methods have been used to determine the areal density of the $^{7}\mathrm{Be}$ target. The inferred zero-energy $S$ factor from the present experiment is ${S}_{17}(0)=0.0216\ifmmode\pm\else\textpm\fi{}0.0025$ keV b. This value reduces the predicted $^{37}\mathrm{Cl}$ solar-neutrino capture rate by \ensuremath{\sim}25%.
TL;DR: In this paper, the number operator for excess pions present in nuclei due to the pion exchange forces between nucleons was constructed using variational wave functions obtained from a realistic Hamiltonian.
Abstract: The authors construct, in the static potential approximation, the number operator for excess pions present in nuclei due to the pion-exchange forces between nucleons. Expectation values are calculated with use of variational wave functions obtained from a realistic Hamiltonian. Results are presented for systems ranging from the deuteron to nuclear matter: For example $^{56}\mathrm{Fe}$ is estimated to have \ensuremath{\sim}7 extra pions, over and above the pion clouds associated with the individual nucleons.
TL;DR: An overview of pathways for bioavailability of cadmium and lead from diet to mother to fetus during pregnancy and to neonate during lactation is presented.