Showing papers by "National Institute of Standards and Technology published in 1984"
TL;DR: In this article, a metallic solid with long-range orientational order, but with icosahedral point group symmetry, which is inconsistent with lattice translations, was observed and its diffraction spots are as sharp as those of crystals but cannot be indexed to any Bravais lattice.
Abstract: We have observed a metallic solid (Al-14-at.%-Mn) with long-range orientational order, but with icosahedral point group symmetry, which is inconsistent with lattice translations. Its diffraction spots are as sharp as those of crystals but cannot be indexed to any Bravais lattice. The solid is metastable and forms from the melt by a first-order transition.
5,702 citations
TL;DR: Multiplicities in the resonances of chemically equivalent carbons, which appear in the solid-state carbon-13 nuclear magnetic resonance spectra of native celluloses, have been examined at high resolution and are consistent with the existence of two distinct crystalline forms.
Abstract: Multiplicities in the resonances of chemically equivalent carbons, which appear in the solid-state carbon-13 nuclear magnetic resonance spectra of native celluloses, have been examined at high resolution. The patterns of variation are consistent with the existence of two distinct crystalline forms. One form is dominant in bacterial and algal celluloses, whereas the other is dominant in celluloses from higher plants.
1,092 citations
640 citations
TL;DR: The structure of form II crystals of bovine pancreatic trypsin inhibitor has been investigated by joint refinement of X-ray and neutron data and eleven amide hydrogens were found to be protected from exchange after three months of soaking the crystals in deuterated mother liquor at pH 8·2.
457 citations
TL;DR: In this paper, a commercially available specimen of single-crystal MgF2 was determined for both the ordinary and extraordinary rays at selected wavelengths from 0.2026 to 7.04 μm.
Abstract: The refractive indices of a commercially available specimen of single-crystal MgF2 were determined for both the ordinary and extraordinary rays at selected wavelengths from 0.2026 to 7.04 μm. Measurements were made by means of the minimum-deviation method on a precision spectrometer near 19°C. The experimentally determined index values for each polarization were fitted to a three-term Sellmeier-type dispersion equation of the form
n2-1=∑Ajλ2(λ2-λj2), where n is the refractive index, λ is the wavelength of interest, λj is the calculated wavelength of an oscillator, and Aj is the strength of the oscillator at λj. The birefringence was computed as a function of wavelength from the calculated index values obtained for the two polarizations. The dispersion coefficients were also determined for the 0 ray and for the birefringence. The results of this study are compared with previously reported work on the refractive properties of MgF2.
371 citations
TL;DR: The crystal structures of three lithium titanates by neutron diffraction powder profile analysis were determined in this article, where the lithium partially occupies the highly distorted octahedral interstices in the anatase framework in fivefold-coordination with oxygen.
308 citations
TL;DR: In this article, the thermodynamics of stressed crystals that can change phase and composition are examined with particular attention to hypotheses used and approximations made, and the effects of vacancies, and their equilibrium within a solid and near surfaces are critically examined and previous formulas are found to be first order approximation.
Abstract: The thermodynamics of stressed crystals that can change phase and composition is examined with particular attention to hypotheses used and approximations made. Bulk and surface conditions are obtained and for each of them practical expressions are given in terms of experimentally measurable quantities. The concept of open-system elastic constants leads to the reformulation of internal elastochemical equilibrium problems into purely elastic problems, whose solutions are then used to compute the composition distribution. The atmosphere around a dislocation in a cubic crystal is one of several examples that are completely worked out. The effects of vacancies, and their equilibrium within a solid and near surfaces are critically examined and previous formulas are found to be first order approximations. Consequences of the boundary equations that govern phase changes are studied with several examples. Finally, problems connected with diffusional kinetics and diffusional creep are discussed.
288 citations
TL;DR: In this paper, a hybridization of local electron gas theory for short distances and the asymptotic form of the polarization potential is proposed for electron-molecule collisions.
Abstract: A model potential that includes both correlation and polarization effects is proposed for electron-molecule collisions. It is based, as suggested by O'Connell and Lane, on a hybridization of local electron-gas theory for short distances and the asymptotic form of the polarization potential. It is energy independent and very simple to apply, depending only on the molecular charge density and polarizabilities. The potential has been calculated for several molecules (H/sub 2/, N/sub 2/, CO/sub 2/, HF, HCl, and CO); the crossing point between the correlation and polarization potentials is remarkably constant, averaging 0.96 eV. Application in scattering calculations for H/sub 2/ and N/sub 2/ yields very encouraging results.
272 citations
TL;DR: In this paper, a general formulation of quantum mechanics within the lowest Landau level in two dimensions was developed, making use of Bargmann's Hilbert space of analytic functions and a simple algorithm for the projection of any quantum operator onto the subspace of the lowest landau level.
Abstract: We develop a general formulation of quantum mechanics within the lowest Landau level in two dimensions. Making use of Bargmann's Hilbert space of analytic functions we obtain a simple algorithm for the projection of any quantum operator onto the subspace of the lowest Landau level. With this scheme we obtain the Schr\"odinger equation in both real-space and coherent-state representations. A Gaussian interaction among the particles leads to a particularly simple form in which the eigenvalue condition reduces to a purely algebraic property of the polynomial wave function. Finally, we formulate path integration within the lowest Landau level using the coherent-state representation. The techniques developed here should prove to be convenient for the study of the anomalous quantum Hall effect and other phenomena involving electron-electron interactions.
245 citations
TL;DR: In this paper, the authors explore the recent discoveries by Williams of unusual phase diagram features for coherent phase equilibrium and explore a model that leads to a simple formulation involving only the minimization of a polynomial free energy function that includes an elastic energy term.
238 citations
TL;DR: In this article, the density effect correction for the ionization energy loss of charged particles has been evaluated as a function of the particle velocity for a total of 278 substances, including 98 cases of elements of the periodic table (12 gases and 86 condensed materials, including liquid hydrogen and graphite of three different densities) and 180 chemical compounds and substances of biological interest.
TL;DR: In this paper, the critical Landau-level filling factor for the transition from Laughlin's liquid state to a Wigner crystal was determined by comparing the energies of these states.
Abstract: The critical Landau-level filling factor ${\ensuremath{
u}}_{c}$ for the transition from Laughlin's liquid state to a Wigner crystal is determined by comparing the energies of these states. The Wigner-crystal energy is substantially improved over the Hartree-Fock result by using a variational wave function which includes particle correlations. The liquid-state energy is obtained from the Monte Carlo calculation of Levesque, Weis, and Mac-Donald. We find ${\ensuremath{
u}}_{c}$ to be slightly larger than ? which is consistent with the experimental observation by Mendez and co-workers that the fractional quantum-Hall effect does not occur for $\ensuremath{
u}l~\frac{1}{7}$. The improvement in the crystal energy by correlation is essential to this agreement since without correlations, ${\ensuremath{
u}}_{c}\ensuremath{\sim}\frac{1}{10}$. In addition the crystal correlation energy explains the very low temperatures required to see the $\ensuremath{
u}=\frac{1}{5}$ liquid state.
TL;DR: In this paper, a series of Ag-Cu alloys between 1 wt pct Cu and the eutectic composition (28.1 wtpct Cu) at speeds between 1.5 and 400 cm per second were used for beam solidification.
Abstract: Electron beam solidification passes have been performed on a series of Ag-Cu alloys between 1 wt pct Cu and the eutectic composition (28.1 wt pct Cu) at speeds between 1.5 and 400 cm per second. At low growth rates conventional dendritic or eutectic structures are obtained. The maximum growth rate of eutectic structure is 2.5 cm per second. At high growth rates microsegregation-free single phase structures are obtained for all compositions. The velocity required to produce this structure increases with composition for dilute alloys and agrees with the theory of absolute stability of a planar liquid-solid interface with equilibrium partitioning. For alloys between 15 and 28 wt pct Cu, the velocity required to produce the microsegregation-free extended solid solution decreases with composition and is related to nonequilibrium trapping of solute at the liquid solid interface. At intermediate growth rates for alloys with 9 wt pct Cu or greater, a structure consisting of alternating bands of cellular and cell-free material is obtained. The bands form approximately parallel to the local interface.
TL;DR: In this article, shape change transitions of elastically misfitting inclusions were predicted to occur when the inclusions are softer than the matrix, and the shape is dictated by minimizing interfacial energy without regard to the elastic contribution.
TL;DR: In this article, the possible information content in lineshapes observed in vibrational spectroscopy of molecules adsorbed on surfaces is considered by drawing analogies with similar situations in other spectroscopic areas where the systematics are more completely understood.
TL;DR: In this article, the combination of lines from a waveguide CO2 laser, with its larger tuning range, with lines from CO2, N2O, and CO2 isotopic lasers, with complete coverage of the entire far-infrared band from 100 to 5000 GHz (3-200 per cm) with stepwise-tunable CW radiation was demonstrated.
Abstract: Tunable, CW, far-infrared radiation has been generated by nonlinear mixing of radiation from two CO2 lasers in a metal-insulator-metal (MIM) diode. The FIR difference-frequency power radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO2 lasers. The combination of lines from a waveguide CO2 laser, with its larger tuning range, with lines from CO2, N2O, and CO2 isotopic lasers promises complete coverage of the entire far-infrared band from 100 to 5000 GHz (3-200 per cm) with stepwise-tunable CW radiation. To demonstrate the usefulness of the technique, the J = 4-5 line of CO was observed at 567 GHz.
TL;DR: In this paper, a fast algorithm for solving the multiparticle diffusion problem (MDP) is described, permitting simulation of coarsening dynamics by cyclic time-stepping and updating the diffusion solution for large random particle arrays.
Abstract: Phase coarsening, also termed Ostwald ripening, is generally thought to be a slow, diffusion-controlled process which occurs subsequent to phase separation under extremely small under- or over-saturation levels. The theory due to Lifshitz, Slyozov, and Wagner (LSW), which predicts the coarsening kinetics and the particle distribution function, are applicable todilute systems only, in which particle-particle interactions are unimportant. Most liquid phase sintered systems, however, have large enough volume fractions of the dispersed phase to violate the essential assumptions of LSW theory. Recent progress will be described on simulating Ostwald ripening in randomly dispersed, high volume fraction systems. A fast algorithm for solving the multiparticle diffusion problem (MDP) will be described, permitting simulation of coarsening dynamics by cyclic time-stepping and updating the diffusion solution for large random particle arrays. The rate constants, controlling the growth of the average particle, and the particle distribution functions were obtained by numerical simulations up to a volume fraction of 0.55. A new statistical mean field theory has now been developed which reproduces the MDP simulation data accurately, and finally makes clear how the linear mean-field approximations employed by LSW theory must be modified to describe real systems. The predictions of the mean field are found to compare favorably with experimental measurements made over a wide range of volume fraction solid of the kinetics of Ostwald ripening in liquid phase sintered Fe-Cu alloys. The new theory provides a comprehensive approach to understanding microstructural coarsening in liquid phase sintered systems.
TL;DR: In this paper, the Gibbs energies for the binary alloy systems Ag-Cu and Cd-Zn have been modeled for the area of rapid solidification, and the phase equilibria and chemical spinodals have been calculated.
Abstract: Gibbs energies have been modeled for the binary alloy systems Ag-Cu and Cd-Zn, simple eutectic systems of interest in the area of rapid solidification. Parameters of the thermodynamic functions are derived from phase diagram and thermochemical data. Metastable phase equilibria have then been calculated, as well as the chemical spinodals and the locus of compositions and temperatures where liquid and solid have equal Gibbs energies (T
0).
TL;DR: In this paper, a simple model to describe radiation effects on MOSFET electrical characteristics is presented, where the key assumption is that mobility degradation in an enhancement mode is predominantly due to charged interface traps.
Abstract: A simple model to describe radiation effects on MOSFET electrical characteristics is presented. The key assumption is that mobility degradation in an enhancement mode MOSFET is predominantly due to charged interface traps. Model predictions are compared with measured values of interface trap density and device I - V curves.
TL;DR: In this article, the direct absorption spectra of the 1'1B+u←1'1A−g transitions of gas phase butadiene, deuterated and methylated butadienes, and the cis and trans isomers of hexatriene cooled to low rotational and vibrational temperatures in supersonic molecular jets are reported.
Abstract: In the present paper, we report the direct absorption spectra of the 1 1B+u←1 1A−g transitions of gas phase butadiene, deuterated and methylated butadienes, and the cis and trans isomers of hexatriene cooled to low rotational and vibrational temperatures in supersonic molecular jets. These jet absorption spectra allow the more accurate determinations of Franck–Condon factors, upper state vibrational intervals and vibronic band homogeneous widths. We discuss the experimental constraints that the measurements reported here and in the previous paper of this series impose on theoretical models of the equilibrium structures and relaxation dynamics of the 1 1B+u excited states of the small linear polyenes.
TL;DR: In this article, an experimental system employing laser-induced Rayleigh light scattering with digital data acquisition as a time-resolved quantitative concentration probe in the turbulent flow field of a binary gas mixture is described.
Abstract: This work describes the development and characterization of an experimental system employing laser-induced Rayleigh light scattering with digital data acquisition as a time-resolved quantitative concentration probe in the turbulent flow field of a binary gas mixture. Equations for the expected signal and noise levels are given. Estimates of these parameters for the experimental system used here are in satisfactory agreement with experiment. It is demonstrated that the laser Rayleigh-light-scattering technique provides measurements having high spatial and temporal resolution for various locations within the concentration flow field. Measurements at various positions in the flow field of an axisymmetric methane jet issuing into a slow flow of air are reported and, where possible, compared with appropriate literature results. The statistical properties of the turbulent concentration fluctuations are found to be in good agreement with other independent measurements. Conditionally sampled measurements are also reported and shown to behave in the same manner as the limited number of similar measurements in the literature. The capability of calculating power spectra and correlation functions for the time behaviour of the methane concentration is also demonstrated. Raman and Rayleigh scattering techniques are compared as measurement techniques of scalar values in turbulent flow fields.
TL;DR: This article presented at the Journal of Quality Technology Session of the 27th Annual Fall Technical Conference of the Chemical and Process Industries Division of the American Society for Quality Control and the Section on Physical and Engineering.
Abstract: (This paper was presented at the Journal of Quality Technology Session of the 27th Annual Fall Technical Conference of the Chemical and Process Industries Division of the American Society for Quality Control and the Section on Physical and Engineering S..
TL;DR: In this article, it was shown that the usual Kubo formula for thermal response functions is invalid if a magnetic field is present, due to a lack of time-reversal symmetry.
Abstract: We demonstrate that the usual Kubo formula for thermal response functions is invalid if a magnetic field is present. There exists a fundamental correction due to a lack of time-reversal symmetry. We show in particular that, in addition to being of general importance in the theory of transport, this leads to a novel thermoelectric effect in a weakly disordered two-dimensional electron gas subject to a quantizing magnetic field. The thermopower tensor is calculated within the self-consistent Born approximation using a generalized Mott formula, which is derived.
TL;DR: In this paper, it was shown that thickness changes contribute about 2/3 of the piezoelectric activity of transducer films, due to displacement of the electrodes in the fields of the constant dipole moments of the crystals.
Abstract: Consideration of the molecular and bulk structures of PVDF and related semicrystalline polymers, and the effects of processing to make transducer films, leads to a novel way of analysing the elastic and piezoelectric constant data. The results of this analysis support the conclusion that thickness changes contribute about 2/3 of the piezoelectric activity. An increase in thickness decreases the charge on the electrodes. The probable mechanism is simply the displacement of the electrodes in the fields of the constant dipole moments of the crystals. The remaining 1/3 of the activity is attributed to changes in the film's dipole moment at constant thickness. Strains in the orientation direction of the film increase the charge on the surface while strains in the plane of the film normal to the orientation direction decrease it. Eight separate possible contributions to the change in moment are discussed, and qualitative evaluations of their importance are given.
TL;DR: In this article, the initial density dependences of both viscosity and thermal conductivity are calculated according to a microscopically based theory which includes effects due to collisional transfer (from only free two-body phase space), three-monomer collisions, and monomer-dimer collisions.
TL;DR: In this paper, the authors describe the theory of a single sensor to perform simultaneous electric and magnetic near-field measurements using a loop antenna terminated with identical loads at two diametrically opposite points.
Abstract: This paper describes the theory of a single sensor to perform simultaneous electric and magnetic near-field measurements. The theory indicates that it is possible to measure the magnetic-loop and electricdipole currents using a loop antenna terminated with identical loads at two diametrically opposite points. The theory also indicates that it is possible to choose an ideal load impedance for achieving equal electric and magnetic-field responses of the loop. Preliminary experiments have been performed using a plane-wave field to verify these results.
TL;DR: For a face-centered-cubic steel, new measurements of the monocrystal Voigt elastic-stiffness constants C11, C12, C44 are given in this article.
Abstract: For a face-centered-cubic steel, new measurements of the monocrystal Voigt elastic-stiffness constants C11, C12, C44 are given. The monocrystal steel, Fe19Cr10Ni, corresponds closely to the well-known AISI-304 austenitic stainless steel. Considering seven theories for the monocrystalpolycrystal elastic constants, it is found that the Hershey-Kroner-Eshelby theory agrees best with measurements. It predicts the shear modulus within 2% of observation, where the Voigt-Beuss first-order bounds differ by 49%. Ten sets of FeCrNi Cij results are reviewed with the finding that both Zener's elastic anisotropy and the C12/C11 ratio are constant within 5%.
TL;DR: In this article, a model is developed for evaluating stresses in the surfaces of brittle materials from changes in indentation crack dimensions, and the underlying basis of the model is a stress intensity formulation incorporating the solution for a penny-like crack system subjected to a constant stress over a relatively thin surface layer.
Abstract: A model is developed for evaluating stresses in the surfaces of brittle materials from changes in indentation crack dimensions. The underlying basis of the model is a stress intensity formulation incorporating the solution for a penny-like crack system subjected to a constant stress over a relatively thin surface layer. Results from a previous study of surface damage in proton-irradiated glass are used to illustrate the scope of the method. The indentation fracture analysis also provides some fresh insight into the susceptibility of brittle surfaces to spontaneous cracking. Implications of the study concerning the potential effect of surface stresses on mechanical properties, such as strength, erosion and wear, are briefly discussed.
TL;DR: In this article, the effect of silica pre-treatment on phase synthesis and column selectivity was also examined for wide and narrow-pore substrates, with the greatest changes in selectivity occurring for the polymeric phases.
TL;DR: In this article, a defect in silicon carbide whiskers made from rice hulls was identified and analyzed using transmission electron microscopy, which resulted in complex mixtures of β and α polytypes arranged in thin lamellae normal to the whisker axis.
Abstract: Defects in silicon carbide whiskers made from rice hulls were identified and analyzed using transmission electron microscopy. The whiskers were characterized by a high density of planar faults lying on close-packed planes perpendicular to the whisker axis. The faulting resulted in complex mixtures of β and α polytypes arranged in thin lamellae normal to the whisker axis. Core regions of whiskers were often filled with small cavities ranging in size from 1 to 20 nm. Partial dislocations accompanied the cavities and were analyzed through specimen tilting experiments.