Showing papers by "Sandia National Laboratories published in 1980"

Approximations of the critical region of the fbietkan statistic

Abstract: The Friedman (1937) test for the randomized complete block design is used to test the hypothesis of no treatment effect among k treatments with b blocks. Difficulty in determination of the size of the critical region for this hypothesis is com¬pounded by the facts that (1) the most recent extension of exact tables for the distribution of the test statistic by Odeh (1977) go up only to the case with k6 and b6, and (2) the usual chi-square approximation is grossly inaccurate for most commonly used combinations of (k,b). The purpose of this paper 2 is to compare two new approximations with the usual x2 and F large sample approximations. This work represents an extension to the two-way layout of work done earlier by the authors for the one-way Kruskal-Wallis test statistic.

Vesiculation of mafic magma during replenishment of silicic magma reservoirs

Abstract: Mafic inclusions are lower in bulk density than the andesitic and dacitic lavas in which they occur, and apparently represent a foam inflated during rapid cooling of wet mafic magma in contact with cooler, more silicic reservoir magma. This process occurs as mafic magma enters the base of the reservoir, so that the mafic/silicic interface becomes unstable in Rayleigh–Taylor fashion. Mixing in these reservoirs thus depends on water content of mafic magma and pressure.

A model for the toughness of epoxy-rubber particulate composites

Abstract: Epoxy resins are toughened significantly by a dispersion of rubber precipitates. Microscopic examinations of propagating cracks in epoxy-rubber composites reveal that the brittle epoxy matrix cracks, leaving ligaments of rubber attached to the two crack surfaces. The rubber particles are stretched as the crack opens and fail by tearing at large, critical extensions. This fracture mechanism is the basis of a new analytical model for toughening. An increase in toughness (ΔGIC) of the composite is identified with the amount of elastic energy stored in the rubber during stretching which is dissipated irreversibly (e.g. as heat) when the particles fail. The model predicts the failure strain of the particles in terms of their size. It also relates the toughness increase to the volume fraction and tearing energy of the rubber particles. Direct measurements of the tearing strains of rubber particles, and toughness data obtained from epoxy-rubber composites, are in good agreement with the model. The particle-stretching model provides a quantitative explanation, in contribution to existing qualitative theories, for the toughening of epoxy-rubber composites.

SCOAP: Sandia Controllability/Observability Analysis Program

Abstract: SCOAP is a program developed at Sandia National Laboratories for the analysis of digital circuit testability. Testability is related to the difficulty of controlling and observing the logical values of internal nodes from circuit inputs and outputs, respectively. This paper reviews the testability analysis algorithms and describes their implementation in the SCOAP program.

Lennard-Jones triple-point bulk and shear viscosities. Green-Kubo theory, Hamiltonian mechanics, and nonequilibrium molecular dynamics

Abstract: A new Hamiltonian method for deformation simulations is related to the Green-Kubo fluctuation theory through perturbation theory and linear-response theory. Numerical results for the bulk and shear viscosity coefficients are compared to corresponding Green-Kubo calculations. Both viscosity coefficients depend similarly on frequency, in a way consistent with enhanced "long-time tails."

Determination of the Fe-Ni and Fe-Ni-P phase diagrams at low temperatures (700 to 300 °C)

Abstract: The α + γ two-phase fields of the Fe-Ni and Fe-Ni (P saturated) phase diagrams have been determined in the composition range 0 to 60 wt pet Ni and in the temperature range 700 to 300 °C. The solubility of Ni in (FeNi)3P was measured in the same temperature range. Homogeneous alloys were austenitized and quenched to form α2, martensite, then heat treated to formα (ferrite) + γ (austenite). The compositions of the α and γ phases were determined with electron microprobe and scanning transmission electron microscope techniques. Retrograde solubility for the α/(α + γ) solvus line was demonstrated exper-imentally. P was shown to significantly decrease the size of the α + γ two-phase field. The maximum solubility of Ni in α is 6.1 ± 0.5 wt pct at 475 °C and 7.8± 0.5 wt pct at 450 °C in the Fe-Ni and Fe-Ni (P saturated) phase diagrams, respectively. The solubility of Ni in α is 4.2 ± 0.5 wt pct Ni and 4.9 ± 0.5 wt pct Ni at 300 °C in the Fe-Ni and Fe-Ni (P saturated) phase diagrams. Ternary Fe-Ni-P isothermal sections were constructed between 700 and 300 °C.

Intense pulsed ion beams for fusion applications

Abstract: The subject of this review is the field of intense pulsed ion beam generation and its potential application to fusion research Considerable progress has been made in the past six years Power levels of the order of 1000 MW/cm2 have been obtained for pulse-lengths from 10−8 to 10−6 s Light-ion beams with currents approaching 1 MA and energies exceeding 1 MeV have been produced The first half of the paper treats the physics and technology of beam generation Following a unified discussion of the theory of ion injectors, experimental work since 1973 is reviewed Diagnostic techniques appropriate to high-flux ion beams are summarized The general problem of high-current ion beam transport in vacuum and through plasmas is also considered The second part of the paper is devoted to applications to fusion research Applications in both magnetic confinement and inertial confinement fusion are considered Intense ion beams have a number of features which make them ideally suited as inertial fusion drivers Discussions are given of the physics of inertial fusion targets, options for ion beam production, experiments on light-ion beam focusing, and high-current multi-stage accelerators

Properties of vibrational energy levels in the quasi periodic and stochastic regimes

Abstract: Several aspects of the quantal energy spectrum are explored for the Henon–Heiles Hamiltonian system: a striking and initially unexpected continuation of sequences of eigenvalues from the quasiperiodic to the stochastic regime, the origin of large second differences Delta2Ei of eigenvalues arising from variation of a parameter, the comparison of classical and quantal spectra, and a comparison of the "classical" and quantal number of states. In the study of the second differences we find both "crossings" and "avoided crossings" of the eigenvalues. We discuss the importance of overlapping avoided crossings as a basis for a possible theory of "quantum stochasticity".

Improved Sensitivity of Infrared Spectroscopy by the Application of Least Squares Methods

Abstract: Improved sensitivity and precision in the quantitative analysis of trace gases by Fourier transform infrared spectroscopy have been achieved by the application of new spectral least squares methods. By relating all of the spectral information present in the reference spectrum of a trace gas to that of the unknown sample and by appropriately fitting the baseline, detections of trace gases can be obtained even though the individual spectral features may lie well below the noise level. Four least squares methods incorporating different baseline assumptions were in vestigated and compared using calibrated gases of CO, N2O, and CO2 in dry air. These methods include: (I) baseline known, (II) baseline linear over the spectral region of interest, (III) baseline linear over each spectral peak, and (IV) negligible baseline shift between successive data points. Methods III and IV were found to be most reliable for the gases studied. When method III is applied to the spectra of these trace gases, detection limits improved by factors of 5 to 7 over conventional methods applied to the same data. "Three sigma" detection limits are equal to 0.6, 0.2, and 0.08 ppm for CO, N2O, and CO2, respectively, when a 10-cm pathlength at a total pressure of 640 Torr is used with a ∼35 min measurement time at 0.06 cm−1 resolution.

Suppression of acoustic noise in speech using two microphone adaptive noise cancellation

Abstract: Acoustic noise with energy greater or equal to the speech can be suppressed by adaptively filtering a separately recorded correlated version of the noise signal and subtracting it from the speech waveform. It is shown that for this application of adaptive noise cancellation, large filter lengths are required to account for a highly reverberant recording environment and that there is a direct relation between filter misadjustment and induced echo in the output speech. The second reference noise signal is adaptively filtered using the least mean squares, LMS, and the lattice gradient algorithms. These two approaches are compared in terms of degree of noise power reduction, algorithm convergence time, and degree of speech enhancement. Both methods were shown to reduce ambient noise power by at least 20 dB with minimal speech distortion and thus to be potentially powerful as noise suppression preprocessors for voice communication in severe noise environments.

Strain-rate dependent fracture initiation

Abstract: The theory of linear elastic dynamic fracture mechanics for Heaviside loading of an isolated crack is employed to formulate the response to constant strain-rate loading of a single crack. Numerical integration of the Heaviside solution is shown to lead to fracture initiation stresses that are dependent upon the imposed strain rate. These fracture initiation stresses are also shown to be relatively independent of the crack size and crack shape. The results are used to explain the strain-rate dependent fracture stress observed in some rocks as being a structural response, rather than a basic material property.

The effect of nitrogen on stacking fault energy of Fe-Ni-Cr-Mn steels

Abstract: The effect of nitrogen content on stacking fault energy (SFE) has been measured in a series of Fe-21Cr-6Ni-9Mn alloys. Stacking fault energies were determined from node measurements using weak beam imaging techniques in transmission electron microscopy. Nitrogen additions lower the SFE from 53 mJ/m2 at 0.21 wt pct to 33 mJ/m2 at 0.24 wt pct. Further increases to 0.52 wt pct do not markedly change the SFE. Carbon and silicon had no effect on SFE in the ranges 0.010 to 0.060 wt pct C and 0.17 to 0.25 wt pct Si. The shift in SFE from 0.21 to 0.24 wt pct N is accompanied by a transition to a more planar plastic deformation mode. The sharp transition precludes the use of linear regression analysis for relating SFE to nitrogen content in this class of alloys.

Adaptive Grid Method for Problems in Fluid Mechanics and Heat Transfer

Abstract: A new method for generating adaptive grids for time-dependent and steady problems in multidimensional fluid mechanics and heat transfer has been developed. The method can be used with many existing grid generation schemes or can be used as an independent grid generation technique. The present adaptive method is based upon the placement of grid points in proportion to the gradients that appear in the dependent variable. The multidimensional results presented in the paper are for the unsteady heat conduction equation and have included steep gradients due to geometry and unsteady boundary conditions. The method has performed in an impressive fashion, although there is a need to control grid skewness better. A study of one-dimensional problems associated with combustion and cell Reynolds number has demonstrated the technique's accuracy and versitility. The paper also discusses the relationship of the method to other grid generation techniques, as well as extensions of the new method.

Criteria for impulsive rock fracture

Abstract: Explosive or percussive breakage of rock relies on impulsive rock fracture and both the fracture stress and fracture energy under such conditions are observed to be significantly greater than measured quasi-statically. The implication of rate dependence has been verified in recent tensile fracture studies and in the present report this data has been compiled, significant trends noted, and comparisons made with earlier impulsive fracture criteria.

Bifurcation Phenomena in Burner-Stabilized Premixed Flames

Abstract: The one-dimensional stability of an isobaric burner-stabilized premixed flame is investigated for arbitrary Lewis number and stoichiometry in the asymptotic limit of large activation energy. Assuming a one-step irreversible chemical reaction in which fuel and oxidizer react to form a product, a linear stability analysis is Used to calculate the neutral stability boundary in Lewis number-activation energy space as a function of incoming flow velocity (or equivalently, the burned temperature) The major result is that although a steady-state adiabatic flame is likely to be stable for typical parameter values, a value of the incoming flow velocity sufficiently less than the adiabatic flame speed is destabilizing to the extent that the unstable region becomes feasible for many flames. Consequently, if all other parameters are fixed, there exists for such flames a critical value of the incoming flow velocity at which the time-asymptotic solution to the time-dependent problem bifurcates from the nontriv...

Glasses and glass ceramics for sealing to aluminum alloys

Abstract: We have developed alkali alkaline earth phosphate glasses which hermetically seal to aluminum alloys. They have coefficients of thermal expansion greater than 200 × 10−7 °C−I and glass transition temperature below 400°C. The relatively low fracture toughness values (KIC) of the glasses, 0.43 to 0.53 MPa (m) 1 2 , (KIC of silica = 0.9 MPa 1 2 ) increase by approximately 25% when the glasses are converted into glass ceramics. Depending upon parent glass compositions and heat treatment, crystal phases of sodium metaphosphate, sodium trimetaphosphate, sodium barium phosphate, or sodium calcium phosphate may develop. DC electrical resistivities of the glasses are 106 to 1010 ohm-cm at 230°C.

Observation of an optical Stark effect on vibrational and rotational transitions

Abstract: Vibrational and rotational Raman transitions are shown to be shifted to lower frequencies in the presence of a nonresonant, high-intensity optical field. Experimental results using coherent anti-Stokes Raman spectroscopy for hydrogen and nitrogen are presented. The magnitude of the observed shift is in agreement with a calculation which considers the coupling of the optical field to the internuclear separation via the molecular electronic polarizability. The magnitude of the shift is predicted to be proportional to the optical field intensity.

Correlation of nosetip boundary-layer transition data measured in ballistics-range experiments

Abstract: Preablated nosetips of various carbonaceous materials were tested in a ballistics range. Surface-temperature contours, measured with image-converter cameras, were used to define boundary-layer transition-front contours. Measurements of surface roughness, surface temperature, average transition-front location, and freestream environment were combined with calculations of nosetip flowfields, and with calculations of laminar boundary-layer development in these flowfields, to transform all data into various dimensionless parameters. These parameters were defined by previous attempts to correlate existing wind-tunnel data for transition on rough/blunt bodies. Of the available correlating techniques, only one, based on the concept of a constant (critical) roughness Reynolds number for transition, was found to successfully describe both the wind-tunnel and ballistics-range data, thereby validating the extrapolation of this concept to actual re-entry vehicle materials and environments.

An adaptive lattice algorithm for recursive filters

Abstract: The purpose of this correspondence is to introduce an adaptive algorithm for recursive filters, which are implemented via a lattice structure. The motivation for doing so is that stability can be achieved during the adaptation process. For convenience, the corresponding algorithm is referred to as an "adaptive lattice algorithm" for recursive filters. Results pertaining to using this algorithm in a system-identification experiment are also included.

A macroscopic theory for the existence of the hysteresis and butterfly loops in ferroelectricity

Abstract: We present in this paper a minimal macroscopic theory leading to the hysteresis loop and the butterfly loop in ferroelectricity. This theory is based on the notion that as domains switch under the ...

Piezoelectricity in polymers

Abstract: Piezoelectricity and related properties of polymers are reviewed. After presenting a historical overview of the field, the mathematical basis of piezo- and pyroelectricity is summarized. We show how the experimentally measured quantities are related to the changes in polarization and point out the serious inequlity between direct and converse piezoelectric coefficients in polymers. Theoretical models of the various origins of piezo- and pyroelectricity, which include piezoelectricity due to inhomogeneous material properties and strains, are reviewed. Relaxational effects are also considered. Experimental techniques are examined and the results for different materials are presented. Because of the considerable work in recent years polyimylidene fluoride, this polymer receives the majority of the attention. The numerous applications of piezo-and pyroelectric polymers are mentioned. This article concludes with a discussion of the possible role of piezo- and pyroelectricity in biological system.