Showing papers by "Sandia National Laboratories published in 1988"
TL;DR: In this article, Amdahl et al. describe a "blocage mental" contre le parallelisme massif impose par une mauvaise utilisation of the formule de Amdahls.
Abstract: Dans cet article, il est question de l'importance, pour la communaute scientifique informatique, de venir a bout du «blocage mental» contre le parallelisme massif impose par une mauvaise utilisation de la formule de Amdahl
1,280 citations
TL;DR: In this article, the authors reviewed the structural trends of monomeric alkoxysilanes and organylalkoxysinanes utilized in sol-gel processing and observed structural trends on the basis of the pH and [H2O] dependence of the hydrolysis, condensation, and dissolution reactions.
Abstract: The hydrolysis and condensation reactions of monomeric alkoxysilanes and organylalkoxysilanes utilized in sol-gel processing are reviewed. Both reactions occur by acid or base-catalyzed bimolecular displacement reactions. The acid-catalyzed mechanisms are preceded by protonation of OH or OR substituents attached to Si, whereas under basic conditions hydroxyl or silanolate anions attack Si directly. Many of the observed structural trends are understood on the basis of the pH and [H2O] dependence of the hydrolysis, condensation, and dissolution reactions.
1,077 citations
TL;DR: This study investigates the applicability of three widely used techniques to three computer models having large uncertainties and varying degrees of complexity in order to highlight some of the problem areas that must be addressed in actual applications.
Abstract: Many different techniques have been proposed for performing uncertainty and sensitivity analyses on computer models for complex processes. The objective of the present study is to investigate the applicability of three widely used techniques to three computer models having large uncertainties and varying degrees of complexity in order to highlight some of the problem areas that must be addressed in actual applications. The following approaches to uncertainty and sensitivity analysis are considered: (1) response surface methodology based on input determined from a fractional factorial design; (2) Latin hypercube sampling with and without regression analysis; and (3) differential analysis. These techniques are investigated with respect to (1) ease of implementation, (2) flexibility, (3) estimation of the cumulative distribution function of the output, and (4) adaptability to different methods of sensitivity analysis. With respect to these criteria, the technique using Latin hypercube sampling and regression analysis had the best overall performance. The models used in the investigation are well documented, thus making it possible for researchers to make comparisons of other techniques with the results in this study.
529 citations
TL;DR: In this paper, two conditions are proposed which place constraints on the processes of dynamic spall in condensed media, and determine inequalities which bound the spall strength, fragment size, and failure time.
Abstract: Two conditions are proposed which place constraints on the processes of dynamic spall in condensed media, and determine inequalities which bound the spall strength, fragment size, and failure time. Spall is defined as rupture within a body due to stress states in excess of the tensile strength of the material. The first is a horizon condition which establishes a domain of communication, consistent with the time to failure, within which spall must be independent of the surrounding environment. The second is an energy condition which requires that the potential and kinetic energy associated with the tensile loading process exceed the fracture energy of the material. Equality in the relations established from these conditions corresponds to energy-limited spall and provides specific analytic expressions for the spall properties. Inequality implies flaw-limited spall and requires more detailed material property information before spall can be characterized. Energy-limited spall is determined by the material fracture toughness in brittle solids and the material flow stress in ductile solids. Calculated spall properties, assuming energy-limited spall, compare well with experimental spall data for various materials. Under certain conditions, a transition from brittle to ductile spall (definition in text) with increasing strain rate is predicted. Comparison is made with spall data on 6061-T6 aluminum for which a brittle-to-ductile transition is predicted to occur at a critical strain rate of approximately 4 × 105 s−1. Energy-limited spall in liquids within their range of Newtonian fluid behavior is governed by surface energy and viscosity. Spall is predicted to be dominated by surface energy at low strain rates and viscous dissipation at high rates. Examples of each appear to exist within the scant experimental spall data available for liquids.
485 citations
TL;DR: Neutron-diffraction measurements as a function of temperature show that the phase separation occurs reversibly near 320 K.
Abstract: Superconducting samples of ${\mathrm{La}}_{2}\mathrm{Cu}{\mathrm{O}}_{4+\ensuremath{\delta}}$ are shown by neutron powder diffraction to consist of two nearly identical orthorhombic phases. The primary phase has a stoichiometry near ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$. The second phase is an oxygen-rich phase that is superconducting. The abundance of the second phase increases with the oxygen pressure at which the samples are annealed. Neutron-diffraction measurements as a function of temperature show that the phase separation occurs reversibly near 320 K.
462 citations
TL;DR: The nonlinear scalar field equation governing the propagation of an unsteadily convected interface is used to derive a convenient expression for the average volume flux through such an interface in a homogeneous flow field, facilitating analysis based on renormalized perturbation theory and numerical simulation.
Abstract: The nonlinear scalar field equation governing the propagation of an unsteadily convected interface is used to derive a convenient expression for the average volume flux through such an interface in a homogeneous flow field. For a particular choice of the initial scalar field, the average volume flux through any such interface is expressed as a volume-averaged functional of the evolving scalar field, facilitating analysis based on renormalized perturbation theory and numerical simulation. It is noted that this process belongs to a different universality class from the propagation model of M. Kardar, G. Parisi, and Y.-C. Zhang (Phys. Rev. Lett. 56, 889 (1986)).
401 citations
21 Aug 1988
TL;DR: Although it is implicit, it is almost never stated explicitly that in a single-key cryptographic communications link, the transmitter and the receiver must unconditionally trust each other since either can do anything that the other can.
Abstract: In information based systems, the integrity of the information (from unauthorized scrutiny or disclosure, manipulation or alteration, forgery, false dating, etc.) is commonly provided for by requiring operation(s) on the information that one or more of the participants, who know some private piece(s) of information not known to all of the other participants, can carry out but which (probably) can’t be carried out by anyone who doesn’t know the private information. Encryption/decryption in a single key cryptoalgorithm is a paradigm of such an operation, with the key being the private (secret) piece of information. Although it is implicit, it is almost never stated explicitly that in a single-key cryptographic communications link, the transmitter and the receiver must unconditionally trust each other since either can do anything that the other can.
329 citations
TL;DR: In this paper, the authors simulate the transport and mixing of diffusive scalars in turbulent flows using a novel representation of the temporal evolution along a transverse line moving with the mean fluid velocity, where the scalar field along this line evolves by Fickian diffusion, representing molecular processes and by randomly occurring events called block inversions.
Abstract: Transport and mixing of diffusive scalars in turbulent flows are simulated computationally based on a novel representation of the temporal evolution along a transverse line moving with the mean fluid velocity. The scalar field along this line evolves by Fickian diffusion, representing molecular processes, and by randomly occurring events called block inversions. Block inversion, representing the effect of turbulent convection, consists of the random selection of an interval (Y0 − 1/2, Y0 + 1/2) of the line, where the interval size l may he either fixed or randomly selected, and replacement of the scalar field θ(y) within that interval by θ(2y0 For fixed l, the model requires a single input parameter, the Peclet number. To demonstrate the performance of the model, this formulation is used to compute the spatial development of diffusive scalar fields downstream of several source configurations in homogeneous turbulence. Generalization to inhomogeneous turbulence is discussed, as well as a formulati...
320 citations
01 May 1988
TL;DR: The general principles that underlie all authentication schemes are reviewed and illustrated using the examples of an early telegraphy cable code, a US military authentication protocol, and authentication of electronic funds transfers in the US Federal Reserve System.
Abstract: The general principles that underlie all authentication schemes are reviewed and illustrated using the examples of an early telegraphy cable code, a US military authentication protocol, and authentication of electronic funds transfers in the US Federal Reserve System. Authentication threats from inside the system (i.e. untrustworthy sender or receiver) are described. The classification of authentication schemes as computationally secure, provably secure, or unconditionally secure is explained, and theoretical results are presented showing that a large number of encoding rules must be available in any unconditionally secure authentication code. Current authentication practices are examined. >
269 citations
TL;DR: The liquidus relations in the system YO1.5-BaO-CuOx in air in the compositional region near the superconducting oxide YBa2Cu3Ox were studied by differential thermal analysis, x-ray diffraction, electron microprobe analysis, and visual observation as discussed by the authors.
Abstract: The liquidus relations in the system YO1.5–BaO–CuOx in air in the compositional region near the superconducting oxide YBa2Cu3Ox were studied by differential thermal analysis, x-ray diffraction, electron microprobe analysis, and visual observation. The temperatures of 11 invariant points and the corresponding reactions were determined. YBa2Cu3Ox was found to melt incogruently at 1015 °C to Y2BaCuO5, which in turn melts incongruently to Y2O3 at 1270 °C. These reactions mean that preparing the superconducting phase by melting and rapid cooling will result in the presence of these two phases as well. The peritectic reaction YBa2Cu3Ox + CuO⇉Y2BaCuO5 + liquid at 940 °C accounts for the observation of partial melting, improved synthesis purity, and grain growth at temperatures of 950 °C. The determination of these invariant temperatures and reactions provide insight into optimal processing conditions.
263 citations
TL;DR: In this paper, the authors unambiguously relate the 608 cm −1 Raman “defect” in a-SiO 2 with reduced Si-OSi bond angles indicative of strained 3-membered rings of silicate tetrahedra.
Abstract: Solid state 29 Si magic angle sample spinning nuclear magnetic resonance spectroscopy and Raman spectroscopy were used to investigate the local silicon environment and siloxane ring vibrations in amorphous silica gels. Our results unambiguously relate the 608 cm −1 Raman “defect” in a-SiO 2 with reduced SiOSi bond angles indicative of strained 3-membered rings of silicate tetrahedra.
TL;DR: In this paper, the concentrations of various functional groups (alkoxy, silanol and Si-O-Si bond) in an acid-catalyzed Si(OCH 3 ) 4 (TMOS):CH 3 OH:H 2 O sol-gel solution were measured using 29 Si NMR.
Abstract: 1 H and 29 Si NMR were used to measure the concentrations of the various functional groups (alkoxy, silanol and SiOSi bond) in an acid-catalyzed Si(OCH 3 ) 4 (TMOS):CH 3 OH:H 2 O sol-gel solution. There are three kinds of functional group reactions: hydrolysis, water producing condensation and alcohol producing condensation. The hydrolysis rate constant was found to be greater than 0.2 1/(mol min). The water-producing condensation and alcohol-producing condensation rate constants are 0.006 and 0.001 1/(mol min), respectively. The rate of hydrolysis is much faster than either rate of condensation. Both condensation pathways are significant for typical sol-gel reaction conditions.
TL;DR: This paper describes a model implementation and test software for the Level 2 Basic Linear Algebra Subprograms (Level 2 BLAS), targeted at matrix-vector operations with the aim of providing more efficient, but portable, implementations of algorithms on high-performance computers.
Abstract: This paper describes a model implementation and test software for the Level 2 Basic Linear Algebra Subprograms (Level 2 BLAS). Level 2 BLAS are targeted at matrix-vector operations with the aim of providing more efficient, but portable, implementations of algorithms on high-performance computers. The model implementation provides a portable set of FORTRAN 77 Level 2 BLAS for machines where specialized implementations do not exist or are not required. The test software aims to verify that specialized implementations meet the specification of Level 2 BLAS and that implementations are correctly installed.
TL;DR: The postirradiation response of CMOS transistors with 30-60-nm gate oxides is investigated as a function of radiation energy, total dose, dose rate, and annealing time and no 'true' dose-rate effects on MOS device response are observed.
Abstract: The postirradiation response of CMOS transistors with 30-60-nm gate oxides is investigated as a function of radiation energy, total dose, dose rate, and annealing time. Measurements of threshold voltage, oxide-trapped charge, and interface traps are reported for times ranging from 10 ms to 4 months following LINAC, Co-60, Cs-137, and 10-keV X-ray irradiations. Exposure dose rates vary by 11 orders of magnitude: from 0.05 to 6*10/sup 9/ rad(SiO/sub 2/)/s. To within the +or-10% uncertainty in the overall dosimetry, no 'true' dose-rate effects on MOS device response are observed. Interface trap and oxide-trapped charge densities are linear with total dose. Preliminary recommendations are made for lot acceptance testing of hardened CMOS circuits and devices intended for use in space and strategic environments. >
TL;DR: In this article, the reaction of labradorite feldspar with an aqueous solution was examined by complementing dissolution rate measurements with analysis of mineral surface chemistry, and the results indicated that the silicon-rich surface of feld spar continually repolymerizes during reaction, and that this repolymersization eliminates hydrogen from the hydration layer.
TL;DR: In this paper, the P/sub b/ centers associated with thermal oxides grown on (111) silicon substrates at 850 /sup 0/C were measured with electron paramagnetic resonance.
Abstract: This paper is concerned with the determination of the kinetic parameters and the chemical reactions that characterize the passivation of P/sub b/ centers with molecular hydrogen. P/sub b/ centers are paramagnetic defects at the (111) Si-SiO/sub 2/ interface. In this study P/sub b/ centers associated with thermal oxides grown on (111) silicon substrates at 850 /sup 0/C were measured with electron paramagnetic resonance. We observe that the P/sub b/ resonance appears to be unaffected by subsequent in situ vacuum anneals for temperatures up to at least 850 /sup 0/C.
TL;DR: In this paper, the evolution of the two-and three-dimensional structures in a temporally growing plane shear layer is numerically simulated with the discrete vortex dynamics method, and the formation of concentrated streamwise vortices in the braid region between the spanwise rollers is observed to grow only initially.
Abstract: The evolution of the two- and three-dimensional structures in a temporally growing plane shear layer is numerically simulated with the discrete vortex dynamics method. We include two signs of vorticity and thus account for the effect of the weaker boundary layer leaving the splitter plate which is used to create a spatially developing mixing layer. The interaction between the two layers changes the symmetry properties seen in a single vorticity-layer calculation and results in closer agreement with experimental observations of the interface between the two streams. Our calculations show the formation of concentrated streamwise vortices in the braid region between the spanwise rollers, whereas the spanwise core instability is observed to grow only initially. Comparison with flow visualization experiments is given, and we find that the processes dominating the early stages of the mixing-layer development can be understood in terms of essentially inviscid vortex dynamics.
TL;DR: In this article, the repeated-root eigenvector derivatives are calculated for the symmetric structural eigen problem and compared with linear approximations to the calculated eigenvectors.
Abstract: In structural optimization and system identification, eigenvector derivatives provide important information for updating design/model parameters. When the current parameter values yield repeated eigenvalues, it has not been possible previously to calculate unique eigenvector derivatives. Recent work has provided a method for determining unique eigenvalue derivatives for this case, but methods for calculating the eigenvector sensitivities have been incomplete. In this work, a complete method for calculation of repeated-root eigenvector derivatives is shown for the real, symmetric structural eigenproblem. The derivation is completed by using information from the second derivative of the eigen problem and is limited to the case of distinct eigenvalue sensitivities. As an example, the repeated-root eigenvector sensitivities are calculated for a simple three degree-of-freedom beam grillage. Comparisons of linear approximations (using these derivatives) to the calculated eigenvectors support the accuracy of the formulation.
TL;DR: In this paper, the authors developed engineering models for forces on rigid, long rods with spherical, ogival, and conical noses that penetrated rate independent, elastic-perfectly plastic targets.
Abstract: We developed engineering models for forces on rigid, long rods with spherical, ogival, and conical noses that penetrated rate independent, elastic-perfectly plastic targets. The spherical and cylindrical, cavity-expansion approximations simplified the target analyses, so we obtained closed-form penetration equations. To verify our models, we performed terminal-ballistic experiments with 7.1-mm dia., 0.024 kg, marging steel rods and 152-mm dia., 6061-T651 aluminum targets. The models predicted penetration depths that were in reasonable agreement with the data for impact velocities between 0.4-1.4 km/s.
TL;DR: The melting and solidification behavior of Alloy 625 has been investigated with differential thermal analysis (DTA) and electron microscopy as discussed by the authors, showing that all alloying additions decreased liquidus and solidus temperatures and also increased the melting temperature range.
Abstract: The melting and solidification behavior of Alloy 625 has been investigated with differential thermal analysis (DTA) and electron microscopy. A two-level full-factorial set of chemistries involving the elements Nb, C, and Si was studied. DTA results revealed that all alloying additions decreased the liquidus and solidus temperatures and also increased the melting temperature range. Terminal solidification reactions were observed in the Nb-bearing alloys. Solidification microstructures in gastungsten-arc welds were characterized with transmission electron microscopy (TEM) techniques. All alloys solidified to an austenitic (γ) matrix. The Nb-bearing alloys terminated solidification by forming various combinations of γ/MC(NbC), γ/Laves, and γ/M6C eutectic-like constituents. Carbon additions (0.035 wt pct) promoted the formation of the γ/MC(NbC) constituent at the expense of the γ/Laves constituent. Silicon (0.4 wt pct) increased the formation of the yJLaves constituent and promoted formation of the γ/M6C carbide constituent at low levels (<0.01 wt pct) of carbon. When both Si (0.4 wt pct) and C (0.035 wt pct) were present, the γ/MC(NbC) and γ/Laves constituents were observed. Regression analysis was used to develop equations for the liquidus and solidus temperatures as functions of alloy composition. Partial derivatives of these equations taken with respect to the alloying variables (Nb, C, Si) yielded the liquidus and solidus slopes t(m
L
, m
S
) for these elements in the multicomponent system. Ratios of these liquidus to solidus slopes gave estimates of the distribution coefficients (k) for these same elements in Alloy 625.
TL;DR: In this paper, a general procedure has been developed for combining a set of elementary chemical reactions into a reduced mechanism, based on independent, approximate relations which permit calculation of concentrations of some species in terms of other known concentrations.
Abstract: Simplification of a detailed reaction mechanism is possible if there exist independent, approximate relations which permit calculation of concentrations of some species in terms of other known concentrations. Given these independent relations, a general procedure has been developed for combining a set of elementary chemical reactions into a reduced mechanism.
Journal Article•
TL;DR: In this article, Raman et al. describe a transmission of modifications de structure au cours de la lixiviation du verre B 2 O 3 -Na 2 O-SiO 2 (pour differentes compositions) a pH=1,2; 9 et 12
Abstract: Etude par spectrometrie Raman et spectrometrie RMN de 29 Si, 11 B, 17 O et 23 Na et par microscopie electronique a transmission des modifications de structure au cours de la lixiviation du verre B 2 O 3 -Na 2 O-SiO 2 (pour differentes compositions) a pH=1,2; 9 et 12
TL;DR: This laser melting technique is applicable to nucleation studies in a wide variety of materials and bounds the interface energy between amorphous Si and liquid Si to be >0.20 Jm/sup 2/.
Abstract: Bulk nucleation of crystalline Si at a supercooling of 505 K was observed following pulsedlaser-induced melting of thin films. If the nucleation was homogeneous, the estimated nucleation rate of ${10}^{29}$ events/${\mathrm{m}}^{3}$ \ifmmode\cdot\else\textperiodcentered\fi{} s implies a liquid-Si-crystalline-Si interfacial energy of 0.34\ifmmode\pm\else\textpm\fi{}0.02 J/${\mathrm{m}}^{2}$. In addition, observation of crystalline nucleation bounds the interface energy between amorphous Si and liquid Si to be g 0.20 J/${\mathrm{m}}^{2}$. This laser melting technique is applicable to nucleation studies in a wide variety of materials.
TL;DR: In this paper, a variety of analytical tools have been combined to show that bulk superconducting La2CuO4+δ has a La to Cu ratio of 2.00 (± 0.02) and an oxygen stoichiometry of 4.13 (±0.1).
Abstract: A variety of analytical tools have been combined to show that bulk superconducting La2CuO4+δ has a La to Cu ratio of 2.00 (±0.02) and an oxygen stoichiometry of 4.13 (±0.1). The combination of these analytical results and magnetization data with a model leads us to suggest that the excess charged oxygen is introduced as O-2.
01 May 1988
TL;DR: The author surveys a collection of protocols in which the level of security or authentication required by the system is actually attained, not because of a failure of the cryptoalgorithm used, but rather because of shortcomings in the design of the protocol.
Abstract: When a cryptoalgorithm is used to solve data security or authentication problems, it is implemented within the context of a protocol that specifies the appropriate procedures for data handling. The purpose of the protocol is to ensure that when the cryptosystem is applied, the level of security or authentication required by the system is actually attained. The author surveys a collection of protocols in which this goal has not been met, not because of a failure of the cryptoalgorithm used, but rather because of shortcomings in the design of the protocol. Guidelines for the development of sound protocols are extracted from an analysis of these failures. >
TL;DR: In this article, the microstructural mechanisms that lead to solder joint failures in thermal fatigue were investigated and it was found that the elevated temperature portion of the thermal cycle was the most significant factor in the heterogeneous coarsening and failure of the solder joints.
Abstract: When an electronic package encounters thermal fluctuations, cyclical shear strain is imposed on the solder joint interconnections. The thermal cycling leads to a condition of thermal fatigue and eventual solder joint failure. This study was performed in order to understand the microstructural mechanisms that lead to solder joint failures in thermal fatigue. Thermal cycling tests were performed on 60Sn-40Pb joints using a -55° C to 125° C cycle and 19% imposed shear strain. A heterogeneously coarsened region of both Pb and Sn-rich phases develops within the 60Sn-40Pb solder joints. Cracks initiate in the heterogeneously coarsened Sn-rich phase at the Sn-Sn grain boundaries. Heterogeneous coarsening and failure occurs in both high (35 to 125° C) and low (-55 to 35° C) thermal cycles. The elevated temperature portion of the thermal cycle was found to be the most significant factor in the heterogeneous coarsening and failure of the solder joints.
TL;DR: The growth of mm-sized polycrystals in the Tl-Ca-Ba-Cu-O and Bi-Ca Sr-Cu O superconductor systems shows the common presence of syntactic intergrowth crystals, which can be described as normal single crystals as discussed by the authors.
Abstract: The growth of mm-sized crystals in the Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O superconductor systems shows the common presence of polycrystals, which can be described as syntactic intergrowth crystals, as well as normal single crystals. Three distinct phases with superconducting transitions at 103 K, 106–108 K and 112–114 K have been grown in the Tl-Ca-Ba-Ca-O system. The newly identified 103 K phase is TlCaBa 2 Cu 2 O 7 which is structurally similar to YBa 2 Cu 3 O 7 but without the presence of chains. Transmission electron diffraction and electron microprobe analysis on several polycrystals show that they are composed of interlayers of these distinct phases grown epitaxially along the c -axis. Crystals have been grown for two phases in the Bi-Ca-Sr-Cu-O system that exhibit transition temperatures at 80 K and at 92 K. Oxygen annealing substantially improves the superconducting properties of most of the crystals.
01 Mar 1988
TL;DR: In this paper, the authors studied flame-generated (fumed) silica particles in situ by static and dynamic light scattering and ex situ by transmission electron microscopy, and found that the growth and aggregation of the particles were followed as a function of height in the flame.
Abstract: We studied flame-generated (fumed) silica particles in situ by static and dynamic light scattering and ex situ by transmission electron microscopy. The growth and aggregation of the particles was followed as a function of height in the flame. The scattered intensity appeared to be consistent with a fractal aggregate structure having a fractal dimension of D = 1.49 (smaller than previously reported ex situ measurements of fumed silica) although the data are too limited to determine D with certainty. From the dynamic light scattering results, corrected for polydispersity, the growth trend appeared to deviate from free-molecular behavior for long residence times. From the electron microscopy, we noted a surprising tendency for the silica monomers to shrink with residence time.