Showing papers by "Sandia National Laboratories published in 1992"
TL;DR: In a comprehensive study, the modified embedded-atom method is extended to a variety of cubic materials and impurities, including metals, semiconductors, and diatomic gases, all of which exhibit different types of bonding.
Abstract: In a comprehensive study, the modified embedded-atom method is extended to a variety of cubic materials and impurities. In this extension, all functions are analytic and computationally simple. The basic equations of the method are developed and applied to 26 elements: ten fcc, ten bcc, three diamond cubic, and three gaseous materials. The materials modeled include metals, semiconductors, and diatomic gases, all of which exhibit different types of bonding. Properties of these materials, including equation of state, elastic moduli, structural energies and lattice constants, simple defects, and surfaces, are calculated. The formalism for applying the method to combinations of these elements is developed and applied to the calculation of dilute heats of solution. In all cases, comparison is made to experiment or higher-level calculations when possible.
1,683 citations
TL;DR: This work simulates an apparatus that learns to excite specified rotational states in a diatomic molecule and uses a learning procedure to direct the production of pulses based on fitness'' information provided by a laboratory measurement device.
Abstract: We simulate a method to teach a laser pulse sequences to excite specified molecular states. We use a learning procedure to direct the production of pulses based on ``fitness'' information provided by a laboratory measurement device. Over a series of pulses the algorithm learns an optimal sequence. The experimental apparatus, which consists of a laser, a sample of molecules and a measurement device, acts as an analog computer that solves Schr\"odinger's equation n/Iexactly, in real time. We simulate an apparatus that learns to excite specified rotational states in a diatomic molecule.
1,426 citations
TL;DR: This paper surveys the work on gross-motion planning, including motion planners for point robots, rigid robots, and manipulators in stationary, time-varying, constrained, and movable-object environments.
Abstract: Motion planning is one of the most important areas of robotics research. The complexity of the motion-planning problem has hindered the development of practical algorithms. This paper surveys the work on gross-motion planning, including motion planners for point robots, rigid robots, and manipulators in stationary, time-varying, constrained, and movable-object environments. The general issues in motion planning are explained. Recent approaches and their performances are briefly described, and possible future research directions are discussed.
909 citations
TL;DR: In this article, a chemical kinetic model was proposed to predict the growth of higher hydrocarbons in a lightly sooting C2H2/O2/Ar flame, and the predictions of the model compare favorably with the experimental results of Bastin et al. (20th Combustion Symposium).
850 citations
TL;DR: In this article, a combination of coating theory and experiment is used to define coating protocols to tailor the deposition process to specific applications, which can be used to tailor coating protocols for specific applications.
Abstract: Sol-gel thin films are formed by gravitational or centrifugal draining accompanied by vigorous drying. Drying largely establishes the shape of the fluid profile, the timescale of the deposition process, and the magnitude of the forces exerted on the solid phase. The combination of coating theory and experiment should define coating protocols to tailor the deposition process to specific applications.
537 citations
TL;DR: In this article, a review of hydrogen interactions with imperfections in crystalline metals and semiconductors is presented, focusing on mechanistic experiments and theoretical advances contributing to predictive understanding.
Abstract: Hydrogen interactions with imperfections in crystalline metals and semiconductors are reviewed. Emphasis is given to mechanistic experiments and theoretical advances contributing to predictive understanding. Important directions for future research are discussed.
427 citations
TL;DR: A new beam-propagation method is presented whereby the exact scalar Helmholtz propagation operator is replaced by any one of a sequence of higher-order Pade approximant operators, resulting in a matrix equation of bandwidth 2n + 1 that is solvable by using Standard implicit solution techniques.
Abstract: A new beam-propagation method is presented whereby the exact scalar Helmholtz propagation operator is replaced by any one of a sequence of higher-order (n, n) Pade approximant operators. The resulting differential equation may then be discretized to obtain (in two dimensions) a matrix equation of bandwidth 2n + 1 that is solvable by using Standard implicit solution techniques. The final algorithm allows (for n = 2) accurate propagation at angles of greater than 55 deg from the propagation axis as well as propagation through materials with widely differing indices of refraction.
421 citations
TL;DR: In this article, a new boundary condition was proposed for beam propagation calculations that passes outgoing radiation freely with minimum reflection coefficient (as low as 3*10/sup -8/).
Abstract: A new boundary condition is presented for use in beam propagation calculations that passes outgoing radiation freely with minimum reflection coefficient (as low as 3*10/sup -8/). In conjunction with a standard Crank-Nicholson finite difference scheme, the assumption that the radiation field behaves as a complex exponential near the boundary is shown to result in a specific transparent boundary condition algorithm. In contrast to the commonly used absorber method, this algorithm contains no adjustable parameters, and is thus problem independent. It is shown to be accurate and robust for both two- and three-dimensional problems. >
392 citations
Journal Article•
TL;DR: The Ulysses solar wind plasma experiment, termed the Solar Wind Observations Over the Poles of the Sun (SWOOPS) as mentioned in this paper, includes measurements of the solar-wind global properties, the nonlinear MHD disturbances in the solar wind, and the internal state of the plasma.
Abstract: The scientific objectives of the Ulysses solar wind plasma experiment, termed the Solar Wind Observations Over the Poles of the Sun (SWOOPS) include measurements of the solar-wind global properties, the nonlinear MHD disturbances in the solar wind, the internal state of the solar wind plasma, and the solar-wind interaction with Jupiter's magnetic field. In this paper, special attention is given to the two instrumental packages of SWOOPS experiment that will simultaneously perform measurements on electrons and ions of solar plasma: the ion analyzer and the electron analyzer. Results obtained in the initial phases of the SWOOPS experiment are presented.
386 citations
TL;DR: Most applications of the exponentially weighted moving average (EWMA) for process monitoring have concentrated on the problem of detecting shifts in the mean level of a process as mentioned in this paper, but perhaps more important is detecting increases in process var..
Abstract: Most applications of the exponentially weighted moving average (EWMA) for process monitoring have concentrated on the problem of detecting shifts in the mean level of a process. Perhaps more important is the problem of detecting increases in process var..
326 citations
TL;DR: In this paper, the authors extend these results to a nonlinear n-DOF system and prove its stability, using nonlinear, multidimensional networks to characterize the nonlinear equations for the master and slave manipulators, the time-delayed communication systems, the human o...
Abstract: A bilateral system consists of a local master manipulator and a remotely located slave manipulator. Velocity commands are sent forward from the master to the slave, and force information is "re flected "back from the slave to the master. Often there is a transmission delay when communicating between the two subsys tems, which causes instability in the force-reflecting teleoperator. Recently, a solution for this instability problem was found, based on mimicking the behavior of a lossless transmission line. Al though the resulting control law was shown to stabilize an actual single-DOF teleoperator system, and although the control law is intuitively stable because of its passivity properties, stability for the system has not yet been proven. In this article we extend these results to a nonlinear n-DOF system and prove its stability. Non linear, multidimensional networks are used to characterize the nonlinear equations for the master and slave manipulators, the time-delayed communication systems, the human o...
TL;DR: In this paper, the terminology for oxide charges developed in 1979 was updated to include near-interfacial oxide traps that communicate with the underlying Si and that these defects collectively be called border traps.
Abstract: The author recommends that the terminology for oxide charges developed in 1979 be updated to include near-interfacial oxide traps that communicate with the underlying Si and that these defects collectively be called border traps. Justification for this nomenclature is presented and defining features of border traps are discussed. Border traps play an important role in determining low-frequency (1/f) noise levels in metal-oxide-semiconductor (MOS) transistors and also appear to have been observed in recent spin-dependent recombination studies on irradiated devices at microwave frequencies. This terminology is intended to add focus to discussions of defect type and location in MOS structures. >
TL;DR: In this article, the authors conducted perforation experiments with 254mm diameter, 050-kg, 30-caliber radius head, ogival-nose rods and 178mm-thick concrete slabs with 48 MPa and 140 MPa unconfined compressive strengths for impact velocities between 300 and 1100 m/s.
TL;DR: In this article, the authors developed penetration equations for ogival-nose projectiles that penetrated soil targets after normal impact, using spherical cavity-expansion approximation simplified the target analysis and obtained closed-form penetration equations.
24 May 1992
TL;DR: In this article, the authors present a method of speeding up a fixed element g of a group (generally Z/qZ) by using precomputed values to reduce the number of multiplications needed.
Abstract: In several cryptographic systems, a fixed element g of a group (generally Z/qZ) is repeatedly raised to many different powers. In this paper we present a practical method of speeding up such systems. using precomputed values to reduce the number of multiplications needed. In practice this provides a substantial improvement over the level of performance that can be obtained using addition chains, and allows the computation of gn for n < N in O(log N/log log N) group multiplications. We also show how these methods can he parallelized, to compute powers in O(log log N) group multiplications with O(log N/ log log N) processors.
TL;DR: Asymmetric photoelectron angular distributions for atomic rubidium are measured and interference between the even- and odd-parity free-electron wave functions allows us to control the direction of maximum electron flux by varying the relative phase of the two laser fields.
Abstract: We have measured asymmetric photoelectron angular distributions for atomic rubidium. Ionization is induced by a one-photon interaction with 280 nm light and by a two-photon interaction with 560 nm light. Interference between the even- and odd-parity free-electron wave functions allows us to control the direction of maximum electron flux by varying the relative phase of the two laser fields.
TL;DR: The use of IDDQ testing for IC quality improvement through increased defect and fault detection is described, and implementation issues are considered, including test pattern generation software, hardware instrumentation, limit setting, IC design guidelines, and defect diagnosis.
Abstract: Quiescent power supply current (I
DDQ
) testing of CMOS integrated circuits is a technique for production quality and reliability improvement, design validation, and failure analysis. It has been used for many years by a few companies and is now receiving wider acceptance as an industry tool. This article begins with a brief history of CMOS ICs to provide perspective on the origin of I
DDQ
testing. Next, the use of I
DDQ
testing for IC quality improvement through increased defect and fault detection is described. Then implementation issues are considered, including test pattern generation software, hardware instrumentation, limit setting, IC design guidelines, and defect diagnosis. An extended reference list is provided to help the reader obtain more information on specific aspects.
TL;DR: In this article, the authors described a self-assembled monolayer and its sensitivity from a mass-sensitive surface acoustic wave (SAW) device, which takes advantage of the interaction between organophosphonate nerve-agent simulants and a composite monoline, consisting of Cu[sup 2+] tethered to the SAW device by an ordered, carboxylate-terminated n-alkanethiol monoline.
Abstract: The device described in this report derives its selectivity, reversibility, and durability from a simple, self-assembled monolayer and its sensitivity from a mass-sensitive surface acoustic wave (SAW) device. The coating design takes advantage of the interaction between organophosphonate nerve-agent simulants and a composite monolayer, consisting of Cu[sup 2+] tethered to the SAW device by an ordered, carboxylate-terminated n-alkanethiol monolayer. The rationale for this design is that Cu[sup 2+] and some of its chelates are hydrolysis catalysts for certain nerve agents. Thus, a surface layer of coordinatively unsaturated Cu[sup 2+] might be expected to provide selective and reversible binding sites for organophosphonates. The authors have demonstrated that this simple fabrication procedure incorporates all of the essential features of an ideal sensor: (1) it is selective for organophosphonates; (2) it is sensitive to 100 ppb of an important nerve-gas simulant; (3) it provides a reversible and proportional response to target analytes; (4) it is durable for periods of months. 19 refs., 3 figs.
TL;DR: In this paper, the Pade approximant wide-angle propagation operator is factored into a series of simpler Pade (1, 1) operators, thus leading naturally to a multistep method whose component steps are each solvable by using readily available paraxiallike solution techniques.
Abstract: A new beam-propagation method is presented whereby the Pade approximant wide-angle propagation operator is factored into a series of simpler Pade (1, 1) operators, thus leading naturally to a multistep method whose component steps are each solvable by using readily available paraxiallike solution techniques. The resulting method allows accurate approximations to true Helmholtz propagation while incurring only a modest numerical penalty. In addition, the tridiagonal form of the component steps allows the straightforward use of the previously reported transparent boundary condition.
TL;DR: It is proved that, for any graphG having maximum degreed, there is a perfect secret sharing scheme realizingG in which the information rate is at least 2/(d+3), which improves the best previous general bound by a factor of almost two.
Abstract: In this paper we study secret sharing schemes for access structures based on graphs. A secret sharing scheme enables a secret key to be shared among a set of participants by distributing partial information called shares. Suppose we desire that some specified pairs of participants be able to compute the key. This gives rise in a natural way to a graphG which contains these specified pairs as its edges. The secret sharing scheme is calledperfect if a pair of participants corresponding to a nonedge ofG can obtain no information regarding the key. Such a perfect secret sharing scheme can be constructed for any graph. In this paper we study the information rate of these schemes, which measures how much information is being distributed as shares compared with the size of the secret key. We give several constructions for secret sharing schemes that have a higher information rate than previously known schemes. We prove the general result that, for any graphG having maximum degreed, there is a perfect secret sharing scheme realizingG in which the information rate is at least 2/(d+3). This improves the best previous general bound by a factor of almost two.
TL;DR: In this paper, multilayer Molybdenum disulfide (MoS 2 ) solid lubricant films were prepared by r.f. magnetron sputtering on 440C steel, 52100 steel, and silicon substrates.
Abstract: Molybdenum disulfide (MoS 2 ) solid lubricant films were prepared by r.f. magnetron sputtering on 440C steel, 52100 steel, and silicon substrates. This study concentrated on films that were multilayer coatings of MoS 2 with either nickel or Au-(20%)Pd metal interlayers. Multilayer thicknesses ranged from 0.2 nm to 1.0 nm while the multilayer periodic spacing ranged from 3 to 10 nm. Scanning electron microscopy and X-ray diffraction revealed that the multilayer films had dense microstructures that, in some cases, exhibited significant orientation of their basal planes parallel to the substrate. Film endurance was assessed in sliding contact using thrust washer tests and in rolling contact using thrust bearing tests. Some film microstructures exhibited excellent endurance. Brale indentation indicated that the metal layers can improve film fracture toughness. Friction in air and ultrahigh vacuum (UHV) was investigated using a UHV-compatible test apparatus. Friction coefficients between 0.05 and 0.08 were measured in UHV.
TL;DR: Light scattering and precision calorimetry show that the nematic ordering of octylcyanobiphenyl (8CB) filling the connected network of pores of a silica aerogel does not occur via the first-order phase transition characteristic of the bulk.
Abstract: Light scattering and precision calorimetry show that the nematic ordering of octylcyanobiphenyl (8CB) filling the connected network of pores of a silica aerogel does not occur via the first-order phase transition characteristic of the bulk. Rather, ordering is continuous with an orientational correlation length never increasing beyond the aerogel pore size. The heat-capacity anomly of the second-order nematic--smectic-A phase transition seen in the bulk is absent or greatly broadened in the aerogel.
TL;DR: The unique properties of degenerate four-wave mixing, a nonlinear optical technique, have recently been found to provide powerful capabilities for a wide range of applications.
Abstract: Spectroscopies that make use of laser light have provided an important tool to modern researchers for the nonintrusive analysis of chemical systems. The strengths and limitations of these spectroscopic techniques often determine the viability of scientific investigations. The unique properties of degenerate four-wave mixing, a nonlinear optical technique, have recently been found to provide powerful capabilities for a wide range of applications.
TL;DR: In this paper, it was shown that dissolution rates of compositionally distinct orthosilicate minerals scale in a fashion similar to rates of water exchange around the corresponding dissolved, divalent cation.
Abstract: COMMON rock-and soil-forming minerals are complicated structures of varying composition. Despite some encouraging progress1,2 there is as yet no comprehensive rationale for predicting the dissolution rates of these minerals. Here we test the hypothesis3 that dissolution rates of compositionally distinct orthosilicate minerals scale in a fashion similar to rates of water exchange around the corresponding dissolved, divalent cation. Although dissolution rates span several orders of magnitude, the hypothesis is sustained. Minerals containing alkaline-earth cations dissolve at rates that correlate with ionic size, whereas minerals containing first-row transition metals dissolve at rates that vary with the number of cationd-electrons. Both types of behaviour are consistent with the control of dissolution rate by the character of the bonds between the divalent cation and neighbouring oxygen atoms. This result supports the proposed link3–6 between the mechanisms of mineral dissolution and the mechanisms by which a dissolved metal exchanges ligands. With this link it may be possible to predict dissolution rates for other nearly isostructural minerals that vary in composition.
TL;DR: A water-rich magmatic gas phase escaped explosively from Mount Pinatubo on June 15, 1991, taking with it a load of crystalline and molten material sufficient to form pumice and tephra deposits with an estimated total dense-rock-equivalent volume of 3-5 km 3 and carrying in it enough sulfur to form a 20 Mt SO 2 cloud in the stratosphere as discussed by the authors.
Abstract: A water-rich magmatic gas phase escaped explosively from Mount Pinatubo on June 15, 1991, taking with it a load of crystalline and molten material sufficient to form pumice and tephra deposits with an estimated total dense-rock-equivalent volume of 3-5 km 3 (Scott et al., 1991), and carrying in it enough sulfur to form a 20 Mt SO 2 cloud in the stratosphere. Application of the "petrologic method" for estimating sulfur degassing during the climactic event from the sulfur content of trapped glass inclusions and matrix glasses in the pumice deposits requires an unacceptably large volume of erupted magma to account for SO 2 in the stratospheric cloud. The ubiquitous presence of primary vapor bubbles in glass inclusions and unaltered anhydrite phenocrysts in the pumice suggest that sulfur was present in a separate H 2 O-rich gas phase of the Pinatubo magma before eruption. Thus, for this eruption, and perhaps others, the petrologic method for estimating sulfur degassing is prone to substantial underestimation of sulfur release and the potential climatic impact of past explosive eruptions.
TL;DR: In this paper, the physical and chemical structures of gels dried from aprotic solvents were studied by a series of techniques (29 Si MAS-NMR, nitrogen adsorption, SAXS, elemental analysis, TGA).
Abstract: A two-step acid/base-catalyzed silica gel has been aged in alcohol and water baths followed by various aprotic solvents with a wide range of surface tensions. Low temperature (CO 2 ) and high temperature (ethanol) aerogels were also prepared. The physical and chemical structures of gels dried from aprotic solvents were studied by a series of techniques ( 29 Si MAS-NMR, nitrogen adsorption, SAXS, elemental analysis, TGA). The aprotic solvents isolated the effects of pore fluid surface tension during drying since they do not participate in condensation and other reactions. For aprotic solvents, a linear decrease in xerogel surface area was observed with increasing surface tension. Pore volume and pore size distribution followed a similar trend. Depending upon whether the gel had been washed in ethanol or water prior to the aprotic solvent, the final pore volume was changed significantly for a given surface tension. This indicates that both surface area and pore volume may be independently controlled.
TL;DR: In this article, the authors show that no lattice exhibits periodic behavior in uniaxial extensional flow, even though Adler & Brenner have established the existence of compatibility.
TL;DR: Using the newly developed interfacial-force microscope, the first measurements of the mechanical relaxation of a Au supported, self-assembled monolayer film interacting with a microscopic tungsten tip are presented.
Abstract: Using the newly developed interfacial-force microscope, we present results for the first measurements of the mechanical relaxation of a Au supported, self-assembled monolayer film interacting with a microscopic tungsten tip. For a methyl-terminated n-alkanethiol film, we observe negligible adhesive film-tip interaction and complete passivation of tip-substrate bonding. The mechanical behavior of the film itself shows a time-dependent, elastic response.
TL;DR: In this article, a numerical and experimental study of hydroxyl radical chemiluminescence from methane-air flames was performed, and it was found that the chemilumininescence intensity was highly dependent on the equivalence ratio.
Abstract: A numerical and experimental study of hydroxyl radical chemiluminescence from methane-air flames was performed. Measurements of the chemiluminescence per unit flame area for lean methane-air flames were obtained, and a model for use in predicting chemiluminescence was developed. The model was one-dimensional and unsteady, incorporating the equations of species continuity and energy, with temperature- and concentration-dependent transport and thermodynamic properties. The reaction mechanism included the chemiluminescent reaction, as well as reactions that both produced and quenched electronically excited OH. It was found, both experimentally and numerically, that the chemiluminescent intensity was highly dependent on the equivalence ratio. For !he range of equivalence ratios studied experimentally (0·65 < φ < 0·90) there was an exponential dependence of chemiluminescence on equivalence ratio. The predicted chemiluminescent intensity was most sensitive to the rate constant of the reaction, , in bot...
TL;DR: An analytical model with no free parameters has been developed which accurately describes thermally-stimulated-current (TSC) measurements spanning more than a factor of 50 in average heating rate.
Abstract: An analytical model with no free parameters has been developed which accurately describes thermally-stimulated-current (TSC) measurements spanning more than a factor of 50 in average heating rate. The model incorporates Schottky electric-field-induced barrier lowering and a temperature-dependent 'attempt-to-escape frequency' equal to approximately 10/sup 14/ Hz at 300 degrees C. Applying this model to TSC measurements provides significantly improved estimates of the energy distribution of trapped holes in irradiated SiO/sub 2/. All devices examined, including soft and (wet and dry) hard oxides from five process technologies, show similar energy distributions, with a minor peak at approximately 1.2 eV and a broad major peak centered approximately 1.7-2.0 eV above the SiO/sub 2/ valance band. It is found that the trapped-electron density in irradiated SiO/sub 2/ is proportional to the trapped-hole density over a wide range of irradiation conditions. >