Showing papers by "Oak Ridge National Laboratory published in 1992"

An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments

Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.

On the generality of the relationship among contact stiffness, contact area, and elastic modulus during indentation

Abstract: Results of Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space are used to show that a simple relationship exists between the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch. The generality of the relationship has important implications for the measurement of mechanical properties using load and depth sensing indentation techniques and in the measurement of small contact areas such as those encountered in atomic force microscopy.

Screening, predicting, and computer experiments

Abstract: Many scientific phenomena are now investigated by complex computer models or codes. Given the input values, the code produces one or more outputs via a complex mathematical model. Often the code is expensive to run, and it may be necessary to build a computationally cheaper predictor to enable, for example, optimization of the inputs. If there are many input factors, an initial step in building a predictor is identifying (screening) the active factors. We model the output of the computer code as the realization of a stochastic process. This model has a number of advantages. First, it provides a statistical basis, via the likelihood, for a stepwise algorithm to determine the important factors. Second, it is very flexible, allowing nonlinear and interaction effects to emerge without explicitly modeling such effects. Third, the same data are used for screening and building the predictor, so expensive runs are efficiently used. We illustrate the methodology with two examples, both having 20 input variables. I...

The deformation behavior of ceramic crystals subjected to very low load (nano)indentations

Abstract: The ultra-low load indentation response of ceramic single crystal surfaces (Al2O3, SiC, Si) has been studied with a software-controlled hardness tester (Nanoindenter) operating in the load range 2–60 mN. In all cases, scanning and transmission electron microscopy have been used to characterize the deformation structures associated with these very small-scale hardness impressions. Emphasis has been placed on correlating the deformation behavior observed for particular indentations with irregularities in recorded load-displacement curves. For carefully annealed sapphire, a threshold load (for a given indenter) was observed below which the only surface response was elastic flexure and beyond which dislocation loop nucleation occurred at, or near, the theoretical shear strength to create the indentation. This onset of plasticity was seen as a sudden displacement discontinuity in the load-displacement response. At higher loads, indentations appeared to be accommodated predominantly by dislocation activity, though microcracks were observed to form at contact loads of only tens of milliNewtons. Possibly such cracks are the incipient slip-induced nuclei for the much larger, indentation-induced cracks usually apparent only on the surface at much higher loads and often used for estimating indentation toughness. By contrast, silicon did not show this behavior but exhibited unusually large amounts of depth recovery within indentations, resulting in a characteristic reverse thrust on the indenter during unloading. TEM studies of indentations in silicon revealed less evidence of obvious dislocation activity than in sapphire (particularly at the lowest loads used) but did show residual highly imperfect–and often amorphous–structures within the indentations, consistent with a densification transformation occurring at the very high hydrostatic stresses produced under the indenter. The reverse thrust is caused by the relaxation of densified material during unloading. Thus, it appears that the low-load hardness response of silicon is controlled by a pressure-sensitive phase transformation. Though SiC has been predicted to undergo a densification transformation similar to silicon, its load-displacement behavior was found to be similar to Al2O3 suggesting that, for these contact experiments at least, the critical resolved shear stress for dislocation nucleation is exceeded before the critical hydrostatic pressure for densification is reached. In all cases, residual, plastically formed indentations were measured to be smaller than the fully loaded indentation depths would suggest, confirming that a significant portion of the deformation is elastic surface flexure. However, there is some doubt as to whether silicon displays elastic-only deformation even at very small penetration depths. The use of microstructural studies to complement nanoindentation experiments is shown to be a key route not only to interpreting the recorded load-displacement responses, but also to examining the deformation mechanisms controlling the mechanical behavior of ceramics to surface contacts at these small spatial scales.

Omniview motionless camera orientation system

Abstract: A device for omnidirectional image viewing providing pan-and-tilt orientation, rotation, and magnification within a hemispherical field-of-view that utilizes no moving parts. The imaging device is based on the effect that the image from a fisheye lens (1), which produces a circular image of an entire hemispherical field-of-view, which can be mathematically corrected using high speed electronic circuitry (5, 6, 7, 12 and 13). More specifically, an incoming fisheye image from any image acquisition source (2) is captured in memory (4) of the device, a transformation is performed for the viewing region of interest and viewing direction, and a corrected image is output as a video image signal for viewing, recording, or analysis. As a result, this device can be accomplish the functions of pan, tilt, rotation, and zoom throughout a hemispherical field-of-view without the need for any mechanical mechanisms. The preferred embodiment of the image transformation device can provide corrected images at real-time rates, compatible with standard video equipment. The device can be used for any application where a conventional pan-and-tilt or orientation mechanism might be considered including inspection, monitoring, surveillance, and target acquisition.

Fabrication and characterization of amorphous lithium electrolyte thin films and rechargeable thin-film batteries

Abstract: Amorphous oxide and oxynitride lithium electrolyte thin films were synthesized by r.f. magnetron sputtering of lithium silicates and lithium phosphates in Ar, Ar + O2, Ar + N2, or N2. The composition, structure, and electrical properties of the films were characterized using ion and electron beam, X-ray, optical, photoelectron, and a.c. impedance techniques. For the lithium phosphosilicate films, lithium ion conductivities as high as 1.4 × 10−6 S/cm at 25 °C were observed, but none of these films selected for extended testing were stable in contact with lithium. On the other hand, a new thin-film lithium phosphorus oxynitride electrolyte, synthesized by sputtering Li3PO4 in pure N2, was found to have a conductivity of 2 × 10-6 S/cm at 25 °C and excellent long-term stability in contact with lithium. Thin-films cells consisting of a 1 μm thick amorphous V2O5 cathode, a 1 μm thick oxynitride electrolyte film, and a 5 μm thick lithium anode were cycled between 3.7 and 1.5 V using discharge rates of up to 100 μA/cm2 and charge rates of up to 20 μA/cm2. The open-circuit voltage of 3.6 to 3.7 V of fully-charged cells remained virtually unchanged after months of storage.

ScaLAPACK: a scalable linear algebra library for distributed memory concurrent computers

Abstract: The authors describe ScaLAPACK, a distributed memory version of the LAPACK software package for dense and banded matrix computations. Key design features are the use of distributed versions of the Level 3 BLAS as building blocks, and an object-oriented interface to the library routines. The square block scattered decomposition is described. The implementation of a distributed memory version of the right-looking LU factorization algorithm on the Intel Delta multicomputer is discussed, and performance results are presented that demonstrate the scalability of the algorithm. >

Productivity and compensatory responses of yellow-poplar trees in elevated C0 2

Abstract: INCREASED forest growth in response to globally rising CO2 concentrations could provide an additional sink for the excess carbon added to the atmosphere from fossil fuels1,2. The response of trees to increased CO2, however, can be expected to be modified by the interactions of other environmental resources and stresses, higher-order ecological interactions and internal feedbacks inherent in the growth of large, perennial organisms3,4. To test whether short-term stimulation of tree growth by elevated CO2 can be sustained without inputs from other environmental resources, we grew yellow-poplar (Liriodendron tulipifera L.) saplings for most of three growing seasons with continuous exposure to ambient or elevated concentrations of atmospheric CO2. Despite a sustained increase in leaf-level photosynthesis and lower rates of foliar respiration in CO2-enriched trees, whole-plant carbon storage did not increase. The absence of a significant growth response is explained by changes in carbon allocation patterns, specifically a relative decrease in leaf production and an increase in fine root production. Although these compensatory responses reduced the potential increase in carbon storage in increased CO2 concentrations, they also favour the efficient use of resources over the longer term.

Alkylphenol ethoxylates in the environment

Abstract: A comprehensive monitoring study, sponsored by the Chemical Manufacturers Association and designed in cooperation with the Environmental Protection Agency (EPA), measured the levels of nonylphenol (NP) and its ethoxylates (NPE) in 30 rivers. The sites, all receiving municipal or industrial wastewater, were selected at random from EPA’s United States river reach database by a statistical procedure. Water column and bottom sediment samples were collected along a perpendicular transect at each site. All samples were assayed for NP and NPE1, and the higher ethoxylates (NPE2 to NPE17) were determined in the water samples. Analysis was by high-performance liquid chromatography (HPLC) with fluorescence detection of microgram quantities of NPE obtained by extractive steam distillation (NP and NPE1) or a dualcolumn extraction procedure (NPE2 to NPE17). Sample collection and analytical procedures were validated according to rigorous EPA guidelines, and quality assurance standards were met throughout the study. NP and NPE concentrations in river water were mostly (60 to 75% of the samples) below their detection limits (about 0.1 ppb for NP, NPE1, and NPE2; 1.6 ppb for NPE3–17). The highest levels found were about 1 ppb for NP, NPE1, and NPE2, 15 ppb for NPE3–17. A majority of sediment samples contained detectable amounts of NP and NPE1, ranging up to 3000 ppb for NP and 170 ppb for NPE1. Sediment interstitial water concentrations of NP were estimated to be similar to concentrations in the water column.

Fullerenes from the geological environment.

Abstract: By means of high-resoluton transmission electron microscopy, both C60 and C70 fullerenes have been found in a, carbon-rich Precambrian rock from Russia The fullerenes were confirmed by Fourier transform mass spectrometry with both laser desorption and thermal desorption/electron-capture methods to verify that the fullerenes were indeed present in the geological sample and were not generated by the laser ionization event. The mass spectra were measured under conditions sufficient to resolve the 13C/12C isotopic ratios for C60 and C70 and indicate that these ratios correspond to the normal range of isotopic values.

Regulation of nutrient concentrations in a temperate forest stream: Roles of upland, riparian, and instream processes

Abstract: The roles of terrestrial and instream processes in controlling stream-water N and P concentrations were studied over a 2-yr period in a deciduous forest stream in eastern Tennessee. Upper soil horizons were highly effective sinks for inorganic N and P in throughfall, and weathering of the parent dolomite was the dominant source of inorganic P to the stream. The riparian zone was a potential source of NH,+ and P to the stream when dissolved oxygen concentrations in riparian groundwater were low, but a sink for P when dissolved oxygen concentrations were high. High rates of instream immobilization of inorganic N and P were observed from late autumn to spring, primarily as a result of uptake by microbes on decomposing leaves and secondarily by algae. Immobilization of inorganic N and P resulted in longitudinal declines in concentrations with distance downstream from groundwater inputs (springs), thereby increasing the importance of organic forms of these nutrients in stream water in downstream reaches. The seasonal pattern of winter minima and summer maxima in stream-water N and P concentrations observed here is opposite to the pattern observed in many northern streams, suggesting the importance of winter nutrient cycling processes in soils and streams in warmer climates.

Electrochemical Origin of Radical Cations Observed in Electrospray Ionization Mass Spectra

Abstract: A variety of experimental data is presented that implicates electrochemical oxidation of analytes in the electrospray (ES) needle as the mechanism for formation of molecular radical cations observed in the ES ionization mass spectra of alkylsubstituted metalloporphyrins, polycyclic aromatic hydrocarbons (PAH`s), and other compound types. Analyte structural characteristics and solution-phase half-wave oxidation potentials (which correlate with gas-phase ionization energies) can be used to evaluate the likelihood of forming and observing a particular compound as a radical cation. Use of an appropriate solvent is critical in the observation of radical cations generated by the ES process. In addition to dissolving the analyte and providing a stable electrospray, the solvent-(s) must {open_quotes}stabilize{close_quotes} or otherwise protect the radical cation from reactions in solution. Appropriate solvent systems (e.g., methylene chloride/0.1% trifluoroacetic acid) are much the same as used in traditional studies of electrochemically generated radical cations. The ability to produce radical cations in the ES process expands the utility of ES ionization mass spectrometry to include compound classes not normally amenable to the technique (e.g., neutral, nonpolar compounds such as PAH`s) and provides for generation of a different type of molecular species than normally produced in positive-ion ES ionization (i.e., M{sup {sm_bullet}+} versus (Mmore » + H){sup +}, (M + Na){sup +}, etc.).« less

Network-based concurrent computing on the PVM system

Abstract: Concurrent computing environments based on loosely coupled networks have proven effective as resources for multiprocessing. Experiences with and enhancements to PVM (Parallel Virtual Machine) are described in this paper. PVM is a software package that allows the utilization of a heterogeneous network of parallel and serial computers as a single computational resource. This report also describes an interactive graphical interface to PVM, and porting and performance results from production applications. 23 refs., 5 figs., 5 tabs.

Grain-Size-Dependent Transformation Behavior in Polycrystalline Tetragonal Zirconia

Abstract: In this paper experimental observations of the tetragonal phase transformation behavior in polycrystalline zirconias and the related toughening contribution are presented. An analysis which considers transformation thermodynamics and residual stresses is developed to describe the influence of grain size on tetragonal-to-monoclinic transformation temperature. The model is based on the promotion of the transformation by local internal tensile stress concentrations whose effects scale with grain size. The analysis is supported by observations of the martensite start temperature---grain size behavior in polycrystalline tetragonal zirconia containing 12 mol% ceria (12 CeTZP). Next, the analysis considers the grain-size-dependent behavior of the transformation-toughening contribution, {Delta}K{sup T}, and the transformation zone size, r{sup T}.

Solution conformation of the major adduct between the carcinogen (+)-anti-benzo[a]pyrene diol epoxide and DNA.

Abstract: We have synthesized, separated, and purified approximately 10 mg of a deoxyundecanucleotide duplex containing a single centrally positioned covalent adduct between (+)-anti-benzo[a]pyrene (BP) diol epoxide and the exocyclic amino group of guanosine. Excellent proton NMR spectra are observed for the (+)-trans-anti-BP diol epoxide-N2-dG adduct positioned opposite dC and flanked by G.C pairs in the d[C1-C2-A3-T4-C5-(BP)G6-C7-T8-A9-C10-C11].d[12- G13-T14-A15-G16-C17-G18-A19-T20-G 21-G22] duplex +ADdesignated (BP)G.C 11-mer+BD. We have determined the solution structure centered about the BP covalent adduct site in the (BP)G.C 11-mer duplex by incorporating intramolecular and intermolecular proton-proton distance bounds deduced from the NMR data sets as constraints in energy minimization computations. The BP ring is positioned in the minor groove and directed toward the 5' end of the modified strand. One face of the BP ring of (BP)G6 is stacked over the G18 and A19 sugar-phosphate backbone on the partner strand and the other face is exposed to solvent. A minimally perturbed B-DNA helix is observed for the d[T4-C5-(BP)G6-C7-T8].d[A15-G16-C17-G18-A19] segment centered about the adduct site with Watson-Crick alignment for both the (BP)G6.C17 pair and flanking G.C pairs. A widening of the minor groove at the adduct site is detected that accommodates the BP ring whose long axis makes an angle of approximately 45 degrees with the average direction of the DNA helix axis. Our study holds future promise for the characterization of other steroisomerically pure adducts of BP diol epoxides with DNA to elucidate the molecular basis of structure-activity relationships associated with the stereoisomer-dependent spectrum of mutational and carcinogenic activities.

Current Issues and Problems in Welding Science

Abstract: Losses of life and property due to catastrophic failure of structures are often traced to defective welds. However, major advances have taken place in welding science and technology in the last few decades. With the development of new methodologies at the crossroad of basic and applied sciences, the promise of science-based tailoring of composition, structure, and properties of the weldments may be fulfilled. This will require resolution of several contemporary issues and problems concerning the structure and properties of the weldments as well as intelligent control and automation of the welding processes.

Foliar δ13C within a temperate deciduous forest: spatial, temporal, and species sources of variation.

Abstract: Foliar 13C-abundance (δ13C) was analyzed in the dominant trees of a temperate deciduous forest in east Tennessee (Walker Branch Watershed) to investigate the variation in foliar δ13C as a function of time (within-year and between years), space (canopy height, watershed topography and habitat) and species (deciduous and coniferous taxa). Various hypotheses were tested by analyzing (i) samples collected from the field during the growing season and (ii) foliar tissues maintained in an archived collection. The δ13C-value for leaves from the tops of trees was 2 to 3%. more positive than for leaves sampled at lower heights in the canopy. Quercus prinus leaves sampled just prior to autumn leaf fall had significantly more negative δ13C-values than those sampled during midsummer. On the more xeric ridges, needles of Pinus spp. had more positive δ13C-values than leaves from deciduous species. Foliar δ13C-values differed significantly as a function of topography. Deciduous leaves from xeric sites (ridges and slopes) had more positive δ13C-values than those from mesic (riparian and cove) environments. On the more xeric sites, foliar δ13C was significantly more positive in 1988 (a dry year) relative to that in 1989 (a year with above-normal precipitation). In contrast, leaf δ13C in trees from mesic valley bottoms did not differ significantly among years with disparate precipitation. Patterns in foliar δ13C indicated a higher ratio of net CO2 assimilation to transpiration (A/E) for trees in more xeric versus mesic habitats, and for trees in xeric habitats during years of drought versus years of normal precipitation. However, A/E (units of mmol CO2 fixed/mol H2O transpired) calculated on the basis of δ13C-values for leaves from the more xeric sites was higher in a wet year (6.6±1.2) versus a dry year (3.4±0.4). This difference was attributed to higher transpiration (and therefore lower A/E) in the year with lower relative humidity and higher average daily temperature. The calculated A/E values for the forest in 1988–89, based on δ13C, were within ±55% of estimates made over a 17 day period at this site in 1984 using micrometeorological methods.

Microwave Sintering of Solid Oxide Fuel Cell Materials: I, Zirconia‐8 mol% Yttria

Abstract: This paper reports that the successful microwave sintering of zirconia demonstrates the necessity to understand both the materials and electromagnetic field aspects of microwave processing. It was difficult to produce crack-free parts in the multimode microwave furnace employed in this investigation. Nonuniformities in the microwave field, and dielectric properties that increased rapidly with temperature, produced hot spots in the parts, which led to differential sintering and subsequent cracking. To produce crack-free sintered parts, an indirect heating method was developed that eliminated the severe differential heating. Using this indirect heating method, it was demonstrated that the sintering temperature of zirconia could be lowered from 1375{degrees} to 1200{degrees}C by microwave processing and that the resulting grain size was finer.

Nonlinear oscillations of viscous liquid drops

Abstract: A fundamental understanding of nonlinear oscillations of a viscous liquid drop is needed in diverse areas of science and technology. In this paper, the moderate- to large-amplitude axisymmetric oscillations of a viscous liquid drop, which is immersed in dynamically inactive surroundings, are analysed by solving the free boundary problem comprised of the Navier–Stokes system and appropriate interfacial conditions at the drop–ambient fluid interface. The means are the Galerkin/finite-element technique, an implicit predictor-corrector method, and Newton's method for solving the resulting system of nonlinear algebraic equations. Attention is focused here on oscillations of drops that are released from an initial static deformation. Two dimensionless groups govern such nonlinear oscillations: a Reynolds number, Re, and some measure of the initial drop deformation. Accuracy is attested by demonstrating that (i) the drop volume remains virtually constant, (ii) dynamic response to small-and moderate-amplitude disturbances agrees with linear and perturbation theories, and (iii) large-amplitude oscillations compare well with the few published predictions made with the marker-and-cell method and experiments. The new results show that viscous drops that are released from an initially two-lobed configuration spend less time in prolate form than inviscid drops, in agreement with experiments. Moreover, the frequency of oscillation of viscous drops released from such initially two-lobed configurations decreases with the square of the initial amplitude of deformation as Re gets large for moderate-amplitude oscillations, but the change becomes less dramatic as Re falls and/or the initial amplitude of deformation rises. The rate at which these oscillations are damped during the first period rises as initial drop deformation increases; thereafter the damping rate is lower but remains virtually time-independent regardless of Re or the initial amplitude of deformation. The new results also show that finite viscosity has a much bigger effect on mode coupling phenomena and, in particular, on resonant mode interactions than might be anticipated based on results of computations incorporating only an infinitesimal amount of viscosity.