Showing papers by "Oak Ridge National Laboratory published in 1989"

Effects of changing spatial scale on the analysis of landscape pattern

Abstract: The purpose of this study was to observe the effects of changing the grain (the first level of spatial resolution possible with a given data set) and extent (the total area of the study) of landscape data on observed spatial patterns and to identify some general rules for comparing measures obtained at different scales. Simple random maps, maps with contagion (i.e., clusters of the same land cover type), and actual landscape data from USGS land use (LUDA) data maps were used in the analyses. Landscape patterns were compared using indices measuring diversity (H), dominance (D) and contagion (C). Rare land cover types were lost as grain became coarser. This loss could be predicted analytically for random maps with two land cover types, and it was observed in actual landscapes as grain was increased experimentally. However, the rate of loss was influenced by the spatial pattern. Land cover types that were clumped disappeared slowly or were retained with increasing grain, whereas cover types that were dispersed were lost rapidly. The diversity index decreased linearly with increasing grain size, but dominance and contagion did not show a linear relationship. The indices D and C increased with increasing extent, but H exhibited a variable response. The indices were sensitive to the number (m) of cover types observed in the data set and the fraction of the landscape occupied by each cover type (P k); both m and P kvaried with grain and extent. Qualitative and quantitative changes in measurements across spatial scales will differ depending on how scale is defined. Characterizing the relationships between ecological measurements and the grain or extent of the data may make it possible to predict or correct for the loss of information with changes in spatial scale.

Bifurcation theory of poloidal rotation in tokamaks: A model for L-H transition.

Abstract: It is shown that the poloidal momentum balance equation in tokamaks has bifurcated solutions. The poloidal flow velocity ${U}_{p}$ can suddenly become more positive when the ion collisionality decreases. The corresponding radial electric field ${E}_{r}$ becomes more negative and hence suppresses the turbulent fluctuations. Thus, plasma confinement is improved. The theory is employed to explain the L-H transition observed in tokamaks.

Mechanisms of dissolved organic carbon adsorption on soil

Abstract: (…) In this study, the sources of DOC adsorption on two proposed waste-site soils are defined, and the chemical mechanisms operative during the adsorption process are specified. Adsorption isotherms for the two soils determined at constant pH, ionic strength (I), and temperature indicated that DOC adsorption increased with increasing soil profile depth. Different adsorption capacities were exhibited by the two soils, however, which was related to their contrasting indigenous organic matter contents and mineralogies. (…)

A theory of the spatial and temporal dynamics of plant communities

Abstract: An individual-based model of plant competition for light that uses a definition of plant functional types based on adaptations for the simultaneous use of water and light can reproduce the fundamental spatial and temporal patterns of plant communities. This model shows that succession and zonation result from the same basic processes. Succession is interpreted as a temporal shift in species dominance, primarily in response to autogenic changes in light availability. Zonation is interpreted as a spatial shift in species dominance, primarily in response to the effect of allogenic changes in water availability on the dynamics of competition for light. Patterns of succession at different points along a moisture gradient can be used to examine changes in the ecological roles of various functional types, as well as to address questions of shifts in patterns of resource use through time.

A hierarchical framework for the analysis of scale

Abstract: Landscapes are complex ecological systems that operate over broad spatiotemporal scales. Hierarchy theory conceptualizes such systems as composed of relatively isolated levels, each operating at a distinct time and space scale. This paper explores some basic properties of scaled systems with a view toward taking advantage of the scaled structure in predicting system dynamics. Three basic properties are explored: (1) hierarchical structuring, (2) disequilibrium, and (3) metastability. These three properties lead to three conclusions about complex ecological systems. First, predictions about landscape dynamics can often be based on constraints that directly result from scaled structure. Biotic potential and environmental limits form a constraint envelope, analogous to a niche hypervolume, within which the landscape system must operate. Second, within the constraint envelope, thermodynamic and other limiting factors may produce attractors toward which individual landscapes will tend to move. Third, because of changes in biotic potential and environmental conditions, both the constraint envelope and the local attractors change through time. Changes in the constraint structure may involve critical thresholds that result in radical changes in the state of the system. An attempt is made to define measurements to predict whether a specific landscape is approaching a critical threshold.

Predicting across scales: Theory development and testing

Abstract: Landscape ecologists deal with processes that occur at a variety of temporal and spatial scales. The ability to make predictions at more than one level of resolution requires identification of the processes of interest and parameters that affect this process at different scales, the development of rules to translate information across scales, and the ability to test these predictions at the relevant spatial and temporal scales. This paper synthesizes discussions from a workshop on ‘Predicting Across Scales: Theory Development and Testing’ that was held to discuss current research on scaling and to identify key research issues.

Reference values for resting blood flow to organs of man.

Abstract: The lack of a reliable quantitative description of blood flow in man has hampered the development of accurate biokinetic models of essential elements, drugs, imaging agents, and carcinogens. In this paper we review and analyse data on blood flow and identify representative percentages of cardiac output and absolute blood flow rates to organs and tissues of man for use as reference values for biokinetic models. To keep the review and analysis to a manageable size we have limited attention to the resting state and have suggested reference values for absolute and relative flow rates only for adult males and females.

The behavior and chemical toxicity of U in the kidney: a reassessment

Abstract: By the late 1950s, the views had evolved that 1) U does not enter cells but damages the kidneys by binding to the luminal membranes of renal tubular cells, interfering with reabsorption of glucose, sodium, amino acids, protein, water, and other substances, and causing slow cell death by suppression of respiration; and 2) U does not cause significant damage to the kidneys at concentrations below 3 micrograms U g-1 kidney. Although there has not been a major unified effort in the past three decades to update the toxicology of U as a nephrotoxin, there have been numerous isolated studies that may be useful in reevaluating these longstanding views on the behavior and action of U in the kidneys and the renal U concentration at which toxic effects may become evident. This paper is a brief review and synthesis of current information on U nephrotoxicity. Much more experimental research and reevaluation of existing data are needed concerning U nephrotoxicity, particularly for the case of chronic exposure.

Sodium-calcium ion exchange in the weathering of shales: Implications for global weathering budgets

Abstract: Unpolluted rivers and streams that drain marine shales show an excess of sodium compared to chloride and a deficiency of calcium and magnesium compared to sulfate and alkalinity. This is due in part to cation exchange of sodium for divalent cations on clay minerals. Consideration of the global weathering budget suggests that up to 34% of the sodium in the total dissolved stream load may be due to cation exchange rather than sodium production via silicate dissolution weathering reactions. These results suggest that the weathering budgets for sodium and calcium are in need of revision because of the inclusion of cation-exchange processes in the weathering cycle. This implies that silicate dissolution is less important in determining the composition of global river water than was previously thought.

Experimental and Thermodynamic Study of Nonstoichiometry in 〈YBa2Cu3O7‐x〉

Abstract: This paper reports on the dependence of the nonstoichiometry of (YBa{sub 2}Cu{sub 3}O{sub 7 {minus} x}) (solid), studied over 5 orders of magnitude in oxygen pressure and from 573 to 1173 K. Hydrogen-reduction methods for determining the absolute oxygen-to-metal ratio were developed. The resulting data were used to derive a chemical thermodynamic representation of the experimental variables. The data were also compared with several other investigations to identify the self-consistent sets of data. The present data and thermodynamic data from the literature were correlated on an Ellingham diagram.

Detection of anomalous computer session activity

Abstract: The authors discusses Wisdom and Sense (W&S), a computer security anomaly detection system. W&S is statistically based. It automatically generates rules from historical data and, in terms of those rules, identifies computer transactions that are at variance with historically established usage patterns. Issues addressed include how W&S generates rules from a necessarily small sample of all possible transactions, how W&S deals with inherently categorical data, and how W&S assists system security officers in their review of audit logs. Preliminary results with W&S show that the software does periodically detect anomalies of high interest even in data though to be free of such events. >

Productive Capacity of Periphyton as a Determinant of Plant-Herbivore Interactions in Streams

Abstract: To investigate the influence of plant productivity on plant-herbivore inter- actions in stream ecosystems, we varied the productive capacity of algal assemblages by exposing periphyton to three levels of irradiance and two levels of grazing. We studied interactions between algal assemblages (grown from algae obtained from four Oregon streams) and herbivorous snails (Juga silicula) in 15 laboratory streams containing either 250 snails/m2 or no snails. Biomass, production, export, and taxonomic structure of the algal community were measured at intervals throughout the 75-d study. Ingestion rate and assimilation efficiency of snails also were measured on six different dates using dual-isotope labeling, and snail growth was measured at the end of the experiment. Rates of primary production, algal biomass accumulation, and dominance by chloro- phytes generally increased with higher irradiance, although these patterns were modified by herbivores. Ungrazed periphyton at low irradiance (photon flux density: 20 ,umol-m-2- s-1) accumulated little biomass, which was further reduced by grazing snails. At inter- mediate (100 ,umol.m-2 s-) and high (400 ,Lmol.m-2-s-1) irradiance, snails delayed the accumulation of algal biomass but did not affect the final biomass attained. After 43 d, net primary production (NPP) at high irradiance was unaffected by grazing, whereas grazing increased NPP at both low and intermediate irradiance. Algal export increased with both irradiance and the presence of grazers and constituted a significant loss of plant biomass from the streams. Grazing by Juga delayed algal succession and altered algal taxonomic structure and assemblage physiognomy by reducing the relative abundance of erect and non-attached algae, while increasing the abundance of adnate diatoms. Snails grew slowly at low irradiance, due to scant food resources, but had high growth rates at intermediate and high irradiance, probably because food was not limiting. Assim- ilation efficiencies for snails generally varied from 40 to 70% and were highest at low irradiance. At low irradiance, 90% ofbenthic production was harvested by grazers, whereas only 10% accumulated as attached biomass or was exported. At higher irradiances, 85% persisted as attached algae or was exported. In these stream ecosystems, the biomass and production of grazers were influenced by abiotic constraints placed on algal productive capacity (i.e., the ability of a plant assemblage to generate biomass). The structure and metabolism of algal assemblages were affected, in turn, by consumptive demand of herbivores. The productive capacity of periphyton mod- ified the nature and outcome of plant-herbivore interactions. This capacity therefore has important implications for the operation of stream ecosystems.

Luminescence of F and F+ centers in magnesium oxide.

Abstract: Time-resolved spectra of luminescence from F and ${F}^{+}$ centers in MgO excited at 248 nm are reported over 8 decades of time and intensity, from 20 ns to 2 s. The decay time of F and ${F}^{+}$ luminescence has been measured at temperatures ranging from 90 to 573 K. The luminescence yield and spectra were studied as a function of excitation-power density at 248 nm over a span of 10 decades, from 1 mW/${\mathrm{cm}}^{2}$ to 38 MW/${\mathrm{cm}}^{2}$. Higher pump-power density favors F luminescence over ${F}^{+}$ luminescence in thermochemically reduced crystals, and the luminescence yield saturates above about 50 kW/${\mathrm{cm}}^{2}$ of pump intensity. Transient absorption spectra were measured in the microsecond-to-seconds time range. The luminescence data show that the decay kinetics of excited F and ${F}^{+}$ centers are dominated by ionization from the excited state and charge recapture from traps which include the ${H}^{\mathrm{\ensuremath{-}}}$ center in thermochemically reduced MgO. It is furthermore inferred that electrons are the charge carriers having primary influence on kinetics of both F and ${F}^{+}$ centers. This implies that the ${F}^{+}$ first-excited state lies close to the conduction-band edge. We confirm that excitation at 248 nm also causes release of valence holes, and propose a mechanism which may explain the hole release, the increase of the F-to-${F}^{+}$ intensity ratio with increasing pump intensity, and the saturation of luminescence with increasing pump intensity.

Development of microstructures in Fe-15Ni-15Cr single crystal electron beam welds

Abstract: A detailed analysis of the microstructures produced in an autogenously welded single crystal of Fc−15Ni−15Cr was performed in order to investigate the relationship between growth crystallography and solidification behavior. Electron beam welds were made at various speeds on the (001) surface of single crystals in either the [100] or [110] directions. A geometrical analysis was carried out in order to relate the dendrite growth velocities in the three 〈100〉 directions to the weld velocities for the different crystallographic orientations examined. From this analysis, the preferred dendrite trunk directions were determined as a function of the solidification front orientation based upon a minimum velocity or minimum undercooling criterion. A thorough examination of the weld microstructures and a comparison with the geometrical relationships developed in this work permitted a three-dimensional reconstruction of the weld pool shape to be performed. In addition, the dendrite spacings were measured, and the variation in spacings as a function of growth velocity was compared with theoretical predictions. It was found that the range of velocities over which dendritic growth is expected agreed with the experimental findings, and, furthermore, the change in dendrite spacing with growth velocity varied as predicted by theory. These results clearly demonstrate the effect of crystallography on the micro-structural development during weld pool solidification. The results also show that the resultant microstructures and pool shapes can be explained by geometrical analysis in conjunction with existing solidification models.

Effect of chromium on properties of Fe3Al

Abstract: The effects of the addition of chromium on several properties of Fe3Al, including tensile strength and ductility, fracture behavior, and slip and dislocation characteristics, were studied. Alloying with up to 6 at. % chromium results in an increase in room temperature ductility from approximately 4% to 8–10%. Along with this increase in ductility, the addition of chromium produces a change in fracture mode from transgranular cleavage to a mixed mode of intergranular-transgranular cleavage, and a change in slip behavior from coarse straight slip to fine wavy slip. These phenomena are discussed in terms of the effect of chromium on the antiphase boundary energies and dislocation characteristics.

Nutrient dynamics and food-web stability

Abstract: The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships. What are the effects of limiting nutrients on the stability of ecosystem food webs Most of the literature on food web stability centers around the dynamics of population numbers and/or biomasses. Nevertheless, a growing body of theoretical and empirical research considers the role that both nutrient limitation and recycling can play in stability. In this paper, it is the authors objective to summarize the current understanding of several important types of stability. The theoretical and empirical evidence relating these types of stability and nutrient cycling is described. A central generalization is produced in each case.

Personal glucose monitor

Abstract: A device for the non-invasive determination of blood glucose of a patient. This glucose monitor is based upon the effect of glucose in rotating polarized infrared light. More specifically, two orthogonal and equal polorized states of infrared light of minimal absorption are passed through a tissue containing blood, and an accurate determination of change in signal intensity is made due to the angle of rotation of these states. This rotation depends upon the glucose level. In order to compensate for absorption in the tissue, another two orthogonal and equal polarized states of infrared light are used, with the wavelength being selected to maximize absorption. At least two embodiments of forming the polarized states are described: an electro-optic switching unit, such as a lithium tantalate crystal with appropriately applied orthogonal voltages; and an infrared beam splitter using two light sources. The device can be applied to a patient, for example, to monitor glucose levels and provide signals to an insulin pump so as to be an artificial pancreas.

Slowing-down time of energetic atoms in solids.

Abstract: Computer simulation models for the slowing down of energetic atoms in matter are often based on the binary collision approximation (BCA) Such models typically ignore the temporal aspects of the problem A method is described whereby calculations of the times at which energetic particles reach their collision points may be included in such BCA simulations without altering the ``event-driven'' structure of the model The enhanced model is illustrated by calculations of the time required by 10-eV to 10-keV Cu atoms to slow down in both crystalline and amorphous Cu targets In addition to the mean slowing-down time, distributions of slowing-down times and correlations between slowing-down times and particle ranges are presented The utility of range-time correlations in studying penetration problems is demonstrated

Crystallization history of Obsidian Dome, Inyo Domes, California

Abstract: Samples obtained by U.S. Department of Energy research drilling at the 600-year-old Obsidian Dome volcano provide the rare opportunity to examine the transition from volcanic (dome) to plutonic (intrusion) textures in a silicic magma system. Textures in the lavas from Obsidian Dome record multiple periods of crystallization initiated in response to changes in undercooling (ΔT) related to variable degassing in the mag-ma. Phenocr)ysts formed first at low ΔT. A drastic increase in ΔT, related to loss of a vapor phase during initial stages of eruption, caused nucleation of microlites. All of the lavas thus contain phenocrysts and microlites. Extrusion and subsequent devitrification of the dry (0.1 wt% H2O) magma crystallized spherulites and fine-grained rhyolite at high ΔT. A granophyric texture, representing crystallization at a moderate ΔT, formed in the intrusions beneath Obsidian Dome. Textures in the intrusion apparently represent crystallization of hydrous (1–2 wt% H2O) rhyolitic magma at shallow depths.

Quantifying scale-dependent effects of animal movement with simple percolation models

Abstract: A simple model of animal movement on random and patterned landscapes was used to explore the problems of extrapolating information across a range of spatial scales. Simulation results indicate that simple relation- ships between pattern and process will produce a variety of scale-dependent effects. These theoretical studies can be used to design experiments for determining the nature of scale-dependent processes and to estimate parameters for extrapolating information across scales.

On the economic incentives for taking bribes

Abstract: This paper presents an empirical analysis of the factors affecting bribe taking by public officials. Factors influencing the acceptance of bribes include: the probability of being convicted, severity of punishment, government salary relative to private sector income, the demonstration effect, and the unemployment rate. Our results indicate that higher probability of being convicted discourages the acceptance of bribes as does more severe punishment. Low relative earnings, high unemployment, and the demonstration effect of aggregate advertising all lead to increased bribe taking.