Showing papers by "Oak Ridge National Laboratory published in 1984"

Aboveground Production and N and P Cycling Along a Nitrogen Mineralization Gradient on Blackhawk Island, Wisconsin

Abstract: Net aboveground production (4.1-9.5 Mg ha- Iyr-') across a series of edaphic climax forests was highly correlated with field measurements of soil N mineralization (26-84 kg ha-- yr-'; r2 = 0.902, P < .001) and with soil silt + clay content (5-74%; r2 = 0.883, P < .001). Soil N min- eralization was positively correlated with litter production and N and P return in litter. Soil N min- eralization was negatively correlated with litter C:N and C:P ratios and with efficiency of P use in litter production. Efficiency of N use in litter production declined with increasing N mineralization except for inefficient use of N in a hemlock stand at low N mineralization. Changes in litter quality across the mineralization-soil texture gradient were due to species replacement rather than changes in litter quality within each species. Nitrification was not correlated with aboveground production. Both mineralization and nitrification were highly correlated with humus P content. Differences in nitrification among the soils appeared to be related to P04-P supply in the spring and early summer and to NH4-N supply in mid- to late summer.

Toughening Behavior in Sic-Whisker-Reinforced Alumina

Abstract: The development of hot-pressed Sic-whisker-reinforced alumina has resulted in composites with fracture toughness values ∼;8.7 MPa·m112 at 20 vol% SiC. Whisker orientation during processing leads to anisotropy in both fracture toughness and fracture strength. Fracture strengths are also limited by the ability to disperse the Sic whiskers; however, use of both fine alumina powders and ultrasonic dispersion techniques yields strengths ∼;800 MPa.

Physical Properties of Polymers

Abstract: The third edition of this well known textbook discusses the diverse physical states and associated properties of polymeric materials. The contents of the book have been conveniently divided into two general parts, 'Physical States of Polymers' and 'Characterization Techniques'. Written by seven of the leading figures in the polymer science community, this third edition has been thoroughly updated and expanded. As in the second edition, all of the chapters contain general introductory material and comprehensive literature citations designed to give newcomers to the field an appreciation of the subject and how it fits into the general context of polymer science. Containing numerous problem sets and worked examples this third edition provides enough core material for a one semester survey course at the advanced undergraduate or graduate level.

Ductile ordered intermetallic alloys

Abstract: Many ordered intermetallic alloys have attractive high-temperature properties; however, low ductility and brittle fracture limit their use for structural applications. The embrittlement in these alloys is mainly caused by an insufficient number of slip systems (bulk brittleness) and poor grain-boundary cohesion. Recent studies have shown that the ductility and fabricability of ordered intermetallics can be substantially improved by alloying processes and control of microstructural features through rapid solidification and thermomechanical treatments. These results demonstrate that the brittleness problem associated with ordered intermetallics can be overcome by using physical metallurgical principles. Application of these principles will be illustrated by results on Ni(3)Al and Ni(3)V-Co(3)V-Fe(3)V. The potential for developing these alloys as a new class of high-temperature structural materials is discussed.

Improvements in mechanical properties in SiC by the addition of TiC particles

Abstract: Silicon carbide ceramics containing up to 24.6 vol% dispersed TiC particles yielded fully dense composites by hot-pressing at 2000/sup 0/C with 1 wt% Al and 1 wt% C added. The microstructure consists of fine TiC particles in a fine-grained SiC matrix. Addition of TiC particles increases the critical fracture toughness of SiC (to approx. =6 MPa /SUP ./ m /SUP 1/2/ at 24.6 vol% TiC) and yields high flexure strength (greater than or equal to 680 MPa), with both properties increasing with increasing volume fraction of TiC. The strengths at high temperatures are also improved by the TiC additions. Observations of the fracture path indicate that the improved toughness and strength are a result of crack deflection by the TiC particles.

Data Compendium for Plasma-Surface Interactions

Abstract: A review of particle-solid processes pertinent to modelling plasma-wall interactions is presented, and sets of recommended data are given. Analytic formulas are used where possible; otherwise, data are presented in the form of tables and graphs. The incident particles considered are e−, H, D, T, He, C, O, and selfions. The materials include the metals aluminum, beryllium, copper, molybdenum, stainless steel, titanium, and tungsten and the nonmetals carbon and TiC. The processes covered are light ion reflection, hydrogen and helium trapping and detrapping, desorption, evaporation, sputtering, chemical effects in sputtering, blistering caused by implantation of helium and hydrogen, secondary electron emission by electrons and particles, and arcing.

Lead-Iron Phosphate Glass: A Stable Storage Medium for High-Level Nuclear Waste

Abstract: Results are presented which show that lead-iron phosphate glasses are a promising new waste form for the safe immobilization of both high-level defense and high-level commercial radioactive waste. Relative to the borosilicate nuclear waste glasses that are currently the "reference" waste form for the long-term disposal of nuclear waste, lead-iron phosphate glasses have several distinct advantages: (i) an aqueous corrosion rate that is about 1000 times lower, (ii) a processing temperature that is 100 degrees to 250 degrees C lower, and (iii) a much lower melt viscosity in the temperature range from 800 degrees to 1000 degrees C. Most significantly, the lead-iron phosphate waste form can be processed using a technology similar to that developed for borosilicate nuclear waste glasses.

Trace elements in tree rings: evidence of recent and historical air pollution.

Abstract: Annual growth rings from short-leaf pine trees in the Great Smoky Mountains National Park show suppressed growth and increased iron content between 1863 and 1912, a period of smelting activity and large sulfur dioxide releases at Copperhill, Tennessee, 88 kilometers upwind. Similar growth suppression and increases of iron and other metals were found in rings formed in the past 20 to 25 years, a period when regional fossil fuel combustion emissions increased about 200 percent. Metals concentrations in phloem and cambium are high, but whether they exceed toxic thresholds for these tissues is not known.

Triiodide ion formation equilibrium and activity coefficients in aqueous solution

Abstract: The equilibrium quotient for the formation of triiodide was studied as a function of temperature, 3.8–209.0°C, and ionic strength, 0.02–6.61. The best-fit value for the molal equilibrium constant at 25°C is 698±10 and the corresponding partial molal enthalphy, entropy, and heat capacity of formation are: ΔHo=−17.0±0.6 kJ-mol−1, ΔSo=−0.6±0.3 J-K−1-mol−1, and ΔC p o =−21±8 J-K−1-mol−1. Activity coefficients of iodine were determined as a function of ionic strength (NaClO4) at 25°C and conclusions are drawn as to the corresponding ionic strength dependence of the triiodide anion.

Kinetics of water loss and the likelihood of intracellular freezing in mouse ova. Influence of the method of calculating the temperature dependence of water permeability.

Abstract: To avoid intracellular freezing and its usually lethal consequences, cells must lose their freezable water before reaching their ice-nucleation temperature. One major factor determining the rate of water loss in the temperature dependence of the water permeability,L p (hydraulic conductivity). Because of the paucity of water permeability measurements at subzero temperatures, that temperature dependence has usually been extrapolated from above-zero measurements. The extrapolation has often been based on an exponential dependence ofL p on temperature. This paper compares the kinetics of water loss based on that extrapolation with that based on an Arrhenius relation betweenL p and temperature, and finds substantial differences below −20 to −25°C. Since the ice-nucleation temperature of mouse ova in the cryoprotectants DMSO and glycerol is usually below −30°C, the Arrhenius form of the water-loss equation was used to compute the extent of supercooling in ova cooled at rates between 1 and 8°C/min and the consequent likelihood of intracellular freezing. The predicted likelihood agrees well with that previously observed. The water-loss equation was also used to compute the volumes of ova as a function of cooling rate and temperature. The computed cell volumes agree qualitatively with previously observed volumes, but differ quantitatively.

Interpolation of data on the surface of a sphere

Abstract: The problem treated is that of constructing a C ~ interpolant of data values associated with arbitrarily distributed nodes on the surface of a sphere. A local interpolation method that has proved very successful for fitting data on the plane consists of generating a triangulation of the nodes, estimating gradients at the nodes, and constructing a triangle-based mterpolant of the data and gradient estamates Methods and software that extend thas solution procedure to the surface of the sphere are described, and test results are presented. The method is shown to be quite efficient and accurate for data taken from a variety of test functions.

Kinetics and Mechanisms of High-Temperature Creep in Silicon Carbide. II. Chemically Vapor Deposited,

Abstract: Chemically vapor deposited (CVD) silicon carbide was subjected to constant compressive stresses (110 to 220 MN/m2) at high temperatures (1848 to 2023 K) in order to determine the controlling steady-state creep mechanisms under these conditions. An extensive TEM study was also conducted to facilitate this determination. The strong preferred crystallographic orientation of this material causes the creep rate to be very dependent on specimen orientation. The stress exponent, n, in the equation eασn was calculated to be 2.3 below 1923 K and 3.7 at 1923 K. The activation energy for steady-state creep was determined to be 175 ± 5 kJ/mol throughout the temperature range employed. At temperatures between 1673 and 1873 K, the controlling creep mechanism for CVD Sic is dislocation glide, which is believed to be controlled by the Peierls stress. Although the activation energy does not change, the increase in the stress exponent for samples deformed at 1923 K suggests that the controlling creep mechanism becomes dislocation glide/climb controlled by climb.

The wear behavior of nitrogen-implanted metals

Abstract: The effect of nitrogen implantation on the wear behavior of a range of metals has been studied. Hardness measurements and pin-on-disc wear tests which characterize specifically the properties of the thin implanted layer have been carried out. It is shown that large improvements in wear resistance can be obtained by nitrogen implantation and that a loose correlation exists between reduced wear and increased surface hardness. However, it is demonstrated, on the basis of detailed examination of the wear tracks, that the best improvements in wear performance occur only when implantation produces a change in the dominant mode of wear. It is further shown that the formation of surface oxide layers during the wear process is often associated with these changes in wear behavior. The wear mechanisms, and the changes thereof, are described and discussed in detail for Ti-6Al-4V, hard chromium electroplate, and a range of ferrous alloys.

Tumor Induction in BALB/c Mice after Fractionated or Protracted Exposures to Fission-Spectrum Neutrons

Abstract: This study has examined the effect of dose rate or fractionation on the carcinogenic effects of fission neutrons with emphasis on the dose range below 50 rad. The induction of lung adenocarcinomas, mammary adenocarcinomas, and ovarian tumors in female BALB/c mice was examined after whole-body neutron irradiation delivered at a high dose rate as a single exposure, or delivered as two equal fractions separated by intervals of 24 hr or 30 days and compared these effects to those after neutron irradiation at low dose rates. The dose responses for ovarian tumorigenesis after the split-dose fractionation regimen were similar to that observed after single high-dose-rate neutron exposure. However, lowering the dose rate reduced the incidence over the dose range of 0-50 rad. For lung and mammary tumors the results were more complex. These data suggest that fractionation and dose-rate effects are different for different tumor types presumably because of the different mechanisms of tumorigenesis that may be involved.

Sulfur cycling in forests

Abstract: Sulfur is essential for the production of certain amino acids in plants. As amino acid sulfur is the major form of sulfur in trees, there is a strong relationship between organic S and organic N in tree tissue. Sulfur deficiencies occur in parts of southeastern Australia and northwestern North America, remote from pollutant inputs. Since bilogical S requirements of forests are modest (< 5 kg · ha−1 yr−1 for net vegetative increment), however, atmospheric S inputs in polluted regions (10–80 kg · ha−1 yr−1 ) often exceed not only the forest ecosystem S requirement but also its ability to biologically accumulate S. There is some increase in the SO2− 4−S content of forest vegetation in response to elevated atmospheric S inputs, but this capacity is apparently easily saturated. Soil SO2−2 4adsorption is often the dominant feature of S cycling in polluted ecosystems and often accounts for net ecosytem S accumulations.

Murine susceptibility to two-stage skin carcinogenesis is influenced by the agent used for promotion

Abstract: Several approaches were employed to investigate whether murine stock and strain differences in susceptibility to two-stage skin carcinogenesis are due to differences in the metabolism of the initiating aromatic hydrocarbons, or the consequences of the agents used for promotion. A cell-mediated mutagenesis assay was used to quantitatively compare the abilities of cultured newborn SENCAR, DBA/2, C57BL/6 and BALB/c keratinocytes to metabolize dimethylbenz[a]anthracene (DMBA) to mutagenic and cytotoxic metabolites. At equivalent concentrations of DMBA, throughout a 25-fold range in promutagen concentration, C57BL/6, BALB/c and SENCAR keratinocyte-dependent mutant frequencies were very similar and approximately twice DBA/2 keratinocyte-dependent mutant frequencies. In in vivo tumor studies, C57BL/6 mice were more sensitive than SENCAR mice to complete skin carcinogenesis protocols employing repetitive weekly treatments with DMBA and benzo[a]pyrene (BP). At equivalent concentrations of either DMBA or BP, C57BL/6 mice developed carcinomas sooner, and had a greater number of carcinomas per animal. SENCAR mice were very sensitive to two-stage skin carcinogenesis protocols employing BP and DMBA as initiators and benzoyl peroxide and 12-O-tetradecanoylphorbol-13-acetate (TPA) as promoters. C57BL/6 mice were relatively refractory to TPA promotion but sensitive to promotion with benzoyl peroxide. These findings suggest that murine stock and strain-dependent differences in sensitivity to two-stage skin carcinogenesis may not be due to major differences in the metabolism of the initiating hydrocarbons, but are partially the consequences of the agents used for promotion.

Second ionization of carbonic acid in NaCl media to 250°C

Abstract: The equilibrium quotients for the first ionization of aqueous carbon dioxide were previously determined at this laboratory. A similar potentiometric technique has now been employed to determine the second ionization quotients in NaCl media to 5m and from 50 to 250°C. The results have been combined with selected information in the literature and modeled to derive thermodynamic parameters including equilibrium constants, activity coefficient quotients, changes in enthalpies and changes in heat capacity along the saturation pressure curve. Approximate values for pressure coefficients were obtained to permit the short extrapolations from experimental conditions to the saturation pressure condition. The results demonstrate that log K2/Kw, when plotted vs. 1/T, gives nearly a straight line as has been observed for a number of other such processes. This provides the best means of extrapolation beyond the temperature of the measurements. The results have been applied to an examination of the solubility of calcite (calcium carbonate) as a function of hydrogen ion molality (in a given NaCl medium) for the condition where the calcium ion molality equals the total carbonate molality (in all forms).