Showing papers by "Oak Ridge National Laboratory published in 1986"
TL;DR: In this article, a computer simulation that assembles a model ecosystem which links these biotic and abiotic interactions through equations that predict decomposition processes, actual evapo-transpiration, soil water balance, nutrient uptake, growth of trees, and light penetration through the canopy.
Abstract: The interactions between the biotic processes of reproduction, growth, and death and the abiotic processes which regulate temperature and water availability, and the interplay between the biotic and abiotic processes regulating N and light availabilities are important in the dynamics of forest ecosystems. We have developed a computer simulation that assembles a model ecosystem which links these biotic and abiotic interactions through equations that predict decomposition processes, actual evapo-transpiration, soil water balance, nutrient uptake, growth of trees, and light penetration through the canopy. The equations and parameters are derived directly from field studies and observations of forests in eastern North America, resulting in a model that can make accurate quantitative predictions of biomass accumulation, N availability, soil humus development and net primary production.
659 citations
TL;DR: In this paper, a Green's function method is used to obtain an integral equation over a toroidal domain φ = Σφ mn sin( mθ − nζ ).
638 citations
TL;DR: Dry deposition was an important mechanism of atmospheric input to the foliar canopy, occurring primarily by vapor uptake for sulfur, nitrogen, and free acidity and by particle deposition for calcium and potassium.
Abstract: Airborne particles and vapors contributed significantly to the nutrient requirements and the pollutant load of a mixed hardwood forest in the eastern United States. Dry deposition was an important mechanism of atmospheric input to the foliar canopy, occurring primarily by vapor uptake for sulfur, nitrogen, and free acidity and by particle deposition for calcium and potassium. The canopy retained 50 to 70 percent of the deposited free acidity and nitrogen, but released calcium and potassium. Atmospheric deposition supplied 40 and 100 percent of the nitrogen and sulfur requirements, respectively, for the annual woody increment. This contribution was underestimated significantly by standard bulk deposition collectors.
522 citations
TL;DR: The temporal response of forests to CO2-induced climate changes was examined for eastern North America and it was found that transient responses in species composition and carbon storage continued as much as 300 years after simulated climate changes ceased.
Abstract: The temporal response of forests to CO2-induced climate changes was examined for eastern North America. A forest stand simulation model was used with the assumption that climate will change at a constant rate as atmospheric CO2 doubles, and then as CO2 doubles again. Before being used to project future vegetation trends, the simulation model FORENA was verified by its ability to reproduce long, temporal sequences of plant community change recorded by fossil pollen and by its ability to reproduce today's vegetation. The simulated effects of changing monthly temperature and precipitation included a distinctive dieback of extant trees at most locations, with only partial recovery of biomass in areas of today's temperate deciduous forest. In the southern portion of today's deciduous-coniferous transition forests the simulated dieback was indistinct and recovery by deciduous tree species was rapid. In more northerly transition areas, the dieback not only was clearly expressed, but occurred twice, when new dominant species replaced extant conifers, then were themselves replaced, as climate change continued. Boreal conifers also underwent diebacks and were replaced by deciduous hardwoods more slowly in the north than in the south. Transient responses in species composition and carbon storage continued as much as 300 years after simulated climate changes ceased.
388 citations
TL;DR: The results demonstrate that a growth response to CO(2) enrichment is possible in nutrient-limited systems, and that the mechanisms of response may include either increased nutrient supply or decreased physiological demand.
Abstract: One-year-old dormant white oak (Quercus alba L.) seedlings were planted in a nutrient-deficient forest soil and grown for 40 weeks in growth chambers at ambient (362 microliters per liter) or elevated (690 microliters per liter) levels of CO2. Although all of the seedlings became severely N deficient, CO2 enrichment enhanced growth by 85%, with the greatest enhancement in root systems. The growth enhancement did not increase the total water use per plant, so water-use efficiency was significantly greater in elevated CO2. Total uptake of N, S, and B was not affected by CO2, therefore, tissue concentrations of these nutrients were significantly lower in elevated CO2. An increase in nutrient-use efficiency with respect to N was apparent in that a greater proportion of the limited N pool in the CO2-enriched plants was in fine roots and leaves. The uptake of other nutrients increased with CO2 concentration, and P and K uptake increased in proportion to growth. Increased uptake of P by plants in elevated CO2 may have been a result of greater proliferation of fine roots and associated mycorrhizae and rhizosphere bacteria stimulating P mineralization. The results demonstrate that a growth response to CO2 enrichment is possible in nutrient-limited systems, and that the mechanisms of response may include either increased nutrient supply or decreased physiological demand.
359 citations
TL;DR: Comparisons with available experimental data show that new theoretical results are clearly superior to earlier calculations based on linear theory for stopping power and effective charge based on nonlinear density-functional calculations.
Abstract: Theoretical calculations of the stopping power of the electron gas for slow ions, v${v}_{F}$, are reviewed. New results are presented for stopping power and effective charge based on nonlinear density-functional calculations. Extensive comparisons with available experimental data show that these new theoretical results are clearly superior to earlier calculations based on linear theory.
268 citations
TL;DR: In the gastro-intestinal tract of mice and rats, BHT enhances the development of dimethylhydrazine-induced tumours, but is without effect on tumours produced by methylnitrosourea.
268 citations
TL;DR: A microscopic magnetic antiphase domain structure has been observed in a single-crystal Gd-Y superlattice by neutron diffraction and oscillatory behavior is consistent with recent theoretical speculation that the Gd moments are coupled through the intervening Y via the Ruderman-Kittel-Kasuya-Yosida interaction.
Abstract: A microscopic magnetic antiphase domain structure has been observed in a single-crystal Gd-Y superlattice by neutron diffraction. Furthermore, this long-range antiferromagnetic correlation is found to occur in a multibilayer, in which each bilayer consists of ${N}_{\mathrm{Gd}}$ ferromagnetic atomic planes of Gd followed by ${N}_{\mathrm{Y}}$ planes of nonmagnetic Y, for ${N}_{\mathrm{Y}}={N}_{\mathrm{Gd}}=10$ but not for ${N}_{\mathrm{Y}}=6 or 20$. This oscillatory behavior is consistent with recent theoretical speculation that the Gd moments are coupled through the intervening Y via the Ruderman-Kittel-Kasuya-Yosida interaction.
257 citations
TL;DR: In this paper, a variational principle is developed for computing accurate values of local plasma transport coefficients in nonsymmetric toroidal confinement configurations, and numerical solutions of the linearized drift Fokker-Planck equation are used to obtain the thermodynamic fluxes as functions of collision frequency and the radial electric field.
Abstract: A variational principle is developed for computing accurate values of local plasma transport coefficients in nonsymmetric toroidal confinement configurations. Numerical solutions of the linearized drift Fokker–Planck equation are used to obtain the thermodynamic fluxes as functions of collision frequency and the radial electric field. Effects resulting from the variation of the longitudinal adiabatic invariant J along an orbit (resulting from particle transitions from helically trapped to toroidally trapped orbits) are treated. The velocity‐space distribution resulting from trapped, circulating, and transition particle orbits is well represented by a Legendre polynomial expansion in the pitch angle coordinate. The computational effort is significantly reduced from that required with Monte Carlo methods through use of an efficient treatment of the disparity between the time scales of collisionless and collisional particle dynamics. Numerical computations for a stellarator configuration are presented.
252 citations
TL;DR: In this paper, the authors discuss the difference between the dispersion relations which hold for nucleus-nucleus scattering on the one hand and for nucleon nucleus scattering in the other hand, and the shape of the apparent anomaly in the framework of several models.
235 citations
TL;DR: In limestones and dolomites, the pore surfaces are effectively smooth above 50 \AA{}, but there is evidence for roughening on shorter length scales, and the fractal dimension is nonuniversal.
Abstract: The microstructure of sedimentary rocks is studied by small-angle neutron scattering for length scales between 5 and 500 \AA{}. In limestones and dolomites, we find that the pore surfaces are effectively smooth above 50 \AA{}, but there is evidence for roughening on shorter length scales. In sandstones and shales, the pore surfaces show fractal character due to the presence of clay. The fractal dimension is nonuniversal. We attribute these observations to impurity effects, which can lower the surface tension and maximize the surface area.
TL;DR: In this article, the effects of solar radiation, vapor pressure deficit and the aerodynamic and canopy resistances on mass and energy exchanges were examined over a fully-leafed deciduous forest in eastern Tennessee.
Abstract: Fluxes of CO2, latent heat and sensible heat were measured above a fully-leafed deciduous forest in eastern Tennessee with the eddy correlation technique. These are among the first reported observations over such a surface. The influences of solar radiation, vapor pressure deficit and the aerodynamic and canopy resistances on these mass and energy exchanges are examined. Following a concept introduced by McNaughton and Jarvis (1983), examination of our data suggest that the water vapor exchange of a deciduous forest is not as strongly coupled with net radiation as is that of agricultural crops. The degree of decoupling is smaller than in the case of a coniferous forest. This difference may be attributable in part to the greater aerodynamic resistance to water vapor transfer in a deciduous forest. It appears that the concept of decoupling may be extended to the CO2 exchange of a deciduous forest as well.
TL;DR: In this article, the effect of elastic anisotropy on the temperature dependence of yield stress is analyzed in the case of Ni/sub 3/Al and it is shown that the effect is equally important in interpreting the main feature of all the experimental data available.
TL;DR: In this paper, the role of marketing and implementation of incentive programs for residential energy efficiency is examined to assess the roles of the size and type of incentive and of non-financial aspects of the programs and to infer lessons for policy.
Abstract: Studies evaluating incentive programs for residential energy efficiency are examined to assess the roles of the size and type of incentive and of nonfinancial aspects of the programs and to infer lessons for policy. Larger incentives are found to increase participation, but marketing and implementation may be more important than incentive size: participation varies tenfold between programs offering identical financial incentives, with more participation in programs operated by trusted organizations and aggressively marketed by word of mouth and other attention-getting methods. Preference for grants versus loans varies with income and other household characteristics. Low-income households can be reached by strong incentives if marketing and implementation are designed carefully.
TL;DR: The atmospheric flux of cosmogenic 7Be (53.3-day half-life) and the mode of 7Be deposition in river-estuarine and coastal environments have been examined in this article.
Abstract: The atmospheric flux of cosmogenic 7Be (53.3-day half-life) and the mode of 7Be deposition in river-estuarine and coastal environments have been examined. The atmospheric flux of 7Be commonly supports inventories ranging from 1.0 to 2.0 pCi/cm2 (1 pCi = 0.037 Bq). Beryllium 7 concentrations in water phase samples, collected across salinity gradients in several estuaries along the eastern coastline of the United States, range from 0.03 to 0.53 pCi/L and primarily reflect variations in 7Be supply and sorption kinetics. The major process controlling the concentration of 7Be on estuarine suspended particles appears to be the length of time that these particles remain in the water column. Field particle-to-water distribution coefficients for 7Be have a median value of about 4 × 104 but range over an order of magnitude reflecting short-term variations in 7Be input, particle dynamics, and particulate iron content rather than equilibrium sorption-desorption responses to changes in water salinity or particle type. Residence times of 7Be in the water column range from a few days in estuarine areas of rapid fine-particle deposition, to several weeks in high-energy environments where pronounced sediment resuspension reintroduces deposited 7Be back into the water column. Inventories of 7Be in sediments range from nondetectable to 3.3 pCi/cm2, with the highest inventories in areas where fine particles are accumulating rapidly. Such sites are also major repositories for other particle-reactive substances. A 7Be budget for the James estuary indicates that less than 5% of the expected 7Be input is in the water column and that the short-term estuarine trapping efficiency for atmospherically derived 7Be is somewhere between 50 and 100%.
TL;DR: The experimental acidification of Lake 223 (Experimental Lakes Area, northwestern Ontario) with sulfuric acid in 1976-1983 allowed a detailed examination of the capacity of the lake to neutralize hydrogen ion.
Abstract: The experimental acidification of Lake 223 (Experimental Lakes Area, northwestern Ontario) with sulfuric acid in 1976-1983 allowed a detailed examination of the capacity of the lake to neutralize hydrogen ion. A whole-lake alkalinity and ion budget for Lake 223 showed that 6681% of the added sulfuric acid was neutralized by alkalinity production in the lake. Nearly 85% of in situ alkalinity production was accounted for by net loss of sulfate through bacterial sulfate reduction, coupled with iron reduction and iron sulfide formation, in littoral sediments (60%) and in the hypolimnion (25%). Exchange of hydrogen ion for calcium and manganese in the sediments accounted for 19% of the alkalinity generated, while other cations were net sinks for alkalinity. Alkalinity input from the watershed of Lake 223 was very small, averaging about 5% of that produced in the lake. The seasonal production of 1,000 peq liter-* alkalinity in the anoxic hypolimnion of this softwater lake could be attributed to bacterial sulfate reduction coupled with iron sulfide formation, ammonium production, and iron (II) production. Only the alkalinity produced from bacterial sulfate reduction coupled with iron sulfide formation remained throughout the annual cycle.
TL;DR: It is concluded that the effect of BHT on tumor development depends on strain and target organ examined and possibly also on the chemical carcinogen used.
TL;DR: It is suggested that the prolonged myocardial retention observed with DMIPP in vivo may result from inhibition of β oxidation, and [123I]DMIPP should be useful for evaluation of aberrations in regionalMyocardial uptake.
Abstract: The effects of 3-methyl substitution on the heart retention and metabolism of 3-R,S-methyl-(BMIPP) and 3,3-dimethyl-(DMIPP) analogues of 15-(p-iodophenyl)-pentadecanoic acid (IPP) were studied in rats. Methyl substitution considerably increased the myocardial half-time values in fasted rats: IPP, 5-10 min; BMIPP, 30-45 min; DMIPP, 6-7 h. Because of the observed differences in the relative myocardial uptake and retention of these agents, an evaluation of the subcellular distribution profiles and the distribution of radioactivity within various lipid pools extracted from cell components was performed. Studies with DMIPP in food-deprived rats have shown high levels of the free fatty acid and only slow conversion to triglycerides. These data are in contrast to the rapid clearance of the straight chain IPP analogue and rapid incorporation into triglycerides, and suggest that the prolonged myocardial retention observed with DMIPP in vivo may result from inhibition of beta oxidation. Subcellular distribution studies have shown predominant association of DMIPP and BMIPP with the mitochondrial and microsomal fractions, while IPP was primarily found in the cytoplasm. Because of the unique "trapping" properties and the high heart:blood ratios, [123I]DMIPP should be useful for evaluation of aberrations in regional myocardial uptake.
TL;DR: The ubiquitous occurrence of charcoal in the forest soils of the Upper Rio Negro region of Colombia and Venezuela indicates the presence of frequent and widespread fires in the Amazon Basin, possibly associated with extremely dry periods or human disturbances as discussed by the authors.
TL;DR: Strong evidence is provided that the double-capture process involves electron-correlation effects whose analysis leads beyond the independent-electron model.
Abstract: Production of LMM-Auger and ${\mathrm{L}}_{1}$${\mathrm{L}}_{23}$M-Coster-Kronig electrons in 60-keV ${\mathrm{O}}^{6+}$+He and 40-keV ${\mathrm{C}}^{4+}$+He collisions were measured with high resolution by the method of 0\ifmmode^\circ\else\textdegree\fi{} Auger spectroscopy. Oxygen impact is found to create intense Coster-Kronig lines attributed to the configurations 1${\mathrm{s}}^{2}$2pnl with n\ensuremath{\ge}6 which are produced by double-electron capture. Strong evidence is provided that the double-capture process involves electron-correlation effects whose analysis leads beyond the independent-electron model.
TL;DR: The results suggest that episodes of liquid water in the past or future of Titan might lead to major further steps in prebiological organic chemistry on that body.
TL;DR: The Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory (ORNL) is the world's largest stellarator experiment when it begins operation in early 1987 as discussed by the authors.
Abstract: The Advanced Toroidal Facility (ATF), now under construction at Oak Ridge National Laboratory, will be the world’s largest stellarator experiment when it begins operation in early 1987. It will hav...
TL;DR: Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state is calculated.
Abstract: Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, we calculated the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state.
TL;DR: Time-resolved reflectivity measurements on silicon and germanium indicate that, during the melt-in process, the near-surface region does not melt homogeneously, but rather consists of a mixturemore of solid and liquid phases.
Abstract: Time-resolved reflectivity measurements on silicon and germanium have been made during pulsed KrF excimer laser irradiation (248 nm). The reflectivity was measured simultaneously with probe-laser wavelengths of 632.8 and 1152 nm, and the energy density of each laser pulse was recorded. From these measurements, we were able to determine the reflectivity of the hot solid just before the onset of melting, the reflectivity of the melt, the melt duration, and the time of the onset of melting. Melting-model calculations were also performed, with the reflectivity of solid and liquid Si and Ge treated as parameters for fitting the experimental values of the melt duration and the time of the onset of melting. The resulting parameter values are in agreement with those obtained from self-reflectivity measurements. Near the melting threshold, it was observed that the melt duration was never less than 20 ns for Si and 25 ns for Ge, while the maximum reflectivity increased from its value for the hot solid to that for the liquid over a finite energy range. These results, together with a reinterpretation of time-resolved ellipsometry measurements, indicate that, during the melt-in process, the near-surface region does not melt homogeneously, but rather consists of a mixture of solid and liquid phases.
TL;DR: In this article, a series of laboratory experiments were conducted to measure the rate constants for the decomposition of acetate (acetic acid and sodium acetate) in the presence of titanium, silica, stainless steel, gold, and magnetite.
TL;DR: In this paper, a physical model of nonlinear boiling water reactor (BWR) dynamics was developed and employed to calculate the amplitude of limit cycle oscillations and their effects on fuel integrity over a
Abstract: A physical model of nonlinear boiling water reactor (BWR) dynamics has been developed and employed to calculate the amplitude of limit cycle oscillations and their effects on fuel integrity over a
TL;DR: The dependence of the nonequilibrium partition coefficient k of Bi in Si upon solidification velocity v has been measured with sufficient accuracy to distinguish between proposed solute-trapping mechanisms.
Abstract: The dependence of the nonequilibrium partition coefficient $k$ of Bi in Si upon solidification velocity $v$ has been measured with sufficient accuracy to distinguish between proposed solute-trapping mechanisms. For the range of measured velocities, 2-14 m/s, we observe a much more gradual increase in $k$ with increasing $v$ than those previously reported and no evidence for a "saturation" effect, i.e., $\frac{\mathrm{dk}}{\mathrm{dv}}\ensuremath{\rightarrow}0$ at $kl1$. The continuous-growth model of Aziz fits the data quite well; the Aziz stepwise-growth model and the two-level Baker model yield values of $\frac{\mathrm{dk}}{\mathrm{dv}}$ that are too high.
Journal Article•
TL;DR: The responses of forest trees to atmospheric CO(2) enrichment will depend in part on carbon-nutrient linkages, and the rates of litter decomposition might not be greatly affected by CO() enrichment, but the total amount of nitrogen returned to soil would be lower in elevatedCO(2).
Abstract: Summary The responses of forest trees to atmospheric CO, enrichment will depend in part on carbon-nutrient linkages. Insights into the possible long-term ecological consequences of CO? enrichment can be gained from studying physiological responses in short-term experiments. One-year-old white oak (Quercus alba L.) seedlings were grown in unfertilized forest soil for 40 weeks in controlledenvironment chambers with ambient (362 ~1 1-l) or elevated (690 ~1 l- ‘) CO*. As previously reported, seedling dry weight was 85% greater in the elevated CO* environment, despite severe nitrogen deficiency in all seedlings. The increase in growth occurred without a concomitant increase in nitrogen uptake, indicating an increase in nitrogen-use efficiency in elevated CO,. The weight of new buds was greater in elevated CO*, suggesting that shoot growth in the next year would have been enhanced relative to that of seedlings in ambient CO 2. However, there was less translocatable nitrogen in perennial woody tissue in elevated C02; thus, further increases in nitrogen-use efficiency may not be possible. The leaves that abscised from seedlings in elevated CO, contained higher amounts of soluble sugars and tannin and a lower amount of lignin compared with amounts in abscised leaves in ambient CO*. Based on 1ignin:N and 1ignin:P ratios, the rates of litter decomposition might not be greatly affected by CO* enrichment, but the total amount of nitrogen returned to soil would be lower in elevated CO,.