Showing papers by "Oak Ridge National Laboratory published in 2002"
••
Oak Ridge National Laboratory1, University of California, Berkeley2, Institut national de la recherche agronomique3, University of Amsterdam4, Carnegie Institution for Science5, Swedish University of Agricultural Sciences6, University of Göttingen7, Oregon State University8, University of Edinburgh9, University of Colorado Boulder10, San Diego State University11, University of Nebraska–Lincoln12
TL;DR: A comprehensive evaluation of energy balance closure is performed across 22 sites and 50 site-years in FLUXNET, a network of eddy covariance sites measuring long-term carbon and energy fluxes in contrasting ecosystems and climates as mentioned in this paper.
2,052 citations
••
United States Department of Energy1, Kyoto University2, Marine Biological Laboratory3, University of Queensland4, Stanford University5, University of California, Berkeley6, McGill University7, National Institute of Genetics8, Aix-Marseille University9, Dalhousie University10, University of Tokyo11, Tokyo Metropolitan University12, Tohoku University13, University of South Florida14, Hokkaido University15, Stazione Zoologica Anton Dohrn16, IBM17, University of Maryland, College Park18, University of California, San Francisco19, University of Edinburgh20, Oak Ridge National Laboratory21, Los Alamos National Laboratory22
TL;DR: A draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis, is generated, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development.
Abstract: The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.
1,582 citations
••
Oregon State University1, University of Bayreuth2, University of California, Berkeley3, Climate Monitoring and Diagnostics Laboratory4, Institut national de la recherche agronomique5, University of Minnesota6, Wageningen University and Research Centre7, University of California, Davis8, University of Virginia9, Swedish University of Agricultural Sciences10, United States Department of Agriculture11, University of Antwerp12, University of Edinburgh13, Technical University of Denmark14, Duke University15, Tuscia University16, Oak Ridge National Laboratory17, University of Colorado Boulder18, Harvard University19, San Diego State University20, University of Nebraska–Lincoln21, University of Helsinki22
TL;DR: The authors compared seasonal and annual estimates of CO2 and water vapor exchange across sites in forests, grasslands, crops, and tundra that are part of an international network called FLUXNET, and investigated the responses of vegetation to environmental variables.
1,199 citations
••
TL;DR: In this paper, a full C cycle analysis has been completed for agricultural inputs, resulting in estimates of net C flux for three crop types across three tillage intensities, including primary fuels, electricity, fertilizers, lime, pesticides, irrigation, seed production, and farm machinery.
1,199 citations
••
TL;DR: In this article, a new indicator of glass-forming ability (GFA) for bulk metallic glasses (BMGs) is proposed based on crystallization processes during cooling and reheating of the supercooled liquid.
1,121 citations
••
[...]
21 Feb 2002-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: BABAR as discussed by the authors is a detector for the SLAC PEP-II asymmetric e+e-B Factory operating at the upsilon 4S resonance, which allows comprehensive studies of CP-violation in B-meson decays.
Abstract: BABAR, the detector for the SLAC PEP-II asymmetric e+e- B Factory operating at the upsilon 4S resonance, was designed to allow comprehensive studies of CP-violation in B-meson decays. Charged particle tracks are measured in a multi-layer silicon vertex tracker surrounded by a cylindrical wire drift chamber. Electromagentic showers from electrons and photons are detected in an array of CsI crystals located just inside the solenoidal coil of a superconducting magnet. Muons and neutral hadrons are identified by arrays of resistive plate chambers inserted into gaps in the steel flux return of the magnet. Charged hadrons are identified by dE/dx measurements in the tracking detectors and in a ring-imaging Cherenkov detector surrounding the drift chamber. The trigger, data acquisition and data-monitoring systems, VME- and network-based, are controlled by custom-designed online software. Details of the layout and performance of the detector components and their associated electronics and software are presented.
789 citations
••
TL;DR: A new metric is needed to quantify the human disturbance of the Earth's surface-energy budget, and this ‘regional climate change potential’ could offer a new metric for developing a more inclusive climate protocol.
Abstract: Our paper documents that land-use change impacts regional and global climate through the surface-energy budget, as well as through the carbon cycle. The surface-energy budget effects may be more important than the carbon-cycle effects. However, land-use impacts on climate cannot be adequately quantified with the usual metric of 'global warming potential'. A new metric is needed to quantify the human disturbance of the Earth's surface-energy budget. This 'regional climate change potential' could offer a new metric for developing a more inclusive climate protocol. This concept would also implicitly provide a mechanism to monitor potential local-scale environmental changes that could influence biodiversity.
767 citations
••
TL;DR: In this paper, a fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum, but at PEO levels greater than 5%, the blends could not be stabilized without the individual fibers fusing together.
722 citations
••
TL;DR: In this article, the authors show that the indentation size effect for pyramidal and spherical indenters can be correlated, based on geometrically necessary dislocations and work-hardening.
Abstract: Experimental results are presented which show that the indentation size effect for pyramidal and spherical indenters can be correlated. For a pyramidal indenter, the hardness measured in crystalline materials usually increases with decreasing depth of penetration, which is known as the indentation size effect. Spherical indentation also shows an indentation size effect. However, for a spherical indenter, hardness is not affected by depth, but increases with decreasing sphere radius. The correlation for pyramidal and spherical indenter shapes is based on geometrically necessary dislocations and work-hardening. The Nix and Gao indentation size effect model (J. Mech. Phys. Solids 46 (1998) 411) for conical indenters is extended to indenters of various shapes and compared to the experimental results.
706 citations
••
TL;DR: A three-dimensional X-ray microscopy technique that uses polychromatic synchrotron X-rays to probe local crystal structure, orientation and strain tensors with submicrometre spatial resolution is described, applicable to single-crystal, polycrystalline, composite and functionally graded materials.
Abstract: Advanced materials and processing techniques are based largely on the generation and control of non-homogeneous microstructures, such as precipitates and grain boundaries. X-ray tomography can provide three-dimensional density and chemical distributions of such structures with submicrometre resolution; structural methods exist that give submicrometre resolution in two dimensions; and techniques are available for obtaining grain-centroid positions and grain-average strains in three dimensions. But non-destructive point-to-point three-dimensional structural probes have not hitherto been available for investigations at the critical mesoscopic length scales (tenths to hundreds of micrometres). As a result, investigations of three-dimensional mesoscale phenomena--such as grain growth, deformation, crumpling and strain-gradient effects--rely increasingly on computation and modelling without direct experimental input. Here we describe a three-dimensional X-ray microscopy technique that uses polychromatic synchrotron X-ray microbeams to probe local crystal structure, orientation and strain tensors with submicrometre spatial resolution. We demonstrate the utility of this approach with micrometre-resolution three-dimensional measurements of grain orientations and sizes in polycrystalline aluminium, and with micrometre depth-resolved measurements of elastic strain tensors in cylindrically bent silicon. This technique is applicable to single-crystal, polycrystalline, composite and functionally graded materials.
689 citations
••
TL;DR: The chemical evolution of seawater during the Phanerozoic is still a matter of debate as mentioned in this paper, and the available data for the composition of fluid inclusions in marine halite and for the mineralogy of marine evaporites.
••
TL;DR: Results of these spectroscopic studies confirm the heterogeneous nature of NOM, and point out the importance of isolation and improved characterization of various NOM subcomponents in order to better understand the behavior and roles of Nom in the natural environment.
••
University of Bayreuth1, University of California, Berkeley2, Climate Monitoring and Diagnostics Laboratory3, Institut national de la recherche agronomique4, Dresden University of Technology5, University of Nebraska–Lincoln6, University of Edinburgh7, Pennsylvania State University8, Swedish University of Agricultural Sciences9, United States Forest Service10, University of Antwerp11, Duke University12, Oregon State University13, Oak Ridge National Laboratory14, University of Colorado Boulder15, Harvard University16, San Diego State University17, University of California, Davis18, University of Helsinki19, Max Planck Society20
TL;DR: In this paper, seasonal patterns of gross primary productivity (FGPP), and ecosystem respiration (FRE) of boreal and temperate, deciduous and coniferous forests, Mediterranean evergreen systems, a rainforest, temperate grasslands, and C3 and C4 crops were analyzed.
••
TL;DR: Examination of soil samples taken from the surface, vadose zone, and saturated subsurface using a small-subunit rRNA-based cloning approach found that spatial isolation could limit competition in surface soils, thereby supporting the high diversity and a uniform community structure.
Abstract: To begin defining the key determinants that drive microbial community structure in soil, we examined 29 soil samples from four geographically distinct locations taken from the surface, vadose zone, and saturated subsurface using a small-subunit rRNA-based cloning approach. While microbial communities in low-carbon, saturated, subsurface soils showed dominance, microbial communities in low-carbon surface soils showed remarkably uniform distributions, and all species were equally abundant. Two diversity indices, the reciprocal of Simpson's index (1/D) and the log series index, effectively distinguished between the dominant and uniform diversity patterns. For example, the uniform profiles characteristic of the surface communities had diversity index values that were 2 to 3 orders of magnitude greater than those for the high-dominance, saturated, subsurface communities. In a site richer in organic carbon, microbial communities consistently exhibited the uniform distribution pattern regardless of soil water content and depth. The uniform distribution implies that competition does not shape the structure of these microbial communities. Theoretical studies based on mathematical modeling suggested that spatial isolation could limit competition in surface soils, thereby supporting the high diversity and a uniform community structure. Carbon resource heterogeneity may explain the uniform diversity patterns observed in the high-carbon samples even in the saturated zone. Very high levels of chromium contamination (e.g., >20%) in the high-organic-matter soils did not greatly reduce the diversity. Understanding mechanisms that may control community structure, such as spatial isolation, has important implications for preservation of biodiversity, management of microbial communities for bioremediation, biocontrol of root diseases, and improved soil fertility.
••
TL;DR: Cascading failure in a simplified transmission system model as load power demand is increased is examined and it is found that operation near critical points can produce power law tails in the blackout size probability distribution similar to those observed.
Abstract: From the analysis of a 15-year time series of North American electric power transmission system blackouts, we have found that the frequency distribution of the blackout sizes does not decrease exponentially with the size of the blackout, but rather has a power law tail. The existence of a power tail suggests that the North American power system has been operated near a critical point. To see if this is possible, here we explore the critical points of a simple blackout model that incorporates circuit equations and a process through which outages of lines may happen. In spite of the simplifications, this is a complex problem. Understanding the different transition points and the characteristic properties of the distribution function of the blackouts near these points offers a first step in devising a dynamical model for the power transmission systems.
••
TL;DR: Data from Barrow, AK, at 71 degrees N show that rapid, photochemically driven oxidation of boundary-layer Hg0 after polar sunrise creates a rapidly depositing species of oxidized gaseous mercury in the remote Arctic troposphere at concentrations in excess of 900 pg m(-3).
Abstract: Gaseous elemental mercury (Hg0) is a globally distributed air toxin with a long atmospheric residence time. Any process that reduces its atmospheric lifetime increases its potential accumulation in the biosphere. Our data from Barrow, AK, at 71 degrees N show that rapid, photochemically driven oxidation of boundary-layer Hg0 after polar sunrise, probably by reactive halogens, creates a rapidly depositing species of oxidized gaseous mercury in the remote Arctic troposphere at concentrations in excess of 900 pg m(-3). This mercury accumulates in the snowpack during polar spring at an accelerated rate in a form that is bioavailable to bacteria and is released with snowmelt during the summer emergence of the Arctic ecosystem. Evidence suggests that this is a recent phenomenon that may be occurring throughout the earth's polar regions.
••
••
TL;DR: In this article, a simple model is developed based on observations from finite element simulations of indentation of elastic-plastic materials by a rigid cone that provides a physical explanation for the behavior.
Abstract: Experiments have shown that nanoindentation unloading curves obtained with Berkovich triangular pyramidal indenters are usually welldescribed by the power-law relation P = α(h − hf)m, where hf is the final depth after complete unloading and α and m are material constants. However, the power-law exponent is not fixed at an integral value, as would be the case for elastic contact by a conical indenter (m = 2) or a flat circular punch (m = 1), but varies from material to material in the range m = 1.2–1.6. A simple model is developed based on observations from finite element simulations of indentation of elastic–plastic materials by a rigid cone that provides a physical explanation for the behavior. The model, which is based on the concept of an indenter with an “effective shape” whose geometry is determined by the shape of the plastic hardness impression formed during indentation, provides a means by which the material constants in the power law relation can be related to more fundamental material properties such as the elastic modulus and hardness. Simple arguments are presented from which the effective indenter shape can be derived from the pressure distribution under the indenter.
••
TL;DR: Four methods for measuring diffusion coefficients were compared on a microfabricated fluidic device using rhodamine 6G as the analyte and the diffusion coefficient measured dynamically was 11% larger than that measured statically.
••
TL;DR: In this paper, the authors developed a comprehensive global database on net primary productivity (NPP) using field measurements of biomass and associated environmental data for multiple study sites in major grassland types worldwide.
Abstract: To address the need for a high quality data set based upon field observations suitable for parameterization, calibration, and validation of terrestrial biosphere models, we have developed a comprehensive global database on net primary productivity (NPP). We have compiled field measurements of biomass and associated environmental data for multiple study sites in major grassland types worldwide. Where sufficient data were available, we compared aboveground and total NPP estimated by six computational methods (algorithms) for 31 grassland sites. As has been found previously, NPP estimates were 2–5 times higher using methods which accounted for the dynamics of dead matter, compared with what is still the most commonly applied estimate of NPP (maximum peak live biomass). It is suggested that assumptions such as the use of peak biomass as an indicator of NPP in grasslands may apply only within certain subbiomes, e.g. temperate steppe grasslands. Additional data on belowground dynamics, or other reliable estimates of belowground productivity, are required if grasslands are to be fully appreciated for their role in the global carbon cycle.
••
[...]
TL;DR: In this paper, the authors highlight recent advances toward more efficient thermoelectric materials that may find wider application in refrigeration and power generation if production costs can be reduced, but they do not discuss the potential of these materials in other applications.
Abstract: Thermoelectric materials have long been investigated for use in refrigeration. However, they currently occupy only niche markets because of their low efficiency. In his Perspective,
Sales
highlights recent advances toward more efficient thermoelectric materials that may find wider application in refrigeration and power generation if production costs can be reduced.
••
TL;DR: In this article, the authors present a cross-site synthesis of annual carbon storage estimates, comparing meteorological and biometric approaches, and also comparing biometric estimates based on analyses of autotrophic carbon pools and heterotropic carbon fluxes (net ecosystem production, NEP).
••
TL;DR: It is suggested that the hydraulic principles that govern water transport provide an integrating framework that would allow CO2-induced changes in stomatal conductance, leaf water potential, root growth and other processes to be uniquely evaluated within the context of whole-plant hydraulic conductance and water transport efficiency.
Abstract: Long-term exposure of plants to elevated [CO 2 ] leads to a number of growth and physiological effects, many of which are interpreted in the context of ameliorating the negative impacts of drought. However, despite considerable study, a clear picture in terms of the influence of elevated [CO 2 ] on plant water relations and the role that these effects play in determining the response of plants to elevated [CO 2 ] under water-limited conditions has been slow to emerge. In this paper, four areas of research are examined that represent critical, yet uncertain, themes related to the response of plants to elevated [CO 2 ] and drought. These include (1) fine-root proliferation and implications for whole-plant water uptake; (2) enhanced water-use efficiency and consequences for drought tolerance; (3) reductions in stomatal conductance and impacts on leaf water potential; and (4) solute accumulation, osmotic adjustment and dehydration tolerance of leaves. A survey of the literature indicates that the growth of plants at elevated [CO 2 ] can lead to conditions whereby plants maintain higher (less negative) leaf water potentials. The mechanisms that contribute to this effect are not fully known, although CO 2 -induced reductions in stomatal conductance, increases in whole-plant hydraulic conductance and osmotic adjustment may be important. Less understood are the interactive effects of elevated [CO 2 ] and drought on fine-root production and water-use efficiency, and the contribution of these processes to plant growth in water-limited environments. Increases in water-use efficiency and reductions in water use can contribute to enhanced soil water content under elevated [CO 2 ]. Herbaceous crops and grasslands are most responsive in this regard. The conservation of soil water at elevated [CO 2 ] in other systems has been less studied, but in terms of maintaining growth or carbon gain during drought, the benefits of CO 2 -induced improvements in soil water content appear relatively minor. Nonetheless, because even small effects of elevated [CO 2 ] on plant and soil water relations can have important implications for ecosystems, we conclude that this area of research deserves continued investigation. Future studies that focus on cellular mechanisms of plant response to elevated [CO 2 ] and drought are needed, as are whole-plant investigations that emphasize the integration of processes throughout the soil‐plant‐ atmosphere continuum. We suggest that the hydraulic principles that govern water transport provide an integrating framework that would allow CO 2 -induced changes in stomatal conductance, leaf water potential, root growth and other processes to be uniquely evaluated within the context of whole-plant hydraulic conductance and water transport efficiency.
••
TL;DR: In this article, a multiple-scale analysis of forest fragmentation based on 30m (0.09 ha pixel 1 ) landcover maps for the conterminous United States is presented.
Abstract: We report a multiple-scale analysis of forest fragmentation based on 30-m (0.09 ha pixel 1 ) landcover maps for the conterminous United States. Each 0.09-ha unit of forest was classified according to fragmentation indexes measured within the surrounding landscape, for five landscape sizes including 2.25, 7.29, 65.61, 590.49, and 5314.41 ha. Most forest is found in fragmented landscapes. With 65.61-ha landscapes, for example, only 9.9% of all forest was contained in a fully forested landscape, and only 46.9% was in a landscape that was more than 90% forested. Overall, 43.5% of forest was located within 90 m of forest edge and 61.8% of forest was located within 150 m of forest edge. Nevertheless, where forest existed, it was usually dominant—at least 72.9% of all forest was in landscapes that were at least 60% forested for all landscape sizes. Small (less than 7.29 ha) perforations in otherwise continuous forest cover accounted for about half of the fragmentation. These results suggest that forests are connected over large regions, but fragmentation is so pervasive that edge effects potentially influence ecological processes on most forested lands.
••
TL;DR: In this article, the authors argue that as the force of humanity increases on the planet, ecosystem service valuation will need to switch from choosing among resources to valuing the avoidance of catastrophic ecosystem change.
••
TL;DR: In this article, structural models for the different surfaces of ZnO surfaces are proposed and related to the stability and reactivity of the surfaces, based on these results, structural models are proposed.
••
TL;DR: In this paper, the applied field that imposes the vortex lattice also induces'striped' antiferromagnetic order in high-T-c superconductors, which provides the best starting point for a pairing theory.
Abstract: One view of the high-transition-temperature (high-T-c) copper oxide superconductors is that they are conventional superconductors where the pairing occurs between weakly interacting quasi-particles (corresponding to the electrons in ordinary metals), although the theory has to be pushed to its limit(1). An alternative view is that the electrons organize into collective textures (for example, charge and spin stripes) which cannot be 'mapped' onto the electrons in ordinary metals. Understanding the properties of the material would then need quantum field theories of objects such as textures and strings, rather than point-like electrons(2-6). In an external magnetic field, magnetic flux penetrates type II superconductors via vortices, each carrying one flux quantum(7). The vortices form lattices of resistive material embedded in the non-resistive superconductor, and can reveal the nature of the ground state-for example, a conventional metal or an ordered, striped phase-which would have appeared had superconductivity not intervened, and which provides the best starting point for a pairing theory. Here we report that for one high-T-c superconductor, the applied field that imposes the vortex lattice also induces 'striped' antiferromagnetic order. Ordinary quasiparticle models can account for neither the strength of the order nor the nearly field-independent antiferromagnetic transition temperature observed in our measurements.
••
TL;DR: The energy absorption capability of a composite material is critical to developing improved human safety in an automotive crash as discussed by the authors, and energy absorption is dependent on many parameters like fiber type, m...
Abstract: The energy absorption capability of a composite material is critical to developing improved human safety in an automotive crash. Energy absorption is dependent on many parameters like fiber type, m...
••
TL;DR: In this paper, size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica were observed in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force.
Abstract: We have observed size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica. The ${\mathrm{VO}}_{2}$ nanoprecipitates are produced by the stoichiometric coimplantation of vanadium and oxygen and subsequent thermal processing. The observed size dependence in the transition temperature and hysteresis loops of the semiconductor-to-metal phase transition in ${\mathrm{VO}}_{2}$ is described in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force.
••
TL;DR: Hydrodynamic shock code simulations supported the observed data and indicated highly compressed, hot (106 to 107 kelvin) bubble implosion conditions, as required for nuclear fusion reactions.
Abstract: In cavitation experiments with deuterated acetone, tritium decay activity above background levels was detected. In addition, evidence for neutron emission near 2.5 million electron volts was also observed, as would be expected for deuterium-deuterium fusion. Control experiments with normal acetone did not result in tritium activity or neutron emissions. Hydrodynamic shock code simulations supported the observed data and indicated highly compressed, hot (10 6 to 10 7 kelvin) bubble implosion conditions, as required for nuclear fusion reactions.