Showing papers by "Oak Ridge National Laboratory published in 2004"
TL;DR: In this article, a new hybrid exchange-correlation functional named CAM-B3LYP is proposed, which combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al.
10,882 citations
TL;DR: In this article, the authors review the current understanding of the mechanics governing elastic-plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how they now implement the method to make the most accurate mechanical property measurements.
Abstract: The method we introduced in 1992 for measuring hardness and elastic modulus by instrumented indentation techniques has widely been adopted and used in the characterization of small-scale mechanical behavior. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques as well as from advances in our understanding of the mechanics of elastic–plastic contact. Here, we review our current understanding of the mechanics governing elastic–plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how we now implement the method to make the most accurate mechanical property measurements. The limitations of the method are also discussed.
6,616 citations
University of Washington1, University of Wisconsin–Milwaukee2, École Normale Supérieure3, University of British Columbia4, University of Wisconsin-Madison5, Princeton University6, Martek Biosciences Corporation7, University of California, Santa Barbara8, University of Melbourne9, University of California, San Diego10, Sandia National Laboratories11, University of California, Santa Cruz12, University of Regensburg13, Oak Ridge National Laboratory14, University of Hull15, Joint Genome Institute16, Academy of Sciences of the Czech Republic17, University of Massachusetts Medical School18, Woods Hole Oceanographic Institution19, Alfred Wegener Institute for Polar and Marine Research20, San Francisco State University21, University of California, Berkeley22
TL;DR: The 34 million-base-pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand base-pair mitochondrial genomes were reported in this article.
Abstract: Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for approximately 20% of global carbon fixation. We report the 34 million-base pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand-base pair mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, use of a range of nitrogenous compounds, and a complete urea cycle, all attributes that allow diatoms to prosper in aquatic environments.
1,945 citations
TL;DR: The Global Ocean Data Analysis Project (GLODAP) as mentioned in this paper uses ocean sampling data from the World Ocean Circulation Experiment (WOCE), the Joint Global Ocean Flux Study (JGOFS), and the Ocean Atmosphere Carbon Exchange Study (OACES) to produce objectively gridded property maps at a 1° resolution on 33 depth surfaces chosen to match existing climatologies for temperature, salinity, oxygen, and nutrients.
Abstract: [1] During the 1990s, ocean sampling expeditions were carried out as part of the World Ocean Circulation Experiment (WOCE), the Joint Global Ocean Flux Study (JGOFS), and the Ocean Atmosphere Carbon Exchange Study (OACES). Subsequently, a group of U.S. scientists synthesized the data into easily usable and readily available products. This collaboration is known as the Global Ocean Data Analysis Project (GLODAP). Results were merged into a common format data set, segregated by ocean. For comparison purposes, each ocean data set includes a small number of high-quality historical cruises. The data were subjected to rigorous quality control procedures to eliminate systematic data measurement biases. The calibrated 1990s data were used to estimate anthropogenic CO2, potential alkalinity, CFC watermass ages, CFC partial pressure, bomb-produced radiocarbon, and natural radiocarbon. These quantities were merged into the measured data files. The data were used to produce objectively gridded property maps at a 1° resolution on 33 depth surfaces chosen to match existing climatologies for temperature, salinity, oxygen, and nutrients. The mapped fields are interpreted as an annual mean distribution in spite of the inaccuracy in that assumption. Both the calibrated data and the gridded products are available from the Carbon Dioxide Information Analysis Center. Here we describe the important details of the data treatment and the mapping procedure, and present summary quantities and integrals for the various parameters.
1,580 citations
Vanderbilt University1, University of Southern California2, University of Texas MD Anderson Cancer Center3, University of Wisconsin-Madison4, University of California, Los Angeles5, National Center for Genome Resources6, Portland VA Medical Center7, University of Colorado Boulder8, University of Pennsylvania9, Hannover Medical School10, Johns Hopkins University11, Oregon Health & Science University12, Cornell University13, University of Michigan14, University of Tennessee Health Science Center15, Washington University in St. Louis16, University of Toronto17, University of Memphis18, Medical Research Council19, University of Massachusetts Medical School20, Hebrew University of Jerusalem21, Université de Montréal22, Purdue University23, University of California, Davis24, Academy of Sciences of the Czech Republic25, University at Buffalo26, Emory University27, University of Cincinnati28, University of Texas Southwestern Medical Center29, New York University30, University of Groningen31, Rutgers University32, Stanford University33, Max Planck Society34, National Institutes of Health35, University of Alabama at Birmingham36, International Livestock Research Institute37, Heidelberg University38, Medical College of Wisconsin39, Icahn School of Medicine at Mount Sinai40, Oak Ridge National Laboratory41, Charité42, University of Antwerp43, RWTH Aachen University44, Paul Sabatier University45, University of California, San Francisco46, McGill University47, Pasteur Institute48, University of Western Australia49, Yale University50, University of Oxford51, Case Western Reserve University52, Roswell Park Cancer Institute53, University of Kentucky54, University of Helsinki55, University of Nebraska–Lincoln56, Harvard University57, Merck & Co.58, King's College London59, Northwestern University60, Shriners Hospitals for Children61, Thomas Jefferson University62, Novartis63, University of North Carolina at Chapel Hill64, Southern Illinois University Carbondale65, University of Rochester66
TL;DR: The Collaborative Cross will provide a common reference panel specifically designed for the integrative analysis of complex systems and will change the way the authors approach human health and disease.
Abstract: The goal of the Complex Trait Consortium is to promote the development of resources that can be used to understand, treat and ultimately prevent pervasive human diseases. Existing and proposed mouse resources that are optimized to study the actions of isolated genetic loci on a fixed background are less effective for studying intact polygenic networks and interactions among genes, environments, pathogens and other factors. The Collaborative Cross will provide a common reference panel specifically designed for the integrative analysis of complex systems and will change the way we approach human health and disease.
1,040 citations
TL;DR: The sequenced genome of Phanerochaete chrysosporium strain RP78 reveals an impressive array of genes encoding secreted oxidases, peroxidases and hydrolytic enzymes that cooperate in wood decay, and provides a framework for further development of bioprocesses for biomass utilization, organopollutant degradation and fiber bleaching.
Abstract: White rot fungi efficiently degrade lignin, a complex aromatic polymer in wood that is among the most abundant natural materials on earth. These fungi use extracellular oxidative enzymes that are also able to transform related aromatic compounds found in explosive contaminants, pesticides and toxic waste. We have sequenced the 30-million base-pair genome of Phanerochaete chrysosporium strain RP78 using a whole genome shotgun approach. The P. chrysosporium genome reveals an impressive array of genes encoding secreted oxidases, peroxidases and hydrolytic enzymes that cooperate in wood decay. Analysis of the genome data will enhance our understanding of lignocellulose degradation, a pivotal process in the global carbon cycle, and provide a framework for further development of bioprocesses for biomass utilization, organopollutant degradation and fiber bleaching. This genome provides a high quality draft sequence of a basidiomycete, a major fungal phylum that includes important plant and animal pathogens.
883 citations
TL;DR: The synthesis of well-defined porous carbon films involves four steps: monomer-block copolymer film casting, structure refining through solvent annealing, polymerization of the carbon precursor, and carbonization.
Abstract: The synthesis of well-defined porous carbon films involves four steps: (1) monomer-block copolymer film casting, (2) structure refining through solvent annealing, (3) polymerization of the carbon precursor, and (4) carbonization. The resulting films, such as that depicted, have potential as separation membranes, chemical sensors, and catalysts.
784 citations
TL;DR: The genome sequence of R. palustris is described, which reveals genes that confer a remarkably large number of options within a given type of metabolism, including three nitrogenases, five benzene ring cleavage pathways and four light harvesting 2 systems.
Abstract: Rhodopseudomonas palustris is among the most metabolically versatile bacteria known. It uses light, inorganic compounds, or organic compounds, for energy. It acquires carbon from many types of green plant-derived compounds or by carbon dioxide fixation, and it fixes nitrogen. Here we describe the genome sequence of R. palustris, which consists of a 5,459,213-base-pair (bp) circular chromosome with 4,836 predicted genes and a plasmid of 8,427 bp. The sequence reveals genes that confer a remarkably large number of options within a given type of metabolism, including three nitrogenases, five benzene ring cleavage pathways and four light harvesting 2 systems. R. palustris encodes 63 signal transduction histidine kinases and 79 response regulator receiver domains. Almost 15% of the genome is devoted to transport. This genome sequence is a starting point to use R. palustris as a model to explore how organisms integrate metabolic modules in response to environmental perturbations.
704 citations
TL;DR: In this article, the authors provide a quantitative overview of DNA's electronic states as obtained from density-functional theory, focusing on dependence on structure, on molecular stretching and twisting, and on water and counterions.
Abstract: The DNA molecule, well known from biology for containing the genetic code of all living species, has recently caught the attention of chemists and physicists. A major reason for this interest is DNA's potential use in nanoelectronic devices, both as a template for assembling nanocircuits and as an element of such circuits. Without question, a truly conducting form of DNA would have a major impact on developments in nanotechnology. It has also been suggested that extended electronic states of DNA could play an important role in biology, e.g., through the processes of DNA damage sensing or repair or through long-range charge transfer. However, the electronic properties of DNA remain very controversial. Charge-transfer reactions and conductivity measurements show a large variety of possible electronic behavior, ranging from Anderson and band-gap insulators to effective molecular wires and induced superconductors. Indeed, understanding the conductance of a complicated polyelectrolytic aperiodic system is by itself a major scientific problem. In this Colloquium, the authors summarize the wide-ranging experimental and theoretical results and look for any consistencies between them. They also pose simple questions regarding the electronic states of DNA within the framework of generalized H\"uckel and Slater-Koster theories. The Colloquium provides a quantitative overview of DNA's electronic states as obtained from density-functional theory, focusing on dependence on structure, on molecular stretching and twisting, and on water and counterions. While there is no clear theoretical basis for truly metallic DNA, situations are discussed in which very small energy gaps might arise in the overall DNA/water/counterion complex, leading to thermally activated conduction at room temperature.
685 citations
TL;DR: In this paper, a new zero-voltage-switching (ZVS) bidirectional dc-dc converter is proposed for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required.
Abstract: This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented.
684 citations
TL;DR: In this paper, the authors measured the centrality dependence of transverse momentum distributions and particle yields at the PHENIX experiment at the Relativistic Heavy Ion Collider (HIC).
Abstract: The centrality dependence of transverse momentum distributions and yields for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},{K}^{\ifmmode\pm\else\textpm\fi{}},p$, and $\overline{p}$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$ in ${p}_{T}$. Both mean transverse momenta and particle yields per participant pair increase from peripheral to midcentral and saturate at the most central collisions for all particle species. We also measure particle ratios of ${\ensuremath{\pi}}^{\ensuremath{-}}∕{\ensuremath{\pi}}^{+}$, ${K}^{\ensuremath{-}}∕{K}^{+}$, $\overline{p}∕p$, $K∕\ensuremath{\pi}$, $p∕\ensuremath{\pi}$, and $\overline{p}∕\ensuremath{\pi}$ as a function of ${p}_{T}$ and collision centrality. The ratios of equal mass particle yields are independent of ${p}_{T}$ and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta $\ensuremath{\sim}1.5--4.5\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$, proton and antiproton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.
National Institutes of Health1, Wellcome Trust Sanger Institute2, University of Pennsylvania3, University of Utah4, University of Wisconsin-Madison5, Harvard University6, Rockefeller University7, University of Manitoba8, New York University9, University of North Carolina at Chapel Hill10, University of California, Davis11, University of Toronto12, GlaxoSmithKline13, Oak Ridge National Laboratory14, Fred Hutchinson Cancer Research Center15, Cold Spring Harbor Laboratory16, Dresden University of Technology17, Memorial Sloan Kettering Cancer Center18, Salk Institute for Biological Studies19, Merck & Co.20, Goethe University Frankfurt21, Max Planck Society22, Regeneron23, University of California, San Francisco24
TL;DR: It is time to harness new technologies and efficiencies of production to mount a high-throughput international effort to produce and phenotype knockouts for all mouse genes, and place these resources into the public domain.
Abstract: Mouse knockout technology provides a powerful means of elucidating gene function in vivo, and a publicly available genome-wide collection of mouse knockouts would be significantly enabling for biomedical discovery. To date, published knockouts exist for only about 10% of mouse genes. Furthermore, many of these are limited in utility because they have not been made or phenotyped in standardized ways, and many are not freely available to researchers. It is time to harness new technologies and efficiencies of production to mount a high-throughput international effort to produce and phenotype knockouts for all mouse genes, and place these resources into the public domain.
TL;DR: The complete genomic sequence of Y. pseudotuberculosis IP32953 is reported and provides a sobering example of how a highly virulent epidemic clone can suddenly emerge from a less virulent, closely related progenitor.
Abstract: Yersinia pestis, the causative agent of plague, is a highly uniform clone that diverged recently from the enteric pathogen Yersinia pseudotuberculosis. Despite their close genetic relationship, they differ radically in their pathogenicity and transmission. Here, we report the complete genomic sequence of Y. pseudotuberculosis IP32953 and its use for detailed genome comparisons with available Y. pestis sequences. Analyses of identified differences across a panel of Yersinia isolates from around the world reveal 32 Y. pestis chromosomal genes that, together with the two Y. pestis-specific plasmids, to our knowledge, represent the only new genetic material in Y. pestis acquired since the the divergence from Y. pseudotuberculosis. In contrast, 149 other pseudogenes (doubling the previous estimate) and 317 genes absent from Y. pestis were detected, indicating that as many as 13% of Y. pseudotuberculosis genes no longer function in Y. pestis. Extensive insertion sequence-mediated genome rearrangements and reductive evolution through massive gene loss, resulting in elimination and modification of preexisting gene expression pathways, appear to be more important than acquisition of genes in the evolution of Y. pestis. These results provide a sobering example of how a highly virulent epidemic clone can suddenly emerge from a less virulent, closely related progenitor.
TL;DR: A review of recent results in developing improved control of growth, doping, and fabrication processes for ZnO devices with possible applications to ultraviolet (UV) light emitters, spin functional devices, gas sensors, transparent electronics, and surface acoustic wave devices is given in this article.
TL;DR: In this article, equal channel angular processing is shown to induce a strong deformation texture, which persists after recrystallization, and the enhancement in the tensile ductility along the extrusion axis originally reported by Mukai et al. [Scripta Mater 45 (2001) 89] is discussed in terms of magnesium's deformation mechanisms, plastic anisotropy, and texture itself.
TL;DR: The discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods are reported, which showed interesting physical, magnetic, and mechanical properties, along with high thermal stability.
Abstract: Recent advancement in bulk metallic glasses, whose properties are usually superior to their crystalline counterparts, has stimulated great interest in fabricating bulk amorphous steels. While a great deal of effort has been devoted to this field, the fabrication of structural amorphous steels with large cross sections has remained an alchemist's dream because of the limited glass-forming ability (GFA) of these materials. Here we report the discovery of structural amorphous steels that can be cast into glasses with large cross-section sizes using conventional drop-casting methods. These new steels showed interesting physical, magnetic, and mechanical properties, along with high thermal stability. The underlying mechanisms for the superior GFA of these materials are discussed.
TL;DR: It is shown that the recently proposed conceptually simple and easily calculated measure of permutation entropy can be effectively used to detect qualitative and quantitative dynamical changes.
Abstract: Timely detection of unusual and/or unexpected events in natural and man-made systems has deep scientific and practical relevance. We show that the recently proposed conceptually simple and easily calculated measure of permutation entropy can be effectively used to detect qualitative and quantitative dynamical changes. We illustrate our results on two model systems as well as on clinically characterized brain wave data from epileptic patients.
TL;DR: Direct images from an aberration-corrected scanning TEM are presented that resolve a lattice in which the atomic columns are sepa-rated by less than 0.1 nanometer.
Abstract: Despite the use of electrons with wavelengths of just a few picometers, spatial resolution in a transmission electron microscope (TEM) has been limited by spherical aberration to typically around 0.15 nanometer. Individual atomic columns in a crystalline lattice can therefore only be imaged for a few low-order orientations, limiting the range of defects that can be imaged at atomic resolution. The recent development of spherical aberration correctors for transmission electron microscopy allows this limit to be overcome. We present direct images from an aberration-corrected scanning TEM that resolve a lattice in which the atomic columns are separated by less than 0.1 nanometer.
TL;DR: In this paper, the authors demonstrate the importance of examining the combined effects of the gradually rising concentration of atmospheric CO2 and the climatic change that attends it, and propose an alternative approach to gain a thorough understanding of the modes of action of single factors, and rely on our understanding (as represented in models) to inform us of the probable interactions.
Abstract: Summary
Analyses of ecosystem responses to global change must embrace the reality of multiple, interacting environmental factors. Ecosystem models demonstrate the importance of examining the combined effects of the gradually rising concentration of atmospheric CO2 and the climatic change that attends it. Models to forecast future changes need data support to be useful, and data–model fusion has become essential in global change research. There is a wealth of information on plant responses to CO2 and temperature, but there have been few ecosystem-scale experiments investigating the combined or interactive effects of CO2 enrichment and warming. Factorial experiments to investigate interactions can be difficult to design, conduct, and interpret, and their results may not support predictions at the ecosystem scale – in the context of global change they will always be case studies. An alternative approach is to gain a thorough understanding of the modes of action of single factors, and rely on our understanding (as represented in models) to inform us of the probable interactions. Multifactor (CO2 × temperature) experiments remain important, however, for testing concepts, demonstrating the reality of multiple-factor influences, and reminding us that surprises can be expected.
TL;DR: GOTree Machine has a broad application in functional genomic, proteomic and other high-throughput methods that generate large sets of interesting genes; its primary purpose is to help users sort for interesting patterns in gene sets.
Abstract: Background
Microarray and other high-throughput technologies are producing large sets of interesting genes that are difficult to analyze directly. Bioinformatics tools are needed to interpret the functional information in the gene sets.
TL;DR: In this article, the authors present longitudinal studies of 23 extant mammal species, modelling ecological niches and predicting geographical distributions reciprocally between the Last Glacial Maximum and present to test this evolutionary conservatism.
Abstract: Aim Theoretical work suggests that species’ ecological niches should remain relatively constant over long-term ecological time periods, but empirical tests are few. We present longitudinal studies of 23 extant mammal species, modelling ecological niches and predicting geographical distributions reciprocally between the Last Glacial Maximum and present to test this evolutionary conservatism. Location This study covered distributional shifts in mammal species across the lower 48 states of the United States.
TL;DR: In this paper, a highly ordered array of parallel multi-wall CNTs in an alumina matrix was fabricated and the damage was examined by scanning electron microscopy, and the quantitative indentation data and computational models were used to determine the multiwall axial Young's modulus as 200-570 GPa, depending on the nanotube geometry and quality.
01 Nov 2004
TL;DR: A new class of multilevel inverters based on a multileVEL DC link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes or capacitors is presented.
Abstract: This paper presents a new class of multilevel inverters based on a multilevel dc link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes, or capacitors. An MLDCL can be a diode-clamped phase leg, a flying-capacitor phase leg, or cascaded half-bridge cells with each cell having its own dc source. A multilevel voltage-source inverter can be formed by connecting one of the MLDCLs with a single-phase bridge inverter. The MLDCL provides a dc voltage with the shape of a staircase approximating the rectified shape of a commanded sinusoidal wave, with or without pulsewidth modulation, to the bridge inverter, which in turn alternates the polarity to produce an ac voltage. Compared with the cascaded H-bridge, diode-clamped, and flying-capacitor multilevel inverters, the MLDCL inverters can significantly reduce the switch count as well as the number of gate drivers as the number of voltage levels increases. For a given number of voltage levels m, the required number of active switches is 2/spl times/(m-1) for the existing multilevel inverters but is m+3 for the MLDCL inverters. Simulation and experimental results are included to verify the operating principles of the MLDCL inverters.
TL;DR: In this paper, the role of canopy storage terms from canopy water content and photosynthesis is usually neglected in the surface energy balance of crops, and data from a research flux tower in central Illinois were used to evaluate these storage terms and their impact on the closure of the surface Energy balance.
TL;DR: A derivatized porphyrin with long alkyl chains, 5,10,15,20-tetrakis(hexadecyloxyphenyl)-21H,23H-porphine, is selective toward semiconducting single-walled carbon nanotubes (SWNTs) in presumably noncovalent interactions, resulting in significantly enriched semiconductor SWNTs in the solubilized sample.
Abstract: A derivatized porphyrin with long alkyl chains, 5,10,15,20-tetrakis(hexadecyloxyphenyl)-21H,23H-porphine, is selective toward semiconducting single-walled carbon nanotubes (SWNTs) in presumably noncovalent interactions, resulting in significantly enriched semiconducting SWNTs in the solubilized sample and predominantly metallic SWNTs in the residual solid sample according to Raman, near-IR absorption, and bulk conductivity characterizations.
University of Wyoming1, University of Oregon2, Oak Ridge National Laboratory3, Northern Arizona University4, Marine Biological Laboratory5, University of Nevada, Reno6, Oregon State University7, University of Oklahoma8, Smithsonian Environmental Research Center9, Lund University10, Colorado State University11
TL;DR: In this article, the current status of below-ground responses to elevated CO2 and temperature and potential feedback effects, methodological challenges, and approaches to integrating models and measurements are discussed, as well as approaches to integrate models and data to predict long-term, net carbon storage in ecosystems.
Abstract: Rising atmospheric CO2 and temperatures are probably altering ecosystem carbon cycling, causing both positive and negative feedbacks to climate. Below-ground processes play a key role in the global carbon (C) cycle because they regulate storage of large quantities of C, and are potentially very sensitive to direct and indirect effects of elevated CO2 and temperature. Soil organic matter pools, roots and associated rhizosphere organisms all have distinct responses to environmental change drivers, although availability of C substrates will regulate all the responses. Elevated CO2 increases C supply below-ground, whereas warming is likely to increase respiration and decomposition rates, leading to speculation that these effects will moderate one another. However, indirect effects on soil moisture availability and nutrient supply may alter processes in unexpected directions. Detailed, mechanistic understanding and modelling of below-ground flux components, pool sizes and turnover rates is needed to adequately predict long-term, net C storage in ecosystems. In this synthesis, we discuss the current status of below-ground responses to elevated CO2 and temperature and potential feedback effects, methodological challenges, and approaches to integrating models and measurements.
TL;DR: Root-system dynamics can explain differences among ecosystems in their response to elevated atmospheric CO(2); hence, accurate assessments of carbon flux and storage in forests in a globally changing atmosphere must account for this unseen and difficult-to-measure component.
Abstract: Fine-root production and turnover are important regulators of the biogeochemical cycles of ecosystems and key components of their response to global change. We present a nearly continuous 6-year record of fine-root production and mortality from minirhizotron analysis of a closed-canopy, deciduous sweetgum forest in a free-air CO2 enrichment experiment. Annual production of fine roots was more than doubled in plots with 550 ppm CO2 compared with plots in ambient air. This response was the primary component of the sustained 22% increase in net primary productivity. Annual fine-root mortality matched annual production, and the mean residence time of roots was not altered by elevated CO2, but peak fine-root standing crop in midsummer was significantly higher in CO2-enriched plots, especially deeper in the soil profile. The preferential allocation of additional carbon to fine roots, which have a fast turnover rate in this species, rather than to stemwood reduces the possibility of long-term enhancement by elevated CO2 of carbon sequestration in biomass. However, sequestration of some of the fine-root carbon in soil pools is not precluded, and there may be other benefits to the tree from a seasonally larger and deeper fine-root system. Root-system dynamics can explain differences among ecosystems in their response to elevated atmospheric CO2; hence, accurate assessments of carbon flux and storage in forests in a globally changing atmosphere must account for this unseen and difficult-to-measure component.
TL;DR: In this paper, the applicability of small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) techniques for determining the porosity, pore size distribution and internal specific surface area in coals is discussed.
TL;DR: In this paper, a modified standard approximation is proposed that involves expansion in the orthogonal complement to the span of orbital basis set (OBS) for linear R12 theories.