bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plane‐layered models for the analysis of wave propagation in reservoir environments1
Authors: Carcione José M. 
Published: April 2006

AbstractThe long‐wavelength propagation and attenuation characteristics of three geological structures that frequently occur in reservoir environments are investigated using a theoretical model that consists of a stack of fine and viscoelastic plane layers, with the layers being either solid or fluid. Backus theory properly describes fine layering and a set of fluid‐filled microfractures, under the assumption that interfaces between different materials are bonded. The effects of saturation on wave attenuation are modelled by the relative values of the bulk and shear quality factors.The anisotropic quality factor in a fine‐layered system shows a variety of behaviours depending on the saturation and velocities of the single constituents. The wave is less attenuated along the layering direction when the quality factors are proportional to velocity, and vice versa when inversely proportional to velocity. Fractured rocks have very anisotropic wavefronts and quality factors, in particular for the shear modes which are strongly dependent on the characteristics of the fluid filling the microfractures.When the size of the boundary layer is much smaller than the thickness of the fluid layer, the stack of solid‐fluid layers becomes a layered porous media of the Biot type. This behaviour is caused by the slip‐wall condition at the interface between the solid and the fluid. As in Biot theory, there are two compressional waves, but here the medium is anisotropic and the slow wave does not propagate perpendicular to the layers. Moreover, this wave shows pronounced cusps along the layering direction, like shear waves in a very anisotropic single‐phase medium.
Estimation of effective source signatures from marine VSP data1
Authors: Hokstad K. , Landrø M. , Mittet R. 
Published: April 2006

AbstractWe present a simple method for estimating an effective source wavelet from the first arrival in marine vertical seismic profiling (VSP) data. The method, which utilizes the free‐space Green's function of the Helmholz equation, is simple and very computer efficient. We show examples from synthetic and real offset and walkaway VSP data.In the synthetic examples, we show that data modelled with the estimated wavelet give small residuals when subtracted from the reference data. In the real data examples, we show that when modelling with the wavelet estimated from the real data, in a smooth macromodel, we obtain a good fit between the first arrivals in the real and modelled data.
Optimum expression for computation of the magnetic field of a homogeneous polyhedral body12
Authors: Ivan M. 
Published: April 2006

AbstractAn expression which is optimum with respect to the simplicity of the numerical computations is obtained for the magnetic field of a polyhedron with constant magnetization. The high accuracy of the results is illustrated using a realistic numerical model.The existence of the magnetic field at points inside the source and on its boundary is discussed and related to real magnetic data modelling.
An iterative method for finding small magnetic objects in the subsurface by linear and non‐linear inversion1
Authors: Mirzaei M. , Bredewout J.W. 
Published: April 2006

AbstractA method to determine the position and magnetization vector of buried objects producing a magnetic anomaly is described. The data used were collected in boreholes. Since the anomaly is due to a number of objects, a ‘stripping’ procedure is employed for finding them, and therefore the process of inversion for finding all objects causing the anomaly consists of a few inversion steps.In each inversion step, two dipoles are considered as a model which approximates an object. The position and magnetic moments of the dipoles are the unknown parameters. The initial parameters are optimized by minimization of an objective function. The optimization procedure consists of a combination of linear and non‐linear inversion. The solution of the linear inversion is obtained by singular value decomposition and that of the non‐linear inversion by a six‐dimensional simplex method (polytope algorithm). After finding one object, its effect is subtracted (‘stripped’) from the data and a new inversion step is started with new initial models and with a reduced data set. The inversion steps for finding different objects are continued until the absolute norm of the data becomes less than some adjustable value.The data will also be inverted assuming a three‐dipole model in order to find the effect of using a more complex model in the inversion.The efficiency of the method is demonstrated using synthetic and real borehole data.
A numerical laboratory for simulation and visualization of seismic wavefields1
Authors: Serón F. J. , Badal J. , Sabadell F. J. 
Published: April 2006

AbstractComputational seismic modelling (CSM) plays an important role in the geophysical industry as an established aid to seismic interpreters. Numerical solution of the elastic wave equations has proved to be a very important tool for geophysicists in both forward modelling and migration. Among the techniques generally used in CSM, we consider the finite‐element method (FEM) and investigate its computational and visualization requirements. The CSMFEM program, designed for this purpose and developed on an IBM 3090 computer with vector facility, is described in detail. It constitutes a numerical laboratory for performing computer experiments. Two Newmark type algorithms for time integration are compared with other time integration schemes, and both direct and iterative methods for solving the corresponding large sparse system of linear algebraic equations are analysed. Several numerical experiments to simulate seismic energy propagation through heterogeneous media are performed. Synthetics in the form of common shot gathers, vertical seismic profiles and snapshots are suitably displayed, since with the large amounts of data obtained from CSM research, methods for visualization of the computed results must be developed. The FEM is compared with other numerical tools, such as finite‐difference and pseudo‐spectral methods.
Climatic severity and the response to temperature elevation of Arctic aphids
Authors: STRATHDEE A.T. , BALE J.S. , STRATHDEE F.C. , BLOCK W.C. , COULSON S.J. , WEBB N.R. , HODKINSON I. D. 
Published: April 2006

Abstract

Theory suggests that any given rise in temperature resulting from climate change will have its greatest effect on high Arctic ecosystems where growing seasons are short and temperatures low.
A small temperature rise, similar to that predicted for the middle of the next century, has profound effects on a population of the high Arctic, Dryas‐feeding aphid Acyrthosiphon svalbardicum on Spitsbergen (Strathdee et al. 1993a).
Here comparative experiments on a closely related Dryas‐feeding species, A. brevicorne, at two contrasting sub‐Arctic sites are described. Together with the results from Spitsbergen these sites represent two colder sites (high Arctic and upland sub‐Arctic) and one warmer site (lowland sub‐Arctic).
Differential responses in aphid population density and overwintering egg production to temperature elevation support the hypothesis that the ecological effects are greatest at sites with the most severe climates; however, there is no similar gradient in advancement of host plant phenology with warming.
Early‐season effects of supplemented solar UV‐B radiation on seedling emergence, canopy structure, simulated stand photosynthesis and competition for light
Authors: BARNES PAUL W. , FLINT STEPHAN D. , CALDWELL MARTYN M. 
Published: April 2006

AbstractMixtures and monocultures of wheat (Triticum aestivum) and wild oat (Avena fatua), a common weedy competitor of wheat, were exposed to enhanced solar UV‐B radiation simulating a 20% reduction in stratospheric ozone to assess the timing and seasonal development of the UV‐B effects on light competition in these species. Results from two years of field study revealed that UV‐B enhancement had no detectable effect on the magnitude or timing of seedling emergence in either species. End‐of‐season measurements showed significant UV‐B inhibition of leaf insertion height in wild oat in mixture and monoculture in the second year (irrigated year) but not in the first year (drought year). Leaf insertion height of wheat was not affected by UV‐B in either year. The UV‐B treatment had no detectable effect on monoculture or total (combined species) mixture LAI but did significantly increase (5–7%) the fractional contribution of wheat to the mixture LAI after four weeks of growth in both years. In addition, the UV‐B treatment had subtle effects on LAI height profiles with early season mixtures showing significant reductions in wild oat LAI in lower canopy layers in both years while midseason Year 2 mixtures showed significant reductions in wild oat LAI in upper canopy layers. The changes in canopy structure were found to significantly increase (6–7%) the proportional simulated clear sky canopy photosynthesis and light interception of wheat in mixture. These findings, and others, indicate that the effects of UV‐B enhancement on competition are realized very early in canopy development and provide additional support for the hypothesis that UV‐B enhancement may shift the balance of competition between these species indirectly by altering competitive interactions for light.
Leaf gas exchange and nitrogen dynamics of N2‐fixing, field‐grown Alnus glutinosa under elevated atmospheric CO2
Authors: VOGEL CHRISTOPH S. , CURTIS PETER S. 
Published: April 2006

AbstractFew studies have investigated the effects of elevated CO2 on the physiology of symbiotic N2‐fixing trees. Tree species grown in low N soils at elevated CO2 generally show a decline in photosynthetic capacity over time relative to ambient CO2 controls. This negative adjustment may be due to a reallocation of leaf N away from the photosynthetic apparatus, allowing for more efficient use of limiting N. We investigated the effect of twice ambient CO2 on net CO2 assimilation (A), photosynthetic capacity, leaf dark respiration, and leaf N content of N2‐fixing Alnus glutinosa (black alder) grown in field open top chambers in a low N soil for 160 d.At growth CO2, A was always greater in elevated compared to ambient CO2 plants. Late season A vs. internal leaf p(CO2) response curves indicated no negative adjustment of photosynthesis in elevated CO2 plants. Rather, elevated CO2 plants had 16% greater maximum rate of CO2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO2 on an area basis, but unaffected by CO2 on a mass or N basis. In elevated CO2 plants, leaf N content (μg N cm−2) increased 50% between Julian Date 208 and 264. Leaf N content showed little seasonal change in ambient CO2 plants. A single point acetylene reduction assay of detached, nodulated root segments indicated a 46% increase in specific nitrogenase activity in elevated compared to ambient CO2 plants. Our results suggest that N2‐fixing trees will be able to maintain high A with minimal negative adjustment of photosynthetic capacity following prolonged exposure to elevated CO2 on N‐poor soils.
Terrestrial ecosystems and the carbon cycle
Authors: SCHIMEL DAVID S. 
Published: April 2006

AbstractThe terrestrial biosphere plays an important role in the global carbon cycle. In the 1994 Intergovernmental Panel Assessment on Climate Change (IPCC), an effort was made to improve the quantification of terrestrial exchanges and potential feedbacks from climate, changing CO2, and other factors; this paper presents the key results from that assessment, together with expanded discussion. The carbon cycle is the fluxes of carbon among four main reservoirs: fossil carbon, the atmosphere, the oceans, and the terrestrial biosphere. Emissions of fossil carbon during the 1980s averaged 5.5 Gt y−1. During the same period, the atmosphere gained 3.2 Gt C y−1 and the oceans are believed to have absorbed 2.0 Gt C y−1. The regrowing forests of the Northern Hemisphere may have absorbed 0.5 Gt C y−1 during this period. Meanwhile, tropical deforestation is thought to have released an average 1.6 Gt C y−1 over the 1980s. While the fluxes among the four pools should balance, the average 198Ds values lead to a ‘missing sink’ of 1.4 Gt C y−1 Several processes, including forest regrowth, CO2 fertilization of plant growth (c. 1.0 Gt C y−1), N deposition (c. 0.6 Gt C y−1), and their interactions, may account for the budget imbalance. However, it remains difficult to quantify the influences of these separate but interactive processes. Uncertainties in the individual numbers are large, and are themselves poorly quantified. This paper presents detail beyond the IPCC assessment on procedures used to approximate the flux uncertainties.Lack of knowledge about positive and negative feedbacks from the biosphere is a major limiting factor to credible simulations of future atmospheric CO2 concentrations. Analyses of the atmospheric gradients of CO2 and 13 CO2 concentrations provide increasingly strong evidence for terrestrial sinks, potentially distributed between Northern Hemisphere and tropical regions, but conclusive detection in direct biomass and soil measurements remains elusive.Current regional‐to‐global terrestrial ecosystem models with coupled carbon and nitrogen cycles represent the effects of CO2 fertilization differently, but all suggest longterm responses to CO2 that are substantially smaller than potential leaf‐ or laboratory whole plant‐level responses. Analyses of emissions and biogeochemical fluxes consistent with eventual stabilization of atmospheric CO2 concentrations are sensitive to the way in which biospheric feedbacks are modeled by c. 15%. Decisions about land use can have effects of 100s of Gt C over the next few centuries, with similarly significant effects on the atmosphere.Critical areas for future research are continued measurements and analyses of atmospheric data (CO2 and 13CO2) to serve as large‐scale constraints, process studies of the scaling from the photosynthetic response to CO2 to whole‐ecosystem carbon storage, and rigorous quantification of the effects of changing land use on carbon storage.
Elevated carbon dioxide affects leaf‐miner performance and plant growth in docks (Rumex spp.)
Authors: SALT D. T. , BROOKS G. L. , WHITTAKER J. B. 
Published: April 2006

AbstractExposure of R. crispus and R. obtusifolius to elevated CO2 (600 ppm) resulted in an increased C:N ratio of leaf tissue and greater leaf areas. Larvae of P. nigritarsis mining leaves of R. obtusifolius during exposure produced significantly bigger mines in elevated than in ambient (350 ppm) conditions. There were no significant treatment effects on pupal weight although in both host species mean weight was greater in ambient than in elevated conditions. These results are consistent with the hypothesis that insect herbivores compensate for increased C:N ratios by increased food consumption. This response by herbivores may partially offset predicted increases in plant biomass in a future high CO2 environment.
Climate change, interannual weather differences and conflicting responses among crop characteristics: the case of forage quality
Authors: SELIGMAN NO'AM G. , SINCLAIR THOMAS R. 
Published: April 2006

AbstractYield and quality of cultivated forage crops are important determinants of animal production efficiency and both forage traits are sensitive to weather. Consequently, it can be presumed that these traits will respond to anticipated changes in the global environment associated with increases in [CO2] and temperature. Because of the large inter‐ and intra‐annual weather variation that exists in most agricultural regions, it is not clear what the forage production response will be to predicted changes. This uncertainty in forage response to global environment change as compared to interannual weather variation was analysed using a mechanistic simulation model of plant development and growth. The results indicated that low soil‐nutrient availability restricts forage production to such a degree that the global environment effects of higher [CO2] and temperature on quality are essentially irrelevant. When the nitrogen constraint was relaxed, higher [CO2] caused dry matter and digestibility to increase and protein concentration and leaf:stem ratio to decrease. Increased temperature had opposite effects. The combined effects of [CO2] and temperature were complex and annual weather variations were dominant, especially in rainfed situations. Limited reliability of predictions of crop response decades into the future indicates that it may be prudent to direct research effort to prepare for a wide range of climatic contingencies.
The effects of elevated CO2concentrations on the root growth of Lolium perenne and Trifolium repens grown in a FACE* system
Authors: JONGEN MARJAN , JONES MIKE B. , HEBEISEN THOMAS , BLUM HERBERT , HENDREY GEORGE 
Published: April 2006

AbstractLolium perenneandTrifolium repenswere grown in a Free Air CO2Enrichment (FACE) system at elevated (600 μimol mol‐1) and ambient (340 μmol mol‐1) carbon dioxide concentrations during a whole growing season. Using a root ingrowth bag technique the extent to which CO2enrichment influenced the growth ofL, perenneandT. repensroots under two contrasting nutrient regimes was examined. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It was also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of bothL. perenneandT. repensincreased under elevated CO2conditions. InL. perenne, root ingrowth decreased with increasing nutrient fertilizer level, but forT. repensthe root ingrowth was not affected by the nutrient application rate. Besides biomass measurements, root length estimates were made forT, repens.These showed an increase under elevated CO2concentrations. Root decomposition appeared to decrease under elevated CO2concentrations. A possible explanation for this effect is the observed changes in tissue composition, such as the increase in the carbon: nitrogen ratio in roots ofL. perenneat elevated CO2concentrations.
Effects of global environmental change on carbon partitioning in vegetative plants of Triticum aestivum and closely related Aegilops species
Authors: LAMBERS HANS , VAN DEN BOOGAARD RIKI , VENEKLAAS ERIK J. , VILLAR RAFAEL 
Published: April 2006

AbstractThe use of fossil fuel is predicted to cause an increase of the atmospheric CO2 concentration, which will affect the global pattern of temperature and precipitation. It is therefore essential to incorporate effects of temperature and water supply on carbon partitioning of plants to predict effects of elevated [CO2] on growth and yield of Triticum aestivum.Although earlier papers have emphasized that elevated [CO2] favours investment of biomass in roots relative to that in leaves, it has now become clear that these are indirect effects, due to the more rapid depletion of nutrients in the root environment as a consequence of enhanced growth. Broadly generalized, the effect of temperature on biomass allocation in the vegetative stage is that the relative investment of biomass in roots is lowest at a certain optimum temperature and increases at both higher and lower temperatures. This is found not only when the temperature of the entire plant is varied, but also when only root temperature is changed whilst shoot temperature is kept constant. Effects of temperature on the allocation pattern can be explained largely by the effect of root temperature on the roots' capacity to transport water. Effects of a shortage in water supply on carbon partitioning are unambiguous: roots receive relatively more carbon.The pattern of biomass allocation in the vegetative stage and variation in water‐use efficiency are prime factors determining a plant's potential for early growth and yield in different environments. In a comparison of a range of T. aestivum cultivars, a high water‐use efficiency at the plant level correlates positively with a large investment in both leaf and root biomass, a low stomatal conductance and a large investment in photosynthetic capacity. We also present evidence that a lower investment of biomass in roots is not only associated with lower respiratory costs for root growth, but also with lower specific costs for ion uptake. We suggest the combination of a number of traits in future wheat cultivars, i.e. a high investment of biomass in leaves, which have a low stomatal conductance and a high photosynthetic capacity, and a low investment of biomass in roots, which have low respiratory costs. Such cultivars are considered highly appropriate in a future world, especially in the dryer regions. Although variation for the desired traits already exists among wheat cultivars, it is much larger among wild Aegilops species, which can readily be crossed with T. aestivum. Such wild relatives may be exploited to develop new wheat cultivars well‐adapted to changed climatic conditions.
Interaction between atmospheric CO2 concentration and water deficit on gas exchange and crop growth: testing of ecosys with data from the Free Air CO2 Enrichment (FACE) experiment
Authors: GRANT R.F. , GARCIA R.L. , PINTER J P.J. , HUNSAKER D. , WALL G.W. , KIMBALL B.A. , LaMORTE R.L. 
Published: April 2006

AbstractSoil water deficits are likely to influence the response of crop growth and yield to changes in atmospheric CO2 concentrations (Ca), but the extent of this influence is uncertain. To study the interaction of water deficits and Ca on crop growth, the ecosystem simulation model ecosys was tested with data for diurnal gas exchange and seasonal wheat growth measured during 1993 under high and low irrigation at Ca= 370 and 550 μmol mol−1 in the Free Air CO2 Enrichment (FACE) experiment near Phoenix, AZ. The model, supported by the data from canopy gas exchange enclosures, indicated that under high irrigation canopy conductance (gc) at Ca= 550 μmol mol−1 was reduced to about 0.75 that at Ca= 370 μmol mol−1, but that under low irrigation, gc was reduced less. Consequently when Ca was increased from 370 to 550 μmol mol−1, canopy transpiration was reduced less, and net CO2 fixation was increased more, under low irrigation than under high irrigation. The simulated effects of Ca and irrigation on diurnal gas exchange were also apparent on seasonal water use and grain yield. Simulated vs. measured seasonal water use by wheat under high irrigation was reduced by 6% vs. 4% at Ca= 550 vs. 370 μmol mol−1 but that under low irrigation was increased by 3% vs. 5%. Simulated vs. measured grain yield of wheat under high irrigation was increased by 16% vs. 8%, but that under low irrigation was increased by 38% vs. 21%. In ecosys, the interaction between Ca and irrigation on diurnal gas exchange, and hence on seasonal crop growth and water use, was attributed to a convergence of simulated gc towards common values under both Ca as canopy turgor declined. This convergence caused transpiration to decrease comparatively less, but CO2 fixation to increase comparatively more, under high vs. low Ca. Convergence of gc was in turn attributed to improved turgor maintenance under elevated Ca caused by greater storage C concentrations in the leaves, and by greater rooting density in the soil.