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  • 1
    Electronic Resource
    Electronic Resource
    The photosynthesis – leaf nitrogen relationship at ambient and elevated atmospheric carbon dioxide: a meta-analysis (1999)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Estimation of leaf photosynthetic rate (A) from leaf nitrogen content (N) is both conceptually and numerically important in models of plant, ecosystem, and biosphere responses to global change. The relationship between A and N has been studied extensively at ambient CO2 but much less at elevated CO2. This study was designed to (i) assess whether the A–N relationship was more similar for species within than between community and vegetation types, and (ii) examine how growth at elevated CO2 affects the A–N relationship. Data were obtained for 39 C3 species grown at ambient CO2 and 10 C3 species grown at ambient and elevated CO2. A regression model was applied to each species as well as to species pooled within different community and vegetation types. Cluster analysis of the regression coefficients indicated that species measured at ambient CO2 did not separate into distinct groups matching community or vegetation type. Instead, most community and vegetation types shared the same general parameter space for regression coefficients. Growth at elevated CO2 increased photosynthetic nitrogen use efficiency for pines and deciduous trees. When species were pooled by vegetation type, the A–N relationship for deciduous trees expressed on a leaf-mass basis was not altered by elevated CO2, while the intercept increased for pines. When regression coefficients were averaged to give mean responses for different vegetation types, elevated CO2 increased the intercept and the slope for deciduous trees but increased only the intercept for pines. There were no statistical differences between the pines and deciduous trees for the effect of CO2. Generalizations about the effect of elevated CO2 on the A–N relationship, and differences between pines and deciduous trees will be enhanced as more data become available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00234.x
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  • 2
    Electronic Resource
    Electronic Resource
    Quantifying the response of photosynthesis to changes in leaf nitrogen content and leaf mass per area in plants grown under atmospheric CO2 enrichment (1999)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 22 (1999), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Previous modelling exercises and conceptual arguments have predicted that a reduction in biochemical capacity for photosynthesis (Aarea) at elevated CO2 may be compensated by an increase in mesophyll tissue growth if the total amount of photosynthetic machinery per unit leaf area is maintained (i.e. morphological upregulation). The model prediction was based on modelling photosynthesis as a function of leaf N per unit leaf area (Narea), where Narea = Nmass×LMA. Here, Nmass is percentage leaf N and is used to estimate biochemical capacity and LMA is leaf mass per unit leaf area and is an index of leaf morphology. To assess the relative importance of changes in biochemical capacity versus leaf morphology we need to control for multiple correlations that are known, or that are likely to exist between CO2 concentration, Narea, Nmass, LMA and Aarea. Although this is impractical experimentally, we can control for these correlations statistically using systems of linear multiple-regression equations. We developed a linear model to partition the response of Aarea to elevated CO2 into components representing the independent and interactive effects of changes in indexes of biochemical capacity, leaf morphology and CO2 limitation of photosynthesis. The model was fitted to data from three pine and seven deciduous tree species grown in separate chamber-based field experiments. Photosynthetic enhancement at elevated CO2 due to morphological upregulation was negligible for most species. The response of Aarea in these species was dominated by the reduction in CO2 limitation occurring at higher CO2 concentration. However, some species displayed a significant reduction in potential photosynthesis at elevated CO2 due to an increase in LMA that was independent of any changes in Narea. This morphologically based inhibition of Aarea combined additively with a reduction in biochemical capacity to significantly offset the direct enhancement of Aarea caused by reduced CO2 limitation in two species. This offset was 100% for Acer rubrum, resulting in no net effect of elevated CO2 on Aarea for this species, and 44% for Betula pendula. This analysis shows that interactions between biochemical and morphological responses to elevated CO2 can have important effects on photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1999.00489.x
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  • 3
    Electronic Resource
    Electronic Resource
    EcoCELLs: tools for mesocosm scale measurements of gas exchange (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We describe the use of a unique plant growth facility, which has as its centerpiece four ‘EcoCELLs’, or 5x7 m mesocosms designed as open-flow, mass-balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifically to bridge the gap between measurement scales during long-term experiments examining the function and development of model ecosystems. There are several advantages to using EcoCELLs, including (i) the same theory of operation as leaf level gas exchange systems, but with continuous operation at a much larger scale: (ii) the ability to independently evaluate canopy-level and ecosystem models; (iii) simultaneous manipulation of environmental factors and measurement of system-level responses, and (iv) maximum access to, and manipulation of, a large rooting volume.In addition to discussing the theory, construction and relative merits of EcoCELLs, we describe the calibration and use of the EcoCELLs during a ‘proof of concept’ experiment. This experiment involved growing soybeans under two ambient CO2 concentrations (−360 and 710μmol mol−1. During this experiment, we asked ‘How accurate is the simplest model that can be used to scale from leaf-level to canopy-level responses?’ in order to illustrate the utility of the EcoCELLs in validating canopy-scale models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00437.x
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  • 4
    Electronic Resource
    Electronic Resource
    Pseudoacids. I. 4- and 5-Oxoacids (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 162-173 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Certain 4- and 5-oxoacids may exist in their cyclic lactol (or pseudoacid) forms. These commonly occur in compounds with proximate carboxylic acid and carbonyl (aldehyde or ketone) functions for the formation of five- or six-membered rings. Examples include trans-2,3-disubstituted aliphatic, (Z)-2,3-olefinic and o-disubstituted aromatic acids. Crystal structures of compounds in these categories are reported: trans-4-methyl-3-oxo-6-hydroxytetrahydropyran-3-carboxylic acid (6), monoclinic, C2/c, a = 25.412 (5), b = 6.291 (1), c = 10.757 (2) Å, β = 104.84 (3)°; penicillic acid (7), 4-methoxy-5-hydroxy-5-(2′-propenyl)dihydrofuran-2-one, tetragonal, P42/n, a = b = 15.83 (2), c = 7.016 (11) Å; mucochloric acid (8), (Z)-3,4-dichloro-5-hydroxydihydrofuran-2-one, triclinic, P1¯, a = 6.227 (5), b = 8.085 (5), c = 12.369 (9) Å, α = 99.50 (5), β = 102.38 (6), γ = 90.29 (6)°; 2-methanoylbenzoic acid (9), 3-hydroxy-1-(3H)-isobenzofuranone, monoclinic, P21, a = 4.006 (1), b = 11.489 (2), c = 7.347 (1) Å, β = 97.50 (3)°; 2-ethanoylbenzoic acid (10), 3-hydroxy-3-methyl-1-(3H)-isobenzofuranone, orthorhombic, P212121, a = 5.199 (6), b = 9.651 (14), c = 15.950 (17) Å; 2-(2′-oxoethyl)benzoic acid (11), 3-hydroxy-3,4-dihydroisobenzopyran-1-one, monoclinic, P21/n, a = 4.651 (3), b = 11.886 (7), c = 14.312 (11) Å, β = 90.86 (6)°. These compounds also exist in the cyclic forms in chloroform solution. A trimeric cyclic trioxane structure, analogous to paracetaldehyde, is confirmed as the solid form of 5-oxopentanoic acid (1), triclinic, P1¯, a = 5.640 (4), b = 8.571 (8), c = 18.962 (13) Å, α = 78.68 (6), β = 84.34 (5), γ = 80.38 (6)°. In solution (NMR), mixtures of the open aldoacid, trimeric acid and cyclic pseudoacid exist. In both furanoid and pyranoid pseudoacids, endocyclic lactol C—O bond lengths are lengthened (1.46–1.48 Å), while the exocyclic C—O(H) bonds are shortened (1.38 Å). Pseudoacids commonly form hydrogen-bonded chains linking the lactol hydroxy and carbonyl groups, but 3-hydroxy-3,4-dihydroisobenzopyran-1-one forms distinctive hydrogen-bonded dimers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876819701149X
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  • 5
    Electronic Resource
    Electronic Resource
    An analysis of the characteristics of rough bed turbulent shear stresses in an open channel (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 193-210 
    Details
    ISSN: 1436-3259
    Keywords: Turbulence ; sediment ; fluvial ; river ; bursting process ; statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Entrainment of sediment particles from channel beds into the channel flow is influenced by the characteristics of the flow turbulence which produces stochastic shear stress fluctuations at the bed. Recent studies of the structure of turbulent flow has recognized the importance of bursting processes as important mechanisms for the transfer of momentum into the laminar boundary layer. Of these processes, the sweep event has been recognized as the most important bursting event for entrainment of sediment particles as it imposes forces in the direction of the flow resulting in movement of particles by rolling, sliding and occasionally saltating. Similarly, the ejection event has been recognized as important for sediment transport since these events maintain the sediment particles in suspension. In this study, the characteristics of bursting processes and, in particular, the sweep event were investigated in a flume with a rough bed. The instantaneous velocity fluctuations of the flow were measured in two-dimensions using a small electromagnetic velocity meter and the turbulent shear stresses were determined from these velocity fluctuations. It was found that the shear stress applied to the sediment particles on the bed resulting from sweep events depends on the magnitude of the turbulent shear stress and its probability distribution. A statistical analysis of the experimental data was undertaken and it was found necessary to apply a Box-Cox transformation to transform the data into a normally distributed sample. This enabled determination of the mean shear stress, angle of action and standard error of estimate for sweep and ejection events. These instantaneous shear stresses were found to be greater than the mean flow shear stress and for the sweep event to be approximately 40 percent greater near the channel bed. Results from this analysis suggest that the critical shear stress determined from Shield's diagram is not sufficient to predict the initiation of motion due to its use of the temporal mean shear stress. It is suggested that initiation of particle motion, but not continuous motion, can occur earlier than suggested by Shield's diagram due to the higher shear stresses imposed on the particles by the stochastic shear stresses resulting from turbulence within the flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427915
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  • 6
    Electronic Resource
    Electronic Resource
    Experience with cardiac tamponade following open heart surgery (1996)
    Springer
    Heart and vessels 11 (1996), S. 39-43 
    Details
    ISSN: 1615-2573
    Keywords: Open heart surgery ; cardiac tamponade ; percutaneous pericardiocentesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Cardiac tamponade following open heart surgery is well described, although, fortunately, uncommon. Unlike more classical “primary” tamponade, the clinical features are not specific, and this can delay diagnosis. In practice, the threshold for investigation must be low, and echocardiography has been invaluable in the detection and localization of pericardial collections. Several factors are believed to contribute to the likelihood of postoperative tamponade, but the mechanisms are not clearly understood. Resternotomy, under general anesthesia, or subxiphoid pericardiotomy, under local or general anesthesia, are effective forms of treatment. However, recent success with the use of percutaneous pericardiocentesis under echocardiographic guidance has shown that postoperative tamponade can be treated safely and effectively by this method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01744598
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  • 7
    Electronic Resource
    Electronic Resource
    Sarason interpolation and Toeplitz corona theorem for almost periodic matrix functions (1998)
    Springer
    Integral equations and operator theory 32 (1998), S. 243-281 
    Details
    ISSN: 1420-8989
    Keywords: Primary 42A75 ; Secondary 46D05 ; 47B35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Sarason interpolation and Toeplitz corona problems are studied for almost periodic matrix functions. Recent results on almost periodic factorization and related generalized Toeplitz operators are the main tools in the study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01203771
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  • 8
    Electronic Resource
    Electronic Resource
    Two-sided Nudelman interpolation for input-output operators of discrete time-varying systems (1995)
    Springer
    Integral equations and operator theory 21 (1995), S. 174-211 
    Details
    ISSN: 1420-8989
    Keywords: Primary 47A57 ; 93A25 ; Secondary 93C55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01203093
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  • 9
    Electronic Resource
    Electronic Resource
    Nudelman interpolation and the band method (1997)
    Springer
    Integral equations and operator theory 27 (1997), S. 253-284 
    Details
    ISSN: 1420-8989
    Keywords: primary 47A57 ; secondary 30E05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In previous work the authors developed a new addition of the band method based on a Grassmannian approach for solving a completion/extension problem in a general, abstract framework. This addition allows one to obtain a linear fractional representation of all solutions of the abstract completion problem from special extensions which are not necessarily band extensions (for the positive case) or triangular extensions (for the contractive case). In this work we extend this framework to a somewhat more general setting and show how one can obtain formulas for the required special extensions from solutions of a system of linear equations. As an application we show how the formalism can be applied to the bitangential Nevanlinna-Pick interpolation problem, a case which, up to now, was not amenable to the band method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01324728
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  • 10
    Electronic Resource
    Electronic Resource
    Continuity Properties and Global Attractors of Generalized Semiflows and the Navier-Stokes Equations (1997)
    Springer
    Journal of nonlinear science 7 (1997), S. 475-502 
    Details
    ISSN: 1432-1467
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: The existence of a global attractor for the 3D incompressible Navier-Stokes equations is established under the (unproved) hypothesis that all weak solutions are continuous from $(0,\infty)$ to L 2 .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003329900037
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