The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Joseph A Tucker - One of the best experts on this subject based on the ideXlab platform.
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compositional analysis of Biomer
Journal of Biomedical Materials Research, 1990Co-Authors: Jon Belisle, Susan K Maier, Joseph A TuckerAbstract:: Biomer, a segmented polyether polyurethane, has been analyzed via hydrolysis/gas chromatography to determine its composition. In addition to the previously reported 4,4'-methylene bis(phenyl isocyanate) (MDI), polytetramethylene glycol (PTMO), and ethylenediamine, we now report the presence of diethylamine, 1,3-diaminocyclohexane and poly(diisopropylaminoethyl methacrylate-co-decyl methacrylate), Biomer's cloudy insoluble phase. In addition, a method is presented to characterize the methacrylate additive by molecular weight based on GPC. Also found by chromatography were the antioxidants Santowhite Powder and BHT. XPS shows no Si (silicone) on the Biomer surface, and a total chloride analysis reports no chloride (less than 0.03%). Time-of-flight SIMS data suggest evidence for the methacrylate additive at the surface, and mass spectroscopy can be interpreted as evidence for a diaminocyclohexane.
Stuart L Cooper - One of the best experts on this subject based on the ideXlab platform.
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biostability and blood contacting properties of sulfonate grafted polyurethane and Biomer
Journal of Biomaterials Science-polymer Edition, 1993Co-Authors: Hugh Wabers, Timothy J Mccoy, Ann T Okkema, Robert W Hergenrother, Michael F Wolf, Stuart L CooperAbstract:Sulfonate-containing polyurethanes were evaluated for in vivo biodegradation using subcutaneously implanted tensile bars. In addition, these anionically charged polyurethanes were evaluated for in vivo activation of human complement C3a and ex vivo platelet deposition in arteriovenouslyshunted canines. The sulfonate derivatized polymers included laboratory synthesized polyurethane and Biomer. Other polymers used for references included IntramedicTM polyethylene, SilasticTM and a poly(ethylene oxide) based polyurethane. The biodegradation results indicated that Biomer and the laboratory sulfonated Biomer (both manufactured with stabilizers), remained mechanically stable, retaining both tensile strength and elasticity after 4 weeks of subcutaneous implantation. The unstabilized polyurethanes (with or without sulfonation), however, showed marked cracking and a loss of mechanical properties after the same period of subcutaneous implantation. Sulfonated polyurethanes depressed human complement C3a activation i...
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physical and blood contacting characteristics of propyl sulphonate grafted Biomer
Biomaterials, 1991Co-Authors: Ann T Okkema, Xuehai Yu, Stuart L CooperAbstract:Abstract Propyl sulphonate groups were grafted on to the backbone of Biomer ®, a polyetherurethaneurea, in an attempt to improve its blood-contacting properties. The bulk, surface and blood-contacting properties of this series of sulphonated polymers were evaluated. Differential scanning calorimetry and dynamic mechanical analysis indicated that propyl sulphonate incorporation increased the microphase separation of the polymers. The ultimate tensile strength was also increased with sulphonation at the expense of the polymer's extensibility. Dynamic contact angle analysis showed that, in water, the sulphonated Biomer® surfaces were more polar than the Biomer® sample indicating the propyl sulphonate groups were enriched at the surface. Canine ex vivo blood-contacting results showed that the incorporation of propyl sulphonate groups dramatically reduced the number and activation of platelets adherent to the polymer surface. In addition, fibrinogen deposition increased with increasing sulphonate content, despite the low level of platelet activation.
E D Schulze - One of the best experts on this subject based on the ideXlab platform.
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co2 balance of boreal temperate and tropical forests derived from a global database
Global Change Biology, 2007Co-Authors: E D Schulze, Sebastiaan Luyssaert, Ilaria Inglima, Martin Jung, Andrew D Richardson, Markus Reichstein, Dario Papale, Shilong Piao, Lisa WingateAbstract:Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 °C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for.
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Maximum rooting depth of vegetation types at the global scale
Oecologia, 1996Co-Authors: Judit Canadell, R B Jackson, James R. Ehleringer, H. A. Mooney, O. E. Sala, E D SchulzeAbstract:The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance, as well as for carbon and nutrient cycling. Here we summarize what we know about the maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 253 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 194 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6±0.5 m. Maximum rooting depth by biome was 2.0±0.3 m for boreal forest. 2.1±0.2 m for cropland, 9.5±2.4 m for desert, 5.2±0.8 m for sclerophyllous shrubland and forest, 3.9±0.4 m for temperate coniferous forest, 2.9±0.2 m for temperate deciduous forest, 2.6±0.2 m for temperate grassland, 3.7±0.5 m for tropical deciduous forest, 7.3±2.8 m for tropical evergreen forest, 15.0±5.4 m for tropical grassland/savanna, and 0.5±0.1 m for tundra. Grouping all the species across biomes (except croplands) by three basic functional groups: trees, shrubs, and herbaceous plants, the maximum rooting depth was 7.0±1.2 m for trees, 5.1±0.8 m for shrubs, and 2.6±0.1 m for herbaceous plants. These data show that deep root habits are quite common in woody and herbaceous species across most of the terrestrial biomes, far deeper than the traditional view has held up to now. This finding has important implications for a better understanding of ecosystem function and its application in developing ecosystem models.
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A global analysis of root distributions for terrestrial biomes
Oecologia, 1996Co-Authors: R B Jackson, Judit Canadell, James R. Ehleringer, Osvaldo E Sala, Harold A. Mooney, E D SchulzeAbstract:Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. We compiled a database of 250 root studies, subdividing suitable results into 11 biomes, and fitted the depth coefficient +¦ to the data for each biome (Gale and Grigal 1987). +¦ is a simple numerical index of rooting distribution based on the asymptotic equation Y=1-+¦d, where d = depth and Y = the proportion of roots from the surface to depth d. High values of +¦ correspond to a greater proportion of roots with depth. Tundra, boreal forest, and temperate grasslands showed the shallowest rooting profiles (+¦=0.913, 0.943, and 0.943, respectively), with 80-90% of roots in the top 30 cm of soil; deserts and temperate coniferous forests showed the deepest profiles (+¦=0.975 and 0.976, respectively) and had only 50% of their roots in the upper 30 cm. Standing root biomass varied by over an order of magnitude across biomes, from approximately 0.2 to 5 kg m-2. Tropical evergreen forests had the highest root biomass (5 kg m-2), but other forest biomes and sclerophyllous shrublands were of similar magnitude. Root biomass for croplands, deserts, tundra and grasslands was below 1.5 kg m-2. Root/shoot (R/S) ratios were highest for tundra, grasslands, and cold deserts (ranging from 4 to 7); forest ecosystems and croplands had the lowest R/S ratios (approximately 0.1 to 0.5). Comparing data across biomes for plant functional groups, grasses had 44% of their roots in the top 10 cm of soil. (+¦=0.952), while shrubs had only 21% in the same depth increment (+¦=0.978). The rooting distribution of all temperate and tropical trees was +¦=0.970 with 26% of roots in the top 10 cm and 60% in the top 30 cm. Overall, the globally averaged root distribution for all ecosystems was +¦=0.966 (r2=0.89) with approximately 30%, 50%, and 75% of roots in the top 10 cm, 20 cm, and 40 cm, respectively. We discuss the merits and possible shortcomings of our analysis in the context of root biomass and root functioning.
Jon Belisle - One of the best experts on this subject based on the ideXlab platform.
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compositional analysis of Biomer
Journal of Biomedical Materials Research, 1990Co-Authors: Jon Belisle, Susan K Maier, Joseph A TuckerAbstract:: Biomer, a segmented polyether polyurethane, has been analyzed via hydrolysis/gas chromatography to determine its composition. In addition to the previously reported 4,4'-methylene bis(phenyl isocyanate) (MDI), polytetramethylene glycol (PTMO), and ethylenediamine, we now report the presence of diethylamine, 1,3-diaminocyclohexane and poly(diisopropylaminoethyl methacrylate-co-decyl methacrylate), Biomer's cloudy insoluble phase. In addition, a method is presented to characterize the methacrylate additive by molecular weight based on GPC. Also found by chromatography were the antioxidants Santowhite Powder and BHT. XPS shows no Si (silicone) on the Biomer surface, and a total chloride analysis reports no chloride (less than 0.03%). Time-of-flight SIMS data suggest evidence for the methacrylate additive at the surface, and mass spectroscopy can be interpreted as evidence for a diaminocyclohexane.
O.Lars Hedin - One of the best experts on this subject based on the ideXlab platform.
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Scaling of C : N : P Stoichiometry in Forests Worldwide : Implications of Terrestrial Redfield- Type Ratios
Ecology, 2004Co-Authors: Megan E Mcgroddy, Tanguy Daufresne, O.Lars HedinAbstract:Inspired by the importance of globally well-constrained carbon: nitrogen: phosphorus {(C:N:P)} ratios in planktonic biomass to the understanding of nutrient cycles and biotic feedbacks in marine ecosystems, we looked for analogous patterns in forest ecosystems worldwide. We used data from the literature to examine the stoichiometry of C, N, and P in forest foliage and litter on both global and biome levels. Additionally, we examined the scaling of nutrient investments with biomass and production both globally and within biomes to determine if and when these ratios respond to macroscale ecosystem properties (such as nutrient availability). We found that, while global forest {C:N:P} ratios in both foliage and litter were more variable than those of marine particulate matter, biome level (temperate broadleaf, temperate coniferous, and tropical) ratios were as constrained as marine ratios and statistically distinct from one another. While we were more interested in the relative constancy of the {C:N:P} ratios than their numerical value we did note, as have others, that the atomic ratios calculated for foliage (1212:28:1) and litter (3007:45:1) reflect the increased proportion of C-rich structural material characteristic of terrestrial vegetation. Carbon: nutrient ratios in litter were consistently higher than in comparable foliar data sets, suggesting that resorption of nutrients is a globally important mechanism, particularly for R Litter {C:N} ratios were globally constant despite biome-level differences in foliar {C:N;} we speculate that this strong coupling may be caused by the significant contribution of immobile cell wall bound proteins to the total foliar N pool. Most ratios scaled isometrically across the range of biomass stocks and production in all biomes suggesting that ratios arise directly from physiological constraints and are insensitive to factors leading to shifts in biomass and production. There were, however, important exceptions to this pattern: nutrient investment in broadleaf forest litter and coniferous forest foliage increased disproportionately relative to C with increasing biomass and production suggesting a systematic influence of macroscopic factors on ratios.
