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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 312 (1995), S. 191-208 
    ISSN: 1573-5117
    Keywords: index of biotic integrity ; stream ; fish ; erosion ; sediment ; physical habitat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Indices of biotic integrity (1131) were computed for two annual fish collections from 27 locations along the bluffline bordering the Mississippi River alluvial plain in northwestern Mississippi. Study sites exhibited varying degrees of physical habitat degradation due to accelerated channel erosion. Objectives of index application were to quantify existing environmental quality and to test the IBI as a tool for relating fish population characteristics to physical degradation. Physical habitat data were collected concurrently with fish at all sites, and physical habitat descriptors were compared with the IBI scores and component metrics. Three to 23 fish species were captured from each site, and species richness explained 64–70% of the variance in IBI scores. Fish collections were dominated by insectivores tolerant of habitat and water quality degradation. Suckers and piscivores were relatively uncommon. The IBI scores were generally not reflective of physical habitat conditions. Variation in IBI scores was indicative of only the grossest differences in physical habitat quality. Weak relationships between physical habitat quality and IBI scores may have been due to large temporal variations in biotic integrity typical of degraded habitats. Alternatively, water quality degradation, which we did not measure, may have confounded relationships between physical habitat and fish metrics. Regional application of the IBI as a habitat assessment tool in landscapes with widespread physical degradation must overcome lack of suitable reference sites, large temporal variation in IBI scores, and small numbers of fish per collection, leading to lower confidence levels for IBI scores. The scarcity of lightly impacted sites may hinder detection of biotic integrity response along gradients of physical habitat quality.
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  • 2
    ISSN: 1573-5117
    Keywords: stream restoration ; fish ; erosion ; sediment ; physical habitat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Channel incision has major impacts on stream corridor ecosystems, leading to reduced spatial habitat heterogeneity, greater temporal instability, less stream-floodplain interaction, and shifts in fish community structure. Most literature dealing with channel incision examines physical processes and erosion control. A study of incised warmwater stream rehabilitation was conducted to develop and demonstrate techniques that would be economically feasible for integration with more orthodox, extensively employed watershed stabilization techniques (e.g., structural bank protection, grade control structures, small reservoirs, and land treatment). One-km reaches of each of five northwest Mississippi streams with contributing drainage areas between 16 and 205 km2 were selected for a 5-year study. During the study two reaches were modified by adding woody vegetation and stone structure to rehabilitate habitats degraded by erosion and channelization. The other three reaches provided reference data, as two of them were degraded but not rehabilitated, and the third was only lightly degraded. Rehabilitation approaches were guided by conceptual models of incised channel evolution and fish community structure in small warmwater streams. These models indicated that rehabilitation efforts should focus on aggradational reaches in the downstream portions of incising watersheds, and that ecological status could be improved by inducing formation and maintenance of stable pool habitats. Fish and physical habitat attributes were sampled from each stream during the Spring and Fall for 5 years, and thalweg and cross-section surveys were performed twice during the same period. Rehabilitation increased pool habitat availability, and made the treated sites physically more similar to the lightly degraded reference site. Fish communities generally responded as suggested by the aforementioned conceptual model of fish community structure. Species composition shifted away from small colonists (principally cyprinids and small centrarchids) toward larger centrarchids, catostomids, and ictalurids. Fish density and species richness increased at one rehabilitated site but remained stable at the other, suggesting that the sites occupied different initial states and endpoints within the conceptual model, and differed in their accessibility to sources of colonizing organisms. These experiments suggest that major gains in stream ecosystem rehabilitation can be made through relatively modest but well-designed efforts to modify degraded physical habitats.
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  • 3
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Nylon-based membranes of greater dialyzing capacity than Cuprophan have been prepared by solution casting. Good permeability is being achieved by the use of diluents such as dimethylsulfoxide in the casting solution. Modifying resins, primarily epoxies, contribute to higher permeability, good aging stability, and heat-sealing properties. Drying time between film casting and water immersion as well as the temperature and composition of the immersion bath are important factors in membrane performance. Methods for attaching heparin to the film surface have been developed, thus imparting good blood compatibility to the membranes.
    Additional Material: 1 Ill.
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  • 4
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A major part of current effort in improving artificial hemodialysis techniques concerns the development of improved membrane structures. Although blood compatibility of membranes is a part of the Battelle program, this discussion is confined to membrane composition, structure, and transport. On the basis of a need for improved hemodialysis techniques, membranes for use in the artificial kidney were prepared and evaluated for urea, creatinine, and uric acid permeability. Water-soluble polymers were crosslinked to form insoluble, but swellable, membranes. Faster metabolic waste transfer than with the conventional cellulosic membranes was obtained with diisocyanate-crosslinked poly (vinyl pyrrolidone) and poly (vinyl pyrrolidone)-dextran membranes and with membranes obtained by crosslinking poly (vinyl alcohol) with polyfunctional aldehydes. Membranes prepared from emulsions of vinyl pyrrolidone-ethyl acrylate and vinyl pyrrolidone-styrene copolymers had exceptionally high urea and creatinine dialysis rates, but were deficient in uric acid transfer. This shortcoming was corrected by incorporating solutes such as sucrose into the membranes followed by leaching. Another important approach concerned the development of a relatively high-strength membrane based on an impermeable nylon resin. Permeability of these membranes which have dialysis characteristics superior to those currently used was obtained through the addition of DMSO and one of several other additives to the coating solution.
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 20 (1982), S. 173-189 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The activity of a solid, polymer-supported catalyst (a semicrystalline polyethylene film containing grafted, sulfonated styrene) was shown to be altered by cold drawing. The catalytic activity was measured by a test reaction, the dehydration of isopropyl alcohol to give propylene. Catalytic reaction rates were measured with variously drawn films clamped in a differential flow reactor operated at 100°C and 1 atm. The catalytic activity increased with the elongation of the polymer up to a draw ratio of 2.5; the activity decreased upon further drawing. The drawn films were characterized by x-ray diffraction, dynamic mechanical measurements, electron microscopy, birefringence, and density measurements. Since no evidence was found for the formation of surface sites by creation of microcracks, the changes in activity are attributed to modifications in the polymer structure induced by drawing. The kinetics of the catalytic reaction and the data giving percentage crystallinity and crystalline and amorphous orientation factors suggest that, in the undrawn polymer, the catalytically active —SO3H groups form a hydrogen-bonded network, which is excluded from the crystalline regions. Initial elongation partially breaks up the network, allowing more —SO3H groups to bond to alcohol and become catalytically engaged. Elongation beyond a draw ratio of 2.5 leads to a separation of —SO3H groups greater than that required for the formation of the reaction intermediate, which involves the alcohol hydrogen bonded to several —SO3H groups. The combined results of the catalytic kinetics experiments and structural characterizations imply that the preliminary deformation response of the semicrystalline polymer occurs predominantly within the noncrystalline regions and is accommodated by the rigid slip and tilting of crystal lamellae. The hydrogen bonding among the —SO3H groups in the noncrystalline regions hinders lamellar breakup and suppresses the formation of highly aligned fibrillar morphologies.
    Additional Material: 6 Ill.
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