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  • 1990-1994  (4)
  • 1965-1969
  • Chemistry  (3)
  • Biogeochemistry  (1)
  • 1
    Electronic Resource
    Electronic Resource
    The role of surface and sub-surface runoff processes in controlling cation export from a wetland watershed (1994)
    Springer
    Aquatic sciences 56 (1994), S. 80-96 
    Details
    ISSN: 1420-9055
    Keywords: Biogeochemistry ; hydrology ; wetland ; cation ; snow melt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Water and cation budgets were calculated for two sub-basins within a small low relief watershed in South-Central Ontario during a period of ephemeral runoff which was initiated by spring snow melt. The hydrology of one (upland) sub-basin was strongly influenced by seasonal fluctuations in the level of regional ground water. Saturated contributing areas formed in low lying regions adjacent to the stream channel where the water table rose to the surface, and stream discharge was a mixture of ground water and saturation overland flow. In the second sub-basin a wetland provided a large and spatially less variable saturated contributing area. Clay soils underlying the wetland resulted in a shallow perched water table, poorly drained and highly organic soils, and greatly reduced inputs of regional ground water. Stream discharge was largely the result of surface runoff from the wetland and adjacent areas of saturated soil. Inter-basin variations in water export were by far greater than variations in stream chemistry. As a result, inter-basin variations in cation export strongly reflected variations in water export over the time interval in which the majority of a given ion was lost from the watershed. Spatial differences in water export were least at the onset of runoff when basin saturation was greatest and overland flow made large contributions to the discharge from both sub-basins. Potassium and hydrogen had high concentrations at this time which caused these ions to show only small spatial differences in export. With decreases in the areal extent of soil saturation, and increases in the storage capacity of the wetland, the hydrologic contrast between sub-basins increased. Greater water loss from the upland area resulted from a greater discharge of regional ground water, and a more rapid expansion of the saturated contributing areas during storm events. Calcium, magnesium, and sodium concentrations increased steadily during the first 3 weeks of runoff, so that the peak export of these cations occurred later in the runoff period at times of higher concentration, but lower and spatially more variable discharges. Consequently, spatial differences in the loss of these ions was great and favoured the upland sub-basin, since the majority of export occurred when the hydrologic contrast between sub-basins was largest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00877437
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Experimental and numerical investigations of the vacuum-forming process (1992)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1163-1173 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper exmines the influence of process variables on final thickness distributions for vacuum-formed thermoplastic parts. The process variables investigated include evacuation rate, sheet surface temperature, mold temperature, and material slip over the mold surface. The experimental data presented include, in addition to thicknesses, sheet surface temperature obtained via infrared thermography. A finite element program to model the vacuum-forming process is discussed, and the wall thickness distribution predicted by this program for a vacuum-formed part is compared with the results of the experiments.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760321613
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Thermomechanical properties of 1C molding compoundsPresented at the Annual Meeting of American Institute of Chemical Engineers in San Francisco, California on November 6, 1989. (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 609-617 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Eight commercial semiconductor grade epoxy compounds that are used to encapsulate 1C (integrated circuit) devices have been evaluated for their ability to minimize the development of thermal stresses which can cause failure during device temperature cycling. Thermal expansion, dynamic modulus and adhesion studies are used to describe the mechanical interaction between the plastic package and the silicon device it surrounds. A “figure of merit” is defined for the development of stress on the 1C device as it is cooled after the packaging process. The stress is shown to be proportional to the product of three terms: (αp-αs) Ep (Tanch-T) where αp and αs are the expansion coefficients for the plastic and silicon, respectively, Ep is the modulus of the epoxy and Tanch is the temperature at which the epoxy becomes anchored to the silicon device during transfer molding. In addition, the importance of good adhesion between the epoxy encapsulant and the silicon device to prevent package cracking has been demonstrated by finite element analysis and a novel adhesion test.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760301008
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Three-dimensional finite element simulation of thermoforming (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1314-1322 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The development of a finite element program specifically designed to simulate thermoforming in complex three-dimensional geometries is described. The large strain finite element model developed for simulating thermoforming processes is based on a total Lagrangian formulation which results in a nonlinear system of equations that must be solved iteratively. The nonlinear material behavior and contact between the polymer and mold surf aces ieads to additional complications in the numerical solution of the thermoforming simulation problem. In an effort to verify the accuracy of the finite element model developed in this study, analyses are compared with measurements obtained from three-dimensional three-formed parts.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760302009
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    Paper (German National Licenses)
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