Showing papers by "Michigan Technological University published in 1983"

Detritivory in neotropical fish communities

Abstract: Fish communities of major river systems in South America contain a high proportion of detritivorous fishes in the families Prochilodontidae and Curimatidae. These families include important fish stocks that in some regions comprise over 50 percent of the community ichthyomass. As a group, detritivores have anatomical-physiological adaptations for collection and digestion of detritus, but the actual mechanisms of these presumed adaptations have to-date only been inferred. Dietary requirements have not been identified. Behavioral adaptation is implied by feeding habitat selection but its nutritional significance is unknown. Because many of these species have commercial importance, and because ongoing construction of impoundments threatens to disrupt seasonal migrations between spawning and feeding areas, an understanding of the feeding biology of detritivores is important.

Gas emissions and the eruptions of mount st. Helens through 1982.

Abstract: The monitoring of gas emissions from Mount St. Helens includes daily airborne measurements of sulfur dioxide in the volcanic plume and monthly sampling of gases from crater fumaroles. The composition of the fumarolic gases has changed slightly since 1980: the water content increased from 90 to 98 percent, and the carbon dioxide concentrations decreased from about 10 to 1 percent. The emission rates of sulfur dioxide and carbon dioxide were at their peak during July and August 1980, decreased rapidly in late 1980, and have remained low and decreased slightly through 1981 and 1982. These patterns suggest steady outgassing of a single batch of magma (with a volume of not less than 0.3 cubic kilometer) to which no significant new magma has been added since mid-1980. The gas data were useful in predicting eruptions in August 1980 and June 1981.

The mechanical theory of fluid interfaces and Maxwell's rule

Abstract: By operating within a recently developed mechanical theory of fluid interfaces we find that Maxwell's equal area rule fails to hold unless certain molecular conditions are satisfied. In view of these conditions various statistical models for fluid interfaces which have previously been proposed need to be restricted if they are to be compatible with the equal area rule. We show that in both concept and fact the mechanical theory is more general than previous interfacial theories which as a rule assume the existence of thermodynamic functions and the validity of thermodynamic relations within the spinodal set. In particular, we list necessary and sufficient conditions for the reduction of the mechanical theory to the modified and original van der Waals theories of fluid interfaces. These conditions are also molecular in nature, the reduction being accomplished without the use of thermodynamic reasoning within the spinodal region. Finally, we consider three-dimensional interfaces and note that when the conditions for Maxwell's rule and van der Waals' theory are not satisfied, then the interfaces are generally planar, cylindrical, or spherical at equilibrium.

Redution Kinetics of Hematite and Magnetite Pellets Containing Coal Char

Abstract: The rate of reduction of hematite and magnetite pellets containing coal char in a nitrogen atmosphere and at the temperatures between 800°C and 1200°C was investigated. The reduction rate was found to increase with increasing temperatures, and increasing calcium oxide content of the pellets. The reduction was not stepwise. That is, iron, hematite, magnetite and wustite were detected by X-ray analysis as coexisting phases during early stages of the reduction process. Large temperature differences were found between the core and surface of the pellets, indicating that the reduction process occurred under non-isothermal conditions.Calculated values for the apparent activation energy ranged between 38kcal/mol to 51kcal/mol. These values are lower than those reported by previous workers, but still within the accepted range for chemically controlled processes. The rate of the carbon gasification reaction and the rate of heat transfer from the furnace wall to the reacting pellet were found to exert the strongest influence on the overall rate of the process. Considering the observed non-isothermal conditions, the highly endotermic nature of the carbon gasification reaction and the large increase in the reduction rate with increasing temperature, it appeared that the overall process was heat transfer controlled.

Subsurface chlorophyll maximum and associated Cyclotella pulse in Lake Superior

Abstract: An investigation of the subsurface chlorophyll layer (SCL) in Lake Superior was conducted from 1 May through 15 October. During spring unstratified conditions (1 May–17 July), chlorophyll a and phytoplankton biomass were vertically and temporally uniform. Phytoflagellates such as Rhodomonas minuta, Cryptomonas spp., and Ochromonas spp. were dominant at this time. The photosynthetic maximum was associated with the depth receiving 10% of surface irradiance, ca. 15–25 m. Once thermal stratification occurred, a SCL developed around 20 m. Although epilimnetic chlorophyll concentrations remained similar to spring mixing levels, concentrations in the SCL increased 3-fold. In situ production was the principal process associated with the development of the SCL. The upper portion of the SCL was dominated by Cyclotella species; C. stelligera, C. comensis, and C. ocellata. The increased abundance of Cyclotella appeared to be related to stable irradiance fields produced during thermal stratification.

Equilibrium solutions in the mechanical theory of fluid microstructures

Abstract: A mechanical-molecular theory for fluid microstructures is outlined. It is assumed that average molecular densities and forces vary continuously across the fluid microstructure in accordance with the mechanical principles of conservation of mass and momentum. To account for the large density gradients, and therefore for the long-range molecular interactions, it is also assumed that the molecular forces can be represented in terms of the gradients of the molecular densities. In contrast to previous theories of fluid microstructures, which are seriously restricted by the use of classical thermodynamic structure within the spinodal region, the mechanical theory is free of thermodynamics. We confine attention to equilibrium, and prove that the differential equation governing a one-dimensional fluid microstructure has only three types of solutions possible: transitions, reversals, and oscillations. Physically, they correspond to liquid-vapor interfaces, thin films, and layered structures.

An Evaluation of Anisotropic Effective Stress-Strain Criteria for the Biaxial Yield and Flow of 2024 Aluminum Tubes

Abstract: 2024 aluminum tubes, heat treated to a T6 and T8 temper, were tested in combinations of tension-internal pressure and tension-torsion loading Yield loci and flow behavior were determined for both modes of loading and compared to theoretical predictions Both tempers of 2024 aluminum exhibited crystallographic textures and anisotropic yield and flow Hill's quadratic yield criterion and the associated flow rule under-estimate balanced biaxial yield and flow, which is consistent with hydraulic bulge data on other face-centered cubic metals Hill's nonquadratic criterion, which adds one additional parameter, and Bassani's criterion, which adds two parameters, predict the anisotropic yield behavior much more accurately Predictions of the complete flow behavior, including strain paths, with these anisotropic criteria could be improved markedly by including provisions for planar anisotropy

Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char

Abstract: The structural changes that occurred during the reduction of hematite and magnetite pellets containing coal char, in the temperature range between 900°C and 1200°C, were studied.The behavior of the pellets was complex. Significant temperature gradients within the pellet were attained during the process, and the reduction was accompanied by catastrophic swelling of the pellets between 900°C and 1000°C, while shrinkage was observed at 1100 and 1200°C. Observed microstructural features such as intragranular porosity and cracking of oxide grains resulted from severe lattice disturbances occurring upon transformation of hematite to magnetite.The catastrophic swelling observed for hematite and magnetite pellets 900 and 1000°C was due to the filamentary or whisker growth of iron outward from the wustite surfaces. The whisker formation appears to be due to a changing reducing potential of the gas phase within the pellet coupled with the presence of calcium oxide on the wustite surface. The shrinkage reported at 1100 and 1200°C is accounted for in terms of sintering of iron filaments.The pellets strength was found to decrease between 900°C and 1000°C, and increased at higher temperatures. The weakness at low temperatures was due to the absence of bonding between iron filaments or whiskers. The high strength obtained at higher temperatures (1100 and 1200°C) was produced by sintering of iron filaments.

Factors regulating the spatial and temporal distribution of Cladophora and Ulothrix in the Laurentian Great Lakes

Abstract: The attached filamentous green algae Ulothrix zonata and Cladophora glomerata are important members of the periphyton community in the rocky littoral zone of the Laurentian Great Lakes. When these algae occur together, Ulothrix occupies the splash zone and Cladophora grows in deeper water. The two algae show definite seasonal patterns of abundance as well as distinct geographic distributions within the Great Lakes basin. We examined the role of light, temperature, and phosphorus supply in regulating the geographic, seasonal, and spatial distribution of these two filamentous algae. Phosphorus availability plays a major role in determining the geographic distribution of attached algae in the Great Lakes. Light intensity, acting through the balance between photosynthesis and respiration, appears to have a significant effect upon the pattern of vertical zonation. Optimum photosynthesis in Ulothrix occurs at high light levels (1200 µE/m2 · sec), while the optimum for Cladophora lies at 300 µE/m2 · sec. Seasonal patterns of abundance in Ulothrix and Cladophora are consistent with their respective temperature optima for photosynthesis. It is suggested, however, that the timing and extent of reproduction in Ulothrix are also of importance in determining the shift in dominance of the periphyton community from Ulothrix to Cladophora.

A program form based on data dependency in predicate regions

Abstract: A new program representation is presented which permits certain optimizations to be performed at less expense than with other forms. This paper describes code motion, common subexpression elimination and induction variable detection. Scalar propagation and constant folding are sketched here, but detailed elsewhere. The powerful code motion strategy allows entire regions of the program to be moved. The representation described may be used as a compiler intermediate form or simply as a model for program analysis. It has great potential for use in translation for parallel machines.

Dialkyldimethylammonium halides as wood preservatives

Abstract: Laboratory decay tests using brown, white and soft rot fungi on wood treated with a series of dialkyldimethylammonium halides show that maximum fungitoxicity is exhibited by compounds with alkyl chains of 10 and 12 carbon atoms. Both the cation and the anion appear to influence effectiveness with bromide salts showing greater activity values than chloride analogs. The anion presumably influences effectiveness through distribution, fixation, and availability of the compounds rather than directly by changes in fungitoxicity. Monobromination of one of the alkyl chains caused a decrease in fungitoxicity, though the alkyl chain length-fungitoxicity relationship was the same as for the unsubstituted series of compounds. Addition of certain copper or organic biocides to alkylammonium compound formulations increased activity, particularly against soft rot. While this result is a significant advance, the complex relationships involved in such formulations will demand considerable further research in respect of efficacy, fixation, leaching, treatability, and environmental aspects before such a product could be commercialized.

Process for recovering terephthalic acid from waste polyethylene terephthalate

Abstract: Terephthalic acid (TPA) is recovered from used polyethylene terephthalate beverage containers by reacting comminuted containers in a reaction zone with an aqueous medium containing ammonium hydroxide at elevated temperatures and pressures to form a water soluble diammonium salt of TPA, separating any undissolved solids from the reaction product, acidifying the remaining reaction product to liberate TPA, and separating the precipitated TPA. A portion of the liquid remaining after separation of TPA can be mixed with lime or slaked lime, the resulting mixture treated in an ammonia stripper to remove ammonia therefrom and the ammonia overheads from the stripper blended with another portion of the liquid remaining after separation of TPA to form a stream containing ammonium hydroxide which is recycled to the reaction zone. Ethylene glycol can be recovered from the bottoms from the ammonia stripper by distillation.

Deformation and fracture of strongly textured Ti alloy sheets in uniaxial tension

Abstract: The influence of crystallographic texture on the deformation and fracture behavior of strongly textured Ti alloy sheet has been investigated. Uniaxial tensile tests have been performed on Ti-6A1-4V and Ti-5A1-2.5 Sn sheet with both a basal and a basal-transverse texture. The results indicate that, by controlling the ease of through-thickness slip, the crystallographic texture strongly affects the plastic anisotropy of the material but has relatively little effect on the strain-rate sensitivity and work-hardening rates at large strains. A strong resistance to through-thickness slip, manifested by a high R-value, enhances the post-uniform elongation and the ability of the material to retain the load-carrying capacity beyond maximum load. This behavior can be qualitatively understood in terms of the effect of R on the hardening which occurs as the strain state within the diffuse neck shifts from uniaxial tension toward plane strain. A higher R-value also increases significantly the limit strain at the onset of localized necking as well as the fracture strain. The effects of R-value on the limit strain can be qualitatively understood in terms of a critical thickness strain criterion and can be quantitatively predicted by two analyses, one of which assumes an imperfection to be present while the other does not.

Large deflections of point loaded cantilevers with nonlinear behaviour

Abstract: Thin beams, being flexible, form a curve with large deflections when subjected to sufficiently large transverse loads. Therefore, geometrical nonlinearity occurs, and the problem must be formulated in terms of the nonlinear theory of bending. In this paper, the beam is constructed from nonlinear elastic material, and subjected to several transverse concentrated loads. Due to the large deflection of the beam, the exact expression of the curvature of the deflected shape is used in the Bernoulli-Euler relationship. Therefore, this leads to a second order nonlinear differential equation for the transverse deflection. The solution of this equation is obtained by using the fourth-order Runge-Kutta method, and the arc length is evaluated using Simpson's Rule. The results obtained from this procedure are compared with previously published results for thin beams of linear elastic materials in order to verify the theory and the method of analysis.

The effect of hydrogen on the multiaxial stress-strain behavior of titanium tubing

Abstract: The influence of internal hydrogen on the multiaxial stress-strain behavior of commercially pure titanium has been studied. Thin-walled tubing specimens containing either 20 or 1070 ppm hydrogen have been tested at constant stress ratios in combined tension and internal pressure. The addition of hydrogen lowers the yield strength for all loading paths but has no significant effect on the strain hardening behavior at strains e ≥ 0.02. Thus, the hydrogen embrittlement of titanium under plain strain or equibiaxial loading is not a consequence of changes of flow behavior. The yielding behavior of this anisotropic material is described well by Hill’s quadratic yield criterion. As measured mechanically and by pole figure analysis, the plastic anisotropy changes with deformation in a manner which depends on stress state. Hill’s criterion and the associated flow rule do not describe the multiaxial flow behavior well because of their inability to account for changes of texture which depend on multiaxial stress path. Hence, a strain dependent, texture-induced strengthening effect in equibiaxial tension is observed, this effect having the form of an enhanced strain hardening rate.

The Effects of a Porous Ceramic Particulate Trap on the Physical, Chemical and Biological Character of Diesel Particulate Emissions

Abstract: Physical, chemical, and biological characterization data for the particulate emissions from a caterpillar 3208 diesel engine with and without Corning porous ceramic particulate traps are presented. Measurements made at EPA modes 3,4,5,9,10 and 11 include total hydrocarbon, oxides of nitrogen and total particulate matter emissions including the solid fraction (SOL), soluble organic fraction (SOF) and sulfate fraction (SO4). Chemical character was defined by fractionation of the SOF while biological character was defined by analysis of Ames Salmonella/microsome bioassay data. The trap produced a wide range of total particulate reduction efficiencies (0-97%) depending on the character of the particulate. The chemical character of the SOF was significantly changed through the trap as was the biological character. The mutagenic specific activity of the SOF was generally increased through the trap but this was offset by a decrease in SOF mass emissions. Some extremely biologically active subfractions were found at mode 4 with the Corning trap. NO2 emissions and HC emissions were generally decreased through the trap. A computer performance model based on membrane filter theory was used to explain the solid particulate filtering efficiency data. The model showed how key variables influence particulate trapping efficiency.

The rate of dissolution of pre-reduced iron in molten steel.

Abstract: The rate of dissolution of sponge iron into molten steel has been studied. Reduced pellets from Midrex and HyL processes and pellets containing coal char were used. The dissolution of the pellets is accompanied by continuous gas evolution which is due mainly to the reduction of iron oxides remaining in the pellets by the carbon within the system. It was found that HyL pellets dissolved faster than Midrex and Midrex pellets dissolved faster than Sartenejas. The rate of heat transfer from the bath to the pellet was found to increase with increasing gas evolution. The melting process was simulated by a mathematical model by assuming heat transfer control. This model allowed the calculation of the heat transfer coefficient as a function of the instantaneous radius of the pellet.