2,182 research outputs found
Impacts of phytoplankton activity on dissolved nitrogen fluxes in the tidal reaches and estuary of the Tweed (North East UK)
No full textMonthly surveys were conducted from April to August 1997 to quantify the uptake of dissolved nitrogen species (nitrate, ammonium and urea) and oxygen production in the tidal reaches and estuary of the Tweed. 15N isotope labelling was used in conjunction with in situ incubation methods to determine the uptake of dissolved nitrogen in surface water samples. Respiration, gross and net oxygen production were measured simultaneously. Phytoplankton activity in the Tweed resulted in low rates of dissolved nitrogen uptake (<0.4 nmol N l?1 h?1) and caused small changes in the dissolved oxygen concentration. Uptake of nitrate and urea was associated with phytoplankton biomass and was highest during periods of net autotrophic production (May, June and August). Reductions in the total downstream fluxes of dissolved nitrogen due to phytoplankton activity were appreciable despite the low rates of uptake of dissolved nitrogen and were found to be strongly dependent on the flushing time of the estuar
Refining experimental method for fluid flow experiments on MSW wastes in a large-scale uniaxial compression cell
No full textProvisional analysis of the effect of compression on transport in degrading municipal solid waste
No full textMultiple-tracer tests for contaminant transport process identification in saturated municipal solid waste
No full textTwo column tests were performed in conditions emulating vertical flow beneath the leachate table in a biologically active landfill to determine dominant transport mechanisms occurring in landfills. An improved understanding of contaminant transport process in wastes is required for developing better predictions about potential length of the long term aftercare of landfills, currently measured in timescales of centuries. Three tracers (lithium, bromide and deuterium) were used. Lithium did not behave conservatively. Given that lithium has been used extensively for tracing in landfill wastes, the tracer itself and the findings of previous tests which assume that it has behaved conservatively may need revisiting. The smaller column test could not be fitted with continuum models, probably because the volume of waste was below a representative elemental volume. Modelling compared advection-dispersion (AD), dual porosity (DP) and hybrid AD-DP models. Of these models, the DP model was found to be the most suitable. Although there is good evidence to suggest that diffusion is an important transport mechanism, the breakthrough curves of the different tracers did not differ from each other as would be predicted based on the free-water diffusion coefficients. This suggested that solute diffusion in wastes requires further stud
Investigating the effect of compression on solute transport through degrading municipal solid waste
No full textThe effect of applied compression on the nature of liquid flow and hence the movement of contaminants within municipal solid waste was examined by means of thirteen tracer tests conducted on five separate waste samples. The conservative nature of bromide, lithium and deuterium tracers was evaluated and linked to the presence of degradation in the sample. Lithium and deuterium tracers were non-conservative in the presence of degradation, whereas the bromide remained effectively conservative under all conditions. Solute diffusion times into and out of less mobile blocks of waste were compared for each test under the assumption of dominantly dual-porosity flow. Despite the fact that hydraulic conductivity changed strongly with applied stress, the block diffusion times were found to be much less sensitive to compression. A simple conceptual model, whereby flow is dominated by sub-parallel low permeability obstructions which define predominantly horizontally aligned less mobile zones, is able to explain this result. Compression tends to narrow the gap between the obstructions, but not significantly alter the horizontal length scale. Irrespective of knowledge of the true flow pattern, these results show that simple models of solute flushing from landfill which do not include depth dependent changes in solute transport parameters are justified
Influence of higher order effects on the vortex instability of thermal boundary layer flow in a wedge shaped domain
No full textWe reconsider the onset of streamwise vortices in the thermal boundary layer flow induced by an inclined upward-facing heated semi-infinite surface placed within a Newtonian fluid. Particular emphasis is laid upon how the induced flow in the isothermal region outside the boundary layer affects the boundary layer itself at higher order, and how this, in turn, affects the stability criterion for the onset of vortices. We find that the stability criterion for thermal boundary layers in air is less susceptible to changes in external geometry than for boundary layers in water. In general, we conclude that the variation of the stability criterion with wedge angle (between the heated and the outer boundary surface) is too great for the theory to predict reliably where disturbances first begin to grow
STRUCTURE OF THE ART-SPACE IN THE STORY "I" BY A.P. POTEMKIN
No full textThe author performs the analysis of the art space structure in A.P. Potemkin's story "I". Several interrelated spatial models are allocated and described: household space, natural space, social space, psychological space, transpersonal space
Pressure drop and turbulence statistics in transpired pipe flow
No full textMeasurements of turbulent flow in a horizontal pipe subjected to wall transpiration are presented. Results include data on global flow rates and pressure drop, and local mean and fluctuating velocity profiles. Two distinct flow transpiration rates are studied, = / = 0.0005 and 0.001. The effects of flow transpiration on the friction-coefficient are compared with theoretical predictions. The theory furnishes predictions accurate to 3\%
Fully Turbulent Mean Velocity Profile for Purely Viscous non-Newtonian Fluids
No full textThe characteristic near wall behavior of turbulent flow of purely-viscous non-Newtonian fluids is discussed for both power-law (P.-L.) and Herschel-Bulkley (H.-B.) rheological models. A proper scaling is presented for H.-B. fluids to establish an analogy with power-law fluids with same flow index. To provide reference data for turbulent flow of non-Newtonian fluids, DNS simulations of power-law fluids are conducted in a rectangular channel for a large range of power-law indices ( = 0.5, 0.69, 0.75, 0.9, 1, 1.2). The DNS data show that the mean velocity profile in the viscous and logarithmic layers follow expressions of the form and respectively, where shows a logarithmic dependency on the flow index.Comparison with some experimental data shows the above formulation to be valid for Reynolds numbers (based on shear velocity) as high as 1000
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