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Tracer Concentrations (tracer + concentration)
Selected AbstractsAn optical device to measure in-line residence time distribution curves during extrusionPOLYMER ENGINEERING & SCIENCE, Issue 1 2002Tomás Jeferson A. Mélo This paper proposes a setup for in-line measurement of residence time distribution (RTD) curves during extrusion. The detection system is composed of a slit die with transparent borosilicate glass windows fixed at the extruder exit, an optical arrangement with an incandescent light microbulb with fixed luminescence, and a Light Dependent Resistor (LDR) photocell of CdS. As the tracer passes through the light path, the reduction in the transmitted light intensity is followed by changes in the voltage induced by the photocell to an electric circuit. The signal is collected by an external interface and sent to a computer. Software acquires the data, does all calculations, and presents all curves and calculated variables to the monitor. The validation of the system was done by checking for data reproducibility and linearity with tracer concentration. The response of the LDR sensor with respect to the concentration of the tracer was calibrated using a set of slight dark film, obtaining a logarithmic relationship. Thus the signal enhances any disturbance, if present, particularly in the tail-region of the curves. Measurements were taken from a Werner-Pfleiderer ZSK 30 twin-screw extruder equipped with K-Tron gravimetric feeders operating with various screw speeds, feeding rates and screw configurations. In this last case, the presence of kneading elements was taken into account. [source] Multi-year tracking of sediment sources in a small agricultural watershed using rare earth elementsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2006A. Kimoto Abstract Rare earth elements (REEs) have been successfully used as a sediment tracer, but the REE technique has never been used for studying sediment sources for a multi-year period. A nearly four-year field experiment was conducted on a small agricultural watershed near Coshocton, OH, USA, to assess the applicability of the REE technique for a multi-year period and to evaluate the relative contributions of sediment sources in the watershed. Tracer depletion and tracer enrichment ratio (ratio of the tracer concentrations in sediment to the concentrations in the soil in the areas of application) were evaluated to examine the applicability and accuracy of the technique. A minimum of 91 per cent of the mass of the applied elements was still available on any individual morphological element at the end of the experimental period. The tracer enrichment ratio varied from 0·4 to 2·3, and it was not significantly related to time. The relative contributions of six morphological elements within the watershed were evaluated as proportions to total sediment yield. The relative contribution of the lower channel was significantly increased as a function of the amount of sediment yield, while that of the lower backslope was significantly decreased. The relative contribution of the lower channel significantly decreased as a function of cumulative sediment yield, while the contributions of the shoulder and the upper backslope significantly increased. Our results showed that the REE technique can be used to track sediment sources for a relatively long period with two limitations or potential sources of error associated with a selective depletion of tracers and a contamination of downslope areas with tagged sediments from upslope areas. Copyright © 2006 John Wiley & Sons, Ltd. [source] Single- and dual-porosity modelling of multiple tracer transport through soil columns: effects of initial moisture and mode of applicationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2001T. Kätterer Summary We investigated the effect of initial moisture contents and mode of application on the displacement of multiple conservative tracers through undisturbed columns of a Humic Gleysol. Bromide was applied at the soil surface and chloride was injected at 5 cm depth. The columns were irrigated with deuterium-enriched water. A dual-porosity model and two single-porosity models were calibrated separately to Br, and Cl, elution curves in the two columns. Elution curves were almost identical for Br, and Cl, under initially wet conditions, whereas the displacement of Br, was faster than that of Cl, in the initially dry column, indicating rapid transport with preferential flow. Only the dual-porosity model described the long-tailing breakthrough of Cl, in the initially dry column adequately. The parameter values giving acceptable fits for ,Br dry' were not compatible with the description of the three other elution curves, which could be adequately modelled with a single set of parameter values. The estimated set of common parameters was validated by comparing with the elution curves of deuterium water, nitrate and sulphate, as well as with resident tracer concentrations at four depths. The results showed that solutes can be displaced much faster when applied at the surface of initially dry soil than when applied to wet soil or when resident in the soil matrix. The simulation results suggest that solute transport under initially dry conditions was governed by preferential flow of infiltration water through macropores by-passing the matrix due to shrinkage cracks and water repellence of matrix surfaces. [source] Suspended-sediment sources in an urban watershed, Northeast Branch Anacostia River, MarylandHYDROLOGICAL PROCESSES, Issue 11 2010Olivia H. Devereux Abstract Fine sediment sources were characterized by chemical composition in an urban watershed, the Northeast Branch Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible land-based sediment sources and suspended sediment collected from the water column at the watershed outlet during storm events. These tracer concentrations were used to determine the relative quantity of suspended sediment contributed by each source. Although this is an urbanized watershed, there was not a distinct urban signature that can be evaluated except for the contributions from road surfaces. We identified the sources of fine sediment by both physiographic province (Piedmont and Coastal Plain) and source locale (streambanks, upland and street residue) by using different sets of elemental tracers. The Piedmont contributed the majority of the fine sediment for seven of the eight measured storms. The streambanks contributed the greatest quantity of fine sediment when evaluated by source locale. Street residue contributed 13% of the total suspended sediment on average and was the source most concentrated in anthropogenically enriched elements. Combining results from the source locale and physiographic province analyses, most fine sediment in the Northeast Branch watershed is derived from streambanks that contain sediment eroded from the Piedmont physiographic province of the watershed. Sediment fingerprinting analyses are most useful when longer term evaluations of sediment erosion and storage are also available from streambank-erosion measurements, sediment budget and other methods. Copyright © 2010 John Wiley & Sons, Ltd. [source] Process-oriented catchment modelling and multiple-response validationHYDROLOGICAL PROCESSES, Issue 2 2002S. Uhlenbrook Abstract The conceptual rainfall runoff model TAC (tracer-aided catchment model) has been developed based on the experimental results of tracer hydrological investigations at the mountainous Brugga and Zastler basins (40 and 18·4 km2). The model contains a physically realistic description of the runoff generation, which includes seven unit types each with characteristic dominating runoff generation processes. These processes are conceptualized by different linear and non-linear reservoir concepts. The model is applied to a period of 3·2 years on a daily time step with good success. In addition, an extensive model validation procedure was executed. Therefore, additional information (i.e. runoff in subbasins and a neighbouring basin, tracer concentrations and calculated runoff components) was used besides the simulated discharge of the basin investigated. This study shows the potential of tracer data for hydrological modelling. On the one hand, they are good tools to investigate the runoff generation processes. This is the basis for developing more realistic conceptualizations of the runoff generation routine. On the other hand, tracer data can serve as multi-response data to assess and validate a model. Copyright © 2002 John Wiley & Sons, Ltd. [source] Numerical investigation of gas mixing in gas-solid fluidized bedsAICHE JOURNAL, Issue 9 2010Tingwen Li Abstract Gas mixing in a tall narrow fluidized bed operated in the slugging fluidization regime is simulated with the aid of computational fluid dynamics. In the first part, a parametric study is conducted to investigate the influence of various parameters on the gas mixing. Among the parameters studied, the specularity coefficient for the partial-slip solid-phase wall boundary condition had the most significant effect on gas mixing. It was found that the solid-phase wall boundary condition needs to be specified with great care when gas mixing is modeled, with free slip, partial slip and no-slip wall boundary conditions giving substantial differences in the extent of gas back mixing. Axial and radial tracer concentration profiles for different operating conditions are generally in good agreement with experimental data from the literature. Detailed analyses of tracer back mixing are carried out in the second part. Two parameters, the tracer backflow fraction and overall gas backflow fraction, in addition to axial profiles of cross-sectional averaged tracer concentrations, are evaluated for different flow conditions. Qualitative trends are consistent with reported experimental findings. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Wheat field erosion rates and channel bottom sediment sources in an intensively cropped northeastern Oregon drainage basin,LAND DEGRADATION AND DEVELOPMENT, Issue 1 2004G. N. Nagle Abstract Sediment tracers were used to quantify erosion from cultivated fields and identify major source areas of channel bottom sediment within the Wildhorse Creek drainage, an intensively cropped tributary of the Umatilla River in northeastern Oregon, USA. Available data indicated that Wildhorse Creek was one of the largest sediment yielding tributaries of the Umatilla River. Carbon, nitrogen and the nuclear bomb-derived radionuclide 137Cs were used as tracers to fingerprint sediment sources. Sediment was collected from the stream bottom and active floodplain and compared to samples from cultivated fields and channel banks. Samples were characterized on the basis of tracer concentrations and a simple mixing model was used to estimate the relative portion of bottom sediment derived from cultivated surface and channel banks. The results indicate that the amount of bottom sediment derived from cultivated surface sources was less than 26,per,cent for the 1998 winter season, although this estimate has a high margin of error. Cesium-137 was also used to estimate surface erosion from three cultivated fields in the watershed. Annual estimates of erosion since 1963 from the three sampled fields were from 3 to 7,5,t,ha,1 yr,1. For the 1998 season, it appears that most channel-bottom sediment was of subsurface origin with much of it likely coming from channel and gully banks indicating that significant reductions in sediment in Wildhorse Creek might be accomplished by the stabilization of eroding riparian areas and swales on the lower slopes of agricultural fields. Published in 2004 by John Wiley & Sons, Ltd. [source] Characteristics of Underground Water Flow at Different Water Levels in Tianshengan Karst Area, Yunnan, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010Janja KOGOV Abstract: Three tracing tests from the same injection point executed at low, medium, and high water levels in the karst aquifer near Tianshengan village, Lunan Stone Forest, Yunnan Province, China, have revealed the basic properties of underground water flow. They showed the general directions of water flows; tracer concentrations were observed at six successive points allowing for the calculation of apparent dominant flow velocities at these sections towards the Dalongtan karst spring. For the high water level, the discharge between single sections was between two and 10 times greater than that at low water level. For the medium water level, the flow velocity at different sections was between 1.4 and 3.7 times faster than that at low water level; and for high water level, it was between 1.3 and 2.7 times faster than that at medium water level. The fastest water flow appeared at the first section (23 cm/s at medium water level); and the slowest (0.6 cm/s at low water level) appeared where water flow must cross the Tianshengan fault (north-south direction), and later, a layer of 20-30 m thickness of quartz sandstone and shale clay-stones. It was also possible to calculate the recovery of the tracer for point 4, Dakenyan, where discharge was measured. At the medium water level, 50% of the injected tracer was detected a half-day after its first appearance and at low water level after more than 3 days. The previously published research illustrates the transport velocities of possible contaminants and their solubilities in water at different hydrological conditions. [source] | ||||||||||