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Transport Regime (transport + regime)
Selected AbstractsPostglacial topographic evolution of glaciated valleys: a stochastic landscape evolution modelEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2005Simon J. Dadson Abstract The retreat of valley glaciers has a dramatic effect on the stability of glaciated valleys and exerts a prolonged influence on the subsequent fluvial sediment transport regime. We have studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model. The model incorporates a stochastic process to represent deep-seated landsliding, non-linear diffusion to represent shallow landsliding and an approximation of the Bagnold relation to represent fluvial sediment transport. It was calibrated using field data from several recent surveys within British Columbia, Canada. We present ensemble model results and compare them with results from a deterministic linear-diffusion model to show that explicit representation of large landslides is necessary to reproduce the morphology and channel network structure of a typical postglacial valley. Our model predicts a rapid rate of fluvial sediment transport following deglaciation with a subsequent gradual decline, similar to that inferred for Holocene time. We also describe how changes in the model parameters affect the estimated magnitude and duration of the paraglacial sediment pulse. Copyright © 2005 John Wiley & Sons, Ltd. [source] Suspended sediment transport regime in a debris-flow gully on Vancouver Island, British ColumbiaHYDROLOGICAL PROCESSES, Issue 4 2005Craig J. Nistor Abstract In debris-flow-prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris-flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s,1, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ,supply limited'; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain-on-snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd. [source] Spatially Resolved Potential Distribution in Carbon Nanotube Cross-Junction DevicesADVANCED MATERIALS, Issue 25-26 2009Eduardo J. H. Lee Crossed-nanotube junctions, the basic constituents of carbon nanotube networks, are investigated by scanning photocurrent microscopy. The location of the predominant electrostatic potential drop, at the electrical contacts or at the junction, is found to be highly dependent on the transport regime. Also, whereas Schottky barriers are formed at M-S (metal,semiconductor) nanotube crossings, isotype heterojunctions are formed at S-S ones (figure). [source] Investigation of a modified sequential iteration approach for solving coupled reactive transport problemsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2006David J. Z. Chen Abstract When contaminants enter the soil or groundwater, they may interact physically, geochemically and biochemically with the native water, microorganisms and solid matrix. A realistic description of a reactive transport regime that includes these processes requires joint consideration of multiple chemical species. Currently there are three common numerical approaches for coupling multispecies reaction and solute transport: the one-step approach, the sequential non-iterative approach (SNIA), and the sequential iterative approach (SIA). A modification of the SNIA method is the Strang-splitting method. In this study, a new modified sequential iteration approach (MSIA) for solving multicomponent reactive transport in steady state groundwater flow is presented. This coupling approach has been applied to two realistic reactive transport problems and its performance compared with the SIA and the Strang-splitting methods. The comparison shows that MSIA consistently converges faster than the other two coupling schemes. For the simulation of nitrogen and related species transport and reaction in a riparian aquifer, the total CPU time required by MSIA is only about 38% of the total CPU time required by the SIA, and only 50% of the CPU time required by the Strang-splitting method. The test problem results indicate that the SIA has superior accuracy, while the accuracy of MSIA is marginally better than that of the Strang-splitting method. The overall performance of MSIA is considered to be good, especially for simulations in which computational time is a critical factor. Copyright © 2005 John Wiley & Sons, Ltd. [source] A method for improving predictions of bed-load discharges to reservoirsLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 2 2007Vicente L. Lopes Abstract Effective management options for mitigating the loss of reservoir water storage capacity to sedimentation depend on improved predictions of bed-load discharges into the reservoirs. Most predictions of bed-load discharges, however, are based on the assumption that the rates of bed-load sediment availability equal the transport capacity of the flow, ignoring the spatio-temporal variability of the sediment supply. This paper develops a semiquantitative method to characterize bed-load sediment transport in alluvial channels, assuming a channel reach is non-supply limited when the bed-load discharge of a given sediment particle-size class is functionally related to the energy that is available to transport that fraction of the total bed-load. The method was applied to 22 alluvial stream channels in the USA to determine whether a channel reach had a supply-limited or non-supply-limited bed-load transport regime. The non-supply-limited transport regime was further subdivided into two groups on the basis of statistical tests. The results indicated the pattern of bed-load sediment transport in alluvial channels depends on the complete spectrum of sediment particle sizes available for transport rather than individual particle-size fractions represented by one characteristic particle size. The application of the method developed in this paper should assist reservoir managers in selecting bed-load sediment transport equations to improve predictions of bed-load discharge in alluvial streams, thereby significantly increasing the efficiency of management options for maintaining the storage capacity of waterbodies. [source] Dynamic culture of droplet-confined cell arraysBIOTECHNOLOGY PROGRESS, Issue 1 2010Elisa Cimetta Abstract Responding to the need of creating an accurate and controlled microenvironment surrounding the cell while meeting the requirements for biological processes or pharmacological screening tests, we aimed at designing and developing a microscaled culture system suitable for analyzing the synergic effects of extracellular matrix proteins and soluble environments on cell phenotype in a high-throughput fashion. We produced cell arrays deposing micrometer-scale protein islands on hydrogels using a robotic DNA microarrayer, constrained the culture media in a droplet-like volume and developed a suitable perfusion system. The droplet-confined cell arrays were used either with conventional culture methods (batch operating system) or with automated stable and constant perfusion (steady-state operating system). Mathematical modeling assisted the experimental design and assessed efficient mass transport and proper fluidodynamic regimes. Cells cultured on arrayed islands (500 ,m diameter) maintained the correct phenotype both after static and perfused conditions, confirmed by immunostaining and gene expression analyses through total RNA extraction. The mathematical model, validated using a particle tracking experiment, predicted the constant value of velocities over the cell arrays (less than 10% variation) ensuring the same mass transport regime. BrdU analysis on an average of 96 cell spots for each experimental condition showed uniform expression inside each cell island and low variability in the data (average of 13%). Perfused arrays showed longer doubling times when compared with static cultures. In addition, perfused cultures showed a reduced variability in the collected data, allowing to detect statistically significant differences in cell behavior depending on the spotted ECM protein. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Suspended sediment transport in a small Mediterranean agricultural catchmentEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2009Joan Estrany Abstract The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km2) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004,2005 to 2006,2007). An annual average SSC of 17.3 mg l,1, with a maximum of 2270 mg l,1, was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright © 2009 John Wiley & Sons, Ltd. [source] Sediment infiltration traps: their use to monitor salmonid spawning habitat in headwater tributaries of the Cascapédia River, QuébecHYDROLOGICAL PROCESSES, Issue 20 2005André E. Zimmermann Abstract Sediment infiltration can clog salmon nests and reduce egg survival. As a countermeasure, environmental managers often deploy infiltration traps to monitor sediment infiltration. Traps provide a repeatable means of measuring infiltration and enable comparisons to be made between sites. Results from infiltration rates measured with traps have also been used to estimate infilling rates into salmon nests. Application of these data is questionable, as the composition of the bed and the amount of fine sediment within the bed is known to affect infiltration rates. Thus, infiltration rates measured with infiltration traps may differ from the infiltration rates occurring in redd and riffle gravels. To examine how relationships between sediment infiltration rates varied between four watersheds, we continuously monitored suspended sediment transport, shear stress and infiltration rates at four sites over 5 months. We also compared infiltration rates measured with infiltration traps with changes in the hydraulic conductivity and subsurface grain size distribution of adjacent artificially constructed salmon nests and natural riffle gravels. Among the four watersheds, clear differences in sediment infiltration rates were observed. The differences correlated with the subsurface silt content but no strong relationship existed between land-use or basin physiography/geology. Despite observing an average of 30 kg m,2 of sediment finer than 2 mm being deposited in the infiltration traps during the study, no change in redd or riffle substrate was observed. If the deposition rates measured with the traps reflect the processes in redds, enough sediment would have been deposited to inhibit egg emergence. However, no reduction in egg survival to the eyed stage was observed. In summary, our results show that infiltration traps with clean gravels can be used to detect intersite differences in sediment transport regimes. Extrapolations of sediment infiltration rates measured with such collectors to estimate infiltration rates in redds or riffles is, however, flawed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Effect of various parameters on the solid circulation rate in a liquid,solid circulating fluidized bedASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008P. Natarajan Abstract A liquid,solid circulating fluidized bed (LSCFB) is operated at high liquid velocity, where particle entrainment is highly significant, and between the conventional liquid fluidized bed and the dilute-phase liquid transport regimes. In the present work, systematic experiments were carried out in a 0.094 m i.d. and 2.4 m height laboratory-scale LSCFB apparatus by using various solid particles and tap water as fluidizing medium to study the hydrodynamics. The effects of operating parameters, i.e. primary liquid flow rate in the riser (jf), auxiliary liquid flow rate (ja), total liquid flow rate (jl), particle density (,s), particle diameter (dp) and solid feed pipe diameter (do) on the solid circulation rate were analyzed from the experimental data. Finally, a correlation was developed from the experimental data to estimate solid velocity (solid circulation rate), and was compared with the present experimental and available data in the literature. They agree well with a maximum root mean-square (RMS) deviation of 12%. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | |||||||||||||