Showing papers on "Water flow published in 2006"

Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes

Abstract: We report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. The measured gas flow exceeds predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations. The gas and water permeabilities of these nanotube-based membranes are several orders of magnitude higher than those of commercial polycarbonate membranes, despite having pore sizes an order of magnitude smaller. These membranes enable fundamental studies of mass transport in confined environments, as well as more energy-efficient nanoscale filtration.

Large Slip of Aqueous Liquid Flow over a Nanoengineered Superhydrophobic Surface

Abstract: While many recent studies have confirmed the existence of liquid slip over certain solid surfaces, there has not been a deliberate effort to design and fabricate a surface that would maximize the slip under practical conditions. Here, we have engineered a nanostructured superhydrophobic surface that minimizes the liquid-solid contact area so that the liquid flows predominantly over a layer of air. Measured through a cone-and-plate rheometer system, the surface has demonstrated dramatic slip effects: a slip length of approximately 20 microm for water flow and approximately 50 microm for 30 wt % glycerin. The essential geometrical characteristics lie with the nanoposts populated on the surface: tall and slender (i.e., needlelike) profile and submicron periodicity (i.e., pitch).

Will African agriculture survive climate change

Abstract: Measurement of the likely magnitude of the economic impact of climate change on African agriculture has been a challenge. Using data from a survey of more than 9,000 farmers across 11 African countries, a cross-sectional approach estimates how farm net revenues are affected by climate change compared with current mean temperature. Revenues fall with warming for dryland crops (temperature elasticity of -1.9) and livestock (-5.4), whereas revenues rise for irrigated crops (elasticity of 0.5), which are located in relatively cool parts of Africa and are buffered by irrigation from the effects of warming. At first, warming has little net aggregate effect as the gains for irrigated crops offset the losses for dryland crops and livestock. Warming, however, will likely reduce dryland farm income immediately. The final effects will also depend on changes in precipitation, because revenues from all farm types increase with precipitation. Because irrigated farms are less sensitive to climate, where water is available, irrigation is a practical adaptation to climate change in Africa.

Environment and plasticity of myogenesis in teleost fish.

Abstract: Embryonic development in teleosts is profoundly affected by environmental conditions, particularly temperature and dissolved oxygen concentrations. The environment determines the rate of myogenesis, the composition of sub-cellular organelles, patterns of gene expression, and the number and size distribution of muscle fibres. During the embryonic and larval stages, muscle plasticity to the environment is usually irreversible due to the rapid pace of ontogenetic change. In the early life stages, muscle can affect locomotory performance and behaviour, with potential consequences for larval survival. Postembryonic growth involves myogenic progenitor cells (MPCs) that originate in the embryo. The embryonic temperature regime can have long-term consequences for the growth of skeletal muscle in some species, including the duration and intensity of myotube formation in adult stages. In juvenile and adult fish, abiotic (temperature, day-length, water flow characteristics, hypoxia) and biotic factors (food availability, parasitic infection) have complex effects on the signalling pathways regulating the proliferation and differentiation of MPCs, protein synthesis and degradation, and patterns of gene expression. The phenotypic responses observed to the environment frequently vary during ontogeny and are integrated with endogenous physiological rhythms, particularly sexual maturation. Studies with model teleosts provide opportunities for investigating the underlying genetic mechanisms of muscle plasticity that can subsequently be applied to non-model species of more ecological or commercial interest.

Climate Change Effects on Hydroecology of Arctic Freshwater Ecosystems

Abstract: In general, the arctic freshwater-terrestrial system will warm more rapidly than the global average, particularly during the autumn and winter season. The decline or loss of many cryospheric components and a shift from a nival to an increasingly pluvial system will produce numerous physical effects on freshwater ecosystems. Of particular note will be reductions in the dominance of the spring freshet and changes in the intensity of river-ice breakup. Increased evaporation/evapotranspiration due to longer ice-free seasons, higher air/water temperatures and greater transpiring vegetation along with increase infiltration because of permafrost thaw will decrease surface water levels and coverage. Loss of ice and permafrost, increased water temperatures and vegetation shifts will alter water chemistry, the general result being an increase in lotic and lentic productivity. Changes in ice and water flow/levels will lead to regime-specific increases and decreases in habitat availability/quality across the circumpolar Arctic.

Regional differences in response of flow in glacier-fed Himalayan rivers to climatic warming

Abstract: River flow from glacierized areas in the Himalaya is influenced both by intra-annual variations in precipitation and energy availability, and by longer term changes in storage of water as glacier ice. High specific discharge from ice melt often dominates flow for considerable distances downstream, particularly where other sources of runoff are limited, providing a major water resource. Should Himalayan glaciers continue to retreat rapidly, water shortages might be widespread within a few decades. However, given the difference in climate between the drier western and monsoonal eastern ends of the region, future warming is unlikely to affect river flow uniformly throughout. A simple temperature-index-based hydro-glaciological model, in which glacier dimensions are allowed to decline through time, has been developed with a view to assessing, in data-sparse areas, by how much and when climate warming will reduce Himalayan glacier dimensions and affect downstream river flows. Two glaciers having the same initial geometries were located (one each) in the headwaters of two identical nests of hypothetical catchments, representing contrasting climates in the west and east of the region. The hypothetical catchments were nested such that percentage ice cover declined with increasing basin area. Model parameters were validated against available but limited mass-balance and river flow measurements. The model was applied for 150 years from an arbitrary start date (1990), first with standard-period (1961-1990) climate data and then with application of a 0·06 °C year-1 transient climatic warming scenario. Under this warming scenario, Himalayan rivers fed by large glaciers descending through considerable elevation range will respond in a broadly similar manner, except that summer snowfall in the east will suppress the rate of initial flow increase, delay peak discharge and postpone eventual disappearance of the ice. Impacts of declining glacier area on river flow will be greater in smaller and more highly glacierized basins in both the west and east, and in the west, where precipitation is scarce, for considerable distances downstream

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties

Abstract: Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

Modeling xylem and phloem water flows in trees according to cohesion theory and Münch hypothesis

Abstract: Water and solute flows in the coupled system of xylem and phloem were modeled together with predictions for xylem and whole stem diameter changes. With the model we could produce water circulation between xylem and phloem as presented by the Munch hypothesis. Viscosity was modeled as an explicit function of solute concentration and this was found to vary the resistance of the phloem sap flow by many orders of magnitude in the possible physiological range of sap concentrations. Also, the sensitivity of the predicted phloem translocation to changes in the boundary conditions and parameters such as sugar loading, transpiration, and hydraulic conductivity were studied. The system was found to be quite sensitive to the sugar-loading rate, as too high sugar concentration, (approximately 7 MPa) would cause phloem translocation to be irreversibly hindered and soon totally blocked due to accumulation of sugar at the top of the phloem and the consequent rise in the viscosity of the phloem sap. Too low sugar loading rate, on the other hand, would not induce a sufficient axial water pressure gradient. The model also revealed the existence of Munch “counter flow”, i.e., xylem water flow in the absence of transpiration resulting from water circulation between the xylem and phloem. Modeled diameter changes of the stem were found to be compatible with actual stem diameter measurements from earlier studies. The diurnal diameter variation of the whole stem was approximately 0.1 mm of which the xylem constituted approximately one-third.

Localization and quantification of plasma membrane aquaporin expression in maize primary root: a clue to understanding their role as cellular plumbers

Abstract: Water movement across root tissues occurs by parallel apoplastic, symplastic, and transcellular pathways that the plant can control to a certain extent. Because water channels or aquaporins (AQPs) play an important role in regulating water flow, studies on AQP mRNA and protein expression in different root tissues are essential. Here, we quantified and localized the expression of Zea mays plasma membrane AQPs (ZmPIPs) in primary root tip using in situ and quantitative RT-PCR and immunodetection approaches. All ZmPIP genes except ZmPIP2;7 were expressed in primary roots. Expression was found to be dependent on the developmental stage of the root, with, in general, an increase in expression towards the elongation and mature zones. Two genes, ZmPIP1;5 and ZmPIP2;5, showed the greatest increase in expression (up to 11- and 17-fold, respectively) in the mature zone, where they accounted for 50% of the total expressed ZmPIPs. The immunocytochemical localization of ZmPIP2;1 and ZmPIP2;5 in the exodermis and endodermis indicated that they are involved in root radial water movement. In addition, we detected a polar localization of ZmPIP2;5 to the external periclinal side of epidermal cells in root apices, suggesting an important role in water uptake from the root surface. Finally, protoplast swelling assays showed that root cells display a variable, but globally low, osmotic water permeability coefficient (Pf < 10 microm/s). However, the presence of a population of cells with a higher Pf (up to 26 microm/s) in mature zone of the root might be correlated with the increased expression of several ZmPIP genes.

Documentation of the Unsaturated-Zone Flow (UZF1) Package for modeling Unsaturated Flow Between the Land Surface and the Water Table with MODFLOW-2005

Abstract: Percolation of precipitation through unsaturated zones is important for recharge of ground water Rain and snowmelt at land surface are partitioned into different pathways including runoff, infiltration, evapotranspiration, unsaturated-zone storage, and recharge A new package for MODFLOW2005 called the Unsaturated-Zone Flow (UZF1) Package was developed to simulate water flow and storage in the unsaturated zone and to partition flow into evapotranspiration and recharge The package also accounts for land surface runoff to streams and lakes A kinematic wave approximation to Richards’ equation is solved by the method of characteristics to simulate vertical unsaturated flow The approach assumes that unsaturated flow occurs in response to gravity potential gradients only and ignores negative potential gradients; the approach further assumes uniform hydraulic properties in the unsaturated zone for each vertical column of model cells The Brooks-Corey function is used to define the relation between unsaturated hydraulic conductivity and water content Variables used by the UZF1 Package include initial and saturated water contents, saturated vertical hydraulic conductivity, and an exponent in the Brooks-Corey function Residual water content is calculated internally by the UZF1 Package on the basis of the difference between saturated water content and specific yield The UZF1 Package is a substitution for the Recharge and Evapotranspiration Packages of MODFLOW-2005 The UZF1 Package differs from the Recharge Package in that an infiltration rate is applied at land surface instead of a specified recharge rate directly to ground water The applied infiltration rate is further limited by the saturated vertical hydraulic conductivity The UZF1 Package differs from the Evapotranspiration Package in that evapotranspiration losses are first removed from the unsaturated zone above the evapotranspiration extinction depth, and if the demand is not met, water can be removed directly from ground water whenever the depth to ground water is less than the extinction depth The UZF1 Package also differs from the Evapotranspiration Package in that water is discharged directly to land surface whenever the altitude of the water table exceeds land surface Water that is discharged to land surface, as well as applied infiltration in excess of the saturated vertical hydraulic conductivity, may be routed directly as inflow to specified streams or lakes if these packages are active; otherwise, this water is removed from the model The UZF1 Package was tested against the US Geological Survey’s Variably-Saturated Two-Dimensional Flow and Transport Model for a vertical unsaturated flow problem that includes evapotranspiration losses This report also includes an example in which MODFLOW-2005 with the UZF1 Package was used to simulate a realistic surfacewater/ground-water flow problem that includes time and space variable infiltration, evapotranspiration, runoff, and groundwater discharge to land surface and to streams Another simpler problem is presented so that the user may use the input files as templates for new problems and to verify proper code installation

Live-Bed Local Pier Scour Experiments

Abstract: Local clear-water and live-bed scour tests were performed for a range of water depths and flow velocities with two different uniform cohesionless sediment diameters (0.27 and 0.84 mm ) and a circular pile with a diameter of 0.15 m . The tests were performed in a tilting flume ( 1.5 m wide, 1.2 m deep, and 45 m long) located in the Hydraulics Laboratory at the University of Auckland in Auckland, New Zealand. These tests extend local scour data obtained in controlled experiments to velocity ratio (V∕ Vc ) values as high as 6. This is near the velocity where the peak live-bed scour occurs for the sediment and flow conditions. Scour depth predictions are made with four different local scour equations for the conditions of the tests and the results compared with the measured values.

Evidence from Amazonian forests is consistent with isohydric control of leaf water potential

Abstract: Climate modelling studies predict that the rain forests of the Eastern Amazon basin are likely to experience reduc- tions in rainfall of up to 50% over the next 50-100 years. Efforts to predict the effects of changing climate, especially drought stress, on forest gas exchange are currently limited by uncertainty about the mechanism that controls stomatal closure in response to low soil moisture. At a through-fall exclusion experiment in Eastern Amazonia where water was experimentally excluded from the soil, we tested the hypothesis that plants are isohydric, that is, when water is scarce, the stomata act to prevent leaf water potential from dropping below a critical threshold level. We made diurnal measurements of leaf water potential ( Ψ l ), stomatal con- ductance ( g s ), sap flow and stem water potential ( Ψ stem ) in the wet and dry seasons. We compared the data with the predictions of the soil-plant-atmosphere (SPA) model, which embeds the isohydric hypothesis within its stomatal conductance algorithm. The model inputs for meteorology, leaf area index (LAI), soil water potential and soil-to-leaf hydraulic resistance ( R ) were altered between seasons in accordance with measured values. No optimization param- eters were used to adjust the model. This 'mechanistic' model of stomatal function was able to explain the individ- ual tree-level seasonal changes in water relations ( r 2 = 0.85, 0.90 and 0.58 for Ψ l , sap flow and g s , respectively). The model indicated that the measured increase in R was the dominant cause of restricted water use during the dry sea- son, resulting in a modelled restriction of sap flow four times greater than that caused by reduced soil water poten- tial. Higher resistance during the dry season resulted from an increase in below-ground resistance (including root and soil-to-root resistance) to water flow.

Seasonal export of carbon, nitrogen, and major solutes from Alaskan catchments with discontinuous permafrost

Abstract: [1] Frequent measurements of stream chemistry during snowmelt and summer storms were used in three watersheds that differ in permafrost coverage (high, 53%; medium, 18%; and low, 4%) to determine the role of water flow paths on the fluxes of carbon, nitrogen, and major solutes from Alaskan catchments. Permafrost was important in the seasonal pattern of stream chemistry as there was a distinct shift in chemistry and flow from winter through snowmelt and into summer in the permafrost-dominated catchment. Furthermore, the active layer above the permafrost was important for the late summer release of NO3 and DOC, suggesting a deeper active layer may increase N and C loss in permafrost-dominated areas. Overall, permafrost constrained water flow to the active layer, resulting in higher DOC but lower dissolved mineral fluxes (Ca 2+ Mg 2+ K + Na + )i n the high-permafrost watershed than in the watersheds with less permafrost coverage. However, the decline in dissolved mineral fluxes was not linearly related to permafrost coverage across watersheds. The flux of weathering ions may also be explained by total water runoff, since the medium-permafrost watershed, which had the greatest runoff on an areal basis, yielded the greatest loss of all major elements (Ca 2+ Mg 2+ K + Na + SO4 NO3 NH4 Cl) except DOC. Despite differences among watersheds in permafrost coverage, hydrologic flow paths, area, and total runoff, all watersheds were net sources of every individual ions or elements (Cl ,P O4 ,S O4 , DOC, DON, NO3 ,N a + ,K + Mg 2+ , Ca 2+ ) except NH4 , which was a small fraction of the total N concentration in streams.

Cells move when ions and water flow.

Abstract: Cell migration is a process that plays an important role throughout the entire life span. It starts early on during embryogenesis and contributes to shaping our body. Migrating cells are involved in maintaining the integrity of our body, for instance, by defending it against invading pathogens. On the other side, migration of tumor cells may have lethal consequences when tumors spread metastatically. Thus, there is a strong interest in unraveling the cellular mechanisms underlying cell migration. The purpose of this review is to illustrate the functional importance of ion and water channels as part of the cellular migration machinery. Ion and water flow is required for optimal migration, and the inhibition or genetic ablation of channels leads to a marked impairment of migration. We briefly touch cytoskeletal mechanisms of migration as well as cell–matrix interactions. We then present some general principles by which channels can affect cell migration before we discuss each channel group separately.

Colloid-Facilitated Solute Transport in Variably Saturated Porous Media: Numerical Model and Experimental Verification

Abstract: Strongly sorbing chemicals (e.g., heavy metals, radionuclides, pharmaceuticals, and explosives) in porous media are associated predominantly with the solid phase, which is commonly assumed to be stationary. However, recent field- and laboratory-scale observations have shown that in the presence of mobile colloidal particles (e.g., microbes, humic substances, clays, and metal oxides), colloids can act as pollutant carriers and thus provide a rapid transport pathway for strongly sorbing contaminants. To address this problem, we developed a one-dimensional numerical model based on the HYDRUS-1D software package that incorporates mechanisms associated with colloid and colloid-facilitated solute transport in variably saturated porous media. The model accounts for transient variably saturated water flow, and for both colloid and solute movement due to advection, diffusion, and dispersion, as well as for solute movement facilitated by colloid transport. The colloid transport module additionally considers the processes of attachment/detachment to/from the solid phase and/or the air–water interface, straining, and/or size exclusion. Various blocking and depth dependent functions can be used to modify the attachment and straining coefficients. The solute transport module uses the concept of two-site sorption to describe nonequilibrium adsorption–desorption reactions to the solid phase. The module further assumes that contaminants can be sorbed onto surfaces of both deposited and mobile colloids, fully accounting for the dynamics of colloid movement between different phases. Application of the model is demonstrated using selected experimental data from published saturated column experiments, conducted to investigate the transport of Cd in the presence of Bacillus subtilis spores in alluvial gravel aquifer media. Numerical results simulating bacteria transport, as well as the bacteria-facilitated Cd transport, are compared with experimental results. A sensitivity analysis of the model to various parameters is also presented.

Relationships among probability distributions of stream discharges in floods, climate, bed load transport, and river incision

Abstract: per unit area of drainage basin (an effective precipitation rate P )t oa: a � 1 / P n , where n � 1.6. Using this relationship, we confirm that rivers in arid regions should incise less rapidly as climate becomes yet more arid. (If no water flows, the ‘‘river’’ transports no sediment.) Whether aridification of an initially humid environment leads to increased or decreased incision rates, however, depends on the minimum (threshold) discharge capable not only of transporting bed load but also sufficient to scour alluvium from the riverbed and then erode the bedrock. The curve fit relating P to a implies that for aridification to accelerate incision, floods that recur only once or twice per millennium (or less frequently) must carry out most of the incision. An overestimate of n could permit smaller, more frequent floods to incise, but it appears that in only special circumstances will aridification accelerate steam incision.

Comparison of artificial neural network and regression pedotransfer functions for prediction of soil water retention and saturated hydraulic conductivity

Abstract: Modeling water flow and solute transport in vadose zone requires knowledge of soil hydraulic properties, which are water retention and hydraulic conductivity curves. As an alternative to direct measurement, indirect determination of these functions from basic soil properties using pedotransfer functions (PTFs) has attracted the attention of researchers in a variety of fields such as soil scientists, hydrologists, and agricultural and environmental engineers. In this study, PTFs for point and parametric (van Genuchten's parameters) estimation of soil hydraulic parameters from basic soil properties such as particle-size distribution, bulk density, and three different pore sizes were developed and validated using artificial neural network (ANN) and multiple-linear regression methods and the predictive capabilities of the two methods was compared using some evaluation criteria. Total of 195 soil samples was divided into two groups as 130 for the development and 65 for the validation of PTFs. Although the differences between the two methods were not statistically significant (p > 0.05), regression predicted point and parametric variables of soil hydraulic parameters better than ANN. Both methods had lower accuracy in parametric predictions than in point predictions. Accuracy of the predictions was evaluated by the coefficient of determination (R2) and the root mean square error (RMSE) between the measured and predicted parameter values. The R2 and RMSE varied from 0.637 to 0.979 and from 0.013 to 0.938 for regression, and varied from 0.444 to 0.952 and from 0.020 to 3.511 for ANN, respectively. Even though regression performs insignificantly better than ANN in this case, ANN produces promising results and its advantages can be utilized by developing or using new algorithms in future studies.

Implementing plant hydraulic architecture within the LPJ Dynamic Global Vegetation Model

Abstract: Aim To implement plant hydraulic architecture within the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM), and to test the model against a set of observational data. If the model can reproduce major patterns in vegetation and ecosystem processes, we consider this to be an important linkage between plant physiology and larger-scale ecosystem dynamics. Location The location is global, geographically distributed. Methods A literature review was carried out to derive model formulations and parameter values for representing the hydraulic characteristics of major global plant functional types (PFTs) in a DGVM. After implementing the corresponding formulations within the LPJ-DGVM, present-day model output was compared to observational data. Results The model reproduced observed broad-scale patterns in potential natural vegetation, but it failed to distinguish accurately between different types of grassland and savanna vegetation, possibly related to inadequate model representations of water fluxes in the soil and wildfire effects. Compared to a version of the model using an empirical formulation for calculating plant water supply without considering plant hydraulic architecture, the new formulation improved simulated patterns of vegetation in particular for dry shrublands. Global-scale simulation results for runoff and actual evapotranspiration (AET) corresponded well to available data. The model also successfully reproduced the magnitude and seasonal cycle of AET for most EUROFLUX forests, while modelled variation in NPP across a large number of sites spanning several biomes showed a strong correlation with estimates from field measurements. Main conclusions The model was generally confirmed by comparison to observational data. The novel model representation of water flow within plants makes it possible to resolve mechanistically the effects of hydraulic differences between plant functional groups on vegetation structure, water cycling, and competition. This may be an advantage when predicting ecosystem responses to nonextant climates, in particular in areas dominated by dry shrubland vegetation.

Mandibular and dental variation and the evolution of suction feeding in odontoceti

Abstract: Comprehensive morphometric analysis of osteological and necropsy specimens indicates that blunt heads and wide jaws, both of which create a more circular mouth opening and thus improve water flow for suction feeding, are common in Odontoceti and found in all families except freshwater river dolphins (Platanistoidea), which are exclusively long-snouted. Mandibular bluntness, here termed amblygnathy, correlates with dental reduction in odontocetes; there is a further association of reduced dentition with increased body length. Examination of quantitative data reveals that many odontocetes, especially globicephaline delphinids, have a blunter cranial profile (partly from facial musculature and other soft tissues) and fewer exposed teeth for grasping prey than is generally supposed, especially when the researcher relies solely on examination of skeletal materials. Numerous teeth present in cleaned skulls and jaws remain unerupted even in adults, as verified by necropsy tooth counts, rendering tooth counts from museum specimens unreliable indicators of in vivo conditions. Amblygnathy and smaller, rounder mouth openings correlate with other anatomical, ecological, and behavioral traits associated with suction feeding. It is likely that odontocete suction ingestion evolved independently in multiple lineages from use of suction to transport grasped prey in long-jawed ancestors, with consequent loss of the grasp and transport step as prey are sucked directly into the oral cavity or oropharynx.