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Sample records for coupled water transport

  1. Coupled water transport by rat proximal tubule.

    PubMed

    Green, R; Giebisch, G; Unwin, R; Weinstein, A M

    1991-12-01

    Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to examine water reabsorption by this epithelium. Osmolality of the luminal solution was varied with changes in NaCl concentration and by the addition of raffinose. Capillary perfusates contained either low (2 g/dl) or high (16 g/dl) concentrations of albumin. We used low-bicarbonate perfusates for both lumen and capillary so that we might apply the nonequilibrium thermodynamic model of transport for a single solute (NaCl) to interpret our observations. Linear regression with the volume flux equation Jv = -Lp delta II - Lp sigma delta C + Jav (where Jv is volume flux, Lp is hydraulic conductance, delta II is oncotic force, sigma is osmotic reflection coefficient, delta C is salt concentration difference, and Jav is the component of Jv not attributed to transepithelial hydrostatic or osmotic forces) revealed a tubule water permeability (Pf = 0.11 +/- 0.01 cm/s) and a sigma (0.74 +/- 0.08) in agreement with previous determinations. These transport parameters were unaffected by changes in peritubular protein. We also found that Jav was substantial, approximately three-fourths of the rate of isotonic transport under these perfusion conditions. Further, this component of water transport nearly doubled with the transition from low- to high-protein peritubular capillary perfusion. When expressed as a capacity for water reabsorption against an osmotic gradient, the salt concentration differences required to null volume flux were 13.2 +/- 2.4 and 29.4 +/- 4.0 mosmol/kgH2O under low and high peritubular protein. Our data suggest that this protein effect is, most likely, an increase in solute transport by the tubule epithelial cells.

  2. Numerical modeling of coupled water flow and heat transport in soil and snow

    Treesearch

    Thijs J. Kelleners; Jeremy Koonce; Rose Shillito; Jelle Dijkema; Markus Berli; Michael H. Young; John M. Frank; William Massman

    2016-01-01

    A one-dimensional vertical numerical model for coupled water flow and heat transport in soil and snow was modified to include all three phases of water: vapor, liquid, and ice. The top boundary condition in the model is driven by incoming precipitation and the surface energy balance. The model was applied to three different terrestrial systems: A warm desert bare...

  3. Numerical Modeling of Coupled Water Flow and Heat Transport in Soil and Snow

    NASA Astrophysics Data System (ADS)

    Kelleners, T.

    2015-12-01

    A numerical model is developed to calculate coupled water flow and heat transport in seasonally frozen soil and snow. Both liquid water flow and water vapor flow are included. The effect of dissolved ions on soil water freezing point depression is included by combining an expression for osmotic head with the Clapeyron equation and the van Genuchten soil water retention function. The coupled water flow and heat transport equations are solved using the Thomas algorithm and Picard iteration. Ice pressure is always assumed zero and frost heave is neglected. The new model is tested using data from a high-elevation rangeland soil that is subject to significant soil freezing and a mountainous forest soil that is snow-covered for about 8 months of the year. Soil hydraulic parameters are mostly based on measurements and only vegetation parameters are fine-tuned to match measured and calculated soil water content, soil & snow temperature, and snow height. Modeling statistics for both systems show good performance for temperature, intermediate performance for snow height, and relatively low performance for soil water content, in accordance with earlier results with an older version of the model.

  4. Coupled Water Flow and Heat Transport in Seasonally Frozen Soils with Snow Accumulation

    NASA Astrophysics Data System (ADS)

    King, J. M.; Kasurak, A.; Kelly, R. E.; Duguay, C. R.; Derksen, C.

    2011-12-01

    A numerical model is developed to calculate coupled water flow and heat transport in seasonally frozen soil and snow. Separate equations are used to describe both unsaturated and saturated soil water flow. The effect of dissolved ions on soil water freezing point depression is included by combining an expression for osmotic head with the Clapeyron equation and the van Genuchten soil water retention function. The coupled water flow and heat transport equations are solved using the Thomas algorithm and Picard iteration. Ice pressure is always assumed zero and frost heave is neglected. The new model is tested using data from an existing laboratory soil column freezing experiment and an ongoing field experiment in a high-elevation rangeland soil. A dimensionless impedance factor describing the effect of ice pore blocking on soil hydraulic conductivity is treated as a calibration parameter for both cases. Calculated values of total water content for the laboratory soil column freezing experiment compare well with measured values, especially during the early stages of the experiment, as is also found by others. Modeling statistics for the rangeland field experiment show varied performance for soil water content and excellent performance for soil temperature, in accordance with earlier results with an older version of the model.

  5. Coupled Water Flow and Heat Transport in Seasonally Frozen Soils with Snow Accumulation

    NASA Astrophysics Data System (ADS)

    kelleners, T.

    2013-12-01

    A numerical model is developed to calculate coupled water flow and heat transport in seasonally frozen soil and snow. Separate equations are used to describe both unsaturated and saturated soil water flow. The effect of dissolved ions on soil water freezing point depression is included by combining an expression for osmotic head with the Clapeyron equation and the van Genuchten soil water retention function. The coupled water flow and heat transport equations are solved using the Thomas algorithm and Picard iteration. Ice pressure is always assumed zero and frost heave is neglected. The new model is tested using data from an existing laboratory soil column freezing experiment and an ongoing field experiment in a high-elevation rangeland soil. A dimensionless impedance factor describing the effect of ice pore blocking on soil hydraulic conductivity is treated as a calibration parameter for both cases. Calculated values of total water content for the laboratory soil column freezing experiment compare well with measured values, especially during the early stages of the experiment, as is also found by others. Modeling statistics for the rangeland field experiment show varied performance for soil water content and excellent performance for soil temperature, in accordance with earlier results with an older version of the model.

  6. Analysis of the sodium recirculation theory of solute-coupled water transport in small intestine

    PubMed Central

    Larsen, Erik Hviid; Sørensen, Jakob Balslev; Sørensen, Jens Nørkær

    2002-01-01

    Our previous mathematical model of solute-coupled water transport through the intestinal epithelium is extended for dealing with electrolytes rather than electroneutral solutes. A 3Na+–2K+ pump in the lateral membranes provides the energy-requiring step for driving transjunctional and translateral flows of water across the epithelium with recirculation of the diffusible ions maintained by a 1Na+-1K+–2Cl− cotransporter in the plasma membrane facing the serosal compartment. With intracellular non-diffusible anions and compliant plasma membranes, the model describes the dependence on membrane permeabilities and pump constants of fluxes of water and electrolytes, volumes and ion concentrations of cell and lateral intercellular space (lis), and membrane potentials and conductances. Simulating physiological bioelectrical features together with cellular and paracellular fluxes of the sodium ion, computations predict that the concentration differences between lis and bathing solutions are small for all three ions. Nevertheless, the diffusion fluxes of the ions out of lis significantly exceed their mass transports. It is concluded that isotonic transport requires recirculation of all three ions. The computed sodium recirculation flux that is required for isotonic transport corresponds to that estimated in experiments on toad small intestine. This result is shown to be robust and independent of whether the apical entrance mechanism for the sodium ion is a channel, a SGLT1 transporter driving inward uphill water flux, or an electroneutral Na+–K+–2Cl− cotransporter. PMID:12096047

  7. A Mathematical Model of Solute Coupled Water Transport in Toad Intestine Incorporating Recirculation of the Actively Transported Solute

    PubMed Central

    Larsen, Erik Hviid; Sørensen, Jakob Balslev; Sørensen, Jens Nørkær

    2000-01-01

    A mathematical model of an absorbing leaky epithelium is developed for analysis of solute coupled water transport. The non-charged driving solute diffuses into cells and is pumped from cells into the lateral intercellular space (lis). All membranes contain water channels with the solute passing those of tight junction and interspace basement membrane by convection-diffusion. With solute permeability of paracellular pathway large relative to paracellular water flow, the paracellular flux ratio of the solute (influx/outflux) is small (2–4) in agreement with experiments. The virtual solute concentration of fluid emerging from lis is then significantly larger than the concentration in lis. Thus, in absence of external driving forces the model generates isotonic transport provided a component of the solute flux emerging downstream lis is taken up by cells through the serosal membrane and pumped back into lis, i.e., the solute would have to be recirculated. With input variables from toad intestine (Nedergaard, S., E.H. Larsen, and H.H. Ussing, J. Membr. Biol. 168:241–251), computations predict that 60–80% of the pumped flux stems from serosal bath in agreement with the experimental estimate of the recirculation flux. Robust solutions are obtained with realistic concentrations and pressures of lis, and with the following features. Rate of fluid absorption is governed by the solute permeability of mucosal membrane. Maximum fluid flow is governed by density of pumps on lis-membranes. Energetic efficiency increases with hydraulic conductance of the pathway carrying water from mucosal solution into lis. Uphill water transport is accomplished, but with high hydraulic conductance of cell membranes strength of transport is obscured by water flow through cells. Anomalous solvent drag occurs when back flux of water through cells exceeds inward water flux between cells. Molecules moving along the paracellular pathway are driven by a translateral flow of water, i.e., the model

  8. Water-transporting proteins.

    PubMed

    Zeuthen, Thomas

    2010-04-01

    Transport through lipids and aquaporins is osmotic and entirely driven by the difference in osmotic pressure. Water transport in cotransporters and uniporters is different: Water can be cotransported, energized by coupling to the substrate flux by a mechanism closely associated with protein. In the K(+)/Cl(-) and the Na(+)/K(+)/2Cl(-) cotransporters, water is entirely cotransported, while water transport in glucose uniporters and Na(+)-coupled transporters of nutrients and neurotransmitters takes place by both osmosis and cotransport. The molecular mechanism behind cotransport of water is not clear. It is associated with the substrate movements in aqueous pathways within the protein; a conventional unstirred layer mechanism can be ruled out, due to high rates of diffusion in the cytoplasm. The physiological roles of the various modes of water transport are reviewed in relation to epithelial transport. Epithelial water transport is energized by the movements of ions, but how the coupling takes place is uncertain. All epithelia can transport water uphill against an osmotic gradient, which is hard to explain by simple osmosis. Furthermore, genetic removal of aquaporins has not given support to osmosis as the exclusive mode of transport. Water cotransport can explain the coupling between ion and water transport, a major fraction of transepithelial water transport and uphill water transport. Aquaporins enhance water transport by utilizing osmotic gradients and cause the osmolarity of the transportate to approach isotonicity.

  9. Solute transport modelling in a coupled water and heat flow system applied to cold regions hydrogeology

    NASA Astrophysics Data System (ADS)

    Frampton, Andrew; Destouni, Georgia

    2016-04-01

    In cold regions, flow in the unsaturated zone is highly dynamic with seasonal variability and changes in temperature, moisture, and heat and water fluxes, all of which affect ground freeze-thaw processes and influence transport of inert and reactive waterborne substances. In arctic permafrost environments, near-surface groundwater flow is further restricted to a relatively shallow and seasonally variable active layer, confined by perennially frozen ground below. The active layer is typically partially saturated with ice, liquid water and air, and is strongly dependent on seasonal temperature fluctuations, thermal forcing and infiltration patterns. Here there is a need for improved understanding of the mechanisms controlling subsurface solute transport in the partially saturated active layer zone. Studying solute transport in cold regions is relevant to improve the understanding of how natural and anthropogenic pollution may change as activities in arctic and sub-arctic regions increase. It is also particularly relevant for understanding how dissolved carbon is transported in coupled surface and subsurface hydrological systems under climate change, in order to better understand the permafrost-hydrological-carbon climate feedback. In this contribution subsurface solute transport under surface warming and degrading permafrost conditions is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in subsurface water flows and solute transport travel times are analysed for different modelled geological configurations during a 100-year warming period. Results show that for all simulated cases, the minimum and mean travel times increase non-linearly with warming irrespective of geological configuration and heterogeneity structure. The travel time changes are shown to depend on combined warming effects of increase in pathway length due to deepening of the active layer, reduced transport

  10. Lagrangian transport of water vapor and CFCs in a coupled Chemistry Climate Model

    NASA Astrophysics Data System (ADS)

    Hoppe, Charlotte; Müller, Rolf; Hoffmann, Lars; Konopka, Paul; Plöger, Felix; Grooß, Jens-Uwe

    2013-04-01

    We describe the implementation of a Lagrangian transport core in a chemistry climate model (CCM). Thereby we address the common problem of properly representing trace gas distributions in a classical Eulerian framework with a fixed model grid, particularly in regions with strong trace gas gradients. A prominent example is stratospheric water vapor, which is an important driver of surface climate change on decadal scales. In this case, the transport representation is particularly important in the tropical tropopause layer (TTL), where tropospheric air enters into the stratosphere. We have coupled the Chemical Lagrangian Model of the Stratosphere (CLaMS) with the ECHAM-MESSy Atmospheric Chemistry Model (EMAC). The latter includes the ECHAM5 climate model, and the MESSy interface, which allows for flexible coupling and switching between different submodels. The chemistry transport model CLaMS provides a fully Lagrangian transport representation to calculate constituent transport for an ensemble of air parcels that move along trajectories. To facilitate the calculation of long time-series a simplified chemistry scheme was implemented. Various studies show that the CLaMS model is particularly suited to properly represent dynamics and chemistry in the UT/LS region. The analysis of mean age of stratospheric air gives insight into the different transport characteristics of the Eulerian and the Lagrangian transport schemes. Mean age of air, calculated in both frameworks, is compared regarding the representation of important processes, i.e. descent in the polar vortex, upwelling in the tropical pipe, and isentropic in-mixing in subtropical regions. We also compared the zonal mean distributions and photochemical lifetimes of CFC-11 and CFC-12 with climatologies from different satellite experiments (ACE-FTS, HIRDLS, and MIPAS). CLaMS stratospheric water vapor distributions show remarkable differences compared to the stratospheric water vapor simulated by ECHAM, especially in

  11. Development of a Coupled Ocean-Hydrologic Model to Simulate Pollutant Transport in Singapore Coastal Waters

    NASA Astrophysics Data System (ADS)

    Chua, V. P.

    2015-12-01

    Intensive agricultural, economic and industrial activities in Singapore and Malaysia have made our coastal areas under high risk of water pollution. A coupled ocean-hydrologic model is employed to perform three-dimensional simulations of flow and pollutant transport in Singapore coastal waters. The hydrologic SWAT model is coupled with the coastal ocean SUNTANS model by outputting streamflow and pollutant concentrations from the SWAT model and using them as inputs for the SUNTANS model at common boundary points. The coupled model is calibrated with observed sea surface elevations and velocities, and high correlation coefficients that exceed 0.97 and 0.91 are found for sea surface elevations and velocities, respectively. The pollutants are modeled as Gaussian passive tracers, and are released at five upstream locations in Singapore coastal waters. During the Northeast monsoon, pollutants released in Source 1 (Johor River), Source 2 (Tiram River), Source 3 (Layang River) and Source 4 (Layau River) enter the Singapore Strait after 4 days of release and reach Sentosa Island within 9 days. Meanwhile, pollutants released in Source 5 (Kallang River) reach Sentosa Island after 4 days. During the Southwest monsoon, the dispersion time is roughly doubled, with pollutants from Sources 1 - 4 entering the Singapore Strait only after 12 days of release due to weak currents.

  12. Constraining Water Vapor Abundance on Mars using a Coupled Heat-Water Transport Model and Seasonal Frost Observations

    NASA Astrophysics Data System (ADS)

    Bapst, J.; Byrne, S.

    2016-12-01

    The stability of water ice on Mars' surface is determined by its temperature and the density of water vapor at the bottom of the atmosphere. Multiple orbiting instruments have been used to study column-integrated water abundance in the martian atmosphere, resolving the global annual water cycle. However, poor knowledge of the vertical distribution of water makes constraining its abundance near the surface difficult. One must assume a mixing regime to produce surface vapor density estimates. More indirectly, one can use the appearance and disappearance of seasonal water frost, along with ice stability models, to estimate this value. Here, we use derived temperature and surface reflectance data from MGS TES to constrain a 1-D thermal diffusion model, which is coupled to an atmospheric water transport model. TES temperatures are used to constrain thermal properties of our modeled subsurface, while changes in TES albedo can be used to determine the timing of water frost. We tune the density of water vapor in the atmospheric model to match the observed seasonal water frost timing in the northern hemisphere, poleward of 45°N. Thus, we produce a new estimate for the water abundance in the lower atmosphere of Mars and how it varies seasonally and geographically. The timing of water frost can be ambiguous in TES data, especially at lower latitudes where the albedo contrast between frosted and unfrosted surfaces is lower (presumably due to lesser areal coverage of water frost). The uncertainty in frost timing with our approach is <20° LS ( 40 sols), and will be used to define upper and lower bounds in our estimate of vapor density. The implications of our derived vapor densities on the stability of surface and subsurface water ice will be discussed.

  13. Coupled Soil Water and Heat Transport Near the Land Surface in Arid and Semiarid Regions - Multi-Domain Modeling

    NASA Astrophysics Data System (ADS)

    Mohanty, Binayak; Yang, Zhenlei

    2016-04-01

    Understanding and simulating coupled water and heat transfer appropriately in the shallow subsurface is of vital significance for accurate prediction of soil evaporation that would improve the coupling between land surface and atmosphere, which consequently could enhance the reliability of weather as well as climate forecast. The theory of Philip and de Vries (1957), accounting for water vapor diffusion only, was considered physically incomplete and consequently extended and improved by several researchers by explicitly taking water vapor convection, dispersion or air flow into account. It is generally believed that the soil moisture is usually low in the near surface layer under highly transient field conditions, particularly in arid and semiarid regions, and that accurate characterization of water vapor transport is critical when modeling simultaneous water and heat transport in the shallow field soils. The first objective of this study is thus mainly to test existing coupled water and heat transport theories and to develop reasonable and simplified numerical models using field experimental data collected under semi-arid and arid hydro-climatic conditions. In addition, more complex multi-domain models are developed for ubiquitous heterogeneous terrestrial surfaces such as horizontal textural contrasts or structured heterogeneity including macropores (fractures, cracks, root channels, etc.). This would make coupled water and heat transfer models applicable in such non-homogeneous soils more meaningful and enhance the skill of land-atmosphere interaction models at a larger context.

  14. Kinetics of coupling water and cryoprotectant transport across cell membranes and applications to cryopreservation.

    PubMed

    Weng, Lindong; Li, Weizhong; Chen, Cong; Zuo, Jianguo

    2011-12-15

    Thermodynamic and kinetic models can provide a wealth of information on the physical response of living cells and tissues experiencing cryopreservation procedures. Both isothermal and nonisothermal models have been proposed so far, accompanied by experimental verification and cryoapplications. But the cryoprotective solution is usually assumed to be dilute and ideal in the models proposed in the literature. Additionally, few nonisothermal models are able to couple the transmembrane transport of water and cryoprotectant during cooling and warming of cells. To overcome these limitations, this study develops a whole new set of equations that can quantify the cotransport of water and cryoprotectant across cell membranes in the nondilute and nonideal solution during the freezing and thawing protocols. The new models proposed here can be simplified into ones consistent with the classic models if some specific assumptions are included. For cryobiological practice, they are applied to predict the volumetric change for imprinting control region (ICR) mouse spermatozoa and human corneal keratocytes in the freezing protocol. The new models can determine the intracellular concentration of cryoprotectant more precisely than others by abandoning the assumptions such as dilute and ideal solutions and nonpermeability of membranes to cryoprotectant. Further, the findings in this study will offer new insights into the physical response of cells undergoing cryopreservation.

  15. Coupled water transport in standing gradient models of the lateral intercellular space.

    PubMed Central

    Weinstein, A M; Stephenson, J L

    1981-01-01

    A standing gradient model of the lateral intercellular space is presented which includes a basement membrane of finite solute permeability. The solution to the model equations is estimated analytically using the "isotonic convection approximation" of Segel. In the case of solute pumps uniformly distributed along the length of the channel, the achievement of isotonic transport depends only on the water permeability of the cell membranes. The ability of the model to transport water against an adverse osmotic gradient is the sum of two terms: The first term is simply that for a well-stirred compartment model and reflects basement membrane solute permeability. The second term measures the added strength due to diffusion limitation within the interspace. It is observed, however, that the ability for uphill water transport due to diffusion limitation is diminished by high cell membrane water permeability. For physiologically relevant parameters, it appears that the high water permeability required for isotonic transport renders the contribution of the standing gradient relatively ineffective in transport against an osmotic gradient. Finally, when the model transports both isotonically and against a gradient, it is shown that substantial intraepithelial solute polarization effects are unavoidable. Thus, the measured epithelial water permeability will grossly underestimate the water permeability of the cell membranes. The accuracy of the analytic approximation is demonstrated by numerical solution of the complete model equations. PMID:7260315

  16. Coupling between inter-helical hydrogen bonding and water dynamics in a proton transporter.

    PubMed

    del Val, Coral; Bondar, Luiza; Bondar, Ana-Nicoleta

    2014-04-01

    Long-distance proton transfers by proton pumps occurs in discrete steps that may involve the direct participation of protein sidechains and water molecules, and coupling of protonation changes to structural rearrangements of the protein matrix. Here we explore the role of inter-helical hydrogen bonding in long-distance protein conformational coupling and dynamics of internal water molecules. From molecular dynamics simulations of wild type and nine different bacteriorhodopsin mutants we find that both intra- and inter-helical hydrogen bonds are important determinants of the local protein structure, dynamics, and water interactions. Based on molecular dynamics and bioinformatics analyses, we identify an aspartate/threonine inter-helical hydrogen-bonding motif involved in controlling the local conformational dynamics. Perturbation of inter-helical hydrogen bonds can couple to rapid changes in water dynamics.

  17. Coupled full core neutron transport/CFD simulations of pressurized water reactors

    SciTech Connect

    Kochunas, B.; Stimpson, S.; Collins, B.; Downar, T.; Brewster, R.; Baglietto, E.; Yan, J.

    2012-07-01

    Recently as part of the CASL project, a capability to perform 3D whole-core coupled neutron transport and computational fluid dynamics (CFD) calculations was demonstrated. This work uses the 2D/1D transport code DeCART and the commercial CFD code STAR-CCM+. It builds on previous CASL work demonstrating coupling for smaller spatial domains. The coupling methodology is described along with the problem simulated and results are presented for fresh hot full power conditions. An additional comparison is made to an equivalent model that uses lower order T/H feedback to assess the importance and cost of high fidelity feedback to the neutronics problem. A simulation of a quarter core Combustion Engineering (CE) PWR core was performed with the coupled codes using a Fixed Point Gauss-Seidel iteration technique. The total approximate calculation requirements are nearly 10,000 CPU hours and 1 TB of memory. The problem took 6 coupled iterations to converge. The CFD coupled model and low order T/H feedback model compared well for global solution parameters, with a difference in the critical boron concentration and average outlet temperature of 14 ppm B and 0.94 deg. C, respectively. Differences in the power distribution were more significant with maximum relative differences in the core-wide pin peaking factor (Fq) of 5.37% and average relative differences in flat flux region power of 11.54%. Future work will focus on analyzing problems more relevant to CASL using models with less approximations. (authors)

  18. A fully coupled model for water-gas-heat reactive transport with methane oxidation in landfill covers.

    PubMed

    Ng, C W W; Feng, S; Liu, H W

    2015-03-01

    Methane oxidation in landfill covers is a complex process involving water, gas and heat transfer as well as microbial oxidation. The coupled phenomena of microbial oxidation, water, gas, and heat transfer are not fully understood. In this study, a new model is developed that incorporates water-gas-heat coupled reactive transport in unsaturated soil with methane oxidation. Effects of microbial oxidation-generated water and heat are included. The model is calibrated using published data from a laboratory soil column test. Moreover, a series of parametric studies are carried out to investigate the influence of microbial oxidation-generated water and heat, initial water content on methane oxidation efficiency. Computed and measured results of gas concentration and methane oxidation rate are consistent. It is found that the coupling effects between water-gas-heat transfer and methane oxidation are significant. Ignoring microbial oxidation-generated water and heat can result in a significant difference in methane oxidation efficiency by 100%. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Coupled modeling of water transport and air-droplet interaction in the electrode of a proton exchange membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Esposito, Angelo; Pianese, Cesare; Guezennec, Yann G.

    In this work, an accurate and computationally fast model for liquid water transport within a proton exchange membrane fuel cell (PEMFC) electrode is developed by lumping the space-dependence of the relevant variables. Capillarity is considered as the main transport mechanism within the gas diffusion layer (GDL). The novelty of the model lies in the coupled simulation of the water transport at the interface between gas diffusion layer and gas flow channel (GFC). This is achieved with a phenomenological description of the process that allows its simulation with relative simplicity. Moreover, a detailed two-dimensional visualization of such interface is achieved via geometric simulation of water droplets formation, growth, coalescence and detachment on the surface of the GDL. The model is useful for optimization analysis oriented to both PEMFC design and balance of plant. Furthermore, the accomplishment of reduced computational time and good accuracy makes the model suitable for control strategy implementation to ensure PEM fuel cells operation within optimal electrode water content.

  20. Simulating Water and Nutrient Transport in an Urbanizing Agricultural Watershed with Lake-Level Regulation Using a Coupled Modeling Approach

    NASA Astrophysics Data System (ADS)

    Chen, X.; Motew, M.; Booth, E.; Carpenter, S. R.; Steven, L. I.; Kucharik, C. J.

    2015-12-01

    The Yahara River basin located in southern Wisconsin is a watershed with long-term eutrophication issues due largely to a thriving dairy industry upstream of the Madison chain of lakes. Steady phosphorus loading from manure production and other sources has contributed directly to blue-green algae blooms and poor water quality in the lakes and river system, and is often viewed as the most important environmental problem to solve in the region. In this study, the daily streamflow and monthly nitrogen (N), sediment and phosphorus (P) transport, as well as the lake levels in the Yahara River basin are simulated using a physically-based hydrologic routing model: the Terrestrial Hydrology Model with Biogeochemistry (THMB). The original model includes representation of water and nitrogen transport but as part of this work, P transport and lake regulation are added into the model. The modified THMB model is coupled with the AgroIBIS-VSF agroecosystem model to represent dynamic coupling between agricultural management in the watershed, and N, P, and sediment transport to lakes and streams. We will present model calibration and validation results that demonstrate the hydrologic routing capability of THMB for a spatial resolution of 220m, several orders of magnitude finer than attempted previously with THMB. The calibrated modeling system is being used to simulate the impacts of climate change and land management on biogeochemistry in the Yahara watershed under four different pathways of change to the year 2070 (Yahara 2070). These scenarios are Abandonment and Renewal, Accelerated Innovation, Connected Communities and Nested Watersheds, which are used to better understand how future decision-making influences the provisioning and trade-offs of ecosystem services.

  1. Towards a Fully Distributed Characterization of Water Residence and Transit Time by Coupled Hydrology-Transport Modeling

    NASA Astrophysics Data System (ADS)

    Remondi, F.; Fatichi, S.; Burlando, P.

    2015-12-01

    Water residence and transit time are crucial elements in flow pathways and catchment response characterization. The temporal distribution of catchment transit times has been generally studied and modelled with lumped parameter approaches. However, understanding the dominant controls in a more holistic manner requires attention to the spatially distributed catchment properties also in relation to their control on the basin response to different type of precipitation events. A tool that looks both at the time and space distribution of water residence and transport can be useful for predicting water and solute fluxes and ultimately for better understanding the dependence of catchment transit and residence times on geomorphological and climatic factors. To this purpose we couple a fully distributed, yet essential, process-based watershed model with a component to simulate solute transport. Key features of the developed tool include: (a) reduced complexity spatially-distributed hydrological model; (b) spatially-distributed water age and conservative tracer concentration; (c) possibility to explicitly compute transit time distributions for different precipitation events and locations. The presented framework is tested on the Plynlimon watershed (UK), where long-term records of hydrological variables are available. Among them, discharge and chloride concentration are used to investigate the model behavior. We present the integrated model concept, the underlying methodologies, the results from the case study application, as well as preliminary virtual experiments that allow exploring the full statistical space of travel and residence times.

  2. Numerical Modeling of Coupled Heat Transport and Liquid Water and Water Vapor Flow in Geothermally Heated Ground at Norris Geyser Basin

    NASA Astrophysics Data System (ADS)

    Mohamed, R. A. M.; Jones, S. B.; Neale, C. M. U.

    2016-12-01

    Long-term monitoring of ground surface temperature and heat flow near hydrothermally active areas in Yellowstone National Park can help determine possible changes of the subsurface heat flow. Some of these changes may alter the safety of the park's visitors, rangers and scientists. The geothermal heated ground in Norris Geyser Basin in Yellowstone National Park receives heat from both the geothermal gradient and the atmospheric shortwave and longwave radiations. In this study a one dimensional numerical model was used to model the coupled movement of liquid water, water vapor, and heat in the top 10 cm soil layer near a hydrothermal crater in Norris Geyser Basin. The Hydrus 1D numerical model was used to simulate the coupled processes in order to optimize the soil hydraulic parameters. Parameter optimization was done using Marquardt-Levenberg type parameter optimization algorithm for variably saturated soil under steady state and transient flow conditions. The simulation of coupled heat transport and liquid water and water vapor flow in geothermally heated ground is a new application to Hydrus 1D. Preliminary results, however, showed that the calculated temperature and water content correlated well with observed patterns on both dry sunny days and wet days. The study explained the coupled processes at the ground-atmosphere boundary layer which can help determine possible changes within the subsurface heat flow from the geothermal source.

  3. Coupling of water and carbon transport in trees: -Could water limitations of phloem transport speed up carbon starvation and tree mortality?

    NASA Astrophysics Data System (ADS)

    Sevanto, S.; McDowell, N. G.; Dickman, L. T.; Pangle, R.; Pockman, W.

    2011-12-01

    Understanding the mechanisms behind tree mortality is increasingly important because climate change appears to be increasing drought severity and duration worldwide, with concomitant increases in mortality. Carbon starvation is one of the mechanisms suggested to be responsible for mortality, especially for species that close stomata at low xylem water tensions. Such plants would be under negative carbon balance during drought. Carbohydrate transport in plants relies on the availability of apoplastic water and therefore, shortage of water could lead to inability to distribute sugars and speed up carbon starvation even if carbohydrate reserves existed. To test these ideas we conducted a greenhouse study where pinon pine (Pinus edulis) trees were killed using two treatments: water limitation (complete drought) and carbon limitation (complete darkness). We collected tissue samples for non-structural carbohydrate content analysis weekly and monitored changes in xylem and phloem water potentials using stem diameter variation measurements. To follow changes in the physiological status of the trees we measured shoot gas exchange, leaf water potential and sap flow rate. Carbon-limited trees continued respiring at relatively high rates and maintained both xylem and phloem transport despite rapidly diminishing carbohydrate pools. Water-limited trees, on the other hand, exhibited reduced respiration and xylem and phloem transport rates as soon as drought inhibited stomatal opening; even before any significant drop in leaf water potential. This suggests that respirationmetabolic rate is strongly controlled by soil water availability, and instead of speeding up mortality, reduced carbohydrate transport and utilization rate may be a valuable strategy to enhance tree survival during long droughts.

  4. The Coupled Mars Dust and Water Cycles: Understanding How Clouds Affect the Vertical Distribution and Meridional Transport of Dust and Water

    NASA Astrophysics Data System (ADS)

    Kahre, M. A.

    2015-12-01

    The dust and water cycles are crucial to the current Martian climate, and they are coupled through cloud formation. Dust strongly impacts the thermal structure of the atmosphere and thus greatly affects atmospheric circulation, while clouds provide radiative forcing and control the hemispheric exchange of water through the modification of the vertical distributions of water and dust. Recent improvements in the quality and sophistication of both observations and climate models allow for a more comprehensive understanding of how the interaction between the dust and water cycles (through cloud formation) affects the dust and water cycles individually. We focus here on the effects of clouds on the vertical distribution of dust and water, and how those vertical distributions control the net meridional transport of water. For this study, we utilize observations of temperature, dust and water ice from the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO) combined with the NASA ARC Mars Global Climate Model (MGCM). We demonstrate that the magnitude and nature of the net meridional transport of water between the northern and southern hemispheres during NH summer is sensitive to the vertical structure of the simulated aphelion cloud belt. We further examine how clouds influence the atmospheric thermal structure and thus the vertical structure of the cloud belt. Our goal is to identify and understand the importance of radiative/dynamic feedbacks due to the physical processes involved with cloud formation and evolution on the current climate of Mars.

  5. The Coupled Mars Dust and Water Cycles: Understanding How Clouds Affect the Vertical Distribution and Meridional Transport of Dust and Water.

    NASA Technical Reports Server (NTRS)

    Kahre, M. A.

    2015-01-01

    The dust and water cycles are crucial to the current Martian climate, and they are coupled through cloud formation. Dust strongly impacts the thermal structure of the atmosphere and thus greatly affects atmospheric circulation, while clouds provide radiative forcing and control the hemispheric exchange of water through the modification of the vertical distributions of water and dust. Recent improvements in the quality and sophistication of both observations and climate models allow for a more comprehensive understanding of how the interaction between the dust and water cycles (through cloud formation) affects the dust and water cycles individually. We focus here on the effects of clouds on the vertical distribution of dust and water, and how those vertical distributions control the net meridional transport of water. For this study, we utilize observations of temperature, dust and water ice from the Mars Climate Sounder (MCS) on the Mars Reconnaissance Orbiter (MRO) combined with the NASA ARC Mars Global Climate Model (MGCM). We demonstrate that the magnitude and nature of the net meridional transport of water between the northern and southern hemispheres during NH summer is sensitive to the vertical structure of the simulated aphelion cloud belt. We further examine how clouds influence the atmospheric thermal structure and thus the vertical structure of the cloud belt. Our goal is to identify and understand the importance of radiative/dynamic feedbacks due to the physical processes involved with cloud formation and evolution on the current climate of Mars.

  6. Coupled inverse modeling of vadose zone water, heat, and solute transport: Calibration constraints, parameter nonuniqueness, and predictive uncertainty

    USGS Publications Warehouse

    Friedel, M.J.

    2005-01-01

    In this study, an inverse methodology is presented and used to evaluate the effect that calibration of a synthetic artificial recharge model, constrained by different combinations of measurements (pressure head, temperature, and concentration), has on estimated vadose zone model parameter-value nonuniqueness and predictive water, heat, and solute transport uncertainty. Several findings are arrived at following model calibration and predictive analysis. First, composite scaled sensitivities revealed that all calibration measurement combinations contributed to the estimation of 30 water, heat, and solute transport parameters by inverting a set of vadose zone transport equations that were coupled explicitly through dependent variables and implicitly through parameters and fluid properties. Second, despite excellent model quality and perfect match of simulated-to-measured dependent field variables, the limitations in information content of field measurements used to constrain the calibration process promoted correlation among parameters; correlation among parameters promoted parameter nonuniqueness; and parameter nonuniqueness promoted predictive uncertainty. Consequently, simulations by transport models calibrated against field information represent a single realization associated with some quantifiable range of predictive uncertainty. Third, a primary reduction in uncertainty was achieved by increasing the number of calibration-constraint measurements, but reductions in uncertainty appeared restricted implying a practical limit to parameterization detail. Fourth, for a fixed number of measurements, a less prominent reduction in the range of predictive uncertainty could be realized through selective use of measurement types to constrain the calibration process. Therefore, field measurement types used to constrain the calibration process should be matched to target predictions. Fifth, because correlation among parameters contributes to predictive uncertainty, it may be

  7. Beta-adrenergic activation of solute coupled water uptake by toad skin epithelium results in near-isosmotic transport.

    PubMed

    Nielsen, Robert; Larsen, Erik Hviid

    2007-09-01

    Transepithelial potential (V(T)), conductance (G(T)), and water flow (J(V)) were measured simultaneously with good time resolution (min) in isolated toad (Bufo bufo) skin epithelium with Ringer on both sides. Inside application of 5 microM isoproterenol resulted in the fast increase in G(T) from 1.2+/-0.3 to 2.4+/-0.4 mS x cm(-2) and slower increases in equivalent short circuit current, I(SC)(Eqv) = -G(T) x V(T), from 12.7+/-3.2 to 33.1+/-6.8 microA cm(-2), and J(V) from 0.72+/-0.17 to 3.01+/-0.49 nL cm(-2) s(-1). Amiloride in the outside solution abolished I(SC)(Eqv) (-1.6+/-0.1 microA cm(-2)) while J(V) decreased to 0.50+/-0.15 nL cm(-2) x s(-1), which is significantly different from zero. Isoproterenol decreased the osmotic concentration of the transported fluid, C(osm) approximately 2 x I(SC)(Eqv)/J(V), from 351+/-72 to 227+/-28 mOsm (Ringer's solution: 252.8 mOsm). J(V) depicted a saturating function of [Na+]out in agreement with Na+ self-inhibition of ENaC. Ouabain on the inside decreased I(SC)(Eqv) from 60+/-10 to 6.1+/-1.7 microA cm(-2), and J(V) from 3.34+/-0.47 to 1.40+/-0.24 nL cm(-2) x s(-1). Short-circuited preparations exhibited a linear relationship between short-circuit current and J(V) with a [Na+] of the transported fluid of 130+/-24 mM ([Na+]Ringer's solution = 117.4 mM). Addition of bumetanide to the inside solution reduced J(V). Water was transported uphill and J(V) reversed at an excess outside osmotic concentration, deltaC(S,rev) = 28.9+/-3.9 mOsm, amiloride decreased deltaC(S,rev) to 7.5+/-1.5 mOsm. It is concluded that water uptake is accomplished by osmotic coupling in the lateral intercellular space (lis), and hypothesized that a small fraction of the Na+ flux pumped into lis is recirculated via basolateral NKCC transporters.

  8. Coupled mode transport theory for sound transmission through an ocean with random sound speed perturbations: coherence in deep water environments.

    PubMed

    Colosi, John A; Chandrayadula, Tarun K; Voronovich, Alexander G; Ostashev, Vladimir E

    2013-10-01

    Second moments of mode amplitudes at fixed frequency as a function of separations in mode number, time, and horizontal distance are investigated using mode-based transport equations and Monte Carlo simulation. These second moments are used to study full-field acoustic coherence, including depth separations. Calculations for low-order modes between 50 and 250 Hz are presented using a deep-water Philippine Sea environment. Comparisons between Monte Carlo simulations and transport theory for time and depth coherence at frequencies of 75 and 250 Hz and for ranges up to 500 km show good agreement. The theory is used to examine the accuracy of the adiabatic and quadratic lag approximations, and the range and frequency scaling of coherence. It is found that while temporal coherence has a dominant adiabatic component, horizontal and vertical coherence have more equal contributions from coupling and adiabatic effects. In addition, the quadratic lag approximation is shown to be most accurate at higher frequencies and longer ranges. Last the range and frequency scalings are found to be sensitive to the functional form of the exponential decay of coherence with lag, but temporal and horizontal coherence show scalings that fall quite close to the well-known inverse frequency and inverse square root range laws.

  9. Large Eddy Simulation of Coupled Water and Carbon Exchange and Transport Through and Above Forest Canopies

    NASA Astrophysics Data System (ADS)

    Drewry, D. T.; Albertson, J. D.

    2002-12-01

    There are outstanding questions surrounding the measurement and modeling of carbon and water fluxes over complex landscapes. Typically, forest fluxes are measured with the eddy covariance technique from a single tower. A unique study over a loblolly pine stand in the Duke Forest yielded high frequency velocity, temperature, water vapor and carbon dioxide fluxes from a network of six instrumented towers, simultaneously. In this talk we explore the canopy-atmosphere dynamics active during this experiment through the use of a Large Eddy Simulation (LES) code. The LES includes a numerical representation of the plant canopy structure, a biophysical process sub-model, and mixes the sources and sinks through the boundary layer with a filtered form of the Navier-Stokes equations. Through this combination of a spatially distributed dataset and a 3D model of canopy flows and processes we investigate the relative influences of canopy structure and meteorological forcing on observed and modeled fluxes. This work has implications for our understanding of the effects of canopy turbulence on eddy covariance flux measurements.

  10. Modeling coupled water flow, solute transport and geochemical reactions affecting heavy metal migration in a podzol soil

    USDA-ARS?s Scientific Manuscript database

    Many or most subsurface pollution problems at the field scale involve such simultaneous processes as water flow, multicomponent solute transport, heat transport and biogeochemical processes and reactions. Process-based models that integrate these various processes can be valuable tools for investiga...

  11. Water transport by Na+-coupled cotransporters of glucose (SGLT1) and of iodide (NIS). The dependence of substrate size studied at high resolution

    PubMed Central

    Zeuthen*, Thomas; Belhage, Bo; Zeuthen, Emil

    2006-01-01

    The relation between substrate and water transport was studied in Na+-coupled cotransporters of glucose (SGLT1) and of iodide (NIS) expressed in Xenopus oocytes. The water transport was monitored from changes in oocyte volume at a resolution of 20 pl, more than one order of magnitude better than previous investigations. The rate of cotransport was monitored as the clamp current obtained from two-electrode voltage clamp. The high resolution data demonstrated a fixed ratio between the turn-over of the cotransporter and the rate of water transport. This applied to experiments in which the rate of cotransport was changed by isosmotic application of substrate, by rapid changes in clamp voltage, or by poisoning. Transport of larger substrates gave rise to less water transport. For the rabbit SGLT1, 378 ± 20 (n = 18 oocytes) water molecules were cotransported along with the 2 Na+ ions and the glucose-analogue α-MDG (MW 194); using the larger sugar arbutin (MW 272) this number was reduced by a factor of at least 0.86 ± 0.03 (15). For the human SGLT1 the respective numbers were 234 ± 12 (18) and 0.85 ± 0.8 (7). For NIS, 253 ± 16 (12) water molecules were cotransported for each 2 Na+ and 1 thiocyanate (SCN−, MW 58), with I− as anion (MW 127) only 162 ± 11 (19) water molecules were cotransported. The effect of substrate size suggests a molecular mechanism for water cotransport and is opposite to what would be expected from unstirred layer effects. Data were analysed by a model which combined cotransport and osmosis at the membrane with diffusion in the cytoplasm. The combination of high resolution measurements and precise modelling showed that water transport across the membrane can be explained by cotransport of water in the membrane proteins and that intracellular unstirred layers effects are minute. PMID:16322051

  12. Interpretation of MSL REMS data using 1D coupled heat and water vapor transport model of Mars subsurface

    NASA Astrophysics Data System (ADS)

    Gloesener, Elodie; Karatekin, Özgür; Dehant, Véronique

    2016-04-01

    MSL Rover Environmental Monitoring Station (REMS) performed high-resolution measurements of temperature and relative humidity during more than one Martian year. In this work, a 1D subsurface model is used to study water vapor exchange between the atmosphere and the subsurface at Gale crater using REMS data. The thermal model used includes several layers of varying thickness with depth and properties that can be changed to correspond to those of Martian rocks at locations studied. It also includes the transport of water vapor through porous Martian regolith and the different phases considered are vapor, ice and adsorbed H2O. The total mass flux is given by the sum of diffusive and advective transport. The role of an adsorbing regolith on water transfer as well as the range of parameters with significant effect on water transport in Martian conditions are investigated. In addition, kinetics of the adsorption process is considered to examine its influence on the water vapor exchange between the subsurface and the atmosphere.

  13. Mobility of ions, sugar, and water in the cytoplasm of Xenopus oocytes expressing Na+-coupled sugar transporters (SGLT1)

    PubMed Central

    Zeuthen, Thomas; Zeuthen, Emil; Klaerke, Dan A

    2002-01-01

    A model was set up to study water transport in membrane proteins expressed in Xenopus oocytes. The model was tested experimentally using human and rabbit Na+-glucose cotransporters (SGLT1), and was used to explain controversies regarding unstirred layer effects. Cotransport of Na+, sugar and water was monitored by two-electrode voltage clamp and online measurements of oocyte volume. The specific resistance of the oocyte cytoplasm was found by means of microelectrodes to be 263 ± 91 Ω cm (s.d., n = 52), or 2.5 times that of Kulori medium, in agreement with reported values of intracellular ion concentrations and diffusion constants. Osmotically induced volume and resistance changes were compatible with a model of the oocyte in which 37 ± 17 % (s.d., n = 66) of the intracellular volume acts as a free solution while the remainder is inert, being occupied by organelles, etc. The model explains the results of several types of experiments: rapid changes in rates of water cotransport induced by changes in clamp voltage followed by osmotic equilibration in sugar-free conditions; volume changes induced by Na+ transport via the ionophore gramicidin; and uphill water transport. Ethanol (0.5 %) induced a marked swelling of the oocytes of about 16 pl s−1. If the specific inhibitor of SGLT1 phlorizin is added from stock solutions in ethanol, the effect of ethanol obfuscates the effects of the inhibitor. We conclude that the transport parameters derived for water cotransport by the SGLT1 can be attributed to the protein residing in the plasma membrane with no significant influences from unstirred layer effects. PMID:12096052

  14. Cation-Coupled Bicarbonate Transporters

    PubMed Central

    Aalkjaer, Christian; Boedtkjer, Ebbe; Choi, Inyeong; Lee, Soojung

    2016-01-01

    Cation-coupled HCO3− transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3− and associated with Na+ and Cl− movement. The first Na+-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na+-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na+-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3− transporters of the SLC4-family. PMID:25428855

  15. Cation-coupled bicarbonate transporters.

    PubMed

    Aalkjaer, Christian; Boedtkjer, Ebbe; Choi, Inyeong; Lee, Soojung

    2014-10-01

    Cation-coupled HCO3(-) transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3(-) and associated with Na(+) and Cl(-) movement. The first Na(+)-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na(+)-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na(+)-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3(-) transporters of the SLC4-family.

  16. Coordination and transport of water and carbohydrates in the coupled soil-root-xylem-phloem leaf system

    NASA Astrophysics Data System (ADS)

    Katul, Gabriel; Huang, Cheng-Wei

    2017-04-01

    In response to varying environmental conditions, stomatal pores act as biological valves that dynamically adjust their size thereby determining the rate of CO2 assimilation and water loss (i.e., transpiration) to the atmosphere. Although the significance of this biotic control on gas exchange is rarely disputed, representing parsimoniously all the underlying mechanisms responsible for stomatal kinetics remain a subject of some debate. It has been conjectured that stomatal control in seed plants (i.e., angiosperm and gymnosperm) represents a compromise between biochemical demand for CO2 and prevention of excessive water loss. This view has been amended at the whole-plant level, where xylem hydraulics and sucrose transport efficiency in phloem appear to impose additional constraints on gas exchange. If such additional constraints impact stomatal opening and closure, then seed plants may have evolved coordinated photosynthetic-hydraulic-sugar transporting machinery that confers some competitive advantages in fluctuating environmental conditions. Thus, a stomatal optimization model that explicitly considers xylem hydraulics and maximum sucrose transport is developed to explore this coordination in the leaf-xylem-phloem system. The model is then applied to progressive drought conditions. The main findings from the model calculations are that (1) the predicted stomatal conductance from the conventional stomatal optimization theory at the leaf and the newly proposed models converge, suggesting a tight coordination in the leaf-xylem-phloem system; (2) stomatal control is mainly limited by the water supply function of the soil-xylem hydraulic system especially when the water flux through the transpiration stream is significantly larger than water exchange between xylem and phloem; (3) thus, xylem limitation imposed on the supply function can be used to differentiate species with different water use strategy across the spectrum of isohydric to anisohydric behavior.

  17. Coupled Neutron Transport for HZETRN

    NASA Technical Reports Server (NTRS)

    Slaba, Tony C.; Blattnig, Steve R.

    2009-01-01

    Exposure estimates inside space vehicles, surface habitats, and high altitude aircrafts exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward-backward (FB) and directionally coupled forward-backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETC-HEDS, FLUKA, and MCNPX, and the DC model is shown to agree closely with the Monte Carlo results. Finally, it is found in the development of either model that the decoupling of low energy neutrons from the light particle transport procedure adversely affects low energy light ion fluence spectra and exposure quantities. A first order correction is presented to resolve the problem, and it is shown to be both accurate and efficient.

  18. Documentation and verification of VST2D; a model for simulating transient, Variably Saturated, coupled water-heat-solute Transport in heterogeneous, anisotropic 2-Dimensional, ground-water systems with variable fluid density

    USGS Publications Warehouse

    Friedel, Michael J.

    2001-01-01

    This report describes a model for simulating transient, Variably Saturated, coupled water-heatsolute Transport in heterogeneous, anisotropic, 2-Dimensional, ground-water systems with variable fluid density (VST2D). VST2D was developed to help understand the effects of natural and anthropogenic factors on quantity and quality of variably saturated ground-water systems. The model solves simultaneously for one or more dependent variables (pressure, temperature, and concentration) at nodes in a horizontal or vertical mesh using a quasi-linearized general minimum residual method. This approach enhances computational speed beyond the speed of a sequential approach. Heterogeneous and anisotropic conditions are implemented locally using individual element property descriptions. This implementation allows local principal directions to differ among elements and from the global solution domain coordinates. Boundary conditions can include time-varying pressure head (or moisture content), heat, and/or concentration; fluxes distributed along domain boundaries and/or at internal node points; and/or convective moisture, heat, and solute fluxes along the domain boundaries; and/or unit hydraulic gradient along domain boundaries. Other model features include temperature and concentration dependent density (liquid and vapor) and viscosity, sorption and/or decay of a solute, and capability to determine moisture content beyond residual to zero. These features are described in the documentation together with development of the governing equations, application of the finite-element formulation (using the Galerkin approach), solution procedure, mass and energy balance considerations, input requirements, and output options. The VST2D model was verified, and results included solutions for problems of water transport under isohaline and isothermal conditions, heat transport under isobaric and isohaline conditions, solute transport under isobaric and isothermal conditions, and coupled water

  19. Coupled transport in rotor models

    NASA Astrophysics Data System (ADS)

    Iubini, S.; Lepri, S.; Livi, R.; Politi, A.

    2016-08-01

    Steady nonequilibrium states are investigated in a one-dimensional setup in the presence of two thermodynamic currents. Two paradigmatic nonlinear oscillators models are investigated: an XY chain and the discrete nonlinear Schrödinger equation. Their distinctive feature is that the relevant variable is an angle in both cases. We point out the importance of clearly distinguishing between energy and heat flux. In fact, even in the presence of a vanishing Seebeck coefficient, a coupling between (angular) momentum and energy arises, mediated by the unavoidable presence of a coherent energy flux. Such a contribution is the result of the ‘advection’ induced by the position-dependent angular velocity. As a result, in the XY model, the knowledge of the two diagonal elements of the Onsager matrix suffices to reconstruct its transport properties. The analysis of the nonequilibrium steady states finally allows to strengthen the connection between the two models.

  20. Moss hair water transport

    NASA Astrophysics Data System (ADS)

    Pan, Zhao; Wu, Nan; Hurd, Randy; Thomson, Scott; Pitt, William; Truscott, Tadd

    2013-11-01

    We present an investigation of water transportation on a moss (Syntrichia caninervis) indigenous to temperate deserts. The moss typically appears to be in a dry, brown state, but is rehydrated by water during the wet season, making the desert green. Small hairs (500-2000 μm in length, and 40 μm in diameter, d) growing out from the tip of the moss leaves transport water back to the leaves. Through high speed observations and mathematical modeling it appears that this transportation is driven by two different mechanisms. 1) Droplet transport is achieved in three ways: i) A large (10d) droplet attached between two intersecting fibers will move toward the bases of the leaves by the changing angle between the two hairs. ii) The shape of the moss hair is conical, thicker at the base, producing a gradient that moves fluid (5d) toward the leaf similar to cactus spines. iii) We also observe that in some cases a Plateau-Rayleigh instability trigger a series of droplets moving toward the base. 2) Micro-grooves on the moss hair transport a film of water along the moss hair when larger droplets are not available. These various water transportation strategies combine to help the moss to survive in the desert and provide valuable insight.

  1. Water promoting electron hole transport between tyrosine and cysteine in proteins via a special mechanism: double proton coupled electron transfer.

    PubMed

    Chen, Xiaohua; Ma, Guangcai; Sun, Weichao; Dai, Hongjing; Xiao, Dong; Zhang, Yanfang; Qin, Xin; Liu, Yongjun; Bu, Yuxiang

    2014-03-26

    The proton/electron transfer reactions between cysteine residue (Cys) and tyrosinyl radical (Tyr(•)) are an important step for many enzyme-catalyzed processes. On the basis of the statistical analysis of protein data bank, we designed three representative models to explore the possible proton/electron transfer mechanisms from Cys to Tyr(•) in proteins. Our ab initio calculations on simplified models and quantum mechanical/molecular mechanical (QM/MM) calculations on real protein environment reveal that the direct electron transfer between Cys and Tyr(•) is difficult to occur, but an inserted water molecule can greatly promote the proton/electron transfer reactions by a double-proton-coupled electron transfer (dPCET) mechanism. The inserted H2O plays two assistant roles in these reactions. The first one is to bridge the side chains of Tyr(•) and Cys via two hydrogen bonds, which act as the proton pathway, and the other one is to enhance the electron overlap between the lone-pair orbital of sulfur atom and the π-orbital of phenol moiety and to function as electron transfer pathway. This water-mediated dPCET mechanism may offer great help to understand the detailed electron transfer processes between Tyr and Cys residues in proteins, such as the electron transfer from Cys439 to Tyr730(•) in the class I ribonucleotide reductase.

  2. Thermodynamically coupled mass transport processes in a saturated clay

    SciTech Connect

    Carnahan, C.L.

    1984-11-01

    Gradients of temperature, pressure, and fluid composition in saturated clays give rise to coupled transport processes (thermal and chemical osmosis, thermal diffusion, ultrafiltration) in addition to the direct processes (advection and diffusion). One-dimensional transport of water and a solute in a saturated clay subjected to mild gradients of temperature and pressure was simulated numerically. When full coupling was accounted for, volume flux (specific discharge) was controlled by thermal osmosis and chemical osmosis. The two coupled fluxes were oppositely directed, producing a point of stagnation within the clay column. Solute flows were dominated by diffusion, chemical osmosis, and thermal osmosis. Chemical osmosis produced a significant flux of solute directed against the gradient of solute concentration; this effect reduced solute concentrations relative to the case without coupling. Predictions of mass transport in clays at nuclear waste repositories could be significantly in error if coupled transport processes are not accounted for. 14 references, 8 figures, 1 table.

  3. Fuel cell water transport

    DOEpatents

    Vanderborgh, Nicholas E.; Hedstrom, James C.

    1990-01-01

    The moisture content and temperature of hydrogen and oxygen gases is regulated throughout traverse of the gases in a fuel cell incorporating a solid polymer membrane. At least one of the gases traverses a first flow field adjacent the solid polymer membrane, where chemical reactions occur to generate an electrical current. A second flow field is located sequential with the first flow field and incorporates a membrane for effective water transport. A control fluid is then circulated adjacent the second membrane on the face opposite the fuel cell gas wherein moisture is either transported from the control fluid to humidify a fuel gas, e.g., hydrogen, or to the control fluid to prevent excess water buildup in the oxidizer gas, e.g., oxygen. Evaporation of water into the control gas and the control gas temperature act to control the fuel cell gas temperatures throughout the traverse of the fuel cell by the gases.

  4. Coupled transport processes in semipermeable media

    SciTech Connect

    Carnahan, C.L.; Jacobsen, J.S.

    1990-04-01

    The thermodynamics of irreversible processes (TTIP) is used to derive governing equations and phenomenological equations for transport processes and chemical reactions in water-saturated semipermeable media. TTIP is based on three fundamental postulates. The first postulate, the assumption of local equilibrium, allows the formulation of balance equations for entropy. These equations are the bases for the derivation of governing equations for the thermodynamic variables, temperature, pressure, and composition. The governing equations involve vector fluxes of heat and mass and scalar rates of chemical reactions; in accordance with the second postulate of TTIP, these fluxes and rates are related, respectively, to all scalar driving forces (gradients of thermodynamic variables) acting within the system. The third postulate of TTIP states equality (the Onsager reciprocal relations) between certain of the phenomenological coefficients relating forces and fluxes. The description by TTIP of a system undergoing irreversible processes allows consideration of coupled transport processes such as thermal osmosis, chemical osmosis, and ultrafiltration. The coupled processes can make significant contributions to flows of mass and energy in slightly permeable, permselective geological materials such as clays and shales.

  5. Testing of a reactive transport processes module for a coupled (groundwater/surface water) physically based model on a vegetative buffer strip (Beaujolais, France).

    NASA Astrophysics Data System (ADS)

    Gatel, L.; Lauvernet, C.; Carluer, N.; Paniconi, C.

    2016-12-01

    In the context of the European Water Framework Directive (WFD, 2000/60/EC), which aims to achieve a good ecological and chemical status for all natural aquatic environments, tools to help understand and quantify pesticide transfers in agricultural watersheds are necessary. Models which are physically based and spatially distributed can be particularly useful for representing in detail processes and interactions between the soil surface and subsurface and thus to evaluate the management of landscape elements remediation. The present study aims to test and validate a recently added reactive transport to the coupled surface water/groundwater model CATHY, in order to represent pesticide transfers. Contaminant reactions implemented in CATHY for this study are linear adsorption and degradation (first order kinetics). The advection part of the model is solved according to the finite volume method and reactions are computed on volumes using a sequential non-iterative approach. The CATHY model has been tested on laboratory data and with a Morris sensitivity analysis and is applied now in real field conditions, on a vegetative buffer strip monitored by Irstea in a vineyard catchment (Beaujolais, France). The site is instrumented with lysimeters, flow and solute concentration measurement devices. This test represents a complex step into the model validation, initial and boundary conditions are not fully controlled, and field parameters measurement are not fully known.

  6. Modeling thermal dynamics of active layer soils and near-surface permafrost using a fully coupled water and heat transport model

    USGS Publications Warehouse

    Jiang, Yueyang; Zhuang, Qianlai; O'Donnell, Jonathan A.

    2012-01-01

    Thawing and freezing processes are key components in permafrost dynamics, and these processes play an important role in regulating the hydrological and carbon cycles in the northern high latitudes. In the present study, we apply a well-developed soil thermal model that fully couples heat and water transport, to simulate the thawing and freezing processes at daily time steps across multiple sites that vary with vegetation cover, disturbance history, and climate. The model performance was evaluated by comparing modeled and measured soil temperatures at different depths. We use the model to explore the influence of climate, fire disturbance, and topography (north- and south-facing slopes) on soil thermal dynamics. Modeled soil temperatures agree well with measured values for both boreal forest and tundra ecosystems at the site level. Combustion of organic-soil horizons during wildfire alters the surface energy balance and increases the downward heat flux through the soil profile, resulting in the warming and thawing of near-surface permafrost. A projection of 21st century permafrost dynamics indicates that as the climate warms, active layer thickness will likely increase to more than 3 meters in the boreal forest site and deeper than one meter in the tundra site. Results from this coupled heat-water modeling approach represent faster thaw rates than previously simulated in other studies. We conclude that the discussed soil thermal model is able to well simulate the permafrost dynamics and could be used as a tool to analyze the influence of climate change and wildfire disturbance on permafrost thawing.

  7. Water intensity of transportation.

    PubMed

    King, Carey W; Webber, Michael E

    2008-11-01

    As the need for alternative transportation fuels increases, it is important to understand the many effects of introducing fuels based upon feedstocks other than petroleum. Water intensity in "gallons of water per mile traveled" is one method to measure these effects on the consumer level. In this paper we investigate the water intensity for light duty vehicle (LDV) travel using selected fuels based upon petroleum, natural gas, unconventional fossil fuels, hydrogen, electricity, and two biofuels (ethanol from corn and biodiesel from soy). Fuels more directly derived from fossil fuels are less water intensive than those derived either indirectly from fossil fuels (e.g., through electricity generation) or directly from biomass. The lowest water consumptive (<0.15 gal H20/mile) and withdrawal (<1 gal H2O/mile) rates are for LDVs using conventional petroleum-based gasoline and diesel, nonirrigated biofuels, hydrogen derived from methane or electrolysis via nonthermal renewable electricity, and electricity derived from nonthermal renewable sources. LDVs running on electricity and hydrogen derived from the aggregate U.S. grid (heavily based upon fossil fuel and nuclear steam-electric power generation) withdraw 5-20 times and consume nearly 2-5 times more water than by using petroleum gasoline. The water intensities (gal H20/mile) of LDVs operating on biofuels derived from crops irrigated in the United States at average rates is 28 and 36 for corn ethanol (E85) for consumption and withdrawal, respectively. For soy-derived biodiesel the average consumption and withdrawal rates are 8 and 10 gal H2O/mile.

  8. Physiological and ecological implications of coupled heat and water transport mechanisms of endotherms and tundra vegetation. Progress report

    SciTech Connect

    Porter, W.P.; Stewart, W.E.

    1986-01-01

    This research seeks to extend a current quantitative general heat and mass transfer model developed for the porous insulation of endotherms to include the porous media of tundra vegetation, to test the model's predictions for endotherm heat generation requirements and water loss rates for different insulations under conditions measured in the laboratory and in the field on various inanimate objects and live endotherms, and to integrate the porous media model with microclimate models to calculate heat and mass fluxes through the low canopies of tundra vegetation and the soil. 9 refs., 6 figs.

  9. Diffusive Transport Properties Across Coupling Regimes

    NASA Astrophysics Data System (ADS)

    Dharuman, G.; Murillo, M. S.; Verboncoeur, J.; Christlieb, A.

    2014-10-01

    Transport properties are poorly known across coupling regimes, therefore understanding them is of importance for theoretical and practical reasons. A useful tool is an ultracold plasma system because of the experimental capability to tune the system to attain Coulomb coupling Γ ranging from 0.1 to 1 to 10 with the screening parameter κ ranging from 0 to 4 to 8, spanning the regions of the phase diagram from weak to moderate to strongly coupled and screened systems. Strong coupling is possible if Disorder Induced Heating is mitigated which requires a correlated initial ion state. Of particular interest is Rydberg blockaded gas of ultracold atoms where the local blockade effect results in correlations. Predictions of higher coupling in ultracold plasma created from a Rydberg blockaded gas have been reported. In this work we examine the diffusive transport properties of ultracold plasma system using molecular dynamics simulations for experimentally realizable values of Γ and κ as discussed above.

  10. Coupled electron-photon radiation transport

    SciTech Connect

    Lorence, L.; Kensek, R.P.; Valdez, G.D.; Drumm, C.R.; Fan, W.C.; Powell, J.L.

    2000-01-17

    Massively-parallel computers allow detailed 3D radiation transport simulations to be performed to analyze the response of complex systems to radiation. This has been recently been demonstrated with the coupled electron-photon Monte Carlo code, ITS. To enable such calculations, the combinatorial geometry capability of ITS was improved. For greater geometrical flexibility, a version of ITS is under development that can track particles in CAD geometries. Deterministic radiation transport codes that utilize an unstructured spatial mesh are also being devised. For electron transport, the authors are investigating second-order forms of the transport equations which, when discretized, yield symmetric positive definite matrices. A novel parallelization strategy, simultaneously solving for spatial and angular unknowns, has been applied to the even- and odd-parity forms of the transport equation on a 2D unstructured spatial mesh. Another second-order form, the self-adjoint angular flux transport equation, also shows promise for electron transport.

  11. Coupled experimetal and theoretical study of photon absorption and charge transport in BiVO4 photoanodes for solar water splitting

    NASA Astrophysics Data System (ADS)

    Ping, Yuan; Kim, Tae Woo; Galli, Giulia; Choi, Kyoung-Shin

    Bismuth vanadate (BiVO4) has been identified as one of the most promising photoanode materials for water-splitting photoelectrochemical cells. The major limitations of BiVO4 are its relatively wide bandgap (2.5 eV) and low electron mobility (0.2 cm-2V-2S-1), which limit its solar-to-hydrogen conversion efficiency. In this talk we will present the results of a coupled experimental and ab initio theoretical study showing that nitrogen doping together with extra oxygen vacancies lead to both a reduction of BiVO4 band gap and to an increase of the majority carrier density and mobility. In turn these improvements lead to the applied bias photon-to-current efficiency over 2%, a record for a single oxide photon absorber, to the best of our knowledge. The ``codoping'' method adopted in our work could also be applied to simultaneously enhance photon absorption and charge transport in other oxides, providing new possibilities for photocatalytic materials. This work was supported by the National Science Foundation (NSF) under the NSF Center (CHE-1305124). Computer time was provided by NERSC.

  12. Energy coupling mechanisms of MFS transporters

    PubMed Central

    Zhang, Xuejun C; Zhao, Yan; Heng, Jie; Jiang, Daohua

    2015-01-01

    Major facilitator superfamily (MFS) is a large class of secondary active transporters widely expressed across all life kingdoms. Although a common 12-transmembrane helix-bundle architecture is found in most MFS crystal structures available, a common mechanism of energy coupling remains to be elucidated. Here, we discuss several models for energy-coupling in the transport process of the transporters, largely based on currently available structures and the results of their biochemical analyses. Special attention is paid to the interaction between protonation and the negative-inside membrane potential. Also, functional roles of the conserved sequence motifs are discussed in the context of the 3D structures. We anticipate that in the near future, a unified picture of the functions of MFS transporters will emerge from the insights gained from studies of the common architectures and conserved motifs. PMID:26234418

  13. Coupled transport processes in semipermeable media

    SciTech Connect

    Jacobsen, J.S.; Carnahan, C.L.

    1990-03-01

    The thermodynamics of irreversible processes leads to nonlinear governing equations for direct and coupled mass transport processes. Analytical solutions of linearized versions of these equations can be used to verify numerical solutions of the nonlinear equations under conditions such that nonlinear terms are relatively small. This report presents derivations of the analytical solutions for one-dimensional and axisymmetric geometries. 7 refs.

  14. Lagrangian Transport in a coupled Chemistry Climate Model

    NASA Astrophysics Data System (ADS)

    Hoppe, C.; Müller, R.; Günther, G.; Hoffmann, L.

    2012-04-01

    We describe the implementation of a Lagrangian transport core in a chemistry climate model (CCM). This is motivated by the problem that in many cases trace gas distributions in the stratosphere can not be represented properly in a classical Eulerian framework with a fixed model grid, especially in regions where strong trace gas gradients occur. Here, we focus on stratospheric water vapor, which is an important driver of surface climate change on decadal scales. In this case, the transport representation is particularly important in the tropical tropopause layer (TTL), where tropospheric air enters into the stratosphere, i.e. , where the entry level of stratospheric water vapor is determined. For this purpose, the Chemical Lagrangian Model of the Stratosphere (CLaMS) is coupled with the ECHAM/MESSy Atmospheric Chemistry Model (EMAC). The latter includes the ECHAM5 climate model, and a coupling interface, which allows for flexible coupling and switching between different submodels. The chemistry transport model CLaMS provides a full Lagrangian transport representation to calculate constituent transport on a set of air parcels that move along trajectories. In the Lagrangian frame of reference, different vertical velocity representations can be used to drive the trajectories: - kinematic transport in isobaric coordinates with omega as vertical velocity, - diabatic transport in isentropic coordinates, where thetadot calculated from diabatic heatingrates is used as vertical velocity. Since vertical winds in the statosphere derived with the kinematic method from the continuity equation often suffer from excessive numerical noise and errors, we expect that constituent transport using the diabatic method will improve the simulations of stratospheric water vapor. We will present preliminary results illustrating how the different transport representations influence simulated tracer distributions.

  15. Mixing and transport. [Water pollution

    SciTech Connect

    Roberts, P.J.W.

    1982-06-01

    The mixing and transport of water pollution is the subject of this literature review with 110 references. The environmental transport of pollutants is examined in streams, rivers, reservoirs, ponds, estuaries, salt marshes and coastal waters. The dynamics of fluid flow, and the physical properties of jets, plumes, and stratified fluids are discussed. (KRM)

  16. Coupled transport processes in semipermeable media

    SciTech Connect

    Jacobsen, J.S.; Carnahan, C.L.

    1990-04-01

    A numerical simulator has been developed to investigate the effects of coupled processes on heat and mass transport in semipermeable media. The governing equations on which the simulator is based were derived using the thermodynamics of irreversible processes. The equations are nonlinear and have been solved numerically using the n-dimensional Newton's method. As an example of an application, the numerical simulator has been used to investigate heat and solute transport in the vicinity of a heat source buried in a saturated clay-like medium, in part to study solute transport in bentonite packing material surrounding a nuclear waste canister. The coupled processes considered were thermal filtration, thermal osmosis, chemical osmosis and ultrafiltration. In the simulations, heat transport by coupled processes was negligible compared to heat conduction, but pressure and solute migration were affected. Solute migration was retarded relative to the uncoupled case when only chemical osmosis was considered. When both chemical osmosis and thermal osmosis were included, solute migration was enhanced. 18 refs., 20 figs.

  17. Students' Conceptions of Water Transport

    ERIC Educational Resources Information Center

    Rundgren, Carl-Johan; Rundgren, Shu-Nu Chang; Schonborn, Konrad J.

    2010-01-01

    Understanding diffusion of water into and out of the cell through osmosis is fundamental to the learning and teaching of biology. Although this process is thought of as occurring directly across the lipid bilayer, the majority of water transport is actually mediated by specialised transmembrane water-channels called aquaporins. This study…

  18. Students' Conceptions of Water Transport

    ERIC Educational Resources Information Center

    Rundgren, Carl-Johan; Rundgren, Shu-Nu Chang; Schonborn, Konrad J.

    2010-01-01

    Understanding diffusion of water into and out of the cell through osmosis is fundamental to the learning and teaching of biology. Although this process is thought of as occurring directly across the lipid bilayer, the majority of water transport is actually mediated by specialised transmembrane water-channels called aquaporins. This study…

  19. Conformational changes couple Na+ and glucose transport

    PubMed Central

    Loo, Donald D. F.; Hirayama, Bruce A.; Gallardo, Elsa M.; Lam, Jason T.; Turk, Eric; Wright, Ernest M.

    1998-01-01

    The mechanism by which cotransport proteins couple their substrates across cell membranes is not known. A commonly proposed model is that cotransport results from ligand-induced conformational transitions that change the accessibility of ligand-binding sites from one side of the membrane to the other. To test this model, we have measured the accessibility of covalent probes to a cysteine residue (Q457C) placed in the putative sugar-translocation domain of the Na+/glucose cotransporter (SGLT1). The mutant protein Q457C was able to transport sugar, but transport was abolished after alkylation by methanethiosulfonate reagents. Alkylation blocked sugar translocation but not sugar binding. Accessibility of Q457C to alkylating reagents required external Na+ and was blocked by external sugar and phlorizin. The voltage dependence of accessibility was directly correlated with the presteady–state charge movement of SGLT1. Voltage-jump experiments with rhodamine-6-maleimide-labeled Q457C showed that the time course and level of changes in fluorescence closely followed the presteady–state charge movement. We conclude that conformational changes are responsible for the coupling of Na+ and sugar transport and that Q457 plays a critical role in sugar translocation by SGLT1. PMID:9636229

  20. Plasma transport theory spanning weak to strong coupling

    SciTech Connect

    Daligault, Jérôme; Baalrud, Scott D.

    2015-06-29

    We describe some of the most striking characteristics of particle transport in strongly coupled plasmas across a wide range of Coulomb coupling strength. We then discuss the effective potential theory, which is an approximation that was recently developed to extend conventional weakly coupled plasma transport theory into the strongly coupled regime in a manner that is practical to evaluate efficiently.

  1. Challenges in Coupling Acidity and Salinity Transport in Porous Media.

    PubMed

    McNeece, Colin J; Hesse, Marc A

    2017-09-26

    Salinity is an increasingly prescient issue in reactive transport, from low salinity water flooding to fracking brine leakage. Of primary concern is the effect of salinity on surface chemistry. Transport and batch experiments show a strong coupling of salinity and acidity through chemical interactions at the mineral-liquid interface. This coupling is ascribed to the combined effects of ionic strength on electrostatic behavior of the interface and competitive sorption between protons and other cations for binding sites on the surface. The effect of these mechanisms is well studied in batch settings and readily describes observed behavior. In contrast, the transport literature is sparse, primarily applied to synthetic materials, and offers only qualitative agreement with observations. To address, this gap in knowledge, we conduct a suite of column flood experiments through silica sand, systematically varying salinity and acidity conditions. Experiments are compared to a reactive transport model incorporating the proposed coupling mechanisms. The results highlight the difficulty in applying such models to realistic media under both basic and acidic conditions with a single set of parameters. The analysis and experimental results show the observed error is the result of electrostatic assumptions within the surface chemistry model and provide a strong constraint on further model development.

  2. High-resolution reactive transport: A coupled parallel hydrogeochemical model

    NASA Astrophysics Data System (ADS)

    Beisman, J. J.; Maxwell, R. M.; Steefel, C. I.; Sitchler, A.; Molins, S.

    2013-12-01

    Subsurface hydrogeochemical systems are an especially complex component of the terrestrial environment and play host to a multitude of interactions. Parameterizations of these interactions are perhaps the least understood component of terrestrial systems, presenting uncertainties in the predictive understanding of biogeochemical cycling and transport. Thorough knowledge of biogeochemical transport processes is critical to the quantification of carbon/nutrient fluxes in the subsurface, and to the development of effective contaminant remediation techniques. Here we present a coupled parallel hydrogeochemical model, ParCrunchFlow, as a tool to further our understanding of governing processes and interactions in natural hydrogeochemical systems. ParCrunchFlow is a coupling of the reactive transport simulator CrunchFlow with the hydrologic model ParFlow. CrunchFlow is a multicomponent reactive flow and transport code that can be used to simulate a range of important processes and environments, including reactive contaminant transport, chemical weathering, carbon sequestration, biogeochemical cycling, and water-rock interaction. ParFlow is a parallel, three-dimensional, variably-saturated, coupled surface-subsurface flow and transport code with the ability to simulate complex topography, geology, and heterogeneity. ParCrunchflow takes advantage of the efficient parallelism built into Parflow, allowing the numerical simulation of reactive transport processes in chemically and physically heterogeneous media at high spatial resolutions. This model provides an ability to further examine the interactions and feedbacks between biogeochemical systems and complex subsurface flow fields. In addition to the details of model construction, results will be presented that show floodplain nutrient cycling and the effects of heterogeneity on small-scale mixing reactions at the Department of Energy's Old Rifle Legacy site.

  3. A coupled energy transport and hydrological model for urban canopies

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Bou-Zeid, E.; Smith, J. A.

    2011-12-01

    Urban land-atmosphere interaction has been attracting more research efforts in order to understand the complex physics of flow and mass and heat transport in urban surfaces and the lower urban atmosphere. In this work, we developed and implemented a new physically-based single-layer urban canopy model, coupling the surface exchange of energy and the subsurface transport of water/soil moisture. The new model incorporates sub-facet heterogeneity for each urban surface (roof, wall or ground). This better simulates the energy transport in urban canopy layers, especially over low-intensity built (suburban type) terrains that include a significant fraction of vegetated surfaces. We implemented detailed urban hydrological models for both natural terrains (bare soil and vegetation) and porous engineered materials with water-holding capacity (concrete, gravel, etc). The skill of the new scheme was tested against experimental data collected through a wireless sensor network deployed over the campus of Princeton University. The model performance was found to be robust and insensitive to changes in weather conditions or seasonal variability. Predictions of the volumetric soil water content were also in good agreement with field measurements, highlighting the model capability of capturing subsurface water transport for urban lawns. The new model was also applied to a case study assessing different strategies, i.e. white versus green roofs, in the mitigation of urban heat island effect.

  4. Understanding the transport and fate of multiple pollutants: development and testing of a coupled surface-groundwater flow and water quality model

    NASA Astrophysics Data System (ADS)

    Sinha, Sumit; Wade, Andrew

    2017-04-01

    The problem of river pollutant diversity, especially in the south-east of UK, is typically associated with sediment, nutrients and micro-organic chemicals such as pesticides. The pollution problem is further exacerbated by climate change and population growth. Given this policy makers and environmental regulators need catchment scale water quantity and quality model that could be potentially used to assess multiple pollutants in catchments with a large groundwater contribution. The research presented here details development of a spatially explicit, coupled surface- groundwater model and its application in an exemplar lowland catchment in the south-east of UK with extensive surface and groundwater datasets available. More specifically, the fully distributed mesoscale hydrological model (mHM) is coupled with MODFLOW in the Enborne catchment (150 km2). Simulations are conducted on daily time step with spatial resolution of 1 km2 grid cell between 1970 and 2010. The spatially explicit nature of the modelling framework is being used to explore aquifer recharge and water and solute residence times to ultimately explore the lags between changes to pollutant loadings, the introduction of small-scale pollution control measures and the within stream response.

  5. Transport zonation limits coupled nitrification-denitrification in permeable sediments.

    PubMed

    Kessler, Adam J; Glud, Ronnie N; Cardenas, M Bayani; Cook, Perran L M

    2013-01-01

    Measurement of biogeochemical processes in permeable sediments (including the hyporheic zone) is difficult because of complex multidimensional advective transport. This is especially the case for nitrogen cycling, which involves several coupled redox-sensitive reactions. To provide detailed insight into the coupling between ammonification, nitrification and denitrification in stationary sand ripples, we combined the diffusion equilibrium thin layer (DET) gel technique with a computational reactive transport biogeochemical model. The former approach provided high-resolution two-dimensional distributions of NO3(-) and (15)N-N2 gas. The measured two-dimensional profiles correlate with computational model simulations, showing a deep pool of N2 gas forming, and being advected to the surface below ripple peaks. Further isotope pairing calculations on these data indicate that coupled nitrification-denitrification is severely limited in permeable sediments because the flow and transport field limits interaction between oxic and anoxic pore water. The approach allowed for new detailed insight into subsurface denitrification zones in complex permeable sediments.

  6. The human proton-coupled folate transporter

    PubMed Central

    Desmoulin, Sita Kugel; Hou, Zhanjun; Gangjee, Aleem; Matherly, Larry H.

    2012-01-01

    This review summarizes the biology of the proton-coupled folate transporter (PCFT). PCFT was identified in 2006 as the primary transporter for intestinal absorption of dietary folates, as mutations in PCFT are causal in hereditary folate malabsorption (HFM) syndrome. Since 2006, there have been major advances in understanding the mechanistic roles of critical amino acids and/or domains in the PCFT protein, many of which were identified as mutated in HFM patients, and in characterizing transcriptional control of the human PCFT gene. With the recognition that PCFT is abundantly expressed in human tumors and is active at pHs characterizing the tumor microenvironment, attention turned to exploiting PCFT for delivering novel cytotoxic antifolates for solid tumors. The finding that pemetrexed is an excellent PCFT substrate explains its demonstrated clinical efficacy for mesothelioma and non-small cell lung cancer, and prompted development of more PCFT-selective tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine antifolates that derive their cytotoxic effects by targeting de novo purine nucleotide biosynthesis. PMID:22954694

  7. Particles in Surface Waters: Coagulation and Transport.

    NASA Astrophysics Data System (ADS)

    Culkin, Gerald William

    Conventional water quality assessment and simulation of particles in natural waters focus on bulk concentrations of the suspended solid phase. These analyses rely directly or indirectly on a linear, 'average particle' approach to describe processes that are nonlinear and highly size -dependent. Size-dependent transport and transformation mechanisms were simulated in this research to identify conditions in which coagulation is important. Explicit finite difference schemes for two-dimensional, laterally-averaged, unsteady particle transport were developed to approximate the size -dependent particle transport processes, which included advection, dispersion, and settling. Coupled exchange of discrete particles between the water column and sediment bed was modeled using size-dependent particle sedimentation and resuspension. Simultaneous particle-particle flocculation was integrated over time in parallel with transport. Model simulations of systems with idealized morphometry and forcing provided greater insight to competing processes that drive particle behavior in natural systems. Application of the model to a real system gave plausible results and suggested explanations for observed conditions.

  8. Entrainment in coupled salt-water oscillators

    NASA Astrophysics Data System (ADS)

    Miyakawa, Kenji; Yamada, Kazuhiko

    1999-03-01

    The properties of coupling between two salt-water oscillators were studied. Two salt-water oscillators were coupled through the window of the partition wall. With an increase of the area of the window, the quasi-periodic mode, the in-phase mode, the bistable mode, and the out-of-phase mode appeared successively. A phase diagram of coupling was obtained in the plane of the area of the window and the diameter of the orifice of the cup. Furthermore, the effect of viscosity on coupling behaviors was investigated. In the boundary region between quasi-periodic coupling and in-phase coupling, the mode coupled with the phase difference of approximately π/4 was found. The experimental results were reproduced by the numerical simulation using coupled non-linear differential equations.

  9. Coupled transport of p24 family members.

    PubMed

    Emery, G; Rojo, M; Gruenberg, J

    2000-07-01

    Recent studies show that small trans-membrane proteins of approximately 22-24 kDa (the p24 family), which are grouped into 4 sub-families by sequence homology (p23, p24, p25 and p26), are involved in the early secretory pathway. In this study, we have investigated the mutual requirements of ectopically expressed members of the p24 family for targeting to their proper cellular destination. We find that coexpression of p23 and p24 is both necessary and sufficient for each protein to be transported to the cis-Golgi network/Golgi complex. Proteins from other subfamilies did not substitute for either p23 or p24, even after multiple coexpression. However, trafficking of the p23/p24 couple was facilitated by coexpression of proteins from other sub-families. In addition, we find that the sequence resembling an endoplasmic reticulum retrieval signal present in the cytoplasmic domain of p23 (but not p24) is dispensable. In contrast, the conserved coiled-coil region in the lumenal domain is absolutely required in both p23 and p24 for proper targeting of the p23/p24 couple. These data demonstrate that p23 and p24 must interact with each other to reach their destination, but that this strict requirement is combined with a mutual dependence amongst p24 proteins. We speculate that p24 proteins can form different oligomeric complexes, which contribute to confer specialized sorting/trafficking properties to membranes of the early secretory pathway, perhaps serving as membrane organizers.

  10. Water transport through welded tuff

    SciTech Connect

    Hadley, G.R.

    1984-08-01

    Water transport through welded tuff was studied with the aid of three drying experiments and one imbibition experiment performed on a single 0.15-m-long core. The specimen was saturated using a novel technique which measures the volume of water imbibed as a function of time in order to insure complete saturation. Profiles of saturation vs axial position along the core were provided by measuring the intensity of a beam of 662 keV gamma ray photons after passing through the sample in a direction normal to the axis of the cylinder. Measurements were made at different axial locations by moving the sample chamber past the beam with a precision translation table. Results indicate that the drying process is, in general, not characterized by a receding evaporation front as has been previously assumed, but rather by evaporation throughout the sample. Water appears to move through the sample under the action of both capillary forces and vapor pressure gradients induced by temperature gradients. Profiles resembling those of a receding evaporation front were observed when the temperature gradient was aligned in the direction of moisture transport. This work was performed in support of the Nevada Nulcear Waste Storage Investigation Project, which is responsible for examining the feasibility of siting a repository for commercial high-level nuclear wastes at Yucca Mountain and adjacent to the Nevada Test Site. 11 references, 9 figures.

  11. Development, Testing, and Application of a Coupled Hydrodynamic Surface-Water/Groundwater Model (FTLOADDS) with Heat and Salinity Transport in the Ten Thousand Islands/Picayune Strand Restoration Project Area, Florida

    USGS Publications Warehouse

    Swain, Eric D.; Decker, Jeremy D.

    2009-01-01

    A numerical model application was developed for the coastal area inland of the Ten Thousand Islands (TTI) in southwestern Florida using the Flow and Transport in a Linked Overland/Aquifer Density-Dependent System (FTLOADDS) model. This model couples a two-dimensional dynamic surface-water model with a three-dimensional groundwater model, and has been applied to several locations in southern Florida. The model application solves equations for salt transport in groundwater and surface water, and also simulates surface-water temperature using a newly enhanced heat transport algorithm. One of the purposes of the TTI application is to simulate hydrologic factors that relate to habitat suitability for the West Indian Manatee. Both salinity and temperature have been shown to be important factors for manatee survival. The inland area of the TTI domain is the location of the Picayune Strand Restoration Project, which is designed to restore predevelopment hydrology through the filling and plugging of canals, construction of spreader channels, and the construction of levees and pump stations. The effects of these changes are simulated to determine their effects on manatee habitat. The TTI application utilizes a large amount of input data for both surface-water and groundwater flow simulations. These data include topography, frictional resistance, atmospheric data including rainfall and air temperature, aquifer properties, and boundary conditions for tidal levels, inflows, groundwater heads, and salinities. Calibration was achieved by adjusting the parameters having the largest uncertainty: surface-water inflows, the surface-water transport dispersion coefficient, and evapotranspiration. A sensitivity analysis did not indicate that further parameter changes would yield an overall improvement in simulation results. The agreement between field data from GPS-tracked manatees and TTI application results demonstrates that the model can predict the salinity and temperature

  12. Distinct transport regimes for two elastically coupled molecular motors.

    PubMed

    Berger, Florian; Keller, Corina; Klumpp, Stefan; Lipowsky, Reinhard

    2012-05-18

    Cooperative cargo transport by two molecular motors involves an elastic motor-motor coupling, which can reduce the motors' velocity and/or enhance their unbinding from the filament. We show theoretically that these interference effects lead, in general, to four distinct transport regimes. In addition to a weak coupling regime, kinesin and dynein motors are found to exhibit a strong coupling and an enhanced unbinding regime, whereas myosin motors are predicted to attain a reduced velocity regime. All of these regimes, which we derive by explicit calculations and general time scale arguments, can be explored experimentally by varying the elastic coupling strength.

  13. Numerical and Experimental Quantification of coupled water and water vapor fluxes in very dry soils.

    NASA Astrophysics Data System (ADS)

    Madi, Raneem; de Rooij, Gerrit

    2015-04-01

    In arid and semi-arid regions with deep groundwater and very dry soils, vapor movement in the vadose zone may be a major component in the total water flux. Therefore, the coupled movement of liquid water, water vapor and heat transport in the unsaturated zone should be explicitly considered to quantify subsurface water fluxes in such regions. Only few studies focused on the importance of vapor water diffusion in dry soils and in many water flow studies in soil it was neglected. We are interested in the importance of water vapor diffusion and condensation in very dry sand. A version of Hydrus-1D capable of solving the coupled water vapor and heat transport equations will be used to do the numerical modeling. The soil hydraulic properties will be experimentally determined. A soil column experiment was developed with negligible liquid flow in order to isolate vapor flux for testing. We have used different values of initial water contents trying to generate different scenarios to assess the role of the water vapor transport in arid and semi-arid soils and how it changes the soil water content using different soil hydraulic parametrization functions. In the session a preliminary experimental and modelling results of vapor and water fluxes will be presented.

  14. Water transport by GLUT2 expressed in Xenopus laevis oocytes

    PubMed Central

    Zeuthen, Thomas; Zeuthen, Emil; MacAulay, Nanna

    2007-01-01

    The glucose transporter GLUT2 has been shown to also transport water. In the present paper we investigated the relation between sugar and water transport in human GLUT2 expressed in Xenopus oocytes. Sugar transport was determined from uptakes of non-metabolizable glucose analogues, primarily 3-O-methyl-d-glucopyranoside; key experimental results were confirmed using d(+)-glucose. Water transport was derived from changes in oocyte volume monitored at a high resolution (20 pl, 1 s). Expression of GLUT2 induced a sugar permeability, PS, of about 5 × 10−6 cm s−1 and a passive water permeability, Lp, of 5.5 × 10−5 cm s−1. Accordingly, the passive water permeability of a GLUT2 protein is about 10 times higher than its sugar permeability. Both permeabilities were abolished by phloretin. Isosmotic addition of sugar to the bathing solution (replacing mannitol) induced two parallel components of water influx in GLUT2, one by osmosis and one by cotransport. The osmotic driving force arose from sugar accumulation at the intracellular side of the membrane and was given by an intracellular diffusion coefficient for sugar of 10−6 cm2 s−1, one-fifth of the free solution value. The diffusion coefficient was determined in oocytes coexpressing GLUT2 and the water channel AQP1 where water transport was predominantly osmotic. By the cotransport mechanism about 35 water molecules were transported for each sugar molecule by a mechanism within the GLUT2. These water molecules could be transported uphill, against an osmotic gradient, energized by the flux of sugar. This capacity for cotransport is 10 times smaller than that of the Na+-coupled glucose transporters (SGLT1). The physiological role of GLUT2 for intestinal transport under conditions of high luminal sugar concentrations is discussed. PMID:17158169

  15. Transport optimization of coupled flashing ratchets in viscoelastic media

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Yan; Bao, Jing-Dong

    2017-08-01

    In the paper, we investigate the transport properties of coupled flashing ratchets in viscoelastic media. Using generalized Langevin equation, subvelocity Vα, subdiffusive coefficient Dα and generalized Peclet number Peα are calculated as functions of the temperature T and the flashing period τ with different subdiffusive exponents α. The results show that the transport of coupled flashing ratchets can be optimized in viscoelastic media.

  16. Transportation dynamics on coupled networks with limited bandwidth

    PubMed Central

    Li, Ming; Hu, Mao-Bin; Wang, Bing-Hong

    2016-01-01

    The communication networks in real world often couple with each other to save costs, which results in any network does not have a stand-alone function and efficiency. To investigate this, in this paper we propose a transportation model on two coupled networks with bandwidth sharing. We find that the free-flow state and the congestion state can coexist in the two coupled networks, and the free-flow path and congestion path can coexist in each network. Considering three bandwidth-sharing mechanisms, random, assortative and disassortative couplings, we also find that the transportation capacity of the network only depends on the coupling mechanism, and the fraction of coupled links only affects the performance of the system in the congestion state, such as the traveling time. In addition, with assortative coupling, the transportation capacity of the system will decrease significantly. However, the disassortative coupling has little influence on the transportation capacity of the system, which provides a good strategy to save bandwidth. Furthermore, a theoretical method is developed to obtain the bandwidth usage of each link, based on which we can obtain the congestion transition point exactly. PMID:27966624

  17. Transportation dynamics on coupled networks with limited bandwidth

    NASA Astrophysics Data System (ADS)

    Li, Ming; Hu, Mao-Bin; Wang, Bing-Hong

    2016-12-01

    The communication networks in real world often couple with each other to save costs, which results in any network does not have a stand-alone function and efficiency. To investigate this, in this paper we propose a transportation model on two coupled networks with bandwidth sharing. We find that the free-flow state and the congestion state can coexist in the two coupled networks, and the free-flow path and congestion path can coexist in each network. Considering three bandwidth-sharing mechanisms, random, assortative and disassortative couplings, we also find that the transportation capacity of the network only depends on the coupling mechanism, and the fraction of coupled links only affects the performance of the system in the congestion state, such as the traveling time. In addition, with assortative coupling, the transportation capacity of the system will decrease significantly. However, the disassortative coupling has little influence on the transportation capacity of the system, which provides a good strategy to save bandwidth. Furthermore, a theoretical method is developed to obtain the bandwidth usage of each link, based on which we can obtain the congestion transition point exactly.

  18. Transportation dynamics on coupled networks with limited bandwidth.

    PubMed

    Li, Ming; Hu, Mao-Bin; Wang, Bing-Hong

    2016-12-14

    The communication networks in real world often couple with each other to save costs, which results in any network does not have a stand-alone function and efficiency. To investigate this, in this paper we propose a transportation model on two coupled networks with bandwidth sharing. We find that the free-flow state and the congestion state can coexist in the two coupled networks, and the free-flow path and congestion path can coexist in each network. Considering three bandwidth-sharing mechanisms, random, assortative and disassortative couplings, we also find that the transportation capacity of the network only depends on the coupling mechanism, and the fraction of coupled links only affects the performance of the system in the congestion state, such as the traveling time. In addition, with assortative coupling, the transportation capacity of the system will decrease significantly. However, the disassortative coupling has little influence on the transportation capacity of the system, which provides a good strategy to save bandwidth. Furthermore, a theoretical method is developed to obtain the bandwidth usage of each link, based on which we can obtain the congestion transition point exactly.

  19. The maltose ABC transporter: action of membrane lipids on the transporter stability, coupling and ATPase activity.

    PubMed

    Bao, Huan; Dalal, Kush; Wang, Victor; Rouiller, Isabelle; Duong, Franck

    2013-08-01

    The coupling between ATP hydrolysis and substrate transport remains a key question in the understanding of ABC-mediated transport. We show using the MalFGK2 complex reconstituted into nanodiscs, that membrane lipids participate directly to the coupling reaction by stabilizing the transporter in a low energy conformation. When surrounded by short acyl chain phospholipids, the transporter is unstable and hydrolyzes large amounts of ATP without inducing maltose. The presence of long acyl chain phospholipids stabilizes the conformational dynamics of the transporter, reduces its ATPase activity and restores dependence on maltose. Membrane lipids therefore play an essential allosteric function, they restrict the transporter ATPase activity to increase coupling to the substrate. In support to the notion, we show that increasing the conformational dynamics of MalFGK2 with mutations in MalF increases the transporter ATPase activity but decreases the maltose transport efficiency.

  20. Modeling greenhouse gas emissions (CO2, N2O, CH4) from managed arable soils with a fully coupled hydrology-biogeochemical modeling system simulating water and nutrient transport and associated carbon and nitrogen cycling at catchment scale

    NASA Astrophysics Data System (ADS)

    Klatt, Steffen; Haas, Edwin; Kraus, David; Kiese, Ralf; Butterbach-Bahl, Klaus; Kraft, Philipp; Plesca, Ina; Breuer, Lutz; Zhu, Bo; Zhou, Minghua; Zhang, Wei; Zheng, Xunhua; Wlotzka, Martin; Heuveline, Vincent

    2014-05-01

    The use of mineral nitrogen fertilizer sustains the global food production and therefore the livelihood of human kind. The rise in world population will put pressure on the global agricultural system to increase its productivity leading most likely to an intensification of mineral nitrogen fertilizer use. The fate of excess nitrogen and its distribution within landscapes is manifold. Process knowledge on the site scale has rapidly grown in recent years and models have been developed to simulate carbon and nitrogen cycling in managed ecosystems on the site scale. Despite first regional studies, the carbon and nitrogen cycling on the landscape or catchment scale is not fully understood. In this study we present a newly developed modelling approach by coupling the fully distributed hydrology model CMF (catchment modelling framework) to the process based regional ecosystem model LandscapeDNDC for the investigation of hydrological processes and carbon and nitrogen transport and cycling, with a focus on nutrient displacement and resulting greenhouse gas emissions in a small catchment at the Yanting Agro-ecological Experimental Station of Purple Soil, Sichuan province, China. The catchment hosts cypress forests on the outer regions, arable fields on the sloping croplands cultivated with wheat-maize rotations and paddy rice fields in the lowland. The catchment consists of 300 polygons vertically stratified into 10 soil layers. Ecosystem states (soil water content and nutrients) and fluxes (evapotranspiration) are exchanged between the models at high temporal scales (hourly to daily) forming a 3-dimensional model application. The water flux and nutrients transport in the soil is modelled using a 3D Richards/Darcy approach for subsurface fluxes with a kinematic wave approach for surface water runoff and the evapotranspiration is based on Penman-Monteith. Biogeochemical processes are modelled by LandscapeDNDC, including soil microclimate, plant growth and biomass allocation

  1. Mathematical Simulation of Sediment and Radionuclide Transport in Surface Waters

    SciTech Connect

    ,

    1981-04-01

    The study objective of "The Mathematical Simulation of Sediment and Radionuclide Transport in Surface Waters" is to synthesize and test radionuclide transport models capable of realistically assessing radionuclide transport in various types of surface water bodies by including the sediment-radionuclide interactions. These interactions include radionuclide adsorption by sediment; desorption from sediment into water; and transport, deposition, and resuspension of sorbed radionuclides controlled by the sediment movements. During FY-1979, the modification of sediment and contaminant (radionuclide) transport model, FETRA, was completed to make it applicable to coastal waters. The model is an unsteady, two-dimensional (longitudinal and lateral) model that consists of three submodels (for sediment, dissolved-contaminant, and particulate-contaminant transport), coupled to include the sediment-contaminant interactions. In estuaries, flow phenomena and consequent sediment and radionuclide migration are often three-dimensional in nature mainly because of nonuniform channel cross-sections, salinity intrusion, and lateral-flow circulation. Thus, an unsteady, three-dimensional radionuclide transport model for estuaries is also being synthesized by combining and modifying a PNL unsteady hydrothermal model and FETRA. These two radionuclide transport models for coastal waters and estuaries will be applied to actual sites to examine the validity of the codes.

  2. Effects of diversity and coupling on transport properties of globally coupled active Brownian particles

    NASA Astrophysics Data System (ADS)

    Wu, Dan; Zhu, Shiqun

    2013-03-01

    Based on recent work [B. Lindner and E. M., Nicola, Phys. Rev. Lett. 101 (2008) 190603], the transport of N globally coupled Brownian motors with diversity is investigated. By applying the mean-field approximation, the effects of the diversity disturbance and the coupling strength on the transport of the coupled system are discussed both theoretically and numerically. It is found that the diversity reduces the diffusion dramatically for small bias and increases the diffusion gradually for large bias. The collective motion shows a resonant dependence on the coupling strength in a region of small bias.

  3. The Mechanism of Isotonic Water Transport

    PubMed Central

    Diamond, Jared M.

    1964-01-01

    The mechanism by which active solute transport causes water transport in isotonic proportions across epithelial membranes has been investigated. The principle of the experiments was to measure the osmolarity of the transported fluid when the osmolarity of the bathing solution was varied over an eightfold range by varying the NaCl concentration or by adding impermeant non-electrolytes. An in vitro preparation of rabbit gall bladder was suspended in moist oxygen without an outer bathing solution, and the pure transported fluid was collected as it dripped off the serosal surface. Under all conditions the transported fluid was found to approximate an NaCl solution isotonic to whatever bathing solution used. This finding means that the mechanism of isotonic water transport in the gall bladder is neither the double membrane effect nor co-diffusion but rather local osmosis. In other words, active NaCl transport maintains a locally high concentration of solute in some restricted space in the vicinity of the cell membrane, and water follows NaCl in response to this local osmotic gradient. An equation has been derived enabling one to calculate whether the passive water permeability of an organ is high enough to account for complete osmotic equilibration of actively transported solute. By application of this equation, water transport associated with active NaCl transport in the gall bladder cannot go through the channels for water flow under passive conditions, since these channels are grossly too impermeable. Furthermore, solute-linked water transport fails to produce the streaming potentials expected for water flow through these passive channels. Hence solute-linked water transport does not occur in the passive channels but instead involves special structures in the cell membrane, which remain to be identified. PMID:14212146

  4. Water transport with a carbon nanotube pump.

    PubMed

    Duan, Wen Hui; Wang, Quan

    2010-04-27

    Transportation of water molecules in a carbon nanotube based on an energy pump concept is investigated by molecular dynamics simulations. A small portion of the initially twisted wall of a carbon nanotube is employed to function as an energy pump for possible smooth transportation of water molecules. The momentum and resultant force on a water molecule and the corresponding displacement and velocity of the molecule are particularly studied to disclose the transportation process. The efficiency of the transportation is found to be dependent on the size of the energy pump. Once the process for the transportation of one molecule is elucidated, transportations of 20 water molecules are simulated to investigate the effect of the environmental temperature and fluctuations in the nanotube channel on the transportation. It is revealed that the accelerated period of multiple water molecules is longer than that in the transportation of a single water molecule. In addition, the fluctuations in the nanotube wall due to the buckling propagation and a higher environmental temperature will all lead to obvious decreases in the water velocity and hence retard the transportation process.

  5. The Physiological Relevance of Na+-Coupled K+-Transport.

    PubMed Central

    Maathuis, FJM.; Verlin, D.; Smith, F. A.; Sanders, D.; Fernandez, J. A.; Walker, N. A.

    1996-01-01

    Plant roots utilize at least two distinct pathways with high and low affinities to accumulate K+. The system for high-affinity K+ uptake, which takes place against the electrochemical K+ gradient, requires direct energization. Energization of K+ uptake via Na+ coupling has been observed in algae and was recently proposed as a mechanism for K+ uptake in wheat (Triticum aestivum L.). To investigate whether Na+ coupling has general physiological relevance in energizing K+ transport, we screened a number of species, including Arabidopsis thaliana L. Heynh. ecotype Columbia, wheat, and barley (Hordeum vulgare L.), for the presence of Na+-coupled K+ uptake. Rb+-flux analysis and electrophysiological K+-transport assays were performed in the presence and absence of Na+ and provided evidence for a coupling between K+ and Na+ transport in several aquatic species. However, all investigated terrestrial species were able to sustain growth and K+ uptake in the absence of Na+. Furthermore, the addition of Na+ was either without effect or inhibited K+ absorption. The latter characteristic was independent of growth conditions with respect to Na+ status and pH. Our results suggest that in terrestrial species Na+-coupled K+ transport has no or limited physiological relevance, whereas in certain aquatic angiosperms and algae this type of secondary transport energization plays a significant role. PMID:12226467

  6. Osmotic water transport in aquaporins: evidence for a stochastic mechanism

    PubMed Central

    Zeuthen, Thomas; Alsterfjord, Magnus; Beitz, Eric; MacAulay, Nanna

    2013-01-01

    We test a novel, stochastic model of osmotic water transport in aquaporins. A solute molecule present at the pore mouth can either be reflected or permeate the pore. We assume that only reflected solute molecules induce osmotic transport of water through the pore, while permeating solute molecules give rise to no water transport. Accordingly, the rate of water transport is proportional to the reflection coefficient σ, while the solute permeability, PS, is proportional to 1 –σ. The model was tested in aquaporins heterologously expressed in Xenopus oocytes. A variety of aquaporin channel sizes and geometries were obtained with the two aquaporins AQP1 and AQP9 and mutant versions of these. Osmotic water transport was generated by adding 20 mm of a range of different-sized osmolytes to the outer solution. The osmotic water permeability and the reflection coefficient were measured optically at high resolution and compared to the solute permeability obtained from short-term uptake of radio-labelled solute under isotonic conditions. For each type of aquaporin there was a linear relationship between solute permeability and reflection coefficient, in accordance with the model. We found no evidence for coupling between water and solute fluxes in the pore. In confirmation of molecular dynamic simulations, we conclude that the magnitude of the osmotic water permeability and the reflection coefficient are determined by processes at the arginine selectivity filter located at the outward-facing end of the pore. PMID:23959676

  7. A coupled nearfield and farfield large-eddy simulation for oil transport from deep-water blowouts - a study of the effects of dispersant in the Deepwater Horizon accident

    NASA Astrophysics Data System (ADS)

    Chamecki, M.; Chen, B.; Yang, D.; Meneveau, C. V.

    2016-12-01

    The Deepwater Horizon accident and the ensuing oil leak at 1.5 km depth in the Gulf of Mexico focused attention on the challenges associated with underwater blowouts in the deep ocean. The strategy adopted for use of chemical dispersants during the leak was, and it still is, one of the most controversial points in the response effort. This work investigates the effects of dispersant applications to oil transport using idealized high-resolution numerical simulations. Deep-water blowouts generate plumes of oil droplets and gas bubbles that rise through, and interact with, various layers of the ocean. The different scales and physical processes governing the dynamics of the oil plume at each layer require different numerical simulation strategies. We develop a high-fidelity turbulence-resolving numerical model using the large-eddy simulation technique which consists of two modules targeting two distinguished stages of the oil plume dispersion: "nearfiled" and "farfield". The "nearfield module" simulates the dynamics of the multiphase plume containing gas bubbles and oil droplets originating from the oil well and rising through the 1.5 km stratified water column. The formation of deep-water intrusions and the separation of oil and gas plumes due to weak crossflow is captured by LES. As the oil plume approaches the bottom of the ocean mixed layer, the "farfield module" takes over and simulates the near-surface oil transport using a new numerical approach called ENDLESS (extended nonperiodic domain LES for scalars) to accommodate the fairly large horizontal extent of the plume. ENDLESS is a multiscale plume modeling approach, which permits simulations of oil plumes including effects of submesoscale eddies, surface waves, Langmuir cells, and 3D small-scale turbulence with reasonable computing power. The two simulation modules are coupled, allowing the representation of the entire plume in a turbulence-resolving context. Simulations are performed to elucidate the effect of

  8. MODELING COUPLED HYDROLOGICAL AND CHEMICAL PROCESSES: LONG-TERM URANIUM TRANSPORT FOLLOWING PHOSPHOROUS-FERTILIZATION

    USDA-ARS?s Scientific Manuscript database

    Contaminants in the vadose zone are affected by the physical processes of water flow, heat movement and multicomponent transport, as well as generally by a range of interacting biogeochemical processes. Coupling these various processes within one integrated numerical simulator provides a process-ba...

  9. Plant water relations I: uptake and transport

    USDA-ARS?s Scientific Manuscript database

    Plants, like all living things, are mostly water. Water is the matrix of life, and its availability determines the distribution and productivity of plants on earth. Vascular plants evolved structures that enable them to transport water long distances with little input of energy, but the hollow trach...

  10. Transport of radon in still water

    NASA Astrophysics Data System (ADS)

    Syahrir

    2005-11-01

    A new method was developed to measure the effectiveness of water in reducing the release of radon emanating from 226Ra-bearing sand into air. Fick's law on diffusion was used to model the transport of radon in water including the impact associated with radioactive decay. A multi-region, one-dimensional, steady-state transport model was used to analyze the movement of radon through a sequential column of air, water and air. An effective diffusion coefficient was determined by varying the thickness of the water column to predict the transport of 222Rn through particular thickness of water. A one-region, one-dimensional transient diffusion equation was developed to investigate the build up of radon at the end of the water column until a steady-state, equilibrium condition was achieved. This build up with time is characteristic of the transport rate of radon in water and established the basis for estimating the effective diffusion coefficient for 222 Rn in water. The results suggest that convective forces other than molecular diffusion impact the transport of 222Rn through the water barrier. An effective diffusion coefficient is defined that includes effects of molecular diffusion and convection to describe the transport of radon in water. Several experimental arrangements were evaluated to examine the influence of physical parameters on the radon transport. The effective diffusion coefficients measured in these experiments are 6.8 x 10 -4 +/- 28% and 3.5 x 10-4 +/- 34% cm2 sec-1 for the steady-state and transient diffusion approaches, respectively. Water barriers ranging in thickness from 30--50 cm reduce the amount of radon released from the radium-bearing source material by a factor of 0.3--0.1, respectively.

  11. Quantum transport in coupled resonators enclosed synthetic magnetic flux

    NASA Astrophysics Data System (ADS)

    Jin, L.

    2016-07-01

    Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov-Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms.

  12. Transport signatures in topological systems coupled to ac fields

    NASA Astrophysics Data System (ADS)

    Ruocco, Leonard; Gómez-León, Álvaro

    2017-02-01

    We study the transport properties of a topological system coupled to an ac electric field by means of Floquet-Keldysh formalism. We consider a semi-infinite chain of dimers coupled to a semi-infinite metallic lead and obtain the density of states and current when the system is out of equilibrium. Our formalism is nonperturbative and allows us to explore, in the thermodynamic limit, a wide range of regimes for the ac field, arbitrary values of the coupling strength to the metallic contact and corrections to the wide-band limit (WBL). We find that hybridization with the contact can change the dimerization phase, and that the current dependence on the field amplitude can be used to discriminate between them. We also show the appearance of side bands and nonequilibrium zero-energy modes, characteristic of the Floquet systems. Our results directly apply to the stability of nonequilibrium topological phases, when transport measurements are used for their detection.

  13. Variations of Connecticut River Water Pathways and Its Water Age: A Coupled Modeling Study

    NASA Astrophysics Data System (ADS)

    Jia, Y.; Whitney, M. M.

    2016-02-01

    As the largest freshwater source to the east-west oriented Long Island Sound (LIS), the Connecticut River (CR) delivers water on the north shore near the sound's mouth. The pathways the river water follows through LIS are impacted by river discharge, tides, winds, and complex topography. Using the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System, with passive dyes and age tracers, the main routes of CR water through the estuary and onto the shelf are determined with their corresponding time scales. During a high discharge period, the CR plume occupies the northern half of eastern LIS and extends farther west than during average discharge conditions. Most of the river water inside the central LIS is transported through this surface plume. After being mixed to deeper depths and farther offshore, the river water that is still within LIS is transported westward. During periods of low discharge, freshwater is initially more prevalent between the CR and the LIS mouth. Later, CR water mixed to depths still moves westward, reaching the estuary's head in approximately 3 weeks. Neap tide allows more CR water to quickly escape to the open shelf through Block Island Sound (BIS) while spring tide allows more CR water back into the central LIS at depth. BIS has a uniform water age ranging from 40 to 50 days throughout the water column. Lower discharge leads to older age in BIS. In western LIS, CR water age at depth increases from 50 to 75 days as discharge decreases and is several days younger than water closer to the surface. These results suggest a bottom-in/surface-out transport pattern exists for CR water in LIS for at least part of the year.

  14. Turbulent Water Coupling in Shock Wave Lithotripsy

    PubMed Central

    Lautz, Jaclyn; Sankin, Georgy; Zhong, Pei

    2013-01-01

    Previous studies have demonstrated that stone comminution decreases with increased pulse repetition frequency as a result of bubble proliferation in the cavitation field of a shock wave lithotripter (Pishchalnikov et al., 2011). If cavitation nuclei remain in the propagation path of successive lithotripter pulses, especially in the acoustic coupling cushion of the shock wave source, they will consume part of the incident wave energy, leading to reduced tensile pressure in the focal region and thus lower stone comminution efficiency. We introduce a method to remove cavitation nuclei from the coupling cushion between successive shock exposures using a jet of degassed water. As a result, pre-focal bubble nuclei lifetime quantified by B-mode ultrasound imaging was reduced from 7 s to 0.3 s by a jet with an exit velocity of 62 cm/s. Stone fragmentation (percent mass < 2 mm) after 250 shocks delivered at 1 Hz was enhanced from 22 ± 6% to 33 ± 5% (p = 0.007) in water without interposing tissue mimicking materials. Stone fragmentation after 500 shocks delivered at 2 Hz was increased from 18 ± 6% to 28 ± 8% (p = 0.04) with an interposing tissue phantom of 8 cm thick. These results demonstrate the critical influence of cavitation bubbles in the coupling cushion on stone comminution and suggest a potential strategy to improve the efficacy of contemporary shock wave lithotripters. PMID:23322027

  15. Turbulent water coupling in shock wave lithotripsy.

    PubMed

    Lautz, Jaclyn; Sankin, Georgy; Zhong, Pei

    2013-02-07

    Previous studies have demonstrated that stone comminution decreases with increased pulse repetition frequency as a result of bubble proliferation in the cavitation field of a shock wave lithotripter (Pishchalnikov et al 2011 J. Acoust. Soc. Am. 130 EL87-93). If cavitation nuclei remain in the propagation path of successive lithotripter pulses, especially in the acoustic coupling cushion of the shock wave source, they will consume part of the incident wave energy, leading to reduced tensile pressure in the focal region and thus lower stone comminution efficiency. We introduce a method to remove cavitation nuclei from the coupling cushion between successive shock exposures using a jet of degassed water. As a result, pre-focal bubble nuclei lifetime quantified by B-mode ultrasound imaging was reduced from 7 to 0.3 s by a jet with an exit velocity of 62 cm s(-1). Stone fragmentation (percent mass <2 mm) after 250 shocks delivered at 1 Hz was enhanced from 22 ± 6% to 33 ± 5% (p = 0.007) in water without interposing tissue mimicking materials. Stone fragmentation after 500 shocks delivered at 2 Hz was increased from 18 ± 6% to 28 ± 8% (p = 0.04) with an interposing tissue phantom of 8 cm thick. These results demonstrate the critical influence of cavitation bubbles in the coupling cushion on stone comminution and suggest a potential strategy to improve the efficacy of contemporary shock wave lithotripters.

  16. Quantum transport in coupled resonators enclosed synthetic magnetic flux

    SciTech Connect

    Jin, L.

    2016-07-15

    Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov–Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms. -- Highlights: •The light transport is investigated through ring array of coupled resonators enclosed synthetic magnetic field. •Aharonov–Bohm ring interferometer of arbitrary configuration is investigated. •The half-integer magnetic flux quantum leads to destructive interference and transmission zeros for two-arm at equal length. •Complete transmission is available via tuning synthetic magnetic flux.

  17. Coupled surface-water and ground-water model

    USGS Publications Warehouse

    Swain, Eric D.; Wexler, Eliezer J.

    1991-01-01

    In areas with dynamic and hydraulically well connected ground-water and surface-water systems, it is desirable that stream-aquifer interaction be simulated with models of equal sophistication and accuracy. Accordingly, a new, coupled ground-water and surface-water model was developed by combining the U.S. Geological Survey models MODFLOW and BRANCH. MODFLOW is the widely used modular three-dimensional, finite-difference, ground-water model and BRANCH is a one-dimensional numerical model commonly used to simulate flow in open-channel networks. Because time steps used in ground-water modeling commonly are much longer than those used in surface-water simulations, provision has been made for handling multiple BRANCH time steps within one MODFLOW time step. Verification testing of the coupled model was done using data from previous studies and by comparing results with output from a simpler four-point implicit open-channel flow model linked with MODFLOW.

  18. Linking phloem function to structure: analysis with a coupled xylem-phloem transport model.

    PubMed

    Hölttä, T; Mencuccini, M; Nikinmaa, E

    2009-07-21

    We carried out a theoretical analysis of phloem transport based on Münch hypothesis by developing a coupled xylem-phloem transport model. Results showed that the maximum sugar transport rate of the phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the phloem. Because xylem water potential affected both xylem and phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the phloem and vice versa.

  19. Effective Potential Theory for Transport Coefficients across Coupling Regimes

    NASA Astrophysics Data System (ADS)

    Baalrud, Scott D.

    2013-10-01

    Plasmas in several modern experiments, including dense, ultracold and dusty plasmas, can reach strong coupling where the Coulomb potential energy of interacting particles exceeds their average kinetic energy. Understanding how the many-body physics of correlations affects plasma transport properties in this regime is interesting both from a basic physics standpoint and as a practical matter. Transport coefficients are essential input required for accurate hydrodynamic modeling of these systems, which can include weakly coupled and strongly coupled components simultaneously. We discuss a physically motivated extension of plasma transport theory that is computationally efficient and versatile enough that it can be applied to essentially any transport property. Like conventional plasma theories, ours is based on a binary collision picture, but where particles interact via an effective potential that accounts for average affects of the intervening medium. This includes both correlations and screening. Hypernetted chain (HNC) theory, which is a well-established approximation for the pair correlation function, is used to derive the effective potential. The theory is shown to compare well with ion velocity relaxation in an ultracold plasma experiment, as well as classical molecular dynamics simulations of temperature relaxation in electron-ion plasmas, and diffusion in both one-component plasmas and ionic mixtures. This research was conducted in collaboration with Jerome Daligault and was supported by a Richard P. Feynman Postdoctoral Fellowship and the LDRD program at Los Alamos National Laboratory.

  20. Transport properties of elastically coupled fractional Brownian motors

    NASA Astrophysics Data System (ADS)

    Lv, Wangyong; Wang, Huiqi; Lin, Lifeng; Wang, Fei; Zhong, Suchuan

    2015-11-01

    Under the background of anomalous diffusion, which is characterized by the sub-linear or super-linear mean-square displacement in time, we proposed the coupled fractional Brownian motors, in which the asymmetrical periodic potential as ratchet is coupled mutually with elastic springs, and the driving source is the external harmonic force and internal thermal fluctuations. The transport mechanism of coupled particles in the overdamped limit is investigated as the function of the temperature of baths, coupling constant and natural length of the spring, the amplitude and frequency of driving force, and the asymmetry of ratchet potential by numerical stimulations. The results indicate that the damping force involving the information of historical velocity leads to the nonlocal memory property and blocks the traditional dissipative motion behaviors, and it even plays a cooperative role of driving force in drift motion of the coupled particles. Thus, we observe various non-monotonic resonance-like behaviors of collective directed transport in the mediums with different diffusion exponents.

  1. Transport Theory for Shallow Water Propagation with Rough Boundaries

    SciTech Connect

    Thorsos, Eric I.; Henyey, Frank S.; Elam, W. T.; Hefner, Brian T.; Reynolds, Stephen A.; Yang Jie

    2010-09-06

    At frequencies of about 1 kHz and higher, forward scattering from a rough sea surface (and/or a rough bottom) can strongly affect shallow water propagation and reverberation. The need exists for a fast, yet accurate method for modeling such propagation where multiple forward scattering occurs. A transport theory method based on mode coupling is described that yields the first and second moments of the field. This approach shows promise for accurately treating multiple forward scattering in one-way propagation. The method is presently formulated in two space dimensions, and Monte-Carlo rough surface PE simulations are used for assessing the accuracy of transport theory results.

  2. News and views on mitochondrial water transport.

    PubMed

    Gena, Patrizia; Fanelli, Elena; Brenner, Catherine; Svelto, Maria; Calamita, Giuseppe

    2009-01-01

    The osmotic movement of water into and out of the mitochondrial matrix underlies the extraordinary plasticity that characterizes mitochondria, a feature of pivotal importance to cell bioenergetics and signaling, and of critical relevance to life-and-death cell decision. However, the biophysics and identity of mitochondrial water transport had remained mostly unexplored, until recent works suggesting high water permeability and the presence of multiple facilitated pathways of water diffusion in liver mitochondria. Here, we attempt to summarize our current view of the mechanisms of mitochondrial water transport and possible relevance of the channel-mediated pathways created by mitochondrial permeability transition, aquaporins and protein/lipid specializations. Assessing the molecular bases and dynamics of mitochondrial water permeability will help to answer the much-debated question over the role of mitochondria.

  3. Validation of a coupled reactive transport code in porous media

    NASA Astrophysics Data System (ADS)

    Mugler, C.; Montarnal, P.; Dimier, A.

    2003-04-01

    The safety assessment of nuclear waste disposals needs to predict the migration of radionuclides and chemical species through a geological medium. It is therefore necessary to develop and assess qualified and validated tools which integrate both the transport mechanisms through the geological media and the chemical mechanisms governing the mobility of radionuclides. In this problem, both geochemical and hydrodynamic phenomena are tightly linked together. That is the reason why the French Nuclear Energy Agency (CEA) and the French Agency for the Management of Radioactive Wastes (ANDRA) are conjointly developping a coupled reactive transport code that solves simultaneously a geochemical model and a transport model. This code, which is part of the software project ALLIANCES, leans on the libraries of two geochemical codes solving the complex ensemble of reacting chemical species: CHESS and PHREEQC. Geochemical processes considered here include ion exchange, redox reactions, acid-base reactions, surface complexation and mineral dissolution and/or precipitation. Transport is simulated using the mixed-hybrid finite element scheme CAST3M or the finite volume scheme MT3D. All together solve Darcy's law and simulate several hydrological processes such as advection, diffusion and dispersion. The coupling algorithm is an iterative sequential algorithm. Several analytical test cases have been defined and used to validate the reactive transport code. Numerical results can be compared to analytical solutions.

  4. [Research advances in simulating land water-carbon coupling].

    PubMed

    Liu, Ning; Sun, Peng-Sen; Liu, Shi-Rong

    2012-11-01

    The increasing demand of adaptive management of land, forest, and water resources under the background of global change and water resources crisis has promoted the comprehensive study of coupling ecosystem water and carbon cycles and their restrictive relations. To construct the water-carbon coupling model and to approach the ecosystem water-carbon balance and its interactive response mechanisms under climate change at multiple spatiotemporal scales is nowadays a major concern. After reviewing the coupling relationships of water and carbon at various scales, this paper explored the implications and estimation methods of the key processes and related parameters of water-carbon coupling, the construction of evapotranspiration model at large scale based on RS, and the importance of this model in water-carbon coupling researches. The applications of assimilative multivariate data in water-carbon coupling researches under future climate change scenarios were also prospected.

  5. Ion sampling and transport in Inductively Coupled Plasma Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Farnsworth, Paul B.; Spencer, Ross L.

    2017-08-01

    Quantitative accuracy and high sensitivity in inductively coupled plasma mass spectrometry (ICP-MS) depend on consistent and efficient extraction and transport of analyte ions from an inductively coupled plasma to a mass analyzer, where they are sorted and detected. In this review we examine the fundamental physical processes that control ion sampling and transport in ICP-MS and compare the results of theory and computerized models with experimental efforts to characterize the flow of ions through plasma mass spectrometers' vacuum interfaces. We trace the flow of ions from their generation in the plasma, into the sampling cone, through the supersonic expansion in the first vacuum stage, through the skimmer, and into the ion optics that deliver the ions to the mass analyzer. At each stage we consider idealized behavior and departures from ideal behavior that affect the performance of ICP-MS as an analytical tool.

  6. Analysis of coupled heat and moisture transport on parallel computers

    NASA Astrophysics Data System (ADS)

    Koudelka, Tomáš; Krejčí, Tomáš

    2017-07-01

    Coupled analysis of heat and moisture transport in complicated structural elements or in whole structures deserves a special attention because after space discretization, large number of degrees of freedom are needed. This paper describes possible solution of such problems based on domain decomposition methods executed on parallel computers. The Schur complement method is used with respect to nonsymmetric systems of algebraic equations. The method described is an alternative to other methods, e.g. two or more scale homogenization.

  7. Electron Transport in Water Vapour

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Satoru; Satoh, Kohki; Itoh, Hidenori

    2015-09-01

    Sets of electron collision cross sections for water vapour previously reported are examined by comparing calculated electron swarm parameters with measured parameters. Further, reliable cross section set of water vapour is estimated by the electron swarm method using Monte Carlo simulation to ensure the accuracy of the swarm parameter calculation. The values of an electron drift velocity, a longitudinal diffusion coefficient, and an effective ionisation coefficient calculated from Yousfi and Benabdessadok's set and those calculated from Itikawa and Mason's set do not necessarily agree with measured data. A new cross section set of water vapour, which consists of three kinds of rotational excitation, two kinds of vibrational excitation, three kinds of electron attachment, twenty-six kinds of electronic excitation, and six kinds of ionisation cross sections, and an elastic collision cross section, is estimated, and an anisotropic electron scattering for elastic and rotational excitation collision is considered. The swarm parameters calculated from the estimated cross section set is in good agreement with measured data in a wide range of reduced electric field.

  8. Revised Ion/Substrate Coupling Stoichiometry of GABA Transporters.

    PubMed

    Eskandari, Sepehr; Willford, Samantha L; Anderson, Cynthia M

    2017-01-01

    The purpose of this review is to highlight recent evidence in support of a 3 Na(+): 1 Cl(-): 1 GABA coupling stoichiometry for plasma membrane GABA transporters (SLC6A1 , SLC6A11 , SLC6A12 , SLC6A13 ) and how the revised stoichiometry impacts our understanding of the contribution of GABA transporters to GABA homeostasis in synaptic and extrasynaptic regions in the brain under physiological and pathophysiological states. Recently, our laboratory probed the GABA transporter stoichiometry by analyzing the results of six independent measurements, which included the shifts in the thermodynamic transporter reversal potential caused by changes in the extracellular Na(+), Cl(-), and GABA concentrations, as well as the ratio of charge flux to substrate flux for Na(+), Cl(-), and GABA under voltage-clamp conditions. The shifts in the transporter reversal potential for a tenfold change in the external concentration of Na(+), Cl(-), and GABA were 84 ± 4, 30 ± 1, and 29 ± 1 mV, respectively. Charge flux to substrate flux ratios were 0.7 ± 0.1 charges/Na(+), 2.0 ± 0.2 charges/Cl(-), and 2.1 ± 0.1 charges/GABA. We then compared these experimental results with the predictions of 150 different transporter stoichiometry models, which included 1-5 Na(+), 0-5 Cl(-), and 1-5 GABA per transport cycle. Only the 3 Na(+): 1 Cl(-): 1 GABA stoichiometry model correctly predicts the results of all six experimental measurements. Using the revised 3 Na(+): 1 Cl(-): 1 GABA stoichiometry, we propose that the GABA transporters mediate GABA uptake under most physiological conditions. Transporter-mediated GABA release likely takes place under pathophysiological or extreme physiological conditions.

  9. Coupled ATPase-adenylate kinase activity in ABC transporters.

    PubMed

    Kaur, Hundeep; Lakatos-Karoly, Andrea; Vogel, Ramona; Nöll, Anne; Tampé, Robert; Glaubitz, Clemens

    2016-12-22

    ATP-binding cassette (ABC) transporters, a superfamily of integral membrane proteins, catalyse the translocation of substrates across the cellular membrane by ATP hydrolysis. Here we demonstrate by nucleotide turnover and binding studies based on (31)P solid-state NMR spectroscopy that the ABC exporter and lipid A flippase MsbA can couple ATP hydrolysis to an adenylate kinase activity, where ADP is converted into AMP and ATP. Single-point mutations reveal that both ATPase and adenylate kinase mechanisms are associated with the same conserved motifs of the nucleotide-binding domain. Based on these results, we propose a model for the coupled ATPase-adenylate kinase mechanism, involving the canonical and an additional nucleotide-binding site. We extend these findings to other prokaryotic ABC exporters, namely LmrA and TmrAB, suggesting that the coupled activities are a general feature of ABC exporters.

  10. Coupled ATPase-adenylate kinase activity in ABC transporters

    PubMed Central

    Kaur, Hundeep; Lakatos-Karoly, Andrea; Vogel, Ramona; Nöll, Anne; Tampé, Robert; Glaubitz, Clemens

    2016-01-01

    ATP-binding cassette (ABC) transporters, a superfamily of integral membrane proteins, catalyse the translocation of substrates across the cellular membrane by ATP hydrolysis. Here we demonstrate by nucleotide turnover and binding studies based on 31P solid-state NMR spectroscopy that the ABC exporter and lipid A flippase MsbA can couple ATP hydrolysis to an adenylate kinase activity, where ADP is converted into AMP and ATP. Single-point mutations reveal that both ATPase and adenylate kinase mechanisms are associated with the same conserved motifs of the nucleotide-binding domain. Based on these results, we propose a model for the coupled ATPase-adenylate kinase mechanism, involving the canonical and an additional nucleotide-binding site. We extend these findings to other prokaryotic ABC exporters, namely LmrA and TmrAB, suggesting that the coupled activities are a general feature of ABC exporters. PMID:28004795

  11. Electron transport in coupled double quantum wells and wires

    SciTech Connect

    Harff, N.E.; Simmons, J.A.; Lyo, S.K.

    1997-04-01

    Due to inter-quantum well tunneling, coupled double quantum wells (DQWs) contain an extra degree of electronic freedom in the growth direction, giving rise to new transport phenomena not found in single electron layers. This report describes work done on coupled DQWs subject to inplane magnetic fields B{sub {parallel}}, and is based on the lead author`s doctoral thesis, successfully defended at Oregon State University on March 4, 1997. First, the conductance of closely coupled DQWs in B{sub {parallel}} is studied. B{sub {parallel}}-induced distortions in the dispersion, the density of states, and the Fermi surface are described both theoretically and experimentally, with particular attention paid to the dispersion anticrossing and resulting partial energy gap. Measurements of giant distortions in the effective mass are found to agree with theoretical calculations. Second, the Landau level spectra of coupled DQWs in tilted magnetic fields is studied. The magnetoresistance oscillations show complex beating as Landau levels from the two Fermi surface components cross the Fermi level. A third set of oscillations resulting from magnetic breakdown is observed. A semiclassical calculation of the Landau level spectra is then performed, and shown to agree exceptionally well with the data. Finally, quantum wires and quantum point contacts formed in DQW structures are investigated. Anticrossings of the one-dimensional DQW dispersion curves are predicted to have interesting transport effects in these devices. Difficulties in sample fabrication have to date prevented experimental verification. However, recently developed techniques to overcome these difficulties are described.

  12. Water transport dynamics in trees and stands

    SciTech Connect

    Pallardy, S.G.; Cermak, J.; Ewers, F.W.; Kaufmann, M.R.; Parker, W.C.; Sperry, J.S.

    1995-07-01

    Water transport dynamics in trees and stands of conifers have certain features that are characteristic of this group and are at least rare among angiosperms. Among these features is the xylem transport system that is dependent on tracheids for long-distance water transport. Tracheid-containing xylem is relatively inefficient, a property that can reduce submaximum allowable rates of gas exchange, but tracheids also offer substantial capacity for water storage and high resistance to freezing-induced dysfunction. Thus, they are quite compatible with the typical evergreen habit and long transpiration season of conifers. At the stand level, canopy transpiration in conifers is primarily controlled by stomatal conductance. In contrast, in dense canopies of angio-sperms, particularly those of tropical forests with limited air mixing, stand transpiration is limited by radiation input rather than by stomatal control. Because of their evergreen habit a greater proportion of evapotranspiration in conifer forests is associated with evaporation of water intercepted by the tree crowns. Other features of transport dynamics are characteristic of most conifers, but are not unique to this group. Among these features are typically shallow root systems that often must supply water in winter to replace transpiration needs of evergreen species, common occurrence of mycorrhizae that enhance mineral and water uptake, and drought tolerance adaptations that include elements of both dehydration avoidance (e.g., stomatal closure under water stress, shifts in allocation of dry matter to below-ground sinks) and dehydration tolerance (e.g., capacity for acclimation of photosynthetic apparatus to drought, osmotic adjustment). Transpiration rates from conifer foliage often are lower than those of deciduous angiosperms, probably because of the lower maximum capacity of tracheid-bearing xylem to transport water.

  13. A coupled heat and water flow apparatus

    SciTech Connect

    Mohamed, A.M.O.; Caporouscio, F.; Yong, R.N. ); Cheung, C.H. ); Kjartanson, B.H. )

    1993-03-01

    Safe and permanent disposal of radioactive waste requires isolation of a number of diverse chemical elements form the environment. The Canadian Nuclear Fuel Waste Management Program is assessing the concept of disposing of waste in a vault excavated at a depth of 500 to 1000 m below the ground surface in plutonic rock of the Canadian Shield. The temperatures and hydraulic potential in the buffer and back fill material were investigated. To study the performance of a compacted buffer material under thermal and isothermal conditions, a coupled heat and water flow apparatus is designed and presented. In the preliminary design, a one-dimensional flow of heat and water was not achieved. however, control of temperature gradient, existence of one-dimensional flow, and uniformity of temperature and volumetric water content distributions at any cross section within the specimen are achieved in the modified design. Experimental results have shown that the temperature stabilizes very rapidly after a period of approximately 0. 107 days. The moisture moves away from the hot end along the longitudinal direction of the specimen due to imposed thermal gradient. The time required for moisture to stabilize is in order of days. 17 refs., 17 figs., 3 tabs.

  14. CFEST Coupled Flow, Energy & Solute Transport Version CFEST005 Theory Guide

    SciTech Connect

    Freedman, Vicky L.; Chen, Yousu; Gupta, Sumant K.

    2005-11-01

    This document presents the mathematical theory implemented in the CFEST (Coupled Flow, Energy, and Solute Transport) simulator. The simulator is a three-dimensional finite element model that can be used for evaluating flow and solute mass transport. Although the theory for thermal transport is presented in this guide, it has not yet been fully implemented in the simulator. The flow module is capable of simulating both confined and unconfined aquifer systems, as well as constant and variable density fluid flows. For unconfined aquifers, the model uses a moving boundary for the water table, deforming the numerical mesh so that the uppermost nodes are always at the water table. For solute transport, changes in concentration of a single dissolved chemical constituent are computed for advective and hydrodynamic transport, linear sorption represented by a retardation factor, and radioactive decay. Once fully implemented, transport of thermal energy in the groundwater and solid matrix of the aquifer can also be used to model aquifer thermal regimes. Mesh construction employs “collapsible”, hexahedral finite elements in a three-dimensional coordinate system. CFEST uses the Galerkin finite element method to convert the partial differential equations to algebraic form. To solve the coupled equations for momentum, solute and heat transport, either Picard or Newton-Raphson iterative schemes are used to treat nonlinearities. An upstream weighted residual finite-element method is used to solve the advective-dispersive transport and energy transfer equations, which circumvents problems of numerical oscillation problems. Matrix solutions of the flow and transport problems are performed using efficient iterative solvers available in ITPACK and PETSc, solvers that are available in the public domain. These solvers are based on the preconditioned conjugate gradient and ORTHOMIN methods for symmetric and a nonsymmetric matrices, respectively.

  15. Vibronic coupling effect on the electron transport through molecules

    NASA Astrophysics Data System (ADS)

    Tsukada, Masaru; Mitsutake, Kunihiro

    2007-03-01

    Electron transport through molecular bridges or molecular layers connected to nano-electrodes is determined by the combination of coherent and dissipative processes, controlled by the electron-vibron coupling, transfer integrals between the molecular orbitals, applied electric field and temperature. We propose a novel theoretical approach, which combines ab initio molecular orbital method with analytical many-boson model. As a case study, the long chain model of the thiophene oligomer is solved by a variation approach. Mixed states of moderately extended molecular orbital states mediated and localised by dress of vibron cloud are found as eigen-states. All the excited states accompanied by multiple quanta of vibration can be solved, and the overall carrier transport properties including the conductance, mobility, dissipation spectra are analyzed by solving the master equation with the transition rates estimated by the golden rule. We clarify obtained in a uniform systematic way, how the transport mode changes from a dominantly coherent transport to the dissipative hopping transport.

  16. An analytical model for predicting transport in a coupled vadose/phreatic system

    SciTech Connect

    Tomasko, D.

    1997-05-01

    A simple analytical model is presented for predicting the transport of a contaminant in both the unsaturated (vadose) and saturated (phreatic) zones following a surficial spill. The model incorporates advection, dispersion, adsorption, and first-order decay in both zones and couples the transport processes at the water table. The governing equation is solved by using the method of Laplace transforms, with numerical inversion of the Laplace space equation for concentration. Because of the complexity of the functional form for the Laplace space solution, a numerical methodology using the real and imaginary parts of a Fourier series was implemented. To reduce conservatism in the model, dilution at the water table was also included. Verification of the model is demonstrated by its ability to reproduce the source history at the surface and to replicate appropriate one-dimensional transport through either the vadose or phreatic zone. Because of its simplicity and lack of detailed input data requirements, the model is recommended for scoping calculations.

  17. Sediment Transport and Water Quality Model of Cedar Lake, Indiana

    NASA Astrophysics Data System (ADS)

    James, S. C.; Jones, C. A.; Roberts, J. D.; Ahlmann, M.; Bucaro, D. A.

    2006-12-01

    The EPA-supported Environmental Fluid Dynamics Code, EFDC, is used to model hydrodynamics, sediment transport, and water quality in coastal regions, estuaries, rivers, and lakes. However, the empirical formulations used for sediment transport are not always adequate to accurately characterize cohesive sediment erosion and transport. New sediment transport subroutines have been incorporated into EFDC and the new model is called SNL-EFDC. The updated model provides an improved, coupled hydrodynamics, sediment transport, and water quality framework. The newly incorporated sediment transport subroutines facilitate direct use of measured erosion rate data from the Sediment Erosion with Depth Flume (SEDflume). Erosion rates are included as functions of both depth within the sediment bed and applied shear stresses. This bypasses problems associated with empirical erosion formulations often based on disaggregated particle size. Restoration alternatives are under consideration for Cedar Lake in Indiana and SNL-EFDC models its hydrodynamics, sediment transport, and water quality. The water quality model as implemented on Cedar Lake tracks algae, oxygen, temperature, carbon, phosphorous, and nitrogen kinetics, as well as, sediment bed diagenesis. Environmental conditions, wind, temperature, rainfall, and sunlight, were based on data collected in 2005. Tributary loading was modeled using L-THIA and provided influxes of water, nutrients (phosphorous, nitrogen, etc.), and sediments. The calibrated model was used to simulate a nine month period from March to November 2005. Results suggest that the model simulates sediments transport and associated water quality correctly. The calibrated model is being used to evaluate several restoration measures throughout the lake and watershed and their effect on water quality. Because Cedar Lake is a nitrogen limited lake, changes in the level of eutrophication from each measure are being tracked by calculating the Carlson trophic state index

  18. Inertial effect on spin-orbit coupling and spin transport

    NASA Astrophysics Data System (ADS)

    Basu, B.; Chowdhury, Debashree

    2013-08-01

    We theoretically study the renormalization of inertial effects on the spin dependent transport of conduction electrons in a semiconductor by taking into account the interband mixing on the basis of k→ṡp→ perturbation theory. In our analysis, for the generation of spin current we have used the extended Drude model where the spin-orbit coupling plays an important role. We predict enhancement of the spin current resulting from the renormalized spin-orbit coupling effective in our model in cubic and non-cubic crystals. Attention has been paid to clarify the importance of gauge fields in the spin transport of this inertial system. A theoretical proposition of a perfect spin filter has been done through the Aharonov-Casher like phase corresponding to this inertial system. For a time dependent acceleration, effect of k→ ṡp→ perturbation on the spin current and spin polarization has also been addressed. Furthermore, achievement of a tunable source of polarized spin current through the non uniformity of the inertial spin-orbit coupling strength has also been discussed.

  19. The effect of coupled transport phenomena in the Opalinus Clay and implications for radionuclide transport.

    PubMed

    Soler, J M

    2001-12-01

    In this study, the potential effects of coupled transport phenomena on radionuclide transport in the vicinity of a repository for vitrified high-level radioactive waste (HLW) and spent nuclear fuel (SF) hosted by the Opalinus Clay in Switzerland, at times equal to or greater than the expected lifetime of the waste canisters (about 1000 years), are addressed. The solute fluxes associated with advection, chemical diffusion, thermal and chemical osmosis, hyperfiltration and thermal diffusion have been incorporated into a simple one-dimensional transport equation. The analytical solution of this equation, with appropriate parameters. shows that thermal osmosis is the only coupled transport mechanism that could, on its own, have a strong effect on repository performance. Based on the results from the analytical model, two-dimensional finite-difference models incorporating advection and thermal osmosis, and taking conservation of fluid mass into account, have been formulated. The results show that, under the conditions in the vicinity of the repository at the time scales of interest, and due to the constraints imposed by conservation of fluid mass, the advective component of flow will oppose and cancel the thermal-osmotic component. The overall conclusion is that coupled phenomena will only have a very minor impact on radionuclide transport in the Opalinus Clay, in terms of fluid and solute fluxes, at least under the conditions prevailing at times equal to or greater than the expected lifetime of the waste canisters (about 1000 years).

  20. ATP-dependent substrate transport by the ABC transporter MsbA is proton-coupled

    PubMed Central

    Singh, Himansha; Velamakanni, Saroj; Deery, Michael J.; Howard, Julie; Wei, Shen L.; van Veen, Hendrik W.

    2016-01-01

    ATP-binding cassette transporters mediate the transbilayer movement of a vast number of substrates in or out of cells in organisms ranging from bacteria to humans. Current alternating access models for ABC exporters including the multidrug and Lipid A transporter MsbA from Escherichia coli suggest a role for nucleotide as the fundamental source of free energy. These models involve cycling between conformations with inward- and outward-facing substrate-binding sites in response to engagement and hydrolysis of ATP at the nucleotide-binding domains. Here we report that MsbA also utilizes another major energy currency in the cell by coupling substrate transport to a transmembrane electrochemical proton gradient. The dependence of ATP-dependent transport on proton coupling, and the stimulation of MsbA-ATPase by the chemical proton gradient highlight the functional integration of both forms of metabolic energy. These findings introduce ion coupling as a new parameter in the mechanism of this homodimeric ABC transporter. PMID:27499013

  1. Coupled model of root water uptake, mucilage exudation and degradation

    NASA Astrophysics Data System (ADS)

    Kroener, Eva; Ahmed, Mutez A.; Carminati, Andrea

    2017-04-01

    Although the fact that root mucilage plays a prominent role in soil-plant water relations is becoming more and more accepted, many aspects of how mucilage distribution and root water uptake interact with each other remain unexplored. First, it is not clear how long mucilage persists in soil. Furthermore, the effects of water content and root water uptake (i.e. convective fluxes) on the diffusion of mucilage from the root surface into the soil are not included in current models of water uptake. The aims of this study were: i) to measure the effect of soil moisture on mucilage decomposition; ii) to develop a coupled model of root water uptake and mucilage diffusion and degradation during root growth. C4 root mucilage from maize was added as single pulses to a C3 soil of two different moisture levels. We have then employed the Richards Equation for water flow and an advection-dispersion equation to describe the dynamic distribution of mucilage in a single-root model. Most of the mucilage was decomposed under optimum water supply. Drought significantly suppressed mucilage mineralization. Opposed to classical solute transport models the water flow in the rhizosphere was affected by the local concentration of mucilage. Namely a higher concentration of mucilage results in (a) an increase in equilibrium water retention curve, (b) a reduction of hydraulic conductivity at a given water content and (c) a non-equilibrium water retention curve caused by swelling and shrinking dynamics of mucilage in the pore space. The dispersion coefficient, on the other hand, depends on the water content. The parameters of mucilage diffusion have been fitted to observations on real plants. The model shows that mucilage exuded in wet soils diffuses far from the roots and it is rapidly degraded. On the contrary, mucilage of plants growing in dry soil is not easily degradable and it remains at higher concentrations in a narrow region around the roots, resulting in a marked increase in water

  2. Isothermal titration calorimetry of ion-coupled membrane transporters.

    PubMed

    Boudker, Olga; Oh, SeCheol

    2015-04-01

    Binding of ligands, ranging from proteins to ions, to membrane proteins is associated with absorption or release of heat that can be detected by isothermal titration calorimetry (ITC). Such measurements not only provide binding affinities but also afford direct access to thermodynamic parameters of binding--enthalpy, entropy and heat capacity. These parameters can be interpreted in a structural context, allow discrimination between different binding mechanisms and guide drug design. In this review, we introduce advantages and limitations of ITC as a methodology to study molecular interactions of membrane proteins. We further describe case studies where ITC was used to analyze thermodynamic linkage between ions and substrates in ion-coupled transporters. Similar type of linkage analysis will likely be applicable to a wide range of transporters, channels, and receptors.

  3. Heat transport along a chain of coupled quantum harmonic oscillators

    NASA Astrophysics Data System (ADS)

    de Oliveira, Mário J.

    2017-04-01

    I study the heat transport properties of a chain of coupled quantum harmonic oscillators in contact at its ends with two heat reservoirs at distinct temperatures. My approach is based on the use of an evolution equation for the density operator which is a canonical quantization of the classical Fokker-Planck-Kramers equation. I set up the evolution equation for the covariances and obtain the stationary covariances at the stationary states from which I determine the thermal conductance in closed form when the interparticle interaction is small. The conductance is finite in the thermodynamic limit implying an infinite thermal conductivity.

  4. Coupled transport/hyperelastic model for nastic materials

    NASA Astrophysics Data System (ADS)

    Homison, Chris; Weiland, Lisa M.

    2006-03-01

    Nastic materials are high energy density active materials that mimic processes used in the plant kingdom to produce large deformations through the conversion of chemical energy. These materials utilize the controlled transport of charge and fluid across a selectively-permeable membrane to achieve bulk deformation in a process referred to in the plant kingdom as nastic movements. The nastic material being developed consists of synthetic membranes containing biological ion pumps, ion channels, and ion exchangers surrounding fluid-filled cavities embedded within a polymer matrix. In this paper the formulation of a biological transport model and its coupling with a hyperelastic finite element model of the polymer matrix is discussed. The transport model includes contributions from ion pumps, ion exchangers, and solvent flux. This work will form the basis for a feedback loop in material synthesis efforts. The goal of these studies is to determine the relative importance of the various parameters associated with both the polymer matrix and the biological transport components.

  5. Osmotic water transport through carbon nanotube membranes

    PubMed Central

    Kalra, Amrit; Garde, Shekhar; Hummer, Gerhard

    2003-01-01

    We use molecular dynamics simulations to study osmotically driven transport of water molecules through hexagonally packed carbon nanotube membranes. Our simulation setup comprises two such semipermeable membranes separating compartments of pure water and salt solution. The osmotic force drives water flow from the pure-water to the salt-solution compartment. Monitoring the flow at molecular resolution reveals several distinct features of nanoscale flows. In particular, thermal fluctuations become significant at the nanoscopic length scales, and as a result, the flow is stochastic in nature. Further, the flow appears frictionless and is limited primarily by the barriers at the entry and exit of the nanotube pore. The observed flow rates are high (5.8 water molecules per nanosecond and nanotube), comparable to those through the transmembrane protein aquaporin-1, and are practically independent of the length of the nanotube, in contrast to predictions of macroscopic hydrodynamics. All of these distinct characteristics of nanoscopic water flow can be modeled quantitatively by a 1D continuous-time random walk. At long times, the pure-water compartment is drained, and the net flow of water is interrupted by the formation of structured solvation layers of water sandwiched between two nanotube membranes. Structural and thermodynamic aspects of confined water monolayers are studied. PMID:12878724

  6. Understanding transport in model water desalination membranes

    NASA Astrophysics Data System (ADS)

    Chan, Edwin

    Polyamide based thin film composites represent the the state-of-the-art nanofiltration and reverse osmosis membranes used in water desalination. The performance of these membranes is enabled by the ultrathin (~100 nm) crosslinked polyamide film in facilitating the selective transport of water over salt ions. While these materials have been refined over the last several decades, understanding the relationships between polyamide structure and membrane performance remains a challenge because of the complex and heterogeneous nature of the polyamide film. In this contribution, we present our approach to addressing this challenge by studying the transport properties of model polyamide membranes synthesized via molecular layer-by-layer (mLbL) assembly. First, we demonstrate that mLbL can successfully construct polyamide membranes with well-defined nanoscale thickness and roughness using a variety of monomer formulations. Next, we present measurement tools for characterizing the network structure and transport of these model polyamide membranes. Specifically, we used X-ray and neutron scattering techniques to characterize their structure as well as a recently-developed indentation based poromechanics approach to extrapolate their water diffusion coefficient. Finally, we illustrate how these measurements can provide insight into the original problem by linking the key polyamide network properties, i.e. water-polyamide interaction parameter and characteristic network mesh size, to the membrane performance.

  7. Transport properties of supercooled confined water

    NASA Astrophysics Data System (ADS)

    Mallamace, F.; Branca, C.; Broccio, M.; Corsaro, C.; Gonzalez-Segredo, N.; Spooren, J.; Stanley, H. E.; Chen, S.-H.

    2008-07-01

    This article presents an overview of recent experiments performed on transport properties of water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We report data of nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, studying water confined in nanometer-scale environments. When contained within small pores, water does not crystallise, and can be supercooled well below its homogeneous nucleation temperature Th. On this basis it is possible to carry out a careful analysis of the well known thermodynamical anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, water in the liquid state is a mixture of two different local structures, characterised by different densities, namely the low density liquid (LDL) and the high-density liquid (HDL). The LLPT line should terminate at a special transition point: a low-T liquid-liquid critical point. We discuss the following experimental findings on liquid water: (i) a crossover from non-Arrhenius behaviour at high T to Arrhenius behaviour at low T in transport parameters; (ii) a breakdown of the Stokes-Einstein relation; (iii) the existence of a Widom line, which is the locus of points corresponding to maximum correlation length in the p-T phase diagram and which ends in the liquid-liquid critical point; (iv) the direct observation of the LDL phase; (v) a minimum in the density at approximately 70 K below the temperature of the density maximum. In our opinion these results represent the experimental proofs of the validity of the LLPT hypothesis.

  8. Polyacrylamide Transport in Water Delivery Canals

    NASA Astrophysics Data System (ADS)

    Chen, L.; Zhu, J.; Young, M.

    2007-12-01

    Linear, anionic polyacrylamide (PAM) is being considered in the western United States as a technology to reduce seepage in unlined water delivery canals. A broad laboratory and field testing program has been undertaken to understand the benefits and potential environmental impacts of PAM use. The ability to predict the fate and transport of PAM in water delivery canals could prove to be a useful planning tool for PAM application. However, one key area of uncertainty of this type of canal treatment is the hydration, reaction, and settling rates of PAM after the dry powder is added to the canal water. In this study, we have developed a model that incorporates a number of known physical and chemical processes that can affect PAM transport, such as convection, dispersion, dissolution, flocculation, and settling, while solving the governing convection-dispersion transport equation. The model uses a mixed analytical and advanced numerical approach, and implements a transient partitioning of PAM mass between the canal water, the substrate soil, and potentially to open water bodies downstream of the application point. All source terms are modeled based on physical and chemical mechanisms as well as laboratory or field determined parameters. To more closely simulate field treatment of some canals, where PAM application moves upstream in time, the model is capable of implementing either a fixed or mobile upper boundary. In the latter treatment, the PAM can be added discretely or continuously in both time and space. A number of test situations have been simulated thus far, including theoretical and hypothetical cases for a wide range of conditions. The model also performed well when predicting PAM concentrations from a full-scale canal treatment experiment. The model provides a useful tool for predicting PAM fate and transport in water delivery canals, and therefore can play an important role in evaluating the efficacy of PAM application for water resources management

  9. Water transport in plants obeys Murray's law.

    PubMed

    McCulloh, Katherine A; Sperry, John S; Adler, Frederick R

    2003-02-27

    The optimal water transport system in plants should maximize hydraulic conductance (which is proportional to photosynthesis) for a given investment in transport tissue. To investigate how this optimum may be achieved, we have performed computer simulations of the hydraulic conductance of a branched transport system. Here we show that the optimum network is not achieved by the commonly assumed pipe model of plant form, or its antecedent, da Vinci's rule. In these representations, the number and area of xylem conduits is constant at every branch rank. Instead, the optimum network has a minimum number of wide conduits at the base that feed an increasing number of narrower conduits distally. This follows from the application of Murray's law, which predicts the optimal taper of blood vessels in the cardiovascular system. Our measurements of plant xylem indicate that these conduits conform to the Murray's law optimum as long as they do not function additionally as supports for the plant body.

  10. Coupling of volatile transport and internal heat flow on Triton

    NASA Technical Reports Server (NTRS)

    Brown, Robert H.; Kirk, Randolph L.

    1994-01-01

    Recently Brown et al. (1991) showed that Triton's internal heat source could amount to 5-20% of the absorbed insolation on Triton, thus significantly affecting volatile transport and atmospheric pressure. Subsequently, Kirk and Brown (1991a) used simple analytical models of the effect of internal heat on the distribution of volatiles on Triton's surface, confirming the speculation of Brown et al. that Triton's internal heat flow could strongly couple to the surface volatile distribution. To further explore this idea, we present numerical models of the permanent distribution of nitrogen ice on Triton that include the effects of sunlight, the two-dimensional distribution of internal heat flow, the coupling of internal heat flow to the surface distribution of nitrogen ice, and the finite viscosity of nitrogen ice. From these models we conclude that: (1) The strong vertical thermal gradient induced in Triton's polar caps by internal heat-flow facilitates viscous spreading to lower latitudes, thus opposing the poleward transport of volatiles by sunlight, and, for plausible viscosities and nitrogen inventories, producing permanent caps of considerable latitudinal extent; (2) It is probable that there is a strong coupling between the surface distribution of nitrogen ice on Triton and internal heat flow; (3) Asymmetries in the spatial distribution of Triton's heat flow, possibly driven by large-scale, volcanic activity or convection in Triton's interior, can result in permanent polar caps of unequal latitudinal extent, including the case of only one permanent polar cap; (4) Melting at the base of a permanent polar cap on Triton caused by internal heat flow can significantly enhance viscous spreading, and, as an alternative to the solid-state greenhouse mechanism proposed by Brown et al. (1990), could provide the necessary energy, fluids, and/or gases to drive Triton's geyser-like plumes; (5) The atmospheric collapse predicted to occur on Triton in the next 20 years

  11. Coupling of volatile transport and internal heat flow on Triton

    NASA Technical Reports Server (NTRS)

    Brown, Robert H.; Kirk, Randolph L.

    1994-01-01

    Recently Brown et al. (1991) showed that Triton's internal heat source could amount to 5-20% of the absorbed insolation on Triton, thus significantly affecting volatile transport and atmospheric pressure. Subsequently, Kirk and Brown (1991a) used simple analytical models of the effect of internal heat on the distribution of volatiles on Triton's surface, confirming the speculation of Brown et al. that Triton's internal heat flow could strongly couple to the surface volatile distribution. To further explore this idea, we present numerical models of the permanent distribution of nitrogen ice on Triton that include the effects of sunlight, the two-dimensional distribution of internal heat flow, the coupling of internal heat flow to the surface distribution of nitrogen ice, and the finite viscosity of nitrogen ice. From these models we conclude that: (1) The strong vertical thermal gradient induced in Triton's polar caps by internal heat-flow facilitates viscous spreading to lower latitudes, thus opposing the poleward transport of volatiles by sunlight, and, for plausible viscosities and nitrogen inventories, producing permanent caps of considerable latitudinal extent; (2) It is probable that there is a strong coupling between the surface distribution of nitrogen ice on Triton and internal heat flow; (3) Asymmetries in the spatial distribution of Triton's heat flow, possibly driven by large-scale, volcanic activity or convection in Triton's interior, can result in permanent polar caps of unequal latitudinal extent, including the case of only one permanent polar cap; (4) Melting at the base of a permanent polar cap on Triton caused by internal heat flow can significantly enhance viscous spreading, and, as an alternative to the solid-state greenhouse mechanism proposed by Brown et al. (1990), could provide the necessary energy, fluids, and/or gases to drive Triton's geyser-like plumes; (5) The atmospheric collapse predicted to occur on Triton in the next 20 years

  12. Water transport control in carbon nanotube arrays

    PubMed Central

    2014-01-01

    Based on a recent scaling law of the water mobility under nanoconfined conditions, we envision novel strategies for precise modulation of water diffusion within membranes made of carbon nanotube arrays (CNAs). In a first approach, the water diffusion coefficient D may be tuned by finely controlling the size distribution of the pore size. In the second approach, D can be varied at will by means of externally induced electrostatic fields. Starting from the latter strategy, switchable molecular sieves are proposed, where membranes are properly designed with sieving and permeation features that can be dynamically activated/deactivated. Areas where a precise control of water transport properties is beneficial range from energy and environmental engineering up to nanomedicine. PMID:25313305

  13. Waveguide transport mediated by strong coupling with atoms

    NASA Astrophysics Data System (ADS)

    Cheng, Mu-Tian; Xu, Jingping; Agarwal, Girish S.

    2017-05-01

    We investigate single-photon scattering properties in a one-dimensional waveguide coupled to a quantum emitter's chain with dipole-dipole interaction (DDI). The photon transport is extremely sensitive to the location of the evanescently coupled atoms. The analytical expressions of reflection and transmission amplitudes for the chain containing two emitters with DDI are deduced by using a real-space Hamiltonian. Two cases, where the two emitters symmetrically or asymmetrically couple to the waveguide, are discussed in detail. It shows that the reflection and transmission typical spectra split into two peaks due to the DDI. The Fano minimum in the spectra can be used to estimate the strength of the DDI. Furthermore, the DDI makes spectra strongly asymmetric and creates a transmission window in the region where there was zero transmission. The scattering spectra for the chain consisting of multiple emitters are also given. Our key finding is that DDI can broaden the frequency bandwidth for high reflection when the chain consists of many emitters.

  14. Electronic transport in partially ionized water plasmas

    NASA Astrophysics Data System (ADS)

    French, Martin; Redmer, Ronald

    2017-09-01

    We use ab initio simulations based on density functional theory to calculate the electrical and thermal conductivities of electrons in partially ionized water plasmas at densities above 0.1 g/cm3. The resulting conductivity data are then fitted to analytic expressions for convenient application. For low densities, we develop a simple and fully analytic model for electronic transport in low-density plasmas in the chemical picture using the relaxation-time approximation. In doing so, we derive a useful analytic expression for electronic transport cross sections with neutral particles, based on a model potential. In the regime of thermal ionization, electrical conductivities from the analytic model agree with the ab initio data within a factor of 2. Larger deviations are observed for the thermal conductivity, and their origin is discussed. Our results are relevant for modeling the interior and evolution of water-rich planets as well as for technical plasma applications.

  15. Human platelet osmotic water and nonelectrolyte transport.

    PubMed

    Meyer, M M; Verkman, A S

    1986-10-01

    The osmotic water (Pf) and nonelectrolyte permeability (Ps) properties of human platelets were characterized using the stopped-flow light-scattering technique. At 37 degrees C, Pf = 0.007 +/- 0.001 cm/s, the urea reflection coefficient (sigma urea) = 0.95 +/- 0.04, and Ps for a series of permeant nonelectrolytes was (in cm X s-1 X 10(-6)) 2.1 (urea), 3.5 (glycerol), 3.8 (thiourea), 17 (ethylene glycol), 18 (acetamide), 23 (formamide), and 24 (butyramide). Pf did not depend on the size of the osmotic gradient or on the direction of volume flow. Mercurial sulfhydryl reagents did not inhibit osmotic water transport, and phloretin and phenylurea did not inhibit urea transport. There was a discontinuity in the temperature dependence for both Pf and urea permeability (P urea) at 36 degrees C; enthalpy (delta H) = 25 (greater than 36 degrees C) and 4.4 kcal/mol (less than 36 degrees C) for Pf, and delta H = 26 (greater than 36 degrees C) and 7 kcal/mol (less than 36 degrees C) for P urea. In contrast to the facilitated water and urea transport systems in the red blood cell, these results suggest that the mechanism for water and urea transport in the platelet is primarily by diffusion through membrane phospholipid. A computer-simulated model of platelet circulation through the renal medulla, based on the measured values for Pf, P urea, and sigma urea, indicated that platelets undergo an approximately 40% decrease in volume in the inner medulla and an approximately 20% overshoot in volume as they return to the external isosmotic environment.

  16. Novel macrocyclic carriers for proton-coupled liquid membrane transport

    SciTech Connect

    Lamb, J.D.

    1991-06-10

    The objective of our research program is to elucidate the chemical principles which are responsible for the cation selectivity and permeability of liquid membranes containing macrocyclic carriers. Several new macrocyclic carriers were synthesized during the last three year period, including selenium-containing macrocycles, new crown-4 structures, and several new crown structures containing nitrogen based heterocycles as substituents in the principal macrocyclic ring. The cation binding properties of these macrocycles were investigated by potentiometric titration, calorimetric titration, solvent extraction, and NMR techniques. In addition, hydrophobic macrocycles were incorporated into dual hollow fiber membrane systems to investigate their membrane performance, especially in the proton-coupled transport mode. It was found that the dual hollow fiber system maintains the cation selectivity and permeability of supported liquid membranes, while enhancing membrane stability. The diffusion limited transport model was expanded to account for membrane solvent effects. Furthermore, Eu{sup 2+} transport was found to be similar to that of strontium and much higher than that of the lanthanides, in supported liquid membrane systems.

  17. Coupled groundwater flow and transport: 1. Verification of variable density flow and transport models

    NASA Astrophysics Data System (ADS)

    Kolditz, Olaf; Ratke, Rainer; Diersch, Hans-Jörg G.; Zielke, Werner

    This work examines variable density flow and corresponding solute transport in groundwater systems. Fluid dynamics of salty solutions with significant density variations are of increasing interest in many problems of subsurface hydrology. The mathematical model comprises a set of non-linear, coupled, partial differential equations to be solved for pressure/hydraulic head and mass fraction/concentration of the solute component. The governing equations and underlying assumptions are developed and discussed. The equation of solute mass conservation is formulated in terms of mass fraction and mass concentration. Different levels of the approximation of density variations in the mass balance equations are used for convection problems (e.g. the Boussinesq approximation and its extension, fully density approximation). The impact of these simplifications is studied by use of numerical modelling. Numerical models for nonlinear problems, such as density-driven convection, must be carefully verified in a particular series of tests. Standard benchmarks for proving variable density flow models are the Henry, Elder, and salt dome (HYDROCOIN level 1 case 5) problems. We studied these benchmarks using two finite element simulators - ROCKFLOW, which was developed at the Institute of Fluid Mechanics and Computer Applications in Civil Engineering and FEFLOW, which was developed at the Institute for Water Resources Planning and Systems Research Ltd. Although both simulators are based on the Galerkin finite element method, they differ in many approximation details such as temporal discretization (Crank-Nicolson vs predictor-corrector schemes), spatial discretization (triangular and quadrilateral elements), finite element basis functions (linear, bilinear, biquadratic), iteration schemes (Newton, Picard) and solvers (direct, iterative). The numerical analysis illustrates discretization effects and defects arising from the different levels of the density of approximation. We contribute

  18. Water dynamics in the rhizosphere - a new model of coupled water uptake and mucilage exudation

    NASA Astrophysics Data System (ADS)

    Kroener, Eva; Holz, Maire; Ahmed, Mutez; Zarebanadkouki, Mohsen; Bittelli, Marco; Carminati, Andrea

    2016-04-01

    The flow of water from soil to plant roots is affected by the narrow region of soil close to the roots, the so-called rhizosphere. The rhizosphere is influenced by mucilage, a polymeric gel exuded by roots that alters the hydraulic properties of the rhizosphere. Here we present a model that accounts for: (a) an increase in equilibrium water retention curve caused by the water holding capacity of mucilage, (b) a reduction of hydraulic conductivity at a given water content due to the higher viscosity of mucilage and (c) the swelling and shrinking dynamics by decoupling water content and water potential and introducing a non-equilibrium water retention curve. The model has been tested for mixtures of soil and mucilage and we applied it to simulate observations of previous experiments with real plants growing in soil that show evidences of altered hydraulic dynamics in the rhizosphere. Furthermore we present results about how the parameters of the model depend on soil texture and root age. Finally we couple our hydraulic model to a diffusion model of mucilage into the soil. Opposed to classical solute transport models here the water flow in the rhizosphere is affected by the concentration distribution of mucilage.

  19. Modular structure of sodium-coupled bicarbonate transporters.

    PubMed

    Boron, Walter F; Chen, Liming; Parker, Mark D

    2009-06-01

    Mammalian genomes contain 10 SLC4 genes that, between them, encode three Cl-HCO(3) exchangers, five Na(+)-coupled HCO(3) transporters (NCBTs), one reported borate transporter, and what is reported to be a fourth Cl-HCO(3) exchanger. The NCBTs are expressed throughout the body and play important roles in maintaining intracellular and whole-body pH, as well as contributing to transepithelial transport processes. The importance of NCBTs is underscored by the genetic association of dysfunctional NCBT genes with blindness, deafness, epilepsy, hypertension and metal retardation. Key to understanding the action and regulation of NCBTs is an appreciation of the diversity of NCBT gene products. The transmembrane domains of human NCBT paralogs are 50-84% identical to each other at the amino acid level, and are capable of a diverse range of actions, including electrogenic Na/HCO(3) cotransport (i.e. NBCe1 and NBCe2) and electroneutral Na/HCO(3) cotransport (i.e. NBCn1 and NBCn2), as well as Na(+)-dependent Cl-HCO(3) exchange (i.e. NDCBE). Furthermore, by the use of alternative promoters and alternative-splicing events, individual SLC4 genes have the potential to generate multiple splice variants (as many as 16 in the case of NBCn1), each of which could have unique temporal and spatial patterns of distribution, unitary transporter activity (i.e. flux mediated by one molecule), array of protein-binding partners, and complement of regulatory stimuli. In the first section of this review, we summarize our present knowledge of the function and distribution of mammalian NCBTs and their multiple variants. In the second section of this review we consider the molecular consequences of NCBT variation.

  20. Coupled Eulerian-Lagrangian transport of large debris by tsunamis

    NASA Astrophysics Data System (ADS)

    Conde, Daniel A. S.; Ferreira, Rui M. L.; Sousa Oliveira, Carlos

    2016-04-01

    Tsunamis are notorious for the large disruption they can cause on coastal environments, not only due to the imparted momentum of the incoming wave but also due to its capacity to transport large quantities of solid debris, either from natural or human-made sources, over great distances. A 2DH numerical model under development at CERIS-IST (Ferreira et al., 2009; Conde, 2013) - STAV2D - capable of simulating solid transport in both Eulerian and Lagrangian paradigms will be used to assess the relevance of Lagrangian-Eulerian coupling when modelling the transport of solid debris by tsunamis. The model has been previously validated and applied to tsunami scenarios (Conde, 2013), being well-suited for overland tsunami propagation and capable of handling morphodynamic changes in estuaries and seashores. The discretization scheme is an explicit Finite Volume technique employing flux-vector splitting and a reviewed Roe-Riemann solver. Source term formulations are employed in a semi-implicit way, including the two-way coupling of the Lagrangian and Eulerian solvers by means of conservative mass and momentum transfers between fluid and solid phases. The model was applied to Sines Port, a major commercial port in Portugal, where two tsunamigenic scenarios are considered: an 8.5 Mw scenario, consistent with the Great Lisbon Earthquake and Tsunami of the 1st November 1755 (Baptista, 2009), and an hypothetical 9.5 Mw worst-case scenario based on the same historical event. Open-ocean propagation of these scenarios were simulated with GeoClaw model from ClawPack (Leveque, 2011). Following previous efforts on the modelling of debris transport by tsunamis in seaports (Conde, 2015), this work discusses the sensitivity of the obtained results with respect to the phenomenological detail of the employed Eulerian-Lagrangian formulation and the resolution of the mesh used in the Eulerian solver. The results have shown that the fluid to debris mass ratio is the key parameter regarding the

  1. Coupling of hydrologic transport and chemical reactions in a stream affected by acid mine drainage

    USGS Publications Warehouse

    Kimball, B.A.; Broshears, R.E.; Bencala, K.E.; McKnight, Diane M.

    1994-01-01

    Experiments in St. Kevin Gulch, an acid mine drainage stream, examined the coupling of hydrologic transport to chemical reactions affecting metal concentrations. Injection of LiCl as a conservative tracer was used to determine discharge and residence time along a 1497-m reach. Transport of metals downstream from inflows of acidic, metal-rich water was evaluated based on synoptic samples of metal concentrations and the hydrologic characteristics of the stream. Transport of SO4 and Mn was generally conservative, but in the subreaches most affected by acidic inflows, transport was reactive. Both 0.1-??m filtered and particulate Fe were reactive over most of the stream reach. Filtered Al partitioned to the particulate phase in response to high instream concentrations. Simulations that accounted for the removal of SO4, Mn, Fe, and Al with first-order reactions reproduced the steady-state profiles. The calculated rate constants for net removal used in the simulations embody several processes that occur on a stream-reach scale. The comparison between rates of hydrologie transport and chemical reactions indicates that reactions are only important over short distances in the stream near the acidic inflows, where reactions occur on a comparable time scale with hydrologic transport and thus affect metal concentrations.

  2. Spin transport at interfaces with spin-orbit coupling: Formalism

    NASA Astrophysics Data System (ADS)

    Amin, V. P.; Stiles, M. D.

    2016-09-01

    We generalize magnetoelectronic circuit theory to account for spin transfer to and from the atomic lattice via interfacial spin-orbit coupling. This enables a proper treatment of spin transport at interfaces between a ferromagnet and a heavy-metal nonmagnet. This generalized approach describes spin transport in terms of drops in spin and charge accumulations across the interface (as in the standard approach), but additionally includes the responses from in-plane electric fields and offsets in spin accumulations. A key finding is that in-plane electric fields give rise to spin accumulations and spin currents that can be polarized in any direction, generalizing the Rashba-Edelstein and spin Hall effects. The spin accumulations exert torques on the magnetization at the interface when they are misaligned from the magnetization. The additional out-of-plane spin currents exert torques via the spin-transfer mechanism on the ferromagnetic layer. To account for these phenomena we also describe spin torques within the generalized circuit theory. The additional effects included in this generalized circuit theory suggest modifications in the interpretations of experiments involving spin-orbit torques, spin pumping, spin memory loss, the Rashba-Edelstein effect, and the spin Hall magnetoresistance.

  3. A coupled vegetation/sediment transport model for dryland environments

    NASA Astrophysics Data System (ADS)

    Mayaud, Jerome R.; Bailey, Richard M.; Wiggs, Giles F. S.

    2017-04-01

    Dryland regions are characterized by patchy vegetation, erodible surfaces, and erosive aeolian processes. Understanding how these constituent factors interact and shape landscape evolution is critical for managing potential environmental and anthropogenic impacts in drylands. However, modeling wind erosion on partially vegetated surfaces is a complex problem that has remained challenging for researchers. We present the new, coupled cellular automaton Vegetation and Sediment TrAnsport (ViSTA) model, which is designed to address fundamental questions about the development of arid and semiarid landscapes in a spatially explicit way. The technical aspects of the ViSTA model are described, including a new method for directly imposing oblique wind and transport directions onto a cell-based domain. Verification tests for the model are reported, including stable state solutions, the impact of drought and fire stress, wake flow dynamics, temporal scaling issues, and the impact of feedbacks between sediment movement and vegetation growth on landscape morphology. The model is then used to simulate an equilibrium nebkha dune field, and the resultant bed forms are shown to have very similar size and spacing characteristics to nebkhas observed in the Skeleton Coast, Namibia. The ViSTA model is a versatile geomorphological tool that could be used to predict threshold-related transitions in a range of dryland ecogeomorphic systems.

  4. Transport and mixing in strongly coupled dusty plasma medium

    NASA Astrophysics Data System (ADS)

    Dharodi, Vikram; Das, Amita; Patel, Bhavesh

    2016-10-01

    The generalized hydrodynamic (GHD) fluid model has been employed to study the transport and mixing properties of Dusty plasma medium in strong coupling limit. The response of lighter electron and ion species to the dust motion is taken to be instantaneous i.e. inertia-less. Thus the electron and ion density are presumed to follow the Boltzman relation. In the incompressible limit (i-GHD) the model supports Transverse Shear wave in contrast to the Hydrodynamic fluids. It has been shown that the presence of these waves leads to a better mixing of fluid in this case. Several cases of flow configuration have been considered for the study. The transport and mixing attributes have been quantified by studying the dynamical evolution of tracer particles in the system. The diffusion and clustering of these test particles are directly linked to the mixing characteristic of a medium. The displacement of these particles provides for a quantitative estimate of the diffusion coefficient of the medium. It is shown that these test particles often organize themselves in spatially inhomogeneous pattern leading to the phenomena of clustering.

  5. Generic Procedure for Coupling the PHREEQC Geochemical Modeling Framework with Flow and Solute Transport Simulators

    NASA Astrophysics Data System (ADS)

    Wissmeier, L. C.; Barry, D. A.

    2009-12-01

    Computer simulations of water availability and quality play an important role in state-of-the-art water resources management. However, many of the most utilized software programs focus either on physical flow and transport phenomena (e.g., MODFLOW, MT3DMS, FEFLOW, HYDRUS) or on geochemical reactions (e.g., MINTEQ, PHREEQC, CHESS, ORCHESTRA). In recent years, several couplings between both genres of programs evolved in order to consider interactions between flow and biogeochemical reactivity (e.g., HP1, PHWAT). Software coupling procedures can be categorized as ‘close couplings’, where programs pass information via the memory stack at runtime, and ‘remote couplings’, where the information is exchanged at each time step via input/output files. The former generally involves modifications of software codes and therefore expert programming skills are required. We present a generic recipe for remotely coupling the PHREEQC geochemical modeling framework and flow and solute transport (FST) simulators. The iterative scheme relies on operator splitting with continuous re-initialization of PHREEQC and the FST of choice at each time step. Since PHREEQC calculates the geochemistry of aqueous solutions in contact with soil minerals, the procedure is primarily designed for couplings to FST’s for liquid phase flow in natural environments. It requires the accessibility of initial conditions and numerical parameters such as time and space discretization in the input text file for the FST and control of the FST via commands to the operating system (batch on Windows; bash/shell on Unix/Linux). The coupling procedure is based on PHREEQC’s capability to save the state of a simulation with all solid, liquid and gaseous species as a PHREEQC input file by making use of the dump file option in the TRANSPORT keyword. The output from one reaction calculation step is therefore reused as input for the following reaction step where changes in element amounts due to advection

  6. Transport of organelles by elastically coupled motor proteins.

    PubMed

    Bhat, Deepak; Gopalakrishnan, Manoj

    2016-07-01

    Motor-driven intracellular transport is a complex phenomenon where multiple motor proteins simultaneously attached on to a cargo engage in pulling activity, often leading to tug-of-war, displaying bidirectional motion. However, most mathematical and computational models ignore the details of the motor-cargo interaction. A few studies have focused on more realistic models of cargo transport by including elastic motor-cargo coupling, but either restrict the number of motors and/or use purely phenomenological forms for force-dependent hopping rates. Here, we study a generic model in which N motors are elastically coupled to a cargo, which itself is subjected to thermal noise in the cytoplasm and to an additional external applied force. The motor-hopping rates are chosen to satisfy detailed balance with respect to the energy of elastic stretching. With these assumptions, an (N + 1) -variable master equation is constructed for dynamics of the motor-cargo complex. By expanding the hopping rates to linear order in fluctuations in motor positions, we obtain a linear Fokker-Planck equation. The deterministic equations governing the average quantities are separated out and explicit analytical expressions are obtained for the mean velocity and diffusion coefficient of the cargo. We also study the statistical features of the force experienced by an individual motor and quantitatively characterize the load-sharing among the cargo-bound motors. The mean cargo velocity and the effective diffusion coefficient are found to be decreasing functions of the stiffness. While the increase in the number of motors N does not increase the velocity substantially, it decreases the effective diffusion coefficient which falls as 1/N asymptotically. We further show that the cargo-bound motors share the force exerted on the cargo equally only in the limit of vanishing elastic stiffness; as stiffness is increased, deviations from equal load sharing are observed. Numerical simulations agree with

  7. Intrauterine insemination results in couples requiring extended semen transport time.

    PubMed

    Randall, Gary W; Gantt, Pickens A

    2007-01-01

    The purpose of the present study is to compare intrauterine insemination (IUI) pregnancy rates (PR) as a function of diagnosis and ovulation protocol utilizing an extended semen transport time. This allowed clients to conveniently collect IUI specimens in the comfort and privacy of their home. A single IUI per treatment cycle was performed. Three-hundred-ten consecutive infertilty couples having unexplained, male factor, ovulatory dysfunction, endometriosis, tubal factor or combined diagnostic factors receiving a total of 584 cycles of IUI were included. Ovulation protocols included LH surge, clomiphene citrate (CC)-hCG, CC-gonadotropins(Gn)-hCG, Gn-hCG or leuprolide acetate (L)-Gn-hCG followed 36-42 hours by a single IUI. Pregnancy rates per cycle (fecundity) and per couple (fertility) as a function of diagnosis, ovulation protocol and cycle number were evaluated. In each cycle the couples processed the specimen by adding sperm washing medium at room temperature to the specimen 30 min following collection and allowed it to incubate for two hours prior to IUI during transport. Overall, fecundity was 11.8% (69/584) and fertility was 22.3% (69/310); respectively by diagnosis was: unexplained 22.6%, 38.8%; male factor 18.8%, 42.9%; ovulatory dysfunction 12.4, 22.6%; endometriosis 5.3%, 11.1%; tubal factor 7.6%,13.3%; and combined factors 9.7%, 20.0%. Unexplained vs endometriosis (P < 0.0001, P < 0.005), tubal factor (fecundity P < 0.008) and ovulatory dysfunction (fecundity P < 0.027) was statistically different. Male factor vs endometriosis (P < 0.011, P < 0.036) was significantly different. Ovulatory dysfunction vs endometriosis was significantly different (fecundity P < 0.027). Pregnancies by ovulation protocol: LH surge 4.5%,10.5%; CC-hCG 9.4%,14.9%; CC-Gn-hCG 13.7%, 23.7%; Gn-hCG 17.5%, 45.3%; L-Gn-hCG 3.5%, 6.7%. For Gn-hCG vs L-Gn-hCG (P < 0.009, P < 0.030) and LH surge (fecundity P < 0.033). CC-Gn-hCG vs CC-hCG (fertility P < 0.050) and L-Gn-hCG (P < 0.033, P

  8. Thermocapillary transport of energy during water evaporation.

    PubMed

    Duan, Fei; Badam, V K; Durst, F; Ward, C A

    2005-11-01

    When evaporation occurs at a spherical water-vapor interface maintained at the circular mouth of a small funnel, studies of the energy transport have indicated that thermal conduction alone does not provide enough energy to evaporate the liquid at the observed rate. If the Gibbs model of the interface is adopted and the "surface-thermal capacity" is assigned a value of 30.6+/-0.8 kJ/(m2 K), then for evaporation experiments with the interfacial temperature in the range -10 degrees C< or =TLV< or =3.5 degrees C and Marangoni number (Ma) in the range 100transport by both thermocapillary convection and thermal conduction were taken into account, conservation of energy was fully satisfied. The question addressed herein is whether the assigned value of the surface-thermal capacity is an ad hoc empirical parameter or a property of the water-vapor interface that can be used in other circumstances. Accordingly, a series of experiments has been conducted in which water evaporated at cylindrical interfaces that were, on average, 4.4 times larger in area than that of the spherical interfaces used to measure the surface-thermal capacity initially. It is shown that using the value of the surface-thermal capacity determined at a spherical interface, the energy transported by thermocapillary convection and thermal conduction at a cylindrical interface is sufficient to evaporate the liquid at the observed rate. Knowing the value of the surface-thermal capacity also allows the local evaporation flux to be calculated from the measured temperature profiles in the liquid and vapor phases. The calculated local evaporation flux can then be used with statistical rate theory to calculate the vapor-phase pressure along the interface. The predicted mean vapor-phase pressure is in close agreement with that measured, and the predicted pressure gradient is consistent with that expected when thermocapillary convection is present.

  9. Modeling coupled nanoparticle aggregation and transport in porous media: A Lagrangian approach

    NASA Astrophysics Data System (ADS)

    Taghavy, Amir; Pennell, Kurt D.; Abriola, Linda M.

    2015-01-01

    Changes in nanoparticle size and shape due to particle-particle interactions (i.e., aggregation or agglomeration) may significantly alter particle mobility and retention in porous media. To date, however, few modeling studies have considered the coupling of transport and particle aggregation processes. The majority of particle transport models employ an Eulerian modeling framework and are, consequently, limited in the types of collisions and aggregate sizes that can be considered. In this work, a more general Lagrangian modeling framework is developed and implemented to explore coupled nanoparticle aggregation and transport processes. The model was verified through comparison of model simulations to published results of an experimental and Eulerian modeling study (Raychoudhury et al., 2012) of carboxymethyl cellulose (CMC)-modified nano-sized zero-valent iron particle (nZVI) transport and retention in water-saturated sand columns. A model sensitivity analysis reveals the influence of influent particle concentration (ca. 70 to 700 mg/L), primary particle size (10-100 nm) and pore water velocity (ca. 1-6 m/day) on particle-particle, and, consequently, particle-collector interactions. Model simulations demonstrate that, when environmental conditions promote particle-particle interactions, neglecting aggregation effects can lead to under- or over-estimation of nanoparticle mobility. Results also suggest that the extent to which higher order particle-particle collisions influence aggregation kinetics will increase with the fraction of primary particles. This work demonstrates the potential importance of time-dependent aggregation processes on nanoparticle mobility and provides a numerical model capable of capturing/describing these interactions in water-saturated porous media.

  10. Mesoscopic modeling of liquid water transport in polymer electrolyte fuel cells

    SciTech Connect

    Mukherjee, Partha P; Wang, Chao Yang

    2008-01-01

    A key performance limitation in polymer electrolyte fuel cells (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. Liquid water leads to the coverage of the electrochemically active sites in the catalyst layer (CL) rendering reduced catalytic activity and blockage of the available pore space in the porous CL and fibrous gas diffusion layer (GDL) resulting in hindered oxygen transport to the active reaction sites. The cathode CL and the GDL therefore playa major role in the mass transport loss and hence in the water management of a PEFC. In this article, we present the development of a mesoscopic modeling formalism coupled with realistic microstructural delineation to study the profound influence of the pore structure and surface wettability on liquid water transport and interfacial dynamics in the PEFC catalyst layer and gas diffusion layer.

  11. Highly efficient optical coupling and transport phenomena in chains of dielectric microspheres

    NASA Astrophysics Data System (ADS)

    Chen, Zhigang; Taflove, Allen; Backman, Vadim

    2006-02-01

    Using the generalized multiparticle Mie theory, we investigate optical coupling and transport through chains of dielectric microspheres. We identify two distinct coupling mechanisms of optical transport in terms of the coupling efficiency between neighboring microspheres, namely, evanescent coupling and nanojet coupling. We demonstrate that perfect whispering gallery mode propagation through a chain of evanescently coupled microspheres can be achieved. However, optical coupling and transport through a chain of nanojet-inducing microspheres is less efficient due to the radiative nature of photonic nanojets. Understanding these two optical coupling mechanisms is critical for selecting appropriate microspheres to build coupled resonator optical waveguides and other photon-manipulation devices for effective and low-loss guiding of photons.

  12. Highly efficient optical coupling and transport phenomena in chains of dielectric microspheres.

    PubMed

    Chen, Zhigang; Taflove, Allen; Backman, Vadim

    2006-02-01

    Using the generalized multiparticle Mie theory, we investigate optical coupling and transport through chains of dielectric microspheres. We identify two distinct coupling mechanisms of optical transport in terms of the coupling efficiency between neighboring microspheres, namely, evanescent coupling and nanojet coupling. We demonstrate that perfect whispering gallery mode propagation through a chain of evanescently coupled microspheres can be achieved. However, optical coupling and transport through a chain of nanojet-inducing microspheres is less efficient due to the radiative nature of photonic nanojets. Understanding these two optical coupling mechanisms is critical for selecting appropriate microspheres to build coupled resonator optical waveguides and other photon-manipulation devices for effective and low-loss guiding of photons.

  13. Neutron Transport Models and Methods for HZETRN and Coupling to Low Energy Light Ion Transport

    NASA Technical Reports Server (NTRS)

    Blattnig, S.R.; Slaba, T.C.; Heinbockel, J.H.

    2008-01-01

    Exposure estimates inside space vehicles, surface habitats, and high altitude aircraft exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward-backward (FB) and directionally coupled forward-backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETCHEDS and FLUKA, and the DC model is shown to agree closely with the Monte Carlo results. Finally, it is found in the development of either model that the decoupling of low energy neutrons from the light ion (A<4) transport procedure adversely affects low energy light ion fluence spectra and exposure quantities. A first order correction is presented to resolve the problem, and it is shown to be both accurate and efficient.

  14. Neutron Transport Models and Methods for HZETRN and Coupling to Low Energy Light Ion Transport

    NASA Technical Reports Server (NTRS)

    Blattnig, S.R.; Slaba, T.C.; Heinbockel, J.H.

    2008-01-01

    Exposure estimates inside space vehicles, surface habitats, and high altitude aircraft exposed to space radiation are highly influenced by secondary neutron production. The deterministic transport code HZETRN has been identified as a reliable and efficient tool for such studies, but improvements to the underlying transport models and numerical methods are still necessary. In this paper, the forward-backward (FB) and directionally coupled forward-backward (DC) neutron transport models are derived, numerical methods for the FB model are reviewed, and a computationally efficient numerical solution is presented for the DC model. Both models are compared to the Monte Carlo codes HETCHEDS and FLUKA, and the DC model is shown to agree closely with the Monte Carlo results. Finally, it is found in the development of either model that the decoupling of low energy neutrons from the light ion (A<4) transport procedure adversely affects low energy light ion fluence spectra and exposure quantities. A first order correction is presented to resolve the problem, and it is shown to be both accurate and efficient.

  15. WATER TRANSPORT IN INVERTEBRATE PERIPHERAL NERVE FIBERS

    PubMed Central

    Nevis, Arnold H.

    1958-01-01

    Osmotic and diffusion permeabilities (Pf and Pd) of invertebrate nerve fibers to tritiated water were measured to determine what water flux studies could reveal about "the nerve membrane" and to directly test the possibility of active transport of water into or out of invertebrate nerve fibers. Pf/Pd ratios for lobster walking leg nerve fibers were found to be about 20 ± 7 at 14°C. Pd measurements were made for squid giant axons at 25°C. and found to yield a value of 4 x 10–4 cm.–1 sec.–1. When combined with the data of D. K. Hill for Pf, a Pf/Pd ratio of 21 ± 5 is obtained. These Pf/Pd ratios correspond to "effective pore radii" of about 16 ± 4 angstrom units, according to theories developed by Koefoed-Johnsen and Ussing and independently by Pappenheimer and his colleagues. Variations of water flux ratios with temperatures were studied and apparent activation energies calculated for both diffusion experiments and osmotic filtration experiments using the Arrhenius equation, and found to be close to 3 to 5 cal. per mole of water transferred. Cyanide (5 x 10–3 molar) and iodoacetate (1 x 10–3 molar) poisoned lobster leg nerve fibers showed no appreciable change in diffusion or osmotic filtration water effluxes. Caution in interpreting these proposed channels as simple pores was emphasized, but the possibility that such channels exist and are related to ionic flow is not incompatible with electrophysiological data. PMID:13525675

  16. Long-term modeling of alteration-transport coupling: Application to a fractured Roman glass

    NASA Astrophysics Data System (ADS)

    Verney-Carron, Aurélie; Gin, Stéphane; Frugier, Pierre; Libourel, Guy

    2010-04-01

    To improve confidence in glass alteration models, as used in nuclear and natural applications, their long-term predictive capacity has to be validated. For this purpose, we develop a new model that couples geochemical reactions with transport and use a fractured archaeological glass block that has been altered for 1800 years under well-constrained conditions in order to test the capacity of the model. The chemical model considers three steps in the alteration process: (1) formation of a hydrated glass by interdiffusion, whose kinetics are controlled by a pH and temperature dependent diffusion coefficient; (2) the dissolution of the hydrated glass, whose kinetics are based on an affinity law; (3) the precipitation of secondary phases if thermodynamic saturation is reached. All kinetic parameters were determined from experiments. The model was initially tested on alteration experiments in different solutions (pure water, Tris, seawater). It was then coupled with diffusive transport in solution to simulate alteration in cracks within the glass. Results of the simulations run over 1800 years are in good agreement with archaeological glass block observations concerning the nature of alteration products (hydrated glass, smectites, and carbonates) and crack alteration thicknesses. External cracks in direct contact with renewed seawater were altered at the forward dissolution rate and are filled with smectites (400-500 μm). Internal cracks are less altered (by 1 or 2 orders of magnitude) because of the strong coupling between alteration chemistry and transport. The initial crack aperture, the distance to the surface, and sealing by secondary phases account for these low alteration thicknesses. The agreement between simulations and observations thus validates the predictive capacity of this coupled geochemical model and increases more generally the robustness and confidence in glass alteration models to predict long-term behavior of nuclear waste in geological disposal or

  17. CFEST Coupled Flow, Energy & Solute Transport Version CFEST005 User’s Guide

    SciTech Connect

    Freedman, Vicky L.; Chen, Yousu; Gilca, Alex; Cole, Charles R.; Gupta, Sumant K.

    2006-07-20

    The CFEST (Coupled Flow, Energy, and Solute Transport) simulator described in this User’s Guide is a three-dimensional finite-element model used to evaluate groundwater flow and solute mass transport. Confined and unconfined aquifer systems, as well as constant and variable density fluid flows can be represented with CFEST. For unconfined aquifers, the model uses a moving boundary for the water table, deforming the numerical mesh so that the uppermost nodes are always at the water table. For solute transport, changes in concentra¬tion of a single dissolved chemical constituent are computed for advective and hydrodynamic transport, linear sorption represented by a retardation factor, and radioactive decay. Although several thermal parameters described in this User’s Guide are required inputs, thermal transport has not yet been fully implemented in the simulator. Once fully implemented, transport of thermal energy in the groundwater and solid matrix of the aquifer can also be used to model aquifer thermal regimes. The CFEST simulator is written in the FORTRAN 77 language, following American National Standards Institute (ANSI) standards. Execution of the CFEST simulator is controlled through three required text input files. These input file use a structured format of associated groups of input data. Example input data lines are presented for each file type, as well as a description of the structured FORTRAN data format. Detailed descriptions of all input requirements, output options, and program structure and execution are provided in this User’s Guide. Required inputs for auxillary CFEST utilities that aide in post-processing data are also described. Global variables are defined for those with access to the source code. Although CFEST is a proprietary code (CFEST, Inc., Irvine, CA), the Pacific Northwest National Laboratory retains permission to maintain its own source, and to distribute executables to Hanford subcontractors.

  18. Noncontact transportation in water using ultrasonic traveling waves.

    PubMed

    Nomura, Shinfuku; Matula, Thomas J; Satonobu, Jun; Crum, Lawrence A

    2007-03-01

    A noncontact transport experiment in water using ultrasonic traveling waves was investigated. Acrylic, aluminum, and brass discs were used as test objects. Traveling waves were generated using two ultrasonic transducers attached at the ends of a vibrating plate. One side was used as the wave-source side and the other side was used as the wave-receiving side. Acrylic plates cemented to the sides of the vibrating plate formed a tank to hold water. Object transportation was accomplished by adding a small amount of water to the vibrating structure. The transport velocity of floating objects in water is faster than for floating transport in air because of buoyancy. The transport velocity of an object depends on water height. The minimum value of the velocity occurs when the disc thickness is equal to the water height. The transport velocity increases as the height of water increases. For very shallow depths, the largest velocity is obtained when cavitation-induced streaming occurs.

  19. Water transport in graphene nano-channels

    NASA Astrophysics Data System (ADS)

    Wagemann, Enrique; Oyarzua, Elton; Walther, J. H.; Zambrano, Harvey

    2015-11-01

    The transport of water in nanopores is of both fundamental and practical interest. Graphene Channels (GCs) are potential building blocks for nanofluidic devices due to their molecularly smooth walls and exceptional mechanical properties. Numerous studies have found a significant flow rate enhancement, defined as the ratio of the computed flow rate to that predicted from the classical Poiseuille model. Moreover, these studies point to the fact that the flow enhancement is a function of channel height and the fluid-wall physical-chemistry. In spite of the intensive research, an explicit relation between the chirality of the graphene walls and the slip length has not been established. In this study, we perform non-equilibrium molecular dynamics simulations of water flow in single- and multi-walled GCs. We examine the influence on the flow rates of dissipating the viscous heat produced by connecting the thermostat to the water molecules, the CNT wall atoms or both of them. From the atomic trajectories, we compute the fluid flow rates in GCs with zig-zag and armchair walls, heights from 1 to 4 nm and different number of graphene layers on the walls. A relation between the chirality, slip length, and flow enhancement is found. We aknowledge partial support from Fondecyt project 11130559 and Redoc udec.

  20. Atmospheric Heat Transport Feedbacks to Freshwater Forcing in the Coupled GCM GISS Model

    NASA Astrophysics Data System (ADS)

    Legrande, A. N.; Schmidt, G. A.

    2005-12-01

    We perform a range of North Atlantic fresh water forcing simulations in the GISS ModelE coupled GCM. Here we present results from two sets of experiments designed to explore the sensitivity of the model to varying fresh water pulses: (1) 12 relatively small simulations emulate the magnitude and placement of 8kyr event and (2) much larger and longer PhosMIP2 hosing experiments (0.1 Sv rate and 1 Sv rate). We find that within the first set of simulations, the modeled THC response to the freshwater forcing is stochastic - the largest volume of fresh water produces neither the largest response, nor the longest perturbation of THC. We evaluate the nature of modeled THC response given (1) a range of volumes, rates, and lengths of freshwater forcing; (2) two locations of fresh water input; and (3) two base states prior to the freshwater forcing. In all simulations, reduced overturning circulation in the Atlantic results in reduced northward heat transport by the ocean (OHT); we evaluate the response of heat transport in the atmosphere (AHT) and address to what extent the rest of the climate system compensates for the reduced OHT.

  1. Active H+ transport in the turtle urinary bladder. Coupling of transport to glucose oxidation

    PubMed Central

    1976-01-01

    The turtle urinary bladder acidifies the contents of its lumen by actively transporting protons. H+ secretion by the isolated bladder was measured simultaneously with the rate of 14CO2 evolution from [14C]glucose. The application of an adverse pH gradient resulted in a decline in the rate of H+ secretion (JH) and in the rate of glucose oxidation (JCO2). The changes in JH and JCO2 were linear functions of the pH difference across the membrane. Hence, JH and JCO2 were linearly related to each other. The slope, deltaJH/deltaJCO2 was found to be similar in half-bladders from the same animal but was seen to vary widely in a population of turtles. To investigate the effect of pH gradients on deltaJH/deltaJCO2, two experiments were performed in each of 14 hemibladders. In one, JH and JCO2 were altered by changing the luminal pH. In the other, they were altered by changing the ambient pCO2 while the luminal pH was kept constant. The average slope, deltaJH/deltaJCO2, in the presence of pH gradients was 14.45 eq-mol-1. In the absence of gradients in the same hemibladders it was 14.72, delta = 0.27 +/- 1.46. The results show that H+ transport is organized in such a way that leaks to protons in parallel to the pump are negligible. Analysis of the transport system by use of the Essig-Caplan linear irreversible thermodynamic formalism shows that the system is tightly coupled. The degree of coupling, q, given by that analysis was measured and found to be at or very near the maximum theoretical value. PMID:11270

  2. Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model

    USGS Publications Warehouse

    Warner, J.C.; Sherwood, C.R.; Signell, R.P.; Harris, C.K.; Arango, H.G.

    2008-01-01

    We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection-diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave-current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay. ?? 2008 Elsevier Ltd. All rights reserved.

  3. Eddy transport of water vapor in the Martian atmosphere

    NASA Technical Reports Server (NTRS)

    Murphy, J. R.; Haberle, Robert M.

    1993-01-01

    Viking orbiter measurements of the Martian atmosphere suggest that the residual north polar water-ice cap is the primary source of atmospheric water vapor, which appears at successively lower northern latitudes as the summer season progresses. Zonally symmetric studies of water vapor transport indicate that the zonal mean meridional circulation is incapable of transporting from north polar regions to low latitudes the quantity of water vapor observed. This result has been interpreted as implying the presence of nonpolar sources of water. Another possibility is the ability of atmospheric wave motions, which are not accounted for in a zonally symmetric framework, to efficiently accomplish the transport from a north polar source to the entirety of the Northern Hemisphere. The ability or inability of the full range of atmospheric motions to accomplish this transport has important implications regarding the questions of water sources and sinks on Mars: if the full spectrum of atmospheric motions proves to be incapable of accomplishing the transport, it strengthens arguments in favor of additional water sources. Preliminary results from a three dimensional atmospheric dynamical/water vapor transport numerical model are presented. The model accounts for the physics of a subliming water-ice cap, but does not yet incorporate recondensation of this sublimed water. Transport of vapor away from this water-ice cap in this three dimensional framework is compared with previously obtained zonally symmetric (two dimensional) results to quantify effects of water vapor transport by atmospheric eddies.

  4. Water Transport in Maize Roots 1

    PubMed Central

    Steudle, Ernst; Oren, Ram; Schulze, Ernst-Detlef

    1987-01-01

    A root pressure probe has been used to measure the root pressure (Pr) exerted by excised main roots of young maize plants (Zea Mays L.). Defined gradients of hydrostatic and osmotic pressure could be set up between root xylem and medium to induce radial water flows across the root cylinder in both directions. The hydraulic conductivity of the root (Lpr) was evaluated from root pressure relaxations. When permeating solutes were added to the medium, biphasic root pressure relaxations were observed with water and solute phases and root pressure minima (maxima) which allowed the estimation of permeability (PSr) and reflection coefficients (σsr) of roots. Reflection coefficients were: ethanol, 0.27; mannitol, 0.74; sucrose, 0.54; PEG 1000, 0.82; NaCl, 0.64; KNO3, 0.67, and permeability coefficients (in 10−8 meters per second): ethanol, 4.7; sucrose, 1.6; and NaCl, 5.7. Lpr was very different for osmotic and hydrostatic gradients. For hydrostatic gradients Lpr was 1·10−7 meters per second per megapascal, whereas in osmotic experiments the hydraulic conductivity was found to be an order of magnitude lower. For hydrostatic gradients, the exosmotic Lpr was about 15% larger than the endosmotic, whereas in osmotic experiments the polarity in the water movement was reversed. These results either suggest effects of unstirred layers at the osmotic barrier in the root, an asymmetrical barrier, and/or mechanical effects. Measurements of the hydraulic conductivity of individual root cortex cells revealed an Lp similar to Lpr (hydrostatic). It is concluded that, in the presence of external hydrostatic gradients, water moves primarily in the apoplast, whereas in the presence of osmotic gradients this component is much smaller in relation to the cell-to-cell component (symplasmic plus transcellular transport). PMID:16665588

  5. Numerical Investigation of Laser Propulsion for Transport in Water Environment

    SciTech Connect

    Han Bing; Li Beibei; Zhang Hongchao; Chen Jun; Shen Zhonghua; Lu Jian; Ni Xiaowu

    2010-10-08

    Problems that cumber the development of the laser propulsion in atmosphere and vacuum are discussed. Based on the theory of interaction between high-intensity laser and materials, as air and water, it is proved that transport in water environment can be impulsed by laser. The process of laser propulsion in water is investigated theoretically and numerically. It shows that not only the laser induced plasma shock wave, but also the laser induced bubble oscillation shock waves and the pressure induced by the collapsing bubble can be used. Many experimental results show that the theory and the numerical results are valid. The numerical result of the contribution of every propulsion source is given in percentage. And the maximum momentum coupling coefficient Cm is given. Laser propulsion in water environment can be applied in many fields. For example, it can provide highly controllable forces of the order of micro-Newton ({mu}N) in microsystems, such as the MEMS (Micro-electromechanical Systems). It can be used as minimally invasive surgery tools of high temporal and spatial resolution. It can be used as the propulsion source in marine survey and exploitation.

  6. Numerical Investigation of Laser Propulsion for Transport in Water Environment

    NASA Astrophysics Data System (ADS)

    Han, Bing; Li, Bei-Bei; Zhang, Hong-Chao; Chen, Jun; Shen, Zhong-Hua; Lu, Jian; Ni, Xiao-Wu

    2010-10-01

    Problems that cumber the development of the laser propulsion in atmosphere and vacuum are discussed. Based on the theory of interaction between high-intensity laser and materials, as air and water, it is proved that transport in water environment can be impulsed by laser. The process of laser propulsion in water is investigated theoretically and numerically. It shows that not only the laser induced plasma shock wave, but also the laser induced bubble oscillation shock waves and the pressure induced by the collapsing bubble can be used. Many experimental results show that the theory and the numerical results are valid. The numerical result of the contribution of every propulsion source is given in percentage. And the maximum momentum coupling coefficient Cm is given. Laser propulsion in water environment can be applied in many fields. For example, it can provide highly controllable forces of the order of micro-Newton (μN) in microsystems, such as the MEMS (Micro-electromechanical Systems). It can be used as minimally invasive surgery tools of high temporal and spatial resolution. It can be used as the propulsion source in marine survey and exploitation.

  7. Water electrolyte transport through corrugated carbon nanopores.

    PubMed

    Moghimi Kheirabadi, A; Moosavi, A

    2014-07-01

    We investigate the effect of wall roughness on water electrolyte transport characteristics at different temperatures through carbon nanotubes by using nonequilibrium molecular dynamics simulations. Our results reveal that shearing stress and the nominal viscosity increase with ion concentration in corrugated carbon nanotubes (CNTs), in contrast to cases in smooth CNTs. Also, the temperature increase leads to the reduction of shearing stress and the nominal viscosity at moderate degrees of wall roughness. At high degrees of wall roughness, the temperature increase will enhance radial movements and increases resistance against fluid motion. As the fluid velocity increases, the particles do not have enough time to fully adjust their positions to minimize system energy, which causes shearing stress and the nominal viscosity to increase. By increasing roughness amplitude or decreasing roughness wavelength, the shearing stress will increase. Synergistic effects of such parameters (wall roughness, velocity, ion concentration, and temperature) inside corrugated CNTs are studied and compared with each other. The molecular mechanisms are considered by investigating the radial density profile and the radial velocity profile of confined water inside modified CNT.

  8. The transport of 'suspended' sediment by water

    NASA Astrophysics Data System (ADS)

    Parsons, Anthony; Cooper, James; Wainwright, John; Sekiguichi, Tomohiro

    2013-04-01

    Coherent turbulent flow structures, such as eddy-like, macro-turbulent structures and smaller scale bursting events, cause a two-way vertical exchange of momentum between the sediment bed and the water surface. Thus movement of suspended particles in open channel flows has a strong correlation with the advection and propagation of these turbulent flow structures, controlling entrainment , travel and deposition. Consequently, there is an argument in favour of the view that suspended sediment merely travels in suspension, but that its distance of travel is finite, and that between periods of travel it is at rest on the bed of the river. To test his hypothesis we added 25 kg of fluorescent sand, fine enough to be transported in suspension, into a steady flow discharge of 0.95 cumecs in the 160-m-long flume at Tsukuba University. After the flow event, a few grains of the sand were identified less than 5 m from the point of introduction and progressively (but irregularly) more downflume. Although our results are both limited and preliminary due to the nature of the existing flume, they clearly show that suspended sediment has a virtual velocity that is less than that of the flow in which the sediment is suspended. For the sediment-size range and flow velocity used in our experiment this virtual velocity is of the order of 50% of the water velocity.

  9. A coupling kinetics model for pollutant release and transport in the process of landfill settlement.

    PubMed

    Zhao, Ying; Xue, Qiang; Liu, Lei

    2012-09-27

    A coupling kinetics model is developed to simulate the release and transport of landfill leachate pollutants in a deformable municipal solid waste landfill by taking into account of landfill settlement, seepage of leachate water, hydrolyse of insoluble and degradable organic pollutants in solid phase, biodegradation of soluble and degradable organic pollutants in solid phase and aqueous one, growth of aerobic and anaerobic microorganism, and consumption of dissolved oxygen. The release and transport of organic pollutants and microorganisms in landfills in the process of landfill settlement was simulated by considering no hydraulic effect. Simulation results demonstrated that the interaction between landfill settlement and the release, transport and biodegradation of landfill leachate pollutants was significant. Porosity and saturated hydraulic conductivity were not constants because of the landfill settlement, which affected the release, transport and biodegradation of landfill leachate pollutants, and furthermore acted on the landfill settlement. The simulation results accorded with the practical situation, which preliminarily verified the reliability of the mathematical model and the numerical program in this paper.

  10. A Coupling Kinetics Model for Pollutant Release and Transport in the Process of Landfill Settlement

    PubMed Central

    Zhao, Ying; Xue, Qiang; Liu, Lei

    2012-01-01

    A coupling kinetics model is developed to simulate the release and transport of landfill leachate pollutants in a deformable municipal solid waste landfill by taking into account of landfill settlement, seepage of leachate water, hydrolyse of insoluble and degradable organic pollutants in solid phase, biodegradation of soluble and degradable organic pollutants in solid phase and aqueous one, growth of aerobic and anaerobic microorganism, and consumption of dissolved oxygen. The release and transport of organic pollutants and microorganisms in landfills in the process of landfill settlement was simulated by considering no hydraulic effect. Simulation results demonstrated that the interaction between landfill settlement and the release, transport and biodegradation of landfill leachate pollutants was significant. Porosity and saturated hydraulic conductivity were not constants because of the landfill settlement, which affected the release, transport and biodegradation of landfill leachate pollutants, and furthermore acted on the landfill settlement. The simulation results accorded with the practical situation, which preliminarily verified the reliability of the mathematical model and the numerical program in this paper. PMID:23202755

  11. Target analysis studies of red cell water and urea transport.

    PubMed

    Dix, J A; Ausiello, D A; Jung, C Y; Verkman, A S

    1985-12-05

    Radiation inactivation was used to determine the nature and molecular weight of water and urea transporters in the human red cell. Red cells were frozen to -50 degrees C in a cryoprotectant solution, irradiated with 1.5 MeV electrons, thawed, washed and assayed for osmotic water and urea permeability by stopped-flow light scattering. The freezing and thawing process did not affect the rates of water or urea transport or the inhibitory potency of p-chloromercuribenzenesulfonate (pCMBS) on water transport and of phloretin on urea transport. Red cell urea transport inactivated with radiation (0-4 Mrad) with a single target size of 469 +/- 36 kDa. 40 microM phloretin inhibited urea flux by approx. 50% at each radiation dose, indicating that urea transporters surviving radiation were inhibitable. Water transport did not inactivate with radiation; however, the inhibitory potency of 2.5 mM pCMBS decreased from 86 +/- 1% to 4 +/- 9% over a 0-2 Mrad dose range. These studies suggest that red cell water transport either required one or more low-molecular-weight proteins, or is lipid-mediated, and that the pCMBS-binding site which regulates water flow inactivates with radiation. These results also suggest that red cell urea transport is mediated by a specific, high-molecular-weight protein. These results do not support the hypothesis that a band 3 dimer (190 kDa) mediates red cell osmotic water and urea transport.

  12. Radiation transport within oceanic (case 1) water

    NASA Astrophysics Data System (ADS)

    Morel, André; Gentili, Bernard

    2004-06-01

    A spectral model of the inherent optical properties (IOP) of oceanic case 1 waters, as previously developed for studying the near-surface bidirectional reflectance, provides the input parameters for the present computations of radiative transport (RT), now extended throughout the water column (three times the euphotic zone). All spectral apparent optical properties (AOP) are computed at each of the levels (30) for six chlorophyll values (from 0.03 to 10 mg m-3) and for six values of the zenith Sun angle (from 0° to 75°). The Raman emission is accounted for. From the irradiances and radiances values the various attenuation coefficients (K), the average cosines (?), and the reflectance (R) are derived for all depths and layers. Their variations resulting from the Sun's position are also studied, which removes the static character of previous empirical models inasmuch as the diurnal changes of the parameters describing the in-water light field can be predicted. The AOPs observed within the deepest levels are also compared to values independently derived from an asymptotic (iterative) solution of the RT. The rate of approach to the asymptotic regime is numerically analyzed; this rate is actually governed by τb, i.e., this fraction of τ (the optical thickness) that corresponds only to scattering. Practical applications of these systematic computations are examined, such as the change (with solar position) of the euphotic depth, the time- and wavelength-dependent scalar irradiance that controls during the day the energy available for photosynthesis (or the heating rate), and the interpretation of radiometric field experiments involving upward and downward irradiance measurements. Some approximate expressions relating AOPs to IOPs are examined in the light of exact computations.

  13. Vapor Transport Modeling of Continental Water Isotope Gradients

    NASA Astrophysics Data System (ADS)

    Ritch, A. J.; Caves, J. K.; Ibarra, D. E.; Winnick, M. J.; Chamberlain, C. P.

    2015-12-01

    Stable isotopes have been widely used to reconstruct past climatic conditions and topographic histories of mountain belts. However, many studies do not account for the influences of evapotranspiration and vapor recycling on downstream meteoric water isotopic compositions. Here we present a case study of the modern Sierra Nevada and Basin and Range to illustrate the value of using process-based models across larger spatial scales to reconstruct the conditions driving local- to regional-scale water isotopic compositions. We use a one-dimensional reactive vapor transport model, driven by the National Centers for Environmental Prediction (NCEP) high-resolution North American Regional Reanalysis (NARR) dataset, to simulate the isotopic composition of modern meteoric waters (δ18O and δD) along storm tracks across the Sierra Nevada and Basin and Range. Storm track pathways are generated using NOAA's Air Resources Laboratory's Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. In addition, we couple the vapor transport model with a soil moisture model to simulate depth profiles of the oxygen isotopic composition of authigenic carbonate along our storm tracks. We show that, given reasonable estimates of the modern partitioning between evaporation and transpiration, our model output is in agreement with modern isotopic data both from compilations of published meteoric water samples and from newly collected soil carbonate samples along a transect across the northern Sierra Nevada and Basin and Range (~38-42° N). These results demonstrate that our modeling approach can be used to analyze the relative contributions of climate and topography to observed isotopic gradients. Future studies can apply this modeling framework to isotopes preserved in the geologic record to provide a quantitative means of understanding the paleoclimatic influences on spatial isotopic distributions.

  14. Ion transport asymmetry and functional coupling in bovine pigmented and nonpigmented ciliary epithelial cells.

    PubMed

    Edelman, J L; Sachs, G; Adorante, J S

    1994-05-01

    The solute and water transport properties of the bovine ciliary epithelium were studied using isolated pigmented (PE) and nonpigmented (NPE) cells. It was shown that these cells were functionally coupled by demonstrating dye diffusion between paired PE and NPE cells after microinjection of lucifer yellow. Electronic cell sizing was used to measure cell volume changes of isolated PE and NPE cells in suspension after anisosmotic perturbations and after transport inhibition under isosmotic conditions. The PE cells showed the presence of a regulatory volume increase when subjected to osmotic shrinkage with NaCl, whereas the NPE cells did not demonstrate a regulatory volume increase under these conditions. In contrast, the NPE cells exhibited a regulatory volume decrease when subjected to osmotic swelling, whereas the PE cells did not recover from swelling. The regulatory volume decrease in NPE cells was inhibited by increased bath K or pretreatment with quinine (1 mM). The presence of a bumetanide-sensitive mechanism capable of moving measurable amounts of solute and water, probably Na-K-2Cl cotransport, was demonstrated in the PE cells but absent in the NPE cells. Bumetanide produced a dose-dependent shrinkage of PE cells at concentrations as low as 1 microM. Isosmotically reducing bath Cl, Na, or K concentration caused a rapid shrinkage of PE cells that was bumetanide inhibitable. The asymmetry of transport properties in PE and NPE cells supports a functional syncytium model of aqueous humor formation (39) across the two layers of the ciliary epithelium wherein ion uptake from the blood is carried out by the PE cells and ion extrusion by the NPE cells. Gap-junction coupling between the cells allows the ions taken up by the PE cells to move into the NPE cells. Extrusion of Na by the Na-K pump across the aqueous facing (basolateral) membranes of the NPE cells, most likely accompanied by Cl, determines the formation of the aqueous humor.

  15. Determining the climatic drivers of speleothem proxy variability: coupling modern cave monitoring with a multicomponent reactive transport model

    NASA Astrophysics Data System (ADS)

    Covey, A. K.; Oster, J. L.; Druhan, J. L.; Lawrence, C. R.

    2015-12-01

    Speleothem isotopic and geochemical proxy records can illuminate changes in climate patterns, soils, vegetation, and the amount of seepage water flow into a cave. However, the number of potential chemical and transport mechanisms that influence drip water composition can complicate speleothem records. A thorough understanding of processes affecting isotopic and geochemical compositions of modern cave waters is essential for interpreting proxies in a climate context. We couple a reactive transport model, CrunchTope, with modern measurements from Blue Spring Cave, Tennessee to understand the factors controlling proxy variability. For 2 years we have monitored surface and soil temperature, precipitation and soil moisture, cave temperature and pCO2, drip rate, and drip water chemistry, δ18O, and δ13C of dissolved inorganic carbon (DIC). The range of variability in drip water δ18O indicates some drips are fed by fracture flow from the surface, while others are fed by more diffuse flow paths. For both drip types, δ13CDIC is inversely correlated with monthly rainfall. Cave air pCO2 suggests seasonal ventilation driven by surface air temperature change. Drip water Sr/Ca and Mg/Ca indicate prior carbonate precipitation (PCP) occurs in the epikarst, but do not appear to reflect cave ventilation. To improve interpretations of drip water geochemical variation, we parameterize CrunchTope with horizons representing soil, epikarst and karst. We use this model to simulate water chemistry changes due to coupled fluid transport and water-mineral interactions in the soils and bedrock. Initial model runs reproduce mean drip water [Sr] and [Mg]. Accurate simulation of drip water [Ca] requires inclusion of a low pCO2 layer that drives PCP. With the inclusion of isotope systematics, a baseline model calibrated with modern data will be available to simulate the effects of long-term climate change on cave waters, thus enhancing the quantitative interpretation of speleothem proxy

  16. How LeuT shapes our understanding of the mechanisms of sodium-coupled neurotransmitter transporters.

    PubMed

    Penmatsa, Aravind; Gouaux, Eric

    2014-03-01

    Neurotransmitter transporters are ion-coupled symporters that drive the uptake of neurotransmitters from neural synapses. In the past decade, the structure of a bacterial amino acid transporter, leucine transporter (LeuT), has given valuable insights into the understanding of architecture and mechanism of mammalian neurotransmitter transporters. Different conformations of LeuT, including a substrate-free state, inward-open state, and competitive and non-competitive inhibitor-bound states, have revealed a mechanistic framework for the transport and transport inhibition of neurotransmitters. The current review integrates our understanding of the mechanistic and pharmacological properties of eukaryotic neurotransmitter transporters obtained through structural snapshots of LeuT.

  17. A two-dimensional coupled flow-mass transport model based on an improved unstructured finite volume algorithm.

    PubMed

    Zhou, Jianzhong; Song, Lixiang; Kursan, Suncana; Liu, Yi

    2015-05-01

    A two-dimensional coupled water quality model is developed for modeling the flow-mass transport in shallow water. To simulate shallow flows on complex topography with wetting and drying, an unstructured grid, well-balanced, finite volume algorithm is proposed for numerical resolution of a modified formulation of two-dimensional shallow water equations. The slope-limited linear reconstruction method is used to achieve second-order accuracy in space. The algorithm adopts a HLLC-based integrated solver to compute the flow and mass transport fluxes simultaneously, and uses Hancock's predictor-corrector scheme for efficient time stepping as well as second-order temporal accuracy. The continuity and momentum equations are updated in both wet and dry cells. A new hybrid method, which can preserve the well-balanced property of the algorithm for simulations involving flooding and recession, is proposed for bed slope terms approximation. The effectiveness and robustness of the proposed algorithm are validated by the reasonable good agreement between numerical and reference results of several benchmark test cases. Results show that the proposed coupled flow-mass transport model can simulate complex flows and mass transport in shallow water.

  18. Proton-coupled sugar transport in the prototypical major facilitator superfamily protein XylE.

    PubMed

    Wisedchaisri, Goragot; Park, Min-Sun; Iadanza, Matthew G; Zheng, Hongjin; Gonen, Tamir

    2014-08-04

    The major facilitator superfamily (MFS) is the largest collection of structurally related membrane proteins that transport a wide array of substrates. The proton-coupled sugar transporter XylE is the first member of the MFS that has been structurally characterized in multiple transporting conformations, including both the outward and inward-facing states. Here we report the crystal structure of XylE in a new inward-facing open conformation, allowing us to visualize the rocker-switch movement of the N-domain against the C-domain during the transport cycle. Using molecular dynamics simulation, and functional transport assays, we describe the movement of XylE that facilitates sugar translocation across a lipid membrane and identify the likely candidate proton-coupling residues as the conserved Asp27 and Arg133. This study addresses the structural basis for proton-coupled substrate transport and release mechanism for the sugar porter family of proteins.

  19. Kumada–Grignard-type biaryl couplings on water

    PubMed Central

    Bhattacharjya, Anish; Klumphu, Piyatida; Lipshutz, Bruce H.

    2015-01-01

    Well-established, traditional Kumada cross-couplings involve preformed Grignard reagents in dry ethereal solvent that typically react, e.g., with aryl halides via Pd catalysis to afford products of net substitution. Therefore, in the work described, which appears to be counterintuitive, exposure of these same aromatic halides to catalytic amounts of Pd(II) and excess magnesium metal in pure water leads to symmetrical/unsymmetrical biaryls, indicative of a net Kumada-like biaryl coupling. Evidence is presented suggesting that Grignard reagents, formed in situ in water, may be involved. PMID:26084774

  20. Water transport inside carbon nanotubes mediated by phonon-induced oscillating friction

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Grey, François; Shen, Luming; Urbakh, Michael; Wu, Shuai; Liu, Jefferson Zhe; Liu, Yilun; Zheng, Quanshui

    2015-08-01

    The emergence of the field of nanofluidics in the last decade has led to the development of important applications including water desalination, ultrafiltration and osmotic energy conversion. Most applications make use of carbon nanotubes, boron nitride nanotubes, graphene and graphene oxide. In particular, understanding water transport in carbon nanotubes is key for designing ultrafiltration devices and energy-efficient water filters. However, although theoretical studies based on molecular dynamics simulations have revealed many mechanistic features of water transport at the molecular level, further advances in this direction are limited by the fact that the lowest flow velocities accessible by simulations are orders of magnitude higher than those measured experimentally. Here, we extend molecular dynamics studies of water transport through carbon nanotubes to flow velocities comparable with experimental ones using massive crowd-sourced computing power. We observe previously undetected oscillations in the friction force between water and carbon nanotubes and show that these oscillations result from the coupling between confined water molecules and the longitudinal phonon modes of the nanotube. This coupling can enhance the diffusion of confined water by more than 300%. Our results may serve as a theoretical framework for the design of new devices for more efficient water filtration and osmotic energy conversion devices.

  1. K9 water searches: scent and scent transport considerations.

    PubMed

    Osterkamp, Tom

    2011-07-01

    Increased use of water search dogs for detecting submerged bodies has created the need for a better understanding of scent emanating from the bodies and how it transits the water to the dog's nose. A review of recent literature identifies likely scent sources, potential scent transport processes, and research needs. Scent sources include gases in bubbles or dissolved in the water, liquids as buoyant plumes and droplets or dissolved in the water, and solids consisting of buoyant particulates with secretions, bacteria, and body fluids. Potential transport processes through the water include buoyancy, entrainment, and turbulence. Transport processes from the water surface into the air include volatilization and evaporation enhanced by bubble bursting, breaking waves, splashing, and wind spray. Implications for the use of water search dogs are examined. Observations of submerged, decomposing bodies are needed to quantify the physical and chemical characteristics of the scent and scent transport processes.

  2. Transport of Water in Semicrystalline Block Copolymer Membranes

    NASA Astrophysics Data System (ADS)

    Hallinan, Daniel; Oparaji, Onyekachi

    Poly(styrene)-block-poly(ethylene oxide) (PS- b-PEO) is a semicrystalline block copolymer (BCP) with interesting properties. It is mechanically tough, amphiphilic, and has a polar phase. The mechanical toughness is due to the crystallinity of PEO and the high glass transition temperature of PS, as well as the morphological structure of the BCP. The polymer has high CO2, water, and salt solubility that derive from the polar PEO component. Potential applications include CO2 separation, water purification, and lithium air batteries. In all of the aforementioned applications, water transport is an important parameter. The presence of water can also affect thermal and mechanical properties. Water transport and thermal and mechanical properties of a lamellar PS- b-PEO copolymer have been measured as a function of water activity. Water transport can be affected by the heterogeneous nature of a semicrystalline BCP. Therefore, Fourier transform infrared - attenuated total reflectance (FTIR-ATR) spectroscopy has been employed, because water transport and polymer swelling can be measured simultaneously. The effect of BCP structure on transport has been investigated by comparing water transport in PS- b-PEO to a PEO homopolymer. The crystalline content of the PEO and the presence of glassy PS lamellae will be used to explain the transport results.

  3. Coupling Protein Dynamics with Proton Transport in Human Carbonic Anhydrase II

    PubMed Central

    2016-01-01

    The role of protein dynamics in enzyme catalysis is one of the most highly debated topics in enzymology. The main controversy centers around what may be defined as functionally significant conformational fluctuations and how, if at all, these fluctuations couple to enzyme catalyzed events. To shed light on this debate, the conformational dynamics along the transition path surmounting the highest free energy barrier have been herein investigated for the rate limiting proton transport event in human carbonic anhydrase (HCA) II. Special attention has been placed on whether the motion of an excess proton is correlated with fluctuations in the surrounding protein and solvent matrix, which may be rare on the picosecond and subpicosecond time scales of molecular motions. It is found that several active site residues, which do not directly participate in the proton transport event, have a significant impact on the dynamics of the excess proton. These secondary participants are shown to strongly influence the active site environment, resulting in the creation of water clusters that are conducive to fast, moderately slow, or slow proton transport events. The identification and characterization of these secondary participants illuminates the role of protein dynamics in the catalytic efficiency of HCA II. PMID:27063577

  4. Coupling fine particle and bedload transport in gravel-bedded streams

    NASA Astrophysics Data System (ADS)

    Park, Jungsu; Hunt, James R.

    2017-09-01

    Fine particles in the silt- and clay-size range are important determinants of surface water quality. Since fine particle loading rates are not unique functions of stream discharge this limits the utility of the available models for water quality assessment. Data from 38 minimally developed watersheds within the United States Geological Survey stream gauging network in California, USA reveal three lines of evidence that fine particle release is coupled with bedload transport. First, there is a transition in fine particle loading rate as a function of discharge for gravel-bedded sediments that does not appear when the sediment bed is composed of sand, cobbles, boulders, or bedrock. Second, the discharge at the transition in the loading rate is correlated with the initiation of gravel mobilization. Third, high frequency particle concentration and discharge data are dominated by clockwise hysteresis where rising limb discharges generally have higher concentrations than falling limb discharges. These three observations across multiple watersheds lead to a conceptual model that fine particles accumulate within the sediment bed at discharges less than the transition and then the gravel bed fluidizes with fine particle release at discharges above the transition discharge. While these observations were individually recognized in the literature, this analysis provides a consistent conceptual model based on the coupling of fine particle dynamics with filtration at low discharges and gravel bed fluidization at higher discharges.

  5. Water Alignment, Dipolar Interactions, and Multiple Proton Occupancy during Water-Wire Proton Transport

    PubMed Central

    Chou, Tom

    2004-01-01

    A discrete multistate kinetic model for water-wire proton transport is constructed and analyzed using Monte Carlo simulations. In the model, each water molecule can be in one of three states: oxygen lone-pairs pointing leftward, pointing rightward, or protonated (H3O+). Specific rules for transitions among these states are defined as protons hop across successive water oxygens. Our model also includes water-channel interactions that preferentially align the water dipoles, nearest-neighbor dipolar coupling interactions, and Coulombic repulsion. Extensive Monte Carlo simulations were performed and the observed qualitative physical behaviors discussed. We find the parameters that allow the model to exhibit superlinear and sublinear current-voltage relationships, and show why alignment fields, whether generated by interactions with the pore interior or by membrane potentials, always decrease the proton current. The simulations also reveal a “lubrication” mechanism that suppresses water dipole interactions when the channel is multiply occupied by protons. This effect can account for an observed sublinear-to-superlinear transition in the current-voltage relationship. PMID:15111400

  6. Kinetic Modeling of Biogeochemical Processes in Subsurface Environments: Coupling Transport, Microbial Metabolism and Geochemistry

    NASA Astrophysics Data System (ADS)

    Wang, Y.

    2002-12-01

    Microbial reactions play an important role in regulating pore water chemistry (e.g., pH and Eh) as well as secondary mineral distribution in many subsurface systems and therefore directly control trace metal migration and recycling in those systems. In this paper, we present a multicomponent kinetic model that explicitly accounts for the coupling of microbial metabolism, microbial population dynamics, advective/dispersive transport of chemical species, aqueous speciation, and mineral precipitation/dissolution in porous geologic media. A modification to the traditional microbial growth kinetic equation is proposed, to account for the likely achievement of quasi-steady state biomass accumulations in natural environments. A scale dependence of microbial reaction rates is derived based on both field observations and the scaling analysis of reactive transport equations. As an example, we use the model to simulate a subsurface contaminant migration scenario, in which a water flow containing both uranium and a complexing organic ligand is recharged into an oxic carbonate aquifer. The model simulation shows that Mn and Fe oxyhydroxides may vary significantly along a flow path. The simulation also shows that uranium (VI) can be reduced and therefore immobilized in the anoxic zone created by microbial degradation. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy (US DOE) under Contract DE-AC04-94AL85000.

  7. Water Transport through Cohesion-Tension in Porous Structures

    NASA Astrophysics Data System (ADS)

    Kosaraju, Srinivas

    2015-11-01

    The predominant theory to explain water transport through plant xylem is the cohesion-tension theory. According to the theory, negative pressure is created due to water evaporation through millions of microscopic capillary pores from tree leaves. The negative pressures are large enough to lift water hundreds of feet against gravity. In an attempt to replicate the process, multiple structures with varying porosity are tested to create negative pressures through water evaporation. The negative pressure created is used to support a water column. The current research is aimed to create artificial leaves using porous structures and be able to transport water in high rise buildings using renewable energy sources such as solar power.

  8. Temperature influence on water transport in hardened cement pastes

    SciTech Connect

    Drouet, Emeline; Poyet, Stéphane; Torrenti, Jean-Michel

    2015-10-15

    Describing water transport in concrete is an important issue for the durability assessment of radioactive waste management reinforced concrete structures. Due to the waste thermal output such structures would be submitted to moderate temperatures (up to 80 °C). We have then studied the influence of temperature on water transport within hardened cement pastes of four different formulations. Using a simplified approach (describing only the permeation of liquid water) we characterized the properties needed to describe water transport (up to 80 °C) using dedicated experiments. For each hardened cement paste the results are presented and discussed.

  9. Numerical Modeling of Coupled Groundwater and Surface Water Interactions in an Urban Setting

    SciTech Connect

    Rihani, J F; Maxwell, R M

    2007-09-26

    balance and hydrology of DCW, a parallel, distributed watershed model that treats flow in groundwater and surface water in a dynamically coupled manner will be used to build a flow model of the watershed. This coupled model forms the basis for modeling and understanding the transport of contaminants through the Dominguez Channel Watershed, which can be used in designing and implementing TMDLs to manage the water quality in this basin. In this report, the coupled surface water-groundwater flow model of DCW will be presented. This flow model was calibrated against a storm that occurred in February 21st, 2004. The model and approach are explained further in the following sections.

  10. Modeling substrate-bacteria-grazer interactions coupled to substrate transport in groundwater

    NASA Astrophysics Data System (ADS)

    Bajracharya, Bijendra M.; Lu, Chuanhe; Cirpka, Olaf A.

    2014-05-01

    Models of microbial dynamics coupled to solute transport in aquifers typically require the introduction of a bacterial capacity term to prevent excessive microbial growth close to substrate-injection boundaries. The factors controlling this carrying capacity, however, are not fully understood. In this study, we propose that grazers or bacteriophages may control the density of bacterial biomass in continuously fed porous media. We conceptualize the flow-through porous medium as a series of retentostats, in which the dissolved substrate is advected with water flow whereas the biomasses of bacteria and grazers are considered essentially immobile. We first model a single retentostat with Monod kinetics of bacterial growth and a second-order grazing law, which shows that the system oscillates but approaches a stable steady state with nonzero concentrations of substrate, bacteria, and grazers. The steady state concentration of the bacteria biomass is independent of the substrate concentration in the inflow. When coupling several retentostats in a series to mimic a groundwater column, the steady state bacteria concentrations thus remain at a constant level over a significant travel distance. The one-dimensional reactive transport model also accounts for substrate dispersion and a random walk of grazers influenced by the bacteria concentration. These dispersive-diffusive terms affect the oscillations until steady state is reached, but hardly the steady state value itself. We conclude that grazing, or infection by bacteriophages, is a possible explanation of the maximum biomass concentration frequently needed in bioreactive transport models. Its value depends on parameters related to the grazers or bacteriophages and is independent of bacterial growth parameters or substrate concentration, provided that there is enough substrate to sustain bacteria and grazers.

  11. Effect of spin rotation coupling on spin transport

    SciTech Connect

    Chowdhury, Debashree Basu, B.

    2013-12-15

    We have studied the spin rotation coupling (SRC) as an ingredient to explain different spin-related issues. This special kind of coupling can play the role of a Dresselhaus like coupling in certain conditions. Consequently, one can control the spin splitting, induced by the Dresselhaus like term, which is unusual in a semiconductor heterostructure. Within this framework, we also study the renormalization of the spin-dependent electric field and spin current due to the k{sup →}⋅p{sup →} perturbation, by taking into account the interband mixing in the rotating system. In this paper we predict the enhancement of the spin-dependent electric field resulting from the renormalized spin rotation coupling. The renormalization factor of the spin electric field is different from that of the SRC or Zeeman coupling. The effect of renormalized SRC on spin current and Berry curvature is also studied. Interestingly, in the presence of this SRC-induced SOC it is possible to describe spin splitting as well as spin galvanic effect in semiconductors. -- Highlights: •Studied effect of spin rotation coupling on the spin electric field, spin current and Berry curvature. •In the k{sup →}⋅p{sup →} framework we study the renormalization of spin electric field and spin current. •For an inertial system we have discussed the spin splitting. •Expression for the Berry phase in the inertial system is discussed. •The inertial spin galvanic effect is studied.

  12. Geometry and transport in a model of two coupled quadratic nonlinear waveguides.

    PubMed

    Stirling, James R; Bang, Ole; Christiansen, Peter L; Zakynthinaki, Maria S; Johansen, Steffen Kjaer

    2008-03-01

    This paper applies geometric methods developed to understand chaos and transport in Hamiltonian systems to the study of power distribution in nonlinear waveguide arrays. The specific case of two linearly coupled chi((2)) waveguides is modeled and analyzed in terms of transport and geometry in the phase space. This gives us a transport problem in the phase space resulting from the coupling of the two Hamiltonian systems for each waveguide. In particular, the effect of the presence of partial and complete barriers in the phase space on the transfer of intensity between the waveguides is studied, given a specific input and range of material properties. We show how these barriers break down as the coupling between the waveguides is increased and what the role of resonances in the phase space has in this. We also show how an increase in the coupling can lead to chaos and global transport and what effect this has on the intensity.

  13. Water/Ice Heat Sink With Quick-Connect Couplings

    NASA Technical Reports Server (NTRS)

    Lomax, Curtis; Webbon, Bruce

    1996-01-01

    Report presents additional detailed information on apparatus described in "Direct-Interface, Fusible Heat Sink" (ARC-11920). Describes entire apparatus, with special emphasis on features of quick-disconnect couplings governing flow of water under various operating conditions and plumbing configuration.

  14. Coupling of Volatile Transport and Internal Heatflow on Triton

    NASA Technical Reports Server (NTRS)

    Brown, R. H.; Kirk, R. L.

    1993-01-01

    Recently Brown et al. (Science 250, 1991) showed that Trition's internal heat source could amount to 5-20% of the absorbed insolation on Trition, thus significantly affecting volatile transport and stmospheric pressure.

  15. Development and applications of a Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System

    NASA Astrophysics Data System (ADS)

    Warner, J. C.; Armstrong, B. N.; He, R.; Zambon, J. B.; Olabarrieta, M.; Voulgaris, G.; Kumar, N.; Haas, K. A.

    2012-12-01

    Understanding processes responsible for coastal change is important for managing both our natural and economic coastal resources. Coastal processes respond from both local scale and larger regional scale forcings. Understanding these processes can lead to significant insight into how the coastal zone evolves. Storms are one of the primary driving forces causing coastal change from a coupling of wave and wind driven flows. Here we utilize a numerical modeling approach to investigate these dynamics of coastal storm impacts. We use the Coupled Ocean - Atmosphere - Wave - Sediment Transport (COAWST) Modeling System that utilizes the Model Coupling Toolkit to exchange prognostic variables between the ocean model ROMS, atmosphere model WRF, wave model SWAN, and the Community Sediment Transport Modeling System (CSTMS) sediment routines. The models exchange fields of sea-surface temperature, ocean currents, water levels, bathymetry, wave heights, lengths, periods, bottom orbital velocities, and atmospheric surface heat and momentum fluxes, atmospheric pressure, precipitation, and evaporation. Data fields are exchanged using regridded flux conservative sparse matrix interpolation weights computed from the SCRIP spherical coordinate remapping interpolation package. We describe the modeling components and the model field exchange methods. As part of the system, the wave and ocean models run with cascading, refined, spatial grids to provide increased resolution, scaling down to resolve nearshore wave driven flows simulated by the vortex force formulation, all within selected regions of a larger, coarser-scale coastal modeling system. The ocean and wave models are driven by the atmospheric component, which is affected by wave dependent ocean-surface roughness and sea surface temperature which modify the heat and momentum fluxes at the ocean-atmosphere interface. We describe the application of the modeling system to several regions of multi-scale complexity to identify the

  16. Impact of pore size variability and network coupling on electrokinetic transport in porous media

    NASA Astrophysics Data System (ADS)

    Alizadeh, Shima; Bazant, Martin Z.; Mani, Ali

    2016-11-01

    We have developed and validated an efficient and robust computational model to study the coupled fluid and ion transport through electrokinetic porous media, which are exposed to external gradients of pressure, electric potential, and concentration. In our approach a porous media is modeled as a network of many pores through which the transport is described by the coupled Poisson-Nernst-Planck-Stokes equations. When the pore sizes are random, the interactions between various modes of transport may provoke complexities such as concentration polarization shocks and internal flow circulations. These phenomena impact mixing and transport in various systems including deionization and filtration systems, supercapacitors, and lab-on-a-chip devices. In this work, we present simulations of massive networks of pores and we demonstrate the impact of pore size variation, and pore-pore coupling on the overall electrokinetic transport in porous media.

  17. Coupled modeling of transport and biogeochemical processes in aquifers - Model requirements, strength and limitations

    NASA Astrophysics Data System (ADS)

    Mayer, K.

    2003-12-01

    Microbially mediated geochemical changes in aquifers may trigger a series of secondary reactions that include aqueous and surface complexation, ion exchange, and mineral dissolution-precipitation. Due to the coupled nature and the multitude of processes involved it is often difficult to identify the reactions controlling the system's overall evolution. Numerical models can be a useful component for identifying gaps and inconsistencies in conceptual models and for performing a more quantitative investigation of these systems. Suitable computer codes must allow for a general description of transport and reaction processes to facilitate the investigation of site-specific conditions. In recent years significant advances have been made in terms of model generality and applicability. Major advances include the consideration of mass balance equations for reactants and reaction products, the integration of biodegradation and thermodynamic models, and the development of novel approaches for simulating biogeochemical processes and reactive transport under variably saturated conditions. MIN3P is one of the codes capable of simulating coupled biogeochemical and hydrological processes on an increasingly mechanistic level. The simulation of column experiments and a hypothetical case study at the field scale illustrate how reactive transport modeling can be used. Modeling column experiments can be particularly fruitful, because detailed data can be collected to support the mechanistic approach. However, analysis of conceptual models is also beneficial on the field scale. The case study considered here describes natural attenuation of a petroleum hydrocarbon spill in an unconfined aquifer by multiple electron acceptors. The simulations also consider geochemical reactions triggered by contaminant degradation including the re-oxidation of reaction products during transport away from the source area. Comparing the results to contaminant plumes described in the literature suggests

  18. On diagonalization of coupled hydrologic transport and geochemical reaction equations

    SciTech Connect

    Yeh, Gour-Tsyh; Cheng, Hwai-Ping

    1996-12-31

    Two basic ingredients present in modeling the transport of reactive multi-components: the transport is described by a set of advection-dispersion-reactive partial differential equations (PDEs) based on the principle of mass balance; the chemical reactions, under the assumptions of local equilibrium, are described by a set of highly nonlinear algebraic equations (AEs) base on the principles of mole balance and mass action. For a typical application, the complete set of nonlinear PDEs and AEs consist of more than one hundred simultaneous equations. Thus, it is impractical to solve this set of equations simultaneously. General practice is to divide this set of equations into two subsets: one is the primary governing equations (PGEs) consisting of mainly the transport equations and the other one is the secondary governing equations consisting of mainly the geochemical reaction equations. The PGEs are solved for the chosen primary dependent variables (PDVs) and the SGEs are used to compute for the secondary dependent variables (SDVs). The major difficulties in simulating the reactive transport is the numerical solution of PGEs. From the computational point of view, the solution of the set of highly nonlinear PDEs are solved either with the direct substitution approach (DSA) or with the sequential iteration approach (SIA). For DSA, geochemical equilibrium reaction equations are substituted into the hydrologic transport equations to results in a set of nonlinear partial differential equations.

  19. Structure-function relationships in sapwood water transport and storage.

    Treesearch

    Barbara L. Gartner; Frederick C. Meinzer

    2005-01-01

    Primary production by plants requires the loss of substantial quantities of water when the stomata are open for carbon assimilation. The delivery of that water to the leaves occurs through the xylem. The structure, condition, and quantity of the xylem control not only the transport efficiency but also the release of water from storage. For example, if there is high...

  20. Crystal Structure of a Phosphorylation-coupled Saccharide Transporter

    SciTech Connect

    Y Cao; X Jin; E Levin; H Huang; Y Zong; W Hendrickson; J Javitch; K Rajashankar; M Zhou; et al.

    2011-12-31

    Saccharides have a central role in the nutrition of all living organisms. Whereas several saccharide uptake systems are shared between the different phylogenetic kingdoms, the phosphoenolpyruvate-dependent phosphotransferase system exists almost exclusively in bacteria. This multi-component system includes an integral membrane protein EIIC that transports saccharides and assists in their phosphorylation. Here we present the crystal structure of an EIIC from Bacillus cereus that transports diacetylchitobiose. The EIIC is a homodimer, with an expansive interface formed between the amino-terminal halves of the two protomers. The carboxy-terminal half of each protomer has a large binding pocket that contains a diacetylchitobiose, which is occluded from both sides of the membrane with its site of phosphorylation near the conserved His250 and Glu334 residues. The structure shows the architecture of this important class of transporters, identifies the determinants of substrate binding and phosphorylation, and provides a framework for understanding the mechanism of sugar translocation.

  1. Coupled transport and heating in EBT and EBS

    SciTech Connect

    Hedrick, C.L.; Batchelor, D.B.; Chen, G.L.; Goldfinger, R.C.; Hastings, D.E.; Jaeger, E.F.; Lee, D.K.; Owen, L.W.; Spong, D.A.; Tolliver, J.S.

    1984-01-01

    In ELMO Bumpy Torus (EBT) and EBT-like devices, hot electron rings form at the edge of the warm core plasma. As early as 1975 it was recognized that microwave heating, which plays such a significant role in electron dynamics, should be incorporated into transport models. Recent theoretical microwave heating and transport studies suggest that this is critical for explaining EBT experiments. In particular, descriptions of the electron distribution as a sum of only two distributions (i.e., one for the core and one for the rings) are inadequate to understand either the heating or the losses in any depth. Here we discuss the interplay of heating and transport from a kinetic standpoint and point out phenomena associated with the microwave heating at the fundamental and second harmonic of the electron cyclotron frequency. We also compare and contrast these phenomena for the EBT magnetic configuration to those for a variant of the standard EBT - the ELMO Bumpy Square (EBS).

  2. Transport behavior of water molecules through two-dimensional nanopores

    SciTech Connect

    Zhu, Chongqin; Li, Hui; Meng, Sheng

    2014-11-14

    Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.

  3. Hydrology and phosphorus transport simulation in a lowland polder by a coupled modeling system.

    PubMed

    Yan, Renhua; Huang, Jiacong; Li, Lingling; Gao, Junfeng

    2017-08-01

    Modeling the rain-runoff processes and phosphorus transport processes in lowland polders is critical in finding reasonable measures to alleviate the eutrophication problem of downstream rivers and lakes. This study develops a lowland Polder Hydrology and Phosphorus modeling System (PHPS) by coupling the WALRUS-paddy model and an improved phosphorus module of a Phosphorus Dynamic model for lowland Polder systems (PDP). It considers some important hydrological characteristics, such as groundwater-unsaturated zone coupling, groundwater-surface water feedback, human-controlled irrigation and discharge, and detailed physical and biochemical cycles of phosphorus in surface water. The application of the model in the Jianwei polder shows that the simulated phosphorus matches well with the measured values. The high precision of this model combined with its low input data requirement and efficient computation make it practical and easy to the water resources management of Chinese polders. Parameter sensitivity analysis demonstrates that Kuptake, cQ2, cW1, and cQ1 exert a significant effect on the modeled results, whereas KresuspensionMax, Ksettling, and Kmineralization have little effect on the modeled total phosphorus. Among the three types of uncertainties (i.e., parameter, initial condition, and forcing uncertainties), forcing uncertainty produces the strongest effect on the simulated phosphorus. Based on the analysis result of annual phosphorus balance when considering the high import from irrigation and fertilization, lowland polder is capable of retaining phosphorus and reducing phosphorus export to surrounding aquatic ecosystems because of their special hydrological regulation regime. Copyright © 2016 Elsevier Ltd. All rights reserved.

  4. Coupling ANIMO and MT3DMS for 3D regional-scale modeling of nutrient transport in soil and groundwater

    NASA Astrophysics Data System (ADS)

    Janssen, G.; Del Val Alonso, L.; Groenendijk, P.; Griffioen, J.

    2012-12-01

    We developed an on-line coupling between the 1D/quasi-2D nutrient transport model ANIMO and the 3D groundwater transport model code MT3DMS. ANIMO is a detailed, process-oriented model code for the simulation of nitrate leaching to groundwater, N- and P-loads on surface waters and emissions of greenhouse gasses. It is the leading nutrient fate and transport code in the Netherlands where it is used primarily for the evaluation of fertilization related legislation. In addition, the code is applied frequently in international research projects. MT3DMS is probably the most commonly used groundwater solute transport package worldwide. The on-line model coupling ANIMO-MT3DMS combines the state-of-the-art descriptions of the biogeochemical cycles in ANIMO with the advantages of using a 3D approach for the transport through the saturated domain. These advantages include accounting for regional lateral transport, considering groundwater-surface water interactions more explicitly, and the possibility of using MODFLOW to obtain the flow fields. An additional merit of the on-line coupling concept is that it preserves feedbacks between the saturated and unsaturated zone. We tested ANIMO-MT3DMS by simulating nutrient transport for the period 1970-2007 in a Dutch agricultural polder catchment covering an area of 118 km2. The transient groundwater flow field had a temporal resolution of one day and was calculated with MODFLOW-MetaSWAP. The horizontal resolution of the model grid was 100x100m and consisted of 25 layers of varying thickness. To keep computation times manageable, we prepared MT3DMS for parallel computing, which in itself is a relevant development for a large community of groundwater transport modelers. For the parameterization of the soil, we applied a standard classification approach, representing the area by 60 units with unique combinations of soil type, land use and geohydrological setting. For the geochemical parameterization of the deeper subsurface, however, we

  5. Hybrid Upwind Discretization for the Implicit Simulation of Three-Phase Coupled Flow and Transport with Gravity

    NASA Astrophysics Data System (ADS)

    Hamon, F. P.; Mallison, B.; Tchelepi, H.

    2015-12-01

    The systems of algebraic equations arising from implicit (backward-Euler) finite-volume discretization of the conservation laws governing multiphase flow in porous media are quite challenging for nonlinear solvers. In the presence of counter-current flow due to buoyancy, the coupling between flow (pressure) and transport (saturations) is often the cause of nonlinear problems when single-point Phase-Potential Upwinding (PPU) is used. To overcome such convergence problems in practice, the time step is reduced and Newton's method is restarted from the solution at the previous converged time step. Here, we generalize the work of Lee, Efendiev and Tchelepi [Advances in Water Resources, 2015] to propose an Implicit Hybrid Upwinding (IHU) scheme for coupled flow and transport. In the pure transport problem, we show that the numerical flux obtained with IHU is differentiable, monotone and consistent for two and three-phase flow. For coupled flow and transport, we prove saturation physical bounds as well as the existence of a solution to our scheme. Challenging two- and three-phase heterogeneous multi-dimensional numerical tests confirm that the new scheme is non-oscillatory and convergent, and illustrate the superior convergence rate of our IHU-based Newton solver for large time steps.

  6. Substrate-bound outward-open state of the betaine transporter BetP provides insights into Na+ coupling

    NASA Astrophysics Data System (ADS)

    Perez, Camilo; Faust, Belinda; Mehdipour, Ahmad Reza; Francesconi, Kevin A.; Forrest, Lucy R.; Ziegler, Christine

    2014-07-01

    The Na+-coupled betaine symporter BetP shares a highly conserved fold with other sequence unrelated secondary transporters, for example, with neurotransmitter symporters. Recently, we obtained atomic structures of BetP in distinct conformational states, which elucidated parts of its alternating-access mechanism. Here, we report a structure of BetP in a new outward-open state in complex with an anomalous scattering substrate, adding a fundamental piece to an unprecedented set of structural snapshots for a secondary transporter. In combination with molecular dynamics simulations these structural data highlight important features of the sequential formation of the substrate and sodium-binding sites, in which coordinating water molecules play a crucial role. We observe a strictly interdependent binding of betaine and sodium ions during the coupling process. All three sites undergo progressive reshaping and dehydration during the alternating-access cycle, with the most optimal coordination of all substrates found in the closed state.

  7. Quantum mechanical study of the coupling of plasmon excitations to atomic-scale electron transport.

    PubMed

    Song, Peng; Nordlander, Peter; Gao, Shiwu

    2011-02-21

    The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics.

  8. Synchronization of elastically coupled processive molecular motors and regulation of cargo transport.

    PubMed

    Kohler, Felix; Rohrbach, Alexander

    2015-01-01

    The collective work of motor proteins plays an important role in cellular transport processes. Since measuring intermotor coupling and hence a comparison to theoretical predictions is difficult, we introduce the synchronization as an alternative observable for motor cooperativity. This synchronization can be determined from the ratio of the mean times of motor resting and stepping. Results from a multistate Markov chain model and Brownian dynamics simulations, describing the elastically coupled motors, coincide well. Our model can explain the experimentally observed effect of strongly increased transport velocities and powers by the synchronization and coupling of myosin V and kinesin I.

  9. FY05 LDRD Final Report Coupled Turbulenc/Transport Model for Edge-Plasmas

    SciTech Connect

    Rognlien, T; Cohen, R; LoDestro, L; Palasek, R; Umansky, M; Xu, X

    2006-02-09

    An edge-plasma simulation for tokamak fusion devices is developed that couples 3D turbulence and 2D transport, including detailed sources and sinks, to determine self-consistent steady-state plasma profiles. Relaxed iterative coupling is shown to be effective when edge turbulence is partially suppressed, for example, by shear E x B shear flow as occurs during the favorable H-mode region. Unsuppressed turbulence is found to lead to large, intermittent edge transport events where the coupling procedure can lead to substantial inaccuracies in describing the true time-averaged plasma behavior.

  10. Coupled Effects of Vadose Zone Hydrodynamics and Anionic Surfactant Aerosol-22 on the Transport of Cryptosporidium parvum in Soil

    NASA Astrophysics Data System (ADS)

    Darnault, C. J.; Jacobson, A. R.; Powelson, D.; Baveye, P.; Peng, Z.; Yu, C.

    2013-12-01

    Cryptosporidium parvum is a microbial pathogen that may be found in soil, surface and groundwater resources. We studied their transport behavior under conditions where both C. parvum oocysts and chemicals that may affect their mobility are present in soils. Surfactants occur widely in soils due to agricultural practices such as wastewater irrigation and application of agrichemicals. Surfactants decrease the surface tension of the soil solution, which may reduce the ability of C. parvum oocysts to be retained at gas-water interfaces. Understanding the fate and transport of C. parvum oocysts following land application of manure and use of surfactants in rural and agricultural watersheds is critical to assess the threat to water resources. We investigated the coupled effects of vadose zone hydrodynamics and an anionic surfactant Aerosol-22 on the transport of C. parvum oocysts in natural structured and non-structured agricultural or range soils from Illinois and Utah. Column transport experiments consisted of unsaturated flow subject to macropore and fingered flows resulting from simulated rainfall with and without surfactant. To assess the behavior of C. parvum oocysts in soils, the breakthrough and distribution of C. parvum oocysts in soil profiles were obtained using qPCR. We observed that surfactant enhanced the transport of C. parvum oocysts when preferential flow paths are present. However, when the interconnection between macropores is not established in the soils, surfactant limited the transport of C. parvum oocysts through the soil matrix by forming oocyst-surfactant-Ca flocs.

  11. Allosteric Mechanisms of Molecular Machines at the Membrane: Transport by Sodium-Coupled Symporters.

    PubMed

    LeVine, Michael V; Cuendet, Michel A; Khelashvili, George; Weinstein, Harel

    2016-06-08

    Solute transport across cell membranes is ubiquitous in biology as an essential physiological process. Secondary active transporters couple the unfavorable process of solute transport against its concentration gradient to the energetically favorable transport of one or several ions. The study of such transporters over several decades indicates that their function involves complex allosteric mechanisms that are progressively being revealed in atomistic detail. We focus on two well-characterized sodium-coupled symporters: the bacterial amino acid transporter LeuT, which is the prototype for the "gated pore" mechanism in the mammalian synaptic monoamine transporters, and the archaeal GltPh, which is the prototype for the "elevator" mechanism in the mammalian excitatory amino acid transporters. We present the evidence for the role of allostery in the context of a quantitative formalism that can reconcile biochemical and biophysical data and thereby connects directly to recent insights into the molecular structure and dynamics of these proteins. We demonstrate that, while the structures and mechanisms of these transporters are very different, the available data suggest a common role of specific models of allostery in their functions. We argue that such allosteric mechanisms appear essential not only for sodium-coupled symport in general but also for the function of other types of molecular machines in the membrane.

  12. Coupled ion Binding and Structural Transitions Along the Transport Cycle of Glutamate Transporters

    SciTech Connect

    Verdon, Gregory; Oh, SeCheol; Serio, Ryan N.; Boudker, Olga

    2014-05-19

    Membrane transporters that clear the neurotransmitter glutamate from synapses are driven by symport of sodium ions and counter-transport of a potassium ion. Previous crystal structures of a homologous archaeal sodium and aspartate symporter showed that a dedicated transport domain carries the substrate and ions across the membrane. We report new crystal structures of this homologue in ligand-free and ions-only bound outward- and inward-facing conformations. We then show that after ligand release, the apo transport domain adopts a compact and occluded conformation that can traverse the membrane, completing the transport cycle. Sodium binding primes the transport domain to accept its substrate and triggers extracellular gate opening, which prevents inward domain translocation until substrate binding takes place. Moreover, we describe a new cation-binding site ideally suited to bind a counter-transported ion. We suggest that potassium binding at this site stabilizes the translocation-competent conformation of the unloaded transport domain in mammalian homologues.

  13. Two-dimensional transport model of coupled Brownian particles driven by biharmonic forces and constant forces

    NASA Astrophysics Data System (ADS)

    Wu, Weixia; Meng, Tao

    2017-01-01

    A directed transport model of coupled Brownian particles in a two-dimensional potential is established. In this model, the system of Brownian particles is driven by biharmonic forces and constant forces. By numerical simulation, the cooperative transport behaviours of the system are investigated. The results show that the average velocity of the system is significantly independent of the frequencies and intensities of the harmonic forces, the barrier height of the ratchet potential, coupling strength and noise intensity. The average velocity increases monotonically with increasing the intensities of the harmonic forces, and can reach some maximum values when the two frequencies are equal. In addition, the average velocity presents stochastic resonance and generalized resonance for noise intensity, coupling strength and the barrier height of the ratchet potential. Moreover, when a constant force is exerted on the ratchet potential direction, it will promote the directed transport of the system. But, when on the non-ratchet potential direction, the transport will not be affected.

  14. TICKET-UWM: a coupled kinetic, equilibrium, and transport screening model for metals in lakes.

    PubMed

    Farley, Kevin J; Carbonaro, Richard F; Fanelli, Christopher J; Costanzo, Robert; Rader, Kevin J; Di Toro, Dominic M

    2011-06-01

    The tableau input coupled kinetic equilibrium transport-unit world model (TICKET-UWM) has been developed as a screening model for assessing potential environmental risks associated with the release of metals into lakes. The model is based on a fully implicit, one-step solution algorithm that allows for simultaneous consideration of dissolved and particulate phase transport; metal complexation to organic matter and inorganic ligands; precipitation of metal hydroxides, carbonates, and sulfides; competitive interactions of metals and major cations with biotic ligands; a simplified description of biogeochemical cycling of organic carbon and sulfur; and dissolution kinetics for metal powders, massives, and other solid forms. Application of TICKET-UWM to a generalized lake in the Sudbury area of the Canadian Shield is presented to demonstrate the overall cycling of metals in lakes and the nonlinear effects of chemical speciation on metal responses. In addition, the model is used to calculate critical loads for metals, with acute toxicity of Daphnia magna as the final endpoint. Model results show that the critical loads for Cu, Ni, Pb, and Zn varied from 2.5 to 39.0 g metal/m(2) -year and were found to be one or more orders of magnitude higher than comparable loads for pesticides (lindane, 4,4'-DDT) and several polyaromatic hydrocarbon (PAH) compounds. In sensitivity calculations, critical metal-loading rates were found to vary significantly as a function of the hydraulic detention time, water hardness, and metal dissolution kinetic rates.

  15. Analysis of Porphyra membrane transporters demonstrates gene transfer among photosynthetic eukaryotes and numerous sodium-coupled transport systems.

    PubMed

    Chan, Cheong Xin; Zäuner, Simone; Wheeler, Glen; Grossman, Arthur R; Prochnik, Simon E; Blouin, Nicolas A; Zhuang, Yunyun; Benning, Christoph; Berg, Gry Mine; Yarish, Charles; Eriksen, Renée L; Klein, Anita S; Lin, Senjie; Levine, Ira; Brawley, Susan H; Bhattacharya, Debashish

    2012-04-01

    Membrane transporters play a central role in many cellular processes that rely on the movement of ions and organic molecules between the environment and the cell, and between cellular compartments. Transporters have been well characterized in plants and green algae, but little is known about transporters or their evolutionary histories in the red algae. Here we examined 482 expressed sequence tag contigs that encode putative membrane transporters in the economically important red seaweed Porphyra (Bangiophyceae, Rhodophyta). These contigs are part of a comprehensive transcriptome dataset from Porphyra umbilicalis and Porphyra purpurea. Using phylogenomics, we identified 30 trees that support the expected monophyly of red and green algae/plants (i.e. the Plantae hypothesis) and 19 expressed sequence tag contigs that show evidence of endosymbiotic/horizontal gene transfer involving stramenopiles. The majority (77%) of analyzed contigs encode transporters with unresolved phylogenies, demonstrating the difficulty in resolving the evolutionary history of genes. We observed molecular features of many sodium-coupled transport systems in marine algae, and the potential for coregulation of Porphyra transporter genes that are associated with fatty acid biosynthesis and intracellular lipid trafficking. Although both the tissue-specific and subcellular locations of the encoded proteins require further investigation, our study provides red algal gene candidates associated with transport functions and novel insights into the biology and evolution of these transporters.

  16. Momentum transport from nonlinear mode coupling of magnetic fluctuations

    PubMed

    Hansen; Almagri; Craig; Den Hartog DJ; Hegna; Prager; Sarff

    2000-10-16

    A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets of tearing modes produce internal torques that redistribute momentum. Evidence for the nonlinear torque is acquired by detecting the correlation of momentum redistribution with the mode triplets, with the elimination of one of the modes in the triplet, and with the external driving of one of the modes.

  17. Coupled transport, mixing and biogeochemical reactions in fractured media: experimental observations and modelling at the Ploemeur fractured rock observatory

    NASA Astrophysics Data System (ADS)

    Le Borgne, T.; Bochet, O.; Klepikova, M.; Kang, P. K.; Shakas, A.; Aquilina, L.; Dufresne, A.; Linde, N.; Dentz, M.; Bour, O.

    2016-12-01

    Transport processes in fractured media and associated reactions are governed by multiscale heterogeneity ranging from fracture wall roughness at small scale to broadly distributed fracture lengths at network scale. This strong disorder induces a variety of emerging phenomena, including flow channeling, anomalous transport and heat transfer, enhanced mixing and reactive hotspot development. These processes are generally difficult to isolate and monitor in the field because of the high degree of complexity and coupling between them. We report in situ experimental observations from the Ploemeur fractured rock observatory (http://hplus.ore.fr/en/ploemeur) that provide new insights on the dynamics of transport and reaction processes in fractured media. These include dipole and push pull tracer tests that allow understanding and modelling anomalous transport processes characterized by heavy-tailed residence time distributions (Kang et al. 2015), thermal push pull tests that show the existence of highly channeled flow with a strong control on fracture matrix exchanges (Klepikova et al. 2016) and time lapse hydrogeophysical monitoring of saline tracer tests that allow quantifying the distribution of transport length scales governing dispersion processes (Shakas et al. 2016). These transport processes are then shown to induce rapid oxygen delivery and mixing at depth leading to massive biofilm development (Bochet et al., in prep.). Hence, this presentation will attempt to link these observations made at different scales to quantify and model the coupling between flow channeling, non-Fickian transport, mixing and chemical reactions in fractured media. References: Bochet et al. Biofilm blooms driven by enhanced mixing in fractured rock, in prep. Klepikova et al. 2016, Heat as a tracer for understanding transport processes in fractured media: theory and field assessment from multi-scale thermal push-pull tracer tests, Water Resour. Res. 52Shakas et al. 2016, Hydrogeophysical

  18. The influence of eddy parameterizations on the transport of the Antarctic Circumpolar Current in coupled climate models

    NASA Astrophysics Data System (ADS)

    Kuhlbrodt, T.; Smith, R. S.; Wang, Z.; Gregory, J. M.

    2012-08-01

    The transport of the Antarctic Circumpolar Current (ACC) varies strongly across the coupled GCMs (general circulation models) used for the IPCC AR4. This note shows that a large fraction of this across-model variance can be explained by relating it to the parameterization of eddy-induced transports. In the majority of models this parameterization is based on the study by Gent and McWilliams (1990). The main parameter is the quasi-Stokes diffusivity κ (often referred to less accurately as "thickness diffusion"). The ACC transport and the meridional density gradient both correlate strongly with κ across those models where κ is a prescribed constant. In contrast, there is no correlation with the isopycnal diffusivity κiso across the models. The sensitivity of the ACC transport to κ is larger than to the zonal wind stress maximum. Experiments with the fast GCM FAMOUS show that changing κ directly affects the ACC transport by changing the density structure throughout the water column. Our results suggest that this limits the role of the wind stress magnitude in setting the ACC transport in FAMOUS. The sensitivities of the ACC and the meridional density gradient are very similar across the AR4 GCMs (for those models where κ is a prescribed constant) and among the FAMOUS experiments. The strong sensitivity of the ACC transport to κ needs careful assessment in climate models.

  19. Electron transfer activation of a second water channel for proton transport in [FeFe]-hydrogenase

    SciTech Connect

    Sode, Olaseni; Voth, Gregory A.

    2014-12-14

    Hydrogenase enzymes are important because they can reversibly catalyze the production of molecular hydrogen. Proton transport mechanisms have been previously studied in residue pathways that lead to the active site of the enzyme via residues Cys299 and Ser319. The importance of this pathway and these residues has been previously exhibited through site-specific mutations, which were shown to interrupt the enzyme activity. It has been shown recently that a separate water channel (WC2) is coupled with electron transport to the active site of the [FeFe]-hydrogenase. The water-mediated proton transport mechanisms of the enzyme in different electronic states have been studied using the multistate empirical valence bond reactive molecular dynamics method, in order to understand any role WC2 may have in facilitating the residue pathway in bringing an additional proton to the enzyme active site. In a single electronic state A{sup 2−}, a water wire was formed through which protons can be transported with a low free energy barrier. The remaining electronic states were shown, however, to be highly unfavorable to proton transport in WC2. A double amino acid substitution is predicted to obstruct proton transport in electronic state A{sup 2-} by closing a cavity that could otherwise fill with water near the proximal Fe of the active site.

  20. Low-pressure water-cooled inductively coupled plasma torch

    DOEpatents

    Seliskar, C.J.; Warner, D.K.

    1984-02-16

    An inductively coupled plasma torch is provided which comprises an inner tube, including a sample injection port to which the sample to be tested is supplied and comprising an enlarged central portion in which the plasma flame is confined; an outer tube surrounding the inner tube and containing water therein for cooling the inner tube, the outer tube including a water inlet port to which water is supplied and a water outlet port spaced from the water inlet port and from which water is removed after flowing through the outer tube; and an rf induction coil for inducing the plasma in the gas passing into the tube through the sample injection port. The sample injection port comprises a capillary tube including a reduced diameter orifice, projecting into the lower end of the inner tube. The water inlet is located at the lower end of the outer tube and the rf heating coil is disposed around the outer tube above and adjacent to the water inlet.

  1. Low-pressure water-cooled inductively coupled plasma torch

    DOEpatents

    Seliskar, Carl J.; Warner, David K.

    1988-12-27

    An inductively coupled plasma torch is provided which comprises an inner tube, including a sample injection port to which the sample to be tested is supplied and comprising an enlarged central portion in which the plasma flame is confined; an outer tube surrounding the inner tube and containing water therein for cooling the inner tube, the outer tube including a water inlet port to which water is supplied and a water outlet port spaced from the water inlet port and from which water is removed after flowing through the outer tube; and an r.f. induction coil for inducing the plasma in the gas passing into the tube through the sample injection port. The sample injection port comprises a capillary tube including a reduced diameter orifice, projecting into the lower end of the inner tube. The water inlet is located at the lower end of the outer tube and the r.f. heating coil is disposed around the outer tube above and adjacent to the water inlet.

  2. Impact of inflow transport approximation on light water reactor analysis

    NASA Astrophysics Data System (ADS)

    Choi, Sooyoung; Smith, Kord; Lee, Hyun Chul; Lee, Deokjung

    2015-10-01

    The impact of the inflow transport approximation on light water reactor analysis is investigated, and it is verified that the inflow transport approximation significantly improves the accuracy of the transport and transport/diffusion solutions. A methodology for an inflow transport approximation is implemented in order to generate an accurate transport cross section. The inflow transport approximation is compared to the conventional methods, which are the consistent-PN and the outflow transport approximations. The three transport approximations are implemented in the lattice physics code STREAM, and verification is performed for various verification problems in order to investigate their effects and accuracy. From the verification, it is noted that the consistent-PN and the outflow transport approximations cause significant error in calculating the eigenvalue and the power distribution. The inflow transport approximation shows very accurate and precise results for the verification problems. The inflow transport approximation shows significant improvements not only for the high leakage problem but also for practical large core problem analyses.

  3. Unstirred Water Layers and the Kinetics of Organic Cation Transport

    PubMed Central

    Shibayama, Takahiro; Morales, Mark; Zhang, Xiaohong; Martinez, Lucy; Berteloot, Alfred; Secomb, Timothy W.; Wright, Stephen H.

    2015-01-01

    Purpose Unstirred water layers (UWLs) present an unavoidable complication in the measurement of transport kinetics in cultured cells and the high rates of transport achieved by overexpressing heterologous transporters exacerbate the UWL effect. This study examined the correlation between measured Jmax and Kt values and the effect of manipulating UWL thickness or transport Jmax on the accuracy of experimentally determined kinetics of the multidrug transporters, OCT2 and MATE1. Methods Transport of TEA and MPP was measured in CHO cells that stably expressed human OCT2 or MATE1. UWL thickness was manipulated by vigorous reciprocal shaking. Several methods were used to manipulate maximal transport rates. Results Vigorous stirring stimulated uptake of OCT2-mediated transport by decreasing apparent Kt (Ktapp) values. Systematic reduction in transport rates was correlated with reduction in Ktapp values. The slope of these relationships indicated a 1500 µm UWL in multiwell plates. Reducing the influence of UWLs (by decreasing either their thickness or the Jmax of substrate transport) reduced Ktapp by 2-fold to >10-fold. Conclusions Failure to take into account the presence of UWLs in experiments using cultured cells to measure transport kinetics can result in significant underestimates of the affinity of multidrug transporters for substrates. PMID:25791216

  4. A model for radionuclide transport in the Cooling Water System

    SciTech Connect

    Kahook, S.D.

    1992-08-01

    A radionuclide transport model developed to assess radiological levels in the K-reactor Cooling Water System (CWS) in the event of an inadvertent process water (PW) leakage to the cooling water (CW) in the heat exchangers (HX) is described. During and following a process water leak, the radionuclide transport model determines the time-dependent release rates of radionuclide from the cooling water system to the environment via evaporation to the atmosphere and blow-down to the Savannah River. The developed model allows for delay times associated with the transport of the cooling water radioactivity through cooling water system components. Additionally, this model simulates the time-dependent behavior of radionuclides levels in various CWS components. The developed model is incorporated into the K-reactor Cooling Tower Activity (KCTA) code. KCTA allows the accident (heat exchanger leak rate) and the cooling tower blow-down and evaporation rates to be described as time-dependent functions. Thus, the postulated leak and the consequence of the assumed leak can be modelled realistically. This model is the first of three models to be ultimately assembled to form a comprehensive Liquid Pathway Activity System (LPAS). LPAS will offer integrated formation, transport, deposition, and release estimates for radionuclides formed in a SRS facility. Process water and river water modules are forthcoming as input and downstream components, respectively, for KCTA.

  5. A model for radionuclide transport in the Cooling Water System

    SciTech Connect

    Kahook, S.D.

    1992-08-01

    A radionuclide transport model developed to assess radiological levels in the K-reactor Cooling Water System (CWS) in the event of an inadvertent process water (PW) leakage to the cooling water (CW) in the heat exchangers (HX) is described. During and following a process water leak, the radionuclide transport model determines the time-dependent release rates of radionuclide from the cooling water system to the environment via evaporation to the atmosphere and blow-down to the Savannah River. The developed model allows for delay times associated with the transport of the cooling water radioactivity through cooling water system components. Additionally, this model simulates the time-dependent behavior of radionuclides levels in various CWS components. The developed model is incorporated into the K-reactor Cooling Tower Activity (KCTA) code. KCTA allows the accident (heat exchanger leak rate) and the cooling tower blow-down and evaporation rates to be described as time-dependent functions. Thus, the postulated leak and the consequence of the assumed leak can be modelled realistically. This model is the first of three models to be ultimately assembled to form a comprehensive Liquid Pathway Activity System (LPAS). LPAS will offer integrated formation, transport, deposition, and release estimates for radionuclides formed in a SRS facility. Process water and river water modules are forthcoming as input and downstream components, respectively, for KCTA.

  6. Novel macrocyclic carriers for proton-coupled liquid membrane transport

    SciTech Connect

    Lamb, J.D.; Bradshaw, J.S.; Izatt, R.M.

    1992-07-01

    A number of new macrocyclic ligands was prepared for transport studies. The cryptands were prpepared (18-40% yield) by a new metal carbonate-catalyzed one-step method from 1 mole oligoethyleneoxy diamine and 2 moles diahlide derivative of oligoethylene glycol. Bis-crown ethers were also isolated in 17-30% yields. Cage compounds were also prepared; they interact with various metal ions and protons. Back extraction and dual module hollow fiber membrane separation experiments were used to study the cation selectivity of new ligands, including crown thioethers. An isothermal flow calorimeter is being constructed for studies of macrocycle-cation reactions. 3 figs, 2 tabs.

  7. Scaling behaviour for the water transport in nanoconfined geometries

    PubMed Central

    Chiavazzo, Eliodoro; Fasano, Matteo; Asinari, Pietro; Decuzzi, Paolo

    2014-01-01

    The transport of water in nanoconfined geometries is different from bulk phase and has tremendous implications in nanotechnology and biotechnology. Here molecular dynamics is used to compute the self-diffusion coefficient D of water within nanopores, around nanoparticles, carbon nanotubes and proteins. For almost 60 different cases, D is found to scale linearly with the sole parameter θ as D(θ)=DB[1+(DC/DB−1)θ], with DB and DC the bulk and totally confined diffusion of water, respectively. The parameter θ is primarily influenced by geometry and represents the ratio between the confined and total water volumes. The D(θ) relationship is interpreted within the thermodynamics of supercooled water. As an example, such relationship is shown to accurately predict the relaxometric response of contrast agents for magnetic resonance imaging. The D(θ) relationship can help in interpreting the transport of water molecules under nanoconfined conditions and tailoring nanostructures with precise modulation of water mobility. PMID:24699509

  8. Water, proton, and ion transport: from nanotubes to proteins

    NASA Astrophysics Data System (ADS)

    Hummer, Gerhard

    Remarkably, protein channels transporting polar substances such as water, protons, and ions are often lined by predominantly non-polar residues. The unique structural, dynamic, and thermodynamic properties of water and ions in molecular confinement help explain this puzzling observation. Computer simulations of solvated nanotubes and proteins show that weakly polar cavities can be filled by water at equilibrium, but such filling is highly sensitive to small variations in the polarity of the cavity. In the filled state, water forms wires and clusters held together by tight hydrogen bonds. Simulations on quantum energy surfaces also show that 1D water wires in hydrophobic environments facilitate rapid proton motion. The unique properties of water in weakly polar channels help explain the rapid flow of water through molecular pores, the controlled proton flow in enzymes, the gating of ion transport through membrane channels, and the function of mitochondrial proton pumps.

  9. Conformational coupling of the nucleotide-binding and the transmembrane domains in ABC transporters.

    PubMed

    Wen, Po-Chao; Tajkhorshid, Emad

    2011-08-03

    Basic architecture of ABC transporters includes two transmembrane domains (TMDs) and two nucleotide-binding domains (NBDs). Although the transport process takes place in the TMDs, which provide the substrate translocation pathway across the cell membrane and control its accessibility between the two sides of the membrane, the energy required for the process is provided by conformational changes induced in the NBDs by binding and hydrolysis of ATP. Nucleotide-dependent conformational changes in the NBDs, therefore, need to be coupled to structural changes in the TMDs. Using molecular dynamics simulations, we have investigated the structural elements involved in the conformational coupling between the NBDs and the TMDs in the Escherichia coli maltose transporter, an ABC importer for which an intact structure is available both in inward-facing and outward-facing conformations. The prevailing model of coupling is primarily based on a single structural motif, known as the coupling helices, as the main structural element for the NBD-TMD coupling. Surprisingly, we find that in the absence of the NBDs the coupling helices can be conformationally decoupled from the rest of the TMDs, despite their covalent connection. That is, the structural integrity of the coupling helices and their tight coupling to the core of the TMDs rely on the contacts provided by the NBDs. Based on the conformational and dynamical analysis of the simulation trajectories, we propose that the core coupling elements in the maltose transporter involve contributions from several structural motifs located at the NBD-TMD interface, namely, the EAA loops from the TMDs, and the Q-loop and the ENI motifs from the NBDs. These three structural motifs in small ABC importers show a high degree of correlation in motion and mediate the necessary conformational coupling between the core of TMDs and the helical subdomains of NBDs. A comprehensive analysis of the structurally known ABC transporters shows a high degree

  10. Aquaporin-4-dependent K(+) and water transport modeled in brain extracellular space following neuroexcitation.

    PubMed

    Jin, Byung-Ju; Zhang, Hua; Binder, Devin K; Verkman, A S

    2013-01-01

    Potassium (K(+)) ions released into brain extracellular space (ECS) during neuroexcitation are efficiently taken up by astrocytes. Deletion of astrocyte water channel aquaporin-4 (AQP4) in mice alters neuroexcitation by reducing ECS [K(+)] accumulation and slowing K(+) reuptake. These effects could involve AQP4-dependent: (a) K(+) permeability, (b) resting ECS volume, (c) ECS contraction during K(+) reuptake, and (d) diffusion-limited water/K(+) transport coupling. To investigate the role of these mechanisms, we compared experimental data to predictions of a model of K(+) and water uptake into astrocytes after neuronal release of K(+) into the ECS. The model computed the kinetics of ECS [K(+)] and volume, with input parameters including initial ECS volume, astrocyte K(+) conductance and water permeability, and diffusion in astrocyte cytoplasm. Numerical methods were developed to compute transport and diffusion for a nonstationary astrocyte-ECS interface. The modeling showed that mechanisms b-d, together, can predict experimentally observed impairment in K(+) reuptake from the ECS in AQP4 deficiency, as well as altered K(+) accumulation in the ECS after neuroexcitation, provided that astrocyte water permeability is sufficiently reduced in AQP4 deficiency and that solute diffusion in astrocyte cytoplasm is sufficiently low. The modeling thus provides a potential explanation for AQP4-dependent K(+)/water coupling in the ECS without requiring AQP4-dependent astrocyte K(+) permeability. Our model links the physical and ion/water transport properties of brain cells with the dynamics of neuroexcitation, and supports the conclusion that reduced AQP4-dependent water transport is responsible for defective neuroexcitation in AQP4 deficiency.

  11. Electric field geometries dominate quantum transport coupling in silicon nanoring

    SciTech Connect

    Lee, Tsung-Han E-mail: sfhu.hu@gmail.com; Hu, Shu-Fen E-mail: sfhu.hu@gmail.com

    2014-03-28

    Investigations on the relation between the geometries of silicon nanodevices and the quantum phenomenon they exhibit, such as the Aharonov–Bohm (AB) effect and the Coulomb blockade, were conducted. An arsenic doped silicon nanoring coupled with a nanowire by electron beam lithography was fabricated. At 1.47 K, Coulomb blockade oscillations were observed under modulation from the top gate voltage, and a periodic AB oscillation of ΔB = 0.178 T was estimated for a ring radius of 86 nm under a high sweeping magnetic field. Modulating the flat top gate and the pointed side gate was performed to cluster and separate the many electron quantum dots, which demonstrated that quantum confinement and interference effects coexisted in the doped silicon nanoring.

  12. Modeling multispecies reactive transport in ground water

    SciTech Connect

    Clement, T.P.; Sun, Y.; Hooker, B.S.; Petersen, J.N.

    1998-12-31

    In this paper, the details of RT3D, a general purpose, multispecies, reactive transport code, are presented. The code uses MODFLOW to simulate flow and several MT3D sub-programs to simulate advection and dispersion. A set of reaction modules were developed and incorporated into RT3D to simulate various types of multispecies reactive transport. This new computer model can be used for analyzing different types of subsurface contaminant reactions, microbial metabolisms, and microbial transport kinetics. Details of the model and numerical solution procedure are presented. The numerical formulation of the code is general enough to allow description of any type of reaction with any number of mobile/immobile species. Several example problems are presented to test the performance of the code, and to illustrate its features. The presented numerical model is shown to be a useful tool for analyzing different types of subsurface bioremediation systems. Prediction based on this model can be used for screening remediation alternatives including natural attenuation and/or for forecasting contaminant exposure levels and environmental risks at sensitive, downgradient receptors.

  13. A process-based evapotranspiration model incorporating coupled soil water-atmospheric controls

    NASA Astrophysics Data System (ADS)

    Haghighi, Erfan; Kirchner, James

    2016-04-01

    Despite many efforts to develop evapotranspiration models (in the framework of the Penman-Monteith equation) with improved parametrizations of various resistance terms to water vapor transfer into the atmosphere, evidence suggests that estimates of evapotranspiration and its partitioning are prone to bias. Much of this bias could arise from the exclusion of surface hydro-thermal properties and of physical interactions close to the surface where heat and water vapor fluxes originate. Recent progress has been made in mechanistic modeling of surface-turbulence interactions, accounting for localized heat and mass exchange rates from bare soil surfaces covered by protruding obstacles. We seek to extend these results partially vegetated surfaces, to improve predictive capabilities and accuracy of remote sensing techniques quantifying evapotranspiration fluxes. The governing equations of liquid water, water vapor, and energy transport dynamics in the soil-plant-atmosphere system are coupled to resolve diffusive vapor fluxes from isolated pores (plant stomata and soil pores) across a near-surface viscous sublayer, explicitly accounting for pore-scale transport mechanisms and environmental forcing. Preliminary results suggest that this approach offers unique opportunities for directly linking transport properties in plants and adjacent bare soil with resulting plant transpiration and localized bare soil evaporation rates. It thus provides an essential building block for interpreting and upscaling results to field and landscape scales for a range of vegetation cover and atmospheric conditions.

  14. Arctic warming induced by atmospheric transport of water vapour

    NASA Astrophysics Data System (ADS)

    Grand Graversen, Rune

    2015-04-01

    The atmospheric northward energy transport plays a crucial role for the Arctic climate; the transport brings to the Arctic an amount of energy comparable to that provided directly by the sun. During recent decades warming of the Arctic surface air has been more than twice as large as the warming averaged over the Northern Hemisphere. This is known as Arctic amplification. Climate models predict that Arctic amplification will continue during the 21st century. The models also show that the atmospheric energy transport to the Arctic will remain almost unchanged or will even decrease in the future. This has led to the conclusion that atmospheric energy transport does not contribute but rather opposes Arctic amplification. Here we show that the atmospheric energy transport will indeed contribute to Arctic amplification even while decreasing. A split of the transport into latent and dry-static components reveals that a change of the latent transport compared to a change of the dry-static has a much larger effect on the Arctic climate. This is because the latent transport brings not only energy, but also water vapour into the Arctic. This water vapour enhances the local greenhouse effect, both in itself and through the formation of clouds. An increase of the latent transport at the Arctic boundary therefore causes Arctic warming, both directly due to latent heat release, and indirectly due to an enhancement of the local greenhouse effect. Climate models tend to agree that the latent energy transport will increase on the expense of the dry-static transport in future simulations. Our results imply that the Arctic cooling caused by the reduction of the dry-static transport is more than compensated for by the warming induced by the latent transport.

  15. Models of Fate and Transport of Pollutants in Surface Waters

    ERIC Educational Resources Information Center

    Okome, Gloria Eloho

    2013-01-01

    There is the need to answer very crucial questions of "what happens to pollutants in surface waters?" This question must be answered to determine the factors controlling fate and transport of chemicals and their evolutionary state in surface waters. Monitoring and experimental methods are used in establishing the environmental states.…

  16. Models of Fate and Transport of Pollutants in Surface Waters

    ERIC Educational Resources Information Center

    Okome, Gloria Eloho

    2013-01-01

    There is the need to answer very crucial questions of "what happens to pollutants in surface waters?" This question must be answered to determine the factors controlling fate and transport of chemicals and their evolutionary state in surface waters. Monitoring and experimental methods are used in establishing the environmental states.…

  17. Water footprint of U.S. transportation fuels.

    PubMed

    Scown, Corinne D; Horvath, Arpad; McKone, Thomas E

    2011-04-01

    In the modern global economy, water and energy are fundamentally connected. Water already plays a major role in electricity generation and, with biofuels and electricity poised to gain a significant share of the transportation fuel market, water will become significantly more important for transportation energy as well. This research provides insight into the potential changes in water use resulting from increased biofuel or electricity production for transportation energy, as well as the greenhouse gas and freshwater implications. It is shown that when characterizing the water impact of transportation energy, incorporating indirect water use and defensible allocation techniques have a major impact on the final results, with anywhere between an 82% increase and a 250% decrease in the water footprint if evaporative losses from hydroelectric power are excluded. The greenhouse gas impact results indicate that placing cellulosic biorefineries in areas where water must be supplied using alternative means, such as desalination, wastewater recycling, or importation can increase the fuel's total greenhouse gas footprint by up to 47%. The results also show that the production of ethanol and petroleum fuels burden already overpumped aquifers, whereas electricity production is far less dependent on groundwater.

  18. Does water transport scale universally with tree size?

    Treesearch

    F.C. Meinzer; B.J. Bond; J.M. Warren; D.R. Woodruff

    2005-01-01

    1. We employed standardized measurement techniques and protocols to describe the size dependence of whole-tree water use and cross-sectional area of conducting xylem (sapwood) among several species of angiosperms and conifers. 2. The results were not inconsistent with previously proposed 314-power scaling of water transport with estimated above-...

  19. Coupling of solute transport and cell expansion in pea stems

    NASA Technical Reports Server (NTRS)

    Schmalstig, J. G.; Cosgrove, D. J.

    1990-01-01

    As cells expand and are displaced through the elongation zone of the epicotyl of etiolated pea (Pisum sativum L. var Alaska) seedlings, there is little net dilution of the cell sap, implying a coordination between cell expansion and solute uptake from the phloem. Using [14C] sucrose as a phloem tracer (applied to the hypogeous cotyledons), the pattern of label accumulation along the stem closely matched the growth rate pattern: high accumulation in the growing zone, little accumulation in nongrowing regions. Several results suggest that a major portion of phloem contents enters elongating cells through the symplast. We propose that the coordination between phloem transport and cell expansion is accomplished via regulatory pathways affecting both plasmodesmata conductivity and cell expansion.

  20. Coupling of solute transport and cell expansion in pea stems

    NASA Technical Reports Server (NTRS)

    Schmalstig, J. G.; Cosgrove, D. J.

    1990-01-01

    As cells expand and are displaced through the elongation zone of the epicotyl of etiolated pea (Pisum sativum L. var Alaska) seedlings, there is little net dilution of the cell sap, implying a coordination between cell expansion and solute uptake from the phloem. Using [14C] sucrose as a phloem tracer (applied to the hypogeous cotyledons), the pattern of label accumulation along the stem closely matched the growth rate pattern: high accumulation in the growing zone, little accumulation in nongrowing regions. Several results suggest that a major portion of phloem contents enters elongating cells through the symplast. We propose that the coordination between phloem transport and cell expansion is accomplished via regulatory pathways affecting both plasmodesmata conductivity and cell expansion.

  1. Coupling of solute transport and cell expansion in pea stems.

    PubMed

    Schmalstig, J G; Cosgrove, D J

    1990-01-01

    As cells expand and are displaced through the elongation zone of the epicotyl of etiolated pea (Pisum sativum L. var Alaska) seedlings, there is little net dilution of the cell sap, implying a coordination between cell expansion and solute uptake from the phloem. Using [14C] sucrose as a phloem tracer (applied to the hypogeous cotyledons), the pattern of label accumulation along the stem closely matched the growth rate pattern: high accumulation in the growing zone, little accumulation in nongrowing regions. Several results suggest that a major portion of phloem contents enters elongating cells through the symplast. We propose that the coordination between phloem transport and cell expansion is accomplished via regulatory pathways affecting both plasmodesmata conductivity and cell expansion.

  2. Quantum transport in chains with noisy off-diagonal couplings.

    PubMed

    Pereverzev, Andrey; Bittner, Eric R

    2005-12-22

    We present a model for conductivity and energy diffusion in a linear chain described by a quadratic Hamiltonian with Gaussian noise. We show that when the correlation matrix is diagonal, the noise-averaged Liouville-von Neumann equation governing the time evolution of the system reduces to the [Lindblad, Commun. Math. Phys. 48, 119 (1976)] equation with Hermitian Lindblad operators. We show that the noise-averaged density matrix for the system expectation values of the energy density and the number density satisfies discrete versions of the heat and diffusion equations. Transport coefficients are given in terms of model Hamiltonian parameters. We discuss conditions on the Hamiltonian under which the noise-averaged expectation value of the total energy remains constant. For chains placed between two heat reservoirs, the gradient of the energy density along the chain is linear.

  3. Water and heat transport in hilly red soil of southern China: I. Experiment and analysis.

    PubMed

    Lu, Jun; Huang, Zhi-Zhen; Han, Xiao-Fei

    2005-05-01

    Studies on coupled transfer of soil moisture and heat have been widely carried out for decades. However, little work has been done on red soils, widespread in southern China. The simultaneous transfer of soil moisture and heat depended on soil physical properties and the climate conditions. Red soil is heavy clay and high content of free iron and aluminum oxide. The climate conditions are characterized by the clear four seasons and the serious seasonal drought. The great air temperature differences annually and diurnally result in significant fluctuation in soil temperature in top layer. The closed and evaporating columns experiments with red soil were conducted to simulate the coupled transfer of soil water and heat under the overlaying and opening fields' conditions, and to analyze the effects of soil temperature gradient on the water transfer and the effects of initial soil water contents on the transfer of soil water and heat. The closed and evaporating columns were designed similarly with about 18 degrees C temperatures differences between the top and bottom boundary, except of the upper end closed or exposed to the air, respectively. Results showed that in the closed column, water moved towards the cold end driven by temperature gradient, while the transported water decreased with the increasing initial soil water content until the initial soil water content reached to field capacity equivalent, when almost no changes for the soil moisture profile. In the evaporating column, the net transport of soil water was simultaneously driven by evaporation and temperature gradients, and the drier soil was more influenced by temperature gradient than by evaporation. In drier soil, it took a longer time for the temperature to reach equilibrium, because of more net amount of transported water.

  4. Edge and coupled core/edge transport modeling in tokamak

    SciTech Connect

    Pearlstein, L D; Casper, T A; Cohen, R H; LoDestro, L L; Mattor, N; Porter, G D; Rensink, M E; Rognlien, T D; Ryutov, D D; Scott, H A; Wan, A

    1998-10-14

    Recent advances in the theory and modelling of tokamak edge, scrape-off-layer and divertor plasmas are described. The effects of the poloidal ExB drift on inner/outer divertor-plate asymmetries within a 1D analysis are shown to be in good agreement with experimental observations; above a critical v ExB, the model predicts transitions to supersonic SOL flow at the inboard midplane. Two-dimensional simulations show the importance of ExB flow in the private-flux region and B-drift effects. A theory of rough plasma-facing surfaces is given, and interesting effects, some traveling back up the magnetic field-lines to the SOL plasma, are predicted. The parametric dependence of detached-plasma states in slab geometry has been explored; with sufficient pumping, the location of the ionization front can be controlled; otherwise only fronts at the plate or the X-point are stable. Studies with a more accurate Monte-Carlo neutrals model and a detailed non-LTE radiation-transport code indicate various effects are important for quantitative rnodelling. Long-lived oscillatory UEDGE solutions in both ITER and DIII-D are reported. Detailed simulations of the DIII-D core and edge are presented; impurity and plasma flow are shown to be well modelled with UEDGE, and the roles of impurity and neutral transport in the edge and SOL are discussed.

  5. Crystal structure of a folate energy-coupling factor transporter from Lactobacillus brevis.

    PubMed

    Xu, Ke; Zhang, Minhua; Zhao, Qin; Yu, Fang; Guo, Hui; Wang, Chengyuan; He, Fangyuan; Ding, Jianping; Zhang, Peng

    2013-05-09

    ATP-binding cassette (ABC) transporters, composed of importers and exporters, form one of the biggest protein superfamilies that transport a variety of substrates across the membrane, powered by ATP hydrolysis. Most ABC transporters are composed of two transmembrane domains and two cytoplasmic nucleotide-binding domains. Also, importers from prokaryotes usually have extra solute-binding proteins in the periplasm that are responsible for the binding of substrates. Structures of importers have been reported that suggested a two-state model for the transport mechanism. Energy-coupling factor (ECF) transporters belong to a new class of ATP-binding cassette importers. Each ECF transporter comprises an energy-coupling module consisting of a transmembrane T protein (EcfT), two nucleotide-binding proteins (EcfA and EcfA'), and another transmembrane substrate-specific binding S protein (EcfS). Despite the similarities with ABC transporters, ECF transporters have different organizational and functional properties. The lack of solute-binding proteins in ECF transporters differentiates them clearly from the canonical ABC importers. Previously reported structures of the EcfS proteins RibU and ThiT clearly demonstrated the binding site of substrate riboflavin and thiamine, respectively. However, the organization of the four different components and the transport mechanism of ECF transporters remain unknown. Here we present the structure of an intact folate ECF transporter from Lactobacillus brevis at a resolution of 3 Å. This structure was captured in an inward-facing, nucleotide-free conformation with no bound substrate. The folate-binding protein FolT is nearly parallel to the membrane and is bound almost entirely by EcfT, which adopts an L shape and connects to EcfA and EcfA' through two coupling helices. Two conserved XRX motifs from the coupling helices of EcfT have a vital role in energy coupling by docking into EcfA-EcfA'. We propose a transport model that involves a

  6. Evaluation of the Water Vapor Transport over the Yellow River Basin in CMIP5 Models

    NASA Astrophysics Data System (ADS)

    Bao, Jiawei; Feng, Jinming

    2014-05-01

    Temperature, precipitation and water vapor transport in China, particularly in the Yellow River Basin simulated by the 16 models participating in phase 5 of the Coupled Model Inter-comparison Project (CMIP5) were evaluated for the period 1979-2005. Results suggest that most CMIP5 models are able to capture the climatological distribution patterns and inter-annual variations of surface air temperature, but with cold bias. Most models reproduce the spatial distribution pattern of warming trends identical with observations. Models tend to overestimate precipitation with relative biases ranging from 4.59 % to 61.46 %. Compared with observations, most models simulate more precipitation over the east of Tibetan Plateau and less in southeastern coastal regions. The spatial distribution of precipitation trends displayed in the observations cannot be well simulated by most models. The underestimation of temperature and the overestimation of precipitation simulated by some models over the east of Tibetan Plateau may be related to the anomalously strong western Pacific subtropical high and sufficient water vapor transport from Indian Ocean and western Pacific Ocean. In terms of the Yellow River Basin, modeled water vapor mainly flows in from eastern boundary and out from the western boundary. Water vapor also flows in through the southern boundary, but with smaller intensity. Owing to the overestimation of water vapor convergence, some models tend to exaggerate the climatological precipitation. Additionally, we found that the summer water vapor budget and precipitation keep pace with each other, which is well reflected by the FIO-ESM model. Models can also reproduce this relation in the lower reaches, with the total water vapor budget correlated strongly with water vapor transport from eastern, western and southern boundaries, indicating that water vapor budget and even the precipitation are strongly influenced by the water vapor transport from Indian Ocean and western

  7. Understanding Surface water Ground water Interactions in Arkansas-Red River Basin using Coupled Modeling

    NASA Astrophysics Data System (ADS)

    Joshi, C.; Mohanty, B. P.

    2006-12-01

    Subsurface water exists primarily as groundwater and also in small quantity as soil water in the unsaturated zone. This soil water plays a vital role in the hydrologic cycle by supporting plant growth, regulating the amount of water lost to evapo-transpiration and affecting the surface water groundwater interaction to a certain extent. As such, the interaction between surface water and groundwater is complex and little understood. This study aims at investigating the surface water groundwater interaction in the Arkansas-Red river basin, using a coupled modeling platform. For this purpose, an ecohydrological model (SWAP) has been coupled with the groundwater model (MODFLOW). Inputs to this coupled model are collected from NEXRAD precipitation data at a resolution of ~4 km, meteorological forcings from Oklahoma mesonet and NCDC sites, STATSGO soil property data, LAI (Leaf Area Index) data from MODIS at a resolution of ~1 km, and DEM (Digital Elevation Model). For numerical modeling, a spatial resolution of ~1 km and a temporal resolution of one day is used. The modeled base flow and total groundwater storage change would be tested using ground water table observation data. The modeled ground water storage is further improved using GRACE (Gravity Recovery and Climate Experiment) satellite data at a resolution of ~400 km, with the help of appropriate data assimilation technique.

  8. Adaptive resolution simulations coupling atomistic water to dissipative particle dynamics

    NASA Astrophysics Data System (ADS)

    Zavadlav, Julija; Praprotnik, Matej

    2017-09-01

    Multiscale methods are the most efficient way to address the interlinked spatiotemporal scales encountered in soft matter and molecular liquids. In the literature reported hybrid approaches span from quantum to atomistic, coarse-grained, and continuum length scales. In this article, we present the hybrid coupling of the molecular dynamics (MD) and dissipative particle dynamics (DPD) methods, bridging the micro- and mesoscopic descriptions. The interfacing is performed within the adaptive resolution scheme (AdResS), which is a linear momentum conserving coupling technique. Our methodology is hence suitable to simulate fluids on the micro/mesoscopic scale, where hydrodynamics plays an important role. The presented approach is showcased for water at ambient conditions. The supramolecular coupling is enabled by a recently developed clustering algorithm SWINGER that assembles, disassembles, and reassembles clusters as needed during the course of the simulation. This allows for a seamless coupling between standard atomistic MD and DPD models. The developed framework can be readily applied to various applications in the fields of materials and life sciences, e.g., simulations of phospholipids and polymer melts, or to study the red blood cells behavior in normal and disease states.

  9. Adaptive resolution simulations coupling atomistic water to dissipative particle dynamics.

    PubMed

    Zavadlav, Julija; Praprotnik, Matej

    2017-09-21

    Multiscale methods are the most efficient way to address the interlinked spatiotemporal scales encountered in soft matter and molecular liquids. In the literature reported hybrid approaches span from quantum to atomistic, coarse-grained, and continuum length scales. In this article, we present the hybrid coupling of the molecular dynamics (MD) and dissipative particle dynamics (DPD) methods, bridging the micro- and mesoscopic descriptions. The interfacing is performed within the adaptive resolution scheme (AdResS), which is a linear momentum conserving coupling technique. Our methodology is hence suitable to simulate fluids on the micro/mesoscopic scale, where hydrodynamics plays an important role. The presented approach is showcased for water at ambient conditions. The supramolecular coupling is enabled by a recently developed clustering algorithm SWINGER that assembles, disassembles, and reassembles clusters as needed during the course of the simulation. This allows for a seamless coupling between standard atomistic MD and DPD models. The developed framework can be readily applied to various applications in the fields of materials and life sciences, e.g., simulations of phospholipids and polymer melts, or to study the red blood cells behavior in normal and disease states.

  10. Single-photon nonreciprocal transport in one-dimensional coupled-resonator waveguides

    NASA Astrophysics Data System (ADS)

    Xu, Xun-Wei; Chen, Ai-Xi; Li, Yong; Liu, Yu-xi

    2017-06-01

    We study the transport of a single photon in two coupled one-dimensional semi-infinite coupled-resonator waveguides (CRWs), in which both end sides are coupled to a dissipative cavity. We demonstrate that a single photon can transfer from one semi-infinite CRW to the other nonreciprocally. Based on such nonreciprocity, we further construct a three-port single-photon circulator by a T-shaped waveguide, in which three semi-infinite CRWs are pairwise mutually coupled to each other. The single-photon nonreciprocal transport is induced by the breaking of the time-reversal symmetry and the optimal conditions for these phenomena are obtained analytically. The CRWs with broken time-reversal symmetry will open up a kind of quantum device with versatile applications in quantum networks.

  11. Coupled Modeling of Flow, Transport, and Deformation during Hydrodynamically Unstable Displacement in Fractured Rocks

    NASA Astrophysics Data System (ADS)

    Jha, B.; Juanes, R.

    2015-12-01

    Coupled processes of flow, transport, and deformation are important during production of hydrocarbons from oil and gas reservoirs. Effective design and implementation of enhanced recovery techniques such as miscible gas flooding and hydraulic fracturing requires modeling and simulation of these coupled proceses in geologic porous media. We develop a computational framework to model the coupled processes of flow, transport, and deformation in heterogeneous fractured rock. We show that the hydrocarbon recovery efficiency during unstable displacement of a more viscous oil with a less viscous fluid in a fractured medium depends on the mechanical state of the medium, which evolves due to permeability alteration within and around fractures. We show that fully accounting for the coupling between the physical processes results in estimates of the recovery efficiency in agreement with observations in field and lab experiments.

  12. Controlling photon transport in the single-photon weak-coupling regime of cavity optomechanics

    NASA Astrophysics Data System (ADS)

    Zhang, Wen-Zhao; Cheng, Jiong; Liu, Jing-Yi; Zhou, Ling

    2015-06-01

    We study the photon statistics properties of few-photon transport in an optomechanical system where an optomechanical cavity couples to two empty cavities. By analytically deriving the one- and two-photon currents in terms of a zero-time-delayed two-order correlation function, we show that a photon blockade can be achieved in both the single-photon strong-coupling regime and the single-photon weak-coupling regime due to the nonlinear interacting and multipath interference. Furthermore, our systems can be applied as a quantum optical diode, a single-photon source, and a quantum optical capacitor. It is shown that this the photon transport controlling devices based on photon antibunching does not require the stringent single-photon strong-coupling condition. Our results provide a promising platform for the coherent manipulation of optomechanics, which has potential applications for quantum information processing and quantum circuit realization.

  13. Methane oxidation coupled to oxygenic photosynthesis in anoxic waters.

    PubMed

    Milucka, Jana; Kirf, Mathias; Lu, Lu; Krupke, Andreas; Lam, Phyllis; Littmann, Sten; Kuypers, Marcel M M; Schubert, Carsten J

    2015-09-01

    Freshwater lakes represent large methane sources that, in contrast to the Ocean, significantly contribute to non-anthropogenic methane emissions to the atmosphere. Particularly mixed lakes are major methane emitters, while permanently and seasonally stratified lakes with anoxic bottom waters are often characterized by strongly reduced methane emissions. The causes for this reduced methane flux from anoxic lake waters are not fully understood. Here we identified the microorganisms and processes responsible for the near complete consumption of methane in the anoxic waters of a permanently stratified lake, Lago di Cadagno. Interestingly, known anaerobic methanotrophs could not be detected in these waters. Instead, we found abundant gamma-proteobacterial aerobic methane-oxidizing bacteria active in the anoxic waters. In vitro incubations revealed that, among all the tested potential electron acceptors, only the addition of oxygen enhanced the rates of methane oxidation. An equally pronounced stimulation was also observed when the anoxic water samples were incubated in the light. Our combined results from molecular, biogeochemical and single-cell analyses indicate that methane removal at the anoxic chemocline of Lago di Cadagno is due to true aerobic oxidation of methane fuelled by in situ oxygen production by photosynthetic algae. A similar mechanism could be active in seasonally stratified lakes and marine basins such as the Black Sea, where light penetrates to the anoxic chemocline. Given the widespread occurrence of seasonally stratified anoxic lakes, aerobic methane oxidation coupled to oxygenic photosynthesis might have an important but so far neglected role in methane emissions from lakes.

  14. Methane oxidation coupled to oxygenic photosynthesis in anoxic waters

    PubMed Central

    Milucka, Jana; Kirf, Mathias; Lu, Lu; Krupke, Andreas; Lam, Phyllis; Littmann, Sten; Kuypers, Marcel MM; Schubert, Carsten J

    2015-01-01

    Freshwater lakes represent large methane sources that, in contrast to the Ocean, significantly contribute to non-anthropogenic methane emissions to the atmosphere. Particularly mixed lakes are major methane emitters, while permanently and seasonally stratified lakes with anoxic bottom waters are often characterized by strongly reduced methane emissions. The causes for this reduced methane flux from anoxic lake waters are not fully understood. Here we identified the microorganisms and processes responsible for the near complete consumption of methane in the anoxic waters of a permanently stratified lake, Lago di Cadagno. Interestingly, known anaerobic methanotrophs could not be detected in these waters. Instead, we found abundant gamma-proteobacterial aerobic methane-oxidizing bacteria active in the anoxic waters. In vitro incubations revealed that, among all the tested potential electron acceptors, only the addition of oxygen enhanced the rates of methane oxidation. An equally pronounced stimulation was also observed when the anoxic water samples were incubated in the light. Our combined results from molecular, biogeochemical and single-cell analyses indicate that methane removal at the anoxic chemocline of Lago di Cadagno is due to true aerobic oxidation of methane fuelled by in situ oxygen production by photosynthetic algae. A similar mechanism could be active in seasonally stratified lakes and marine basins such as the Black Sea, where light penetrates to the anoxic chemocline. Given the widespread occurrence of seasonally stratified anoxic lakes, aerobic methane oxidation coupled to oxygenic photosynthesis might have an important but so far neglected role in methane emissions from lakes. PMID:25679533

  15. CO2-ECBM related coupled physical and mechanical transport processes

    NASA Astrophysics Data System (ADS)

    Gensterblum, Y.; Sartorius, M.; Busch, A.; Krooss, B. M.; Littke, R.

    2012-12-01

    The interrelation of cleat transport processes and mechanical properties was investigated by permeability tests at different stress levels (60% to 130% of in-situ stress) with sorbing (CH4, CO2) and inert gases (N2, Ar, He) on a subbituminous A coal from the Surat Basin, Queensland Australia (figure). From the flow tests under controlled triaxial stress conditions the Klinkenberg-corrected "true" permeability coefficients and the Klinkenberg slip factors were derived. The "true"-, absolute or Klinkenberg-corrected permeability depends on gas type. Following the approach of Seidle et al. (1992) the cleat volume compressibility (cf) was calculated from observed changes in apparent permeability upon variation of external stress (at equal mean gas pressures). The observed effects also show a clear dependence on gas type. Due to pore or cleat compressibility the cleat aperture decreases with increasing effective stress. Vice versa, with increasing mean pore pressure at lower confining pressure an increase in permeability is observed, which is attributed to a widening of cleat aperture. Non-sorbing gases like helium and argon show higher apparent permeabilities than sorbing gases like methane and CO2. Permeability coefficients measured with successively increasing mean gas pressures were consistently lower than those determined at decreasing mean gas pressures. The kinetics of matrix transport processes were studied by sorption tests on different particle sizes at various moisture contents and temperatures (cf. Busch et al., 2006). Methane uptake rates were determined from the pressure decline curves recorded for each particle-size fraction, and "diffusion coefficients" were calculated using several unipore and bidisperse diffusion models. While the CH4 sorption capacity of moisture-equilibrated coals was significantly lower (by 50%) than that of dry coals, no hysteresis was observed between sorption and desorption on dry and moisture-equilibrated samples and the

  16. Coupled DEM-CFD Investigation of Granular Transport in a Fluid Channel

    NASA Astrophysics Data System (ADS)

    Zhao, T.; Dai, F.; Xu, N. W.

    2015-09-01

    This paper presents three dimensional numerical investigations of granular transport in fluids, analysed by the Discrete Element Method (DEM) coupled with Computational Fluid Mechanics (CFD). By employing this model, the relevance of flow velocity and granular depositional morphology has been clarified. The larger the flow velocity is, the further distance the grains can be transported to. In this process, the segregation of solid grains has been clearly identified. This research reveals that coarse grains normally accumulate near the grain source region, while the fine grains can be transported to the flow front. Regardless of the different flow velocities used in these simulations, the intensity of grains segregation remains almost unchanged. The results obtained from the DEM-CFD coupled simulations can reasonably explain the grain transport process occurred in natural environments, such as river scouring, evolution of river/ocean floor, deserts and submarine landslides.

  17. Nanoparticle growth and transport mechanisms in capacitively coupled silane discharges: a numerical investigation

    SciTech Connect

    Bleecker, K. de; Bogaerts, A.; Goedheer, W.J.

    2005-10-31

    A self-consistent 1D fluid model is used to investigate the formation, growth and transport mechanisms of sub-micrometer particles in a low pressure capacitively coupled radio-frequency silane (SiH4) discharge. In this contribution we analyze the competition between the different forces governing the transport of nanometer-sized particles and the specific role of the thermophoretic force arising from a thermal gradient in gas temperature induced by heating or cooling of the electrodes. Further growth of the nanoparticles due to coagulation is also described by coupling the 1D fluid model with an aerosol dynamics model.

  18. Andreev transport through quantum dots coupled to ferromagnetic and superconducting leads

    NASA Astrophysics Data System (ADS)

    Weymann, Ireneusz; Wojcik, Krzysztof; Trocha, Piotr

    2014-03-01

    The local and nonlocal Andreev transport through the system consisting of quantum dot coupled to one superconducting electrode and two ferromagnetic leads is studied theoretically. The magnetizations of the leads are assumed to form either parallel or antiparallel magnetic configuration. To calculate basic transport characteristics, like Andreev current, local and nonlocal conductance, tunneling magnetoresistance, we employ the real-time diagrammatic technique assuming weak tunnel coupling of the dot to ferromagnetic leads. We study the effect of cotunneling processes on Andreev transport in the Coulomb blockade regime. We find a zero-bias anomaly of the Andreev differential conductance in the parallel configuration, which is associated with a nonequilibrium spin accumulation in the dot. We also analyze the linear response transport properties in the case of strong coupling to ferromagnetic leads, when the electronic correlations can lead to the Kondo effect. This transport regime is addressed by means of the numerical renormalization group method. We show that the linear conductance due to Andreev processes strongly depends on the magnitude of exchange field due to the presence of ferromagnetic leads, and the coupling strength to the superconducting lead. We acknowledge support from the project No. IP2011 059471 and the EU grant No. CIG-303 689.

  19. Hyperfine coupling of the hydrogen atom in high temperature water.

    PubMed

    Nuzhdin, Kirill; Bartels, David M

    2013-03-28

    The hyperfine coupling constant of the hydrogen atom has been measured in pressurized liquid water up to 300 °C. The reduced constant A(water)∕A(vacuum) is 0.9939 at room temperature, and decreases to a minimum of 0.9918 at 240 °C. The reduced constant then increases at higher temperature. The g-factor is 2.002244(10) at room temperature and decreases to 2.00221(1) at 240 °C. The change in g-factor is proportional to the change in hyperfine coupling. The behavior below 110 °C is in excellent agreement with a previously proposed model in which the H atom is confined to a harmonic solvent cage, and vibrations within the cage mix "p-type" character into the wavefunction, resulting inA(water)∕A(vacuum) < 1. The harmonic model breaks down above 130 °C. We demonstrate that a classical binary collision model using approximate partial molar volume information can recover the observed minima near 240 °C.

  20. CO2-ECBM related coupled physical and mechanical transport processes

    NASA Astrophysics Data System (ADS)

    Gensterblum, Y.; Sartorius, M.; Busch, A.; Cumming, D.; Krooss, B. M.

    2012-04-01

    The interrelation of cleat transport processes and mechanical properties was investigated by permeability tests at different stress levels (60% to 130% of in-situ stress) with sorbing (CH4, CO2) and inert gases (N2, Ar, He) on a sub bituminous A coal from the Surat Basin, Queensland Australia. From the flow tests under controlled triaxial stress conditions the Klinkenberg-corrected "true" permeability coefficients and the Klinkenberg slip factors were derived. The "true"-, absolute or Klinkenberg corrected permeability shows a gas type dependence. Following the approach of Seidle et al. (1992) the cleat volume compressibility (cf) was calculated from observed changes in apparent permeability upon variation of external stress (at equal mean gas pressures). The observed effects also show a clear dependence on gas type. Due to pore or cleat compressibility the cleat aperture decreases with increasing effective stress. Vice versa we observe with increasing mean pressure at lower confining pressure an increase in permeability which we attribute to a cleat aperture widening. The cleat volume compressibility (cf) also shows a dependence on the mean pore pressure. Non-sorbing gases like helium and argon show higher apparent permeabilities than sorbing gases like methane. Permeability coefficients measured with successively increasing mean gas pressures were consistently lower than those determined at decreasing mean gas pressures. This permeability hysteresis is in accordance with results reported by Harpalani and McPherson (1985). The kinetics of matrix transport processes were studied by sorption tests on different particle sizes at various moisture contents and temperatures (cf. Busch et al., 2006). Methane uptake rates were determined from the pressure decline curves recorded for each particle-size fraction, and "diffusion coefficients" were calculated using several unipore and bidisperse diffusion models. While the CH4 sorption capacity of moisture-equilibrated coals

  1. CO2-ECBM related coupled physical and mechanical transport processes

    NASA Astrophysics Data System (ADS)

    Gensterblum, Yves; Satorius, Michael; Busch, Andreas; Krooß, Bernhard

    2013-04-01

    The interrelation of cleat transport processes and mechanical properties was investigated by permeability tests at different stress levels (60% to 130% of in-situ stress) with sorbing (CH4, CO2) and inert gases (N2, Ar, He) on a sub bituminous A coal from the Surat Basin, Queensland Australia. From the flow tests under controlled triaxial stress conditions the Klinkenberg-corrected "true" permeability coefficients and the Klinkenberg slip factors were derived. The "true"-, absolute or Klinkenberg corrected permeability shows a gas type dependence. Following the approach of Seidle et al. (1992) the cleat volume compressibility (cf) was calculated from observed changes in apparent permeability upon variation of external stress (at equal mean gas pressures). The observed effects also show a clear dependence on gas type. Due to pore or cleat compressibility the cleat aperture decreases with increasing effective stress. Vice versa we observe with increasing mean pressure at lower confining pressure an increase in permeability which we attribute to a cleat aperture widening. The cleat volume compressibility (cf) also shows a dependence on the mean pore pressure. Non-sorbing gases like helium and argon show higher apparent permeabilities than sorbing gases like methane. Permeability coefficients measured with successively increasing mean gas pressures were consistently lower than those determined at decreasing mean gas pressures. This permeability hysteresis is in accordance with results reported by Harpalani and McPherson (1985). The kinetics of matrix transport processes were studied by sorption tests on different particle sizes at various moisture contents and temperatures (cf. Busch et al., 2006). Methane uptake rates were determined from the pressure decline curves recorded for each particle-size fraction, and "diffusion coefficients" were calculated using several unipore and bidisperse diffusion models. While the CH4 sorption capacity of moisture-equilibrated coals

  2. A Coupled Modeling System to Simulate Water Resources in the Rio Grande Basin

    SciTech Connect

    Bossert, J.E.; Breshears, D.D.; Campbell, K.; Costigan, K.R.; Greene, R.K.; Keating, E.H.; Kleifgen, L.M.; Langley, D.L.; Martens, S.N.; Sanderson, J.G.; Springer, E.P.; Stalker, J.R.; Tartakovsky, D.M.; Winter, C.L.; Zyvoloski, G.A.

    1999-01-11

    Limited availability of fresh water in arid and semi-arid regions of the world requires prudent management strategies from accurate, science-based assessments. These assessments demand a thorough understanding of the hydrologic cycle over long time periods within the individual water-sheds that comprise large river basins. Measurement and simulation of the hydrologic cycle is a tremendous challenge, involving a coupling between global to regional-scale atmospheric precipitation processes with regional to local-scale land surface and subsurface water transport. Los Alamos National Laboratory is developing a detailed modeling system of the hydrologic cycle and applying this tool at high resolution to assess the water balance within the upper Rio Grande river basin. The Rio Grande is a prime example of a river system in a semiarid environment, with a high demand from agricultural, industrial, recreational, and municipal interests for its water supply. Within this river basin, groundwater supplies often augment surface water. With increasing growth projected throughout the river basin, however, these multiple water users have the potential to significantly deplete groundwater resources, thereby increasing the dependence on surface water resources.

  3. Coupled modeling of groundwater flow solute transport, chemical reactions and microbial processes in the 'SP' island

    SciTech Connect

    Samper, Javier; Molinero, Jorg; Changbing, Yang; Zhang, Guoxiang

    2003-12-01

    The Redox Zone Experiment was carried out at the Aespoe HRL in order to study the redox behavior and the hydrochemistry of an isolated vertical fracture zone disturbed by the excavation of an access tunnel. Overall results and interpretation of the Redox Zone Project were reported by /Banwart et al, 1995/. Later, /Banwart et al, 1999/ presented a summary of the hydrochemistry of the Redox Zone Experiment. Coupled groundwater flow and reactive transport models of this experiment were carried out by /Molinero, 2000/ who proposed a revised conceptual model for the hydrogeology of the Redox Zone Experiment which could explain simultaneously measured drawdown and salinity data. The numerical model was found useful to understand the natural system. Several conclusions were drawn about the redox conditions of recharge waters, cation exchange capacity of the fracture zone and the role of mineral phases such as pyrite, calcite, hematite and goethite. This model could reproduce the measured trends of dissolved species, except for bicarbonate and sulfate which are affected by microbially-mediated processes. In order to explore the role of microbial processes, a coupled numerical model has been constructed which accounts for water flow, reactive transport and microbial processes. The results of this model is presented in this report. This model accounts for groundwater flow and reactive transport in a manner similar to that of /Molinero, 2000/ and extends the preliminary microbial model of /Zhang, 2001/ by accounting for microbially-driven organic matter fermentation and organic matter oxidation. This updated microbial model considers simultaneously the fermentation of particulate organic matter by yeast and the oxidation of dissolved organic matter, a product of fermentation. Dissolved organic matter is produced by yeast and serves also as a substrate for iron-reducing bacteria. Model results reproduce the observed increase in bicarbonate and sulfate concentration, thus

  4. A multi-substrate single-file model for ion-coupled transporters.

    PubMed Central

    Su, A; Mager, S; Mayo, S L; Lester, H A

    1996-01-01

    Ion-coupled transporters are simulated by a model that differs from contemporary alternating-access schemes. Beginning with concepts derived from multi-ion pores, the model assumes that substrates (both inorganic ions and small organic molecules) hop a) between the solutions and binding sites and b) between binding sites within a single-file pore. No two substrates can simultaneously occupy the same site. Rate constants for hopping can be increased both a) when substrates in two sites attract each other into a vacant site between them and b) when substrates in adjacent sites repel each other. Hopping rate constants for charged substrates are also modified by the membrane field. For a three-site model, simulated annealing yields parameters to fit steady-state measurements of flux coupling, transport-associated currents, and charge movements for the GABA transporter GAT1. The model then accounts for some GAT1 kinetic data as well. The model also yields parameters that describe the available data for the rat 5-HT transporter and for the rabbit Na(+)-glucose transporter. The simulations show that coupled fluxes and other aspects of ion transport can be explained by a model that includes local substrate-substrate interactions but no explicit global conformational changes. Images FIGURE 1 FIGURE 2 FIGURE 9 PMID:8789093

  5. Single photon transport in two waveguides chirally coupled by a quantum emitter.

    PubMed

    Cheng, Mu-Tian; Ma, Xiao-San; Zhang, Jia-Yan; Wang, Bing

    2016-08-22

    We investigate single photon transport in two waveguides coupled to a two-level quantum emitter (QE). With the deduced analytical scattering amplitudes, we show that under condition of the chiral coupling between the QE and the photon in the two waveguides, the QE can play the role of ideal quantum router to redirect a single photon incident from one waveguide into the other waveguide with a probability of 100% in the ideal condition. The influences of cross coupling between two waveguides and dissipations on the routing are also shown.

  6. A new look at water transport regulation in plants.

    PubMed

    Martínez-Vilalta, Jordi; Poyatos, Rafael; Aguadé, David; Retana, Javier; Mencuccini, Maurizio

    2014-10-01

    Plant function requires effective mechanisms to regulate water transport at a variety of scales. Here, we develop a new theoretical framework describing plant responses to drying soil, based on the relationship between midday and predawn leaf water potentials. The intercept of the relationship (Λ) characterizes the maximum transpiration rate per unit of hydraulic transport capacity, whereas the slope (σ) measures the relative sensitivity of the transpiration rate and plant hydraulic conductance to declining water availability. This framework was applied to a newly compiled global database of leaf water potentials to estimate the values of Λ and σ for 102 plant species. Our results show that our characterization of drought responses is largely consistent within species, and that the parameters Λ and σ show meaningful associations with climate across species. Parameter σ was ≤1 in most species, indicating a tight coordination between the gas and liquid phases of water transport, in which canopy transpiration tended to decline faster than hydraulic conductance during drought, thus reducing the pressure drop through the plant. The quantitative framework presented here offers a new way of characterizing water transport regulation in plants that can be used to assess their vulnerability to drought under current and future climatic conditions. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.

  7. Investigating water transport through the xylem network in vascular plants.

    PubMed

    Kim, Hae Koo; Park, Joonghyuk; Hwang, Ildoo

    2014-04-01

    Our understanding of physical and physiological mechanisms depends on the development of advanced technologies and tools to prove or re-evaluate established theories, and test new hypotheses. Water flow in land plants is a fascinating phenomenon, a vital component of the water cycle, and essential for life on Earth. The cohesion-tension theory (CTT), formulated more than a century ago and based on the physical properties of water, laid the foundation for our understanding of water transport in vascular plants. Numerous experimental tools have since been developed to evaluate various aspects of the CTT, such as the existence of negative hydrostatic pressure. This review focuses on the evolution of the experimental methods used to study water transport in plants, and summarizes the different ways to investigate the diversity of the xylem network structure and sap flow dynamics in various species. As water transport is documented at different scales, from the level of single conduits to entire plants, it is critical that new results be subjected to systematic cross-validation and that findings based on different organs be integrated at the whole-plant level. We also discuss the functional trade-offs between optimizing hydraulic efficiency and maintaining the safety of the entire transport system. Furthermore, we evaluate future directions in sap flow research and highlight the importance of integrating the combined effects of various levels of hydraulic regulation.

  8. Transport of Cryptosporidium parvum in Surface Waters: Interplay of Hydrodynamic Processes, Sediments, and Biofilms

    NASA Astrophysics Data System (ADS)

    Searcy, K. E.; Packman, A. I.; Atwill, E. R.; Harter, T.

    2005-05-01

    Understanding the movement of pathogens in the environment is necessary to ensure the safety and protection of municipal water supply systems. Cryptosporidium parvum is a human pathogen of particular concern as it is common in surface waters of the United States, it can survive for long periods of time in the environment, and it is difficult to disinfect in water treatment plants. The transport of oocysts through watersheds can be mediated by interactions with the stream channel and suspended particles in the water column. For example, the association of C. parvum oocysts with suspended particles can alter the effective physical properties of the oocysts and increase their settling velocity. The hydrodynamic coupling of the overlying water with the pore water of the sediment bed can carry oocysts from the surface water into the sediment bed. Surface-attached communities of microorganisms, called biofilms, are ubiquitous in surface water systems and can capture C. parvum oocysts. Laboratory experiments were conducted at multiple scales (flowcell, batch, and flume) to determine the association of oocysts with sediments and biofilm communities and to assess the impact of this association on C. parvum transport. The effects of flow conditions, water chemistry, sediment composition, biofilm composition, and biofilm structure on these associations were all evaluated. The experimental results demonstrate that oocyst-sediment-biofilm interactions have significant implications for the propagation of C. parvum oocysts through watersheds and should generally be considered when predicting the fate of pathogens in the environment.

  9. Coupling biological processes and gaseous transport in models describing GHG emission from soils

    NASA Astrophysics Data System (ADS)

    Blagodatsky, S.; Smith, P.

    2012-04-01

    The precise coupling of gaseous transport and biochemistry in models describing the emission of greenhouse gases (GHG) from soil is necessary because CH4 and N2O can be both produced and consumed in soil. Eventual fluxes to the atmosphere depends on the position of reaction sites and the escape pathways for these gases. The CO2 production rate depends in turn on the efficiency of oxygen transport in the soil. Basing on models published in literature and our own experience the main principles leading to the best simulation results can be summarized as: 1) keeping a balanced level of detail in coupled model systems describing biochemical reactions and transport; 2) reduction of unnecessary complexity by means of using the most essential relationships elucidated by comprehensive statistical model testing; 3) consideration of all transport mechanisms in relation to prevailing ecological conditions. We will show examples of the successful application of coupled model systems for the prediction of three main GHG: CO2, N2O and CH4 as well as results of application of our model MICNIT designed for the simulation of CO2 and N2O emission and microbial C and N turnover in soil. We conclude that coupled gas transport and decomposition models lack the latest findings in modelling microbial growth in soil. So, models including an explicit description of microbial growth, i.e. growth rate and efficiency, humification ratios and their relationship with N availability (Blagodatsky, Richter, 1998; Moorhead and Sinsabaugh, 2006; Eliasson, and Ågren, 2011) need to be coupled with well-developed soil physics models with appropriate description of transport processes.

  10. Experimental and numerical investigation of the coupling of turbulence and sediment transport over dunes

    NASA Astrophysics Data System (ADS)

    Schmeeckle, M. W.; Leary, K. P.

    2016-12-01

    We investigate the spatiotemporal coupling of sediment transport over dunes using a turbulence- and particle-resolving numerical model and high-speed video in a laboratory flume. The model utilizes the Large Eddy Simulation (LES) for the fluid turbulence and a Discrete Element Method (DEM) simulation for the sediment. Previous experiments assessing the effects of flow separation on downstream fluid turbulent structures and bedload transport suggest that localized, intermittent, high-magnitude transport events, called permeable splat events, play an important role in both downstream and cross-stream transport near flow reattachment. The flume was lined with 17 concrete ripples that had a 2 cm high crest and were 30 cm long. A high-speed camera observed sediment transport along the entirety of the bedform at 250 Hz. Downstream and vertical fluid velocity was observed at 1mm and 3 mm above the bed using Laser Doppler Velocitmetry (LDV) at 15 distances along bedform profile. As observed in our previous backward-facing step experiments and simulations, mean downstream fluid velocity increases nonlinearly with increasing distance along the ripple. Observed sediment transport, however, increases linearly with increasing distance along the ripple with an exception at the crest of the bedform, where both mean downstream fluid velocity and sediment transport decrease significantly. Previous experiments assessing only the effect of flow separation showed that calculating sediment transport as a function of boundary shear stress using a Meyer-Peter Müller type equation, produced a zone of underestimated transport near flow reattachment. Results reported here show that calculating sediment transport in this way underestimates observed sediment transport along the entire profile of the bedform, not just near flow reattachment. Preliminary sediment transport time-series data show a zone of high-magnitude cross-stream transport near flow reattachment, suggesting that permeable

  11. Coupled Particle Transport and Pattern Formation in a Nonlinear Leaky-Box Model

    NASA Technical Reports Server (NTRS)

    Barghouty, A. F.; El-Nemr, K. W.; Baird, J. K.

    2009-01-01

    Effects of particle-particle coupling on particle characteristics in nonlinear leaky-box type descriptions of the acceleration and transport of energetic particles in space plasmas are examined in the framework of a simple two-particle model based on the Fokker-Planck equation in momentum space. In this model, the two particles are assumed coupled via a common nonlinear source term. In analogy with a prototypical mathematical system of diffusion-driven instability, this work demonstrates that steady-state patterns with strong dependence on the magnetic turbulence but a rather weak one on the coupled particles attributes can emerge in solutions of a nonlinearly coupled leaky-box model. The insight gained from this simple model may be of wider use and significance to nonlinearly coupled leaky-box type descriptions in general.

  12. Barriers to superfast water transport in carbon nanotube membranes.

    PubMed

    Walther, Jens H; Ritos, Konstantinos; Cruz-Chu, Eduardo R; Megaridis, Constantine M; Koumoutsakos, Petros

    2013-05-08

    Carbon nanotube (CNT) membranes hold the promise of extraordinary fast water transport for applications such as energy efficient filtration and molecular level drug delivery. However, experiments and computations have reported flow rate enhancements over continuum hydrodynamics that contradict each other by orders of magnitude. We perform large scale molecular dynamics simulations emulating for the first time the micrometer thick CNTs membranes used in experiments. We find transport enhancement rates that are length dependent due to entrance and exit losses but asymptote to 2 orders of magnitude over the continuum predictions. These rates are far below those reported experimentally. The results suggest that the reported superfast water transport rates cannot be attributed to interactions of water with pristine CNTs alone.

  13. Coupled Normal Heat and Matter Transport in a Simple Model System

    NASA Astrophysics Data System (ADS)

    Mejía-Monasterio, C.; Larralde, H.; Leyvraz, F.

    2001-06-01

    We introduce the first simple mechanical system that shows fully realistic transport behavior while still being exactly solvable at the level of equilibrium statistical mechanics. The system is a Lorentz gas with fixed freely rotating circular scatterers which scatter point particles via perfectly rough collisions. Upon imposing either a temperature gradient and/or a chemical potential gradient, a stationary state is attained for which local thermal equilibrium holds. Transport in this system is normal in the sense that the transport coefficients which characterize the flow of heat and matter are finite in the thermodynamic limit. Moreover, the two flows are nontrivially coupled, satisfying Onsager's reciprocity relations.

  14. Coupling Radar Rainfall to Hydrological Models for Water Abstraction Management

    NASA Astrophysics Data System (ADS)

    Asfaw, Alemayehu; Shucksmith, James; Smith, Andrea; MacDonald, Ken

    2015-04-01

    The impacts of climate change and growing water use are likely to put considerable pressure on water resources and the environment. In the UK, a reform to surface water abstraction policy has recently been proposed which aims to increase the efficiency of using available water resources whilst minimising impacts on the aquatic environment. Key aspects to this reform include the consideration of dynamic rather than static abstraction licensing as well as introducing water trading concepts. Dynamic licensing will permit varying levels of abstraction dependent on environmental conditions (i.e. river flow and quality). The practical implementation of an effective dynamic abstraction strategy requires suitable flow forecasting techniques to inform abstraction asset management. Potentially the predicted availability of water resources within a catchment can be coupled to predicted demand and current storage to inform a cost effective water resource management strategy which minimises environmental impacts. The aim of this work is to use a historical analysis of UK case study catchment to compare potential water resource availability using modelled dynamic abstraction scenario informed by a flow forecasting model, against observed abstraction under a conventional abstraction regime. The work also demonstrates the impacts of modelling uncertainties on the accuracy of predicted water availability over range of forecast lead times. The study utilised a conceptual rainfall-runoff model PDM - Probability-Distributed Model developed by Centre for Ecology & Hydrology - set up in the Dove River catchment (UK) using 1km2 resolution radar rainfall as inputs and 15 min resolution gauged flow data for calibration and validation. Data assimilation procedures are implemented to improve flow predictions using observed flow data. Uncertainties in the radar rainfall data used in the model are quantified using artificial statistical error model described by Gaussian distribution and

  15. Coupled binding mechanism of three sodium ions and aspartate in the glutamate transporter homologue GltTk

    PubMed Central

    Guskov, Albert; Jensen, Sonja; Faustino, Ignacio; Marrink, Siewert J.; Slotboom, Dirk Jan

    2016-01-01

    Glutamate transporters catalyse the thermodynamically unfavourable transport of anionic amino acids across the cell membrane by coupling it to the downhill transport of cations. This coupling mechanism is still poorly understood, in part because the available crystal structures of these transporters are of relatively low resolution. Here we solve crystal structures of the archaeal transporter GltTk in the presence and absence of aspartate and use molecular dynamics simulations and binding assays to show how strict coupling between the binding of three sodium ions and aspartate takes place. PMID:27830699

  16. The Transportation of Debris by Running Water

    USGS Publications Warehouse

    Gilbert, Grove Karl; Murphy, Edward Charles

    1914-01-01

    Scope.-The finer debris transported by a stream is borne in suspension. The coarser is swept along the channel bed. The suspended load is readily sampled and estimated, and much is known as to its quantity. The bed load is inaccessible and we are without definite information as to its amount. The primary purpose of the investigation was to learn the laws which control the movement of bed load, and especially to determine how the quantity of load is related to the stream's slope and discharge and to the degree of comminution of the debris. Method.-To this end a laboratory was equipped at Berkeley, Cal., and experiments were performed in which each of the three conditions mentioned was separately varied and the resulting variations of load were observed and measured. Sand and gravel were sorted by sieves into grades of uniform size. Determinate discharges were used. In each experiment a specific load was fed to a stream of specific width and discharge, and measurement was made of the slope to which the stream automatically adjusted its bed so as to enable the current to transport the load. The slope factor.-For each combination of discharge, width, and grade of debris there is a slope, called competent slope, which limits transportation. With lower slopes there is no load, or the stream has no capacity for load. With higher slopes capacity exists; and increase of slope gives increase of capacity. The value of capacity is approximately proportional to a power of the excess of slope above competent slope. If S equal the stream's slope and sigma equal competent slope, then the stream's capacity varies as (S - sigma)n. This is not a deductive, but an empiric law. The exponent n has not a fixed value, but an indefinite series of values depending on conditions. Its range of values in the experience of the laboratory is from 0.93 to 2.37, the values being greater as the discharges are smaller or the debris is coarser. The discharge factor.-For each combination of width

  17. Incomplete water securitization in coupled hydro-human production sytems

    NASA Astrophysics Data System (ADS)

    van den Boom, B.; Pande, S.

    2012-04-01

    Due to the dynamics, the externalities and the contingencies involved in managing local water resource for production, the water allocation at basin-level is a subtle balance between laws of nature (gravity; flux) and laws of economics (price; productivity). We study this balance by looking at inter-temporal basin-level water resource allocations in which subbasins enjoy a certain degree of autonomy. Each subbasin is represented as an economic agent i, following a gravity ordering with i=1 representing the most upstream area and i=I the downstream boundary. The water allocation is modeled as a decentralized equilibrium in a coupled conceptual hydro-human production system. Agents i=1,2,...,I in the basin produce a composite good according to a technology that requires water as a main input and that is specific to the subbasin. Agent i manages her use Xi and her storage Si, conceptualizing surface and subsurface water, of water with the purpose of maximizing the utility derived from consumption Ci of the composite good, where Ci is a scalar and Xi and Si are vectors which are composed of one element for each time period and for each contingency. A natural way to consume the good would be to absorb the own production. Yet, the agent may have two more option, namely, she might get a social transfer from other agents or she could use an income from trading water securities with her contiguous neighbors. To study these options, we compare water allocations (Ci, Xi, Si) all i=1,2,...,I for three different settings. We look at allocations without water securitization (water autarky equilibrium EA) first. Next, we describe the imaginary case of full securitization (contingent water markets equilibrium ECM) and, in between, we study limited securitization (incomplete water security equilibrium EWS). We show that allocations under contingent water markets ECM are efficient in the sense that, for the prevailing production technologies, no other allocation exists that is at

  18. Meridional energy transport in the coupled atmosphere-ocean system: Compensation and partitioning

    NASA Astrophysics Data System (ADS)

    Farneti, R.; Vallis, G. K.

    2012-04-01

    The variability and compensation of the energy transport in the atmosphere and ocean are discussed with a hierarchy of coupled models. A state-of-the-art Coupled Model (GFDL CM2.1), an Intermediate Complexity Climate Model (GFDL ICCM) and a simple Energy Balance Model (EBM) are used in this study. For decadal time scales, a high degree of compensation is found for the transport in the Northern Hemisphere in the Atlantic sector. The variability of the total, or planetary, heat transport (PHT) is much smaller than the variability in either the atmosphere (AHT) or ocean (OHT) alone, a feature sometimes referred to as `Bjerknes compensation'. In the coupled models used, natural decadal variability stems from the Atlantic meridional overturning circulation (AMOC), and variations in the strength of the AMOC tend to lead the variability in the OHT. Furthermore, the PHT is positively correlated with the OHT, implying that the atmosphere is compensating, but imperfectly, for variations in the ocean transport. In the Southern Hemisphere no significant anticorrelation is found between OHT and AHT, consistent with the absence of decadal scale variability in the ocean. For both coupled models, the strongest anticorrelation between transports is found at the period of AMOC variability and decreases as the time scale decreases. Unlike the AHT and AMOC, the AHT and the transport in the oceanic gyres are positively correlated, suggesting that coupling between the wind-driven ocean circulation and the atmosphere militates against long-term variability involving the wind-driven flow. Moisture and sensible heat transports in the atmosphere are also positively correlated at decadal time scales. In the Northern Hemisphere compensation is weaker at low latitudes than at high. This is consistent with the notion that at low latitudes a larger fraction of the oceanic transport is due to the wind-driven warm cell, and the atmospheric and wind-driven oceanic energy transports vary in unison

  19. Computational study of effect of water finger on ion transport through water-oil interface

    NASA Astrophysics Data System (ADS)

    Kikkawa, Nobuaki; Wang, Lingjian; Morita, Akihiro

    2016-07-01

    When an ion transports from water to oil through water-oil interface, it accompanies hydrated water molecules and transiently forms a chain of water, called "water finger." We thoroughly investigated the role of the water finger in chloride ion transport through water-dichloromethane interface by using molecular dynamics technique. We developed a proper coordinate w to describe the water finger structure and calculated the free energy landscape and the friction for the ion transport as a function of ion position z and the water finger coordinate w. It is clearly shown that the formation and break of water finger accompanies an activation barrier for the ion transport, which has been overlooked in the conventional free energy curve along the ion position z. The present analysis of the friction does not support the hypothesis of augmented local friction (reduced local diffusion coefficient) at the interface. These results mean that the experimentally observed rate constants of interfacial ion transfer are reduced from the diffusion-limited one because of the activation barrier associated to the water finger, not the anomalous local diffusion. We also found that the nascent ion just after the break of water finger has excessive hydration water than that in the oil phase.

  20. Computational study of effect of water finger on ion transport through water-oil interface.

    PubMed

    Kikkawa, Nobuaki; Wang, Lingjian; Morita, Akihiro

    2016-07-07

    When an ion transports from water to oil through water-oil interface, it accompanies hydrated water molecules and transiently forms a chain of water, called "water finger." We thoroughly investigated the role of the water finger in chloride ion transport through water-dichloromethane interface by using molecular dynamics technique. We developed a proper coordinate w to describe the water finger structure and calculated the free energy landscape and the friction for the ion transport as a function of ion position z and the water finger coordinate w. It is clearly shown that the formation and break of water finger accompanies an activation barrier for the ion transport, which has been overlooked in the conventional free energy curve along the ion position z. The present analysis of the friction does not support the hypothesis of augmented local friction (reduced local diffusion coefficient) at the interface. These results mean that the experimentally observed rate constants of interfacial ion transfer are reduced from the diffusion-limited one because of the activation barrier associated to the water finger, not the anomalous local diffusion. We also found that the nascent ion just after the break of water finger has excessive hydration water than that in the oil phase.

  1. Surface excess properties from energy transport measurements during water evaporation.

    PubMed

    Duan, Fei; Ward, C A

    2005-11-01

    When water evaporates at high rates, recent studies indicate thermal conduction to the interface does not provide enough energy to evaporate water at the observed rate and that it is perhaps thermocapillary convection that transports the remaining energy. This possibility is examined by applying the Gibbs dividing-surface approximation to develop an expression for the energy transported along the interface. When this energy transport rate is compared with that required to evaporate the liquid at the observed rate, it is found that a Gibbs excess property, the "surface-thermal capacity," can be evaluated. A series of 19 evaporation experiments has been conducted under conditions for which there was no buoyancy-driven convection and for which the evaporation rate was progressively increased. For Marangoni numbers, (Ma) less than approximately 100, the interface was quiescent and thermal conduction (the Stefan condition) correctly predicted the energy transport rate to the surface. For experiments with 100transport. However, if the surface-thermal capacity is assigned a value of 30.6+/-0.8 kJ/(m2K), then energy transport by thermocapillary convection and conduction provides the energy transport required to evaporate the liquid at the observed rate. For experiments with Ma>22,000, the interfacial flow was turbulent and viscous dissipation became important.

  2. Coupling Seepage and Radionuclide Transport in and Around Emplacement Drifts at Yucca Mountain

    NASA Astrophysics Data System (ADS)

    Zhang, G.; Spycher, N.; Sonnenthal, E.; Steefel, C.

    2007-12-01

    The proposed nuclear waste repository of the United States is located at Yucca Mountain, Nevada. Waste packages will be placed in deep (~350 m) underground drifts in volcanic tuff. Seepage may potentially occur at the repository drifts when the drifts get rewetted after a dryout period. The potential seepage water will be quickly evaporated or boiled to near dryness as long as it falls on the top of the hot waste package leading to formation of brine, precipitation of salts and volatilization of gases. These processes may potentially impact the long-term safety of waste packages in the drift. The objectives of this study are to: (1) develop a quantitative model of coupled thermal, hydrological, and chemical (THC) processes potentially leading to brine formation, salt precipitation and gas volatilization on top of waste packages and/or a drip shield and (2) dynamically integrate such a model into the larger-scale models of processes within and around waste emplacement drifts, as well as into the smaller-scale waste-package corrosion models. Process models were implemented into an existing reactive transport numerical simulator, TOUGHREACT, to allow modeling of (1) evaporative concentration to very high ionic strength (up to 40 molal), (2) boiling point elevation due to dissolved salts, (3) boiling/evaporation to dryness, and (4) salt deliquescence. An integrated near-field and in-drift THC simulation was run using a vertical 2-D grid extending from near the ground surface to the groundwater table, and covering a width equal to half the design drift spacing of 81 m. The integrated model was then used to simulate a discrete dripping event within the drift. The model considered the release of radionuclides into seepage water as this water contacts the waste package and flows through the invert. The precipitation of uranophane and Np-uranophane was also considered. These minerals form in the invert from the neutralization of mildly acidic seepage water by clay minerals

  3. Aquarius, a reusable water-based interplanetary human spaceflight transport

    NASA Astrophysics Data System (ADS)

    Adamo, Daniel R.; Logan, James S.

    2016-11-01

    Attributes of a reusable interplanetary human spaceflight transport are proposed and applied to example transits between the Earth/Moon system and Deimos, the outer moon of Mars. Because the transport is 54% water by mass at an interplanetary departure, it is christened Aquarius. In addition to supporting crew hydration/hygiene, water aboard Aquarius serves as propellant and as enhanced crew habitat radiation shielding during interplanetary transit. Key infrastructure and technology supporting Aquarius operations include pre-emplaced consumables and subsurface habitat at Deimos with crew radiation shielding equivalent to sea level on Earth, resupply in a selenocentric distant retrograde orbit, and nuclear thermal propulsion.

  4. NUTRIENT SOUIRCES, TRANSPORT, AND FATE IN COUPLED WATERSHED-ESTUARINE SYSTEMS OF COASTAL ALABAMA

    EPA Science Inventory

    The processes regulating sources, transport, and fate of nutrients were studied in 3 coupled watershed-estuarine systems that varied mainly by differences in the dominant land use-land cover (LULC), i.e. Weeks Bay -- agriculture, Dog River -- urban, and Fowl River -- forest. Mea...

  5. Coupled Factors Influencing Concentration Dependent Colloid Transport and Retention in Saturated Porous Media

    USDA-ARS?s Scientific Manuscript database

    The coupled influence of input suspension concentration (Ci), ionic strength (IS) and hydrodynamics on the transport and retention of 1.1 'm carboxyl modified latex colloids in saturated quartz sand (150 'm) was investigated. Results from batch experiments and interaction energy calculations indica...

  6. Coupled Factors Influencing the Transport and Retention of Cryptosporidium Parvum Oocysts in Saturated Porous Media

    USDA-ARS?s Scientific Manuscript database

    The coupled role of solution ionic strength (IS), system hydrodynamics and pore structure on the transport and retention of viable Cryptosporidium parvum oocyst was investigated via batch, packed-bed column, and micromodel systems. The experiments were conducted over a wide range of IS (0.1-100 mM)...

  7. Second order transport coefficient from the chiral anomaly at weak coupling: Diagrammatic resummation

    NASA Astrophysics Data System (ADS)

    Jimenez-Alba, Amadeo; Yee, Ho-Ung

    2015-07-01

    We compute one of the second order transport coefficients arising from the chiral anomaly in a high-temperature weakly coupled regime of quark-gluon plasma. This transport coefficient is responsible for the C P -odd current that is proportional to the time derivative of the magnetic field, and can be considered as a first correction to the chiral magnetic conductivity at finite, small frequency. We observe that this transport coefficient has a nonanalytic dependence on the coupling as ˜1 /(g4log (1 /g )) at the weak coupling regime, which necessitates a resummation of infinite ladder diagrams with leading pinch singularities to get a correct leading log result, a feature quite similar to what one finds in the computation of electric conductivity. We formulate and solve the relevant C P -odd Schwinger-Dyson equation in real-time perturbation theory that reduces to a coupled set of second order differential equations at leading log order. Our result for this second order transport coefficient indicates that chiral magnetic current has some resistance to the time change of the magnetic field; this shall be called the "chiral induction effect." We also discuss the case of color current induced by a color magnetic field.

  8. NUTRIENT SOUIRCES, TRANSPORT, AND FATE IN COUPLED WATERSHED-ESTUARINE SYSTEMS OF COASTAL ALABAMA

    EPA Science Inventory

    The processes regulating sources, transport, and fate of nutrients were studied in 3 coupled watershed-estuarine systems that varied mainly by differences in the dominant land use-land cover (LULC), i.e. Weeks Bay -- agriculture, Dog River -- urban, and Fowl River -- forest. Mea...

  9. A model of epithelial water transport. The corneal endothelium.

    PubMed Central

    Liebovitch, L S; Weinbaum, S

    1981-01-01

    To try to understand how an epithelial tissue can transport water between bathing solutions of equal tonicity and how intracellular solute and protein concentration are related to the structural specialization of the cell membrane at its apical, basal, and lateral margins, we have formulated and solved, using approximate analytical techniques, a new model which combines the detailed transport of local osmotic flow in extracellular channel with the multicompartment approach of thermodynamic models requiring the overall conservation of water and solute for the entire cell layer. Thus, unlike most previous models, which dealt exclusively with either the average properties of the cell layer or the local transport in the extracellular channel, we are able to solve simultaneously for the interaction of the cell with its environments across its apical, basal, and lateral cell membranes as well as the detailed transport in the extracellular channel. The model is then applied to corneal endothelium to obtain new insight into the water flow movement in this tissue under in vitro and in vivo conditions. Then in vitro solution shows that the cell at 297 mosmol/liter is slightly hypotonic to the 300-mosmol/liter external bathing solutions which drive water equally out both the aqueous (apical) and stromal (basal) cell faces. This water is replaced from the extracellular channel. There is a net flow of water because more water enters the channel through its open stromal end than through the higher resistance tight junction. In vivo, the solution predicts that the stromal swelling pressure forces water through the tight junctions towards the stroma so that there is no net flow. The interesting new features of our solution are the water recirculation pattern and the role of the osmotically active proteins in making the cell hypertonic relative to the channel. PMID:7272441

  10. Water and heat transport in hilly red soil of southern China: II. Modeling and simulation.

    PubMed

    Lu, Jun; Huang, Zhi-Zhen; Han, Xiao-Fei

    2005-05-01

    Simulation models of heat and water transport have not been rigorously tested for the red soils of southern China. Based on the theory of nonisothermal water-heat coupled transfer, a simulation model, programmed in Visual Basic 6.0, was developed to predict the coupled transfer of water and heat in hilly red soil. A series of soil column experiments for soil water and heat transfer, including soil columns with closed and evaporating top end, were used to test the simulation model. Results showed that in the closed columns, the temporal and spatial distribution of moisture and heat could be very well predicted by the model, while in the evaporating columns, the simulated soil water contents were somewhat different from the observed ones. In the heat flow equation from Taylor and Lary (1964), the effects of soil water evaporation on the heat flow is not involved, which may be the main reason for the differences between simulated and observed results. The predicted temperatures were not in agreement with the observed one with thermal conductivities calculated by de Vries and Wierenga equations, so that it is suggested that K(h), soil heat conductivity, be multiplied by 8.0 for the first 6.5 h and by 1.2 later on. Sensitivity analysis of soil water and heat coefficients showed that the saturated hydraulic conductivity, K(S), and the water diffusivity, D(theta), had great effects on soil water transport; the variation of soil porosity led to the difference of soil thermal properties, and accordingly changed temperature redistribution, which would affect water redistribution.

  11. Spatiotemporal Coupling of cAMP Transporter to CFTR Chloride Channel Function in the Gut Epithelia

    PubMed Central

    Li, Chunying; Krishnamurthy, Partha C.; Penmatsa, Himabindu; Marrs, Kevin L.; Wang, Xue Qing; Zaccolo, Manuela; Jalink, Kees; Li, Min; Nelson, Deborah J.; Schuetz, John D.; Naren, Anjaparavanda P.

    2007-01-01

    SUMMARY Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated chloride channel localized at apical cell membranes and exists in macromolecular complexes with a variety of signaling and transporter molecules. Here we report that the multidrug resistance protein 4 (MRP4), a cAMP transporter, is functionally and physically associates with CFTR. Adenosine-stimulated CFTR-mediated chloride currents are potentiated by MRP4 inhibition, and this potentiation is directly coupled to attenuated cAMP efflux through the apical cAMP transporter. CFTR single-channel recordings and FRET-based intracellular cAMP dynamics suggest that a compartmentalized coupling of cAMP transporter and CFTR occurs via the PDZ scaffolding protein, PDZK1, forming a macromolecular complex at apical surfaces of gut epithelia. Disrupting this complex abrogates the functional coupling of cAMP transporter activity to CFTR function. MRP4 knockout mice are more prone to CFTR-mediated secretory diarrhea. Our findings have important implications for disorders such as inflammatory bowel disease and secretory diarrhea. PMID:18045536

  12. Spatiotemporal coupling of cAMP transporter to CFTR chloride channel function in the gut epithelia.

    PubMed

    Li, Chunying; Krishnamurthy, Partha C; Penmatsa, Himabindu; Marrs, Kevin L; Wang, Xue Qing; Zaccolo, Manuela; Jalink, Kees; Li, Min; Nelson, Deborah J; Schuetz, John D; Naren, Anjaparavanda P

    2007-11-30

    Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated chloride channel localized at apical cell membranes and exists in macromolecular complexes with a variety of signaling and transporter molecules. Here, we report that the multidrug resistance protein 4 (MRP4), a cAMP transporter, functionally and physically associates with CFTR. Adenosine-stimulated CFTR-mediated chloride currents are potentiated by MRP4 inhibition, and this potentiation is directly coupled to attenuated cAMP efflux through the apical cAMP transporter. CFTR single-channel recordings and FRET-based intracellular cAMP dynamics suggest that a compartmentalized coupling of cAMP transporter and CFTR occurs via the PDZ scaffolding protein, PDZK1, forming a macromolecular complex at apical surfaces of gut epithelia. Disrupting this complex abrogates the functional coupling of cAMP transporter activity to CFTR function. Mrp4 knockout mice are more prone to CFTR-mediated secretory diarrhea. Our findings have important implications for disorders such as inflammatory bowel disease and secretory diarrhea.

  13. Coupling Substrate and Ion Binding to Extracellular Gate of a Sodium-Dependent Aspartate Transporter

    SciTech Connect

    Boudker,O.; Ryan, R.; Yernool, D.; Shimamoto, K.; Gouaux, E.

    2007-01-01

    Secondary transporters are integral membrane proteins that catalyze the movement of substrate molecules across the lipid bilayer by coupling substrate transport to one or more ion gradients, thereby providing a mechanism for the concentrative uptake of substrates. Here we describe crystallographic and thermodynamic studies of Glt{sub Ph}, a sodium (Na{sup +})-coupled aspartate transporter, defining sites for aspartate, two sodium ions and D,L-threo-{beta}-benzyloxyaspartate, an inhibitor. We further show that helical hairpin 2 is the extracellular gate that controls access of substrate and ions to the internal binding sites. At least two sodium ions bind in close proximity to the substrate and these sodium-binding sites, together with the sodium-binding sites in another sodium-coupled transporter, LeuT, define an unwound {alpha}-helix as the central element of the ion-binding motif, a motif well suited to the binding of sodium and to participation in conformational changes that accompany ion binding and unbinding during the transport cycle.

  14. Transport and sorption of volatile organic compounds and water vapor in porous media

    SciTech Connect

    Lin, Tsair-Fuh

    1995-07-01

    To gain insight on the controlling mechanisms for VOC transport in porous media, the relations among sorbent properties, sorption equilibrium and intraparticle diffusion processes were studied at the level of individual sorbent particles and laboratory columns for soil and activated carbon systems. Transport and sorption of VOCs and water vapor were first elucidated within individual dry soil mineral grains. Soil properties, sorption capacity, and sorption rates were measured for 3 test soils; results suggest that the soil grains are porous, while the sorption isotherms are nonlinear and adsorption-desorption rates are slow and asymmetric. An intragranular pore diffusion model coupled with the nonlinear Freundlich isotherm was developed to describe the sorption kinetic curves. Transport of benzene and water vapor within peat was studied; partitioning and sorption kinetics were determined with an electrobalance. A dual diffusion model was developed. Transport of benzene in dry and moist soil columns was studied, followed by gaseous transport and sorption in activated carbon. The pore diffusion model provides good fits to sorption kinetics for VOCs to soil and VOC to granular activated carbon and activated carbon fibers. Results of this research indicate that: Intraparticle diffusion along with a nonlinea sorption isotherm are responsible for the slow, asymmetric sorption-desorption. Diffusion models are able to describe results for soil and activated carbon systems; when combined with mass transfer equations, they predict column breakthrough curves for several systems. Although the conditions are simplified, the mechanisms should provide insight on complex systems involving transport and sorption of vapors in porous media.

  15. Subunit composition of an energy-coupling-factor-type biotin transporter analysed in living bacteria.

    PubMed

    Finkenwirth, Friedrich; Neubauer, Olivia; Gunzenhäuser, Julia; Schoknecht, Janna; Scolari, Silvia; Stöckl, Martin; Korte, Thomas; Herrmann, Andreas; Eitinger, Thomas

    2010-11-01

    BioMNY, a bacterial high-affinity biotin transporter, is a member of the recently defined class of ECF (energy-coupling factor) transporters. These systems are composed of ABC (ATP-binding-cassette) ATPases (represented by BioM in the case of the biotin transporter), a universally conserved transmembrane protein (BioN) and a core transporter component (BioY), in unknown stoichiometry. The quaternary structure of BioY, which functions as a low-affinity biotin transporter in the absence of BioMN, and of BioMNY was investigated by a FRET (Förster resonance energy transfer) approach using living recombinant Escherichia coli cells. To this end, the donor-acceptor pair, of Cerulean and yellow fluorescent protein respectively, were fused to BioM, BioN and BioY. The fusion proteins were stable and the protein tags did not interfere with transport and ATPase activities. Specific donor-acceptor interactions were characterized by lifetime-based FRET spectroscopy. The results suggest an oligomeric structure for the solitary BioY core transporter and oligomeric forms of BioM and BioY in BioMNY complexes. We surmise that oligomers of BioY are the functional units of the low- and high-affinity biotin transporter in the living cell. Beyond its relevance for clarifying the supramolecular organization of ECF transporters, the results demonstrate the general applicability of lifetime-based FRET studies in living bacteria.

  16. Correlation-driven transport asymmetries through coupled spins in a tunnel junction

    PubMed Central

    Muenks, Matthias; Jacobson, Peter; Ternes, Markus; Kern, Klaus

    2017-01-01

    Spin–spin correlations can be the driving force that favours certain ground states and are key in numerous models that describe the behaviour of strongly correlated materials. While the sum of collective correlations usually lead to a macroscopically measurable change in properties, a direct quantification of correlations in atomic scale systems is difficult. Here we determine the correlations between a strongly hybridized spin impurity on the tip of a scanning tunnelling microscope and its electron bath by varying the coupling to a second spin impurity weakly hybridized to the sample surface. Electronic transport through these coupled spins reveals an asymmetry in the differential conductance reminiscent of spin-polarized transport in a magnetic field. We show that at zero field, this asymmetry can be controlled by the coupling strength and is related to either ferromagnetic or antiferromagnetic spin–spin correlations in the tip. PMID:28074832

  17. Analysis of coupling between high-speed railway and common speed railway system in transportation corridor

    NASA Astrophysics Data System (ADS)

    Zhou, Hongchang; Li, Haijun; Chen, Xiaohong; Zhu, Changfeng

    2017-04-01

    The high-speed railway and common speed railway subsystems as important components of the railway transportation system, can make railway traffic organization more orderly, when there are a rational division and balance development between them. In order to quantitatively evaluate the coordinate relations between high-speed railway subsystem and common speed railway subsystem, this paper takes the railway transportation corridor from Baoji to Lanzhou as an example. Firstly, using Logit model and grey forecasting model predict the passenger volume, passenger turnover and time value of high-speed railway and common speed railway in the Baoji-Lanzhou corridor. And then, the coupling forecast model of these two subsystems is established. Lastly, the coupling and coupling coordination of these two subsystems using are predicted and analyzed at theatrically level.

  18. Correlation-driven transport asymmetries through coupled spins in a tunnel junction

    NASA Astrophysics Data System (ADS)

    Muenks, Matthias; Jacobson, Peter; Ternes, Markus; Kern, Klaus

    2017-01-01

    Spin-spin correlations can be the driving force that favours certain ground states and are key in numerous models that describe the behaviour of strongly correlated materials. While the sum of collective correlations usually lead to a macroscopically measurable change in properties, a direct quantification of correlations in atomic scale systems is difficult. Here we determine the correlations between a strongly hybridized spin impurity on the tip of a scanning tunnelling microscope and its electron bath by varying the coupling to a second spin impurity weakly hybridized to the sample surface. Electronic transport through these coupled spins reveals an asymmetry in the differential conductance reminiscent of spin-polarized transport in a magnetic field. We show that at zero field, this asymmetry can be controlled by the coupling strength and is related to either ferromagnetic or antiferromagnetic spin-spin correlations in the tip.

  19. Well-to-Wheels Water Consumption: Tracking the Virtual Flow of Water into Transportation

    NASA Astrophysics Data System (ADS)

    Lampert, D. J.; Elgowainy, A.; Hao, C.

    2015-12-01

    Water and energy resources are fundamental to life on Earth and essential for the production of consumer goods and services in the economy. Energy and water resources are heavily interdependent—energy production consumes water, while water treatment and distribution consume energy. One example of this so-called energy-water nexus is the consumption of water associated with the production of transportation fuels. The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model is an analytical tool that can be used to compare the environmental impacts of different transportation fuels on a consistent basis. In this presentation, the expansion of GREET to perform life cycle water accounting or the "virtual flow" of water into transportation and other energy sectors and the associated implications will be discussed. The results indicate that increased usage of alternative fuels may increase freshwater resource consumption. The increased water consumption must be weighed against the benefits of decreased greenhouse gas and fossil energy consumption. Our analysis highlights the importance of regionality, co-product allocation, and consistent system boundaries when comparing the water intensity of alternative transportation fuel production pathways such as ethanol, biodiesel, compressed natural gas, hydrogen, and electricity with conventional petroleum-based fuels such as diesel and gasoline.

  20. Concerted orientation induced unidirectional water transport through nanochannels.

    PubMed

    Wan, Rongzheng; Lu, Hangjun; Li, Jinyuan; Bao, Jingdong; Hu, Jun; Fang, Haiping

    2009-11-14

    The dynamics of water inside nanochannels is of great importance for biological activities as well as for the design of molecular sensors, devices, and machines, particularly for sea water desalination. When confined in specially sized nanochannels, water molecules form a single-file structure with concerted dipole orientations, which collectively flip between the directions along and against the nanotube axis. In this paper, by using molecular dynamics simulations, we observed a net flux along the dipole-orientation without any application of an external electric field or external pressure difference during the time period of the particular concerted dipole orientations of the molecules along or against the nanotube axis. We found that this unique special-directional water transportation resulted from the asymmetric potential of water-water interaction along the nanochannel, which originated from the concerted dipole orientation of the water molecules that breaks the symmetry of water orientation distribution along the channel within a finite time period. This finding suggests a new mechanism for achieving high-flux water transportation, which may be useful for nanotechnology and biological applications.

  1. Water transport within carbon nanotubes on a wave.

    PubMed

    Li, Jin-Yi; Wu, Zeng-Qiang; Xu, Jing-Juan; Chen, Hong-Yuan; Xia, Xing-Hua

    2016-12-07

    Water molecules possess discontinuous properties in confined surroundings as compared to the bulk, their transport velocity shows a step change with the increase in the radius of hydrophobic carbon nanotubes (CNTs). Here, we report that the chain of water molecules in CNTs behaves as a "spring" owing to hydrogen bonding. Thus, the transport of water molecules in confined systems proceeds as a wave motion with eigen frequencies in the terahertz region which is determined by the CNT size. Water velocities derived from molecular dynamics (MD) fit well with the ones from finite element methods (FEM) on consideration of both the no-slip and slip boundary conditions for CNT diameters less than 1 nm and more than 1 nm, respectively. The present work helps clarify the features of mass and momentum transfers in confined surroundings, and provides perspectives for mass transfer applications.

  2. Water and Molecular Transport across Nanopores in Monolayer Graphene Membranes

    NASA Astrophysics Data System (ADS)

    Jang, Doojoon; O'Hern, Sean; Kidambi, Piran; Boutilier, Michael; Song, Yi; Idrobo, Juan-Carlos; Kong, Jing; Laoui, Tahar; Karnik, Rohit

    2015-11-01

    Graphene's atomic thickness and high tensile strength allow it to outstand as backbone material for next-generation high flux separation membrane. Molecular dynamics simulations predicted that a single-layer graphene membrane could exhibit high permeability and selectivity for water over ions/molecules, qualifying as novel water desalination membranes. However, experimental investigation of water and molecular transport across graphene nanopores had remained barely explored due to the presence of intrinsic defects and tears in graphene. We introduce two-step methods to seal leakage across centimeter scale single-layer graphene membranes create sub-nanometer pores using ion irradiation and oxidative etching. Pore creation parameters were varied to explore the effects of created pore structures on water and molecular transport driven by forward osmosis. The results demonstrate the potential of nanoporous graphene as a reliable platform for high flux nanofiltration membranes.

  3. Role of water states on water uptake and proton transport in Nafion using molecular simulations and bimodal network

    SciTech Connect

    Hwang, Gi Suk; Kaviany, Massoud; Gostick, Jeffrey T.; Kientiz, Brian; Weber, Adam Z.; Kim, Moo Hwan

    2011-04-07

    In this paper, using molecular simulations and a bimodal-domain network, the role of water state on Nafion water uptake and water and proton transport is investigated. Although the smaller domains provide moderate transport pathways, their effectiveness remains low due to strong, resistive water molecules/domain surface interactions. Finally, the water occupancy of the larger domains yields bulk-like water, and causes the observed transition in the water uptake and significant increases in transport properties.

  4. Heat and water transport in a polymer electrolyte fuel cell electrode

    SciTech Connect

    Mukherjee, Partha P; Mukundan, Rangachary; Borup, Rod L; Ranjan, Devesh

    2010-01-01

    In the present scenario of a global initiative toward a sustainable energy future, the polymer electrolyte fuel cell (PEFC) has emerged as one of the most promising alternative energy conversion devices for various applications. Despite tremendous progress in recent years, a pivotal performance limitation in the PEFC comes from liquid water transport and the resulting flooding phenomena. Liquid water blocks the open pore space in the electrode and the fibrous diffusion layer leading to hindered oxygen transport. The electrode is also the only component in the entire PEFC sandwich which produces waste heat from the electrochemical reaction. The cathode electrode, being the host to several competing transport mechanisms, plays a crucial role in the overall PEFC performance limitation. In this work, an electrode model is presented in order to elucidate the coupled heat and water transport mechanisms. Two scenarios are specifically considered: (1) conventional, Nafion{reg_sign} impregnated, three-phase electrode with the hydrated polymeric membrane phase as the conveyer of protons where local electro-neutrality prevails; and (2) ultra-thin, two-phase, nano-structured electrode without the presence of ionomeric phase where charge accumulation due to electro-statics in the vicinity of the membrane-CL interface becomes important. The electrode model includes a physical description of heat and water balance along with electrochemical performance analysis in order to study the influence of electro-statics/electro-migration and phase change on the PEFC electrode performance.

  5. Explicit and implicit coupling during solute transport through clay membrane barriers

    NASA Astrophysics Data System (ADS)

    Malusis, Michael A.; Shackelford, Charles D.

    2004-08-01

    Simulations of salt (KCl) flux through a 1-m-thick clay membrane barrier (CMB) based on coupled solute transport theory are compared to simulated fluxes based on traditional advective-dispersive transport theory. The simulations are based on measured values for the effective salt-diffusion coefficient ( Ds*) and chemico-osmotic efficiency coefficient ( ω) for a bentonite-based barrier material subjected to KCl solutions. The results indicate that the exit salt flux is reduced due to both explicit coupling (hyperfiltration and chemico-osmotic counter-advection) and an implicit coupling effect resulting from the decrease in Ds* due to a decrease in the apparent tortuosity factor, τa, with an increase in ω. Implicit coupling is shown to be more significant than explicit coupling for reducing and retarding salt flux through a CMB under diffusion-dominated conditions. Failure to account for the implicit coupling effect may result in unrealistic results, such as the existence of salt flux through a perfect (ideal) clay membrane (i.e., ω=1).

  6. A Coupled Multiphase Fluid Flow And Heat And Vapor Transport Model For Air-Gap Membrane Distillation

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Sumit

    2010-05-01

    Membrane distillation (MD) is emerging as a viable desalination technology because of its low energy requirements that can be provided from low-grade, waste heat and because it causes less fouling. In MD, desalination is accomplished by transporting water vapour through a porous hydrophobic membrane. The vapour transport process is governed by the vapour pressure difference between the two sides of a membrane. A variety of configurations have been tested to impose this vapour pressure gradient, however, the air-gap membrane distillation (AGMD) has been found to be the most efficient. The separation mechanism of AGMD and its overall efficiency is based on vapour-liquid equilibrium (VLE). At present, little knowledge is available about the optimal design of such a transmembrane VLE-based evaporation, and subsequent condensation processes. While design parameters for MD have evolved mostly through experimentations, a comprehensive mathematical model is yet to be developed. This is primarily because the coupling and non-linearity of the equations, the interactions between the flow, heat and mass transport regimes, and the complex geometries involved pose a challenging modelling and simulation problem. Yet a comprehensive mathematical model is needed for systematic evaluation of the processes, design parameterization, and performance prediction. This paper thus presents a coupled fluid flow, heat and mass transfer model to investigate the main processes and parameters affecting the performance of an AGMD.

  7. Coupled effects of solution chemistry and hydrodynamics on the mobility and transport of quantum dot nanomaterials in the vadose zone

    NASA Astrophysics Data System (ADS)

    Uyusur, Burcu; Darnault, Christophe J. G.; Snee, Preston T.; Kokën, Emre; Jacobson, Astrid R.; Wells, Robert R.

    2010-11-01

    To investigate the coupled effects of solution chemistry and hydrodynamics on the mobility of quantum dot (QD) nanoparticles in the vadose zone, laboratory scale transport experiments involving single and/or sequential infiltrations of QDs in unsaturated and saturated porous media, and computations of total interaction and capillary potential energies were performed. As ionic strength increased, QD retention in the unsaturated porous media increased; however, this retention was significantly suppressed in the presence of a non-ionic surfactant in the infiltration suspensions as indicated by surfactant enhanced transport of QDs. In the vadose zone, the non-ionic surfactant limited the formation of QD aggregates, enhanced QD mobility and transport, and lowered the solution surface tension, which resulted in a decrease in capillary forces that not only led to a reduction in the removal of QDs, but also impacted the vadose zone flow processes. When chemical transport conditions were favorable (ionic strength of 5 × 10 -4 M and 5 × 10 -3 M, or ionic strengths of 5 × 10 -2 M and 0.5 M with surfactant), the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were meso-scale processes, where infiltration by preferential flow results in the rapid transport of QDs. When chemical transport conditions were unfavorable (ionic strength of 5 × 10 -2 M and 0.5 M) the dominating phenomena controlling the mobility and transport of QDs in the vadose zone were pore-scale processes governed by gas-water interfaces (GWI) that impact the mobility of QDs. The addition of surfactant enhanced the transport of QDs both in favorable and unfavorable chemical transport conditions. The mobility and retention of QDs was controlled by interaction and capillary forces, with the latter being the most influential. GWI were found to be the dominant mechanism and site for QD removal compared with solid-water interfaces (SWI) and pore straining. Additionally

  8. CFD Model of Water Droplet Transport for ISS Hygiene Activity

    NASA Technical Reports Server (NTRS)

    Son, Chang H.

    2011-01-01

    The goal of the study is to assess the impacts of free water propagation in the Waste and Hygiene Compartment (WHC). Free water can be generated inside the WHC in small quantities due to crew hygiene activity. To mitigate potential impact of free water in Node 3 cabin the WHC doorway is enclosed by a waterproof bump-out, Kabin, with openings at the top and bottom. At the overhead side of the rack, there is a screen that prevents large drops of water from exiting. However, as the avionics fan in the WHC causes airflow toward the deck side of the rack, small quantities of free water may exit at the bottom of the Kabin. A Computational Fluid Dynamics (CFD) analysis of Node 3 cabin airflow made possible to identify the paths of water transport. The Node 3 airflow was computed for several ventilation scenarios. To simulate the droplet transport the Lagrangian discrete phase approach was used. Various initial droplet distributions were considered in the study. The droplet diameter was varied in the range of 2-20 mm. The results of the computations showed that most of the drops fall to the rack surface not far from the WHC curtain. The probability of the droplet transport to the adjacent rack surface with electronic equipment was predicted.

  9. Eolian transport of geogenic hexavalent chromium to ground water

    USGS Publications Warehouse

    Wood, W.W.; Clark, D.; Imes, J.L.; Councell, T.B.

    2010-01-01

    A conceptual model of eolian transport is proposed to address the widely distributed, high concentrations of hexavalent chromium (Cr+6) observed in ground water in the Emirate of Abu Dhabi, United Arab Emirates. Concentrations (30 to more than 1000 μg/L Cr+6) extend over thousands of square kilometers of ground water systems. It is hypothesized that the Cr is derived from weathering of chromium-rich pyroxenes and olivines present in ophiolite sequence of the adjacent Oman (Hajar) Mountains. Cr+3 in the minerals is oxidized to Cr+6 by reduction of manganese and is subsequently sorbed on iron and manganese oxide coatings of particles. When the surfaces of these particles are abraded in this arid environment, they release fine, micrometer-sized, coated particles that are easily transported over large distances by wind and subsequently deposited on the surface. During ground water recharge events, the readily soluble Cr+6 is mobilized by rain water and transported by advective flow into the underlying aquifer. Chromium analyses of ground water, rain, dust, and surface (soil) deposits are consistent with this model, as are electron probe analyses of clasts derived from the eroding Oman ophiolite sequence. Ground water recharge flux is proposed to exercise some control over Cr+6 concentration in the aquifer.

  10. An Isotopic view of water and nitrogen transport through the ...

    EPA Pesticide Factsheets

    Groundwater nitrate contamination affects thousands of households in Oregon’s southern Willamette Valley and many more across the Pacific Northwest. The southern Willamette Valley Groundwater Management Area (SWV GWMA) was established in 2004 due to nitrate levels in the groundwater exceeding the human health standard of 10 mg nitrate-N L-1. Much of the nitrogen inputs to the GWMA comes from agricultural nitrogen use, and thus efforts to reduce N inputs to groundwater are focused upon improving N management. However, the effectiveness of these improvements on groundwater quality is unclear because of the complexity of nutrient transport through the vadose zone and long groundwater residence times. Our objective was to focus on vadose zone transport and understand the dynamics and timing of N and water movement below the rooting zone in relation to N management and water inputs. Stable isotopes are a powerful tool for tracking water movement, and understanding nitrogen transformations within the vadose zone. In partnership with local farmers, and state agencies, we established lysimeters and groundwater wells in multiple agricultural fields in the GWMA, and have monitored nitrate, nitrate isotopes, and water isotopes weekly for multiple years. Our results indicate that vadose zone transport is highly complex, and the residence time of water collected in lysimeters was much longer than expected. While input precipitation water isotopes were highly variab

  11. The importance of coupled modelling of variably saturated groundwater flow-heat transport for assessing river-aquifer interactions

    NASA Astrophysics Data System (ADS)

    Engeler, I.; Hendricks Franssen, H. J.; Müller, R.; Stauffer, F.

    2011-02-01

    SummaryThis paper focuses on the role of heat transport in river-aquifer interactions for the study area Hardhof located in the Limmat valley within the city of Zurich (Switzerland). On site there are drinking water production facilities of Zurich water supply, which pump groundwater and infiltrate bank filtration water from river Limmat. The artificial recharge by basins and by wells creates a hydraulic barrier against the potentially contaminated groundwater flow from the city. A three-dimensional finite element model of the coupled variably saturated groundwater flow and heat transport was developed. The hydraulic conductivity of the aquifer and the leakage coefficient of the riverbed were calibrated for isothermal conditions by inverse modelling, using the pilot point method. River-aquifer interaction was modelled using a leakage concept. Coupling was considered by temperature-dependent values for hydraulic conductivity and for leakage coefficients. The quality of the coupled model was tested with the help of head and temperature measurements. Good correspondence between simulated and measured temperatures was found for the three pumping wells and seven piezometers. However, deviations were observed for one pumping well and two piezometers, which are situated in an area, where zones with important hydrogeological heterogeneity are expected. A comparison of simulation results with isothermal leakage coefficients with those of temperature-dependent leakage coefficients shows that the temperature dependence is able to reduce the head residuals close to the river by up to 30%. The largest improvements are found in the zone, where the river stage is considerably higher than the groundwater level, which is in correspondence with the expectations. Additional analyses also showed that the linear leakage concept cannot reproduce the seepage flux in a downstream section during flood events. It was found that infiltration is enhanced during flood events, which is

  12. Proton-coupled oligopeptide transporter (POT) family expression in human nasal epithelium and their drug transport potential.

    PubMed

    Agu, Remigius; Cowley, Elizabeth; Shao, Di; Macdonald, Christopher; Kirkpatrick, David; Renton, Ken; Massoud, Emad

    2011-06-06

    The molecular and functional expression of peptide transporters (PEPT1 and PEPT2, PHT1, PHT2) in human nasal epithelium was investigated. Quantitative/reverse transcriptase polymerase chain reaction (qPCR/RT-PCR), Western blotting and indirect immuno-histochemistry were used to investigate the functional gene and protein expression for the transporters. Uptake and transport studies were performed using metabolically stable peptides [β-alanyl-L-lysyl-Nε-7-amino-4-methyl-coumarin-3-acetic acid (β-Ala-Lys-AMCA) and β-alanyl-L-histidine (carnosine)]. The effects of concentration, temperature, polarity, competing peptides, and inhibitors on peptide uptake and transport were investigated. PCR products corresponding to PEPT1 (150 bp), PEPT2 (127 bp), PHT1 (110 bp) and PHT2 (198 bp) were detected. Immunohistochemistry and Western blotting confirmed the functional expression of PEPT1 and PEPT2 genes. The uptake of β-Ala-Lys-AMCA was concentration-dependent and saturable (Vmax =4.1 ( 0.07 μmol/min/mg protein, Km = 0.6 ( 0.07 μM). The optimal pH for intracellular accumulation of β-Ala-Lys-AMCA was 6.5. Whereas dipeptides and carbonyl cyanide m-chlorophenylhydrazone (CCCP) significantly inhibited peptide uptake and transport, L-Phe had no effect on peptide transport. The permeation of β-alanyl-L-histidine was concentration-, direction-, and temperature-dependent. The uptake, permeation, qPCR/RT-PCR and protein expression data showed that the human nasal epithelium functionally expresses proton-coupled oligopeptide transporters.

  13. Coupled atmospheric, land surface, and subsurface modeling: Exploring water and energy feedbacks in three-dimensions

    NASA Astrophysics Data System (ADS)

    Davison, Jason H.; Hwang, Hyoun-Tae; Sudicky, Edward A.; Lin, John C.

    2015-12-01

    Human activities amplified by climate change pose a significant threat to the sustainability of water resources. Coupled climate-hydrologic simulations commonly predict these threats by combining shallow 1-D land surface models (LSMs) with traditional 2-D and 3-D hydrology models. However, these coupled models limit the moisture and energy-feedback dynamics to the shallow near-surface. This paper presents a novel analysis by applying an integrated variably-saturated subsurface/surface hydrology and heat transport model, HydroGeoSphere (HGS), as a land surface model (LSM). Furthermore, this article demonstrates the coupling of HGS to a simple 0-D atmospheric boundary layer (ABL) model. We then applied our coupled HGS-ABL model to three separate test cases and reproduced the strong correlation between the atmospheric energy balance to the depth of the groundwater table. From our simulations, we found that conventional LSMs may overestimate surface temperatures for extended drought periods because they underestimate the heat storage in the groundwater zone. Our final test case of the atmospheric response to drought conditions illustrated that deeper roots buffered the atmosphere better than shallow roots by maintaining higher latent heat fluxes, lower sensible heat fluxes, and lower surface and atmospheric temperatures.

  14. Molecular transport through surfactant-covered oil-water interfaces: role of physical properties of solutes and surfactants in creating energy barriers for transport.

    PubMed

    Ahn, Yong Nam; Gupta, Ashish; Chauhan, Anuj; Kopelevich, Dmitry I

    2011-03-15

    Mechanisms of molecular transport across oil-water interfaces covered by nonionic surfactants are investigated using coarse-grained molecular dynamics simulations. Resistance of the surfactant monolayer to the solute transport is shown to be controlled by dense regions in the monolayer. The dense regions are formed on both sides of the dividing surface and the barrier to the solute transport is created by those of them experiencing unfavorable interactions with the solute. Resistance to the transport of a hydrophobic (hydrophilic) solute increases with the excess density of the head (tail) group region of the monolayer, which in turn increases with the length of the surfactant head (tail) group. Barriers for solute transport through surfactant monolayers are also influenced by the solute size. However, the extent of this influence is determined by the monolayer thickness and the solute structure and composition. For example, it is shown that resistance offered by thin monolayers to transport of linear oligomers is relatively insensitive to the solute length. The barrier sensitivity to the length of these solutes increases with the monolayer thickness. In addition to the static barriers, the solute transport is shown to be affected by dynamic barriers due to a nonadiabatic coupling of the monolayer surface with the solute position and configuration. This coupling leads to deviations of the system dynamics from the minimum energy path. The deviations are most significant in the neighborhood of the static energy barrier, which effectively leads to an increase of the barrier for the solute transport.

  15. Coupled electrochemical and heat/mass transport characteristics in passive direct methanol fuel cells

    NASA Astrophysics Data System (ADS)

    Chen, Rong

    indicated that the thermal management is a key factor for improving the performance of the passive DMFC. To enhance oxygen transport on the air-breathing cathode and to reduce the heat loss from the cathode, a porous current collector for the passive DMFC was proposed to replace conventional perforated-plate current collectors. Because of its high specific area of transport and effectiveness in removing the liquid water as a result of the capillary action in the porous structure, the porous current collector enables a significant enhancement of oxygen supply to the fuel cell. In addition, because of the lower effective thermal conductivity of the porous structure, the heat loss from the fuel cell to ambient air can be reduced. The experimental results showed that the passive DMFC having the porous current collector yielded much higher and much more stable performance than did the cell having the conventional perforated-plate current collector with high methanol concentration operation. As a following up to oxygen transport enhancement, a new design of membrane electrode assembly (MEA) was proposed, in which the conventional cathode gas diffusion layer (CGDL) is eliminated while utilizing a porous metal structure for transporting oxygen and collecting current. We show theoretically that the new MEA enables a higher mass transfer rate of oxygen and thus better performance. Moreover, the measured polarization and constant-current discharging behavior showed that the passive DMFC with the new MEA yielded higher and much more stable performance than did the cell having the conventional MEA. Besides the experimental investigations, to further theoretically study the thermal effect on the cell performance, a one-dimension single-phase model is developed by considering inherently coupled heat and mass transport along with the electrochemical reactions occurring in passive DMFCs. The analytical solutions predicting the performance of this type of fuel cell operating with different

  16. Water Transport in Trees--An Artificial Laboratory Tree

    ERIC Educational Resources Information Center

    Susman, K.; Razpet, N.; Cepic, M.

    2011-01-01

    Water transport in tall trees is an everyday phenomenon, seldom noticed and not completely understood even by scientists. As a topic of current research in plant physiology it has several advantages for presentation within school physics lectures: it is interdisciplinary and clearly shows the connection between physics and biology; the…

  17. Pupils' Response to a Model for Water Transport.

    ERIC Educational Resources Information Center

    Johnstone, A. H.; Mahmoud, N. A.

    1981-01-01

    Described is a model, based on the physical sciences, designed to teach secondary students about water transport through the use of an animated film. Pupils (N=440) taught by this method developed a self-consistent, although reduced, picture and understanding of osmosis. (Author/DC)

  18. Pupils' Response to a Model for Water Transport.

    ERIC Educational Resources Information Center

    Johnstone, A. H.; Mahmoud, N. A.

    1981-01-01

    Described is a model, based on the physical sciences, designed to teach secondary students about water transport through the use of an animated film. Pupils (N=440) taught by this method developed a self-consistent, although reduced, picture and understanding of osmosis. (Author/DC)

  19. Classroom Techniques to Illustrate Water Transport in Plants

    ERIC Educational Resources Information Center

    Lakrim, Mohamed

    2013-01-01

    The transport of water in plants is among the most difficult and challenging concepts to explain to students. It is even more difficult for students enrolled in an introductory general biology course. An easy approach is needed to demonstrate this complex concept. I describe visual and pedagogical examples that can be performed quickly and easily…

  20. Water Transport in Trees--An Artificial Laboratory Tree

    ERIC Educational Resources Information Center

    Susman, K.; Razpet, N.; Cepic, M.

    2011-01-01

    Water transport in tall trees is an everyday phenomenon, seldom noticed and not completely understood even by scientists. As a topic of current research in plant physiology it has several advantages for presentation within school physics lectures: it is interdisciplinary and clearly shows the connection between physics and biology; the…

  1. Classroom Techniques to Illustrate Water Transport in Plants

    ERIC Educational Resources Information Center

    Lakrim, Mohamed

    2013-01-01

    The transport of water in plants is among the most difficult and challenging concepts to explain to students. It is even more difficult for students enrolled in an introductory general biology course. An easy approach is needed to demonstrate this complex concept. I describe visual and pedagogical examples that can be performed quickly and easily…

  2. Sediment Transport at Density Fronts in Shallow Water

    DTIC Science & Technology

    2012-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Sediment Transport at Density Fronts in Shallow Water...tidal inundation cycle as it travels across the intertidal zone, and - combine the observations and model results to (1) quantify sediment suspension...S) 12. DISTRIBUTION /AVAILABILITY STATEMENT Approved for public release, distribution unlimited 13. SUPPLEMENTARY NOTES The original document

  3. Sodium-coupled and electrogenic transport of B-complex vitamin nicotinic acid by slc5a8, a member of the Na/glucose co-transporter gene family

    PubMed Central

    Gopal, Elangovan; Fei, You-Jun; Miyauchi, Seiji; Zhuang, Lina; Prasad, Puttur D.; Ganapathy, Vadivel

    2005-01-01

    SMCT (sodium-coupled monocarboxylate transporter; slc5a8) is a Na+-coupled transporter for lactate, pyruvate and short-chain fatty acids. Similar to these already known substrates of SMCT, the water-soluble B-complex vitamin nicotinic acid also exists as a monocarboxylate anion (nicotinate) under physiological conditions. Therefore we evaluated the ability of SMCT to mediate the uptake of nicotinate. In mammalian cells, the cloned mouse SMCT (slc5a8) induced the uptake of nicotinate. The SMCT-induced uptake was Na+-dependent. The Michaelis constant for the uptake process was 296±88 μM. The Na+-activation kinetics indicated that at least two Na+ ions are involved in the process. Among the various structural analogues tested, nicotinate was the most effective substrate. Nicotinamide and methylnicotinate were not recognized by the transporter. 2-Pyrazine carboxylate and isonicotinate interacted with the transporter to a moderate extent. SMCT-mediated uptake of nicotinate was inhibited by lactate and pyruvate. In the Xenopus laevis oocyte expression system, SMCT-mediated nicotinate transport was electrogenic, as evident from the nicotinate-induced inward currents under voltage-clamp conditions. Substrate-induced currents in this expression system corroborated the substrate specificity determined in the mammalian cell expression system. The kinetic parameters with regard to the affinity of the transporter for nicotinate and the Hill coefficient for Na+ activation, determined by using the oocyte expression system, were also similar to those obtained from the mammalian cell expression system. We conclude that SMCT functions not only as a Na+-coupled transporter for short-chain fatty acids and lactate but also as a Na+-coupled transporter for the water-soluble vitamin nicotinic acid. PMID:15651982

  4. Structural insight in the toppling mechanism of an energy-coupling factor transporter

    PubMed Central

    Swier, Lotteke J. Y. M.; Guskov, Albert; Slotboom, Dirk J.

    2016-01-01

    Energy-coupling factor (ECF) transporters mediate uptake of micronutrients in prokaryotes. The transporters consist of an S-component that binds the transported substrate and an ECF module (EcfAA′T) that binds and hydrolyses ATP. The mechanism of transport is poorly understood but presumably involves an unusual step in which the membrane-embedded S-component topples over to carry the substrate across the membrane. In many ECF transporters, the S-component dissociates from the ECF module after transport. Subsequently, substrate-bound S-components out-compete the empty proteins for re-binding to the ECF module in a new round of transport. Here we present crystal structures of the folate-specific transporter ECF–FolT from Lactobacillus delbrueckii. Interaction of the ECF module with FolT stabilizes the toppled state, and simultaneously destroys the high-affinity folate-binding site, allowing substrate release into the cytosol. We hypothesize that differences in the kinetics of toppling can explain how substrate-loaded FolT out-competes apo-FolT for association with the ECF module. PMID:27026363

  5. Quantum transport through a Coulomb blockaded quantum emitter coupled to a plasmonic dimer.

    PubMed

    Goker, A; Aksu, H

    2016-01-21

    We study the electron transmission through a Coulomb blockaded quantum emitter coupled to metal nanoparticles possessing plasmon resonances by employing the time-dependent non-crossing approximation. We find that the coupling of the nanoparticle plasmons with the excitons results in a significant enhancement of the conductance through the discrete state with higher energy beyond the unitarity limit while the other discrete state with lower energy remains Coulomb blockaded. We show that boosting the plasmon-exciton coupling well below the Kondo temperature increases the enhancement adding another quantum of counductance upon saturation. Finite bias and increasing emitter resonance energy tend to reduce this enhancement. We attribute these observations to the opening of an additional transport channel via the plasmon-exciton coupling.

  6. Transport through an impurity tunnel coupled to a Si/SiGe quantum dot

    SciTech Connect

    Foote, Ryan H. Ward, Daniel R.; Thorgrimsson, Brandur; Savage, D. E.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.; Prance, J. R.; Gamble, John King; Nielsen, Erik; Saraiva, A. L.

    2015-09-07

    Achieving controllable coupling of dopants in silicon is crucial for operating donor-based qubit devices, but it is difficult because of the small size of donor-bound electron wavefunctions. Here, we report the characterization of a quantum dot coupled to a localized electronic state and present evidence of controllable coupling between the quantum dot and the localized state. A set of measurements of transport through the device enable the determination that the most likely location of the localized state is consistent with a location in the quantum well near the edge of the quantum dot. Our results are consistent with a gate-voltage controllable tunnel coupling, which is an important building block for hybrid donor and gate-defined quantum dot devices.

  7. Conformational cycle and ion-coupling mechanism of the Na+/hydantoin transporter Mhp1

    PubMed Central

    Kazmier, Kelli; Sharma, Shruti; Islam, Shahidul M.; Roux, Benoît; Mchaourab, Hassane S.

    2014-01-01

    Ion-dependent transporters of the LeuT-fold couple the uptake of physiologically essential molecules to transmembrane ion gradients. Defined by a conserved 5-helix inverted repeat that encodes common principles of ion and substrate binding, the LeuT-fold has been captured in outward-facing, occluded, and inward-facing conformations. However, fundamental questions relating to the structural basis of alternating access and coupling to ion gradients remain unanswered. Here, we used distance measurements between pairs of spin labels to define the conformational cycle of the Na+-coupled hydantoin symporter Mhp1 from Microbacterium liquefaciens. Our results reveal that the inward-facing and outward-facing Mhp1 crystal structures represent sampled intermediate states in solution. Here, we provide a mechanistic context for these structures, mapping them into a model of transport based on ion- and substrate-dependent conformational equilibria. In contrast to the Na+/leucine transporter LeuT, our results suggest that Na+ binding at the conserved second Na+ binding site does not change the energetics of the inward- and outward-facing conformations of Mhp1. Comparative analysis of ligand-dependent alternating access in LeuT and Mhp1 lead us to propose that different coupling schemes to ion gradients may define distinct conformational mechanisms within the LeuT-fold class. PMID:25267652

  8. Conformational cycle and ion-coupling mechanism of the Na+/hydantoin transporter Mhp1.

    PubMed

    Kazmier, Kelli; Sharma, Shruti; Islam, Shahidul M; Roux, Benoît; Mchaourab, Hassane S

    2014-10-14

    Ion-dependent transporters of the LeuT-fold couple the uptake of physiologically essential molecules to transmembrane ion gradients. Defined by a conserved 5-helix inverted repeat that encodes common principles of ion and substrate binding, the LeuT-fold has been captured in outward-facing, occluded, and inward-facing conformations. However, fundamental questions relating to the structural basis of alternating access and coupling to ion gradients remain unanswered. Here, we used distance measurements between pairs of spin labels to define the conformational cycle of the Na(+)-coupled hydantoin symporter Mhp1 from Microbacterium liquefaciens. Our results reveal that the inward-facing and outward-facing Mhp1 crystal structures represent sampled intermediate states in solution. Here, we provide a mechanistic context for these structures, mapping them into a model of transport based on ion- and substrate-dependent conformational equilibria. In contrast to the Na(+)/leucine transporter LeuT, our results suggest that Na(+) binding at the conserved second Na(+) binding site does not change the energetics of the inward- and outward-facing conformations of Mhp1. Comparative analysis of ligand-dependent alternating access in LeuT and Mhp1 lead us to propose that different coupling schemes to ion gradients may define distinct conformational mechanisms within the LeuT-fold class.

  9. Water transport in limestone by X-ray CAT scanning

    USGS Publications Warehouse

    Mossoti, Victor G.; Castanier, Louis M.

    1989-01-01

    The transport of water through the interior of Salem limestone test briquettes can be dynamically monitored by computer aided tomography (commonly called CAT scanning in medical diagnostics). Most significantly, unless evaporation from a particular face of the briquette is accelerated by forced air flow (wind simulation), the distribution of water in the interior of the briquette remains more or less uniform throughout the complete drying cycle. Moreover, simulated solar illumination of the test briquette does not result in the production of significant water gradients in the briquette under steady-state drying conditions.

  10. Experimental and modeling analysis of coupled non-Fickian transport and sorption in natural soils

    NASA Astrophysics Data System (ADS)

    Rubin, Shira; Dror, Ishai; Berkowitz, Brian

    2012-05-01

    We present experimental breakthrough curve (BTC) data and a modeling investigation of conservative and sorbing tracer transport in natural soils. By analyzing the data using the continuous time random walk (CTRW) model, we probe the traditional approach of using conservative tracer model parameters as a basis for quantifying the transport of sorbing solutes in the same domain when non-Fickian transport is present. Many known contaminants in groundwater are sorbed to the host solid porous medium, to varying extents, while being transported; this enhances the long tailing of BTCs which often already occurs because of the inherent non-Fickian nature of the transport. The CTRW framework has been shown to account very well for non-Fickian conservative (nonsorbing) transport. Here, we examine two BTC data sets in laboratory columns packed with natural soils; the first (previously analyzed by Mao and Ren (2004)) comprises transport of (conservative) bromide and (sorbing) atrazine tracers, while the second presents new data with bromide and tribromoneopentyl alcohol (TBNPA), a key flame retardant, as a sorbing solute. TBNPA has received little attention in the past, and is shown to be sorbed onto Bet Dagan soil in a nonlinear manner. We find that the transport behavior of bromide is non-Fickian in all cases, which is caused by the heterogeneity of the soil. Comparative model analysis of the non-Fickian BTCs of the conservative, and sorbing tracers and examination of the fitting parameters, exemplify the coupling between transport and adsorption/desorption processes. The difference in transport parameters used to match the conservative and sorbing data sets shows that conservative tracer parameters (average velocity and dispersion coefficient) are not valid for the transport of reactive tracers.

  11. Experimental and modeling analysis of coupled non-Fickian transport and sorption in natural soils

    NASA Astrophysics Data System (ADS)

    Rubin, S.; Berkowitz, B.

    2011-12-01

    We present experimental breakthrough curve (BTC) data and a modeling investigation of conservative and sorbing tracer transport in natural soils. By analyzing the data using the continuous time random walk (CTRW) model, we probe the traditional approach of using conservative tracer model parameters as a basis for quantifying the transport of sorbing solutes in the same domain. Many known contaminants in groundwater are sorbed to the host solid porous medium, to varying extents, while being transported; this enhances the long tailing of BTCs which already arise because of the inherent non-Fickian nature of the transport. The CTRW framework has been shown to account very well for non-Fickian conservative (nonsorbing) transport. Here, we examine two BTC data sets in laboratory columns packed with natural soils; the first (previously published) comprises transport of (conservative) bromide and (sorbing) atrazine tracers, while the second comprises new data with bromide and tribromoneopentyl alcohol (TBNPA), a common flame retardant, as a sorbing solute. We find that the transport behavior of bromide is non-Fickian in all cases, which is caused by the heterogeneity of the soil. Analysis of the relation between the non-Fickian transport of the conservative and sorbing tracers demonstrates the coupling between transport and adsorption/desorption, and the result that transport parameters (average velocity and dispersion coefficient) calibrated for the conservative tracer parameters are not applicable to the transport of reactive tracers. Our analyses further confirm the relevance and applicability of CTRW theory to the case of laboratory-scale observations of sorbing solutes.

  12. External forces influence the elastic coupling effects during cargo transport by molecular motors.

    PubMed

    Berger, Florian; Keller, Corina; Klumpp, Stefan; Lipowsky, Reinhard

    2015-02-01

    Cellular transport is achieved by the cooperative action of molecular motors which are elastically linked to a common cargo. When the motors pull on the cargo at the same time, they experience fluctuating elastic strain forces induced by the stepping of the other motors. These elastic coupling forces can influence the motors' stepping and unbinding behavior and thereby the ability to transport cargos. Based on a generic single motor description, we introduce a framework that explains the response of two identical molecular motors to a constant external force. In particular, we relate the single motor parameters, the coupling strength and the external load force to the dynamics of the motor pair. We derive four distinct transport regimes and determine how the crossover lines between the regimes depend on the load force. Our description of the overall cargo dynamics takes into account relaxational displacements of the cargo caused by the unbinding of one motor. For large forces and weak elastic coupling these back-shifts dominate the displacements. To develop an intuitive understanding about motor cooperativity during cargo transport, we introduce a time scale for load sharing. This time scale allows us to predict how the regulation of single motor parameters influences the cooperativity. As an example, we show that up-regulating the single motor processivity enhances load sharing of the motor pair.

  13. Coupling mechanical forces to electrical signaling: molecular motors and the intracellular transport of ion channels.

    PubMed

    Barry, Joshua; Gu, Chen

    2013-04-01

    Proper localization of various ion channels is fundamental to neuronal functions, including postsynaptic potential plasticity, dendritic integration, action potential initiation and propagation, and neurotransmitter release. Microtubule-based forward transport mediated by kinesin motors plays a key role in placing ion channel proteins to correct subcellular compartments. PDZ- and coiled-coil-domain proteins function as adaptor proteins linking ionotropic glutamate and GABA receptors to various kinesin motors, respectively. Recent studies show that several voltage-gated ion channel/transporter proteins directly bind to kinesins during forward transport. Three major regulatory mechanisms underlying intracellular transport of ion channels are also revealed. These studies contribute to understanding how mechanical forces are coupled to electrical signaling and illuminating pathogenic mechanisms in neurodegenerative diseases.

  14. A COMSOL-GEMS interface for modeling coupled reactive-transport geochemical processes

    NASA Astrophysics Data System (ADS)

    Azad, Vahid Jafari; Li, Chang; Verba, Circe; Ideker, Jason H.; Isgor, O. Burkan

    2016-07-01

    An interface was developed between COMSOL MultiphysicsTM finite element analysis software and (geo)chemical modeling platform, GEMS, for the reactive-transport modeling of (geo)chemical processes in variably saturated porous media. The two standalone software packages are managed from the interface that uses a non-iterative operator splitting technique to couple the transport (COMSOL) and reaction (GEMS) processes. The interface allows modeling media with complex chemistry (e.g. cement) using GEMS thermodynamic database formats. Benchmark comparisons show that the developed interface can be used to predict a variety of reactive-transport processes accurately. The full functionality of the interface was demonstrated to model transport processes, governed by extended Nernst-Plank equation, in Class H Portland cement samples in high pressure and temperature autoclaves simulating systems that are used to store captured carbon dioxide (CO2) in geological reservoirs.

  15. Experimental validation of a coupled neutron-photon inverse radiation transport solver

    NASA Astrophysics Data System (ADS)

    Mattingly, John; Mitchell, Dean J.; Harding, Lee T.

    2011-10-01

    Sandia National Laboratories has developed an inverse radiation transport solver that applies nonlinear regression to coupled neutron-photon deterministic transport models. The inverse solver uses nonlinear regression to fit a radiation transport model to gamma spectrometry and neutron multiplicity counting measurements. The subject of this paper is the experimental validation of that solver. This paper describes a series of experiments conducted with a 4.5 kg sphere of α-phase, weapons-grade plutonium. The source was measured bare and reflected by high-density polyethylene (HDPE) spherical shells with total thicknesses between 1.27 and 15.24 cm. Neutron and photon emissions from the source were measured using three instruments: a gross neutron counter, a portable neutron multiplicity counter, and a high-resolution gamma spectrometer. These measurements were used as input to the inverse radiation transport solver to evaluate the solver's ability to correctly infer the configuration of the source from its measured radiation signatures.

  16. Experimental validation of GADRAS's coupled neutron-photon inverse radiation transport solver.

    SciTech Connect

    Mattingly, John K.; Mitchell, Dean James; Harding, Lee T.

    2010-08-01

    Sandia National Laboratories has developed an inverse radiation transport solver that applies nonlinear regression to coupled neutron-photon deterministic transport models. The inverse solver uses nonlinear regression to fit a radiation transport model to gamma spectrometry and neutron multiplicity counting measurements. The subject of this paper is the experimental validation of that solver. This paper describes a series of experiments conducted with a 4.5 kg sphere of {alpha}-phase, weapons-grade plutonium. The source was measured bare and reflected by high-density polyethylene (HDPE) spherical shells with total thicknesses between 1.27 and 15.24 cm. Neutron and photon emissions from the source were measured using three instruments: a gross neutron counter, a portable neutron multiplicity counter, and a high-resolution gamma spectrometer. These measurements were used as input to the inverse radiation transport solver to evaluate the solver's ability to correctly infer the configuration of the source from its measured radiation signatures.

  17. Plasmodium falciparum chloroquine resistance transporter is a H+-coupled polyspecific nutrient and drug exporter

    PubMed Central

    Juge, Narinobu; Moriyama, Sawako; Miyaji, Takaaki; Kawakami, Mamiyo; Iwai, Haruka; Fukui, Tomoya; Nelson, Nathan; Omote, Hiroshi; Moriyama, Yoshinori

    2015-01-01

    Extrusion of chloroquine (CQ) from digestive vacuoles through the Plasmodium falciparum CQ resistance transporter (PfCRT) is essential to establish CQ resistance of the malaria parasite. However, the physiological relevance of PfCRT and how CQ-resistant PfCRT gains the ability to transport CQ remain unknown. We prepared proteoliposomes containing purified CQ-sensitive and CQ-resistant PfCRTs and measured their transport activities. All PfCRTs tested actively took up tetraethylammonium, verapamil, CQ, basic amino acids, polypeptides, and polyamines at the expense of an electrochemical proton gradient. CQ-resistant PfCRT exhibited decreased affinity for CQ, resulting in increased CQ uptake. Furthermore, CQ competitively inhibited amino acid transport. Thus, PfCRT is a H+-coupled polyspecific nutrient and drug exporter. PMID:25733858

  18. The Origin of Coupled Chloride and Proton Transport in a Cl–/H+ Antiporter

    PubMed Central

    2016-01-01

    The ClC family of transmembrane proteins functions throughout nature to control the transport of Cl– ions across biological membranes. ClC-ec1 from Escherichia coli is an antiporter, coupling the transport of Cl– and H+ ions in opposite directions and driven by the concentration gradients of the ions. Despite keen interest in this protein, the molecular mechanism of the Cl–/H+ coupling has not been fully elucidated. Here, we have used multiscale simulation to help identify the essential mechanism of the Cl–/H+ coupling. We find that the highest barrier for proton transport (PT) from the intra- to extracellular solution is attributable to a chemical reaction, the deprotonation of glutamic acid 148 (E148). This barrier is significantly reduced by the binding of Cl– in the “central” site (Cl–cen), which displaces E148 and thereby facilitates its deprotonation. Conversely, in the absence of Cl–cen E148 favors the “down” conformation, which results in a much higher cumulative rotation and deprotonation barrier that effectively blocks PT to the extracellular solution. Thus, the rotation of E148 plays a critical role in defining the Cl–/H+ coupling. As a control, we have also simulated PT in the ClC-ec1 E148A mutant to further understand the role of this residue. Replacement with a non-protonatable residue greatly increases the free energy barrier for PT from E203 to the extracellular solution, explaining the experimental result that PT in E148A is blocked whether or not Cl–cen is present. The results presented here suggest both how a chemical reaction can control the rate of PT and also how it can provide a mechanism for a coupling of the two ion transport processes. PMID:27783900

  19. Channel morphology effect on water transport through graphene bilayers

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Wu, Renbing; Law, Adrian Wing-Keung; Feng, Xi-Qiao; Bai, Lichun; Zhou, Kun

    2016-12-01

    The application of few-layered graphene-derived functional thin films for molecular filtration and separation has recently attracted intensive interests. In practice, the morphology of the nanochannel formed by the graphene (GE) layers is not ideally flat and can be affected by various factors. This work investigates the effect of channel morphology on the water transport behaviors through the GE bilayers via molecular dynamics simulations. The simulation results show that the water flow velocity and transport resistance highly depend on the curvature of the graphene layers, particularly when they are curved in non-synergic patterns. To understand the channel morphology effect, the distributions of water density, dipole moment orientation and hydrogen bonds inside the channel are investigated, and the potential energy surface with different distances to the basal GE layer is analyzed. It shows that the channel morphology significantly changes the distribution of the water molecules and their orientation and interaction inside the channel. The energy barrier for water molecules transport through the channel also significantly depends on the channel morphology.

  20. Modeling Nitrogen Fate and Transport at the Sediment-Water ...

    EPA Pesticide Factsheets

    Diffusive mass transfer at media interfaces exerts control on the fate and transport of pollutants originating from agricultural and urban landscapes and affects the con-ditions of water bodies. Diffusion is essentially a physical process affecting the distribution and fate of various environmental pollutants such as nutrients, pesticides, metals, PCBs, PAHs, etc. Environmental problems caused by excessive use of agricultural chemicals (e.g., pesticides and fertilizers) and improper discharge of industrial waste and fuel leaks are all influenced by the diffusive nature of pollutants in the environment. Eutrophication is one such environmental problem where the sediment-water interface exerts a significant physical and geochemical control on the eutrophic condition of the stressed water body. Exposure of streams and lakes to contaminated sediment is another common environmental problem whereby transport of the contaminant (PCBs, PAHs, and other organic contaminants) across the sediment water can increase the risk for exposure to the chemicals and pose a significant health hazard to aquatic life and human beings. This chapter presents analytical and numerical models describing fate and transport phenomena at the sediment-water interface in freshwater ecosystems, with the primary focus on nitrogen cycling and the applicability of the models to real-world environmental problems and challenges faced in their applications. The first model deals with nitrogen cycling

  1. Transports and pathways of overflow water in the Rockall Trough

    NASA Astrophysics Data System (ADS)

    Johnson, Clare; Sherwin, Toby; Cunningham, Stuart; Dumont, Estelle; Houpert, Loïc; Holliday, N. Penny

    2017-04-01

    Water mass analysis reveals a persistent core of deep overflow water within the Rockall Trough which hugs the northern and western boundaries of the basin. Mean speeds within this overflow are 10-15 cm s-1 giving a transport time from the Wyville Thomson Ridge to the central basin of <50 days. Analysis of the 40-year Extended Ellett Line record shows proportions of Norwegian Sea Deep Water associated with the deep core exceed 15% around one quarter of the time. We present the first transport estimates for overflow water in the Rockall Trough. This flux is for overflow water modified by mixing with a density greater than 27.65 kg m-3. Mean values calculated both from a newly deployed mooring array (OSNAP project) and indirectly from the Extended Ellett Line time-series are -0.3±0.04 Sv. Although the flux is highly variable there is no long term trend. As some overflow appears to exit into the Iceland Basin via channels between the northern banks, we suggest that the volume transport will likely increase as the flow pathway is traced back around the boundary of the Rockall Trough towards the Wyville Thomson Ridge.

  2. An Isotopic view of water and nitrogen transport through the ...

    EPA Pesticide Factsheets

    Background/Question/MethodsGroundwater nitrate contamination affects thousands of households in Oregon's southern Willamette Valley and many more across the Pacific Northwest. The southern Willamette Valley Groundwater Management Area (SWV GWMA) was established in 2004 due to nitrate levels in the groundwater exceeding the human health standard of 10 mg nitrate-N L-1. Much of the nitrogen inputs to the GWMA comes from agricultural nitrogen use, and thus efforts to reduce N inputs to groundwater are focused upon improving N management. However, the effectiveness of these improvements on groundwater quality is unclear because of the complexity of nutrient transport through the vadose zone and long groundwater residence times. Our objective was to focus on vadose zone transport and understand the dynamics and timing of N and water movement below the rooting zone in relation to N management and water inputs. Stable isotopes are a powerful tool for tracking water movement, and understanding nitrogen transformations within the vadose zone. In partnership with local farmers, and state agencies, we established lysimeters and groundwater wells in multiple agricultural fields in the GWMA, and have monitored nitrate, nitrate isotopes, and water isotopes weekly for multiple years Results/ConclusionsOur results indicate that vadose zone transport is highly complex, and the residence time of water collected in lysimeters was much longer than expected. While input precipitatio

  3. Interfacial Water-Transport Effects in Proton-Exchange Membranes

    SciTech Connect

    Kienitz, Brian; Yamada, Haruhiko; Nonoyama, Nobuaki; Weber, Adam

    2009-11-19

    It is well known that the proton-exchange membrane is perhaps the most critical component of a polymer-electrolyte fuel cell. Typical membranes, such as Nafion(R), require hydration to conduct efficiently and are instrumental in cell water management. Recently, evidence has been shown that these membranes might have different interfacial morphology and transport properties than in the bulk. In this paper, experimental data combined with theoretical simulations will be presented that explore the existence and impact of interfacial resistance on water transport for Nafion(R) 21x membranes. A mass-transfer coefficient for the interfacial resistance is calculated from experimental data using different permeation cells. This coefficient is shown to depend exponentially on relative humidity or water activity. The interfacial resistance does not seem to exist for liquid/membrane or membrane/membrane interfaces. The effect of the interfacial resistance is to flatten the water-content profiles within the membrane during operation. Under typical operating conditions, the resistance is on par with the water-transport resistance of the bulk membrane. Thus, the interfacial resistance can be dominant especially in thin, dry membranes and can affect overall fuel-cell performance.

  4. Channel morphology effect on water transport through graphene bilayers

    PubMed Central

    Liu, Bo; Wu, Renbing; Law, Adrian Wing-Keung; Feng, Xi-Qiao; Bai, Lichun; Zhou, Kun

    2016-01-01

    The application of few-layered graphene-derived functional thin films for molecular filtration and separation has recently attracted intensive interests. In practice, the morphology of the nanochannel formed by the graphene (GE) layers is not ideally flat and can be affected by various factors. This work investigates the effect of channel morphology on the water transport behaviors through the GE bilayers via molecular dynamics simulations. The simulation results show that the water flow velocity and transport resistance highly depend on the curvature of the graphene layers, particularly when they are curved in non-synergic patterns. To understand the channel morphology effect, the distributions of water density, dipole moment orientation and hydrogen bonds inside the channel are investigated, and the potential energy surface with different distances to the basal GE layer is analyzed. It shows that the channel morphology significantly changes the distribution of the water molecules and their orientation and interaction inside the channel. The energy barrier for water molecules transport through the channel also significantly depends on the channel morphology. PMID:27929106

  5. Electrical coupling between the human serotonin transporter and voltage-gated Ca(2+) channels.

    PubMed

    Ruchala, Iwona; Cabra, Vanessa; Solis, Ernesto; Glennon, Richard A; De Felice, Louis J; Eltit, Jose M

    2014-07-01

    Monoamine transporters have been implicated in dopamine or serotonin release in response to abused drugs such as methamphetamine or ecstasy (MDMA). In addition, monoamine transporters show substrate-induced inward currents that may modulate excitability and Ca(2+) mobilization, which could also contribute to neurotransmitter release. How monoamine transporters modulate Ca(2+) permeability is currently unknown. We investigate the functional interaction between the human serotonin transporter (hSERT) and voltage-gated Ca(2+) channels (CaV). We introduce an excitable expression system consisting of cultured muscle cells genetically engineered to express hSERT. Both 5HT and S(+)MDMA depolarize these cells and activate the excitation-contraction (EC)-coupling mechanism. However, hSERT substrates fail to activate EC-coupling in CaV1.1-null muscle cells, thus implicating Ca(2+) channels. CaV1.3 and CaV2.2 channels are natively expressed in neurons. When these channels are co-expressed with hSERT in HEK293T cells, only cells expressing the lower-threshold L-type CaV1.3 channel show Ca(2+) transients evoked by 5HT or S(+)MDMA. In addition, the electrical coupling between hSERT and CaV1.3 takes place at physiological 5HT concentrations. The electrical coupling between monoamine neurotransmitter transporters and Ca(2+) channels such as CaV1.3 is a novel mechanism by which endogenous substrates (neurotransmitters) or exogenous substrates (like ecstasy) could modulate Ca(2+)-driven signals in excitable cells.

  6. Renewable Water: Direct Contact Membrane Distillation Coupled With Solar Ponds

    NASA Astrophysics Data System (ADS)

    Suarez, F. I.; Tyler, S. W.; Childress, A. E.

    2010-12-01

    The exponential population growth and the accelerated increase in the standard of living have increased significantly the global consumption of two precious resources: water and energy. These resources are intrinsically linked and are required to allow a high quality of human life. With sufficient energy, water may be harvested from aquifers, treated for potable reuse, or desalinated from brackish and seawater supplies. Even though the costs of desalination have declined significantly, traditional desalination systems still require large quantities of energy, typically from fossil fuels that will not allow these systems to produce water in a sustainable way. Recent advances in direct contact membrane distillation can take advantage of low-quality or renewable heat to desalinate brackish water, seawater or wastewater. Direct contact membrane distillation operates at low pressures and can use small temperature differences between the feed and permeate water to achieve a significant freshwater production. Therefore, a much broader selection of energy sources can be considered to drive thermal desalination. A promising method for providing renewable source of heat for direct contact membrane distillation is a solar pond, which is an artificially stratified water body that captures solar radiation and stores it as thermal energy at the bottom of the pond. In this work, a direct contact membrane distillation/solar pond coupled system is modeled and tested using a laboratory-scale system. Freshwater production rates on the order of 2 L day-1 per m2 of solar pond (1 L hr-1 per m2 of membrane area) can easily be achieved with minimal operating costs and under low pressures. While these rates are modest, they are six times larger than those produced by other solar pond-powered desalination systems - and they are likely to be increased if heat losses in the laboratory-scale system are reduced. Even more, this system operates at much lower costs than traditional desalination

  7. Pore Water PAH Transport in Amended Sediment Caps

    NASA Astrophysics Data System (ADS)

    Gidley, P. T.; Kwon, S.; Ghosh, U.

    2009-05-01

    Capping is a common remediation strategy for contaminated sediments that creates a physical barrier between contaminated sediments and the water column. Diffusive flux of contaminants through a sediment cap is small. However, under certain hydrodynamic conditions such as groundwater potential and tidal pumping, groundwater advection can accelerate contaminant transport. Hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) could be transported through the cap under advective conditions. To better understand PAH migration under these conditions, physical models of sediment caps were evaluated in the laboratory through direct measurement of pore water using solid phase micro-extraction with gas chromatography and mass spectrometry. Contaminated sediment and capping material was obtained from an existing Superfund site that was capped at Eagle Harbor, Washington. A PAH dissolution model linked to an advection-dispersion equation with retardation using published organic carbon-water partitioning coefficients (Koc) was compared to measured PAHs in the sediment and cap porewater of the physical model.

  8. Combined effect of boron and salinity on water transport

    PubMed Central

    del Carmen Martínez-Ballesta, Maria; Bastías, Elizabeth

    2008-01-01

    Boron toxicity is an important disorder that can limit plant growth on soils of arid and semi arid environments throughout the world. Although there are several reports about the combined effect of salinity and boron toxicity on plant growth and yield, there is no consensus about the experimental results. A general antagonistic relationship between boron excess and salinity has been observed, however the mechanisms for this interaction is not clear and several options can be discussed. In addition, there is no information, concerning the interaction between boron toxicity and salinity with respect to water transport and aquaporins function in the plants. We recently documented in the highly boron- and salt-tolerant the ecotype of Zea mays L. amylacea from Lluta valley in Northern Chile that under salt stress, the activity of specific membrane components can be influenced directly by boron, regulating the water uptake and water transport through the functions of certain aquaporin isoforms. PMID:19704850

  9. GoAmazon – Scaling Amazon Carbon Water Couplings

    SciTech Connect

    Dubey, Manvendra Krishna

    2016-09-06

    Forests soak up 25% of the carbon dioxide (CO2) emitted by anthropogenic fossil energy use (10 Gt C y-1) moderating its atmospheric accumulation. How this terrestrial CO2 uptake will evolve with climate change in the 21st century is largely unknown. Rainforests are the most active ecosystems with the Amazon basin storing 120 Gt C as biomass and exchanging 18 Gt C y-1 of CO2 via photosynthesis and respiration and fixing carbon at 2-3 kg C m-2 y-1. Furthermore, the intense hydrologic and carbon cycles are tightly coupled in the Amazon where about half of the water is recycled by evapotranspiration and the other half imported from the ocean by Northeasterly trade winds. Climate models predict a drying in the Amazon with reduced carbon uptake while observationally guided assessments indicate sustained uptake. We will resolve this huge discrepancy in the size and sign of the future Amazon carbon cycle by performing the first simultaneous regional scale high frequency measurements of atmospheric CO2, H2O, HOD, CH4, N2O and CO at the T3 site in Manacupuru, Brazil as part of DOE's GoAmazon project. Our data will be used to inform and develop DOE's CLM on the tropical carbon-water couplings at the appropriate grid scale (10-50km). Our measurements will also validate the CO2 data from Japan's GOSAT and NASA's imminent OCO-2 satellite (launch date July 2014).

  10. Electron-vibron coupling effects on electron transport via a single-molecule magnet

    NASA Astrophysics Data System (ADS)

    McCaskey, Alexander; Yamamoto, Yoh; Warnock, Michael; Burzurí, Enrique; van der Zant, Herre S. J.; Park, Kyungwha

    2015-03-01

    We investigate how the electron-vibron coupling influences electron transport via an anisotropic magnetic molecule, such as a single-molecule magnet (SMM) Fe4, by using a model Hamiltonian with parameter values obtained from density-functional theory (DFT). The magnetic anisotropy parameters, vibrational energies, and electron-vibron coupling strengths of the Fe4 are computed using DFT. A giant spin model is applied to the Fe4 with only two charge states, specifically a neutral state with a total spin S =5 and a singly charged state with S =9 /2 , which is consistent with our DFT result and experiments on Fe4 single-molecule transistors. In sequential electron tunneling, we find that the magnetic anisotropy gives rise to new features in the conductance peaks arising from vibrational excitations. In particular, the peak height shows a strong, unusual dependence on the direction as well as magnitude of applied B field. The magnetic anisotropy also introduces vibrational satellite peaks whose position and height are modified with the direction and magnitude of applied B field. Furthermore, when multiple vibrational modes with considerable electron-vibron coupling have energies close to one another, a low-bias current is suppressed, independently of gate voltage and applied B field, although that is not the case for a single mode with a similar electron-vibron coupling. In the former case, the conductance peaks reveal a stronger B -field dependence than in the latter case. The new features appear because the magnetic anisotropy barrier is of the same order of magnitude as the energies of vibrational modes with significant electron-vibron coupling. Our findings clearly show the interesting interplay between magnetic anisotropy and electron-vibron coupling in electron transport via the Fe4. Similar behavior can be observed in transport via other anisotropic magnetic molecules.

  11. Simulation of atmospheric carbon dioxide variability with a global coupled Eulerian-Lagrangian transport model

    NASA Astrophysics Data System (ADS)

    Koyama, Y.; Maksyutov, S.; Mukai, H.; Thoning, K.; Tans, P.

    2010-11-01

    This study assesses the advantages of using a coupled atmospheric-tracer transport model, comprising a global Eulerian model and a global Lagrangian particle dispersion model, for reproducibility of tracer gas variation affected by near field around observation sites. The ability to resolve variability in atmospheric composition on an hourly time scale and a spatial scale of several kilometers would be beneficial for analyzing data from continuous ground-based monitoring and upcoming space-based observations. The coupled model yields increased horizontal resolution of transport and fluxes, and has been tested in regional-scale studies of atmospheric chemistry. By applying the Lagrangian component to the global domain, we extend this approach to the global scale, thereby enabling global inverse modeling and data assimilation. To validate the coupled model, we compare model-simulated CO2 concentrations with continuous observations at two sites operated by the National Oceanic and Atmospheric Administration, USA and one site operated by National Institute for Environmental Studies, Japan. As the purpose of this study is limited to demonstration of the new modeling approach, we select a small subset of 3 sites to highlight use of the model in various geographical areas. To explore the capability of the coupled model in simulating synoptic-scale meteorological phenomena, we calculate the correlation coefficients and variance ratios between deseasonalized model-simulated and observed CO2 concentrations. Compared with the Eulerian model alone, the coupled model yields improved agreement between modeled and observed CO2 concentrations.

  12. Modeling Unsaturated-Saturated Coupled Heat and Groundwater Transport in a Warming Watershed with Seasonal Frozen Ground and Snowmelt

    NASA Astrophysics Data System (ADS)

    Evans, S. G.; Ge, S.; Voss, C.

    2016-12-01

    Controls on groundwater discharge to streams in cold regions that experience freeze-thaw cycles remain an outstanding question in hydrogeology. This question is particularly relevant for mountainous regions, as warming at these high altitudes has led to increasing frozen ground degradation, an earlier onset of snowmelt, and potential water resource insecurity. To evaluate how changes in frozen ground, snowmelt, and warming will alter groundwater discharge to streams, we construct one of the first two-dimensional unsaturated-saturated coupled flow and freeze/thaw heat transport hydrogeologic models. The model simulates seasonally-frozen ground by allowing for pore water freeze and thaw, and by incorporating variable permeability associated with changes in ice and liquid water contents. We apply the model to a high-altitude snowmelt-dominated watershed in the Rocky Mountains of central Colorado, USA. Snowmelt time series are reconstructed from a 12-year dataset of hydrometeorological records and satellite-derived snow-covered area in concert with field measurements from the 2015-2016 snowmelt season. Simulation analyses illustrate that annual groundwater recharge and discharge is limited according to the persistence of seasonal freezing in the subsurface. Climate warming increases groundwater discharge to streams and decreases groundwater discharge to seepage faces. With projected warming trends of 4.8°C/100 years, for the first decade of warming, simulations predict that annual groundwater discharge to streams will increase about 6%, while seepage to the ground surface will decrease by about 5%. Should these changes continue over longer time periods, they may cause significant local ecological and downstream hydrologic impacts. This study has implications for the temporal variability of water resources in a warming global climate and demonstrates the utility of coupled modeling of flow and heat transport in unsaturated-saturated media in cold regions.

  13. Competition for light and water in a coupled soil-plant system

    DOE PAGES

    Manoli, Gabriele; Huang, Cheng -Wei; Bonetti, Sara; ...

    2017-08-14

    Here, it is generally accepted that resource availability shapes the structure and function of many ecosystems. Within the soil-plant-atmosphere (SPA) system, resource availability fluctuates in space and time whereas access to resources by individuals is further impacted by plant-to-plant competition. Likewise, transport and transformation of resources within an individual plant is governed by numerous interacting biotic and abiotic processes. The work here explores the co-limitations on water losses and carbon uptake within the SPA arising from fluctuating resource availability and competition. In particular, the goal is to unfold the interplay between plant access and competition for water and light, asmore » well as the impact of transport/redistribution processes on leaf-level carbon assimilation and water fluxes within forest stands. A framework is proposed that couples a three-dimensional representation of soil-root exchanges with a one-dimensional description of stem water flow and storage, canopy photosynthesis, and transpiration. The model links soil moisture redistribution, root water uptake, xylem water flow and storage, leaf potential and stomatal conductance as driven by supply and demand for water and carbon. The model is then used to investigate plant drought resilience of overstory-understory trees simultaneously competing for water and light. Simulation results reveal that understory-overstory interactions increase ecosystem resilience to drought (i.e. stand-level carbon assimilation rates and water fluxes can be sustained at lower root-zone soil water potentials). This resilience enhancement originates from reduced transpiration (due to shading) and hydraulic redistribution in soil supporting photosynthesis over prolonged periods of drought. In particular, the presence of different rooting systems generates localized hydraulic redistribution fluxes that sustain understory transpiration through overstory-understory interactions. Such complex SPA

  14. Competition for light and water in a coupled soil-plant system

    NASA Astrophysics Data System (ADS)

    Manoli, Gabriele; Huang, Cheng-Wei; Bonetti, Sara; Domec, Jean-Christophe; Marani, Marco; Katul, Gabriel

    2017-10-01

    It is generally accepted that resource availability shapes the structure and function of many ecosystems. Within the soil-plant-atmosphere (SPA) system, resource availability fluctuates in space and time whereas access to resources by individuals is further impacted by plant-to-plant competition. Likewise, transport and transformation of resources within an individual plant is governed by numerous interacting biotic and abiotic processes. The work here explores the co-limitations on water losses and carbon uptake within the SPA arising from fluctuating resource availability and competition. In particular, the goal is to unfold the interplay between plant access and competition for water and light, as well as the impact of transport/redistribution processes on leaf-level carbon assimilation and water fluxes within forest stands. A framework is proposed that couples a three-dimensional representation of soil-root exchanges with a one-dimensional description of stem water flow and storage, canopy photosynthesis, and transpiration. The model links soil moisture redistribution, root water uptake, xylem water flow and storage, leaf potential and stomatal conductance as driven by supply and demand for water and carbon. The model is then used to investigate plant drought resilience of overstory-understory trees simultaneously competing for water and light. Simulation results reveal that understory-overstory interactions increase ecosystem resilience to drought (i.e. stand-level carbon assimilation rates and water fluxes can be sustained at lower root-zone soil water potentials). This resilience enhancement originates from reduced transpiration (due to shading) and hydraulic redistribution in soil supporting photosynthesis over prolonged periods of drought. In particular, the presence of different rooting systems generates localized hydraulic redistribution fluxes that sustain understory transpiration through overstory-understory interactions. Such complex SPA dynamics

  15. Differentiation of transport for particulate and dissolved water chemistry load indices in rainfall runoff from urban source area watersheds

    NASA Astrophysics Data System (ADS)

    Sheng, Y.; Ying, G.; Sansalone, J.

    2008-10-01

    SummaryControl of coupled hydrology and pollutant transport from urban areas generally specify a runoff (or rainfall) depth for treatment. Incarnations of such coupled transport and control include the "first flush" and recent, albeit similar, "water quality volume" (WQV) concepts. For a century the first flush, a mass limited behavior, has been held as the singular transport phenomena for urban areas. In contrast, this study hypothesizes that load transport can have two classifications; mass or flow limited for pollutant phases (dissolved and particulate). Recognition, quantification, and differentiation of two limiting behaviors and phases, is less common. Differentiation is defined physically (exponential or linear); and examined statistically (logistical regression, discriminant analysis); deriving load transport rules using only calibrated hydrologic parameters. The study is supported by 28 Baton Rouge and 14 Cincinnati events; both urban, paved source areas. Once calibrated with pollutant data, statistical approaches for such rules provide promise for transport differentiation based on more economical hydrologic data. Results demonstrate load transport from source areas can be differentiated into mass or flow limited behavior. Results also indicate that within a given event, pollutant phases exhibit differing transport. With hydrologic and chemical pollutant phase transport data, calibrated event-based differentiation rules can be combined with continuous simulations in tools such as SWMM. Such a combination allows time series differentiation of load transport behavior and unit operation volumetric requirements for urban source areas.

  16. Evidence for a Revised Ion/Substrate Coupling Stoichiometry of GABA Transporters.

    PubMed

    Willford, Samantha L; Anderson, Cynthia M; Spencer, Shelly R; Eskandari, Sepehr

    2015-08-01

    Plasma membrane γ-aminobutyric acid (GABA) transporters (GATs) are electrogenic transport proteins that couple the cotranslocation of Na(+), Cl(-), and GABA across the plasma membrane of neurons and glia. A fundamental property of the transporter that determines its ability to concentrate GABA in cells and, hence, regulate synaptic and extra-synaptic GABA concentrations, is the ion/substrate coupling stoichiometry. Here, we scrutinized the currently accepted 2 Na(+):1 Cl(-):1 GABA stoichiometry because it is inconsistent with the measured net charge translocated per co-substrate (Na(+), Cl(-), and GABA). We expressed GAT1 and GAT3 in Xenopus laevis oocytes and utilized thermodynamic and uptake under voltage-clamp measurements to determine the stoichiometry of the GABA transporters. Voltage-clamped GAT1-expressing oocytes were internally loaded with GABA, and the reversal potential (V rev) of the transporter-mediated current was recorded at different external concentrations of Na(+), Cl(-), or GABA. The shifts in V rev for a tenfold change in the external Na(+), Cl(-), and GABA concentration were 84 ± 4, 30 ± 1, and 29 ± 1 mV, respectively. To determine the net charge translocated per Na(+), Cl(-), and GABA, we measured substrate fluxes under voltage clamp in cells expressing GAT1 or GAT3. Charge flux to substrate flux ratios were 0.7 ± 0.1 charge/Na(+), 2.0 ± 0.2 charges/Cl(-), and 2.1 ± 0.1 charges/GABA. Altogether, our results strongly suggest a 3 Na(+):1 Cl(-):1 GABA coupling stoichiometry for the GABA transporters. The revised stoichiometry has important implications for understanding the contribution of GATs to GABAergic signaling in health and disease.

  17. Nonequilibrium steady state transport of collective-qubit system in strong coupling regime

    NASA Astrophysics Data System (ADS)

    Wang, Chen; Sun, Ke-Wei

    2015-11-01

    We investigate the steady state photon transport in a nonequilibrium collective-qubit model. By adopting the noninteracting blip approximation, which is applicable in the strong photon-qubit coupling regime, we describe the essential contribution of indirect qubit-qubit interaction to the population distribution, mediated by the photonic baths. The linear relations of both the optimal flux and noise power with the qubits system size are obtained. Moreover, the inversed power-law style for the finite-size scaling of the optimal photon-qubit coupling strength is exhibited, which is proposed to be universal.

  18. Osmotic water transport with glucose in GLUT2 and SGLT.

    PubMed

    Naftalin, Richard J

    2008-05-15

    Carrier-mediated water cotransport is currently a favored explanation for water movement against an osmotic gradient. The vestibule within the central pore of Na(+)-dependent cotransporters or GLUT2 provides the necessary precondition for an osmotic mechanism, explaining this phenomenon without carriers. Simulating equilibrative glucose inflow via the narrow external orifice of GLUT2 raises vestibular tonicity relative to the external solution. Vestibular hypertonicity causes osmotic water inflow, which raises vestibular hydrostatic pressure and forces water, salt, and glucose into the outer cytosolic layer via its wide endofacial exit. Glucose uptake via GLUT2 also raises oocyte tonicity. Glucose exit from preloaded cells depletes the vestibule of glucose, making it hypotonic and thereby inducing water efflux. Inhibiting glucose exit with phloretin reestablishes vestibular hypertonicity, as it reequilibrates with the cytosolic glucose and net water inflow recommences. Simulated Na(+)-glucose cotransport demonstrates that active glucose accumulation within the vestibule generates water flows simultaneously with the onset of glucose flow and before any flow external to the transporter caused by hypertonicity in the outer cytosolic layers. The molar ratio of water/glucose flow is seen now to relate to the ratio of hydraulic and glucose permeability rather than to water storage capacity of putative water carriers.

  19. Charge Compensation Mechanism of a Na+-coupled, Secondary Active Glutamate Transporter*

    PubMed Central

    Grewer, Christof; Zhang, Zhou; Mwaura, Juddy; Albers, Thomas; Schwartz, Alexander; Gameiro, Armanda

    2012-01-01

    Forward glutamate transport by the excitatory amino acid carrier EAAC1 is coupled to the inward movement of three Na+ and one proton and the subsequent outward movement of one K+ in a separate step. Based on indirect evidence, it was speculated that the cation binding sites bear a negative charge. However, little is known about the electrostatics of the transport process. Valences calculated using the Poisson-Boltzmann equation indicate that negative charge is transferred across the membrane when only one cation is bound. Consistently, transient currents were observed in response to voltage jumps when K+ was the only cation on both sides of the membrane. Furthermore, rapid extracellular K+ application to EAAC1 under single turnover conditions (K+ inside) resulted in outward transient current. We propose a charge compensation mechanism, in which the C-terminal transport domain bears an overall negative charge of −1.23. Charge compensation, together with distribution of charge movement over many steps in the transport cycle, as well as defocusing of the membrane electric field, may be combined strategies used by Na+-coupled transporters to avoid prohibitive activation barriers for charge translocation. PMID:22707712

  20. Quantized Water Transport: Ideal Desalination through Graphyne-4 Membrane

    NASA Astrophysics Data System (ADS)

    Zhu, Chongqin; Li, Hui; Zeng, Xiao Cheng; Wang, E. G.; Meng, Sheng

    2013-11-01

    Graphyne sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. Extensive molecular dynamics simulations on pore-size effects suggest that γ-graphyne-4, with 4 acetylene bonds between two adjacent phenyl rings, has the best performance with 100% salt rejection and an unprecedented water permeability, to our knowledge, of ~13 L/cm2/day/MPa, 3 orders of magnitude higher than prevailing commercial membranes based on reverse osmosis, and ~10 times higher than the state-of-the-art nanoporous graphene. Strikingly, water permeability across graphyne exhibits unexpected nonlinear dependence on the pore size. This counter-intuitive behavior is attributed to the quantized nature of water flow at the nanoscale, which has wide implications in controlling nanoscale water transport and designing highly effective membranes.

  1. Quantized Water Transport: Ideal Desalination through Graphyne-4 Membrane

    PubMed Central

    Zhu, Chongqin; Li, Hui; Zeng, Xiao Cheng; Wang, E. G.; Meng, Sheng

    2013-01-01

    Graphyne sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. Extensive molecular dynamics simulations on pore-size effects suggest that γ-graphyne-4, with 4 acetylene bonds between two adjacent phenyl rings, has the best performance with 100% salt rejection and an unprecedented water permeability, to our knowledge, of ~13 L/cm2/day/MPa, 3 orders of magnitude higher than prevailing commercial membranes based on reverse osmosis, and ~10 times higher than the state-of-the-art nanoporous graphene. Strikingly, water permeability across graphyne exhibits unexpected nonlinear dependence on the pore size. This counter-intuitive behavior is attributed to the quantized nature of water flow at the nanoscale, which has wide implications in controlling nanoscale water transport and designing highly effective membranes. PMID:24196437

  2. Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene.

    PubMed

    Hegele, P R; Mumford, K G

    2014-09-01

    The effective remediation of chlorinated solvent source zones using in situ thermal treatment requires successful capture of gas that is produced. Replicate electrical resistance heating experiments were performed in a thin bench-scale apparatus, where water was boiled and pooled dense non-aqueous phase liquid (DNAPL) trichloroethene (TCE) and water were co-boiled in unconsolidated silica sand. Quantitative light transmission visualization was used to assess gas production and transport mechanisms. In the water boiling experiments, nucleation, growth and coalescence of the gas phase into connected channels were observed at critical gas saturations of Sgc=0.233±0.017, which allowed for continuous gas transport out of the sand. In experiments containing a colder region above a target heated zone, condensation prevented the formation of steam channels and discrete gas clusters that mobilized into colder regions were trapped soon after discontinuous transport began. In the TCE-water experiments, co-boiling at immiscible fluid interfaces resulted in discontinuous gas transport above the DNAPL pool. Redistribution of DNAPL was also observed above the pool and at the edge of the vapor front that propagated upwards through colder regions. These results suggest that the subsurface should be heated to water boiling temperatures to facilitate gas transport from specific locations of DNAPL to extraction points and reduce the potential for DNAPL redistribution. Decreases in electric current were observed at the onset of gas phase production, which suggests that coupled electrical current and temperature measurements may provide a reliable metric to assess gas phase development.

  3. Gas production and transport during bench-scale electrical resistance heating of water and trichloroethene

    NASA Astrophysics Data System (ADS)

    Hegele, P. R.; Mumford, K. G.

    2014-09-01

    The effective remediation of chlorinated solvent source zones using in situ thermal treatment requires successful capture of gas that is produced. Replicate electrical resistance heating experiments were performed in a thin bench-scale apparatus, where water was boiled and pooled dense non-aqueous phase liquid (DNAPL) trichloroethene (TCE) and water were co-boiled in unconsolidated silica sand. Quantitative light transmission visualization was used to assess gas production and transport mechanisms. In the water boiling experiments, nucleation, growth and coalescence of the gas phase into connected channels were observed at critical gas saturations of Sgc = 0.233 ± 0.017, which allowed for continuous gas transport out of the sand. In experiments containing a colder region above a target heated zone, condensation prevented the formation of steam channels and discrete gas clusters that mobilized into colder regions were trapped soon after discontinuous transport began. In the TCE-water experiments, co-boiling at immiscible fluid interfaces resulted in discontinuous gas transport above the DNAPL pool. Redistribution of DNAPL was also observed above the pool and at the edge of the vapor front that propagated upwards through colder regions. These results suggest that the subsurface should be heated to water boiling temperatures to facilitate gas transport from specific locations of DNAPL to extraction points and reduce the potential for DNAPL redistribution. Decreases in electric current were observed at the onset of gas phase production, which suggests that coupled electrical current and temperature measurements may provide a reliable metric to assess gas phase development.

  4. Pedestal Fueling Simulations with a Coupled Kinetic-kinetic Plasma-neutral Transport Code

    SciTech Connect

    D.P. Stotler, C.S. Chang, S.H. Ku, J. Lang and G.Y. Park

    2012-08-29

    A Monte Carlo neutral transport routine, based on DEGAS2, has been coupled to the guiding center ion-electron-neutral neoclassical PIC code XGC0 to provide a realistic treatment of neutral atoms and molecules in the tokamak edge plasma. The DEGAS2 routine allows detailed atomic physics and plasma-material interaction processes to be incorporated into these simulations. The spatial pro le of the neutral particle source used in the DEGAS2 routine is determined from the uxes of XGC0 ions to the material surfaces. The kinetic-kinetic plasma-neutral transport capability is demonstrated with example pedestal fueling simulations.

  5. Energy Conservation Tests of a Coupled Kinetic-kinetic Plasma-neutral Transport Code

    SciTech Connect

    Stotler, D. P.; Chang, C. S.; Ku, S. H.; Lang, J.; Park, G.

    2012-08-29

    A Monte Carlo neutral transport routine, based on DEGAS2, has been coupled to the guiding center ion-electron-neutral neoclassical PIC code XGC0 to provide a realistic treatment of neutral atoms and molecules in the tokamak edge plasma. The DEGAS2 routine allows detailed atomic physics and plasma-material interaction processes to be incorporated into these simulations. The spatial pro le of the neutral particle source used in the DEGAS2 routine is determined from the uxes of XGC0 ions to the material surfaces. The kinetic-kinetic plasma-neutral transport capability is demonstrated with example pedestal fueling simulations.

  6. Ion Transport Induced by Polycations and its Relationship to Loose Coupling of Corn Mitochondria 1

    PubMed Central

    Hanson, J. B.

    1972-01-01

    Treatment of corn mitochondria (Zea mays L., WF9 (Tms) × M14) with polycations (protamine, pancreatic ribonuclease, or polylysine) releases acceptorless respiration if phosphate is present. Concurrently, there is extensive active swelling which is reversed when respiration is uncoupled or stopped. Mersalyl, the phosphate transport inhibitor, blocks both the release of respiration and the active swelling. Diversion of energy into phosphate transport lowers respiratory control and ADP: O ratios. This response is termed “loose coupling” in distinction to “uncoupling” in which energy is made unavailable for either transport or ATP formation. Corn mitochondria as used here are endogenously loose coupled to some extent, and show state 4 respiration linked to active transport. The action of polycations can be partially mimicked by lowering pH of the suspending medium; both give swelling in sucrose medium and increased light absorbancy. Triton X-100, a nonionic detergent, will uncouple and accentuate active swelling, but unlike polycations it will not release state 4 respiration. Calcium ion acts something like polycation in activating phosphate transport and releasing respiration, and polycation appears to block entry of Ca2+. It is speculated that neutralization of certain negatively charged acid groups on the membranes by polycations increases permeability to solutes and decreases coulombic repulsion of phosphate in approaching transport sites. In consequence, respiration rates and active transport rates increase. PMID:16658034

  7. Experimental validation of a coupled neutron-photon inverse radiation transport solver.

    SciTech Connect

    Mattingly, John K.; Harding, Lee; Mitchell, Dean James

    2010-03-01

    Forward radiation transport is the problem of calculating the radiation field given a description of the radiation source and transport medium. In contrast, inverse transport is the problem of inferring the configuration of the radiation source and transport medium from measurements of the radiation field. As such, the identification and characterization of special nuclear materials (SNM) is a problem of inverse radiation transport, and numerous techniques to solve this problem have been previously developed. The authors have developed a solver based on nonlinear regression applied to deterministic coupled neutron-photon transport calculations. The subject of this paper is the experimental validation of that solver. This paper describes a series of experiments conducted with a 4.5-kg sphere of alpha-phase, weapons-grade plutonium. The source was measured in six different configurations: bare, and reflected by high-density polyethylene (HDPE) spherical shells with total thicknesses of 1.27, 2.54, 3.81, 7.62, and 15.24 cm. Neutron and photon emissions from the source were measured using three instruments: a gross neutron counter, a portable neutron multiplicity counter, and a high-resolution gamma spectrometer. These measurements were used as input to the inverse radiation transport solver to characterize the solver's ability to correctly infer the configuration of the source from its measured signatures.

  8. Quantifying impacts of coupled chemical and physical heterogeneity on water quality evolution during Aquifer Storage and Recovery

    NASA Astrophysics Data System (ADS)

    Deng, H.; Descourvieres, C.; Seibert, S.; Harris, B.; Atteia, O.; Siade, A. J.; Prommer, H.

    2014-12-01

    Aquifer storage and recovery (ASR) is an important water management option in water-scarce regions. During wet periods surplus water is injected into suitable aquifers for storage and later recovery. ASR sites are, however, also ideal natural laboratories that provide opportunities for studying coupled physical and geochemical processes and water quality evolution at field-scale under well-controlled hydrological conditions. In this study, we use reactive transport modelling to assess the impacts of physical and chemical heterogeneities on the water quality evolution during the injection of oxic surface water into the anoxic, pyrite-bearing Leederville aquifer in Perth, Western Australia. Physical heterogeneity was identified from geophysical well logs and time lapse temperature logs. Those data were used to define the spatial, depth-varying alternation of three lithofacies (sandstone, siltstone and clay). Chemical heterogeneity was incorporated through distinct chemical zones, based on data derived from a comprehensive pre-trial geochemical characterization and from dedicated laboratory respirometer experiments. Calibration of flow and conservative transport parameters was constrained by the spatially varying measured chloride breakthrough behavior. Subsequent reactive transport modeling discerned the key geochemical processes that affected the water quality evolution during ASR. Clearly identified processes included oxidation of pyrite, mineralization of sedimentary organic carbon, ion exchange, dissolution of calcite and precipitation of ferrihydrite and siderite. We use the calibrated model to analyze the individual and the combined effects of the physical and chemical heterogeneities on the chemical composition of the recovered water during ASR.

  9. A turbulent transport network model in MULTIFLUX coupled with TOUGH2

    SciTech Connect

    Danko, G.; Bahrami, D.; Birkholzer, J.T.

    2011-02-15

    A new numerical method is described for the fully iterated, conjugate solution of two discrete submodels, involving (a) a transport network model for heat, moisture, and airflows in a high-permeability, air-filled cavity; and (b) a variably saturated fractured porous medium. The transport network submodel is an integrated-parameter, computational fluid dynamics solver, describing the thermal-hydrologic transport processes in the flow channel system of the cavity with laminar or turbulent flow and convective heat and mass transport, using MULTIFLUX. The porous medium submodel, using TOUGH2, is a solver for the heat and mass transport in the fractured rock mass. The new model solution extends the application fields of TOUGH2 by integrating it with turbulent flow and transport in a discrete flow network system. We present demonstrational results for a nuclear waste repository application at Yucca Mountain with the most realistic model assumptions and input parameters including the geometrical layout of the nuclear spent fuel and waste with variable heat load for the individual containers. The MULTIFLUX and TOUGH2 model elements are fully iterated, applying a programmed reprocessing of the Numerical Transport Code Functionalization model-element in an automated Outside Balance Iteration loop. The natural, convective airflow field and the heat and mass transport in a representative emplacement drift during postclosure are explicitly solved in the new model. The results demonstrate that the direction and magnitude of the air circulation patterns and all transport modes are strongly affected by the heat and moisture transport processes in the surrounding rock, justifying the need for a coupled, fully iterated model solution such as the one presented in the paper.

  10. Linear coupling of alignment with transport in a polymer electrolyte membrane

    NASA Astrophysics Data System (ADS)

    Li, Jing; Park, Jong Keun; Moore, Robert B.; Madsen, Louis A.

    2011-07-01

    Polymer electrolyte membranes (PEMs) selectively transport ions and polar molecules in a robust yet formable solid support. Tailored PEMs allow for devices such as solid-state batteries,‘artificial muscle’ actuators and reverse-osmosis water purifiers. Understanding how PEM structure and morphology relate to mobile species transport presents a challenge for designing next-generation materials. Material length scales from subnanometre to 1 μm (refs , ) influence bulk properties such as ion conductivity and water transport. Here we employ multi-axis pulsed-field-gradient NMR (ref. ) to measure diffusion anisotropy, and 2H NMR spectroscopy and synchrotron small-angle X-ray scattering to probe orientational order as a function of water content and of membrane stretching. Strikingly, transport anisotropy linearly depends on the degree of alignment, signifying that membrane stretching affects neither the nanometre-scale channel dimensions nor the defect structure,causing only domain reorientation. The observed reorientation of anisotropic domains without perturbation of the inherent nematic-like domain character parallels the behaviour of nematic elastomers, promises tailored membrane conduction and potentially allows understanding of tunable shape-memory effects in PEM materials. This quantitative understanding will drive PEM design efforts towardsoptimal membrane transport, thus enabling more efficient polymeric batteries, fuel cells, mechanical actuators and water purification.

  11. Linear coupling of alignment with transport in a polymer electrolyte membrane.

    PubMed

    Li, Jing; Park, Jong Keun; Moore, Robert B; Madsen, Louis A

    2011-06-19

    Polymer electrolyte membranes (PEMs) selectively transport ions and polar molecules in a robust yet formable solid support. Tailored PEMs allow for devices such as solid-state batteries,'artificial muscle' actuators and reverse-osmosis water purifiers. Understanding how PEM structure and morphology relate to mobile species transport presents a challenge for designing next-generation materials. Material length scales from subnanometre to 1 μm influence bulk properties such as ion conductivity and water transport. Here we employ multi-axis pulsed-field-gradient NMR to measure diffusion anisotropy, and (2)H NMR spectroscopy and synchrotron small-angle X-ray scattering to probe orientational order as a function of water content and of membrane stretching. Strikingly, transport anisotropy linearly depends on the degree of alignment, signifying that membrane stretching affects neither the nanometre-scale channel dimensions nor the defect structure,causing only domain reorientation. The observed reorientation of anisotropic domains without perturbation of the inherent nematic-like domain character parallels the behaviour of nematic elastomers, promises tailored membrane conduction and potentially allows understanding of tunable shape-memory effects in PEM materials. This quantitative understanding will drive PEM design efforts towards optimal membrane transport, thus enabling more efficient polymeric batteries, fuel cells, mechanical actuators and water purification.

  12. Grid resolution study of ground water flow and transport.

    PubMed

    Bower, Kathleen M; Gable, Carl W; Zyvoloski, George A

    2005-01-01

    Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.

  13. Nanoscale transport of electrons and ions in water

    NASA Astrophysics Data System (ADS)

    Boynton, Paul Christopher

    The following dissertation discusses the theoretical study of water on the nanoscale, often involved with essential biological molecules such as DNA and proteins. First I introduce the study of water on the nanoscale and how experimentalists approach confinement with nanopores and nanogaps. Then I discuss the theoretical method we choose for understanding this important biological medium on the molecular level, namely classical molecular dynamics. This leads into transport mechanisms that utilize water on the nanoscale, in our case electronic and ionic transport. On the scale of mere nanometers or less electronic transport in water enters the tunneling regime, requiring the use of a quantum treatment. In addition, I discuss the importance of water in ionic transport and its known effects on biological phenomena such as ion selectivity. Water also has great influence over DNA and proteins, which are both introduced in the context of nanopore sequencing. Several techniques for nanopore sequencing are examined and the importance of protein sequencing is explained. In Chapter 2, we study the effect of volumetric constraints on the structure and electronic transport properties of distilled water in a nanopore with embedded electrodes. Combining classical molecular dynamics simulations with quantum scattering theory, we show that the structural motifs water assumes inside the pore can be probed directly by tunneling. In Chapter 3, we propose an improvement to the original sequencing by tunneling method, in which N pairs of electrodes are built in series along a synthetic nanochannel. Each current time series for each nucleobase is cross-correlated together, reducing noise in the signals. We show using random sampling of data from classical molecular dynamics, that indeed the sequencing error is significantly reduced as the number of pairs of electrodes, N, increases. In Chapter 4, we propose a new technique for de novo protein sequencing that involves translocating a

  14. Risk-based water resources planning: Coupling water allocation and water quality management under extreme droughts

    NASA Astrophysics Data System (ADS)

    Mortazavi-Naeini, M.; Bussi, G.; Hall, J. W.; Whitehead, P. G.

    2016-12-01

    The main aim of water companies is to have a reliable and safe water supply system. To fulfil their duty the water companies have to consider both water quality and quantity issues and challenges. Climate change and population growth will have an impact on water resources both in terms of available water and river water quality. Traditionally, a distinct separation between water quality and abstraction has existed. However, water quality can be a bottleneck in a system since water treatment works can only treat water if it meets certain standards. For instance, high turbidity and large phytoplankton content can increase sharply the cost of treatment or even make river water unfit for human consumption purposes. It is vital for water companies to be able to characterise the quantity and quality of water under extreme weather events and to consider the occurrence of eventual periods when water abstraction has to cease due to water quality constraints. This will give them opportunity to decide on water resource planning and potential changes to reduce the system failure risk. We present a risk-based approach for incorporating extreme events, based on future climate change scenarios from a large ensemble of climate model realisations, into integrated water resources model through combined use of water allocation (WATHNET) and water quality (INCA) models. The annual frequency of imposed restrictions on demand is considered as measure of reliability. We tested our approach on Thames region, in the UK, with 100 extreme events. The results show increase in frequency of imposed restrictions when water quality constraints were considered. This indicates importance of considering water quality issues in drought management plans.

  15. Long-Distance Water Transport in Aquatic Plants.

    PubMed Central

    Pedersen, O.

    1993-01-01

    Acropetal mass flow of water is demonstrated in two submerged angiosperms, Lobelia dortmanna L. and Sparganium emersum Rehman by means of guttation measurements. Transpiration is absent in truly submerged plants, but the presence of guttation verifies that long-distance water transport takes place. Use of tritiated water showed that the water current arises from the roots, and the main flow of water is channeled to the youngest leaves. This was confirmed by measurement of guttation, which showed the highest rates in young leaves. Guttation rates were 10-fold larger in the youngest leaf of S. emersum (2.1 [mu]L leaf-1 h-1) compared with the youngest leaf of L. dortmanna (0.2 [mu]L leaf-1 h-1). This is probably due to profound species differences in the hydraulic conductance (2.7 x 10-17 m4 Pa-1 s-1 for S. emersum and 1.4 x 10-19 m4 Pa-1 s-1 for L. dortmanna). Estimates derived from the modified Hagen-Poiseuille equation showed that the maximum flow velocity in xylem vessels was 23 to 84 cm h-1, and the required root pressure to drive the flow was small compared to that commonly found in terrestrial plants. In S. emersum long-distance transport of water was shown to be dependent on energy conversion in the roots. The leaves ceased to guttate when the roots were cooled to 4[deg]C from the acclimatization level at 15[deg]C, whereas the guttation was stimulated when the temperature was increased to 25[deg]C. Also, the guttation rate decreased significantly when vanadate was added to the root medium. The observed water transport is probably a general phenomenon in submerged plants, where it can act as a translocation system for nutrients taken up from the rich root medium and thereby assure maximum growth. PMID:12232030

  16. Production and pipeline transport of oil-water dispersions

    SciTech Connect

    Carniani, E.; Celsi, A.; Ercolani, D.

    1997-07-01

    Oil-water dispersions are becoming increasingly important for their potential application in the economical exploitation of heavy-oil fields and as novel fuels to be utilized for gasification in industrial power plants and in small heating systems. Snamprogetti in co-operation with Agip and Eniricerche is involved in a research project, partially supported by the Holding Company ENI and Europen Union (Thermie project), for the developing of a new integrated process to produce heavy crude oil from the marginal fields located in the Adriatic Sea as oil-water dispersions. The process scheme provides the multiphase pipeline transportation of the oil in reservoir water dispersion (primary dispersion) from the platform to the onshore processing Oil Centre for oil production and for the preparation of a very stable dispersion of oil in fresh water (secondary dispersion) to be utilized for direct burning. To obtain the necessary information for the design of the production, transportation and processing systems Snamprogetti has equipped a pilot plant to perform dispersion preparations and characterizations, single phase and multiphase transportation tests. The present work provides experimental data relevant to pumping tests of primary and secondary dispersions showing a stable flow configuration for the secondary and a tendency to stratification for the primary in certain flow conditions. During multiphase pumping tests of primary dispersions a markedly non-newtonian behavior has been observed when strong segregation phenomena occur. A comparison with results obtained by one-phase and multiphase flow programs is also presented.

  17. Water transport and cell survival in cryobiological procedures.

    PubMed

    Farrant, J

    1977-03-29

    Living cells may be cooled to 77 K (liquid nitrogen) either to destroy them selectively or to store them for long periods. Water transport across the cell membranes during freezing and thawing is a primary factor determining whether the cells survive. These water movements are controlled by phase changes both intracellular and extracellular and by other factors such as the nature of any cryoprotective agent present, and the rates of cooling and thawing. The relation between cooling procedure, water transport and cell survival is discussed. In particular, the crucial rôle of dilution shock is emphasized: this is the damage to cells induced during the dilution that occurs both as ice melts during rewarming and when any cryoprotective additives are removed after thawing. Apart from the usefulness of understanding these processes for maximizing preservation or controlling selective destruction, the diverse responses of cells to different combinations of water transport and temperature changes appear likely to provide basic information on the properties of cell membranes.

  18. The Transport of Salt and Water across Isolated Rat Ileum

    PubMed Central

    Clarkson, T. W.

    1967-01-01

    The flows of sodium, potassium, and chloride under electrical and chemical gradients and of salt and water in the presence of osmotic pressure gradients are described by phenomenological equations based on the thermodynamics of irreversible processes. The aim was to give the simplest possible description, that is to postulate the least number of active transport processes and the least number of separate pathways across the intestine. On this basis, the results were consistent with the following picture of the intestine: Two channels exist across this tissue, one allowing only passive transport of ions and the other only active. In the passive channel, the predominant resistance to ion flow is friction with the water in the channel. The electroosmotic flow indicates that the passive channel is lined with negative fixed charged groups having a surface charge density of 3000 esu cm-2. The values of the ion-water frictional coefficients, and the relationship between ionic concentrations and flows indicate that the passive channel is extracellular. The active channel behaves as two membranes in series, the first membrane being semipermeable but allowing active transport of sodium, and the second membrane being similar to the passive channel. Friction with the ions in the second "membrane" is the predominant resistance to water flow. PMID:11526854

  19. Single-photon transport through a waveguide coupling to a quadratic optomechanical system

    NASA Astrophysics Data System (ADS)

    Qiao, Lei

    2017-07-01

    We study the coherent transport of a single photon, which propagates in a one-dimensional waveguide and is scattered by a quadratic optomechanical system. Our approach, which is based on the Lippmann-Schwinger equation, gives an analytical solution to describe the single-photon transmission and reflection properties. We analyze the transport spectra and find they are not only related to the optomechanical system's energy-level structure, but also dependent on the optomechanical system's inherent parameters. For the existence of atomic degrees of freedom, we get a Rabi-splitting-like or an electromagnetically induced transparency (EIT)-like spectrum, depending on the atom-cavity coupling strength. Here, we focus on the single-photon strong-coupling regime so that single-quantum effects could be seen.

  20. Long-range correlations in a simple stochastic model of coupled transport

    NASA Astrophysics Data System (ADS)

    Larralde, Hernán; Sanders, David P.

    2009-08-01

    We study coupled transport in the nonequilibrium stationary state of a model consisting of independent random walkers, moving along a one-dimensional channel, which carry a conserved energy-like quantity, with density and temperature gradients imposed by reservoirs at the ends of the channel. In our model, walkers interact with other walkers at the same site by sharing energy at each time step, but the amount of energy carried does not affect the motion of the walkers. We find that already in this simple model long-range correlations arise in the nonequilibrium stationary state which are similar to those observed in more realistic models of coupled transport. We derive an analytical expression for the source of these correlations, which we use to obtain semi-analytical results for the correlations themselves assuming a local-equilibrium hypothesis. These are in very good agreement with results from direct numerical simulations.

  1. Spin-polarized transport through a laterally coupled Aharonov-Bohm ring with two magnetic impurities

    NASA Astrophysics Data System (ADS)

    Cattapan, G.; Lotti, P.

    2012-04-01

    We consider spin-polarized electron transport through an Aharonov-Bohm ring threaded by magnetic flux, side coupled to a quantum waveguide. The ring contains two magnetic defects symmetrically placed with respect to the stub. In the framework of the quantum-waveguide approach, we treat the transport process as a multi-channel scattering problem, the possible spin channels being degenerate in energy. We study both the phase coherence of the electron's wave function, and the entanglement formation between the impurities spins due to the scattering process, in correspondence to various initial spin configurations. To this end, we consider both a suitable spin-flip parameter, and the transmission concurrencies for the outgoing state. In particular, we find that phase coherence is preserved in correspondence to the maximally entangled singlet state of the impurities, in close analogy to what has been found in the literature for a serially coupled ring.

  2. Coupling lattice Boltzmann and continuum equations for flow and reactive transport in porous media.

    SciTech Connect

    Coon, Ethan; Porter, Mark L.; Kang, Qinjun; Moulton, John D.; Lichtner, Peter C.

    2012-06-18

    In spatially and temporally localized instances, capturing sub-reservoir scale information is necessary. Capturing sub-reservoir scale information everywhere is neither necessary, nor computationally possible. The lattice Boltzmann Method for solving pore-scale systems. At the pore-scale, LBM provides an extremely scalable, efficient way of solving Navier-Stokes equations on complex geometries. Coupling pore-scale and continuum scale systems via domain decomposition. By leveraging the interpolations implied by pore-scale and continuum scale discretizations, overlapping Schwartz domain decomposition is used to ensure continuity of pressure and flux. This approach is demonstrated on a fractured medium, in which Navier-Stokes equations are solved within the fracture while Darcy's equation is solved away from the fracture Coupling reactive transport to pore-scale flow simulators allows hybrid approaches to be extended to solve multi-scale reactive transport.

  3. Phase controlled swapping effect in electron transport through asymmetric parallel coupled quantum dot system

    NASA Astrophysics Data System (ADS)

    Brogi, Bharat Bhushan; Chand, Shyam; Ahluwalia, P. K.

    2015-03-01

    We present a theoretical study of the role of asymmetry and magnetic flux on electronic transport through various configurations of coupled quantum dot system, by using Non-Equilibrium Green Function formalism. Transport properties (Transmission Probability, Current-Voltage Characteristics and Differential Conductance) of the different configurations of coupled quantum dot system have been studied by self-consistent approach, in the presence of on-dot Coulomb interaction. Fano effect, appearing in Transmission probability, has been explored during transition of the system from series to symmetric parallel configuration and in response to the variation in magnetic flux threading the system. The results show Fano peaks for asymmetric and symmetric parallel configurations. By adjusting the magnetic flux, swapping effect in Fano peaks appears due to the exchange of states, which sustains despite strong Coulomb blockade effect. The transmission probability spectrum shows mirror symmetry whenever the sum of two values of magnetic flux threading the system is 2 π.

  4. Quantized Water Transport: Ideal Desalination through Graphyne-4 Membrane

    NASA Astrophysics Data System (ADS)

    Zhu, Chongqin; Li, Hui; Zeng, Xiao Cheng; Wang, E. G.; Meng, Sheng

    2014-03-01

    The shortage of clean and fresh water is one of most pervasive problems afflicting human being's life in the world. Desalination is one viable solution to produce clean water, since 98% of the available water in the form of salty water. Using molecular dynamics simulations, we demonstrate that graphyne sheet exhibits promising potential for nanoscale desalination to achieve both high water permeability and salt rejection rate. In addition, Graphyne sheets also are mechanically robust with high tolerance to deformation. Especially, γ-graphyne-4 has the best performance with 100% slat rejection and an unprecedented water permeability of ~ 13L/cm2/day/MPa. 3 orders of magnitude higher than prevailing commercial membranes based on reverse osmosis, and ~ 10 times higher than the state-of-the-art nanoporous graphene. Strikingly, water permeability across graphyne exhibits unexpected nonlinear dependence on the pore area. This counter-intuitive behavior is attributed to the quantized nature of water flow at the nanoscale, which has wide implications in controlling nanoscale water transport and designing highly effective membrane.

  5. Water transport by the bacterial channel alpha-hemolysin

    NASA Technical Reports Server (NTRS)

    Paula, S.; Akeson, M.; Deamer, D.

    1999-01-01

    This study is an investigation of the ability of the bacterial channel alpha-hemolysin to facilitate water permeation across biological membranes. alpha-Hemolysin channels were incorporated into rabbit erythrocyte ghosts at varying concentrations, and water permeation was induced by mixing the ghosts with hypertonic sucrose solutions. The resulting volume decrease of the ghosts was followed by time-resolved optical absorption at pH 5, 6, and 7. The average single-channel permeability coefficient of alpha-hemolysin for water ranged between 1.3x10-12 cm/s and 1.5x10-12 cm/s, depending on pH. The slightly increased single-channel permeability coefficient at lower pH-values was attributed to an increase in the effective pore size. The activation energy of water transport through the channel was low (Ea=5.4 kcal/mol), suggesting that the properties of water inside the alpha-hemolysin channel resemble those of bulk water. This conclusion was supported by calculations based on macroscopic hydrodynamic laws of laminar water flow. Using the known three-dimensional structure of the channel, the calculations accurately predicted the rate of water flow through the channel. The latter finding also indicated that water permeation data can provide a good estimate of the pore size for large channels.

  6. Water transport by the bacterial channel alpha-hemolysin

    NASA Technical Reports Server (NTRS)

    Paula, S.; Akeson, M.; Deamer, D.

    1999-01-01

    This study is an investigation of the ability of the bacterial channel alpha-hemolysin to facilitate water permeation across biological membranes. alpha-Hemolysin channels were incorporated into rabbit erythrocyte ghosts at varying concentrations, and water permeation was induced by mixing the ghosts with hypertonic sucrose solutions. The resulting volume decrease of the ghosts was followed by time-resolved optical absorption at pH 5, 6, and 7. The average single-channel permeability coefficient of alpha-hemolysin for water ranged between 1.3x10-12 cm/s and 1.5x10-12 cm/s, depending on pH. The slightly increased single-channel permeability coefficient at lower pH-values was attributed to an increase in the effective pore size. The activation energy of water transport through the channel was low (Ea=5.4 kcal/mol), suggesting that the properties of water inside the alpha-hemolysin channel resemble those of bulk water. This conclusion was supported by calculations based on macroscopic hydrodynamic laws of laminar water flow. Using the known three-dimensional structure of the channel, the calculations accurately predicted the rate of water flow through the channel. The latter finding also indicated that water permeation data can provide a good estimate of the pore size for large channels.

  7. Benchmark solutions for the galactic heavy-ion transport equations with energy and spatial coupling

    NASA Technical Reports Server (NTRS)

    Ganapol, Barry D.; Townsend, Lawrence W.; Lamkin, Stanley L.; Wilson, John W.

    1991-01-01

    Nontrivial benchmark solutions are developed for the galactic heavy ion transport equations in the straightahead approximation with energy and spatial coupling. Analytical representations of the ion fluxes are obtained for a variety of sources with the assumption that the nuclear interaction parameters are energy independent. The method utilizes an analytical LaPlace transform inversion to yield a closed form representation that is computationally efficient. The flux profiles are then used to predict ion dose profiles, which are important for shield design studies.

  8. Simulation of variability in atmospheric carbon dioxide using a global coupled Eulerian - Lagrangian transport model

    NASA Astrophysics Data System (ADS)

    Koyama, Y.; Maksyutov, S.; Mukai, H.; Thoning, K.; Tans, P.

    2011-04-01

    This study assesses the advantages of using a coupled atmospheric-tracer transport model, comprising a global Eulerian model and a global Lagrangian particle dispersion model, to improve the reproducibility of tracer-gas variations affected by the near-field surface emissions and transport around observation sites. The ability to resolve variability in atmospheric composition on an hourly time-scale and a spatial scale of several kilometers would be beneficial for analyzing data from continuous ground-based monitoring and from upcoming space-based observations. The coupled model yields an increase in the horizontal resolution of transport and fluxes, and has been tested in regional-scale studies of atmospheric chemistry. By applying the Lagrangian component to the global domain, we extend this approach to the global scale, thereby enabling computationally efficient global inverse modeling and data assimilation. To validate the coupled model, we compare model-simulated CO2 concentrations with continuous observations at three sites: two operated by the National Oceanic and Atmospheric Administration, USA, and one operated by the National Institute for Environmental Studies, Japan. As the goal of this study is limited to introducing the new modeling approach, we selected a transport simulation at these three sites to demonstrate how the model may perform at various geographical areas. The coupled model provides improved agreement between modeled and observed CO2 concentrations in comparison to the Eulerian model. In an area where variability in CO2 concentration is dominated by a fossil fuel signal, the correlation coefficient between modeled and observed concentrations increases by between 0.05 to 0.1 from the original values of 0.5-0.6 achieved with the Eulerian model.

  9. Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

    USGS Publications Warehouse

    Molins, S.; Mayer, K.U.

    2007-01-01

    The two-way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate-rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.

  10. Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study

    NASA Astrophysics Data System (ADS)

    Molins, S.; Mayer, K. U.

    2007-05-01

    The two-way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate-rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.

  11. Transport of dissolved organic carbon from soil to surface water: Identifying the transport pathways

    NASA Astrophysics Data System (ADS)

    Van Gaelen, Nele

    2013-04-01

    Over the last decades, increasing concentrations of dissolved organic carbon (DOC) have been found in surface waters. It has also become clear that land use is an important driver for DOC export. However, causal factors controlling this temporal and spatial variation are not clear. Efforts to model DOC export on a catchment scale are rare. In this research, we aim to determine the factors controlling variations in DOC concentration and quality in surface waters. Secondly, the importance of the different pathways (surface runoff, subsurface flow and groundwater flow) for the transport of dissolved organic matter from the soil to the surface water is investigated. Six headwater catchments (100 - 400 ha) were selected in Belgium, representing three different types of land use, namely forest, grassland and arable land. At the outlet of each catchment, a flow-proportional sampler has been collecting samples of base flow and peak discharge since January 2010. In addition, samples of groundwater, subsurface water and precipitation water were collected on a regular base in three of the catchments. Samples were analyzed for DOC, specific UV absorbance (SUVA) and dissolved silica (DSi). Elemental analysis was carried out using ICP-OES. Since 2012, precipitation water and a selection of river water samples was also analyzed for O and H isotopes. Overall, DOC concentrations were highest in forest catchments and lowest in grassland catchments. For all land use types, measured DOC concentrations were highest during peak discharge. The rise in DOC concentrations was associated with a change in DOC quality. During periods of greater discharge, higher SUVA values were measured, indicating DOC with higher aromaticity (humic and fulvic fractions) reaches the outlet. ICP and DSi results also showed a significant difference in geochemical composition of the river water if peak events are compared to base flow samples. During an event, Ca, Mg, Na, S and DSi concentrations were lowered

  12. Investigation of hurricane Ivan using the coupled ocean-atmosphere-wave-sediment transport (COAWST) model

    USGS Publications Warehouse

    Zambon, Joseph B.; He, Ruoying; Warner, John C.

    2014-01-01

    The coupled ocean–atmosphere–wave–sediment transport (COAWST) model is used to hindcast Hurricane Ivan (2004), an extremely intense tropical cyclone (TC) translating through the Gulf of Mexico. Sensitivity experiments with increasing complexity in ocean–atmosphere–wave coupled exchange processes are performed to assess the impacts of coupling on the predictions of the atmosphere, ocean, and wave environments during the occurrence of a TC. Modest improvement in track but significant improvement in intensity are found when using the fully atmosphere–ocean-wave coupled configuration versus uncoupled (e.g., standalone atmosphere, ocean, or wave) model simulations. Surface wave fields generated in the fully coupled configuration also demonstrates good agreement with in situ buoy measurements. Coupled and uncoupled model-simulated sea surface temperature (SST) fields are compared with both in situ and remote observations. Detailed heat budget analysis reveals that the mixed layer temperature cooling in the deep ocean (on the shelf) is caused primarily by advection (equally by advection and diffusion).

  13. Dynamical coupling between magnetic equilibrium and transport in tokamak scenario modelling, with application to current ramps

    NASA Astrophysics Data System (ADS)

    Fable, E.; Angioni, C.; Ivanov, A. A.; Lackner, K.; Maj, O.; Medvedev, S. Yu; Pautasso, G.; Pereverzev, G. V.; Treutterer, W.; the ASDEX Upgrade Team

    2013-07-01

    The modelling of tokamak scenarios requires the simultaneous solution of both the time evolution of the plasma kinetic profiles and of the magnetic equilibrium. Their dynamical coupling involves additional complications, which are not present when the two physical problems are solved separately. Difficulties arise in maintaining consistency in the time evolution among quantities which appear in both the transport and the Grad-Shafranov equations, specifically the poloidal and toroidal magnetic fluxes as a function of each other and of the geometry. The required consistency can be obtained by means of iteration cycles, which are performed outside the equilibrium code and which can have different convergence properties depending on the chosen numerical scheme. When these external iterations are performed, the stability of the coupled system becomes a concern. In contrast, if these iterations are not performed, the coupled system is numerically stable, but can become physically inconsistent. By employing a novel scheme (Fable E et al 2012 Nucl. Fusion submitted), which ensures stability and physical consistency among the same quantities that appear in both the transport and magnetic equilibrium equations, a newly developed version of the ASTRA transport code (Pereverzev G V et al 1991 IPP Report 5/42), which is coupled to the SPIDER equilibrium code (Ivanov A A et al 2005 32nd EPS Conf. on Plasma Physics (Tarragona, 27 June-1 July) vol 29C (ECA) P-5.063), in both prescribed- and free-boundary modes is presented here for the first time. The ASTRA-SPIDER coupled system is then applied to the specific study of the modelling of controlled current ramp-up in ASDEX Upgrade discharges.

  14. Axial and radial water transport and internal water storage in tropical forest canopy trees.

    Treesearch

    Shelley A. James; Frederick C. Meinzer; Guillermo Goldstein; David Woodruff; Timothy Jones; Teresa Restom; Monica Mejia; Michael Clearwater; Paula. Campanello

    2003-01-01

    Heat and stable isotope tracers were used to study axial and radial water transport in relation to sapwood anatomical characteristics and internal water storage in four canopy tree species of a seasonally dry tropical forest in Panama. Anatomical characteristics of the wood and radial profiles of sap flow were measured at the base, upper trunk, and crown of a single...

  15. Rapid water transportation through narrow one-dimensional channels by restricted hydrogen bonds.

    PubMed

    Ohba, Tomonori; Kaneko, Katsumi; Endo, Morinobu; Hata, Kenji; Kanoh, Hirofumi

    2013-01-29

    Water plays an important role in controlling chemical reactions and bioactivities. For example, water transportation through water channels in a biomembrane is a key factor in bioactivities. However, molecular-level mechanisms of water transportation are as yet unknown. Here, we investigate water transportation through narrow and wide one-dimensional (1D) channels on the basis of water-vapor adsorption rates and those determined by molecular dynamics simulations. We observed that water in narrow 1D channels was transported 3-5 times faster than that in wide 1D channels, although the narrow 1D channels provide fewer free nanospaces for water transportation. This rapid transportation is attributed to the formation of fewer hydrogen bonds between water molecules adsorbed in narrow 1D channels. The water-transportation mechanism provides the possibility of rapid communication through 1D channels and will be useful in controlling reactions and activities in water systems.

  16. Stochastic analysis of transverse dispersion in density-coupled transport in aquifers

    USGS Publications Warehouse

    Welty, C.; Kane, A. C.; Kauffman, L.J.

    2003-01-01

    Spectral perturbation techniques have been used previously to derive integral expressions for dispersive mixing in concentration-dependent transport in three-dimensional, heterogeneous porous media, where fluid density and viscosity are functions of solute concentration. Whereas earlier work focused on evaluating longitudinal dispersivity in isotropic media and incorporating the result in a mean one-dimensional transport model, the emphasis of this paper is on evaluation of the complete dispersion tensor, including the more general case of anisotropic media. Approximate analytic expressions for all components of the macroscopic dispersivity tensor are derived, and the tensor is shown to be asymmetric. The tensor is separated into its symmetric and antisymmetric parts, where the symmetric part is used to calculate the principal components and principal directions of dispersivity, and the antisymmetric part of the tensor is shown to modify the velocity of the solute body compared to that of the background fluid. An example set of numerical simulations incorporating the tensor illustrates the effect of density-coupled dispersivity on a sinking plume in an aquifer. The simulations show that the effective transverse vertical spreading in a sinking plume to be significantly greater than would be predicted by a standard density-coupled transport model that does not incorporate the coupling in the dispersivity tensor.

  17. Insights into the ion-coupling mechanism in the MATE transporter NorM-VC

    NASA Astrophysics Data System (ADS)

    Krah, Alexander; Zachariae, Ulrich

    2017-08-01

    Bacteria have developed a variety of different mechanisms to defend themselves from compounds that are toxic to them, such as antibiotics. One of these defence mechanisms is the expulsion of drugs or other noxious compounds by multidrug efflux pumps. Multidrug and toxic compound extrusion (MATE) transporters are efflux pumps that extrude metabolic waste and a variety of antibiotics out of the cell, using an ion gradient as energy source. They function via an alternating-access mechanism. When ions bind in the outward facing conformation, a large conformational change to the inward facing conformation is induced, from which the ion is released and the extruded chemical compound is bound. NorM proteins, which are usually coupled to a Na+ gradient, are members of the MATE family. However, for NorM-VC from Vibrio cholerae, it has been shown that this MATE transporter is additionally coupled to protons. How H+ and Na+ binding are coupled mechanistically to enable drug antiport is not well understood. In this study, we use molecular dynamics simulations to illuminate the sequence of ion binding events that enable efflux. Understanding this antiport mechanism is important to support the development of novel compounds that specifically inhibit the functional cycle of NorM transporters.

  18. Coupled porohyperelastic mass transport (PHEXPT) finite element models for soft tissues using ABAQUS.

    PubMed

    Vande Geest, Jonathan P; Simon, B R; Rigby, Paul H; Newberg, Tyler P

    2011-04-01

    Finite element models (FEMs) including characteristic large deformations in highly nonlinear materials (hyperelasticity and coupled diffusive/convective transport of neutral mobile species) will allow quantitative study of in vivo tissues. Such FEMs will provide basic understanding of normal and pathological tissue responses and lead to optimization of local drug delivery strategies. We present a coupled porohyperelastic mass transport (PHEXPT) finite element approach developed using a commercially available ABAQUS finite element software. The PHEXPT transient simulations are based on sequential solution of the porohyperelastic (PHE) and mass transport (XPT) problems where an Eulerian PHE FEM is coupled to a Lagrangian XPT FEM using a custom-written FORTRAN program. The PHEXPT theoretical background is derived in the context of porous media transport theory and extended to ABAQUS finite element formulations. The essential assumptions needed in order to use ABAQUS are clearly identified in the derivation. Representative benchmark finite element simulations are provided along with analytical solutions (when appropriate). These simulations demonstrate the differences in transient and steady state responses including finite deformations, total stress, fluid pressure, relative fluid, and mobile species flux. A detailed description of important model considerations (e.g., material property functions and jump discontinuities at material interfaces) is also presented in the context of finite deformations. The ABAQUS-based PHEXPT approach enables the use of the available ABAQUS capabilities (interactive FEM mesh generation, finite element libraries, nonlinear material laws, pre- and postprocessing, etc.). PHEXPT FEMs can be used to simulate the transport of a relatively large neutral species (negligible osmotic fluid flux) in highly deformable hydrated soft tissues and tissue-engineered materials.

  19. Free energy calculation of water addition coupled to reduction of aqueous RuO4-.

    PubMed

    Tateyama, Yoshitaka; Blumberger, Jochen; Ohno, Takahisa; Sprik, Michiel

    2007-05-28

    Free energy calculations were carried out for water addition coupled reduction of aqueous ruthenate, RuO4-+H2O+e--->[RuO3(OH)2]2-, using Car-Parrinello molecular dynamics simulations. The full reaction is divided into the reduction of the tetrahedral monoanion, RuO4-+e--->RuO4(2-), followed by water addition, RuO4(2-)+H2O-->[RuO3(OH)2]2-. The free energy of reduction is computed from the fluctuations of the vertical energy gap using the MnO4-+e--->MnO(4)2- reaction as reference. The free energy for water addition is estimated using constrained molecular dynamics methods. While the description of this complex reaction, in principle, involves multiple reaction coordinates, we found that reversible transformation of the reactant into the product can be achieved by control of a single reaction coordinate consisting of a suitable linear combination of atomic distances. The free energy difference of the full reaction is computed to be -0.62 eV relative to the normal hydrogen electrode. This is in good agreement with the experimental value of -0.59 eV, lending further support to the hypothesis that, contrary to the ruthenate monoanion, the dianion is not tetrahedral but forms a trigonal-bipyramidal dihydroxo complex in aqueous solution. We construct an approximate two-dimensional free energy surface using the coupling parameter for reduction and the mechanical constraint for water addition as variables. Analyzing this surface we find that in the most favorable reaction pathway the reduction reaction precedes water addition. The latter takes place via the protonated complex [RuO3(OH)]- and subsequent transport of the created hydroxide ion to the fifth coordination site of Ru.

  20. Effect of wind forcing on the meridional heat transport in a coupled climate model: equilibrium response

    NASA Astrophysics Data System (ADS)

    Yang, Haijun; Dai, Haijin

    2015-09-01

    The effect of the ocean surface winds on the meridional heat transports is studied in a coupled model. Shutting down the global surface winds causes significant reductions in both wind-driven and thermohaline ocean circulations, resulting in a remarkable decrease in the poleward oceanic heat transport (OHT). The sea surface temperature responds with significant warming in the equator and cooling off the equator, causing an enhancement and equatorward shift in the Hadley cell. This increases the poleward atmospheric heat transport (AHT), which in turn compensates the decrease in the OHT. This compensation implies a fundamental constraint in changes of ocean-atmosphere energy transports. Several other compensation changes are also identified. For the OHT components, the changes in the Eulerian mean and bolus OHT are compensated with each other in the Southern Ocean, since a stronger wind driven Ekman transport is associated with a stronger meridional density gradient (stronger bolus circulation) and vice versa. For the AHT components, the changes in the dry static energy (DSE) and latent energy transports are compensated within the tropics (30°N/S), because a stronger Hadley cell causes a stronger equatorward convergence of moisture. In the extratropics, the changes in the mean and eddy DSE transports show perfect compensation, as a result of the equatorward shift of the Ferrell Cell and enhancement of atmospheric baroclinicity in mid-high latitudes, particularly over the North Atlantic. This work also shows how the Earth's climate is trying to maintain the balance between two hemispheres: the ocean in the Northern Hemisphere is colder than that in the Southern Hemisphere due to much reduced northward heat transports cross the Equator in the Atlantic, therefore, the atmosphere responds to the ocean with temperature colder in the Southern Hemisphere than in the Northern Hemisphere by transporting more heat northward cross the equator over the Pacific, in association

  1. gamma. -Aminobutyric acid transport in reconstituted preparations from rat brain: coupled sodium and chloride fluxes

    SciTech Connect

    Keynan, S.; Kanner, B.I.

    1988-01-12

    Transport of ..gamma..-aminobutyric acid (GABA) is electrogenic and completely depends on the presence of both sodium and chloride ions. These ions appear to be cotransported with ..gamma..-aminobutyric acid through its transporter. Using proteoliposomes into which a partially purified ..gamma..-aminobutyric acid transporter preparation was reconstituted. The authors have been able-for the first time-to provide direct evidence for sodium- and chloride-coupled ..gamma..-aminobutyric acid transport. This has been done by measuring the fluxes of /sup 22/Na/sup +/, /sup 36/Cl/sup -/, and (/sup 3/H)GABA. These fluxes have the following characteristics: There are components of the net fluxes of sodium and chloride that are ..gamma..-aminobutyric acid dependent. The sodium flux is chloride dependent. The chloride flux is sodium dependent. Thus, the ..gamma..-aminobutyric acid dependent sodium and chloride fluxes appear to be catalyzed by the transporter. Using these fluxes they have attempted to determine the stoichiometry of the process. They measured the initial rate of sodium-dependent ..gamma..-aminobutyric acid fluxes and that of ..gamma..-aminobutyric acid dependent sodium fluxes. Similarly, they measured the stoichiometry between chloride and ..gamma..-aminobutyric acid. The half-maximal effect obtained when the ..gamma..-aminobutyric acid concentration dependence of Cl/sup -/ and Na/sup +/ transport is determined is much higher than the known K/sub m/ of this system. Reexamination of the kinetics of ..gamma..-aminobutyric acid transport reveals that there are two transport systems for it. The sodium, chloride, and ..gamma..-aminobutyric acid fluxes probably originate from the low-affinity transporter.

  2. Structural basis of water-specific transport through the AQP1 water channel

    NASA Astrophysics Data System (ADS)

    Sui, Haixin; Han, Bong-Gyoon; Lee, John K.; Walian, Peter; Jap, Bing K.

    2001-12-01

    Water channels facilitate the rapid transport of water across cell membranes in response to osmotic gradients. These channels are believed to be involved in many physiological processes that include renal water conservation, neuro-homeostasis, digestion, regulation of body temperature and reproduction. Members of the water channel superfamily have been found in a range of cell types from bacteria to human. In mammals, there are currently 10 families of water channels, referred to as aquaporins (AQP): AQP0-AQP9. Here we report the structure of the aquaporin 1 (AQP1) water channel to 2.2Å resolution. The channel consists of three topological elements, an extracellular and a cytoplasmic vestibule connected by an extended narrow pore or selectivity filter. Within the selectivity filter, four bound waters are localized along three hydrophilic nodes, which punctuate an otherwise extremely hydrophobic pore segment. This unusual combination of a long hydrophobic pore and a minimal number of solute binding sites facilitates rapid water transport. Residues of the constriction region, in particular histidine 182, which is conserved among all known water-specific channels, are critical in establishing water specificity. Our analysis of the AQP1 pore also indicates that the transport of protons through this channel is highly energetically unfavourable.

  3. Fano effect dominance over Coulomb blockade in transport properties of parallel coupled quantum dot system

    SciTech Connect

    Brogi, Bharat Bhushan Ahluwalia, P. K.; Chand, Shyam

    2015-06-24

    Theoretical study of the Coulomb blockade effect on transport properties (Transmission Probability and I-V characteristics) for varied configuration of coupled quantum dot system has been studied by using Non Equilibrium Green Function(NEGF) formalism and Equation of Motion(EOM) method in the presence of magnetic flux. The self consistent approach and intra-dot Coulomb interaction is being taken into account. As the key parameters of the coupled quantum dot system such as dot-lead coupling, inter-dot tunneling and magnetic flux threading through the system can be tuned, the effect of asymmetry parameter and magnetic flux on this tuning is being explored in Coulomb blockade regime. The presence of the Coulomb blockade due to on-dot Coulomb interaction decreases the width of transmission peak at energy level ε + U and by adjusting the magnetic flux the swapping effect in the Fano peaks in asymmetric and symmetric parallel configuration sustains despite strong Coulomb blockade effect.

  4. A coupling model of the radiative transport equation for calculating photon migration in biological tissue

    NASA Astrophysics Data System (ADS)

    Fujii, Hiroyuki; Okawa, Shinpei; Yamada, Yukio; Hoshi, Yoko; Watanabe, Masao

    2015-12-01

    Development of a physically accurate and computationally efficient photon migration model for turbid media is crucial for optical computed tomography such as diffuse optical tomography. For the development, this paper constructs a space-time coupling model of the radiative transport equation with the photon diffusion equation. In the coupling model, a space-time regime of the photon migration is divided into the ballistic and diffusive regimes with the interaction between the both regimes to improve the accuracy of the results and the efficiency of computation. The coupling model provides an accurate description of the photon migration in various turbid media in a wide range of the optical properties, and reduces computational loads when compared with those of full calculation of the RTE.

  5. Fano effect dominance over Coulomb blockade in transport properties of parallel coupled quantum dot system

    NASA Astrophysics Data System (ADS)

    Brogi, Bharat Bhushan; Chand, Shyam; Ahluwalia, P. K.

    2015-06-01

    Theoretical study of the Coulomb blockade effect on transport properties (Transmission Probability and I-V characteristics) for varied configuration of coupled quantum dot system has been studied by using Non Equilibrium Green Function(NEGF) formalism and Equation of Motion(EOM) method in the presence of magnetic flux. The self consistent approach and intra-dot Coulomb interaction is being taken into account. As the key parameters of the coupled quantum dot system such as dot-lead coupling, inter-dot tunneling and magnetic flux threading through the system can be tuned, the effect of asymmetry parameter and magnetic flux on this tuning is being explored in Coulomb blockade regime. The presence of the Coulomb blockade due to on-dot Coulomb interaction decreases the width of transmission peak at energy level ɛ + U and by adjusting the magnetic flux the swapping effect in the Fano peaks in asymmetric and symmetric parallel configuration sustains despite strong Coulomb blockade effect.

  6. Particle transport and flow modification in planar temporally evolving laminar mixing layers. I. Particle transport under one-way coupling

    NASA Astrophysics Data System (ADS)

    Narayanan, Chidambaram; Lakehal, Djamel

    2006-09-01

    Simulations of two-dimensional, particle-laden mixing layers were performed for particles with Stokes numbers of 0.3, 0.6, 1, and 2 under the assumption of one-way coupling using the Eulerian-Lagrangian method; two-way coupling is addressed in Part II. Analysis of interphase momentum transfer was performed in the Eulerian frame of reference by looking at the balance of fluid-phase mean momentum, mean kinetic energy, modal kinetic energy, and particle-phase mean momentum. The differences in the dominant mechanisms of vertical transport of streamwise momentum between the fluid and particle phases is clearly brought out. In the fluid phase, growth of the mixing layer is due to energy transfer from the mean flow to the unstable Kelvin-Helmholtz modes, and transport of mean momentum by these modes. In contrast, in the particle phase, the primary mechanism of vertical transport of streamwise momentum is convection due to the mean vertical velocity induced by the centrifuging of particles by the spanwise Kelvin-Helmholtz vortices. Although the drag force and the particle-phase modal stress play an important role in the early stages of the evolution of the mixing layer, their role is shown to decrease during the pairing process. After pairing, the particle-phase mean streamwise momentum balance is accounted for by the convection and drag force term. The particle-phase modal stress term is shown to be strongly connected to the fluid phase modal stress with a Stokes-number-dependent time lag in its evolution.

  7. Momentum transport in strongly coupled anisotropic plasmas in the presence of strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Finazzo, Stefano Ivo; Critelli, Renato; Rougemont, Romulo; Noronha, Jorge

    2016-09-01

    We present a holographic perspective on momentum transport in strongly coupled, anisotropic non-Abelian plasmas in the presence of strong magnetic fields. We compute the anisotropic heavy quark drag forces and Langevin diffusion coefficients and also the anisotropic shear viscosities for two different holographic models, namely, a top-down deformation of strongly coupled N =4 super-Yang-Mills theory triggered by an external Abelian magnetic field, and a bottom-up Einstein-Maxwell-dilaton (EMD) model which is able to provide a quantitative description of lattice QCD thermodynamics with (2 +1 ) flavors at both zero and nonzero magnetic fields. We find that, in general, energy loss and momentum diffusion through strongly coupled anisotropic plasmas are enhanced by a magnetic field being larger in transverse directions than in the direction parallel to the magnetic field. Moreover, the anisotropic shear viscosity coefficient is smaller in the direction of the magnetic field than in the plane perpendicular to the field, which indicates that strongly coupled anisotropic plasmas become closer to the perfect fluid limit along the magnetic field. We also present, in the context of the EMD model, holographic predictions for the entropy density and the crossover critical temperature in a wider region of the (T , B ) phase diagram that has not yet been covered by lattice simulations. Our results for the transport coefficients in the phenomenologically realistic magnetic EMD model could be readily used as inputs in numerical codes for magnetohydrodynamics.

  8. Water generation and transport below Europa's strike-slip faults

    NASA Astrophysics Data System (ADS)

    Kalousová, Klára; Souček, Ondřej; Tobie, Gabriel; Choblet, Gaël.; Čadek, Ondřej

    2016-12-01

    Jupiter's moon Europa has a very young surface with the abundance of unique terrains that indicate recent endogenic activity. Morphological models as well as spectral observations suggest that it might possess shallow lenses of liquid water within its outer ice shell. Here we investigate the generation and possible accumulation of liquid water below the tidally activated strike-slip faults using a numerical model of two-phase ice-water mixture in two-dimensional Cartesian geometry. Our results suggest that generation of shallow partially molten regions underneath Europa's active strike-slip faults is possible, but their lifetime is constrained by the formation of Rayleigh-Taylor instabilities due to the negative buoyancy of the melt. Once formed, typically within a few million years, these instabilities efficiently transport the meltwater through the shell. Consequently, the maximum water content in the partially molten regions never exceeds 10% which challenges their possible detection by future exploration mission.

  9. Why are carbon nanotubes fast transporters of water?

    PubMed

    Joseph, Sony; Aluru, N R

    2008-02-01

    Extraordinarily fast transport of water in carbon nanotubes (CNTs) in recent experiments has been generally attributed to the smoothness of the CNT surface. Using molecular dynamics simulations we investigate water flow in (16,16) CNTs and show that the enhanced flow rates over Hagen-Poiseuille flow arise from a velocity "jump" in a depletion region at the water nanotube interface and that the water orientations and hydrogen bonding at the interface significantly affect the flow rates. For nanotube with the same smooth wall structure but with more hydrophilic Lennard-Jones (LJ) parameters of silicon, the enhancement is greatly reduced because it does not have "free" OH bonds pointing to the wall as in CNTs that would reduce the number of hydrogen bonds in the depletion layer. Roughness in the tube walls causes strong hydrogen-bonding network and no significant flow enhancement is attained in rough tubes.

  10. Studies of soil-water transport by MRI.

    PubMed

    Amin, M H; Richards, K S; Chorley, R J; Gibbs, S J; Carpenter, T A; Hall, L D

    1996-01-01

    Sequential spin-echo spin-warp MRI pulse sequences have been used to study soil-water transport processes including infiltration, redistribution, and drainage of water in soil columns. Those images provide a means for monitoring and quantifying spatial and temporal changes of soil-water distributions and the movement of wetting fronts. In addition, temporal-geometric changes of unstable wetting fronts during water redistribution were estimated from 2D images and the temporal development of the longest length of finger was described by a fractal relation t approximately L1.38. Bulk dispersion-time-dependent displacement and velocity spectra, as well as 2D maps of flow velocities and dispersion coefficients in soil macropores during saturated steady-state flow, were reconstructed from data obtained using the alternating-pulsed-field-gradient (APFG) pulse sequences.

  11. SUPG and discontinuity-capturing methods for coupled fluid mechanics and electrochemical transport problems

    NASA Astrophysics Data System (ADS)

    Kler, Pablo A.; Dalcin, Lisandro D.; Paz, Rodrigo R.; Tezduyar, Tayfun E.

    2013-02-01

    Electrophoresis is the motion of charged particles relative to the surrounding liquid under the influence of an external electric field. This electrochemical transport process is used in many scientific and technological areas to separate chemical species. Modeling and simulation of electrophoretic transport enables a better understanding of the physicochemical processes developed during the electrophoretic separations and the optimization of various parameters of the electrophoresis devices and their performance. Electrophoretic transport is a multiphysics and multiscale problem. Mass transport, fluid mechanics, electric problems, and their interactions have to be solved in domains with length scales ranging from nanometers to centimeters. We use a finite element method for the computations. Without proper numerical stabilization, computation of coupled fluid mechanics, electrophoretic transport, and electric problems would suffer from spurious oscillations that are related to the high values of the local Péclet and Reynolds numbers and the nonzero divergence of the migration field. To overcome these computational challenges, we propose a stabilized finite element method based on the Streamline-Upwind/Petrov-Galerkin (SUPG) formulation and discontinuity-capturing techniques. To demonstrate the effectiveness of the stabilized formulation, we present test computations with 1D, 2D, and 3D electrophoretic transport problems of technological interest.

  12. The evolution of water transport in plants: an integrated approach.

    PubMed

    Pittermann, J

    2010-03-01

    This review examines the evolution of the plant vascular system from its beginnings in the green algae to modern arborescent plants, highlighting the recent advances in developmental, organismal, geochemical and climatological research that have contributed to our understanding of the evolution of xylem. Hydraulic trade-offs in vascular structure-function are discussed in the context of canopy support and drought and freeze-thaw stress resistance. This qualitative and quantitative neontological approach to palaeobotany may be useful for interpreting the water-transport efficiencies and hydraulic limits in fossil plants. Large variations in atmospheric carbon dioxide levels are recorded in leaf stomatal densities, and may have had profound impacts on the water conservation strategies of ancient plants. A hypothesis that links vascular function with stomatal density is presented and examined in the context of the evolution of wood and/or vessels. A discussion of the broader impacts of plant transport on hydrology and climate concludes this review.

  13. Coupled Hydrogeophysical Inversion for Characterizing Heterogeneous Permeability Field at a Groundwater-River Water Interaction Zone

    NASA Astrophysics Data System (ADS)

    Chen, X.; Johnson, T. C.; Hammond, G. E.; Zachara, J. M.

    2014-12-01

    The hydrological and biogeochemical processes at the groundwater and river water interface are largely controlled by the exchange dynamics between the two water bodies. Accurate characterization of the heterogeneous permeability field at such interface is critical for modeling the bulk flow as well as the biogeochemical processes that are coupled with the flow. Taking advantage of the distinct conductivities in groundwater and rive water, time lapse electrical resistivity tomography (ERT) can provide rich spatial and temporal data for characterizing the permeability field, by imaging the change in subsurface electric conductivity driven by river water intrusion and retreat. We installed a large-scale (300 m by 300 m) 3-dimensional ERT array to monitor river water intrusion and retreat through time at a major river corridor, and the 4-dimensional electrical geophysical data is assimilated to invert for the underlying permeability field using ensemble-based algorithms (e.g., ensemble Kalman filter and ensemble smoother). We developed a new high-performance hydrogeophysical code by coupling an ERT imaging code E4D (Johnson et al., 2010) with a site-scale flow and transport code, PFLOTRAN (Hammond et al., 2012). The coupled code provides the key modeling capability of multi-physics processes, parallel efficiency, and multi-realization simulation capability for hydrogeophysical inversion. We assimilated both well-based point measurements of water table and specific conductance and spatially continuous ERT images in a sequential Bayesian way. Our study demonstrates the effectiveness of joint hydrogeophysical inversion for large-scale characterization of subsurface properties in the groundwater and river water interaction zone. Our investigation of spatial versus temporal data assimilation strategies have inspired systematic data worth analyses to identify the most valuable data sets for hydrogeophysical inversion. The high performance computing is performed on the Hopper

  14. Upregulation of Na-coupled glucose transporter SGLT1 by Tau tubulin kinase 2.

    PubMed

    Alesutan, Ioana; Sopjani, Mentor; Dërmaku-Sopjani, Miribane; Munoz, Carlos; Voelkl, Jakob; Lang, Florian

    2012-01-01

    The Tau-tubulin-kinase 2 (TTBK2) is a serine/threonine kinase expressed in various tissues including tumors. Up-regulation of TTBK2 increases resistance of tumor cells against antiangiogenic treatment and confers cell survival. Tumor cell survival critically depends on cellular uptake of glucose, which is partially accomplished by SGLT1 (SLC5A1) mediated Na(+)-coupled glucose transport. The present study explored whether TTBK2 participates in the regulation of SGLT1 activity. To this end, electrogenic glucose transport was determined in Xenopus oocytes expressing SGLT1 with or without wild-type TTBK2, truncated TTBK2([1-450]) or kinase inactive mutants TTBK2-KD and TTBK2-KD([1-450]). TTBK2, but not TTBK2([1-450]), TTBK2-KD or TTBK2-KD([1-450]), increased membrane carrier protein abundance and electrogenic glucose transport capacity in SGLT1-expressing Xenopus oocytes. Thus TTBK2 is a completely novel regulator of Na(+)-coupled glucose transport.

  15. The Effect of Yaw Coupling in Turning Maneuvers of Large Transport Aircraft

    NASA Technical Reports Server (NTRS)

    McNeill, Walter E.; Innis, Robert C.

    1965-01-01

    A study has been made, using a piloted moving simulator, of the effects of the yaw-coupling parameters N(sub p) and N(sub delta(sub a) on the lateral-directional handling qualities of a large transport airplane at landing-approach airspeed. It is shown that the desirable combinations of these parameters tend to be more proverse when compared with values typical of current aircraft. Results of flight tests in a large variable-stability jet transport showed trends which were similar to those of the simulator data. Areas of minor disagreement, which were traced to differences in airplane geometry, indicate that pilot consciousness of side acceleration forces can be an important factor in handling qualities of future long-nosed transport aircraft.

  16. EmrE, a model for studying evolution and mechanism of ion-coupled transporters.

    PubMed

    Schuldiner, Shimon

    2009-05-01

    EmrE is a small (110 residues) SMR transporter from Escherichia coli that extrudes positively charged aromatic drugs in exchange for two protons, thus rendering bacteria resistant to a variety of toxic compounds. Due to its size, stability and retention of its function upon solubilization in detergent, EmrE provides a unique experimental paradigm for the biochemical and biophysical studies of membrane based ion-coupled transporters. In addition, EmrE has been in center stage in the past two years because it provides also a paradigm for the study of the evolution of membrane proteins. Controversy around this topic is still going on and some novel concepts are surfacing that may contribute to our understanding of evolution of topology of membrane proteins. Furthermore, based on the findings that the cell multidrug transporters interact functionally we introduce the concept of a cell Resistosome.

  17. Large-voltage behavior of charge transport characteristics in nanosystems with weak electron–vibration coupling

    PubMed Central

    Belzig, Wolfgang

    2015-01-01

    Summary We study analytically the Full Counting Statistics of the charge transport through a nanosystem consisting of a few electronic levels weakly coupled to a discrete vibrational mode. In the limit of large transport voltage bias the cumulant generating function can be evaluated explicitly based solely on the intuitive physical arguments and classical master equation description of the vibration mode. We find that for the undamped vibrational modes mutual dynamical interplay between electronic and vibronic degrees of freedom leads to strongly nonlinear (in voltage) transport characteristics of the nanosystem. In particular, we find that for large voltages the k-th cumulant of the current grows as V 2k to be contrasted with the linear dependence in case of more strongly externally damped and thus thermalized vibrational modes. PMID:26425436

  18. Interwire coupling for I n(4 ×1 )/Si(111) probed by surface transport

    NASA Astrophysics Data System (ADS)

    Edler, F.; Miccoli, I.; Demuth, S.; Pfnür, H.; Wippermann, S.; Lücke, A.; Schmidt, W. G.; Tegenkamp, C.

    2015-08-01

    The In/Si(111) system reveals an anisotropy in the electrical conductivity and is a prototype system for atomic wires on surfaces. We use this system to study and tune the interwire interaction by adsorption of oxygen. Through rotational square four-tip transport measurements, both the parallel (σ||) and perpendicular (σ⊥) components are measured separately. The analysis of the I(V) curves reveals that σ⊥ is also affected by adsorption of oxygen, showing clearly an effective interwire coupling, in agreement with density-functional-theory-based calculations of the transmittance. In addition to these surface-state mediated transport channels, we confirm the existence of conducting parasitic space-charge layer channels and address the importance of substrate steps by performing the transport measurements of In phases grown on Si(111) mesa structures.

  19. Ethylene Enhances Water Transport in Hypoxic Aspen1

    PubMed Central

    Kamaluddin, Mohammed; Zwiazek, Janusz J.

    2002-01-01

    Water transport was examined in solution culture grown seedlings of aspen (Populus tremuloides) after short-term exposures of roots to exogenous ethylene. Ethylene significantly increased stomatal conductance, root hydraulic conductivity (Lp), and root oxygen uptake in hypoxic seedlings. Aerated roots that were exposed to ethylene also showed enhanced Lp. An ethylene action inhibitor, silver thiosulphate, significantly reversed the enhancement of Lp by ethylene. A short-term exposure of excised roots to ethylene significantly enhanced the root water flow (Qv), measured by pressurizing the roots at 0.3 MPa. The Qv values in ethylene-treated roots declined significantly when 50 μm HgCl2 was added to the root medium and this decline was reversed by the addition of 20 mm 2-mercaptoethanol. The results suggest that the response of Qv to ethylene involves mercury-sensitive water channels and that root-absorbed ethylene enhanced water permeation through roots, resulting in an increase in root water transport and stomatal opening in hypoxic seedlings. PMID:11891251

  20. Numerical Modeling of Coupled Water, Vapor and Energy in Soils and at the Soil-Atmosphere Interface

    NASA Astrophysics Data System (ADS)

    Simunek, J.; Bristow, K. L.; Saito, H.

    2015-12-01

    It is broadly accepted that mass and energy fluxes in the subsurface in general, and in arid and semi-arid regions in particular, are closely coupled and cannot be evaluated without considering their mutual interactions. However, only a few numerical models (if any) consider coupled water, vapor and energy transport in both the subsurface and at the soil-atmosphere interface. While the subsurface is commonly implemented in existing models, which often consider both isothermal and thermally induced water and vapor flow, the effects of slope inclination, slope azimuth, variable surface albedo and plant shading on incoming radiation and spatially variable surface mass and energy balance, and consequently soil moisture distribution, is rarely considered. In this presentation we discuss these missing elements and our attempts to implement them into the HYDRUS model. We demonstrate implications of some of their interactions, their impact on the spatial distributions of soil temperature and water content, and their effect on soil evaporation.

  1. Cost Analysis of Water Transport for Climate Change Impact Assessment

    NASA Astrophysics Data System (ADS)

    Szaleniec, V.; Buytaert, W.

    2012-04-01

    It is expected that climate change will have a strong impact on water resources worldwide. Many studies exist that couple the output of global climate models with hydrological models to assess the impact of climate change on physical water availability. However, the water resources topology of many regions and especially that of cities can be very complex. Changes in physical water availability do therefore not translate easily into impacts on water resources for cities. This is especially the case for cities with a complex water supply topology, for instance because of geographical barriers, strong gradients in precipitation patterns, or competing water uses. In this study we explore the use of cost maps to enable the inclusion of water supply topologies in climate change impact studies. We use the city of Lima as a case study. Lima is the second largest desert city in the world. Although Peru as a whole has no water shortage, extreme gradients exist. Most of the economic activities including the city of Lima are located in the coastal desert. This region is geographically disconnected from the wet Amazon basin because of the Andes mountain range. Hence, water supply is precarious, provided by a complex combination of high mountain ecosystems including wetlands and glaciers, as well as groundwater aquifers depending on recharge from the mountains. We investigate the feasibility and costs of different water abstraction scenarios and the impact of climate change using cost functions for different resources. The option of building inter basins tunnels across the Andes is compared to the costs of desalinating seawater from the Pacific Ocean under different climate change scenarios and population growth scenarios. This approach yields recommendations for the most cost-effective options for the future.

  2. Numerical modeling of watershed-scale radiocesium transport coupled with biogeochemical cycling in forests

    NASA Astrophysics Data System (ADS)

    Mori, K.; Tada, K.; Tawara, Y.; Tosaka, H.; Ohno, K.; Asami, M.; Kosaka, K.

    2015-12-01

    Since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, intensive monitoring and modeling works on radionuclide transfer in environment have been carried out. Although Cesium (Cs) concentration has been attenuating due to both physical and environmental half-life (i.e., wash-off by water and sediment), the attenuation rate depends clearly on the type of land use and land cover. In the Fukushima case, studying the migration in forest land use is important for predicting the long-term behavior of Cs because most of the contaminated region is covered by forests. Atmospheric fallout is characterized by complicated behavior in biogeochemical cycle in forests which can be described by biotic/abiotic interactions between many components. In developing conceptual and mathematical model on Cs transfer in forest ecosystem, defining the dominant components and their interactions are crucial issues (BIOMASS, 1997-2001). However, the modeling of fate and transport in geosphere after Cs exports from the forest ecosystem is often ignored. An integrated watershed modeling for simulating spatiotemporal redistribution of Cs that includes the entire region from source to mouth and surface to subsurface, has been recently developed. Since the deposited Cs can migrate due to water and sediment movement, the different species (i.e., dissolved and suspended) and their interactions are key issues in the modeling. However, the initial inventory as source-term was simplified to be homogeneous and time-independent, and biogeochemical cycle in forests was not explicitly considered. Consequently, it was difficult to evaluate the regionally-inherent characteristics which differ according to land uses, even if the model was well calibrated. In this study, we combine the different advantages in modeling of forest ecosystem and watershed. This enable to include more realistic Cs deposition and time series of inventory can be forced over the land surface. These processes are integrated

  3. Proton transport in photooxidation of water: A new perspective on photosynthesis

    PubMed Central

    Arnon, Daniel I.; Tsujimoto, Harry Y.; Tang, George M.-S.

    1981-01-01

    The currently prevalent concept of the generation of photosynthetic reducing power in oxygen-evolving cells envisions a linear (noncyclic) electron flow from water to ferredoxin (and thence to NADP+) that requires the collaboration of photosystems I and II (PSI and PSII) joined by plastoquinone and other electron carriers (the Z scheme). The essence of the Z scheme is that only PSI can reduce ferredoxin—i.e., that, after being energized to an intermediate reducing potential by PSII, electrons from water are transported via plastoquinone to PSI which energizes the electrons to their ultimate reducing potential adequate for the reduction of ferredoxin. Basic to the Z scheme is the function of plastoquinone as the obligatory link in electron transport from PSII to PSI. However, we have found that, when plastoquinone function was inhibited, ferredoxin was photoreduced by water without the collaboration of PSI. We now report evidence for an important function of plastoquinone in the translocation of protons liberated inside the thylakoid membrane by photooxidation of water. When the oxygenic photoreduction (i.e., by water) of ferredoxin was blocked by plastoquinone inhibitors, dibromothymoquinone or dinitrophenol ether of iodonitrothymol, the photoreduction of ferredoxin was restored by each of four chemically diverse uncouplers, similar only in their ability to facilitate proton movement across membranes. Similar results were obtained for the oxygenic reduction of NADP+. Our results suggest that the light-induced electron flow from water cannot be maintained unless the simultaneously liberated protons are removed from inside the membrane via plastoquinone. The new evidence is embodied in a concept of an oxygenic photosystem for photosynthetic electron and proton transport, which we propose as an alternative to the Z scheme, to account for photoreduction of ferredoxin-NADP+ by water and the coupled oxygenic (formerly noncyclic) ATP formation without involving PSI. The

  4. Co-regulation of water and K(+) transport in sunflower plants during water stress recovery.

    PubMed

    Benlloch, Manuel; Benlloch-González, María

    2016-06-01

    16-day-old sunflower (Helianthus annuus L.) plants were subjected to deficit irrigation for 12 days. Following this period, plants were rehydrated for 2 days to study plant responses to post-stress recovery. The moderate water stress treatment applied reduced growth in all plant organs and the accumulation of K(+) in the shoot. After the rehydration period, the stem recovered its growth and reached a similar length to the control, an effect which was not observed in either root or leaves. Moreover, plant rehydration after water stress favored the accumulation of K(+) in the apical zone of the stem and expanding leaves. In the roots of plants under water stress, watering to field capacity, once the plants were de- topped, rapidly favored K(+) and water transport in the excised roots. This quick and short-lived response was not observed in roots of plants recovered from water stress for 2 days. These results suggest that the recovery of plant growth after water stress is related to coordinated water and K(+) transport from the root to the apical zone of the ​​stem and expanding leaves. This stimulation of K(+) transport in the root and its accumulation in the cells of the growing zones of the ​​stem must be one of the first responses induced in the plant during water stress recovery. Copyright © 2016 Elsevier GmbH. All rights reserved.

  5. Geoelectrical Evidence of Bicontinuum Transport in Ground Water

    NASA Astrophysics Data System (ADS)

    Singha, K.; Day-Lewis, F. D.; Lane, J. W.

    2007-12-01

    The fate and transport of chemicals in ground water is commonly described by advection and dispersion processes. In many settings, however, observed transport behavior appears inconsistent with the standard advective-dispersive model; instead, concentration histories show long tailing behavior, non-Gaussian breakthrough, and/or rebound after pumping for mass removal has ceased. These phenomena have prompted the consideration of dual-domain, rate-limited mass transfer (RLMT) as a controlling process. Determination of parameters describing mass-transfer between mobile and immobile domains - or even verifying the occurrence of RLMT - is problematic because geochemical data-collection methods preferentially sample the mobile component of the pore space. We present direct evidence of RLMT at the field scale during an aquifer storage and recovery experiment. We observe a hysteretic relation between measurements of pore-fluid conductivity (from borehole fluid samples) and bulk earth conductivity (from borehole electrical-resistivity). This hysteresis contradicts advective-dispersive transport and the standard petrophysical model relating pore-fluid and bulk conductivity, but can be explained by bicontinuum transport models that include first-order RLMT. Using a simple model, we demonstrate that geoelectrical methods can be used to bound estimates of mass transfer-rates and immobile porosity that are otherwise difficult to estimate in situ. These findings suggest that RLMT is one of the fundamental processes controlling solute transport and the efficiency of aquifer remediation, and suggest that similar analyses in other geologic settings may help evaluate the prevalence of RLMT.

  6. Water flow and multicomponent solute transport in drip-irrigated lysimeters

    NASA Astrophysics Data System (ADS)

    Raij, Iael; Šimûnek, Jiří; Ben-Gal, Alon; Lazarovitch, Naftali

    2016-08-01

    Controlled experiments and modeling are crucial components in the evaluation of the fate of water and solutes in environmental and agricultural research. Lysimeters are commonly used to determine water and solute balances and assist in making sustainable decisions with respect to soil reclamation, fertilization, or irrigation with low-quality water. While models are cost-effective tools for estimating and preventing environmental damage by agricultural activities, their value is highly dependent on the accuracy of their parameterization, often determined by calibration. The main objective of this study was to use measured major ion concentrations collected from drip-irrigated lysimeters to calibrate the variably saturated water flow model HYDRUS (2D/3D) coupled with the reactive transport model UNSATCHEM. Irrigation alternated between desalinated and brackish waters. Lysimeter drainage and soil solution samples were collected for chemical analysis and used to calibrate the model. A second objective was to demonstrate the potential use of the calibrated model to evaluate lower boundary design options of lysimeters with respect to leaching fractions determined using drainage water fluxes, chloride concentrations, and overall salinity of drainage water, and exchangeable sodium percentage (ESP) in the profile. The model showed that, in the long term, leaching fractions calculated with electrical conductivity values would be affected by the lower boundary condition pressure head, while those calculated with chloride concentrations and water fluxes would not be affected. In addition, clear dissimilarities in ESP profiles were found between lysimeters with different lower boundary conditions, suggesting a potential influence on hydraulic conductivities and flow patterns.

  7. Carbon dioxide and climate: The effects of water transport in radiative-convective models

    NASA Astrophysics Data System (ADS)

    Hummel, John R.; Reck, Ruth A.

    1981-12-01

    Considerable attention is being focused on the possible climatic effects resulting from increases in the concentration of atmospheric carbon dioxide. In calculating CO2 influence on the thermal structure of the atmosphere, the role of clouds is critically important. Not only are the cloud properties, such as amount, numbers of clouds, altitudes, and optical properties important but also whether or not these properties are fixed or coupled to model temperatures. The transport of water vapor determines whether or not a region has clouds, the cloud properites, and the water vapor profiles appropriate for clear and cloudy skies. Results are presented of the change in surface temperature with changes in carbon dioxide content for two radiative-convective models with three different cloud coverages. We used (1) the Manabe-Wetherald radiative-convective model in which three clouds with fixed pressures, thicknesses, and optical properties and a single water vapor profile are inputed and (2) the Hummel-Kuhn model, which couples radiative heating, convection, and water vapor transport in order to calculate locations and thicknesses. The Hummel-Kuhn model yields temperature increases for doubled CO2 larger than the Manabe-Wetherald model for various assumed total cloud cover amounts. For assumed standard cloud cover amounts the Hummel-Kuhn estimate is 20% larger than the Manabe-Wetherald estimate. For reduced and enhanced cloud cover amounts the Hummel-Kuhn estimates are 37% and 17% larger, respectively. The calculated cloud locations and thicknesses did not change in the calculations; therefore the increased sensitivity in the Hummel-Kuhn model is due to the larger water vapor amounts in the Hummel-Kuhn model and the added infrared absorption by the water vapor dimer.

  8. Integrating Water Flow, Solute Transport and Crop Production Models At The Farm-scale

    NASA Astrophysics Data System (ADS)

    Assinck, F. B. T.; de Vos, J. A.

    Minimising nitrate pollution of ground and surface water and optimising agricultural yields are problems which have to be addressed at the farm-scale. However, simulation models usually operate at the field-scale. We coupled the subsurface hydrology model SWAP with other existing deterministic (sub)models for solute transport, organic mat- ter dynamics, crop growth, and dairy farm management at the farm-scale, resulting in the model WATERPAS. The (sub)models are coupled in a Framework environment obeying the principles of object oriented modelling. Based on daily weather data, groundwater regimes, soil and farm characteristics WATERPAS is able to simulate the water and nutrient balances, grass production, economical benefits, nitrate leaching and greenhouse gas emissions at a farm. Problems of coupling, such as data-transfer, quality checks, over-parameterisation, complexity and sensitivity of the systems are discussed. Application of deducted simpler models and expert judgement can be use- ful for practical use. However, we believe that integrated models are a powerful tool to understand the complex relationships between the different processes. It also gives opportunities to perform scenario analysis for future boundary conditions, i.e. due to changing farm management, (sea) water levels and climate change.

  9. Molecular level water and solute transport in reverse osmosis membranes

    NASA Astrophysics Data System (ADS)

    Lueptow, Richard M.; Shen, Meng; Keten, Sinan

    2015-11-01

    The water permeability and rejection characteristics of six solutes, methanol, ethanol, 2-propanol, urea, Na+, and Cl-, were studied for a polymeric reverse osmosis (RO) membrane using non-equilibrium molecular dynamics simulations. Results indicate that water flux increases with an increasing fraction of percolated free volume in the membrane polymer structure. Solute molecules display Brownian motion and hop from pore to pore as they pass through the membrane. The solute rejection depends on both the size of the solute molecule and the chemical interaction of the solute with water and the membrane. When the open spaces in the polymeric structure are such that solutes have to shed at least one water molecule from their solvation shell to pass through the membrane molecular structure, the water-solute pair interaction energy governs solute rejection. Organic solutes more easily shed water molecules than ions to more readily pass through the membrane. Hydrogen-bonding sites for molecules like urea also lead to a higher rejection. These findings underline the importance of the solute's solvation shell and solute-water-membrane chemistry in solute transport and rejection in RO membranes. Funded by the Institute for Sustainability and Energy at Northwestern with computing resources from XSEDE (NSF grant ACI-1053575).

  10. Water mass structure and transport in the Tourbillon eddy

    NASA Astrophysics Data System (ADS)

    Harvey, John; Glynn, Simon

    1985-06-01

    CTD data collected during the Tourbillon Experiment have been used to identify the water masses present in a mesoscale eddy in the eastern North Atlantic, and their transports during the 50-day period of the Experiment. The core of the eddy was found to comprise North Atlantic Central Water within the temperature range 10 to 11°C, and evidence of downward movement of this water between 150 and 700 db and upward movement between 750 and 820 db is presented. Mediterranean Water (MW) was drawn around the eddy in a tongue which broke into separate patches during the Experiment. There is evidence of this MW having a dynamical role in the eddy: whilst it was present as a continuous tongue it did not progress around the eddy as fast as other water. There is also an indication of upward movement of this MW. The distribution of Labrador Sea Water showed some positive relationship to the location of the eddy centre, whilst low concentrations were noted beneath the MW tongue. Both θ-S analysis and charts of the planetary component of potential vorticity are used in an attempt to identify the source region of the eddy; it is concluded that the eddy had not moved far (perhaps 200 km) from its place of origin, and that the homogeneous water in its core may have been formed by deep winter convection somewhere between north and west of the area where the Experiment was conducted.

  11. Evaluation of bremsstrahlung contribution to photon transport in coupled photon-electron problems

    NASA Astrophysics Data System (ADS)

    Fernández, Jorge E.; Scot, Viviana; Di Giulio, Eugenio; Salvat, Francesc

    2015-11-01

    The most accurate description of the radiation field in x-ray spectrometry requires the modeling of coupled photon-electron transport. Compton scattering and the photoelectric effect actually produce electrons as secondary particles which contribute to the photon field through conversion mechanisms like bremsstrahlung (which produces a continuous photon energy spectrum) and inner-shell impact ionization (ISII) (which gives characteristic lines). The solution of the coupled problem is time consuming because the electrons interact continuously and therefore, the number of electron collisions to be considered is always very high. This complex problem is frequently simplified by neglecting the contributions of the secondary electrons. Recent works (Fernández et al., 2013; Fernández et al., 2014) have shown the possibility to include a separately computed coupled photon-electron contribution like ISII in a photon calculation for improving such a crude approximation while preserving the speed of the pure photon transport model. By means of a similar approach and the Monte Carlo code PENELOPE (coupled photon-electron Monte Carlo), the bremsstrahlung contribution is characterized in this work. The angular distribution of the photons due to bremsstrahlung can be safely considered as isotropic, with the point of emission located at the same place of the photon collision. A new photon kernel describing the bremsstrahlung contribution is introduced: it can be included in photon transport codes (deterministic or Monte Carlo) with a minimal effort. A data library to describe the energy dependence of the bremsstrahlung emission has been generated for all elements Z=1-92 in the energy range 1-150 keV. The bremsstrahlung energy distribution for an arbitrary energy is obtained by interpolating in the database. A comparison between a PENELOPE direct simulation and the interpolated distribution using the data base shows an almost perfect agreement. The use of the data base increases

  12. Dispersive transport dynamics in a strongly coupled groundwater-brine flow system

    SciTech Connect

    Oldenburg, C.M.; Pruess, K.

    1995-02-01

    Many problems in subsurface hydrology involve the flow and transport of solutes that affect liquid density. When density variations are large (>5%), the flow and transport are strongly coupled. Density variations in excess of 20% occur in salt dome and bedded-salt formations which are currently being considered for radioactive waste repositories. The widely varying results of prior numerical simulation efforts of salt dome groundwater-brine flow problems have underscored the difficulty of solving strongly coupled flow and transport equations. We have implemented a standard model for hydrodynamic dispersion in our general purpose integral finite difference simulator, TOUGH2. The residual formulation used in TOUGH2 is efficient for the strongly coupled flow problem and allows the simulation to reach a verifiable steady state. We use the model to solve two classic coupled flow problems as verification. We then apply the model to a salt dome flow problem patterned after the conditions present at the Gorleben salt dome, Germany, a potential site for high-level nuclear waste disposal. Our transient simulations reveal the presence of two flow regimes: (1) recirculating and (2) swept forward. The flow dynamics are highly sensitive to the strength of molecular diffusion, with recirculating flows arising for large values of molecular diffusivity. For pure hydrodynamic dispersion with parameters approximating those at Gorleben, we find a swept-forward flow field at steady state rather than the recirculating flows found in previous investigations. The time to steady state is very sensitive to the initial conditions, with long time periods required to sweep out an initial brine pool in the lower region of the domain. Dimensional analysis is used to demonstrate the tendency toward brine recirculation. An analysis based on a dispersion timescale explains the observed long time to steady state when the initial condition has a brine pool in the lower part of the system.

  13. Simulating Salt Movement and Transformation using a Coupled Reactive Transport Model in Variably-Saturated Groundwater Systems

    NASA Astrophysics Data System (ADS)

    Tavakoli Kivi, S.; Bailey, R. T.; Gates, T.

    2016-12-01

    Salinization is one of the major concerns in irrigated agricultural landscapes. Increasing salinity concentrations are due principally to evaporative concentration; dissolution of salts from weathered minerals and bedrock; and a high water table that results from excessive irrigation, canal seepage, and a lack of efficient drainage systems; leading to decreasing crop yield. High groundwater salinity loading to nearby river systems also impacts downstream areas, with saline river water diverted for application on irrigated fields. In this study, a solute transport model coupled with equilibrium chemistry reactions has been developed to simulate transport of individual salt ions in regional-scale aquifer systems and thereby investigate strategies for salinity remediation. The physically-based numerical model is based on the UZF-RT3D variably-saturated, multi-species groundwater reactive transport modeling code, and accounts for advection, dispersion, carbon and nitrogen cycling, oxidation-reduction reactions, and salt ion equilibrium chemistry reactions such as complexation, ion exchange, and precipitation/dissolution. Each major salt ion (sulfate, chloride, bicarbonate, calcium, sodium, magnesium, potassium) is included. The model has been tested against measured soil salinity at a small scale (soil profile) and against soil salinity, groundwater salinity, and groundwater salinity loading to surface water at the regional scale (500 km2) in the Lower Arkansas River Valley (LARV) in southeastern Colorado, an area acutely affected by salinization for many decades and greatly influenced by gypsum deposits. Preliminary results of using the model in scenario analysis suggest that increasing irrigation efficiency, sealing earthen canals, and rotational fallowing of land can decrease the groundwater salt load to the Arkansas River by 50 to 70% and substantially lower soil salinity in the root zone.

  14. Tunable transport through a quantum dot chain with side-coupled Majorana bound states

    SciTech Connect

    Jiang, Cui; Lu, Gang; Gong, Wei-Jiang

    2014-09-14

    We investigate the transport properties of a quantum dot (QD) chain side-coupled to a pair of Majorana bound states (MBSs). It is found that the zero-bias conductance is tightly dependent on the parity of QD number. First, if a Majorana zero mode is introduced to couple to one QD of the odd-numbered QD structure, the zero-bias conductance is equal to (e{sup 2})/(2h) , but the zero-bias conductance will experience a valley-to-peak transition if the Majorana zero mode couples to the different QDs of the even-numbered QD structure. On the other hand, when the inter-MBS coupling is nonzero, the zero-bias conductance spectrum shows a peak in the odd-numbered QD structure, and in the even-numbered QD structure one conductance valley appears at the zero-bias limit. These results show the feasibility to manipulate the current in a multi-QD structure based on the QD-MBS coupling. Also, such a system can be a candidate for detecting the MBSs.

  15. Tunable transport through a quantum dot chain with side-coupled Majorana bound states

    NASA Astrophysics Data System (ADS)

    Jiang, Cui; Lu, Gang; Gong, Wei-Jiang

    2014-09-01

    We investigate the transport properties of a quantum dot (QD) chain side-coupled to a pair of Majorana bound states (MBSs). It is found that the zero-bias conductance is tightly dependent on the parity of QD number. First, if a Majorana zero mode is introduced to couple to one QD of the odd-numbered QD structure, the zero-bias conductance is equal to e/22h, but the zero-bias conductance will experience a valley-to-peak transition if the Majorana zero mode couples to the different QDs of the even-numbered QD structure. On the other hand, when the inter-MBS coupling is nonzero, the zero-bias conductance spectrum shows a peak in the odd-numbered QD structure, and in the even-numbered QD structure one conductance valley appears at the zero-bias limit. These results show the feasibility to manipulate the current in a multi-QD structure based on the QD-MBS coupling. Also, such a system can be a candidate for detecting the MBSs.

  16. Full counting statistics of transport electrons through a two-level quantum dot with spin–orbit coupling

    SciTech Connect

    Wang, Z.M.; Xue, H.B.; Xue, N.T.; Liang, J.-Q.

    2015-02-15

    We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.

  17. Water, heat and salt transport through the Strait of Otranto

    NASA Astrophysics Data System (ADS)

    Yari, Sadegh; Gačić, Miroslav; Kovačević, Vedrana; Cardin, Vanessa

    2010-05-01

    The water, heat and salt transports through the Strait of Otranto are estimated applying direct method to historical current and hydrographical data (from December 94 through November 95). A variational inverse method based on a variational principle and a finite element solver is used to reconstruct the current, temperature and salinity fields across the Strait section from sparse measurements. The mean annual inflow and outflow water transport rates are estimated as 0.901±0.039 Sv and -0.939±0.315 Sv, respectively, and the net transport for the period of study is equal to -0.032±0.208 Sv. Thus, on a yearly time interval, the inflow and the outflow are practically compensated. The heat and salt transports due to advection process are estimated for five monthly periods, namely December 1994, February, May, August and November 1995. Considering these five periods representative of the seasonal cycle during the year, their average values show that there is a net heat advection into the Adriatic Sea on a yearly basis. The estimated value of advected heat and the corresponding error are 2.408±0.490 TW, which is equivalent to a heat gain of 17.37±3.53 W m-2 for the whole basin. This value is compared to the heat loss of -36±152 (std) W m-2 through the air-sea interface calculated by means of bulk formulas over the Adriatic Sea. The two values are expected to be balance each other in order to close the heat budget of the basin. The possible reasons for this difference to occur are discussed. On a yearly basis, the salt transport is estimated as an input of salt equal to 0.05×106 Kg s-1. The average annual fresh water budget is estimated as -0.002 Sv, equivalent to the mass of fresh water of 2.00×106Kg s-1 or to the level of 0.45 m yr-1 for the entire Adriatic Sea. The import of salt that is less than the gain of fresh water is in agreement with the fact that the Adriatic Sea is a dilution basin.

  18. Chancellor Water Colloids: Characterization and Radionuclide Associated Transport

    SciTech Connect

    Reimus, Paul William; Boukhalfa, Hakim

    2014-09-26

    Column transport experiments were conducted in which water from the Chancellor nuclear test cavity was transported through crushed volcanic tuff from Pahute Mesa. In one experiment, the cavity water was spiked with solute 137Cs, and in another it was spiked with 239/240Pu(IV) nanocolloids. A third column experiment was conducted with no radionuclide spike at all, although the 137Cs concentrations in the water were still high enough to quantify in the column effluent. The radionuclides strongly partitioned to natural colloids present in the water, which were characterized for size distribution, mass concentration, zeta potential/surface charge, critical coagulation concentration, and qualitative mineralogy. In the spiked water experiments, the unanalyzed portion of the high-concentration column effluent samples were combined and re-injected into the respective columns as a second pulse. This procedure was repeated again for a third injection. Measurable filtration of the colloids was observed after each initial injection of the Chancellor water into the columns, but the subsequent injections (spiked water experiments only) exhibited no apparent filtration, suggesting that the colloids that remained mobile after relatively short transport distances were more resistant to filtration than the initial population of colloids. It was also observed that while significant desorption of 137Cs from the colloids occurred after the first injection in both the spiked and unspiked waters, subsequent injections of the spiked water exhibited much less 137Cs desorption (much greater 137Cs colloid-associated transport). This result suggests that the 137Cs that remained associated with colloids during the first injection represented a fraction that was more strongly adsorbed to the mobile colloids than the initial 137Cs associated with the colloids. A greater amount of the 239/240

  19. A Local Incident Flux Response Expansion Transport Method for Coupling to the Diffusion Method in Cylindrical Geometry

    SciTech Connect

    Dingkang Zhang; Farzad Rahnema; Abderrafi M. Ougouag

    2013-09-01

    A local incident flux response expansion transport method is developed to generate transport solutions for coupling to diffusion theory codes regardless of their solution method (e.g., fine mesh, nodal, response based, finite element, etc.) for reactor core calculations in both two-dimensional (2-D) and three-dimensional (3-D) cylindrical geometries. In this approach, a Monte Carlo method is first used to precompute the local transport solution (i.e., response function library) for each unique transport coarse node, in which diffusion theory is not valid due to strong transport effects. The response function library is then used to iteratively determine the albedo coefficients on the diffusion-transport interfaces, which are then used as the coupling parameters within the diffusion code. This interface coupling technique allows a seamless integration of the transport and diffusion methods. The new method retains the detailed heterogeneity of the transport nodes and naturally constructs any local solution within them by a simple superposition of local responses to all incoming fluxes from the contiguous coarse nodes. A new technique is also developed for coupling to fine-mesh diffusion methods/codes. The local transport method/module is tested in 2-D and 3-D pebble-bed reactor benchmark problems consisting of an inner reflector, an annular fuel region, and a controlled outer reflector. It is found that the results predicted by the transport module agree very well with the reference fluxes calculated directly by MCNP in both benchmark problems.

  20. Optical measurement of osmotic water transport in cultured cells. Role of glucose transporters

    PubMed Central

    1992-01-01

    Methodology was developed to measure osmotic water permeability in monolayer cultured cells and applied to examine the proposed role of glucose transporters in the water pathway (1989. Proc. Natl. Acad. Sci. USA. 86:8397-8401). J774 macrophages were grown on glass coverslips and mounted in a channel-type perfusion chamber for rapid fluid exchange without cell detachment. Relative cell volume was measured by 45 degrees light scattering using an inverted microscope; measurement accuracy was validated by confocal imaging microscopy. The time required for greater than 90% fluid exchange was less than 1 s. In response to a decrease in perfusate osmolality from 300 to 210 mosM, cells swelled without lag at an initial rate of 4.5%/s, corresponding to a water permeability coefficient of (6.3 +/- 0.4) x 10(-3) cm/s (SE, n = 20, 23 degrees C), assuming a cell surface-to-volume ratio of 4,400 cm-1. The initial rate of cell swelling was proportional to osmotic gradient size, independent of perfusate viscosity, and increased by amphotericin B (25 micrograms/ml), and had an activation energy of 10.0 +/- 1 kcal/mol (12-39 degrees C). The compounds phloretin (20 microM) and cytochalasin B (2.5 micrograms/ml) inhibited glucose transport by greater than 85% but did not influence Pf in paired experiments in which Pf was measured before and after inhibitor addition. The mercurials HgCl2 (0.1 mM) and p-chloromercuribenzoate (1 mM) did not inhibit Pf. A stopped-flow light scattering technique was used to measure Pf independently in J774 macrophages grown in suspension culture. Pf in suspended cells was (4.4 +/- 0.3) x 10(-3) cm/s (assuming a surface-to-volume ratio of 8,800 cm-1), increased more than threefold by amphotericin B, and not inhibited by phloretin and cytochalasin B under conditions of strong inhibition of glucose transport. The glucose reflection coefficient was 0.98 +/- 0.03 as measured by induced osmosis, assuming a unity reflection coefficient for sucrose. These results

  1. The SLC36 family of proton-coupled amino acid transporters and their potential role in drug transport

    PubMed Central

    Thwaites, David T; Anderson, Catriona MH

    2011-01-01

    Members of the solute carrier (SLC) 36 family are involved in transmembrane movement of amino acids and derivatives. SLC36 consists of four members. SLC36A1 and SLC36A2 both function as H+-coupled amino acid symporters. SLC36A1 is expressed at the luminal surface of the small intestine but is also commonly found in lysosomes in many cell types (including neurones), suggesting that it is a multipurpose carrier with distinct roles in different cells including absorption in the small intestine and as an efflux pathway following intralysosomal protein breakdown. SLC36A1 has a relatively low affinity (Km 1–10 mM) for its substrates, which include zwitterionic amino and imino acids, heterocyclic amino acids and amino acid-based drugs and derivatives used experimentally and/or clinically to treat epilepsy, schizophrenia, bacterial infections, hyperglycaemia and cancer. SLC36A2 is expressed at the apical surface of the human renal proximal tubule where it functions in the reabsorption of glycine, proline and hydroxyproline. SLC36A2 also transports amino acid derivatives but has a narrower substrate selectivity and higher affinity (Km 0.1–0.7 mM) than SLC36A1. Mutations in SLC36A2 lead to hyperglycinuria and iminoglycinuria. SLC36A3 is expressed only in testes and is an orphan transporter with no known function. SLC36A4 is widely distributed at the mRNA level and is a high-affinity (Km 2–3 µM) transporter for proline and tryptophan. We have much to learn about this family of transporters, but from current knowledge, it seems likely that their function will influence the pharmacokinetic profiles of amino acid-based drugs by mediating transport in both the small intestine and kidney. LINKED ARTICLES This article is part of a themed section on Transporters. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2011.164.issue-7 PMID:21501141

  2. Heat and water transport in soils and across the soil-atmosphere interface: 1. Theory and different model concepts

    NASA Astrophysics Data System (ADS)

    Vanderborght, Jan; Fetzer, Thomas; Mosthaf, Klaus; Smits, Kathleen M.; Helmig, Rainer

    2017-02-01

    Evaporation is an important component of the soil water balance. It is composed of water flow and transport processes in a porous medium that are coupled with heat fluxes and free air flow. This work provides a comprehensive review of model concepts used in different research fields to describe evaporation. Concepts range from nonisothermal two-phase flow, two-component transport in the porous medium that is coupled with one-phase flow, two-component transport in the free air flow to isothermal liquid water flow in the porous medium with upper boundary conditions defined by a potential evaporation flux when available energy and transfer to the free airflow are limiting or by a critical threshold water pressure when soil water availability is limiting. The latter approach corresponds with the classical Richards equation with mixed boundary conditions. We compare the different approaches on a theoretical level by identifying the underlying simplifications that are made for the different compartments of the system: porous medium, free flow and their interface, and by discussing how processes not explicitly considered are parameterized. Simplifications can be grouped into three sets depending on whether lateral variations in vertical fluxes are considered, whether flow and transport in the air phase in the porous medium are considered, and depending on how the interaction at the interface between the free flow and the porous medium is represented. The consequences of the simplifications are illustrated by numerical simulations in an accompanying paper.

  3. Janus Copper Mesh Film with Unidirectional Water Transportation Ability toward High Efficiency Oil/Water Separation.

    PubMed

    Cheng, Zhongjun; Wang, Bohan; Lai, Hua; Liu, Pengchang; Zhang, Dongjie; Tian, Da; Liu, Hongwei; Yu, Xiaoyan; Sun, Bo; Sun, Kening

    2017-08-17

    Inspired by the special asymmetric wettability and controllable permeation function of cell membranes, we report a Janus nanostructured copper mesh film with unidirectional water transportation ability. Water can permeate from the hydrophobic side to the hydrophilic side, but is retained in the opposite direction. Notably, based on this special unidirectional water permeation property, both heavy oil/water mixtures (ρoil >ρwater ) and light oil/water mixtures (ρoil <ρwater ) can be separated. Additionally, the film demonstrates high separation efficiency and good recyclability. This paper reports a new Janus film that achieved highly efficient oil/water separation based on smart control of the wettability of the film. It is believed to have the potential to be used in many practical applications, such as wastewater treatment and oil-spill cleanup. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Use of boundary fluxes when simulating solute transport with the MODFLOW ground-water transport process

    USGS Publications Warehouse

    Konikow, L.F.; Hornberger, G.Z.

    2003-01-01

    This report describes modifications to a U.S. Geological Survey (USGS) threedimensional solute-transport model (MODFLOWGWT), which is incorporated into the USGS MODFLOW ground-water model as the Ground- Water Transport (GWT) Process. The modifications improve the capability of MODFLOW-GWT to accurately simulate solute transport in simulations that represent a nonzero flux across an aquifer boundary. In such situations, the new Boundary Flux Package (BFLX) will allow the user flexibility to assign the flux to specific cell faces, although that flexibility is limited for certain types of fluxes (such as recharge and evapotranspiration, which can only be assigned to the top face if either is to be represented as a boundary flux). The approach is consistent with that used in the MODPATH model. The application of the BFLX Package was illustrated using a test case in which the Lake Package was active. The results using the BFLX Package showed noticeably higher magnitudes of velocity in the cells adjacent to the lake than previous results without the BFLX Package. Consequently, solute was transported slightly faster through the lake-aquifer system when the BFLX Package is active. However, the overall solute distributions did not differ greatly from simulations made without using the BFLX Package.

  5. Applications of the compensating pressure theory of water transport.

    PubMed

    Canny, M

    1998-07-01

    Some predictions of the recently proposed theory of long-distance water transport in plants (the Compensating Pressure Theory) have been verified experimentally in sunflower leaves. The xylem sap cavitates early in the day under quite small water stress, and the compensating pressure P (applied as the tissue pressure of turgid cells) pushes water into embolized vessels, refilling them during active transpiration. The water potential, as measured by the pressure chamber or psychrometer, is not a measure of the pressure in the xylem, but (as predicted by the theory) a measure of the compensating pressure P. As transpiration increases, P is increased to provide more rapid embolism repair. In many leaf petioles this increase in P is achieved by the hydrolysis of starch in the starch sheath to soluble sugars. At night P falls as starch is reformed. A hypothesis is proposed to explain these observations by pressure-driven reverse osmosis of water from the ground parenchyma of the petiole. Similar processes occur in roots and are manifested as root pressure. The theory requires a pump to transfer water from the soil into the root xylem. A mechanism is proposed by which this pump may function, in which the endodermis acts as a one-way valve and a pressure-confining barrier. Rays and xylem parenchyma of wood act like the xylem parenchyma of petioles and roots to repair embolisms in trees. The postulated root pump permits a re-appraisal of the work done by evaporation during transpiration, leading to the proposal that in tall trees there is no hydrostatic gradient to be overcome in lifting water. Some published observations are re-interpreted in terms of the theory: doubt is cast on the validity of measurements of hydraulic conductance of wood; vulnerability curves are found not to measure the cavitation threshold of water in the xylem, but the osmotic pressure of the xylem parenchyma; if measures of xylem pressure and of hydraulic conductance are both suspect, the accepted

  6. Modeling greenhouse gas emissions and nutrient transport in managed arable soils with a fully coupled hydrology-biogeochemical modeling system

    NASA Astrophysics Data System (ADS)

    Haas, Edwin; Klatt, Steffen; Kiese, Ralf; Butterbach-Bahl, Klaus; Kraft, Philipp; Breuer, Lutz

    2015-04-01

    The use of mineral nitrogen fertilizer sustains the global food production and therefore the livelihood of human kind. The rise in world population will put pressure on the global agricultural system to increase its productivity leading most likely to an intensification of mineral nitrogen fertilizer use. The fate of excess nitrogen and its distribution within landscapes is manifold. Process knowledge on the site scale has rapidly grown in recent years and models have been developed to simulate carbon and nitrogen cycling in managed ecosystems on the site scale. Despite first regional studies, the carbon and nitrogen cycling on the landscape or catchment scale is not fully understood. In this study we present a newly developed modelling approach by coupling the fully distributed hydrology model CMF (catchment modelling framework) to the process based regional ecosystem model LandscapeDNDC for the investigation of hydrological processes and carbon and nitrogen transport and cycling, with a focus on nutrient displacement and resulting greenhouse gas emissions in various virtual landscapes / catchment to demonstrate the capabilities of the modelling system. The modelling system was applied to simulate water and nutrient transport at the at the Yanting Agro-ecological Experimental Station of Purple Soil, Sichuan province, China. The catchment hosts cypress forests on the outer regions, arable fields on the sloping croplands cultivated with wheat-maize rotations and paddy rice fields in the lowland. The catchment consists of 300 polygons vertically stratified into 10 soil layers. Ecosystem states (soil water content and nutrients) and fluxes (evapotranspiration) are exchanged between the models at high temporal scales (hourly to daily) forming a 3-dimensional model application. The water flux and nutrients transport in the soil is modelled using a 3D Richards/Darcy approach for subsurface fluxes with a kinematic wave approach for surface water runoff and the

  7. Ion and water transport in charge-modified graphene nanopores

    NASA Astrophysics Data System (ADS)

    Qiu, Ying-Hua; Li, Kun; Chen, Wei-Yu; Si, Wei; Tan, Qi-Yan; Chen, Yun-Fei

    2015-10-01

    Porous graphene has a high mechanical strength and an atomic-layer thickness that makes it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solutions are a type of strong long-range interaction that may greatly influence fluid transport through nanopores. In this study, molecular dynamic simulations were conducted to investigate ion and water transport through 1.05-nm diameter monolayer graphene nanopores, with their edges charge-modified. Our results indicated that these nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase-decrease profile while the co-ion currents monotonically decrease. The co-ion rejection can reach 76.5% and 90.2% when the nanopores are negatively and positively charged, respectively. The Cl- ion current increases and reaches a plateau, and the Na+ current decreases as the charge amount increases in systems in which Na+ ions act as counterions. In addition, charge modification can enhance water transport through nanopores. This is mainly due to the ion selectivity of the nanopores. Notably, positive charges on the pore edges facilitate water transport much more strongly than negative charges. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB707601 and 2011CB707605), the National Natural Science Foundation of China (Grant No. 50925519), the Fundamental Research Funds for the Central Universities, Funding of Jiangsu Provincial Innovation Program for Graduate Education, China (Grant No. CXZZ13_0087), and the Scientific Research Foundation of Graduate School of Southeast University (Grant No. YBJJ 1322).

  8. Spectroscopic study of optical confinement and transport effects in coupled microspheres and pillar cavities

    NASA Astrophysics Data System (ADS)

    Yang, Seungmoo

    In this thesis we investigated the spatial and spectral mode profiles, and the optical transport properties of single and multiple coupled cavities. We performed numerical modeling of whispering gallery modes (WGMs) in such cavities in order to explain recent experiments on semiconductor micropillars. High quality (Q up to 20 000) WGMs with small mode volumes V ˜0.3 mum 3 in 4-5 mum micropillars were reproduced. The WGM spectra were found to be in a good agreement with the experimental data. The coupling between size-matched spheres from 2.9 to 6.0 mum in diameter was characterized using spectroscopy. We observed peculiar kites in the spectral images of such coherently coupled bispheres. The origin of these kites was explained due to the coupling of multiple pairs of azimuthal modes. We quantified the coupling constant for WGMs located in the equatorial plane of spheres parallel to the substrate which plays the most important role in the transport of WGMs in such structures. It was shown that in long (>10 spheres) chains of size-disordered polystyrene microspheres the transmission properties are dominated by photonic nanojet-induced modes (NIMs) leading to periodic focusing of light along the chain. In the transmission spectra of such chains we observed Fabry-Perot fringes with propagation losses of only 0.08 dB per sphere at the maxima of the transmission peaks. The fringes of NIMs are found to be in a good agreement with the results of numerical modeling. These modes can be used in various biomedical applications requiring tight focusing of the beams.

  9. Stable Janus superhydrophilic/hydrophobic nickel foam for directional water transport.

    PubMed

    Si, Yifan; Chen, Liwei; Yang, Fuchao; Guo, Fei; Guo, Zhiguang

    2017-09-08

    Janus superhydrophilic/hydrophobic macroporous nickel foam for directional water transport has been demonstrated via a simple floating strategy. Water can transport from hydrophobic to superhydrophilic layer through Janus nickel foam, but cannot transfer from superhydrophilic to hydrophobic layer. This "3D water diode" Janus nickel foam shows extremely high transport rate and outstanding stability. After damaged by abrasion, its directional water transport property retains well. Copyright © 2017 Elsevier Inc. All rights reserved.

  10. Coupled Continuous Time Random Walks for Anomalous Transport in Media Characterized by Heterogeneous Mass Transfer Properties

    NASA Astrophysics Data System (ADS)

    Comolli, A.; Dentz, M.

    2015-12-01

    Solute transport in geological media is in general non-Fickian as it cannot be explained in terms of equivalent homogeneous media. This anomalous character can be traced back to the existence of multiscale heterogeneity and strong correlations within the medium. Here we investigate the impact of fast heterogeneous mass transfer properties as represented by a spatially varying retardation coefficient (mass exchange between mobile and immobile regions, linear sorption-desorption reactions, variable porosity). In order to estimate the effects of spatial correlation, and disorder distribution on the average transport, we consider 2D media characterized by complex multiscale geometries and point distributions of retardation of increasing heterogeneity. Within a Lagrangian framework, we coarse-grain the Langevin equation for the transport of solute particles due to advection and diffusion in the heterogeneous medium. The large-scale transport properties are derived within a stochastic modeling approach by ensemble averaging of the coarse-grained Langevin equation . This approach shows that the effective particle motion can be described by a coupled CTRW that is fully parametrized by the distribution of the retardation coefficient and the spatial medium organization. This allows for the explicit relation of the heterogeneous medium properties to observed anomalous transport in terms of solute dispersion, breakthrough curves and spatial concentration profiles.

  11. Modeling the coupled mechanics, transport, and growth processes in collagen tissues.

    SciTech Connect

    Holdych, David J.; Nguyen, Thao D.; Klein, Patrick A.; in't Veld, Pieter J.; Stevens, Mark Jackson

    2006-11-01

    The purpose of this project is to develop tools to model and simulate the processes of self-assembly and growth in biological systems from the molecular to the continuum length scales. The model biological system chosen for the study is the tendon fiber which is composed mainly of Type I collagen fibrils. The macroscopic processes of self-assembly and growth at the fiber scale arise from microscopic processes at the fibrillar and molecular length scales. At these nano-scopic length scales, we employed molecular modeling and simulation method to characterize the mechanical behavior and stability of the collagen triple helix and the collagen fibril. To obtain the physical parameters governing mass transport in the tendon fiber we performed direct numerical simulations of fluid flow and solute transport through an idealized fibrillar microstructure. At the continuum scale, we developed a mixture theory approach for modeling the coupled processes of mechanical deformation, transport, and species inter-conversion involved in growth. In the mixture theory approach, the microstructure of the tissue is represented by the species concentration and transport and material parameters, obtained from fibril and molecular scale calculations, while the mechanical deformation, transport, and growth processes are governed by balance laws and constitutive relations developed within a thermodynamically consistent framework.

  12. Transport and coordination in the coupled soil-root-xylem-phloem leaf system

    NASA Astrophysics Data System (ADS)

    Huang, C. W.; Katul, G. G.; Pockman, W.; Litvak, M. E.; Domec, J. C.; Palmroth, S.

    2016-12-01

    In response to varying environmental conditions, stomatal pores act as biological valves that dynamically adjust their size thereby determining the rate of CO2 assimilation and water loss (i.e., transpiration) to the dry atmosphere. Although the significance of this biotic control on gas exchange is rarely disputed, representing parsimoniously all the underlying mechanisms responsible for stomatal kinetics remain a subject of some debate. It has been conjectured that stomatal control in seed plants (i.e., angiosperm and gymnosperm) represents a compromise between biochemical demand for CO2 and prevention of excessive water loss. This view has been amended at the whole-plant level, where xylem hydraulics and sucrose transport efficiency in phloem appear to impose additional constraints on gas exchange. If such additional constraints impact stomatal opening and closure, then seed plants may have evolved coordinated photosynthetic-hydraulic-sugar transporting machinery that confers some competitive advantages in fluctuating environmental conditions. Thus, a stomatal optimization model that explicitly considers xylem hydraulics and maximum sucrose transport is developed to explore this coordination in the leaf-xylem-phloem system. The model is then applied to progressive drought conditions. The main findings from the model calculations are that (1) the predicted stomatal conductance from the conventional stomatal optimization theory at the leaf and the newly proposed models converge, suggesting a tight coordination in the leaf-xylem-phloem system; (2) stomatal control is mainly limited by the water supply function of the soil-xylem hydraulic system especially when the water flux through the transpiration stream is significantly larger than water exchange between xylem and phloem; (3) thus, xylem limitation imposed on the supply function can be used to differentiate species with different water use strategy across the spectrum of isohydric to anisohydric behavior

  13. Woody debris transport modelling by a coupled DE-SW approach

    NASA Astrophysics Data System (ADS)

    Persi, Elisabetta; Petaccia, Gabriella; Sibilla, Stefano

    2016-04-01

    The presence of wood in rivers is gaining more and more attention: on one side, the inclusion of woody debris in streams is emphasized for its ecological benefits; on the other hand, particular attention must be paid to its management, not to affect hydraulic safety. Recent events have shown that wood can be mobilized during floodings (Comiti et al. 2008, Lange and Bezzola 2006), aggravating inundations, in particular near urban areas. For this reason, the inclusion of woody debris influence on the prediction of flooded areas is an important step toward the reduction of hydraulic risk. Numerical modelling plays an important role to this purpose. Ruiz-Villanueva et al. (2014) use a two-dimensional numerical model to calculate the kinetics of cylindrical woody debris transport, taking into account also the hydrodynamic effects of wood. The model here presented couples a Discrete Element approach (DE) for the calculation of motion of a cylindrical log with the solution of the Shallow Water Equations (SW), in order to simulate woody debris transport in a two-dimensional stream. In a first step, drag force, added mass force and side force are calculated from flow and log velocities, assuming a reference area and hydrodynamic coefficients taken from literature. Then, the equations of dynamics are solved to model the planar roto-translation of the wooden cylinder. Model results and its physical reliability are clearly affected by the values of the drag and side coefficients, which in turn depend upon log submergence and angle towards the flow direction. Experimental studies to evaluate drag and side coefficients can be found for a submerged cylinder, with various orientations (Gippel et al. 1996; Hoang et al. 2015). To extend such results to the case of a floating (non-totally submerged) cylinder, the authors performed a series of laboratory tests whose outcomes are implemented in the proposed DE-SW model, to assess the effects of these values on the dynamic of woody

  14. Control of unidirectional transport of single-file water molecules through carbon nanotubes in an electric field.

    PubMed

    Su, Jiaye; Guo, Hongxia

    2011-01-25

    The transport of water molecules through nanopores is not only crucial to biological activities but also useful for designing novel nanofluidic devices. Despite considerable effort and progress that has been made, a controllable and unidirectional water flow is still difficult to achieve and the underlying mechanism is far from being understood. In this paper, using molecular dynamics simulations, we systematically investigate the effects of an external electric field on the transport of single-file water molecules through a carbon nanotube (CNT). We find that the orientation of water molecules inside the CNT can be well-tuned by the electric field and is strongly coupled to the water flux. This orientation-induced water flux is energetically due to the asymmetrical water-water interaction along the CNT axis. The wavelike water density profiles are disturbed under strong field strengths. The frequency of flipping for the water dipoles will decrease as the field strength is increased, and the flipping events vanish completely for the relatively large field strengths. Most importantly, a critical field strength E(c) related to the water flux is found. The water flux is increased as E is increased for E ≤ E(c), while it is almost unchanged for E > E(c). Thus, the electric field offers a level of governing for unidirectional water flow, which may have some biological applications and provides a route for designing efficient nanopumps.

  15. Coupled Reactive Transport Modeling of CO2 Injection in Mt. Simon Sandstone Formation, Midwest USA

    NASA Astrophysics Data System (ADS)

    Liu, F.; Lu, P.; Zhu, C.; Xiao, Y.

    2009-12-01

    CO2 sequestration in deep geological formations is one of the promising options for CO2 emission reduction. While several large scale CO2 injections in saline aquifers have shown to be successful for the short-term, there is still a lack of fundamental understanding on key issues such as CO2 storage capacity, injectivity, and security over multiple spatial and temporal scales that need to be addressed. To advance these understandings, we applied multi-phase coupled reactive mass transport modeling to investigate the fate of injected CO2 and reservoir responses to the injection into Mt. Simon Formation. We developed both 1-D and 2-D reactive transport models in a radial region of 10,000 m surrounding a CO2 injection well to represent the Mt. Simon sandstone formation, which is a major regional deep saline reservoir in the Midwest, USA. Supercritical CO2 is injected into the formation for 100 years, and the modeling continues till 10,000 years to monitor both short-term and long-term behavior of injected CO2 and the associated rock-fluid interactions. CO2 co-injection with H2S and SO2 is also simulated to represent the flue gases from coal gasification and combustion in the Illinois Basin. The injection of CO2 results in acidified zones (pH ~3 and 5) adjacent to the wellbore, causing progressive water-rock interactions in the surrounding region. In accordance with the extensive dissolution of authigenic K-feldspar, sequential precipitations of secondary carbonates and clay minerals are predicted in this zone. The vertical profiles of CO2 show fingering patte