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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. PMID:1750518

  2. Models of coupled salt and water transport across leaky epithelia.

    PubMed

    Weinstein, A M; Stephenson, J L

    1981-05-15

    A general formulation is presented for the verification of isotonic transport and for the assignment of a degree of osmotic coupling in any epithelial model. In particular, it is shown that the concentration of the transported fluid in the presence of exactly equal bathing media is, in general, not a sufficient calculation by which to decide the issue of isotonicity of transport. Within this framework, two epithelial models are considered: (1) A nonelectrolyte compartment model of the lateral intercellular space is presented along with its linearization about the condition of zero flux. This latter approximate model is shown to be useful in the estimation of deviation from isotonicity, intraepithelial solute polarization effects, and the capacity to transport water against a gradient. In the case of uphill water transport, some limitations of a model of fixed geometry are indicated and the advantage of modeling a compliant interspace is suggested. (2) A comprehensive model of cell and channel is described which includes the major electrolytes and the possible presence of intraepithelial gradients. The general approach to verification of isotonicity is illustrated for this numerical model. In addition, the insights about parameter dependence gained from the linear compartment model are shown to be applicable to understanding this large simulation. PMID:6264088

  3. Models for coupling of salt and water transport; Proximal tubular reabsorption in Necturus kidney.

    PubMed

    Sackin, H; Boulpaep, E L

    1975-12-01

    Models for coupling of salt and water transport are developed with two important assumptions appropriate for leaky epithelia. (a) The tight junction is permeable to both sale and water. (b) Active Na transport into the lateral speces is assumed to occur uniformly along the length of the channel. The proposed models deal specifically with the intraepithelial mechanism of proximal tubular resbsorption in the Necturus kidney although they have implications for epithelial transport in the gallbladder and small intestine as well. The first model (continuous version) is similar to the standing gradient model devised by Diamond and Bossert but used different boundary conditions. In contrast to Diamond and Bossert's model, the predicted concentration profiles are relatively flat with no sizable gradients along the interspace. The second model (compartment version) expands Curran's model of epithelial salt and water transport by including additional compartments and considering both electrical and chemical driving forces for individual Na and Cl ions as well as hydraulic and osmotic driving forces for water. In both models, ion and water fluxes are investigated as a function of the transport parameters. The behavior of the models is consistent with previously suggested mechanisms for the control of net transport, particularly during saline diuresis. Under all conditions the predicted ratio of net solute to solvent flux, or emergent concentration, deviates from exact isotonicity (except when the basement membrane has an appreciable salt reflection coefficient). However, the degree of hypertonicity may be small enough to be experimentally indistinguishable from isotonic transport. PMID:1104761

  4. 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.

  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. 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

  7. 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. PMID:20091162

  8. 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

  9. CTSPAC: MATHEMATICAL MODEL FOR COUPLED TRANSPORT OF WATER, SOLUTES, AND HEAT IN THE SOIL-PLANT-ATMOSPHERE CONTINUUM. VOLUME 1. MATHEMATICAL THEORY AND TRANSPORT CONCEPTS

    EPA Science Inventory

    The mathematical structure of the model consists of the coupling of a model for the transport through soils to a model for transport through plants. The coupled model describes uptake of water and solutes by plants from the soil solution. The rate of uptake is a function of the e...

  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. 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%. PMID:25489976

  13. Validation of water vapour transport in the tropical tropopause region in coupled Chemistry Climate Models

    NASA Astrophysics Data System (ADS)

    Kremser, S.; Rex, M.; Langematz, U.; Dameris, M.; Wohltmann, I.

    2008-06-01

    In this study backward trajectories from the tropical lower stratosphere were calculated for the Northern Hemisphere (NH) winters 1995-1996, 1997-1998 (El Niño) and 1998-1999 (La Niña) and summers 1996, 1997 and 1999 using both ERA-40 reanalysis data of the European Centre for Medium-Range Weather Forecast (ECMWF) and coupled chemistry climate model (CCM) data. The calculated trajectories were analyzed to determine the distribution of points where individual air masses encounter the minimum temperature and thus minimum water vapour mixing ratio during their ascent through the tropical tropopause layer (TTL) into the stratosphere. The geographical distribution of these dehydration points and the local conditions there determine the overall water vapour entry into the stratosphere. Results of two CCMs are presented: the ECHAM4.L39(DLR)/CHEM (hereafter: E39/C) from the German Aerospace Center (DLR) and the Freie Universität Berlin Climate Middle Atmosphere Model with interactive chemistry (hereafter: FUB-CMAM-CHEM). In the FUB-CMAM-CHEM model the minimum temperatures are overestimated by about 7 K in Northern Hemisphere (NH) winter as well as in NH summer, resulting in too high water vapour entry values compared to ERA-40. However, the geographical distribution of dehydration points is fairly reproduced for NH winter 1995-1996 and 1998-1999 and in all boreal summers. The distribution of dehydration points suggests an influence of the Indian monsoon upon the water vapour transport. The E39/C model displays a temperature bias of about +3 K. Hence, the minimum water vapour mixing ratios are higher relative to ERA-40. The geographical distribution of dehydration points is satisfactory in NH winter 1995-1996 and 1997-1998 with respect to ERA-40. The distribution is not reproduced for the NH winter 1998-1999 (La Niña event) compared to ERA-40. There is excessive mass flux through warm regions e.g. Africa, leading to excessive water vapour flux in the NH winter and

  14. 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.

  15. Delineating the extracellular water-accessible surface of the proton-coupled folate transporter.

    PubMed

    Duddempudi, Phaneendra Kumar; Goyal, Raman; Date, Swapneeta Sanjay; Jansen, Michaela

    2013-01-01

    The proton-coupled folate transporter (PCFT) was recently identified as the major uptake route for dietary folates in humans. The three-dimensional structure of PCFT and its detailed interplay with function remain to be determined. We screened the water-accessible extracellular surface of HsPCFT using the substituted-cysteine accessibility method, to investigate the boundaries between the water-accessible surface and inaccessible buried protein segments. Single-cysteines, engineered individually at 40 positions in a functional cysteine-less HsPCFT background construct, were probed for plasma-membrane expression in Xenopus oocytes with a bilayer-impermeant primary-amine-reactive biotinylating agent (sulfosuccinimidyl 6-(biotinamido) hexanoate), and additionally for water-accessibility of the respective engineered cysteine with the sulfhydryl-selective biotinylating agent 2-((biotinoyl)amino)ethyl methanethiosulfonate. The ratio between Cys-selective over amine-selective labeling was further used to evaluate three-dimensional models of HsPCFT generated by homology / threading modeling. The closest homologues of HsPCFT with a known experimentally-determined three-dimensional structure are all members of one of the largest membrane protein super-families, the major facilitator superfamily (MFS). The low sequence identity--14% or less--between HsPCFT and these templates necessitates experiment-based evaluation and model refinement of homology/threading models. With the present set of single-cysteine accessibilities, the models based on GlpT and PepTSt are most promising for further refinement. PMID:24205192

  16. Electric field-controlled water permeation coupled to ion transport through a nanopore

    NASA Astrophysics Data System (ADS)

    Dzubiella, J.; Allen, R. J.; Hansen, J.-P.

    2004-03-01

    We report molecular dynamics simulations of a generic hydrophobic nanopore connecting two reservoirs which are initially at different Na+ concentrations, as in a biological cell. The nanopore is impermeable to water under equilibrium conditions, but the strong electric field caused by the ionic concentration gradient drives water molecules in. The density and structure of water in the pore are highly field dependent. In a typical simulation run, we observe a succession of cation passages through the pore, characterized by approximately bulk mobility. These ion passages reduce the electric field, until the pore empties of water and closes to further ion transport, thus providing a possible mechanism for biological ion channel gating.

  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. Magnetically Coupled Transport System

    SciTech Connect

    Breshears, S.A.

    1999-01-26

    Throughout the DOE complex, materials are routinely transported within glovebox processing lines. Cylindrical product cans, crucibles, sample containers, tools, and waste products are all examples of items that are moved between equipment stations during glovebox operations. Traditional transport methods have included manual handling using tongs, chain and belt conveyors, carts with pull wires, and overhead hoists on monorails. These methods rely on hands-on operations and/or utilize high maintenance equipment located inside the gloveboxes, which can lead to high radiation exposure to personnel and can generate large amounts of radioactive waste. One innovative approach incorporates linear induction motors (LIMs) so that high maintenance items are located outside the gloveboxes, but LIMs produce heat, do not move smoothly over a wide range of velocities, and are not locked in position at zero velocity. Savannah River Technology Center (SRTC) engineers have developed and demonstrated a concept for a magnetically coupled transport system to transfer material within process lines and from line to line. This automated system significantly reduces hands-on operations. Linear actuators and lead screws provide smooth horizontal and vertical movement. Rare earth magnetic coupling technology allows the majority of the equipment to be located outside the glovebox, simplifying maintenance and minimizing radioactive waste.

  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. A bimodel climate response controlled by water vapor transport in a coupled ocean-atmosphere box model

    NASA Astrophysics Data System (ADS)

    Birchfield, G. Edward; Wang, Huaxiao; Wyant, Matthew

    1990-06-01

    The importance of the hydrological cycle as a controlling factor on the magnitude of the thermohaline circulation is illustrated in a simple one-hemisphere coupled ocean-atmosphere box model. The ocean model includes differential surface heating and evaporation, horizontal and vertical exchange of heat and salt between boxes, and a simply parameterized thermohaline circulation. Surface heat fluxes and evaporation are determined through the coupled ocean and energy balance atmosphere models which treat fluxes of long- and short-wave radiation and sensible and latent heat. Two parameters represent the most important physics: µ controls the magnitude of the thermohaline circulation; ɛ controls the strength of the hydrological cycle. For fixed µ, two regimes are distinguished. One, associated with small values of ɛ, has weak latitudinal water vapor transport in the atmosphere, a strong thermohaline circulation with sinking in high latitudes, upwelling in low latitudes, and strong latitudinal transport of heat by the ocean. The second regime for larger ɛ is characterized by strong latitudinal water vapor transport which, by reducing the surface salinity in high latitudes, shuts down the thermohaline circulation and has reduced ocean and net latitudinal heat transport. The bimodal response in the model is shown to be the consequence of a shift in the mechanism of supply of salt to the high-latitude surface ocean from predominantly thermohaline transport, a nonlinear process, to or from predominantly eddy mixing transport, a linear process. In climatological terms, the bimodality represents two distinct climate regimes, one with an active ocean meridional circulation and relatively warm ocean and atmosphere temperatures in high latitudes, and the other with a less active ocean circulation and an increased latitudinal temperature gradient in atmosphere and ocean. The regime with an active thermohaline circulation tends to be less stable than the other, exhibiting over

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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. PMID:24116510

  6. Water vapour transport in the tropical tropopause region in coupled Chemistry-Climate Models and ERA-40 reanalysis data

    NASA Astrophysics Data System (ADS)

    Kremser, Stefanie; Wohltmann, Ingo; Rex, Markus; Langematz, Ulrike; Dameris, Martin; Kunze, Markus

    2009-04-01

    In this study backward trajectories from the tropical lower stratosphere were calculated for the Northern Hemisphere (NH) winters 1995-1996, 1997-1998 (El Niño) and 1998-1999 (La Niña) and summers 1996, 1997 and 1999 using both ERA-40 reanalysis data of the European Centre for Medium-Range Weather Forecast (ECMWF) and coupled Chemistry-Climate Model (CCM) data. The calculated trajectories were analysed to determine the distribution of points where individual air masses encounter the minimum temperature and thus minimum water vapour mixing ratio during their ascent through the tropical tropopause layer (TTL) into the stratosphere. The geographical distribution of these dehydration points and the local conditions there determine the overall water vapour entry into the stratosphere. Results of two CCMs are presented: the ECHAM4.L39(DLR)/CHEM (hereafter: E39/C) from the German Aerospace Center (DLR) and the Freie Universität Berlin Climate Middle Atmosphere Model with interactive chemistry (hereafter: FUB-CMAM-CHEM). In the FUB-CMAM-CHEM model the minimum temperatures are overestimated by about 9 K in NH winter and about 3 K in NH summer, resulting in too high water vapour entry values compared to ERA-40. However, the geographical distribution of dehydration points is fairly similar to ERA-40 for NH winter 1995-1996 and 1998-1999. The distribution of dehydration points in the boreal summer 1996 suggests an influence of the Indian monsoon upon the water vapour transport. The E39/C model displays a temperature bias of about +5 K. Hence, the minimum water vapour mixing ratios are higher relative to ERA-40. The geographical distribution of dehydration points is fairly well in NH winter 1995-1996 and 1997-1998 with respect to ERA-40. The distribution is not reproduced for the NH winter 1998-1999 (La Niña event) compared to ERA-40. There is an excessive water vapour flux through warm regions e.g. Africa in the NH winter and summer. The possible influence of the Indian

  7. Coupled Fluid Energy Solute Transport

    Energy Science and Technology Software Center (ESTSC)

    1992-02-13

    CFEST is a Coupled Fluid, Energy, and Solute Transport code for the study of a multilayered, nonisothermal ground-water system. It can model discontinuous as well as continuous layers, time-dependent and constant source/sinks, and transient as well as steady-state flow. The finite element method is used for analyzing isothermal and nonisothermal events in a confined aquifer system. Only single-phase Darcian flow is considered. In the Cartesian coordinate system, flow in a horizontal plane, in a verticalmore » plane, or in a fully three-dimensional region can be simulated. An option also exists for the axisymmetric analysis of a vertical cross section. The code employs bilinear quadrilateral elements in all two dimensional analyses and trilinear quadrilateral solid elements in three dimensional simulations. The CFEST finite element formulation can approximate discontinuities, major breaks in slope or thickness, and fault zones in individual hydrogeologic units. The code accounts for heterogeneity in aquifer permeability and porosity and accommodates anisotropy (collinear with the Cartesian coordinates). The variation in the hydraulic properties is described on a layer-by-layer basis for the different hydrogeologic units. Initial conditions can be prescribed hydraulic head or pressure, temperature, or concentration. CFEST can be used to support site, repository, and waste package subsystem assessments. Some specific applications are regional hydrologic characterization; simulation of coupled transport of fluid, heat, and salinity in the repository region; consequence assessment due to natural disruption or human intrusion scenarios in the repository region; flow paths and travel-time estimates for transport of radionuclides; and interpretation of well and tracer tests.« less

  8. Micro-Scale Simulation of Water Transport in Porous Media Coupled with Phase Change

    NASA Astrophysics Data System (ADS)

    Etemad, Sahand; Behrang, Arash; Mohammadmoradi, Peyman; Hejazi, Hossein; Kantzas, Apostolos

    2015-11-01

    Sub-pore scale modeling of flow in porous media is gaining momentum. The concept of Digital Core Analysis deals with measurements of virtual core and the purpose of such modeling is to replace conventional and special core analysis when the latter are not feasible. Single phase flow phenomena are nowadays fairly easy to model given a good representation of the porous medium by its digital counterpart. Two phase flow modeling has proven more difficult to represent due to the complexities introduced by the insert of interfaces. These problems were at least partially overcome by the implementation of the ``Volume of Fluid'' method. OpenFOAM is the CFD package of choice in this work. The aforementioned approach is currently being extended in the modeling of phase change within a porous medium. Surface roughness is introduced by the incorporation of wedges of variable density and amplitude on the pore surface. A further introduced complication is that the individual grains are of different mineralogy and thus of different wettability. The problem of steam condensation in such media is addressed. It is observed that steam condenses first in the smallest of wedges, which act a nucleation sites. Water spreads on water-wet surfaces. Snap-off is observed in several cases leading to temporary trapping of vapor. Grid size effects are also addressed. The application of this modeling effort is the condensation of steam in thermal recovery methods.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  10. 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.

  11. 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. PMID:25428855

  12. 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

  13. 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.

  14. 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

  15. Mammalian ion-coupled solute transporters.

    PubMed Central

    Hediger, M A; Kanai, Y; You, G; Nussberger, S

    1995-01-01

    Active transport of solutes into and out of cells proceeds via specialized transporters that utilize diverse energy-coupling mechanisms. Ion-coupled transporters link uphill solute transport to downhill electrochemical ion gradients. In mammals, these transporters are coupled to the co-transport of H+, Na+, Cl- and/or to the countertransport of K+ or OH-. By contrast, ATP-dependent transporters are directly energized by the hydrolysis of ATP. The development of expression cloning approaches to select cDNA clones solely based on their capacity to induce transport function in Xenopus oocytes has led to the cloning of several ion-coupled transporter cDNAs and revealed new insights into structural designs, energy-coupling mechanisms and physiological relevance of the transporter proteins. Different types of mammalian ion-coupled transporters are illustrated by discussing transporters isolated in our own laboratory such as the Na+/glucose co-transporters SGLT1 and SGLT2, the H(+)-coupled oligopeptide transporters PepT1 and PepT2, and the Na(+)- and K(+)-dependent neuronal and epithelial high affinity glutamate transporter EAAC1. Most mammalian ion-coupled organic solute transporters studied so far can be grouped into the following transporter families: (1) the predominantly Na(+)-coupled transporter family which includes the Na+/glucose co-transporters SGLT1, SGLT2, SGLT3 (SAAT-pSGLT2) and the inositol transporter SMIT, (2) the Na(+)- and Cl(-)-coupled transporter family which includes the neurotransmitter transporters of gamma-amino-butyric acid (GABA), serotonin, dopamine, norepinephrine, glycine and proline as well as transporters of beta-amino acids, (3) the Na(+)- and K(+)-dependent glutamate/neurotransmitter family which includes the high affinity glutamate transporters EAAC1, GLT-1, GLAST, EAAT4 and the neutral amino acid transporters ASCT1 and SATT1 reminiscent of system ASC and (4) the H(+)-coupled oligopeptide transporter family which includes the intestinal H

  16. 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.

  17. 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.

  18. COUPLED TRANSPORT SYSTEMS FOR CONTROL OF HEAVY METAL POLLUTANTS

    EPA Science Inventory

    This report describes a process for separating and concentrating heavy metals from electroplating rinse waters. Metal ions can be 'chemically pumped' across a coupled transport membrane against large concentration gradients by allowing the counterflow of a coupled ion such as hyd...

  19. 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.

  20. 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.

  1. 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.

  2. 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. PMID:19031873

  3. 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.

  4. 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.

  5. 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.

  6. 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)

  7. 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.

  8. 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…

  9. 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.

  10. Water Transport in Yeasts.

    PubMed

    Sabir, Farzana; Prista, Catarina; Madeira, Ana; Moura, Teresa; Loureiro-Dias, Maria C; Soveral, Graça

    2016-01-01

    Water moves across membranes through the lipid bilayer and through aquaporins, in this case in a regulated manner. Aquaporins belong to the MIP superfamily and two subfamilies are represented in yeasts: orthodox aquaporins considered to be specific water channels and aquaglyceroporins (heterodox aquaporins). In Saccharomyces cerevisiae genome, four aquaporin isoforms were identified, two of which are genetically close to orthodox aquaporins (ScAqy1 and ScAqy2) and the other two are more closely related to the aquaglyceroporins (ScFps1 and ScAqy3). Advances in the establishment of water channels structure are reviewed in this chapter in relation with the mechanisms of selectivity, conductance and gating. Aquaporins are important for key aspects of yeast physiology. They have been shown to be involved in sporulation, rapid freeze-thaw tolerance, osmo-sensitivity, and modulation of cell surface properties and colony morphology, although the underlying exact mechanisms are still unknown. PMID:26721272

  11. 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.

  12. 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.

  13. 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. PMID:24224741

  14. Influence of surfactants on unsaturated water flow and solute transport

    NASA Astrophysics Data System (ADS)

    Karagunduz, Ahmet; Young, Michael H.; Pennell, Kurt D.

    2015-04-01

    Surfactants can reduce soil water retention by changing the surface tension of water and the contact angle between the liquid and solid phases. As a result, water flow and solute transport in unsaturated soil may be altered in the presence of surfactants. In this study, the effects of a representative nonionic surfactant, Triton X-100, on coupled water flow and nonreactive solute transport during unsaturated flow conditions were evaluated. Batch reactor experiments were conducted to measure the surfactant sorption characteristics, while unsaturated transport experiments were performed in columns packed with 40-270 mesh Ottawa sand at five initial water contents. Following the introduction of surfactant solution, the rate of water percolation through the sand increased; however, this period of rapid water drainage was followed by decreased water percolation due to the reduction in soil water content and the corresponding decrease in unsaturated hydraulic conductivity behind the surfactant front. The observed changes in water percolation occurred sequentially, and resulted in faster nonreactive solute transport than was observed in the absence of surfactant. A one-dimensional mathematical model accurately described coupled water flow, surfactant, and solute transport under most experimental conditions. Differences between model predictions and experimental data were observed in the column study performed at the lowest water content (0.115 cm3/cm3), which was attributed to surfactant adsorption at the air-water interface. These findings demonstrate the potential influence of surfactants additives on unsaturated water flow and solute transport in soils, and demonstrate a methodology to couple these processes in a predictive modeling tool.

  15. Water transport into epoxy resins and composites

    SciTech Connect

    Tsou, H.S.

    1987-01-01

    The processing-property relationships were established for the epoxy system of tetraglycidyl 4,4'-diaminodiphenyl methane (TGDDM) cured with diaminodiphenyl sulfone (DDS). The TGDDM-DDS epoxy system was selected for analysis as the ensuing polymer matrix is most common in high-performance fiber-reinforced epoxy composites. Experiments on water transport in epoxy resins with varying compositions were performed and a relaxation-coupled transport behavior was observed in these epoxy resins. By post-curing vitrified epoxy resins, the additional free volume usually measured in them was removed and maximum water uptake was reduced. Since epoxy resins were in a quasi-equilibrium glassy state after the post-cure, Fick's law with a constant diffusion coefficient could adequately describe the water sorption behavior. A network formation model based on the branching theory was developed, taking into account the difference in reactivities of primary and secondary amines and the etherification reaction. Using this network formation model, water uptake in post-cured epoxy resins was found to be proportional to tertiary amine concentration.

  16. SiSPAT-Isotope, a coupled heat, water and stable isotope (HDO and H 218O) transport model for bare soil. Part II. Evaluation and sensitivity tests using two laboratory data sets

    NASA Astrophysics Data System (ADS)

    Braud, I.; Bariac, T.; Vauclin, M.; Boujamlaoui, Z.; Gaudet, J. P.; Biron, Ph.; Richard, P.

    2005-07-01

    Stable water isotopes are tracers of water movement within the soil-vegetation-atmosphere system. They have the potential for a better understanding of water vapour transport within soils, evaporation and transpiration processes. To better understand those potentialities and possible lack of knowledge, a coupled heat-water and stable isotope transport model, called SiSPAT-Isotope was developed for bare soil. We presented the theoretical basis of the model in the first part of the paper, including a first validation of the likelihood of model results and a comparison with existing analytical solutions. In this companion paper, we go a step further by comparing the model results with two data sets collected on laboratory columns. In both cases, five soil columns were saturated and let drying during 173 and 253 days, respectively. At selected dates, one of the column was cut into slices and analysed to determine the volumetric water content, the deuterium and oxygen 18 concentrations profiles. The first data set was acquired on disturbed soil columns. The second one was collected on non-disturbed soil columns and it included a complete monitoring of atmospheric variables. It was not the case for the first one and a sensitivity analysis of model results to the air humidity was performed, showing its large influence on surface isotope concentrations. For both data sets, we also conducted a sensitivity analysis to the formulation of the kinetic fractionation factor, conditioning the resistance to isotope transport between the soil surface and the atmosphere, and to the value of soil tortuosity. The results showed that the model was able to reproduce the behaviour of the observed concentration profiles. A fair agreement between measured and calculated values was obtained for all profiles for the disturbed soil. Near surface concentrations were in general overestimated for the undisturbed soil, raising the question of possible influence of immobile water on concentrations

  17. 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

  18. 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.

  19. The lateral intercellular space as osmotic coupling compartment in isotonic transport.

    PubMed

    Larsen, E H; Willumsen, N J; Møbjerg, N; Sørensen, J N

    2009-01-01

    Solute-coupled water transport and isotonic transport are basic functions of low- and high-resistance epithelia. These functions are studied with the epithelium bathed on the two sides with physiological saline of similar composition. Hence, at transepithelial equilibrium water enters the epithelial cells from both sides, and with the reflection coefficient of tight junction being larger than that of the interspace basement membrane, all of the water leaves the epithelium through the interspace basement membrane. The common design of transporting epithelia leads to the theory that an osmotic coupling of water absorption to ion flow is energized by lateral Na(+)/K(+) pumps. We show that the theory accounts quantitatively for steady- and time dependent states of solute-coupled fluid uptake by toad skin epithelium. Our experimental results exclude definitively three alternative theories of epithelial solute-water coupling: stoichiometric coupling at the molecular level by transport proteins like SGLT1, electro-osmosis and a 'junctional fluid transfer mechanism'. Convection-diffusion out of the lateral space constitutes the fundamental problem of isotonic transport by making the emerging fluid hypertonic relative to the fluid in the lateral intercellular space. In the Na(+) recirculation theory the 'surplus of solutes' is returned to the lateral space via the cells energized by the lateral Na(+)/K(+) pumps. We show that this theory accounts quantitatively for isotonic and hypotonic transport at transepithelial osmotic equilibrium as observed in toad skin epithelium in vitro. Our conclusions are further developed for discussing their application to solute-solvent coupling in other vertebrate epithelia such as small intestine, proximal tubule of glomerular kidney and gallbladder. Evidence is discussed that the Na(+) recirculation theory is not irreconcilable with the wide range of metabolic cost of Na(+) transport observed in fluid-transporting epithelia. PMID:18983444

  20. Electrogenicity of Na(+)-coupled bile acid transporters.

    PubMed Central

    Weinman, S. A.

    1997-01-01

    The Na(+)-bile acid cotransporters NTCP and ASBT are largely responsible for the Na(+)-dependent bile acid uptake in hepatocytes and intestinal epithelial cells, respectively. This review discusses the experimental methods available for demonstrating electrogenicity and examines the accumulating evidence that coupled transport by each of these bile acid transporters is electrogenic. The evidence includes measurements of transport-associated currents by patch clamp electrophysiological techniques, as well as direct measurement of fluorescent bile acid transport rates in whole cell patch clamped, voltage clamped cells. The results support a Na+:bile acid coupling stoichiometry of 2:1. PMID:9626753

  1. CHARACTERIZING COUPLED CHARGE TRANSPORT WITH MULTISCALE MOLECULAR DYNAMICS

    SciTech Connect

    Swanson, Jessica

    2011-08-31

    This is the final progress report for Award DE-SC0004920, entitled 'Characterizing coupled charge transport with multi scale molecular dynamics'. The technical abstract will be provided in the uploaded report.

  2. Implications of Lagrangian transport for coupled chemistry-climate simulations

    NASA Astrophysics Data System (ADS)

    Stenke, A.; Dameris, M.; Grewe, V.; Garny, H.

    2008-10-01

    For the first time a purely Lagrangian transport algorithm is applied in a fully coupled chemistry-climate model (CCM). We use the Lagrangian scheme ATTILA for the transport of water vapour, cloud water and chemical trace species in the ECHAM4.L39(DLR)/CHEM (E39C) CCM. The advantage of the Lagrangian approach is that it is numerically non-diffusive and therefore maintains steeper and more realistic gradients than the operational semi-Lagrangian transport scheme. In case of radiatively active species changes in the simulated distributions feed back to model dynamics which in turn affect the modelled transport. The implications of the Lagrangian transport scheme for stratospheric model dynamics and tracer distributions in the upgraded model version E39C-ATTILA (E39C-A) are evaluated by comparison with observations and results of the E39C model with the operational semi-Lagrangian advection scheme. We find that several deficiencies in stratospheric dynamics in E39C seem to originate from a pronounced modelled wet bias and an associated cold bias in the extra-tropical lowermost stratosphere. The reduction of the simulated moisture and temperature bias in E39C-A leads to a significant advancement of stratospheric dynamics in terms of the mean state as well as annual and interannual variability. As a consequence of the favourable numerical characteristics of the Lagrangian transport scheme and the improved model dynamics, E39C-A generally shows more realistic stratospheric tracer distributions: Compared to E39C high stratospheric chlorine (Cly) concentrations extend further downward and agree now well with analyses derived from observations. Therefore E39C-A realistically covers the altitude of maximum ozone depletion in the stratosphere. The location of the ozonopause, i.e. the transition from low tropospheric to high stratospheric ozone values, is also clearly improved in E39C-A. Furthermore, the simulated temporal evolution of stratospheric Cly in the past is

  3. 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

  4. Flux coupling in the human serotonin transporter.

    PubMed Central

    Adams, Scott V; DeFelice, Louis J

    2002-01-01

    The serotonin (5-hydroxytryptamine; 5HT) transporter (SERT) catalyzes the movement of 5HT across cellular membranes. In the brain, SERT clears 5HT from extracellular spaces, modulating the strength and duration of serotonergic signaling. SERT is also an important pharmacological target for antidepressants and drugs of abuse. We have studied the flux of radio-labeled 5HT through the transporter stably expressed in HEK-293 cells. Analysis of the time course of net transport, the equilibrium 5HT gradient sustained, and the ratio of the unidirectional influx to efflux of 5HT indicate that mechanistically, human SERT functions as a 5HT channel rather than a classical carrier. This is especially apparent at relatively high [5HT](out) (> or =10 microM), but is not restricted to this regime of external 5HT. PMID:12496095

  5. Flux coupling in the human serotonin transporter.

    PubMed

    Adams, Scott V; DeFelice, Louis J

    2002-12-01

    The serotonin (5-hydroxytryptamine; 5HT) transporter (SERT) catalyzes the movement of 5HT across cellular membranes. In the brain, SERT clears 5HT from extracellular spaces, modulating the strength and duration of serotonergic signaling. SERT is also an important pharmacological target for antidepressants and drugs of abuse. We have studied the flux of radio-labeled 5HT through the transporter stably expressed in HEK-293 cells. Analysis of the time course of net transport, the equilibrium 5HT gradient sustained, and the ratio of the unidirectional influx to efflux of 5HT indicate that mechanistically, human SERT functions as a 5HT channel rather than a classical carrier. This is especially apparent at relatively high [5HT](out) (> or =10 microM), but is not restricted to this regime of external 5HT. PMID:12496095

  6. Modeling of coupled geochemical and transport processes: An overview

    SciTech Connect

    Carnahan, C.L.

    1989-10-01

    Early coupled models associated with fluid flow and solute transport have been limited by assumed conditions of constant temperature, fully saturated fluid flow, and constant pore fluid velocity. Developments including coupling of chemical reactions to variable fields of temperature and fluid flow have generated new requirements for experimental data. As the capabilities of coupled models expand, needs are created for experimental data to be used for both input and validation. 25 refs.

  7. Visualizing the kinetic power stroke that drives proton-coupled Zn(II) transport

    PubMed Central

    Gupta, Sayan; Chai, Jin; Cheng, Jie; D'Mello, Rhijuta; Chance, Mark R.; Fu, Dax

    2014-01-01

    The proton gradient is a principal energy source for respiration-dependent active transport, but the structural mechanisms of proton-coupled transport processes are poorly understood. YiiP is a proton-coupled zinc transporter found in the cytoplasmic membrane of E. coli, and the transport-site of YiiP receives protons from water molecules that gain access to its hydrophobic environment and transduces the energy of an inward proton gradient to drive Zn(II) efflux1,2. This membrane protein is a well characterized member3-7 of the protein family of cation diffusion facilitators (CDFs) that occurs at all phylogenetic levels8-10. X-ray mediated hydroxyl radical labeling of YiiP and mass spectrometric analysis showed that Zn(II) binding triggered a highly localized, all-or-none change of water accessibility to the transport-site and an adjacent hydrophobic gate. Millisecond time-resolved dynamics revealed a concerted and reciprocal pattern of accessibility changes along a transmembrane helix, suggesting a rigid-body helical reorientation linked to Zn(II) binding that triggers the closing of the hydrophobic gate. The gated water access to the transport-site enables a stationary proton gradient to facilitate the conversion of zinc binding energy to the kinetic power stroke of a vectorial zinc transport. The kinetic details provide energetic insights into a proton-coupled active transport reaction. PMID:25043033

  8. 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.

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

    PubMed

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

    1996-12-01

    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

  10. 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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  12. 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

  13. 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.

  14. Hydraulic Transport of Ice-Water Mixtures

    NASA Astrophysics Data System (ADS)

    Fujita, Toshihiko

    When an ice thermal storage system is introduced into a district cooling system,the hydraulic ice transport system must have an advantage over a conventional water transport system in saving pipe sizes and pumping powers. Referring to the literature providing direct information on the hydraulic transport of ice-water mixtures,the author comments on the following subjects : •Definitions of an ice packing factor. • The capacity of heat transported with ice-water mixtures. • District distribution system. • Flow patterns in ice-water two-phase flow in straight pipes. • General expressions for pressure losses in solid-liquid two-phase flow. • The characteristics of pressure losses in ice-water two-phase flow. •Choking phenomena in channels.

  15. Plant water relations I: uptake and transport

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  16. 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.

  17. Modeling Reactive Transport in Coupled Groundwater-Conduit Systems

    NASA Astrophysics Data System (ADS)

    Spiessl, S. M.; Sauter, M.; Zheng, C.; Viswanathan, H. S.

    2002-05-01

    Modeling reactive transport in coupled groundwater-conduit systems requires consideration of two transport time scales in the flow and transport models. Consider for example a subsurface mine consisting of a network of highly conductive shafts, drifts or ventilation raises (i.e., conduits) within the considerably less permeable ore material (i.e., matrix). In the conduits, potential contaminants can travel much more rapidly than in the background aquifer (matrix). Since conduits cannot necessarily be regarded as a continuum, double continuum models are only of limited use for simulation of contaminant transport in such coupled groundwater-conduit systems. This study utilizes a "hybrid" flow and transport model in which contaminants can in essence be transported at a slower time scale in the matrix and at a faster time scale in the conduits. The hybrid flow model uses an approach developed by Clemens et al. (1996), which is based on the modelling of flow in a discrete pipe network, coupled to a continuum representing the low-permeability inter-conduit matrix blocks. Laminar or turbulent flow can be simulated in the different pipes depending on the flow conditions in the model domain. The three-dimensional finite-difference groundwater flow model MODFLOW (Harbaugh and McDonald, 1996) is used to simulate flow in the continuum. Contaminant transport within the matrix is simulated with a continuum approach using the three-dimensional multi-species solute transport model MT3DMS (Zheng and Wang, 1999), while that in the conduit system is simulated with a one-dimensional advective transport model. As a first step for reactive transport modeling in such systems, only equilibrium reactions among multiple species are considered by coupling the hybrid transport model to a geochemical speciation package. An idealized mine network developed by Viswanathan and Sauter (2001) is used as a test problem in this study. The numerical experiment is based on reference date collected from

  18. Isotonic water transport in secretory epithelia.

    PubMed

    Swanson, C H

    1977-01-01

    The model proposed by Diamond and Bossert [1] for isotonic water transport has received wide acceptance in recent years. It assumes that the local driving force for water transport is a standing osmotic gradient produced in the lateral intercellular spaces of the epithelial cell layer by active solute transport. While this model is based on work done in absorptive epithelia where the closed to open direction of the lateral space and the direction of net transport are the same, it has been proposed that the lateral spaces could also serve as the site of the local osmotic gradients for water transport in secretory epithelia, where the closed to open direction of the lateral space and net transport are opposed, by actively transporting solute out of the space rather than into it. Operation in the backward direction, however, requires a lower than ambient hydrostatic pressure within the lateral space which would seem more likely to cause the space to collapse with loss of function. On the other hand, most secretory epithelia are characterized by transport into a restricted ductal system which is similar to the lateral intercellular space in the absorptive epithelia in that its closed to open direction is the same as that of net transport. In vitro micropuncture studies on the exocrine pancreas of the rabbit indicate the presence of a small but statistically significant increase in juice osmolality, 6 mOsm/kg H(2)O, at the site of electrolyte and water secretion in the smallest extralobular ducts with secretin stimulation which suggests that the ductal system in the secretory epithelia rather than the lateral intercellular space is the site of the local osmotic gradients responsible for isotonic water transport. PMID:331693

  19. 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.

  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. 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.

  2. Charge transport in strongly coupled quantum dot solids

    NASA Astrophysics Data System (ADS)

    Kagan, Cherie R.; Murray, Christopher B.

    2015-12-01

    The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design.

  3. Wentzel-Bardeen singularity in coupled Luttinger liquids: Transport properties

    SciTech Connect

    Martin, T.

    1994-08-26

    The recent progress on 1 D interacting electrons systems and their applications to study the transport properties of quasi one dimensional wires is reviewed. We focus on strongly correlated elections coupled to low energy acoustic phonons in one dimension. The exponents of various response functions are calculated, and their striking sensitivity to the Wentzel-Bardeen singularity is discussed. For the Hubbard model coupled to phonons the equivalent of a phase diagram is established. By increasing the filling factor towards half filling the WB singularity is approached. This in turn suppresses antiferromagnetic fluctuations and drives the system towards the superconducting regime, via a new intermediate (metallic) phase. The implications of this phenomenon on the transport properties of an ideal wire as well as the properties of a wire with weak or strong scattering are analyzed in a perturbative renormalization group calculation. This allows to recover the three regimes predicted from the divergence criteria of the response functions.

  4. Transport Properties in Superconducting Wires Coupled to Ferromagnetic Leads

    NASA Astrophysics Data System (ADS)

    Chen, Qiao; Zhang, Ya-Min; Xu, H. Q.; Xu, Ning

    2016-02-01

    We investigate the transport properties of a pair of Majorana bound states in both serial configuration and T-shape configuration with ferromagnetic leads. By using a non-equilibrium Green's function method, the formula of current and shot noise are obtained. The numerical results show that the coupling between the Majorana bounds states at the ends of a wire can be tuned by the polarization P and polarization angle θ intimately in serial configuration. However, this coupling in T-shape configuration is only affected by ferromagnetic leads faintly. In addition, the Fano factor in both configurations is influenced by the polarization P and polarization angle θ intimately at low bias region. Because of the different transport mechanisms, the serial configuration and T-shape configuration show sub-Poissonian and super-Poissonian shot noise at low bias, respectively.

  5. The proton-coupled folate transporter: physiological and pharmacological roles.

    PubMed

    Zhao, Rongbao; Goldman, I David

    2013-12-01

    Recent studies have identified the proton-coupled folate transporter (PCFT) as the mechanism by which folates are absorbed across the apical brush-border membrane of the small intestine and across the basolateral membrane of the choroid plexus into the cerebrospinal fluid. Both processes are defective when there are loss-of-function mutations in this gene as occurs in the autosomal recessive disorder hereditary folate malabsorption. Because this transporter functions optimally at low pH, antifolates are being developed that are highly specific for PCFT in order to achieve selective delivery to malignant cells within the acidic environment of solid tumors. PCFT has a spectrum of affinities for folates and antifolates that narrows and increases at low pH. Residues have been identified that play a role in folate and proton binding, proton coupling, and oscillation of the carrier between its conformational states. PMID:24383099

  6. 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.

  7. 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.

  8. Current density fluctuations, nonlinear coupling, and transport in MST

    SciTech Connect

    Prager, S.C.; Almagri, A.F.; Assadi, S.; Cekic, M.; Chapman, B.E.; Crocker, N.; Den Hartog, D.J.; Dexter, R.N.; Fiksel, G.; Fonck, R.J.; Henry, J.S.; Hokin, S.A.; Holly, D.J.; Ji, H.; Rempel, T.D.; Sarff, J.S.; Scime, E.; Shen, W.; Sidikman, K.L.; Sprott, J.C.; Stoneking, M.R.; Watts, C.

    1992-09-01

    New information on magnetic fluctuations and transport in toroidal devices has been obtained in the MST reversed field pinch through measurement of nonlinear coupling of three waves in k-space, and measurement of current density fluctuations. Measurements of nonlinear coupling of magnetic fluctuations reveals that (1) two poloidal mode number m = 1 modes couple strongly to an m = 2 mode, (2) toroidal mode coupling is broad extending up to n = 20, (3) these features agree with predictions for tearing fluctuations from a nonlinear MHD code, (4) during a sawtooth crash the number of modes involved in nonlinear interactions increases dramatically and the k-spectrum broadens simultaneously. Measurements of current density fluctuations over the outer 20% of the minor radius reveal that (1) low frequency fluctuations are consistent with tearing modes, (2) high frequency fluctuations are localized turbulence which maintains resonance with the equilibrium field as q changes with radius, (3) particle transport from magnetic fluctuations is ambipolar (i.e., <{delta}j{sub {parallel}}B{sub r}> = O).

  9. 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.

  10. An exploration of coupled surface-subsurface solute transport in a fully integrated catchment model

    NASA Astrophysics Data System (ADS)

    Liggett, Jessica E.; Partington, Daniel; Frei, Sven; Werner, Adrian D.; Simmons, Craig T.; Fleckenstein, Jan H.

    2015-10-01

    Coupling surface and subsurface water flow in fully integrated hydrological codes is becoming common in hydrological research; however, the coupling of surface-subsurface solute transport has received much less attention. Previous studies on fully integrated solute transport focus on small scales, simple geometric domains, and have not utilised many different field data sources. The objective of this study is to demonstrate the inclusion of both flow and solute transport in a 3D, fully integrated catchment model, utilising high resolution observations of dissolved organic carbon (DOC) export from a wetland complex during a rainfall event. A sensitivity analysis is performed to span a range of transport conditions for the surface-subsurface boundary (e.g. advective exchange only, advection plus diffusion, advection plus full mechanical dispersion) and subsurface dispersivities. The catchment model captures some aspects of observed catchment behaviour (e.g. solute discharge at the catchment outlet, increasing discharge from wetlands with increased stream discharge, and counter-clockwise concentration-discharge relationships), although other known behaviours are not well represented in the model (e.g. slope of concentration-discharge plots). Including surface-subsurface solute transport aids in evaluating internal model processes, however there are challenges related to the influence of dispersion across the surface-subsurface interface, and non-uniqueness of the solute transport solution. This highlights that obtaining solute field data is especially important for constraining integrated models of solute transport.

  11. 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.

  12. HEAT AND WATER TRANSPORT IN A POLYMER ELECTROLYTE FUEL CELL

    SciTech Connect

    Mukherjee, Partha P

    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 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.

  13. Coupled polaronic and ion transport in nanocrystalline metal oxide electrodes

    NASA Astrophysics Data System (ADS)

    Rosso, Kevin

    2012-02-01

    We report new computational methods and fundamental understanding in the dynamics of coupled charge and ion transport in nanoscale metal oxides. The methods attack the multi-scale problem of simulating the collective diffusivities of ions and charge compensating e-/h+ carriers in single crystal particles, across particle-particle grain boundaries, and through networks of grains for select systems. Methods include embedded quantum mechanical clusters at the DFT and MP2 levels of theory for atomic-scale polaronic and ion transport kinetics, classical DFT-based free energy calculations for grain-scale conductivity in the framework of the Poisson-Nernst-Planck formalism, and phase field simulation of charged particle diffusivity for conductivity at the grain network scale. This combination of approaches is one of a kind in terms of its multi-scale range, scaling, and computational efficiency. We are presently focused on coupled electron and Li+ ion transport in polymorphs of TiO2, and also in mixed valence spinel oxides, for electrode conductivity optimization and improving energy storage materials performance for Li+ batteries.

  14. 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.

  15. 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

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

    PubMed

    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

  17. 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

  18. Energy-coupled outer membrane transport proteins and regulatory proteins.

    PubMed

    Braun, Volkmar; Endriss, Franziska

    2007-06-01

    FhuA and FecA are two examples of energy-coupled outer membrane import proteins of gram-negative bacteria. FhuA transports iron complexed by the siderophore ferrichrome and serves as a receptor for phages, a toxic bacterial peptide, and a toxic protein. FecA transports diferric dicitrate and regulates transcription of an operon encoding five ferric citrate (Fec) transport genes. Properties of FhuA mutants selected according to the FhuA crystal structure are described. FhuA mutants in the TonB box, the hatch, and the beta-barrel are rather robust. TonB box mutants in FhuA FecA, FepA, Cir, and BtuB are compared; some mutations are suppressed by mutations in TonB. Mutant studies have not revealed a ferrichrome diffusion pathway, and tolerance to mutations in the region linking the TonB box to the hatch does not disclose a mechanism for how energy transfer from the cytoplasmic membrane to FhuA changes the conformation of FhuA such that bound substrates are released, the pore is opened, and substrates enter the periplasm, or how surface loops change their conformation such that TonB-dependent phages bind irreversibly and release their DNA into the cells. The FhuA and FecA crystal structures do not disclose the mechanism of these proteins, but they provide important information for specific functional studies. FecA is also a regulatory protein that transduces a signal from the cell surface into the cytoplasm. The interacting subdomains of the proteins in the FecA --> FecR --> FecI --> RNA polymerase signal transduction pathway resulting in fecABCDE transcription have been determined. Energy-coupled transporters transport not only iron and vitamin B12, but also other substrates of very low abundance such as sugars across the outer membrane; transcription regulation of the transport genes may occur similarly to that of the Fec transport genes. PMID:17370038

  19. Isothermal titration calorimetry of ion-coupled membrane transporters

    PubMed Central

    SeCheol, Oh

    2015-01-01

    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. PMID:25676707

  20. Strain engineering water transport in graphene nanochannels.

    PubMed

    Xiong, Wei; Liu, Jefferson Zhe; Ma, Ming; Xu, Zhiping; Sheridan, John; Zheng, Quanshui

    2011-11-01

    Using equilibrium and nonequilibrium molecular dynamic simulations, we found that engineering the strain on the graphene planes forming a channel can drastically change the interfacial friction of water transport through it. There is a sixfold change of interfacial friction stress when the strain changes from -10% to 10%. Stretching the graphene walls increases the interfacial shear stress, while compressing the graphene walls reduces it. Detailed analysis of the molecular structure reveals the essential roles of the interfacial potential energy barrier and the structural commensurateness between the solid walls and the first water layer. Our results suggest that the strain engineering is an effective way of controlling the water transport inside nanochannels. The resulting quantitative relations between shear stress and slip velocity and the understanding of the molecular mechanisms will be invaluable in designing graphene nanochannel devices. PMID:22181520

  1. 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.

  2. 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

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

    NASA Astrophysics Data System (ADS)

    Kroener, E.

    2015-12-01

    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 same 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 presen 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 experiments the water flow in the rhizosphere is affected by the concentration distribution of mucilage.

  4. 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.

  5. Trapping and transport of indirect excitons in coupled quantum wells

    NASA Astrophysics Data System (ADS)

    Wuenschell, Jeffrey K.

    Spatially indirect excitons are optically generated composite bosons with a radiative lifetime sufficient to reach thermal equilibrium. This work explores the physics of indirect excitons in coupled quantum wells in the GaAs/AlGaAs system, specifically in the low-temperature, high-density regime. Particular attention is paid to a technique whereby a spatially inhomogeneous strain field is used as a trapping potential. In the process of modeling the trapping profile in wide quantum wells, dramatic effects due to intersubband coupling were observed at high strain. Experimentally, this regime coincides with the abrupt appearance of a dark population of indirect excitons at trap center, an effect originally suspected to be related to Bose-Einstein condensation. Here, the role of band mixing due to the strain-induced distortion of the crystal symmetry will be explored in detail in the context of this effect. Experimental studies presented here and in the literature suggest that Bose-Einstein condensation in indirect exciton systems may be difficult to detect with optical means (e.g., coherence measurements, momentum-space narrowing), possibly due to the strong dipole interaction between indirect excitons. Due to similarities between this system and liquid helium, it may be more fruitful to look for transport-related signatures of condensation, such as super fluidity. Here, a method for performing transport measurements on optically generated indirect excitons is also outlined and preliminary results are presented.

  6. Diagnostics for transport phenomena in strongly coupled dusty plasmas

    NASA Astrophysics Data System (ADS)

    Goree, J.; Liu, Bin; Feng, Yan

    2013-12-01

    Experimental methods are described for determining transport coefficients in a strongly coupled dusty plasma. A dusty plasma is a mixture of electrons, ions and highly charged microspheres. Due to their large charges, the microspheres are a strongly coupled plasma, and they arrange themselves like atoms in a crystal or liquid. Using a video microscopy diagnostic, with laser illumination and a high speed video camera, the microspheres are imaged. Moment-method image analysis then yields the microspheres' positions and velocities. In one approach, these data in the particle paradigm are converted into the continuum paradigm by binning, yielding hydrodynamic quantities like number density, flow velocity and temperature that are recorded on a grid. To analyze continuum data for two-dimensional laboratory experiments, they are fit to the hydrodynamic equations, yielding the transport coefficients for shear viscosity and thermal conductivity. In another approach, the original particle data can be used to obtain the diffusion and viscosity coefficients, as is discussed in the context of future three-dimensional microgravity experiments.

  7. 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.

  8. A Coupled Model of Multiphase Flow, Reactive Biogeochemical Transport, Thermal Transport and Geo-Mechanics.

    NASA Astrophysics Data System (ADS)

    Tsai, C. H.; Yeh, G. T.

    2015-12-01

    In this investigation, a coupled model of multiphase flow, reactive biogeochemical transport, thermal transport and geo-mechanics in subsurface media is presented. It iteratively solves the mass conservation equation for fluid flow, thermal transport equation for temperature, reactive biogeochemical transport equations for concentration distributions, and solid momentum equation for displacement with successive linearization algorithm. With species-based equations of state, density of a phase in the system is obtained by summing up concentrations of all species. This circumvents the problem of having to use empirical functions. Moreover, reaction rates of all species are incorporated in mass conservation equation for fluid flow. Formation enthalpy of all species is included in the law of energy conservation as a source-sink term. Finite element methods are used to discretize the governing equations. Numerical experiments are presented to examine the accuracy and robustness of the proposed model. The results demonstrate the feasibility and capability of present model in subsurface media.

  9. 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.

  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. 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.

  12. Coupled ER to Golgi Transport Reconstituted with Purified Cytosolic Proteins

    PubMed Central

    Barlowe, Charles

    1997-01-01

    A cell-free vesicle fusion assay that reproduces a subreaction in transport of pro-α-factor from the ER to the Golgi complex has been used to fractionate yeast cytosol. Purified Sec18p, Uso1p, and LMA1 in the presence of ATP and GTP satisfies the requirement for cytosol in fusion of ER-derived vesicles with Golgi membranes. Although these purified factors are sufficient for vesicle docking and fusion, overall ER to Golgi transport in yeast semi-intact cells depends on COPII proteins (components of a membrane coat that drive vesicle budding from the ER). Thus, membrane fusion is coupled to vesicle formation in ER to Golgi transport even in the presence of saturating levels of purified fusion factors. Manipulation of the semi-intact cell assay is used to distinguish freely diffusible ER- derived vesicles containing pro-α-factor from docked vesicles and from fused vesicles. Uso1p mediates vesicle docking and produces a dilution resistant intermediate. Sec18p and LMA1 are not required for the docking phase, but are required for efficient fusion of ER- derived vesicles with the Golgi complex. Surprisingly, elevated levels of Sec23p complex (a subunit of the COPII coat) prevent vesicle fusion in a reversible manner, but do not interfere with vesicle docking. Ordering experiments using the dilution resistant intermediate and reversible Sec23p complex inhibition indicate Sec18p action is required before LMA1 function. PMID:9382859

  13. 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

  14. Two-Dimensional Ground Water Transport

    Energy Science and Technology Software Center (ESTSC)

    1992-03-05

    FRACFLO computes the two-dimensional, space, time dependent, convective dispersive transport of a single radionuclide in an unbounded single or multiple parallel fracture system with constant aperture. It calculates the one-dimensional diffusive transport into the rock matrix as well as the mass flux and cumulative mass flux at any point in the fracture. Steady-state isothermal ground water flow and parallel streamlines are assumed in the fracture, and the rock matrix is considered to be fully saturatedmore » with immobile water. The model can treat a single or multiple finite patch source or a Gaussian distributed source subject to a step or band release mode.« less

  15. 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

  16. Mechanism of isotonic water transport in glands.

    PubMed

    Ussing, H H; Eskesen, K

    1989-07-01

    Since water and electrolytes pass cell membranes via separate channels, there can be no interactions in the membranes, and osmotic interactions between water and solutes can be expressed as the product of solute flux, frictional coefficient of solute, and length of pathway. It becomes clear that isotonic transport via a cell is impossible. In glands, where cation-selective junctions impede anion flux between the cells, isotonic water transport is only possible if sodium, after having passed the junction, is reabsorbed in the acinus and returned to the serosal side. Thus it can be recycled via the cation-selective junction and exert its drag on water more than once. This hypothesis was tested on frog skin glands. Skins were mounted in flux chambers with identical Ringer solutions on both sides. Na channels of the principal cells were closed with amiloride in the outside solution, and secretion stimulated with noradrenaline in the inside solution. Influx and efflux of Na, K and Br (used as tracer for Cl) were measured on paired half-skins during the constant-secretion phase. Flux ratios for both Na and K were higher than expected for electrodiffusion, indicating outgoing solvent drag. Flux ratios for K were much higher than those for Na. This is an agreement with the concept that Na is reabsorbed in the acinus and K is not. Two independent expressions for the degree of sodium recycling are developed. Under all experimental conditions these expressions give values for the recycling which are in good agreement. PMID:2473601

  17. Coherent transport of nanowire surface plasmons coupled to quantum dots.

    PubMed

    Chen, Wei; Chen, Guang-Yin; Chen, Yueh-Nan

    2010-05-10

    The coherent transport of surface plasmons with nonlinear dispersion relations on a metal nanowire coupled to two-level emitters is investigated theoretically. Real-space Hamiltonians are used to obtain the transmission and reflection spectra of the surface plasmons. For the single-dot case, we find that the scattering spectra can show completely different features due to the non-linear quadratic dispersion relation. For the double-dot case, we obtain the interference behavior in transmission and reflection spectra, similar to that in resonant tunneling through a double-barrier potential. Moreover, Fano-like line shape of the transmission spectrum is obtained due to the quadratic dispersion relation. All these peculiar behaviors indicate that the dot-nanowire system provides a onedimensional platform to demonstrate the bandgap feature widely observed in photonic crystals. PMID:20588891

  18. 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

  19. 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.

  20. 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

  1. Electron transport analysis in water vapor

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Satoru; Takahashi, Kazuhiro; Satoh, Kohki; Itoh, Hidenori

    2016-07-01

    A reliable set of electron collision cross sections for water vapor, including elastic, rotational, vibrational, and electronic excitation, electron attachment, and ionization cross sections, is estimated by the electron swarm method. In addition, anisotropic electron scattering for elastic and rotational excitation collisions is considered in the cross section set. Electron transport coefficients such as electron drift velocity, longitudinal diffusion coefficient, and effective ionization coefficient are calculated from the cross section set by Monte Carlo simulation in a wide range of E/N values, where E and N are the applied electric field and the number density of H2O molecules, respectively. The calculated transport coefficients are in good agreement with those measured. The obtained results confirm that the anisotropic electron scattering is important for the calculation at low E/N values. Furthermore, the cross section set assuming the isotropic electron scattering is proposed for practical use.

  2. Coupling methodology and application of a fully integrated model for contaminant transport in the subsurface system

    NASA Astrophysics Data System (ADS)

    Zhu, Yan; Shi, Liangsheng; Yang, Jinzhong; Wu, Jingwei; Mao, Deqiang

    2013-09-01

    An efficient integrated modeling approach is developed to simulate the contaminant transport in the subsurface system. The unsaturated zone is divided into a number of horizontal sub-areas according to the atmospheric boundary conditions, land use types and hydrological conditions. Solute migration through the unsaturated zone of each sub-area is assumed to be vertical and can be represented by the one-dimensional advection-dispersion equation, which is then coupled to the three-dimensional advection-dispersion equation representing the subsequent groundwater transport. The finite element method is adopted to discretize the vertical solute equation, while the hybrid finite element and finite difference method is used to discretize the three-dimensional saturated solute transport equation, which is split into the horizontal and vertical equations based on the concept of the horizontal/vertical splitting. The unsaturated and saturated solute transport equations are combined into a unified matrix by the mass balance analysis for the adjacent nodes located at the one-dimensional soil column and at the water table. Two hypothetical cases and two field cases are simulated to test the validity of the model with the results compared with those from HYDRUS-1D, SWMS2D and the measured data. The limitations of the model are discussed as well. The analysis of the four cases demonstrates that the proposed model can calculate the water flow and solute transport reasonably even with complex boundary and variable topography conditions. It also shows that the model is efficient to simulate the water flow and solute transport in regional-scale areas with small computational costs. However, the model will lose accuracy when the lateral dispersion effect is dominant in the unsaturated zone.

  3. 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.

  4. An Interpretation of Some Whole Plant Water Transport Phenomena

    PubMed Central

    Fiscus, Edwin L.; Klute, Arnold; Kaufmann, Merrill R.

    1983-01-01

    A treatment of water flow into and through plants to the evaporating surface of the leaves is presented. The model is driven by evaporation from the cell wall matrix of the leaves. The adsorptive and pressure components of the cell wall matric potential are analyzed and the continuity between the pressure component and the liquid tension in the xylem established. Continuity of these potential components allows linking of a root transport function, driven by the tension in the xylem, to the leaf water potential. The root component of the overall model allows for the solvent-solute interactions characteristic of a membrane-bound system and discussion of the interactions of environmental variables such as root temperature and soil water potentials. A partition function is developed from data in the literature which describes how water absorbed by the plant might be divided between transpiration and leaf growth over a range of leaf water potentials. Relationships between the overall system conductance and the conductance coefficients of the various plant parts (roots, xylem, leaf matrix) are established and the influence of each of these discussed. The whole plant flow model coupled to the partition function is used to simulate several possible relationships between leaf water potential and transpiration rate. The effects of changing some of the partition function coefficients, as well as the root medium water potential on these simulations is illustrated. In addition to the general usefulness of the model and its ability to describe a wide range of situations, we conclude that the relationships used, dealing with bulk fluid flow, diffusion, and solute transport, are adequate to describe the system and that analogically based theoretical systems, such as the Ohm's law analogy, probably ought to be abandoned for this purpose. PMID:16662912

  5. An interpretation of some whole plant water transport phenomena.

    PubMed

    Fiscus, E L; Klute, A; Kaufmann, M R

    1983-04-01

    A treatment of water flow into and through plants to the evaporating surface of the leaves is presented. The model is driven by evaporation from the cell wall matrix of the leaves. The adsorptive and pressure components of the cell wall matric potential are analyzed and the continuity between the pressure component and the liquid tension in the xylem established. Continuity of these potential components allows linking of a root transport function, driven by the tension in the xylem, to the leaf water potential. The root component of the overall model allows for the solvent-solute interactions characteristic of a membrane-bound system and discussion of the interactions of environmental variables such as root temperature and soil water potentials. A partition function is developed from data in the literature which describes how water absorbed by the plant might be divided between transpiration and leaf growth over a range of leaf water potentials.Relationships between the overall system conductance and the conductance coefficients of the various plant parts (roots, xylem, leaf matrix) are established and the influence of each of these discussed.The whole plant flow model coupled to the partition function is used to simulate several possible relationships between leaf water potential and transpiration rate. The effects of changing some of the partition function coefficients, as well as the root medium water potential on these simulations is illustrated.In addition to the general usefulness of the model and its ability to describe a wide range of situations, we conclude that the relationships used, dealing with bulk fluid flow, diffusion, and solute transport, are adequate to describe the system and that analogically based theoretical systems, such as the Ohm's law analogy, probably ought to be abandoned for this purpose. PMID:16662912

  6. Regulated traffic of anion transporters in mammalian Brunner's glands: a role for water and fluid transport

    PubMed Central

    Collaco, Anne M.; Jakab, Robert L.; Hoekstra, Nadia E.; Mitchell, Kisha A.; Brooks, Amos

    2013-01-01

    The Brunner's glands of the proximal duodenum exert barrier functions through secretion of glycoproteins and antimicrobial peptides. However, ion transporter localization, function, and regulation in the glands are less clear. Mapping the subcellular distribution of transporters is an important step toward elucidating trafficking mechanisms of fluid transport in the gland. The present study examined 1) changes in the distribution of intestinal anion transporters and the aquaporin 5 (AQP5) water channel in rat Brunner's glands following second messenger activation and 2) anion transporter distribution in Brunner's glands from healthy and disease-affected human tissues. Cystic fibrosis transmembrane conductance regulator (CFTR), AQP5, sodium-potassium-coupled chloride cotransporter 1 (NKCC1), sodium-bicarbonate cotransporter (NBCe1), and the proton pump vacuolar ATPase (V-ATPase) were localized to distinct membrane domains and in endosomes at steady state. Carbachol and cAMP redistributed CFTR to the apical membrane. cAMP-dependent recruitment of CFTR to the apical membrane was accompanied by recruitment of AQP5 that was reversed by a PKA inhibitor. cAMP also induced apical trafficking of V-ATPase and redistribution of NKCC1 and NBCe1 to the basolateral membranes. The steady-state distribution of AQP5, CFTR, NBCe1, NKCC1, and V-ATPase in human Brunner's glands from healthy controls, cystic fibrosis, and celiac disease resembled that of rat; however, the distribution profiles were markedly attenuated in the disease-affected duodenum. These data support functional transport of chloride, bicarbonate, water, and protons by second messenger-regulated traffic in mammalian Brunner's glands under physiological and pathophysiological conditions. PMID:23744739

  7. Coupled Deterministic-Monte Carlo Transport for Radiation Portal Modeling

    SciTech Connect

    Smith, Leon E.; Miller, Erin A.; Wittman, Richard S.; Shaver, Mark W.

    2008-01-14

    Radiation portal monitors are being deployed, both domestically and internationally, to detect illicit movement of radiological materials concealed in cargo. Evaluation of the current and next generations of these radiation portal monitor (RPM) technologies is an ongoing process. 'Injection studies' that superimpose, computationally, the signature from threat materials onto empirical vehicle profiles collected at ports of entry, are often a component of the RPM evaluation process. However, measurement of realistic threat devices can be both expensive and time-consuming. Radiation transport methods that can predict the response of radiation detection sensors with high fidelity, and do so rapidly enough to allow the modeling of many different threat-source configurations, are a cornerstone of reliable evaluation results. Monte Carlo methods have been the primary tool of the detection community for these kinds of calculations, in no small part because they are particularly effective for calculating pulse-height spectra in gamma-ray spectrometers. However, computational times for problems with a high degree of scattering and absorption can be extremely long. Deterministic codes that discretize the transport in space, angle, and energy offer potential advantages in computational efficiency for these same kinds of problems, but the pulse-height calculations needed to predict gamma-ray spectrometer response are not readily accessible. These complementary strengths for radiation detection scenarios suggest that coupling Monte Carlo and deterministic methods could be beneficial in terms of computational efficiency. Pacific Northwest National Laboratory and its collaborators are developing a RAdiation Detection Scenario Analysis Toolbox (RADSAT) founded on this coupling approach. The deterministic core of RADSAT is Attila, a three-dimensional, tetrahedral-mesh code originally developed by Los Alamos National Laboratory, and since expanded and refined by Transpire, Inc. [1

  8. Endothelin and Renal Ion and Water Transport

    PubMed Central

    Speed, Joshua S.; Fox, Brandon M.; Johnston, Jermaine G.; Pollock, David M.

    2015-01-01

    The renal tubular epithelial cells produce more endothelin-1 (ET-1) than any other cell type in the body. Moving down the nephron, the amount of ET-1 produced appears fairly consistent until reaching the inner medullary collecting duct, which produces at least 10 times more ET-1 than any other segment. ET-1 inhibits Na+ transport in all parts of the nephron through activation of the ETB receptor, and to a minor extent, the ETA receptor. These effects are most prominent in the collecting duct where ETB receptor activation inhibits activity of the epithelial Na+ channel. Effects in other parts of the nephron include inhibition of Na+/H+ exchange in the proximal tubule and the Na+, K+, 2Cl− co-transporter in the thick ascending limb. In general, the renal epithelial ET-1 system is an integral part of the body’s response to a high salt intake in order to maintain homeostasis and normal blood pressure. Loss of ETB receptor function results in salt sensitive hypertension. The goal of this article is to review the role of renal ET-1 and how it affects Na+ and water transport throughout the nephron. PMID:25966345

  9. 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.

  10. 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.

  11. Radionuclide transport coupled with bentonite extrusion in a saturated fracture system

    NASA Astrophysics Data System (ADS)

    Borrelli, Robert Angelo

    The study in this dissertation focuses on the characterization of radionuclide migration in a water saturated fracture. The near field of a high level radioactive waste repository contains the engineered barrier system, which provides manufactured components designed to limit radionuclide releases to the environment. A major component in this system involves the utilization of bentonite as a buffer to protect the degraded waste package and limit release of radionuclides into intersecting fractures that pose possible pathways for transport to the environment. A model is derived for radionuclide migration through this fracture. The model incorporates the features of bentonite: extrusion into the fracture, sorption, and the effect of bentonite swelling on groundwater flow. The resulting derivation of this model is a coupled system of differential equations. The differential equation describing the mass conservation of radionuclides is coupled to the equation system for bentonite extrusion. The models are coupled through the parameters in the radionuclide transport model, which are dependent on the spatial distribution of solid material in the domain. Numerical evaluations of the solution to this radionuclide transport model were conducted for neptunium, a weakly sorbing radionuclide and americium, a strongly sorbing radionuclide. Results were presented in terms normalized spatial distribution of radionuclide concentration in the fluid phase and normalized radionuclide release rate in the fluid phase. Major findings of the study conducted for this dissertation are provided. (1) Bentonite extrusion affects fluid phase advection resulting in groundwater flow countercurrent to the direction of extrusion to the direction of radionuclide migration. (2) The sorption distribution coefficient is the most important parameter affecting radionuclide behavior in this system for this model. (3) Simulations of the model for americium, a highly sorbing radionuclide, indicate that

  12. 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

  13. Water governance across competing scales: Coupling land and water management

    NASA Astrophysics Data System (ADS)

    Daniell, Katherine A.; Barreteau, Olivier

    2014-11-01

    Water governance is becoming an increasingly important area of study for hydrologists, as the impacts of human decisions on water flows and their various management scales are recognised. Hydrology has long tackled issues of water flow and quality across basins-from rain to soil and sub-soil, from upstream to downstream, between surface water and groundwater systems, and through interlinked watersheds-with the understanding that these stocks and flows can be modified en-route due to the actions of people, including through organised water management and governance processes. In this setting, one common aim of water governance is to develop management processes and infrastructure systems that can control hydrological variability at different levels of spatial and temporal scales. For example, water storages, distribution systems and drainage networks are developed for long-term seasonal and inter-decadal variability-in the case of large dams and irrigation systems-as well as shorter-term variability, such as flooding events, that may take place over hours (e.g. urban flash floods), days (e.g. catchment-based river flooding) or months (e.g. basin-wide flood-plain inundation events). Particularly when looking at water supply issues, water allocation rules are elaborated and negotiated in order to provide water to people when and where they most need it, rather than when and where it would naturally be available.

  14. 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.

  15. 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.

  16. Coupled Thermal and Water Management in Polymer-Electrolyte FuelCells

    SciTech Connect

    Weber, Adam Z.; Newman, John

    2006-11-01

    Thermal and water management are intricately coupled in polymer-electrolyte fuel cells. In this paper, we simulate fuel-cell performance and account for nonisothermal phenomena. The transport of water due to a temperature gradient and its associated effects on performance are described, with the increase of reactant dilution by the water-vapor partial pressure being the most dominant. In addition, simulations are undergone to find the optimum operating temperature and maximum power density as a function of external heat-transfer coefficient. The shape of the optimization curves and the magnitudes of the nonisothermal phenomena are also detailed and explained.

  17. 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.

  18. 3D multi-scale analysis of coupled heat and moisture transport and its parallel implementation

    NASA Astrophysics Data System (ADS)

    Kruis, Jaroslav

    2016-06-01

    Parallel implementation of two-scale model of coupled heat and moisture transport is described. The coupled heat and moisture transport is based on the Künzel model. Motivation for the two-scale analysis comes from the requirement to describe distribution of the relative humidity and temperature in historical masonry structures.

  19. Coupled transport and reaction kinetics control the nitrate source-sink function of hyporheic zones

    NASA Astrophysics Data System (ADS)

    Zarnetske, Jay P.; Haggerty, Roy; Wondzell, Steven M.; Bokil, Vrushali A.; GonzáLez-Pinzón, Ricardo

    2012-11-01

    The fate of biologically available nitrogen (N) and carbon (C) in stream ecosystems is controlled by the coupling of physical transport and biogeochemical reaction kinetics. However, determining the relative role of physical and biogeochemical controls at different temporal and spatial scales is difficult. The hyporheic zone (HZ), where groundwater-stream water mix, can be an important location controlling N and C transformations because it creates strong gradients in both the physical and biogeochemical conditions that control redox biogeochemistry. We evaluated the coupling of physical transport and biogeochemical redox reactions by linking an advection, dispersion, and residence time model with a multiple Monod kinetics model simulating the concentrations of oxygen (O2), ammonium (NH4), nitrate (NO3), and dissolved organic carbon (DOC). We used global Monte Carlo sensitivity analyses with a nondimensional form of the model to examine coupled nitrification-denitrification dynamics across many scales of transport and reaction conditions. Results demonstrated that the residence time of water in the HZ and the uptake rate of O2 from either respiration and/or nitrification determined whether the HZ was a source or a sink of NO3 to the stream. We further show that whether the HZ is a net NO3 source or net NO3 sink is determined by the ratio of the characteristic transport time to the characteristic reaction time of O2 (i.e., the Damköhler number, DaO2), where HZs with DaO2 < 1 will be net nitrification environments and HZs with DaO2 ≪ 1 will be net denitrification environments. Our coupling of the hydrologic and biogeochemical limitations of N transformations across different temporal and spatial scales within the HZ allows us to explain the widely contrasting results of previous investigations of HZ N dynamics which variously identify the HZ as either a net source or sink of NO3. Our model results suggest that only estimates of residence times and O2uptake rates

  20. 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

  1. 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.

  2. Simulating Sediment Transport Processes in San Francisco Bay Using Coupled Hydrodynamic, Wave, and Sediment Transport Models

    NASA Astrophysics Data System (ADS)

    Bever, A. J.; MacWilliams, M.

    2012-12-01

    Under the conceptual model of sediment transport in San Pablo Bay, a sub-embayment of San Francisco Bay, proposed by Krone (1979), sediment typically enters San Pablo Bay during large winter and spring flows and is redistributed during summer conditions through wind wave resuspension and transport by tidal currents. A detailed understanding of how the waves and tides redistribute sediment within San Francisco Bay is critical for predicting how future sea level rise and a reduction in the sediment supply to the Bay will impact existing marsh and mudflat habitat, tidal marsh restoration projects, and ongoing maintenance dredging of the navigation channels. The three-dimensional UnTRIM San Francisco Bay-Delta Model was coupled with the Simulating WAves Nearshore (SWAN) wave model and the SediMorph morphological model, to develop a three-dimensional hydrodynamic, wind wave, and sediment transport model of the San Francisco Bay and the Sacramento-San Joaquin Delta. Numerical simulations of sediment resuspension due to tidal currents and wind waves and the subsequent transport of this sediment by tidal currents are used to quantify the spatial and temporal variability of sediment fluxes on the extensive shoals in San Pablo Bay under a range of tidal and wind conditions. The results demonstrate that suspended sediment concentration and sediment fluxes within San Pablo Bay are a complex product of tides and waves interacting spatially throughout the Bay, with concentrations responding to local resuspension and sediment advection. Sediment fluxes between the San Pablo Bay shoals and the deeper channel are highest during spring tides, and are elevated for up to a week following wave events, even though the greatest influence of the wave event occurs abruptly.

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

    PubMed

    Zhao, Ying; Xue, Qiang; Liu, Lei

    2012-10-01

    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

  4. Downregulation of mouse intestinal Na(+)-coupled glucose transporter SGLT1 by gum arabic (Acacia Senegal).

    PubMed

    Nasir, Omaima; Artunc, Ferruh; Wang, Kan; Rexhepaj, Rexhep; Föller, Michael; Ebrahim, Ammar; Kempe, Daniela S; Biswas, Raja; Bhandaru, Madhuri; Walter, Michael; Mohebbi, Nilufar; Wagner, Carsten A; Saeed, Amal M; Lang, Florian

    2010-01-01

    Intestinal Na(+)-coupled glucose transporter SGLT1 determines the rate of glucose transport, which in turn influences glucose-induced insulin release and development of obesity. The present study explored effects of Gum Arabic (GA), a dietary polysaccharide from dried exudates of Acacia Senegal, on intestinal glucose transport and body weight in wild-type C57Bl/6 mice. Treatment with GA (100 g/l) in drinking water for four weeks did not affect intestinal SGLT1 transcript levels but decreased SGLT1 protein abundance in jejunal brush border membrane vesicles. Glucose-induced jejunal short-circuit currents revealed that GA treatment decreased electrogenic glucose transport. Drinking a 20% glucose solution for four weeks significantly increased body weight and fasting plasma glucose concentrations, effects significantly blunted by simultaneous treatment with GA. GA further significantly blunted the increase in body weight, fasting plasma glucose and fasting insulin concentrations during high fat diet. In conclusion, the present observations disclose a completely novel effect of gum arabic, i.e. its ability to decrease intestinal SGLT1 expression and activity and thus to counteract glucose-induced obesity. PMID:20110681

  5. 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

  6. 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.

  7. Laser coupling with a multimode water-jet waveguide

    NASA Astrophysics Data System (ADS)

    Couty, Philippe; Wagner, Frank R.; Hoffmann, Patrik W.

    2005-06-01

    The coupling of a laser focused into a water microjet is studied. Using a high-power laser, the light guided in the jet is used to process various materials. To explain the observed ablation patterns, the propagation of a low-power and highly coherent laser beam coupled into a laminar water jet is studied. The light of a He-Ne laser (5 mW) is focused into the water jet, which behaves as a multimode waveguide. The distribution of the light intensity in the jet impinging on a glass plate cutting the jet perpendicularly to its propagation direction is recorded for various laser coupling conditions. The influence of the jet diameter, as well as the influence of the depth of focus of the incident beam and its position with respect to the center of the jet is studied. A nearly homogeneous grain size was observed over the whole jet cross section. The characteristic grain size was then compared with predictions from standard multimode fiber theory. Finally, it is confirmed that the structures resulting from material ablation using the laser-microjet technology when coupling Q-switched Nd:YAG (λ=1064 and 355 nm) are closely related to the predicted light intensity distributions. Furthermore, recommendations are made concerning the coupling conditions for optimizing the laser processing applications.

  8. 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. PMID:23878376

  9. 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.

  10. 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. PMID:25686488

  11. 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.

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

    PubMed Central

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

    2014-01-01

    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. PMID:25088546

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

    PubMed

    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. PMID:26149236

  14. Influence of root-water-uptake parameterization on simulated heat transport in a structured forest soil

    NASA Astrophysics Data System (ADS)

    Votrubova, Jana; Vogel, Tomas; Dohnal, Michal; Dusek, Jaromir

    2015-04-01

    Coupled simulations of soil water flow and associated transport of substances have become a useful and increasingly popular tool of subsurface hydrology. Quality of such simulations is directly affected by correctness of its hydraulic part. When near-surface processes under vegetation cover are of interest, appropriate representation of the root water uptake becomes essential. Simulation study of coupled water and heat transport in soil profile under natural conditions was conducted. One-dimensional dual-continuum model (S1D code) with semi-separate flow domains representing the soil matrix and the network of preferential pathways was used. A simple root water uptake model based on water-potential-gradient (WPG) formulation was applied. As demonstrated before [1], the WPG formulation - capable of simulating both the compensatory root water uptake (in situations when reduced uptake from dry layers is compensated by increased uptake from wetter layers), and the root-mediated hydraulic redistribution of soil water - enables simulation of more natural soil moisture distribution throughout the root zone. The potential effect on heat transport in a soil profile is the subject of the present study. [1] Vogel T., M. Dohnal, J. Dusek, J. Votrubova, and M. Tesar. 2013. Macroscopic modeling of plant water uptake in a forest stand involving root-mediated soil-water redistribution. Vadose Zone Journal, 12, 10.2136/vzj2012.0154. The research was supported by the Czech Science Foundation Project No. 14-15201J.

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

    PubMed

    Taraphder, Srabani; Maupin, C Mark; Swanson, Jessica M J; Voth, Gregory A

    2016-08-25

    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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Implications of Lagrangian transport for simulations with a coupled chemistry-climate model

    NASA Astrophysics Data System (ADS)

    Stenke, A.; Dameris, M.; Grewe, V.; Garny, H.

    2009-08-01

    For the first time a purely Lagrangian transport algorithm is applied in a fully coupled chemistry-climate model (CCM). We use the numerically non-diffusive Lagrangian scheme ATTILA instead of the operational semi-Lagrangian scheme for the transport of water vapour, cloud water and chemical trace species in the CCM E39C. The new model version including the Lagrangian scheme is referred to as E39C-A. The implications of the Lagrangian transport scheme for stratospheric model dynamics and tracer distributions in E39C-A are evaluated by comparison with observations and results of the previous model version E39C. We found in a previous paper that several deficiencies in stratospheric dynamics in E39C originate from a pronounced modelled wet bias and an associated cold bias in the extra-tropical lowermost stratosphere. Contrary to the semi-Lagrangian scheme ATTILA shows a largely reduced meridional transport of water vapour from the tropical upper troposphere into the extratropical lowermost stratosphere. The reduction of the moisture and temperature bias in E39C-A leads to a significant advancement of stratospheric dynamics in terms of the mean state as well as annual and interannual variability. In this study we show that as a consequence of both, the favourable numerical characteristics of the Lagrangian transport scheme and the improved model dynamics, E39C-A generally shows more realistic distributions of chemical trace species: Compared to E39C high stratospheric chlorine (Cly) concentrations extend further downward. Therefore E39C-A realistically covers the altitude of maximum ozone depletion in the stratosphere. The location of the ozonopause, i.e. the transition from low tropospheric to high stratospheric ozone values, is also clearly improved in E39C-A. Not only the spatial distribution but also the temporal evolution of stratospheric Cly in the past is realistically reproduced in E39C-A which is an important step towards a more reliable projection of future

  3. H+-coupled nutrient, micronutrient and drug transporters in the mammalian small intestine

    PubMed Central

    Thwaites, David T.; Anderson, Catriona M.H.

    2009-01-01

    The H+-electrochemical gradient was originally considered as a driving force for solute transport only across cellular membranes of bacteria, plants and yeast. However, in the mammalian small intestine a H+electrochemical gradient is present at the epithelial brush-border membrane in the form of an acid microclimate. Over recent years a large number of H+-coupled cotransport mechanisms have been identified at the luminal membrane of the mammalian small intestine. These transporters are responsible for the initial stage in absorption of a remarkable variety of essential and non-essential nutrients and micronutrients including protein digestion products (di/tripeptides and amino acids), vitamins, short-chain fatty acids and divalent metal ions. Proton-coupled cotransporters expressed at the mammalian small intestinal brush-border membrane include: the di/tripeptide transporter PepT1 (SLC15A1); the proton-coupled amino-acid transporter PAT1 (SLC36A1); the divalent metal transporter DMT1 (SLC11A2); the organic anion transporting polypeptide OATP2B1 (SLC02B1); the monocarboxylate transporter MCT1 (SLC16A1); the proton-coupled folate transporter PCFT (SLC46A1); the sodium-glucose linked cotransporter SGLT1 (SLC5A1); and the excitatory amino acid carrier EAAC1 (SLC1A1). Emerging research demonstrates that the optimal intestinal absorptive capacity of certain H+-coupled cotransporters (PepT1 and PAT1) is dependent upon function of the brush-border Na+/H+ exchanger NHE3 (SLC9A3). The high oral bioavailability of a large number of pharmaceutical compounds is due, in part, to absorptive transport via these same H+-coupled cotransporters. Drugs undergoing H+-coupled cotransport across the intestinal brush-border membrane include those used to treat bacterial infections, hypercholesterolaemia, hypertension, hyperglycaemia, viral infections, allergies, epilepsy, schizophrenia, rheumatoid arthritis and cancer. PMID:17468205

  4. H+-coupled nutrient, micronutrient and drug transporters in the mammalian small intestine.

    PubMed

    Thwaites, David T; Anderson, Catriona M H

    2007-07-01

    The H(+)-electrochemical gradient was originally considered as a driving force for solute transport only across cellular membranes of bacteria, plants and yeast. However, in the mammalian small intestine, a H(+)-electrochemical gradient is present at the epithelial brush-border membrane in the form of an acid microclimate. Over recent years, a large number of H(+)-coupled cotransport mechanisms have been identified at the luminal membrane of the mammalian small intestine. These transporters are responsible for the initial stage in absorption of a remarkable variety of essential and non-essential nutrients and micronutrients, including protein digestion products (di/tripeptides and amino acids), vitamins, short-chain fatty acids and divalent metal ions. Proton-coupled cotransporters expressed at the mammalian small intestinal brush-border membrane include: the di/tripeptide transporter PepT1 (SLC15A1); the proton-coupled amino-acid transporter PAT1 (SLC36A1); the divalent metal transporter DMT1 (SLC11A2); the organic anion transporting polypeptide OATP2B1 (SLC02B1); the monocarboxylate transporter MCT1 (SLC16A1); the proton-coupled folate transporter PCFT (SLC46A1); the sodium-glucose linked cotransporter SGLT1 (SLC5A1); and the excitatory amino acid carrier EAAC1 (SLC1A1). Emerging research demonstrates that the optimal intestinal absorptive capacity of certain H(+)-coupled cotransporters (PepT1 and PAT1) is dependent upon function of the brush-border Na(+)-H(+) exchanger NHE3 (SLC9A3). The high oral bioavailability of a large number of pharmaceutical compounds results, in part, from absorptive transport via the same H(+)-coupled cotransporters. Drugs undergoing H(+)-coupled cotransport across the intestinal brush-border membrane include those used to treat bacterial infections, hypercholesterolaemia, hypertension, hyperglycaemia, viral infections, allergies, epilepsy, schizophrenia, rheumatoid arthritis and cancer. PMID:17468205

  5. Peptide Selectivity of the Proton-Coupled Oligopeptide Transporter from Neisseria meningitidis.

    PubMed

    Sharma, Neha; Aduri, Nanda G; Iqbal, Anna; Prabhala, Bala K; Mirza, Osman

    2016-01-01

    Peptide transport in living organisms is facilitated by either primary transport, hydrolysis of ATP, or secondary transport, cotransport of protons. In this study, we focused on investigating the ligand specificity of the Neisseria meningitidis proton-coupled oligopeptide transporter (NmPOT). It has been shown that the gene encoding this transporter is upregulated during infection. NmPOT conformed to the typical chain length preference as observed in prototypical transporters of this family. In contrast to prototypical transporters, it was unable to accommodate a positively charged peptide residue at the C-terminus position of the substrate peptide. Sequence analysis of the active site of NmPOT displayed a distinctive aromatic patch, which has not been observed in any other transporters from this family. This aromatic patch may be involved in providing NmPOT with its atypical preferences. This study provides important novel information towards understanding how these transporters recognize their substrates. PMID:27438044

  6. 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.

  7. 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.

  8. 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.

  9. Proline residues in two tightly coupled helices of the sulphate transporter, SHST1, are important for sulphate transport.

    PubMed Central

    Shelden, M C; Loughlin, P; Tierney, M L; Howitt, S M

    2001-01-01

    The sulphate transporter SHST1, from Stylosanthes hamata, features three tightly coupled transmembrane helices which include proline residues that are conserved in most related transporters. We used site-directed mutagenesis and expression of the mutant transporters in yeast to test whether these proline residues are important for function. Four proline residues were replaced by both alanine and leucine. Only one of these proline residues, Pro-144, was essential for sulphate transport. However, mutation of either Pro-133 or Pro-160 resulted in a severe decrease in sulphate transport activity; this was due more to a decrease in transport activity than to a decrease in the amount of mutant SHST1 in the plasma membrane. These results suggest that all three proline residues are important for transport, and that the conformation of the three tightly coupled helices may play a critical role in sulphate transport. We also show that SHST1 undergoes a post-translational modification that is required for trafficking to the plasma membrane. PMID:11368789

  10. 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.

  11. Diagnosing coupled watershed processes using a fully-coupled groundwater, land-surface, surface water and mesoscale atmospheric model

    NASA Astrophysics Data System (ADS)

    Maxwell, R. M.; Kollet, S. J.; Chow, F. K.

    2007-12-01

    A variably-saturated groundwater flow model with an integrated overland flow component, a land-surface model and a mesoscale atmospheric model is used to examine the interplay between coupled water and energy processes. These processes are influenced by land-surface topography and subsurface heterogeneity. This parallel, integrated model simulates spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. Spatial statistics are used to demonstrate spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land surface temperatures trigger shifts in wind behavior, such as during early morning surface heating. Additionally, spectral transforms of subsurface arrival times are computed using a transient Lagrangian transport simulation. Macrodispersion is used to mimic the effects of subsurface heterogeneity for a range of Peclet numbers. The slopes of these transforms indicate fractal scaling of this system over a range of timescales. All of these techniques point to importance of realistically representing coupled processes and the need to understand and diagnose these processes in nature. This work was conducted under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory (LLNL) under contract W-7405-Eng-48. This project was funded by the Laboratory Directed Research and Development Program at LLNL

  12. Water access points and hydration pathways in CLC H+/Cl− transporters

    PubMed Central

    Han, Wei; Cheng, Ricky C.; Maduke, Merritt C.; Tajkhorshid, Emad

    2014-01-01

    CLC transporters catalyze transmembrane exchange of chloride for protons. Although a putative pathway for Cl− has been established, the pathway of H+ translocation remains obscure. Through a highly concerted computational and experimental approach, we characterize microscopic details essential to understanding H+-translocation. An extended (0.4 µs) equilibrium molecular dynamics simulation of membrane-embedded, dimeric ClC-ec1, a CLC from Escherichia coli, reveals transient but frequent hydration of the central hydrophobic region by water molecules from the intracellular bulk phase via the interface between the two subunits. We characterize a portal region lined by E202, E203, and A404 as the main gateway for hydration. Supporting this mechanism, site-specific mutagenesis experiments show that ClC-ec1 ion transport rates decrease as the size of the portal residue at position 404 is increased. Beyond the portal, water wires form spontaneously and repeatedly to span the 15-Å hydrophobic region between the two known H+ transport sites [E148 (Gluex) and E203 (Gluin)]. Our finding that the formation of these water wires requires the presence of Cl− explains the previously mystifying fact that Cl− occupancy correlates with the ability to transport protons. To further validate the idea that these water wires are central to the H+ transport mechanism, we identified I109 as the residue that exhibits the greatest conformational coupling to water wire formation and experimentally tested the effects of mutating this residue. The results, by providing a detailed microscopic view of the dynamics of water wire formation and confirming the involvement of specific protein residues, offer a mechanism for the coupled transport of H+ and Cl− ions in CLC transporters. PMID:24379362

  13. Water vapor transport in the lower stratosphere during summer linked to Asian monsoon and horizontal transport

    NASA Astrophysics Data System (ADS)

    Ploeger, Felix; Mueller, Rolf; Riese, Martin; Konopka, Paul

    We compare global water vapor observations from Microwave Limb Sounder (MLS) and simulations with the Lagrangian chemistry transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) to investigate the pathways of water vapor into the lower stratosphere during northern hemisphere (NH) summer. We find good agreement between the simulation and observations, with an effect of the satellite averaging kernel especially at high latitudes. The Asian and American monsoons emerge as regions of particularly high water vapor mixing ratios in the lower stratosphere during boreal summer. In NH mid latitudes and high latitudes, a clear anticorrelation between water vapor and ozone daily tendencies reveals a large region influenced by frequent horizontal transport from low latitudes, extending up to about 450K during summer and fall. Analysis of the zonal mean tracer continuity equation shows that close to the subtropics, this horizontal transport is mainly caused by the residual circulation. In contrast, at higher latitudes, poleward of about 50N, eddy mixing dominates the horizontal water vapor transport. Model simulations with transport barriers confirm that almost the entire annual cycle of water vapor in NH mid latitudes above about 360K, with maximum mixing ratios during summer and fall, is caused by horizontal transport from low latitudes. In the model, highest water vapor mixing ratios in this region are clearly linked to upward transport within the Asian monsoon in the subtropics and subsequent poleward horizontal transport.

  14. 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.

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

    SciTech Connect

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. 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.

  18. 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

  19. 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.

  20. Global simulation of coupled carbon and oxygen transport in a Czochralski furnace for silicon crystal growth

    NASA Astrophysics Data System (ADS)

    Gao, B.; Kakimoto, K.

    2010-10-01

    For accurate prediction of carbon and oxygen impurities in a single crystal produced by the Czochralski method, global simulation of coupled oxygen and carbon transport in the whole furnace was implemented. Both gas-phase transportation and liquid-phase transportation of oxygen and carbon were considered. With five chemical reactions considered, SiO and CO concentrations in gas and C and O atom concentrations in silicon melt were solved simultaneously. The simulation results show good agreement with experimental data.

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

    PubMed

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

    2014-01-01

    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. PMID:25023443

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

    PubMed

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

    2016-06-01

    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. PMID:26892914

  3. 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.

  4. Modeling the coupling between flow and transport developed by chemical reactions and density differences using TOUGHREACT.

    SciTech Connect

    Kim, Jeongkon; Scwartz, Franklin W.; Shi, Jianyou; Xu, Tianfu

    2003-04-01

    A complex pattern of coupling between fluid flow and mass transport develops when heterogeneous reactions occur. For instance, dissolution and precipitation reactions can change the physical properties of a medium, such as permeability and pore geometry. These changes influence fluid flow, which in turn impact the composition of dissolved constituents and solid-phase, and the rate and direction of advective transport. Two-dimensional modeling studies using TOUGHREACT were conducted to investigate the coupling between flow and transport developed as a consequence of difference in density, dissolution/precipitation, and medium heterogeneity. The model includes equilibrium reactions for aqueous species, kinetic reactions between the solid phases and aqueous constituents, and full coupling of porosity and permeability changes resulting from precipitation and dissolution reactions in porous media. Generally, the evolutions in the concentrations of the aqueous phase are intimately related to the reaction-front dynamics. Plugging of the medium contributed to significant transients in patterns of flow and mass transport.

  5. MULTIDIMENSIONAL COUPLED PHOTON-ELECTRON TRANSPORT SIMULATIONS USING NEUTRAL PARTICLE SN CODES

    SciTech Connect

    Ilas, Dan; Williams, Mark L; Peplow, Douglas E.; Kirk, Bernadette Lugue

    2008-01-01

    During the past two years a study was underway at ORNL to assess the suitability of the popular SN neutral particle codes ANISN, DORT and TORT for coupled photon-electron calculations specific to external beam therapy of medical physics applications. The CEPXS-BFP code was used to generate the cross sections. The computational tests were performed on phantoms typical of those used in medical physics for external beam therapy, with materials simulated by water at different densities and the comparisons were made against Monte Carlo simulations that served as benchmarks. Although the results for one-dimensional calculations were encouraging, it appeared that the higher dimensional transport codes had fundamental difficulties in handling the electron transport. The results of two-dimensional simulations using the code DORT with an S16 fully symmetric quadrature set agree fairly with the reference Monte Carlo results but not well enough for clinical applications. While the photon fluxes are in better agreement (generally, within less than 5% from the reference), the discrepancy increases, sometimes very significantly, for the electron fluxes. The paper, however, focuses on the results obtained with the three-dimensional code TORT which had convergence difficulties for the electron groups. Numerical instabilities occurred in these groups. These instabilities were more pronounced with the degree of anisotropy of the problem.

  6. 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. PMID:21381089

  7. A new paradigm for local-global coupling in whole-core neutron transport.

    SciTech Connect

    Lewis, E.; Smith, M.; Palmiotti, G,; Nuclear Engineering Division; Northwestern Univ.; INL

    2009-01-01

    A new paradigm that increases the efficiency of whole-core neutron transport calculations without lattice homogenization is introduced. Quasi-reflected interface conditions are formulated to partially decouple periodic lattice effects from global flux gradients. The starting point is the finite subelement form of the variational nodal code VARIANT that eliminates fuel-coolant homogenization through the use of heterogeneous nodes. The interface spherical harmonics expansions that couple pin-cell-sized nodes are divided into low-order and high-order terms, and reflected interface conditions are applied to the high-order terms. Combined with an integral transport method within the node, the new approach dramatically reduces both the formation time and the dimensions of the nodal response matrices and leads to sharply reduced memory requirements and computational time. The method is applied to the two-dimensional C5G7 problem, an Organisation for Economic Co-operation and Development/Nuclear Energy Agency pressurized water reactor benchmark containing mixed oxide (MOX) and UO{sub 2} fuel assemblies, as well as to a three-dimensional MOX fuel assembly. Results indicate the new approach results in very little loss of accuracy relative to the corresponding full spherical harmonics expansions while reducing computational times by well over an order of magnitude.

  8. Mitochondrial Electron Transport and Glycolysis are coupled in Articular Cartilage

    PubMed Central

    Martin, James A.; Martini, Anne; Molinari, Alexander; Morgan, Walter; Ramalingam, Wendy; Buckwalter, Joseph A.; McKinley, Todd O.

    2012-01-01

    Objective Although the majority of the ATP in chondrocytes is made by glycolysis rather than by oxidative phosphorylation in mitochondria there is evidence to suggest that reactive oxygen species produced by mitochondrial electron transport help to maintain cellular redox balance in favor of glycolysis. The objective of this study was to test this hypothesis by determining if rotenone, which inhibits electron transport and blocks oxidant production inhibits glycolytic ATP synthesis. Design Bovine osteochondral explants were treated with rotenone, an electron transport inhibitor; or oligomycin an ATP synthase inhibitor; or 2-fluoro-2-deoxy-D-glucose, a glycolysis inhibiter; or peroxide, an exogenous oxidant; or mitoquinone, a mitochondria-targeted anti-oxidant. Cartilage extracts were assayed for ATP, NAD+, and NADH, and culture medium was assayed for pyruvate and lactate after 24 hours of treatment. Imaging studies were used to measure superoxide production in cartilage. Results Rotenone and 2-fluoro-2-deoxy-D-glucose caused a significant decline in cartilage ATP (p < 0.001). In contrast, ATP levels were not affected by oligomycin. Peroxide treatment blocked rotenone effects on ATP, while treatment with MitoQ significantly suppressed ATP levels. Rotenone and 2-fluoro-2-deoxy-D-glucose caused a significant decline in pyruvate, but not in lactate production. NADH:NAD+ ratios decreased significantly in both rotenone and 2-fluoro-2-deoxy-D-glucose-treated explants (p < 0.05). Rotenone also significantly reduced superoxide production Conclusions These findings showing a link between glycolysis and electron transport are consistent with previous reports on the critical need for oxidants to support normal chondrocyte metabolism. They suggest a novel role for mitochondria in cartilage homeostasis that is independent of oxidative phosphorylation. PMID:22305999

  9. Formation of a ravine network by seepage: coupling groundwater to sediment transport

    NASA Astrophysics Data System (ADS)

    Devauchelle, O.; Petroff, A. P.; Abrams, D. M.; Rothman, D.

    2009-12-01

    The formation of a ravine network by seepage of an aquifer can produce a highly complex pattern, even when sediment properties and precipitation are uniform. The steephead streams of the Apalachicola Bluffs and Ravines Preserve on the Florida Panhandle are a simple example of this type of landscape. We report comparisons of theoretical predictions for stream elevation profiles against field observations and analyses of high resolution LIDAR maps of this system. An initially flat seepage face is prone to develop channels due to water sapping, in a way that is similar to the fluid-dynamical interfacial instability that occurs when a non-viscous fluid is pushed into a viscous one. However there are significant differences. We investigate this mechanism by means of a two-dimensional model for the water table. The higher the curvature of a ravine tip, the more groundwater it attracts, causing tips to be unstable. However, ravines are stabilized by the requirement that all the sediment detached from the head must be removed by the stream. This analysis reproduces the 20 m spacing between nascent tips. Once a tip is formed, water flowing through it transports sediment removed from the tip, thus allowing the ravine to grow forward. Although the size and discharge of the streams vary considerably across the ravine networks, the hydraulic force exerted on the bed remains close to the minimum value required to move a sand grain. This equilibrium condition imposes a strong constraint on the stream elevation profile, thus coupling the sediment transport process to the groundwater flow. From this model we show that, in the neighborhood of the channel head, stream elevation profiles increase with the distance from the tip to the power two thirds. This result, supported by field data, relates the shape of the stream to the amount of water captured by its tip. In particular, sediment transport into the stream influences not only the landscape around the head, but also the ravine

  10. 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.

  11. 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

  12. 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.

  13. Ballistic transport through coupled T-shaped quantum wires

    NASA Astrophysics Data System (ADS)

    Lin, Yuh-Kae; Lin, Kao-Chin; Chuu, Der-San

    2004-05-01

    The ballistic conductance of a coupled T-shaped semiconductor quantum wire (CTQW) is studied. Two types of CTQW are considered, one of which is a Π-shaped quantum wire ( ΠQW) which consists of two vertical arms on the same side of the horizontal arm and the other a Π-clone quantum wire ( ΠCQW) which consists of two vertical armes on the opposite sides of the horizontal arm. The mode matching method and Landauer-Buttiker theory are employed to study the energy dependence of the ballistic conductance. Most of transmission profiles of ΠQW and ΠCQW are found to be distinguishable for large separation d between the two vertical arms. The transmission probability manifests oscillatory behavior when d is increased. When a potential is applied to the connection region, it results in decoupling or coupling effects between the two T-shaped quantum wires according to whether it is positive or negative. When magnetic field is applied to CTQW, the transmission profiles are found to be affected prominently even if the electron passes through the field free region only.

  14. 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.

  15. Computing and the electrical transport properties of coupled quantum networks

    NASA Astrophysics Data System (ADS)

    Cain, Casey Andrew

    In this dissertation a number of investigations were conducted on ballistic quantum networks in the mesoscopic range. In this regime, the wave nature of electron transport under the influence of transverse magnetic fields leads to interesting applications for digital logic and computing circuits. The work specifically looks at characterizing a few main areas that would be of interest to experimentalists who are working in nanostructure devices, and is organized as a series of papers. The first paper analyzes scaling relations and normal mode charge distributions for such circuits in both isolated and open (terminals attached) form. The second paper compares the flux-qubit nature of quantum networks to the well-established spintronics theory. The results found exactly contradict the conventional school of thought for what is required for quantum computation. The third paper investigates the requirements and limitations of extending the Thevenin theorem in classic electric circuits to ballistic quantum transport. The fourth paper outlines the optimal functionally complete set of quantum circuits that can completely satisfy all sixteen Boolean logic operations for two variables.

  16. Water transportation across narrow channel of nanometer dimension

    NASA Astrophysics Data System (ADS)

    Wan, Rongzheng; Fang, Haiping

    2010-06-01

    Since the discovery of the carbon nanotube and aquaporin, the study of the transportation of water across nanochannels has become one of the hot subjects. When the radius of a nanochannel is only about one nanometer or a little larger, water confined in those nanoscale channels usually exhibits dynamics different from those in bulk system, such as the wet-dry transition due to the confinement, concerted hydrogen-bond orientations and flipping, concerted motion of water molecules, and strong interactions with external charges. Those dynamics correlate with the unique behavior of the water transportation across the channels, such as the extra-high permeability, excellent on-off gating behavior with response to the external mechanical and electrical signals and noises, enhancement by structure outside the channel, directional transportation driven by charges close to a channel or electric field. In this article, we review some of the recent progress on the study of the water molecules inside those narrow nanochannels.

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

    PubMed

    Wen, Po-Chao; Tajkhorshid, Emad

    2011-08-01

    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

  18. 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.

  19. Reactions in water: alkyl nitrile coupling reactions using Fenton's reagent.

    PubMed

    Keller, Christopher L; Dalessandro, James D; Hotz, Richard P; Pinhas, Allan R

    2008-05-01

    The coupling reaction of water-soluble alkyl nitriles using Fenton's reagent (Fe(II) and H2O2) is described. The best metal for the reaction is iron(II), and the greatest yields are obtained when the concentration of the metal is kept low. Hydrogen-atom abstraction is selective, preferentially producing the radical alpha to the nitrile. In order to increase the production of dinitrile, in situ reduction of iron(III) to iron(II), using a variety of reducing agents, was investigated. PMID:18363368

  20. Dynamics of magnetosphere-ionosphere coupling including turbulent transport

    NASA Technical Reports Server (NTRS)

    Lysak, R. L.; Dum, C. T.

    1982-01-01

    A two dimensional two-fluid MHD model including anomalous resistivity was used to investigate the dynamics of magnetosphere-ionosphere coupling. When a field-aligned current is generated on auroral field lines, the disturbance propagates towards the ionosphere in the form of a kinetic Alfven wave. When the current exceeds a critical value, microscopic turbulence is produced, which modifies the propagation of the Alfven wave. This process is modeled by a nonlinear collision frequency, which increases with the excess of the drift velocity over the critical value. Turbulence leads to absorption and reflection of the Alfven wave, partially decoupling the generator from the ionosphere. The approach to a steady-state is strongly dependent on the presence or absence of the turbulence. The current is self-limiting, since a current in excess of critical causes a diffusion of the magnetic field perturbation and a reduction of current.

  1. 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.

  2. Scaling behaviour for the water transport in nanoconfined geometries

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  3. 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

  4. Evaluating the costs of desalination and water transport

    NASA Astrophysics Data System (ADS)

    Zhou, Yuan; Tol, Richard S. J.

    2005-03-01

    Many regions of the world are facing formidable freshwater scarcity. Although there is substantial scope for economizing on the consumption of water without affecting its service level, the main response to water scarcity has been to increase the supply. To a large extent, this is done by transporting water from places where it is abundant to places where it is scarce. At a smaller scale and without a lot of public and political attention, people have started to tap into the sheer limitless resource of desalinated water. This study looks at the development of desalination and its costs over time. The unit costs of desalinated water for five main processes are evaluated, followed by regressions to analyze the main influencing factors to the costs. The unit costs for all processes have fallen considerably over the years. This study suggests that a cost of $1/m3 for seawater desalination and $0.6/m3 for brackish water would be feasible today. The costs will continue to decline in the future as technology progresses. In addition, a literature review on the costs of water transport is conducted in order to estimate the total cost of desalination and the transport of desalinated water to selected water stress cities. Transport costs range from a few cents per cubic meter to over a dollar. A 100 m vertical lift is about as costly as a 100 km horizontal transport ($0.05-0.06/m3). Transport makes desalinated water prohibitively expensive in highlands and continental interiors but not elsewhere.

  5. Evaluating the costs of desalination and water transport

    NASA Astrophysics Data System (ADS)

    Zhou, Yuan; Tol, Richard S. J.

    2005-03-01

    Many regions of the world are facing formidable freshwater scarcity. Although there is substantial scope for economizing on the consumption of water without affecting its service level, the main response to water scarcity has been to increase the supply. To a large extent, this is done by transporting water from places where it is abundant to places where it is scarce. At a smaller scale and without a lot of public and political attention, people have started to tap into the sheer limitless resource of desalinated water. This study looks at the development of desalination and its costs over time. The unit costs of desalinated water for five main processes are evaluated, followed by regressions to analyze the main influencing factors to the costs. The unit costs for all processes have fallen considerably over the years. This study suggests that a cost of 1/m3 for seawater desalination and 0.6/m3 for brackish water would be feasible today. The costs will continue to decline in the future as technology progresses. In addition, a literature review on the costs of water transport is conducted in order to estimate the total cost of desalination and the transport of desalinated water to selected water stress cities. Transport costs range from a few cents per cubic meter to over a dollar. A 100 m vertical lift is about as costly as a 100 km horizontal transport ($0.05-0.06/m3). Transport makes desalinated water prohibitively expensive in highlands and continental interiors but not elsewhere.

  6. 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.

  7. 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.

  8. Spin-polarized transport through a coupled double-dot

    NASA Astrophysics Data System (ADS)

    Yu, Hui; Liang, J.-Q.

    2006-10-01

    We propose, theoretically, a new type of design that generates the spin-polarized current through a mesoscopic device composed of lateral double-quantum-dot in the company of time oscillating and spin-polarization dependent tunneling. A formula for the spin-dependent current is obtained and is applied to discuss the transport properties. We demonstrate that the spin and charge currents are controllable by adjusting the gate voltage, the frequency of driving field and the magnitude of the magnetic field as well. In particular an interesting resonance phenomenon of the spin current is qualitatively explained in terms of the exact solutions of a time-dependent Schrödinger equation for an electron moving between the two quantum dots.

  9. 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.

  10. 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

  11. Aquaporin-4–dependent K+ and water transport modeled in brain extracellular space following neuroexcitation

    PubMed Central

    Jin, Byung-Ju; Zhang, Hua; Binder, Devin K.

    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. PMID:23277478

  12. 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

  13. Thermal radiation transport in a fluidized dry water system

    NASA Astrophysics Data System (ADS)

    Taylan, Onur; Berberoglu, Halil

    2013-05-01

    This paper reports a numerical study on thermal radiation transport in a novel material called dry water. Dry water is a water-in-air inverse foam which consists of micrometer-sized water droplets encapsulated by hydrophobic fumed-silica nanoparticles. First, the size distribution of dry water was measured using a particle size analyzer. Then, the radiation characteristics of dry water were obtained using the Mie theory for coated spheres. One-dimensional, steady radiative transport in fluidized dry water system was modeled using the radiative transport equation (RTE) and was solved spectrally with the discrete ordinates method. The effects of silica coating and water droplet size as well as the volume fraction of dry water particles on reducing radiative heat transfer were studied parametrically. The results obtained using the size distributions from experimental measurements at a volume fraction of 10-4 showed that dry water reduced the local radiative heat flux by more than 60% with respect to that by silica particles alone whereas its performance was comparable to that of fine water mists. Moreover, reduction of the diameter of dry water particles from 150 to 50 μm and increasing their volume fraction from 10-4 to 10-3 decreased the radiative heat flux by 45% and 67%, respectively. Dry water is a novel and unique material that does not require high pressure fluid lines for producing fine mists and features a silica shell that can serve to encapsulate water soluble compounds, retard water evaporation from the core as well as increase scattering. With these unique features, dry water finds diverse engineering applications serving as a base for photo-catalytic nanoreactors, gas and chemical storage and delivery systems, as well as alternative mist systems in firefighting.

  14. 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.…

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

    PubMed Central

    Lu, Jun; Huang, Zhi-zhen; Han, Xiao-fei

    2005-01-01

    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 depends 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 annual and diurnal air temperature differences 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 °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. PMID:15822143

  16. 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. PMID:15822143

  17. Dynamics of magnetosphere-ionosphere coupling including turbulent transport

    NASA Technical Reports Server (NTRS)

    Lysak, R. L.; Dum, C. T.

    1983-01-01

    The dynamics of magnetosphere-ionosphere coupling has been investigated by means of a two-dimensional two-fluid MHD model including anomalous resistivity. When field-aligned current is generated on auroral field lines, the disturbance propagates toward the ionosphere in the form of a kinetic Alfven wave. When the current exceeds a critical value, microscopic turbulence is produced, which modifies the propagation of the Alfven wave. This process is modeled by a nonlinear collision frequency, which increases with the excess of the drift velocity over the critical value. The system evolves toward an electrostatic structure, with the perpendicular electric field having a shorter scale than the field-aligned current. The approach to a steady state is strongly dependent on the presence or absence of the turbulence and on the boundary conditions imposed in the generator. As current is increased or scale size is decreased, the turbulent region reflects and absorbs most of the Alfven wave energy, decoupling the generator from the ionosphere.

  18. 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

  19. 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

  20. Liquid water transport mechanism in the gas diffusion layer

    NASA Astrophysics Data System (ADS)

    Zhou, P.; Wu, C. W.

    We developed an equivalent capillary model of a microscale fiber-fence structure to study the microscale evolution and transport of liquid in a porous media and to reveal the basic principles of water transport in gas diffusion layer (GDL). Analytical solutions using the model show that a positive hydraulic pressure is needed to drive the liquid water to penetrate through the porous GDL even consisting of the hydrophilic fibers. Several possible contributions for the water configuration, such as capillary pressure, gravity, vapor condensation, wettability and microstructures of the GDL, are discussed using the lattice Boltzmann method (LBM). It is found that the distribution manners of the fibers and the spatial mixed-wettability in the GDL also play an important role in the transport of liquid water.

  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. 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

  3. Release of Entropic Spring Reveals Conformational Coupling Mechanism in the ABC Transporter BtuCD-F.

    PubMed

    Prieß, Marten; Schäfer, Lars V

    2016-06-01

    Substrate translocation by ATP-binding cassette (ABC) transporters involves coupling of ATP binding and hydrolysis in the nucleotide-binding domains (NBDs) to conformational changes in the transmembrane domains. We used molecular dynamics simulations to investigate the atomic-level mechanism of conformational coupling in the ABC transporter BtuCD-F, which imports vitamin B12 across the inner membrane of Escherichia coli. Our simulations show how an engineered disulfide bond across the NBD dimer interface reduces conformational fluctuations and hence configurational entropy. As a result, the disulfide bond is under substantial mechanical stress. Releasing this entropic spring, as is the case in the wild-type transporter, combined with analyzing the pairwise forces between individual residues, unravels the coupling mechanism. The identified pathways along which force is propagated from the NBDs via the coupling helix to the transmembrane domains are composed of highly conserved residues, underlining their functional relevance. This study not only reveals the details of conformational coupling in BtuCD-F, it also provides a promising approach to other long-range conformational couplings, e.g., in ABC exporters or other ATP-driven molecular machines. PMID:27276259

  4. The "independence principle" in the processes of water transport.

    PubMed Central

    Hernández, J A; Fischbarg, J

    1994-01-01

    The processes of membrane transport exhibiting permeability coefficients depending on the species activities do not obey the "independence principle" and are assumed to take place by a mechanism of discrete nature, analyzable by a kinetic formalism. In this article, we study the dependence of the osmotic permeability coefficient on the water activities, from the steady-state analysis of a kinetic model of single-file water transport that simultaneously incorporates the vacancy-mediated and "knock-on" mechanisms into the state diagram. In particular, we study the relation between the near-equilibrium osmotic permeability (Pe) and the equilibrium water activity of the compartments (w). The analysis and numerical calculations performed for a simple case of the model show that, for values of the parameters consistent with experimental data, Pe exhibits only a small variation with w within the physiological range in the majority of the situations considered here. It is not possible to predict, from the study of these simple models, whether more complicated kinetic diagrams of water transport may be characterized by permeability coefficients with a more evident dependence on the water activities. Nevertheless, the results obtained here suggest that, for the case of physiological water pores, the analysis of the kinetic dependence of the permeability coefficients on the water activities may not yield evidence pointing to a discrete nature for the transport process. PMID:7529582

  5. 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

  6. 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

  7. TACK—a program coupling chemical kinetics with a two-dimensional transport model in geochemical systems

    NASA Astrophysics Data System (ADS)

    Källvenius, Göran; Ekberg, Christian

    2003-05-01

    The Transport And Chemical Kinetics (TACK) program has been designed to make predictions of the chemistry in the vicinity of a planned repository for nuclear waste, i.e. SFL 3-5, where SFL is the Swedish abbreviation for "Swedish repository for long-lived waste". This implies modelling transport and chemistry in fractured rock. The system concerned in the modelling of SFL is leaching water from decommissioning waste in concrete. The concrete will raise the pH in the water to between 12 and 13.5. So far, only a few calculations have been made on such systems. Coupled transport and chemical reaction programs should be used, since the system is important for safety assessments of the repository. At least two of programs can be used for this kind of problem, for example OS3D/GIMRT and PHAST. As it is also important to consider the uncertainty of the model, the TACK program fills an important purpose here. A slightly different approach to the problem may give significantly different results. Because validation is generally not possible, using several programs is the only key to identifying conceptual uncertainties. To illustrate this point, comparative calculations have been made between TACK and the PHAST program. The calculations gave qualitatively similar result but quantitatively somewhat differing results. The TACK program couples the well known PHREEQC geochemical program with a two-dimensional transport model. The PHREEQC calculations include speciation of solutions and mineral reactions involving kinetics. The reasons for choosing this program are that it is quite a general one and is relatively stable at the high pH values present in the systems used. The transport phenomena taken into account in the model are advection, diffusion and dispersion in two dimensions.

  8. Active water transport in unicellular algae: where, why, and how.

    PubMed

    Raven, John A; Doblin, Martina A

    2014-12-01

    The occurrence of active water transport (net transport against a free energy gradient) in photosynthetic organisms has been debated for several decades. Here, active water transport is considered in terms of its roles, where it is found, and the mechanisms by which it could occur. First there is a brief consideration of the possibility of active water transport into plant xylem in the generation of root pressure and the refilling of embolized xylem elements, and from an unsaturated atmosphere into terrestrial organisms living in habitats with limited availability of liquid water. There is then a more detailed consideration of volume and osmotic regulation in wall-less freshwater unicells, and the possibility of generation of buoyancy in marine phytoplankton such as large-celled diatoms. Calculations show that active water transport is a plausible mechanism to assist cells in upwards vertical movements, requires less energy than synthesis of low-density organic solutes, and potentially on a par with excluding certain ions from the vacuole. PMID:25205578

  9. 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. PMID:27557274

  10. 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.

  11. 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. PMID:24609652

  12. 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.

  13. 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

  14. 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.

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

    PubMed

    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. PMID:27394116

  16. 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

  17. 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

  18. 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...

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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)...

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  1. 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.

  2. The Transporter-Opsin-G protein-coupled receptor (TOG) Superfamily

    PubMed Central

    Yee, Daniel C.; Shlykov, Maksim A.; Västermark, Åke; Reddy, Vamsee S.; Arora, Sumit; Sun, Eric I.; Saier, Milton H.

    2013-01-01

    Visual Rhodopsins (VR) are recognized members of the large and diverse family of G protein-coupled receptors (GPCRs), but their evolutionary origin and relationships to other proteins, are not known. In an earlier publication (Shlykov et al., 2012), we characterized the 4-Toulene Sulfonate Uptake Permease (TSUP) family of transmembrane proteins, showing that these 7 or 8 TMS proteins arose by intragenic duplication of a 4 TMS-encoding gene, sometimes followed by loss of a terminal TMS. In this study, we show that the TSUP, GPCR and Microbial Rhodopsin (MR) families are related to each other and to six other currently recognized transport protein families. We designate this superfamily the Transporter-Opsin-G protein-coupled receptor (TOG) Superfamily. Despite their 8 TMS origins, members of most constituent families exhibit 7 TMS topologies that are well conserved, and these arose by loss of either the N-terminal (more frequent) or the C-terminal (less frequent) TMS, depending on the family. Phylogenetic analyses revealed familial relationships within the superfamily and protein relationships within each of the nine families. The statistical analyses leading to the conclusion of homology were confirmed using HMMs, Pfam, and 3D superimpositions. Proteins functioning by dissimilar mechanisms (channels, primary active transporters, secondary active transporters, group translocators and receptors) are interspersed on a phylogenetic tree of the TOG superfamily, suggesting that changes in the transport and energy-coupling mechanisms occurred multiple times during the evolution of this superfamily. PMID:23981446

  3. Controllable single-photon transport between remote coupled-cavity arrays

    NASA Astrophysics Data System (ADS)

    Qin, Wei; Nori, Franco

    2016-03-01

    We develop an approach for controllable single-photon transport between two remote one-dimensional coupled-cavity arrays, used as quantum registers, mediated by an additional one-dimensional coupled-cavity array, acting as a quantum channel. A single two-level atom located inside one cavity of the intermediate channel is used to control the long-range coherent quantum coupling between two remote registers, thereby functioning as a quantum switch. With a time-independent perturbative treatment, we find that the leakage of quantum information can in principle be made arbitrarily small. Furthermore, our method can be extended to realize a quantum router in multiregister quantum networks, where single-photons can be either stored in one of the registers or transported to another on demand. These results are confirmed by numerical simulations.

  4. 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.

  5. Structural Determinants of Water Permeation through the Sodium-Galactose Transporter vSGLT

    PubMed Central

    Adelman, Joshua L.; Sheng, Ying; Choe, Seungho; Abramson, Jeff; Wright, Ernest M.; Rosenberg, John M.; Grabe, Michael

    2014-01-01

    Sodium-glucose transporters (SGLTs) facilitate the movement of water across the cell membrane, playing a central role in cellular homeostasis. Here, we present a detailed analysis of the mechanism of water permeation through the inward-facing state of vSGLT based on nearly 10 μs of molecular dynamics simulations. These simulations reveal the transient formation of a continuous water channel through the transporter that permits water to permeate the protein. Trajectories in which spontaneous release of galactose is observed, as well as those in which galactose remains in the binding site, show that the permeation rate, although modulated by substrate occupancy, is not tightly coupled to substrate release. Using a, to our knowledge, novel channel-detection algorithm, we identify the key residues that control water flow through the transporter and show that solvent gating is regulated by side-chain motions in a small number of residues on the extracellular face. A sequence alignment reveals the presence of two insertion sites in mammalian SGLTs that flank these outer-gate residues. We hypothesize that the absence of these sites in vSGLT may account for the high water permeability values for vSGLT determined via simulation compared to the lower experimental estimates for mammalian SGLT1. PMID:24655503

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Quantification of Water Absorption and Transport in Parchment

    NASA Astrophysics Data System (ADS)

    Herringer, Susan N.; Bilheux, Hassina Z.; Bearman, Greg

    Neutron radiography was utilized to quantify water absorption and desorption in parchment at the High Flux Isotope Reactor CG-1D imaging facility at Oak Ridge National Laboratory (ORNL). Sequential 60s radiographs of sections of a 15th century parchment were taken as the parchment underwent wetting and drying cycles. This provided time-resolved visualization and quantification of water absorption and transport in parchment.