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1

Soil Water Retention Curves and Their Impact on Evaporation  

NASA Astrophysics Data System (ADS)

An accurate description of soil moisture dynamics in both the liquid and vapor phases is crucial to properly estimate soil evaporation. Soil moisture dynamics are largely dependent on the soil water retention. In the most commonly used models the water retention curve diverges at residual water content, the value below which liquid connectivity is lost and liquid flow stops. Not only this is physically unrealistic but results in incorrect evaporation modeling near dry conditions since the water vapor role is limited. We consider two of the main parametrizations that allow vapor flux below residual water content (modified models): one consists in a re-fit of the standard retention curve with zero residual water content, the other, supported by some laboratory measurements, considers a linear extension (on a semi-log plot) of the standard retention curve in the dry region. For a medium-textured sand and a loam we numerically investigate the effects of both the modified and the standard Van Genuchten models on the liquid and vapor transport during the simulated drying process, with and without surface radiative forcing. In the isothermal case, we show how all the models almost identically describe the capillary-dominated evaporative regime whereas when vapor diffusion is the dominant evaporative mechanism the modified models yield larger and longer sustained vapor fluxes, significantly increasing soil water removal. In the presence of diurnal radiative forcing at the soil surface, we focus on the effects of temperature fluctuations on soil water retention. The impact on liquid and vapor fluxes is analyzed in order to assess whether temperature-dependent and dry-extended retention curves may 'fill the gap' or not between theory and some still debated field experimental evidences (e.g. the midday moisture content rise) without the need of introducing any questionable and ad-hoc empirical terms such as vapor enhancement and/or liquid gain factors.

Ciocca, F.; Lunati, I.; Parlange, M. B.

2013-12-01

2

Average Soil Water Retention Curves Measured by Neutron Radiography  

SciTech Connect

Water retention curves are essential for understanding the hydrologic behavior of partially-saturated porous media and modeling flow transport processes within the vadose zone. In this paper we report direct measurements of the main drying and wetting branches of the average water retention function obtained using 2-dimensional neutron radiography. Flint sand columns were saturated with water and then drained under quasi-equilibrium conditions using a hanging water column setup. Digital images (2048 x 2048 pixels) of the transmitted flux of neutrons were acquired at each imposed matric potential (~10-15 matric potential values per experiment) at the NCNR BT-2 neutron imaging beam line. Volumetric water contents were calculated on a pixel by pixel basis using Beer-Lambert s law after taking into account beam hardening and geometric corrections. To remove scattering effects at high water contents the volumetric water contents were normalized (to give relative saturations) by dividing the drying and wetting sequences of images by the images obtained at saturation and satiation, respectively. The resulting pixel values were then averaged and combined with information on the imposed basal matric potentials to give average water retention curves. The average relative saturations obtained by neutron radiography showed an approximate one-to-one relationship with the average values measured volumetrically using the hanging water column setup. There were no significant differences (at p < 0.05) between the parameters of the van Genuchten equation fitted to the average neutron radiography data and those estimated from replicated hanging water column data. Our results indicate that neutron imaging is a very effective tool for quantifying the average water retention curve.

Cheng, Chu-Lin [ORNL; Perfect, Edmund [University of Tennessee, Knoxville (UTK); Kang, Misun [ORNL; Voisin, Sophie [ORNL; Bilheux, Hassina Z [ORNL; Horita, Juske [Texas Tech University (TTU); Hussey, Dan [NIST Center for Neutron Research (NCRN), Gaithersburg, MD

2011-01-01

3

Water retention curves and thermal insulating properties of Thermosand  

NASA Astrophysics Data System (ADS)

The heat loss and the efficiency of isolating material surrounding heat supply pipes are essential issues for the energy budget of heat supply pipe lines. Until now heat loss from the pipe is minimized by enlarging the polyurethane (PU) - insulation thickness around the pipe. As a new approach to minimize the heat loss a thermally insulating bedding material was developed and investigated. Conventional bedding sands cover all necessary soil mechanical properties, but have a high thermal conductivity from ? =1,5 to 1,7 W/(m K). A newly developed embedding material 'Thermosand' shows thermal properties from ?=0,18 W/(m K) (dry) up to 0,88 W/(m K) (wet). The raw material originates from the waste rock stockpiles of a coal mine near Fohnsdorf, Austria. With high temperatures up to nearly 1000 ° C and a special mineral mixture, a natural burned reddish material resembling clinker arises. The soilmechanical properties of Thermosand has been thoroughly investigated with laboratory testing and in situ investigations to determine compaction-, permeability- and shear-behaviour, stiffness and corresponding physical parameters. Test trenches along operational heat pipes with temperature-measurement along several cross-sections were constructed to compare conventional embedding materials with 'Thermosand'. To investigate the influence of varying moisture content on thermal conductivity a 1:1 large scale model test in the laboratory to simulate real insitu-conditions was established. Based on this model it is planned to develop numerical simulations concerning varying moisture contents and unsaturated soil mechanics with heat propagation, including the drying out of the soil during heat input. These simulations require the knowledge about the water retention properties of the material. Thus, water retention curves were measured using both steady-state tension and pressure techniques and the simplified evaporation method. The steady-state method employs a tension table (sand box) at tensions below 100 hPa and a pressure extractor at tensions between 300 hPa and 15,000 hPa; the water content is measured by weighing after the sample has equilibrated at the tension value set on the table or plate. In the transient evaporation method two tensiometers with a measurement range between 0 and 850 hPa are installed at a depth of 1.25 cm and 3.75 cm in a sample of 5 cm in height; the mean values of the two tensiometers and the water contents measured by weighting are used to obtain the water retention curve. First results of both methods show that the Thermosand samples release water over the entire tension range measured above 10 hPa. Because of the limited measurement range of the tensiometers used for the evaporation method, the measured curve must be extrapolated between 850 hPa and 15,000 hPa, to allow comparison with the steady-state method. To this end, it was attempted to match the Van-Genuchten and a bimodal Van-Genuchten retention function to the data from the evaporation experiments. This involves a simultaneous fit of both the water-retention and the hydraulic-conductivity function. As one first result only the Van-Genuchten model was found to be able to produce satisfactorily fits to the data. The extrapolated water retention curves (above 850 hPa) however do not match the data from the steady-state method. This suggests that alternative soil hydraulic functions are needed to provide an adequate representation of the water retention characteristics of the Thermosand. It has to be considered that especially for the heat flow simulation water retention and hydraulic conductivity functions above 15,000 hPa have to be determined.

Leibniz, Otto; Winkler, Gerfried; Birk, Steffen

2010-05-01

4

Closing the loop of the soil water retention curve  

USGS Publications Warehouse

The authors, to their knowledge for the first time, produced two complete principal soil water retention curves (SWRCs) under both positive and negative matric suction regimes. An innovative testing technique combining the transient water release and imbibition method (TRIM) and constant flow method (CFM) was used to identify the principal paths of SWRC in the positive pore-water pressure regime under unsaturated conditions. A negative matric suction of 9.8 kPa is needed to reach full saturation or close the loop of the SWRC for a silty soil. This work pushes the understanding of the interaction of soil and water into new territory by quantifying the boundaries of the SWRC over the entire suction domain, including both wetting and drying conditions that are relevant to field conditions such as slope wetting under heavy rainfall or rapid groundwater table rise in earthen dams or levees.

Lu, Ning; Alsherif, N; Wayllace, Alexandra; Godt, Jonathan W.

2015-01-01

5

Soil Water Thermodynamic to Unify Water Retention Curve by Pressure Plates and Tensiometer  

NASA Astrophysics Data System (ADS)

The pressure plate method is a standard method for measuring the pF curves, also called soil water retention curves, in a large soil moisture range from saturation to a dry state corresponding to a tension pressure of near 1500 kPa. However, the pressure plate can only provide discrete water retention curves represented by a dozen measured points. In contrast, the measurement of the soil water retention curves by tensiometer is direct and continuous, but limited to the range of the tensiometer reading: from saturation to near 70-80 kPa. The two methods stem from two very different concepts of measurement and the compatibility of both methods has never been demonstrated. The recently established thermodynamic formulation of the pedostructure water retention curve, will allow the compatibility of the two curves to be studied, both theoretically and experimentally. This constitutes the object of the present article. We found that the pressure plate method provides accurate measurement points of the pedostructure water retention curve h(W), conceptually the same as that accurately measured by the tensiometer. However, contrarily to what is usually thought, h is not equal to the applied air pressure on the sample, but rather, is proportional to its logarithm, in agreement with the thermodynamic theory developed in the article. The pF curve and soil water retention curve, as well as their methods of measurement are unified in a same physical theory. It is the theory of the soil medium organization (pedostructure) and its interaction with water. We show also how the hydrostructural parameters of the theoretical curve equation can be estimated from any measured curve, whatever the method of measurement. An application example using published pF curves is given.

Braudeau, Erik; Hovhannissian, Gaghik; Assi, Amjad; Mohtar, Rabi

2014-10-01

6

A Global Optimization Method to Calculate Water Retention Curves  

NASA Astrophysics Data System (ADS)

Water retention curves (WRC) have a key role for the hydraulic characterization of soils and rocks. The behaviour of the medium is defined by relating the unsaturated water content to the matric potential. The experimental determination of WRCs requires an accurate and detailed measurement of the dependence of matric potential on water content, a time-consuming and error-prone process, in particular for rocky media. A complete experimental WRC needs at least a few tens of data points, distributed more or less uniformly from full saturation to oven dryness. Since each measurement requires to wait to reach steady state conditions (i.e., between a few tens of minutes for soils and up to several hours or days for rocks or clays), the whole process can even take a few months. The experimental data are fitted to the most appropriate parametric model, such as the widely used models of Van Genuchten, Brooks and Corey and Rossi-Nimmo, to obtain the analytic WRC. We present here a new method for the determination of the parameters that best fit the models to the available experimental data. The method is based on differential evolution, an evolutionary computation algorithm particularly useful for multidimensional real-valued global optimization problems. With this method it is possible to strongly reduce the number of measurements necessary to optimize the model parameters that accurately describe the WRC of the samples, allowing to decrease the time needed to adequately characterize the medium. In the present work, we have applied our method to calculate the WRCs of sedimentary carbonatic rocks of marine origin, belonging to 'Calcarenite di Gravina' Formation (Middle Pliocene - Early Pleistocene) and coming from two different quarry districts in Southern Italy. WRC curves calculated using the Van Genuchten model by simulated annealing (dashed curve) and differential evolution (solid curve). The curves are calculated using 10 experimental data points randomly extracted from the full experimental dataset. Simulated annealing is not able to find the optimal solution with this reduced data set.

Maggi, S.; Caputo, M. C.; Turturro, A. C.

2013-12-01

7

Hysteresis and uncertainty in soil water-retention curve parameters  

USGS Publications Warehouse

Accurate estimates of soil hydraulic parameters representing wetting and drying paths are required for predicting hydraulic and mechanical responses in a large number of applications. A comprehensive suite of laboratory experiments was conducted to measure hysteretic soil-water characteristic curves (SWCCs) representing a wide range of soil types. Results were used to quantitatively assess differences and uncertainty in three simplifications frequently adopted to estimate wetting-path SWCC parameters from more easily measured drying curves. They are the following: (1) ?w=2?d, (2) nw=nd, and (3) ?ws=?ds, where ?, n, and ?s are fitting parameters entering van Genuchten’s commonly adopted SWCC model, and the superscripts w and d indicate wetting and drying paths, respectively. The average ratio ?w/?d for the data set was 2.24±1.25. Nominally cohesive soils had a lower ?w/?d ratio (1.73±0.94) than nominally cohesionless soils (3.14±1.27). The average nw/nd ratio was 1.01±0.11 with no significant dependency on soil type, thus confirming the nw=nd simplification for a wider range of soil types than previously available. Water content at zero suction during wetting (?ws) was consistently less than during drying (?ds) owing to air entrapment. The ?ws/?ds ratio averaged 0.85±0.10 and was comparable for nominally cohesive (0.87±0.11) and cohesionless (0.81±0.08) soils. Regression statistics are provided to quantitatively account for uncertainty in estimating hysteretic retention curves. Practical consequences are demonstrated for two case studies.

Likos, William J.; Lu, Ning; Godt, Jonathan W.

2014-01-01

8

Estimating water retention curves for sandy soils at the Dońana National Park, SW Spain  

Technology Transfer Automated Retrieval System (TEKTRAN)

The determination of soil water retention curves (SWRC) in the laboratory is a slow and tedious task, which is especially challenging for sandy soils due to their low water retention capacity and large water content changes for small pressure head differences. Due to spatial variability within larg...

9

Effects of the water retention curve on evaporation from arid soils  

NASA Astrophysics Data System (ADS)

Water retention curves approaching infinitely negative matric potentials at residual water content are widely employed to model soil moisture dynamics. When used in numerical simulations, these retention curves fail to satisfactorily describe evaporation from arid soil (moisture-limited regime) because they do not allow the soil to dry below residual water content. We show that simple modifications can be introduced to prevent unrealistic water retention at residual water content and predict more physically sound moisture dynamics. Modified retention models that allow drying below residual predict a moisture-limited regime characterized by a thin subsurface evaporation zone and produce vapor fluxes up to 3 times larger than classical retention models. This might reduce the need to introduce empirical enhancement factors and improve the capability of modeling evaporation into the atmosphere and runoff in arid regions.

Ciocca, Francesco; Lunati, Ivan; Parlange, Marc B.

2014-05-01

10

Performance Evaluation of Models that Describe the Soil Water Retention Curve between Saturation and Oven Dryness  

Technology Transfer Automated Retrieval System (TEKTRAN)

The objective of this work was to evaluate eight closed-form unimodal analytical expressions that describe the soil-water retention curve over the complete range of soil water contents. To meet this objective, the eight models were compared in terms of their accuracy (root mean square error, RMSE), ...

11

Multiple pixel-scale soil water retention curves quantified by neutron radiography  

NASA Astrophysics Data System (ADS)

The soil water retention function is needed for modeling multiphase flow in porous media. Traditional techniques for measuring the soil water retention function, such as the hanging water column or pressure cell methods, yield average water retention data which have to be modeled using inverse procedures to extract relevant point parameters. In this study, we have developed a technique for directly measuring multiple point (pixel-scale) water retention curves for a repacked sand material using 2-D neutron radiography. Neutron radiographic images were obtained under quasi-equilibrium conditions at nine imposed basal matric potentials during monotonic drying of Flint sand at the High Flux Isotope Reactor (HFIR) Cold Guide (CG) 1D beamline at Oak Ridge National Laboratory. All of the images were normalized with respect to an image of the oven dry sand column. Volumetric water contents were computed on a pixel by pixel basis using an empirical calibration equation after taking into account beam hardening and geometric corrections. Corresponding matric potentials were calculated from the imposed basal matric potential and pixel elevations. Volumetric water content and matric potential data pairs corresponding to 120 selected pixels were used to construct 120 point water retention curves. Each curve was fitted to the Brooks and Corey equation using segmented non-linear regression in SAS. A 98.5% convergence rate was achieved resulting in 115 estimates of the four Brooks and Corey parameters. A single Brooks and Corey point water retention function was constructed for Flint sand using the median values of these parameter estimates. This curve corresponded closely with the point Brooks and Corey function inversely extracted from the average water retention data using TrueCell. Forward numerical simulations performed using HYDRUS 1-D showed that the cumulative outflows predicted using the point Brooks and Corey functions from both the direct (neutron radiography) and inverse (TrueCell) methods were in good agreement with independent measurements of cumulative outflow determined with a transducer. Our results indicate that neutron radiography can be used to quantify the point water retention curve of homogeneous mineral particles. Further research will be needed to extend this approach to more heterogeneous porous media.

Kang, M.; Perfect, E.; Cheng, C. L.; Bilheux, H. Z.; Lee, J.; Horita, J.; Warren, J. M.

2014-03-01

12

Extrapolative Capability of Two Models That Estimating Soil Water Retention Curve between Saturation and Oven Dryness  

PubMed Central

Accurate estimation of soil water retention curve (SWRC) at the dry region is required to describe the relation between soil water content and matric suction from saturation to oven dryness. In this study, the extrapolative capability of two models for predicting the complete SWRC from limited ranges of soil water retention data was evaluated. When the model parameters were obtained from SWRC data in the 0–1500 kPa range, the FX model (Fredlund and Xing, 1994) estimations agreed well with measurements from saturation to oven dryness with RMSEs less than 0.01. The GG model (Groenevelt and Grant, 2004) produced larger errors at the dry region, with significantly larger RMSEs and MEs than the FX model. Further evaluations indicated that when SWRC measurements in the 0–100 kPa suction range was applied for model establishment, the FX model was capable of producing acceptable SWRCs across the entire water content range. For a higher accuracy, the FX model requires soil water retention data at least in the 0- to 300-kPa range to extend the SWRC to oven dryness. Comparing with the Khlosi et al. (2006) model, which requires measurements in the 0–500 kPa range to reproduce the complete SWRCs, the FX model has the advantage of requiring less SWRC measurements. Thus the FX modeling approach has the potential to eliminate the processes for measuring soil water retention in the dry range. PMID:25464503

Lu, Sen; Ren, Tusheng; Lu, Yili; Meng, Ping; Sun, Shiyou

2014-01-01

13

Comparison of Optimization and Two-point Methods in Estimation of Soil Water Retention Curve  

NASA Astrophysics Data System (ADS)

Soil water retention curve (SWRC) is one of the soil hydraulic properties in which its direct measurement is time consuming and expensive. Since, its measurement is unavoidable in study of environmental sciences i.e. investigation of unsaturated hydraulic conductivity and solute transport, in this study the attempt is to predict soil water retention curve from two measured points. By using Cresswell and Paydar (1996) method (two-point method) and an optimization method developed in this study on the basis of two points of SWRC, parameters of Tyler and Wheatcraft (1990) model (fractal dimension and air entry value) were estimated and then water content at different matric potentials were estimated and compared with their measured values (n=180). For each method, we used both 3 and 1500 kPa (case 1) and 33 and 1500 kPa (case 2) as two points of SWRC. The calculated RMSE values showed that in the Creswell and Paydar (1996) method, there exists no significant difference between case 1 and case 2. However, the calculated RMSE value in case 2 (2.35) was slightly less than case 1 (2.37). The results also showed that the developed optimization method in this study had significantly less RMSE values for cases 1 (1.63) and 2 (1.33) rather than Cresswell and Paydar (1996) method.

Ghanbarian-Alavijeh, B.; Liaghat, A. M.; Huang, G.

2009-04-01

14

Prediction of water retention curves for dry soils from an established pedotransfer function: Evaluation of the Webb model  

NASA Astrophysics Data System (ADS)

The van Genuchten curve, and its prediction by various pedotransfer functions, has long been an established method to describe the water retention curve (WRC) in soils, but it cannot be used to describe water retention under conditions dryer then the wilting point. Water retention under dry conditions follows a log linear function, which does not agree with the extrapolated van Genuchten curve. As a remedy Webb (2000) proposed an approach that predicts this linear function for the dry range with a smooth transition to the van Genuchten curve that has been fitted to experimental data for the moist range. In this work we present the prediction of water retention curves for 31 soils under dry conditions using the approach presented by Webb. In addition to the larger number of soils that we use for evaluation we deviate from the original Webb approach in two ways: (a) we use predicted (Rosetta) rather than fitted van Genuchten curves and (b) we use a corrected endpoint at zero water content. The outcome reveals good results for the prediction of water retention curves for the dry region and provides a smooth transition between the moist and the dry region of the water retention curve. Occasional inferior performance for some data is likely due to uncertainties in the texture data or in the choice of the right bulk density rather than due to conceptual shortcomings of the Webb approach. This work shows that the WRC for the whole humidity range, from oven dryness to full saturation, can be described by two functions with a smooth transition whose parameters can all be predicted by Rosetta without the need of experimental information.

Schneider, M.; Goss, K.-U.

2012-06-01

15

Modeling the Soil Water Retention Curves of Soil-Gravel Mixtures with Regression Method on the Loess Plateau of China  

PubMed Central

Soil water retention parameters are critical to quantify flow and solute transport in vadose zone, while the presence of rock fragments remarkably increases their variability. Therefore a novel method for determining water retention parameters of soil-gravel mixtures is required. The procedure to generate such a model is based firstly on the determination of the quantitative relationship between the content of rock fragments and the effective saturation of soil-gravel mixtures, and then on the integration of this relationship with former analytical equations of water retention curves (WRCs). In order to find such relationships, laboratory experiments were conducted to determine WRCs of soil-gravel mixtures obtained with a clay loam soil mixed with shale clasts or pebbles in three size groups with various gravel contents. Data showed that the effective saturation of the soil-gravel mixtures with the same kind of gravels within one size group had a linear relation with gravel contents, and had a power relation with the bulk density of samples at any pressure head. Revised formulas for water retention properties of the soil-gravel mixtures are proposed to establish the water retention curved surface models of the power-linear functions and power functions. The analysis of the parameters obtained by regression and validation of the empirical models showed that they were acceptable by using either the measured data of separate gravel size group or those of all the three gravel size groups having a large size range. Furthermore, the regression parameters of the curved surfaces for the soil-gravel mixtures with a large range of gravel content could be determined from the water retention data of the soil-gravel mixtures with two representative gravel contents or bulk densities. Such revised water retention models are potentially applicable in regional or large scale field investigations of significantly heterogeneous media, where various gravel sizes and different gravel contents are present. PMID:23555040

Wang, Huifang; Xiao, Bo; Wang, Mingyu; Shao, Ming'an

2013-01-01

16

Interrelations among the soil-water retention, hydraulic conductivity, and suction-stress characteristic curves  

USGS Publications Warehouse

The three fundamental constitutive relations that describe fluid flow, strength, and deformation behavior of variably saturated soils are the soil-water retention curve (SWRC), hydraulic conductivity function (HCF), and suction-stress characteristic curve (SSCC). Until recently, the interrelations among the SWRC, HCF, and SSCC have not been well established. This work sought experimental confirmation of interrelations among these three constitutive functions. Results taken from the literature for six soils and those obtained for 11 different soils were used. Using newly established analytical relations among the SWRC, HCF, and SSCC and these test results, the authors showed that these three constitutive relations can be defined by a common set of hydromechanical parameters. The coefficient of determination for air-entry pressures determined independently using hydraulic and mechanical methods is >0.99, >0.98 for the pore size parameter, and 0.94 for the residual degree of saturation. One practical implication is that one of any of the four experiments (axis-translation, hydraulic, shear-strength, or deformation) is sufficient to quantify all three constitutive relations.

Lu, Ning; Kaya, Murat; Godt, Jonathan W.

2014-01-01

17

Soil water retention curve of agrogray soils: Influence of anisotropy and the scaling factor  

NASA Astrophysics Data System (ADS)

The soil water characteristic or soil water retention curve (WRC) of medium-loamy gray forest soil horizons was studied in cylinder-shaped samples of disturbed and undisturbed structure. The sample height varied within 2-4 cm and the diameter within 4.5-10 cm. The soil monoliths were sampled in three profiles: vertically, along the slope, and across the slope in accordance with the intrasoil paleorelief formed by the funnel-shaped surface of the second humus horizon. The experimental WRC were approximated with the van Genuchten equation. The statistical analysis of the WRc approximation parameters proved to differ significantly in filled soil samples and monoliths, and a number of parameters differ for samples of the maximal height and diameter. The reliable differences of the parameters were also noted for the different sampling directions, most often, for those across the paleorelief slope. The noted variation in the WRC approximation parameters may substantially influence the predictive estimation of the spring water reserve for example. This fact suggests the necessity to strictly indicate the sampling procedure, in particular, with respect to the soil profile, the asymmetry in the soil properties, and the sample sizes (scaling factor) used for analyzing the hydrological properties of structured soils.

Umarova, A. B.; Shein, E. V.; Kukharuk, N. S.

2014-12-01

18

Water Repellency of Organic Growing Media and Its Consequences on Hysteretic Behaviours of the Water Retention Curve  

E-print Network

Science, Univ. Laval, QC, G1K 7P4, Canada Keywords: peat, pine bark, modelling, hydrophobicity Abstract, (), of peat and pine bark during a drying/wetting cycle. Major differences in the hydraulic behaviour curve (21%) and also in the contact angle/water potential relation- ship, ((), 20%), whereas in pine

Paris-Sud XI, Université de

19

Relationship between specific surface area and the dry end of the water retention curve for soils with varying clay and organic carbon contents  

NASA Astrophysics Data System (ADS)

Accurate description of the soil water retention curve (SWRC) at low water contents is important for simulating water dynamics and biochemical vadose zone processes in arid environments. Soil water retention data corresponding to matric potentials of less than -10 MPa, where adsorptive forces dominate over capillary forces, have also been used to estimate soil specific surface area (SA). In the present study, the dry end of the SWRC was measured with a chilled-mirror dew point psychrometer for 41 Danish soils covering a wide range of clay (CL) and organic carbon (OC) contents. The 41 soils were classified into four groups on the basis of the Dexter number (n = CL/OC), and the Tuller-Or (TO) general scaling model describing water film thickness at a given matric potential (<-10 MPa) was evaluated. The SA estimated from the dry end of the SWRC (SA_SWRC) was in good agreement with the SA measured with ethylene glycol monoethyl ether (SA_EGME) only for organic soils with n > 10. A strong correlation between the ratio of the two surface area estimates and the Dexter number was observed and applied as an additional scaling function in the TO model to rescale the soil water retention curve at low water contents. However, the TO model still overestimated water film thickness at potentials approaching ovendry condition (about -800 MPa). The semi-log linear Campbell-Shiozawa-Rossi-Nimmo (CSRN) model showed better fits for all investigated soils from -10 to -800 MPa and yielded high correlations with CL and SA. It is therefore recommended to apply the empirical CSRN model for predicting the dry part of the water retention curve (-10 to -800 MPa) from measured soil texture or surface area. Further research should aim to modify the more physically based TO model to obtain better descriptions of the SWRC in the very dry range (-300 to -800 MPa).

Resurreccion, Augustus C.; Moldrup, Per; Tuller, Markus; Ferré, T. P. A.; Kawamoto, Ken; Komatsu, Toshiko; de Jonge, Lis Wollesen

2011-06-01

20

Evolution of water repellency of organic growing media used in Horticulture and consequences on hysteretic behaviours of the water retention curve  

NASA Astrophysics Data System (ADS)

Most of growing media used in horticulture (particularly peat substrates) shows hysteresis phenomena during desiccation and rehydration cycles, which greatly affects their hydraulic properties. The origins of these properties have often been related to one or several of the specific mechanisms such as the non-geometrical uniformity of the pores (also called ‘ink bottle' effect), presence of trapped air, shrinkage-swelling phenomena, and changes in water repellency. However, recent results showed that changes in wettability during desiccation and rehydration could be considered as one of the main factors leading to hysteretic behaviour in these materials with high organic matter contents (Naasz et al., 2008). The general objective was to estimate the evolutions of changes in water repellency on the water retention properties and associated hysteresis phenomena in relation to the intensity and the number of drying/wetting cycles. For this, simultaneous shrinkage/swelling and water retention curves were obtained using method previously developed for soil shrinkage analysis by Boivin (2006) that we have adapted for growing media and to their physical behaviours during rewetting. The experiment was performed in a climatic chamber at 20°C. A cylinder with the growing medium tested was placed on a porous ceramic disk which is used to control the pressure and to full/empty water of the sample. The whole of the device was then placed on a balance to record the water loss/storage with time; whereas linear displacement transducers were used to measure the changes in sample height and diameter upon drying and wetting in the axial and radial directions. Ceramic cups (2 cm long and 0.21 cm diameter) connected to pressure transducers were inserted in the middle of the samples to record the water pressure head. In parallell, contact angles were measured by direct droplet method at different steps during the drying/rewetting cycles. First results obtained on weakly decomposed peat samples with or without surfactants showed isotropic shrinkage and swelling, and highlighted hysteresis phenomena in relation to the intensity of drying/wetting cycle. Contact angle measurements are in progress. Other measurements on highly decomposed peat (more repellent than weakly decomposed), composted pine bark (without volume change during dryin/wetting cycles), and coco fiber (expected as non repellent organic growing media) are also in progress.

Michel, Jean-Charles; Qi, Guifang; Charpentier, Sylvain; Boivin, Pascal

2010-05-01

21

Analysis of water retention curve as a potential tool in comparing the effect of different soil management in two olive orchard in southern Spain  

NASA Astrophysics Data System (ADS)

Water soil erosion is one of the major concerns in agricultural areas in Southern Spain, and the use of cover crops has been recommended as an alternative to tillage to prevent, or mitigate, soil erosion. This change of soil management implies a progressive modification of soil chemical, biological and physical properties which to date, have been documented by a limited number of studies. In this communication we describe a methodology based on the modification of the water retention curves of intact cores, present the results obtained in two olive orchards in Southern Spain, and compare them with several chemical and physical properties measured simultaneously in the orchards. The experimental areas were located in Benacazón and Pedrera, Seville province in Southern Spain, and at each location two experimental plots were established. One of the plots was under traditional tillage management and the other under cover crop soil management. The slope at the plots was 12 and 4% respectively. Soil samples were taken at both plots differentiating between the inter tree areas and the under the olive canopy areas, between two different depths: 0-10 cm and 10-20 cm. These resulted in eight different sampling areas (2x2x2). Samples were taken three year after establishing the experiments. Water retention curves of soils were obtained as the average of replications per and using the Eijkelkamp Sand and Sand/Kaolin suction tables (0-500 hPa) and a Decagon's WP4-T dewpoint potentiometer (0-300•106 hPa). The latest was used to determine the residual water content. Experimental water retention curves were to two different models: van Genuchten (1980) and Kosugi (1994). Once modeling was done, the slope value of the curves at the inflexion point, proposed by Dexter (2004a, b, c) to estimate physical quality of soils, was calculated. This study presents and discusses the advantages and problems of the different approaches for determining the water retention curves, the potential of these curves to evaluate physical modifications of the soils, and compares them with the other soil properties measured at the experiments. References: Dexter, A. R. 2004. a.- Soil physical quality. Part I. Theory, effects of soil texture, density, and organic matter, and effects on root growth. Geoderma 120 (2004) 201-214. Dexter, A. R. 2004. b.- Soil physical quality. Part II. Friability, tillage, tilth and hardsetting. Geoderma 120 (2004) 215-225. Dexter, A. R. 2004. c.- Soil physical quality. Part III: Unsaturated hydraulic conductivity and general conclusions about S-theory. Geoderma 120 (2004) 227-239. Kosugi, K. 1994. Three-parameter lognormal distribution model for soil water retention. Water Resour. Re. 30: 891-901. van Genutchen, M.Th. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils, Soil Science Society of America Journal, v.44, p.892-898,1980.

Guzmán, G.; Gómez, J. A.; Giráldez, J. V.

2010-05-01

22

Deriving NMR surface relaxivities, pore size distributions and water retention curves by NMR relaxation experiments on partially de-saturated rocks  

NASA Astrophysics Data System (ADS)

Nuclear magnetic resonance (NMR) is a method used over a wide field of geophysical applications to non-destructively determine transport and storage properties of rocks and soils. In NMR relaxometry signal amplitudes correspond directly to the rock's fluid (water, oil) content. On the other hand the NMR relaxation behavior, i.e. the longitudinal (T1) and transverse (T2) NMR relaxation times, can be used to derive pore sizes and permeability as it is linearly linked to the pore's surface-to-volume-ratio and physiochemical properties of the rock-fluid interface by the surface relaxivity ?_s This parameter, however, is dependent on the type and mineral constituents of the investigated rock sample and thus has to be determined and calibrated prior to estimating pore sizes from NMR relaxometry measurements. Frequently used methods to derive surface relaxivity to calibrate NMR pore sizes comprise mercury injection, pulsed field gradients (PFG-NMR) or grain size analysis. This study introduces an alternative approach to jointly estimate NMR surface relaxivity and pore radii distributions using NMR relaxation data obtained from partially de-saturated rocks. In this, inverse modeling is carried on a linked Young Laplace equation for capillary bundles and the Brownstein and Tarr equations. Subsequently, this approach is used to predict water retention curves of the investigated rocks. The method was tested and validated on simulated and laboratory transverse NMR data. Calculated inverse models are generally in a good agreement with results obtained from mercury injection and drainage measurements. Left: Measured and predicted water retention (pF) curves. Center: NMR relaxometry data, fit and error. Right: Mercury injection data (HgPor, dashed line) and jointly derived pore radii distributions and surface relaxivity by joint inverse modelling

Mohnke, O.; Nordlund, C. L.; Klitzsch, N.

2013-12-01

23

2.5 SOIL WATER POTENTIAL ESTIMATES Soil moisture retention curves were evaluated for representative A, AE, and EB horizon soils  

E-print Network

ESTIMATES Soil moisture retention curves were evaluated for representative A, AE, and EB horizon soils, additional litter and soil temperature measurements were conducted periodically from 1994 through 1996 to determine if the TDE infrastructure had a microclimatic effect that differed with the extent of leaf

24

High-resolution Land Cover Datasets, Composite Curve Numbers, and Storm Water Retention in the Tampa Bay, FL region  

EPA Science Inventory

Policy makers need to understand how land cover change alters storm water regimes, yet existing methods do not fully utilize newly available datasets to quantify storm water changes at a landscape-scale. Here, we use high-resolution, remotely-sensed land cover, imperviousness, an...

25

Retention Curve Measurement for Sands Using a TDR-based Long Column and Modified Tempe Cell  

NASA Astrophysics Data System (ADS)

Long column and Tempe cell are typical methods for measuring the water retention curves for soils. In the conventional long column method utilizing a stack of rings, water saturation profile is determined gravimetrically. X-ray or gamma ray attenuation are non-destructive methods but require complex and expensive devices and involve the use of photon sources. Time domain reflectometry (TDR) is an alternative to these radioactive methods for measuring water content profile along the column. Typical Tempe cells have a sample height of 3 to 6 cm. Suction is applied to the sample to induce drainage and monitored outflow is used to calculate the average water saturation of the sample, which potentially leads to obscuring the distinct displacement pressure value and results in a smoothed retention curve. In this study, we assumed that direct point-wise measurements provide retention curves that represent the physical behavior of the porous medium. We first determined retention curves for a number of well-sorted industrial silica sands using a long column that allows such point-wise measurements by TDR probes horizontally installed at eleven different elevations. Then, we modified a commercially available Tempe cell so that water saturation and capillary pressure head at a physical point in the cell, as well as the conventional height-averaged water saturation, can be measured simultaneously. Comparison of the conventional and point- measured retention curves that were obtained simultaneously for the identical sand samples revealed that 1) point-measured retention curves were identical to the ones measured in the long column, 2) the artifact of using height-averaged saturation values as pointed out by Dane et al. [1992] was experimentally confirmed. We further show that the displacement pressure head can possibly be underestimated especially for coarse soils when height-averaged water saturation is used. This is more significant for oil-water and DNAPL-water systems where the displacement pressure values are typically smaller than those in air-water systems.

Sakaki, T.; Illangasekare, T. H.

2006-12-01

26

Water retention and gas relative permeability of two industrial concretes  

SciTech Connect

This experimental study aims at identifying the water retention properties of two industrial concretes to be used for long term underground nuclear waste storage structures. Together with water retention, gas transfer properties are identified at varying water saturation level, i.e. relative gas permeability is assessed directly as a function of water saturation level S{sub w}. The influence of the initial de-sorption path and of the subsequent re-saturation are analysed both in terms of water retention and gas transfer properties. Also, the influence of concrete microstructure upon water retention and relative gas permeability is assessed, using porosity measurements, analysis of the BET theory from water retention properties, and MIP. Finally, a single relative gas permeability curve is proposed for each concrete, based on Van Genuchten-Mualem's statistical model, to be used for continuous modelling approaches of concrete structures, both during drying and imbibition.

Chen Wei; Liu Jian; Brue, Flore; Skoczylas, Frederic [Univ Lille Nord de France, F-59000 Lille (France); ECLille, LML, BP 48, F-59650 Villeneuve d'Ascq (France); CNRS, UMR 8107, F-59650 Villeneuve d'Ascq (France); Davy, C.A., E-mail: catherine.davy@ec-lille.fr [Univ Lille Nord de France, F-59000 Lille (France); ECLille, LML, BP 48, F-59650 Villeneuve d'Ascq (France); CNRS, UMR 8107, F-59650 Villeneuve d'Ascq (France); Bourbon, Xavier; Talandier, Jean [Andra, 1-7 rue Jean Monnet, F-92298 Chatenay-Malabry Cedex (France)

2012-07-15

27

Micromechanical analysis of water retention phenomenon  

NASA Astrophysics Data System (ADS)

We investigate the water distribution and the link between suction and water content in granular media. Firstly, we examine the effect of suction on the shape and the volume of the liquid bridge for different parameters (grain radius, inter-particle distance, contact angle, surface tension). This local behaviour is then used in a discrete element study of a sample composed of several thousands of grains. We focus our study on the pendular state. The existence of a liquid film around the grains which involves the continuity of the liquid phase is assumed. The water distribution and the water content associated with a given suction are calculated. Then retention curves of the granular media are built. Four different methods are used. The first is based on the local expression of the capillary force coupled with the "gorge method," the second is based on the Laplace equation, and the third and the fourth are based on the integration of the differential equation that defines the liquid bridge shape. A parametric study is made to bring to light the effect of macroscopic parameters (grain-size distribution, density) and physical parameters (liquid/air surface tension, contact angle) on the water retention curve. Finally, numerical data are compared to experimental results.

Gras, J.-P.; Delenne, J.-Y.; Soulié, F.; El Youssoufi, M. S.

2009-06-01

28

In situ soil water retention measurements with TDR and polymer tensiometers and comparison with computed water retention relations  

NASA Astrophysics Data System (ADS)

The soil water retention relation is of widespread interest in unsaturated zone hydrology. The standard procedure for determining this relation is to take soil cores, subject these cores to predetermined pressures and record the subsequent soil water contents. A disadvantage of this method is that it needs to be determined in the laboratory, and is often the main drying curve is considered. However, the water retention relationship's nature is hysteretic, and field soils will often go through multiple cycles of drying and wetting. To fully understand unsaturated processes in dry soils it is highly desirable to measure in situ soil water retention relations. Combining measurements of polymer tensiometers and TDR-probes it is possible to determine an in situ soil water retention relation until a matric potential of -1.6 MPa (pF=4.2). In an experimental setup polymer tensiometers were paired to TDR probes in a setup of two evaporation boxes, one containing sand (97.6% sand, 1.6% silt, 0.8% clay), and one containing loam (42.8% sand, 38.8% silt, 18.4% clay). Results were compared with laboratory determined water retention relations, and frequently used water retention models. Some water retention models may implicitly assume the averaged value of the matric pressure over a soil sample, a point that was illuminated by Liu and Dane (1995). As polymer tensiometers measure a more local value of the matric pressure within the soil, the use of such models on in situ determined water relations may lead to extreme parameter values. Liu, H.H. and J.H. Dane. 1995. Improved computational procedure for water retention relations of immicible fluids using pressure cells. This research was funded by the Dutch Technology Foundation (STW).

van der Ploeg, M. J.; Gooren, H. P. A.; Hoogendam, C. W.; Bakker, G.; Huiskes, C.; Koopal, L. K.; Kruidhof, H.; de Rooij, G. H.

2009-04-01

29

Pore-Scale Model for Water Retention in Unsaturated Sand  

NASA Astrophysics Data System (ADS)

A model for water retention in pores representative of unsaturated granular media is described. Retention behavior in an idealized angular pore is upscaled to the bulk scale using a statistical framework for pore size distribution that independently accounts for partially filled pores in the form of liquid bridges and completely filled pores in the form of saturated pockets. This distinction allows the water retention curve to be modeled over the complete range of saturation (pendular, funicular, and capillary regimes). Material properties including surface area, porosity, and grain size distribution are used to constrain the model calculations. Development and characteristics of the model are described; model predictions are compared with experimental measurements for unsaturated sand.

Likos, William J.

2009-06-01

30

Running heading: Water retention properties of the clay in clayey soils Water retention properties of the clay in soils developed  

E-print Network

1 Running heading: Water retention properties of the clay in clayey soils Water retention. E-mail: ary.bruand@orleans.inra.fr Summary We have investigated the water retention properties retention properties have been studied from -10 hPa to -15 000 hPa water potential using small clods

Paris-Sud XI, Université de

31

Wildfire impacts on soil-water retention in the Colorado Front Range, United States  

NASA Astrophysics Data System (ADS)

This work examined the plot-scale differences in soil-water retention caused by wildfire in the area of the 2010 Fourmile Canyon Fire in the Colorado Front Range, United States. We measured soil-water retention curves on intact cores and repacked samples, soil particle-size distributions, and organic matter content. Estimates were also made of plant-available water based on the soil-water retention curves. Parameters for use in soil-hydraulic property models were estimated; these parameters can be used in unsaturated flow modeling for comparing burned and unburned watersheds. The primary driver for measured differences in soil-water retention in burned and unburned soils was organic matter content and not soil-particle size distribution. The tendency for unburned south-facing soils to have greater organic matter content than unburned north-facing soils in this field area may explain why unburned south-facing soils had greater soil-water retention than unburned north-facing soils. Our results suggest that high-severity wildfire can "homogenize" soil-water retention across the landscape by erasing soil-water retention differences resulting from organic matter content, which for this site may be affected by slope aspect. This homogenization could have important implications for ecohydrology and plant succession/recovery in burned areas, which could be a factor in dictating the window of vulnerability of the landscape to flash floods and erosion that are a common consequence of wildfire.

Ebel, Brian A.

2012-12-01

32

Upscaled soil-water retention using van Genuchten's function  

USGS Publications Warehouse

Soils are often layered at scales smaller than the block size used in numerical and conceptual models of variably saturated flow. Consequently, the small-scale variability in water content within each block must be homogenized (upscaled). Laboratory results have shown that a linear volume average (LVA) of water content at a uniform suction is a good approximation to measured water contents in heterogeneous cores. Here, we upscale water contents using van Genuchten's function for both the local and upscaled soil-water-retention characteristics. The van Genuchten (vG) function compares favorably with LVA results, laboratory experiments under hydrostatic conditions in 3-cm cores, and numerical simulations of large-scale gravity drainage. Our method yields upscaled vG parameter values by fitting the vG curve to the LVA of water contents at various suction values. In practice, it is more efficient to compute direct averages of the local vG parameter values. Nonlinear power averages quantify a feasible range of values for each upscaled vG shape parameter; upscaled values of N are consistently less than the harmonic means, reflecting broad pore-size distributions of the upscaled soils. The vG function is useful for modeling soil-water retention at large scales, and these results provide guidance for its application.

Green, T.R.; Constantz, J.E.; Freyberg, D.L.

1996-01-01

33

Estimating soil water retention using soil component additivity model  

NASA Astrophysics Data System (ADS)

Soil water retention is a major soil hydraulic property that governs soil functioning in ecosystems and greatly affects soil management. Data on soil water retention are used in research and applications in hydrology, agronomy, meteorology, ecology, environmental protection, and many other soil-related fields. Soil organic matter content and composition affect both soil structure and adsorption properties; therefore water retention may be affected by changes in soil organic matter that occur because of both climate change and modifications of management practices. Thus, effects of organic matter on soil water retention should be understood and quantified. Measurement of soil water retention is relatively time-consuming, and become impractical when soil hydrologic estimates are needed for large areas. One approach to soil water retention estimation from readily available data is based on the hypothesis that soil water retention may be estimated as an additive function obtained by summing up water retention of pore subspaces associated with soil textural and/or structural components and organic matter. The additivity model and was tested with 550 soil samples from the international database UNSODA and 2667 soil samples from the European database HYPRES containing all textural soil classes after USDA soil texture classification. The root mean square errors (RMSEs) of the volumetric water content estimates for UNSODA vary from 0.021 m3m-3 for coarse sandy loam to 0.075 m3m-3 for sandy clay. Obtained RMSEs are at the lower end of the RMSE range for regression-based water retention estimates found in literature. Including retention estimates of organic matter significantly improved RMSEs. The attained accuracy warrants testing the 'additivity' model with additional soil data and improving this model to accommodate various types of soil structure. Keywords: soil water retention, soil components, additive model, soil texture, organic matter.

Zeiliger, A.; Ermolaeva, O.; Semenov, V.

2009-04-01

34

Soil water retention and maximum capillary drive from saturation to oven dryness  

USGS Publications Warehouse

This paper provides an alternative method to describe the water retention curve over a range of water contents from saturation to oven dryness. It makes two modifications to the standard Brooks and Corey [1964] (B-C) description, one at each end of the suction range. One expression proposed by Rossi and Nimmo [1994] is used in the high-suction range to a zero residual water content. (This Rossi-Nimmo modification to the Brooks-Corey model provides a more realistic description of the retention curve at low water contents.) Near zero suction the second modification eliminates the region where there is a change in suction with no change in water content. Tests on seven soil data sets, using three distinct analytical expressions for the high-, medium-, and low-suction ranges, show that the experimental water retention curves are well fitted by this composite procedure. The high-suction range of saturation contributes little to the maximum capillary drive, defined with a good approximation for a soil water and air system as H(cM) = {???)/(o) k(rw) dh(c), where k(rw) is relative permeability (or conductivity) to water and h(c) is capillary suction, a positive quantity in unsaturated soils. As a result, the modification suggested to describe the high-suction range does not significantly affect the equivalence between Brooks-Corey (B-C) and van Genuchten [1980] parameters presented earlier. However, the shape of the retention curve near 'natural saturation' has a significant impact on the value of the capillary drive. The estimate using the Brooks-Corey power law, extended to zero suction, will exceed that obtained with the new procedure by 25 to 30%. It is not possible to tell which procedure is appropriate. Tests on another data set, for which relative conductivity data are available, support the view of the authors that measurements of a retention curve coupled with a speculative curve of relative permeability as from a capillary model are not sufficient to accurately determine the (maximum) capillary drive. The capillary drive is a dynamic scalar, whereas the retention curve is of a static character. Only measurements of infiltration rates with time can determine the capillary drive with precision for a given soil.

Morel-Seytoux, H. J.; Nimmo, J.R.

1999-01-01

35

Evolutionary Computing for Detection of Retentive Structures in Coastal Waters  

E-print Network

Evolutionary Computing for Detection of Retentive Structures in Coastal Waters Marc Segond, Denis. To verify this hypothesis, an automatic detection tool is needed to process a database of thousands to automatically detect these retentive structures. Our heuristics are shown to be competitive with human experts

Fernandez, Thomas

36

Determination of water retention in stratified porous materials  

USGS Publications Warehouse

Predicted and measured water-retention values, ??(??), were compared for repacked, stratified core samples consisting of either a sand with a stone-bearing layer or a sand with a clay loam layer in various spatial orientations. Stratified core samples were packed in submersible pressure outflow cells, then water-retention measurements were performed between matric potentials, ??, of 0 to -100 kPa. Predictions of ??(??) were based on a simple volume-averaging model using estimates of the relative fraction and ??(??) values of each textural component within a stratified sample. In general, predicted ??(??) curves resembled measured curves well, except at higher saturations in a sample consisting of a clay loam layer over a sand layer. In this case, the model averaged the air-entry of both materials, while the air-entry of the sample was controlled by the clay loam in contact with the cell's air-pressure inlet. In situ, avenues for air-entry generally exist around clay layers, so that the model should adequately predict air-entry for stratified formations regardless of spatial orientation of fine versus coarse layers. Agreement between measured and predicted volumetric water contents, ??, was variable though encouraging, with mean differences between measured and predicted ?? values in the range of 10%. Differences in ?? of this magnitude are expected due to variability in pore structure between samples, and do not indicate inherent problems with the volume averaging model. This suggets that explicit modeling of stratified formations through detailed characterization of the stratigraphy has the potential of yielding accurate ??(??) values. However, hydraulic-equilibration times were distinctly different for each variation in spatial orientation of textural layering, indicating that transient behavior during drainage in stratified formations is highly sensitive to the stratigraphic sequence of textural components, as well as the volume fraction of each textural component in a formation. This indicates that prolonged residence times of water, nutrients, and pollutants are likely within finer-textured layers, when ?? conditions have resulted in drainage of underlying coarser-textured strata. ?? 1995 Kluwer Academic Publishers.

Constantz, J.

1995-01-01

37

Nitrogen surface water retention in the Baltic Sea drainage basin  

NASA Astrophysics Data System (ADS)

In this paper, we estimate the surface water retention of nitrogen (N) in all the 117 drainage basins to the Baltic Sea with the use of a statistical model (MESAW) for source apportionment of riverine loads of pollutants. Our results show that the MESAW model was able to estimate the N load at the river mouth of 88 Baltic Sea rivers, for which we had observed data, with a sufficient degree of precision and accuracy. The estimated retention parameters were also statistically significant. Our results show that around 380 000 t of N are annually retained in surface waters draining to the Baltic Sea. The total annual riverine load from the 117 basins to the Baltic Sea was estimated at 570 000 t of N, giving a total surface water N retention of around 40%. In terms of absolute retention values, three major river basins account for 50% of the total retention in the 117 basins; i.e. around 104 000 t of N are retained in Neva, 55 000 t in Vistula and 32 000 t in Oder. The largest retention was found in river basins with a high percentage of lakes as indicated by a strong relationship between N retention (%) and share of lake area in the river drainage areas. For example in Göta älv, we estimated a total N retention of 72%, whereof 67% of the retention occurred in the lakes of that drainage area (Lake Vänern primarily). The obtained results will hopefully enable the Helsinki Commission (HELCOM) to refine the nutrient load targets in the Baltic Sea Action Plan (BSAP), as well as to better identify cost-efficient measures to reduce nutrient loadings to the Baltic Sea.

Stĺlnacke, P.; Pengerud, A.; Vassiljev, A.; Smedberg, E.; Mörth, C.-M.; Hägg, H. E.; Humborg, C.; Andersen, H. E.

2015-02-01

38

Nitrogen surface water retention in the Baltic Sea drainage basin  

NASA Astrophysics Data System (ADS)

In this paper, we estimate the surface water retention of nitrogen (N) in all the 117 drainage basins to the Baltic Sea with the use of a statistical model (MESAW) for source apportionment of riverine loads of pollutants. Our results show that the MESAW model was able to estimate the N load at the river mouth of 88 Baltic Sea rivers, for which we had observed data, with a sufficient degree of precision and accuracy. The estimated retention parameters were also statistically significant. Our results show that around 380 000 t of N are annually retained in surface waters draining to the Baltic Sea. The total annual riverine load from the 117 basins to the Baltic Sea was estimated to 570 000 t of N, giving a total surface water N retention of around 40%. In terms of absolute retention values, three major river basins account for 50% of the total retention in the 117 basins; i.e. around 104 000 t of N is retained in Neva, 55 000 t in Vistula and 32 000 t in Oder. The largest retention was found in river basins with a high percentage of lakes as indicated by a strong relationship between N retention (%) and share of lake area in the river drainage areas. For example in Göta älv, we estimated a total N retention of 72%, whereof 67% of the retention occurred in the lakes of that drainage area (Lake Vänern primarily). The obtained results will hopefully enable the Helsinki Commission (HELCOM) to refine the nutrient load targets in the Baltic Sea Action Plan (BSAP), as well as to better identify cost-efficient measures to reduce nutrient loadings to the Baltic Sea.

Stĺlnacke, P.; Pengerud, A.; Vassiljev, A.; Smedberg, E.; Mörth, C.-M.; Hägg, H. E.; Humborg, C.; Andersen, H. E.

2014-09-01

39

Variation of Water Retention in Various Soils of Kuwait  

Microsoft Academic Search

Soil properties varied in water retention; due to soil texture and organic matter content. Variations of texture in many soils are effected mostly to soil forming factors of parent materials of the soil; biological activities; climactic variation; and duration of soil reaction. While the organic matter contents are affected totally by the environmental conditions of the soils. Water holding capacity

M. Abdal; M. Suleiman; M. Albaho

2002-01-01

40

Variation Of Water Retention In Various Soils Of Kuwait  

Microsoft Academic Search

Soil properties varied in water retention; due to soil texture and organic matter content. Variations of texture in many soils are effected mostly to soil forming factors of parent materials of the soil, biological activities, climactic variation, and duration of soil reaction. While the organic matter contents are affected totally by the environmental conditions of the soils. Water holding capacity

M. Abdal; M. Suleiman; S. Al-Ghawas

2002-01-01

41

Is the Water Heating Curve as Described?  

ERIC Educational Resources Information Center

We analysed the heating curve of water which is described in textbooks. An experiment combined with some simple heat transfer calculations is discussed. The theoretical behaviour can be altered by changing the conditions under which the experiment is modelled. By identifying and controlling the different parameters involved during the heating…

Riveros, H. G.; Oliva, A. I.

2008-01-01

42

Modelling Soil Water Retention Using Support Vector Machines with Genetic Algorithm Optimisation  

PubMed Central

This work presents point pedotransfer function (PTF) models of the soil water retention curve. The developed models allowed for estimation of the soil water content for the specified soil water potentials: –0.98, –3.10, –9.81, –31.02, –491.66, and –1554.78?kPa, based on the following soil characteristics: soil granulometric composition, total porosity, and bulk density. Support Vector Machines (SVM) methodology was used for model development. A new methodology for elaboration of retention function models is proposed. Alternative to previous attempts known from literature, the ?-SVM method was used for model development and the results were compared with the formerly used the C-SVM method. For the purpose of models' parameters search, genetic algorithms were used as an optimisation framework. A new form of the aim function used for models parameters search is proposed which allowed for development of models with better prediction capabilities. This new aim function avoids overestimation of models which is typically encountered when root mean squared error is used as an aim function. Elaborated models showed good agreement with measured soil water retention data. Achieved coefficients of determination values were in the range 0.67–0.92. Studies demonstrated usability of ?-SVM methodology together with genetic algorithm optimisation for retention modelling which gave better performing models than other tested approaches. PMID:24772030

Lamorski, Krzysztof; S?awi?ski, Cezary; Moreno, Felix; Barna, Gyöngyi; Skierucha, Wojciech; Arrue, José L.

2014-01-01

43

Biodestruction of strongly swelling polymer hydrogels and its effect on the water retention capacity of soils  

NASA Astrophysics Data System (ADS)

The biodestruction of strongly swelling polymer hydrogels (water adsorbing soil conditioners of the new generation) has been studied at the quantitative level using original mathematical models. In laboratory experiments, a relationship between the hydrogel degradation rate and the temperature has been obtained, and the effect of the biodestruction on the water retention curve of soil compositions with hydrogels (used as an index of their water retention capacity) has been assessed. From the automatic monitoring data of the temperature regime of soils, the potential biodestruction of hydrogels has been predicted for different climatic conditions. The loss of hydrogels during three months of the vegetation period because of destruction can exceed 30% of their initial content in irrigated agriculture under arid climatic conditions and more than 10% under humid climatic conditions. Thus, the biodestruction of hydrogels is one of the most important factors decreasing their efficiency under actual soil conditions.

Smagin, A. V.; Sadovnikova, N. B.; Smagina, M. V.

2014-06-01

44

Closed-form expressions for water retention and conductivity data  

Microsoft Academic Search

Closed-form expressions for quantifying the unsaturated soil hydraulic properties are widely used in computer programs to model subsurface flow and transport in porous media and to investigate indirect methods for estimating these properties. For example, water retention data, which relate soil-water pressure head (h) and effective water saturation (S{sub e}), are frequently used to predict the unsaturated hydraulic conductivity (K).

Feike J. Leij; Walter B. Russell; Scott M. Lesch

1997-01-01

45

Transport and Retention of Stabilized Silver Nanoparticles in Water-Saturated Porous Media  

NASA Astrophysics Data System (ADS)

Water-saturated column experiments were conducted to investigate the transport and retention of surfactant stabilized silver nanoparticles (AgNPs) in quartz sand. The mobility of AgNPs was enhanced with an increase in water velocity, sand grain size, and AgNP input concentration (Co), and a decrease in solution ionic strength (IS). Retention profiles (RPs) for AgNPs exhibited uniform, nonmonotonic, or hyperexponential shapes depending on physicochemical conditions. The experimental breakthrough curves (BTCs) and RPs were described using a numerical model that considers time/concentration- and depth-dependent retention. The simulated maximum retained concentration on the solid phase (Smax) and the retention rate coefficient (k1) increased with IS and as the grain size and/or Co decreased. The RPs were more hyperexponential in finer textured sand and at lower Co, were nonmonotonic or uniform at higher Co and in coarser sand, and tended to exhibit higher peak concentrations in the RPs at lower velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when Smax was approaching filled conditions. The sensitivity of the nonmonotonic RPs to IS and velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary minimum and largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity. The competitive retention of AgNPs and surfactants close to the column inlet was observed when additional surfactants were added into the system. Nonmonotonic RPs had peak concentrations at a greater distance in the presence of larger amount of surfactant. This implies that the existence of natural occurring organic matter will likely facilitate NP transport deeper into the subsurface environment and increase the risk potential of ground water contamination. Y. Liang, S. A. Bradford, J. Simunek, H.Vereecken, E. Klumpp. Sensitivity of the Transport and Retention of Stabilized Silver Nanoparticles to Physicochemical Factors. Water Research. Submitted.

Liang, Yan; Bradford, Scott A.; Simunek, Jiri; Vereecken, Harry; Klumpp, Erwin

2013-04-01

46

EFFECT OF SOIL AGGREGATE SIZE DISTRIBUTION ON WATER RETENTION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Quantitative information on soil water retention is in demand in hydrology, agrometeorology, agronomy, contaminant transport, and other soil-related disciplines of earth and environmental sciences. Soil aggregate composition is an important characteristic of soil structure and, as such, has been exp...

47

Phosphorus Retention Mechanisms of a Water Treatment Residual  

Microsoft Academic Search

Water treatment residuals (WTRs) are a by-product of municipal drinking water treatment plants and can have the,capacity to adsorb tremendous amounts of P. Understanding the WTR phosphorus ad- sorption process is important for discerning the mechanrism and tenac- ity of P retention. We studied P adsorbing mechanism(s) of an alumi- num-based (A12(SO 4),14H 2O) WTR from Englewood, CO. In a

J. A. Ippolito; K. A. Barbarick; D. M. Heil; J. P. Chandler; E. F. Redente

2003-01-01

48

Decline in urinary retention incidence in 805 patients after prostate brachytherapy: The effect of learning curve?  

SciTech Connect

Purpose: To evaluate the incidence and factors predictive of acute urinary retention (AUR) in 805 consecutive patients treated with prostate brachytherapy monotherapy and to examine the possible effect of a learning curve. Methods and Materials: Between July 1998 and November 2002, 805 patients were treated with prostate brachytherapy. Low-risk patients (Gleason Score (GS) {<=}6; prostate specific antigen (PSA) {<=}10, and {<=} T2b [UICC 1997]) received implant alone. Patients with prostate volume of 50 cc or more, GS = 7, or PSA = 10 to 15 received 6 months of androgen suppression (AS) with brachytherapy. Patient, treatment, and dosimetric factors examined include baseline prostate symptom score (IPSS), diabetes, vascular disease, PSA, Gleason score, clinical stage, AS, ultrasound planning target volume (PUTV), postimplant prostate volume (obtained with 'Day 30' postimplant CT), CT:PUTV ratio (surrogate for postimplant edema), number of seeds, number of needles, number of seeds per needle, dosimetric parameters (V100, V150, and D90), date of implant (learning curve), and implanting oncologists. Univariate and multivariate analyses were carried out. Results: Acute urinary retention in the first 200 patients was 17% vs. 6.3% in the most recently treated 200 patients (p = 0.002). Overall AUR was 12.7%, and prolonged urinary obstruction incidence (>20 days) was 5%. On multivariate analysis, factors predictive of any AUR include baseline IPSS (p = < 0.004), CT:PUTV ratio (p = < 0.001), PUTV (p = < 0.001), and implant order (learning curve) (p = 0.001). Factors predictive for 'prolonged' catheterization (>20 days) on multivariate analysis include IPSS (p < 0.01), number of needles (p < 0.001), diabetes mellitus (p = 0.048), and CT:PUTV ratio (p < 0.001) Conclusion: Over the years, our AUR rate has fallen significantly (from 17% to 6.3%). On multivariate analysis, highly significant factors include IPSS, PUTV, CT:PUTV ratio (i.e., degree of prostate edema), and order of implant (learning curve). Over the course of the program, we have deliberately reduced the number of needles and OR time per patient, which have potentially minimized intraoperative trauma and may have contributed to less toxicity. A learning curve in prostate brachytherapy programs affect not only the outcome but also the toxicity from the treatment.

Keyes, Mira [Department of Radiation Oncology, Vancouver Cancer Centre, Vancouver, BC (Canada)]. E-mail: mkeyes@bccancer.bc.ca; Schellenberg, Devin [Department of Radiation Oncology, Vancouver Cancer Centre, Vancouver, BC (Canada); Moravan, Veronika M.Sc. [Population and Preventive Oncology, British Columbia Cancer Agency, Vancouver, BC (Canada); McKenzie, Michael [Department of Radiation Oncology, Vancouver Cancer Centre, Vancouver, BC (Canada); Agranovich, Alexander [Fraser Valley Cancer Centre, Vancouver, BC (Canada); Pickles, Tom [Department of Radiation Oncology, Vancouver Cancer Centre, Vancouver, BC (Canada); Wu, Jonn [Department of Radiation Oncology, Vancouver Cancer Centre, Vancouver, BC (Canada); Liu, Mitchell [Fraser Valley Cancer Centre, Vancouver, BC (Canada); Bucci, Joseph M.B.B.S. [Department of Radiation Oncology, St. George Hospital, University of New South Wales, Sydney (Australia); Morris, W. James [Department of Radiation Oncology, Vancouver Cancer Centre, Vancouver, BC (Canada)

2006-03-01

49

Water retention, hydraulic conductivity of hydrophilic polymers in sandy soil as affected by temperature and water quality  

NASA Astrophysics Data System (ADS)

SummaryHydrophilic polymers can swell by absorbing huge volumes of water or aqueous solutions. This property has led to many practical applications of these new materials, particularly in arid regions for improving water retention in sandy soils and the water supply to plants grown on them. The effects of two hydrophilic polymers, carboxymethylcellulose (RF) and isopropyl acrylamide (BF) on the water holding capacity and saturated hydraulic conductivity ( KS) of a sandy soil at varying soil temperature and water quality were evaluated. The RF was less efficient in absorbing water than BF, but the efficiency of BF in retaining water was negatively affected by its thermo-sensitivity and the quality of water. The temperature dependence of the water absorption was not clear for the soils treated with RF, whereas, the efficiency of BF treatment in absorbing water decreased significantly ( P < 0.05) with increasing soil temperature. The dependence of the KS on soil temperature differed with the type of hydrophilic polymer used. The KS of the control soil remained nearly constant as the soil temperature increased. The KS of the BF treated soil increased significantly ( P < 0.05) and linearly with increasing soil temperature, while that of soil treated with RF showed a quadratic response. The soil-absorbent mixtures exhibited different water retention characteristics under different soil temperature conditions. The increase in soil temperature did not affect the water retention characteristics curve of the control. The effect of soil temperature on the water potential curve of the soil treated with RF was not clear particularly when the temperature increased from 25 to 35 °C. The water potential curve for soil-BF mixtures showed that the water content value at field capacity shifted from 0.21 to 0.10 cm 3 cm -3 for 0.1% and from 0.27 to 0.12 cm 3 cm -3 for 0.2%, as the soil temperature increased from 15 to 35 °C. This implies that the soil-BF absorbent mixtures would release some moisture as the soil temperature would increase from 15 to 35 °C, and this water could be lost by percolation or taken up by plant. It was found that available water content increased up to four times with RF as compared to control soil whereas it increased up to five times with BF treatment. At high temperature, the difference was much reduced except for RF at 0.2%. This understanding of the characteristics of the absorbents and the interactions among absorbents, soil, and temperature would be of help in water management in sandy soil.

Andry, H.; Yamamoto, T.; Irie, T.; Moritani, S.; Inoue, M.; Fujiyama, H.

2009-06-01

50

LIGHTWEIGHT GREEN ROOF WATER RETENTION SYSTEM  

EPA Science Inventory

During Phase I, we have forged numerous necessary partnerships, which will allow us to begin our implementation tests. Working with the Philadelphia Water Department (PWD) and Drexel Smart House (DSH) we have 3 to 4 prime test sites for our system. We plan to execute our insta...

51

Correcting the errors from variable sea salt retention and water of hydration in loss on ignition analysis: Implications for studies of estuarine and coastal waters  

NASA Astrophysics Data System (ADS)

The standard technique of determining the concentrations of total suspended solids (TSSs), particulate inorganic matter (PIM), and particulate organic matter (POM) by filtration with glass fiber filters is subject to an error or bias from sea salt plus water of hydration retention, when applied to saline waters. The sea salt plus water of hydration retention by the filters occurs even after washing the filter with 300 ml of deionized water, a greater volume than any wash recommended in the literature. We determined that the mass retention on a glass fiber filter, at a given salinity, is essentially constant, no matter the volume of seawater passed through the filter. We also determined that the sea salt plus water of hydration retention on glass fiber filters is directly proportional to the salinity of the seawater filtered. Sea salt plus water of hydration retention causes an overestimate of TSS; sea salt retention causes an overestimate of PIM; volatilization of water of hydration causes an overestimate of POM. Thus a correction curve is required for sea salt and water of hydration errors in the determination of TSS and PIM. Corrected POM comes from the difference between the two. Also, filter blanks (procedural control filters), run with deionized (DI) water rather than the seawater sample, are required to correct for possible filter mass loss during the analysis. We demonstrate correction curves for sea salt plus water of hydration retention for Whatman GF/F filters, 47 mm diameter, utilizing the methods of the APHA Manual, Standard Methods for the Examination of Water and Wastewater. Application of other glass fiber filter types or an analytical technique differing significantly from that employed here requires a different correction curve for retention of sea salt and water of hydration. These methods can be used to reanalyze older data on PIM, POM, and TSS. We apply these corrections to PIM and POM data from the northern Gulf of Mexico and examine the interactions of these filter corrections with corrections for structural water volatilization from suspended clay minerals in the determinations of PIM and POM. We analyze published data on PIM and POM determinations and their application to remote sensing. We conclude that sea salt and water of hydration retention on filters has an adverse effect on remote-sensing algorithms inverting radiance reflectance to estimate concentrations of suspended matter.

Stavn, Robert H.; Rick, Hans J.; Falster, Alexander V.

2009-03-01

52

Variation of Retention Curves in the Past 70 years in the Tatsunokuchi-yama Forested Experimental Watershed  

NASA Astrophysics Data System (ADS)

Long-term variation of the retention curves were examined for better understanding of forest and water interaction in the Kita-tani catchment (17 ha) and the Minami-tani catchment (23 ha) in the Tatsunokuchi-yama experimental watershed (34°42'N, 133°58'E, 36-257 m) where rainfall and runoff observations started in 1937. The retention curve in watershed basis is expressed as relationship between rainfall (P) and loss of rainfall (L); L=S{1-exp(-KP)}. L is the difference between P and direct runoff. When P is infinity, L equals S. Hence S is sometimes called maximum water-holding capacity of watershed. As K gets larger, L becomes larger at same P when S is same. Unit flood hydrographs (peak runoff ≥ 1 mm/d) were extracted from daily runoff data, then P and L were estimated for each unit hydrograph. P and L were regressed in every five years with yearly step. Consequently, annual S and K were obtained. Coefficients of correlation were greater than 0.8 except 2005-2009 in the Kita-tani (r>0.7). Relationship between variation of moving median of these regression parameters and changes of vegetation cover condition were summarized as follows; S approximately ranged from 50 to 400 mm. S became larger when forest was thickly growing. In contrast, S became smaller when clearcut was conducted, forest fire occurred, or pine wilt disease occurred. If these variation of S were brought mainly by changes of canopy interception loss, it is not suitable to call S as water-holding capacity. K ranged from about 0.002 to 0.018. K showed antiphase that K becomes lager when S becomes smaller. Each catchment has individual variation of S and K as they have different history of vegetation cover. Annual rainfall in Tatsunokuchi-yama is about 1200 mm in average, but there is interannual fluctuation about 1000 mm (ranges about 600 to 1600 mm). In addition, direct runoffs' fluctuation influenced by antecedent rainfall condition is quite large because of seasonal deviation of rainfall and geology that is primarily underlain by crack rich Paleozoic sedimentary rocks of forearc accretionary prism. Although these circumstances exist, it is thought that vegetation cover condition can be explained by annual S and K.

Hosoda, I.

2010-12-01

53

No tillage effect on water retention characteristics of soil aggregates in rainfed semiarid conditions.  

NASA Astrophysics Data System (ADS)

The evaluation of changes in soil moisture retention characteristics associated to alterations in soil structure is of great interest in tillage studies. Most of these studies have evaluated soil properties in samples of total soil but not in individual aggregates. However, soil behavior at a macroscale level depends on the aggregate properties. A better knowledge of aggregate characteristics, as the water retention properties, will help to explain, for example, the response of soil to tillage, compaction and crop growth, and hence, to plan adequate soil management practices. In this study we determine the water retention curve of soil aggregates of different sizes from a soil under two tillage systems (conventional and no tillage). The study was carried out in a silty clay loam soil of semiarid Aragon (NE Spain). Two tillage systems were compared: no tillage (NT) and conventional tillage with mouldboard plough (CT). Water retention curves (WRC) were determined for soil surface aggregates (0-5 cm) of three different sizes (8-4, 4-2 and 2-1 mm in diameter) by using the TDR-pressure cell (Moret et al. 2008. Soil Till. Res, 100, 114-119). The TDR-pressure cell is a non-destructive method which permits determining WRC with the only one and same soil sample. Thus, the pressure cell was filled with aggregates up to 4 cm height, weighted and wetted to saturation from the bottom. Pressure steps were sequentially applied at -0.5, -1.5, -3, -5, -10, -33, -100, -300 kPa, and water content of each aggregate sample was measured gravimetrically and by TDR 24 h after starting each pressure head step. The volume of the sample within the cell was also determined at this moment in order to obtain the bulk density and thus calculate the volumetric water content. A good relationship was obtained between the volumetric water content calculated from the gravimetric water content and the corresponding values measured by TDR (r2=0.907; p?0.05). Within the same tillage treatment, no significant differences in WRC were found among soil aggregate sizes. Soil aggregates under CT retained more water at lower pressure heads in all aggregate sizes; in contrast the retention was more effective in those from NT at high pressure level. The extensive structural degradation of the CT aggregates observed during wetting with the consequent decrease in the soil volume within the transparent cell, can help to explain the different behaviour of both soils. The CT aggregates were probably disintegrated by slaking, causing a reduction in water drainage and, therefore, an increase in soil water content at low pressure heads. This idea was also confirmed with the application of the double exponential function proposed by Dexter et al. (2008. Geoderma 173, 243-253). The WRC curves measured by TDR were successfully fitted to the theoretical model proposed by Dexter (r2=0.986; p?0.05). Thus, the model estimated that the large porosity between aggregates retain slightly more water under CT (0.36-0.39 m3 m-3) than under NT (0.31-0.35 m3 m-3). On the contrary, pores inside the aggregates tend to storage more water in NT (0.16-0.20 m3 m-3vs. 0.13-0.17 m3 m-3 in CT). These results show the suitability of NT to reduce the risk of soil crusting and compaction in agricultural lands of Aragón.

Blanco-Moure, Nuria; López, M. Victoria; Moret, David

2010-05-01

54

Background: Subsurface Water Retention Technology (SWRT) Durable and easy to install: Water  

E-print Network

Background: Subsurface Water Retention Technology (SWRT) Benefits Durable and easy to install: Water retaining membranes can last at least 40 years and can be installed quickly and costeffectively permeable marginal soils converting them to much higher production levels of food crops. Better water

55

Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions  

PubMed Central

[1] For characterizing water flow in the vadose zone, the water retention curve (WRC) of the soil must be known. Because conventional WRC measurements demand much time and effort in the laboratory, alternative methods with shortened measurement duration are desired. The WRC can be estimated, for instance, from the cumulative pore size distribution (PSD) of the investigated material. Geophysical applications of nuclear magnetic resonance (NMR) relaxometry have successfully been applied to recover PSDs of sandstones and limestones. It is therefore expected that the multiexponential analysis of the NMR signal from water-saturated loose sediments leads to a reliable estimation of the WRC. We propose an approach to estimate the WRC using the cumulative NMR relaxation time distribution and approximate it with the well-known van-Genuchten (VG) model. Thereby, the VG parameter n, which controls the curvature of the WRC, is of particular interest, because it is the essential parameter to predict the relative hydraulic conductivity. The NMR curves are calibrated with only two conventional WRC measurements, first, to determine the residual water content and, second, to define a fixed point that relates the relaxation time to a corresponding capillary pressure. We test our approach with natural and artificial soil samples and compare the NMR-based results to WRC measurements using a pressure plate apparatus and to WRC predictions from the software ROSETTA. We found that for sandy soils n can reliably be estimated with NMR, whereas for samples with clay and silt contents higher than 10% the estimation fails. This is the case when the hydraulic properties of the soil are mainly controlled by the pore constrictions. For such samples, the sensitivity of the NMR method for the pore bodies hampers a plausible WRC estimation. Citation: Costabel, S., and U. Yaramanci (2013), Estimation of water retention parameters from nuclear magnetic resonance relaxation time distributions, Water Resour. Res., 49, 2068-2079, doi:10.1002/wrcr.20207. PMID:23935225

Costabel, Stephan; Yaramanci, Ugur

2013-01-01

56

Water Retention and Rheology of Ti-doped, Synthetic Olivine  

NASA Astrophysics Data System (ADS)

Upper mantle flow laws are currently based almost entirely on experiments with olivine from San Carlos in Arizona. Synthetically produced olivine enables the exploration of the effects of trace elements on the rheology. We have conducted a range of experiments in a gas medium apparatus with solution-gelation derived olivine that show that titanium is the most effective in binding water in the olivine structure. The FTIR signature of this structurally bound water is most similar to that of water-undersaturated natural olivine with absorption bands at 3575 and 3525 cm-1. Water added, titanium-free solgel contains little water after hotpressing and shows adsorption bands at wavenumbers near 3200 cm-1. Noble metal capsules such as Pt or AuPd, providing more oxidizing conditions, are more effective in retaining water. Experiments with NiFe-lined welded Pt capsules retain no more water than NiFe lined samples without Pt capsule. Water retention is, however, again dependent on trace element content, with Ti doped samples containing tens of ppm after hotpressing. By comparison undoped samples run under the same conditions contain little water, again with different FTIR spectra to Ti-doped samples. Our experiments suggest that Ti by itself, or with water contents at the FTIR detection limit enhances diffusion creep rates relative to undoped, dry solgel olivine. Water contents around 10 ppm in NiFe wrapped samples show an enhancement of strain rates of more than one order of magnitude. The addition of Ti, together with the presence of water, also enhances grain growth. For more coarse-grained samples in the dislocation creep regime the enhancement of the stain rate as a function of water content is approximately consistent with the flow laws of Hirth and Kohlstedt (2003).

Faul, U.; Jackson, I.; Fitz Gerald, J. D.

2012-12-01

57

A model for soil surface evaporation based on Campbell's retention curve  

NASA Astrophysics Data System (ADS)

SummaryThe objective of this study was to develop and verify a simple analytical model for one-dimensional non-steady upward flow from shallow and falling water table with minimum input data. Consequently, an analytical model was derived based on the Richards' equation with the Campbell's parametric retention model. This study proposes a model that uses the measurement of water table depth drawdown and some soil physical properties to estimate evaporation, instead of measuring evaporation rate itself. Nine relatively large lysimeters were packed with sandy loam, silty clay loam, and silty clay soil textures to obtain the data needed for evaluating the proposed model. The results indicate a reasonable agreement between the experimental data and the proposed model (root mean square error, RMSE = 2.11-4.22 mm/day). For the experimental period (64 days), however, there is some discrepancy between observation and simulation data. The reasons for this discrepancy may be attributed to vapor upward flow, evaporation which takes place from the lysimeters side gaps resulting from soil shrinkage and collapse of macropores resulting from soil packing.

Zarei, Ghasem; Homaee, Mehdi; Liaghat, Abdol Majid; Hoorfar, Abdol Hosain

2010-01-01

58

Thermodynamic assessment of the effect of strongly swelling polymer hydrogels on the water retention capacity of model porous media  

NASA Astrophysics Data System (ADS)

The effect of different rates and fractions of strongly swelling polymer hydrogel (SSPH) based on radiation-grafted polyacrylamide on the water retention capacity and structural state of model porous media in the form of quartz sand fractions with different degrees of dispersion has been studied. The water retention curve (WRC) of sandy porous media obtained by the capillarimetric method has been used as a basic thermodynamic parameter. An original method has been proposed for the comparative study of the effect of SSPHs on the WRC based on the approximation of data by the nonlinear van Genuchten function followed by differential analysis. Equations are given for the calculation of capillary water capacity and structural curves of pore size distribution. SSPH concentrations in the range 0.05-0.2% of enclosing material weight reliably increase the water retention capacity of sandy fractions and the total, capillary, and field capacities (determined by the Voronin secant method) by 2-3 times; as well as the range of available water and the contents of fine macropores and mesopores. Factors limiting the swelling of SSPHs in model porous media have been revealed.

Sadovnikova, N. B.; Smagin, A. V.; Sidorova, M. A.

2014-04-01

59

Marked differences between van Genuchten soil water-retention parameters for temperate and tropical soils: a new water-retention pedo-transfer functions developed for tropical soils  

Microsoft Academic Search

All of the physical, chemical and soil water-retention data suitable for the derivation of a Pedo-Transfer Functions (PTF) for water retention for tropical soils (771 suitable horizons) were extracted from the IGBP-DIS soil database. The parameters ?s, ?r, ? and n of the van Genuchten (vG) [Soil Sci. Soc. Am. J. 44 (1980) 892] equation were derived and compared with

M. G. Hodnett; J. Tomasella

2002-01-01

60

Influence of Soil Management on Water Retention from Saturation to Oven Dryness and Dominant Soil Water States in a Vertisol under Crop Rotation  

NASA Astrophysics Data System (ADS)

Unique water transfer and retention properties of Vertisols strongly affect their use in rainfed agriculture in water-limited environments. Despite the agricultural importance of the hydraulic properties of those soils, water retention data dryer than the wilting point are generally scarce, mainly as a result of practical constraints of traditional water retention measurement methods. In this work we provide a detailed description of regionalized water retention data from saturation to oven dryness, obtained from 54 minimally disturbed topsoil (0-0.05m) samples collected at a 3.5-ha experimental field in SW Spain where conventional tillage (CT) and direct drilling (DD) is compared in a wheat-sunflower-legume crop rotation on a Vertisol. Water retention was measured from saturation to oven dryness using sand and sand-kaolin boxes, a pressure plate apparatus and a dew point psychrometer, respectively. A common shape of the water retention curve (WRC) was observed in both tillage systems, with a strong discontinuity in its slope near -0.4 MPa and a decreasing spread from the wet to the dry end. A continuous function, consisting of the sum of a double exponential model (Dexter et al, 2008) and the Groenevelt and Grant (2004) model could be fitted successfully to the data. Two inflection points in the WRC were interpreted as boundaries between the structural and the textural pore spaces and between the textural and the intra-clay aggregate pore spaces. Water retention was significantly higher in DD (p<0.05) for pressure heads ranging from -0.006 to -0.32 MPa, and from -1.8 to -3.3 MPa. The magnitude of these differences ranged from 0.006 to 0.015 kg kg-1. The differential water capacity and associated equivalent pore-size distribution showed that these differences could be attributed to a combined effect of tillage and compaction, increasing and decreasing the amount of the largest pores in CT and DD, respectively, but resulting in a proportionally larger pore space with relevant pore-sizes for water dynamics and agronomic performance. Significant differences in water retention and equivalent pore-sizes at the dry end of the WRC could be associated with the higher organic matter content found in DD. These results explain the superior performance of DD over CT in satisfying high crop water demands, especially at the end of spring when atmospheric water demands become very high, resulting in an extension of the growing period under DD. The results provide also an explanation for the observed soil water dynamics pattern in the field, with rapid transitions between persistent wet and dry water content states. References Dexter, A.R., E.A. Czy?, G. Richard, A. Reszkowska, 2008. A user-friendly water retention function that takes account of the textural and structural pore spaces in soil. Geoderma, 143:243-253. Groenevelt, P.A., C.D. Grant, 2004. A new model for the soil-water retention curve that solves the problem of residual water contents. Eur. J. Soil Sci. 55:479-485.

Vanderlinden, Karl; Pachepsky, Yakov; Pederera, Aura; Martinez, Gonzalo; Espejo, Antonio Jesus; Giraldez, Juan Vicente

2014-05-01

61

Saturated hydraulic conductivity and soil water retention properties across a soil-slope transition  

E-print Network

Saturated hydraulic conductivity and soil water retention properties across a soil-slope transition measured saturated hydraulic conductivity (Ksat) and soil water retention functions at two (15 and 30 cm Area Research and Extension Center, Santa Clara, California Abstract. The hydraulic properties of soil

Mohanty, Binayak P.

62

Resolving structural influences on water-retention properties of alluvial deposits  

USGS Publications Warehouse

With the goal of improving property-transfer model (PTM) predictions of unsaturated hydraulic properties, we investigated the influence of sedimentary structure, defined as particle arrangement during deposition, on laboratory-measured water retention (water content vs. potential [??(??)]) of 10 undisturbed core samples from alluvial deposits in the western Mojave Desert, California. The samples were classified as having fluvial or debris-flow structure based on observed stratification and measured spread of particle-size distribution. The ??(??) data were fit with the Rossi-Nimmo junction model, representing water retention with three parameters: the maximum water content (??max), the ??-scaling parameter (??o), and the shape parameter (??). We examined trends between these hydraulic parameters and bulk physical properties, both textural - geometric mean, Mg, and geometric standard deviation, ??g, of particle diameter - and structural - bulk density, ??b, the fraction of unfilled pore space at natural saturation, Ae, and porosity-based randomness index, ??s, defined as the excess of total porosity over 0.3. Structural parameters ??s and Ae were greater for fluvial samples, indicating greater structural pore space and a possibly broader pore-size distribution associated with a more systematic arrangement of particles. Multiple linear regression analysis and Mallow's Cp statistic identified combinations of textural and structural parameters for the most useful predictive models: for ??max, including Ae, ??s, and ??g, and for both ??o and ??, including only textural parameters, although use of Ae can somewhat improve ??o predictions. Textural properties can explain most of the sample-to-sample variation in ??(??) independent of deposit type, but inclusion of the simple structural indicators Ae and ??s can improve PTM predictions, especially for the wettest part of the ??(??) curve. ?? Soil Science Society of America.

Winfield, K.A.; Nimmo, J.R.; Izbicki, J.A.; Martin, P.M.

2006-01-01

63

27. CUSHMAN POWER PLANT NO. 1, WATER CURVE SPILLWAY ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

27. CUSHMAN POWER PLANT NO. 1, WATER CURVE - SPILLWAY OVERFLOW CHANNEL. July 1928. Reference BT-109 - Cushman No. 1 Hydroelectric Power Plant, Spillway, North Fork of Skokomish River, 5 miles West of Hood Canal, Hoodsport, Mason County, WA

64

Soil-Water Characteristic Curve Modeling at Low Water Content: Empirical and Semi-Empirical Approaches  

E-print Network

Soil-Water Characteristic Curve Modeling at Low Water Content: Empirical and Semi model, the Modified Kovacs (MK) model for the determination of soil-water characteristic curve at the low water contents of two horizons of a soil from Burkina Faso. Combining terms from capillary state

Paris-Sud XI, Université de

65

Water Retention Capacity in Root Segments Differing in the Degree of Exodermis Development  

Microsoft Academic Search

Water loss from roots back into drying soil is a problem of practical importance in plants growing under conditions of very low substrate water potential, such as dry or saline areas. Root exodermis is relatively impermeable and has been suggested to play a protective role against water loss. The relative water retention ability was compared in root segments from exodermal

E. TALEISNIK; G. PEYRANO; A. CÓRDOBA; C. ARIAS

1999-01-01

66

Transparent hydrogel with enhanced water retention capacity by introducing highly hydratable salt  

E-print Network

Transparent hydrogel with enhanced water retention capacity by introducing highly hydratable salt 2014; published online 14 October 2014) Polyacrylamide hydrogels containing salt as electrolyte have of polyacrylamide hydrogel by introducing highly hydratable salts into the hydrogel. These hydrogels show enhanced

Suo, Zhigang

67

THE EFFECTS OF FOREST DEGRADATION ON SOIL WATER RETENTION IN NOTHERN VIETNAM  

E-print Network

Abstract THE EFFECTS OF FOREST DEGRADATION ON SOIL WATER RETENTION IN NOTHERN VIETNAM This study in northern Vietnam: moderate tree volume forest, poor tree volume forest, rehabilitation forest, and mixed

68

Pore-Scale Effects of Soil Structure And Microbial EPS Production On Soil Water Retention  

NASA Astrophysics Data System (ADS)

Climate-induced changes to the hydrological cycle will increase the frequency of extreme weather events including powerful storms and prolonged droughts. Moving forward, one of the major factors limiting primary productivity in terrestrial ecosystems will be sub-optimal soil moisture. We focus here on the ability of soils to retain moisture under drying conditions. A soil's ability to retain moisture is influenced by many factors including its texture, its structure, and the activities of soil microbes. In soil microcosms, the addition of small amounts of microbially-produced extracellular polymeric substances (EPS) can dramatically shift moisture retention curves. The objective of this research is to better understand how soil structure and EPS may act together to retain moisture in unsaturated soils. Replicate micromodels with exactly-conserved 2-D physical geometry were initially filled with aqueous suspensions of one of two types of bacteria: one mutant was ultra- muccoid and the other was non-muccoid. Replicate micromodels were held at a fixed, external, relative humidity, and the position of the air-water interface was imaged over time as water evaporates. There was no forced convection of air or water inside the micromodels: drying was achieved by water evaporation and diffusion alone. We used a fully automated, inverted microscope to image replicate drying lanes each with dimensions of 1 mm x 10 mm. A complete set of images was collected every 30 minutes for 30 hours. The results show devices loaded with the highly muccoid strain remained >40% hydrated for 13 h, while devices loaded with the non-muccoid remained >40% hydrated for only 6 h, and were completely dry by 13 h. Current work is comparing interfacial water fluxes in structured and unstructured settings, and is attempting to model the synergistic effects of soil structure and EPS content on moisture retention in real soils. This research may allow more accurate description of naturally-occurring feedbacks between the soil carbon and water cycles, and may enable agriculture biotechnology that enhances natural soil processes for improved resiliency of terrestrial ecosystems.

Orner, E.; Anderson, E.; Rubinstein, R. L.; Chau, J. F.; Shor, L. M.; Gage, D. J.

2013-12-01

69

Soil water retention at varying matric potentials following repeated wetting with modestly saline-sodic water and subsequent air drying  

SciTech Connect

Coal bed natural gas (CBNG) development in the Powder River (PR) Basin produces modestly saline, highly sodic wastewater. This study assessed impacts of wetting four textural groups (0-11%, 12-22%, 23 -33%, and > 33% clay (g clay/100 g soil) x 100%))with simulated PR or CBNG water on water retention. Soils received the following treatments with each water quality: a single wetting event, five wetting and drying events, or five wetting and drying events followed by leaching with salt-free water. Treated samples were then resaturated with the final treatment water and equilibrated to -10, -33, -100, -500, or -1,500 kPa. At all potentials, soil water retention increased significantly with increasing clay content. Drought-prone soils lost water-holding capacity between saturation and field capacity with repeated wetting and drying, whereas finer textured soils withstood this treatment better and had increased water-retention capacity at lower matric potentials.

Browning, L.S.; Hershberger, K.R.; Bauder, J.W. [Montana State University, Bozeman, MT (United States). Dept. of Land Resources & Environmental Science

2007-07-01

70

Experimental Investigation on Role of Root Mucilage and Microbial Exudates on Soil Water Retention Dynamics  

NASA Astrophysics Data System (ADS)

The release of organic molecules by soil microbes and plant roots to adapt their surrounding represents a substantial portion of the energy use by these organisms. The hypothesis in this study is that the long-chain molecules and hydrophilic nature of the released organic compounds deposited on soil surfaces drastically alters the dynamism of the soil water retention curves (SWRC) of the rhizosphere relative to the bulk soil through direct effect besides the well-known indirect influence of the organic matter by modifying the soil structure and providing energy for the biogeochemical processes. The experiment was set up in such away that it suppresses the indirect effect of organic matter (OM) and rather it traces only its immediate effect on SWRC. To achieve this goal inert and uniform size (0.1-0.11 mm) glassbeads were used. We assumed that wet mixing of the glass beads with OM and slow drying the mixture (40-50oC) for 1-day will lead to deposition of the OM only at the surface of the glass beads, the short time being not enough for aggregate formation. This way we can simulate the natural deposition of OM on soil surfaces. Our argument is that this deposited OM has its own distinct time-dependent SWRC which is different from that of bulk soil. Model exudates including PGA, XA, and SPA are used to mimic the behavior of plant root mucilages, bacterial and fungal exudates respectively. These model exudates at varying concentration (0, 0.008, 0.04, and 0.2 gm/l) were wet mixed with glass beads. SWRC was determined using both water-hanging column and pressure plate for both low and high suction ranges respectively. We will present the effect of exudate type and level of concentration on the dynamic behavior of SWRC of the glassbeads by determining: i) the SWRC for each treatment; ii) the rate of drying and wetting at different intervals; iii) the hysteresis of the retention curves; iv) the saturated hydraulic conductivity.

Gebrenegus, T. B.; Ghezzehei, T.

2011-12-01

71

Post-retention Development of Curve of Spee in Pre-adjusted Edgewise Appliance Cases, Its Correlation to Dentoskeletal Parameters: An In vitro Study  

PubMed Central

Background: Curve of Spee was first described by Ferdin and Graf Von Spee in 1890. The curve of Spee is an important characteristic of the mandibular dental arch. One of the most frequently encountered problems in the treatment of orthodontic patients is an excessive overbite. Deep bite has been found to be associated with abnormal mandibular function. Temporomandibular joint disorders also have potentially detrimental effects on mandibular development. Andrews advocated leveling the curve of Spee to aflat curve, in order to facilitate construction of an optimal occlusion and that a flat plane should be given as a form of over treatment. There is no reliable information currently available from the literature about the long-term stability of the curve of Spee and the factors influencing the same. The objective of this study was to assess the post-retention development of the curve of Spee and to evaluate the dental and skeletal parameters as predictors of its post-retention stability. Materials and Methods: Pre-treatment (Tl), post-treatment (T2) and post-retention (T3) dental casts and lateral cephalograms of 24 orthodontically treated patients having a mean age of 14.5 years were evaluated. The mean period of the study group after retention was up to 2.6 years (range = 1-5 years). Pre-treatment T1, post-treatment T2, and post-retention T3 casts and radiographs were measured. The data were tabulated and statistically analyzed. Results: A highly significant positive correlation was observed between the changes in the curve of Spee during treatment (T2-T1) and the net result after retention (T3-T2). This means that much of the treatment results remained stable at T3. However, slight change was noticed in curve of Spee’s depth during the time interval T3-T2. This finding was very negligible and was not statistically significant. Conclusion: The leveling of the curve of Spee during the treatment is a stable treatment objective on long term basis. There was a mild correlation existing between the curve of Spee and the different dental and skeletal parameters. PMID:25395790

Ahammed, A R Yusuf; Ganiger, Channamallappa C; Shetty, Vikranth; Sunny, Sunil; Shetty, Sadashiva; Pawar, Renuka; Suresh, K V

2014-01-01

72

Soil Water Retention as Indicator for Soil Physical Quality - Examples from Two SoilTrEC European Critical Zone Observatories  

NASA Astrophysics Data System (ADS)

Soil water retention is of primary importance for majority of soil functions. The characteristics derived from Soil Water Retention Curve (SWRC) are directly related to soil structure and soil water regime and can be used as indicators for soil physical quality. The aim of this study is to present some parameters and relationships based on the SWRC data from the soil profiles characterising the European SoilTrEC Critical Zone Observatories Fuchsenbigl and Koiliaris. The studied soils are representative for highly productive soils managed as arable land in the frame of soil formation chronosequence at "Marchfeld" (Fuchsenbigl CZO), Austria and heavily impacted soils during centuries through intensive grazing and farming, under severe risk of desertification in context of climatic and lithological gradient at Koiliaris, Crete, Greece. Soil water retention at pF ? 2.52 was determined using the undisturbed soil cores (100 cm3 and 50 cm3) by a suction plate method. Water retention at pF = 4.2 was determined by a membrane press method and at pF ? 5.6 - by adsorption of water vapour at controlled relative humidity, both using ground soil samples. The soil physical quality parameter (S-parameter) was defined as the slope of the water retention curve at its inflection point (Dexter, 2006), determined with the obtained parameters of van Genuhten (1980) water retention equation. The S-parameter values were categorised to assess soil physical quality as follows: S < 0.020 very poor, 0.020 ? S < 0.035 poor, 0.035 ? S < 0.050 good, S ? 0.050 very good (Dexter, 2004). The results showed that most of the studied topsoil horizons have good physical quality according to both the S-parameter and the Plant-Available Water content (PAW), with the exception of the soils from croplands at CZO Fuxenbigl (F4, F5) which are with poor soil structure. The link between the S-parameter and the indicator of soil structure stability (water stable soil aggregates with size 1-3 mm) is not well defined. The scattering is due to high values of S in subsoil, which does not always coincide with favourable physical properties, as it can be seen from the relationship with the PAW content. It was found that values of S ? 0.05 correspond to PAW > 20 % vol. in the topsoil horizons. The high values of S in subsoil horizons are due to the low PAW and restrict the application of the S categories in these cases. Well defined links are found between the PAW content and the S-parameter when the data from the topsoil horizons are grouped in 2 groups according to the ratio between air-filled pores (at pF 2.52) and plant available water: <2 and ? 2. The authors acknowledge gratefully the European Commission Research Directorate-General for funding the SoilTrEC project (Contract No 244118) under its 7th Framework Programme.

Rousseva, Svetla; Kercheva, Milena; Shishkov, Toma; Dimitrov, Emil; Nenov, Martin; Lair, Georg J.; Moraetis, Daniel

2014-05-01

73

Relationship Study Between Reversed Phase HPLC Retention and Octanol\\/Water Partition Among Amphoteric Compoundsw  

Microsoft Academic Search

The retention of eight non-congeneric amphoteric compounds was followed in a reversed phase (RP HPLC) system (C18\\/methanol-water vol. 50:50) in the pH range 4–9. The chromatographic behavior of the amphoterics is explained by means of their species distribution diagram (pH profile of the protonation macro- and microspecies) in the same pH interval.Maximum retention was observed at the isoelectric point of

K. Takács-Novák; Gy. Szász; Zs. Budvári-Bárány; M. Józan; A. Löe

1995-01-01

74

Aspect influences on soil water retention and storage I. J. Geroy,1  

E-print Network

studied water release mechanisms. The storage capacity of a soil profile depends on soil depthAspect influences on soil water retention and storage I. J. Geroy,1 M. M. Gribb,2 H. P. Marshall,3 Abstract: Many catchment hydrologic and ecologic processes are impacted by the storage capacity of soil

Marshall, Hans-Peter

75

Prediction of soil water retention properties after stratification by combining texture, bulk density and the type of horizon  

E-print Network

1 Prediction of soil water retention properties after stratification by combining texture, bulk water retention properties at continental and national scales because only very basic soils data (topsoil and subsoil). The performance of these class-PTFs was validated against water retained at -33

Paris-Sud XI, Université de

76

Nuclear magnetic relaxation dispersion investigations of water retention mechanism by cellulose ethers in mortars  

SciTech Connect

We show how nuclear magnetic spin-lattice relaxation dispersion of proton-water (NMRD) can be used to elucidate the effect of cellulose ethers on water retention and hydration delay of freshly-mixed white cement pastes. NMRD is useful to determine the surface diffusion coefficient of water, the specific area and the hydration kinetics of the cement-based material. In spite of modifications of the solution's viscosity, we show that the cellulosic derivatives do not modify the surface diffusion coefficient of water. Thus, the mobility of water present inside the medium is not affected by the presence of polymer. However, these admixtures modify significantly the surface fraction of mobile water molecules transiently present at solid surfaces. This quantity measured, for the first time, for all admixed cement pastes is thus relevant to explain the water retention mechanism.

Patural, Laetitia [Ecole Nationale Superieure des Mines de Saint-Etienne, Centre SPIN, LPMG FRE 3312, 158 Cours Fauriel, 42023 Saint-Etienne Cedex 2 (France)] [Ecole Nationale Superieure des Mines de Saint-Etienne, Centre SPIN, LPMG FRE 3312, 158 Cours Fauriel, 42023 Saint-Etienne Cedex 2 (France); Korb, Jean-Pierre, E-mail: jean-pierre.korb@polytechnique.fr [Physique de la Matiere Condensee, Ecole Polytechnique-CNRS, Route de Saclay, 91128 Palaiseau Cedex (France)] [Physique de la Matiere Condensee, Ecole Polytechnique-CNRS, Route de Saclay, 91128 Palaiseau Cedex (France); Govin, Alexandre; Grosseau, Philippe [Ecole Nationale Superieure des Mines de Saint-Etienne, Centre SPIN, LPMG FRE 3312, 158 Cours Fauriel, 42023 Saint-Etienne Cedex 2 (France)] [Ecole Nationale Superieure des Mines de Saint-Etienne, Centre SPIN, LPMG FRE 3312, 158 Cours Fauriel, 42023 Saint-Etienne Cedex 2 (France); Ruot, Bertrand; Deves, Olivier [Universite Paris-Est, Centre Scientifique et Technique du Batiment, Departement Enveloppe et Revetements/Division Enduits, Mortiers et Colles, 84 avenue Jean Jaures, 77447 Marne-la-Vallee Cedex 2 (France)] [Universite Paris-Est, Centre Scientifique et Technique du Batiment, Departement Enveloppe et Revetements/Division Enduits, Mortiers et Colles, 84 avenue Jean Jaures, 77447 Marne-la-Vallee Cedex 2 (France)

2012-10-15

77

Peat properties and water retention in boreal forested peatlands subject to wildfire  

NASA Astrophysics Data System (ADS)

Peat cores from a recently burned peatland and one over 75 years since fire in Alberta, Canada were analyzed for physical properties and water retention. Wildfire exposed denser peat at the peat surface, more so in hollow than hummock microforms. Water retention in peat has implications for postfire Sphagnum regeneration, as this more dense peat requires smaller volumes of water loss before a critical growth-inhibiting pore-water pressure of -100 mb is reached. Simulations of water retention after fire showed that hollow microforms are at a higher risk of losing low-density surface peat, which moderates water table (WT) declines via high specific yield. Exposure of dense peat to the surface after fire increases surface moisture under a constant WT. The net effect of decreasing specific yield and increasing water retention at the surface has implications on hydrologic stability and resilience of boreal peatlands to future wildfire risk under a changing climate. Earth system models incorporating wildfire disturbance in boreal peatlands would benefit from the inclusion of these hydrological feedbacks in this globally significant carbon reservoir.

Thompson, Dan K.; Waddington, James M.

2013-06-01

78

Effect of boundary conditions on measured water retention behavior within soils  

NASA Astrophysics Data System (ADS)

The Soil Water Characteristic Curve (SWCC) is a practical representation of the behavior of soil water by relating the suction (difference between the air and water pressures to the moisture content (water saturation). The SWCC is characterized by a hysteresis loop, which is thought to be unique in that any drainage-imbibition cycle lies within a main hysteresis loop limited by two different curves for drainage and imbibition. This 'uniqueness' is the main argument for considering the SWCC as a material-intrinsic feature that characterizes the pore structure and its interaction with fluids. Models have been developed with the SWCC as input data to describe the evolution of the water saturation and the suction within soils. One example of these models is the widely used Richard's equation [1]. In this work we present a series of numerical simulations to evaluate the 'unique' nature of the SWCC. The simulations involves the use of the Lattice Boltzmann Method (LBM) [2] within a regular soil, modelling the flow behavior of two immiscible fluids: wetting and non-wetting. The soil is packed within a cubic domain to resemble the experimental setups that are commonly used for measuring the SWCC[3]. The boundary conditions ensure that the non-wetting phase enters through one cubic face and the wetting phase enters trough the opposite phase, with no flow boundary conditions in the remaining 4 cubic faces. The SWCC known features are inspected including the presence of the common limit curves for different cycles involving varying limits for the suction. For this stage of simulations, the SWCC is indeed unique. Later, different boundary conditions are applied with the two fluids each injected from 3 opposing faces into the porous medium. The effect of this boundary condition change is a net flow direction, which is different from that in the previous case. A striking result is observed when both SWCC are compared and found to be noticeable different. Further analysis is conducted to examine how the fluids are distributed inside the porous medium. This distribution is quantified by the measurement of the interfacial area which behaves also differently between the two configurations. Hassanizadeh proposed an unique relation among saturation, suction and interfacial area, which has been validated experimentally [4]. However we found that such relation is not 'unique' and instead depends on the flow and boundary conditions. While future experimental tests on these results need to be carried out, the simulated SWCC behaviors raise serious questions about the current experimental set-up for measuring the soil water retention characteristics. References. 1. Serrano, S.E., Modeling infiltration with approximate solutions to Richard's equation. Journal of Hydrologic Engineering, 2004. 9(5): p. 421-432. 2. Galindo-Torres, S.A., et al., A Lattice Boltzmann model for studying transient effects during imbibition-drainage cycles in unsaturated soils. Computer Physics Communications, 2013. 184(4): p. 1086-1093. 3. Drake, S.S., D.M. O'Carroll, and J.I. Gerhard, Wettability contrasts between fresh and weathered diesel fuels. Journal of contaminant hydrology, 2012. 4. Culligan, K.A., et al., Interfacial area measurements for unsaturated flow through a porous medium. Water Resources Research, 2004. 40(12).

Galindo-torres, S.; Scheuermann, A.; Pedroso, D.; Li, L.

2013-12-01

79

Influence of leaf hydrophobicity and water droplet retention on rainfall interception  

NASA Astrophysics Data System (ADS)

Climate change, coupled with land use and land cover changes, influence the geographic pattern and composition of vegetation. These vegetation changes strongly influence hydrological processes such as rainfall interception. Rainfall interception is influenced by several variables, including canopy surface area, canopy architecture, and wind. Leaf hydrophobicity and water droplet retention may additionally be important canopy parameters that explain differences in rainfall interception under different canopies with constant leaf area. Different species with the same canopy area, but with differences in leaf hydrophobicity and water droplet retention, may produce different values of rainfall interception. The objective of this study was to investigate if leaf hydrophobicity and water droplet retention are additional influences on rainfall interception. Specifically, this study tested the hypothesis that species with the highest leaf hydrophobicity and the lowest water droplet retention had the lowest rainfall interception on a per leaf area basis. Twenty species from Colorado, U.S.A. were selected for experimentation. Five branches from each species were lopped, positioned under a rainfall simulator, and connected to a balance to record the mass gain of the branches by rainfall interception during 17 minutes of rainfall simulation. Additionally, five separate branches of each species were analyzed using the immersion method to determine maximum rainfall interception. Each branch was destructively sampled following the two separate methods to calculate the leaf and woody surface areas. The rank-order of maximum leaf surface storages for each species corresponded to the rank-order of leaf hydrophobicity and water droplet retention for each species. Species with the highest leaf surface storage had the lowest leaf hydrophobicity and the lowest water droplet retention. The significance of leaf hydrophobicity and water droplet retention as variables that influence rainfall interception is a largely unexplored topic in ecohydrology. Humans have consistently altered vegetation in watersheds by replacing existing species with new species. Additionally, climate change influences species composition in watersheds. Changes in vegeation type in watersheds may influence the discharge from watersheds because of the influence that leaf hydrophobicity and water droplet retention has on interception processes. Understanding differences in rainfall interception between species provides important information for the better management of forests under changing environments.

Holder, C.

2012-12-01

80

An Empirical Test of Environmental Kuznets Curve for Water Pollution  

Microsoft Academic Search

The Environmental Kuznets Curve (EKC) on water pollution was investigated with both semiparametric and parametric models using watershed level data for the state of Louisiana, USA. The parametric model indicated the turning points within the range $10241–$12993, $6636–$13877, and $6467–$12758 for nitrogen (N), phosphorus (P), and dissolved oxygen (DO), respectively. However, only the parameters associated with N EKC were found

Krishna P. Paudel; Hector Zapata; Dwi Susanto

2005-01-01

81

Water retention and hydraulic conductivity of a loamy sand soil as influenced by crop rotation and fertilization  

Microsoft Academic Search

Measurements are reported of soil organic carbon content, dry bulk density, water retention characteristics, and saturated hydraulic conductivity of a sandy loam soil with two different crop rotations and two levels of fertilization. The water retention characteristics were fitted to the van Genuchten equation. Values of unsaturated hydraulic conductivity were estimated by calculation. It was found that crop rotation has

A. R. Dexter; E. A. Czy?; J. Niedzwiecki; C. Ma?kowiak

2001-01-01

82

INFLUENCE OF CELLULOSE ETHER PARTICLE SIZE ON WATER RETENTION OF FRESHLY-MIXED  

E-print Network

induce excellent water retention thanks to the possible superposition of two phenomena. Mortar rheology), in order to impart some specific properties to the mortar, from the fresh paste to the hardened material [1 phenomena [2]: · a rheological effect similar to the one produced by other polysaccharides · an effect

Paris-Sud XI, Université de

83

A Simple Approach for Demonstrating Soil Water Retention and Field Capacity  

ERIC Educational Resources Information Center

It is difficult to demonstrate the soil water retention relationship and related concepts because the specialized equipment required for performing these measurements is unavailable in most classrooms. This article outlines a low-cost, easily visualized method by which these concepts can be demonstrated in most any classroom. Columns (62.5 cm…

Howard, A.; Heitman, J. L.; Bowman, D.

2010-01-01

84

SENSITIVITY ANALYSIS OF THE NON-PARAMETRIC NEAREST NEIGHBOR APPROACH TO ESTIMATE WATER RETENTION  

Technology Transfer Automated Retrieval System (TEKTRAN)

One type of non-parametric lazy learning algorithm, a k-Nearest Neighbor (k-NN) algorithm has been applied to estimate water retention at –33 and –1500 kPa matric potentials. We used a hierarchical set of input attributes using soil texture, bulk density and organic matter content, and varied the si...

85

DEVELOPING JOINT PROBABILITY DISTRIBUTIONS OF SOIL WATER RETENTION CHARACTERISTICS  

EPA Science Inventory

A method is presented for developing probability density functions for parameters of soil moisture relationships of capillary head and hydraulic conductivity. These soil moisture parameters are required for the assessment of water flow and solute transport in unsaturated media. T...

86

Integrated vegetation designs for enhancing water retention and recycling in agroecosystems  

Microsoft Academic Search

Long term studies have shown strong links between vegetation clearing and rainfall declines and more intense droughts. Many\\u000a agroecosystems are exposed to more extreme weather and further declines in rainfall under climate change unless adaptations\\u000a increase the retention of water in landscapes, and its recycling back to the lower atmosphere. Vegetation systems provide\\u000a vital feedbacks to mechanisms that underpin water

Justin G. RyanClive; Clive A. McAlpine; John A. Ludwig

2010-01-01

87

Soil Water Retention and Relative Permeability for Conditions from Oven-Dry to Full Saturation  

SciTech Connect

Common conceptual models for unsaturated flow often rely on the oversimplified representation of medium pores as a bundle of cylindrical capillaries and assume that the matric potential is attributed to the capillary force only. The adsorptive surface forces are ignored. It is often assumed that aqueous flow is negligible when a soil is near or at the residual water content. These models are successful at high and medium water contents but often give poor results at low water contents. These models do not apply to conditions at which the water content is less than the residual water content. We extend the lower bound of existing water-retention functions and conductivity models from residual water content to the oven-dry condition (i.e., zero water content) by defining a state-dependent, residual-water content for a soil drier than a critical value. Furthermore, a hydraulic conductivity model for smooth uniform spheres was modified by introducing a correction factor to describe the film flow-induced hydraulic conductivity for natural porous media. The total unsaturated hydraulic conductivity is the sum of those due to capillary and film flow. The extended retention and conductivity models were verified measurements. Results show that, when the soil is at high and intermediate water content, there is no difference between the un-extended and the extended models; when the soil is at low water content, the un-extended models overestimate the water content but underestimate the conductivity. The extended models match the retention and conductivity measurements well.

Zhang, Z. F.

2011-11-04

88

Soil Water Retention and Relative Permeability for Full Range of Saturation  

SciTech Connect

Common conceptual models for unsaturated flow often rely on the oversimplified representation of medium pores as a bundle of cylindrical capillaries and assume that the matric potential is attributed to capillary forces only. The adsorptive surface forces are ignored. It is often assumed that aqueous flow is negligible when a soil is near or at the residual water content. These models are successful at high and medium water contents but often give poor results at low water contents. These models do not apply to conditions at which water content is less than the residual water content. We extend the lower bound of existing water-retention functions and conductivity models from residual water content to the oven-dry condition (i.e., zero water content) by defining a state-dependent, residual-water content for a soil drier than a critical value. Furthermore, a hydraulic conductivity model for smooth uniform spheres was modified by introducing a correction factor to describe the film flow-induced hydraulic conductivity for natural porous media. The total unsaturated hydraulic conductivity is the sum of those due to capillary and film flow. The extended retention and conductivity models were verified with six datasets from the literature. Results show that, when the soil is at high and intermediate water content, there is no difference between the un-extended and the extended models; when the soil is at low water content, the un-extended models overestimate the water content but under-estimate the conductivity while the extended models match the retention and conductivity measurements well.

Zhang, Z. F.

2010-09-28

89

Developing joint probability distributions of soil water retention characteristics  

Microsoft Academic Search

A method is presented for developing probability density functions for parameters of soil moisture relationships of capillary head (h(Phi)) and hydraulic conductivity (K(Phi)). These soil moisture parameters are required for the assessment of water flow and solute transport in unsaturated media. The method employs a statistical multiple regression equations proposed in the literature for estimating (h(Phi)) or (K(Phi)) relationships using

Robert F. Carsel; Rudolph S. Parrish

1988-01-01

90

Phosphorus retention in a newly constructed wetland receiving agricultural tile drainage water.  

PubMed

One measure used in Sweden to mitigate eutrophication of waters is the construction of small wetlands (free water surface wetland for phosphorus retention [P wetlands]) to trap particulate phosphorus (PP) transported in ditches and streams. This study evaluated P retention dynamics in a newly constructed P wetland serving a 26-ha agricultural catchment with clay soil. Flow-proportional composite water samples were collected at the wetland inlet and outlet over 2 yr (2010-2011) and analyzed for total P (TP), dissolved P (DP), particulate P (PP), and total suspended solids (TSS). Both winters had unusually long periods of snow accumulation, and additional time-proportional water samples were frequently collected during snowmelt. Inflow TP and DP concentrations varied greatly (0.02-1.09 mg L) during the sampling period. During snowmelt in 2010, there was a daily oscillation in P concentration and water flow in line with air temperature variations. Outflow P concentrations were generally lower than inflow concentrations, with net P losses observed only in August and December 2010. On an annual basis, the wetland acted as a net P sink, with mean specific retention of 69 kg TP, 17 kg DP, and 30 t TSS ha yr, corresponding to a reduction in losses of 0.22 kg TP ha yr from the agricultural catchment. Relative retention was high (36% TP, 9% DP, and 36% TSS), indicating that small constructed wetlands (0.3% of catchment area) can substantially reduce P loads from agricultural clay soils with moderately undulating topography. PMID:23673852

Kynkäänniemi, Pia; Ulén, Barbro; Torstensson, Gunnar; Tonderski, Karin S

2013-01-01

91

Epiphyte Water Retention and Evaporation in Native and Invaded Tropical Montane Cloud Forests in Hawaii  

NASA Astrophysics Data System (ADS)

Epiphyte water retention was quantified at two montane cloud forest sites in Hawai'i Volcanoes National Park, one native and the other invaded by an alien tree species. Water storage elements measured included all epiphytic mosses, leafy liverworts, and filmy ferns. Tree surface area was estimated and a careful survey was taken to account for all epiphytes in the sample area of the forest. Samples were collected and analyzed in the lab for epiphyte water retention capacity (WRC). Based on the volume of the different kinds of epiphytes and their corresponding WRC, forest stand water retention capacity for each survey area was estimated. Evaporation from the epiphyte mass was quantified using artificial reference samples attached to trees that were weighed at intervals to determine changes in stored water on days without significant rain or fog. In addition, a soil moisture sensor was wrapped in an epiphyte sample and left in the forest for a 6-day period. Epiphyte biomass at the Native Site and Invaded Site were estimated to be 2.89 t ha-1 and 1.05 t ha-1, respectively. Average WRC at the Native Site and Invaded Site were estimated at 1.45 mm and 0.68 mm, respectively. The difference is likely due to the presence of the invasive Psidium cattleianum at the Invaded Site because its smooth stem surface is unable to support a significant epiphytic layer. The evaporation rate from the epiphyte mass near WSC for the forest stand at the Native Site was measured at 0.38 mm day-1, which represented 10.6 % of the total ET from the forest canopy at the Native Site during the period. The above research has been recently complemented by a thorough investigation of the WSC of all water storage elements (tree stems, tree leaves, shrubs, grasses, litter, fallen branches, and epiphytes) at six forested sites at different elevations within, above, and below the zone of frequent cloud-cover. The goal of this study was to create an inexpensive and efficient methodology for acquiring estimates of above-ground water retention in different types of forests by means of minimally-destructive sampling and surveying. The results of this work serve as baseline data providing a range of possible values of the water retention of specific forest elements and the entire above-ground total where no values have been previously recorded.

Mudd, R. G.; Giambelluca, T. W.

2006-12-01

92

Water retention and drainage in different brands of microcrystalline cellulose: effect of measuring conditions.  

PubMed

Interaction between water and microcrystalline cellulose (MCC) measured as retention and cumulative drainage of water (WR% and CDW%) is investigated for unmilled and micronized standard (Avicel and Emcocel) and silicified (Prosolv) MCC brands. A centrifuge method was applied with increasing duration and different porosity and thickness of cylindrical powder beds (specimens), in order to establish optimal determination conditions and quantify alterations in interaction between water and different MCC brands. Also, changes of specimen thickness due to presence of water (swelling) were followed. It was found that the effect of specimen porosity and thickness on water drainage (CDW%) appears to be opposite to that on water retention (WR%), while two patterns of WR% and CDW% change with specimen porosity and thickness can be distinguished depending on the centrifugation time. Also, WR% and CDW% are affected by the MCC brand and the micronization. Unmilled silicified MCC brand (Prosolv) shows significantly lower retention and higher drainage of water compared to standard unmilled brands (Avicel and Emcocel), while differences between the unmilled standard Avicel and Emcocel brands are not easily distinguished. Micronization, in general, increases greatly the WR% and decreases CDW% for all the tested MCC brands, and enhances their differences even between Avicel and Emcocel. Swelling of specimen due to presence of water was observed, which was significantly reduced with the micronization, the specimen porosity, and centrifugation as well, but showed slight variation between the different MCC brands. Values of specimen porosity between 60% and 70%, thickness/diameter ratio between 0.75 and 1.0, and centrifugation time between 5 and 20 min provide optimal measuring settings for comparison of MCC brands. PMID:16527466

Nikolakakis, Ioannis; Tsarvouli, Konstantina; Malamataris, Stavros

2006-07-01

93

Development of a world data set of soil water retention properties using pedotransfer rules  

Microsoft Academic Search

The World Inventory of Soil Emission Potentials (WISE) database is used to compile a standardized and spatially explicit data set of soil water retention properties. WISE holds 4353 globally distributed profiles considered to be representative of the soil units shown on a 1\\/2° latitude by 1\\/2° longitude version of the corrected and digitized 1:5 M FAO-Unesco Soil Map of the

N. H. Batjes

1996-01-01

94

Heat island mitigation using water retentive pavement sprinkled with reclaimed wastewater.  

PubMed

In Japan, reclaimed wastewater has been recycled widely for non-potable urban applications and it is to be used for sprinkling roads to mitigate heat island in urban areas. To assess the heat island mitigation effects of the sprinkling reclaimed wastewater on water retentive pavement, we carried out a survey at Shiodome-District, Tokyo. The temperatures of air and roads, humidity, and WBGT (Wet-bulb globe temperature) were measured and heat flux was estimated to compare the condition of the areas with/without sprinkling. The following results were obtained. 1) Sprinkling reclaimed wastewater decreased the road surface temperature by 8 degrees during the daytime and by 3 degrees at night: temperatures equal to those on planting zones. Nevertheless sprinkling was done only in the daytime, the temperature decrease effect was not only obtained during the daytime: it continued through the night, due to the water retentive pavement. 2) Sprinkling reclaimed wastewater reduced the amount of sensible heat flux and increased that of latent heat flux. These results suggest that sprinkling reclaimed wastewater on water retentive pavement can effectively mitigate the heat island phenomenon. PMID:18401150

Yamagata, H; Nasu, M; Yoshizawa, M; Miyamoto, A; Minamiyama, M

2008-01-01

95

Investigation of the use of nanofluids to enhance the In-Vessel Retention capabilities of Advanced Light Water Reactors  

E-print Network

Nanofluids at very low concentrations experimentally exhibit a substantial increase in Critical Heat Flux (CHF) compared to water. The use of a nanofluid in the In-Vessel Retention (IVR) severe accident management strategy, ...

Hannink, Ryan Christopher

2007-01-01

96

MODELING SHALLOW GROUNDWATER TABLE CONTRIBUTION TO SOIL WATER RETENTION IN THE UNSATURATED ZONE OF A CALCAREOUS SOIL OF SOUTH  

E-print Network

1 MODELING SHALLOW GROUNDWATER TABLE CONTRIBUTION TO SOIL WATER RETENTION IN THE UNSATURATED ZONE dreams and professional goals. #12;5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES

Migliaccio, Kati White

97

Soil Organic Carbon and Water Retention after Conversion of Grasslands to Pine Plantations in the Ecuadorian Andes  

Microsoft Academic Search

Tree plantations in the high elevations of the tropics constitute a growing land use, but their effect on ecosystem processes and services is not well known. We examined changes in soil organic carbon (C) and water retention in a chronosequence of Pinus radiata stands planted in páramo grasslands in Cotopaxi province, Ecuador. Water retention at 10, 33, and 1,500 kPa declined

Kathleen A. Farley; Eugene F. Kelly; Robert G. M. Hofstede

2004-01-01

98

Organic matter controls of soil water retention in an alpine grassland and its significance for hydrological processes  

NASA Astrophysics Data System (ADS)

Soil water retention influences many soil properties and soil hydrological processes. The alpine meadows and steppes of the Qilian Mountains on the northeast border of the Qinghai-Tibetan Plateau form the source area of the Heihe River, the second largest inland river in China. The soils of this area therefore have a large effect on water movement and storage of the entire watershed. In order to understand the controlling factors of soil water retention and how they affect regional eco-hydrological processes in an alpine grassland, thirty-five pedogenic horizons in fourteen soil profiles along two facing hillslopes in typical watersheds of this area were selected for study. Results show that the extensively-accumulated soil organic matter plays a dominant role in controlling soil water retention in this alpine environment. We distinguished two mechanisms of this control. First, at high matric potentials soil organic matter affected soil water retention mainly through altering soil structural parameters and thereby soil bulk density. Second, at low matric potentials the water adsorbing capacity of soil organic matter directly affected water retention. To investigate the hydrological functions of soils at larger scales, soil water retention was compared by three generalized pedogenic horizons. Among these soil horizons, the mattic A horizon, a diagnostic surface horizon of Chinese Soil Taxonomy defined specially for alpine meadow soils, had the greatest soil water retention over the entire range of measured matric potentials. Hillslopes with soils having these horizons are expected to have low surface runoff. This study promotes the understanding of the critical role of alpine soils, especially the vegetated surface soils in controlling the eco-hydrological processes in source regions of the Heihe River watershed.

Yang, Fei; Zhang, Gan-Lin; Yang, Jin-Ling; Li, De-Cheng; Zhao, Yu-Guo; Liu, Feng; Yang, Ren-Min; Yang, Fan

2014-11-01

99

Soil water retention after natural and simulated rainfall on a temperate grassland  

NASA Astrophysics Data System (ADS)

Recent climate change scenarios resulting from elevated trace gasses may alter environmental temperature and moisture. The ecological consequences, however, are uncertain requiring an understanding of how soil-plant systems will respond to different conditions. This study examines the temporal characteristics of soil water retention in a temperate grassland following natural and simulated summer showers. We have used weighting lysimeters located in grassland stands of 360 m2, 2.25 m2 and lone lysimeters measuring 0.07 m2. Water deposited from natural summer rainfall on these grasslands is likely to be lost in less than two days because 92% of the rainshowers are < 10 mm having residence times of less than two days. Showers > 10 mm did, however, consistently remain in the soil-plant system for periods longer than light showers. When the largest plots (360 m2) were wetted by small (< 3 mm) natural rainfall events covering a portion of the entire valley (30 70 km2), soil water depletion rates were not significantly different than if just the 360 m2 plots were wetted by irrigations of the same size. If anthopogenetic changes occur in the rainfall amounts of summer showers in the Northern Great Plains, our results support the contention that soil water retention and associated ecosystem processes may be significantly altered in Agropyron smithii (Rybd.) grasslands.

Welker, J. M.; McClelland, S.; Weaver, T.

1991-09-01

100

Using Bezier curves for the calculation of retention indices of polycyclic aromatic hydrocarbons in the so-called Lee's scale in temperature-programmed gas chromatography with mass spectrometry detection.  

PubMed

The retention indices of some polycyclic aromatic hydrocarbons (PAHs) separated by temperature-programmed gas chromatography are computed by smoothing reference data with Bezier curves of orders 6 are more consistent with the scheme of this retention parameter, and they present standard deviations systematically smaller than those associated with classical retention indices. The Bezier curve possesses the property of local control, (i.e., their graphs are modified only in the neighbourhood of the displaced point). The values thus obtained were compared with the corresponding ones calculated in a classical way. Detailed statistical analysis is presented to describe the retention indices of PAHs expressed in the so-called Lee's scale as a function of retention temperatures (in degrees C). As a training set, experimental retention data of PAHs obtained on a PE-5 phase is used for correlation. As prediction sets, literature experimental retention indices expressed in the so-called Lee's scale obtained on a DB-5 slightly polar stationary phase are applied for comparison. The method developed is successfully used for estimating and predicting the capillary gas chromatography retention index of PAHs. PMID:17254379

Jamoussi, Bassem; Kanzari, Fehmi; Ben Hassine, Béchir; Abderrabba, Abdelmanef

2007-01-01

101

Assessing the Use of Sunken Lanes for Water Retention in a Landscape  

NASA Astrophysics Data System (ADS)

Newly-designed structures and landscaping elements are often used for flood protection. This article assesses the use of existing sunken lanes for retaining water in a landscape and the sedimentation of washed-off soil. The article also describes ways how to preserve or, at least minimally disrupt, existing biotopes and landscape segments. Geodetic data from one specific sunken lane in South Moravia in the Czech Republic were transferred to a digital terrain model; 9 models were subsequently generated, each with a different longitudinal sunken lane bed slope. Retention dams consisting of gabions were placed in them. The number of dams, the volume of structures made of steel gabions, and the retention area volume behind the dams were determined for each model specifically. It was determined that the number of dams, as well as their total volume, increased with the average longitudinal slope of the sunken lane bed. It was also discovered that the retention volume remained almost the same, as it only very slightly decreases with an increasing longitudinal slope.

Zlatuška, Karel

2012-12-01

102

Assessing the Use of Sunken Lanes for Water Retention in a Landscape  

NASA Astrophysics Data System (ADS)

Newly-designed structures and landscaping elements are often used for flood protection. This article assesses the use of existing sunken lanes for retaining water in a landscape and the sedimentation of washed-off soil. The article also describes ways how to preserve or, at least minimally disrupt, existing biotopes and landscape segments. Geodetic data from one specific sunken lane in South Moravia in the Czech Republic were transferred to a digital terrain model; 9 models were subsequently generated, each with a different longitudinal sunken lane bed slope. Retention dams consisting of gabions were placed in them. The number of dams, the volume of structures made of steel gabions, and the retention area volume behind the dams were determined for each model specifically. It was determined that the number of dams, as well as their total volume, increased with the average longitudinal slope of the sunken lane bed. It was also discovered that the retention volume remained almost the same, as it only very slightly decreases with an increasing longitudinal slope.

Zlatuška, Karel

2012-12-01

103

Analysis of water-level fluctuations of the US Highway 90 retention pond, Madison, Florida  

USGS Publications Warehouse

A closed basin stormwater retention pond, located 1 mile west of Madison, Florida, has a maximum storage capacity of 134.1 acre-feet at the overtopping altitude of 100.2 feet. The maximum observed altitude (July 1982 to March 1984) was 99.52 feet (126.7 acre-feet) on March 28, 1984. This report provides a technique for simulating net monthly change-in-altitude in response to rainfall and evaporation. A regression equation was developed which relates net monthly change in altitude (dependent variable) to rainfall and evaporation (independent variables). Rainfall frequency curves were developed using a log-Pearson Type III distribution of the annual, January through April, June through August, and July monthly rainfall totals for the years 1908-72, 1974, 1976-82. The altitude of the retention pond increased almost 7 feet during the 4-month period January through April 1983. The rainfall total was 35.1 inches, and the recurrence interval exceeded the 100-year January-April rainfall. (USGS)

Bridges, W.C.

1985-01-01

104

Regularities of Anthocyanins Retention in RP HPLC for “Water–Acetonitrile–Phosphoric Acid” Mobile Phases  

PubMed Central

The influence of exchange of HCOOH (System 2) by phosphoric acid (System 1) for acidification of the “acetonitrile–water” mobile phases for reversed-phase HPLC of anthocyanins was investigated in the framework of relative retention analysis. The differences and similarities of anthocyanins separation were revealed. It has been shown that some common features of the quantitative relationships may be used for preliminary anthocyanins structure differentiation, according to the number of OH-groups in anthocyanidin backbone as well as to a number of saccharide molecules in glycoside radicals in position 3 of the anthocyanin without MS detection. PMID:25692073

Deineka, V. I.; Deineka, L. A.; Saenko, I. I.

2015-01-01

105

Regularities of Anthocyanins Retention in RP HPLC for "Water-Acetonitrile-Phosphoric Acid" Mobile Phases.  

PubMed

The influence of exchange of HCOOH (System 2) by phosphoric acid (System 1) for acidification of the "acetonitrile-water" mobile phases for reversed-phase HPLC of anthocyanins was investigated in the framework of relative retention analysis. The differences and similarities of anthocyanins separation were revealed. It has been shown that some common features of the quantitative relationships may be used for preliminary anthocyanins structure differentiation, according to the number of OH-groups in anthocyanidin backbone as well as to a number of saccharide molecules in glycoside radicals in position 3 of the anthocyanin without MS detection. PMID:25692073

Deineka, V I; Deineka, L A; Saenko, I I

2015-01-01

106

Increased Water Retention in Polymer Electrolyte Membranes at Elevated Temperatures Assisted by Capillary Condensation  

SciTech Connect

We establish a new systematic methodology for controlling the water retention of polymer electrolyte membranes. Block copolymer membranes comprising hydrophilic phases with widths ranging from 2 to 5 nm become wetter as the temperature of the surrounding air is increased at constant relative humidity. The widths of the moist hydrophilic phases were measured by cryogenic electron microscopy experiments performed on humid membranes. Simple calculations suggest that capillary condensation is important at these length scales. The correlation between moisture content and proton conductivity of the membranes is demonstrated.

Park, M.J.; Downing, K.H.; Jackson, A.; Gomez, E.D.; Minor, A.M.; Cookson, D.; Weber, A.Z.; Balsara, N.P. (UCB); (NIST); (LBNL); (UC)

2008-10-03

107

Investigating and simulating the impact of surface water retention potential in Western Siberia  

NASA Astrophysics Data System (ADS)

The Western Siberian lowland is characterised through an extreme climate with a yearly temperature difference of more than 60°C. An intensive growth period of five months follows the most important hydrological event of the year, the snowmelt, which defines more than 90% of the yearly runoff. The geophysical setting is mainly influenced through low hydraulic gradients, clayey soils, retention basins, landscape depressions and embankments that lead to a high water rentention potential on the surface and the soil. During snowmelt, this leads to a runoff delay. In hand with high evaporation, the described characteristics cause low runoff generation during the rest of the year, even after intense rainfall events. Within the scope of the project "Sustainable land management and adaptation stategies to climate change for the Western Siberian corn-belt" (SASCHA) the hydrological processes are simulated in three catchments, in a gradient from the pre-taiga to the forest steppe. The three catchments are Pyschma (16.762 km˛), Vagai (2.851 km˛) and Loktinka (334 km˛). The special challenges in the simulations are: (1) the correct simulation of the half-year long snow cover and its melting, (2) the scarce historical flow data, which could only be extended in 2013 through own measurement campaings and (3) to quantify and simulate the impact of the water retention potential on the catchment hydrology using raw and filled digital elevation models and landscape characteristics. Against the background of these challenges, we present the hydrological simulations with the Soil and Water Assessment Tool (SWAT).

Kiesel, Jens; Kolychalow, Olga; Sheludkov, Artyom; Marciniak, Hasmik; Abramenko, Katya; Schmalz, Britta; Conrad, Yvonne; Pfannerstill, Matthias; Veshkurseva, Tatyana; Khoroshavin, Vitaliy; Tolstikov, Andrey; Fohrer, Nicola

2014-05-01

108

Nitrate retention in riparian ground water at natural and elevated nitrate levels in North Central Minnesota  

USGS Publications Warehouse

The relationship between local ground water flows and NO3- transport to the channel was examined in three well transects from a natural, wooded riparian zone adjacent to the Shingobee River, MN. The hillslope ground water originated as recharge from intermittently grazed pasture up slope of the site. In the hillslope transect perpendicular to the stream, ground water NO3- concentrations decreased from ???3 mg N L-1 beneath the ridge (80 m from the channel) to 0.01 to 1.0 mg N L-1 at wells 1 to 3 m from the channel. The Cl- concentrations and NO3/Cl ratios decreased toward the channel indicating NO3- dilution and biotic retention. In the bankside well transect parallel to the stream, two distinct ground water environments were observed: an alluvial environment upstream of a relict beaver dam influenced by stream water and a hillslope environment downstream of the relict beaver dam. Nitrate was elevated to levels representative of agricultural runoff in a third well transect looted ???5 m from the stream to assess the effectiveness of the riparian zone as a NO3- sink. Subsurface NO3- injections revealed transport of up to 15 mg N L-1 was nearly conservative in the alluvial riparian environment. Addition of glucose stimulated dissolved oxygen uptake and promoted NO3- retention under both background and elevated NO 3- levels in summer and winter. Disappearance of added NO3- was followed by transient NO2- formation and, in the presence of C2H2, by N2O formation, demonstrating potential denitrification. Under current land use, most NO3- associated with local ground water is biotically retained or diluted before reaching the channel. However, elevating NO 3- levels through agricultural cultivation would likely result in increased NO3- transport to the channel. ?? ASA, CSSA, SSSA.

Duff, J.H.; Jackman, A.P.; Triska, F.J.; Sheibley, R.W.; Avanzino, R.J.

2007-01-01

109

A Correlation Between Water Maser Emission and the Visual Light Curve of RX Bootis  

Microsoft Academic Search

We investigate the emission from the 22.2 GHz maser line of water, and compare it to the visual light curve for the semi-regular variable star RX Boo. There appears to be a correlation between the maser emission and light curve, however, the correlation is not as clear as for the regular Mira variables. The water emission appears over a broad

Jennifer Hedden; Priscilla J. Benson; Irene R. Little-Marenin; Robert R. Cadmus

1991-01-01

110

Impact of storm water on groundwater quality below retention/detention basins.  

PubMed

Groundwater from 33 monitoring of peripheral wells of Karachi, Pakistan were evaluated in terms of pre- and post-monsoon seasons to find out the impact of storm water infiltration, as storm water infiltration by retention basin receives urban runoff water from the nearby areas. This may increase the risk of groundwater contamination for heavy metals, where the soil is sandy and water table is shallow. Concentration of dissolved oxygen is significantly low in groundwater beneath detention basin during pre-monsoon season, which effected the concentration of zinc and iron. The models of trace metals shown in basin groundwater reflect the land use served by the basins, while it differed from background concentration as storm water releases high concentration of certain trace metals such as copper and cadmium. Recharge by storm water infiltration decreases the concentration and detection frequency of iron, lead, and zinc in background groundwater; however, the study does not point a considerable risk for groundwater contamination due to storm water infiltration. PMID:19241126

Zubair, Arif; Hussain, Asif; Farooq, Mohammed A; Abbasi, Haq Nawaz

2010-03-01

111

Surface Water Ground Water Interaction Inferred from Discharge vs. Basin Area Curves  

NASA Astrophysics Data System (ADS)

Peak discharge (Qp) vs. basin area (A) curves have been studied for long time leading to the development of some of the promising hydrological response models. In this study we also analyze discharge vs. basin area curves for recession periods. We define the characteristic discharge, Qn, as the discharge observed in the n-th day after a peak, then for each value of n we analyze Qn vs. A curves, which typically follow a power law equation of type: Qp ? A?n. The exponent ? n for n=0 is known to take value between 0.5 and 1 (note that Qn = Qp for n=0), and the commonly accepted theoretical explanation for it is that Qp is controlled by width of channel network and effective rainfall duration. This premise is based on the assumption that surface flow dominates during a flood event in a basin and that flow velocity is constant everywhere in the stream network of the basin. As n increases, i.e. during recession periods, Qn is expected to be controlled by subsurface flow. According to the geomorphological recession flow model Qn for higher values of n is controlled by the dynamics of saturated channel network, and for this case the value of ? n is close to 1. Results here show that ? n increases and approaches 1 as n increases, confirming the notion that a transition from surface water dominated flow process to subsurface water dominated flow process occurs with time during a recession event.

Biswal, B.; D, N.

2012-12-01

112

Influence of vegetative filter strips on heavy metal retention in runoff waters: a laboratory evaluation  

NASA Astrophysics Data System (ADS)

Point-polluted industrial sites can be exposed to water erosion, leading to a dispersion of, e.g., heavy metal contaminated soil particles. Sowing vegetative buffer strips could limit this problem. We therefore investigated the influence of different vegetative filter strips on heavy metal retention, for runoff water loaded with two different polluted sediments. An experimental flume was built in order to simulate sediment retention by short vegetative buffer strips for different runoff discharges, slopes and sediment concentrations. At the lower bound of the flume, a 0.58 m wide x 1 m long x 0.1 m deep cage filled with soil could be inserted. Three treatments were considered: bare soil and soil sown with either Trifolium repens or Lolium perenne. The plants were allowed to grow for 2 months after germination. The setup allowed characterizing the water and sediment discharge at the outlet of the vegetative strips by means of a tipping bucket with splitter device. Heavy metal-polluted soils were collected at two industrial sites highly polluted with 1) arsenic and lead (Ath), and 2) cadmium and zinc (Prayon). We investigated the effects of the three different covers for these two sediment types (4 replications by treatment), with a slope of 8%, a discharge of 1.7 m3/h and a sediment concentration of 10g/l. Besides sediment mass, we determined heavy metal concentrations and particle size of the sediments collected both at the outlet of the flume and in the sediment deposits upstream of the strips. Following these experiments, size separation of the initial soils was performed, to analyze heavy metal concentrations of each size class. Finally, selective extractions (water, CaCl2 and EDTA) were performed, allowing estimation of heavy metal soluble fractions not retained by vegetative filter strips. Ath Prayon As [%] Pb [%] Cd [%] Zn [%] Lolium perenne 24.1 21.5 23.7 21.2 Trifolium repens 47.8 40.5 55 52.4 Bare soil 20.5 10.9 26.5 22.1 Concentrations [mg/kg] 800 40000 42 2400 Heavy metal retention by vegetative filter strips and mean concentrations [mg/kg] of soils. Heavy metal concentrations increased at the outlet of the flume because of selective sedimentation. Vegetative filter strips with Trifolium repens were the most effective to trap sediments and heavy metals. These strips slowed significantly the flow, leading to important sediment deposits upstream. Lolium perenne were not more efficient than bare soil, because of its erected posture and its low number of tillers after 2 months.

Lambrechts, Thomas; de Braekeleer, Charlotte; Iserentant, Anne; Rentmeesters, Guido; Lutts, Stanley; Bielders, Charles

2010-05-01

113

Source or Sink: Investigating the role of storm water retention ponds in the urban landscape (Invited)  

NASA Astrophysics Data System (ADS)

The impact of human activities on surface water, groundwater and soil is nowhere more apparent than in urban and suburban systems. Dramatic changes to watersheds in urbanizing areas have led to changes in hydrology and an associated increase in the flux of sediment and contaminants to surface and ground waters. In an effort to mediate these impacts, Best Management Practices (BMP) have been established in order to increase infiltration of runoff and trap sediment and particulates derived from impervious surfaces before they enter surface waters. Perhaps the most ubiquitous BMP are storm water retention ponds. While these structures are designed to reduce runoff and particulate loading to urban streams, their addition to the urban landscape has created a large number of new wetland habitats. In the Red Run watershed, just outside of Baltimore, Maryland, 186 discrete natural or man-made wetland areas have been identified. Of these 186 wetland areas, 165 were created to manage stormwater and most were specifically designed as stormwater management ponds (i.e., human-created basins or depressions that hold runoff for some period during the annual hydrological year). Despite their abundance in the landscape, very little is known about how these systems impact the flux of stormwater pollutants or affect the organisms using these ponds as habitat. Results from a series of related projects in the Red Run watershed are presented here in an effort to summarize the range of issues associated with stormwater management ponds. The Red Run watershed is situated inside the Urban-Rural Demarcation Line (URDL) around Baltimore City and has been identified as a smart growth corridor by Baltimore County. This region is one of two areas in Baltimore County where new development is focused. In a series of investigations of soils, surface and ground waters, and amphibian and earthworm use of 68 randomly selected stormwater retention ponds from the Red Run watershed, a range of hydrologic, ecologic, and geochemical conditions have been identified. Results from these investigations suggest that pollutant conditions, specifically trace metals and chloride, limit the use of these ponds by amphibians and effect the distribution of earthworms within ponds. The soils in ponds associated with high use roadways contain elevated levels of PAHs, Zn and Cu and the groundwater beneath these same ponds tends to have elevated chloride levels year round. Pond and associated flood plain soils in these systems have been altered and exhibit elevated Na+ or Ca2+ concentrations suggesting years of interaction with road salt contaminated discharge. These Na+ and Ca2+ form soils affect the retention of dissolved trace metals with Ca-enriched soils potentially increasing the dissolved metal concentrations of surface and pore waters and enabling the transport of roadway derived metals to surface waters and Na-enriched soils scavenging trace metals from incoming runoff. The increase in dissolved metals may also increase the toxicity to amphibians and other organisms inhabiting the storm water ponds and ultimately, streams fed by ground water recharge from ponds. Our results to date suggest both the intended and unintended function of storm water ponds in urban landscapes are complicated and deserving of more attention.

Lev, S.; Casey, R.; Ownby, D.; Snodgrass, J.

2009-12-01

114

Buried particulate organic carbon stimulates denitrification and nitrate retention in stream sediments at the groundwater-surface water interface  

USGS Publications Warehouse

The interface between ground water and surface water in streams is a hotspot for N processing. However, the role of buried organic C in N transformation at this interface is not well understood, and inferences have been based largely on descriptive studies. Our main objective was to determine how buried particulate organic C (POC) affected denitrification and NO3? retention in the sediments of an upwelling reach in a sand-plains stream in Wisconsin. We manipulated POC in mesocosms inserted in the sediments. Treatments included low and high quantities of conditioned red maple leaves (buried beneath combusted sand), ambient sediment (sand containing background levels of POC), and a control (combusted sand). We measured denitrification rates in sediments by acetylene-block assays in the laboratory and by changes in N2 concentrations in the field using membrane inlet mass spectrometry. We measured NO3?, NH4+, and dissolved organic N (DON) retention as changes in concentrations and fluxes along groundwater flow paths in the mesocosms. POC addition drove oxic ground water to severe hypoxia, led to large increases in dissolved organic C (DOC), and strongly increased denitrification rates and N (NO3? and total dissolved N) retention relative to the control. In situ denitrification accounted for 30 to 60% of NO3? retention. Our results suggest that buried POC stimulated denitrification and NO3? retention by producing DOC and by creating favorable redox conditions for denitrification.

Stelzer, Robert S.; Scott, J. Thad; Bartsch, Lynn A.

2015-01-01

115

The Role of Environmental Forcing in Controlling Water Retention Gyres in Subsystems of Narragansett Bay  

NASA Astrophysics Data System (ADS)

Greenwich Bay and the Providence River represent two subsystems of the Narragansett Bay (RI) estuary with chronic water quality problems. Both underway and moored Acoustic Doppler Current Profiler (ADCP) observations have shown the presence of large-scale, subtidal gyres within these subsystems. Prior numerical models of Narragansett Bay, developed using the Regional Ocean Modeling System (ROMS), indicate that prevailing summer sea breeze conditions are favorable to the evolution of stable circulation gyres, which increase retention times within each subsystem. Fluid dynamics laboratory models of the Providence River, conducted in the Geophysical Fluid Dynamics Laboratory of the Research School of Earth Sciences (Australian National University), reproduce gyres that match first order features of the ADCP data. These laboratory models also reveal details of small-scale eddies along the edges of the retention gyre. We report results from spatially and temporally detailed current meter deployments (using SeaHorse Tilt Current Meters) in both subsystems, which reveal details on the growth and decay of gyres under various spring-summer forcing conditions. In particular, current meters were deployed during the severe flooding events in the Narragansett Bay watershed during March, 2010. A combination of current meter data and high-resolution ROMS modeling is used to show how gyres effectively limit subtidal exchange from the Providence River and Greenwich Bay and to understand the forcing conditions that favor efficient flushing. The residence times of stable gyres within these regions can be an order of magnitude larger than values predicted by fraction of water methods. ROMS modeling is employed to characterize gyre energy, stability, and flushing rates for a wide range of seasonal, wind and runoff scenarios.

Balt, C.; Kincaid, C. R.; Ullman, D. S.

2010-12-01

116

Evaluation of a computer program used to estimate water characteristic curve  

Technology Transfer Automated Retrieval System (TEKTRAN)

The soil water characteristic curve, h(theta), can be used to estimate a variety of parameters in unsaturated soils. One practical application of h(theta) is its use by DRAINMOD, a drainage model that has been widely used in shallow water table regions, to determine the water table depth–drainage v...

117

ESTIMATING WATER TREATMENT COSTS. VOLUME 2. COST CURVES APPLICABLE TO 1 TO 200 MGD TREATMENT PLANTS  

EPA Science Inventory

This report discusses unit processes and combinations of unit processes that are capable of removing contaminants included in the National Interim Primary Drinking Water Regulations. Construction and operation and maintenance cost curves are presented for 99 unit processes that a...

118

Carbon isotope discrimination and water stress in trembling aspen following variable retention harvesting.  

PubMed

Variable retention harvesting (VRH) has been proposed as a silvicultural practice to maintain biodiversity and ecosystem integrity. No previous study has examined tree carbon isotope discrimination to provide insights into water stress that could lead to dieback and mortality of trees following VRH. We measured and compared the carbon isotope ratios (delta(13)C) in stem wood of trembling aspen (Populus tremuloides Michx.) before and after VRH. Eight trees were sampled from isolated residual, edge and control (interior of unharvested stand) positions from each of seven plots in three regions (Calling Lake and Drayton Valley, Alberta and Lac Duparquet, Québec). After VRH, the general trend in mean delta(13)C was residual > edge > control trees. Although this trend is indicative of water stress in residual trees, it also suggests that edge trees received some sheltering effect, reducing their stress compared with that of residuals. A strong inverse relationship was found between the delta(13)C values and the mean annual precipitation in each region. The trend in mean delta(13)C signature was Calling Lake > Drayton Valley > Lac Duparquet trees. These results suggest that residual or edge trees in drier regions are more likely to suffer water stress following VRH. We also observed a trend of greater delta(13)C in stout trees compared with slender trees, both before and after VRH. The evidence of greater water stress in stout trees likely occurred because of a positive relationship between stem diameter and crown volume per basal area. Our results provide evidence that water stress could be the driving mechanism leading to dieback and mortality of residual trees shortly after VRH. Additionally, the results from edge trees indicate that leaving hardwood residuals in larger patches or more sheltered landscape positions could reduce the water stress to which these trees are subjected, thereby reducing dieback and mortality. PMID:17403660

Bladon, Kevin D; Silins, Uldis; Landhäusser, Simon M; Messier, Christian; Lieffers, Victor J

2007-07-01

119

Simulation of water flow and retention in earthen-cover materials overlying uranium mill tailings  

SciTech Connect

The water retention characteristics of a multilayer earthen cover for uranium mill tailings were simulated under arid weather conditions common to Grand Junction, Colorado. The multilayer system described in this report consists of a layer of wet clay/gravel (radon barrier), which is separated from a surface covering of fill soil by a washed rock material used as a capillary barrier. The capillary barrier is designed to prevent the upward migration of water and salt from the tailings to the soil surface and subsequent loss of water from the wet clay. The flow model, UNSATV, described in this report uses hydraulic properties of the layered materials and historical climatic data for two years (1976 and 1979) to simulate long-term hydrologic response of the multilayer system. Application of this model to simulate the processes of infiltration, evaporation and drainage is described in detail. Simulations over a trial period of one relatively wet and two dry years indicated that the clay-gravel layer remained near saturation, and hence, that the layer was an effective radon barrier. Estimates show that the clay-gravel layer would not dry out (i.e., revert to drying dominated by isothermal vapor-flow conditions) for at least 20 years, provided that the modeled dry-climate period continues.

Simmons, C.S.; Gee, G.W.

1981-09-01

120

IPhO 2012: how magnets curve the water  

NASA Astrophysics Data System (ADS)

An overview of the 43rd International Physics Olympiad (held in Tallinn and Tartu, Estonia) is given; this includes short summaries of the problems and competition results. Experimental problem no 1 is discussed in detail, including the full text, solution, and additional theoretical analysis. In this experiment, laser beam reflection from the water surface is used to calculate the recession depth of the water surface above a strong permanent magnet; this result is used to determine the magnetic permeability of the water.

Kalda, J.; Kikas, J.; Heidelberg, M.; Ainsaar, S.; Lőhmus, R.

2013-07-01

121

Characterizing Scale and Location-Dependent Correlation of Water Retention Parameters with Soil Physical Properties Using Wavelet Techniques  

Microsoft Academic Search

Understanding the correlation between soil hydraulic parameters and soil physical properties is a prerequisite for the prediction of soil hydraulic properties from soil physical properties. Th e objective of this study was to examine the scale- and location-dependent correlation between two water retention parameters (? and n) in the van Genuchten (1980) function and soil physical properties (sand content, bulk

Qiaosheng Shu; Zuoxin Liu; Bingcheng Si

2008-01-01

122

Continuum percolation theory for water retention and hydraulic conductivity of fractal soils: estimation of the critical volume fraction for percolation  

Microsoft Academic Search

Systematic experimental deviations from theoretical predictions for water retention characteristics of fractal porous media develop at a moisture content, ?d. Below ?d larger suction pressures are required than would otherwise be predicted from the implied fractal pore-size distribution. Inferred values of ?d were shown to be compatible with observed values of the volumetric moisture content, ?t, at which solute diffusion

A. G Hunt

2004-01-01

123

Controlling suction by vapour equilibrium technique at different temperatures, application to the determination of the water retention properties of MX80 clay  

E-print Network

Problems related to unsaturated soils are frequently encountered in geotechnical or environmental engineering works. In most cases, for the purpose of simplicity, the problems are studied by considering the suction effects on volume change or shear strength under isothermal conditions. Under isothermal condition, very often, a temperature independent water retention curve is considered in the analysis, which is obviously a simplification. When the temperature changes are too significant to be neglected, it is necessary to account for the thermal effects. In this paper, a method for controlling suction using the vapour equilibrium technique at different temperatures is presented. First, calibration of various saturated saline solutions was carried out from temperature of 20 degrees C to 60 degrees C. A mirror psychrometer was used for the measurement of relative humidity generated by saturated saline solutions at different temperatures. The results obtained are in good agreement with the data from the literatu...

Tang, Anh-Minh

2005-01-01

124

USING ENSEMBLES OF PEDOTRANSFER FUNCTIONS FOR SOIL WATER RETENTION IN FIELD-SCALE WATER FLOW SIMULATIONS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Using pedotransfer functions (PTF) to estimate soil hydraulic properties may be necessary in soil water flow simulations for large-scale projects or in pilot studies. The accuracy of a PTF outside of its development dataset is generally unknown. The existence of multiple models that are developed an...

125

FIELD-SCALE WATER FLOW SIMULATIONS USING ENSEMBLES OF PEDOTRANFER FUNCTIONS FOR SOIL WATER RETENTION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Using pedotransfer functions (PTF) to estimate soil hydraulic properties may be necessary in soil water flow simulations for large-scale projects or in a pilot studies. The accuracy of a PTF outside of its development dataset is unknown. Existence of several models that are developed and tested in o...

126

Water retention and runoff retardation in a drained wetland after heavy rainfall events  

NASA Astrophysics Data System (ADS)

Wetlands are often described as a sponge; they are believed to buffer surplus water coming from precipitation or inflow from the catchment and to emit it slowly to the downstream part of the river basin. However, in Middle or Western Europe anthropogenically influenced wetlands outnumber natural ones. In the last 200 years many wetlands have been drained to use the land for agriculture or forestry. Their water balance is nowadays regulated by water management systems consisting of ditches, weirs and sometimes pumping stations. Still, typical wetland characteristics are maintained: Groundwater levels only a few decimeters below the land surface, small surface slopes, high evapotranspiration, the domination of peat soils and extensive grasslands as the prevailing form of land use. Two main issues arise and are discussed in different contexts: (i) the extent to which the behavior of anthropogenically influenced wetlands differs from that of natural wetlands and (ii) their buffering capacities. The objective of our study was to investigate how a drained, agricultural wetland reacted to heavy rainfall events and to determine the influencing factors. In total 29 rainfall events with amounts greater than 10 mm were selected in the period between April 2010 and October 2012. The reactions of groundwater and ditch water levels were analysed, as well as the water balance of the rainfall events. The latter was determined using a weighable groundwater lysimeter installed in the Spreewald wetland in northeast Germany, whose groundwater level was adjusted to the surrounding grassland site. Our measurements showed that on average 70% of the rainfall was stored in the wetland, while only 10% was discharged. In dry periods, when sub-irrigation was present at the beginning of the rainfall event, more water was stored (83%) than in wet periods (51%) while the share of runoff was nearly halved. Evapotranspiration played an important role during the runoff process. The wetland had a high retardation effect, since in most cases the maximum ditch water level lagged several hours behind the peak in groundwater level. Besides a multitude of process-influencing factors, it was shown that in flat areas even drained wetlands can display a marked retention effect.

Dietrich, Ottfried; Fahle, Marcus; Steidl, Jörg

2014-05-01

127

Transport and retention of phosphorus in surface water in an urban slum area  

NASA Astrophysics Data System (ADS)

The transport of excessive phosphorus (P) discharged from unsewered informal settlements (slums) due to poor on-site sanitation is largely unknown. Hence, we investigated the processes governing P transport in a 28 km2 slum-dominated catchment in Kampala, Uganda. During high runoff events and a period of base flow, we collected hourly water samples (over 24 h) from a primary channel draining the catchment and from a small size tertiary channel draining one of the contributing slum areas (0.5 km2). Samples were analyzed for orthophosphate (PO4-P), particulate P (PP), total P (TP) and selected hydro-chemical parameters. Channel bed and suspended sediments were collected to determine their sorption potential, geo-available metals and dominant P forms. We found that P inputs in the catchment originated mainly from domestic wastewater as evidenced by high concentrations of Cl (36-144 mg L-1), HCO3 and other cations in the channels. Most P discharged during low flow conditions was particulate implying that much of it was retained in bed sediments. Retained P was mostly bound to Ca and Fe/Al oxides. Hence, we inferred that mineral precipitation and adsorption to Ca-minerals were the dominant P retention processes. Bed sediments were P-saturated and showed a tendency to release P to discharging waters. P released was likely due to Ca-bound P because of the strong correlation between Ca and total P in sediments (r2 = 0.9). High flows exhibited a strong flush of PP and SS implying that part of P retained was frequently flushed out of the catchment by surface erosion and resuspension of bed sediment. Our findings suggest that P accumulated in the channel bed during low flows and then was slowly released into surface water. Hence, it will likely take some time, even with improved wastewater management practices, before P loads to downstream areas can be significantly reduced.

Nyenje, P. M.; Meijer, L. M. G.; Foppen, J. W.; Kulabako, R.; Uhlenbrook, S.

2013-08-01

128

Impact of oxy-fuel combustion gases on mercury retention in activated carbons from a macroalgae waste: Effect of water.  

PubMed

The aim of this study is to understand the different sorption behaviors of mercury species on activated carbons in the oxy-fuel combustion of coal and the effect of high quantities of water vapor on the retention process. The work evaluates the interactions between the mercury species and a series of activated carbons prepared from a macroalgae waste (algae meal) from the agar-agar industry in oxy-combustion atmospheres, focussing on the role that the high concentration of water in the flue gases plays in mercury retention. Two novel aspects are considered in this work (i) the impact of oxy-combustion gases on the retention of mercury by activated carbons and (ii) the performance of activated carbons prepared from biomass algae wastes for this application. The results obtained at laboratory scale indicate that the effect of the chemical and textural characteristics of the activated carbons on mercury capture is not as important as that of reactive gases, such as the SOx and water vapor present in the flue gas. Mercury retention was found to be much lower in the oxy-combustion atmosphere than in the O2+N2 (12.6% O2) atmosphere. However, the oxidation of elemental mercury (Hg(0)) to form oxidized mercury (Hg(2+)) amounted to 60%, resulting in an enhancement of mercury retention in the flue gas desulfurization units and a reduction in the amalgamation of Hg(0) in the CO2 compression unit. This result is of considerable importance for the development of technologies based on activated carbon sorbents for mercury control in oxy-combustion processes. PMID:25585865

Lopez-Anton, M A; Ferrera-Lorenzo, N; Fuente, E; Díaz-Somoano, M; Suarez-Ruíz, I; Martínez-Tarazona, M R; Ruiz, B

2015-04-01

129

Modeling gravity effects on water retention and gas transport characteristics in plant growth substrates  

NASA Astrophysics Data System (ADS)

Growing plants to facilitate life in outer space, for example on the International Space Station (ISS) or at planned deep-space human outposts on the Moon or Mars, has received much attention with regard to NASA’s advanced life support system research. With the objective of in situ resource utilization to conserve energy and to limit transport costs, native materials mined on Moon or Mars are of primary interest for plant growth media in a future outpost, while terrestrial porous substrates with optimal growth media characteristics will be useful for onboard plant growth during space missions. Due to limited experimental opportunities and prohibitive costs, liquid and gas behavior in porous substrates under reduced gravity conditions has been less studied and hence remains poorly understood. Based on ground-based measurements, this study examined water retention, oxygen diffusivity and air permeability characteristics of six plant growth substrates for potential applications in space, including two terrestrial analogs for lunar and Martian soils and four particulate substrates widely used in reduced gravity experiments. To simulate reduced gravity water characteristics, the predictions for ground-based measurements (1 - g) were scaled to two reduced gravity conditions, Martian gravity (0.38 - g) and lunar gravity (0.16 - g), following the observations in previous reduced gravity studies. We described the observed gas diffusivity with a recently developed model combined with a new approach that estimates the gas percolation threshold based on the pore size distribution. The model successfully captured measured data for all investigated media and demonstrated the implications of the poorly-understood shift in gas percolation threshold with improved gas percolation in reduced gravity. Finally, using a substrate-structure parameter related to the gaseous phase, we adequately described the air permeability under reduced gravity conditions.

Chamindu Deepagoda, T. K. K.; Jones, Scott B.; Tuller, Markus; de Jonge, Lis Wollesen; Kawamoto, Ken; Komatsu, Toshiko; Moldrup, Per

2014-08-01

130

QSPR models of boiling point, octanol–water partition coefficient and retention time index of polycyclic aromatic hydrocarbons  

Microsoft Academic Search

A Quantitative Structure–Property Relationship (QSPR) analysis and study of polycyclic aromatic hydrocarbons (PAHs) is presented. Three physicochemical properties related to their environmental impact are studied: boiling point (bp), octanol–water partition coefficient (logKow) and retention time index (RI) for reversed-phase liquid chromatography analysis. The geometry of all PAHs were optimized by the semi-empirical method AM1 and used to calculate thermodynamic, electronic,

Fabiana Alves de Lima Ribeiro; Márcia Miguel Castro Ferreira

2003-01-01

131

An approach to bioassessment of water quality using diversity measures based on species accumulative curves.  

PubMed

Traditional community-based bioassessment is time-consuming because they rely on full species-abundance data of a community. To improve bioassessment efficiency, the feasibility of the diversity measures based on species accumulative curves for bioassessment of water quality status was studied based on a dataset of microperiphyton fauna. The results showed that: (1) the species accumulative curves well fitted the Michaelis-Menten equation; (2) the ?- and ?-diversity, as well as the number of samples to 50% of the maximum species number (Michaelis-Menten constant K), can be statistically estimated based on the formulation; (3) the rarefied ?-diversity represented a significant negative correlation with the changes in the nutrient NH4-N; and (4) the estimated ?-diversity and the K constant were significantly positively related to the concentration of NH4-N. The results suggest that the diversity measures based on species accumulative curves might be used as a potential bioindicator of water quality in marine ecosystems. PMID:25499181

Xu, Guangjian; Zhang, Wei; Xu, Henglong

2015-02-15

132

EXPERIMENTAL STUDY OF CRITICAL HEAT FLUX WITH ALUMINA-WATER NANOFLUIDS IN DOWNWARD-FACING CHANNELS FOR IN-VESSEL RETENTION APPLICATIONS  

E-print Network

The Critical Heat Flux (CHF) of water with dispersed alumina nanoparticles was measured for the geometry and flow conditions relevant to the In-Vessel Retention (IVR) situation which can occur during core melting sequences ...

Park, R.J.

133

The infrared light curve of Periodic Comet Halley 1986 III and its relationship to the visual light curve, C2, and water production rates  

NASA Technical Reports Server (NTRS)

The near-IR light curve of Periodic Comet Halley 1986 III is analyzed and compared with C2 production, water production, and the visual light curve. This is the most complete IR light curve compiled to date for any comet. The scattering phase function at small sun-comet-earth angles is shown to affect the slope of near-IR light curve significantly. P/Halley's dust production, as inferred from the IR light curve showed an increased production rate near perihelion which appears to be correlated with the onset of significant jet activity. The near-IR light curve, visual light curve, C2, and water production rates displayed different heliocentric variations, suggesting that one parameter cannot be accurately estimated from another. This is particularly true of the early preperihelion visual light curve. A peak of 0.3-0.5 magnitude in the visual magnitude, representing the integrated brightness of the comet's visible coma, lagged the other parameters by about a day. The near-IR color, J-H, was less red during periods of strong dust activity.

Morris, Charles S.; Hanner, Martha S.

1993-01-01

134

Nitrogen in river basins: sources, retention in the surface waters and peatlands, and fluxes to estuaries in Finland.  

PubMed

Nitrogen export from diffuse and point sources and its retention in the major river basins of Finland is quantified and discussed. The estimated total export from river-basins in Finland was 119,000 tonnes N a(-1) for the period 1993 to 1998 based on N export from different land use types defined in a GIS-based assessment model, incorporated with estimates of N inputs from atmospheric deposition and point sources. Agriculture contributes 38% of the total export, varying in the range 35-85% in the south-western basins and 0-25% in the northern basins. This estimate of N export from agriculture was based on regional N balances together with data from small agricultural research catchments. Forestry contributes on average 9%, with increasing dominance towards eastern and northern parts of the country: from 2% to 15% in the southern-mid-western Finland basins to 10-30% in the large northern basins. 'Background' N export from forests on both mineral and organic soils contributes 27% on average; in the northern basins it may contribute from 40% up to 90% of the total load. The estimate was calculated based on practically all data available from 42 small, experimental catchments in Finland. Of the total N input to Finnish river-systems, 0% to 68% was retained in surface waters and/or peatlands, with a mean retention of 22%. The highest retention of N (36-61%) was observed in the basins with the highest lake percentages. The lowest retention (0-10%) of N was in the coastal basins with practically no lakes. In the national N mass balance, 38,000 tonnes N a(-1) (32%) was estimated as lake retention and 4,000 tonnes N a(-1) (3%) as retention in peatlands. On the basis of mass balances and sensitivity analysis, retention was in most cases estimated to be in the range of 7.5-12.5 kg ha(-1)a(-1) in lakes and 0-1.5 kg ha(-1)a(-1) in peatlands. The model results were tested using the split-sample technique and uncertainty estimates for different data sources are provided and discussed. PMID:16624380

Lepistö, Ahti; Granlund, Kirsti; Kortelainen, Pirkko; Räike, Antti

2006-07-15

135

Regularities of retention of benzoic acids on microdispersed detonation nanodiamonds in water-methanol mobile phases  

NASA Astrophysics Data System (ADS)

The dependences of the retention of benzoic acids on microdispersed sintered detonation nanodiamond (MSDN) on the concentration of the organic solvent in the eluent and the temperature of the chromatographic column under conditions of high-performance liquid chromatography (HPLC) are investigated. It is found that in the investigated range of methanol concentrations, the acids are retained by different mechanisms: at methanol contents of the eluent lower than 85%, retention decreases with increasing methanol concentration and increases at higher concentrations of the organic solvent. It is shown that retention of benzoic acids on MSDN under these conditions depends on the dissociation constant of the investigated substances. A comparison is made between the properties of MSDN and analogous properties of porous graphitic carbon.

Fedyanina, O. N.; Nesterenko, P. N.

2011-10-01

136

Estimation of fatigue strain-life curves for austenitic stainless steels in light water reactor environments.  

SciTech Connect

The ASME Boiler and Pressure Vessel Code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels (SSs) in light water reactor (LWR) environments. Unlike those of carbon and low-alloy steels, environmental effects on fatigue lives of SSs are more pronounced in low-dissolved-oxygen (low-DO) water than in high-DO water, This paper summarizes available fatigue strain vs. life data on the effects of various material and loading variables such as steel type, DO level, strain range, and strain rate on the fatigue lives of wrought and cast austenitic SSs. Statistical models for estimating the fatigue lives of these steels in LWR environments have been updated with a larger data base. The significance of the effect of environment on the current Code design curve has been evaluated.

Chopra, O. K.; Smith, J. L.

1998-02-12

137

Comparing the Effects of Hot Pack and Lukewarm-Water-Soaked Gauze on Postoperative Urinary Retention; A Randomized Controlled Clinical Trial  

PubMed Central

Background: Urinary retention is a common postoperative complication that mandates urinary catheterization. Urinary catheterization is associated with different physical, mental, and financial problems for both patients and healthcare systems. The patient inconvenience, urinary tract infections, and increase in hospital stay and expenses are common problems of urinary retention and urinary catheterization. Therefore, alternative ways of relieving urinary retention, preferably noninvasive interventions, are of great interest. Objectives: The aim of this study was to compare the effects of placing hot pack and lukewarm-water-soaked gauze on the suprapubic region on male patients with postoperative urinary retention. Patients and Methods: This was a three-group, randomized, controlled trial. A convenience sample of 126 male patients who had undergone general, orthopedic, or urologic surgeries were recruited. The block randomization method was used for allocating patients to either the two experimental groups (the hot pack and the lukewarm-water-soaked gauze groups) or the control one. Patients in the experimental groups were treated by placing either hot pack or lukewarm-water-soaked gauze on the suprapubic region. All patients were monitored for 20 minutes for urinary retention relief. If they did not experience urinary retention relief (starting urine flow and bladder evacuate), urinary catheterization would be performed. The data was collected using information sheet. Elimination of urinary retention was compared among study groups. The one-way analysis of variance and the Chi-square tests were used for analyzing data. Results: Respectively, 59.5%, 71.4%, and 7.1% of patients in the hot pack, the soaked gauze, and the control groups experienced relief from urinary retention and the bladder was emptied. There was a significant difference among study groups in percentage of patients who experienced urinary retention relief. However, the difference between the two experimental groups was not significant. The time to urinary retention relief in hot pack, soaked gauze, and control groups was 15.45 ± 3.15, 13.83 ± 3.80, and 14.59 ± 3.29 minutes, respectively. The difference among the study groups in time to urinary retention relief was not statistically significant. Conclusions: Both the lukewarm-water-soaked gauze and the hot pack techniques had significant effects on postoperative urinary retention and significantly reduced the need for urinary catheterization. Using these two simple and cost-effective techniques for managing postoperative urinary retention is recommended. PMID:25741518

Afazel, Mohammad Reza; Jalali, Ehsan; Sadat, Zohre; Mahmoodi, Hossein

2014-01-01

138

Formation and Retention of Hydroxyl and Water on the Lunar Surface  

NASA Astrophysics Data System (ADS)

Spectral reflectance observations by the Moon Mineralogy Mapper (M3) showed that both hydroxyl and (molecular) water (hereafter referred to collectively as H/OH) vary spatially as a function of solar illumination geometry. At low solar incidence angles, the observed strengths of the H/OH spectral features are stronger than at higher angles, suggesting that the abundance varies with the diurnal cycle. This is also demonstrated in the increasing abundances with increasing latitude, such that above ~60 degrees there is little reduction in the depth of the water-related spectral absorption bands. It was immediately recognized that the wide-spread occurrence of H/OH across the lunar surface was the result of solar wind-induced hydroxylation, a phenomenon that was predicted almost 50 years ago. The lunar soil has a finite capacity to retain implanted hydrogen, and over time, the surface reaches a steady state, or background H/OH abundance, which is manifested in spectra of the mature soil. In addition to maturity, the retention of H/OH is a function of composition and texture (i.e., crystallinity and surface/volume). There are two hypotheses for how solar wind-implanted H/OH is retained in the soil: 1) H/OH adsorbs onto active surface sites on fresh soil particles. 2) H/OH is trapped in vesicles in agglutinates and amorphous coatings on soil grains created by space weathering. Undoubtedly both of these mechanisms occur, but one process is ultimately responsible for the observed steady state mature soil abundance, and this can be studied by measuring the strength of the H/OH spectral feature from soils as a function of variable composition, texture, and maturity. Space weathering is capable of both activating and neutralizing grain surfaces. Micrometeorite and larger impacts can activate mineral surfaces through mechanical forces, such as crushing and shattering of minerals, which creates fresh surfaces with partially unsatisfied chemical bonds. The freshly fractured crystalline materials provide defect lattice sites and dangling bonds often providing an electronegative surface that would enhance adsorption (chemisorption) of solar wind hydrogen. Continual irradiation by solar-wind protons will pacify broken bonds through sputtering and impact vaporization and deposition. These space weathering processes create amorphous rims on soil particles, turning a once active surface electroneutral. If hypothesis #1 is the dominant process, the ejecta of fresh craters in crystalline materials will have relatively strong H/OH spectral features, which decrease with increasing maturity. Agglutinitic glass and submicroscopic Fe^0 are products of the space weathering process, and their abundance is proportional to maturity. Heating and melting of the soil by micro-impacts facilitates reduction of FeO by implanted H/OH to submicroscopic Fe^0 and H2O. Some of these volatiles could not escape the melt before quenching, and are trapped within agglutinitic glass and amorphous coatings on soil particles. If hypothesis #2 is the dominant process, the H/OH absorption features increases with increasing maturity, regardless of composition or texture. Using M3 spectra, we are testing these hypotheses on diverse regions of the Moon, including highlands, mare, impact melts, pyroclastic deposits, and most interestingly, the lunar swirls.

Kramer, G. Y.; Clark, R. N.; Combe, J.; Noble, S. K.

2012-12-01

139

A Nonparametric Instrumental Variable Approach to Estimating the Environmental Kuznets Curve for Water Pollutants at the Global Level  

E-print Network

for Water Pollutants at the Global Level Krishna P. Paudel1 , C.-Y. Cynthia Lin2 , Mahesh Pandit the Environmental Kuznets Curve for Water Pollutants at the Global Level Abstract We examine the relationship between income and water pollutants using country- level global water quality data over the period 1980

Lin, C.-Y. Cynthia

140

Mathematical relationships between vapor pressure, water solubility, Henry's law constant, n-octanol\\/water partition coefficent and gas chromatographic retention index of polychlorinated-dibenzo-dioxins  

Microsoft Academic Search

Mathematical relationships between vapor pressures (P), water solubilities (S), Henry's law constants (Hc), n-octanol\\/water partition coefficients (Kow) and gas chromatograph retention indices (GC-RIs) of polychlorinated-dibenzo-dioxins (PCDDs) were established. A model equation was established between GC-RIs (=RI) and other physico-chemical parameters (K) of PCDDs in the form of logK=aRI2+bRI+c with correlation coefficients (R2) greater than 0.97, except Hc. These equations were

Y. H. Wang; P. K. Wong

2002-01-01

141

The disappearing Environmental Kuznets Curve: a study of water quality in the Lower Mekong Basin (LMB).  

PubMed

The literature is flush with articles focused on estimating the Environmental Kuznets Curve (EKC) for various pollutants and various locations. Most studies have utilized air pollution variables; far fewer have utilized water quality variables, all with mixed results. We suspect that mixed evidence of the EKC stems from model and error specification. We analyze annual data for four water quality indicators, three of them previously unstudied - total phosphorus (TOTP), dissolved oxygen (DO), ammonium (NH4) and nitrites (NO2) - from the Lower Mekong Basin region to determine whether an Environmental Kuznets Curve (EKC) is evident for a transboundary river in a developing country and whether that curve is dependent on model specification and/or pollutant. We build upon previous studies by correcting for the problems of heteroskedasticity, serial correlation and cross-sectional dependence. Unlike multi-country EKC studies, we mitigate for potential distortion from pooling data across geographically heterogeneous locations by analyzing data drawn from proximate locations within a specific international river basin in Southeast Asia. We also attempt to identify vital socioeconomic determinants of water pollution by including a broad list of explanatory variables alongside the income term. Finally, we attempt to shed light on the pollution-income relationship as it pertains to trans-boundary water pollution by examining data from an international river system. We do not find consistent evidence of an EKC for any of the 4 pollutant indicators in this study, but find the results are entirely dependent on model and error specification as well as pollutant. PMID:24211570

Wong, Yoon Loong Andrew; Lewis, Lynne

2013-12-15

142

ESTIMATING WATER TREATMENT COSTS. VOLUME 3. COST CURVES APPLICABLE TO 2,500 GPD TO 1 MGD TREATMENT PLANTS  

EPA Science Inventory

This report discusses unit processes and combinations of unit processes that are capable of removing contaminants included in the National Interim Primary Drinking Water Regulations. Construction and operation and maintenance cost curves are presented for 99 unit processes that a...

143

Retention of chromium (VI) on a macroporous char following ChemChar gasification and successive leaching with water and acids.  

PubMed

A granular macroporous char, triple-reverse-burn (TRB) char, was loaded with 23.40 mg Cr/g TRB char from an aqueous solution, and the retained metal was leached by water, 0.66 M nitric acid, concentrated nitric acid, and concentrated hydrochloric acid before and after treatment by a reductive thermal gasification process (ChemChar process developed by ChemChar Research, Inc., Columbia, Missouri). The chromium leachate was analyzed by flame atomic adsorption. Reverse- and forward-mode gasifications were performed on the metal-laden char. With the exception of a 10% mass loss of carbon, the reverse mode gasification process does not change the physical characteristics of the granular char, but does increase the retention of the chromium from 16.7 to 24.2%, depending on the leachant. The forward mode gasification process produces a vitrified (or glasslike) ash residue. There was an 11.6 to 13.1% increase in the retention of the chromium by the slag and ash when compared to the nongasified chromium-loaded TRB char. Chromium (VI) was effectively removed from solution by TRB char and found to be retained to a higher degree on the char after a reductive thermal treatment. PMID:15816678

Marrero, Thomas W; Manahan, Stanley E

2005-01-01

144

Performance Evaluation of Four-Parameter Models of the Soil-Water Characteristic Curve  

PubMed Central

Soil-water characteristic curves (SWCCs) are important in terms of groundwater recharge, agriculture, and soil chemistry. These relationships are also of considerable value in geotechnical and geoenvironmental engineering. Their measurement, however, is difficult, expensive, and time-consuming. Many empirical models have been developed to describe the SWCC. Statistical assessment of soil-water characteristic curve models found that exponential-based model equations were the most difficult to fit and generally provided the poorest fit to the soil-water characteristic data. In this paper, an exponential-based model is devised to describe the SWCC. The modified equation is similar to those previously reported by Gardner (1956) but includes exponential variable. Verification was performed with 24 independent data sets for a wide range of soil textures. Prediction results were compared with the most widely used models to assess the model's performance. It was proven that the exponential-based equation of the modified model provided greater flexibility and a better fit to data on various types of soil. PMID:24971384

Taha, Mohd Raihan

2014-01-01

145

Soil water repellency characteristic curves for soil profiles with natural organic carbon gradients  

NASA Astrophysics Data System (ADS)

Soil water repellency (SWR) is a phenomenon that influences many soil hydrologic processes such as reduction of infiltration, increase in overland flow, and enhanced preferential flow. SWR has been observed in various soil types and textures, and the degree of SWR is greatly controlled by soil moisture content and levels of organic matter and clay. One of the key topics in SWR research is how to describe accurately the seasonal and temporal variation of SWR with the controlling factors such as soil moisture, organic matter, and clay contents for soil profiles with natural organic carbon gradients. In the present study, we summarize measured SWR data for soil profiles under different land uses and vegetation in Japan and New Zealand, and compared these with literature data. We introduce the contact angle-based evaluation of SWR and predictive models for soil water repellency characteristic curves, in which the contact angle is a function of the moisture content. We also discuss a number of novel concepts, including i) the reduction in the contact angle with soil-water contact time to describe the time dependence of SWR, ii) the relationship between the contact angles from the measured scanning curves under controlled wetting and drying cycles, and iii) the initial contact angles measured by the sessile drop method.

Kawamoto, Ken; Müller, Karin; Moldrup, Per; de Jonge, Lis; Clothier, Brent; Hiradate, Syuntaro; Komatsu, Toshiko

2014-05-01

146

Sustainable Water Practices at Pomona's Parks: Improving Irrigation Use and Stormwater Runoff Retention  

E-print Network

rates that depend on the natural processes of the hydrologic cycle. Unsustainable water use is a problemSustainable Water Practices at Pomona's Parks: Improving Irrigation Use and Stormwater Runoff;1 Abstract The need for water sustainability has emerged as a response to urbanization and the depletion

Young, Terence

147

Potential Water Retention Capacity as a Factor in Silage Effluent Control: Experiments with High Moisture By-product Feedstuffs  

PubMed Central

The role of moisture absorptive capacity of pre-silage material and its relationship with silage effluent in high moisture by-product feedstuffs (HMBF) is assessed. The term water retention capacity which is sometimes used in explaining the rate of effluent control in ensilage may be inadequate, since it accounts exclusively for the capacity of an absorbent incorporated into a pre-silage material prior to ensiling, without consideration to how much the pre-silage material can release. A new terminology, ‘potential water retention capacity’ (PWRC), which attempts to address this shortcoming, is proposed. Data were pooled from a series of experiments conducted separately over a period of five years using laboratory silos with four categories of agro by-products (n = 27) with differing moisture contents (highest 96.9%, lowest 78.1% in fresh matter, respectively), and their silages (n = 81). These were from a vegetable source (Daikon, Raphanus sativus), a root tuber source (potato pulp), a fruit source (apple pomace) and a cereal source (brewer’s grain), respectively. The pre-silage materials were adjusted with dry in-silo absorbents consisting wheat straw, wheat or rice bran, beet pulp and bean stalks. The pooled mean for the moisture contents of all pre-silage materials was 78.3% (±10.3). Silage effluent decreased (p<0.01), with increase in PWRC of pre-silage material. The theoretical moisture content and PWRC of pre-silage material necessary to stem effluent flow completely in HMBF silage was 69.1% and 82.9 g/100 g in fresh matter, respectively. The high correlation (r = 0.76) between PWRC of ensiled material and silage effluent indicated that the latter is an important factor in silage-effluent relationship. PMID:25049587

Razak, Okine Abdul; Masaaki, Hanada; Yimamu, Aibibula; Meiji, Okamoto

2012-01-01

148

Covariance in water- and nutrient budgets of Dutch peat polders: what governs nutrient retention?  

Microsoft Academic Search

Water and nutrient budgets were constructed for 13 low-lying peat polders in the Netherlands that varied in elevation relative\\u000a to sea level (?0.2 to ?2.4 m below sea level), land use (7–70% of the total polder area covered by agriculture; largely dairy\\u000a farming), and surface water prevalence (6–43%). Water balances were verified with chloride budgets and accepted when both\\u000a met the

Jan E. Vermaat; Fritz Hellmann

2010-01-01

149

Surfactant and Irrigation Effects on Runoff, Erosion, and Water Retention of Three Wettable Soils  

Technology Transfer Automated Retrieval System (TEKTRAN)

Surfactants are chemical compounds that change the contact angle of water on solid surfaces and are commonly used to increase infiltration into hydrophobic soil. Since production fields with water-repellent soil often contain areas of wettable soil, surfactants applied to such fields will likely be ...

150

Surfactant and irrigation effects on wettable soils: Runoff, erosion, and water retention responses  

Technology Transfer Automated Retrieval System (TEKTRAN)

Surfactants are chemical compounds that change the contact angle of water on solid surfaces and are commonly used to increase infiltration into hydrophobic soil. Since production fields with water-repellent soil often contain areas of wettable soil, surfactants applied to such fields will likely be ...

151

Software to estimate –33 and –1500 kPa soil water retention using the non-parametric k-Nearest Neighbor technique  

Technology Transfer Automated Retrieval System (TEKTRAN)

A computer tool has been developed that uses a k-Nearest Neighbor (k-NN) lazy learning algorithm to estimate soil water retention at –33 and –1500 kPa matric potentials and its uncertainty. The user can customize the provided source data collection to accommodate specific local needs. Ad hoc calcula...

152

Importance of intercellular lipids in water-retention properties of the stratum corneum: induction and recovery study of surfactant dry skin  

Microsoft Academic Search

In order to further clarify the role of intercellular lipids in the water-retention properties of the stratum corneum, forearm skin of six healthy male volunteers was treated with 5% sodium dodecyl sulfate (SDS) for 1, 10, and 30 min. All treatment periods induced chapping and scaling of the stratum corneum without any inflammatory reaction, accompanied by a significant decrease in

G. Imokawa; S. Akasaki; Y. Minematsu; M. Kawai

1989-01-01

153

Evaluation of the “DSPM” model on a titania membrane: measurements of charged and uncharged solute retention, electrokinetic charge, pore size, and water permeability  

Microsoft Academic Search

The DSPM (Donnan steric partitioning pore model) was evaluated in the case of a titania membrane with “nanofiltration properties” by measuring the electrokinetic charge, pore size, and water permeability of the membrane, along with charged and uncharged solute retention. The zeta potential values (?) were determined from measurements of the electrophoretic mobility (EM) of titania powder forming the filtering layer

C. Labbez; P. Fievet; F. Thomas; A. Szymczyk; A. Vidonne; A. Foissy; P. Pagetti

2003-01-01

154

Development of a quasi-adiabatic calorimeter for the determination of the water vapor pressure curve  

NASA Astrophysics Data System (ADS)

Progress in the knowledge of the water saturation curve is required to improve the accuracy of the calibrations in humidity. In order to achieve this objective, the LNE-CETIAT and the LNE-CNAM have jointly built a facility dedicated to the measurement of the saturation vapor pressure and temperature of pure water. The principle is based on a static measurement of the pressure and the temperature of pure water in a closed, temperature-controlled thermostat, conceived like a quasi-adiabatic calorimeter. A copper cell containing pure water is placed inside a temperature-controlled copper shield, which is mounted in a vacuum-tight stainless steel vessel immersed in a thermostated bath. The temperature of the cell is measured with capsule-type standard platinum resistance thermometers, calibrated with uncertainties below the millikelvin. The vapor pressure is measured by calibrated pressure sensors connected to the cell through a pressure tube whose temperature is monitored at several points. The pressure gauges are installed in a thermostatic apparatus ensuring high stability of the pressure measurement and avoiding any condensation in the tubes. Thanks to the employment of several technical solutions, the thermal contribution to the overall uncertainty budget is reduced, and the remaining major part is mainly due to pressure measurements. This paper presents a full description of this facility and the preliminary results obtained for its characterization.

Mokdad, S.; Georgin, E.; Hermier, Y.; Sparasci, F.; Himbert, M.

2012-07-01

155

Development of a quasi-adiabatic calorimeter for the determination of the water vapor pressure curve.  

PubMed

Progress in the knowledge of the water saturation curve is required to improve the accuracy of the calibrations in humidity. In order to achieve this objective, the LNE-CETIAT and the LNE-CNAM have jointly built a facility dedicated to the measurement of the saturation vapor pressure and temperature of pure water. The principle is based on a static measurement of the pressure and the temperature of pure water in a closed, temperature-controlled thermostat, conceived like a quasi-adiabatic calorimeter. A copper cell containing pure water is placed inside a temperature-controlled copper shield, which is mounted in a vacuum-tight stainless steel vessel immersed in a thermostated bath. The temperature of the cell is measured with capsule-type standard platinum resistance thermometers, calibrated with uncertainties below the millikelvin. The vapor pressure is measured by calibrated pressure sensors connected to the cell through a pressure tube whose temperature is monitored at several points. The pressure gauges are installed in a thermostatic apparatus ensuring high stability of the pressure measurement and avoiding any condensation in the tubes. Thanks to the employment of several technical solutions, the thermal contribution to the overall uncertainty budget is reduced, and the remaining major part is mainly due to pressure measurements. This paper presents a full description of this facility and the preliminary results obtained for its characterization. PMID:22852731

Mokdad, S; Georgin, E; Hermier, Y; Sparasci, F; Himbert, M

2012-07-01

156

Effect of the water content on the retention and enantioselectivity of albendazole and fenbendazole sulfoxides using amylose-based chiral stationary phases in organic-aqueous conditions.  

PubMed

Four commercially available immobilized amylose-derived CSPs (Chiralpak IA-3, Chiralpak ID-3, Chiralpak IE-3 and Chiralpak IF-3) were used in the HPLC analysis of the chiral sulfoxides albendazole (ABZ-SO) and fenbendazole (FBZ-SO) and their in vivo sulfide precursor (ABZ and FBZ) and sulfone metabolite (ABZ-SO2 and FBZ-SO2) under organic-aqueous mode. U-shape retention maps, established by varying the water content in the acetonitrile- and ethanol-water mobile phases, were indicative of two retention mechanisms operating on the same CSP. The dual retention behavior of polysaccharide-based CSPs was exploited to design greener enantioselective and chemoselective separations in a short time frame. The enantiomers of ABZ-SO and FBZ-SO were baseline resolved with water-rich mobile phases (with the main component usually being 50-65% water in acetonitrile) on the IF-3 CSP and ethanol-water 100:5 mixture on the IA-3 and IE-3 CSPs. A simultaneous separation of ABZ (or FBZ), enantiomers of the corresponding sulfoxide and sulfone was achieved on the IA-3 using ethanol-water 100:60 (acetonitrile-water 100:100 for FBZ) as a mobile phase. PMID:24411094

Materazzo, Sabrina; Carradori, Simone; Ferretti, Rosella; Gallinella, Bruno; Secci, Daniela; Cirilli, Roberto

2014-01-31

157

Fate of Nitrogenand Phosphorus in a Waste-water RetentionReservoir Containing Aquatic Macrophytes1  

E-print Network

) cattails (Typha latifolia L.) and elodea (Egeria densa P), and (iv) control (no macrophytes). Labeled "N such as water hyacinths (Eichhornia crassipes [Mart] Solms), duckweed (Lemna minor), and cattails (Typha sp

Florida, University of

158

Preliminary investigation to estimate soil NAPL retention using parametric pedotransfer functions  

NASA Astrophysics Data System (ADS)

Organic liquid retention of soils is a primary input variable for modelling the nonaqueous phase liquid transport and behaviour in the subsurface. In environmental and soil physical practice, it is mainly determined by scaling based on the water retention of soils or with charts of average empirical values of organic liquid retention or the fitting parameters of hydraulic functions. Predicting the fitting parameters of organic liquid retention curves with pedotransfer functions might be a promising alternative method, but this topic has only been researched to a limited extent. Thus we investigated the applicability of different hydraulic functions (3- and 4- parameter form of the van Genuchten equation and Brutsaert equation) for fitting organic liquid retention characteristics. Multivariate linear regression was used to build and develop pedotransfer functions, modelling relations between original and transformed values of basic soil properties and organic liquid retention. We attempted to generate parametric pedotransfer functions. According to our results, the applicability of hydraulic functions for fitting nonaqueous phase liquid retention curves to the experimental data was proven. The investigations gave promising results for the possibility to estimate soil nonaqueous phase liquid retention with parametric pedotransfer functions.

Hernádi, Hilda; Makó, András

2014-10-01

159

Water retention of selected microorganisms and Martian soil simulants under close to Martian environmental conditions  

NASA Astrophysics Data System (ADS)

Based on the latest knowledge about microorganisms resistant towards extreme conditions on Earth and results of new complex models on the development of the Martian atmosphere we quantitatively examined the water-bearing properties of selected extremophiles and simulated Martian regolith components and their interaction with water vapor under close to Martian environmental conditions. Three different species of microorganisms have been chosen and prepared for our study: Deinococcus geothermalis, Leptothrix sp. OT_B_406, and Xanthoria elegans. Further, two mineral mixtures representing the early and the late Martian surface as well as montmorillonite as a single component of phyllosilicatic minerals, typical for the Noachian period on Mars, were selected. The thermal mass loss of the minerals and bacteria-samples was measured by thermoanalysis. The hydration and dehydration properties were determined under close to Martian environmental conditions by sorption isotherm measurements using a McBain-Bakr quartz spring balance. It was possible to determine the total water content of the materials as well as the reversibly bound water fraction as function of the atmospheres humidity by means of these methods. Our results are important for the evaluation of future space mission outcomes including astrobiological aspects and can support the modeling of the atmosphere/surface interaction by showing the influence on the water inventory of the upper most layer of the Martian surface.

Jänchen, J.; Bauermeister, A.; Feyh, N.; de Vera, J.-P.; Rettberg, P.; Flemming, H.-C.; Szewzyk, U.

2014-08-01

160

Critical evaluation of a simple retention time predictor based on LogKow as a complementary tool in the identification of emerging contaminants in water.  

PubMed

There has been great interest in environmental analytical chemistry in developing screening methods based on liquid chromatography-high resolution mass spectrometry (LC-HRMS) for emerging contaminants. Using HRMS, compound identification relies on the high mass resolving power and mass accuracy attainable by these analyzers. When dealing with wide-scope screening, retention time prediction can be a complementary tool for the identification of compounds, and can also reduce tedious data processing when several peaks appear in the extracted ion chromatograms. There are many in silico, Quantitative Structure-Retention Relationship methods available for the prediction of retention time for LC. However, most of these methods use commercial software to predict retention time based on various molecular descriptors. This paper explores the applicability and makes a critical discussion on a far simpler and cheaper approach to predict retention times by using LogKow. The predictor was based on a database of 595 compounds, their respective LogKow values and a chromatographic run time of 18min. Approximately 95% of the compounds were found within 4.0min of their actual retention times, and 70% within 2.0min. A predictor based purely on pesticides was also made, enabling 80% of these compounds to be found within 2.0min of their actual retention times. To demonstrate the utility of the predictors, they were successfully used as an additional tool in the identification of 30 commonly found emerging contaminants in water. Furthermore, a comparison was made by using different mass extraction windows to minimize the number of false positives obtained. PMID:25882420

Bade, Richard; Bijlsma, Lubertus; Sancho, Juan V; Hernández, Felix

2015-07-01

161

INVESTIGATION OF PHASE AND EMULSION BEHAVIOR, SURFACTANT RETENTION, AND CONDENSATE RECOVERY FOR CONDENSATE/WATER/ETHANOL MIXTURES  

SciTech Connect

This semi-annual technical progress report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period April 01, 2003 to September 30, 2003 which covers the second six months of the project. Presently work is in progress to characterize phase and emulsion behavior for ethylbenzene/water/ethanol system. During this reporting period, salinity scans were completed for 0, 5, 10, 20, 50, 100, 250, 500, and 1000 mM salt concentrations at room temperature to identify optimal salinity intervals in which all three phases coexist for this system. Temperature scans are in progress at Morehouse College to identify the optimal temperature, and the temperature intervals in which all three phases coexist for this system. Coreflooding experiments are being conducted by our industrial partner in this project, Surtek, CO, to measure the effectiveness for surfactant retention and condensate recovery in flooding processes. Review of the current literature in the subject area, and modeling efforts that were established in our previous studies to predict electrical conductivities and inversion phenomena was continued from the previous reporting period. Based on the review a computer model to predict electrical conductivities of the ethylbenzene (that has the equivalent carbon number of the condensate)/water/ethanol system is being developed.

Ramanathan Sampath

2003-10-01

162

Sulfonated polyimide/acid-functionalized graphene oxide composite polymer electrolyte membranes with improved proton conductivity and water-retention properties.  

PubMed

Sulfonated polyimide (SPI)/sulfonated propylsilane graphene oxide (SPSGO) was assessed to be a promising candidate for polymer electrolyte membranes (PEMs). Incorporation of multifunctionalized (-SO3H and -COOH) SPSGO in SPI matrix improved proton conductivity and thermal, mechanical, and chemical stabilities along with bound water content responsible for slow dehydration of the membrane matrix. The reported SPSGO/SPI composite PEM was designed to promote internal self-humidification, responsible for water-retention properties, and to promote proton conduction, due to the presence of different acidic functional groups. Strong hydrogen bonding between multifunctional groups thus led to the presence of interconnected hydrophobic graphene sheets and organic polymer chains, which provides hydrophobic-hydrophilic phase separation and suitable architecture of proton-conducting channels. In single-cell direct methanol fuel cell tests, SPI/SPSGO-8 exhibited 75.06 mW·cm(-2) maximum power density (in comparison with commercial Nafion 117 membrane, 62.40 mW·cm(-2)) under 2 M methanol fuel at 70 °C. PMID:25207457

Pandey, Ravi P; Thakur, Amit K; Shahi, Vinod K

2014-10-01

163

Trinarization of ?X-ray CT images of partially saturated sand at different water-retention states using a region growing method  

NASA Astrophysics Data System (ADS)

The trinarization of micro-computed tomography (CT) images for partially saturated soils at different water-retention states has been performed to clearly identify the three phases, i.e., the soil particles, the pore water and the pore air. We have proposed a trinarization technique for partially saturated soils whose histograms of the gray values for the three phases overlap each other. The segmentation method used in this study is the region growing method that ensures the spatial continuity of the phases extracted by the segmentation. Micro CT images of a dense sand specimen during the wetting process in a water retention test have been obtained. It has been found that the trinarization of the CT images in a high pore saturation regime provides reasonable results, while that in a low pore saturation regime overestimates the local void ratio. This is because the gray values of the mixels of the soil particle phase and the air phase, due to the partial volume effect, are similar to those of the water phase. It is necessary, therefore, to validate the trinarization results, by a comparison with the test results, because it is difficult to theoretically evaluate the partial volume effect. The correction of the tolerance value for the low pore saturation case with validation has provided better trinarization results. Through the trinarized CT images, the form of the existing pore water at different water-retention states has been discussed.

Higo, Yosuke; Oka, Fusao; Morishita, Ryoichi; Matsushima, Yoshiki; Yoshida, Tatsuya

2014-04-01

164

Field-Obtained Soil Water Characteristic Curves and Hydraulic Conductivity Functions  

NASA Astrophysics Data System (ADS)

A compacted clay liner (test pad) was constructed and instrumented with volumetric water content and soil matric potential sensors to determine soil water characteristic curves (SWCC) and hydraulic conductivity (k) functions. Specifically, the compacted clay liner was subjected to an infiltration cycle during a sealed double ring infiltrometer (SDRI) test followed by a drying cycle. After the drying cycle, Shelby tube samples were collected from the compacted clay liner and flexible wall permeability (FWP) tests were conducted on sub-samples to determine the saturated hydraulic conductivity. Moreover, two computer programs (RETC and UNSAT-H) were utilized to model the SWCCs and k-functions of the soil based on obtained measurements including the volumetric water content, the soil matric potential, and the saturated hudraulic conductivity (ks). Results obtained from the RETC program (s, r, ?, n and ks) were ingested into UNSAT-H program to calculate the movement of water (rate and location) through the compacted clay liner. Although a linear wetting front (location of water infiltration as a function of time) is typically utilized for SDRI calculations, the use of a hyperbolic wetting front is recommended as a hyperbolic wetting front was modeled from the testing results. The suggested shape of the wetting front is associated with utilization of the desorption SWCC instead of the sorption SWCC and with relatively high values of ks (average value of 7.2E-7 cm/sec) were measured in the FWP tests while relatively low values of ks (average value of 1.2E-7 cm/sec) were measured in the SDRI test.

Elvis, Ishimwe

165

Use of a storm water retention system for conservation of regionally endangered fishes  

USGS Publications Warehouse

Maintaining aquatic biodiversity in urban or suburban areas can be problematic because urban landscapes can be nearly devoid of aquatic habitats other than engineered basins for storm water management. These areas are usually of questionable value for fish, but we examined a case study in which five regionally imperiled fish species were reintroduced into an artificial storm water detention pond and subsequently thrived. Although not a formal experiment, postintroduction survey data suggested that three of the five species maintained high population densities for 10 years after initial stocking, and two persisted in lower numbers. Success was likely due to a combination of unique design features and prior habitat preparation that resulted in clear water conditions that supported dense vegetation. Stocked fish persisted despite occasional bouts of low dissolved oxygen and increased chloride levels resulting from road salt application within the watershed. Transplanted fish served as a source population for both research and further reintroduction experiments. We suggest that, for some fish species, habitat preservation has a middle ground between natural habitats and completely artificial environments that require constant husbandry and that storm water systems could be used to create engineered sanctuaries within the human landscape that have many potential benefits for both humans and fish.

Schaeffer, Jeffrey S.; Bland, James K.; Janssen, John

2012-01-01

166

Evaluation of the "DSPM" model on a titania membrane: measurements of charged and uncharged solute retention, electrokinetic charge, pore size, and water permeability.  

PubMed

The DSPM (Donnan steric partitioning pore model) was evaluated in the case of a titania membrane with "nanofiltration properties" by measuring the electrokinetic charge, pore size, and water permeability of the membrane, along with charged and uncharged solute retention. The zeta potential values (zeta) were determined from measurements of the electrophoretic mobility (EM) of titania powder forming the filtering layer of the membrane. Zeta potential values were converted into membrane volume charge (X) by assuming two limiting cases: a constant surface charge (sigma(s)(cst)) and a constant surface potential (psi(s)(cst)). The mean pore radius and thickness/porosity ratio of the membrane were determined by permporometry and from water permeability measurements, respectively. Retention measurements were carried out as a function of the permeate volume flux for both neutral solutes (polyethylene glycol PEG of different size) and salts (KCl, MgSO4, K2SO4, and MgCl2) at various pH values. Ionic retentions showed minimum values near the IEP of the membrane. Retention data were analyzed using the DSPM. Very good agreement was found between the pore radius calculated by the model and that determined by permporometry. X values calculated from fitting retention data using the DSPM were also in satisfactorily agreement with X values calculated from EM measurements assuming a constant surface potential for a large pH range. Furthermore, the DSPM leads to X values (X(DSPM)) between those calculated from EM (X(EM)) using the two limiting bounds. In other words, X(DSPM) was higher than X(EM) assuming psi(s)(cst) at pH values far from the isoelectric point (IEP) and lower than X(EM) assuming sigma(s)(cst). These results show that the DSPM is in qualitative agreement with the charge regulation theory (increase of the pore surface potential and decrease of the pore surface charge density with decreasing the pore size). On the other hand, the thickness/porosity ratio of the membrane calculated from solute retention data differed significantly from that determined from water permeability measurements. Moreover, a single value of Deltax/Ak could not be determined from PEG and salt retention data. This means that the Deltax/Ak parameter loses its physical meaning and includes physical phenomena which are not taken into account by the DSPM. Nevertheless, the model satisfactorily predicted the limiting retention, as this is not influenced by the Deltax/Ak parameter. PMID:16256596

Labbez, C; Fievet, P; Thomas, F; Szymczyk, A; Vidonne, A; Foissy, A; Pagetti, P

2003-06-01

167

Continuous radon measurements in upper catchments to determine soil water retention  

NASA Astrophysics Data System (ADS)

Perennial rivers flow all year, even during long periods of drought. From baseflow separation analysis, it is known that approximately 10 to 40% of the total discharge during dry periods is derived from the adjacent riverbanks and the regional groundwater in the lowland areas of rivers. However, these amounts do not even constitute half of the total discharge. This suggests that other reservoirs within the catchment hold water from wetter seasons and release them slowly during the rest of the year. While the volume of small alluvial deposits in mountain valleys and the groundwater can only account for a fraction of the 'missing' discharge components, the soil cover has a large capacity to store and release water, but is often neglected in traditional hydrogeological studies. Hydrogeochemical tracers are often used to determine the contributions from upper catchment reservoirs; however, sampling intervals are often too large to show all of the process involved in the stream flow generation process. 222Rn is a naturally produced radioactive isotopic tracer that is commonly used to quantify groundwater discharge to streams, rivers, and wetlands. Traditional sampling and analysis techniques are usually confined to point measurements taken at a specific time. However, it is difficult to constrain short- or medium-term processes occurring at the groundwater-surface water interface using single measurements. We have developed a new technique to extract dissolved gases from surface water, which allows continuous 222Rn and CO2 measurements. The technique is ideal for determining the time scales for the contribution of groundwater discharge and interflow to upper catchment creeks. The first results from the continuous measurement techniques in combination with continuous electrical conductivity measurements and weekly sampling for major ion chemistry, stable isotopes, DIC and Si in a small headwater catchment in Australia (Lyrebird Creek Catchment, Victoria, Australia) show that direct continuous measurements capture variations in runoff processes and related chemistry changes in short-time scales (

Hofmann, H.; Gilfedder, B.; Cartwright, I.

2012-04-01

168

Involvement of cell shape and flagella in the bacterial retention during percolation of contaminated water through soil columns in tropical region.  

PubMed

Microorganisms' retention in soil contributes to the natural purification of groundwater. Bacteria found in groundwater are generally of various shapes. The aim of this study was to assess the importance of cell shape and flagella in bacterial retention during polluted water percolation through two soil columns CA and CB, in the equatorial region in Central Africa. Percolation tests were carried out using different water loads samples which were contaminated by Escherichia coli (straight rods, peritrichous flagella), Vibrio parahaemolyticus (rods bacteria, polar flagella), and Staphylococcus saprophyticus (spherical, free-flagellum). It has been noted that showed that through soil column CA, the mean values of cells retention ratios (T(R)) varied with bacteria species considered, and from one applied water load sample to another. E. coli T(R) and that of S. saprophyticus were not significantly different (P> 0.05) for the two soil columns. V. parahaemolyticus T(R) significantly differed from that of E. coli and S. saprophyticus through soil column CA (P< 0.01) when the highest water load was applied, and through soil column CB (P< 0.05) for each of water load applied. A relative hierarchical arrangement of retained cells based on the T(R) showed that V. parahaemolyticus was less retained through the 2 soil columns. S. saprophyticus in most cases was more retained than others. The physical properties of the bacterial cell must be taken into consideration when evaluating the transfer of bacteriological pollutants towards groundwater. PMID:20658409

Nola, Moise; Ewoti, Olive V Noah; Nougang, Mireille; Moungang, Marlyse L; Chihib, Nour-Eddine; Krier, Francois; Servais, Pierre; Hornez, Jean-Pierre; Njine, Thomas

2010-09-01

169

Role of air on local water retention behavior in the shallow heterogeneous vadose zone  

NASA Astrophysics Data System (ADS)

In the presence of a subsurface source, air flowing through the unsaturated soil can transport toxic vapor into subsurface structures due to pressure gradients created by, e.g., a pressure drop within the building. Development of dynamic air pathways in the subsurface are largely controlled by the geological heterogeneity and the spatial and temporal distribution of soil moisture. To better understand how these air pathways are developed, it is crucial to know how water is retained in heterogeneous medium at spatial resolutions that are finer than those adopted in typical hydrologic and soil physics applications. Although methods for soil water pressure measurement can be readily found in literature, a technique for measuring “air pressure” in wet soil is not well-established or documented. Hydrophobic porous ceramic cups have been used to measure non-wetting NAPL phase pressure in two-phase systems. However, our preliminary tests using the hydrophobic ceramic cups installed in highly wet soil showed that under conditions of fast drainage of the wetting fluid that is replaced by air, it typically took some time before the cups responded to register the air pressure. Therefore, an attempt was made to develop a more robust method where the time lag is minimized. The tested materials were; 1) ceramic porous cups, 2) sintered stainless steel cups, 3) porous glass discs, and 4) non-woven PTFE fabric. The ceramic cups, sintered stainless steel cups and sintered porous glass discs required hydrophobic treatment, whereas the non-woven PTFE fabric is hydrophobic by itself. To treat the ceramic porous cups, the method proposed by Parker and Lenhard [1988] was adopted. The sintered porous stainless steel cups and porous glass discs were treated by a commercially available water repellant compound. For those four materials, contact angle, water entry pressure, and time lag to respond to an imposed pressure were measured. The best performing material was then tested in a simple heterogeneous column. The column was packed using two sands to form three layers where the coarser sand was sandwitched by two layers of a finer sand. In each layer, soil moisture, water pressure and air pressure were monitored. The soil was initially saturated and suction at the bottom was gradually increased to induce wetting fluid drainage, and followed by a wetting cycle. In the drainage cycle, the coarse middle layer did not drain until air front reached the bottom of the top fine layer. Once the air front reached the fine-coarse interface, air was quickly pulled into the coarse layer. The results showed that the newly developed hydrophobic material showed very small time lag and captured the abrupt air pressure change in the wet soil. In the wetting cycle, we observed positive air pressure which indicated entrapment of air and its compression as wetting proceeded. This behavior cannot be evaluated properly without the rapid measurement of air pressure. The method is currently being applied in a large 2D vertical aquifer with a structured heterogeneity to investigate how air pathways are formed under various flux/temperature conditions at the soil surface.

Sakaki, T.; Limsuwat, A.; Illangasekare, T. H.

2009-12-01

170

Superhydrophobic surfaces of the water bug Notonecta glauca: a model for friction reduction and air retention  

PubMed Central

Summary Superhydrophobic surfaces of plants and animals are of great interest for biomimetic applications. Whereas the self-cleaning properties of superhydrophobic surfaces have been extensively investigated, their ability to retain an air film while submerged under water has not, in the past, received much attention. Nevertheless, air retaining surfaces are of great economic and ecological interest because an air film can reduce friction of solid bodies sliding through the water. This opens perspectives for biomimetic applications such as low friction fluid transport or friction reduction on ship hulls. For such applications the durability of the air film is most important. While the air film on most superhydrophobic surfaces usually lasts no longer than a few days, a few semi-aquatic plants and insects are able to hold an air film over a longer time period. Currently, we found high air film persistence under hydrostatic conditions for the elytra of the backswimmer Notonecta glauca which we therefore have chosen for further investigations. In this study, we compare the micro- and nanostructure of selected body parts (sternites, upper side of elytra, underside of elytra) in reference to their air retaining properties. Our investigations demonstrate outstanding air film persistence of the upper side of the elytra of Notonecta glauca under hydrostatic and hydrodynamic conditions. This hierarchically structured surface was able to hold a complete air film under hydrostatic conditions for longer than 130 days while on other body parts with simple structures the air film showed gaps (underside of elytra) or even vanished completely after a few days (sternites). Moreover, the upper side of the elytra was able to keep an air film up to flow velocities of 5 m/s. Obviously the complex surface structure with tiny dense microtrichia and two types of larger specially shaped setae is relevant for this outstanding ability. Besides high air film persistence, the observation of a considerable fluid velocity directly at the air–water interface indicates the ability to reduce friction significantly. The combination of these two abilities makes these hierarchically structured surfaces extremely interesting as a biomimetic model for low friction fluid transport or drag reduction on ship hulls. PMID:21977425

Schneider, Erik S; Melskotte, Jan-Erik; Brede, Martin; Leder, Alfred

2011-01-01

171

Retention and loss of water extractable carbon in soils: effect of clay properties.  

PubMed

Clay sorption is important for organic carbon (C) sequestration in soils, but little is known about the effect of different clay properties on organic C sorption and release. To investigate the effect of clay content and properties on sorption, desorption and loss of water extractable organic C (WEOC), two experiments were conducted. In experiment 1, a loamy sand alone (native) or mixed with clay isolated from a surface or subsoil (78 and 96% clay) resulting in 90, 158 and 175 g clay kg(-1) soil. These soil treatments were leached with different WEOC concentrations, and then CO2 release was measured for 28 days followed by leaching with reverse osmosis water at the end of experiment. The second experiment was conducted to determine WEOC sorption and desorption of clays isolated from the loamy sand (native), surface soil and subsoil. Addition of clays isolated from surface and subsoil to sandy loam increased WEOC sorption and reduced C leaching and cumulative respiration in percentage of total organic C and WEOC added when expressed per g soil and per g clay. Compared to clays isolated from the surface and subsoil, the native clay had higher concentrations of illite and exchangeable Ca(2+), total organic C and a higher CEC but a lower extractable Fe/Al concentration. This indicates that compared to the clay isolated from the surface and the subsoil, the native clay had fewer potential WEOC binding sites because it had lower Fe/Al content thus lower number of binding sites and the existing binding sites are already occupied native organic matter. The results of this study suggest that in the soils used here, the impact of clay on WEOC sorption and loss is dependent on its indigenous organic carbon and Fe and/or Al concentrations whereas clay mineralogy, CEC, exchangeable Ca(2+) and surface area are less important. PMID:24144942

Nguyen, Trung-Ta; Marschner, Petra

2014-02-01

172

In the Way of Peacemaker Guide Curve between Water Supply and Flood Control for Short Term Reservoir Operation  

NASA Astrophysics Data System (ADS)

Effective management of a controlled reservoir system where it involves multiple and sometimes conflicting objectives is a complex problem especially in real time operations. Yuvac?k Dam Reservoir, located in the Marmara region of Turkey, is built to supply annual demand of 142 hm3 water for Kocaeli city requires such a complex management strategy since it has relatively small (51 hm3) effective capacity. On the other hand, the drainage basin is fed by both rainfall and snowmelt since the elevation ranges between 80 - 1548 m. Excessive water must be stored behind the radial gates between February and May in terms of sustainability especially for summer and autumn periods. Moreover, the downstream channel physical conditions constraint the spillway releases up to 100 m3/s although the spillway is large enough to handle major floods. Thus, this situation makes short term release decisions the challenging task. Long term water supply curves, based on historical inflows and annual water demand, are in conflict with flood regulation (control) levels, based on flood attenuation and routing curves, for this reservoir. A guide curve, that is generated using both water supply and flood control of downstream channel, generally corresponds to upper elevation of conservation pool for simulation of a reservoir. However, sometimes current operation necessitates exceeding this target elevation. Since guide curves can be developed as a function of external variables, the water potential of a basin can be an indicator to explain current conditions and decide on the further strategies. Besides, releases with respect to guide curve are managed and restricted by user-defined rules. Although the managers operate the reservoir due to several variable conditions and predictions, still the simulation model using variable guide curve is an urgent need to test alternatives quickly. To that end, using HEC-ResSim, the several variable guide curves are defined to meet the requirements by taking inflow, elevation, precipitation and snow water equivalent into consideration to propose alternative simulations as a decision support system. After that, the releases are subjected to user-defined rules. Thus, previous year reservoir simulations are compared with observed reservoir levels and releases. Hypothetical flood scenarios are tested in case of different storm event timing and sizing. Numerical weather prediction data of Mesoscale Model 5 (MM5) can be used for temperature and precipitation forecasts that will form the inputs for a hydrological model. The estimated flows can be used for real time short term decisions for reservoir simulation based on variable guide curve and user defined rules.

Uysal, G.; Sensoy, A.; Yavuz, O.; Sorman, A. A.; Gezgin, T.

2012-04-01

173

Moisture retention properties of a mycorrhizal soil  

Microsoft Academic Search

The water relations of arbuscular mycorrhizal plants have been compared often, but virtually nothing is known about the comparative water relations of mycorrhizal and nonmycorrhizal soils. Mycorrhizal symbiosis typically affects soil structure, and soil structure affects water retention properties; therefore, it seems likely that mycorrhizal symbiosis may affect soil water relations. We examined the water retention properties of a Sequatchie

Robert M. Augel; Ann J. W. Stodola; Jayme E. Tims; Arnold M. Saxton

2001-01-01

174

Decentralised water retention along the river channels in a mesoscale catchment in south-eastern Germany  

NASA Astrophysics Data System (ADS)

Throughout the Ore Mountains, a low mountain area located in the German-Czech border region, storm runoff frequently causes severe damage in headwater areas as well as in lower reaches. Settlements along smaller tributaries and towns at the receiving water are affected simultaneously, so measures distributed throughout the entire drainage area (decentralised measures) have to be considered for flood protection planning in such areas. The concept of decentralised flood protection, which is well established in the German literature, offers a large number of potential flood control schemes including measures along the river channels, in agriculture and forestry as well as in settlements. The investigations presented here focus on the group of measures along the river channels, including small, distributed retarding basins, river renaturation and afforestation of floodplains. Based on rainfall-runoff models, its aim is to show how such measures influence flood hydrographs in low mountain areas with a 100-year recurrence interval, using the example of the Upper Flöha watershed in the Central Ore Mountains. The results indicate that along the tributaries of the Flöha very high local peak reductions can be achieved with small retarding basins. The efficiency of the basins is related to the available storage capacity in the valleys upstream of the settlements. On a supralocal level, i.e. at the Flöha River, an additional reduction of the peak discharge occurs in the model. Other significant supralocal effects can be observed for the scenarios with an increased floodplain roughness (afforestation). In a combination of both scenarios the supralocal effects increase further, whereas the local effects are as high as in the retarding basin scenario. By contrast, the river renaturation scenario does not show a significant impact on the flood hydrographs. However, the limited effect is a result of the local characteristics of the study area, where the number of suitable river sections is limited and the slope gradients are high. On the whole, it can be concluded that decentralised measures along the rivers can be efficient elements in the framework of flood protection strategies. The reduction of flood peaks includes not only the receiving water, but also the tributaries, so that an improvement of flood protection extending across the entire watershed can be achieved.

Reinhardt, Christian; Bölscher, Jens; Schulte, Achim; Wenzel, Robert

2011-01-01

175

Modeling water retention of sludge simulants and actual saltcake tank wastes  

SciTech Connect

The Ferrocyanide Tanks Safety Program managed by Westinghouse hanford Company has been concerned with the potential combustion hazard of dry tank wastes containing ferrocyanide chemical in combination with nitrate salts. Pervious studies have shown that tank waste containing greater than 20 percent of weight as water could not be accidentally ignited. Moreover, a sustained combustion could not be propagated in such a wet waste even if it contained enough ferrocyanide to burn. Because moisture content is a key critical factor determining the safety of ferrocyanide-containing tank wastes, physical modeling was performed by Pacific Northwest National laboratory to evaluate the moisture-retaining behavior of typical tank wastes. The physical modeling reported here has quantified the mechanisms by which two main types of tank waste, sludge and saltcake, retain moisture in a tank profile under static conditions. Static conditions usually prevail after a tank profile has been stabilized by pumping out any excess interstitial liquid, which is not naturally retained by the waste as a result of physical forces such as capillarity.

Simmons, C.S.

1996-07-01

176

Regional water balance modelling using flow-duration curves with observational uncertainties  

NASA Astrophysics Data System (ADS)

Robust and reliable water-resource mapping in ungauged basins requires estimation of the uncertainties in the hydrologic model, the regionalisation method, and the observational data. In this study we investigated the use of regionalised flow-duration curves (FDCs) for constraining model predictive uncertainty, while accounting for all these uncertainty sources. A water balance model was applied to 36 basins in Central America using regionally and globally available precipitation, climate and discharge data that were screened for inconsistencies. A rating-curve analysis for 35 Honduran discharge stations was used to estimate discharge uncertainty for the region, and the consistency of the model forcing and evaluation data was analysed using two different screening methods. FDCs with uncertainty bounds were calculated for each basin, accounting for both discharge uncertainty and, in many cases, uncertainty stemming from the use of short time series, potentially not representative for the modelling period. These uncertain FDCs were then used to regionalise a FDC for each basin, treating it as ungauged in a cross-evaluation, and this regionalised FDC was used to constrain the uncertainty in the model predictions for the basin. There was a clear relationship between the performance of the local model calibration and the degree of data set consistency - with many basins with inconsistent data lacking behavioural simulations (i.e. simulations within predefined limits around the observed FDC) and the basins with the highest data set consistency also having the highest simulation reliability. For the basins where the regionalisation of the FDCs worked best, the uncertainty bounds for the regionalised simulations were only slightly wider than those for a local model calibration. The predicted uncertainty was greater for basins where the result of the FDC regionalisation was more uncertain, but the regionalised simulations still had a high reliability compared to the locally calibrated simulations and often encompassed them. The regionalised FDCs were found to be useful on their own as a basic signature constraint; however, additional regionalised signatures could further constrain the uncertainty in the predictions and may increase the robustness to severe data inconsistencies, which are difficult to detect for ungauged basins.

Westerberg, I. K.; Gong, L.; Beven, K. J.; Seibert, J.; Semedo, A.; Xu, C.-Y.; Halldin, S.

2014-08-01

177

Wettability of poultry litter biochars at variable pyrolysis temperatures and their impact on soil wettability and water retention relationships  

NASA Astrophysics Data System (ADS)

To reduce the impact of poultry farming on greenhouse gas emissions, poultry farming waste - poultry litter - can be converted to biofuel and biochar through slow-pyrolysis, with the biochar added to agricultural soil for nutrient enrichment and carbon sequestration. While biochars from source materials other than poultry litter have been shown to sequester carbon and increase soil fertility, there is considerable variability in biochar behavior - even with biochars created from the same source material. This situation is exacerbated by our limited understanding of how biochars alter physical, chemical, and biological processes in agricultural soils. The focus of this work is to develop a mechanistic understanding of how poultry litter (PL) biochars affect the hydrology, microbial communities, N2O emissions, and nitrogen cycling in agricultural soils. The initial focus is on the impact of PL biochar on soil hydrology. PL from Perdue AgriRecycle, LLC (Seaford, Delaware) was used to produce biochars at pyrolysis temperatures from 300°C to 600°C. To explore the impact of these biochars on soil wettability, the PL biochars were mixed with a 30/40 Accusand in mass fractions from 0% to 100%. The water contact angle was then measured using a goniometer on these sand/biochar mixtures using the sessile drop method and a single layer of sample particles. The PL biochars produced at temperatures between 300°C to 400°C were hydrophobic, while those pyrolized at > 400°C were hydrophilic. Water contact angles for samples with 100% biochar varied systematically with pyrolysis temperature, decreasing from 101.12° to 20.57° as the pyrolysis temperature increased from 300 to 600°C. Even for small amounts of hydrophobic biochar added to the hydrophilic sand, the contact angle of the mixture was altered: for sand/biochar mixtures containing only 2% hydrophobic PL biochar by weight, the contact angle of the mixture increased from ~ 8° (0% biochar) to 20° (2% biochar). For higher mass fractions, the impact of hydrophobic PL biochar on the sand/mixture contact angle was more dramatic: for a sand/biochar mixture with 15% PL biochar, the contact angle was 40.12°. Water drop penetration tests were also performed on these samples, and results were consistent with contact angles measured with the sessile drop method. To further explore the cause of the varying contact angle with pyrolysis temperature, the PL biochars were vigorously rinsed with deionized water or heated for 24 hours at 105°C, and the contact angle measurements repeated. Both rinsing and heating samples rendered hydrophobic PL biochar hydrophilic. Rinsate samples were analyzed for total organic carbon and with GC-MS. These data suggest that bio-oils produced during slow-pyrolysis at temperatures < 400°C condensed on biochar and caused hydrophobicity. These bio-oils could be removed through vigorous washing with deionized water or heating to 105°C. The implication of these changes in water contact angle from PL biochar addition on water retention relationships for soil and on water distribution within pores will be discussed.

Yi, S. C.; Witt, B.; Guo, M.; Chiu, P.; Imhoff, P. T.

2012-12-01

178

THE SIGNIFICANCE OF "STAGNATION CURVES" FOR LEAD AND COPPER, AND WATER QUALITY FACTORS AFFECTING THEM  

EPA Science Inventory

"Stagnation curves" are the response of metal levels, particularly lead and copper, to time under conditions of no water flow. Research on lead pipe in the early 1980's in the United States, Germany, and in the United Kingdom suggested that they were characterized by rapid incre...

179

Introducing Hysteresis in Snow Depletion Curves to Improve the Water Budget of a Land Surface Model in an Alpine Catchment  

E-print Network

Introducing Hysteresis in Snow Depletion Curves to Improve the Water Budget of a Land Surface Model), a distributed land surface model (LSM) with a multilayer, physically based snow model, has been applied of the accu- mulation and ablation of the snow cover using Moderate Resolution Imaging Spectroradiometer

180

Investigation of downward facing critical heat flux with water-based nanofluids for In-Vessel Retention applications  

E-print Network

In-Vessel Retention ("IVR") is a severe accident management strategy that is power limiting to the Westinghouse AP1000 due to critical heat flux ("CHF") at the outer surface of the reactor vessel. Increasing the CHF level ...

DeWitt, Gregory L

2011-01-01

181

Water Retention Characteristics and State-Dependent Mechanical and Petro-Physical Properties of a Clay Shale  

NASA Astrophysics Data System (ADS)

A series of clay shale specimens in equilibrium with various humidity conditions were used to establish the water retention characteristics, the influence of suction on ultrasonic p-wave velocity and rock mechanical properties such as Young's modulus, Poisson's ratio, onset of dilatancy, unconfined compressive strength and Brazilian tensile strength. Opalinus Clay, a clay shale considered as host rock for the disposal of nuclear waste in Switzerland was utilized. The results showed that the p-wave velocity normal to bedding ( v p,n) dropped sharply upon desaturation until suction approached the air-entry value. The sharp decrease was associated with desiccation cracks solely oriented parallel to bedding. For suction in excess of the air-entry value, v p,n was constant, indicating no further desiccation damage. The suction at the shrinkage limit and at the air-entry point is similar in magnitude. The p-wave velocity parallel to bedding ( v p,p) remained constant in the entire range of suction investigated in this study. The constant v p,p with increasing suction might be associated with the disproportional decrease in the Poisson's ratio and Young's modulus and its opposing effect on p-wave velocity. An almost linear increase in unconfined compressive strength, Brazilian tensile strength, stress at the onset of dilatancy and Young's modulus with increasing suction was observed up to a suction of 56.6 MPa. For suction larger than 56.6 MPa, relatively constant strength and stiffness was observed. The increase is associated with the net contribution of suction to strength/stiffness, which decreases nonlinearly with decreasing volumetric water content. The rate of increase in tensile strength and unconfined compressive strength with increasing suction is different depending on the rock anisotropy. Compared to the strength values (Brazilian tensile and uniaxial compressive strength) obtained from specimens loaded parallel to bedding, the tensile strength parallel to bedding and the unconfined compressive strength obtained from specimens loaded normal to bedding are considerably more affected by increasing suction or decreasing water content. The reasons for the different rates in strength increase are considered to be related to local variations in suction (i.e., local suction) as a consequence of zones of contrasting pore-size distribution. These variations may influence the effect of suction on strength, especially when the load is applied parallel to bedding and crack growth occurs predominately along bedding layers with comparably low suction.

Wild, Katrin M.; Wymann, Linda P.; Zimmer, Sebastian; Thoeny, Reto; Amann, Florian

2015-03-01

182

Predicting the soil moisture retention curve, from soil particle size distribution and bulk density data using a packing density scaling factor  

NASA Astrophysics Data System (ADS)

A substantial number of models predicting the soil moisture characteristic curve (SMC) from particle size distribution (PSD) data underestimate the dry range of the SMC especially in soils with high clay and organic matter contents. In this study, we applied a continuous form of the PSD model to predict the SMC, and subsequently we developed a physically based scaling approach to reduce the model's bias at the dry range of the SMC. The soil particle packing density was considered as a metric of soil structure and used to define a soil particle packing scaling factor. This factor was subsequently integrated in the conceptual SMC prediction model. The model was tested on 82 soils, selected from the UNSODA database. The results show that the scaling approach properly estimates the SMC for all soil samples. In comparison to the original conceptual SMC model without scaling, the scaling approach improves the model estimations on average by 30%. Improvements were particularly significant for the fine- and medium-textured soils. Since the scaling approach is parsimonious and does not rely on additional empirical parameters, we conclude that this approach may be used for estimating SMC at the larger field scale from basic soil data.

Meskini-Vishkaee, F.; Mohammadi, M. H.; Vanclooster, M.

2014-10-01

183

Physically based estimation of soil water retention from textural data: General framework, new models, and streamlined existing models  

USGS Publications Warehouse

Numerous models are in widespread use for the estimation of soil water retention from more easily measured textural data. Improved models are needed for better prediction and wider applicability. We developed a basic framework from which new and existing models can be derived to facilitate improvements. Starting from the assumption that every particle has a characteristic dimension R associated uniquely with a matric pressure ?? and that the form of the ??-R relation is the defining characteristic of each model, this framework leads to particular models by specification of geometric relationships between pores and particles. Typical assumptions are that particles are spheres, pores are cylinders with volume equal to the associated particle volume times the void ratio, and that the capillary inverse proportionality between radius and matric pressure is valid. Examples include fixed-pore-shape and fixed-pore-length models. We also developed alternative versions of the model of Arya and Paris that eliminate its interval-size dependence and other problems. The alternative models are calculable by direct application of algebraic formulas rather than manipulation of data tables and intermediate results, and they easily combine with other models (e.g., incorporating structural effects) that are formulated on a continuous basis. Additionally, we developed a family of models based on the same pore geometry as the widely used unsaturated hydraulic conductivity model of Mualem. Predictions of measurements for different suitable media show that some of the models provide consistently good results and can be chosen based on ease of calculations and other factors. ?? Soil Science Society of America. All rights reserved.

Nimmo, J.R.; Herkelrath, W.N.; Laguna, Luna A.M.

2007-01-01

184

Multivariate curve resolution-assisted determination of pseudoephedrine and methamphetamine by HPLC-DAD in water samples.  

PubMed

In the present study, a simple strategy based on solid-phase extraction (SPE) with a cation exchange sorbent (Finisterre SCX) followed by fast high-performance liquid chromatography (HPLC) with diode array detection coupled with chemometrics tools has been proposed for the determination of methamphetamine and pseudoephedrine in ground water and river water. At first, the HPLC and SPE conditions were optimized and the analytical performance of the method was determined. In the case of ground water, determination of analytes was successfully performed through univariate calibration curves. For river water sample, multivariate curve resolution and alternating least squares was implemented and the second-order advantage was achieved in samples containing uncalibrated interferences and uncorrected background signals. The calibration curves showed good linearity (r(2) > 0.994).The limits of detection for pseudoephedrine and methamphetamine were 0.06 and 0.08 ?g/L and the average recovery values were 104.7 and 102.3% in river water, respectively. PMID:24920656

Vosough, Maryam; Mohamedian, Hadi; Salemi, Amir; Baheri, Tahmineh

2015-02-01

185

Biexponential Characterization of Prostate Tissue Water Diffusion Decay Curves Over an Extended b-factor Range  

PubMed Central

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging exams at 1.5 T, a single 10 mm thick axial slice was scanned with a line scan diffusion imaging (LSDI) sequence in which 14 equally spaced b- factors from 5 to 3500 s/mm2 were sampled along three orthogonal diffusion sensitization directions in 6 minutes. Due to the combination of long scan time and limited volume coverage associated with the multi-b- factor, multi-directional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed non-cancerous regions of interest (ROI’s) within the central gland (CG) and peripheral zone (PZ). Histology from pre-scan biopsy (N = 9) and post-surgical resection (N = 4) was subsequently employed to help confirm that the ROIs sampled were non-cancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia (BPH) which is prevalent in this population. The water signal decays with b- factor from all ROI’s were clearly non-monoexponential and better served with bi- vs monoexponential fits, as tested using ?2 based F-test analyses. Fits to biexponential decay functions yielded inter-subject fast diffusion component fractions on the order of 0.73 ± 0.08 for both CG and PZ ROIs, fast diffusion coefficients of 2.68 ± 0.39 and 2.52 ± 0.38 ?m2/ms and slow diffusion coefficients of 0.44 ± 0.16 and 0.23 ± 0.16 um2/ms for CG and PZ ROI’s, respectively. The difference between the slow diffusion coefficients within CG and PZ was statistically significant as assessed with a Mann-Whitney non-parametric test (P < 0.05). We conclude that a monoexponential model for water diffusion decay in prostate tissue is inadequate when a large range of b- factors is sampled and that biexponential analyses are better suited for characterizing prostate diffusion decay curves. PMID:16735177

Mulkern, Robert V.; Barnes, Agnieszka Szot; Haker, Steven J.; Hung, Yin P.; Rybicki, Frank J.; Maier, Stephan E.; Tempany, Clare M.C.

2006-01-01

186

Biexponential characterization of prostate tissue water diffusion decay curves over an extended b-factor range.  

PubMed

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging examinations at 1.5 T, a single 10-mm-thick axial slice was scanned with a line scan diffusion imaging sequence in which 14 equally spaced b factors from 5 to 3,500 s/mm(2) were sampled along three orthogonal diffusion sensitization directions in 6 min. Due to the combination of long scan time and limited volume coverage associated with the multi-b-factor, multidirectional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed noncancerous regions of interest (ROIs) within the central gland (CG) and peripheral zone (PZ). Histology from prescan biopsy (n=9) and postsurgical resection (n=4) was subsequently employed to help confirm that the ROIs sampled were noncancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia, which is prevalent in this population. The water signal decays with b factor from all ROIs were clearly non-monoexponential and better served with bi- vs. monoexponential fits, as tested using chi(2)-based F test analyses. Fits to biexponential decay functions yielded intersubject fast diffusion component fractions in the order of 0.73+/-0.08 for both CG and PZ ROIs, fast diffusion coefficients of 2.68+/-0.39 and 2.52+/-0.38 microm(2)/ms and slow diffusion coefficients of 0.44+/-0.16 and 0.23+/-0.16 um(2)/ms for CG and PZ ROIs, respectively. The difference between the slow diffusion coefficients within CG and PZ was statistically significant as assessed with a Mann-Whitney nonparametric test (P<.05). We conclude that a monoexponential model for water diffusion decay in prostate tissue is inadequate when a large range of b factors is sampled and that biexponential analyses are better suited for characterizing prostate diffusion decay curves. PMID:16735177

Mulkern, Robert V; Barnes, Agnieszka Szot; Haker, Steven J; Hung, Yin P; Rybicki, Frank J; Maier, Stephan E; Tempany, Clare M C

2006-06-01

187

Climate Change Adaptation in the Western U.S.: the Case for Dynamic Rule Curves in Water Resources Management  

NASA Astrophysics Data System (ADS)

Climate change in the Western U.S. will bring systematic hydrologic changes affecting many water resources systems. Successful adaptation to these changes, which will be ongoing through the 21st century, will require the 'rebalancing' of competing system objectives such as water supply, flood control, hydropower production, and environmental services in response to hydrologic (and other) changes. Although fixed operating policies for the operation of reservoirs has been a traditional approach to water management in the 20th century, the rapid pace of projected climate shifts (~0.5 F per decade), and the prohibitive costs of recursive policy intervention to mitigate impacts, suggest that more sophisticated approaches will be needed to cope with climate change on a long term basis. The use of 'dynamic rule curves' is an approach that maintains some of the key characteristics of current water management practice (reservoir rule curves) while avoiding many of the fundamental drawbacks of traditional water resources management strategies in a non-stationary climate. In this approach, water resources systems are optimized for each operational period using ensemble streamflow and/or water demand forecasts. The ensemble of optimized reservoir storage traces are then analyzed to produce a set of unique reservoir rule curves for each operational period reflecting the current state of the system. The potential advantage of this approach is that hydrologic changes associated with climate change (such as systematically warmer temperatures) can be captured explicitly in operational hydrologic forecasts, which would in turn inform the optimized reservoir management solutions, creating water resources systems that are largely 'self tending' as the climate system evolves. Furthermore, as hydrologic forecasting systems improve (e.g. in response to improved ENSO forecasting or other scientific advances), so does the performance of reservoir operations. An example of the approach is given for flood control in the Columbia River basin.

Lee, S.; Hamlet, A. F.; Burges, S. J.

2008-12-01

188

4, 407437, 2007 Fitting of soil water  

E-print Network

Interactive Discussion EGU Abstract The soil hydraulic parameters for analyzing soil water movement can be determined by fitting a soil water retention curve to a certain function, i.e., a soil hydraulic model of matric potential), is the volumetric water content, and K is the unsaturated hydraulic conductivity

Boyer, Edmond

189

RETENTION BASIN Definition  

E-print Network

A retention basin is a stormwater facility which includes a permanent impoundment, or pool of water, and, therefore, is normally wet, even during non-rainfall periods. Inflows from stormwater runoff may be temporarily stored above this permanent pool. Purpose A retention basin provides for long-term water quality enhancement of stormwater runoff. Stormwater inflows may also be temporarily stored above the permanent pool for downstream flood control and channel erosion control. A retention basin is considered one of the most reliable and versatile BMPs available. Water Quality Enhancement High removal rates of particulate and soluble pollutants (nutrients) can be achieved in retention basins through gravitational settling, biological uptake and decomposition. When an even higher degree of pollutant removal efficiency is required, the basin can be enhanced by using various modifications relating to the size and design of the permanent pool. Monitoring studies have shown sediment removal efficiencies to range from 50-90%, total phosphorus removal efficiencies to range from 30-90 % and soluble nutrient removal efficiencies to

Figure Figures Page

190

Distribution of Typical Freshwater Bacterial Groups Is Associated with pH, Temperature, and Lake Water Retention Time  

Microsoft Academic Search

The distribution of 15 typical freshwater bacterial groups in 15 diverse lakes in northern Europe was investigated using reverse line blot hybridization. Statistical evaluation of the data in relation to the charac- teristics of the lakes showed that pH, temperature, and the theoretical hydrological retention time of the lakes were most strongly related to variations in the distribution of bacterial

Eva S. Lindstrom; Miranda P. Kamst-Van Agterveld; Gabriel Zwart

2005-01-01

191

Distribution of typical freshwater bacterial groups is associated with pH, temperature and lake water retention time  

Microsoft Academic Search

The distribution of 15 typical freshwater bacterial groups in 15 diverse lakes in northern Europe was investigated using reverse line blot hybridization. Statistical evaluation of the data in relation to the characteristics of the lakes showed that pH, temperature, and the theoretical hydrological retention time of the lakes were most strongly related to variations in the distribution of bacterial taxa.

E. S. Lindström; Agterveld Kamst-van M. P; G. Zwart

2005-01-01

192

Soil and Water Science Department University of Florida Developing retention indices and modeling transport of CCA in Florida soils at  

E-print Network

on preliminary characterization of the leaching and transport properties of CCA in Florida soils, with emphasis on the arsenic, chromium, and copper species in the subsurface. The primary objective of the laboratory study is to develop retention indices for the three elements that can potentially leach out from CCA-treated wood (Cu

Ma, Lena

193

Dehydration of aloe vera: simulation of drying curves and evaluation of functional properties  

Microsoft Academic Search

The effect of air-drying temperature (from 30°C to 80°C) on dehydration curves and functional properties (water retention capacity, WRC; swelling, SW; fat adsorption capacity, FAC) of aloe vera cubes has been investigated. A diffusional model taking into account sample shrinkage has been proposed and solved by using a finite difference method. The effective diffusivities estimated with the proposed model varied

S Simal; A Femen??a; P Llull; C Rosselló

2000-01-01

194

Diffusivity in 2-butoxyethanol/water mixtures of noncritical composition approaching the liquid/liquid coexistence curve  

NASA Astrophysics Data System (ADS)

Results of dynamic light scattering experiments are reported which demonstrate that the mutual diffusion coefficient of 2-butoxyethanol/water mixtures of noncritical composition exhibits a characteristic temperature and composition dependence: The diffusion coefficients of the two phases of noncritical composition coexisting along the liquid/liquid coexistence curve decrease by an order of magnitude in the temperature range (Tp-Tc)<10 K approaching the lower critical point (Tp, temperature of phase separation; Tc, critical temperature). In the homogeneous 1-fluid phase region of the phase diagram, the D vs (T-Tp) curves of mixtures of noncritical composition are shifted to smaller values of D with decreasing values of ?y-yc? (y, mass fraction of 2-butoxyethanol; yc, critical mass fraction). These findings are discussed on the basis of the model of regular mixtures.

Schmitz, J.; Belkoura, L.; Woermann, D.

1994-07-01

195

Enhancing water retention and low-humidity proton conductivity of sulfonated poly(ether ether ketone) composite membrane enabled by the polymer-microcapsules with controllable hydrophilicity-hydrophobicity  

NASA Astrophysics Data System (ADS)

Four kinds of polymer microcapsules (PMCs) with different hydrophilicity-hydrophobicity are synthesized via distillation-precipitation polymerization (polymer microcapsules form by self-crosslinking of monomers/crosslinkers in this process) and incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare composite membranes. To improve the water retention of the PMCs, the hydrophilicity-hydrophobicity of the PMCs is manipulated by regulating the proportion of hydrophilic ethylene glycol dimethacrylate (EGDMA) and hydrophobic divinylbenzene (DVB) crosslinkers in the synthesis formula. The hydrophilicity of the PMCs decreases with increasing the content of polyDVB in the PMCs. The four kinds of PMCs exhibit different water retention properties. The PMCs with appropriate hydrophilic/hydrophobic balance (EGDMA: DVB = 1:1) possess the best water retention properties. Incorporation of PMCs into SPEEK matrix enhances the water-retention properties, and consequently increases proton conductivity to 0.0132 S cm-1 under 20% relative humidity, about thirteen times higher than that of the SPEEK control membrane. Moreover, the incorporation of PMCs reduces the activation energy for proton conduction and the methanol permeability of the membranes. This study may be helpful to rational design of excellent water-retention materials.

He, Guangwei; Li, Yifan; Li, Zongyu; Nie, Lingli; Wu, Hong; Yang, Xinlin; Zhao, Yuning; Jiang, Zhongyi

2014-02-01

196

Role of the air-water interface in the retention of TiO2 nanoparticles in porous media during primary drainage.  

PubMed

The increasing use of nanomaterials in commercial products has resulted in increased concerns about their potential environmental impacts. The overall mobility of nanomaterials in the environment may depend in part on their mobility in the unsaturated zone of the subsurface, which may provide a sink for nanomaterials, preventing their spread, or a long-term contaminant source. The objective of this work was to study the dynamic unsaturated transport of titanium dioxide (TiO2) during primary drainage to examine the role of air-water interface formation on nanomaterial retention. A specialized automated system was used to track depletion of TiO2 in the pore solution of a porous medium during dynamic drainage, while simultaneously measuring capillary pressure (Pc) and saturation (S). A continuous mass balance was used to calculate the mass of retained TiO2 nanoparticles. Experiments were specifically designed to minimize TiO2 interactions with solid surfaces to allow direct assessment of the role of the air-water interface. Results indicate that the mass of retained TiO2 increases as saturation decreases at all drainage rates, with slower drainage rates corresponding to greater retention at a given saturation. Normalizing the retained mass (M) bythe measured air-water interfacial area (A) shows near-constant M/A values at high saturations (S > 0.4) and increasing M/A values with decreasing saturation as saturation drops below 0.4. This result may indicate air-water interfacial adsorption at high saturations, with increasing contributions from film straining at lower saturations. PMID:18409613

Chen, Lixia; Sabatini, David A; Kibbey, Tohren C G

2008-03-15

197

Water retention and granular rheological behavior of fresh C 3S paste as a function of concentration 1 1 This paper was originally submitted to Advanced Cement Based Materials. It was received at the Editorial Office of Cement and Concrete Research on 27 August 1998 and accepted in final form on 28 May 1999  

Microsoft Academic Search

Water retention and rheological behavior of fresh C3S paste have been analysed as a function of C3S volume fraction. Three investigation techniques have been used : (1) the test of water demand, (2) filtration under gas pressure, and (3) shear rheology with normal stress measurements. Cross correlations between shear rheological parameters, dilatancy, and water retention measurement results allow for the

S. Mansoutre; P. Colombet; H. Van Damme

1999-01-01

198

Visual techniques for the detection of water quality trends: Double-mass curves and cusum functions  

Microsoft Academic Search

There is a great need for quantitative techniques to assess changes in water quality related to progressive watershed land-use developments, water-related impoundments or to evaluate the impact of recent sanitation programs. In choosing a physically representative variate for the water quality of the run-off, both concentrations and fluxes of pollutants must be taken into account. The importance of the climatic

Daniel A. Cluis; GI V

1983-01-01

199

River inflow and retention time affecting spatial heterogeneity of chlorophyll and water-air CO2 fluxes in a tropical hydropower reservoir  

NASA Astrophysics Data System (ADS)

Much research has been devoted to understanding the complexity of biogeochemical and physical processes responsible for the greenhouse gas (GHG) emissions from hydropower reservoirs. Spatial complexity and heterogeneity of GHG emission may be observed in these systems because it is dependent on flooded biomass, river inflow, primary production and dam operation. In this study, we investigate the relationships between water-air CO2 fluxes and phytoplanktonic biomass in Funil Reservoir, an old and stratified tropical reservoir, where intense phytoplankton blooms and low partial pressure of CO2 (pCO2) are observed. Our results showed that Funil Reservoir seasonal and spatial variability of chlorophyll concentration (Chl) and pCO2 is more related to changes in river inflow over the year than environmental factor such as air temperature and solar radiation. Field data and hydrodynamic simulations reveal that the river inflow contributes to increased heterogeneity in dry season due to the variation of reservoir retention time and river temperature. Contradictory conclusion can be drawn if temporal data collected only near the dam is considered instead of spatial data to represent CO2 fluxes in whole reservoir. The average CO2 fluxes was -17.6 and 22.1 mmol m-2d-2 considering data collected near the dam and spatial data, respectively, in periods of low retention time. In this case, the lack of spatial information can change completely the role of Funil Reservoir regarding GHG emissions. Our results support the idea that Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in river inflow and retention time is potentially more important force driving both Chl and pCO2 spatial variability than in-system ecological factors.

Pacheco, F. S.; Soares, M. C. S.; Assireu, A. T.; Curtarelli, M. P.; Roland, F.; Abril, G.; Stech, J. L.; Alvalá, P. C.; Ometto, J. P.

2014-06-01

200

Evaluation of pollutant loads from stormwater BMPs to receiving water using load frequency curves with uncertainty analysis.  

PubMed

This study examined pollutant loads released to receiving water from a typical urban watershed in the Los Angeles (LA) Basin of California by applying a best management practice (BMP) performance model that includes uncertainty. This BMP performance model uses the k-C model and incorporates uncertainty analysis and the first-order second-moment (FOSM) method to assess the effectiveness of BMPs for removing stormwater pollutants. Uncertainties were considered for the influent event mean concentration (EMC) and the aerial removal rate constant of the k-C model. The storage treatment overflow and runoff model (STORM) was used to simulate the flow volume from watershed, the bypass flow volume and the flow volume that passes through the BMP. Detention basins and total suspended solids (TSS) were chosen as representatives of stormwater BMP and pollutant, respectively. This paper applies load frequency curves (LFCs), which replace the exceedance percentage with an exceedance frequency as an alternative to load duration curves (LDCs), to evaluate the effectiveness of BMPs. An evaluation method based on uncertainty analysis is suggested because it applies a water quality standard exceedance based on frequency and magnitude. As a result, the incorporation of uncertainty in the estimates of pollutant loads can assist stormwater managers in determining the degree of total daily maximum load (TMDL) compliance that could be expected from a given BMP in a watershed. PMID:22578429

Park, Daeryong; Roesner, Larry A

2012-12-15

201

REVERSED-PHASE SEPARATION OF ESTUARINE INTERSTITIAL WATER FRACTIONS AND THE CONSEQUENCES OF C18 RETENTION OF ORGANIC MATTER  

EPA Science Inventory

Data are presented on the application of the reversed-phase separation technique for the determination of dissolved organic compounds in estuarine interstitial water. hirty-seven neutral, nonpolar organic compounds were equilibrated with interstitial water, extracted by emulsion-...

202

The effect of traces of hexyloxyethoxyethanol on the 2-butoxyethanol + water liquid-liquid coexistence curve  

NASA Astrophysics Data System (ADS)

A cloudy region found in the liquid system 2-butoxyethanol + water with traces of 2-(2-hexyloxyethoxy) ethanol, at the water-rich part of the phase diagram, is studied with light scattering. Our results indicate that the cloudy region corresponds to a phase separation. We present the cloud points for two series of mixtures at constant 2-(2-hexyloxyethoxy) ethanol concentration (I and 1.5 wt% ). Some comments are made to explain the apparent stability of that cloudy region.

Castillo, R.; Rivera, M.

1995-05-01

203

Lake retention of manufactured nanoparticles.  

PubMed

For twenty-five world lakes and three engineered nanoparticles (ENP), lake retention was calculated using a uniformly mixed lake mass balance model. This follows similar approaches traditionally used in water quality management. Lakes were selected such that lake residence times, depths and areal hydraulic loadings covered the widest possible range among existing lakes. Sedimentation accounted for natural colloid as well as suspended solid settling regimes. An ENP-specific mixed sedimentation regime is proposed. This regime combines ENP sedimentation through slow settling with natural colloids from the water column, with faster settling with suspended solids from a selected part of the water column. Although sedimentation data and hydrodynamic concepts as such were not new, their first time combination or application to ENPs shows in which cases lake retention is important for these particles. In combination with ENP emission data, lake retention translates directly into potential risks of ENPs for lake benthic communities. PMID:25463711

Koelmans, A A; Quik, J T K; Velzeboer, I

2015-01-01

204

Visual techniques for the detection of water quality trends: Double-mass curves and cusum functions.  

PubMed

There is a great need for quantitative techniques to assess changes in water quality related to progressive watershed land-use developments, water-related impoundments or to evaluate the impact of recent sanitation programs. In choosing a physically representative variate for the water quality of the run-off, both concentrations and fluxes of pollutants must be taken into account. The importance of the climatic seasonal and hydrological factors associated with unstable event-related contributions of point and non-point pollution sources of the pollutants has lead us to simultaneously study water-discharge and pollutant flux time-series. The mass-discharge time-series are, in practice, far from being ideal for the application of classical trend analysis: they are relatively short and inaccurate: their distribution, orginating from mixed parent populations is very often highly skewed; they show a high level of serial dependence and the seasonal effects represent a large percentage of the variance, concealing possible long-term trends. Faced with the poor structure of these series which prohibits the use of statistical tests, experiments have been carried out with progressive-regressive inertial techniques, which imply the stationarity of water discharges. The double-mass technique was developed originally as a visual technique, to assess the homogeneity of precipitation records and was extended to study variations in sediment transport in modified watersheds. More recently confidence 'rails' and slope change detection have rendered its use more quantitative. Based on the same inertial principles, the Cumulative Sum (CUSUM) functions allow simultaneous evaluation of the covariability of the two series. An example involving weekly sampled nitrate concentrations and continuously monitored water discharges is developed. PMID:24258934

Cluis, D A

1983-06-01

205

Effects of a Long-Acting Ophthalmic Formulation of Carteolol Containing Alginic Acid on the Corneal Epithelial Barrier Function and Water Retentive Effect  

PubMed Central

Abstract Purpose Effects of a long-acting ophthalmic formulation of carteolol containing alginic acid on the corneal epithelial barrier function and its water retentive effect were investigated. Methods Using 10 healthy adult subjects, 2% Mikelan Ophthalmic Solution® (MK) was instilled in the eye once daily for 7 days (MK group) and then after a washout period of at least 28 days, 2% Mikelan LA Ophthalmic Solution® (MKLA) was instilled in the eye once daily for 7 days (LA group). As an index of the corneal epithelial barrier function, the fluorescein uptake was measured using Kowa FL-500. A Schirmer test was conducted to evaluate the tear dynamics. In another 10 subjects, 0.5% Timoptol® (TM) was instilled in the eye unilaterally twice daily for 7 days (TM group), and the tests were conducted in the same manner. Results Concerning the fluorescein uptake before and after initiation of instillation, the levels before and at 7 days after initiation of instillation were 20.7 and 26.5?ng/mL, respectively, in the LA group and 20.6 and 26.4?ng/mL, respectively, in the MK group, showing no significant difference between levels before and after initiation of instillation in either group. In the TM group, the levels were 21.4 and 65.5?ng/mL, respectively, showing a significant increase after initiation of instillation. In the Schirmer test, the values before and after initiation of instillation were 16.8 and 20.7?mm, respectively, in the LA group and 13.7 and 12.7?mm, respectively, in the MK group, showing a trend toward increase in the LA group. Conclusions The findings suggest that the long-acting ophthalmic formulation of carteolol containing alginic acid does not affect the corneal epithelial barrier function and that it may possess a water retentive action. PMID:22217390

Inoue, Jun; Yamazaki, Izumi; Ueno, Satoki; Fujisawa, Sigeki

2012-01-01

206

Low temperature sugar-water equilibrium curve by a rapid calorimetric method  

Microsoft Academic Search

A simple rapid enthalpic method based upon a unique calorimetric measurement was developed and applied to sugar solutions at low temperatures to determine the amount of unfreezable water. The experimental results were in good agreement with those obtained by the usual freezing point depression method. The experimental data were also used to test the validity of several literature semi-empirical models

V. Hoff; S CORRERA

1995-01-01

207

Uptake and Retention of Mirex by Fish Maintained on Formulated and Natural Diets in Lake Ontario Waters  

Microsoft Academic Search

Fish with no detectable levels of the contaminant mirex were grown in Lake Ontario waters under conditions simulating commercial aquaculture. Benthic black bullheads (Ameiurus melas) were grown in cages placed in a bay of the lake. Pelagic rainbow trout (Oncorhynchus mykiss) were grown in terrestrial raceways served with Lake Ontario waters. Contaminant-free fingerlings were reared to a large size on

Joseph C. Makarewicz; Joseph K. Buttner; Theodore W. Lewis

1993-01-01

208

The influence of acid mist upon transpiration, shoot water potential and pressure—volume curves  

E-print Network

The influence of acid mist upon transpiration, shoot water potential and pressure and night transpiration rates were determined on 16/11/87 for 10 entire seedlings, of pH 2.5 and pH 5 transpiration rates were 1.19 ± 0.06 mmol's-1.tree-1 (day) and 0.54 ± 0.06 mmol's-1.tree-1 (night) for whole

Paris-Sud XI, Université de

209

Biexponential characterization of prostate tissue water diffusion decay curves over an extended b-factor range  

Microsoft Academic Search

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging examinations at 1.5 T, a single 10-mm-thick axial slice was scanned with a line scan diffusion imaging sequence in which 14 equally spaced

Robert V. Mulkern; Agnieszka Szot Barnes; Steven J. Haker; Yin P. Hung; Frank J. Rybicki; Stephan E. Maier; Clare M. C. Tempany

2006-01-01

210

Transport and retention from single to multiple fractures in crystalline rock at Äspö (Sweden): 1. Evaluation of tracer test results and sensitivity analysis  

NASA Astrophysics Data System (ADS)

We evaluate the breakthrough curves obtained within a comprehensive experimental program for investigating the retention properties of crystalline rock, referred to as Tracer Retention Understanding Experiments (TRUE). The tracer tests were conducted at the Äspö Hard Rock Laboratory (Sweden) in two phases jointly referred to as TRUE Block Scale (TBS); the TBS tests comprise a total of 17 breakthrough curves with nonsorbing and a range of sorbing tracers. The Euclidian length scales are between 10 and 30 m, compared to 5 m for the earlier tests TRUE-1. The unlimited diffusion model is consistent with measured breakthrough curves and is adopted here for evaluation. The model has four independent parameters, two of which are related to advection and dispersion, one which is related to diffusion-sorption, and one which is related to surface sorption; the individual retention parameters or properties cannot be inferred from breakthrough curves alone and require additional constraints. The mean water residence times for the TBS tests are in the range 15-250 h, whereas the coefficient of variation of the water residence times is in the range 0.4-0.6. A consistent trend is found in the calibrated retention parameters with the sorption affinities of the tracers involved. Using Bode sensitivity functions, it is shown that sensitivity increases for the retention parameter with increasing sorption affinity; for nonsorbing tracers, diffusion and hydrodynamic dispersion are shown to "compete," exhibiting similar effects; hence, their estimates are uncertain. The analysis presented here exposes a few fundamental limitations and sensitivities when evaluating diffusion-controlled retention in the subsurface; it is general and applicable to any site with comparable tracer test data. In part 2, it will be shown how discrete fracture network simulations based on the hydrostructural information available can be used for further constraining individual retention parameters, in particular, the active specific surface area (sf) and the rock matrix porosity (?).

Cvetkovic, V.; Cheng, H.; ByegâRd, J.; Winberg, A.; Tullborg, E.-L.; Widestrand, H.

2010-05-01

211

Role of mixed boundaries on flow in open capillary channels with curved air-water interfaces.  

PubMed

Flow in unsaturated porous media or in engineered microfluidic systems is dominated by capillary and viscous forces. Consequently, flow regimes may differ markedly from conventional flows, reflecting strong interfacial influences on small bodies of flowing liquids. In this work, we visualized liquid transport patterns in open capillary channels with a range of opening sizes from 0.6 to 5.0 mm using laser scanning confocal microscopy combined with fluorescent latex particles (1.0 ?m) as tracers at a mean velocity of ?0.50 mm s(-1). The observed velocity profiles indicate limited mobility at the air-water interface. The application of the Stokes equation with mixed boundary conditions (i.e., no slip on the channel walls and partial slip or shear stress at the air-water interface) clearly illustrates the increasing importance of interfacial shear stress with decreasing channel size. Interfacial shear stress emerges from the velocity gradient from the adjoining no-slip walls to the center where flow is trapped in a region in which capillary forces dominate. In addition, the increased contribution of capillary forces (relative to viscous forces) to flow on the microscale leads to increased interfacial curvature, which, together with interfacial shear stress, affects the velocity distribution and flow pattern (e.g., reverse flow in the contact line region). We found that partial slip, rather than the commonly used stress-free condition, provided a more accurate description of the boundary condition at the confined air-water interface, reflecting the key role that surface/interface effects play in controlling flow behavior on the nanoscale and microscale. PMID:22867425

Zheng, Wenjuan; Wang, Lian-Ping; Or, Dani; Lazouskaya, Volha; Jin, Yan

2012-09-01

212

The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water-air CO2 fluxes in a tropical hydropower reservoir  

NASA Astrophysics Data System (ADS)

Abundant research has been devoted to understanding the complexity of the biogeochemical and physical processes that are responsible for greenhouse gas (GHG) emissions from hydropower reservoirs. These systems may have spatially complex and heterogeneous GHG emissions due to flooded biomass, river inflows, primary production and dam operation. In this study, we investigated the relationships between the water-air CO2 fluxes and the phytoplanktonic biomass in the Funil Reservoir, which is an old, stratified tropical reservoir that exhibits intense phytoplankton blooms and a low partial pressure of CO2 (pCO2). Our results indicated that the seasonal and spatial variability of chlorophyll concentrations (Chl) and pCO2 in the Funil Reservoir are related more to changes in the river inflow over the year than to environmental factors such as air temperature and solar radiation. Field data and hydro-dynamic simulations revealed that river inflow contributes to increased heterogeneity during the dry season due to variations in the reservoir retention time and river temperature. Contradictory conclusions could be drawn if only temporal data collected near the dam were considered without spatial data to represent CO2 fluxes throughout the reservoir. During periods of high retention, the average CO2 fluxes were 10.3 mmol m-2 d-1 based on temporal data near the dam versus -7.2 mmol m-2 d-1 with spatial data from along the reservoir surface. In this case, the use of solely temporal data to calculate CO2 fluxes results in the reservoir acting as a CO2 source rather than a sink. This finding suggests that the lack of spatial data in reservoir C budget calculations can affect regional and global estimates. Our results support the idea that the Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in the river inflow and retention time are potentially a more important force driving both the Chl and pCO2 spatial variability than the in-system ecological factors.

Pacheco, F. S.; Soares, M. C. S.; Assireu, A. T.; Curtarelli, M. P.; Abril, G.; Stech, J. L.; Alvalá, P. C.; Ometto, J. P.

2015-01-01

213

Remote community drinking water supply : mechanisms of uranium retention and adsorption by ultrafiltration, nanofiltration and reverse osmosis   

E-print Network

Worldwide, around 884 million people lack access to safe drinking water. To address this, groundwater sources such as boreholes and wells are often installed in remote locations especially in developing countries. However, ...

Schulte-Herbruggen, Helfrid Maria Albertina

2012-11-29

214

Trichomes related to an unusual method of water retention and protection of the stem apex in an arid zone perennial species.  

PubMed

It is well known that trichomes protect plant organs, and several studies have investigated their role in the adaptation of plants to harsh environments. Recent studies have shown that the production of hydrophilic substances by glandular trichomes and the deposition of this secretion on young organs may facilitate water retention, thus preventing desiccation and favouring organ growth until the plant develops other protective mechanisms. Lychnophora diamantinana is a species endemic to the Brazilian 'campos rupestres' (rocky fields), a region characterized by intense solar radiation and water deficits. This study sought to investigate trichomes and the origin of the substances observed on the stem apices of L. diamantinana. Samples of stem apices, young and expanded leaves were studied using standard techniques, including light microscopy and scanning and transmission electron microscopy. Histochemical tests were used to identify the major groups of metabolites present in the trichomes and the hyaline material deposited on the apices. Non-glandular trichomes and glandular trichomes were observed. The material deposited on the stem apices was hyaline, highly hydrophilic and viscous. This hyaline material primarily consists of carbohydrates that result from the partial degradation of the cell wall of uniseriate trichomes. This degradation occurs at the same time that glandular trichomes secrete terpenoids, phenolic compounds and proteins. These results suggest that the non-glandular trichomes on the leaves of L. diamantinana help protect the young organ, particularly against desiccation, by deposition of highly hydrated substances on the apices. Furthermore, the secretion of glandular trichomes probably repels herbivore and pathogen attacks. PMID:25527474

Lusa, Makeli Garibotti; Cardoso, Elaine Cristina; Machado, Silvia Rodrigues; Appezzato-da-Glória, Beatriz

2014-01-01

215

Circulation, retention, and mixing of waters within the Weddell-Scotia Confluence, Southern Ocean: The role of stratified Taylor columns  

NASA Astrophysics Data System (ADS)

waters of the Weddell-Scotia Confluence (WSC) lie above the rugged topography of the South Scotia Ridge in the Southern Ocean. Meridional exchanges across the WSC transfer water and tracers between the Antarctic Circumpolar Current (ACC) to the north and the subpolar Weddell Gyre to the south. Here, we examine the role of topographic interactions in mediating these exchanges, and in modifying the waters transferred. A case study is presented using data from a free-drifting, intermediate-depth float, which circulated anticyclonically over Discovery Bank on the South Scotia Ridge for close to 4 years. Dimensional analysis indicates that the local conditions are conducive to the formation of Taylor columns. Contemporaneous ship-derived transient tracer data enable estimation of the rate of isopycnal mixing associated with this column, with values of O(1000 m2/s) obtained. Although necessarily coarse, this is of the same order as the rate of isopycnal mixing induced by transient mesoscale eddies within the ACC. A picture emerges of the Taylor column acting as a slow, steady blender, retaining the waters in the vicinity of the WSC for lengthy periods during which they can be subject to significant modification. A full regional float data set, bathymetric data, and a Southern Ocean state estimate are used to identify other potential sites for Taylor column formation. We find that they are likely to be sufficiently widespread to exert a significant influence on water mass modification and meridional fluxes across the southern edge of the ACC in this sector of the Southern Ocean.

Meredith, Michael P.; Meijers, Andrew S.; Naveira Garabato, Alberto C.; Brown, Peter J.; Venables, Hugh J.; Abrahamsen, E. Povl; Jullion, Loďc.; Messias, Marie-José

2015-01-01

216

Effectiveness of using pedo-transfer functions to quantify the spatial variability of soil water retention characteristics  

Microsoft Academic Search

Accurate knowledge of soil hydraulic properties is of crucial importance for reliable applications of recently developed distributed models to environmental studies and land-use planning. To provide such information in a cost-effective way, indirect estimation of water transport parameters from easily measurable or already available soil data using pedo-transfer functions (PTFs) is becoming increasingly popular. However, distributed hydrological modeling requires that

Nunzio Romano; Alessandro Santini

1997-01-01

217

Investigation of Phase and Emulsion Behavior, Surfactant Retention and Condensate Recovery for Condensate/Water/Ethanol Mixtures  

SciTech Connect

This semi-annual technical progress report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period October 01, 2003 to March 31, 2004 which covers the third six months of the project. Presently work is in progress to characterize phase and emulsion behavior for ethylbenzene/water/ethanol system. Ethylbenzene that has the equivalent carbon number is used as the model condensate. During this reporting period, temperature scans were performed mixing equal volumes of ethylbenzene and 10mM NaCl water with various concentrations of ethanol ranging from 2 to 70 vol%. For the range of temperatures tested (2 to 70 C), results indicate that temperature is invariant and produced a single phase for ethanol concentrations greater than 60 vol%. For ethanol concentrations less than 60 vol%, only two phases were obtained with aqueous rich bottom phase more in volume than that of the ethylbenzene rich top phase. Linear coreflooding experiments were completed by our industrial partner in this project, Surtek, CO, to measure the condensate recovery in flooding processes. It was found about 30% ethylbenzene recovery was obtained by the waterflooding, however, 2wt% ethanol flooding did not produce incremental recovery of the ethylbenzene. Radial coreflooding with ethanol injection prior to water injection is in progress to assess the effectiveness of the surfactant flooding in the recovery of condensate.

Ramanathan Sampath

2004-03-31

218

Ogive Curves  

NSDL National Science Digital Library

This page contains a discussion of ogive curves, logistic regression curves, and architecture. Nice photographs of architectural applications are included. The classic Birthday Problems is included as an example of an ogive curve.

2008-01-01

219

Relating soil specific surface area, water film thickness, and water vapor adsorption  

NASA Astrophysics Data System (ADS)

Estimation of soil specific surface area (SSA) and dry-end water vapor adsorption are important for porous media characterization and for prediction of water and vapor fluxes in arid environments. The objective of the presented study was to model water adsorption, film thickness, and SSA based on the t-curve theory originally developed for N2 adsorption. Data from 21 source soils with clay contents ranging from 0.6 to 52.2% were used to estimate specific surface area based on water retention, a t-curve type method, the linear prediction method, and a simplified monolayer method. The water retention and the t-curve methods were found to be mathematically analogous and were among the most accurate with regard to correlation coefficient (r = 0.97) and root-mean-square error (RMSE = 11.36 × 103 m2/kg) when compared to measurements obtained with the standard ethylene glycol monoethyl ether (EGME) method. The corrected t-curve method significantly overestimated SSA when compared to EGME data. Comparison of all considered methods with N2-BET (BET) measurements disclosed lower correlation coefficients. For soil studies, the vapor adsorption in conjunction with the t-curve or water retention methods should be preferred for SSA estimation as they show much higher correlation with soil clay content and EGME measurements.

Leăo, Tairone Paiva; Tuller, Markus

2014-10-01

220

Investigation of Phase and Emulsion Behavior, Surfactant Retention and Condensate Recovery for Condensate/Water/Ethanol Mixtures  

SciTech Connect

This semi-annual technical progress report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period April 01, 2004 to September 30, 2004 which covers the fourth six months of the project. Presently work is in progress to characterize phase and emulsion behavior for ethylbenzene/water/ethanol system. Ethylbenzene that has the equivalent carbon number is used as the model condensate. During this reporting period, work was under way and the electrical conductivity experimental system was set up at the Atlanta University Center. Following the set-up of the emulsion measurement system, the electronic instruments and data acquisition modules involved were tested for proper operation of the system. Then, the conductivity output was normalized with that obtained for 10mM NaCl water. Radial coreflooding experiments with ethanol injection prior to and after water injection were completed to assess the effectiveness of the surfactant flooding in the recovery of condensate by our industrial partner, Surtek, CO, in this reporting period. In Run 1, 10 mM NaCl without ethanol injection recovered 31.5% of the initial ethyl benzene saturation. Injection of ethanol following 10 mM NaCl produced a tertiary ethyl benzene bank with maximum ethyl benzene cuts of 32%. In Run 2, 50 vol% of pure (100%) ethanol was injected and flowed through the Berea sandstone after Ethyl Benzene Saturation. 69% of the initial ethyl benzene was recovered. Results of the radial corefloods are very encouraging. Emulsion conductivity measurements for conjugate pair phases are in progress at Morehouse.

Ramanathan Sampath

2004-09-30

221

Investigation of Phase and Emulsion Behavior, Surfactant Retention and Condensate Recovery for Condensate/Water/Ethanol Mixtures  

SciTech Connect

This semi-annual technical progress report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period October 01, 2002 to April 01, 2003 which covers the first six months of the project. Presently work is in progress to characterize phase and emulsion behavior for condensate/water/ethanol system. Temperature and salinity scans are planned to identify the optimal salinity and temperature, and the temperature and salinity intervals in which all three phases coexist for this system. Test matrix to perform salinity and temperature scans has been established. Supply requests to obtain hydrocarbons, surfactant, etc., were processed and supplies obtained. Current literature in the subject area, and modeling efforts that were established in our previous studies to predict electrical conductivities and inversion phenomena were reviewed. Based on the review a computer model to predict electrical conductivities of the ethylbenzene (that has the equivalent carbon number of the condensate)/water/ethanol system is being developed. These activities resulted in one published conference abstract during this reporting period.

Ramanathan Sampath

2003-03-31

222

Investigation of Phase and Emulsion Behavior, Surfactant Retention and Condensate Recovery for Condensate/Water/Ethanol Mixtures  

SciTech Connect

This semi-annual technical progress report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period October 01, 2004 to March 31, 2005 which covers the fifth six months of the project. Presently work is in progress to characterize phase and emulsion behavior for ethylbenzene/water/ethanol system. Ethylbenzene that has the equivalent carbon number is used as the model condensate. During this reporting period, electrical conductivity measurements for bottom, and top phases, as well as bottom/top, and top/bottom conjugate pair phases of the ethylbenzene/water/ethanol system were performed for various ethanol volume percentage of the mixtures starting from 2% to 60%. Preliminary findings are that electrical conductivity of the bottom phase decreased as ethanol volume fraction of the mixture increased. Conductivity of the top phase was small and remained almost the same for variations in ethanol volume fraction of the mixture. Conductivity of the emulsion of the conjugate pair phases decreased as the fraction of volume of the top phase was increased and vice versa. Also inversion phenomena was observed. Detailed analyses are in progress including the prediction of conductivity data using the theoretical model already developed in this project.

Ramanathan Sampath

2005-03-31

223

Investigation of Phase and Emulsion Behavior, Surfactant Retention and Condensate Recovery for Condensate/Water/Ethanol Mixtures  

SciTech Connect

This semi-annual technical progress report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period April 01, 2005 to September 30, 2005 which covers the sixth six months of the project. Presently work is in progress to characterize phase and emulsion behavior for ethylbenzene/water/ethanol system. Ethylbenzene that has the equivalent carbon number is used as the model condensate. In the last reporting period, electrical conductivity measurements for bottom/top, and top/bottom conjugate pair phases of the ethylbenzene/water/ethanol system were performed for various ethanol volume percentage in the mixture: 2,10,20,33,43,50, and 56. During this reporting period, prediction of electrical conductivity data obtained in the past was conducted employing a theoretical model already developed in this project. Results of the comparisons for 2, and 10% ethanol volume in the mixture are presented here. A good agreement was obtained between the predicted emulsion conductivities and the measured values. To date about 99% of the proposed work has been completed. Conductivity prediction for 56% ethanol volume in the mixture is in progress. Following this prediction, a final report will be developed describing the research activities conducted through the entire project period including results and conclusions.

Ramanathan Sampath

2005-09-30

224

Quantifying colloid retention in partially saturated porous media  

NASA Astrophysics Data System (ADS)

The transport of colloid-contaminant complexes and colloid-sized pathogens through soil to groundwater is of concern. Visualization and quantification of pore-scale colloid behavior will enable better description and simulation of retention mechanisms at individual surfaces, in contrast to breakthrough curves which only provide an integrated signal. We tested two procedures for quantifying colloid movement and retention as observed in pore-scale image sequences. After initial testing with static images, three series of images of synthetic microbead suspensions passing through unsaturated sand were examined. The region procedure (implemented in ImageJ) and the Boolean procedure (implemented in KS400) yielded nearly identical results for initial test images and for total colloid-covered areas in three image series. Because of electronic noise resulting in pixel-level brightness fluctuations the Boolean procedure tended to underestimate attached colloid counts and conversely overestimate mobile colloid counts. The region procedure had a smaller overestimation error of attached colloids. Reliable quantification of colloid retention at pore scale can be used to improve current understanding on the transport mechanisms of colloids in unsaturated porous media. For example, attachment counts at individual air/water meniscus/solid interface were well described by Langmuir isotherms.

Zevi, Yuniati; Dathe, Annette; Gao, Bin; Richards, Brian K.; Steenhuis, Tammo S.

2006-12-01

225

INVESTIGATION OF PHASE AND EMULSION BEHAVIOR, SURFACTANT RETENTION, AND CONDENSATE RECOVERY FOR CONDENSATE/WATER/ETHANOL MIXTURES  

SciTech Connect

This final technical report describes work performed at Morehouse College under DOE Grant No. DE-FG26-02NT15447 during the period October 01, 2002 to September 30, 2005, which covers the total performance period of the project. During this period, work was conducted to characterize phase and emulsion behavior for ethylbenzene/water/ethanol system. Ethylbenzene that has the equivalent carbon number was used as the model condensate. Salinity scans were performed for 0, 5, 10, 20, 50, 100, 250, 500, and 1000 mM salt concentrations at room temperature to identify the optimal salinity and salinity intervals in which all phases coexisted. It was found that only two phases formed, and salinity has no significant effect in the volumes of the phases formed. Experiments were repeated at 30 C and observed salinity has no effect at higher temperatures as well. Following the salinity experiments, measurements were made with 10mM NaCl water for surfactant concentrations from 2 to 70 volume percent at room temperature. It was found that only two phases were formed upto 60 vol% concentration of the surfactant. Above 60 vol% surfactant, the mixture produced only a single phase. Experiments were repeated from 2 to 70 C and observed that temperature has no significant effect on the number of phases formed. At the temperatures and surfactant concentration tested, volume fraction of the aqueous bottom phase was found to be larger than that of the top phase. Electrical conductivity measurements were then conducted for bottom/top, and top/bottom conjugate pair phases of the ethylbenzene/water/ethanol system formed by mixing ethanol at various volume percentages including 2,10,33,and 56% while keeping the volumes of ethylbenzene and water the same in the mixture. Electrical conductivity of the bottom phase decreased as ethanol volume fraction in the mixture increased. Conductivity of the top phase was found small and remained almost the same for variations in ethanol volume fraction in the mixture. Also inversion phenomena was observed. Prediction of the conductivity data obtained was then conducted employing a theoretical model developed in this project based on Maxwell relations. Results of the comparisons for 2, 10, 33, and 56% ethanol volume in the mixture are presented here. A good agreement was obtained between the predicted emulsion conductivities and the measured values. Work was also conducted at Surtek, Golden, CO, our industrial partner in this project, to measure the effectiveness for condensate recovery employing coreflooding techniques. In Run 1 of the radial coreflooding experiments conducted, 10 mM NaCl without ethanol injection recovered 31.5% of the initial ethyl benzene saturation. Injection of ethanol following 10 mM NaCl produced a tertiary ethyl benzene bank with maximum ethyl benzene cuts of 32%. In Run 2, 50 vol% of pure (100%) ethanol was injected and flowed through the Berea sandstone after Ethyl Benzene Saturation. 69% of the initial ethyl benzene was recovered. While 50 vol% of ethanol injection does not make economic sense when injecting a large fraction of a pore volume, injection of sufficient volume to remove water and condensate from around the near well bore area of a gas well could be economic.

Ramanathan Sampath

2005-12-01

226

Transport and retention of multi-walled carbon nanotubes in saturated porous media: effects of input concentration and grain size.  

PubMed

Water-saturated column experiments were conducted to investigate the effect of input concentration (C?) and sand grain size on the transport and retention of low concentrations (1, 0.01, and 0.005 mg L?ą) of functionalized ą?C-labeled multi-walled carbon nanotubes (MWCNT) under repulsive electrostatic conditions that were unfavorable for attachment. The breakthrough curves (BTCs) for MWCNT typically did not reach a plateau, but had an asymmetric shape that slowly increased during breakthrough. The retention profiles (RPs) were not exponential with distance, but rather exhibited a hyper-exponential shape with greater retention near the column inlet. The collected BTCs and RPs were simulated using a numerical model that accounted for both time- and depth-dependent blocking functions on the retention coefficient. For a given C?, the depth-dependent retention coefficient and the maximum solid phase concentration of MWCNT were both found to increase with decreasing grain size. These trends reflect greater MWCNT retention rates and a greater number of retention locations in the finer textured sand. The fraction of the injected MWCNT mass that was recovered in the effluent increased and the RPs became less hyper-exponential in shape with higher C? due to enhanced blocking/filling of retention locations. This concentration dependency of MWCNT transport increased with smaller grain size because of the effect of pore structure and MWCNT shape on MWCNT retention. In particular, MWCNT have a high aspect ratio and we hypothesize that solid phase MWCNT may create a porous network with enhanced ability to retain particles in smaller grain sized sand, especially at higher C?. Results demonstrate that model simulations of MWCNT transport and fate need to accurately account for observed behavior of both BTCs and RPs. PMID:23228890

Kasel, Daniela; Bradford, Scott A; Šim?nek, Ji?í; Heggen, Marc; Vereecken, Harry; Klumpp, Erwin

2013-02-01

227

Field experiments of Controlled Drainage of agricultural clay soils show positive effects on water quantity (retention, runoff) and water quality (nitrate leaching).  

NASA Astrophysics Data System (ADS)

Despite best management practices, agriculture is still facing major challenges to reduce nutrients leaching to the aquatic environment. In deltas, most of total nutrient losses from artificially drained agricultural soils are discharged via drains. Controlled drainage is a promising measure to prevent drainage of valuable nutrients, improve water quality and agricultural yield and adapt to climate change (reduce peak runoff, manage water scarcity and drought). In The Netherlands, this technique has attracted much attention by water managers and farmers alike, yet field studies to determine the expected (positive) effects for Dutch conditions were scarce. Recently, a field experiment was set up on clay soils. Research questions were: how does controlled, subsurface drainage perform on clay soils? Will deeper tile drains function just as well? What are the effects on drain water quality (especially with respect to nitrogen and salt) and crop yield? An agricultural field on clay soils was used to test different tile drainage configurations. Four types of tile drainage systems were installed, all in duplicate: eight plots in total. Each plot has its own outlet to a control box, where equipment was installed to control drain discharge and to measure the flow, concentrations of macro-ions, pH, nitrogen, N-isotopes and heavy metals. In each plot, groundwater observation wells and suction cups are installed in the saturated and vadose zones, at different depths, and crop yield is determined. Four plots discharge into a hydrologic isolated ditch, enabling the determination of water- and nutrient balances. Automatic drain water samplers and innovative nitrate sensors were installed in four plots. These enable identification and unravelling so-called first flush effects (changes in concentrations after a storm event). Water-, chloride- and nitrogen balances have been set up, and the interaction between groundwater and surface water has been quantified. The hydrological processes in the soil have been modelled with simulation model SWAP. The experiment started in 2010 and is ongoing. Data, collected so far show that the plots with controlled drainage (all compared with plots equipped with conventional drainage) conserve more rain water (higher groundwater tables in early spring), lower discharges under average weather conditions and storm events, reduce N-loads and saline seepage to surface waters, enhance denitrification, show a different 'first flush' effect and show similar crop yields. The results of the experiments will contribute to a better understanding of the impact of controlled drainage on complex hydrological en geochemical processes in agricultural clay soils, the interaction between ground- en surface water and its effects on drain water quantity, quality and crop yield.

schipper, peter; stuyt, lodewijk; straat, van der, andre; schans, van der, martin

2014-05-01

228

Effects of Age and Calving Season on Lactation Curves of Milk Production Traits in Italian Water Buffaloes  

Microsoft Academic Search

Test day (TD) records of milk production traits (milk yield, fat, and protein percentages) of 534 Italian buf- falo cows were analyzed with a mixed linear model in order to estimate lactation curves pertaining to differ- ent ages at calving and different seasons of calving. Milk yield lactation curves of younger animals were lower than those of older animals until

G. Catillo; N. P. P. Macciotta; A. Carretta; A. Cappio-Borlino

2002-01-01

229

The effect of dietary carbohydrate composition on apparent total tract digestibility, feed mean retention time, nitrogen and water balance in horses.  

PubMed

A total of four diets with different carbohydrate composition were investigated in a 4×4 Latin square design experiment with four Norwegian Coldblooded trotter horses. The objective of the present study was to increase the fermentable fibre content and reduce the starch intake of the total ration obtained by partly substituting mature hay and barley with sugar beet pulp (SBP), a soluble fibre source. The diets investigated were hay only (HAY), hay (85% of dry matter intake (DMI)) and molassed SBP (15% of DMI) (SBP), hay (68% of DMI) and barley (32% of DMI) (BAR), and hay (68% of DMI), barley (26% of DMI) and SBP (6% of DMI) (BAR+SBP). The feeding level was 18.5, 17.3, 15.7 and 15.7 g DM/kg BW per day for the HAY, SBP, BAR and BAR+SBP diets, respectively. Each diet was fed for 18 days followed by 10 days of data collection, where apparent total tract digestibility (ATTD), total mean retention time (TMRT) of ytterbium-labelled hay, water balance, digestible energy (DE) intake and nitrogen balance were measured. An enzymatic chemical dietary fibre (DF) method was used to get detailed information on the composition and ATTD of the fibre fraction. Inclusion of SBP in the diet increased the ATTD of the constituent sugars galactose and arabinose (P<0.01). Feeding the HAY and SBP diets resulted in a lower TMRT owing to a higher DF intake than the BAR and BAR+SBP diets (P<0.01). There was no difference in water intake between HAY and SBP, but faecal dry matter was lower for HAY than the other diets (P=0.017), indicating that water was more tightly bound to fibre in the HAY diet. The diets were iso-energetic and provided enough DE and protein for light to moderate exercise for a 550 kg horse. In conclusion, this study showed that the DF intake had a larger effect on TMRT than partly substituting hay or barley with SBP, and that highly fermentable pectin-rich soluble DF from SBP maintains high nutrient utilization in horses. PMID:25018093

Jensen, R B; Austbř, D; Bach Knudsen, K E; Tauson, A-H

2014-11-01

230

Optimized Delivery System Achieves Enhanced Endomyocardial Stem Cell Retention  

PubMed Central

Background Regenerative cell-based therapies are associated with limited myocardial retention of delivered stem cells. The objective of this study is to develop an endocardial delivery system for enhanced cell retention. Methods and Results Stem cell retention was simulated in silico using one and three-dimensional models of tissue distortion and compliance associated with delivery. Needle designs, predicted to be optimal, were accordingly engineered using nitinol – a nickel and titanium alloy displaying shape memory and super-elasticity. Biocompatibility was tested with human mesenchymal stem cells. Experimental validation was performed with species-matched cells directly delivered into Langendorff-perfused porcine hearts or administered percutaneously into the endocardium of infarcted pigs. Cell retention was quantified by flow cytometry and real time quantitative polymerase chain reaction methodology. Models, computing optimal distribution of distortion calibrated to favor tissue compliance, predicted that a 75°-curved needle featuring small-to-large graded side holes would ensure the highest cell retention profile. In isolated hearts, the nitinol curved needle catheter (C-Cath) design ensured 3-fold superior stem cell retention compared to a standard needle. In the setting of chronic infarction, percutaneous delivery of stem cells with C-Cath yielded a 37.7±7.1% versus 10.0±2.8% retention achieved with a traditional needle, without impact on biocompatibility or safety. Conclusions Modeling guided development of a nitinol-based curved needle delivery system with incremental side holes achieved enhanced myocardial stem cell retention. PMID:24326777

Behfar, Atta; Latere, Jean-Pierre; Bartunek, Jozef; Homsy, Christian; Daro, Dorothee; Crespo-Diaz, Ruben J.; Stalboerger, Paul G.; Steenwinckel, Valerie; Seron, Aymeric; Redfield, Margaret M.; Terzic, Andre

2014-01-01

231

Control of ice chromatographic retention mechanism by changing temperature and dopant concentration.  

PubMed

A liquid phase coexists with solid water ice in a typical binary system, such as NaCl-water, in the temperature range between the freezing point and the eutectic point (t(eu)) of the system. In ice chromatography with salt-doped ice as the stationary phase, both solid and liquid phase can contribute to solute retention in different fashions; that is, the solid ice surface acts as an adsorbent, while a solute can be partitioned into the liquid phase. Thus, both adsorption and partition mechanisms can be utilized for ice chromatographic separation. An important feature in this approach is that the liquid phase volume can be varied by changing the temperature and the concentration of a salt incorporated into the ice stationary phase. Thus, we can control the relative contribution from the partition mechanism in the entire retention because the liquid phase volume can be estimated from the freezing depression curve. Separation selectivity can thereby be modified. The applicability of this concept has been confirmed for the solutes of different adsorption and partition abilities. The predicted retention based on thermodynamics basically agrees well with the corresponding experimental retention. However, one important inconsistency has been found. The calculation predicts a step-like discontinuity of the solute retention at t(eu) because the phase diagram suggests that the liquid phase abruptly appears at t(eu) when the temperature increases. In contrast, the corresponding experimental plots are continuous over the wider range including the subeutectic temperatures. This discrepancy is explained by the existence of the liquid phase below t(eu). A difference between predicted and measured retention factors allows the estimation of the volume of the subeutectic liquid phase. PMID:22053829

Tasaki, Yuiko; Okada, Tetsuo

2011-12-15

232

9 CFR 441.10 - Retained water.  

Code of Federal Regulations, 2013 CFR

...determine the amount or percentage of water absorption and retention that is unavoidable using...describe variable factors that affect water absorption and retention. In poultry processing...Additional factors that may affect water absorption and retention are scalding...

2013-01-01

233

9 CFR 441.10 - Retained water.  

Code of Federal Regulations, 2011 CFR

...determine the amount or percentage of water absorption and retention that is unavoidable using...describe variable factors that affect water absorption and retention. In poultry processing...Additional factors that may affect water absorption and retention are scalding...

2011-01-01

234

9 CFR 441.10 - Retained water.  

Code of Federal Regulations, 2014 CFR

...determine the amount or percentage of water absorption and retention that is unavoidable using...describe variable factors that affect water absorption and retention. In poultry processing...Additional factors that may affect water absorption and retention are scalding...

2014-01-01

235

9 CFR 441.10 - Retained water.  

Code of Federal Regulations, 2010 CFR

...determine the amount or percentage of water absorption and retention that is unavoidable using...describe variable factors that affect water absorption and retention. In poultry processing...Additional factors that may affect water absorption and retention are scalding...

2010-01-01

236

9 CFR 441.10 - Retained water.  

Code of Federal Regulations, 2012 CFR

...determine the amount or percentage of water absorption and retention that is unavoidable using...describe variable factors that affect water absorption and retention. In poultry processing...Additional factors that may affect water absorption and retention are scalding...

2012-01-01

237

Biochar from Sugarcane Filtercake Reduces Soil CO2 Emissions Relative to Raw Residue and Improves Water Retention and Nutrient Availability in a Highly-Weathered Tropical Soil  

PubMed Central

In Brazil, the degradation of nutrient-poor Ferralsols limits productivity and drives agricultural expansion into pristine areas. However, returning agricultural residues to the soil in a stabilized form may offer opportunities for maintaining or improving soil quality, even under conditions that typically promote carbon loss. We examined the use of biochar made from filtercake (a byproduct of sugarcane processing) on the physicochemical properties of a cultivated tropical soil. Filtercake was pyrolyzed at 575°C for 3 h yielding a biochar with increased surface area and porosity compared to the raw filtercake. Filtercake biochar was primarily composed of aromatic carbon, with some residual cellulose and hemicellulose. In a three-week laboratory incubation, CO2 effluxes from a highly weathered Ferralsol soil amended with 5% biochar (dry weight, d.w.) were roughly four-fold higher than the soil-only control, but 23-fold lower than CO2 effluxes from soil amended with 5% (d.w.) raw filtercake. We also applied vinasse, a carbon-rich liquid waste from bioethanol production typically utilized as a fertilizer on sugarcane soils, to filtercake- and biochar-amended soils. Total CO2 efflux from the biochar-amended soil in response to vinasse application was only 5% of the efflux when vinasse was applied to soil amended with raw filtercake. Furthermore, mixtures of 5 or 10% biochar (d.w.) in this highly weathered tropical soil significantly increased water retention within the plant-available range and also improved nutrient availability. Accordingly, application of sugarcane filtercake as biochar, with or without vinasse application, may better satisfy soil management objectives than filtercake applied to soils in its raw form, and may help to build soil carbon stocks in sugarcane-cultivating regions. PMID:24897522

Eykelbosh, Angela Joy; Johnson, Mark S.; Santos de Queiroz, Edmar; Dalmagro, Higo José; Guimarăes Couto, Eduardo

2014-01-01

238

Curved Mirrors  

NSDL National Science Digital Library

This inquiry activity will be used before discussing curved mirrors in class. Students will discover how curved mirrors act and how the size and the orientation of the image are related to the distance from the mirror. Ray diagrams for curved mirrors are

Michael Horton

2009-05-30

239

An Analytical Method for Deriving Reservoir Operation Curves to Maximize Social Benefits from Multiple Uses of Water in the Willamette River Basin  

NASA Astrophysics Data System (ADS)

A central characteristic of large river basins in the western US is the spatial and temporal disjunction between the supply of and demand for water. Water sources are typically concentrated in forested mountain regions distant from municipal and agricultural water users, while precipitation is super-abundant in winter and deficient in summer. To cope with these disparities, systems of reservoirs have been constructed throughout the West. These reservoir systems are managed to serve two main competing purposes: to control flooding during winter and spring, and to store spring runoff and deliver it to populated, agricultural valleys during the summer. The reservoirs also provide additional benefits, including recreation, hydropower and instream flows for stream ecology. Since the storage capacity of the reservoirs cannot be used for both flood control and storage at the same time, these uses are traded-off during spring, as the most important, or dominant use of the reservoir, shifts from buffering floods to storing water for summer use. This tradeoff is expressed in the operations rule curve, which specifies the maximum level to which a reservoir can be filled throughout the year, apart from real-time flood operations. These rule curves were often established at the time a reservoir was built. However, climate change and human impacts may be altering the timing and amplitude of flood events and water scarcity is expected to intensify with anticipated changes in climate, land cover and population. These changes imply that reservoir management using current rule curves may not match future societal values for the diverse uses of water from reservoirs. Despite a broad literature on mathematical optimization for reservoir operation, these methods are not often used because they 1) simplify the hydrologic system, raising doubts about the real-world applicability of the solutions, 2) exhibit perfect foresight and assume stationarity, whereas reservoir operators face uncertainty and risk daily, and 3) require complex computer programming. The proposed research addresses these critiques by pursuing a novel approach - the development of an analytical method to demonstrate how reservoir management could adapt to anticipated changes in water supply and demand, which incorporates some of the complexity of the hydrologic system, includes stochasticity, and can be readily implemented. Employing a normative economic framework of social welfare maximization, the research will 1) estimate the social benefits associated with reservoir uses, 2) analytically derive conditions for maximizing the benefits of reservoir operation, and 3) estimate the resulting optimal operating rules under future trajectories of climate, land cover, and population. The findings of this analysis will be used to address the following research questions: 1) How do the derived optimal operating rules compare to the existing rule curves? 2) How does the shape of the derived rule curves change under different scenarios of global change? 3) What is the change in net social benefits resulting from the use of these derived rule curves as compared to existing rule curves? 4) To the extent possible, what are the distributional and social justice implications of the derived changes in the rule curves?

Moore, K. M.; Jaeger, W. K.; Jones, J. A.

2013-12-01

240

Parametric Curves parametric curves (Splines)  

E-print Network

curves (Splines) · polygonal meshes #12;2 Roller coaster · Next programming assignment involves creating a 3D roller coaster animation · We must model the 3D curve describing the roller coaster, but how

Treuille, Adrien

241

A Nonparametric Instrumental Variable Approach to Estimating the Environmental Kuznets Curve for Water Pollutants at the Global Level1  

E-print Network

for Water Pollutants at the Global Level1 C.-Y. Cynthia Lin,2 Krishna P. Paudel, Mahesh Pandit for Water Pollutants at the Global Level Abstract We examine the relationship between income and water pollutants using country- level global water quality data over the period 1980 to 2012. We include civil

Lin, C.-Y. Cynthia

242

Quantum Curves  

NASA Astrophysics Data System (ADS)

One says that a pair (P, Q) of ordinary differential operators specify a quantum curve if {[P,Q]=hbar} . If a pair of difference operators (K, L) obey the relation KL = q LK, where {q =e^{hbar}} , we say that they specify a discrete quantum curve. This terminology is prompted by well known results about commuting differential and difference operators, relating pairs of such operators with pairs of meromorphic functions on algebraic curves obeying some conditions. The goal of this paper is to study the moduli spaces of quantum curves. We will relate the moduli spaces for different {hbar} . We will show how to quantize a pair of commuting differential or difference operators (i.e., to construct the corresponding quantum curve or discrete quantum curve).

Schwarz, Albert

2015-02-01

243

Lance water injection tests adjacent to the 281-3H retention basin at the Savannah River Site, Aiken, South Carolina  

SciTech Connect

A pilot-scale field demonstration of waste isolation using viscous- liquid containment barriers has been planned for the 281-3H retention basin at the Savannah River Site, Aiken, SC. The 281-3H basin is a shallow retention/seepage basin contaminated mainly by radionuclides. The viscous-liquid containment barrier utilizes the permeation of liquid grout to either entomb the contaminants within a monolithic grout structure or to isolate the waste by drastically reducing the permeability, of the soils around the plume. A clear understanding of the hydrogeologic setting of the retention basin is necessary for proper design of the viscous liquid barrier. To aid in the understanding of the hydrogeology of the 281-3H retention basin, and to obtain critical parameters necessary for grout injection design, a series of tests were undertaken in a region immediately adjacent to the basin. The objectives of the LWIT were: 1. To evaluate the general performance of the Lance Injection Technique for grout emplacement at the site, including the range and upper limits of injection pressures, the flow rates applicable for site conditions, as well as the mechanical forces needed for lance penetration. 2. To obtain detailed information on the injectability of the soils immediately adjacent to the H-area retention basin. 3. To identify any high permeability zones suitable for injection and evaluate their spatial distribution. 4. To perform ground penetrating radar (GPR) to gain information on the structure of the soil column and to compare the results with LWIT data. This report will focus on results pertinent to these objectives.

Freifeld, B.; Myer, L.; Moridis, G.; Cook, P.; James, A.; Pellerin, L.; Pruess, K.

1996-09-01

244

Assessing Chemical Retention Process Controls in Ponds  

NASA Astrophysics Data System (ADS)

Small ponds are a ubiquitous component of the landscape and have earned a reputation as effective chemical retention devices. The most common characterization of pond chemical retention is the retention coefficient, Ri= ([Ci]inflow-[Ci] outflow)/[Ci]inflow. However, this parameter varies widely in one pond with time and among ponds. We have re-evaluated literature reported (Borden et al., 1998) monthly average retention coefficients for two ponds in North Carolina. Employing a simple first order model that includes water residence time, the first order process responsible for species removal have been separated from the water residence time over which it acts. Assuming the rate constant for species removal is constant within the pond (arguable at least), the annual average rate constant for species removal is generated. Using the annual mean rate constant for species removal and monthly water residence times results in a significantly enhanced predictive capability for Davis Pond during most months of the year. Predictive ability remains poor in Davis Pond during winter/unstratified periods when internal loading of P and N results in low to negative chemical retention. Predictive ability for Piedmont Pond (which has numerous negative chemical retention periods) is improved but not to the same extent as Davis Pond. In Davis Pond, the rate constant for sediment removal (each month) is faster than the rate constant for water and explains the good predictability for sediment retention. However, the removal rate constant for P and N is slower than the removal rate constant for sediment (longer water column residence time for P,N than for sediment). Thus sedimentation is not an overall control on nutrient retention. Additionally, the removal rate constant for P is slower than for TOC (TOC is not the dominate removal process for P) and N is removed slower than P (different in pond controls). For Piedmont Pond, sediment removal rate constants are slower than the removal rate constant for water indicating significant sediment resuspension episodes. It appears that these sediment resuspension events are aperiodic and control the loading and the chemical retention capability of Piedmont Pond for N,P,TOC. These calculated rate constants reflect the differing internal loading processes for each component and suggest means and mechanisms for the use of ponds in water quality management.

Torgersen, T.; Branco, B.; John, B.

2002-05-01

245

Gradient retention prediction of acid-base analytes in reversed phase liquid chromatography: a simplified approach for acetonitrile-water mobile phases.  

PubMed

In previous work, a two-parameter model to predict chromatographic retention of ionizable analytes in gradient mode was proposed. However, the procedure required some previous experimental work to get a suitable description of the pKa change with the mobile phase composition. In the present study this previous experimental work has been simplified. The analyte pKa values have been calculated through equations whose coefficients vary depending on their functional group. Forced by this new approach, other simplifications regarding the retention of the totally neutral and totally ionized species also had to be performed. After the simplifications were applied, new prediction values were obtained and compared with the previously acquired experimental data. The simplified model gave pretty good predictions while saving a significant amount of time and resources. PMID:25454137

Andrés, Axel; Rosés, Martí; Bosch, Elisabeth

2014-11-28

246

Light Curves  

NSDL National Science Digital Library

This is a game about light curves that will test your ability to figure out things about an asteroid from just a graph of its brightness. Astronomers use telescopes to collect light curves - measurements of the brightness of distant asteroids over time. It is part of the Killer Asteroids Web Site. The site also features a background overview of the differences between asteroids and comets, information on different types of asteroids (rubble piles vs monoliths), a discussion of how at risk Earth really is to an asteroid or comet impact, and background information on light curves.

2013-02-12

247

Drug Retention Times  

SciTech Connect

The purpose of this monograph is to provide information on drug retention times in the human body. The information provided is based on plausible illegal drug use activities that might be engaged in by a recreational drug user.

Center for Human Reliability Studies

2007-05-01

248

Drug Retention Times  

SciTech Connect

The purpose of this monograph is to provide information on drug retention times in the human body. The information provided is based on plausible illegal drug use activities that might be engaged in by a recreational drug user

Center for Human Reliability Studies

2007-05-01

249

A technique to minimize uncertainties in load duration curves (LDCs) for water quality-impaired ungauged sites  

EPA Science Inventory

For many water quality-impaired stream segments, streamflow and water quality monitoring sites are not available. Lack of available streamflow data at impaired ungauged sites leads to uncertainties in total maximum daily load (TMDL) estimation. We developed a technique to minimiz...

250

Climate Change Adaptation in the Western U.S.: the Case for Dynamic Rule Curves in Water Resources Management  

Microsoft Academic Search

Climate change in the Western U.S. will bring systematic hydrologic changes affecting many water resources systems. Successful adaptation to these changes, which will be ongoing through the 21st century, will require the 'rebalancing' of competing system objectives such as water supply, flood control, hydropower production, and environmental services in response to hydrologic (and other) changes. Although fixed operating policies for

S. Lee; A. F. Hamlet; S. J. Burges

2008-01-01

251

Controlling suction by vapour equilibrium technique at different temperatures, application to the determination of the water  

E-print Network

1 Controlling suction by vapour equilibrium technique at different temperatures, application-mail : cui@cermes.enpc.fr #12;2 Controlling suction by vapour equilibrium technique at different temperatures, very often, a temperature independent water retention curve is considered in the analysis, which

Paris-Sud XI, Université de

252

Chemical retention during dry growth riming  

Microsoft Academic Search

Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversion of liquid water to ice in clouds can impact distributions of chemicals in precipitation and in the poststorm troposphere. In this paper, we extend a theoretical scaling model of chemical retention during hydrometeor freezing to all dry growth riming conditions. We account for spreading of drops

A. L. Stuart; M. Z. Jacobson

2004-01-01

253

Stress-Strain Curves of Adsorbed Protein Layers at the Air\\/Water Interface Measured with Surface Shear Rheology  

Microsoft Academic Search

Interfacial shear properties of adsorbed protein layers at the air\\/water interface were determined using a Couette-type surface shear rheometer. Such experiments are often used to determine a steady-state ratio between stress and rate of strain, which is then denoted as \\

A. H. Martin; M. A. Bos; M. A. Cohen Stuart; T. van Vliet

2002-01-01

254

DEVELOPMENT OF DURATION-CURVE BASED METHODS FOR QUALIFYING VARIABILITY AND CHANGE IN WATERSHED HYDROLOGY AND WATER QUALITY  

EPA Science Inventory

During the past decades, U.S. Environmental Protection Agency (EPA), U.S. Department of Agriculture (USDA) and other Federal program administrative and regulatory agencies spent considerable amounts of time and money to manage risks to surface waters associated with agricultural ...

255

Curved Knives  

Microsoft Academic Search

IT may interest your correspondent, Dr. Otis T. Mason, to know that the curved ``drawing-knife'' described by him has representatives in Western (British) India. The Kolis (fishing races) of the Bombay coast wore lately, and some still wear, knives made by local blacksmiths, of which the blade, 2 to 3 inches long, was shaped and edged like that of an

W. F. Sinclair

1897-01-01

256

Stubble retention and nitrogen fertilisation in a fallow-wheat rainfed cropping system. 1. Soil water and nitrogen conservation, crop growth and yield  

Microsoft Academic Search

In semi-arid environments where water supply is the factor usually limiting grain yield, fallowing provides a way to increase water and nitrogen supply. An experiment was maintained from 1980 to 1990 at the Wimmera Research Station, Dooen, Australia. In each year, water use, growth and yield of wheat (Triticum aestivum L.) were measured following three tillage methods of year-long fallow.

C. Cantero-Martinez; G. J. O'Leary; D. J. Connor

1995-01-01

257

Uncertainty analysis of transport of water and pesticide in an unsaturated layered soil profile using fuzzy set theory  

Microsoft Academic Search

Incomplete information is notoriously common in planning soil and groundwater remediation. For making decisions groundwater flow and transport models are commonly used. However, uncertainty in prediction arises due to imprecise information on flow and transport parameters like saturated\\/unsaturated hydraulic conductivity, water retention curve parameters, precipitation and evapo-transpiration rates as well as factors governing the fate of pollutant in soil like

P. Verma; P. Singh; K. V. George; H. V. Singh; S. Devotta; R. N. Singh

2009-01-01

258

Biofilm Roughness Determines Cryptosporidium parvum Retention in Environmental Biofilms  

PubMed Central

The genus Cryptosporidium is a group of waterborne protozoan parasites that have been implicated in significant outbreaks of gastrointestinal infections throughout the world. Biofilms trap these pathogens and can contaminate water supplies through subsequent release. Biofilm microbial assemblages were collected seasonally from three streams in eastern Pennsylvania and used to grow biofilms in laboratory microcosms. Daily oocyst counts in the influx and efflux flow allowed the calculation of daily oocyst retention in the biofilm. Following the removal of oocysts from the influx water, oocyst attachment to the biofilm declined to an equilibrium state within 5 days that was sustained for at least 25 days. Varying the oocyst loading rate for the system showed that biofilm retention could be saturated, suggesting that discrete binding sites determined the maximum number of oocysts retained. Oocyst retention varied seasonally but was consistent across all three sites; however, seasonal oocyst retention was not consistent across years at the same site. No correlation between oocyst attachment and any measured water quality parameter was found. However, oocyst retention was strongly correlated with biofilm surface roughness and roughness varied among seasons and across years. We hypothesize that biofilm roughness and oocyst retention are dependent on environmentally driven changes in the biofilm community rather than directly on water quality conditions. It is important to understand oocyst transport dynamics to reduce risks of human infection. Better understanding of factors controlling biofilm retention of oocysts should improve our understanding of oocyst transport at different scales. PMID:22492449

Hargreaves, B. R.; Jellison, K. L.

2012-01-01

259

Data protection — retention policies  

Microsoft Academic Search

A data retention policy is a bit of an enigmatic beast. Everyone knows what it is, and most companies recognize that it is vital to have a policy in place but what should it look like? What should be included in the policy and how much detail is required?

Rowan Middleton; Herbert Smith

2003-01-01

260

Three Exemplary Retention Programs.  

ERIC Educational Resources Information Center

Describes three retention programs for regularly admitted students of color. Outlines each program's history and inception; its funding, staffing, and facilities; how the program has become institutionalized and marketed. The key components of the program and assessment of program effectiveness are presented, as well as the crises encountered and…

Carreathers, Kevin R.; And Others

1996-01-01

261

Secrets of Retention  

ERIC Educational Resources Information Center

Recruiting students is one thing, but keeping them in a chorus, orchestra, or band is another. Although a music director has no control over some variables, there is much that can be done to help students to stay. Several experts share their advice on retention. One expert said a teacher's own attitude and classroom strategies may be two of the…

Poliniak, Susan

2012-01-01

262

Data Show Retention Disparities  

ERIC Educational Resources Information Center

New nationwide data collected by the U.S. Department of Education's civil rights office reveal stark racial and ethnic disparities in student retentions, with black and Hispanic students far more likely than white students to repeat a grade, especially in elementary and middle school. The contrast is especially strong for African-Americans. In the…

Adams, Caralee J.; Robelen, Erik W.; Shah, Nirvi

2012-01-01

263

QSPR models of boiling point, octanolwater partition coefficient and retention time index of polycyclic aromatic hydrocarbons  

E-print Network

QSPR models of boiling point, octanol­water partition coefficient and retention time index) is presented. Three physicochemical properties related to their environmental impact are studied: boiling point

Ferreira, Márcia M. C.

264

Mobile Learning and Student Retention  

ERIC Educational Resources Information Center

Student retention in open and distance learning (ODL) is comparatively poor to traditional education and, in some contexts, embarrassingly low. Literature on the subject of student retention in ODL indicates that even when interventions are designed and undertaken to improve student retention, they tend to fall short. Moreover, this area has not…

Fozdar, Bharat Inder; Kumar, Lalita S.

2007-01-01

265

Curved Space or Curved Vacuum?  

E-print Network

While the simple picture of a spatially flat, matter plus cosmological constant universe fits current observation of the accelerated expansion, strong consideration has also been given to models with dynamical vacuum energy. We examine the tradeoff of ``curving'' the vacuum but retaining spatial flatness, vs. curving space but retaining the cosmological constant. These different breakdowns in the simple picture could readily be distinguished by combined high accuracy supernovae and cosmic microwave background distance measurements. If we allow the uneasy situation of both breakdowns, the curvature can still be measured to 1%, but at the price of degrading estimation of the equation of state time variation by 60% or more, unless additional information (such as weak lensing data or a tight matter density prior) is included.

Eric V. Linder

2005-10-11

266

Colloidal particle transport in unsaturated porous media: Influence of flow velocity and ionic strength on colloidal particle retention  

NASA Astrophysics Data System (ADS)

Recently, anthropogenic colloidal particles are increasingly present into the environment. They can carry contaminants or constitute themselves a risk for the environment. Several factors can influence the fate of colloidal particles in soils. This work presents the investigation of effects of flow velocity and ionic strength on colloidal particles retention in unsaturated porous media. Experiments were carried out in laboratory column (D = 10 cm, L = 30 cm) with compacted mixture sand-gravel from a fluvioglacial basin of Lyon, France. Fluorescents nanoparticles (D = 50 to 60 nm) of silica doped with fluorescent organic molecules (fluorescein) have been used to simulate colloid particle transport. A solution of a non-reactive tracer, Br-, was used to determine the water flow behavior. Three different unsaturated water flow velocities (i.e. V = 0.025, 0.064 and 0.127 cm/min) and five ionic strengths (i.e. IS = 1, 5, 50, 100 and 200 mM at pH=8.5) have been tested for the case of a pulse injection of a colloidal particle solution at a concentration of 2 mg/L. Breakthrough curves are modeled by the non-equilibrium transfer model MIM (mobile and immobile water fraction), taking into account a sink term to reflect the colloidal particles adsorption. Results show that, when the flow velocity increases, the colloidal particle retention decreases. The decrease in flow velocity allows a better homogenization of the flow. In addition, colloidal entrapment is favored by the fact that their pore velocity is reduced. The retention of colloidal particle is function of ionic strength as well. Indeed, when the ionic strength increases, the retention increases. However for ionic strength higher than 50 mM, the retention decreases suggesting that there is a threshold value for the ionic strength with respect to the retention of colloidal particles. The retention profiles at the end of experiments indicate that the colloidal particles are retained at the inlet of the columns. Experimental and simulation results can be used to understand the mechanisms that are responsible for the transfer of colloidal particles in the environment and then to improve remediation techniques for contaminated soils. Keys words: colloidal particles, flow velocity, ionic strength, unsaturated soil

Predelus, Dieuseul; Coutinho, Paiva Artur; Lassabatere, Laurent; Winiarsky, Thierry; Angulo Jaramillo, Rafael

2014-05-01

267

Curved microchannels and bacterial streamers  

NASA Astrophysics Data System (ADS)

Bacterial biofilms are commonly identified as microbial communities attached to a surface and encased in a self-secreted extracellular matrix. Due to their increased resistance to antimicrobial agents, biofilms have an enormous impact on health and medicine (e.g., wound healing, implant-associated infections, disease transmission). On the other hand, they constitute a major component of the stream ecosystem by increasing transport of nutrients and retention of suspended particles. In this talk, we present an experimental study of bacterial biofilm development in a microfluidic device. In particular, we show the formation of filamentous structures, or streamers, in curved channels and how these suspended biofilms are linked to the underlying hydrodynamics.

Rusconi, Roberto; Lecuyer, Sigolene; Guglielmini, Laura; Stone, Howard

2010-03-01

268

Automated headspace-solid-phase micro extraction-retention time locked-isotope dilution gas chromatography-mass spectrometry for the analysis of organotin compounds in water and sediment samples.  

PubMed

An automated method for the simultaneous determination of six important organotin compounds namely monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TPhT) in water and sediment samples is described. The method is based on derivatization with sodium tetraethylborate followed by automated headspace-solid-phase micro extraction (SPME) combined with GC-MS under retention time locked (RTL) conditions. Home-synthesized deuterated organotin analogues were used as internal standards. Two high abundant fragment ions corresponding to the main tin isotopes Sn118 and Sn120 were chosen; one for quantification and one as qualifier ion. The method was validated and excellent figures of merit were obtained. Limits of quantification (LOQs) are from 1.3 to 15 ng l(-1) (ppt) for water samples and from 1.0 to 6.3 microg kg(-1) (ppb) for sediment samples. Accuracy for sediment samples was tested on spiked real-life sediment samples and on a reference PACS-2 marine harbor sediment. The developed method was used in a case-study at the harbor of Antwerp where sediment samples in different areas were taken and subsequently screened for TBT contamination. Concentrations ranged from 15 microg kg(-1) in the port of Antwerp up to 43 mg kg(-1) near a ship repair unit. PMID:16038329

Devosa, Christophe; Vliegen, Maarten; Willaert, Bart; David, Frank; Moens, Luc; Sandra, Pat

2005-06-24

269

An ATP-binding cassette subfamily G full transporter is essential for the retention of leaf water in both wild barley and rice  

PubMed Central

Land plants have developed a cuticle preventing uncontrolled water loss. Here we report that an ATP-binding cassette (ABC) subfamily G (ABCG) full transporter is required for leaf water conservation in both wild barley and rice. A spontaneous mutation, eibi1.b, in wild barley has a low capacity to retain leaf water, a phenotype associated with reduced cutin deposition and a thin cuticle. Map-based cloning revealed that Eibi1 encodes an HvABCG31 full transporter. The gene was highly expressed in the elongation zone of a growing leaf (the site of cutin synthesis), and its gene product also was localized in developing, but not in mature tissue. A de novo wild barley mutant named “eibi1.c,” along with two transposon insertion lines of rice mutated in the ortholog of HvABCG31 also were unable to restrict water loss from detached leaves. HvABCG31 is hypothesized to function as a transporter involved in cutin formation. Homologs of HvABCG31 were found in green algae, moss, and lycopods, indicating that this full transporter is highly conserved in the evolution of land plants. PMID:21737747

Chen, Guoxiong; Komatsuda, Takao; Ma, Jian Feng; Nawrath, Christiane; Pourkheirandish, Mohammad; Tagiri, Akemi; Hu, Yin-Gang; Sameri, Mohammad; Li, Xinrong; Zhao, Xin; Liu, Yubing; Li, Chao; Ma, Xiaoying; Wang, Aidong; Nair, Sudha; Wang, Ning; Miyao, Akio; Sakuma, Shun; Yamaji, Naoki; Zheng, Xiuting; Nevo, Eviatar

2011-01-01

270

ENHANCED RETENTION AND SENSITIVITY IN THE ANALYSIS OF CYANURIC ACID IN WATER USING POROUS GRAPHITIC CARBON AND UV DETECTION IN HPLC  

EPA Science Inventory

Cyanuric acid (CA) has found application as a chlorine stabilizer in pool waters. The National Swimming Pool Foundation recommends CA levels between 30-50 ppm and a chlorine residual of 1.0-3.0 ppm. These chlorine levels are needed to destroy harmful pathogenic organisms. Develo...

271

ENHANCED RETENTION AND SENSITIVITY IN THE ANALYSIS OF CYANURIC ACID IN WATER USING POROUS GRAPHITIC CARBON AND UV DETECTION IN HIGH PRESSURE LIQUID CHROMATOGRAPHY  

EPA Science Inventory

Cyanuric acid (CA) has found application as a chlorine stabilizer in pool waters. The National Swimming Pool Foundation recommends CA levels between 30-50 ppm and a chlorine residual of 1.0-3.0 ppm. These chlorine levels are needed to destroy harmful pathogenic organisms. Develo...

272

Hyperexponential and nonmonotonic retention of polyvinylpyrrolidone-coated silver nanoparticles in an Ultisol  

NASA Astrophysics Data System (ADS)

The increasing application of engineered nanoparticles (ENPs) has heightened the concern that these ENPs would eventually be released to the environment and may enter into life cycle of living beings. In this regard, it is essential to understand how these ENPs transport and retain in natural soils because they are considered to be a major repository for ENPs. Herein, transport and retention of polyvinylpyrrolidone (PVP)-coated silver nanoparticles (PVP-AgNPs) were investigated over a wide range of physicochemical factors in water-saturated columns packed with an Ultisol rich in clay-size particles. Higher mobility of PVP-AgNPs occurred at larger soil grain size, lower solution ionic strength and divalent cation concentration, higher flow rate, and greater PVP concentrations. Most breakthrough curves (BTCs) for PVP-AgNPs exhibited significant amounts of retardation in the soil due to its large surface area and quantity of retention sites. In contrast to colloid filtration theory, the shapes of retention profiles (RPs) for PVP-AgNPs were either hyperexponential or nonmonotonic (a peak in particle retention down-gradient from the column inlet). The BTCs and hyperexponential RPs were successfully described using a 1-species model that considered time- and depth-dependent retention. Conversely, a 2-species model that included reversibility of retained PVP-AgNPs had to be employed to better simulate the BTCs and nonmonotonic RPs. As the retained concentration of species 1 approached the maximum solid-phase concentration, a second mobile species (species 2, i.e., the same PVP-AgNPs that are reversibly retained) was released that could be retained at a different rate than species 1 and thus yielded the nonmonotonic RPs. Some retained PVP-AgNPs were likely to irreversibly deposit in the primary minimum associated with microscopic chemical heterogeneity (favorable sites). Transmission electron microscopy and energy-dispersive X-ray spectroscopy analysis suggested that these favorable sites were positively charged sites on montmorillonite edges and goethite surfaces in the soil. Overall, our study highlights that the transport and especially retention of PVP-AgNPs are highly sensitive to the physicochemical factors, but mathematical modeling can accurately predict the fate of these ENPs in porous media which is important for better understanding the fate of these ENPs in point of exit and in the environment.

Wang, Dengjun; Ge, Liqiang; He, Jianzhou; Zhang, Wei; Jaisi, Deb P.; Zhou, Dongmei

2014-08-01

273

Nutrient retention in plant biomass and sediments from the salt marsh in Hangzhou Bay estuary, China.  

PubMed

Nutrient load into the ocean can be retained during the process of plant uptake and sedimentation in marshes along the bay zone. Seasonal variations of biomass and nutrient concentration in three dominated plant assemblages and associated sediments were monitored in this study area to determine effects of salt marsh on nutrient retention. Results showed that plant aboveground biomass displayed a unimodal curve with nutrient concentration generally decreased from spring to winter. Belowground biomass was relatively low during the rapid growth period with nutrient concentration tending to decrease and then increase during this period. Plant total nitrogen (TN) pools are higher than total phosphorus (TP) pools, and both pools showed significant seasonal variations. Water purification coefficients (WPC) of nutrients by plant assimilation were 34.4/17.3, 19.3/24.0, and 5.14/6.04 t/(m(2) year) (TN/TP) for Phragmites australis, Spartina alterniflora, and Scirpus mariqueter, respectively. Overall, these results suggest that higher annual plant biomass and nutrient assimilation contribute to greater nutrient retention capacity and accumulation in sediments, thereby enabling reduced eutrophication in transitional waters. PMID:23589271

Shao, Xuexin; Wu, Ming; Gu, Binhe; Chen, Yinxu; Liang, Xinqiang

2013-09-01

274

Selenide retention by mackinawite.  

PubMed

The isotope (79)Se may be of great concern with regard to the safe disposal of nuclear wastes in deep geological repositories due to its long half-life and potential mobility in the geosphere. The Se mobility is controlled by the oxidation state: the oxidized species (Se(IV)) and (Se(VI)) are highly mobile, whereas the reduced species (Se(0) and Se(-II)) form low soluble solids. The mobility of this trace pollutant can be greatly reduced by interacting with the various barriers of the repository. Numerous studies report on the oxidized species retention by mineral phases, but only very scarce studies report on the selenide (Se(-II)) retention. In the present study, the selenide retention by coprecipitation with and by adsorption on mackinawite (FeS) was investigated. XRD and SEM analyses of the samples reveal no significant influence of Se on the mackinawite precipitate morphology and structure. Samples from coprecipitation and from adsorption are characterized at the molecular scale by a multi-edge X-ray absorption spectroscopy (XAS) investigation. In the coprecipitation experiment, all elements (S, Fe, and Se) are in a low ionic oxidation state and the EXAFS data strongly point to selenium located in a mackinawite-like sulfide environment. By contacting selenide ions with FeS in suspension, part of Se is located in an environment similar to that found in the coprecipitation experiment. The explanation is a dynamical dissolution-recrystallization mechanism of the highly reactive mackinawite. This is the first experimental study to report on selenide incorporation in iron monosulfide by a multi-edge XAS approach. PMID:22900520

Finck, N; Dardenne, K; Bosbach, D; Geckeis, H

2012-09-18

275

RETENTION TIME EFFECT ON METAL REMOVAL BY PEAT COLUMNS  

SciTech Connect

The potential use of a peat bed to treat the H-12 Outfall discharge to bring it to new compliance limits was previously investigated and reported utilizing a 7 hour retention time. The influence of retention time (contact time) of water with peat moss on the removal of copper from the water was investigated under laboratory conditions using vertical flow peat moss columns. Reduction of the necessary retention time has a large influence on the design sizing of any peat bed that would be constructed to treat the H-12 discharge on a full scale basis. Retention times of 5 hours, 3 hours and 1 hour were tested to determine the copper removal by the peat columns using vertical flow. Water samples were collected after 4, 8, 12, and 16 water volumes had passed through the columns and analyzed for a suite of metals, with quantitative emphasis on copper. Laboratory results indicated that copper removal was very high at each of the 3 retention times tested, ranging from 99.6 % removal at 5 and 3 hours to 98.8% removal at 1 hour. All these values are much lower that the new compliance limit for the outfall. The results also indicated that most divalent metals were removed to their normal reporting detection limit for the analytical methods used, including zinc. Lead levels in the H-12 discharge used in this study were below PQL in all samples analyzed. While each of the retention times studied removed copper very well, there were indications that 1 hour is probably too short for an operational, long-term facility. At that retention time, there was about 6% compaction of the peat in the column due to the water velocity, and this may affect long term hydraulic conductivity of the peat bed. At that retention time, copper concentration in the effluent was higher than the other times tested, although still very low. Because of the potential compacting and somewhat reduced removal efficiency at a 1 hour retention time, it would be prudent to design to at least a 3 hour retention time for water in any peat bed system that is proposed for the H-12 Outfall. A scope to design and install a pilot level study at H-12 is currently under development. This study will be designed to examine some of the engineering issues that are of concern regarding the scaling of an actual peat bed to treat the volumes of water that are typically discharged through the H-12 Outfall. Different hydraulic paths and configurations are expected to be part of that scope.

Nelson, E

2007-02-28

276

Soluble reactive phosphorus transport and retention in tropical, rainforest streams draining a volcanic and geothermally active landscape in Costa Rica.: Long-term concentration patterns, pore water environment and response to ENSO events  

USGS Publications Warehouse

Soluble reactive phosphorus (SRP) transport/retention was determined at four sites in three rainforest streams draining La Selva Biological Station, Costa Rica. La Selva is located at the base of the last remaining intact rainforest transect from 30 m above sea level to 3000 m along the entire Caribbean slope of Central America. Steam SRP levels can be naturally high there due to regional, geothermal groundwater discharged at ambient temperature. Monitoring since 1988 has revealed distinctive long-term differences in background SRP and total P (TP) for three streams in close proximity, and identified the impact of ENSO (El Nino Southern Oscillation) events on SRP-enriched reaches. Mean interannual SRP concentrations (?? standard deviation) were 89 ?? 53??g/l in the Salto (1988-1996), 21 ?? 39??g/l in the Pantano (1988-1998), and 26 ?? 35??g/l in the Sabalo (1988-1996). After January, 1997 the separate upland-lowland contributions to discharge and SRP load were determined monthly in the Salto. SRP in Upper Salto was low (19 ?? 8??g/l, 1997-2002) until enriched at the upland-lowland transition by regional groundwater. Mean SRP concentration in Lower Salto (108 ?? 104??g/l) was typically highest February-April, the driest months, and lowest July-September, the wettest. SRP concentration was positively correlated to the inverse of discharge in Lower Salto when ENSO data were omitted (1992 and 1998-1999), but not in the Upper Salto, Pantano, or Sabalo. TP was positively correlated to the inverse of discharge in all three streams when ENSO data were omitted. High SRP springs and seeps along the Lower Salto contributed 36% of discharge but 85% of SRP export 1997-2001. Annual SRP flux from the total Salto watershed (1997-2001) averaged 2.9 kg/ha year, but only 0.6 kg/ha year from the Upper Salto. A dye tracer injection showed that pore water environments were distinctly different between Upper and Lower Salto. Upper Salto had high surface water-pore water exchange, high dissolved oxygen, low SRP, and low conductivity similar to surface water, and Lower Salto had low surface water-pore water exchange, low dissolved oxygen, high SRP, and high conductivity reflecting geothermal groundwater influence. SRP export from the Salto was controlled by regional groundwater transfer, which in similar volcanic settings could be a significant P source. However, ENSO events modified the SRP concentration in the Salto suggesting that long-term monitoring is required to understand underlying SRP dynamics and P flux to downstream communities. ?? 2006 Springer Science+Business Media, Inc.

Triska, F.J.; Pringle, C.M.; Duff, J.H.; Avanzino, R.J.; Ramirez, A.; Ardon, M.; Jackman, A.P.

2006-01-01

277

Curves and Their Properties.  

ERIC Educational Resources Information Center

This volume, a reprinting of a classic first published in 1952, presents detailed discussions of 26 curves or families of curves, and 17 analytic systems of curves. For each curve the author provides a historical note, a sketch or sketches, a description of the curve, a discussion of pertinent facts, and a bibliography. Depending upon the curve,…

Yates, Robert C.

278

Retention of 2,4,6-trinitrotoluene and heavy metals from industrial waste water by using the low cost adsorbent pine bark in a batch experiment.  

PubMed

Pine bark is a low cost sorbent originating from the forest industry. In recent years, it has been found to show promise as an adsorbent for metals and organic substances in contaminated water, especially landfill leachates and storm water. This study aims to investigate if pine bark can replace commercial adsorbents such as active carbon. An industrial effluent, collected from a treatment plant of a demilitarization factory, was diluted to form concentration ranges of contaminants and shaken with pine bark for 24 hours. Metals (e.g. Pb, Zn, Cd, As and Ni) and explosives, e.g., 2,4,6-trinitrotoluene (TNT), were analysed before and after treatment. The aim of the experiment was twofold; firstly, it was to investigate whether metals are efficiently removed in the presence of explosives and secondly, if adsorption of explosive substances to pine bark was possible. Langmuir and Freundlich isotherms were used to describe the adsorption process where this was possible. It was found that metal uptake was possible in the presence of TNT and other explosive contaminants. The uptake of TNT was satisfactory with up to 80% of the TNT adsorbed by pine bark. PMID:22105128

Nehrenheim, E; Odlare, M; Allard, B

2011-01-01

279

Influence of sodium chloride and pH during acidic marination on water retention and mechanical properties of turkey breast meat.  

PubMed

Turkey breast cubes underwent acidic marination in the presence of salt. The transfer of water, salt and acid was measured, and texture was assessed on the cooked meat. While significant mass gains were observed during marination, from 20 minutes of immersion onwards, only long durations produced an overall matter balance greater than that of non-marinated meat. From the first minutes of immersion, these transfers caused hardening, regardless of the presence of salt in the marinade. For longer durations, only in the absence of salt was significant tenderizing seen in comparison to the non-marinated control. This effect appears to be due on the one hand to passing the isoelectric pH of the meat during acidification, and on the other hand to setting up antagonistic mechanisms breaking down or reinforcing connective tissues by acid and salt respectively. The high degree of tenderization observed in a water-acid solution can be explained partly by dilution of the fiber load per section unit due to protein solubilization. PMID:24334031

Goli, T; Ricci, J; Bohuon, P; Marchesseau, S; Collignan, A

2014-03-01

280

Absorption and retention of aluminum from drinking water. 1. Effect of citric and ascorbic acids on aluminum tissue levels in rabbits  

SciTech Connect

Adult, male New Zealand rabbits (three per group) were administered drinking water containing aluminum chloride (0, 100, or 500 mg Al/liter) together with citrate (0.11 M), ascorbate (0.11 M), or no added ligand ad libitum for 12 weeks. They were fed ad libitum regular rabbit chow analyzed to contain 297 mg Al/kg. Treatment had no effect upon food and water intake or weight gain during the experimental period. No effect of aluminum was observed on tissue levels of the essential metals zinc, copper, and iron, or on hemoglobin and hematocrit values. Aluminum levels were found to increase in a dose-dependent manner in stomach and intestinal mucosa, kidney, bone, urine, and feces. There was only a slight accumulation in liver, and no accumulation in brain (cerebral cortex or hippocampus). Although plasma aluminum was directly related to aluminum intake, whole blood aluminum bore no relation to aluminum dose. Citrate had no effect on aluminum accumulation in the stomach or intestine, but significantly enhanced plasma and bone aluminum levels. Ascorbate did not enhance aluminum accumulation in any tissue studied and even prevented accumulation in bone. Both citrate and ascorbate enhanced excretion of aluminum. Ascorbate therapy may be of potential clinical use to enhance aluminum excretion.

Fulton, B.; Jeffery, E.H. (Univ. of Illinois, Urbana-Champaign (USA))

1990-05-01

281

Determination of partition coefficients n-octanol/water for treosulfan and its epoxy-transformers: an example of a negative correlation between lipophilicity of unionized compounds and their retention in reversed-phase chromatography.  

PubMed

For the last decade an alkylating agent treosulfan (TREO) has been successfully applied in clinical trials in conditioning prior to hematopoietic stem cell transplantation. Pharmacological activity of the pro-drug depends on its epoxy-transformers, monoepoxide (S,S-EBDM) and diepoxide (S,S-DEB), which are formed in a non-enzymatic consecutive reaction accompanied by a release of methanesulfonic acid. In the present study partition coefficient n-octanol/water (POW) of TREO as well as its biologically active epoxy-transformers was determined empirically (applying a classical shake-flask method) and in silico for the first time. In vitro the partition was investigated at 37°C in the system composed of the pre-saturated n-octanol and 0.05 M acetate buffer pH 4.4 adjusted with sodium and potassium chloride to ionic strength of 0.16 M. Concentration of the analytes was quantified by reversed-phase high performance liquid chromatography (RP-HPLC) method in which retention time increased from S,S-DEB to TREO. It was shown that neither association nor dissociation of the tested compounds in the applied phases occurred. Calculated logPOW (TREO: -1.58±0.04, S,S-EBDM: -1.18±0.02, S,S-DEB: -0.40±0.03) indicate the hydrophilic character of the all three entities, corresponding to its pharmacokinetic parameters described in the literature. Experimentally determined logPOW of the compounds were best comparable to the values predicted by algorithm ALOGPs. Interestingly, the POW values determined in vitro as well as in silico were inversely correlated with the retention times observed in the endcapped RP-HPLC column. It might be explained by the fact that a cleavage of methansulfonic acid from a small molecule of TREO generates significant changes in the molecular structure. Consequently, despite the common chemical origin, TREO, S,S-EBDM and S,S-DEB do not constitute a 'congeneric' series of compounds. We concluded that this might occur in other low-weight species, therefore measurement of their POW by RP-HPLC had to be applied with a special care. PMID:23500352

G?ówka, Franciszek K; Roma?ski, Micha?; Siemi?tkowska, Anna

2013-04-01

282

SULFUR RETENTION IN COAL ASH  

EPA Science Inventory

The report gives results of an analytical study to assess the potential for sulfur retention in various types of coal-fired boilers. Results of a field test of 10 industrial coal-fired boilers were used to evaluate the impact on sulfur retention of the operating variables (load a...

283

Toward a Record Retention Policy  

ERIC Educational Resources Information Center

An academic library working group was charged in 2005 to create a records retention schedule and policy applicable to records containing personally identifiable information of library patrons. This group conducted a survey and extensive research, culminating in an adopted library records retention schedule and policy implemented in 2006.

Vaughan, Jason

2007-01-01

284

Retention and release of oil-in-water emulsions from filled hydrogel beads composed of calcium alginate: impact of emulsifier type and pH.  

PubMed

Delivery systems based on filled hydrogel particles (microgels) can be fabricated from natural food-grade lipids and biopolymers. The potential for controlling release characteristics by modulating the electrostatic interactions between emulsifier-coated lipid droplets and the biopolymer matrix within hydrogel particles was investigated. A multistage procedure was used to fabricate calcium alginate beads filled with lipid droplets stabilized by non-ionic, cationic, anionic, or zwitterionic emulsifiers. Oil-in-water emulsions stabilized by Tween 60, DTAB, SDS, or whey protein were prepared by microfluidization, mixed with various alginate solutions, and then microgels were formed by simple extrusion into calcium solutions. The microgels were placed into a series of buffer solutions with different pH values (2 to 11). Lipid droplets remained encapsulated under acidic and neutral conditions, but were released under highly basic conditions (pH 11) due to hydrogel swelling when the alginate concentration was sufficiently high. Lipid droplet release increased with decreasing alginate concentration, which could be attributed to an increase in the pore size of the hydrogel matrix. These results have important implications for the design of delivery systems to entrap and control the release of lipophilic bioactive components within filled hydrogel particles. PMID:25646949

Zeeb, Benjamin; Saberi, Amir Hossein; Weiss, Jochen; McClements, David Julian

2015-03-01

285

7 CFR 3015.21 - Retention period.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Retention period. 3015.21 Section 3015.21...UNIFORM FEDERAL ASSISTANCE REGULATIONS Record Retention and Access Requirements § 3015.21 Retention period. (a) Except as provided...

2010-01-01

286

49 CFR 576.7 - Retention.  

Code of Federal Regulations, 2010 CFR

... 7 2010-10-01 2010-10-01 false Retention. 576.7 Section 576.7 Transportation...DEPARTMENT OF TRANSPORTATION (CONTINUED) RECORD RETENTION § 576.7 Retention. Duplicate copies need not be retained....

2010-10-01

287

7 CFR 3015.21 - Retention period.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Retention period. 3015.21 Section 3015.21...UNIFORM FEDERAL ASSISTANCE REGULATIONS Record Retention and Access Requirements § 3015.21 Retention period. (a) Except as provided...

2011-01-01

288

49 CFR 576.7 - Retention.  

Code of Federal Regulations, 2011 CFR

... 7 2011-10-01 2011-10-01 false Retention. 576.7 Section 576.7 Transportation...DEPARTMENT OF TRANSPORTATION (CONTINUED) RECORD RETENTION § 576.7 Retention. Duplicate copies need not be retained....

2011-10-01

289

Retention of water-borne bacteria by membrane filters. Part I: Bacterial challenge tests on 0.2 and 0.22 micron rated filters.  

PubMed

The results of bacterial challenge tests conducted on several 0.2 and 0.22 micron rated "sterilizing grade" filter cartridge types with bacteria from a natural water source are presented. Eight different 0.2/0.22 micron rated "sterilizing grade" filter types from four different filter manufacturers, claimed to be capable of retaining Brevundimonas diminuta at a challenge level of 10(7) CFU/cm2, were tested. The filters tested included nylon 6.6 and polyamide filters from two manufacturers, modified or hydrophilic PVDF filters from two manufacturers, modified or asymmetric PES filters from three manufacturers, and cellulose acetate filters from a single manufacturer. Consistent bacterial penetration was observed, over the 18-24 h challenge period, for all twenty-five integral 0.2 and 0.22 micron rated filter cartridges tested, at challenge levels of about 10(1)-10(4) CFU/cm2, indicating that natural waterborne bacteria were more penetrative than B. diminuta. The observed penetration was thus qualitatively independent of filter media type or manufacturer. These results add to the growing body of evidence that shows 0.2 and 0.22 micron rated filters may not remove all microorganisms under all conditions. These results further establish that bacterial penetration of 0.2/0.22 micron rated filters is not limited just to (1) specific membrane types, or (2) extended duration challenges (> 24 h), or (3) extremely high challenge levels, or (4) bacteria that can only exist in a penetrative state in an artificial laboratory setting. PMID:11310322

Sundaram, S; Eisenhuth, J; Howard, G; Brandwein, H

2001-01-01

290

Quantitative structure-retention and retention-activity relationships of beta-blocking agents by micellar liquid chromatography.  

PubMed

Sixteen beta-blocking agents (acebutolol, alprenolol, atenolol, bisoprolol, carteolol, celiprolol, esmolol, labetalol, metoprolol, nadolol, oxprenolol, pindolol, practolol, propranolol, sotalol and timolol) showing a large range of hydrophobicity (octanol-water partition coefficients, log P between -0.026 and 2.81) were subjected to micellar liquid chromatography with sodium dodecyl sulfate as micelle forming agent, and n-propanol as organic modifier. The correlation between log P and the retention factor extrapolated to a mobile phase free of micelles and organic modifier was investigated. The use of an interpolated retention factor or the retention factor for specific individual experimental mobile phases was however advantageous since the retention factors of all beta-blocking agents were measurable in the selected mobile phases. Good correlations with log P and with in vitro biological parameters (cellular permeability coefficients in Caco-2 monolayers and apparent permeability coefficients in rat intestinal segments) were found. PMID:11330791

Detroyer, A; Vander Heyden, Y; Carda-Broch, S; García-Alvarez-Coque, M C; Massart, D L

2001-04-01

291

Transport and retention of colloid particles in partially saturated porous media: effect of surfactant and ionic strength  

NASA Astrophysics Data System (ADS)

The effect of surfactant and ionic strength concentration on colloid transport through saturated or partially saturated media has typically been studied inferentially using breakthrough curves. In this work, we made pore-scale observations in a small flow chamber to count colloids retained on the grain, air and liquid interfaces using a confocal microscope system and public domain image analysis software ImageJ. Stacks of images were analyzed for colloid retention in which the ionic strength and concentration of surfactant (nonionic Surfynol 485) were varied. The number of mobile (free in the water phase) colloids and attached colloids (retained at the surface of sand grains) for each image were quantified. We found that as ionic strength increased, the location where the colloids were retained changed from the air/water meniscus/solid (AWmS) interface to the water/solid (WS) interface. In addition, we observed that increasing the surfactant concentration reduced the retention of colloids due to decreased contact angle and surface tension.

Zevi, Y.; Dathe, A.; Gao, B.; Cakmak, M.; Richards, B. K.; Parlange, J.; Steenhuis, T. S.

2006-12-01

292

Alteration, adsorption and nucleation processes on clay-water interfaces: Mechanisms for the retention of uranium by altered clay surfaces on the nanometer scale  

NASA Astrophysics Data System (ADS)

Nano-scale processes on the solid-water interface of clay minerals control the mobility of metals in the environment. These processes can occur in confined pore spaces of clay buffers and barriers as well as in contaminated sediments and involve a combination of alteration, adsorption and nucleation processes of multiple species and phases. This study characterizes nano-scale processes on the interface between clay minerals and uranyl-bearing solution near neutral pH. Samples of clay minerals with a contact pH of ?6.7 are collected from a U mill and mine tailings at Key Lake, Saskatchewan, Canada. The tailings material contains Cu-, As-, Co-, Mo-, Ni-, Se-bearing polymetallic phases and has been deposited with a surplus of Ca(OH)2 and Na2CO3 slaked lime. Small volumes of mill-process solutions containing sulfuric acid and U are occasionally discharged onto the surface of the tailings and are neutralized after discharge by reactions with the slaked lime. Transmission electron microscopy (TEM) in combination with the focused ion beam (FIB) technique and other analytical methods (SEM, XRD, XRF and ICP-OES) are used to characterize the chemical and mineralogical composition of phases within confined pore spaces of the clay minerals montmorillonite and kaolinite and in the surrounding tailings material. Alteration zones around the clay minerals are characterized by different generations of secondary silicates containing variable proportions of adsorbed uranyl- and arsenate-species and by the intergrowth of the silicates with the uranyl-minerals cuprosklodowskite, Cu[(UO2)2(SiO3OH)2](H2O)6 and metazeunerite, Cu[(UO2)(AsO4)2](H2O)8. The majority of alteration phases such as illite, illite-smectite, kaolinite and vermiculite have been most likely formed in the sedimentary basin of the U-ore deposit and contain low amounts of Fe (<5 at.%). Iron-enriched Al-silicates or illite-smectites (Fe >10 at.%) formed most likely in the limed tailings at high contact pH (?10.5) and their structure is characterized by a low degree of long-range order. Adsorption of U and nucleation of metazeunerite and cuprosklodowskite are strongly controlled by the presence of the adsorbed oxy-anion species arsenate and silica on the Fe-enriched silicates. Heterogeneous nucleation of nano-crystals of the uranyl minerals occurs most likely on adsorption sites of binary uranyl-, arsenate- and silica-complexes as well as on ternary uranyl-arsenate or uranyl-silicate complexes. The uranyl minerals occur as aggregates of misoriented nano-size crystals and are the result of supersaturated solutions and a high number of nucleation sites that prevented the formation of larger crystals through Oswald ripening. The results of this study provide an understanding of interfacial nano-scale processes between uranyl species and altered clay buffers in a potential Nuclear Waste repository as similar alteration conditions of clays may occur in a multi-barrier system.

Schindler, Michael; Legrand, Christine A.; Hochella, Michael F.

2015-03-01

293

Effective retention time of the Hanford 107 reactor effluent retention basins  

Microsoft Academic Search

Studies of the radioactive decay of the gross beta particle emitters in reactor effluent water indicated that the retention time for basins at the different reactor areas varied from 1.5 hours to 4.0 hours for flow rates occurring during the last three years. A statistical analysis of the data from 100-B, 100-D, and 100-F indicated a significant relationship between the

J. K. Soldat; G. R. Quimby

1953-01-01

294

Nitrate-nitrogen retention in wetlands in the Mississippi River Basin  

Microsoft Academic Search

Nitrate-nitrogen retention as a result of river water diversions is compared in experimental wetland basins in Ohio for 18 wetland-years (9 years×2 wetland basins) and a large wetland complex in Louisiana (1 wetland basin×4 years). The Ohio wetlands had an average nitrate-nitrogen retention of 39g-Nm?2year?1, while the Louisiana wetland had a slightly higher retention of 46g-Nm?2year?1 for a similar loading

William J. Mitsch; John W. Day; Li Zhang

2005-01-01

295

Data Retention and Anonymity Services  

NASA Astrophysics Data System (ADS)

The recently introduced legislation on data retention to aid prosecuting cyber-related crime in Europe also affects the achievable security of systems for anonymous communication on the Internet. We argue that data retention requires a review of existing security evaluations against a new class of realistic adversary models. In particular, we present theoretical results and first empirical evidence for intersection attacks by law enforcement authorities. The reference architecture for our study is the anonymity service AN.ON, from which we also collect empirical data. Our adversary model reflects an interpretation of the current implementation of the EC Directive on Data Retention in Germany.

Berthold, Stefan; Böhme, Rainer; Köpsell, Stefan

296

Isolated Curves for Hyperelliptic Curve Cryptography  

E-print Network

We introduce the notion of isolated genus two curves. As there is no known efficient algorithm to explicitly construct isogenies between two genus two curves with large conductor gap, the discrete log problem (DLP) cannot be efficiently carried over from an isolated curve to a large set of isogenous curves. Thus isolated genus two curves might be more secure for DLP based hyperelliptic curve cryptography. We establish results on explicit expressions for the index of an endomorphism ring in the maximal CM order, and give conditions under which the index is a prime number or an almost prime number for three different categories of quartic CM fields. We also derived heuristic asymptotic results on the densities and distributions of isolated genus two curves with CM by any fixed quartic CM field. Computational results, which are also shown for three explicit examples, agree with heuristic prediction with errors within a tolerable range.

Wang, Wenhan

2012-01-01

297

Payload retention device  

NASA Astrophysics Data System (ADS)

A payload retention device for grappling and retaining a payload in docked position on a supporting structure in the cargo bay of a space vehicle is presented. The device comprises a two-fault tolerant electromagnetic grappling system comprising electromagnets for attracting and grappling a grapple strike plate affixed to the payload when in proximity thereto and an electromechanical latching assembly comprising a pair of independent latching subassemblies. Each subassembly comprises a set of latching pawls which are driven into latching and unlatching positions relative to a grappled payload by a pair of gearmotors, each equipped with a ratchet clutch drive mechanism which is two-fault tolerant with respect to latching such that only one gearmotor of the four needs to be operational to effect a latch of the payload but is single fault tolerant with respect to release of a latched payload. Sensors are included for automatically sensing the magnetic grappling of a payload and for automatically de-energizing the gearmotors of the latching subassemblies when a latch condition is achieved.

Monford, Leo G., Jr.

1992-06-01

298

Mechanisms of colloid retention, mobilization, and transport in unsaturated porous media (Invited)  

NASA Astrophysics Data System (ADS)

Colloid retention, mobilization, and transport in porous media have been attracting considerable scientific attention due to concerns of potentially enhanced transport of contaminants by mobile colloids and transport of pathogenic microorganisms and nanoparticles. An understanding of colloid retention, mobilization, and transport in subsurface environments is also essential for the design of effective water treatment and bioremediation strategies. Mechanisms of colloid retention and transport in unsaturated vadoes zone are complex due to flow discontinuity, interfacial processes, wetting history, and transient effects, and remain poorly understood. Our primary research objective is to quantify two complementary modes of colloid retention: accumulation at the air-water interface vs. accumulation in the (small) volume of water associated with the air-water-solid contact line. We address this objective through experiments and modeling, driven by the fact that the rate of colloid retention and the capacity of retention depend strongly upon the geometry of the configuration of the air and water phases. Additionally, the rate of retention, as well as colloid mobilization, will also depend upon how readily the water phase can access the air-water interface and the region near the contact line. In this talk, I will present results from experiments conducted at pore scale using micromodels, in columns, as well as from modeling to address these issues.

Jin, Y.; Zevi, Y.; Lazouskaya, V.; Rodriguez, E.; Prodanovic, M.; Bryant, S. L.

2009-12-01

299

Ammonia-water mixtures at high pressures - Melting curves of ammonia dihydrate and ammonia monohydrate and a revised high-pressure phase diagram for the water-rich region. [in primordial solar system ices  

NASA Technical Reports Server (NTRS)

The phase relations of some mixtures of ammonia and water are investigated to create a phase diagram in pressure-temperature-composition space relevant to the geophysical study of bodies in the outer solar system. The mixtures of NH3(x)H2O(1-x), where x is greater than 0.30 but less than 0.51, are examined at pressures and temperatures ranging from 0-6.5 GPa and 125-400 K, respectively. The ruby luminescence technique monitors the pressure and a diamond-anvil cell compresses the samples, and the phases are identified by means of normal- and polarized-light optical microscopy. The melting curve for NH3H2O(2) is described by the equation T = 176 + 60P - 8.5P squared for the ranges of 0.06-1.4 GPa and 179-243 K. The equation for NH3H2O is T = 194 + 37P - P squared, which represents a minor correction of a previous description by Johnson et al. (1985). Observed phase transitions are consistent with the high-pressure stability limit of NH3H2O(2), and the transition boundary is found to be linear.

Boone, S.; Nicol, M. F.

1991-01-01

300

EA Shuttle Document Retention Effort  

NASA Technical Reports Server (NTRS)

This slide presentation reviews the effort of code EA at Johnson Space Center (JSC) to identify and acquire databases and documents from the space shuttle program that are adjudged important for retention after the retirement of the space shuttle.

Wagner, Howard A.

2010-01-01

301

Turnover: strategies for staff retention.  

PubMed

This discussion has focused on a number of areas where organizations may find opportunities for more effectively managing employee retention. Given the multitude of causes and consequences, there is no one quick fix. Effective management of employee retention requires assessment of the entire human resources process, that is, recruitment, selection, job design, compensation, supervision, work conditions, etc. Regular and systematic diagnosis of turnover and implementation of multiple strategies and evaluation are needed (Mobley, 1982). PMID:10106673

SnowAntle, S

1990-01-01

302

Elementary Grade Retention: Making the Decision.  

ERIC Educational Resources Information Center

Reviews historic approaches to grade retention, what research does and does not show about retention, and some factors to weigh when considering retention. Focuses on models developed by H. Wayne Light and Laurence Lieberman. Includes a sample elementary school promotion policy and a sample retention referral form. (IW)

Bucko, Richard L.

1986-01-01

303

Elliptic Curves An Introduction  

E-print Network

. The growing practical relevance of elliptic curves in modern cryptography is another issue missing. This listElliptic Curves ­ An Introduction ­ Expanded notes from a mini-workshop held at Mary Immaculate. Group law on the cubic curve 29 4. Theta Functions 53 5. Rank two vector bundles on elliptic curves 75

Babinkostova, Liljana

304

Elliptic Curves Number Theory  

E-print Network

Elliptic Curves Number Theory and Cryptography Second Edition © 2008 by Taylor & Francis Group, LLC Washington, Lawrence C. Elliptic curves : number theory and cryptography / Lawrence C. Washington. -- 2nd ed, elliptic curves started being used in cryptography and elliptic curve techniques were developed

Babinkostova, Liljana

305

Phosphorus Retention in Streams and Wetlands: A Review  

Microsoft Academic Search

Wetlands and streams buffer the interactions among uplands and adjacent aquatic systems. Phosphorus (P) is often the key nutrient found to be limiting in both estuarine and freshwater ecosystems. As such, the ability of wetlands and streams to retain P is key to determining downstream water quality. This article reviews the processes and factors regulating P retention in streams and

K. R. Reddy; R. H. Kadlec; E. Flaig; P. M. Gale

1999-01-01

306

Equilibrium retention in the nozzle of oxygen hydrogen propulsion systems  

NASA Technical Reports Server (NTRS)

Arguments are presented for the retention of vibrational equilibrium of species in the nozzle of the Space Shuttle Main Engine which are especially applicable to water and the hydroxyl radical. It is shown that the reaction OH + HH yields HOH + H maintains equilibrium as well. This is used to relate OH to H, the temperature, and the oxidizer-to-fuel ratio.

Ford, D. I.

1987-01-01

307

HEAVY METAL RETENTION WITHIN A POROUS PAVEMENT STRUCTURE  

Microsoft Academic Search

Porous pavements with reservoir structure for infiltration of runoff from parking spaces and residential streets offer the opportunity to dispose water without using additional space in urban areas. However, pollutants in urban runoff endanger soils and groundwater, when pol- lutant retention in the structure is not sufficient. Porous pavement structures with four differ- ent subbase materials were tested in rigs.

C. Dierkes; A. Holte; W. F. Geiger

308

Water relations of Robinia pseudoacacia?L.: do vessels cavitate and refill diurnally or are R-shaped curves invalid in Robinia?  

PubMed

Since 2005, an unresolved debate has questioned whether R-shaped vulnerability curves (VCs) might be an artefact of the centrifuge method of measuring VCs. VCs with R-shape show loss of stem conductivity from approximately zero tension, and if true, this suggests that some plants either refill embolized vessels every night or function well with a high percentage of vessels permanently embolized. The R-shaped curves occur more in species with vessels greater than half the length of the segments spun in a centrifuge. Many have hypothesized that the embolism is seeded by agents (bubbles or particles) entering the stem end and travelling towards the axis of rotation in long vessels, causing premature cavitation. VCs were measured on Robinia pseudoacacia?L. by three different techniques to yield three different VCs; R-shaped: Cavitron P50 ?=?0.30?MPa and S-shaped: air injection P50 ?=?1.48?MPa and bench top dehydration P50 ?=?3.57?MPa. Stem conductivity measured in the Cavitron was unstable and is a function of vessel length when measured repeatedly with constant tension, and this observation is discussed in terms of stability of air bubbles drawn into cut-open vessels during repeated Cavitron measurement of conductivity; hence, R-shaped curves measured in a Cavitron are probably invalid. PMID:24588635

Wang, Ruiqing; Zhang, Lingling; Zhang, Shuoxin; Cai, Jing; Tyree, Melvin T

2014-12-01

309

Prediction of the retention values associated to the ultrafiltration of mixtures of metal ions and high molecular weight water-soluble polymers as a function of the initial ionic strength  

Microsoft Academic Search

The equations that relate the dissociation constants between divalent metal ions and polymer chains in aqueous solutions with the ionic strength are developed from a model previously discussed that gives account for the experimental results obtained in ultrafiltration experiments. The relations found are used to predict the retention values at high filtration factors in ultrafiltration experiments corresponding to the systems

Bernabé L. Rivas; Ignacio Moreno-Villoslada

2000-01-01

310

Effect of moisture on alachlor retention in the soil  

E-print Network

loam. Greatest loss s occurred at 0, relative humid-tv and were at", . ributed to chemical decom~ositio, of the herbicide by acidic soil wate: ~ At 3S C& maximum re- tent" on r!as noted at 31/ relative humidity, and ~ ~ 46 C, maximum retention... periods. Alachlor retention was deter- mined by a direc r, comparison with the 0 hr values. Pield capacity of soils utilized was approximated by measuring the amount of water held against gravityo At field capacity the moisture content of' Sawyer fine...

Hargrove, Raford Stanley

1970-01-01

311

Odonata, Amphibia and Environmental Characteristics in Motorway Stormwater Retention Ponds (Southern France)  

Microsoft Academic Search

Water and its protection against pollution is an urgent priority for all countries around the world. In that context, France, through its Water Law in 1992 obliged the motorway companies to build stormwater retention ponds along roads in order to protect the water resource from transport pollution and to control water flow during rainstorms. We propose to evaluate how much

Olivier Scher; Alain Thičry

2005-01-01

312

Lead Retention and Complexation in a Magnesium Smectite (Hectorite)  

Microsoft Academic Search

The retention and complexation of Pb2+ in the interlayer of a smectite clay (hectorite) was investigated. Based on XRD results, the Ca-Pb exchanged clays most likely exhibit random interstratification. A random alternation of one-water-layer (? 12.5 Ĺ) and two-water-layer (? 15.5 Ĺ) hydrates as well as an irrational set of basal reflections are observed. At a specified humidity, the basal

Darsa P. Siantar; José J. Fripiat

1995-01-01

313

Exploring particulate retention mechanisms through visualization of E. coli transport through a single, saturated fracture  

NASA Astrophysics Data System (ADS)

Groundwater is an extremely valuable resource; a large body of work has been conducted towards remediating, tracking and reducing its contamination. Even so, there are large gaps within the current understanding of groundwater flow and contaminant transport, particularly within fractured media. Fractured media has the ability transport contaminants over longer distances in less time relative to porous media. Furthermore, colloids display unique transport characteristics in comparison to dissolved constituents, including the fact that they typically exhibit earlier initial arrival times. Of particular concern to human health are pathogenic microorganisms, which often originate from fecal contamination. Escherichia coli is a common indicator for fecal contamination; some strains are pathogenic, causing acute illness and sometimes death, in humans. A comprehensive understanding of the transport and retention of E. coli in fractured media will improve our ability to accurately assess whether a site is at risk of becoming contaminated by pathogenic microorganisms. Therefore, the goal of this work is to expand our mechanistic understanding particulate retention, specifically E. coli, in fractures, and the influence of flow rate on these mechanisms. In order to achieve this goal, clear epoxy casts were fabricated of two dolomitic limestone fractures retrieved from a quarry in Guelph, Ontario. Each aperture field was characterized through hydraulic and tracer tests, and measured directly using the light transmission technique. E. coli RS2-GFP, which is a non-pathogenic strain of E. coli that has been tagged with a green fluorescent protein, was injected into the cast under three separate specific discharges ranging from 5 - 30 m/d. These experiments were conducted on an ultraviolet light source, and a high resolution charged-couple device (CCD) camera was employed to take photos at regular intervals in order to capture the dominant flow paths and the areas of retention within the epoxy fracture. Samples were drawn downstream to obtain the E. coli breakthrough curve and determine the percent retained within the fracture. This paper will present the dominant retention mechanisms of E. coli at various effective flow rates as determined from an analysis of the images showing trapped E. coli, together with the aperture field information from the direct measurement. This information will help to improve the robustness and of contaminant transport models in fractures, and will therefore improve the ability to assess the risk posed by using bedrock aquifers as drinking water sources.

Burke, M. G.; Dickson, S. E.; Schutten, M.

2011-12-01

314

Twinned principal curves  

Microsoft Academic Search

Principal Curves are extensions of Principal Component Analysis and are smooth curves, which pass through the middle of a data set. We extend the method so that, on pairs of data sets which have underlying non-linear correlations, we have pairs of curves which go through the ‘centre’ of data sets in such a way that the non-linear correlations between the

Jos Koetsier; Ying Han; Colin Fyfe

2004-01-01

315

Total fatigue curve  

SciTech Connect

The fatigue failure mechanisms operative on different segments of the total fatigue curve are discussed. The need for experimental determination of this curve is emphasized; once known, this curve will make possible a deeper insight into the transitional zones associated with a change in the cumulative fatigue damage mechanism.

Sosnovskii, L.A.; Makhutov, N.A. [A.A. Blagonravov Inst. of Machine Engineering, Moscow (Russian Federation)

1995-11-01

316

Nuclear reactor melt-retention structure to mitigate direct containment heating  

DOEpatents

A light water nuclear reactor melt-retention structure to mitigate the extent of direct containment heating of the reactor containment building. The structure includes a retention chamber for retaining molten core material away from the upper regions of the reactor containment building when a severe accident causes the bottom of the pressure vessel of the reactor to fail and discharge such molten material under high pressure through the reactor cavity into the retention chamber. In combination with the melt-retention chamber there is provided a passageway that includes molten core droplet deflector vanes and has gas vent means in its upper surface, which means are operable to deflect molten core droplets into the retention chamber while allowing high pressure steam and gases to be vented into the upper regions of the containment building. A plurality of platforms are mounted within the passageway and the melt-retention structure to direct the flow of molten core material and help retain it within the melt-retention chamber. In addition, ribs are mounted at spaced positions on the floor of the melt-retention chamber, and grid means are positioned at the entrance side of the retention chamber. The grid means develop gas back pressure that helps separate the molten core droplets from discharged high pressure steam and gases, thereby forcing the steam and gases to vent into the upper regions of the reactor containment building.

Tutu, Narinder K. (Manorville, NY); Ginsberg, Theodore (East Setauket, NY); Klages, John R. (Mattituck, NY)

1991-01-01

317

From principal curves to granular principal curves.  

PubMed

Principal curves arising as an essential construct in dimensionality reduction and data analysis have recently attracted much attention from theoretical as well as practical perspective. In many real-world situations, however, the efficiency of existing principal curves algorithms is often arguable, in particular when dealing with massive data owing to the associated high computational complexity. A certain drawback of these constructs stems from the fact that in several applications principal curves cannot fully capture some essential problem-oriented facets of the data dealing with width, aspect ratio, width change, etc. Information granulation is a powerful tool supporting processing and interpreting massive data. In this paper, invoking the underlying ideas of information granulation, we propose a granular principal curves approach, regarded as an extension of principal curves algorithms, to improve efficiency and achieve a sound accuracy-efficiency tradeoff. First, large amounts of numerical data are granulated into C intervals-information granules developed with the use of fuzzy C-means clustering and the two criteria of information granulation, which significantly reduce the amount of data to be processed at the later phase of the overall design. Granular principal curves are then constructed by determining the upper and the lower bounds of the interval data. Finally, we develop an objective function using the criteria of information confidence and specificity to evaluate the granular output formed by the principal curves. We also optimize the granular principal curves by adjusting the level of information granularity (the number of clusters), which is realized with the aid of the particle swarm optimization. A number of numeric studies completed for synthetic and real-world datasets provide a useful quantifiable insight into the effectiveness of the proposed algorithm. PMID:23996588

Zhang, Hongyun; Pedrycz, Witold; Miao, Duoqian; Wei, Zhihua

2014-06-01

318

Sensitivity of the transport and retention of stabilized silver nanoparticles to physicochemical factors  

Technology Transfer Automated Retrieval System (TEKTRAN)

Saturated sand-packed column experiments were conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized silver nanoparticles (AgNPs). The normalized concentration in breakthrough curves (BTCs) of AgNPs increased with a decrease in solut...

319

Employee voice and employee retention.  

PubMed

This study investigates the relationship between the extent to which employees have opportunities to voice dissatisfaction and voluntary turnover in 111 short-term, general care hospitals. Results show that, whether or not a union is present, high numbers of mechanisms for employee voice are associated with high retention rates. Implications for theory and research as well as management practice are discussed. PMID:10278801

Spencer, D G

1986-09-01

320

Enhancing student retention and employability  

Microsoft Academic Search

Retention of first year students in the Faculty of Engineering is a significant problem. There appears to be a pattern of loss of students early in Semester 1 with students failing to engage with their program of learning and again in Semester 2 after the publication of results of the January exam diet. This project aimed to address these problems

D. Ballance; A. Browitt; J. Davies; J. Pritchard; S. Roy; W. Stewart; M. Vezza; L. Walker; A. Whittaker

321

Teacher Retention: An Appreciative Approach  

ERIC Educational Resources Information Center

Nationally, the problem of teacher retention compounds the unstable nature of the educational situation, especially in urban, high-needs schools. Much of the instability of urban schools is due to teacher movement, the migration of teachers from school to another school within or between school districts, particularly from high-needs schools.…

Pesavento-Conway, Jennifer Jean

2010-01-01

322

Course Retention Analysis. Focus Study.  

ERIC Educational Resources Information Center

A study was conducted at Mount San Antonio College (MSAC), California, to analyze patterns in credit course retention between fall 1986 and spring 1989. The study investigated the development of course prerequisites based on faculty perceptions of the skills necessary for success and minimal skill levels associated with success; student assessment…

Mount San Antonio Coll., Walnut, CA.

323

Strategies for improving employee retention.  

PubMed

This article proposes a solution to the perennial problem of talent retention in the clinical laboratory. It includes the presentation of 12 strategies that may be used to significantly improve institutional identity formation and establishment of the psychological contract that employees form with laboratory management. Identity formation and psychological contracting are deemed as essential in helping reduce employee turnover and increase retention. The 12 conversational strategies may be used as a set of best practices for all employees, but most importantly for new employees, and should be implemented at the critical moment when employees first join the laboratory. This time is referred to as "retention on-boarding"--the period of induction and laboratory orientation. Retention on-boarding involves a dialogue between employees and management that is focused on the psychological, practical, cultural, and political dimensions of the laboratory. It is placed in the context of the modern clinical laboratory, which is faced with employing and managing Generation X knowledge workers. Specific topics and broad content areas of those conversations are outlined. PMID:17394785

Verlander, Edward G; Evans, Martin R

2007-01-01

324

Root water uptake and rhizosphere dynamics  

NASA Astrophysics Data System (ADS)

Is root water uptake controlled by the hydraulic properties of the rhizosphere? Recent experiments showed that during drying the rhizosphere held more water than the bulk soil. After irrigation the rhizosphere remained temporarily dry and it slowly rewetted after a few days. How to explain such hysteretic and dynamic behavior of the rhizosphere? And what are the implications for soil-plant water relations? Our hypothesis is that the observed hydraulic behavior was caused by mucilage exuded by roots. Mucilage is a polymeric material that is capable of holding large amount of water, but that contains also lipids that makes it hydrophobic when it dries. Here it is proposed a model of root water uptake coupled with shrinking/swelling of mucilage. Water flow is modeled solving the Richards' equation in radial coordinates. During drying, mucilage is in equilibrium with the bulk water and the rhizosphere is at the equilibrium water retention curve. After irrigation, which typically is a quick process, mucilage does not rehydrate immediately and the rhizosphere rewets only partly. The swelling rate of mucilage is driven by the difference between the water potential in the rhizosphere and the potential that the rhizosphere would have at the actual water content. The calculations reproduce well the observed water dynamics in the rhizosphere. According to this model the rhizosphere conductivity is not univocally determined by the soil water potential, but it is variable and depends on the drying/wetting history. The study illustrates the dynamic and interacting nature of the water flow to roots.

Carminati, A.

2012-04-01

325

High retention membrane bioreactors: challenges and opportunities.  

PubMed

Extensive research has focussed on the development of novel high retention membrane bioreactor (HR-MBR) systems for wastewater reclamation in recent years. HR-MBR integrates high rejection membrane separation with conventional biological treatment in a single step. High rejection membrane separation processes currently used in HR-MBR applications include nanofiltration, forward osmosis, and membrane distillation. In these HR-MBR systems, organic contaminants can be effectively retained, prolonging their retention time in the bioreactor and thus enhancing their biodegradation. Therefore, HR-MBR can offer a reliable and elegant solution to produce high quality effluent. However, there are several technological challenges associated with the development of HR-MBR, including salinity build-up, low permeate flux, and membrane degradation. This paper provides a critical review on these challenges and potential opportunities of HR-MBR for wastewater treatment and water reclamation, and aims to guide and inform future research on HR-MBR for fast commercialisation of this innovative technology. PMID:24996563

Luo, Wenhai; Hai, Faisal I; Price, William E; Guo, Wenshan; Ngo, Hao H; Yamamoto, Kazuo; Nghiem, Long D

2014-09-01

326

Managing Chemotherapy Side Effects: Swelling (Fluid Retention)  

MedlinePLUS

... institutes of health Managing Chemotherapy Side Effects Swelling (Fluid retention) “My hands and feet were swollen and ... at one time. Managing Chemotherapy Side Effects: Swelling (Fluid retention) Weigh yourself. l Weigh yourself at the ...

327

7 CFR 70.54 - Retention authorities.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Retention authorities... AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices...THE AGRICULTURAL MARKETING ACT OF 1946 AND...Products § 70.54 Retention authorities....

2011-01-01

328

7 CFR 57.426 - Retention.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Retention. 57.426 ...AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices...THE AGRICULTURAL MARKETING ACT OF 1946 AND...Inspection of Eggs Retention § 57.426...

2010-01-01

329

7 CFR 56.38 - Retention authorities.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Retention authorities... AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices...THE AGRICULTURAL MARKETING ACT OF 1946 AND...Products § 56.38 Retention authorities....

2011-01-01

330

7 CFR 70.54 - Retention authorities.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Retention authorities... AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices...THE AGRICULTURAL MARKETING ACT OF 1946 AND...Products § 70.54 Retention authorities....

2010-01-01

331

7 CFR 57.426 - Retention.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 false Retention. 57.426 ...AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing Practices...THE AGRICULTURAL MARKETING ACT OF 1946 AND...Inspection of Eggs Retention § 57.426...

2011-01-01

332

12 CFR 609.945 - Records retention.  

Code of Federal Regulations, 2010 CFR

...retention. 609.945 Section 609.945 Banks and Banking FARM CREDIT ADMINISTRATION FARM CREDIT SYSTEM ELECTRONIC COMMERCE Standards for Boards and Management § 609.945 Records retention. Records stored electronically must...

2010-01-01

333

Retention of orthodontic bands with new fluoride-releasing cements.  

PubMed

The prevalence of enamel decalcification beneath orthodontic bands has indicated the need for a fluoride-releasing, enamel-adhesive orthodontic luting cement. The purpose of this study was to compare the retentive bond strengths of orthodontic bands cemented with two new fluoride-releasing cements, a zinc polycarboxylate and a glass ionomer, with the retentive bond strength of bands cemented with the standard orthodontic cement zinc phosphate. The site of cement failure was also evaluated. One hundred eighty extracted human molar teeth were embedded in resin blocks and randomly assigned to three cement groups. Adapted bands were cemented by a clinically acceptable technique. The cemented teeth were then assigned to one of three time intervals--24 hours, 7 days, and 60 days--and thermocycled in synthetic saliva. The force required to initially fracture the cement bond was used as a measure of cement retention. By means of the Instron, a tensile load was applied to each cemented band. The maximum retentive strength (cement failure) was interpreted from the stress-strain curve at the point where linearity deviated. The failure site was judged subjectively: between cement and enamel, within the cement, or between cement and the band. Using stress at failure, an analysis of variance showed no significant differences among the retentive strengths of the three cements. The chi-square test revealed a significant difference (P less than 0.01) between failure sites of the zinc phosphate and glass ionomer cements. Significantly more bands cemented with the glass ionomer failed at the cement/band interface, leaving the cement adhered to the tooth.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:3513596

Norris, D S; McInnes-Ledoux, P; Schwaninger, B; Weinberg, R

1986-03-01

334

Water  

MedlinePLUS

... to drink more water Other drinks How much water do you need? top Water is very important, ... you probably need more water. What about bottled water? top Some people like bottled water for its ...

335

Transport and retention of dormant copepods in the Gulf of Maine  

NASA Astrophysics Data System (ADS)

Variability in the availability of dormant copepods to seed productive shelf areas has been hypothesized to influence the abundance of the dominant copepod species Calanus finmarchicus in several regions of the North Atlantic. One source of this variability is advection of dormant copepods in deep water. Using Lagrangian particle simulations, we examined the influence of environmental forcing and copepod behavior on transport and retention of dormant C. finmarchicus in the deep Gulf of Maine, in the northwestern Atlantic. Retention in the Gulf of Maine was relatively high, >40% over 6 months, under all conditions simulated. Transport within the Gulf of Maine was high, resulting in shifts of eastern copepods into the western Gulf and of upstream copepods, from slope and Scotian Shelf waters, into the eastern Gulf. Copepod behavior during dormancy was a major source of uncertainty, but it is probably not a major source of interannual variability in retention. Retention increased with the initial depth of dormant copepods, and vertical positioning behavior had a strong influence on retention for simulations started at depths greater than 150 m, because copepods that can stay below basin sill depths are retained. Mean cross-shore winds reduced retention slightly (<2% absolute difference), and mean alongshore winds increased retention by 4-8%. Wind-driven interannual variability in retention was low. Variability in Scotian Shelf inflow had a greater influence on retention than did variability in winds, and inflow-driven changes in retention may contribute to interannual variability in copepod abundance associated with changes in deep-water temperature. However, estimates of advective loss are relatively low compared to measured reductions in dormant copepod abundance, and mortality is probably a major factor in this reduction.

Johnson, Catherine; Pringle, James; Chen, Changsheng

2006-11-01

336

Scale and Seasonal Controls on Nitrate and Sediment Retention in Freshwater Tidal Wetlands  

NASA Astrophysics Data System (ADS)

Channel networks in freshwater tidal wetlands convey water, sediment, and solutes into marsh interiors where sediment deposition and biogeochemical processes, such as denitrification and nitrogen uptake occur. Tidal inlets that connect these channel network systems to the main estuary define the initial solute or sediment load into these systems, but channel, soil, and vegetation characteristics influence nitrate and sediment retention. We used field measurements and remotely sensed images to determine marsh area, stream length, inlet morphology, and channel morphology for the 267 marshes in the freshwater tidal ecosystem. Discharge and water volume over high tidal cycles was measured at selected inlets representative of the range of inlet sizes in the ecosystem. Aquatic vegetation distribution and density was also measured at these inlets. These data were used to develop geomorphic-hydraulic relationships for the marshes for winter (no vegetation) and summer (vegetated) conditions. Nitrate and sediment retention were determined from field mass balance measurements based on water flux and concentration measurements taken over tidal cycle at inlets to selected marshes of varying size over a 3-year period. These mass balance data indicate that net nitrate retention is a simple function of tidal water volume for marshes of different sizes and for various vegetated conditions. These data suggest that nitrate retention is transport limited for the range of initial nitrate concentrations observed in this system. Although nitrate retention was a function of tidal water volume, it was also seasonally variable due to restrictions in water flow and volume caused by aquatic vegetation in summer months. Sediment retention is seasonally variable due to the strong controls exerted by emergent and submerged aquatic vegetation and decoupled from the water volume dependence observed for nitrate retention. Variations in sediment retention caused by vegetation resulted in channel morphology that oscillates between summer and winter conditions.

Prestegaard, K. L.; Seldomridge, E.; Statkiewicz, A.

2013-12-01

337

Elementary Grade Retention: Making the Decision.  

ERIC Educational Resources Information Center

Today's administrators must exercise caution in using student retention as a means of responding to changing social values and to the current media attention on declining standardized test scores. Recent reviews of hundreds of studies of student retention have concluded that some low achieving students do benefit from retention, but the majority…

Bucko, Richard

338

Reframing Retention Strategy: A Focus on Progress  

ERIC Educational Resources Information Center

Few words have dominated the vocabulary of college retention as has the word "persistence." Many institutions still struggle to engage faculty and administrators in building campuswide retention efforts, to find the organizational levers that translate the abstractions and complexities of retention theory into scalable and durable initiatives, and…

Spittle, Brian

2013-01-01

339

Reframing Retention Strategy: A Focus on Profile  

ERIC Educational Resources Information Center

Over 35 years of retention theory and literature have acknowledged the importance of institutional and student profiles in accounting for cross-sectional differences in retention and completion rates between types of colleges and universities. The first "P" within a 4 Ps framework of student retention--"profile"--recognizes that an institution's…

Kalsbeek, David H.; Zucker, Brian

2013-01-01

340

A RETENTION INDEX SCHEME FOR USE WITH SULFUR SPECIFIC DETECTORS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Retention indices are very important for compound identification when using gas chromatography. Retention indices are important because they remain static under different conditions and instruments while retention times vary dramatically. Generally, a retention index is generated using a series of...

341

5 CFR 536.204 - Period of grade retention.  

Code of Federal Regulations, 2010 CFR

...false Period of grade retention. 536.204 Section...REGULATIONS GRADE AND PAY RETENTION Grade Retention...under § 536.208, an employee is entitled to retain...the employee to grade retention, the employee must continue...

2010-01-01

342

5 CFR 536.201 - Mandatory grade retention.  

Code of Federal Regulations, 2010 CFR

...REGULATIONS GRADE AND PAY RETENTION Grade Retention...201 Mandatory grade retention. (a) Subject...must provide grade retention to an employee who moves from a position under a covered pay system to a...

2010-01-01

343

5 CFR 536.301 - Mandatory pay retention.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Mandatory pay retention. 536.301 Section 536.301 Administrative...MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Pay Retention § 536.301 Mandatory pay retention....

2011-01-01

344

5 CFR 536.201 - Mandatory grade retention.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Mandatory grade retention. 536.201 Section 536.201 Administrative...MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.201 Mandatory grade retention....

2011-01-01

345

5 CFR 536.204 - Period of grade retention.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Period of grade retention. 536.204 Section 536.204 Administrative...MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.204 Period of grade retention....

2011-01-01

346

5 CFR 536.202 - Optional grade retention.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Optional grade retention. 536.202 Section 536.202 Administrative...MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.202 Optional grade retention....

2011-01-01

347

48 CFR 4.704 - Calculation of retention periods.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false Calculation of retention periods. 4.704 Section 4.704 Federal...ADMINISTRATIVE MATTERS Contractor Records Retention 4.704 Calculation of retention periods. (a) The retention...

2010-10-01

348

5 CFR 536.302 - Optional pay retention.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Optional pay retention. 536.302 Section 536.302 Administrative...MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Pay Retention § 536.302 Optional pay retention....

2011-01-01

349

48 CFR 4.704 - Calculation of retention periods.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Calculation of retention periods. 4.704 Section 4.704 Federal...ADMINISTRATIVE MATTERS Contractor Records Retention 4.704 Calculation of retention periods. (a) The retention...

2011-10-01

350

Comparative characteristics of HPLC columns based on quantitative structure–retention relationships (QSRR) and hydrophobic-subtraction model  

Microsoft Academic Search

The study was aimed at quantitative comparison of retention properties of modern stationary phases for reversed-phase HPLC. Three approaches, the calculated logarithm of octanol\\/water partition coefficient (clogP)-based model, the molecular modeling descriptors-based model and the hydrophobic-subtraction model, were compared and discussed. Gradient retention time, tR, of a series of test analytes was a dependent variable in the quantitative structure–retention relationship

Tomasz B?czek; Roman Kaliszan; Kate?ina Novotná; Pavel Jandera

2005-01-01

351

Supply Curves of Conserved Energy  

SciTech Connect

Supply curves of conserved energy provide an accounting framework that expresses the potential for energy conservation. The economic worthiness of a conservation measure is expressed in terms of the cost of conserved energy, and a measure is considered economical when the cost of conserved energy is less than the price of the energy it replaces. A supply curve of conserved energy is independent of energy prices; however, the economical reserves of conserved energy will depend on energy prices. Double-counting of energy savings and error propagation are common problems when estimating conservation potentials, but supply curves minimize these difficulties and make their consequences predictable. The sensitivity of the cost of conserved energy is examined, as are variations in the optimal investment strategy in response to changes in inputs. Guidelines are presented for predicting the consequences of such changes. The conservation supply curve concept can be applied to peak power, water, pollution, and other markets where consumers demand a service rather than a particular good.

Meier, Alan Kevin

1982-05-01

352

Mathematical Curve Conjectures  

NSDL National Science Digital Library

In this activity, a six-foot length of nylon rope is suspended at both ends to model a mathematical curve known as the hyperbolic cosine. In a write-pair-share activity, students are asked to make a conjecture concerning the nature of the curve and then embark on a guided discovery in which they attempt to determine a precise mathematical description of the curve using function notation.

James Rutledge

353

Characterization of retention processes and their effect on the analysis of tracer tests in fractured reservoirs  

SciTech Connect

Retention processes such as adsorption and diffusion into an immobile region can effect tracer movement through a fractured reservoir. This study has conducted experimental work and has developed a two-dimensional model to characterize retention processes. A method to directly determine some important flow parameters, such as the fracture aperture, from the analysis of tracer tests has been developed as a result of the new two-dimensional model. The experimental work consisted of batch experiments designed to both reproduce earlier work and to determine the magnitude of the retention effects. Negligible retention was observed from which it was concluded that the batch experiments were not sensitive enough and that more sensitive flowing tests were needed. A two-dimensional model that represents a fractured medium by a mobile region, in which convention, diffusion, and adsorption are allowed, and an immobile region in which only diffusion and adsorption are allowed has been developed. It was possible to demonstrate how each of the mass-transfer processes included in the model affect tracer return curves by producing return curves for any set of the defining variables. Field data from the New Zealand was numerically fit with the model. The optimum values of the parameters determined from curve fitting provided a direct estimate of the fracture width and could be used to estimate other important flow parameters if experimentally determinable values were known. 25 refs., 22 figs., 6 tabs.

Walkup, G.W. Jr.

1984-06-01

354

Modelling global nutrient retention by river damming: Phosphorus and silicon  

NASA Astrophysics Data System (ADS)

The phosphorus to silicon (P:Si) nutrient ratio is a key variable affecting ecosystem health in many aquatic environments. River damming represents a major anthropogenic perturbation of natural material flows along the aquatic continuum, with the potential to profoundly modify absolute and relative nutrient availabilities in surface waters. In this study, a multi-tiered approach for estimating global nutrient retention in man-made reservoirs is presented. We illustrate its application to the global riverine flux of reactive Si, using a database of dissolved reactive Si (DSi) budgets for 24 natural lakes and 22 artificial reservoirs. The database includes information on bedrock geology, surface water pH, water residence time, reservoir age and function, climate, and trophic status. Statistical analyses (ANOVA, t-test, PCA, linear plus non-linear regressions) are used to identify the best predictors of DSi retention and delineate how reservoir properties modulate nutrient dynamics. Results indicate that (1) reservoirs retain significantly less DSi than natural lakes, and (2) the water residence time, reservoir age and function (e.g., hydroelectrical production, irrigation, flood control) are the main system variables controlling DSi retention by dams. Next, a biogeochemical Si model is used to reproduce the previously derived statistical trends for DSi retention. Calibration of the model yields a relationship that enables one to predict annual in-reservoir siliceous productivity as a function of the external reactive Si supply. The model further accounts for the transition from reservoirs where reactive Si retention is primarily due to burial of allochtonous Si to those where in-reservoir DSi uptake by diatoms dominates. Finally, the statistical and mechanistic relationships are extrapolated to estimate that 25-28 Tg SiO2 yr-1 are retained worldwide by dams, or 7% of the annual reactive Si load to watersheds. We are currently applying the same multi-tiered approach to the global P cycle. Our goal is to predict not only the effect of dams on reactive P retention, but also to determine how they are changing the P:Si ratios in river systems. Our preliminary results indicate that reservoirs are more effective in retaining nutrient P than Si.

Maavara, Taylor; Dürr, Hans; Van Cappellen, Philippe

2014-05-01

355

Mechanism of retention loss when C 8 and C 18 HPLC columns are used with highly aqueous mobile phases  

Microsoft Academic Search

We describe investigations into the cause of retention losses encountered when C8 and C18 HPLC columns are used with highly aqueous (>90% water) mobile phases. A procedure for quantifying these losses is described, involving stopping and restarting the flow. This procedure was used to study the dependence of retention loss on the pore size, surface concentration, and chemical structure of

Thomas H. Walter; Pamela Iraneta; Mark Capparella

2005-01-01

356

Functional models for colloid retention in porous media at the triple line1 Annette Dathe1,2,*  

E-print Network

1 Functional models for colloid retention in porous media at the triple line1 Annette Dathe1 can aid in resolving the functional8 form of retention rates of colloids at the AWS interface in the water as10 independent variable by the cumulative colloids passing by. In order of increasing11 number

Walter, M.Todd

357

The Curved Cube  

NSDL National Science Digital Library

Take a solid cube with rods attached at diagonally opposite vertices. Hold the rods horizontally and rapidly spin the cube. (See Figure 1.) You should see a curved outline formed by the spinning cube. The objective of this demos is to discover how the straight edges of the cube become curved. The demo is physically based, but can be simulated within various software packages.

Hill, David R.

2003-02-24

358

CPR: curved planar reformation  

Microsoft Academic Search

Visualization of tubular structures such as blood vessels is an important topic in medical imaging. One way to display tubular structures for diagnostic purposes is to generate longitudinal cross-sections in order to show their lumen, wall, and surrounding tissue in a curved plane. This process is called Curved Planar Reformation (CPR). We present three different methods to generate CPR images.

Armin Kanitsar; Dominik Fleischmann; Rainer Wegenkittl; Petr Felkel; Meister Eduard Gröller

2002-01-01

359

Crystallography on Curved Surfaces  

Microsoft Academic Search

We present a theoretical and numerical study of the static and dynamical properties that distinguish two dimensional curved crystals from their flat space counterparts. Experimental realizations include block copolymer mono-layers on lithographically patterned substrates and self-assembled colloidal particles on a curved interface. At the heart of our approach lies a simple observation: the packing of interacting spheres constrained to lie

Vincenzo Vitelli; Julius Lucks; David Nelson

2007-01-01

360

Anodic Polarization Curves Revisited  

ERIC Educational Resources Information Center

An experiment published in this "Journal" has been revisited and it is found that the curve pattern of the anodic polarization curve for iron repeats itself successively when the potential scan is repeated. It is surprising that this observation has not been reported previously in the literature because it immediately brings into…

Liu, Yue; Drew, Michael G. B.; Liu, Ying; Liu, Lin

2013-01-01

361

Tempo curves considered harmful  

Microsoft Academic Search

In the literature of musicology, computer music research and the psychology of music, timing or tempo measurements are mostly presented in the form of continuous curves. The notion of these tempo curves is dangerous, despite its widespread use, because it lulls its users into the false impression that a continuous concept of temporal flow has an independent existence, a musical

Peter Desain; Henkjan Honing

1993-01-01

362

Pairings on hyperelliptic curves  

Microsoft Academic Search

We assemble and reorganize the recent work in the area of hyperelliptic pairings: We survey the research on constructing hyperelliptic curves suitable for pairing-based cryptography. We also showcase the hyperelliptic pairings proposed to date, and develop a unifying framework. We discuss the techniques used to optimize the pairing computation on hyperelliptic curves, and present many directions for further research.

Jennifer Balakrishnan; Juliana Belding; Sarah Chisholm; Kirsten Eisentraeger; Katherine E. Stange; Edlyn Teske

2009-01-01

363

Nonequilibrium water dynamics in the rhizosphere: How mucilage affects water flow in soils  

NASA Astrophysics Data System (ADS)

The flow of water from soil to plant roots is controlled by the properties of the narrow region of soil close to the roots, the rhizosphere. In particular, the hydraulic properties of the rhizosphere are altered by mucilage, a polymeric gel exuded by the roots. In this paper we present experimental results and a conceptual model of water flow in unsaturated soils mixed with mucilage. A central hypothesis of the model is that the different drying/wetting rate of mucilage compared to the bulk soil results in nonequilibrium relations between water content and water potential in the rhizosphere. We coupled this nonequilibrium relation with the Richards equation and obtained a constitutive equation for water flow in soil and mucilage. To test the model assumptions, we measured the water retention curve and the saturated hydraulic conductivity of sandy soil mixed with mucilage from chia seeds. Additionally, we used neutron radiography to image water content in a layer of soil mixed with mucilage during drying and wetting cycles. The radiographs demonstrated the occurrence of nonequilibrium water dynamics in the soil-mucilage mixture. The experiments were simulated by numerically solving the nonequilibrium model. Our study provides conceptual and experimental evidences that mucilage has a strong impact on soil water dynamics. During drying, mucilage maintains a greater soil water content for an extended time, while during irrigation it delays the soil rewetting. We postulate that mucilage exudation by roots attenuates plant water stress by modulating water content dynamics in the rhizosphere.

Kroener, Eva; Zarebanadkouki, Mohsen; Kaestner, Anders; Carminati, Andrea

2014-08-01

364

The human body retention time of environmental organically bound tritium.  

PubMed

Tritium in the UK environment causes low radiation doses to the public, but uncertainty exists in the dose coefficient for the organically bound component of tritium (OBT). This can affect the assessment of effective doses to representative persons. Contributing to that uncertainty is poor knowledge of the body retention time of OBT and how this varies for different OBT compounds in food. This study was undertaken to measure the retention time of tritium by volunteers after eating sole from Cardiff Bay, which may contain OBT from discharges from the GE Healthcare Ltd plant. Five volunteers provided samples of excreta over periods up to 150 days after intake. The results, which are presented in raw form to allow independent analysis, suggest retention of total tritium with body half-times ranging from 4 to 11 days, with no evidence (subject to experimental noise) of a significant contribution due to retention with a longer half-time. This range covers the half-time of 10 days used by the ICRP for tritiated water. The short timescale could be due to rapid hydrolysis in body tissues of the particular form of OBT used in this study. Implications for the dose coefficient for OBT are that the use of the ICRP value of 4.2 x 10(-11) Sv Bq(-1) may be cautious in this specific situation. These observations on dose coefficients are separate from any implications of recent discussion on whether the tritium radiation weighting factor should be increased from 1 to 2. PMID:19225188

Hunt, John; Bailey, Trevor; Reese, Allan

2009-03-01

365

Phosphorus retention and remobilization along hydrological pathways in karst terrain.  

PubMed

Karst landscapes are often perceived as highly vulnerable to agricultural phosphorus (P) loss, via solution-enlarged conduits that bypass P retention processes. Although attenuation of P concentrations has been widely reported within karst drainage, the extent to which this results from hydrological dilution, rather than P retention, is poorly understood. This is of strategic importance for understanding the resilience of karst landscapes to P inputs, given increasing pressures for intensified agricultural production. Here hydrochemical tracers were used to account for dilution of P, and to quantify net P retention, along transport pathways between agricultural fields and emergent springs, for the karst of the Ozark Plateau, midcontinent USA. Up to ? 70% of the annual total P flux and ? 90% of the annual soluble reactive P flux was retained, with preferential retention of the most bioavailable (soluble reactive) P fractions. Our results suggest that, in some cases, karst drainage may provide a greater P sink than previously considered. However, the subsequent remobilization and release of the retained P may become a long-term source of slowly released "legacy" P to surface waters. PMID:24720609

Jarvie, Helen P; Sharpley, Andrew N; Brahana, Van; Simmons, Tarra; Price, April; Neal, Colin; Lawlor, Alan J; Sleep, Darren; Thacker, Sarah; Haggard, Brian E

2014-05-01

366

Water and heat fluxes in desert soils: 2. Numerical simulations  

NASA Astrophysics Data System (ADS)

Transient one-dimensional fluxes of soil water (liquid and vapor) and heat in response to 1 year of atmospheric forcing were simulated numerically for a site in the Chihuahuan Desert of Texas. The model was initialized and evaluated using the monitoring data presented in a companion paper (Scanlon, this issue). Soil hydraulic and thermal properties were estimated a priori from a combination of laboratory measurements, models, and other published information. In the first simulation, the main drying curves were used to describe soil water retention, and hysteresis was ignored. Remarkable consistency was found between computed and measured water potentials and temperatures. Attenuation and phase shift of the seasonal cycle of water potentials below the shallow subsurface active zone (0.0- to 0.3-m depth) were similar to those of temperatures, suggesting that water potential fluctuations were driven primarily by temperature changes. Water fluxes in the upper 0.3 m of soil were dominated by downward and upward liquid fluxes that resulted from infiltration of rain and subsequent evaporation from the surface. Upward flux was vapor dominated only in the top several millimeters of the soil during periods of evaporation. Below a depth of 0.3 m, water fluxes varied slowly and were dominated by downward thermal vapor flux that decreased with depth, causing a net accumulation of water. In a second simulation, nonhysteretic water retention was instead described by the estimated main wetting curves; the resulting differences in fluxes were attributed to lower initial water contents (given fixed initial water potential) and unsaturated hydraulic conductivities that were lower than they were in the first simulation. Below a depth of 0.3 m, the thermal vapor fluxes dominated and were similar to those in the first simulation. Two other simulations were performed, differing from the first only in the prescription of different (wetter) initial water potentials. These three simulations yielded identical solutions in the upper 0.2 m of soil after infiltration of summer rain; however, the various initial water potentials were preserved throughout the year at depths greater than 0.2 m. Comparison of all four simulations showed that the predominantly upward liquid fluxes below a depth of 0.2 m were very sensitive to the differences in water retention functions and initial water potentials among simulations, because these factors strongly affected hydraulic conductivities. Comparison of numerical modeling results with chemical tracer data showed that values of downward vapor flux below the surface evaporation zone were of the same order of magnitude as those previously estimated by analysis of depth distributions of bomb 3H (volatile) and bomb 36Cl (nonvolatile).

Scanlon, Bridget R.; Milly, P. C. D.

1994-03-01

367

Demand Curves and the Pricing of Money Management  

Microsoft Academic Search

One reason why funds charge different prices to their investors is that they face different demand curves. One source of differentiation is asset retention: Performance-sensitive investors migrate from worse to better prospects, taking their performance sensitivity with them. In the cross-section we show that past attrition significantly influences the current pricing of retail but not institutional funds. In time-series we

Susan E. K. Christoffersen; David K. Musto

2002-01-01

368

Automated solid-phase extraction of herbicides from water for gas chromatographic-mass spectrometric analysis  

USGS Publications Warehouse

An automated solid-phase extraction (SPE) method was developed for the pre-concentration of chloroacetanilide and triazine herbicides, and two triazine metabolites from 100-ml water samples. Breakthrough experiments for the C18 SPE cartridge show that the two triazine metabolites are not fully retained and that increasing flow-rate decreases their retention. Standard curve r2 values of 0.998-1.000 for each compound were consistently obtained and a quantitation level of 0.05 ??g/l was achieved for each compound tested. More than 10,000 surface and ground water samples have been analyzed by this method.

Meyer, M.T.; Mills, M.S.; Thurman, E.M.

1993-01-01

369

NASA's Potential Contributions for Remediation of Retention Ponds Using Solar Ultraviolet Radiation and Photocatalysis  

NASA Technical Reports Server (NTRS)

This Candidate Solution uses NASA Earth science research on atmospheric ozone and aerosols data (1) to help improve the prediction capabilities of water runoff models that are used to estimate runoff pollution from retention ponds, and (2) to understand the pollutant removal contribution and potential of photocatalytically coated materials that could be used in these ponds. Models (the EPA's SWMM and the USGS SLAMM) exist that estimate the release of pollutants into the environment from storm-water-related retention pond runoff. UV irradiance data acquired from the satellite mission Aura and from the OMI Surface UV algorithm will be incorporated into these models to enhance their capabilities, not only by increasing the general understanding of retention pond function (both the efficacy and efficiency) but additionally by adding photocatalytic materials to these retention ponds, augmenting their performance. State and local officials who run pollution protection programs could then develop and implement photocatalytic technologies for water pollution control in retention ponds and use them in conjunction with existing runoff models. More effective decisions about water pollution protection programs could be made, the persistence and toxicity of waste generated could be minimized, and subsequently our natural water resources would be improved. This Candidate Solution is in alignment with the Water Management and Public Health National Applications.

Underwood, Lauren W.; Ryan, Robert E.

2007-01-01

370

Membrane retention of herbicides from single and multi-solute media: The effect of ionic environment  

Microsoft Academic Search

Results are reported for a systematic study on retention of three selected herbicides, in single solute or multi-solute feed-waters, by three commercial NF\\/ULPRO membranes, using stirred cells in the dead-end filtration mode. The effect of ionic environment on the retention of herbicides is also examined by controlling sodium and calcium concentration. The results are interpreted on the basis of the

K. V. Plakas; A. J. Karabelas

2008-01-01

371

Retention at Departments of Physics  

NASA Astrophysics Data System (ADS)

A thriving physics department is the end result of many actions, taken over time, that results in the development of a sense of community between the faculty and the students. As part of this sense of community, gifted students must receive special attention and innovative ideas must be incorporated to successfully accommodate the needs of these students. We have found that the best retention strategy for gifted undergraduates is the total involvement of them in undergraduate research projects and also the development of leadership in extracurricular activities within the department. A careful employment strategy is needed to secure a faculty committed to the goals of the community.

Muller, Rafael; Rosa, Luis

2013-03-01

372

space curves and surfaces 1 Plotting Space Curves  

E-print Network

space curves and surfaces 1 Plotting Space Curves the twisted cubic with matplotlib four subplots 2013 Scientific Software (MCS 507 L-16) space curves and surfaces 2 October 2013 1 / 43 #12;space curves and surfaces 1 Plotting Space Curves the twisted cubic with matplotlib four subplots

Verschelde, Jan

373

Weak Curves In Elliptic Curve Cryptography Peter Novotney  

E-print Network

Weak Curves In Elliptic Curve Cryptography Peter Novotney March 2010 Abstract Certain choices of elliptic curves and/or underlying fields reduce the security of an elliptical curve cryptosystem of an elliptical curve that reduce the security in this manner, as well as a discussion of the attacks that cause

Stein, William

374

GENERALIZED MORDELL CURVES, GENERALIZED FERMAT CURVES, AND THE HASSE PRINCIPLE  

E-print Network

GENERALIZED MORDELL CURVES, GENERALIZED FERMAT CURVES, AND THE HASSE PRINCIPLE NGUYEN NGOC DONG. The descending chain condition on sequences of curves 18 6. Certain generalized Fermat curves violating the Hasse of generalized Fermat curves 33 9. Epilogue 35 Acknowledgements 45 References 45 Abstract. A generalized Mordell

Nguyen, Dong Quan Ngoc

375

Retention force measurement of telescopic crowns  

Microsoft Academic Search

This study deals with the determination of the retentive force between primary and secondary telescopic crowns under clinical\\u000a conditions. Forty-three combined fixed–removable prostheses with a total of 140 double crowns were used for retention force\\u000a measurement of the telescopic crowns prior to cementation. The crowns had a preparation of 1–2°. A specifically designed measuring\\u000a device was used. The retentive forces

Stefan Bayer; Helmut Stark; Sebastian Mues; Ludger Keilig; Anja Schrader; Norbert Enkling

2010-01-01

376

Simulation of optically conditioned retention and mass occurrences of Periphylla periphylla  

PubMed Central

Jellyfish blooms are of increasing concern in many parts of the world, and in Norwegian fjords an apparent increase in mass occurrences of the deep water jellyfish Periphylla periphylla has attracted attention. Here we investigate the hypothesis that changes in the water column light attenuation might cause local retention and thereby facilitate mass occurrences. We use a previously tested individual-based model of light-mediated vertical migration in P. periphylla to simulate how retention is affected by changes in light attenuation. Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined. In category 1, increased light attenuation turns fjords into dark “deep-sea” environments which increase the habitat and retention of P. periphylla. In category 2, an optimal light attenuation facilitates the maximum retention and likelihood for mass occurrences. In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention. This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection. PMID:20454515

Dupont, Nicolas; Aksnes, Dag L.

2010-01-01

377

Simulation of optically conditioned retention and mass occurrences of Periphylla periphylla.  

PubMed

Jellyfish blooms are of increasing concern in many parts of the world, and in Norwegian fjords an apparent increase in mass occurrences of the deep water jellyfish Periphylla periphylla has attracted attention. Here we investigate the hypothesis that changes in the water column light attenuation might cause local retention and thereby facilitate mass occurrences. We use a previously tested individual-based model of light-mediated vertical migration in P. periphylla to simulate how retention is affected by changes in light attenuation. Our results suggest that light attenuation, in combination with advection, has a two-sided effect on retention and that three fjord categories can be defined. In category 1, increased light attenuation turns fjords into dark "deep-sea" environments which increase the habitat and retention of P. periphylla. In category 2, an optimal light attenuation facilitates the maximum retention and likelihood for mass occurrences. In category 3, further increase in light attenuation, however, shoals the habitat so that individuals are increasingly exposed to advection and this results in loss of individuals and decreased retention. This classification requires accurate determinations of the organism's light preference, the water column light attenuation and topographical characteristics affecting advection. PMID:20454515

Dupont, Nicolas; Aksnes, Dag L

2010-06-01

378

Radionuclide Retention in Concrete Wasteforms  

SciTech Connect

Assessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e., sorption or precipitation); the mechanism of contaminant release; the significance of contaminant release pathways; how wasteform performance is affected by the full range of environmental conditions within the disposal facility; the process of wasteform aging under conditions that are representative of processes occurring in response to changing environmental conditions within the disposal facility; the effect of wasteform aging on chemical, physical, and radiological properties; and the associated impact on contaminant release. This knowledge will enable accurate prediction of radionuclide fate when the wasteforms come in contact with groundwater. Data collected throughout the course of this work will be used to quantify the efficacy of concrete wasteforms, similar to those used in the disposal of LLW and MLLW, for the immobilization of key radionuclides (i.e., uranium, technetium, and iodine). Data collected will also be used to quantify the physical and chemical properties of the concrete affecting radionuclide retention.

Wellman, Dawn M.; Jansik, Danielle P.; Golovich, Elizabeth C.; Cordova, Elsa A.

2012-09-24

379

Enhanced retention of linuron, alachlor and metalaxyl in sandy soil columns intercalated with wood barriers.  

PubMed

A study has been made of the effect a reactive barrier made of pine (softwood) or oak (hardwood) wood intercalated in a sandy soil column has on the retention of linuron, alachlor and metalaxyl (pesticides with contrasting physicochemical characteristics). The leaching of pesticides has been carried out under a saturated flow regime and breakthrough curves (BTCs) have been obtained at flow rates of 1 m Lmin(-1) (all pesticides) and 3 m Lmin(-1) (linuron). The cumulative curves in the unmodified soil indicate a leaching of pesticides >80% of the total amount of compound added. After barrier intercalation, linuron leaching decreases significantly and a modification of the leaching kinetics of alachlor and metalaxyl has been observed. The theoretical R factors increased ?2.6-3.3, 1.2-1.6-fold, and 1.4-1.7-fold and the concentration of the maximum peak decreased ?6-12-fold, 2-4-fold and 1.2-2-fold for linuron, alachlor and metalaxyl, respectively. When considering the three pesticides, significant correlations have been found between the theoretical retardation factor (R) and the pore volume corresponding to the maximum peaks of the BTCs (r=0.77; p<0.05) or the total volume leached (r=-0.78; p<0.05). The results reveal the efficacy of reactive wood barriers to decrease the leaching of pesticides from point sources of pollution depends on the type of wood, the hydrophobicity of the pesticide and the adopted water flow rate. Pine was more effective than oak in decreasing the leaching of hydrophobic pesticide linuron or in decreasing the maximum peak concentration of the less hydrophobic pesticides in soils. Efficacy of these wood barriers was limited for the least hydrophobic pesticide metalaxyl. PMID:21183199

Rodríguez-Cruz, M S; Ordax, J M; Arienzo, M; Sánchez-Martín, M J

2011-03-01

380

Another Hilbert Curve Generator  

NSDL National Science Digital Library

Students work step-by-step through the generation of a different Hilbert-like Curve (a fractal made from deforming a line by bending it), allowing them to explore number patterns in sequences and geometric properties of fractals.

381

Logistic Curve Demo  

NSDL National Science Digital Library

This interactive demo illustrates the generation of a logistic curve. This demo is appropriate for a pre-calculus course, but is quite effective in a calculus class immediately after a discussion of inflection points.

Roberts, Lila F.

2002-02-03

382

The Bell Curve  

NSDL National Science Digital Library

This lesson is designed to introduce students to the normal distribution or bell curve. The lesson also discusses controversy behind the interpretation of the bell curve. This lesson provides links to discussions and activities related to the normal distribution as well as suggested ways to integrate them into the lesson. Finally, the lesson provides links to follow-up lessons designed for use in succession with the current one.

2011-05-23

383

Adult Student Retention: A Practical Approach to Retention Improvement through Learning Enhancement  

ERIC Educational Resources Information Center

Adult student retention is an issue of growing concern for many institutions. It differs from traditional retention much like traditional students differ from adult students. As the majority of student body growth comes from adult students, adult student retention management will become critical to the majority of colleges and universities. To…

Fincher, Mark

2010-01-01

384

“The nurse satisfaction, service quality and nurse retention chain” : Implications for management of recruitment and retention  

Microsoft Academic Search

This paper presents the findings of a qualitative study, based on interviews with over 130 nurses and midwives in four London Trust hospitals on: the main factors influencing nurse satisfaction and retention; empirical support for the robustness of a conceptual framework or model “the nurse satisfaction, service quality and nurse retention chain”; and some managerial considerations for recruitment and retention.

Karin Newman; Uvanney Maylor; Bal Chansarkar

2002-01-01

385

Mechanisms affecting the transport and retention of bacteria, bacteriophage and microspheres in laboratory-scale saturated fractures  

NASA Astrophysics Data System (ADS)

Groundwater is becoming an increasingly important water source due to the ever-increasing demands from agricultural, residential and industrial consumers. In search of more secure sources, wells are routinely finished over large vertical depths in bedrock aquifers, creating new hydraulic pathways and thus increasing the risk of cross contamination. Moreover, hydraulic pathways are also being altered and created by increasing water withdrawal rates from these wells. Currently, it is not well understood how biological contaminants are transported through, and retained in, fractured media thereby making risk assessment and land use decisions difficult. Colloid transport within fractured rock is a complex process with several mechanisms affecting transport and retention, including: advection, hydrodynamic dispersion, diffusion, size exclusion, adsorption, and decay. Several researchers have investigated the transport of bacteria, bacteriophage, and microspheres (both carboxylated and plain) to evaluate the effects of surface properties and size on transport and retention. These studies have suggested that transport is highly dependent on the physico-chemical properties of the particle, the fracture, and the carrying fluid. However, these studies contain little detail regarding the specific mechanisms responsible for transport beyond speculating about their existence. Further, little work has been done to compare the transport of these particulate materials through the same fracture, allowing for direct observations based on particulate size and surface properties. This research examines the similarities and differences in transport and retention between four different particles through two different laboratory-scale, saturated fractures. This work is designed to explore the effects of particle size, surface properties, ionic strength of the carrying solution, and aperture field characteristics on transport and retention in single, saturated fractures. The particulates chosen for this work include E.coli RS2-GFP, MS2, and carboxylated microspheres with diameters of 0.0425 ?m and 0.525 ?m. The results of this work will contribute to the understanding of risk posed by contaminants to bedrock aquifer sources. Dolomite rock samples were collected from the DoLime quarry in Guelph, Ontario. A single fracture was induced in the sample by applying a uniaxial force. Lengthwise edges were sealed to create no-flow boundaries, and flow cells were fitted on the up- and down-stream ends of the fracture. Aperture size and variability were characterized using hydraulic and solute tracer tests. Particulate tracer tests were conducted by injecting a pulse of particles (E.coli RS2-GFP, MS2, or microspheres) into the upstream flow cell, and measuring the subsequent effluent concentration profile. From these tests, the percent recovery and mean residence time of the particulate were analyzed. Generally, it was found that microspheres are a poor indication of biological particulate transport, likely due to differences in surface properties affecting the retention mechanisms. This talk will provide an analysis of the breakthrough curves, with specific details regarding the transport and retention mechanisms for the various types and sizes of particles employed in these experiments.

Seggewiss, G.; Dickson, S. E.

2013-12-01

386

Water  

NSDL National Science Digital Library

Water is an environmental chemistry Flash video designed to give students and educators an informative look into Water Treatment and Waste Water Treatment. It covers a variety of water and waste water treatment plants and processes including: Watersheds, Ozonation, Chlorination, Flocculation, Sand Filtration, Trickling Filters, Activated Sludge, and more. This program includes both live video and animations.~~~~

Dr. Frank Dunnivant

2008-02-20

387

Estimating steady-state evaporation rates from bare soils under conditions of high water table  

USGS Publications Warehouse

A procedure that combines meteorological and soil equations of water transfer makes it possible to estimate approximately the steady-state evaporation from bare soils under conditions of high water table. Field data required include soil-water retention curves, water table depth and a record of air temperature, air humidity and wind velocity at one elevation. The procedure takes into account the relevant atmospheric factors and the soil's capability to conduct 'water in liquid and vapor forms. It neglects the effects of thermal transfer (except in the vapor case) and of salt accumulation. Homogeneous as well as layered soils can be treated. Results obtained with the method demonstrate how the soil evaporation rates·depend on potential evaporation, water table depth, vapor transfer and certain soil parameters.

Ripple, C.D.; Rubin, J.; Van Hylckama, T. E. A.

1970-01-01

388

Retention and transport of nutrients in a mature agricultural impoundment  

NASA Astrophysics Data System (ADS)

Small impoundments intended for irrigation, livestock watering, and hydropower are numerous in agricultural regions of the world. Many of these artificial water bodies are well positioned to intercept fertilizer runoff and pollutants but could be vulnerable to long-term sedimentation, management intervention, or failure. We examined solute retention in a mature, sediment-filled, run-of-river impoundment created by a small, >100 year old dam in agricultural Wisconsin, United States. To do so, we measured instantaneous net fluxes of inorganic and organic solutes through the system, which contained wetlands. The impoundment was a persistent net sink for sulfate and, during the warm season only, a net sink for nitrate, ammonium, and soluble reactive phosphorus. There was also a negative relationship between nitrate and sulfate retention, suggestive of nitrate-stimulated sulfate production. Impoundment hydraulics were then altered by a management manipulation (dam removal) that caused mean water travel time to decrease by approximately 40%. Following manipulation, autoregressive modeling of solute time series indicated a decrease in mean net retention of nitrate, sulfate, ammonium, and soluble reactive phosphorus. There was also a decrease in the variability (coefficient of variation) of instantaneous net exports of dissolved organic nitrogen and dissolved organic phosphorus. These biogeochemical changes were consistent with predictions based on hydraulics (reduced water travel time), with the exception of ammonium release immediately following reservoir dewatering. Our results emphasize the biogeochemical importance of reservoir-wetland ecosystems, which are expanding with impoundment sedimentation but are threatened by infrastructure aging. We suggest that reservoir wetlands be considered in the management of dams and surface water pollution.

Powers, S. M.; Julian, J. P.; Doyle, M. W.; Stanley, E. H.

2013-03-01

389

Retentive shear strengths of various bonding attachment bases.  

PubMed

The purpose of this study was to determine whether any of the commercially available attachment bases had significantly better retentive properties. This was determined by their shear strengths after all were bonded to bovine incisors with Auto-Tach. The mean shear strengths of sixteen bases were statistically compared to each other at 24 hours and at 30 days. In addition, the data were converted to pounds per square inch to ascertain if the size of the base significantly influenced the mean shear strength. It was concluded that (1). one of the foil mesh bases tested for shear strength was significantly superior to the two other base designs (indents with undercuts and solid bases with perforations); (2). mechanical retention of the attachment bases to the adhesive was not significantly affected after being placed in distilled water at 37 degrees C. either for 24 hours or for 30 days; (3). smaller foil mesh bases could be used without sacrificing significant shear strength. PMID:6992590

Lopez, J I

1980-06-01

390

Water  

MedlinePLUS

... to groundwater (the fresh water found under the Earth’s surface that supplies wells and springs). Everything that ... body is water. 4. How much of the earth’s surface is water? About 80 percent of the ...

391

Metal Cycling in Polymictic Suburban Retention Ponds  

NASA Astrophysics Data System (ADS)

Stratified conditions in lakes have been demonstrated to enhance metal species mobilization as well as the potential for mercury methylation. However, few studies have been conducted in shallow engineered systems. Although each system is relatively small in area, the overall number of such engineered systems is large (and increasing) and warrants consideration within overall landscape nutrient cycling. Previous research has documented strong diel stratification cycles and the frequent development of anoxia within the bottom waters of such polymictic systems compared with larger, dimictic lakes. We examined the impact of polymixis and the shorter hydraulic residence time on the bioavailability and the downstream transport of Hg species and other trace metals. Filtered and unfiltered lake water samples were collected at 15 and 50 cm above the sediment as well as the surface of the 1-m deep Mirror Lake retention pond on the University of Connecticut Storrs campus. Additional samples were collected from the lake outlet under baseflow and elevated discharge conditions, including the capture of initial mobilization during precipitation events. Samples were analyzed for Hg speciation as well as dissolved organic carbon (DOC), total suspended solids, cations (including Cu, Zn and Pb) and anions. We measured stage height at the lake outlet to calculate flux. Lake total Hg (THg) concentrations were generally less than 4 ng/L with the majority in the particulate phase. Outlet THg increased to 32 ng/L and dissolved THg increased to 1.2 ng/L during high flow events likely due to enhanced mobilization of particulates from the sediment and runoff from impervious surfaces, respectively. In contrast, DOC concentrations decreased as runoff contributions increased and were not correlated with dissolved THg. In addition, THg concentrations increased following copper algaecide applications, possibly due to re- suspension in the water column of biotic material.

Segal, C. A.; Bushey, J. T.; Torgersen, T.

2009-05-01

392

Rainwater runoff retention on an aged intensive green roof.  

PubMed

Urban areas are characterised by large proportions of impervious surfaces which increases rainwater runoff and the potential for surface water flooding. Increased precipitation is predicted under current climate change projections, which will put further pressure on urban populations and infrastructure. Roof greening can be used within flood mitigation schemes to restore the urban hydrological balance of cities. Intensive green roofs, with their deeper substrates and higher plant biomass, are able to retain greater quantities of runoff, and there is a need for more studies on this less common type of green roof which also investigate the effect of factors such as age and vegetation composition. Runoff quantities from an aged intensive green roof in Manchester, UK, were analysed for 69 rainfall events, and compared to those on an adjacent paved roof. Average retention was 65.7% on the green roof and 33.6% on the bare roof. A comprehensive soil classification revealed the substrate, a mineral soil, to be in good general condition and also high in organic matter content which can increase the water holding capacity of soils. Large variation in the retention data made the use of predictive regression models unfeasible. This variation arose from complex interactions between Antecedant Dry Weather Period (ADWP), season, monthly weather trends, and rainfall duration, quantity and peak intensity. However, significantly lower retention was seen for high rainfall events, and in autumn, which had above average rainfall. The study period only covers one unusually wet year, so a longer study may uncover relationships to factors which can be applied to intensive roofs elsewhere. Annual rainfall retention for Manchester city centre could be increased by 2.3% by a 10% increase in intensive green roof construction. The results of this study will be of particular interest to practitioners implementing greenspace adaptation in temperate and cool maritime climates. PMID:23712113

Speak, A F; Rothwell, J J; Lindley, S J; Smith, C L

2013-09-01

393

Headwaters Retention Potential Assessment with Respect to Hydrological Extremes  

NASA Astrophysics Data System (ADS)

Urgent need of solving of issues dealing with protection against hydrological extremes calls also for detailed clarification of runoff generation mechanisms. The topicality of this subject is associated with recent climate change and the intensification of hydrometeorological extremes, taking place in Central Europe as well. Suitable conditions for the research realization at present is related to the highly peaty Otava River headwaters, sw. Czechia. To understand and clarify the runoff generation process and the effect of various physical-geographic factors on its dynamics, the analyses of runoff regime in chosen experimental catchments were done. In order to evaluate the study area retention potential peat bogs hydrological function assessment had to be carried out. Attention was also focused on findings of a runoff dynamics dependence on the ground water table in the peatland. Hydrochemical and geochemical approaches including isotope hydrology principles were used to explain the mechanisms of streamflow generation processes in the highly peaty catchments. On the base of acquired results and time series statistical analyses it could be stated that more distinct runoff variability is typical for streams draining catchments with the significant proportion of peatland. The fact that the existence of bogs has the negative effect on the runoff process, especially during extreme hydrological situations, was confirmed by hydropedological, hydrochemical and geochemical approaches. Implementation of unforceable measures, such as the use of potential accumulation and retention spaces in the catchment area, could contribute significantly to reduction of peak flows and to increase of water resources during eventual extreme droughts in future. Key words: hydrological extremes, runoff formation, retention potential, Otava River, automatic stations, experimental catchment, peat bogs hydrological function, oxygen isotopes, snow cover, retention and accumulation spaces, climate change

Kocum, Jan; Jansky, Bohumir; Vlcek, Lukas

2014-05-01

394

Transmural migration of gastrostomy tube retention discs  

Microsoft Academic Search

Background Accidental dislodgment is one of the most frequent causes of avoidable cost and consternation related to gastrostomy tubes. The Sacks–Vine gastrostomy tube, inserted in an antegrade fashion by a percutaneous technique, is extremely stable due to the construction of its disc retention device. However, transmural migration of the retention disc is a known severe delayed complication associated with this

AnneMarie Cahill; Kevin M. Baskin; Robin D. Kaye; Charles R. Fitz; Richard B. Towbin

2004-01-01

395

The Grade Retention/Social Promotion Debate.  

ERIC Educational Resources Information Center

This publication focuses on the retention/promotion debate regarding failing and low-achieving students. An introductory essay describes the inherent limitation in the research done on this issue--the impossibility of obtaining an appropriate control group--and suggests that the retention/promotion quandary can best be resolved by accommodating…

Lindelow, John

1985-01-01

396

Factors Affecting Students' Retention at Kuwait University  

ERIC Educational Resources Information Center

This article addresses the factors that affect students' retention at Kuwait University. Five hundred seventy students participated in the study. A survey of 22 retention factors was designed to measure student perceptions. Students presented their agreement on factors which included: achieving personal aspiration, getting jobs, free-of-charge…

AlKandari, Nabila

2008-01-01

397

Unconditioned Stimulus Intensity and Retention Interval Effects  

Microsoft Academic Search

In single-element taste-aversion learning, retention interval effects are seen if taste aversions are paradoxically weak when they are tested 1 day after conditioning than when they are tested 3 or more days after conditioning. One explanation of this phenomenon is that weaker taste aversions may increase in strength across a retention interval. To test this possibility, rats were given saccharin

W. ROBERT BATSELL; JOHN W. GEORGE

1996-01-01

398

Healthcare Learning Community and Student Retention  

ERIC Educational Resources Information Center

Teaching, learning, and retention processes have evolved historically to include multifaceted techniques beyond the traditional lecture. This article presents related results of a study using a healthcare learning community in a southwest Georgia university. The value of novel techniques and tools in promoting student learning and retention

Johnson, Sherryl W.

2014-01-01

399

Profile in Action: Linking Admission and Retention  

ERIC Educational Resources Information Center

A profile-oriented retention strategy embraces the admission process as a powerful lever in improving retention and completion rates and recognizes that the student profile can be shaped by changes in admission policies or priorities--even within the current market position of the institution. In addition, the student body can be oriented toward…

Cortes, Carla M.

2013-01-01

400

A Marketing Model for Student Retention.  

ERIC Educational Resources Information Center

Presents a model to help student personnel administrators develop cost effective approaches for improving student retention, based on the marketing process. The marketing model can be used to systematically respond to the needs of students, faculty, and the community. Outlines retention tactics at Prince Georges Community College. (JAC)

Lewis, Chad T.; And Others

1983-01-01

401

MONOGRAPH - Recruitment & Retention of Engineering Technology Students  

NSDL National Science Digital Library

Identifying strategies to assist with recruitment and retention of engineering technology students particularly women and minorities was the focus of a 1998 Retention Forum, held in Columbia, SC, and sponsored by the South Carolina Advanced Technological Education (SC ATE) Center of Excellence. The Center is funded by the National Science Foundation and the South Carolina State Board for Technical and Comprehensive Education. Approximately 90 Retention Forum participants discussed results from research on enrollment and retention of engineering technology (ET) students in South Carolinas technical college system. The SC ATE Center of Excellence commissioned the research report, Determinants of Enrollment and Retention in South Carolina Engineering Technology Programs, by Dr. W. Douglas Evans. Forum participants also heard a report on what SC technical colleges are doing well to recruit and retain women and minorities in ET fields. During the forum, a panel of women and minority ET students from South Carolina technical colleges shared their perspectives and experiences. In conclusion, participants met in focus groups to discuss new ways of enhancing recruitment and retention of engineering technology students. These research activities reveal some significant findings, which are being used to develop new retention strategies. In addition to an in-depth examination of opinions and attitudes of first- and second-year engineering technology students and engineering technology faculty and administrators, the research takes a closer look at recruitment and retention of women and minority students. The various components of this research activity by the SC ATE Center of Excellence are presented in this monograph.

Craft, Elaine

402

Measuring Up: Benchmarking Graduate Retention. IES Report.  

ERIC Educational Resources Information Center

Retention of college graduates by employers across the United Kingdom was examined. Data were collected through a survey of 362 organizations and interviews with 36 employers and their graduate employees. Most employers were unworried by their levels of graduate retention; two-thirds expected to keep new recruits for the foreseeable future. Rates…

Tyers, C.; Perryman, S.; Barber, L.

403

Managing human resources to improve employee retention.  

PubMed

Managers face increased challenges as the demand for health care services increases while the supply of employees with the requisite skills continues to lag. Employee retention will become more important in the effort to service health care needs. Appropriate human resource management strategies and policies implemented effectively can significantly assist managers in dealing with the employee retention challenges ahead. PMID:15923925

Arnold, Edwin

2005-01-01

404

Classroom Techniques for Black Male Student Retention.  

ERIC Educational Resources Information Center

This paper describes and encourages the application of 20 classroom techniques to enhance the retention and success of black male college students. Though retention enhancement programs work best when institution-wide support and commitment are behind them, the techniques described here can be implemented in the classroom with significant results…

Gardenhire, John Fouts

405

Novel Word Retention in Sequential Bilingual Children  

ERIC Educational Resources Information Center

Children's ability to learn and retain new words is fundamental to their vocabulary development. This study examined word retention in children learning a home language (L1) from birth and a second language (L2) in preschool settings. Participants were presented with sixteen novel words in L1 and in L2 and were tested for retention after…

Kan, Pui Fong

2014-01-01

406

The Psychology Underlying Successful Retention Practices.  

ERIC Educational Resources Information Center

Describes the psychological processes that lead to academic and social integration based on a retention model proposed by the authors. Describes how successful retention programs such as learning communities, freshman interest groups, tutoring, and orientation rely on psychological processes. Four psychological theories form the basis for…

Bean, John; Eaton, Shevawn Bogdan

2002-01-01

407

How work environment impacts retention.  

PubMed

Work environment is a major aspect of the day-to-day grind that drives the retention (or turnover) of RNs. When opportunities abound, it is easy to jump ship, and when turnover begins, it is usually the best and brightest who are first to depart. Recent research reported a whopping 27.1% average voluntary turnover rate among new graduate nurses during their first year of employment. Aging of the nurse workforce may be the largest factor impacting health care work environments, as employers struggle to diminish the physical effect of lifting thousands of pounds and walking several miles during each shift. Every influence on the work environment (management, peer behavior, patient acuity, equipment availability, the physical plant) should be assessed for impact on the workforce. While we cannot hope to create paradise in each work setting, we can promote an environment that is healing both to patient and to caregiver. PMID:18979696

Christmas, Kate

2008-01-01

408

Radionuclide Retention in Concrete Wasteforms  

SciTech Connect

Assessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e., sorption or precipitation); the mechanism of contaminant release; the significance of contaminant release pathways; how wasteform performance is affected by the full range of environmental conditions within the disposal facility; the process of wasteform aging under conditions that are representative of processes occurring in response to changing environmental conditions within the disposal facility; the effect of wasteform aging on chemical, physical, and radiological properties; and the associated impact on contaminant release. This knowledge will enable accurate prediction of radionuclide fate when the wasteforms come in contact with groundwater. The information present in the report provides data that (1) measures the effect of concrete wasteform properties likely to influence radionuclide migration; and (2) quantifies the rate of carbonation of concrete materials in a simulated vadose zone repository.

Bovaird, Chase C.; Jansik, Danielle P.; Wellman, Dawn M.; Wood, Marcus I.

2011-09-30

409

A comparison of the retention of pathogenic Escherichia coli?O157 by sprouts, leaves and fruits.  

PubMed

The retention (binding to or association with the plant) of Escherichia coli by cut leaves and fruits after vigorous water washing was compared with that by sprouts. Retention by fruits and leaves was similar but differed from retention by sprouts in rate, effect of wounding and requirement for poly-?,1-6-N-acetyl-D-glucosamine. Escherichia coli was retained by cut ends of lettuce leaves within 5?min while more than 1?h was required for retention by the intact epidermis of leaves and fruits, and more than 1 day for sprouts. Retention after 5?min at the cut leaf edge was specific for E.?coli and was not shown by the plant-associated bacteria Agrobacterium tumefaciens and Sinorhizobium meliloti.?Escherichia coli was retained by lettuce, spinach, alfalfa, bean, tomato, Arabidopsis thaliana, cucumber, and pepper leaves and fruits faster than by sprouts. Wounding of leaves and fruits but not sprouts increased bacterial retention. Mutations in the exopolysaccharide synthesis genes yhjN and wcaD reduced the numbers of bacteria retained. PgaC mutants were retained by cut leaves and fruits but not by sprouts. There was no significant difference in the retention of an O157 and a K12 strain by fruits or leaves. However, retention by sprouts of O157 strains was significantly greater than K12 strains. These findings suggest that there are differences in the mechanisms of E? coli retention among sprouts, and leaves and fruits. PMID:25351040

Mathews, Stephanie L; Smith, Rachel B; Matthysse, Ann G

2014-11-01

410

A comparison of the retention of pathogenic Escherichia coli?O157 by sprouts, leaves and fruits  

PubMed Central

The retention (binding to or association with the plant) of Escherichia coli by cut leaves and fruits after vigorous water washing was compared with that by sprouts. Retention by fruits and leaves was similar but differed from retention by sprouts in rate, effect of wounding and requirement for poly-?,1-6-N-acetyl-D-glucosamine. Escherichia coli was retained by cut ends of lettuce leaves within 5 min while more than 1 h was required for retention by the intact epidermis of leaves and fruits, and more than 1 day for sprouts. Retention after 5 min at the cut leaf edge was specific for E. coli and was not shown by the plant-associated bacteria Agrobacterium tumefaciens and Sinorhizobium meliloti.?Escherichia coli was retained by lettuce, spinach, alfalfa, bean, tomato, Arabidopsis thaliana, cucumber, and pepper leaves and fruits faster than by sprouts. Wounding of leaves and fruits but not sprouts increased bacterial retention. Mutations in the exopolysaccharide synthesis genes yhjN and wcaD reduced the numbers of bacteria retained. PgaC mutants were retained by cut leaves and fruits but not by sprouts. There was no significant difference in the retention of an O157 and a K12 strain by fruits or leaves. However, retention by sprouts of O157 strains was significantly greater than K12 strains. These findings suggest that there are differences in the mechanisms of E coli retention among sprouts, and leaves and fruits. PMID:25351040

Mathews, Stephanie L; Smith, Rachel B; Matthysse, Ann G

2014-01-01

411

Trend analyses with river sediment rating curves  

USGS Publications Warehouse

Sediment rating curves, which are fitted relationships between river discharge (Q) and suspended-sediment concentration (C), are commonly used to assess patterns and trends in river water quality. In many of these studies it is assumed that rating curves have a power-law form (i.e., C = aQb, where a and b are fitted parameters). Two fundamental questions about the utility of these techniques are assessed in this paper: (i) How well to the parameters, a and b, characterize trends in the data? (ii) Are trends in rating curves diagnostic of changes to river water or sediment discharge? As noted in previous research, the offset parameter, a, is not an independent variable for most rivers, but rather strongly dependent on b and Q. Here it is shown that a is a poor metric for trends in the vertical offset of a rating curve, and a new parameter, â, as determined by the discharge-normalized power function [C = â (Q/QGM)b], where QGM is the geometric mean of the Q values sampled, provides a better characterization of trends. However, these techniques must be applied carefully, because curvature in the relationship between log(Q) and log(C), which exists for many rivers, can produce false trends in â and b. Also, it is shown that trends in â and b are not uniquely diagnostic of river water or sediment supply conditions. For example, an increase in â can be caused by an increase in sediment supply, a decrease in water supply, or a combination of these conditions. Large changes in water and sediment supplies can occur without any change in the parameters, â and b. Thus, trend analyses using sediment rating curves must include additional assessments of the time-dependent rates and trends of river water, sediment concentrations, and sediment discharge.

Warrick, Jonathan

2015-01-01

412

Functional models for colloid retention in porous media at the triple line.  

PubMed

Spectral confocal microscope visualizations of microsphere movement in unsaturated porous media showed that attachment at the Air Water Solid (AWS) interface was an important retention mechanism. These visualizations can aid in resolving the functional form of retention rates of colloids at the AWS interface. In this study, soil adsorption isotherm equations were adapted by replacing the chemical concentration in the water as independent variable by the cumulative colloids passing by. In order of increasing number of fitted parameters, the functions tested were the Langmuir adsorption isotherm, the Logistic distribution, and the Weibull distribution. The functions were fitted against colloid concentrations obtained from time series of images acquired with a spectral confocal microscope for three experiments performed where either plain or carboxylated polystyrene latex microspheres were pulsed in a small flow chamber filled with cleaned quartz sand. Both moving and retained colloids were quantified over time. In fitting the models to the data, the agreement improved with increasing number of model parameters. The Weibull distribution gave overall the best fit. The logistic distribution did not fit the initial retention of microspheres well but otherwise the fit was good. The Langmuir isotherm only fitted the longest time series well. The results can be explained that initially when colloids are first introduced the rate of retention is low. Once colloids are at the AWS interface they act as anchor point for other colloids to attach and thereby increasing the retention rate as clusters form. Once the available attachment sites diminish, the retention rate decreases. PMID:24234754

Dathe, Annette; Zevi, Yuniati; Richards, Brian K; Gao, Bin; Parlange, J-Yves; Steenhuis, Tammo S

2014-08-01

413

Developing Sediment Retention Model for the Ecoservice Model InVEST  

NASA Astrophysics Data System (ADS)

The Integrated Valuation of Environmental Services and Tradeoffs (InVEST) model has been gaining popularity internationally as a tool to evaluate and value services provided by nature. The sediment retention sub-model is one of the key components of the InVEST model that assesses potentials of landscape and landcover to retain sediments preventing them from reaching the waterways and reservoirs. Based on the outputs of the sediment retention sub-model, InVEST estimates landcover's economic values of avoiding water quality pollution and reservoir sedimentation. The current version of the sediment retention sub-model uses retention-coefficient approach based solely on landcover type in estimating the quantities of sediment retained and transported downstream. The purpose of this study was to develop and test a sediment-delivery-ratio approach that integrates more catchment characteristics, including slope and flow length, in addition to the landcover characteristics. This approach was tested in Midwestern U.S. using distributed sediment data. Results show that the sediment-delivery-ratio approach has improved performance in identifying sediment transport and retention processes. Incorporating this approach into the InVEST tool will enhance the model's capability in more accurately estimating the economic values of avoiding water quality pollution and reservoir sedimentation. Keywords: ecosystem service, modeling, sediment delivery ratio, sediment retention

Ghebremichael, L.; Ziv, G.; Ghile, Y.

2012-12-01

414

5 CFR 536.302 - Optional pay retention.  

Code of Federal Regulations, 2010 CFR

...authorized agency official may provide pay retention to an employee not entitled to pay retention under § 536.301, but whose payable...conjunction with an action that may entitle the employee to pay retention under paragraph (a) of this...

2010-01-01

415

5 CFR 536.202 - Optional grade retention.  

Code of Federal Regulations, 2010 CFR

...Optional grade retention. (a...provide grade retention to an employee moving from...under a covered pay system to...different covered pay system is a...c) When an employee is offered...with grade retention under...

2010-01-01

416

5 CFR 536.208 - Termination of grade retention.  

Code of Federal Regulations, 2010 CFR

...to grade retention terminates...section, the employee's rate of basic pay must be set...positions). An employee is not entitled to pay retention under subpart...in basic pay resulting...waiver of the employee's grade retention...

2010-01-01

417

7 CFR 3015.22 - Starting date of retention period.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Starting date of retention period. 3015.22 Section 3015...FEDERAL ASSISTANCE REGULATIONS Record Retention and Access Requirements § 3015.22 Starting date of retention period. (a) General....

2010-01-01

418

48 CFR 4.705 - Specific retention periods.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Specific retention periods. 4.705 Section 4.705 Federal... ADMINISTRATIVE MATTERS Contractor Records Retention 4.705 Specific retention periods. The contractor shall retain...

2011-10-01

419

49 CFR 239.203 - Retention of emergency preparedness plan.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Retention of emergency preparedness plan. 239...PREPAREDNESS Review, Approval, and Retention of Emergency Preparedness Plans § 239.203 Retention of emergency preparedness plan....

2011-10-01