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1

A Technique for Producing Soil Water Retention Curves  

Microsoft Academic Search

Water retention curves compiled for specific soil types are an essential management and research tool in evaluating plant stress. The method of producing water retention curves by means of the 1500 kPa pressure extractor is described.

L. van der Merwe

1990-01-01

2

Advances in modelling hysteretic water retention curve in deformable soils  

Microsoft Academic Search

Experimental findings on the hysteretic nature of the soil water retention curve, relating the degree of saturation to the matric suction, have generally to be superimposed with the aspects due to the deformability of the soil matrix. Indeed, most state-of-the-art models for retention curves only feature one of these two essential features, that is either capillary hysteresis or void ratio

Mathieu Nuth; Lyesse Laloui

2008-01-01

3

Temperature dependence of the water retention curve for dry soils  

Microsoft Academic Search

Water retention curves (WRCs) are equivalent to water adsorption isotherms that display the soil water content as a function of water activity in the pore space. The use of water activity implies that pure (unbound) water at the given temperature is considered to be a reference state. In this study we measured the temperature dependence of WRCs for nine European

M. Schneider; K.-U. Goss

2011-01-01

4

Soil water retention curve analysis using radial basis function network  

Microsoft Academic Search

The soil water retention curve (SWRC) shows the relationship between soil suction pressure and water content, which is one of the key hydraulic properties to study the flow and solute transports in unsaturated zone. A radial basis function network (RBFN) was developed to describe the SWRC with the observed soil suction pressure and simultaneous soil water content derived from laboratory

Jin Gao; Yanfeng Liu

2010-01-01

5

Estimating soil mass fractal dimensions from water retention curves  

Microsoft Academic Search

The drying branch of the water retention curve is widely used for modeling hydrologic processes and contaminant transport in porous media. A prefractal model is presented for this function based on the capillary equation and a randomized Menger sponge algorithm with upper and lower scaling limits. The upper limit is the air entry value (?0) and the lower limit is

E. Perfect

2000-01-01

6

An Improved Fractal Equation for The Soil Water Retention Curve  

Microsoft Academic Search

The water retention curve, ?(?), is important for predicting soil physical properties and processes. Until recently, equations for the ?(?) were empirical. Advances in fractal geometry have led to the derivation of physical models for the ?(?). However, both existing fractal equations have only two parameters and thus are relatively inflexible. We derived a new three-parameter fractal model for the

E. Perfect; N. B. McLaughlin; B. D. Kay; G. C. Topp

1996-01-01

7

Modeling water retention curves of sandy soils using neural networks  

Microsoft Academic Search

We used neural networks (NNs) to model the drying water retention curve (WRC) of 204 sandy soil samples from particle-size distribution (PSD), soil organic matter content (SOM), and bulk density (BD). Neural networks can relate multiple model input data to multiple model output data without the need of an a priori model concept. In this way a high performance black-box

Marcel G. Schaap; Willem Bouten

1996-01-01

8

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

9

An improved fractal equation for the soil water retention curve  

Microsoft Academic Search

The water retention curve, theta(psi), is important for predicting soil physical properties and processes. Until recently, equations for the theta(psi) were empirical. Advances in fractal geometry have led to the derivation of physical models for the theta(psi). However, both existing fractal equations have only two parameters and thus are relatively inflexible. We derived a new three-parameter fractal model for the

E. Perfect; N. B. McLaughlin; B. D. Kay; G. C. Topp

1996-01-01

10

Pedotransfer functions for point and parametric estimations of soil water retention curve  

Microsoft Academic Search

A water retention curve is required for the simulation studies of water and solute transport in unsaturated or va- dose zone. Unlike the direct measurement of water retention data, pedotransfer functions (PTFs) have attracted the attention of researchers for determining water retention curves from basic soil properties. The objective of this study was to develop and validate point and parametric

H. Merdun

2006-01-01

11

Application of a Soil Water Hysteresis Model to Simple Water Retention Curves  

Microsoft Academic Search

The Parlange hysteresis model is reformulated as a pair of recurrence relations to provide relationships between wetting and drying phases to any order. The model is applied to the classical van Genuchten model for soil water retention used as the main wetting curve. The nonphysical behaviour of these retention curves is related to the existence of a point of inflection

R. D. Braddock; J.-Y. Parlange; H. Lee

2001-01-01

12

Models of the water retention curve for soils w@h a fractal , pore size distribution  

Microsoft Academic Search

The relationship between water content and water potential for a soil is termed its water retention curve. This basic hydraulic property is closely related to the soil pore size distribution, for which it serves as a conventional method of measurement. In this paper a general model of the water retention curve is derived for soils whose pore size distribution is

Edith Perrier; Michel Rieu; Gliislain de Marsily

1996-01-01

13

Models of the water retention curve for soils with a fractal pore size distribution  

Microsoft Academic Search

The relationship between water content and water potential for a soil is termed its water retention curve. This basic hydraulic property is closely related to the soil pore size distribution, for which it serves as a conventional method of measurement. In this paper a general model of the water retention curve is derived for soils whose pore size distribution is

Edith Perrier; Michel Rieu; Garrison Sposito; Ghislain de Marsily

1996-01-01

14

Errors in water retention curves determined with pressure plates and their effect on soil hydraulic properties  

Microsoft Academic Search

Pressure plates are commonly used to measure the soil water retention curve. Low plate and soil conductance, lack of plate-soil contact, and soil dispersion, however, make this method often unreliable at low water potentials. In this paper, we investigate how errors in the determination of the water retention curve affect the soil hydraulic properties and the computation of plant available

M. Bittelli; M. Flury

2009-01-01

15

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

Microsoft Academic Search

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

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

2009-01-01

16

A physically based model for the water retention curve of clay pastes  

Microsoft Academic Search

Available approaches for modeling the soil water retention curve are based on parameters to be fitted using observed data. Due to the formal fitting to the data the soil water retention curves of nonswelling and swelling soils are frequently considered on equal grounds, and the data of both soil types are used as examples in validation. The objective of this

V. Y. Chertkov

2003-01-01

17

A physically based model for the water retention curve of clay pastes  

Microsoft Academic Search

Available approaches for modeling the soil water retention curve are based on parameters to be fitted using observed data. Due to the formal fitting to the data the soil water retention curves of nonswelling and swelling soils are frequently considered on equal grounds, and the data of both soil types are used as examples in validation. The objective of this

V. Y. Chertkov

2004-01-01

18

Measurement errors of water retention curve using pressure plates: consequences on parameterization  

NASA Astrophysics Data System (ADS)

Pressure plates are very common experimental devices to measure the soil water retention curve. However, recent studies have demonstrated the lack of reliability of pressure plates when measuring the soil water retention curve in the dry range, due to low plate and soil conductance, lack of soil-plate contact and soil dispersion. In a recent investigation on a silt loam soil, water retention data were determined using pressure plates only and a combination of pressure plates and a dew point meter, showing errors in the measurement of the soil water retention curve at potentials less than 20 m-H2O. This error led to unreliable evaluation of soil hydraulic properties and their parameterization. We extended the investigation on the effects of water retention measurement error to eighteen soils having different textural properties, by comparing measurements of soil water retention curves obtained with a combination of Stackman's beds and pressure plates and soil water retention curves obtained with the chilled-mirror dew point technique. The aim of this research was to investigate the differences between the soil water retention curves as function of different soil textural properties and their effect of soil hydraulic properties and water drainage. Comparison between retention curves and fitting van Genuchten parameters, showed an error in measurements made by the combination Stackman's beds and Richards' pressure plates, for potential values below 1 m-H2O to 57 m-H2O. By characterizing textural properties by using geometric mean diameters, a clear relationship between texture and errors in water retention was established. In particular coarser soil displayed errors at lower potential (in absolute value) with respect to finer textures. The occurrence of these errors in the water retention measurement performed with pressure plates showed that it is advisable to use a combination of methodologies to correctly measure an entire soil retention curve and current parameters database should be used with caution.

Bittelli, M.; Solone, R.

2012-04-01

19

Errors in water retention curves determined with pressure plates: Effects on the soil water balance  

NASA Astrophysics Data System (ADS)

Pressure plates apparatus are very common experimental devices utilized to measure the soil water retention curve. Many studies have demonstrated the lack of reliability of pressure plates apparatus when they are used to measure the soil water retention curve in the dry range, due to low plate and soil conductance, lack of hydrostatic equilibrium, lack of soil-plate contact and soil dispersion. In this research, we investigated measurements of soil water retention curves obtained with a combination of Stackman's tables, pressure plates apparatus and the chilled-mirror dew point technique. Specifically, the aim of this research was: (a) to investigate the differences in the measured soil water retention curves by the different experimental methods, (b) evaluate relationships between the experimental differences and soil texture, (c) analyze the effect of experimental differences on hydraulic properties parameterization and (d) investigate the effects of the different parameters set on water transport computation. The results showed differences in measurements made by the combination of Stackman's tables and Richards' pressure plates apparatus as compared to the dew point method, for fine textured soils, while no significant differences were detected for coarse textured soils. Computed cumulative drainage and evaporation displayed lower values if soil water retention curves were obtained from data obtained with the Stackman's tables and Richards' pressure plates apparatus instead of the dew point method. In soils, where the soil water retention curve was measured with traditional methods (Stackman's tables and Richards' pressure plates apparatus) average cumulative drainage was 173 mm, with respect to a combination of methods including the dew point methods, where the average cumulative drainage was 184 mm. Average cumulative evaporation was 77 mm for the traditional methods, while it was 91 mm, for the combination of methods. Overall, when simulation models are used for studies related to solute transport, polluted soil remediation, irrigation management and others, erroneous measurement of the SWRC for fine textured soils, may lead to erroneous computation of the soil water balance.

Solone, R.; Bittelli, M.; Tomei, F.; Morari, F.

2012-11-01

20

A conceptual model of the soil water retention curve  

Microsoft Academic Search

A conceptual model based on the assumption that soil structure evolves from a uniform random fragmentation process is proposed to define the water retention function. The fragmentation process determines the particle size distribution of the soil. The transformation of particles volumes into pore volumes via a power function and the adoption of the capillarity equation lead to an expression for

S. Assouline; D. Tessier; A. Bruand

1998-01-01

21

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

Microsoft Academic Search

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 larger areas and difficulties to obtain minimally disturbed soil samples, especially under dry conditions,

M. Luisa Prados Garcia; Karl Vanderlinden; Carolina Guardiola-Albert; Juan Vicente Giraldez Cervera; Andrey K. Guber; Yakov A. Pachepsky

2010-01-01

22

Estimating the water retention curve from soil properties: comparison of linear, nonlinear and concomitant variable methods  

Microsoft Academic Search

The unsaturated soil hydraulic functions involving the soil–water retention curve (SWRC) and the hydraulic conductivity provide useful integrated indices of soil quality. Existing and newly devised methods were used to formulate pedotransfer functions (PTFs) that predict the SWRC from readily available soil data. The PTFs were calibrated using a large soils database from Hungary. The database contains measured soil–water retention

Kálmán Rajkai; Sándor Kabos; M. Th. van Genuchten

2004-01-01

23

Estimating soil water retention curve in rhodic ferralsols from basic soil data  

Microsoft Academic Search

Determining soil water retention curve by field methods is expensive, laborious and time consuming. Several indirect methods have been developed to circumvent these setbacks. However, tropical soils have hardly benefited from these innovations. In this work, pedo-transfer functions (PTFs) and fractal analysis were used to predict the soil water characteristic curve of a Rhodic Ferralsol, collected from the three western

Mohamed Tarawally; Alicia del Valle; Mar??a Elena Ruiz

2002-01-01

24

Use of a fractal model for determining soil water retention curves  

Microsoft Academic Search

In the light of the practical application of deducing soil water retention ?(h) and hydraulic conductivity functions K(?) from some simply determined physical properties, due consideration was given to physico-empirical models in the literature based on the transformation of particle-size distribution into a retention curve. In particular, forecasting potentials were evaluated with regard to a fractal model proposed by Tyler

Vincenzo Comegna; Paolo Damiani; Angelo Sommella

1998-01-01

25

Soil porous system changes quantified by analyzing soil water retention curve modifications  

Microsoft Academic Search

Soil water retention curves (SWRCs) relate soil water pressure head (h) to soil water content (?) and can also be used to find information regarding soil pore distribution. To analyze SWRCs in relation to pore size distribution (PSD), changes due to wetting and drying (W–D) cycles were studied in three different tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN; Rhodic

Luiz F. Pires; Fabio A. M. Cássaro; Klaus Reichardt; Osny O. S. Bacchi

2008-01-01

26

An innovative device for determining the soil water retention curve under high suction at different temperatures  

Microsoft Academic Search

To characterise the water retention behaviour of fine soils, high suction values are applied. In this range of values, the\\u000a vapour equilibrium technique is usually used. This paper presents an innovative device, a sorption bench that permits the\\u000a determination of the water retention curve of soil. With this new testing method, the time required for testing is significantly\\u000a reduced. In

Simon Salager; Marta Rizzi; Lyesse Laloui

27

Estimating Mass Fractal Dimension of Soil Water Retention Curve using Neural Networks  

Microsoft Academic Search

Soil water retention curve (SWRC) representing the relationship between soil water content and matric potential, is one of the most important soil hydraulic properties which its direct measurement is time consuming and expensive. The objective of this study was to develop an Artificial Neural Networks (ANNs) model to estimate the mass fractal dimension of SWRC from readily available parameters such

B. Ghanbarian-Alavijeh; G. Huang; A. M. Liaghat; R. Taghizadeh-Mehrjerdi

2009-01-01

28

Generating hydraulic properties from non-equilibrium water-retention curves  

NASA Astrophysics Data System (ADS)

Water retention curves, particularly those obtained from ceramic plate experiments, tend overestimate the equilibrium water content at high tensions and thus imply unrealistic amounts of water present in films etc. We have previously reported a method to predict non-equilibrium water-retention data from known fractal equilibrium water-retention curves. This method relates actual water loss to the product of the equilibrium water loss and the ratio of two different percolation-based calculations of the hydraulic conductivity. Here we reverse the process and generate the equilibrium water-retention curve from data. No particular form of pore- size distribution is assumed, although extrapolation procedures and a posteriori checks are used. The results we obtained make sense and imply water film contents of roughly 0.01 instead of 0.05 or higher in the coarse Hanford site soils investigated. From a reliable equilibrium pore-size distribution, percolation theory yields all flow and transport properties. Work supported by NSF grant EAR-0609884.

Hunt, A. G.; Skinner, T. E.

2008-12-01

29

ESTIMATING THE WATER RETENTION CURVE FROM SOIL PROPERTIES: COMPARISON OF LINEAR, NONLINEAR AND CONCOMITANT VARIABLE METHODS  

Technology Transfer Automated Retrieval System (TEKTRAN)

The unsaturated soil hydraulic functions involving the soil-water retention curve (SWRC) and the hydraulic conductivity provide useful integrated indices of soil quality. Existing and newly devised methods were used to formulate pedotransfer functions (PTFs) that predict the SWRC from readily avail...

30

Analysis of physical quality of soil using the water retention curve: Validity of the S-index  

Microsoft Academic Search

Among the various soil indicators established in order to discuss physical properties of soils is the S-index, derived from the slope of the soil water retention curve at its inflection point, used by a number of authors. In this publication we discuss the value of the slope at the inflection point of the soil water retention curve according to the

Glenio Guimarães Santos; Euzebio Medrado da Silva; Robélio Leandro Marchão; Pedro Marques da Silveira; Ary Bruand; Francois James; Thierry Becquer

2011-01-01

31

Eliminating kinetic effects on the pore size distribution as determined from water-retention curves  

NASA Astrophysics Data System (ADS)

The procedure described requires some knowledge of a critical moisture content for percolation as described by the Moldrup et al. (2001) experimental results for a moisture content at which solute diffusion vanishes. This can be obtained experimentally by using N2 BET measurements or theoretically from the particle size distribution. Alternatively one can estimate the critical moisture content as the residual moisture content on a water retention curve. We use critical path analysis to find the saturation S dependence of the hydraulic conductivity from the pore size distribution inferred from a water-retention curve. As S is reduced towards the critical value we test our calculated K with K obtained by universal percolation scaling. When the latter formulation predicts the more rapid drop of K with decreasing moisture content, we assume that equilibration effects (as described in a previous publication) interfere with the interpretation that the water retention curve reflects only medium properties and renormalize the water retention by kinetic effects. We then use the inverse of this renormalization to extract a "true" pore size distribution.

Hunt, A. G.; Skinner, T. E.

2007-12-01

32

The effect of earthworm coprolites on the soil water retention curve  

NASA Astrophysics Data System (ADS)

The effect of earthworm coprolites on the water retention curves in soils of different geneses and textures was investigated by the method of equilibrium centrifuging. Coprolites sampled in the field were compared with the surrounding soil. The effect of earthworms on a soddy-podzolic light loamy soil (from Moscow oblast) was comprehensively analyzed in the course of a special model experiment in a laboratory. This experiment was necessary because it was difficult to separate the coprolites from the soil, in which additional coprolites could appear under natural conditions. In all the variants of the experiment, the differences between the water retention curves of the coprolites and the surrounding soil (or control substrates unaffected by earthworms) were statistically significant. The development of coprolites favored a considerable increase (up to 20 wt.% and more) of the soil water retention capacity upon equivalent water potentials within the range from 0 to -1000 kPa. In most cases, the soil water retention capacity increased within the entire range of the soil moisture contents. This could be explained by the fact that strongly swelling hygroscopic plant remains (detritus) were included into the coprolites and by the formation of a specific highly porous aggregate structure.

Smagin, A. V.; Prusak, A. V.

2008-06-01

33

Column-centrifugation method for determining water retention curves of soils and disperse sediments  

NASA Astrophysics Data System (ADS)

A new instrumental method was proposed for the rapid estimation of the water-retention capacity of soils and sediments. The method is based on the use of a centrifugal field to remove water from distributed soil columns. In distinction from the classical method of high columns, the use of a centrifugal force field stronger than the gravity field allowed reducing the height of the soil samples from several meters to 10-20 cm (the typical size of centrifuge bags). In distinction from equilibrium centrifugation, the proposed method obtained an almost continuous water retention curve during the rotation of the soil column only at one-two centrifuge speeds. The procedure was simple in use, had high accuracy, and obtained reliable relationships between the capillary-sorption water potential and the soil water content in a wide range from the total water capacity to the wilting point.

Smagin, A. V.

2012-04-01

34

Simple modification to describe the soil water retention curve between saturation and oven dryness  

NASA Astrophysics Data System (ADS)

Prediction of water and vapor flow in porous media requires an accurate estimation of the soil water retention curve describing the relation between matric potential and the respective soil water content from saturation to oven dryness. In this study, we modified the Kosugi (1999) function to represent soil water retention at all matric potentials. This modification retains the form of the original Kosugi function in the wet range and transforms to an adsorption equation in the dry range. Following a systems identification approach, the extended function was tested against observed data taken from literature that cover the complete range of water contents from saturation to almost oven dryness with textures ranging from sand to silty clay. The uncertainty of parameter estimates (confidence intervals) as well as the correlation between parameters was studied. The predictive capability of the extended model was evaluated under two reduced sets of data that do not contain observations below a matric potential of -1500 and -100 kPa. This evaluation showed that the extended model successfully predicted the water content with acceptable uncertainty. These results add confidence into the proposed modification and suggest that it can be used to better predict the soil water retention curve, particularly under reduced data sets.

Khlosi, Muhammed; Cornelis, Wim M.; Gabriels, Donald; Sin, Gürkan

2006-11-01

35

SWRC fit - a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure  

Microsoft Academic Search

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. For this purpose, the program \\

K. Seki

2007-01-01

36

Temperature dependence of large-scale water-retention curves: a case study  

Microsoft Academic Search

A local-scale model for temperature-dependence of water-retention curves may be applicable to large scales. Consideration of this temperature dependence is important for modeling unsaturated flow and transport in the subsurface in numerous cases. Although significant progress has been made in understanding and modeling this temperature effect, almost all the previous studies have been limited to small scales (on the order

Hui-Hai Liu; G. S. Bodvarsson; J. H. Dane

2006-01-01

37

A TDR-pressure cell design for measuring the soil-water retention curve  

Microsoft Academic Search

This paper presents a new type of pressure cell associated with a zigzag-shaped time domain reflectometry (TDR) probe for determining the soil-water retention (?(?)) curve of disturbed thin soil samples. The pressure cell, designed for pressures ranging between 0 and ?500kPa, consisted of a zigzag copper rod (150-mm long, 2mm in diameter) vertically installed in a clear plastic cylinder (60-mm

D. Moret-Fernández; J. L. Arrúe; V. Pérez; M. V. López

2008-01-01

38

A new model for predicting relative nonwetting phase permeability from soil water retention curves  

NASA Astrophysics Data System (ADS)

Relative permeability of the nonwetting phase in a multiphase flow in porous media is a function of phase saturation. Specific expressions of this function are commonly determined by combining soil water retention curves with relative nonwetting phase permeability models. Experimental evidence suggests that the relative permeability of the nonwetting phase can be significantly overestimated by the existing relative permeability models. A new model for the prediction of relative nonwetting phase permeability from soil water retention curves is proposed in this paper. A closed form expression can be obtained in combination with soil water retention curves. The model is mathematically simple and can easily and efficiently be implemented in numerical models of multiphase flow processes in porous media. The predicting capability of the proposed model is contrasted with well-supported models by comparing the measured and predicted relative air permeability data for 11 soils, representing a wide range of soil textures, from sand to silty clay loam. In most of the cases the proposed model improves the agreement between the predicted relative air permeability and the measured data.

Kuang, Xingxing; Jiao, Jiu Jimmy

2011-08-01

39

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

NASA Astrophysics Data System (ADS)

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 larger areas and difficulties to obtain minimally disturbed soil samples, especially under dry conditions, laboratory measurements of the SWRCs are only suitable for guidance, as a consequence of their low representativity and accuracy. This work was developed within the framework of a research project on the ecohydrological behaviour of the soil-plant-atmosphere system within the Doñana National Park (SW Spain). In order to characterise the hydrological behaviour of the soils, a good estimation of water retention curves and hydraulic parameters is needed. Ten locations within the study area were equipped with soil moisture sensors (ECH2O-EC20, Decagon Devices Inc.) to monitor volumetric water content at different depths throughout the vadose zone. These data allow the estimation of water fluxes and recharge of the underlying aquifer, which plays a crucial role in the wetland system of the Park, declared by UNESCO as Biosphere Reserve. In this work three methods for estimating SWRCs were developed and compared. First, sand and kaolin suction tables were used to obtain SWRCs for both minimally disturbed and disturbed samples. Second, SWRC were estimated with HYDRUS-1D using the monitored volumetric soil water content data. Finally, SWRCs were estimated using the additivity hypothesis, based on the idea that SWRCs can be approximated by summing up SWRCs corresponding to different particle-size and pore-space classes of which the soil is composed. Particle-size distributions were determined in the laboratory while water retention data for the different particle-size classes were taken from literature. The comparison of these three methods allowed us to define their strengths and weaknesses with respect to accurate estimation of SWRCs in sandy soils and to improve the estimation of water fluxes and recharge.

Prados Garcia, M. Luisa; Vanderlinden, Karl; Guardiola-Albert, Carolina; Giraldez Cervera, Juan Vicente; Guber, Andrey K.; Pachepsky, Yakov A.

2010-05-01

40

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

41

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

42

Differences of water retention curves obtained through capillary rise and steady-state equilibrium experiments  

Microsoft Academic Search

Capillary rise experiments were performed under constant temperature in columns of Metea sandy loam soil packed at different bulk densities. Moisture retention curves were obtained following the capillary rise activity. All curves exhibited a theta-straight region, followed by a parabolic region flattened at higher suctions. The parabolic region, when plotted on log-log scales, could be separated into three distinct zones

George C. Zalidis; Raymond J. Kunze

1994-01-01

43

Identifying a parameterisation of the soil water retention curve from on-ground GPR measurements  

NASA Astrophysics Data System (ADS)

We show the potential of on-ground Ground-Penetrating Radar (GPR) to identify the parameterisation of the soil water retention curve, i.e. its functional form, with a semi-quantitative analysis based on numerical simulations of the radar signal. An imbibition and drainage experiment has been conducted at the ASSESS-GPR site to establish a fluctuating water table, while an on-ground GPR antenna recorded traces over time at a fixed location. These measurements allow to identify and track the capillary fringe in the soil. The typical dynamics of soil water content with a transient water table can be deduced from the recorded radargrams. The characteristic reflections from the capillary fringes in model soils that are described by commonly used hydraulic parameterisations are investigated by numerical simulations. The parameterisations used are (i) full van Genuchten, (ii) simplified van Genuchten with m = 1 - 1/n and (iii) Brooks-Corey. All three yield characteristically different reflections, which allows the identification of an appropriate parameterisation by comparing to the measured signals. We show that for the sand used here, these signals are not consistent with the commonly used simplified van Genuchten parameterisation with m = 1 - 1/n.

Dagenbach, A.; Buchner, J. S.; Klenk, P.; Roth, K.

2013-02-01

44

Modeling the soil water retention curves of soil-gravel mixtures with regression method on the Loess Plateau of China.  

PubMed

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

2013-03-15

45

Regionalization of soil water retention curves in a highly variable soilscape, II. Comparison of regionalization procedures using a pedotransfer function  

Microsoft Academic Search

As measuring soil water retention curves (WRCs) is time-consuming and costly, pedotransfer functions (PTFs) which predict WRCs from the fundamental soil properties bulk density (Db), texture, and organic C (Corg) are in common use. The regionalization of WRCs with a PTF can be performed in two different ways. (1) Interpolate first the fundamental properties, and apply then the PTF to

W. Sinowski; A. C. Scheinost; K. Auerswald

1997-01-01

46

Use of a lognormal distribution model for estimating soil water retention curves from particle-size distribution data  

Microsoft Academic Search

Particle-size distribution (PSD) of soils has been widely used to estimate water retention curves (WRCs). Lognormal distribution model, which estimates the WRC directly from the PSD data by applying a lognormal distribution law to both PSD and void-size distribution (VSD), has been recently developed and successfully applied to sandy soils. The objective of this study was to investigate in detail

Sang Il. Hwang; Sang Il. Choi

2006-01-01

47

Experimental corrections of simplified methods for predicting water retention curves in clay-loamy soils from particle-size determination  

Microsoft Academic Search

The Arya and Paris model for predicting soil water retention curves from particle-size distribution data is a commonly accepted method for rigid soils with medium grain size but limitations to its application for fine textured soils occur, due to the dominant role of internal structure in such soils. Moving from the consideration that simplified models for determining soil hydraulic characteristics

Angelo Basile; Guido D'Urso

1997-01-01

48

Determination of water retention curves of rocks by a differential evolution algorithm  

NASA Astrophysics Data System (ADS)

Several different parametric models have been developed to describe fluid flow and mass transport in unsaturated media. The experimental data can be fitted to the models obtaining a water retention curve (WRC) which best describes the hydraulic properties of the soil or rock under investigation. However, all these models need a complete data set and require an accurate measurement of the dependence of the matric potential () on water content (?) from saturation to oven dryness using methods that are time consuming and error-prone, especially when investigating rock media. In this work, a new approach for the determination of the model parameters that best fit the WRC of rocks is presented. The approach uses a differential evolution algorithm (DE), an evolutionary computation algorithm particularly useful for multidimensional real-valued problems, to calculate the parameters that best fit the models to the available experimental data. We show here that with DE it is possible to strongly decrease the number of experimental data needed to obtain model parameters that accurately describe the hydraulic properties of the rocks. In this work, we have applied DE to calculate the WRCs of rock samples, using several widely used models. The measurements have been performed on samples 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.

Turturro, Antonietta Celeste; Clementina Caputo, Maria; Maggi, Sabino

2013-04-01

49

Estimating Saturated Hydraulic Conductivity from Soil Water Retention Curve using Neural Networks  

Microsoft Academic Search

Study of soil hydraulic properties like saturated and unsaturated hydraulic conductivity is required in the environmental investigations. Since, direct measurement of soil hydraulic properties is time consuming and expensive, indirect methods such as pedotransfer function and artificial neural networks (ANN) have been developed based on the readily available soil characteristics. In this study, we used soil water retention data i.e.

B. Ghanbarian-Alavijeh; A. M. Liaghat; S. Sohrabi

2009-01-01

50

Water retention curves of loamy-sandy soils: Transient evaporation method versus steady-state tension and pressure techniques  

Microsoft Academic Search

Water retention curves of loamy-sandy soils at the agricultural test site Wagna (Austria) were measured using both the simplified evaporation method according to Schindler (Arch. Acker- u. Pflanzenbau u. Bodenkd. Berlin 24, 1-7, 1980) and steady-state tension and pressure techniques. The soil was sampled with 250-ccm and 100-ccm steel pipes for the evaporation method and the steady-state technique, respectively. In

G. Winkler; E. Eberhard; J. Fank; S. Birk

2009-01-01

51

Determination of the Soil Water Retention Curve and the Unsaturated Hydraulic Conductivity from the Particle Size Distribution  

Microsoft Academic Search

Because of the complexity of the metrological determination of the soil water retention curve (SWRC), so-called pedotransfer\\u000a functions (PTF) have been developed for several years. Mostly these PTF are based on a more or less simple regression analysis\\u000a using a limited set of data. In such methods the SWRC is predicted with data on the amount of soil components sometimes

Alexander Scheuermann; Andreas Bieberstein

52

Complete characterization of pore size distribution of tilled and orchard soil using water retention curve, mercury porosimetry, nitrogen adsorption, and water desorption methods  

Microsoft Academic Search

Pore size distribution (PSD) affects numerous soil functions and root growth. The PSD is largely influenced by soil management practices. We have compared the PSD in a wide pore size range of conventionally tilled (CT) and orchard (OR) loamy soil, determined by different methods. Water retention curve, mercury intrusion porosimetry, nitrogen adsorption isotherm and water desorption isotherm were used to

M. Hajnos; J. Lipiec; R. ?wieboda; Z. Soko?owska; B. Witkowska-Walczak

2006-01-01

53

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

Microsoft Academic Search

Measurements with pressure plate overestimated water contents at ?1.5 MPaTuller-Or model needs additional scaling function for retention curveLinear Campbell-Shiozawa-Rossi-Nimmo (CSRN) model showed better fits to data

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

2011-01-01

54

Estimating Saturated Hydraulic Conductivity from Soil Water Retention Curve using Neural Networks  

NASA Astrophysics Data System (ADS)

Study of soil hydraulic properties like saturated and unsaturated hydraulic conductivity is required in the environmental investigations. Since, direct measurement of soil hydraulic properties is time consuming and expensive, indirect methods such as pedotransfer function and artificial neural networks (ANN) have been developed based on the readily available soil characteristics. In this study, we used soil water retention data i.e. fractal dimension, air entry value and effective porosity, as well as bulk density and developed artificial neural networks in order to estimate saturated hydraulic conductivity. Total of 142 soil samples of the UNSODA, GRIZZLY and Puckett et al. (1985) databases was divided into two groups as 114 for the development and 28 for the validation of ANN model. We used multi-layer perceptron model with 4 layers as the inputs and one layer as the output of ANN model and back propagation algorithm for training procedure. The activation function was selected LOGSIG in the middle and exist layers. The values of statistical parameters such as coefficient of determination (R2) and mean square error (MSE) showed that the best number of neurons in the middle layer of ANN model was 24. We also compared the developed ANN model with Rawls et al. (1993) and Rawls et al. (1998) models using 28 soil samples. The results showed that developed ANN model estimates saturated hydraulic conductivity better than the other methods. The AIC values of ANN, Rawls et al. (1993) and Rawls et al. (1998) were obtained 291.8, 322.3 and 316.4, respectively.

Ghanbarian-Alavijeh, B.; Liaghat, A. M.; Sohrabi, S.

2009-04-01

55

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

Microsoft Academic Search

their accuracy (RMSE), linearity (coeffi cient of determination, R 2 , and adjusted coeffi cient of determination, R 2 adj ), and pre- diction potential. Th e latter was evaluated by correlating the model parameters to basic soil properties. Retention data for 137 undisturbed soils from the Unsaturated Soil Hydraulic Database (UNSODA) were used for the model comparison. Th e

Muhammed Khlosi; Wim M. Cornelis; Ahmed Douaik; Martinus Th. van Genuchten; Donald Gabriels

2008-01-01

56

Estimating soil mass fractal dimensions from water retention curves 1 Kentucky Agric. Exp. Stn. Contribution No. 97-06-141. 1  

Microsoft Academic Search

The drying branch of the water retention curve is widely used for modeling hydrologic processes and contaminant transport in porous media. A prefractal model is presented for this function based on the capillary equation and a randomized Menger sponge algorithm with upper and lower scaling limits. The upper limit is the air entry value (?0) and the lower limit is

E. Perfect

1999-01-01

57

Uncertainty in soil water retention curves of Havana province as estimated from site-specific pedotransfer functions: effects of incorporating residual errors  

Microsoft Academic Search

The characterization of the soil water retention curves (SWRC) using pedotransfer functions (PTFs) has been widely discussed in the literature. However, still limited attention has been paid to the validity of these approaches to deal with soil spatial variability issues at relatively large scales. The objective of this work is to quantify the spatial uncertainty of estimated SWRC in Havana

Jorge García; Nunzio Romano

2010-01-01

58

Use of a lognormal distribution model for estimating soil water retention curves from particle-size distribution data  

NASA Astrophysics Data System (ADS)

Particle-size distribution (PSD) of soils has been widely used to estimate water retention curves (WRCs). Lognormal distribution model, which estimates the WRC directly from the PSD data by applying a lognormal distribution law to both PSD and void-size distribution (VSD), has been recently developed and successfully applied to sandy soils. The objective of this study was to investigate in detail the applicability of the lognormal distribution model for a broader range of soil textures. Performance of the model was evaluated on five aggregated USDA texture classes (coarse-, moderately coarse-, medium-, moderately fine-, and fine-texture soils) using 229 ‘undisturbed’ soils (159 soils for model calibration and 70 soils for validation). The model performed worst for moderately fine-textured soils, since the PSDs and VSDs of soils included in this texture did not strongly follow the lognormal distribution. In general, performance of the model decreased with increase in fine particle fraction, possibly because of the surface sorption behavior of clay particles.

Hwang, Sang Il.; Choi, Sang Il.

2006-05-01

59

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

60

Methods for predicting the optimum and the range of soil water contents for tillage based on the water retention curve  

Microsoft Academic Search

Information is needed on the range of soil water contents for tillage. The objective of the work was to develop methods for the prediction of the soil water contents at which tillage may be done satisfactorily. Three water contents are considered: the lower (dry) limit, the optimum water content, and the upper (wet) limit. This paper makes a synthesis of

A. R Dexter; N. R. A Bird

2001-01-01

61

Retention Curves of Two Bentonites at High Temperature  

Microsoft Academic Search

Two methods were developed to determine the retention curve for a fixed dry density and at high temperature. The materials\\u000a used are the MX–80 and the FEBEX bentonites. The retention capacity of the FEBEX bentonite is higher than that of MX–80, i.e.\\u000a for a given suction and dry density, the water content of the FEBEX bentonite is higher. However, the

María Victoria Villar; Roberto Gòmez-Espina

62

Moisture retention curve in landfilled waste  

Microsoft Academic Search

Moisture content and moisture movement are key factors in controlling the progress and rate of biodegradation within a landfill as it is the aqueous environment that facilitates the transport of nutrients and microbes. The modelling of infiltration and water movement requires information on the moisture retention and hydraulic conductivity properties, usually in the form of empirical functions such as those

Y. Kazimoglu; J. McDougall; I. Pyrah

63

A Retention Curve Prediction for Unsaturated Clay Soils  

Microsoft Academic Search

In order to obtain the retention curve of unsaturated soil which is defined as the relationship between water content and\\u000a suction, numerous laboratory tests have been done for many soils with different clay contents. The laboratory tests concern\\u000a different types of soils; the swelling and not swelling clays (natural clay with high silt content and the bentonite clay).\\u000a Two complementary

Mehrez Jamei; H. Guiras; N. Mokni

64

Spatial Variability of Physical Properties of a Tropical Soil. II. Soil Water Retention Curves and Hydraulic Conductivity.  

National Technical Information Service (NTIS)

The characterization of a field site from the soil physics point of view, the improvement of the use of soil and water resources under a particular condition and the development of means for controlling the dynamics of soil-water movement are presented. S...

K. Reichardt P. L. Libardi S. V. Queiroz F. Grohmann

1976-01-01

65

Interlaboratory Comparison of the Measurement of Retention Curves  

Microsoft Academic Search

The results of an interlaboratory comparison of the measurement of apparent density, solid density, open porosity and retention curves are presented. Baumberger sandstone and Sander sandstone were used as test materials.Repeatability standard deviation and reproducibility standard deviation for the measurement of apparent density, solid density, open porosity and retention curve moisture content have been estimated from the results of the

Morten Hjorslev Hansen; Geert Houvenaghel; Mårten Janz; Martin Krus; Kenneth Strømdahl

1999-01-01

66

Comparison of Two Techniques to Develop Pedotransfer Functions for Water Retention  

Microsoft Academic Search

the parameters control position and shape of the water retention equation. Two pedotransfer function (PTF) approaches can be used for ob- If both soil basic data and soil water retention infor- taining the analytical expression of the whole retention curve: (i) soil basic data is used to estimate soil water retention at specific water mation are available for a set

J. Tomasella; Ya. Pachepsky; S. Crestana; W. J. Rawls

2003-01-01

67

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

68

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

Microsoft Academic Search

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

T. Sakaki; T. H. Illangasekare

2006-01-01

69

On the influence of coarse fragments on soil water retention  

NASA Astrophysics Data System (ADS)

The classical determination of the soil water retention curve (SWRC) by measuring soil water content ? at different matric potentials ? using undisturbed soil samples is time consuming and expensive. Furthermore, undisturbed soil sampling can be an intricate task when coarse soil fragments (>2 mm) are present. The objective of this study was to test whether tension infiltrometry could be used to estimate the SWRC of stony soils and to investigate to what extent the coarse fragments affected the SWRC. Tension infiltrometer measurements were conducted at 44 sites with stony soils in arid Chile. Soil water retention curves obtained through inverse modeling were compared with laboratory-determined water retention (?, ?) data pairs. Differences were found to be small, confirming the applicability of the inverse modeling method. Rock fragments had a significant indirect influence on water retention for matric potentials higher than -0.30 kPa, which could be attributed to their direct influence on pore size distribution.

Baetens, J. M.; Verbist, K.; Cornelis, W. M.; Gabriels, D.; Soto, G.

2009-07-01

70

Moisture Retention Curves of Topopah Spring Tuff at Elevated Temperatures  

Microsoft Academic Search

Knowledge of unsaturated flow and transport in porous media is critical for understanding the movement of water and solute through the unsaturated zone. The suction potential of rock determines the imbibition of water and, therefore, the moisture retention in the matrix. That, in turn, affects the relative importance of matrix flow and fracture flow, and their interaction, because greater suction

W. Lin; J. Roberts; E. Carlberg; D. Ruddle; R. Pletcher

2001-01-01

71

Evaluation of Hydrogel Application on Soil Water Retention Characteristics  

Microsoft Academic Search

Hydrogels can absorb irrigation and rain water and help to reduce deep percolation by using gravitational water as well as capillary water. The objective of this study was to evaluate the effect of hydrogels on soil water retention characteristic curve (WRC) using RETC computer model. The hydrogels, PR3005A and Tarawat A100 in four levels, 2, 4, 6, and 8 g\\/kg,

Jahangir Abedi-Koupai; Farahnaz Sohrab; Gareth Swarbrick

2008-01-01

72

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

Microsoft Academic Search

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

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

2010-01-01

73

Predicting relative permeability from water retention: A direct approach based on fractal geometry  

Microsoft Academic Search

Commonly, a soil's relative permeability curve is predicted from its measured water retention curve by fitting equations that share parameters between the two curves (e.g., Brooks\\/Corey-Mualem and van Genuchten-Mualem). We present a new approach to predict relative permeability by direct application of measured soil water retention data without any fitting procedures. The new relative permeability model, derived from a probabilistic

Abdullah Cihan; John S. Tyner; Edmund Perfect

2009-01-01

74

A physical–chemical model for the static water retention characteristic of unsaturated porous media  

Microsoft Academic Search

Water retention characteristic or water retention curve (WRC) is an important constitutive feature of porous media, and also meanwhile is an indispensable requirement in hydraulic transport modelling. Previous experiments have indicated that the specific surface area of porous media has effects on the WRC. It has also been observed that a linear relationship generally exists between the air–water interface area

Y. Wang; S. M. Grove; M. G. Anderson

2008-01-01

75

SHEARING AND WATER RETENTION BEHAVIOR OF UNSATURATED LOAM WITH MODELING  

NASA Astrophysics Data System (ADS)

Unsaturated triaxial tests were carried out to study deformation behavior, effective stress path and water retention property of consolidated loam during consolidation and shearing processes. Initial matric suction was set as 0, 50, and 90 kPa, and confining pressures (net normal stresses) were set as 100 kPa. Then shearing processes were done under undrained and drained conditions. We clarified the relation between void ratio and Van Genuchten model parameter by using water retention curve. To predict the unsaturated shearing behavior, a modified Cam Clay model considering void ratio dependent Van Genuchten parameter was proposed. Those numerical test results were agreed well with laboratory tests results.

Kiyohara, Yukoh; Kazama, Motoki

76

Optimal employee retention when inferring unknown learning curves  

Microsoft Academic Search

This paper formulates an employer's hiring and retention decisions as an infinite-armed bandit problem and characterizes the structure of optimal hiring and retention policies. We develop approximations that allow us to explicitly calculate these policies and to evaluate their benefit. The solution involves a balance of two types of learning: the learning that reflects the improvement in performance of employees

Alessandro Arlotto; Noah Gans; Stephen E. Chick

2010-01-01

77

Preliminary Exploration of Dynamic Effect in a Field Soil Retention Curves: Direct Laboratory Quantification of Material Coefficient  

NASA Astrophysics Data System (ADS)

The constitutive relationship between capillary pressure and wetting fluid saturation (retention curve) is needed in the modeling of multi-phase flow in porous media. This relationship is usually measured under equilibrium conditions of the two phases (wetting and non-wetting). The question is whether such curves adequately describe the relationships between capillary pressure and saturation in drainage or imbibition events with a time scale of in the order of hours. Hassanizadeh et al. pointed out that the difference in capillary pressures in static and dynamic retention curves on the rate of change of saturation is due to dynamic effects. A very few experimental approaches exists to quantify this effect properly. Typically, the increase in capillary pressure due to dynamic effect is defined as a product of a material coefficient (tau) and rate of change in wetting phase saturation (-dSw/dt). The study based on inverse modeling using multi-step outflow column experiment data showed that tau may be a function of wetting fluid saturation rather than a constant. In this study, we attempted to measure tau in a more direct manner. A vertical column was filled with water-saturated field soil (Ohji fine sand). At the midpoint of the column, pressure and water content sensors were installed. Initially saturated column was first drained very slowly and primary drainage retention curve was obtained. The sample was wetted very slowly and subjected to three secondary drainage cycles with different drainage rates. The retention curves presented a slight increase in the displacement pressure as the drainage rate increased. Based on the difference in the retention curves and the rate of saturation change, tau was calculated. Although the data were somewhat scattered, overall trend indicated that tau for Ohji fine sand decreases as saturation decreases.

Komatsu, M.; Sakaki, T.; Illangasekare, T. H.

2006-12-01

78

WATER RETENTION PEDOTRANSFER FUNCTION FOR A HORIZON  

Technology Transfer Automated Retrieval System (TEKTRAN)

Reports about the relationship between soil water retention and organic carbon content are contradictory. We hypothesized that this relationship is affected by both proportions of textural components and amount of organic carbon. We examined the relationship between total clay, sand and silt, textur...

79

Simulation of Soil Moisture Profiles Using K ( h ) from Coupling Experimental Retention Curves and One-Step Outflow Data  

Microsoft Academic Search

In the present work, the effect on the soil moisture profiles development and the cumulative infiltration when three different\\u000a equations for calculating the diffusivity versus volumetric water content, D(?) function, from one-step outflow experimental data are used, is investigated. These D(?) functions are coupled with moisture retention curves ?(h) (h being the soil matric potential) obtained independently for the determination

I. Argyrokastritis; G. Kargas; P. Kerkides

2009-01-01

80

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

Microsoft Academic Search

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

Hubert J. Morel-Seytoux; John R. Nimmo

1999-01-01

81

On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve  

Microsoft Academic Search

In comparison with direct measurements of unsaturated hydraulic conductivity, the methods of calculations from the moisture retention curve are attractive for their fast and simple use and low cost. These are the main reasons for their increasing use, mainly in spatial variability studies. On the other hand, it is known that their applicability is limited. The possibility of the use

Tomas Vogel; Milena Cislerova

1988-01-01

82

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

83

Shirnkage and water retention characteristic in a fine-textured mollisol compacted under different axle loads  

Microsoft Academic Search

In areas where heavy vehicles are used, the subsoils often become very compacted. Freezing-thawing and wetting-drying have not been effective at reducing compaction. In this study, the type of soil shrinkage related to compaction was investigated to explain these amelioration failures. In conjunction with a shrinkage curve, the water retention characteristic was also measured because both can be related to

L. Wu; R. R. Allmaras; D. Gimenez; D. M. Huggins

1997-01-01

84

Estimating Dry-Range Water Retention Properties Using Specific Surface Area and Particle-Size Measurements  

Microsoft Academic Search

To test whether the slope of the dry-range water retention curve can be correlated directly with particle size and specific surface area, measurements were completed for core samples from the Mojave Desert and the Idaho National Engineering and Environmental Laboratory. Samples ranged in texture from gravelly sands to silt loams. Each core sample was split into representative, 1-3 g subsamples,

K. A. Winfield; J. R. Nimmo

2001-01-01

85

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

86

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

NASA Astrophysics Data System (ADS)

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 HcM = ?0?krw dhc, where krw is relative permeability (or conductivity) to water and hc 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, Hubert J.; Nimmo, John R.

1999-07-01

87

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

88

Effect of Intercropping Coconut Lands on Soil Water Retention  

Microsoft Academic Search

This study was conducted to evaluate the effect of intercropping coconut lands on soil water retention, available water, porosity and their relationship with organic matter contents. The results showed that the water holding capacity and available water increased significantly at both depths (0–20 and 20–40 cm) investigated. The increase in available water was mainly due to increase in field capacity

Ranjith B. Mapa

1995-01-01

89

Study of the sensitivity of PTF specific to the contribution of the structural state on variation in soil water retention  

NASA Astrophysics Data System (ADS)

The objective of this study was to analyze the sensitivity of estimating water retention properties of 54 soil samples collected from Lower Cheliff (northwestern of Algeria) by pedotransfer functions, our results show that training models for input and method adopted, reacts differently in estimation of water retention, and also influenced by the size and mode of particle assembly and differences in clay content. The water retention curve, which was established for three classes, proves to be an essential element for understanding the hydrodynamic behavior of soil. Additional, in soil texture clay and clay-loam and silty clay, nonlinear methods based on variables including clay fraction, behave much better in estimating of mean water retention curve. In contrast, in well structured soils the multiple linear regression showed a better quality of estimation, based on the bulk density and sand fraction as inputs. The results suggest that the PTF parametric derived should be used to estimate retention curves rather than PTF point. Keywords: Pedotransfer Function, Water Retention curve, sensitivity

Touil, Sami; Degre, Aurore; Nacer Chabaca, Mohamed

2013-04-01

90

Using Entropy to Quantify Soil Structure from Water Retention and Texture Data  

NASA Astrophysics Data System (ADS)

Soil structure embodies complex interactions between particle sizes (texture) and environmental factors that lead to the formation of structural units of different sizes and shapes. Water retention curves of structured soils reflect those interactions on the distribution and connectivity of pores. The main hypothesis of this work is that a measure of soil structure is given by the entropic distance between pore systems resulting from the same particle size distribution arranged randomly (reference distribution) and in structural units. It was also hypothesized that such distance can be derived from water retention curves by assuming that the reference and structured pore systems follow lognormal distributions and that textural pore systems are the result of random arrangements of particles sizes. Reference pore size distributions were obtained from texture using an empirical model to convert from particle to pore size distributions. Soil clods were sampled in triplicate from each of 24 horizons of soil profiles under forest and agriculture management. Disturbed samples were collected to measure texture and organic matter. Soil clods were used to measure bulk density and water retention by the hanging column and pressure extractor methods (7 points between -0.3 to -10 kPa). Clods were then disturbed and water retention measured on packed soil (13 points between-0.3 to -1500 kPa on disturbed samples). Water retention data were fit with the Kosugi lognormal water retention model and the parameters from the model used to calculate the entropic or Kullback-Leibler Distance (KLD) between measured and reference pore size distributions. Values of KLD estimated from undisturbed clods were significantly (P<0.05) greater than the corresponding values estimated from the disturbed clods. The KLD measure of undisturbed soil exhibited distinctive trends with soil texture and aggregate size classes. The proposed measure could serve as a link between qualitative field description of soil structure and a quantitative measure of the effect of soil structure on pore size distribution.

Gimenez, D.; Yoon, S.-W.

2012-04-01

91

Determination of water retention in stratified porous materials  

Microsoft Academic Search

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

Jim Constantz

1995-01-01

92

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

Microsoft Academic Search

Modeling water flow and solute transport in vadose zone requires knowledge of soil hydraulic properties, which are water retention and hydraulic conductivity curves. As an alternative to direct measurement, indirect determination of these functions from basic soil properties using pedotransfer functions (PTFs) has attracted the attention of researchers in a variety of fields such as soil scientists, hydrologists, and agricultural

Hasan Merdun; Özer Ç?nar; Ramazan Meral; Mehmet Apan

2006-01-01

93

Comparison of Soil Freezing Curve and Soil Water Curve Data for Windsor Sandy Loam,  

National Technical Information Service (NTIS)

Unfrozen water content as a function of temperature was measured in the laboratory using nuclear magnetic resonance (NMR) for a Windsor sandy loam soil. The data were related to previously measured soil moisture retention data through the modified Clapeyr...

A. R. Tice P. B. Black

1988-01-01

94

The nature of the minimal water retentive capacity  

Microsoft Academic Search

A soil uniform in texture is able to retain some water in equilibrium against gravity, providing that neither temperature nor tension gradients are effective. Such soil water is referred to as suspended moisture. The intrinsic minimal retentive capacity corresponds to maximal content of suspended moisture. The tension gradient does not operate after the solum has wetted through, and all gravitational

A. A. Rode

95

Correlated Moisture Content, Pressure and Temperature Data for Development of Hysteretic Moisture Retention Curves.  

NASA Astrophysics Data System (ADS)

This study was performed as the first part of an effort to collect high quality, repeatable, hydrologic data in a laboratory environment to provide a sound basis for future macropore model development, validation, and calibration. The objective of the experiment was to study the hysteretic function (drainage/wetting/scanning) of soils and the role of hysteresis in fluid transport. Our hysteretic dataset provides detailed information of coupled fluid transport behavior that includes temperature, moisture, and concentration. Hysteretic data collected has been further correlated with soil matric potential and temperature to define moisture-retention curves in replicates of a coarse-sandy, mixed, mesic Fluventic Hapludoll, loam soil (Eudora loam of the Kansas River Valley). Large (28 L-soil core) volume minimized statistical uncertainty that customarily accompany small cores and provided robust results in determining scanning curves (wetting and drying). Integration of a bromide tracer applied to the large cores at saturation indicated that macropore transport occurred within the range of 0-20 kPa thereafter, transport was via soil matrix flow. The tracer also provided further information about the physical and chemical properties of the soil, which can be utilized in the future development and calibration of robust, versatile computer models. Continuing research of these same cores will focus on macropore transport as it correlates to our existing research.

Little, J. J.; Tindall, J. A.; Friedel, M.

2004-12-01

96

Effectiveness of Glycerol Ingestion for Enhanced Body Water Retention during Cold Water Immersion.  

National Technical Information Service (NTIS)

The efficacy of ingesting an aqueous glycerol (GLY) solution to reduce diuresis and enhance body water retention during prolonged cold water dives was tested. Six subjects were assigned to either a water treatment (WT) or glycerol treatment (GT) group. Du...

H. W. Goforth D. A. Arnall

1989-01-01

97

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

98

Comparison of soil freezing curve and soil water curve data for Windsor sandy loam  

Microsoft Academic Search

Unfrozen water content as a function of temperature was measured in the laboratory using pulsed nuclear magnetic resonance (PNMR) for a Windsor sandy loam soil. The PNMR data were related to previously measured soil moisture retention data through the modified Clausius-Clapeyron equation, with suitable adjustment for surface tension. The transformed measured unfrozen water content data and the previously measured soil

Patrick B. Black; Allen R. Tice

1989-01-01

99

Model and experimental investigations of water retention of repellent and subcritical repellent soils  

NASA Astrophysics Data System (ADS)

Soil organic matter can modify the surface properties of the soil mineral phase by changing the surface tension of the mineral surfaces. This modifies the soil's solid-water contact angle, which in turn would be expected to affect its water retention curve (SWRC). Here we model the impact of differences in the soil pore-water contact angle on capillarity in non-cylindrical pores by accounting for their complex pore-geometry. Theoretical modeling, assuming a constant surface tension of soil particle surfaces, supported by experimental observations using materials with different water repellency levels (‘model soil' soils containing grains that exhibit ‘permanent' hydrophobicity and field soil samples), demonstrate that (i) water retention depends strongly on the solid-water wetting angle for the wetting curve, but has little impact on the drying curve and (ii) that water retention is a feature not of only wettable soils, but also soils that are in a water repellent state. This behavior cannot be explained on the basis of the commonly used, but vastly simplifying, capillary bundle model for soil pores. The new model presented here takes account of the wavy nature of soil pores and explains the experimental observations made on model and field soils. Although the model is based on a simplified (‘permanent') hydrophobicity of soil particle surfaces, its principles and implications are relevant also to more complex scenarios in which particle surface hydrophobicity may change during wetting and drying phases. The currently used methods for measuring the Young's wetting angle on soil samples are insufficient in representing the variable wetting angle in the soil pore space and hence its impact on the SWRC. The theoretical predictions and experimental results obtained here indicate that small changes in wetting angle can cause switches between wettable and water repellent soil behaviour of the soil pore space. This may explain the common observation that relatively small changes in soil water content can cause substantial changes in soil wettability irrespective of changes in surface tension (i.e. hydrophobicity) of individual soil particle surfaces. The model derived here would also help to explain the substantial reductions in water repellency observed following soil compaction, which results in changes in pore geometry and hence wetting angle. The above findings are not only relevant for soils, but also for predicting wettability and water retention of other, potentially water repellent, porous media such as reservoir rocks containing hydrocarbons, or the wide variety of man-made materials used in engineering, construction or medicine.

Czachor, Henryk; Doerr, Stefan H.; Lichner, Lubomir

2010-05-01

100

Investigation of the spatial distribution of the maximum water retention capacity of soil in a small river basin  

Microsoft Academic Search

The maximum water retention capacity of soils is crucial for runoff generation, flow regime and hence also for the watershed behaviour during rainfall events. High infiltration rates of soils lead to a decreased in peak discharge reducing flood risk in river basins. In catchments where agricultural lands are prevailing, American Soil Conservation Service (SCS) - Runoff Curve Number Method is

Angelantonio Calabrese; Anna Maria de Girolamo; Antonio Lo Porto; Giuseppe Pappagallo; Gerardina Santese

2010-01-01

101

Simultaneous scaling of soil water retention and unsaturated hydraulic conductivity functions assuming lognormal pore-size distribution  

Microsoft Academic Search

Using simultaneous scaling, soil spatial variability of hydraulic functions can be described from a single set of scaling factors. The conventional scaling approach is based on empirical curve fitting, without paying much attention to the physical significance of the scaling factors. In this study, the concept of simultaneous scaling of the soil water retention and unsaturated hydraulic conductivity functions is

A. Tuli; K. Kosugi; J. W. Hopmans

2001-01-01

102

Modified soil water retention functions for all matric suctions  

Microsoft Academic Search

The Brooks-Corey and van Genuchten functions were modified to adequately represent retention at all matric suctions. The modification consisted of replacing the residual water content with an adsorption equation. The modified functions retain the form of the original functions in the wet range and the form of an adsorption equation in the dry range. The modified functions provided excellent fits

Michael J. Fayer; C. Steven Simmons

1995-01-01

103

Modeling of soil water retention from saturation to oven dryness  

Microsoft Academic Search

Most analytical formulas used to model moisture retention in unsaturated porous media have been developed for the wet range and are unsuitable for applications in which low water contents are important. We have developed two models that fit the entire range from saturation to oven dryness in a practical and physically realistic way with smooth, continuous functions that have few

Cinzia Rossi; John R. Nimmo

1994-01-01

104

Assessment of Stormwater Retention Basin Water Quality in Winnipeg, Canada  

Microsoft Academic Search

The water quality behaviour of 58 stormwater retention basins in Winnipeg, Canada, was intensively studied during a 5-month summer period (May to September). Dissolved oxygen (DO), temperature, turbidity, transparency and depth were measured onsite. Samples analyzed in the laboratory included: total suspended solids (TSS), pH, chlorophyll a, fecal coliforms (FC), total kjeldahl nitrogen (TKN), ammonia, nitrate, total phosphorus (TP) and

SARAH C. WAKELIN; PANAGIOTIS ELEFSINIOTIS; DAVID G. WAREHAM

2003-01-01

105

Pathophysiology of Sodium and Water Retention in Heart Failure  

Microsoft Academic Search

Heart failure is a leading cause of morbidity and mortality. In the United States, there are more than 5 million patients with heart failure and over 500,000 newly diagnosed cases each year. Numerous advances have been made in our understanding of the pathophysiologic mechanisms contributing to sodium and water retention in this condition. Important alterations in the sympathetic nervous system

Melissa A. Cadnapaphornchai; Andrei K. Gurevich; Howard D. Weinberger; Robert W. Schrier

2001-01-01

106

DRAINAGE AND RETENTION OF WATER BY CLADDING SYSTEMS  

Microsoft Academic Search

This laboratory study investigated the drainage, retention and isothermal drying of various wall cladding systems to determine behavioral characteristics and factors affecting their ability to dry. The full scale laboratory wall tests included EIFS adhesively attached to the OSB sheathing with a liquid applied water penetration barrier (3 manufacturers), direct-applied vinyl siding (2 profiles), hardboard siding (2 profiles), wood siding

Donald Onysko; Constance Thivierge; Silvio Plescia; Barry Craig

107

INFLUENCE OF CATION LEACHING ON WATER RETENTIVITY OF DRINKING WATER SLUDGE  

NASA Astrophysics Data System (ADS)

It is important for waste management and sound material-cycle society to clarify the change of the physico-chemical properties of reusable material. In this study, the influence of cation leaching on water retentivity of drinking water sludge was investigated. The column leaching test was executed using drinking water sludge to simulate rainwater percolation, and the water retentivity test of the degraded sludge was executed. As a result, the water retentivity of drinking water sludge decreased after cation leaching. The cation exchangeable capacity of drinking water sludge and its microscopic structure were almost stable during the leaching test. The results indicate a possibility that Al leaching decreases the hydrophilic part of flocculating agent which relates to water retention of drinking water sludge.

Watanabe, Yasutaka; Komine, Hideo; Yasuhara, Kazuya; Murakami, Satoshi; Toyoda, Kazuhiro

108

Estimating Dry-Range Water Retention Properties Using Specific Surface Area and Particle-Size Measurements  

NASA Astrophysics Data System (ADS)

To test whether the slope of the dry-range water retention curve can be correlated directly with particle size and specific surface area, measurements were completed for core samples from the Mojave Desert and the Idaho National Engineering and Environmental Laboratory. Samples ranged in texture from gravelly sands to silt loams. Each core sample was split into representative, 1-3 g subsamples, with 3 replicates per sample. Specific surface areas were determined by the BET (Brunauer-Emmett-Teller) method of nitrogen adsorption. A chilled mirror hygrometer was used to measure the relative humidity and temperature of each replicate, which were directly implemented in the Kelvin equation to calculate water potentials. Sample weights obtained immediately after the hygrometer measurements, the oven-dry weights, and the original core bulk densities were used to calculate volumetric water contents. For each sample, about 7 points on the retention curve were determined by allowing the replicates to dry for 15 to 120 minutes in a desiccating chamber and by repeating the hygrometer and weight measurements. Measured water potentials fell in the range of -105 to -106 cm-water and volumetric water contents in the range of 0.05 to 0.007 cm3/cm3, typically below the equilibrium water content under laboratory conditions at about 50 % relative humidity and 22 ° C. Measurements of specific surface area ranged from 0.5 to 25 m2/g. At low water potentials water exists as thin films on solid surfaces rather than filling pores, therefore the dry-range retention slope should be dominated by texture, with structure having negligible influence, and should correlate with specific surface area for samples having similar mineralogies. Initial correlations show that the dry-range retention slope becomes steeper as the mean particle size of the sample decreases and as the clay content increases. The slope also approximates a direct linear proportionality to specific surface area. Correlations between dry-range retention properties, particle size, and specific surface area provide the foundation for the development of property transfer models that are applicable over the low-water-content range of interest at many arid region sites. These models will permit the estimation of hydraulic properties, which are especially difficult to measure at low water contents, from less complicated bulk property measurements.

Winfield, K. A.; Nimmo, J. R.

2001-12-01

109

Soil-Moisture Retention Curves, Capillary Pressure Curves, and Mercury Porosimetry: A Theoretical and Computational Investigation of the Determination of the Geometric Properties of the Pore Space  

Microsoft Academic Search

Immiscible displacement protocols have long been used to infer the geometric properties of the void space in granular porous media. The three most commonly used experimental techniques are the measurement of soil-moisture retention curves and relative permeability-capillary pressure-saturation relations, as well as mercury intrusion porosimetry experiments. A coupled theoretical and computational investigation was performed that provides insight into the limitations

T. E. Strand; H. F. Wang

2003-01-01

110

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...

111

A soil-water retention function that includes the hyper-dry region through the BET adsorption isotherm  

NASA Astrophysics Data System (ADS)

Most existing full-range soil-water retention functions extend standard capillary pressure curves into the dry region to zero water content at a finite matric pressure. A description of dryness is commonly taken as oven-dry conditions given by a matric suction of about 109 Pa at zero liquid saturation. However, no finite pressure can be exerted by a zero amount of water, so a possibly more realistic situation necessarily implies that as water content approaches zero, suction tends to infinity. In this study we propose a full-range water retention function that takes advantage of the physical consistence of the Brunauer-Emmett-Teller (BET) adsorption isotherm to describe the very dry end, and preserves the capillary behavior of the classical Brooks and Corey function in the wet range. The transition from capillary to adsorption mechanisms is accounted for by a generalization of the Bradley's isotherm. Tests on seven widely studied soil data sets show that the experimental water retention curves are well fitted by the proposed retention model. In order to test the present approach, our simulations were compared to experimental data, for water transport under dry conditions, found in the literature. The present model was also compared with a recently proposed extended retention function in a hypothetical experiment designed to test the influence of predicted soil humidity on solute volatilization. These comparisons showed that, under severe dryness, the water dynamics is well described by the proposed model. Moreover, in these conditions the retention function determines the soil humidity, to which solute volatilization calculations can be very sensitive.

Silva, Orlando; Grifoll, Jordi

2007-11-01

112

Interpretation of water retention field measurements in relation to hysteresis phenomena  

Microsoft Academic Search

Knowledge of the soil water retention function is fundamental to quantifying the flow of water and dissolved contaminants in the vadose zone. This function is usually determined by fitting a particular model (see, for example, van Genuchten (1980) or Brooks-Corey (1964)) to observed retention points. Independent of the model chosen, interpretation and identification of the water retention parameters are subjective

Davide Canone; Stefano Ferraris; Graham Sander; Randel Haverkamp

2008-01-01

113

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

114

Studies on water retention and water release from some protein systems  

Microsoft Academic Search

The hydrogen-bond properties (WBI index), water retention and water release from the protein-water systems gluten-water, soya protein- water and casein-water, have been investigated using differential scanning calorimetry in the temperature range 223–423 K. The proteins were characterized by their isoelectric point, contents of carboxyl groups and sulfur-containing groups, and readiness of undergo chloromethylation. It was concluded that the marked difference

R. Silvonen; J. J. Lindberg; C. Seppälä; M. Ervasti; C. Hauta-Aho

1982-01-01

115

Modeling of soil water retention from saturation to oven dryness  

NASA Astrophysics Data System (ADS)

Most analytical formulas used to model moisture retention in unsaturated porous media have been developed for the wet range and are unsuitable for applications in which low water contents are important. We have developed two models that fit the entire range from saturation to oven dryness in a practical and physically realistic way with smooth, continuous functions that have few parameters. Both models incorporate a power law and a logarithmic dependence of water content on suction, differing in how these two components are combined. In one model, functions are added together (model "sum"); in the other they are joined smoothly together at a discrete point (model "junction"). Both models also incorporate recent developments that assure a continuous derivative and force the function to reach zero water content at a finite value of suction that corresponds to oven dryness. The models have been tested with seven sets of water retention data that each cover nearly the entire range. The three-parameter sum model fits all data well and is useful for extrapolation into the dry range when data for it are unavailable. The two-parameter junction model fits most data sets almost as well as the sum model and has the advantage of being analytically integrable for convenient use with capillary-bundle models to obtain the unsaturated hydraulic conductivity.

Rossi, Cinzia; Nimmo, John R.

1994-03-01

116

Scaling soil water retention functions using particle-size distribution  

NASA Astrophysics Data System (ADS)

The application of spatially distributed hydrological model is a challenging problem, particularly because of the difficulties arising in the identification of the model parameters describing the soil hydraulic properties and their spatial variability. Generally soil data are available just for a limited number of locations across the study area and very often the available data consist of soil physical and chemical properties rather than direct measurements of the soil hydraulic properties. Thus indirect methods are often required for an assessment of model parameters describing the soil hydraulic properties, based on a limited number of measurements. This study presents a methodology for assessing the variability of soil water retention from soil texture and bulk density measurements, based on a combination of the scaling approach proposed by Kosugi and Hopmans (1998) and the Arya-Paris (AP) physico-empirical pedotransfer function. The approach proposed by Kosugi and Hopmans (1998) represents the spatial variability of soil hydraulic properties by scaling factors which relate the soil hydraulic functions in any location to a single reference function, provided that soils are characterised by geometric similitude within the study area. The Arya-Paris (AP) physico-empirical pedotransfer function estimates the soil water retention from the soil particle-size distribution and bulk density. The proposed method has been evaluated in two different areas of Southern Italy. Laboratory-measured and AP-predicted reference water retention functions are compared by evaluating the lognormal distributions of the corresponding scaling factors. The method proved to be effective even with a limited number of soil samples (30-40 soil samples), provided that the study region is classified according to homogeneous soil textural classes, to ensure the geometric similitude within each soil sample set. This method can be potentially used as an effective tool for identifying homogeneous soil hydrologic response units at the catchment scale.

Nasta, P.; Chirico, G. B.; Kamai, T.; Hopmans, J. W.; Romano, N.

2009-04-01

117

Scaling soil water retention functions using particle-size distribution  

NASA Astrophysics Data System (ADS)

The application of spatially distributed hydrological model is a challenging problem, particularly because of the difficulties arising in the identification of the model parameters describing the soil hydraulic properties and their spatial variability. Generally soil data are available just for a limited number of locations across the study area and very often the available data consist of soil physical and chemical properties rather than direct measurements of the soil hydraulic properties. Thus indirect methods are often required for an assessment of model parameters describing the soil hydraulic properties, based on a limited number of measurements. This study presents a methodology for assessing the variability of soil water retention from soil texture and bulk density measurements, based on a combination of the scaling approach and the Arya-Paris (AP) physico-empirical pedotransfer function. The approach represents the spatial variability of soil hydraulic properties by scaling factors which relate the soil hydraulic functions in any location to a single reference function, provided that soils are characterised by geometric similitude within the study area. The Arya-Paris (AP) physico-empirical pedotransfer function estimates the soil water retention from the soil particle-size distribution and bulk density. The proposed method has been evaluated in two different areas of Southern Italy. Laboratory-measured and AP-predicted reference water retention functions are compared by evaluating the lognormal distributions of the corresponding scaling factors. The method proved to be effective even with a limited number of soil samples (30-40 soil samples), provided that the study region is classified according to homogeneous soil textural classes, to ensure the geometric similitude within each soil sample set. This method can be potentially used as an effective tool for identifying homogeneous soil hydrologic response units at the catchment scale.

Nasta, P.; Hopmans, J. W.; Kamai, T.; Romano, N.; Chirico, G.

2009-12-01

118

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.

Costabel, Stephan; Yaramanci, Ugur

2013-01-01

119

Characterizing scale- and location-dependent correlation of water retention parameters with soil physical properties using wavelet techniques.  

PubMed

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. The objective of this study was to examine the scale- and location-dependent correlation between two water retention parameters (alpha and n) in the van Genuchten (1980) function and soil physical properties (sand content, bulk density [Bd], and organic carbon content) using wavelet techniques. Soil samples were collected from a transect from Fuxin, China. Soil water retention curves were measured, and the van Genuchten parameters were obtained through curve fitting. Wavelet coherency analysis was used to elucidate the location- and scale-dependent relationships between these parameters and soil physical properties. Results showed that the wavelet coherence between alpha and sand content was significantly different from red noise at small scales (8-20 m) and from a distance of 30 to 470 m. Their wavelet phase spectrum was predominantly out of phase, indicating negative correlation between these two variables. The strong negative correlation between alpha and Bd existed mainly at medium scales (30-80 m). However, parameter n had a strong positive correlation only with Bd at scales between 20 and 80 m. Neither of the two retention parameters had significant wavelet coherency with organic carbon content. These results suggested that location-dependent scale analyses are necessary to improve the performance for soil water retention characteristic predictions. PMID:18948482

Shu, Qiaosheng; Liu, Zuoxin; Si, Bingcheng

2008-10-23

120

Neural Network-Based Multi-scale Pedo-Transfer Functions for Soil Water Retention  

NASA Astrophysics Data System (ADS)

Pedo Transfer Functions (PTFs) based on Artificial Neural Networks (ANNs) have been used in the field of hydrology for some time. However, while most previous studies derive and adopt these parameters at matching spatial scales (1:1) of input and output data, here we present two methodologies to derive the soil water retention function at the point or local scale using PTFs trained with coarser scale input data. In the first study, a conventional ANN was trained using soil texture and bulk density data from the SSURGO database (scale 1:24,000) and then used for predicting the soil water contents at different pressure heads with point scale data (1:1) inputs. Suitable bias correction was applied to the resulting output and used to construct the van Genuchten soil water characteristic curve. The results show good agreement between the soil water retention curves constructed from the ANN-based PTFs and the field observations at the local scale. In the second study we employed a Markov Chain Monte Carlo (MCMC) based Bayesian Neural Network to derive the soil water content values. While conventional ANN training attempts to describe the target variable as a function of the input vector and the training weights, Bayesian training attempts to update the weight vector with information available in the data. Comparisons of the outputs from the two methodologies are presented and their respective advantages and disadvantages are highlighted. These methods have potential as suitable tools to tackle the dual problems of parameter estimation and their scaling in one simple package.

Jana, R. B.; Mohanty, B. P.

2006-12-01

121

Influence of air and water temperature on fill characteristics curve  

SciTech Connect

In a previous paper, the author discussed approximations of the Merkel Theory, as well as other approximations included in the CTI recommended method of calculation of the Demand curves. The paper concluded that the familiar difference of enthalpies, used as a cooling potential, which is the Merkel Theory, could continue to be used by simply adding a corrective multiplying factor derived from a direct comparison of the exact theory and the Merkel Theory. At the end of the paper the author briefly showed that the corrections to the Demand curve was only one part of the picture and that there was also an influence of the temperatures of the Characteristic curve side. The object of this paper is to now review the influence of the air and water temperature on the Characteristic curve. This completes the work presented last year.

Lefevre, M.R.

1985-01-01

122

Influences affecting the soil-water characteristic curve  

Microsoft Academic Search

The soil-water characteristic curve (SWCC) is the primary partially saturated soil information as its behavior and properties can be derived from it. Although there have been many studies of unsaturated soils and the SWCC, there is still no combined constitutive model that can simulate soil characteristics accurately. In cases when hydraulic hysteresis is dominant (e.g. under cyclic loading) it is

ZHOU Jian; YU Jian-lin

2005-01-01

123

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

Microsoft Academic Search

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

Anh-Minh Tang; Yu-Jun Cui

2007-01-01

124

Considering rating curve uncertainty in water level predictions  

NASA Astrophysics Data System (ADS)

Streamflow cannot be measured directly and is typically derived with a rating curve model. Unfortunately, this causes uncertainties in the streamflow data and also influences the calibration of rainfall-runoff models if they are conditioned on such data. However, it is currently unknown to what extent these uncertainties propagate to rainfall-runoff predictions. This study therefore presents a quantitative approach to rigorously consider the impact of the rating curve on the prediction uncertainty of water levels. The uncertainty analysis is performed within a formal Bayesian framework and the contributions of rating curve versus rainfall-runoff model parameters to the total predictive uncertainty are addressed. A major benefit of the approach is its independence from the applied rainfall-runoff model and rating curve. In addition, it only requires already existing hydrometric data. The approach was successfully tested on a small urbanized basin in Poland, where a dedicated monitoring campaign was performed in 2011. The results of our case study indicate that the uncertainty in calibration data derived by the rating curve method may be of the same relevance as rainfall-runoff model parameters themselves. A conceptual limitation of the approach presented is that it is limited to water level predictions. Nevertheless, regarding flood level predictions, the Bayesian framework seems very promising because it (i) enables the modeler to incorporate informal knowledge from easily accessible information and (ii) better assesses the individual error contributions. Especially the latter is important to improve the predictive capability of hydrological models.

Sikorska, A. E.; Scheidegger, A.; Banasik, K.; Rieckermann, J.

2013-03-01

125

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

126

Improved estimation of soil water retention characteristics from hydrostatic column experiments  

NASA Astrophysics Data System (ADS)

The soil water retention characteristic, ?(h), is required for modeling and predicting water and solute transport in unsaturated porous media. Commonly, ?(h) is determined by relating pressure heads, h, to mean water contents, ?, that are measured in column experiments under hydrostatic equilibrium conditions and fitting a parametric retention function to these data pairs. Implicit to this method is the assumption that the mean water content of the column is equivalent to a point measurement in the column center. Dependent on the nonlinearity of the vertical water content distribution, ?(z), in the column, this assumption may be invalid and introduces a systematic error. A sensitivity analysis shows that the magnitude of the error caused by neglecting the nonlinearity of the water content distribution may reach several percent if coarse materials with low air entry values and tall soil columns are investigated. Furthermore, neglecting ?(z) yields a smoothed retention characteristic and thus may lead to wrong conclusions about the most appropriate parametric model for the water retention characteristic. If the hydraulic conductivity function K(h) is predicted from such an incorrect retention function, it can differ greatly from the true function. In this paper, we propose to consider the measured water content of a soil column explicitly as an integral of the equilibrium water content distribution with depth. We show that this eliminates systematic parameter estimation errors and leads to improved estimates of the soil water retention function.

Peters, A.; Durner, W.

2006-11-01

127

Role of air-water interfaces on retention of viruses under unsaturated conditions  

NASA Astrophysics Data System (ADS)

We investigated transport of viruses through saturated and unsaturated sand columns. Unsaturated experiments were conducted under conditions of uniform saturation and steady state water flow. The water saturation ranged from 1 to 0.5. Bacteriophages MS2 and ?X174 were used as surrogates for pathogenic viruses in these studies. Phosphate-buffered solutions with different pH values (7.5, 6.2, 5.5, and 5) were utilized. Virus transport was modeled assuming first-order kinetic adsorption for interactions to the solid-water interface (SWI) and the air-water interface (AWI). Under saturated conditions, virus retention increased as pH decreased, and a one-site kinetic model produced a good fit to the breakthrough curves. Under unsaturated conditions a two-site kinetic model was needed to fit the breakthrough curves satisfactorily. The second site was attributed to the adsorption of phages to the AWI. According to our results, ?X174 exhibits a high affinity to the AWI at pH values below 6.6 (the isoelectric point of ?X174). Although it is believed that MS2 is more hydrophobic than ?X174, MS2 had a lower affinity to the AWI than ?X174, presumably because of the lower isoelectric point of MS2, which is equal to 3.9. Under unsaturated conditions, viruses captured within the column could be recovered in the column outflow by resaturating and immediately draining the column. Draining columns under saturated conditions, however, did not result in any recovery of viruses. Therefore the recovery can be attributed to the release of viruses adsorbed to the AWI. Our results suggest that electrostatic interactions of viruses with the AWI are much more important than hydrophobicity.

Torkzaban, S.; Hassanizadeh, S. M.; Schijven, J. F.; van den Berg, H. H. J. L.

2006-12-01

128

Water films and scaling of soil characteristic curves at low water contents  

Microsoft Academic Search

Individual contributions of capillarity and adsorptive surface forces to the matric potential are seldom differentiated in determination of soil water characteristic (SWC) curves. Typically, capillary forces dominate at the wet end, whereas adsorptive surface forces dominate at the dry end of a SWC where water is held as thin liquid films. The amount of adsorbed soil water is intimately linked

Markus Tuller

2005-01-01

129

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

130

SPATIAL VARIABILITY OF SOIL WATER RETENTION FUNCTIONS IN A SILT LOAM SOIL  

Microsoft Academic Search

a structured variance witha range of influence between 12 and 30.The number of parameters needed to char-acterize the field variability was 912 forthe retention model. Scaling theory appliedto the water retention data signifi4 Applied Geosciences Unit, E. G. and G. Idaho Inc.,Idaho National Engineering Lab., Idaho Falls, ID.Received March 17, 1994; accepted Aug. 16, 1994.contribution from the USDA-ARES U.S.Salinity Laboratory,

P. J. SHOUSE; W. B. RUSSELL; D. S. BURDEN; H. M. SELIM; J. B. SISSON; M. T. H. VAN GENUCHTEN

1995-01-01

131

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

132

Wet-End Deviations from Scaling of the Water Retention Characteristics of Fractal Porous Media  

Microsoft Academic Search

A previous investigation demonstrated that dry-end deviations from fractal scaling of the water retention of USDOE Hanford site soils set on at a moisture content closely related to the moisture content at which solute diffusion vanishes. This result was interpreted in terms of a minimum water content for percolation of filled capillaries. We now find that wet-end deviations from fractal

Allen G. Hunt; Glendon W. Gee

2003-01-01

133

Applicability of Uni and Bimodal Retention Functions for Water Flow Modeling in a Tropical Acrisol  

Microsoft Academic Search

Modeling soil water fluxes is an important part of many agricultural and environmental investigations and applications. A prerequisite for accurate modeling results is a sound parameterization of the soil hydraulic functions. The aim of this study was to investigate whether the unimodal retention function is sufficient to simulate the soil water regime of an Acrisol in Northern Thailand. The van

Klaus Spohrer; Ludger Herrmann; Joachim Ingwersen; Karl Stahr

2006-01-01

134

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

135

Hydraulic Conductivity Limited Equilibration: Effect on Water Retention Characteristics  

Microsoft Academic Search

the transient flow case than for the static equilibrium and steady-state cases. The effects of the percolation phase transition on equilibration of Our work concerns only nonequilibrium effects on porous media during drainage are shown to set on at moisture con- drainage curves; the fundamental hysteresis between tents,,somewhatlargerthanthecriticalmoisturecontentforpercola- tion, t. An algorithm is developed, which yields the typical upward drainageandimbibitionhasalreadybeentreated(Hunt,

A. G. Hunt; T. E. Skinner

2005-01-01

136

Retention characteristics of water-soluble compounds on water-holding adsorbents with immobilized zwitterionic copolymers having different ionicities.  

PubMed

Three kinds of water-holding adsorbents with immobilized zwitterionic copolymers having different cationic ionicities were synthesized. To investigate the influence of the charge balance and the ionicity of the cation site, the retention properties of the water-soluble solutes on the zwitterionic adsorbents were measured by HPLC. These adsorbents had high water contents, and the hydrating water contents depended on the amounts of immobilized copolymer. The retentions of water-soluble solutes depended on the hydrophilic interaction, and were in the order of logP(o/w) (logarithm of octanol-water partition coefficient). This suggests that the partition to the hydration layer was the main retention mechanism on the zwitterionic adsorbents. On the other hand, the electrostatic interaction based on the cation site on the adsorbents was also observed. The electrostatic interaction could be reduced by decreasing the ionicity of the cation sites. These results indicate that the retentions of the water-soluble solutes on the zwitterionic adsorbents were greatly influenced by the ionicity of the cation sites on the adsorbents. PMID:22997146

Kamichatani, Waka; Inoue, Yoshinori; Saito, Mitsuru; Kobayashi, Yasuyuki; Yamamoto, Atsushi

2012-09-20

137

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...

138

Hyperthermia Impairs Retention of an Overtrained Spatial Task in the Morris Water Maze,  

National Technical Information Service (NTIS)

Fifteen rats were trained to learn the location of a spatially fixed platform hidden in a Morris water maze (40 + or - 2 C). Then retention of the spatial task was assessed immediately after raising core body temperature (T sub c) to 42, 40 or 37 C (the n...

D. I. Welch L. Gallego T. M. Rauch

1988-01-01

139

Pilot Scale Microfiltration–Coagulation for Treatment of Retention Pond Water  

Microsoft Academic Search

An evaluation of two commonly used coagulants, alum and ferric chloride was conducted to treat retention pond water using microfiltration. To determine the effectiveness of these coagulants in removing turbidity, color, and total suspended solids two different sets of the experiments were performed. Preliminary test was carried out to evaluate the optimum dosages of coagulants. Optimum turbidity removal was achieved

Katayon Saed; Megat Johari Megat Mohd Noor; Abdul Ghani Liew Abdullah; Mohd Razman Salim; Hiroshi Nagaoka; Hidenori Aya

2004-01-01

140

Wavelet-based multifractal analysis of field scale variability in soil water retention  

NASA Astrophysics Data System (ADS)

Better understanding of spatial variability of soil hydraulic parameters and their relationships to other soil properties is essential to scale-up measured hydraulic parameters and to improve the predictive capacity of pedotransfer functions. The objective of this study was to characterize scaling properties and the persistency of water retention parameters and soil physical properties. Soil texture, bulk density, organic carbon content, and the parameters of the van Genuchten water retention function were determined on 128 soil cores from a 384-m transect with a sandy loam soil, located at Smeaton, SK, Canada. The wavelet transform modulus maxima, or WTMM, technique was used in the multifractal analysis. Results indicate that the fitted water retention parameters had higher small-scale variability and lower persistency than the measured soil physical properties. Of the three distinct scaling ranges identified, the middle region (8-128 m) had a multifractal-type scaling. The generalized Hurst exponent indicated that the measured soil properties were more persistent than the fitted soil hydraulic parameters. The relationships observed here imply that soil physical properties are better predictors of water retention values at larger spatial scales than at smaller scales.

Zeleke, Takele B.; Si, Bing C.

2007-07-01

141

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

Microsoft Academic Search

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

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

1991-01-01

142

Technical note Characterisation of geotextiles water retention using a modified capillary pressure cell  

Microsoft Academic Search

This paper presents water retention data, on the drying path, of a non-woven polyester geotextile obtained from a modified capillary pressure cell. The results were evaluated and compared to a hanging column test results. A good correlation was found between the two test methods. The modified capillary cell allowed the testing to be conducted in a very short time compared

Hani Nahlawi; Abdelmalek Bouazza; Jayantha Kodikara

143

Clay-based heat insulator composites: Thermal and water retention properties  

Microsoft Academic Search

The formulation of unsaturated polyester composite as an insulating material that gives the best in terms of thermal and water retention properties was investigated as a function of filler type and content. Different types of local fillers were used in the formulations. Bentonite-based unsaturated polyester composite which is denoted as BBUPEC was found to have stable and compatible thermal, physical,

Kamal Al-Malah; Basim Abu-Jdayil

2007-01-01

144

Wetting process and soil water retention of a minesoil amended with composted and thermally dried sludges  

Microsoft Academic Search

Composting or thermally-drying sludges are becoming commonly used in soil rehabilitation of degraded land. Sludge amendments increase soil organic matter, but can reduce soil wettability due to hydrophobic compounds. The main objective of this study is to analyse how composted and thermally dried sludges influence soil wettability and water retention properties of a minesoil obtained from limestone extraction during quarrying

G. Ojeda; S. Mattana; J. M. Alcañiz; G. Marando; M. Bonmatí; S. K. Woche; J. Bachmann

2010-01-01

145

Retention in hydrophobic interaction chromatography and dissolution of nonpolar gases in water  

Microsoft Academic Search

The retention data of dansyl amino acids in hydrophobic interaction chromatography (HIC) is interpreted in terms of physicochemical properties of the eluites and solvent and the results are compared to data for the dissolution in water of nonpolar gases. Isothermodynamic temperatures, certain linear relationships between thermodynamic quantities and molecular structure as well as the hermeneutics of the solvophobic theory are

Anant Vailaya; Csaba Horváth

1996-01-01

146

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

147

Prediction of water retention in soils of Castilla-La Mancha (Spain) with artificial neural networks  

Microsoft Academic Search

The direct measurement of the water retention in soil at a defined matric potential is a tedious and hard action. To estimate it indirectly from other soil parameters, which are easily measured, statistical models have been developed, and nowadays they are also used artificial neural networks (ANN). The aim of this study has been to see if the ANN application

ARTIGAO Alfonso; FELIPE Beatriz; ORTEGA José Fernando

148

Development of class pedotransfer functions of soil water retention—A refinement  

Microsoft Academic Search

This paper reviews an existing method of class pedotransfer function development, ‘the Wösten method’, reproducing previous results by this method, and introduces a statistically more stringent refinement, ‘the Transformation method’. Direct comparison of the Wösten method and a Box–Cox Transformation method shows that these two methods produce equivalent predictions of the average values of water retention, and errors in these

L. Baker

2008-01-01

149

Wavelet-based multifractal analysis of field scale variability in soil water retention  

Microsoft Academic Search

Better understanding of spatial variability of soil hydraulic parameters and their relationships to other soil properties is essential to scale-up measured hydraulic parameters and to improve the predictive capacity of pedotransfer functions. The objective of this study was to characterize scaling properties and the persistency of water retention parameters and soil physical properties. Soil texture, bulk density, organic carbon content,

Takele B. Zeleke; Bing C. Si

2007-01-01

150

Alluvial Characteristics, Groundwater-Surface Water Exchange and Hydrological Retention in Headwater Streams  

NASA Astrophysics Data System (ADS)

Conservative solute injections were conducted in three first-order montane streams of different geological composition to assess the influence of parent lithology and alluvial characteristics on the hydrological retention of nutrients. Three study sites were established: (1) Aspen Creek, in a sandstone-siltstone catchment with a fine-grained alluvium of low hydraulic conductivity (1·3×10-4 cm/s), (2) Rio Calaveras, which flows through volcanic tuff with alluvium of intermediate grain size and hydraulic conductivity (1·2×10-3 cm/s), and (3) Gallina Creek, located in a granite/gneiss catchment of coarse, poorly sorted alluvium with high hydraulic conductivity (4·1×10-3 cm/s). All sites were instrumented with networks of shallow groundwater wells to monitor interstitial solute transport. The rate and extent of groundwater-surface water exchange, determined by the solute response in wells, increased with increasing hydraulic conductivity. The direction of surface water-groundwater interaction within a stream was related to local variation in vertical and horizontal hydraulic gradients. Experimental tracer responses in the surface stream were simulated with a one-dimensional solute transport model with inflow and storage components (OTIS). Model-derived measures of hydrological retention showed a corresponding increase with increasing hydraulic conductivity.To assess the temporal variability of hydrological retention, solute injection experiments were conducted in Gallina Creek under four seasonal flow regimes during which surface discharge ranged from baseflow (0·75 l/s in October) to high (75 l/s during spring snowmelt). Model-derived hydrological retention decreased with increasing discharge.The results of our intersite comparison suggest that hydrological retention is strongly influenced by the geologic setting and alluvial characteristics of the stream catchment. Temporal variation in hydrological retention at Gallina Creek is related to seasonal changes in discharge, highlighting the need for temporal resolution in studies of the dynamics of surface water-groundwater interactions in stream ecosystems.

Morrice, John A.; Valett, H. Maurice; Dahm, Clifford N.; Campana, Michael E.

1997-03-01

151

Potassium Release Kinetics and Water Retention of Controlled-Release Fertilizers Based on Chitosan Hydrogels  

Microsoft Academic Search

Controlled release fertilizer (CRF) hydrogels were prepared from poly(vinyl alcohol), poly(vinyl alcohol)\\/chitosan and chitosan\\u000a using glutaraldehyde as a crosslinker. Intermolecular interactions of the CRF hydrogels were elucidated using FTIR. Water\\u000a absorbency characteristics of the CRF hydrogels were also studied. It was found that the CRF hydrogels exhibited the equilibrium\\u000a swelling ratio (SR) in the range 70–300%. The water retention of

Tongsai Jamnongkan; Supranee Kaewpirom

2010-01-01

152

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

153

Hysteresis of Soil Point Water Retention Functions Determined by Neutron Radiography  

NASA Astrophysics Data System (ADS)

Soil point water retention functions are needed for modeling flow and transport in partially-saturated porous media. Such functions are usually determined by inverse modeling of average water retention data measured experimentally on columns of finite length. However, the resulting functions are subject to the appropriateness of the chosen model, as well as the initial and boundary condition assumptions employed. Soil point water retention functions are rarely measured directly and when they are the focus is invariably on the main drying branch. Previous direct measurement methods include time domain reflectometry and gamma beam attenuation. Here we report direct measurements of the main wetting and drying branches of the point water retention function using neutron radiography. The measurements were performed on a coarse sand (Flint #13) packed into 2.6 cm diameter x 4 cm long aluminum cylinders at the NIST BT-2 (50 ?m resolution) and ORNL-HFIR CG1D (70 ?m resolution) imaging beamlines. The sand columns were saturated with water and then drained and rewetted under quasi-equilibrium conditions using a hanging water column setup. 2048 x 2048 pixel images of the transmitted flux of neutrons through the column were acquired at each imposed suction (~10-15 suction values per experiment). Volumetric water contents were calculated on a pixel by pixel basis using Beer-Lambert’s law in conjunction with beam hardening and geometric corrections. The pixel rows were averaged and combined with information on the known distribution of suctions within the column to give 2048 point drying and wetting functions for each experiment. The point functions exhibited pronounced hysteresis and varied with column height, possibly due to differences in porosity caused by the packing procedure employed. Predicted point functions, extracted from the hanging water column volumetric data using the TrueCell inverse modeling procedure, showed very good agreement with the range of point functions measured within the column using neutron radiography. Extension of these experiments to 3-dimensions using neutron tomography is planned.

Perfect, E.; Kang, M.; Bilheux, H.; Willis, K. J.; Horita, J.; Warren, J.; Cheng, C.

2010-12-01

154

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

155

Submersible pressure outflow cell for measurement of soil water retention and diffusivity from 5 to 95oC.  

USGS Publications Warehouse

The technique is designed to measure soil water retention characteristics and to make transient outflow estimates of the soil water diffusivity at temperatures from 5 to 95oC. We also used the technique to determine the isobaric temperature dependence of water retention in soil. Results indicate that at constant capillary pressure, the relationship between moisture content and temperature is hysteretic.-from Authors

Constantz, J.; Herkelrath, W. N.

1984-01-01

156

Electrocapillary Curves of Chloride Ions in Water-Hydrogen Flouride Mixtures  

Microsoft Academic Search

We have determined the electrocapillary curves of the mercury electrode with a mixture of hydrogen fluoride and water contaning 40% (by weight) of HF, using the mercury electrode drop time formation technique. The addition of KCl at concentrations from 0.01 to 0.5 M provokes a displacement of the electrocapillary curves showing a possible specific adsorption of HCl at the electrode.

Hugues Ménard; Francine Leblond-routhier; Jean-Luc Roux; Jacques Devynck

1979-01-01

157

Shape of dielectric relaxation curves of ethylene glycol oligomer-water mixtures  

NASA Astrophysics Data System (ADS)

Dielectric measurements of water mixtures of ethylene glycol oligomer (EGO) with 1-6 repeat units were carried out in the frequency range of 100 MHz-30 GHz at 25 °C. One relaxation process due to water and EGO was observed for each mixture. If the number of repeat units of EGO is larger than three, the water mixtures show a broad and symmetric relaxation curve. On the other hand, if the number of repeat units of EGO is two or less, the mixtures show a broad and asymmetric relaxation curve. The two types of relaxation curves observed in the EGO-water mixtures reflect the size of the EGO molecule. The asymmetric relaxation curve is due to the cooperative motion of water and EGO molecules in the EGO-water cluster for smaller EGO-water mixtures. In contrast, the symmetric dielectric relaxation curve is a result of the variation of local structure in larger EGO-water mixtures. The larger EGO molecules cannot move cooperatively and behave as a geometrical constraint to the motion of water clusters.

Shinyashiki, Naoki; Sudo, Seiichi; Abe, Wataru; Yagihara, Shin

1998-12-01

158

Predicting the permeability function for unsaturated soils using the soil-water characteristic curve  

Microsoft Academic Search

The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 10 6 kPa), was proposed by the first two authors in another paper. This equation

D. G. Fredlund; ANQUING XING; Shangyan Huang

1994-01-01

159

Eliminating kinetic effects on the pore size distribution as determined from water-retention curves  

Microsoft Academic Search

The procedure described requires some knowledge of a critical moisture content for percolation as described by the Moldrup et al. (2001) experimental results for a moisture content at which solute diffusion vanishes. This can be obtained experimentally by using N2 BET measurements or theoretically from the particle size distribution. Alternatively one can estimate the critical moisture content as the residual

A. G. Hunt; T. E. Skinner

2007-01-01

160

Direct measurement of the soil water retention curve using X-ray absorption  

Microsoft Academic Search

X-ray absorption measurements have been explored as a fast experimental approach to determine soil hydraulic properties and to study rapid dynamic processes. As examples, the pressure-saturation relation theta(Psi) for a uniform sand column has been considered as has capillary rise in an initially dry sintered glass column. The theta(Psi)-relation is in reasonable agreement with that obtained by inverting a traditional

A. Bayer; H.-J. Vogel; K. Roth

2004-01-01

161

Estimating Soil Water Retention Curve from Particle-Size Distribution Data Based on Polydisperse Sphere Systems  

Microsoft Academic Search

ABSTRACT,form that can fit very well to a wide range of soils. Al- though these models,offer simple functional expressions Soilhydraulicpropertiesarenecessaryforunderstandingwaterand that can be easily incorporated,into the modeling,of solute movement in subsurface vadose zone environments. Previous unsaturated flow, they lack a sound theoretical basis statistical models of soil hydraulic properties have postulated a pore- size distribution from the particle-size distribution by

T. P. Chan; R. S. Govindaraju

2004-01-01

162

Electrical-impedance spectroscopy of sedimentary rocks: prediction of hydraulic conductivity and soil water retention curves  

Microsoft Academic Search

The broadband electrical-impedance response of rocks and soils is a complex function of the pore solution chemistry, the sample microgeometry, and the surface chemical properties of the system. The conductivity and dielectric responses, which are obtained from impedance measurements, are also strong functions of the measurement frequency. The dispersion in the conductivity and dielectric responses is controlled by physiochemical polarization

D. Lesmes

2003-01-01

163

Cattle manure effects on structural stability and water retention capacity of a granitic sandy soil in Zimbabwe  

Microsoft Academic Search

The evaluation of soil aggregate stability and water retention is important in the assessment of soil management options. A 3-year study was conducted in 1999 to determine the effects of two cattle manure application methods on soil aggregate stability and water retention capacity of a sandy soil (Haplic Lixisol). Manure application increased soil organic C by 10–38% in the 0–10cm

J Nyamangara; J Gotosa; S. E Mpofu

2001-01-01

164

Applying Pedo-transfer Functions to Simulate Spatial Heterogeneity of Cinnamon Soil Water Retention Characteristics in Western Liaoning Province  

Microsoft Academic Search

In this study, by measuring soil water retention characteristics and fitting them to van Genuchten Equation, three types of\\u000a pedo-transfer functions (PTFs) were estimated using linear regression (MLR3) and nonlinear regression (ENR3) based on three\\u000a textural classifications, and using linear regression (MLR7) based on seven textural classification. And their abilities to\\u000a quantify soil water retention characteristics and spatial heterogeneity in

Zuoxin Liu; Qiaosheng Shu; Zhenying Wang

2007-01-01

165

Effect of the initial soil moisture content on the spatial distribution of the water retention  

NASA Astrophysics Data System (ADS)

The initial soil moisture content affects the water flow and solute transport through the vadose zone, but researchers are in disagreement about the extent and nature of its effects. Better understanding of the initial moisture effect on the water movement will help to prevent groundwater contamination and increase crop production by improving the efficiency of water use in irrigation practice. Therefore, in this study, the effect of the initial moisture content on the spatial distribution of the water retention was investigated in the field. A total of 4 cm of water was applied to duplicate plots with each of three initial moisture conditions within 2 h using a rainfall simulator. Following the application and a 2-h redistribution period, 100 soil samples were taken from different depths of each plot using a grid sampling system to be analyzed for their gravimetric water content in the laboratory. Statistical and geostatistical analyses were performed to analyze the spatial structure of the collected data. The results showed that the preferential flow was more evident in the case of the dry initial soil water content than for the two wetter initial conditions. Both the classical and geostatistical analyses supported that the overall water retention was uniformly distributed throughout the profile except at 20-30 cm, where the coefficient of variation and the percent nugget to total semivariance ratio were high, indicating some degree of preferential flow through large pores (macropores). These results suggest that similar studies should be conducted on different field soils under more different initial moisture conditions so that the effect of the macropores on the water flow and chemical transport can be better understood.

Merdun, H.; Meral, R.; Riza Demirkiran, A.

2008-10-01

166

Improved water retention links high species richness with increased productivity in arctic tundra moss communities.  

PubMed

A positive relationship between plant species richness and ecosystem functioning has been found in a number of experimental studies. Positive species interactions at high species numbers have been suggested as a cause, but mechanisms driving positive interactions have not often been tested. In this experiment we asked three questions: (1) What is the relationship between species richness and productivity in experimentally constructed moss communities? (2) Is this relationship affected by plant density? and (3) Can changes in moisture absorption and retention explain observed relationships? To answer these questions we exposed arctic tundra moss communities of different species richness levels (1-11 species) and two different densities in the greenhouse to two levels of drought (short and long). Biomass (by the community and individual species), height and community moisture absorption and retention were measured as response variables. High species diversity increased productivity (more so in low-density plots than in high-density plots), but only when plots were watered regularly. Plot moisture retention was improved at high species richness as well, and plant height and variation in height was increased compared to plants in monoculture. Under high-density and short-drought conditions 10 out of 12 species grew better in mixture than in monoculture, but under the long drought treatment only six species did. A positive feedback loop between biomass and improved humidity under high diversity was supported by path analysis. We conclude that in this community the relationship between species richness and productivity depends on moisture availability and density, with improved water absorption and retention likely to be the mechanism for increased plant growth when drought periods are short. Furthermore, since this is the opposite of what has been found for temperate moss communities, conclusions from one system cannot automatically be extrapolated to other systems. PMID:16044351

Rixen, Christian; Mulder, Christa P H

2005-07-26

167

Ecological effects of water retention in the River Rhine valley: a review assisting future retention basin classification  

Microsoft Academic Search

This review paper summarizes the ecological effects of the use of floodplains and flood retention basins to control river flow in the River Rhine (Rhein) valley. Early River Rhine regulation strategies including channel straightening are assessed. The subsequent disappearance of alluvial hardwood forests has been highlighted as the major disadvantage. The response of trees to more recent strategies such as

M. Scholz

2007-01-01

168

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

169

Water retention properties of porous geopolymers for use in cooling applications  

Microsoft Academic Search

A series of geopolymers were prepared with varying ratios of sodium silicate, metakaolinite, NaOH and H2O and their porous properties, water retention and mechanical properties were determined, to develop materials for counteracting heat island effects. Samples were prepared with the molar ratios SiO2:Al2O3:Na2O:H2O of 3.66:1:x:y, where x=0.92–1.08 and y=14.2–19.5. The porous and mechanical properties of the geopolymers showed a good

Kiyoshi Okada; Asami Ooyama; Toshihiro Isobe; Yoshikazu Kameshima; Akira Nakajima; Kenneth J. D. MacKenzie

2009-01-01

170

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

2009-02-25

171

Biological impacts associated with the proposed retention basin and ground water projects at Lawrence Livermore National Laboratory (LLNL), and the ground water projects at Site 300  

SciTech Connect

This document discusses impacts for the proposed retention basin and ground water projects at Lawrence Livermore Laboratory. Topics discussed include positive impacts, negative impacts, mitigation and monitoring. 4 refs. (KJD)

Not Available

1990-05-30

172

Constant Flow Method for Concurrently Measur- ing Soil-Water Characteristic Curve and Hydraulic Conductivity Function  

Microsoft Academic Search

A constant-flow laboratory testing method CFM is presented for concurrently measuring the soil-water characteristic curve SWCC and hydraulic conductivity function HCF of unsaturated coarse-grained soils. Two computer-automated syringe pumps are employed to control the volumetric water content of a specimen and to periodically impose constant volumetric flow rates through the specimen, respectively. Hydraulic conductivity k corresponding to each water content

Ning Lu; Alexandra Wayllace; Jiny Carrera; William J. Likos

173

Vulnerability curves from conifer sapwood sections exposed over solutions with known water potentials.  

PubMed

The cohesion-tension (CT) theory requires stability of liquid water in conducting elements under high tensions. This stability has been measured using different methods, some of which yielded contradictory results. In this study a method is presented to establish known tensions in the water inside conifer tracheids, to detect cavitation events under these conditions and to construct vulnerability curves. Tangential sapwood sections of Juniperus virginiana L. were placed closely over the surface of NaCl solutions with water potentials ranging from -0.91 to -7.57 MPa. Water potentials were measured with a thermocouple hygrometer in contact with the section, and ultrasound acoustic emissions (UAE) from the sections were registered with an ultrasound transducer. The emission rate of signals increased with the concentration of the solution. Exposure of 100 microm sections in the airspace over a solution provided optimal conditions for the rupture of the water column: many tracheid walls bordered on air, and water in the lumen came under high tension. Nevertheless, the water remained in the metastable liquid state for periods of many hours. The vulnerability obtained from simultaneous measurements of water potentials and ultrasound acoustic emissions on sapwood sections was substantially higher than from conventionally measured curves of detached branches. It is argued that the isolation of tracheids in a massive organ as well as the rate of potential decline will influence the probability of cavitations at a given water potential and thus the parameters of the vulnerability curve. PMID:12867547

Kikuta, Silvia B; Hietz, Peter; Richter, Hanno

2003-07-16

174

Absorption and retention of uranium from drinking water by rats and rabbits.  

PubMed

Uranium in the form of uranyl nitrate hexahydrate was administered in drinking water to Sprague-Dawley rats for periods of 28 and 91 d and New Zealand White rabbits for 91 d. The animals consumed food and water ad libitum. Subgroups of rabbits were followed for recovery periods of up to 91 d; 24-h collections of urine and feces were performed for some of the rabbits at various times during the exposure and recovery periods. At the end of the experiment, all animals were sacrificed and femur and kidney samples were analyzed for uranium residues. The results show that both rats and rabbits absorb about 0.06% of ingested uranium in the gastrointestinal (GI) tract. The distribution and retention of uranium in the skeleton and kidneys of rats are comparable to parameters reported for humans. The retention half-time in rabbit bone is substantially longer than for humans. The implications of extrapolating from animal data to effects on humans are discussed. PMID:1727413

Tracy, B L; Quinn, J M; Lahey, J; Gilman, A P; Mancuso, K; Yagminas, A P; Villeneuve, D C

1992-01-01

175

Free water content and sludge retention time: impact on oxygen transfer in activated sludge.  

PubMed

To investigate the effect of sludge retention time (SRT) and the concentration of mixed liquid volatile suspended solids (MLVSS) on oxygen transfer in activated sludge, we studied mass transfer coefficients (k(L)a) in a pilot-scale membrane bioreactor, which treated synthetic greywater. Additionally, experiments with iron hydroxide flocs were performed to examine the role of free water content in oxygen transfer. The results demonstrate that the alpha-factor is reduced when free water content decreases and floc volume increases. Because the MLVSS concentration in activated sludge mainly regulates floc volume, a reduction of oxygen transfer with increasing MLVSS concentration was observed. If the floc volume remains unchanged, oxygen transfer increases with increasing SRT. PMID:20028052

Henkel, Jochen; Cornel, Peter; Wagner, Martin

2009-11-15

176

Studies on Microbial Heavy Metal Retention from Uranium Mine Drainage Water with Special Emphasis on Rare Earth Elements  

Microsoft Academic Search

Microbial heavy metal retention was studied using seepage water sampled from a former uranium mining site in Eastern Thuringia, Germany. The seepage water has a low pH and contains high concentrations of metals, including uranium, rare earth elements (REE), and other heavy metals. Microbial influence on sorption and\\/or active uptake of heavy metals was studied using REE patterns. Incubation of

D. Merten; E. Kothe; G. Büchel

2004-01-01

177

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

178

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

179

Leak-Free Pressure Plate Extractor For Measuring the Soil Water Characteristic Curve  

Microsoft Academic Search

An ew pressure plate extractor, referred to as the leak-free pressure plate extractor (LFPPE), is described where air leakage around the ceramic plate effectively is eliminated. The LFPPE was designed so that it would be robust, easy to use, and readily assembled and disassembled for testing and maintenance. An example shows that the LFPPE yields a soil water characteristic curve

Xiaodong Wang; Craig H. Benson; X Wang

2004-01-01

180

Relationship between porosimetry measurement and soil–water characteristic curve for an unsaturated residual soil  

Microsoft Academic Search

Soil–water characteristic curve (SWCC) is an important tool for determining the engineering properties of unsaturated soil. This depends on the size and distribution of pore structures which control the permeability and amount of volume change. Mercury Intrusion Porosimetry tests can be used to determine the size, amount and distribution of pore spaces of the soil in a shorter time period

K. K. Aung; H. Rahardjo; E. C. Leong; D. G. Toll

2001-01-01

181

Pore pressure versus confining pressure and their effect on oil–water relative permeability curves  

Microsoft Academic Search

Reservoir petrophysical properties such as relative permeability are influenced by the state of stresses acting on the reservoir rock. Production and water flooding operations induce changes in the net effective pressure due to changes in pore pressure that affects relative permeability curves. Previous studies conducted to investigate the effect of net pressure on relative permeability were conducted by varying the

Abdulrahman Al-Quraishi; M. Khairy

2005-01-01

182

Statistical assessment of soil-water characteristic curve models for geotechnical engineering  

Microsoft Academic Search

A number of empirical equations have been proposed for the soil-water characteristic curve. A nonlinear, least squares method was used to determine best-fit parameters for several empirical equations that were best-fit to 230 water content versus soil suction data sets. In addition, two proposed correction methods to accommodate high soil suctions up to 1 000 000 kPa were applied to

W. Scott Sillers; Delwyn G. Fredlund

2001-01-01

183

A computer simulation study of the liquid-vapor coexistence curve of water  

Microsoft Academic Search

The liquid–vapor coexistence curve of a model water (the extended simple point charge model, SPCE) is evaluated by molecular dynamics simulation in the (N,V,E) ensemble. It is shown that the simulated system (N=256 water molecules) is too small to present a spinodal decomposition and, hence, can be described by a classical equation of state whose the critical parameters (Tc=651.7 K,

Yves Guissani; Bertrand Guillot

1993-01-01

184

Assessment of retention basin volume and outlet capacity in urban stormwater drainage systems with respect to water quality  

Microsoft Academic Search

The quality of river water or other surface waters is detrimentally affected by the contaminants carried by the rainfall runoff\\u000a in urban areas. The control of pollution moved by rainfall runoff is achieved by installing outlets and small retention basins\\u000a in stormwater collection systems, thereby allowing only a certain amount of rainfall water to overflow and leading the remaining\\u000a to

Mehmet A. Yurdusev; Ahmet A. Kumanlio?lu; Bekir Solmaz

2005-01-01

185

Water Repellency Effects on Water Retention in Heat Pre-treated Volcanic Ash Soil  

Microsoft Academic Search

Water repellency (WR) in soil is a common phenomenon after forest fires all over the world. It can induce hydrological problems such as preferential flow in soils and reduced water infiltration rate which in turn can lead to surface runoff and erosion. In this study, we examined the hydrophobicity for pre-heated volcanic ash soil samples with different temperatures between 60

T. Chhoden; A. Karunarathna; K. Kawamoto; T. Komatsu; P. Moldrup

2009-01-01

186

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

187

Relation between retention factors of immunosuppressive drugs in microemulsion electrokinetic chromatography with biosurfactants and octanol–water partition coefficients  

Microsoft Academic Search

Retention (capacity) factors (k? values) of immunosuppressive drugs were determined in microemulsion electrokinetic chromatography (MEEKC) systems as a tool for the indirect estimation of partition coefficients (POW) between 1-octanol and water. The microemulsions were based on phosphatidylcholine (PC) and bile acids (BAs) as biosurfactants and isopropyl myristate (IPM) as oil. Immunosuppressants were azathioprine (AZA), mycophenolate mofetil (MMF), tacrolimus (FK506) and

Silvia E Lucangioli; Ernst Kenndler; Adriana Carlucci; Valeria P Tripodi; Silvia L Scioscia; Clyde N Carducci

2003-01-01

188

Preliminary permeability and water-retention data for nonwelded and bedded tuff samples, Yucca Mountain area, Nye County, Nevada  

Microsoft Academic Search

Measurements of rock-matrix hydrologic properties at Yucca Mountain, a potential site for a high-level nuclear waste repository, are needed to predict rates and direction of water flow in the unsaturated zone. The objective of this study is to provide preliminary data on intrinsic and relative permeability and moisture retention on rock core samples and to present the methods used to

L. E. Flint; A. L. Flint

1990-01-01

189

Evaluation of the effects of incorporation rate and depth of water-retentive amendment materials in sports turf constructions  

Microsoft Academic Search

The objective of the current laboratory study was to assess the effects of a number of amendment materials and the depth of incorporation on water retention. 300 mm rootzone profiles were established in 150 mm diameter plastic cylinders over a 50 mm gravel drainage layer. Five amendment materials (sphagnum peat, compost, zeolite, TerraCottem and Stockosorb) were mixed with a medium-coarse

Stanislav Hejduk; Stephen W. Baker; Christian A. Spring

2012-01-01

190

Water flow and retention in coarse soil pockets in the shallow subsurface  

NASA Astrophysics Data System (ADS)

Soil moisture processes in the near-land-surface subsurface, referred to here as the shallow subsurface, plays a crucial role in the hydrologic cycle and global water budget. In addition, this critical zone is associated with emerging problems in hydrology, climate, the environment and relates to multiple direct and tangential short- and long-term national security interests. Some of the problems associated with the shallow subsurface such as detection of buried landmines and evaporation from disturbed soils require the understanding of spatial distribution of soil moisture at much higher spatial resolutions than what is needed in traditional soil physics applications. In landmine detection in naturally heterogeneous shallow subsurface, where soil properties change at smaller scales, soil moisture as measured by remote sensing techniques may provide anomalies that result in falsely interpreted sensing signals to conclude that a mine is present. To improve our fundamental understanding of how variation of soil properties at small scales affect soil moisture distribution, the water flow and retention behaviors in a heterogeneous system with two pockets of different sands that are coarser than the background sand were investigated. Drainage was slowly induced in a two-dimensional test sand tank, followed by wetting, secondary drainage, and precipitation cycles. Throughout the experiments, water and air pressures and water content were continuously monitored at 25 locations on the tank. To monitor air pressure in highly wet soils, we used newly-developed hydrophobic tensiometers. In the primary drainage cycle, the pockets of coarse sands drained rapidly when air reached the coarse-fine interface. During the rapid drainage, air pressure in the pockets suddenly became negative as the water was released. In the wetting cycle, water bypassed through fine sand and air was trapped in the pockets. At the top portion of the coarse pocket, significant amount of air was trapped and saturation remained very low. In the subsequent drainage cycle, similar behavior in the primary drainage, i.e., rapid drainage in the pockets as soon as the air reaches the coarse-fine interface was observed. During precipitation, water bypassed through the fine sand and saturation in the pockets, although increased very slowly, remained very low. These observations suggest that a pocket of soil that is coarser than the background soil can keep the air trapped during wetting/precipitation or artificial water spraying that lead to anomalies in soil moisture imagery. Furthermore, as soil moisture controls thermal conductivity of soil, anomalies in soil moisture can result in those in temperature distribution. Finally, when modeling local water flow and retention in pockets of coarse soils, the single-phase approach using Richard’s equation breaks down suggesting that the air pressure variations can not be neglected. A better prediction based on two-phase flow approach can ultimately improve the prediction of soil moisture variations at high spatial resolutions.

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

2010-12-01

191

Field-Scale Water Flow Simulations Using Ensembles of Pedotransfer Functions for Soil Water Retention  

Microsoft Academic Search

Using pedotransfer functions (PTF) to estimate soil hydraulic prop- erties may be necessary in soil water flow simulations for large-scale projects or in pilot studies. The accuracy of a PTF outside of its devel- opment dataset is generally unknown. The existence of multiple models that are developed and tested in one region, but may perform relatively poorly in other regions,

A. K. Guber; Ya. A. Pachepsky; M. Th. van Genuchten; W. J. Rawls; J. Simunek; D. Jacques; T. J. Nicholson; R. E. Cady

2006-01-01

192

Lattice Boltzmann model for shallow water flows in curved and meandering channels  

Microsoft Academic Search

Meandering channel flows are simulated using two-dimensional lattice Boltzmann models (LBM) for the shallow water equations. A boundary approach is designed for curved boundary treatment, which is applicable to no-slip, semi-slip and slip boundaries at a second-order accuracy. The large eddy simulation model is added in the lattice Boltzmann model, so that the turbulence can be taken into account and

Haifei Liu; Guo Jian Zhou; Richard Burrows

2009-01-01

193

Receiver Operating Characteristic Curve Analysis of Beach Water Quality Indicator Variables  

PubMed Central

Receiver operating characteristic (ROC) curve analysis is a simple and effective means to compare the accuracies of indicator variables of bacterial beach water quality. The indicator variables examined in this study were previous day's Enterococcus density and antecedent rainfall at 24, 48, and 96 h. Daily Enterococcus densities and 15-min rainfall values were collected during a 5-year (1996 to 2000) study of four Boston Harbor beaches. The indicator variables were assessed for their ability to correctly classify water as suitable or unsuitable for swimming at a maximum threshold Enterococcus density of 104 CFU/100 ml. Sensitivity and specificity values were determined for each unique previous day's Enterococcus density and antecedent rainfall volume and used to construct ROC curves. The area under the ROC curve was used to compare the accuracies of the indicator variables. Twenty-four-hour antecedent rainfall classified elevated Enterococcus densities more accurately than previous day's Enterococcus density (P = 0.079). An empirically derived threshold for 48-h antecedent rainfall, corresponding to a sensitivity of 0.75, was determined from the 1996 to 2000 data and evaluated to ascertain if the threshold would produce a 0.75 sensitivity with independent water quality data collected in 2001 from the same beaches.

Morrison, Ann Michelle; Coughlin, Kelly; Shine, James P.; Coull, Brent A.; Rex, Andrea C.

2003-01-01

194

Retention of ionizable compounds in high-performance liquid chromatography. IX. Modelling retention in reversed-phase liquid chromatography as a function of pH and solvent composition with acetonitrile-water mobile phases.  

PubMed

The influence of pH and solvent composition of acetonitrile-water mobile phases on the retention of acids and bases on a polymeric stationary phase is studied. Very good relationships between retention and mobile phase pH are obtained if the pH is measured in the proper pH scale. The fit of retention to pH for a particular solvent composition provides the pKa values of the equilibria between the different acid-base species and the retention parameters of these species at this solvent composition. Several models are tested that relate these parameters to solvent composition and properties in order to propose a general model to predict retention for any mobile phase pH and composition. PMID:11873997

Espinosa, Sonia; Bosch, Elisabeth; Rosés, Martí

2002-02-15

195

The water method for aiding colonoscope insertion: the learning curve of an experienced colonoscopist  

PubMed Central

Background The water method has promising features for colonoscopy but the learning curve to master the technique is unknown. Aims To describe the learning phase, and pitfalls of the water method and its impact on procedural outcomes by an experienced colonoscopist. Design Review of prospectively collected data in a performance improvement project Setting endoscopy Unit at a VA medical center Patients 200 consecutive veterans undergoing colonoscopy Methods An experienced colonoscopist examined 4 consecutive groups of 25 patients each using the water method to define the learning curve. Outcomes were compared to a historical cohort (n=100) examined by the same colonoscopist using usual air insufflation. Main outcome measures Intent-to-treat (ITT) cecal intubation rate. Results ITT cecal intubation rate increased from 76% (first) to 96% (fourth quartile). Cecal intubation time in the first 2 quartiles was significantly longer (8.9±1.0 and 8.2±0.8 min, respectively) than that in the historical cohort (5.8±0.4 min) but decreased and became comparable to control values in the next 2 quartiles (7.2±0.9 and 6.6±0.6 min, respectively). Overall adenoma detection rate as a group (55%), compared favorably to the historical cohort (46%). Conclusions The water method is relatively easy to learn for an experienced colonoscopist. Mastery of the method resulted in cecal intubation rate and overall adenoma detection rate meeting quality performance standards.

Leung, Felix W

2011-01-01

196

Influence of water level on oil–water separation by residence time distribution curves investigations  

Microsoft Academic Search

The separation of crude oil and water mixtures is an important process in the oil and chemical industries. This work studied the flow behavior of crude oil and water in a pilot scale oil–water separator. This gravity separator (diameter of 1.2m and length of 5.2m) was operated by Drood oil of the Iranian Offshore Oil Company (IOOC) located in Kharg

J. Behin; M. Aghajari

2008-01-01

197

Linopirdine (DUP 996; AVIVA): Its effects in the morris water escape task and on retention of an incompletely acquired bar-press response in rodents  

Microsoft Academic Search

The present study assessed the effects of linopirdine, a putative cognition-enhancing drug, on the acquisition and retention of a bar-press response [continous reinforcement schedule (CRF)] in young Wistar rats. It was also investigated whether this substance influenced the acquisition and retention of a standard Morris water escape task by young NMRI mice and by young and old Wistar rats. Linopirdine

Iris Flagmeyer; Franz Josef van der Staay

1995-01-01

198

International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance  

Microsoft Academic Search

In order to define the phase boundary between the solid phase (ice) and the fluid phase (liquid and gas) of ordinary (light) water substance in pressure-temperature coordinates, correlation equations for the pressure along the melting curve of the various modifications of ice as well as for the pressure along the sublimation curve are presented. The five equations for the melting

Wolfgang Wagner; A. Saul; A. Pruss

1994-01-01

199

Effect of water velocity on growth and retention of cultured Greenshell™ mussel spat, Perna canaliculus (Gmelin, 1791)  

Microsoft Academic Search

The GreenshellTM mussel, Perna canaliculus, is a commercially important species forming New Zealand’s largest aquaculture export product. Losses of P. canaliculus spat from culture ropes between larval settlement and the time mussels reach initial reseeding size (c. 10 mm) are common. To test whether water velocity affects growth and retention of post-settlement P. canaliculus spat, and whether there is a threshold

Barbara J. Hayden; Chris M. C. Woods

200

The roles of texture and structure in the water retention capacity of burnt Mediterranean soils with varying rainfall  

Microsoft Academic Search

Differences in soil texture, structure and water retention capacity between burnt and unburnt soils were studied in an area affected periodically by forest fires in SE Spain. The burnt and unburnt soils were sampled at altitudes ranging from 100 to 1000 m a.s.l., with slight differences in climate between the sampling sites. Comparisons were made at three levels: all-sites, between-sites

Carolina Boix Fayos

1997-01-01

201

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

202

Soil water retention and carbon pools in tropical forested wetlands and marshes of the Gulf of Mexico  

Microsoft Academic Search

The ability of marshes and forested wetlands to provide environmental services (water retention in soil and carbon storage) was evaluated at three locations along the coast of Veracruz, Mexico. Hydro-periods were obtained for the different vegetation communities of marshes and forested wetlands. Total organic carbon contents were 26.2% in Pachira swamp, 23.1% in Ficus swamp and 11.2% in marsh soils.

Adolfo Campos C; María E. Hernández; Patricia Moreno-Casasola; Eduardo Cejudo Espinosa; Alezandra Robledo R; Dulce Infante Mata

2011-01-01

203

Measurement of soil-water characteristic curves for fine-grained soils using a small-scale centrifuge  

Microsoft Academic Search

Considerably long periods of time are required to measure soil-water characteristic curves using conventional equipment such as pressure plate apparatus or a Tempe cell. A commercially available, small-scale medical centrifuge with a swinging type rotor assembly was used to measure the soil-water characteristic curves on statically compacted, fine-grained soil specimens. A specimen holder was specially designed to obtain multiple sets

R. M. Khanzode; S. K. Vanapalli; D. G. Fredlund

2002-01-01

204

An Internal Water-Retention Site in the Rhomboid Intramembrane Protease GlpG Ensures Catalytic Efficiency  

PubMed Central

SUMMARY Rhomboid proteases regulate key cellular pathways, but their biochemical mechanism including how water is made available to the membrane-immersed active site remains ambiguous. We performed four prolonged molecular dynamics simulations initiated from both gate-open and gate-closed states of Escherichia coli rhomboid GlpG in a phospholipid bilayer. GlpG was notably stable in both gating states, experiencing similar tilt and local membrane thinning, with no observable gating transitions, highlighting that gating is rate-limiting. Analysis of dynamics revealed rapid loss of crystallographic waters from the active site, but retention of a water cluster within a site formed by His141, Ser181, Ser185 and/or Gln189. Experimental interrogation of 14 engineered mutants revealed an essential role for at least Gln189 and Ser185 in catalysis with no effect on structural stability. Our studies indicate that spontaneous water supply to the intra-membrane active site of rhomboid proteases is rare, but its availability is ensured by an unanticipated active site element, the water-retention site.

Zhou, Yanzi; Moin, Syed M.; Urban, Sinisa; Zhang, Yingkai

2012-01-01

205

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

206

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

Microsoft Academic Search

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

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

2010-01-01

207

Wading through a swamp of complete confusion: how to choose a method for estimating soil water retention parameters for crop models  

Microsoft Academic Search

A minimum input for water dynamics simulation in crop models are soil water content at field capacity (DUL, drained upper limit), wilting point (LL, lower limit) and, often, saturation (SAT). Eight methods for estimating these water-retention parameters were compared using the following procedure: [1] Stepping through the texture triangle in increments of 1% clay and 1% sand, LL, DUL and

A. J. Gijsman; S. S. Jagtap; J. W. Jones

2002-01-01

208

On the Way to Determination of the Vapor-Pressure Curve of Pure Water  

NASA Astrophysics Data System (ADS)

The determination of the physical properties of pure water, especially the vapor-pressure curve of water, is one of the major issues identified by the Consultative Committee for Thermometry of the International Committee for Weights and Measures (CIPM) to improve the accuracy of the national references in humidity. At the present time the saturation-pressure data, corresponding to ice or liquid-vapor equilibrium, at low temperature are scarce and unreliable. This study presents new measurements of vapor and sublimation pressures of, respectively, water and ice, using a static apparatus. Prior to saturation-pressure measurements, the temperature and pressure sensors of the static apparatus were calibrated against reference gauges in use at the LNE- CETIAT laboratories. The effect of thermal transpiration has been studied. The explored temperature range lies between 250 K and 374 K, and the pressure range between 70 Pa and 105 Pa. An automatic data acquisition program was developed to monitor the pressure and temperature. The obtained results have been compared with available literature data. The preliminary uncertainty budget took into account several components: pressure measurements, temperature measurements, and environmental error sources such as thermal transpiration and hydrostatic correction.

Mokdad, S.; Georgin, E.; Mokbel, I.; Jose, J.; Hermier, Y.; Himbert, M.

2012-09-01

209

The unusual coexistence curve of 2-butanol + water. An experimental and theoretical study  

NASA Astrophysics Data System (ADS)

The coexistence curve of the 2-butanol + water system has been measured at P ? 1 bar, with a higher precision and a more detailed description of the pinch-off region than in previous experimental studies. The data points in the vicinity of the UCST have been fitted to a simple scaling expression to obtain the critical point coordinates and an estimation of the range of validity of simple scaling. The experimental binodal has been used to test two Ising-like models including directional interactions: an asymmetric decorated lattice one and a lattice-gas model with fluctuating orientational degrees of freedom. Both models offered comparable results when a symmetrized composition variable was used.

Aizpiri, Arturo G.; Chazarra, Pedro; Rubio, Ramón G.; Pena, Mateo Diaz

1990-09-01

210

Adsorption-partition switching of retention mechanism in ice chromatography with NaCl-doped water-ice.  

PubMed

A liquid phase is coexistent with water-ice prepared from a brine solution at any temperature above the eutectic point of the system. Ice chromatographic measurements have provided information on the liquid phase in an ice particle prepared from NaCl. The growth of the liquid phase causes the alternation of the dominant separation mechanism from the adsorption on the ice surface to the partition into the liquid phase, resulting in an increase in the retention of a water-soluble probe. When the liquid phase is developed, the retention is well explained by the partition coefficient determined with bulk solvents, suggesting that all of the liquid pools in a water-ice particle are connected to each other. In contrast, only a part of the liquid pools act as a stationary phase when the volume of the liquid phase is small. A model, which assumes the homogenous distribution of a salt in an ice particle and spherical shapes of a liquid pool, has allowed the estimation of its size. PMID:19212050

Tasaki, Yuiko; Okada, Tetsuo

2009-02-01

211

Hexadecyltrimethylammonium bromide\\/ethanol\\/water systems as mobie phase in reverse phase high performance liquid chromatography. Study of metal-diethyldithiocarbamate complexes retention  

Microsoft Academic Search

Summary  This paper presents the, chromatographic retention of Co(II), Ni(II) and Cu(II) as diethyldithiocarbamate complexes in the\\u000a presence of hexadecyltrimethylammonium bromide\\/ethanol\\/water systems, as mobile phase, by reversed phase high performance\\u000a liquid chromatography. The presence of an organic modifier reduces the retention times and improves the efficiency. In order\\u000a to evaluate the interaction between the metal complexes and the mixed micellar system

M. P. San Andrés; M. J. Barroso; S. Vera

1998-01-01

212

A biokinetic model for predicting the retention of 3H in the human body after intakes of tritiated water.  

PubMed

Scarce published data on the long-term excretion of tritiated water from the human body have been re-evaluated in order to develop a biokinetic model describing the retention in the human body of 3H from tritiated water (HTO) that could be used for both prospective and retrospective radiation protection. A three-component exponential function is proposed to describe the elimination of 3H from HTO with biological half-times of 10 d (99.00%), 40 d (0.98%) and 350 d (0.02%) respectively. The model predicts a committed effective dose of 1.7 x 10(-11) Sv Bq(-1), comparable with that of the current ICRP Publication 56 and 72 models, and estimates the retention of 3H to within a factor of about 2 of the measured values up to 40 d after intake and about 5 at times longer than 100 d. The derivation of the model and the uncertainties associated with the various parameters are discussed. PMID:14526960

Taylor, D M

2003-01-01

213

[Renal and extra-renal mechanisms of sodium and water retention in cirrhosis with ascites].  

PubMed

In this work we analyze the renal and systemic factors involved in the sodium retention in two conditions: in extracellular volume depletion and in edema forming states, particularly liver cirrhosis with ascitis. In this paper we accept that the volume loss of body fluids stimulates the "effective arterial blood volume" (VAE). This term results from a decrease in the arterial blood volume secondary to a fall in cardiac output or a peripheral arterial vasodilatation. The reduction in the VAE stimulates: the high pressure baroreceptors (carotid sinus and aortic arch); the intrarrenal mechanisms, such as the yuxtaglomerular apparatus and the renin angiotensin aldosterone system; the sympathetic adrenergic system; the non osmotic release of antidiuretic hormone; prostaglandins (PGE1, Tromboxane) and endothelin; and inhibits the atrial natriuretic peptide. We also describe the sodium transport mechanisms along the nephron during physiological conditions and after volume depletion, and in edema formation states, specially hepatic cirrhosis with ascitis. We speculate that the intrarenal mechanisms are more important and persistent than the systemic mechanisms. It is possible that the sodium retention of these states might be the result of direct stimuli of the tubular sodium transport mechanisms in the different segments of the nephron, mediated by the co and counter transports, ATPase activity or by the second messengers cyclic AMP and cyclic GMP. The clonation and structural characterization of the different sodium transports may help us to establish, more precisely, the intracellular tubular mechanisms responsible for the tendency of the body to retain sodium. The amount of information generated in the future may help us to demonstrate, with more precision, the mechanisms responsible for the sodium retention and excretion in normal and pathological conditions, particularly the edema forming states such as cardiac failure, nephrotic syndrome and hepatic cirrhosis with ascitis. PMID:7777718

Peña, J C

214

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

215

Continuum Percolation Theory for Water Retention and Hydraulic Conductivity of Fractal Soils: Estimation of the Critical Volume Fraction for Percolation and Extension to Non-Equilibrium  

Microsoft Academic Search

Systematic experimental deviations from theoretical predictions derived for water retention characteristics of fractal porous media have previously been interpreted in terms of continuum percolation theory (at low moisture contents, below the critical volume fraction of water, ?c, capillary flow ceases). In other work, continuum percolation theory was applied to find the hydraulic conductivity as a function of saturation for saturations

AG Hunt

216

Liquid chromatography and differential scanning calorimetry studies on the states of water in hydrophilic polymer gel packings in relation to retention selectivity  

Microsoft Academic Search

The amounts of water which exhibit selectivity to solutes in water-swollen hydrophilic polymer gel packings were determined by a liquid chromatographic method designed on the basis of the mobile phase electrolyte effects on the retention of ionic solutes. The estimated amounts of the water in three types of water-swollen hydrophilic polymer gels, a cross-linked dextran, poly(vinyl alcohol) and polyacrylamide, agree

Masami Shibukawa; Kaoru Aoyagi; Ryosaku Sakamoto; Koichi Oguma

1999-01-01

217

Multiresponse multilayer vadose zone model calibration using Markov chain Monte Carlo simulation and field water retention data  

NASA Astrophysics Data System (ADS)

In the past two decades significant progress has been made toward the application of inverse modeling to estimate the water retention and hydraulic conductivity functions of the vadose zone at different spatial scales. Many of these contributions have focused on estimating only a few soil hydraulic parameters, without recourse to appropriately capturing and addressing spatial variability. The assumption of a homogeneous medium significantly simplifies the complexity of the resulting inverse problem, allowing the use of classical parameter estimation algorithms. Here we present an inverse modeling study with a high degree of vertical complexity that involves calibration of a 25 parameter Richards'-based HYDRUS-1D model using in situ measurements of volumetric water content and pressure head from multiple depths in a heterogeneous vadose zone in New Zealand. We first determine the trade-off in the fitting of both data types using the AMALGAM multiple objective evolutionary search algorithm. Then we adopt a Bayesian framework and derive posterior probability density functions of parameter and model predictive uncertainty using the recently developed differential evolution adaptive metropolis, DREAMZS adaptive Markov chain Monte Carlo scheme. We use four different formulations of the likelihood function each differing in their underlying assumption about the statistical properties of the error residual and data used for calibration. We show that AMALGAM and DREAMZS can solve for the 25 hydraulic parameters describing the water retention and hydraulic conductivity functions of the multilayer heterogeneous vadose zone. Our study clearly highlights that multiple data types are simultaneously required in the likelihood function to result in an accurate soil hydraulic characterization of the vadose zone of interest. Remaining error residuals are most likely caused by model deficiencies that are not encapsulated by the multilayer model and can not be accessed by the statistics and likelihood function used. The utilization of an explicit autoregressive error model of the remaining error residuals does not work well for the water content data with HYDRUS-1D prediction uncertainty bounds that become unrealistically large.

WöHling, Thomas; Vrugt, Jasper A.

2011-04-01

218

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...

219

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

220

Soil-Moisture Retention Curves for Evaluating Plant Moisture Availability of Cover Materials and Coal Refuse from the Staunton 1 Reclamation Demonstration Project.  

National Technical Information Service (NTIS)

Availability of soil water to plants was investigated at the Staunton 1 reclamation demonstration site in southwestern Illinois. Field cores for determination of gravimetric moisture content were taken during July and August 1977 from research plots with ...

B. K. Mueller P. A. Vance

1981-01-01

221

Effect of the initial soil moisture content on the spatial distribution of the water retention  

Microsoft Academic Search

The initial soil moisture content affects the water flow and solute transport through the vadose zone, but researchers are\\u000a in disagreement about the extent and nature of its effects. Better understanding of the initial moisture effect on the water\\u000a movement will help to prevent groundwater contamination and increase crop production by improving the efficiency of water\\u000a use in irrigation practice.

H. Merdun; R. Meral; A. Riza Demirkiran

2008-01-01

222

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

PubMed Central

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. This suggests that pH and temperature are steering factors in the selection of taxa and supports the notion that communities in lakes with short water turnover times are influenced by the input of bacterial cells from the drainage areas. Within the beta subdivision of the Proteobacteria (Betaproteobacteria), as well as within the divisions Actinobacteria and Verrucomicrobia, different subgroups were associated differently with environmental variables.

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

2005-01-01

223

Improving water quality in agricultural catchments: sediment and nutrient retention in field wetlands  

NASA Astrophysics Data System (ADS)

A recent update of Water Framework Directive classifications in the UK indicates that only 28% of water bodies currently achieve good ecological status and that agriculture is one of the main sectors responsible for the pressures contributed by sediment and nutrients. The use of edge-of-field features, such as field wetlands - small sediment and pollutant trapping features (

Ockenden, M. C.; Deasy, C.; Quinton, J. N.; Stoate, C.

2012-04-01

224

Absorption and retention of uranium from drinking water by rats and rabbits  

Microsoft Academic Search

Uranium in the form of uranyl nitrate hexahydrate was administered in drinking water to Sprague-Dawley rats for periods of 28 and 91 d and New Zealand White rabbits for 91 d. The animals consumed food and water ad libitum. Subgroups of rabbits were followed for recovery periods of up to 91 d; 24-h collections of urine and feces were performed

B. L. Tracy; J. M. Quinn; J. Lahey; A. P. Gilman; K. Mancuso; A. P. Yagminas; D. C. Villeneuve

1992-01-01

225

Drought tolerance in cereals in terms of water retention, photosynthesis and antioxidant enzyme activities  

Microsoft Academic Search

Experiments were carried out on three bread wheat varieties, one barley and one durum wheat variety grown in pots in the phytotron\\u000a and subjected to water withdrawal for 7 days during grain-filling. Leaf water loss, net assimilation rate and transpiration\\u000a showed marked differences, allowing the genotypes to be ranked. Although the most resistant variety had the highest activity\\u000a for ascorbate

Szilvia Bencze; Zsuzsanna Bamberger; Tibor Janda; Krisztina Balla; Zoltán Bed?; Ottó Veisz

2011-01-01

226

Water content of roasted coffee: impact on grinding behaviour, extraction, and aroma retention  

Microsoft Academic Search

Normal and long time roasting trials were carried out on industrial scale. Different amounts of water were applied during\\u000a quenching, resulting in water contents in the range of 2.3–8.8 g\\/100 g wb. Coffees were ground immediately after cooling,\\u000a and after equilibration times of 6 and 24 h. Particle size distribution of ground coffees, percolation time, and extraction\\u000a properties were investigated on an espresso coffee

Juerg Baggenstoss; Rainer Perren; Felix Escher

2008-01-01

227

Geographical variation in antibiotic resistance profiles of Escherichia coli isolated from swine, poultry, beef and dairy cattle farm water retention ponds in Florida1  

Microsoft Academic Search

Aims: The aim of this study was to assess geographical variation in multiple antibiotic resistance (MAR) profiles of livestock Escherichia coli as well as to evaluate the ability of MAR profiles to differentiate sources of faecal pollution. Methods and Results: More than 2000 E. coli isolates were collected from water retention ponds and manure of swine, poultry, beef and dairy

S. Parveen; J. Lukasik; T. M. Scott; M. L. Tamplin; K. M. Portier; S. Sheperd; K. Braun; S. R. Farrah

2006-01-01

228

The effect of salt precipitation and high sodium concentrations on soil hydraulic conductivity and water retention  

Microsoft Academic Search

Controlled irrigation management of moderate to poor quality water must assure sufficient movement of solution through the root zone to maintain a salinity regime which a crop can tolerate while at the same time minimizing the deterioration of groundwater or river quality. One proposal for accomplishing this objective is a policy of high-frequency irrigation and minimum leaching, which encourages precipitation

H. Frenkel; A. Hadas; W. A. Jury

1978-01-01

229

THE EFFECT OF TOTAL WATER REUSE AND ALUM CONTROL ON FIRST PASS RETENTION  

EPA Science Inventory

Product quality deterioration, caused by poor wet end control and the resulting build up of dissolved inorganic and organic contaminants, has hampered achieving complete water reuse in paper manufacturing. By using pulp-derived dissolved organic material, the study makes use of a...

230

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

Microsoft Academic Search

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.

Zhang

2011-01-01

231

Soil Water Retention and Relative Permeability for Full Range of Saturation  

Microsoft Academic Search

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

Zhang

2010-01-01

232

Water retention and plasma and urine composition in toads ( Bufo viridis Laur.) under burrowing conditions  

Microsoft Academic Search

Osmoregulation in the terrestrial toad,Bufo viridis, was studied under burrowing conditions in the laboratory. The toads can live for over 3 months burrowed in soil containing 9–10% moisture, maintaining constant body volume due to a large increase in the plasma osmolality, contributed mainly by urea. Water content of the tissues remains constant. Relatively large volumes of urine are stored in

Uri Katz; S. Gabbay

1986-01-01

233

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

234

The Effect of Wood Fiber Mulch on Water Retention, Soil Temperature and Growth of Vegetable Plants  

Microsoft Academic Search

The suitability of wood fiber materials as soil cover mulch in relation to soil moisture and temperature was investigated. The uncomposted wood fiber applied with adhesives formed a sturdy mat after spreading onto the soil. Evaporation of water was reduced and temperature fluctuations in the soil were dampened compared with bare soil. This was determined in incubation experiments as well

Nazim Gruda

2008-01-01

235

THE BALANCED ENTROPY INDEX TO CHARACTERIZE SOIL TEXTURE FOR SOIL WATER RETENTION ESTIMATION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Pedotransfer procedures are often used to estimate soil hydraulic properties from soil basic data available from soil surveys. Soil particle size distribution, or texture, is known to be a leading soil property affecting soils' ability to retain and transmit water and solutes. A substantial effort h...

236

Metal retention by iron oxide precipitation from acidic ground water in Dalarna, Sweden  

Microsoft Academic Search

This study provides a characterization of goethite and lepidocrocite precipitates that form from ground water contaminated by acid mine leachate in Dalarna, Sweden. Chemical extraction techniques and electron microprobe analyses indicate that Al, Cu, Ni, S, Si, Ti, and Zn may be retained in the goethite structure. The metals are retained by either isomorphic substitution for Fe in goethite or

Roger B. Herbert

1996-01-01

237

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

238

Water flow and retention in coarse soil pockets in the shallow subsurface  

Microsoft Academic Search

Soil moisture processes in the near-land-surface subsurface, referred to here as the shallow subsurface, plays a crucial role in the hydrologic cycle and global water budget. In addition, this critical zone is associated with emerging problems in hydrology, climate, the environment and relates to multiple direct and tangential short- and long-term national security interests. Some of the problems associated with

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

2010-01-01

239

Vertical soil water retention in newly?sodded, drained turfgrass sites  

Microsoft Academic Search

Drained golf greens, athletic fields, and various other turfgrass planting sites are frequently backfilled with specially?prescribed coarse or very coarse?textured root growth media to compensate for the effects of the shallow (20 to 50 cm deep), perched water table which forms at the drainage level. These areas are often planted with sod grown on much finer?textured soils. This study examined

L. Art Spomer; A. J. Turgeon

1977-01-01

240

Protective and retentive effects of liposomes on water-degradable hydrocortisone acetate in dermatological applications  

Microsoft Academic Search

Various dermatological samples containing Liposomes as a drug carrier were prepared, and the effects of variations in the\\u000a dermatological formulations, such as liposornal encapsulation, base materials, and the purity of lipid products, on drug stability\\u000a and characteristics for effective topical drug delivery were investigated. Hydrocortisone-21-acetate, a hydrophobic and water-degradable,\\u000a anti-inflammatory agent, was used as the model drug. It was found

Soo Kyoung Bae; Jin-Chul Kim; Ung Kil Jee; Jong-Duk Kim

1999-01-01

241

Melting Curve of Water Studied in Externally Heated Diamond-Anvil Cell  

Microsoft Academic Search

The melting curve of ice VII was measured to a maximum pressure of 38GPa (temperature of about 1000 K). Experiments were carried out in an externally heated diamond anvil cell and melting was monitored by the disappearance of X-ray difiraction from ice VII. The melting line of H2O was found to be well described by the Simon equation P =

Natalia Dubrovinskaia; Leonid Dubrovinsky

2003-01-01

242

INCORPORATING NATURAL VARIABILITY, UNCERTAINTY, AND RISK INTO WATER-QUALITY EVALUATIONS USING DURATION CURVES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Quantifying natural variability, uncertainty, and risk is one of the greatest challenges facing those engaged in TMDL development because of regulatory, natural, and analytical constraints. Duration curves (DCs) are tools that can solve some of these problems, as are plots of percent exceedance ver...

243

Retention and transport of silver nanoparticles in a ceramic porous medium used for point-of-use water treatment.  

PubMed

The retention and transport of silver nanoparticles (Ag-NPs) through a ceramic porous medium used for point-of-use drinking water purification is investigated. Two general types of experiments were performed: (i) pulse injections of suspensions of Ag-NPs in aqueous MgSO4 solutions were applied to the ceramic medium, and effluent silver was quantified over time; (ii) Ag-NPs were applied directly to the porous medium during fabrication using a paint-on, dipping, or fire-in method, a synthetic, moderately hard water sample with monovalent and divalent inorganic ions was applied to the ceramic medium, and effluent silver was quantified over time. These latter experiments were performed to approximate real-world use of the filter medium. For experiments with Ag-NPs suspended in the inflow solution, the percentage of applied Ag-NPs retained in the ceramic porous medium ranged from about 13 to 100%. Ag-NP mobility decreased with increasing ionic strength for all cases and to a lesser extent with increasing nanoparticle diameter. Citrate-capped particles were slightly less mobile than proteinate-capped particles. For ceramic disks fabricated with Ag-NPs by the paint-on and dipping methods (where the Ag-NPs are applied to the disks after firing), significant release of nanoparticles into the filter disk effluent was observed relative to the fire-in method (where the nanoparticles are combined with the clay, water, grog, and flour before firing). These results suggest that the fire-in method may be a new and significant improvement to ceramic filter design. PMID:23496137

Ren, Dianjun; Smith, James A

2013-04-01

244

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

245

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.

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

2011-01-01

246

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

PubMed

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

Ditsche-Kuru, Petra; Schneider, Erik S; Melskotte, Jan-Erik; Brede, Martin; Leder, Alfred; Barthlott, Wilhelm

2011-03-10

247

Estimating Soil Water Retention Parameters Using Remote Sensing Platforms and Data Assimilation Tools  

NASA Astrophysics Data System (ADS)

Using air and space-borne remote sensing soil moisture data, insitu profile soil moisture at discrete depths, a physics-based soil hydrology model, and Genetic Algorithm (GA) we have developed (1) near-surface and (2) layer-specific soil-moisture assimilation schemes. This study quantifies the soil hydraulic properties of the near surface (0-5 cm) and root zone (0-200 cm) in a homogeneous/layered soil column (for individual layers) under various scenarios of vegetation type, bottom boundary conditions, and soil layering. We have conducted numerical (synthetic) studies and field experimental validation using simulation-optimization with genetic algorithm (SWAP-GA). In this study, it is demonstrated that soil texture, bottom boundary conditions, soil layers and heterogeneity of various soil types and vertical arrangements influence uncertainties for quantifying the soil hydraulic parameters in the layered soil domain. We envisage that our findings will help in the estimations of effective soil hydraulic parameters at large (remote sensing) footprints for land surface models under soil layering, vertical heterogeneity sequence, different vegetation and land covers, and ground water table depths.

Mohanty, B. P.; Shin, Y.; Ines, A.

2011-12-01

248

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

249

Thermodynamic study of the retention behaviour of selected macrocycles using reversed-phase high-performance thin-layer chromatography plates and methanol-water mobile phases  

Microsoft Academic Search

The influence of temperature and mobile-phase composition on retention of ?-, ß-, and ?-cyclodextrins and two macrocyclic antibiotics (rifamycin B and rifampicin) has been examined by reversed-phase thin-layer chromatography, using wide-range (0–100%) binary mixtures of methanol-water. Retardation factors (RF) of the solute molecules were measured at different temperatures from 5 to 60°C. Temperature changes of the chromatographic conditions produce significant

Pawe? K. Zarzycki; Joanna Nowakowska; Aleksandra Chmielewska; Maria Wierzbowska; Henryk Lamparczyk

1997-01-01

250

Boresight Retention.  

National Technical Information Service (NTIS)

This report provides a method of evaluating the boresight retention capability of gun control systems mounted in combat vehicles. It describes equipment and instrumentation including installation of reference telescopes. It also includes angular measureme...

1976-01-01

251

Boresight Retention.  

National Technical Information Service (NTIS)

This TOP describes procedures for evaluating the boresight retention capability of gun control systems mounted in combat vehicles other than field artillery weapons. The tests are designed to detect angular changes between gun and sighting systems after v...

1983-01-01

252

Apodemus sylvaticus (LOXT) is a suitable mouse strain for testing spatial memory retention in the Morris water maze.  

PubMed

Information on the difference in cognitive function between laboratory and wild-caught mice is anecdotal and this question has not been systematically studied. Moreover, studying a wild-caught mouse strain per se may add information to the repertoire of mouse strains available. We aimed to study spatial memory in a wild mouse strain (Apodemus sylvaticus, AS) as compared to two individual laboratory mouse strains. Male AS (n=20), CD1 (n=19) and C57BL/6J mice (n=19), 12-14 weeks old, were used in the experiments. The Morris water maze (MWM) was used for determination of spatial memory and time spent in the target quadrant at time points 5 (D5) and 12 days (D12) was evaluated. During the acquisition phase latency to reach the platform and path length to reach the platform was evaluated. Following four training days on day 5 (D5), time spent in the target quadrant was highest in AS>CD1>C57BL/6J (P<0.006). On day 12 (D12), time spent in the target quadrant was significantly higher in AS than in both other strains (P<0.001). All animals learned the task and during the acquisition phase, latency to reach the platform as well as path length decreased significantly in AS. It is concluded that the AS is the most suitable strain for the evaluation of spatial memory in the MWM and is presenting with memory retention superior to laboratory mouse strains CD1 and C57BL/6J. PMID:18242105

Patil, Sudarshan S; Sunyer, Berta; Höger, Harald; Lubec, Gert

2008-01-31

253

Retention of ionizable compounds on HPLC. 4. Mobile-phase pH measurement in methanol/water  

PubMed

The different procedures used in HPLC to measure the pH of a mobile phase are evaluated in terms of the rigorous IUPAC definition of pH. The three procedures evaluated are as follows: measurement of the pH of the aqueous HPLC buffer before mixing it with the organic modifier, measurement of the pH of the HPLC buffer after mixing it with the organic modifier using a pH electrode system calibrated with aqueous buffers, and measurement of the pH of the HPLC buffer after mixing it with the organic modifier but calibrating the electrode system with reference buffers prepared in the same mixed solvent used as mobile phase. Following IUPAC definitions and recommendations, the three pH values can be related with the pH scales: w(w)pH, s(w)pH, and s(s)pH, respectively. The relationships between these three pH scales are also presented. The retention of several compounds with acid/base behavior in a C-18 and a polymeric column with buffered methanol/water as mobile phase is related to the mobile phase pH value measured in the three pH scales. It is demonstrated that the s(w)pH and s(s)pH scales give better relationships than the w(w)pH scale (pH measured in the aqueous buffer before mixing it with the organic modifier), commonly used on HPLC. The s(w)pH scale is specially recommended because of its simplicity of measurement: the pH is measured after mixing the aqueous buffer with the organic modifier, but the pH calibration is performed with the common aqueous reference buffers. PMID:10784145

Canals; Portal; Bosch; Roses

2000-04-15

254

Surface retention capacity calculation  

NASA Astrophysics Data System (ADS)

Flood wave transformation in the floodplain is the phenomenon which is researched within interdisciplinary project NIVA - Water Retention in Floodplains and Possibilities of Retention Capacity Increase. The project focuses on broad range of floodplain ecosystem services and mitigation of flooding is one of them. Despite main influence on flood wave transformation is due to flow retardation, retention in surface depressions within floodplain has been analyzed to get better overview of whole transformation process. Detail digital relief model (DRM) has been used for given purposes to be able to analyze terrain depressions volumes. The model was developed with use of stereophotogrammetric evaluation of airborne images with high resolution of 10 cm. It was essential for purposes of presented analysis not to apply pit removal routines which are often used for generation of DRM for hydrological modelling purposes. First, the methodology of analysis was prepared and tested on artificial surface. This surface was created using random raster generation, filtration and resampling with final resolution of 1000 x 1000 units and height of maximum 10 units above datum. The methodology itself is based on analysis of areas inundated by water at different elevation levels. Volume is than calculated for each depression using extraction of terrain elevations under corresponding water level. The method was then applied on the area of Lužnice River floodplain section to assess retention capacity of real floodplain. The floodplain had to be cut into sections perpendicular to main river orientation for analyses as the method was tested for square shaped area without any significant inclination. Results obtained by mentioned analysis are presented in this paper. Acknowledgement Presented research was accomplished within national project NIVA - Water Retention in Floodplains and Possibilities of Retention Capacity Increase, nr. QH82078. The project is funded by Ministry of Agriculture of the Czech Republic. The support is highly acknowledged.

David, Vaclav; Dostal, Tomas

2010-05-01

255

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

256

DRYING OF WATER GELS: DETERMINATION OF THE CHARACTERISTIC CURVE OF AGAR-AGAR  

Microsoft Academic Search

Agar-agar is a polysaccharide extracted as a hydrocolloid from red seaweed, whose gels are homogeneous, stable and transparent. The characterization of ternary equilibrium and mass transfer kinetics in the agar-water-air system is essential for designing operations in the extractive process as well as for ascertaining the behaviour of these gels and sols during evaporation. humectation and swelling.In this work, the

O. Iglesias; A. Garcia; M. Roques; J. L. Bueno

1993-01-01

257

Safety implications of an integrated boiling curve model for water-cooled divertor channels  

Microsoft Academic Search

The international fusion community is actively researching advanced heat transfer methods for removal of high thermal loads from next-generation divertor assemblies. Such advanced techniques may indeed optimize the operational and economical performance of future divertor designs. However, with its extensive operational database, water-cooling remains as one of the optimum choices for near-term divertor designs. Critical heat flux (CHF) is the

T Marshall

2002-01-01

258

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

259

Freshman Retention  

Microsoft Academic Search

Aggregate college data are used to help understand how college characteristics influence the decision for freshman to remain in school another year. Taking advantage of the aggregate data, we estimate a three-stage least squares model which takes retention, enrollment and SAT scores as all endogenous. Our results highlight interactions between the three endogenous variables which confirms our suspicion of the

John S. Heywood; Richard D. Marcus

1989-01-01

260

Frequency curves  

USGS Publications Warehouse

This manual describes graphical and mathematical procedures for preparing frequency curves from samples of hydrologic data. It also discusses the theory of frequency curves, compares advantages of graphical and mathematical fitting, suggests methods of describing graphically defined frequency curves analytically, and emphasizes the correct interpretations of a frequency curve.

Riggs, H. C.

1968-01-01

261

Apparent paradox of neurohumoral axis inhibition after body fluid volume depletion in patients with chronic congestive heart failure and water retention.  

PubMed Central

BACKGROUND--Hypovolaemia stimulates the sympathoadrenal and renin systems and water retention. It has been proposed that in congestive heart failure reduction of cardiac output and any associated decrease in blood pressure cause underfilling of the arterial compartment, which promotes and perpetuates neurohumoral activation and the retention of fluid. This study examined whether an intravascular volume deficit accounts for patterns that largely exceed the limits of a homoeostatic response, which are sometimes seen in advanced congestive heart failure. METHODS AND RESULTS--In 22 patients with congestive heart failure and water retention the body fluid mass was reduced by ultrafiltration and the neurohumoral reaction was monitored. A Diafilter, which was part of an external venous circuit was regulated to produce 500 ml/hour of ultrafiltrate (mean (SD) 3122 (1199) ml) until right atrial pressure was reduced to 50% of baseline. Haemodynamic variables, plasma renin activity, noradrenaline, and aldosterone were measured before and within 48 hours of ultrafiltration. After ultrafiltration, which produced a 20% reduction of plasma volume and a moderate decrease in cardiac output and blood pressure (consistent with a diminished degree of filling of the arterial compartment), there was an obvious decrease in noradrenaline, plasma renin activity, and aldosterone. In the next 48 hours plasma volume, cardiac output, and blood pressure recovered; the neurohumoral axis was depressed; and there was a striking enhancement of water and sodium excretion with resolution of the peripheral oedema and organ congestion. The neurohumoral changes and haemodynamic changes were not related. There were significant correlations between the neurohumoral changes and increase in urinary output and sodium excretion. CONCLUSIONS--In advanced congestive heart failure arterial underfilling was not the main mechanism for activating the neurohumoral axis and retaining fluid. Because a decrease in circulating hormones was associated with reabsorption of extravascular fluid it is likely that hypoperfusion and/or congestion of organs, such as the kidney and lung, reduce the clearance of circulating noradrenaline and help to keep plasma concentrations of renin and aldosterone raised. A positive feedback loop between fluid retention and plasma hormone concentrations may be responsible for progression of congestive heart failure.

Guazzi, M D; Agostoni, P; Perego, B; Lauri, G; Salvioni, A; Giraldi, F; Matturri, M; Guazzi, M; Marenzi, G

1994-01-01

262

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

Horton, Michael

2009-05-30

263

Retention of ionizable compounds on HPLC. 6. pH measurements with the glass electrode in methanol–water mixtures  

Microsoft Academic Search

The relationship, ? values, between the two rigorous pH scales, sspH (pH measured in a methanol–water mixture and referred to the same mixture as standard state) and swpH (pH measured in a methanol–water mixture but referred to water as standard state), in several methanol–water mixtures was determined (?=swpH?sspH). ? values were measured using a combined glass electrode and a wide

Immaculada Canals; Fadoua Z. Oumada; Mart?? Rosés; Elisabeth Bosch

2001-01-01

264

Evaluation of the physical properties of water treatment residue for use as a soil substitute compared with decomposed granite soil  

Microsoft Academic Search

To evaluate water treatment residue (WTR) as a soil substitute material, its physical properties were investigated and compared with decomposed granite soil (DGS). For comparison purposes, relative gas diffusivity (D\\/D0), saturated hydraulic conductivity (Ks), water retention curve, porosity and readily available water were measured for both the WTR and the DGS. The measured D\\/D0, Ks, water retention ability and porosity

Seok-Gon Park; Mizue Ohashi; Kiyoshi Kurosawa; Young-Jin Kim; Hisashi Yahata

2010-01-01

265

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.

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

2012-01-01

266

Mapping water quality-related ecosystem services: concepts and applications for nitrogen retention and pesticide risk reduction  

Microsoft Academic Search

One of the challenges of using the ecosystem service (ES) framework in the context of planning and decision support is the question of how to map these services in an appropriate way. For water quality-related ESs, this implies a movement from the display of classical water quality indicators towards the mapping of the service itself. We explore the potential of

Sven Lautenbach; Joachim Maes; Mira Kattwinkel; Ralf Seppelt; Michael Strauch; Mathias Scholz; Christiane Schulz-Zunkel; Martin Volk; Jens Weinert; Carsten F. Dormann

2012-01-01

267

Retention of Microcystis aeruginosa and microcystin by salad lettuce ( Lactuca sativa) after spray irrigation with water containing cyanobacteria  

Microsoft Academic Search

Colonies and single cells of Microcystis aeruginosa and the hepatotoxin microcystin were retained by salad lettuce after growth with spray irrigation water containing the microcystin-producing cyanobacteria. These findings are discussed in terms of crop spray irrigation with water containing cyanobacteria and potential human exposure to cyanobacterial toxins via plant foods grown in such circumstances.

Geoffrey A Codd; James S Metcalf; Kenneth A Beattie

1999-01-01

268

Estimation of water transport based on in situ measurements of relative humidity and temperature in a dry Tanzanian soil  

Microsoft Academic Search

In situ measurements of relative humidity (RH) and temperature have been conducted along the profile of an air-dry soil over the course of 3 months. Soil water content data were calculated from RH measurements and the experimentally determined soil water retention curves at various temperatures. In addition, soil water potential data were directly derived from RH measurements, and the water

Kai-Uwe Goss; Michael Madliger

2007-01-01

269

Effect of Aquasorb and Organic Compost Amendments on Soil Water Retention and Evaporation with Different Evaporation Potentials and Soil Textures  

Microsoft Academic Search

Aquasorb PR3005A, a hydrophilic polymer (a salt copolymer polyacrylamide), and garden waste compost were added to a loamy sand and a loam soil in pots to assess their impact upon soil physical properties at two different evaporation potentials. Compost was mulched and incorporated, the Aquasorb was incorporated, and their effect on temperature and amelioration of soil water content and evaporation

M. Taban; S. A. R. Movahedi Naeini

2006-01-01

270

Preliminary permeability and water-retention data for nonwelded and bedded tuff samples, Yucca Mountain area, Nye County, Nevada.  

National Technical Information Service (NTIS)

Measurements of rock-matrix hydrologic properties at Yucca Mountain, a potential site for a high-level nuclear waste repository, are needed to predict rates and direction of water flow in the unsaturated zone. The objective of this study is to provide pre...

L. E. Flint A. L. Flint

1990-01-01

271

The flood on the Elbe river in August 2002 and the efficiency of water retention in the Havel detention basins  

Microsoft Academic Search

The flood at the Elbe\\/Labe River in August 2002 has reached the highest ever measured water level at many gauging stations and caused extraordinarily high damages. The event caused 19 fatalities in Germany. The estimates about the material losses range from 10,000 to 25,000 MEuro for Germany alone. The flood event at the lower part of the Elbe was still

A. Bronstert

2003-01-01

272

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

273

RETENTION OF ARIZONA DEER HUNTING CUSTOMERS  

Microsoft Academic Search

Trends in retention of Arizona deer hunting customers were examined to determine which factors influence retention. Much of Arizona experienced drought conditions fiom 1989 through the present. The resulting impact on vegetation and available water has contributed to a decline in deer population numbers. The Arizona Game and Fish Commission has responded by reducing the number of deer hunting permits

TICE SUPPLEE; AMBER A. MUNIG

274

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

275

Validation of a hyperspectral curve-fitting model for the estimation of plant water content of agricultural canopies  

Microsoft Academic Search

The estimation of plant water content is essential to the integration of remote sensing into precision agriculture. Hyperspectral models developed to estimate plant water content have had limited application under field conditions and have not been rigorously validated. A physical model using a spectrum matching technique was applied to hyperspectral data to directly calculate the canopy equivalent water thickness (EWT)

Catherine M Champagne; Karl Staenz; Abdou Bannari; Heather McNairn; Jean-Claude Deguise

2003-01-01

276

Water exchange and suction removal of all residual air in the colonic lumen both contribute to attenuation of insertion pain in a learning curve study  

PubMed Central

Purpose Water exchange colonoscopy significantly reduces insertion pain. We report a learning curve experience. Method Historic cohort was examined by usual air insufflation during scope insertion. Water exchange in consecutive groups using escalating volumes (group 1 to 3) of infused water, and transitioned from leaving residual air initially unattended (group 1 and 2) to suction removal of all residual air in subsequent practice (group 3). pain (0=none, 10=most severe) was assessed at 2 to 3-minute intervals during insertion or at any time the patient voiced discomfort. Procedural outcomes were recorded. Results Compared with the historic cohort examined by air insufflation, We produced a significantly lower proportion of patients with poor bowel preparation (?6% vs. 18.9%, p=0.005). From group 1 to 2, in the presence of a significant increase in volume of water exchanged (volume infused, 954±283 vs. 791±263, p=0.004; volume aspirated, 776±376 vs. 657±183, p=0.120) without suction removal of residual air, there was a non-significant reduction of insertion pain (2.4±2.9 vs. 3.2±3.1, p=0.198). suction removal of all residual air necessitated exchange of even larger volumes of water (1074±533, p=0.023) in group 3; and a further significant decrease of pain score to 1.3±2.4 (p=0.043). a progressive significant increase in insertion time was noted as the volume of water exchanged escalated alongside residual air aspirated (p=0.001). Conclusion Unrestricted water exchange enhances pain reduction. suction removal of all residual air in the colonic lumen further attenuates insertion pain. Both maneuvers contribute to optimizing reduction of insertion pain in the current learning curve study.

Hsieh, Jin-Jian; Leung, Felix W

2013-01-01

277

Linear viscoelastic master curves of neat and laponite-filled poly(ethylene oxide)–water solutions  

Microsoft Academic Search

Aqueous solutions composed of dispersed nanoparticles and entangled polymers are shown to exhibit common viscoelasticity over a range of particle and polymer concentrations. Time–temperature superposition and time–concentration superposition are applied to generate rheological master curves for neat and laponite-filled aqueous solutions of poly(ethylene oxide). The shift factors were correlated in terms of temperature and concentration and are found to differ

Vikram K. Daga; Norman J. Wagner

2006-01-01

278

Determination of sulphate in water and biodiesel samples by a sequential injection analysis—Multivariate curve resolution method  

Microsoft Academic Search

A spectrophotometric sequential injection analysis (SIA-DAD) method linked to multivariate curve resolution-alternating least squares (MCR-ALS) has been developed for sulphate determination. This method involves the reaction, inside the tubes of the SIA system, of sulphate with barium-dimethylsulphonazo (III) complex, Ba-DMSA (III), displacing Ba2+ from the complex and forming DMSA (III). When the reaction products reach the detector a data matrix

Vanessa del Río; M. Soledad Larrechi; M. Pilar Callao

2010-01-01

279

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

280

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

281

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

282

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

283

Ultrasonic spectroscopy allows a rapid determination of the relative water content at the turgor loss point: a comparison with pressure-volume curves in 13 woody species.  

PubMed

The turgor loss point (TLP), which is considered a threshold for many physiological processes, may be useful in plant-breeding programs or for the selection of reforestation species. Obtaining TLP through the standard pressure-volume (p-v) curve method in a large set of species is highly time-consuming and somewhat subjective. To solve this problem, we present an objective and a less time-consuming technique based on the leaf resonance able to calculate the relative water content (RWC) at TLP (RWCTLP). This method uses air-coupled broadband ultrasonic spectroscopy to obtain the sigmoidal relation between RWC and the standardized resonant frequency (f/fo). For the 13 species measured, the inflexion point of the RWC-f/fo relationship ( ) was not statistically different from the value of RWC at the TLP obtained with the p-v curves (RWCTLP p-v). PMID:23933828

Sancho-Knapik, Domingo; Peguero-Pina, José Javier; Fariñas, María Dolores; Alvarez-Arenas, Tomás Gómez; Gil-Pelegrín, Eustaquio

2013-07-01

284

New insights on the retention mechanism of non-polar solutes in reversed-phase liquid chromatographic columns.  

PubMed

A clarification of the retention mechanism of non-polar solutes in octadecyl reversed-phase chromatographic columns is attempted based on a systematic comparison of the retention in C18 and C2 columns under the assumption that the retention in C2 columns is due to adsorption. The comparison involves curve fitting procedures and tests based on the properties of special functions suggested in the present paper. For the application of this approach the retention behaviour of six non-polar solutes, benzene, toluene, ethylbenzene, propylbenzene, isopropylbenzene and tert-butylbenzene, is studied from aqueous mobile phases modified with methanol, isopropanol, acetonitrile and tetrahydrofuran using C18 and C2 reversed-phase columns. It was found that the retention mechanism in C18 columns is not the same in the four modifiers. In particular, our results show that the adsorption mechanism has a significant contribution in mobile phases modified by acetonitrile and tetrahydrofuran, the partition mechanism is likely to predominate in isopropanol-water mobile phases provided that the mole fraction of isopropanol is higher than 0.2, whereas the case of MeOH is rather obscure, since the various tests did not give a clear picture about the retention mechanism in methanol-water mobile phases. PMID:15116913

Nikitas, P; Pappa-Louisi, A; Agrafiotou, P

2004-04-23

285

Bimodal Probability Law Model for Unified Description of Water Retention, Air and Water Permeability, and Gas Diffusivity in Variably Saturated Soil  

Microsoft Academic Search

Air and water permeabilities and gas diffusivity as functions of soil fluid phase (air or water) contents are governing chemical transport and fate processes in the vadose zone, and have frequently been iden- tified as the three main transport parameters determining time and ef- ficiency during soil vapor extraction (soil venting) at polluted soil sites. A mathematically flexible function that

Tjalfe G. Poulsen; Per Moldrup; Seiko Yoshikawa; Toshiko Komatsu

2006-01-01

286

Association of methanol and water in ionic liquids elucidated by infrared spectroscopy using two-dimensional correlation and multivariate curve resolution.  

PubMed

Water and methanol associations in ionic liquids (ILs) have been studied by means of FTIR spectroscopy. Spectra at different concentrations of water or methanol in ILs were obtained by means of on-line dilution using a flow injection analysis system. Spectral features in the OH stretching region revealed that most of the water and methanol molecules tended to be isolated from each other and to interact with the anion of the IL via H bonding. By means of two-dimensional correlation spectroscopy, the formation of methanol and water dimers was also detected. Multivariate curve resolution was used to recover pure spectra and concentration profiles of the different species. Methanol dimers form at concentrations higher than 0.8% (w/w) in the three studied ILs, 1-ethyl-3-methylimidazolium tetrafluoroborate (emimBF4), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). Self-association of water molecules takes place in emimBF4 and bmimBF4 at a molar ratio similar to that of methanol molecules; however, water dimers cannot be detected in bmimPF6, the most hydrophobic IL studied. No evidence was found that bigger water clusters are formed in these ILs at the studied cosolvent concentrations. PMID:16771342

López-Pastor, Mercedes; Ayora-Cañada, María José; Valcárcel, Miguel; Lendl, Bernhard

2006-06-01

287

Skill retention and relearning – a proposed cyclical model  

Microsoft Academic Search

Some of the conventions regarding relearning of complex tasks (requiring both psychomotor and procedural skills) are well known, especially as relating to retention curves. Still lacking, however, is information which better clarifies the relationship between relearning and skill retention. The purpose of this study was to examine this relationship while identifying the parameter affecting the duration between training intervals, in

S. Ginzburg; E. M. Dar-El

2000-01-01

288

Football curves  

NASA Astrophysics Data System (ADS)

Straight lines, zigzag, parabolas (possibly truncated), circles and spirals are the main curves which can be observed in football (in the European sense, soccer elsewhere). They are, respectively, associated to heavy kick, knuckleball, lob and banana kicks. We discuss their physical origin and determine their respective domain of existence.

Dupeux, Guillaume; Cohen, Caroline; Le Goff, Anne; Quéré, David; Clanet, Christophe

2011-07-01

289

Bayesian approach to daily rainfall modelling to estimate monthly net infiltration using the Thornthwaite water budget and Curve Number methods  

Microsoft Academic Search

The Thornthwaite and Mather water budget is a simple and frequently applicable tool to estimate surpluses of water, which are not stored in the soil profile. Combining it with the empiric CN-method of the US Soil Conservation Service (US-SCS), which is applied to daily rainfall records, it is possible to estimate the runoff, and this way, from the difference between

E. Zimmermann

2006-01-01

290

N Retention in Urbanizing Headwater Catchments  

Microsoft Academic Search

Urbanization can potentially alter watershed nitrogen (N) retention via combined changes in N loading, water runoff, and N\\u000a processing potential. We examined N export and retention for two headwater catchments (?4 km2) of contrasting land use (16% vs. 79% urban) in the Plum Island Ecosystem (PIE-LTER) watershed, MA. The study period included\\u000a a dry year (2001–2002 water year) and a

Wilfred M. Wollheim; Brian A. Pellerin; Charles J. Vörösmarty; Charles S. Hopkinson

2005-01-01

291

Typewriting: Retention and Relearning.  

National Technical Information Service (NTIS)

Retention and relearning of straight-copy typewriting skill among 38 Administrative Specialists, 71L Military Occupational Specialty, were examined after the no-practice retention interval between Advanced Individual Training (AIT) graduation and unit dut...

J. D. Hagman

1979-01-01

292

Preliminary Assessment of Infiltration Rates and Effects on Water Quality of Selected Infiltration Media for Use in Highway Runoff Retention Basins in Washington State.  

National Technical Information Service (NTIS)

Infiltration experiments were undertaken to investigate an infiltration medium that could be used in retention basins to decrease the infiltration rate to between 5 and 10 inches per hour and to also decrease the concentrations of some pollutants in highw...

K. C. Ames E. L. Inkpen L. M. Frans W. R. Bidlake

2001-01-01

293

Solute Retention in Column Liquid Chromatography. X. Determination of Solute Infinite-Dilution Activity Coefficients in Methanol, Water, and Their Mixtures, by Combined Gas-Liquid and Liquid-Liquid Chromatography  

Microsoft Academic Search

The Raoult's-law activity coefficients of 3- to 7-carbon aliphatic aldehyde, ketone, ester, and alcohol solutes at infinite dilution in methanol, water, and mixtures of the two and in polydimethylsiloxane, all at 293–308 K, have been determined for the first time by appropriate combination of GLC and LLC retention data. The latter data are reported in terms of mole fractions, while

R. A. Djerki; R. J. Laub

1988-01-01

294

Rating curves and estimation of average water depth at the upper Negro River based on satellite altimeter data and modeled discharges  

NASA Astrophysics Data System (ADS)

The objective of this study is to derive the stage discharge relationship for 21 “virtual gauge stations” located at the upper Negro River (Amazon Basin, Brazil). A virtual station can be defined as any crossing of water body surface (i.e., large rivers) by radar altimeter satellite tracks. Rating curve parameters are estimated by fitting with a power law the temporal series of water surface altitude derived from satellite measurements and the discharge. Discharges are calculated using ProGUM, a flow routing model based on the Muskingum Cunge (M C) approach considering a diffusion-cum-dynamic wave propagation [Leon, J.G., Bonnet, M.P., Cauhope, M., Calmant, S., Seyler, F., submitted for publication. Distributed water flow estimates of the upper Negro River using a Muskingum Cunge routing model based on altimetric spatial data. J. Hydrol.]. Among these parameters is the height of effective zero flow. Measured from the WGS84 ellipsoid used as reference, it is shown that the height of effective zero flow is a good proxy of the mean water depth from which bottom slope of the reaches can be computed and Manning roughness coefficients can be evaluated. Mean absolute difference lower than 1.1 m between estimated equivalent water depth and measured water depth indicates the good reliability of the method employed. We computed the free surface water slope from ENVISAT altimetry data for dry and rainy seasons. These profiles are in good agreement with the bottom profile derived from the aforementioned water depths. Also, the corresponding Manning coefficients are consistent with the admitted ranges for natural channels with important flows (superficial width >30.5 m [Chow, V.T., 1959. Open Channel Hydraulics. McGraw-Hill, New York]) and irregular section.

Leon, J. G.; Calmant, S.; Seyler, F.; Bonnet, M.-P.; Cauhopé, M.; Frappart, F.; Filizola, N.; Fraizy, P.

2006-09-01

295

Exclusion and retention of compensatory kosmotropes by HPLC columns  

Microsoft Academic Search

With water as the elution solvent, zwitterionic solutes and polyols were retained on HPLC columns, more than was water, by totally hydrophobic packing materials. Relative retentions were systematically affected by oxygen functional groups in the packing material, explicable as specific retention of water. Reproducible elution sequences of 20 solutes at a variety of hydrophobic surfaces (aromatic and both long- and

Michael Lever

1998-01-01

296

Influence of River Rating Curves Interpolation Methods on In-stream Water Level Assessment and Stream-aquifer Exchanges in a Regional Distributed Hydro(Geo)logical Model  

NASA Astrophysics Data System (ADS)

The main objective of this study is to provide a realistic simulation of river stage in regional river networks in order to improve the quantification of stream-aquifer exchanges. The study focuses on the Oise basin (4 500 km2, part of the 65 000 km2-Seine basin in Northern France) where two original methodologies of rating curves estimations are proposed. The general framework is the distributed model Eau-Dyssée, which couples existing specialized models to address water resources in river basins. In particular, it simulates flow in aquifer units with a finite difference pseudo 3D model and river flow with a Muskingum model. Rating curves are used in the regional distributed hydro(geo)logical model to deduce river stage from the routed discharge, which permits to calculate the exchanges between aquifer units and rivers. The first methodology, which was already validated in the Oise basin, is based on simulating the main rivers with a 1D Saint-Venant model, from which functional stage-discharge relationships, or rating curves, are derived at a 200-m resolution and projected onto each 1-km grid-cell of the regional model. Such method can only be developed on well instrumented basins. In order to estimate river height on most basins (even those where the St Venant approach is not valid or cannot be set up due to lack of data), a second methodology is developed using data calculated with models at lower resolution (? 500 m): Rating curves at each center of the river network at regional scale are thus interpolated, based on a segmentation of the space compatible with the hydraulics and the regional model. This second methodology has been carried out over half the Seine basin river network, and the aim of the study is to validate it in the Oise basin with regards to the results of the first one. Assessed by the first method, average stream-aquifer exchanges are 39 mm.yr-1 for aquifer to streams fluxes and 2 mm.yr-1 for streams to aquifer fluxes, mainly due to storage in aquifer units during storm events. The stream to aquifer fluxes during high flow periods involve a longer transfer time in the aquifer units near to the river network, what corresponds to an increase of stored water in the aquifer system. In terms of spatial impact on simulated piezometric heads, the area influenced by in-stream water level fluctuations extends across 3 to 20 km around the streams, depending on the hydrogeological setting of the aquifer unit (confined/unconfined), with deviations of the simulated piezometric heads from their average ranging from a few centimeters to more than 1 m in aquifer grid-cells near the main stream. The second methodology leads to similar results offering a low computational cost opportunity for taking into account in-stream water level fluctuations in regional distributed process-based hydro(geo)logical models. It is an efficient way to improve the physics of the stream-aquifer interactions and better assess soil water content at the regional scale, with a limited computational burden owing to the pre-computation of the rating curves.

Saleh, F.; Flipo, N.; de Fouquet, C.; Ducharne, A.; Oudin, L.; Habets, F.; Ledoux, E.

2011-12-01

297

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 ...

298

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

299

Effects of agricultural practices on hydraulic properties and water movement in soils in Brittany (France)  

Microsoft Academic Search

The intensive agricultural use of soils in the Brittany region (western France) has increased the need for a better understanding of soil water dynamics. The aim of the present study is to compare quantitatively the differences produced by two agricultural practices on soil hydraulic properties (water retention curve and hydraulic conductivity) as well as the infiltration and drainage fluxes in

Babacar Ndiaye; Jérôme Molénat; Vincent Hallaire; Chantal Gascuel; Yannick Hamon

2007-01-01

300

Simulating Water Transfers at a Forest Field Site by Using Pedo-Transfer Functions  

Microsoft Academic Search

Pedo-transfer functions (PTFs) are an essential building block for the modelling of water flow in soils. Many such functions have been developed for estimating the water retention curve and hydraulic conductivity from measured soil properties. Studies have previously been conducted to evaluate the performance of such functions against independent data sets obtained by laboratory measurements. Three PTFs, which have performed

F. Gerard; M. Tinsley; K. U. Mayer

2003-01-01

301

A new Automated Laboratory Instrument for Soil Water Characteristic Determination. System Validation at Oregon State University  

Microsoft Academic Search

The soil water characteristic (SWC) is a fundamental descriptor of soil water retention properties. While tension table apparatus for defining drainage curves in the near-saturated region (0 to -100 cm H20) has been available for many decades, there has been little advance in automating the process, particularly when measurements of wetting, drying are combined. We describe a new automated tension

K. Vache; J. J. McDonneIl; C. Graham; J. Ekanayake; T. Davie

302

Variation of the relaxographic "shutter-speed" for transcytolemmal water exchange affects the CR bolus-tracking curve shape.  

PubMed

Contrast reagents (CRs) may enter the tissue interstitium for a period after a vascular bolus injection. As the amount of interstitial CR increases, the longitudinal relaxographic NMR "shutter-speed" (T(-1)) for the equilibrium transcytolemmal water exchange process increases. The quantity T(-1) is given by |r(1o)[CR(o)] + R(1o0) - R(1i)| (where r(1o) and [CR(o)] represent the interstitial (extracellular) CR relaxivity and concentration, respectively, and R(1o0) and R(1i) are the extra- and intracellular (1)H(2)O relaxation rate constants, respectively, in the absence of exchange). The increase of T(-1) with [CR(o)] causes the kinetics of the water exchange equilibrium to appear to decrease. Here, analytical theory for two-site-exchange processes is combined with that for pharmacokinetic CR delivery, extraction, and distribution in a method termed BOLus Enhanced Relaxation Overview (BOLERO(Copyright )). The shutter-speed effect alters the shape of the bolus-tracking (B-T) time-course. It is shown that this is mostly accounted for by the inclusion of only one additional parameter, which measures the mean intracellular lifetime of a water molecule. Simulated and real data demonstrate that the effect of shutter-speed variation on pharmacokinetic parameters can be very significant: neglecting this effect can lead to an underestimation of the parameter values by 50%. This phenomenon can be heterogeneous. Within a tiny gliosarcoma implanted in the rat brain, the interstitial CR in the tumor core never rises to a level sufficient to cause apparent slowing of the exchange process. However, within the few microns needed to reach the proliferating rim, this occurs to a significant degree. Thus, even relative pharmacokinetic quantities can be incorrectly represented in a parametric map that neglects this effect. The BOLERO analysis shows promise for in vivo vascular phenotyping in pathophysiology. It also includes a provision for approximating the separation of the perfusion and permeability contributions to CR extravasation. PMID:14648563

Yankeelov, Thomas E; Rooney, William D; Li, Xin; Springer, Charles S

2003-12-01

303

Generic soil descriptions for modelling water and chloride dynamics in the unsaturated zone based on Swedish soils  

Microsoft Academic Search

Information about soil hydraulic properties is a prerequisite for modelling water and solute dynamics in the unsaturated zone. Providing that this information is available and the uncertainty is within an acceptable range, computer models can be helpful tools in quantifying environmental effects. This study describes the water retention curve and hydraulic conductivity for three soil types: clay, glacial till and

Annika Lundmark; Per-Erik Jansson

2009-01-01

304

Neurogenic urinary retention  

Microsoft Academic Search

This review article on neurogenic urinary retention is divided into three main sections. The first covers the neuroanatomy of the bladder and urethral sphincters, developing the peripheral innervation as well as the spinal cord organization and the cortical and subcortical brain control of micturition. The second discusses the main central and peripheral neurological lesions and diseases causing urinary retention. The

A. G. Herbaut

1993-01-01

305

Fuel retention in tokamaks  

Microsoft Academic Search

Tritium retention constitutes an outstanding problem for ITER operation and future fusion reactors, particularly for the choice of the first wall materials. In present day tokamaks, fuel retention is evaluated by two complementary methods. The in situ gas balance allows evaluation of how much fuel is retained during a discharge and, typically, up to one day of experiments. Post-mortem analysis

T. Loarer

2009-01-01

306

Wrestling with Retention.  

ERIC Educational Resources Information Center

|In Long Beach, California, a courageous, communitywide conversation devised a new approach to enforcing K-8 promotion standards. Retention programs will not be a repeat of services, but offer retained children a significantly different academic experience. Retention criteria will comprise multiple measures, based on proficiency with content…

DeVries, Karen E.; Cohn, Carla A.

1998-01-01

307

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

308

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

309

Voltage Shift Effect on Retention Failure in Ferroelectric Memories  

NASA Astrophysics Data System (ADS)

We investigated the origin of retention failure in ferroelectric memories (FeRAMs) with SrBi2(Ta, Nb)2O9 (SBTN) memory cell capacitors by considering the time-dependent behavior of polarization vs. voltage (P-V ) curves of the capacitors during high-temperature storage. Since the SBTN capacitors exhibited no marked decrease in the nonvolatile component of polarization even after high-temperature storage, we focused on the effect of voltage shift observed in P-V curves. We calculated bitline voltage along the storage from the P-V curves and the bitline capacitance, and successfully estimated a decrease in the bitline voltage, which is in agreement with the retention failure in FeRAMs. In addition, the calculation indicated that the lifetime limited by the retention failure in FeRAMs with SBTN capacitors at 125°C exceeds 10 years.

Nakao, Keisaku; Judai, Yuji; Azuma, Masamichi; Shimada, Yasuhiro; Otsuki, Tatsuo

1998-09-01

310

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

311

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

312

Standard Mastery Curves and Skew Curves.  

ERIC Educational Resources Information Center

The objective of the study is to convince educational researchers of the necessity for "standard mastery curves" for the graphical representation of scores on summative tests for a group of students. Attention is drawn to the study of theoretical and empirical skew curves in education and biology. Use of standard mastery curves and study of skew…

Warries, Egbert

313

Performance of pedotransfer functions in predicting soil water characteristics of soils in Norway  

Microsoft Academic Search

Pedotransfer functions (PTFs), predicting the soil water retention curve (SWRC) from basic soil physical properties, need to be validated on arable soils in Norway. In this study we compared the performance of PTFs developed by Riley (1996), Rawls and Brakensiek (1989), Vereecken et al. (1989), Wösten et al. (1999) and Schaap et al. (2001). We compared SWRCs calculated using textural

Sigrun Hjalmarsdottir Kværnø; Lars Egil Haugen

2011-01-01

314

SCALING INFILTRATION AND OTHER SOIL WATER PROCESSES ACROSS DIVERSE SOIL TEXTURAL CLASSES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Our studies showed that the pore-size distribution index (lambda) can scale Brooks-Corey (B-C) formulation of the soil-water retention curves below the air-entry pressure head across dissimilar (Sandy to clayey) soils, and other key B-C hydraulic parameters ( Ksat, air-entry pressure head, and depen...

315

Retention Time Effect on Metal Removal by Peat Columns (U).  

National Technical Information Service (NTIS)

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 ...

E. A. Nelson

2007-01-01

316

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

317

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

318

Modeling of the Transport and Retention of Fullerene C60 Aggregates in Porous Media  

NASA Astrophysics Data System (ADS)

Buckminster fullerene (C60) has recently gained wide application in many commercial products. Given its widespread use, release of C60 into the environment during manufacture, transportation, and/or application is likely. Although C60 has negligible solubility in water, it is capable of acquiring charge and form highly stable nano-scale aggregates (nC60) in aqueous systems. In recent years, several laboratory research efforts have been devoted to studying the potential fate and transport of nC60 in porous media representative of the natural subsurface environment. Traditional clean-bed filtration theory is typically applied to analyze the experimental results. Far less attention has focused on the applicability of filtration theory to nC60 transport under different soil and solution conditions. In this work, we simulate column transport of nC60 under progressively more complex conditions and compare with laboratory observations. For nC60 transport in columns packed with Ottawa sand and simple electrolyte solutions, i.e. 1mM CaCl2 and 1mM NaCl, simulation results reveal that traditional clean-bed filtration theory is not sufficient to model the asymmetric breakthrough curves and relatively flat retention profiles observed in these systems. Modification of the filtration model, incorporating a maximum retention capacity term, can provide remarkably improved modeling results. The second application is for transport of nC60 in Ottawa sand coated with surfactant. The observed retention profiles in these experiments exhibit a hyper-exponential feature. Modeling results demonstrate that coupled simulation of both surfactant and nC60 transport is required to correctly capture the hyper-exponential retention profile in these systems. Finally, efforts to model the transport of nC60 in real soils, including Appling and Webster soils, are presented, suggesting that modification of filtration theory is also necessary in this case, to capture the shape of the observed retention profiles.

Li, Y.; Wang, Y.; Pennell, K.; Abriola, L.

2008-12-01

319

Moisture retention of a swelling soil under capillary and overburden pressures  

Microsoft Academic Search

The moisture content in a rigid soil varies with capillary pressure. On the other hand the moisture retention properties of a swelling soil are functions of capillary pressure and overburden pressure. An unloaded moisture retention curve for a swelling soil can be determined following the same laboratory procedures used for the rigid soils. Determination of the moisture contents due to

Ata-ur-Rehman Tariq; Deanna S. Durnford

1997-01-01

320

Modelling of arsenic retention in constructed wetlands.  

PubMed

A new model was developed in order to simulate the most significant arsenic retention processes that take place in constructed wetlands (CWs) treating high arsenic waters. The present contribution presents the implementation phases related to plants (arsenic uptake and accumulation, root arsenic adsorption, and root oxygen release), showing the first simulation results of the complete model. Different approaches with diverse influent configurations were simulated. In terms of total arsenic concentrations in effluent, the simulated data closely matched the data measured in all evaluated cases. The iron and arsenic species relationships, and the arsenic retention percentages obtained from simulations, were in agreement with the experimental data and literature. The arsenic retention efficiency increased whenever a new phase was implemented, reaching a maximum efficiency range of 85-95%. According to the quality of the obtained results, it can be considered that the implementation of all steps of RCB-ARSENIC provided reasonably good response values. PMID:23994963

Llorens, Esther; Obradors, Joshua; Alarcón-Herrera, María Teresa; Poch, Manel

2013-08-09

321

Principals Retention. Research Brief  

ERIC Educational Resources Information Center

Many districts are struggling with the problem of administrator retention. Hoffman (2004) identifies some of the reasons for this: (1) Increased accountability expectations; (2) Diminished or static levels of resources to support reform efforts; (3) Greater administrator vulnerability to sanctions; (4) The complex demands of government and the…

Muir, Mike

2005-01-01

322

Recruitment, Retention, Attrition Project.  

ERIC Educational Resources Information Center

|Based on a series of faculty workshops conducted at Jefferson Community College (KY) in 1978 and 1980, this handbook outlines 95 practical suggestions for increasing student retention rates. After introductory material describing these workshops, the first 22 suggestions recommend ways to foster positive student/teacher interaction. Methods are…

Horvath, Ronald J., Ed.

323

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

324

Exposure to brackish water, upon feeding, leads to enhanced conservation of nitrogen and increased urea synthesis and retention in the Asian freshwater stingray Himantura signifer  

Microsoft Academic Search

The white-edge freshwater whip ray Himantura signifer is ammonotelic in freshwater, but retains the capacities of urea synthesis and ureosmotic osmoregulation to survive in brackish water. The first objective of this study was to examine whether exposure to brackish water would lead to increases in food intake, and\\/or conservation of nitrogen in H. signifer upon daily feeding. Results obtained showed

Shit F. Chew; Nirmala K. Poothodiyil; Wai P. Wong; Yuen K. Ip; Nanyang Walk

2006-01-01

325

The relation of retention to the distribution of relearning  

Microsoft Academic Search

Experiments to test the inference made by several authorities that, since the rate of forgetting is very rapid at first and more gradual later on, relearning of a given material should come more frequently at first and at longer intervals later. Paired associates were used; the curve of retention for this material showed negative acceleration. 72 subjects, divided into 3

L. S. Tsai

1927-01-01

326

Liposome retention in size exclusion chromatography  

PubMed Central

Background Size exclusion chromatography is the method of choice for separating free from liposome-encapsulated molecules. However, if the column is not presaturated with lipids this type of chromatography causes a significant loss of lipid material. To date, the mechanism of lipid retention is poorly understood. It has been speculated that lipid binds to the column material or the entire liposome is entrapped inside the void. Results Here we show that intact liposomes and their contents are retained in the exclusion gel. Retention depends on the pore size, the smaller the pores, the higher the retention. Retained liposomes are not tightly fixed to the beads and are slowly released from the gels upon direct or inverted eluent flow, long washing steps or column repacking. Further addition of free liposomes leads to the elution of part of the gel-trapped liposomes, showing that the retention is transitory. Trapping reversibility should be related to a mechanism of partitioning of the liposomes between the stationary phase, water-swelled polymeric gel, and the mobile aqueous phase. Conclusion Retention of liposomes by size exclusion gels is a dynamic and reversible process, which should be accounted for to control lipid loss and sample contamination during chromatography.

Ruysschaert, Tristan; Marque, Audrey; Duteyrat, Jean-Luc; Lesieur, Sylviane; Winterhalter, Mathias; Fournier, Didier

2005-01-01

327

Generic Recruitment and Retention Plan  

Cancer.gov

February 23, 2010 Version 3 Division of Cancer Prevention Recruitment Retention and Adherence Plan TemplateInstructions NCI DCP requires a study-specific recruitment, retention and adherence (RRA) plan for each cancer chemoprevention study. Each participating

328

Biofilm roughness determines Cryptosporidium parvum retention in environmental biofilms.  

PubMed

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

DiCesare, E A Wolyniak; Hargreaves, B R; Jellison, K L

2012-04-06

329

Retention of metal ions in ultrafiltration of mixtures of divalent metal ions and water-soluble polymers at constant ionic strength based on Freundlich and Langmuir isotherms  

Microsoft Academic Search

The interactions of water-soluble polymers with metal ions are studied by ultrafiltration using a molecular-weight cut off of 5000Da polyethersulfone ultrafiltration membrane. The technique allowed analyzing mathematically the distribution of metal ions bound to previously fractionated high molecular-weight water-soluble polymers or free in the solution from variables experimentally measurable. The Langmuir and Freundlich adsorption isotherms for the system poly(sodium 4-styrenesulfonate)

Ignacio Moreno-Villoslada; Bernabé L Rivas

2003-01-01

330

Academic Advising, Retention, and Transfer.  

ERIC Educational Resources Information Center

|Stresses the central role of academic advising in student retention. Reviews Tinto's model of retention stressing the importance of student academic and social integration. Describes studies demonstrating the predictive validity of integration for retention, and identifying attitudinal and behavioral correlates of attrition. Reviews obstacles to…

King, Margaret C.

1993-01-01

331

Teacher Retention: Problems and Solutions  

ERIC Educational Resources Information Center

There is a teacher retention crisis in the United States. The purpose of this paper is to answer the following questions: What contributes to teachers leaving the field? How has "No Child Left Behind" affected teacher retention? What can be done to retain good teachers? What impact do school administrators have on teacher retention? After…

McLaurin, Sidney E.; Smith, Willis; Smillie, Amanda

2009-01-01

332

Research Synopsis: Spring 1983 Retention.  

ERIC Educational Resources Information Center

An analysis of spring 1983 retention rates and grade distributions within the Peralta Community College District (PCCD) revealed: (1) College of Alameda had the highest successful retention rate in the PCCD, defined as the total of all students who completed the term with a grade of A, B, C, D, or CR (credit); (2) the PCCD's successful retention

Peralta Community Coll. District, Oakland, CA. Office of Research, Planning and Development.

333

Retention: A Model  

NASA Astrophysics Data System (ADS)

Bowie State University, one of six institutions, received a Model Institution for Excellence Award through the National Science Foundation and was funded by the National Aeronautic Space Administration - Goddard Space Flight Center. The primary goals for the Initiative are to increase Science Mathematics Engineering and Technology (SMET)student enrollment, retention and graduation rates and the number of minorities and women entering graduate school and SMET related workforces. Additionally, a satellite operations and control center was established at Bowie State University to provide training for students interested in space science. Thus far, the number of students entering the SMET domain has increase, the retention rate is up to 72-75%, graduation rate is up 80% and approximately 70 certifications have been awarded to students as Command Controllers, Spacecraft Analysts or Mission Planners as a result of their training in the Bowie State Satellite Operations and Control Center (BSOCC). The partnership between NASA and Bowie State University has been extremely beneficial to both and has established a model for the retention of science, mathematics, engineering and technology students.

Davis, E. J.; Strand, D.; Wiggs, M.

2004-12-01

334

Lead Retention by Soils at Field Moisture Contents  

Microsoft Academic Search

Majority of studies pertaining to lead retention by clays and soils have examined the mechanisms, kinetics and adsorption isotherms using the batch experiment technique that employ solid: water extracts of 1:10 and 1:20 Field soil deposits generally have much lower gravimetric water contents ranging between 9 and 45%. Given the wide disparity in the solids: water ratio employed in the

Sudhakar M. Rao; Kumar Gaurave; Ayyavoo Sarvanan

2012-01-01

335

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.

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

336

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

337

Efficient elliptic curve exponentiation  

Microsoft Academic Search

Elliptic curve cryptosystems, proposed by Koblitz([8]) andMiller([11]), can be constructed over a smaller definition field than theElGamal cryptosystems([5]) or the RSA cryptosystems([16]). This is whyelliptic curve cryptosystems have be un to attract notice. There aremainly two types in elliptic curve cryptosystems, elliptic curves E overIF 2 r and E over IFp . Some current systems based on ElGamal or RSAmay

Atsuko Miyaji; Takatoshi Ono; Henri Cohen

1997-01-01

338

Standard Decrement Curves  

Microsoft Academic Search

For circuit breaker and relay application, it is frequently necessary to determine the decrement in power system short-circuit currents. For this purpose certain ``standard decrement curves'' approved by the National Electrical Manufacturers Association have been in general use. The original curves appeared in 1918 and a revised set was prepared in 1923. New decrement curves given in the present paper

W. C. Hahn; C. F. Wagner

1932-01-01

339

Cooperative multimodal retention of IgG, fragments, and aggregates on hydroxyapatite  

PubMed Central

Retention mapping of chimeric monoclonal IgG1, Fc, Fab, F(ab?)2, and aggregated antibody was conducted on hydroxyapatite (HA) by systematically varying phosphate and chloride concentrations during gradient elution in order to characterize the interactions of each solute with calcium and phosphate residues on the solid phase. Lysozyme was used as a control to model cation exchange-dominant interactions. Bovine serum albumin was used as a control for calcium affinity-dominant interactions. Calcium affinity and phosphoryl cation exchange were positively cooperative for IgG-related species. Fc retention was dominated by calcium affinity, while retention of Fab was dominated by cation exchange. F(ab?)2 exhibited a curve shape similar to Fab, but stronger retention. The retention curve for intact IgG incorporated the distinctive elements of its fragments but stronger retention than that predicted by their addition to one another. Aggregate retention paralleled the curve for non-aggregated antibody, with stronger retention by both binding mechanisms. Experimental data revealed evidence of charge repulsion between IgG carboxyls and HA phosphate at low conductivity values. Electrostatic repulsion of amino residues and attraction of carboxyls by HA calcium appeared to be blocked by strong complexation of calcium with mobile phase phosphate.

Gagnon, Pete; Cheung, Chia-Wei; Yazaki, Paul J.

2011-01-01

340

Modelling the Hydrological Performance of Stormwater Management Retention Ponds in Scotland  

NASA Astrophysics Data System (ADS)

The work presented here is part of a wider modelling study into the long-term performance of Sustainable Urban Drainage Systems in Scotland, a stormwater management technique employed by the Scottish Environment Protection Agency to protect watercourses from flooding and water quality deterioration. In particular, the study aims to predict how retention ponds perform under varying inflow conditions and climate change scenarios to assess the long-term impact of this form of stormwater management on Scotland's future water resources. A suite of simulations was conducted to explore the flow attenuation characteristics of conical retention ponds that have outflows controlled by triangular notch weirs. The inflows were represented as triangular hydrographs using a range of peak flows. Optimum flow attenuation occurs when peak outflow is reduced and hydrograph time lags are prolonged. Analysis of the results has shown that the Temporary Storage Volume available in the retention pond during any given storm exercises a critical control on flow attenuation performance of the pond. Factors which increase Temporary Storage Volume such as increasing pond radius, decreasing water level at the start of a storm, decreasing pond side slope gradient and increasing weir crest elevation lead to a marked improvement in pond flow attenuation performance. Conversely, factors which decrease Temporary Storage Volume result in poor flow attenuation performance. These simulations also demonstrate the secondary control that weir angle has on flow attenuation performance through its influence on the Dynamic Storage Volume, which is only effective once outflow through the weir has begun. Larger weir angles reduce the flow attenuation performance of ponds; however caution must be exercised in using smaller weir angles, which despite improving performance, may lead to an increased risk of overtopping. Other simulations show that ponds suffer a reduction in performance when subject to larger inflow volumes and that the provision of an additional outflow device can have a marked, but complex, effect on performance. With regard to the latter, for example, a low-level orifice outlet may decrease flow attenuation (by increasing the peak outflow and decreasing lags), but will decrease the risk of the pond not being well drawn down at the start of the next storm. Clearly, there is a trade off between the attenuation of a current and a subsequent storm. Although these trends are not unexpected, there is little published information that quantifies them in such a way that the performance of a retention pond can be predicted over the range of conditions likely to be encountered during its operating life. The generation of performance curves from the simulations being carried out in this study should lead to a better design process for retention ponds, for both single-event and event sequence scenarios.

Morgan, C. T.; Wallis, S. G.; Lunn, R. J.; Heal, K.

2004-12-01

341

An integrated approach with Trichoderma harzianum DGA01 and hot water treatment on control of crown rot disease and retention of overall quality in banana  

Microsoft Academic Search

A biological control of crown rot disease of banana fruit was analysed using an integrated approach combining hot water treatment and Trichoderma harzianum strain DGA01. Treated fruit were stored at 22–25°C and 90–95% relative humidity for 2 weeks. The bioefficacy of fungal antagonist in vitro towards crown rot-causing pathogens namely: Lasiodiplodia theobromae, Thielaviopsis paradoxa, Colletotrichum musae, and Fusarium verticillioides, was

Dionisio G. Alvindia; Miriam A. Acda

2012-01-01

342

Role of adipocytes in the muscle tissue of Atlantic salmon ( Salmo salar ?) in the uptake, release and retention of water-soluble fraction of crude oil hydrocarbons  

Microsoft Academic Search

The uptake and depuration of the water-sol?uble fraction (WSF) of hydrocarbons of crude petroleum by Atlantic salmon (Salmosalar) has previously been examined in terms of whole muscle. The hypothesis that the tainting WSF in the muscle was retained primarily\\u000a by adipocytes has been investigated by the isolation of adipocytes and the subsequent analysis for hydrocarbons in adipocytes.\\u000a After 96?h exposure

S. Zhou; H. Heras; R. G. Ackman

1997-01-01

343

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

2012-09-04

344

Metals Retention in Constructed Wetland Sediments  

SciTech Connect

The A-01 wetland treatment system (WTS) was designed to remove metals from the effluent at the A-01 NPDES outfall at the Savannah River Site, Aiken, SC. Sequential extraction data was used to evaluate remobilization and retention of Cu, Pb, Zn, Mn, and Fe in the wetland sediment. Remobilization of metals was determined by the Potentially Mobile Fraction (PMF) and metal retention by the Recalcitrant Factor (RF). The PMF, which includes water soluble, exchangeable, and oxides fractions, is the contaminant fraction that has the potential to enter into the mobile aqueous phase under changeable environmental conditions. PMF values were low for Cu, Zn and Pb (about 20 percent) and high for Fe and Mn (about 60 to 70 percent). The RF, which includes crystalline oxides, sulfides or silicates and aluminosilicates, is the ratio of strongly bound fractions to the total concentration of elements in sediment. RF values were about 80 percent for Cu, Zn and Pb, indicating high retention in the sediment and 30 percent to above 40 percent for Fe and Mn indication low retention.

KNOX, ANNA

2004-10-27

345

Estimating Retention Properties of Components of a Block Scale Fracture Network an Example from the Äspö Hard Rock Laboratory, Sweden.  

NASA Astrophysics Data System (ADS)

Crystalline rock is typically viewed as consisting of essentially impervious rock blocks separated by fractures. These fractures include both high-conductivity structures along which most of the flow takes place, and lower- conductivity fractures which are either hydraulically inactive, or carry very low flow. A number of tracer tests ("Tracer Retention Understanding Experiments"-TRUE) have been carried out along high-conductivity fractures (T >10-7 m2/s) since 1995 at the Äspö Hard Rock Laboratory (Sweden), with the purpose of characterizing their retention properties. However, from the safety assessment point of view, lower conductivity fractures (often referred to as "background fractures") could play an important role for the overall retention of radionuclides, since such fractures are most likely to be exposed to the initial release from a leaky radioactive waste canister. The most recent series of tracer tests performed at the Äspö HRL (TRUE Block Scale Continuation) address the issue of radionuclide retention in network pathway including a background fracture. Two tracer injections were performed in a forced flow field involving a high-conductivity fracture/fault (referred to as structure #19) and a pathway including a background fracture (referred to as BG1). These tracer experiments were carried out using a cocktail of tracers with varying sorption properties. In the first case, both injection and pumping were within structure #19, whereas in the second case tracers were injected in BG1 and pumped in structure #19. The Euclidean distance from injection location to extraction location is in both cases about 20 m. However, the hydrostructural model shows that while the actual pathway distance for the Structure #19 pathway may actually be 20 m, the pathway distance for the network pathway including BG1 is probably between 50 and 70 m. The retention properties of fracture BG1 were estimated indirectly, by inferring retention properties of structure #19 from the breakthrough curve of the first injection, and then using that result to deduce retention properties of BG1. We find that the retention material parameter group of BG1 is considerably lower than that of structure #19, but the hydrodynamic control parameter is one order of magnitude higher due to higher water residence time and smaller aperture. This is consistent with the significantly longer path length inferred from the hydrostructural model, and the geologic characterization of BG1 as a "non-fault" fracture. These results provide a clear indication that although the immobile zone retention properties are weaker in BG1, the overall retention is stronger for the BG1 pathway than for structure #19. These results indicate that assessment of transport properties needs to be made as a combination of discrete fracture network analysis to evaluate the pathway geometry, and immobile zone geochemical experiments to assess the retention properties of fractures and fracture populations. The uncertainty of the analysis interpretations presented has been evaluated quantitatively, demonstrating that the uncertainty about the hydrodynamic (pathway length and velocity) parameter group is greater than that for the retention (physical and geochemical) parameter group. This analysis, together with the quantitative analysis of uncertainty supports the development of more realistic retention properties of fractures in discrete fracture network simulations for hazardous chemical and radionuclide transport in crystalline rock.

Cheng, H.; Cvetkovic, V.; Winberg, A.; Dershowitz, W.

2006-12-01

346

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

347

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

2013-04-16

348

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

349

Use of the root contact concept, an empirical leaf conductance model and pressure-volume curves in simulating crop water relations  

Microsoft Academic Search

A simulation model “DanStress” was developed for studying the integrated effects of soil, crop and climatic conditions on\\u000a water relations and water use of field grown cereal crops. The root zone was separated into 0.1 m deep layers of topsoil and\\u000a subsoil. For each layer the water potential at the root surface was calculated by a single root model, and

C. R. Jensen; H. Svendsen; M. N. Andersen; R. Lösch

1993-01-01

350

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

351

Ranking intersecting Lorenz curves  

Microsoft Academic Search

This paper is concerned with the problem of ranking Lorenz curves in situations where the Lorenz curves intersect and no unambiguous\\u000a ranking can be attained without introducing weaker ranking criteria than first-degree Lorenz dominance. To deal with such\\u000a situations two alternative sequences of nested dominance criteria between Lorenz curves are introduced. At the limit the systems\\u000a of dominance criteria appear

Rolf Aaberge

2009-01-01

352

Equivalent Curves in Surfaces  

Microsoft Academic Search

We consider various notions of equivalence for homotopy classes of curves on hyperbolic surfaces based on topological, algebraic, and geometric structures, and find the relationships between these equivalences.

Christopher J. Leininger

2003-01-01

353

Multiple linear regression analysis of the retention data for several polynuclear aromatic hydrocarbons  

SciTech Connect

The retention data for benzene, toluene, naphthalene, cumeme, biphenyl, and durene in ternary (methanol, tetrahydrofuran, water) and quaternary (methanol, tegrahydrofuran, acetonitrile, water) solvent systems has been reduced to linear equations relating the retention volume to solvent composition. In particular, attention is focused on the biphenyl, naphthalene, cumene system and comments are made as to the optimum separation conditions. 3 tables.

Walters, F.H.

1983-01-01

354

Pedotransfer functions for the estimation of moisture retention characteristics of Ferralsols and related soils  

Microsoft Academic Search

The determination of water retention characteristics of soils in tropical regions is hampered by the lack of adequate laboratory equipment and high cost of analysis. In this paper the possibilities of estimating water retention characteristics from routinely determined properties of Ferralsols\\/Oxisols and related soils are investigated. Two sets of data on soils from South America, Africa and South East Asia,

M. van den Berg; E. Klamt; L. P. van Reeuwijk; W. G. Sombroek

1997-01-01

355

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

356

Strategies to improve engineering retention  

Microsoft Academic Search

Victoria University of Wellington in partnership with the regional polytechnic, WelTec, undertook a major exercise to identify, and where possible, resolve, barriers to recruitment and retention in the “digital” engineering specializations. This paper focuses on the retention aspects of this research. Informed by student surveys, focus groups and secondary school academic achievement data, we identified contributing issues of academic preparation,

Dale. A. Carnegie; Craig Watterson; Will N. Browne; James MacKay; Mel Lock; John Williams; Michael Forret

2012-01-01

357

Solvent Retention and Fibre Chemistry.  

National Technical Information Service (NTIS)

The aim of this study was to understand in which way different chemical and physical treatments affect the solvent retention properties of pulps used in the middle layer of folding boxboard. The solvent retention properties of the treated pulps were exami...

M. Rantanen

2003-01-01

358

Mechanical Retention of Resin Veneers.  

National Technical Information Service (NTIS)

Mechanical retention of resin veneers is provided for by a number of means, including the use of retentive beads. Studies have been reported in which resin-gold bonds were evaluated using beads, but no known effort had been made to determine the number be...

J. W. O'Hara W. G. Richardson R. J. Leupold G. B. Pelleu

1974-01-01

359

Retention: Are Students Good Predictors?  

Microsoft Academic Search

The retention rates of engineering students, in general, are much lower than they should be. Of particular concern is the fact that women and underrepresented minorities are not only recruited in small numbers, but their retention rates are also low. Research has shown that there are many actions that can be done to help retain students. In order to better

Mary R. Anderson-Rowland

360

Bridging the Gaps in Retention.  

ERIC Educational Resources Information Center

This paper reviews the literature on student retention at urban colleges and explores notions of student involvement and academic and social integration especially in relation to nontraditional students. It describes some programmatic interventions designed to improve retention. The paper concludes that partnerships with public schools may have a…

Pacheco, Arturo

1994-01-01

361

Sacral neuromodulation for urinary retention  

Microsoft Academic Search

Urinary retention without an identifiable urological cause presents a diagnostic and therapeutic challenge. Patients with nonobstructive chronic urinary retention usually have to rely on intermittent self-catheterization or indwelling suprapubic or transurethral catheters, which significantly affect quality of life. For some patients, however, sacral neuromodulation (SNM) offers an effective therapeutic alternative, and women with primary disorder of urethral sphincter relaxation (Fowler's

Clare J Fowler; Thomas M Kessler

2008-01-01

362

Leaf retention and cassava productivity  

Microsoft Academic Search

Increased longevity of leaves, or improved leaf retention, has been suggested as a possible means to increase productivity of cassava (Manihot esculenta Crantz). This study evaluated variation in leaf retention and its relation to cassava productivity under irrigated and stressed conditions. In the first trial 1350 clones were evaluated on the North Coast of Colombia with a 5-month dry period

J. I. Lenis; F. Calle; G. Jaramillo; J. C. Perez; H. Ceballos; J. H. Cock

2006-01-01

363

Increasing undergraduate student retention rates  

Microsoft Academic Search

Based on data from a questionnaire survey of the new undergraduate intake to the University of Birmingham, the factors which influence withdrawal\\/retention rates in the first term were examined. The effectiveness of counselling intervention with first-year undergraduate students at risk of leaving university in their first term is also explored. The implications for universities wishing to increase retention rates and

Barbara Rickinson; Desmond Rutherford

1995-01-01

364

Grading on the Curve.  

ERIC Educational Resources Information Center

Discusses some of the myths surrounding grading on the curve. Provides a simple explanation of such statistical terms as histograms, relative frequency, normal distribution, mean, and standard deviation. Describes how to restructure the curve, including the program listing for a computer program that will assist the teacher. (TW)

Wall, Charles R.

1987-01-01

365

Classification Using Growth Curves  

Microsoft Academic Search

Classification using the growth curve model is analyzed according to whether the covariance matrix structure is known to be compound symmetric. A new classification procedure appropriate for classification in the case of models with means that follow a Potthoff and Roy [Potthoff, R. F., Roy, S. N. (1964). A generalized multivariate analysis of variance model useful especially for growth curve

Graciela B. Mentz; Anant M. Kshirsagar

2005-01-01

366

Analyzing population growth curves  

Microsoft Academic Search

Assessing animal population growth curves is an essential feature of field studies in ecology and wildlife management. We used five models to assess population growth rates with a number of sets of population growth rate data. A 'generalized' logistic curve provides a better model than do four other popular models. Use of difference equations for fitting was checked by a

L. L. Eberhardt; J. M. Breiwick; D. P. Demaster

2008-01-01

367

AND NEGATIVELY CURVED SPACES  

Microsoft Academic Search

The paper sketches a recent progress and formulates several open prob- lems in studying equivariant quasiconformal and quasisymmetric homeomorphisms in negatively curved spaces as well as geometry and topology of noncompact geo- metrically finite negatively curved manifolds and their boundaries at infinity having Carnot-Caratheodory structures. Especially, the most interesting are complex hy- perbolic manifolds with Cauchy-Riemannian structure at infinity, which

Boris Apanasov

368

Hyperelliptic Curves and Cryptography  

Microsoft Academic Search

In 1989, Koblitz proposed using the jacobian of a hyperel- liptic curve deflned over a flnite fleld to implement discrete logarithm cryptographic protocols. This paper provides an overview of algorithms for performing the group law (which are necessary for the e-cient imple- mentation of the protocols), and algorithms for solving the hyperelliptic curve discrete logarithm problem (whose intractability is essential

Michael Jacobson; Alfred Menezes; Andreas Stein

2004-01-01

369

Stellar Blackbody Radiation Curves  

NSDL National Science Digital Library

Stellar Blackbody Radiation Curves model simulates the blackbody radiation curve of stars and how this leads to the observed color and luminosity of the star. If a star can be treated as a blackbody, the blackbody radiation curve of the star, the power density per area (or intensity) per wavelength (energy/time/volume) vs wavelength, is dependent on the star's temperature (spectral class). In the simulation, the star is shown along with its luminosity and spectral class. In separate graph, the blackbody radiation curve, the visible part of the spectrum, and the integrated stellar surface intensity (integrating the blackbody curve over all wavelengths) are shown. In another window the HR diagram can be shown indicating the current star's parameters. The radius of the star (in Rsun) and the temperature of the star in Kelvin (5780 K is Tsun) can be changed.

Belloni, Mario

2010-11-11

370

Comparative analysis of base flow recession curves for different Andean catchments  

NASA Astrophysics Data System (ADS)

Little is known in the Paute River basin, Ecuador about the groundwater resources, the relation between aquifers and their recharge zones and interaction with rivers. The pressure from human activities in the river basin is increasing and impacting the surface water quality and quantity, therefore it becomes increasingly useful to estimate the potential of groundwater exploitation as an alternative resource. Due to the lack of specific groundwater data and information, assessment of suitable alternative methods for groundwater research at different scales is considered. In low flow hydrology literature it is noted that the majority of natural gains to streamflow during low-flow periods are derived from releases from groundwater storage, moreover baseflow is generally suggested to be an indicator of groundwater or other delayed sources. Analysis of flow recession curves allows the determination of characteristics of the groundwater reservoir, which is a prerequisite for the separation of baseflow from total discharge and the estimation of groundwater storage and recharge. The flow recession curve at a river cross section is defined as the discharge hydrograph of the basin during a rainless or dry period. Its analysis yields information on the retention characteristics of the basin and of groundwater storage and depletion. In the Paute River basin baseflows are assumed to be originating from Paramo storage, which is largely determined by the high water retention capacity of the soils in combination with their slopes. In the case of the sub-catchment of the Tarqui River, there are evidences based on topography, hydromorphology, discharges and soils that suggest the presence of a major aquifer in the valley. Hence, the goal of this contribution is the comparison and analysis of groundwater conditions based on baseflow recession analysis for the Tarqui and Yanuncay River sub-catchments. Baseflow analyses are translated in recharge and groundwater resources characteristics, as well as relationships with land cover, morphology, geology and rainfall are established and presented. The results are discussed within the framework of increasing pressures on the water system.

Guzman, P.; Batelaan, O.; Wyseure, G.

2012-04-01

371

Simple-closed-curve sculptures of knots and links  

Microsoft Academic Search

We present a method for creating simple closed curves that divide the plane into two regions that, when coloured differently from one another, resemble knots and links. By cutting along these curves with a laser or water jet cutter, we obtain two-piece sculptures ideal for illustrating the Jordan curve theorem.

Robert Bosch

2010-01-01

372

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

373

Curved Girder Computer Manual.  

National Technical Information Service (NTIS)

This report presents three computer programs based on analytical techniques of the slope deflection Fourier Series previously developed under this HP and R study. The COBRA (Curved Orthotropic Bridge Analysis) slope deflection computer programs can be use...

L. C. Bell C. P. Heins

1969-01-01

374

Bragg Curve Spectroscopy  

SciTech Connect

An alternative utilization is presented for the gaseous ionization chamber in the detection of energetic heavy ions, which is called Bragg Curve Spectroscopy (BCS). Conceptually, BCS involves using the maximum data available from the Bragg curve of the stopping heavy ion (HI) for purposes of identifying the particle and measuring its energy. A detector has been designed that measures the Bragg curve with high precision. From the Bragg curve the range from the length of the track, the total energy from the integral of the specific ionization over the track, the dE/dx from the specific ionization at the beginning of the track, and the Bragg peak from the maximum of the specific ionization of the HI are determined. This last signal measures the atomic number, Z, of the HI unambiguously.

Gruhn, C.R.

1981-05-01

375

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.; Hill, David R.

2002-02-03

376

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.

2010-01-01

377

Post-operative urinary retention.  

PubMed

Urinary retention is a common complication of surgery and anaesthesia. The risk of post-operative urinary retention is increased following certain surgical procedures and anaesthetic modalities, and with patients' advancing age. Patients at increased risk of post-operative urinary retention should be identified before surgery or the condition should be identified and treated in a timely manner following surgery. If conservative measures do not help the patient to pass urine, the bladder will need to be drained using either an intermittent catheter or an indwelling urethral catheter, which can result in catheter-associated urinary tract infections. This article provides an overview of normal bladder function, risk factors for developing post-operative urinary retention, and treatment options. Guidance drawn from the literature aims to assist nurses in identifying at-risk patients and inform patient care. PMID:24093416

Steggall, Martin; Treacy, Colm; Jones, Mark

2013-10-01

378

Diversity and Retention in Engineering  

ERIC Educational Resources Information Center

|The authors describe three initiatives designed to increase the academic achievement and retention of historically underrepresented students (including females and underrepresented students of color) in engineering. (Contains 2 tables.)|

Davis, Cinda-Sue G.; Finelli, Cynthia J.

2007-01-01

379

Rip Current Retention  

NASA Astrophysics Data System (ADS)

Here, we show for the first time spatially synoptic estimates of rip current flow patterns and Lagrangian transport behavior using a fleet of 30 position-tracking surfzone drifters over multiple rip current systems in Sand City, Monterey Bay, CA. The rotational characteristics of the rip current resulted in a high number of Lagrangian observations that temporally and spatially iterated. Only 10% of the drifters that entered a rip current exited the surf zone resulting in high surfzone retention with maxima occurring in the center of the rip current vortices. Rip current diffusivities in the cross-shore have a periodic response, which modulates at ~300s, the time required for a drifter to complete one revolution around a rip current cell, before decreasing to an asymptotic limit. This suggests that material initially (t<90 s; ?xx = 4.9 - 6.1 m2/s) diffuses, then re-collects, reaching a lower asymptote (t>200 s; ?xx = 0.9 - 2.2 m2/s). The alongshore diffusivity is also periodic, but its asymptotic limit is larger (?yy = 2.8 - 3.9 m2/s), as the drifters spread to neighboring rip currents, whereas the cross-shore offshore limited by the surf zone width, reducing material transport. Asymptotic rip current diffusivities are similar to other asymptotic diffusivities of surf zones that support non-rip current circulation patterns. New thoughts of rip current behaviors are presented suggesting that rip currents retain more floatsom material within the surf zone as opposed to transporting floatsom material offshore.

Thornton, E.; Macmahan, J.; Reniers, A.; Brown, J.; Stanton, T.; Brown, J.

2008-12-01

380

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

381

College Counseling and Student Retention  

Microsoft Academic Search

Although it is commonly believed that college counseling positively affects student retention and further, that there are convincing data and evidence to support such a belief, an extensive literature search found no objective evidence at all on the relationship of a counseling center's conventional one-to-one counseling and therapy activities with short-term student retention. Two program evaluations which attempt to relate

Norman S Giddan; David M Levy; Ronald M Estroff; John C Cline; Erika B Altman; Karen A Isham; Steven J Weiss

1987-01-01

382

Disease risk curves.  

PubMed

ABSTRACT Disease risk curves are simple graphical relationships between the probability of need for treatment and evidence related to risk factors. In the context of the present article, our focus is on factors related to the occurrence of disease in crops. Risk is the probability of adverse consequences; specifically in the present context it denotes the chance that disease will reach a threshold level at which crop protection measures can be justified. This article describes disease risk curves that arise when risk is modeled as a function of more than one risk factor, and when risk is modeled as a function of a single factor (specifically the level of disease at an early disease assessment). In both cases, disease risk curves serve as calibration curves that allow the accumulated evidence related to risk to be expressed on a probability scale. When risk is modeled as a function of the level of disease at an early disease assessment, the resulting disease risk curve provides a crop loss assessment model in which the downside is denominated in terms of risk rather than in terms of yield loss. PMID:23531177

Hughes, G; Burnett, F J; Havis, N D

2013-11-01

383

Retention Rate by Ethnicity. Information Capsule.  

ERIC Educational Resources Information Center

|This document discusses retention rate based on ethnicity for Miami-Dade Community College (M-DCC) for December 2002. The study found that the 2001 Fall-Spring retention rates increased among all ethnic groups. The total college retention rate rose by 2.7 percentage points to 75.2%. Among individual groups, the highest retention rate of 76.9% was…

Baldwin, Anne

384

The retention behaviour of amino acids in hydrophilic interaction liquid chromatography on zwitterionic stationary phases.  

PubMed

The retention behaviour of amino acids was studied in hydrophilic LC on zwitterionic stationary phases. Evaluation of the influences of acetonitrile/water content, ammonium acetate (NH4Ac) concentration and mobile phase pH values was performed. Fourteen amino acids were tested and they were all retained to varying extents, with poorer retention in high water content eluents. The linear relationship between the logarithm of retention factor and log(water content) indicated that adsorption dominated or at least was partly involved in the separation mechanism. Electrostatic and hydrophilic interactions also contributed to the retention of these amino acids under different separation conditions with various mobile phase pH values and NH4Ac concentrations. Thus, the overall retention mechanism could be explained as a combination of adsorption, electrostatic and hydrophilic interactions. The magnitude and contribution of each mechanism is dependent on the nature of the analyte and the separation conditions applied. PMID:23650211

Wu, Ze-Ying; Liu, Junfeng; Shi, Hong; Marriott, Philip J

2013-06-18

385

Dynamics of curved interfaces  

SciTech Connect

Stochastic growth phenomena on curved interfaces are studied by means of stochastic partial differential equations. These are derived as counterparts of linear planar equations on a curved geometry after a reparametrization invariance principle has been applied. We examine differences and similarities with the classical planar equations. Some characteristic features are the loss of correlation through time and a particular behavior of the average fluctuations. Dependence on the metric is also explored. The diffusive model that propagates correlations ballistically in the planar situation is particularly interesting, as this propagation becomes nonuniversal in the new regime.

Escudero, Carlos [Instituto de Ciencias Matematicas, Consejo Superior de Investigaciones Cientificas, C/ Serrano 123, 28006 Madrid (Spain)], E-mail: cel@imaff.cfmac.csic.es

2009-08-15

386

Liquefaction Probability Curves for Surficial Geologic Units  

NASA Astrophysics Data System (ADS)

Liquefaction probability curves that predict the probability of surface manifestations of earthquake-induced liquefaction are developed for 14 different surficial geologic deposits. The geologic units include alluvial fan, beach ridge, river delta, eolian dune, point bar, floodbasin, natural river levee, abandoned river channel, deep-water lake, lagoonal, sandy artificial fill, and valley train deposits. Probability is conditioned on earthquake magnitude and peak ground acceleration. Curves are developed for water table depths of 1.5 and 5.0 m. Probabilities were derived from complementary cumulative frequency distributions of the liquefaction potential index (LPI) that were computed from 935 cone penetration tests. Most of the curves can be fit with a 3-parameter logistic function, which facilitates computations of probability. For natural deposits with a water table at 1.5 m depth and subjected to an M7.5 earthquake with a PGA = 0.25 g, probabilities range from <0.03 for alluvial fan and lacustrine deposits to >0.5 for fluvial point bar, barrier island beach ridge, and deltaic deposits. Retrospective predictions of liquefaction during historical earthquakes based on the curves compare favorably to post-earthquake observations. We also have used the curves to assign ranges of liquefaction probabilities to the susceptibility categories proposed by Youd and Perkins (1978) for different geologic deposits. For the earthquake loading and conditions described above, probabilities range from 0-0.08 for low, 0.09-0.30 for moderate, 0.31-0.62 for high, to 0.63-1.00 for very high susceptibility. Liquefaction probability curves have two primary practical applications. First, the curves can be combined with seismic source characterizations to transform surficial geologic maps into probabilistic liquefaction hazard maps. Geographic specific curves are clearly desirable, but in the absence of such information, generic liquefaction probability curves provide a first approximation of liquefaction hazard. Such maps are useful both to delineate regional liquefaction hazard and to develop regulatory hazard zones. Second, the curves enable preliminary estimates of liquefaction hazard along paths of lifelines. Lifelines typically cross multiple types of surficial geologic deposits. Liquefaction probability curves can be used to estimate the likelihood of liquefaction during the lifetimes of these structures.

Holzer, T. L.; Noce, T. E.; Bennett, M. J.

2009-12-01

387

Study on optimization of moisture retention for golf green rootzone soil mixtures  

Microsoft Academic Search

Most golf course green have been constructed with pure sand or sand-based rootzone mixes. As we know, high sand content provides rapid drainage despite sand’s inefficiency in retaining moisture. However, drainage capability and water retention are both essential elements to the golf course green, and the addition of peat could increase the soil moisture retention, therefore, the research on the

Shao-Hua Yin; Zhi-Hui Chang; Lie-Bao Han; Xin-Shi Lu

388

Nuclear reactor melt-retention structure to mitigate direct containment heating  

Microsoft Academic Search

This patent describes a nuclear reactor melt-retention structure that functions to retain molten core material within a melt retention chamber to mitigate the extent of direct containment heating. The structure being adapted to be positioned within or adjacent to a pressurized or boiling water nuclear reactor containment building at a location such that at least a portion of the melt

N. K. Tutu; T. Ginsberg; J. R. Klages

1991-01-01

389

Nuclear reactor melt-retention structure to mitigate direct containment heating  

Microsoft Academic Search

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

Narinder K. Tutu; Theodore Ginsberg; John R. Klages

1991-01-01

390

Capillary electrochromatography with monolithic stationary phases. III. Evaluation of the electrochromatographic retention of neutral and charged solutes on cationic stearyl-acrylate monoliths and the separation of water-soluble proteins and membrane proteins.  

PubMed

This article, which is closely related to part II, is concerned with the evaluation of the retentive properties of cationic stearyl-acrylate monoliths (i.e. cationic C17 monoliths) over a wide range of elution conditions with various uncharged and charged solutes including proteins. The retention parameters for charged solutes including the retention factor k* observed under capillary electrochromatography conditions and the velocity factor k(ep)*, which reflects the electrophoretic process, were measured for weak, moderate and strong basic compounds. These retention parameters allowed the assessment of the respective contributions from electrophoretic and partitioning separation mechanisms. The cationic C17 monoliths exhibited sufficient hydrophobic interactions with relatively weak basic solutes. Moderate and strong bases showed migration behaviors dominated by their relatively strong electrophoretic mobility with marginal chromatographic partitioning. At low pH, the cationic C17 monoliths allowed the separation of proteins with minimum electrostatic interactions between proteins and the cationic sites on the surface of the stationary phase. The utility of the cationic C17 monoliths was demonstrated in the rapid and efficient separation of two crude extracts of membrane proteins, namely galactosyl transferase and cytochrome c reductase. Short capillary columns (8.5 cm effective length) of the cationic C17 monoliths allowed rapid and efficient separations of neutral and charged pesticides and metabolites, phenylthiohydrantoin amino acids and proteins at the time scale of seconds at relatively high flow velocity. PMID:14604107

Bedair, Mohamed; El Rassi, Ziad

2003-09-26

391

Recession slope curve analysis under human interferences  

NASA Astrophysics Data System (ADS)

To study the base flow recession at the watershed scale, the log-scale plot of - dQ/ dt ˜ Q proposed by Brutsaert and Nieber [10] has been used to estimate the recession parameters, i.e., the slope and interception of the theoretical recession slope curve. The lower envelope or the best fit in some studies is usually used to determine the recession slope curve for natural watersheds. However, human interferences exist in most watersheds around the world. This paper discusses the impact of human interferences, which include groundwater pumping, water diversion and return flow, on the determination of the recession slope curve and the cloud shape of the data points of - dQ/ dt ˜ Q. First, values of - dQ/ dt generated for hypothetical watersheds are analyzed. Then real data for three watersheds in Illinois is analyzed to verify the hypothetical analysis. The placement of the recession slope curve depends on the coexistence and relative amount of the evapotranspiration, groundwater pumping or even water diversion if it exists, and the return flow. When the water consumption rate is small, the recession slope curve can even be located at the upper envelope of the cloud of points representing historical data. These results suggest that the use of the lower envelope as a guideline for estimating recession parameters for watersheds subject to human interferences can result in biased estimates.

Wang, Dingbao; Cai, Ximing

2010-09-01

392

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

393

Uncertainty propagation: Curve fitting  

NSDL National Science Digital Library

Students will learn a sample-variance curve fitting method that can be used to determine whether a set of experimental data appears to have been generated by a model. This method is based on minimizing the reduced chi-squared value. This video includes a reminder to inspect normalized residuals before reporting fitted parameters.

Liao, David

394

Curved Solids Nets  

ERIC Educational Resources Information Center

The transformation of a solid to its net is based on something quite different from simple perceptual impression. It is a mental operation performed by manipulating mental images. The aim of this study was to observe pre-service and in-service teachers' ability to visualize the transformation of a curved solid to its net and vice versa, and to try…

Cohen, Nitsa

2003-01-01

395

RATIONAL NORMAL CURVE  

Microsoft Academic Search

The paper has two goals: the study of the associated graded ring of contracted homogeneous ideals in K(x, y) and the study of the Grobner fan of the ideal P of the rational normal curve in Pd. These two problems are, quite surprisingly, very tightly related. We completely classify the contracted ideals with a Cohen-Macaulay associated graded rings in terms

ALDO CONCA; EMANUELA DE NEGRI; MARIA EVELINA ROSSI

396

The Carnegie Curve  

NASA Astrophysics Data System (ADS)

The Earth's fair weather atmospheric electric field shows, in clean air, an average daily variation which follows universal time, globally independent of the measurement position. This single diurnal cycle variation (maximum around 19UT and minimum around 03UT) is widely known as the Carnegie curve, after the geophysical survey vessel of the Carnegie Institution of Washington on which the original measurement campaigns demonstrating the universal time variation were undertaken. The Carnegie curve's enduring importance is in providing a reference variation against which atmospheric electricity measurements are still compared; it is believed to originate from regular daily variations in atmospheric electrification associated with the different global disturbed weather regions. Details of the instrumentation, measurement principles and data obtained on the Carnegie's seventh and final cruise are reviewed here, also deriving new harmonic coefficients allowing calculation of the Carnegie curve for different seasons. The additional harmonic analysis now identifies changes in the phasing of the maximum and minimum in the Carnegie curve, which shows a systematic seasonal variation, linked to the solstices and equinoxes, respectively.

Harrison, R. Giles

2013-03-01

397

Electrostatic curved electrode actuators  

Microsoft Academic Search

This paper presents the design and performance of an electrostatic actuator consisting of a laterally compliant cantilever beam and a fixed curved electrode, both suspended above a ground plane. A theoretical description of the static behavior of the cantilever as it is pulled into contact with the rigid fixed-electrode structure is given. Two models are presented: a simplified semi-analytical model

Rob Legtenberg; John Gilbert; Stephen D. Senturia; Miko Elwenspoek

1997-01-01

398

HUMAN GROWTH CURVE.  

PubMed

The human growth curve shows two (and only two) outstanding periods of accelerated growth-the circumnatal and the adolescent. The circumnatal growth cycle attains great velocity, which reaches a maximum at the time of birth. The curve of this cycle is best fitted by a theoretical skew curve of Pearson's Type I. It has a theoretical range of 44 months and a standard deviation of 5.17 months. The modal velocity is 10.2 kilos per year. The adolescent growth cycle has less maximum velocity and greater range in time than the circumnatal cycle. The best fitting theoretical curve is a normal frequency curve ranging over about 10 years with a standard deviation of about 21 months and a modal velocity of 4.5 kilos per year. The two great growth accelerations are superimposed on a residual curve of growth which measures a substratum of growth out of which the accelerations arise. This probably extends from conception to 55 years, on the average. It is characterized by low velocity, averaging about 2 kilos per year from 2 to 12 years. It is interpreted as due to many growth operations coincident or closely blending in time. Our curve shows no third marked period of acceleration at between the 3rd and 6th years. The total growth in weight of the body is the sum of the weight of its constituent organs. In some cases these keep pace with the growth of the body as a whole; great accelerations of body growth are due to great accelerations in growth of the constituent organs. In other cases one of the organs of the body (like the thymus gland) may undergo a change in weight that is not in harmony with that of the body as a whole. The development of the weight in man is the resultant of many more or less elementary growth processes. These result in two special episodes of growth and numerous smaller, blending, growth operations. Hypotheses are suggested as to the basis of the special growth accelerations. PMID:19872316

Davenport, C B

1926-11-20

399

Retention of hydrogen in graphite  

SciTech Connect

The retention of hydrogen in POCO AXF-5Q graphite has been measured at room temperature as a function of fluence and flux for H/sub 2//sup +/ ions at energies from 250 to 500 eV provided by a glow discharge. More than 2 x 10/sup 18/ H/cm/sup 2/ has been retained, and no indication of saturation has been observed to a fluence of 5 x 10/sup 19/ H/cm/sup 2/. In this experiment, retention was found to increase linearly with fluence for constant flux. A flux dependence was observed; that is, the retention rate was observed to decrease monotonically as the flux increased. A change-over experiment, deuterium to hydrogen, was conducted; the results show that significant change-over occurs (i.e., about 30% change-over for a fluence of 5 x 10/sup 17/ D/cm/sup 2/).

Langley, R.A.

1986-10-01

400

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 Thièry

2005-01-01

401

Parameterization of multiple Bragg curves for scanning proton beams using simultaneous fitting of multiple curves.  

PubMed

Although Bortfeld's analytical formula is useful for describing Bragg curves, measured data can deviate from the values predicted by the model. Thus, we sought to determine the parameters of a closed analytical expression of multiple Bragg curves for scanning proton pencil beams using a simultaneous optimization algorithm and to determine the minimum number of energies that need to be measured in treatment planning so that complete Bragg curves required by the treatment planning system (TPS) can be accurately predicted. We modified Bortfeld's original analytical expression of Bragg curves to accurately describe the dose deposition resulting from secondary particles. The parameters of the modified analytical expression were expressed as the parabolic cylinder function of the ranges of the proton pencil beams in water. Thirty-nine discrete Bragg curves were measured in our center using a PTW Bragg Peak chamber during acceptance and commission of the scanning beam proton delivery system. The coefficients of parabolic function were fitted by applying a simultaneous optimization algorithm to seven measured curves. The required Bragg curves for 45 energies in the TPS were calculated using our parameterized analytical expression. Finally, the 10 cm width of spread-out Bragg peaks (SOBPs) of beams with maximum energies of 221.8 and 121.2 MeV were then calculated in the TPS and compared with measured data. Compared with Bortfeld's original formula, our modified formula improved fitting of the measured depth dose curves at depths around three-quarters of the maximum range and in the beam entrance region. The parabolic function described the relationship between the parameters of the analytic expression of different energies. The predicted Bragg curves based on the parameters fitted using the seven measured curves accurately described the Bragg curves of proton pencil beams of 45 energies configured in our TPS. When we used the calculated Bragg curves as the input to TPS, the standard deviations of the measured and calculated data points along the 10 cm SOBPs created with proton pencil beams with maximum energies of 221.8 and 121.2 MeV were 1.19% and 1.18%, respectively, using curves predicted by the algorithm generated from the seven measured curves. Our method would be a valuable tool to analyze measured Bragg curves without the need for time-consuming measurements and correctly describe multiple Bragg curves using a closed analytical expression. PMID:22085829

Zhang, Xiaodong; Liu, Wei; Li, Yupeng; Li, Xiaoqiang; Quan, Michelle; Mohan, Radhe; Anand, Aman; Sahoo, Narayan; Gillin, Michael; Zhu, Xiaorong R

2011-11-16

402

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

403

Curve and Surface Interrogation  

Microsoft Academic Search

\\u000a Interrogation is the process of extraction of information from a geometric model. In this chapter we focus on free-form curve and surface\\u000a interrogation. Free form surface, also called sculptured surface, are widely used in scientific and engineering applications.\\u000a For example, the hydrodynamic shape of propeller blades has an important role in marine applications, and the aerodynamic\\u000a shape of turbine blades

Nicholas M. Patrikalakis; Takashi Maekawa

404

Dosimetry of intravenously administered oxygen-15 labelled water in man: a model based on experimental human data from 21 subjects  

Microsoft Academic Search

Models based on uniform distribution of tracer in total body water underestimate the absorbed dose from H215O because of the short half-life (2.04 min) of 15O, which leads to non-uniform distribution of absorbed dose and also complicates the direct measurement of organ retention curves. However, organ absorbed doses can be predicted by the present kinetic model based on the convolution

Terry Smith; Carrison Tong; Adriaan A. Lammertsma; Kenneth R. Butler; Leonard Schnorr; John D. G. Watson; Stuart Ramsay; John C. Clark; Terry Jones

1994-01-01

405

Quantization on Curves  

NASA Astrophysics Data System (ADS)

Deformation quantization on varieties with singularities offers perspectives that are not found on manifolds. The Harrison component of Hochschild cohomology, vanishing on smooth manifolds, reflects information about singularities. The Harrison 2-cochains are symmetric and are interpreted in terms of abelian *-products. This paper begins a study of abelian quantization on plane curves over mathbb{C}, being algebraic varieties of the form {mathbb{C}}^2/R, where R is a polynomial in two variables; that is, abelian deformations of the coordinate algebra mathbb{C}[x,y]/(R). To understand the connection between the singularities of a variety and cohomology we determine the algebraic Hochschild (co)homology and its Barr Gerstenhaber Schack decomposition. Homology is the same for all plane curves mathbb{C}[x,y]/R, but the cohomology depends on the local algebra of the singularity of R at the origin. The Appendix, by Maxim Kontsevich, explains in modern mathematical language a way to calculate Hochschild and Harrison cohomology groups for algebras of functions on singular planar curves etc. based on Koszul resolutions.

Frønsdal, Christian; Kontsevich, Maxim

2007-02-01

406

Short-Term Effects of Grade Retention on the Growth Rate of Woodcock-Johnson III Broad Math and Reading Scores  

ERIC Educational Resources Information Center

|We investigated the effects of grade retention in first grade on the growth of the Woodcock-Johnson broad mathematics and reading scores over three years using linear growth curve modeling on an academically at-risk sample. A large sample (n=784) of first grade children who were at risk for retention was initially identified based on low literacy…

Wu, Wei; West, Stephen G.; Hughes, Jan N.

2008-01-01

407

Meeting Individual Needs Fosters Retention.  

ERIC Educational Resources Information Center

|A 1991 study of non-returning students at Del Mar College (DMC), in Corpus Christi, Texas, revealed that only 37.9% of these students were actual dropouts (i.e., had failed to accomplish their educational goals, and had no plans to take up further study). Retention studies conducted in Texas between 1985 and 1989 have shown that DMC has…

Artman, Johanne I.; Gore, Robert C.

408

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

409

JCC Recruitment, Retention, Attrition Project.  

ERIC Educational Resources Information Center

|In an effort to reduce the class attrition rate of 40% at Jefferson Community College (JCC), and to investigate the entire process of recruitment, retention, and attrition (RRA), a series of four faculty workshops were held. The plan was to look at the RRA process from the student's point of view in terms of four phases: (1) the pre-enrollment…

Horvath, Ronald J.

410

Improving Hunter Recruitment and Retention  

Microsoft Academic Search

Current trends show that despite overall support for hunting, fewer Americans are participating in the activity. Traditional recruitment and retention methods in which hunting families initiate, train, and socialize their children or other family members into hunting tradition are still the primary routes to recruiting and retaining new hunters. With declining numbers of hunters, however, this approach alone will not

Elizabeth L. Ryan; Bret Shaw

2011-01-01

411

Standards, Retention, and Social Promotion.  

ERIC Educational Resources Information Center

Describes origin and elements of the standards movement. Reviews research on grade retention and social promotion and concludes that both are failed strategies to improve student achievement. Describes principal's role in meeting standards. Discusses the use of systemic and classroom interventions to help students meet state standards. (Contains…

Owings, William A.; Kaplan, Leslie S.

2001-01-01

412

Institutionalization of a Retention Model  

NASA Astrophysics Data System (ADS)

Bowie State University and NASA Goddard Space Flight Center have, for the past 10 years, worked diligently together to enhance the science, mathematics, engineering and technology (SMET) domain. Efforts made, because of a Model Institutions for Excellence (MIE) Award, have changed the landscape of the SMET domain by increasing the retention and graduation rates, the number of students entering graduate and professional schools, and the number of students entering SMET related careers for minorities and women. Several initiatives a Scholarship Program, PRISEM Tutoring Center, Safety-net Program, Research emphasis, Focused Mentoring, a Summer Academy for accepted incoming students, a Bridge Program for students needing assistance being admitted to the University, the RISE Program and the Bowie State Satellite Operations and Control Center (BSOCC) provide the nurturing, mentoring, and opportunities for our students. As a result of efforts made, the retention rate has increase to approximately 80%, the graduation rate has increased 40%, and 85% of the SMET students are now interested or entering graduate and professional schools. Successes that have been documented by various assessment activities have led to the institutionalization of the Retention Model of the MIE Initiative. It is anticipated that University-wide application of the retention model will prove the incentives necessary to obtain similar results as the MIE Initiative.

Davis, E. J.; Campbell, A.

2006-05-01

413

Educational Advising for Student Retention.  

ERIC Educational Resources Information Center

Drawing from the literature and research on educational advising and student retention, this handbook provides practical guidelines on advising students, based on five propositions. The propositions are that: (1) educational advisement should be designed to provide accurate, consistent, accessible information for students concerning their progress…

Santa Rita, Emilio

414

Meeting Individual Needs Fosters Retention.  

ERIC Educational Resources Information Center

A 1991 study of non-returning students at Del Mar College (DMC), in Corpus Christi, Texas, revealed that only 37.9% of these students were actual dropouts (i.e., had failed to accomplish their educational goals, and had no plans to take up further study). Retention studies conducted in Texas between 1985 and 1989 have shown that DMC has…

Artman, Johanne I.; Gore, Robert C.

415

Effects on retention of posttraining amphetamine injections in mice: Interaction with pretraining experience  

Microsoft Academic Search

These experiments examined the effects of d-amphetamine on retention of one-trial inhibitory (passive) avoidance training in mice. Water-deprived mice were pretrained to lick from a water spout at the end of a darkened compartment. Footschock was administered during licking after 4, 6, or 7 days of pretraining. Retention performance (latency to lick) was measured 24 h after training. The effects

John W. Haycock; Roderick Buskirk; Paul E. Gold

1977-01-01

416

9 CFR 354.73 - Retention labels.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Retention labels. 354.73 Section 354.73 Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE...Packaging § 354.73 Retention labels. An inspector may use such labels, devices, and methods...

2013-01-01

417

Liquefaction probability curves for surficial geologic deposits  

USGS Publications Warehouse

Liquefaction probability curves that predict the probability of surface manifestations of earthquake-induced liquefaction are developed for 14 different types of surficial geologic units. The units consist of alluvial fan, beach ridge, river delta topset and foreset beds, eolian dune, point bar, flood basin, natural river and alluvial fan levees, abandoned river channel, deep-water lake, lagoonal, sandy artificial fill, and valley train deposits. Probability is conditioned on earthquake magnitude and peak ground acceleration. Curves are developed for water table depths of 1.5 and 5.0 m. Probabilities are derived from complementary cumulative frequency distributions of the liquefaction potential index (LPI) that were computed from 927 cone penetration tests. For natural deposits with a water table at 1.5 m and subjected to a M7.5 earthquake with peak ground acceleration (PGA) ?=? 0.25g, probabilities range from 0.5 for beach ridge, point bar, and deltaic deposits. The curves also were used to assign ranges of liquefaction probabilities to the susceptibility categories proposed previously for different geologic deposits. For the earthquake described here, probabilities for susceptibility categories have ranges of 0–0.08 for low, 0.09–0.30 for moderate, 0.31–0.62 for high, and 0.63–1.00 for very high. Retrospective predictions of liquefaction during historical earthquakes based on the curves compare favorably to observations.

Holzer, Thomas L.; Noce, Thomas E.; Bennett, Michael J.

2011-01-01

418

Retention of phytoplankton by an eddy  

NASA Astrophysics Data System (ADS)

A patch of high phytoplankton biomass, approximately 109 m2 in area, remained apparently stationary off King George Island, South Shetland Islands, over a period of at least 11 days. The patch was centred on an eddy at the apex of a tight meander formed by water passing round the eastern end of King George Island and being turned back immediately by the strong northeastern flow of water within the Bransfield Strait. Chlorophyll a biomass approached 1 g m2 and was concentrated within the top 50 75 m of water. The community consisted mainly of diatoms, which were growing actively. Growth in situ might have been sufficient to generate the observed high biomass from the general concentration of phytoplankton observed locally but only if all production had been retained within the patch. However, elevated biomass downcurrent of the patch suggested that physical retention was only about 50% efficient. It is concluded that the patch was derived from a pulse of high biomass which had been transported into the area and partially retained by the horizontal recirculation of water within the eddy. Dominant diatom species, Odontella weissflogii, Proboscia ‘alata’, Chaetoceros curvisetum and Thalassiosira tumida, were also predominant in a phytoplankton maximum off Brabant Island, upcurrent of the study site. This may have provided the seed population for the patch off King George Island. Vertical migration may have prevented krill accumulation within the eddy and it is concluded that some shallow eddies may partially insulate phytoplankton communities from heavy grazing pressure.

Heywood, R. B.; Priddle, J.

1987-08-01

419

CURVED PHOTON MAPPING: BEYOND THE CURVED RAY TRACING ALGORITHM  

Microsoft Academic Search

Several natural phenomena, such as mirages, are owed to inhomogeneous media in which the index of refraction is not constant, and therefore light travels a curved path. One way to simulate Global Illumination in inhomogeneous media is using a curved ray tracing algorithm, but this approach presents some problems that need to be solved. This paper introduces both a curved

MUÑOZ ORBAÑANOS; GUTIERREZ PEREZ; JIMENEZ CHAPRESTO; SERON ARBELOA; Francisco José

420

Hyperelliptic Curve Cryptosystems: Closing the Performance Gap to Elliptic Curves  

Microsoft Academic Search

For most of the time since they were proposed, it was widely believed that hyperelliptic curve cryptosystems (HECC) carry a substantial performance penalty compared to elliptic curve cryptosystems (ECC) and are, thus, not too attractive for practical applications. Only quite recently improvements have been made, mainly restricted to curves of genus 2. The work at hand advances the state-of-the- art

Jan Pelzl; Thomas J. Wollinger; Jorge Guajardo; Christof Paar

2003-01-01

421

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,…

Spittle, Brian

2013-01-01

422

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

423

Toward a perspective on orthodontic retention?  

Microsoft Academic Search

Retention is one of the most difficult challenges facing the clinician in orthodontics. In this article we collate current knowledge regarding the origin of orthodontic relapse and attempt to rationalize the necessary factors in planning orthodontic retention. Despite extensive research, the various elements leading to relapse of treated malocclusions are incompletely understood, giving rise to wide variation in retention protocols

Colin Melrose; Declan T. Millett

1998-01-01

424

Effective Retention Strategies for Engineering Students  

Microsoft Academic Search

Engineering Programs in the US have been working to improve retention rates of students for many years. Today universities in Europe and other countries are becoming increasingly interested in improving retention and student success. Improving retention rates is especially important in order to increase the nu mber of students who obtain engineering degrees. Many of t he programs developed in

Kerri A. Sleeman; Sheryl A. Sorby

425

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

426

Designing Online Courses to Promote Student Retention  

ERIC Educational Resources Information Center

|Although the issue of student retention is a campus-wide one, it is of special interest in online distance learning courses, where retention rates are reported to be lower than in face-to-face classes. Among the explanations and theories of retention rates in online courses, one that struck us as most useful is a structural one, namely, course…

Dietz-Uhler, Beth; Fisher, Amy; Han, Andrea

2008-01-01

427

AN ORIENTATION COURSE AND COMMUNITY COLLEGE RETENTION  

Microsoft Academic Search

Orientation and retention programs are common in institutions of higher education. The potential association between orientation programs and student retention, particularly within the community college sector, has long been neglected. This study presents an institutional view of a potential associative relationship between an orientation course and student retention measures. A chi-square analysis revealed a significant association among orientation program, student

Dustin C. Derby; Thomas Smith

2004-01-01

428

Evaluating freshmen retention efforts in engineering housing  

Microsoft Academic Search

Freshman engineering retention is a national problem. At Arizona State University, freshmen retention is a major focus of the Office of Student Affairs in the College of Engineering and Applied Sciences (CEAS). The CEAS Fall 2000 freshmen class numbered 969 students. Major programs that have been developed to increase CEAS freshmen retention include engineering residence hall floors and academic and

Mary R. Anderson-Rowland; Joseph E. Urban

2001-01-01

429

Do We Have a Retention Problem ... Or Do We Have a Problem "about" Retention?  

ERIC Educational Resources Information Center

This paper deals with the "problem" of student retention in higher education. But unlike most, this paper focuses not on the problem of retention "per se" but rather on how institutional leaders think about student retention, completion, and success--how the way they frame their concerns about retention can give rise to a different sort of…

Butler, Lawrence

2011-01-01

430

Disk galaxy rotation curves  

NASA Astrophysics Data System (ADS)

We show that simple axisymmetric Newtonian calculation suffices to consistently connect disk galaxy rotation curves to underlying mass distribution and vice versa, without need for any dark matter. To this end, we connect mass density profiles of five galaxies of varying sizes with observed galaxy rotation curves. The five galaxies are: NGC6822 (4.8 kpc), Large Magellanic Cloud (9 kpc), The Milky Way (17 kpc), NGC3198 (30 kpc) and UGC9133 (102.5 kpc). The mass and mass density profiles of these galaxies have been computed using the scientific computing s/w package MATLAB taking the already available velocity profiles of the galaxies as the input, and without considering any dark matter contribution. We have plotted these profiles after computing them according to three different theories of gravity (and dynamics): Newtonian, Modified Newtonian Dynamics (MOND) and Vacuum Modified Gravity. We also consider how the profile due to the Newtonian theory would modify if we use a cosmological constant = 5 × 10^{-56} cm^{-2}. Comparing these mass and mass density profiles, we try to form an idea regarding what could be a realistic theory of gravity and whether we need dark matter to explain the results.

Banhatti, Dilip G.; Datta, Rahul

431

Degree formulae for offset curves  

Microsoft Academic Search

In this paper, we present three different formulae for computing the degree of the offset of a real irreducible affine plane curve C given implicitly, and we see how these formulae particularize to the case of rational curves. The first formula is based on an auxiliary curve, called S, that is defined depending on a non-empty Zariski open subset of

Fernando San Segundo; J. Rafael Sendra

2005-01-01

432

Enumerating singular curves on surfaces  

Microsoft Academic Search

We enumerate the singular algebraic curves in a complete linear system on a smooth projective surface. The system must be suitably ample in a rather precise sense. The curves may have up to eight nodes, or a triple point of a given type and up to three nodes. The curves must also pass through appropriately many general points. The number

Steven Kleiman; Ragni Piene

1999-01-01

433

Titration Curves: Fact and Fiction.  

ERIC Educational Resources Information Center

|Discusses ways in which datalogging equipment can enable titration curves to be measured accurately and how computing power can be used to predict the shape of curves. Highlights include sources of error, use of spreadsheets to generate titration curves, titration of a weak acid with a strong alkali, dibasic acids, weak acid and weak base, and…

Chamberlain, John

1997-01-01

434

Acute urinary retention among astronauts.  

PubMed

Although acute urinary retention (AUR) is not commonly thought of as a life-threatening condition, its presentation in orbit can lead to a number of medical complications that could compromise a space mission. We report on a middle-aged astronaut who developed urinary retention during two spaceflights. On the first mission of note, the astronaut initially took standard doses of promethazine and scopolamine before launch, and developed AUR immediately after entering orbit. For the first 3 d, the astronaut underwent intermittent catheterizations with a single balloon-tipped catheter. Due to the lack of iodine solution on board and the need for the astronaut to complete certain duties without interruption, the catheter was left in place for a total of 4 d. Although the ability to void returned after day 7, a bout of AUR reemerged on day 10, 1 d before landing. On return to Earth, a cystometrogram was unremarkable. During the astronaut's next mission, AUR again recurred for the first 24 h of microgravity exposure, and the astronaut was subsequently able to void spontaneously while in space. This report details the presentation of this astronaut, the precautions that were taken for space travel subsequent to the initial episode of AUR, and the possible reasons why space travel can predispose astronauts to urinary retention while in orbit. The four major causes of AUR--obstructive, pharmacologic, psychogenic, and neurogenic-are discussed, with an emphasis on how these may have played a role in this case. PMID:17511293

Stepaniak, Philip C; Ramchandani, Suneil R; Jones, Jeffrey A

2007-04-01

435

Multipulse phase resetting curves  

NASA Astrophysics Data System (ADS)

In this paper, we introduce and study systematically, in terms of phase response curves, the effect of dual-pulse excitation on the dynamics of an autonomous oscillator. Specifically, we test the deviations from linear summation of phase advances resulting from two small perturbations. We analytically derive a correction term, which generally appears for oscillators whose intrinsic dimensionality is >1. The nonlinear correction term is found to be proportional to the square of the perturbation. We demonstrate this effect in the Stuart-Landau model and in various higher dimensional neuronal models. This deviation from the superposition principle needs to be taken into account in studies of networks of pulse-coupled oscillators. Further, this deviation could be used in the verification of oscillator models via a dual-pulse excitation.

Krishnan, Giri P.; Bazhenov, Maxim; Pikovsky, Arkady

2013-10-01

436

Understanding curved detonation waves  

SciTech Connect

The reaction zone of a detonation wave is very small compared to the dynamic length scale for a typical application. Consequently, it is impractical for numerical calculations to fully resolve the reaction zone. A non-zero reaction zone width is critical to describe curved detonation waves because it affects the wave speed. The curvature effect is the result of an the interaction between the rate of energy release and geometric source terms within the reaction zone. When the reaction zone width is determined by the computational cell size rather than the physical scale, the numerics introduces an artificial curvature effect which frequently dominates the physical effect and leads to mesh dependence of simulations. Modified Hugoniot jump conditions are derived which characterize the curvature effect. They express the conservation laws and are not sensitive to the detailed reaction dynamics but instead depend only on the reaction zone width, and averages of pressure and of mass, momentum and energy densities.

Bukiet, B.G. (New Jersey Inst. of Tech., Newark, NJ (United States)); Lackner, K.S.; Menikoff, R. (Los Alamos National Lab., NM (United States))

1993-01-01

437

Understanding curved detonation waves  

SciTech Connect

The reaction zone of a detonation wave is very small compared to the dynamic length scale for a typical application. Consequently, it is impractical for numerical calculations to fully resolve the reaction zone. A non-zero reaction zone width is critical to describe curved detonation waves because it affects the wave speed. The curvature effect is the result of an the interaction between the rate of energy release and geometric source terms within the reaction zone. When the reaction zone width is determined by the computational cell size rather than the physical scale, the numerics introduces an artificial curvature effect which frequently dominates the physical effect and leads to mesh dependence of simulations. Modified Hugoniot jump conditions are derived which characterize the curvature effect. They express the conservation laws and are not sensitive to the detailed reaction dynamics but instead depend only on the reaction zone width, and averages of pressure and of mass, momentum and energy densities.

Bukiet, B.G. [New Jersey Inst. of Tech., Newark, NJ (United States); Lackner, K.S.; Menikoff, R. [Los Alamos National Lab., NM (United States)

1993-06-01

438

Generating Resources Supply Curves.  

SciTech Connect

This report documents Pacific Northwest supply curve information for both renewable and other generating resources. Resources are characterized as ''Renewable'' and ''Other'' as defined in section 3 or the Pacific Northwest Electric Power Planning and Conservation Act. The following resources are described: renewable: (cogeneration; geothermal; hydroelectric (new); hydroelectric (efficiency improvement); solar; and wind); other (nonrenewable generation resources: coal; combustion turbines; and nuclear. Each resource has the following information documented in tabular format: (1) Technical Characteristics; (2) Costs (capital and O and M); (3) Energy Distribution by Month; and (4) Supply Forecast (energy). Combustion turbine (CT) energy supply is not forecasted because of CT's typical peaking application. Their supply is therefore unconstrained in order to facilitate analysis of their operation in the regional electrical supply system. The generic nuclear resource is considered unavailable to the region over the planning horizon.

United States. Bonneville Power Administration. Division of Power Resources Planning.

1985-07-01

439

Holomorphic curves from matrices  

NASA Astrophysics Data System (ADS)

Membranes holomorphically embedded in flat non-compact space are constructed in terms of the degrees of freedom of an infinite collection of 0-branes. To each holomorphic curve we associate infinite-dimensional matrices which are static solutions to the matrix theory equations of motion, and which can be interpreted as the matrix theory representation of the holomorphically embedded membrane. The problem of finding such matrix representations can be phrased as a problem in geometric quantization, where ?~lP3/R plays the role of the Planck constant and parametrizes families of solutions. The concept of Bergman projection is used as a basic tool, and a local expansion for the action of the projection in inverse powers of curvature is derived. This expansion is then used to compute the required matrices perturbatively in ?. The first two terms in the expansion correspond to the standard geometric quantization result and to the result obtained using the metaplectic correction to geometric quantization.

Cornalba, Lorenzo; Taylor, Washington, IV

1998-12-01

440

Variation of curve number with storm depth  

NASA Astrophysics Data System (ADS)

The NRCS Curve Number (known also as SCS-CN) method is well known as a tool in predicting flood runoff depth from small ungauged catchment. The traditional way of determination the CNs, based on soil characteristics, land use and hydrological conditions, seemed to have tendency to overpredict the floods in some cases. Over 30 year rainfall-runoff data, collected in two small (A=23.4 & 82.4 km2), lowland, agricultural catchments in Center of Poland (Banasik & Woodward 2010), were used to determine runoff Curve Number and to check a tendency of changing. The observed CN declines with increasing storm size, which according recent views of Hawkins (1993) could be classified as a standard response of watershed. The analysis concluded, that using CN value according to the procedure described in USDA-SCS Handbook one receives representative value for estimating storm runoff from high rainfall depths in the analyzes catchments. This has been confirmed by applying "asymptotic approach" for estimating the watershed curve number from the rainfall-runoff data. Furthermore, the analysis indicated that CN, estimated from mean retention parameter S of recorded events with rainfall depth higher than initial abstraction, is also approaching the theoretical CN. The observed CN, ranging from 59.8 to 97.1 and from 52.3 to 95.5, in the smaller and the larger catchment respectively, declines with increasing storm size, which has been classified as a standard response of watershed. The investigation demonstrated also changeability of the CN during a year, with much lower values during the vegetation season. Banasik K. & D.E. Woodward (2010). "Empirical determination of curve number for a small agricultural watrshed in Poland". 2nd Joint Federal Interagency Conference, Las Vegas, NV, June 27 - July 1, 2010 (http://acwi.gov/sos/pubs/2ndJFIC/Contents/10E_Banasik_ 28_02_10. pdf). Hawkins R. H. (1993). "Asymptotic determination of curve numbers from data". Journal of Irrigation and Drainage Division. American Society of Civil Engineers, 119(2). pp. 334-345. ACKNOWLEDGMENTS The investigation described in the paper is part of the research project no. N N305 396238 founded by PL-Ministry of Science and Higher Education. The support provided by this organization is gratefully acknowledged.

Banasik, K.; Hejduk, L.

2012-04-01

441

Automated reasoning about cubic curves.  

SciTech Connect

It is well known that the n-ary morphisms defined on projective algebraic curves satisfy some strong local-to-global equational rules of derivation not satisfied in general by universal algebras. For example, every rationally defined group law on a cubic curve must be commutative. Here we extract from the geometry of curves a first order property (gL) satisfied by all morphisms defined on these curves such that the equational consequences known for projective curves can be derived automatically from a set of six rules (stated within the first-order logic with equality). First, the rule (gL) is implemented in the theorem-proving program Otter. Then we use Otter to automatically prove some incidence theorems on projective curves without any further reference to the underlying geometry or topology of the curves.

Padmanabhan, R.; McCune, W.; Mathematics and Computer Science; Univ. of Manitoba

1995-01-01

442

Incorporating ecological requirement into multipurpose reservoir operating rule curves for adaptation to climate change  

NASA Astrophysics Data System (ADS)

We incorporate ecological requirement into multipurpose reservoir operating rule curves.We explore how multipurpose reservoir operating rule curves adapt to future climate change.Ecological supply water operation will alleviate negative effect of dam on river ecosystem.

Zhou, Yanlai; Guo, Shenglian

2013-08-01

443

Juvenile densities relative to water regime in mainstem reservoirs of the Tennessee River, USA  

USGS Publications Warehouse

Successful reproduction and development of strong year classes of fish in storage reservoirs are commonly associated with reproductive seasons of high water level and extensive flooding. Responses to flooding are likely to be less pronounced or altogether different in mainstem navigation reservoirs that experience limited water level fluctuation. In these reservoirs, water regime characteristics such as timing of flooding, instability of water level, and water retention could supersede the effects of water level. We examined existing data to identify aspects of the water regime that have detectable consequence on juveniles of selected taxa in a sequence of four reservoirs of the Tennessee River that exhibited relatively small annual rises. Empirical models relating density of selected age-0 centrarchids to water regime suggested that descriptors of spring and summer flow through the reservoirs, water level instability, and summer water level were better related to juvenile densities than was spring water level. Different water regimes had different effects on the study species, and presumably other species in the fish communities. Therefore, a diversity of water regimes rather than a rigid rule curve is likely most beneficial to the long-term permanence of the fish assemblages of the study reservoirs. Fixed rule curves produce drawdown zones devoid of vegetation consisting primarily of mudflats of limited ecological value to floodplain species, and maintenance of water levels within the rule curve force operational drops and rises that adversely affect littoral spawners. In developing water management plans, regulatory agencies should consider incorporating managed randomness into rule curves. ?? 2007 Blackwell Publishing Asia Pty Ltd.

Miranda, L. E.; Lowery, D. R.

2007-01-01

444

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

445

Feature grid neural networks for curve partitioning  

Microsoft Academic Search

Presents a neural network method for partitioning image curves into perceptual entities called generic curve segments (GCSs). GCSs are perceptual classes of primitive curve objects, which are qualitative descriptors for grouping curve shapes. The success of GCS classification and curve grouping relies on correctly locating curve partitioning points (CPPs), i.e. points from where the curves are broken down into GCSs.

Mao Tan; Qigang Gao

2000-01-01

446

Impact of various food ingredients on the retention of furan in foods.  

PubMed

Since furan is classified as "possibly carcinogenic to humans," many studies investigated furan concentrations in foods. However, no data are available on the impact of food ingredients on the retention or release of furan from food. These data are important, since they explain the differences in furan removal during domestic food preparation. Furan retention was studied by spiking various samples with D(4)-furan and comparing D(4)-furan evaporation from these samples with comparable aqueous solutions. In addition, furan concentrations were determined. Furan retention caused by starch gels was negligible. Oils caused high furan retention: peak areas of furan in oils ranged from 22 to 25% of the corresponding aqueous solutions. In addition, in coffee, furan retention was mainly caused by the lipophilic fraction. However, since furan retention was also found in defatted coffee and coffee grounds, other coffee constituents also have the ability to retain furan. Peak areas of furan in the headspace of baby foods ranged from 71 to 97% of those in water. In addition, in this case, the highest retention was found in baby foods with added oils. Baby food containing spinach showed the highest furan concentration (172 ppb) as well as the highest furan retention. PMID:19862771

Van Lancker, Fien; Adams, An; Owczarek, Agnieszka; De Meulenaer, Bruno; De Kimpe, Norbert

2009-12-01

447

Estimates of the hydrologic impact of drilling water on core samples taken from partially saturated densely welded tuff  

SciTech Connect

The purpose of this work is to determine the extent to which drill water might be expected to be imbibed by core samples taken from densely welded tuff. In a related experimental study conducted in G-Tunnel, drill water imbibition by the core samples was observed to be minimal. Calculations were carried out with the TOUGH code with the intent of corroborating the imbibition observations. Due to the absence of hydrologic data pertaining directly to G-Tunnel welded tuff, it was necessary to apply data from a similar formation. Because the moisture retention curve was not available for imbibition conditions, the drainage curve was applied to the model. The poor agreement between the observed and calculated imbibition data is attributed primarily to the inappropriateness of the drainage curve. Also significant is the value of absolute permeability (k) assumed in the model. Provided that the semi-log plot of the drainage and imbibition moisture retention curves are parallel within the saturation range of interest, a simple relationship exists between the moisture retention curve, k, and porosity ({phi}) which are assumed in the model and their actual values. If k and {phi} are known, we define the hysteresis factor {lambda} to be the ratio of the imbibition and drainage suction pressures for any saturation within the range of interest. If k and {phi} are unknown, {lambda} also accounts for the uncertainties in their values. Both the experimental and modeling studies show that drill water imbibition by the core has a minimal effect on its saturation state. 22 refs., 6 figs., 2 tabs.

Buscheck, T.A.; Nitao, J.J.

1987-09-01

448

Unwrapping Closed Timelike Curves  

NASA Astrophysics Data System (ADS)

Closed timelike curves (CTCs) appear in many solutions of the Einstein equation, even with reasonable matter sources. These solutions appear to violate causality and so are considered problematic. Since CTCs reflect the global properties of a spacetime, one can attempt to extend a local CTC-free patch of such a spacetime in a way that does not give rise to CTCs. One such procedure is informally known as unwrapping. However, changes in global identifications tend to lead to local effects, and unwrapping is no exception, as it introduces a special kind of singularity, called quasi-regular. This “unwrapping” singularity is similar to the string singularities. We define an unwrapping of a (locally) axisymmetric spacetime as the universal cover of the spacetime after one or more of the local axes of symmetry is removed. We give two examples of unwrapping of essentially 2+1 dimensional spacetimes with CTCs, the Gott spacetime and the Gödel spacetime. We show that the unwrapped Gott spacetime, while singular, is at least devoid of CTCs. In contrast, the unwrapped Gödel spacetime still contains CTCs through every point. A “multiple unwrapping” procedure is devised to remove the remaining circular CTCs. We conclude that, based on the given examples, CTCs appearing in the solutions of the Einstein equation are not simply a mathematical artifact of coordinate identifications. Alternative extensions of spacetimes with CTCs tend to lead to other pathologies, such as naked quasi-regular singularities.

Slobodov, Sergei

2008-12-01

449

Symmetries of curved superspace  

NASA Astrophysics Data System (ADS)

The formalism to determine (conformal) isometries of a given curved super-space was elaborated almost two decades ago in the context of the old minimal formulation for {N}=1 supergravity in four dimensions (4D). This formalism is universal, for it may readily be generalized to supersymmetric backgrounds associated with any supergravity theory formulated in superspace. In particular, it has already been used to construct rigid supersymmetric field theories in 5D {N}=1 , 4D {N}=2 and 3D ( p, q) anti-de Sitter super-spaces. In the last two years, there have appeared a number of publications devoted to the construction of supersymmetric backgrounds in off-shell 4D {N}=1 supergravity theories using component field considerations. Here we demonstrate how to read off the key results of these recent publications from the more general superspace approach developed in the 1990s. We also present a universal superspace setting to construct supersymmetric backgrounds, which is applicable to any of the known off-shell formulations for {N}=1 supergravity. This approach is based on the realizations of the new minimal and non-minimal supergravity theories as super-Weyl invariant couplings of the old minimal supergravity to certain conformal compensators.

Kuzenko, Sergei M.

2013-03-01

450

Calculation of radioimmunoassay standard curves  

Microsoft Academic Search

A method for calculating radioimmunoassay standard curves, based on the theory of Ekins et al., is described. Because a four-parameter model is used, nonlinear standard curves are the result. The calibration curve is fitted to the measured standard points by means of a weighted least-squares method. The program based on this model can be easily processed on a desk-top calculator.

A. J. Naus; P. S. Kuppens; A. Borst

1977-01-01

451

Photosynthetic light-response curves  

Microsoft Academic Search

Gradients in photosynthetic capacity through the leaf affect the shape of the irradiance-response curve. These gradients in photosynthetic capacity were manipulated by restraining leaves in different orientations. The shape or curvature of the light-response curve can be defined by T, where T=0 is a rectangular hyperbola and T=1 is a Blackman curve. Horizontal leaves had the highest T values when

J. R. Evans; I. Jakobsen; E. Ögren

1993-01-01

452

Synthetic RR Lyrae velocity curves  

SciTech Connect

An amplitude correlation between the pulsation velocity curves and visual light curves of ab-type RR Lyrae stars is derived from a large number of RR Lyrae that have high-precision radial-velocity and photometric data. Based on the determined AVp, AV ralation, a synthetic radial-velocity curve for a typical ab-type RR Lyrae star is constructed. This would be of particular use in determining the systemic velocities of RR Lyrae. 17 refs.

Liu, Tianxing (California Univ., Los Angeles (USA) Boston Univ., MA (USA))

1991-02-01

453

Synthetic RR Lyrae velocity curves  

NASA Astrophysics Data System (ADS)

An amplitude correlation between the pulsation velocity curves and visual light curves of ab-type RR Lyrae stars is derived from a large number of RR Lyrae that have high-precision radial-velocity and photometric data. Based on the determined AVp, AV ralation, a synthetic radial-velocity curve for a typical ab-type RR Lyrae star is constructed. This would be of particular use in determining the systemic velocities of RR Lyrae.

Liu, Tianxing

1991-02-01

454

Deuterium Retention in Liquid Lithium  

NASA Astrophysics Data System (ADS)

Flowing liquid Li as a plasma-facing material in a tokamak offers potential advantages over solid materials. The high-thermal conductivity of Li allows heat loads to be effectively removed and erosion lifetime is no longer a significant concern as a flowing liquid surface is self-repairing. In addition to this, it has also been demonstrated that lithium surfaces are effective in providing low-recycling boundaries. Oxygen, carbon and hydrogen are readily gettered by lithium and it is expected that fuel control should also be possible though the retention of deuterium. However, it is not clear that Li, in its liquid state, offers the same low-recycling properties. As part of the liquid-metals research effort being undertaken at the UCSD, we are examining the practicality of fuel control through studies of the retention of deuterium in liquid Li. Samples of solid and liquid Li have been exposed to deuterium plasma in the UCSD PISCES B linear plasma facility and characterized using secondary-ion mass spectrometry (SIMS), x-ray-photoelectron spectroscopy (XPS) and thermal-desorption mass spectrometry (TDS). Results will be presented and discussed at the meeting.

Baldwin, M. J.; Doerner, R. P.; Luckhardt, S. C.; Conn, R. W.; Seraydarian, R.; Whyte, D. G.

2000-10-01