Sample records for water retention curve

  1. Average Soil Water Retention Curves Measured by Neutron Radiography

    SciTech Connect

    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

    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.

  2. Mapping soil water retention curves via spatial Bayesian hierarchical models

    NASA Astrophysics Data System (ADS)

    Yang, Wen-Hsi; Clifford, David; Minasny, Budiman

    2015-05-01

    Soil water retention curves are an important parameter in soil hydrological modeling. These curves are usually represented by the van Genuchten model. Two approaches have previously been taken to predict curves across a field - interpolation of field measurements followed by estimation of the van Genuchten model parameters, or estimation of the parameters according to field measurements followed by interpolation of the estimated parameters. Neither approach is ideal as, due to their two-stage nature, they fail to properly track uncertainty from one stage to the next. In this paper we address this shortcoming through a spatial Bayesian hierarchical model that fits the van Genuchten model and predicts the fields of hydraulic parameters of the van Genuchten model as well as fields of the corresponding soil water retention curves. This approach expands the van Genuchten model to a hierarchical modeling framework. In this framework, soil properties and physical or environmental factors can be treated as covariates to add into the van Genuchten model hierarchically. Consequently, the effects of covariates on the hydraulic parameters of the van Genuchten model can be identified. In addition, our approach takes advantage of Bayesian analysis to account for uncertainty and overcome the shortcomings of other existing methods. The code used to fit these models are available as an appendix to this paper. We apply this approach to data surveyed from part of the alluvial plain of the river Rhône near Yenne in Savoie, France. In this data analysis, we demonstrate how the inclusion of soil type or spatial effects can improve the van Genuchten model's predictions of soil water retention curves.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  4. Laboratory and Field Investigations of Dynamic Effects in Soil Water Retention Curve

    NASA Astrophysics Data System (ADS)

    Chiu, Yung-Chia; Tseng, Yen-Huiang; Ye, Jiun-Yan

    2015-04-01

    The unsaturated soil is a multi-phase system and the embedded physical mechanisms and chemical reactions are very complicated. The characteristics of groundwater flow and mechanisms of mass transport are still ambiguous so far. In order to fully understand the flow and transport in the unsaturated zone, the soil water retention curve plays an important role in description of water flow. However, the measurements and calculations of soil water retention curve are usually obtained under the static condition or steady state (equilibrium), in which the dynamic effects (non-equilibrium) are not considered, and the obtained relationship between capillary pressure and saturation is skeptical. Therefore, the sandbox experiments and field tests will be conducted to discuss the dynamic effects in the soil water retention curve and hysteresis effect in this study. In the laboratory, the relations between capillary pressure, saturation, the rate of change of water content, and dynamic constant are evaluated through different setting of boundary conditions and different sizes of particles. In the field, the tests are conducted to describe the soil water retention curve through the rain simulator and artificial evaporation. Besides, the dynamic dewpoint potentiameter is used to analyze the hysteresis effect of soil samples, and its results are compared with the results obtained from sandbox and field experiments. Finally, through a series of experiments, the relationship between capillary pressure and saturation under the dynamic effects is established, and the associated theories and mechanisms are discussed. The works developed in this study can provide as reference tools for the hydrogeological investigation and contaminated site remediation in the future. Keywords: capillary pressure, saturation, soil water retention curve, hysteresis, sandbox experiment, field test

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

    E-print Network

    Jiao, Jiu Jimmy

    relative air permeability and the measured data. Citation: Kuang, X., and J. J. Jiao (2011), A new model a comprehensive review on laboratory measurement of air permeability. [4] There are basically two categoriesA new model for predicting relative nonwetting phase permeability from soil water retention curves

  6. Analysis of physical quality of soil using the water retention curve: validity of the S-index

    E-print Network

    Paris-Sud XI, Université de

    1 Analysis of physical quality of soil using the water retention curve: validity of the S Among the various soil indicators established in order to discuss physical properties of soils is the S the physical properties of soil using a water retention curve plotted with an arithmetic expression of suction

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

    NASA Astrophysics Data System (ADS)

    Smagin, A. V.

    2012-04-01

    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.

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

    PubMed Central

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

    2013-01-01

    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

  9. Scale effect on the water retention curve of a volcanic ash

    NASA Astrophysics Data System (ADS)

    Damiano, Emilia; Comegna, Luca; Greco, Roberto; Guida, Andrea; Olivares, Lucio; Picarelli, Luciano

    2015-04-01

    During the last decades, a number of flowslides and debris flows triggered by intense rainfall affected a wide mountainous area surrounding the "Campania Plain" (southern Italy). The involved slopes are constituted by shallow unsaturated air-fall deposits of pyroclastic nature, which stability is guaranteed by the contribution of suction on shear strength. To reliably predict the onset of slope failure triggered by critical precipitations, is essential to understand the infiltration process and the soil suction distribution in such granular deposits. The paper presents the results of a series of investigation performed at different scales to determine the soil water retention curve (SWRC) of a volcanic ash which is an es-sential element in the analysis of the infiltration processes. The soil, a silty sand, was taken at Cervinara hillslope, 30 km East of Naples, just aside an area which had been subjected to a catastrophic flowslide. The SWRC was obtained through: - standard tests in a suction-controlled triaxial apparatus (SCTX), in a pressure plate and by the Wind technique (1968) on small natural and reconstituted soil samples (sample dimensions in the order of the 1•10-6m3) ; - infiltration tests on small-scale model slopes reconstituted in an instrumented flume (sample dimensions in the order of 5•10-3m3); - suction and water content monitoring at the automatic station installed along the Cervinara hillslope. The experimental points generally were defined by coupling suction measurements through jet-fill tensiometers and water content through TDR probes installed close each others. The obtained data sets individuate three different curves characterized by different shapes in the transition zone: at larger volume element dimensions correspond curves which exhibit steeper slopes and lower values of the water content in the transition zone. This result confirms the great role of the volume element dimensions in the de-termination of hydraulic characteristics of the soil which cannot be neglected if a reli-able prediction of the slope behaviour has to be done.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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 the transient evaporation method two tensiometers with a measurement range between 0 and 850 hPa are installed at a depth of 1.25 cm and 3.75 cm in a sample of 5 cm in height; the mean values of the two tensiometers and the water contents measured by weighing are used to obtain the water retention curve. The steady-state method employs a tension table (sand box) at tensions below 100 hPa and a pressure extractor at tensions between 300 hPa and 15,000 hPa; the water content is measured by weighing after the sample has equilibrated at the tension value set on the table or plate. First results of both methods suggest that the soil samples release water over the entire tension range measured. In particular, the release of water at very low tension values may suggest the presence of macropores. Despite the generally good agreement between the two methods, the values appear to deviate systematically close to saturation. This is potentially caused by the large relative error of the tension measurement close to saturation. Alternatively, the different size of the samples used for the evaporation experiment (250 ccm) and the steady-state method (100 ccm) might play a role. Because of the limited measurement range of the tensiometers used for the evaporation method, the measured curve must be extrapolated between 850 hPa and 15,000 hPa to allow comparison with the steady-state method. To this end, it was attempted to match the Brooks-Corey, the Van-Genuchten, and a bimodal Van-Genuchten retention function to the data from the evaporation experiments. This involves a simultaneous fit of both water-retention and hydraulic-conductivity function. Only the bimodal Van-Genuchten model was found to be able to produce satisfactory fits to the data. The extrapolated water retention curves, however, do not match the data from the steady-state method. This suggests that alternative soil hydraulic functions are needed to provide an adequate representation of the water retention characteristics of the loamy-sandy soils considered in this investigation.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  12. Water retention of arctic zone soils (Spitsbergen)

    NASA Astrophysics Data System (ADS)

    Melke, J.; Witkowska-Walczak, B.; Bartmi?ski, P.

    2013-12-01

    The water retention characteristics of the arctic zone soils ((TurbicCryosol (Skeletic), TurbicCryosols (Siltic, Skeletic) and BrunicTurbicCryosol (Arenic)) derived in different micro-relief forms were determined. Water retention curves were similar in their course for the mud boils, cell forms, and sorted circles ie for TurbicCryosols. For these forms, the mud boils showed the highest water retention ability, whereas the sorted circles - the lowest one. Water retention curves for the tundra polygons (Brunic TurbicCryosol, Arenic) were substantially different from these mentioned above. The tundra polygons were characterized by the lowest bulk density of 1.26 g cm-3, whereas the sorted circles (TurbicCryosol, Skeletic) - the highest: 1.88 g cm-3. Total porosity was the highest for the tundra polygons (52.4 and 55.5%) and the lowest - for the sorted circles (28.8 and 26.2%). Pore size distribution of the investigated soils showed that independently of depths, the highest content of large and medium pores was noticed for the tundra polygons ie 21.2-24.2 and 19.9-18.7%, respectively. The lowest content of large pores was observed for the cell forms (6.4-5.9%) whereas the mud boils exhibited the lowest amount of medium sized pores (12.2-10.4%) (both TurbicCryosols Siltic, Skeletic). The highest content of small pores was detected in the mud boils - 20.4 and 19.0%.

  13. Water retention and gas relative permeability of two industrial concretes

    SciTech Connect

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

    2012-07-15

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

  14. Analysis of Soil Water Retention Data Using Artificial Neural Networks

    Microsoft Academic Search

    Sharad K. Jain; Vijay P. Singh

    2004-01-01

    Many studies of water flow and solute transport in the vadose zone require estimates of the unsaturated soil hydraulic properties, including the soil water retention curve ~WRC! describing the relationship between soil suction and water content. An artificial neural network ~ANN! approach was developed to describe the WRC using observed data from several soils. The ANN approach was found to

  15. Estimating In-situ Soil-Water Retention and Field Water Capacity in Two Contrasting Soil Textures

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A priori knowledge of the in-situ soil field water capacity (FWC) and the soil-water retention curve for soils is important for the effective irrigation management and scheduling of many crops. The primary objective of this study was to estimate the in-situ FWC using the soil-water retention curve d...

  16. In-situ Field Capacity and Soil Water Retention Measurements in Two Contrasting Soil Textures

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Knowledge of the in-situ field capacity and soil-water retention curve for soils is important for effective irrigation management and scheduling. The primary objective of this study was to estimate in-situ field capacity and soil water retention curves in the field using continually monitoring soil ...

  17. In-situ field capacity and soil water retention measurements in two contrasting soil textures

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Knowledge of the in-situ field capacity and soil-water retention curve for soils is important for effective irrigation management and scheduling. The primary objective of this study was to estimate in-situ field capacity and soil water retention curves in the field using continually monitoring soil ...

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  19. Water retention capacity of tissue cultured plants

    Microsoft Academic Search

    Klerk de G. J. M; F. Wijnhoven

    2005-01-01

    Leaves rapidly close their stomata after detachment resulting in a strong reduction of water loss. It has been reported that detached leaves of in vitro produced plants show continuous water loss indicating that they are unable to close the stomata properly and\\/or that their cuticle is malfunctioning. We examined the water retention capacity (WRC) of detached primary leaves of in

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

    NASA Astrophysics Data System (ADS)

    Ebel, Brian A.

    2012-12-01

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

  1. Upscaled soil-water retention using van Genuchten's function

    USGS Publications Warehouse

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

    1996-01-01

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

  2. Estimation of hydraulic conductivities of Yucca Mountain tuffs from sorptivity and water retention measurements

    SciTech Connect

    Zimmerman, R.W.; Bodvarsson, G.S.

    1995-06-01

    The hydraulic conductivity functions of the matrix rocks at Yucca Mountain, Nevada, are among the most important data needed as input for the site-scale hydrological model of the unsaturated zone. The difficult and time-consuming nature of hydraulic conductivity measurements renders it infeasible to directly measure this property on large numbers of cores. Water retention and sorptivity measurements, however, can be made relatively rapidly. The sorptivity is, in principle, a unique functional of the conductivity and water retention functions. It therefore should be possible to invert sorptivity and water retention measurements in order to estimate the conductivity; the porosity is the only other parameter that is required for this inversion. In this report two methods of carrying out this inversion are presented, and are tested against a limited data set that has been collected by Flint et al. at the USGS on a set of Yucca Mountain tuffs. The absolute permeability is usually predicted by both methods to within an average error of about 0.5 - 1.0 orders of magnitude. The discrepancy appears to be due to the fact that the water retention curves have only been measured during drainage, whereas the imbibition water retention curve is the one that is relevant to sorptivity measurements. Although the inversion methods also yield predictions of the relative permeability function, there are yet no unsaturated hydraulic conductivity data against which to test these predictions.

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

    E-print Network

    Paris-Sud XI, Université de

    1 Running heading: Water retention properties of the clay in clayey soils Water retention properties of the clay in soils developed on clayey sediments: Significance of parent material and soil of clayey subsoils horizons according to the variation of clay characteristics. The horizons studied

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

    USGS Publications Warehouse

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

    1999-01-01

    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.

  5. 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)

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

    2013-04-01

    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

  6. Determination of water retention in stratified porous materials

    USGS Publications Warehouse

    Constantz, J.

    1995-01-01

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

  7. Evaluation of the Arya-Paris model for estimating water retention characteristics of lignitic mine soils

    SciTech Connect

    Buczko, U.; Gerke, H.H. [Brandenburg University of Technology, Cottbus (Germany)

    2005-07-01

    Mine soil materials may be viewed as man-made systems that consist of spatially disordered soil and sediment components, which are in an initial stage of soil development. A question is whether methods and approaches developed for natural soils, may also be used for such artificially created soil materials. The applicability of the Arya and Paris pedotransfer function to obtain hydraulic properties from the particle size distribution and bulk density was tested for lignitic mine soil material of the Lusatian Lignite Mining District in eastern Germany. The scaling factor a in this model was evaluated by (I) fitting of the water retention curves estimated with the Arya-Paris model (APM) to measured water retention data and (ii) interpretation of a as a fractal dimension of the pore channels and derivation of this fractal dimension from the fractal dimension of the particle size distribution. The two tested fractal approaches resulted in relatively inaccurate predictions of the water content. The use of a single fitted a value for each depth yielded a values between 1.05 and 1.47. Because of the inability of the APM to account for residual water contents in this sandy soil material, a correction was applied. The cumulative mass fraction fractal method did not improve the estimation in comparison with the retention curves calculated with a constant a value of 1.38. The closest fits with the data were obtained by using a variable a value that depended on the particle size. The accuracy of the predictions of the APM in the higher suction range could be improved (lower mean deviations and root mean square deviations of water content) by using a linear water content-dependent correction factor. Better estimates of water retention in the relatively dry range may be significant for simulation of water budgets of mine spoil sites in the Lusatian Mining District.

  8. Modelling soil water retention using support vector machines with genetic algorithm optimisation.

    PubMed

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

    2014-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  10. INFLUENCE OF CATION LEACHING ON WATER RETENTIVITY OF DRINKING WATER SLUDGE

    NASA Astrophysics Data System (ADS)

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

    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.

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

    Microsoft Academic Search

    Orlando Silva; Jordi Grifoll

    2007-01-01

    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,

  12. Assessment of Stormwater Retention Basin Water Quality in Winnipeg, Canada

    Microsoft Academic Search

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

    2003-01-01

    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

  13. Phosphorus Retention Mechanisms of a Water Treatment Residual

    Microsoft Academic Search

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

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

  15. 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...

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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 and 200oC and non pre-heated samples (20oC) from a single surface soil profile down to 25 cm depth. Moreover, the pre-heated samples were used to investigate the effects of pre-heat treatment and hydrophobic severity on soil-water retention properties. We first assessed the degree of water repellency for pre-heated samples by the Water Droplet Penetration Time test and Molarity of Ethanol Droplet test and categorized the water repellency into four different classes (extremely, severely, strongly and non-WR) as proposed by Bisdom et al. (1993). The depth profiles of soil organic carbon (SOC) content for the pre-heated samples were also measured. Results showed the categorized WR classes changed depending on pre-heated temperatures and residual SOC contents. For top surface soil with 0-5cm depth, pre-heated samples at 105, 125, 150 and 175oC exhibited extremely WR, pre-heated samples at 60oC exhibited severely WR, non pre-heated samples (20oC) exhibited strongly WR, and pre-heated samples at 200oC exhibited non-WR. Moreover, the threshold value of SOC above which WR occurs was found to be around 7.4% based on the measured WR classes and SOC profiles. The water supply/drainage controlled hanging column setup equipped with a newly-developed mini tensiometer-TDR coil probe (5 cm in length and 0.5 cm in diameter) was used to measure wetting and drying processes of the soil-water retention curves (SWRCs) for the pre-heated samples. Results showed that the SWRCs on the wetting process were highly affected by the degree of water repellency. Clear water-entry pressures (hwe) were observed in the SWRCs for the preheated samples categorized as extremely and severely WR and the measured hwe values were between -1.5 and 2 cm H2O.

  17. Water Retention and Rheology of Ti-doped, Synthetic Olivine

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  18. Hamerschlag Hall Green Roof Storm Water Retention and Runoff Reduction Performance Lucheng Chen

    E-print Network

    Andrews, Peter B.

    Hamerschlag Hall Green Roof Storm Water Retention and Runoff Reduction Performance ......................................................................................................................... 2 2. Hamerschlag Hall Green Roof ............................................................................................................................ 6 3.2. Ultrasonic Sensors

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  20. Water Retention and Structure Stability in Smectitic or Kaolinitic Loam and Clay Soils Affected by Polyacrylamide Addition

    NASA Astrophysics Data System (ADS)

    Mamedov, Amirakh; Levy, Guy

    2015-04-01

    Studying the effects of polyacrylamide (PAM) on soil aggregate and structure stability is important in developing effective soil and water conservation practices and in sustaining soil and water quality. Five concentrations of an anionic PAM (0, 25, 50, 100 and 200 mg L-1) with a high molecular weight were tested on loam and clay soils having either a predominant smectitic or kaolinitic clay mineralogy. The effects of the PAM and of soil texture on soil water retention at near saturation and on aggregate and structure stability were investigated using the high energy moisture characteristic (HEMC) method. The S-shaped water retention curves obtained by the HEMC method were characterized by the modified van Genuchten (1980) model that provided: (i) the model parameters ? and n, which represent the location of the inflection point and the steepness of the water retention curve, respectively; and (ii) the soil structure index, SI =VDP/MS, where VDP is the volume of drainable pores, an indicator of the quantity of water released by a soil over the range of applied suctions (0-5 J kg-1), and MS is the modal suction representing the most frequent pore sizes (> 60 ?m). In general, the treatments tested (clay mineralogy, soil type and PAM concentration) resulted in: (i) a considerable modification of the shape of the water retention curves as indicated by the changes in the ? and n values; and; (ii) substantial effects on the stability indices and other model parameters. The contribution of PAM concentration to soil structure stability depended on the clay mineralogy, being more effective in the smectitic soils than in the kaolinitic ones. Although kaolinitic soils are usually more stable than smectitic soils, when the latter were treated with PAM (25-200 mg L-1) the opposite trend was observed. In the loam soils, increasing the PAM concentration notably decreased the differences between values of the stability indices of the smectitic and kaolinitic samples. The results suggest that determining the efficacy of different PAM applications in the field in improving water retention and soil structure is complex. Therefore soil properties (clay mineralogy, soil texture) and field conditions (moisture content) should be considered when determining the optimal rate of PAM application. The mechanisms responsible for PAM-soil interaction impacts on soil structure, stability indices and model parameters are discussed in the paper.

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

    E-print Network

    Perfect, Ed

    relative permeability by direct application of measured soil water retention data without any fitting] Because measurement of relative permeability is dif- ficult, attempts to predict this function from is an alternative approach to predict relative permeability from measured water retention data [Fischer and Celia

  2. REGIONAL SOIL WATER RETENTION IN THE CONTIGUOUS US: SOURCES OF VARIABILITY AND VOLCANIC SOIL EFFECTS

    EPA Science Inventory

    Water retention of mineral soil is often well predicted using algorithms (pedotransfer functions) with basic soil properties but the spatial variability of these properties has not been well characterized. A further source of uncertainty is that water retention by volcanic soils...

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

    SciTech Connect

    Bai, Yuanyuan; Xiang, Feng; Wang, Hong, E-mail: hwang@mail.xjtu.edu.cn, E-mail: suo@seas.harvard.edu [Electronic Materials Research Laboratory, School of Electronics and Information Engineering, Xi'an Jiaotong University, Xi'an 710049 (China); Chen, Baohong; Zhou, Jinxiong [State Key Laboratory for Strength and Vibration of Mechanical Structures, International Center for Applied Mechanics and School of Aerospace, Xi'an Jiaotong University, Xi'an 710049 (China); Suo, Zhigang, E-mail: hwang@mail.xjtu.edu.cn, E-mail: suo@seas.harvard.edu [School of Engineering and Applied Sciences, Kavli Institute of Bionano Science and Technology, Harvard University, Cambridge, Massachusetts 02138 (United States)

    2014-10-13

    Polyacrylamide hydrogels containing salt as electrolyte have been used as highly stretchable transparent electrodes in flexible electronics, but those hydrogels are easy to dry out due to water evaporation. Targeted, we try to enhance water retention capacity of polyacrylamide hydrogel by introducing highly hydratable salts into the hydrogel. These hydrogels show enhanced water retention capacity in different level. Specially, polyacrylamide hydrogel containing high content of lithium chloride can retain over 70% of its initial water even in environment with relative humidity of only 10% RH. The excellent water retention capacities of these hydrogels will make more applications of hydrogels become possible.

  4. Enhancing the Effectiveness of Heuristic Rule Curves for Water

    E-print Network

    Painter, Kevin

    Enhancing the Effectiveness of Heuristic Rule Curves for Water Supply Reservoir Operation Adebayo economic benefits from the ubiquitous water resources Raise international profile of the nation as world leader in water management practices Develop a water centre of expertise with international reach

  5. Retention of radium from thermal waters on sand filters and adsorbents

    Microsoft Academic Search

    C. Elejalde; M. Herranz; R. Idoeta; F. Legarda; F. Romero; A. Baeza

    2007-01-01

    This study was focussed on laboratory experiences of retention of radium from one thermal water on sand filters and adsorbents, trying to find an easy method for the elimination in drinkable waters polluted with this natural radio-nuclide. A thermal water from Cantabria (Spain) was selected for this work.Retention experiences were made with columns of 35mm of diameter containing 15cm layers

  6. Validity of the centrifuge method for determining the water retention properties of tropical soils

    E-print Network

    Paris-Sud XI, Université de

    1 Validity of the centrifuge method for determining the water retention properties of tropical.Bruand@univ-orleans.fr (A. Bruand) ABSTRACT This study compared the centrifuge and pressure plate methods with appropriate retention recorded by using the pressure plate and centrifuge methods. The results showed good agreement (R2

  7. Comparison of the lateral retention forces on sessile and pendant water drops on a solid surface

    E-print Network

    Rafael de la Madrid; Taylor Whitehead; George Irwin

    2015-05-15

    We present a simple experiment that demonstrates how a water drop hanging from a Plexiglas surface (pendant drop) experiences a lateral retention force that is comparable to, and in some cases larger than, the lateral retention force on a drop resting on top of the surface (sessile drop). The experiment also affords a simple demonstration of the Coriolis effect in two dimensions.

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

    E-print Network

    Suo, Zhigang

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    E-print Network

    Paris-Sud XI, Université de

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

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

    E-print Network

    Marshall, Hans-Peter

    aspect retain as much as 25% more water at any given soil water pressure than samples from the south methods are commonly used to describe the distribution of soil moisture (Famiglietti et al., 1998; GraysonAspect influences on soil water retention and storage I. J. Geroy,1 M. M. Gribb,2 H. P. Marshall,3

  12. Primer on Condition Curves for Water Mains

    EPA Science Inventory

    ABSTRACT The development of economical tools to prioritize pipe renewal based upon structural condition and remaining asset life is essential to effectively manage water infrastructure assets for both large and small diameter pipes. One tool that may facilitate asset management...

  13. Study of CPAM\\/ bentonite microparticle retention system on reducing pollution load of papermaking white water

    Microsoft Academic Search

    Sha Li-zheng; Zhao Hui-fang

    2010-01-01

    In order to investigate the effects of CPAM\\/bentonite microparticle retention system on reducing pollution load of papermaking white water, the dynamic drainage jar was used to simulate the wet end of low grammage fresh-keeping case board production. The turbidity and CODcr of the filtrate were measured to express the pollution load of white water. Results showed that the turbidity and

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

    Microsoft Academic Search

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

    2010-01-01

    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

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

    E-print Network

    Paris-Sud XI, Université de

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

  16. Chromatographic impulse response technique with curve fitting to measure binary diffusion coefficients and retention factors using polymer-coated capillary columns

    Microsoft Academic Search

    Chang Yi Kong; Toshitaka Funazukuri; Seiichiro Kagei

    2004-01-01

    The theoretical basis of a Gaussian-like approximate solution was applied to a chromatographic impulse response technique with curve fitting for measuring binary diffusion coefficients and retention factors using a polymer-coated capillary column. The formulae were derived for evaluating both the accuracy of the approximate solution and the sensitivity of the parameters. The validity of the solution also was confirmed experimentally

  17. Testing a full-range soil-water retention function in modeling water potential and temperature

    USGS Publications Warehouse

    Andraski, B.J.; Jacobson, E.A.

    2000-01-01

    Recent work has emphasized development of full-range water-retention functions that are applicable under both wet and dry soil conditions, but evaluation of such functions in numerical modeling has been limited. Here we show that simulations using the Rossi-Nimmo (RN) full-range function compared favorably with those using the common Brooks-Corey function and that the RN function can improve prediction of water potentials in near-surface soil, particularly under dry conditions. Simulations using the RN function also improved prediction of temperatures throughout the soil profile. Such improvements could be important for calculations of liquid and vapor flow in near-surface soils and in deep unsaturated zones of arid and semiarid regions.

  18. Effect of boundary conditions on measured water retention behavior within soils

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  19. PREVENTING LOSS AND RESTORING WATER RETENTION VALUES TO PULP BY FIBER LOADING

    E-print Network

    Abubakr, Said

    PREVENTING LOSS AND RESTORING WATER RETENTION VALUES TO PULP BY FIBER LOADING John H. Klungness Gifford Pinchot Drive Madison, WI 53705-2398 ABSTRACT Significant paper strength loss occurs when never-dried bleached kraft pulps are dried prior to paper manufacture. This loss in strength is a problem for the use

  20. Hysteresis of Soil Point Water Retention Functions Determined by Neutron Radiography

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  1. 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...

  2. An Empirical Test of Environmental Kuznets Curve for Water Pollution

    Microsoft Academic Search

    Krishna P. Paudel; Hector Zapata; Dwi Susanto

    2005-01-01

    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

  3. Effects of Ranchland Water Retention on Water and Nutrient Discharges in the Lake Okeechobee basin

    NASA Astrophysics Data System (ADS)

    Shrestha, N. K.; Shukla, S.; Hendricks, G.

    2014-12-01

    A long-term study was conducted for runoff and water quality evaluation of the water retention (WR) best management practice (BMP) implemented at two pastures (sites1 and 2) in a ranch in the Lake Okeechobee (LO) watershed, Florida. The BMP was implemented by raising the spillage levels using drainage structures in the ditch that drained the wetland and upland areas. Four-year pre-BMP and 5-year post-BMP data from Site 1 and 3-year pre-BMP and 6-year post-BMP data from Site 2 were used to evaluate the BMP. We compared runoff, Total phosphorus (TP) and Total nitrogen (TN) loads and concentrations between pre- and post-BMP periods. Compared to pre-BMP, annual post-BMP runoff reduced for Site 1 (60%) and Site 2 (54%). These reductions were only statistically significant for Site 2 (p = 0.096). For the wetter part of the rainy season (July-October), when damaging excessive flows to the LO occur, the post-BMP runoff reduced significantly (p= 0.049) for Site 1 but not for Site 2. Reductions were mainly due to increased water storage while the reductions in nutrient loads and average concentrations were due to reduced runoff volume as well as P retention by soil and plants. Despite reductions in average concentrations, the wet-season post-BMP TP flow weighted concentration (FWC) increased significantly (p= 0.05) at Site 1. Increased TP FWC was likely due to increased inundation in wetland and its connectivity with upland pasture during the post-BMP period. This connectivity increased the surface transport of P, the preferred mode for particulate and dissolved P transport. Unlike Site 1, the TP FWC at Site 2 decreased significantly (p = 0.002) during the wet season due to absence of P hotspots and their connectivity to the wetland. Results indicate that while pasture WR can reduce runoff from the ranchlands, it may increase the TP loads depending on the topographic and drainage characteristics and presence of P hotspots within a ranch.

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

    SciTech Connect

    Zhang, Z. F.

    2011-11-04

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

  5. Water retention of treated stratum corneum measured by a coupling method: thermal desorption-mass spectrometry.

    PubMed

    Gournay, A; Navarro, R; Mathieu, J; Riviere, M

    1995-08-01

    Synopsis A thermal desorption autosampler coupled to a mass spectrometer has been used to measure the in vitro water retention of human stratum corneum as a function of treatment applied. Samples were treated with ingredients possessing good hygroscopic properties which are used in the formulation of moisturizing creams. After being treated, stratum corneum samples were dried and rehydrated and then analysed. The paper describes the method used to quantify their hygroscopic capacity in terms of the percentage of water retained. Ten humectants were examined, of which urea, glycerine, ammonium lactate and a new salt of an alpha-hydroxy acid were found to have the highest activities. This method can also be used to quantify the water retention capacity of various types of pathological skin such as ichthyosis and psoriasis. PMID:19245485

  6. Applying application of aerial photos to estimate a retention volume of Chi-Shui river water in Taiwan

    NASA Astrophysics Data System (ADS)

    Chang, I.; Zheng, Y.; Huang, Y.; Huang, S.; Wen, J.

    2013-12-01

    In groundwater hydrology, retention volume of water is an important parameter for recharge. However, get value of retention volume of river water is not efficiency. In this paper, we used the fixed wing Unmanned Aerial Vehicles(UAVs) (swinglet CAM; senseFly Ltd., Switzerland) to collect images of Chi-Shui river in Taiwan. We also used these images to make aerial photos to estimate retention volume of river. Our interesting area is channel of Chi-Shui river located in Changhua and Yuunlin regions, Taiwan. We find the change obviously at river of terrain features. Taking aerial photo with Geographic Information System(GIS) together can make relief map of river landforms. Because we can get the information from this relief map, we estimate retention volume by three steps. Firstly, we build a relief map before retention. Secondly, building other one after retention. Finally, to compare with two period of relief map and get the retention volume of river water by GIS. In conclusion, we found a retention volume in this method. We can take advantage to the data, which is in used our study, can get a new retention volume immediately.

  7. Developing joint probability distributions of soil water retention characteristics

    Microsoft Academic Search

    Robert F. Carsel; Rudolph S. Parrish

    1988-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    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.

  9. A new water retention and hydraulic conductivity model accounting for contact angle

    NASA Astrophysics Data System (ADS)

    Diamantopoulos, Efstathios; Durner, Wolfgang

    2013-04-01

    The description of soil water transport in the unsaturated zone requires the knowledge of the soil hydraulic properties, i.e. the water retention and the hydraulic conductivity function. A great amount of parameterizations for this can be found in the literature, the majority of which represent the complex pore space of soils as a bundle of cylindrical capillary tubes of various sizes. The assumption of zero contact angles between water and surface of the grains is also made. However, these assumptions limit the predictive capabilities of these models, leading often to enormous errors in the prediction of water dynamics in soils. We present a pore scale analysis for equilibrium liquid configurations (retention) in angular pores taking the effect of contact angle into account. Furthermore, we propose an alternative derivation of the hydraulic conductivity function, again as a function of the contact angle, assuming flow perpendicular to pore cross sections. Finally, we upscale our model from the pore to the sample scale by assuming a gamma statistical distribution of the pore sizes. Closed form expressions are derived for both sample water retention and conductivity functions. The new model was tested against experimental data from multistep inflow/outflow (MSI/MSO) experiments for a sandy material. They were conducted using ethanol and water as the wetting liquid. Ethanol was assumed to form a zero contact angle with the soil grains. The proposed model described both imbibition and drainage of water and ethanol very well. Lastly, the consideration of the contact angle allowed the description of the observed hysteresis.

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

    E-print Network

    Hannink, Ryan Christopher

    2007-01-01

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

  11. Comment on "A model for soil surface evaporation based on Campbell's retention curve" by G. Zarei, M. Homaee, A.M. Liaghat, A.H. Hoorfar

    NASA Astrophysics Data System (ADS)

    Sadeghi, Morteza

    2015-06-01

    Zarei et al. (2010) developed an analytical solution to soil evaporation under conditions of a falling (or fluctuating) water table (WT). They described the soil evaporation rate as a function of water table depth drawdown and soil physical properties (e.g. Campbell's retention model parameters). I want to demonstrate how the basic assumptions used in the derivation of this solution are not valid and thus the analytical model is in need of correction.

  12. Retention of contaminants in northern natural peatlands treating mine waste waters

    NASA Astrophysics Data System (ADS)

    Palmer, Katharina; Ronkanen, Anna-Kaisa; Klöve, Björn

    2014-05-01

    The mining industry in Finland is growing, leading to an increasing number of working and proposed mine sites. As a consequence, the amount of mine waste waters created is likewise increasing. This poses a great challenge for water management and purification, as these mine waste waters can lead to severe environmental and health consequences when released to receiving water bodies untreated. In the past years, the use of natural peatlands for cost-effective passive waste water treatment has been increasing. In this study, the fate of mine water contaminants in a treatment peatland receiving process waters from the Kittilä gold mine was investigated. Special attention was paid to the fate of potentially harmful substances such as arsenic, antimony or nickel. During the 4 years of operation, the peatland removed contaminants from process waters at varying efficiencies. While arsenic, antimony and nickel were retained at high efficiencies (>80% retention), other contaminants such as zinc, sulfate or iron were not retained or even leaching from the peatland. Soil samples taken in 2013 showed a linear increase of arsenic, antimony and nickel concentration in the peatland as compared to earlier sampling times, in agreement with the good retention efficiencies for those contaminants. Measured concentrations exceeded guideline values for contaminated soils, indicating that the prolonged use of treatment peatlands leads to high soil contamination and restrict further uses of the peatlands without remediation measures. Soil and pore water samples were taken along a transect with varying distance from the process water distribution ditch and analyzed for total and more easily mobile concentrations of contaminants (peat soil) as well as total and dissolved contaminants (water samples). Concentrations of contaminants such as arsenic, manganese or antimony in peat and pore water samples were highest near the distribution ditch and decreased with increasing distance from the ditch. Moreover, ratios of dissolved and total concentrations in pore water and of mobile and total concentrations in peat changed along the transect. Higher ratios of dissolved contaminants in water in greater distance from the distribution ditch indicate a decrease of particulate matter. Additionally, higher ratios of mobile contaminants in peat at greater distance from the distribution ditch indicate efficient immobilization of contaminants by chemical adsorption or sedimentation of particulate contaminants near the distribution ditch. Other contaminants such as sulfur/sulfate, sodium, magnesium and zinc showed similar concentrations in peat and pore water at all points of the transect, as well as similar concentration ratios, indicating that there is only minor net retention of those contaminants. This is in good agreement with the low retention efficiencies obtained for those contaminants. In conclusion, the study revealed that (i) removal efficiencies are variable depending on the individual contaminant, (ii) major contaminants are enriched to a degree which exceeds guideline values for contaminated soils, (iii) concentrational changes with distance from the process water distribution ditch can give further insights on the fate of individual contaminants. Even though the dominant processes involved in contaminant removal are not clearly identified to date, further analysis of the data obtained in this study will provide new insights on the fate of mine water contaminants in treatment peatlands and help evaluate potential consequences of the use of peatlands for mine water treatment.

  13. Transportation and Bioavailability of Copper and Zinc in a Storm Water Retention Pond

    NASA Astrophysics Data System (ADS)

    Camponelli, K.; Casey, R. E.; Wright, M. E.; Lev, S. M.; Landa, E. R.

    2006-05-01

    Highway runoff has been identified as a non-point source of metals to storm water retention ponds. Zinc and copper are major components of tires and brake pads, respectively. As these automobile parts degrade, they deposit particulates onto the roadway surface. During a storm event, these metal containing particulates are washed into a storm water retention pond where they can then accumulate over time. These metals may be available to organisms inhabiting the pond and surrounding areas. This study focuses on tracking the metals from their deposition on the roadway to their transport and accumulation into a retention pond. The retention pond is located in Owings Mills, MD and collects runoff from an adjacent four lane highway. Pond sediments, background soils, road dust samples, and storm events were collected and analyzed. Copper and zinc concentrations in the pond sediments are higher than local background soils indicating that the pond is storing anthropogenically derived metals. Storm event samples also reveal elevated levels of copper and zinc transported through runoff, along with a large concentration of total suspended solids. After looking at the particulate and dissolved fractions of both metals in the runoff, the majority of the Zn and Cu are in the particulate fraction. Changes in TSS are proportional with changes in particulate bound Zn, indicating that the solid particulates that are entering into the pond are a major contributor of the total metal loading. Sequential extractions carried out on the road dust show that the majority of zinc is extracted in the second and third fractions and could become available to organisms in the pond. There is a small amount of Cu that is being released in the more available stages of the procedure; however the bulk of the Cu is seen in the more recalcitrant steps. In the pond sediments however, both Cu and Zn are only being released from the sediments in the later steps and are most likely not highly available.

  14. Removing the impact of water abstractions on flow duration curves

    NASA Astrophysics Data System (ADS)

    Masoero, Alessandro; Ganora, Daniele; Galeati, Giorgio; Laio, Francesco; Claps, Pierluigi

    2015-04-01

    Changes and interactions between human system and water cycle are getting increased attention in the scientific community. Commonly discharge data needed for water resources studies were collected close to urban or industrial settlements, thus in environments where the interest for surveying was not merely scientific, but also for socio-economical purposes. Working in non-natural environments we must take into account human impacts, like the one due to water intakes for irrigation or hydropower generation, while assessing the actual water availability and variability in a river. This can became an issue in alpine areas, where hydropower exploitation is heavy and it is common to have water abstraction before a gauge station. To have a gauge station downstream a water intake can be useful to survey the environmental flow release and to record the maximum flood values, which should not be affected by the water abstraction. Nevertheless with this configuration we are unable to define properly the water volumes available in the river, information crucial to assess low flows and investigate drought risk. This situation leads to a substantial difference between observed data (affected by the human impact) and natural data (as would have been without abstraction). A main issue is how to correct these impacts and restore the natural streamflow values. The most obvious and reliable solution would be to ask for abstraction data to water users, but these data are hard to collect. Usually they are not available, because not public or not even collected by the water exploiters. A solution could be to develop a rainfall-run-off model of the basin upstream the gauge station, but this approach needs a great number of data and parameters Working in a regional framework and not on single case studies, our goal is to provide a consistent estimate of the non-impacted statistics of the river (i.e. mean value, L-moments of variation and skewness). We proposed a parsimonious method, based on few easy-access parameters, of correction of the water abstraction impact. The model, based on an exponential form of the river Flow Duration Curve (FDC), allows completely analytical solutions. Hence the method can be applied extensively. This is particularly relevant when working on a general outlook on water resources (regional or basin scale), given the high number of water abstractions that should be considered. The correction method developed is based on only two hard data that can be easily found: i) the design maximum discharge of the water intake and ii) the days of exercise, between a year. Following the same correction hypothesis also the abstracted discharge statistics have been reconstructed analytically and combined with the statistics of the receiving reach, that can be different from the original one. This information can be useful when we are assessing water availability in a river network interconnected by derivation channels. The goodness of the correction method proposed is proven by the application to a case study in North-West Italy, along a second order tributary of the Po River. Flow values recorded at the river gauge station were affected, significantly, by the presence of a 5 MW hydropower plant. Knowing the amount of water abstracted daily by the power plant we are able to reconstruct, empirically, the natural discharge on the river and compare its main statistics with the ones computed analytically using the proposed correction model. An extremely low difference between empirical and analytical reconstructed mean discharge and L-moment of variation was founded. Also, the importance of the day of exercise information was highlighted. The correction proposed in this work is able to give a correct indication of the non-impacted natural streamflows characteristics, especially in alpine regions where water abstraction impact is a main issue.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Zlatuška, Karel

    2012-12-01

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

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

    PubMed Central

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

    2015-01-01

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

  18. The role of water nitrogen retention in integrated nutrient management: assessment in a large basin using different modelling approaches

    NASA Astrophysics Data System (ADS)

    Grizzetti, Bruna; Passy, Paul; Billen, Gilles; Bouraoui, Fayçal; Garnier, Josette; Lassaletta, Luis

    2015-06-01

    Assessing the removal of nitrogen (temporary and permanent) in large river basins is complex due to the dependency on climate, hydrological and physical characteristics, and ecosystems functioning. Measurements are generally limited in number and do not account for the full integration of all processes contributing to nitrogen retention in the river basin. However, the estimation of nitrogen retention by the ecosystems is crucial to understanding the nitrate water pollution and the N2O emissions to the atmosphere, as well as the lag time between the implementation of agri-environmental measures to reduce nitrogen pollution and the improvement of water quality. Models have often been used to understand the dynamics of the river basin system. The objective of this study was to assess nitrogen retention in a large river basin, the Seine basin (?65 000 km2, in France), through the application of three models with different levels of complexity developed for different specific purposes: the GREEN, SWAT and RiverStrahler models. The study analyses the different modelling approaches and compares their estimates of water nitrogen retention over an 11-year period. Then reflexions on the role played by nitrogen retention by aquatic ecosystems in integrated nutrient management are presented. The results of this study are relevant for the understanding of nitrogen retention processes at the large river basin scale and for the analysis of mitigation measure scenarios designed to reduce nitrogen impacts on aquatic ecosystems and climate.

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

    Microsoft Academic Search

    D. Merten; E. Kothe; G. Büchel

    2004-01-01

    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

  20. Ear-tag retention and identification methods for extensively managed water buffalo (Bubalus bubalis) in Trinidad.

    PubMed

    Fosgate, G T; Adesiyun, A A; Hird, D W

    2006-03-16

    Thirty-two young domestic water buffalo were studied to evaluate ear-tag retention during an epidemiologic field trial. Plastic ear-tags were placed in both ears before the start of the trial, which was implemented in an extensively managed domestic water buffalo herd of approximately 1000 animals in Trinidad from 1999-2001. The presence or absence of ear-tags was recorded at the times of animal handling. The rate of ear-tag loss was modeled using a parametric survival analysis assuming an exponential rate of loss. A gamma distribution was used to estimate the amount of time that each animal would be positively identified based only on the presence or absence of one or more ear-tags. The overall median ear-tag retention was 272 days. The estimated rate of ear-tag loss was 0.0024 ear-tags lost per day. The use of ear-tags alone might not be sufficient for long-term identification of extensively managed animal populations. PMID:16242197

  1. Water proof and strength retention properties of thermoplastic starch based biocomposites modified with glutaraldehyde.

    PubMed

    Yeh, Jen-Taut; Hou, Yuan-Jing; Cheng, Li; Wang, Ya-Zhou; Yang, Liang; Wang, Chuen-Kai

    2015-08-20

    Water proof and strength retention properties of thermoplastic starch (TPS) resins were successfully improved by reacting glutaraldehyde (GA) with starch molecules during their gelatinization processes. Tensile strength (?f) values of initial and aged TPS100BC0.02GAx and (TPS100BC0.02GAx)75PLA25 specimens improved significantly to a maximal value as GA contents approached an optimal value, while their moisture content and elongation at break values reduced to a minimal value, respectively, as GA contents approached the optimal value. The ?f retention values of (TPS100BC0.02GA0.5)75PLA25 specimen aged for 56 days are more than 50 times higher than those of correspoding aged TPS and TPS100BC0.02 specimens, respectively. New melting endotherms and diffraction peaks of VH-type starch crystals were found on DSC thermograms and WAXD patterns of aged TPS or TPS100BC0.02 specimens, respectively, while negligible retrogradation effect was found for most aged TPS100BC0.02GAx and/or (TPS100BC0.02GAx)75PLA25 specimens. PMID:25965466

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

    USGS Publications Warehouse

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

    2015-01-01

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

  3. Optimising the weighting of the water retention index using sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Becker, William; Vandecasteele, Ine

    2015-04-01

    A robust composite indicator was developed to assess the capacity of the landscape to regulate and retain water passing through it at Pan-European scale. The "Water Retention Index" (WRI) takes into account the role of interception by vegetation, the water-holding capacity of the soil, and the relative capacity of the bedrock to allow percolation of water, as well as the influence of soil sealing and slope gradient. A delicate issue in composite indicators is however the relative weighting of each variable used in the indicator - strong correlations and skewness are known to cause unequal influence of the input variables, even though the weighting coefficients are equal (Paruolo et al, 2013). To understand the effects of the weightings in the WRI, penalised splines were used to calculate the first order sensitivity index of each variable used in the construction of the WRI, allowing the true influence of each input to be determined. Furthermore, the weighting coefficients were optimised using an iterative nonlinear algorithm to find the coefficients which resulted in the most equal influence of each input to the indicator. In principle, this approach can be used to improve the weighting of many different kinds of composite indicator, the results of which are often used as the basis for important policy decisions at the European level. Paruolo, Paolo, Michaela Saisana, and Andrea Saltelli. "Ratings and rankings: voodoo or science?." Journal of the Royal Statistical Society: Series A (Statistics in Society) 176.3 (2013): 609-634.

  4. Multi-decadal water-table manipulation alters peatland hydraulic structure and moisture retention.

    NASA Astrophysics Data System (ADS)

    Moore, Paul; Morris, Paul; Waddington, James

    2015-04-01

    Peatlands are a globally important store of freshwater and soil carbon. However, there is a concern that these water and carbon stores may be at risk due to climate change as vapour pressure deficits, evapotranspiration and summer moisture deficits are expected to increase, leading to greater water table (WT) drawdown in northern continental regions where peatlands are prevalent. We argue that in order to evaluate the hydrological response (i.e. changes in WT level, storage, surface moisture availability, and moss evaporation) of peatlands under future climate change scenarios, the hydrophysical properties of peat and disparities between microforms must be well understood. A peatland complex disturbed by berm construction in the 1950's was used to examine the long-term impact of WT manipulation on peatland hydraulic properties and moisture retention at three adjacent sites with increasing average depth to WT (WET, INTermediate reference, and DRY). All three sites exhibited a strong depth dependence for hydraulic conductivity, specific yield, and bulk density. Moreover, the effect of microform on near-surface peat properties tended to be greater than the site effect. Bulk density was found to explain a high amount of variance (r2 > 0.69) in moisture retention across a range of pore water pressures (-15 to -500 cm H2O), where bulk density tended to be higher in hollows. The estimated residual water content for surface Sphagnum samples, while on average lower in hummocks (0.082 m3 m-3) versus hollows (0.087 m3 m-3), increased from WET (0.058 m3 m-3) to INT (0.088 m3 m-3) to DRY (0.108 m3 m-3) which has important implications for moisture stress under conditions of persistent WT drawdown. While we did not observe significant differences between sites, we did observe a greater proportional coverage and greater relative height of hummocks at the drier sites. Given the potential importance of microtopographic succession for altering peatland hydraulic structure, our findings point to the need for a better understanding of what controls the relative height and proportional coverage of hummocks in relation to long-term disturbance-response dynamics. While current peatland models can simulate bulk density that varies as a result of changes in rates of production and decomposition for different plant functional types and different microforms, the spatial component of microtopographic succession is missing. We argue that the effects of microtopographic succession on the spatial pattern of bulk density and associated hydrophysical properties are important for capturing changes in hydraulic structure that result from disturbance.

  5. Preparation and properties of a double-coated slow-release NPK compound fertilizer with superabsorbent and water-retention.

    PubMed

    Wu, Lan; Liu, Mingzhu; Rui Liang

    2008-02-01

    A double-coated slow-release NPK compound fertilizer with superabsorbent and water-retention was prepared by crosslinked poly(acrylic acid)/diatomite - containing urea (the outer coating), chitosan (the inner coating), and water-soluble granular fertilizer NPK (the core). The effects of the amount of crosslinker, initiator, degree of neutralization of acrylic acid, initial monomer and diatomite concentration on water absorbency were investigated and optimized. The water absorbency of the product was 75 times its own weight if it was allowed to swell in tap water at room temperature for 2 h. Atomic absorption spectrophotometer and element analysis results showed that the product contained 8.47% potassium (shown by K(2)O), 8.51% phosphorus (shown by P(2)O(5)), and 15.77% nitrogen. We also investigated the water-retention property of the product and the slow release behavior of N, P and K in the product. This product with excellent slow release and water-retention capacity, being nontoxic in soil and environment-friendly, could be especially useful in agricultural and horticultural applications. PMID:17320380

  6. Determining factors for anodic polarization curves of typical structural materials of boiling water reactors in high temperature – high purity water

    Microsoft Academic Search

    Masahiko Tachibana; Kazushige Ishida; Yoichi Wada; Ryosuke Shimizu; Nobuyuki Ota; Nobuyoshi Hara

    2012-01-01

    In order to examine the anodic polarization characteristics of typical structural materials of boiling water reactors (BWRs), the anodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in deaerated high purity water at 553 K using the previously reported measurement method which was confirmed suitable for high temperature – high purity water. In order to

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

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

    PubMed

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

    2015-04-01

    The aim of this study is to understand the different sorption behaviors of mercury species on activated carbons in the oxy-fuel combustion of coal and the effect of high quantities of water vapor on the retention process. The work evaluates the interactions between the mercury species and a series of activated carbons prepared from a macroalgae waste (algae meal) from the agar-agar industry in oxy-combustion atmospheres, focussing on the role that the high concentration of water in the flue gases plays in mercury retention. Two novel aspects are considered in this work (i) the impact of oxy-combustion gases on the retention of mercury by activated carbons and (ii) the performance of activated carbons prepared from biomass algae wastes for this application. The results obtained at laboratory scale indicate that the effect of the chemical and textural characteristics of the activated carbons on mercury capture is not as important as that of reactive gases, such as the SOx and water vapor present in the flue gas. Mercury retention was found to be much lower in the oxy-combustion atmosphere than in the O2+N2 (12.6% O2) atmosphere. However, the oxidation of elemental mercury (Hg0) to form oxidized mercury (Hg2+) amounted to 60%, resulting in an enhancement of mercury retention in the flue gas desulfurization units and a reduction in the amalgamation of Hg0 in the CO2 compression unit. This result is of considerable importance for the development of technologies based on activated carbon sorbents for mercury control in oxy-combustion processes. PMID:25585865

  10. Utilization of wheat straw for the preparation of coated controlled-release fertilizer with the function of water retention.

    PubMed

    Xie, Lihua; Liu, Mingzhu; Ni, Boli; Wang, Yanfang

    2012-07-18

    With the aim of improving fertilizer use efficiency and minimizing the negative impact on the environment, a new coated controlled-release fertilizer with the function of water retention was prepared. A novel low water solubility macromolecular fertilizer, poly(dimethylourea phosphate) (PDUP), was "designed" and formulated from N,N'-dimethylolurea (DMU) and potassium dihydrogen phosphate. Simultaneously, an eco-friendly superabsorbent composite based on wheat straw (WS), acrylic acid (AA), 2-acryloylamino-2-methyl-1-propanesulfonic acid (AMPS), and N-hydroxymethyl acrylamide (NHMAAm) was synthesized and used as the coating to control the release of nutrient. The nitrogen release profile and water retention capacity of the product were also investigated. The degradation of the coating material in soil solution was studied. Meanwhile, the impact of the content of N-hydroxymethyl acrylamide on the degradation extent was examined. The experimental data showed that the product with good water retention and controlled-release capacities, being economical and eco-friendly, could be promising for applications in agriculture and horticulture. PMID:22730900

  11. Why biochar application did not improve the soil water retention of a sandy soil: An investigation into the underlying mechanisms.

    NASA Astrophysics Data System (ADS)

    Jeffery, Simon; Meinders, Marcel B. J.; Stoof, Cathelijne; Bezemer, T. Martijn; vande Voorde, Tess F. J.; Mommer, Liesje; Willem van Groenigen, Jan

    2015-04-01

    Biochar application to soil is currently being widely touted as a means to improve soil quality and to enhance the provision of numerous ecosystem services, including water storage, in soils. However, evidence for hydrological effects in the primary literature remain inconclusive with contradictory effects reported. The mechanisms behind such contradictory results are not yet elucidated. As such we aimed to investigate the effects of biochar on soil water retention and infiltration, as well as the underlying mechanisms. To do so we set up two field experiments with biochar produced from herbaceous feedstock through slow pyrolysis at two temperatures (400°C and 600°C). In the first experiment both biochars were applied at a rate of 10 t ha-1 to separate plots in a sandy soil in a North European grassland. In a separate experiment, the biochar produced at 400°C was applied to a different set of plots in the same grassland at rates equivalent to 1, 5, 20 and 50 t ha-1. Soils from these experiments were analysed for soil water retention and infiltration rate as well as aggregate stability and other soil physical parameters. The pore structure of the biochar was fully characterised using X-ray computed micro-tomography (XRT) and hydrophobicity determined using contact angle measurements. There were no significant effects of biochar application on soil water retention, field saturated conductivity or aggregate stability in either experiment. XRT analysis of the biochars confirmed that the biochars were highly porous, with 48% and 57% porosity for the 400°C and 600°C biochars, respectively. More than 99% of internal pores of the biochar particles were connected to the surface, suggesting a potential role for biochars in improving soil water retention. However, the biochars were highly hydrophobic as demonstrated by the high contact angles when water was applied. We suggest that this hydrophobicity greatly diminished water infiltration into the biochar particles, prohibiting an effect on soil water retention. Our results indicate that, in addition to characterizing pore space, biochars should be analysed for hydrophobicity when assessing their capacity for improving soil physical properties.

  12. Impact of regression methods on improved effects of soil structure on soil water retention estimates

    NASA Astrophysics Data System (ADS)

    Nguyen, Phuong Minh; De Pue, Jan; Le, Khoa Van; Cornelis, Wim

    2015-06-01

    Increasing the accuracy of pedotransfer functions (PTFs), an indirect method for predicting non-readily available soil features such as soil water retention characteristics (SWRC), is of crucial importance for large scale agro-hydrological modeling. Adding significant predictors (i.e., soil structure), and implementing more flexible regression algorithms are among the main strategies of PTFs improvement. The aim of this study was to investigate whether the improved effect of categorical soil structure information on estimating soil-water content at various matric potentials, which has been reported in literature, could be enduringly captured by regression techniques other than the usually applied linear regression. Two data mining techniques, i.e., Support Vector Machines (SVM), and k-Nearest Neighbors (kNN), which have been recently introduced as promising tools for PTF development, were utilized to test if the incorporation of soil structure will improve PTF's accuracy under a context of rather limited training data. The results show that incorporating descriptive soil structure information, i.e., massive, structured and structureless, as grouping criterion can improve the accuracy of PTFs derived by SVM approach in the range of matric potential of -6 to -33 kPa (average RMSE decreased up to 0.005 m3 m-3 after grouping, depending on matric potentials). The improvement was primarily attributed to the outperformance of SVM-PTFs calibrated on structureless soils. No improvement was obtained with kNN technique, at least not in our study in which the data set became limited in size after grouping. Since there is an impact of regression techniques on the improved effect of incorporating qualitative soil structure information, selecting a proper technique will help to maximize the combined influence of flexible regression algorithms and soil structure information on PTF accuracy.

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

    Microsoft Academic Search

    Fabiana Alves de Lima Ribeiro; Márcia Miguel Castro Ferreira

    2003-01-01

    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,

  14. Passive cooling effect of RC roof covered with the ceramics having high water retention and evaporation capacity

    NASA Astrophysics Data System (ADS)

    Yamazaki, M.; Kanaya, M.; Shimazu, T.; Ohashi, T.; Kato, N.; Horikoshi, T.

    2011-10-01

    Hot days in metropolitan cities have increased remarkably by the heat island phenomenon these days. Thus the authors tried to develop the porous ceramics with high water retention and evaporation capacity as a maintenance-free material to improve thermal environment. The developed ceramic pellets have high water retention of more than 60 % of water absorption and high water evaporation which is similar to water surface. In this study, three types of 5 meter squared large flat-roofed structural specimen simulated reinforced concrete (RC) slab were constructed on the outside. The variation of water content and temperature of the specimens and atmosphere temperature around the specimens were measured from summer in 2009. In the case of the ceramic pellets, the temperature under RC slab was around 15 degree C lower than that of the control. The results were probably contributed by passive cooling effect of evaporated rain water, and the effect was similar to in the case of the grasses. From the viewpoint of thermal environment improvement, substitution of a rooftop gardening by the porous ceramics could be a promising method.

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

    PubMed Central

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

    2014-01-01

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

  16. Evaluating changes to reservoir rule curves using historical water-level data

    USGS Publications Warehouse

    Mower, Ethan; Miranda, Leandro E.

    2013-01-01

    Flood control reservoirs are typically managed through rule curves (i.e. target water levels) which control the storage and release timing of flood waters. Changes to rule curves are often contemplated and requested by various user groups and management agencies with no information available about the actual flood risk of such requests. Methods of estimating flood risk in reservoirs are not easily available to those unfamiliar with hydrological models that track water movement through a river basin. We developed a quantile regression model that uses readily available daily water-level data to estimate risk of spilling. Our model provided a relatively simple process for estimating the maximum applicable water level under a specific flood risk for any day of the year. This water level represents an upper-limit umbrella under which water levels can be operated in a variety of ways. Our model allows the visualization of water-level management under a user-specified flood risk and provides a framework for incorporating the effect of a changing environment on water-level management in reservoirs, but is not designed to replace existing hydrological models. The model can improve communication and collaboration among agencies responsible for managing natural resources dependent on reservoir water levels.

  17. A new approach for the in situ determination of soil water retention characteristics for shallow groundwater systems

    NASA Astrophysics Data System (ADS)

    Dettmann, Ullrich; Bechtold, Michel

    2015-04-01

    Obtaining representative effective hydraulic properties for the pedon to field scale as input for models is a major challenge in hydrology. Hydraulic properties are often determined by laboratory measurements on small soil cores. Due to the high small-scale variability, many samples are needed to obtain representative values, which is time consuming and costly. Here, we present a new approach which is focused on the in situ determination of the soil water retention characteristics that is applicable to shallow groundwater systems. The method integrates over small-scale heterogeneity (appr. several meters) and uses only precipitation and water-level data. Our approach is built on two assumptions: i) for shallow groundwater systems (with water table depths of appr. < 0.5 to 1 m) , e.g. wetlands, with medium- to high conductive soils the soil moisture profile is close to hydrostatic equilibrium before and after rain events (Dettmann et al., 2014, J Hydrol, 515, 103-115) and ii) over short time periods lateral fluxes into and out of the system are negligible. Given these assumptions, the height of a water level rise after a precipitation event only depends on the soil water retention characteristics, the precipitation amount of the event and the initial water table depths. We use this dependency, to determine van Genuchten-parameters by Bayesian inversion. The applicability of the method is proved by synthetic data. Water retention characteristics are very well-constrained for the low suction range. At high suctions uncertainties strongly increase as this suction range is not covered by the approach. With real field data, some phenomena make an accurate determination more difficult. Wetlands are typically characterized by a distinct microrelief leading to partly inundated areas around a monitoring well in dependence of the water level. For field application, we thus developed a model that takes into account the microrelief by assuming frequency distributions. Furthermore, preferential flow phenomena were accounted for by waiting for the system to equilibrate a few hours after the rain events. The inversely-determined parameters are compared against laboratory data.

  18. Estimation of mortality coefficients and survivorship curves for minke whales (Balaenoptera acutorostrata) in Korean waters

    Microsoft Academic Search

    Chang Ik Zhang; Kyung-Jun Song; Jong-Hun Na

    2010-01-01

    Population ecological characteristics of growth and mortality play an important role in understanding the population dynamics of marine mammals. The instantaneous coefficients of natural and bycatch mortality were estimated for minke whales (Balaenoptera acutorostrata) in Korean waters using a population assessment model composed of bycatch and abundance data. The survivorship curve of this population was fitted to the data, and

  19. Satellite observation of winter season subsurface liquid melt water retention on the Greenland ice sheet using spectroradiometer and scatterometer data

    NASA Astrophysics Data System (ADS)

    Miller, J. Z.; Forster, R. R.; Long, D. G.; Brewer, S.

    2013-12-01

    The recently discovered perennial firn aquifer (PFA) represents a new glacier facie and a previously undefined liquid water storage mechanism on the Greenland ice sheet (GrIS). The current hypothesis suggests that at least two geophysical processes control the formation of the PFA: 1) high melt rates that saturate snow and firn layers with liquid water during the melt season, and 2) high snow accumulation rates that subsequently insulate this saturated layer allowing it to be retained in liquid form during the winter season. The PFA is potentially an important component in ice sheet mass and energy budget calculations, however, large-scale observations linking surface melt, subsurface liquid melt water retention, and the PFA currently do not exist. Satellite-borne spectroradiometers and scatterometers are frequently used to detect the presence of liquid water content over the GrIS. The sensor's penetration depth is dependent on the frequency (which determines wavelength) and time-varying geophysical properties (which determine absorption and scattering characteristics). At shorter spectral wavelengths, penetration depths are limited at the interface between the ice sheet surface and the atmosphere. Spectroradiometer-derived retrievals of liquid water content represent an integrated response on the order of a few millimeters. At longer microwave wavelengths (C- and Ku-band), penetration depths are increased. Scatterometer-derived retrievals of liquid water content represent an integrated response on the order of a few centimeters to several meters. We combine spectroradiometer data acquired from the Moderate Resolution Imaging Spectroradiometer aboard Terra and Aqua (MODIS) and C- and Ku-band scatterometer data acquired from MetOP-A (ASCAT) and OceanSAT-2 (OSCAT) to investigate the spatiotemporal variability of subsurface liquid water content on the GrIS. Penetration depth differences are exploited to distinguish between the detection of liquid water content controlled by surface heat flux and the detection of subsurface liquid water content controlled by the retention process. Surface freeze-up is identified using MODIS-derived ice surface temperatures. We then identify distinct microwave signatures suggesting the presence of subsurface liquid water content, characterize the stratigraphy and geophysical processes controlling the observed response, and derive a retrieval algorithm using a simple radiative transfer model. Over the 4 year time series (2009-2013), results indicate subsurface liquid melt water persists within Ku-band penetration depth up to ~1 month and within C-band penetration depth between ~1-5 months following surface-freeze-up. Detection occurs exclusively in regions where the PFA has previously been mapped using field (Arctic Circle Traverse) and airborne (IceBridge) observations and the spatial extent is consistent with regional climate model (RACMO2) simulations.

  20. A feasibility assessment of the use of nanofluids to enhance the in-vessel retention capability in light-water reactors

    Microsoft Academic Search

    J. Buongiorno; L. W. Hu; G. Apostolakis; R. Hannink; T. Lucas; A. Chupin

    2009-01-01

    Nanofluids, colloidal dispersions of nanoparticles, exhibit a substantially higher critical heat flux (CHF) compared to water. As such, they could be used to enhance the in-vessel retention (IVR) capability in the severe accident management strategy implemented by certain light-water reactors. It is envisioned that, at normal operating conditions, the nanofluid would be stored in dedicated storage tanks, which, upon actuation,

  1. 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

    Masami Shibukawa; Kaoru Aoyagi; Ryosaku Sakamoto; Koichi Oguma

    1999-01-01

    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

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

    E-print Network

    Florida, University of

    ) pennywort (Hydrocotyle umbellata L.), (ii) water hyacinth (Eich- hornia crassipes [Mart] Solms), (iii through precipitation and adsorption reactions. Additional Index Words: water hyacinth, pennywort such as water hyacinths (Eichhornia crassipes [Mart] Solms), duckweed (Lemna minor), and cattails (Typha sp

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

    PubMed

    Peña, J C

    1995-01-01

    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

  4. Plant-Water Relations in Seasonally Dry Tropical Montane Cloud Forests

    E-print Network

    Goldsmith, Gregory Rubin

    2012-01-01

    Soil-lysimeter and ground water sampling locations and methodssoil sampling, antecedent precipitation indices were calculated for the 15 days prior to both dates following the methodssoil water retention curve without intensive or destructive sampling. However, the filter paper method

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

    PubMed Central

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

    2012-01-01

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

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

    PubMed Central

    Leung, Felix W

    2011-01-01

    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. PMID:22163078

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

    PubMed

    Wong, Yoon Loong Andrew; Lewis, Lynne

    2013-12-15

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

  8. Thermodynamic Basis of Budyko Curve for Annual Water Balance: Proportionality Hypothesis and Maximum Entropy Production

    NASA Astrophysics Data System (ADS)

    Wang, Dingbao; Zhao, Jianshi; Tang, Yin; Sivapalan, Murugesu

    2015-04-01

    Recently, Wang and Tang [2014] demonstrated that the validity of the Proportionality Hypothesis extends to the partitioning of precipitation into runoff and evaporation at the annual time scale as well, and that the Budyko Curve could then be seen as the straightforward outcome of the application of the Proportionality Hypothesis to estimate mean annual water balance. In this talk, we go further and demonstrate that the Proportionality Hypothesis itself can be seen as a result of the application of the thermodynamic principle of Maximum Entropy Production (MEP), provided that the conductance coefficients assumed for evaporation and runoff are linearly proportional to their corresponding potential values. In this way, on the basis of this common hydrological assumption, we demonstrate a possible physical (thermodynamic) basis for the Proportionality Hypothesis, and consequently for the Budyko Curve.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  10. Analysis of the deviations from the "average" curve of sediment transport vs water flow

    NASA Astrophysics Data System (ADS)

    Nones, Michael; di Silvio, Giampaolo; Bisiacco, Mauro

    2010-05-01

    Recent studies about analytical solutions of the 1-D morphodynamic model (Fasolato et al., 2009) have shown that any river reach maintains an equilibrium configuration (namely a stationary morphological situation) under the hypothesis that the boundaries of the river reach are in equilibrium as far as solid and liquid inputs are concerned. This hypothesis means that the bottom profile of the river and the grainsize composition of the bed should, in principle, remain constant in time, provided that sediments and water entering the reach are related by an equilibrium relation (transport formula). Obviously, this condition is not always satisfied, especially in the mountain rivers, as the formation mechanisms of water and sediment inputs are quite different and seasonally delayed. These initial perturbations give place to important deviations from the "average" curve of sediment transport vs water flow, namely from the curve calculated in equilibrium conditions. This study presents a general approach that can be used to explain and possibly predict these deviations. The approach is based on the deterministic analytical solution of the harmonic river (Fasolato et al., 2009), combined with a recursive model of ARMA type, with unknown parameters, which can be estimated by minimizing a suitable mean square error, in order to obtain the best ARMA model from two different points of view: its performances both in fitting the available (measured) data and in providing a prediction algorithm for the future evolutions. The recursive model for a synthetic river reach will provide the instantaneous sediment discharge as a function of the instantaneous water flow (namely equilibrium conditions) and the water flow measured at one or more previous time (non-equilibrium conditions). This model is calibrated against a relatively small dataset of measurements about an important Italian water course: the Adige River, which flows from the Alps to the Adriatic Sea south of Venice. The analysis is limited to two gauge stations: Trento (typical mountain river reach) and Boara Pisani (typical lowland river reach).

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

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

    E-print Network

    Young, Terence

    Sustainable Water Practices at Pomona's Parks: Improving Irrigation Use and Stormwater Runoff represents a large portion of the United States total water usage. Further, the majority of stormwater runoff and utilizing stormwater runoff, such as the two parks of this study: Kellogg Park and John F. Kennedy Park

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

    PubMed

    Wan, Y H; Wong, P K

    2002-01-01

    Mathematical relationships between vapor pressures (P), water solubilities (S), Henry's law constants (Hc). noctanol/water partition coefficients (Kow) and gas chromatograph retention indices (GC-RIs) of polychlorinated-dibenzo-dioxins (PCDDs) were established. A model equation was established between GC-RIs (= RI) and other physico-chemical parameters (K) of PCDDs in the form of log K = aRI2 + bRI + c with correlation coefficients (R2) greater than 0.97, except Hc. These equations were derived from 56 experimental data of PCDDs reported previously. The values of P, S, Hc and Kow of PCDDs predicted by these equations based on their GC-RIs in the present study deviated from those calculated by the SOFA method in a previous study by only 0.19, 0.13, 0.18 and 0.096 log units, respectively. PMID:11766813

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

    PubMed Central

    Taha, Mohd Raihan

    2014-01-01

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

  15. Performance evaluation of four-parameter models of the soil-water characteristic curve.

    PubMed

    Matlan, Siti Jahara; Mukhlisin, Muhammad; Taha, Mohd Raihan

    2014-01-01

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

  16. Evaluation of the performance of the van Genuchten equation using a large database on soil water retention of tropical soils in Brazil

    NASA Astrophysics Data System (ADS)

    Ottoni, M. V.; Van Genuchten, M.; Lopes Assad, M. L. R. C.; Monteiro, A. E.

    2014-12-01

    The van Genuchten equation is used often to provide an empirical description of soil water retention data. The equation is commonly used for modeling hydrologic processes for environmental and agricultural applications, including irrigation. Most applications involved soils of temperate or arid climatic regions. Soil of tropical zones often have distinct textural compositions with a predominance of clay and sand, which may lead to multimodal pore size distributions that are not conducive to applications of the standard van Genuchten equation. This study aims to evaluate the performance of the van Genuchten equation using a large database on soil water retention of tropical soils in Brazil, where almost 6 million hectares are irrigated and responsible for about 70% of water consumption in Brazil. We selected 1058 undisturbed soil samples with water retention data covering a wide matric potentials. The results show that the root-mean-squared error (RMSE) of the water retention estimates was larger than 4% for only 10 samples. For the remaining datasets, the RMSE distribution behaved as follows: 27 samples had an RMSE from 3 to 4%, 70 samples had an RMSE from 2 to 3%, 332 samples had an RMSE from 1 to 2%, and 619 samples had an RMSE from 0 to 1%. Because of the bimodal pore size distribution of many soils, a dual porosity retention model is probably more appropriate for samples having the higher RMSE values. Overall, the van Genuchten equation was found to be appropriate for Brazilian soil conditions. Work is underway to see if soil or landscape properties can be used to predict the presence of the bimodal pore-size distributions.

  17. Geologic and geophysical investigation of a small water retention structure, Salado, Tx 

    E-print Network

    Carter, James Lewis

    2002-01-01

    incorporated to identify the causes of the water losses in the pond. The presence of a spring identified during field investigations, the identification of the creek as a lineament, and the indication of a subsurface linear conductive feature...

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

    PubMed

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

    2015-07-01

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

  19. Humidity interaction of lichens under astrobiological aspects: the impact of UVC exposure on their water retention properties

    NASA Astrophysics Data System (ADS)

    Jänchen, J.; Meeßen, J.; Herzog, T. H.; Feist, M.; de la Torre, R.; Devera, J.-P. P.

    2015-07-01

    We quantitatively studied the hydration and dehydration behaviour of the three astrobiological model lichens Xanthoria elegans, Buellia frigida and Circinaria gyrosa by thermoanalysis and gravimetric isotherm measurements under close-to-Martian environmental conditions in terms of low temperature and low pressure. Additionally, the impact of UVC exposure on the isolated symbionts of B. frigida and X. elegans was studied by thermoanalysis and mass spectrometry as well as by gravimetric isotherm measurements. The thermal analysis revealed whewellite as a component of C. gyrosa which was not found in B. frigida and X. elegans. Neither the water retention nor the thermal behaviour of symbionts changed when irradiated with UVC under dry conditions. On the other hand, UVC irradiation of the wet mycobiont of B. frigida had a distinct impact on the hydration/dehydration ability which was not observed for the mycobiont of X. elegans. Possibly the melanin of B. frigida's mycobiont, that is not present in X. elegans, or a specifically damaged acetamido group of the chitin of B. frigida may be the sources of additional UVC-induced sorption sites for water associated with the UVC exposure.

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

    SciTech Connect

    Ramanathan Sampath

    2003-10-01

    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.

  1. Cathodic polarization curves of the oxygen reduction reaction on various structural materials of boiling water reactors in high temperature–high purity water

    Microsoft Academic Search

    Masahiko Tachibana; Kazushige Ishida; Yoichi Wada; Ryosuke Shimizu; Nobuyuki Ota; Nobuyoshi Hara

    2012-01-01

    Cathodic polarization curves of the O2 reduction reaction were measured by using electrodes made from typical structural materials of boiling water reactors (BWRs) to evaluate the effects of kind of material on the electrochemical corrosion potential (ECP) calculation. To estimate ECPs at any region in the BWRs on the basis of the BWR environmental conditions, anodic and cathodic polarization curves

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

    USGS Publications Warehouse

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

    2012-01-01

    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.

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

    PubMed

    Ren, Dianjun; Smith, James A

    2013-04-16

    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

  4. Development of Duration-Curve Based Methods for Quantifying Variability and Change in Watershed Hydrology and Water Quality

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Little is known about effectiveness of land activities to control water quality. The objective was to explore the duration curve (DC) concept for comparing hydrology and water quality data from watersheds. DCs are plots of the percent of time that a given value of a variable (e.g., flow rate) is ex...

  5. Retention capacity of correlated surfaces.

    PubMed

    Schrenk, K J; Araújo, N A M; Ziff, R M; Herrmann, H J

    2014-06-01

    We extend the water retention model [C. L. Knecht et al., Phys. Rev. Lett. 108, 045703 (2012)] to correlated random surfaces. We find that the retention capacity of discrete random landscapes is strongly affected by spatial correlations among the heights. This phenomenon is related to the emergence of power-law scaling in the lake volume distribution. We also solve the uncorrelated case exactly for a small lattice and present bounds on the retention of uncorrelated landscapes. PMID:25019758

  6. A feasibility study on the estimation of water retention parameters from surface nuclear magnetic resonance measurements in the vadose zone

    NASA Astrophysics Data System (ADS)

    Costabel, S.; Guenther, T.; Meyer, U.

    2012-12-01

    The surface nuclear magnetic resonance (SNMR) method is usually applied for groundwater prospection. Its unique property - distinct from other hydrogeophysical methods - is the direct sensitivity to water content in the subsurface. The inversion of SNMR data yields the subsurface water content distribution without the need of a specific petrophysical model. Recent developments in instrumentation, i.e., decreased instrumental dead times and advanced noise cancellation strategies enable the use of this method for investigating the vadose zone. The first attempt to interpret SNMR measurements with the focus on hydraulic parameters is the inversion approach of Costabel and Yaramanci (2011).Their inversion directly provides WR parameters by parameterizing the capillary fringe (CF) by means of soil-physical water retention (WR) models. We have developed and investigated this inversion approach further to assess its general applicability. A sensitivity study based on both synthetic and real data analyzes the resolution properties, the uncertainties and the covariances of the involved parameters: the saturated and the residual water content, a parameter for the height of the CF, a parameter describing the gradient of the water content increase in the CF, and the water table. We found that it is not meaningful to invert for all parameters at once. At least, an estimate of the CF's height or the water table must be available as a-priori information. Otherwise the CF inversion cannot reliably be applied, even when the noise level is unrealistically low. The water content of the saturated zone is generally estimated with high accuracy, i.e., errors of less than 1%. Depending on the actual noise level, the uncertainties of the other WR parameters are in the range of 10 to 100%. We conclude that, for moderate noise conditions, this kind of inversion provides WR parameters sufficiently accurate to estimate the unsaturated hydraulic conductivity roughly. However, a serious conceptual shortcoming of this approach is the inconsistency between observing a static system on the one hand and estimating dynamic parameters on the other hand. A promising approach to overcome this problem is to do time-lapse measurements. To assess the potential of SNMR for such experiments, we combine hydraulic simulations and SNMR forward modeling calculations to develop and investigate adequate measurement strategies based upon realistic field scenarios. We found that the common SNMR measurement scheme must be modified to allow faster repetitions, e.g., when monitoring infiltration of water with high dynamics. Otherwise it is not possible to realize an appropriate resolution in time. For such modifications one must accept the loss of spatial resolution. However, the direct sensitivity of the SNMR method for dynamic water content changes is an important benefit and we expect that future SNMR inversion approaches will provide hydraulic parameters, at least for the vertical water flux through the vadose zone. References: Costabel, S. and Yaramanci, U. (2011). Relative hydraulic conductivity in the vadose zone from magnetic resonance sounding - Brooks-Corey parameterization of the capillary fringe. Geophysics, 76 (3):B1-B11.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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.

  8. Field-Obtained Soil Water Characteristic Curves and Hydraulic Conductivity Functions

    NASA Astrophysics Data System (ADS)

    Elvis, Ishimwe

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

  9. Bimodal and multimodal descriptions of soil-water characteristic curves for structural soils.

    PubMed

    Liu, Shiyu; Yasufuku, Noriyuki; Liu, Qiang; Omine, Kiyoshi; Hemanta, Hazarika

    2013-01-01

    In the last decades several approaches have been developed to describe bimodal or multimodal soil-water characteristic curves (SWCCs). Unfortunately, most of these models were derived empirically. In the presented study, physically based bimodal and multimodal SWCC functions have been developed for structural soils. The model involved two or more continual pore series; the probability density functions for each pore series were assumed to be lognormal distribution and can be superposed to obtain the overall probability density function of the structural soils. The proposed functions were capable of simulating bimodal or multimodal SWCCs using parameters which can be related to physical properties of the structural soils. The experimental SWCC data were used to verify the proposed method. The fitting results showed that the proposed approaches resulted in good agreement between measurement and simulation. These functions can potentially be used as effective tools for indentifying hydraulic porosities in the structural mediums. PMID:23579828

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  11. Water management at Rocky Flats: Design of wet ponds for optimal interception, retention, and remediation of metals from surface and groundwaters

    SciTech Connect

    Fiehweg, R. [EG& G/Rocky Flats Plant, Golden, CO (United States); Waugh, P. [Wright Water Engineers, Inc., Denver, CO (United States); Weiner, E. [Univ. of Denver, CO (United States)

    1993-12-31

    All waters leaving the Rocky Flats Plant site are obligated to meet and are meeting stringent downstream water quality standards in Walnut Creek. All surface water, groundwater, and sewage treatment plant effluent coming from the plant site is intercepted and retained in a series of wet ponds. The ponds are unique in that they: (1) are situated and constructed to intercept all water coming from the plant site, (2) are large, thus allowing long retention times, and (3) are interconnected by a series of underground pipelines and valves allowing great latitude in water management. Data show that metals concentrations are significantly reduced as water passes through the ponds. Mechanisms for metals remediation will be discussed.

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

    E-print Network

    DeWitt, Gregory L

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    USGS Publications Warehouse

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

    2007-01-01

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

  15. 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...

  16. A Method to Recover Useful Geothermal-Reservoir Parameters from Production Characteristic Curves (2) Hot Water Reservoirs

    Microsoft Academic Search

    E. Iglesias; V. Arellano; R. Molinar

    1983-01-01

    In this paper we develop and demonstrate a method to estimate the reservoir pressure, a mass productivity index, and a thermal power productivity index for vertical water-fed geothermal wells, from its production characteristic (also called output) curves. In addition, the method allows to estimate the radius of influence of the well, provided that a value of the reservoir transmisivity is

  17. Effects of dietary electrolyte balance and addition of electrolyte-betaine supplements in feed or water on performance, acid-base balance and water retention in heat-stressed broilers.

    PubMed

    Sayed, M A M; Downing, J

    2015-04-01

    The effects of dietary electrolyte balance (DEB) and electrolyte-betaine (El-Be) supplements on heat-stressed broiler performance, acid-base balance and water retention were evaluated during the period 31-40 d of age in a 2 × 3 factorial arrangement of treatments. A total of 240 broilers were assigned to 6 treatment groups each with 8 replicates of 5 birds per cage and were exposed to cyclic high temperature (32 - 24 ± 1°C). Birds were provided with diets having DEB of either 180 or 220 mEq/kg. El-Be supplements were either added to the diet, water or not added to either of them to complete the array of 6 treatment groups. An additional 80 birds were kept at thermoneutral temperature (20 ± 1°C) and were provided with tap water and diets with DEB of either 180 or 220 mEq/kg to serve as negative controls. Exposure to high temperature depressed growth performance, increased rectal temperature and decreased potassium (K(+)) retention. In high-temperature room, birds fed on diets with DEB of 220 mEq/kg tended to increase BW from 35-40 d of age. However, at thermoneutral temperature, broilers fed on diets with DEB of 220 mEq/kg increased K(+) retention. Adding El-Be supplements in feed or water improved feed conversion ratio (FCR), enhanced water consumption and increased K(+) and sodium (Na(+)) retention. Interactions between DEB and El-Be supplements tended to affect body weight gain and FCR during the periods 35-40 and 31-40 d of age, respectively. It is suggested that when using a diet with DEB of 180 mEq/kg, adding the El-Be supplements in drinking water was more beneficial than in feed. Adding the supplements in feed or water was equally useful when using DEB of 220 mEq/kg. PMID:25558900

  18. Urinary Retention

    MedlinePLUS

    ... indicates the bladder does not empty completely. A health care provider performs this test during an office visit. The patient often receives ... more urodynamic tests to diagnose urinary retention. The health care provider will perform these tests during an office visit. For tests that use ...

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

    Microsoft Academic Search

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

    2000-01-01

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

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

    PubMed Central

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

    1994-01-01

    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. PMID:7857735

  1. 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...

  2. Determination of n-octanol/water partition coefficient for DDT-related compounds by RP-HPLC with a novel dual-point retention time correction.

    PubMed

    Han, Shu-ying; Qiao, Jun-qin; Zhang, Yun-yang; Yang, Li-li; Lian, Hong-zhen; Ge, Xin; Chen, Hong-yuan

    2011-03-01

    n-Octanol/water partition coefficients (P) for DDTs and dicofol were determined by reversed-phase high performance liquid chromatography (RP-HPLC) on a C(18) column using methanol-water mixture as mobile phase. A dual-point retention time correction (DP-RTC) was proposed to rectify chromatographic retention time (t(R)) shift resulted from stationary phase aging. Based on this correction, the relationship between logP and logk(w), the logarithm of the retention factor extrapolated to pure water, was investigated for a set of 12 benzene homologues and DDT-related compounds with reliable experimental P as model compounds. A linear regression logP=(1.10±0.04) logk(w) - (0.60±0.17) was established with correlation coefficient R(2) of 0.988, cross-validated correlation coefficient R(cv)(2) of 0.983 and standard deviation (SD) of 0.156. This model was further validated using four verification compounds, naphthalene, biphenyl, 2,2-bis(4-chlorophenyl)-1,1-dichloroethane (p,p'-DDD) and 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (p,p'-DDE) with similar structure to DDT. The RP-HPLC-determined P values showed good consistency with shake-flask (SFM) or slow-stirring (SSM) results, especially for highly hydrophobic compounds with logP in the range of 4-7. Then, the P values for five DDT-related compounds, 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1,1-trichloroethane (o,p'-DDT), 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethane (o,p'-DDD), 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethene (o,p'-DDE), and 2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol (dicofol) and its main degradation product 4,4'-dichlorobenzophenone (p,p'-DBP) were evaluated by the improved RP-HPLC method for the first time. The excellent precision with SD less than 0.03 proved that the novel DP-RTC protocol can significantly increases the determination accuracy and reliability of P by RP-HPLC. PMID:21300395

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

    EPA Science Inventory

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

  4. Comparing risk of failure models in water supply networks using ROC curves

    Microsoft Academic Search

    A. Debón; A. Carrión; E. Cabrera; H. Solano

    2010-01-01

    The problem of predicting the failure of water mains has been considered from different perspectives and using several methodologies in engineering literature. Nowadays, it is important to be able to accurately calculate the failure probabilities of pipes over time, since water company profits and service quality for citizens depend on pipe survival; forecasting pipe failures could have important economic and

  5. Comparison of soil water potential sensors

    NASA Astrophysics Data System (ADS)

    Degre, Aurore; van der Ploeg, Martine; Caldwell, Todd; Gooren, Harm

    2015-04-01

    Temporal and spatial monitoring of soil water potential and soil water content are necessary for quantifying water flow in the domains of hydrology, soil science and crop production as knowledge of the soil water retention curve is important for solving Richards' equation. Numerous measurement techniques exist nowadays that use various physical properties of the soil-water complex to record changes in soil water content or soil water potential. Laboratory techniques are very useful to determine static properties of the soil water retention curve, and have been used to show the impacts of hysteresis. Yet, other spatiotemporal dynamics resulting from for example growing root systems, biological activity, periodic tillage and their impact on the soil structure cannot satisfactory be quantified in static setups in the laboratory. ). To be able to quantify the influence of soil heterogeneity, and spatiotemporal dynamics on the soil water retention curve, an in situ approach combining soil moisture and soil water potential measurements could provide useful data. Such an in situ approach would require sensors that can measure a representative part of the soil water retention curve. The volumetric soil water content is often measured using time domain reflectometry, and has gained widespread acceptance as a standard electronic means of volumetric water content measurement. To measure the soil water potential, water filled tensiometers are used in most studies. Unfortunately, their range remains limited due to cavitation. Recently, several new sensors for use under in situ conditions have been proposed to cover a wider range of pressure head: Polymer tensiometers, MPS (Decagon) and pF-meter (ecoTech). In this study, we present the principles behind each measurement technique. Then we present the results of a fully controlled experiment where we compared two MPS sensors, two pF-meter sensors and two POT sensors in the same repacked soil. It allows us to discuss advantages and disadvantages of each method. A CS616 volumetric water content probe was installed to compare in situ measured retention curves with laboratory measured retention curves for each method.

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

    PubMed

    Park, Daeryong; Roesner, Larry A

    2012-12-15

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

  7. Desorption of water from distinct step types on a curved silver crystal.

    PubMed

    Janlamool, Jakrapan; Bashlakov, Dima; Berg, Otto; Praserthdam, Piyasan; Jongsomjit, Bunjerd; Juurlink, Ludo B F

    2014-01-01

    We have investigated the adsorption of H2O onto the A and B type steps on an Ag single crystal by temperature programmed desorption. For this study, we have used a curved crystal exposing a continuous range of surface structures ranging from [5(111) × (100)] via (111) to [5(111) × (110)]. LEED and STM studies verify that the curvature of our sample results predominantly from monoatomic steps. The sample thus provides a continuous array of step densities for both step types. Desorption probed by spatially-resolved TPD of multilayers of H2O shows no dependence on the exact substrate structure and thus confirms the absence of thermal gradients during temperature ramps. In the submonolayer regime, we observe a small and linear dependence of the desorption temperature on the A and B step density. We argue that such small differences are only observable by means of a single curved crystal, which thus establishes new experimental benchmarks for theoretical calculation of chemically accurate binding energies. We propose an origin of the observed behavior based on a "two state" desorption model. PMID:25068782

  8. Titration Curves: A Useful Instrument for Assessing the Buffer Systems of Acidic Mining Waters (10 pp)

    Microsoft Academic Search

    Oliver Totsche; Andrew Fyson; Margarete Kalin; Christian Steinberg

    2006-01-01

    Background, Aims and Scope   The acidification of mine waters is generally caused by metal sulfide oxidation, related to mining activities. These waters\\u000a are characterized by low pH and high acidity due to strong buffering systems. The standard acidity parameter, the Base Neutralization\\u000a Capacity (BNC) is determined by endpoint titration, and reflects a cumulative parameter of both hydrogen ions and all

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

    E-print Network

    Schulte-Herbruggen, Helfrid Maria Albertina

    2012-11-29

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

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

    PubMed Central

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

    2015-01-01

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

  11. Acoustic Ducting, Reflection, Refraction, and Dispersion by Curved Nonlinear Internal Waves in Shallow Water

    Microsoft Academic Search

    James F. Lynch; Ying-Tsong Lin; Timothy F. Duda; Arthur E. Newhall

    2010-01-01

    Nonlinear internal waves in shallow water have been shown to be effective ducts of acoustic energy, through theory, numerical modeling, and experiment. To date, most work on such ducting has concentrated on rectilinear internal wave ducts or those with very slight curvature. In this paper, we examine the acoustic effects of significant curvature of these internal waves. (By significant curvature,

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

    Microsoft Academic Search

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

    1993-01-01

    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

  13. Need probability affects retention: a direct demonstration.

    PubMed

    Anderson, R B; Tweney, R D; Rivardo, M; Duncan, S

    1997-11-01

    Recent memory theory has emphasized the concept of need probability--that is, the probability that a given piece of learned information will be tested at some point in the future. It has been proposed that, in real-world situations, need probability declines over time and that the memory-loss rate is calibrated to match the progressive reduction in need probability (J.R. Anderson & Schooler, 1991). The present experiments were designed to examine the influence of the slope of the need-probability curve on the slope of the retention curve. On each of several trials, subjects memorized a list of digits, then retained the digits in memory for 1, 2, 4, 8, or 16 sec. Some trials ended with a recall test; other trials ended with the message, "no test." In Experiment 1, the likelihood of encountering a memory test (i.e., the need probability) was made to either increase or decrease as the retention interval increased; in Experiment 2, need probability either was flat (invariant across retention intervals) or decreased as the retention interval increased. The results indicated that the shape of the need-probability curve influenced the slope of the retention curve (Experiment 1) and that the effect became larger as the experimental session progressed (Experiment 2). The findings support the notion that memory adapts to need probabilities and that the rate of forgetting is influenced by the slope of the need-probability curve. In addition, all of the forgetting curves approximated a power function, suggesting that need probability influences the slope but not the form of forgetting. PMID:9421573

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

    SciTech Connect

    Ramanathan Sampath

    2004-03-31

    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.

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

    SciTech Connect

    Ramanathan Sampath

    2004-09-30

    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.

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

    SciTech Connect

    Ramanathan Sampath

    2005-09-30

    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.

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

    SciTech Connect

    Ramanathan Sampath

    2005-03-31

    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.

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

    SciTech Connect

    Ramanathan Sampath

    2003-03-31

    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.

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

    SciTech Connect

    Ramanathan Sampath

    2005-12-01

    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.

  20. Stabilities of thiomolybdate complexes of iron; implications for retention of essential trace elements (Fe, Cu, Mo) in sulfidic waters.

    PubMed

    Helz, George R; Erickson, Britt E; Vorlicek, Trent P

    2014-06-01

    In aquatic ecosystems, availabilities of Fe, Mo and Cu potentially limit rates of critical biological processes, including nitrogen fixation, nitrate assimilation and N2O decomposition. During long periods in Earth's history when large parts of the ocean were sulfidic, what prevented these elements' quantitative loss from marine habitats as insoluble sulfide phases? They must have been retained by formation of soluble complexes. Identities of the key ligands are poorly known but probably include thioanions. Here, the first determinations of stability constants for Fe(2+)-[MoS4](2-) complexes in aqueous solution are reported based on measurements of pyrrhotite (hexagonal FeS) solubility under mildly alkaline conditions. Two linear complexes, [FeO(OH)MoS4](3-) and [(Fe2S2)(MoS4)2](4-), best explain the observed solubility variations. Complexes that would be consistent with cuboid cluster structures were less successful, implying that such clusters probably are minor or absent in aqueous solution under the conditions studied. The new data, together with prior data on stabilities of Cu(+)-[MoS4](2-) complexes, are used to explore computationally how competition of Fe(2+) and Cu(+) for [MoS4](2-), as well as competition of [MoS4](2-) and HS(-) for both metals would be resolved in solutions representative of sulfidic natural waters. Thiomolybdate complexes will be most important at sulfide concentrations near the [MoO4](2-)-[MoS4](2-) equivalence point. At lower sulfide concentrations, thiomolybdates are insufficiently stable to be competitive ligands in natural waters and at higher sulfide concentrations HS(-) ligands out-compete thiomolybdates. PMID:24226648

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

    PubMed

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

    2014-11-01

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

  2. Ogive Curves

    NSDL National Science Digital Library

    2008-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  4. Biochar from sugarcane filtercake reduces soil CO2 emissions relative to raw residue and improves water retention and nutrient availability in a highly-weathered tropical soil.

    PubMed

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

    2014-01-01

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

  5. Multiresolution curves

    Microsoft Academic Search

    Adam Finkelstein; David H. Salesin

    1994-01-01

    We describe a multiresolution curve representation, based on wavelets, that conveniently supports a variety of operations: smoothing a curve; editing the overall form of a curve while preserving its details; and approximating a curve within any given error tolerance for scan conversion. We present methods to support continuous levels of smoothing as well as direct manipulation of an arbitrary portion

  6. Frequency curves

    USGS Publications Warehouse

    Riggs, H.C.

    1968-01-01

    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.

  7. 2012 Retention Review Guide Online Annual Retention Review

    E-print Network

    Tennessee, University of

    2012 Retention Review Guide Online Annual Retention Review Of TenureTrack Faculty The University of Tennessee Office of Information Technology 08/30/2012 Online Performance Review System Retention Review Steps...................................................4 How to access the Online

  8. Improvement in the water retention characteristics of sandy loam soil using a newly synthesized poly(acrylamide-co-acrylic acid)/AlZnFe2O4 superabsorbent hydrogel nanocomposite material.

    PubMed

    Shahid, Shaukat Ali; Qidwai, Ansar Ahmad; Anwar, Farooq; Ullah, Inam; Rashid, Umer

    2012-01-01

    The use of some novel and efficient crop nutrient-based superabsorbent hydrogel nanocomposites (SHNCs), is currently becoming increasingly important to improve the crop yield and productivity, due to their water retention properties. In the present study a poly(Acrylamide-co-acrylic acid)/AlZnFe2O4 superabsorbent hydrogel nanocomposite was synthesized and its physical properties characterized using Energy Dispersive X-ray (EDX), FE-SEM and FTIR spectroscopic techniques. The effects of different levels of SHNC were studied to evaluate the moisture retention properties of sandy loam soil (sand 59%, silt 21%, clay 19%, pH 7.4, EC 1.92 dS/m). The soil amendment with 0.1, 0.2, 0.3 and 0.4 w/w% of SHNC enhanced the moisture retention significantly at field capacity compared to the untreated soil. Besides, in a separate experiment, seed germination and seedling growth of wheat was found to be notably improved with the application of SHNC. A delay in wilting of seedlings by 5-8 days was observed for SHNC-amended soil, thereby improving wheat plant growth and establishment. PMID:22864245

  9. Neurogenic urinary retention

    Microsoft Academic Search

    A. G. Herbaut

    1993-01-01

    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

  10. Failing Grades for Retention.

    ERIC Educational Resources Information Center

    Natriello, Gary

    1998-01-01

    Although prevailing research indicates that holding back students carries negative effects, retention is becoming ever more popular. Administrators seeking secure funding for retention alternatives face considerable resistance, while the decision to add a full year of expenditures for a retained student is made without considering budgetary…

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

    SciTech Connect

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

    1996-09-01

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

  12. Two-dimensional array of particles originating from dipole-dipole interaction as evidenced by potential curve measurements at vertical oil/water interfaces.

    PubMed

    Sakka, Tetsuo; Kozawa, Daichi; Tsuchiya, Kiyoto; Sugiman, Nao; Øye, Gisle; Fukami, Kazuhiro; Nishi, Naoya; Ogata, Yukio H

    2014-08-28

    We propose a new method to evaluate the interaction potential energy between the particles adsorbed at an oil/water interface as a function of interparticle distance. The method is based on the measurement of the interparticle distance at a vertical oil/water interface, at which the gravitational force is naturally applied to compress the particle monolayer in the in-plane direction. We verified the method by examining whether we obtained the same potential curve upon varying the gravitational acceleration by tilting the interface. The present method is applicable in the force range from ?0.1 to ?100 pN, determined by the effective weight of the particles at the interface. The method gives a rather simple procedure to estimate a long range interaction among the particles adsorbed at oil/water interfaces. We applied this method to polystyrene particles at the decane/aqueous surfactant solution interface, and obtained the interparticle potential curves. All the potential curves obtained by the present method indicated that the interparticle repulsion is due to the electrical dipole-dipole interaction based on the negative charge of the particles. The mechanism of the dipole-dipole interaction is further discussed on the basis of the effects of surfactants. PMID:25005863

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. Quantum curves

    E-print Network

    Albert Schwarz

    2014-08-16

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

  15. Flow-duration curves

    USGS Publications Warehouse

    Searcy, James Kincheon

    1959-01-01

    The flow-duration curve is a cumulative frequency curve that shows the percent of time specified discharges were equaled or exceeded during a given period. It combines in one curve the flow characteristics of a stream throughout the range of discharge, without regard to the sequence of occurrence. If the period upon which the curve is based represents the long-term flow of a stream, the curve may be used to predict the distribution of future flows for water- power, water-supply, and pollution studies. This report shows that differences in geology affect the low-flow ends of flow-duration curves of streams in adjacent basins. Thus, duration curves are useful in appraising the geologic characteristics of drainage basins. A method for adjusting flow-duration curves of short periods to represent long-term conditions is presented. The adjustment is made by correlating the records of a short-term station with those of a long-term station.

  16. Drug Retention Times

    SciTech Connect

    Center for Human Reliability Studies

    2007-05-01

    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.

  17. Drug Retention Times

    SciTech Connect

    Center for Human Reliability Studies

    2007-05-01

    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

  18. 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...

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

    Microsoft Academic Search

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

    2010-01-01

    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

  20. Importance of sediment deposition and denitrification for nutrient retention in floodplain wetlands

    Microsoft Academic Search

    Harry Olde Venterink; Jan E. Vermaat; Mario Pronk; Frank Wiegman; Lee van der G. E. M; Hoorn van den M. W; Jos T. A. Verhoeven

    2006-01-01

    Questions: Various floodplain communities may differ in their relative abilities to influence water quality through nutrient retention and denitrification. Our main questions were: (1) what is the importance of sediment deposition and denitrification for plant productivity and nutrient retention in floodplains; (2) will rehabilitation of natural floodplain communities (semi-natural grassland, reedbed, woodland, pond) from agricultural grassland affect nutrient retention? Location:

  1. 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

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

    1995-01-01

    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.

  2. Light Curves

    NSDL National Science Digital Library

    2013-02-12

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

  3. "Assistants Retention in

    E-print Network

    Turner, Monica G.

    The Impact ofTeaching "Assistants on Student Retention in the Sciences Lessons for TA Training courses. A majority ofscience, technology, engineering, and mathematics (STEM) bachelor's degrees have on underclass students' plans to major in or leave the sciences? Literature on student attrition

  4. Secrets of Retention

    ERIC Educational Resources Information Center

    Poliniak, Susan

    2012-01-01

    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…

  5. Tritium retention in TFTR

    Microsoft Academic Search

    C. H. Skinner; D. Mueller; R. T. Walters; R. Causey; S. Luckhardt; J. Hirooka

    1996-01-01

    The large tritium inventories projected for ITER pose an important constraint in the design of plasma facing components and the selection of first wall materials. Three years of deuterium-tritium operation in TFTR has provided a special opportunity to address the issues of tritium retention in a tokamak environment. More than 18 kCi of tritium has been injected into the torus

  6. The origin of the "snap-in" in the force curve between AFM probe and the water/gas interface of nanobubbles.

    PubMed

    Song, Yang; Zhao, Binyu; Zhang, Lijuan; Lü, Junhong; Wang, Shuo; Dong, Yaming; Hu, Jun

    2014-02-24

    The long-range attractive force or "snap-in" is an important phenomenon usually occurring when a solid particle interacts with a water/gas interface. By using PeakForce quantitative nanomechanics the origin of snap-in in the force curve between the atomic force microscopy (AFM) probe and the water/gas interface of nanobubbles has been investigated. The snap-in frequently happened when the probe was preserved for a certain time or after being used for imaging solid surfaces under atmospheric conditions. In contrast, imaging in liquids rarely induced a snap-in. After a series of control experiments, it was found that the snap-in can be attributed to hydrophobic interactions between the water/gas interface and the AFM probe, which was either modified or contaminated with hydrophobic material. The hydrophobic contamination could be efficiently removed by a conventional plasma-cleaning treatment, which prevents the occurring of the snap-in. In addition, the adsorption of sodium dodecyl sulfate onto the nanobubble surface changed the water/gas interface into hydrophilic, which also eliminated the snap-in phenomenon. PMID:24478257

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  8. Teacher Retention: Problems and Solutions

    ERIC Educational Resources Information Center

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

    2009-01-01

    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…

  9. 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

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

    2006-01-01

    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

  10. 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 ...

  11. Modelling the Hydrological Performance of Stormwater Management Retention Ponds in Scotland

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    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.

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

    Microsoft Academic Search

    B. Fulton; E. H. Jeffery

    1990-01-01

    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

  13. 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

    Ignacio Moreno-Villoslada; Bernabé L Rivas

    2003-01-01

    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)

  14. Retention: A Model

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    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.

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

    PubMed

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

    2014-08-01

    The increasing application of engineered nanoparticles (ENPs) has heightened the concern that these ENPs would eventually be released to the environment and may enter into life cycle of living beings. In this regard, it is essential to understand how these ENPs transport and retain in natural soils because they are considered to be a major repository for ENPs. Herein, transport and retention of polyvinylpyrrolidone (PVP)-coated silver nanoparticles (PVP-AgNPs) were investigated over a wide range of physicochemical factors in water-saturated columns packed with an Ultisol rich in clay-size particles. Higher mobility of PVP-AgNPs occurred at larger soil grain size, lower solution ionic strength and divalent cation concentration, higher flow rate, and greater PVP concentrations. Most breakthrough curves (BTCs) for PVP-AgNPs exhibited significant amounts of retardation in the soil due to its large surface area and quantity of retention sites. In contrast to colloid filtration theory, the shapes of retention profiles (RPs) for PVP-AgNPs were either hyperexponential or nonmonotonic (a peak in particle retention down-gradient from the column inlet). The BTCs and hyperexponential RPs were successfully described using a 1-species model that considered time- and depth-dependent retention. Conversely, a 2-species model that included reversibility of retained PVP-AgNPs had to be employed to better simulate the BTCs and nonmonotonic RPs. As the retained concentration of species 1 approached the maximum solid-phase concentration, a second mobile species (species 2, i.e., the same PVP-AgNPs that are reversibly retained) was released that could be retained at a different rate than species 1 and thus yielded the nonmonotonic RPs. Some retained PVP-AgNPs were likely to irreversibly deposit in the primary minimum associated with microscopic chemical heterogeneity (favorable sites). Transmission electron microscopy and energy-dispersive X-ray spectroscopy analysis suggested that these favorable sites were positively charged sites on montmorillonite edges and goethite surfaces in the soil. Overall, our study highlights that the transport and especially retention of PVP-AgNPs are highly sensitive to the physicochemical factors, but mathematical modeling can accurately predict the fate of these ENPs in porous media which is important for better understanding the fate of these ENPs in point of exit and in the environment. PMID:24926609

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  17. Water quality, streamflow conditions, and annual flow-duration curves for streams of the San Juan–Chama Project, southern Colorado and northern New Mexico, 1935-2010

    USGS Publications Warehouse

    Falk, Sarah E.; Anderholm, Scott K.; Hafich, Katya A.

    2013-01-01

    The Albuquerque–Bernalillo County Water Utility Authority supplements the municipal water supply for the Albuquerque metropolitan area, in central New Mexico, with water diverted from the Rio Grande. Water diverted from the Rio Grande for municipal use is derived from the San Juan–Chama Project, which delivers water from streams in the southern San Juan Mountains in the Colorado River Basin in southern Colorado to the Rio Chama watershed and the Rio Grande Basin in northern New Mexico. The U.S. Geological Survey, in cooperation with Albuquerque–Bernalillo County Water Utility Authority, has compiled historical streamflow and water-quality data and collected new water-quality data to characterize the water quality and streamflow conditions and annual flow variability, as characterized by annual flow-duration curves, of streams of the San Juan–Chama Project. Nonparametric statistical methods were applied to calculate annual and monthly summary statistics of streamflow, trends in streamflow conditions were evaluated with the Mann–Kendall trend test, and annual variation in streamflow conditions was evaluated with annual flow-duration curves. The study area is located in northern New Mexico and southern Colorado and includes the Rio Blanco, Little Navajo River, and Navajo River, tributaries of the San Juan River in the Colorado River Basin located in the southern San Juan Mountains, and Willow Creek and Horse Lake Creek, tributaries of the Rio Chama in the Rio Grande Basin. The quality of water in the streams in the study area generally varied by watershed on the basis of the underlying geology and the volume and source of the streamflow. Water from the Rio Blanco and Little Navajo River watersheds, primarily underlain by volcanic deposits, volcaniclastic sediments and landslide deposits derived from these materials, was compositionally similar and had low specific-conductance values relative to the other streams in the study area. Water from the Navajo River, Horse Lake Creek, and Willow Creek watersheds, which are underlain mostly by Cretaceous-aged marine shale, was compositionally similar and had large concentrations of sulfate relative to the other streams in the study area, though the water from the Navajo River had lower specific-conductance values than did the water from Horse Lake Creek above Heron Reservoir and Willow Creek above Azotea Creek. Generally, surface-water quality varied with streamflow conditions throughout the year. Streamflow in spring and summer is generally a mixture of base flow (the component of streamflow derived from groundwater discharged to the stream channel) diluted with runoff from snowmelt and precipitation events, whereas streamflow in fall and winter is generally solely base flow. Major- and trace-element concentrations in the streams sampled were lower than U.S. Environmental Protection Agency primary and secondary drinking-water standards and New Mexico Environment Department surface-water standards for the streams. In general, years with increased annual discharge, compared to years with decreased annual discharge, had a smaller percentage of discharge in March, a larger percentage of discharge in June, an interval of discharge derived from snowmelt runoff that occurred later in the year, and a larger discharge in June. Additionally, years with increased annual discharge generally had a longer duration of runoff, and the streamflow indicators occurred at dates later in the year than the years with less snowmelt runoff. Additionally, the seasonal distribution of streamflow was more strongly controlled by the change in the amount of annual discharge than by changes in streamflow over time. The variation of streamflow conditions over time at one streamflow-gaging station in the study area, Navajo River at Banded Peak Ranch, was not significantly monotonic over the period of record with a Kendall’s tau of 0.0426 and with a p-value of 0.5938 for 1937 to 2009 (a trend was considered statistically significant at a p-value ? 0.05). There was a relation, however, such that annua

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

    PubMed Central

    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

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

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

    EPA Science Inventory

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

  20. RETENTION TIME EFFECT ON METAL REMOVAL BY PEAT COLUMNS

    SciTech Connect

    Nelson, E

    2007-02-28

    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.

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

    SciTech Connect

    Walters, F.H.

    1983-01-01

    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.

  2. Transport and Retention of Emulsion Droplets in Sandy Porous Media

    NASA Astrophysics Data System (ADS)

    Esahani, S. G.; Muller, K.; Chapra, S. C.; Ramsburg, A.

    2014-12-01

    Emulsions are commonly used as amendments during remediation; yet, the processes controlling the distribution of droplets within the subsurface are not well understood. Given that inadequate spatial and/or temporal delivery of amendments often leads to ineffective treatment, there is a need to better understand emulsion transport. Experiments were conducted to evaluate the transport and retention of emulsion droplets in columns containing Ottawa sands. Breakthrough curves and deposition profiles from these experiments were interrogated using a mathematical model capable of describing attachment, detachment, and straining to begin to elucidate the physical processes controlling delivery. Emulsions were constructed by stabilizing soybean oil droplets within a continuous aqueous phase. Physical properties of the resulting oil-in-water emulsions were favorable for subsurface delivery (nominal properties: 1 g/mL density; 10 cP viscosity; and 1.5 ?m droplet d50). Emulsions were introduced to the columns for approximately two pore volumes and followed by an extended flush of background solution. Effluent droplet size distributions did not vary significantly over the course of the experiment and remained similar to those measured for the influent emulsion. Emulsion breakthrough curves exhibited tailing, and deposition profiles were found to be hyper-exponential and unaffected by extended periods of background flow. Depending on emulsion composition and flow characteristics, 10-30% of the injected emulsion was retained on the sand suggesting a non-negligible influence on accessible porosity over the course of the experiment. Experimental results were further interpreted using a droplet transport model that accounts for temporal and spatial variation in porosity due to the retention of the emulsion droplets. At present the model assumes a uniform size distribution of inelastic emulsion droplets which are transported by advection and dispersion, and exchanged with the solid phase through attachment, detachment, and straining processes. Results examine the relative roles of attachment-detachment and straining in reducing the accessible porosity. Evaluation of how the porosity change influences the flow regime for moderately and slightly clogged media is currently under investigation.

  3. 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

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

    2006-01-01

    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.

  4. Water-retention properties of porous ceramics prepared from mixtures of allophane and vermiculite for materials to counteract heat island effects

    Microsoft Academic Search

    Kiyoshi Okada; Shunsuke Matsui; Toshihiro Isobe; Yoshikazu Kameshima; Akira Nakajima

    2008-01-01

    Porous ceramics for anti-heat island effect were prepared from mixtures of allophane and vermiculite (VA samples). Allophane and vermiculite which had been ground for 0.5–2h was mixed in various mass ratios, formed into pellets by uniaxial pressing at 40MPa, and heated at 600–800°C to form porous ceramics. The large thermal expansion of the vermiculite upon explosive dehydration of interlayer water

  5. 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

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

    1997-01-01

    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

  6. [Acute urinary retention in children].

    PubMed

    Marans, Rachel; Mandel, Asaf; Gielchinsky, Ilan; Tenenbaum, Ariel

    2012-06-01

    Acute urinary retention is defined as failure to urinate in spite of an adequate amount of urine in the bladder. Acute urinary retention in children is rare, and may cause pain and distress. Diagnosis and urgent treatment are essential. Identification and treatment of underlying medical conditions such as constipation, neurological impairment or adverse reactions to medications may prevent recurrence of retention. We describe six cases of children who were hospitalized with acute urinary retention and review the medical literature on the subject. PMID:22991857

  7. Refining the M {sub BH}-V {sub c} scaling relation with H I rotation curves of water megamaser galaxies

    SciTech Connect

    Sun, Ai-Lei; Greene, Jenny E. [Department of Astrophysics, Princeton University, Princeton, NJ 08540 (United States); Impellizzeri, C. M. Violette; Braatz, James A. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Kuo, Cheng-Yu [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Tuttle, Sarah [McDonald Observatory, The University of Texas, Austin, TX 78712 (United States)

    2013-11-20

    Black-hole-galaxy scaling relations provide information about the coevolution of supermassive black holes and their host galaxies. We compare the black-hole mass-circular-velocity (M {sub BH}-V {sub c}) relation with the black-hole-mass-bulge-stellar-velocity-dispersion (M {sub BH}-?{sub *}) relation to see whether the scaling relations can passively emerge from a large number of mergers or require a physical mechanism, such as feedback from an active nucleus. We present Very Large Array H I observations of five galaxies, including three water megamaser galaxies, to measure the circular velocity. Using 22 galaxies with dynamical M {sub BH} measurements and V {sub c} measurements extending to large radius, our best-fit M {sub BH}-V {sub c} relation, log?M{sub BH}=?+?log?(V{sub c}/200 km s{sup ?1}), yields ?=7.43{sub ?0.13}{sup +0.13}, ?=3.68{sub ?1.20}{sup +1.23}, and an intrinsic scatter ?{sub int}=0.51{sub ?0.09}{sup +0.11}. The intrinsic scatter may well be higher than 0.51, as we take great care to ascribe conservatively large observational errors. We find comparable scatter in the M {sub BH}-?{sub *} relations, ?{sub int}=0.48{sub ?0.08}{sup +0.10}, while pure merging scenarios would likely result in a tighter scaling with the dark halo (as traced by V {sub c}) properties rather than the baryonic (?{sub *}) properties. Instead, feedback from the active nucleus may act on bulge scales to tighten the M {sub BH}-?{sub *} relation with respect to the M {sub BH}-V {sub c} relation, as observed.

  8. Assessing plant water relations based on hidden in formation in the hyper-spectral signatures: Parameterization of olive leaf P-V curve and estimation of water potential components

    NASA Astrophysics Data System (ADS)

    Rallo, Giovanni; Provenzano, Giuseppe; Jones, Hamlyn G.

    2015-04-01

    The Soil Plant Atmosphere Continuum (SPAC) is characterized by complex structures and biophysical processes acting over a wide range of temporal and spatial scales. Additionally, in olive grove systems, the plant adaptive strategies to respond to soil water-limited conditions make the system even more complex. One of the greatest challenges in hydrological research is to quantify changing plant water relations. A promising new technology is provided by the advent of new field spectroscopy detectors, characterized by very high resolution over the spectral range between 300 and 2500 nm, allowing the detection of narrow reflectance or absorptance peaks, to separate close lying peaks and to discover new information, hidden at lower resolutions. The general objective of the present research was to investigate a range of plant state function parameters in a non-destructive and repeatable manner and to improve methodologies aimed to parameterize hydrological models describing the entire SPAC, or each single compartment (soil or plant). We have investigated the use of hyperspectral sensing for the parameterization of the hydraulic pressure-volume curve (P-V) for olive leaf and for the indirect estimation of the two principal leaf water potential components, i.e. turgor and osmotic potentials. Experiments were carried out on an olive grove in Sicily, during the mature phase of the first vegetative flush. Leaf spectral signatures and associated P-V measurements were acquired on olive leaves collected from well-irrigated plants and from plants maintained under moderate or severe water stress. Leaf spectral reflectance was monitored with a FieldSpec 4 spectro-radiometer (Analytical Spectral Device, Inc.), in a range of wavelengths from VIS to SWIR (350-2500 nm), with sampling intervals of 1.4 nm and 2.0 nm, respectively in the regions from 350 to 1000 nm and from 1000 to 2500 nm. Measurements required the use of contact probe and leaf clip (Analytical Spectral Device, Inc.), specifically designed for plant leaves. Immediately after each spectral acquisition, water potential was measured on the same leaf with a Scholander pressure chamber (Skye, Powys, UK), by following the standard procedure usually adopted to detect leaf P-V curves (Vilagrosa et al. 2003). The relationship between pressure and volume was represented by means of the Höfler diagram (Richter, 1978) and modeled following an analytical approach. In order to parameterize the the P-V curve and to estimate the leaf water potential components, spectral indices were then examined, considering the features of water absorption in SWIR domain, sensitive to changes in leaf water content, and in NIR domain of the spectrum, sensitive to changes in leaf internal structure. A number of spectral indices were found to be related to patterns in the Höfler diagram, for leaves collected under different intensities of crop water stress. Moreover, results show that a fundamental characteristic point of the Höfler diagram, the turgor loss point, can be identified when indices accounting for both SWIR and NIR domains are considered. Acknowledgements The research was carried out thanks to the Alexander Goetz support program 2014, which provided the tools for spectral measurements and technical assistance during experiments.

  9. Derivation of Soil Moisture Retention Characteristics from Saturated Hydraulic Conductivity

    E-print Network

    Kumar, C.P.

    : Knowledge of the physics of soil water movement is crucial to the solution of many problems in watershed1 Derivation of Soil Moisture Retention Characteristics from Saturated Hydraulic Conductivity C. P systems require knowledge of the relationships between soil moisture content (), soil water pressure (h

  10. [Retention or adhesion?].

    PubMed

    Sharon, E; Lipovezky-Adler, M; Haramaty, O; Smidt, A

    2013-04-01

    One of the reasons for immediate or late failure of restorations is the detachment of the restoration from the tooth. Retention for the restoration could be achieved from axial walls (macromechanical retention) or from adhesion of the restoration to the remaining tooth structure. Adhesion relies on bonding of resin cement to enamel or dentin on one side and to the restorative material on the other side. Bonding to enamel is predictable. Good bonding to dentin is more of a challenge especially with indirect restorations. In those cases the restoration is delivered usually a few days after the tooth was prepared during this time the exposed dentin might be contaminated or damaged. The question is whether you can rely on adhesion when cementing indirect restorations? In order to achieve the maximal bonding strength to dentin, the hybrid layer on the dentin must be built immediately after tooth preparation. This procedure is called Immediate Dentin Sealing. In vitro and clinical studies have shown better performance of restorations cemented following the IDS procedure. The article discusses the rational and the protocol of this procedure. A clinical case is presented as an example for the possibilities following this philosophy. PMID:24020243

  11. Introduction Elliptic curves

    E-print Network

    Kwak, Do Young

    Introduction Elliptic curves Modular curves Elliptic curves and modular forms Application to number theory y-coordinates of elliptic curves Dong Hwa Shin Department of Mathematical Sciences KAIST January 11, 2010 #12;Introduction Elliptic curves Modular curves Elliptic curves and modular forms

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

    PubMed

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

    2013-04-01

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

  13. Pesticide and trace metal occurrence and aquatic benchmark exceedances in surface waters and sediments of urban wetlands and retention ponds in Melbourne, Australia.

    PubMed

    Allinson, Graeme; Zhang, Pei; Bui, AnhDuyen; Allinson, Mayumi; Rose, Gavin; Marshall, Stephen; Pettigrove, Vincent

    2015-07-01

    Samples of water and sediments were collected from 24 urban wetlands in Melbourne, Australia, in April 2010, and tested for more than 90 pesticides using a range of gas chromatographic (GC) and liquid chromatographic (LC) techniques, sample 'hormonal' activity using yeast-based recombinant receptor-reporter gene bioassays, and trace metals using spectroscopic techniques. At the time of sampling, there was almost no estrogenic activity in the water column. Twenty-three different pesticide residues were observed in one or more water samples from the 24 wetlands; chemicals observed at more than 40 % of sites were simazine (100 %), atrazine (79 %), and metalaxyl and terbutryn (46 %). Using the toxicity unit (TU) concept, less than 15 % of the detected pesticides were considered to pose an individual, short-term risk to fish or zooplankton in the ponds and wetlands. However, one pesticide (fenvalerate) may have posed a possible short-term risk to fish (log10TUf > -3), and three pesticides (azoxystrobin, fenamiphos and fenvalerate) may have posed a risk to zooplankton (logTUzp between -2 and -3); all the photosystem II (PSII) inhibiting herbicides may have posed a risk to primary producers in the ponds and wetlands (log10TUap and/or log10TUalg > -3). The wetland sediments were contaminated with 16 different pesticides; no chemicals were observed at more than one third of sites, but based on frequency of detection and concentrations, bifenthrin (33 %, maximum 59 ?g/kg) is the priority insecticide of concern for the sediments studied. Five sites returned a TU greater than the possible effect threshold (i.e. log10TU > 1) as a result of bifenthrin contamination of their sediments. Most sediments did not exceed Australian sediment quality guideline levels for trace metals. However, more than half of the sites had threshold effect concentration quotients (TECQ) values >1 for Cu (58 %), Pb (50 %), Ni (67 %) and Zn (63 %), and 75 % of sites had mean probable effect concentration quotients (PECQ) >0.2, suggesting that the collected sediments may have been having some impact on sediment-dwelling organisms. PMID:25697552

  14. Retention in Grade: Lethal Lessons?

    ERIC Educational Resources Information Center

    Sherwood, Charles

    Despite a growing trend toward retention in grade of low-achieving students and apparent public support for the practice, many educators and psychologists disagree with the perception that flunking is an appropriate response to poor academic performance. Research reported in the past two decades indicates that grade-level retention produces little…

  15. Teacher Retention in Catholic Schools

    ERIC Educational Resources Information Center

    Przygocki, Walter F.

    2004-01-01

    Teacher attrition is a concern in all educational sectors but is of special importance to Catholic schools because of the salary disparity between public and Catholic schools. This review examines the research on teacher retention in general with a view to understanding how this knowledge might inform teacher recruitment and retention strategies…

  16. Flavor Retention During Drying1

    Microsoft Academic Search

    Gary A. Reineccius; S. T. Coulter

    1969-01-01

    The influence of spray dryer operating conditions (drying temperatures, extract solids content, nozzle orifice size, and in- feed spray pressure) and of variations in the proportions of individual skin~- milk components in the extract to be dried, upon flavor retention during drying, was investigated. The influence of those variables upon flavor retention was evalu- ated by adding either acetoin, acetone,

  17. Nitrogen retention in natural Mediterranean wetlands affected by agricultural runoff

    NASA Astrophysics Data System (ADS)

    García García, V.; Gómez, R.; Vidal-Abarca, M. R.; Suárez, M. L.

    2009-08-01

    Nitrogen retention efficiency in natural Mediterranean wetlands affected by agricultural runoff was quantified and the effect of season and hydrological/chemical loading was examined from March 2007 to June 2008 in two wetland-streams located in Southeast Spain. Nitrate-N (NO3--N), ammonium-N (NH4+-N), total organic nitrogen-N (TON-N) and chloride (Cl-) concentrations were analyzed to calculate nitrogen retention efficiencies. These wetlands consistently reduced water nitrogen concentration throughout the year with higher values for NO3--N (72.3%), even though the mean values of inflow NO3--N concentrations were above 20 mg l-1. Additionally, they usually acted as sinks for TON-N (45.4%), but as sources for NH4+-N. Over the entire study period, the Taray and Parra wetlands were capable of removing a mean value of 1.6 and 0.8 kg NO3--N a day-1, respectively. Retention efficiencies were not affected by temperature variation and did not follow a seasonal pattern. The temporal variability for NO3--N retention efficiency was positively and negatively explained by the net hydrologic retention and the inflow NO3--N concentration (R2adj=0.832, p<0.001), respectively. TON-N retention efficiency was only positively explained by the net hydrologic retention (R2adj=0.1997, p<0.05). No significant regression model was found for NH4+-N. Finally, the conservation of these Mediterranean wetland-streams may act as a tool to not only improves the surface water quality in agricultural catchments, but to also achieve a good ecological status for surface waters, this being the Water Framework Directive's ultimate purpose.

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

    PubMed

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

    2015-03-21

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

  19. The effect of resin cements and primer on retentive force of zirconia copings bonded to zirconia abutments with insufficient retention

    PubMed Central

    Kim, Seung-Mi; Yoon, Ji-Young; Lee, Myung-Hyun

    2013-01-01

    PURPOSE The purpose of this study was to investigate the effect of resin cements and primer on the retentive force of zirconia copings bonded to zirconia abutments with insufficient retention. MATERIALS AND METHODS Zirconia blocks (Lava, 3M ESPE, St. Paul, MN, USA) were obtained and forty sets of zirconia abutments and copings were fabricated using CAD/CAM technology. They were grouped into 4 categories as follows, depending on the types of resin cements used, and whether the primer is applied or not:Panavia F2.0 (P), Panavia F2.0 using Primer (PRIME Plus, Bisco Inc, Schaumburg, IL, USA) (PZ), Superbond C&B (S), and Superbond C&B using Primer (SZ). For each of the groups, the cementation was conducted. The specimens were kept in sterilized water (37?) for 24 hours. Retentive forces were tested and measured, and a statistical analysis was carried out. The nature of failure was recorded. RESULTS The means and standard deviations of retentive force in Newton for each group were 265.15 ± 35.04 N (P), 318.21 ± 22.24 N (PZ), 445.13 ± 78.54 N (S) and 508.21 ± 79.48 N (SZ). Superbond C&B groups (S & SZ) showed significantly higher retentive force than Panavia F2.0 groups (P & PZ). In Panavia F2.0 groups, the use of primer was found to contribute to the increase of retentive force. On the other hand, in Superbond C&B groups, the use of primer did not influence the retention forces. Adhesive failure was observed in all groups. CONCLUSION This study suggests that cementation of the zirconia abutments and zirconia copings with Superbond C&B have a higher retentive force than Panavia F2.0. When using Panavia F2.0, the use of primer increases the retentive force. PMID:23755347

  20. Retrofitting a stormwater retention pond using a deflector island.

    PubMed

    Khan, S; Melville, B W; Shamseldin, A Y

    2011-01-01

    Stormwater retention ponds are one of the principal methods to treat stormwater runoff. Analysis of residence time distribution (RTD) curves can be used to evaluate the capability of these ponds for sediment removal. Deflector islands have been suggested as a means of improving the performance of retention ponds, due to their diffusing the inlet jet. In this study, the effect of an island on retention pond performance was investigated using a physical model of an existing stormwater retention pond. The physical model is a trapezoidal pond having top dimensions 4.1 x 1.5 x 0.23 m and side slopes of 2:1 (h:v). Three different arrangements were studied. The results show that placing an island to deflect the influent to a stormwater retention pond does not improve pond performance, rather it stimulates short-circuiting. This unexpected behaviour, in relation to previous studies, is considered to be a consequence of the model pond incorporating sloping walls; which is a novel aspect of this paper. PMID:22049712

  1. Fluid retention in cirrhosis: pathophysiology and management.

    PubMed

    Kashani, A; Landaverde, C; Medici, V; Rossaro, L

    2008-02-01

    Accumulation of fluid as ascites is the most common complication of cirrhosis. This is occurring in about 50% of patients within 10 years of the diagnosis of cirrhosis. It is a prognostic sign with 1-year and 5-year survival of 85% and 56%, respectively. The most acceptable theory for ascites formation is peripheral arterial vasodilation leading to underfilling of circulatory volume. This triggers the baroreceptor-mediated activation of renin-angiotensin-aldosterone system, sympathetic nervous system and nonosmotic release of vasopressin to restore circulatory integrity. The result is an avid sodium and water retention, identified as a preascitic state. This condition will evolve in overt fluid retention and ascites, as the liver disease progresses. Once ascites is present, most therapeutic modalities are directed on maintaining negative sodium balance, including salt restriction, bed rest and diuretics. Paracentesis and albumin infusion is applied to tense ascites. Transjugular intrahepatic portosystemic shunt is considered for refractory ascites. With worsening of liver disease, fluid retention is associated with other complications; such as spontaneous bacterial peritonitis. This is a primary infection of ascitic fluid caused by organisms originating from large intestinal normal flora. Diagnostic paracentesis and antibiotic therapy plus prophylactic regimen are mandatory. Hepatorenal syndrome is a state of functional renal failure in the setting of low cardiac output and impaired renal perfusion. Its management is based on drugs that restore normal renal blood flow through peripheral arterial and splanchnic vasoconstriction, renal vasodilation and/or plasma volume expansion. However, the definitive treatment is liver transplantation. PMID:18184668

  2. Data Retention and Anonymity Services

    NASA Astrophysics Data System (ADS)

    Berthold, Stefan; Böhme, Rainer; Köpsell, Stefan

    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.

  3. Retention in orthodontics.

    PubMed

    Johnston, C D; Littlewood, S J

    2015-02-16

    Retention is necessary following orthodontic treatment to prevent relapse of the final occlusal outcome. Relapse can occur as a result of forces from the periodontal fibres around the teeth which tend to pull the teeth back towards their pre-treatment positions, and also from deflecting occlusal contacts if the final occlusion is less than ideal. Age changes, in the form of ongoing dentofacial growth, as well as changes in the surrounding soft tissues, can also affect the stability of the orthodontic outcome. It is therefore essential that orthodontists, patients and their general dental practitioners understand the importance of wearing retainers after orthodontic treatment. This article will update the reader on the different types of removable and fixed retainers, including their indications, duration of wear, and how they should be managed in order to minimise any unwanted effects on oral health and orthodontic outcomes. The key roles that the general dental practitioner can play in supporting their patients wearing orthodontic retainers are also emphasised. PMID:25686428

  4. Payload retention device

    NASA Technical Reports Server (NTRS)

    Monford, Leo G., Jr. (inventor)

    1992-01-01

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

  5. EA Shuttle Document Retention Effort

    NASA Technical Reports Server (NTRS)

    Wagner, Howard A.

    2010-01-01

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

  6. Parent lithology, surface-groundwater exchange, and nitrate retention in headwater streams

    Microsoft Academic Search

    H. Maurice Valett; John A. Morrice; N. Dahm

    1996-01-01

    We address the ecological ramifications of variation in hydrologic interaction between streams and alluvial aquifers in catchments with alluvium derived from parent materials of contrasting geologic composition. We present a conceptual model in which solute retention in streams results from hydrologic retention (increased water residence time resulting from surface-groundwater exchange), biological nutrient cycling, and chemical processes. Solute injection experiments were

  7. Grade Retention and School Performance

    Microsoft Academic Search

    Ann R. McCoy; Arthur J. Reynolds

    1999-01-01

    A follow-up study of the predictors and consequences of grade retention up to age 14 was conducted. This study investigated the effects of retention on school achievement, perceived school competence, and delinquency. The study sample included 1,164 low-income, minority (95% Black, 5% Hispanic) children from the Chicago Longitudinal Study. This was 93% of the original study by Reynolds (1992). Twenty-eight

  8. Turnover: strategies for staff retention.

    PubMed

    SnowAntle, S

    1990-01-01

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

  9. Quantifying flow retention due to vegetation in an earthen experimental channel using the Aggregated Dead Zone (ADZ) dilution approach

    NASA Astrophysics Data System (ADS)

    Carling, Paul; Kleinhans, Maarten; Leyland, Julian; Besozzi, Louison; Duranton, Pierre; Trieu, Hai; Teske, Roy

    2014-05-01

    Understanding of flow resistance of forested floodplains is essential for floodplain flow routing and floodplain reforestation projects. Although the flow resistance of grass-lined channels is well-known, flow retention due to flow-blocking by trees is poorly understood. Flow behaviour through tree-filled channels or over forested floodplain surfaces has largely been addressed using laboratory studies of artificial surfaces and vegetation. Herein we take advantage of a broad, shallow earthen experimental outdoor channel with headwater and tailwater controls. The channel was disused and left undisturbed for more than 20 years. During this time period, small deciduous trees and a soil cover of grass, herbs and leaf-litter established naturally. We measured flow resistance and fluid retention in fifteen controlled water discharge experiments for the following conditions: (a) natural cover of herbs and trees; (b) trees only and; (c) earthen channel only. In the b-experiments the herbaceous groundcover was first removed carefully and in the c-experiments the trees were first cut flush with the earthen channel floor. Rhodamine-B dye was used to tag the flow and the resultant fluorescence of water samples were systematically assayed through time at two stations along the length of the channel. Dilution-curve data were analysed within the Aggregated Dead Zone (ADZ) framework to yield bulk flow parameters including dispersion, fluid retention and flow resistance parameters after the procedure of Richardson & Carling (2006). The primary response of the bulk flow to vegetation removal was an increase in bulk velocity, with depth and wetted width decreasing imperceptibly at the resolution of measurement. An overall reduction in flow resistance and retention occurred as discharge increased in all experiments and flow retention. Retentiveness was more prominent during low flow and for all three experimental conditions tended to converge on a constant low value for high discharges. Reach mean travel times and the advective time delays decreased very slightly from experiments (a) to (b) which is not surprising given the sparse nature of the herbaceous soil cover. Thus in these two initial experiments, the trees provided the majority of the resistance in contrast to the aggregate effect of grass, herbs and litter. Removing the trees leaving an earthen channel further decreased travel times such that the ADZ residence time was more than halved moving from (a) to (c). The overall bulk flow effect of tree cover on retention is here expressed by the dispersive fraction parameter, indicating retention volume and time, which reduced from typically 0.4 to closer to 0.2 when vegetation was removed. The Darcy-Weisbach friction factor during low discharges was higher for experiments (a) compared with (b) but the friction factors converged on the low earthen channel value as discharge increased. In conclusion the effect of vegetation on hydraulic retention compared with an unvegetated channel is prominent during low discharges but becomes negligible during high discharges as momentum increasingly dominates the flow.

  10. Mars: retention of ice.

    PubMed

    Smoluchowski, R

    1968-03-22

    Water in the form of ice can exist on Mars as permafrost that is either in equilibrium with the water content of the atmosphere or gradually evaporating through a protective layer of soil. The latter situation is evaluated quantitatively, and the required thicknesses of the protective layers are estimated. The presence of subsurface ice may explain the higher radar reflectivity of the dark areas than of the bright areas. Observation of its seasonal variations is suggested. PMID:17791161

  11. Structural stability-chromatographic retention relationship on exenatide diastereomer separation.

    PubMed

    Tsai, Ching-Wei; Kao, Wei-Hung; Chang, Li-Chiao; Ruaan, Ruoh-Chyu; Chen, Wen-Yih

    2012-11-01

    In this study, the relationship of the structural stability of peptide diastereomers in elution solvents and their retention behaviors in reversed-phase chromatography (RPC) was examined to provide guidance on the solvent selection for a better separation of peptide diastereomers. We investigated the chromatographic retention behaviors of exenatide, a peptide drug for the treatment of type II diabetes mellitus and its three diastereomers using RPC and implicit molecular dynamics (MD) simulation analysis. Three diastereomers involved in the single serine residue mutation of D-form at the 11th, 32nd, and 39th residues were investigated in this study. Results show that the order of the solution structural stability of exenatide and its diastereomers is consistent with their retention order by 36 % acetonitrile/water elution. The sample loading solvent also affects the retention behaviors of exenatide peptide diastereomers in RPC column. Furthermore, a larger solution conformation energy difference of the critical pair of exenatide and its diastereomer (D-Ser39) at the elution solvent of 32 % tetrahydrofuran/water were obtained by MD simulation, and baseline separation was proved experimentally. In summary, we demonstrated that the solution structural stability-chromatographic retention relationship could be a powerful tool for elution solvent selection in peptide chromatographic purification, especially valuable for the separation of critical pair of diastereomers. PMID:22945556

  12. Equilibrium retention in the nozzle of oxygen hydrogen propulsion systems

    NASA Technical Reports Server (NTRS)

    Ford, D. I.

    1987-01-01

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

  13. Hydrogen peroxide retention in rime ice

    NASA Astrophysics Data System (ADS)

    Snider, Jefferson R.; Montague, Derek C.; Vali, Gabor

    1992-05-01

    The extent to which H2O2 dissolved in cloud droplets is trapped in rime ice affects the composition of precipitation and the rate of H2O2 removal from the atmosphere. Measurements were conducted in winter stratiform clouds at a remote mountain-top site in southeastern Wyoming, thus avoiding the difficulties of preparing laboratory clouds whose chemical and physical properties are similar to natural clouds. Quantities directly observed were H2O2 concentrations in cloud water collected as rime, air temperature, gaseous H2O2, O3, and SO2, and cloud liquid water concentration. Values of the retention coefficient, ?, defined as the ratio of the H2O2 concentration in the melted rime sample divided by the equilibrium concentration in the supercooled droplets, were always less than unity (?¯=0.24±0.07). Corrections to account for the rapid reaction between dissolved H2O2 and sulfur(IV) increase the average value of the retention coefficient to only 0.30. An observed correlation between ? and riming rate suggests that H2O2 is released to the gas phase during riming. These field measurements do not agree with laboratory determinations of ?.

  14. A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF PASO ROBLES AUTHORIZING THE MODIFICATION OF THE UTILITIES MANAGER POSITION AND THE RETENTION OF A WATER RESOURCE AND WASTE WATER RESOURCE MANAGER

    Microsoft Academic Search

    Deborah D. Robinson

    2008-01-01

    WHEREAS, Consultant support to replace employees can range from 120% to 200% of the position's annual salary. Additionally, operating efficiency can be impeded without continuous and consistent supervision. THEREFORE, BE IT RESOLVED AS FOLLOWS: SECTION 1. The City Council of the City of Paso Robles does approve deletion of the City Utilities Manager position and instead implement one each, Water

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

    NASA Technical Reports Server (NTRS)

    Boone, S.; Nicol, M. F.

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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.

  17. Isolated Curves for Hyperelliptic Curve Cryptography

    E-print Network

    Wang, Wenhan

    2012-01-01

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

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

    Microsoft Academic Search

    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

    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

  19. A successful Minority Retention Project.

    PubMed

    Gardner, Janelle D

    2005-12-01

    Racial and ethnic minorities are underrepresented in the nursing profession. The high attrition rate of minority students from nursing schools contributes to this problem. Academic leaders are calling for change in nursing education and asking educators to work diligently to retain minority students. This article describes a Minority Retention Project that included interventions designed to enhance the integration of minority students into a supportive learning environment, assist them in using the available resources, and help them feel connected and supported by their peers and faculty. At the end of the first year of the project, the nursing school experienced 100% retention of minority nursing students. Increasing the retention and graduation of minority nursing students supports the continued effort to provide culturally competent health care. PMID:16402740

  20. Comparative analysis of base flow recession curves for different Andean catchments

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  1. Nuclear reactor melt-retention structure to mitigate direct containment heating

    DOEpatents

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

    1991-01-01

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

  2. The retention of a simple running response after varying amounts of reinforcement

    Microsoft Academic Search

    F. W. Finger

    1943-01-01

    Four groups of 11 rats each were trained in a simple runway problem, with 4, 8, 16, and 32 acquisition trials, respectively. Twenty-four hours later the animals were tested for retention, and 10 points on the extinction curves determined. Strength of response was measured in terms of latent period. At the end of acquisition the groups which had received 4

  3. High retention membrane bioreactors: challenges and opportunities.

    PubMed

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

    2014-09-01

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

  4. Understanding curved detonation waves

    SciTech Connect

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

    1992-01-01

    A wave curve is the set of final states to which an initial state may be connected by a traveling wave. In gas dynamics, for example, the wave curve consists of the shock Hugoniot curve for compressive waves and the rarefaction curve for expansive waves. In this paper, we discuss the wave curve for an undriven planar detonation and for general planar detonations. We then extend the wave curve concept to detonations in converging and diverging geometry. We also discuss the application of these wave curves to the numerical computation of detonation problems.

  5. Understanding curved detonation waves

    SciTech Connect

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

    1992-10-01

    A wave curve is the set of final states to which an initial state may be connected by a traveling wave. In gas dynamics, for example, the wave curve consists of the shock Hugoniot curve for compressive waves and the rarefaction curve for expansive waves. In this paper, we discuss the wave curve for an undriven planar detonation and for general planar detonations. We then extend the wave curve concept to detonations in converging and diverging geometry. We also discuss the application of these wave curves to the numerical computation of detonation problems.

  6. Maslow's Hierarchy and Student Retention.

    ERIC Educational Resources Information Center

    Brookman, David M.

    1989-01-01

    Abraham Maslow's hierarchy of needs offers perspective on student motivation and a rationale for college retention programing. Student affairs and faculty interventions addressing student safety needs and engaging students' sense of purpose reinforce persistence. A mentor program is a possible cooperative effort between student personnel and…

  7. Retention-Oriented Curricular Design

    ERIC Educational Resources Information Center

    Milanovic, Ivana; Eppes, Tom A.; Girouard, Janice; Townsend, Lee

    2010-01-01

    This paper presents a retention-oriented approach to the educational value stream within the STEM undergraduate area. Faced with several strategic challenges and opportunities, a Flex Advantage Plan was developed to enhance the undergraduate engineering technology programs and better utilize the curricular flexibilities inherent in the current…

  8. JCC Recruitment, Retention, Attrition Project.

    ERIC Educational Resources Information Center

    Horvath, Ronald J.

    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…

  9. Educational Advising for Student Retention.

    ERIC Educational Resources Information Center

    Santa Rita, Emilio

    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…

  10. Award-Winning Approaches to Retention.

    ERIC Educational Resources Information Center

    Hammer, Ben

    2003-01-01

    Describes retention programs for at-risk freshmen that have been recognized as successful in a study by the consulting firm Noel-Levitz. Provides details about the retention efforts at 10 colleges and universities. (SLD)

  11. Managing Chemotherapy Side Effects: Swelling (Fluid Retention)

    MedlinePLUS

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

  12. Pharmaceutical Retention Mechanisms by Nanofiltration Membranes 

    E-print Network

    Nghiem, Long D.; Schäfer, Andrea; Elimelech, Menachem

    2005-01-01

    by steric (size) exclusion, whereas both electrostatic repulsion and steric exclusion govern the retention of ionizable pharmaceuticals by a loose NF membrane. In the latter case, speciation of pharmaceuticals may lead to a dramatic change in retention as a...

  13. Phosphorus retention patterns along the Tisza River, Hungary.

    PubMed

    Kovács, A; Kozma, Zs; Istvánovics, V; Honti, M

    2009-01-01

    The aim of this study was to assess in-stream retention of suspended solids (SS) and total phosphorus (TP) at low flow condition in a large watercourse, the Tisza River. The analysis was based on a longitudinal water quality profile obtained in July 2006 during a cruise along the Hungarian section of the river (nearly 600 km). Water samples were taken manually for SS and TP every half an hour (ca. 5.5 km). Additionally, concentration of SS was calculated from on-line turbidity records taken every 6 s (ca. 10 m). Velocity field was calculated with a 1D hydrodynamic model calibrated for low flow conditions. To describe the transport, a simple first-order equation was adjusted to the SS profile after estimating the potential maximum of SS that the flow with the given velocity could transport. Specific P content of SS was related to velocity to estimate longitudinal TP profile. Retention of TP amounted to 42% along the Hungarian section of the Tisza River at a flow of 110 m(3) s(-1). Storage reservoirs significantly influenced the longitudinal retention pattern. Upstream of Dam II (river kilometre 404), net TP retention reached 73%, while the downstream section was a source of TP. PMID:19182352

  14. Reframing Retention Strategy: A Focus on Profile

    ERIC Educational Resources Information Center

    Kalsbeek, David H.; Zucker, Brian

    2013-01-01

    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…

  15. 2014 Action Plan for Retention and

    E-print Network

    Thomas, Andrew

    best practices leading to incremental improvement of retention rates, graduation rates, and student2014 Action Plan for Retention and Graduation #12;1 Background Provost Jeffrey Hecker assembled the Advisory Group on Retention and Graduation in fall 2013 and charged it with collecting data and evaluating

  16. Knowledge retention in knowledge management system: Review

    Microsoft Academic Search

    Akbar Dehghani Ghahfarokhi; Mohamad Shanudin Zakaria

    2009-01-01

    Knowledge retention is a topic that comes up in many discussions of knowledge management. The primary concern is how to tap the brains of employees who are retiring, moving on to new jobs or otherwise leaving the company. Of course, there is no one way to create good knowledge retention. This necessitates different approaches for knowledge sharing or knowledge retention.

  17. A RETENTION INDEX SCHEME FOR USE WITH SULFUR SPECIFIC DETECTORS

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  18. Water

    MedlinePLUS

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

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

    PubMed

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

    2014-12-01

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

  20. On the inherent data fitting problems encountered in modeling retention behavior of analytes with dual retention mechanism.

    PubMed

    Tyteca, Eva; Desmet, Gert

    2015-07-17

    Some valuable insights have been obtained in the inherent fitting problems when trying to predict the retention time of complex, multi-modal retention modes such as encountered in HILIC and SFC. In this study, we used mathematical models with known input parameters to generate different sets of numerical test curves representative for systems exhibiting a complex, non-LSS dual retention behavior. Subsequently, we tried to fit these data sets using some popular (non-linear) literature models. Even in cases where a physical fitting model exists (e.g., the mixed model in case of pure additive adsorptive and partitioning retention), the fitting quality can only be expected to be relatively good (prediction errors expressed in terms of a normalized resolution error ?Rs) when carefully selecting the scouting runs and the appropriate starting values for the fitting algorithm. The latter can best be done using a comprehensive grid search scanning a wide range of different starting values. This becomes even more important when no good physical model is available and one has to use a non-physical fitting model, such as the empirical Neue-model. The use of higher-order models is found to be quasi indispensable to keep the prediction errors on the order of some ?Rs=0.05. Also, the choice of the scouting runs becomes even more important using these higher-order models. For highly retained compounds we recommend using scouting runs with long tG/t0-values or to include a run with a higher fraction of eluting solvent at the start of the gradient. When trying to predict gradient retention, errors with which the isocratic retention behavior is fitted are much less important for high retention factors k than errors made in the range of k near the one at the point of elution. The results obtained with a so-called segmented Neue-model (containing 7 parameters) were less good and thus practically not interesting (because of the high number of initial runs). PMID:26044381

  1. N=1 Curve

    E-print Network

    Dan Xie

    2014-09-29

    N=1 curve is defined for four dimensional class S theory using Cayley-Hamilton theorem for two commuting matrices. The curve consists of three ingredients: 1: A set of N+1 degree N equations defining a curve; 2: a set of constraints relating the coefficients in the curve; 3: a canonically defined differential. We then extract from spectral curve various physical information such as the space of moduli fields, chiral ring relations, full moduli space, etc. Many examples are discussed, and the curve recovers the intricate vacua structure which often involves highly non-trivial field theory dynamics such as monopole condensation, dynamical generated superpotential, Seiberg duality, etc.

  2. Scavenging and retention of metals by zooplankton fecal pellets and marine snow

    NASA Astrophysics Data System (ADS)

    Fisher, Nicholas S.; Nolan, Canice V.; Fowler, Scott W.

    1991-10-01

    The scavenging and retention of nine metals in different batches of zooplankton fecal pellets and marine snow were studied in the laboratory using radiotracer techniques. Dissolved 60Co, 65Zn, 106Ru, 109Cd, 110mAg, 141Ce, 154Eu, 237Pu and 241AM were scavenged from seawater onto euphausiid fecal pellets, marine snow and copepod fecal pellets recovered from sediment traps and onto copepod fecal pellets freshly produced in the laboratory. Kd values for the different radioisotopes ranged from 8.4 × 10 2 to 1.9 × 10 5. The radiolabeled fecal pellets and marine snow, resuspended into unlabelled seawater at 2 and 15°C, displayed metal depurations curves generally conforming to a two-compartment model, with overall retention half-times ( t r 1/2s) varying with each metal and type of debris. 109Cd was retained least effectively and 106Ru was generally retained for the longest periods, with t r 1/2s up to 66 days. The t r 1/2s of 141Ce, 154Eu, 237Pu and 241Am in each type of debris were comparable and were not appreciably affected by temperature. 60Co, 65Zn, 109Cd and 110mAg were released into the dissolved phase more rapidly at 15 than at 2°C. Metal binding on copepod fecal pellets and marine snow was generally greater than on euphausiid fecal pellets. These results provide direct evidence that fecal pellets and marine snow can effectively scavenge metals from seawater; of the metals examined, zinc and cadmium are likely to be remineralized most rapidly in surface waters, while the others are likely to be vertically transported hundreds to thousands of meters.

  3. Instrument parameters controlling retention precision in gradient elution reversed-phase liquid chromatography.

    PubMed

    Beyaz, Ayse; Fan, Wenzhe; Carr, Peter W; Schellinger, Adam P

    2014-10-01

    The precision of retention time in RPLC is important for compound identification, for setting peak integration time windows and in fundamental studies of retention. In this work, we studied the effect of temperature (T), initial (?o) and final mobile phase (?f) composition, gradient time (tG), and flow rate (F) on the retention time precision under gradient elution conditions for various types of low MW solutes. We determined the retention factor in pure water ( [Formula: see text] ) and the solute-dependent solvent strength (S) parameters of Snyder's linear solvent strength theory (LSST) as a function of temperature for three different groups of solutes. The effect of small changes in the chromatographic variables (T, ?o, ?f, tG and F) by use of the LSST gradient retention equation were estimated. Peaks at different positions in the chromatogram have different sensitivities to changes in these instrument parameters. In general, absolute fluctuations in retention time are larger at longer gradient times. Drugs showed less sensitivity to changes in temperature compared to relatively less polar solutes, non-ionogenic solutes. Surprisingly we observed that fluctuations in temperature, mobile phase composition and flow rate had less effect on retention time under gradient conditions as compared to isocratic conditions. Overall temperature and the initial mobile phase composition are the most important variables affecting retention reproducibility in gradient elution chromatography. PMID:25459648

  4. Colloid transport in unsaturated porous media: the role of water content and ionic strength on particle straining.

    PubMed

    Torkzaban, Saeed; Bradford, Scott A; van Genuchten, Martinus Th; Walker, Sharon L

    2008-02-19

    Packed column and mathematical modeling studies were conducted to explore the influence of water saturation, pore-water ionic strength, and grain size on the transport of latex microspheres (1.1 microm) in porous media. Experiments were carried out under chemically unfavorable conditions for colloid attachment to both solid-water interfaces (SWI) and air-water interfaces (AWI) using negatively charged and hydrophilic colloids and modifying the solution chemistry with a bicarbonate buffer to pH 10. Interaction energy calculations and complementary batch experiments were conducted and demonstrated that partitioning of colloids to the SWI and AWI was insignificant across the range of the ionic strengths considered. The breakthrough curve and final deposition profile were measured in each experiment indicating colloid retention was highly dependent on the suspension ionic strength, water content, and sand grain size. In contrast to conventional filtration theory, most colloids were found deposited close to the column inlet, and hyper-exponential deposition profiles were observed. A mathematical model, accounting for time- and depth-dependent straining, produced a reasonably good fit for both the breakthrough curves and final deposition profiles. Experimental and modeling results suggest that straining--the retention of colloids in low velocity regions of porous media such as grain junctions--was the primary mechanism of colloid retention under both saturated and unsaturated conditions. The extent of stagnant regions of flow within the pore structure is enhanced with decreasing water content, leading to a greater amount of retention. Ionic strength also contributes to straining, because the number of colloids that are held in the secondary energy minimum increases with ionic strength. These weakly associated colloids are prone to be translated to stagnation regions formed at grain-grain junctions, the solid-water-air triple point, and dead-end pores and then becoming trapped. PMID:18068262

  5. Retention characteristics of aliphatic compounds on cellulose acetates as a stationary phase with an aqueous mobile phase

    Microsoft Academic Search

    Y. Kiso; T. Kitao; Ge Yong-Sheng; K. Jinno

    1989-01-01

    Cellulose and cellulose mono-, di-, and triacetate were used as stationary phases for liquid chromatography with water as a mobile phase, and the retention behavior of alcohols, ethers, ketones, and chlorides was examined. For cellulose acetate columns, the logarithm of the specific retention volume, (logV

  6. A micropuncture study of renal sodium retention in nephrotic syndrome in rats: Evidence for increased resistance to tubular fluid flow

    Microsoft Academic Search

    Shigeomi Kuroda; Hagop S Aynedjian; Norman Bank

    1979-01-01

    A micropuncture study of renal sodium retention in nephrotic syndrome in rats: Evidence for increased resistance to tubular fluid flow. Micropuncture studies were carried out in surface nephrons of rats with nephrotoxic-serum (NTS) -induced nephrotic syndrome during a period of active sodium and water retention. It was found that hydrostatic pressure and tubular diameter were increased in the proximal tubules

  7. Evaluation of nutrient retention in four restored Danish riparian wetlands

    Microsoft Academic Search

    Carl Chr. Hoffmann; Brian Kronvang; Joachim Audet

    2011-01-01

    During the last 15–20 years, re-establishment of freshwater riparian wetlands and remeandering of streams and rivers have\\u000a been used as a tool to mitigate nutrient load in downstream recipients in Denmark. The results obtained on monitoring four\\u000a different streams and wetland restoration projects are compared with respect to hydrology, i.e. flow pattern and discharge\\u000a of ground or surface water, retention of

  8. An extraordinary origami curve

    Microsoft Academic Search

    Frank Herrlich; Gabriela Schmithusen

    2008-01-01

    We study a special Teichmueller curve in the moduli space of curves of genus\\u000a3 that is intersected by infinitely many other Teichmueller curves. The Veech\\u000agroup of the underlying translation surface is SL_2(Z). All occurring\\u000aTeichmueller curves are induced by origamis, i.e. unramified coverings of the\\u000aonce punctured torus.

  9. Modelling global nutrient retention by river damming: Phosphorus and silicon

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  10. Root numbers of curves

    Microsoft Academic Search

    MARIA SABITOVA

    2004-01-01

    We generalize a theorem of D. Rohrlich concerning root numbers of elliptic curves over the field of rational numbers. Our result applies to curves of all higher genera over number fields. Namely, under certain conditions which naturally extend the conditions used by D. Rohrlich, we show that the root number associated to a smooth projective curve over a number field

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

    USGS Publications Warehouse

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

    2007-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Underwood, Lauren W.; Ryan, Robert E.

    2007-01-01

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

  13. From principal curves to granular principal curves.

    PubMed

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

    2014-06-01

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

  14. Effects of a novel poly (AA-co-AAm)/AlZnFe?O?/potassium humate superabsorbent hydrogel nanocomposite on water retention of sandy loam soil and wheat seedling growth.

    PubMed

    Shahid, Shaukat Ali; Qidwai, Ansar Ahmad; Anwar, Farooq; Ullah, Inam; Rashid, Umer

    2012-01-01

    A novel poly(acrylic acid-co-acrylamide)AlZnFe?O?/potassium humate( )superabsorbent hydrogel nanocomposite (PHNC) was synthesized and its physical properties characterized using SEM, Energy Dispersive X-ray (EDX) and FTIR spectroscopic techniques. Air dried sandy loam soil was amended with 0.1 to 0.4 w/w% of PHNC to evaluate its soil moisture retention attributes. Effect of PHNC amendment on pH, electrical conductivity (EC), porosity, bulk density and hydraulic conductivity of sandy loam soil was also studied. The soil amendment with 0.1 to 0.4 w/w% of PHNC remarkably enhanced the moisture retention at field capacity as compared to the un-amended soils. Seed germination and seedling growth of wheat (Triticum aestivum L.) was considerably increased and a delay by 6-9 days in wilting of seedlings was observed in the soil amended with PHNC, resulting in improved wheat plant establishment and growth. PMID:23099615

  15. Fractionation of process water in thermomechanical pulp mills.

    PubMed

    Persson, T; Krawczyk, H; Nordin, A-K; Jönsson, A-S

    2010-06-01

    In this work process water from a thermomechanical pulp mill was divided into five fractions by filtration and membrane filtration. Suspended matter was mainly isolated in the retentate from the drum filter, extractives in the microfiltration retentate, hemicelluloses in the ultrafiltration retentate and lignin in the nanofiltration retentate. The final water fraction was of fresh water quality. For each tonne of pulp produced, about 10kg of suspended matter, more than 0.3kg of extractives, 11kg of hemicelluloses and 8kg of aromatic compounds (lignin) could be recovered from the drum filtration retentate, the microfiltration retentate, the ultrafiltration retentate and the nanofiltration retentate, respectively. About 40% of the treated process water could be recovered as fresh water. PMID:20137925

  16. A coupled reference interaction site model/molecular dynamics study of the potential of mean force curve of the SN2 Cl- + CH3Cl reaction in water.

    PubMed

    Freedman, Holly; Truong, Thanh N

    2005-03-17

    An application of the coupled reference interaction site model (RISM)/simulation methodology to the calculation of the potential of mean force (PMF) curve in aqueous solution for the identity nucleophilic substitution reaction Cl(-) + CH(3)Cl is performed. The free energy of activation is calculated to be 27.1 kcal/mol which compares very well with the experimentally determined barrier height of 26.6 kcal/mol. Furthermore, the calculated PMF is almost superimposed with that previously calculated using the computationally rigorous Monte Carlo with importance sampling method (Chandrasekhar, J.; Smith, S. F.; Jorgensen, W. L. J. Am. Chem. Soc. 1985, 107, 154). Using the calculated PMF, a crude estimate of the solvated kinetic transmission coefficient also compares well with that of previous more accurate simulations. These results indicate that the coupled RISM/simulation method provides a cost-effective methodology for studying reactions in solution. PMID:16851554

  17. Influence of hydrologic loading rate on phosphorus retention and ecosystem productivity in created wetlands. Final report

    SciTech Connect

    Mitsch, W.J.; Cronk, J.K.

    1995-01-01

    Four 2- to 3-ha constructed freshwater riparian wetlands in Lake County, Illinois, were subjected to two hydrologic regimes of pumped river water to simulate nonpoint source pollution. The experimental wetlands at the Des Plaines River Wetland Demonstration Project were designed to develop and test wetland design principles, construction methods, and management programs needed to create and maintain wetlands for the purposes of water quality management, flood control, and fish and wildlife habitat. High-flow wetlands (HFW) with short retention times received 34 to 38 cm of river water per week, and low-flow wetlands (LFW) with high retention times received 10 to 15 cm per week. This report summarizes research results for phosphorus dynamics and retention, macrophyte development, periphyton productivity, and overall water column metabolism through 1992. All of these functions were hypothesized to be related to hydrologic conditions.

  18. Water

    MedlinePLUS

    ... consuming only bottled water or water from a filtration system that has been certified by an independent ... recommends using bottled water or water from a filtration system that has been certified by an independent ...

  19. Supply Curves of Conserved Energy

    SciTech Connect

    Meier, Alan Kevin

    1982-05-01

    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.

  20. Nutrient Retention Efficiency in Streams Receiving Inputs from Wastewater Treatment Plants

    Microsoft Academic Search

    Eugènia Marti; Jordi Aumatell; Lluís Godé; Manel Poch; Francesc Sabater

    2004-01-01

    documented declines in water quality (Howarth et al., 1996). Degradation of water quality is a universal issue We tested the effect of nutrient inputs from wastewater treatment because it directly affects human health and the ecologi- plants (WWTPs) on stream nutrient retention efficiency by examining the longitudinal patterns of ammonium, nitrate, and phosphate con- cal integrity of freshwater ecosystems. centrations

  1. Woody Shrubs for Stormwater Retention Practices 1 A portion of the

    E-print Network

    Pawlowski, Wojtek

    conditions, which is detrimental to aquatic life · Bacterial contamination of water sources especially retention practices. What is Stormwater? Stormwater is rain or snowmelt which flows over the ground and does when the rate of rainfall or snowmelt was greater than the rate at which water could be absorbed

  2. Radionuclide Retention in Concrete Wasteforms

    SciTech Connect

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

    2012-09-24

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

  3. Adult Student Retention: A Practical Approach to Retention Improvement through Learning Enhancement

    ERIC Educational Resources Information Center

    Fincher, Mark

    2010-01-01

    Adult student retention is an issue of growing concern for many institutions. It differs from traditional retention much like traditional students differ from adult students. As the majority of student body growth comes from adult students, adult student retention management will become critical to the majority of colleges and universities. To…

  4. Theoretical considerations of soil retention. [dirtying of solar energy devices

    NASA Technical Reports Server (NTRS)

    Cuddihy, E. F.

    1980-01-01

    The performance of solar energy devices is adversely affected by surface soiling, and generally, the loss of performance increases with increases in the quantity of soil retained on their surfaces. To minimize performance losses caused by soiling, solar devices should not only be deployed in low soiling geographical areas, but employ surfaces or surfacing materials having low affinity for soil retention, maximum susceptibility to be naturally cleaned by wind, rain and snow, and to be readily cleanable by simple and inexpensive maintenance cleaning techniques. This article describes known and postulated mechanisms of soil retention on surfaces, and infers from these mechanisms that low soiling and easily cleanable surfaces should have low surface energy, and be hard, smooth, hydrophobic and chemically clean of sticky materials and water soluble salts.

  5. A comparison of the retention of pathogenic Escherichia coli?O157 by sprouts, leaves and fruits

    PubMed Central

    Mathews, Stephanie L; Smith, Rachel B; Matthysse, Ann G

    2014-01-01

    The retention (binding to or association with the plant) of Escherichia coli by cut leaves and fruits after vigorous water washing was compared with that by sprouts. Retention by fruits and leaves was similar but differed from retention by sprouts in rate, effect of wounding and requirement for poly-?,1-6-N-acetyl-D-glucosamine. Escherichia coli was retained by cut ends of lettuce leaves within 5 min while more than 1 h was required for retention by the intact epidermis of leaves and fruits, and more than 1 day for sprouts. Retention after 5 min at the cut leaf edge was specific for E. coli and was not shown by the plant-associated bacteria Agrobacterium tumefaciens and Sinorhizobium meliloti.?Escherichia coli was retained by lettuce, spinach, alfalfa, bean, tomato, Arabidopsis thaliana, cucumber, and pepper leaves and fruits faster than by sprouts. Wounding of leaves and fruits but not sprouts increased bacterial retention. Mutations in the exopolysaccharide synthesis genes yhjN and wcaD reduced the numbers of bacteria retained. PgaC mutants were retained by cut leaves and fruits but not by sprouts. There was no significant difference in the retention of an O157 and a K12 strain by fruits or leaves. However, retention by sprouts of O157 strains was significantly greater than K12 strains. These findings suggest that there are differences in the mechanisms of E coli retention among sprouts, and leaves and fruits. PMID:25351040

  6. Rainwater runoff retention on an aged intensive green roof.

    PubMed

    Speak, A F; Rothwell, J J; Lindley, S J; Smith, C L

    2013-09-01

    Urban areas are characterised by large proportions of impervious surfaces which increases rainwater runoff and the potential for surface water flooding. Increased precipitation is predicted under current climate change projections, which will put further pressure on urban populations and infrastructure. Roof greening can be used within flood mitigation schemes to restore the urban hydrological balance of cities. Intensive green roofs, with their deeper substrates and higher plant biomass, are able to retain greater quantities of runoff, and there is a need for more studies on this less common type of green roof which also investigate the effect of factors such as age and vegetation composition. Runoff quantities from an aged intensive green roof in Manchester, UK, were analysed for 69 rainfall events, and compared to those on an adjacent paved roof. Average retention was 65.7% on the green roof and 33.6% on the bare roof. A comprehensive soil classification revealed the substrate, a mineral soil, to be in good general condition and also high in organic matter content which can increase the water holding capacity of soils. Large variation in the retention data made the use of predictive regression models unfeasible. This variation arose from complex interactions between Antecedant Dry Weather Period (ADWP), season, monthly weather trends, and rainfall duration, quantity and peak intensity. However, significantly lower retention was seen for high rainfall events, and in autumn, which had above average rainfall. The study period only covers one unusually wet year, so a longer study may uncover relationships to factors which can be applied to intensive roofs elsewhere. Annual rainfall retention for Manchester city centre could be increased by 2.3% by a 10% increase in intensive green roof construction. The results of this study will be of particular interest to practitioners implementing greenspace adaptation in temperate and cool maritime climates. PMID:23712113

  7. Functional models for colloid retention in porous media at the triple line.

    PubMed

    Dathe, Annette; Zevi, Yuniati; Richards, Brian K; Gao, Bin; Parlange, J-Yves; Steenhuis, Tammo S

    2014-01-01

    Spectral confocal microscope visualizations of microsphere movement in unsaturated porous media showed that attachment at the Air Water Solid (AWS) interface was an important retention mechanism. These visualizations can aid in resolving the functional form of retention rates of colloids at the AWS interface. In this study, soil adsorption isotherm equations were adapted by replacing the chemical concentration in the water as independent variable by the cumulative colloids passing by. In order of increasing number of fitted parameters, the functions tested were the Langmuir adsorption isotherm, the Logistic distribution, and the Weibull distribution. The functions were fitted against colloid concentrations obtained from time series of images acquired with a spectral confocal microscope for three experiments performed where either plain or carboxylated polystyrene latex microspheres were pulsed in a small flow chamber filled with cleaned quartz sand. Both moving and retained colloids were quantified over time. In fitting the models to the data, the agreement improved with increasing number of model parameters. The Weibull distribution gave overall the best fit. The logistic distribution did not fit the initial retention of microspheres well but otherwise the fit was good. The Langmuir isotherm only fitted the longest time series well. The results can be explained that initially when colloids are first introduced the rate of retention is low. Once colloids are at the AWS interface they act as anchor point for other colloids to attach and thereby increasing the retention rate as clusters form. Once the available attachment sites diminish, the retention rate decreases. PMID:24234754

  8. Low power integrated scan-retention mechanism

    Microsoft Academic Search

    Victor V. Zyuban; Stephen V. Kosonocky

    2002-01-01

    This paper presents a methodology for unifying the scan mechanism and data retention in latches which leads to scannable latches with the data retention capability achieved at a very low power overhead during the active mode. A detailed analysis of power and area overhead is presented, with layout examples for various common latch styles. Implications of using different power gating

  9. Academic Advising to Facilitate Student Retention.

    ERIC Educational Resources Information Center

    Kapraun, E. Daniel; Coldren, Doris W.

    Seven components of an academic advising program that emphasizes student retention are examined. These components are as follows: an institutional commitment to academic advising, a faculty-endorsed statement of adviser responsibilities (with retention as a major emphasis), the training of advisers, an adviser evaluation and recognition for…

  10. Retention Implementation Task Force Final Report

    E-print Network

    Cinabro, David

    in terms of student retention and graduation rates for some time, and when various sub-groups including before we see the effects of these improvements on graduation rates. Wayne State University cannot fulfill its mission without significantly improving the retention and graduation rates of its students

  11. Sulfonate retention and residual oil saturation

    Microsoft Academic Search

    Presley

    1981-01-01

    An empirical relationship between sulfonate retention and final residual oil saturation achieved by a micellar-polymer oil recovery process was found. Using this relationship and certain assumptions, expressions were derived for predicting oil recovery performance in core flood experiments. The equations contain two experimental constants. One is sulfonate retention. The other is a factor related to the oil recovery efficiency of

  12. University Record Retention Policy Policy # FA-002

    E-print Network

    Xia, Yu "Brandon"

    University Record Retention Policy Policy # FA-002 Effective Date: June 1, 2009 Policy Statement Boston University requires that University records be retained for specific periods of time, and has that are outlined in this document. Reason for Policy Boston University is committed to effective records retention

  13. PROJECT LASER - LONGITUDINAL ADF STUDY EVALUATING RETENTION

    Microsoft Academic Search

    Nicole Barton

    Personnel retention and turnover behaviour have received much attention in both the civilian and military environments as employers contend with a competitive labour market and the challenges of skill shortages and changing population demographics. To improve current personnel research in the Australian Defence Force (ADF) and subsequently, the quality of retention initiatives, a longitudinal research program based on a customized

  14. The Psychology Underlying Successful Retention Practices.

    ERIC Educational Resources Information Center

    Bean, John; Eaton, Shevawn Bogdan

    2002-01-01

    Describes the psychological processes that lead to academic and social integration based on a retention model proposed by the authors. Describes how successful retention programs such as learning communities, freshman interest groups, tutoring, and orientation rely on psychological processes. Four psychological theories form the basis for…

  15. Healthcare Learning Community and Student Retention

    ERIC Educational Resources Information Center

    Johnson, Sherryl W.

    2014-01-01

    Teaching, learning, and retention processes have evolved historically to include multifaceted techniques beyond the traditional lecture. This article presents related results of a study using a healthcare learning community in a southwest Georgia university. The value of novel techniques and tools in promoting student learning and retention

  16. Profile in Action: Linking Admission and Retention

    ERIC Educational Resources Information Center

    Cortes, Carla M.

    2013-01-01

    A profile-oriented retention strategy embraces the admission process as a powerful lever in improving retention and completion rates and recognizes that the student profile can be shaped by changes in admission policies or priorities--even within the current market position of the institution. In addition, the student body can be oriented toward…

  17. Nitrogen retention in natural Mediterranean wetland-streams affected by agricultural runoff

    NASA Astrophysics Data System (ADS)

    García-García, V.; Gómez, R.; Vidal-Abarca, M. R.; Suárez, M. L.

    2009-12-01

    Nitrogen retention efficiency in natural Mediterranean wetland-streams affected by agricultural runoff was quantified and the effect of the temporal variability and hydrological/chemical loading was examined from March 2007 to June 2008 in two wetland-streams located in Southeast Spain. Nitrate-N (NO-3-N), ammonium-N (NH+4-N), total nitrogen-N (TN-N), total organic nitrogen-N (TON-N) and chloride (Cl-) concentrations were analyzed to calculate nitrogen retention efficiencies. These wetland-streams consistently reduced water nitrogen concentration throughout the year with higher values for NO-3-N (72.3%), even though the mean value of inflow NO-3-N concentrations was above 20 mg l-1. Additionally, they usually acted as sinks for TON-N (8.4%), but as sources for NH+4-N. Over the entire study period, the Taray and Parra wetland-streams were capable of removing on average 1.6 and 0.8 kg NO-3-N a day-1, respectively. Retention efficiencies were not affected by temperature variation. NO-3-N retention efficiency followed a seasonal pattern with the highest retention values in summer (June-September). The temporal variability for NO-3-N retention efficiency was positively and negatively explained by the hydrologic retention and the inflow NO-3-N concentration (R2adj=0.815, p<0.01), respectively. No significant regression model was found for TON-N and NH+4-N. Finally, the conservation of these Mediterranean wetland-streams may help to not only improve the surface water quality in agricultural catchments, but to also achieve good ecological status for surface waters, this being the Water Framework Directive's ultimate purpose.

  18. A comparison study of methods for measuring retention in HIV medical care.

    PubMed

    Crawford, Timothy N; Sanderson, Wayne T; Thornton, Alice

    2013-11-01

    The purpose of this study was to compare multiple measures of retention in HIV medical care by determining their ability to predict viral suppression. Patients who sought care between 2003 and 2011 were eligible. Visit constancy, gaps-in-care, and HRSA measure were the measures compared. Multiple logistic regressions and area under the curve statistics were employed to determine which measure most accurately discerned between patients with or without viral suppression. There were 850 patients included in the study. The mean follow-up time among the cohort was 5.6 years and less than half were consistently retained in care. All three measures had similar area under the curves, but only visit constancy and gaps in care were significantly associated with viral suppression. Retention in care should be defined consistently across studies and interventions should be set in place to increase the number of optimal retainers. PMID:23868692

  19. 5 CFR 536.202 - Optional grade retention.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

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

  20. 5 CFR 536.204 - Period of grade retention.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

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

  1. 5 CFR 536.202 - Optional grade retention.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Optional grade retention. 536.202 Section 536.202 Administrative...PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.202 Optional grade...

  2. 5 CFR 536.201 - Mandatory grade retention.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Mandatory grade retention. 536.201 Section 536.201 Administrative...PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.201 Mandatory grade...

  3. 5 CFR 536.208 - Termination of grade retention.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...2011-01-01 2011-01-01 false Termination of grade retention. 536.208 Section 536.208 Administrative...PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.208 Termination of grade...

  4. 5 CFR 536.201 - Mandatory grade retention.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

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

  5. 5 CFR 536.204 - Period of grade retention.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Period of grade retention. 536.204 Section 536.204 Administrative...PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.204 Period of grade...

  6. 5 CFR 536.208 - Termination of grade retention.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Termination of grade retention. 536.208 Section 536.208 Administrative...PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS GRADE AND PAY RETENTION Grade Retention § 536.208 Termination of grade...

  7. 5 CFR 351.401 - Determining retention standing.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 false Determining retention standing. 351.401 Section 351.401 Administrative...Competition § 351.401 Determining retention standing. Each agency shall determine the retention standing of each competing employee on the basis...

  8. 5 CFR 351.506 - Effective date of retention standing.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 false Effective date of retention standing. 351.506 Section 351.506 Administrative...REGULATIONS REDUCTION IN FORCE Retention Standing § 351.506 Effective date of retention standing. Except for applying the...

  9. THE UNIVERSITY OF UTAH UNDERGRADUATE RETENTION & GRADUATION REPORTS

    E-print Network

    Provancher, William

    1 GRADUATION RATES 2 SUMMED RETENTION AND GRADUATION RATES 3 NEW UNDERGRADUATE TRANSFER STUDENTS: RETENTION RATES 4 GRADUATION RATES 5 SUMMED RETENTION AND GRADUATION RATES 6 FIRSTTIME, FIRST YEAR STUDENT BY GENDER

  10. 5 CFR 317.801 - Retention of SES provisions.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...2013-01-01 2013-01-01 false Retention of SES provisions. 317.801 Section 317.801...IN THE SENIOR EXECUTIVE SERVICE Retention of SES Provisions § 317.801 Retention of SES provisions. (a) Coverage. This subpart...

  11. 5 CFR 317.801 - Retention of SES provisions.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...2014-01-01 2014-01-01 false Retention of SES provisions. 317.801 Section 317.801...IN THE SENIOR EXECUTIVE SERVICE Retention of SES Provisions § 317.801 Retention of SES provisions. (a) Coverage. This subpart...

  12. 5 CFR 317.801 - Retention of SES provisions.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...2012-01-01 2012-01-01 false Retention of SES provisions. 317.801 Section 317.801...IN THE SENIOR EXECUTIVE SERVICE Retention of SES Provisions § 317.801 Retention of SES provisions. (a) Coverage. This subpart...

  13. 5 CFR 317.801 - Retention of SES provisions.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...2011-01-01 2011-01-01 false Retention of SES provisions. 317.801 Section 317.801...IN THE SENIOR EXECUTIVE SERVICE Retention of SES Provisions § 317.801 Retention of SES provisions. (a) Coverage. This subpart...

  14. 5 CFR 317.801 - Retention of SES provisions.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Retention of SES provisions. 317.801 Section 317.801...IN THE SENIOR EXECUTIVE SERVICE Retention of SES Provisions § 317.801 Retention of SES provisions. (a) Coverage. This subpart...

  15. Radionuclide Retention in Concrete Wasteforms

    SciTech Connect

    Bovaird, Chase C.; Jansik, Danielle P.; Wellman, Dawn M.; Wood, Marcus I.

    2011-09-30

    Assessing long-term performance of Category 3 waste cement grouts for radionuclide encasement requires knowledge of the radionuclide-cement interactions and mechanisms of retention (i.e., sorption or precipitation); the mechanism of contaminant release; the significance of contaminant release pathways; how wasteform performance is affected by the full range of environmental conditions within the disposal facility; the process of wasteform aging under conditions that are representative of processes occurring in response to changing environmental conditions within the disposal facility; the effect of wasteform aging on chemical, physical, and radiological properties; and the associated impact on contaminant release. This knowledge will enable accurate prediction of radionuclide fate when the wasteforms come in contact with groundwater. The information present in the report provides data that (1) measures the effect of concrete wasteform properties likely to influence radionuclide migration; and (2) quantifies the rate of carbonation of concrete materials in a simulated vadose zone repository.

  16. CPR: curved planar reformation

    Microsoft Academic Search

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

    2002-01-01

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

  17. The Skipping Rope Curve

    ERIC Educational Resources Information Center

    Nordmark, Arne; Essen, Hanno

    2007-01-01

    The equilibrium of a flexible inextensible string, or chain, in the centrifugal force field of a rotating reference frame is investigated. It is assumed that the end points are fixed on the rotation axis. The shape of the curve, the skipping rope curve or "troposkien", is given by the Jacobi elliptic function sn. (Contains 3 figures.)

  18. ?-function for analytic curves

    Microsoft Academic Search

    I. K. Kostov; I. Krichever; M. Mineev-Weinstein; P. B. Wiegmann; A. Zabrodin

    We review the concept of ?-function for simple analytic curves. The ?-function gives a formal solution to the 2D inverse potential problem and appears as the ?-function of the integrable hierarchy which describes conformal maps of simply- connected domains bounded by analytic curves to the unit disk. The ?-function also emerges in the context of topological gravity and enjoys an

  19. The Curved Cube

    NSDL National Science Digital Library

    Hill, David R.

    2003-02-24

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

  20. Anodic Polarization Curves Revisited

    ERIC Educational Resources Information Center

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

    2013-01-01

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

  1. Analyzing population growth curves

    Microsoft Academic Search

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

    2008-01-01

    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

  2. Quantification of Colloid Retention in Unsaturated Porous Media Using Microscopic Image Analysis Data

    NASA Astrophysics Data System (ADS)

    Dathe, A.; Zevi, Y.; Gao, B.; Richards, B. K.; Steenhuis, T. S.

    2006-05-01

    The movement of contaminants via colloidal transport mechanisms through the vadose zone to groundwater is of growing concern. Normally-immobile contaminants can enter an aquifer via colloid-facilitated transport, and pathogens themselves (e.g. Cryptosporidium parvum) are colloidal in scale. Little is known about the complex pore-scale mechanisms of transport and retention of colloids in soils. Measurements of colloid and microbial transport have been typically limited to the evaluation of breakthrough curves from column experiments (which yield only an integrated signal of all retention processes in the column) or to the visualization in micromodels with limited applicability to realistic conditions. The objective of the work discussed here is to observe and model colloid transport and retention on the pore scale. Flow experiments were run in a horizontal flow chamber containing clean quartz sand as the porous medium. Synthetic fluorescent microspheres were used as easily-detected colloid surrogates. A syringe inlet pump and peristaltic outlet pump controlled the chamber moisture content and flow rate. The chamber was mounted under a Laser Scanning Confocal Microscope (Leica TCS SP2, 10x 0.40 UV objective) which allowed the acquisition of time series images and 3D reconstruction of pore-scale images. Three spectral channels were used to detect: 1) fluorescent microsphere emissions (500 to 540 nm) excited at 488 nm by an argon laser; 2) water phase emissions (555 to 650 nm) due to Rhodamine B stain excited at 543 nm by a green HeNe laser; and 3) reflectance of laser light at the grain surfaces. Three 8-bit images were detected simultaneously for every time step. The system is also capable of obtaining image stacks in the z-direction, which allow the determination of the position of attached colloids relative to the interface between air, water menisci, and solid grains. The 3D z-axis stacks reveal that the colloids are attaching at the air/water meniscus/solid (AWmS) interface, our term for the region where the water menisci diminish into a thin film covering the grains. Methods of digital image analysis are presented for quantification of the number and area of both moving and retained colloids. After thresholding the argon laser channel images (in which the microsphere location information is stored), binary images are obtained. The total number and area of white pixels in selected regions are counted for each image sequence. Pixels are counted as colloids attached to the AWmS interface when they appear at exactly the same location in sequential images, as determined by using a Boolean logical operator in a measurement loop. The difference between total and attached particles represents mobile (suspended) particles. The results show that once the first colloid is attached at the AWmS interface, the attachment rate increases until the number of locations where the colloids can be attached near other colloids becomes limiting. A Langmuir model is presented that is capable of predicting the observed colloid attachment processes. Forces acting on the colloids are discussed.

  3. In addition to general retention and graduation rates, NIU calculates retention and graduation rates by certain financial aid categories. For this purpose, retention and graduation rate calculations only

    E-print Network

    Karonis, Nicholas T.

    In addition to general retention and graduation rates, NIU calculates retention and graduation rates by certain financial aid categories. For this purpose, retention and graduation rate calculations a PELL Grant Total Number = 896 % % 1-year Retention Rate 70.8 4-year Graduation Rate 12.8 2-year

  4. Famous Curves Index

    NSDL National Science Digital Library

    Throughout history, there have been many famous curves. In this case, the famous curves profiled here have names such as rhodonea, right strophoid, and the Kampyle of Eudoxus. These curves belong to the world of the mathematical sciences, and they are offered up for teachers and the generally curious by the staff at the School of Mathematics and Statistics at the University of St. Andrews. Visitors can scroll through the complete list of curves (there are over eighty here), and click on each one for an illustration and a listing of the equation that would create such a curve. The site is rounded out by an interactive map that lets users learn about the birthplaces of famous mathematicians from Leibniz to Babbage.

  5. Tripod configurations of curves

    NASA Astrophysics Data System (ADS)

    Chen, Eric; Lourie, Nick

    2015-03-01

    Tripod configurations of plane curves, formed by certain triples of normal lines coinciding at a point, were introduced by Tabachnikov, who showed that C2 closed convex curves possess at least two tripod configurations. Later, Kao and Wang established the existence of tripod configurations for C2 closed locally convex curves. In this paper we generalize these results, answering a conjecture of Tabachnikov on the existence of tripod configurations for all closed plane curves by proving existence for a generalized notion of tripod configuration. We then demonstrate the existence of the natural extensions of these tripod configurations to the spherical and hyperbolic geometries for a certain class of convex curves, and discuss an analogue of the problem for regular plane polygons.

  6. Xenon-133 hepatic retention ratio: A useful index for fatty liver quantification

    SciTech Connect

    Yeh, S.H.; Wu, L.C.; Wang, S.J.; Lin, H.C.; Liu, R.S.; Lee, S.D.; Wu, J.C. (Veterans General Hospital, Taipei (Taiwan))

    1989-10-01

    Xenon-133 hepatic retention ratio was developed for quantifying fatty liver. Data were acquired in frame mode in the hepatic region and both lung bases for 5 min after rebreathing 20 mCi of gaseous {sup 133}Xe and for another 5 min during washout. Static ({sup 99m}Tc)sulfur colloid liver imaging was performed with the patient in the identical position immediately after the ventilation study and data were stored for liver localization. A hepatic time-activity curve corrected for background activity was generated. The 133Xe retention ratio was derived by dividing the activity at 3.5 min after washout by the peak activity. The data of 16 controls and 20 patients with fatty liver were analyzed. The retention ratio (mean +/- s.d.) was greatly increased in patients with fatty infiltration (0.43 +/- 0.20 vs. 0.04 +/- 0.08 in controls, p less than 0.001). There was a strong positive correlation between the {sup 133}Xe retention ratios and percentage of fat on biopsy as assessed by the amount of the liver tissue occupied by fat globules on H E stained sections. The {sup 133}Xe hepatic retention ratio is a simple, accurate and clinically useful index of detecting, quantifying and managing fatty infiltration of the liver.

  7. Retention Loss of Resin Based Fissure Sealants - a Valid Predictor for Clinical Outcome?

    PubMed Central

    Mickenautsch, Steffen; Yengopal, Veerasamy

    2013-01-01

    Purpose: The null-hypothesis that retention loss of resin fissure sealants predicts caries manifestation no more accurately than random values was tested. Methods: Systematic reviews were checked and electronic databases searched for clinical trials. Trials reporting on the retention of resin sealants and caries occurrence in permanent molar teeth, with minimum 24-month follow-up period, were included. Extracted data: number of sealed teeth, number of teeth without completely retained sealants, number of sealed teeth with caries. The number of teeth with complete sealant retention and absence of carious lesions/cavities was calculated; the predictive outcomes: true/false positive; false/true negative were established. Random values were generated as control-data. Diagnostic Odds ratios (DOR) were computed and tested for statistical difference. Summary Receiver Operating Characteristic curves were plotted. Results: 95 trials were found. Median DOR values were 1.21 and 0.28 for test- and control data, respectively. Wilcoxon test (z = 0.56; p = 0.58) and Sign test (z = 1.38; p = 0.17) results were statistically non-significant. The null-hypothesis was not rejected. Conclusions: Predictions based on the retention loss of resin sealants, regarding caries manifestation, was no more accurate than random guesses. Sealant retention loss appears not to be a valid predictor for clinical outcome. PMID:24078856

  8. Predictors of retention in community-based methadone maintenance treatment program in Pearl River Delta, China

    PubMed Central

    2013-01-01

    Background The aims were to identify predictors of treatment retention in methadone maintenance treatment (MMT) clinics in Pearl River Delta, China. Methods Retrospective longitudinal study. Participants: 6 MMT clinics in rural and urban area were selected. Statistical analysis: Stratified random sampling was employed, and the data were analyzed using Kaplan-Meier survival curves and life table method. Protective or risk factors were explored using Cox’s proportional hazards model. Independent variables were enrolled in univariate analysis and among which significant variables were analyzed by multivariate analysis. Results A total of 2728 patients were enrolled. The median of the retention duration was 13.63 months, and the cumulative retention rates at 1,2,3 years were 53.0%, 35.0%, 20.0%, respectively. Multivariate Cox analysis showed: age, relationship with family, live on support from family or friends, income, considering treatment cost suitable, considering treatment open time suitable, addiction severity (daily expense for drug), communication with former drug taking peer, living in rural area, daily treatment dosage, sharing needles, re-admission and history of being arrested were predictors for MMT retention. Conclusions MMT retention rate in Guangdong was low and treatment skills and quality should be improved. Meanwhile, participation of family and society should be encouraged. PMID:23497263

  9. Microcapsules for Enhanced Cargo Retention and Diversity.

    PubMed

    Zieringer, Maximilian A; Carroll, Nick J; Abbaspourrad, Alireza; Koehler, Stephan A; Weitz, David A

    2015-06-01

    Prevention of undesired leakage of encapsulated materials prior to triggered release presents a technological challenge for the practical application of microcapsule technologies in agriculture, drug delivery, and cosmetics. A microfluidic approach is reported to fabricate perfluoropolyether (PFPE)-based microcapsules with a high core-shell ratio that show enhanced retention of encapsulated actives. For the PFPE capsules, less than 2% leakage of encapsulated model compounds, including Allura Red and CaCl2 , over a four week trial period is observed. In addition, PFPE capsules allow cargo diversity by the fabrication of capsules with either a water-in-oil emulsion or an organic solvent as core. Capsules with a toluene-based core begin a sustained release of hydrophobic model encapsulants immediately upon immersion in an organic continuous phase. The major contribution on the release kinetics stems from the toluene in the core. Furthermore, degradable silica particles are incorporated to confer porosity and functionality to the otherwise chemically inert PFPE-based polymer shell. These results demonstrate the capability of PFPE capsules with large core-shell ratios to retain diverse sets of cargo for extended periods and make them valuable for controlled release applications that require a low residual footprint of the shell material. PMID:25693141

  10. University of Arizona Water Sustainability Program Conservation Easement Monitoring

    E-print Network

    Fay, Noah

    regulation of hydrological flows, storage and retention of water, and waste treatment and detoxificationUniversity of Arizona Water Sustainability Program Conservation Easement Monitoring: Development Initiative Fund 2008/2009, Water Sustainability Graduate Student Fellowship Program #12;Water in Arizona

  11. Retention characteristics of porous graphitic carbon in subcritical fluid chromatography with carbon dioxide-methanol mobile phases.

    PubMed

    West, C; Lesellier, E; Tchapla, A

    2004-09-01

    Numerous relationships usually used in high-performance liquid chromatography (HPLC) for describing the retention on porous graphitic carbon (PGC) have been applied in subcritical fluid chromatography, with CO2-methanol mobile phases. As reported in HPLC, octanol-water partition coefficient failed to fit the retention, whereas satisfactory results were obtained with the sum of partial negative charges. A better fit was reached by using the solvation parameter model, allowing a better understanding of the interactions developed between the solute, the stationary and the mobile phases. Results show that the dominant contribution to retention was given by the polarizability (E) and the volume (V), while the hydrogen-bond basicity (B) was not selected in the retention model, whatever the methanol content. The increase in methanol percentage favours the retention decrease, mainly through the volume for hydrophobic compounds, and through the hydrogen-bond acidity for polar compounds. PMID:15453424

  12. Elliptic Curves Kenneth A. Ribet

    E-print Network

    Ribet, Kenneth A.

    Elliptic Curves Kenneth A. Ribet UC Berkeley PARC Forum October 17, 2008 Kenneth A. Ribet Elliptic Curves #12;In talking about elliptic curves, one can do no better than to quote the Yale mathematician endlessly on elliptic curves. (This is not a threat.) Kenneth A. Ribet Elliptic Curves #12;Although I have

  13. Logistic Curve Demo

    NSDL National Science Digital Library

    Roberts, Lila F.

    2002-02-03

    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.

  14. Terrestrial Exoplanet Light Curves

    E-print Network

    Eric Gaidos; Nicholas Moskovitz; Darren M. Williams

    2005-11-23

    The phase or orbital light curves of extrasolar terrestrial planets in reflected or emitted light will contain information about their atmospheres and surfaces complementary to data obtained by other techniques such as spectrosopy. We show calculated light curves at optical and thermal infrared wavelengths for a variety of Earth-like and Earth-unlike planets. We also show that large satellites of Earth-sized planets are detectable, but may cause aliasing effects if the lightcurve is insufficiently sampled.

  15. Trend analyses with river sediment rating curves

    USGS Publications Warehouse

    Warrick, Jonathan

    2015-01-01

    Sediment rating curves, which are fitted relationships between river discharge (Q) and suspended-sediment concentration (C), are commonly used to assess patterns and trends in river water quality. In many of these studies it is assumed that rating curves have a power-law form (i.e., C = aQb, where a and b are fitted parameters). Two fundamental questions about the utility of these techniques are assessed in this paper: (i) How well to the parameters, a and b, characterize trends in the data? (ii) Are trends in rating curves diagnostic of changes to river water or sediment discharge? As noted in previous research, the offset parameter, a, is not an independent variable for most rivers, but rather strongly dependent on b and Q. Here it is shown that a is a poor metric for trends in the vertical offset of a rating curve, and a new parameter, â, as determined by the discharge-normalized power function [C = â (Q/QGM)b], where QGM is the geometric mean of the Q values sampled, provides a better characterization of trends. However, these techniques must be applied carefully, because curvature in the relationship between log(Q) and log(C), which exists for many rivers, can produce false trends in â and b. Also, it is shown that trends in â and b are not uniquely diagnostic of river water or sediment supply conditions. For example, an increase in â can be caused by an increase in sediment supply, a decrease in water supply, or a combination of these conditions. Large changes in water and sediment supplies can occur without any change in the parameters, â and b. Thus, trend analyses using sediment rating curves must include additional assessments of the time-dependent rates and trends of river water, sediment concentrations, and sediment discharge.

  16. Effects of Bioreactor Retention Time on Aerobic Microbial Decomposition of CELSS Crop Residues

    NASA Technical Reports Server (NTRS)

    Strayer, R. F.; Finger, B. W.; Alazraki, M. P.

    1997-01-01

    The focus of resource recovery research at the KSC-CELSS Breadboard Project has been the evaluation of microbiologically mediated biodegradation of crop residues by manipulation of bioreactor process and environmental variables. We will present results from over 3 years of studies that used laboratory- and breadboard-scale (8 and 120 L working volumes, respectively) aerobic, fed-batch, continuous stirred tank reactors (CSTR) for recovery of carbon and minerals from breadboard grown wheat and white potato residues. The paper will focus on the effects of a key process variable, bioreactor retention time, on response variables indicative of bioreactor performance. The goal is to determine the shortest retention time that is feasible for processing CELSS crop residues, thereby reducing bioreactor volume and weight requirements. Pushing the lower limits of bioreactor retention times will provide useful data for engineers who need to compare biological and physicochemical components. Bioreactor retention times were manipulated to range between 0.25 and 48 days. Results indicate that increases in retention time lead to a 4-fold increase in crop residue biodegradation, as measured by both dry weight losses and CO2 production. A similar overall trend was also observed for crop residue fiber (cellulose and hemicellulose), with a noticeable jump in cellulose degradation between the 5.3 day and 10.7 day retention times. Water-soluble organic compounds (measured as soluble TOC) were appreciably reduced by more than 4-fold at all retention times tested. Results from a study of even shorter retention times (down to 0.25 days), in progress, will also be presented.

  17. 10 CFR 490.810 - Record retention.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...2013-01-01 2013-01-01 false Record retention. 490.810 Section 490.810 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ALTERNATIVE FUEL TRANSPORTATION PROGRAM Alternative Compliance § 490.810 Record...

  18. 10 CFR 490.810 - Record retention.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...2011-01-01 2011-01-01 false Record retention. 490.810 Section 490.810 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ALTERNATIVE FUEL TRANSPORTATION PROGRAM Alternative Compliance § 490.810 Record...

  19. 10 CFR 490.810 - Record retention.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 2010-01-01 false Record retention. 490.810 Section 490.810 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ALTERNATIVE FUEL TRANSPORTATION PROGRAM Alternative Compliance § 490.810 Record...

  20. 10 CFR 490.810 - Record retention.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...2014-01-01 2014-01-01 false Record retention. 490.810 Section 490.810 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ALTERNATIVE FUEL TRANSPORTATION PROGRAM Alternative Compliance § 490.810 Record...

  1. 10 CFR 490.810 - Record retention.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...2012-01-01 2012-01-01 false Record retention. 490.810 Section 490.810 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ALTERNATIVE FUEL TRANSPORTATION PROGRAM Alternative Compliance § 490.810 Record...

  2. 32 CFR 240.6 - Retention program.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...employees may apply for a master's or doctoral degree program; enlisted personnel...part-time. There are no part-time doctoral programs. All candidates must meet the...f) Retention students shall fulfill post-academic service obligations...

  3. 32 CFR 240.6 - Retention program.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...employees may apply for a master's or doctoral degree program; enlisted personnel...part-time. There are no part-time doctoral programs. All candidates must meet the...f) Retention students shall fulfill post-academic service obligations...

  4. 32 CFR 240.6 - Retention program.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...employees may apply for a master's or doctoral degree program; enlisted personnel...part-time. There are no part-time doctoral programs. All candidates must meet the...f) Retention students shall fulfill post-academic service obligations...

  5. 40 CFR 35.6705 - Records retention.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...Agreement § 35.6705 Records retention. (a...requirement applies to all financial and programmatic records, supporting documents...must maintain all records for 10 years following...submission of the final Financial Status Report...

  6. 40 CFR 35.6705 - Records retention.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...Agreement § 35.6705 Records retention. (a...requirement applies to all financial and programmatic records, supporting documents...must maintain all records for 10 years following...submission of the final Financial Status Report...

  7. 40 CFR 35.6705 - Records retention.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...Agreement § 35.6705 Records retention. (a...requirement applies to all financial and programmatic records, supporting documents...must maintain all records for 10 years following...submission of the final Financial Status Report...

  8. 40 CFR 35.6705 - Records retention.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...Agreement § 35.6705 Records retention. (a...requirement applies to all financial and programmatic records, supporting documents...must maintain all records for 10 years following...submission of the final Financial Status Report...

  9. 40 CFR 35.6705 - Records retention.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...Agreement § 35.6705 Records retention. (a...requirement applies to all financial and programmatic records, supporting documents...must maintain all records for 10 years following...submission of the final Financial Status Report...

  10. Tritium retention and removal on TFTR

    SciTech Connect

    Mueller, D.; Blanchard, W. [Princeton Plasma Physics Lab., NJ (United States); Doyle, B.L. [Sandia National Labs., Albuquerque, NM (United States)] [and others

    1997-10-01

    Tritium retention and removal are critical issues for the success of ITER or any DT fusion reactor. The Tokamak Fusion Test Reactor, TFTR, is the first fusion facility to afford the opportunity to study the tritium retention and removal over an extended period. In TFTR, tritium accumulates on all surfaces with line of sight to the plasma by codeposition of tritium with carbon. Measurements of both deuterium and tritium retention fractions have yielded retention between 0.2 and 0.6 of the injected fuel in the torus. Tritium has been successfully removed from TFTR by glow discharge cleaning and by air purges. The in-vessel inventory was reduced by a factor of 2, facilitating machine maintenance. In TFTR, the amount of dust recovered from the TFTR vacuum vessel has varied from several grams to a few kilograms.

  11. Tritium retention and removal on TFTR

    SciTech Connect

    Mueller, D.; Blanchard, W. [Princeton Univ., NJ (United States). Princeton Plasma Physics Lab.; Doyle, B.L. [Sandia National Labs., Albuquerque, NM (United States)] [and others

    1997-11-01

    Tritium retention and removal are critical issues for the success of ITER or any DT fusion reactor. The Tokamak Fusion Test Reactor, TFTR, is the first fusion facility to afford the opportunity to study the tritium retention and removal over an extended period. In TFTR, tritium accumulates on all surfaces with line of sight to the plasma by codeposition of tritium with carbon. Measurements of both deuterium and tritium retention fractions have yielded retention between 0.2 and 0.6 of the injected fuel in the torus. Tritium has been successfully removed from TFTR by glow discharge cleaning and by air purges. The in-vessel inventory was reduced by a factor of 2, facilitating machine maintenance. In TFTR, the amount of dust recovered from the TFTR vacuum vessel has varied from several grams to a few kilograms.

  12. Residential Refrigerator Recycling Ninth Year Retention Study

    E-print Network

    Residential Refrigerator Recycling Ninth Year Retention Study Study ID Nos. 546B, 563 Prepared RECYCLING PROGRAMS Study ID Nos. 546B and 563 Prepared for Southern California Edison Rosemead, California

  13. 50 CFR 401.15 - Record retention.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...COMMERCE); ENDANGERED SPECIES COMMITTEE REGULATIONS SUBCHAPTER A ANADROMOUS FISHERIES CONSERVATION, DEVELOPMENT AND ENHANCEMENT § 401.15 Record retention. All records of accounts and reports with supporting documentation thereto, as set...

  14. 50 CFR 401.15 - Record retention.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...COMMERCE); ENDANGERED SPECIES COMMITTEE REGULATIONS SUBCHAPTER A ANADROMOUS FISHERIES CONSERVATION, DEVELOPMENT AND ENHANCEMENT § 401.15 Record retention. All records of accounts and reports with supporting documentation thereto, as set...

  15. 50 CFR 401.15 - Record retention.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...COMMERCE); ENDANGERED SPECIES COMMITTEE REGULATIONS SUBCHAPTER A ANADROMOUS FISHERIES CONSERVATION, DEVELOPMENT AND ENHANCEMENT § 401.15 Record retention. All records of accounts and reports with supporting documentation thereto, as set...

  16. 39 CFR 946.10 - Record retention.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...THE DISPOSITION OF STOLEN MAIL MATTER AND PROPERTY ACQUIRED BY THE POSTAL INSPECTION...retention. Records regarding property subject to this part will be...3 years following return of the property to its owner or a...

  17. 39 CFR 946.10 - Record retention.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...THE DISPOSITION OF STOLEN MAIL MATTER AND PROPERTY ACQUIRED BY THE POSTAL INSPECTION...retention. Records regarding property subject to this part will be...3 years following return of the property to its owner or a...

  18. 39 CFR 946.10 - Record retention.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...THE DISPOSITION OF STOLEN MAIL MATTER AND PROPERTY ACQUIRED BY THE POSTAL INSPECTION...retention. Records regarding property subject to this part will be...3 years following return of the property to its owner or a...

  19. 39 CFR 946.10 - Record retention.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...THE DISPOSITION OF STOLEN MAIL MATTER AND PROPERTY ACQUIRED BY THE POSTAL INSPECTION...retention. Records regarding property subject to this part will be...3 years following return of the property to its owner or a...

  20. Spinal morphine anesthesia and urinary retention.

    PubMed

    Mahan, K T; Wang, J

    1993-11-01

    Spinal anesthetic is a common form of surgical anesthetic used in foot and ankle surgery. Spinal morphine anesthetic is less common, but has the advantage of providing postoperative analgesia for 12 to 24 hr. A number of complications can occur with spinal anesthesia, including urinary retention that may be a source of severe and often prolonged discomfort and pain for the patient. Management of this problem may require repeated bladder catheterization, which may lead to urinary tract infections or impairment of urethrovesicular function. This study reviews the incidence of urinary retention in 80 patients (40 after general anesthesia and 40 after spinal anesthesia) who underwent foot and ankle surgery at Saint Joseph's Hospital, Philadelphia, PA. Twenty-five percent of the patients who had spinal anesthesia experienced urinary retention, while only 7 1/2% of the group who had general anesthesia had this complication. Predisposing factors, treatment regimen, and recommendations for the prevention and management of urinary retention are presented. PMID:8258772

  1. Transport and retention from single to multiple fractures in crystalline rock at Äspö (Sweden): 2. Fracture network simulations and generic retention model

    NASA Astrophysics Data System (ADS)

    Cvetkovic, V.; Frampton, A.

    2010-05-01

    Hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges. In this work we use comprehensive hydrostructural information and present a detailed simulation study of flow and advective transport in a discrete fracture network (DFN) that replicates the Tracer Retention Understanding Experiments (TRUE) Block Scale rock volume at the Äspö Hard Rock Laboratory (Sweden). Simulated water residence time ? and hydrodynamic retention parameter ? are used as independent constraints for estimating material retention properties as presented in paper 1 of this series, whereas simulated mean water residence times are compared with observed values. We find that the DFN simulations reproduce water residence times reasonably well, indicating that the characterization data are sufficient and that the DFN model does capture dominant features of the flow paths analyzed. The empirical quadratic law that relates aperture and transmissivity seems to better reproduce calibrated mean water residence times than the theoretical cubic law for the five flow paths. The active specific surface area (?/?) [1/L] as inferred from simulations is used for defining a generic retention model for the dominant rock type (Äspö diorite) that matches fairly well the entire range of calibrated retention parameters of the TRUE tests. The combination of paper 1 and this work provides a general, comprehensive methodology for evaluating tracer test results in crystalline rock where a comparable amount of information is available; critical to this methodology is that tracer tests are carried out using tracers with sufficiently different sorption affinities (of factor 10-100).

  2. Sulfonate Retention and Residual Oil Saturation

    Microsoft Academic Search

    C. Presley

    1983-01-01

    This paper describes an empirical relationship between sulfonate retention and final residual oil saturation achieved by a micellar\\/polymer oil-recovery process. Using this relationship and certain assumptions, one can derive expressions for predicting oil recovery performance in coreflood experiments. The equations contain two experimental constants: sulfonate retention and a factor related to the oil-recovery efficiency of the sulfonate slug in cores,

  3. Factors affecting water coning 

    E-print Network

    Parker, Randy Keith

    1977-01-01

    . The interpolated curve was essentially the same as the simulation curve during the later production history. The values of the interpolated curve during the transition period had lower water oil ratios than the simulation curve. This is due to using linear... (December 1977) Randy Keith Parker, B. S. , Texas ASM University Chairman of Advisory Conmittee: Dr. Richard A. Morse The production of oil that is underlain by water, through a partially penetrating well at a production rate greater than a certain...

  4. Phosphate retention by New Zealand soils and its relationship to free sesquioxides, organic matter, and other soil properties

    Microsoft Academic Search

    W. M. H. Saunders

    1965-01-01

    Phosphate retention from KH2PO4 solution at pH 4.6 was measured in some New Zealand soil profiles, arranged in sequences of increasing weathering and leaching, from sedimentary and volcanic parent materials. P retention from KH2PO4 solution correlated closely with Pretention measured by adding solid Ca(H2PO4)2H2O to moist soil and subsequently measuring water-soluble P.P retention by topsoils correlated closely with organic carbon,

  5. Biogenic structure enhances landscape retention on intertidal flats at extensive spatial scales

    NASA Astrophysics Data System (ADS)

    Nieuwhof, Sil; van Belzen, Jim; Oteman, Bas; van de Koppel, Johan; Herman, Peter; van der Wal, Daphne

    2015-04-01

    Ecosystem engineering species can structure their environment at multiple spatial scales, locally where the organisms are found, but this can also extend to significant distance. Such structural change of the landscape can have important consequences for ecosystem functioning, increasing retention of valuable resources in the system, such as water or nutrients. Yet, the relative effect of structure added by ecosystem engineers as opposed to the physical landscape structure on retention remains poorly understood. Using remote sensing techniques, we reveal that on intertidal flats, water retention is greatly enhanced by the reef structure created by shellfish, where the effects exceed significantly beyond the physical borders of the reef system. Furthermore, real and simulated landscapes show that changes in retention capacity brought about by ecosystem engineering depends on the underlying landscape configuration. Strikingly, shellfish reefs enhance retention even at low densities, and this effect is largest and most extensive in space on relatively flat landscapes. Our results provide valuable new insights into the importance and context dependence of biogenic structure to landscapes.

  6. Least Limiting Water Range of soils in the Colonia Agrícola de Turen, Venezuela

    NASA Astrophysics Data System (ADS)

    Perez, Maiby Yolanda; Florentino de Andreu, Adriana

    2013-04-01

    Soil physical degradation is a major problem affecting the soil quality for crops production in Venezuelan agricultural areas. The least limiting water range (LLWR) is considered a soil physical quality index defined as the range in soil water content within which the limitations to plant response associated with water potential, poor aeration and high mechanical resistance are minimal. The study was carried out to characterize the LLWR and to determine the LLWR response to structural changes on soils of the Colonia Agricola de Turen, Venezuela. The soils were cropped with maize under different tillage systems (no tillage, conventional and conventional - fallow) and non-cropped under native forest. Hundred and seventy undisturbed samples were taken from specific sites under each of the above soil conditions to determine the water retention curve, the soil resistance curve and bulk density. Disturbed samples were also taken from each site to determine particle size and organic matter content. Pedotransfer functions relating the water retention curve and soil resistance curve with particle size distribution, organic matter content and bulk density were developed and use to calculate the LLWR for each site. According to the results, soil physical degradation under conventional tillage and high clay content had the highest negative impact on the LLWR. For this case (silty clay loam soil), the LLWR became narrower due to the lower water content associated with poor aeration and the higher water content associated with high mechanical resistance. In contrast, for non degraded soils with high sand content (sandy loam) the LLWR showed the highest values associated with the water content at field capacity and the water content at permanent wilting point, both the upper and lower critical limits of LLWR. For silty loam and loam soils the LLWR declined with increasing bulk density and clay content associated with water content at field capacity and water content at high mechanical resistance. Soil resistance to root penetration determined the lower limit of LLWR in 41 % of the soils and the water content at field capacity determined the upper limit of LLWR in 94% of the soils. Further studies are recommended to determine the nature and magnitude of the association between the LLWR and crop yield under different soils and climate conditions.

  7. Reactive barriers for 137Cs retention

    NASA Astrophysics Data System (ADS)

    Krumhansl, James L.; Brady, Patrick V.; Anderson, Howard L.

    2001-02-01

    137Cs was dispersed globally by cold war activities and, more recently, by the Chernobyl accident. Engineered extraction of 137Cs from soils and groundwaters is exceedingly difficult. Because the half-life of 137Cs is only 30.2 years, remediation might be more effective (and less costly) if 137Cs bioavailability could be demonstrably limited for even a few decades by use of a reactive barrier. Essentially permanent isolation must be demonstrated in those few settings where high nuclear level wastes contaminated the environment with 135Cs (half-life 2.3×10 6 years) in addition to 137Cs. Clays are potentially a low-cost barrier to Cs movement, though their long-term effectiveness remains untested. To identify optimal clays for Cs retention, Cs desorption was measured for five common clays: Wyoming Montmorillonite (SWy-1), Georgia Kaolinites (KGa-1 and KGa-2), Fithian Illite (F-Ill), and K-Metabentonite (K-Mbt). Exchange sites were pre-saturated with 0.16 M CsCl for 14 days and readily exchangeable Cs was removed by a series of LiNO 3 and LiCl washes. Washed clays were then placed into dialysis bags and the Cs release to the deionized water outside the bags measured. Release rates from 75 to 139 days for SWy-1, K-Mbt and F-Ill were similar; 0.017% to 0.021% sorbed Cs released per day. Both kaolinites released Cs more rapidly (0.12% to 0.05% of the sorbed Cs per day). In a second set of experiments, clays were Cs-doped for 110 days and subjected to an extreme and prolonged rinsing process. All the clays exhibited some capacity for irreversible Cs uptake. However, the residual loading was greatest on K-Mbt (˜0.33 wt.% Cs). Thus, this clay would be the optimal material for constructing artifical reactive barriers.

  8. Techniques for estimating specific yield and specific retention from grain-size data and geophysical logs from clastic bedrock aquifers

    USGS Publications Warehouse

    Robson, S.G.

    1993-01-01

    Specific yield and specific retention are aquifer characteristics that are important in determining the volume of water in storage in an aquifer. These characteristics can be determined by laboratory analyses of undisturbed samples of aquifer material. However. quicker, less costly alternatives to these laboratory analyses are needed. This report presents techniques for estimating specific yield and specific retention based on grain-size analyses, and based on interpretation of borehole geophysical logs.

  9. Modelling the Hydrological Performance of Stormwater Management Retention Ponds in Scotland

    Microsoft Academic Search

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

    2004-01-01

    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

  10. Liquid Drops on an Inclined Plane: The Relation between Contact Angles, Drop Shape, and Retentive Force

    Microsoft Academic Search

    Charles W. Extrand; Y. Kumagai

    1995-01-01

    Contact angle hysteresis, drop shape, and drop retention were studied with a tiltable plane. Contact liquids were water and ethylene glycol. Four polymers and silicon wafers were used as substrates. When the plane was inclined, the shape of drops distorted, exhibiting advancing and receding contact angles. Drops remained stationary until a critical angle of tilt was exceeded, and then they

  11. AIRWAY RETENTION OF MATERIALS OF DIFFERENT SOLUBILITY FOLLOWING LOCAL INTRABRONCHIAL DEPOSITION IN DOGS

    EPA Science Inventory

    We used a gamma camera to monitor the retention and clearance of radiolabeled human serum albumin (HSA), a water-soluble material with molecular weight of 66,000 Daltons, and radiolabeled sulfur colloid (SC), an insoluble submicron (0.22 microm) particle, following localized depo...

  12. Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

    Microsoft Academic Search

    Kaouakeb Elkhattabi; Ahmed Bouhaouss; Laura Scrano; Filomena Lelario; Sabino A. Bufo

    2007-01-01

    The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of C labeled isoproturon have been determined in two Moroccan soils by ? -counting–liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis\\/scintillation-detected

  13. Developing Novel Reservoir Rule Curves Using Seasonal Inflow Projections

    NASA Astrophysics Data System (ADS)

    Tseng, Hsin-yi; Tung, Ching-pin

    2015-04-01

    Due to significant seasonal rainfall variations, reservoirs and their flexible operational rules are indispensable to Taiwan. Furthermore, with the intensifying impacts of climate change on extreme climate, the frequency of droughts in Taiwan has been increasing in recent years. Drought is a creeping phenomenon, the slow onset character of drought makes it difficult to detect at an early stage, and causes delays on making the best decision of allocating water. For these reasons, novel reservoir rule curves using projected seasonal streamflow are proposed in this study, which can potentially reduce the adverse effects of drought. This study dedicated establishing new rule curves which consider both current available storage and anticipated monthly inflows with leading time of two months to reduce the risk of water shortage. The monthly inflows are projected based on the seasonal climate forecasts from Central Weather Bureau (CWB), which a weather generation model is used to produce daily weather data for the hydrological component of the GWLF. To incorporate future monthly inflow projections into rule curves, this study designs a decision flow index which is a linear combination of current available storage and inflow projections with leading time of 2 months. By optimizing linear relationship coefficients of decision flow index, the shape of rule curves and the percent of water supply in each zone, the best rule curves to decrease water shortage risk and impacts can be developed. The Shimen Reservoir in the northern Taiwan is used as a case study to demonstrate the proposed method. Existing rule curves (M5 curves) of Shimen Reservoir are compared with two cases of new rule curves, including hindcast simulations and historic seasonal forecasts. The results show new rule curves can decrease the total water shortage ratio, and in addition, it can also allocate shortage amount to preceding months to avoid extreme shortage events. Even though some uncertainties in historic forecasts would result unnecessary discounts of water supply, it still performs better than M5 curves during droughts.

  14. Floppy Curves with Applications to Real Algebraic Curves

    Microsoft Academic Search

    Patrick M. Gilmer

    1996-01-01

    We show how one may sometimes perform singular ambient surgery on the complex\\u000alocus of a real algebraic curve and obtain what we call a floppy curve. A\\u000afloppy curve is a certain kind of singular surface in CP(2), more general than\\u000athe complex locus of a real nodal curve. We derive analogs for floppy curves of\\u000aknown restrictions on

  15. Biological plasticity in penguin heat-retention structures.

    PubMed

    Thomas, Daniel B; Fordyce, R Ewan

    2012-02-01

    Insulation and vascular heat-retention mechanisms allow penguins to forage for a prolonged time in water that is much cooler than core body temperature. Wing-based heat retention involves a plexus of humeral arteries and veins, which redirect heat to the body core rather than to the wing periphery. The humeral arterial plexus is described here for Eudyptes and Megadyptes, the only extant penguin genera for which wing vascular anatomy had not previously been reported. The erect-crested (Eudyptes sclateri) and yellow-eyed (Megadyptes antipodes) penguins both have a plexus of three humeral arteries on the ventral surface of the humerus. The wing vascular system shows little variation between erect-crested and yellow-eyed penguins, and is generally conserved across the six extant genera of penguins, with the exception of the humeral arterial plexus. The number of humeral arteries within the plexus demonstrates substantial variation and correlates well with wing surface area. Little penguins (Eudyptula minor) have two humeral arteries and a wing surface area of ? 75 cm(2) , whereas emperor penguins (Aptenodytes forsteri) have up to 15 humeral arteries and a wing surface area of ? 203 cm(2) . Further, the number of humeral arteries has a stronger correlation with wing surface area than with sea water temperature. We propose that thermoregulation has placed the humeral arterial plexus under a strong selection pressure, driving penguins with larger wing surface areas to compensate for heat loss by developing additional humeral arteries. PMID:22213564

  16. IGMtransmission: Transmission curve computation

    NASA Astrophysics Data System (ADS)

    Harrison, Christopher M.; Meiksin, Avery; Stock, David

    2015-04-01

    IGMtransmission is a Java graphical user interface that implements Monte Carlo simulations to compute the corrections to colors of high-redshift galaxies due to intergalactic attenuation based on current models of the Intergalactic Medium. The effects of absorption due to neutral hydrogen are considered, with particular attention to the stochastic effects of Lyman Limit Systems. Attenuation curves are produced, as well as colors for a wide range of filter responses and model galaxy spectra. Photometric filters are included for the Hubble Space Telescope, the Keck telescope, the Mt. Palomar 200-inch, the SUBARU telescope and UKIRT; alternative filter response curves and spectra may be readily uploaded.

  17. Considering Student Retention as a Complex System: A Possible Way forward for Enhancing Student Retention

    ERIC Educational Resources Information Center

    Forsman, Jonas; van den Bogaard, Maartje; Linder, Cedric; Fraser, Duncan

    2015-01-01

    This study uses multilayer minimum spanning tree analysis to develop a model for student retention from a complex system perspective, using data obtained from first-year engineering students at a large well-regarded institution in the European Union. The results show that the elements of the system of student retention are related to one another…

  18. Record Retention Policy Page 1 of 3 10.7 Record Retention Policy

    E-print Network

    Yang, Eui-Hyeok

    Record Retention Policy Page 1 of 3 10.7 Record Retention Policy Policy Number & Name: 10.7 Record and destruction of records received or created in the course of University operations (as further defined below, "Records"). It is the intention of this Policy to ensure that the University: (a) Establishes the minimum

  19. Use of a Graphical Method to Predict the Retention Times of Selected Flavonoids in HPLC from Thin-Layer Chromatographic Data

    Microsoft Academic Search

    M. Tatarczak; J. Flieger; H. Szumi?o

    2005-01-01

    Similarities and differences between the retention characteristics of octadecylsilica wettable with water used in TLC and RP-18 used in HPLC have been elucidated by use of the linear relationships between log k and RM. The stationary phases compared were investigated with the same mobile phases—binary mixtures of methanol and water, acetonitrile and water, and tetrahydrofuran and water. For these adsorbents

  20. Liquefaction probability curves for surficial geologic deposits

    USGS Publications Warehouse

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

    2011-01-01

    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.

  1. WATER AND ATRAZINE MOVEMENT IN A CALCAREOUS COMPOST APPLIED SOIL DURING SIMULATED MULTIPLE STORM EVENTS.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Agricultural soils in the region are mainly composed of crushed limestone, which has a low water and chemical retention capacity. Therefore, sustaining a profitable agricultural system requires appropriate applications of fertilizer, pesticides and irrigation. The retention and transport of atrazi...

  2. RELATIVE PERMEABILITY CURVES DURING HYDRATE DISSOCIATION IN DEPRESSURIZATION

    Microsoft Academic Search

    Yoshihiro Konno; Yoshihiro Masuda; Chie Lin Sheu; Hiroyuki Oyama; Hisanao Ouchi; Masanori Kurihara

    2008-01-01

    Depressurization is thought to be a promising method for gas recovery from methane hydrate reservoirs, but considerable water production is expected when this method is applied to the hydrate reservoir of high initial water saturation. In this case, the prediction of water production is a critical problem. This study examined relative permeability curves during hydrate dissociation by comparing numerical simulations

  3. Water power generator

    Microsoft Academic Search

    Borgren

    1982-01-01

    A water power generator for generating electrical energy from a moving body of water comprising structural means interposed in the path of water flow. The structural means includes at least one side wall which is longitudinally curved from a diverting point at the outer end thereof to a gradually flattened curve at the inner end thereof. The wall is transversely

  4. Water

    MedlinePLUS

    You might not give much thought to water or how it gets to you. You just turn on the faucet and there it is. Do you ever wonder how it flows ... concern that it might make you sick. Your water can come from a lake, a river, a ...

  5. Simulation of the fluid retention effects of a vasopressin analog using the Guyton model of circulation.

    PubMed

    Srinivasan, R S; Simanonok, K E; Fortney, S M; Charles, J B

    1993-01-01

    Fluid-loading (FL) consisting of water and salt tablets equivalent of 32 oz of isotonic saline is a countermeasure currently in use by NASA to improve the orthostatic tolerance of astronauts during Shuttle reentry. However, the effectiveness of this countermeasure has been observed to decrease with the duration of space flight. Possible ways to improve fluid retention and thus the effectiveness of FL include use of analogs of vasopressin such as lypressin (LVP). This study used a computer simulation approach to analyze the potential benefits on fluid retention with LVP administered before FL. PMID:11537416

  6. The effects of wood species and treatment retention on kinetics of CCA-C fixation reactions

    Microsoft Academic Search

    Suzana Radivojevic; Paul A. Cooper

    2010-01-01

    Reaction kinetics of fixation of CCA-C (chromated copper arsenate type C) preservative was studied at 30°C in ground wood\\u000a of trembling aspen, red pine, and red maple at treatment retentions of 4.0, 6.4, 9.6, and 30 kg\\/m3, and red maple pre-extracted with hot water at retentions of 6.4 and 30 kg\\/m3. Reaction orders of cumulative Cr, Cu, and As reactions decreased gradually

  7. Electrostatic curved electrode actuators

    Microsoft Academic Search

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

    1997-01-01

    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

  8. Throwing a Curve

    E-print Network

    Wedge, Philip

    2000-09-01

    134 Aethlon XVIII: 1 / Fall 2000 Throwing A Curve Coming home from Roy's team picture, we stop to show off the brand-new uniform - Blue Jays stenciled on the front, stockings, the works. Out of mischief or shyness hes at the edge of the room...

  9. Uncertainty propagation: Curve fitting

    NSDL National Science Digital Library

    2013-06-21

    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.

  10. Parametric Curves Introduction

    E-print Network

    Vickers, James

    in three dimensional space. 9 8 6 7 Prerequisites Before starting this Section you should.3: Parametric Curves 2 #12;i.e. x2 4 + y2 9 = 1 which we easily recognise as an ellipse whose major = 3 sin t together with the parametric range 0 t /2 describe that part of the ellipse x2 4 + y2 9

  11. Straightening Out Learning Curves

    ERIC Educational Resources Information Center

    Corlett, E. N.; Morecombe, V. J.

    1970-01-01

    The basic mathematical theory behind learning curves is explained, together with implications for clerical and industrial training, evaluation of skill development, and prediction of future performance. Brief studies of textile worker and typist training are presented to illustrate such concepts as the reduction fraction (a consistent decrease in…

  12. Characteristic Curves of PEMFC

    NSDL National Science Digital Library

    This in-class exercise will allow students hands-on experience working with a proton exchange membrane fuel cell, or PEMFC. The class will examine the characteristic curve of one of these fuel cells and measure the voltage and current output of the cell. Step by step instructions are provided for the experiment. This document may be downloaded in PDF file format.

  13. Curve Fit Challenge

    ERIC Educational Resources Information Center

    Harper, Suzanne R.; Driskell, Shannon

    2005-01-01

    Graphic tips for using the Geometer's Sketchpad (GSP) are described. The methods to import an image into GSP, define a coordinate system, plot points and curve fit the function using a graphical calculator are demonstrated where the graphic features of GSP allow teachers to expand the use of the technology application beyond the classroom.

  14. Symbolic Parametrization of Curves

    Microsoft Academic Search

    J. Rafael Sendra; Franz Winkler

    1991-01-01

    If algebraic varieties like curves or surfaces are to be manipulated by computers, it is essential to be able to represent these geometric objects in an appropriate way. For some applications an implicit representation by algebraic equations is desirable, whereas for others an explicit or parametric representation is more suitable. Therefore, transformation algorithms from one representation to the other are

  15. Heavy metal contamination of settling particles in a retention pond along the A-71 motorway in Sologne, France

    Microsoft Academic Search

    Pyeong-Koo Lee; Jean-Claude Touray; Patrick Baillif; Jean-Pierre Ildefonse

    1997-01-01

    A retention pond is a part of a drainage system designed to control water flow during rainstorms and to trap contaminated solid particles washed off by runoff water from a motorway. A series of studies have been carried out concerning the physico-chemical characteristics of the particles which settle down in such a pond in order to evaluate the effectiveness of

  16. Influence of pH on Phosphorus Retention in Oxidized Lake Sediments O. G. Olila* and K. R. Reddy

    E-print Network

    Florida, University of

    Influence of pH on Phosphorus Retention in Oxidized Lake Sediments O. G. Olila* and K. R. Reddy ABSTRACT Diel pH changes in lake waters resulting from high photosynthetic activity may regulate water studies were conducted to determine the pH effect on P fractions and P sorption kinetics in oxidized

  17. Crown retention for non-retentive preparations using adhesive resin cements.

    PubMed

    Osman, Saad A; Walls, A W G; McCabe, John F

    2010-12-01

    This study examines the effect of preparing teeth with six varying convergence angles (ranging between 12 and 120 degrees) and height (1 and 2 mm) on the retention of cast gold crowns. Six groups of 4 human premolar teeth were prepared to give a flat occlusal surface in dentine with very short axial wall heights (1 or 2 mm) and variation in axial wall convergence (between 12 and 120 degrees). Impressions were recorded of the prepared teeth and custom castings made using a high copper content precious metal alloy. The castings were luted with an adhesive resin and stored in water at 37 degrees C for 24 hours prior to determining the pull-off force in an Instron Universal testing Machine at a cross head speed of 1mm min(-1). Twenty two of the twenty four tested specimens failed within the dentine of the tooth, irrespective of preparation orientation. Statistical testing using ANOVA demonstrated that there were no differences between the bond strength values for any of the preparation convergence angles or between preparations with 1 and 2 mm axial wall heights. This suggests that attachment strength of adhesively bonded castings with minimal axial wall height preparations is not influenced by the convergence angle of the preparation. The attachment strength exceeded that cohesive strength of the underlying dentine in nearly all of the adhesively luted restorations. PMID:21265433

  18. The Effects of Denture Cleansing Solutions on the Retention of Attachments of Implant Supported Overdentures

    PubMed Central

    Derafshi, Reza; Mohaghegh, Mina; Saki, Maryam; Safari, Anahita; Rabee Haghighi, Mohammad

    2015-01-01

    Statement of the Problem Implant-retained overdenture can improve the stability of dentures and prevent bone loss. Overdenture-wearing patients need special hygiene care. Purpose The aim of this study was to evaluate the effects of various denture cleansers on the retention of Dio orange O-rings. Method and Materials In this experimental study, 40 Dio orange O-rings were divided into 4 groups (10 O-rings each) and each group was soaked for equivalent of 6 months in the following solutions: 5.25% NaOCl (1:10 dilution), Corega cleanser tabs, Professional cleanser tabs and water (as the control group). After 6 months, O-rings were tested for 2inch/minutes of tensile force. The peak load-to-dislodgement was recorded. Data were imported to SPSS18 and were analyzed by One-Way ANOVA and Tukey HSD test (p? 0.05). Results Denture cleansing solutions have significant effects on the reduction of retentive value of O-rings (p? 0.001). Corega tabs caused the reduction of 15.7% (9.91±0.53 N) in the retentive value of O-rings and Professional tabs caused 15% (10.00±0.86 N). NaOCl caused significant decrease (48%) in retentive value of O-rings (6.10±0.91 N in comparison with the control group (11.76±1 N). Conclusion This in-vitro study demonstrated that the retention of O-rings was affected when soaked in cleansing solutions. NaOCl caused more reduction in retentive value compared to effervescent cleansers and would not be recommended for cleansing O-rings. These results should be interpreted clinically and the role of other factors in the retention of O-rings should be considered in order to recommend the best cleanser for O-ring overdentures.

  19. Retention mechanisms in super/subcritical fluid chromatography on packed columns.

    PubMed

    Lesellier, E

    2009-03-01

    Whereas the retention rules of achiral compounds are well defined in high-performance liquid chromatography, on the basis of the nature of the stationary phase, some difficulties appear in super/subcritical fluid chromatography on packed columns. This is mainly due to the supposed effect of volatility on retention behaviours in supercritical fluid chromatography (SFC) and to the nature of carbon dioxide, which is not polar, thus SFC is classified as a normal-phase separation technique. Moreover, additional effects are not well known and described. They are mainly related to density changes of the mobile phase or to adsorption of fluid on the stationary phase causing a modification of its surface. It is admitted that pressure or temperature modifications induce variation in the eluotropic strength of the mobile phase, but effects of flow rate or column length on retention factor changes are more surprising. Nevertheless, the retention behaviour in SFC first depends on the stationary phase nature. Working with polar stationary phases induces normal-phase retention behaviour, whereas using non-polar bonded phases induces reversed-phase retention behaviour. These rules are verified for most carbon dioxide-based mobile phases in common use (CO(2)/MeOH, CO(2)/acetonitrile or CO(2)/EtOH). Moreover, the absence of water in the mobile phase favours the interactions between the compounds and the stationary phase, compared to what occurs in hydro-organic liquids. Other stationary phases such as aromatic phases and polymers display intermediate behaviours. In this paper, all these behaviours are discussed, mainly by using log k-log k plots, which allow a simple comparison of stationary phase properties. Some examples are presented to illustrate these retention properties. PMID:18996534

  20. Retention and remobilization dynamics of fine particles and microorganisms in pastoral streams.

    PubMed

    Drummond, J D; Davies-Colley, R J; Stott, R; Sukias, J P; Nagels, J W; Sharp, A; Packman, A I

    2014-12-01

    Both microbial metabolism and pathogen retention and remobilization are dependent on downstream transport of fine particles, which migrate in a series of deposition and resuspension events. All fine particles, including clay minerals, particulate organic carbon, nutrients and microbes, are often considered to be transported similarly in the environment because of a lack of specific observations comparing their relative transport. We conducted a tracer injection study to compare the transport and retention of the fecal indicator bacterium Escherichia coli, synthetic inert fluorescent fine particles, and a dissolved conservative tracer. We found that the fluorescent fine particles and bacteria were transported similarly, with both having greater retention than the solute tracer. We used a stochastic model to evaluate in-stream retention and migration of the solute, fluorescent particles, and E. coli. The best-fit model parameters indicate that different stream reaches had varied retention characteristics, but always showed greater retention of fluorescent particles and E. coli compared to the solute tracer. Direct measurements within known retention areas after the injection showed that the majority of the fluorescent particles and E. coli were retained near the sediment-water interface in macrophyte stands or filtered within the top 3 cm of the streambed sediment. Both the tracer particles and E. coli were retained within these regions for multiple months following the injection experiment. The stochastic model properly captured the wide range of storage timescales and processes we observed in the stream. Our results demonstrate the importance of the streambed sediment and in-stream macrophytes as short- and long-term reservoirs for fine organic particles and microbes in streams. PMID:25243658

  1. Rapid Estimation of Octanol–Water Partition Coefficient for Triazole Fungicides by MEKC with Sodium Deoxycholate as Surfactant

    Microsoft Academic Search

    Wan Aini Wan Ibrahim; Dadan Hermawan; Mohamed Noor Hasan; Hassan Y. Aboul Enein; M. Marsin Sanagi

    2008-01-01

    A rapid estimation of octanol–water partition coefficient (log P\\u000a ow) was developed for triazole fungicides by micellar electrokinetic chromatography (MEKC). Five standard compounds with known\\u000a log P\\u000a ow values from 2.9 to 4.3 (cyproconazole, bromuconazole, epoxiconazole, bitertanol and difenoconazole) were used for constructing\\u000a the calibration curve of the log P\\u000a ow against the MEKC retention factor, log k. A linear

  2. Modelling the impact of retention-detention units on sewer surcharge and peak and annual runoff reduction.

    PubMed

    Locatelli, Luca; Gabriel, Søren; Mark, Ole; Mikkelsen, Peter Steen; Arnbjerg-Nielsen, Karsten; Taylor, Heidi; Bockhorn, Britta; Larsen, Hauge; Kjølby, Morten Just; Blicher, Anne Steensen; Binning, Philip John

    2015-01-01

    Stormwater management using water sensitive urban design is expected to be part of future drainage systems. This paper aims to model the combination of local retention units, such as soakaways, with subsurface detention units. Soakaways are employed to reduce (by storage and infiltration) peak and volume stormwater runoff; however, large retention volumes are required for a significant peak reduction. Peak runoff can therefore be handled by combining detention units with soakaways. This paper models the impact of retrofitting retention-detention units for an existing urbanized catchment in Denmark. The impact of retrofitting a retention-detention unit of 3.3 m(3)/100 m(2) (volume/impervious area) was simulated for a small catchment in Copenhagen using MIKE URBAN. The retention-detention unit was shown to prevent flooding from the sewer for a 10-year rainfall event. Statistical analysis of continuous simulations covering 22 years showed that annual stormwater runoff was reduced by 68-87%, and that the retention volume was on average 53% full at the beginning of rain events. The effect of different retention-detention volume combinations was simulated, and results showed that allocating 20-40% of a soakaway volume to detention would significantly increase peak runoff reduction with a small reduction in the annual runoff. PMID:25812100

  3. Variables affecting athletes' retention of coaches' feedback.

    PubMed

    Januário, Nuno M S; Rosado, Antonio F; Mesquita, Isabel

    2013-10-01

    Athletes' retention of information conveyed in coaches' feedback during training was examined, considering the nature of the information transmitted by each coach (extensions, total number of ideas transmitted, and total number of repeated ideas), athletes' characteristics, (ages, genders, school levels, and practice levels), and athletes' perceptions (relevance and acceptance of coaches' information, task motivational levels, and athletes' attention levels). Participants were 193 athletes (79 boys, 114 girls; 9 to 13 years of age) and 6 coaches. Feedback was both audio and video recorded and all athletes were interviewed. All coaches' feedback and athletes' recollections were subjected to content analysis. Information was completely retained in 31.60% of feedback episodes. Athletes' mean per-episode information retention was 63.0%. Three variables appeared to b e predictiveathletes' retention: athletes' practice levels (p = -.25), attention to coaches' provision of feedback (P = .17), and the number of different ideas transmitted by each coach (P = -.90). PMID:24611244

  4. Deuterium Retention in NSTX with Lithium Conditioning

    SciTech Connect

    C.H. Skinner, J.P. Allain, W. Blanchard, H.W. Kugel, R. Maingi, L. Roquemore, V. Soukhanovskii, C.N. Taylor

    2010-06-02

    High (? 90%) deuterium retention was observed in NSTX gas balance measurements both withand without lithiumization of the carbon plasma facing components. The gas retained in ohmic discharges was measured by comparing the vessel pressure rise after a discharge to that of a gasonly pulse with the pumping valves closed. For neutral beam heated discharges the gas input and gas pumped by the NB cryopanels were tracked. The discharges were followed by outgassing of deuterium that reduced the retention. The relationship between retention and surface chemistry was explored with a new plasma-material interface probe connected to an in-vacuo surface science station that exposed four material samples to the plasma. XPS and TDS analysis showed that the binding of D atoms is fundamentally changed by lithium - in particular atoms are weakly bonded in regions near lithium atoms bound to either oxygen or the carbon matrix.

  5. Influence of ionic complexation on release rate profiles from multiple water-in-oil-in-water (W/O/W) emulsions.

    PubMed

    Bonnet, Marie; Cansell, Maud; Placin, Frédéric; David-Briand, Elisabeth; Anton, Marc; Leal-Calderon, Fernando

    2010-07-14

    Water-in-oil-in-water (W/O/W) double emulsions were prepared, and the kinetics of release of magnesium ions from the internal to the external water phase was followed. Different chelating agents (phosvitin and gluconate) were used to bind magnesium within the prospect of improving the ion retention in the internal aqueous droplets. Magnesium release was monitored for 1 month of storage, for each formulation, with and without chelation, at two storage temperatures (4 and 25 degrees C). Leakage occurred without film rupturing (coalescence) and was mainly due to entropically driven diffusion/permeation phenomena. The experimental results revealed a clear correlation between the effectiveness of chelating agents to delay the delivery and their binding capacity characterized by the equilibrium affinity constant. The kinetic data (percent released versus time curves) were interpreted within the framework of a kinetic model based on diffusion and taking into account magnesium chelation. PMID:20545343

  6. Enhanced retention of encapsulated ions in cross-linked polymersomes.

    PubMed

    Wang, Guanglin; Hoornweg, Arentien; Wolterbeek, Hubert T; Franken, Linda E; Mendes, Eduardo; Denkova, Antonia G

    2015-03-19

    Polymer vesicles (polymersomes) composed of poly(butadiene-b-poly(ethylene oxide)) (PB-b-PEO) are known for their stability and limited permeability. However, when these vesicles are diluted, substances, such as ions, encapsulated in the aqueous cavity can be released due to vesicle disruption. In previous studies, we have shown that these vesicles can be loaded efficiently with sufficient quantities of radionuclides to allow application in radionuclide therapy and pharmacokinetics evaluation, provided that there is no loss of the encapsulated radionuclides when diluted in the bloodstream. In this paper, in order to stabilize the carriers, we propose to cross-link the hydrophobic part of the polymersome membrane and to investigate whether such cross-linking induced by ? radiation can enhance the retention of ions (radionuclides). Retention of ions encapsulated in the lumen in such cross-linked carriers has not been previously quantitatively evaluated, although it is of ultimate importance in any medical application. Here, we also investigate how cross-linking affects the transport of radionuclides (loading) through the membrane of the vesicles. The integrity of the vesicles as a function of the radiation dose is also investigated, including morphological changes. The results show that cross-linking hinders the transport of ions through the membrane, which also leads to higher retention of ions encapsulated prior to cross-linking in the vesicles. Electron micrographs show that the shape of the polymersomes is not greatly affected by ? radiation when left in the original solvent (phosphate buffered saline (PBS) or Milli-Q water), but when diluted in a good solvent for both blocks, i.e., tetrahydrofuran (THF), disintegration of the vesicles and the appearance of droplet-like structures is observed, which had not been reported previously. The results of the present study help to formulate polymersomes as carriers for radionuclide therapy, demonstrating a way to prevent in vivo release of radionuclides, caused by dilution-induced destabilization of the nanocarriers. PMID:25734478

  7. Strong Agreement of Nationally Recommended Retention Measures from the Institute of Medicine and Department of Health and Human Services

    PubMed Central

    Rebeiro, Peter F.; Horberg, Michael A.; Gange, Stephen J.; Gebo, Kelly A.; Yehia, Baligh R.; Brooks, John T.; Buchacz, Kate; Silverberg, Michael J.; Gill, John; Moore, Richard D.; Althoff, Keri N.

    2014-01-01

    Objective We sought to quantify agreement between Institute of Medicine (IOM) and Department of Health and Human Services (DHHS) retention indicators, which have not been compared in the same population, and assess clinical retention within the largest HIV cohort collaboration in the U.S. Design Observational study from 2008–2010, using clinical cohort data in the North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD). Methods Retention definitions used HIV primary care visits. The IOM retention indicator was: ?2 visits, ?90 days apart, each calendar year. This was extended to a 2-year period; retention required meeting the definition in both years. The DHHS retention indicator was: ?1 visit each semester over 2 years, each ?60 days apart. Kappa statistics detected agreement between indicators and C statistics (areas under Receiver-Operating Characteristic curves) from logistic regression analyses summarized discrimination of the IOM indicator by the DHHS indicator. Results Among 36,769 patients in 2008–2009 and 34,017 in 2009–2010, there were higher percentages of participants retained in care under the IOM indicator than the DHHS indicator (80% vs. 75% in 2008–2009; 78% vs. 72% in 2009–2010, respectively) (p<0.01), persisting across all demographic and clinical characteristics (p<0.01). There was high agreement between indicators overall (??=?0.83 in 2008–2009; ??=?0.79 in 2009–2010, p<0.001), and C statistics revealed a very strong ability to predict retention according to the IOM indicator based on DHHS indicator status, even within characteristic strata. Conclusions Although the IOM indicator consistently reported higher retention in care compared with the DHHS indicator, there was strong agreement between IOM and DHHS retention indicators in a cohort demographically similar to persons living with HIV/AIDS in the U.S. Persons with poorer retention represent subgroups of interest for retention improvement programs nationally, particularly in light of the White House Executive Order on the HIV Care Continuum. PMID:25375099

  8. Green roof stormwater retention: effects of roof surface, slope, and media depth.

    PubMed

    VanWoert, Nicholaus D; Rowe, D Bradley; Andresen, Jeffrey A; Rugh, Clayton L; Fernandez, R Thomas; Xiao, Lan

    2005-01-01

    Urban areas generate considerably more stormwater runoff than natural areas of the same size due to a greater percentage of impervious surfaces that impede water infiltration. Roof surfaces account for a large portion of this impervious cover. Establishing vegetation on rooftops, known as green roofs, is one method of recovering lost green space that can aid in mitigating stormwater runoff. Two studies were performed using several roof platforms to quantify the effects of various treatments on stormwater retention. The first study used three different roof surface treatments to quantify differences in stormwater retention of a standard commercial roof with gravel ballast, an extensive green roof system without vegetation, and a typical extensive green roof with vegetation. Overall, mean percent rainfall retention ranged from 48.7% (gravel) to 82.8% (vegetated). The second study tested the influence of roof slope (2 and 6.5%) and green roof media depth (2.5, 4.0, and 6.0 cm) on stormwater retention. For all combined rain events, platforms at 2% slope with a 4-cm media depth had the greatest mean retention, 87%, although the difference from the other treatments was minimal. The combination of reduced slope and deeper media clearly reduced the total quantity of runoff. For both studies, vegetated green roof systems not only reduced the amount of stormwater runoff, they also extended its duration over a period of time beyond the actual rain event. PMID:15888889

  9. Nitrogen Saturation in Highly Retentive Watersheds?

    NASA Astrophysics Data System (ADS)

    Daley, M. L.; McDowell, W. H.

    2009-12-01

    Watershed managers are often concerned with minimizing the amount of N delivered to N-limited estuaries and coastal zones. A major concern is that watersheds might reach N saturation, in which N delivered to coastal zones increases due to declines in the efficiency of N retention despite constant or even reduced N inputs. We have quantified long-term changes in N inputs (atmospheric deposition, imported food and agricultural fertilizers), outputs (N concentration and export) and retention in the urbanizing Lamprey River watershed in coastal NH. Overall, the Lamprey watershed is 70% forested, receives about 13.5 kg N/ha/yr and has a high rate of annual N retention (85%). Atmospheric deposition (8.7 kg/ha/yr) is the largest N input to the watershed. Of the 2.2 kg N/ha/yr exported in the Lamprey River, dissolved organic N (DON) is the dominant form (50% of total) and it varies spatially throughout the watershed with wetland cover. Nitrate accounts for 30% of the N exported, shows a statistically significant increase from 1999 to 2009, and its spatial variability in both concentration and export is related to human population density. In sub-basins throughout the Lamprey, inorganic N retention is high (85-99%), but the efficiency of N retention declines sharply with increased human population density and associated anthropogenic N inputs. N assimilation in the vegetation, denitrification to the atmosphere and storage in the groundwater pool could all be important contributors to the current high rates of N retention. The temporal and spatial patterns that we have observed in nitrate concentration and export are driven by increases in N inputs and impervious surfaces over time, but the declining efficiency of N retention suggests that the watershed may also be reaching N saturation. The downstream receiving estuary, Great Bay, already suffers from low dissolved oxygen levels and eelgrass loss in part due to N loading from the Lamprey watershed. Targeting and reducing anthropogenic sources of N that are not retained in the watershed and maintaining high rates of N retention will be of utmost concern for coastal managers.

  10. Different approaches to quantitative structure-retention relationships in the prediction of oligonucleotide retention.

    PubMed

    Studzi?ska, Sylwia; Buszewski, Bogus?aw

    2015-06-01

    Quantitative structure-retention relationships studies were performed for cholesterol and alkylamide stationary phases, which were previously applied in the analysis of nucleotides and oligonucleotides. An octadecyl column was also tested. Twenty-four oligonucleotides of various sequences and length were chosen; next, their structural descriptors were determined with the use of quantum-mechanics method. The sequence features were related mainly to their surface area, hydrophobicity, and the nature of nucleobases. Moreover, for the first time models employing experimentally derived descriptors (the sum of retention factor for individual nucleotides) were developed in the quantitative structure-retention relationship studies of these compounds. The retention of oligonucleotides for alkylamide and cholesterol stationary phases may be effectively predicted with the use of quantitative structure-retention relationship models based only on molecularly modeled descriptors, as well as with models employing experimentally derived descriptors. Therefore, we recommend the first approach, since descriptors may be easily and quickly calculated. However, oligonucleotide retention prediction for octadecyl phases gives better results, when individual nucleotide retention factors are known and utilized for the creation of a mathematical model. PMID:25866200

  11. A Simple Calorimetric Experiment that Highlights Aspects of Global Heat Retention and Global Warming

    ERIC Educational Resources Information Center

    Burley, Joel D.; Johnston, Harold S.

    2007-01-01

    In this laboratory experiment, general chemistry students measure the heating curves for three different systems: (i) 500 g of room-temperature water heated by a small desk lamp, (ii) 500 g of an ice-water mixture warmed by conduction with room-temperature surroundings, and (iii) 500 g of an ice-water mixture heated by a small desk lamp and by…

  12. Trishear for curved faults

    NASA Astrophysics Data System (ADS)

    Brandenburg, J. P.

    2013-08-01

    Fault-propagation folds form an important trapping element in both onshore and offshore fold-thrust belts, and as such benefit from reliable interpretation. Building an accurate geologic interpretation of such structures requires palinspastic restorations, which are made more challenging by the interplay between folding and faulting. Trishear (Erslev, 1991; Allmendinger, 1998) is a useful tool to unravel this relationship kinematically, but is limited by a restriction to planar fault geometries, or at least planar fault segments. Here, new methods are presented for trishear along continuously curved reverse faults defining a flat-ramp transition. In these methods, rotation of the hanging wall above a curved fault is coupled to translation along a horizontal detachment. Including hanging wall rotation allows for investigation of structures with progressive backlimb rotation. Application of the new algorithms are shown for two fault-propagation fold structures: the Turner Valley Anticline in Southwestern Alberta, and the Alpha Structure in the Niger Delta.

  13. Connecting curves for dynamical systems

    E-print Network

    R. Gilmore; Jean-Marc Ginoux; Timothy Jones; C. Letellier; U. S. Freitas

    2010-03-08

    We introduce one dimensional sets to help describe and constrain the integral curves of an $n$ dimensional dynamical system. These curves provide more information about the system than the zero-dimensional sets (fixed points) do. In fact, these curves pass through the fixed points. Connecting curves are introduced using two different but equivalent definitions, one from dynamical systems theory, the other from differential geometry. We describe how to compute these curves and illustrate their properties by showing the connecting curves for a number of dynamical systems.

  14. Anatomical curve identification

    PubMed Central

    Bowman, Adrian W.; Katina, Stanislav; Smith, Joanna; Brown, Denise

    2015-01-01

    Methods for capturing images in three dimensions are now widely available, with stereo-photogrammetry and laser scanning being two common approaches. In anatomical studies, a number of landmarks are usually identified manually from each of these images and these form the basis of subsequent statistical analysis. However, landmarks express only a very small proportion of the information available from the images. Anatomically defined curves have the advantage of providing a much richer expression of shape. This is explored in the context of identifying the boundary of breasts from an image of the female torso and the boundary of the lips from a facial image. The curves of interest are characterised by ridges or valleys. Key issues in estimation are the ability to navigate across the anatomical surface in three-dimensions, the ability to recognise the relevant boundary and the need to assess the evidence for the presence of the surface feature of interest. The first issue is addressed by the use of principal curves, as an extension of principal components, the second by suitable assessment of curvature and the third by change-point detection. P-spline smoothing is used as an integral part of the methods but adaptations are made to the specific anatomical features of interest. After estimation of the boundary curves, the intermediate surfaces of the anatomical feature of interest can be characterised by surface interpolation. This allows shape variation to be explored using standard methods such as principal components. These tools are applied to a collection of images of women where one breast has been reconstructed after mastectomy and where interest lies in shape differences between the reconstructed and unreconstructed breasts. They are also applied to a collection of lip images where possible differences in shape between males and females are of interest. PMID:26041943

  15. Curved PN triangles

    Microsoft Academic Search

    Alex Vlachos; Jörg Peters; Chas Boyd; Jason L. Mitchell

    2001-01-01

    To improve the visual quality of existing triangle-based art in real- time entertainment, such as computer games, we propose replacing flat triangles with curved patches and higher-order normal variation. At the hardware level, based only on the three vertices and three vertex normals of a given flat triangle, we substitute the geometry of a three-sided cubic Bezier patch for the

  16. Diffusion in Curved Spacetimes

    E-print Network

    Matteo Smerlak

    2011-11-18

    Using simple kinematical arguments, we derive the Fokker-Planck equation for diffusion processes in curved spacetimes. In the case of Brownian motion, it coincides with Eckart's relativistic heat equation (albeit in a simpler form), and therefore provides a microscopic justification for his phenomenological heat-flux ansatz. Furthermore, we obtain the small-time asymptotic expansion of the mean square displacement of Brownian motion in static spacetimes. Beyond general relativity itself, this result has potential applications in analogue gravitational systems.

  17. Brody curves omitting hyperplanes

    E-print Network

    For the recent work on Brody curves we refer to [3, 10, 11, 12, 13]. A. general reference .... We are going to prove first that. u0(z) ? u?(z) + 4(n + 1)|z| sup. C. f . (5). 4 ... On the other hand, |f0(z1)| = |fk(z1)|?|fj(z1)| for all j ? {1,...,n}, so. f (z1) ?

  18. Quantization on Curves

    NASA Astrophysics Data System (ADS)

    Frønsdal, Christian; Kontsevich, Maxim

    2007-02-01

    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.

  19. Transforming Curves into Curves with the Same Shape.

    ERIC Educational Resources Information Center

    Levine, Michael V.

    Curves are considered to have the same shape when they are related by a similarity transformation of a certain kind. This paper extends earlier work on parallel curves to curves with the same shape. Some examples are given more or less explicitly. A generalization is used to show that the theory is ordinal and to show how the theory may be applied…

  20. space curves and surfaces 1 Plotting Space Curves

    E-print Network

    Verschelde, Jan

    the twisted cubic give the azimuth : -30 give the elevation : 10 Scientific Software (MCS 507 L-16) space=30, elev=30) plt.show() Scientific Software (MCS 507 L-16) space curves and surfaces 2 October 2013space curves and surfaces 1 Plotting Space Curves the twisted cubic with matplotlib four subplots

  1. COMPARTMENTAL MODEL OF NITRATE RETENTION IN STREAMS

    EPA Science Inventory

    A compartmental modeling approach is presented to route nitrate retention along a cascade of stream reach sections. A process transfer function is used for transient storage equations with first order reaction terms to represent nitrate uptake in the free stream, and denitrifica...

  2. Testing to Enhance Retention in Human Anatomy

    ERIC Educational Resources Information Center

    Logan, Jessica M.; Thompson, Andrew J.; Marshak, David W.

    2011-01-01

    Recent work in cognitive psychology has shown that repeatedly testing one's knowledge is a powerful learning aid and provides substantial benefits for retention of the material. To apply this in a human anatomy course for medical students, 39 fill-in-the-blank quizzes of about 50 questions each, one for each region of the body, and four about the…

  3. Factors affecting career retention among naval aviators

    Microsoft Academic Search

    Gerald D. Gibb; Daniel L. Dolgin

    1988-01-01

    Typically, retention studies have emphasized those who separate rather than those who choose a naval career. The present study examined factors that contribute to career satisfaction and aviators' decisions to remain in naval aviation. Primary reasons for remaining in naval aviation were the enjoyment of flying, coupled with the self-esteem associated with being a naval aviator. Career satisfaction for aviators

  4. Retention of First Year Community College Students

    ERIC Educational Resources Information Center

    Windham, Melissa H.

    2012-01-01

    Although close to half of all community college students leave before obtaining their stated goals, most retention studies are still being conducted at the four-year college and university level. There is still little research conducted at the community college level. In order to determine what student characteristics increase community college…

  5. Entering Fall One Year Retention 2006 Cohort

    E-print Network

    Years 77% Graduation Rates by Gender: Female 79% Male 74% Graduation Rates by Ethnicity: Native amer 75% Graduation Rates by Financial Aid Status: Pell Grants 73% Non-Pell Subsidized Loan 74% Other-Year Graduation Rate by Gender, by Ethnicity and by Financial Aid Status Retention and Graduation Rates Six

  6. Student Retention: Catalyst for Institutional Change.

    ERIC Educational Resources Information Center

    Meha, Arapata T.

    The conceptual model for institutional change presented in this report was developed within the context of the University of Hawaii's Native Hawaiian Vocational Education Project (NHVEP), a systemwide initiative for increasing minority student persistence at community colleges. Chapter 1 discusses the problem of low retention among Native Hawaiian…

  7. Copper Retention Kinetics in Acid Soils

    Microsoft Academic Search

    José Eugenio López-Periago; Manuel Arias-Estévez; Juan Carlos Nóvoa-Muñoz; David Fernández-Calviño; Benedicto Soto; Cristina Pèrez-Novo; Jesus Simal-Gándara

    2008-01-01

    Retention and release kinetics of Cu on four acid Typic haplumbrepts developed on two dif- ferent types of parent rock material (granite and amphibolite) were studied with a stirred-fl ow chamber (SFC) method. The granitic soils were lower in organic material and lower in Fe and Al oxides than the soils formed in amphibolite. The kinetic parameters were assessed in

  8. Measuring Learning Retention after Program Funding.

    ERIC Educational Resources Information Center

    Meckler, Terry Anne; Vogler, James D.

    The study investigated retention of gains in reading/language skills after one year by 378 eighth-grade students in 18 health studies classrooms. Six classrooms were assigned to each of three groups, two experimental and one control, taught by health science teachers who were: (1) trained in reading/language techniques; (2) not trained in…

  9. Sediment retention in rangeland riparian buffers.

    PubMed

    Hook, Paul B

    2003-01-01

    Controlling nonpoint-source sediment pollution is a common goal of riparian management, but there is little quantitative information about factors affecting performance of rangeland riparian buffers. This study evaluated the influence of vegetation characteristics, buffer width, slope, and stubble height on sediment retention in a Montana foothills meadow. Three vegetation types (sedge wetland, rush transition, bunchgrass upland) were compared using twenty-six 6- x 2-m plots spanning 2 to 20% slopes. Plots were clipped moderately (10-15 cm stubble) or severely (2-5 cm stubble). Sediment (silt + fine sand) was added to simulated overland runoff 6, 2, or 1 m above the bottom of each plot. Runoff was sampled at 15-s to > 5-min intervals until sediment concentrations approached background levels. Sediment retention was affected strongly by buffer width and moderately by vegetation type and slope, but was not affected by stubble height. Mean sediment retention ranged from 63 to > 99% for different combinations of buffer width and vegetation type, with 94 to 99% retention in 6-m-wide buffers regardless of vegetation type or slope. Results suggest that rangeland riparian buffers should be at least 6 m wide, with dense vegetation, to be effective and reliable. Narrower widths, steep slopes, and sparse vegetation increase risk of sediment delivery to streams. Vegetation characteristics such as biomass, cover, or density are more appropriate than stubble height for judging capacity to remove sediment from overland runoff, though stubble height may indirectly indicate livestock impacts that can affect buffer performance. PMID:12809315

  10. Return on Investment: Libraries and Student Retention

    ERIC Educational Resources Information Center

    Mezick, Elizabeth M.

    2007-01-01

    Using data on libraries collected by the Association of Research Libraries (ARL) and the Association of College and Research Libraries (ACRL), as well as fall-to-fall retention rates obtained from the Integrated Postsecondary Education Data System (IPEDS) of the National Center for Education Statistics (NCES), this study employs statistical…

  11. An Examination of Master's Student Retention & Completion

    ERIC Educational Resources Information Center

    Barry, Melissa; Mathies, Charles

    2011-01-01

    This study was conducted at a research-extensive public university in the southeastern United States. It examined the retention and completion of master's degree students across numerous disciplines. Results were derived from a series of descriptive statistics, T-tests, and a series of binary logistic regression models. The findings from binary…

  12. Relationship of Personality Traits to Student Retention

    ERIC Educational Resources Information Center

    Liang, John Paul

    2010-01-01

    Carl Jung's theory of psychological types has been the basis for the development of personality categorization, including tests such as Myers-Briggs Type Indicator (MBTI). This study analyzed the extent of the relationship between MBTI and Tinto (1993) retention factors that influence Oriental medicine students' choice of staying or dropping out…

  13. Involving Graduate Assistants in Student Retention Efforts.

    ERIC Educational Resources Information Center

    Boger, Ruth E.

    1994-01-01

    The efforts of five Bowling Green State University (Ohio) graduate students to design, develop, and implement a student retention training program using graduate assistants are described. Special techniques used to train participants and lessons learned in the process are noted. (MSE)

  14. RECORDS RETENTION POLICY Table of Contents

    E-print Network

    Shihadeh, Alan

    - Definitions Section 4 - General Section 5 - Program and Administrative Files Section 6 - Financial Accounting and Reporting Documents Section 7 - Human Resources Section 8 - Intellectual Property Appendix I - Inventory operating efficiency. 4. Minimizes the cost of records retention. 5. Identifies and preserves records

  15. Recruitment and Retention in Clinical Research

    E-print Network

    Carmichael, Owen

    Recruitment and Retention in Clinical Research June 24, 2011 Linda Ziegahn, Ph.D. Sergio Aguilar the community in clinical research? It takes an average of 17 years for only 14% of new scientific. #12;NIH Policy on Inclusion in Clinical Research Mandated by Congress, 1993 PL 10343 Women

  16. 49 CFR 219.903 - Retention of drug testing records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...2014-10-01 false Retention of drug testing records. 219.903 Section...Requirements § 219.903 Retention of drug testing records. (a) General requirement...Records related to employee training: (i) Materials...

  17. 5 CFR 575.306 - Authorizing a retention incentive.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...who, with minimal training, cost, or disruption...in addition to a retention incentive, such as special training and work scheduling...for authorizing a retention incentive for a group...required rating of record. (While a...

  18. 5 CFR 575.306 - Authorizing a retention incentive.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...who, with minimal training, cost, or disruption...in addition to a retention incentive, such as special training and work scheduling...for authorizing a retention incentive for a group...required rating of record. (While a...

  19. 49 CFR 219.901 - Retention of alcohol testing records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...2012-10-01 false Retention of alcohol testing records. 219.901 Section...Requirements § 219.901 Retention of alcohol testing records. (a) General requirement...Records related to employee training: (i) Materials...

  20. 49 CFR 219.901 - Retention of alcohol testing records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...2013-10-01 false Retention of alcohol testing records. 219.901 Section...Requirements § 219.901 Retention of alcohol testing records. (a) General requirement...Records related to employee training: (i) Materials...

  1. 49 CFR 219.903 - Retention of drug testing records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...2013-10-01 false Retention of drug testing records. 219.903 Section...Requirements § 219.903 Retention of drug testing records. (a) General requirement...Records related to employee training: (i) Materials...

  2. 49 CFR 219.903 - Retention of drug testing records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...2012-10-01 false Retention of drug testing records. 219.903 Section...Requirements § 219.903 Retention of drug testing records. (a) General requirement...Records related to employee training: (i) Materials...

  3. 5 CFR 575.306 - Authorizing a retention incentive.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...who, with minimal training, cost, and disruption...in addition to a retention incentive, such as special training and work scheduling...for authorizing a retention incentive for a group...required rating of record. (While a...

  4. 49 CFR 219.901 - Retention of alcohol testing records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...2014-10-01 false Retention of alcohol testing records. 219.901 Section...Requirements § 219.901 Retention of alcohol testing records. (a) General requirement...Records related to employee training: (i) Materials...

  5. 20 CFR 655.167 - Document retention requirements.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...2013-04-01 false Document retention requirements. 655.167 Section 655.167 Employees' Benefits EMPLOYMENT AND TRAINING...H-2A Workers) Labor Certification Determinations § 655.167 Document retention requirements. (a)...

  6. 20 CFR 655.1319 - Document retention requirements.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...2010-04-01 false Document retention requirements. 655.1319 Section 655.1319 Employees' Benefits EMPLOYMENT AND TRAINING...Employment in the United States (H-2A Workers) § 655.1319 Document retention requirements....

  7. 20 CFR 655.167 - Document retention requirements.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...2011-04-01 false Document retention requirements. 655.167 Section 655.167 Employees' Benefits EMPLOYMENT AND TRAINING...H-2A Workers) Labor Certification Determinations § 655.167 Document retention requirements. (a)...

  8. 20 CFR 655.167 - Document retention requirements.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...2010-04-01 false Document retention requirements. 655.167 Section 655.167 Employees' Benefits EMPLOYMENT AND TRAINING...H-2A Workers) Labor Certification Determinations § 655.167 Document retention requirements. (a)...

  9. 20 CFR 655.1319 - Document retention requirements.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...2014-04-01 false Document retention requirements. 655.1319 Section 655.1319 Employees' Benefits EMPLOYMENT AND TRAINING...Employment in the United States (H-2A Workers) § 655.1319 Document retention requirements....

  10. 20 CFR 655.1319 - Document retention requirements.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...2011-04-01 false Document retention requirements. 655.1319 Section 655.1319 Employees' Benefits EMPLOYMENT AND TRAINING...Employment in the United States (H-2A Workers) § 655.1319 Document retention requirements....

  11. 20 CFR 655.1319 - Document retention requirements.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...2013-04-01 false Document retention requirements. 655.1319 Section 655.1319 Employees' Benefits EMPLOYMENT AND TRAINING...Employment in the United States (H-2A Workers) § 655.1319 Document retention requirements....

  12. 20 CFR 655.167 - Document retention requirements.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...2012-04-01 false Document retention requirements. 655.167 Section 655.167 Employees' Benefits EMPLOYMENT AND TRAINING...H-2A Workers) Labor Certification Determinations § 655.167 Document retention requirements. (a)...

  13. 20 CFR 655.167 - Document retention requirements.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...2014-04-01 false Document retention requirements. 655.167 Section 655.167 Employees' Benefits EMPLOYMENT AND TRAINING...H-2A Workers) Labor Certification Determinations § 655.167 Document retention requirements. (a)...

  14. 20 CFR 655.1319 - Document retention requirements.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...2012-04-01 false Document retention requirements. 655.1319 Section 655.1319 Employees' Benefits EMPLOYMENT AND TRAINING...Employment in the United States (H-2A Workers) § 655.1319 Document retention requirements....

  15. 49 CFR 655.71 - Retention of records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... false Retention of records. 655.71 Section 655.71 Transportation Other Regulations... Administrative Requirements § 655.71 Retention of records. ...provide an adequate urine or breathe sample. (2) Records related to...

  16. 49 CFR 655.71 - Retention of records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... false Retention of records. 655.71 Section 655.71 Transportation Other Regulations... Administrative Requirements § 655.71 Retention of records. ...provide an adequate urine or breathe sample. (2) Records related to...

  17. 49 CFR 655.71 - Retention of records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... false Retention of records. 655.71 Section 655.71 Transportation Other Regulations... Administrative Requirements § 655.71 Retention of records. ...provide an adequate urine or breathe sample. (2) Records related to...

  18. 49 CFR 655.71 - Retention of records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... false Retention of records. 655.71 Section 655.71 Transportation Other Regulations... Administrative Requirements § 655.71 Retention of records. ...provide an adequate urine or breathe sample. (2) Records related to...

  19. 49 CFR 655.71 - Retention of records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... false Retention of records. 655.71 Section 655.71 Transportation Other Regulations... Administrative Requirements § 655.71 Retention of records. ...provide an adequate urine or breathe sample. (2) Records related to...

  20. ORIGINAL PAPER Digesta retention time in roe deer Capreolus

    E-print Network

    Paris-Sud XI, Université de

    ORIGINAL PAPER Digesta retention time in roe deer Capreolus capreolus, as measured with cerium assessing the passage kinetics of different-sized particles, we measured the mean retention time in roe deer

  1. 49 CFR 219.901 - Retention of alcohol testing records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...2011-10-01 false Retention of alcohol testing records. 219.901 Section...DEPARTMENT OF TRANSPORTATION CONTROL OF ALCOHOL AND DRUG USE Recordkeeping Requirements § 219.901 Retention of alcohol testing records. (a) General...

  2. 49 CFR 219.901 - Retention of alcohol testing records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...2010-10-01 false Retention of alcohol testing records. 219.901 Section...DEPARTMENT OF TRANSPORTATION CONTROL OF ALCOHOL AND DRUG USE Recordkeeping Requirements § 219.901 Retention of alcohol testing records. (a) General...

  3. 39 CFR 262.6 - Retention and disposal.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Retention and disposal. 262.6 Section 262.6 Postal Service UNITED STATES...INFORMATION MANAGEMENT DEFINITIONS § 262.6 Retention and disposal. (a... A directive describing records series that are maintained by...

  4. 27 CFR 40.185 - Retention of records.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...2010-04-01 false Retention of records. 40.185 Section 40.185 Alcohol, Tobacco Products and Firearms ALCOHOL...by Manufacturers of Tobacco Products Records § 40.185 Retention of records. All records...

  5. 47 CFR 42.6 - Retention of telephone toll records.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...2013-10-01 false Retention of telephone toll records. 42.6 Section 42...Instructions § 42.6 Retention of telephone toll records. Each carrier that offers or bills toll telephone service shall retain for a...

  6. 47 CFR 42.6 - Retention of telephone toll records.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...2010-10-01 false Retention of telephone toll records. 42.6 Section 42...Instructions § 42.6 Retention of telephone toll records. Each carrier that offers or bills toll telephone service shall retain for a...

  7. 47 CFR 42.6 - Retention of telephone toll records.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...2014-10-01 false Retention of telephone toll records. 42.6 Section 42...Instructions § 42.6 Retention of telephone toll records. Each carrier that offers or bills toll telephone service shall retain for a...

  8. 47 CFR 42.6 - Retention of telephone toll records.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...2011-10-01 false Retention of telephone toll records. 42.6 Section 42...Instructions § 42.6 Retention of telephone toll records. Each carrier that offers or bills toll telephone service shall retain for a...

  9. 47 CFR 42.6 - Retention of telephone toll records.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...2012-10-01 false Retention of telephone toll records. 42.6 Section 42...Instructions § 42.6 Retention of telephone toll records. Each carrier that offers or bills toll telephone service shall retain for a...

  10. 24 CFR 792.202 - PHA retention of proceeds.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 4 2011-04-01 2011-04-01 false PHA retention of proceeds. 792.202 Section... Recovery of Section 8 Funds § 792.202 PHA retention of proceeds. (a) Where the PHA is the principal party initiating or...

  11. 24 CFR 792.202 - PHA retention of proceeds.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 4 2013-04-01 2013-04-01 false PHA retention of proceeds. 792.202 Section... Recovery of Section 8 Funds § 792.202 PHA retention of proceeds. (a) Where the PHA is the principal party initiating or...

  12. 24 CFR 792.202 - PHA retention of proceeds.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 4 2010-04-01 2010-04-01 false PHA retention of proceeds. 792.202 Section... Recovery of Section 8 Funds § 792.202 PHA retention of proceeds. (a) Where the PHA is the principal party initiating or...

  13. 24 CFR 792.202 - PHA retention of proceeds.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 4 2014-04-01 2014-04-01 false PHA retention of proceeds. 792.202 Section... Recovery of Section 8 Funds § 792.202 PHA retention of proceeds. (a) Where the PHA is the principal party initiating or...

  14. 24 CFR 792.202 - PHA retention of proceeds.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 4 2012-04-01 2012-04-01 false PHA retention of proceeds. 792.202 Section... Recovery of Section 8 Funds § 792.202 PHA retention of proceeds. (a) Where the PHA is the principal party initiating or...

  15. On planar rational cuspidal curves

    E-print Network

    Liu, Tiankai

    2014-01-01

    This thesis studies rational curves in the complex projective plane that are homeomorphic to their normalizations. We derive some combinatorial constraints on such curves from a result of Borodzik-Livingston in Heegaard-Floer ...

  16. West Virginia University -Main Campus Student Retention and Graduation Rates

    E-print Network

    Mohaghegh, Shahab

    West Virginia University - Main Campus Student Retention and Graduation Rates First-Time, Full ---------------------------------------------------------------------Continuation Rates and Cumulative Graduation Rates

  17. Understanding recruitment and retention in neurological research.

    PubMed

    Newberry, Alyssa; Sherwood, Paula; Hricik, Allison; Bradley, Sarah; Kuo, Jean; Crago, Elizabeth; Hoffman, Leslie A; Given, Barbara A

    2010-02-01

    Cognitive deficits in participants and the abrupt and traumatic way in which many neurological conditions present are two examples of the unique challenges in recruiting and retaining participants with neurological injury for research studies. The purpose of this investigation was to identify obstacles to recruitment and retention in three ongoing research studies. These studies involve persons with neurological disorders across the continuum of care, from those newly diagnosed and with emergent presentation to those with more established chronic neurological conditions. For this analysis, we evaluated the effectiveness of the strategies employed to improve participation rates. The first study was a project funded by the National Institutes of Health designed to identify biomarkers of vasospasm in persons (n = 496) with aneurysmal subarachnoid hemorrhage who presented to the neurovascular intensive care unit (National Institute of Nursing Research, R01 NR004339). The purpose of the second study was to examine biobehavioral interactions in family caregivers (n = 59) of persons with a primary malignant brain tumor recruited in the community setting. The third project involved recruiting persons (n = 1,019) within an outpatient neurosurgical center to participate in a research registry. To determine differential effectiveness of strategies, consent and attrition rates were calculated at serial points over time in three studies, and recruitment and retention strategies were compared. Sentinel time points in participants' disease trajectories played a key role in determining whether those who were approached to participate gave consent and were retained, particularly in the studies involving persons with aneurysmal subarachnoid hemorrhage (consent = 85%; retention = 89%) and persons with primary malignant brain tumors and their caregivers (consent = 68%; retention = 83%). In addition, several specific recruiter and interviewer training techniques were associated with higher recruitment and retention. Targeted strategies to improve participation rates are vital for neuroscience nurses involved in any aspect of clinical research, including those who conduct studies, assist with data collection, and recruit potential participants. PMID:20187349

  18. Titration Curves: Fact and Fiction.

    ERIC Educational Resources Information Center

    Chamberlain, John

    1997-01-01

    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…

  19. Dragon curves revisited S. Tabachnikov

    E-print Network

    Tabachnikov, Sergei

    Dragon curves revisited S. Tabachnikov It has happened several times in recent history mathematical object of comparable beauty, the Dragon curves, whose theory was created by Chandler Davis with previously unpublished addendum).1 Mathematical Intelligencer wrote about Dragon curves more than 30 years

  20. Guide to Elliptic Curve Cryptography

    E-print Network

    Babinkostova, Liljana

    Guide to Elliptic Curve Cryptography Darrel Hankerson Alfred Menezes Scott Vanstone Springer #12;Guide to Elliptic Curve Cryptography Springer New York Berlin Heidelberg Hong Kong London Milan Paris Tokyo #12;#12;Darrel Hankerson Alfred Menezes Scott Vanstone Guide to Elliptic Curve Cryptography

  1. Shared project studies, revises hospital record retention policies.

    PubMed

    Domanico, L; Leverette, T J

    1978-05-16

    Through their shared service organization, six hospitals conducted a study that showed that they had similar practical needs and legal requirements for medical record retention but widely varying retention policies. Written policies that were developed for and jointly adopted by the hospitals have ensured consistent, cost-effective retention practices. PMID:640605

  2. Oregon State University Retention and Graduation Rate Report

    E-print Network

    Escher, Christine

    Oregon State University Retention and Graduation Rate Report Cohort Classes: Fall Term 1994 ­ Fall-737-9600 March 31, 2011 #12;2 Oregon State University Retention and Graduation Rate Report Cohort Classes: Fall Term 1994 ­ Fall Term 2009 This retention and graduation rate document contains the following sections

  3. Education for Sustainable Development and Retention: Unravelling a Research Agenda

    ERIC Educational Resources Information Center

    Lotz-Sisitka, Heila

    2010-01-01

    This paper considers the question of what education for sustainable development (ESD) research might signify when linked to the concept of "retention", and how this relation (ESD and retention) might be researched. It considers two different perspectives on retention, as revealed through educational research trajectories, drawing on existing…

  4. Modeling the Keeling Curve

    NSDL National Science Digital Library

    In this problem set, learners will refer to the tabulated data used to create the Keeling Curve of atmospheric carbon dioxide to create a mathematical function that accounts for both periodic and long-term changes. They will use this function to answer a series of questions, including predictions of atmospheric concentration in the future. A link to the data, which is in an Excel file, as well as the answer key are provided. This is part of Earth Math: A Brief Mathematical Guide to Earth Science and Climate Change.

  5. Curve walking in crayfish

    PubMed

    Cruse; Saavedra

    1996-01-01

    Curve walking of crayfish Astacus leptodactylus was investigated by exploiting their optomotor response. The animal walked while spatially fixed on a motor-driven treadmill and turning behaviour was induced by an optical stimulus, a pattern consisting of vertical stripes moving in a horizontal direction. In this open-loop situation, the crayfish maintains the same step frequency for the legs on both sides of the body for low and intermediate turning speeds, but increases the step amplitude of the outer legs 2, 3 and 4 by shifting the posterior extreme position (PEP) of these legs in a posterior direction and reduces the step amplitude of inner leg 5 by shifting the PEP of this leg in an anterior direction. Furthermore, the main movement direction of the legs can change relative to the body. This was observed for outer leg 5 and also, at higher turning speeds, for outer leg 2. As coordinating influences between contra- and ipsilateral legs were found directly to influence only the anterior extreme position of the legs, these results indicate that the mechanisms controlling curve walking may be different from those controlling normal leg coordination. PMID:9319377

  6. Strategies to improve retention in randomised trials

    PubMed Central

    Brueton, Valerie C; Tierney, Jayne; Stenning, Sally; Harding, Seeromanie; Meredith, Sarah; Nazareth, Irwin; Rait, Greta

    2013-01-01

    Background Loss to follow-up from randomised trials can introduce bias and reduce study power, affecting the generalisability, validity and reliability of results. Many strategies are used to reduce loss to follow-up and improve retention but few have been formally evaluated. Objectives To quantify the effect of strategies to improve retention on the proportion of participants retained in randomised trials and to investigate if the effect varied by trial strategy and trial setting. Search methods We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, PreMEDLINE, EMBASE, PsycINFO, DARE, CINAHL, Campbell Collaboration's Social, Psychological, Educational and Criminological Trials Register, and ERIC. We handsearched conference proceedings and publication reference lists for eligible retention trials. We also surveyed all UK Clinical Trials Units to identify further studies. Selection criteria We included eligible retention trials of randomised or quasi-randomised evaluations of strategies to increase retention that were embedded in 'host' randomised trials from all disease areas and healthcare settings. We excluded studies aiming to increase treatment compliance. Data collection and analysis We contacted authors to supplement or confirm data that we had extracted. For retention trials, we recorded data on the method of randomisation, type of strategy evaluated, comparator, primary outcome, planned sample size, numbers randomised and numbers retained. We used risk ratios (RR) to evaluate the effectiveness of the addition of strategies to improve retention. We assessed heterogeneity between trials using the Chi2 and I2 statistics. For main trials that hosted retention trials, we extracted data on disease area, intervention, population, healthcare setting, sequence generation and allocation concealment. Main results We identified 38 eligible retention trials. Included trials evaluated six broad types of strategies to improve retention. These were incentives, communication strategies, new questionnaire format, participant case management, behavioural and methodological interventions. For 34 of the included trials, retention was response to postal and electronic questionnaires with or without medical test kits. For four trials, retention was the number of participants remaining in the trial. Included trials were conducted across a spectrum of disease areas, countries, healthcare and community settings. Strategies that improved trial retention were addition of monetary incentives compared with no incentive for return of trial-related postal questionnaires (RR 1.18; 95% CI 1.09 to 1.28, P value < 0.0001), addition of an offer of monetary incentive compared with no offer for return of electronic questionnaires (RR 1.25; 95% CI 1.14 to 1.38, P value < 0.00001) and an offer of a GBP20 voucher compared with GBP10 for return of postal questionnaires and biomedical test kits (RR 1.12; 95% CI 1.04 to 1.22, P value < 0.005). The evidence that shorter questionnaires are better than longer questionnaires was unclear (RR 1.04; 95% CI 1.00 to 1.08, P value = 0.07) and the evidence for questionnaires relevant to the disease/condition was also unclear (RR 1.07; 95% CI 1.01 to 1.14). Although each was based on the results of a single trial, recorded delivery of questionnaires seemed to be more effective than telephone reminders (RR 2.08; 95% CI 1.11 to 3.87, P value = 0.02) and a 'package' of postal communication strategies with reminder letters appeared to be better than standard procedures (RR 1.43; 95% CI 1.22 to 1.67, P value < 0.0001). An open trial design also appeared more effective than a blind trial design for return of questionnaires in one fracture prevention trial (RR 1.37; 95% CI 1.16 to 1.63, P value = 0.0003). There was no good evidence that the addition of a non-monetary incentive, an offer of a non-monetary incentive, 'enhanced' letters, letters delivered by priority post, additional reminders, or questionnaire question order either increased or decreased trial questionnaire response/reten

  7. An unsteady state retention model for fluid desorption from sorbents.

    PubMed

    Bazargan, Alireza; Sadeghi, Hamed; Garcia-Mayoral, Ricardo; McKay, Gordon

    2015-07-15

    New studies regarding the sorption of fluids by solids are published every day. In performance testing, after the sorbent has reached saturation, it is usually removed from the sorbate bath and allowed to drain. The loss of liquid from the sorbents with time is of prime importance in the real-world application of sorbents, such as in oil spill response. However, there is currently no equation used for modeling the unsteady state loss of the liquid from the dripping sorbent. Here, an analytical model has been provided for modeling the dynamic loss of liquid from the sorbent in dripping experiments. Data from more than 60 sorbent-sorbate systems has been used to validate the model. The proposed model shows excellent agreement with experimental results and is expressed as: U(t)=U(L)e(-Kt)+U(e) In which U(t) (kg/kg) is the uptake capacity of the sorbent at any time t (s) during dripping, U(L) (kg/kg) is the uptake capacity lost due to dripping, and U(e) (kg/kg) is the equilibrium uptake capacity reached after prolonged dripping. K (1/s) is defined as the Kamaan coefficient and controls the curvature of the retention profile. Kamaan ([symbol: see text] IPA phonetics: kæm?n) is an Iranian (Farsi/Persian) word meaning "arc" or "curve" and hence the letter K has been designated. PMID:25814100

  8. From vigilance to violence: mate retention tactics in married couples.

    PubMed

    Buss, D M; Shackelford, T K

    1997-02-01

    Although much research has explored the adaptive problems of mate selection and mate attraction, little research has investigated the adaptive problem of mate retention. We tested several evolutionary psychological hypotheses about the determinants of mate retention in 214 married people. We assessed the usage of 19 mate retention tactics ranging from vigilance to violence. Key hypothesized findings include the following: Men's, but not women's, mate retention positively covaried with partner's youth and physical attractiveness. Women's, but not men's, mate retention positively covaried with partner's income and status striving. Men's mate retention positively covaried with perceived probability of partner's infidelity. Men, more than women, reported using resource display, submission and debasement, and intrasexual threats to retain their mates. Women, more than men, reported using appearance enhancement and verbal signals of possession. Discussion includes an evolutionary psychological analysis of mate retention in married couples. PMID:9107005

  9. Place Learning in the Morris Water Task: Making the Memory Stick

    ERIC Educational Resources Information Center

    Bolding, Kevin; Rudy, Jerry W.

    2006-01-01

    Although the Morris water task has been used in hundreds of studies of place learning, there have been no systematic studies of retention of the place memory. We report that retention, as measured by selective search behavior on a probe trial, is excellent when the retention interval is short (5-10 min). However, performance rapidly deteriorates,…

  10. Improving student retention in computer engineering technology

    NASA Astrophysics Data System (ADS)

    Pierozinski, Russell Ivan

    The purpose of this research project was to improve student retention in the Computer Engineering Technology program at the Northern Alberta Institute of Technology by reducing the number of dropouts and increasing the graduation rate. This action research project utilized a mixed methods approach of a survey and face-to-face interviews. The participants were male and female, with a large majority ranging from 18 to 21 years of age. The research found that participants recognized their skills and capability, but their capacity to remain in the program was dependent on understanding and meeting the demanding pace and rigour of the program. The participants recognized that curriculum delivery along with instructor-student interaction had an impact on student retention. To be successful in the program, students required support in four domains: academic, learning management, career, and social.

  11. Science Teacher Retention: Mentoring and Renewal

    NSDL National Science Digital Library

    2003-01-01

    "Some forty percent of all new science teachers leave the profession within five years, and too many science teachers are wedded to their textbooks and the routines they acquired during their collegiate years." What can be done to retain new science teachers and reinvigorate more experienced science teachers? Allow Science Teacher Retention: Mentoring and Renewal to "mentor" you as you reach toward this lofty but attainable goal. For this book, Jack Rhoton and Patricia Bowers assembled some of the country's most noted science educators and asked them to offer ideas to resolve the problems of science teacher retention and renewal. Their suggestions are designed to keep the brightest and most motivated new teachers in the profession and help all science teachers to continue to learn and to treat their own profession like science itself--that is, by basing it on questions, suggesting answers, and using their interests and abilities to test the validity of these answers.

  12. Recruitment, retention, and blinding in clinical trials.

    PubMed

    Page, Stephen J; Persch, Andrew C

    2013-01-01

    The recruitment and retention of participants and the blinding of participants, health care providers, and data collectors present challenges for clinical trial investigators. This article reviews challenges and alternative strategies associated with these three important clinical trial activities. Common recruiting pitfalls, including low sample size, unfriendly study designs, suboptimal testing locations, and untimely recruitment are discussed together with strategies for overcoming these barriers. The use of active controls, technology-supported visit reminders, and up-front scheduling is recommended to prevent attrition and maximize retention of participants. Blinding is conceptualized as the process of concealing research design elements from key players in the research process. Strategies for blinding participants, health care providers, and data collectors are suggested. PMID:23433269

  13. Birational maps that send biquadratic curves to biquadratic curves

    NASA Astrophysics Data System (ADS)

    Roberts, John A. G.; Jogia, Danesh

    2015-02-01

    Recently, many papers have begun to consider so-called non-Quispel?Roberts?Thompson (QRT) birational maps of the plane. Compared to the QRT family of maps which preserve each biquadratic curve in a fibration of the plane, non-QRT maps send a biquadratic curve to another biquadratic curve belonging to the same fibration or to a biquadratic curve from a different fibration of the plane. In this communication, we give the general form of a birational map derived from a difference equation that sends a biquadratic curve to another. The necessary and sufficient condition for such a map to exist is that the discriminants of the two biquadratic curves are the same (and hence so are the j-invariants). The result allows existing examples in the literature to be better understood and allows some statements to be made concerning their generality.

  14. Tracer injection techniques in flowing surface water

    NASA Astrophysics Data System (ADS)

    Wörman, A.

    2009-04-01

    Residence time distributions for flowing water and reactive matter are commonly used integrated properties of the transport process for determining technical issues of water resource management and in eco-hydrological science. Two general issues for tracer techniques are that the concentration-vs-time relation following a tracer injection (the breakthrough curve) gives unique transport information in different parts of the curve and separation of hydromechanical and reactive mechanisms often require simultaneous tracer injections. This presentation discusses evaluation methods for simultaneous tracer injections based on examples of tracer experiments in small rivers, streams and wetlands. Tritiated water is used as a practically inert substance to reflect the actual hydrodynamics, but other involved tracers are Cr(III)-51, P-32 and N-15. Hydromechanical, in-stream dispersion is reflected as a symmetrical spreading of the spatial concentration distribution. This requires that the transport distance over water depth is larger than about five times the flow Peclet number. Transversal retention of both inert and reactive solutes is reflected in terms of the tail of the breakthrough curve. Especially, reactive solutes can have a substantial magnification of the tailing behaviour depending on reaction rates or partitioning coefficients. To accurately discriminate between the effects of reactions and hydromechanical mixing its is relevant to use simultaneous injections of inert and reactive tracers with a sequential or integrated evaluation procedure. As an example, the slope of the P-32 tailing is consistently smaller than that of a simultaneous tritium injection in Ekeby wetland, Eskilstuna. The same applies to N-15 injected in the same experiment, but nitrogen is affected also by a systematic loss due to denitrification. Uptake in stream-bed sediments can be caused by a pumping effect arising when a variable pressure field is created on the stream bottom due to bed irregularities. The so-called pumping model provided good estimates of the storage in the hyporheic zone under different stream discharges and stream flow conditions along streams. Evaluations Hobøl River, Norway, and Säva Brook, Sweden, at two occasions in both stream indicate that the relative residence time in the hyporheic zone is linearly proportional to the squared Froude Number. The residence time is scaled with water depth and hydraulic conductivity of the bed. The effect of such transient storage in e.g. the hyporheic zone gives rise to a tailing, but the breakthrough curve become increasingly symmetrical with Damköhler number. Such a symmetrical breakthrough can be erroneously taken as an effect of in-stream dispersion, even though this similarity is merely due to the physical analogy of various advection velocities over the transport cross-section, differential advection.

  15. Exchange of phosphorus across the sediment-water interface

    Microsoft Academic Search

    Bengt Boström; Jens M. Andersen; Siegfried Fleischer; Mats Jansson

    1988-01-01

    In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact

  16. Postmenopausal Estrogen Replacement and Tooth Retention

    Microsoft Academic Search

    1997-01-01

    PURPOSE To determine if estrogen replacement therapy (ERT) is associated with improved tooth retention and lower risk of edentulism (no natural teeth remaining) in a cohort of elderly women.PATIENTS AND METHODS Subjects were 488 women, aged 72 to 95, who participated in the 23rd examination cycle (1994 to 1995) of the Framingham Heart Study, a population-based study begun in 1948.

  17. 300 Area Building Retention Evaluation Mitigation Plan

    SciTech Connect

    D. J. McBride

    2007-07-03

    Evaluate the long-term retention of several facilities associated with the PNNL Capability Replacement Laboratory and other Hanfor mission needs. WCH prepared a mitigation plan for three scenarios with different release dates for specific buildings. The evaluations present a proposed plan for providing utility services to retained facilities in support of a long-term (+20 year) lifespan in addition to temporary services to buildings with specified delayed release dates.

  18. Generating Resources Supply Curves.

    SciTech Connect

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

    1985-07-01

    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.

  19. Catenary curve revisited

    SciTech Connect

    Huang, T. [Univ. of Texas, Arlington, TX (United States); Chucheepsakul, S. [King Mongkut`s Inst. of Tech. Thonburi, Bangkok (Thailand)

    1993-12-31

    One common approach to derive the catenary curve of a suspended cable is to minimize the total potential energy of the system. This is accomplished via the calculus of variation and it is an isoperimetric problem. This paper identifies that the conventional way of formulation follows the Eulerian viewpoint. An alternative way of formulation is given, which follows the Lagrangian viewpoint. An important distinction between these two formulations is the different meaning of the Lagrange multiplier in the modified energy functional. In the formulation based on the Eulerian viewpoint it is a constant which depends on the datum from which the gravitational potential is evaluated; while in that based on the Lagrangian viewpoint this multiplier is a variable which represents the cable tension.

  20. Gelfond-Bezier Curves

    E-print Network

    Ait-Haddou, Rachid; Nomura, Taishin

    2011-01-01

    We show that the generalized Bernstein bases in Muntz spaces defined by Hirschman and Widder [7] and extended by Gelfond [6] can be obtained as limits of the Chebyshev-Bernstein bases in Muntz spaces with respect to an interval [a,1] as the real number, a, converges to zero. Such a realization allows for concepts of curve design such as de Casteljau algorithm, blossom, dimension elevation to be translated from the general theory of Chebyshev blossom in Muntz spaces to these generalized Bernstein bases that we termed here as Gelfond-Bernstein bases. The advantage of working with Gelfond-Bernstein bases lies in the simplicity of the obtained concepts and algorithms as compared to their Chebyshev-Bernstein bases counterparts.