bluuebunny/crossref_metadata_2025 huggingface dataset:
A composite analytical model for analysis of pumping tests affected by well bore storage and finite thickness skin
Authors: Novakowski Kent S.
Published: February 2008

A composite analytical model is developed for analyzing the results of pumping tests where the influence of well bore storage and a skin region of finite thickness are present at the pumping well. The solution of the boundary value problem for dimensionless drawdown in the pumping well, skin region, and formation is derived using the Laplace transform method. The solution is verified by comparison to solutions of pumping test problems with well bore storage only, with a composite formation only, and with well bore storage and infinitesimally thin skin. Type curves obtained by numerically inverting the solution for drawdown in the formation are used to illustrate the influence of well bore storage, the effect of skin region characteristics, and the effect of radial distance. These show that the influence of a finite thickness skin of reduced permeability is clearly identifiable over a fairly broad range of radial distance from the pumping well when well bore storage effects are minimized. Conversely, the effects of finite skin of enhanced permeability are more easily identified where the influence of well bore storage is greater. In both cases the type curves are uniquely defined provided that the skin region is of nonzero thickness. Type curves obtained for the solution for drawdown in the skin region are used to illustrate the effect of outer or far‐field boundary conditions. These type curves show that early time data not influenced by well bore storage effects are required to detect the presence of outer boundaries of reduced permeability. Drawdown data at late time, although less influenced by well bore storage effects, are subject to nonuniqueness with regard to the characteristics of the skin and formation regions. Outer boundaries of enhanced permeability are identified only at early time and are almost entirely masked by well bore storage at later time.
Numerical analysis of solute transport during transient irrigation: 1. The effect of hysteresis and profile heterogeneity
Authors: Russo David , Jury William A. , Butters Greg L.
Published: February 2008

Most of the existing data on vadose zone field scale solute transport have been obtained from experiments conducted under transient, nonmonotonic water flow. However, the majority of the theoretical analyses of these experiments have used models which assume monotonic steady state water flow and uniform water content for the entire profile. In this study, transport of nonreactive solutes under nonmonotonic, transient water flow is analyzed numerically. The effect of hysteresis on solute transport is evaluated by making the soil hydraulic properties hysteretic using the procedure of Kool and Parker (1987). The effect of profile heterogeneity on solute transport is analyzed by assuming that the medium is scale heterogeneous in a vertical direction, with a random scale factor. Results of the simulations show that under transient water flow, analysis of solute transport data with a steady state water flow model may considerably overestimate the effective vertical pore water velocity. Under nonmonotonic water flow, when the hysteretic characteristics of the soil are important, transient flow models which neglect hysteresis can also seriously overestimate the solute velocity. In addition, failure to account for profile heterogeneity will also overestimate the solute velocity, because both hysteresis and profile heterogeneity change the water content profile and concurrently retard solute transport relative to the movement predicted if the soil water system is considered as homogeneous and nonhysteretic. Analyses of the computed breakthrough curves suggest that direct stimates of the amount of water drained below a given depth may improve the goodness of fit of the solution of the convection dispersion equation with constant effective parameters to the breakthrough curves obtained under transient conditions. The fitted parameters, however, are depth dependent and the resulting effective solute velocity is smaller than the steady state pore water velocity.
Interpretation of oscillatory water levels in observation wells during aquifer tests in fractured rock
Authors: Shapiro Allen M.
Published: February 2008

Oscillatory water levels in observation wells have commonly been recorded at the beginning of aquifer tests in highly transmissive fractured formations. In this paper, oscillatory water levels are predicted by the equations coupling the fluid movement in the observation well and the fluid movement in the surrounding formation. The equivalent‐porous medium and dual‐porosity models of fractured rock are two models considered in this analysis; however, other conceptual models of fractured media can also be coupled with the model presented here for fluid movement in the observation well. Type curves for the response of water levels in observation wells due to pumping in another well are generated by numerical inversion of the Laplace transform solution to the governing equations. Overdamped conditions, where inertial effects are insignificant, and underdamped conditions, where oscillations arise, are predicted by the solution to the governing equations. By matching water level measurements with the appropriate type curve, a conceptual model of the formation can be identified, and aquifer properties can be estimated. This analysis is applied in the interpretation of an aquifer test conducted in a fractured dolomite in northeastern Illinois. If the early time oscillations are ignored, the measured water levels can be explained by an equivalent‐porous medium model. By analyzing the early time oscillations, however, the formation is shown to respond as a dual‐porosity medium with a storativity of the fracture porosity that is an order of magnitude smaller than the storativity estimated from the equivalent‐porous medium model.
One‐dimensional steady state infiltration in heterogeneous soils
Authors: Yeh T.‐C. Jim
Published: February 2008

The effects of heterogeneity on one‐dimensional, steady state infiltration are studied using numerical simulations where the soil hydrologic properties are assumed to be spatial stochastic processes. Analytical solutions to one‐dimensional, steady state infiltration in heterogeneous soils are developed and applied to the stochastic random fields. The effects of spatial variability of parameters of an exponential unsaturated hydraulic conductivity model on the soil‐water pressure profiles are examined. The amount of variation in pressure heads is found to vary with infiltration rates and mean pressure heads, while the cross‐correlation between parameters is shown to have important influences on the value of the head variance. An inverse procedure is developed to determine the effective hydraulic conductivity parameters. The effective parameter is found to vary with mean pressures. Effective hydraulic conductivities and pressure head variances estimated from the numerical simulations were compared with those obtained from a spectral method by Yeh et al. (1985a, b, c). A unit mean gradient approach was used to estimate the effective unsaturated hydraulic conductivity, and the result shows that this approach is adequate for heterogeneous soils.
Solute transport in a stream‐aquifer system: 1. Derivation of a dynamic model
Authors: Dietrich C. R. , Jakeman A. J. , Thomas G. A.
Published: February 2008

A dynamic model is derived for the transport of a conservative solute along a stream connected to an aquifer contaminated by the solute. It relates downstream concentration to upstream concentration, stream discharge, and piezometric levels in the aquifer. Submodels for solute travel time in the stream and aquifer inflow into the stream are presented. In paper 2, (Jakeman et al., this issue), the model is applied to a reach of the River Murray in Australia and the model structure and probability distribution of parameter values are determined using linear system identification methods.
Solute Transport in a Stream‐aquifer system: 2. Application of model identification to the River Murray
Authors: Jakeman A. J. , Dietrich C. R. , Thomas G. A.
Published: February 2008

In paper 1 (Dietrich et al., this issue) a model was derived for the transport of a conservative solute along a stream connected to an aquifer. In this paper the model is applied to a 207‐km reach of the River Murray in Australia. The appropriate model structure and its parameter values are determined using principles of system identification. The major tools applied are instrumental variable estimation techniques. Accurate downstream salinity prediction is obtained on independent data sets not used for model calibration.
Analysis of pulse interference tests
Authors: Novakowski Kentner S.
Published: February 2008

Pulse interference tests, which are conducted by monitoring the response in an observation well to a slug test conducted in a source well, are an attractive alternative to the pumping test method for determining the transmissivity and storativity of low‐storativity geological formations. An analytical model for analyzing the results of pulse interference tests affected by well bore storage in the observation well is developed in this paper using the Laplace transform method. By numerically inverting the Laplace space solution the practical range of the pulse interference test method and the influence of radial distance and well bore storage on the response in the observation well are explored. Results show that the influence of observation well storage can be significant, particularly for larger well bore storage coefficients and for almost all practical radial distances. In addition, a graphical method, based on the analytical model, is developed for analyzing the results of pulse interference tests in which observation well bore storage is negligible and for the case where the source and observation well storage coefficients are equal. A field example is also presented to illustrate and compare the use of the analytical model and graphical method for the field case where observation well storage is present and the case where it is not.
The analysis of slug tests in the frequency domain
Authors: Marschall Paul , Barczewski Baldur
Published: February 2008

In this paper a generalized analytical frequency domain method for the evaluation of transmissivity tests is presented. For a confined homogeneous aquifer the Kelvin functions represent a satisfactory set of solutions for the equation of radial flow in the frequency domain. Depending on the type of transmissivity test, simple analytical frequency‐dependent transfer functions can be defined, which relate the reaction of the aquifer to any pressure disturbance. Hence a numerical Fourier transform of the field data can be performed to determine a transfer function of data, which can be fitted with the analytical one. In order to estimate the hydraulic parameters a special logarithmic Fourier transform was used to analyze synthetic data of a slug test to verify this approach. The consideration of transmissivity tests in the frequency domain leads to some promising prospects. With this method a radius of penetration for each excitation frequency can be defined. Furthermore, analytical solutions for radial symmetric permeability distributions are available (e.g., consideration of a gravel pack or a developed zone). The frequency domain approach is also extended to a new type of low‐cost transmissivity test, the hydraulic impedance test.
Analytical solution of a convection‐dispersion model with time‐dependent transport coefficients
Authors: Barry D. A. , Sposito Garrison
Published: February 2008

Mathematical studies of solute transport in porous media have often utilized “equivalent” models of the transport process to remove undesired variability in the transport coefficients at the space and time scales of direct interest. Both deterministic and stochastic approaches in this genre produce an “effective” convection‐dispersion equation with time‐dependent coefficients. This type of equation in one spatial dimension is investigated mathematically in the present paper. A closed‐form solution of the solute transport equation is derived for a semi‐infinite spatial domain with arbitrary initial and boundary flux conditions. It is shown that the solution reduces to well‐known results for special forms of the time‐dependent coefficients. In general, however, a Volterra integral equation of the second kind must be solved to evaluate the analytical solution of the transport equation. We present a stable and convergent numerical scheme, utilizing a trapezoidal quadrature rule, for the solution of the Volterra equation. The method of solution developed should be applicable to a broad variety of solute transport problems, including particularly those in heterogeneous porous media.
On the applicability of the second‐order dispersion model
Authors: Klotz Konrad
Published: February 2008

The convective transport of a dissolved chemical species in a pipe is studied both for an injection and pulse problem. The entire solutions of the equations of the second‐order dispersion model for the averaged mass fraction of the solute are derived in the case of no molecular diffusion. Although the exact representation of
and
deviate from corresponding constitutive equations proposed by A. F. B. Tompson and W. G. Gray (1986a), they do not reflect the influence of diffusion in the overall dispersion processes considered in A. F. B. Tompson and W. G. Gray's (1986b) validation exercises. The dispersion coefficient of the injection problem considered clearly exhibits a scale effect.
Regional analyses of precipitation annual maxima in Washington State
Authors: Schaefer M. G.
Published: February 2008

Regional analyses of precipitation data were conducted using an index flood type methodology and probability weighted moments parameter estimates for the generalized extreme value distribution. Annual maximum series data were collected at 115 stations for durations of 2 and 6 hours and at 315 stations for the 24‐hour duration. Because the climate in Washington State varies from arid to rain forest, the issues of homogeneity and region definition posed major problems. Those problems were circumvented by considering the state to be a heterogeneous superregion. Climatologically homogenous subregions within the superregion were defined in terms of mean annual precipitation (MAP) rather than geographic location. The subregional values of the coefficients of variation Cv and skew γ were found to vary systematically with MAP across the superregion. This allowed the superregional values of Cv and γ to be expressed as continuous variables instead of conventional fixed values and eliminated the boundary problems normally associated with subregion definition. The values of Cv and γ for the superregion were found to be largest for arid areas and shorter durations. Smaller values of Cv and γ were associated with humid and rain forest environments. All subregional solutions were within, or near, the extreme value type II family.
Analysis of solute redistribution in a heterogeneous field
Authors: van der Zee Sjoerd E. A. T. M.
Published: February 2008

The redistribution of a solute present in the topsoil is simulated assuming adsorption according to the Langmuir isotherm. A parameter sensitivity analysis showed that the effect of the thickness (xs) of the initially solute‐containing layer on the concentration distribution can be accounted for by transforming time. Both this thickness and adsorption parameters (A) control how fast the concentration decreases in the topsoil, when the feed concentration does not contain solute. At large times the concentration increases gradually until the penetration depth, which is the mean downstream front position. There the concentration decreases abruptly to the initial value in the subsoil. When randomness of xs, and A is taken into account, no such well‐defined subsoil front is seen. With a simple approximation valid for a constant feed concentration larger than zero and for linear adsorption, it is shown when pore scale dispersion may be discarded.
A comparison of regional flood frequency estimation methods using a resampling method
Authors: Potter Kenneth W. , Lettenmaier Dennis P.
Published: February 2008

Most comparisons of flood frequency estimation methods have been based on Monte Carlo simulation. An alternative method which does not require the choice of a parent distribution is to resample from the historical record. The relative performance of 10 flood frequency estimation methods, including four at‐site methods, four regional index flood methods, and two variations of the U.S. Water Resources Council regional method, was evaluated using a resampling method. Performance measures were based on two statistics. The first was a flood damage surrogate, which was defined as a power of the excess of the flood peak over a fixed threshold approximately equal to the median annual flood; the second was the estimator of the 100‐year flood. For each subsampling of the historical record, the expected flood loss and 100‐year flood quantile conditioned on the estimated parameters were computed. From the remainder of the record, an empirical estimate of the mean damage was computed. The performance of the methods is summarized in terms of the mean and variance of the difference between the conditional expectation and the empirical damages, and the variance of the 100‐year flood estimates. The results are qualitatively similar to those reported in earlier Monte Carlo studies. The U.S. Water Resources Council method, in particular, produced variability in the damage estimates that was much greater than that for any of the index flood methods tested. Estimates of the 100‐year flood were about twice as variable on average as 100‐year flood estimates obtained using any of the regional index flood methods. For the Wisconsin and New England flood records tested, the regional Generalized Extreme Value estimators yielded 100‐year flood estimates with lower variability at virtually all sites than the U.S. Water Resources Council method.
On the nature of the dispersive flux in saturated heterogeneous porous media
Authors: Naff R. L.
Published: February 2008

A method is presented for evaluating the mean transport of a tracer in saturated heterogeneous porous media when the hydraulic conductivity can be represented by a stochastic process; no assumption concerning stationarity of the concentration field is made. The analysis results in a transform‐space solution for the dispersive flux associated with the mean concentration in a mean uniform flow field when the tracer is conservative. For a pulse input of tracer, general forms for the first four moments in the longitudinal direction are presented; these forms are solved for specific cases of interest. A general form for the global dispersive flux, associated with mean transport, is presented for the case where local dispersion, relative to the length scale of heterogeneity, is negligible. The global dispersive flux takes the form of a convolution, over time, of the concentration gradient weighted by the correlation function of the velocity field; in large time, this integral asymptotically approaches a classical Fickian form. The convolution formulation of the global flux manifests itself in early time in the form of non‐Gaussian behavior of the mean tracer concentration. Beyond a travel distance equivalent to approximately 20 length scales of the hydraulic conductivity process, Gaussian behavior of the mean tracer cloud dominates.
Predicting the vertical structure of tidal current and salinity in San Francisco Bay, California
Authors: Ford Michael , Wang Jia , Cheng Ralph T.
Published: February 2008

A two‐dimensional laterally averaged numerical estuarine model is developed to study the vertical variations of tidal hydrodynamic properties in the central/north part of San Francisco Bay, California. Tidal stage data, current meter measurements, and conductivity, temperature, and depth profiling data in San Francisco Bay are used for comparison with model predictions. An extensive review of the literature is conducted to assess the success and failure of previous similar investigations and to establish a strategy for development of the present model. A σ plane transformation is used in the vertical dimension to alleviate problems associated with fixed grid model applications in the bay, where the tidal range can be as much as 20–25% of the total water depth. Model predictions of tidal stage and velocity compare favorably with the available field data, and prototype salinity stratification is qualitatively reproduced. Conclusions from this study as well as future model applications and research needs are discussed.
Transport in heterogeneous porous formations: Spatial moments, ergodicity, and effective dispersion
Authors: Dagan Gedeon
Published: February 2008

Transport of inert solutes in natural porous formations is dominated by convection and by the large‐scale heterogeneity of permeability. A solute body inserted in the formation spreads because of the variation of velocity among and along the stream tubes which cross the plume. With neglect of the slow effect of pore‐scale dispersion the solute particles preserve their initial concentration, but the body as a whole spreads in an irregular manner (Figures 1, 2, and ). The transport theory, based on representation of permeability and velocity as random space functions, can predict the expected value and variance of concentration, but under the above conditions, the coefficient of variation may be large. In contrast, the spatial moments of the solute body are less susceptible to uncertainty, depending on the transverse dimensions of the plume and on the travel time. The first and second spatial moments are regarded as random functions of time, and their expected value and variance are derived in terms of the velocity field. The moments are assumed to satisfy the ergodic hypothesis if their coefficients of variation are negligible. The conditions which ensure the fulfillment of this requirement are examined. The “effective dispersion coefficients” are defined with the aid of the spatial moments and are shown to depend generally on the initial size of the solute body and on travel time. The results are illustrated by an analytical solution of transport in a stratified formation with the average velocity parallel to the bedding.
A general mass‐conservative numerical solution for the unsaturated flow equation
Authors: Celia Michael A. , Bouloutas Efthimios T. , Zarba Rebecca L.
Published: February 2008

Numerical approximations based on different forms of the governing partial differential equation can lead to significantly different results for unsaturated flow problems. Numerical solution based on the standard h‐based form of Richards equation generally yields poor results, characterized by large mass balance errors and erroneous estimates of infiltration depth. Conversely, numerical solutions based on the mixed form of Richards equation can be shown to possess the conservative property, so that mass is perfectly conserved. This leads to significant improvement in numerical solution performance, while requiring no additional computational effort. However, use of the mass‐conservative method does not guarantee good solutions. Accurate solution of the unsaturated flow equation also requires use of a diagonal time (or mass) matrix. Only when diagonal time matrices are used can the solution be shown to obey a maximum principle, which guarantees smooth, nonoscillatory infiltration profiles. This highlights the fact that proper treatment of the time derivative is critical in the numerical solution of unsaturated flow.
An efficient deterministic‐probabilistic approach to modeling regional groundwater flow: 1. Theory
Authors: Yen Chung‐Cheng , Guymon Gary L.
Published: February 2008

An efficient probabilistic model is developed and cascaded with a deterministic model for predicting water table elevations in regional aquifers. The objective is to quantify model uncertainty where precise estimates of water table elevations may be required. The probabilistic model is based on the two‐point probability method which only requires prior knowledge of uncertain variables mean and coefficient of variation. The two‐point estimate method is theoretically developed and compared with the Monte Carlo simulation method. The results of comparisons using hypothetical determinisitic problems indicate that the two‐point estimate method is only generally valid for linear problems where the coefficients of variation of uncertain parameters (for example, storage coefficient and hydraulic conductivity) is small. The two‐point estimate method may be applied to slightly nonlinear problems with good results, provided coefficients of variation are small. In such cases, the two‐point estimate method is much more efficient than the Monte Carlo method provided the number of uncertain variables is less than eight.
Gas exchange rates for a first‐order stream determined with deliberate and natural tracers
Authors: Wanninkhof R. , Mulholland P. J. , Elwood J. W.
Published: February 2008

Gas transfer velocities have been determined for a first‐order stream by performing a 3‐hour release of the volatile tracer sulfur hexafluoride, SF6, and the nonvolatile tracer tritiated water, 3H2O. The average gas transfer velocity for the 292‐m reach was 29 cm/h which corresponds to a reaeration coefficient for oxygen at 25°C of 134 day−1. Groundwater inflow along the stream was corrected for by measuring the downstream dilution of the 3H2O spike. Downstream discharge increased from 0.5 L/s, 2 m downstream of the point of tracer release, to 19.3 L/s at a point 292 m downstream. As an alternative to using (radioactive) 3H2O, we investigated the possibility of using natural radon, 222Rn, as a groundwater tag and using the variation of SF6 and 222Rn along the stream to determine gas exchange rates and groundwater inflow. The method yielded an average transfer velocity of 21 cm/h and underestimated the groundwater inflow by a factor of 3. This large discrepancy is attributed to a doubling of stream discharge between the time the stream was sampled for radon and the tracer experiment and the limited number of radon samples.
The willingness to pay for groundwater protection
Authors: Shultz Steven D. , Lindsay Bruce E.
Published: February 2008

To determine the willingness to pay (WTP) for a hypothetical groundwater protection plan in Dover, New Hampshire, a mail contingent valuation survey was conducted. The median WTP value among Dover residents was estimated to be $40 per household, and the community WTP value is estimated to be at least $100,000 annually for a groundwater protection plan. The assessed land values of respondents as well as their incomes were shown to positively influence their WTP values, while their ages had a negative influence on WTP. A variety of other socioeconomic variables were shown to have no influence on individuals WTP for groundwater protection. This research illustrates a methodology that other researchers, and water resource managers can use to estimate the value which people place on various water resources and can help to predict whether water policies and projects will be accepted by the public.
Tidal dynamics of the water table in beaches
Authors: Nielsen Peter
Published: February 2008

Tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations. Only the movements forced by the tide are considered, so a beach with negligible wave activity was chosen for the field measurements. The data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level. Also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide. This latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter. The observed behavior of the water table is explained in terms of perturbation extensions to the classical “deep aquifer solution.” One extension deals with the nonlinearity in the interior, the other with the boundary condition at the sloping beach face.
Biofilm growth and the related changes in the physical properties of a porous medium: 2. Permeability
Authors: Taylor Stewart W. , Milly P. C. D. , Jaffé Peter R.
Published: February 2008

Growth of a biofilm in a porous medium reduces the total volume and the average size of the pores. The change in the pore size distributions is easily quantified when certain geometric assumptions are made. Existing models of permeability or of relative permeability can be manipulated to yield estimates of the resulting reduction in permeability as a function of biofilm thickness. The associated reductions in porosity and specific surface can be estimated as well. Based on a sphere model of the medium, the Kozeny‐Carman permeability model predicts physically realistic results for this problem. Using a cut‐and‐random‐rejoin‐type model of the medium, the permeability model of Childs and Collis‐George yields qualitatively reasonable results for this problem, as does a generalization of the relative permeability model of Mualem. Permeability models of Kozeny‐Carman and of Millington and Quirk lead to unrealistic results for a cut‐and‐random‐rejoin‐type medium. The Childs and Collis‐George and the Mualem models predict that the permeability reduction for a given volume of biomass is greatest when the porous medium has uniform pore sizes.
Substrate and biomass transport in a porous medium
Authors: Taylor Stewart W. , Jaffé Peter R.
Published: February 2008

A model describing the transport of substrate and biomass in porous media is formulated which accounts for the transport, growth and decay of biomass suspended in the water phase and attached to the solid matrix as a biofilm. Interphase transport of biomass between the water phase and attached biofilm phase due to fluid mechanical shear and filtration is considered as well. Special attention is given to changes in the porosity, permeability, and dispersivity resulting from the biofilm altering the microscopic geometry of the pore space. A numerical solution to the governing equations is obtained by the finite element method. The model is calibrated and verified against experimental data. An application is presented which assesses the effects of pulsed substrate loading, flow rate, and flow duration on the clogging of porous media by biomass.
Stochastic analysis of unsaturated flow: One‐dimensional Monte Carlo simulations and comparisons with spectral perturbation analysis and field observations
Authors: Ünlü K. , Nielsen D. R. , Biggar J. W.
Published: February 2008

A numerical experiment was designed to study the stochastic behavior of one‐dimensional transient unsaturated flow in a Monte Carlo setting. Soil hydraulic properties, log‐saturated hydraulic conductivity ln Ks, pore size distribution parameter α, and the specific water capacity C are assumed to be statistically homogeneous random fields described by exponential correlation functions with identical correlation lengths. Fifty realizations of each soil hydraulic property, with statistical properties obtained from a field experiment, are generated by using a nearest‐neighbor model. Numerical solutions of the one‐dimensional flow equation are used repeatedly to obtain realizations of soil water pressure head ψ and flux q corresponding to the realizations of In Ks, α, and C. The dependence of ψ and q on the statistical properties of ln Ks, α, and C and the magnitude of the hydraulic head gradient G prevailing at the lower boundary are investigated. In addition, results of Monte Carlo analysis and spectral perturbation analyses are compared with field observations. The greatest variability of ψ and q are observed when soil hydraulic properties are uncorrelated and have large variances and integral scales and when G at the lower boundary is unity. The Monte Carlo and spectral perturbation analyses tend to agree reasonably well for the flow domains in which ergodicity of local soil hydraulic properties is assured. Results of the Monte Carlo and spectral perturbation analyses are also supported by field observations.
Stochastic analysis of the concentration variability in a three‐dimensional heterogeneous aquifer
Authors: Vomvoris Efstratios G. , Gelhar Lynn W.
Published: February 2008

A spectrally based perturbation approach is used to evaluate the concentration variability for a steady concentration field in a three‐dimensional statistically homogeneous and anisotropic aquifer. The analysis assumes small, locally stationary concentration perturbations, and consequently, is valid only after mean displacements that are large compared to the scale of aquifer heterogeneity. It is shown that the concentration variance is proportional to the square of the local mean concentration gradient and the variance and the correlation scales of log‐hydraulic conductivity (ln K) and is inversely proportional to the local dispersivity. The concentration covariance function is highly anisotropic, with the largest correlation length aligned to the mean flow direction. Another important finding is the sensitivity of the longitudinal persistence of the concentration field to the high wave number behavior of the input ln K spectrum. The commonly employed exponential‐type covariance function, which corresponds to a nondifferentiable random field, results in extremely large concentration correlation lengths along the flow direction. Input spectra corresponding to differentiable fields with more rapid high wave number cutoffs produce a significant reduction of the longitudinal correlation length.
At‐a‐Point Bed Load Sampling in the Presence of Dunes
Authors: Gomez Basil , Hubbell D. W. , Stevens H. H.
Published: February 2008

Even during constant, or virtually constant, flow conditions, bed load transport rates are known to vary over a range of temporal scales. Previous studies have emphasized that, in order to provide an accurate estimate of the mean bed load transport rate at a given point, either many samples must be collected repeatedly or the sampling time must be long. We systematically evaluate errors associated with at‐a‐point bed load sampling during steady flow conditions in the presence of dunes and provide an indication of the way in which sampling should proceed in order to minimize sampling errors. The analysis is undertaken using laboratory data and a theoretical probability distribution function. It is assumed that bed load samplers have an efficiency of 100% and that the flow conditions and the configuration of the primary bed forms remain constant during the sampling period. In the presence of dunes, sampling should be accomplished using (1) the shortest practicable sampling time for each sample, (2) short, equally spaced time intervals between samples, and (3) as long a sampling period as is necessary to ensure that at least one primary bed form has passed the sampling point. Such procedures will provide information about high‐ and low‐frequency fluctuations in at‐a‐point bed load transport rates and a reasonably reliable estimate of the mean bed load transport rate. Only about 21 sequential samples are required to estimate the mean bed load transport rate at any given point. However, because the sampling time generally is short in comparison with the time that it takes a dune to pass the sampling point, between 50 and 100 samples are needed to define both high‐ and low‐frequency at‐a‐point rate variations. A knowledge of the prevailing bed configuration is necessary in order to ensure that sampling proceeds in accordance with these requirements.
A Systematized Drillstem Test
Authors: Karasaki Kenzi
Published: February 2008

A solution of the well response to a drillstem test (DST) is presented. The advantages of a DST over conventional slug tests are discussed. A systematized procedure of a DST is proposed, where a slug test is terminated in the midpoint of the flow period, and the subsequent shut‐in data are recorded and analyzed. This method requires a downhole shut‐in device and a pressure transducer, which is no more than the conventional deep‐well slug testing. As opposed to slug tests, which are ineffective when a skin is present, more accurate estimate of formation permeability can be made using a DST. Premature termination also shortens the test duration considerably. Because in most cases no more information is gained by completing a slug test to the end, the author recommends that conventional slug tests be replaced by the premature termination technique.
Hydrologic Flow Path Definition and Partitioning of Spring Meltwater
Authors: Maulé C. P. , Stein J.
Published: February 2008

More than half of the annual acidic deposition to Canada's boreal forests is released during spring snowmelt. To evaluate the impact of this acidity upon the aquatic environment, the sources and hydrologic pathways must be defined. Two environmental tracers, oxygen 18 and silica, were used to meet this objective for spring snowmelt at Lac Laflamme. Stream water could be partitioned into four distinct waters based upon event and flow path; however, similar division for lake water was not possible due to inconsistencies between tracer contents in the lake water. In terms of the major source of acidity, snow meltwater, stream water had an average meltwater content of 70% while near‐shore lake water ranged from greater than 70% at spring melt commencement to less than 45% at the end. These high amounts of meltwater represent a severe hazard for the potential occurrence of “acid shock” of nearshore spawning grounds.
Quenching of highly vibrationally excited pyrimidine by collisions with CO2
Authors: Johnson Jeremy A. , Duffin Andrew M. , Hom Brian J. , Jackson Karl E. , Sevy Eric T.
Published: February 2008

Relaxation of highly vibrationally excited pyrimidine (C4N2H4) by collisions with carbon dioxide has been investigated using diode laser transient absorption spectroscopy. Vibrationally hot pyrimidine (E′=40635cm−1) was prepared by 248-nm excimer laser excitation, followed by rapid radiationless relaxation to the ground electronic state. The nascent rotational population distribution (J=58–80) of the 0000 ground state of CO2 resulting from collisions with hot pyrimidine was probed at short times following the excimer laser pulse. Doppler spectroscopy was used to measure the CO2 recoil velocity distribution for J=58–80 of the 0000 state. Rate constants and probabilities for collisions populating these CO2 rotational states were determined. The measured energy transfer probabilities, indexed by final bath state, were resorted as a function of ΔE to create the energy transfer distribution function, P(E,E′), from E′−E∼1300–7000cm−1. P(E,E′) is fitted to a single exponential and a biexponential function to determine the average energy transferred in a single collision between pyrimidine and CO2 and parameters that can be compared to previously studied systems using this technique, pyrazine∕CO2, C6F6∕CO2, and methylpyrazine∕CO2. P(E,E′) parameters for these four systems are also compared to various molecular properties of the donor molecules. Finally, P(E,E′) is analyzed in the context of two models, one which suggests that the shape of P(E,E′) is primarily determined by the low-frequency out-of-plane donor vibrational modes and one which suggests that the shape of P(E,E′) can be determined by how the donor molecule final density of states changes with ΔE.
Soft x-ray resonant magnetic scattering investigation of stable magnetic configurations in patterned rings
Authors: Ogrin F. Y. , Sirotkin E. , van der Laan G. , Beutier G. , Ross C. A. , Jung W. , Menon R.
Published: February 2008

The first experimental results of soft x-ray resonant magnetic scattering from a pattern of microscopic Permalloy rings are reported. Experimental measurements and simulations of the scattering from the stable magnetic configurations such as “vortex” and “onion” commonly observed for the ring structures are presented. Variations in the diffraction profile as a function of field are discussed in the context of the simulation results, which show a good agreement with the behavior of the experimental data.
High field performance of nanodiamond doped MgB2 superconductor
Authors: Vajpayee Arpita , Awana V. P. S. , Kishan H. , Narlikar A. V. , Bhalla G. L. , Wang X. L.
Published: February 2008

The results from magnetotransport and magnetization of nanodiamond doped MgB2-nDx are reported. Superconducting transition temperature (Tc) is not affected significantly by x up to x=0.05 and latter decreases slightly for higher x>0.05. R(T) vs H measurements show higher Tc values under same applied magnetic fields for the nanodiamond added samples, resulting in higher estimated Hc2 values. From the magnetization measurements, it was found that irreversibility field value Hirr for the pristine sample is 7.5T at 4K and the same is increased to 13.5T for 3wt% nD added sample at the same temperature. The Jc(H) plots at all temperatures show that Jc value is lowest at all applied fields for pristine MgB2 and the sample doped with 3wt% nD gives the best Jc values at all fields. These results are discussed in terms of extrinsic pinning due to dispersed n-diamond in the host MgB2 matrix along with the intrinsic pinning due to possible substitution of C at boron site and increased interband scattering for highly doped samples resulting in extraordinary performance of the doped system.
Illuminating the connection between contact angle saturation and dielectric breakdown in electrowetting through leakage current measurements
Authors: Papathanasiou A. G. , Papaioannou A. T. , Boudouvis A. G.
Published: February 2008

Recent findings on the connection between the dielectric breakdown strength and the contact angle saturation in electrowetting triggered further investigation of the underlying mechanisms towards reporting the consequences of the proposed relation. High sensitivity current measurements are conducted to monitor the dielectric leakage current during a standard electrowetting experiment by testing thin (15–500 nm) dielectric films of materials widely used in microelectronics industry (SiO2, tetra-ethoxy-silane, Si3N4). The measurements confirmed that the current is negligible as long as the applied, direct current, voltage is kept below a critical value at saturation onset. This current, however, exhibits a sharp increase at higher voltages. By exploiting the increased breakdown strength of stacked oxide-nitride-oxide dielectrics, the appearance of the contact angle saturation is inhibited, suggesting the use of such composites for the design of efficient electrowetting devices.
Plasmonic engineering of singlet oxygen generation
Authors: Zhang Yongxia , Aslan Kadir , Previte Michael J. R. , Geddes Chris D.
Published: February 2008

In this article, we report metal-enhanced singlet oxygen generation (ME
1
O
2
). We demonstrate a direct relationship between the singlet oxygen yield of a common photosensitizer (Rose Bengal) and the theoretical electric field enhancement or enhanced absorption of the photosensitizer in proximity to metallic nanoparticles. Using a series of photosensitizers, sandwiched between silver island films (SiFs), we report that the extent of singlet oxygen enhancement is inversely proportional to the free space singlet oxygen quantum yield. By modifying plasmon coupling parameters, such as nanoparticle size and shape, fluorophore/particle distance, and the excitation wavelength of the coupling photosensitizer, we can readily tune singlet oxygen yields for applications in singlet oxygen-based clinical therapy.
History-dependent random processes
Authors: Clifford Peter , Stirzaker David
Published: February 2008

Ulam has defined a history-dependent random sequence by the recursionXn+1=Xn+XU(n), where (U(n);n≥1) is a sequence of independent random variables withU(n) uniformly distributed on {1, …, n} andX1=1. We introduce a new class of continuous-time history-dependent random processes regulated by Poisson processes. The simplest of these, a univariate process regulated by a homogeneous Poisson process, replicates in continuous time the essential properties of Ulam's sequence, and greatly facilitates its analysis. We consider several generalizations and extensions of this, including bivariate and multivariate coupled history-dependent processes, and cases when the dependence on the past is not uniform. The analysis of the discrete-time formulations of these models would be at the very least an extremely formidable project, but we determine the asymptotic growth rates of their means and higher moments with relative ease.
The effect of the Convention on International Trade in Endangered Species on scientific collections
Authors: Roberts David L , Solow Andrew R
Published: February 2008

The Convention on International Trade in Endangered Species (CITES) was conceived in the spirit of cooperation, with the aim of ensuring that the international trade in wild animals and plants, including all parts and derivatives, did not threaten their survival. However, concerns have been raised by scientists that CITES hinders the cross-border movement of scientific specimens. To our knowledge, no empirical analysis has been undertaken to demonstrate the existence of this effect. We test for a CITES effect on the collection record of orchids from Brazil and Costa Rica using the collection records of bromeliads, which are not covered by CITES, as a control. Highly significant effects are found in both countries.
Sperm motility and cryopreservation of spermatozoa in freshwater gobies
Authors: Yokoi K. , Ohta H. , Hosoya K.
Published: February 2008

Testicular sperm motility and methods for the cryopreservation of spermatozoa in the freshwater goby Rhinogobius sp. CB (Cross Band type) were examined. Spermatozoa were almost immotile upon dilution with 300 mOsm kg−1 of NaCl, KCl and mannitol solutions but began to swim in solutions with concentrations <200 mOsm kg−1. The highest percentage and longest duration of motility was obtained in the 0 and 100–200 mOsm kg−1 solutions, respectively. The highest post‐thaw motility, c. 50% of motility before cryopreservation, was obtained when spermatozoa were diluted with an extender of 10% methanol and 90% artificial seminal plasma, cooled at −10·0 ± 1·1° C min−1 (mean ±s.e.) to −50° C and plunged into liquid nitrogen. Spermatozoa were cryopreserved in a 50 μl acrylic haematocrit tube to store the small amount of milt. As the cryopreservation method described above was applicable to the endangered Rhinogobius sp. BI (Bonin Island type), it is probable that this method can be used for other species of freshwater gobies.
Ovarian contraction in various teleost families
Authors: Bills M. L. , Callaway S. B. , Kessler A. T. , Taylor M. H.
Published: February 2008

Fishes from 12 species (a minimum of three fish of each species), representing nine families were examined for ovarian contraction. An ovary from each fish was removed, placed in a muscle bath and assessed for contractions using a force‐displacement transducer. After at least 30 min of observation for spontaneous contractions, acetylcholine (ACh) was added to the muscle bath to assess the ovary’s capacity for contraction. At least one third of the ovaries from each species contracted spontaneously or in response to 10−5 M ACh. Mean ±s.e. frequencies of spontaneous contractions ranged from 7·5 ± 2·0 h−1 in the Atlantic silverside Menidia menidia to 380·3 ± 101·5 h−1 in the sheepshead minnow Cyprinodon variegatus. Simultaneously tested ovaries from a single white perch Morone americana contracted at rates of 31·4 and 81·9 h−1. This is consistent with independent generation of the contractile rhythm in the two ovaries. In three species (goldfish Carassius auratus, mummichog Fundulus heteroclitus and white perch), the tunica albuginea was removed from the ovary and found to be capable of independent contraction. This suggests that this membrane contributes to the observed contractions. The presence of ovarian contractions in this varied group of fish species indicates that the contractions play an important role in reproduction.