bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring groundwater transport through lake sediments by advection and diffusion
Authors: Cornett R. J. , Risto B. A. , Lee D. R.
Published: February 2008

A method for estimating low rates of groundwater inflow and outflow through the bottom sediments of surface waters was developed and tested. A one‐dimensional advection‐diffusion model was fitted to measured pore water profiles of two nonreactive solutes, tritiated water and chloride, and the advection rate was calculated by a nonlinear least squares technique. Using 3H profiles measured 0–0.5 m below the sediment‐water interface, rates of groundwater advection into a lake through interbedded sands and gyttja were estimated to be about 1.0 m/year. In midlake locations underlain by soft organic gyttja, rates of advection were much lower (<0.1 m/year). Knowledge of the rate and direction of groundwater flow substantially altered the interpretation of pore water profiles within the sediments and the fluxes of solutes. This technique can be used to estimate flow rates less than 2 m/annum with minimal disturbance, without enclosing the sediments in a container, in a diversity of systems.
The Laplace Transform Galerkin Technique: A time‐continuous finite element theory and application to mass transport in groundwater
Authors: Sudicky E. A.
Published: February 2008

A time‐continuous numerical technique, referred to as the Laplace Transform Galerkin (LTG) method, is developed and applied to the problem of solute transport in porous media. After application of Galerkin's procedure and subdivision of the domain into finite elements, the method involves a simple application of the Laplace transformation to eliminate the temporal derivatives appearing in the space‐discretized set of ordinary differential equations. Then, by solving the resulting transformed system of algebraic equations in Laplace p space, numerical inversion of the Laplace‐transformed nodal concentration is performed using the robust and accurate Crump (1976) algorithm. The Crump algorithm permits the concentration to be evaluated from a range of time values from a single set of Laplace p space solutions. Because each of the needed p space solutions are independent, the algorithm is well suited for execution on multiprocessor parallel computers. It is demonstrated by means of a series of examples that the LTG scheme is capable of providing highly accurate solutions essentially devoid of numerical dispersion for grid Peclet numbers in excess of 30. Examination of the complex‐valued, Laplace‐domain concentration profiles reveal that they are generally smooth, well‐behaved oscillatory functions compared to the profiles in the time domain, thus permitting the use of a coarse finite element grid. Because of the nature of the Laplace transformation, the LTG method is particularly well suited to the problem of transient groundwater flow and solute transport in fractured porous media or multiple aquifer‐aquitard systems based on the dual‐porosity integrodifferential equation approach.
Numerical analysis of solute transport during transient irrigation: 2. The effect of immobile water
Authors: Russo David , Jury William A. , Butters Greg L.
Published: February 2008

In this study, the two‐component mobile‐immobile water model is modified to describe solute transport under transient water flow induced by periodic cycles of irrigation, evaporation, and redistribution. To characterize transient flow, the soil water content is divided into a time‐invariant immobile water content Θi, and a time‐dependent mobile water content Θm which obeys the Richards equation. Solute transport is described by the two‐component mobile‐immobile water model, modified to take into account the time dependence of Θm. Results of the calculations show important differences between the behavior of the flux and residence concentrations under steady state water flow, particularly when the mass transfer coefficient α is relatively small. In this case, both resident and flux concentrations show a dispersion scale effect in their rate of spreading about the center of mass position in the soil. There were significant differences in solute transport predicted by the transient two‐component model compared to the steady state model. The apparent velocity derived from the time variations of the position of the center of mass of the resident concentration decreased with time in the transient model, but was relatively constant in the steady state one. Apparent dispersion about the center of mass increased with time in both models, but was much higher in the transient model, caused principally by a buildup of solute at the surface during evaporation cycles.
Bed material sampling error in sand bed rivers
Authors: Ashmore P. E. , Yuzyk T. R. , Herrington R.
Published: February 2008

A total of 468 bed material samples were collected at cross sections of the sand bed of the South Saskatchewan River at Saskatoon to assess the random and systematic errors in the results from four commonly used samplers. Statistically significant differences in particle size distribution occur between the results obtained from different samplers at the same location, in part due to variability in retention of the small particles. The differences are greatest in silty sand and least in well‐sorted, medium sand. The precision of results from repetitive samples at the same location using the same sampler depends on both the sampler and the composition of the bed material. Except in well‐sorted, medium sand, a single sample at a vertical is inadequate to determine the particle size of a given size fraction to within 10% with a probability of error of 0.1. In some cases 10 or more samples may be required. The magnitude of these statistical errors at a given location is generally less than the within‐reach variability in bed material particle size, and therefore the appropriate choice of sample location is critical.
Economic targeting of nonpoint pollution abatement for fish habitat protection
Authors: Braden John B. , Herricks Edwin E. , Larson Robert S.
Published: February 2008

A model is presented which relates farm economics, pollutant delivery, fisheries habitat quality and reliability, and spatial optimization. The model identifies the most profitable cropping practices which provide an acceptable level of risk of impairment to the physical and chemical fish habitat. The potential of the model as a watershed management aid is demonstrated with an application to salmonid habitat in a Lake Michigan tributary.
Hydrologic sensitivities of the Sacramento‐San Joaquin River Basin, California, to global warming
Authors: Lettenmaier Dennis P. , Gan Thian Yew
Published: February 2008

The hydrologic sensitivities of four medium‐sized mountainous catchments in the Sacramento and San Joaquin River basins to long‐term global warming were analyzed. The hydrologic response of these catchments, all of which are dominated by spring snowmelt runoff, were simulated by the coupling of the snowmelt and the soil moisture accounting models of the U.S. National Weather Service River Forecast System. In all four catchments the global warming pattern, which was indexed to CO2 doubling scenarios simulated by three (global) general circulation models, produced a major seasonal shift in the snow accumulation pattern. Under the alternative climate scenarios more winter precipitation fell as rain instead of snow, and winter runoff increased while spring snowmelt runoff decreased. In addition, large increases in the annual flood maxima were simulated, primarily due to an increase in rain‐on‐snow events, with the time of occurrence of many large floods shifting from spring to winter.
A statistical log piecewise linear model of at‐a‐station hydraulic geometry
Authors: Bates Bryson C.
Published: February 2008

A new log piecewise linear model of at‐a‐station hydraulic geometry and a statistical methodology for fitting the model to observed data are described. The proposed parameterization provides a continuity relationship between the model parameters and allows the model to reduce to the Leopold and Maddock power function model when one of the parameters is set equal to zero. Applications of the new model, the Leopold and Maddock model, and the Richards log quadratic model are made to 22 gauging stations in New South Wales, Australia. Ordinary least squares (OLS) procedures are used to fit the models to the data. Results indicate that the new model is superior to the existing models in that it allows the identification of the points at which there are breaks in the slopes of the width‐, mean depth‐, and mean velocity‐discharge relations. In addition, it often produces smaller residual variances and residuals that more frequently conform with the OLS error assumptions. However, more sophisticated procedures for parameter estimation may be needed in some instances if statistical inferences are to be drawn from these regression models.
A comparison of erosion and water pollution control strategies for an agricultural watershed
Authors: Prato Tony , Shi Hongqi
Published: February 2008

The effectiveness and efficiency of two erosion control strategies and one water pollution control (riparian) strategy are compared for Idaho's Tom Beall watershed. Erosion control strategies maximize annualized net returns per hectare on each field and restrict field erosion rates to no more than 11.2 or 16.8 tons per hectare. The riparian strategy uses good vegetative cover on all fields adjacent to the creek and in noncropland areas and the resource management system that maximizes annualized net returns per hectare on remaining fields. The Agricultural Nonpoint Source Pollution model is used to simulate the levels and concentrations of sediment, nitrogen, phosphorus, and chemical oxygen demand at the outlet of the watershed. Erosion control strategies generate less total erosion and water pollution but are less efficient than the riparian strategy. The riparian strategy is less equitable for farmers than the erosion control strategies.
Analysis of one‐dimensional solute transport through porous media with spatially variable retardation factor
Authors: Chrysikopoulos Constantinos V. , Kitanidis Peter K. , Roberts Paul V.
Published: February 2008

A closed‐form analytical small‐perturbation (or first‐order) solution to the one‐dimensional advection‐dispersion equation with spatially variable retardation factor is derived to investigate the transport of sorbing but otherwise nonreacting solutes in hydraulically homogeneous but geochemically heterogeneous porous formations. The solution is developed for a third‐ or flux‐type inlet boundary condition, which is applicable when considering resident (volume‐averaged) solute concentrations, and a semi‐infinite porous medium. For mathematical simplicity it is hypothesized that the sorption processes are based on linear equilibrium isotherms and that the local chemical equilibrium assumption is valid. The results from several simulations, compared with predictions based on the classical advection‐dispersion equation with constant coefficients, indicate that at early times, spatially variable retardation affects the transport behavior of sorbing solutes. The zeroth moments corresponding to constant and variable retardation are not necessarily equal. The impact of spatially variable retardation increases with increasing Péclet number. The center of mass appears to move more slowly, and solute spreading is enhanced in the variable retardation case. At late times, when the travel distance is much larger than the correlation scale of the retardation factor, the zeroth moment for the variable retardation case is identical to the case of invariant retardation. The small‐perturbation solution agrees closely with a finite difference numerical approximation.
Modeling transient storage and nitrate uptake kinetics in a flume containing a natural periphyton community
Authors: Kim B. K. , Jackman A. P. , Triska F. J.
Published: February 2008

An existing transport model including storage zones was combined with a submodel describing biotic retention of nutrient based on Michaelis‐Menten kinetics. This transport/retention model was used to simulate the results of an experiment in which the inflows to flumes containing nitrate‐limited natural stream periphyton on artificial substrates were amended with chloride and nitrate. Hydrodynamic parameters were determined by fitting the model to the chloride data. The Michaelis‐Menten maximum uptake rate parameter was determined by fitting the model to the nitrate data. The transport/retention model accurately simulated the responses of the flumes to the amendments. Independent batch experiments to determine Michaelis‐Menten parameters were performed on periphyton from a control flume. The maximum uptake rate parameters from the two experiments are in good agreement. Both experiments indicate possible inadequacies of the Michaelis‐Menten kinetic model for describing nutrient uptake in a complex field community.
A two‐phase decomposition method for optimal design of looped water distribution networks
Authors: Fujiwara Okitsugu , Khang Do Ba
Published: February 2008

A two‐phase decomposition method is proposed for the optimal design of new looped water distribution networks as well as for the parallel expansion of existing ones. The main feature of the method is that it generates a sequence of improving local optimal solutions. The first phase of the method takes a gradient approach with the flow distribution and pumping heads as decision variables and is an extension of the linear programming gradient method proposed by Alperovits and Shamir (1977) for nonlinear modeling. The technique is iterative and produces a local optimal solution. In the second phase the link head losses of this local optimal solution are fixed, and the resulting concave program is solved for the link flows and pumping heads; these then serve to restart the first phase to obtain an improved local optimal solution. The whole procedure continues until no further improvement can be achieved. Some applications and extensions of the method are also discussed.
Particle velocity interpolation in block‐centered finite difference groundwater flow models
Authors: Goode Daniel J.
Published: February 2008

A block‐centered, finite difference model of two‐dimensional groundwater flow yields velocity values at the midpoints of interfaces between adjacent blocks. Method of characteristics, random walk and particle‐tracking models of solute transport require velocities at arbitrary particle locations within the finite difference grid. Particle path lines and travel times are sensitive to the spatial interpolation scheme employed, particularly in heterogeneous aquifers. This paper briefly reviews linear and bilinear interpolation of velocity and introduces a new interpolation scheme. Linear interpolation of velocity is consistent with the numerical solution of the flow equation and preserves discontinuities in velocity caused by abrupt (blocky) changes in transmissivity or hydraulic conductivity. However, linear interpolation yields discontinuous and somewhat unrealistic velocities in homogeneous aquifers. Bilinear interpolation of velocity yields continuous and realistic velocities in homogeneous and smoothly heterogeneous aquifers but does not preserve discontinuities in velocity at abrupt transmissivity boundaries. The new scheme uses potentiometric head gradients and offers improved accuracy for nonuniform flow in heterogeneous aquifers with abrupt changes in transmissivity. The new scheme is equivalent to bilinear interpolation in homogeneous media and is equivalent to linear interpolation where gradients are uniform. Selecting the best interpolation scheme depends, in part, on the conceptualization of aquifer heterogeneity, that is, whether changes in transmissivity occur abruptly or smoothly.
Explicit Monte Carlo Simulation head moment estimates for stochastic confined groundwater flow
Authors: Jones LaDon
Published: February 2008

A methodology is presented for expressing the head moment estimates as explicit functions of the pumping rates for confined groundwater flow with parameter uncertainty. The technique combines a single Monte Carlo simulation (MCS) and the statistical moment estimators to express the mean head estimate as an explicit linear function of the pumping rates and the head variance estimate as an explicit quadratic function of the pumping rates. With a change in the pumping rates, instead of again applying MCS, the MCS head moment estimates can be found from the explicit equations with trivial computational effort. The results are limited to systems where the dependent variable can be expressed as a linear function of the control variable. To demonstrate the results, a simulation example is presented for steady confined groundwater flow, with the transmissivity treated as a spatially correlated, lognormally distributed random variable. The explicit MCS head moment estimates are also used in a simple management model for dewatering under parameter uncertainty. The objective is to minimize the total pumping, while meeting constraints on the probability of the head exceeding an upper bound at the control nodes. The explicit MCS head moment estimates and a Gaussian assumption for the head distribution are used in a chance constraint formulation to express the head level constraints as explicit functions of the pumping rates. Solution of the management model requires modest computational effort due to the explicit nature of the head level constraints. Also examined is the effect on the optimal solution of the management model of (1) changes in the acceptable probability of exceeding the head upper bound, (2) changes in the number of samples used for the explicit MCS head moment estimates, and (3) the Gaussian assumption for the head distribution.
Exact solution for flow of slightly compressible fluids through multiple‐porosity, multiple‐permeability media
Authors: Liu M.‐X. , Chen Z.‐X.
Published: February 2008

This paper presents a model describing the flow of a slightly compressible fluid through a multiple‐porosity, multiple‐permeability medium. The model considers flow within each porous system and the cross flow between any two different porous systems using a matrix of cross‐flow coefficients. An exact solution for a bounded, closed cylindrical reservoir with a concentric well producing at a constant rate is obtained rigorously. Moreover, the solution is expressed in terms of Bessel functions, so there are no particular difficulties in computing the solution numerically. The key to the method of solution is an orthogonal matrix transformation that makes the n‐coupled governing equations uncoupled.
Cokriging to assess regional stream quality in the Southern Blue Ridge Province
Authors: Jager Henriette I. , Sale Michael J. , Schmoyer Richard L.
Published: February 2008

Cokriging is used to predict stream chemistry at unsampled locations with the use of spatial and intervariable correlation. The technique is used in this study to predict the acid neutralizing capacity (ANC) of streams in the Southern Blue Ridge Province (SBRP). ANC measurements between pairs of streams surveyed in this region were found to be spatially correlated over distances up to around 40 km. Predictions were improved by including elevation in the analysis to represent the combined influence of elevational gradients in climate, geology, soils, hydrology, and vegetation on stream ANC. The cokriging analysis identified specific stream reaches predicted to be most sensitive to acidification and located areas of high uncertainty. Stream ANC levels below 50 μeq/L were predicted for one‐fifth of the upper nodes associated with digitized headwater reaches in the SBRP. The majority of these were located in the higher elevations of the Great Smoky Mountains National Park, in the vicinity of Mount Mitchell, and in the Blue Ridge Mountains in southern North Carolina.
A multilayered sharp interface model of coupled freshwater and saltwater flow in coastal systems: Model development and application
Authors: Essaid Hedeff I.
Published: February 2008

A quasi three‐dimensional, finite difference model, that simulates freshwater and saltwater flow separated by a sharp interface, has been developed to study layered coastal aquifer systems. The model allows for regional simulation of coastal groundwater conditions, including the effects of saltwater dynamics on the freshwater system. Vertically integrated freshwater and saltwater flow equations incorporating the interface boundary condition are solved within each aquifer. Leakage through confining layers is calculated by Darcy's law, accounting for density differences across the layer. The locations of the interface tip and toe, within grid blocks, are tracked by linearly extrapolating the position of the interface. The model has been verified using available analytical solutions and experimental results. Application of the model to the Soquel‐Aptos basin, Santa Cruz County, California, illustrates the use of the quasi three‐dimensional, sharp interface approach for the examination of freshwater‐saltwater dynamics in regional systems. Simulation suggests that the interface, today, is still responding to long‐term Pleistocene sea level fluctuations and has not achieved equilibrium with present day sea level conditions.
Response of the water level in a well to Earth tides and atmospheric loading under unconfined conditions
Authors: Rojstaczer Stuart , Riley Francis S.
Published: February 2008

The response of the water level in a well to Earth tides and atmospheric loading under unconfined conditions can be explained if the water level is controlled by the aquifer response averaged over the saturated depth of the well. Because vertical averaging tends to diminish the influence of the water table, the response is qualitatively similar to the response of a well under partially confined conditions. When the influence of well bore storage can be ignored, the response to Earth tides is strongly governed by a dimensionless aquifer frequency Q′u. The response to atmospheric loading is strongly governed by two dimensionless vertical fluid flow parameters: a dimensionless unsaturated zone frequency, R, and a dimensionless aquifer frequency Qu. The differences between Q′u and Qu are generally small for aquifers which are highly sensitive to Earth tides. When Q′u and Qu are large, the response of the well to Earth tides and atmospheric loading approaches the static response of the aquifer under confined conditions. At small values of Q′u and Qu, well response to Earth tides and atmospheric loading is strongly influenced by water table drainage. When R is large relative to Qu, the response to atmospheric loading is strongly influenced by attenuation and phase shift of the pneumatic pressure signal in the unsaturated zone. The presence of partial penetration retards phase advance in well response to Earth tides and atmospheric loading. When the theoretical response of a phreatic well to Earth tides and atmospheric loading is fit to the well response inferred from cross‐spectral estimation, it is possible to obtain estimates of the pneumatic diffusivity of the unsaturated zone and the vertical hydraulic conductivity of the aquifer.
Experimental testing of transient unsaturated flow theory at low water content in a centrifugal field
Authors: Nimmo John R.
Published: February 2008

Experimental measurements and theoretical predictions of transient moisture conditions have been compared for a sandy soil approaching hydrostatic equilibrium in a centrifugal field. Starting near saturation, samples were centrifuged at constant speed with a constant suction at the outflow boundary. Water flowed freely out of the sample through a porous plate. Step increases in centrifuge speed produced transient moisture conditions suitable for comparison between experiment and theory. Measurements of electrical conductivity by a direct contact four‐electrode technique indicated the water content according to a calibration based on known moisture conditions at various equilibrium states. A specially modified centrifuge permitted electrical measurements during centrifugation. For comparison, the transient water contents were computed by a finite‐difference solution of Richards' equation (modified by replacing gravitational with centrifugal potential), using soil characteristics measured previously by steady state techniques. The time dependence of water content changes, used as the basis for comparison between experiment and theory, shows agreement which is reasonable given the degree of uncertainty of the measurements. The experiment confirms, within a factor of 4, the validity of Richards' equation for moisture conditions as dry as 25% of saturation, over a hydraulic conductivity range of 5 × 10−11to 1 × 10−8m/s, and in a centrifugal field up to about 200g.
Theoretical model of optimal drainage networks
Authors: Howard Alan D.
Published: February 2008

A simulation model of drainage network optimization is presented in which channels shift to minimize total stream power pgQS within the network. The simulation model starts from an arbitrary initial stream network developed on a square matrix, such as produced by random headward growth. Discrete stream capture then is simulated within the network, occurring wherever a new stream linkage would produce a steeper course than the original. Such capture produces a network with minimum power optimization but flow directions constrained to eight directions. Individual segment end points are then allowed to migrate by iterative relaxation with a direction and rapidity of motion governed by the gradient of stream power at the node. This valley migration is subject to the constraint that the sources and outlet remain fixed. The resulting networks are visually and morphometrically more similar to natural stream networks than the original networks produced by the random headward growth model.
Statistical characteristics of some estimators of sediment and nutrient loadings
Authors: Clarke Robin T.
Published: February 2008

This paper explores some of the statistical characteristics of estimators of sediment load which require the integration over time of the product of a concentration (c) with a discharge (q). Using a bivariate lognormal distribution for the discrete variables (ci, qi), (i = 1, …, n), approximate confidence intervals are calculated for an unbiassed estimator of sediment yield, and the exact sampling distribution of the estimator is obtained by numerical integration of a Fourier transform. This permits an investigation of the rapidity with which the estimator tends to normality. Provided the data sequences are serially independent, the same technique can be used to obtain the distribution of an estimator without the assumption of bivariate lognormality. Some characteristics of an “extrapolation” estimate of sediment yield are derived, in which power law regression is used to estimate concentration from discharge when measurements of the latter are more plentiful than the former. Subject to model assumptions, the extrapolation estimate is found to underestimate the true sediment load, although its variance is smaller; this confirms results obtained by other workers who use empirical sampling and alternative theoretical approaches.
Technology, institutions, and politics: Still out of balance
Authors: Howe Charles W.
Published: February 2008

Let me start by reiterating Allen Kneese's message in his guest editorial concerning the excitement of the early days of Water Resources Research [Kneese, 1990]. My commitment to the study of water resources began through studies of inland waterway transportation. That led to the publication of an article in the very first issue of the journal. I then was fortunate to be asked to join Resources for the Future, Incorporated (RFF) in 1965, where I had the privilege of learning from and working with many great scholars in the field, among them Irving Fox, Allen Kneese, John Krutilla, and Walter Langbein.
Calibration of time domain reflectometry for water content measurement using a composite dielectric approach
Authors: Roth Kurt , Schulin Rainer , Flühler Hannes , Attinger Werner
Published: February 2008

Time domain reflectometry (TDR) has been developed to an operational level for the measurement of soil water content during the past decade. Because it is able to provide fast, precise and nondestructive in situ measurements, it has become an alternative to the neutron scattering method, in particular for monitoring water content under field conditions. One of the major disadvantages of the neutron scattering technique is that, due to the relatively high sensitivity of the signal to factors other than water content, site‐specific calibration is usually required. In this paper a calibration curve for the TDR method is presented which is not restricted to specific soil conditions. The calibration is based on the dielectric mixing model of Dobson et al. (1985). Measurements of volumetric water content and dielectric number at eleven different field sites representing a wide range of soil types were used to determine the parameter of the model by weighted nonlinear regression. The uncertainty (root mean square error) of water content values calculated with the optimized calibration curve was estimated not to exceed 0.013 cm3/cm3. This value is comparable to the precision of the thermogravimetric method. From a sensitivity analysis it was determined that the temperature dependence of the TDR signal may have to be corrected to obtain optimum accuracy.
Coupled inverse problems in groundwater modeling: 2. Identifiability and experimental design
Authors: Sun Ne‐Zheng , Yeh William W.‐G.
Published: February 2008

Parameter identifiability and experimental design in the context of solving the coupled inverse problem in groundwater modeling are considered in part 2 of the two‐paper series. The following three new definitions of extended identifiability for a distributed parameter system are presented: interval identifiability (INI), prediction equivalence identifiability (PEI), and management equivalence identifiability (MEI). The uniqueness requirement of the inverse solution is relaxed by these definitions. An identified parameter is said to be extendedly identifiable if it is able to satisfy an accuracy requirement in a specific application of the model. When a generalized least squares norm is used, the proposed identifiabilities are applicable to any coupled problems in which the state variables and parameters may have different order of magnitudes. A salient feature of the new definitions is that the extended identifiabilities are closely related to experimental design. Consequently, the sufficiency of an experimental design for assuring a given level of an extended identifiability can be estimated prior to field experiments. The methodology developed can be used to determine the reliability of an experimental design even for nonlinear models. A numerical example on the management of a wastewater disposal is given to explain how the concepts and methods presented in this paper can be used for solving practical problems.
Periodic‐stochastic modeling of separation of precipitation into rainfall and snowfall
Authors: Yevjevich Vujica , Harmancioğlu Nilgün Bayraktar
Published: February 2008

Modelers must separate precipitation into rainfall and snowfall because the two processes have significant differences as inputs to runoff. The purpose of the present study is to model this separation, provided that available data permit the coding of observed precipitation as rainfall, snowfall, and/or mixed rainfall‐snowfall. Modeling of precipitation is realized by a simple approach such as the periodic‐stochastic Markov chain description of occurrence and nonoccurrence of time interval precipitation. The exponential probability distribution based functions, with periodic parameters, are used for modeling the nonzero values of precipitation. The generated series are then separated into rainfall and snowfall components by means of the rainfall‐precipitation ratio. This ratio is modeled as a periodic‐stochastic process in the range zero to one. The bounded (0, 1)‐beta distribution function is selected as the appropriate distribution function to describe the ratio when it can also assume values between zero and unity. Most parameters in modeling precipitation and the ratio show periodicity, often fitted well by one‐ or two‐harmonic Fourier functions. Two sets of daily precipitation series, each ten years long, are used to demonstrate the results of modeling daily precipitation and daily rainfall‐precipitation ratio: the Besanson precipitation gauging station in the Durance River basin, France (as a point process), and the W‐3 watershed area, near Danville, Vermont (as a daily average areal precipitation process). The investigation shows the feasibility of modeling the separation when observed precipitation is coded for rainfall, snowfall, and/or mixed rainfall‐snowfall.
Naturally Occurring Radon 222 as a Tracer for Streamflow Generation: Steady State Methodology and Field Example
Authors: Genereux David P. , Hemond Harold F.
Published: February 2008

This paper presents a quantitative framework for the use of naturally occurring 222Rn as a hydrologic flow path tracer under conditions of steady streamflow. The methodology consists of two distinct parts, the first of which is the determination of
, the average 222Rn content of the water feeding a given stream reach.
is determined by measuring the concentrations of 222Rn and two injected tracers (one conservative, the other volatile) in the stream water and solving a mass balance equation for 222Rn around the reach of interest. The second part of the methodology involves using
values to determine the sources of stream inflow (and, implicitly, the flow paths important in streamflow generation). One means of accomplishing this, simple “geographic source” separations, is presented here. Both parts of the methodology were illustrated with a field experiment at the Bickford watershed in central Massachusetts. The injected tracers used were NaCl (conservative) and propane (volatile). The value of
(700 disintegrations per minute (dpm)/L) was found to be closer to the 222Rn content of vadose zone water (500 dpm/L) than to that of saturated zone water (2000 dpm/L), suggesting that lateral unsaturated flow was important in supplying base flow at the study site.
Stabilization of surface reaction intermediates by added metal atoms on metal surfaces of low free energy
Authors: Zhou Ling , Gao Weiwei , Klust Andreas , Madix Robert J.
Published: February 2008

Dynamic restructuring of the Ag(111) surface occurs during the reaction of sulfur dioxide with Ag(111)-p(4×4)-O at 300K, resulting in the incorporation of added silver atoms into the unit cells of both adsorbed sulfite and sulfate. This result clearly demonstrates that incorporation of metal atoms into the structures of adsorbates and reaction intermediates is not restricted to more open, higher free energy single crystal planes. These observations indicate that the participation of added metal atoms must be considered in the theoretical treatment of metal catalyzed reactions.
Study of etched (210)-oriented thin garnet films
Authors: Tkachuk S. , Bowen D. , Nistor I. , Krafft C. , Mayergoyz I.
Published: February 2008

The study of BiPrGdLu garnet films epitaxially grown on (210)-oriented substrates for use as magneto-optical imagers is reported. These garnet films exhibit the phenomena of easy magnetization plane which makes them attractive in imaging applications. It is demonstrated that the thickness reduction of garnet films through chemical etching enhances the clarity and spatial resolution of magneto-optical imaging.
Interaction effects in Permalloy nanowire systems
Authors: Pardavi-Horvath M. , Si P. E. , Vazquez M. , Rosa W. O. , Badini G.
Published: February 2008

Two series of self-organized hexagonal arrays of uniaxial Permalloy nanowires are grown by electroplating, filling of nanopores in anodic alumina films. Nanowires with periodicities of 65 and 105nm and wire diameter of 25–60nm were investigated by magnetization and ferromagnetic resonance (FMR) measurements. The length of the wires is 2.5μm, the volume ratio 0.13⩽v⩽0.43. A crossover transition from a one-dimensional easy axis “wire” behavior of weakly interacting uniaxial nanowires to a two-dimensional behavior of strongly coupled “wire film” having an easy plane anisotropy is determined from FMR measurements. The crossover occurs at v=0.27 for 105nm periodicity, and v=0.43 for 65nm periodicity. The system of the thinnest nanowires corresponds to a statistical ensemble of weakly interacting uniaxial particles, characterized by the highest coercivity of 1276Oe, the highest switching field distribution, and highest FMR linewidth, resulting from the broad distribution of individual wires. The coercivity monotonously decreases to 440Oe with increasing nanowire radius and volume fraction, as the wire shape anisotropy is reduced and the array anisotropy takes over due to dipolar interwire interaction, smoothing out the individuality of the wires. The behavior of coercivity, switching field distribution, and FMR linewidth is in accordance with the increase of the coupling of the nanowires.
Orbital order in electron-doped manganites
Authors: Schlottmann P.
Published: February 2008

In electron-doped LaMnO3, La is partially substituted by tetravalent Ce, and Mn has a valence between 2 and 3. Mn2+ ions have five localized 3d electrons (half-filled shell) and a spin S*=5∕2. The Mn3+ configuration corresponds to an eg hole in the half-filled shell yielding a total spin S=2. A mean-field slave-boson formulation for hole doping has been extended to electron doping. For eg holes in two orbitals with excluded multiple occupancy and Hund’s rule coupling between the eg and t2g states, we study the conditions for staggered orbital order in the A phase for electron doping. The long-range staggered order of the eg orbitals arises due to the competition of the superexchange, the double exchange, and the Jahn–Teller effect.
Single cell gap and wide-view transflective liquid crystal display using fringe field switching and embedded wire grid polarizer
Authors: Ge Zhibing , Wu Thomas X. , Wu Shin-Tson
Published: February 2008

A single cell gap and wide-view transflective liquid crystal display (TR-LCD) using fringe field switching and embedded wire grid polarizer as polarization dependent reflector is developed. Such a device structure does not require any quarter-wave plate or in-cell phase retarder. Through optimizing the pixel electrode width and gap, high transmittance and reflectance and a single gamma curve are obtained. Potential application of this TR-LCD for mobile displays is emphasized.
RimO, a MiaB-like enzyme, methylthiolates the universally conserved Asp88 residue of ribosomal protein S12 in
Escherichia coli
Authors: Anton Brian P. , Saleh Lana , Benner Jack S. , Raleigh Elisabeth A. , Kasif Simon , Roberts Richard J.
Published: February 2008

Ribosomal protein S12 undergoes a unique posttranslational modification, methylthiolation of residue D88, in
Escherichia coli
and several other bacteria. Using mass spectrometry, we have identified the enzyme responsible for this modification in
E. coli
, the
yliG
gene product. This enzyme, which we propose be called RimO, is a radical-
S
-adenosylmethionine protein that bears strong sequence similarity to MiaB, which methylthiolates tRNA. We show that RimO and MiaB represent two of four subgroups of a larger, ancient family of likely methylthiotransferases, the other two of which are typified by
Bacillus subtilis
YqeV and
Methanococcus jannaschii
Mj0867, and we predict that RimO is unique among these subgroups in its modification of protein as opposed to tRNA. Despite this, RimO has not significantly diverged from the other three subgroups at the sequence level even within the C-terminal TRAM domain, which in the methyltransferase RumA is known to bind the RNA substrate and which we presume to be responsible for substrate binding and recognition in all four subgroups of methylthiotransferases. To our knowledge, RimO and MiaB represent the most extreme known case of resemblance between enzymes modifying protein and nucleic acid. The initial results presented here constitute a bioinformatics-driven prediction with preliminary experimental validation that should serve as the starting point for several interesting lines of further inquiry.
Efficacy of Personal Response Systems (“Clickers”) in Large, Introductory Psychology Classes
Authors: Morling Beth , McAuliffe Meghan , Cohen Lawrence , DiLorenzo Thomas M.
Published: February 2008

Four sections of introductory psychology participated in a test of personal response systems (commonly called “clickers”). Two sections used clickers to answer multiple-choice quiz questions for extra credit; 2 sections did not. Even though we used clickers very minimally (mainly to administer quizzes and give immediate feedback in class), their use had a small, positive effect on exam scores. On anonymous course evaluations, students in 1 clicker section reported that regular attendance was more important, but otherwise, students in clicker sections (compared to traditional sections) did not report feeling significantly more engaged during class. We suggest that future researchers might combine clicker technology with other, established pedagogical techniques.
The clonal composition of biramous and uniramous arthropod limbs
Authors: Wolff Carsten , Scholtz Gerhard
Published: February 2008

We present the first comparative cell lineage analysis of uniramous and biramous limbs of an arthropod, the crustaceanOrchestia cavimana. Via single cell labelling of the cells that are involved in limb development, we are able to present the first complete clonal composition of an arthropod limb. We show that the two main branches of crustacean limbs, exopod and endopod, are formed by a secondary subdivision of the growth zone of the main limb axis. Additional limb outgrowths such as exites result from the establishment of new axes. In contrast to general belief, uniramous limbs inOrchestiaare not formed by the loss of the exopod but by suppression of the split into exopod and endopod. Our results offer a developmental approach to discriminate between the different kinds of branches of arthropod appendages. This leads to the conclusion that a ‘true’ biramous limb comprising an endopod and an exopod might have occurred much later in euarthropod evolution than has previously been thought, probably either in the lineage of the Mandibulata or that of the Tetraconata.
Sheep in wolf's clothing: host nestling vocalizations resemble their cowbird competitor's
Authors: Pagnucco Katie , Zanette Liana , Clinchy Michael , Leonard Marty L
Published: February 2008

Nestlings of many avian brood parasites are virtuosos at mimicking host nestling vocalizations, which, like egg mimicry, presumably ensures acceptance by host parents. Having been accepted, parasitic nestlings then often exaggerate the aspects of the host's display to increase parental care. Host nestlings may, in turn, exaggerate their vocalizations to keep up with the parasite, though this possibility has not been evaluated. We experimentally parasitized song sparrow (Melospiza melodia) nests with a brown-headed cowbird (Molothrus ater) chick to evaluate how host nestlings respond. Vocalizations emitted from experimentally parasitized nests were higher in frequency, and louder, than those from unparasitized nests, consistent with the cowbird exaggerating its signalling. In response, host nestlings exaggerated the frequency and amplitude of their vocalizations, such that they resembled the cowbird's while they ‘scaled back’ on calls per parental provisioning bout. Sparrows in parasitized nests were fed equally often as sparrows in unparasitized nests, suggesting that exaggerating some aspects of vocalization while scaling back on others can help host nestlings confronted with a cowbird. Our results support the recently proposed hypothesis that signalling in parasitized nests involves a dynamic interaction between parasitic and host nestlings, rather than a one-way process of mimicry by the parasite.
Sex‐specific somatic–otolith growth relationship in two Gadidae
Authors: Vallisneri M. , Trotta V. , Cavicchi S. , Piccinetti C.
Published: February 2008

Otolith and somatic mass of two Gadidae (Merlangius merlangus and Trisopterus minutus) were compared in order to analyse the sex‐specific relationship between otolith and somatic growth at age. In the present study, otolith mass appeared a reliable indicator of age in both species. Otolith growth reflected somatic growth, but the relationship between these characters varied and differed between species and sexes.
First record of saddleback syndrome in wild parrotfish Sparisoma cretense (L., 1758) (Perciformes, Scaridae)
Authors: Koumoundouros G.
Published: February 2008

The saddleback syndrome is recorded for the first time in a wild fish population of the Mediterranean Sea. The deformed specimen belongs to Sparisoma cretense and presents the typical saddleback phenotype of missing spines in the dorsal fin.
Embryonic mortality and predation on egg capsules of the Port Jackson shark Heterodontus portusjacksoni (Meyer)
Authors: Powter D. M. , Gladstone W.
Published: February 2008

Egg capsules of the Port Jackson shark Heterodontus portusjacksoni were examined during underwater visual census surveys at two sites in New South Wales, Australia, during the 2002–2005 reproductive seasons (austral winter). Embryonic mortality was high (0·783–0·896 per annum) with the majority (99·2%) resulting from predation. The crested horn shark Heterodontus galeatus and common tent shell Astralium tentoriformis (Gastropoda, Turbinidae) were positively identified as egg predators. Gastropod predation was insignificant, accounting for only 2·0 and 2·1% of total mortality at Terrigal Haven and Dent Rock, respectively. Most capsules appeared to have been depredated by large predatory fishes with the eastern blue groper Achoerodus viridis (Labridae) and the black stingray Dasyatis thetidis (Dasyatidae) as possible candidate predators. The rate of embryonic mortality in H. portusjacksoni is higher than that reported for other oviparous elasmobranchs. This high level of mortality has significant consequences for the conservation and management of this species, especially when combined with an understanding of their low fecundity, late maturity and protracted reproductive life.
Ultrastructural changes induced in cutaneous collagen by ultraviolet‐A1 and psoralen plus ultraviolet A therapy in systemic sclerosis
Authors: SAKAKIBARA Noriyuki , SUGANO Shigeru , MORITA Akimichi
Published: February 2008

In the present study, we examined the ultrastructural alterations in collagen fibrils clinically softened by ultraviolet‐A1 (UVA1, 340–400 nm) therapy and psoralen plus long‐wave ultraviolet (PUVA) therapy and compared collagen fibril diameters in four patients with systemic sclerosis (SSc). In skin sclerosis, the dermis is compacted from the epidermal layer to the sweat glands, and the collagen bundles are thicker with decreased space between them. We obtained skin specimens before and after UVA1 or PUVA therapy, and compared cutaneous alterations in one diffuse‐type patient and one limited‐type patient following UVA1 therapy, and in two diffuse‐type patients following PUVA treatment. Ultramicroscopic analysis revealed that UVA1 treatment decreased the diameter of the broad collagen fibrils, mainly in the upper reticular layer. PUVA induced similar alterations in the collagen fibrils, extending to the upper and middle reticular layers. PUVA therapy induced alterations in collagen fibril diameter in deeper layers than did UVA1 therapy, which might be related to the direct action of UV light and the depth of the light penetration. In three of four patients, collagen fibril diameter decreased, collagen fibril thickness equalized, and new, thin fibrils developed among the collagen fibrils, suggesting that collagen degradation and synthesis underlie the alterations induced by UVA1 and PUVA phototherapies.