bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiparticle simulation methods applied to the micromechanics of bed load transport
Authors: Jiang Z. , Haff P. K.
Published: February 2004

We solve the Newtonian equations of motion to follow the trajectories of each of a large number of two‐dimensional circular bed load particles as they move in response to stresses exerted by an overlying fluid. The fluid is modeled as a moving layer or “slab” which exerts a velocity‐dependent drag force on embedded particles and satisfies its own momentum balance equation. Bed load mass flux and hop length and hop height statistics of simulated beds resemble those observed in the laboratory. By marking particles originally residing on the surface, vertical mixing of sediment is investigated. An injection of fine particles into a bed load system of coarse particles under traction illustrates the early stages of the evolution of sedimentary stratigraphy. Friction angles and their distribution are investigated as a function of bed transport history and particle size. The main thrust of the paper, however, is to describe and test a microscopic bed load model which engineers, geologists, and biologists may find useful for applications where particle arrangement and relative particle motion are important.
Steady infiltration from a semicircular cylindrical trench and a hemispherical pond into unsaturated soil
Authors: Waechter R. T. , Mandal A. C.
Published: February 2004

The boundary layer methods which have been used to describe wave propagation past obstacles in the regions of glancing incidence have particular relevance to the asymptotic treatment, for large s, of steady infiltration as modeled by Philip's quasi‐linearization. Here s(= αl/2) is defined as the ratio of the characteristic length l of the water supply surface (in fact, its radius) to the sorptive length 2α−1 of the soil. In this paper the steady infiltration from surface sources which are either semicircular in cross section or hemispherical are considered. Unlike the cases of buried sources considered by Waechter and Philip (1985), where an exact solution is available, we do not have an exact solution here. However, we resolve the structure of the large s asymptotics using the advantages of the scattering analog with the elegance of boundary layer methods. In particular, we calculate the mean infiltration rates (4/π)(1 + 0.6954s−2/3) and (1 + 1.3909s−2/3) for trench and hemispherical pond respectively and compare these with those for the corresponding cases of buried sources. We also compare our dimensionless total flux for a trench with that for a shallow trench of Pullan and Collins (1987) and our dimensionless total flux for a hemispherical cavity with that for a large shallow pond of Weir (1986).
Modeling of carbon dioxide transport and production in soil: 2. Parameter selection, sensitivity analysis, and comparison of model predictions to field data
Authors: Suarez Donald L. , Šimůnek Jiří
Published: February 2004

In paper 1 of this two‐paper series (Šimůnek and Suarez, this issue) we presented a description of the numerical model, SOILCO2, for CO2 transport and production in the unsaturated zone. In paper 2 the model sensitivity to various parameters is evaluated by both steady state and transient simulations, with a range in the parameter values typically found under field conditions. We also select parameter values for optimal plant and microbial CO2 production and production dependence on temperature, water content, osmotic potential and gas composition for plant and microbial respiration, all based on literature review. The predictive capabilities of the SOILCO2 model are evaluated by comparing model simulations to published field data from Missouri for three different crops and two growing seasons under transient conditions as well as a data set collected in Riverside, California, under relatively constant water content at depth. The model provided good prediction of the CO2 flux to the atmosphere as well as the concentrations in the root zone for all data sets.
An entropy‐based morphological analysis of river basin networks
Authors: Fiorentino Mauro , Claps Pierluigi , Singh Vijay P.
Published: February 2004

Under the assumption that the only information available on a drainage basin is its mean elevation, the connection between entropy and potential energy is explored to analyze drainage basins morphological characteristics. The mean basin elevation is found to be linearly related to the entropy of the drainage basin. This relation leads to a linear relation between the mean elevation of a subnetwork and the logarithm of its topological diameter. Furthermore, the relation between the fall in elevation from the source to the outlet of the main channel and the entropy of its drainage basin is found to be linear and so is also the case between the elevation of a node and the logarithm of its distance from the source. When a drainage basin is ordered according to the Horton‐Strahler ordering scheme, a linear relation is found between the drainage basin entropy and the basin order. This relation can be characterized as a measure of the basin network complexity. The basin entropy is found to be linearly related to the logarithm of the magnitude of the basin network. This relation leads to a nonlinear relation between the network diameter and magnitude, where the exponent is found to be related to the fractal dimension of the drainage network. Also, the exponent of the power law relating the channel slope to the network magnitude is found to be related to the fractal dimension of the network. These relationships are verified on three drainage basins in southern Italy, and the results are found to be promising.
Experimental constraints on bar migration through bends: Implications for meander wavelength selection
Authors: Whiting Peter J. , Dietrich William E.
Published: February 2004

The bed of an initially straight channel often deforms into a series of migrating alternate bars that can cause bank erosion and the development of periodic planform curvature which is often expressed as a meandering channel trace. The planform curvature in turn leads to topography similar to alternate bars, but stationary with respect to the meander. The migration of alternate bars over this steady topography may lead to interactions influencing meander initiation and wavelength selection. We studied these interactions in flume channels with bends of various lengths and angles, and having various width‐to‐depth ratios. In channels whose wavelength was equal to the length of bars in straight channels (nearly eight channel widths), bars migrated through sine‐generated channels with angles up to 10°. The critical bend angle was smaller for channels of longer wavelength and smaller width‐to‐depth ratio. Migration was nonuniform, and bars temporarily stalled when in phase with the curvature‐induced topography, leading to amplification of the topography. Flow against an opposing bank can lead to such a strong boundary shear stress divergence that migration of the bars is prevented because sediment that otherwise would have led to bar migration is scoured from the bar front. We propose that the amplification of bar‐pool topography in bends where free alternate bars are stalled enhances scour of the bank which leads to selection of a meander wavelength equal to that of the alternate bars.
Stochastic analysis of unsaturated steady state flow through bounded heterogeneous formations
Authors: Indelman Peter , Or Dani , Rubin Yoram
Published: February 2004

The effect of heterogeneity in saturated hydraulic conductivity (Ks) and in a pore‐scale distribution parameter (α) on unsaturated steady state flow in bounded domains is studied. The properties are assumed to be random space functions having stationary means and covariances. An analytic model based on small‐perturbation approximation in Ks and α for predicting the spatial moments of the pressure head from the moments of the input variables is developed. The solution applies to the entire unsaturated domain without invoking the unit mean hydraulic gradient assumption. Under conditions of small‐scale variability the solution simplfies considerably resulting in closed‐form expressions for the moments of the pressure head. These expressions are tested in synthetically generated random fields of α and Ks having prescribed statistical properties.
Horton's Laws and the fractal nature of streams
Authors: Beer Tom , Borgas Michael
Published: February 2004

Stream networks and catchment basins are characterized by numerous fractal dimensions, the traditional one being the mainstream length as a function of length scale which we denote by d. We consider an ideal Horton system and define fractal dimensions based on (1) the subcatchment length‐area relationship, which gives D1; (2) the total length of streams as a function of scale, which gives a network similarity dimension D2; (3) the mainstream length‐area relationship (D3), and (4) the total area of streams as a function of areal scale (D4). These fractal dimensions are related to the values of the bifurcation ratio, the stream length ratio, and the stream area ratio. Their value should be indirectly estimated from these Horton parameters. An improved understanding of the relationships between the fractal dimension and Horton's laws is obtained by defining an eigenarea of a stream of a particular Horton order. This is the area of the drainage basin which is not drained by streams of immediately lower order. The variation of eigenareas with scale controls the value of D1, which equals D3 for hydrologically realistic systems. In such cases D4 = 2. This paper assumes that river systems are Hortonian in nature and that measured departures from Hortonianity are due to statistical variability. Estimates of the Horton parameters and of the fractal dimensions are therefore subject to uncertainty. Two sources of statistical variability are considered herein: The first source of statistical variability is due to the fluctuations in stream numbers, stream lengths, and stream areas. These fluctuations affect the values of the Horton parameters, which are traditionally estimated using a graphical technique. We show that an analytical technique (which corresponds to a constrained graphical technique) is preferable. The second source of variability that we consider arises from the fact that estimates of Horton's parameters and fractal dimensions are always made on truncated systems because the particular scales of measurement determine the order of the catchment. In a Horton system it is straight forward to estimate D1, which is defined exactly at all scales. Direct attempts to estimate D2 and D3 (as opposed to indirect attempts via the Horton parameters) are difficult because their true value is approached asymptotically in the limit of infinite‐order catchments.
New control concepts for uncertain water resources systems: 2. Reservoir management
Authors: Yao Huaming , Georgakakos Aris P.
Published: February 2004

Reservoir management decisions continuously strive to balance conflicting risks and benefits. Hydrologic uncertainty is a major complicating factor, especially during extreme events when data are sparse and probabilistic characterizations are less reliable. The set control approach offers an alternative by assuming that inputs are unknown but bounded. The solution provides a set of control actions which guarantee that the system will operate within the stated constraints for a certain time horizon. The method is applied to a three‐reservoir system in the southeastern United States.
Real‐time rainfall prediction at small space‐time scales using a two‐dimensional stochastic advection‐diffusion model
Authors: Jinno Kenji , Kawamura Akira , Berndtsson Ronny , Larson Magnus , Niemczynowicz Janusz
Published: February 2004

A model based on the two‐dimensional stochastic advection‐diffusion equation is developed to forecast properties of individual rain cells in urban areas such as speed and spatial rainfall intensity. Two different modeling approaches are employed, and examples of the results are given. The first approach involves a Gaussian distribution as an analytic solution to the advection‐diffusion equation, whereas the second one entails a double Fourier series expansion of the rainfall intensity field. Both modeling approaches are used to predict the rainfall intensity field over a small 12‐gage urban catchment in southern Sweden. The model parameters are continuously updated by extended Kalman filtering. The Fourier series approach is shown to be the most flexible for practical applications and to give the most accurate forecasts. This model approach gives acceptable forecasts for a lead time of 1–5 min. It gives consistently smaller prediction errors compared to both the Gaussian solution and simple extrapolation calculations. The effect of system noise level on the forecast accuracy and model performance is discussed. The model can be used not only to predict in real time the spatial rainfall, but also to parameterize the variability pattern of small‐scale spatial rainfall into a set of physically based parameters, thus separating the effects of advective velocity, turbulent diffusion, and development/decay.
A simplified Newton Iteration Method with linear finite elements for transient unsaturated flow
Authors: Li C. W.
Published: February 2004

A simplified Newton iteration method with Galerkin linear finite elements is developed for the solution of the nonlinear transient unsaturated flow equation in “mixed” form. The use of the Galerkin linear finite element method in the spatial discretization produces a recurrence equation in which the interaode hydraulic conductivity is represented by an integrated average expression which generates the exact Darcy flow flux through each element under the steady horizontal flow condition. The numerical computation of the integrated average hydraulic conductivity using Simpson's 1/3 rule leads to an accurate solution even in the presence of a sharp front. In the time discretization using a backward Euler scheme, the standard Newton iteration method is simplified by taking account of the integrated average expression of the hydraulic conductivity and the diffusion‐dominated nature of the flow process. The resulting two‐level scheme is of the same efficiency on a per‐iteration basis as the modified Picard scheme but converges at a faster rate.
Optimal channel networks: A framework for the study of river basin morphology
Authors: Rigon Riccardo , Rinaldo Andrea , Rodriguez‐Iturbe Ignacio , Bras Rafael L. , Ijjasz‐Vasquez Ede
Published: February 2004

Optimal channel networks (OCNs) are dendritic structures obtained by minimizing the local and global rates of energy dissipation in a continuously fed (in space and time) plane aggregation system reminiscent, and based on the properties, of the planform of three‐dimensional natural drainage networks. Geomorphological and fractal properties of OCNs are known from earlier studies by the authors. This paper explores further the structures derived by optimization of energy dissipation rates. Optimality of subnetworks and of basin shapes is investigated as a by‐product of competition for drainage. A new perspective on the possible prediction of the width function of a basin network, and hence of its hydrologic response, is obtained by exploiting OCN techniques, requiring only the definition of the outer boundaries of the basin. The interplay between hillslope processes and the development of drainage networks is addressed, aiming at the relative role and the mutual interrelations of geology and optimal organization in the structure of mature river basins. Also addressed is the issue of multiscaling and multifractality in the spatial organization of the network. It is concluded that OCN approaches provide a comprehensive framework for the study of the morphology of geophysical structures.
The sizes of salmonid spawning gravels
Authors: Kondolf G. Mathias , Wolman M. Gordon
Published: February 2004

The availability of suitably sized spawning gravels limits salmonid (salmon and trout) populations in many streams. We compiled published and original size distribution data to determine distinguishing characteristics of spawning gravels and how gravel size varies with size of the spawning fish. Median diameters of 135 size distributions ranged from 5.4 to 78 mm, with 50% falling between 14.5 and 35 mm. All but three spawning gravel size distributions were negatively skewed (on a log‐transformed basis), with 50% of the skewness coefficients falling between −0.24 and −0.39. Fewer than 20% of the distributions were bimodal. Although tending to be coarser, spawning gravels had sorting and skewness values similar to other fluvial gravels reported in the literature. The range of gravel sizes used by fish of a given species or length is great, but the relation between fish size and size of gravel can be described by an envelope curve. In general, fish can spawn in gravels with a median diameter up to about 10% of their body length.
Algebraic models for disc tension permeameters
Authors: Hussen A. A. , Warrick A. W.
Published: February 2004

Four infiltration models for disc tension permeameters were compared to field and simulated data. Comparisons were made in order to assess the alternative values of sorptivity and steady state flow rates. Model 1 was the conventional analysis with assumptions of one‐dimensional flow at small times and Wooding's steady state flow rate at large times. Model 2 was a modified Horton equation defined to fit one‐dimensional infiltration at small times with an exponential decay to a steady state value for large times. Model 3 assumed linear diffusion for a soil with constant diffusivity ignoring gravity. Model 4 was based on “linearized” flow with gravity. The number of unknown parameters to be estimated ranged from one to four. Sorptivity data using models 2 and 3 generally agreed with the conventional method (model 1) both for the field and simulated data. For the steady state infiltration rate, all of the models gave generally consistent results. Model 2 with four parameters was the best fitting model to field and simulated data. The simulated data allowed comparisons of results based on the total time over which the parameters were evaluated. Results were sensitive to the time of evaluation up to 0.3–1.3 hours for the sandy loam soil.
Enhancement of uranium 234 in springwaters of Águas da Prata, São Paulo, Brazil
Authors: Bonotto Daniel Marcos
Published: February 2004

Springwater samples were collected at Águas da Prata, an important spa in Sāo Paulo State, Brazil. The 238U and 234U isotopes were evaluated for Platina, Paiol, Villela, Prata‐Radioativa, Prata‐Nova, Boi, Vitória, and Prata‐Antiga springs. An inverse logarithmic correlation was found between 234U/238U activity ratio and 222Rn content of the studied waters, which was related to different solution mechanisms of 222Rn and 234U nuclides at the rock‐water interface. A linear correlation also exists between the 234U/238U activity ratios of the studied waters and total dissolved solids, ionic strength, CO2 partial pressure, and index of base exchange, which indicates that the enhancement of 234U in solution increases with the degree of weathering in the aquifers. A higher 234U/238U activity ratio was found to be directly related to a higher value of dissolution rate.
The influence of hydrologic conditions and peat oxia on the phosphorus and nitrogen dynamics of a conifer swamp
Authors: Devito Kevin J. , Dillon Peter J.
Published: February 2004

A mass balance approach was used to determine the factors influencing phosphorus and nitrogen dynamics in wetlands common to headwater catchments of the Precambrian Shield. The relationships of runoff, water level, water temperature, and anoxia to the annual and seasonal total phosphorus (TP) and total nitrogen (TN) retentions of a headwaterSphagnum‐conifer swamp during 1987–1988 were examined. Annual retentions of TP (4%) and TN (10%) were low in the swamp. On an annual basis, inputs exceeded outputs of total reactive P, NO3‐N, and NH4‐N and outputs exceeded inputs of total unreactive P and total organic N. Seasonal trends in P and N retention were inversely correlated with runoff. Positive monthly retention coincided with low runoff and increased biotic assimilation during the growing season. Water table drawdown during the summer was associated with peat aeration and increased levels of P and N in surface and pore water. High levels of P and N in the swamp surface water during the fall and winter were coupled with increased runoff, saturated overland flow, and potentially low biotic assimilation resulting in a net release of TP and TN. Large flow through of waterborne inputs and flushing of regenerated P and N occurred during peak snowmelt runoff resulting in low annual retention.
Geophysical‐hydrological identification of field permeabilities through Bayesian updating
Authors: Copty Nadim , Rubin Yoram , Mavko Gary
Published: February 2004

A new Bayesian method is developed to identify the spatial distribution of permeabilities. In addition to sparsely sampled permeability and pressure data, this approach incorporates densely sampled seismic velocity data along with semiempirical relationships between seismic and hydraulic soil properties. The procedure consists first of performing a hydrological inversion based solely on the permeability and pressure data. In light of the available seismic data, the velocity‐permeability‐pressure relationships are then used to update, in a Bayesian sense, the image of the permeability field. To investigate the usefulness of this approach, synthetic case studies are performed. These studies demonstrate that, even when the seismic data are corrupted by a significant level of error, a joint geophysical‐hydrological inversion can produce improved images of permeability. Moreover, this paper derives rigorously the bounds on the error that can be tolerated in seismic velocities such that they are still useful for hydrological purposes.
Long‐term trends in Pamlico River Estuary nutrients, chlorophyll, dissolved oxygen, and watershed nutrient production
Authors: Stanley Donald W.
Published: February 2004

Trends in Pamlico River estuary ammonia nitrogen (NH4), nitrate nitrogen (NO3), phosphate phosphorus (PO4), chlorophyll a (chl a) and dissolved oxygen (DO) during the past 20–24 years were analyzed, and estimates of annual N and P production in the watershed over the past century were computed. The goal of the study was to determine whether or not the estuary is becoming more eutrophic. NO3 has decreased in the upper and middle regions of the estuary by 3–6% yr−1 since 1970, and NH4 has decreased throughout the estuary at an annual rate of 5.5–7.7% yr−1. Since 1967 PO4 has increased by 2% yr−1 in the lower two thirds of the estuary due to discharges from a phosphate mining facility. Thus the inorganic N:P ratio has decreased, which suggests that N is now potentially more limiting than in the past. In the upper estuary, chl a increased at a rate of 6.6% yr−1 since 1970, and bottom water DO decreased very slightly; neither showed trends in the middle and lower estuary regions. The weight of the evidence is that the Pamlico has not become more eutrophic during the past two decades. This finding is corroborated by the lack of a trend since 1970 in calculated N and P production from point and nonpoint sources in the watershed. Watershed nutrient production is estimated to have increased severalfold between 1880 and 1970, but appears to have stabilized after 1970, due primarily to decreased application of fertilizer on croplands.
Multilayered leaky aquifer systems: 1. Pumping well solutions
Authors: Cheng A. H.‐D. , Morohunfola O. K.
Published: February 2004

This paper presents an analytical solution of a radial flow to a pumping well at constant discharge located in a multilayered leaky aquifer system. The aquifer system is composed of alternating layer of aquifers and aquitards and is modeled after the theory of Neuman‐Witherspoon and Herrera. The resulting coupled integrodifferential equation system is handled by the Laplace transform technique which removes not only the time variable but also the convolutional integral. Green's functions for the coupled elliptic partial differential equations are then sought. Utilizing a numerical Laplace inversion algorithm, the drawdown at any given time and location in any layer can be evaluated. Several examples are given for validation and exploration purposes.
Reliability assessment of water supply systems with storage and distribution networks
Authors: Fujiwara Okitsugu , Ganesharajah Tharmarajah
Published: February 2004

The water supply system studied in this paper consists of a water treatment plant, a ground‐level storage, a pumping station, and a distribution network in series. Expected served demand is employed to measure reliability taking into account both insufficient heads and flows at individual nodes in the network since it is the most important service level index provided to individual users. A basic method proposed is to assume that the insufficient nodal head reduces the effectiveness of flow supplied at the node and that the authority provides the maximum service to customers so that the real‐time pump and network flow operations maximize the effective served system demand. The average value of the maximum effective served system demand relative to the total system demand over all system states is defined as system reliability, and the nodal reliability for each demand node is similarly defined. The Markov chain method introduced by Beim and Hobbs (1988) is employed to describe the evolution of the storage level over time so that the real‐time pump and network flow operations can be accurately implemented by solving a nonlinear programming model. Two example systems are presented to demonstrate numerically the advantage of the method proposed in its consideration of the distribution network and nodal reliabilities.
Series solutions for steady seepage through hillsides with arbitrary flow boundaries
Authors: Read W. W. , Volker R. E.
Published: February 2004

Quantification of seepage through hillsides is important to the understanding of landscape hydrology, run‐off generation, erosion processes, and the transport of solutes. For complicated flow domains, numerical solutions have the propensity to be computationally expensive and inaccurate. Analytical solutions are therefore inherently valuable; they also provide a means of checking the accuracy of numerical solutions and, because they provide continuous velocity fields, are extremely useful in generating descriptions of solute transport. This paper presents a method for obtaining analytical solutions for seepage in the saturated zone of homogeneous hillsides with arbitrary surface geometry, using a least squares method to determine the coefficients in a series expansion of the Laplace equation. It determines the (initially unknown) water table location and accommodates arbitrary shapes of the lower impermeable boundary. Flow solutions for a variety of flow domain geometries are provided, with the upper and lower boundaries expressed as cubic splines and piecewise linear polynomials.
Effect of mud penetration on borehole skin properties
Authors: Abboud Nelly M. , Corapcioglu M. Yavuz
Published: February 2004

Clay particles in drilling muds can form a filter cake (skin) on the walls of the well and migrate into the adjacent formation. In general, filter cakes are formed when a liquid phase containing solid particles is forced through a pervious surface which allows liquid transport, while retaining solid particles. Following a literature survey, the governing equations for the concentration of suspended solid particles in the pore fluid, cake permeability, and solid velocity are obtained by considering the mass balance equations for the fluid phase and suspended and captured solid particles. The capture mechanism is represented by a kinetic equation with rate constants for particle trapping and cake erosion. Numerical solutions for the cake permeability, cake resistance, solid particle velocity (cake compression rate), and concentration of suspended particles are obtained by utilizing experimentally available porosity and pressure variations along the dimensionless cake thickness. The results compared for a simplified experimental case, show excellent match. A sensitivity analysis shows that cake permeability and cake resistance are more sensitive to the rate constant of cake erosion than they are to the rate constant of particle capture. It was also determined that the permeability has larger values along the entire cake thickness when the rate constant of particle capture is zero in comparison to values obtained with a nonzero rate constant. Cake permeability is small when the rate constant of cake erosion is large.
Numerical simulation of chemical migration in physically and chemically heterogeneous porous media
Authors: Tompson Andrew F. B.
Published: February 2004

A series of chemical transport simulations in saturated porous media are conducted to examine the coupled impacts on chemical mobility induced by nonuniform sorption reactions and heterogeneous flow fields. The simulations involve the calculation of fluid flow and chemical migration within highly resolved, three‐dimensional cubic regions with synthetically derived material properties. Nonuniformities in subsurface materials are represented as randomly correlated hydraulic conductivity and sorption partition coefficent fields. Transport computations are based upon a random walk particle model, appropriately modified to treat equilibrium sorption reactions. Current experiments focus on four hypothetical constituents, one being inert, and the other three independently obeying linear, Freundlich, and Langmuir partitioning relationships. Results show distinct effects of the nonuniform flow and sorption processes on the overall displacement, dispersion, and partitioning/retardation and the breakthrough behavior of the constituent plumes, as well as on the sharpening fronts and skewed concentration profiles associated with nonlinear partitioning models.
Analytical models of steady state organic species transport in the vadose zone with kinetically controlled volatilization and dissolution
Authors: Zaidel Jacob , Russo David
Published: February 2004

Kinetically controlled volatilization and dissolution of nonaqueous phase liquids (NAPLs) may play an important role in the transport of volatile compounds in the unsaturated (vadose) zone. In this study, some one‐ and two‐dimensional steady state transport problems are solved analytically. The one‐dimensional case is pertinent to pollution by a relatively long, mainly horizontally spread leak of NAPL. The two‐dimensional case corresponds to situations in which the pollution spreads primarily vertically, originating at the ground surface and migrating to the top of the capillary fringe, and in which the solution domain may be represented by a cross‐sectional model. Solutions of the steady state transport problems are used to investigate effects of several parameters, characterizing the advective‐dispersive and purely diffusive transport regimes, on the NAPL concentration distribution for the one‐ and two‐dimensional cases, respectively. Results of this analysis indicate that the mass exchange between NAPL and other phases may not reach equilibrium, even for relatively large mass transfer rate coefficients and small water infiltration rates, if this zone has relatively small vertical or horizontal extent and is located close to the fully open ground surface. Analysis of local volatilization and dissolution fluxes shows that, under equilibrium conditions, the main losses of the organic phase take place at the upper part of the NAPL zone.
Correction of stream quality trends for the effects of laboratory measurement bias
Authors: Alexander Richard B. , Smith Richard A. , Schwarz Gregory E.
Published: February 2004

We present a statistical model relating measurements of water quality to associated errors in laboratory methods. Estimation of the model allows us to correct trends in water quality for long‐term and short‐term variations in laboratory measurement errors. An illustration of the bias correction method for a large national set of stream water quality and quality assurance data shows that reductions in the bias of estimates of water quality trend slopes are achieved at the expense of increases in the variance of these estimates. Slight improvements occur in the precision of estimates of trend in bias by using correlative information on bias and water quality to estimate random variations in measurement bias. The results of this investigation stress the need for reliable, long‐term quality assurance data and efficient statistical methods to assess the effects of measurement errors on the detection of water quality trends.
Experimental Studies of bed topography and flow patterns in large‐amplitude meanders: 2. Mechanisms
Authors: Whiting Peter J. , Dietrich William E.
Published: February 2004

Large‐amplitude river meanders develop multiple scour holes within a single bend that are observed to be part of overlapping shingle bars (Whiting and Dietrich, this issue). These bars, having wavelengths near 4 channel widths, consist of a pool along the outer concave bank and a depositional lobe along the inner convex bank. The development of multiple pools and lobes within a bend has been shown to cause localized bank erosion and channel trace distortion expressed as planform asymmetry and compound heads. In this second paper we describe experiments designed specifically to test hypotheses that propose multiple pools to be the result of an overshoot phenomenon, to be a consequence of an alternate bar‐like instability, or to develop from a flow/planform instability. Although our experiments favor the hypothesis that multiple bars in bends of large amplitude arise from an alternate bar‐like instability, experiments conducted over an immobile flat bed also reveal longitudinal oscillations in flow that may arise in these long bends. This secondary effect interacts with shingle bars to amplify pool expression at particular points along the channel.
An approximate solution for steady vertical flux of moisture through an unsaturated homogeneous soil
Authors: Salvucci Guido Daniel
Published: February 2004

An approximate solution is found to the differential equation governing the steady state vertical flux of moisture through an unsaturated homogeneous soil for which the dependence of hydraulic conductivity on tension head is given in the form K(Ψ) = A(B+Ψn)−1. The solution expresses the depth from the water table as a function of the capillary tension for a given rate of percolation or capillary rise. It is easily inverted to obtain explicit expressions both for the capillary tension as a function of depth and flow rate, and for the steady flow rate in terms of the capillary tension at a given depth. The latter is shown to compare favorably both to existing limiting case solutions of percolation to a water table at infinite depth, and to capillary rise from a shallow water table to an infinitely dry surface. More importantly, this solution applies to the intermediate condition where the magnitude and direction of flow are sensitive to both the near‐surface capillary tension and the water table depth.
PPARγ ligands, 15‐deoxy‐Δ12,14‐prostaglandin J2 and rosiglitazone regulate human cultured airway smooth muscle proliferation through different mechanisms
Authors: Ward Jane E , Gould Haslinda , Harris Trudi , Bonacci John V , Stewart Alastair G
Published: February 2004

The influence of two peroxisome proliferator‐activated receptor γ (PPARγ) ligands, a thiazolidinedione, rosiglitazone (RG) and the prostaglandin D2 metabolite 15‐deoxy‐Δ12,14‐prostaglandin J2 (15d‐PGJ2) on the proliferation of human cultured airway smooth muscle (HASM) was examined.

The increases in HASM cell number in response to basic fibroblast growth factor (bFGF, 300 pM) or thrombin (0.3 U ml−1) were significantly inhibited by either RG (1–10 μM) or 15d‐PGJ2 (1–10 μM). The effects of RG, but not 15d‐PGJ2, were reversed by the selective PPARγ antagonist GW9662 (1 μM).

Neither RG nor 15d‐PGJ2 (10 μM) decreased cell viability, or induced apoptosis, suggesting that the regulation of cell number was due to inhibition of proliferation, rather than increased cell death.

Flow‐cytometric analysis of HASM cell cycle distribution 24 h after bFGF addition showed that RG prevented the progression of cells from G1 to S phase. In contrast, 15d‐PGJ2 caused an increase in the proportion of cells in S phase, and a decrease in G2/M, compared to bFGF alone.

Neither RG nor 15d‐PGJ2 inhibited ERK phosphorylation measured 6 h post mitogen addition. The bFGF‐mediated increase in cyclin D1 protein levels after 8 h was reduced in the presence of 15d‐PGJ2, but not RG.

Although both RG and 15d‐PGJ2 can inhibit proliferation of HASM irrespective of the mitogen used, only the antiproliferative effects of RG appear to be PPARγ‐dependent. The different antimitogenic mechanisms of 15d‐PGJ2 and synthetic ligands for PPARγ may be exploited to optimise the potential for these compounds to inhibit airway remodelling in asthma.

British Journal of Pharmacology (2004) 141, 517–525. doi:10.1038/sj.bjp.0705630
Expansion Kinematics are an Intrinsic Property of Leaf Development and are Scaled from Cell to Leaf Level at Different Nutrient Availabilities
Authors: Walter A. , Roggatz U. , Schurr U.
Published: February 2004

Abstract: Leaves of Nicotiana tabacum L. and Ricinus communis L. develop with a wide range of different final sizes due to leaf position and nutrient availability. The aim of this study was to investigate, on different organizational levels of leaf growth, which parameters are affected by external nutrient availability and which parameters are not affected and might thus be intrinsic, general patterns of growth that govern plant architecture. We found that leaf size and final cell size was larger with higher external nutrient availability, and that hexose concentrations in N. tabacum were lower with higher nutrient availability. Despite these differences, several dynamic parameters of leaf development were not affected by the nutrient treatment. Leaves of all sizes within a species exhibited the same relationship between relative leaf growth rate and relative leaf area (RLA), which is defined as the ratio of momentary and final leaf area. External nutrient availability did not affect chlorophyll concentration per parenchyma cell, which increased linearly with leaf development. Leaves of identical RLA exhibited identical cell density patterns within their interveinal tissue layers. This indicates a close connection between the kinematics of cell expansion and RLA and, hence, reveals that kinematics are an intrinsic property of growing leaves that can be scaled from the cell to the leaf level.
Controllable Josephson current through a pseudospin-valve structure
Authors: Bell C. , Burnell G. , Leung C. W. , Tarte E. J. , Kang D.-J. , Blamire M. G.
Published: February 2004

A thin Co/Cu/permalloy (Ni80Fe20) pseudospin-valve structure is sandwiched between superconducting Nb contacts. When the current is passed perpendicular to the plane of the film a Josephson critical current (IC) is observed at 4.2 K, in addition to a magnetoresistance (MR) of ∼0.5% at high bias. The hysteresis loop of the spin-valve structure can be cycled to modulate the zero field IC of the junction in line with the MR measurements. These modulations of resistance and IC occur both smoothly and sharply with the field applied. For each type of behavior there is a strong correlation between the shape of the MR loops and the IC modulation.
Radiative and nonradiative excitonic transitions in nonpolar (112̄0) and polar (0001̄) and (0001) ZnO epilayers
Authors: Koida T. , Chichibu S. F. , Uedono A. , Sota T. , Tsukazaki A. , Kawasaki M.
Published: February 2004

Polarized optical reflectance and photoreflectance spectra of an out-plane nonpolar (112̄0) ZnO epilayer grown by laser molecular-beam epitaxy exhibited anisotropic exciton resonance structures according to the polarization selection rules for anisotropically strained hexagonal material. Consistently, the electric field component of its excitonic photoluminescence (PL) peak was polarized perpendicular to the [0001] axis. Different from the case for GaN, nonradiative PL lifetime at 293 K and the S parameter, which is a measure of Zn vacancy-related defect density obtained by positron annihilation spectroscopy, of the (112̄0) ZnO were comparable to those of state-of-the-art polar (0001̄) and (0001) epilayers. Since the polar epilayers exhibited pronounced exciton–polariton emissions, the negligible impact of growth direction on the defect incorporation suggests a potential use of epitaxial (112̄0) ZnO as polarization-sensitive optoelectronic devices operating in ultraviolet spectral regions.
Influence of growth flux and surface supersaturation on InGaAs/GaAs strain relaxation
Authors: Lynch C. , Chason E. , Beresford R. , Hong S. K.
Published: February 2004

We present results showing that the strain relaxation rate in heteroepitaxial layers depends strongly on the presence of the growth flux. These results are based on real-time stress measurements made during molecular beam epitaxy of InxGa1−xAs/GaAs (x=0.16±0.01) films grown at 452, 477, and 502 °C. Our measurements indicate that the increased relaxation rate during growth is due to an enhancement in the dislocation glide velocity. We propose a model for the dislocation velocity increase in which the growth-induced supersaturation of adatoms lowers the barrier to single kink nucleation.
Large spontaneous emission factor (>0.1) in the photonic crystal monopole-mode laser
Authors: Ryu H. Y. , Notomi M. , Kuramoti E. , Segawa T.
Published: February 2004

1.55-μm-InGaAsP photonic crystal lasers operating in the monopole mode of a triangular lattice defect cavity are realized by room-temperature optical pumping with a low threshold of <0.5 mW. By analyzing rate equations and the light–light characteristic curve, we evaluate the spontaneous emission factor (β) of this laser to be larger than 0.1, an extremely high value for photonic crystal lasers. The achievement of this large β is attributed to the facts that the investigated monopole-mode laser operates at the peak of the spontaneous emission spectrum and it shows a single-mode operation in a wide spectral range. In addition, nonclamping of carrier density near threshold and the β>0.1 are confirmed by the investigation of carrier-density dependent wavelength blueshift of the lasing mode.
Picosecond dynamics of spin-related optical nonlinearities in InxGa1−xAs multiple quantum wells at 1064 nm
Authors: Jarasiunas K. , Gudelis V. , Aleksiejunas R. , Sudzius M. , Iwamoto S. , Nishioka M. , Shimura T. , Kuroda K. , Arakawa Y.
Published: February 2004

Light-induced absorption and diffraction measurements of resonantly excited 10-nm-width InGaAs multiple quantum wells have been carried out, using circularly polarized beams at 1064 nm. Spin relaxation time τs≃280±15 ps has been determined by monitoring dynamics of light absorption bleaching at 0.04 mJ/cm2, while a nonlinearly compressed spin component in diffraction varied from 220±20 ps to 115±15 ps with excitation. The kinetics of carrier grating with randomized spins allowed the determination of the bipolar diffusion coefficient D=11.5 cm2/s, hole mobility of 230 cm2/V s, and carrier lifetime τR=0.73–1 ns.
Optical pulse compression using cascaded quadratic nonlinearities in periodically poled lithium niobate
Authors: Ashihara Satoshi , Shimura Tsutomu , Kuroda Kazuo , Yu Nan Ei , Kurimura Sunao , Kitamura Kenji , Cha Myoungsik , Taira Takunori
Published: February 2004

Efficient pulse compression was achieved by the use of cascaded quadratic nonlinearities in 10-mm-long periodically poled MgO-doped lithium niobate. An off-diagonal component of the nonlinear coefficient was utilized for group-velocity matched cascaded interactions at the fundamental wavelength of 1560 nm. Simultaneously compressed fundamental and second-harmonic pulses of ∼35 fs duration were obtained from the 110-fs-pump pulses.
Enhancement of magnetic properties by nitrogen implantation to Mn-implanted p-type GaN
Authors: Baik Jeong Min , Shon Yoon , Kang Tae Won , Lee Jong-Lam
Published: February 2004

N and Mn ions were co-implanted into p-type GaN and subsequently annealed at 700–900 °C. Compared with Mn-implanted sample, the (Mn+N)-implanted sample revealed a larger ferromagnetic signal. This was attributed to the increase of Ga–Mn magnetic phases. Mn–N compounds, such as Mn6N2.58 and Mn3N2, decreased and the resistivity significantly increased, meaning a reduction of N vacancies. It is suggested that enhancement in ferromagnetic properties in the (Mn+N)-implanted GaN originated from the reduction of N vacancies and the increase of Ga–Mn magnetic phases.
Probing the nanoscale electro-optical properties in ferroelectrics
Authors: Otto T. , Grafström S. , Chaib H. , Eng L. M.
Published: February 2004

We present an approach to inspecting the electro-optical properties of a ferroelectric crystal on the nanometer scale by applying a confined electric field E between a pointed optical fiber and the sample under investigation. Monitoring the optical transmission of barium titanate (BaTiO3) provides a complete image of the ferroelectric domain distribution in a single scan, including also antiparallel domains. The spatial resolution of ∼250 nm in this experiment is determined by the confinement of the electric field.
Analysis of Gold in Solutions Containing Ionic Liquids by Inductively Coupled Plasma Atomic Emission Spectrometry
Authors: Whitehead Jacqueline A. , Lawrance Geoffrey A. , McCluskey Adam
Published: February 2004

The analysis of gold by inductively coupled plasma atomic emission spectrometry (ICP-AES) in aqueous solution in the presence of up to 50% w/v of ionic liquid is reported. The ionic liquids investigated contain the 1-butyl-3-methyl-imidazolium (bmIm) cation with the anions Cl–, BF4–, HSO4–, or N(CN)2–. A facile route to the HSO4– salt is also described. The presence of ionic liquids alter the nebulization efficiency and sample transport properties, and the AES signal intensity and apparent concentration of gold in solution is usually suppressed as a result, principally, of increased viscosity of solutions containing an ionic liquid. However, the counterplay between a lower surface tension and a higher viscosity is illustrated by the results for the [bmIm][BF4] ionic liquid. The presence of this liquid at low concentrations causes an enhanced apparent concentration of gold whereas at higher concentrations the apparent concentration is diminished as the viscosity of the solution increases. Comparative data with simple sodium salts is also reported. Use of the standard addition method to compensate for matrix effects in the presence of ionic liquids is effective.
Indium-Mediated Addition of 4-Bromocrotonic Acid to Aldehydes and Ketones—A Simple, High Yielding Route to α-Allyl-β-Hydroxy Carboxylic Acids
Authors: Bowyer Michael C. , Gordon Charles M. , Leitch Sarah K. , McCluskey Adam , Ritchie Craig
Published: February 2004

We report a simple procedure for the indium-mediated addition of 4-bromocrotonic acid to a variety of aldehydes and ketones. In all instances the reaction proceeds exclusively with α-addition and typically in moderate to good yields (42–100%). The effect of solvent is minimal allowing a wide choice of conditions (methanol, ethanol, ethanol/water, water, tetrahydrofuran, and the ionic liquid [bmIm][BF4]).
Thermal Degradation of Ionic Liquids at Elevated Temperatures
Authors: Baranyai Krisztian J. , Deacon Glen B. , MacFarlane Douglas R. , Pringle Jennifer M. , Scott Janet L.
Published: February 2004

Ionic liquids based on the imidazolium cation are found to degrade, yielding volatile degradation products, at temperatures significantly lower than previously reported and thus a parameter Tz/x (the maximum operating temperature) is developed to provide a more appropriate estimate of thermal stability.