bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of dissolved organic carbon in forested and disturbed catchments, Westland, New Zealand: 2. Larry River
Authors: Moore T. R. , Jackson R. J.
Published: February 2008

Dissolved organic carbon (DOC) dynamics were investigated in three small wetland catchments: one covered by a scrub forest and the other two cleared, V‐bladed, and planted with pine, 1 and 4 years before sampling. Over a 4‐month sampling period, DOC concentrations averaged 1.4, 20.9, 47.1, 46.0, and 45.7 mg/L in precipitation, throughfall, stemflow, surface soil water, and subsoil water, respectively, in the scrub forest catchment. DOC concentration in the stream draining the catchment averaged 43.4 mg/L, reflecting the inability of the Larry River subsoils to adsorb DOC and the pathways taken by water. In 1986, discharge‐weighted DOC concentrations in the streams ranged from 29.9 mg/L in the catchment disturbed 4 years before sampling to 35.0 mg/L in the recently disturbed catchment and 37.9 mg/L in the catchment covered by scrub forest. DOC export from the catchments in 1986 was estimated to be 30.6, 43.8, and 41.7 g m−2 yr−1, suggesting that disturbance had a minor effect on DOC export. The role of the high DOC concentrations on the chemistry of the stream water was revealed by a large anion deficit, an average anion deficit:DOC relationship of 5.7 meq/g, and an annual export of acidity of 184–263 meq m−2 yr−1. Within‐storm sampling showed that pH and DOC were related inversely and base titration suggested acid dissociation constants (pKa) ranging from 4.4 to 4.9.
An approximate solution for one‐dimensional absorption in unsaturated porous media
Authors: Zimmerman Robert W. , Bodvarsson Gudmundur S.
Published: February 2008

The “boundary layer” or “integral” method is used to derive a closed‐form approximate solution for one‐dimensional absorption of water in an unsaturated porous medium whose characteristic curves are of the van Genuchten type. In this approach, an assumed saturation profile is substituted into the governing equation, and integrated from the boundary out to the wetting front. This yields closed‐form solutions for the front location and the instantaneous liquid flux at the boundary. The accuracy of this solution in predicting the flux, as determined by comparison with numerical solutions utilizing a Boltzmann‐type transformation, is always within 15%, for any value of the initial saturation. As an example of the use of this approximate solution, saturation profiles are calculated for absorption into the Topopah Spring volcanic tuff at Yucca Mountain, Nevada, the site of the proposed nuclear waste repository.
Assessing the value of hydrogeologic information for risk‐based remedial action decisions
Authors: Reichard Eric G. , Evans John S.
Published: February 2008

Remedial action decisions for groundwater contamination are made under conditions of uncertainty regarding both human exposure levels and chemical potency. The value of groundwater monitoring in reducing exposure uncertainty can be estimated within a decision‐analytic framework. The value of information from a particular monitoring strategy will depend on the expected accuracy of the strategy in estimating exposure, prior uncertainty about exposure and potency, the costs and efficiencies of the alternative remedial actions, and values assumed for the discount rate and the cost per unit risk. The proposed framework for assessing the value of hydrogeologic information at a groundwater contamination site consists of three steps: (1) determine a probability distribution for average lifetime exposure; (2) estimate the value of perfect exposure information in reducing the expected opportunity losses of decision making; and (3) compare hydrogeologic monitoring costs with the expected value of the sample information provided.
Analysis of the linear programming gradient method for optimal design of water supply networks
Authors: Kessler Avner , Shamir Uri
Published: February 2008

A theoretical analysis of the linear programming (LP) gradient method for optimal design of water distribution networks is presented. The method was first proposed by A. Alperovits and U. Shamir (1977) and has received much attention in the last 10 years. It consists of two stages that are solved in alteration: (1) a LP problem is solved for a given feasible flow distribution and (2) a search is conducted in the space of flow variables, based on the gradient of the objective function (GOF). In this paper a matrix formulation is given for both stages using well‐known graph theory matrices. It is proven that the mathematical expression of the GOF is independent of the choice of the sets of loops and paths along which the head constraints are formulated. This is contrary to the claim made by I. C. Goulter et al. (1986). The original GOF expression is shown to have been an approximation of the steepest direction, but still gives good results. Finally, the search procedure is improved by using the projected gradient method.
Analysis of natural groundwater level variations for hydrogeologic conceptualization, Hanford Site, Washington
Authors: Nevulis Richard H. , Davis Donald R. , Sorooshian Soroosh
Published: February 2008

This study involves the analysis of groundwater level time series for the purpose of obtaining details for a conceptual hydrogeologic model at a time when conventional hydraulic stress testing was not feasible due to regulatory considerations. The study area is located in south central Washington in the Pasco Basin which was a candidate site for underground disposal of high‐level radioactive nuclear wastes. Advantages of such passive methods of analysis may include relative simplicity, low cost, and avoidance of disturbances typically associated with stress testing of aquifers. Through this approach, natural and incidental man‐made groundwater level variations, most of which are quite small, are examined by statistical and analytical methods in conjunction with hydrogeologic models to draw inferences on the hydrogeology. Vertical connectivity of the hydrostratigraphic units is also examined by analyzing groundwater level time series of five units at three piezometer nests. It is concluded that a combination of statistical/analytical approaches used in a complementary fashion can provide useful information about the hydrogeology of a given area. A meaningful analysis requires that there is (1) a source of influence on the groundwater levels, (2) a response to that influence, (3) a sufficiently long data record, and (4) measurement and analytical techniques which allow the detection and identification of the influence and response.
Frequency distribution for suspended sediment loads
Authors: Parker R. S. , Troutman Brent M.
Published: February 2008

A method is described for deriving a frequency distribution for suspended sediment loads. The method uses a curvilinear regression relation between the logarithm of annual flood peaks and the logarithm of suspended sediment loads associated with that flood peak. It combines this relation with a log‐Pearson type III distribution for annual floods to produce a sediment load frequency distribution. Suspended sediment and peak streamflow data collected at a gaging station are used to evaluate the frequency of given sediment discharges. Because the annual flood series is generally a much longer record than the suspended sediment record, this method provides a mechanism to reduce the time sampling error (i.e., error due to shortness of record) in sediment load estimates. Sediment load frequency curves are derived for seven gaging stations in different hydrologic regimes.
A model for hysteretic constitutive relations governing multiphase flow: 3. Refinements and numerical simulations
Authors: Lenhard R. J. , Parker J. C. , Kaluarachchi J. J.
Published: February 2008

Refinements are proposed to a constitutive model for hysteretic three‐phase permeability‐saturation‐pressure relations which we have described in papers 1 and 2 of this series. The modifications involve distinguishing between various mechanisms of air entrapment in water and oil phases required to ensure consistency in mass balance calculations. Analytical saturation‐pressure derivatives for the three‐phase hysteretic k‐S‐P model are derived which provide exact representations of fluid pair capacities needed for implicit numerical solution of the governing equations for three‐phase flow. The hysteretic constitutive model was incorporated into a finite element multiphase flow code to enable simulation of transient three‐phase flow under conditions of arbitrary saturation path history. Simulations were conducted for a scenario involving the injection of an oil slug into a vertical soil profile subjected to a fluctuating groundwater table. In addition to simulations with the full hysteresis model, runs were performed with a model which considers hysteresis due to nonwetting fluid entrapment effects only and to a model which disregards hysteresis entirely. Full hysteresis and trapped fluid only analyses yielded very similar results. The hysteretic models predicted about two‐thirds of the 7.5 cm of injected oil would become trapped by a 50‐cm increase in water table elevation. Ignoring fluid entrapment thus may lead to large errors in predicted fluid distributions during periods of rising water tables.
An optimization approach for groundwater quality monitoring network design
Authors: Loaiciga Hugo A.
Published: February 2008

The optimal sampling plan for groundwater quality monitoring is formulated as a mixed integer programming (MIP) problem. A sampling plan consists of the number and locations of sampling sites as well as the temporal sampling frequency. The MIP network problem is defined by the minimization of the variance of estimation error subject to resource and unbiasedness constraints. The mean and covariance of the spatial/temporal variable (chloride concentration measurements) are derived from the advection‐dispersion equation governing mass transport. The solution for the optimal sampling proceeds in two stages: (1) parameter estimation and (2) network optimization. The MIP model was successfully tested with a network design problem in a buried valley aquifer in Butler County, Ohio. The application illustrates the role of objective function, resource constraint, mass transport processes, and hydrogeologic setting in groundwater quality monitoring network design.
Matching a field tracer test with some simple models
Authors: Bullivant D. P. , O'sullivan M. J.
Published: February 2008

Simple models of fluid flow and dispersion in a porous rock matrix are compared and used to match the results of tracer tests at the Wairakei (New Zealand) geothermal field. It is found that models which allow transient diffusion from fractures into the surrounding rock matrix give a better match to test results than either a model which allows only longitudinal dispersion or a pseudo steady state double porosity model. For some tests a model which includes two fractures is required to match the field data.
Sources of acidic storm flow in an Appalachian Headwater Stream
Authors: Swistock Bryan R. , DeWalle David R. , Sharpe William E.
Published: February 2008

A study was conducted to quantify the source of increased dissolved aluminum concentrations during acidic storm flows on a small Pennsylvania stream. Data for six episodes during fall 1986 and spring 1987 showed depressions in stream pH and increases in sulfates, conductivity, dissolved organic carbon, and dissolved aluminum. Flow separation analyses were conducted using 18O as a tracer in a three‐component mass balance tracer model. Results showed that soil water and groundwater are the dominant flow sources, accounting for approximately 20 and 75% of total flow during storms, respectively. Channel precipitation generally provided less than 5% of total flows. Hydrograph separation using aluminum agreed with 18O results, while other chemical parameters produced unsatisfactory results. The data support Hewlett's (1982) variable source area concept of storm flow generation with inputs of older, deep circulating groundwater from low‐elevation source areas early in an event and later inputs of younger soil water and possibly shallow groundwater from expanding source areas at higher elevations. The results suggest that the most toxic runoff events for aquatic life occur during large storms when the greatest inputs of soil water cause elevated stream dissolved aluminum concentrations. Reductions in storm flow acidity and dissolved aluminum concentrations on this catchment will be most dependent upon changes in soil water and/or groundwater chemistry.
Density‐driven flow of gas in the unsaturated zone due to the evaporation of volatile organic compounds
Authors: Falta Ronald W. , Javandel Iraj , Pruess Karsten , Witherspoon Paul A.
Published: February 2008

A theoretical investigation of factors affecting the gas phase transport of evaporating organic liquids in the unsaturated zone is presented. Estimates of density‐driven advective gas flow using a simple analytic expression indicate that significant advective gas flow will result from the evaporation of volatile liquids in soils having a high permeability. Numerical simulations using a two‐dimensional cylindrical geometry and including the effects of phase partitioning between the solid, gas, water, and organic liquid phases show that mass transfer due to density‐driven flow may dominate the gas phase transport of some organic chemical vapors in the unsaturated zone.
Topographic distribution of clear‐sky radiation over the Konza Prairie, Kansas
Authors: Dubayah Ralph , Dozier Jeff , Davis Frank W.
Published: February 2008

This research analyzes the topographic distribution of clear‐sky incoming solar radiation over the tallgrass Konza Prairie, site of FIFE, the First ISLSCP (International Satellite Land Surface Climatology Program) Field Experiment. Using a two‐stream atmospheric radiation model and digital elevation grids of 25‐, 50‐, and 100‐m grid spacing, clear‐sky radiation is simulated throughout the day for three dates: December 15, March 15, and June 15. Geostatistical analysis is used to characterize the spatial and temporal variability in modeled radiation at each grid spacing. The variance and spatial autocorrelation of simulated incoming radiation depend on Sun angle and elevation grid spacing. The behavior of the variance as a function of Sun angle, optical depth, and mean terrain slope can be explained by considering direct radiation variability on a simplified terrain model of uniform albedo where slopes are equal and azimuths are distributed uniformly in all directions. For this constant‐slope model it can be shown analytically that the solar zenith angle at which variance is maximized is a function of optical depth only and is independent of elevation, slope, and aspect. Results from the two‐stream simulations support this conclusion and suggest its applicability to real terrain.
On thermohydrologic conditions near high‐level nuclear wastes emplaced in partially saturated fractured tuff: 2. Effective continuum approximation
Authors: Pruess K. , Wang J. S. Y. , Tsang Y. W.
Published: February 2008

This paper presents an effective continuum approximation for modeling of fluid and heat flow in fractured porous media. The approximation is based on the thermohydrologic behavior observed in detailed simulations with explicit consideration of fracture effects (see the companion paper, part 1.) The crucial concept in the development of an effective continuum approximation is the notion of local thermodynamic equilibrium between rock matrix and fractures. Where applicable it provides a substantial simplification of the description of fluid and heat flow in fractured porous media. We derive formulas for effective continuum characteristic curves (relative permeabilities and capillary pressures) in terms of the properties of fracture and matrix continua, respectively. Numerical simulations demonstrate that under favorable conditions the effective continuum approximation closely matches predictions obtained from an explicit modeling of fracture effects. It is also demonstrated that the approximation breaks down under unfavorable conditions (very tight rock matrix). A simple criterion for the applicability of an effective continuum approximation is derived from consideration of diffusive processes. A quantitative evaluation shows the criterion to be consistent with results of our numerical simulations.
Analytical solutions of the one‐dimensional advection equation and two‐ or three‐dimensional dispersion equation
Authors: Leij Feike J. , Dane J. H.
Published: February 2008

For many transport problems involving one‐dimensional flow a significant amount of solute might move in the direction transverse to the flow. In this study the advection‐dispersion equation was solved analytically to evaluate transient solute transport in a two‐dimensional semi‐infinite isotropic porous medium (half plane) with a step change in concentration along the inlet during one‐dimensional flow. The solution was obtained with Laplace and Fourier transforms and verified with various numerical and analytical solutions. The same technique was used to obtain analytical solutions for some other concentration distributions at the inlet under conditions of either two‐ or three‐dimensional dispersion.
The zero‐curtain effect: Heat and mass transfer across an isothermal region in freezing soil
Authors: Outcalt Samuel I. , Nelson Frederick E. , Hinkel Kenneth M.
Published: February 2008

The term zero curtain refers to the effect of latent heat in maintaining temperatures near 0°C over extended periods in freezing or thawing soils. Analysis of thermal data from an arctic site and a mid‐latitude location suggests that the phenomenon may be a universal characteristic of wet, medium‐textured mineral and organic soils during freezing. Nonconductive processes play an important role in formation and maintenance of the zero‐curtain effect. Water advection, condensation, and evaporation events are recognizable in mappings of thermal and ion concentration records on time‐depth meshes. The zero curtain appears to be produced and maintained by vapor transport and internal distillation mechanisms, driven by osmotic potential variations induced by freeze‐thaw events at the soil surface. The term zero curtain is applicable to locations outside permafrost regions, but units of measurements should not be assigned to it.
An assessment of a conceptual rainfall‐runoff model's ability to represent the dynamics of small hypothetical catchments: 1. Models, model properties, and experimental design
Authors: Gan Thian Yew , Burges Stephen J.
Published: February 2008

A set of tests is proposed to determine the reliability of soil moisture accounting rainfall‐runoff models for prediction beyond the calibration experience and for extreme event forecasts under dry and wet antecedent conditions. The tests are developed for small (less than 0.5 km2) hypothetical hillslope catchments whose hydrologic response to rainfall and evapotranspiration (ET) fluxes is modeled with an accurate physically based model (S‐H) developed by Smith and Hebbert (1983). The tests are based on the assumption that the climatic and resulting S‐;H streamflow time series are error free. The conceptual model explored is a modified version of the Sacramento model (used by the U.S. National Weather Service) reprogrammed for inputs at various time increments as small as 1 min. A Nelder and Mead (1965) direct search optimization scheme is also included in this modified model (denoted SMA) to assist in model calibration. The set of tests is designed to illuminate differences in modeled ET fluxes, streamflow time series, and the relative amounts of Hortonian and saturated overland flow and subsurface flow under a wide variety of climate and hillslope combinations. The test scheme ensures that the conceptual model is tested for a number of hydrodynamic conditions where flow responses range from primarily surface, to primarily subsurface, to relatively even amounts of surface and subsurface flow for humid and subhumid environments. It also provides direct comparisons of the physical (hillslope catchments) and conceptual model storages, and explicit evaluation of the combined influence of conceptual model structure and calibration errors. Specific model structure differences between S‐H and SMA are detailed to elucidate any differences between model responses reported in the companion paper. Hydrologic responses are evaluated with statistical measures and graphical comparisons for time increments ranging from minutes to years.
Nitrous oxide dissolved in soil solution: An insignificant pathway of nitrogen loss from a southeastern hardwood forest
Authors: Davidson Eric A. , Swank Wayne T.
Published: February 2008

Nitrous oxide is soluble and can accumulate in soil solution when gaseous diffusion is restricted. The importance of N losses via degassing of N2O from groundwater entering surface streams is unknown. Measurements of N2O in soil solution revealed patterns of seasonal and spatial variation that were consistent with ecosystem regulation of denitrification. The highest concentrations were observed in the riparian zone in May, when soil NO3−, temperature, and moisture were conducive for denitrification. At each of the other sample dates and sites, at least one of these factors appeared to prevent significant N2O accumulation in soil solution. Extrapolation of the highest observed N2O concentrations to an annual basis corresponded to a loss of only 56 g N ha−1yr−1. Denitrification in the riparian zone may be an important fate of N in this hardwood forest, but N2O in soil solution does not appear to be a significant pathway of N loss. This site might be expected to produce N2O at higher rates than most hardwood forests, but extrapolation of the highest calculated losses frorn soil solution over the global area occupied by hardwood forest indicates that this source of N2O is insignificant for global atmospheric budgets.
A capillarity correction for free surface flow revisited
Authors: Parlange J.‐Y. , Brutsaert Wilfried , Fink James P. , El‐Kadi Aly I.
Published: February 2008

In general, the usual treatment of the initial response of the water table to a sudden drawdown involves a discontinuity at the outflow end of the aquifer. In the description of this problem by means of the diffusion equation of Boussinesq, this discontinuity is damped rapidly and presents no special difficulties. However, when a capillary correction, or a similar source term, is applied to this equation, the additional term may exhibit singular behavior. A procedure is presented to circumvent this.
Strategy for cost recovery in the rural water sector: A case study of Nsukka District, Anambra State, Nigeria
Authors: Whittington Dale , Okorafor Apia , Okore Augustine , McPhail Alexander
Published: February 2008

In‐depth interviews were conducted with 395 households in three rural communities in the Nsukka district of Anambra State, Nigeria, concerning their household water use practices, water expenditures to vendors, willingness to pay for improved water supplies, and household socioeconomic characteristics. Households in Nsukka district do not want to pay for water in advance or commit themselves to a fixed monthly payment for water. They want the freedom to buy water only when they use it, partly due to the seasonal nature of water use and partly because they want control over their cash flow in order to meet other more immediately pressing needs. Equally important, they do not trust government to provide a reliable public water supply. They do not want to pay in advance for a service they are not sure they will ever get. If they are required to pay a fixed fee every month, households are willing to pay only relatively small amounts for improved services, even less than they are currently paying water vendors. Current arrangements for cost recovery, fixed monthly fees for both public taps and unmetered private connections, are inappropriate. Kiosk systems, or kiosk systems with metered private connections for some households, are the most promising way to improve cost recovery and meet consumers' cash flow needs.
Numerical simulation of gravel river widening
Authors: Pizzuto James E.
Published: February 2008

A numerical model is described which simulates bank erosion in a straight channel composed of noncohesive sediment. The model predicts the distribution of boundary shear stress, cross‐channel sediment transport rates and the evolution of the bed topography. When erosion produces a bank slope which exceeds the angle of repose, widening occurs by a planar bank failure. Equilibrium channels produced by the model have flat beds and curved bank regions which are similar to the classical cosine stable bank profile. Equilibrium values of dimensionless depth are inversely proportional to the slope, as suggested by previous studies. The model also reproduces the exponential cross sections created during laboratory experiments. However, as the computations proceed, the exponential profiles slowly develop a flat bed and a curved bank region, suggesting that past flume experiments of channel widening may have frequently been terminated before a stable equilibrium form had evolved.
Pretest analyses of water demand in thirty communities
Authors: Griffin Ronald C. , Chang Chan
Published: February 2008

Using 3 years of monthly data for 30 carefully selected Texas communities, several characteristics of community water demand are investigated. The average price versus marginal price specification issue is examined in the same manner as preceding literature and again demonstrates the superiority of the average price approach. More original contributions identify (1) the need to include sewer rates in water demand models, (2) the importance of studying seasonal demand rather than annual demand, (3) seasonal variations in the price elasticity of demand, and (4) an interesting index for relating monthly community water demand to monthly climatic conditions.
Width and depth of self‐formed straight gravel rivers with bank vegetation
Authors: Ikeda Syunsuke , Izumi Norihiro
Published: February 2008

The influence of bank vegetation on the stable channel cross‐sectional geometry of stable, straight gravel rivers is studied theoretically. Singular perturbation and matched asymptotic expansion techniques are employed to derive the lateral distribution of depth‐averaged fluid velocity and the bed shear stress. A condition of sediment incipient motion is imposed at the junctions of the bed and the banks to derive the stable depth, and a formula for resistance to flow is used to obtain the stable width. The theory reveals that a thicker vegetation yields a larger depth and a smaller width. Increasing discharge increases the effect of vegetation. The analysis agrees reasonably well with available field data.
Predicting runoff from Rangeland Catchments: A comparison of two models
Authors: Wilcox Bradford P. , Rawls W. J. , Brakensiek D. L. , Wight J. Ross
Published: February 2008

This is a comparison of two very different hydrology models, both designed to predict runoff from ungaged rural catchments. One is the commonly used and conceptually simple Soil Conservation Service curve number method. The other is a process oriented model based on the Green and Ampt equation. The Green and Ampt model employs newly developed techniques for parameterizing the Green and Ampt equation based on readily available soil and vegetation information. Annual, monthly and daily predicted runoff were compared to observed on six uncalibrated rangeland catchments located in Texas, Oklahoma, Arizona, Nebraska and Idaho. Model parameterization was based strictly on individual catchment characteristics. No model calibration was performed. Results indicate that the Green and Ampt model is a potentially useful tool for predicting runoff. These results are important because they demonstrate the utility of complex physically based models as management tools for predicting land use impacts to runoff and infiltration.
A Hybrid Model for Forecasting Daily Rainfall
Authors: Wasimi Saleh A.
Published: February 2008

In a hydrologic basin where precipitation rates have strong seasonal characteristics, simple seasonal forecasts of rainfall along with regression analysis on a few related meteorological observations can be used to obtain an estimate of the anticipated rainfall rate one day in advance. In this paper a model for forecasting daily rainfall with one day lead time is presented. The model uses smoothed normal daily rainfall rates as seasonal forecasts and a linear regression model on deviations of atmospheric pressure, temperature, and humidity from their seasonal mean values for estimating departures from seasonal rainfall forecasts. The model has been applied to and tested with daily rainfall data of Dhaka (Dacca) city in Bangladesh.
Approximate Analytical Solutions for Overland Flows
Authors: Govindaraju R. S. , Kavvas M. L. , Jones S. E.
Published: February 2008

Following the study of Govindaraju et al. (1988), approximate analytical solutions are presented to the diffusion and kinematic wave models subject to space and time‐varying rainfall. An approximation in the form of the first term of an infinite sine series has been considered. This converts the partial differential equation to an ordinary differential equation, and analytical solutions for both rising and recession phases of the hydrograph can be developed. Time variation in rainfall is found to play a key role. Comparisons with full Saint‐Venant solutions, the kinematic wave approximation and experimental results are presented for validating the proposed solution methodology. The one‐term analytical solution is shown to perform well in some cases of physical interest. It is concluded that the analytical solution is useful for estimating runoff from steep overland flow sections.
Chemical Weathering in the Loch Vale Watershed, Rocky Mountain National Park, Colorado
Authors: Mast M. Alisa , Drever James I. , Baron Jill
Published: February 2008

Mineralogic, hydrologic, and geochemical data were used to determine the source of solutes to surface waters draining the Loch Vale Watershed (LVWS), an alpine‐subalpine drainage located in the Front Range of Colorado. The flux of dissolved solids from LVWS is primarily controlled by interactions between snowmelt and materials derived from the local bedrock; the biomass has only a minor effect on solute budgets except for ammonium. LVWS is underlain by Precambrian granite and gneiss, the major minerals include quartz, microcline, plagioclase, biotite, and sillimanite. Small amounts of calcite were found along hydrothermally altered zones in the bedrock. Mass balance calculations indicate that the weathering of calcite contributes nearly 40% of the cations derived within the basin. The importance of calcite weathering in LVWS is a result of its chemical reactivity and the high rate of physical erosion in this alpine environment. The average cationic denudation rate in the drainage (390 eq/ha/yr) is similar to long‐term rates in forested Adirondack watersheds (500–600 eq/ha/yr), but much lower than the average for the North American Continent (3800 eq/ha/yr). Surface waters in LVWS are susceptible to acidification should acid deposition from the atmosphere increase.
The Identifiability of Conceptual Hydrochemical Models
Authors: Kleissen F. M. , Beck M. B. , Wheater H. S.
Published: February 2008

Estimating a uniquely best set of values for the parameters of conceptual hydrological models has long been a problem of considerable concern. More recent interest in using these models to determine the flow paths of water passing through catchments experiencing acidification has sharpened the focus of such concern on the role of tracer observations in model and parameter identifiability. The paper examines the question of a priori identifiability in both deterministic and stochastic frameworks. Working with relatively simple linear and nonlinear two‐store models, the deterministic analysis involves merely algebraic manipulation of the model's state space description. It is apparent that, while this form of analysis is of limited applicability (even with the assistance of systems of computer algebra), the availability of tracer observations enhances model identifiability in all the cases examined. More complex model structures, and the effects of model and observation uncertainty, can be explored within a stochastic framework based on filtering theory. It is found that the availability of two tracer signals does not necessarily improve identifiability beyond what is possible with just a single tracer measurement. There is also evidence of a basis for the cross referencing of identifiability results between the deterministic and stochastic frameworks.
Hydrogeochemical Response of a Forested Watershed to Storms: Effects of Preferential Flow Along Shallow and Deep Pathways
Authors: Mulholland Patrick J. , Wilson Glenn V. , Jardine Philip M.
Published: February 2008

Hydrology and solute chemistry were monitored during four storms in a forested watershed in karst terrain in eastern Tennessee at spatial scales ranging from a 0.5‐ha upper hillslope subcatchment to a 38.4‐ha watershed drained by a first‐order stream. Storm flow was generated from large portions of the watershed as a result of subsurface preferential flow initiated by zones of perched saturation in the soil profile. For most storms, runoff per unit area increased with increasing catchment size, indicating that preferential flow was primarily vertical along relatively deep pathways that emerged in the lower portions of the watershed. However, when antecedent soil moisture was high and rainfall was large, runoff was similar across catchment sizes, indicating that preferential flow was largely lateral along shallow paths (<2.5 m deep). Concentrations of some solutes differed for shallow and deep flow paths because dominant sources and sinks are stratified vertically in the watershed. Runoff generated by preferential flow along shallow flow paths resulted in higher exports of Cl, Al, SO4, and dissolved organic carbon and lower exports of alkalinity, Ca, Mg, and soluble reactive phosphorus than an equivalent amount of runoff generated by preferential flow via deeper flow paths.
Influence of Temperature and Mineral Surface Characteristics on Feldspar Weathering Rates in Natural and Artificial Systems: A First Approximation
Authors: Velbel Michael Anthony
Published: February 2008

Rates of alkali feldspar hydrolysis in the near‐neutral pH range are up to 3 orders of magnitude slower in natural systems than in laboratory experiments. Correcting for differences in temperature between natural weathering and laboratory systems reduces the disparity by as much as a factor of 5. Any remaining disparity can be accounted for by differences in the ratio of effective surface area to total surface area; the ratio of effective‐to‐total surface area in natural systems is generally considerably smaller than in laboratory systems. This may be related, at least in part, to experimental preparation artifacts and to the fact that naturally weathered feldspars have lost much of their most reactive surface to the formation of etch pits. Hydrological factors such as inhomogeneous access of percolating fluids to mineral surfaces may also reduce the proportion of mineral surface area reacting in natural systems.
Theoretical study of Sutherland fluids with long-range, short-range, and highly short-range potential parameters
Authors: Mi Jianguo , Tang Yiping , Zhong Chongli
Published: February 2008

On the basis of the first-order mean spherical approximation (FMSA) theory the behavior of Sutherland fluids with a number of parameters (γ=3.1−36) is investigated. The investigation includes its modification by the simplified exponent approximation, renormalization group (RG) transformation, and density functional theory (DFT). For long-range parameters, the original FMSA is found sufficiently good to describe the global phase behavior, including inside the critical region. For short-range parameters, the modified FMSA by the simplified exponent approximation outside the critical region and RG transform inside the critical region are applied. For extremely short-range forces, the success is achieved by its combination with the DFT. This work gives a general sense about the capability of a theory for different ranges of potential, as well as for different thermodynamic states.
The oxidation of SmCo magnets
Authors: Pragnell W. M. , Williams A. J. , Evans H. E.
Published: February 2008

SmCo alloys form the basis of excellent permanent magnets with potential service applications to 500°C. It is suspected, however, that their oxidation behavior may limit their usefulness but this is a relatively unstudied subject. Two grades of Sm2(Co,Fe,Cu,Zr)17-based alloys were aged in air at temperatures between 300 and 600°C and the oxidation reaction characterized by post-test scanning electron microscopy examination. Both alloys formed a thin external oxide scale composed of Cu and mixed Fe∕Co oxides and an extensive internal oxidation layer consisting of Sm-rich oxide within a CoFe matrix. The depth of the internal oxidation zone was typically an order of magnitude thicker than the surface oxides and increased parabolically with time. This internal oxidation is an important degradation phenomenon because the transformation to CoFe causes a loss of magnetic properties proportional to the volume consumed. The morphologies of the oxidation zones, nature, and mechanisms of various precipitated phases and the differences between the two alloys’ oxidation behavior is also discussed.
Positive mass theorems for higher dimensional Lorentzian manifolds
Authors: Ding Lu
Published: February 2008

We extend Witten’s proof [“A new proof of the positive energy theorem,” Commun. Math. Phys. 80, 381–402 (1981)] of the positive mass theorem to a rigorous proof for Lorentzian manifolds of any dimension. This includes the original higher-dimensional positive mass theorem proved by spinors [Parker, T. and Taubes, C., “On Witten’s proof of the positive energy theorem,” Commun. Math. Phys. 84, 223–238 (1982)] for dimension 4 and [Zhang, X., “Positive mass conjecture for five-dimensional Lorentzian manifolds,” J. Math. Phys. 40, 3540–3552 (1999)] for dimension 5. Stimulated by the article of Zhang [“Positive mass theorem for hypersurface in 5-dimensional Lorentzian manifolds,” Commun. Anal. Geom. 8, 635–652 (2000)], we weaken the spin condition on the spacelike hypersurface to require only a spinc structure and give a modified positive mass theorem for Lorentzian manifolds for dimensions 4, 5, and 6.
Electrowetting-based valve for the control of the capillary flow
Authors: Satoh Wataru , Yokomaku Hiroomi , Hosono Hiroki , Ohnishi Noriyuki , Suzuki Hiroaki
Published: February 2008

The behavior of a microfluidic device based on transport by capillary action and control by direct electrowetting was examined by changing the device parameters. The device was constructed with a polydimethylsiloxane (PDMS) substrate with a flow channel and a glass substrate with electrodes to control electrowetting. The microfluidic transport and valve action could be explained by Washburn’s model, which suggests that the model can be used for designing such a device. The device could be used for the timely delivery of a solution into many flow channels as well as for the mixing of solutions.
Size and pressure effects in the atom-phonon coupling model for spin crossover compounds
Authors: Rotaru Aurelian , Linares Jorge , Codjovi Epiphane , Nasser Jamil , Stancu Alexandru
Published: February 2008

The smallest size of a spin crossover particle which still exhibits hysteric behavior is an open question. It is clear that spin crossover is a cooperative phenomenon, which implies the dependence of the high spin fraction variation on the number of molecules within the system. We use the “atom-phonon coupling” model to explain the different results that have been recently published with regard to the critical dimension of a spin crossover system. In the second part of the paper, the applicability of the model to the pressure induced transition has been developed, and the results are in good agreement with what has been observed experimentally.
Thickness dependence of magnetic film edge properties in Ni80Fe20 stripes
Authors: McMichael Robert D. , Ross C. A. , Chuang Vivian P.
Published: February 2008

Measurements of “trapped spin wave” edge modes in transversely magnetized stripe arrays of Ni80Fe20 largely confirm previous theoretical predictions for the thickness dependence of the edge saturation field Hsat and the effective out-of-plane edge anisotropy field H2. The stripes were patterned using optical interference lithography with film thicknesses in the range from 10to65nm. Large linewidth values for edge modes relative to bulk modes indicate inhomogeneity of the edges. Elimination of an antireflective coating underlayer dramatically decreases the edge mode linewidth without affecting the bulk mode linewidth.
Alignment-free process for asymmetric contact electrodes and their application in light-emitting organic field-effect transistors
Authors: Sakanoue Tomo , Yahiro Masayuki , Adachi Chihaya , Burroughes Jeremy H. , Oku Yoshiaki , Shimoji Noriyuki , Takahashi Takayoshi , Toshimitsu Akio
Published: February 2008

We developed an alignment-free process for asymmetric contacts of Au and Al and applied it to light-emitting organic field-effect transistors. Because electrons were injected efficiently from Al contacts, the emission intensity and onset voltages for light were significantly better than those in a device with conventional Au∕Cr contacts. Moreover, a device with 1μm channel length asymmetric contacts of Au and Al showed about 50 times higher current than that of the device with conventional Au∕Cr contacts. This significant improvement can be ascribed to both dual space-charge formation of holes and electrons and low carrier injection barriers.
A possible source of spin-polarized electrons: The inert graphene/Ni(111) system
Authors: Dedkov Yu. S. , Fonin M. , Laubschat C.
Published: February 2008

We report on an investigation of spin-polarized secondary electron emission from the chemically inert system: graphene/Ni(111). An ordered passivation graphene layer (monolayer of graphite) was formed on Ni(111) surface via cracking of propylene gas. The spin polarization of secondary electrons obtained from this system upon photoemission is only slightly lower than the one from the clean Ni surface but does not change upon large oxygen exposure. These results suggest to use such passivated Ni(111) surface as a source of spin-polarized electrons stable against adsorption of reactive gases.
Accelerating Self-Motion Displays Produce More Compelling Vection in Depth
Authors: Palmisano Stephen , Allison Robert S , Pekin Fiona
Published: February 2008

We examined the vection in depth induced when simulated random self-accelerations (jitter) and periodic self-accelerations (oscillation) were added to radial expanding optic flow (simulating constant-velocity forward self-motion). Contrary to the predictions of sensory-conflict theory frontal-plane jitter and oscillation were both found to significantly decrease the onsets and increase the speeds of vection in depth. Depth jitter and oscillation had lesser, but still significant, effects on the speed of vection in depth. A control experiment demonstrated that adding global perspective motion which simulated a constant-velocity frontal-plane self-motion had no significant effect on vection in depth induced by the radial component of the optic flow. These results are incompatible with the notion that constant-velocity displays produce optimal vection. Rather, they indicate that displays simulating self-acceleration can often produce more compelling experiences of self-motion in depth.
Differential Effects of Full and Partial Notes on Learning Outcomes and Attendance
Authors: Cornelius Tara L. , Owen-DeSchryver Jamie
Published: February 2008

Although college instructors are increasingly providing students with online notes, research is equivocal on how such notes affect student outcomes. This study examined partial versus full notes in introductory psychology classes while controlling for initial levels of student knowledge and academic ability. Results suggested that students receiving partial notes performed better on examinations later in the semester and on conceptual questions during the cumulative final examination than students receiving full notes. Students receiving full notes also self-reported more negative effects on attendance. We provide possible interpretations of these data and suggest areas for further investigation.
Short Article: Newly Learned Spoken Words Show Long-Term Lexical Competition Effects
Authors: Tamminen Jakke , Gaskell M. Gareth
Published: February 2008

Newly learned spoken words (e.g., “cathedruke”) become fully engaged in the mental lexicon, as measured via lexical competition with their pre-existing phonological neighbours (e.g., “cathedral”), over the course of several hours or days, and this lexical restructuring is associated with sleep (Dumay & Gaskell, 2007). Here, we investigated the longer-term effects of word learning for three sets of novel words learned at different times using phoneme monitoring and repetition tasks. The effects of these exposure sessions on lexical memory were assessed in a battery of tests. Lexical decision latencies to pre-existing neighbouring words showed that lexical competition effects for the novel words remained observable 8 months after initial exposure. Furthermore, the order-of-acquisition of the novel words affected their production speed (but not recognition speed), with an advantage for earlier acquired words. The results suggest that the consolidation of novel words results in a long-term and stable change in the lexical competition process.
On the characterization of the deterministic/stochastic and linear/nonlinear nature of time series
Authors: Mandic D.P , Chen M , Gautama T , Van Hulle M.M , Constantinides A
Published: February 2008

The need for the characterization of real-world signals in terms of their linear, nonlinear, deterministic and stochastic nature is highlighted and a novel framework for signal modality characterization is presented. A comprehensive analysis of signal nonlinearity characterization methods is provided, and based upon local predictability in phase space, a new criterion for qualitative performance assessment in machine learning is introduced. This is achieved based on a simultaneous assessment of nonlinearity and uncertainty within a real-world signal. Next, for a given embedding dimension, based on the target variance of delay vectors, a novel framework for heterogeneous data fusion is introduced. The proposed signal modality characterization framework is verified by comprehensive simulations and comparison against other established methods. Case studies covering a range of machine learning applications support the analysis.