Dissolved Oxygen and pH Modeling of a Periphyton Dominated, Nutrient Enriched River

Nutrient enrichment of the South Umpqua River, Oregon was linked to periphyton growth and large diel fluctuations in dissolved oxygen and hydrogen ion (pH) concentrations using the water quality model QUAL2Kw. The available data provide a good case study for the relatively new water quality model. QUAL2Kw simulates a dynamic diel heat budget and water quality kinetics for a one-dimensional, steady-flow system and is part of a family of models meant to serve as an update to the widely used QUAL2E. The model was used to quantify nonpoint source loading, determine the pollutant of concern, estimate natural conditions, and calculate a phosphorus total maximum daily load during summer, low-flow conditions. Control of both nonpoint and point sources is required to achieve the low instream phosphorus concentrations necessary to meet water quality criteria. To our knowledge, this is the first paper that reports on the application of a model for computing the maximum allowable load necessary to manage the diel variation in pH.     

Fuzzy Waste Load Allocation Model: Simulation-Optimization Approach

The problem of waste load allocation (WLA) for water quality management of a river system is addressed with a simulation-optimization approach. The WLA model developed in the study provides the best compromise solutions to the pollution control agency (PCA) responsible for maintaining the water quality and the dischargers disposing pollutants into the river system. A previously developed fuzzy waste load allocation model (FWLAM) is extended to incorporate QUAL2E, a water quality simulation model developed by the U.S. Environmental Protection Agency for modeling the pollutant transport in a river. The imprecision associated with establishing water quality standards and the aspirations of the PCA and dischargers are quantified using fuzzy goals with appropriate membership functions. The membership functions of the fuzzy goals represent the variation of the goal satisfaction in the system. A genetic algorithim (GA) is used as an optimization tool to find optimal fraction removal levels to the dischargers and the corresponding satisfaction level. Because a GA is an unconstrained optimization tool, it is extended to handle constraints by complementing it with homomorphous mapping (HM), a constraint handling method for evolutionary algorithms. The GA directs the decision vector in an encoded form to HM. HM, after a few interactions with QUAL2E, redirects the decoded solution back to the GA. The GA assigns a fitness value to the feasible solution vector and applies operators to refine the solution. This interaction among the GA, HM, and QUAL2E continues until a prespecified criterion for global optimality is met. Application of the model is illustrated with a case study of the Tunga-Bhadra River in South India.     

Development of a Simple Phosphorus Model for a Large Urban Watershed: A Case Study

Often, the initiation of a total maximum daily load (TMDL) program is delayed until intensive monitoring data can be collected—even in watersheds where large historical data sets exist. This paper provides a case study of a modeling effort that utilizes available historical data to fulfill an intermediate goal of a TMDL program for the Passaic River Basin. The subject model is developed to simulate total phosphorus concentrations (and loads) within the basin’s effluent-dominated streams. The model is based on the assumption that the primary process controlling in-stream total phosphorus concentrations is the dilution of the cumulative upstream effluent load—which was computed on a continuous (daily) basis. Model comparisons indicate a generally good fit to long-term river-monitoring data at several key sites. Model results, and data analyses, suggest that secondary processes have a relatively minor impact on total phosphorus (TP) concentrations in this relatively large, urbanized system. This finding is consistent with a previous QUAL2E model study of the system, and consistent with the relatively conservative behavior of TP reported in many medium-to-large river systems throughout the United States. Model results are used to facilitate TMDL planning efforts for a major water supply reservoir in the basin.     

Empirical Relations for Longitudinal Dispersion in Streams

Although several methods are available for dispersion in natural streams, no method is accurate enough to satisfactorily predict the time variation of stream pollution concentration. Further, limited studies exist for dispersion of nonconservative pollutants. In this paper a six-parameter concentration equation for dispersion of conservative and nonconservative pollutants has been proposed. The parameters of the equation have been related to hydraulic variables and stream geometry. Using these predictors, the equation is fairly accurate for concentration predictions. It is hoped that the equation is useful in water quality management studies.     

Dimensional Analysis of Reaeration Rate in Streams

Atmospheric reaeration at the free surface of lakes and streams is a relevant process for water quality, thus the amount of oxygen transferred to the water body should be carefully estimated. Recent studies have demonstrated that available equations for estimation of the reaeration rate offer a poor fit with field data different from those for which each equation was originally developed. Thus, none of the available equations is applicable to all stream hydrodynamic conditions; on the contrary, they remain stream-specific, probably since some parameters involved in the process have been neglected in their formulation and their expressions are too simplistic. This paper proposes a comprehensive approach to the mass-transfer process at the air-water interface that is based on dimensional analysis. Careful inspection of equations in the literature shows that the mass-transfer process at the air-water interface has been affected by 14 different parameters. The application of dimensional analysis produces, for a wide rectangular section if wind speed is negligible, a dimensionless equation for the mass-transfer rate, where this rate is a function of the Froude number, channel slope, Reynolds number, Sherwood number, Weber number, and relative roughness. This expression is further developed to address the reaeration process in streams and rivers. As a result, at a fixed temperature, the dimensionless reaeration rate KaND (where ND denotes nondimensional) is finally a function of only the Froude number, channel slope, Reynolds number, and relative roughness. Moreover, the application of the Darcy-Wiesbach equation allows this dimensionless rate KaND to be considered as a function of only three of the aforementioned parameters. This result provides a comprehensive approach to the reaeration process that can also explain the unreliability of the literature equations available up to now.     

Sorption Behavior and Long-Term Retention of Reactive Solutes in the Hyporheic Zone of Streams

This paper analyzes the transport of sorbing solutes by extending the advective storage path model developed for longitudinal transport of inert solutes in streams coupled with flow-induced uptake in the hyporheic zone. Independent observations of a conservative (3H) and a reactive (51Cr) tracer in both the stream water and the hyporheic zone were used to differentiate between hydraulic and sorption processes. The method of temporal moments was found to be inadequate for parameter determination, whereas fitting versus the entire tracer breakthrough curves with special emphasis on the tail indicates that the proposed model could be used to represent both conservative and reactive transport. Information on the tracer inventory of the conservative tracer in the hyporheic zone was found to be of vital importance to the evaluation of the hydraulic exchange. A model evaluation based on stream water data alone can yield predictions of a wash-out in the hyporheic zone that deviates markedly from the observed wash-out. This prohibits long-term predictions of the wash-out from the hyporheic zone as well as the evaluation of sorption properties. The sorption in the hyporheic zone was found to follow a two-step model, where the first step is instantaneous and the second kinetic. A model with a single-step sorption process could not reproduce the observed breakthrough curves. An evaluation of the relative importance of including sorption kinetics in solute stream transport models is elucidated by means of the analytical expressions for the temporal moments. The omission of the kinetics in the second sorption step in the hyporheic zone will result in relative errors in the moments of second order or higher. The error will increase with decreasing residence time in the hyporheic zone. Especially, long-term predictions of the wash-out from the hyporheic zone require consideration of the rate-limited sorption.     

On the tensile properties of a fiber reinforced titanium matrix composite—I. Unnotched behavior

An investigation of the ultimate tensile strength and fracture strain of a fiber-reinforced Ti-matrix composite has been conducted. Comparisons have been made between experimental measurements and predictions of two micromechanical models: one assumes that the fibers behave independently of the matrix, i.e. as in a dry fiber bundle, and the other assumes frictional coupling between the fibers and the matrix, characterized by a constant interfacial sliding stress. To conduct such comparisons, a number of constituent properties have been measured, including the fiber strength distribution, the thermal residual stress and the interfacial sliding stress. In addition, the effects of gauge length on the tensile properties of the composite have been studied. The comparisons indicate that the model prediction based on frictional coupling provide a good representation of the experimental results. In constrast, predictions based on the dry fiber bundle approach strongly underestimate both the ultimate strength and the fracture strain and predict a gaunge length dependence that is inconsistent with the experiments.     

Modeling Resuspension in a Dynamic Water Supply Reservoir

Enhancements to the two-dimensional lake and reservoir water quality model W2Tn to simulate the effects of currents and waves on sediment resuspension and turbidity are described. Bed stress attributable to currents was computed by the hydrothermal component of W2Tn, whereas a surface wave component was added to W2Tn to determine bed stress owing to waves. Resuspension flux is computed from bed stress and is included as a source of turbidity to the water column. The model is tested through application to Schoharie Reservoir, a drinking water supply that experiences episodes of elevated turbidity caused by runoff events and exacerbated by drawdown. Model predictions of bed stress attributed to currents are validated by using measurements obtained from acoustic Doppler instrumentation. The surface wave component of the model is established on a framework that has been previously validated for Schoharie Reservoir. Testing of the enhanced turbidity component of W2Tn was completed for a 3.5-year period of historical observations, which included a number of runoff events covering a range of severity and variations in reservoir drawdown. The enhanced model performed well in simulating observed conditions in the water column. The resuspension mechanism made a significant contribution to the predicted turbidity during periods of reservoir drawdown and during a severe runoff event. The model also performed well in simulating the observed turbidity of the drinking water withdrawal. Resuspension of particles contributing to turbidity was largely attributable to reservoir currents with surface wave-induced resuspension playing a smaller role. The potential application of this model to other water bodies and water quality issues is discussed.     

Hybrid-Cells-in-Series Model for Solute Transport in Streams and Relation of Its Parameters with Bulk Flow Characteristics

The conceptualized hybrid-cells-in-series model, consists of a plug flow zone and two thoroughly mixed unequal reservoirs, all connected in series, has three time parameters, namely: (1) residence time of solute in the plug flow zone; and (2) residence times of solute in the two thoroughly mixed reservoirs. The model simulates closely advection-dispersion solute transport in natural streams. The resident time parameters are related to the velocity of flow, width of water surface, and depth of flow in the stream. Through the Péclet number, defined as Pe = (Δxu)/DL (in which Δx=process unit size; u=mean flow velocity; and DL=longitudinal dispersion coefficient), the relations of the model parameters with the longitudinal dispersion coefficient and with the bulk stream flow characteristics have been established. For a given reach of a stream, the parameters are inversely proportional to the flow velocity. By decoupling of pure advection by the plug flow component and dispersion of tracer by the two thoroughly mixed reservoir components, a robust fitting to the observed concentration-time data in natural streams was achieved.     

Models Quantify the Total Maximum Daily Load Process

Mathematical models have been used for many years to assist in the management of water quality. The total maximum daily load (TMDL) process is no exception; models represent the means by which the assimilative capacity of a water body can be quantified and a waste load allocation can be determined such that the assimilative capacity is not exceeded. Unfortunately, in many TMDLs, the use of models has not always adhered to the best modeling practices that have been developed over the past half-century. This paper presents what are felt to be the most important principles of good modeling practice relative to all of the steps in developing and applying a model for computing a TMDL. These steps include: Problem definition and setting management objectives; data synthesis for use in modeling; model selection; model calibration and, if possible confirmation; model application; iterative modeling; and model postaudit. Since mathematical modeling of aquatic systems is not an exact science, it is essential that these steps be fully transparent to all TMDL stakeholders through comprehensive documentation of the entire process, including specification of all inputs and assumptions. The overriding consideration is that data richness and quality govern the level of model complexity that can be applied to a given system. The model should never be more complex than the data allow. Also, in applying a model, one should always attempt to quantify the uncertainty in predictions. In general, quantifying uncertainty is easier with simple models, which is another reason to begin with a simple framework.     

Ultimate Bed Slope in Calabrian Streams Upstream of Check Dams: Field Study

In this paper a number of proposed criteria are analyzed that predict the ultimate equilibrium bed slope in streams upstream of a check dam. The analysis is based on a comprehensive data set that includes 132 reaches in streams located in southern Italy. The results of this study show that the procedures suggested by Ferro et al. and Julien and Wargadalam do not lead to satisfactory results. Better predictions of the ultimate bed slope are achieved using the criterion suggested by Gessler, which is based on the stochastic analysis of incipient motion in nonuniform bed material. This analysis is based on a design discharge corresponding to a return period of 1.2 years and accounts for the armoring process at the bed surface. The procedure allows an estimate of the equilibrium slope of a nonhomogeneous bed material.     

A Steady State Thermal and Material Balance Model for an Iron Making Blast Furnace and Its Validation with Operational Data

In view of scarcity and depletion in the quality of raw materials as well as stringent environmental regulations, judicious use of resource and adoption of optimal operating practices have become the prime concern in iron and steel industries. Real time forecasting and supervision of the process behavior is an important step in addressing these issues. As a part of the tool termed “Real Time Process Simulator (RTPS)”, containing several reduced order models for real time monitoring and prediction of the internal dynamics of iron making blast furnace, a mathematical model for material and thermal analysis has been developed, mainly to predict the top gas composition, raw material consumption and overall heat balance. The model predictions have been tested against actual plant data. The raceway adiabatic flame temperature has been calculated using data similar to that of an operating plant. The calculated heat distribution of the process has been presented in the form of a SHANKEY diagram. The RTPS, containing the present model has been implemented in an Indian integrated steel plant. Prior to implementation, the model has been tested and validated in the plant operational range with the help of a virtual platform.     

A mediational model of quality of life for individuals with severe mental health problems

BACKGROUND: Despite the increasing importance of quality of life in the mental health field, the theoretical conceptualization of the construct remains poorly developed. A proposed mediational model of quality of life, which links subjective quality of life with self-related constructs, is examined with a group of long-term psychiatric hostel residents. The present study aims to develop a measure of quality of life based on the proposed model, to explore the data and their implications for service development and finally to conduct a preliminary analysis of the model's predictions. METHODS: A cross-sectional research design was employed. Quality of life interviews, using a modified version of Lehman's Quality of Life Interview, were carried out with 54 psychiatric residents in Greece. The model's predictions were examined by using a series of regression analyses. RESULTS: The results indicate that perceived improvements in lifestyle, greater autonomy and positive self-concept are significantly and directly associated with better quality of life. In contrast, a direct relationship between objective indicators and subjective quality of life was not found. CONCLUSIONS: The traditional two-part quality of life model that includes objective indicators of life circumstances and subjective indicators is extended to included the constructs of self-concept and perceived autonomy. The present extended mediational model of quality of life for individuals with long-term mental health problems appears to have important implications for the planning and delivery of mental health programmes.     

Parameter Estimation of the Transient Storage Model for Stream–Subsurface Exchange

The transient storage model (TSM) is the most commonly used model for stream–subsurface exchange of solutes. The TSM provides a convenient, simplified representation of hyporheic exchange, but its lack of a true physical basis causes its parameters to be difficult to predict. However, the simple formulation makes the model a useful practical tool for many applications. This work compares the TSM with a physically based pumping model. This comparison is advantageous for two reasons: Advective pumping is known to be an important hyporheic exchange process in many streams, and the pumping model can be used to derive dimensionless transient storage parameters that are properly scaled with important physical stream parameters. Transient storage model parameters are shown to be dependent on both the timescale of observation and the shape of the breakthrough curve, i.e., on the temporal evolution of the solute concentration in the surface water. This indicates that the transient storage model can, in practice, lead to incorrect predictions when model parameters are obtained without consideration of the stream flow dynamics, the properties of the stream bed, or the process timescale. This work emphasizes the limitations of simplified models for hyporheic transport, and indicates that such models need to be carefully applied.     

Parameter Sensitivity and Predictive Uncertainty in a New Water Quality Model, Q2

A new dynamic model of water quality, Q2, has recently been developed, capable of simulating large branched river systems. This paper describes the application of a generalized sensitivity analysis (GSA) to Q2 for single reaches of the River Thames in southern England. Focusing on the simulation of dissolved oxygen (DO) (since this may be regarded as a proxy for the overall health of a river); the GSA is used to identify key parameters controlling model behavior and provide a probabilistic procedure for model calibration. It is shown that, in the River Thames at least, it is more important to obtain high quality forcing functions than to obtain improved parameter estimates once approximate values have been estimated. Furthermore, there is a need to ensure reasonable simulation of a range of water quality determinands, since a focus only on DO increases predictive uncertainty in the DO simulations. The Q2 model has been applied here to the River Thames, but it has a broad utility for evaluating other systems in Europe and around the world.     

Mathematical modeling of mixing phenomena in a gas stirred liquid bath

A macroscopic, steady state energy balance model has been formulated to describe mixing phenom-ena in a liquid bath stirred by injecting gas through a straight nozzle fitted axially at the bottom of the vessel. This, along with experimental data on a water model previously reported, was employed to make predictions. Input energy terms considered in the model consist of buoyancy energy and empirically determined fraction of gas kinetic energy. Dissipation of energy was attributed to liquid circulation and bubble slip. The two-phase plume was assumed to be a truncated cone whose dimen-sions depended upon operating conditions. Numerical solution of model equations gave liquid velocity and gas hold-up inside the plume as well as liquid circulation rate and liquid velocity in the region outside the plume. Influence of process variables, e.g., gas flow rate, bath height, and nozzle diameter, have been predicted. Validity of the model has been established by comparing some pre-dicted entrainment ratios with those experimentally measured by other investigators. Empirical cor-relations to predict circulation time and circulation number have been proposed. Circulation number was found to vary between 2 and 12 in contrast to the existing assumption in the literature of a con-stant value of 3. Usefulness of these correlations in predicting mixing time for industrial vessels has been demonstrated. Formerly a Graduate Student in the De-partment of Metallurgical Engineering at the Indian Institute of Technol-ogy, Kanpur     

Adaptation reveals multiple levels of representation in auditory stream segregation.

When presented with alternating low and high tones, listeners are more likely to perceive 2 separate streams of tones (“streaming”) than a single coherent stream when the frequency separation (Δ?) between tones is greater and the number of tone presentations is greater (“buildup”). However, the same large-Δ? sequence reduces streaming for subsequent patterns presented after a gap of up to several seconds. Buildup occurs at a level of neural representation with sharp frequency tuning. The authors used adaptation to demonstrate that the contextual effect of prior Δ? arose from a representation with broad frequency tuning, unlike buildup. Separate adaptation did not occur in a representation of Δ? independent of frequency range, suggesting that any frequency-shift detectors undergoing adaptation are also frequency specific. A separate effect of prior perception was observed, dissociating stimulus-related (i.e., Δ?) and perception-related (i.e., 1 stream vs. 2 streams) adaptation. Viewing a visual analogue to auditory streaming had no effect on subsequent perception of streaming, suggesting adaptation in auditory-specific brain circuits. These results, along with previous findings on buildup, suggest that processing in at least 3 levels of auditory neural representation underlies segregation and formation of auditory streams. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Plasmachrome process for ferrochrome production – thermochemical modelling and application to process data

Plasmachrome is a new process for the production of ferrochrome and chargechrome using a variety of chromium bearing materials. In this paper a thermochemical model has been developed for the Plasmachrome process. The model is based on the equilibrium approach and considers mass and heat balances for the shaft and smelting zone of the reactor. A review of available literature has been made and gaps in thermodynamic data of relevance to the process have been identified. The model has been applied to available plant data for the process. Calculations show a good agreement between model predictions and plant data. It has been shown that the equilibrium approach can be effectively used for process analysis. The model has been used to study the possible effect of different types of material additions on process performance. The results indicate the process to be flexible, permitting many process variations to enable optimal use of different raw materials.     

Mathematical Modelling of the Liquid-Liquid Extraction Separation of Rare Earths

Abstract

An empirical mathematical model has been developed for the simulation of an integrated solvent extraction circuit consisting of an extractor, scrubber and a stripper. This model is designed to simulate the separation of any lanthanide from a mixed lanthanide feed. The Kremser equation is used to calculate the separation occurring in each section of the circuit. The inputs required for the simulation are the feed composition, separation factors, equilibrium data of the key element under a wide range of conditions, the number of stages and flow rates of the aqueous and organic streams in the circuit. This model has been validated with the experimental data for the separation of Nd from a mixed lanthanide chloride feed with 2-ethylhexyl phosphonic acid mono 2-ethyl-hexyl ester (EHPNA) as an extractant.     

A kinetic model of the Peirce-Smith converter: Part II. Model application and discussion

A sensitivity analysis of a kinetics-based model of the Peirce-Smith converter has been carried out, and the model has then been applied to an analysis of copper converter operation. The results of the sensitivity analysis indicate that only factors relating to the mass-transfer rates have a significant effect on the model predictions. However, even with large changes in diffusivities, the model predictions remain within the error of the plant measurements. The converter analysis indicates that considerable improvements to converter productivity can be made, particularly through changes to gas injection practices.