Set Of Model Parameter Values Research Articles

Branched pore kinetic model analysis of geosmin adsorption on super-powdered activated carbon

Super-powdered activated carbon (S-PAC) is activated carbon of much finer particle size than powdered activated carbon (PAC). Geosmin is a naturally occurring taste and odor compound that impairs aesthetic quality in drinking water. Experiments on geosmin adsorption on S-PAC and PAC were conducted, and the results using adsorption kinetic models were analyzed. PAC pulverization, which produced the S-PAC, did not change geosmin adsorption capacity, and geosmin adsorption capacities did not differ between S-PAC and PAC. Geosmin adsorption kinetics, however, were much higher on S-PAC than on PAC. A solution to the branched pore kinetic model (BPKM) was developed, and experimental adsorption kinetic data were analyzed by BPKM and by a homogeneous surface diffusion model (HSDM). The HSDM describing the adsorption behavior of geosmin required different surface diffusivity values for S-PAC and PAC, which indicated a decrease in surface diffusivity apparently associated with activated carbon particle size. The BPKM, consisting of macropore diffusion followed by mass transfer from macropore to micropore, successfully described the batch adsorption kinetics on S-PAC and PAC with the same set of model parameter values, including surface diffusivity. The BPKM simulation clearly showed geosmin removal was improved as activated carbon particle size decreased. The simulation also implied that the rate-determining step in overall mass transfer shifted from intraparticle radial diffusion in macropores to local mass transfer from macropore to micropore. Sensitivity analysis showed that adsorptive removal of geosmin improved with decrease in activated carbon particle size down to 1 μm, but further particle size reduction produced little improvement.

Integrating human indoor air pollutant exposure within Life Cycle Impact Assessment.

Neglecting health effects from indoor pollutant emissions and exposure, as currently done in Life Cycle Assessment (LCA), may result in product or process optimizations at the expense of workers’ or consumers’ health. To close this gap, methods for considering indoor exposure to chemicals are needed to complement the methods for outdoor human exposure assessment already in use. This paper summarizes the work of an international expert group on the integration of human indoor and outdoor exposure in LCA, within the UNEP/SETAC Life Cycle Initiative. A new methodological framework is proposed for a general procedure to include human-health effects from indoor exposure in LCA. Exposure models from occupational hygiene and household indoor air quality studies and practices are critically reviewed and recommendations are provided on the appropriateness of various model alternatives in the context of LCA. A single-compartment box model is recommended for use as a default in LCA, enabling one to screen occupational and household exposures consistent with the existing models to assess outdoor emission in a multimedia environment. An initial set of model parameter values was collected. The comparison between indoor and outdoor human exposure per unit of emission shows that for many pollutants, intake per unit of indoor emission may be several orders of magnitude higher than for outdoor emissions. It is concluded that indoor exposure should be routinely addressed within LCA.

Extracting Risk Insights from Performance Assessments for High-Level Radioactive Waste Repositories

Performance assessments (PAs) are important sources of information for societal decisions in high-level radioactive waste (HLW) management, particularly in evaluating safety cases for proposed HLW repository development. Assessing risk from geologic repositories for HLW poses a significant challenge due to the uncertainties in modeling complex systems of such large temporal and spatial scales. Because of the extensive uncertainties, a typical safety case for a proposed HLW repository is comprised of PA results coupled with various defense-in-depth elements, such as the multibarrier requirement for repository design, and insights from supplementary analyses. This paper proposes an additional supplementary analysis, the Strategic Partitioning of Assumption Ranges and Consequences (SPARC), that could be used (a) in a safety case to help build confidence in a repository system and (b) to provide risk information for decisions on how to allocate resources for future research. The SPARC method extracts risk information from existing PAs and supporting databases by uncovering new information—namely, what sets of model parameter values taken together could produce substantially increased doses (SIDs) from the repository—and displays the results in SPARC trees. These sets of parameter values correspond to the failure scenarios of reactor probabilistic risk assessments. The SPARC method is applied to the proposed Yucca Mountain HLW repository, as a demonstrative example, and the results indicate that just one or a couple of the repository features working alone could “save” the repository from SIDs even in extremely challenging conditions. Such insights produced with the SPARC method could help significantly in focusing resources on future research to build confidence in the repository.

Pseudospin-electron model spectrum in alloy analogy approximation

Energy spectrum of the pseudospin-electron model is investigated in the alloy analogy approximation within the framework of the dynamical mean field theory (DMFT). The case of two near Hubbard-like electron subbands, which determine the location of chemical potential at a certain set of model parameter values, is considered. The conditions of gap appearance in the spectrum are established. The effect of the asymmetry field h and tunneling-like splitting of levels in the local anharmonic well on the critical value Ucrit of the on-site Hubbard interaction constant is investigated.

Verification of 3-PG growth and water-use predictions in twelve Eucalyptus plantation stands in Zululand, South Africa

Process-based forestry models are seen by the South African forestry industry as potentially useful tools for improving predictions of growth and water use in forest plantations. The 3-PG process-based forest model was evaluated in South Africa using limited Eucalyptus and Pinus trial data, with encouraging results. Some uncertainty exists, however, over whether 3-PG will prove to be a practical forest management tool on forestry estates that typically comprise scores of compartments (planted even-aged stands) covering a wide range of site conditions, species/clone and tree age. Two important questions require answers: (i) is 3-PG capable of modelling growth over a wide range of site growth potential to useful accuracy and (ii) are there practical methods for estimating or measuring all of the required parameter values for the model? To answer these questions, 12 stands of Eucalyptus grandis×camaldulensis hybrid clones, representing early, mid and late rotation age, and covering a wide range of site growth potential in the Zululand region (KwaZulu-Natal Province), were intensively studied over a period of 12 months. Measurements of initial and final biomass, leaf area index, biomass allometric ratios, litterfall, specific leaf area, sap-flow rates, pre-dawn xylem pressure potential and weather conditions were made throughout the year. Two influential site parameter values (maximum available soil-water capacity and a soil fertility rating) required indirect estimation, since relevant information was lacking and difficult to obtain from the field. A pragmatic approach to estimating these parameters is described. Annual tree growth predicted by the model, and daily ranges of sap flow, were compared to field measurements. Predictions of annual growth increment (dry mass of stems and branches) were acceptable for 11 of the 12 stands ( Y=0.85 X+1.7, r 2=0.84). The twelfth stand, which had an extremely high annual growth increment, high leaf area and year-long access by the trees to shallow groundwater, was substantially underpredicted. This is attributed to likely physiological adaptions to the long-term absence of water stress at this site. We conclude that 3-PG can realistically simulate growth and water use over a wide range of rotation age and growth conditions. Preliminary sets of model parameter values for a range of diverse stands may be estimated over a relatively short period using simple field equipment and techniques. Further testing of these parameter values at physiologically significant times over the remainder of the rotation is recommended to test model output and permit fine-tuning of parameters.

Validation of a decision support system for use in drug development: pharmacokinetic data.

Single dose pharmacokinetic data from several individuals can be used to predict the fraction of the population that is expected to be within a therapeutic range. Without having some measure of its reliability, however, that prediction is only likely to marginally influence critical drug development decision making. The system (Forecaster) described generates an approximate prediction interval that contains the original prediction and where, for example, the probability is approximately 85% that a similar prediction from a new set of data will also be within the range. The goal is to validate that the system functions as designed. The strategy requires having a Surrogate Population (SP), which is a large number (> or = 1500) of hypothetical individuals each represented by set of model parameter values having unique attributes. The SP is generated so that a sample taken from it will give data that is statistically indistinguishable from the available experimental data. The automated method for building the SP is described. Validation studies using 300 independent samples document that for this example the SP can be used to make useful predictions, and that the approximate prediction interval functions as designed. For the boundary conditions and assumptions specified, the Forecaster can make valid predictions of pharmacokinetic-based population targets that without a SP would not be possible. Finally, the approximate prediction interval does provide a useful measure of prediction reliability.

Effect of improved subgrid scale transport of tracers on uptake of bomb radiocarbon in the GFDL Ocean General Circulation Model

We show that the Gent‐McWilliams tracer transport parameterization greatly improves the ability of the GFDL ocean general circulation model to simulate vertical profiles of both temperature and bomb radiocarbon with a single set of model parameter values. This parameterization, which includes new advection terms as well as isopycnal mixing, has previously been shown to greatly improve simulated temperature fields. Here, we show that it does not markedly affect the already good simulation of oceanic absorption of bomb radiocarbon, and discuss the reasons for this result.

Muscle-joint models incorporating activation dynamics, moment-angle, and moment-velocity properties.

Muscle input/output models incorporating activation dynamics, moment-angle, and moment-velocity factors are commonly used to predict the moment produced by muscle during nonisometric contractions; the three factors are generally assumed to be independent. We examined the ability of models with independent factors, as well as models with coupled factors, to fit input/output data measured during simultaneous modulation of the fraction of muscle stimulated (recruitment) and joint angle inputs. The models were evaluated in stimulated cat soleus muscles producing ankle extension moment, with regard to their potential applications in neuroprostheses with either fixed parameters or parameter adaptation. Both uncoupled and coupled models predicted the output moment well for random angle perturbation sizes ranging from 10 degrees to 30 degrees. For the uncoupled model, the best parameter values depended on the range of perturbations and the mean angle. Introducing coupling between activation and velocity in the model reduced this parameter sensitivity; one set of model parameter values fit the data for all perturbation sizes and also fit the data under isometric or constant stimulation conditions. Thus, the coupled model would be the most appropriate for applications requiring fixed parameter values. In contrast, with continuous parameter adaptation, errors due to changing test conditions decreased more quickly for the uncoupled model, suggesting that it would perform well in adaptive control of neuroprostheses.

Modelling the impact of mass vaccination against hepatitis B. I. Model formulation and parameter estimation.

A new model of the transmission dynamics of hepatitis B virus in countries with high transmission rates is presented. The model is age and sex stratified, and includes details of host demography. Details of hepatitis B natural history, such as the existence of infectious and non-infectious carriers, are included. The biological assumptions of the model are discussed in full and related to the model's equations. Hepatitis B epidemiological data is reviewed with special emphasis on the estimation of model parameter values from field data. A full set of model parameter values are derived. Possible uses of the model in the assessment of strategies of mass vaccination are discussed.

Significance of conductances in Hodgkin-Huxley models.

1. We explore the roles of conductances in Hodgkin-Huxley (HH) models using a method that allows the explicit linking of HH model input-output behavior to parameter values for maximal conductances, voltage shifts, and time constants. The procedure can be used to identify not only the parameter values most critical to supporting a neuronal activity pattern of interest but also the relationships between parameters which may be required, e.g., limited ranges of relative magnitudes. 2. The method is the repeated use of stochastic search to find hundreds or even thousands of different sets of model parameter values that allow a HH model to produce a desired behavior, such as current-frequency transduction, to within a desired tolerance, e.g., frequency match to within 10 Hz. Graphical or other analysis may then be performed to reveal the shape and boundaries of the parameter solution regions that support the desired behavior. 3. The shape of these parameter regions can reveal parameter values and relationships essential to the behavior. For instance, graphical display may reveal covariances between maximal conductance values, or a much wider range of variation in some maximal conductance values than in others. 4. We demonstrate the use of these techniques with simple, representative HH models, primarily that of Connor et al. for crustacean walking leg axons, but also some extensions of the results are explored using the more complex model of McCormick and Huguenard for thalamocortical relay neurons. Both models are single compartment. Behaviors studied include current-to-frequency transduction, the time delay to first action potential in response to current steps, and the timing of action potential occurrences in response to both square-wave current injection and the injection of currents derived from in vitro records of excitatory postsynaptic currents. 5. Using these simple models, we find that relatively general behaviors such as current-frequency (I/F) curves may be supported by very broad, but bounded parameter solution regions, with the shape of the solution regions revealing the relative importance of the maximal conductances of a model in creating the behavior. Furthermore, we find that a focus on increasingly specific behaviors, such as I/F behavior, defined by tolerances of only a few hertz combined with strict requirements for action potential height, inevitably leads to increasingly narrow, and eventually nonphysiologically narrow, regions of acceptable parameter values. 6. We use the Connor et al. model to reproduce the in vitro action potential timing responses of a rat brain stem neuron to various stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Solute transport in aggregated porous media: Comparing model independent and dependent parameter estimation

In many studies on solute transport soil column experiments arc used to obtain the transport characteristics for Convection-Dispersion-Models. Early breakthrough of the solute pulse has been attributed to a non-equilibrium in phase exchange. It is a standard procedure to determine several model parameter values from such breakthrough curves (BTC). This investigation is focused on the physical significance of simultaneously fitted parameter values used in the convection and diffusion-controlled mass transfer model (mobile — immobile phase concept). Saturated column experiments were conducted with solid phases consisting of porous and solid glass beads. One set of model parameter values was obtained from the breakthrough curves by simultaneous optimization and a second set was determined by independent measurements of individual parameter values. Both sets of parameter values described the BTCs equally well but deviated substantially from each other. These discrepancies were analysed in terms of local parameter sensitivities.

Theoretical Treatment of Magnetic Field Dependent In-cage Backward Electron Transfer During Photooxidation of Ru(II) Complexes

A theoretical treatment is presented of the magnetic field dependence of in-cage backward electron transfer within the primary redox pair originating from electron transfer between photoexcited Ru(II)-trisbipyridyl [Ru(bpy)~+] and methylviologen (MV2+). The treatment is based on the numerical solution of a stochastic Liouville equation for a density matrix represented in the basis of an explicitly given set of spin-orbit states of the redox pair [Ru(bpyH + ... MV'']. Calculations with various sets of model parameter values were performed in order to obtain the best fit to the experimentally observed magnetic field dependence of the efficiency ofcage escape. A reasonable simulation required the assumption of substantial initial singlet character of the primary redox pair and a very high rate of relaxation within the set of its four lowest spin-orbit states. A rate constant of about 1011 s-1 for a hypothetically spin-allowed backward electron transfer was evaluated.

Comparison of proton and neutron spectra: The extended Griffin model, pairing and isospin

The energy spectra of protons and neutrons emitted in proton induced reactions on the targets103Rh,159Tb, and169Tm were measured at a bombarding energy of 18 MeV and at a variety of emission angles. Angle-integrated emission spectra were calculated and compared with preequilibrium model predictions. The general validity of the extended Griffin model with a systematic empirical set of model parameter values was verified. Evidence was obtained for the conservation (partial or complete) of isospin as a quantum number and for the possible utility of including a pairing energy shift in the calculations.