Nonlinear Regression (nonlinear + regression)

Distribution by Scientific Domains

Terms modified by Nonlinear Regression

  • nonlinear regression analysis

  • Selected Abstracts


    Nonlinear Regression with R by RITZ, C. and STREIBIG, J. C.

    BIOMETRICS, Issue 3 2009
    Article first published online: 14 SEP 200
    No abstract is available for this article. [source]


    Spectroelectrochemical and Voltammetric Studies of L -DOPA

    ELECTROANALYSIS, Issue 2 2003
    Xiaoqiang Liu
    Abstract The electrooxidation of L -dopa at GC electrode was studied by in situ UV-vis spectroelectrochemistry (SEC) and cyclic voltammetry. The mechanism of electrooxidation and some reaction parameters were obtained. The results showed that the whole electrooxidation reaction of L -dopa at glassy carbon (GC) electrode was an irreversible electrochemical process followed by a chemical reaction in neutral solution (EC mechanism). The spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E0=228,mV, the apparent electron-transfer number of the electrooxidation reaction ,n=0.376 (R=0.99, SD=0.26), the standard electrochemical rate constant k0=(3.93±0.12)×10,4,cm s,1 (SD=1.02×10,2), and the formation equilibrium constant of the following chemical reaction kc=(5.38±0.34)×10,1,s,1 (SD=1.02×10,2) were also obtained. [source]


    Estimation of the soil,water partition coefficient normalized to organic carbon for ionizable organic chemicals,

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2008
    Antonio Franco
    Abstract The sorption of organic electrolytes to soil was investigated. A dataset consisting of 164 electrolytes, composed of 93 acids, 65 bases, and six amphoters, was collected from literature and databases. The partition coefficient log KOW of the neutral molecule and the dissociation constant pKa were calculated by the software ACD/Labs®. The Henderson-Hasselbalch equation was applied to calculate dissociation. Regressions were developed to predict separately for the neutral and the ionic molecule species the distribution coefficient (Kd) normalized to organic carbon (KOC) from log KOW and pKa. The log KOC of strong acids (pKa < 4) was not correlated to these parameters. The regressions derived for weak acids and bases (undissociated at environmental pH) were similar. The highest sorption was found for strong bases (pKa > 7.5), probably due to electrical interactions. Nonetheless, their log KOC was highly correlated to log KOW. For bases, a nonlinear regression was developed, too. The new regression equations are applicable in the whole pKa range of acids, bases, and amphoters and are useful in particular for relatively strong bases and amphoters, for which no predictive methods specifically have been developed so far. [source]


    Bacterial energetics, stoichiometry, and kinetic modeling of 2,4-Dinitrotoluene biodegradation in a batch respirometer

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2004
    Chunlong Zhang
    Abstract A stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, ,max, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium. [source]


    Predicting ready biodegradability in the Japanese ministry of international trade and industry test

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2000
    Jay Tunkel
    Abstract Two new predictive models for assessing a chemical's biodegradability in the Japanese Ministry of International Trade and Industry (MITI) ready biodegradation test have been developed. The new methods use an approach similar to that in the existing BIOWIN© program, in which the probability of rapid biodegradation is estimated by means of multiple linear or nonlinear regression against counts of 36 chemical substructures (molecular fragments) plus molecular weight (mol wt). The data set used to develop the new models consisted of results (pass/no pass) from the MITI test for 884 discrete organic chemicals. This data set was first divided into randomly selected training and validation sets, and new coefficients were derived for the training set using the BIOWIN fragment library and mol wt as independent variables. Based on these results, the fragment library was then modified by deleting some fragments and adding or refining others, and the new set of independent variables (42 substructures and mol wt) was fit to the MITI data. The resulting linear and nonlinear regression models accurately classified 81% of the chemicals in an independent validation set. Like the established BIOWIN models, the MITI models are intended for use in chemical screening and in setting priorities for further review. [source]


    Three lines of evidence in a sediment toxicity evaluation for hexachlorobutadiene

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2000
    Phyllis C. Fuchsman
    Abstract Three approaches were used in a site-specific sediment toxicity evaluation for hexachlorobutadiene (HCBD), a chemical not previously tested for toxicity in sediment. The results of a sediment dilution study, spiked sediment toxicity tests, and a probabilistic model based on equilibrium partitioning theory were used to estimate ecological effects thresholds for HCBD in sediments of a Gulf Coast estuary. Twenty-nine sediment samples, including 11 undiluted samples and six dilution series, were tested for toxicity under estuarine conditions (10%0 salinity) using Hyalella azteca and Leptocheirus plumulosus. Site sediment was used as diluent, and all samples were assayed for a range of organic and inorganic chemicals. A logistic relationship was observed between HCBD concentrations and organism response, and nonlinear regression explained approximately 90% of the observed variation in amphipod survival as a function of HCBD. Spiked sediment toxicity test results generally agreed with the results of the dilution study, demonstrating the causality of the observed concentration,response relationship. Effects thresholds were estimated as HCBD concentrations corresponding to 80% amphipod survival. The most conservative effects thresholds from the spiked sediment and dilution studies were 0.63 mg/kg normalized to 1% total organic carbon (mg/kg1%OC) for H. azteca and 1.4 mg/kg1%OC for L. plumulosus. Aquatic LC50s for 10 species and a measured acute,chronic ratio from the published literature were used to predict a distribution of sediment effects thresholds for HCBD, with 10th and 90th percentile values of 2.6 and 45 mg/kg1%OC, respectively. The predicted and observed sediment effects thresholds thus agreed relatively well, although the H. azteca and L. plumulosus test results from this study seem to be somewhat more conservative than the majority of published aquatic toxicity test results. [source]


    Phytotoxicity assay for seed production using Brassica rapa L.

    INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 4 2010
    David Olszyk
    Abstract Although pesticide drift can affect crop yield adversely, current plant testing protocols emphasize only the potential impacts on vegetative plant growth. The present study was conducted to determine whether a plant species with a short life cycle, such as Brassica rapa L. Wisconsin Fast Plants®, can be used to indicate potential effects on seed production of herbicides applied at relatively low levels (e.g., low field application rates [FAR]). The effects of ,0.1,×,FAR of aminopyralid, cloransulam, glyphosate, primisulfuron, or sulfometuron applied 14 d after emergence (DAE), were evaluated for B. rapa grown in mineral soil in pots under greenhouse conditions. Effects were expressed as the effective concentration of the herbicide producing a 25% reduction in a response (EC25) based on nonlinear regression. Brassica rapa seed dry weight was reduced by sulfometuron at an EC25 of 0.00014,×,a field application rate (FAR) of 53,g active ingredient (a.i.) ha,1, primisulfuron at 0.008 (experiment 1) or 0.0050 (experiment 2),×,FAR of 40,g,a.i.,ha,1, cloransulam at 0.022,×,FAR of 18,g,a.i.,ha,1, glyphosate at 0.0399,×,FAR of 834,g,a.i.,ha,1, and by aminopyralid at 0.005,×,FAR of 123,g,a.i.,ha,1, but only for 1 of 2 experiments. Reduced seed production occurred at less than the FAR that reduced shoot dry weight with sulfometuron and primisulfuron, whereas neither aminopyralid, cloransulam, nor glyphosate affected shoot dry weight. A short life cycle form of B. rapa could be used to indicate reduced seed production with plants grown only 1 week longer (,35,DAE) than as the current vegetative vigor test for nontarget herbicide effects on plants. Integr Environ Assess Manag 2010;6:725,734. © 2010 SETAC [source]


    Heterogeneity of the coumarin anticoagulant targeted vitamin K epoxide reduction system.

    JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 5 2006
    Study of kinetic parameters in susceptible, resistant mice (Mus musculus domesticus)
    Abstract Vitamin K epoxide reductase (VKOR) activity in liver microsomes from a susceptible and a genetically warfarin-resistant strain of mice (Mus Musculus domesticus) was analyzed to determine the mechanism of resistance to this 4-hydroxycoumarin derivative. Kinetic parameters for VKOR were calculated for each strain by incubating liver microsomes with vitamin K epoxide ± warfarin. In susceptible mice, an Eadie,Hofstee plot of the data was not linear and suggested the involvement of at least two different components. Apparent kinetic parameters were obtained by nonlinear regression using a Michaelis--Menten model, which takes into account two enzymatic components. Component A presents a high Km and a high Vm, and as a consequence only an enzymatic efficiency Vm/Km was obtained (0.0024 mL/min/mg). Estimated warfarin Ki was 0.17 ,M. Component B presented an apparent Km of 12.73 ,M, an apparent Vm of 0.32 nmol/min/mg, and an apparent Ki for warfarin of 6.0 ,M. In resistant mice, the enzymatic efficiency corresponding to component A was highly decreased (0.0003,0.00066 mL/min/mg) while the Ki for warfarin was not modified. The apparent Vm of component B was poorly modified between susceptible and resistant mice. The apparent Km of component B observed in resistant mice was similar to the Km observed in susceptible mice. These modifications of the catalytic properties are associated with a single nucleotide polymorphism (T175G) in the VKOR-C1 gene, which corresponds to a Trp59Gly mutation in the protein. © 2006 Wiley Periodicals, Inc. J Biochem Mol Toxicol 20:221,229, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20144 [source]


    Patterns of species richness on very small islands: the plants of the Aegean archipelago

    JOURNAL OF BIOGEOGRAPHY, Issue 7 2006
    Maria Panitsa
    Abstract Aim, To investigate the species,area relationship (SAR) of plants on very small islands, to examine the effect of other factors on species richness, and to check for a possible Small Island Effect (SIE). Location, The study used data on the floral composition of 86 very small islands (all < 0.050 km2) of the Aegean archipelago (Greece). Methods, We used standard techniques for linear and nonlinear regression in order to check several models of the SAR, and stepwise multiple regression to check for the effects of factors other than area on species richness (,habitat diversity', elevation, and distance from nearest large island), as well as the performance of the Choros model. We also checked for the SAR of certain taxonomic and ecological plant groups that are of special importance in eastern Mediterranean islands, such as halophytes, therophytes, Leguminosae and Gramineae. We used one-way anova to check for differences in richness between grazed and non-grazed islands, and we explored possible effects of nesting seabirds on the islands' flora. Results, Area explained a small percentage of total species richness variance in all cases. The linearized power model of the SAR provided the best fit for the total species list and several subgroups of species, while the semi-log model provided better fits for grazed islands, grasses and therophytes. None of the nonlinear models explained more variance. The slope of the SAR was very high, mainly due to the contribution of non-grazed islands. No significant SIE could be detected. The Choros model explained more variance than all SARs, although a large amount of variance of species richness still remained unexplained. Elevation was found to be the only important factor, other than area, to influence species richness. Habitat diversity did not seem important, although there were serious methodological problems in properly defining it, especially for plants. Grazing was an important factor influencing the flora of small islands. Grazed islands were richer than non-grazed, but the response of their species richness to area was particularly low, indicating decreased floral heterogeneity among islands. We did not detect any important effects of the presence of nesting seabird colonies. Main conclusions, Species richness on small islands may behave idiosyncratically, but this does not always lead to a typical SIE. Plants of Aegean islets conform to the classical Arrhenius model of the SAR, a result mainly due to the contribution of non-grazed islands. At the same time, the factors examined explain a small portion of total variance in species richness, indicating the possible contribution of other, non-standard factors, or even of stochastic effects. The proper definition of habitat diversity as pertaining to the taxon examined in each case is a recurrent problem in such studies. Nevertheless, the combined effect of area and a proxy for environmental heterogeneity is once again superior to area alone in explaining species richness. [source]


    Onium salt reduces the inhibitory polymerization effect from an organic solvent in a model dental adhesive resin

    JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008
    Fabrício A. Ogliari
    Abstract This study evaluated the effect of organic solvent concentration on the polymerization kinetics for a model dental adhesive resin containing a ternary photoinitiator system. A monomer blend based on the bis-GMA, TEGDMA, and HEMA was used as a model dental adhesive resin, which was polymerized using a binary system [camphorquinone (CQ) and ethyl 4-dimethylamine benzoate (EDAB)] and a ternary system [CQ, EDAB, and diphenyliodonium hexafluorphosphate (DPIHFP)]. Additionally, these blends had 0, 10, 20, 30, and 40 wt % ethanol added. Real-time Fourier transform infrared spectroscopy was used to investigate the polymerization reaction over photoactivation time. Data were plotted, and Hill's three-parameter nonlinear regression was performed for curve fitting. The addition of a solvent to the monomer blends decreased the polymerization kinetics, directly affecting the rate of polymerization, delaying vitrification, and attenuating the Trommsdorf effect. The introduction of DPIHFP displayed a strong increase in reaction kinetics, reducing the solvent inhibition effect. After 10 s of photoactivation, the binary system obtained in 0, 10, 20, 30, and 40% of ethanol, a degree of conversion of 44.6, 26.3, 13.4, 1.15, and 0.0%, respectively, whereas when a ternary system was used, the values were 54.6, 40.5, 27.4, 14.5, and 3.4%. An improvement was observed in the polymerization kinetics of a model dental adhesive resin when using a ternary photoinitiation system, making the material less sensitive to the residual presence of a solvent before photoactivation. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]


    Currency forecasting based on an error components-seemingly unrelated nonlinear regression model

    JOURNAL OF FORECASTING, Issue 8 2005
    Winston T. Lin
    Abstract This paper proposes to forecast foreign exchange rates by means of an error components-seemingly unrelated nonlinear regression (EC-SUNR) model and, simultaneously, explore the interrelationships among currencies from newly industrializing economies with those of highly industrialized countries. Based on the empirical results, we find that the EC-SUNR model improves on the performance of forecasting foreign exchange rates in comparison with an intrinsically nonlinear dynamic speed of adjustment model that has been shown to outperform several other important models in the forecasting literature. We also find evidence showing that the foreign exchange markets of the newly industrializing countries are influenced by those of the highly industrialized countries and vice versa, and that such interrelationships affect the accuracy of currency forecasting. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Multivariable real-time optimal control of a cooling and antisolvent semibatch crystallization process

    AICHE JOURNAL, Issue 10 2009
    Milana Trifkovic
    Abstract This article presents an experimental study of simultaneous optimization with respect to two variables (cooling rate and flow-rate of antisolvent) in an offline and online (real-time) manner on a semibatch crystallizer. The nucleation and growth kinetic parameters of paracetamol in an isopropanol-water cooling, antisolvent batch crystallizer were estimated by nonlinear regression in terms of the moments of the crystal population density. Moments of crystal population were estimated from the measured chord length distribution, generated by the FBRM®, and the supersaturation was calculated from the measured concentration by attenuated total reflectance-fourier transform infrared spectroscopy. The results of real-time optimization showed a substantial improvement of the end of batch properties (the volume-weighted mean size and yield). For the same objective function, the real-time optimization method resulted in an increase in the volume-weighted mean size by ,100 ,m and 15% of theoretical yield compared with the best result obtained in an offline optimization manner. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


    Unifying redox kinetics for standard and fast NH3 -SCR over a V2O5 -WO3/TiO2 catalyst

    AICHE JOURNAL, Issue 6 2009
    Isabella Nova
    Abstract A dynamic Mars,van Krevelen kinetic model that unifies Standard and Fast SCR reactions into a single redox approach is herein proposed for V-based catalysts for NOx removal from Diesel exhausts. Such a mechanistic model is consistent with the detailed catalytic chemistry proposed for the NH3 -NO/NO2 reacting system in which NO2 disproportionates to form nitrites and nitrates, nitrates are reduced by NO to nitrites in a key redox step, and nitrites react with NH3 to form N2 via decomposition of unstable ammonium nitrite. Intrinsic kinetic parameters were estimated by global multiresponse nonlinear regression of 42 transient runs. The model accounts for stoichiometry, selectivity, and kinetics of the global SCR process, reproducing successfully both the steady-state and transient behaviors of the SCR reacting system over the full range (0,1) of NO2/NOx feed ratios in the 175,425°C temperature range. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


    Kinetic modeling of the photocatalytic degradation of air-borne pollutants

    AICHE JOURNAL, Issue 5 2004
    H. Ibrahim
    Abstract The photocatalytic conversion of organic model pollutants (acetone, acetaldehyde, and isopropanol) in a novel Photo-CREC-Air unit is considered. This photocatalytic unit features: (1) external near-UV lamps placed in parabolic reflectors, (2) a basket supporting the irradiated glass mesh holding TiO2 loadings to achieve high photoconversion rates, and (3) a fluid flow pattern securing high gas velocities in the near-mesh region. Given the high quantum efficiencies observed in Photo-CREC-Air and, as a result, the high prospects for this novel design, rate equations and associated mechanistic formulations are investigated. With this goal, a Langmuir,Hinshelwood model, involving a one-site model pollutant mechanism, is considered. The associated kinetic parameters with the related statistical indicators are established, using least-square nonlinear regression. It is found that this model is adequate for describing the photodegradation of acetone on both Degussa P25 and Hombikat UV-100. It is also observed that the same type of reaction rate model is less adequate for the photodegradation of acetaldehyde and isopropanol, in particular, for predicting the formation of carbon dioxide. © 2004 American Institute of Chemical Engineers AIChE J 50: 1017,1027, 2004 [source]


    A novel method for deriving true density of pharmaceutical solids including hydrates and water-containing powders

    JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2004
    Changquan (Calvin) Sun
    Abstract True density is commonly measured using helium pycnometry. However, most water-containing powders, for example, hydrates, amorphous drugs and excipients, and most tablet formulations, release water when exposed to a dry helium atmosphere. Because released water brings significant errors to the measured true density and drying alters the nature of water-containing solids, the helium pycnometry is not suitable for those substances. To overcome this problem, a novel method has been developed to accurately calculate powder true density from compaction data. No drying treatment of powder samples is required. Consequently, the true density thus obtained is relevant to tableting characterization studies because no alteration to the solid is induced by drying. This method involves nonlinear regression of compaction pressure-tablet density data based on a modified Heckel equation. When true density values of water-free powders derived by this novel method were plotted against values measured using pycnometry, a regression line with slope close to unity and intercept close to zero was obtained. Thus, the validity of this method was supported. Using this new method, it was further demonstrated that helium pycnometry always overestimates true densities of water containing powders, for example, hydrates, microcrystalline cellulose (MCC), and tablet formulations. The calculated true densities of powders were the same for different particle shapes and sizes of each material. This further suggests that true density values calculated using this novel method are characteristic of given materials and independent of particulate properties. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:646,653, 2004 [source]


    Determination of dissociation constants of ten alkaloids by capillary zone electrophoresis

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 6-7 2003
    Suxuan Gong
    Abstract The dissociation constants of ten alkaloids, berbamine, (+)-tetrandrine, thalifaretine, thalifaricine, northaltive, matrine, sophocarpine, sophoridine, oxymatrine, and oxysophocarpine isolated from herbal medicines Thalictrum and Sophoraflavescens, were determined by capillary zone electrophoresis (CZE). The analysis time for each alkaloid was within 10 min under the following experimental conditions: acetate (pH 3.81,5.55) and phosphate buffer (pH 6.05,9.29) with ionic strength set at 0.03, applied voltage 30 kV, UV detection at 210 nm, capillary temperature 25°C. Effective mobility for each alkaloid and corresponding pH were fitted to an equilibrium expression by using nonlinear regression as well as linear regression, showing that the two models give comparable results for all studied alkaloids. The correlation coefficients were between 0.987 and 1.00 in the linear regression model, and between 0.978 and 1.00 in the nonlinear model. The measured pKa values for the ten alkaloids were from 5.7 to 7.8. The pKa values changed with the addition of organic additive to the buffer system. [source]


    MEASUREMENT OF FIRMNESS OF FRESH-CUT SLICED TOMATO USING PUNCTURE TESTS , STUDIES ON SAMPLE SIZE, PROBE SIZE AND DIRECTION OF PUNCTURE

    JOURNAL OF TEXTURE STUDIES, Issue 5 2007
    MILZA M. LANA
    ABSTRACT In order to investigate the firmness of tomato slices, two experiments were performed. In the first one, Monte Carlo simulation was used to study the variation in firmness within and between slices. Adding more slices and more measurements per slice reduced the SD, but in general, the efficiency of adding more slices was higher. In the second experiment, the firmness of tomato slices was measured by puncture test during storage, using one of three flat-tipped cylindrical probes (3.5-, 2.5- and 1.5-mm diameter) in two directions, along or perpendicular to the main axis of the fruit. Changes in firmness were studied by nonlinear regression analysis. The same model could be applied to all combinations of probe size and direction with the same correction for shear and compression. It suggests that shear and compression forces decay with storage time according to the same mechanism, irrespective of the measurement direction. PRACTICAL APPLICATIONS Methodologies for both firmness evaluation and data analysis were presented. Monte Carlo simulation was used to optimize the number of samples for firmness assays. After calculating the experimental SD from preliminary experimental results, simulations were performed with different numbers of replicates and measurements per replicate, to find an optimal experimental design where the SD is minimized. Using nonlinear regression, the effects on firmness of probe size, puncture direction in relation to the plant tissue and storage time can be analyzed simultaneously. The incorporation of a correction factor to account for differences in firmness due to probe size was proposed. The relative influence of shear (s) and compression force (c) on the observed force is estimated. Results of interest for the industry were presented, confirming previous findings that the firmness of ripened tomato slices measured by puncture analysis does not change significantly during short-term storage at low temperature. [source]


    Synthesis and Characterization of Poly(N -vinylimidazole- co -acrylonitrile) and Determination of Monomer Reactivity Ratios

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2004
    Nursel Pekel
    Abstract Summary: Radical-initiated solution copolymerization of N -vinylimidazole (VIM) and acrylonitrile (AN) was carried out with 2,2, -azobisisobutyronitrile (AIBN) as an initiator in benzene at 70,°C in nitrogen atmosphere. The structure and composition of synthesized copolymers for a wide range of monomer feeds were determined by FTIR, 1H and 13C NMR spectroscopy with the aid of recorded analytical absorption bands for VIM (667 cm,1, CN of imidazole ring) and AN (2,242 cm,1, CN group), as well as by using the areas of proton and carbon atom signals from corresponding functional groups of monomer units. Monomer reactivity ratios for VIM (M1)-AN (M2) pair were determined by nonlinear regression (NLR), Kelen,Tüdös (KT) and Fineman,Ross (FR) methods. They were found to be r1,=,0.24 and r2,=,0.15 for the NLR method, r1,=,0.22 and r2,=,0.094 for the KT method, and r1,=,0.24 and r2,=,0.12 for the FR method, respectively. The relatively high activity observed of VIM growing macroradical and the results of FTIR and 1H NMR structural analysis of copolymers suggest the formation of complexed linkages between monomers and growing radicals in chain propagation reactions. Similar complexation between monomer,comonomer units in the structure of formed macromolecules showed an increase in isotactic triad fractions in the copolymer. Complex formation between the imidazole ring and nitrile group in both the monomer mixture and chain growing reactions. [source]


    QRS Amplitude and Shape Variability in Magnetocardiograms

    PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 2 2000
    MARKUS HUCK
    In magnetocardiography, averaging of QRS complexes is often used to improve the signal-to-noise ratio. However, averaging of QRS complexes ignores the variation in amplitude and shape of the signals caused, for example, by respiration. This may lead to suppression of signal portions within the QRS complexes. Furthermore, for inverse source, reconstructions of dipoles and of current density distributions errors in the special arrangement may occur. To overcome these problems we developed a method for separating and selective averaging QRS complexes with different shapes and amplitudes. The method is based on a spline interpolation of the QRS complex averaged by a standard procedure. This spline function then is fitted to each QRS complex in the raw data by means of nonlinear regression (Levenberg-Marquardt method). Five regression parameters are applied: a linear amplitude scaling, two parameters describing the baseline drift, a time scaling parameter, and a time shift parameter. We found that both amplitude and shape of the QRS complex are influenced by respiration. The baseline shows a weaker influence of the respiration. The regression parameters of two neighboring measurement channels correlate linearly. Thus, selective averaging of a larger number of sensors can be performed simultaneously. [source]


    Robust sequential designs for nonlinear regression

    THE CANADIAN JOURNAL OF STATISTICS, Issue 4 2002
    Sanjoy Sinha
    Abstract The authors introduce the formal notion of an approximately specified nonlinear regression model and investigate sequential design methodologies when the fitted model is possibly of an incorrect parametric form. They present small-sample simulation studies which indicate that their new designs can be very successful, relative to some common competitors, in reducing mean squared error due to model misspecifi-cation and to heteroscedastic variation. Their simulations also suggest that standard normal-theory inference procedures remain approximately valid under the sequential sampling schemes. The methods are illustrated both by simulation and in an example using data from an experiment described in the chemical engineering literature. Les auteurs définissent formellement le concept de modéle de régression non linéaire approxima-tif et proposentdes plans d'expérience séquentiels pour les situations o4uG la forme paramétrique du modéle ajusté est inexacte. Ils présentent une étude de simulation qui montre que, pour de petits échantillons, leurs nouveaux plans sont largement préférables aux plans usuels en terme de réduction de I'erreur quadratique moyenne associée à rinadéquation du modéle et à l'hétéroscédasticité. Leurs simulations montrent aussi que les procédures d'inférence classiques associées au paradigme normal restent valables, à peu de choses prés, pour ces plans expéimentaux se'quentiels. La methodologie proposde est illustrée par voie de simulation et au moyen d'une application concréte tirée de la pratique du génie chimique. [source]


    Application in stochastic volatility models of nonlinear regression with stochastic design

    APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 2 2010
    Ping Chen
    Abstract In regression model with stochastic design, the observations have been primarily treated as a simple random sample from a bivariate distribution. It is of enormous practical significance to generalize the situation to stochastic processes. In this paper, estimation and hypothesis testing problems in stochastic volatility model are considered, when the volatility depends on a nonlinear function of the state variable of other stochastic process, but the correlation coefficient |,|,±1. The methods are applied to estimate the volatility of stock returns from Shanghai stock exchange. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    3-Fluoro-2,4-dioxa-3-phosphadecalins as Inhibitors of Acetylcholinesterase.

    CHEMISTRY & BIODIVERSITY, Issue 3 2009
    A Reappraisal of Kinetic Mechanisms, Diagnostic Methods
    Abstract A systematic survey of the acetylcholine-mimetic 2,4-dioxa-3-phosphadecalins as irreversible inhibitors of acetylcholinesterase revealed hitherto overlooked properties as far as the kinetic mechanisms of interaction are concerned. As a support to past and future work in this field, we describe the kinetics of eight reaction schemes that may be found in irreversible enzyme modification and compare them with two mechanism of reversible, slow-binding inhibition. The relevant kinetic equations and their associated graphical representations are given for all mechanisms, and concrete examples illustrate their practical use. Since irreversible inhibition is a time-dependent phenomenon, kinetic analysis is greatly facilitated by fitting the appropriate integrated rate equations to reaction-progress curves by nonlinear regression. This primary scrutiny provides kinetic parameters that are indispensable tools for diagnosing the kinetic mechanism and for calculating inhibition constants. Numerical integration of sets of differential equations is an additional useful investigation tool in critical situations, e.g., when inhibitors are unstable and/or act as irreversible modifiers only temporarily. [source]


    Parametric study on the silica gel,calcium chloride composite desiccant rotary wheel employing fractal BET adsorption isotherm

    INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 1 2005
    X. J. Zhang
    Abstract In this paper a family of new silica gel,calcium chloride composite adsorbents is presented for desiccant rotary wheel in dehumidification system. For these desiccants the water sorption equilibrium has been measured in a wide relative vapour pressure range. This experimental study shows that the vapour adsorption properties of the composites using calcium chloride as impregnated salt can be controllably modified by varying the amount of the salt inside the pores. The thermodynamic performance of such desiccant rotary wheel is analysed based on the adsorption equilibrium equations obtained through nonlinear regressions using fractal BET theory. The simulation results show that the new composite desiccants can be effectively used in a rotary wheel dehumidifier and to improve its performance, various optimum operational/system parameters have been identified. Copyright © 2005 John Wiley & Sons, Ltd. [source]


    Spatial patterns in species,area relationships and species distribution in a West African forest,savanna mosaic

    JOURNAL OF BIOGEOGRAPHY, Issue 4 2005
    Thomas Hovestadt
    Abstract Aim, To investigate the relationship between the slope z of the species,area relationship (SAR) and the intensity of spatial patterns in species number and dissimilarity for woody plants with different modes of seed dispersal. According to island theory we expect, for any given archipelago, steeper slopes and more pronounced spatial patterns for groups of less dispersive species. Location, Ivory Coast, West Africa. Methods, In a West African forest,savanna mosaic we collected presence,absence data for woody plant species in 49 forest islands. The parameters of the SARs were fitted by nonlinear regressions and then compared for plant species aggregated according to their mode of seed dispersal. We used the Mantel test to calculate the intensity of spatial patterns in species number, i.e. residual deviation from SAR, and species dissimilarity. Results, The z -value for bird-dispersed species was lower (0.11) than that for wind-dispersed species (0.27), with mammal-dispersed species taking an intermediate value (0.16). This result suggests that, as a group, bird-dispersed species are better colonizers. The spatial pattern in species number as well as species similarity was more pronounced for bird- compared with wind-dispersed species. Main conclusions, The standard interpretation of the theory of island biogeography claims that shallow slopes in the SAR imply low isolation of islands, i.e. good dispersal abilities of species. The results of our study appear to contradict this statement. The contradiction can eventually be resolved by a more detailed account of the colonization process, i.e. by distinguishing between dispersal and consecutive establishment of populations. [source]


    DIMENSIONLESS CORRELATIONS FOR CONVECTIVE HEAT TRANSFER IN CANNED PARTICULATE FLUIDS UNDER AXIAL ROTATION PROCESSING

    JOURNAL OF FOOD PROCESS ENGINEERING, Issue 2010
    MRITUNJAY DWIVEDI
    ABSTRACT Dimensionless correlations for estimating heat transfer coefficients (U and hfp) in canned high viscosity Newtonian liquids (with and without particles) were developed using stepwise multiple nonlinear regressions of statistically significant dimensionless groups using tangent as an estimate and Newton as search method. Data on overall heat transfer coefficient U and fluid-to-particle heat transfer coefficients hfpwere obtained for several processing conditions and were analyzed separately for particle and particle-free conditions. In free axial mode, a newly developed form, combining natural and forced convection, provided higher R2 = 0.93. In the absence of particles in end-over-end mode, introducing natural convection term (Gr × Pr), improved R2 from 0.81 to 0.97. Combination of the reel radius, radius of the can and radius of the particles was chosen as characteristics length. PRACTICAL APPLICATIONS Most earlier dimensionless correlations for a canned liquid particulate mixture subjected to free axial mode of agitation are present for either U or hfp individually due to the difficulties in obtaining time,temperature profiles of the liquid and particles simultaneously; however, the time,temperature prediction at the particle center requires appropriate correlations for both U and hfp and cannot be made with only one of these coefficients. Additionally, importance of natural convection in forced convection heat transfer correlations has been demonstrated by developing the U and hfp correlations using the mixed convection approach as the combination of natural and forced convection heat transfer. These developed correlations would help in modeling the time,temperature profiles of a canned particulate mixture and will be helpful in determining the contribution of natural and forced convection heat transfer. These dimensional numbers would give a better understanding of the physical phenomenon and can also be easily used for scale-up purposes. [source]