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Curve Fitting (curve + fitting)
Selected AbstractsTemperature-Dependent Optical Reflectivity of Tetragonal-Prime Yttria-Stabilized ZirconiaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006John A. Nychka The optical reflectance of dense, metastable, tetragonal-prime zirconia plates, made by densifying electron beam physical vapor-deposited powder, is reported as a function of temperature up to 1673 K (1400°C) over the range of 400,1500 cm,1 (6.67,25 ,m). Curve fitting of the reflectance as a function of temperature was performed using two different damped oscillator models, each with three infrared (IR)-active modes. Oscillator parameters were then used to calculate the values of the indices of refraction and absorption as a function of temperature using the classical dispersion theory. The reflectance data of tetragonal-prime yttria-stabilized zirconia at room temperature are qualitatively similar to that reported for the equilibrium tetragonal phase in that it can be fit with three IR-active modes. [source] Nonlinear Damping Identification in Precast Prestressed Reinforced Concrete BeamsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2009P. Franchetti Integrated static and dynamic experiments were carried out on three precast PRC beam specimens. The static loading induced different levels of damage to the beams. At each damage level, impulsive loading was applied to the beams and the free vibration response was measured. The dynamic response data were processed using different methods including the multi-input multi-output (MIMO) curve fitting and the Hilbert transform techniques. A strong correlation is observed between the level of concrete damage (cracks) and the amount of nonlinear energy dissipation that can be modeled by means of quadratic damping. The nonlinear damping can be extracted from the free vibration response for each vibration mode. The proposed method is suited for quality control when manufacturing precast PRC members, and can be further extended for in situ detection of damage in concrete structures under ambient vibration. [source] Effect of urea on analyte complexation by 2,6-dimethyl-,-CD in peptide enantioseparations by CEELECTROPHORESIS, Issue 21 2009Manuela Hammitzsch-Wiedemann Abstract The aim of the present study was the investigation of the effect of urea on analyte complexation in CD-mediated separations of peptide enantiomers by CE in the pH range of about 2,5. pH-independent complexation and mobility parameters in the absence and presence of 2,M urea were obtained by three-dimensional, non-linear curve fitting of the effective analyte mobility as a function of pH and heptakis-(2,6-di- O -methyl)-,-CD concentration. Urea led to decreased binding strength of the CD towards the protonated and neutral analyte enantiomers as well as to decreased mobilities of the free analytes. In contrast, mobilities of the fully protonated enantiomer,CD complexes as well as the pKa values of the free and complexed analytes increased. The effect of urea on separation efficiency varied with pH and CD concentration. In the case of Ala-Tyr and Ala-Phe, separations improved in the presence of urea at pH 2.2. In contrast, separations were impaired by urea at pH 3.8 and low concentrations of the CD. Decreased separation efficiency was noted for Asp-PheOMe and Glu-PheNH2 at low CD concentrations when urea was added but separations improved at higher CD concentrations over the entire pH range studied. The effect of urea on analyte complexation appeared to be primarily non-stereoselective. Furthermore, the pH-dependent reversal of the enantiomer migration order observed for Ala-Tyr and Ala-Phe can be rationalized by the complexation and mobility parameters. [source] Calix[4]arene-Based Chromogenic Chemosensor for the ,-Phenylglycine Anion: Synthesis and Chiral RecognitionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2006Guang-Yan Qing Abstract Calix[4]arene-based two-armed chiral anion receptors 3a and 3b have been synthesized and examined for their chiral anion-binding abilities by UV/Vis absorption and 1H NMR spectroscopy. The results of nonlinear curve fitting indicate that 3a and 3b form 1:1 stoichiometric complexes with the L - or D -,-phenylglycine anion by multiple hydrogen-bonding interactions and exhibit good enantioselective recognition for the enantiomers of the ,-phenylglycine anions (3a: Kass(L)/Kass(D) = 4.76; 3b: Kass(D)/Kass(L) = 2.84). The marked colour changes observed for the complexation of 3a with the chiral anions and the good enantioselective recognition reveal that receptor 3a could be used as a good chiral chromogenic chemosensor for the enantiomers of the ,-phenylglycine anion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Fityk: a general-purpose peak fitting programJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5-1 2010Marcin Wojdyr Fityk is portable, open-source software for nonlinear curve fitting and data analysis. It specializes in fitting a sum of bell-shaped functions to experimental data. In particular, it enables Pawley refinement of powder diffraction data and size,strain analysis. [source] Onium salt reduces the inhibitory polymerization effect from an organic solvent in a model dental adhesive resinJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Fabrício 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] Monitoring of a second-order reaction by electronic absorption spectroscopy using combined chemometric and kinetic modelsJOURNAL OF CHEMOMETRICS, Issue 6 2003Tom J. Thurston Abstract This paper reports the application of 11 methods for obtaining kinetic constants from a second-order reaction, that between phenylhydrazine and benzophenone. In this type of reaction the number of absorbing species is lower than the number of steps in the reaction minus one, resulting in a rank-deficient response matrix. The methods used include traditional univariate curve fitting, classical least squares using previously recorded pure spectra, alternating least squares methods with both kinetic and non-negativity constraints, and target-testing methods using principal component scores. An additional recently proposed method based on difference spectra is also examined, suitable for any single-step closed reaction. The methods that performed best were difference spectra, kinetically constrained alternating least squares, and target-testing approaches. Limitations of the traditional methods are described. Copyright © 2003 John Wiley & Sons, Ltd. [source] A study of collective motions in liquid tert -butanol from low-wavenumber Raman scatteringJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2009P. Sassi Abstract The collective properties of liquid tert -butyl alcohol (TBA) were analysed by low-wavenumber Raman (LWR) scattering spectroscopy. Vibrational and relaxation phenomena of this H-bonding system were assessed in pure liquid phase at different temperatures in the 15,70 °C range, and in solution with 2,2,-dimethyl butane (2,2,-DMB) and water as a function of composition in the 0.7,xTBA,0.9 range at constant temperature (T = 25 °C). The LWR spectrum of pure TBA (below 150 cm,1) was expressed by the dynamical (or Raman) susceptibility ???? and reproduced by curve fitting using three functional forms. The high-wavenumber band, whose intensity is poorly dependent on the temperature, was assigned to the ultrafast librational mode; the remaining components with an intensity that increased with temperature were attributed to relaxation dynamics in the range of picosecond (,slow' 3 ps) and sub-picosecond (,fast', 0.4 ps) timescales. Adding 2,2,-DMB to TBA had no significant effect on the intermolecular interactions in alcohol-rich solutions, with almost unchanged LWR scattering features. On the other hand, water added to TBA determined an increase in interactions, similar to the effect of a temperature decrease in pure liquid alcohol; this was clearly depicted by the LWR profiles. Moreover, through the analysis of the OH stretching bands of water in solution, the confinement of aqueous pools in the hydrophilic spaces of alcohol-rich solutions was confirmed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Michaelis-Menten Elimination Kinetics of Acetaldehyde During Ethanol OxidationALCOHOLISM, Issue 2002Tatsuya Fujimiya Background Acetaldehyde (AcH) is a toxic metabolite of ethanol (EtOH). The pharmacokinetics of blood AcH during EtOH oxidation was studied with or without the administration of aldehyde dehydrogenase 2 inhibitor (cyanamide) in rabbits. Methods An bolus of EtOH saline solution (0.25, 0.5, 1.0, 1.5, and 2.0 g/kg) was injected intravenously. Cyanamide was administered intraperitoneally (25 mg/kg body weight) to the cyanamide-treated group. Blood EtOH and AcH concentrations were measured by using head-space gas chromatography. Results In the control group, the first peak of the blood AcH appeared immediately and the second elevation appeared 1 to 4 hr after administration at a high EtOH dose. The blood AcH levels other than the second elevation part were significantly correlated to the blood EtOH levels. In the cyanamide-treated group, a peak and a plateau formed at the time corresponding to the second peak in the control group. The peak and plateau concentration of AcH increased markedly. We attempted simultaneous curve fitting, using the five blood EtOH and AcH concentration-time curves, to determine the pharmacokinetic model. Consequently, the AcH elimination was best described by a Michaelis-Menten kinetic model in both groups. Conclusions The blood AcH profile was suggested to consist of the first and second components that are related to the blood EtOH concentration itself and the metabolic formation of AcH, respectively. With higher EtOH doses or aldehyde dehydrogenase 2 inhibition, the second component becomes prominent as a result of the capacity-limited property of the metabolism of AcH, which is described by Michaelis-Menten elimination kinetics. [source] Proton Conductivity Measurements in Yttrium Barium Cerate by Impedance SpectroscopyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2002W. Grover Coors Proton-conducting solid-electrolyte perovskite ceramics based on acceptor-doped barium and strontium cerates have become the focus of extensive investigations as candidate materials for fuel cells that operate at moderate temperatures. To assess the suitability of a material for this application, it is necessary that bulk electrolyte conductivity be measured at the operating temperature. However, very little reliable published conductivity data exist above 600°C. Protonic conductivity in yttrium-doped barium cerate has been observed to be less at high temperatures than would be expected, based on the activation energy and preexponential for hydrogen transport at temperatures <300°C. Conductivity data obtained from impedance spectroscopy on BaCe0.9Y0.1O3,, over the extended temperature range of 100°,900°C are presented. An Arrhenius plot of the data shows two distinct linear regions, suggesting that two different rate-limiting processes occur in series with a break-over transition at ,250°C. The decrease in conductivity is apparently not due to dehydration. An activation energy for protonic transport of 0.26 eV, about one-half of the low-temperature value, is proposed, based on curve fitting of the high-temperature data. [source] Quantitative analysis of spatial proteoglycan content in articular cartilage with Fourier transform infrared imaging spectroscopy: Critical evaluation of analysis methods and specificity of the parametersMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2010L. Rieppo Abstract Objective: To evaluate the specificity of the current Fourier transform infrared imaging spectroscopy (FT-IRIS) methods for the determination of depthwise proteoglycan (PG) content in articular cartilage (AC). In addition, curve fitting was applied to study whether the specificity of FT-IRIS parameters for PG determination could be improved. Methods: Two sample groups from the steer AC were prepared for the study (n = 8 samples/group). In the first group, chondroitinase ABC enzyme was used to degrade the PGs from the superficial cartilage, while the samples in the second group served as the controls. Samples were examined with FT-IRIS and analyzed using previously reported direct absorption spectrum techniques and multivariate methods and, in comparison, by curve fitting. Safranin O-stained sections were measured with digital densitometry to obtain a reference for depthwise PG distribution. Results: Carbohydrate region-based absorption spectrum methods showed a statistically weaker correlation with the PG reference distributions than the results of the curve fitting (subpeak located approximately at 1,060 cm,1). Furthermore, the shape of the depthwise profiles obtained using the curve fitting was more similar to the reference profiles than with the direct absorption spectrum analysis. Conclusions: Results suggest that the current FT-IRIS methods for PG analysis lack the specificity for quantitative measurement of PGs in AC. The curve fitting approach demonstrated that it is possible to improve the specificity of the PG analysis. However, the findings of the present study suggest that further development of the FT-IRIS analysis techniques is still needed. Microsc. Res. Tech. 2010. © 2009 Wiley-Liss, Inc. [source] Using combined measurements of gas exchange and chlorophyll fluorescence to estimate parameters of a biochemical C3 photosynthesis model: a critical appraisal and a new integrated approach applied to leaves in a wheat (Triticum aestivum) canopyPLANT CELL & ENVIRONMENT, Issue 5 2009XINYOU YIN ABSTRACT We appraised the literature and described an approach to estimate the parameters of the Farquhar, von Caemmerer and Berry model using measured CO2 assimilation rate (A) and photosystem II (PSII) electron transport efficiency (,2). The approach uses curve fitting to data of A and ,2 at various levels of incident irradiance (Iinc), intercellular CO2 (Ci) and O2. Estimated parameters include day respiration (Rd), conversion efficiency of Iinc into linear electron transport of PSII under limiting light [,2(LL)], electron transport capacity (Jmax), curvature factor (,) for the non-rectangular hyperbolic response of electron flux to Iinc, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) CO2/O2 specificity (Sc/o), Rubisco carboxylation capacity (Vcmax), rate of triose phosphate utilization (Tp) and mesophyll conductance (gm). The method is used to analyse combined gas exchange and chlorophyll fluorescence measurements on leaves of various ages and positions in wheat plants grown at two nitrogen levels. Estimated Sc/o (25 °C) was 3.13 mbar µbar,1; Rd was lower than respiration in the dark; Jmax was lower and , was higher at 2% than at 21% O2; ,2(LL), Vcmax, Jmax and Tp correlated to leaf nitrogen content; and gm decreased with increasing Ci and with decreasing Iinc. Based on the parameter estimates, we surmised that there was some alternative electron transport. [source] Extension of a biochemical model for the generalized stoichiometry of electron transport limited C3 photosynthesisPLANT CELL & ENVIRONMENT, Issue 10 2004X. YIN ABSTRACT The widely used steady-state model of Farquhar et al. (Planta 149: 78,90, 1980) for C3 photosynthesis was developed on the basis of linear whole-chain (non-cyclic) electron transport. In this model, calculation of the RuBP-regeneration limited CO2 -assimilation rate depends on whether it is insufficient ATP or NADPH that causes electron transport limitation. A new, generalized equation that allows co-limitation of NADPH and ATP on electron transport is presented herein. The model is based on the assumption that other thylakoid pathways (the Q-cycle, cyclic photophosphorylation, and pseudocyclic electron transport) interplay with the linear chain to co-contribute to a balanced production of NADPH and ATP as required by stromal metabolism. The original model assuming linear electron transport limited either by NADPH or by ATP, predicts quantum yields for CO2 uptake that represent the highest and the lowest values, respectively, of the range given by the new equation. The applicability of the new equation is illustrated for a number of C3 crop species, by curve fitting to gas exchange data in the literature. In comparison with the original model, the new model enables analysis of photosynthetic regulation via the electron transport pathways in response to environmental stresses. [source] Gaussian Process Functional Regression Modeling for Batch DataBIOMETRICS, Issue 3 2007J. Q. Shi Summary A Gaussian process functional regression model is proposed for the analysis of batch data. Covariance structure and mean structure are considered simultaneously, with the covariance structure modeled by a Gaussian process regression model and the mean structure modeled by a functional regression model. The model allows the inclusion of covariates in both the covariance structure and the mean structure. It models the nonlinear relationship between a functional output variable and a set of functional and nonfunctional covariates. Several applications and simulation studies are reported and show that the method provides very good results for curve fitting and prediction. [source] Calix[4]arene-Based Enantioselective Fluorescent Sensors for the Recognition of N-Acetyl-aspartateCHINESE JOURNAL OF CHEMISTRY, Issue 4 2008Guang-Yan QING Abstract Two-armed chiral anion receptors (1 and 2), calix[4]arenes bearing dansyl fluorophore and (1R,2R)- or (1S,2S)-1,2-diphenylethylenediamine binding sites, were prepared and examined for their chiral amino acid anion binding abilities by the fluorescence spectra in dimethylsulfoxide (DMSO). The results of non-linear curve fitting indicate that 1 or 2 forms a 1:1 stoichiometry complex with N -acetyl- L - or D -aspartate by multiple hydrogen bonding interactions, exhibiting good enantioselective fluorescent recognition for the enantiomers of N -acetyl-aspartate, [receptor 1:Kass(D)/Kass(L)=6.74; receptor 2:Kass(L)/Kass(D)=6.48]. The clear fluorescent response difference indicates that receptors 1 and 2 could be used as a fluorescent chemosensor for N -Acetyl-aspartate. [source] Combined Wavelet Transform with Curve-fitting for Objective Optimization of the Parameters in Fourier Self-deconvolutionCHINESE JOURNAL OF CHEMISTRY, Issue 10 2001Xiu-Qi Zhang Abstract Fourier self-deconvolution was the most effective technique in resolving overlapping bands, in which deconvolution function results in deconvolution and apodization smoothes the magnified noise. Yet, the choice of the original half-width of each component and breaking point for truncation is often very subjective. In this paper, the method of combined wavelet transform with curve fitting was described with the advantages of an enhancement of signal to noise ratio as well as the improved fitting condition, and was applied to objective optimization of the original half-widths of components in unresolved bands for Fourier self-deconvolution. Again, a noise was separated from a noisy signal by wavelet transform, therefore, the breaking point of apodization function can be determined directly in frequency domain. Accordingly, some artifacts in Fourier self-deconvolution were minimized significantly. [source] | |||||||||||||||||||