Good Data Fitting Research Articles

Forward and inverse modelling approaches for prediction of light stimulus from electrophysiological response in plants

In this paper, system identification approach has been adopted to develop a novel dynamical model for describing the relationship between light as an environmental stimulus and the electrical response as the measured output for a bay leaf (Laurus nobilis) plant. More specifically, the target is to predict the characteristics of the input light stimulus (in terms of on–off timing, duration and intensity) from the measured electrical response – leading to an inverse problem. We explored two major classes of system estimators to develop dynamical models – linear and nonlinear – and their several variants for establishing a forward and also an inverse relationship between the light stimulus and plant electrical response. The best class of models are given by the Nonlinear Hammerstein–Wiener (NLHW) estimator showing good data fitting results over other linear and nonlinear estimators in a statistical sense. Consequently, a few set of models using different functional variants of NLHW has been developed and their accuracy in detecting the on–off timing and intensity of the input light stimulus are compared for 19 independent plant datasets (including 2 additional species viz. Zamioculcas zamiifolia and Cucumis sativus) under similar experimental scenario.

Solution thermodynamics and solubility prediction of glibenclamide in Transcutol + water co-solvent mixtures at 298.15–333.15 K

Solution thermodynamics and solubility of glibenclamide (GBN) in binary co-solvent mixtures of Transcutol + water at temperature range of 298.15-333.15 K were investigated in present study. The modified Apelblat model was used to predict the solubility of GBN in co-solvent mixtures at various temperatures. The highest and lowest solubility of GBN were observed in pure Transcutol and pure water, respectively. Moreover, all co-solvent mixtures had highest solubility at 333.15 K. The experimental solubility data of GBN was correlated well with the modified Apelblat model at each temperature studied with relative absolute deviation in the range of 0.008-5.903 %. The correlation coefficients in co-solvent mixtures were observed in the range of 0.995-0.999 which indicated good fitting of experimental data with calculated one. The enthalpies and entropies for GBN dissolution were observed in the range of 2.012-38.215 kJ mol(-1) and 6.748-114.709 J mol(-1) K(-1), respectively indicating its dissolution is endothermic and an entropy-driven process. These results indicated that Transcutol can be used as a co-solvent in preformulation studies and formulation development of GBN.

Triaxial Compressive Strength of Concrete Subjected to High Temperatures

AbstractAn experimental study was undertaken to develop an extension of Mohr-Coulomb and Newman models to predict the failure of concrete subjected to elevated temperatures. Concrete specimens of 83×166-mm dimensions were prepared and subjected to various temperature levels of 300, 500, and 700°C. The tests were carried out in triaxial cell using various confining stress levels. The applied confining pressures varied between 1.4 and 24 MPa, corresponding to 3 and 54% of the uniaxial compressive strength. Test results indicated that the increase in temperature and/or confining pressure lead to a significant change in the mechanical properties of concrete. Furthermore, the Mohr-Coloumb and Newman models did not provide good fitting of the experimental data obtained on concrete subjected to high temperature of up to 700°C. A dehydrate index is introduced and used to define new variables in the existing models. The modified models are shown to adequately predict the residual strength of concrete that has been...

Study of interactions between oppositely charged dendrigraft poly-l-lysine and human serum albumin by continuous frontal analysis capillary electrophoresis and fluorescence spectroscopy

Dendrigraft poly-l-lysine (DGL) are biomacromolecules of great interest for many applications including antibacterial activity, drug delivery systems, gene therapy and production of antibodies. As human serum albumin (HSA) is the most abundant serum protein, the study of interactions between these two compounds is crucial for the use of DGL in drug or gene delivery systems. The present work aims at determining the number of binding sites and the corresponding successive equilibrium constants between DGL of generation 3 (G3) and HSA in physiological conditions. To meet this end, continuous frontal analysis capillary electrophoresis (FACCE) and fluorescence spectroscopic methods were implemented and compared. FACCE was performed on a polycationic modified capillary in combination with a co-pressure that allowed for selectively introducing the free G3 from the G3/HSA mixtures. FACCE studies demonstrated that HSA has 2 binding sites with DGL G3 with the following successive constants K1=31.2×103M−1 and K2=30.6×103M−1. For a 1g/L concentration in G3 and assuming a plasmatic HSA concentration of 40g/L, these binding constants lead to only 5% free DGL in the medium. It was also shown that the interactions between G3 and HSA corresponded to a model of cooperative sites. These results are in good agreement with the presence of two negatively charged domains in the HSA. Good fitting of the fluorescence spectroscopy data was obtained using the equilibrium constants derived from FACCE. Nevertheless, due to the high number of fitting parameters, it was difficult to fit the fluorescence spectroscopic data independently of the results obtained by FACCE.

Modelling 18O2 and 16O2 unidirectional fluxes in plants. IV: Role of conductance and laws of its regulation in C3 plants

Numerous studies focus on the measurement of conductances for CO2 transfer in plants and especially on their regulatory effects on photosynthesis. Measurement accuracy is strongly dependent on the model used and on the knowledge of the flow of photochemical energy generated by light in chloroplasts. The only accurate and precise method to quantify the linear electron flux (responsible for the production of reductive energy) is the direct measurement of O2 evolution, by 18O2 labelling and mass spectrometry. The sharing of this energy between the carboxylation (P) and the oxygenation of photorespiration (PR) depends on the plant specificity factor (Sp) and on the corresponding atmospheric concentrations of CO2 and O2 (André, 2013). The concept of plant specificity factor simplifies the equations of the model. It gives a new expression of the effect of the conductance (g) between atmosphere and chloroplasts. Its quantitative effect on photosynthesis is easy to understand because it intervenes in the ratio of the plant specificity factor (Sp) to the specificity of Rubisco (Sr). Using this ‘simple’ model with the data of 18O2 experiments, the calculation of conductance variations in response to CO2 and light was carried out.The good fitting of experimental data of O2 and CO2 exchanges confirms the validity of the simple model. The calculation of conductance variation during the increase of external CO2 concentration reveals a linear law of regulation between external and internal CO2 concentrations. During CO2 variations, the effects of g regulation tend to maintain a higher level of oxygenation (PR) in expense of a better carboxylation (P). Contrary to CO2, the variation of O2 creates a negative feedback effect compatible with a stabilization of atmospheric O2. The regulation of g amplifies this result. The effect of light in combination with CO2 is more complex. Below 800μmolquantam–2s–1 the ratio PR/P is maintained unchangeable in expense of carboxylation efficiency. Above that irradiance value, PR/P increases dramatically. It appears that the saturation curves of photosynthesis under high light could be simply due to the regulation by the conductance g and not by any biochemical or biophysical limitation. In conclusion, the regulatory effect of conductance operates in a way that it preserves the rate of photorespiration. This confirms a positive and protective role of photorespiration at the biochemical, whole plant and atmosphere levels. Since the effects of photorespiration are linked to the properties of Rubisco, they add new arguments for a co-evolution of plant and atmosphere, including the evolution of CO2 conductance.

Semi-Idealized Study on Estimation of Partly and Fully Space Varying Open Boundary Conditions for Tidal Models

Two strategies for estimating open boundary conditions (OBCs) with adjoint method are compared by carrying out semi-idealized numerical experiments. In the first strategy, the OBC is assumed to be partly space varying and generated by linearly interpolating the values at selected feature points. The advantage is that the values at feature points are taken as control variables so that the variations of the curves can be reproduced by the minimum number of points. In the second strategy, the OBC is assumed to be fully space varying and the values at every open boundary points are taken as control variables. A series of semi-idealized experiments are carried out to compare the effectiveness of two inversion strategies. The results demonstrate that the inversion effect is in inverse proportion to the number of feature points which characterize the spatial complexity of open boundary forcing. The effect of ill-posedness of inverse problem will be amplified if the observations contain noises. The parameter estimation problems with more control variables will be much more sensitive to data noises, and the negative effects of noises can be restricted by reducing the number of control variables. This work provides a concrete evidence that ill-posedness of inverse problem can generate wrong parameter inversion results and produce an unreal “good data fitting.”

Determining the biomechanical properties of human intracranial blood vessels through biaxial tensile test and fitting them to a hyperelastic model

Article history: Received January 20, 2013 Received in Revised form July, 2, 2013 Accepted 6 August 2013 Available online 7 August 2013 Understanding mechanical properties of healthy and unhealthy cerebral vessels is a key element in the development of their science and the relevant clinical diagnosis, prevention and treatment. Thirteen healthy samples were obtained from 23 middle cerebral arteries. The changes of force and deformation until the vessel rupture were recorded using a biaxial device. Thereafter, the stress-strain curve was plotted and fitted with a hyperelastic five-parameter Mooney-Rivlin model and the model parameters (C1, C2, C3, C4, and C5) were determined according to the best fit. For statistical comparison, the samples were divided into three age and two gender groups and subjected to non-parametric statistical analyses. Comparison of obtained results for different age groups showed that there is a significant difference between the old group and the other two groups (middle-aged and young). There was no significant difference between male and female groups. Therefore, the results demonstrate the changes of blood vessel wall properties with aging. The results also depicted that the arterial wall is stiffer in the circumferential direction than the axial direction. Anisotropy of cerebral vessels was confirmed by all of the tests. Therefore, the significance of the biaxial tests is in the spot light in the derived data. Moreover, good fitting of data illuminated that the use of multiple-parameter constitutive models is useful for mathematical demonstration of cerebral vessel tissue behavior. In conclusion, good fitting of data illuminated that the use of multiple-parameter constitutive models is useful for mathematical demonstration of cerebral vessel tissue behavior.

Effective dielectric constant of two phase systems: Application to mixed conducting systems

Theoretical approaches to electrical characterization of two phase systems are mostly limited to the systems where the individual components exhibit the same type of conductivity (pure dielectric or pure conductive systems). In this article, the brick wall geometry is extended to the mixed conductive systems with percolation. Impedance spectroscopy techniques were used for experimental investigation of slurries. Various metal oxide powders and host liquids were analyzed using a wide range of solids loadings. Comparison of experimental results with theoretical predictions shows good fitting of the experimental data. Parameters (the values of permittivity for both phases and percolation threshold) calculated from this fitting match the corresponding values of components of two phase systems. Analysis of both low frequency (less than 10 kHz) as well as high frequency (10 kHz to 1 MHz) responses of impedance spectra allows determining of permittivity of dielectric powders suspended in various liquids. Low frequency response provides better accuracy for systems with high dielectric contrast between components, while high frequency response is more accurate for low contrast systems.

Studying the abrasion behavior of rubbery materials with combined design of experiment-artificial neural network

In this study, an application of artificial neural network (ANN) has been presented in modeling and studying the effect of compounding variables on abrasion behavior of rubber formulations. Three case studies were carried out in which the experiment data were collected according to classical response surface designs. Besides developing the ANN models, we developed response surface methodology (RSM) to confirm the ANN predictions. A simple relation was employed for determination of relative importance of each variable according to ANN models. It was shown through these case studies that ANN models delivered very good data fitting and their simulating curves could help the researchers to better understand the abrasion behavior.

Adsorption characteristics of [Fe(III)–EDTA]− on granular activated carbon from aqueous solutions

In this study, the adsorption of [Fe(III)–EDTA]− on coconut‐activated carbon from aqueous solutions has been studied in a batch stirred cell. Experiments have been carried out to investigate the effects of temperature, [Fe(III)–EDTA]− concentration, pH, and activated carbon mass on [Fe(III)–EDTA]− adsorption. The experimental results manifest that high temperature is favorable to the adsorption of [Fe(III)–EDTA]− on the activated carbon. The [Fe(III)–EDTA]− adsorption on activated carbon increases with its concentration in the aqueous solutions. However, the [Fe(III)–EDTA]− adsorption on activated carbon decreases as the pH rises. The [Fe(III)–EDTA]− adsorption on per gram of activated carbon decreases as the activated carbon mass increases. The kinetic study shows that [Fe(III)–EDTA]− adsorption on the activated carbon is in good compliance with the pseudo‐second‐order kinetic model. The Langmuir and Freundlich equilibrium isotherm models are found to provide a good fitting of the adsorption data. Thermodynamic parameters such as Ea, ΔG0, ΔH0, and ΔS0 for adsorption reaction are estimated. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 470–479, 2013

Kinetics of forced aerated biodegradation of digested sewage sludge-reed mixtures at different temperatures

This work presents a kinetic analysis of the aerobic biodegradation of anaerobically digested sewage sludge and dried reed mixtures at different temperatures. Batch experiments were conducted in laboratory-scale reactors with temperature (T) control and forced aeration of the solid mixture. The biowaste mixture was treated at four different temperatures: 25, 40, 50 and 60 °C, with moisture controlled and samples taken weekly for carbon (C) and volatile solids (VS) measurements. The duration of experiments was either 90 d (at 25 °C) or 60 d (at 40, 50 and 60 °C). Two different kinetic models were used to fit the carbon mineralisation curves: the 2C model, which considers two organic fractions (biodegradable and non-biodegradable) and the 3C model, which considers three fractions (easily biodegradable, slowly biodegradable and non-biodegradable). In both cases, the kinetic rate constants were calculated by mathematical fitting and were compared with previously reported values. The temperature influence on the rate constants was studied for both models using a T-dependent equation. The calculated kinetic rate constants were in agreement with previously published values, and good fitting of the experimental data was obtained with both models. Similar rate constant values were obtained for mineralisation of the biodegradable fraction (2C model) and the easily biodegradable fraction (3C model). The rate constants for the slowly biodegradable fraction (3C model) were much lower. A good correlation between rate constants and T was observed. Different optimum temperature values were obtained for each rate constant depending on which carbon fraction was degraded. The T-dependent rate constant values obtained could be used for modelling the C mineralisation of real variable-temperature composting processes.

Heterogeneous studies in pulping of wood: Modelling mass transfer of dissolved lignin

A kinetic model is proposed for the mass transfer of dissolved lignin from the interior of the chip to the bulk liquor, during the kraft pulping of Eucalyptus globulus wood. The model is based on extensive experimental data which include the dissolved lignin concentration both inside and outside the chips, along pulping time. The lignin concentration in the entrapped liquor was shown to be much higher than the one in the free liquor, and reached a maximum value during the cook. The model follows a lumped parameter estimation approach, where the spatial concentration profile of lignin inside the chip is represented by its average. This strategy enables estimating the effective diffusion coefficient that characterizes the internal resistance to mass transfer. This coefficient was expressed by an Arrhenius-type equation with an activation energy for diffusion of 29 kJ mol −1, multiplied by the cooking yield raised to an exponent whose estimated value was 5. This high value corresponds to an increasing resistance to lignin diffusion along pulping time. The resistance to mass transfer in the film surrounding the wood chips was found to have a contribution of 20–30% to the overall mass transfer resistance at the beginning of the cook, which is significant and should not be neglected. The model proved to enable a good fitting of the experimental data on the dissolved lignin concentration in the free liquor.

Biosorption of cadmium ions using Pleurotus ostreatus: Growth kinetics, isotherm study and biosorption mechanism

The mycelial growth kinetics, cadmium biosorption capacity and main governing biosorption mechanism of Pleurotus ostreatus (oyster mushroom) have been determined in this study. The fungus mycelium exhibits a sigmoidal (S-shaped) growth curve in which the growth rates for the lag and exponential phases are 0.1 and 0.31 g/L·day, respectively. The grown fungus is subjected to elemental, infra-red and scanning electron microscopy-energy dispersive x-ray spectroscopy analyses, while biosorption data are fitted to established adsorption isotherm models, namely, Langmuir, Freundlich and Dubinin-Radushkevich. It is strongly suggested that the main governing mechanism involved is chemisorption due to good fitting of biosorption data to Langmuir and Dubinin-Radushkevich models with possibility of involvement of both ion exchange and complexation. Data presented in the study are very useful for design of future pilot- or industrial-scale biosorption water purification systems.

Modelling the Adsorption of p-Nitrophenol by the Boyd Method in Conjunction with the Finite Element Method

Adsorption kinetics are often studied by non-dimensional models that allow a good fitting of the experimental data. Nevertheless, their physical interpretation is very limited because the particle geometry is not considered. In this work, the adsorption kinetics of p-nitrophenol onto two commercial activated carbons with different textural and geometrical characteristics was studied. For this purpose, two types of models were used: zero-dimensional models which do not take the system geometry into account; and the Boyd model, which takes the shape of the adsorbent molecule into account. In contrast to previous published works, the Boyd model was solved by means of the finite element method using the commercial software COMSOL. This paper provides a new insight into the modelling of adsorption kinetics when non-spherical adsorbents are employed.

Adsorption of EDTA on activated carbon from aqueous solutions

In this study, the adsorption of EDTA on activated carbon from aqueous solutions has been investigated in a batch stirred cell. Experiments have been carried out to investigate the effects of temperature, EDTA concentration, pH, activated carbon mass and particle size on EDTA adsorption. The experimental results manifest that the EDTA adsorption rate increases with its concentration in the aqueous solutions. EDTA adsorption also increases with temperature. The EDTA removal from the solution increases as activated carbon mass increases. The Langmuir and Freundlich equilibrium isotherm models are found to provide a good fitting of the adsorption data, with R 2 = 0.9920 and 0.9982, respectively. The kinetic study shows that EDTA adsorption on the activated carbon is in good compliance with the pseudo-second-order kinetic model. The thermodynamic parameters ( E a , Δ G 0, Δ H 0, Δ S 0) obtained indicate the endothermic nature of EDTA adsorption on activated carbon.

A formulation to model the nonlinear viscoelastic properties of the vascular tissue

Nearly all soft tissues, including the vascular tissue, present a certain degree of viscoelastic material response, which becomes apparent performing multiple relaxation tests over a wide range of strain levels and plotting the resulting stress relaxation curves, nonlinear viscoelasticity of the tissue. Changes in relaxation rate at each strain may occur at multiple strain levels. A constitutive formulation considering the particular features of the vascular tissue, such as anisotropy, together with these nonlinear viscoelastic phenomena is here presented and used to fit stress–stretch curves from experimental relaxation tests. This constitutive model was used to fit several data set of in vitro experimental stress relaxation tests performed on ovine and porcine aorta. The good fitting of the experimental data shows the capability of the model to reproduce the viscoelastic response of the vascular tissue.

Kinetics and Modeling of the Flexible Fuel Reformer: n-Hexadecane Steam Reforming and Combustion

Steam reforming of liquid hydrocarbon fuels provides one possible solution for the production of hydrogen for solid oxide fuel cells (SOFCs). However, the design of the reformer is dependent on the kinetics of the catalytic reaction, which is not widely reported. Because reforming is highly endothermic, we have investigated the use of a heat exchange device, designated the flexible fuel reformer (FFR), as a reactor in which combustion and reforming can be simultaneously accomplished. In the present study, we evaluated the reforming and combustion kinetics of n-hexadecane (used as an analog for diesel) over the rhodium/nickel catalyst supported on alumina. Reforming data obtained over the temperature range of 500−750 °C was compared against three different mechanistic models: Eley−Rideal, Langmuir−Hinshelwood bimolecular adsorption, and Langmuir−Hinshelwood dual site. Among all, Eley−Rideal produced good data fitting and fulfilled the thermodynamic criteria in every case. Combustion kinetics of hexadecane was also studied, since our proposed reactor configuration uses the heat from the exothermic combustion reaction as a driver for the endothermic reforming reaction. It was found that power-law model produced the best fit among all the models and this result was further corroborated using statistical analysis. The kinetic results can be combined with the reactor design model to predict the performance and demonstrate the benefit obtained from simultaneous reforming and combustion.

Characterization of a chitosan sample extracted from Brazilian shrimps and its application to obtain insoluble complexes with a commercial whey protein isolate

The rheological behaviour of chitosan solutions in 250 mM acetate buffer was studied at different pHs (25 °C). The intrinsic viscosity decreased from ∼17 dL/g to ∼14 dL/g when the pH increased from 4.7 to 6.0. Concentrated solutions (0.5–3.0% w/w) exhibited a shear-thinning behaviour which increased with increasing chitosan concentration and decreasing pH. A good fitting of the experimental data to the Cross and Carreau flow models was obtained. The elasticity of the solutions decreased with increasing pH and decreasing chitosan concentration, as a consequence of increased chain flexibility. The interaction of chitosan with whey proteins (WPI) was studied by isothermal titration calorimetry (ITC) and turbidity measurements, at different pHs (3.0–6.0) and ionic strengths (100 and 250 mM). ITC results showed that electrostatics is the main driving force for chitosan:WPI interaction, as an increase in ionic strength lead to a smaller interaction. A pH and chitosan:WPI ratio dependence of aggregate formation was clearly observed by turbidimetry. At pH 3.0, there was no change in turbidity upon addition of chitosan, whereas at pH 4.0 and 6.0, the turbidity values varied with chitosan:WPI ratio and were smaller at 250 mM than those at 100 mM. The rheology of chitosan:WPI coacervates was studied in acetate buffer (100 and 250 mM), at pH 5.5, mixing ratios of 0.25:1 and 0.10:1. Time dependent flow behaviour, higher G′ and G″ values and higher elasticity were observed for the coacervates, originating mainly from the electrostatic interactions between the protein and the polysaccharide chains.

Statistical information of ASAR observations over wetland areas: An interaction model interpretation

This paper presents the results obtained after studying the relation between the statistical parameters that describe the backscattering distribution of junco marshes and their biophysical variables. The results are based on the texture analysis of a time series of Envisat ASAR C-band data (APP mode, V V +HH polarizations) acquired between October 2003 and January 2005 over the Lower Paraná River Delta, Argentina. The image power distributions were analyzed, and we show that the K distribution provides a good fitting of SAR data extracted from wetland observations for both polarizations. We also show that the estimated values of the order parameter of the K distribution can be explained using fieldwork and reasonable assumptions. In order to explore these results, we introduce a radiative transfer based interaction model to simulate the junco marsh σ0 distribution. After analyzing model simulations, we found evidence that the order parameter is related to the junco plant density distribution inside the junco marsh patch. It is concluded that the order parameter of the K distribution could be a useful parameter to estimate the junco plant density. This result is important for basin hydrodynamic modeling, since marsh plant density is the most important parameter to estimate marsh water conductance.

Adsorption Kinetics for the Removal of Fluoride from Aqueous Solution by Activated Carbon Adsorbents Derived from the Peels of Selected Citrus Fruits

Activated carbons (ACs) were prepared from the peels of Citrus documana, Citrus medica and Citrus aurantifolia fruits. Adsorption of fluoride onto these activated carbons was investigated. Effect of contact time in the removal of fluoride from aqueous solution at neutral pH was studied. Five kinetic models; the pseudo first‐ and second‐order equations, intraparticle diffusion, pore diffusion and the Elovich equation, were selected to follow adsorption process. Adsorption of fluoride onto adsorbents could be described by pseudo second‐order equation. Kinetic parameters; rate constants, equilibrium adsorption capacities and correlation coefficients, for each kinetic equation were calculated and discussed. The good fitting of kinetic data to pore diffusion and Elovich equations indicate that pore diffusion plays a vital role in controlling the rate of the reaction.