جستجوی مقالات مرتبط با کلیدواژه « Correlation » در نشریات گروه « شیمی »

This study focuses on developing a new method that represents user-accessible correlation for the estimation of water-based nanofluids viscosity. For this, an evolutionary algorithm, namely Gene Expression Programming (GEP), was adapted based on a wide selection of literature published databanks including 819 water-based nanofluids viscosity points. The developed model utilized the base fluid viscosity as well as volume fraction and size of the nanoparticles as the inputs of the model. Several statistical parameters integrated with graphical plots were employed in order to assess the accuracy of the proposed GEP-based model. Results of the evaluation demonstrate fairly enough accuracy of the developed model with statistical parameters of AARD%=11.7913, RMSE=0.3567, and SD=0.1851. Furthermore, the trend analysis indicates that the GEP calculated points satisfactorily follow the trend of the nanofluid viscosity variation as a function of different model inputs. To provide more verification, the proposed GEP model was compared with some literature theoretical and empirical correlations leading to the supremacy of the developed model here. The applied sensitivity analysis reveals that the highest impact value is assigned to the volume fraction of the nanoparticle. Moreover, the outlier’s detection by Williams’ technique illustrates that about 96.5% of the GEP estimates are in the applicability domain resulting in the validity of the proposed model in this study. At last, the results of this study demonstrate that the new method here outperforms other literature-published correlations from the standpoint of accuracy and reliability.

Among the various methods for CO2 removal from the atmosphere, CO2 absorption is considered as the most applicable one. Although several studies have been performed on CO2 absorption by using chemical solvents, there are not many studies on using improved absorbents. Therefore, the aim of this study was to measure the solubility of CO2 in utilized aqueous blends of 2-amino-2-methyl-1-propanol (AMP) and hexamethylenediamine (HMDA). In the present research, the equilibrium set up for measuring CO2 solubility in aqueous solvents was assembled. CO2 solubility experiments were carried out over a various range of CO2 partial pressures (8.44, 25.33, and 42.22 kPa) temperatures (303, 313, and 323 K) and solvent concentration (0.4, 1.8, 2, and 3 M). The results showed that increasing CO2 partial pressure or decreasing the temperature would lead to an increase in CO2 loading. Furthermore, with increasing HMDA concentration, CO2 loading reached a maximum value before it followed a slight decrease. The experimental results were fitted to the thermodynamic Deshmukh Mather model and the required parameters in this model were generated. The results showed that there is a good agreement between theoretical and experimental results of CO2 loading.

Opium poppy(Papaver  somniferum L.), a member of family Papaveraceae is an important source of several benzylisoquinoline derived alkaloids known to the human race since the ancient civilizations for their therapeutic and narcotic values. In the present study a total number of 47 accessions/genotypes of Opium poppywere procured from various resources and screened for economic yield, variability, heritability, correlation and path coefficient. Among them G-18 was identified as highest seed yielding 10.45 g/plant, G-3 & G-6 (0.092%, 0.086%) as high morphine containing accessions. Maximum Genotypic Coefficient of Variance (GCV) recorded for papaverine content. The estimate of heritability in the broad sense was recorded higher side for morphine content (99.96%) and papaverine (99.85 %) while lower for days to 50% flowering (4.22%). The genotypic and phenotypic correlation coefficient amongst codeine and thebaine content were found highly significant and positively associated with morphine content followed by narcotine content. The path coefficient analysis revealed that the highest direct contribution to seed yield was made by capsule straw yield (0.8730) followed by days to maturity (0.3758).

In recent years, there is great attention by researchers in ionic liquid due to the huge potential for separation and reaction technology. Also, the heat capacity of ionic liquids is a substantial parameter for conclusive process designs and engineering calculations. A database for the heat capacity of ionic liquids created by compiling experimental data onto literature covering the period from 1971 to 2016 is reported. In this work, a temperature-dependent equation to the heat capacity for 141 pure ionic liquids is proposed. A database containing 6961 experimental data was used for the development of this model. Finally, a 7-parameter simple equation with the capability for predicting the heat capacity of ionic liquids is presented. The accuracy of the new model has been compared to the most precise models in the literature and the comparison indicates that the proposed method provides more accurate results than other models considered in this work. The average absolute percentage deviation from the new model is only 3.83%.

This work investigates the modeling of the surface tension and the interface of liquid mixtures. Nine binary liquid mixtures of (DMSO+alcohols), (2-Propanol+2,2,4-trimethylpentane), (Tetrahydrofuran+2-Propanol), (Tetrahydrofuran+2,2,4-trimethylpentane), and (ethano+glycerol) are considered. Additionally, one ternary liquid mixture of (Tetrahydrofuran+2-Propanol+2,2,4-trimethylpentane) is considered. Firstly, two correlations were used to model the surface tension. One of these correlations has one adjustable parameter, and the other has five fitting parameters. Then the model based on the equality of the chemical potentials at the interface and the liquid phase was used. The surface tension and interfacial composition are computed by using this model. This approach was used in two ways, including activity-based and fugacity-based models. The UNIFAC activity model and PSRK EOS equation of state were applied to compute activity and fugacity, respectively. Moreover, the effect of the partial molar volume on predictions was investigated. The results of the applied models show that the correlation with five adjustable parameters and the fugacity-based model have the best results. Also, the increase in the non-ideality of these systems results in a better performance of the fugacity-based model, therefore the application of the partial molar volume is necessary.

An investigation was carried out to assess the genetic variability, genetic divergence and association of pheno-morphic and agronomic traits along with major chemical constituents of essential oil in 41 accessions of spearmint (Mentha spicata L.). Highly significant differences were noted for all 10 economic traits indicating the existence of considerable genetic variability among 41 accessions. High heritability (h2) and high genetic advance was noted for herb yield (120.64 %). On the basis of Mahalnobis D2 values, all 41 spearmint accessions were grouped into six diverse clusters. The cluster-I was largest group which consist of 20 accessions. A significant and positive correlation was observed for plant height with herb yield (0.58 * *; ** = significant at 1% probability level). The herb yield showed a highest direct effect (0.194) for oil yield. According to results, a significant genetic variability was present among 41 accessions, simple selection can be employed to improve essential oil content. More importance should be given to plant height, leaf length, leaf width and herb yield during selection to improve essential oil yield in spearmint.

Thermodynamic data on environmental refrigerants have attracted considerable interest in the optimization and design of heat compressors, exchangers and other refrigeration equipment. In this study, An optimization algorithm was used to obtain the constant parameters of the new empirical model by fitting them to the source databank. The model was used to calculate the constant coefficients of the new equation for 15474 data of 27 refrigerants (temperatures between 92 and 486 K) by fitting them with source data. The accuracy of the presented equation was compared with commonly used models. Results indicated that the developed model provides more accurate results than those of other considered equations, with an average absolute percentage deviation of 3.46%.

The ability of a material to supply heat by means of conduction is called thermal conductivity, which is defined by Fourier's equation. Thermodynamic data on environmental refrigerants have attracted considerable interest in the design and optimization of refrigeration equipment, such as heat compressors and exchangers. After analysis of statistical effects, a new simple correlation was developed for the thermal conductivity of refrigerants as a function of temperature. An optimization algorithm was used to obtain the constant parameters of the new equation by fitting them to the source databank. The accuracy of the presented equation was compared with commonly used models. Results indicated that the developed model provides more accurate results than those of other considered equations, with an average absolute percentage deviation of 3.46%.

In this work, we develop a correlative model based on the surface tension data in order to calculate thermodynamic parameters, such as interaction energy between components (Uij), activity coefficients and etc. In the new approach, by using Li et al. (LWW) model, a three-parameter surface tension equation is derived for liquid mixtures. The surface tension data of 54 aqueous and 73 non-aqueous binary mixtures have been correlated as a function of composition using the new model, then the interaction energy between two compounds (Uij) of mixtures and their activity coefficients have been calculated with the results of this model. The average relative error obtained from the comparison of experimental and calculated surface tension values for 127 binary systems is less than 2.8%.In order to evaluate new method, the obtained values using this method were comparable with the results of the UNIFAC group contribution model.

Plant secondary metabolites have innumerable benefits in regard to human health. From the available 106 divergent lines of five Plantago species, a screening program was conducted to explore putative lines having best resources of aucubin and β-carotene. HPLC results indicated that seeds of selection LP3 of P. ovata contained highest (9.53%) and P. arenaria contained least (7.79%) β-carotene. Investigation was also conducted to assess the genetic variability, correlations and character contribution of β-carotene and aucubin content with other traits towards seed yield in a set of ten selected accessions in relation to seven traits in Plantago species. Results indicated that none of the accessions of any other species apart from P. lanceolata contained aucubin. PL-61 accession was detected to have maximum concentration (0.23%) of aucubin while the lowest (0.02%) was detected in PL-66. This opened the possibilities for nutritional value addition of β-carotene in seeds of isabgol.

The examination of available vapor pressure data in the case of the methane, ethane, propane and butane halogenated refrigerants, allowed recommendations of standard equations for this property. In this study, three new models include a general correlation; a substance-dependent correlation and an artificial neural network (ANN) approach have been developed to estimate the saturated vapor pressure of refrigerants. With the presented approaches, vapor pressures have been calculated and compared with source data bank for 5600 data points of 28 refrigerants. The accuracies of new correlations and ANN have been compared with most commonly used correlations and the comparison indicates that all new models provide more accurate results than other literature correlations considered in this work.

A three-parameter cubic equation of state has been proposed for predicting PVT of pure refrigerants such as R236ea, R236fa, R245fa, R245ca, R218, R227ea, and R717, from freezing point up to critical point temperature and pressures up 650 atm. We explore the theory of the equation of state from the view point of Ihm–Song–Mason (ISM) equation of state, which has been derived on the basis of statistical mechanical perturbation theory, and is characterized by three temperature dependent parameters, a, b, B2 , and a free parameter λ. The second virial coefficients are calculated from a correlation based on the heat of vaporization, ΔHvap, and the liquid density at the normal boiling point, ρnb. α(T ) and b(T ) can also be calculated from second virial coefficients by a scaling rule. The theory has considerable predictive power, since it permits the construction of the PVT surface from the heat of vaporization and the liquid density at the normal boiling point. The results indicate that the liquid densities can be predicted with very good agreement over a wide range of temperatures, 100–400 K.

Polythiophenes are of considerable interest as synthetic metals. The optical properties of polythiophenes can be easily affected by alkyl chain or other side groups to the thiophene ring. The effect of polymerization degree on the energy gap was studied in the case of polythiophene as a conjugated polymer at B3LYP/6-31(3d,3p) level of theory. Up to n = 16 could be confident that this degree of polymerization represents the bulk of polymer. The effect of the substitution of different groups in functionalized-bithiophene and -terthiophene on the polarizability was studied. The correlation study was performed between descriptors representing the molecular structure and refractive index for the set of 9 oligothiophenes. Three descriptor models including energy gap, polarizability and heat of formation were developed to estimate the refractive index with R2 = 0.81 and S = 0.068 by multi-linear regression analysis. The obtained model was used to predict the refractive indices of other six oligothiophenes. The model may be improved to predict the refractive index of the other oligothiophene derivatives.

Prediction of available vapor pressure data in the case of compounds containing C-H-O led to derivations and recommendations of standard equations for this property. The accuracy of vapor pressure estimations is essential to use as a basis to calculate acentric factor, thermal and equilibrium properties. In this study, according to the previous work, an accurate equation to estimate vapor pressure is developed to 130 pure C-H-O compounds as a function of reduced temperature and critical pressure. With new proposed equation, vapor pressures have been calculated in comparison with experimental data reported in literature for 2019 data points of 130 pure C-H-O compounds and the overall average absolute relative deviation is only 0.333%. The accuracy of the developed equation has been compared to that of Antoine and other mostly used equations. Our comparisons show that new equation leads to more accurate results than those of literature methods.

In recent years there has been a great deal of attention paid by researchers in investigating ionic liquids (ILs) mainly due to the tremendous potential that ionic liquids have in reaction and separation technology. Sonic speed is an important thermodynamic property of ionic liquids (ILs) and always chosen as a source to determine other properties. A database for the sonic speed of pure ILs created by collecting experimental data from literature covering the period from 2005 to 2013 is presented. In this study, based on sonic speed experimental data, for the first time the relationship between boiling temperature, reduced temperature and pressure for 2198 data of 29 ionic liquids covering wide ranges of temperature, pressure, and sonic speed has been examined. In results, a 6-parameter model with ability for predicts the sonic speed of ionic liquids is presented. The obtained model has an average absolute relative deviation (AARD%) of 1.30%,a determination coefficient (R2) of 0.987, and a root mean square error (RSMD) of 1.85.

A three-parameter cubic equation of state has been proposed for predicting PVT of pure refrigerants such as R236ea, R236fa, R245fa, R245ca, R218, R227ea, and R717, from freezing point up to critical point temperature and pressures up 650 atm. We explore the theory of the equation of state from the view point of Ihm–Song–Mason (ISM) equation of state, which has been derived on the basis of statistical mechanical perturbation theory, and is characterized by three temperature dependent parameters, a, b, B2, and a free parameter λ. The second virial coefficients are calculated from a correlation based on the heat of vaporization, ΔHvap, and the liquid density at the normal boiling point, ρnb. α(T) and b(T) can also be calculated from second virial coefficients by a scaling rule. The theory has considerable predictive power, since it permits the construction of the PVT surface from the heat of vaporization and the liquid density at the normal boiling point. The results indicate that the liquid densities can be predicted with very good agreement over a wide range of temperatures, 100–400 K.

In the first part of this work, correlation between optical activity and elements of magnetic susceptibility tensor (MST) for five classes of model small molecules containing a single chiral center has been studied using quantum computational techniques at DFT-B3LYP level of theory with 6-311G basis set. Several molecular properties are used to reduce the MST elements prior to the examination of the correlation. This study showed a close correlation between optical activity and the off-diagonal MST elements reduced by the electronic spatial extent . In the second part of this work, effects of the type of substitutions and their distances from the chiral center on the optical activity of these molecules have been investigated. Results of this work show that optical activity is reduced effectively upon distancing the substitution groups from the chiral center. Furthermore, the set of substitutions with higher electron densities and larger differences in their electronic structures result in higher optical activity.

Lighthydrocarbons are commonly used to evaluatecrude oils to determine oil families in reservoirs undergone some kind of alteration process. In this study crude oil contentsfromNorthwestern IranDelta (samples A, B and C)were analyzed in order to evaluate the IranDelta petroleum system independent of higher molecular weight markers. Ultra high resolution gas chromatography was used in separation and analysis of the light hydrocarbons.Heptane ratio, invariance, maturity,aromaticity and paraffinicity parameters among the C7 light hydrocarbons discriminated the oils into two families namely marine and terrigenous and also revealed the Northwestern IranDelta oils as supermature. Further confirmation of these two sources for crude oils in the Northwestern IranDeltawas obtained from multivariate plots of each crude oil on a star diagram. Sample B and sample C oils were closely matched by their similar path on the star diagram and grossly different from sample A oil which followed a different pattern.