Non-empirical Models Research Articles

A kinetic model for multicomponent gas transport in shale gas reservoirs and its applications

An accurate gas transport model is of vital importance to the simulation and production optimization of unconventional gas reservoirs. Although great success has been achieved in the development of single-component transport models, limited progress has been made in multicomponent systems. The major challenge of developing non-empirical multicomponent gas transport models lies in the absence of the quantification of the concentration impact on the fluid dynamic properties. To fill such a gap, this work presents a comprehensive transport model for multicomponent gas transport in shale and tight reservoirs. In developing the model, we first conducted molecular dynamic simulations to qualitatively understand the differential release of hydrocarbons from unconventional shale and tight reservoirs. It is found that the gas slippage, differential adsorption, and surface diffusion are the primary transport mechanisms in the working range of Knudsen number during reservoir production. Based on the molecular dynamic study, a quantitative transport model has been developed and validated, which extends existing models from single-component systems to multiple-component systems. The kinetic theory of gases is adopted and modified to model the multicomponent slippage effect. A generalized Maxwell–Stefan formulation with extended Langmuir adsorption isotherm is used to model the multicomponent surface diffusion process. The accuracy of the proposed model is above 90% for low to moderate Knudsen numbers in modeling the differential release phenomenon in unconventional reservoirs.

Prediction of the mechanical properties of isotropic pure metal-based and two-phase alloy-based porous materials using modified analytical models

This work investigates the applicability and accuracy of the five fundamental analytical models commonly used to estimate the thermophysical properties of porous materials for the prediction of the mechanical behaviour, both compressive and tensile, of isotropic pure metal-based and two-phase alloy-based porous materials. In literature, the prediction of the mechanical behaviour of these advanced engineering materials requires the development of semi-empirical models, which are material-specific and, thus, require empirical constants. The significance of the current investigation is the possibility to optimise the mechanical behaviour of porous metallic materials through the rapid and accurate prediction of their mechano-physical behaviour using non-empirical physically-based prediction models. The work is complemented with the derivation of new combined models with increased accuracy prediction of up to approx. 90% with respect to fundamental models. Although developed for porous materials, the derived combined models could be applied for the accurate and rapid prediction of the thermophysical and mechanical properties of multi-phase materials with unknown microstructure such as two-ductile-phase alloys, nanocomposites, hetero- and harmonic-structured materials, and immiscible alloys.

Input/output inconsistencies of daily evapotranspiration conducted empirically using remote sensing data in arid environments

Abstract The reliable quantification of daily evapotranspiration (ET) over vast croplands is a quest in many scholarly works aimed at the precise practice of water resources management. Remote sensing–based empirical and nonempirical models were developed to overcome large-scale quantification issues, which are usually experienced when using conventional approaches for the estimation of ET. The surface energy balance system (SEBS) model was used to quantify the daily ET in the arid/semi-arid over Wadi Ad-Dwaser, Saudi. SEBS input variables are parametrically sensitive and climatic dependent, and the model input/output dependencies are of high comprehensibility; therefore, the optimization analysis of SEBS input/output parameters is the target of the current research. SEBS inputs reciprocal inconsistencies were determined using the artificial neural network analysis, while the output dependencies on the daily ET estimation were mapped. Results demonstrated that the temperature and relative humidity are the most sensitive parameters to be considered in the routine crop monitoring procedure. SEBS output thematic maps showed the robust proportional correlation between the daily ET and the conducted temperature map. Moreover, the estimated daily ET was inversely correlated with the estimated cold sensible heat fluxes. The findings suggest systematic monitoring and forecasting procedures for efficient water-saving management plans in Saudi Arabia.

A non-empirical intermolecular force-field for trinitrobenzene and its application in crystal structure prediction.

An anisotropic atom-atom distributed intermolecular force-field (DIFF) for rigid trinitrobenzene (TNB) is developed using distributed multipole moments, dipolar polarizabilities, and dispersion coefficients derived from the charge density of the isolated molecule. The short-range parameters of the force-field are fitted to first- and second-order symmetry-adapted perturbation theory dimer interaction energy calculations using the distributed density-overlap model to guide the parameterization of the short-range anisotropy. The second-order calculations are used for fitting the damping coefficients of the long-range dispersion and polarization and also for relaxing the isotropic short-range coefficients in the final model, DIFF-srL2(rel). We assess the accuracy of the unrelaxed model, DIFF-srL2(norel), and its equivalent without short-range anisotropy, DIFF-srL0(norel), as these models are easier to derive. The model potentials are contrasted with empirical models for the repulsion-dispersion fitted to organic crystal structures with multipoles of iterated stockholder atoms (ISAs), FIT(ISA,L4), and with Gaussian Distributed Analysis (GDMA) multipoles, FIT(GDMA,L4), commonly used in modeling organic crystals. The potentials are tested for their ability to model the solid state of TNB. The non-empirical models provide more reasonable relative lattice energies of the three polymorphs of TNB and propose more sensible hypothetical structures than the empirical force-field (FIT). The DIFF-srL2(rel) model successfully has the most stable structure as one of the many structures that match the coordination sphere of form III. The neglect of the conformational flexibility of the nitro-groups is a significant approximation. This methodology provides a step toward force-fields capable of representing all phases of a molecule in molecular dynamics simulations.

Empirical treatment of asymptomatic contacts of gonorrhoea: patient views.

We conducted an anonymous cross-sectional survey of patients attending sexual health centres in New South Wales, Australia, on the acceptability of empirical and non-empirical treatment models and patients' concerns about antimicrobial resistance. Most of the 823 survey participants were willing to wait for treatment until their results were reported; 77% and 53% would agree to wait for treatment if results were available in 2 and 7 days respectively. Participants were less likely to agree to non-empirical treatment if they lived in regional and remote areas compared with those in a major city (odds ratio (OR) 0.5; 95% confidence interval (CI) 0.35-0.73). Most participants (70%) were worried about infections becoming resistant to antibiotics, with heterosexual men and women being less likely than gay and bisexual men to be worried (heterosexual men: OR 0.64, 95% CI 0.44-0.94; women: OR 0.64 95%, CI 0.44-0.92). Non-empirical treatment was acceptable to most participants, but patient preference, ability to return for treatment and timeliness of results are factors that should inform individual treatment decisions.

Supercomputer modelling of an electronic structure for KCl nanocrystal with edge dislocation with the use of semiempirical and nonempirical models

In the present work we used semiempirical and non-empirical models for electronic states of KCl nanocrystal containing edge dislocation for comparison of the obtained results. Electronic levels and local densities of states were calculated. As a result we found a reasonable qualitative correlation of semiempirical and non-empirical results. Using the results of computer modelling we discuss the problem of localization of electronic states near the line of edge dislocation.

Model for Calculating the Activity Coefficients of Electrolytes in the 0 to 16 mol/L Range of Concentrations

Based on the plasma-like theory of electrolyte solutions, areas of concentration with minimum activity coefficients are found, and the predominance of association phenomena leading to the formation of ionic associates or molecular solvates is explained. Alternative nonempirical models for estimating the activity coefficients of electrolytes are developed that produce values close to or coinciding with the available literature data in the 0 to 16 mol/L range of concentrations.

Validated real-time energy models for small-scale grid-connected PV-systems

Abstract This paper presents validated real-time energy models for small-scale grid-connected PV-systems suitable for domestic application. The models were used to predict real-time AC power output from a PV-system in Dublin, Ireland using 30-min intervals of measured performance data between April 2009 and March 2010. Statistical analysis of the predicted results and measured data highlight possible sources of errors and the limitations and/or adequacy of existing models, to describe the temperature and efficiency of PV-cells and consequently, the accuracy of power prediction models. PV-system AC output power predictions using empirical models for PV-cell temperature and efficiency prediction showed lower percentage mean absolute errors (PMAEs) of 7.9–11.7% while non-empirical models had errors of 10.0–12.4%. Cumulative errors for PV-system AC output power predictions were 1.3% for empirical models and 3.3% for non-empirical models. The proposed models are suitable for predicting PV-system AC output power at time intervals suitable for smart metering.

Methodology of Lifetime Prediction in Polymer Aging

Abstract Two approaches for lifetime prediction in polymer aging are compared: the “simulation approach” and the “ideal approach.” The widely used “simulation approach,” based on the hypotheses which were never clearly formulated, consists of finding a set of exposure conditions such that accelerated aging leads to the same structural states as natural aging. Using simple kinetic models it is demonstrated, that in the general case it is impossible to obtain a “good simulation.” Anyhow, in this approach, the problem of the relationship between accelerated aging and natural lifetimes remains unresolved. The “ideal approach” uses nonempirical kinetic models, taking into account structural changes at all the pertinent scales, and also uses polymer physics to establish the link between the polymer structure and the property under consideration. An important characteristic of this approach is that the accelerated aging serves only to determine the model parameters.

Photophysical properties of 2,6-dicyano- N, N, N ′, N ′-tetramethyl- p-phenylenediamine

Photophysical properties of 2,6-dicyano- N, N, N ′, N ′-tetramethyl- p-phenylenediamine (DCTMPPD) are reported. Fluorescence quantum yields range from 0.37 to 0.58 and fluorescence lifetimes from 12.2 to 22.9 ns in 28 different solvents. The triplet energy is determined to be 16.8 kK. Steady-state and time-resolved emission anisotropies in glycerol are given. Three correlation times with τ 1 < 0.8 ns τ 2 = 20 ns and τ 3 > 80 ns are found. The fluorescence solvatochromism is analyzed using empirical one- and multiparameter approaches as well as classical non-empirical continuum models. The excited state dipole moment is estimated to be between 10 and 12 D, depending on the model applied. The ground state p K a is determined to be 2.5, while for the excited state p K a ∗ a range of 0.5–2 can be estimated.

Is HAM/3 (hydrogenic atoms in molecules, version 3) a semiempirical version of dft (density functional theory) for ionization processes?

We calculated valence-electron vertical ionization potentials (VIPs) of nine small molecules, plus uracil and C2F4, by several different methods: semiempirical HAM/3 and AM1 methods, different nonempirical DFT models such as uDI(B88-P86)/cc-pVTZ and -e(SAOP)/TZP, and ab initio Hartree-Fock (HF) /cc-pVTZ. HAM/3 reproduced numerical values more closely to those calculated by the nonempirical DFTs than to those obtained by HF method. Core-electron binding energies (CEBEs) of aniline, nitrobenzene and p-nitro aniline, were also calculated by HAM/3 and nonempirical DFT using DE method. A nonempirical DFT model, designated as DEKS (PW86-PW91)/TZP model, resulted accurate CEBEs (average absolute deviation of 0.14 eV) with high efficiency. Although absolute magnitude of HAM/3 CEBEs has error as much as 3 eV, the error in the chemical shifts DCEBE is much smaller at 0.55 eV. While the CEBE results do not lead to any definite answer to the question in the title, the trends in valence-electron VIPs indicate that HAM/3 does not approximate DFT with accurate exchange-correlation potentials, but seems to simulate approximate functionals such as B88-P86.

Quantifying intermolecular interactions and their use in computational crystal structure prediction

Intermolecular interactions control the crystal structures adopted by rigid organic molecules. Methods of quantifying the intermolecular forces from the ab initio charge density of the molecule have been extended to organic molecules, albeit more approximately than for small polyatomics. This has led to some almost non-empirical models being used to study organic packing, including crystal structure prediction studies. These studies are highlighted, with particular emphasis on what they reveal about the transferability assumptions that underpin the use of empirical atom–atom intermolecular potentials and intuitive crystal design.

Mathematical models of solute retention in gas chromatography as sources of thermodynamic data. Part III. Alkylbenzenes as the test analytes.

Direct determination of thermodynamic data has always been a complicated and troublesome experimental task. Gas chromatography is among long-established working tools well suited to performing this particular task indirectly. Our own results were first presented in the papers by Ciazynska-Halarewicz and Kowalska (1,2), and this article is Part III in the series. Present experiments are carried out on low- and medium-polarity stationary phases at five different temperatures ranging from 323K to 423K. They enable determination of two thermodynamic properties of the alkylbenzenes, molar enthalpy of vaporization (DeltaH(vap)), and the chemical potential of partitioning of the methylene group between the two phases of the chromatographic system (Delta micro (p(-CH2-))). These properties are obtained from eight nonempirical models and, as is apparent from their derivation (3-7), the terms of the models have clearly defined physical meaning, which enables calculation of thermodynamic properties.

Finding the global minima of clusters with non-empirical models: a comparison of results

Abstract The energetics and the structural properties of some of the smaller ionic clusters of neon atoms ( Ne n + , with n up to 25) are examined using different modeling for the interactions within each cluster moiety. A new, very simple model for the global interaction, the polygon growth model or PGM, is presented and discussed in detail. The results of the calculations, and the physical reliability of the methods, are then examined in comparison with earlier theoretical results and with some available experimental data. In spite of the simplicity of the PGM scheme, the present treatment shows it to be able to reproduce all the important features known for these clusters from earlier calculations and from measurements.

Anisotropic Repulsion Potentials for Cyanuric Chloride (C3N3Cl3) and Their Application to Modeling the Crystal Structures of Azaaromatic Chlorides

A series of nonempirical intermolecular potentials has been developed for the cyanuric chloride dimer, using the overlap model to determine the anisotropy of the repulsive wall around each atom. Calibration against intermolecular perturbation theory calculations enables the penetration and charge-transfer energy to be explicitly included with the exchange-repulsion to give a simple repulsion model in an anisotropic atom−atom form. These model repulsion potentials are used in conjunction with an atomic multipole electrostatic model and an atom−atom dispersion model to give nonempirical potential models, which are tested for their ability to reproduce the crystal structure of cyanuric chloride. The best nonempirical potential is successfully used to construct a simpler transferable model for closely related azaaromatic chlorides. The nonempirical potential reproduces the experimental space group of cyanuric chloride, unlike some empirically fitted repulsion−dispersion potentials. This first nonempirical rep...

Quantitative modeling of soil sorption for xenobiotic chemicals.

Experimentally determining soil sorption behavior of xenobiotic chemicals during the last 10 years has been costly, time-consuming, and very tedious. Since an estimated 100,000 chemicals are currently in common use and new chemicals are registered at a rate of 1000 per year, it is obvious that our human and material resources are insufficient to experimentally obtain their soil sorption data. Much work is being done to find alternative methods that will enable us to accurately and rapidly estimate the soil sorption coefficients of pesticides and other classes of organic pollutants. Empirical models, based on water solubility and n-octanol/water partition coefficients, have been proposed as alternative, accurate methods to estimate soil sorption coefficients. An analysis of the models has shown (a) low precision of water solubility and n-octanol/water partition data, (b) varieties of quantitative models describing the relationship between the soil sorption and above-mentioned properties, and (c) violations of some basic statistical laws when these quantitative models were developed. During the last 5 years considerable efforts were made to develop nonempirical models that are free of errors imminent to all models based on empirical variables. Thus far molecular topology has been shown to be the most successful structural property for describing and predicting soil sorption coefficients. The first-order molecular connectivity index was demonstrated to correlate extremely well with the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and heterosubstituted PAHs, and halogenated phenols. The average difference between predicted and observed soil sorption coefficients is only 0.2 on the logarithmic scale (corresponding to a factor of 1.5). A comparison of the molecular connectivity model with the empirical models described earlier shows that the former is superior in accuracy, performance, and range of applicability. It is possible to extend this model, with the addition of a single, semiempirical variable, to take care of polar and ionic compounds and to accurately predict the soil sorption coefficients for almost 95% of all organic chemicals whose coefficients have been reported. No empirical or nonempirical models have ever predicted the soil sorption coefficients to such a high degree of accuracy on such a broad selection of structurally diverse compounds. An additional advantage of the molecular connectivity model is that it is sufficient to know the structural formulas to make predictions about soil sorption coefficients.(ABSTRACT TRUNCATED AT 400 WORDS)

Investigation of the shape of the imaginary part of the optical-model potential for electron scattering by rare gases

We present a comparative study of several empirical and nonempirical models for the absorption potential, which is the imaginary part of an optical-model potential, for electron scattering by rare gases. We show that the elastic differential cross section is most sensitive to the absorption potential for high-impact energy and large scattering angles. We compare differential cross sections calculated by several models for the absorption potential and by several arbitrary modifications of these model potentials. We are able to associate the effect of the absorption potential on the elastic differential cross section with its form at small electron-atom distances $r$, and we are able to deduce various qualitative features that the absorption potential must possess at small and large $r$ in order to predict both accurate differential cross sections and accurate absorption cross sections. Based on these observations, the Pauli blocking conditions of the quasifree scattering model for the absorption potential are modified empirically, thus producing a more accurate model that may be applied to other systems; e.g., electron-molecule scattering, with no adjustable parameters.