Set Of Interaction Parameters Research Articles

Phase behavior of supercritical CO2 + nonionic ethoxylated surfactants + methanol: Experimental data and modeling with PC-SAFT equation of state

The use of surfactants for oil and gas purposes has been explored and extensively applied. However, such systems' thermodynamic and predictability behavior still needs further investigation. This work aims to describe the phase behavior of the systems composed of nonionic ethoxylated surfactants (nonylphenyl ethoxylated surfactants—IGEPAL CO-630 and CO-720) + carbon dioxide (CO2) with additional methanol in wide ranges of temperature (T = 313 to 413 K), pressure (P = 0.8 to 54.8 MPa), and CO2 molar compositions (up to 90.0 %). It was observed for all systems studied that CO2 solubility was inversely proportional to temperature and the number of ethoxylated units for pure surfactants. The addition of methanol greatly increases the overall CO2 solubility. The thermodynamic modeling through the PC-SAFT equation of state was also evaluated. Bubble pressure deviations of 13.63 % and 13.49 % were obtained for pure IGEPAL CO-630 and IGEPAL CO-720 + CO2, respectively, and 12.63 % for the ternary system (IGEPAL CO-720 + methanol + CO2). A new set of binary interaction parameters was also provided for IGEPAL CO-630 and IGEPAL CO-720 + CO2.

Free energy curves for the Volmer reaction obtained from molecular dynamics simulation based on quantum chemistry

Hydrogen desorption from Au(111) at a constant electrode charge has been studied by a DFT-based tight binding theory (DFTB). Free energy curves have been obtained from molecular dynamics with umbrella sampling. The activation energy increases linearly with the applied negative charge and decreases with temperature, so that the Butler-Volmer law does not hold in its strict form. The activation energy is determined by the reorganization of the accepting water molecule and its surroundings, which becomes more facile with temperature. A separation of the free energy curves into a constant chemical part and an electrostatic part, which varies with the charge, does not hold. Because of its speed DFTB is very suitable for the investigation of electrochemical reactions, but is presently hampered by a lack of sets of interaction parameters.

Investigation of the relationship between mirror proton radii and neutron-skin thickness* *This study is partially Supported by the National Natural Science Foundation of China (11925502, 11935001, 11961141003, 11890714, 12147101), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB34030000) and the National Key R&D Program of China (2018YFA0404404)

Through systematic investigations using the axially deformed solutions of the Skyrme-Hartree-Fock-Bogoliubov equations with 132 sets of Skyrme interaction parameters, it is confirmed that the neutron-skin thickness () of a neutron-rich nucleus is proportional to the difference between the proton radii of mirror nuclei (). This indicates that may be deduced from . Compared with the results of the Skyrme-Hartree-Fock model, pairing effects are found to enhance the correlation for most mirror pairs, whereas deformation effects may weaken the correlation. Furthermore, the correlation between and is studied for isotones with and , which reveals a stronger linear correlation with increasing . This result demonstrates that it is possible to extract the neutron-skin thickness of an unstable nucleus from the proton radii difference of the mirror nuclei of its isotones.

Raman spectroscopy of bimagnon and trimagnon excitations and rotonlike points in a distorted triangular lattice antiferromagnet

We investigate the experimental signatures of Raman spectroscopy of bi- and tri-magnon excitations in the distorted triangular lattice antiferromagnets alpha-LCr2O4 (L=Sr, Ca). We utilize spin wave theory to analyze the nearly 120 degree spin-3/2 spiral ordered antiferromagnetic ground state to compute the single-magnon density of states, single-magnon dispersion, and bimagnon and trimagnon Raman spectra (polarized and unpolarized). It is found that Raman scattering is capable of capturing the effect of the rotonlike M and M' points on the bimagnon Raman spectrum. Our calculation confirms the connection between single-magnon rotonlike excitation energy and bimagnon Raman excitation spectrum observed experimentally. The roton energy minimum in momentum space is half of the energy of a bimagnon excitation signal. The experimental magnetic Raman scattering result displays two peaks which have a Raman shift of 15 meV and 40 meV, respectively. Theoretical modeling and analysis of the experimental spectrum of alpha-SrCr2O4 within our distorted Heisenberg Hamiltonian lattice suggests that the low-energy peak at 15 meV is associated with the bimagnon excitation, whereas the high-energy peak around 40 meV is primarily a trimagnon excitation. Based on our fitting procedure we propose a new set of magnetic interaction parameters for alpha-SrCr2O4. These parameters reproduce not only the experimental Raman spectrum, but also the inelastic neutron scattering response (including capturing high energy magnon branches). We also compute the unpolarized bimagnon and trimagnon Raman spectra for alpha-CaCr2O4. Furhtermore, we found that the polarization sensitivity of Raman spectrum can be utilized to distinguish the bi- and tri-magnon excitation channels.

Simplified Approach to the Parameterization of the NRTL Model for Partially Miscible Binary Systems: Tττ LLE Methodology

A new approach to parameterizing the NRTL model for binary liquid–liquid equilibria (LLE) is presented. It allows for the incorporation of a priori knowledge into the parameterization procedure rather than using the “black box” approach often employed. The method first converts the compositional Txx data to a set of unique binary interaction parameters, Tττ data. Thereafter, the second step improves the parameterization of frequently used temperature-dependent parameters (TDPs) by reducing the traditional nonlinear regression problem to simpler linear regression. This method is less susceptible to poor initial guesses, finding local minima, and significantly reduces computational requirements, with comparable/improved performance to published parameters. A total of 29 binary systems, including upper and/or lower critical solution temperatures, were evaluated using the approach to provide generalized recommendations and understanding of the TDP requirements for each system type. Inclusion of such information and use of the approach will significantly simplify multicomponent LLE model parameterization.

Marginal log-linear models and mediation analysis

After reviewing some not well known results about marginal log-linear models, the paper derives some new ones and shows how they might be relevant in mediation analysis when all variables are categorical. By focusing on the interactions between treatment and response, both marginally and jointly with respect to the mediating variables, a new relation between these parameters is derived. In addition, the paper describes a new class of models in which linear constraints may be imposed simultaneously on these two sets of interaction parameters. An application to education transmission from parents to their children is used as an illustration.

Development of a more accurate Geant4 quantum molecular dynamics model for hadron therapy

Objective. Although in heavy-ion therapy, the quantum molecular dynamics (QMD) model is one of the most fundamental physics models providing an accurate daughter-ion production yield in the final state, there are still non-negligible differences with the experimental results. The aim of this study is to improve fragment production in water phantoms by developing a more accurate QMD model in Geant4. Approach. A QMD model was developed by implementing modern Skyrme interaction parameter sets, as well as by incorporating with an ad hoc α-cluster model in the initial nuclear state. Two adjusting parameters were selected that can significantly affect the fragment productions in the QMD model: the radius to discriminate a cluster to which nucleons belong after the nucleus–nucleus reaction, denoted by R, and the squared standard deviation of the Gaussian packet, denoted by L. Squared Mahalanobis’s distance of fragment yields and angular distributions with 1, 2, and the higher atomic number for the produced fragments were employed as objective functions, and multi-objective optimization (MOO), which make it possible to compare quantitatively the simulated production yields with the reference experimental data, was performed. Main results. The MOO analysis showed that the QMD model with modern Skyrme parameters coupled with the proposed α-cluster model, denoted as SkM* α, can drastically improve light fragments yields in water. In addition, the proposed model reproduced the kinetic energy distribution of the fragments accurately. The optimized L in SkM* α was confirmed to be realistic by the charge radii analysis in the ground state formation. Significance. The proposed framework using MOO was demonstrated to be very useful in judging the superiority of the proposed nuclear model. The optimized QMD model is expected to improve the accuracy of heavy-ion therapy dosimetry.

Multi-objective optimization of equation of state molecular parameters: SAFT-VR Mie models for water

The determination of a suitable set of molecular interaction parameters for use with an equation of state (EoS) can be viewed as a multi-objective optimization (MOO) problem, where each objective quantifies the quality of the description for a particular type of thermodynamic property. We outline a methodology for the determination of a set of Pareto-optimal interaction parameters. The Pareto front is generated efficiently using a sandwich algorithm where one solves a sequence of weighted-sum scalarized single objective optimization problems. The algorithm presented can be used for any number of objective functions, allowing for the consideration of multiple thermodynamic property types as competing objectives in the MOO. The methodology is applied to the determination of suitable parameter sets for models of water within the SAFT-VR Mie framework. Three competing property targets are considered as objective functions: saturated-liquid density, vapour pressure and isobaric heat capacity. Two different types of molecular models are considered: spherical models of water, and non-spherical model of water. We analyse the two- and three-dimensional Pareto surfaces and parameter sets obtained for different property combinations in the MOO. The proposed methodology can be used to provide a rigorous comparison between different model types. Numerous Pareto-optimal parameter sets for SAFT-VR Mie water models are documented, and we recommend two new models (one spherical model and one non-spherical model) with an appropriate compromise between the competing objectives.

Bose-Einstein condensation in finite drops of α particles

Ground-state properties of finite drops of $\ensuremath{\alpha}$ particles (Q-balls) are studied within a field-theoretical approach in the mean-field approximation. The strong interaction of $\ensuremath{\alpha}$'s is described by the scalar field with a sextic Skyrme-like potential. The radial profiles of scalar and Coulomb fields are found by solving the coupled system of Klein-Gordon and Poisson equations. The formation of shell-like nuclei, with vanishing density around the center, is predicted at high enough attractive strength of Skyrme potential. The equilibrium values of energy and baryon number of Q-balls and Q-shells are calculated for different sets of interaction parameters. Empirical binding energies of $\ensuremath{\alpha}$-conjugate nuclei are reproduced only if the gradient term in the Lagrangian is strongly enhanced. It is demonstrated that this enhancement can be explained by a finite size of $\ensuremath{\alpha}$ particles.

Thermodynamic assessment of the Ca–Sn system

Abstract Thermodynamic modelling of the Ca–Sn binary system was carried out. The thermodynamic parameters related to this system were determined from experimental phase diagram and thermodynamic information available in the literature. In this system the liquid phase was modelled by the association model with the “Ca2Sn” associated complex. This consideration permits to well restore experimental values. A set of thermodynamic interaction parameters, the calculated phase diagram as well as the comparison with experimental data are presented.

Modelling low pressure LLE and VLE of methanol/alkane mixtures with a modified Peng-Robinson EoS and the Huron-Vidal mixing rules

In this work, it is assessed the capabilities and limitations of a simple cubic EoS/GE thermodynamic model to describe the phase equilibria of methanol/alkane mixtures using generalized binary interaction parameters. In first place, the critical properties of the n-alkanes were selected to generalize the parameters of the model by fitting the liquid-liquid equilibria (LLE) of binary mixtures formed by methanol with pentane, heptane and decane respectively. Adequate description of the LLE coexistence curve can be obtained at atmospheric pressure for mixtures with n-alkanes in the 4-10 carbon number range. Also, it is possible to represent the mathematical behavior of the UCST of the methanol alkane series according to literature. Finally, some predictions were made for vapor liquid equilibria (VLE) and vapor-liquid-liquid equilibria (VLLE) conditions at low and high pressure. In general, predictions are unsatisfactory. In some cases, at low pressures, qualitative predictions for the azeotropic behavior can be obtained. In second place, a second set of generalized parameters were obtained by fitting the VLE of binary mixtures formed by methanol with propane, pentane and hexane. Using this new set, the model is capable to reproduce in qualitative way the high-pressure vapor-liquid equilibria of methanol/alkane mixtures between propane and decane. However, for LLE equilibria the results are inadequate from qualitative and quantitative points of view. Based on the results found in this work, it can be established that the selected model is not capable to describe simultaneously the VLE and LLE of methanol/alkane type mixtures reasonably with a single set of binary interaction parameters.

The Effect of Functional Groups on the Phase Behavior of Carbon Dioxide Binaries and Their Role in CCS.

In recent years we have focused our efforts on investigating various binary mixtures containing carbon dioxide to find the best candidate for CO2 capture and, therefore, for applications in the field of CCS and CCUS technologies. Continuing this project, the present study investigates the phase behavior of three binary systems containing carbon dioxide and different oxygenated compounds. Two thermodynamic models are examined for their ability to predict the phase behavior of these systems. The selected models are the well-known Peng–Robinson (PR) equation of state and the General Equation of State (GEOS), which is a generalization for all cubic equations of state with two, three, and four parameters, coupled with classical van der Waals mixing rules (two-parameter conventional mixing rule, 2PCMR). The carbon dioxide + ethyl acetate, carbon dioxide + 1,4-dioxane, and carbon dioxide + 1,2-dimethoxyethane binary systems were analyzed based on GEOS and PR equation of state models. The modeling approach is entirely predictive. Previously, it was proved that this approach was successful for members of the same homologous series. Unique sets of binary interaction parameters for each equation of state, determined for the carbon dioxide + 2-butanol binary model system, based on k12–l12 method, were used to examine the three systems. It was shown that the models predict that CO2 solubility in the three substances increases globally in the order 1,4-dioxane, 1,2-dimethoxyethane, and ethyl acetate. CO2 solubility in 1,2-dimethoxyethane, 1.4-dioxane, and ethyl acetate reduces with increasing temperature for the same pressure, and increases with lowering temperature for the same pressure, indicating a physical dissolving process of CO2 in all three substances. However, CO2 solubility for the carbon dioxide + ether systems (1,4-dioxane, 1,2-dimethoxyethane) is better at low temperatures and pressures, and decreases with increasing pressures, leading to higher critical points for the mixtures. By contrast, the solubility of ethyl acetate in carbon dioxide is less dependent on temperatures and pressures, and the mixture has lower pressures critical points. In other words, the ethers offer better solubilization at low pressures; however, the ester has better overall miscibility in terms of lower critical pressures. Among the binary systems investigated, the 1,2-dimethoxyethane is the best solvent for CO2 absorption.

Neutron scattering study of magnetic anisotropy in the tetragonal antiferromagnet Bi2CuO4

Using neutron spectroscopy, the authors map out the full magnon dispersion in the easy-plane antiferromagnet Bi${}_{2}$CuO${}_{4}$ and determine its complete spin Hamiltonian. In particular, they solve a long-standing puzzle in this material by determining its small anisotropic spin interactions. Equipped with the complete set of interaction parameters, the authors establish Bi${}_{2}$CuO${}_{4}$ as a rare example of quantum order by disorder, where quantum fluctuations break the in-plane spin degeneracy and are manifested as a spin-flop transition observed by neutron scattering.

Conical order, magnetic compensation, and sign reversible exchange bias in spinel structured AB2O4 compounds: A Monte Carlo study

$A{B}_{2}{\mathrm{O}}_{4}$ are a special class of spinel structured compounds exhibiting unique multiferroic properties. Recent experimental observation confirms switchable polarization in $A{\text{Cr}}_{2}{\text{O}}_{4}$ $(A=\text{Co}, \mathrm{Mn}, \mathrm{Fe})$, arising out of noncollinear magnetic spin order. In this paper we unfold the microscopic origin behind such magnetic spin order, hysteresis, polarization, and the so-called magnetic compensation effect in $A{\text{Cr}}_{2}{\text{O}}_{4}$ $(A=\text{Co}, \mathrm{Mn}, \mathrm{Fe}, \mathrm{Ni})$ using Monte Carlo simulation. We have carefully constructed a set of exchange interaction parameters, which help to explain various experimental findings such as magnetization vs temperature $(T)$, conical stability, magnetic ordering, and polarization in a representative compound ${\text{CoCr}}_{2}{\text{O}}_{4}$. When substituted with Fe, ${\text{CoCr}}_{2}{\text{O}}_{4}$ shows few exotic phenomena such as sign reversible exchange bias effect and magnetic compensation. ${\text{CoMn}}_{2}{\text{O}}_{4}$ and ${\text{CoFe}}_{2}{\text{O}}_{4}$ are two other compounds in the spinel family where we found no conical spin order and polarization, and thus facilitate a distinct contrast compared to others.

Understanding charged vesicle suspensions as Wigner glasses: dynamical aspects

Suspensions of charged vesicles in water with added salt are widespread in nature and industrial production. Here we investigate, via Brownian dynamics simulations, a model that grasps the key features of these systems, with bidisperse colloidal beads interacting via a hard-core and an electrostatic double layer potential. Our goal is to focus on a set of interaction parameters that is not generic but measured in recent experiments, and relevant for a class of consumer products, such as liquid fabric softeners. On increasing the volume fraction in a range relevant to real formulation, we show that the dynamics become progressively slower and heterogeneous, displaying the typical signatures of an approaching glass transition. On lowering the salt concentration, which corresponds to increasing the strength and range of the electrostatic repulsion, the emergence of glassy dynamics becomes significantly steeper, and, remarkably, occurs at volume fractions well below the hard-sphere glass transition. The volume fraction dependence of the structural relaxation time at different salt concentration is well described through a functional law inspired by a recently proposed model (Krausser et al 2015 Proc. Natl Acad. Sci. USA 112 13762). According to our results, the investigated system may be thought of as a Wigner glass, i.e. a low-density glassy state stabilized by long-range repulsive interactions. Overall, our study suggests that glassy dynamics plays an important role in controlling the stability of these suspensions.

Energy deposition parameters revealed in the transition from 3D to 1D femtosecond laser ablation of fluorite at high-NA focusing

Ultrashort-pulse laser surface and bulk nano- and micromachining of dielectrics have multiple promising applications in micro-optics, microfluidics, and memory storage. The fundamental principles relate intrinsic inter-band multi-photon (MPA) and laser-induced intra-band free-carrier absorption (FCA) to particular ablation mechanisms and features. These principles are yet to be quantified into a complete set of basic experimental laser-matter interaction parameters, describing photoexcitation, relaxation, and final ablation. In this study, we considered the characteristic double-crater structure of single-shot ablation spots on dielectric surfaces and single-shot transmission spectra to extract crucial information about the underlying basic processes of ultrafast photoexcitation and laser energy deposition. Specifically, energy-dependent crater profiles and accompanying prompt self-phase modulation (SPM) spectral broadening were studied in single-shot surface ablation experiments on fluorite (CaF2) surface photo-excited by tightly focused 515- or 1030-nm, 300-fs laser pulses. Crater size dependence demonstrated two slopes, scaling proportionally to the squared focal 1/e-radius at higher energies (intensities) for larger ablated spots, and a much smaller squared 1/e-radius at lower energies (intensities) for (sub) micron-wide ablated spots, indicating a transition from 1D to 3D-ablation. As a result, these slopes were related to lower-intensity wavelength-dependent multi-photon inter-band transitions and wavelength-independent higher-intensity linear absorption in the emerging near-critical electron-hole plasma (EHP), respectively. Crater depth dependences on the local laser intensity fitted in the corresponding ranges by multi- and one-photon absorption provided the corresponding absorption coefficients. Spectral broadening measurements indicated even values for the red and blue shoulders of the laser pulse spectrum, representing the SPM effect in the weakly excited fluorite at the leading pulse front and providing the corresponding Kerr coefficient. In the second regime, the blue-shoulder broadening value saturated, indicating the appearance of near-critical plasma screening at the trailing pulse front, which is consistent with our calculations. These complementary experiments and related analysis provided an important set of key basic parameters, characterizing not only surface ablation, but also propagation of high-intensity ultrashort laser pulses in bulk fluorite, and enabling precise forecasting of optimal energy deposition for high-efficiency ultrashort-laser micro-structuring of this dielectric material.

Temperature dependence of interaction parameters for Al–Li liquid alloy

ABSTRACT In the studies related to thermodynamic and structural functions of liquid alloys at high temperatures using linear temperature-dependent interaction parameters, in some cases, artificial miscibility gaps or artefacts are noticed. These artificial miscibility gaps in these functions at higher temperatures are usually asymmetric with respect to the concentration. The presence of the artificial miscibility gaps in the properties of the alloys at higher temperatures makes them less reliable and such data cannot be accepted at all. In the present work, we have computed thermodynamic and structural properties of liquid Al–Li alloy at temperatures 800, 1300 and 2000 K in the framework of Redlich–Kister (R-K) polynomials assuming interaction parameters to be linear temperature dependent and some artefacts were observed in these functions at around 2000 K. We have then obtained the optimised set of exponential temperature-dependent interaction parameters and computed the properties of the alloy again from the same polynomials where no miscibility gap was noticed at higher temperatures.

Coarse-Grained Parameters for Divalent Cations within the SIRAH Force Field.

Although molecular dynamics simulations allow for the study of interactions among virtually all biomolecular entities, metal ions still pose significant challenges in achieving an accurate structural and dynamical description of many biological assemblies, particularly to coarse-grained (CG) models. Although the reduced computational cost of CG methods often makes them the technique of choice for the study of large biomolecular systems, the parameterization of metal ions is still very crude or not available for the vast majority of CG force fields. Here, we show that incorporating statistical data retrieved from the Protein Data Bank (PDB) to set specific Lennard-Jones interactions can produce structurally accurate CG molecular dynamics simulations using the SIRAH force field. We provide a set of interaction parameters for calcium, magnesium, and zinc ions, which cover more than 80% of the metal-bound structures reported in the PDB. Simulations performed on several proteins and DNA systems show that it is possible to preclude the use of topological constraints by modifying specific Lennard-Jones interactions.

Development of a coarse-grained lipid model, LIME 2.0, for DSPE using multistate iterative Boltzmann inversion and discontinuous molecular dynamics simulations

We suggest an improved version of the intermediate resolution implicit solvent model for lipids, LIME, that was previously developed for use with discontinuous molecular dynamics (DMD) simulations. LIME gets its geometrical and energy parameters between bonded and nonbonded pairs of coarse-grained (CG) sites from atomistic simulations. The improved model, LIME 2.0, uses multiple square wells rather than the single square well used in original LIME to obtain intermolecular interactions that more faithfully mimic those from atomistic simulations. The multi-state iterative Boltzmann inversion (MS-IBI) scheme is used to determine the interaction parameters. This means that a single set of interaction parameters between coarse-grained sites can be used to represent the lipid bilayers at different temperatures. The physical properties of CG DSPE lipid bilayer are calculated using CG simulations and compared to atomistic simulations results to verify the improved model. The phase transition temperature of the lipid bilayer is measured accurately and the lipid translocation phenomenon, “flip-flop” is observed through CG simulation. These results suggest that CG parameterization using multiple square-wells and the MS-IBI scheme is well suited to the study of lipid bilayers across a range of temperatures with DMD simulations.

Estimation of Solubility of BTEX, Light Hydrocarbons and Sour Gases in Triethylene Glycol Using the SAFT Equation of State

An accurate prediction of the absorption and desorption of Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) is important for the estimation of BTEX emissions from glycol units in natural gas processing plants. This work presents an approach to accurately model the solubilities of BTEX in triethylene glycol (TEG). The absorption of gases studied in this work into TEG is physical in nature, and therefore is treated as physisorption in modeling. The Huang-Radosz version of Statistical Associating Fluid Theory (SAFT-HR) Equation of State (EoS) was utilized to estimate the solubilities of BTEX in TEG. A new set of SAFT parameters for TEG, as well as a new set of binary interaction parameters between TEG and other components were obtained by fitting experimental vapor pressure and liquid density of TEG and available experimental binary VLE data, respectively. Using these parameters, solubility of multicomponent gases in TEG are accurately predicted. To have an estimate of the relative accuracy of SAFT-HR EoS, the results from Perturbed–Chain SAFT (PC–SAFT) and Peng–Robinson (PR) EoS are also reported. The overall average of root–mean–square deviation (RMSD) for binary and ternary systems studied in this work, using SAFT-HR, PC–SAFT, and PR EoS obtained equal to 0.12, 0.20, and 1.56, respectively.