Concentration Dependence Of Density Research Articles

Global well-posedness and convergence to equilibrium for the Abels-Garcke-Grün model with nonlocal free energy

We investigate the nonlocal version of the Abels-Garcke-Grün (AGG) system, which describes the motion of a mixture of two viscous incompressible fluids. This consists of the incompressible Navier-Stokes-Cahn-Hilliard system characterized by concentration-dependent density and viscosity, and an additional flux term due to interface diffusion. In particular, the Cahn-Hilliard dynamics of the concentration (phase-field) is governed by the aggregation/diffusion competition of the nonlocal Helmholtz free energy with singular (logarithmic) potential and constant mobility. We first prove the existence of global strong solutions in general two-dimensional bounded domains and their uniqueness when the initial datum is strictly separated from the pure phases. The key points are a novel well-posedness result of strong solutions to the nonlocal convective Cahn-Hilliard equation with singular potential and constant mobility under minimal integral assumption on the incompressible velocity field, and a new two-dimensional interpolation estimate for the L4(Ω) control of the pressure in the stationary Stokes problem. Secondly, we show that any weak solution, whose existence was already known, is globally defined, enjoys the propagation of regularity and converges towards an equilibrium (i.e., a stationary solution) as t→∞. Furthermore, we demonstrate the uniqueness of strong solutions and their continuous dependence with respect to general (not necessarily separated) initial data in the case of matched densities and unmatched viscosities (i.e., the nonlocal model H with variable viscosity, singular potential and constant mobility). Finally, we provide a stability estimate between the strong solutions to the nonlocal AGG model and the nonlocal Model H in terms of the difference of densities.

Computational calculations for temperature and concentration-dependent density effects on creeping motion of Carreau fluid: biological applications

The sperm density through the cervical canal plays a vital role in promoting the pregnancy processes of living organisms. So, the density of fluid distribution is studied in a dependent case on concentration and temperature. A new mechanism of creeping flow of non-Newtonian fluid in a cervical channel is proposed. Carreau fluid system or physical model is rearranged using non-dimensional quantities, and then numerically reappearances using adaptive (AST) shooting technique. Results for axial velocity u(y) profile, temperature , and concentration distribution are numerically obtained with aid of a computer algorithm in AST by Mathematica 13.1.1. Confirmation check of acquired results is verified with numerical values comparison with nearest available results. The main point output shows that the dependent values of fluid concentration and temperature parameters make the velocity distribution better active. Further, the creeping flow concentration behavior gets better as the fluid density changes with the concentration and temperature, and the sperms become more active in the cervical channel.

On the analogy between the restricted primitive model and capacitor circuits. Part II: A generalized Gibbs-Duhem consistent extension of the Pitzer-Debye-Hückel term with corrections for low and variable relative permittivity

We present a novel, thermodynamically consistent modification of the Pitzer-Debye-Hückel term and its extension for concentration dependent density, molar mass and relative permittivity. This extension is validated for ionic liquids by comparison with a reference model from the literature and, in contrast to similar extensions, also applied to conventional salts with small spherical ions in aqueous, mixed and non-aqueous solvents. The central novelty is the inclusion of a modified parameter of closest approach, which improves the overall qualitative performance of the Pitzer-Debye-Hückel term over the complete relative permittivity range. Gibbs-Duhem consistency is retained in the modified extension and sample calculations for aqueous [BMIM][BF4] and aqueous NaCl are provided. The novel, modified and extended term with concentration dependent properties is combined with the predictive COSMO-RS-ES model for the calculation of phase equilibria and activity coefficients in electrolytes with conventional salts. The performance of the COSMO-RS-ES model for predictions of salt solubility in fully non-aqueous media improves significantly upon introduction of concentration dependent properties within the long-range electrostatics. Modelling performance with the modified extended Pitzer-Debye-Hückel term outperforms modelling with the unmodified extensed term as well as with the conventional term. The correlated relative permittivity of the mixture is overestimated with respect to experimental values and kinetic depolarization effects provide a plausible explanation for this observation. Overall, our results support the consistent introduction of concentration dependent properties within the electrostatic theory in order to improve the modelling of electrolytes with particular emphasis on non-aqueous electrolytes.

Deciphering Ethanol-Driven Swelling, Rupturing, Aggregation, and Fusion of Lipid Vesicles Using Coarse-Grained Molecular Dynamics Simulations.

Traditionally, liquid ethanol is known to enhance the permeability of lipid membranes and causes vesicle aggregation and fusion. However, how the amphiphilic ethanol molecules perturb the lipid vesicles to facilitate their aggregation or fusion has not been addressed at any level of molecular simulations. Herein, not only have we developed a coarse-grained (CG) model for liquid ethanol, its aqueous mixture, and hydrated lipid membranes for molecular dynamics (MD) simulations, but also utilized it to delineate the aggregation and fusion of lipid vesicles using CG-MD simulations with multimillion particles. We have systematically parametrized the force-field for pure ethanol and its interactions with hydrated POPC and POPE model lipid membranes. In this process, we have successfully reproduced the bulk ethanol structure and concentration-dependent density of aqueous ethanol. To quantify the interaction of ethanol with lipid membranes, we have reproduced the transfer free energy of the ethanol molecule across the hydrated bilayers, and the concentration-dependent distribution of ethanol molecules across the lipid bilayers. After having acceptable force-field parameters for ethanol-membrane interactions, we have checked the effect of ethanol toward the vesicles comprising POPC lipids. We observe a rapid increase in the size of the POPC lipid vesicles with increasing amounts of ethanol up to 30 mol %. We unambiguously observe swelling and decrease in the thickness of the POPC vesicles with increasing amounts of ethanol up to 30 mol %, beyond which the vesicles begin to lose their integrity and rupture at higher mol % of ethanol. The fusion study of two vesicles demonstrates that fused vesicles can be obtained from 20 to 30 mol % of ethanol provided that they are brought closer than a critical distance at a particular mol %. The multivesicle simulations show that along with the increase in the sizes of vesicles the propensity of vesicle aggregation increases as the mol % of ethanol increases.

Role of density gradients on miscible Rayleigh–Taylor fingers in porous media

We investigate the effect of density gradients on miscible Rayleigh–Taylor fingers in homogeneous porous media using two families of concentration-dependent density profiles: (a) monotonic and (b) nonmonotonic. The first family consists of linear, quadratic, and cubic functions of the solute concentration, while the latter is described as a quadratic function of the solute concentration such that the density maximum (minimum) appears in time as diffusion relaxes the concentration gradient. With the help of these simple models, we are able to address one of the most puzzling questions about the fingering instabilities with nonmonotonic density profiles. Using linear stability analysis and nonlinear simulations, we show that density gradients play a pivotal role in controlling instability.

Transferable Ion Force Fields in Water from a Simultaneous Optimization of Ion Solvation and Ion-Ion Interaction.

The poor performance of many existing nonpolarizable ion force fields is typically blamed on either the lack of explicit polarizability, the absence of charge transfer, or the use of unreduced Coulomb interactions. However, this analysis disregards the large and mostly unexplored parameter range offered by the Lennard-Jones potential. We use a global optimization procedure to develop water-model-transferable force fields for the ions K+, Na+, Cl–, and Br– in the complete parameter space of all Lennard-Jones interactions using standard mixing rules. No extra-thermodynamic assumption is necessary for the simultaneous optimization of the four ion pairs. After an optimization with respect to the experimental solvation free energy and activity, the force fields reproduce the concentration-dependent density, ionic conductivity, and dielectric constant with high accuracy. The force field is fully transferable between simple point charge/extended and transferable intermolecular potential water models. Our results show that a thermodynamically consistent force field for these ions needs only Lennard-Jones and standard Coulomb interactions.

Mechanism of transient stagnant formation in convection of binary mixtures

Two-dimensional convection rolls are usually stable near the critical Rayleigh number in single component fluids. However, in binary mixtures, it has been reported that the roll patterns become unstable over time and that stagnant domains are transiently formed. The formation of transient stagnant domains (TSD) occurs in systems where one component is more viscous than the other. Meanwhile, the mechanism of the TSD formation has been unclear yet. Here, we use experiments using well-mixed silicone oils and colloidal suspensions to show that the formation of transient stagnant regions is chiefly related to the concentration dependence of the kinematic viscosity rather than spatially averaged properties. Furthermore, we find that the concentration dependence of density is also related to the formation of stagnant regions. The coupling between density, viscosity and concentration fluctuations may play an important role for thermal convection in multi-component mixtures.

Well-posedness of the two-dimensional Abels–Garcke–Grün model for two-phase flows with unmatched densities

We study the Abels–Garcke–Grün (AGG) model for a mixture of two viscous incompressible fluids with different densities. The AGG model consists of a Navier–Stokes–Cahn–Hilliard system characterized by a (non-constant) concentration-dependent density and an additional flux term due to interface diffusion. In this paper we address the well-posedness problem in the two-dimensional case. We first prove the existence of local strong solutions in general bounded domains. In the space periodic setting we show that the strong solutions exist globally in time. In both cases we prove the uniqueness and the continuous dependence on the initial data of the strong solutions. Lastly, we show a stability result for the strong solutions to the AGG model and the model H in terms of the density values.

Thermal energy dissipation capability of garnet nanofluids

The nano garnet particle is dispersed into SN500 grade lubricating oil through Digital probe sonicator for formulating garnet nanofluids. The temperature and particle concentration dependent density and heat dissipation rate are experimentally investigated. The results show that the density of base fluid increases with the addition of nanoparticles. Also, the homogeneous dispersion of garnet nanoparticles into the base fluid has the considerable effect on the nanoparticle concentration and temperature dependent thermal energy dissipation capability.

Determination of excited state dipole moments in solution via thermochromic methods

The method basically combines the existing ideas of excited state dipole moment determination via thermochromic fluorescence spectroscopy with the determination of the solvent cavity volume via concentration dependent density measurements of the solution densities at different weight fractions. Additionally, the determination of the cavity volume in dependence of the solvent temperature is included here, which provides a better accuracy of the excited state dipole moment determination. With this step two major sources of errors are eliminated: the use of the very imprecise Onsager radius and the assumption, that the cavity size is temperature independent.•Thermochromic absorption and fluorescence spectroscopy.•Cavity volume determination by density measurements.•Temperature dependent cavity volume determination.

Неустойчивость двойной диффузии при сонаправленной диффузии растворенных компонент

Diffusion can have a destabilizing effect on the development of convective flows in multicomponent liquid mixtures with different diffusion rates of components. The movement that arises in this case, which is generally called double (or differential) diffusive instability, is an important mechanism for intensifying mass and heat transfer in many natural and technological systems. As components that affect the overall density distribution in a liquid medium, heat and a dissolved substance or two dissolved substances can act. In the latter, isothermal case, the standard formulation of the problem includes the study of the stability of a two-layer system under counter diffusion of components dissolved in adjacent layers. The possibility of developing instability during co-directional diffusion of components having a different sign of the concentration dependence of density and initially dissolved in one of the layers was experimentally investigated for the first time. Such a statement of the problem is closest to a number of oceanological applications, where the development of instability is due to the uneven distribution of temperature and salinity of sea water. In present work, the development of double diffusive instability was found and it was shown that the structure of the resulting convective flow is determined by the ratios of the density increments due to the dissolution of the components and the diffusion coefficients. Based on the research results, a set of dimensionless parameters is proposed and a map of the regimes of the observed convective flows is constructed, which allows us to systematize the experimental data.

Nonlinear Convective Flow of Non-Newtonian Fluid over an Inclined Plate with Convective Surface Condition: A Darcy–Forchheimer Model

A problem of mixed convective flow of a non-Newtonian power-law fluid over an inclined plate embedded in a non-Darcy porous medium under convective thermal boundary condition is attempted in the present investigation. In addition, the nonlinear temperature–concentration-dependent density relation taken into account to address thermal and solutal transport phenomena in some thermal systems which are performed at high-level temperatures. Initially, the flow equations of the present model are cast into a sequence of ordinary differential equations by the local non-similarity technique. Then the modified set of equations is evaluated by applying a successive linearization method. This numerical study explores the impact of pertinent parameters on the fluid flow characteristics through graphs and the salient features are discussed in detail.

Physico-chemical properties of the C60-l-threonine water solutions

The paper presents novel data on physico-chemical investigation of the C60-l-threonine water solutions. The data on temperature dependence of solubility and viscosity, concentration dependences of density, specific conductivity, molar conductivity, dissociation constant, activity coefficients as well as experimental data on dynamic light scattering are presented and discussed. The excess thermodynamic functions were calculated using Virial Decomposition Asymmetric Model (VD-AS) based on virial expansion of the excess molar Gibbs energy by mole fractions of the solution components.

Physico-chemical properties of the C60-l-lysine water solutions

The paper describes the experimental data on physico-chemical study of the C60-l-lysine derivative water solutions. The data on temperature dependence of solubility in water, concentration dependence of density, specific conductivity, molar conductivity, dissociation constant as well as experimental data on dynamic light scattering are presented and discussed.

Trapping of Li(+) Ions by [ThFn](4-n) Clusters Leading to Oscillating Maxwell-Stefan Diffusivity in the Molten Salt LiF-ThF4.

A molten salt mixture of lithium fluoride and thorium fluoride (LiF-ThF4) serves as a fuel as well as a coolant in the most sophisticated molten salt reactor (MSR). Here, we report for the first time dynamic correlations, Onsager coefficients, Maxwell-Stefan (MS) diffusivities, and the concentration dependence of density and enthalpy of the molten salt mixture LiF-ThF4 at 1200 K in the composition range of 2-45% ThF4 and also at eutectic composition in the temperature range of 1123-1600 K using Green-Kubo formalism and equilibrium molecular dynamics simulations. We have observed an interesting oscillating pattern for the MS diffusivity for the cation-cation pair, in which ĐLi-Th oscillates between positive and negative values with the amplitude of the oscillation reducing as the system becomes rich in ThF4. Through the velocity autocorrelation function, vibrational density of states, radial distribution function analysis, and structural snapshots, we establish an interplay between the local structure and multicomponent dynamics and predict that formation of negatively charged [ThFn](4-n) clusters at a higher ThF4 mole % makes positively charged Li(+) ions oscillate between different clusters, with their range of motion reducing as the number of [ThFn](4-n) clusters increases, and finally Li(+) ions almost get trapped at a higher ThF4% when the electrostatic force on Li(+) exerted by various surrounding clusters gets balanced. Although reports on variations of density and enthalpy with temperature exist in the literature, for the first time we report variations of the density and enthalpy of LiF-ThF4 with the concentration of ThF4 (mole %) and fit them with the square root function of ThF4 concentration, which will be very useful for experimentalists to obtain data over a range of concentrations from fitting the formula for design purposes. The formation of [ThFn](4-n) clusters and the reduction in the diffusivity of the ions at a higher ThF4% may limit the percentage of ThF4 that can be used in the MSR to optimize the neutron economy.

Physico-chemical properties of the water-soluble C70-tris-malonic solutions

The paper presents some data on physico-chemical study of the C70-carboxyfullerene water solutions. The data on temperature dependence of solubility in water, concentration dependence of density, specific conductivity, molar conductivity, dissociation constant, and dynamic light scattering are presented and characterized; composition of equilibrium solid phase in binary C70-carboxyfullerene+water system is determined.

Physico-chemical properties of the C60-arginine water solutions

The paper presents experimental data on physico-chemical study of the C60-arginine derivative water solutions. The data on temperature dependence of solubility in water, concentration dependence of density, specific conductivity, molar conductivity, dissociation constant, and dynamic light scattering are presented and characterized.

Concentration dependences of density, viscosity, refractive index, and other derived properties of metoclopramide aqueous solutions at 303.15 K

Density (ρ), viscosity (η) and refractive index (nD) of an antiemetic drug metoclopramide (4-amino-5-chloro-N-(2-(diethylamino)ethyl)-2-methoxybenzamide hydrochloride) solutions containing amino acids (glycine, D-alanine, L-cystine and L-histidine) were measured in the concentration range 0.01–0.17 mol/dm3 at 303.15 K. The apparent molar volume (φv) of this drug in aqueous amino acid solutions was calculated from the density data and fitted to the Massons relation, and the partial molar volume φv0 of the drug was determined graphically. The partial molar volumes of transfer (Δtrφv0) of drug at infinite dilution from pure water to aqueous amino acid solutions were calculated and interpreted in terms of different interactions between the drug and amino acids.

Optical Absorption of Erbium Doped Zinc Phosphate Glass Containing Fe<sub>3</sub>O<sub>4</sub> Nanoparticles

Modifying the optical properties of rare earth doped phosphate glasses in a tunable fashion via the embedment of magnetic nanoparticles (NPs) is challenging for magneto-optic devices. Glasses with compositions (69-x)P2O5-30ZnO-1Er2O3-(x)Fe3O4, where x = 0 to 1.5 mol% are prepared by conventional melt quenching method. The Fe3O4 NPs concentration dependent density, molar volume, refractive index and optical properties are determined. Density and molar volume shows strong correlation with structural alteration in the presence of NPs. The XRD spectra confirm the disordered nature of the glass and TEM micrograph display the presence of spherical NPs with average size ~26 nm. The optical band gap and Urbach energy calculated from the room temperature absorption spectra recorded in the range of 350-1700 nm reveal significant improvement. The density and refractive index increases and the molar volume decreases with the increase of Fe3O4 contents. The energy band gap for direct and indirect transitions varies in the range of 4.47-3.64 eV and 4.27-3.53 eV, respectively. The Urbach energy increases from 0.15 to 0.19 eV as the NPs concentration increases from 0 to 1.5 mol%.

Influence of Fe3O4 nanoparticles on structural, optical and magnetic properties of erbium doped zinc phosphate glass

Tunable modifications of physical and optical properties of metallic nanoparticles (NPs) embedded rare earth (RE) doped inorganic binary glasses are the key issue. Series of glass with composition (69-x)P2O5–30ZnO–1Er2O3–(x)Fe3O4, where 0 ≤ x ≤ 2 mol% containing Fe3O4 NPs are prepared by melt quenching method and characterized using XRD, UV–Vis–NIR, PL, TEM and vibrating sample magnetometer (VSM) techniques. The Fe3O4 NPs concentration dependent density, molar volume, structural, magnetic and optical properties are determined. The XRD pattern confirms the amorphous nature of all samples. The glass density is found increase and molar volume decrease with the increase of NPs concentration. The TEM micrographs reveal the presence of spherical NPs of average diameter ∼26 nm with homogenous distribution. The UV–Vis–NIR absorption spectra exhibit ten absorption bands centered at 376, 406, 448, 486, 522, 546, 652, 798, 976 and 1534 nm corresponding to the absorption from 4I15/2 ground state to various excited states of Er3+ ions. The optical band gap energy for direct (4.47–3.64 eV) and indirect (4.27–3.53 eV) transitions and Urbach energy (0.65–0.15 eV) are found to decrease with the increase of Fe3O4 contents. The decrease in band gap energy is ascribed to the creation of non bridging oxygen (NBO) ions in the glass network. The emission spectra at 478 nm excitations display two prominent peaks centered at 532 and 634 nm originate from 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. Furthermore, increasing NPs concentration dependent luminescence quenching is attributed to the energy transfer from the erbium ion to NPs. These glasses displaying ferrimagnetic behavior in the concentration range of 1.5–2 mol% of NPs verify the presence of iron oxide or ferrite in the glass sample are useful for magneto-optic devices.