Structure Of Fluid Research Articles

Simulations of dipolar fluids using effective many-body isotropic interactions.

The partition function of a system with pairwise-additive anisotropic dipole-dipole interactions is equal to that of a hypothetical system with many-body isotropic interactions [G. Stell, Phys. Rev. Lett. 32, 286 (1974)]. The effective many-body interactions contain n-body contributions of all orders. Each contribution is known as an expansion in terms of the particle-particle distances r, and the coefficients are temperature dependent. The leading-order two-body term is the familiar -r(-6) attraction, and the leading-order three-body term is equivalent to the Axilrod-Teller interaction. In this work, a fluid of particles with the leading-order two-body and three-body interactions is compared to an equivalent dipolar soft-sphere fluid. Molecular simulations are used to determine the conditions under which the effective many-body interactions reproduce the fluid-phase structures of the dipolar system. The effective many-body interaction works well at moderately high temperatures but fails at low temperatures where particle chaining is expected to occur. It is shown that an adjustment of the coefficients of the two-body and three-body terms leads to a good description of the structure of the dipolar fluid even in the chaining regime, due primarily to the ground-state linear configuration of the three-body Axilrod-Teller interaction. The vapor-liquid phase diagrams of systems with different Axilrod-Teller contributions are determined. As the strength of the three-body interaction is increased, the critical temperature and density both decrease and disappear completely above a threshold strength, where chaining eventually suppresses the condensation transition.

Вплив зовнішніх факторів на структуру двокомпонентних рідин в стаціонарному стані

Вплив зовнішніх факторів на структуру двокомпонентних рідин в стаціонарному стані

Two-Yukawa fluid at a hard wall: Field theory treatment.

We apply a field-theoretical approach to study the structure and thermodynamics of a two-Yukawa fluid confined by a hard wall. We derive mean field equations allowing for numerical evaluation of the density profile which is compared to analytical estimations. Beyond the mean field approximation, analytical expressions for the free energy, the pressure, and the correlation function are derived. Subsequently, contributions to the density profile and the adsorption coefficient due to Gaussian fluctuations are found. Both the mean field and the fluctuation terms of the density profile are shown to satisfy the contact theorem. We further use the contact theorem to improve the Gaussian approximation for the density profile based on a better approximation for the bulk pressure. The results obtained are compared to computer simulation data.

Interstitial hydraulic conductivity and interstitial fluid pressure for avascular or poorly vascularized tumors

A correct description of the hydraulic conductivity is essential for determining the actual tumor interstitial fluid pressure (TIFP) distribution. Traditionally, it has been assumed that the hydraulic conductivities both in a tumor and normal tissue are constant, and that a tumor has a much larger interstitial hydraulic conductivity than normal tissue. The abrupt transition of the hydraulic conductivity at the tumor surface leads to non-physical results (the hydraulic conductivity and the slope of the TIFP are not continuous at tumor surface). For the sake of simplicity and the need to represent reality, we focus our analysis on avascular or poorly vascularized tumors, which have a necrosis that is mostly in the center and vascularization that is mostly on the periphery. We suggest that there is an intermediary region between the tumor surface and normal tissue. Through this region, the interstitium (including the structure and composition of solid components and interstitial fluid) transitions from tumor to normal tissue. This process also causes the hydraulic conductivity to do the same. We introduce a continuous variation of the hydraulic conductivity, and show that the interstitial hydraulic conductivity in the intermediary region should be monotonically increasing up to the value of hydraulic conductivity in the normal tissue in order for the model to correspond to the actual TIFP distribution. The value of the hydraulic conductivity at the tumor surface should be the lowest in value.

Thermal and structural properties of ionic fluids.

The electrostatic interaction in ionic fluids is well known to give rise to a characteristic phase behavior and structure. Sometimes its long range is proposed to single out the electrostatic potential over other interactions with shorter ranges. Here the importance of the range for the phase behavior and the structure of ionic fluids is investigated by means of grandcanonical Monte Carlo simulations of the lattice restricted primitive model (LRPM). The long-ranged electrostatic interaction is compared to various types of short-ranged potentials obtained by sharp and/or smooth cutoff schemes. Sharply cutoff electrostatic potentials are found to lead to a strong dependence of the phase behavior and the structure on the cutoff radius. However, when combined with a suitable additional smooth cutoff, the short-ranged LRPM is found to exhibit quantitatively the same phase behavior and structure as the conventional long-ranged LRPM. Moreover, the Stillinger-Lovett perfect screening property, which is well known to be generated by the long-ranged electrostatic potential, is also fulfilled by short-ranged LRPMs with smooth cutoffs. By showing that the characteristic phase behavior and structure of ionic fluids can also be found in systems with short-ranged potentials, one can conclude that the decisive property of the electrostatic potential in ionic fluids is not the long range but rather the valency dependence.

Predicting the structure of fluids with piecewise constant interactions: Comparing the accuracy of five efficient integral equation theories.

We use molecular dynamics simulations to test integral equation theory predictions for the structure of fluids of spherical particles with eight different piecewise-constant pair-interaction forms comprising a hard core and a combination of two shoulders and/or wells. Since model pair potentials like these are of interest for discretized or coarse-grained representations of effective interactions in complex fluids (e.g., for computationally intensive inverse optimization problems), we focus here on assessing how accurately their properties can be predicted by analytical or simple numerical closures including Percus-Yevick, hypernetted-chain, and reference hypernetted-chain closures and first-order mean spherical and modified first-order mean spherical approximations. To make quantitative comparisons between the predicted and simulated radial distribution functions, we introduce a cumulative structural error metric. For equilibrium fluid state points of these models, we find that the reference hypernetted-chain closure is the most accurate of the tested approximations as characterized by this metric or related thermodynamic quantities.

The Action of inVestigational Drugs of Brucella abortus in the L- and S-forms on the Subpopulations of Blood Cells and Peritoneal Fluid of White Mice (Communication 2)

We have estimated the effects of the Brucella abortus 19 ВА inactivated vaccine, thermo extracts of Brucella abortus I-206 in the L- and S-forms and corpuscular antigen of Brucella abortus I-206 in L-form on the population and subpopulation structure of blood cells and peritoneal fluid of white mice. It was showed that the antigen preparations of Brucella abortus I-206 in L-form didn't caused endogenous intoxication of the organism of experimental animals in distinction from the inactivated vaccine of Brucella abortus 19 BA.

High overtone quasinormal modes of analog black holes and the small scale structure of the background fluid

The goal of this paper is to build a foundation for, and explore the possibility of, using high overtone quasinormal modes (QNMs) of analog black holes to probe the small scale (microscopic) structure of a background fluid in which an analog black hole is formed. This may provide a tool to study the small scale structure of some interesting quantum systems such as Bose–Einstein condensates (BECs). In order to build this foundation, we first look into the hydrodynamic case where we calculate the high overtone QNM frequencies of a 3+1 dimensional canonical non-rotating acoustic black hole. The leading order calculations have been done earlier in the literature. Here, we obtain the first order correction. We then analyze the high overtone QNMs of acoustic black holes in a BEC using the linearized Gross–Pitaevskii equation. We point out that at the high overtone QNM limit, the only term that is important in the linearized Gross–Pitaevskii equation is the quantum potential term, which is a small scale effect.

Pressure Tensor of Nanoscopic Liquid Drops

This study describes the structure of an inhomogeneous fluid of one or several components that forms a spherical interface. Using the stress tensor of Percus–Romero, which depends on the density of one particle and the intermolecular potential, it provides an analytical development leading to the microscopic expressions of the pressure differences and the interfacial properties of both systems. The results are compared with a previous study and agree with the description of the mean field.

Scaling Law of the Disjoining Pressure Reveals 2D Structure of Polymeric Fluids

A scaling relation for the disjoining pressure of strongly confined polymer fluids is proposed for the first time, which yields directly the scaling exponent ν of the radius of gyration for polymers. To test the proposed scaling relation we performed extensive particle-based, coarse-grained computer simulations of polymers confined under θ-solvent conditions and found that the value of ν agrees with the expected value for strictly two dimensional chains, ν = 4/7, which points towards the essential correctness of our scaling relation. New approaches are suggested for experimental tests of this scaling law. This work opens up the way to look for other scaling exponents that may reveal new physical regimes and it constitutes an efficient route to determine ν because the scaling exponent can be obtained with chains of a single polymerization degree by simply reducing the distance between the confining plates.

Web applet for predicting structure and thermodynamics of complex fluids

Based on a recently introduced analytical strategy [Hollingshead et al., J. Chem. Phys. 139, 161102 (2013)], we present a web applet that can quickly and semi-quantitatively estimate the equilibrium radial distribution function and related thermodynamic properties of a fluid from knowledge of its pair interaction. We describe the applet's features and present two (of many possible) examples of how it can be used to illustrate concepts of interest for introductory statistical mechanics courses: the transition from ideal gas-like behavior to correlated-liquid behavior with increasing density, and the tradeoff between dominant length scales with changing temperature in a system with ramp-shaped repulsions. The latter type of interaction qualitatively captures distinctive thermodynamic properties of liquid water, because its energetic bias toward locally open structures mimics that of water's hydrogen-bond network.

The effects of inserting a tiny sphere in the center of a nanospherical pore on the structure, adsorption, and capillary condensation of a confined fluid (a DFT study).

The modified fundamental measure theory (MFMT) has been employed to investigate the effects of inserting a tiny sphere in the center of a nanospherical pore on the structure, adsorption, and capillary condensation of fluids confined in it. In the first part of this Article, we have solved the weighted density integrals for all pores with spherical symmetries, including spherical and bispherical pores. In the second part, we show that the structure, amount of adsorption, and position of the fluid's capillary condensation change drastically when even a very thin sphere, R(s) = 0.01σ, is inserted into the center of a spherical pore (SP). In fact, the existence of a forbidden region around the inner sphere for the case of bispherical pores, even when R(s) = 0.01σ, causes a remarkable shift in both the amount of adsorption and the bulk density at which the capillary condensation occurs. Moreover, the insertion causes a sudden increase in the value of the contact density of the liquid, or the liquid in equilibrium with its vapor, at the wall of the outer sphere compared to that for an SP. In other words, the insertion of a tiny sphere in an SP causes the liquid droplet, which is formed in the center of the SP, to sprinkle throughout the whole nanopore. Also, we have demonstrated that the critical temperature and densities decrease with decreasing radius of the inner sphere.

The rate of convergence of the virial series in confined systems

We examine cluster-series methods for the behaviour of simple fluids under confinement, applying the Mayer-sampling Monte Carlo method to evaluate the necessary cluster integrals. We examine two series formulations, one based on the density of a bulk phase in equilibrium with the confined phase (effectively specifying the chemical potential), and another based on the density of the confined phase. The theory and methods are used to calculate the structure and properties of hard-sphere fluids confined between parallel planar hard walls. We present the effects of width of the confined region on the inhomogeneous virial coefficients, and through them, on the thermodynamics of the confined system.

J0540307 二原子分子流体の臨界点近傍における静的・動的ゆらぎ構造の分子動力学的解析

In our study, we investigated fluctuation structure of diatomic fluids around the critical point. We used molecular dynamics simulation to evaluate the principle of corresponding state of fluctuation structure of 2-center-Lennard-Jones fluid which has molecular elongation as a parameter. We evaluated the static fluctuation structure by calculating dispersion of number of molecules at divided cells and static structure factor. As results, the principle of corresponding state on the static fluctuation structure is satisfied because static fluctuation structure does not have dependence on molecular elongation. On the other hand, dynamic fluctuation structure of fluid which has longer molecular elongation disagrees with dynamic fluctuation structure of fluid which has shorter molecular elongation. Therefore, it was found that the principle of corresponding state of dynamic fluctuation structure might not be satisfied.

Predicting the structure and interfacial activity of diblock brush, mixed brush, and Janus-grafted nanoparticles.

A modeling framework is developed to describe the structure and properties of fluid interfaces stabilized with grafted nanoparticles. The framework is demonstrated on nanoparticles functionalized with polymers of various grafting architectures; we find that the conformation of the grafted chains plays an important role in the interfacial tension.

Modelling the rheology of anisotropic particles adsorbed on a two-dimensional fluid interface.

We present a general approach based on nonequilibrium thermodynamics for bridging the gap between a well-defined microscopic model and the macroscopic rheology of particle-stabilised interfaces. Our approach is illustrated by starting with a microscopic model of hard ellipsoids confined to a planar surface, which is intended to simply represent a particle-stabilised fluid-fluid interface. More complex microscopic models can be readily handled using the methods outlined in this paper. From the aforementioned microscopic starting point, we obtain the macroscopic, constitutive equations using a combination of systematic coarse-graining, computer experiments and Hamiltonian dynamics. Exemplary numerical solutions of the constitutive equations are given for a variety of experimentally relevant flow situations to explore the rheological behaviour of our model. In particular, we calculate the shear and dilatational moduli of the interface over a wide range of surface coverages, ranging from the dilute isotropic regime, to the concentrated nematic regime.

超臨界流体の局所構造とナノ物質生成

超臨界流体の局所構造とナノ物質生成

Microdynamics and arrest of coarsening during spinodal decomposition in thermoreversible colloidal gels.

Coarsening and kinetic arrest of colloidal systems undergoing spinodal decomposition (SD) is a conserved motif for forming hierarchical, bicontinuous structures. Although the thermodynamic origins of SD in colloids are widely known, the microstructural processes responsible for its coarsening and associated dynamics en route to arrest remain elusive. To better elucidate the underlying large-scale microdynamical processes, we study a colloidal system with moderate-range attractions which displays characteristic features of arrested SD, and study its dynamics during coarsening through a combination of differential dynamic microscopy and real-space tracking. Using these recently developed imaging techniques, we reveal directly that the coarsening arises from collective dynamics of dense domains, which undergo slow, intermittent, and ballistic motion. These collective motions indicate interfacial effects to be the driving force of coarsening. The nature of the gelation enables control of the arrested length scale of coarsening by the depths of quenching into the spinodal regime, which we demonstrate to provide an effective means to control the elasticity of colloidal gels.

Cryopreserved and Lyophylized Amniotic Fluids using Levine’s Conservation Model: A Breakthough in the Process of Wound Healing

Healing restores continuity and form through cell replication; hence, conserving structural integrity. Early detection and management of wounds by nurses reduces tissue destruction, which also conserves structural integrity. In response to the worldwide pressing problem of chronic wounds in the healthcare delivery system, the researcher aims to provide effective intervention to preserve the structural integrity of the person. The cryopreserved and lyophilized amniotic fluids are sophisticated processes in formulating a drug in the form of ointment. These methods preserved the cell structure of amniotic fluid from term fetus and embed into two (2) concentrations (1.5 % and 1.0 %) of an absorption-based ointment. The total protein concentration of Cryopreserved and Lyophilized Amniotic Membrane in full term fetus was determined by the Biuret and Bradford methods, which are based on UV-visible spectroscopy. The percentages of protein presence in 9.5 mg (mass total sample) of Amniotic fluids ranges between 14.77 – 14.46 % in Bradford method, while slightly lower to 13.78 – 13.80 % concentration in Biuret method, respectively. Bradford method evidently showed higher sensitivity for proteins than Biuret test. Overall, the amniotic membrane, composed principally of proteins, proved its healing abilities. Levine’s conservation model emphasized that it was the nurse’s duty to promote healing as well as protect the patient from external factors that may contribute to physical breakdown and complications. Keywords - Wounds, Healing, Amniotic membrane ointments

Multifractality in dilute magnetorheological fluids under an oscillating magnetic field.

A study of the multifractal characteristics of the structure formed by magnetic particles in a dilute magnetorheological fluid is presented. A quasi-two-dimensional magnetorheological fluid sample is simultaneously subjected to a static magnetic field and a sinusoidal magnetic field transverse to each other. We analyzed the singularity spectrum f(α) and the generalized dimension D(q) of the whole structure to characterize the distribution of the aggregates under several conditions of particle concentration, magnetic field intensities, and liquid viscosity. We also obtained the fractal dimension D(g), calculated from the radius of gyration of the chains, to describe the internal distribution of the particles. We present a thermodynamic interpretation of the multifractal analysis, and based on this, we discussed the characteristics of the structure formed by the particles and its relation with previous studies of the average chain length. We have found that this method is useful to quantitatively describe the structure of magnetorheological fluids, especially in systems with high particle concentration where the aggregates are more complex than simple chains or columns.