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We propose an estimator that allows us to calculate the value of a simple system's partition function using finite sampling. The core idea is to neglect the contribution from high energy microstates, which are difficult to be sampled properly, and then calculate a volume correction term to compensate for this. As a proof of concept, the estimator is applied to calculate the partition function for several model systems, ranging from a simple harmonic oscillator to a Lennard-Jones fluid with hundreds of particles. Our results agree well with the numerically exact solutions or reference data, demonstrating that efficiently estimating partition functions for the studied example cases is possible and computationally affordable. [ABSTRACT FROM AUTHOR]

Field-theoretic simulations are numerical methods for polymer field theory, which include fluctuation corrections beyond the mean-field level, successfully capturing various mesoscopic phenomena. Most field-theoretic simulations of polymeric fluids use the auxiliary field (AF) theory framework, which employs Hubbard–Stratonovich transformations for the particle-to-field conversion. Nonetheless, the Hubbard–Stratonovich transformation imposes significant limitations on the functional form of the non-bonded potentials. Removing this restriction on the non-bonded potentials will enable studies of a wide range of systems that require multi-body or more complex potentials. An alternative representation is the hybrid density-explicit auxiliary field theory (DE-AF), which retains both a density field and a conjugate auxiliary field for each species. While the DE-AF representation is not new, density-explicit field-theoretic simulations have yet to be developed. A major challenge is preserving the real and non-negative nature of the density field during stochastic evolution. To address this, we introduce positivity-preserving schemes that enable the first stable and efficient density-explicit field-theoretic simulations (DE-AF FTS). By applying the new method to a simple fluid, we find thermodynamically correct results at high densities, but the algorithm fails in the dilute regime. Nonetheless, DE-AF FTS is shown to be broadly applicable to dense fluid systems including a simple fluid with a three-body non-bonded potential, a homopolymer solution, and a diblock copolymer melt. [ABSTRACT FROM AUTHOR]

The stochastic dynamics of small elastic objects in fluid are central to many important and emerging technologies. It is now possible to measure and use the higher modes of motion of elastic structures when driven by Brownian motion alone. Although theoretical descriptions exist for idealized conditions, computing the stochastic multimodal dynamics for the complex conditions of an experiment is very challenging. We show that this is possible using deterministic finite-element calculations with the fluctuation dissipation theorem by exploring the multimodal stochastic dynamics of a doubly clamped nanobeam. We use a very general, and flexible, finite-element computational approach to quantify the stochastic dynamics of multiple modes simultaneously using only a single deterministic simulation. We include the experimentally relevant features of an intrinsic tension in the beam and the influence of a nearby rigid boundary on the dynamics through viscous fluid interactions. We quantify the stochastic dynamics of the first 11 flexural modes of the beam when immersed in air or water. We compare the numerical results with theory, where possible, and find excellent agreement. We quantify the limitations of the computational approach and describe its range of applicability. These results pave the way for computational studies of the stochastic dynamics of complex 3D elastic structures in a viscous fluid where theoretical descriptions are not available. [ABSTRACT FROM AUTHOR]

DNA is now firmly established as a versatile and robust platform for achieving synthetic nanostructures. While the folding of single molecules into complex structures is routinely achieved through engineering basepair sequences, very little is known about the emergence of structure on larger scales in DNA fluids. The fact that polymeric DNA fluids can undergo phase separation into dense fluid and dilute gas opens avenues to design hierachical and multifarious assemblies. Here, we investigate to which extent the phase behavior of single-stranded DNA fluids can be captured by a minimal model of semiflexible charged homopolymers while neglecting specific hybridization interactions. We first characterize the single-polymer behavior and then perform direct coexistence simulations to test the model against experimental data. While low-resolution models show great promise to bridge the gap to relevant length and time scales, obtaining consistent and transferable parameters is challenging. In particular, we conclude that counterions not only determine the effective range of direct electrostatic interactions but also contribute to the effective attractions. [ABSTRACT FROM AUTHOR]

Critical Casimir forces emerge among particles or surfaces immersed in a near-critical fluid, with the sign of the force determined by surface properties and with its strength tunable by minute temperature changes. Here, we show how such forces can be used to trap a colloidal particle and levitate it above a substrate with a bull's-eye pattern consisting of a ring with surface properties opposite to the rest of the substrate. Using the Derjaguin approximation and mean-field calculations, we find a rich behavior of spherical colloids at such a patterned surface, including sedimentation toward the ring and levitation above the ring (ring levitation) or above the bull's-eye's center (point levitation). Within the Derjaguin approximation, we calculate a levitation diagram for point levitation showing the depth of the trapping potential and the height at which the colloid levitates, both depending on the pattern properties, the colloid size, and the solution temperature. Our calculations reveal that the parameter space associated with point levitation shrinks if the system is driven away from a critical point, while, surprisingly, the trapping force becomes stronger. We discuss the application of critical Casimir levitation for sorting colloids by size and for determining the thermodynamic distance to criticality. Our results show that critical Casimir forces provide rich opportunities for controlling the behavior of colloidal particles at patterned surfaces. [ABSTRACT FROM AUTHOR]

Diffusion in complex heterogeneous media, such as biological tissues or porous materials, typically involves constrained displacements in tortuous structures and sticky environments. Therefore, diffusing particles experience both entropic (excluded-volume) forces and the presence of complex energy landscapes. In this situation, one may describe transport through an effective diffusion coefficient. In this paper, we examine comb structures with finite-length 1D and finite-area 2D fingers, which act as purely diffusive traps. We find that there exists a critical width of 2D fingers, above which the effective diffusion along the backbone is faster than for an equivalent arrangement of 1D fingers. Moreover, we show that the effective diffusion coefficient is described by a general analytical form for both 1D and 2D fingers, provided the correct scaling variable is identified as a function of the structural parameters. Interestingly, this formula corresponds to the well-known general situation of diffusion in a medium with fast reversible adsorption. Finally, we show that the same formula describes diffusion in the presence of dilute potential energy traps, e.g., through a landscape of square wells. While diffusion is ultimately always the result of microscopic interactions (with particles in the fluid, other solutes, and the environment), effective representations are often of great practical use. The results reported in this paper help clarify the microscopic origins and the applicability of global, integrated descriptions of diffusion in complex media. [ABSTRACT FROM AUTHOR]

We perform large-scale atomistic simulations of a system containing 12 × 106 atoms, comprising an oxygen gas-filled bubble immersed in water, to understand the stability and cavitation induced by ultrasound. First, we propose a method to construct a bubble/water system. For a given bubble radius, the pressure inside the bubble is estimated using the Young–Laplace equation. Then, this pressure is used as a reference for a constant temperature, constant pressure simulation of an oxygen system, enabling us to extract a sphere of oxygen gas and place it into a cavity within an equilibrated water box. This ensures that the Young–Laplace equation is satisfied and the bubble is stable in water. Second, this stable bubble is used for ultrasound-induced cavitation simulations. We demonstrate that under weak ultrasound excitation, the bubble undergoes stable cavitation, revealing various fluid velocity patterns, including the first-order velocity field and microstreaming. These fluid patterns emerge around the bubble on a nanometer scale within a few nanoseconds, a phenomenon challenging to observe experimentally. With stronger ultrasound intensities, the bubble expands significantly and then collapses violently. The gas core of the collapsed bubble, measuring 3–4 nm, exhibits starfish shapes with temperatures around 1500 K and pressures around 6000 bar. The simulation results are compared with those from Rayleigh–Plesset equation modeling, showing good agreement. Our simulations provide insights into the stability and cavitation of nanosized bubbles. [ABSTRACT FROM AUTHOR]

Introduced by Pitzer in 1955, the acentric factor (ω) has been used to evaluate a molecule's deviation from the corresponding state principle. Pitzer devised ω based on a concept called perfect liquid (or centric fluid), a hypothetical species perfectly adhering to this principle. However, its physical significance remains unclear. This work attempts to clarify the centric fluid from an excess entropy perspective. We observe that the excess entropy per particle of centric fluids approximates −kB at their critical points, akin to the communal entropy of an ideal gas in classical cell theory. We devise an excess entropy dissection and apply it to model fluids (square-well, Lennard-Jones, Mie n-6, and the two-body ab initio models) to interpret this similarity. The dissection method identifies both centricity-independent and centricity-dependent entropic features. Regardless of the acentric factor, the attractive interaction contribution to the excess entropy peaks at the density where local density is most enhanced due to the competition between the local attraction and critical fluctuations. However, only in centric fluids does the entropic contribution from the local attractive potential become comparable to that of the hard sphere exclusion, making the centric fluid more structured than acentric ones. These findings elucidate the physical significance of the centric fluid as a system of particles where the repulsive and attractive contributions to the excess entropy become equal at its gas–liquid criticality. We expect these findings to offer a way to find suitable intermolecular potentials and assess the physical adequacy of equations of state. [ABSTRACT FROM AUTHOR]

This Response addresses critiques raised about the Binding Debye–Hückel (BiDH) theory [Naseri Boroujeni et al., J. Chem. Phys. 159, 154503 (2023)] by Simonin and Bernard [J.-P. Simonin and O. Bernard, J. Chem. Phys. 161, 057102 (2024)]. The critiques questioned the foundational framework of the Debye–Hückel (DH) theory, the relevance of ion pairing in primitive model fluids, and the accuracy of the BiDH model compared to mean spherical approximation model. Through a systematic rebuttal, supported by extensive literature review and comparison with Monte Carlo simulation data, this Response addresses these concerns. It demonstrates the efficacy of DH theory in describing real electrolyte solutions, validates the relevance of ion pairing in primitive model fluids, and establishes the BiDH model's accuracy in describing electrolyte properties. [ABSTRACT FROM AUTHOR]

We present the first systematic application of the integral equation implementation of the replica method to the study of arrested states in fluids with microscopic competing interactions (short-range attractive and long-range repulsive, SALR), as exemplified by the prototype Lennard-Jones–Yukawa model. Using a wide set of potential parameters, we provide as many as 11 different phase diagrams on the density (ρ)–temperature (T) plane, embodying both the cluster-phase boundary, TC(ρ), and the locus below which arrest takes place, TD(ρ). We describe how the interplay between TC and TD—with the former falling on top of the other, or the other way around, depending on thermodynamic conditions and potential parameters—gives rise to a rich variety of non-ergodic states interspersed with ergodic ones, of which both the building blocks are clusters or single particles. In a few cases, we find that the TD locus does not extend all over the density range subtended by the TC envelope; under these conditions, the λ-line is within reach of the cluster fluid, with the ensuing possibility to develop ordered microphases. Whenever a comparison is possible, our predictions favorably agree with previous numerical results. Thereby, we demonstrate the reliability and effectiveness of our scheme to provide a unified theoretical framework for the study of arrested states in SALR fluids, irrespective of their nature. [ABSTRACT FROM AUTHOR]

We numerically investigate the dynamics and linear rheology of disordered systems made of patchy particles, focusing on the role of valence, temperature, and bonding mechanism. We demonstrate that the dynamics is enslaved to bonding, giving rise to an activated behavior at low temperatures. By independently computing the diffusion constant and the viscosity from the simulations, we also confirm the validity of the Stokes–Einstein relation in valence-limited systems, with two caveats: (i) the diffusion constant requires a finite-size correction, at least at the intermediate density we investigate, and (ii) there is the onset of a breakdown that appears at the lowest temperatures considered. Finally, our results show that the storage and loss moduli of mixtures of divalent and M-valent particles exhibit an apparent power-law dependence on frequency, hinting at the possibility of using the composition to finely tune the rheological response of these materials. Our results compare well with literature experimental data on valence-limited DNA nanostars. In addition, the wealth of data we present and analyze here will help develop and test theoretical frameworks aimed at describing the dynamics of flexible limited-valence particles that self-assemble into disordered networks. [ABSTRACT FROM AUTHOR]

This study introduces recommendations for conducting molecular simulations of vapor adsorption, with an emphasis on enhancing the accuracy, reproducibility, and comparability of results. The first aspect we address is consistency in the implementation of some details of typical molecular models, including tail corrections and cutoff distances, due to their significant influence on generated data. We highlight the importance of explicitly calculating the saturation pressures at relevant temperatures using methods such as Gibbs ensemble Monte Carlo simulations and illustrate some pitfalls in extrapolating saturation pressures using this method. For grand canonical Monte Carlo (GCMC) simulations, the input fugacity is usually calculated using an equation of state, which often requires the critical parameters of the fluid. We show the importance of using critical parameters derived from the simulation with the same model to ensure internal consistency between the simulated explicit adsorbate phase and the implicit bulk phase in GCMC. We show the advantages of presenting isotherms on a relative pressure scale to facilitate easier comparison among models and with experiment. Extending these guidelines to a practical case study, we evaluate the performance of various isoreticular metal–organic frameworks (MOFs) in adsorption cooling applications. This includes examining the advantages of using propane and isobutane as working fluids and identifying MOFs with a superior performance. [ABSTRACT FROM AUTHOR]

The focus of our study is an in-depth investigation of the quantum effects associated with the surface tension and other thermodynamic properties of nanoscopic liquid drops. The behavior of drops of quantum Lennard-Jones fluids is investigated with path-integral Monte Carlo simulations, and the test-area method is used to determine the surface tension of the spherical vapor–liquid interface. As the thermal de Broglie wavelength, λB, becomes more significant, the average density of the liquid drop decreases, with the drop becoming mechanically unstable at large wavelengths. As a consequence, the surface tension is found to decrease monotonically with λB, vanishing altogether for dominant quantum interactions. Quantum effects can be significant, leading to values that are notably lower than the classical thermodynamic limit, particularly for smaller drops. For planar interfaces (with infinite periodicity in the direction parallel to the interface), quantum effects are much less significant with the same values of λB but are, nevertheless, consequential for values representative of hydrogen or helium-4 at low temperatures corresponding to vapor–liquid coexistence. Large quantum effects are found for small drops of molecules with quantum interactions corresponding to water, ethane, methanol, and carbon dioxide, even at ambient conditions. The notable decrease in the density and tension has important consequences in reducing the Gibbs free-energy barrier of a nucleating cluster, enhancing the nucleation kinetics of liquid drops and of bubble formation. This implies that drops would form at a much greater rate than is predicted by classical nucleation theory. [ABSTRACT FROM AUTHOR]

It is shown that the transport coefficients (self-diffusion, shear viscosity, and thermal conductivity) of the Weeks–Chandler–Andersen (WCA) fluid along isotherms exhibit a freezing density scaling (FDS). The functional form of this FDS is essentially the same or closely related to those in the Lennard-Jones fluid, hard-sphere fluid, and some liquefied noble gases. This proves that this FDS represents a quasi-universal corresponding state principle for simple classical fluids with steep interactions. Some related aspects, such as a Stokes–Einstein relation without a hydrodynamic diameter and gas-to-liquid dynamical crossover, are briefly discussed. Simple fitting formulas for the transport coefficients of the dense WCA fluid are suggested. [ABSTRACT FROM AUTHOR]

Entropy scaling is applied to the shear viscosity, self-diffusion coefficient, and thermal conductivity of simple monatomic fluids. An extensive molecular dynamics simulation series is performed to obtain these transport properties and the residual entropy of three potential model classes with variable repulsive exponents: n, 6 Mie (n = 9, 12, 15, and 18), Buckingham's exponential-six (α = 12, 14, 18, and 30), and Tang–Toennies (αT = 4.051, 4.275, and 4.600). A wide range of liquid and supercritical gas- and liquid-like states is covered with a total of 1120 state points. Comparisons to equations of state, literature data, and transport property correlations are made. Although the absolute transport property values within a given potential model class may strongly depend on the repulsive exponent, it is found that the repulsive steepness plays a negligible role when entropy scaling is applied. Hence, the plus-scaled transport properties of n, 6 Mie, exponential-six, and Tang–Toennies fluids lie basically on one master curve, which closely corresponds with entropy scaling correlations for the Lennard-Jones fluid. This trend is confirmed by literature data of n, 6 Mie, and exponential-six fluids. Furthermore, entropy scaling holds for state points where the Pearson correlation coefficient R is well below 0.9. The condition R > 0.9 for strongly correlating liquids is thus not necessary for the successful application of entropy scaling, pointing out that isomorph theory may be a part of a more general framework that is behind the success of entropy scaling. Density scaling reveals a strong influence of the repulsive exponent on this particular approach. [ABSTRACT FROM AUTHOR]

A new free-energy functional is proposed for inhomogeneous associating fluids. The general formulation of Wertheim's thermodynamic perturbation theory is considered as the starting point of the derivation. We apply the hypotheses of the statistical associating fluid theory in the classical density functional theory (DFT) framework to obtain a tractable expression of the free-energy functional for inhomogeneous associating fluids. Specific weighted functions are introduced in our framework to describe association interactions for a fluid under confinement. These weighted functions have a mathematical structure similar to the weighted densities of the fundamental-measure theory (i.e., they can be expressed as convolution products) such that they can be efficiently evaluated with Fourier transforms in a 3D space. The resulting free-energy functional can be employed to determine the microscopic structure of inhomogeneous associating fluids of arbitrary 3D geometry. The new model is first compared with Monte Carlo simulations and previous versions of DFT for a planar hard wall system in order to check its consistency in a 1D case. As an example of application in a 3D configuration, we then investigate the extreme confinement of an associating hard-sphere fluid inside an anisotropic open cavity with a shape that mimics a simplified model of zeolite. Both the density distribution and the corresponding molecular bonding profile are given, revealing complementary information to understand the structure of the associating fluid inside the cavity network. The impact of the degree of association on the preferential positions of the molecules inside the cavity is investigated as well as the competition between association and steric effect on adsorption. [ABSTRACT FROM AUTHOR]

We present a comprehensive study using dissipative particle dynamics simulations to investigate phase separation kinetics (PSK) in three-dimensional (3d) polymeric fluids under random photo-illumination. We consider two scenarios: polymer blends with active radicals at one end of each immiscible chain and block copolymer (BCP) melts with photosensitive bonds linking incompatible blocks. The phase separation (PS) is induced by temperature quench of the initial homogeneously mixed system. Simultaneously, the system experiences random photo-illumination, simulated by two concurrent random events: (a) the recombination of active radicals in polymer blends and (b) the breaking of photosensitive bonds in BCP chains. Variations in the bond-breaking probability, Pb, mimic the change in light intensity. The length scale follows power law growth, R(t) ∼ tϕ, where ϕ represents the growth exponent. Increasing Pb results in a gradual transition in growth kinetics from micro-PS to macro-PS, accompanied by corresponding transition probabilities for both systems. Micro-PSK dominates the evolution process at low Pb values. The scaling functions exhibit data overlap for most scaled distances, indicating the statistical self-similarity of evolving patterns. Our study enhances the understanding of PSK in polymeric fluids, revealing the impact of photosensitive bonds and active radicals. Furthermore, it suggests the potential for designing novel polymeric materials with desired properties. [ABSTRACT FROM AUTHOR]

Beyond well-documented confinement and surface effects arising from the large internal surface and severely confining porosity of nanoporous hosts, the transport of nanoconfined fluids remains puzzling in many aspects. With striking examples such as memory, i.e., non-viscous effects, intermittent dynamics, and surface barriers, the dynamics of fluids in nanoconfinement challenge classical formalisms (e.g., random walk, viscous/advective transport)—especially for molecular pore sizes. In this context, while molecular frameworks such as intermittent Brownian motion, free volume theory, and surface diffusion are available to describe the self-diffusion of a molecularly confined fluid, a microscopic theory for collective diffusion (i.e., permeability), which characterizes the flow induced by a thermodynamic gradient, is lacking. Here, to fill this knowledge gap, we invoke the concept of "De Gennes narrowing," which relates the wavevector-dependent collective diffusivity D0(q) to the fluid structure factor S(q). First, using molecular simulation for a simple yet representative fluid confined in a prototypical solid (zeolite), we unravel an essential coupling between the wavevector-dependent collective diffusivity and the structural ordering imposed on the fluid by the crystalline nanoporous host. Second, despite this complex interplay with marked Bragg peaks in the fluid structure, the fluid collective dynamics is shown to be accurately described through De Gennes narrowing. Moreover, in contrast to the bulk fluid, the departure from De Gennes narrowing for the confined fluid in the macroscopic limit remains small as the fluid/solid interactions in severe confinement screen collective effects and, hence, weaken the wavevector dependence of collective transport. [ABSTRACT FROM AUTHOR]

We present a derivation from the first principles of the coupled equations of motion of an active self-diffusiophoretic Janus motor and the hydrodynamic densities of its fluid environment that are nonlinearly displaced from equilibrium. The derivation makes use of time-dependent projection operator techniques defined in terms of slowly varying coarse-grained microscopic densities of the fluid species number, total momentum, and energy. The exact equations of motion are simplified using time scale arguments, resulting in Markovian equations for the Janus motor linear and angular velocities with average forces and torques that depend on the fluid densities. For a large colloid, the fluid equations are separated into bulk and interfacial contributions, and the conditions under which the dynamics of the fluid densities can be accurately represented by bulk hydrodynamic equations subject to boundary conditions on the colloid are determined. We show how the results for boundary conditions based on continuum theory can be obtained from the molecular description and provide Green–Kubo expressions for all transport coefficients, including the diffusiophoretic coupling and the slip coefficient. [ABSTRACT FROM AUTHOR]

Coarse-graining of fluids is challenging because fluid particles are unbound and diffuse long distances in time. One approach creates coarse-grain variables that group all particles within a region centered on specific points in space and accounts for the movement of particles among such regions. In our previous work, we showed that in many cases, potential interactions for such a scheme adopted a generalized quadratic form, whose parameters depend on means, variances, and correlation coefficients among the coarse-grain variables. In this work, we use statistical mechanics to derive analytic expressions for these parameters, using properties of the fluid, including pair distribution functions. These expressions are compared against simulation-derived values and shown to be in good agreement. This approach can be used to calculate a priori the potential for any homogeneous, simple fluid, without the need for fitting procedures or matching, thus increasing the ease of use of this coarse-grain scheme and creating a foundation for large-scale bottom-up simulations. Furthermore, these expressions provide a quantitative way of studying the boundary between discrete (atomic) and continuum models of fluids. [ABSTRACT FROM AUTHOR]

A generalized Coleman-Noll procedure is applied to analyze thermoviscoelastic solids of grade 3, namely, solids with constitutive equations depending on the third spatial gradient of the deformation. Some new forms of stress tensor and specific entropy are obtained. For small deformations, the equilibrium problem is studied for onedimensional systems. An explicit form of the displacement is calculated. A comparison with the equilibrium theory of Korteweg fluids is carried out. [ABSTRACT FROM AUTHOR]

Benzyltoluene (BT) and dibenzyltoluene (DBT) mixtures are promising liquid organic hydrogen carriers (LOHCs) due to their high hydrogen storage capacity, excellent thermal stability and safety of storage and transportation. This study investigates the thermodynamic properties of BT + DBT mixtures to develop an accurate prediction model for hybrid LOHCs. Experimental measurements of liquid density were performed over a wide temperature range (293.15–433.15 K) and pressures up to 20 MPa, revealing the effects of temperature, pressure, and composition on thermodynamic properties. An empirical model using the Tait equation achieved an average absolute deviation of 0.027%. Drawing on experimental data, the model parameters of perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) were optimized separately for low-pressure and high-pressure regions, improving prediction accuracy and enabling the evaluation of bubble-point pressure and saturated densities. Additionally, simulations were conducted to analyze the variation of hydrogen mole fraction with pressure and temperature in both the dehydrogenation reactor and the condenser. Derived thermodynamic properties, including excess molar volume, isothermal compressibility, thermal expansion coefficient, and heat capacity, were calculated to support LOHC system design. This work provides foundational data and a reliable theoretical model to optimize hydrogen storage and dehydrogenation processes for BT + DBT mixtures. The results offer valuable insights for future applications of LOHC technology in energy-efficient hydrogen storage and transport systems. • Liquid density of BT + DBT was measured at elevated temperatures and pressures. • Influence of mole fraction, temperature and pressure on density was elucidated. • SAFT-type EoSs were developed to predict the thermodynamic properties of BT + DBT. • Mole fraction of hydrogen in dehydrogenation facilities was discussed. [ABSTRACT FROM AUTHOR]

The use of hybrid nanofluids (HNF) in heat transfer applications has become the subject of studies during recent periods. Its ability to transfer heat is superior to single nanofluids, and this has been proven in many research. Shell and tube heat exchanger is one of the most common types and are therefore always under research to improve their performance. This study is a practical study that examines the effectiveness of HNF in their use as operating fluids in shell-and-tube heat exchangers instead of traditional operating fluids. A laboratory heat exchanger was used to complete this study. A group of HNF (MWCNTs- Al2O3/water) was synthesized at different concentration rates ranging from 0.4 to 2%. Tests were conducted for Reynolds values in the range from 2500 to 12,560. By measuring the variables in the tests and calculating some factors the results showed that, in comparison between the use of HNF and distilled water, it was found that there is an increase in the value of the Nusselt number for the HNF over the distilled water in a range of 10- 28.5%. The effectiveness increased when using the HNF by up to 22.7% compared to distilled water. Through experiments, an equation was deduced to calculate the value of the Nusselt number. There is good agreement between the results of this research and previous literature. [ABSTRACT FROM AUTHOR]

In this paper, the three-dimensional magneto-micropolar fluid equations with partial dissipation is studied on $ \mathbb {R}^3 $ R 3 . The main purpose of this paper is to establish global solutions with a small initial value. More specifically, we demonstrate the global stability of the perturbation solutions near the background magnetic field. The proof is mainly based on the energy estimate, the tricky interpolation techniques and bootstrapping argument. [ABSTRACT FROM AUTHOR]

Serum and pleural fluid tumor markers are well-recognized auxiliary diagnostic tools for malignant pleural effusion (MPE). Here, we discuss some pearls and pitfalls regarding the role of tumor markers in MPE management. The following issues are discussed in this article: What is the appropriate clinical scenario for evaluating pleural tumor markers? Which tumor markers should be advocated for diagnosing MPE? Can extremely high levels of tumor markers be employed to establish a diagnosis of MPE? Does the serum-to-pleural fluid ratio of a tumor marker have the same diagnostic efficacy as the measurement of that marker alone in the pleural fluid? Can tumor markers be used to estimate the risk of specific cancers? What should be considered when interpreting the diagnostic accuracy of tumor markers? How should tumor marker studies be performed? We addressed these issues with published works, particularly systematic reviews and meta-analyses. [ABSTRACT FROM AUTHOR]

This paper delivers the characterization of a pseudo B -symmetric spacetimes and we illustrate that a pseudo B -symmetric spacetime admitting Codazzi type of B -tensor represents a perfect fluid spacetime and if this spacetime admits the time-like convergence criterion, then the pseudo B -symmetric spacetime fulfills cosmic strong energy criterion and contains pure matter. Besides, we find in a pseudo B -symmetric spacetime with Codazzi type of B -tensor the electric part of the Weyl tensor vanishes and has Riemann and Weyl compatible vector fields. Furthermore, it is established that the chosen spacetime with Codazzi type of B -tensor is conformally flat and represents a Robertson–Walker spacetime. Also, we calculate the scale factor Ψ (t) for these spacetimes in a spatially flat Robertson–Walker spacetime. Finally, we study the impact of this spacetime under f (R) gravity scenario and deduce several energy conditions by considering a new model f (ℛ) = e (α ℛ) − ln (β ℛ) in which α and β are positive constants. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel curvature tensor called the -curvature tensor, which is formed by combining the Weyl tensor and the 2 -curvature tensor. It is proved that a semi-Riemannian manifold with traceless -curvature tensor is Einstein, while a -curvature flat semi-Riemannian manifold exhibits constant sectional curvature. We show that a space-time with traceless -curvature tensor or -curvature flat represents dark energy era. A semi-Riemannian manifold with divergence-free -curvature tensor is Weyl harmonic. In a space-time where the -curvature tensor is of divergence-free, both the isotropic pressure and energy density are constants. Under certain conditions, it is shown that a pseudo- -symmetric semi-Riemannian manifold reduces to a pseudo-Riemannian manifold. It is demonstrated that pseudo- -symmetric space-times can be regarded as generalized Robertson–Walker (GRW) space-times. Finally, a concrete example of pseudo- -symmetric semi-Riemannian manifolds is presented. [ABSTRACT FROM AUTHOR]

The principal aim of this paper is to find the expression of *-Bach tensors on (κ , μ) ′ -almost-Kenmotsu manifolds. It is shown that if the metric of a (κ , μ) ′ -almost-Kenmotsu manifold admits a generalized closed *-Bach soliton, then the metric is *-Bach flat under certain restrictions. We also prove that the metric of a generalized gradient *-Bach soliton on a (κ , μ) ′ -almost-Kenmotsu manifold is *-Bach flat, for a soliton function which is invariant under the Reeb vector field. Further, we characterize generalized *-Bach solitons with trace-free *-Bach tensors on (κ , μ) ′ -almost-Kenmotsu manifolds and results are verified by an example. As an application of these solitons, we study generalized almost-Bach solitons whose metrics are associated with the Lorentzian metric of the perfect fluid spacetimes. [ABSTRACT FROM AUTHOR]

This article explores the evolving nature of volunteering in fluid forms of organizing and their potential for civic action. While previous research suggests that highly individualized volunteering can undermine collectivity and disconnect tasks from change-oriented goals, thus diminishing its civic character, this study employs Lichterman and Eliasoph's conceptual framework of civic action and Dewey's concept of ends-in-view to demonstrate how civic action arises in fluid forms of organizing through the ongoing coordination of organizational maintenance. Drawing on an 18-month ethnographic study of female breakers aiming to improve women's access to a male-dominated street dance scene, we find that fluid organizing produces a distinct form of volunteering that invigorates a collective and change-oriented endeavor. Our findings highlight the importance of understanding and investigating new contexts and forms of volunteering to shed new light on contemporary volunteerism, its multifaceted nature, and its potential to mobilize collective efforts for societal change. [ABSTRACT FROM AUTHOR]

This article captures a convergence of its authors' life experiences and existent data, made possible by Complex Instruction (CI). There is a pressing need to study and support the foundational practice of assigning competence, which requires that a teacher first recognise students' strengths and publicly name their academic contributions. However, a teacher cannot name what they have not noticed. Collectively, we wondered what we could learn from one teacher's fluid ability to effectively assign competence. We embraced CI principles to co-author our article. [ABSTRACT FROM AUTHOR]

This paper deals with a study on an initial-boundary value problem for incompressible non-Newtonian fluids of degree two, in a bounded and simply connected open set Ω of ℝ 3 . It will be shown that the global-in-time weak solution is uniformly stable (i.e. the behavior of the solution changes continuously with the data), and consequently this solution is unique. Furthermore, an exponential decay rate for the energy of the weak solution will also be established. [ABSTRACT FROM AUTHOR]

This election article explains Malaysia's winding democratization trajectory from one-coalition predominance (1957–1990) to aggregated bipartism (1990–2015, with intermissions) to fluid multipartism (particularly in the aftermath of 2020 to the present day), with the help of multilevel party system framework. The findings demonstrate that state-level dynamics can facilitate or impede the formation and sustenance of aggregated bipartism, known as the Two-Coalition System, in Malaysia. I identify the state-level factors that affect the emergence of, and disruptions to, aggregated bipartism in 1990-2015, and analyse the outcome of 16 state elections held between May 2018 and March 2022 amidst Malaysia's transition from aggregated bipartism. [ABSTRACT FROM AUTHOR]

This paper concerns with the one dimensional compressible isentropic Navier–Stokes equations with a free boundary separating fluid and vacuum when the viscosity coefficient depends on the density. Precisely, the pressure P and the viscosity coefficient μ are assumed to be proportional to ρ γ and ρ θ respectively, where ρ is the density, and γ and θ are constants. We establish the unique solvability in the framework of global classical solutions for this problem when γ ≥ θ > 1. Since the previous results on this topic are limited to the case when θ ∈ (0 , 1 ] , the result in this paper fills in the gap for θ > 1. Note that the key estimate is to show that the density has a positive lower bound and the new ingredient of the proof relies on the study of the quasilinear parabolic equation for the viscosity coefficient by reducing the nonlocal terms in order to apply the comparison principle. [ABSTRACT FROM AUTHOR]

Local stay of the solutions to the Euler equations for an ideal incompressible fluid in the end‐point Triebel–Lizorkin space F1,∞sℝd$$ {F}_{1,\infty}^s\left({\mathbb{R}}^d\right) $$ with s≥d+1$$ s\ge d+1 $$ is clarified. [ABSTRACT FROM AUTHOR]

This paper focuses on the three‐dimensional (3D) incompressible anisotropic Boussinesq system while the velocity of fluid only involves horizontal dissipation and the temperature has a damping term. By utilizing the structure of the system, the energy methods and the means of bootstrapping argument, we prove the global stability property in the Sobolev space Hk(ℝ3)(k≥3)$$ {H}^k\left({\mathrm{\mathbb{R}}}^3\right)\left(k\ge 3\right) $$ of perturbations near the hydrostatic equilibrium. Moreover, we take an effective approach to obtain the optimal decay rates for the global solution itself as well as its derivatives. In this paper, we aim to reveal the mechanism of how the temperature helps stabilize the fluid. Additionally, exploring the stability of perturbations near hydrostatic equilibrium may provide valuable insights into specific severe weather phenomena. [ABSTRACT FROM AUTHOR]

We consider the motion of an incompressible viscous fluid on a compact Riemannian manifold M with boundary. The motion on M is modeled by the incompressible Navier-Stokes equations, and the fluid is subject to pure or partial slip boundary conditions of Navier type on ∂ M. We establish existence and uniqueness of strong as well as weak (variational) solutions for initial data in critical spaces. Moreover, we show that the set of equilibria consists of Killing vector fields on M that satisfy corresponding boundary conditions, and we prove that all equilibria are (locally) stable. In case M is two-dimensional we show that solutions with divergence free initial condition in L 2 (M ; T M) exist globally and converge to an equilibrium exponentially fast. [ABSTRACT FROM AUTHOR]

The research on the propagation and evolution of the second-mode internal solitary waves(ISWs) is receiving more and more attention. In this study, second-mode internal solitary waves in continuous stratification are physically simulated in a laboratory-stratified fluid flume. Meanwhile, the second-mode ISWs and their induced flow field in the same stratification environment are solved based on the eigenvalue problem of the TG equation (Taylor-Goldstein), combined with the weakly non-linear ISW theoretical models. The experimental and theoretical results show that the symmetry of the second-mode ISW wave-flow field can be improved as the thickness ratio of the upper fluid layer and lower one approaches 1. The ISW speed and horizontal and vertical velocity range values in the continuous pycnocline are positively correlated with the changing ISW amplitude, while only the wavelength is negatively correlated with the iSW amplitude. The waveflow fields of the second-mode ISWs calculated by Korteweg-de Vries (KdV) and extended KdV (eKdV) models in the large amplitude cases are more consistent with the experimental results than those in the small amplitude cases. The two theoretical models used to describe second-mode ISWs can be significantly improved when the thickness ratio of the upper and lower fluid layers approaches 1. In this case, the eKdV model is more applicable than the KdV model. [ABSTRACT FROM AUTHOR]

In this paper, three real fluid mixtures, such as methane+Ar, methane+Kr and methane+Xe, are considered and the viscosity of the mixtures is theoretically calculated. For this purpose, three potential models are chosen. The potential models have the same repulsive terms but different attractive parts. The main purpose of this paper is to study the contribution of the potential attractive term on the viscosity of the fluid mixtures. To this goal, the Ornstein–Zernike (OZ) integral equation is first solved. Then, the viscosity is calculated by the Vesovic–Wakeham (VW) formalism. The obtained results in this work have been compared with the simulation data and also the experimental results. The findings show that the viscosity at low density for the three potential models is in good agreement with the simulation data. But, at high density, one of the potential models gave better agreement with the experimental results. Also, it is found that for each of the aforementioned mixtures, only one potential model gives a better result in comparison with the experimental data. The lowest deviation with the experimental data corresponds to the mixture of methane+Kr (3.0%) and methane+Xe (3.0%) by using different potential models. It means that the attractive term has an important role in predicting the viscosity of the fluid mixtures. [ABSTRACT FROM AUTHOR]

We study h-almost conformal ω-Ricci–Bourguignon solitons and h-almost gradient conformal ω-Ricci–Bourguignon solitons in spacetimes of general relativity. At first, we provide an example of h-almost conformal ω-Ricci–Bourguignon soliton. Next, we prove that if a generalized Robertson–Walker spacetime admits an h-almost conformal ω-Ricci–Bourguignon soliton or an h-almost gradient conformal ω-Ricci–Bourguignon soliton, then it becomes a perfect fluid spacetime. Moreover, we have observed that a spacetime with h-almost conformal ω-Ricci–Bourguignon soliton whose potential vector field is a conformal vector field is an ω-Einstein manifold. [ABSTRACT FROM AUTHOR]

This work introduces a high-throughput setup for Raman analysis of various flowing fluids, both transparent and non-transparent. The setup employs a microfluidic cell, used with an external optical setup, to control the sample flow's position and dimensions via 3-dimensional hydrodynamic focusing. This approach, in contrast to the prevalent use of fused silica capillaries, reduces the risk of sample photodegradation and boosts measurement efficiency, enhancing overall system throughput. The microfluidic cell has been further evolved to laminate two distinct flows from different samples in parallel. Using line excitation, both samples can be simultaneously excited without moving parts, further increasing throughput. This setup also enables real-time monitoring of phenomena like mixing or potential reactions between the two fluids. This development could significantly advance the creation of highly sensitive, high-throughput sensors for fluid composition analysis. [ABSTRACT FROM AUTHOR]

The concept of friction was integrated into the broader field of tribology in the 20th century. Here, we revive the older friction coefficient concept and show that it is the defining parameter for a family of granular materials. We show, for the first time, that kinetic friction coefficients of such systems can be described as a function of the lubricating fluid and the shape of the granules, without any fitting parameters. With this, we define the value and conditions for the minimal friction of this system and show how it can increase depending on the properties of the system. This paper shows that the minimum possible friction for an assembly of granular media is the same universal constant of ¼ that da Vinci identified for kinetic friction between two rigid bodies. [ABSTRACT FROM AUTHOR]

In this study, a well-defined and controlled plasma-droplet two-phase flow millifluidic system was developed. We established a detailed quantitative relationship among plasma discharge characteristics, flow dynamics, and the gas–liquid transport properties of reactive oxygen and nitrogen species (RONS). Under constant energy inputs, the gas–liquid contact area in the two-phase flow initially increases and subsequently decreases with rising liquid flow rates. Efficient gas–liquid transport results in a linear decrease in residual gaseous RONS and a corresponding linear increase in aqueous RONS, both of which align with changes in gas–liquid contact area. Notably, across various two-phase flow conditions, the combined values of residual gaseous RONS and liquid oxidation capacity consistently match the decreased plasma intensity due to droplet involvement in the discharge. The quantitative optimization of fluid characteristics and RONS transport within the two-phase flow millifluidic system significantly boosts the energy efficiency of Methyl Orange decolorization, far exceeding that of traditional methods. [ABSTRACT FROM AUTHOR]