Classical Fluid Research Articles

Von Karman correlation similarity in solar wind magnetohydrodynamic turbulence.

A major development underlying hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth, here extended empirically to plasma turbulence in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here, we analyze an ensemble of Elsässer autocorrelation functions computed from Advanced Composition Explorer data at 1 astronomical unit (AU), and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman's hypothesis applied to weakly compressive magnetohydrodynamic turbulence. This provides a firm empirical basis for employing the similarity decay hypothesis to the Elsässer correlations that represent the incompressive turbulence cascade. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.

Effect of magnetic field and heat transfer on peristaltic flow of a micropolar fluid through a porous medium

This paper presents a numerical study of the peristaltic flow of a micropolar fluid through a porous medium have been studied under the long-wavelength and low Reynolds number approximation. The system of differential equations is solved numerically using the NDSolve Mathematica. The numerical study investigates the effects of magnetic field, heat transfer on the peristaltic flow of a micropolar fluid through a porous medium induced by sinusoidal peristaltic waves traveling down the channel wall in symmetric channel. The effects of various parameters like coupling number, the Hartman number, the micropolar parameter, the permeability, the viscosity constant of the classical fluid dynamics and the thermal radiation, etc. on velocity profiles, temperature and micropolar rotation. Numerical results are computed and discussed numerically and presented through graphs. The impacts of pertinent parameters on the aforementioned quantities are examined by plotting graphs on the basis of computational results. The results indicate that the effect of parameters is very pronounced.

Impact of Newtonian Heating via Fourier and Fick’s Laws on Thermal Transport of Oldroyd-B Fluid by Using Generalized Mittag-Leffler Kernel

In this manuscript, a new approach to study the fractionalized Oldroyd-B fluid flow based on the fundamental symmetry is described by critically examining the Prabhakar fractional derivative near an infinitely vertical plate, wall slip condition on temperature along with Newtonian heating effects and constant concentration. The phenomenon has been described in forms of partial differential equations along with heat and mass transportation effect taken into account. The Prabhakar fractional operator which was recently introduced is used in this work together with generalized Fick’s and Fourier’s law. The fractional model is transfromed into a non-dimentional form by using some suitable quantities and the symmetry of fluid flow is analyzed. The non-dimensional developed fractional model for momentum, thermal and diffusion equations based on Prabhakar fractional operator has been solved analytically via Laplace transformation method and calculated solutions expressed in terms of Mittag-Leffler special functions. Graphical demonstrations are made to characterize the physical behavior of different parameters and significance of such system parameters over the momentum, concentration and energy profiles. Moreover, to validate our current results, some limiting models such as fractional and classical fluid models for Maxwell and Newtonian are recovered, in the presence of with/without slip boundary wall conditions. Further, it is observed from the graphs the velocity curves for classical fluid models are relatively higher than fractional fluid models. A comparative analysis between fractional and classical models depicts that the Prabhakar fractional model explains the memory effects more adequately.

Analysis on Seal Capacity of Magnetic Fluid Seal Using Ring Magnet

Magnetic fluid seal is one of the most mature applications of magnetic fluid. When the shaft has a large radial runout, the classical pole piece is easily damaged. Due to its small size, the commonly used pole piece structure harbors problems like poor seal performance under a large gap and poor processability. By exploring the distribution law of the magnetic field on the magnet’s surface, we provided theoretical support for the magnetic fluid seal using axially-magnetized ring magnets. New structures for the magnetic fluid seal using axially-magnetized slotted ring magnets and the magnetic fluid seal using radially-magnetized ring magnets were proposed. Then, comparisons were made between the classical magnetic fluid seal and the magnetic fluid seal using ring magnets. The results revealed that the magnetic fluid seal using axially-magnetized slotted ring magnets and the magnetic fluid seal using radially-magnetized ring magnets exhibited a certain seal capacity, which could replace the classical magnetic fluid seal structure.

AQP4 labels a subpopulation of white matter-dependent glial radial cells affected by pediatric hydrocephalus, and its expression increased in glial microvesicles released to the cerebrospinal fluid in obstructive hydrocephalus

Hydrocephalus is a distension of the ventricular system associated with ventricular zone disruption, reactive astrogliosis, periventricular white matter ischemia, axonal impairment, and corpus callosum alterations. The condition's etiology is typically attributed to a malfunction in classical cerebrospinal fluid (CSF) bulk flow; however, this approach does not consider the unique physiology of CSF in fetal and perinatal patients. The parenchymal fluid contributes to the glymphatic system, and plays a fundamental role in pediatric hydrocephalus, with aquaporin 4 (AQP4) as the primary facilitator of these fluid movements. Despite the importance of AQP4 in the pathophysiology of hydrocephalus, it’s expression in human fetal life is not well-studied. This manuscript systematically defines the brain expression of AQP4 in human brain development under control (n = 13) and hydrocephalic conditions (n = 3). Brains from 8 postconceptional weeks (PCW) onward and perinatal CSF from control (n = 2), obstructive (n = 6) and communicating (n = 6) hydrocephalic samples were analyzed through immunohistochemistry, immunofluorescence, western blot, and flow cytometry. Our results indicate that AQP4 expression is observed first in the archicortex, followed by the ganglionic eminences and then the neocortex. In the neocortex, it is initially at the perisylvian regions, and lastly at the occipital and prefrontal zones. Characteristic astrocyte end-feet labeling surrounding the vascular system was not established until 25 PCW. We also found AQP4 expression in a subpopulation of glial radial cells with processes that do not progress radially but, rather, curve following white matter tracts (corpus callosum and fornix), which were considered as glial stem cells (GSC). Under hydrocephalic conditions, GSC adjacent to characteristic ventricular zone disruption showed signs of early differentiation into astrocytes which may affect normal gliogenesis and contribute to the white matter dysgenesis. Finally, we found that AQP4 is expressed in the microvesicle fraction (p < 0.01) of CSF from patients with obstructive hydrocephalus. These findings suggest the potential use of AQP4 as a diagnostic and prognostic marker of pediatric hydrocephalus and as gliogenesis biomarker.

Application to Differential Transform Method for MHD Fluid Flow and Heat Transfer

Present study reveals the flow of a classical non-Newtonian fluid based on the Williamson model through a vertical flat plate. The free convective flow is generated because of the effect of buoyancy relating to the temperature. In addition to that, the influence of thermal radiation and heat source/sink in conjunction with the dissipative heat enhances the efficiency of transport phenomenon within the bounding surface. Well-proposed similarity transformation is used to transform the governing equation into ordinary. However, due to the dissipation, the nonlinear coupled problems are complex. For the solution, a semi-analytical approach such as differential transformation method (DTM) in association with the Padé approximant method is used instead of traditional numerical technique. Pade-approximant is useful to get a non-iterative solution without imposing the missing boundary conditions. It is a simple and effective way to determine the solutions of complex nonlinear problems with assumed boundary conditions at infinity. The physical significance of all the contributing parameters distinguished the flow properties are achieved and accessible graphically. Moreover, the validation of the present methodology with the traditional numerical technique is obtained, showing an excellent correlation in particular cases.

Fluid Biomarkers in Alzheimer's Disease and Other Neurodegenerative Disorders: Toward Integrative Diagnostic Frameworks and Tailored Treatments.

The diagnosis of neurodegenerative diseases (NDDs) represents an increasing social burden, with the unsolved issue of disease-modifying therapies (DMTs). The failure of clinical trials treating Alzheimer′s Disease (AD) so far highlighted the need for a different approach in drug design and patient selection. Identifying subjects in the prodromal or early symptomatic phase is critical to slow down neurodegeneration, but the implementation of screening programs with this aim will have an ethical and social aftermath. Novel minimally invasive candidate biomarkers (derived from blood, saliva, olfactory brush) or classical cerebrospinal fluid (CSF) biomarkers have been developed in research settings to stratify patients with NDDs. Misfolded protein accumulation, neuroinflammation, and synaptic loss are the pathophysiological hallmarks detected by these biomarkers to refine diagnosis, prognosis, and target engagement of drugs in clinical trials. We reviewed fluid biomarkers of NDDs, considering their potential role as screening, diagnostic, or prognostic tool, and their present-day use in clinical trials (phase II and III). A special focus will be dedicated to novel techniques for the detection of misfolded proteins. Eventually, an applicative diagnostic algorithm will be proposed to translate the research data in clinical practice and select prodromal or early patients to be enrolled in the appropriate DMTs trials for NDDs.

High-resolution fluid–particle interactions: a machine learning approach

Modelling of fluid–particle interactions is a major area of research in many fields of science and engineering. There are several techniques that allow modelling of such interactions, among which the coupling of computational fluid dynamics (CFD) and the discrete element method (DEM) is one of the most convenient solutions due to the balance between accuracy and computational costs. However, the accuracy of this method is largely dependent upon mesh size, where obtaining realistic results always comes with the necessity of using a small mesh and thereby increasing computational intensity. To compensate for the inaccuracies of using a large mesh in such modelling, and still take advantage of rapid computations, we extended the classical modelling by combining it with a machine learning model. We have conducted seven simulations where the first one is a numerical model with a fine mesh (i.e. ground truth) with a very high computational time and accuracy, the next three models are constructed on coarse meshes with considerably less accuracy and computational burden and the last three models are assisted by machine learning, where we can obtain large improvements in terms of observing fine-scale features yet based on a coarse mesh. The results of this study show that there is a great opportunity in machine learning towards improving classical fluid–particle modelling approaches by producing highly accurate models for large-scale systems in a reasonable time.

Extension of Kelvin’s equation to dipolar colloids

Vapor pressure refers to the pressure exerted by the vapor phase in thermodynamic equilibrium with either its liquid or solid phase. An important class of active matter is field-driven colloids. A suspension of dipolar colloids placed in a high-frequency rotating magnetic field undergoes a nonequilibrium phase transition into a dilute and dense phase, akin to liquid–vapor coexistence in a simple fluid. Here, we compute the vapor pressure of this colloidal fluid. The number of particles that exist as the dilute bulk phase versus condensed cluster phases can be directly visualized. An exponential relationship between vapor pressure and effective temperature is determined as a function of applied field strength, analogous to the thermodynamic expression between vapor pressure and temperature found for pure liquids. Additionally, we demonstrate the applicability of Kelvin’s equation to this field-driven system. In principle, this appears to be in conflict with macroscopic thermodynamic assumptions due to the nonequilibrium and discrete nature of this colloidal system. However, the curvature of the vapor–liquid interface provides a mechanical equilibrium characterized by interfacial tension that connects the condensed clusters observed with these active fluids to classical colligative fluid properties.

Amorphous solids as fuzzy crystals: A Debye-like theory of low-temperature specific heat

The formulation of a fundamental description of amorphous solids is a standing challenge in condensed matter physics. We construct a quantum mechanical model of isotropic amorphous solids as fuzzy crystals and establish an analytical theory of vibrations for glasses at low temperature. Our theoretical framework relies on the basic principle that the disorder in a glass is similar to the disorder in a classical fluid, while the latter is mathematically encoded by noncommutative coordinates in the Lagrange description of fluid mechanics. We find that the density of states in the acoustic branches flattens significantly, leading naturally to a boson peak in the specific heat as a manifestation of a van Hove singularity. The model is valid in the same range as Debye’s theory, namely up to circa 10% of the Debye temperature. Within this range, we find an excellent agreement between the theoretical predictions and the experimental data for two typical glasses, a-GeO2 and Ba8Ga16Sn30-clathrate.Our model supports the conceptual understanding of the nature of the boson peak in glasses as a manifestation of the liquid-like disorder. At the same time, it provides a novel, mathematically simple framework for a unitary treatment of thermodynamical and transport properties of amorphous materials and a solid background for inserting further elements of complexity specific to particular glasses.

Role of odd viscosity in falling viscous fluid

The aim of the present study is to investigate the linear and nonlinear wave dynamics of a falling incompressible viscous fluid when the fluid undergoes an effect of odd viscosity. In fact, such an effect arises in classical fluids when the time-reversal symmetry is broken. The motivation to study this dynamics was raised by recent studies (Ganeshan &amp; Abanov, Phys. Rev. Fluids, vol. 2, 2017, p. 094101; Kirkinis &amp; Andreev, J. Fluid Mech., vol. 878, 2019, pp. 169–189) where the odd viscosity coefficient suppresses thermocapillary instability. Here, we explore the linear surface wave and shear wave dynamics for the isothermal case by solving the Orr–Sommerfeld eigenvalue problem numerically with the aid of the Chebyshev spectral collocation method. It is found that surface and shear instabilities can be weakened by the odd viscosity coefficient. Furthermore, the growth rate of the wavepacket corresponding to the linear spatio-temporal response is reduced as long as the odd viscosity coefficient increases. In addition, a coupled system of a two-equation model is derived in terms of the fluid layer thickness $h(x,t)$ and the flow rate $q(x,t)$. The nonlinear travelling wave solution of the two-equation model reveals the attenuation of maximum amplitude and speed in the presence of an odd viscosity coefficient, which ensures the delay of transition from the primary parallel flow with a flat surface to secondary flow generated through the nonlinear wave interactions. This physical phenomenon is further corroborated by performing a nonlinear spatio-temporal simulation when a harmonic forcing is applied at the inlet.

Multivariate Assessment of Lipoxidative Metabolites, Trace Biometals, and Antioxidant and Detoxifying Activities in the Cerebrospinal Fluid Define a Fingerprint of Preclinical Stages of Alzheimer's Disease.

There exists considerable interest in the identification of molecular traits during early stages of Alzheimer's disease (AD). Mild cognitive impairment (MCI) is considered the closest prodromal stage of AD, and to develop gradually from earlier stages although not always progresses to AD. Classical cerebrospinal fluid (CSF) AD biomarkers, amyloid-β peptides and tau/p-tau proteins, have been measured in prodromal stages yet results are heterogeneous and far from conclusive. Therefore, there exists a pressing need to identify a neurochemical signature for prodromal stages and to predict which cases might progress to AD. Exploring potential CSF biomarkers related to brain oxidative and inorganic biochemistry during prodromal stages of the disease. We have analyzed CSF levels of lipoxidative markers (MDA and 8-isoF2α), biometals (Cu, Zn, Se, Mn, and Fe), iron-transport protein transferrin (TFER), antioxidant enzymes (SOD and GPx4), detoxifying enzymes (GST and BuChE), as well as classical amyloid-β and total and phosphorylated tau, in cognitively healthy controls, patients with MCI, and subjects exhibiting subjective memory complaints (SMC). Inter-group differences for several variables exhibit differentiable trends along the HC ⟶ SMC ⟶ MCI sequence. More interestingly, the combination of Se, Cu, Zn, SOD, TFER, and GST variables allow differentiable fingerprints for control subjects and each prodromal stage. Further, multivariate scores correlate positively with neurocognitive In-Out test, hence with both episodic memory decline and prediction to dementia. We conclude that changes in the CSF biochemistry related to brain oxidative defense and neurometallomics might provide more powerful and accurate diagnostic tools in preclinical stages of AD.

Electrokinetic energy conversion of core-annular flow in a slippery nanotube

In this paper, the electrokinetic energy conversion of core-annular flow (CAF) is investigated theoretically in a slippery nanotube. Two immiscible and undisturbed fluids are full of the whole nanotube, consisting of a two-layer fluid system. The core fluid is assumed to be surrounded by the annular fluid with an ideal flow pattern. Based on the Debye–Hückel linearization, the analytical expressions of flow velocity, streaming potential and electrokinetic energy conversion efficiency have been obtained. Result shows that the CAF can be enhanced obviously by the permittivity and viscosity ratios. Compared with the classical single-layer fluid system, large streaming potential strength can be obtained by altering the annular fluid property in the present two-layer fluid system. This implies that more streaming current can be obtained. Besides, as a significant application of electrokinetic flow, the optimal ratios can also be obtained in the two-layer fluid system and the conversion efficiency attains the maximum at these optimal ratios.

Detectable universes inside regular black holes

While spacetime in the vicinity outside astrophysical black holes is believed to be well understood, the event horizon and the interior remain elusive. Here, we discover a degenerate infinite spectrum of novel general relativity solutions with the same mass-energy and entropy that describe a dark energy universe inside an astrophysical black hole. This regular cosmological black hole is stabilized by a finite tangential pressure applied on the dual cosmological-black hole event horizon, localized up to a quantum indeterminacy. We recover the Bekenstein–Hawking entropy formula from the classical fluid entropy, calculated at a Tolman temperature equal to the cosmological horizon temperature. We further calculate its gravitational quasi-normal modes. We find that cosmological black holes are detectable by gravitational-wave experiments operating within the mu mathrm{Hz}–mathrm{Hz} range, like LISA space-interferometer.

Determination of the Microinjected Cytosolic Concentration by Using Mathematical Models of Fluid Dynamics.

The precise determination of the intracellular concentration of a drug is a major challenge in drug discovery. Microinjection is a very effective technique for the introduction of macromolecules into single cells. However, due to the large number of parameters that need to be adjusted and the complex physical mechanisms involved, there are currently no means by which the concentration of a microinjected intracellular compound could be theoretically estimated. In this paper, we present a method for the theoretical estimation of intracellular drug concentration, based on the framework of classical fluid mechanism theory - specifically, the modified Bernoulli equation. We introduce into Bernoulli's classical equation the effect of friction due to the non-laminar regimes of the injected fluid. We also study the compatibility of our theoretical estimation model with variations in injection time and concentration of the compound inside the microinjection needle. Finally, microinjected calcium concentrations estimated with the theoretical model were compared with those determined experimentally in several cell types, by using a Fura-2-based Ca2+ imaging technique.

A new microscopic look into pressure fields and local buoyancy

Defining local pressures is pivotal to understanding phenomena such as buoyancy and atmospheric physics, which always require space-varying pressure fields to be considered. Such fields have precise definitions within the frameworks of hydro-thermodynamics and the kinetic theory of gases, but a pedagogical approach based on standard statistical mechanics techniques is still lacking. In this paper, we propose a new microscopic definition of local pressure inside a classical fluid, relying upon a local barometer potential that is built into the many-particle Hamiltonian. This setup allows pressure to be locally defined as an ensemble average of the radial force exerted by the barometer potential on the gas' particles. Moreover, this same framework is also employed in a microscopic derivation of buoyancy of immersed bodies in the presence of arbitrary external fields. As instructive examples, buoyant forces are calculated for ideal fluids in the presence of a uniform force field, in the presence of a spherical harmonic confinement field and in rotation with a constant angular velocity.

Coupling and Instability of Electrostatic Waves in Spin Magnetized Degenerate Plasmas

In this article, we study the coupling of low-frequency electrostatic waves in the electron-ion and the electron-ion-beam-spin quantum plasmas. The quantum effect of electrons are introduced via separate spin evolution-quantum hydrodynamic (SSE-QHD) model while the ion dynamics is governed by classical fluid equations. In the case of electron-ion plasma, it is found that the quantum effects shift both the coupling domain and the phase velocities of coupled waves. Furthermore, the coupling is observed to be strong at small propagation angles. In the beam interacting system, two coupling domains occur corresponding to small and large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> -values. In the first domain beam mode excites the ion cyclotron (IC) wave and moves with constant phase velocity while in the second domain it gains energy from the ion acoustic (IA) mode and travels with increasing phase velocity. In addition, the beam parameters affect both the coupling domain and the phase velocity. The presence of beam in electron-ion plasma drives the IC mode unstable. The beam parameters, the spin, and the obliqueness affect the instability. Our findings may be helpful in understanding the energy exchange of plasma waves via coupling phenomenon in degenerate plasma systems.

A classical relativistic hydrodynamical model for strong EM wave-spin plasma interaction

Based on the covariant Lagrangian function and Euler–Lagrange equation, a set of classical fluid equations for strong EM wave-spin plasma interaction is derived. Analysis shows that the relativistic effects may affect the interaction processes by three factors: the relativistic factor, the time component of four-spin, and the velocity-field coupling. This set of equations can be used to discuss the collective spin effects of relativistic electrons in classical regime, such as astrophysics, high-energy laser-plasma systems and so on. As an example, the spin induced ponderomotive force in the interaction of strong EM wave and magnetized plasma is investigated. Results show that the time component of four-spin, which approaches to zero in nonrelativistic situations, can increase the spin-ponderomotive force obviously in relativistic situation.

Natural Convection Inside a 3D Regular Shape Enclosures - A Brief Review

This paper introducing a review of the recent three-dimensional numerical and experimental researches on the laminar natural convection heat transfer inside cavities. Focusing on the previous research’s cavity geometry specially the regular shapes both simple or complex shapes. A wide variety of geometries which having different inclinations, inserted bodies and boundary conditions were presented and discussed. The working fluids of the cavities were also reviewed, classical fluids, nanofluids and else. It can be concluded that there is a gap in the research region of the three-dimensional numerical studies in complex cavities. And generally, lake in the experimental studies for all cavity geometries classical or complex were appointed.

Joint quantum–classical Hamilton variational principle in the phase space

We show that the dynamics of a closed quantum system obeys the Hamilton variational principle. Even though quantum particles lack well-defined trajectories, their evolution in the Husimi representation can be treated as a flow of multidimensional probability fluid in the phase space. By introducing the classical counterpart of the Husimi representation in a close analogy to the Koopman–von Neumann theory, one can largely unify the formulations of classical and quantum dynamics. We prove that the motions of elementary parcels of both classical and quantum Husimi fluid obey the Hamilton variational principle, and the differences between associated action functionals stem from the differences between classical and quantum pure states. The Husimi action functionals are not unique and defined up to the Skodje flux gauge fixing (Skodje et al 1989 Phys. Rev. A 40 2894). We demonstrate that the gauge choice can dramatically alter flux trajectories. Applications of the presented theory for constructing semiclassical approximations and hybrid classical–quantum theories are discussed.