Presence Of Viscosity Research Articles

Особенности биоэлектрической активности коры головного мозга и нарушения мышления у детей с различными пограничными расстройствами резидуально-органического генеза

The article presents the results of a study of the features of cognitive function and bioelectric activity cerebral cortex in children with borderline mental disorders of residually organic genesis. 80 children participated with the following diagnoses: organic emotionally labile [asthenic] disorder [F 06.06]; inorganic enuresis [F 98.0], encopresis [F 98.1], stereotypical motor disorders [F 98.4], other specified emotional and behavioral disorders with onset usually occurring in childhood [F 98.8]. The features of bioelectric activity of the cerebral cortex, the ability to spatial analysis and synthesis, arithmetic counting, assimilation of logical and grammatical structures, the presence of viscosity, detail and diversity intellectual activity were studied in children. Data of electroencephalographic examinations were compared with the results of psychodiagnostic methods using the methods of mathematical statistics. Differences of bioelectric activity and features of thinking in children were investigated depending on features of boundary disorder. It is shown that on the background of asthenization more pronounced cognitive impairment is observed. Children with asthenic disorders [06.06] have the largest scatter of data than patients with enuresis [F98.0], encopresis [F 98.1], stereotypical movement disorders [F 98.4], disorders of behavior [F 98.8]. At the same time, on average, they have the most significant violations of thinking, what happens against the background of increasing spectral power of low-frequency activity of delta and theta rhythms in general, as well as of delta rhythm in the frontal part of the brain. Increase of low-frequency activity in the frontal lobes of both hemispheres leads to more pronounced disorders of thinking, than similar changes in the temporal, parietal, occipital regions of the right hemisphere and speech zones of the left hemisphere. In the first case, they are manifested in violations of spatial analysis and synthesis, viscosity, detail and diversity of thinking, as well as in difficulties in the semantic and symbolic activity, in the assimilation of logical and grammatical structures and arithmetic. In the second case — only in violations of spatial analysis and synthesis, viscosity, detail and diversity of thinking.

Exploring membrane viscosity at the headgroup region utilizing a hemicyanine-based fluorescent probe

Membrane viscosity is an important determinant for several cellular functions. In spite of having vast literature on the interfacial and acyl chain region viscosity of the membrane, there is hardly any report on the membrane viscosity at the headgroup region. In this present work, we have exploited the photophysical properties of a hemicyanine dye covalently linked with a C16 alkyl chain (HC16) to explore the membrane viscosity at the headgroup region. The chromophoric group of HC16 locates at the headgroup region due to its overall positive charge. Methanol-glycerol mixture of known composition and viscosity were used to develop the standard curve of apparent rotational correlation time against viscosity, and utilized this standard curve to evaluate viscosity of dimyristoylphosphatidylcholine (DMPC) membrane as a function of temperature. The result exhibited that there is a 4-fold change in headgroup viscosity of the DMPC membrane between gel and fluid phase; with a sharp change during the phase transition. Moreover, we have monitored the effect of cholesterol on the viscosity of the headgroup region of a biologically relevant lipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), keeping in mind the role of cholesterol on membrane organization, dynamics, and cellular functions. Interestingly, the headgroup viscosity of POPC membrane does not show a significant change in presence of various concentrations of cholesterol, though literature showed remarkable change in interfacial and acyl chain region viscosity in presence of similar concentrations of cholesterol.

Mathematical modelling of acoustic radiation force in transient shear wave elastography in the heart

The aim of this work is to provide a mathematical model and analysis of the excitation and the resulting shear wave propagation in acoustic radiation force (ARF)-based shear wave cardiac elastography. Our approach is based on asymptotic analysis; more precisely, it consists in considering a family of problems, parametrised by a small parameter inversely proportional to the excitation frequency of the probes, the viscosity and the velocity of pressure wave propagation. We derive a simplified model for the expression of the ARF by investigating the limit behaviour of the solution when the small parameter goes to zero. By formal asymptotic analysis – an asymptotic expansion of the solution is used – and energy analysis of the nonlinear elastodynamic problem, we show that the leading-order term of the expansion is solution of the underlying, incompressible, nonlinear cardiac mechanics. Subsequently, two corrector terms are derived. The first is a fast-oscillating pressure wave generated by the probes, solution of a Helmholtz equation at every time. The second corrector term consists in an elastic field with prescribed divergence, having a function of the first corrector as a source term. This field corresponds to the shear acoustic wave induced by the ARF. We also confirm that, in cardiac mechanics, the presence of viscosity in the model is essential to derive an expression of the shear wave propagation from the ARF, and that this phenomenon is related to the nonlinearity of the partial differential equation.

Riemann and Shock Waves in a Porous Liquid-Saturated Geometrically Nonlinear Medium

Within the framework of the classical Biot theory, the propagation of plane longitudinal waves in a porous liquidsaturated medium is considered with account for the nonlinear connection between deformations and displacements of solid phase. It is shown that the mathematical model accounting for the geometrical nonlinearity of the medium skeleton can be reduced to a system of evolution equations for the displacements of the skeleton of medium and of the liquid in pores. The system of evolution equations, in turn, depending on the presence of viscosity, is reduced to the equation of a simple wave or to the equation externally resembling the Burgers equation. The solution of the Riemann equation is obtained for a bell-shaped initial profile; the characteristic wave breaking is shown. In the second case, the solution is found in the form of a stationary shock wave having the profile of a nonsymmetric kink. The relationship between the amplitude and width of the shock wave front has been established. It is noted that the behavior of nonlinear waves in such media differs from the standard one typical of dissipative nondispersing media, in which the propagation of waves is described by the classical Burgers equation.

Heat transfer to supercritical hydrocarbon fuel in horizontal tube: Effects of near-wall pyrolysis at high heat flux

Understanding heat transfer to endothermic hydrocarbon fuels (EHFs) with pyrolysis at high heat flux is a challenging issue for the design of regenerative cooling panels in the fuel-cooled thermal management technology of advanced aircrafts. In this work, the convective heat transfer of supercritical EHFs in presence of pyrolysis reactions was experimentally investigated in horizontal tubes at the heat flux up to 1.836 MW/m2 under 3.5 MPa. A CFD model with an improved kinetics (Chem Eng Sci 2019, 207, 202-214) has been developed and extensively validated to get detailed information on the coupling mechanism of heat transfer and pyrolysis. The heat transfer rate can be enhanced by pyrolysis reactions at relative low heat flux (below 400 kW/m2). With increasing heat flux, the rapid and high-degreed pyrolysis near-wall considerably changes the local composition and thus the thermophysical properties, resulting in the significant heat absorption differences in the cross section and local heat transfer deterioration. Typically, Nub decreases from 108.8 to 73.4 (about 30%) when the heat flux increases from 426 to 758 kW/m2. The possible reasons may be attributed to the weakened near-wall turbulence by the increased fluid viscosity in presence of secondary products, as well as the increased thermal boundary layer effect attributed to the high near-wall heat absorption and huge radial property gradient at high heat flux.

Bulk viscous Bianchi type I cosmological model in Lyra geometry and in the general theory of relativity

In the framework of the gravitational theory based on Lyra geometry and the general theory of relativity, we study Bianchi type I cosmological model in the presence of viscous fluid. A discussion about the suitability of the Sen equations as field equations in Lyra geometry is given. A clear physical meaning for the time component of the displacement vector, introduced in the Sen field equations used in the framework of Lyra geometry, is given by identifying it as a part of the energy momentum tensor (viscosity term). Exact solution of the Einstein field equations is given by assuming the model has a constant deceleration parameter. Moreover, we study the effect of the viscosity term on the entropy of the universe. A formula for calculating the entropy in the presence of viscosity is given by a combination between the second law of thermodynamics and the energy momentum tensor in a conservative manner. We calculate and study the thermodynamic functions (Enthalpy, Gibbs energy and Helmholtz energy) of the universe in the presence of viscosity in Lyra geometry and in the general theory of relativity. The physical and geometrical properties of the obtained models are discussed.

Constraints and cosmography of Lambda CDM in presence of viscosity

In this work, we study two scenarios of the Universe filled by a perfect fluid following the traditional dark energy and a viscous fluid as dark matter. In this sense, we explore the most simple case for the viscosity in the Eckart formalism, a constant, and then, a polynomial function of the redshift. We constrain the phase-space of the model parameters by performing a Bayesian analysis based on Markov Chain Monte Carlo method and using the latest data of the Hubble parameter (OHD), Type Ia Supernovae (SNIa) and Strong Lensing Systems. The first two samples cover the region 0.01<z<2.36. Based on AIC, we find equally support of these viscous models over Lambda-Cold Dark Matter (LCDM) taking into account OHD or SNIa. On the other hand, we reconstruct the cosmographic parameters (q, j, s, l) and find good agreement to LCDM within up to 3sigma CL. Additionally, we find that the cosmographic parameters and the acceleration-deceleration transition are sensible to the parameters related to the viscosity coefficient, making of the viscosity an interesting physical mechanism to modified them.

Inertial Effect on Interaction between Two Earthquake Faults

This study is focused on the inertial effect on slip of and interaction between two earthquake faults based on a two-body slider-slider model in the presence of thermal-pressurized slip-weakening friction and viscosity. The ratio m = m 2 / m 1 , where m 2 and m 1 are the masses of sliders 1 and 2, respectively, is the model parameter to represent the inertial effect. Other model parameters are s (the stiffness ratio), f= f o2 /f o1 (where f oi is the normalized static friction force on the i -th slider, i =1, 2), y=U c2 /U c1 (where U ci is the normalized characteristic displacement of friction law on the i -th slider), and g=h 2 /h 1 (where h i is the normalized viscosity coefficient between the i -th slider and the background plate). Simulation results show that m is important on interaction between the two sliders. Foreshocks and aftershocks/afterslip can be generated on slider 1 or slider 2 when m ≠1. Slider 2 behaves like a slow event when m ≥50. The f, y , and g are the major factors and s is minor one in causing time delay between the two sliders. Slider 2 cannot move when f is higher than a critical value which depends on other model parameters. Interaction and the patterns of motions of the two sliders are different between y 1. The presence of viscosity may increase the predominant period of a slider.

Thiol-ene photo-click immobilization of a chiral chromatographic ligand on silica particles

This work reports procedures for the immobilization of vinyl ligands on silica particles by UV-initiated thiol-ene radical addition reaction (photo-click immobilization). tert‑Butylcarbamoyl quinine was the functional ligand (ene component) for the synthesis of chiral stationary phases. Two distinct surface chemistries were evaluated. In one approach, the ligand was directly attached to 3-mercaptopropyl-silica triggered by radicals generated by UV irradiation from a photoinitiator. In another approach, the ligand was immobilized onto vinyl silica via poly(3-mercaptopropyl-methylsiloxane) (PMPMS) as crosslinker by a photoinitiated double click reaction in which functionalization with chiral ligand and crosslinking to vinylsilica occurred simultaneously in one synthesis step. PMPMS-bonded CSPs were prepared from suspension (slurry method) or solventless after coating of the polythiol onto the vinylsilica surface (film method). Optimization by a design of experiment approach showed that the reaction time is the prime variable to optimize the surface coverage of chiral selector which also increased with PMPMS concentration. When the film formation of the latter approach was assisted by a minute volume of toluene during photo-click immobilization, selector coverage could be significantly increased to 0.73 µmol/m2 in a 2 h synthesis compared to 0.44 µmol/m2 by the solventless film method and 0.47 µmol/m2 by the slurry method under otherwise comparable conditions. The solvent assistance improved the chromatographic efficiency of the film method and resulted equal minimal reduced plate height of 2.6 as the slurry method for a chiral probe (Fmoc-Phe). The mass transfer resistance was around factor 2 smaller with the solvent-assisted film method as compared to the film approach without toluene, presumably due to a more homogenous distribution of the thin polymer film owing to lower dynamic viscosity in presence of toluene.

Mode conversion and damping of MHD waves in stratified viscous solar atmosphere

We study the mode conversion and damping of MHD waves in a gravitationally stratified low-$\beta $ to high-$\beta $ isothermal atmosphere of the Sun permeated by a uniform vertical magnetic field. We solve the MHD equations by MacCormack method to examine the effect of viscosity on amplitudes of physical quantities such as velocity, mass density, gas pressure and magnetic field before and after the $\beta \approx 1$ layer. It is found that mode conversion occurs at the point $z \approx -1.8$ in $\beta \approx 1$ layer and viscosity does not influence the mode conversion phenomenon. In the presence of viscosity, the amplitudes of vertical and horizontal velocity components, horizontal and vertical magnetic field components, gas pressure and mass density decrease and decay of amplitude is stronger for higher values of viscosity. In the low $\beta $ plasma, damping length decreases with the increase in viscosity but remains almost unchanged in the high $\beta $ plasma. When the driving frequency increases, conversion from slow to fast mode decreases.

Rayleigh–Bénard convection in Maxwell nanofluids layer saturated in a rotating porous medium with feedback control subjected to viscosity and thermal conductivity variations

Control strategy on Rayleigh–Benard convection in rotating Darcy–Maxwell nanofluids saturated in porous layer heated from below is studied in the presence of viscosity and thermal conductivity variations for rigid–rigid, free–free, and lower-rigid and upper-free boundaries. Feedback control strategy with an array of sensors situated at the top plate and actuators located at the bottom plate of the nanofluids layer are considered in this study. Linear stability analysis based on normal mode technique has been performed, the eigenvalue problem is obtained numerically by implementing the Galerkin method and computed by using Maple software. Model employed for the nanofluids includes the mechanisms of Brownian motion and thermophoresis. The important effects of feedback control, rotation, Vadasz number, relaxation parameter, viscosity variation, thermal conductivity variation, porosity and nanofluids parameters have been presented graphically and discussed.

Modulated free energy and mean field limit

This is the document corresponding to the talk the first author gave at IH{\'E}S for the Laurent Schwartz seminar on November 19, 2019. It concerns our recent introduction of a modulated free energy in mean-field theory in BrJaWa [4]. This physical object may be seen as a combination of the modulated potential energy introduced by S. Serfaty [See Proc. Int. Cong. Math. (2018)] and of the relative entropy introduced in mean field limit theory by P.-E. Jabin, Z. Wang [See Inventiones 2018]. It allows to obtain, for the first time, a convergence rate in the mean field limit for Riesz and Coulomb repulsive kernels in the presence of viscosity using the estimates in Du [8] and Se1 [20]. The main objective in this paper is to explain how it is possible to cover more general repulsive kernels through a Fourier transform approach as announced in BrJaWa [4] first in the case $\sigma$N $\rightarrow$ 0 when N $\rightarrow$ +$\infty$ and then if $\sigma$ > 0 is fixed. Then we end the paper with comments on the particle approximation of the Patlak-Keller-Segel system which is associated to an attractive kernel and refer to [C.R.

RETRACTED ARTICLE: A uniqueness lemma with applications to regularization and incompressible fluid mechanics

In this paper, we extend our previous result from Levy (2016). We prove that transport equations with rough coefficients do possess a uniqueness property, even in the presence of viscosity. Our method relies strongly on duality and bears a strong resemblance to the well-known DiPerna-Lions theory first developed by DiPerna and Lions (1989). This uniqueness result allows us to reprove the celebrated theorem of Serrin (1962) in a novel way. As a byproduct of the techniques, we derive an L1 bound for the vorticity in terms of a critical Lebesgue norm of the velocity field. We also show that the zero solution is unique for the 2D Euler equations on the torus under a mild integrability assumption.

Gravitational waves in the presence of viscosity

We analyze gravitational waves propagating in an isotropic cosmic fluid endowed with a bulk viscosity [Formula: see text] and a shear viscosity [Formula: see text], assuming these coefficients to vary with fluid density [Formula: see text] as [Formula: see text], with [Formula: see text] favored by experimental evidence. We give the general governing equation for the gravitational waves and focus thereafter on two examples. The first concerns waves in the very late universe, close to the Big Rip, where the fate of the cosmic fluid is dependent highly on the values of the parameters. Our second example considers the very early universe, the lepton era, the motivation for this choice being that the microscopical bulk viscosity as calculated from statistical mechanics is then at maximum. We find that the gravitational waves on such an underlying medium are damped, having a decay constant equal to the inverse of the conformal Hubble parameter. Our results turn out to be in good agreement with other viscosity-based approaches.

Pulsatile vibrations of viscoelastic microtubes conveying fluid

In this paper, the pulsatile coupled vibrations of a viscoelastic microtube conveying pulsatile fluid is examined for the first time. The problem is grouped into the class of parametrically excited, internally damped, gyroscopic where both Coriolis and parametric forces are present in the presence of viscosity. The Kelvin–Voigt approach of the viscosity, the Euler–Bernoulli for the deformation, the modified couple stress theory for the small size, and Hamilton’s principle for deriving differential equations are used. Parametric frequency–response curves are obtained in the vicinity of the parametric resonance near the critical speed for both subcritical and supercritical regimes. The effect of the flow pulsation on the oscillations is investigated.

On weak–strong uniqueness for compressible Navier–Stokes system with general pressure laws

The goal of the present paper is to study the weak–strong uniqueness problem for the compressible Navier–Stokes system with a general barotropic pressure law. Our results include the case of a hard sphere pressure of Van der Waals type with a non-monotone perturbation and a Lipschitz perturbation of a monotone pressure. Although the main tool is the relative energy inequality, the results are conditioned by the presence of viscosity and do not seem extendable to the Euler system.

On Plane Motion of Incompressible Variable Viscosity Fluids with Moderate Peclet Number in Presence of Body Force Via Von-Mises Coordinates

The aim of this article is to use von-Mises coordinates to find a class of new exact solutionsof the equations governing the plane steady motion with moderate Peclet number of incompressible fluid of variable viscosity in presence of body force. An equation relating a differentiable function and a stream function characterizes the class under consideration. When the differentiable function is parabolic and when it is not, in both the cases, it finds exact solutions for given one component of the body force. This discourse shows an infinite set of streamlines and the velocity components, viscosity function, generalized energy function and temperature distribution for moderate Peclet number in presence of body force. Moreover, for parabolic case, it obtains viscosity as a function of temperature distribution for moderate Peclet number.

Cosmological singularities in interacting dark energy models with an ω(q) parametrization

Future singularities arising in a family of models for the expanding universe, characterized by sharing a convenient parametrization of the energy budget in terms of the deceleration parameter, are classified. Finite-time future singularities are known to appear in many cosmological scenarios, in particular, in the presence of viscosity or nongravitational interactions, the last being known to be able to suppress or just change in some cases the type of the cosmological singularity. Here, a family of models with a parametrization of the energy budget in terms of the deceleration parameter are studied in the light of Gaussian processes using reconstructed data from [Formula: see text]-value [Formula: see text] datasets. Eventually, the form of the possible nongravitational interaction between dark energy and dark matter is constructed from these smoothed [Formula: see text] data. Using phase space analysis, it is shown that a noninteracting model with dark energy [Formula: see text] ([Formula: see text] being the deceleration parameter) may evolve, after starting from a matter-dominated unstable state, into a de Sitter universe (the solution being in fact a stable node). Moreover, for a model with interaction term [Formula: see text] ([Formula: see text] is a parameter and [Formula: see text], the Hubble constant) three stable critical points are obtained, which may have important astrophysical implications. In addition, part of the paper is devoted to a general discussion of the finite-time future singularities obtained from direct numerical integration of the field equations, since they appear in many cosmological scenarios and could be useful for future extended studies of the models here introduced. Numerical solutions for the new models, produce finite-time future singularities of Type I or Type III, or an [Formula: see text]-singularity, provided general relativity describes the background dynamics.

On Two-Dimensional Variable Viscosity Fluid Motion with Body Forcefor Intermediate Peclet Number Via von-Mises Coordinates

This article uses von-Mises coordinates to present a class of new exact solutions of the system of partial differential equations for the plane steady motion of incompressible fluid of variable viscosity in presence of body forcefor moderate Peclet number. This communication applies successive transformation technique and characterizes streamlines through an equation relating a differentiable function f(x) and a function of stream function. Considering the function of stream function satisfies a specific relation, the exact solutions for moderate Peclet number with body force are determined for given one component of the body force when f(x) takes a specific value and when it is not. In both the cases, it shows an infinite set of streamlines, the velocity components, viscosity function, generalized energy function and temperature distribution for intermediate Peclet number in presence of body force. When f(x) takes a specific value, a relation between viscosity and temperature function is observed.

A class of exact solutions of equations for plane steady motion of incompressible fluids of variable viscosity in presence of body force

This paper determines a class of exact solutions for plane steady motion of incompressible fluids of variable viscosity with body force term in the Navier-Stokes equations. The class consists of stream function  characterized by equation , in polar coordinates ,  where ,  and  are continuously differentiable functions, derivative of  is non-zero but double derivative of  is zero. We find exact solutions, for a suitable component of body force, considering two cases based on velocity profile. The first case fixes both the functions ,  and provides viscosity as function of temperature. Where as the second case fixes the function , leaves  arbitrary and provides viscosity and temperature for the arbitrary function . In both the cases, we can create infinite set of expressions for streamlines, viscosity function, generalized energy function and temperature distribution in the presence of body force. Â