Hepatitis C virus treatment revolution: need for close monitoring

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Thermocapillary motion of a Newtonian drop in a dilute viscoelastic fluid

In this work we investigate the role played by viscoelasticity on the thermocapillary motion of a deformable Newtonian droplet embedded in an immiscible, otherwise quiescent non-Newtonian fluid. We consider a regime in which inertia and convective transport of energy are both negligible (represented by the limit condition of vanishingly small Reynolds and Marangoni numbers) and free from gravitational effects. A constant temperature gradient is maintained by keeping two opposite sides of the computational domain at different temperatures. Consequently the droplet experiences a motion driven by the mismatch of interfacial stresses induced by the non-uniform temperature distribution on its boundary. The departures from the Newtonian behaviour are quantified via the “thermal” Deborah number, De T and are accounted for by adopting either the Oldroyd-B model, for relatively small De T, or the FENE-CR constitutive law for a larger range of De T. In addition, the effects of model parameters, such as the concentration parameter c=1−β (where β is the viscoelastic viscosity ratio), or the extensibility parameter, L 2, have been studied numerically using a hybrid volume of fluid-level set method. The numerical results show that the steady-state droplet velocity behaves as a monotonically decreasing function of De T, whilst its shape deforms prolately. For increasing values of De T, the viscoelastic stresses show the tendency to be concentrated near the rear stagnation point, contributing to an increase in its local interface curvature

Creeping thermocapillary motion of a Newtonian droplet suspended in a viscoelastic fluid

In this work we consider theoretically the problem of a Newtonian droplet moving in an otherwise quiescent infinite viscoelastic fluid under the influence of an externally applied temperature gradient. The outer fluid is modelled by the Oldroyd-B equation, and the problem is solved for small Weissenberg and Capillary numbers in terms of a double perturbation expansion. We assume microgravity conditions and neglect the convective transport of energy and momentum. We derive expressions for the droplet migration speed and its shape in terms of the properties of both fluids. In the absence of shape deformation, the droplet speed decreases monotonically for sufficiently viscous inner fluids, while for fluids with a smaller inner-to-outer viscosity ratio, the droplet speed first increases and then decreases as a function of the Weissenberg number. For small but finite values of the Capillary number, the droplet speed behaves monotonically as a function of the applied temperature gradient for a fixed ratio of the Capillary and Weissenberg numbers. We demonstrate that this behaviour is related to the polymeric stresses deforming the droplet in the direction of its migration, while the associated changes in its speed are Newtonian in nature, being related to a change in the droplet's hydrodynamic resistance and its internal temperature distribution. When compared to the results of numerical simulations, our theory exhibits a good predictive power for sufficiently small values of the Capillary and Weissenberg numbers.Comment: 18 pages, 7 figures, submitted to J. Fluid Mec

Numerical simulations of the thermocapillary migration of a deformable Newtonian droplet in an Oldroyd-B matrix fluid in stokes flow conditions

In this work we investigate the role of elasticity on the thermal Marangoni migration of a Newtonian droplet surrounded by a viscoelastic fluid matrix in a three‐ dimensional geometry for the case of small Reynolds and Marangoni numbers. The study has been conducted in the framework of a coupled Level‐Set‐Volume of Fluid method implemented using the CFD toolbox OpenFOAM. The resulting approach was validated in a variety of flow conditions by comparing our results with analytical correlations and relevant experimental data available in literature. In the present numerical experiments, we consider a neutrally buoyant system of a Newtonian droplet placed in a container with square cross‐section filled with an Oldroyd‐B fluid (a viscoelastic fluid of constant shear viscosity). We apply a thermal gradient by keeping two sides of the box at a different constant temperature so that the temperature gradients at the liquid‐liquid interface generate an imbalance in the interfacial stresses. Such imbalance in turn is responsible of the motion of the fluid from the higher temperature region to the lower temperature region. This mechanism results in the drop moving in the opposite direction due to the thrust generated by the counter motion of the surrounding phase. In order to quantify the viscoelastic effects, we introduce a new dimensionless parameter measuring the relative importance of thermocapillary and elastic stresses. According to the numerical results, the droplet migration speed and shape are significantly different from those observed for the Newtonian‐Newtonian system. This departure of the observed dynamics from Newtonian behaviour can be ascribed to the complex interplay between different effects, including droplet morphological evolution and related distribution of surface‐tension‐driven and elastic stresses at the interface

Flow focusing with miscible fluids in microfluidic devices

In this work, a series of experiments and numerical simulations performed using a Volume-of-Fluid approach were carried out to investigate the flow of miscible viscous fluid systems through microfluidic flow focusing devices with one central inlet stream (with 'Fluid 1') and two lateral inlet streams (with 'Fluid 2'). The combined effect of the fluid viscosity ratio and the inlet velocity ratio on the characteristics of the central focused outlet stream was assessed in microfluidic channels with different aspect ratios. An analytical expression for the two-dimensional (2D) case, relating the width of the central focused stream in the outlet channel with the velocity ratio and the viscosity ratio, was also derived from first principles. The analytical results are in excellent agreement with the two-dimensional numerical results, and the expression is also able to represent well the experimental findings for the configuration with an aspect ratio of 0.84. The width of the central focused outlet stream at the centre plane is seen to decrease with both the velocity ratio and the viscosity ratio. The results of the three-dimensional numerical simulations and experimental measurements are in good agreement, producing further insight into the curved interface known to exist when high viscosity contrasts are present in parallel flow systems. It was observed that the interface curvature across the depth of the channel cross section is strongly dependent on the ratio of inlet viscosities and microchannel aspect ratio, highlighting the three-dimensional (3D) nature of the flow, in which confinement plays a significant role

Deformation of a ferrofluid droplet in a simple shear flow under the effect of a constant magnetic field

Abstract: In the present work, we investigate the dynamics of a droplet of ferrofluid placed in a shear flow field subjected to the additional action produced by the application of a magnetic field in a direction perpendicular to the flow. The problem is solved in the framework of a moving-boundary method based on the solution of the Navier-Stokes equations complemented with the additional equations required for the determination of the magnetic force. The results reveal interesting changes in the trends displayed by the droplet deformation and inclination angle as a function of the capillary number when the intensity of the magnetic field is varied while maintaining flow conditions corresponding to the Stokes regime. The mechanism of droplet relaxation from equilibrium when the magnetic force is suddenly removed is also investigated. According to our numerical experiments the deformation evolves in time following a harmonic decaying process, which, in the limit of small capillary number, i.e. for very small deformations, can be fairly well represented by the temporal evolution of a simple damped harmonic oscillator

Early improvement of glycaemic control after virus clearance in patients with chronic hepatitis C and severe liver fibrosis: a cohort study

HCV has been recognized as the cause of chronic hepatitis C (CHC) since 1990. CHC is associated with progressive liver damage and extrahepatic conditions. Direct antiviral agents (DAAs), approved in 2014, have shown effectiveness in eradicating HCV in most patients. However, little is known about the effect of viral eradication on hepatic and extra-hepatic damage. We performed a historical cohort study of patients with HCV-related liver diseases who achieved SVR from March 2015 to October 2016 at INMI Lazzaro Spallanzani liver Unit in Rome (Italy). Repeated measures of glycaemia were analysed through a multilevel analysis framework to assess short time kinetics of blood glucose level at different times after therapy and for different levels of HCV viremia. The analysis included 205 patients. A model assessing temporal kinetics and variation of glycaemia according to HCV viremia provided evidence that blood glucose levels significantly dropped in patients with diabetes achieving SVR. Most of the variations occurred at 3-5 weeks of therapy (-17.96 mg/dL; p<0.001) and in coincidence with HCV clearance (-13.92 mg/dL; p<0.001). A weak, non-statistically significant reduction was observed in normoglycemic patients. Our study provides evidence that DAAs therapy may significantly improve glycaemic control in patients with CHC achieving SVR even when liver diseases are already established