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European Physical Journal. E, Soft Matter

Valentina Meschini, Marco D de Tullio, Roberto Verzicco
In this paper a computational model for the ventricular flow with a mitral valve and modeled chordae tendineae is presented. The results are compared with an analogous case in which the chordae are not included and their presence is replaced by kinematic boundary conditions. The problem is studied using direct numerical simulation of the Navier-Stokes equations, two-way coupled with a structural solver for the ventricle and mitral valve dynamics. An experimental validation of the model is performed by a comparison of the results with a companion dedicated experiment...
February 28, 2018: European Physical Journal. E, Soft Matter
Daniela Pimponi, Mauro Chinappi, Paolo Gualtieri
The hydrodynamics of a flagellated microswimmer moving in thin films is discussed. The fully resolved hydrodynamics is exploited by solving the Stokes equations for the actual geometry of the swimmer. Two different interfaces are used to confine the swimmer: a bottom solid wall and a top air-liquid interface, as appropriate for a thin film. The swimmer follows curved clockwise trajectories that can converge towards an asymptotically stable circular path or can result in a collision with one of the two interfaces...
February 28, 2018: European Physical Journal. E, Soft Matter
Yongjian Zhang, Jiaqi Si, Qirui Cui, Gengtao Wang, Yujie Bai
Nanoparticle can adsorb at the air-water interface and gives rise to the special interfacial mechanical properties. With the influence of external stimulus, the adsorption state of the particles may be changed and in turn the mechanical properties of the particle layer. In this work, we study the mechanical properties of a monolayer of silica nanoparticles deposited in the Langmuir trough. The area of the monolayer was varied sinusoidally by two oscillating barriers and the surface pressure was monitored by two orthogonal Wilhelmy plates...
February 28, 2018: European Physical Journal. E, Soft Matter
Shasha Qiao, Qunyang Li, Xi-Qiao Feng
Microstructured surfaces with continuous solid topography have many potential applications in biology and industry. To understand the liquid transport property of microstructured surfaces with continuous solid topography, we studied the sliding behavior of a droplet on microhole-structured surfaces. We found that the sliding friction of the droplet increased with increasing solid area fraction due to enlarged apparent contact area and enhanced contact angle hysteresis. By introducing a correction factor to the modified Cassie-Baxter relation, we proposed an improved theoretical model to better predict the apparent receding contact angle...
February 20, 2018: European Physical Journal. E, Soft Matter
Olga Vlasova, Nikolai Kozlov
The behaviour of a heavy cylindrical body in a rotating horizontal cylindrical cavity filled with viscous liquid is investigated experimentally. Several modes of the body behaviour depending on the rate of the cavity rotation, i.e., the ratio of the centrifugal force of inertia and the gravity, are detected. At a fast rotation rate, the body makes the solid-body rotation, remaining immobile relative to the cavity due to the action of the centrifugal force. In the absence of rotation, under the influence of gravity, the body occupies a position in the lower part of the cavity...
February 20, 2018: European Physical Journal. E, Soft Matter
M Guiral, C Neitzel, M Salvador Castell, N Martinez, M T Giudici-Orticoni, J Peters
Pure phospholipids and membrane fragments from bacterial cells living under various conditions were studied against the influence of the surrounding acidity on the internal dynamics. For that we compared mean square displacements extracted from elastic incoherent neutron scattering data, measured both at low and at neutral pH, of the phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine and of samples from neutralophilic and acidophilic micro-organisms (some being hyperthermophilic and others mesophilic)...
February 16, 2018: European Physical Journal. E, Soft Matter
T Lyubimova, N Lobov, V Shevtsova
The linear stability of a steady convective flow of a ternary mixture placed between differently heated vertical rigid plates is studied. The applied temperature gradient induces concentration gradients due to the Soret effect. The analysis is done for the case when separation ratios of ternary mixture, i.e., Soret coefficients, have different signs but the net separation ratio is negative. The stability maps in terms of the Grashof number and net separation ratio are obtained and discussed for monotonic and oscillatory modes of instability...
February 16, 2018: European Physical Journal. E, Soft Matter
David Urbanik, Shikhar Mani Dwivedi, Colin Denniston
Using simulations that realistically model both hydrodynamic and elastic behavior, we study the motion of a microscopic, driven elastic sphere immersed in water. We first confirm the "jittery" relaxation recently predicted theoretically for an externally driven elastic sphere. The sphere is then divided in two and each section is driven internally with the two sections 180° out of phase. With periodic and perfectly symmetric driving, the elastic sphere spontaneously breaks symmetry and can attain macroscopic average swimming velocities to the right or left, the direction depending only on the initial state...
February 16, 2018: European Physical Journal. E, Soft Matter
Martin James, Michael Wilczek
Cellular suspensions such as dense bacterial flows exhibit a turbulence-like phase under certain conditions. We study this phenomenon of "active turbulence" statistically by using numerical tools. Following Wensink et al. (Proc. Natl. Acad. Sci. U.S.A. 109, 14308 (2012)), we model active turbulence by means of a generalized Navier-Stokes equation. Two-point velocity statistics of active turbulence, both in the Eulerian and the Lagrangian frame, is explored. We characterize the scale-dependent features of two-point statistics in this system...
February 14, 2018: European Physical Journal. E, Soft Matter
Olivier Lombard, Nicolas Viard, Valentin Leroy, Christophe Barrière
This experimental study deals with the propagation of an ultrasonic shock wave in a random heterogeneous medium, constituted of identical 75μm radius bubbles, trapped in a yield-stress fluid. The fundamental frequency of the incident wave (in the MHz range) was much larger than the resonance frequency of bubbles (38kHz). A well-expanded coda, resulting from the multiple scattering of the incident shock wave through the heterogeneous medium, was experimentally measured in transmission. Despite the significant amplitude of the shock wave (90kPa), no sign of nonlinear response of the bubbles was detected...
February 8, 2018: European Physical Journal. E, Soft Matter
Abdallah Daddi-Moussa-Ider, Stephan Gekle
Elastic confinements are an important component of many biological systems and dictate the transport properties of suspended particles under flow. In this paper, we review the Brownian motion of a particle moving in the vicinity of a living cell whose membrane is endowed with a resistance towards shear and bending. The analytical calculations proceed through the computation of the frequency-dependent mobility functions and the application of the fluctuation-dissipation theorem. Elastic interfaces endow the system with memory effects that lead to a long-lived anomalous subdiffusive regime of nearby particles...
February 8, 2018: European Physical Journal. E, Soft Matter
Badr Kaoui
I propose two-dimensional simulations of drug release from a liposome into the bloodstream. I perform the fluid-structure coupling, between the particles deformation (the liposome and the red blood cells) and the plasma flow, using the immersed boundary method. I compute both the flow and the drug mass transport using the lattice Boltzmann method. The simulations allow computing the instantaneous amount of the released drug, its distribution and its accumulation in the blood vessel wall. These quantities are sensitive to multiple factors and parameters...
February 8, 2018: European Physical Journal. E, Soft Matter
Jun-Jie Huang, Jie Wu, Haibo Huang
We propose an alternative method to implement the contact angle boundary condition on a solid wall and apply it in hybrid lattice-Boltzmann finite-difference simulations of two-phase flows with immersed surfaces in which the flow equations are solved by the lattice-Boltzmann method and the interface equations are solved by the finite-difference method. Using the hyperbolic tangent profile of the order parameter across an interface in phase-field theory, we were able to obtain its unknown value at a ghost point from the information at only one point in the fluid domain...
February 7, 2018: European Physical Journal. E, Soft Matter
Sébastien Fumeron, Fernando Moraes, Erms Pereira
One interesting way to control heat is to use devices designed by transformation thermics, where artificial media are used. However, once manufactured (either repelling or concentrating heat, for example), besides being mono-purpose, such devices are designed according to a specific geometric boundary conditions. Another problem is the temperature dependence of the materials employed, since their properties are sometimes considered temperature-invariant. In this paper, we show that a previously proposed bi-objective heat switcher (Phys...
February 2, 2018: European Physical Journal. E, Soft Matter
Chunxi Li, Yuxi Lin, Ran Zhang, Xuemin Ye
A model for the evolution of two droplets laden with insoluble surfactant coalescing on a preset film is established according to the lubrication theory, and the coalescence processes are simulated. The role of the surfactant and its inherent mechanism are investigated, the effects of the Marangoni number, the preset liquid film thickness and the initial spacing between the two droplets on the coalescence are examined. The results show that the droplets encounter each other, gradually overlap, and finally coalesce into a "new" droplet...
January 31, 2018: European Physical Journal. E, Soft Matter
Vaibhav Wasnik
At the point of a second-order phase transition also termed as a critical point, systems display long-range order and their macroscopic behaviors are independent of the microscopic details making up the system. Due to these properties, it has long been speculated that biological systems that show similar behavior despite having very different microscopics, may be operating near a critical point. Recent methods in neuroscience are making it possible to explore whether criticality exists in neural networks. Despite being large in size, many datasets are only a minute sample of the neural system and methods have to be developed to expand these datasets to study criticality...
January 31, 2018: European Physical Journal. E, Soft Matter
Valery Ya Rudyak, Andrey V Minakov
This paper discusses the current state of knowledge of the thermophysical properties of nanofluids. The viscosity, thermal conductivity and heat transfer of nanofluids are considered. Experimental and molecular dynamics data are presented. It is shown that viscosity and thermal conductivity of nanofluids generally cannot be described by classical theories. The transport coefficients of nanofluids depend not only on the volume concentration of the particles but also on their size and material. The viscosity increases with decreasing the particle size while the thermal conductivity increases with increasing the particle size...
January 31, 2018: European Physical Journal. E, Soft Matter
Sutapa Mukherji
In this paper, we study through mathematical modelling the combined effect of transcriptional and translational regulation by proteins and small noncoding RNAs (sRNA) in a genetic feedback motif that has an important role in the survival of E. coli under stress associated with oxygen and energy availability. We show that subtle changes in this motif can bring in drastically different effects on the gene expression. In particular, we show that a threshold response in the gene expression changes to a bistable response as the regulation on sRNA synthesis or degradation is altered...
January 31, 2018: European Physical Journal. E, Soft Matter
Ram M Adar, David Andelman
The properties of ionic solutions between charged surfaces are often studied within the Poisson-Boltzmann framework, by finding the electrostatic potential profile. For example, the osmotic pressure between two charged planar surfaces can be evaluated by solving coupled equations for the electrostatic potential and osmotic pressure. Such a solution relies on symmetry arguments and is restricted to either equally or oppositely charged surfaces. Here, we provide a different and more efficient scheme to derive the osmotic pressure straightforwardly, without the need to find the electrostatic potential profile...
January 29, 2018: European Physical Journal. E, Soft Matter
P Grassia
The pressure-driven growth model for advance of a foam front through an oil reservoir during foam improved oil recovery is considered: specifically the limit of strong heterogeneity in the reservoir permeability is treated, such that permeability variation with depth more than outweighs the tendency of the net pressure driving the front to decay with depth. This means that the fastest moving part of the front is not at the top of the solution domain, but rather somewhere in the interior. Moreover the location of the foam front on the top boundary of the system can no longer be specified as a boundary condition, but instead must be determined as part of the solution of the problem...
January 25, 2018: European Physical Journal. E, Soft Matter
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