Symmetry properties and bifurcations of viscoelastic thermovibrational convection in a square cavity.

To fill a gap in the literature about the specific dynamics of thermovibrational flow in a square cavity filled with a viscoelastic fluid when vibrations and the imposed temperature gradient are concurrent, a parametric investigation has been conducted to investigate the response of this system over a relatively wide subregion of the space of parameters (Pr_{g}=10; viscosity ratio ξ=0.5; nondimensional frequency Ω=25, 50, 75, and 100; and Ra_{ω}∈[Ra_{ω,cr},3.3×10^{4}], where Ra_{ω,cr} is the critical vibrational Rayleigh number).

Competing particle attractee in liquid bridges.

Assuming the so-called particle accumulation structures (PAS) in liquid bridges as archetypal systems for the investigation of particle self-assembly phenomena in laminar time-periodic flows, an attempt is made here to disentangle the complex hierarchy of relationships existing between the multiplicity of the loci of aggregation (streamtubes which coexist in the physical space as competing attractee) and the particle structures effectively showing up. While the former depends on purely topological (fluid-dynamic) arguments, the influential factors driving the outcomes of the fluid-particle interaction seem to obey a much more complex logic, which makes the arrangement of particles different from realization to realization. Through numerical solution of the governing Eulerian and Lagrangian equations for liquid and mass transport, we show that for a fixed aspect ratio of the liquid bridge, particles can be gradually transferred from one streamtube to another as the Stokes number and/or the Marangoni number are varied.

Two-dimensional vibrationally driven solid particle structures in non-uniformly heated fluid containers.

Building on a pre-existing line of inquiry where the presence of solid particle attractors in thermovibrationally driven flows was demonstrated in cavities subjected to a unidirectional temperature gradient, the present work considers cases where the direction of such a gradient is allowed to change inside the fluid. Moreover, the considered configurations differ with regard to the angle that vibrations form with respect to a reference axis. Variations in the orientation of the temperature gradient are made possible by setting a non-uniform temperature distribution along certain walls.

Competition of overstability and stabilizing effects in viscoelastic thermovibrational flow.

Attention is paid to a specific form of thermal convection which encompasses viscoelastic and thermovibrational effects in a single problem or framework. The main objective is understanding the relationship between the phenomenon of overstability and periodic forcing through numerical solution of the governing equations in their complete, time-dependent, and nonlinear form. Fluid motion is found for values of the control parameter one order of magnitude smaller than the threshold to be exceeded in the equivalent Newtonian case.

Three-dimensional simulation of clouds of multi-disperse evaporating saliva droplets in a train cabin.

In line with recent ongoing efforts to collect crucial information about the mechanisms of virus diffusion and put them in relation to the effective complexity of the several natural or artificial environments where human beings leave and operate, the present study deals with the dispersion of evaporating saliva droplets in the cabin of an interregional train. A relevant physical model is constructed taking into account the state of the art in terms of existing paradigms and their ability to represent some fundamental aspects related to the evolution in time of a cloud of multi-disperse droplets. Conveniently, such a theoretical framework is turned into a computational one that relies on low Mach-number asymptotics and can therefore take advantage of the typical benefits (relatively low computational cost) associated with pressure-based methods.

Gravitational thermal flows of liquid metals in 3D variable cross-section containers: Transition from low-dimensional to high-dimensional chaos.

This study extends the numerical results presented in author's past work [M. Lappa and H. Ferialdi, Phys.

Patterning behavior of gravitationally modulated supercritical Marangoni flow in liquid layers.

The objective of the present analysis is the investigation of hybrid convection induced by the joint influence of imposed vibrations (g-jitters) of desired amplitude and frequency and surface-tension-induced forces in a nonisothermal liquid layer. This study may be regarded as the natural extension of an earlier work [V. M.

On the existence and multiplicity of one-dimensional solid particle attractors in time-dependent Rayleigh-Bénard convection.

For the first time evidence is provided that one-dimensional objects formed by the accumulation of tracer particles can emerge in flows of thermogravitational nature (in the region of the space of parameters, in which the so-called OS (oscillatory solution) flow of the Busse balloon represents the dominant secondary mode of convection). Such structures appear as seemingly rigid filaments, rotating without changing their shape. The most interesting (heretofore unseen) feature of such a class of physical attractors is their variety.

Placenta perfusion has hematopoietic and mesenchymal progenitor stem cell potential.

Background: Placenta is a valuable source of stem cells for cell therapy and future application in the field of regenerative medicine. This is due to the plasticity and the immunomodulatory effects of the stem cells that it contains. In this study we present a totally closed method for hematopoietic and nonhematopoietic stem cell isolation from human term placenta.

Discrete layers of interacting growing protein seeds: convective and morphological stages of evolution.

The growth of several macromolecular seeds uniformly distributed on the bottom of a protein reactor (i.e., a discrete layer of N crystals embedded within a horizontal layer of liquid with no-slip boundaries) under microgravity conditions is investigated for different values of N and for two values of the geometrical aspect ratio of the container.

A CFD level-set method for soft tissue growth: theory and fundamental equations.

A level-set method, specifically conceived for the case of soft organic tissue growth from feeding solutions, is introduced and described in detail. The model can handle the morphological evolution of the organic specimen under the influence of external convection (fluid-dynamics of the bioreactor). The analogies and differences between this technique and a previous volume of fraction method are discussed pointing out advantages and limitations of both formulations.

Effect of convective disturbances induced by g-jitter on the periodic precipitation of lysozyme.

Numerical simulations are carried out to investigate the crystallization process of a protein macromolecular substance under two different conditions: pure diffusive regime and microgravity conditions present on space laboratories. The configuration under investigation consists of a protein reactor and a salt chamber separated by an "interface". The interface is strictly related to the presence of agarose gel in one of the two chambers.

Organic tissues in rotating bioreactors: fluid-mechanical aspects, dynamic growth models, and morphological evolution.

This analysis deals with advances in tissue-engineering models and computational methods as well as with novel results on the relative importance of "controlling forces" in the growth of organic constructs. Specifically, attention is focused on the rotary culture system, because this technique has proven to be the most practical solution for providing a suitable culture environment supporting three-dimensional tissue assemblies. From a numerical point of view, the growing biological specimen gives rise to a moving boundary problem.

The growth and the fluid dynamics of protein crystals and soft organic tissues: models and simulations, similarities and differences.

The fluid-dynamic environment within typical growth reactors as well as the interaction of such flow with the intrinsic kinetics of the growth process are investigated in the frame of the new fields of protein crystal and tissue engineering. The paper uses available data to introduce a set of novel growth models. The surface conditions are coupled to the exchange mass flux at the specimen/culture-medium interface and lead to the introduction of a group of differential equations for the nutrient concentration around the sample and for the evolution of the construct mass displacement.

Numerical and experimental analysis of periodic patterns and sedimentation of lysozyme.

This paper deals with experimental investigation, mathematical modelling and numerical simulation of the crystallization processes induced by counter diffusion method of a precipitant agent in a lysozyme protein solution. Novel mathematical strategies are introduced to simulate the experiments and in particular to take into account the kinetics of the growth process and the motion of the crystals due to the combined effect of gravitational force and viscous drag if the sedimenting process is allowed (protein chamber free of gel). Comparison between experimental observations and numerical simulations in the presence of convection and sedimentation and without them provides a validation of the model.

Experimental observations and numerical modelling of diffusion-driven crystallisation processes.

This paper reports experimental results and modelling on the crystallisation processes induced by counter diffusion method of a precipitant agent in a lysozyme protein solution. Comparison between experimental observations and numerical simulations in the presence of convection and sedimentation and without them (suppressed using gel) provides a validation of the model. Different values of the initial protein concentration are used, in order to investigate the effects of supersaturation conditions on the process, and in particular on nucleation.