Nanofluid bioconvection in water-based suspensions containing nanoparticles and oxytactic microorganisms: oscillatory instability

The aim of this article is to propose a novel type of a nanofluid that contains both nanoparticles and motile (oxytactic) microorganisms. The benefits of adding motile microorganisms to the suspension include enhanced mass transfer, microscale mixing, and anticipated improved stability of the nanofluid. In order to understand the behavior of such a suspension at the fundamental level, this article investigates its stability when it occupies a shallow horizontal layer. The oscillatory mode of nanofluid bioconvection may be induced by the interaction of three competing agencies: oxytactic microorganisms, heating or cooling from the bottom, and top or bottom-heavy nanoparticle distribution. The model includes equations expressing conservation of total mass, momentum, thermal energy, nanoparticles, microorganisms, and oxygen. Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model. An approximate analytical solution of the eigenvalue problem is obtained using the Galerkin method. The obtained solution provides important physical insights into the behavior of this system; it also explains when the oscillatory mode of instability is possible in such system

Magnetostatic response and field-controlled haloing in binary superparamagnetic mixtures

The work is devoted to the theoretical and numerical analysis of a two-component superparamagnetic system. Namely, of a rigid superparamagnetic cluster embedded in a superparamagnetic medium and subjected to a uniform magnetic field. Both cluster and the medium contain single-domain nanoparticles of the same diameter and magnetic moment. But the concentration of nanoparticles within the cluster is higher than that in the surrounding medium. Equilibrium magnetic response of the system in wide ranges of concentrations and interaction energies is calculated using Langevin dynamics simulations. Corresponding theoretical predictions are obtained within the analytical framework, previously developed for ferrofluid emulsions. The framework is proven to be accurate in the case when nanoparticles of the medium are immobilized. However, if particles are subjected to a translational Brownian motion, the applied field causes their local redistribution in the cluster vicinity. This behavior is reminiscent of the so-called ``haloing'' effect previously observed experimentally in bimodal magnetorheological fluids. It is shown that the haloing can lead to an anomalous increase of the system magnetization at large enough applied fields.Comment: 11 pages, 7 figure

Automation of Synthesis of Structures, Systems Engineering Strategies for Production

AbstractThe article describes an automated system of support of decision-making structures in the synthesis strategies of industrial engineering systems, based on the method of structural and technological complexity of produced parts. This paper critically evaluates various tool management approaches, identifying the operational tradeoffs and analyzing the models developed to address management decisions involving tooling. The evidence is clear that a lack of attention to structured tool management has resulted in the poor performance of many manufacturing systems. Plant tooling systems affect product design options, machine loading, job batching, capacity scheduling, and real-time part routing decisions. With increasing automation in manufacturing systems, there is a growing need to integrate tool management more thoroughly into system design, planning and control