Magnetic drive micro/nanomotor model

A model of a micro-/nanomotor with a hydrodynamic mechanism of motion due to the action of a rotating uniform external magnetic field is proposed. Micro-/nanomotor - is a chain of three charged particles, one of which has a magnetic moment. The total charge of the system is zero. In the absence of an external field, the particles are in equilibrium due to the action of the forces of attraction and repulsion, which corresponds to the minimum interaction energy. After applying a rotating magnetic field, a particle with a magnetic moment begins to rotate, forming a flow in the surrounding viscous fluid. The flow induces a hydrodynamic force that moves the chain in a specific direction. The forces of hydrodynamic interaction of particles with each other are taken into account, as well as internal forces holding the particles together. The dynamics of six model aggregates with one rotating particle is simulated numerically. The proposed mechanism for moving the chain can be used in the design of micro-/nanomotors and control them to deliver the payload.

10.15507/2079-6900.23.202101.91–109

A hydrodynamic mechanism of movement of a micro/nanomotor with a dipole charge induced by an electro-catalytic reaction on its surface and the formation of charges in the surrounding liquid is proposed. For this, the dynamics of a dipole aggregate in a cloud of small oppositely charged particles in a viscous fluid surrounding it is simulated. Under the action of the field of the aggregate, the particles in the cloud are set in motion, which forms a flow in the surrounding fluid. In turn, the flow creates a hydrodynamic force that moves the aggregate. The hydrodynamic interaction of all particles in the cloud with each other and with the dipole aggregate is taken into account at their different distributions in the liquid around the dipole. The total charge of all small particles can be either equal to zero or have a non-zero value. The calculations carried out confirmed the possibility of the dipole unit to move in all the cases considered as a result of action of the hydrodynamic force created by the formed flow of the surrounding fluid. In this case, the speed and direction of dipole movement significantly depends both on the distribution of small particles in the surrounding liquid and on their total charge. As the result of asymmetry in the distribution of small charged particles in the surrounding fluid, dipole unit will move not only in longitudinal but also in transverse direction. This leads to the need to use some mechanism of controlling its movement. As such a mechanism the action of an external field can be used, orienting the dipole unit in a given direction of motion. It is proposed to use an external magnetic field for such control. In this case, the dipole aggregate must have a magnetic moment due to the presence of a magnetizable nucleus inside the particles.

Centering and symmetry breaking in confined contracting actomyosin networks

Centering and decentering of cellular components is essential for internal organization of cells and their ability to perform basic cellular functions such as division and motility. How cells achieve proper localization of their organelles is still not well-understood, especially in large cells such as oocytes. Here, we study actin-based positioning mechanisms in artificial cells with persistently contracting actomyosin networks, generated by encapsulating cytoplasmic Xenopus egg extracts into cell-sized ‘water-in-oil’ droplets. We observe size-dependent localization of the contraction center, with a symmetric configuration in larger cells and a polar one in smaller cells. Centering is achieved via a hydrodynamic mechanism based on Darcy friction between the contracting network and the surrounding cytoplasm. During symmetry breaking, transient attachments to the cell boundary drive the contraction center to a polar location. The centering mechanism is cell-cycle dependent and weakens considerably during interphase. Our findings demonstrate a robust, yet tunable, mechanism for subcellular localization.

Вклад силы присоединенных масс в формирование пропульсивной силы машущего профиля в вязкой жидкости

In the light of the recently proved general theorem on the added mass of bodies in a viscous incompressible fluid, the mechanism of the formation of the propulsive force of the flapping airfoil, which performs harmonic angular oscillations in the flow of a continuous medium, is investigated. The flow is described by the Navier-Stokes equations. The calculations were performed by a meshless numerical method of viscous vortex domains. The mechanism of the formation of a reversed vortex track in the wake behind the flapping profile in the positive traction mode is explained. The dominant contribution of the force of the added masses to the value of the propulsive force is revealed. The results obtained to some extent reveal the hydrodynamic mechanism of action of the caudal fin of underwater creatures.

On the Mechanism of Atmospheric Vortex Formation and How to Weaken a Tornado

A hydrodynamic mechanism of tornado formation is proposed: it is based on the air density decrease in ascending jets. The empirical verification of this mechanism is considered. The ways are discussed to weaken the tornado by reducing the inflow streams humidity or by introducing the discontinuity of air jets connecting the lower and upper layers of the atmosphere.

Hydrodynamic effect of non-closed elliptical grooves of bi-directional rotation gas face seals

Purpose The purpose of this paper is to improve opening performance of bi-directional rotation gas face seals by investigating the hydrodynamic effect of non-closed elliptical grooves. Design/methodology/approach A model of non-closed elliptical groove bi-directional rotation gas face seal is developed. The distribution of lubricating film pressure is obtained by solving gas Reynolds equations with the finite difference method. The program iterates repeatedly until the convergence criterion on the opening force is satisfied, and the sealing performance is finally obtained. Findings Non-closed elliptical groove presents much stronger hydrodynamic effect than the closed groove because of drop of the gas resistance flowing into grooves. Besides, the non-closed elliptical groove presents significant hydrodynamic effect under bi-directional rotation conditions, and an increase of over 40 per cent is obtained for the opening force at seal pressure 4.5 MPa, as same level as the unidirectional spiral groove gas seal. In the case of bi-directional rotation, the value of the inclination angle is recommended to set as 90° presenting a structure symmetry so as to keep best opening performance for both positive and reverse rotation. Originality/value A model of non-closed elliptical groove bi-directional rotation gas face seal is established. The hydrodynamic mechanism of this gas seal is illustrated. Parametric investigation of inclination angle and integrity rate is presented for the non-closed elliptical groove bi-directional rotation gas face seal.