Springer最新文献

Quasi-stationary hydrodynamic flows have been studied in a small slowly evaporating hemispherical droplet with a pinned contact line on a flat horizontal substrate. Analytical solutions of the Stokes equations have been obtained and visualized for a capillary flow, which corresponds to the so-called “coffee-ring effect,” as well as for the Marangoni flow induced by a surface tension gradient associated with the cooling of the droplet surface due to the evaporation. The flow model corresponds to low Reynolds and Peclet numbers. The boundary conditions corresponding to the presence or absence of liquid slip at the substrate, which facilitate or hinder the Marangoni flow, have been analyzed. A hypothesis has been proposed that a critical Marangoni number corresponds to the system parameters that provide the separation of the flow from the substrate and the transition to the slip mode, in which the liquid velocity immediately at the substrate surface is nonzero. The obtained result can be used to study the flow structure and evaluate the flow rate in an evaporating microdroplet.

The electrostatic interaction of two identical charged dielectric spheroidal particles in a symmetric electrolyte solution has been considered. The finite element method has been used to calculate the repulsive forces between the particles by the Poisson–Boltzmann equation under the condition that their surface charge distribution is independent of the interparticle distance and there is no external electrostatic field. The charge distribution on the surface of each particle is assumed to coincide with that on an isolated individual particle at a given surface potential. It has been found that, depending on the Debye length and the distance between the particle surfaces, an increase in the longitudinal size of the particles upon the passage from oblate to prolate spheroids can either enhance or weaken the interaction force.

In this paper, we investigate the occurrence of Majorana zero modes in carbon nanotubes in contact with a conventional superconductor and placed in a longitudinal magnetic field. The influence of nanotube geometry, determined by chirality indices ((n,m)), on the conditions for the formation of the topological superconducting phase is considered. It is shown that chirality changes the electronic structure of the nanotube, the spin–orbit interaction and the effective chemical potential, which determine the conditions of the topological phase transition. To describe the system, an effective model based on the Bogolyubov–de Gennes Hamiltonian is constructed, which allows one to obtain a criterion for the occurrence of Majorana null modes. Based on the developed model, a method for selecting the most favorable geometries of carbon nanotubes is proposed. Numerical results show that certain chiralities minimize the effective chemical potential and facilitate the transition of the system to the topological phase. The obtained results show that the geometry of the carbon nanotube is an effective parameter for controlling the topological properties of the system and can serve as a criterion for choosing the chiralities that are most promising for the experimental implementation of Majorana zero modes.

An actuator rod (control device) is examined for the stability coefficient under a given load. It was found that commonly known calculation methods do not allow for the geometric features of the rod to be fully taken into account. To take into account the geometric features of the rod, a numerical experiment was carried out in the Compass APM FEM software environment. The numerical experiments conducted allow us to draw the following conclusions. When the ratio of the diameters of the inner hole to the diameter of the rod is 85%, as well as 71%, and when the ratio of the lengths of the inner hole to the length of the rod is from 100 to 31%, the presence of the inner hole greatly affects the safety factor, which varies in the range from 0.54 to 1.6. When the diameter ratio decreases, the length of the inner hole has virtually no effect on the safety factor, but in the range of length ratios from 100 to 50%, the safety factor is less than the recommended 1.8.

This study reports the structural, morphological, mechanical and dielectric behavior of solution-cast poly(methyl methacrylate) (PMMA) films containing trace fractions (0.5 and 1%) of polystyrene (PS). X-ray diffraction shows that all films are amorphous, exhibiting broad halos whose position reflects the average inter-chain spacing; PS incorporation shifts the halo slightly, indicating modestly looser chain packing rather than any crystalline change. FTIR and Raman spectroscopy reveal no new bands and only marginal shifts, confirming the absence of chemical bonding and consistent with the known immiscibility of PMMA and PS. Atomic force microscopy uncovers a composition-driven morphological transition: at 0.5% PS the surface develops a diffusion-limited dendritic network, which reorganizes into a phase-separated pore structure at 1%. Microhardness varies systematically with composition, and dielectric spectroscopy shows that ε′, ε″ and tanδ change measurably with PS content, which we attribute to interfacial polarization at the phase-separated domains. The results establish trace-PS addition as a simple route to tune the morphology and permittivity of PMMA films for dielectric-coating and flexible electronic applications.

A theory has been developed for nanodispersion of a simple liquid under the conditions of thermal evaporation in a supersaturated medium and ultrasonic cavitation. The proposed theory takes into account the size dependence of surface tension. It has been shown that accounting for this dependence decreases the energy barrier of nucleation and the critical nucleus radius, while causing a significant asymmetry in the kinetics of the growth and evaporation of nanodroplets. The modified Rayleigh–Plesset equation has been used to show that the size dependence of the surface tension increases the capillary stiffness of a bubble, suppresses chaotic regimes, and preserves the scale-invariant (fractal) structure of cavitation oscillations. A new criterion has been obtained for the disappearance of the nucleation barrier. It has been shown that, under real conditions of ultrasonic cavitation, the supersaturation reaches values sufficiently high for the transition to the spinodal regime of spontaneous phase separation and the formation of nanodroplets (1–3 nm in size) without an activation delay.

A new neurodynamic model for joint optimization of the traveling salesman problem route and fuzzy cluster partitioning of a set of vertices is proposed. The model’s energy function includes three components: a Hopfield-Tank term encoding route feasibility constraints; a fuzzy means term ensuring geometric compactness of clusters; and a topological matching term penalizing for discontinuities in cluster membership between adjacent vertices along the route. An iterative minimization scheme is developed. The following convergence properties are proven: monotonic energy decrease and convergence of the energy sequence to a limit value. Computational experiments on a test example showed that the proposed model finds solutions that coincide with the global optimum, while the resulting clusters differ significantly from the results of the classical fuzzy c-means algorithm, reflecting the topology of the optimal route. The results of the study can be used for problems of delivery territory zoning, production operation planning, and condensation of large factor models.

The paper presents a methodology for experimental research and a test bench for determining the flow coefficient during the flow of a two-phase working fluid through cracks. The dependences of the influence of the degree of dryness of the wet refrigerant vapor and the gap resistance on the flow coefficient during the outflow of the working fluid through the gap were established. A method for determining the coefficient of flow of wet vapor through cracks is proposed, implemented on the basis of the method of S.E. Zakharenko for dry saturated vapor and a correction function for the degree of dryness of the vapor. Artificial refrigerants used in air conditioning systems, such as R32 and R410a, which belong to the HFC class, and R22, which belongs to the HCFC class, are considered as the working fluid.