Plume neutralization of ionic liquid electrospray thruster: Better insights from Particle-in-cell modelling

Ionic liquid electrospray thrusters with high specific impulse, high thrust accuracy and low thrust noise are very promising for space gravitational wave detection missions. The plume which may lead to surface charging of solar panels and sensitive spacecraft components is a great concern for the applications of electrospray thruster. Therefore, this paper investigates the plume neutralization process of the ionic liquid electrospray thruster through fully kinetic Particle­in­cell simulations. The unipolarity operation mode is firstly simulated and compared with the experimental measurements. The bipolar operation mode is analyzed by considering the premixing and the separation of positive and negative ion beams. At the same time, the effect of beam spacing on the plume characteristics is investigated. The results show that the plume neutralization of the ionic liquid electrospray thruster is achieved by the spatial and temporal oscillations of the ion beams. In the horizontal direction, the spatial oscillations are caused by the different mass and hence velocities of positive and negative ions. In the vertical direction, the spatial oscillations are mainly because of the non-zero beam spacing. The temporal oscillations may be related to the charge separation induced by the different mass and hence velocities of positive and negative ions. As the beam spacing increases, the amplitude of the electric potential oscillations changes scarcely in the horizontal direction while increases in the vertical direction. The ion temperature goes up with the beam spacing and the deviation of the temperature of beam ions does not exceed 15 eV in the horizontal direction but exceeds 100 eV in the vertical direction. Moreover, the plume divergence half angle and the beam spacing are positively correlated, suggesting that the ionic electrospray thrusters with positive and negative polarity need to be placed as close as possible in the spacecraft.

Non-Hermitian indirect exchange interaction in a topological insulator coupled to a ferromagnetic metal

We theoretically demonstrate non-Hermitian indirect interaction between two magnetic impurities placed at the interface between a 3D topological insulator and a ferromagnetic metal. The coupling of topological insulator and the ferromagnet introduces not only Zeeman exchange field on the surface states but also broadening to transfer the charge and spin between the surface states of the topological insulator and the metallic states of the ferromagnet. While the former provides bandgap at the charge neutrality point, the latter causes non-Hermiticity. Using the Green’s function method, we calculate the range functions of magnetic impurity interactions. We show that the charge decay rate provides a coupling between evanescent modes near the bandgap and traveling modes near the band edge. However, the spin decay rate induces a stronger coupling than the charge decay rate so that higher energy traveling modes can be coupled to lower energy evanescent ones. This results in a non-monotonic behavior of the range functions in terms of distance and decay rates in the subgap regime. In the over gap regime, depending on the type of decay rate and on the distance, the amplitude of spatial oscillations would be damped or promoted.

MATHEMATICAL MODEL OF SPATIAL OSCILLATIONS OF A RAILWAY FOUR-AXLE AUTONOMOUS TRACTION MODULE

A description of the original mathematical model of spatial oscillations of a four-axle autonomous traction module during its movement along straight and curved sections of the railway track is proposed. In this case, the design of a four-axle autonomous traction module is presented as a complex mechanical system, and the track is considered as an elastic-viscous inertial system. The equations of motion were compiled using the Lagrange method of the ІІ kind. For each of the solids, the kinetic energy is determined by the Koenig theorem. The potential energy component is obtained by the Clapeyron theorem, as the sum of the energies accumulated in the elastic elements of the system during their deformations. The dissipative energy was also taken into account when compiling the equations of motion. Generalized forces that have no potential, in this case, include the forces of interaction between wheels and rails, which are determined using the creep hypothesis. It is important to note that the model takes into account the forces in the bonds between the bodies of the system and the spatial displacements of the rigid bodies of the mechanical system, taking into account possible restrictions. Moreover, the mathematical model developed by the author is a system of differential equations of the 100th order. This mathematical model is the base for further theoretical studies of the dynamics of railway four-axle autonomous traction modules in single motion or when moving as part of a train. To solve the resulting system of differential equations, the author develops special software that allows for complex theoretical studies of spatial oscillations of a four-axle autonomous tractionmodule to determine the indicators of its dynamic loading and traffic safety.

Theory of creation and practice of using vibrating machines for various technological purposes

The paper presents the results of the study of vibration machines for technological purposes. The theory of joint movement of working bodies of vibrating machines and the processed environments modeled by discrete-continuous systems is developed. The complex approach to the decision of a question of modeling of difficult dynamic systems with variable characteristics of elastic elements at realization of working process is considered. The parameters of resonant vibration systems with directional oscillations for surface compaction, polyphase oscillations and spatial oscillations are determined. The basic principles of such approach to the decision of a question of rational use of materials at designing of cars are resulted. New designs of machines and their components are offered. The data on researches which are introduced in educational process, normative documentation and in the industry are resulted.

Landscape-induced spatial oscillations in population dynamics

We study the effect that disturbances in the ecological landscape exert on the spatial distribution of a population that evolves according to the nonlocal FKPP equation. Using both numerical and analytical techniques, we characterize, as a function of the interaction kernel, the three types of stationary profiles that can develop near abrupt spatial variations in the environmental conditions vital for population growth: sustained oscillations, decaying oscillations and exponential relaxation towards a flat profile. Through the mapping between the features of the induced wrinkles and the shape of the interaction kernel, we discuss how heterogeneities can reveal information that would be hidden in a flat landscape.

Прототип протонного ондуляторного линейного ускорителя

One of the ways to realize undulator acceleration is to ensure particles motion in a magnetostatic undulator, where spatial oscillations of particles in the transverse direction are synchronized with temporal oscillations of transverse high-frequency field, which allows its energy transfer to the accelerated particles. The resonators, tcapable to provide a uniform transverse field, are structurally simpler than resonators with a periodically variable longitudinal field, which makes undulator accelerators an attractive alternative to coventional accelerators.Although the physics of such accelerators was previously descussed in the literature, the task of creating a physical prototype of undulator linac is still not realized. In this paper, we privde a practical description of the project of a proton undulator linear accelerator based on based on this principle, developed by RadiaBeam (USA).

Analysis of the effect of wheel–rail pair contact surface wear on the oscillations of a freight car with an increased axle load

At present, nearly all countries of the world develop and implement measures aimed to increase the competitiveness and efficiency of their railways. One of the priority lines is to increase the carrying capacity of freight trains. In Ukraine, 18-9817 trucks of axle load 25 tf were developed and adopted as basic ones for new-generation freight cars, and the ITM-73-03 wear-resistant wheel profile of flange thickness 32 mm was developed for them too. The aim of this paper is to study the effect of in-service variation in the wheel and rail profile shape on the spatial oscillations of a freight car with 18-9817 trucks and the ITM-73-03 wheel profile. The paper estimates the effect of in-service variation in the wheel and rail profile shape on the dynamic stability and ride performance of the car under consideration. The wear of wheels with the new profile is predicted by solving the geometrical problem of wheel–rail interaction with account for the mutual horizontal lateral displacements of the wheel and the rail, the wheelset angle of attack and angle of roll, the nonlinearity of the contacting surfaces, and the possibility of their conformal contact. The results of calculation of the spatial oscillations of the car in tangents and curves are presented. It is shown that wear-caused variation in the wheel and rail profile shape has little effect of the dynamic performance of a new-generation freight car with 18-9817 trucks with an increased axle load and the ITM-73-03 wear-resistant wheel profile, its dynamic stability and ride performance remaining at a high level. The use of the above car on the Ukrainian railways fully meets the objectives of home rolling stock renewal: vehicle ride performance improvement, running gear life extension, and vehicle and track wear reduction

Mixed Oscillation Flow of Binary Fluid with Minus One Capillary Ratio in the Czochralski Crystal Growth Model

This work presented a series of three-dimensional unsteady numerical simulations on the characteristics of the mixed oscillation flows of binary mixture in a Czochralski crystal growth model. The silicon-germanium melt is investigated and the capillary ratio is minus one. The simulation results showed that, for the special capillary ratio, the thermal and solutocapillary forces are imposed in opposite directions and counteract each other. With the effect of buoyancy, the balance between the capillary forces is disturbed. Mixed with the forced convection driven by rotation, the capillary-buoyancy convection is complex. The basic mixed flow streamlines are presented as various rolling cells. The directions of the rolls are dependent on the combinations of surface and body forces. With the increase of temperature gradient, the basic flow stability is broken, and the oscillations occur. The crucible rotation has an effective influence on the stability enhancement. However, affected by the crystal rotation, the critical condition experiences an increase to a turning point, and then undergoes a sharp reduction to zero. Once the instability is incubated, the surface oscillations are analyzed. For the three-dimensional steady flow, only spatial oscillations are observed circumferentially, and the surface patterns of spokes, rosebud, and pulsating ring are obtained. For the unsteady oscillation flow, the spiral hydrosoultal waves, rotating waves, and superimposition of spirals and spokes are observed, and the oscillation behaviors are also discussed.