Azimuthal Motion Research Articles

Вращение плазменной струи высокочастотными электромагнитными полями и ее использование для масс-сепарации

Equations are obtained that describe the characteristics of the azimuthal motion and radial expansion of a plasma jet under the action of a rotating transverse magnetic field of a dipole configuration in a longitudinal static magnetic field. The analysis was carried out both in the multicomponent approximation and on the basis of MHD equations taking into account the Hall effect. Based on the obtained dependences of the azimuthal and radial ion velocities on the magnetic field values, the separation characteristics of the direct-flow plasma centrifuge are estimated for the separation of a two-component binary mixture simulating spent nuclear fuel. It was shown that the concentration of the heavy uranium-plutonium component in the product flow can be increased from the initial 96 to 99.8% with a fuel component extraction of 0.87.

Mm-Pose: Real-Time Human Skeletal Posture Estimation Using mmWave Radars and CNNs

In this paper, mm-Pose, a novel approach to detect and track human skeletons in real-time using an mmWave radar, is proposed. To the best of the authors' knowledge, this is the first method to detect >15 distinct skeletal joints using mmWave radar reflection signals. The proposed method would find several applications in traffic monitoring systems, autonomous vehicles, patient monitoring systems and defense forces to detect and track human skeleton for effective and preventive decision making in real-time. The use of radar makes the system operationally robust to scene lighting and adverse weather conditions. The reflected radar point cloud in range, azimuth and elevation are first resolved and projected in Range-Azimuth and Range-Elevation planes. A novel low-size high-resolution radar-to-image representation is also presented, that overcomes the sparsity in traditional point cloud data and offers significant reduction in the subsequent machine learning architecture. The RGB channels were assigned with the normalized values of range, elevation/azimuth and the power level of the reflection signals for each of the points. A forked CNN architecture was used to predict the real-world position of the skeletal joints in 3-D space, using the radar-to-image representation. The proposed method was tested for a single human scenario for four primary motions, (i) Walking, (ii) Swinging left arm, (iii) Swinging right arm, and (iv) Swinging both arms to validate accurate predictions for motion in range, azimuth and elevation. The detailed methodology, implementation, challenges, and validation results are presented.

Gödel spacetime: Planar geodesics and gyroscope precession

We study elliptic-like geodesic motion on hyperplanes orthogonal to the cylindrical symmetry axes of the Godel spacetime by using an eccentricity-semi-latus rectum parametrization which is familiar from the Newtonian description of a two-body system. We compute several quantities which summarize the main features of the motion, namely the coordinate time and proper time periods of the radial motion, the frequency of the azimuthal motion, the full variation of the azimuthal angle over a period, etc. Exact as well as approximate (i.e., Taylor-expanded in the limit of small eccentricity) analytic expressions of all these quantities are obtained. Finally, we consider their application to the gyroscope precession frequency along these orbits, generalizing the existing results for the circular case.

Transient flows and reorientations of large-scale convection in a cubic cell

The transient processes of a turbulent large-scale convective circulation (LSC) in a cubic cell are investigated using large-eddy simulations for Rayleigh number Ra = 108 and Prandtl number Pr = 0.7. For the first time, we have explicitly shown that LSC is accompanied by large-scale azimuthal flows with non-zero total angular momentum. It is also shown that solid-body rotation of the entire fluid is not realized. It is found that correlation between rotation of LSC plane and the mean azimuthal motion is high during quasiperiodic oscillations of LSC near the diagonal plane and relatively weak during LSC reorientations. We propose a new plausible scenario for the reorientations of the LSC in a cube that does not involve a mean azimuthal flow. Instead of a single-roll, we introduce the superposition of a pair of large-scale orthogonal quasi-two-dimensional (Q2D) rolls and the reorientation of the LSC occurs as a result of the cessation of one of the Q2D rolls. This scenario is consistent with all known experimental and numerical data.

A stable added-mass partitioned (AMP) algorithm for elastic solids and incompressible flow

A stable added-mass partitioned (AMP) algorithm is developed for fluid-structure interaction (FSI) problems coupling viscous incompressible flow and compressible elastic solids. The hyperbolic system governing the solid is integrated using an explicit upwind (Godunov) scheme. The equations for the fluid are integrated using an implicit-explicit (IMEX) fractional-step scheme whereby the velocity is advanced in one step, treating the viscous terms implicitly, and the pressure is computed in a second step. The AMP interface conditions for the fluid arise from the outgoing characteristic variables in the solid, and they are partitioned into a Robin (mixed) interface condition for the pressure and interface conditions for the velocity. The latter conditions include an impedance-weighted average between fluid and solid velocities using a fluid impedance of a special form. A similar impedance-weighted average is used to define interface values for the solid. Deforming composite grids are used to effectively handle the evolving geometry and large deformations. The new algorithm is verified for accuracy and stability on a number of useful benchmark problems in two space dimensions, including a radial-piston problem for which exact solutions for radial and azimuthal motions are found and tested. Exact traveling wave solutions for a solid disk surrounded by an annular region of fluid are also derived and used to verify the AMP scheme. Fluid flow in a channel past a deformable solid annulus is computed, and the errors are estimated from a self-convergence grid refinement study. The AMP scheme is found to be stable and second-order accurate, without sub-time-step iterations, even for very difficult cases of very light solids when added-mass and added-damping effects are large.

$\boldsymbol{E}\times\boldsymbol{B}$ Drift of Electrons in a Radial Electric Field and Longitudinal Magnetic Field

To examine the effect of the radial electric field on the electron rotational motion under ${E}\times {B}$ field, particularly $E_{r} \times B_{z}$ geometry, for a plasma with magnetized electrons and nonmagnetized ions flowing through a uniform magnetic channel, an experimental study is conducted by applying a steady-state plasma flow along the uniform longitudinal magnetic field $B_{z}$ . The argon plasma flow is generated by atmospheric-pressure dc arc discharge, followed by a continuous expansion into a rarefied gas-wind tunnel with a uniform magnetic field 0.15 T. Inside one of the magnets which is situated at rather a downstream position, a ring electrode is set to apply the radial electric field $E_{r}$ . An up–down probe is employed for the analysis of the electron azimuthal rotational motion. The value of the radial electric field applied in the plasma is about ~150 V/m. The probe measurement indicates the ${E}\times {B}$ rotation of electrons, particularly when the radially inward electric field is externally applied, whose order is about ~1000 m/s. The inward electric field results in the electron rotational motion in the same direction as the diamagnetic current. On the other hand, when the outward electric field is applied, the electron rotational motion is not observed. The order of the observed electron drift velocity is consistent with the theoretical value. ${E}\times {B}$ rotation velocity is found to be almost equal to that by the electron diamagnetic current. Even without the external electric field, the observed electron saturation current indicates that there is a rotational motion of electrons, which is considered to be due to the electron diamagnetic current.

The spontaneous breaking of axisymmetry in shallow rotating flows

We show that the axial symmetry of a shallow rotating flow is spontaneously broken in the absence of an externally forced velocity gradient. It is caused by an instability excited by the gradients that arise from the axisymmetric counter-rotating vortices. The experimental setup consists of an electrolyte poured into a cylindrical container with radius R and height h and subject to electromagnetic forcing caused by an axial magnetic field and a radial current (J) leading to an azimuthal rotation Vθ. The flow motion is considered to be two-dimensional at large aspect ratio (R/h) and low Reynolds number, Re = Vθh/ν, where ν is the kinematic viscosity. At a moderate aspect ratio, we record the existence of an axisymmetric vortex at the edge caused by the no-slip boundary condition at the walls. When Re is increased by changing h or J, the flow becomes unstable at the radial position where gradients exist due to the edge vortices at a critical Reynolds number of about 220. The most unstable mode of this nonaxisymmetric instability is found to be m = 1 followed by m = 2 and other higher mode numbers. Using perturbation theory, we found that two counter-rotating vortices that are in azimuthal motion are unstable when subject to nonaxisymmetric perturbations with the onset of low azimuthal mode numbers in agreement with the experiment. We conclude that the axial symmetry breaking in shallow rotating flows occurs at relatively low Reynolds numbers caused by the gradients generated by the vortices in the height-radial plane.

Passive solar tracker based in the differential thermal expansion of vertical strips

This paper presents a multiple axis passive solar tracking concept that takes advantage of the thermal expansion induced length variation of a material when exposed to sunshine. The differential expansion of three vertical thin flat strips with different orientations is amplified by a lever system to enable tracking of the apparent motion of the sun in the sky. A passive solar tracking system prototype supporting a photovoltaic (PV) module was built and tested. The model and experimental results show that the tracking system can correctly follow the azimuthal motion during the day. The tracking of solar elevation is less pronounced. The use of this tracking system leads to a 28% increase in PV generation during the testing period.

Synchrotron radiography characterization of the liquid core dynamics in a canonical two-fluid coaxial atomizer

The liquid core of a canonical two-fluid coaxial atomizer has been characterized using synchrotron X-rays. The high energy photons allow for high-speed imaging of attenuation through the dense liquid-gas jet core, resolving the internal structures that include entrapped air bubbles and the formation of liquid ligaments and bags. When the gas-to-liquid momentum ratio increases, the liquid core transitions from an intact column, where primary break-up happens several liquid diameters downstream, to a hollow crown with a downstream span comparable to the liquid diameter that disintegrates by shedding ligaments from its rim. At high gas momentum ratios (limited by the sonic velocity at the gas nozzle exit), this crown suffers partial dewetting and, when angular momentum is added to the gas, it dewets on a large section of the liquid injection needle circumference. This partial crown exhibits azimuthal motions along the circumference, on timescales much longer than the relevant flow timescales. The crown attachment to the liquid needle presents a bi-stable nature. The dramatic changes of the liquid core morphology, as the gas momentum and swirl ratios vary, have a strong impact on the gas-liquid boundary layers, which control the liquid break-up mechanisms and the resulting spray characteristics, such as droplet size distributions and the droplet volume fraction across the spray.

Surface Heat Dissipation Dependence of Thermocapillary Convection of Moderate Prandtl Number Fluid in an Annular Pool

In order to understand surface heat dissipation dependence of thermocapillary convection for moderate Prandtl number fluid in a deep annular pool, a series of three-dimensional numerical simulations have been carried out by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are fixed at 0.5 and 1.0, respectively. The working fluid is 0.65cSt silicone oil with Prandtl number of 6.7. Surface heat dissipation Biot (Bi) number is varied from 0 to 50. Results indicate that with the increase of Biot number, the radial temperature gradient near the inner cylindrical wall decreases, and near the outer cylindrical wall it increases, so the flow is enhanced. When 0 < Bi < 10, with the increase of Marangoni number, the axisymmetric steady flow first transits to the standing wave, and then to the azimuthal waves. The standing wave should be attributed to Marangoni-Benard instability. However, the azimuthal waves should be corresponded to hydraulic instability, which is mainly driven by the azimuthal motion of temperature fluctuation from the sudden change of flow direction near the bottom and the inner cylindrical wall. When Bi ≥ 10, when the flow destabilizes, the axisymmetric steady flow transits directly to the azimuthal waves. With the increase of Biot number, the critical Marangoni number of the flow destabilization increases. Furthermore, the fundamental frequency and the wave number of three-dimensional oscillatory flow increase gradually with the increase of Biot number.

The Primordial Solar Wind as a Sculptor of Terrestrial Planet Formation

Abstract Our solar system is almost entirely devoid of material interior to Mercury’s orbit, in sharp contrast to the multiple Earth masses of material commonly residing within the analogous region of extrasolar planetary systems. Recent work has suggested that Jupiter’s orbital migration early in the solar system’s history fragmented primordial planetary material within the inner solar system. However, the reason for the absence of subsequent planet formation within 0.4 au remains unsolved. Here, we show that leftover debris interior to Mercury’s current orbit was susceptible to outward migration driven by the early Solar wind, enhanced by the Sun’s primordial rapid rotation and strong magnetic field. The ram pressure arising from azimuthal motion of the Solar wind plasma transported ∼100 m-sized objects and smaller from 0.1 au out to the terrestrial planet-forming zone within the suspected ∼30–50 Myr timespan of the Earth’s formation. The mass of material within this size class typically exceeds Mercury, and can rival that of Earth. Consequently, the present-day region of terrestrial planets and the asteroid belt has been supplied by a large mass of material from the innermost, hot solar system, providing a potential explanation for the evidence of high-temperature alteration within some asteroids and the high iron content of Mercury.

Transverse motions of a single sphere in hanging or swing configurations under a longitudinal flow

As a result of the reporting of casual observations of the oscillation or rotation of the beacons in transmission line guard cables, some attention has been paid to the stability of the guard cables with beacons.The relatively more frequent observation of these motions has been explained in recent papers dealing with the elastic part of the problem as a consequence of the increasing number of resonant frequencies (one for each additional beacon) that can be excited by appropriate aerodynamic loads. But a model that could explain the aerodynamic forces that can give rise to this motion is still lacking.In this paper we consider the transverse motions of a single sphere in two simplified configurations, (1) hanging (tethered at one point), and (2) swing (tethered at two points) under a longitudinal flow, performing small amplitude swinging oscillations or circular-orbit autorotation about an axis parallel to the main flow direction. The dynamic model here presented is based on the motion equations, which also include a model for the aerodynamic lift and drag forces on the sphere in transverse motion, which considers the effect of changes of flow around the sphere due to the cable interference. These forces are contained in the symmetry plane of the flow relative to the sphere, and, when projected on the lateral direction, give rise to a lateral force, which can explain the existence of the azimuthal motion even at a large reduced velocity, outside the vortex induced vibration (VIV) range The conditions for stable small oscillation motion and circular-orbit autorotation of a sphere in a swing configuration are given.The results for the aerodynamic loads in transverse motion have also been applied to the case of a circular-orbit autorotation of a hanging sphere (spherical pendulum) under a vertical flow. The angular rotation speed and the orbit radius (or cable angle) have been determined as a function of aerodynamic coefficients and configuration parameters.

Effect of the Azimuthal Inhomogeneity of Beam Density on the Dynamics of Electron Bunches in Multiwave Cherenkov Oscillators

Data obtained in a series of computational experiments are used to study features of the formation of charged-particle bunches with strong azimuthal density inhomogeneity of the annular relativistic electron beam in multiwave Cherenkov oscillators. It is shown that the azimuthal motion of particles is negligible under the chosen parameter values. The oscillator radiation remains coherent.

Role of inertial forces in flame-flow interaction during premixed swirl flame flashback

This study investigates the flame-flow interaction during a fully-premixed swirl flame flashback from flame-frame-of-reference. To capture the flame front movement during upstream propagation, high-speed chemiluminescence imaging and simultaneous three-component PIV measurements are taken at 4 kHz. The upstream propagation of the flame occurs along a helical path around the center-body. For low-turbulence and high-swirl conditions (Reh = 4000, Swirl number ∼ 0.9), the lab-frame speed of the flame structure remains nearly constant during the period of investigation. Simultaneously, the leading side of the flame tongue retains its topology during propagation. The steady-state propagation behavior of the flame structure and stationarity of the flame topology allows us to make a frozen-flame-surface assumption. Applying space-time equivalence, the three-dimensional flame surface and flow field are reconstructed by shifting and stacking the time-series of the planar flame front profiles and the three-component planar velocity data. Further, the steady flow in the flame frame-of-reference provides a powerful means of investigating the flame-flow interaction. Quasi-pathlines are constructed in the unburnt and burnt regions of the flow field. The motion of the approach flow along a quasi-pathline is analyzed to understand the role of centrifugal and Coriolis forces. It is shown that the tug-of-war situation between Coriolis and centrifugal forces gets disrupted by the dilatation-driven blockage effect from the flame surface. It leads to a radial deflection of the approach flow, which results in reduction in the flame-normal approach flow speed, thereby assisting in the flame propagation. In the burnt gas, the Coriolis Effect bends the pathlines towards the center-body. We show - for the first time - that the azimuthal motion of the flame assists in the upstream propagation of the flame structure. Error assessment shows that the approximations made to construct the flame-surface and the flow-field retains the physics of flame-flow interactions.

Galactic rotation from Cepheids with Gaia DR2 and effects of non-axisymmetry

We apply a simple axisymmetric disc model to 218 Galactic Cepheids whose accurate measurements of the distance and velocities are obtained by cross-matching an existing Cepheids catalogue with the Gaia DR2 data. Our model fit determines the "local centrifugal speed", $V_\mathrm{c}$ $-$ defined as the rotation speed required to balance the local radial gravitational force $-$ at the Sun's location to be $V_{c}(R_0)=236\pm 3$ km s$^{-1}$ and the Sun's azimuthal and radial peculiar motions to be $V_{\odot}=12.4\pm0.7$ km s$^{-1}$ and $U_{\odot}=7.7\pm0.9$ km s$^{-1}$, respectively. These results are obtained with strong priors on the solar radius, $R_0=8.2\pm0.1$ kpc, and Sun's angular rotation velocity, $\Omega_{\odot}=30.24\pm0.12$ km s$^{-1}$ kpc$^{-1}$. We also applied the axisymmetric model to mock data from an N-body/hydrodynamic simulation of a Milky Way-like galaxy with a bar and spiral arms. We find that our axisymmetric model fit to the young stars recovers the local centrifugal speed reasonably well, even in the face of significant non-axisymmetry. However, the local centrifugal speed determined from our Cepheid sample could suffer from systematic uncertainty as large as 6 km s$^{-1}$.

Mechanism of Cardiac Tropomyosin Transitions on Filamentous Actin As Revealed by All-Atom Steered Molecular Dynamics Simulations.

The three-state model of tropomyosin (Tm) positioning along filamentous actin allows for Tm to act as a gate for myosin head binding with actin. The blocked state of Tm prevents myosin binding, while the open state allows for strong binding. Intermediate to this transition is the closed state. The details of the transition from the blocked to the closed state and then finally to the open state by Tm have not been fully accessible to experiment. Utilizing steered molecular dynamics, we investigate the work required to move the Tm strand through the extant set of proposed transitions. We find that an azimuthal motion around the actin filament by Tm is most probable in spite of increased initial energy barrier from the topographical landscape of actin.

Impacts of Magnetosheath High‐Speed Jets on the Magnetosphere and Ionosphere Measured by Optical Imaging and Satellite Observations

AbstractMagnetosheath high‐speed jets (HSJs) are dayside upstream transient disturbances with enhanced flow velocity and dynamic pressure. They are associated with significant magnetopause perturbations, ultralow frequency waves in the dayside magnetosphere, and localized flow enhancements in the ionosphere. However, whether HSJs have corresponding dayside aurora signatures is still an open question. If auroral signatures are found, 2‐D structure and evolution of HSJ effects on the magnetosphere can be imaged in a much higher precision than possible by other means. In this study, eight HSJ events are identified by the THEMIS satellites located within ±1 MLT of the center of the field‐of‐view of the South Pole station all‐sky imager. In all of those cases, the HSJs are observed to have a nearly one‐to‐one relationship with individual localized discrete/diffuse auroral brightenings. The azimuthal size of HSJ‐related diffuse aurora signatures is ~800 km at 230‐km altitude in the ionosphere and ~3.7 Re in the magnetosphere, which is slightly larger but of the order of the cross‐sectional diameter of HSJs (~1 Re). Furthermore, most of those aurora signatures have azimuthal motion, whose magnitude and direction agree with magnetosheath background flows. This study for the first time shows high‐resolution, two‐dimensional observations of localized structure and fast propagation of precipitation due to magnetosheath HSJs. We conclude that magnetosheath HSJs can have substantial impacts on the coupled magnetosphere‐ionosphere system, causing localized magnetospheric compression and aurora brightening, in a similar manner to responses during interplanetary shocks except with a smaller scale size.

Dirac electrons in quantum rings

We consider quantum rings realized in materials where the dynamics of charge carriers mimics that of two-dimensional (2D) Dirac electrons. A general theoretical description of the ring-subband structure is developed that applies to a range of currently available 2D systems, including graphene, transition-metal dichalcogenides, and narrow-gap semiconductor quantum wells. We employ the scattering-matrix approach to calculate the electronic two-terminal conductance through the ring and investigate how it is affected by Dirac-electron interference. The interplay of pseudo-spin chirality and hard-wall confinement is found to distinctly affect the geometric phase that is experimentally accessible in mesoscopic-conductance measurements. We derive an effective Hamiltonian for the azimuthal motion of charge carriers in the ring that yields deeper insight into the physical origin of the observed transport effects, including the unique behavior exhibited by the lowest ring subband in the normal and topological (i.e., band-inverted) regimes. Our work provides a unified approach to characterizing confined Dirac electrons, which can be used to explore the design of valley- and spintronic devices based on quantum interference and the confinement-tunable geometric phase.

Geometric effects resulting from square and circular confinements for a particle constrained to a space curve

Investigating the geometric effects resulting from the detailed behaviors of the confining potential, we consider square and circular confinements to constrain a particle to a space curve. We find a torsion-induced geometric potential and a curvature-induced geometric momentum just in the square case, while a geometric gauge potential solely in the circular case. In the presence of electromagnetic field, a geometrically induced magnetic moment couples with magnetic field as an induced Zeeman coupling only for the circular confinement, also. As spin-orbit interaction is considered, we find some additional terms for the spin-orbit coupling, which are induced not only by torsion, but also curvature. Moreover, in the circular case, the spin also couples with an intrinsic angular momentum, which describes the azimuthal motions mapped on the space curve. As an important conclusion for the thin-layer quantization approach, some substantial geometric effects result from the confinement boundaries. Finally, these results are proved on a helical wire.

Turning the Azimuthal Motions of Adjacent Tropomyosins into a Coupled N-body Problem in a Brownian Model of Cardiac Thin Filament Activation

During thin filament activation process, tropomyosin (Tm) oscillates over the surface of actin filament in the azimuthal direction to regulate the access of myosin head to actin binding sites. This motion is characterized by the existence of three distinct equilibrium positions, namely; blocked (B), closed (C), and open (M) regulatory states. The exact dynamics and energy landscape that governs Tm motions between these conformational states is not yet fully understood. In this study, we developed a Brownian flashing ratchet model to mathematically describe Tm motions over the surface of actin filament. The model approximates the Tm flexible chain by a system of discrete and coupled Brownian bodies. In other words, the thin filament regulatory units (RUs) are prescribed by a set of N-body stochastic ODEs that govern the azimuthal motion of adjacent tropomyosins. The model explicitly accounts for spatial interactions among nearest neighbor RUs, which were thought to appear from structural coupling of adjacent tropomyosins. This coupling is achieved by assigning each Brownian Tm-body with a local multi-well potential. The energetic barrier, asymmetry, and bias of each individual energy landscape are hypothesized to be influenced by the Tm status of its neighbors. This coupling approach is anticipated to be sufficient to produce observed cooperativity in both force-Ca2+ relationship and twitch dynamic. The present analysis is expected to perform better than many of current phenomenological myofilament models which were mostly derived based on the classical mean-field approximation. Additionally, this analysis draws a more detailed molecular connection between Tm dynamics and sarcomeric twitch production. Therefore, the Brownian ratchet modeling methodology of Tm motions during thin filament activation may offer an enhanced mechanistic approach to describe cardiac muscle contraction.