Center Of Motion Research Articles

Response to “Comment on ‘Modification of Lie's transform perturbation theory for charged particle motion in a magnetic field’” [Phys. Plasmas 30, 104701 (2023)

Dr. Brizard's comment on my work is based on a conceived procedure that does not come from my work. The defense of his claim that the modification of the so-called standard Lie's transform theory is unnecessary is also unsupported. This response reveals in detail the inconsistency issues in the so-called standard Lie's transform theory by analyzing both its results and root causes. The problem in the so-called standard Lie's transform theory is beyond the issue to take into account the ordering difference between the guiding center motion and gyromotion. The inconsistent commutation of derivative and limit causes another issue. In addition, the so-called standard Lie's transform formulation leads to an unnecessarily lengthy and tedious derivation process for a one or two page task under the singular (or renormalized) formalism described in my paper.

DOA estimation based on smoothed sparse reconstruction with time-modulated linear arrays

A novel direction of arrival (DOA) estimation method based on smoothed sparse reconstruction with time-modulated linear arrays (TMLA) is proposed in this paper. With the analysis of the noise variation after time modulation, a closed-form expression for the noise covariance under the optimized unidirectional phase center motion time sequence scheme is derived. Then a reweighted continuous function is designed for the smooth approximation to ℓ0-norm based on the orthogonality between the signal subspace and the noise subspace. Simulation results demonstrate that, compared with conventional DOA estimation method with time-modulated arrays, the proposed method possesses higher estimation accuracy and lower computational complexity, especially for the scenario with small snapshot and low signal-to-noise ratio.

Patterns of localized deformation at pre-fracture stage in carbon steel – stainless steel bimetal

The work is devoted to the study of strain localization at macroscale level during parabolic mechanical hardening and pre-fracture under quasi-static loading of a carbon steel – stainless steel bimetal. The problem of estimating the scale of the phenomena that determine plasticity is decisive in the development of any theories of plastic deformation, in particular, dislocation theories. The main difficulty in constructing such theories is the reconciling the dislocation scales, characteristic for most deformation and mechanical hardening mechanisms, with macroscopic parameters of deformation processes. In the framework of the autowave model of localized plastic deformation, this problem can be reduced to the possibility of obtaining parameters from the results of macroscale observations of localized plastic flow development. During the experiments, it was confirmed that in a bimetal at any forming stage, a specific pattern of localization centers distribution is spontaneously generated - a pattern of localized plastic flow. The shape of such patterns is determined by the law of mechanical hardening acting in the material. It is shown that the observed localization patterns can be used as an informative feature in predicting the plasticity margin. In the process of uniaxial tension at the stage of parabolic mechanical hardening of the bimetal, the deformation mode is realized with the formation of several potential fracture centers. It was established that at the pre-fracture stage, during the time evolution of the wave pattern of deformation localization, the zone of active plastic deformation narrows, but the number of centers in it either remains the same with a decrease in the distance between them, or even increases. The result of this process is the formation of a macroscopic neck, and then fracture. At the pre-fracture stage, the collapse point indicates the place of future fracture and signals the need to stop the deformation process in order to avoid the fracture of the bimetallic material. Thus, the well-known manifestation of deformation macroscopic localization – formation of a neck – is preceded by complex phenomena of mutually coordinated motion of localized plasticity centers at the pre-fracture stage.

Time History of Maximum Bearing Temperature Based on a Simplified Thermohydrodynamic Lubrication Theory

An overshoot phenomenon of bearing temperature in hydrodynamic journal bearings may be observed during a sudden start-up experiment. This phenomenon implies that the maximum bearing temperature in acceleration operation may exceed the predicted one which can be predicted accurately by applying a state-of-the-art steady state thermohydrodynamic lubrication (THL) model. This paper presents the maximum bearing temperature including the one during acceleration operation by using a simplified THL model that is newly proposed for a transient THL analysis. It is found that the overshooted temperature can be qualitatively predicted by using the transient THL model that incorporates properly the interaction between the motion of journal center and the viscous dissipation, even if it is a simple model. Next, the transient temperature during slow acceleration operation and also those toward higher dimensional steady state journal rotational speed are calculated and they are found to be in qualitative agreement with the measurements. The oil film characteristics such as oil film pressure, temperature and thickness after reaching the steady state equilibrium do not depend on the value of initial journal eccentricity ratio in the transient analysis. However, when the values are different, the characteristics immediately after starting rotation change largely. In the case of the value 1.00, it is found to give a prediction that agrees qualitatively with the characteristics measured in the experiment.

Method for detecting the loss of stability of the movement of tractors when towing a trailer or a coupled unit

BACKGROUND:Currently, combines and tractors, being the most energy-intensive transport and technological machines for agricultural purposes, largely determine the possibility of transition to an efficient and environmentally friendly agricultural economy, and also provide the technical aspect of the transformation of the agro-industrial complex into the leading sector of the countrys industry. One of the sources of dynamic loads in the units and subsystems of tractor equipment are self-oscillating modes.
 AIMS:Study of the conditions for the occurrence of self-oscillating processes in the design of wheeled tractor trains and development of methods to increase the handling and safety of their movement by means of reducing the galloping and yawing of the tractor-tractor when towing heavy loads.
 METHODS:It has been established that due to the coupling of oscillations along the longitudinal displacement of a truck tractor and a trailer with oscillations along the vertical displacement of the center of mass and with pitch angle oscillations of the truck tractor, when an auto-oscillatory mode occurs in the interaction zone of an elastic wheel with a solid surface, the same mode of self-oscillation will occur along the mentioned degrees of freedom. Moreover, it is possible to specify the sequence of occurrence of self-oscillating modes in different zones of the tractor train design.
 RESULTS:First, self-oscillations are excited in the contact patch of a wheel with a solid surface when a complete slip occurs, then self-oscillations along the pitch angle of a truck tractor body begin and after that self-oscillations along the vertical displacement of the center of mass of a truck tractor occur. Folding angle oscillations of a tractor train are associated with oscillations of the translational motion of wheel centers, which lead to the emergence of an self-oscillating mode, both with partial and full slip in the interaction zone of an elastic tire with a solid surface. Since the self-oscillations of each of the wheels occur at random times, the self-oscillations of a truck tractor along the folding angle will be chaotic.
 CONCLUSIONS:The practical value of the study lies in the possibility of using the proposed methods to identify the danger of self-oscillating processes in the design of promising types of agricultural machinery.

Thermal effect on magnetoexciton energy spectra in monolayer transition metal dichalcogenides

It is widely comprehended that temperature may cause phonon-exciton scattering, enhancing the energy level's linewidth and leading to some spectrum shifts. However, in the present paper, we suggest a different mechanism that allows the thermal motion of the exciton's center of mass (c.m.) to affect the magnetoexciton energies in monolayer dichalcogenides (TMDCs). By the nontrivial but precise separation of the c.m. motion from an exciton in a monolayer TMDC with a magnetic field, we obtain an equation for the relative motion containing a motional Stark term proportional to the c.m. pseudomomentum, related to the temperature of the exciton gas but neglected in the previous studies. Solving the Schr\"odinger equation without omitting the motional Stark potential at room temperature shows approximately a few meV thermal-magnetic shifts in the exciton energies, significant enough for experimental detection. Moreover, this thermal effect causes a change in exciton radius and diamagnetic coefficient and enhances the exciton lifetime as a consequence. Surprisingly, the thermoinduced motional Stark potential breaks the system's SO(2) symmetry, conducting new peaks in the exciton absorption spectra at room temperature besides those of the $s$ states. This mechanism could be extended for other magnetoquasiparticles such as trions and biexcitons.

Modification of Lie's transform perturbation theory for charged particle motion in a magnetic field

It is pointed out that the conventional Lie transform perturbation theory for the guiding center motion of charged particles in a magnetic field needs to be modified for ordering inconsistency. There are two reasons. First, the ordering difference between the temporal variation of gyrophase and that of the other phase space coordinates needs to be taken into account. Second, it is also important to note that the parametric limit of the derivative of a function is not equivalent to the derivative of the limit function. When these facts are taken into account, the near identity transformation rule for one form related to the Lagrangian is modified. With the modified near identity transformation rule, the drift motion of charged particles can be described in the first order, instead of the second order and beyond through a tedious expansion process as in the conventional formulation. This resolves the discrepancy between the direct and Lie transform treatments in the Lagrangian perturbation theory for charged particle motion in a magnetic field.

Vibration and stability analysis of a spinning shaft with arbitrary boundaries subjected to partial load

This paper deals with the flexural vibration and dynamic stability of a spinning shaft subjected to partial load. Based on the theorem of moment of momentum and the theorem of motion of center of mass, the governing equation of motion for the spinning shaft system is obtained. Four kinds of boundary conditions including pinned-pinned, clamped-clamped, free-free, and elastic supports are considered. The exact whirl frequency equation is derived analytically for different boundary conditions. The obtained model is confirmed by comparing with the results reported in the available literature, and excellent agreement is presented. A numerical investigation is carried out to examine the effects of support stiffness, mass ratio, eccentric distance, and slenderness ratio on the whirl characteristics and stability of the system in terms of the obtained model. The results show that the whirl frequency and critical spinning speed of the system are dependent on these parameters, and the stability is mainly governed by the mass ratio and eccentric distance.

Phase center motion based time modulated arrays with preprocessed time schemes for selective harmonic beamforming in B5G communication systems

AbstractThe possibilities of achieving beamforming antenna arrays for beyond fifth generation (B5G) communication systems by controlling the inherently generated harmonic beam patterns in “time modulation” based antenna arrays, are proposed in this article. The idea of “time modulation” is to assimilate an additional dimension “time” by using high‐speed switches for synthesizing the array radiation patterns. This in turn generates an infinite number of harmonic frequency patterns apart from the main beam at the fundamental frequency. In general, harmonic frequency patterns may be regarded as wastage of power, but with proper controlling, these spatially independent patterns created at multiple harmonics can be selectively utilized for specific purposes. In this article, the lower‐order harmonic frequency patterns of “time modulated” linear arrays (TMLA) are exploited to produce simultaneous multi‐beamforming for B5G multipoint communication. The capabilities of selective harmonic frequency patterns for multi‐beamforming are mathematically verified by proposing different beamforming switching network combinations. In this regard, phase centered motion (PCM) based TMLA is examined for simultaneous, as well as, monopulse beam scanning. PCM‐based unidirectional and bidirectional beamforming patterns with optimal time schemes are proposed. The mathematical validation of preprocessed symmetric and asymmetric time schemes, as well as, the PCM‐based optimized selective harmonic multi‐beamforming radiation patterns are discussed in detail to show the effectiveness of the proposed method.

Equivalent Dynamic of Liquid Sloshing Coupled with Mass Transfer During On-Orbit Refueling

During an on-orbit refueling mission, the liquid fuel partially filling in the tanks will slosh and produce coupled motion with the servicer-to-client transfer, which may bring dangers to the spacecraft and even lead to attitude divergence. To effectively simulate the motion and the inertia of liquid fuel in a cylindrical tank during refueling, equivalent dynamic modeling of liquid fuel sloshing coupled with mass transfer is developed in this paper. A spring–mass–damper model with time-varying elastic and damping coefficients is implemented in the axial direction to equal the motion of the liquid mass center, while a pendulum model with time-varying pendulum length is adopted in the radial direction. An equivalent liquid elliptical cylinder is developed to approximate the inertia of dispersed liquid while sloshing. A series of computational fluid dynamics simulations are carried out to observe the liquid behaviors in the fuel tanks and to verify the proposed equivalent dynamic model. Finally, three-dimensional sloshing is theoretically and numerically analyzed.

Simulating Underwater Human Motions on the Ground With a Cable-Driven Robotic Platform

Human performance and body motions when submerged underwater are highly influenced by buoyancy forces. In this article, we simulate the effect of buoyancy on human motion over ground by using a cable-driven robotic system. The robotic platform was configured to apply buoyancy forces on the human torso, similar to underwater, while subjects performed reaching and assembly tasks. Previous studies have analyzed muscle activity, postural balance, and limb kinematics in aquatic enclosures. However, from these studies, it is difficult to correlate observed human physiology changes with a specific underwater feature. The goal of this article is to expand our knowledge in objectively characterizing how physical underwater features affect human performance. The results of this article could help in designing more efficient overground programs to train divers in performing submarine motor tasks. For this purpose, we investigated motion of body center of mass (COM), ground reaction forces, muscular activity with surface electromyography (sEMG), and limb coordination while participants performed reaching tasks with and without simulated underwater forces. Within the simulated underwater environment with the cable system, buoyancy force significantly displaced the COM to outside the base of support. Additionally, ground reaction forces and sEMG of back muscles were significantly reduced during this condition. The results obtained in the present study are in line with previous experiments performed underwater. The results show the potential applicability of cable-driven platforms to expand our understanding in the future about the influence of aquatics on functional tasks.

On the Dynamics of an Enhanced Coaxial Inertial Exciter for Vibratory Machines

Theoretical investigations into the capabilities of a coaxial inertial drive with various operating modes for vibratory conveyors and screens are conducted in the paper. The coaxial inertial exciter is designed with one asynchronous electric motor and the kinematically synchronized rotation of two unbalanced masses. Three variants of angular speeds ratios, namely ω2/ω1 = 1, ω2/ω1 = –1, and ω2/ω1 = 2, are considered. Based on these relations, the circular, elliptical, and complex motion trajectories of the working members are implemented. In the first two cases, single-frequency harmonic oscillations take place. In the latter case, the double-frequency periodic oscillations are excited. The dynamic behavior of the motor’s shaft during its running-up and running-out is considered. The influence of the inertial parameters of the unbalanced rotors and the relative phase shift angle between them on the elliptical trajectories of the vibratory system’s mass center motion is investigated. The use of forced kinematic synchronization provides the motion stability of the vibratory system for all considered working regimes.

Determination of main performance data of an aircraft threedimensional maneuver split-S with a permissible flight envelope limiter

Due to a steady extension of the flight envelope of modern agile combat aircraft, with the growing requirements for state tests, it is increasingly necessary to study the entire flight envelope and specifically, to determine the main performance data of individual maneuvers. Currently, state tests are based on a flight full-scale experiment, which is cost-ineffective in terms of cost, duration, and limit lines of the flight envelope. The accelerating trends to update state tests are semirealistic simulation and complex simulation modeling. The article presents the various techniques to determine main performance data of a three-dimensional maneuver split-S, which include the calculation method, semirealistic simulation, and simulation modeling. The calculation method is understood as calculation formulas expressed from the system of equations for motion of the aircraft mass center. Semirealistic simulation was carried out using a flight-simulation stand by operator pilots. Simulation modeling was conducted using a complex simulation model of an aircraft, consisting of a pilot’s control actions model based on fuzzy logic. The article provides the description, advantages and disadvantages, comparison of the results of each of the techniques. The calculation method, despite its efficiency, is the most inaccurate due to the complexity and inability to define the average flight parameters. Additionally, this method does not take into consideration such factors as the aircraft flight configuration, atmospheric disturbances, the pilot’s command profile, the logic of the permissible flight envelope limiter operation. The results of semirealistic simulation showed that this method is more accurate than the calculation one, but complex and time consuming in terms of the organization and execution of experiments. The analysis of the study illustrated that the most appropriate way to determine main performance data of split-S is simulation modeling on a complex simulation model of the aircraft, because the given method considerably saves financial and time resources used on state flight tests.

Limitations of phase-sorting based pencil beam scanned 4D proton dose calculations under irregular motion

Objective. 4D dose calculation (4DDC) for pencil beam scanned (PBS) proton therapy is typically based on phase-sorting of individual pencil beams onto phases of a single breathing cycle 4DCT. Understanding the dosimetric limitations and uncertainties of this approach is essential, especially for the realistic treatment scenario with irregular free breathing motion. Approach. For three liver and three lung cancer patient CTs, the deformable multi-cycle motion from 4DMRIs was used to generate six synthetic 4DCT(MRI)s, providing irregular motion (11/15 cycles for liver/lung; tumor amplitudes ∼4–18 mm). 4DDCs for two-field plans were performed, with the temporal resolution of the pencil beam delivery (4–200 ms) or with 8 phases per breathing cycle (500–1000 ms). For the phase-sorting approach, the tumor center motion was used to determine the phase assignment of each spot. The dose was calculated either using the full free breathing motion or individually repeating each single cycle. Additionally, the use of an irregular surrogate signal prior to 4DDC on a repeated cycle was simulated. The CTV volume with absolute dose differences >5% (V dosediff>5%) and differences in CTV V 95% and D 5%–D 95% compared to the free breathing scenario were evaluated. Main results. Compared to 4DDC considering the full free breathing motion with finer spot-wise temporal resolution, 4DDC based on a repeated single 4DCT resulted in V dosediff>5% of on average 34%, which resulted in an overestimation of V 95% up to 24%. However, surrogate based phase-sorting prior to 4DDC on a single cycle 4DCT, reduced the average V dosediff>5% to 16% (overestimation V 95% up to 19%). The 4DDC results were greatly influenced by the choice of reference cycle (V dosediff>5% up to 55%) and differences due to temporal resolution were much smaller (V dosediff>5% up to 10%). Significance. It is important to properly consider motion irregularity in 4D dosimetric evaluations of PBS proton treatments, as 4DDC based on a single 4DCT can lead to an underestimation of motion effects.

Direct Anterior Approach Provides Superior Prosthesis Adaptability in the Early Postoperative Period of Total Hip Arthroplasty.

Prosthesis awareness is the perception of foreign bodies, which has a critical effect on the function of the prosthetic joint. In total hip arthroplasty (THA), the direct anterior approach (DAA) has more advantages than the posterior approach (PA), including superior rehabilitation outcomes. This study was to evaluate the recovery of "prosthesis awareness" through these two approaches. Three hundred and seventy-six patients who received THA with either DAA (n=41) or PA (n=335) from January 2016 to December 2017 were retrospectively analyzed. The Forgotten Joint Score-12 (FJS-12), Harris hip score (HHS), and visual analog scale (VAS) analyses were used to evaluate the recovery of "prosthesis awareness" in these patients 2 weeks, 1, 3, 6, and 12months after surgery. The student t-test, Wilcoxon rank sum test, chi-square test, and MANOVA were used to compare the differences among groups. We found that DAA patients had higher FJS-12 scores than PA patients at 2 weeks (42.15 ± 3.36 vs. 38.09 ± 3.28, p =0.042), 1 month (49.06 ± 5.14 vs. 41.11 ± 5.21, p =0.038), and 3 months (53.23 ± 4.07 vs. 48.09 ± 3.71, t=3.152, p=0.045). And the recovery rates of FJS-12 scores in DAA and PA groups at 2 weeks, 1 month, and 3 months after surgery were 75.46% ± 6.04%, 84.05% ± 6.57%, 91.37% ± 7.13%, and 74.14% ± 5.54%, 78.16% ± 6.01%, 88.23% ± 6.42%, respectively. To compare the recovery effects of the two procedures in more detail, we classified the 12 items in FJS-12 that evaluate different types of gravity center motions into three categories: low-movement group (LG), middle-movement group (MG), and high-movement group (HG). Interestingly, DAA patients had significantly higher HG than PA patients at 2 weeks, 1 month, and 3 months after operation (t=3.225, p=0.022 at 2 weeks, t=3.081, p=0.041 at 1 month and t=2.783, p=0.046 at 3 months), whereas no significant differences were observed in LG- and MG-related items. In addition, there were no significant differences in HHS and VAS scores between DAA and PA patients at 2 weeks (p=0.102, p =0.093), or from 1 month to 12months (each p > 0.05). DAA-mediated THA is superior to PA in terms of prosthesis adaptability and recovery of hip joint motion in the first 3 months after surgery, especially concerning high-movement gravity center motions.

A guiding center implementation for relativistic particle dynamics in the PLUTO code

We present a numerical implementation of the guiding center approximation to describe the relativistic motion of charged test particles in the PLUTO code for astrophysical plasma dynamics. The guiding center approximation (GCA) removes the time step constraint due to particle gyration around magnetic field lines by following the particle center of motion rather than its full trajectory. The gyration can be detached from the guiding center motion if electromagnetic fields vary sufficiently slow compared to the particle gyration radius and period. Our implementation employs a variable step-size linear multistep method, more efficient when compared to traditional one-step Runge Kutta schemes. A number of numerical benchmarks is presented in order to assess the validity of our implementation.

Testing the conservative character of particle simulations: II. Spurious heating of guiding centers and full orbits subject to fluctuations expressed in terms of E and B

For an axisymmetric tokamak plasma, Hamiltonian theory predicts that the orbits of charged particles must stay on invariant tori of conserved energy in the moving frame of reference of a wave that propagates along the torus with fixed angular phase velocity, amplitude, and shape. The mode structure in the poloidal plane is arbitrary if the fluctuations are expressed in terms of potentials Φ and A, which satisfy Faraday's law and the solenoidal condition by definition. Consequently, smoothing operations (such as gyroaveraging and noise suppression) do not violate the conservative laws. However, this is not guaranteed for models expressed in terms of the physical fields E and B. Here, we demonstrate that manipulations of E and B in the poloidal (R, z) plane can cause spurious heating that is independent of time steps or numerical methods, but can be sensitive to geometry. In particular, we show that secular acceleration is enhanced when one imposes nonnormal modes that possess strong up–down asymmetry instead of the usual in–out asymmetry of normal toroidal (eigen)modes. We compare full gyro-orbit and guiding center models and find similar behavior. We also examine the effect of ad hoc N-point gyroaveraging in a guiding center model, as is done in some simulation codes. If one uses Faraday's law to (re)compute B(t) after gyroaveraging E, the guiding center motion remains conservative. Otherwise, spurious heating should be expected and monitored, but it may be tolerable when normal modes dominate.

Micromagnetic Modes of Anisotropy of Magnetic Susceptibility in Natural Magnetite Particles

AbstractAnisotropy of magnetic susceptibility (AMS) is commonly used to assess sedimentation, deformation, tectonics, rock fabric, and texture. Using focused‐ion beam nanotomography, we develop a micromagnetic method to investigate the AMS of individual magnetite inclusions in silicates across the transition between single‐domain (SD) to multidomain behavior. We calculate individual AMS tensors by modeling the magnetization response of a particle to weak applied fields in three orthogonal directions. The main AMS mode of elongated SD particles is not a homogeneous magnetization rotation, but focused alignment of spins at their edges and tips. In single‐vortex particles, vortex displacement is the dominant AMS mode, which focuses the largest magnetization changes in a planar region containing the vortex core, and perpendicular to the direction of vortex motion. In multi‐vortex structures a combined motion of all vortex centers can lead to high degrees of anisotropy when some motion patterns are energetically much easier to achieve than others.

Optical Nonreciprocity in Rotating Diamond with Nitrogen‐Vacancy Color Centers

AbstractA method to realize optical nonreciprocity in rotating nano‐diamond with nitrogen‐vacancy (NV) centers is theoretically proposed here. Because of the relative motion of the NV center with respect to the propagating fields, the frequencies of the fields are shifted due to the Doppler effect. When the control and probe fields are incident to the NV center from the same direction, the two‐photon resonance still holds as the Doppler shifts of the two fields are the same. Thus, due to the electromagnetically‐induced transparency, the probe light can pass through the NV center nearly without absorption. However, when the two fields propagate in opposite directions, the probe light cannot effectively pass through the NV center as a result of the breakdown of two‐photon resonance.

Analytical Model of Hole Diameter and Self-Guiding Machining Mechanism of BTA Deep Hole Drilling

The goal of this study was to explore the self-guided machining mechanism of boring and trepanning association (BTA) deep hole drilling and realize precise control of the machining quality. The motion analysis method was used to analyze the center motion trajectory of the drill during the entrance, and the self-guiding mechanism and hole-forming mechanism of BTA deep hole drilling were revealed. Considering the bending deformation of the drilling tube and the tool structure parameters, according to the elastic-plastic deformation theory and Hertzian contact theory, a novel analytical model of the extrusion contact between the guide pads and the hole wall of the BTA deep hole drilling was established for the theoretical prediction of the extrusion deformation and the machining hole diameter. Combined with the finite element method (FEM) simulation model, the variation law of the contact inclination angle, contact stress, and extrusion deformation of the guide pads and the hole wall with the drilling conditions were studied. The total extrusion deformation between the guide pad and the hole wall was between 10 and 50 μm. The maximum error between the FEM simulation results and the test results was 18.1%, and the maximum error between the analytical model results and the test results was 23.6%. The simulation and experimental results showed that the established extrusion contact model could accurately predict the extrusion deformation of the hole wall and the machining hole diameter.