Uniform Motion Research Articles

The Horizons in Circular Accelerated Motions and Its Consequences

In this work, we study the existence of horizons in circular accelerated motions and its consequences. One particular case is the existence of two horizons in any uniform circular motion. The radiation of the Poincaré invariant vacuum is related to the spontaneous breakdown of the conformal symmetry in Quantum Field Theory The main consequence of the existence of these horizons is the Unruh radiation coming from such horizons. This consequence allows us to study the possible experimental detection of the Unruh radiation in such motions. The radiation of the Poincaré invariant vacuum is related to the spontaneous breakdown of the conformal symmetry in Quantum Field Theory. This radiation is associated with an effective temperature that can be detected using an Unruh–DeWitt detector. In fact, this effective temperature at the relativistic limit depends linearly with respect to the proper acceleration. However, in general, this dependence is not linear, contrary of what happens in the classical Unruh effect. In the relativistic limit and high density case, the uniform circular motion becomes a rotating black hole. This allows for future studies of pre-black hole configurations.

A non-contact vehicle weighing approach based on bridge weigh-in-motion framework and computer vision techniques

Bridge weigh-in-motion (BWIM) system plays increasingly important role in vehicle load monitoring and bridge maintenance due to advantages of high efficiency and little impact on traffic. However, the contact-type sensors in a traditional BWIM system should be installed in advance and is environment-sensitive, which hinders its application. To this end, a vision-based contactless BWIM (cBWIM) system is proposed. The core idea of the current method is to replace the traditional contact-type sensors by two consumer cameras to realize real-time monitoring of bridge displacement and vehicle trajectory. The cBWIM system consists of three modules, including the axle weight identification algorithm, the bridge displacement monitoring system and the vehicle trajectory tracking system. The influence line-based Moses algorithm is utilized for identification of axle weight. For bridge displacement monitoring, the minimum bounding rectangle-based similarity matching method is proposed to achieve high accuracy measurement of displacement and real-time data processing. For vehicle trajectory tracking, a deep learning-based YOLOv5s algorithm is adopted as a detector, combined with DeepSort algorithm to realize real-time tracking of vehicle position. The cBWIM system is applicable for non-uniform motion and vehicle occlusion cases. Laboratory tests covering various cases (i.e. uniform motion, non-uniform motion and visual occlusion) and field measurement on a full-scale bridge have demonstrated that the proposed method is effective and reliable and can provide alternative tool to the current vehicle weighing methods.

Classical relativistic electron-field dynamics: Hamiltonian approach to radiation reaction

Motivated by the renewed interest due to the presently available extreme light sources, the dynamics of a single classical relativistic (spinless) extended electron interacting with a classical electromagnetic field (an incoming radiation and the field radiated by the electron) is revisited. The field is treated in Lorentz gauge, with the Lorentz condition. By assumption, there is a crucial finite cut-off k max on the magnitude of any wavevector contributing to the field (preventing a point electron) and, for a simple formulation, the initial conditions for particle and fields are given in the infinitely remote past. In an infinite three-dimensional vacuum and in an inertial system, Hamilton’s dynamical equations for the particle and the complex field amplitudes acting as canonical variables (a's) yield an exact Lorentz force equation for the former, that includes the incoming radiation and an exact radiation reaction force F RR due to the field radiated by the electron. Uniform motion is obtained as a test of consistency. Based upon numerical computations, some approximations on F RR are given. A covariant formulation is also presented.

Suspending droplets beyond the Rayleigh limit: The interplay of acoustic and gravity forces

In this work, we experimentally investigate the suspension behavior of droplets subjected to standing acoustic waves. We focus on the droplet sizes beyond the Rayleigh limit, i.e., when the droplet size is comparable to the wavelength of the acoustic wave. We show that an acoustic field can disrupt the uniform motion of aqueous droplets in oil and cause them to either suspend or settle, depending on the interplay between acoustic and gravity forces. Remarkably, in contrast to droplets within the Rayleigh limit, the critical acoustic power or minimum pressure amplitude required to suspend droplets beyond the Rayleigh limit is dependent on the droplet size. As the droplet size increases, the critical acoustic power increases significantly. Building upon this understanding, a novel sorting method is proposed based on critical acoustic power.

A coupling FEM/BEM method for acoustic-structural interaction problems in uniform relative motion between structure source and fluid

When a vibrating thin structure moves in a heavy flow field, the effect of sound waves on the structure cannot be ignored. This effect is especially pronounced when the relative velocity of the structure and the flow field increases. The hybrid numerical method of finite element method (FEM) and convective boundary element method (BEM) is proposed to solve acoustic-structural interaction problems in uniform relative motion between structure source and fluid. Besides, an acoustic-analogy Lorentz transform is proposed to handle the direct convective boundary integral equation (BIE), which makes the convective BIE has the same form as traditional BIE so that there are no more convective terms and extra singular integrals. The continuity condition at the fluid-structure interface is also proposed to generate the coupling equation. Compared with the traditional FEM, this hybrid method has the advantages of greatly reducing the number of finite elements outside the structure as well as automatically satisfying the radiation condition at far field. And compared with the direct convective BIE, this method reduces the computational complexity and time. It is potential to deliver a solver with higher accuracy and less memory consumption. Some numerical examples are designed to study the influence of the convective effect. Keywords: Acoustic-structural interaction, Finite element method, Boundary element method, FEM-BEM coupling

Correlation harvesting between particle detectors in uniform motion

Correlation harvesting between particle detectors in uniform motion

Transition from a Uniform Mode of Polaron Motion to an Oscillatory One When the Initial Polaron State Changes

A study of the nature of the motion of a Holstein polaron in a homogeneous polynucleotide chain in a constant electric field, depending on the initial polaron state, was carried out. The calculations performed showed that the duration of the uniform motion of the polaron along the chain is finite and depends on the entire set of system parameters, including the characteristic size of the initial polaron state. It is shown that at a fixed value of the electric field intensity, an increase in the characteristic size of the initial polaron state leads to a decrease in the time of uniform motion of the polaron along the chain. The calculations carried out earlier showed that with the uniform movement of the polaron along the chain, low-density components of the polaron are formed immediately after the electric field is turned on. Moreover, the low-density components of the polaron have their own internal dynamics, which are different from the dynamics of the macro-part of the polaron. With uniform motion, the macro-part of the polaron moves at a constant velocity, maintaining its shape, while the low-density components of the polaron demonstrate such characteristics of Bloch oscillations as the period of Bloch oscillations and the maximum Bloch amplitude. It is also shown that a change in the shape of the initial polaron state exerts influence upon not only the duration of the uniform motion of the polaron along the chain, but also the characteristics of the low-density components of the polaron.

Quantum mechanical Gaussian wavepackets of single relativistic particles

We study the evolutions of selected quasi-(1+1) dimensional wavepacket solutions to the Klein–Gordon equation for a relativistic charged particle in uniform motion or accelerated by a uniform electric field in Minkowski space. We explore how good the charge density of a Klein–Gordon wavepacket can be approximately described by a Gaussian state with the single-particle interpretation. We find that the minimal initial width of a wavepacket for a good Gaussian approximation in position space is about the Compton wavelength of the particle divided by its Lorentz factor at the initial moment. This can be considered as a manifestation of relativistic length contraction, which is also observed numerically in the spreading of the wavepacket’s charge density.

The effects of object size on spatial orientation: an eye movement study.

The processing of visual information in the human brain is divided into two streams, namely, the dorsal and ventral streams, object identification is related to the ventral stream and motion processing is related to the dorsal stream. Object identification is interconnected with motion processing, object size was found to affect the information processing of motion characteristics in uniform linear motion. However, whether the object size affects the spatial orientation is still unknown. Thirty-eight college students were recruited to participate in an experiment based on the spatial visualization dynamic test. Eyelink 1,000 Plus was used to collect eye movement data. The final direction difference (the difference between the final moving direction of the target and the final direction of the moving target pointing to the destination point), rotation angle (the rotation angle of the knob from the start of the target movement to the moment of key pressing) and eye movement indices under conditions of different object sizes and motion velocities were compared. The final direction difference and rotation angle under the condition of a 2.29°-diameter moving target and a 0.76°-diameter destination point were significantly smaller than those under the other conditions (a 0.76°-diameter moving target and a 0.76°-diameter destination point; a 0.76°-diameter moving target and a 2.29°-diameter destination point). The average pupil size under the condition of a 2.29°-diameter moving target and a 0.76°-diameter destination point was significantly larger than the average pupil size under other conditions (a 0.76°-diameter moving target and a 0.76°-diameter destination point; a 0.76°-diameter moving target and a 2.29°-diameter destination point). A relatively large moving target can resist the landmark attraction effect in spatial orientation, and the influence of object size on spatial orientation may originate from differences in cognitive resource consumption. The present study enriches the interaction theory of the processing of object characteristics and motion characteristics and provides new ideas for the application of eye movement technology in the examination of spatial orientation ability.

Estimation and Compensation of Heading Misalignment Angle for Train SINS/GNSS Integrated Navigation System Based on Observability Analysis

The inertial Navigation Systems/global navigation satellite system (SINS/GNSS) has become a research hotspot in the field of train positioning. However, during a uniform straight-line motion period, the heading misalignment angle of the SINS/GNSS is unobservable, resulting in the divergence of the heading misalignment angle and ultimately causing a divergence in the train’s speed and position estimation. To address this issue, this paper proposes an estimation and compensation method for the heading misalignment angle for train SINS/GNSS integrated navigation system based on an observability analysis. When the train enters a straight-line segment, the alignment of the train’s sideslip angle and the satellite velocity heading angle allows the achievement of velocity heading observation values that resolve the issue. In a curved segment, the heading angle becomes observable, allowing for an accurate estimation of the SINS’s heading misalignment angle using GNSS observations. The results showed that, whether the train is on a straight or curved track, the position estimation accuracy meets the simulation design criteria of 0.1 m, and the heading accuracy is better than 0.25°. In comparison to the results of pure GNSS position and velocity-assisted navigation, where heading divergence occurs during constant velocity straight-line segments, the method proposed in this paper not only converges but also achieves an accuracy comparable to the GNSS velocity-based heading alignment. The simulation results demonstrate that the proposed strategy significantly improves the accuracy of the heading misalignment angle estimation, thereby enhancing the accuracy of speed and position estimation under a GNSS-denied environment.

Students’ confusions about the electric field of a uniformly moving charge

In light of a recent direct experimental confirmation of a Lorentz contraction of Coulomb field (an electric field of a point charge in a uniform motion), we revisit some common confusions related to it, to be mindful of in teaching the subject. These include questions about the radial nature of the field, the role of the retardation effect due to a finite speed of information transfer and some issues related to a depiction of Coulomb field by means of the Lorentz contracted field lines.

Effectiveness of silver-magnesium oxide-water hybrid nanofluid in Couette channel

The present article numerically investigates the unsteady magnetohydrodynamic (MHD) Couette flow containing novel (Ag + MgO)-water hybrid nanofluid (HNF). The nanoparticles of silver (Ag) and magnesium oxide (MgO) are supplemented to base fluid water. The top wall is kept in uniform motion while the bottom wall of channel set stationary and stretchable. An external magnetic field is applied perpendicular to lower plate. The governed nonlinear partial differential equations (PDE) are solved employing finite difference method (FDM). The effects of hybrid nanofluid and nanofluid (NF) are compared for the significant parameters and presented graphically. The results illustrate that (Ag + MgO)-water HNF exhibits significant influence over Ag-water NF on velocity and temperature in the Couette channel.

Simulation of sonar reverberation signal considering the ocean multipath and Doppler effect

In order to achieve accurate modeling and simulation of sonar reverberation signals, four types of multi-path underwater reverberation models are established considering Doppler effect under the condition of separating the sound source and hydrophone. The simulation of underwater reverberation signals under static or uniform linear motion conditions is carried out for single point for the separating the sound source and hydrophone transceiver, as well as horizontal linear array. The non-stop-and-hop model of reverberation signals is presented. And the underwater reverberation signals in the array element domain and beam domain are obtained. From the simulation results of the improved model, it can be seen that the spatiotemporal two-dimensional characteristics and Doppler expansion are consistent with theoretical analysis. The frequency shift of the horizontal linear array reverberation signal is approximately sinusoidal with the directionality angle of the linear array. Comparing the simulation results of the improved model with traditional models, the improved model can more accurately simulate sonar reverberation signals.

A Lightweight Visual Odometry Based on LK Optical Flow Tracking

Autonomous mobile robots (AMRs) require SLAM technology for positioning and mapping. Their accuracy and real-time performance are the keys to ensuring that the robot can safely and accurately complete the driving task. The visual SLAM systems based on feature points have high accuracy and robustness but poor real-time performance. A lightweight Visual Odometry (VO) based on Lucas–Kanade (LK) optical flow tracking is proposed. Firstly, a robust key point matching relationship between adjacent images is established by using a uniform motion model and a pyramid-based sparse optical flow tracking algorithm. Then, the grid-based motion statistics algorithm and the random sampling consensus algorithm are used to eliminate the mismatched points in turn. Finally, the proposed algorithm and the ORB-SLAM3 front-end are compared in a dataset to verify the effectiveness of the proposed algorithm. The results show that the proposed algorithm effectively improves the real-time performance of the system while ensuring its accuracy and robustness.

On asymptotic stability of solitons for 2D Maxwell–Lorentz equations

We prove asymptotic stability of solitons for the 2D Maxwell–Lorentz equations with an extended charged particle. Soliton solutions correspond to the uniform motion of a particle. Our main result is as follows: the particle for large times moves asymptotically uniformly, and the Maxwell field asymptotically is the sum of the comoving field and the dispersive wave. The remainder converges to zero in the global energy norm.

Electromechanical control method of rheological and technological characteristics of building mixtures

The paper is devoted to the enhancement of control methods for the rheological and technological properties of building mixtures: foam concrete, injection mortar, and tamponage mortars. For this, a new method for determining these properties and a device that extends the range of measurements in comparison with the widespread ones are developed. This device consists of the DC motor that directly brings the spherical spindle into a uniform motion in the building mixture. It allows for transforming the rheological characteristics into electrical signals during the preparation processes of mixtures. For the first time, the physical-mathematical model of such dependence is obtained. Also, for the first time, the experimental and calculated dependencies between the values of the amperage and the common technological characteristics of the cement mortar and conditional viscosity have been determined. It is established that the viscosity is within 0.23 ÷ 0.07 Pа⋅s, and the current strength is within 60 ÷ 225 mА for sand-cement mortars with the ratio 1:1 ÷ 1:1.5 and W/C 0.7 ÷ 1.2. For cement suspension, the viscosity is equal to 2.7 Pа⋅s for W/C = 0.3 and 1.2 Pа⋅s for W/C = 0.5. Wherein, the amperages comprise 607 and 278 mА for W/C = 0.3, 226 and 116 mА for W/C = 0.5 for spindles of different diameters. Obtained dependencies could be the basis of the software for the development and of the automatic monitoring system of rheological and technological characteristics of cement-sand mortars, as well as the automatic management system for preparing building mixtures with set rheological properties.

Dynamic analysis of 2DFGM porous nanobeams under moving load with surface stress and microstructure effects using Ritz method

This paper investigates the dynamic behavior of micro/nanobeams made of two-dimensional functionally graded porous material (2DFGPM) under accelerated, decelerated, and uniform moving harmonic load, using surface elasticity and modified couple stress theories. The key feature of this formulation is that it deals with a higher order shear deformation beam theory. The non-classical equilibrium equations are developed using Lagrange's equation and the concept of physical neutral surface. The equations of motion are derived using the same approach, accounting for the porosity effect and the modified power-law distribution of material properties. The trigonometric Ritz method is used with sinusoidal trial functions for the displacement field, and the Newmark method is applied to obtain the dynamical response of 2DFGPM nanobeams. The results are compared with previous studies, and the impact of critical parameters such as gradation indices, volume fraction ratio, pattern of porosity, velocity, frequency, and motion type of the applied force are explored. This study highlights the importance of considering the porosity effect, as neglecting it can lead to significant errors in the predicted results. Additionally, the study found that the accelerated and decelerated motions of the applied load have a greater impact on the dynamical deflection of 2DFGPM nanobeams than the uniform motion. The findings of this study can provide guidance for the optimal design of micro/nanobeams subjected to a moving force with multifunctional properties.

Wave Resistance Caused by a Point Load Steadily Moving on the Surface of a Floating Viscoelastic Plate

The wave resistance caused by a point load steadily moving on an infinitely extended viscoelastic plate floating on an inviscid fluid is analytically studied, which can be used to describe the response due to the motion of amphibious air-cushion vehicles on the continuous ice sheet on the ocean. The action of concentrated and distributed point loads are both considered. Under the assumptions that the fluid is incompressible and homogeneous and the motion of the fluid is irrotational, the Laplace equation is taken as the governing equation. For the floating plate, the Kelvin–Voigt viscoelastic model is employed. At the plate–fluid interface, linearized boundary conditions are used when the wave amplitude generated is less than its wavelength. The Fourier integral transform is performed to achieve the formal solution. The residue theorem is applied to derive the response of flexural–gravity wave resistance. It is indicated that for a point load with a uniform rectilinear motion, the wave resistance shows a sharp decrease with the increase in the moving speed when the load velocity is greater than the minimum phase velocity. There is no steady wave resistance when the load velocity is smaller than the minimum phase velocity. The effects of different parameters are obtained. Wave resistance decreases with the increasing plate thickness, viscoelastic parameter, and Poisson’s ratio, especially for a small value of viscoelastic parameter.

Resonance with surface waves induces forbidden velocity bands in dislocation glide

We use molecular dynamics simulations to demonstrate a pronounced influence of free surfaces on the mobility of dislocations at near-sonic velocities. By correlating instantaneous velocities v and resolved stresses τ, we show that the mobility relations of both edge and screw characters are composed of multiple ranges of stable uniform motion separated by bands of forbidden velocity. The lower limiting velocity for uniform motion of both edge and screw dislocations is the Rayleigh wave speed, cR. When forced to propagate at an average velocity greater than cR, dislocations exhibit cyclic, intermittent jumps in instantaneous velocity between cR and higher velocity branches of the mobility relation. Bands of forbidden velocity may be calculated directly from the velocity dependence of dislocation drag functions, which contain peaks near cR and—in the edge case—one other characteristic surface wave speed, which we associate with shear-horizontal (SH) waves. We propose that peaks in the drag function are due to resonance of free surface vibrations forced by nearby moving dislocations.

Understanding of the Intrinsic Difference between n- and p-Doping Propagation in Polymer Light-Emitting Electrochemical Cells: A Numerical Modeling Approach.

Distinct doping propagation characteristics between p-doping and n-doping in light-emitting electrochemical cells (LECs) have been highlighted by intensive reports. Typically, there are significant differences in the doping speeds between p-doping and n-doping, with the former exhibiting a sawtooth frontier and the latter displaying a more uniform frontier profile. In addition, experimental observations demonstrate a uniform motion instead of the theoretically suggested accelerated electrochemical doping frontier propagation. Therefore, there is an urgent need to establish a quantitative model that delves into the underlying mechanisms responsible for doping propagation in LECs. In this study, four variables were selected to investigate the detailed mechanism of electrochemical doping propagation: temperature, voltage, and concentrations of salt and solid electrolyte. Fluorescence imaging revealed that the n-doping and p-doping propagations behaved contrarily with increasing temperature and voltage. By numerically fitting the doping propagation frontier, equations were derived to describe the relationship between the speed of electrochemical doping propagation and temperature/voltage. The underlying mechanisms were elucidated, indicating that anions undergo motion through the cooperative effects of electric field drift and concentration diffusion, while cation transport strongly relies on poly(ethylene oxide) (PEO) segmental motions. In other words, the movement of anions within the electrolyte is characterized by a greater degree of freedom, whereas the motion of cations is significantly dependent on the segmental motions of PEO. The resulting equations were well-fitted with experimental data, providing a solid foundation for further theoretical investigations into electrochemical doping in various devices.