Ballistic Motion Research Articles

Emergent ordering of microswimmers in smectic liquid crystals

Self-propelled agents can interact in many different ways, including by perturbing a shared physical environment, e.g, hydrodynamic interactions. We study motile particles that are embedded into a smectic liquid crystal, locally distorting the smectic layer spacing. This results in interactions mediated by a smectic liquid crystal distortion field and corresponds to a form of “active smectic” liquid crystal. We identify several dynamical phases that emerge in different regimes of the smectic stiffness and particle reorientation time. We characterise these as (i) ballistic motion, (ii) clustering and (iii) collective motion where orientational order emerges even thought the system lacks explicit co-alignment. We further identify an order-to-disorder transition on the addition of angular noise.

Magnetization switching in the inertial regime

We have numerically solved the Landau-Lifshitz-Gilbert (LLG) equation in its standard and inertial forms to study the magnetization switching dynamics in a $3d$ thin film ferromagnet. The dynamics is triggered by ultrashort magnetic field pulses of varying width and amplitude in the picosecond and Tesla range. We have compared the solutions of the two equations in terms of switching characteristic, speed and energy analysis. Both equations return qualitatively similar switching dynamics, characterized by regions of slower precessional behavior and faster ballistic motion. In case of inertial dynamics, ballistic switching is found in a 25 % wider region in the parameter space given by the magnetic field amplitude and width. The energy analysis of the dynamics is qualitatively different for the standard and inertial LLG equations. In the latter case, an extra energy channel, interpreted as the kinetic energy of the system, is available. Such extra channel is responsible for a resonant energy absorption at THz frequencies, consistent with the occurence of spin nutation.

Influence of the Lander Size and Shape on the Ballistic Landing Motion

AbstractThis article investigates the ballistic landing motion and final distribution of the landers in different sizes or shapes near the small celestial body. Three typical shapes, including cubic, cuboid, and cylindrical, are considered for the landers deployed to a tri‐axial ellipsoid model. The Polygonal Contact Model (PCM) is used to detect the contact/collision, where the Hertz model is applied to calculate the continuous contact force. Different‐sized cubic landers (in the edge length of 20, 30, 40, and 50 cm) are numerically simulated to examine how the lander size influences its dynamics. The landing motion of the cuboid‐ and the cylinder‐shaped landers are then analyzed in the same technique. The heights of these asymmetrical landers are assumed to be 25, 30, and 35 cm, respectively, to illustrate the shape effect. Monte Carlo simulations are implemented for various landers to account for the surface motion randomness. The final dispersion, the outgoing velocity after the collision, the horizontal transfer distance, and the settling time are taken to be critical indicators for discussing the landing behavior, which can provide implications for the probe design of future missions.

Numerical Analysis of Golf Swing using Hilbert-Huang Transformation

Golf swing analysis is mainly performed using a high-speed camera and a device called a Trackman. Trackman can collect club data, ball data, putting data, etc., and the high-speed camera can record images at 6000 Hz. However, these devices are quite expensive and difficult to introduce to the general golfer. This research adopts an inexpensive inertial motion capture, Perception Neuron 2.0, to numerically capture motion and identify the differences between motions that result in straight and slice ballistics. In general, the left half of the body opening, and the head up are known to cause a slice ballistic of the golf ball. In this research, the analysis focuses on the front left half body and the head motion. The captured golf swing motion data is then processed by Hilbert-Huang Transform to calculate their instantaneous frequency and instantaneous amplitude. The result of the research found differences at the moment of impact of the golf swing at low frequencies. The amplitude of the straight ballistic motion of the head and the left shoulder increases at the moment of impact of the swing. On the other hand, the amplitude of the slice ballistic motion of the head and the left shoulder increases before impact. These results indicate that the slice ballistic motion is causes by an opening of the left half of the body and head-up from a biomechanical viewpoint.

A perfect probe: Resonance of underdamped scaled Brownian motion

We numerically investigate the resonance of the underdamped scaled Brownian motion in a bistable system for both cases of a single particle and interacting particles. Through the velocity autocorrelation function and mean squared displacement of a single particle, we find that for the steady state, diffusions are free ballistic motion in short time, become the transitions between superdiffusion and subdiffusion in intermediate time, and converge to zero at long times. Via the power spectrum density corresponding to the transitions between superdiffusion and subdiffusion, we find that there exists a nontrivial resonance. For interacting particles, we find that the interaction between the probe particle and other particles can lead to the resonance, too. Thus we propose the system with the Brownian particle as a probe, which can detect the temperature of the system and identify the number of the particles or the types of different coupling strengths in the system. The probe is potentially useful for detecting microscopic and nanometer-scale particles.

Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet

Electrons navigate more easily in a background of ordered magnetic moments than around randomly oriented ones. This fundamental quantum mechanical principle is due to their Bloch wave nature and also underlies ballistic electronic motion in a perfect crystal. As a result, a paramagnetic metal that develops ferromagnetic order often experiences a sharp drop in the resistivity. Despite the universality of this phenomenon, a direct observation of the impact of ferromagnetic order on the electronic quasiparticles in a magnetic metal is still lacking. Here we demonstrate that quasiparticles experience a significant enhancement of their lifetime in the ferromagnetic state of the low-density magnetic semimetal EuCd2As2, but this occurs only in selected bands and specific energy ranges. This is a direct consequence of the magnetically induced band splitting and the multi-orbital nature of the material. Our detailed study allows to disentangle different electronic scattering mechanisms due to non-magnetic disorder and magnon exchange. Such high momentum and energy dependence quasiparticle lifetime enhancement can lead to spin selective transport and potential spintronic applications.

Narrow escape problem in two-shell spherical domains.

Intracellular transport in living cells is often spatially inhomogeneous with an accelerated effective diffusion close to the cell membrane and a ballistic motion away from the centrosome due to active transport along actin filaments and microtubules, respectively. Recently it was reported that the mean first passage time (MFPT) for transport to a specific area on the cell membrane is minimal for an optimal actin cortex width. In this paper, we ask whether this optimization in a two-compartment domain can also be achieved by passive Brownian particles. We consider a Brownian motion with different diffusion constants in the two shells and a potential barrier between the two, and we investigate the narrow escape problem by calculating the MFPT for Brownian particles to reach a small window on the external boundary. In two and three dimensions, we derive asymptotic expressions for the MFPT in the thin cortex and small escape region limits confirmed by numerical calculations of the MFPT using the finite-element method and stochastic simulations. From this analytical and numeric analysis, we finally extract the dependence of the MFPT on the ratio of diffusion constants, the potential barrier height, and the width of the outer shell. The first two are monotonous, whereas the last one may have a minimum for a sufficiently attractive cortex, for which we propose an analytical expression of the potential barrier height matching very well the numerical predictions.

Diffusion in crowded environments: Trapped by the drift.

The diffusion type is determined not only by microscopic dynamics but also by the environment properties. For example, the environment's fractal structure is responsible for the emergence of subdiffusive scaling of the mean square displacement in Markovian systems because the presence of nontrivially placed obstacles puts constraints on possible displacements. We investigate how the additional action of drift changes properties of the diffusion in the crowded environment. It is shown that the action of a constant drift increases chances of trapping, which suppresses the persistent ballistic motion. Such a diffusion becomes anisotropic because the drift introduces a preferred direction of motion which is further altered by interactions with obstacles. Moreover, individual trajectories display a high level of variability, which is responsible for the macroscopic properties of the diffusing front. Overall, the interplay among drift, diffusion, and a crowded environment, as measured by the time-averaged mean square displacement, is responsible for the emergence of superdiffusive and subdiffusive patterns in the very same system. Importantly, in contrast to free motion, the constant drift can enhance signatures of subdiffusive motion as it increases trapping chances.

The scent of fear makes sea urchins go ballistic

BackgroundClassic ecological formulations of predator–prey interactions often assume that predators and prey interact randomly in an information-limited environment. In the field, however, most prey can accurately assess predation risk by sensing predator chemical cues, which typically trigger some form of escape response to reduce the probability of capture. Here, we explore under laboratory-controlled conditions the long-term (minutes to hours) escaping response of the sea urchin Paracentrotus lividus, a key species in Mediterranean subtidal macrophyte communities.MethodsBehavioural experiments involved exposing a random sample of P. lividus to either one of two treatments: (i) control water (filtered seawater) or (ii) predator-conditioned water (with cues from the main P. lividus benthic predator—the gastropod Hexaplex trunculus). We analysed individual sea urchin trajectories, computed their heading angles, speed, path straightness, diffusive properties, and directional entropy (as a measure of path unpredictability). To account for the full picture of escaping strategies, we followed not only the first instants post-predator exposure, but also the entire escape trajectory. We then used linear models to compare the observed results from control and predators treatments.ResultsThe trajectories from sea urchins subjected to predator cues were, on average, straighter and faster than those coming from controls, which translated into differences in the diffusive properties and unpredictability of their movement patterns. Sea urchins in control trials showed complex diffusive properties in an information-limited environment, with highly variable trajectories, ranging from Brownian motion to superdiffusion, and even marginal ballistic motion. In predator cue treatments, variability reduced, and trajectories became more homogeneous and predictable at the edge of ballistic motion.ConclusionsDespite their old evolutionary origin, lack of cephalization, and homogenous external appearance, the trajectories that sea urchins displayed in information-limited environments were complex and ranged widely between individuals. Such variable behavioural repertoire appeared to be intrinsic to the species and emerged when the animals were left unconstrained. Our results highlight that fear from predators can be an important driver of sea urchin movement patterns. All in all, the observation of anomalous diffusion, highly variable trajectories and the behavioural shift induced by predator cues, further highlight that the functional forms currently used in classical predator–prey models are far from realistic.

Local Nonequilibrium Electron Transport in Metals after Femtosecond Laser Pulses: A Multi-Temperature Hyperbolic Model

ABSTRACT The trend toward miniaturization of electronic devices has increased the interest in nano scale heat transport, particularly, in laser-excited solids where electron–electron thermalization and electron-phonon coupling play a key role. Using a multi-temperature hyperbolic model, which takes into account the coupling between initially non-thermalized electrons and different phonon branches, we obtain a hierarchy of heat conduction equations for the electron temperature, which arises due to multi-length and time scales nature of coupling between different excitations. The hierarchy predicts that the ultrashort laser pulse induces a multi-front temperature wave propagating into the bulk of the material, which includes various heat transport regimes, ranging from the ballistic motion of the initially non-thermalized electrons propagating on the shortest time scale without interaction with the lattice as a temperature discontinuity, to the continuous wave-like temperature fronts arising on the intermediate time scale due to coupling between various excitations, and eventually to the classical Fourier transport on the longest time scale. The model is expected to be useful for modeling heat wave propagation phenomena in heterostructures and metamaterials.

Transmission Comparison for Cooperative Robotic Applications

The development of powered assistive devices that integrate exoskeletal motors and muscle activation for gait restoration benefits from actuators with low backdrive torque. Such an approach enables motors to assist as needed while maximizing the joint torque muscles, contributing to movement, and facilitating ballistic motions instead of overcoming passive dynamics. Two electromechanical actuators were developed to determine the effect of two candidate transmission implementations for an exoskeletal joint. To differentiate the transmission effects, the devices utilized the same motor and similar gearing. One actuator included a commercially available harmonic drive transmission while the other incorporated a custom designed two-stage planetary transmission. Passive resistance and mechanical efficiency were determined based on isometric torque and passive resistance. The planetary-based actuator outperformed the harmonic-based actuator in all tests and would be more suitable for hybrid exoskeletons.

Spontaneous Mode Switching of Self-Propelled Droplet Motion Induced by a Clock Reaction in the Belousov-Zhabotinsky Medium.

Interfacial chemical dynamics on a droplet generate various self-propelled motions. For example, ballistic and random motions arise depending on the physicochemical conditions inside the droplet and its environment. In this study, we focus on the relationship between oxidant concentrations in an aqueous droplet and its mode of self-propelled motion in an oil phase including surfactant. We demonstrated that the chemical conditions inside self-propelled aqueous droplets were changed systematically, indicating that random motion appeared at higher concentrations of oxidants, which were H2SO4 and BrO3-, and ballistic motion at lower concentrations. In addition, spontaneous mode switching from ballistic to random motion was successfully demonstrated by adding malonic acid, wherein the initially observed reduced state of the aqueous solution suddenly changed to the oxidized state. Although we only observed one-time transition and have not yet succeeded to realize alternation between ballistic (reduced state) and random motion (oxidized state), such spontaneous transitions are fundamental steps in realizing artificial cells and understanding the fundamental mechanisms of life-like behavior, such as bacterial chemotaxis originating from periodical run-and-tumble motion.

Interplay between Kinetics and Dynamics of Liquid-Liquid Phase Separation in a Protein Solution Revealed by Coherent X-ray Spectroscopy.

Microscopic dynamics of complex fluids in the early stage of spinodal decomposition (SD) is strongly intertwined with the kinetics of structural evolution, which makes a quantitative characterization challenging. In this work, we use X-ray photon correlation spectroscopy to study the dynamics and kinetics of a protein solution undergoing liquid-liquid phase separation (LLPS). We demonstrate that in the early stage of SD, the kinetics relaxation is up to 40 times slower than the dynamics and thus can be decoupled. The microscopic dynamics can be well described by hyper-diffusive ballistic motions with a relaxation time exponentially growing with time in the early stage followed by a power-law increase with fluctuations. These experimental results are further supported by simulations based on the Cahn-Hilliard equation. The established framework is applicable to other condensed matter and biological systems undergoing phase transitions and may also inspire further theoretical work.

Analytical consideration of particle transport in 1D nanostructures

The paper presents an analytical study of one-dimensional fluxes of ballistic quasiparticles in the presence of scattering centers. Such a situation can be realized at very low temperatures or systems of very small sizes – nanostructures. To describe such a situation, the approach of heat transfer by radiation, which goes back to Casimir, is used, in which the interaction of phonons with image boundaries is taken into account, or, for example, the Landauer approach, where the probability of phonon transition from the initial state to the final state is introduced. At the same time, the intermediate regime, the mean free path of phonons due to their interaction with each other, is comparable to the size of the samples; to this day, it remains a rather difficult problem for a theoretical or numerical solution. In this work, we propose the probabilistic approach in the Landauer model to describe heat transfer in the one-dimensional ballistic motion of quasiparticles. Within the framework of the theory of random walks, a model of successive scattering centers is considered. An explicit analytical expression is obtained for the dependence of the flux of quasiparticles on the probability of scattering and the number of scattering centers. In order to explain the physical sense of the obtained result the comparison with the result of iterative approach is made. As well the results are used for description of the problem of the heat flux in multilayered structures, in which one should take into account not only the thermal resistance inside the layers, but also the Kapitsa resistance between the layers. The practical application of the obtained results to one-dimensional nanostructures and to quasi-one-dimensional heat-conducting systems is discussed, various limiting cases are considered and a comparison with experimental data is made.

Optimizing Ballistic Motion of Partially Coherent Multiple Airy Beams by Quadratic and Linear Phases

AbstractBy applying quadratic and linear phase modulations (QPM and LPM), the propagation properties of the partially coherent dual and quad Airy beams which maintain acceleration in free space are studied. They are generated by superimposing two and four partially coherent Airy beams whose phase is modulated in the source field. It is demonstrated that the trajectories of the partially coherent light beams and the location and number of focal points, along with maximum altitude and range of the trajectories can be easily dominated by adjusting the appropriate values of QPM p and LPM l. Furthermore, for the quad case, the transverse spectral density distribution of lacking side lobes exhibits the structure of the optical frame which may be flipped under certain conditions. Both the peak intensity of the beams and the divergence speed of the optical frame can be managed by choosing the different characteristic transverse width of the beams. These results show an energizing new idea in the manipulation of partially coherent multiple fields of accelerating beams.

Random Force in Molecular Dynamics with Electronic Friction.

Originally conceived to describe thermal diffusion, the Langevin equation includes both a frictional drag and a random force, the latter representing thermal fluctuations first seen as Brownian motion. The random force is crucial for the diffusion problem as it explains why friction does not simply bring the system to a standstill. When using the Langevin equation to describe ballistic motion, the importance of the random force is less obvious and it is often omitted, for example, in theoretical treatments of hot ions and atoms interacting with metals. Here, friction results from electronic nonadiabaticity (electronic friction), and the random force arises from thermal electron–hole pairs. We show the consequences of omitting the random force in the dynamics of H-atom scattering from metals. We compare molecular dynamics simulations based on the Langevin equation to experimentally derived energy loss distributions. Despite the fact that the incidence energy is much larger than the thermal energy and the scattering time is only about 25 fs, the energy loss distribution fails to reproduce the experiment if the random force is neglected. Neglecting the random force is an even more severe approximation than freezing the positions of the metal atoms or modelling the lattice vibrations as a generalized Langevin oscillator. This behavior can be understood by considering analytic solutions to the Ornstein–Uhlenbeck process, where a ballistic particle experiencing friction decelerates under the influence of thermal fluctuations.

Quantum boomerang effect: Beyond the standard Anderson model

It was recently shown that wavepackets with skewed momentum distribution exhibit a boomerang-like dynamics in the Anderson model due to Anderson localization: after an initial ballistic motion, they make a U-turn and eventually come back to their starting point. In this paper, we study the robustness of the quantum boomerang effect in various kinds of disordered and dynamical systems: tight-binding models with pseudo-random potentials, systems with band random Hamiltonians, and the kicked rotor. Our results show that the boomerang effect persists in models with pseudo-random potentials. It is also present in the kicked rotor, although in this case with a specific dependency on the initial state. On the other hand, we find that random hopping processes inhibit any drift motion of the wavepacket, and consequently the boomerang effect. In particular, if the random nearest-neighbor hopping amplitudes have zero average, the wavepacket remains in its initial position.

Trajectory tracking analysis of airborne data link antenna

With the development of weapons and equipment and changes in combat concepts, airborne data links have become more and more widely used in war communications. Whether their system performance is stable and reliable has gradually become a key indicator for measuring the combat effectiveness of the Air Force. This article mainly introduces the airborne data link to provide graphical information for combatants, solves the problem that people’s information cannot be shared synchronously, expands the transmission scale of data information, and greatly improves the situational awareness of the battlefield. This paper mainly studies the link between the airborne data link between the computer and the aircraft, and makes a substantial analysis of the trajectory tracking, which is helpful for the combatants to be familiar with the trajectory direction and internal structure, and provide clear trajectory information for the fighters Interpretation, you can see at a glance the graphics, and the information obtained by the combatants is consistent. This paper mainly uses the standard Kalman filter algorithm to study the basic characteristics of the target ballistic group motion, and based on the HLA-simulated development of GBR radar integration and completed the system test to verify the accuracy of the simulation signal processing. The experimental results of this paper show that the information acquisition rate of combatants under the airborne data link has been increased by 40%, and the consistency of simultaneous information acquisition has been improved by 90%. This is the future development direction of the theater.

Generalized description of the Knudsen layer thickness in rarefied gas flows

We provide the first direct calculation of the Knudsen layer (KL) thickness in rarefied gas flows based on the ballistic molecular motions in the direct simulation Monte Carlo simulations. Calculations reproduce a linear relation between the KL thickness and the mean free path (MFP) of the gas, which agrees with the classical gas kinetic theory statement. The ratio of the KL thickness and MFP is only a function of the gas molecular model at slight flow gradients. However, high flow gradient and high surface curvature effects destroy the linear relation between the KL thickness and MFP.

Optimal escape-and-feeding dynamics of random walkers: Rethinking the convenience of ballistic strategies.

Excited random walks represent a convenient model to study food intake in a media which is progressively depleted by the walker. Trajectories in the model alternate between (i) feeding and (ii) escape (when food is missed and so it must be found again) periods, each governed by different movement rules. Here, we explore the case where the escape dynamics is adaptive, so at short times an area-restricted search is carried out, and a switch to extensive or ballistic motion occurs later if necessary. We derive for this case explicit analytical expressions of the mean escape time and the asymptotic growth of the depleted region in one dimension. These, together with numerical results in two dimensions, provide surprising evidence that ballistic searches are detrimental in such scenarios, a result which could explain why ballistic movement is barely observed in animal searches at microscopic and millimetric scales, therefore providing significant implications for biological foraging.