Local Acceleration Research Articles

Solar Energetic Particle Acceleration at a Spherical Shock with the Shock Normal Angle Evolving in Space and Time

We present a 2D kinematic model to study the acceleration of solar energetic particles (SEPs) at a shock driven by a coronal mass ejection. The shock is assumed to be spherical about an origin that is offset from the center of the Sun. This leads to a spatial and temporal evolution of the angle between the magnetic field and the shock-normal direction (θ Bn ) as it propagates through the Parker spiral magnetic field from the lower corona to 1 au. We find that the high-energy SEP intensity varies significantly along the shock front due to the evolution of θ Bn . Generally, the west flank of the shock preferentially accelerates particles to high energies compared to the east flank and shock nose. This can be understood in terms of the rate of acceleration, which is higher at the west flank. Double power-law energy spectra are reproduced in our model as a consequence of the local acceleration and transport effects. These results will help us to better understand the evolution of SEP acceleration and provide new insights into large SEP events observed by multiple spacecraft, especially those close to the Sun, such as Parker Solar Probe and Solar Orbiter.

Study of the influence of current pulse parameters on kinematic and energy characteristics of a plasma actuator based on a moving electric arc

In this work, a parametric study of the flow induced during the movement of an arc channel in a transverse constant magnetic field in initially still air is carried out. The analysis of the flow structure, integral energy and kinematic characteristics of the arc acceleration process is carried out. Instantaneous velocity fields in the induced flow were experimentally obtained for the range of discharge current amplitudes from 8 to 160 A and pulse durations from 40 to 380 μs. A parametric study of the flow structure in the wake behind the arc is carried out by the method of two-dimensional numerical simulation in the MHD approximation. In the particular case of a single-mode current pulse, the shape of the current pulse is optimized to maximize the gas momentum in the near-wall region. It is shown that similar conditions for the balance of local acceleration, convective acceleration and viscous forces are observed for the problem of flow past an arc and a cylinder for regimes with a conditionally steady vortex shedding in the wake. In this case, the coincidence of the vortex shedding frequency occurs when the characteristic scale of the streamlined body is chosen equal to half the height of the thermal cavity.

Abstract 15146: A Flying Saucer- Asymptomatic Migration of an Atrial Septal Defect Occluder Device to the Aortic Arch - No Good Deed Goes Unpunished!

Introduction: Though safe, the transcatheter closure with an atrial septal defect for secundum atrial septal defect (ASD) is associated with complications, such as device dislodgement. Case report: A 51-year-old female with a complex fenestrated secundum ASD (16mm superior defect and 14mm inferior defect with insufficient aortic rim) with hemodynamically significant shunt causing right heart dysfunction underwent placement of two atrial septal defect occluder devices (Amplatzer). While there was no shunting noted on immediate post-procedure transthoracic echocardiogram (TTE), a follow-up TTE after a year showed residual left to right shunting across the ASD. Transesophageal echocardiogram (TEE) showed a single occluder device (inferior) in place and a second device (superior) lodged in the distal aortic arch at the level of the left common carotid and left subclavian artery with mild local flow acceleration (aortic velocity 2.6 ms/s) and no superimposed device thrombus. Her only complaint was recurrent headaches, which pre-dated the procedure and were attributed to ocular migraine by her neurologist. The patient underwent a transcatheter procedure to attempt the retrieval of the dislodged device. The proximal end of the device was found adherent to the aortic wall. Aortogram revealed excellent flow around the device. The procedure was aborted due to the risk of dissection. Since the device did not cause any adverse effects and would likely continue to endothelialization. Conclusion: Atrial septal occluder device dislodgement can occur several months after implantation. Careful monitoring is required particularly when the ASD rim is insufficient. In cases of migration and adherence to the aortic wall without hemodynamic consequences, the device can likely be safely left in place to endothelialize. Despite a faster recovery with percutaneous procedures, a surgical approach should be considered in younger patients to avoid such complications.

Charting Galactic Accelerations with Stellar Streams and Machine Learning

We present a data-driven method for reconstructing the galactic acceleration field from phase-space (position and velocity) measurements of stellar streams. Our approach is based on a flexible and differentiable fit to the stream in phase-space, enabling a direct estimate of the acceleration vector along the stream. Reconstruction of the local acceleration field can be applied independently to each of several streams, allowing us to sample the acceleration field due to the underlying galactic potential across a range of scales. Our approach is methodologically different from previous works, as a model for the gravitational potential does not need to be adopted beforehand. Instead, our flexible neural-network-based model treats the stream as a collection of orbits with a locally similar mixture of energies, rather than assuming that the stream delineates a single stellar orbit. Accordingly, our approach allows for distinct regions of the stream to have different mean energies, as is the case for real stellar streams. Once the acceleration vector is sampled along the stream, standard analytic models for the galactic potential can then be rapidly constrained. We find our method recovers the correct parameters for a ground-truth triaxial logarithmic halo potential when applied to simulated stellar streams. Alternatively, we demonstrate that a flexible potential can be constrained with a neural network, and standard multipole expansions can also be constrained. Our approach is applicable to simple and complicated gravitational potentials alike and enables potential reconstruction from a fully data-driven standpoint using measurements of slowly phase-mixing tidal debris.

On optimal gear shifting in city bicycles

Standard and electric bicycles are expected to become the principal mean of transport for future short-range mobility. Solving the comfort problem is thus becoming more and more urgent, nonetheless it is known to be a hard task, especially because the cyclist is an active agent while pedaling. As far as we are aware, this is the first paper addressing the comfort problem during the gear shifting phase. Under non-restrictive assumptions, an algorithmic solution is developed providing an estimate for the best instant for comfort shifting. This problem is formulated as a local minimum acceleration point seeking. To solve it, the pedaling cadence is estimated from the rear wheel speed, after learning the gear ratios. Experiments performed on a real testing set-up are finally provided to assess the performance of the proposed approach.

Proof of Concept Project: Temperature Measurement Using Lora Sensors on the Bridge Over the Danube River Near Smederevo Kovin

Abstract: On the road network in the Republic of Serbia, is establish monitoring of parameters at certain points of road network for the needs of the organization that deals with road maintenance and implementation of PBMC (Performance based Maintenance Contract), which has a need for mass collection of data from roads and road facilities. One of the parameter is the temperature, whose measurement on the bridge structure over the Danube near Kovin/Smederevo will be the primary focus of this paper. New technology Lo Ra sensors were used to collect temperature data. This type of sensor has low energy consumption so it does not require a specially implemented power supply. The service life of such sensors is estimated at a minimum of 5 years in environmental conditions. Communication is achieved using Lo Ra WAN technology that requires an access communication point at a distance of up to 8 km from the sensor with a bandwidth capacity of 3 kbps to 50 kbps. This sensor allows the measurement and collection of temperature data as a primary function and is also able to measure local acceleration in three axes on the structural element on which it is mounted. This way of collecting data using wireless sensors with low power consumption significantly improves efficiency and economy in the field of road maintenance and monitoring.

Particle Acceleration Controlled by Ambient Density in the Southwestern Rim of RCW 86

The physics of particle acceleration at supernova remnant (SNR) shocks is one of the most intriguing problems in astrophysics. SNR RCW 86 provides a suitable environment for understanding the physics of particle acceleration because one can extract the information on both accelerated particles and acceleration environment in the same regions through the bright X-ray emission. In this work, we study X-ray proper motions and spectral properties of the southwestern region of RCW 86. The proper motion velocities are found to be ∼300–2000 km s−1 at a distance of 2.8 kpc. We find two inward-moving filaments, which are more likely reflected shocks rather than reverse shocks. Based on the X-ray spectroscopy, we evaluate thermal parameters such as the ambient density and temperature, and nonthermal parameters such as the power-law flux and index. From the decrease in flux over time of several nonthermal filaments, we estimate the magnetic field amplitudes to be ∼30–100 μG. Gathering the physical parameters, we then investigate parameter correlations. We find that the synchrotron emission from thermal-dominated filaments is correlated with the ambient density n e as (power-law flux) and (power-law index) , and not or only weakly correlated with the shock velocity and shock obliquity. As an interpretation, we propose a shock–cloud interaction scenario, where locally enhanced magnetic turbulence levels have a great influence on local acceleration conditions.

Off-equatorial effects of the nonlinear interaction of VLF chorus waves with radiation belt electrons

Nonlinear processes are involved in both the growth of VLF chorus waves and the energization of radiation belt electrons trapped in the wave potential. Nonlinear theory has led to analytic formulae describing both these processes. To investigate these processes, observations from the Van Allen Probes twin spacecraft provide simultaneous in situ information on VLF chorus waves, radiation belt and injected electrons, and local plasma parameters. We combine the theoretical treatment summarized by Omura (2021) with these in situ observations to investigate the characteristics and effects of nonlinear radiation belt processes at the off-equatorial location of the spacecraft observations. We show the smooth phase transition between initial subpackets of chorus wave elements, conducive to extended trapping and enhancement of resonant electrons. The structure of the chorus wave element changes as it propagates away from the equator. Frequency dispersion due to the variation of parallel wave group velocity with frequency contributes to the chorus waveform frequency sweep rate observed at an off-equatorial location. Nonlinear damping at the local value of ½ fce progressively erodes wave amplitude at frequencies above ½ fceEQ. We examine the important dependencies of the nonlinear inhomogeneity factor on the time rate of change of the wave frequency and the field-aligned gradient of the magnetic field and discuss their implication for the energization of trapped non-relativistic and MeV electrons. The 0.5–2% energy gain we find for 3–6 MeV seed electrons indicates that prompt local acceleration of highly relativistic and ultra-relativistic radiation belt electrons can take place directly through their nonlinear interaction with an individual VLF chorus wave element.

A consistent method to design and evaluate the performance of Anti-Roll Tanks for ships

ABSTRACT This article presents practical methods to design an Anti-Roll tank (ART) for a ship and to predict the performance of the system ship + ART in a sea state. The methods presented are extensions of existing mathematical models. The prediction of the moment exerted by the tanks has been improved and new models for the lateral force have been derived. Instead of using only the roll angle, a combination of the roll angle and the local lateral acceleration is used as excitation of the motion of the tank. The main advantage of this combined parameter is that it accounts for the distance of the tank bottom to the roll axis and the effect of sway. Experimental and CFD methods have been reviewed and results are shown. Limits of the use of the U and FS-type of ART are separately discussed and quantified. The procedure is demonstrated by a design example.

Towards personalized environment‐aware outdoor gait analysis using a smartphone

AbstractAutomatic gait analysis in free‐living environments using inertial sensors requires individualized approach as local acceleration and velocity profiles vary with the walker and the topological properties of the environment (e.g., walking in the forest vs. walking on sand). Here, we propose a smartphone‐based gait assessment architecture which consists of two data processing modules. The first module employs a set of personalized classifiers for automatic recognition of the walking environment. The second module provides accurate step time estimates by selecting the optimal filtering frequency tailored to the predicted environment. The performance of the architecture was evaluated using experimental data collected from 10 participants walking in 10 different conditions typically encountered during daily living. Compared with ground truth data, the architecture successfully recognized the walking environments; the percentage of correctly classified instances was above 92%. It also estimated step time with high accuracy; the mean absolute error was less than 10 ms, outperforming or at the very least matching the performance levels achieved in controlled laboratory trials (indoor flat surface walking). Compared with using one filtering frequency for all environments, using optimal frequency tailored to each environment reduced step time estimation error by more than 39%. To the best of our knowledge, this is the first study which successfully demonstrates that parameter tuning can improve gait characterization in outdoor environments. However, further research using a larger data set (including more participants with varying demographics and degree of impairment) is needed to confirm this result. Our findings highlight the importance of environment‐aware gait analysis, and lay the groundwork for a smartphone‐based technology that can be used in the community.

An event of extreme relativistic and ultra-relativistic electron enhancements following the arrival of consecutive corotating interaction regions: Coordinated observations by Van Allen Probes, Arase, THEMIS and Galileo satellites

During July to October of 2019, a sequence of isolated Corotating Interaction Regions (CIRs) impacted the magnetosphere, for four consecutive solar rotations, without any interposed Interplanetary Coronal Mass Ejections. Even though the series of CIRs resulted in relatively weak geomagnetic storms, the net effect of the outer radiation belt during each disturbance was different, depending on the electron energy. During the August-September CIR group, significant multi-MeV electron enhancements occurred, up to ultra-relativistic energies of 9.9 MeV in the heart of the outer Van Allen radiation belt. These characteristics deemed this time period a fine case for studying the different electron acceleration mechanisms. In order to do this, we exploited coordinated data from the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms Mission (THEMIS), Arase and Galileo satellites, covering seed, relativistic and ultra-relativistic electron populations, investigating their Phase Space Density (PSD) profile dependence on the values of the second adiabatic invariant K, ranging from near-equatorial to off equatorial mirroring populations. Our results indicate that different acceleration mechanisms took place for different electron energies. The PSD profiles were dependent not only on the μ value, but also on the K value, with higher K values corresponding to more pronounced local acceleration by chorus waves. The 9.9 MeV electrons were enhanced prior to the 7.7 MeV, indicating that different mechanisms took effect on different populations. Finally, all ultra-relativistic enhancements took place below geosynchronous orbit, emphasizing the need for more Medium Earth Orbit (MEO) missions.

Ultrasonic power measurement by Kibble balance

In May 2019, the International System of Units (SI) was revised. The new SI outlines the measurement system that allows the realisation of the kilogram using the Kibble balance. This work aims to develop and use a bench-top Kibble balance to perform ultrasonic power measurements, which are currently performed by a conventional balance. When replacing the traditional balance with a Kibble balance, the local gravity acceleration, one of the variables for measuring the ultrasonic power, is nullified, allowing the ultrasonic power to be measured in any place of the earth, without the need to know the value of the acceleration of the gravity. A low-cost bench-top Kibble balance was built using a 3D printer, a Raspberry microcomputer, an oscilloscope, and Python programming language. The prototype developed was able to measure a radiation power range from 1.4 W to 21.7 W and it obtained uncertainties lower than 5 % for the range above 9.6 W. Therefore, it is concluded that the developed system presented satisfactory results, especially considering that the system was built from a 3D printer. It is proposed that the system can be used as a basis for the development of new ultrasonic power measurement systems using the Kibble balance method.

Prediction of the Height of Water Flowing Fractured Zone Based on the MPSO-BP Neural Network Model

The height of the water flowing fractured zone (HWFFZ) is the key parameter for safe coal mining under water bodies. In order to improve the accuracy of prediction model of the HWFFZ, the grey relational analysis (GRA) is used to quantitatively analyze the influencing factors of the HWFFZ, the main influencing factors of the HWFFZ under the condition of comprehensive mechanized mining and comprehensive top coal caving mining are selected scientifically, and these five factors that include mining depth, mining thickness, inclined length of working face, hard rock lithology proportion coefficient, and coal seam dip angle are selected as the discriminant indexes for predicting the HWFFZ. Nonlinear inertia weight adjustment, linear adjustments of local acceleration factor and global acceleration factor, and Gaussian mutation operation are introduced into particle swarm optimization (PSO) algorithm to improve the performance of PSO algorithm. The modified particle swarm optimization (MPSO) algorithm is used to optimize the initial weights and thresholds of back propagation (BP) neural network, and the prediction model of the HWFFZ based on MPSO-BP neural network algorithm is established according to the measured data. The prediction results are compared with those of PSO-BP neural network model and empirical formulas, the results show that the prediction accuracy of MPSO-BP neural network prediction model is higher than that of PSO-BP neural network prediction model and empirical formulas, and its prediction mean relative error (MRE) is smallest. The model also has good application effect and certain guiding significance for actual production.

Unsteady Friction Modeling Technique for Lagrangian Approaches in Transient Simulations

This study investigates the simulation of celerity attenuation and head damping in transient flows using a Lagrangian approach rather than an Eulerian approach. Typically, the Lagrangian approach requires orders of magnitude fewer calculations, resulting in the rapid solution of very large systems. Additionally, it is based on a simple physical model. As the method is continuous in both time and space, it is less sensitive to the structure of the network and the length of the simulation process. Most recent studies, however, have focused on the development and improvement of computational routines for modeling in an Eulerian environment. This results in the development of adequate models that are suitable for Eulerian models but not applicable in Lagrangian-based models. As a result of this fixation, a bias was created towards using Eulerian approaches in transient simulations. It also diverts resources from further development of Lagrangian models. Consequently, it is necessary to develop a friction model that is more accurate and compatible with Lagrangian methods without compromising their performance. To the authors’ knowledge, such a model is yet to be published in the literature. This study presents a new friction modeling technique that compensates for both the local and convective acceleration terms for the Lagrangian transient modeling approach without compromising the computational time.

Receiver Sand Mitigation Measures along railways: CWE-based conceptual design and preliminary performance assessment

Desert railways are constantly exposed to incoming wind-blown sand. The railway structure locally disturbs the incoming sand drift, induces its accumulation, and ultimately suffers its harmful effects. Receiver Sand Mitigation Measures (SMMs) aerodynamically interact with the track system, induce sand erosion around it, and allow sand transport far downwind it. The conceptual and preliminary design of an innovative Receiver SMM called Sand Blower is developed in this study. The design is grounded on the aerodynamic behaviour of the baseline humped sleeper track system. The flow control strategy is intended to avoid boundary layer separation, and to promote local flow acceleration by means of the Venturi effect. The performance assessment is carried out by Computational Wind Engineering approach. It allows to simulate the local wind flow, to obtain the shear stress field at the wall, and to derive from it sand sedimentation, windward erosion and backward erosion conditions. The results show that the Sand Blower greatly increases the track system performance by reducing sand sedimentation and increasing sand erosion under wide range of wind speeds and directions.

Observation of Magnetic Reconnection in a Region of Strong Turbulence

We examine a rare and interesting observation of magnetic reconnection embedded in a large-scale region of strong turbulence in which magnetic field annihilation is energizing ions and electrons. The magnetic reconnection event is in Earth’s magnetotail and is associated with enhanced energetic particle fluxes indicating local particle acceleration. Despite substantial electric and magnetic field fluctuations throughout the surrounding, large-scale region, the ongoing magnetic reconnection has many similar properties to laminar, 2D magnetic reconnection including Hall electric fields, Hall magnetic fields, a thin electron current sheet, and ion and electron jets. Notably, the electron jet emerging from the electron diffusion region (EDR) appears to transport sufficient off-diagonal momentum to infer that off-diagonal electron stress can support the reconnection electric field in the EDR even in a turbulent environment. Although the electron jet appears to be briefly (∼1 s) deflected or possibly interrupted by an electromagnetic disturbance, the reconnection appears to otherwise continue for a long period (∼30 minutes) as evidenced by a persistent ion jet. This particular finding implies that the fundamental electron-scale processes inside of the EDR in turbulent magnetic reconnection are not necessarily distinct from those in laminar magnetic reconnection. These observations provide direct confirmation that magnetic reconnection can not only be responsible for but also can continue in regions of large-scale turbulence. Because the electric and magnetic fields of strong turbulence are linked to particle acceleration, it follows that particle acceleration also can continue as a consequence of turbulent magnetic reconnection.

Electron dynamics in small magnetospheres

Context. The planet Mercury possesses a small but highly dynamic magnetosphere in which the role and dynamics of electrons are still largely unknown. Aims. We aim to model the global dynamics of solar-wind electrons impinging on Mercury’s magnetosphere. Particular relevance is given to local acceleration processes and the global circulation patterns. Methods. The goals of this work are pursued by means of three-dimensional, fully kinetic particle-in-cell simulations modeling the interaction of the solar wind with the Hermean magnetosphere. This method allows a self-consistent representation of the plasma dynamics from the large planetary scale down to the electron kinetic scale. We carried out numerical simulations using two different solar-wind conditions: purely northward or purely southward interplanetary magnetic field direction. Results. We find a high plasma current (of the order of few μA m−2) flowing at the magnetospheric boundaries (bow shock and magnetopause) dominated by electrons. This current is driven by the small-scale electron physics resolved in our model. Furthermore, we observe strong electron acceleration up to tens of keV as a consequence of magnetic reconnection when the interplanetary magnetic field is directed southward. Such energetic electrons are partially trapped in the dipolar magnetic field of the planet mainly at nightside. Finally, by studying the distribution of electrons in our simulations along Mariner10 and BepiColombo first-Mercury-flyby trajectories, we propose that both spacecraft observed this energetic quasi-trapped electron population around closest approach.

A Short Review on the Preferential Concentration of Particles in Fluid Flow

Particle laden fluid flows are important in many fields of application such as environmental, chemical, astrophysical, and biological flows. They are examples of multicomponent fluid flow where the dispersed component is transported within a carrier fluid, and the dynamics of the flow are mostly dictated by the carrier fluid. The dispersed phase generally consists of particles such as droplets, bubbles, sediments, or nanoparticles while the carrier phase is typically water, oil, and chemical and biological liquids. Preferential concentration is an important characteristic of such multicomponent fluid flow which is defined by a higher density of particles in local regions of flow based on local acceleration, vorticity, strain, and pressure. Due to the intrinsic challenges of dealing with turbulence, mixing, particle tracking, and inter-and intra-component interactions, these flows are complicated to model. Based on the mass ratio of the particles to the fluid, the particles exhibit different preferential concentration patterns. In this article, experimental and numerical works on the preferential concentration of dispersed particles in different fluid flow problems are reviewed and discussed.

Visual recognition of social signals by a tectothalamic neural circuit

Social affiliation emerges from individual-level behavioural rules that are driven by conspecific signals1–5. Long-distance attraction and short-distance repulsion, for example, are rules that jointly set a preferred interanimal distance in swarms6–8. However, little is known about their perceptual mechanisms and executive neural circuits3. Here we trace the neuronal response to self-like biological motion9,10, a visual trigger for affiliation in developing zebrafish2,11. Unbiased activity mapping and targeted volumetric two-photon calcium imaging revealed 21 activity hotspots distributed throughout the brain as well as clustered biological-motion-tuned neurons in a multimodal, socially activated nucleus of the dorsal thalamus. Individual dorsal thalamus neurons encode local acceleration of visual stimuli mimicking typical fish kinetics but are insensitive to global or continuous motion. Electron microscopic reconstruction of dorsal thalamus neurons revealed synaptic input from the optic tectum and projections into hypothalamic areas with conserved social function12–14. Ablation of the optic tectum or dorsal thalamus selectively disrupted social attraction without affecting short-distance repulsion. This tectothalamic pathway thus serves visual recognition of conspecifics, and dissociates neuronal control of attraction from repulsion during social affiliation, revealing a circuit underpinning collective behaviour.

A Copula-Based Simulation of Wave-Induced Pore Water Pressure Gradient and Local Acceleration Within Surf Zone for Natural and Laboratory Barred Beach Profiles

Wave-induced pressure gradients and local accelerations are important interconnected physical mechanisms involving several hydrodynamic and morphodynamic coastal phenomena. Therefore, to provide a reliable and realistic hydrodynamic and morphodynamic simulation, the dependencies among different parameters, such as water level, pressure gradient, local acceleration, and sediment concentration, should be considered. Herein, a copula-based simulation is presented for modeling multivariate parameters and maintaining their statistical characteristics within the surf zone. Archimedean and elliptical copula families are applied to investigate the dependency construction between the parameters in two case studies: one from a field site on the east coast of Japan, and another from a large-scale laboratory barred beach profile. The dependency between variables is evaluated using Kendall’s τ correlation coefficient. The water level, pressure gradient, and local acceleration are shown to be significantly correlated. The correlation coefficients between the variables for the natural beach are lower than the laboratory data. The marginal probabilistic distribution functions and their joint probabilities are estimated to simulate the variables using a copula approach. The performance of the simulations is evaluated via the goodness-of-fit test. The analysis shows that the laboratory data are comparable to the field measurements, implying that the laboratory simulation results can be applied universally to model multivariable joint distributions with similar hydrodynamic conditions.