Formation Track Research Articles

Resilient Time-Varying Formation Tracking for Heterogeneous High-Order Multiagent Systems With Multiple Dynamic Leaders

This paper investigates time-varying output formation tracking problems for heterogeneous multiagent systems in an adversarial environment, where both leaders and followers are vulnerable to cyber-attacks. Despite the presence of adversarial agents, the normal followers not suffering from cyber-attacks seek to achieve a desired for-mation configuration and track a safe trajectory generated by normal leaders' outputs simultaneously. To this end, a resilient time-varying output formation (RTVOF) tracking scheme is presented in this work. Firstly, to counteract the effect of adversarial agents, a safety strategy is proposed for general linear heterogeneous systems, which is a syn-thesis of the mean-subsequence-reduced family algorithms and an attack detection procedure. Secondly, using the neighboring interaction, a resilient distributed observer and a local formation controller are designed for each normal follower to estimate the state and track the output of the safe formation reference. Then, it is proved that the hetero-geneous multiagent system with multiple dynamic leaders and time-varying topologies can accomplish the RTVOF tracking if specific graph-theoretic properties and forma-tion feasibility conditions are satisfied. Finally, simulation examples are given to demonstrate the effectiveness of obtained results.

Adaptive Event-Triggered Time-Varying Output Bipartite Formation Containment of Multiagent Systems Under Directed Graphs.

The time-varying output bipartite formation containment (TVOBFC) problem for linear multiagent systems (MASs) under directed graphs is an important problem. However, the methods in existing works rely on the global information of the MASs or do not use event-triggered communication. This article investigates two kinds of TVOBFC problems for heterogeneous linear MASs under signed digraphs by event-triggered communication. For the first case where leaders have the same dynamics, the innovative fully distributed event-triggered protocol for the follower is proposed. In this case, the followers form the preset formation shape. For the second case where leaders have different dynamics, the leaders are divided into two groups. One group can directly obtain the output information of the virtual leader, while the other group cannot. In order to make leaders achieve the formation shape and track the virtual leader, two kinds of innovative observers are designed for two kinds of leaders to estimate the state of the virtual leader, and the control protocol is designed for each leader based on the designed observers. Then, the control law for each follower is designed to solve the formation containment problem. Finally, two examples are introduced to illustrate the main results.

TAPHONOMY OF TINY TETRAPOD TRACKS IN AN EXAMPLE FROM THE LOWER PERMIAN (CISURALIAN) SŁUPIEC FORMATION (SW POLAND)

Abstract The continental Lower Permian Słupiec Formation (the Sudetes Mountains, southwestern Poland) is well known for the occurrence of fossilized tracks of Early Permian tetrapods. Previous reports have focused on the taxonomy of tracks and their producers. The track assemblage was apparently missing the footprints of amphibians and thus such tetrapods were thought to be truly absent in the Słupiec Early Permian paleohabitat. The present paper utilizes the results of experiments and field surveys in order to test a possibility that tracks of tiny tetrapods (e.g., with body mass < 9 g), including amphibians, could be missing due to taphonomic filtration. The experimental tests were performed to investigate the following: (1) the interplay between the sizes of the penetrator (representation of trackmaker’s pes and manus) and the particles within the substrate, with emphasis on how the size interplay affects the lamina-modification mechanism, e.g., lamina-piercing by sand versus lamina compaction/displacement by sand or clay; (2) undertrack production in laminated sandy substrates by tiny tetrapods; and (3) the taphonomic impact that biofilm may have on the occurrence of tiny tetrapod tracks in clay. The results of experimental tests and the field survey suggest that tiny tetrapod tracks (e.g., amphibians) may be underrepresented in the Słupiec Formation track assemblage due to negative taphonomic filtration.

Study on structural properties of swift heavy ion induced damage in Al2O3

Polycrystalline α-Al2O3 is irradiated using 100 MeV Au ion, with fluences range extended from 1 × 1012 to 1 × 1014 ions/cm2. The objective of this work is to study the impact of swift heavy ion (SHI) on structural and morphological properties of α-Al2O3 and confirm the predicted results with the help of thermal spike (TS) model. XRD result reveals that there is a decrease in peak intensities with an increase in ion fluence. The reduction of peak intensity indicates the increased disorder or defect formation in α-Al2O3 due to SHI irradiation. Further, PL results also corroborated with the XRD outcome. Information on damage formation and molten track radius is extracted from the XRD data, and the molten track radius is obtained to be ∼2.42 ± 0.13 nm. Morphological changes due to SHI irradiation are studied using FESEM and AFM techniques and reveal the increase of surface roughness with the SHI fluences. Furthermore, the radius of latent track formation and radiation-induced lattice temperature spike are estimated for SHI irradiated Al2O3 using three cases; elastic TS model (only Sn), inelastic TS model (only Se), and unified TS model (Sn + Se). The numerically calculated latent track considering the combined contribution of Sn and Se in the unified TS model is around 2.6 nm, which is in good agreement with the experimental determination. The present study investigates the overall performance of structural properties of Al2O3 for SHI irradiation and explains the radiation tolerance of ceramic for corresponding ion fluence.

A Study of Marx's Thoughts on Beauty

In Marx's works, "the way of mastering art" and other expressions about beauty are mentioned. Do these expressions mean that Marx thinks about human existence, human comprehensive development and human liberation from the anthropological intention of beauty? In this paper, Marx's knowledge formation track is investigated from Marx's learning experience from middle school to university and life experience in his youth, tracing the ancient Greek origin of Marx's aesthetic tendency, citing Marx's image data in the eyes of western scholars, and analyzing the implication of Marx's thought on beauty.

Distributed observer based event‐triggered affine formation maneuver control for underactuated surface vessels with positive minimum inter‐event times

AbstractThis article investigates the distributed event‐triggered affine formation maneuver control problem for multiple underactuated surface vessel (USV) systems with positive minimum inter‐event times (MIET). Unlike common formation control methods that only ensure the formation system to keep a fixed geometric shape, the proposed scheme enables multiple USVs maneuver as a group in translation, shearing, rotation, or combinations of them. The proposed control strategy is composed of two parts. First, a distributed event‐triggered observer (DETO) is proposed to observe the time‐varying target formation under the lack of global leaders' information and govern the inter‐vessel communications among the formation group. Besides, the MIET of the designed communication strategy is proved to be strictly positive and computable from formation configurations and control parameters. With these guarantees, the maximum communication frequency can be known in advance. Then, upon the DETO signals, the adaptive local tracking controller is subsequently synthesized for each vessel to realize the target formation track. Rigorous theoretical analysis and simulation results are finally conducted to verify the validness and effectiveness of the proposed algorithm.

Adaptive hybrid formation-search and track controller of UAVs

In this paper, a novel search and track scheme is developed through adaptive hybrid formation- search and track controller of networked unmanned aerial vehicles (UAVs). The search and the track algorithm is carried out with antennas placed on at least four UAVs that kept the ‘+’ formation on the x-y plane. The x-axis is assumed to lie in the east–west direction and the y-axis in the north–south direction. UAVs flying in the ‘+’ formation are divided into 4 main groups: east, west, north, and south. UAVs on the x-axis are driven from the difference in signal strengths of the east group and the west group, and on the y-axis from the difference in signal strengths of the north and south groups respectively. The hybrid controller consists of two discrete modes: (1) formation mode (2) search and track mode. The back-stepping formation controller is derived through Lyapunov stability criteria to make the UAVs fly in ‘+’shape and at a fixed altitude. Then, received signal power consensus-based search and track controller is developed for networked UAV groups flying in a desired ‘+’ formation. Simulation results verify our theoretical claims.

Intelligent multiframe detection aided by Doppler information and a deep neural network

Multiframe detection can be effective for the detection of targets with low signal-to-noise ratios by integrating the target information in several consecutive frames. Traditional methods usually suffer from high computational complexity and insufficient use of available information. In this paper, we propose solving the multiframe detection problem through two sequential steps: Doppler-aided track formation (DTF) and data-driven track detection (DTD). By using the DTF, which considers the coupling relationship between the location measurements and Doppler measurements, the potential tracks can be extracted without introducing too many false tracks. Using DTD, which fuses multiple features along the extracted tracks through a deep neural network, the detection can be sequentially declared. Simulation results show that the detection performance of the proposed method is better than that of the traditional methods for weak targets, and that false alarms can be handled well. Both theoretical analysis and experimental studies corroborate the computational efficiency of the proposed method in real-time implementation.

Research on Tracking Control of A Quadrotor UAV Based on Model Predictive Control and PD Control

In order to solve the problem of path tracking of a quadrotor UAV, this paper proposes a track tracking control method which combines Model Predictive Control algorithm and PD control method. Model Predictive Control algorithm can generate control input for formation flight and track the specified trajectory. PD control can achieve rapid response to attitude and adjust error quickly. The simulation results verify the effectiveness of the proposed control method.

Saurischian dinosaur tracks from the Upper Triassic of southern Queensland: possible evidence for Australia’s earliest sauropodomorph trackmaker

ABSTRACT Fossil footprints provide the only evidence of Triassic-aged dinosaurs in Australia. While historically several Triassic dinosaur tracksites are reported, only one specimen exists for direct study. Evidence for the Rhondda colliery (Ipswich) trackmaker, Upper Triassic Blackstone Formation as a very large-bodied Triassic predatory dinosaur is not supported by the present study because of overestimated footprint length measurements, and we question earlier interpretations that these tracks are Eubrontes-like. Instead, we recognise shared characteristics with the sauropodomorph ichnogenus Evazoum. The track morphology resembles that of Evazoum on account of the distinct shape and position of the impression of the metatarsophalangeal pad for digit IV. The mesaxony of the Blackstone Formation track is also low, but possibly slightly higher than in Evazoum, if the proportions of the digital impressions are correctly interpreted. Finally, the trackway pattern shows constant track inward rotation, a feature observed in typical Evazoum and mostly absent in Eubrontes. Therefore, we assign these Australian tracks as Evazoum ichnosp. indet. If our assessment of the Blackstone Formation tracks is correct, they provide the first and only evidence of basal sauropodomorph dinosaurs from Australia. In addition to this record, we give an overview of other reported (but lost) Australian Triassic dinosaur footprints.

Crocodylian swim tracks from the Gates Formation (Albian), British Columbia, Canada: comparisons with Cretaceous crocodylian ichnology in western USA

Numerous crocodylian swim tracks occur in the late Early Cretaceous and earliest Late Cretaceous of western North America, in coastal plain deposits marginal to the Cretaceous interior seaways. New assemblages from the lower Albian Gates Formation, within the Tumbler Ridge UNESCO Global Geopark Quintette site (TRUGG-Q) in British Columbia, Canada, resemble those from Albian-Cenomanian Dakota Sandstone sites in Colorado, Kansas and Utah, and facilitate comparative analysis of how such assemblages are registered and preserved. The Gates Formation track assemblage formed on the southwest margin of the ‘Moosebar Sea’ that filled the foredeep of the Western Canada Foreland Basin in the Early Albian. Northeast-prograding sandy deltas were backed by low-lying and heavily-vegetated coastal plains, inhabited by track-making dinosaurs, birds, and crocodylians. The base of a tidal channel-fill at the TRUGG-Q site preserves crocodylian swim traces indicating progression largely parallel to the channel axis, as also inferred for some USA sites. Swim track lengths can be categorized on a short–long spectrum which reflects swimming behavior, with short, wide toe tip traces indicating firm digging-in of toes (‘punting’ or ‘poling’ behavior), and elongate scrape marks indicating light touch-down (or substrate ‘raking’) by buoyant animals making intermittent contact with a subaqueous substrate. The body lengths size of crocodylian trackmakers can be calculated from rare complete ‘walking’ track footprints or from the widths, not lengths, in the case of ‘swim’ traces. The mean size of the Canadian tracks indicates individuals with body lengths in the range of ~1.0 m, with larger trackmakers up to ~4.0 m more common at the USA sites.

Opportunity for Early Warnings of Typhoon Lekima from Two Global Ensemble Model Forecasts of Formation with 7-Day Intensities along Medium-Range Tracks

Typhoon Lekima (2019) with its heavy rains and floods is an excellent example of the need to provide the earliest possible warnings of the formation, intensification, and subsequent track before a typhoon makes landfall along a densely populated coast. To demonstrate an opportunity to provide early (10 days in advance) warnings of the threat of Typhoon Lekima, the ensemble models from the European Centre for Medium-Range Weather Forecasts and the National Centers for Environmental Predictions have been used to provide time-to-formation timing and positions along the weighted-mean vector motion track forecasts. In addition, the seven-day intensity forecasts after the formation using a weighted analog intensity prediction technique are provided. A detailed description of one European Center ensemble forecast is provided to describe the methodology for estimating the formation time and generating the intensity forecasts. Validation summary tables of the formation timing and position errors, and the intensity errors versus the Joint Typhoon Warning Center intensities, are presented. The availability of these ensemble forecasts would have been an opportunity to issue alerts/watches/warnings of Lekima even seven days in advance of when Lekima became a Tropical Storm. These ensemble forecasts also represent an opportunity to extend support on the 5–15 day timescale for the decision-making processes of water resource management and hydrological operations.

Multi-formation track initiation method based on Density clustering

Aiming at the problem that the existing track initiation algorithm has a poor effect when starting multiple formation tracks under strong clutter, based on the Hough transform method and its derivative algorithm, a multi-formation Hough transform route based on density clustering is proposed. Trace start algorithm. The algorithm first combines the motion information of the target and the timing parameters of the detection points to filter the detection data set to exclude as many points as possible from non-targets. Then it uses the Hough transform to process the obtained detection point set to obtain a preliminary threshold with a lower threshold Formation track; Finally, according to the characteristics of formation goals, the overall formation track is obtained by density clustering method, which solves the problems of track crossing and chaos. Simulation results show that, compared with the standard Hough transform method and its derivative algorithm, the algorithm can start the track of formation targets under strong clutter, and has good performance.

Moving Area Tracking Formation Control of Multiple Autonomous Agents

This paper investigates a moving area tracking formation control (MATFC) problem of multiple autonomous agents, which aims at driving a group of agents to achieve a desired formation configuration and track a moving area. By using local information interaction among agents, a distributed MATFC protocol is proposed for single integrator dynamics. Without requiring the position and velocity of the center of the sub-area are bounded, the MATFC problem obtains greater application potential. During the moving process, the formation size can be regulated in real time to adapt the complicated environment through a scaling parameter. By adding a rotation matrix, the spatial orientation of each agent is capable of transforming in different cases. Then, based on the Lyapunov stability theory, it is verified that the objective of MATFC problem can be achieved under the proposed control protocol. Finally, numerical simulation results are shown to further demonstrate the effectiveness of the designed MATFC protocol.

Time-varying output formation tracking of heterogeneous linear multi-agent systems with multiple leaders and switching topologies

This paper studies the time-varying output formation tracking problems for heterogeneous linear multi-agent systems with multiple leaders in the presence of switching directed topologies, where the agents can have different system dynamics and state dimensions. The outputs of followers are required to accomplish a given time-varying formation configuration and track the convex combination of leaders’ outputs simultaneously. Firstly, using the neighboring relative information, a distributed observer is constructed for each follower to estimate the convex combination of multiple leaders’ states under the influences of switching directed topologies. The convergence of the observer is proved based on the piecewise Lyapunov theory and the threshold for the average dwell time of the switching topologies is derived. Then, an output formation tracking protocol based on the distributed observer and an algorithm to determine the control parameters of the protocol are presented. Considering the features of heterogeneous dynamics, the time-varying formation tracking feasible constraints are provided, and a compensation input is applied to expand the feasible formation set. Sufficient conditions for the heterogeneous multi-agent systems with multiple leaders and switching directed topologies to achieve the desired time-varying output formation tracking under the designed protocol are proposed. Finally, simulation examples are given to validate the theoretical results.

Formation-containment tracking for general linear multi-agent systems with a tracking-leader of unknown control input

This paper investigates the formation-containment tracking problems for general linear multi-agent systems with a tracking-leader of unknown control input, where the agents are classified into a tracking-leader, several formation-leaders and followers. The formation-leaders are required to accomplish a given time-varying formation configuration and track the desired trajectory generated by the tracking-leader simultaneously, while the followers need to converge to the convex hull spanned by the formation-leaders. Firstly, based on the neighboring relative information, a formation-containment tracking protocol is proposed under the influences of the tracking-leader’s unknown input. Then an algorithm is given to determine the control parameters, where a general formation-containment tracking feasible constraint is presented. It is proved that the given formation-containment tracking can be achieved under the discontinuous protocol. Furthermore, in order to avoid the large chattering of the control inputs, a continuous formation-containment tracking protocol is also presented, under which the errors can converge to an arbitrarily small neighborhood of zero. Finally, a simulation example is given to verify the theoretical results.

Increasing transnational sea‐ice exchange in a changing Arctic Ocean

AbstractThe changing Arctic sea‐ice cover is likely to impact the trans‐border exchange of sea ice between the exclusive economic zones (EEZs) of the Arctic nations, affecting the risk of ice‐rafted contamination. We apply the Lagrangian Ice Tracking System (LITS) to identify sea‐ice formation events and track sea ice to its melt locations. Most ice (52%) melts within 100 km of where it is formed; ca. 21% escapes from its EEZ. Thus, most contaminants will be released within an ice parcel's originating EEZ, while material carried by over 1 00,000 km2 of ice—an area larger than France and Germany combined—will be released to other nations' waters. Between the periods 1988–1999 and 2000–2014, sea‐ice formation increased by ∼17% (roughly 6 million km2 vs. 5 million km2 annually). Melting peaks earlier; freeze‐up begins later; and the central Arctic Ocean is more prominent in both formation and melt in the later period. The total area of ice transported between EEZs increased, while transit times decreased: for example, Russian ice reached melt locations in other nations' EEZs an average of 46% faster while North American ice reached destinations in Eurasian waters an average of 37% faster. Increased trans‐border exchange is mainly a result of increased speed (∼14% per decade), allowing first‐year ice to escape the summer melt front, even as the front extends further north. Increased trans‐border exchange over shorter times is bringing the EEZs of the Arctic nations closer together, which should be taken into account in policy development—including establishment of marine‐protected areas.Plain Language SummaryWe use data from satellite images to identify the formation, drift tracks, and melt locations of sea ice in the Arctic. Most ice melts locally: only about 21% is exported from the exclusive economic zone (EEZ) in which it is formed. That export is nonetheless about 1,000,000 km2 each year. As the ice cover has thinned and the summer sea ice has retreated in a warming Arctic, formation and melt locations have moved further north, ice drifts have accelerated, and the area of ice formation and melt has increased. We looked at ice formation and transport between the EEZs of the Arctic nations, and broke the record into two periods: 1988–1999 and 2000–2014. As the Arctic warms, more ice is transported between EEZs and it is arriving at the receiving EEZ faster, than in the past. Between the two study periods: Sea ice velocity increased by about 14%/decade; Russian ice reached melt locations in other nations' EEZs 46% faster; and North American ice reached Eurasian destinations 37% faster. Exchanges of ice have increased as a result. For example, export of ice from Russia to Norway increased by 11% and export from Alaska to Russia by 16%.

Decentralized minimal‐time planar formation control of multi‐agent system

SummaryIn this paper, the problems of decentralized minimal‐time planar formation control are investigated for both static and dynamic cases. For the static one, the discrete‐time dynamics of multi‐agent system in which each agent exchanges information according to a complex weighted network is studied. On the basis of a minimal polynomial, a decentralized minimal‐time static formation method is proposed to compute the final formation positions of the agents in the minimal number of steps without global coordinates. The proposed method allows an arbitrarily chosen agent in the network to compute its final formation position. For the dynamic one in a leader–follower framework, the path information of the agents satisfies linear regression equations that are determined by interaction topology and input signals. In order to obtain the coefficients of such linear regression equations, a Kronecker‐theorem‐based algorithm is presented. Similar to the results for the static case, any agent is allowed to use the minimum number of successive history state values to compute the future dynamic formation track. The minimal number of steps can be computed by checking the rank condition of the Hankel matrix constructed in terms of the path information. Meanwhile, the simulation examples are given to demonstrate the validity of the proposed minimal‐time planar formation control methods. The results in the paper combine the matrix polynomial analysis into the framework of formation control design and show how to predict the motion of the agents in a decentralized manner. Copyright © 2017 John Wiley & Sons, Ltd.

Insights on dramatic radial fluctuations in track formation by energetic ions.

We report on unexpected dramatic radial variations in ion tracks formed by irradiation with energetic ions (2.3 GeV 208Pb) at a constant electronic energy-loss (~42 keV/nm) in pyrochlore-structured Gd2TiZrO7. Though previous studies have shown track formation and average track diameter measurements in the Gd2TixZr(1−x)O7 system, the present work clearly reveals the importance of the recrystallization process in ion track formation in this system, which leads to more morphological complexities in tracks than currently accepted behavior. The ion track profile is usually considered to be diametrically uniform for a constant value of electronic energy-loss. This study reveals the diameter variations to be as large as ~40% within an extremely short incremental track length of ~20 nm. Our molecular dynamics simulations show that these fluctuations in diameter of amorphous core and overall track diameter are attributed to the partial substitution of Ti atoms by Zr atoms, which have a large difference in ionic radii, on the B-site in pyrochlore lattice. This random distribution of Ti and Zr atoms leads to a local competition between amorphous phase formation (favored by Ti atoms) and defect-fluorite phase formation (favored by Zr atoms) during the recrystallization process and finally introduces large radial variations in track morphology.

Formation Track Association Algorithm in the Presence of Sensor Bias Based on Double Fuzzy Topology

Aiming to solve the track association problem of the formation targets in the presence of sensor bias, a formation track association algorithm based on double fuzzy topology (DFT-FTA) is proposed according to the topology characteristics of the formation tracks. The formations are identified among sensors tracks based on the circulatory threshold model firstly. Then the formation tracks are replaced by their center track so that the first fuzzy topology model is established to realize preparatory association of formation tracks and common tracks. At last, the second fuzzy topology model based on the associated formation tracks and associated common tracks is established to realize formation inner track association. The simulation result shows that the proposed algorithm outperforms the fuzzy track alignment-association algorithm based on target invariable information (TII-FTA) and modified weight track association algorithm (MW-TA).