Multi-agent algorithms with assignment strategy pursuing multiple moving targets in dynamic environments

Devising intelligent agents to successfully plan a path to a target is a common problem in artificial intelligence and in recent years, attention has increased to multi-agent pathfinding problems, especially due to the expansion in computer video games and robotics. Pathfinding for agents in real-world applications is a defined problem of multi-agent systems, where pursuing agents collaborate among themselves and autonomously plan their path to the targets. There are multi-agent algorithms that provide solutions with the shortest path without considering other pursuers and several of those use coordination. However, less attention has been paid to computing an assignment strategy for the pursuers and finding paths that collectively surround the targets. Comparatively fewer studies have been on target algorithms either. Besides, the multi-agent pathfinding problem becomes even more challenging if the goal destinations change over time. Existing solutions consider either a single target with moving capability or multiple targets that are stationary. The work presented in this thesis considers multiple moving targets in multi-agent systems. Therefore, the path planning problem for multiple pursuing agents requires more efficient pathfinding algorithms. In addition, when the target algorithms are improved for advanced behaviour with moving capabilities that smartly evade the pursuers makes the problem even harder. The research reported in this thesis aims to investigate multi-agent search algorithms to address the challenge associated with pursuing agents towards moving targets within a dynamically changing environment. In multi-agent scenarios, agents compute a path towards the target, while these target destinations in some cases are predefined in advance. Thus, this research proposes to investigate a solution to the path planning problem by utilising heuristic algorithms as well as assignment strategies for multiple pursuing agents. Furthermore, a state-of-the-art moving target algorithm, TrailMax, has been enhanced and implemented for multiple agent pathfinding problems, which aims to maximise the capture time if possible until timeout. The focus of this thesis is the investigation of the assignment strategy algorithms to coordinate multiple pursuing agents and explore pathfinding search algorithms to find a route towards moving targets. This will be achieved by dividing it into two stages. The first one is the coupled approach where the assignment strategy with a given criterion finds the optimal combination based on the current position of players. The second stage is the decoupled approach, where each agent independently finds its path towards the moving target. On the other hand, targets flee from pursuing agents using the specified escaping strategy. The novel contributions of the research presented in this thesis are summarised as follows: - A new algorithm is developed that uses existing assignment strategies, sum-of-costs and makespan, to assign targets, and then runs repetitive A* search until reaches the target. - An enhancement is provided for a state-of-the-art target algorithm that takes smart moves by avoiding capture from all pursuers. - To improve efficiency, six new approaches are investigated to find an optimal agent-to-target combination for target assignment. - A novel multi-agent algorithm is developed which uses cover heuristics to maximise its coverage to outmanoeuvre, trap and catch moving targets. The proposed pathfinding solutions and the results presented in this thesis demonstrate a significant contribution towards search algorithms in multi-agent systems

Intrinsic ionic conductances mediate the spontaneous electrical activity of cultured mouse myotubes

AbstractMouse skeletal myotubes differentiated in vitro exhibited spontaneous contractions associated with electrical activity. The ionic conductances responsible for the origin and modulation of the spontaneous activity were examined using the whole-cell patch-clamp technique and measuring [Ca2+]i transients with the Ca2+ indicator, fura 2-AM. Regular spontaneous activity was characterized by single TTX-sensitive action potentials, followed by transient increases in [Ca2+]i. Since the bath-application of Cd2+ (300 μM) or Ni2+ (50 μM) abolished the cell firing, T-type (ICa,T) and L-type (ICa,L) Ca2+ currents were investigated in spontaneously contracting myotubes. The low activation threshold (around −60 mV) and the high density of ICa,T observed in contracting myotubes suggested that ICa,T initiated action potential firing, by bringing cells to the firing threshold. The results also suggested that the activity of ICa,L could sustain the [Ca2+]i transients associated with the action potential, leading to the activation of apamin-sensitive SK-type Ca2+-activated K+ channels and the afterhyperpolarization (AHP) following single spikes. In conclusion, an interplay between voltage-dependent inward (Na+ and Ca2+) and outward (SK) conductances is proposed to mediate the spontaneous pacemaker activity in cultured muscle myotubes during the process of myogenesis

Longitudinal two-photon imaging in somatosensory cortex of behaving mice reveals dendritic spine formation enhancement by subchronic administration of low-dose ketamine

Ketamine, a well-known anesthetic, has recently attracted renewed attention as a fast-acting antidepressant. A single dose of ketamine induces rapid synaptogenesis, which may underlie its antidepressant effect. To test whether repeated exposure to ketamine triggers sustained synaptogenesis, we administered a sub-anesthetic dose of ketamine (10 mg/kg i.p.) once-daily for 5 days, and repeatedly imaged dendritic spines of the YFP-expressing pyramidal neurons in somatosensory cortex of awake female mice using in vivo two-photon microscopy. We found that the spine formation rate became significantly higher at 72-132 h after the first ketamine injection (but not at 6-24 h), while the rate of elimination of pre-existing spines remained unchanged. In contrast to the net gain of spines observed in ketamine-treated mice, the vehicle-injected control mice exhibited a net loss typical for young-adult animals undergoing synapse pruning. Ketamine-induced spinogenesis was correlated with increased PSD-95 and phosphorylated actin, consistent with formation of new synapses. Moreover, structural synaptic plasticity caused by ketamine was paralleled by a significant improvement in the nest building behavioral assay. Taken together, our data show that subchronic low-dose ketamine induces a sustained shift towards spine formation.Peer reviewe

Development of fundamentals of theory and methods of simulation and control of processes of machining workpieces with variable cutting geometry

Available from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

A strategy-based algorithm for moving targets in an environment with multiple agents

Most studies in the field of search algorithms have only focused on pursuing agents, while comparatively less attention has been paid to target algorithms that employ strategies to evade multiple pursuing agents. In this study, a state-of-the-art target algorithm, TrailMax, has been enhanced and implemented for multiple agent pathfinding problems. The presented algorithm aims to maximise the capture time if possible until timeout. Empirical analysis is performed on grid-based gaming benchmarks, measuring the capture cost, the success of escape and statistically analysing the results. The new algorithm, Multiple Pursuers TrailMax, doubles the escaping time steps until capture when compared with existing target algorithms and increases the target’s escaping success by 13% and in some individual cases by 37%

Recovery from desensitization of neuronal nicotinic acetylcholine receptors of rat chromaffin cells is modulated by intracellular calcium through distinct second messengers

The mechanisms through which changes in intracellular Ca2+ concentration ([Ca2+]i) might influence desensitization of neuronal nicotinic receptors (nAChRs) of rat chromaffin cells were investigated by simultaneous patch-clamp recording of membrane currents and confocal microscopy imaging of [Ca2+]i induced by nicotine. Increases in [Ca2+]i that were induced by membrane depolarization or occurred spontaneously did not influence inward currents elicited by focally applied test pulses (10 msec) of nicotine, indicating that raised [Ca2+]i per se did not trigger desensitization of nAChRs. Desensitization of nAChRs, evoked by 2 sec focal application of nicotine, which largely raised [Ca2+]i, was not affected by intracellular application of agents that activate or depress protein kinase C (PKC) or A (PKA) or inhibit phosphatase 1, 2 A and B. Conversely, recovery from desensitization was facilitated by the phorbol ester phorbol 12-myristate 13-acetate (PMA) or the phosphatase 2 B inhibiting complex of cyclosporin A-cyclophilin A, whereas it was impaired by the broad spectrum kinase inhibitor staurosporine. The effects of PMA or staurosporine were prevented by the intracellularly applied Ca2+ chelator BAPTA. The adenylate cyclase activator forskolin accelerated recovery, whereas the selective PKA antagonist Rp-cAMPS had an opposite effect. The action of staurosporine and Rp-cAMPS on recovery from desensitization was additive. It is proposed that when nAChRs are desensitized, they become susceptible to modulation by [Ca2+]i via intracellular second messengers such as serine/threonine kinases and calcineurin. Thus, the phosphorylation state of neuronal nAChRs appears to regulate their rate of recovery from desensitization