The existing results on the leaderless and leader-following consensus problems for discrete-time linear multi-agent systems subject to jointly connected switching networks are limited to undirected ...networks. This note will first study the stability property for a class of discrete-time linear switched systems. This stability result will then be applied to the two consensus problems for discrete-time linear multi-agent systems subject to directed jointly connected switching networks. It is shown that, in some interesting cases, the two problems are solvable by the distributed state feedback control law even if the switching networks are directed and every time disconnected.
In this technical note, we deal with the attitude tracking and disturbance rejection problem of spacecraft for a class of persistent disturbances with unbounded energy which include the sinusoidal ...disturbance as a special case. The approach involves the integration of techniques from robust control, adaptive control, and robust output regulation theory.
A simple motor behaviour or a more complex behaviour is the result of the neural activity of those neural networks responsible for the behaviour. To understand how the network activity is transformed ...into human behaviours, it is necessary to identify task-specific networks and analyse the dynamic network activity that changes with time. Here we report a novel task-fMRI technique to identify task-specific networks and analyse their dynamic activity. Nine subjects participated in a task-fMRI study in which the subjects were cued to perform three different tasks of word-reading, pattern-viewing and finger-tapping. A functional area of unitary pooled activity (FAUPA) is defined as an area in which the temporal variation of the activity is the same across the entire area, and a task-associated FAUPA plays the role of a functional unit for the task. A novel method is presented to (1) identify FAUPAs that are associated with each task as well as their functional groupings; (2) identify the three task-specific networks; and (3) analyse the network activity from trial to trial. Task-associated FAUPAs were identified for each task and each subject. A task-specific large-scale neural network across the whole brain consisted of all FAUPAs that were activated each time the task was performed, and all three task-specific networks were identified for each individual subject. The temporal changes of activation and functional connectivity of the FAUPAs within each network from trial to trial characterized the dynamic activity of the network. The results demonstrated a one-to-one relation between the network activity and the task performance from trial to trial, offering a means of testing the causal relationship between network activity and human task performance by systematically manipulating task performance and measuring corresponding network activity change.
Alzheimer’s disease (AD) is a devastating neurodegenerative disease with a concealed onset and continuous deterioration. Mild cognitive impairment (MCI) is the prodromal stage of AD. Molecule-based ...imaging with positron emission tomography (PET) is critical in tracking pathophysiological changes among AD and MCI patients. PET with novel targets is a promising approach for diagnostic imaging, particularly in AD patients. Our present review overviews the current status and applications of
in vivo
molecular imaging toward neuroinflammation. Although radiotracers can remarkably diagnose AD and MCI patients, a variety of limitations prevent the recommendation of a single technique. Recent studies examining neuroinflammation PET imaging suggest an alternative approach to evaluate disease progression. This review concludes that PET imaging towards neuroinflammation is considered a promising approach to deciphering the enigma of the pathophysiological process of AD and MCI.
In this technical note, we consider the cooperative output regulation of linear multi-agent systems. The overall system consists of two groups of subsystems. While the first group of subsystems can ...access the exogenous signal, the second cannot. As a result, the problem cannot be solved by the decentralized approach. By devising a distributed observer, we can solve the problem by a dynamic full information distributed control scheme. The problem can also be viewed as a generalization of some results of the leader-following consensus problem of multi-agent systems.
We consider symmetry-protected topological (SPT) phases with crystalline point group symmetry, dubbed point group SPT (pgSPT) phases. We show that such phases can be understood in terms of ...lower-dimensional topological phases with on-site symmetry and that they can be constructed as stacks and arrays of these lower-dimensional states. This provides the basis for a general framework to classify and characterize bosonic and fermionic pgSPT phases, which can be applied for arbitrary crystalline point group symmetry and in arbitrary spatial dimensions. We develop and illustrate this framework by means of a few examples, focusing on three-dimensional states. We classify bosonic pgSPT phases and fermionic topological crystalline superconductors with Z2P (reflection) symmetry, electronic topological crystalline insulators (TCIs) with U(1)×Z2P symmetry, and bosonic pgSPT phases with C2v symmetry, which is generated by two perpendicular mirror reflections. We also study surface properties, with a focus on gapped, topologically ordered surface states. For electronic TCIs, we find a Z8×Z2 classification, where the Z8 corresponds to known states obtained from noninteracting electrons, and the Z2 corresponds to a “strongly correlated” TCI that requires strong interactions in the bulk. Our approach may also point the way toward a general theory of symmetry-enriched topological phases with crystalline point group symmetry.
In this note, we first propose an adaptive distributed observer for a linear leader system. This observer only assumes those followers who are the children of the leader know the system matrix of the ...leader system. Then, we further develop a distributed adaptive controller utilizing this adaptive distributed observer to solve the leader-following consensus problem for multiple uncertain Euler-Lagrange systems without assuming that all the followers need to know the system matrix of the leader system.
In this paper, we first establish a stability result for a class of linear switched systems involving Kronecker product. The problem is interesting in that the system matrix does not have to be ...Hurwitz at any time instant. This class of linear switched systems arises in the control of multi-agent systems under switching network topology. As applications of this stability result, we give the solvability conditions for both the leaderless consensus problem and the leader-following consensus problem for general marginally stable linear multi-agent systems under switching network topology. In contrast with some existing results, our results only assume that the dynamic graph is uniformly connected.
In this paper, we consider the leader-following consensus problem for a multiple rigid spacecraft system whose attitude is represented by the unit quaternion. Most results on this problem rely on the ...assumption that every follower can access the state of the leader and are obtained via a decentralized control manner. By developing a nonlinear distributed observer for the leader system, we can solve this problem via a distributed control scheme under the mild assumptions that the state of the leader can reach every follower through a path and that the communication between followers is bidirectional. Moreover, our result can accommodate a class of desired angular velocities generated by a marginally stable linear autonomous system.
We report the discovery of human brain functional areas of unitary pooled activity (FAUPAs) using fMRI. A FAUPA is defined as an area in which the temporal variation of the activity is the same ...across the entire area. This dynamically unitary activity implies a perfect temporal correlation everywhere within the FAUPA for the activity-induced BOLD response, i.e., the corresponding Pearson correlation coefficient (R) is 1 for the BOLD responses of any two locations within the FAUPA. A novel method was developed to identify the FAUPA. In this study, nine subjects had a resting-state (rs) fMRI and a task-fMRI. FAUPAs have been identified for both rs- and task-fMRI, and their determination was objective and automatic, with no a-priori knowledge. The group mean of R was 0.952 ± 0.004 for the rs-fMRI and 0.950 ± 0.002 for the task-fMRI, showing the dynamically unitary activity within each FAUPA. For the finger-tapping (FT) task, the group-mean BOLD signal time course of the FT-associated FAUPAs in the primary motor cortex was almost perfectly correlated with the FT-induced ideal response (R = 0.9330, P = 1.8 × 10
), confirming the association of the FAUPA with the task. A task-associated FAUPA may play the role of a functional unit for a particular neural computation.
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