查看更多>>摘要：This paper is concerned with the recently introduced Sombor index SO, defined as SO = SO(G) = Sigma(vkvl is an element of E(G)) root d(G)(v(k))(2) + d(G) (v(l))(2), where d(G) (v) is the degree of the vertex v of a graph G. We present bounds on SO of trees in terms of order, independence number, and number of pendent vertices, and characterize the extremal cases. In addition, analogous results for quasi-trees are established. (C) 2021 Elsevier Inc. All rights reserved.
Curado, ManuelRodriguez, RocioTortosa, LeandroVicent, Jose F....
15页
查看更多>>摘要：Many scholars have tried to address the identification of critical nodes in complex networks from different perspectives. For instance, by means of the betweenness methods based on shortest paths and random walk, it is possible to measure the global importance of a node as an intermediate node. All these metrics have the common characteristic of not taking into account the density of the clusters. In this paper, we apply an analysis of network centrality, from a perspective oriented to ranking nodes, reinforcing dense communities using evaluating graphs using a two-trip transition probability matrix. We define a new centrality measure based on random walk betweenness. We study and analyse the new metric as a betweenness centrality measure with common characteristics with Pagerank, presenting through its practical implementation in some examples based on synthetic, and testing with well-known real-world networks. This method helps to increase the ranking of nodes belonging to dense clusters with a higher average degree than the remaining clusters, and it can detect the weakness of a network comparing it with the classical betweenness centrality measure. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：In this paper, the H-infinity sliding mode control problem of persistent dwell-time switched non-linear systems is investigated. Due to the limited bandwidth resources, a dynamic event-triggered mechanism is introduced to alleviate the transmission burden. Considering that the system parameters are switched in accordance with the persistent dwell-time switching strategy, a novel switched sliding mode control law is constructed. Then, drawing on the Lyapunov function approach, sufficient conditions are derived, which not only ensure the reachability of the sliding region around the specified sliding surface but also guarantee the globally uniform exponential stability of the system with an H-infinity performance. Moreover, the specific form of the controller gains is derived by utilizing an efficient decoupling method. Eventually, the validity of the proposed method is validated by two numerical examples. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：In a recent work Karakazian and Nassif (2021)[1], two of the authors have formulated the non-linear space-time Hasegawa-Mima plasma equation as a coupled system of two linear PDEs, a solution of which is a pair (u, w), with w = (I - Delta)u. The first equation is of hyperbolic type and the second of elliptic type. Variational frames for obtaining weak solutions to the initial value Hasegawa-Mima problem with periodic boundary conditions were also derived. Using the Fourier basis in the space variables, existence of solutions were obtained. Implementation of algorithms based on Fourier series leads to systems of dense matrices. In this paper, we use a finite element space-domain approach to semi-discretize the coupled variational Hasegawa-Mima model, obtaining global existence of solutions in H-2 on any time interval [0, T], for all T. In the sequel, full-discretization using an implicit time scheme on the semi-discretized system leads to a nonlinear full space-time discrete system. For the existence proof, a condition on the time step is imposed that is independent from the space mesh size h. For the uniqueness proof, a CFL-type of condition on the time step is imposed. Tests on a semi-linear version of the implicit nonlinear full-discrete system are conducted for several initial data, assessing the efficiency of our approach. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：Regional scale forest distribution models are important tools for biogeography and understanding the structure of forest communities in space. These models take climate and geographic variables as input and are therefore helpful for long-term decision support and climate adaptation planning. Generally, local processes of tree germination and seedling survival are resolved probabilistically with explanatory variables such as elevation, latitude, exposure, soil type, moisture availability, climate and weather inputs and 'trained' using landscape and regional presence-absence data and machine learning techniques. How seeds are distributed in these models, that is, determining the dispersal kernel, is far more problematic. The challenge is that variables conditioning vertebrate seed dispersal (motility and probability of utilization or caching in response to cover type) are not represented in large scale distribution models, and in fact vary on scales (10-100 meters) that are much smaller than the smallest pixel size for the distribution model (1-10 kilometers). We present a homogenized seed digestion kernel (HSDK) which incorporates this scale separation. Homogenization naturally links highly variable small-scale processes (like seed foraging and caching by birds and rodents) with large scale effects (like dispersal of seeds over tens of kilometers). We develop a homogenization strategy to predict seed dispersal on landscape scales, analytically linking small-scale variables (landscape fraction cover by tree type, gut residence times and cover type utilization by frugivorous birds) with large scale behaviors. Closed form approximations are developed in two dimensions for two limiting cases of seed handling behavior, and the approach is illustrated using landscape data and pinon-pine dispersal in a 630,000 square kilometer region in the southwestern US. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：This paper considers the data quantization problem for a class of unknown nonaffine nonlinear discrete-time multi-agent systems (MASs) under repetitive operations to achieve bipartite consensus tracking. Here, a quantized distributed model-free adaptive iterative learning bipartite consensus control (QDMFAILBC) approach is proposed based on the dynamic linearization technology, algebraic graph theory, and sector-bound methods. The proposed approach doesn't require each agent's dynamics knowledge and only uses the input/output data of MASs, where the data is coded by the logarithmic quantizer before being transmitted. Moreover, we consider both cooperative and competitive relationships among agents. We rigorously prove the stability of the proposed scheme and analyze the effects of data quantization. Meanwhile, we demonstrate that data quantization does not affect the stability of MASs, and bipartite consensus tracking errors can converge to zero with the processing of the proposed scheme, although the data quantization slows the convergence rate. Furthermore, the results are extended to switching topologies, and three simulation studies further validate the effectiveness of the designed method. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：This paper investigates convergence properties of gradient neural network (GNN) and GNN-based dynamical systems for computing generalized inverses. The main results are exact analytical solutions for the state matrices of the corresponding GNN and GNN-based dynamical systems. The exact solutions are given in each time instant, which enables to express final results as appropriate limiting expressions. This enables more rigorous convergence analysis in terms of exact solutions. Finally, trajectories of state variables in considered dynamical systems can be generated by avoiding time-consuming numerical solving matrix differential equations inside the selected time interval. Using the fact that the stated dynamical systems are in the essence systems of linear equations, explicit solutions can be obtained using known techniques of ordinary differential equations. Main results of the paper are further transformations of obtained exact solutions using main properties of generalized inverses and linear algebra tools. It is important to mention that the convergence results are expressed in terms of expressions involving outer inverses. Several examples are presented and a closed-form expressions for the solutions are given and implemented in package Mathematica. These are compared with the numerical solutions obtained by Matlab Simulink implementation. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：This work has addressed the output-feedback finite-time stabilization issue for a type of asymmetric output-constrained planar systems. The innovation involved in the results of the work owes to the construction of a barrier Lyapunov function (BLF) to the handling of the asymmetric output constraint. By incorporated the BLF into the backstepping-like technique, a state feedback controller is first developed. An implementable observer is subsequently designed to estimate the unmeasurable system state. Lastly, an observer-based finite-time output feedback controller is explicitly proposed. Theoretically, the Lyapunov stability theory is adopted to show that the system states are finite-time stabilized under the presented control scheme. Meanwhile, the violation of a pre-established asymmetric output constraint is circumvented. To testify the derived theoretical results, the case studies of a permanent magnet linear motor system are offered. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：In this work, we study a lower bound of the condition number of a matrix by its combined matrix. In particular, we construct a special combined matrix in such a way that the sums of its columns are lower bounds of the condition number of the matrix. Cases for special matrices as unitary matrices are considered. (C) 2021 The Authors. Published by Elsevier Inc.
查看更多>>摘要：The heterogeneity is a key feature of individual mobility which caused by different comprehensive interferences, including the distinctions of interventions deployed by governments and individuals' self-protection awareness in different regions. Since exposed individuals and infected individuals can infect the susceptible with different transmission rates, we use the Markovian approach to construct a Susceptible-Exposed-Infected-Recovered (SEIR) model with recurrent mobility patterns in the metapopulation network. We first theoretically calculate the epidemic threshold, and then, perform the proposed model in different underlying metapopulation networks, named as ER-like metapopulation network and BA-like metapopulation network. Simulation results indicate that BA-like metapopulation network is more conductive for epidemic spreading. Further research presents that both comprehensive interferences and the initial mobility rate can influence disease propagation heavily. In particular, for ER-like metapopulation network, comprehensive interferences can suppress the disease propagation when the initial mobility rate approaches to one. Whereas for BA-like metapopulation network, comprehensive interferences can contain the disease when the initial mobility rate is greater than a certain value. Meanwhile, implementing stronger interventions in patches with larger populations could reduce epidemic spreading effectively in BA-like metapopulation network. In addition, a long latent period could lead to the spread and infection of disease in both kinds of metapopulation networks. (C) 2021 Elsevier Inc. All rights reserved.
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