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A note on the Cucker-Smale model with time delay and communication failures
Full text linkIn this paper, we deal with a Cucker-Smale model with time-dependent time delay and communication failures. Namely, we investigate the situation in which the agents involved in a flocking process can possibly suspend the exchange of information among themselves at some times. Under a so-called Persistence Excitation Condition, we establish the exponential flocking for the considered model. The exponential decay estimates on the velocity diameters we obtain are independent of the number of agents, which is convenient especially when the number of agents becomes too large. Exponential decay estimates with decay rate depending on the number of agents appear instead in the case of pair-dependent time delays and non-universal interaction, i.e. not all the agents are able to exchange information among themselves. In this paper, we rather consider a universal interaction and the time delay functions do not depend on the pair of agents. The analysis is then extended to a model with distributed time delay, namely the time delay is not pointwise but the agents are influenced by the information received from the other components of the system in a certain time interval
Convergence to consensus results for Hegselmann-Krause type models with attractive-lacking interaction
Full text linkIn this paper, we analyze a Hegselmann-Krause opinion formation model with attractive-lacking interaction. More precisely, we investigate the situation in which the individuals involved in an opinion formation process interact among themselves but can eventually suspend the exchange of information among each other at some times. Under quite general assumptions, we prove the exponential convergence to consensus for the Hegselmann-Krause model in presence of possible lack of interaction. We then extend the analysis to an analogous model in presence of time delays
Energy decay for semilinear evolution equations with memory and time-dependent time delay feedback
No full textIn this paper, we study well-posedness and exponential stability
for semilinear second-order evolution equations with memory and
time-varying delay feedback. The time delay function is assumed to be continuous and bounded. Under a suitable assumption on the delay feedback, we are able to prove that solutions corresponding to small initial data are globally defined and satisfy an exponential decay estimate
Analysis and control of some evolutive models
Full text linkThe aim of this thesis is to investigate the asymptotic behavior of solutions to opinion formation and flocking models and to abstract evolution equations. Most of the models we will deal with involve time delay effects. Time delays, even arbitrarily small, may induce instability phenomena. Hence, the stability analysis for delayed systems is an important issue to deepen.
In this thesis, we will establish consensus results for the Hegselmann-Krause opinion formation model and the Cucker-Smale flocking model, investigating different scenarios. Namely, we will analyze situations where lack of connections, non-universal interactions or repulsive dynamics may occur among the system's agents.
Also, we will provide suitable decay estimates for solutions to linear evolution equations with time-dependent time delays and to semilinear evolution equations with memory and time-dependent time delay feedback
Exponential decay of solutions to linear evolution equations with time-dependent time delay
Full text linkIn this note, we analyze an abstract evolution equation with time-dependent time delay and time-dependent delay feedback coefficient. We assume that the operator corresponding to the nondelayed part of the model generates an exponentially stable semigroup. Under an appropriate assumption on the delay feedback, we prove the well-posedness and an exponential stability estimate for our model. Applications of our abstract results to concrete models are also illustrated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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