A system made up of N interacting species is considered. Self-reaction terms are assumed of the l... more A system made up of N interacting species is considered. Self-reaction terms are assumed of the logistic type. Pairwise interactions take place among species according to different modalities, thus yielding a complex asymmetric disordered graph. A mathematical procedure is introduced and tested to stabilise the ecosystem via an ad hoc rewiring of the underlying couplings. The method implements minimal modifications to the spectrum of the Jacobian matrix which sets the stability of the fixed point and traces these changes back to species-species interactions. Resilience of the equilibrium state appear to be favoured by predator-prey interactions.
We investigate how knowledge percolates and clusters in a given knowledge space. We introduce a s... more We investigate how knowledge percolates and clusters in a given knowledge space. We introduce a simple model of knowledge organization in which each contribution spans a certain number of items. If this contribution overlaps with others above a certain threshold, they form a cluster. A contribution can also merge clusters together. We study the growth of global knowledge and the cluster dynamics, both showing a nontrivial behavior.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires
An important question to be addressed regarding system control on a time interval [0, T ] is whet... more An important question to be addressed regarding system control on a time interval [0, T ] is whether some particular target state in the configuration space is reachable from a given initial state. When the target of interest refers only to a portion of the spatial domain, we speak about regional analysis. Cellular Automata (CA) approach have been recently promoted for the study of control problems on spatially extended systems for which the classical approaches cannot be used. An interesting problem concerns the situation where the subregion of interest is not interior to the domain but a portion of its boundary. In this paper we address the problem of regional controllability of cellular automata via boundary actions, i.e., we investigate the characteristics of a cellular automaton so that it can be controlled inside a given region only acting on the value of sites at its boundaries.
Prestrained elastic networks arise in a number of biological and technological systems ranging fr... more Prestrained elastic networks arise in a number of biological and technological systems ranging from the cytoskeleton of cells to tensegrity structures. To understand the response of such a network as a function of the prestrain, we consider a minimal model in one dimension. We do this by considering a chain (1D network) of elastic springs upon which a random, zero mean, finite variance prestrain is imposed. Numerical simulations and analytical predictions quantify the magnitude of the contraction as a function of the variance of the prestrain, and show that the chain always shrinks. To test these predictions, we vary the topology of the chain and consider more complex connectivity and show that our results are relatively robust to these changes.
In the past three decades, fractional and fractal calculus (that is, calculus of derivatives and ... more In the past three decades, fractional and fractal calculus (that is, calculus of derivatives and integral of any arbitrary real or complex order) appeared to be an important tool for its applications in many fields of science and engineering. This theory allows to face, analytically and/or numerically, fractional differential equations and fractional partial differential equations. In particular, one of the several applications deals with anomalous diffusion processes. The latter phenomena can be clearly described from the statistical viewpoint. Indeed, in various complex systems, the diffusion processes usually no longer follow Gaussian statistics, and thus Fick’s second law fails to describe the related transport behavior. In particular, one observes deviations from the linear time dependence of the mean squared displacement 〈 x (t) 〉 ∝ t, (1)
Dido solved the first isoperimetric problem in history by cutting an oxhide into strips, tying th... more Dido solved the first isoperimetric problem in history by cutting an oxhide into strips, tying them together and surrounding with the resulting rope the portion of land where Carthage was to be built. However, Dido’s feat can be improved on, as can be shown by cutting an opening in a postcard in such a way that a person is able to pass through it.
In teaching physics one works hard to make pupils understand that all masses fall with the same a... more In teaching physics one works hard to make pupils understand that all masses fall with the same acceleration. However, if we drop compound bodies, some parts of them can actually “go faster” than free fall. This experiment can be easily accomplished with a chain and a dumbbell. Here we try to provide a simple explanation for this apparently impossible effect.
Ihusan Adam, 2 Franco Bagnoli, 3 Duccio Fanelli, 3 L. Mahadevan, and Paolo Paoletti Department of... more Ihusan Adam, 2 Franco Bagnoli, 3 Duccio Fanelli, 3 L. Mahadevan, and Paolo Paoletti Department of Information Engineering, University of Florence, Florence, Italy Department of Physics and Astronomy, and CSDC, University of Florence, Sesto Fiorentino, Italy INFN, Florence Section, Sesto Fiorentino, Italy School of Engineering and Applied Sciences, Department of Physics, and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA School of Engineering, University of Liverpool, L69 3GH Liverpool, UK
This review article focuses on studying problems of observability and controllability of cellular... more This review article focuses on studying problems of observability and controllability of cellular automata (CAs) considered in the context of control theory, an important feature of which is the adoption of a state-space model. Our work first consists in generalizing the obtained results to systems described by CAs considered as the discrete counterpart of partial differential equations, and in exploring possible approaches to prove controllability and observability. After having introduced the notion of control and observation in cellular automata models, in a similar way to the case of discrete-time distributed parameter systems, we investigate these key concepts of control theory in the case of complex systems. For the controllability issue, the Boolean class is particularly studied and applied to the regional case, while the observability is approached in the general case and related to the reconstructibility problem for linear or nonlinear CAs.
An impossible interview with a famous physicist, William Thompson Lord Kelvin, is presented, high... more An impossible interview with a famous physicist, William Thompson Lord Kelvin, is presented, highlighting both his scientific contributions and his short temper. Keywords. Heat conduction, Entropy, Cooling of the Earth, Age of the Earth and the Sun. I: Good morning Professor Kelvin (Fig. 1). K: Not to be pedantic, but I am first a Lord and only then a professor. I: Excuse me, Sir Kelvin, it won't happen again. Can you tell us something about your life? K: I was born in Ireland, Belfast, in 1824, as William Thompson. My father was a mathematician and engineering professor; my mother died when I was only 6 years old. In 1832 we moved to Glasgow, and later we traveled to London, Paris, Germany and the Netherlands. I: Where did you study? K: Practically always at university. I entered the University of Glasgow at the age of 10,
International Journal of Parallel, Emergent and Distributed Systems, 2019
Controllability is one of the central concepts of modern control theory that allows a good unders... more Controllability is one of the central concepts of modern control theory that allows a good understanding of a system's behaviour. It consists in constraining a system to reach the desired state from an initial state within a given time interval. When the desired objective affects only a sub-region of the domain, the control is said to be regional. The purpose of this paper is to study a particular case of regional control using cellular automata models since they are spatially extended systems where spatial properties can be easily defined thanks to their intrinsic locality. We investigate the case of boundary controls on the target region using an original approach based on graph theory. Necessary and sufficient conditions are given based on the Hamiltonian Circuit and strongly connected component. The controls are obtained using a preimage approach.
In this paper we describe the results of some experiments about using surprising physics demonstr... more In this paper we describe the results of some experiments about using surprising physics demonstrations, presented as magical phenomena followed by scientific explanations, for introducing physics topics in several teaching contexts. All the demonstrations have been designed to be implemented with easy to get and cheap materials, so that students can reproduce them at home. This approach has been exploited in Italian high schools, Italian elderly people education and French primary schools, with good results.
A general scheme is proposed and tested to control the symmetry breaking instability of a homogen... more A general scheme is proposed and tested to control the symmetry breaking instability of a homogeneous solution of a spatially extended multispecies model, defined on a network. The inherent discreteness of the space makes it possible to act on the topology of the inter-nodes contacts to achieve the desired degree of stabilization, without altering the dynamical parameters of the model. Both symmetric and asymmetric couplings are considered. In this latter setting the web of contacts is assumed to be balanced, for the homogeneous equilibrium to exist. The performance of the proposed method are assessed, assuming the Complex Ginzburg-Landau equation as a reference model. In this case, the implemented control allows one to stabilize the synchronous limit cycle, hence time-dependent, uniform solution. A system of coupled real Ginzburg-Landau equations is also investigated to obtain the topological stabilization of a homogeneous and constant fixed point.
In this paper we present first experimental results about a small group of people exchanging priv... more In this paper we present first experimental results about a small group of people exchanging private and public messages in a virtual community. Our goal is the study of the cognitive network that emerges during a chat seance. We used the Derrida coefficient and the triangle structure under the working assumption that moods and perceived mutual affinity can produce results complementary to a full semantic analysis. The most outstanding outcome is the difference between the network obtained considering publicly exchanged messages and the one considering only privately exchanged messages: in the former case, the network is very homogeneous, in the sense that each individual interacts in the same way with all the participants, whilst in the latter the interactions among different agents are very heterogeneous, and are based on "the enemy of my enemy is my friend"strategy. Finally a recent characterization of the triangular cliques has been considered in order to describe the intimate structure of the network. Experimental results confirm recent theoretical studies indicating that certain 3-vertex structures can be used as indicators for the network aging and some relevant dynamical features.
We investigate the problem of autonomous agents processing pieces of information that may be corr... more We investigate the problem of autonomous agents processing pieces of information that may be corrupted (tainted). Agents have the option of contacting a central database for a reliable check of the status of the message, but this procedure is costly and therefore should be used with parsimony. Agents have to evaluate the risk of being infected, and decide if and when communicating partners are affordable. Trustability is implemented as a personal (one-to-one) record of past contacts among agents, and as a mean-field monitoring of the level of message corruption. Moreover, this information is slowly forgotten in time, so that at the end everybody is checked against the database. We explore the behavior of a homogeneous system in the case of a fixed pool of spreaders of corrupted messages, and in the case of spontaneous appearance of corrupted messages.
ABSTRACT Previous works have analyzed the cluster organization of the cat cortical network using ... more ABSTRACT Previous works have analyzed the cluster organization of the cat cortical network using both traditional multidimensional scaling methods and evolutionary optimization algorithms. Interestingly, the evolutionary optimization principle of previous works is based on the modularity measure used to find communities in network with global algorithms. In this paper, we deepen this point taking into account different community-detection algorithms. We compare the performances of Net Explorer, a local information dynamics algorithm for detecting communities in networks, with six well-known community detection algorithms: Info map, Hierarchical Info map, Lou vain, Modularity Optimization, Label Propagation and Oslom. The results indicate that Net Explorer is able to detect the four functional clusters where misattributions of some areas are explained by their multimodal function. Results are discussed in terms of misattributions of brain areas to the different clusters emphasizing connections which are explainable (or not) by a cognitive point of view.
In this paper we present first experimental results about a small group of people exchanging priv... more In this paper we present first experimental results about a small group of people exchanging private and public messages in a virtual community. Our goal is the study of the cognitive network that emerges during a chat seance. We used the Derrida coefficient and the triangle structure under the working assumption that moods and perceived mutual affinity can produce results complementary to a full semantic analysis. The most outstanding outcome is the difference between the network obtained considering publicly exchanged messages and the one considering only privately exchanged messages: in the former case, the network is very homogeneous, in the sense that each individual interacts in the same way with all the participants, whilst in the latter the interactions among different agents are very heterogeneous, and are based on "the enemy of my enemy is my friend"strategy. Finally a recent characterization of the triangular cliques has been considered in order to describe the intimate structure of the network. Experimental results confirm recent theoretical studies indicating that certain 3-vertex structures can be used as indicators for the network aging and some relevant dynamical features.
A system made up of N interacting species is considered. Self-reaction terms are assumed of the l... more A system made up of N interacting species is considered. Self-reaction terms are assumed of the logistic type. Pairwise interactions take place among species according to different modalities, thus yielding a complex asymmetric disordered graph. A mathematical procedure is introduced and tested to stabilise the ecosystem via an ad hoc rewiring of the underlying couplings. The method implements minimal modifications to the spectrum of the Jacobian matrix which sets the stability of the fixed point and traces these changes back to species-species interactions. Resilience of the equilibrium state appear to be favoured by predator-prey interactions.
We investigate how knowledge percolates and clusters in a given knowledge space. We introduce a s... more We investigate how knowledge percolates and clusters in a given knowledge space. We introduce a simple model of knowledge organization in which each contribution spans a certain number of items. If this contribution overlaps with others above a certain threshold, they form a cluster. A contribution can also merge clusters together. We study the growth of global knowledge and the cluster dynamics, both showing a nontrivial behavior.
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires
An important question to be addressed regarding system control on a time interval [0, T ] is whet... more An important question to be addressed regarding system control on a time interval [0, T ] is whether some particular target state in the configuration space is reachable from a given initial state. When the target of interest refers only to a portion of the spatial domain, we speak about regional analysis. Cellular Automata (CA) approach have been recently promoted for the study of control problems on spatially extended systems for which the classical approaches cannot be used. An interesting problem concerns the situation where the subregion of interest is not interior to the domain but a portion of its boundary. In this paper we address the problem of regional controllability of cellular automata via boundary actions, i.e., we investigate the characteristics of a cellular automaton so that it can be controlled inside a given region only acting on the value of sites at its boundaries.
Prestrained elastic networks arise in a number of biological and technological systems ranging fr... more Prestrained elastic networks arise in a number of biological and technological systems ranging from the cytoskeleton of cells to tensegrity structures. To understand the response of such a network as a function of the prestrain, we consider a minimal model in one dimension. We do this by considering a chain (1D network) of elastic springs upon which a random, zero mean, finite variance prestrain is imposed. Numerical simulations and analytical predictions quantify the magnitude of the contraction as a function of the variance of the prestrain, and show that the chain always shrinks. To test these predictions, we vary the topology of the chain and consider more complex connectivity and show that our results are relatively robust to these changes.
In the past three decades, fractional and fractal calculus (that is, calculus of derivatives and ... more In the past three decades, fractional and fractal calculus (that is, calculus of derivatives and integral of any arbitrary real or complex order) appeared to be an important tool for its applications in many fields of science and engineering. This theory allows to face, analytically and/or numerically, fractional differential equations and fractional partial differential equations. In particular, one of the several applications deals with anomalous diffusion processes. The latter phenomena can be clearly described from the statistical viewpoint. Indeed, in various complex systems, the diffusion processes usually no longer follow Gaussian statistics, and thus Fick’s second law fails to describe the related transport behavior. In particular, one observes deviations from the linear time dependence of the mean squared displacement 〈 x (t) 〉 ∝ t, (1)
Dido solved the first isoperimetric problem in history by cutting an oxhide into strips, tying th... more Dido solved the first isoperimetric problem in history by cutting an oxhide into strips, tying them together and surrounding with the resulting rope the portion of land where Carthage was to be built. However, Dido’s feat can be improved on, as can be shown by cutting an opening in a postcard in such a way that a person is able to pass through it.
In teaching physics one works hard to make pupils understand that all masses fall with the same a... more In teaching physics one works hard to make pupils understand that all masses fall with the same acceleration. However, if we drop compound bodies, some parts of them can actually “go faster” than free fall. This experiment can be easily accomplished with a chain and a dumbbell. Here we try to provide a simple explanation for this apparently impossible effect.
Ihusan Adam, 2 Franco Bagnoli, 3 Duccio Fanelli, 3 L. Mahadevan, and Paolo Paoletti Department of... more Ihusan Adam, 2 Franco Bagnoli, 3 Duccio Fanelli, 3 L. Mahadevan, and Paolo Paoletti Department of Information Engineering, University of Florence, Florence, Italy Department of Physics and Astronomy, and CSDC, University of Florence, Sesto Fiorentino, Italy INFN, Florence Section, Sesto Fiorentino, Italy School of Engineering and Applied Sciences, Department of Physics, and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA School of Engineering, University of Liverpool, L69 3GH Liverpool, UK
This review article focuses on studying problems of observability and controllability of cellular... more This review article focuses on studying problems of observability and controllability of cellular automata (CAs) considered in the context of control theory, an important feature of which is the adoption of a state-space model. Our work first consists in generalizing the obtained results to systems described by CAs considered as the discrete counterpart of partial differential equations, and in exploring possible approaches to prove controllability and observability. After having introduced the notion of control and observation in cellular automata models, in a similar way to the case of discrete-time distributed parameter systems, we investigate these key concepts of control theory in the case of complex systems. For the controllability issue, the Boolean class is particularly studied and applied to the regional case, while the observability is approached in the general case and related to the reconstructibility problem for linear or nonlinear CAs.
An impossible interview with a famous physicist, William Thompson Lord Kelvin, is presented, high... more An impossible interview with a famous physicist, William Thompson Lord Kelvin, is presented, highlighting both his scientific contributions and his short temper. Keywords. Heat conduction, Entropy, Cooling of the Earth, Age of the Earth and the Sun. I: Good morning Professor Kelvin (Fig. 1). K: Not to be pedantic, but I am first a Lord and only then a professor. I: Excuse me, Sir Kelvin, it won't happen again. Can you tell us something about your life? K: I was born in Ireland, Belfast, in 1824, as William Thompson. My father was a mathematician and engineering professor; my mother died when I was only 6 years old. In 1832 we moved to Glasgow, and later we traveled to London, Paris, Germany and the Netherlands. I: Where did you study? K: Practically always at university. I entered the University of Glasgow at the age of 10,
International Journal of Parallel, Emergent and Distributed Systems, 2019
Controllability is one of the central concepts of modern control theory that allows a good unders... more Controllability is one of the central concepts of modern control theory that allows a good understanding of a system's behaviour. It consists in constraining a system to reach the desired state from an initial state within a given time interval. When the desired objective affects only a sub-region of the domain, the control is said to be regional. The purpose of this paper is to study a particular case of regional control using cellular automata models since they are spatially extended systems where spatial properties can be easily defined thanks to their intrinsic locality. We investigate the case of boundary controls on the target region using an original approach based on graph theory. Necessary and sufficient conditions are given based on the Hamiltonian Circuit and strongly connected component. The controls are obtained using a preimage approach.
In this paper we describe the results of some experiments about using surprising physics demonstr... more In this paper we describe the results of some experiments about using surprising physics demonstrations, presented as magical phenomena followed by scientific explanations, for introducing physics topics in several teaching contexts. All the demonstrations have been designed to be implemented with easy to get and cheap materials, so that students can reproduce them at home. This approach has been exploited in Italian high schools, Italian elderly people education and French primary schools, with good results.
A general scheme is proposed and tested to control the symmetry breaking instability of a homogen... more A general scheme is proposed and tested to control the symmetry breaking instability of a homogeneous solution of a spatially extended multispecies model, defined on a network. The inherent discreteness of the space makes it possible to act on the topology of the inter-nodes contacts to achieve the desired degree of stabilization, without altering the dynamical parameters of the model. Both symmetric and asymmetric couplings are considered. In this latter setting the web of contacts is assumed to be balanced, for the homogeneous equilibrium to exist. The performance of the proposed method are assessed, assuming the Complex Ginzburg-Landau equation as a reference model. In this case, the implemented control allows one to stabilize the synchronous limit cycle, hence time-dependent, uniform solution. A system of coupled real Ginzburg-Landau equations is also investigated to obtain the topological stabilization of a homogeneous and constant fixed point.
In this paper we present first experimental results about a small group of people exchanging priv... more In this paper we present first experimental results about a small group of people exchanging private and public messages in a virtual community. Our goal is the study of the cognitive network that emerges during a chat seance. We used the Derrida coefficient and the triangle structure under the working assumption that moods and perceived mutual affinity can produce results complementary to a full semantic analysis. The most outstanding outcome is the difference between the network obtained considering publicly exchanged messages and the one considering only privately exchanged messages: in the former case, the network is very homogeneous, in the sense that each individual interacts in the same way with all the participants, whilst in the latter the interactions among different agents are very heterogeneous, and are based on "the enemy of my enemy is my friend"strategy. Finally a recent characterization of the triangular cliques has been considered in order to describe the intimate structure of the network. Experimental results confirm recent theoretical studies indicating that certain 3-vertex structures can be used as indicators for the network aging and some relevant dynamical features.
We investigate the problem of autonomous agents processing pieces of information that may be corr... more We investigate the problem of autonomous agents processing pieces of information that may be corrupted (tainted). Agents have the option of contacting a central database for a reliable check of the status of the message, but this procedure is costly and therefore should be used with parsimony. Agents have to evaluate the risk of being infected, and decide if and when communicating partners are affordable. Trustability is implemented as a personal (one-to-one) record of past contacts among agents, and as a mean-field monitoring of the level of message corruption. Moreover, this information is slowly forgotten in time, so that at the end everybody is checked against the database. We explore the behavior of a homogeneous system in the case of a fixed pool of spreaders of corrupted messages, and in the case of spontaneous appearance of corrupted messages.
ABSTRACT Previous works have analyzed the cluster organization of the cat cortical network using ... more ABSTRACT Previous works have analyzed the cluster organization of the cat cortical network using both traditional multidimensional scaling methods and evolutionary optimization algorithms. Interestingly, the evolutionary optimization principle of previous works is based on the modularity measure used to find communities in network with global algorithms. In this paper, we deepen this point taking into account different community-detection algorithms. We compare the performances of Net Explorer, a local information dynamics algorithm for detecting communities in networks, with six well-known community detection algorithms: Info map, Hierarchical Info map, Lou vain, Modularity Optimization, Label Propagation and Oslom. The results indicate that Net Explorer is able to detect the four functional clusters where misattributions of some areas are explained by their multimodal function. Results are discussed in terms of misattributions of brain areas to the different clusters emphasizing connections which are explainable (or not) by a cognitive point of view.
In this paper we present first experimental results about a small group of people exchanging priv... more In this paper we present first experimental results about a small group of people exchanging private and public messages in a virtual community. Our goal is the study of the cognitive network that emerges during a chat seance. We used the Derrida coefficient and the triangle structure under the working assumption that moods and perceived mutual affinity can produce results complementary to a full semantic analysis. The most outstanding outcome is the difference between the network obtained considering publicly exchanged messages and the one considering only privately exchanged messages: in the former case, the network is very homogeneous, in the sense that each individual interacts in the same way with all the participants, whilst in the latter the interactions among different agents are very heterogeneous, and are based on "the enemy of my enemy is my friend"strategy. Finally a recent characterization of the triangular cliques has been considered in order to describe the intimate structure of the network. Experimental results confirm recent theoretical studies indicating that certain 3-vertex structures can be used as indicators for the network aging and some relevant dynamical features.
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Papers by Franco Bagnoli