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  • A simulation of a Bitcoin blockchain based on a pseudo-randomly selected block
    Paper
    Alberto Partida, Regino Criado, Miguel Romance.
    The aim of this paper is to present an analysis of a blockchain implementation such as Bitcoin from a  viewpoint based on a complex network model with the aim to identify an initial toy model to which Information Security measures could be applied. As it is known, blockchain finds its roots in cryptography and distributed systems. Those blockchain implementations using decentralised consensus have a simple motto i.e. ``the longest chain wins". This technology can then be used, among many other user cases, to create a ledger book, i.e. a chain of blocks with records representing financial transactions.
    The most popular blockchain implementation is Bitcoin which appeared in 2008  \cite{Nakamoto}. Without mentioning the word blockchain at all, in \cite{Nakamoto} an ongoing chain of hash-based ``proof of work" is described.
    In fact, this is the heart of Bitcoin, ``a purely peer to peer version of electronic cash"  \cite{Nakamoto}.  It combines three powerful artifacts: the blockchain technology, a distributed peer-to-peer network and a fully decentralised consensus-based approach. 
    The entire public Bitcoin blockchain, its distributed ledger, reached in January 2018 a volume over 100
    GB. This database contains Bitcoin addresses, dates, transactions and bitcoin figures. In order
    to model this database as a complex network, our proposal is to start small and focus our attention first on a
    pseudo-randomly selected block. The only requirement to select a transaction block has been
    that one of the ``richest" Bitcoin addresses, according to \cite{bitinfocharts1}, participates in
    that block. The selected block records 2522 transactions. Initially we consider every different Bitcoin address present in the block as a node. The links between the nodes will be the transactions publicly available in \cite{bitinfocharts2}. Some measurements and properties of this network are analyzed: clustering coefficient, modularity, possible existence of motifs and communities.
    The attractiveness of this proposal is that algorithms and steps used to study this block escale
    and can be used to study each completed bitcoin block in the Bitcoin blockchain. It is remarkable that in \cite{Reid} it is also suggested that there is no preferential attachment in the Bitcoin transaction network. The proposed initial link with Information Security is founded on anonymity, although in \cite{Nakamoto} it is concluded that anonymity in Bitcoin is not a pivotal design goal of the Bitcoin system.
     
     
    \begin{thebibliography}{10}
    \bibitem{Nakamoto}
    S. Nakamoto {\it Bitcoin: A Peer-to-Peer Electronic Cash System } Nakamotoinstitute.org (2008)
    \bibitem{bitinfocharts1}
    https://bitinfocharts.com/top-100-richest-bitcoin-addresses.html
    \bibitem{bitinfocharts2}
    https://http://bit.ly/2D3uMnf bitinfocharts.com Bitcoin Block 500700
    \bibitem{Reid}
    F Reid, M. Harrigan {\it An Analysis of Anonymity in the Bitcoin System} Cornell University Library
    (2011) http://arxiv.org/abs/1107.4524
    \end{thebibliography}
    Ver abstract
  • An efficient wavelet iterative process for viscoelastic behavior of erythrocytes' deformability.
    Oral paper
    Ana Maria Korol, S. Bortolato, A. Leguto, P. Vizarri, M. Martin, V. Vampa, B. Riquelme, M. Mancilla Canales, S. Perez.
    Fractal analysis has been applied with great success to different biological tissue, in particular Entropy and Complexity are new quantifiers for red blood cells (RBCs) recognition when belonging to healthy individuals and different hematological diseases, such as chronic lymphocytic leukemia and acute lymphocytic leukemia. The purpose of this work is to make a crossover between new mathematical quantifiers and the loose of deformability on the cells membrane when disease severity increased.
    The dynamic behavior of RBCs has a physiological significance since in vivo the cells continually change their shape and adapt passively to capillary circulation. We analyzed  the photometrically recorde time series of several millions of RBCs which are subjected to well control fluid shear stress, as it happens when the samples are placed on the Rheometer (home- made device developed in our laboratory. The samples are obtained by cubital venipuncture with disposable syringes and large gauge needles to avoid mechanical damage, using anticoagulant Na2EDTA in 40 individuals: 20 healthy controls and 20 leukemia patients. All the individuals gave their informed consent for participating in the study.
    For succeeding on explaining complex behavior, we would like to emphasize the  hemathological dynamic disease instead of the tools. The different RBCs populations were not only clearly characterized by the Entropy of the process but also by the Complexity. The obtained results showed a clear difference:  on one hand while the healthy controls are white noise (random process), the disease ones are coloured noise (have also a deterministic component), with a clear pattern growing on severity leukemia. 
    Present results allowed insights that cannot be obtained that cannot be obtained  with linear methods applied before. Despite leukemia mainly affects white blood cells, we could detect a loose of deformability on the RBCs membrane.   
     
     
    Ver abstract
  • Analyzing disease outbreaks by means of symbolic networks
    Oral paper
    Jose Luis Herrera, Johann MARTÍNEZ, Javier M. Buldú.

    The understanding of disease outbreaks, as well the prevalence and lifetime of contagious diseases have become a challenge in biomedical sciences. The unavoidable difficulties in poorest populations to access valuable medical triages together with the lack of policies to inspect the reported cases in controlled populations, drive to a shortage of the quality of the recorded datasets. Although different interdisciplinary perspectives have been proposed to understand the dynamics of different diseases, recent advances in the understanding of complex systems dynamics suggest alternative viewpoints that may enhance our understanding of the problem. Under this framework, we propose an aggregated-data-based model that shows how the persistence of events in disease outbreaks follows specific progressions that can be identified and characterized thanks to the analysis of the temporal patterns encoded in the number of infected individuals. Our methodology considers aggregated data as the seminal information to extract either the level of complexity and entropy (local and global) of the evolution of a disease, as well as the distribution of hidden temporal patterns. Beyond focusing on a single disease and, with the aim of gaining general intuition about the results of the proposed methodology, we consider different diseases and track their similarities and divergences. Additionally, we build up directed weighted networks associated to the disease dynamics, in which the nodes (edges) represent specific temporal events (progressions between consecutive events). This way, we can study the role of each node (pattern) in the diseases considered, as well as the structure of the complex network related to the disease temporal patterns and find, for instance, the existence of common persistent events (hubs). In this scenario, we identify similarities in the structure of networks associated to different outbreaks and make a dynamical and topological characterization of such networks. These results lead to the primary conclusion that, in general, disease outbreaks maintain specific ordinal patterns, which is translated to specific values of statistical complexity and permutation entropy, when the whole symbolic network is analyzed. Furthermore, there are particular nodes that have an important role in the system which depend on the particular disease considered. Lastly, we consider the possible relations between dynamical-topological-prevalence variables.

    Ver abstract
  • Chimera states in 1D and 2D with mutliple co-existing solutions
    Oral paper
    Flavio Fenton, Andrea Welsh.

    Most chimera states to date require global coupling to produce co-stable solutions. We present here a system that can lead to up to 4 different co-existing solutions  in a system composed of identical oscillators only coupled by diffusion. The single oscillatory system is based on the saline oscillator. In this talk, we first demonstrate the bi-stability of this system experimental as a function of initial conditions and perturbations with a given strength and phase. Then create a mathematical model for this system that when coupled in 1 and 2D by just diffusion allows the existence of up to 4 different solutions co-existing in space at the same time.

    Ver abstract
  • Chimera states in coupled-waveguide Kerr resonators
    Oral paper
    Saliya Coulibaly, Marcel Clerc, Ferre Michel, René Rojas, Mustapha Tlidi.
    Chimera states are spatiotemporal patterns in which an array of oscillators splits into two domains: one coherent and phase locked, the other incoherent and desynchronized \cite{Strogatz,Kuramoto2002}.  A while after their discovery, the main ingredient to explain this counterintuitive state was the weakness or non-local nature of the coupling between the oscillators. However, recent works have reported  on chimera states in globally \cite{Sethia} and, strong and non-locally coupled oscillators \cite{Sethia1}. These works opened the possibility to generate a novel type of chimera state based on other type of oscillators coupling. Here, we study the case of the nearest neighbor local coupling, widely present in nature. To this end we consider an array of coupled-waveguides resonators. Coupled-waveguides play an important role in communication technologies, optical computing, and even quantum information processing. From a fundamental point of view, their dynamic behaviors exhibit interesting states like discrete solutions\cite{Peschel}. Based on a discrete model, we investigate the formation of complex spatiotemporal localized states in an array of coupled-waveguide resonators. The presented localized states correspond to the optical behavior equivalent to the chimera states. By means of the Lyapunov spectrum, we are able to characterize the spatiotemporal chaotic nature of these optical chimera states\cite{Ferre1}.
     
    \begin{thebibliography}{10}
     
    \bibitem{Strogatz}  D. M. Abrams, and S. H. Strogatz, {\it Phys. Rev. Lett.} {\bf 93}, 174102 (2004).
     
    \bibitem{Kuramoto2002}  Y. Kuramoto, and D. Battogtokh, 
    {Nonlinear Phenom. Complex Systems} {\bf 5}, 380, (2002).
    \bibitem{Sethia}G.C. Sethia, and A. Sen,  {\it Phys. Rev. Lett.} {\bf 112}, 144101 (2014). 
    \bibitem{Sethia1}G. C. Sethia, A. Sen, and G. L. Johnston,  {\it Phys. Rev. E} {\bf 88}, 042917,(2013).
    \bibitem{Peschel}U. Peschel, O. Egorov, and F. Lederer, {\it Opt. Lett.} 29, 1909 (2004). 
    \bibitem{Ferre1}M. G. Clerc, M. A. Ferr\'e, S. Coulibaly, R. G. Rojas, and M. Tlidi,  {\it Opt. Lett.} {\bf 42}, 2906-2909, (2017).
    \end{thebibliography}
    Ver abstract
  • Complexity in Brain Structure and Functions
    Paper
    Joaquín Marro, J.J. Torres, A. P. Millán.

    Many intricate aspects of nature are now well understood from the mathematical perspective of the theory of non-equilibrium phase transitions and critical phenomena. It does not therefore came as a surprise that recent studies try to deep on the structure and high-level functions of the brain -where experiments have revealed that complexity may be a main ingredient- by using analogies according to those strategy and ideas and perhaps also involving the concept of chaos. This talk will illustrate and ground this situation. It will be based on the papers “Brain performance versus phase transitions”, Sci. Rep. 5, 12216 (2015), by J.J. Torres and J. Marro, and “The concurrence of structure and function in developing networks: Explanation for synaptic pruning”, Nature Communications to be published (2017), by Ana P. Millán, J. J. Torres, S. Johnson and J. Marro (now available at arxiv.org/abs/1705.02773v1), and will serve as a presentation of the book “La Mente es Crítica ― Descubriendo la Admirable Complejidad del Cerebro”, J. Marro & D. R. Chialvo, Editorial Univ. de Granada 2017. 

    Ver abstract
  • Connectivity and Dynamics in Neuronal Cultures: Experiments, Simulations, and Medical Applications
    Paper
    Jordi Soriano.

    Neuronal cultures offer a unique platform to study collective
    phenomena in neuronal networks. The ability of experimentalists to
    modify the connectivity among neurons and their dynamics offer a
    unique scenario to investigate key open questions in neuroscience,
    including the emergence of spontaneous activity patterns, the
    importance of spatial embedding, network connectivity, and the
    resilience of the networks to damage. Here I will present
    different experiments and theoretic-numerical resources to shed light
    on these questions. In particular, I will pinpoint the potential of
    effective connectivity inference to characterize the behavior of
    neuronal networks affected by Sanfilippo, Alzheimer’s and other
    diseases.

    Ver abstract
  • Control of a spatiotemporal instability affecting the relativistic electrons in synchrotron radiation facilities
    Oral paper
    Clément Evain, Christophe Szwaj, Eléonore Roussel, Marc Le Parquier, Marie-Agnès Tordeux, Marie Labat, Fernand Ribeiro, Nicolas Hubert, Jean-Blaise Brubach, Pascale Roy, Serge Bielawski.

    Synchrotron radiation facilities are sources using the light
    emitted by relativistic electron bunches and dedicated to various
    users of THz, VUV and X-ray radiation. The power delivered generally
    depends of the electron-bunch charge, and synchrotron radiation
    facilities tend to use electron bunches with the highest possible
    charge density.

    However, at high charge density, a spatio-temporal instability affects
    the electron-bunches in most facilities \cite{1} (e.g. ALS in Berkeley,
    BESSY in Berlin, DIAMOND in UK, SOLEIL in France \cite{2} , etc). This
    instability has a fondamental origin: it comes from the interaction of
    the electron bunch with its own radiated electric field. As a
    consequence, microstructures appear in the longitudinal direction of
    the bunch with a complex temporal evolution.

    Here, we present the first results on the control of those
    instabilities using a feedback method. The strategy is directly
    inspired from chaos control method (In particular from the OGY and Pyragas
    methods). The idea is to stabilized a pre-existing unstable periodic
    solution. A feedback system continuously applies small perturbations
    on one of accelerator parameters in function of the deviation between
    the unstable solution and the system state. After numerical studies on
    the system model (Fokker-Planck-Vlasov equations), we succeeded to
    experimentally control this instability at synchrotron SOLEIL
    (France). To this purpose, we used a rather simple elecronic feedback
    system (base on a FPGA board). We will present the results as well as
    the open questions (from the dynamical point of view) raised by this
    study.

    \begin{thebibliography}{10}
    \bibitem{1} Beam instability and microbunching due to coherent synchrotron radiation, G. Stupakov and S. Heifets, Phys. Rev. ST Accel. Beams, 5, 054402 (2002)
    \bibitem{2} Direct observation of spatiotemporal dynamics of short electron bunches in storage rings, C Evain, E Roussel, M Le Parquier, C Szwaj, M-A Tordeux, J-B Brubach, L Manceron, P Roy, S Bielawski, Phys. Rev. Lett. 118, 054801 (2017).
    \end{thebibliography}


     

    Ver abstract
  • Dimension from Covariance Matrices
    Oral paper
    Thomas Carroll.

    I describe a method to estimate embedding dimension from a time series. This method includes an estimate of the probability that the dimension estimate is valid. Such validity estimates are not common in algorithms for calculating the properties of dynamical systems. The algorithm described here compares the eigenvalues of covariance matrices created from an embedded signal to the eigenvalues for a covariance matrix of a Gaussian random process with the same dimension and number of points. A statistical test gives the probability that the eigenvalues for the embedded signal did not come from the Gaussian random process.

    Ver abstract
  • Dynamics, geometry, and topology of fluid turbulence
    Oral paper
    Roman Grigoriev, Balachandra Suri, Jeff Tithof, Logan Kageorge, Ravi Pallantla, Michael Schatz.
    Dramatic progress in understanding fluid turbulence, especially at moderate Reynolds numbers, has been made in the past decade using a deterministic framework based on the state space geometry of unstable solutions of the Navier-Stokes equation. Initial results obtained by restricting attention to minimal flow units capable of sustaining turbulence and imposing unphysical (e.g., spatially periodic) boundary conditions seemed to suggest that fluid turbulence is in many ways similar to low-dimensional chaos, with unstable periodic solutions forming the geometric skeleton for dynamics. However, extending these results to larger flow domains with physical boundary conditions both proved very challenging and produced a number of surprises. In particular, our experimental and numerical studies have shown that unstable equilibria, quasiperiodic states, and heteroclinic connections can play an equally important role. We have also demonstrated that unstable solutions can be used for forecasting the evolution of experimental turbulent flows.
     
    Ver abstract
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