2,299 research outputs found
Fractals in the Nervous System: conceptual Implications for Theoretical Neuroscience
This essay is presented with two principal objectives in mind: first, to
document the prevalence of fractals at all levels of the nervous system, giving
credence to the notion of their functional relevance; and second, to draw
attention to the as yet still unresolved issues of the detailed relationships
among power law scaling, self-similarity, and self-organized criticality. As
regards criticality, I will document that it has become a pivotal reference
point in Neurodynamics. Furthermore, I will emphasize the not yet fully
appreciated significance of allometric control processes. For dynamic fractals,
I will assemble reasons for attributing to them the capacity to adapt task
execution to contextual changes across a range of scales. The final Section
consists of general reflections on the implications of the reviewed data, and
identifies what appear to be issues of fundamental importance for future
research in the rapidly evolving topic of this review
Griffiths phases and localization in hierarchical modular networks
We study variants of hierarchical modular network models suggested by Kaiser
and Hilgetag [Frontiers in Neuroinformatics, 4 (2010) 8] to model functional
brain connectivity, using extensive simulations and quenched mean-field theory
(QMF), focusing on structures with a connection probability that decays
exponentially with the level index. Such networks can be embedded in
two-dimensional Euclidean space. We explore the dynamic behavior of the contact
process (CP) and threshold models on networks of this kind, including
hierarchical trees. While in the small-world networks originally proposed to
model brain connectivity, the topological heterogeneities are not strong enough
to induce deviations from mean-field behavior, we show that a Griffiths phase
can emerge under reduced connection probabilities, approaching the percolation
threshold. In this case the topological dimension of the networks is finite,
and extended regions of bursty, power-law dynamics are observed. Localization
in the steady state is also shown via QMF. We investigate the effects of link
asymmetry and coupling disorder, and show that localization can occur even in
small-world networks with high connectivity in case of link disorder.Comment: 18 pages, 20 figures, accepted version in Scientific Report
Flow-Based Network Analysis of the Caenorhabditis elegans Connectome
We exploit flow propagation on the directed neuronal network of the nematode C. elegans to reveal dynamically relevant features of its connectome. We find flow-based groupings of neurons at different levels of granularity, which we relate to functional and anatomical constituents of its nervous system. A systematic in silico evaluation of the full set of single and double neuron ablations is used to identify deletions that induce the most severe disruptions of the multi-resolution flow structure. Such ablations are linked to functionally relevant neurons, and suggest potential candidates for further in vivo investigation. In addition, we use the directional patterns of incoming and outgoing network flows at all scales to identify flow profiles for the neurons in the connectome, without pre-imposing a priori categories. The four flow roles identified are linked to signal propagation motivated by biological input-response scenarios
Modeling social resilience: Questions, answers, open problems
Resilience denotes the capacity of a system to withstand shocks and its
ability to recover from them. We develop a framework to quantify the resilience
of highly volatile, non-equilibrium social organizations, such as collectives
or collaborating teams. It consists of four steps: (i) \emph{delimitation},
i.e., narrowing down the target systems, (ii) \emph{conceptualization}, .e.,
identifying how to approach social organizations, (iii) formal
\emph{representation} using a combination of agent-based and network models,
(iv) \emph{operationalization}, i.e. specifying measures and demonstrating how
they enter the calculation of resilience. Our framework quantifies two
dimensions of resilience, the \emph{robustness} of social organizations and
their \emph{adaptivity}, and combines them in a novel resilience measure. It
allows monitoring resilience instantaneously using longitudinal data instead of
an ex-post evaluation
Complex network analysis and nonlinear dynamics
This chapter aims at reviewing complex network and nonlinear dynamical
models and methods that were either developed for or applied to socioeconomic
issues, and pertinent to the theme of New Economic Geography. After an introduction
to the foundations of the field of complex networks, the present summary
introduces some applications of complex networks to economics, finance, epidemic
spreading of innovations, and regional trade and developments. The chapter also
reviews results involving applications of complex networks to other relevant
socioeconomic issue
Safe Connectivity Maintenance in Underactuated Multi-Agent Networks for Dynamic Oceanic Environments
Autonomous Multi-Agent Systems are increasingly being deployed in
environments where winds and ocean currents can exert a significant influence
on their dynamics. Recent work has developed powerful control policies for
single agents that can leverage flows to achieve their objectives in dynamic
environments. However, in the context of multi-agent systems, these flows can
cause agents to collide or drift apart and lose direct inter-agent
communications, especially when agents have low propulsion capabilities. To
address these challenges, we propose a Hierarchical Multi-Agent Control
approach that allows arbitrary single agent performance policies that are
unaware of other agents to be used in multi-agent systems, while ensuring safe
operation. We first develop a safety controller solely dedicated to avoiding
collisions and maintaining inter-agent communication. Subsequently, we design a
low-interference safe interaction (LISIC) policy that trades-off the
performance policy and the safety controller to ensure safe and optimal
operation. Specifically, when the agents are at an appropriate distance, LISIC
prioritizes the performance policy, while smoothly increasing the safety
controller when necessary. We prove that under mild assumptions on the flows
experienced by the agents our approach can guarantee safety. Additionally, we
demonstrate the effectiveness of our method in realistic settings through an
extensive empirical analysis with underactuated Autonomous Surface Vehicles
(ASV) operating in dynamical ocean currents where the assumptions do not always
hold.Comment: 8 pages, submitted to 2023 IEEE 62th Annual Conference on Decision
and Control (CDC) Nicolas Hoischen and Marius Wiggert contributed equally to
this wor
Financial stability from a network perspective
This thesis consists of six chapters related to applications of network analysis’ methods for financial stability. The first chapter introduces the network perspective as a new mapping technique for studying and understanding financial markets’architecture. The second chapter breaks down the Colombian sovereign securities market into different layers of interaction corresponding to distinct trading and registering platforms. The third chapter addresses an overlooked issue: How to measure the importance of financial market infrastructures within their corresponding network. The fourth chapter studies the connective and hierarchical structure of the Colombian non-collateralized money market, and uses an information retrieval algorithm for identifying those financial institutions that simultaneously excel at borrowing and lending central bank’s liquidity (i.e. superspreaders). The fifth chapter addresses –for the first time- the question regarding the presence of a modular hierarchy in financial networks, and discusses the main implications for financial stability. The sixth chapter explicitly models the role of financial market infrastructures as financial markets’ “plumbing”, and recognizes that traditional analysis of financial institutions networks is of a virtual or logical nature. The third chapter is published in the Journal of Financial Market Infrastructures (Vol.2 (3), 2014), whereas the fourth chapter is published in the Journal of Financial Stability (Vol.15, 2014)
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