# Cristian HuepeCHuepe Labs Inc. · Complex Systems Research

Cristian Huepe

PhD - Physics

## About

78

Publications

8,766

Reads

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2,799

Citations

Citations since 2017

Introduction

Additional affiliations

September 2014 - present

Education

September 1995 - June 1999

September 1994 - August 1995

March 1989 - December 1993

## Publications

Publications (78)

We investigate the susceptible–infectious–recovered contagion dynamics in a system of self-propelled particles with polar alignment. Using agent-based simulations, we analyze the outbreak process for different combinations of the spatial parameters (alignment strength and Peclet number) and epidemic parameters (infection-lifetime transmissibility a...

We analyze 6 months of Twitter conversations related to the Chilean Covid-19 vaccination process, in order to understand the online forces that argue for or against it and suggest effective digital communication strategies. Using AI, we classify accounts into four categories that emerge from the data as a result of the type of language used. This c...

Experiments with small flocks of sheep show intermittent collective motion events driven by random leaders that guide the group. A model reveals information pooling capabilities, suggesting a mechanism for swarm intelligence.

We study a model of self-propelled particles interacting with their $k$ nearest neighbors through polar alignment. By exploring its phase space as a function of two nondimensional parameters (alignment strength $g$ and Peclet number $\mathrm{Pe}$), we identify two distinct order-disorder transitions. One is continuous, occurs at a low critical $g$...

We investigate the susceptible–infectious–recovered contagion dynamics in a system of self-propelled particles with polar alignment. Using agent-based simulations, we analyze the outbreak process for different combinations of the spatial parameters (alignment strength and Peclet number) and epidemic parameters (infection-lifetime transmissibility a...

We study a set of models of self-propelled particles that achieve collective motion through similar alignment-based dynamics, considering versions with and without repulsive interactions that do not affect the heading directions. We explore their phase space within a broad range of values of two nondimensional parameters (coupling strength and Pecl...

arXiv:2103.07444v2
We study a set of models of self-propelled particles that achieve collective motion through similar alignment-based dynamics, considering versions with and without repulsive interactions that do not affect the heading directions. We explore their phase space within a broad range of values of two nondimensional parameters (couplin...

We investigate the Susceptible-Infectious-Recovered contagion dynamics in a system of self-propelled particles with polar alignment. Using agent-based simulations, we show that the emerging spatial features strongly affect the contagion process, in addition to standard epidemic parameters given by the base reproduction number and duration of the in...

We study a set of models of self-propelled particles that achieve collective motion through similar alignment-based dynamics, considering versions with and without repulsive interactions that do not affect the heading directions. We explore their phase space within a broad range of values of two nondimensional parameters (coupling strength and Pecl...

We introduce a new minimal model for self-propelled agents that attract, repel, and align to their neighbors through elastic interactions. This model has a simple mechanical realization and provides an approximate description of real-world systems ranging from active cell membranes to robotic or animal groups with predictive capabilities. The agent...

We study how the structure of the interaction network affects self-organized collective motion in two minimal models of self-propelled agents: the Vicsek model and the Active-Elastic (AE) model. We perform simulations with topologies that interpolate between a nearest-neighbour network and random networks with different degree distributions to anal...

Achieving efficient and reliable self-organization in groups of autonomous robots is a fundamental challenge in swarm robotics. Even simple states of collective motion, such as group translation or rotation, require nontrivial algorithms, sensors, and actuators to be achieved in real-world scenarios. We study here the capabilities and limitations i...

Social hierarchy is central to decision-making such as the coordinated movement of many swarming species. Here we propose a hierarchical swarm model for collective motion in the spirit of the Vicsek model of self-propelled particles. We show that, as the hierarchy becomes more important, the swarming transition changes dramatically from the weak fi...

Networks that are organized as a hierarchy of modules have been the subject of much research, mainly focusing on algorithms that can extract this community structure from data. The question of why modular hierarchical (MH) organizations are so ubiquitous in nature, however, has received less attention. One hypothesis is that MH topologies may provi...

Networks that are organized as a hierarchy of modules have been the subject of much research, mainly focusing on algorithms that can extract this community structure from data. The question of why modular hierarchical organizations are so ubiquitous in nature, however, has received less attention. One hypothesis is that modular hierarchical topolog...

Self-organized collective coordinated behaviour is an impressive phenomenon, observed in a variety of natural and artificial systems, in which coherent global structures or dynamics emerge from local interactions between individual parts. If the degree of collective integration of a system does not depend on size, its level of robustness and adapti...

We consider a class of adaptive network models where links can only be
created or deleted between nodes in different states. These models provide an
approximate description of a set of systems where nodes represent agents moving
in physical or abstract space, the state of each node represents the agent's
heading direction, and links indicate mutual...

We consider a model of self-propelled agents with spring-like interactions that depend only on relative positions, and not on relative orientations. We observe that groups of these agents self-organize to achieve collective motion (CM) through a mechanism based on the cascading of self-propulsion energy towards lower elastic modes. By computing the...

We explore the connection between complex systems and music by studying different approaches for generating music based on a flocking system. By developing software that links the dynamics of a standard flocking algorithm to a set of sound wave generators and to a musical score, we study how each approach reflects sonically the transition to collec...

We introduce an elasticity-based mechanism that drives active particles to self-organize by cascading self-propulsion energy towards lower-energy modes. We illustrate it on a simple model of self-propelled agents linked by linear springs that reach a collectively rotating or translating state without requiring aligning interactions. We develop an a...

We introduce a simple model of self-propelled particles connected by linear springs that describes a semi-rigid formation of active agents without explicit alignment rules. The model displays a discontinuous transition at a critical noise level, below which the group self-organizes into a collectively translating or rotating state. We identify a no...

Statistics of state transitions for varying definitions of dynamical state. We define the dynamical states as: polar state (P) when Op>1−k and Or<k; milling state (M) when Op 1−k; and swarm state (S) when Op<k and Or<k. The plots show the transition statistics for k = 0.25 (first row), 0.35 (second row and the value used in the paper—included for e...

Average transition paths. Density plot of the smallest distance from the center of mass of the fish shoal to the tank boundary as a function of rotation and polarization. The overlaid arrows are the averaged trajectories of all transitions in the rotation-polarization phase space. For the different group sizes we used dmin = 19.5 cm and dmax = 36 c...

Packing fraction and average speed. Density plots of packing fraction and average individual speed (averaged per frame) as functions of rotation Op and polarization Or for (A) 30 fish, (B) 70 fish and (C) 300 fish.
(TIF)

Relationship between agent speed and order in constant-speed agent based simulation model with 30, 70 and 300 agents. (A) Density plot of agent speed as function of rotation Or and polarization Op, revealing a bistable regime between the milling and the polar states for high speeds in simulations with 30 and 70 agents. For 300 agents the milling st...

30 golden shiners swimming in shallow water in the laboratory. The video plays at 16× normal speed to clearly depict the different dynamical patterns occurring.
(M4V)

70 golden shiners swimming in shallow water in the laboratory. The video plays at 16× normal speed to clearly depict the different dynamical patterns occurring.
(M4V)

Relation between group size and group area and packing fraction. (A) shows the mean group area plotted as a function of group size, including standard deviations. The dashed red line is a linear fit. (B) shows the mean packing fraction as a function of group size, also with standard deviations incuded.
(TIF)

Relation between local polarization and individual speed. The plots show the correlation between individual speed and local polarization estimated in two ways from the underlying density maps. The stapled curves are produced by averaging across individual speeds for each value of the order parameter; the solid curves from averaging across the order...

Radial division of milling state. The figure shows the division of fish in the milling state into shells, where the distance of the outer shell (dashed lines) is defined as the median distance to the group's centre of mass of the five most peripheral fish, and the width of each shell is the radius of the outer shell divided by six.
(TIF)

Tracking accuracy. (A) shows histograms of how many fish are tracked in each frame. The red line in each histogram denotes the threshold for 80% tracking accuracy. The percentage of frames above 80% accuracy are 88% for 30 fish, 91% for 70 fish, 80% for 150 fish and 71% for 300 fish. (B) shows the density distributions of tracking accuracy as a fun...

150 golden shiners swimming in shallow water in the laboratory. The video plays at 16× normal speed to clearly depict the different dynamical patterns occurring.
(M4V)

No signature of handedness. The plot shows the mean and standard deviation of the number of transitions (per replicate) resulting in a clockwise (blue) or counter-clockwise (red) milling state. Transitions into the milling state were no more likely to go clockwise or counterclockwise (GLMM: F1,23 = 0.7191, P = 0.4052), and neither was this affected...

Schematic overview of transitions between dynamical states. The filled circles represent the fraction of time spent in a dynamical state and the arrows represent the fraction of transitions from one dynamical state to another. The absolute number of transitions from one state to another is placed at the tip of the respective transition arrow.
(TIF)

Transition patterns. Density plots of transitions between states for (A) 30 fish and (B) 70 fish. Overlaid the density plots are the corresponding velocity fields of the transition data (in the rotation-polarization phase space).
(TIF)

Transition patterns. Density plots of transitions between states for (A) 150 fish and (B) 300 fish. Overlaid the density plots are the corresponding velocity fields of the transition data (in the rotation-polarization phase space).
(TIF)

300 golden shiners swimming in shallow water in the laboratory. The video plays at 16× normal speed to clearly depict the different dynamical patterns occurring.
(M4V)

The spontaneous emergence of pattern formation is ubiquitous in nature, often arising as a collective phenomenon from interactions among a large number of individual constituents or sub-systems. Understanding, and controlling, collective behavior is dependent on determining the low-level dynamical principles from which spatial and temporal patterns...

We introduce a simple model of self-propelled agents connected by linear
springs, with no explicit alignment rules. Below a critical noise level, the
agents self-organize into a collectively translating or rotating group. We
derive analytical stability conditions for the translating state in an elastic
sheet approximation. We propose an elasticity-...

In flocking, a swarm of robots moves cohesively in a common direction. Traditionally, flocking is realized using two main control rules: proximal control, which controls the cohesion of the swarm using local range-and bearing information about neighboring robots; and alignment control, which allows the robots to align in a common direction and uses...

We explore different approaches for generating music from the flocking dynamics of groups of mobile autonomous agents following a simple decentralized control rule. By developing software that links these dynamics to a set of sound wave generators, we study how each approach reflects sonically the transition to collective order and which produces m...

We consider voter dynamics on a directed adaptive network with fixed out-degree distribution. A transition between an active phase and a fragmented phase is observed. This transition is similar to the undirected case if the networks are sufficiently dense and have a narrow out-degree distribution. However, if a significant number of nodes with low...

Understanding the organization of collective motion in biological systems is
an ongoing challenge. In this Paper we consider a minimal model of
self-propelled particles with variable speed. Inspired by experimental data
from schooling fish, we introduce a power-law dependency of the speed of each
particle on the degree of polarization order in its...

Determining individual-level interactions that govern highly coordinated motion in animal groups or cellular aggregates has been a long-standing challenge, central to understanding the mechanisms and evolution of collective behavior. Numerous models have been proposed, many of which display realistic-looking dynamics, but nonetheless rely on untest...

We propose a simple adaptive-network model describing recent swarming
experiments. Exploiting an analogy with human decision making, we capture the
dynamics of the model by a low-dimensional system of equations permitting
analytical investigation. We find that the model reproduces several
characteristic features of swarms, including spontaneous sym...

We analyze order-disorder phase transitions driven by noise that occur in two kinds of network models closely related to the self-propelled model proposed by Vicsek [Phys. Rev. Lett. 75, 1226 (1995)] to describe the collective motion of groups of organisms. Two different types of noise, which we call intrinsic and extrinsic, are considered. The int...

We compare three simple models that reproduce qualitatively the emergent swarming behavior of bird flocks, fish schools, and other groups of self-propelled agents by using a new set of diagnosis tools related to the agents’ spatial distribution. Two of these correspond in fact to different implementations of the same model, which had been previousl...

We analyze order-disorder phase transitions driven by noise that occur in two kinds of network models closely related to the self-propelled model proposed by Vicsek et. al. to describe the collective motion of groups of organisms [\emph{Phys. Rev. Lett.} {\bf 75}:1226 (1995)]. Two different types of noise, which we call intrinsic and extrinsic, are...

Vortex nucleation in two-dimensional (2D) and three-dimensional (3D) super flows past a cylinder is studied. The superflow
is described by a Nonlinear Schrödinger like equation. In the 2D case, a continuation method is used to characterize the bifurcation
of stationary states leading to vortex formation. Asaddle-no de followed by a secondary pitchf...

Two similar Laplacian-based models for swarms with informed agents are proposed and analyzed analytically and numerically. In these models, each individual adjusts its velocity to match that of its neighbors and some individuals are given a preferred heading direction towards which they accelerate if there is no local velocity consensus. The conver...

An important characteristic of flocks of birds, schools of fish, and many similar assemblies of self-propelled particles is the emergence of states of collective order in which the particles move in the same direction. When noise is added into the system, the onset of such collective order occurs through a dynamical phase transition controlled by t...

We investigate the relationship between the linear surface wave instabilities of a shallow viscous fluid layer and the shape of the periodic, parametric-forcing function (describing the vertical acceleration of the fluid container) that excites them. We find numerically that the envelope of the resonance tongues can only develop multiple minima whe...

We investigate the relationship between the linear surface wave instabilities of a shallow viscous fluid layer and the shape of the periodic, parametric-forcing function (describing the vertical acceleration of the fluid container) that excites them. We find numerically that the envelope of the Arnold resonance tongues only develops multiple minima...

For spatio-temporal chaos observed in numerical simulations of the complex Ginzburg-Landau equation (CGL) and in experiments on inclined-layer convection (ILC) we report numerical and experimental data on the statistics of defects and of defect loops. These loops consist of defect trajectories in space-time that are connected to each other through...

Intermittent behavior is shown to appear in a system of self-driven interacting particles. In the ordered phase, most particles move in the same approximate direction, but the system displays a series of intermittent bursts during which the order is temporarily lost. This intermittency is characterized and its statistical properties are found analy...

Most physical systems are governed by evolution equations of the general form $$
\frac{{\partial \Psi }}{{\partial t}} = L\Psi + W(\Psi )
$$ (1) where L is the Laplacian operator and W represents some combination of multiplicative and nonlinear terms. Some examples are: $$
\frac{{\partial U}}{{\partial t}} = - (U\cdot\nabla )U - \nabla P + \nu {\na...

We consider systems containing a Bose-Einstein condensate described by a macroscopic wave function that obeys a Nonlinear Schrödinger like equation (NLSE). Using a continuation method, we characterize the bifurcation of stationary states.
For attractive Bose condensates confined in isotropic potentials, we show the presence of an Hamiltonian saddle...

The Gross–Pitaevskii equation, also called the nonlinear Schrödinger equation (NLSE), describes the dynamics of low-temperature superflows and Bose–Einstein Condensates (BEC). We review some of our recent NLSE-based numerical studies of superfluid turbulence and BEC stability. The relations with experiments are discussed.

By performing a linear-stability analysis, we study the conditions for the appearance of Faraday waves on the surface of a fluid in a container driven by a periodic sequence of delta-like acceleration impulses. Implicit analytic expressions for the neutral stability curve are found for a finite depth fluid layer described by the Navier-Stokes equat...

We investigate the conditions that produce a phase transition from an ordered to a disordered state in a family of models of two-dimensional elements with a ferromagnetic-like interaction. This family is defined to contain under the same framework, among others, the XY-model and the Self-Driven Particles Model introduced by Vicsek et al. Each model...

Non-Isotropic Attractive Bose-Einstein condensates are investigated with Newton and inverse Arnoldi methods. The stationary solutions of the Gross-Pitaevskii equation and their linear stability are computed. Bifurcation diagrams are calculated and used to find the condensate decay rates corresponding to macroscopic quantum tunneling, two-three body...

The dynamics of the finite-time blowup solutions of a parabolic–elliptic system of partial differential equations is studied. These equations arise when modelling chemotactic aggregation or a dissipative gravitational collapse. Radial self-similar blowup solutions on a bounded domain are analysed by perturbing the known analytic solutions of the co...

The dynamical organization in the presence of noise of a Boolean neural network with random connections is analyzed. For low levels of noise, the system reaches a stationary state in which the majority of its elements acquire the same value. It is shown that, under very general conditions, there exists a critical value
c
of the noise, below which...

Cosmological solutions of a toy homogeneous isotropic universe filled with a superfluid Bose condensate described by a complex scalar field (with relativistic barotropic fluid interpretation) are studied. The eigenvalues of the tangent map for the resulting Hamiltonian system are used to classify the phase space regions and to understand the typica...

The bifurcation diagram corresponding to stationary solutions of the nonlinear Schrödinger equation describing a superflow around a disc is numerically computed using continuation techniques. When the Mach number is varied, it is found that the stable and unstable (nucleation) branches are connected through a primary saddle-node and a secondary pit...