139 research outputs found
Evolutionary Game Dynamics for Two Interacting Populations under Environmental Feedback
We study the evolutionary dynamics of games under environmental feedback
using replicator equations for two interacting populations. One key feature is
to consider jointly the co-evolution of the dynamic payoff matrices and the
state of the environment: the payoff matrix varies with the changing
environment and at the same time, the state of the environment is affected
indirectly by the changing payoff matrix through the evolving population
profiles. For such co-evolutionary dynamics, we investigate whether convergence
will take place, and if so, how. In particular, we identify the scenarios where
oscillation offers the best predictions of long-run behavior by using
reversible system theory. The obtained results are useful to describe the
evolution of multi-community societies in which individuals' payoffs and
societal feedback interact.Comment: 7 pages, submitted to a conferenc
Impactless biped walking on a slope
AbstractWalking without impacts has been considered in dynamics as a motion/force control problem. In order to avoid impacts, an approach for both the specified motion of the biped and its ground reaction forces was presented yielding a combined motion and force control problem. As an application, a walker on a horizontal plane has been considered. In this paper, it is shown how the control of the ground reaction forces and the energy consumption depend on the gradient of a slope. The biped dynamics and the constraints within the biped system and on the ground are discussed. A motion control synthesis is developed using the inverse dynamics principle proven to be most efficient for human walking research, too. The impactless walking with controlled legs is illustrated by a seven-link biped. The “flying” biped has nine degrees of freedom, with six control inputs. During locomotion, the standing leg has three scleronomic constraints, and the trunk has three rheonomic constraints. However, there are three rheonomic constraints for the prescribed leg motion or three scleronomic constraints for reaction forces of the trailing leg, respectively. The nominal control action for impactless walking can be precomputed and stored. The model proposed allows the investigation of several problems: uphill and downhill walking, optimization of step length, stiction of the feet on the slope and many more. All these findings are also of interest in biomechanics
Astrocytes as a mechanism for meta-plasticity and contextually-guided network function
Astrocytes are a ubiquitous and enigmatic type of non-neuronal cell and are
found in the brain of all vertebrates. While traditionally viewed as being
supportive of neurons, it is increasingly recognized that astrocytes may play a
more direct and active role in brain function and neural computation. On
account of their sensitivity to a host of physiological covariates and ability
to modulate neuronal activity and connectivity on slower time scales,
astrocytes may be particularly well poised to modulate the dynamics of neural
circuits in functionally salient ways. In the current paper, we seek to capture
these features via actionable abstractions within computational models of
neuron-astrocyte interaction. Specifically, we engage how nested feedback loops
of neuron-astrocyte interaction, acting over separated time-scales may endow
astrocytes with the capability to enable learning in context-dependent
settings, where fluctuations in task parameters may occur much more slowly than
within-task requirements. We pose a general model of neuron-synapse-astrocyte
interaction and use formal analysis to characterize how astrocytic modulation
may constitute a form of meta-plasticity, altering the ways in which synapses
and neurons adapt as a function of time. We then embed this model in a
bandit-based reinforcement learning task environment, and show how the presence
of time-scale separated astrocytic modulation enables learning over multiple
fluctuating contexts. Indeed, these networks learn far more reliably versus
dynamically homogeneous networks and conventional non-network-based bandit
algorithms. Our results indicate how the presence of neuron-astrocyte
interaction in the brain may benefit learning over different time-scales and
the conveyance of task-relevant contextual information onto circuit dynamics.Comment: 42 pages, 14 figure
Evolutionary dynamics of two communities under environmental feedback:Special Issue on Control and Network Theory for Biological Systems
In this paper, we study the evolutionary dynamics of two different types of communities in an evolving environment. We model the dynamics using an evolutionary differential game consisting of two sub-games: 1) a game between two different communities and 2) a game between communities and the environment. Our interest is to clarify when the two communities and environment can coexist dynamically under the feedback from the changing environment. Mathematically speaking, we show that for specific game payoffs, the corresponding three dimensional replicator dynamics induced by the evolutionary game have an infinite number of periodic orbits
Copper-based charge transfer multiferroics with a configuration
Multiferroics are materials with a coexistence of magnetic and ferroelectric
order allowing the manipulation of magnetism by applications of an electric
field through magnetoelectric coupling effects. Here we propose an idea to
design a class of multiferroics with a configuration using the magnetic
order in copper-oxygen layers appearing in copper oxide high-temperature
superconductors by inducing ferroelectricity. Copper-based charge transfer
multiferroics SnCuO2 and PbCuO2 having the inversion symmetry breaking
polar space group are predicted to be such materials. The active inner s
electrons in Sn and Pb hybridize with O states leading the buckling in
copper-oxygen layers and thus induces ferroelectricity, which is known as the
lone pair mechanism. As a result of the configuration, SnCuO2 and PbCuO2
are charge transfer insulators with the antiferromagnetic ground state of the
moment on Cu retaining some strongly correlated physical properties of parent
compounds of copper oxide high-temperature superconductors. Our work reveals
the possibility of designing multiferroics based on copper oxide
high-temperature superconductors.Comment: 18 pages, 5 figures, 1 tabl
Elemental topological ferroelectrics and polar metals of few-layer materials
Ferroelectricity can exist in elemental phases as a result of charge
transfers between atoms occupying inequivalent Wyckoff positions. We
investigate the emergence of ferroelectricity in two-dimensional elemental
materials with buckled honeycomb lattices. Various multi-bilayer structures
hosting ferroelectricity are designed by stacking-engineering. Ferroelectric
materials candidates formed by group IV and V elements are predicted
theoretically. Ultrathin Bi films show layer-stacking-dependent physical
properties of ferroelectricity, topology, and metallicity. The two-bilayer Bi
film with a polar stacking sequence is found to be an elemental topological
ferroelectric material. Three and four bilayers Bi films with polar structures
are ferroelectric-like elemental polar metals with topological nontrivial edge
states. For Ge and Sn, trivial elemental polar metals are predicted. Our work
reveals the possibility of design two-dimensional elemental topological
ferroelectrics and polar metals by stacking-engineering.Comment: 18 pages, 6 figure
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