61 research outputs found
Collective fluctuations in networks of noisy components
Collective dynamics result from interactions among noisy dynamical
components. Examples include heartbeats, circadian rhythms, and various pattern
formations. Because of noise in each component, collective dynamics inevitably
involve fluctuations, which may crucially affect functioning of the system.
However, the relation between the fluctuations in isolated individual
components and those in collective dynamics is unclear. Here we study a linear
dynamical system of networked components subjected to independent Gaussian
noise and analytically show that the connectivity of networks determines the
intensity of fluctuations in the collective dynamics. Remarkably, in general
directed networks including scale-free networks, the fluctuations decrease more
slowly with the system size than the standard law stated by the central limit
theorem. They even remain finite for a large system size when global
directionality of the network exists. Moreover, such nontrivial behavior
appears even in undirected networks when nonlinear dynamical systems are
considered. We demonstrate it with a coupled oscillator system.Comment: 5 figure
Heterogeneity in connectivity of habitat networks saves stable coexistence of competing species
Coexistence of individuals with different species or phenotypes is often
found in nature in spite of competition between them. Stable coexistence of
multiple types of individuals have implications for maintenance of ecological
biodiversity and emergence of altruism in society, to name a few. Various
mechanisms of coexistence including spatial structure of populations,
heterogeneous individuals, and heterogeneous environments, have been proposed.
In reality, individuals disperse and interact on complex networks. We examine
how heterogeneous degree distributions of networks influence coexistence,
focusing on models of cyclically competing species. We show analytically and
numerically that heterogeneity in degree distributions promotes stable
coexistence.Comment: 4 figure
Pluto’s ocean is capped by gas hydrates
Many icy solar system bodies possess subsurface oceans. At Pluto, Sputnik Planitia’s location near the equator suggests the presence of a subsurface ocean and a locally thinned ice shell. To maintain an ocean, Pluto needs to retain heat inside. On the other hand, to maintain large variations in ice shell thickness, Pluto’s ice shell needs to be cold. Achieving such an interior structure is problematic. Here we show that the presence of a thin layer of clathrate hydrates (gas hydrates) at the base of the ice shell can explain both the long-term survival of the ocean and the maintenance of shell thickness contrasts. Clathrate hydrates act as a thermal insulator, preventing the ocean from complete freezing while keeping the ice shell cold and immobile. The most likely clathrate guest gas is methane either contained in precursor bodies and/or produced by cracking of organic materials in the hot rocky core. Nitrogen molecules initially contained and/or produced later in the core would likely not be trapped as clathrate hydrates, instead supplying the nitrogen-rich surface and atmosphere. The formation of a thin clathrate hydrate layer capping a subsurface ocean may be an important generic mechanism maintaining long-lived subsurface oceans in relatively large but minimally-heated icy satellites and Kuiper Belt Objects
The Correlation of the NA Measurements by Counting 28Si Atoms
open12sìpartially_openembargoed_20160715Mana, G.; Massa, E.; Sasso, C. P.; Stock, M.; Fujii, K.; Kuramoto, N.; Mizushima, S.; Narukawa, T.; Borys, M.; Busch, I.; Nicolaus, A.; Pramann, A.Mana, Giovanni; Massa, Enrico; Sasso, CARLO PAOLO; Stock, M.; Fujii, K.; Kuramoto, N.; Mizushima, S.; Narukawa, T.; Borys, M.; Busch, I.; Nicolaus, A.; Pramann, A
Structure of Cell Networks Critically Determines Oscillation Regularity
Biological rhythms are generated by pacemaker organs, such as the heart
pacemaker organ (the sinoatrial node) and the master clock of the circadian
rhythms (the suprachiasmatic nucleus), which are composed of a network of
autonomously oscillatory cells. Such biological rhythms have notable
periodicity despite the internal and external noise present in each cell.
Previous experimental studies indicate that the regularity of oscillatory
dynamics is enhanced when noisy oscillators interact and become synchronized.
This effect, called the collective enhancement of temporal precision, has been
studied theoretically using particular assumptions. In this study, we propose a
general theoretical framework that enables us to understand the dependence of
temporal precision on network parameters including size, connectivity, and
coupling intensity; this effect has been poorly understood to date. Our
framework is based on a phase oscillator model that is applicable to general
oscillator networks with any coupling mechanism if coupling and noise are
sufficiently weak. In particular, we can manage general directed and weighted
networks. We quantify the precision of the activity of a single cell and the
mean activity of an arbitrary subset of cells. We find that, in general
undirected networks, the standard deviation of cycle-to-cycle periods scales
with the system size as , but only up to a certain system size
that depends on network parameters. Enhancement of temporal precision is
ineffective when . We also reveal the advantage of long-range
interactions among cells to temporal precision
Competency of Education for Interntional Understanding: By analyzing Dircke Geography: For Bilingual Classes in Germany
This paper aims to clarify the characteristics of learning units on Education for International Understanding (EIU) and their structure, appropriate geographical teaching materials on EIU, streategies for competence acquisition, and perspectives of ESD within learning units on EIU by analyzing two learning units “Globalisation” and “Global Disparities” in the geography textbook for bilingual lesson ”Diercke Geography: For Bilingual Classes”. The results of the analysis showed that 1)“Globalisation” focuses on the theories of globalisation and “Global Disparities” aims to learn not only theories but also regionl images; 2) Competency is repeatedly acquired through different learning activities ; 3) “Global Disparities” is designed from the viewpoint of “think globally, act locally”
Formation of feedforward networks and frequency synchrony by spike-timing-dependent plasticity
Spike-timing-dependent plasticity (STDP) with asymmetric learning windows is
commonly found in the brain and useful for a variety of spike-based
computations such as input filtering and associative memory. A natural
consequence of STDP is establishment of causality in the sense that a neuron
learns to fire with a lag after specific presynaptic neurons have fired. The
effect of STDP on synchrony is elusive because spike synchrony implies unitary
spike events of different neurons rather than a causal delayed relationship
between neurons. We explore how synchrony can be facilitated by STDP in
oscillator networks with a pacemaker. We show that STDP with asymmetric
learning windows leads to self-organization of feedforward networks starting
from the pacemaker. As a result, STDP drastically facilitates frequency
synchrony. Even though differences in spike times are lessened as a result of
synaptic plasticity, the finite time lag remains so that perfect spike
synchrony is not realized. In contrast to traditional mechanisms of large-scale
synchrony based on mutual interaction of coupled neurons, the route to
synchrony discovered here is enslavement of downstream neurons by upstream
ones. Facilitation of such feedforward synchrony does not occur for STDP with
symmetric learning windows.Comment: 9 figure
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