2,180 research outputs found
Transitions in active rotator systems: invariant hyperbolic manifold approach
Our main focus is on a general class of active rotators with mean field
interactions, that is globally coupled large families of dynamical systems on
the unit circle with non-trivial stochastic dynamics. Each isolated system is a
diffusion process on a circle, with drift -delta V', where V' is a periodic
function and delta is an intensity parameter. It is well known that the
interacting dynamics is accurately described, in the limit of infinitely many
interacting components, by a Fokker-Planck PDE and the model reduces for
delta=0 to a particular case of the Kuramoto synchronization model, for which
one can show the existence of a stable normally hyperbolic manifold of
stationary solutions for the corresponding Fokker-Planck equation (we are
interested in the case in which this manifold is non-trivial, that happens when
the interaction is sufficiently strong, that is in the synchronized regime of
the Kuramoto model). We use the robustness of normally hyperbolic structures to
infer qualitative and quantitative results on the |delta|< delta0 cases, with
delta0 a suitable threshold: as a matter of fact, we obtain an accurate
description of the dynamics on the invariant manifold for delta=0 and we link
it explicitly to the potential V . This approach allows to have a complete
description of the phase diagram of the active rotators model, at least for
|delta|< delta0, thus identifying for which values of the parameters (notably,
noise intensity and/or coupling strength) the system exhibits periodic pulse
waves or stabilizes at a quiescent resting state. Moreover, some of our results
are very explicit and this brings a new insight into the combined effect of
active rotator dynamics, noise and interaction. The links with the literature
on specific systems, notably neuronal models, are discussed in detail.Comment: 29 pages, 4 figures. Version 2: some changes in introduction, added
reference
Reducing the cost of group communication with semantic view synchrony
View Synchrony (VS) is a powerful abstraction in the design and implementation of de- pendable distributed systems. By ensuring that processes deliver the same set of messages in each view, it allows them to maintain consistency across membership changes. However, experience indicates that it is hard to combine strong reliability guarantees as offered by VS with stable high performance. In this paper we propose a novel abstraction, Semantic View Synchrony (SVS), that exploits the application's semantics to cope with high throughput applications. This is achieved by allowing some messages to be dropped while still preserving consistency when new views are installed. Thus, SVS inherits the elegance of view synchronous communi- cation. The paper describes how SVS can be implemented and illustrates its usefulness in the context of distributed multi-player games
VIOLA - A multi-purpose and web-based visualization tool for neuronal-network simulation output
Neuronal network models and corresponding computer simulations are invaluable
tools to aid the interpretation of the relationship between neuron properties,
connectivity and measured activity in cortical tissue. Spatiotemporal patterns
of activity propagating across the cortical surface as observed experimentally
can for example be described by neuronal network models with layered geometry
and distance-dependent connectivity. The interpretation of the resulting stream
of multi-modal and multi-dimensional simulation data calls for integrating
interactive visualization steps into existing simulation-analysis workflows.
Here, we present a set of interactive visualization concepts called views for
the visual analysis of activity data in topological network models, and a
corresponding reference implementation VIOLA (VIsualization Of Layer Activity).
The software is a lightweight, open-source, web-based and platform-independent
application combining and adapting modern interactive visualization paradigms,
such as coordinated multiple views, for massively parallel neurophysiological
data. For a use-case demonstration we consider spiking activity data of a
two-population, layered point-neuron network model subject to a spatially
confined excitation originating from an external population. With the multiple
coordinated views, an explorative and qualitative assessment of the
spatiotemporal features of neuronal activity can be performed upfront of a
detailed quantitative data analysis of specific aspects of the data.
Furthermore, ongoing efforts including the European Human Brain Project aim at
providing online user portals for integrated model development, simulation,
analysis and provenance tracking, wherein interactive visual analysis tools are
one component. Browser-compatible, web-technology based solutions are therefore
required. Within this scope, with VIOLA we provide a first prototype.Comment: 38 pages, 10 figures, 3 table
Towards a cyber physical system for personalised and automatic OSA treatment
Obstructive sleep apnea (OSA) is a breathing disorder that takes place in the course of the sleep and is produced by a complete or a partial obstruction of the upper airway that manifests itself as frequent breathing stops and starts during the sleep. The real-time evaluation of whether or not a patient is undergoing OSA episode is a very important task in medicine in many scenarios, as for example for making instantaneous pressure adjustments that should take place when Automatic Positive Airway Pressure (APAP) devices are used during the treatment of OSA. In this paper the design of a possible Cyber Physical System (CPS) suited to real-time monitoring of OSA is described, and its software architecture and possible hardware sensing components are detailed. It should be emphasized here that this paper does not deal with a full CPS, rather with a software part of it under a set of assumptions on the environment. The paper also reports some preliminary experiments about the cognitive and learning capabilities of the designed CPS involving its use on a publicly available sleep apnea database
Mean-Field Theory of Meta-Learning
We discuss here the mean-field theory for a cellular automata model of
meta-learning. The meta-learning is the process of combining outcomes of
individual learning procedures in order to determine the final decision with
higher accuracy than any single learning method. Our method is constructed from
an ensemble of interacting, learning agents, that acquire and process incoming
information using various types, or different versions of machine learning
algorithms. The abstract learning space, where all agents are located, is
constructed here using a fully connected model that couples all agents with
random strength values. The cellular automata network simulates the higher
level integration of information acquired from the independent learning trials.
The final classification of incoming input data is therefore defined as the
stationary state of the meta-learning system using simple majority rule, yet
the minority clusters that share opposite classification outcome can be
observed in the system. Therefore, the probability of selecting proper class
for a given input data, can be estimated even without the prior knowledge of
its affiliation. The fuzzy logic can be easily introduced into the system, even
if learning agents are build from simple binary classification machine learning
algorithms by calculating the percentage of agreeing agents.Comment: 23 page
Spontaneous Resonances and the Coherent States of the Queuing Networks
We present an example of a highly connected closed network of servers, where
the time correlations do not go to zero in the infinite volume limit. This
phenomenon is similar to the continuous symmetry breaking at low temperatures
in statistical mechanics. The role of the inverse temperature is played by the
average load.Comment: 3 figures added, small correction
Comparing Fully General Relativistic and Newtonian Calculations of Structure Formation
In the standard approach to studying cosmological structure formation, the
overall expansion of the Universe is assumed to be homogeneous, with the
gravitational effect of inhomogeneities encoded entirely in a Newtonian
potential. A topic of ongoing debate is to what degree this fully captures the
dynamics dictated by general relativity, especially in the era of precision
cosmology. To quantitatively assess this, we directly compare standard N-body
Newtonian calculations to full numerical solutions of the Einstein equations,
for cold matter with various magnitude initial inhomogeneities on scales
comparable to the Hubble horizon. We analyze the differences in the evolution
of density, luminosity distance, and other quantities defined with respect to
fiducial observers. This is carried out by reconstructing the effective
spacetime and matter fields dictated by the Newtonian quantities, and by taking
care to distinguish effects of numerical resolution. We find that the fully
general relativistic and Newtonian calculations show excellent agreement, even
well into the nonlinear regime. They only notably differ in regions where the
weak gravity assumption breaks down, which arise when considering extreme cases
with perturbations exceeding standard values.Comment: 17 pages, 14 figures; revised to match PRD versio
Perturbatively constructed cosmological model with periodically distributed dust inhomogeneities
We constructed a simple cosmological model which approximates the Einstein-de
Sitter background with periodically distributed dust inhomogeneities. By taking
the metric as a power series up to the third order in some perturbative
parameter , we are able to achieve large values of the density
contrast. With a metric explicitly given, many model properties can be
calculated in a straightforward way which is interesting in the context of the
current discussion concerning the averaging of the inhomogeneities and their
backreaction in cosmology. Although the Einstein-de Sitter model can be thought
as the model \emph{average}, the light propagation differs from that of the
Einstein-de Sitter. The angular diameter distance-redshift relation is affected
by the presence of inhomogeneities and depends on the observer's position. The
model construction scheme enables some generalizations in the future, so the
present work is a step towards more realistic cosmological model described by a
relatively simple analytical metric
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