1,941 research outputs found
Living on the edge of chaos: minimally nonlinear models of genetic regulatory dynamics
Linearized catalytic reaction equations modeling e.g. the dynamics of genetic
regulatory networks under the constraint that expression levels, i.e. molecular
concentrations of nucleic material are positive, exhibit nontrivial dynamical
properties, which depend on the average connectivity of the reaction network.
In these systems the inflation of the edge of chaos and multi-stability have
been demonstrated to exist. The positivity constraint introduces a nonlinearity
which makes chaotic dynamics possible. Despite the simplicity of such minimally
nonlinear systems, their basic properties allow to understand fundamental
dynamical properties of complex biological reaction networks. We analyze the
Lyapunov spectrum, determine the probability to find stationary oscillating
solutions, demonstrate the effect of the nonlinearity on the effective in- and
out-degree of the active interaction network and study how the frequency
distributions of oscillatory modes of such system depend on the average
connectivity.Comment: 11 pages, 5 figure
Parametric ordering of complex systems
Cellular automata (CA) dynamics are ordered in terms of two global
parameters, computable {\sl a priori} from the description of rules. While one
of them (activity) has been used before, the second one is new; it estimates
the average sensitivity of rules to small configurational changes. For two
well-known families of rules, the Wolfram complexity Classes cluster
satisfactorily. The observed simultaneous occurrence of sharp and smooth
transitions from ordered to disordered dynamics in CA can be explained with the
two-parameter diagram
Density classification on infinite lattices and trees
Consider an infinite graph with nodes initially labeled by independent
Bernoulli random variables of parameter p. We address the density
classification problem, that is, we want to design a (probabilistic or
deterministic) cellular automaton or a finite-range interacting particle system
that evolves on this graph and decides whether p is smaller or larger than 1/2.
Precisely, the trajectories should converge to the uniform configuration with
only 0's if p1/2. We present solutions to that problem
on the d-dimensional lattice, for any d>1, and on the regular infinite trees.
For Z, we propose some candidates that we back up with numerical simulations
Thalidomide-induced Teratogenesis : History and Mechanisms
Peer reviewedPublisher PD
On the stability of standing matter waves in a trap
We discuss excited Bose-condensed states and find the criterion of dynamical
stability of a kink-wise state, i.e., a standing matter wave with one nodal
plane perpendicular to the axis of a cylindrical trap. The dynamical stability
requires a strong radial confinement corresponding to the radial frequency
larger than the mean-field interparticle interaction. We address the question
of thermodynamic instability related to the presence of excitations with
negative energy.Comment: 4 pages, 3 figure
Topology and Evolution of Technology Innovation Networks
The web of relations linking technological innovation can be fairly described
in terms of patent citations. The resulting patent citation network provides a
picture of the large-scale organization of innovations and its time evolution.
Here we study the patterns of change of patents registered by the US Patent and
Trademark Office (USPTO). We show that the scaling behavior exhibited by this
network is consistent with a preferential attachment mechanism together with a
Weibull-shaped aging term. Such attachment kernel is shared by scientific
citation networks, thus indicating an universal type of mechanism linking ideas
and designs and their evolution. The implications for evolutionary theory of
innovation are discussed.Comment: 6 pages, 5 figures, submitted to Physical Review
Normal Modes of a Vortex in a Trapped Bose-Einstein Condensate
A hydrodynamic description is used to study the normal modes of a vortex in a
zero-temperature Bose-Einstein condensate. In the Thomas-Fermi (TF) limit, the
circulating superfluid velocity far from the vortex core provides a small
perturbation that splits the originally degenerate normal modes of a
vortex-free condensate. The relative frequency shifts are small in all cases
considered (they vanish for the lowest dipole mode with |m|=1), suggesting that
the vortex is stable. The Bogoliubov equations serve to verify the existence of
helical waves, similar to those of a vortex line in an unbounded weakly
interacting Bose gas. In the large-condensate (small-core) limit, the
condensate wave function reduces to that of a straight vortex in an unbounded
condensate; the corresponding Bogoliubov equations have no bound-state
solutions that are uniform along the symmetry axis and decay exponentially far
from the vortex core.Comment: 15 pages, REVTEX, 2 Postscript figures, to appear in Phys. Rev. A. We
have altered the material in Secs. 3B and 4 in connection with the normal
modes that have |m|=1. Our present treatment satisfies the condition that the
fundamental dipole mode of a condensate with (or without) a vortex should
have the bare frequency $\omega_\perp
Factors associated with the decision to investigate child protective services referrals: a systematic review
Background: Limited resources for child protection create challenging decision situations for child protective services (CPS) workers at the point of intake. A body of research has examined the factors associated with worker decisions and processes using a variety of methodological approaches to gain knowledge on decision-making. However, few attempts have been made to systematically review this literature.
Objective: As part of a larger project on decision-making at intake, this systematic review addressed the question of the factors associated with worker decisions to investigate alleged maltreatment referrals.
Methods: Quantitative studies that examined factors associated with screening decisions in CPS practice settings were included in the review. Database and other search methods were used to identify research published in English over a 35-year period (1980-2015).
Findings: Of 1,147 identified sources, 18 studies were selected for full data extraction. The studies were conducted in the U.S., Canada, and Sweden and varied in methodological quality. Most studies examined case factors with few studies examining other domains.
Conclusions: To inform CPS policy and practice, additional research is needed to examine the relationships between decision-making factors and case outcomes. Greater attention needs to be given to the organizational and external factors that influence decision-making
Using Topological Statistics to Detect Determinism in Time Series
Statistical differentiability of the measure along the reconstructed
trajectory is a good candidate to quantify determinism in time series. The
procedure is based upon a formula that explicitly shows the sensitivity of the
measure to stochasticity. Numerical results for partially surrogated time
series and series derived from several stochastic models, illustrate the
usefulness of the method proposed here. The method is shown to work also for
high--dimensional systems and experimental time seriesComment: 23 RevTeX pages, 14 eps figures. To appear in Physical Review
Asymptotically stable phase synchronization revealed by autoregressive circle maps
A new type of nonlinear time series analysis is introduced, based on phases,
which are defined as polar angles in spaces spanned by a finite number of
delayed coordinates. A canonical choice of the polar axis and a related
implicit estimation scheme for the potentially underlying auto-regressive
circle map (next phase map) guarantee the invertibility of reconstructed phase
space trajectories to the original coordinates. The resulting Fourier
approximated, Invertibility enforcing Phase Space map (FIPS map) is well suited
to detect conditional asymptotic stability of coupled phases. This rather
general synchronization criterion unites two existing generalisations of the
old concept and can successfully be applied e.g. to phases obtained from ECG
and airflow recordings characterizing cardio-respiratory interaction.Comment: PDF file, 232 KB, 24 pages, 3 figures; cheduled for Phys. Rev. E
(Nov) 200
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