19,334 research outputs found
Connectivity Influences on Nonlinear Dynamics in Weakly-Synchronized Networks: Insights from Rössler Systems, Electronic Chaotic Oscillators, Model and Biological Neurons
Natural and engineered networks, such as interconnected neurons, ecological and social networks, coupled oscillators, wireless terminals and power loads, are characterized by an appreciable heterogeneity in the local connectivity around each node. For instance, in both elementary structures such as stars and complex graphs having scale-free topology, a minority of elements are linked to the rest of the network disproportionately strongly. While the effect of the arrangement of structural connections on the emergent synchronization pattern has been studied extensively, considerably less is known about its influence on the temporal dynamics unfolding within each node. Here, we present a comprehensive investigation across diverse simulated and experimental systems, encompassing star and complex networks of Rössler systems, coupled hysteresis-based electronic oscillators, microcircuits of leaky integrate-and-fire model neurons, and finally recordings from in-vitro cultures of spontaneously-growing neuronal networks. We systematically consider a range of dynamical measures, including the correlation dimension, nonlinear prediction error, permutation entropy, and other information-theoretical indices. The empirical evidence gathered reveals that under situations of weak synchronization, wherein rather than a collective behavior one observes significantly differentiated dynamics, denser connectivity tends to locally promote the emergence of stronger signatures of nonlinear dynamics. In deterministic systems, transition to chaos and generation of higher-dimensional signals were observed; however, when the coupling is stronger, this relationship may be lost or even inverted. In systems with a strong stochastic component, the generation of more temporally-organized activity could be induced. These observations have many potential implications across diverse fields of basic and applied science, for example, in the design of distributed sensing systems based on wireless coupled oscillators, in network identification and control, as well as in the interpretation of neuroscientific and other dynamical data
Short-time Critical Dynamics of the 3-Dimensional Ising Model
Comprehensive Monte Carlo simulations of the short-time dynamic behaviour are
reported for the three-dimensional Ising model at criticality. Besides the
exponent of the critical initial increase and the dynamic exponent
, the static critical exponents and as well as the critical
temperature are determined from the power-law scaling behaviour of observables
at the beginning of the time evolution. States of very high temperature as well
as of zero temperature are used as initial states for the simulations.Comment: 8 pages with 7 figure
Intrinsic Structural Disorder and the Magnetic Ground State in Bulk EuTiO3
The magnetic properties of single-crystal EuTiO3 are suggestive of nanoscale
disorder below its cubic-tetragonal phase transition. We demonstrate that
electric field cooling acts to restore monocrystallinity, thus confirming that
emergent structural disorder is an intrinsic low-temperature property of this
material. Using torque magnetometry, we deduce that tetragonal EuTiO3 enters an
easy-axis antiferromagnetic phase at 5.6 K, with a first-order transition to an
easy-plane ground state below 3 K. Our data is reproduced by a 3D anisotropic
Heisenberg spin model.Comment: 5 pages, 4 figure
Impurity Effects on Superconductivity on Surfaces of Topological Insulators
A two-dimensional superconductor (SC) on surfaces of topological insulators
(TIs) is a mixture of s-wave and helical p-wave components when induced by
s-wave interactions, since spin and momentum are correlated. On the basis of
the Abrikosov-Gor'kov theory, we reveal that unconventional SCs on the surfaces
of TIs are stable against time-reversal symmetric (TRS) impurities within a
region of small impurity concentration. Moreover, we analyze the stability of
the SC on the surfaces of TIs against impurities beyond the perturbation theory
by solving the real-space Bogoliubov-de Gennes equation for an effective
tight-binding model of a TI. We find that the SC is stable against strong TRS
impurities. The behaviors of bound states around an impurity suggest that the
SC on the surfaces of TIs is not a topological SC.Comment: 17 pages, 14 figures, to appear in J. Phys. Soc. Jp
A New Solid Deuterium Source of Ultra-Cold Neutrons
In polarized neutron decay, the angular correlation between the neutron spin and the
direction of emission of the electron is characterized by the coefficient A. Measuring
A involves determining the forward-backward asymmetry of the decay beta with
respect to the direction of the neutron polarization. The value of A, when combined
with measurements of the neutron lifetime, determines the values of the vector and
axial vector weak coupling constants, Gv and GA. The value of Gv can also be
determined by measurements of superallowed nuclear beta decay and by requiring
that the Cabibo-Kobayashi-Maskawi (CKM) mixing matrix be unitary along with the
measured value of other elements of the CKM matrix
A high-field adiabatic fast passage ultracold neutron spin flipper for the UCNA experiment
The UCNA collaboration is making a precision measurement of the β asymmetry (A) in free neutron decay using polarized ultracold neutrons (UCN). A critical component of this experiment is an adiabatic fast passage neutron spin flipper capable of efficient operation in ambient magnetic fields on the order of 1 T. The requirement that it operate in a high field necessitated the construction of a free neutron spin flipper based, for the first time, on a birdcage resonator. The design, construction, and initial testing of this spin flipper prior to its use in the first measurement of A with UCN during the 2007 run cycle of the Los Alamos Neutron Science Center's 800 MeV proton accelerator is detailed. These studies determined the flipping efficiency of the device, averaged over the UCN spectrum present at the location of the spin flipper, to be ϵ(overbar) = 0.9985(4)
Inter-Intra Molecular Dynamics as an Iterated Function System
The dynamics of units (molecules) with slowly relaxing internal states is
studied as an iterated function system (IFS) for the situation common in e.g.
biological systems where these units are subjected to frequent collisional
interactions. It is found that an increase in the collision frequency leads to
successive discrete states that can be analyzed as partial steps to form a
Cantor set. By considering the interactions among the units, a self-consistent
IFS is derived, which leads to the formation and stabilization of multiple such
discrete states. The relevance of the results to dynamical multiple states in
biomolecules in crowded conditions is discussed.Comment: 7 pages, 7 figures. submitted to Europhysics Letter
Two-dimensional quantum interference contributions to the magnetoresistance of Nd{2-x}Ce{x}CuO{4-d} single crystals
The 2D weak localization effects at low temperatures T = (0.2-4.2)K have been
investigated in nonsuperconducting sample Nd{1.88}Ce{0.12}CuO{4-d} and in the
normal state of the superconducting sample Nd{1.82}Ce{0.18}CuO{4-d} for B>B_c2.
The phase coherence time and the effective thickness of a conducting CuO_2
layer have been estimated by the fitting of 2D weak localization theory
expressions to the magnetoresistivity data for the normal to plane and the
in-plane magnetic fields.Comment: 5 pages, 4 postscript figure
Normal-state resistivity anisotropy in underdoped RBa_2Cu_3O_{6+x} crystals
We have revealed new features in the out-of-plane resistivity rho_c of
heavily underdoped RBa_2Cu_3O_{6+x} (R=Tm,Lu) single crystals, which give
evidence for two distinct mechanisms contributing the c-axis transport. We have
observed a crossover towards "metal-like" (d rho_c/d T > 0) behavior at the
temperature T_m which quickly increases with decreasing doping. The
"metal-like" conductivity contribution dominates at T < T_m and provides a
saturation of the resistivity anisotropy, rho_c / rho_{ab}. The
antiferromagnetic ordering is found to block this "metal-like" part of the
c-axis conductivity and complete decoupling of CuO_2 planes, which may be the
reason of superconductivity disappearance.Comment: RevTex, 4 pages including 4 eps figures. To be published in
Phys.Rev.Let
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