28,121 research outputs found
Cusp-scaling behavior in fractal dimension of chaotic scattering
A topological bifurcation in chaotic scattering is characterized by a sudden
change in the topology of the infinite set of unstable periodic orbits embedded
in the underlying chaotic invariant set. We uncover a scaling law for the
fractal dimension of the chaotic set for such a bifurcation. Our analysis and
numerical computations in both two- and three-degrees-of-freedom systems
suggest a striking feature associated with these subtle bifurcations: the
dimension typically exhibits a sharp, cusplike local minimum at the
bifurcation.Comment: 4 pages, 4 figures, Revte
Possible nodal superconducting gap emerging at the Lifshitz transition in heavily hole-doped Ba0.1K0.9Fe2As2
We performed a high energy resolution ARPES investigation of over-doped
Ba0.1K0.9Fe2As2 with T_c= 9 K. The Fermi surface topology of this material is
similar to that of KFe2As2 and differs from that of slightly less doped
Ba0.3K0.7Fe2As2, implying that a Lifshitz transition occurred between x=0.7 and
x=0.9. Albeit for a vertical node found at the tip of the emerging
off-M-centered Fermi surface pocket lobes, the superconducting gap structure is
similar to that of Ba0.3K0.7Fe2As2, suggesting that the paring interaction is
not driven by the Fermi surface topology.Comment: 5 pages, 4 figure
Tableaux for Policy Synthesis for MDPs with PCTL* Constraints
Markov decision processes (MDPs) are the standard formalism for modelling
sequential decision making in stochastic environments. Policy synthesis
addresses the problem of how to control or limit the decisions an agent makes
so that a given specification is met. In this paper we consider PCTL*, the
probabilistic counterpart of CTL*, as the specification language. Because in
general the policy synthesis problem for PCTL* is undecidable, we restrict to
policies whose execution history memory is finitely bounded a priori.
Surprisingly, no algorithm for policy synthesis for this natural and
expressive framework has been developed so far. We close this gap and describe
a tableau-based algorithm that, given an MDP and a PCTL* specification, derives
in a non-deterministic way a system of (possibly nonlinear) equalities and
inequalities. The solutions of this system, if any, describe the desired
(stochastic) policies.
Our main result in this paper is the correctness of our method, i.e.,
soundness, completeness and termination.Comment: This is a long version of a conference paper published at TABLEAUX
2017. It contains proofs of the main results and fixes a bug. See the
footnote on page 1 for detail
Signatures of charmonium modification in spatial correlation functions
We study spatial correlation functions of charmonium in 2+1 flavor QCD using
an improved staggered formulation. Contrary to the temporal correlation
functions the spatial correlation functions exhibit a strong temperature
dependence above the QCD transition temperature. Above this temperature they
are sensitive to temporal boundary conditions. Both features become significant
at a temperature close to 1.5 Tc and suggest corresponding modifications of
charmonium spectral functions.Comment: 12 pages, LaTeX, 3 figure
Fine Details of the Nodal Electronic Excitations in BiSrCaCuO
Very high energy resolution photoemission experiments on high quality samples
of optimally doped BiSrCaCuO show new features in the
low-energy electronic excitations. A marked change in the binding energy and
temperature dependence of the near-nodal scattering rates is observed near the
superconducting transition temperature, . The temperature slope of the
scattering rate measured at low energy shows a discontinuity at ~. In the
superconducting state, coherent excitations are found with the scattering rates
showing a cubic dependence on frequency and temperature. The superconducting
gap has a d-wave magnitude with negligible contribution from higher harmonics.
Further, the bi-layer splitting has been found to be finite at the nodal point.Comment: 5 pages, 4 figure
ARPES observation of isotropic superconducting gaps in isovalent Ru-substituted Ba(FeRu)As
We used high-energy resolution angle-resolved photoemission spectroscopy to
extract the momentum dependence of the superconducting gap of Ru-substituted
Ba(FeRu)As ( K). Despite a strong
out-of-plane warping of the Fermi surface, the magnitude of the superconducting
gap observed experimentally is nearly isotropic and independent of the
out-of-plane momentum. More precisely, we respectively observed 5.7 meV and 4.5
meV superconducting gaps on the inner and outer -centered hole Fermi
surface pockets, whereas a 4.8 meV gap is recorded on the M-centered electron
Fermi surface pockets. Our results are consistent with the model with
a dominant antiferromagnetic exchange interaction between the next-nearest Fe
neighbors.Comment: 5 pages, 4 figure
An efficient and principled method for detecting communities in networks
A fundamental problem in the analysis of network data is the detection of
network communities, groups of densely interconnected nodes, which may be
overlapping or disjoint. Here we describe a method for finding overlapping
communities based on a principled statistical approach using generative network
models. We show how the method can be implemented using a fast, closed-form
expectation-maximization algorithm that allows us to analyze networks of
millions of nodes in reasonable running times. We test the method both on
real-world networks and on synthetic benchmarks and find that it gives results
competitive with previous methods. We also show that the same approach can be
used to extract nonoverlapping community divisions via a relaxation method, and
demonstrate that the algorithm is competitively fast and accurate for the
nonoverlapping problem.Comment: 14 pages, 5 figures, 1 tabl
Viewing the efficiency of chaos control
This paper aims to cast some new light on controlling chaos using the OGY-
and the Zero-Spectral-Radius methods. In deriving those methods we use a
generalized procedure differing from the usual ones. This procedure allows us
to conveniently treat maps to be controlled bringing the orbit to both various
saddles and to sources with both real and complex eigenvalues. We demonstrate
the procedure and the subsequent control on a variety of maps. We evaluate the
control by examining the basins of attraction of the relevant controlled
systems graphically and in some cases analytically
Universal Magnetic Properties of at Intermediate Temperatures
We present the theory of two-dimensional, clean quantum antiferromagnets with
a small, positive, zero temperature () stiffness , but with the
ratio arbitrary. Universal scaling forms for the uniform
susceptibility (), correlation length(), and NMR relaxation rate
() are proposed and computed in a expansion and by Mont\'{e}-Carlo
simulations. For large , and asymptote
to universal values, while is nearly -independent. We find good
quantitative agreement with experiments and some numerical studies on
.Comment: 14 pages, REVTEX, 1 postscript figure appende
Experimental realization of strange nonchaotic attractors in a quasiperiodically forced electronic circuit
We have identified the three prominent routes, namely Heagy-Hammel,
fractalization and intermittency routes, and their mechanisms for the birth of
strange nonchaotic attractors (SNAs) in a quasiperiodically forced electronic
system constructed using a negative conductance series LCR circuit with a diode
both numerically and experimentally. The birth of SNAs by these three routes is
verified from both experimental and their corresponding numerical data by
maximal Lyapunov exponents, and their variance, Poincar\'e maps, Fourier
amplitude spectrum, spectral distribution function and finite-time Lyapunov
exponents. Although these three routes have been identified numerically in
different dynamical systems, the experimental observation of all these
mechanisms is reported for the first time to our knowledge and that too in a
single second order electronic circuit.Comment: 21 figure
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