7,574 research outputs found
Synchronisation of time--delay systems
We present the linear-stability analysis of synchronised states in coupled
time-delay systems. There exists a synchronisation threshold, for which we
derive upper bounds, which does not depend on the delay time. We prove that at
least for scalar time-delay systems synchronisation is achieved by transmitting
a single scalar signal, even if the synchronised solution is given by a
high-dimensional chaotic state with a large number of positive
Lyapunov-exponents. The analytical results are compared with numerical
simulations of two coupled Mackey-Glass equations
Spontaneous Emergence of Spatio-Temporal Order in Class 4 Automata
We report surprisingly regular behaviors observed for a class 4 cellular
automaton, the totalistic rule 20: starting from disordered initial
configurations the automaton produces patterns which are periodic not only in
time but also in space. This is the first evidence that different types of
spatio-temporal order can emerge under specific conditions out of disorder in
the same discrete rule based algorithm.Comment: 5 pages, 6 color figures, Proceedings Medyfinol 2004, Physica A in
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Raman scattering in a Heisenberg {\boldmath } antiferromagnet on the triangular lattice
We investigate two-magnon Raman scattering from the Heisenberg
antiferromagnet on the triangular lattice, considering both the effect of
renormalization of the one-magnon spectrum by 1/S corrections and final-state
magnon-magnon interactions. The bare Raman intensity displays two peaks related
to one-magnon van-Hove singularities. We find that 1/S self-energy corrections
to the one-magnon spectrum strongly modify this intensity profile. The central
Raman-peak is significantly enhanced due to plateaus in the magnon dispersion,
the high frequency peak is suppressed due to magnon damping, and the overall
spectral support narrows considerably. Additionally we investigate final-state
interactions by solving the Bethe-Salpeter equation to . In contrast to
collinear antiferromagnets, the non-collinear nature of the magnetic ground
state leads to an irreducible magnon scattering which is retarded and
non-separable already to lowest order. We show that final-state interactions
lead to a rather broad Raman-continuum centered around approximately twice the
'roton'-energy. We also discuss the dependence on the scattering geometry.Comment: 7 pages, 5 figure
Orbits of primitive k-homogenous groups on (N − k)-partitions with applications to semigroups
© 2018 American Mathematical Society. The purpose of this paper is to advance our knowledge of two of the most classic and popular topics in transformation semigroups: automorphisms and the size of minimal generating sets. In order to do this, we examine the k-homogeneous permutation groups (those which act transitively on the subsets of size k of their domain X) where |X| = n and k < n/2. In the process we obtain, for k-homogeneous groups, results on the minimum numbers of generators, the numbers of orbits on k-partitions, and their normalizers in the symmetric group. As a sample result, we show that every finite 2-homogeneous group is 2-generated. Underlying our investigations on automorphisms of transformation semigroups is the following conjecture: If a transformation semigroup S contains singular maps and its group of units is a primitive group G of permutations, then its automorphisms are all induced (under conjugation) by the elements in the normalizer of G in the symmetric group. For the special case that S contains all constant maps, this conjecture was proved correct more than 40 years ago. In this paper, we prove that the conjecture also holds for the case of semigroups containing a map of rank 3 or less. The effort in establishing this result suggests that further improvements might be a great challenge. This problem and several additional ones on permutation groups, transformation semigroups, and computational algebra are proposed at the end of the paper
Optimal gradual annuitization : quantifying the costs of switching to annuities
We compute the optimal dynamic asset allocation policy for a retiree with Epstein-Zin utility. The retiree can decide how much he consumes and how much he invests in stocks, bonds, and annuities. Pricing the annuities we account for asymmetric mortality beliefs and administration expenses. We show that the retiree does not purchase annuities only once but rather several times during retirement (gradual annuitization). We analyze the case in which the retiree is restricted to buy annuities only once and has to perform a (complete or partial) switching strategy. This restriction reduces both the utility and the demand for annuities
Deferred Annuities and Strategic Asset Allocation
We derive the optimal portfolio choice and consumption pattern over the lifecycle for households facing labor income, capital market, and mortality risk. In addition to stocks and bonds, households also have access to deferred annuities. Deferred annuities offer a hedge against mortality risk and provide similar benefits as Social Security. We show that a considerable fraction of wealth should be annuitized to skim the return enhancing mortality credit. The remaining liquid wealth (stocks and bonds) is used to hedge labor income risk during work life and to earn the equity premium. We find a marginal difference between a strategy involving deferred annuities and one where the investor can purchase immediate life annuities.
On computational irreducibility and the predictability of complex physical systems
Using elementary cellular automata (CA) as an example, we show how to
coarse-grain CA in all classes of Wolfram's classification. We find that
computationally irreducible (CIR) physical processes can be predictable and
even computationally reducible at a coarse-grained level of description. The
resulting coarse-grained CA which we construct emulate the large-scale behavior
of the original systems without accounting for small-scale details. At least
one of the CA that can be coarse-grained is irreducible and known to be a
universal Turing machine.Comment: 4 pages, 2 figures, to be published in PR
How Will Energy Demand Develop in the Developing World?
Most of the medium-run growth in energy demand is forecast to come from the developing world, which consumed more total units of energy than the developed world in 2007. We argue that the main driver of the growth is likely to be increased incomes among the poor and near-poor. We document that as households come out of poverty and join the middle class, they acquire appliances, such as refrigerators, and vehicles for the first time. These new goods require energy to use and energy to manufacture. The current forecasts for energy demand in the developing world may be understated because they do not accurately capture the dramatic increase in demand associated with poverty reduction.
Intrinsic motivation in open source software development
This papers sheds light on the puzzling evidence that even though open source software (OSS) is a public good, it is developed for free by highly qualified, young and motivated individuals, and evolves at a rapid pace. We show that once OSS development is understood as the private provision of a public good, these features emerge quite naturally. We adapt a dynamic private-provision-of-public-goods model to reflect key aspects of the OSS phenomenon. In particular, instead of relying on extrinsic motives for programmers (e.g. signaling) the present model is driven by intrinsic motives of OSS programmers, such as user-programmers, play value or homo ludens payoff, and gift culture benefits. Such intrinsic motives feature extensively in the wider OSS literature and contribute new insights to the economic analysis. --open source software,public goods,homo ludens,war of attrition
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