22,752 research outputs found
Uni-directional polymerization leading to homochirality in the RNA world
The differences between uni-directional and bi-directional polymerization are
considered. The uni-directional case is discussed in the framework of the RNA
world. Similar to earlier models of this type, where polymerization was assumed
to proceed in a bi-directional fashion (presumed to be relevant to peptide
nucleic acids), left-handed and right-handed monomers are produced via an
autocatalysis from an achiral substrate. The details of the bifurcation from a
racemic solution to a homochiral state of either handedness is shown to be
remarkably independent of whether the polymerization in uni-directional or
bi-directional. Slightly larger differences are seen when dissociation is
allowed and the dissociation fragments are being recycled into the achiral
substrate.Comment: 9 pages, 4 figures, submitted to Astrobiolog
On the Entropy of a Family of Random Substitutions
The generalised random Fibonacci chain is a stochastic extension of the
classical Fibonacci substitution and is defined as the rule mapping and with probability , where with
, and where the random rule is applied each time it acts on
a 1. We show that the topological entropy of this object is given by the growth
rate of the set of inflated generalised random Fibonacci words.Comment: A more appropriate tile and minor misprints corrected, compared to
the previous versio
Forecasting Inflation: the Relevance of Higher Moments
We provide evidence that higher moments of the relative price distribution improve out-of-sample forecasts of inflation. Further, we show how theoretically consistent higher moments can be calculated by expanding the seminal work by Theil (1967). Results presented here are of direct relevance to monetary authorities, policy analysts and academic economistsrelative price distribution, higher moments, out-of-sample inflation forecasting
Spatially self-similar spherically symmetric perfect-fluid models
Einstein's field equations for spatially self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
with the theory of dynamical systems.Comment: 21 pages, 6 eps-figure
Heat capacity mapping mission project HCM-051
There are no author-identified significant results in this report
The state space and physical interpretation of self-similar spherically symmetric perfect-fluid models
The purpose of this paper is to further investigate the solution space of
self-similar spherically symmetric perfect-fluid models and gain deeper
understanding of the physical aspects of these solutions. We achieve this by
combining the state space description of the homothetic approach with the use
of the physically interesting quantities arising in the comoving approach. We
focus on three types of models. First, we consider models that are natural
inhomogeneous generalizations of the Friedmann Universe; such models are
asymptotically Friedmann in their past and evolve fluctuations in the energy
density at later times. Second, we consider so-called quasi-static models. This
class includes models that undergo self-similar gravitational collapse and is
important for studying the formation of naked singularities. If naked
singularities do form, they have profound implications for the predictability
of general relativity as a theory. Third, we consider a new class of
asymptotically Minkowski self-similar spacetimes, emphasizing that some of them
are associated with the self-similar solutions associated with the critical
behaviour observed in recent gravitational collapse calculations.Comment: 24 pages, 12 figure
Faithful fermionic representations of the Kondo lattice model
We study the Kondo lattice model using a class of canonical transformations
that allow us to faithfully represent the model entirely in terms of fermions
without constraints. The transformations generate interacting theories that we
study using mean field theory. Of particular interest is a new manifestly
O(3)-symmetric representation in terms of Majorana fermions at half-filling on
bipartite lattices. This representation suggests a natural O(3)-symmetric trial
state that is investigated and characterized as a gapped spin liquid.Comment: 11 pages, 2 figures, minor update
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