2,281 research outputs found
A Double Auction Market with Signals of Varying Precision
A computerized double auction market with human traders is employed to examine the relation of price and volume under conditions of asymmetric information. In this market, the informed traders receive higher precision signals than the uninformed traders. The relation of price and volume has been suggested as an important factor in the process of information revelation whereby information held by informed traders is transferred to uninformed traders. In contrast, the no-trade theorems suggest that trade should not occur at all between informed and uninformed traders. The results show trading volume within the informed group to be positively correlated with signal precision. In situations of asymmetric information, uninformed trading activity as measured by volume/precision correlations declines significantly as the precision of the signals of informed traders increases. However, the presence of asymmetric information does not lead to a zero trade condition for either the informed or the uninformed traders.Experimental, Double Auction, Information Precision, Trading Volume, Asymmetric Information
Frontier impedance effects and the growth of international exchanges: an empirical analysis for France
On the European Union scale, international traffic is growing faster than intra-national traffic. This phenomenon is often viewed as a consequence of the abatement of the frontier effect. In this article the frontier effect is analyzed, on the basis of data available for road traffic between France and its neighbors and of freight transport data available at the EU level. The concept is discussed in the light of this empirical analysis. The shortcomings of the static approach lead to a critical revaluation by means of a longitudinal approach. In the conclusion some potential directions for future research are discussed.Frontier ; frontier effect ; international flow ; passengers transport ; goods transport ; Europe
Combined analytical and numerical approach to magnetization plateaux in one-dimensional spin tube antiferromagnets
In this paper, we investigate the properties of frustrated three-leg spin
tubes under a magnetic field. We concentrate on two kind of geometries for
these tubes, one of which is relevant for the compound
. We combine an analytical path integral
approach with a strong coupling approach, as well as large-scale Density Matrix
Renormalization Groups (DMRG) simulations, to identify the presence of plateaux
in the magnetization curve as a function of the value of spin . We also
investigate the issue of gapless non-magnetic excitations on some plateaux,
dubbed chirality degrees of freedom for both tubes.Comment: 17 page
Magnetization plateaus of an easy-axis Kagom\'e antiferromagnet with extended interactions
We investigate the properties in finite magnetic field of an extended
anisotropic XXZ spin-1/2 model on the Kagome lattice, originally introduced by
Balents, Fisher, and Girvin [Phys. Rev. B, 65, 224412 (2002)]. The
magnetization curve displays plateaus at magnetization m=1/6 and 1/3 when the
anisotropy is large. Using low-energy effective constrained models (quantum
loop and quantum dimer models), we discuss the nature of the plateau phases,
found to be crystals that break discrete rotation and/or translation
symmetries. Large-scale quantum Monte-Carlo simulations were carried out in
particular for the m=1/6 plateau. We first map out the phase diagram of the
effective quantum loop model with an additional loop-loop interaction to find
stripe order around the point relevant for the original model as well as a
topological Z2 spin liquid. The existence of a stripe crystalline phase is
further evidenced by measuring both standard structure factor and entanglement
entropy of the original microscopic model.Comment: 14 pages, 14 figure
Colour-dressed hexagon tessellations for correlation functions and non-planar corrections
We continue the study of four-point correlation functions by the hexagon
tessellation approach initiated in 1611.05436 and 1611.05577. We consider
planar tree-level correlation functions in supersymmetric
Yang-Mills theory involving two non-protected operators. We find that, in order
to reproduce the field theory result, it is necessary to include colour
factors in the hexagon formalism; moreover, we find that the hexagon approach
as it stands is naturally tailored to the single-trace part of correlation
functions, and does not account for multi-trace admixtures. We discuss how to
compute correlators involving double-trace operators, as well as more general
effects; in particular we compute the whole next-to-leading order in the
large- expansion of tree-level BMN two-point functions by tessellating a
torus with punctures. Finally, we turn to the issue of "wrapping",
L\"uscher-like corrections. We show that colour-dressing reproduces an
earlier empirical rule for incorporating single-magnon wrapping, and we provide
a direct interpretation of such wrapping processes in terms of
supersymmetric Feynman diagrams.Comment: 42 pages, typos correcte
Transportation and access to urban services in Dar es Salaam
Transportation in Dar es Salaam is particularly difficult. Statistical data drawn from the 1993 Human Resources Development Survey confirm that in unplanned settlements, transportation conditions and access to urban services are less favourable than in the rest of the city. The poverty of a majority of city inhabitants, the low quality of urban passenger transport and poor accessibility result in daily mobility reduced to the immediate neighbourhood, while in turn tends to perpetuate poverty.Access to urban services ; daily mobility ; Statistical data (HRDS 1993) ; poverty ; Dar es Salaam
Universal logarithmic corrections to entanglement entropies in two dimensions with spontaneously broken continuous symmetries
We explore the R\'enyi entanglement entropies of a one-dimensional (line)
subsystem of length embedded in two-dimensional square lattice
for quantum spin models whose ground-state breaks a continuous symmetry in the
thermodynamic limit. Using quantum Monte Carlo simulations, we first study the
Heisenberg model with antiferromagnetic nearest-neighbor
and ferromagnetic second-neighbor couplings . The signature of SU(2)
symmetry breaking on finite size systems, ranging from up to
clearly appears as a universal additive logarithmic correction to the R\'enyi
entanglement entropies: with , independent of the
R\'enyi index and values of . We confirm this result using a high
precision spin-wave analysis (with restored spin rotational symmetry) on finite
lattices up to sites, allowing to explore further
non-universal finite size corrections and study in addition the case of U(1)
symmetry breaking. Our results fully agree with the prediction
where is the number of Goldstone modes, by Metlitski and Grover
[arXiv:1112.5166].Comment: 6 pages, 6 figure
Selection of factorizable ground state in a frustrated spin tube: Order by disorder and hidden ferromagnetism
The interplay between frustration and quantum fluctuation in magnetic systems
is known to be the origin of many exotic states in condensed matter physics. In
this paper, we consider a frustrated four-leg spin tube under a magnetic field.
This system is a prototype to study the emergence of a nonmagnetic ground state
factorizable into local states and the associated order parameter without
quantum fluctuation, that appears in a wide variety of frustrated systems. The
one-dimensional nature of the system allows us to apply various techniques: a
path-integral formulation based on the notion of order by disorder,
strong-coupling analysis where magnetic excitations are gapped, and
density-matrix renormalization group. All methods point toward an interesting
property of the ground state in the magnetization plateaus, namely, a quantized
value of relative magnetizations between different sublattices (spin imbalance)
and an almost perfect factorization of the ground state
Improving entanglement and thermodynamic R\'enyi entropy measurements in quantum Monte Carlo
We present a method for improving measurements of the entanglement R\'enyi
entropies in quantum Monte Carlo simulations by relating them with measurements
of participation R\'enyi entropies. Exploiting the capability of building
improved estimators for the latter allows to obtain very good estimates for
entanglement R\'enyi entropies. When considering a full system instead of a
bipartition, the method can be further ameliorated providing access to the
thermodynamic R\'enyi entropies with high accuracy. We also explore a
recently-proposed method for the reconstruction of the entanglement spectrum
from entanglement R\'enyi entropies and finally show how potential entanglement
Hamiltonians may be tested for their validity using a comparison with thermal
R\'enyi entropies.Comment: 15 pages, 11 figure
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