44 research outputs found
From spin liquid to magnetic ordering in the anisotropic kagome Y-Kapellasite Y3Cu9(OH)19Cl8: a single crystal study
Y3Cu9(OH)19Cl8 realizes an original anisotropic kagome model hosting a rich
magnetic phase diagram [M. Hering et al, npj Computational Materials 8, 1
(2022)]. We present an improved synthesis of large phase-pure single crystals
via an external gradient method. These crystals were investigated in details by
susceptibility, specific heat, thermal expansion, neutron scattering and local
muSR and NMR techniques. At variance with polycristalline samples, the study of
single crystals gives evidence for subtle structural instabilities at 33K and
13K which preserve the global symmetry of the system and thus the magnetic
model. At 2.1K the compound shows a magnetic transition to a coplanar (1/3,1/3)
long range order as predicted theoretically. However our analysis of the spin
wave excitations yields magnetic interactions which locate the compound closer
to the phase boundary to a classical jammed spin liquid phase. Enhanced quantum
fluctuations at this boundary may be responsible for the strongly reduced
ordered moment of the Cu2+, estimated to be 0.075muB from muSR
The International-Trade Network: Gravity Equations and Topological Properties
This paper begins to explore the determinants of the topological properties
of the international - trade network (ITN). We fit bilateral-trade flows using
a standard gravity equation to build a "residual" ITN where trade-link weights
are depurated from geographical distance, size, border effects, trade
agreements, and so on. We then compare the topological properties of the
original and residual ITNs. We find that the residual ITN displays, unlike the
original one, marked signatures of a complex system, and is characterized by a
very different topological architecture. Whereas the original ITN is
geographically clustered and organized around a few large-sized hubs, the
residual ITN displays many small-sized but trade-oriented countries that,
independently of their geographical position, either play the role of local
hubs or attract large and rich countries in relatively complex
trade-interaction patterns
The effects of spatial constraints on the evolution of weighted complex networks
Motivated by the empirical analysis of the air transportation system, we
define a network model that includes geographical attributes along with
topological and weight (traffic) properties. The introduction of geographical
attributes is made by constraining the network in real space. Interestingly,
the inclusion of geometrical features induces non-trivial correlations between
the weights, the connectivity pattern and the actual spatial distances of
vertices. The model also recovers the emergence of anomalous fluctuations in
the betweenness-degree correlation function as first observed by Guimer\`a and
Amaral [Eur. Phys. J. B {\bf 38}, 381 (2004)]. The presented results suggest
that the interplay between weight dynamics and spatial constraints is a key
ingredient in order to understand the formation of real-world weighted
networks
Filtering and Tracking with Trinion-Valued Adaptive Algorithms
A new model for three-dimensional processes based on the trinion algebra is introduced for the first time. Compared
with the pure quaternion model, the trinion model is more compact and computationally more efficient, while having similar or
comparable performance in terms of adaptive linear filtering. Moreover, the trinion model can effectively represent the general
relationship of state evolution in Kalman filtering, where the pure quaternion model fails. Simulations on real-world wind
recordings and synthetic data sets are provided to demonstrate the potentials of this new modeling method
Evolution of scaling emergence in large-scale spatial epidemic spreading
Background: Zipf's law and Heaps' law are two representatives of the scaling
concepts, which play a significant role in the study of complexity science. The
coexistence of the Zipf's law and the Heaps' law motivates different
understandings on the dependence between these two scalings, which is still
hardly been clarified.
Methodology/Principal Findings: In this article, we observe an evolution
process of the scalings: the Zipf's law and the Heaps' law are naturally shaped
to coexist at the initial time, while the crossover comes with the emergence of
their inconsistency at the larger time before reaching a stable state, where
the Heaps' law still exists with the disappearance of strict Zipf's law. Such
findings are illustrated with a scenario of large-scale spatial epidemic
spreading, and the empirical results of pandemic disease support a universal
analysis of the relation between the two laws regardless of the biological
details of disease. Employing the United States(U.S.) domestic air
transportation and demographic data to construct a metapopulation model for
simulating the pandemic spread at the U.S. country level, we uncover that the
broad heterogeneity of the infrastructure plays a key role in the evolution of
scaling emergence.
Conclusions/Significance: The analyses of large-scale spatial epidemic
spreading help understand the temporal evolution of scalings, indicating the
coexistence of the Zipf's law and the Heaps' law depends on the collective
dynamics of epidemic processes, and the heterogeneity of epidemic spread
indicates the significance of performing targeted containment strategies at the
early time of a pandemic disease.Comment: 24pages, 7figures, accepted by PLoS ON
Review of Riemannian Distances and Divergences, Applied to SSVEP-based BCI
International audienc
MULTIVARIATE DICTIONARY LEARNING AND SHIFT & 2D ROTATION INVARIANT SPARSE CODING
In this article, we present a new tool for sparse coding: Multivariate DLA which empirically learns the characteristic patterns associated to a multivariate signals set. Once learned, Multivariate OMP approximates sparsely any signal of this considered set. These methods are specified to the 2D rotation-invariant case. Shift and rotationinvariant cases induce a compact learned dictionary. Our methods are applied to 2D handwritten data in order to extract the elementary features of this signals set
3D Rotation Invariant Decomposition of Motion Signals
Abstract. A new model for describing a three-dimensional (3D) trajectory is introduced in this article. The studied object is viewed as a linear combination of rotatable 3D patterns. The resulting model is now 3D rotation invariant (3DRI). Moreover, the temporal patterns are considered as shift-invariant. A novel 3DRI decomposition problem consists of estimating the active patterns, their coefficients, their rotations and their shift parameters. Sparsity allows to select few patterns among multiple ones. Based on the sparse approximation principle, a non-convex optimization called 3DRI matching pursuit (3DRI-MP) is proposed to solve this problem. This algorithm is applied to real and simulated data, and compared in order to evaluate its performances. Key words: 3D, motion trajectory, rotation invariant, shift-invariant, matching pursuit, Procrustes, registration.