371 research outputs found
Anticipated synchronization in coupled inertia ratchets with time-delayed feedback: a numerical study
We investigate anticipated synchronization between two periodically driven
deterministic, dissipative inertia ratchets that are able to exhibit directed
transport with a finite velocity. The two ratchets interact through an
unidirectional delay coupling: one is acting as a master system while the other
one represents the slave system. Each of the two dissipative deterministic
ratchets is driven externally by a common periodic force. The delay coupling
involves two parameters: the coupling strength and the (positive-valued) delay
time. We study the synchronization features for the unbounded, current carrying
trajectories of the master and the slave, respectively, for four different
strengths of the driving amplitude. These in turn characterize differing phase
space dynamics of the transporting ratchet dynamics: regular, intermittent and
a chaotic transport regime. We find that the slave ratchet can respond in
exactly the same way as the master will respond in the future, thereby
anticipating the nonlinear directed transport
Stocks and Cryptocurrencies: Anti-fragile or Robust?
Antifragility was recently defined as a property of complex systems that
benefit from disorder. However, its original formal definition is difficult to
apply. Our approach has been to define and test a much simpler measure of
antifragility for complex systems. In this work we use our antifragility
measure to analyze real data from the stock market and cryptocurrency prices.
Results vary between different antifragility interpretations and for each
system. Our results suggest that the stock market favors robustness rather than
antifragility, as in most cases the highest and lowest antifragility values are
reached either by young agents or constant ones. There are no clear
correlations between antifragility and different good-performance measures,
while the best performers seem to fall within a robust threshold. In the case
of cryptocurrencies, there is an apparent correlation between high price and
high antifragility.Comment: 11 pages, 5 figure
A random walker on a ratchet
We analyze a model for a walker moving on a ratchet potential. This model is
motivated by the properties of transport of motor proteins, like kinesin and
myosin. The walker consists of two feet represented as two particles coupled
nonlinearly through a bistable potential. In contrast to linear coupling, the
bistable potential admits a richer dynamics where the ordering of the particles
can alternate during the walking. The transitions between the two stable states
on the bistable potential correspond to a walking with alternating particles.
We distinguish between two main walking styles: alternating and no alternating,
resembling the hand-over-hand and the inchworm walking in motor proteins,
respectively. When the equilibrium distance between the two particles divided
by the periodicity of the ratchet is an integer, we obtain a maximum for the
current, indicating optimal transport.Comment: 10 pages, 5 figure
Temporal visitation patterns of points of interest in cities on a planetary scale: a network science and machine learning approach
We aim to study the temporal patterns of activity in points of interest of
cities around the world. In order to do so, we use the data provided by the
online location-based social network Foursquare, where users make check-ins
that indicate points of interest in the city. The data set comprises more than
90 million check-ins in 632 cities of 87 countries in 5 continents. We analyzed
more than 11 million points of interest including all sorts of places:
airports, restaurants, parks, hospitals, and many others. With this
information, we obtained spatial and temporal patterns of activities for each
city. We quantify similarities and differences of these patterns for all the
cities involved and construct a network connecting pairs of cities. The links
of this network indicate the similarity of temporal visitation patterns of
points of interest between cities and is quantified with the Kullback-Leibler
divergence between two distributions. Then, we obtained the community structure
of this network and the geographic distribution of these communities worldwide.
For comparison, we also use a Machine Learning algorithm - unsupervised
agglomerative clustering - to obtain clusters or communities of cities with
similar patterns. The main result is that both approaches give the same
classification of five communities belonging to five different continents
worldwide. This suggests that temporal patterns of activity can be universal,
with some geographical, historical, and cultural variations, on a planetary
scale.Comment: 18 pages, 7 figure
Towards a clinical staging for bipolar disorder: defining patient subtypes based on functional outcome.
BACKGROUND: The functional outcome of Bipolar Disorder (BD) is highly variable. This variability has been attributed to multiple demographic, clinical and cognitive factors. The critical next step is to identify combinations of predictors that can be used to specify prognostic subtypes, thus providing a basis for a staging classification in BD. METHODS: Latent Class Analysis was applied to multiple predictors of functional outcome in a sample of 106 remitted adults with BD. RESULTS: We identified two subtypes of patients presenting "good" (n=50; 47.6%) and "poor" (n=56; 52.4%) outcome. Episode density, level of residual depressive symptoms, estimated verbal intelligence and inhibitory control emerged as the most significant predictors of subtype membership at the p<0.05 level. Their odds ratio (OR) and confidence interval (CI) with reference to the "good" outcome group were: episode density (OR=4.622, CI 1.592-13.418), level of residual depressive symptoms (OR=1.543, CI 1.210-1.969), estimated verbal intelligence (OR=0.969; CI 0.945-0.995), and inhibitory control (OR=0.771, CI 0.656-0.907). Age, age of onset and duration of illness were comparable between prognostic groups. LIMITATIONS: The longitudinal stability or evolution of the subtypes was not tested. CONCLUSIONS: Our findings provide the first empirically derived staging classification of BD based on two underlying dimensions, one for illness severity and another for cognitive function. This approach can be further developed by expanding the dimensions included and testing the reproducibility and prospective prognostic value of the emerging classes. Developing a disease staging system for BD will allow individualised treatment planning for patients and selection of more homogeneous patient groups for research purposes
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