37 research outputs found
Supersampling and network reconstruction of urban mobility
Understanding human mobility is of vital importance for urban planning,
epidemiology, and many other fields that aim to draw policies from the
activities of humans in space. Despite recent availability of large scale data
sets related to human mobility such as GPS traces, mobile phone data, etc., it
is still true that such data sets represent a subsample of the population of
interest, and then might give an incomplete picture of the entire population in
question. Notwithstanding the abundant usage of such inherently limited data
sets, the impact of sampling biases on mobility patterns is unclear -- we do
not have methods available to reliably infer mobility information from a
limited data set. Here, we investigate the effects of sampling using a data set
of millions of taxi movements in New York City. On the one hand, we show that
mobility patterns are highly stable once an appropriate simple rescaling is
applied to the data, implying negligible loss of information due to subsampling
over long time scales. On the other hand, contrasting an appropriate null model
on the weighted network of vehicle flows reveals distinctive features which
need to be accounted for. Accordingly, we formulate a "supersampling"
methodology which allows us to reliably extrapolate mobility data from a
reduced sample and propose a number of network-based metrics to reliably assess
its quality (and that of other human mobility models). Our approach provides a
well founded way to exploit temporal patterns to save effort in recording
mobility data, and opens the possibility to scale up data from limited records
when information on the full system is needed.Comment: 14 pages, 4 figure
Statistical Complex Analysis of Taxi Mobility in San Francisco
Projecte final de MĂ ster Oficial realitzat en col.laboraciĂł amb Universitat de Barcelona, Departament de FĂsica Fonamental.English: The recent developments in technology of movement tracking devices such as Global Positioning (GPS), together with the increasing availability of consistent data bases, have lately given rise to the study of human mobility patterns in different environments. In this work a statistical characterization of real mobility GPS high-frequency data from taxis in San Francisco is performed. The di_erent patterns taxi drivers and customers follow are shown through comparing behavior when cabs are empty or full and the information is presented using a weighted directed complex network metric, from which the author obtains some topological information such as correlations between nodes, assortativity and clustering. Some adapted measurements to weighted nets are presented together with some remarks to support the need for new tools for assortativity classification
Synchronization of moving integrate and fire oscillators
We present a model of integrate and fire oscillators that move on a plane.
The phase of the oscillators evolves linearly in time and when it reaches a
threshold value they fire choosing their neighbors according to a certain
interaction range. Depending on the velocity of the ballistic motion and the
average number of neighbors each oscillator fires to, we identify different
regimes shown in a phase diagram. We characterize these regimes by means of
novel parameters as the accumulated number of contacted neighbors.Comment: 9 pages, 5 figure
The configuration multi-edge model: Assessing the effect of fixing node strengths on weighted network magnitudes
Complex networks grow subject to structural constraints which affect their
measurable properties. Assessing the effect that such constraints impose on
their observables is thus a crucial aspect to be taken into account in their
analysis. To this end,we examine the effect of fixing the strength sequence in
multi-edge networks on several network observables such as degrees, disparity,
average neighbor properties and weight distribution using an ensemble approach.
We provide a general method to calculate any desired weighted network metric
and we show that several features detected in real data could be explained
solely by structural constraints. We thus justify the need of analytical null
models to be used as basis to assess the relevance of features found in real
data represented in weighted network form.Comment: 11 pages. 4 figure
Tuning synchronization of integrate-and-fire oscillators through mobility
We analyze the emergence of synchronization in a population of moving integrate-and-fire oscillators. Oscillators, while moving on a plane, interact with their nearest neighbor upon firing time. We discover a nonmonotonic dependence of the synchronization time on the velocity of the agents. Moreover, we find that mechanisms that drive synchronization are different for different dynamical regimes. We report the extreme situation where an interplay between the time scales involved in the dynamical processes completely inhibits the achievement of a coherent state. We also provide estimators for the transitions between the different regimes
The configuration multi-edge model: Assessing the effect of fixing node strengths on weighted network magnitudes
Complex networks grow subject to structural constraints which affect their measurable properties. Assessing the effect that such constraints impose on their observables is thus a crucial aspect to be taken into account in their analysis. To this end,we examine the effect of fixing the strength sequence in multi-edge networks on several network observables such as degrees, disparity, average neighbor properties and weight distribution using an ensemble approach. We provide a general method to calculate any desired weighted network metric and we show that several features detected in real data could be explained solely by structural constraints. We thus justify the need of analytical null models to be used as basis to assess the relevance of features found in real data represented in weighted network form