47 research outputs found
Evacuation time estimate for a total pedestrian evacuation using queuing network model and volunteered geographic information
Estimating city evacuation time is a non-trivial problem due to the
interaction between thousands of individual agents, giving rise to various
collective phenomena, such as bottleneck formation, intermittent flow and
stop-and-go waves. We present a mean field approach to draw relationships
between road network spatial attributes, number of evacuees and resultant
evacuation time estimate (ETE). We divide medium sized UK cities into a
total of catchment areas which we define as an area where all agents
share the same nearest exit node. In these catchment areas, 90% of agents are
within km of their designated exit node. We establish a characteristic
flow rate from catchment area attributes (population, distance to exit node and
exit node width) and a mean flow rate in free-flow regime by simulating total
evacuations using an agent based `queuing network' model. We use these
variables to determine a relationship between catchment area attributes and
resultant ETE. This relationship could enable emergency planners to make rapid
appraisal of evacuation strategies and help support decisions in the run up to
a crisis.Comment: 6 pages, 8 figure
Human Mobility Modelling:Exploration and Preferential Return Meet the Gravity Model
AbstractModeling the properties of individual human mobility is a challenging task that has received increasing attention in the last decade. Since mobility is a complex system, when modeling individual human mobility one should take into account that human movements at a collective level influence, and are influenced by, human movement at an individual level. In this paper we propose the d-EPR model, which exploits collective information and the gravity model to drive the movements of an individual and the exploration of new places on the mobility space. We implement our model to simulate the mobility of thousands synthetic individuals, and compare the synthetic movements with real trajectories of mobile phone users and synthetic trajectories produced by a prominent individual mobility model. We show that the distributions of global mobility measures computed on the trajectories produced by the d-EPR model are much closer to empirical data, highlighting the importance of considering collective information when simulating individual human mobility
An allometry-based approach for understanding forest structure, predicting tree-size distribution and assessing the degree of disturbance
Tree-size distribution is one of the most investigated subjects in plant
population biology. The forestry literature reports that tree-size distribution
trajectories vary across different stands and/or species, while the metabolic
scaling theory suggests that the tree number scales universally as -2 power of
diameter. Here, we propose a simple functional scaling model in which these two
opposing results are reconciled. Basic principles related to crown shape,
energy optimization and the finite size scaling approach were used to define a
set of relationships based on a single parameter, which allows us to predict
the slope of the tree-size distributions in a steady state condition. We tested
the model predictions on four temperate mountain forests. Plots (4 ha each,
fully mapped) were selected with different degrees of human disturbance
(semi-natural stands vs. formerly managed). Results showed that the size
distribution range successfully fitted by the model is related to the degree of
forest disturbance: in semi-natural forests the range is wide, while in
formerly managed forests, the agreement with the model is confined to a very
restricted range. We argue that simple allometric relationships, at individual
level, shape the structure of the whole forest community.Comment: 22 pages, 4 figure
Deep Gravity: enhancing mobility flows generation with deep neural networks and geographic information
The movements of individuals within and among cities influence key aspects of
our society, such as the objective and subjective well-being, the diffusion of
innovations, the spreading of epidemics, and the quality of the environment.
For this reason, there is increasing interest around the challenging problem of
flow generation, which consists in generating the flows between a set of
geographic locations, given the characteristics of the locations and without
any information about the real flows. Existing solutions to flow generation are
mainly based on mechanistic approaches, such as the gravity model and the
radiation model, which suffer from underfitting and overdispersion, neglect
important variables such as land use and the transportation network, and cannot
describe non-linear relationships between these variables. In this paper, we
propose the Multi-Feature Deep Gravity (MFDG) model as an effective solution to
flow generation. On the one hand, the MFDG model exploits a large number of
variables (e.g., characteristics of land use and the road network; transport,
food, and health facilities) extracted from voluntary geographic information
data (OpenStreetMap). On the other hand, our model exploits deep neural
networks to describe complex non-linear relationships between those variables.
Our experiments, conducted on commuting flows in England, show that the MFDG
model achieves a significant increase in the performance (up to 250\% for
highly populated areas) than mechanistic models that do not use deep neural
networks, or that do not exploit geographic voluntary data. Our work presents a
precise definition of the flow generation problem, which is a novel task for
the deep learning community working with spatio-temporal data, and proposes a
deep neural network model that significantly outperforms current
state-of-the-art statistical models