2,092 research outputs found
A Metapopulation Model for Chikungunya Including Populations Mobility on a Large-Scale Network
In this work we study the influence of populations mobility on the spread of
a vector-borne disease. We focus on the chikungunya epidemic event that
occurred in 2005-2006 on the R\'eunion Island, Indian Ocean, France, and
validate our models with real epidemic data from the event. We propose a
metapopulation model to represent both a high-resolution patch model of the
island with realistic population densities and also mobility models for humans
(based on real-motion data) and mosquitoes. In this metapopulation network, two
models are coupled: one for the dynamics of the mosquito population and one for
the transmission of the disease. A high-resolution numerical model is created
out from real geographical, demographical and mobility data. The Island is
modeled with an 18 000-nodes metapopulation network. Numerical results show the
impact of the geographical environment and populations' mobility on the spread
of the disease. The model is finally validated against real epidemic data from
the R\'eunion event.Comment: Accepted in Journal of Theoretical biolog
Spatial networks with wireless applications
Many networks have nodes located in physical space, with links more common
between closely spaced pairs of nodes. For example, the nodes could be wireless
devices and links communication channels in a wireless mesh network. We
describe recent work involving such networks, considering effects due to the
geometry (convex,non-convex, and fractal), node distribution,
distance-dependent link probability, mobility, directivity and interference.Comment: Review article- an amended version with a new title from the origina
A New Phase Transition for Local Delays in MANETs
We consider Mobile Ad-hoc Network (MANET) with transmitters located according
to a Poisson point in the Euclidean plane, slotted Aloha Medium Access (MAC)
protocol and the so-called outage scenario, where a successful transmission
requires a Signal-to-Interference-and-Noise (SINR) larger than some threshold.
We analyze the local delays in such a network, namely the number of times slots
required for nodes to transmit a packet to their prescribed next-hop receivers.
The analysis depends very much on the receiver scenario and on the variability
of the fading. In most cases, each node has finite-mean geometric random delay
and thus a positive next hop throughput. However, the spatial (or large
population) averaging of these individual finite mean-delays leads to infinite
values in several practical cases, including the Rayleigh fading and positive
thermal noise case. In some cases it exhibits an interesting phase transition
phenomenon where the spatial average is finite when certain model parameters
are below a threshold and infinite above. We call this phenomenon, contention
phase transition. We argue that the spatial average of the mean local delays is
infinite primarily because of the outage logic, where one transmits full
packets at time slots when the receiver is covered at the required SINR and
where one wastes all the other time slots. This results in the "RESTART"
mechanism, which in turn explains why we have infinite spatial average.
Adaptive coding offers a nice way of breaking the outage/RESTART logic. We show
examples where the average delays are finite in the adaptive coding case,
whereas they are infinite in the outage case.Comment: accepted for IEEE Infocom 201
Customer mobility and congestion in supermarkets
The analysis and characterization of human mobility using population-level
mobility models is important for numerous applications, ranging from the
estimation of commuter flows in cities to modeling trade flows between
countries. However, almost all of these applications have focused on large
spatial scales, which typically range between intra-city scales to
inter-country scales. In this paper, we investigate population-level human
mobility models on a much smaller spatial scale by using them to estimate
customer mobility flow between supermarket zones. We use anonymized, ordered
customer-basket data to infer empirical mobility flow in supermarkets, and we
apply variants of the gravity and intervening-opportunities models to fit this
mobility flow and estimate the flow on unseen data. We find that a
doubly-constrained gravity model and an extended radiation model (which is a
type of intervening-opportunities model) can successfully estimate 65--70\% of
the flow inside supermarkets. Using a gravity model as a case study, we then
investigate how to reduce congestion in supermarkets using mobility models. We
model each supermarket zone as a queue, and we use a gravity model to identify
store layouts with low congestion, which we measure either by the maximum
number of visits to a zone or by the total mean queue size. We then use a
simulated-annealing algorithm to find store layouts with lower congestion than
a supermarket's original layout. In these optimized store layouts, we find that
popular zones are often in the perimeter of a store. Our research gives insight
both into how customers move in supermarkets and into how retailers can arrange
stores to reduce congestion. It also provides a case study of human mobility on
small spatial scales
Landau levels, edge states and magneto-conductance in GaAs/AlGaAs core-shell nanowires
Magnetic states of the electron gas confined in modulation-doped core-shell
nanowires are calculated for a transverse field of arbitrary strength and
orientation. Magneto-conductance is predicted within the Landauer approach. The
modeling takes fully into account the radial material modulation, the prismatic
symmetry and the doping profile of realistic GaAs/AlGaAs devices within an
envelope-function approach, and electron-electron interaction is included in a
mean-field self-consistent approach. Calculations show that in the low
free-carrier density regime, magnetic states can be described in terms of
Landau levels and edge states, similar to planar two-dimensional electron gases
in a Hall bar. However, at higher carrier density the dominating
electron-electron interaction leads to a strongly inhomogeneous localization at
the prismatic heterointerface. This gives rise to a complex band dispersion,
with local minima at finite values of the longitudinal wave vector, and a
region of negative magneto-resistance. The predicted marked anisotropy of the
magneto-conductance with field direction is a direct probe of the inhomogeneous
electron gas localization of the conductive channel induced by the prismatic
geometry
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