913 research outputs found
Explore Spatiotemporal and Demographic Characteristics of Human Mobility via Twitter: A Case Study of Chicago
Characterizing human mobility patterns is essential for understanding human
behaviors and the interactions with socioeconomic and natural environment. With
the continuing advancement of location and Web 2.0 technologies, location-based
social media (LBSM) have been gaining widespread popularity in the past few
years. With an access to locations of users, profiles and the contents of the
social media posts, the LBSM data provided a novel modality of data source for
human mobility study. By exploiting the explicit location footprints and mining
the latent demographic information implied in the LBSM data, the purpose of
this paper is to investigate the spatiotemporal characteristics of human
mobility with a particular focus on the impact of demography. We first collect
geo-tagged Twitter feeds posted in the conterminous United States area, and
organize the collection of feeds using the concept of space-time trajectory
corresponding to each Twitter user. Commonly human mobility measures, including
detected home and activity centers, are derived for each user trajectory. We
then select a subset of Twitter users that have detected home locations in the
city of Chicago as a case study, and apply name analysis to the names provided
in user profiles to learn the implicit demographic information of Twitter
users, including race/ethnicity, gender and age. Finally we explore the
spatiotemporal distribution and mobility characteristics of Chicago Twitter
users, and investigate the demographic impact by comparing the differences
across three demographic dimensions (race/ethnicity, gender and age). We found
that, although the human mobility measures of different demographic groups
generally follow the generic laws (e.g., power law distribution), the
demographic information, particular the race/ethnicity group, significantly
affects the urban human mobility patterns
Optimal Allocation of Resources for Suppressing Epidemic Spreading on Networks
Efficient allocation of limited medical resources is crucial for controlling
epidemic spreading on networks. Based on the susceptible-infected-susceptible
model, we solve an optimization problem as how best to allocate the limited
resources so as to minimize the prevalence, providing that the curing rate of
each node is positively correlated to its medical resource. By quenched
mean-field theory and heterogeneous mean-field (HMF) theory, we prove that
epidemic outbreak will be suppressed to the greatest extent if the curing rate
of each node is directly proportional to its degree, under which the effective
infection rate has a maximal threshold
where is average degree of the underlying network. For weak infection
region (), we combine a perturbation theory with
Lagrange multiplier method (LMM) to derive the analytical expression of optimal
allocation of the curing rates and the corresponding minimized prevalence. For
general infection region (), the high-dimensional
optimization problem is converted into numerically solving low-dimensional
nonlinear equations by the HMF theory and LMM. Counterintuitively, in the
strong infection region the low-degree nodes should be allocated more medical
resources than the high-degree nodes to minimize the prevalence. Finally, we
use simulated annealing to validate the theoretical results.Comment: 7 pages for two columns, 2 figure
On the Structure of Compatible Rational Functions
A finite number of rational functions are compatible if they satisfy the
compatibility conditions of a first-order linear functional system involving
differential, shift and q-shift operators. We present a theorem that describes
the structure of compatible rational functions. The theorem enables us to
decompose a solution of such a system as a product of a rational function,
several symbolic powers, a hyperexponential function, a hypergeometric term,
and a q-hypergeometric term. We outline an algorithm for computing this
product, and present an application
Discontinuous phase transition in an annealed multi-state majority-vote model
In this paper, we generalize the original majority-vote (MV) model with noise
from two states to arbitrary states, where is an integer no less than
two. The main emphasis is paid to the comparison on the nature of phase
transitions between the two-state MV (MV2) model and the three-state MV (MV3)
model. By extensive Monte Carlo simulation and mean-field analysis, we find
that the MV3 model undergoes a discontinuous order-disorder phase transition,
in contrast to a continuous phase transition in the MV2 model. A central
feature of such a discontinuous transition is a strong hysteresis behavior as
noise intensity goes forward and backward. Within the hysteresis region, the
disordered phase and ordered phase are coexisting.Comment: 12 pages, 6 figure
Energy cost for controlling complex networks
The controllability of complex networks has received much attention recently,
which tells whether we can steer a system from an initial state to any final
state within finite time with admissible external inputs. In order to
accomplish the control in practice at the minimum cost, we must study how much
control energy is needed to reach the desired final state. At a given control
distance between the initial and final states, existing results present the
scaling behavior of lower bounds of the minimum energy in terms of the control
time analytically. However, to reach an arbitrary final state at a given
control distance, the minimum energy is actually dominated by the upper bound,
whose analytic expression still remains elusive. Here we theoretically show the
scaling behavior of the upper bound of the minimum energy in terms of the time
required to achieve control. Apart from validating the analytical results with
numerical simulations, our findings are feasible to the scenario with any
number of nodes that receive inputs directly and any types of networks.
Moreover, more precise analytical results for the lower bound of the minimum
energy are derived in the proposed framework. Our results pave the way to
implement realistic control over various complex networks with the minimum
control cost
). Size Dependency of the Elastic Modulus of ZnO Nanowires: Surface Stress Effect
Relation between the elastic modulus and the diameter (D) of ZnOnanowires was elucidated using a model with the calculated ZnOsurface stresses as input. We predict for ZnOnanowires due to surface stress effect: (1) when D\u3e20nm, the elastic modulus would be lower than the bulk modulus and decrease with the decreasing diameter, (2) when 20nm\u3eD\u3e2nm, the nanowires with a longer length and a wurtzite crystal structure could be mechanically unstable, and (3) when D\u3c2nm, the elastic modulus would be higher than that of the bulk value and increase with a decrease in nanowire diameter
Phase transitions in a multistate majority-vote model on complex networks
We generalize the original majority-vote (MV) model from two states to
arbitrary states and study the order-disorder phase transitions in such a
-state MV model on complex networks. By extensive Monte Carlo simulations
and a mean-field theory, we show that for the order of phase
transition is essentially different from a continuous second-order phase
transition in the original two-state MV model. Instead, for the model
displays a discontinuous first-order phase transition, which is manifested by
the appearance of the hysteresis phenomenon near the phase transition. Within
the hysteresis loop, the ordered phase and disordered phase are coexisting and
rare flips between the two phases can be observed due to the finite-size
fluctuation. Moreover, we investigate the type of phase transition under a
slightly modified dynamics [Melo \emph{et al.} J. Stat. Mech. P11032 (2010)].
We find that the order of phase transition in the three-state MV model depends
on the degree heterogeneity of networks. For , both dynamics produce
the first-order phase transitions.Comment: two-column 7 pages, 1 table and 7 figure
Predicting Young’s Modulus of Nanowires from First-Principles Calculations on their Surface and Bulk Materials
Using the concept of surface stress, we developed a model that is able to predict Young’s modulus of nanowires as a function of nanowire diameters from the calculated properties of their surface and bulk materials. We took both equilibrium strain effect and surface stress effect into consideration to account for the geometric size influence on the elastic properties of nanowires. In this work, we combined first-principles density functional theory calculations of material properties with linear elasticity theory of clamped-end three-point bending. Furthermore, we applied this computational approach to Ag, Au, and ZnOnanowires. For both Ag and Aunanowires, our theoretical predictions agree well with the experimental data in the literature. For ZnOnanowires, our predictions are qualitatively consistent with some of experimental data for ZnO nanostructures. Consequently, we found that surface stress plays a very important role in determining Young’s modulus of nanowires. Our finding suggests that the elastic properties of nanowires could be possibly engineered by altering the surface stress of their lateral surfaces
Robust Keyframe-based Dense SLAM with an RGB-D Camera
In this paper, we present RKD-SLAM, a robust keyframe-based dense SLAM
approach for an RGB-D camera that can robustly handle fast motion and dense
loop closure, and run without time limitation in a moderate size scene. It not
only can be used to scan high-quality 3D models, but also can satisfy the
demand of VR and AR applications. First, we combine color and depth information
to construct a very fast keyframe-based tracking method on a CPU, which can
work robustly in challenging cases (e.g.~fast camera motion and complex loops).
For reducing accumulation error, we also introduce a very efficient incremental
bundle adjustment (BA) algorithm, which can greatly save unnecessary
computation and perform local and global BA in a unified optimization
framework. An efficient keyframe-based depth representation and fusion method
is proposed to generate and timely update the dense 3D surface with online
correction according to the refined camera poses of keyframes through BA. The
experimental results and comparisons on a variety of challenging datasets and
TUM RGB-D benchmark demonstrate the effectiveness of the proposed system.Comment: 12 pages, 9 figure
The simulation of loss of U ions due to charge changing processes in the CSRm ring
Significant beam loss caused by the charge exchange processes and ions impact
induced outgassing play a crucial role in the limitation of the maximum number
of accumulated heavy ions during the high intensity operation in the
accelerators. With the aim to control beam loss due to charge exchange
processes and to confine the generated desorption gas, the tracking of the loss
positions and installing the absorber blocks with low-desorption rate material
at appropriate locations in the CSRm ring will be taken. The loss simulation of
U ions having lost an electron will be presented in this report and the
calculation of the collimation efficiency of the CSRm ring will be continued in
the future.Comment: 4 pages, 5 figure
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