179 research outputs found
Urban Dreams of Migrants: A Case Study of Migrant Integration in Shanghai
Unprecedented human mobility has driven the rapid urbanization around the
world. In China, the fraction of population dwelling in cities increased from
17.9% to 52.6% between 1978 and 2012. Such large-scale migration poses
challenges for policymakers and important questions for researchers. To
investigate the process of migrant integration, we employ a one-month complete
dataset of telecommunication metadata in Shanghai with 54 million users and 698
million call logs. We find systematic differences between locals and migrants
in their mobile communication networks and geographical locations. For
instance, migrants have more diverse contacts and move around the city with a
larger radius than locals after they settle down. By distinguishing new
migrants (who recently moved to Shanghai) from settled migrants (who have been
in Shanghai for a while), we demonstrate the integration process of new
migrants in their first three weeks. Moreover, we formulate classification
problems to predict whether a person is a migrant. Our classifier is able to
achieve an F1-score of 0.82 when distinguishing settled migrants from locals,
but it remains challenging to identify new migrants because of class imbalance.
This classification setup holds promise for identifying new migrants who will
successfully integrate into locals (new migrants that misclassified as locals).Comment: A modified version. The paper was accepted by AAAI 201
Accurate position tracking with a single UWB anchor
Accurate localization and tracking are a fundamental requirement for robotic
applications. Localization systems like GPS, optical tracking, simultaneous
localization and mapping (SLAM) are used for daily life activities, research,
and commercial applications. Ultra-wideband (UWB) technology provides another
venue to accurately locate devices both indoors and outdoors. In this paper, we
study a localization solution with a single UWB anchor, instead of the
traditional multi-anchor setup. Besides the challenge of a single UWB ranging
source, the only other sensor we require is a low-cost 9 DoF inertial
measurement unit (IMU). Under such a configuration, we propose continuous
monitoring of UWB range changes to estimate the robot speed when moving on a
line. Combining speed estimation with orientation estimation from the IMU
sensor, the system becomes temporally observable. We use an Extended Kalman
Filter (EKF) to estimate the pose of a robot. With our solution, we can
effectively correct the accumulated error and maintain accurate tracking of a
moving robot.Comment: Accepted by ICRA202
Evolution of Interlayer Coupling in Twisted MoS2 Bilayers
Van der Waals (vdW) coupling is emerging as a powerful method to engineer and
tailor physical properties of atomically thin two-dimensional (2D) materials.
In graphene/graphene and graphene/boron-nitride structures it leads to
interesting physical phenomena ranging from new van Hove singularities1-4 and
Fermi velocity renormalization5, 6 to unconventional quantum Hall effects7 and
Hofstadter's butterfly pattern8-12. 2D transition metal dichalcogenides
(TMDCs), another system of predominantly vdW-coupled atomically thin layers13,
14, can also exhibit interesting but different coupling phenomena because TMDCs
can be direct or indirect bandgap semiconductors15, 16. Here, we present the
first study on the evolution of interlayer coupling with twist angles in
as-grown MoS2 bilayers. We find that an indirect bandgap emerges in bilayers
with any stacking configuration, but the bandgap size varies appreciably with
the twist angle: it shows the largest redshift for AA- and AB-stacked bilayers,
and a significantly smaller but constant redshift for all other twist angles.
The vibration frequency of the out-of-plane phonon in MoS2 shows similar twist
angle dependence. Our observations, together with ab initio calculations,
reveal that this evolution of interlayer coupling originates from the repulsive
steric effects, which leads to different interlayer separations between the two
MoS2 layers in different stacking configurations
A real-time dynamic obstacle tracking and mapping system for UAV navigation and collision avoidance with an RGB-D camera
The real-time dynamic environment perception has become vital for autonomous
robots in crowded spaces. Although the popular voxel-based mapping methods can
efficiently represent 3D obstacles with arbitrarily complex shapes, they can
hardly distinguish between static and dynamic obstacles, leading to the limited
performance of obstacle avoidance. While plenty of sophisticated learning-based
dynamic obstacle detection algorithms exist in autonomous driving, the
quadcopter's limited computation resources cannot achieve real-time performance
using those approaches. To address these issues, we propose a real-time dynamic
obstacle tracking and mapping system for quadcopter obstacle avoidance using an
RGB-D camera. The proposed system first utilizes a depth image with an
occupancy voxel map to generate potential dynamic obstacle regions as
proposals. With the obstacle region proposals, the Kalman filter and our
continuity filter are applied to track each dynamic obstacle. Finally, the
environment-aware trajectory prediction method is proposed based on the Markov
chain using the states of tracked dynamic obstacles. We implemented the
proposed system with our custom quadcopter and navigation planner. The
simulation and physical experiments show that our methods can successfully
track and represent obstacles in dynamic environments in real-time and safely
avoid obstacles
Resolving spin, valley, and moir\'e quasi-angular momentum of interlayer excitons in WSe2/WS2 heterostructures
Moir\'e superlattices provide a powerful way to engineer properties of
electrons and excitons in two-dimensional van der Waals heterostructures. The
moir\'e effect can be especially strong for interlayer excitons, where
electrons and holes reside in different layers and can be addressed separately.
In particular, it was recently proposed that the moir\'e superlattice potential
not only localizes interlayer exciton states at different superlattice
positions, but also hosts an emerging moir\'e quasi-angular momentum (QAM) that
periodically switches the optical selection rules for interlayer excitons at
different moir\'e sites. Here we report the observation of multiple interlayer
exciton states coexisting in a WSe2/WS2 moir\'e superlattice and unambiguously
determine their spin, valley, and moir\'e QAM through novel resonant optical
pump-probe spectroscopy and photoluminescence excitation spectroscopy. We
demonstrate that interlayer excitons localized at different moir\'e sites can
exhibit opposite optical selection rules due to the spatially-varying moir\'e
QAM. Our observation reveals new opportunities to engineer interlayer exciton
states and valley physics with moir\'e superlattices for optoelectronic and
valleytronic applications
Pan-cancer analysis of the prevalence and associated factors of lung metastasis and the construction of the lung metastatic classification system
This study first presents an analysis of the prevalence and associated factors of the lung metastasis (LM) database and then uses this analysis to construct an LM classification system. Using cancer patient data gathered from the surveillance, epidemiology, and end results (SEER) database, this study shows that the prevalence of LM is not consistent among different cancers; that is, the prevalence of LM ranges from 0.0013 [brain; 95% confidence interval (95% CI); 0.0010–0.0018] to 0.234 (“other digestive organs”; 95% CI; 0.221–0.249). This study finds that advanced age, poor grade, higher tumor or node stage, and metastases including bone, brain, and liver are positively related to LM occurrence, while female gender, income, marital status, and insured status are negatively related. Then, this study generates four categories from 58 cancer types based on prevalence and influence factors and satisfactorily validates these. This classification system reflects the LM risk of different cancers. It can guide individualized treatment and the management of these synchronous metastatic cancer patients and help clinicians better distribute medical resources
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