159 research outputs found
Validating Activity-Based Travel Demand Models Using Mobile Phone Data
Activity-based travel demand models predict travel sequences on a day for each individual in a study region. These sequences serve as important input for travel demand estimate and forecast in the area. However, a reliable method to evaluate the generated sequences has been lacking, hampering further development and application of the models. In this chapter, we use travel behavioral information inferred from mobile phone data for such validation purposes. Our method is composed of three major steps. First, locations where a user made calls on a day are extracted from his/her mobile phone records, and these locations form a location trajectory. All the trajectories from the user across multiple days are then transformed into actual travel sequences. The sequences derived from all phone users are further classified into typical patterns which, along with their relative frequencies, define travel profiles. These profiles characterize current travel behavior in the study region and can thus be utilized for assessing sequences generated from activity-based models. By comparing the obtained profiles with statistics drawn from conventional travel surveys, the validation potential of the proposed method is demonstrated
Systematic Determination of Absolute Absorption Cross-section of Individual Carbon Nanotubes
Determination of optical absorption cross-section is always among the central
importance of understanding a material. However its realization on individual
nanostructures, such as carbon nanotubes, is experimentally challenging due to
the small extinction signal using conventional transmission measurements. Here
we develop a technique based on polarization manipulation to enhance the
sensitivity of single-nanotube absorption spectroscopy by two-orders of
magnitude. We systematically determine absorption cross-section over broad
spectral range at single-tube level for more than 50 chirality-defined
single-walled nanotubes. Our data reveals chirality-dependent one-dimensional
photo-physics through the behaviours of exciton oscillator strength and
lifetime. We also establish an empirical formula to predict absorption spectrum
of any nanotube, which provides the foundation to determine quantum
efficiencies in important photoluminescence and photovoltaic processes
Topological states and braiding statistics using quantum circuits
Using superconducting quantum circuits, we propose an approach to construct a
Kitaev lattice, i.e., an anisotropic spin model on a honeycomb lattice with
three types of nearest-neighbor interactions. We study two particular cases to
demonstrate topological states (i.e., the vortex and bond states) and show how
the braiding statistics can be revealed. Our approach provides an
experimentally realizable many-body system for demonstrating exotic properties
of topological phases.Comment: 4 pages, 2 figure
Modifying Adhesive Materials to Improve the Longevity of Resinous Restorations
Dental caries is a common disease on a global scale. Resin composites are the most popular materials to restore caries by bonding to tooth tissues via adhesives. However, multiple factors, such as microleakage and recurrent caries, impair the durability of resinous restorations. Various innovative methods have been applied to develop adhesives with particular functions to tackle these problems, such as incorporating matrix metalloproteinase inhibitors, antibacterial or remineralizing agents into bonding systems, as well as improving the mechanical/chemical properties of adhesives, even combining these methods. This review will sum up the latest achievements in this field
Quantitative analysis of transient and sustained transforming growth factor-β signaling dynamics
Mathematical modeling and experimental analyses reveal that TGF-β ligand depletion has an important role in converting short-term graded signaling responses to long-term switch-like responses
Exploring the Potential Transmission Risk of Schistosomiasis Japonica in the Lower Reaches of the Yangtze River, China
Vector snails are important in the life cycle of schisosomiasis, the need to understand the ecologic factors that could enhance snails’ survival and trigger schistosomiasis transmission necessitated this study. Therefore, the potential risk of schistosomiasis transmission was explored in Zhangjiagang region, a non-endemic area in lower reaches of Yangtze River, eastern of China. The key indictors, including snail survival rate, spawn rate, hatching rate and gland development, were investigated through the designed experiments, routine snail and infectious source surveillance. The results showed that there was no significant difference in surviving rate, spawn rate, hatching rate and gland development between groups of simulated environments in laboratory, similar finding in field experiments, which suggested that snails stand a high possibility to survive in these non-endemic areas once they spread into these areas from other places. And no snails and infectious source were found either in the previous routine monitoring in the past decades and the snail surveillance we conducted from 2007 to 2013. Therefore, there is little risk in the study areas in the lower reaches of the Yangtze River. However, the sporadic and imported cases are still seen in a few areas adjacent to the endemic or transmission interrupted areas as the important infectious source, thus become a risk of schistosomisis transmission or re-emergence in these areas where the snail exists. Hence, maintaining routine monitoring and surveillance can be one of the effective and efficient ways to prevent the re-emergence of Schistosomiasis
Gate-dependent Pseudospin Mixing in Graphene/Boron Nitride Moire Superlattices
Electrons in graphene are described by relativistic Dirac-Weyl spinors with a
two-component pseudospin1-12. The unique pseudospin structure of Dirac
electrons leads to emerging phenomena such as the massless Dirac cone2,
anomalous quantum Hall effect2, 3, and Klein tunneling4, 5 in graphene. The
capability to manipulate electron pseudospin is highly desirable for novel
graphene electronics, and it requires precise control to differentiate the two
graphene sub-lattices at atomic level. Graphene/boron nitride (graphene/BN)
Moire superlattice, where a fast sub-lattice oscillation due to B-N atoms is
superimposed on the slow Moire period, provides an attractive approach to
engineer the electron pseudospin in graphene13-18. This unusual Moire
superlattice leads to a spinor potential with unusual hybridization of electron
pseudospins, which can be probed directly through infrared spectroscopy because
optical transitions are very sensitive to excited state wavefunctions. Here, we
perform micro-infrared spectroscopy on graphene/BN heterostructure and
demonstrate that the Moire superlattice potential is dominated by a
pseudospin-mixing component analogous to a spatially varying pseudomagnetic
field. In addition, we show that the spinor potential depends sensitively on
the gate-induced carrier concentration in graphene, indicating a strong
renormalization of the spinor potential from electron-electron interactions.
Our study offers deeper understanding of graphene pseudospin structure under
spinor Moire potential, as well as exciting opportunities to control pseudospin
in two-dimensional heterostructures for novel electronic and photonic
nanodevices
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