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

Understanding coupling dynamics of public transportation networks

Abstract Subway and bus networks work as an integrated multiplex transportation system and play an indispensable role in modern big cities. Even though a variety of works have investigated the coupling dynamics of multiplex transportation networks, empirical data that validates the determinant coupling factors are still lacking. In this paper, we employ smartcard data of 2.4 million subway and bus passengers in Shenzhen, China to study the coupling dynamics of subway and bus networks. Surprisingly, the coupling of subway and bus networks is not notably influenced by the time-varying speed ratio of the two network layers but is jointly determined by the distribution of travel demands and transportation facilities. Our findings highlight the important role of real travel demand data in analyzing the coupling dynamics of multiplex transportation networks. They also suggest that the speed ratio of different network layers, which was regarded as a key factor in determining coupling strength, has a negligible effect on travelers’ route selections, and thus the coupling dynamics of multiplex transportation networks

Progress of gene editing technology in ornamental plant breeding

Gene editing breeding technology can change the plant traits and obtain excellent varieties more accurately and efficiently than the traditional breeding. There are few reported researches on ornamental plant breeding by using gene editing technology.In this review, we mainly summarize the progress on gene editing technology and its limitations, especially clustered regularly interspersed short palindromic repeats/CRISPR-associated protein 9(CRISPR/Cas 9)in ornamental plant breeding.The future research directions of gene editing in breeding of ornamental plants were discussed as well, which can provide some reference for its further application

A Data-Driven Urban Metro Management Approach for Crowd Density Control

Large crowding events in big cities pose great challenges to local governments since crowd disasters may occur when crowd density exceeds the safety threshold. We develop an optimization model to generate the emergent train stop-skipping schemes during large crowding events, which can postpone the arrival of crowds. A two-layer transportation network, which includes a pedestrian network and the urban metro network, is proposed to better simulate the crowd gathering process. Urban smartcard data is used to obtain actual passenger travel demand. The objective function of the developed model minimizes the passengers’ total waiting time cost and travel time cost under the pedestrian density constraint and the crowd density constraint. The developed model is tested in an actual case of large crowding events occurred in Shenzhen, a major southern city of China. The obtained train stop-skipping schemes can effectively maintain crowd density in its safety range

Understanding the predictability of path flow distribution in urban road networks using an information entropy approach

Publisher Copyright: © 2024Predicting the distributions of path flow between origin-destination (OD) pairs in an urban road network is crucial for developing efficient traffic control and management strategies. Here, we use the large-scale taxi GPS trajectory data of San Francisco and Shenzhen to study the predictability of path flow distribution in urban road networks. We develop an approach to project the time-varying path flow distributions into a high-dimensional space. In the high-dimensional space, information entropy is used to measure the predictability of path flow distribution. We find that the distributions of path flow between OD pairs are in general characterized with a high predictability. In addition, we analyze the factors affecting the predictability of path flow distribution. Finally, an n-gram model incorporating high-order gram and low-order gram is proposed to predict the distribution of path flow. A relatively high prediction accuracy is achieved.Peer reviewe

An Advanced Multipath Mitigation Method Based on Trend Surface Analysis

Among various ways to eliminate the multipath effect in high-precision global navigation satellite system positioning, the multipath hemispherical map (MHM) is a typical multipath correction method based on spatial domain repeatability, which is suitable for not only static environments, but also some dynamic carriers, such as ships and aircraft. So, it has notable advantages and is widely used. The MHM method divides the sky into grids according to the azimuth and elevation angles of satellite, and calculates the average of the residuals within the grid points as its multipath calibration value. It is easy to implement, but it will inevitably lead to excessive or insufficient multipath correction in the grid. The trend surface analysis-based multipath hemispherical map (T-MHM) method makes up for this deficiency by performing trend surface analysis on the multipath spatial changes within the grid points. However, the effectiveness of T-MHM is limited and less capable of resisting noise interference due to the multicollinearity between the independent variables caused by the special spatial distribution of multipath sampling and the overfitting problem caused by ignoring the multipath anisotropy. Thus, we proposed an improved multipath elimination method named AT-MHM (advanced trend surface analysis-based multipath hemispherical model), which cautiously judges the occurrence of the above problems and gives corresponding solutions. This was extended to double-difference mode, which expands the scope of application. The performance of AT-MHM in GPS pseudorange multipath mitigation was verified on geodetic receiver and low-cost receiver in a strong multipath environment with high occlusion

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An Optical Spectroscopic Study of Air-Degradation of van der Waals Magnetic Semiconductor Cr₂Ge₂Te₆

Two-dimensional (2D) magnetic semiconductors exhibit unique combination of electronic and magnetic properties, holding great promise in potential applications such as spintronics and magneto-optics. However, many of them are air-sensitive, and their properties can be significantly altered upon exposure to air. Here, we showed an optical spectroscopic investigation of the effects of air-degradation on few-layered van der Waals (vdW) magnetic semiconductor Cr2Ge2Te6. It was found that although the partially degraded few-layered Cr2Ge2Te6 showed a significant Raman redshift and a split of Eg peak at room temperature, the magneto-optic Kerr hysteresis loop can remain largely unchanged below the Curie temperature. Temperature-dependent Raman measurements further revealed characteristic blueshifts of phonon energy, which were associated with the ferromagnetic phase transition in partially degraded Cr2Ge2Te6, in agreement with Kerr measurements. Our results provide an optical spectroscopic insight into the air-instability of 2D magnetic semiconductors, and contribute to a better understanding of the relationship between phonon modes and long-range spin order at the presence of defects in ultra-thin vdW magnetic semiconductors

An Oligopeptide-Protected Ultrasmall Gold Nanocluster with Peroxidase-Mimicking and Cellular-Imaging Capacities

Recent decades have witnessed the rapid progress of nanozymes and their high promising applications in catalysis and bioclinics. However, the comprehensive synthetic procedures and harsh synthetic conditions represent significant challenges for nanozymes. In this study, monodisperse, ultrasmall gold clusters with peroxidase-like activity were prepared via a simple and robust one-pot method. The reaction of clusters with H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB) followed the Michaelis-Menton kinetics. In addition, in vitro experiments showed that the prepared clusters had good biocompatibility and cell imaging ability, indicating their future potential as multi-functional materials