Highly directional and coherent emission from dark excitons enabled by bound states in the continuum

A double-edged sword in two-dimensional material science and technology is an optically forbidden dark exciton. On the one hand, it is fascinating for condensed matter physics, quantum information processing, and optoelectronics due to its long lifetime. On the other hand, it is notorious for being optically inaccessible from both excitation and detection standpoints. Here, we provide an efficient and low-loss solution to the dilemma by reintroducing photonics bound states in the continuum (BICs) to manipulate dark excitons in the momentum space. In a monolayer tungsten diselenide under normal incidence, we observed a giant enhancement with an enhancement factor of ~3,100 for dark excitons enabled by transverse magnetic BICs with intrinsic out-of-plane electric fields. By further employing widely tunable Friedrich-Wintgen BICs, we demonstrated highly directional emission from the dark excitons with a divergence angle of merely 7 degrees. We found that the directional emission is coherent at room temperature, unambiguously shown in polarization analyses and interference measurements. Therefore, the BICs reintroduced as a momentum-space photonic environment could be an intriguing platform to reshape and redefine light-matter interactions in nearby quantum materials, such as low-dimensional materials, otherwise challenging or even impossible to achieve

Plasmonic metamaterials as an optoelectronic platform for active and nonlinear nanophotonics

The ultimate goal of this thesis is to develop meta-structured devices that simultaneously sustain both electrical and optical functionalities. An asymmetric plasmonic grating was designed for not only the excitation of dark modes featured with an ultrasharp spectrum but also the generation of an electric potential via a plasmoelectric effect. An electrically tunable second-harmonic signal and optical rectification are both realized from a perfect absorber metamaterial. Beyond the solid state structures, electrically tunable harmonic generation was also demonstrated from plasmonic metamaterials in electrolyte solutions. Moreover, by applying electrically induced nonlinear optics, this thesis demonstrated a decade-old prediction, backward phase-matching in negative-index materials, using a plasmonic waveguide scenario. The results revealed the potential of plasmonic metamaterials as self-contained, dynamic electrooptic systems with intrinsically embedded electrical functions and exotic optical properties for signal processing, light switching, and sensing applications.Ph.D

An incentive mechanism design for bus subsidy based on the route service level

The use of public transit subsidy has become a widely discussed aspect for the development of public transportation. The government uses the subsidy policy to offer incentives to improve the service levels and convenience of residents. This paper presents an incentive subsidy mechanism which is based on the service level of a bus line. The subsidy mechanism overcomes the problem of information asymmetry between public transport companies and the local government in the subsidy process, and thus reinforces that bus companies should provide efficient services on lines of different profitability levels. This paper provides the analytical results of the model and analyzes the optimal results. To broaden the scope of application of this model, this study also provides an example that explains how to regulate the bus company when quality reduction happened if the subsidy occurs at the beginning of the subsidy period. At last, management significance and policy recommendations are offered and possible directions for further research are explored

Methyl Sartortuoate Inhibits Colon Cancer Cell Growth by Inducing Apoptosis and G2/M-Phase Arrest

The potential anti-neoplastic activity of terpenoids is of continued interest. In this study, we investigate whether methyl sartortuoate, a terpenoid isolated from soft coral, induced cell cycle arrest and apoptosis in a human colon cancer cell line. Culture studies found that methyl sartortuoate inhibited colon cancer cell (LoVo and RKO) growth and caused apoptotic death in a concentration- and time-dependent manner, by activation of caspase-8, caspase-9, caspase-3, p53 and Bax, and inactivation of B-cell lymphoma 2 (Bcl-2) apoptosis regulating proteins. Methyl sartortuoate treatment led to reduced expression of cdc2 and up-regulated p21 and p53, suggesting that Methyl sartortuoate induced G2-M arrest through modulation of p53/p21/cdc2 pathways. Methyl sartortuoate also up-regulated phospho-JNK and phospho-p38 expression levels. This resulted in cell cycle arrest at the G2-M phase and apoptosis in LoVo and RKO cells. Treatment with the JNK inhibitor SP600125 and the p38 MAPK inhibitor SB203580 prevented methyl sartortuoate-induced apoptosis in LoVo cells. Moreover, methyl sartortuoate also prevented neoplasm growth in NOD-SCID nude mice inoculated with LoVo cells. Taken together, these findings suggest that methyl sartortuoate is capable of leading to activation of caspase-8, -9, -3, increasing p53 and Bax/Bcl-2 ratio apoptosis through MAPK-dependent apoptosis and results in G2-M phase arrest in LoVo and RKO cells. Thus, methyl sartortuoate may be a promising anticancer candidate