Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers

We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS2, WS2, and WSe2, can be substantially tuned by > 60% in the imaginary part and > 20% in the real part around exciton resonances using CMOS-compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of refractive index. This work may pave the way towards the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits

A Generalized Shuffle Framework for Privacy Amplification: Strengthening Privacy Guarantees and Enhancing Utility

The shuffle model of local differential privacy is an advanced method of privacy amplification designed to enhance privacy protection with high utility. It achieves this by randomly shuffling sensitive data, making linking individual data points to specific individuals more challenging. However, most existing studies have focused on the shuffle model based on $(\epsilon_0,0)$-Locally Differentially Private (LDP) randomizers, with limited consideration for complex scenarios such as $(\epsilon_0,\delta_0)$-LDP or personalized LDP (PLDP). This hinders a comprehensive understanding of the shuffle model's potential and limits its application in various settings. To bridge this research gap, we propose a generalized shuffle framework that can be applied to any $(\epsilon_i,\delta_i)$-PLDP setting with personalized privacy parameters. This generalization allows for a broader exploration of the privacy-utility trade-off and facilitates the design of privacy-preserving analyses in diverse contexts. We prove that shuffled $(\epsilon_i,\delta_i)$-PLDP process approximately preserves $\mu$-Gaussian Differential Privacy with \mu = \sqrt{\frac{2}{\sum_{i=1}^{n} \frac{1-\delta_i}{1+e^{\epsilon_i}}-\max_{i}{\frac{1-\delta_{i}}{1+e^{\epsilon_{i}}}}}}. $ This approach allows us to avoid the limitations and potential inaccuracies associated with inequality estimations. To strengthen the privacy guarantee, we improve the lower bound by utilizing hypothesis testing} instead of relying on rough estimations like the Chernoff bound or Hoeffding's inequality. Furthermore, extensive comparative evaluations clearly show that our approach outperforms existing methods in achieving strong central privacy guarantees while preserving the utility of the global model. We have also carefully designed corresponding algorithms for average function, frequency estimation, and stochastic gradient descent.Comment: Correct some typo

Empirical Essays on Banking Stability

The banking industry is one of the most important components of modern economies, providing a variety of essential economic functions. However, a banking system is inherently fragile, and this has been widely witnessed during the great financial crisis in 2008. Another lesson learnt from the crisis is that the cost of a banking crisis can be substantial. Thus, it is important for us to understand how a banking system could be destabilised and thus consider the prudential policies that could be specifically designed to prevent a banking crisis from occurring. This thesis uses micro-econometric methods to explore factors that could have an impact on banking stability. The first essay examines whether a liquidity shock to a banking system could be transmitted to other economies through a network of bank ownership. First, it constructs cross-border ownership networks for banks located in European countries. Then, it exploits the liquidity crisis generated by the 2010 European sovereign debt crisis as a quasi-natural experiment. The analysis shows that subsidiary banks located outside of Greece, Ireland, Italy, Portugal and Spain (GIIPS) but with ownership linkages to these countries have a lower loan growth rate during the crisis period, which suggests that the liquidity shock experienced by the GIIPS countries was indeed transmitted to those banks through ownership linkages. Larger subsidiary banks and those subsidiaries that were more profitable are found to be more resilient to the shock. Furthermore, It also shows that the parent bank’s characteristics affect the transmission of the shock, supporting the notion of an internal capital market operating within these banking groups. The second essay focuses on the effect of sovereign shocks on banks’ lending activities through their exposures to the distressed sovereigns. Furthermore, it identifies whether bank strength, specifically bank capital, can act as a transmission channel through which poorly capitalised bank tend to be more fragile in response to a sovereign shock. Using a rich dataset on banks’ sovereign exposures from the European Banking Authority, it also disentangles the transmission channel by breaking down the type and accounting classification of the exposure. The results suggest that highly exposed banks tend to have lower lending over the crisis period. But it shows that it is banks’ available-for-sale sovereign exposures that play the key role in the transmission from sovereign distress to bank lending through the capital channel. The third essay explores the relationship between banking competition and banking stability, using the staggered banking deregulation levied by individual states in the U.S. as a natural experiment. Specifically, it identifies the effect of the intensified competition induced by the deregulation on the stability of the U.S. banking sector. The analysis is conducted at state-level as well as bank-level, and the overall result shows that the competition shock improves banking stability at both state- and bank-level. Furthermore, it reveals that there is significant heterogeneity among banks in response to the intensified competition: intra-state competition shock has a greater effect on the stability of small banks while banks with a larger size or better profitability are more likely to be affected by the inter-state competition shock. It also suggests that there is a non-linear relationship between banking competition and stability, as the competition shock has a greater effect on banks operating in a less competitive environment. Overall, the findings from this thesis may help regulatory authorities to maintain the stability of the banking sector in three ways. First, it helps regulators to design micro-prudential policies towards foreign banks to prevent them from transmitting foreign liquidity shocks which could potentially destabilise the domestic banking system. Second, it produces guidance on how the regulatory treatment on banks’ sovereign exposures should be specified in the future macro-prudential policy framework, to better isolate banks from sovereign shocks. Third, it helps regulators to balance between policies on facilitating competition in the banking sector and those on maintaining the stability of the financial system

Research on Multi-specialty Coordination, Multi-discipline and Multifunction Integration Oriented Modeling and Simulation Innovation Technology

AbstractThe paper mainly covers the connotations, the functions and the key techniques of the Aircraft Digital Cooperative Robust Integration Optimization Performance Simulation Technology. The Performance Simulation Airplane Integration Design Platform, which has been established by the Performance Simulation Airplane construction analysis, a series of Standard Specification Establishing, the key modules development and a series of the supporting work implementation. It can be customized and be extended, and it is easy to be demonstrated. The platform contains the engineering database including the Performance Simulation Airplane model, simulation process data, simulation results data, and so on. It also provides the closed development process from the initial design to the optimized design, and end to the final detail design. It carries out the configuration selection and performance analysis for the airplane various configurations under the product development requirements in the entire process. It is applicable for the cooperative simulation analysis about the General Configuration research, the Aerodynamic design, the Structure design, the Strength design and some system specialties. This technique system has brought revolutionary changes to the traditional technological concept and Architecture, and it has been proved that the design period of the product is shortened by more than 25%, and the simulation test period is also shortened by more than 25%

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

A granular landslide impacting a river may lead to the formation of a landslide dam blocking the streamflow, and subsequently create a barrier lake. Should a barrier lake outburst, the flood may be destructive and spell disastrous consequences downstream. The last decade or so has witnessed a number of experimental and numerical investigations on barrier lake outburst flooding, whilst studies on barrier lake formation remain rare – a physically enhanced and practically viable mathematical model is still missing. Generally, barrier lake formation is characterized by multi-physical, interactive processes between water flow, multi-sized sediment transport and morphological evolution. Here, a new double layer-averaged two-phase flow model is proposed, which is an advance on existing continuum models that involve a single-phase flow assumption and presume a single sediment size, and discrete models that preclude fine grains and assume narrow grain size distributions. The proposed model is first validated against data from previous laboratory experiments of waves due to landslides impacting reservoirs and landslide dam formation over dry valleys. Then it is applied to explore the complicated mechanism and threshold for barrier lake formation. The water and grain velocities are shown to be disparate, characterizing the primary role of grains in driving water movement during subaqueous landslide motion and also demonstrating the need for a two-phase flow approach. The grain size effects are revealed, i.e., coarse grains and grain-size uniformity favour barrier lake formation. A new threshold condition is proposed for barrier lake formation, integrating the landslide-to-river momentum ratio and grain size effects. The present work facilitates a promising modelling framework for solving barrier lake formation, thereby underpinning the assessment of flood hazards due to barrier lakes