Quasisymmetric Embeddability of Weak Tangents

In this paper, we study the quasisymmetric embeddability of weak tangents of metric spaces. We first show that quasisymmetric embeddability is hereditary, i.e., if $X$ can be quasisymmetrically embedded into $Y$, then every weak tangent of $X$ can be quasisymmetrically embedded into some weak tangent of $Y$, given that $X$ is proper and doubling. However, the converse is not true in general; we will illustrate this with several counterexamples. In special situations, we are able to show that the embeddability of weak tangents implies global or local embeddability of the ambient space. Finally, we apply our results to expanding dynamics and establish several results on Gromov hyperbolic groups and visual spheres of expanding Thurston maps.Comment: 35 pages, 6 figure

Fiscal Policy, Regional Disparity and Poverty in China: a General Equilibrium Approach

The main objective of this research is to analyze the effects of the fiscal dimension of China’s government transfer and preferential tax policy on regional income disparity and poverty reduction. Using a computable general equilibrium model with a three-region component, we find that the preferential tax policy on the eastern coastal region of China has a significant effect on household income, as well as on the FGT indicator. The simulation results suggest that tax policy is a more effective tool to counter against China’s regional disparity than government transfer.China, Regional Disparity, Fiscal Policy, Government Transfer, Preferential Policy, Poverty, CGE, FGT

High Speed All Optical Switching and Encryption using Ultrafast Devices

The next generation of fiber-optic communication system demands ultra-high speed data processing and switching components. Conventional electro-optical parts have reached their bottleneck both speed-wise and efficiency-wise. The idea of manipulating high speed data in all-optical domain is gaining more popularity. In this PhD dissertation, I showed the design and performance analysis of two kinds of ultra-fast all-optical latches, Set-Reset latch and D-flip-flop, based on two different schemes: (1) cross gain and phase modulation (XGM and XPM) in quantum dot semiconductor optical amplifiers (QD-SOA) and (2) two-photon absorption (TPA) in bulk semiconductor optical amplifiers. Design and simulation of a scheme to realize high speed all-optical encryption and decryption using key-stream generators and XOR gates based on QD-SOA are included in this dissertation. We also proposed and simulated all-optical Boolean logic functions with improved output quality using binary phase shift keyed signal based on QD-SOA. A fiber ring laser system with charcoal nano-particles as saturable absorber inside the cavity has been designed and experimentally demonstrated. This fiber ring laser system can generate optical pulse train @ 20Gb/s with improved stability and smaller pulse width comparing with the system without nano-particles in the cavity