A High Frequency Photoacoustic System for Colorectal Cancer Imaging

While colorectal cancer is the second largest cause of cancer-related deaths in the United States, early detection is a key factor in its survival rate. Compared to conventional imaging modalities, photoacoustic imaging offers benefits in providing angiographic images which are valuable for early-stage tumor detection. This thesis presents the design of a 32-channel 80 MHz photoacoustic image system, whose relatively high frequency offers particular advantages. The system comprises several modules, including a laser system, ultrasound probe, AD convertor, microcontroller (FPGA), and a computer. The system requires programs for the FPGA and the data receiver on the computer. The data transportation accuracy, signal-noise ratio, and transmission speed are analyzed here to understand the system’s performance. The system was tested by standard phantoms, like carbon fiber and black tape, and images were reconstructed by the typical delay-and-sum algorithm. As important parameters of this system, the spatial resolution and signal-to-noise ratio were analyzed. In the future, to improve the lateral resolution of this system and broaden its imaging window, we can expand the 32-channel system up to 256 channels simply by duplicating the 32-channel data acquisition module. This improved system can provide detailed ex-vivo and in-vivo information about colorectal cancer

Information Elicitation from Decentralized Crowd Without Verification

Information Elicitation Without Verification (IEWV) refers to the problem of eliciting high-accuracy solutions from crowd members when the ground truth is unverifiable. A high-accuracy team solution (aggregated from members' solutions) requires members' effort exertion, which should be incentivized properly. Previous research on IEWV mainly focused on scenarios where a central entity (e.g., the crowdsourcing platform) provides incentives to motivate crowd members. Still, the proposed designs do not apply to practical situations where no central entity exists. This paper studies the overlooked decentralized IEWV scenario, where crowd members act as both incentive contributors and task solvers. We model the interactions among members with heterogeneous team solution accuracy valuations as a two-stage game, where each member decides her incentive contribution strategy in Stage 1 and her effort exertion strategy in Stage 2. We analyze members' equilibrium behaviors under three incentive allocation mechanisms: Equal Allocation (EA), Output Agreement (OA), and Shapley Value (SV). We show that at an equilibrium under any allocation mechanism, a low-valuation member exerts no more effort than a high-valuation member. Counter-intuitively, a low-valuation member provides incentives to the collaboration while a high-valuation member does not at an equilibrium under SV. This is because a high-valuation member who values the aggregated team solution more needs fewer incentives to exert effort. In addition, when members' valuations are sufficiently heterogeneous, SV leads to team solution accuracy and social welfare no smaller than EA and OA

Economic Policy Uncertainty and Corporate Mergers and Acquisitions

In recent years, the frequent adjustment of the government’s economic policies and the uncertainty of foreign economic situations have made the degree of uncertainty of China’s economic policies rise continuously. The increasing degree of policy uncertainty will inevitably affect the investment and financing decisions of micro enterprises. Then, how does economic policy uncertainty (EPU) affect mergers and acquisitions (M&A) behavior? What’s the mechanism? Based on the above questions, this paper uses the data of non-financial listed companies in the Shanghai and Shenzhen stock exchanges from 2008 to 2018 as a sample to explore the relationship between EPU and M&A. The study shows that rising EPU will promote corporate M&A behavior, and this effect is more significant in slow-growth companies. The relationship between EPU and M&A is affected by corporate governance, stock price volatility and financing constraints. Specifically, the company’s M&A size is more sensitive to EPU with higher level of corporate governance, higher level of stock price volatility, and lesser financing constraints. Further research shows that the rise of EPU will significantly promote the improvement of M&A performance in the short-term, but this effect does not exist in the long-term. Various robustness checks do not change the empirical results of this paper