Polarity-induced oxygen vacancies at LaAlO3|SrTiO3 interfaces

Using first-principles density functional theory calculations, we find a strong position and thickness dependence of the formation energy of oxygen vacancies in LaAlO3|SrTiO3 (LAO|STO) multilayers and interpret this with an analytical capacitor model. Oxygen vacancies are preferentially formed at p-type SrO|AlO2 rather than at n-type LaO|TiO2 interfaces; the excess electrons introduced by the oxygen vacancies reduce their energy by moving to the n-type interface. This asymmetric behavior makes an important contribution to the conducting (insulating) nature of n-type (p-type) interfaces while providing a natural explanation for the failure to detect evidence for the polar catastrophe in the form of core level shifts

Noncollinearity-modulated electronic properties of the monolayer CrI3_3

Introducing noncollinear magnetization into a monolayer CrI$_3$ is proposed to be an effective approach to modulate the local electronic properties of the two-dimensional (2D) magnetic material. Using first-principles calculation, we illustrate that both the conduction and valence bands in the monolayer CrI$_3$ are lowered down by spin spiral states. The distinct electronic structure of the monolayer noncollinear CrI$_3$ can be applied in nanoscale functional devices. As a proof of concept, we show that a magnetic domain wall can form a one-dimensional conducting channel in the 2D semiconductor via proper gating. Other possible applications such as electron-hole separation and identical quantum dots are also discussed

Essays on Fairness Preferences: An Experimental Approach

Fairness is a central topic in ethics, political science and economics. A variety of economic questions, such as charitable donation, welfare programs, taxation of income and inheritances, are closely associated with people's fairness preferences. Hence it is important to take fairness and justice into account for making appropriate social welfare policy. This dissertation contributes to the related literature in understanding people's fairness preferences by using an experimental approach. It consists of three interrelated essays, all of which focus on fairness preferences and redistributive decision making under risk and uncertainty. The first essay is an experimental investigation into fairness preferences and redistribution under different rooted risks, i.e., pure-luck versus option-luck. Our experimental results reconcile the conflict between the accountability principle and consequential egalitarianism by suggesting that people are more inclined to the accountability principle in the presence of relatively lower income inequality but support consequential egalitarianism in case of large income inequality or salience of extreme low payoff. The second essay explores the dynamic evolution of a laboratory economy in which fairness preferences, risk preferences, and income inequality are jointly determined under different redistributive policies. By using a panel vector auto-regression model, we find different patterns of interplay between subjects under different redistributive regimes. The third essay studies how charitable giving is influenced by the performance of charitable organizations and associated organization costs. We study charitable giving in a laboratory experiment, in which donors are confronted with a tradeoff between helping people in need and the possibility of being cheated. We find evidence that individuals exploit the shadow of fundraising cost to excuse their selfishness with a self-serving biased belief that fundraisers are corrupt. In contrast, the charitable contribution significantly increases when the moral excuse is removed by excluding the manipulation of costs by the fundraisers

JDsearch: A Personalized Product Search Dataset with Real Queries and Full Interactions

Recently, personalized product search attracts great attention and many models have been proposed. To evaluate the effectiveness of these models, previous studies mainly utilize the simulated Amazon recommendation dataset, which contains automatically generated queries and excludes cold users and tail products. We argue that evaluating with such a dataset may yield unreliable results and conclusions, and deviate from real user satisfaction. To overcome these problems, in this paper, we release a personalized product search dataset comprised of real user queries and diverse user-product interaction types (clicking, adding to cart, following, and purchasing) collected from JD.com, a popular Chinese online shopping platform. More specifically, we sample about 170,000 active users on a specific date, then record all their interacted products and issued queries in one year, without removing any tail users and products. This finally results in roughly 12,000,000 products, 9,400,000 real searches, and 26,000,000 user-product interactions. We study the characteristics of this dataset from various perspectives and evaluate representative personalization models to verify its feasibility. The dataset can be publicly accessed at Github: https://github.com/rucliujn/JDsearch.Comment: Accepted to SIGIR 202

Balanced Coarsening for Multilevel Hypergraph Partitioning via Wasserstein Discrepancy

We propose a balanced coarsening scheme for multilevel hypergraph partitioning. In addition, an initial partitioning algorithm is designed to improve the quality of k-way hypergraph partitioning. By assigning vertex weights through the LPT algorithm, we generate a prior hypergraph under a relaxed balance constraint. With the prior hypergraph, we have defined the Wasserstein discrepancy to coordinate the optimal transport of coarsening process. And the optimal transport matrix is solved by Sinkhorn algorithm. Our coarsening scheme fully takes into account the minimization of connectivity metric (objective function). For the initial partitioning stage, we define a normalized cut function induced by Fiedler vector, which is theoretically proved to be a concave function. Thereby, a three-point algorithm is designed to find the best cut under the balance constraint