AN ANALYSIS OF CURRENT PROBLEMS IN CHINA'S AGRICULTURE DEVELOPMENT: AGRICULTURE, RURAL AREAS AND FARMERS

China is the most populous country in the world. Of its 1.3 billion people, 22% of the world population, about 67% are living in rural areas. Although China is the third largest country in terms of area, the arable land is only 7% of the global amount. With relatively meager endowment, it is undoubtedly a daunting task for the agricultural sector to provide adequate supply to fulfil huge needs for food and other agricultural products. In addition, agriculture development in China confronts with challenges to raise the average income and standard of living of the rural population in the long run. Since China's economic reform was launched in 1978, the "People's Commune" system was dismantled and replaced by the "Household Responsibility" system. Agricultural production has achieved rapid growth and income per capita in the rural area has risen 10 times in 20 years. During this transformation process, a number of serious problems have been emerging in the agricultural sector. They include the diminishing size of the arable land, enlarging of income disparity and stagnating of productivity growth, which have been exacerbated by the population growth and increasing demands for agricultural products. The agricultural sector is also plagued by environmental degradation and confronted by township enterprise development. Furthermore, China's recent accession into the World Trade Organization (WTO) brings more tremendous challenges to its agriculture. This paper is intended to provide a concise analysis of the problems and possible policy options associated with current agriculture development. It reveals that the main problems are market partition, inefficiency in government administration in supply and distribution, and price distortions of agricultural products, originating from China's development strategy of preferred industrialization in the industry sector and urban development. This paper also explores and assesses a few government policy options for the alleviation of these problems. Policy options focus on deepening market-oriented reforms, including price deregulation, market integration and property (land) reforms, which also reflect the requirements of the Agriculture Agreement of WTO. Policy options also focus on improvement of government supported programs in investment and subsidies aimed at boosting productivity, narrowing the inequality of income distribution and easing the barriers for mobility of surplus labor into the industry and service sectors in urban areas.International Development,

Emerging exciton physics in two-dimensional semiconductors

Excitons are bosonic quasiparticles composed of a bound electron-hole pair. As one of the most ubiquitous quasiparticles in solid state systems, excitons play a particularly important role in the optical and electronic properties of semiconductors. Two-dimensional materials provide new opportunities for the exploration of interesting exciton physics due to reduced screening of electron-hole interactions and the emergent layer degree of freedom. This dissertation presents a study of different aspects of exciton physics in two-dimensional semiconductors, with emphasis on interlayer exciton condensation in bilayer electron-hole systems. Chapter 1 provides an overview of exciton physics in two-dimensional semiconductors. Starting with a brief historical overview of theoretical and experimental progress in various material platforms, the rest of the chapter provides an introduction to theoretical formulations for the description of excitons and exciton condensation. Chapters 2 to 4 focus on interlayer exciton condensation in electron-hole bilayers. In Chapter 2 we study the electronic properties of an ideal electron-hole bilayer in which interlayer tunneling is suppressed and the carrier densities are tuned by gate and bias voltages. Recent experimental studies based on transition metal dichalcogenide bilayers are discussed. In Chapter 3 we study the influence of an in-plane magnetic field on InAs/GaSb quantum wells, another electron-hole bilayer but with finite p-wave interlayer tunneling. Chapter 4 presents a field-theory study of nonequilibrium electron-hole bilayers in which both bias voltage and interlayer tunneling are present. The next two chapters focus on moiré materials. In Chapter 5 we study the layer pseudospin physics of double-moiré systems and find interlayer coherent states and dipole crystal states as the system parameters vary. In Chapter 6 we study the strong modulation limit of excitons and trions and the associated optical properties of moiré materials by exact diagonalization of a quantum dot model. Finally, Chapter 7 concludes this dissertation with an outlook of the field.Physic

Electrical Control of Two-Dimensional Electron-Hole Fluids in the Quantum Hall Regime

We study the influence of quantizing perpendicular magnetic fields on the ground state of a bilayer with electron and hole fluids separated by an opaque tunnel barrier. In the absence of a field, the ground state at low carrier densities is a condensate of s-wave excitons that has spontaneous interlayer phase coherence. We find that a series of phase transitions emerge at strong perpendicular fields between condensed states and incompressible incoherent states with full electron and hole Landau levels. When the electron and hole densities are unequal, condensation can occur in higher angular momentum electron-hole pair states and, at weak fields, break rotational symmetry. We explain how this physics is expressed in dual-gate phase diagrams, and predict transport and capacitively-probed thermodynamic signatures that distinguish different states

Efficient and Private Federated Trajectory Matching

Federated Trajectory Matching (FTM) is gaining increasing importance in big trajectory data analytics, supporting diverse applications such as public health, law enforcement, and emergency response. FTM retrieves trajectories that match with a query trajectory from a large-scale trajectory database, while safeguarding the privacy of trajectories in both the query and the database. A naive solution to FTM is to process the query through Secure Multi-Party Computation (SMC) across the entire database, which is inherently secure yet inevitably slow due to the massive secure operations. A promising acceleration strategy is to filter irrelevant trajectories from the database based on the query, thus reducing the SMC operations. However, a key challenge is how to publish the query in a way that both preserves privacy and enables efficient trajectory filtering. In this paper, we design GIST, a novel framework for efficient Federated Trajectory Matching. GIST is grounded in Geo-Indistinguishability, a privacy criterion dedicated to locations. It employs a new privacy mechanism for the query that facilitates efficient trajectory filtering. We theoretically prove the privacy guarantee of the mechanism and the accuracy of the filtering strategy of GIST. Extensive evaluations on five real datasets show that GIST is significantly faster and incurs up to 3 orders of magnitude lower communication cost than the state-of-the-arts.Comment: 14 page

Preference-aware task assignment in on-demand taxi dispatching: An online stable matching approach

A central issue in on-demand taxi dispatching platforms is task assignment, which designs matching policies among dynamically arrived drivers (workers) and passengers (tasks). Previous matching policies maximize the profit of the platform without considering the preferences of workers and tasks (e.g., workers may prefer high-rewarding tasks while tasks may prefer nearby workers). Such ignorance of preferences impairs user experience and will decrease the profit of the platform in the long run. To address this problem, we propose preference-aware task assignment using online stable matching. Specifically, we define a new model, Online Stable Matching under Known Identical Independent Distributions (OSM-KIID). It not only maximizes the expected total profits (OBJ-1), but also tries to satisfy the preferences among workers and tasks by minimizing the expected total number of blocking pairs (OBJ-2). The model also features a practical arrival assumption validated on real-world dataset. Furthermore, we present a linear program based online algorithm LP-ALG, which achieves an online ratio of at least 1−1/e on OBJ-1 and has at most 0.6·|E| blocking pairs expectedly, where |E| is the total number of edges in the compatible graph. We also show that a natural Greedy can have an arbitrarily bad performance on OBJ-1 while maintaining around 0.5·|E| blocking pairs. Evaluations on both synthetic and real datasets confirm our theoretical analysis and demonstrate that LP-ALG strictly dominates all the baselines on both objectives when tasks notably outnumber workers