A gyrotron capable of both frequency and power tuning is a promising coherent millimeter-THz wave source. A self-consistent nonlinear theory is applied to investigate the electron cyclotron interaction between electron beam and wave modes of axial nonfixed profiles in an extended W-band TE01 mode cylindrical cavity. It is revealed that tuning the magnetic field strength can excite electron cyclotron resonances on forward wave, backward wave, and even simultaneous on both waves, which makes the system operate under distinctive states, namely the gyrotron backward wave oscillation state and the gyromonotron state. In this paper, a W-band prototype gyrotron oscillator based on an extended cylindrical waveguide cavity is built, and the experiment test indicates that the system starts oscillation in a relative wide range of the operation parameters. The measured frequency spectrum reveals the system iteratively switches between the lower order instability axial modes, and it operates under nonstationary oscillation states. The experimental measurement of highest output power ~8 kW is consistent with the theoretical predictions. An optimized gyrotron circuit with efficiency exceeding 20% and tunable bandwidth over 10 GHz is also presented. The free oscillation behaviors revealed in this paper provide interesting guidance for developing tunable gyrotrons in millimeter-THz wave range.
A three-level trade-off analysis is proposed for decision making in environmental engineering under interval uncertainty, capable of providing both extreme and non-extreme decision alternatives at different risk levels for constraint and objective function violations. The essence of three-level trade-off analysis is the use of both modified interval linear programming and enhanced interval linear programming models to generate risk-based decision alternatives by qualitatively dividing the risk levels of the parameters in both the constraints and the objective function. The generated decision alternatives include two extremes, two appropriate values and one expected value, and two other non-extremes. The results of a numerical example and a real-world case study (Lake Qionghai Watershed, China) indicate that this procedure can support decision-making processes for stakeholders at different levels of risk to system benefits, within absolutely feasible and optimal solution spaces.
In China, booming tourism is considered to be a win-win solution to fight both ecosystem degradation and poverty in pastoral areas. However, whether this alternative livelihood can reduce pressure on rangeland and improve livelihood of indigenous peoples has not yet been explored. To examine tourism’s impacts on pastoral communities, we conducted field surveys at Inner Mongolia and Xinjiang and distributed questionnaires in 12 provinces including most of the grassland areas of China. On the basis of fieldwork and national survey data, we found that different types of operations have different impacts on livelihood and ecosystem in pastoral area. Pastoralists involved in tourism can increase the income of pastoral households during the summer tourism season, but that pastoralism still provides the main guarantee of a sustainable livelihood. However, along with the development of tourism, business enterprises from outside the pastoral area may replace local herders in tourism operations. As a result, a large area of rangeland may be lost to local herders, who only receive money if they rent their pastures or serve as laborers; unfortunately, many residents lack the training to perform better-paid roles. In addition, we found that pure tourism that replaces pastoralism does not necessarily protect the rangeland, as it brings a variety of environmental impacts and disrupts traditional use that the rangeland may be adapted to. On the basis of our findings, we recommend that tourism managed by local operators who also engage in pastoralism should become the main direction for economic development.
With the proliferation of mobile devices, recent years have witnessed an emerging potential to integrate mobile visual search techniques into digital library. Such a mobile application scenario in digital library has posed significant and unique challenges in document image search. The mobile photograph makes it tough to extract discriminative features from the landmark regions of documents, like line drawings, as well as text layouts. In addition, both search scalability and query delivery latency remain challenging issues in mobile document search. The former relies on an effective yet memory-light indexing structure to accomplish fast online search, while the latter puts a bit budget constraint of query images over the wireless link. In this paper, we propose a novel mobile document image retrieval framework, consisting of a robust Local Inner-distance Shape Context (LISC) descriptor of line drawings, a Hamming distance KD-Tree for scalable and memory-light document indexing, as well as a JBIG2 based query compression scheme, together with a Retinex based enhancement and an OTSU based binarization, to reduce the latency of delivering query while maintaining query quality in terms of search performance. We have extensively validated the key techniques in this framework by quantitative comparison to alternative approaches.