Conversion of native desert into irrigated cropland is common in southern Taklimakan desert of China though the effect on soil fertility are not well understood. This study examined the effect of ...cultivation intensity on soil properties and crop productivity using 9-year data from cotton grown at three intensities of no fertilizer, low, and high fertilizer inputs. A native desert with sparse vegetation of Alhagi sparsifolia Shap. was used as a check. Treatment effects on soil properties fluctuated during 2005-2009 due to mineralization of applied manure or weather variation, and kept stable during 2010-2013. Soil organic carbon (SOC) during 2010-2013 increased with intensity, being 1.0-2.4 times greater in the fertilized than unfertilized cotton and desert. Soil total N, plant available N, and P content increased with fertilizer inputs. Available N content in the desert was 28.8 mg kg
−1
, being comparable to the low fertilizer treatment but approximately double that of unfertilized cotton, suggesting N fixing capacity of the leguminosae A. sparsifolia. Available K content was highest in desert and decreased with cultivation intensity. There were positive relationships between SOC and available N and P contents, suggesting SOC as a nutrient reservoir. Soil C:N ratio during 2010-2013 increased with intensity, being 8.7, 9.7, 10.8, and 12.0, for desert, no fertilizer, low, and high fertilizer input, respectively. Fertilizer application increased the 2010-2013 average cotton seed yield by 4.3-6.4 times compared to the unfertilized cotton field. In conclusion, our results suggest the intensive inputs of fertilizers are crucial to accelerate soil fertility and maintain the productivity of the recently converted lands from the desert.
Aedes albopictus is an invasive vector of serious Aedes-borne diseases of global concern. Habitat management remains a critical factor for establishing a cost-effective systematic strategy for ...sustainable vector control. However, the community-based characteristics of Ae. albopictus habitats in complex urbanization ecosystems are still not well understood. A large-scale investigation of aquatic habitats, involving 12 sites selected as representative of four land use categories at three urbanization levels, was performed in Guangzhou, China during 2015-2017. The characteristics and dynamics of these Ae. albopictus habitats were assessed using habitat-type composition, habitat preference, diversity indexes and the Route index (RI), and the temporal patterns of these indexes were evaluated by locally weighted scatterplot smoothing models. The associations of RI with urbanization levels, land use categories and climatic variables were inferred using generalized additive mixed models. A total of 1994 potential habitats and 474 Ae. albopictus-positive habitats were inspected. The majority of these habitats were container-type habitats, with Ae. albopictus showing a particularly higher habitat preference for plastic containers, metal containers and ceramic vessels. Unexpectedly, some non-container-type habitats, especially ornamental ponds and surface water, were found to have fairly high Ae. albopictus positivity rates. Regarding habitats, the land use category residential and rural in Jiangpu (Conghua District, Guangzhou) had the highest number of Ae. albopictus habitats with the highest positive rates. The type diversity of total habitats (H-total) showed a quick increase from February to April and peaked in April, while the H-total of positive habitats (H-positive) and RIs peaked in May. RIs mainly increased with the monthly average daily mean temperature and monthly cumulative rainfall. We also observed the accumulation of diapause eggs in the winter and diapause termination in the following March. Ecological heterogeneity of habitat preferences of Ae. albopictus was demonstrated in four land use categories at three urbanization levels. The results reveal diversified habitat-type compositions and significant seasonal variations, indicating an ongoing adaptation of Ae. albopictus to the urbanization ecosystem. H-positivity and RIs were inferred as affected by climatic variables and diapause behavior of Ae. albopictus, suggesting that an effective control of overwintering diapause eggs is crucial. Our findings lay a foundation for establishing a stratified systematic management strategy of Ae. albopictus habitats in cities that is expected to complement and improve community-based interventions and sustainable vector management.
Resonant frequency shift can occur during operation in the application of ultrasonic actuating device. It affects the resonance amplitude and therefore the performance of the device. To solve this ...problem, an automatic frequency tracking system based on embedded technology was developed. It has the ability to automatically track the resonant frequency shift in response to the load and adjust the excitation frequency accordingly to optimize the performance of the ultrasonic actuating device. The tracking algorithm realized by stm32 ARM processor ensures flexibility to suit different transducers and load conditions. The data acquisition module and serial port can achieve real time operation parameters monitoring and storage on PC. The effectiveness of this frequency tracking system is tested in a trial study of needle visualization during anesthesia procedure using needle actuating device. Results show that the visibility of the needle is greatly improved throughout needle insertion.
With the rapid development of industrial production and micro-packing technology, the demand of thermal conductivity performance of materials becomes increasingly growing. Traditional metal materials ...have been unable to meet the use of certain special occasions. The thermal conductivity of pure polymer materials is poor, however, which can generally be changed by filling thermal conductive composite materials. This method to prepare high performance composite materials attracts more and more attention in recent years. The structures and performances of micro-nano core-shell composite particles can be designed. In this work, we synthesized a few core-shell composite particles with different sizes using sol-gel method, such as SiO 2 /Al 2 O 3 , SiO 2 /AlN, TiO 2 /Al 2 O 3 , Al 2 O 3 /AlN. The composite particles were filled into epoxy resin. The thermal conductivity and mechanical properties of SiO 2 /Al 2 O 3 composite particles filled polymer composites are improved compared to SiO 2 &Al 2 O 3 -physical mixing particles filled polymer composites. The results show that particles of core-shell structure improve the thermal conductivity coefficient of the thermal interface polymer materials and reduce the interfacial heat resistance. The storage modulus in glassy state and rubbery state of SiO 2 / Al 2 O 3 composite particles filled epoxy resin increased 15.4% and 85% compared to the 40wt% physical mixing particles filled epoxy resin and pure epoxy resin respectively. Furthermore, the bending strength of SiO 2 /Al 2 O 3 composite particles filled epoxy resin is 1.9% lower than that of the 40wt% physical mixing particles filled epoxy resin. The thermal conductivity coefficient of epoxy resin with content of 30wt% micro-nano particles of core-shell structure is 34.4% higher than that of pure epoxy resin, and 8.8% higher than that of 30wt% physical mixing particles filled epoxy resin composite. It indicated that the composite particles of core-shell structure have good heat conduction paths to improve the thermal conductivity of thermal interface polymer materials.
PDF
