Browsing by Author "Chen, Wen"

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    Ca(Mg1/3Ta2/3)O3 dielectric thin films: preparation, structure, mechanical and dielectric properties
    (Springer, 2016-05-17) Li, Runrun; Zhou, Jing; Chen, Wen; Zhang, Qi; Bao, Yiwang Bao
    The effects of annealing temperature on the crystallinity, grain size and hence mechanical and dielectric properties of Ca(Mg1/3Ta2/3)O3 (CMT) dielectric films were systematically studied. The CMT thin films were fabricated by an aqueous solution-gel technology and exhibited uniform, smooth and dense morphologies. The optimum pyrolysis temperature and time was 550 °C and 330 s, respectively. All the CMT films annealed from 650 to 800 °C show a single perovskite phase and the crystallization increases with increasing the annealed temperature but a secondary phase is observed in the film annealed at 900 °C. The hardness and reduced modulus were effectively enhanced by increasing the annealing temperature, which can be correlated to the crystallinity and densification improvements. Higher elastic recovery was observed for CMT films annealed at higher temperatures indicating less difficult recoveries for those films. We also noticed that the dielectric constants were improved for the samples annealed at higher temperature, which may enable higher performances for future microwave communication electronics.
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    Communication-aware convoy following guidance for UAVs in a complex urban environment
    (IEEE, 2016-06-30) Oh, Hyondong; Shin, Hyosang; Kim, Seungkeun; Ladosz, Pawel; Chen, Wen
    This paper proposes a communication-aware trajectory planning approach for UAVs to relay data/information (e.g. live surveillance feed) between a ground control station and friendly ground vehicles (a convoy) moving in a complex urban area. UAVs are controlled to stay: i) within the communication-feasible area (having a direct line-of-sight to the moving convoy and within the maximum communication range) and ii) as close as possible to the convoy to have better communication quality, while satisfying their kinematic and dynamic constraints. Numerical simulations and a proof-of-concept indoor flight test have been performed to validate the benefit and feasibility of the proposed algorithm.
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    Development of Crop.LCA, an adaptable screening life cycle assessment tool for agricultural systems: a Canadian scenario assessment
    (Elsevier, 2017-06-22) Goglio, Pietro; Smith, Ward N.; Worth, Devon E.; Grant, Brian B.; Desjardins, Raymond L.; Chen, Wen; Tenuta, Mario; McConkey, Brian G.; Williams, Adrian; Burgess, Paul
    There is an increasing demand for sustainable agricultural production as part of the transition towards a globally sustainable economy. To quantify impacts of agricultural systems on the environment, life cycle assessment (LCA) is ideal because of its holistic approach. Many tools have been developed to conduct LCAs in agriculture, but they are not publicly available, not open-source, and have a limited scope. Here, a new adaptable open-source tool (Crop.LCA) for carrying out LCA of cropping systems is presented and tested in an evaluation study with a scenario assessment of 4 cropping systems using an agroecosystem model (DNDC) to predict soil GHG emissions. The functional units used are hectares (ha) of land and gigajoules (GJ) of harvested energy output, and 4 impact categories were evaluated: cumulative energy demand (CED), 100-year global warming potential (GWP), eutrophication and acidification potential. DNDC was used to simulate 28 years of cropping system dynamics, and the results were used as input in Crop.LCA. Data were aggregated for each 4-year rotation and statistically analyzed. Introduction of legumes into the cropping system reduced CED by 6%, GWP by 23%, and acidification by 19% per ha. These results highlight the ability of Crop.LCA to capture cropping system characteristics in LCA, and the tool constitutes a step forward in increasing the accuracy of LCA of cropping systems as required for bio-economy system assessments. Furthermore, the tool is open-source, highly transparent and has the necessary flexibility to assess agricultural systems.
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    Direct measurement of electric field-induced strains of a single lead zirconate titanate piezoelectric ceramic fibre under various conditions
    (Elsevier, 2014-09-29) Yang, Xiong; Zhou, Jing; Zhang, Sen; Shen, Jie; Chen, Wen; Tian, Jing; Zhang, Qi
    The electric field-induced strains (S-E) of a single PZT piezoelectric fibre were measured using a micro-displacement sensor. The effects of temperature and uniaxial compressive stress on S-E were also investigated. The results demonstrate that the S-E are strongly dependent on these factors. Both the maximum strain (Smax) and depoling field increase with the increase of applied electric field. The Smax value increases with the increase of frequency and remains constant after the frequency exceeds 20 Hz. Meanwhile, the remnant strain (Srem) continues to increase, due to the mismatch between the strain response and loading rates. The recoverable strain (Smax-Srem) goes up with the increase of temperature and reaches the maximum value at 140 °C. Under an increasing uniaxial compressive stress, both Smax and depoling field increase and reach the peak value at 3 MPa, and then decrease with further increase of stress.