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RISS 인기검색어
- 검색키워드
- 저자 : Dawei Shi (검색결과 4 건)
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Influence of oxygen vacancies on the EPIR effect in Nd0.7Sr0.3MnO3 ceramics
Dawei Shi,Shunsheng Chen,Di Liu,Lingfang Xu,Haibo Xiao,Changping Yang,Kaiying Wang 한국물리학회 2015 Current Applied Physics Vol.15 No.8
Nd0.7Sr0.3MnO3 polycrystalline ceramic samples (NSMO) were synthesized by solid state reaction with a post annealing for parts of samples under different partial pressures of oxygen at 1350 ℃ for 12 h. XRD shows that all the samples are in single phase with a perovskite structure. The electrical transport measurement implies that the oxygen concentration has an important influence on the electrical pulse induced resistance, i.e. the EPIR-effect, for NSMO samples. For the oxygen-enriched sample, which probably contains a smaller amount of oxygen vacancies, the I-V characteristic is linear with a very small resistance, and the EPIR-effect is not detectable within the experimental accuracy. However, after sintered and annealed in reducing atmospheres, an EPIR effect appears and even becomes stronger and more stable if the sintering atmosphere is more reducing than that of normal air condition. Besides, the I -V becomes nonlinear and the initial resistance increases with increasing deficiency of oxygen, which means that the oxygen vacancies and their deep level trap states play an important role for the EPIR effect of NSMO. In this manuscript, an oxygen vacancy trapped state model is put forward to explain the relation between oxygen concentration and the EPIR effect.
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LinLin Wang,Tao Shi,Dawei Chang,Haitao Zhang 한국자원공학회 2020 Geosystem engineering Vol.23 No.6
The abundant geochemical information on elements in the autogenous sedimentary rocks can help reconstruct the paleoenvironment of the stratigraphic sedimentation period. Based on the analysis of sedimentary characteristics of Ordovician Majiagou Formation and the trace elements in limestone, dolomite and gypsum rocks in Northern Shaanxi salt basin, the relationship between the distribution of trace elements of Majiagou Formation and the sedimentary environment is discussed. The results display that Majiagou Formation is mainly composed of the sedimentation of carbonate rocks and evaporites, and the subfacies of open platform and restricted platform are developed. The trace element analysis shows that the deposition period of the Majiagou Formation is dominated by dry hot climate, and there are alternating dry and wet seasons in climate evolution. In middle Ordovician, the sedimentary environment of Majiagou Formation was undergoing the transformation of oxygen enrichment-oxygen deficiency-anoxic environment.
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Stiffness matching method for the ball screw feed drive system of machine tools
Gaiyun He,Panpan Shi,Dawei Zhang,Guangming Sun 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.7
The static stiffness of machine tools plays an important role in ensuring the performance of machine tools and improving the machining accuracy. In the design stage, stiffness matching provides a theoretical basis for determining the stiffness of each component. This study proposed a stiffness matching design method for machine tools. First, the deformation model of machine tools is established on the basis of the state space model. Through force analysis, the relationships between the deformations and stiffness of each part are determined. Second, the stiffness model of the machine tool is established by combining these relationships with the deformation model. Third, the objective function is determined by performing sensitivity analysis after obtaining the stiffness range. The stiffness matching design results are obtained through multi-objective linear programming. Lastly, the stiffness simulations, theoretical model, and experimental results are analyzed. The maximum errors among the experimental, simulation, and theoretical results (18.8 % and 19.9 %) are within the acceptable range. In conclusion, the proposed method is suitable for designing ball screw feed drive systems that requires rigidity.
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Comparative Investigation Into Field Performance of Steel Bridge Deck Asphalt Overlay Systems
Xiaoyang Jia,Baoshan Huang,Shangjiang Chen,Dawei Shi 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7
The steel bridge deck overlay provides a smooth surface for riding and protects the deck from influence of traffic and environment factors. The presence of distress on overlay may compromise the serviceability of a bridge. A better understanding of distress is indispensable for designers to make improvements on asphalt overlay to extend the service life. A field investigation into performance of two bridge deck asphalt overlay systems was conducted. The overlay system included an epoxy asphalt overlay and a composite asphalt overlay consisting of Stone-Matrix-Asphalt (SMA) and Gussasphalt (GA). The field investigation was conducted to evaluate the difference in performance between two systems. Chemical analyses were performed on core samples from each bridge to further investigate the distress mechanism of each system. Results indicated that the two overlay systems generally exhibited similar field performance. Each bridge developed different distress, mainly due to the poor bonding between layers or between overlay and steel deck.
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