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排序方式: 共有7059条查询结果,搜索用时 15 毫秒
1.
针对新型机器人多自由度运动机构的需求,提出了一种新型六相双定子螺旋运动永磁执行器。执行器特点在于每个定子均为六相双Y移30°绕组,两个定子铁心采用螺旋形齿槽结构,对两个定子绕组通入六相不同相序电流组合便可产生多自由度运动方式。执行器具有控制方式灵活、容错性能强、可靠性稳定等优点。首先对螺旋运动永磁执行器的结构及运行机理进行分析,推导了执行器的磁链方程、电压方程、转矩和推力方程。最后构建了瞬态三维多自由度数值分析模型,得到了磁链、电压、转矩和推力的波形,验证了运行机理的正确性。 相似文献
2.
Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment
Hongjiang Li Kaili Chu Xingrui Pu Xiaohan Yu Xiaoli Guan Shuaizhao Jin Xiang Liu 《Ceramics International》2021,47(1):94-101
High-density La0.9-xSrxK0.1MnO3 ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr2+ ions, substituting La3+ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K?1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping. 相似文献
3.
Shammya Afroze Nico Torino Md Sumon Reza Nikdalila Radenahmad Quentin Cheok Paul F. Henry Abul K. Azad 《Ceramics International》2021,47(1):541-546
The structural and electrochemical properties of the double perovskite-type oxide, PrBaMnMoO6-δ, was investigated using neutron diffraction with in-situ conductivity measurement under a dry Argon atmosphere from 25 °C to 700 °C. A Rietveld refinement of the neutron diffraction data confirmed monoclinic symmetry in the P21/n space group. Rietveld refinement also confirms the unit cell parameters of a = 5.6567 (1) Å, b = 5.6065 (2) Å, c = 7.9344 (1) Å and β = 84.43° with reliable atomic positions and refinement factors (R-factors). Neutron diffraction data refinement shows two minor phases (<5%), an orthorhombic AB2O5 type phase of PrMn2O5 in the Pbam (No. 32) space group with unit cell parameters, a = 7.9672 (1) Å, b = 8.9043 (2) Å and c = 5.8540 (1) Å and a scheelite phase of BaMoO4 in the tetragonal I41/a (88) space group with the unit cell parameters, a = b = 5.9522 (1) Å, and c = 12.3211 (2) Å. Morphological images revealed a porous and intertwined microstructure. In-situ conductivity measurement shows that the total conductivity of this material was 130.84 Scm?1 at 700 °C. 相似文献
4.
根据现行标准,低压燃气管道应采用锥/锥形式的螺纹连接。通过调研多家燃气企业,发现燃气管道的螺纹连接在实际应用中普遍存在管件选型不当、现场加工螺纹要求不明、密封填料选用不当等问题。针对管道螺纹连接进行理论分析,计算DN 50 mm镀锌钢管螺纹的理论最小机紧圈数与上紧至材料屈服的圈数。分析螺纹牙高、牙型角、螺纹锥度加工误差对螺纹密封间隙的影响,从理论上说明了螺纹连接使用填料、上紧等措施实现密封的必要性。针对存在的问题,提出了解决措施,包括丰富设计文件细节、定期检验螺纹现场加工成品误差、选用合适的螺纹密封材料、规范施工方法。 相似文献
5.
Wire arc additive manufacturing(WAAM)has been investigated to deposit large-scale metal parts due to its high deposition efficiency and low material cost.However,in the process of automatically manufacturing the high-quality metal parts by WAAM,several problems about the heat build-up,the deposit-path optimization,and the stability of the process parameters need to be well addressed.To overcome these issues,a new WAAM method based on the double electrode micro plasma arc welding(DE-MPAW)was designed.The circuit principles of different metal-transfer models in the DE-MPAW deposition process were analyzed theoretically.The effects between the parameters,wire feed rate and torch stand-off distance,in the process of WAAM were investigated experimentally.In addition,a real-time DE-MPAW control system was developed to optimize and stabilize the deposition process by self-adaptively changing the wire feed rate and torch stand-off distance.Finally,a series of tests were performed to evaluate the con-trol system's performance.The results show that the capability against interferences in the process of WAAM has been enhanced by this self-adaptive adjustment system.Further,the deposition paths about the metal part's layer heights in WAAM are simplified.Finally,the appearance of the WAAM-deposited metal layers is also improved with the use of the control system. 相似文献
6.
In this communication, the structural, micro-structural, dielectric, electrical, magnetic, and leakage-current characteristics of a double perovskite (Y2CoMnO6) ceramic material have been reported. The material was synthesized via a high-temperature mixed-oxide route. The compound crystallizes in a monoclinic structure which is confirmed from preliminary X-ray structural study. The morphological study by using scanning electron micrograph reveals the almost homogeneous distribution of grains throughout the surface of the sample. The nature of frequency-dependence of dielectric constant has been described by the Maxwell-Wagner model. The occurrence of a dielectric anomaly in the temperature dependence of dielectric permittivity study demonstrates the ferroelectric-paraelectric phase transition in the material. From the Nyquist plots, we found the existence of both grain and grain boundary effects. The frequency dependence of conductivity was studied by the Jonscher’s Power law, and the conduction phenomenon obeys the large overlapping polaron tunneling model. By using the Arrhenius equation, the activation energy has been calculated which is nearly equal to the energy required for the hoping of the electron. Both impedance and conductivity analysis demonstrate that the sample exhibits negative temperature coefficient of resistance (NTCR) properties indicating the semiconducting type of material at high temperatures. The anti-ferromagnetic character of the material is observed from the nature of magnetic hysteresis loop. The leakage current analysis suggests that the conduction process in the material follows the space charge limited conduction phenomenon. Such material will be helpful for modern electronic devices and spintronic applications. 相似文献
7.
8.
Flash cosintering of a lanthanum strontium cobalt ferrite nanofibre/Gd-doped ceria bilayer structure
《Journal of the European Ceramic Society》2022,42(6):2870-2878
For solid oxide fuel cells, an important structural requirement is that the electrolyte layer needs to be dense and the electrode layer porous, which is difficult to obtain by conventional cosintering. In this work, flash cosintering of a double layer structure consisting of a Gd-doped ceria substrate with a lanthanum strontium cobalt ferrite nanofibre coating is investigated. Experimental and finite element modelling results reveal that when the LSCF layer is connected to the electrode, the heat is concentrated in the LSCF layer, which leads to a huge temperature gradient and introduces severe cracking. When the LSCF layer is electrically isolated from the electrode, the heat is concentrated in the GDC layer, and the temperature gradient is dramatically reduced. In this situation, the density of GDC can reach 92.86% while a high porosity of 52.26% is maintained in the LSCF layer, which is higher than that of the conventional cosintered sample. 相似文献
9.
通常情况下,应用Radon变换压制多次波,一般是对正变换的模型空间进行处理,再反变换回时空域,而Radon域能量团的收敛性直接影响多次波去除效果,且求解过程中需反复进行矩阵的逆运算,计算成本偏高。为此,基于二维抛物Radon变换,借鉴Abbad等的方法,首次提出λ-f(λ为曲率q与频率f的乘积)域三维抛物Radon变换多次波压制方法,将常规三维抛物Radon变换的f-qx-qy(qx、qy分别为横、纵向离散曲率)域转换到一个全新的λx-λy-f(λx=qxf、λy=qyf)域,继承了二维λ-f域Radon变换思路。通过引入新的变量λx和λy,消除常规Radon算子对频率的依赖,减少了矩阵运算次数,显著提高了计算效率;根据一次波和多次波能量在λ-f域空间分布特征,设计三维椎体滤波器,更有效地分离一次波和多次波,降低空间截断效应引起的误差。理论模型及实际数据测试表明:1所提方法降低了空间截断效应的影响,消除了变换算子对频率的依赖,有效减少了矩阵求逆运算次数,较常规三维Radon变换方法的计算效率提高了约8倍以上;2所提方法仍然存在Radon类方法的弊端,即当一次波和多次波速度差异较小时,在近炮检距位置无法得到较理想的多次波压制效果。 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(6):3781-3790
A novel heterostructure of g-C3N4/ZnO/Bi4O5Br2 (ZB-3) was designed, and used in the microbial coupled photocatalytic fuel cell (MPFC). It can effectively improve electron utilization efficiency and pollutant degradation using this double Z-scheme heterojunction structure. The current–time (I–t) curves demonstrated that the current density of ZB-3 was higher than that of ZnO, ZnO/Bi4O5Br2 (ZB-1), g-C3N4/ZnO (ZB-2). Electrochemical impedance spectroscopy (EIS) indicated ZB-3 possessed the minimum charge-transfer resistance. This MPFC for degrading rhodamine B (RhB) and tetracycline (TC) under different conditions were developed using these materials. Even in the dark condition, MPFC with g-C3N4/ZnO/Bi4O5Br2 demonstrated 93% and 82% degradation efficiency for RhB and TC, respectively. Furthermore, the electron transport mechanism of the MPFC and ZB-3 were proposed. It paves the approach for more efficient pollutant degradation via MFC photocatalysis. 相似文献