The influence of the distorted plane of the active phased array antenna on the electromagnetic performance is of great significance to the research on and development of the high-performance antennas. On the bent and ...The influence of the distorted plane of the active phased array antenna on the electromagnetic performance is of great significance to the research on and development of the high-performance antennas. On the bent and bowl-shape distortion, the model is established of the relationship between the electromagnetic performance and the position error of the radiated elements. The method is presented of analyzing the far-field pattern of the distorted rectangular active phased array antenna. The analysis results of a planar phased array antenna with different distortions grades prove the validity of the model. Therefore, by the method, the antenna designers may set the reasonable requirement on the structural tolerance in manufacturing antenna.展开更多
The phase stability and structural distortion of NiO under high pressure were investigated using first-principles calculations based on density-functional theory. Different forms of exchange-correlation functional inc...The phase stability and structural distortion of NiO under high pressure were investigated using first-principles calculations based on density-functional theory. Different forms of exchange-correlation functional including LDA, GGA and GGA+U were used in the present calculations. All of the three methods predict NiO to be AFM II ordering with the cell slightly compressed along [111] direction and also indicate that there is no structural phase transition of NiO under pressure up to 140 GPa, which are in agreement with the experiment. However, both LDA and GGA incorrectly predict the structural distortion under pressure especially above 60 GPa. Only when strong correlations are included in form of GGA+U, structural distortion under high pressure can qualitatively agree with the experiment. The related mechanism was also analyzed and discussed. These results suggest that the strong electronic correlations still play a very important role in the properties of NiO under high pressure.展开更多
Based on the tests of a build-up welding at plate edge (BWPE) and amulti-layer build-up welding on plate (MBWP), the article studies on the solid-state phasetransformations which affect welding distortion process and ...Based on the tests of a build-up welding at plate edge (BWPE) and amulti-layer build-up welding on plate (MBWP), the article studies on the solid-state phasetransformations which affect welding distortion process and on the influence rule of transformationstarting temperature (TST) of welded metal to the welding residual distortion. The weldingdistortion can be decreased or controlled by the transformation volume expansion caused bysolid-state phase transformation of welded metal during the cooling. The test results of BWPE showthat when TST is at about 190 deg C, the bending distortion of welded specimen is the smallest, andits displacements at free end are decreased to 58 percent and 67 percent compared with those ofconventional welding electrodes A102 and E5015, which TST are less than room temperature and equalto 758 deg C respectively. The test results of MBWP show that when TST were at 100 approx 250 deg C.the welded specimen would appear reversible bending distortion compared with those of A102 andE5015. The maximum deflection value of reversible bending distortion in 8 mm thick plate is -2.94 mmat about 170 deg C of TST. The test results provide a valuable method to decrease or to controlwelding residual distortion.展开更多
周期性信号采样中,等效采样利用较低采样频率的A/D转换实现高频周期信号的采集,一定程度上弥补欠采样测量精度低的缺陷。为了有效地提高高频测量中阻抗谱测量精度与稳定性,提出一种基于等效采样思想的均匀相位采样的阻抗谱测量方法。利...周期性信号采样中,等效采样利用较低采样频率的A/D转换实现高频周期信号的采集,一定程度上弥补欠采样测量精度低的缺陷。为了有效地提高高频测量中阻抗谱测量精度与稳定性,提出一种基于等效采样思想的均匀相位采样的阻抗谱测量方法。利用单片机共时钟基准的模/数转换器(digital to analog convertor,DAC)与数/模转换器(analog to digital convertor,ADC)模块,在完成激励信号产生、输入输出信号同步采集的基础上,合理设计激励信号频率、采集频率与信号重构方法,实现高频信号单周期内均匀相位分布的等效高频采样,同时为克服常规A/D转换速度条件下难以准确实现高频阻抗谱测量的问题提供了新思路。从误差假设与拟合算法的角度,理论上分析证明了该方法降低误差的原因。并通过两种等效电路模型的阻抗谱测量对比实验,表明该方法在所设计的20~100 kHz高频段上,阻抗测量精度与稳定性得到了显著的提高。展开更多
X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged...X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged. Structural distortions, such as the rotating and tilting for oxygen octahedron in the unit cell vary with iron content. A phase transition occurs at the Fe content values of 0.2~0.3. The evolutions of rotation and tilting angle of FeO6/MnO6 octahedral may be the vital factors to the structure and magnetism. We believe that the spin configuration of Fe3＋ may vary from the intermediate spin t2g4eg1 （S = 3/2） to the higher spin t2g3eg2 （S = 5/2） near the phase transition.展开更多
基金supported partly by the National Natural Science Foundation of China(50805111)the Natural Science Basic Research Plan in Shaanxi Province of China(SJ08E_203.)
文摘The influence of the distorted plane of the active phased array antenna on the electromagnetic performance is of great significance to the research on and development of the high-performance antennas. On the bent and bowl-shape distortion, the model is established of the relationship between the electromagnetic performance and the position error of the radiated elements. The method is presented of analyzing the far-field pattern of the distorted rectangular active phased array antenna. The analysis results of a planar phased array antenna with different distortions grades prove the validity of the model. Therefore, by the method, the antenna designers may set the reasonable requirement on the structural tolerance in manufacturing antenna.
基金Project(KF0504) supported by Open Program of Key Laboratory of Advanced Materials & Rheological Properties, Ministry of Education
文摘The phase stability and structural distortion of NiO under high pressure were investigated using first-principles calculations based on density-functional theory. Different forms of exchange-correlation functional including LDA, GGA and GGA+U were used in the present calculations. All of the three methods predict NiO to be AFM II ordering with the cell slightly compressed along [111] direction and also indicate that there is no structural phase transition of NiO under pressure up to 140 GPa, which are in agreement with the experiment. However, both LDA and GGA incorrectly predict the structural distortion under pressure especially above 60 GPa. Only when strong correlations are included in form of GGA+U, structural distortion under high pressure can qualitatively agree with the experiment. The related mechanism was also analyzed and discussed. These results suggest that the strong electronic correlations still play a very important role in the properties of NiO under high pressure.
基金This project is supported by National Natural Science Foundation of China (No.50175079) China Postdoctoral Science Foundation (No.2003033348).
文摘Based on the tests of a build-up welding at plate edge (BWPE) and amulti-layer build-up welding on plate (MBWP), the article studies on the solid-state phasetransformations which affect welding distortion process and on the influence rule of transformationstarting temperature (TST) of welded metal to the welding residual distortion. The weldingdistortion can be decreased or controlled by the transformation volume expansion caused bysolid-state phase transformation of welded metal during the cooling. The test results of BWPE showthat when TST is at about 190 deg C, the bending distortion of welded specimen is the smallest, andits displacements at free end are decreased to 58 percent and 67 percent compared with those ofconventional welding electrodes A102 and E5015, which TST are less than room temperature and equalto 758 deg C respectively. The test results of MBWP show that when TST were at 100 approx 250 deg C.the welded specimen would appear reversible bending distortion compared with those of A102 andE5015. The maximum deflection value of reversible bending distortion in 8 mm thick plate is -2.94 mmat about 170 deg C of TST. The test results provide a valuable method to decrease or to controlwelding residual distortion.
文摘周期性信号采样中,等效采样利用较低采样频率的A/D转换实现高频周期信号的采集,一定程度上弥补欠采样测量精度低的缺陷。为了有效地提高高频测量中阻抗谱测量精度与稳定性,提出一种基于等效采样思想的均匀相位采样的阻抗谱测量方法。利用单片机共时钟基准的模/数转换器(digital to analog convertor,DAC)与数/模转换器(analog to digital convertor,ADC)模块,在完成激励信号产生、输入输出信号同步采集的基础上,合理设计激励信号频率、采集频率与信号重构方法,实现高频信号单周期内均匀相位分布的等效高频采样,同时为克服常规A/D转换速度条件下难以准确实现高频阻抗谱测量的问题提供了新思路。从误差假设与拟合算法的角度,理论上分析证明了该方法降低误差的原因。并通过两种等效电路模型的阻抗谱测量对比实验,表明该方法在所设计的20~100 kHz高频段上,阻抗测量精度与稳定性得到了显著的提高。
基金Project supported by the State Key Program for Basic Research of China (Grant No.2010CB923404)the National Natural Science Foundation of China (Grant Nos.11274153,11204124,and 51202108)
文摘X-ray absorption spectra （XAS） at Mn K-edge and Fe K-edge in LaMnl-xFexO3 show that with the increase of Fe substitution the chemical valence of Mn4＋ decreases, while the chemical valence of Fe3＋ remains unchanged. Structural distortions, such as the rotating and tilting for oxygen octahedron in the unit cell vary with iron content. A phase transition occurs at the Fe content values of 0.2~0.3. The evolutions of rotation and tilting angle of FeO6/MnO6 octahedral may be the vital factors to the structure and magnetism. We believe that the spin configuration of Fe3＋ may vary from the intermediate spin t2g4eg1 （S = 3/2） to the higher spin t2g3eg2 （S = 5/2） near the phase transition.
