Black polyimides(BPIs)have attracted increasing attention owing to their growing demand in optoelectronics.However,commonly used black polyimides doped with black fillers suffer from poor mechanical and electrical pro...Black polyimides(BPIs)have attracted increasing attention owing to their growing demand in optoelectronics.However,commonly used black polyimides doped with black fillers suffer from poor mechanical and electrical properties.To address these issues,a new diamine(2,5-bis(4′-amino-[1,1′-biphenyl]-4-yl)-3,4-bis(4-fluorophenyl)cyclopenta-2,4-dien-1-one,TPCPFPDA)bearing a tetraphenylcyclopentadienone(TPCP)moiety bonded with benzene and fluorine units was synthesized.The diamine was reacted with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)to yield a soluble intrinsic black polyimide(TPCPFPPI).Bonding fluorine(auxochrome group)and benzene units to TPCP can increase the conjugation ofπ-electrons systems and facilitate the movement of electron throughout the bigπbond,respectively.Owing to the structural features,the synthesized TPCPFPPI exhibited complete visible-light absorption with high blackness and opacity.Its cutoff wavelength(λ_(cut))and CIE(Commission Internationale de I′Eclairage)parameter L^(*)were 684 nm and 1.33,respectively.Moreover,TPCPFPPI displayed exceptional electrical,mechanical,and thermal properties as well as excellent solubility.A detailed theoretical calculation was conducted to gain better insight into the electronic properties of the TPCPFPPI.Results showed that the blackness of TPCPFPPI was chiefly attributed to the electron transition from highest occupied molecular orbital(HOMO)to lowest unoccupied molecular orbital(LUMO)in the diamines,where the charges primarily migrated from the aryl groups in the 2-and 5-positions to the cyclopentadienone center.The as-obtained intrinsic BPI(TPCPFPPI),exhibiting both high solubility and outstanding overall properties,has important applications in photo-electronics.展开更多
Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing fre...Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the con-sideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of cen-troid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid loca-tion and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel-and 5-pixel-windows’ centroid estimation are less than 2×10-3 pixels and 2×10-4 pixels respectively.展开更多
This paper is concerned with the attitude control of a three-axis-stabilized spacecraft which consists of a central rigid body and a flexible sun-tracking solar array driven by a solar array drive assembly. Based on t...This paper is concerned with the attitude control of a three-axis-stabilized spacecraft which consists of a central rigid body and a flexible sun-tracking solar array driven by a solar array drive assembly. Based on the linearization of the dynamics of the spacecraft and the modal identi- ties about the flexible and rigid coupling matrices, the spacecraft attitude dynamics is reduced to a formally singular system with periodically varying parameters, which is quite different from a space- craft with fixed appendages. In the framework of the singular control theory, the regularity and impulse-freeness of the singular system is analyzed and then admissible attitude controllers are designed by Lyapunov＇s method. To improve the robustness against system uncertainties, an H∞ optimal control is designed by optimizing the H∞ norm of the system transfer function matrix. Comparative numerical experiments are performed to verify the theoretical results.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.51973055&52103004)the Natural Science Foundation of Hunan Province (Grant No.2021JJ50004)+1 种基金the Science Research Project of Hunan Provincial Department of Education (Grant No.21A0364)the Student Innovation and Entrepreneurship Training Program of Hunan Province (Grant No.S202211535096)。
文摘Black polyimides(BPIs)have attracted increasing attention owing to their growing demand in optoelectronics.However,commonly used black polyimides doped with black fillers suffer from poor mechanical and electrical properties.To address these issues,a new diamine(2,5-bis(4′-amino-[1,1′-biphenyl]-4-yl)-3,4-bis(4-fluorophenyl)cyclopenta-2,4-dien-1-one,TPCPFPDA)bearing a tetraphenylcyclopentadienone(TPCP)moiety bonded with benzene and fluorine units was synthesized.The diamine was reacted with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)to yield a soluble intrinsic black polyimide(TPCPFPPI).Bonding fluorine(auxochrome group)and benzene units to TPCP can increase the conjugation ofπ-electrons systems and facilitate the movement of electron throughout the bigπbond,respectively.Owing to the structural features,the synthesized TPCPFPPI exhibited complete visible-light absorption with high blackness and opacity.Its cutoff wavelength(λ_(cut))and CIE(Commission Internationale de I′Eclairage)parameter L^(*)were 684 nm and 1.33,respectively.Moreover,TPCPFPPI displayed exceptional electrical,mechanical,and thermal properties as well as excellent solubility.A detailed theoretical calculation was conducted to gain better insight into the electronic properties of the TPCPFPPI.Results showed that the blackness of TPCPFPPI was chiefly attributed to the electron transition from highest occupied molecular orbital(HOMO)to lowest unoccupied molecular orbital(LUMO)in the diamines,where the charges primarily migrated from the aryl groups in the 2-and 5-positions to the cyclopentadienone center.The as-obtained intrinsic BPI(TPCPFPPI),exhibiting both high solubility and outstanding overall properties,has important applications in photo-electronics.
文摘Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the con-sideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of cen-troid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid loca-tion and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel-and 5-pixel-windows’ centroid estimation are less than 2×10-3 pixels and 2×10-4 pixels respectively.
文摘This paper is concerned with the attitude control of a three-axis-stabilized spacecraft which consists of a central rigid body and a flexible sun-tracking solar array driven by a solar array drive assembly. Based on the linearization of the dynamics of the spacecraft and the modal identi- ties about the flexible and rigid coupling matrices, the spacecraft attitude dynamics is reduced to a formally singular system with periodically varying parameters, which is quite different from a space- craft with fixed appendages. In the framework of the singular control theory, the regularity and impulse-freeness of the singular system is analyzed and then admissible attitude controllers are designed by Lyapunov＇s method. To improve the robustness against system uncertainties, an H∞ optimal control is designed by optimizing the H∞ norm of the system transfer function matrix. Comparative numerical experiments are performed to verify the theoretical results.
