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1.
针对刚性航天器在姿态跟踪控制中存在的系统不确定及外界干扰等问题,提出了一种预定义时间滑模控制器(PTSMC).首先,给出了以四元数为姿态参数的航天器姿态跟踪控制系统,利用误差四元数和误差角速度设计了预定义时间滑模面.然后,考虑了航天器系统的不确定性和外界干扰设计了一种非保守上界的PTSMC,并通过边界层技术降低了系统抖动.最后,通过设计Lyapunov函数,证明了所提出的控制器的预定义时间稳定性和系统收敛时间上界的非保守性.仿真结果表明,刚性航天器的姿态跟踪误差精度可达1.5×10-6 rad,角速度跟踪误差精度可达2×10-6 rad/s.与现有的预定义时间控制器相比,所提出的控制器的稳定时间上限是更加非保守的,与传统PD控制和非奇异终端滑模控制相比,所提出的控制器具有更高的跟踪精度和鲁棒性.通过3自由度气浮平台的姿态跟踪实验进一步说明了控制方案的有效性,其中角度跟踪误差小于0.1 rad,位置跟踪误差小于0.2 m. 相似文献
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Shimei Fu Song Xue Jun Chen Shuai Shang Hui Xiao Yu Zang Xuexi Tang 《International journal of molecular sciences》2021,22(4)
The effects of ultraviolet (UV) radiation, particularly UV-B on algae, have become an important issue as human-caused depletion of the protecting ozone layer has been reported. In this study, the effects of different short-term UV-B radiation on the growth, physiology, and metabolism of Porphyra haitanensis were examined. The growth of P. haitanensis decreased, and the bleaching phenomenon occurred in the thalli. The contents of total amino acids, soluble sugar, total protein, and mycosporine-like amino acids (MAAs) increased under different UV-B radiation intensities. The metabolic profiles of P. haitanensis differed between the control and UV-B radiation-treated groups. Most of the differential metabolites in P. haitanensis were significantly upregulated under UV-B exposure. Short-term enhanced UV-B irradiation significantly affected amino acid metabolism, carbohydrate metabolism, glutathione metabolism, and phenylpropane biosynthesis. The contents of phenylalanine, tyrosine, threonine, and serine were increased, suggesting that amino acid metabolism can promote the synthesis of UV-absorbing substances (such as phenols and MAAs) by providing precursor substances. The contents of sucrose, D-glucose-6-phosphate, and beta-D-fructose-6-phosphate were increased, suggesting that carbohydrate metabolism contributes to maintain energy supply for metabolic activity in response to UV-B exposure. Meanwhile, dehydroascorbic acid (DHA) was also significantly upregulated, denoting effective activation of the antioxidant system. To some extent, these results provide metabolic insights into the adaptive response mechanism of P. haitanensis to short-term enhanced UV-B radiation. 相似文献
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禁行域在圆型限制性三体问题中对第三体的运动有极为重要的影响. 利用零速度曲线讨论天体禁行域与系统参数之间的关系. 禁行域与雅可比常数有关,且能影响天体的运动区域和轨道构型. 利用最大李雅普诺夫指数寻找该模型的混沌轨道,给出混沌轨道在不同系统参数下随天体初始位置的分布. 这些分布说明,当第三天体从两主天体连线的中点处释放时,容易产生混沌运动;当质量参量足够小时,体系无法产生混沌现象. 相似文献
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Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are attracting famous applications in antistatic coating, energy storage and conversion, printed electronics, and biomedical fields due to their conductivity, optical transparency and flexibility. However, PEDOT:PSS has poor dispersion stability during long-term storage and transport. Moreover, the dried PEDOT:PSS films are insoluble in any solvent and cannot be redispersed again. In comparison to bake drying, here, a feasible strategy to achieve mechanically redispersed PEDOT:PSS with the help of freeze-drying process was reported. The redispersed PEDOT:PSS can recover not only the initial characters such as pH, chemical composition, viscosity, and particle size under similar solid contents, but also conductivity and surface morphology of treated films. In addition, the treated film exhibits self-healing properties similar to pristine film in terms of mechanical and electrical properties. This technology enables reuse and overcomes the technical problems of PEDOT:PSS dispersion, realizing real-time processing to meet variable applications. 相似文献
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文章介绍了海外某大型火力发电厂发生的一起发电机定子接地故障的分析和处理过程,对发电厂类似故障的处理和海外发电厂的运行和维护提供了参考。 相似文献
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Dr. Yibin Zhang Dr. Shuai Xia Shulin Wan Tessa E. Steenwinkel Tara Vohs Prof. Rudy L. Luck Prof. Thomas Werner Prof. Haiying Liu 《Chembiochem : a European journal of chemical biology》2021,22(13):2282-2291
Abnormal levels of glutathione, a cellular antioxidant, can lead to a variety of diseases. We have constructed a near-infrared ratiometric fluorescent probe to detect glutathione concentrations in biological samples. The probe consists of a coumarin donor, which is connected through a disulfide-tethered linker to a rhodamine acceptor. Under the excitation of the coumarin donor at 405 nm, the probe shows weak visible fluorescence of the coumarin donor at 470 nm and strong near-infrared fluorescence of the rhodamine acceptor at 652 nm due to efficient Forster resonance energy transfer (FRET) from the donor to the acceptor. Glutathione breaks the disulfide bond through reduction, which results in a dramatic increase in coumarin fluorescence and a corresponding decrease in rhodamine fluorescence. The probe possesses excellent cell permeability, biocompatibility, and good ratiometric fluorescence responses to glutathione and cysteine with a self-calibration capability. The probe was utilized to ratiometrically visualize glutathione concentration alterations in HeLa cells and Drosophila melanogaster larvae. 相似文献
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JAVARIA AFZAL XIUKANG WANG MUHAMMAD HAMZAH SALEEM XUECHENG SUN SHAHID HUSSAIN IMRAN KHAN MUHAMMAD SHOAIB RANA SHAKEEL AHMED SAMRAH AFZAL AWAN SAJID FIAZ OMAR AZIZ KASHIF ALI KUBAR SHAFAQAT ALI CHENGXIAO HU 《Biocell》2021,45(6):1631-1649
Soil contamination with toxic heavy metals [such as cadmium (Cd)] is becoming a serious global problem due
to rapid development of social economy. Iron (Fe), being an important element, has been found effective in enhancing
plant tolerance against biotic and abiotic stresses. The present study investigated the extent to which different levels of
Ferrous sulphate (FeSO4) modulated the Cd tolerance of rice (Oryza sativa L.), when maintained in artificially Cd
spiked regimes. A pot experiment was conducted under controlled conditions for 146 days, by using natural soil,
mixed with different levels of CdCl2 [0 (no Cd), 0.5 and 1 mg/kg] together with the exogenous application of FeSO4
at [0 (no Fe), 1.5 and 3 mg/kg] levels to monitor different growth, gaseous exchange characteristics, oxidative stress,
antioxidative responses, minerals accumulation, organic acid exudation patterns of O. sativa. Our results depicted that
addition of Cd to the soil significantly (P < 0.05) decreased plant growth and biomass, gaseous exchange parameters,
mineral uptake by the plants, sugars (soluble, reducing, and non-reducing sugar) and altered the ultrastructure of
chloroplasts, plastoglobuli, mitochondria, and many other cellular organelles in Cd-stressed O. sativa compared to
those plants which were grown without the addition of Cd in the soil. However, Cd toxicity boosted the production of
reactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication of
oxidative stress in O. sativa and was also manifested by hydrogen peroxide (H2O2) contents and electrolyte leakage to
the membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase
(SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidants like
phenolics, flavonoid, ascorbic acid, anthocyanin and proline contents increased up to a Cd level of 0.5 mg/kg in the
soil but were significantly diminished at the highest Cd level of 1 mg/kg in the soil compared to those plants which
were grown without the addition of Cd in the soil. The negative impacts of Cd injury were reduced by the application
of FeSO4 which increased plant growth and biomass, improved photosynthetic apparatus, antioxidant enzymes, minerals uptake together with diminished exudation of organic acids as well as oxidative stress indicators in roots and
shoots of O. sativa by decreasing Cd retention in different plant parts. These results shed light on the effectiveness of
FeSO4 in improving the growth and upregulation of antioxidant enzyme activities of O. sativa in response to Cd
stress. However, further studies at field levels are required to explore the mechanisms of FeSO4-mediated reduction of
the toxicity of not only Cd, but possibly also other heavy metals in plants. 相似文献