刚性航天器的预定义时间滑模控制

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.     

Effects of Different Short-Term UV-B Radiation Intensities on Metabolic Characteristics of Porphyra haitanensis

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.     

Freeze-drying and mechanical redispersion of aqueous PEDOT:PSS

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.     

Fabrication of Nd-doped Ni–Zn ferrite/multi-walled carbon nanotubes composites with effective microwave absorption properties

The electromagnetic materials are featured by good magnetic permeability and dielectric constant characteristics, which are of significant importance in solving the pollution problem of electromagnetic. In this study, after the complete of the use of sol-gel method, argon gas was then introduced for calcination, and eventually a new type of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ composites was synthesized after the above mentioned procedures. The synthesized MWCNTs were able to be adsorbed on the surface of Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ and could form a good conductive work of 3D. Also, the effect of additional MWCNTs on microwave absorption properties of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄ composites were also observed in this study. The results indicate that the additional MWCNTs function to significantly improve the microwave absorption property of MWCNTs/Ni_0.5Zn_0.5Nd_0.04Fe_1.96O₄. Through altering the amount of MWCNTs, the microwave attenuation performance and impedance matching coefficient of this electromagnetic materials can be effectively improved. The S2 sample presented a minimum reflection loss of ?35.05 dB when its thickness reached 1.6 mm, meanwhile, the effective absorption bandwidth achieved 4.55 GHz. The prepared composites perform well in microwave absorption, which can attribute to the reasonable ratio of composites as well as its interaction with both of the magnetic and dielectric components. This research paved the way for novel ideas to be put in the electromagnetic absorption materials with high-efficient.     

Ratiometric Detection of Glutathione Based on Disulfide Linkage Rupture between a FRET Coumarin Donor and a Rhodamine Acceptor

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.     

小型饮料瓶盖颜色识别系统设计与实现

目的：解决当前饮料瓶盖检测系统功能单一、体积偏大、颜色识别率低的问题。方法：提出一种基于ARM处理器的小型饮料瓶盖颜色识别系统设计方案，通过仿真软件HyperLynx的LineSim工具设计四层PCB板，设置传输线参数并进行阻抗匹配仿真分析；利用编译软件Jupyter Notebook实现阈值设置、目标轮廓检测、目标框出等功能。结果：在强、弱光条件下，识别系统对红、绿、蓝3种颜色瓶盖的识别率达到92.7%。结论：与傅里叶描述子相比，该识别系统识别准确率和精度更高，同时系统也具有人脸识别功能，适用于各种智能应用场景。     

安卓平台上的医用图像信息采集系统的开发设计

为了探讨在安卓平台上构建医用图像采集系统的开发个案,分析通过以智能手机、平板电脑为核心安卓设备通过拍照获得化验单数据后进行文本识别并提交智慧医疗系统的解决方案。本文首先通过二值化算法形成低阈值图像数据,使用卷积神经元网络算法对文本进行逐一识别,使用K-means算法对识别后的单字文本进行字段记录值的整合并形成元数据库服务于其他智慧医疗系统模块。在使用9000组数据对神经元网络进行前期训练的前提下,该系统的识别准确率达到了99.5%以上。本系统具有一定的可行性,对未来智慧医疗的系统开发有实践意义。     

风力发电机组全功率试验台搭建及应用

为了降低风力发电机组现场调试的高成本和高风险,在车间完成对机组整机性能的测试,采用数字仿真模型与全功率拖动平台联合实时测试的方法搭建了风力发电机组全功率试验平台.其中,数字仿真模型使用基于多体动力学的线性变参数(LPV)建模方法对叶片以及塔架等柔性部件进行详细建模,采用仿真计算出的高精度模拟信号作为系统的输入;拖动平台采用伺服拖动系统模拟风轮的气动输入作为系统的执行机构.测试表明,该试验平台能够在不增加复杂装置的情况下,将叶片模态以及塔架模态纳入到测试系统中,使测试结果更加接近现场实际情况,保证机组装机后安全稳定的运行.