Chattering-free full-order recursive sliding mode control for finite-time attitude synchronization of rigid spacecraft

This paper investigates a quaternion-based finite-time cooperative attitude synchronization and tracking of multiple rigid spacecraft with a virtual leader subject to bounded external disturbances. Firstly, the communication network between followers is assumed to be an undirected graph and every follower can get a direct access to the virtual leader, by using two neighborhood attitude error signals, a novel chattering-free recursive full-order sliding mode control algorithm is proposed such that all follower spacecraft synchronize to the virtual leader in finite time. In the proposed algorithm, the sliding mode surface is constructed by two layers of sliding mode surfaces, which are called as the outer and the inner sliding mode surfaces. To achieve finite-time performance of sliding mode dynamics, the outer sliding mode surface is designed as a terminal sliding mode manifold, and the inner one is designed as a fast nonsingular terminal sliding mode manifold, respectively. Then, to reduce the heavy communication burden, a distributed recursive full-order sliding mode control law is designed by introducing a distributed finite-time sliding mode estimator such that only a subset of the group members has access to the virtual leader. Finally, a numerical example is illustrated to demonstrate the validity of the proposed results.     

Fabrication of rigid microstructures with thiol-ene-based soft lithography for continuous-flow cell lysis

In this work, we introduce a method for the soft-lithography-based fabrication of rigid microstructures and a new, simple bonding technique for use as a continuous-flow cell lysis device. While on-chip cell lysis techniques have been reported previously, these techniques generally require a long on-chip residence time, and thus cannot be performed in a rapid, continuous-flow manner. Microstructured microfluidic devices can perform mechanical lysis of cells, enabling continuous-flow lysis; however, rigid silicon-based devices require complex and expensive fabrication of each device, while polydimethylsiloxane (PMDS), the most common material used for soft lithography fabrication, is not rigid and expands under the pressures required, resulting in poor lysis performance. Here, we demonstrate the fabrication of microfluidic microstructures from off-stoichiometry thiol-ene (OSTE) polymer using soft-lithography replica molding combined with a post-assembly cure for easy bonding. With finite element simulations, we show that the rigid microstructures generate an energy dissipation rate of nearly 10⁷, which is sufficient for continuous-flow cell lysis. Correspondingly, with the OSTE device we achieve lysis of highly deformable MDA-MB-231 breast cancer cells at a rate of 85%, while a comparable PDMS device leads to a lysis rate of only 40%.     

Task-space control for industrial robot manipulators with unknown inner loop control architecture

The operational space control of a robot manipulator using external sensors requires stabilizing the compound system {external sensors - outer controller - inner controller - robot manipulator}. The user must access the inner controller to reshape it to achieve this stabilization. Due to intellectual property protection purposes, most industrial robots have an unknown or inaccessible inner controller. Therefore, it is tricky to design a stable control scheme. To solve this problem, an adaptive radial basis function neural network (RBF NN) outer controller is proposed, which approximates the inner controller’s dynamics to eliminate its effect in the closed-loop. An inherent property for RBF NN is used to reduce the number of adaptive parameters. Since this technique introduces approximation errors, it is included in the control scheme, a term that constrains the system to converge rapidly to the performances prescribed by the user. It is proved that all the closed-loop signals are semi-globally uniformly ultimately bounded (SGUUB) through Lyapunov theory. The effectiveness of the proposed approach is verified through simulation comparisons and experimental studies.     

Minimal energy maneuvering control of a rigid spacecraft with momentum transfer

The main goal of this study is to investigate a minimal energy rest-to-rest maneuvering control problem with open final time of a rigid spacecraft actuated by three orthogonal momentum wheels. Different from conventional shooting methods, this control problem is formulated and solved as a constrained nonlinear programming (NLP) one by utilizing an iterative procedure. In this novel method, the count of control steps is fixed initially and the sampling period is treated as a variable in the optimization process. An approach to find the initial feasible solutions of the NLP problem is also proposed. Since initial feasible solutions can be found easily, the optimization process of the NLP problem can be started from different points to find the minimal energy rest-to-rest maneuver of the rigid spacecraft between two attitudes. To show the feasibility of the proposed method, simulation results are included for illustration.     

Yield loci around fiber inclusions

An analysis of the plastic enclaves developed around the end points of rigid fiber inclusions embedded in an elastic plate is undertaken. The plate is subjected to a uniform uniaxial stress at any angle of inclination with the axis of the fiber. It is assumed that the material of the plate is elastic-perfectly plastic and that the deformations are small. A singular solution of the stress field in the vicinity of the end points of the fiber is used in conjunction with the Mises yield criterion to obtain the radius of the plastic zone under conditions of plane strain and generalized plane stress. The dependence of the size and shape of the plastic deformation on the orientation of the fiber, the Poisson's ratio of the plate and the state of stress (plane strain or generalized plane stress) is established.     

索膜结构非线性有限元找形分析基本理论研究

膜结构是近40年发展起来的一种新型建筑结构形式,它以性能优良的柔软织物作为覆盖材料,可以是向膜内充空气,由空气压力支撑膜面,也可以利用柔软的拉索结构或刚性的支撑结构将膜绷紧或撑起,从而形成具有一定刚度、能够覆盖大跨度空间的结构体系。膜结构的突出特点就是它形状的多样性．曲面存在着无限的可能性。以索或骨架支承的膜结构．其曲面就可以随着建筑师的想象力而任意变化,使得膜结构具有广阔的发展前景,将是21世纪空间结构发展的主流。     

Diversity incorporated energy adaptation for A-CDMA systems over slow fading channels

In this paper, a theoretical analysis of diversity incorporated Variable Energy Adaptation (VEA) in an Asynchronous Code Division Multiple Access (A-CDMA) system is discussed for Rayleigh, Rician and Nakagami slow fading channels. The adaptation is accomplished by providing the receiver with the capability of measuring the signal energy-to-noise ratio, and controlling the transmitted signal energy by means of a noise-free feedback loop. System parameters such as fading margin, maximum signal-to-noise ratio, and mean transmitter energy gain are derived and plotted for fading channels as a function of the probability of error specification and the probability of unsatisfactory operation. The mean and median probabilities of error are plotted as a function of energy-to-noise ratios for different fading channels. Error probability distribution and density functions are derived and plotted for various signal-fading distributions.     

Microfluidic blood plasma separation via bulk electrohydrodynamic flows

An effective mechanism for rapid and efficient microfluidic particle trapping and concentration is proposed without requiring any mechanically moving parts. When a voltage beyond the threshold atmospheric ionization value is applied on a sharp electrode tip mounted at an angle above a microfluidic liquid chamber, the bulk electrohydrodynamic air thrust that is generated results in interfacial shear and, hence, primary azimuthal liquid surface recirculation. This discharge driven vortex mechanism, in turn, causes a secondary bulk meridional liquid recirculation, which produces an inward radial force near the bottom of the chamber. Particles suspended in the liquid are then rapidly convected by the bulk recirculation toward the bottom, where the inward radial force causes them to spiral in a helical swirl-like fashion toward a stagnation point. In particular, we show that these flows, similar to Batchelor flows occurring in a cylindrical liquid column between a stationary and rotating disk, can be used for the separation of red blood cells from blood plasma in a miniaturized device.     

矿物填料填充高分子聚合物(PP)的应力-应变特征研究

讨论了矿物填料填充高分子聚合物（ＰＰ）的应力－应变特征．研究表明，矿物填料填充聚合物（ＰＰ）复合物具有刚性填料填充硬性基体复合物的应力－应变行为特征；填充复合物体系的拉伸弹性模量与抗拉强度随矿物填充量的增加分别显示为增大与下降．这些特征主要与刚性矿物填料、硬性聚合物基体本身的性质、矿物填料在聚合物中的分散性以及两者界面的相互作用特点有关．     

Optimal control of a flywheel energy storage system with a radial flux hybrid magnetic bearing

This paper describes the design and implementation of digital controllers for a flywheel energy storage device that incorporates a radial flux hybrid permanent magnetic bearing. Although the uncontrolled device is asymptotically stable, active control is required to: (i) ensure that a finite radial air gap is maintained at all times, and (ii) attenuate the oscillations of the flywheel which reduce the efficiency of the motor generator. The paper presents the design of gain scheduled discrete time linear quadratic regulator (LQR) and linear quadratic Gaussian (LQG) controllers for this rotordynamic system. Real time experiments are conducted to investigate the performance of the controllers. The result indicates that the LQR controller with approximate system velocities is easier to implement than the LQG controller, and also provides superior performance.     

T型刚构桥静载试验及性能评定

本文以广东省境内的一座T型刚构旧桥为背景,通过建立有限元模型进行理论计算,以此为基础制订静载试验方案并进行现场加载,测试桥梁关键截面的挠度和应变数据,最后与理论数据进行对比,对桥梁的受力状态和承载能力进行综合评定,并得到相应的结论,可对同类型的桥梁提供参考。     

科学理解的实践境况及其规范性——基于科学实践哲学视角的探究

科学理解的境况性规范是科学实践哲学的核心论题,阐释了实践境况与科学理解规范性的内在关联,指出境况性科学理解规范的研究内容;分别从物质性维度、时间性维度、话语维度以及权力维度解析作为实践现象整体的科学实践境况,同时揭示了不同实践境况维度对于科学理解的规范涵义。     

A droplet-based novel approach for viable and low volume consumption surface plasmon resonance bio-sensing inside a polydimethylsiloxane microchip

Over the course of last two decades, surface plasmon resonance (SPR) has emerged as a viable candidate for label-free detection and characterization for a large pool of biological interactions, ranging from hybridization of oligonucleotides to high throughput drug-screening. Conventional SPR bio-sensing involves a step-response method where the SPR sensorgram in response to a switched sequential flow of analyte and buffer is plotted in real-time and fitted to an exponential curve to extract the associative and dissociative reaction rates. Such measurement schemes involve continuous flow conditions where a substantial reagent volume is consumed and is subject to dispersive mixing at flow switching zones. In this paper, we demonstrate a new plug-train SPR technique in a microfluidic chip that separates and singulates solvent plugs in analyte and buffer by an immiscible air phase. Bio-samples are first discretized within plug droplets with volumes in order of few hundred nanoliters or less followed by pressure-driven transport onto SPR sensing sites of this hydrophobically modified SPR microdevise. The kinetic constants k_a and k_d for a model protein-small molecule interaction pair are extracted from a plug-train signal and are shown to be in reasonable agreement with our previous reports.     

Temporal Trends of Malondialdehyde in Stored Human Plasma

Malondialdehyde (MDA) is widely used as oxidative stress biomarker in biomedical research. Plasma is stored in deep freezers generally till analysis. Effect of such storage on MDA values, which may be variable and prolong, was incidentally observed in the ongoing study which is to estimate oxidative stress with oral iron. Plasma from blood samples of pregnant women (20–30 years age) in third trimester of singleton pregnancy (n = 139), consuming oral iron tablets was stored at −20 °C with intention of MDA estimation, as soon as possible. However logistic problems led this storage for prolonged and variable period (1–708 days). When values of MDA estimated using “Ohkawa” 79 method and readings were plotted against time to check the temporal effect, it showed a hyperbolic curve. Standard deviation (SD) was lowest when samples were tested within 3 weeks time. The samples analyzed within 3 weeks had mean ± SD value of 31.59 ± 26.11 μmol/L, while 123.7 ± 93.97 and 366.5 ± 189.8 μmol/L for samples stored for 1–3 and 4 months to 1 year respectively. Mean ± SD were 539.9 ± 196.8 in the samples store for more than a year. Rate of change in values was also lowest (0.0433 μmol/L/day) in the samples tested within first 3 weeks, which rose to 1.2 μmol/L/day during 3 month’s storage. This rate peaked at storage of 120 days (1.87 μmol/L/day) and fell to 0.502 μmol/L/day in the second year of storage. It is concluded that at −20 °C, only 3 weeks of storage time should be considered valid for fairly acceptable stability in MDA values.     

刚性地基梁非线性分析的积分方程法

提出了刚性地基梁非线性分析的积分方程法。以地基反力为未知量,导出了刚性地基梁弯曲的积分方程。通过引入梁的边界条件,建立起一组刚性地基梁关于地基反力和挠度的线性互补方程。利用Lemke方法求解得到梁上任一点处的挠度、转角、弯矩和剪力。最后给出了一些数值结果,表明本文数值解与解析解良好吻合。     

师生文化冲突的成因、表现及调适

师生冲突长期存在于教育的发展进程中,由于社会文化良莠不齐、学校文化过于僵硬、家庭文化与学校文化脱节、师生文化隔阂等原因造成师生文化冲突的形成。尽管冲突造成了一定程度的师生间偏见,但是只要发挥冲突的正向功能,便能引导师生文化由冲突走向融合。     

基于ANSYS对低温运输半挂车的内筒支撑管进行应力分析

半挂车在运行过程中,筒体容易上下振动和左右摆动。支撑管是支撑和固定内筒的核心结构。利用ANSYS软件对支撑管建立有限元模型,然后仿真三种典型工况,即半挂车静止、急刹车、急转弯情况下支撑管的受载情况。通过求解,得出支撑管上的等效应力分布状况及危险位置,为工程实践提供指导意义。     

黄连中盐酸小檗碱的提取工艺教学实验改进

采用解吸-内部沸腾两步法改进大学专业实验黄连中盐酸小檗碱的提取工艺,得到最佳提取工艺如下:解吸剂浓度为40%乙醇、解吸剂固液比1:2、热提第一次时间1 min、第二次时间5 min、热提剂固液比1:40。并与传统醇提法相比,提取时间短、乙醇消耗少和浸膏有效成分含量高,有效的提高了实验效率和经济性。     

Microfluidic platform integrated with worm-counting setup for assessing manganese toxicity

We reported a new microfluidic system integrated with worm responders for evaluating the environmental manganese toxicity. The micro device consists of worm loading units, worm observing chambers, and a radial concentration gradient generator (CGG). Eight T-shape worm loading units of the micro device were used to load the exact number of worms into the corresponding eight chambers with the assistance of worm responders and doorsills. The worm responder, as a key component, was employed for performing automated worm-counting assay through electric impedance sensing. This label-free and non-invasive worm-counting technique was applied to the microsystem for the first time. In addition, the disk-shaped CGG can generate a range of stepwise concentrations of the appointed chemical automatically and simultaneously. Due to the scalable architecture of radial CGG, it has the potential to increase the throughput of the assay. Dopaminergic (DAergic) neurotoxicity of manganese on C. elegans was quantitatively assessed via the observation of green fluorescence protein-tagged DAergic neurons of the strain BZ555 on-chip. In addition, oxidative stress triggered by manganese was evaluated by the quantitative fluorescence intensity of the strain CL2166. By scoring the survival ratio and stroke frequency of worms, we characterized the dose- and time-dependent mobility defects of the manganese-exposed worms. Furthermore, we applied the microsystem to investigate the effect of natural antioxidants to protect manganese-induced toxicity.