Adaptive output feedback stabilization for nonlinear systems with unknown polynomial-of-output growth rate and sensor uncertainty

summary:In this paper, the problem of adaptive output feedback stabilization is investigated for a class of nonlinear systems with sensor uncertainty in measured output and a growth rate of polynomial-of-output multiplying an unknown constant in the nonlinear terms. By developing a dual-domination approach, an adaptive observer and an output feedback controller are designed to stabilize the nonlinear system by directly utilizing the measured output with uncertainty. Besides, two types of extension are made such that the proposed methods of adaptive output feedback stabilization can be applied for nonlinear systems with a large range of sensor uncertainty. Finally, numerical simulations are provided to illustrate the correctness of the theoretical results

Contagion processes on the static and activity driven coupling networks

The evolution of network structure and the spreading of epidemic are common coexistent dynamical processes. In most cases, network structure is treated either static or time-varying, supposing the whole network is observed in a same time window. In this paper, we consider the epidemic spreading on a network consisting of both static and time-varying structures. At meanwhile, the time-varying part and the epidemic spreading are supposed to be of the same time scale. We introduce a static and activity driven coupling (SADC) network model to characterize the coupling between static (strong) structure and dynamic (weak) structure. Epidemic thresholds of SIS and SIR model are studied on SADC both analytically and numerically with various coupling strategies, where the strong structure is of homogeneous or heterogeneous degree distribution. Theoretical thresholds obtained from SADC model can both recover and generalize the classical results in static and time-varying networks. It is demonstrated that weak structures can make the epidemics break out much more easily in homogeneous coupling but harder in heterogeneous coupling when keeping same average degree in SADC networks. Furthermore, we show there exists a threshold ratio of the weak structure to have substantive effects on the breakout of the epidemics. This promotes our understanding of why epidemics can still break out in some social networks even we restrict the flow of the population

Photocatalytic regio- and stereoselective C(sp3)–H functionalization of benzylic and allylic hydrocarbons as well as unactivated alkanes

C(sp3)–H键的直接官能团化具有原子、步骤经济、原料来源丰富等特点，备受合成化学家的青睐。然而，这些化学键的高键能、低极性等特征使其反应性差；相近能量化学键的存在也使反应的选择性难以控制。因此，C(sp3)–H键的直接、选择性转化一直是有机合成中的难题。课题组基于近期在手性廉价金属配合物催化自由基可控不对称合成方面的工作基础（Nat.Commun.2019,10,3804、J. Am.Chem.Soc.2018,140,15850、Chem.Sci.2018,9,4562），提出了手性铜、镍、钴配合物与商业化醌类可见光氢转移催化剂共催化的策略，在极为温和的光反应条件下，实现了石油、天然气中原材料向高附加值手性化合物的区域、立体选择性转化，为烃类资源的优化利用及药物分子的后期改造提供了有效手段，也为纯烃分子作为反应试剂直接使用提供了新思路。该方法适用于苄基、烯丙基类化合物、环烷烃、链烷烃等40余种烃类分子，也适用于一些药物及生物活性分子（如celebrex、skelaxin等）的后期官能化中。此外，廉价金属/氢转移光催化剂体系也展现了通过改变催化剂金属中心获得手性反转产物的独特现象，为立体发散性合成提供了极为简便的策略。 本工作由龚磊副教授指导，实验部分由2016级博士生李延军和已毕业硕士生雷梦合作完成.The selective functionalization of inert C(sp3)–H bonds is extremely attractive in organic synthesis and catalysis science, but the conversion of hydrocarbons lacking directing groups into chiral molecules through catalytic C(sp3)–H functionalization is formidably challenging. Here, to address this problem, we have developed a photochemical system consisting of a hydrogen atom transfer organophotocatalyst and a chiral catalyst containing an earth-abundant metal. With the cooperative catalysts and imine partners, a wide range of benzylic, allylic hydrocarbons and unactivated alkanes can be converted to functionalized chiral products. The readily tunable bisoxazoline catalysts of copper or other metals exhibit precise regional recognition and asymmetric induction towards these inert C–H bonds. The reactions are applicable to many compounds including small hydrocarbons, branched alkanes, cycloalkanes and more complex medicinal agents. This method provides an economic and rapid construction of optically active compounds, starting from the most basic chemical feedstocks.We gratefully acknowledge funding from the National Natural Science Foundation of China (grant no. 21572184), the Natural Science Foundation of Fujian Province of China (grant no. 2017J06006) and the Fundamental Research Funds for the Central Universities (grant no. 20720190048). 研究工作得到国家自然科学基金（21572184）、福建省杰出青年基金（2017J06006）、南强青年拔尖人才计划（B类）、厦门大学校长基金（20720190048）等项目支持

Estimation of the Conifer-Broadleaf Ratio in Mixed Forests Based on Time-Series Data

Most natural forests are mixed forests, a mixed broadleaf-conifer forest is essentially a heterogeneously mixed pixel in remote sensing images. Satellite missions rely on modeling to acquire regional or global vegetation parameter products. However, these retrieval models often assume homogeneous conditions at the pixel level, resulting in a decrease in the inversion accuracy, which is an issue for heterogeneous forests. Therefore, information on the canopy composition of a mixed forest is the basis for accurately retrieving vegetation parameters using remote sensing. Medium and high spatial resolution multispectral time-series data are important sources for canopy conifer-broadleaf ratio estimation because these data have a high frequency and wide coverage. This paper highlights a successful method for estimating the conifer-broadleaf ratio in a mixed forest with diverse tree species and complex canopy structures. Experiments were conducted in the Purple Mountain, Nanjing, Jiangsu Province of China, where we collected leaf area index (LAI) time-series and forest sample plot inventory data. Based on the Invertible Forest Reflectance Model (INFORM), we simulated the normalized difference vegetation index (NDVI) time-series of different conifer-broadleaf ratios. A time-series similarity analysis was performed to determine the typical separable conifer-broadleaf ratios. Fifteen Gaofen-1 (GF-1) satellite images of 2015 were acquired. The conifer-broadleaf ratio estimation was based on the GF-1 NDVI time-series and semi-supervised k-means cluster method, which yielded a high overall accuracy of 83.75%. This study demonstrates the feasibility of accurately estimating separable conifer-broadleaf ratios using field measurement data and GF-1 time series in mixed broadleaf-conifer forests

Characterization of severe fever with thrombocytopenia syndrome in rural regions of Zhejiang, China.

Severe fever with thrombocytopenia syndrome virus (SFTSV) infections have recently been found in rural regions of Zhejiang. A severe fever with thrombocytopenia syndrome (SFTS) surveillance and sero-epidemiological investigation was conducted in the districts with outbreaks. During the study period of 2011-2014, a total of 51 SFTSV infection cases were identified and the case fatality rate was 12% (6/51). Ninety two percent of the patients (47/51) were over 50 years of age, and 63% (32/51) of laboratory confirmed cases occurred from May to July. Nine percent (11/120) of the serum samples from local healthy people without symptoms were found to be positive for antibodies to the SFTS virus. SFTSV strains were isolated by culture using Vero, and the whole genomic sequences of two SFTSV strains (01 and Zhao) were sequenced and submitted to the GenBank. Homology analysis showed that the similarity of the target nucleocapsid gene from the SFTSV strains from different geographic areas was 94.2-100%. From the constructed phylogenetic tree, it was found that all the SFTSV strains diverged into two main clusters. Only the SFTSV strains from the Zhejiang (Daishan) region of China and the Yamaguchi, Miyazakj regions of Japan, were clustered into lineage II, consistent with both of these regions being isolated areas with similar geographic features. Two out of eight predicted linear B cell epitopes from the nucleocapsid protein showed mutations between the SFTSV strains of different clusters, but did not contribute to the binding ability of the specific SFTSV antibodies. This study confirmed that SFTSV has been circulating naturally and can cause a seasonal prevalence in Daishan, China. The results also suggest that the molecular characteristics of SFTSV are associated with the geographic region and all SFTSV strains can be divided into two genotypes

Robo-centric ESDF: A Fast and Accurate Whole-body Collision Evaluation Tool for Any-shape Robotic Planning

For letting mobile robots travel flexibly through complicated environments, increasing attention has been paid to the whole-body collision evaluation. Most existing works either opt for the conservative corridor-based methods that impose strict requirements on the corridor generation, or ESDF-based methods that suffer from high computational overhead. It is still a great challenge to achieve fast and accurate whole-body collision evaluation. In this paper, we propose a Robo-centric ESDF (RC-ESDF) that is pre-built in the robot body frame and is capable of seamlessly applied to any-shape mobile robots, even for those with non-convex shapes. RC-ESDF enjoys lazy collision evaluation, which retains only the minimum information sufficient for whole-body safety constraint and significantly speeds up trajectory optimization. Based on the analytical gradients provided by RC-ESDF, we optimize the position and rotation of robot jointly, with whole-body safety, smoothness, and dynamical feasibility taken into account. Extensive simulation and real-world experiments verified the reliability and generalizability of our method.Comment: Accepted at IROS 202

Structural Behavior of Thin-Walled Concrete-Filled Steel Tube Used in Cable Tunnel: An Experimental and Numerical Investigation

One steel grid and five thin-walled concrete-filled steel tubes (CTST) used as the supports of tunnel were tested in site for investigating the mechanical behavior. The mechanical influences of thickness, node form, and concrete on CTST were gained and compared with the impacts on steel grid. It is indicated that high antideformation capacity of CTST improved the stability of surrounding rock in short time. The cementitious grouted sleeve connection exhibited superior flexibility when CTST was erected and built. Although the deformation of rock and soil in the tunnel was increasing, good compression resistance was observed by CTST with the new connection type. It was also seen that vault, tube foot, and connections were with larger absolute strain values. The finite element analysis (FEA) was carried out using ABAQUS program. The results were validated by comparison with experimental results. The FE model could be referred by similar projects