An improved P(V)-N activation strategy for the synthesis of nucleoside diphosphate 6-deoxy-l-sugars

Four nucleoside diphosphate 6-deoxy-l-sugars have been efficiently synthesized by coupling sugar-1-phosphates prepared from the H-phosphonate precursors with nucleoside 5′-phosphoropiperidates in the presence of 4,5-dicyanoimidazole (DCI) as the activator. Compared to the conventional 1H-tetrazole-promoted phosphoromorpholidate method, the new phosphoropiperidate/DCI system significantly shortened the reaction time and afforded nucleoside diphosphate sugars in excellent isolated yields.     

Analysis and design of a novel and compact X-structured vibration isolation mount (X-Mount) with wider quasi-zero-stiffness range

Nonlinear Dynamics - Passive vibration isolation is always preferable in most engineering practices. To this aim, a novel, compact and passive vibration isolation mount is studied in this paper,...     

Nonlinear mechanics of flexible cables in space robotic arms subject to complex physical environment

A nonlinear model of a special cable in space robotic arms is developed in space environment. The mechanic effects of control cables in powerful robots can often be neglected. However, in complex space multi-physics environments, involving ultra-low temperature, radiation, and other extreme conditions of outer space, the externally mounted cables (protected by shielding layers) can induce strong nonlinear interference to robot arms; and this can induce further small-range slow rotations or oscillations of the flexible joint of robots at a specific posture, which consequently affect the precision and operation performance of end effectors. Effective mathematical models on nonlinear mechanics of strong cables under multi-physics environments and their effects on weak robots have not been well developed yet. Complex key factors, such as low gravity, nonlinear friction, and unexpected curved surface constraints, have not been extensively investigated either. In this study, considering all these key factors, a Kirchhoff nonlinear mechanical model of cables in complex space environments is developed, and a relatively improved algorithm based on a trust-region strategy is proposed for solving this nonlinear model, based on which the geometry and terminal force of the modeled robot cable can be obtained. The validity and accuracy of the proposed algorithm and theoretical calculation results are verified via experiments. The theoretical findings revealed in this study are significant to future research on the slow rotations and oscillations of weak robot joints in space exploration with robotic arms.

     

eSHAFTS: Integrated and graphical drug design software based on 3D molecular similarity

With the development of computer technology, computer-aided drug design (CADD) has become an important means for drug research and development, and its representative method is virtual screening. Various virtual screening platforms have emerged in an endless stream and play great roles in the field of drug discovery. With the increasing number of compound molecules, virtual screening platforms face two challenges: low fluency and low visibility of software operations. In this article, we present an integrated and graphical drug design software eSHAFTS based on three-dimensional (3D) molecular similarity to overcome these shortcomings. Compared with other software, eSHAFTS has four main advantages, which are integrated molecular editing and drawing, interactive loading and analysis of proteins, multithread and multimode 3D molecular similarity calculation, and multidimensional information visualization. Experiments have verified its convenience, usability, and reliability. By using eSHAFTS, various tasks can be submitted and visualized in one desktop software without locally installing any dependent plug-ins or software. The software installation package can be downloaded for free at http://lilab.ecust.edu.cn/home/resource.html . © 2019 Wiley Periodicals, Inc.     

Frequency domain analysis and identification of block-oriented nonlinear systems

Block-oriented nonlinear models including Wiener models, Hammerstein models and Wiener-Hammerstein models, etc. have been extensively applied in practice for system identification, signal processing and control. In this study, analytical frequency response functions including generalized frequency response functions (GFRFs) and nonlinear output spectrum of block-oriented nonlinear systems are developed, which can demonstrate clearly the relationship between frequency response functions and model parameters, and also the dependence of frequency response functions on the linear part of the model. The nonlinear part of these models can be a more general multivariate polynomial function. These fundamental results provide a significant insight into the analysis and design of block-oriented nonlinear systems. Effective algorithms are therefore proposed for the estimation of nonlinear output spectrum and for parametric or nonparametric identification of nonlinear systems. Compared with some existing frequency domain identification methods, the new estimation algorithms do not necessarily require model structure information, not need the invertibility of the nonlinearity and not restrict to harmonic inputs. Simulation examples are given to illustrate these new results.